Materials Engineering

introductory overview Materials Engineering - metals technology

„Technology” Greek origin

„Technos”  technical „logos”  logikal

Theory and practice of some technical processes.

Production, planning, organizations (+information and experience) Materials Engineering - metals technology

Meaning changed with time

Before the industrial revolution: the sum of the knowledge of a single worker.

After the industrial revolution, first part of XIX century: Manufacturing industry, technical knowledge and the science are separated into various technologies.

After the industrial revolution, second part of XIX century: Mass production, important technologies: Mechanization, automatization, organization Materials Engineering - metals technology

Meaning changed with time

Since 1960: New disciplines (electronics, informatics, computer science), various scientific background

Increased productivity, the skilled labor is less important Materials Engineering

Metals technology

Metal producing and processing technologies machining industry

Construction

Product Production quality possibilities

Material Technology production abilities Materials Engineering examples

1) Car body  sheet rolling technology  deep drawing

2) Heat exchanger: steel, stainless steel, titanium  different welding technologies Materials Engineering

Materials

Metallic Non metallic

Ferrous -> iron, steel Organic Plastics or polymers Nonferrous Wood, paper, rubber -> Al, Mg, Cu, Ni, Pb Inorganic ceramics (technical ceramics) glass

Composites: utilize more than one type of material Materials Engineering Materials Engineering

The properties of materials are determined by two group of factors:

Internal factors  determine the material’s structure - Chemical composition (impurity and alloying) - Microstructure (equilibrium or non-equilibrium phases, their amount, quality distribution, and sizes)

External factors  determine the service condition of a machine part - Temperature (mean value and amplitude) - Rate of deformation - Stress state - Chemical effects - Corrosion effects - Irradiation effects Materials Engineering

Internal factors are determined by all the - Metal production - Form making - Forming - Heat treating - Surface treating - Joining process Materials Engineering

External factors – service conditions are determined by how the machine part is used

T (°C)

1000

600 e.g.: service temperature range

1950 1960 1970 1980 1990

-200 spacecraft Materials Engineering

Need for better material properties because: a) To decrease the weight of the equipment b) Increasing the quality

In practice 70-80,000 various types of materials are used.

More than 1000 different types of steel Materials Engineering

General layout of the subject

Metal producing technologies: iron and steel making Producing of nonferrous metals

Form making technologies: casting, pre-forming Never pure, contains by plastic deformation impurities Powder metallurgy

Cast ingot, castings, rolled bloom, billet, rod, wire, strip, sheet, forged bar, block Forming processes, machining processes, heat treatments and surface treatments

Joining process: Welding Materials Engineering

Phase transformation Phase diagrams Phase Transformation

Why is it important for us?

o Temperature, chemical composition and pressure can change the properties of materials

o Understanding what happens during heat treating processes

o Understanding the development of the microstructure Phase Transformation

Today’s topics

o Terminology of phase diagrams and phase transformations

o Thermodynamics of phase transformations

o Phase diagrams Phase Transformation

Terminology

Component: Pure metals and/or compounds of which an alloy is composed. e.g. in a copper–zinc brass, the components are Cu and Zn

System: Series of possible alloys consisting of the same components, but without regard to alloy composition

Solid solution consists at least two different types of atoms the solute atoms occupy either substitutional or interstitial positions in the solvent lattice Phase Transformation

Solubility limit A maximum concentration of solute atoms that may dissolve in the solvent to form a solid solution

The solubility of sugar in a sugar–water syrup

Figures from Callister, Mat. Sci. and Eng. An Introduction, 8th edition Phase Transformation

Phase A homogeneous portion of a system that has uniform physical and chemical characteristics.

Own distinct properties • Chemical composition • State of matter (e.g. water+ice) • Crystal structure • …

1 phase Homogeneous system: single-phase system 2 phases Heterogeneous system: two or more phases Phase Transformation

Thermodynamics Internal energy U: the energy needed to create the system Enthalpy (H=U+pV): U+ energy required to make room for it by displacing its environment Enthropy (S): expression of disorder or randomness, the energy not available for work Helmholtz free energy (F=U-TS) Gibbs free energy (free enthalpy)(G=H-TS) G Equilibrium Gsolid A system is at equilibrium if its free energy is

at a minimum under some specified Gliquid combination of temperature, pressure, and composition. T The characteristics of the system do not change with time. Phase Equilibrium

Phase Equilibrium In an equilibrium system the ratio of phases are constant.

3

2

1 Phase Equilibrium

Equilibrium Two component system (A-B) (ideal solution: exchanging any two atoms does not change the enthalpy)

Entropy, S disorder or randomness Processes reduce the state of order of the initial systems.

S

A B Phase Equilibrium

Equilibrium Two component system (A-B), ideal solution Phase Equilibrium

L liquid α phase

T1 T2 L L+α T3

T4 α T5 CL Cα CL Cα Phase Equilibrium

L L+α

α

CL Cα

C L Cα Phase Equilibrium

Metastable state

Often the state of equilibrium is never completely achieved because the rate of approach to equilibrium is extremely slow.

 non-equilibrium or metastable state.

Metastable state or microstructure may persist indefinitely (changes only extremely slight)

Often, metastable structures are of more practical significance than equilibrium ones. Phase Diagrams

Phase or equilibrium diagram

Information about the phase structure of a particular system.

Parameters Informations • Temperature • State of the matter, crystal structure • Pressure • Phase composition • Composition • Chemical composition of the phases

several different varieties (e.g. composition-Temperature, pressure-Temperature) Phase Diagrams

One-component (or unary) phase diagram

Simplest, one-component system p-T phase diagram

Note! phases at equilibrium

Pressure–temperature phase diagram for H2O. Phase Diagrams

Binary phase diagrams

composition-Temperature

transition from one phase to another, or the appearance or disappearance of a phase.

Copper–nickel phase diagram Phase Diagrams

Copper–nickel phase diagram Alloy (2)

Point A: T=1100°C 1 phase: α, solid sol. of Cu and Ni C CNi=60%, CCu=40%

Alloy (1)

Point C: T=1400°C 1 phase: L, liquid

CNi=35%, CCu=65%

(1) (2) Phase Diagrams

Copper–nickel phase diagram

Alloy (1)

Point B: T=1250°C 2 phases: α + L, C solid + liquid phase Composition:

CNi=35%, CCu=65% Mass fraction of phases

Wα=? %, WL= ? % Composition of phases:

α: CNi=? %, CCu=? % L: CNi=? %, CCu=? % (1) (2) Phase Diagrams

Copper–nickel phase diagram L

α L L α

L α α Phase Diagrams

Copper–nickel phase diagram

Lever rule ~ α ~ L

CL C0 Cα Mass fraction of phases

퐶0−퐶퐿 퐶훼−퐶0 푊훼 = 퐶훼−퐶퐿 푊퐿 = 퐶훼−퐶퐿 Phase Diagrams

Copper–nickel phase diagram

Composition of phases ~ α ~ L

CL C0 Cα

wt% of Ni wt% of Ni in liquid phase in α phase

The chemical composition of the phases is changing with the temperature change. Phase Diagrams

Copper–nickel phase diagram Liquid phase: 35% Ni α phase: -

Liquid phase: 34% Ni α phase: 46% Ni

Liquid phase: 32% Ni α phase: 43% Ni

Liquid phase: 35% Ni α phase: 37% Ni

Liquid phase: - α phase: 35% Ni 25 46 Phase Diagrams

Inhomogeneous and equilibrium phase Equilibrium solidification: • only for extremely slow cooling rates. • diffusional processes (diffusion rates are lower for lower temperatures and for solid phases)

High cooling rate Low cooling rate Inhomogeneous Equilibrium structure structure Phase Diagrams

Inhomogeneous and equilibrium phase

Figure from Callister, Mat. Sci. and Eng. An Introduction, 8th edition Phase Diagrams

Eutectic reaction Liquid phase α + (solid phases)

Lead-Tin system Phase Diagrams

Lead-Tin system Phase Diagrams

Lead-Tin system Phase Diagrams

Eutectoid reaction ( solid phase) α + (solid phases)

Peritectic reaction α ( solid phase) + liquid phase (solid phases)

Copper–zinc phase diagram Phase Diagrams Ceramic Phase Diagrams

The two components are compounds that share a common element Similar to metal–metal systems

Al2O2-Cr2O3 phase diagram

Figure from Callister, Mat. Sci. and Eng. An Introduction, 8th edition Ceramic Phase Diagrams

ZrO2-CaZrO3 phase diagram Ceramic Phase Diagrams

BaTiO3 p-T phase diagram

S A Hayward and E K H Salje ,J. Phys.: Condens. Matter 14 No 36 2002 p 599-604 Materials engineering

Iron and steel making Metals: rarely exist in pure state  mostly in ores

Ore: Metallic and other compounds, mostly oxides

Metallic content: Iron ores: 30-70% Fe Copper ores: 0.1-0.8 % Cu Molybdenum: 0.01-0.1% Mo 4 basic way to gain the metallic parts from ore: Reduction by carbon Electrolytic way costs Metallotermical process Dissociation 1) Reduction by carbon MeO + C  Me + CO

FeO + C  [Fe] + {CO}

molten metals gas

3+ 2- 2) Electrolytic way Al2O3  Al2 + 3O on the cathode: Al3+ + 3e-  Al

3) Metallothermical process

TilCl4 + 2Mg [Ti] + 2MgCl

4) Dissociation MeX  [Me] + [x] only at high energy level Iron and steel Iron and steel making

Blast furnace

Foundry

Steel making plant

Foundry Production of molten steel Iron producing processes

Purpose: Iron ore  Pig Iron

ore types: Fe3O4 magnetite ~70% Fe Fe2O3 hematite ~70% Fe FeCO3 siderite ~50% Fe

+ tailings: silicates, sand, other non ferrous

MnO, Al2O3, P2O5, etc Concentration of ore cost cost of pig iron cost of concent- rating

cost of blast furnace

30 ~ 70 % Fe % in ore magnetite Blast Furnace Plant

Blast Furnace Plant

Tasks 1) Reduction of the ore 2) Extraction of tailings 3) Melting  separation of the molten iron from the molten tailings (spec. weight difference)

Charge: Ore + Coke + Limestone

Dimension of the BF: For 1000 t of iron: Diameter: 4-10 m 2000 t ore + Height: 25-30 m 800 t coke + Volume: 300 – 5000 m3 500 t limestone + ~ 4000t hot air Processes in blast furnace

Charge moves down (6-8 hours)

- Preheating by gas: coke burns more efficient Formation of CO CO reacts with iron ore

- Coke reduces CO2 in the gas C + CO2  2CO - CO reduces the surface of the iron ore. Indirect reduction

FeO + CO  Fe + CO2 - Slag producing by limestone.

CaCO3  CaO + CO2 MgCO3  MgO + CO2 - In the bosh the coke burns

C + O2  CO2 + Heat - The coke reduces the molten ore. Direct reduction FeO + C  Fe + CO - Molten limestone + other slag components produce eutectic slag Slag floats over molten iron Processes in blast furnace – thermodynamics

• Gibbs free energy • Reduction of FeO from 690 °C

C+O2CO2 Processes in blast furnace

Carbon reduces the oxides: FeO + C  Fe + CO

MnO + C  Mn + CO alloying elements SiO2 + 2C  Si + 2CO

P2O5 + 5C  2P + 5CO impurities SO2 + 2C  S + 2CO

in molten iron gas

In BF carbon can reduce S, P, Cr, Mn, Si 70-90% and Ti 10-20%

Sulfur and phosphorous are harmful in pig iron, and they must be removed. Processes in blast furnace

Desulfurization FeS + CaO  FeO + CaS

in molten iron in molten slag

Dephosphorization

P2O5 + 5FeO + 5C + 4 CaO  CaO4P2O5 + 5Fe + 5CO

in molten iron in molten slag gas

in molten iron

Result: pig iron

Product of blast furnace

At the bottom of the BF: Slag on the top Molten iron on the bottom with~4% C Near to eutectic composition

Taping at different heights: different composition different purpose

C% Mn% Si% S% P% for casting 3 - 4 < 1 < 4 < 0.1 < 0.1

for steel with Bessemer method 3 - 4 0.4 – 1 ~ 3 < 0.1 < 0.1

for steel with Thomas method 3 - 4 0.4 – 1 ~ 2 < 0.1 < 0.1 for steel with Siemens-Martin 3 - 4 0.4 – 1 ~ 1 < 0.1 < 0.1 method Product of blast furnace

Taping: http://www.youtube.com/watch?v=QBLRIEZZEsU Product of blast furnace

Metallurgy

http://www.youtube.com/watch?v=kPH4dJUVOfc Steel making

Purpose Pig iron  steel by fire – refining treatments that decrease the C content and impurities.

Main steps

1) Charging 2) Oxidation decreasing C content

3) Increasing temp. with decreasing C% the Tmelt increases ! 4) Deoxidation decrease FeO and O in molten steel 5) Alloying 6) Casting, solidification casting of ingots or continuous casting of bars and billets Steel making

Processes . Siemens Martin (open hearth furnace) . Bessemer converter process . Thomas converter process . Oxygen converter process (Linz-Donawitz process - LD) . Electric arc steel furnace Siemens Martin process (1864)

Charging pig iron+scrap pig iron + ore

Capacity 10-900 t 6-12 h

Too expensive

carbon 0,3 %/hour burns out Siemens Martin process (1864) Bessemer process (1856)

Charging molten iron 1210-1250ºC ~3% Si

Capacity 5-60 t 15-20 min

First converter method No external heat Acidic lining (slag react.)

Si + O2  SiO2

from the air Bessemer process (1856)

During the blow C, Si, Mn % decreases.

% ºC 1700ºC

1250ºC

C Si O 4% 3% Mn

1% N

blowing time 15 min. Thomas converter process (1878)

Charging molten iron 1210-1250ºC ~2% P

No external heat

Similar to Bessemer, but basic lining for slag reaction.

4 P +5 O2  2 P2O5

from the air Oxygen-converter process (LD)

Charging molten iron ~3% C ~0.5% Mn ~1% Si ~0.1% P, S

Capacity 15-400 t

No external heat

To avoid overheating when blowing iron ore or scrap are changed. Limestone is changed for desulfurization & dephosphorization. Variants of Oxygen-converter process

OLP process

oxygen – limestone – powder

oxygen & CaO powder is blown through the lance

AOD process

argon – oxygen – decarbonizing oxygen & argon is blown through the lance

Mixed gas system  decreased partial pressure of oxygen  C% decreases

up to 0.002% C e.g. for stainless steels Electric Arc Steel Furnace

Charging scrap + solid pig iron ~3% C ~0.5% Mn ~1% Si ~0.1% P, S

Capacity 5-200 t

For high grade steels

T > 2500ºC intensive reaction, N2 dissociation Electric Arc Steel Furnace

http://www.youtube.com/watch?v=nolpiat6Sk0

Charging scrap Electric Arc Steel Furnace

http://www.youtube.com/watch?v=G6Uxh-xtU-g

during work Electric Arc Steel Furnace

http://www.youtube.com/watch?v=3gg9_zTlg4M

Electrode in the furnace Steel making - oxidization

Purpose decrease C% and oxidize the impurities (S, P)

In open hearth and electric arc furnace

C + FeO  Fe + CO

from scrap turbulence in the charge or iron ore

In air or oxygene blowing converters

2C + O2  2CO

from blowing The dissolved oxygen content air increases Hamilton’s law

At the given temperature [C][O]=constant

O% Stainless steels oxidization requires vacuum 0.1 C < 0.02% O < 0.01% 0.01 p=1bar

0.001

0.0001 p=1mbar

0.01 0.1 1 C% The law of distribution and mass action

The law of distribution At a given temperature the ratio of the amount of a given compound In the molten iron and in the molten slag is constant.

퐹푒푖 ℎ푒 푙푎푔 = 퐹푒푖 ℎ푒 푖 The law of mass action Determines the direction of the reaction

v1 mA + nB pAB v2

p m n v1=k1(CAB) V2=k2(CA) (CB)

At equilibrium v1=v2 Effect of nonmetallic elements S, P, O, N

Effect of sulfur FeS at grain boundaries S does not dissolve, forms FeS eutectic with iron. grain T Crystallization at the grain 1600 boundaries. 1000 Cold and hot brittleness FeS % 0% ~80% 100% To reduce the effect: desulfurization

1) Alloy with Mn 2) Increase S content

FeS + Mn  MnS + Fe generally S < 0.035%

MnS is formable at high temperature Effect of nonmetallic elements S, P, O, N

Effect of sulfur - desulfurization

increases with temperature 퐹푒푂푖 ℎ푒 푙푎푔 = 퐹푒푂푖 ℎ푒 푖

퐶푎푖 ℎ푒 푙푎푔 ∙ 퐹푒푖 ℎ푒 푖 퐶푎푖 ℎ푒 푙푎푔 ∙ 퐹푒푖 ℎ푒 푙푎푔 = = 퐹푒푖 ℎ푒 푖 ∙ 퐶푎푖 ℎ푒 푙푎푔 퐹푒푖 ℎ푒 푖 ∙ 퐶푎푖 ℎ푒 푙푎푔∙

퐶푎푖 ℎ푒 푙푎푔 ∙ 퐹푒푖 ℎ푒 푙푎푔 퐹푒푖 ℎ푒 푖 = ∙ 퐶푎푖 ℎ푒 푙푎푔∙

To achieve low S% • increase L : increase the temperature. • increase CaO content in the slag The slag must be • increase CaS content in the slag changed • increase FeO content in the slag Effect of nonmetallic elements S, P, O, N

Effect of nitrogen

nitride compounds precipitation and/or the solidification of nitrogen in interstitial solid solution.

. Increases strength decreases toughness. . Ageing Effect of nonmetallic elements S, P, O, N

Effect of phosphorous

T Keep P content under 0.035%

γ (0.001%) α 1000

1.2% 15%

Impact energy Rm Rm Rp02 Z Rp02

Z T TTKV TTKV P [%] P% ↑ Effect of nonmetallic elements S, P, O, N

Effect of phosphorous - dephosphorization

2 P + 5 FeO + 4 CaO  (CaO4 · P2O5) + Fe

in molten iron in molten iron in molten slag Dissolves only in slag

5 [퐶푎 · 2] ∙ [퐹푒] [퐶푎 · 2] ∙ [퐹푒] = 2 [] = 퐹푒 [퐶푎] 퐹푒 [퐶푎]

To achieve low P% • decrease the temperature. • increase CaO content in the slag The slag must be • increase phosphate content in the slag changed • increase FeO content in the slag Effect of nonmetallic elements S, P, O, N

stress Effect of oxygen after long service period In form of O or FeO. after forming

initial state Ageing strain

Work done till fracture Impact energy To reduce the effect: deoxidation

Methods: . Settling . Diffusional deox. T TTKV TTKV . Synthetic slag O% ↑ . Ladle metallurgy Brittel-to-ductile transition temperature Effect of nonmetallic elements S, P, O, N

Effect of oxigene

Rm Z

Rm

Z

O [%] Deoxidation: settling

Deoxidizing elements are loaded into the molten steel. General reaction: FeO + Me  MeO + Fe

The amount of deoxidizing elements are limited by their disadvantageous effect on the properties:

Mn < 1% causes grain coarsening & brittleness Si < 0.5 % it decreases the toughness.

V Ti < 0.1 % they decreases the toughness. Al Deoxidation: settling

Effect of deoxidizing element on the dissolved oxygen

O [%]

0.1 Mn Si

0.01 V C

0.001 Al

Ti 0.0001 Zr

Me [%]

0.01 0.1 1 Deoxidation: settling

Rimmed steel Deoxidizing with Mn only susceptible on ageing

Semi-killed steel Deoxidizing with Mn + Al for continuous casting

Killed steel Deoxidizing with Mn + Si lower TTKV than rimmed steel

Dead killed steel Deoxidizing with Mn + Si + Al/V/Ti/Zr best quality from the point of brittleness Deoxidation: diffusional and synthetic slag meth.

Diffusional method

Deoxidizing element loaded on the top of the molten slag. Diffusion of O to slag.

Diffusional synthetic slag method

The molten steel is poured on the top of prepared FeO-free slag. molten steel

FeO free slag Deoxidation: ladle metallurgy

Ladle metallurgy

Powder injection deoxidizing, desulfurizing, and dephosphorising powder with Ar gas are blown into the molten steel.

- Inclusions are lifting to the slag. molten steel - Almost isotropic

This technology with the converter method is the most up-to-date steel making process Vacuum handling

A process for deoxidation and degasification

The effect of vacuum on steel 1) Decreasing the partial pressure of the gas above the molten steel 2) Decrease the content of oxygen. 3) Increase the vaporization rate of low melting point metals (Zn, Pn, Sn, As) 4) Separates the compounds by dissociation.

~10-6 bar ~10-9 bar 10-12-15 bar

Practically Fe4N FeO SiO2 impossible

CrN AlN Al2O3 TiN Vacuum handling

Two type of process

Molten steel

Vacuum chamber

Steel stream Vacuum

ladle

Degasificated steel

Vacuum ladle degassing Vacuum stream degassing Effect of dissolved gases on steel

CO - in the rimmed steel produces gas bubbles

O2 - produces gas inclusions and oxide and silicate inclusions

N2 - increase the ability for aging and nitride inclusions

H2 - flocking – H2 bubbles  cracking Effect of dissolved gases on steel

Tmelting flocking – H2 bubbles reason A4

[H] [H]

A3

Temp

T A3 A4 melting Effect of dissolved gases on steel

H2 – solution let the gas atoms depart by diffusion

• slow cooling after casting (several days) • forging by very soft deformation to make cohesion between the surfaces of the cracks

+ for N make stable nitrides my mircoalloying elements

Al, V, Ti  AlN, VN … Alloying, casting

Alloying

Can only take place after a perfect deoxidation, otherwise alloying elements would burn.

Casting

Two types: casting of ingots continuous casting Casting of ingots

• simple • More homogeneous • High productivity • slow Casting of ingots

Solidification process for ingots - Shrinking effect

- Crystallisation, grain-arrangement, mircostructure

- Segregation Casting of ingots

Shrinking effect

the top 12-15% of the total weight of killed steel ingot must be cut off (rimmed steel only 3-5%) Casting of ingots

Crystallisation, grain-arrangement, mircostructure

R – rate of crystall growing

R N N – number of crystal nuclei

ΔT Supercooling – under the equilibrium Casting of ingots

Segregation – normal segregation

During the solidification the liquid phase becomes enriched with alloying elements and impurities.

T R – rate of crystall growing The difference can be 300% for S P% 500-600% for P

S%

C%

Concentration of the liquid phase cross section of the ingot B [%] Casting of ingots

dendrite Segregation – inverse segregation

Because shrinkage the alloying elements and impurities can move inwards between dendrites. liquid phase

The impuritiy concentration is higher Concentration % between the dendrites’ arm. Casting of ingots

Microstricture and segragation in ingot

http://www.substech.com/ Casting of ingots Continuous casting Continuous casting

• https://www.youtube.com/watch?v=d- 72gc6I-_E Steel refining methods

All of these methods have a remelting and solidification period to:

- Decrease the dissolved gas content and the amount of inclusions - Produce a homogeneous fine grained crystal structure - Produce a homogeneous distribution of alloying elements

Used for

- tool steels - high alloy steels Steel refining methods

Vacuum arc remelting process

. Removal of dissolved gases, such as hydrogen, nitrogen and CO; . Reduction of undesired trace elements with high vapor pressure; . Improvement of oxide cleanliness; . Achievement of directional solidification of the ingot from bottom to top, thus avoiding macro-segregation and reducing micro-segregation. Steel refining methods

Vacuum induction remelting process

. Removal of undesired trace elements with high vapor pressures

. Removal of dissolved gases (hydrogen and nitrogen) Steel refining methods

Electroslag remelting process

Similar technology: electron beam remelting process

http://www.substech.com/ Materials engineering

Steels Outline of todays lecture

• Alloying elements • The effect of carbon • The effect of alloying elements on – microstructure – Grain size – softening during tempering – Embrittlement during tempering – Ductile-brittle Transition temperature – Temperature of recrystallization – Mechanical properties of ferrite – Forming of carbides and nitrides Basic alloying and impurity elements

. Basic alloying elements . C – primer alloying element . Mn – austenite producing element . Si – ferrite producing element

. Main impurity elements . S – hot and cold brittleness . P – hot brittleness . O – gas inclusions (CO) . N – ageing Effect of C% on properties – annealed state

Contraction Z

Impact Energy , KV

Elong.

Hardness HB, Strength (MPa) Strength HB, Hardness (J) E Imp. (%) contraction Strain,

Carbon % Structural steels Tool steels Effect of C% on properties

Quenched state

Annealed state

Non-heat Heat treatable treatable The effect of alloying elements on the properties of steel

1. Solubility – ferrite or austenite producing elements 2. Non-equilibrium  transformation 3. Austenite grain growth γ α 4. Softening during tempering 5. Embrittlement during tempering 6. Ductile-brittle transition temperature 7. Recrystallization's temperature 1. Does it dissolve in the steel?

• Does not dissolve – Produces inclusions, disadvantageous – S, As, Pb…

• Dissolves – Dissolves better in ferrite – ferrite producing element • Cr, Al, Si, W, Mo, V, Ti

– Dissolves better in austenite – austenite producing element • Ni, Mn, C, N, Cu Microstructure, C and alloy content

austenitic

Ledebutitic

Semi-austenitic

Alloy % Alloy %

Ferritic- Ferritic- Ledebutitic Perlitic+ Perlitic+ perlitic perlitic Sec.Cem Sec.Cem

Ferrite producing Austenite producing element element Change of transformation’s temperature 2. Effect of alloying elements on non-equilibrium transformation

• All alloying elements decreases the Ms and Mf temperatures, except Co and Al.

• The present of residual austenite increases. – Deep cooling if necessary

• The CCT curves are shifted to the left. – The critical cooling rate is decreasing.

• Hardenability, trough hardening diameter increases. Conditions of quenching

• Importance of quenching: with quenching&tempering (allotropic transformation) the properties can be influenced in wide range.

• Conditions

– Heating to the temperature of A3 + ~50°C – Keeping at constant temperature till material is fully austenitized – Cooling faster than the critical cooling rate. – Practical condition: C > 0.2% C10 Practical conditions

The alloying decreases the critical cooling rate

MS = 480 °C and the Ms temperature.

vcritical

C45 MS = 340 °C vwater

voil

~0,22 C (%) Effect of through hardenability The trough hardening diameter

The maximal diameter of a bar, which can be quenched to contain 50% of martensite.

(see more: lab practice…)

Martensitic layer

T cooling

vcritf

Temperature distribution Distribution of cooling rate The efect of alloying elements on through hardenability

Mn Mo Cr

Si Ni

Co V austenitizing at 950

D - through hardenability and 1100 °C Alloying (%) Application of Jomminy test results

• Verification of material – Harness according to the

standards Hardness • Technology information – Maximal/minimal hardness by quenching – Harness distribution in the cross section Distance from quenched end 3: The effect of alloying on the austenite grain growth

• Mn, Si and B increases the susceptibility to grain coarsening

• Grain refining effect: Ti, V, Nb, Al, Zr – Producing fine uniformly distributed nitro-carbides on the grain boundaries, what decreases the boundary migration.

• Other has no significant effect of grain coarsening. 4: The effect alloying on softening during tempering

Temperature of 1 hour tempering Temperature of 1 hour tempering 5: The effect of alloying on the embrittlement during tempering

• Cr, Mn causes brittleness if slowly cooled at 500-650°C • Reason: Enrichment of Carbides, nitrides, phosphides at grain boundaries • P makes it worse. • Ni together with Cr and Mn is disadvantageous • 0,2…0,3% Mo or 0,5-0,7% W and fast cooling is

Impact energy Impact advantageous.

Tempering temperature, °C 6: The effect of alloying on the Ductile--brittle Transition temperature

• Ni alloying shifts the Impact energy–temp. diagram to the left. – 1% Ni alloying ~20°C shift

• Grain refinement helps as well – Nb, V, Ti, Al, Zr, N microalloying ~40°C effect

• Impact energy–temp. Diagram is shifted to right (makes it worse) – C, 0.1% C ~25°C – P, 0.1% P ~55°C – N, 0.01% N ~300°C (as solution) – O, 0.01% O ~200°C (as solution) 7: The effect of alloying on the recrystallization temperature

• The alloying increases the heat and creep resistance. – W, Mo ~110°C / at% – V ~55°C / at% – Cr ~30°C / at% Classification of steels Classification according to 1) Steel production methods (old category) 2) Structure at room temperature 3) Content of alloying elements 4) Purpose of utilization Content of alloying elements

Plain (carbon) steels Because of the steel making process contains unavoidable elements Mn < 0.8% Si < 0.6% Cr,Ni,Cu <0.3% Mo,W < 0.2% Al, Ti, V, Nb < 0.05%

Alloyed steels - micro alloyed steels alloy < 0.1% (Ti, Ni, V, …)

- low alloyed steels Σ alloy < 3 % - medium alloyed steels Σ alloy < 10 % - high alloyed steels Σ alloy > 10 % Σ Structure at room temperature

austenitic

Ledebutitic

Semi-austenitic

Alloy Alloy % Alloy %

Ferritic- Ferritic- Ledebutitic Perlitic+ Perlitic+ perlitic perlitic Sec.Cem Sec.Cem

. Ferritic • Ledeburitic - Ferrite producing element • Semi austenitic . Semi ferritic • Austenitic . Hipoeutektoidic . Hipereutektoidic – Austenite producing element Structure at room temperature

• Perlitic • Martensitic • Austenitic • Ferritic • Bainitic Utilization

• Structural steels – Automotive industry, machine industry , steel structures – Toughness is also a requirement – C < 0,6%

• Tool steels – Machining and forming tools – Wear resistance, stiffness, hardness – hardenable, precipitation hardenable alloys

• Special steels and alloys – For a specific purpose • Heat resistance, corrosion resistance etc. Designation of steels

According to different standards Most well-known standards:

. International Standard Organization ISO . American Iron and Steel Institute AISI . Society of Automotive Engineer SAE . American Society for Testing and Materials ASTM Designation of steels

Example: number (werkstoffnummer)

Material group 1 – steels Steel group 2 – heavy metals 3 – light metals 1.43 00 xx 4 – nonmetallic … number

Auxiliary sign Short designation

sign Application Area Main prop. e.g.

S Structural steel ReH (MPa) S235

P Pressure vessel steel ReH (MPa) P275

L Pipe steels ReH (MPa)

E Steels for machines ReH (MPa) E235

B Steels for concrete ReH (MPa) … … …… Designation according to chemical composition

Carbon steels: C22, C60, C90, C120

Alloyed steels: 14NiCrMo13-4

high alloy steels: X8CrNiTi18-10 Structural steels

A: hot rolled structural steels B: flat steel products for pressure vessels Formable, weldable C: Steels for cold forming D: Heat treatable steels E: Case hardening steels F: Nitridable steels G: …other A: Hot rolled unalloyed structural steels

• For general purpose • Hot rolled of forged state

• Certificate: Rm, ReH, A, KV, chem. comp • Can not be used in some cases – Carbon equivalent ( less than 0,5%, see later) • Various types • E.g.: S235JR A: Normalized rolled, weldable, fine-grained steels

• Normalized during rolling • Grain size number greater than 6 • Auxiliary mark: – N: normalized – L: impact energy 27 J at -50°C • E.g.: S275N, S275NL A: Thermomechanical rolled, weldable, fine-grained steels

• Thermomechanical rolling: controlled recrystallization during deformation • Nb alloying increases the recrystallization temperature • The grain refinement is promoted by Ti-alloying • Auxiliary mark: M • E.g.: S355M, S355ML A: Thermomechanical rolled, weldable, fine-grained steels II.

• Hydrogen resistant steels • Problem: H makes the iron carbide dissociate – Higher temperatures speeds up the process (T>200°C) – Tensile stress speeds up the process • Solution: stabile carbide producing alloying elements – Cr, Mo, V, W • Better heat resistance, used in heat treated state • Oil industry, refineries, hydrogen appliances A: atmospheric corrosion resistant (weathering) steels

• The steel corrodes. Pores. • Cu, Cr, P, Ni, Mo alloying (low content!) • Forming of phosphate, sulfate, hydroxide compounds – closes the pores, the corrosion stops. • Passive layer, red-brown color, < 0.3 mm • E.g.: S235J0W, S355J0WP A: Sheets and bands for high strength heat treatable steels

• Welded structures for high load at low or environment temperature. • Containers, bridges cranes etc. • Auxiliary mark: Q • Weldable but susceptible to cold cracking • E.g.: S460QL B: Plain and alloyed steels for elevated temperatures

• Plain steels (e.g.: P235GH) – Yield stress or creep strength is given – Steam boilers, pressure vessels – Up to ~400°C- • Alloyed steels(e.g.: 12CrMo9-10) – Mn, Mo, Cr, V, Nb and Si, Ni for weldability – boilers, heat exchanger, chemistry appliances, flanges, fasteners – Up to ~500-530°C B: Weldable fine-grained normalized steels

• Three sub-classes – Room temperature quality (P…N) • T > -20°C – Heat resistant quality (P…NH) • T= -20…400°C – Sub-zero toughness (P…NL1 and P…NL2) • Not brittle even at T=-40 or -50°C • Grain size number is greater than 6 • Welding: carbon equivalent B: Cryogenic Ni alloyed steels

• The impact energy is prescribed for structures • Below -60°C Ni alloying • FCC lattice not sensitive to embrittlement • Selection according to temperature and thickness • Acceptable impact energy even at -200 °C • Cooling and cryogen technology • E.g.: 11MnNi5-3, 12Ni14, X7Ni9 B: Weldable fine-grained thermomechanical rolled steels

• Nb alloying to increase the recrystallizations temperature • Ti alloying to grain refining • V and Mo alloying to strengthen • Auxiliary mark: M • E.g.: P355ML1 B: Weldable, fine-grained heat treatable steels

• Three sub-classes – Room temperature quality (P…Q) – Heat resistant quality (P…QH) – Sub-zero toughness quality upto -40°C-ig (P…QNL1), up to -50°C-ig (P…QNL2) • Micro alloying elements for grain refining and strengthening (Ti, Nb, V, N, B) • Weldability is influenced by: thickness, input energy, design, welding process, electrode B: Corrosion resistant steels

• Ferritic steels – Weak corrosive environment; pressure vessels, food industry appliances – Up to 350°C 155-215 MPa yield stress • Martensitic steels – Pump parts, valves, turbine impellers – Up to 300°C-ig 530-580 Mpa yield stress • Austenitic steels – Wide range of application – From -196 to 600°C applicable (FCC, no susceptibility to embrittlement after solution heat treatment, there is no TTKV) • Ferritic-austenitic (duplex) steels C: Cold rolled flat products from low carbon steels for cold forming

• Low carbon content, ferritic steel • Very low alloy content • DC01…DC06, : A, or B – surface quality – A: surface insufficiency (e.g. scratch) allowed – B: no surface imperfection allowed • Surface roughness grades – Shiny, matt, normal, rough • E.g.: DC01Am C: Cold rolled uncoated steel band for cold forming

• With less than 600 mm, thickness lass than 10 mm un-alloyed and alloyed steel band • designation: – Annealed (A) – Cold rolled (C ) – Skin passed (LC) – Surface quality MA, MB and MC • E.g.: DC03C440MB C: Hot rolled high strengh steel flat products for cold forming

• For cold forming, hot rolled, weldable high strength, alloyed • Thermo mechanical or normalizing rolled • Low Perlite steels (Ti, Nb, V) – HSLA • E.g.: S420NC, S460MC • Plastically formable, shearable, bendable, machinable • Welded structures, automotive industry DP Steels

• Dual Phase steels – very hard martensite finely distributed in soft ferrite matrix

• Good strength, good formability

• Wheels, car body, bumper, wires, building structures TRIP steels

• TRansformation Induced Plasticity

• Ferritic-austenitic-bainitic microstructure after hot forming

• Austenite transforms to martensite during further forming

• car body, vehicle industry DP / TRIP

DP TRIP IF steels

• Interstitial Free • Extra low content of alloying elements (30-60 ppm) • Good deep drawability, formability, no aging • Household appliances, vehicle overlay parts BH steels

• Bake Hardening • Low carbon content alloys, precipitation hardenable at ~200°C • Increases the yield stress by ~40 MPa though precipitation hardening (C and N) • E.g.: after forming during painting • Vehicle body elements D: Heat treatable steels

• Must be tough enough and resistant to dynamic impacts • Fasteners, pins, joints, beam structures, wrenches, axle, cardan cross, gears, etc. • Unalloyed and alloyed steels • Purpose of alloying: – Increase the trough hardening diameter – Increase toughness, decrease TTKV – Improve fatigue resistance – Decrease softening during tempering D: Unalloyed Heat tretable steels

• Only carbon, no additional alloying element (except elements from production) • Higher toughness, lower strength • Small trough hardening diameter • Wear resistance can be improved by surface quenching

• Rm: 500…1000 MPa, ReH: 300-580 Mpa, A: 20-11%, Z: 50-20% • designation: Cnn, where nn = C% • Auxiliary marks: E: S < 0.035%, R: 0.020 % < S < 0.040% D: Alloyed Heat tretable steels I.

• Mn (1.4-1.65%) – cheap – Increased trough hardening diameter – Susceptibility to over heating and embrittlement during tempering (fast cooling necessary) – Must not be used for parts with service temperature below 0°C – E.g.: 28Mn6 D: Alloyed Heat tretable steels II.

• Cr (even 2%) – Most common alloying element – Strongly Increases the trough hardening diameter and yield stress – Good surface hardenability – For low to middle stresses, engine parts, axles – E.g.: 34Cr4 D: Alloyed Heat tretable steels III.

• Cr-Mo (even 2% Cr, 0.9-1.2% Mo) – Mo eliminates the embrittlement during tempering – Cr and Mo are strong carbide-forming elements, tempering at higher temperatures (~600°C) – Significant strength and good toughness – For middle sized part for high fatigue and impact loads. Axles, parts with teeth – E.g.: 50CrMo4 D: Alloyed heat treatable steels IV.

• Cr-V (0.7-1.1% Cr, 0.1-0.2% V) – Similar to Cr-Mo steels – a little cheaper but worse toughness – For middle sized part for high fatigue and impact loads.

– E.g.: 51CrV4 D: Alloyed heat treatable steels V.

• Ni-Cr-Mo(-V) (0.7-1.1% Cr, 0.1-0.2% Mo) – Large sized parts where the fast cooling can not be realized. • Ni decreases the ductile to brittle temperature (TTKV) • Mo eliminates the embrittlement during tempering – Though hardening diameter increases significantly (~150 mm) – Engine parts, crankshaft, quenched&tempered state – E.g.: 36NiCrMo16 D: Alloyed heat tretable steels VI.

• Boron steels – Mn, Mn-Cr alloying, B micro alloying – Though hardening diameter increases significantly – Delivered generally in hot formed state – Good toughness – E.g.: 20MnB5, 27MnCrB5-2 E: Case hardening steels

• Carbon content below 0.2% • Tough core and wear resistant surface layer ~1%C in the surface layer, 60-63 HRC • Can be used up to the diameter of ~80 mm (through hardenability) • Heat treatable steels have higher strength for the same toughness • No carburizing for fatigue loaded parts, 35-45 HRC E: Unalloyed case hardening steels

• Small size parts for modest loads • pins, gear pumps • Harness: 55-60 HRC • Up to 20-30 mm size • E.g.: C10, C15 E: Alloyed case hardening steels

• Alloying elements are the same as those of heat treatable steels • Low carbon content, C<0,2% • Cr-Mo alloying for middle sized and loaded parts (bush, pin, gears) – Susceptible to overheating, up to the diameter of 40-60 mm • Mn-Cr-Mo alloying for highly loaded parts (gears, chain wheels, axles) – up to the diameter of 70-80 mm • Ni-Cr-Mo alloying for extrem strong dynamic loads tough core, high surface hardness F: Nitridable steels

• They are basically heat treatable steels • Aim: very hard wear resistant surface layer • Addition of nitride-forming elements (Cr, Al, V, Ti) • Results: wear-resistant, hard, better fatigue- resistance. Sensitive to high local pressures • E.g.: 34CrAlNi7-10 Other structural steels

• Free-cutting steels • Steels for roll-bearings • Spring steels • Steels and nickel alloys for cryogenic and Low- Temperature application • Heat resistant steels and nickel alloys • Steels and alloys for valves of internal combustion engines Free-cutting steels

• For high performance machining cells • aim: brittle chip • S and S+Bi alloying • E.g.: 11SMn37, 10S20, 44SMn28 Steels for roll-bearings

• High wear resistance and fatigue limit

• Carbon content 0.85-1.1% - hardness – S < 0.015%, P < 0.025%, O < 0.,002% – Polishing – fatigue

• Quenching, cooling to lower temp. (-30°C), low temperature tempering – 62 HRC

• E.g.: 100Cr6, 100CrMnMoSi8-4-6, 19MnCr5, 18NiCrMo14-6, 70Mn4, KO:X65Cr14, X89CrMoV18-1, 80MoCrV42-16, X82WMoCrV6-5-4 Spring steels I.

• Storing of elastic energy • High yield stress (1000-1350 MPa) and acceptable ultimate tensile strain are necessary (6-8%) • Heat treatable steels, 0.4-0.7% C-content, low temperature tempering (450-480°C) • For different purposes Spring steels II.

• Heat treated springs from hot rolled steels by forming

– Si alloying, ReH increases – Cr-V, Cr-MoV high performance, high dynamic loads – E.g.: 38Si7, 60SiCrV7, 60CrMo3-2 • Cold rolled narrow steels trip for heat treatment

– Good surface quality, Rm up to 2100 MPa – E.g.: C75S • Corrosion resistant steels strip for springs – For corrosive media Steels and nickel alloys for cryogenic, low- temperature and heat resistant application

• Unalloyed / alloyed (corr. resistant too) • Applicable up to 900°C • Mo: carbide-forming increases strength • The corrosion must be taken into account beside of heat-loading. – E.g.: 42CrMo5-6, 25CrMo4, NiCr20TiAl (Ni alloy), X10CrNiMoMnNbVB15-10-1

• Ni alloying for low temperatures – E.g.: 41NiCrMo7-3-2, X8Ni9, X6CrNi18-10 Heat resistant steels and Ni-alloys I.

• Problem: Oxidizing of steels’ surface over 500°C • Austenitic, ferritic, austenitic-ferritic steel • Creep resistant and strength are the characteristic properties • Alloying with Cr, Si, Al • Applicable even at 900°C-ig • Groin coarsening can be a problem • Ni based superalloys (not iron alloys!) Heat resistant steels and Ni-alloys II.

• Ferritic – Susceptible to grain coarsening and embrittlement at 350- 550°C and over 900°C, better in S-containing environment, e.g.: X10CrAlSi18 • Austenitic – Grain coarsening is not significant even at higher temperatures, between 600-800°C the σ-phase causes brittlement, e.g.: X10NiCrAlTi32-21 • Austenitic-ferritic – In oxidizing S-containing environment, e.g.: X15CrNiSi25-4 • Ni alloys – Jet engines, rocket industry, e.g.: NiCr23Fe Steels and alloys for valves of internal combustion engines

• Homogeneous microstructure, high alloying, calculable thermal expansion • Loads: unsteady temperature, corrosion, oxidation, fatigue, strike, wear • Bars, wires • Hot formable, hard to machine • Main types – Martensitic valve steel e.g.: X40CrSiMo10-2 – Austenitic valve steel e.g.: X50CrMnNiNbN21-9, NiFe25Cr20NbTi Hadfield steels

• Austenitic, high alloyed Mn steels – ~1.2%C, ~0.4 Si, ~12.5% Mn • Impact wear resistance, hardening during wear (cold forming) • Inner not-hardened layer gives good toughness • For dynamic and wear loads • Railroad switches, excavator bucket, Tool Steels

• A: Unalloyed tool steels • B: Hot forming tool steels • C: Coldforming tool steels • D: High speed steels General requirements

• Harness, wear resistance • toughness • Heat resistance • Resistance against thermal fatigue • Appropriate trough hardening diameter A: Un alloyed tool steels

• 0.45-1.25% C content – 0.45% C – 54 HRc – 1.125% C – 62 HRc

• Only base alloying and impurity elements (Mn, Si, S, P) • For hand tools • E.g.: C90U, C100U – U mark: un-treated state B: Hot forming tool steels

• Service temperature over 200°C, but hardness and heat resistance even at 600°C (38-46 HRc)

• Main alloying elements: Cr, Mo, W, Ni, Co

• Carbide compounds– hardness at high temperatures

• Closed-dies for forging, die-casting dies

• E.g.: 55NiCrMoV7, X40CrMoV5-1 C: Cold forming tool steels

• Main alloying elements: Mn, Cr, Mo, V, W, Ni • To increase through hardening diameter and improve – strength – Wear resistance – Hardness

• Heat-treated. Service temperature at room temperature (maximum 150-180°C) • E.g. Cutting and punching tools • E.g.: 95MnWCrV5, X210CrW12 E: High speed steels

• For high performance machining. 62-64 HRc harness at ~600°C • Main alloying elements : W, Mo, V, Co • Special heat treatment method. (precipitation hardening) • E.g.: HS6-5-2, HS10-4-3-10 Corrosion resistant steels

• A: Ferritic corrosion resistant steels • B: Martensitic corrosion resistant steels • C: Austenitic corrosion resistant steels • D: Duplex (austenite + ferrite) corrosion resistant steels A: Ferritic corrosion resistant steels

• The alloying element forms a cohesive, non-porous surface layer preventing the further oxidation. • Max 0.08% carbon in ferritic corrosion resistant steels and ~13% Cr alloying

• ReH ~280-320 MPa, A=18-20% • Good formability and weldablility • Good corrosion resistance in wear and modest corrosive media: food industry, beer- and milk industry • For some purposes: semi-ferritic steel – increased strength (chemical industry) • E.g.: X2CrTi12, X6CrMo17-1, X2CrMoTi29-4 B: Martensitic corrosion resistant steels

• ferritic corrosion resistant steels are not strength enough  higher C content & heat treatment

• Heat treatment: quenching + tempering

• C content: between0.08% and 1.2%

• Surgery blades, scalpel, needles, food industry blades

• E.g.: X12Cr13, X105CrMo17, X7CrNiAl17-7 C: Austenitic corrosion resistant steels

• Ferritic corrosion resistant steels does not have good resistance against strong acids. • Austenitic steel – C<0.03% + ~18% Cr + ~10% Ni (Mn, Cu, N)

• Cr-cardibes form at grain boundaries by slow cooling at 600-800°C, which spoils the corrosion resistance – Can prevent by alloying of Ti and Nb

• Difficult to machine • E.g.: X10CrNi18-8, X3CrNiMo17-13-3 D: Duplex corrosion resistant steels

• High Cr and Ni content • ~40-60% austenite at room temperature • Higher strength • Better stress-corrosion resitance • Can be applied as heat resistant steel as well. • E.g.: X2CrNiN23-4, X2CrNiMoCuWN25-7-4 Corrosion resistant steels Materials engineering

Cast Irons Outline

• Properties of cast irons – Microstructure – Mechanical properties

• Types – Gray cast iron – White cast iron – Nodular cast irons – Malleable cast irons Properties

Cast Iron C = 2.1 ~ 6.67%

Properties depend on 1) Carbon content 2) Cooling rate of the casting 3) Alloying elements Carbon content

1) Degree of solution

퐶% 푇 = .−0.푆푖%+푃% T>1 Hypereutectic Ledeburite + Pr. Cementite

T=1 Eutectic Ledeburite

T>1 Hypoeutectic Ledeburite + Perlite Cooling rate

2) Cooling rate

Slow cooling rate Iron + Graphite section size > 10 mm

Quick Cooling rate Iron + Cementite section size < 10 mm Cooling rate

2) Cooling rate Fe - graphite

Fe - cementite Alloying elements

Graphite producing elements Co, P, Cu, Ni, Ti, Si, C, Al

Carbide producing elements W, Mn, Mo, S, Cr, V, Mg, Ce

The microstructure depends on: - Carbon and Silicon content - Section size (cooling rate) Maurer diagram

Gray cast iron (Stable)

Ferrite + Graphite

White cast iron (metastable) Microstructure

Hypoeutectic white cast iron Hypereutectic white cast iron Perlite and ledeburite Primer cementite and ledeburite

Gray cast iron Gray cast iron Ferrite and graphite Ferrite, perlite and graphite Greiner - Klingenstein diagram

At a given C+Si% the graphite producing elements’ effects

increases with increasing section size C + + Si C %

Ferrite + Graphite

Perlite + Graphite

Ledeburite+ 10 20 30 40 50 60 70 Perlite Wall thickness (mm) L + P + G Typical chamical compossition for gray cast iron: C % Si % Mn % S % P % 2.5-3.5 1-3 0.5-1 <0.1 <0.3

Mechanical properties of cast iron

Strength Tensile Tensile

400

100

Ferritic Perlitic microstructure microstructure

Graphite’s effect on Tensile strength - graphite produces notch effect - graphite excludes parts in the matrix Mechanical properties of cast iron

Disadvantage of cast iron - gray cast iron has low strength - gray cast iron has no plastic strain = brittle

Graphite forms in gray cast iron Mechanical properties of cast iron

Advantage of cast iron

- Good compressive strength

- high damping capability (tool machines)

- good machinability

- good wear resistance (graphite as lubricant)

- lower cost Utilization of gray cast iron

Machine stands, engines, etc Increasing the strength of cast iron a) Increase the perlite amount in the matrix b) Modify the shape and distribution of the graphite flakes c) Alternating the graphite’s geometry from flake to spheroidal graphite Increasing the strength of cast iron

Increase the perlite amount in the matrix

Ferrite + Graphite

ASTM A438 TS (ksi) TS (MPa) T Class 20 150 1 30 200 0.94 35 250 0.88 Increasing the strength of cast iron

Modify the size and distribution of graphite flakes

FeSi and CaSi as centers of crystallization (nucleation) Method: Overheating the molten iron and alloy FeSi ~0.5% CaSi 0.5~1% - finer flakes - higher strength

ASTM A438 TS (ksi) TS (MPa) T Class 40 300 0.8 50 350 0.76 60 400 0.72 Increasing the strength of cast iron

Alternating the graphite’s geometry from flake to spheroidal graphite Ductile or Nodular cast iron Mg and Si alloying Mg alloying by Fe-Cu-Mg and Fe-Ni-Mg

F + Sph + Si % C=3.5% Graphite flakes 400 F + P +Sph +

Graphite flakes

spheroidal gr.

+ +

Graphite flakes Graphite flakes

+ + F + P + Sph.

+ +

Ferrite Ferrite 100 F + Sph. + Carbides

Mg % Microstructure

Ductile cast iron Ferrite and spherical graphite

20 µm

spherical graphite in gray cast iron

Ductile cast iron Ferrite, Perlite and spherical graphite Utilization of ductile cast iron

Machine parts, gears, pipes, crankshaft, etc Increasing the strength of cast iron

Ductile or nodular cast irons

ASTM A395 TS (MPa) YS(MPa) El (%) structure

Grade 60-40-18 400 250 18 Ferrite

Elongation (%) Yield Stress (ksi) Tensile strength (ksi)

Grade 80-55-06 600 370 6 F + P Grade 100-70-03 700 420 3 P (AQ) Grade 120-90-02 800 480 2 M (Q+T) Malleable cast iron

Convert iron-carbibe to temper carbon increases the ductility Black heart malleable cast iron

Ferritic structure with temper carbon ASTM A47 TS (MPa) YS(MPa) El (%) Grade 325-10 400 130 10

Ledeburitic-perlitic structure 940 ºC

T (ºC) T neutral Iron carbide dissociates to Fe and C atmosphere Austenite transforms to ferrite and graphite 723 Ferrite + temper carbon

100 12 – 48 hours

time White heart malleable cast iron

Ferritic structure with low carbon content ASTM A47 TS (MPa) YS(Mpa) El (%) Grade 450-06 310 175 6 Grade 600-04 420 250 4 Grade 800-02 550 340 2 Grade 900-01 650 430 1

Ledeburitic-perlitic structure 1000ºC C = ~ 3%

T (ºC) T oxidizing Iron carbide dissociates to Fe and C atmosphere 723 Carbon diffuses to the surface and burns there.

Ferritic structure , low carbon C = ~ 0.1% 100 25 -100 hours time Microstructure

Black heart cast iron Temper-carbon in ferrite matrix Utilization of malleable cast iron

Machine parts, machine stands, etc Materials engineering

Casting Outline

• Solidification of metals • Fluid flow, effect of cooling rate • Cast defects • Metal casting processes – Sand mold casting – Shell-mold casting – Investment casting – Evaporative-pattern Casting – Permanent mold casting – Pressure die casting – Centrifugal casting History

. B.C. 3000-1500 Bronze age (tin-bronze)

. B.C. 224 Colossus of Rhodes (32 m high, bronze)

. 1252 Great Buddha, Japan(120 t (9% Sn, 20% Pb))

. 1400 Yongle Great Bell (China, Beijing) 46 t, 120 dB-20 km)

. 1586 Tsar cannon

. 1709 Cast iron bridge (USA Coalbrookdale)

. 1735 Tsar Bell (193 t) History

1252 Great Buddha, Japan(1252 , 120 t (9% Sn, 20% Pb)) History

Great Bell (China, Beijing, 46 t) 120 dB - 50 km History

Cast iron bridge (1709, USA Coalbrookdale) History

Tsar Cannon (1586, 193 t) History

Tsar Bell (1735, 193 t) Casting process

The casting process basically involves: (a) pouring molten molten metal into the mold cavity (b) solidification and cooling of the metal in the mold (c) removing the part from the mold. Efficience and energy consumption

Utilization of the mat. Process Energy consumption

Casting

Powder metallurgy (1kg product)

Cold and warm forming

Closed die forging

Machining Solidification of pure metals and eutectic alloys

Latent heat Solidification takes place at a constant temperature

Pure metals and eutectic alloys - good castability Solidification of alloys

time

columnar dendrites („tree shape”)

Solidification takes place in a temperature range The effect of cooling rate

Slow cooling rates: coarse dendritic structures

Higher cooling rates: fine structure

Extreme high cooling rates: amorphous structure

As grain size decreases:

the strength and the ductility of the cast alloy increase microporosity in the casting decreases the tendency for the casting to crack during solidification decreases.

Lack of uniformity in grain size and grain distribution: anisotropic properties The fluid flow

Risers (feeders): reservoirs of molten metal prevent porosity due to shrinkage

mold cavity

gating system (sprue, runners, and gates) sand casting: traps contaminants Shrinkage Casting defects Casting defects - porosity

Porosity: caused by shrinkage, entrained or/and dissolved gases

Solution: Adequate liquid metal

Internal or external chills,

Hot isostatic pressing Metal casting processes Metal casting processes

Evaporative Invest- Permanent Centri- Sand Shell Plaster Die pattern ment mold fugal

Non- Non- material All All All ferrous ferrous

Weight 0.01 0.01 0.01 0.01 0.001 0.1 <0.01 0.01 Min

Max No limit 100+ 100+ 50+ 100+ 300 50 5000+

accep- Very Surface good acceptable good good good good table good

Shape Very Very good good good good good good complexity good good Dim. +0.005 - +0.001 - 1.6-4 mm +0.003 +0.005 ±0.015 0.015 tolerance 0.01 0.005 Min. 3 2 2 1 1 2 0.5 2 thickness Min. 10- 1 100 500 10 10 1000 10 000 quantity 10 000 Metal casting processes

Process / mass (kg) 0.01 0.1 1 10 100 1000 10 000 100 000

Sand Ra =100 μm

Shell Ra =10-25 μm

Investment Ra < 10 μm

Permanent Ra = 10-50 m mold μ

Die Ra =1.6 - 10 μm Sand mold casting

Cope (flask)

Pattern

Core-prints

Drag (flask)

Core Casting Shell mold casting

Sand + 2.5-4% 175-370⁰C resin binder Evaporative-pattern Casting (Lost-foam Process)

polystyrene pattern evaporates upon contact with molten metal

Coating with water-based refractory slurry & drying

The degradation products from the polystyrene are vented into the surrounding sand. Investment (precision) Casting

wax can be recovered and reused Permanent mold casting

2 halves of a mold: made from materials with high resistance to erosion and thermal fatigue, (cast iron, steel, bronze, graphite, or refractory metal alloys)

Mold cavity and gating system are machined into the mold + cores made of metal or sand aggregate

The molds are clamped together heated to 150° - 200°C

The process is used mostly for aluminum, magnesium, and copper alloys, gray iron, lower melting points

Steels: graphite or heat-resistant metal molds. good surface finish, close dimensional tolerances, uniform and good mechanical properties, and at high production rates. (Pressure) Die casting

Hot-chamber process

Dies are cooled by circulating water or oil: Pressure: up to 35 MPa - to improve die life - rapid metal cooling (reducing cycle time)

Cycle times: 200 - 300 shots per hour for zinc (Pressure) Die casting

Cold-chamber process

Pressure: 20-70 MPa Centrifugal casting

Sand-mold casting http://www.youtube.com/watch?v=K8SYhISGxN4

Evaporative-pattern Casting http://www.youtube.com/watch?v=HFITqk2KTjw

Investment casting: http://www.youtube.com/watch?v=BX8w-GUPz1w

Hot chamber die casting http://www.youtube.com/watch?v=bzSSfBgkWfc

Centrifugal casting http://www.youtube.com/watch?v=DjWJcCCupaY from 3:00 to 4:00 Materials engineering

Powder metallurgy Outline

• Process of powder metallurgy

• Production of metal powders

• Compaction

• Sintering

• PM products Introduction

. During powder metallurgy processes metal powders are - compacted into desired shapes and - sintered (heated without melting the metal) to form a solid part.

. net-shape forming Process of powder metallurgy

http://www.youtube.com/watch?v=O7U4HWjYcqo Powder producing process

. Reduction of metal-oxide . Atomization of molten . Electrolytic Deposition metal . Carbonyl process . Mechanical comminution Powder producing process

Atomization: injecting molten metal through a small orifice; the stream is broken up by jets of inert gas, air or water

For low melting point materials: Sn, Zn, Al, Cu etc

Drop size: 200-400 μm Powder producing process

Mechanical comminution

Roll crushing Ball milling Hammer milling

For brittle alloys and carbides

Particle size: 20-400 μm Powder producing process

Reduction of metal oxide: W, TiC, Ta

WO3+3H2 → W + 3H2O W + C → WC ~1500°C in vacuum particle size: 0.5 ~10 μm

TiO2 + 2C → TiC + CO2

Co3O4 + 4H2 → 3Co + 4H2O particle size: ~0.5 μm

very fine metallic powder with spherical shapes Powder producing process

Carbonyl process: Unstable carbonyl compound Me + n(CO) → Me(CO)n

Decomposition

Me

Fe, Ni and Co Expensive Extra clean and fine sized (~0.1μm) Fe can be produced Powder producing process

Electro deposition:

Electrolytic deposition utilizes either aqueous solutions or fused salts. One of the purest method. Blending Metal Powders

. Mixing of metal powders according to the desired chemical composition. . Uniformity of mechanical properties throughout the part. . Lubricants can be mixed with the powders to improve their flow characteristics. . Other additives, such as binders Compaction of Metal Powders

. Brittle . High porosity Compaction of Metal Powders

Cold Isostatic Pressing

Hot Isostatic Pressing

uniform grain structure and density

almost 100% density Sintering

A process whereby green parts are heated in a controlled atmosphere furnace to a temperature below the melting point, but sufficiently high to allow bonding by fusion of the powder particles

Initial unsitered Sintered powder powder particles particles

Depending on temperature, time, and the processing history, different structures and porosities can be obtained which affect the properties. PM products

Iron powder products

Volume porosity > 30 % filters 18-30% bearings (oil soaks up into the pores) 7-18% textile machine parts, oil pump gears <7% heat treatable parts, soft magnets

Copper powder products

Oxygen-free Cu – the best conductivity (wire)

Bronze powder products

Copper and Tin powder + small percent of graphite are sintered („solide sponge”)

Porous bronze bearings (oil soaks up into the pores, low friction) PM products: Hard Metals

. High hardness at elevated temperatures (e.g. HRc > 55 at 900°C) . High wear resistance

ISO HV B.S. WC TiC+TaC Co

P 0.1 1300 700 MPa 30 % 64 % 6 % … … … … … … P 50 1800 2100 MPa 68 % 15 % 17 % M 10 1750 1350 MPa 6 % … … … Rem. ~10 % … M 40 1300 2100 MPa 15 %

For cutting For K 0.1 1800 1200 MPa 4 % … … … Rem. 1-4 % … K 50 1300 2100 MPa 12 % G 0.1 1600 1500 MPa 92 % 6 % … … … … 1-2 % …

G 40 950 2800 MPa 69 % 30 %

forming For cold For PM products: ASP High speed steels

. Atomized powder loaded and vacuum sealed into steel container . Compacted at room temperature . Heated to 1150°C and compacted by hot rolling or forging (~ 100 MPa pressure) . Homogeneous carbide distribution . Bending strength is doubled . High hot hardness PM products

Cutting tools PM products

Filters, catalyzers PM products

Bearings PM products Machine parts Metals Technology

nonferrous metals Today’s topic

• Light metals – Aluminium and its alloys – Magnesium and its alloys – Titanium and its alloys • Heavy metals – Copper and its alloys – Other metals with technical importance Light and heavy metals

. Light metals according to the density lighter than 4.5 gcm-3 Al, Mg Be, Li…

. Borderline case… Ti, ρ≈4.5 gcm-3

. Heavy metals heavier than 4.5 gcm-3 Cu, Zn, Sn, Pb, Ni, W, precious metals Physical and mechanical character

-3 ρ (gcm ) ReH (MPa) ReH/ρ Tcreep (°C) Al and alloys 2,70 25-650 9-240 150-250 Mg and alloys 1,70 70-270 40-160 150-250 Ti and alloys 4,50 170-1300 38-300 400-600 Be 1,82 100-700 50-380 ~250 Cu and alloys 8,94 60-1400 7-150 Structural steels 7,90 180-1600 25-200 400-600 Physical and mechanical character

Rm E ρ Rm/ρ E/ρ $/t Cast iron 200 110 7150 280 154 900 Steel -soft 450 210 7860 573 267 600 -hard 1500 210 7800 1923 269 800 -corr. Res. 500 210 7930 631 265 2700 Aluminium -soft 70 70 2710 258 258 2000 -hard 450 70 2800 1601 250 2500 Copper -soft 140 120 8930 156 134 2000 -hard 400 120 8500 471 141 2000 Magnesium 250 42 1740 1436 241 6000 Titanium 1200 120 4580 2620 262 20000 Aluminium

• light, low density (ρ=2.7 gcm-3) • Low melting temperature (660°C) • Good electric conductor (~2/3 of that of Cu) • Good heat conductor • FCC lattice – Good formability, Z~90%, cold and hot • Good corrosion resistance (surface oxide layer) • Low strength

– Rm=40…120 MPa, Rp0,2=20-60 MPa • Low young modulus – E=70 MPa Strengthening

• Increasing the strength – Alloying – Cold plastic deformation – Heat treatment – precipitation hardening – Dispersion hardening – (Composites)

Some extra material with animations

http://aluminium.matter.org.uk/content/html/eng/default.asp?catid=7 1&pageid=2075282087 Alloying

• Produced in „pure” (99.5%) state. Even small amount of alloying elements has a significant effect. – Strengthen: Cu, Mg, Zn, Mn, Si – Decreases the grain size: Ti, Cr – Enhance the corrosion resistance: Mn, Sb – Enhanced the strength at high temperatures: Ni – Enhanced the machinability: Co, Fe, Bi

• Mots important impurities: Fe, Si Solid solution

• Alloying element as substitutional atoms in the lattice – Even H has place only in octahedral lattice sites

– Different effect on strength Yield Stress YieldStress (MPa) Alloying (weight%)

Atomic number

Atomic radius Solid solution - Alloys

Alloying (weight%) Al - Cu Al - Mg Al - Si General Al - Me

Liquid phase

Liquid ph

Liquid ph

C)

° Temperature ( Temperature

Concentration (weight%) Classes according to processing

T

a b

A B

Cast alloys

Formable alloys heat treatable, precipitation hardenable alloys Designation system formable castable Al 1xxx 1xx.x Al-Cu 2xxx 2xx.x Al-Mn 3xxx Al-Si 4xxx 4xx.x Al-Si(-Cu/Mg) 3xx.x Al-Mg 5xxx 5xx.x Al-Mg-Si 6xxx Al-Zn(-Mg) 7xxx 7xx.x Al-Li 8xxx Other elements 9xxx 9xx.x Al-Sn 8xx.x Not used 6xx.x 1xxx

. >99% purity - E.g. Al1050 – 99.5% Al . Can contains Fe and Si impurities . Good formability . Good corrosion resistance . Good conductivity . Sheet for deep drawing, foil, electric cables . Fe/Si influences the formability, - Fe/Si>2.5 advantageous 1xxx 2xxx

• 3-6% Cu alloying – 0.4-2.5% Mg 0.3-1.0% Mn 0.2-1.3% Fe 0.2-1.2% Si 1.0-2.0% Ni

• Heat treatable alloys

– 4% Cu + 2% Mg --- 440 MPa Rm and 320 MPa Rp0,2 – Military technology, automotive and aircraft industry 2xxx 3xxx

• <2% Mn alloying – Above compounds which spoils the properties • Non-heat treatable, can be strengthened by cold forming • Modest strength • Good formability • Good weldability • Good anodizability • Packaging, kitchenware, architecture 3xxx 4xxx

• Up to 17% Si alloying – Si as intermetallic phase, or as elemental Si brittle, non-formable • Low Si% : for cladding filler material for welding • Higher Si %: alloys for casting – Low melting point, low shrinkage, good fluidity • Adding Mg  heat treatable alloy(6xxx) strength increasing • engines, castings for modest loads and sizes, pistons 4xxx 5xxx

• 0.5-0.7% Mg alloying • Strengthening cased by Mg can be enhanced by cold working • Good formability • Good weldability • Good anodizability • Good corrosion resistance • Automotive industry, architecture, shipbuilding, chemical industry • With >3% Mg alloying the corrosion resistance decreases can be balanced with Mn 5xxx 6xxx

• 0.3-1.5% Mg and Si

• Precipitation hardenable alloys (Mg2Si) • Moderate to high strength • Good formability • Good weldability • Good anodizability • Good corrosion resistance • One of the most common Al alloy: electric industry, Automotive industry, architecture, machine industry, commodity • Mn and Cr addition: grain refinement, increased strength and toughness, decreased stress-corrosion resistance 6xxx 7xxx

• 4-6% Zn (and 1-3% Mg), „hard” alloys • Precipitation hardenable At 443°C ~70% Zn solubility  at 20°C 0.1% (!)

• Up to Rp0,2=600 MPa • Outstanding strength and appropriate formability • Automotive industry, architecture, sporting goods 7xxx 8xxx

• 1-5% Li alloying • The most light Al alloys – 1% Li alloying  ~3% decrease in density • Precipitation hardenable alloys • High strength • The production is relative expensive • Military industry, rocket and space technology Overview

Formable alloys Cast alloys Non-heat treateble (weldable) heat treateble - Good corrosion resistance high-strength Non-heat treateble heat treateble Good electric condictivity alloys Good formability Al-Mn Al-Si Al-Si-Mg Al-Mg Al-Mg-Si Al-Mg Al-Si-Cu Al-Mg-Si Al-Mg0.5-Si0,5 Al-Mg-Li Al-Mg-Si Al-Mg-Zn Al-Li-Mg Al-Mg-Li Al-Cu-Mg Al-Cu-Li Al-Cu Al-Cu-Li-Mg Al-Cu-Ni Al-Zn-Mg Al-Li-Cu-Mg Al-Zn-Si Al-Zn-Cu-Mg Al-Zn-Mg

Semiproducts

Primer metal Production of Treatment of Scrap metal molten metal molten metal Alloying e.

Casting of Continuous roll Mold casting ingots/billets casting

rolling Tube extrusion Forging Strip Wire Casting extrusion Hot rolling

drawing Cold rolling

Heat Heat Heat Heat treatment treatment treatment treatment

Holow Forged Strip Sheet Foil Tube Bar wire section part Casting of ingots and billets

• For the purpose of rolling or extrusion

• Basic procedures – Mold casting – Direct chill (or semi continuous) casting

• Possibilities to increase quality – Direct chill casting in electromagnetic mold – Hot top mold direct chill casting – Descaling of ingots Direct chill casting

Continuous roll casting

• Wires and strips • It is followed by rolling generally Continuous roll casting Continuous roll casting Casting of strips

belt Molten metal

Cast strip

Cooled plate

Twin-belt casting

Molten metal Molten metal Cast strip Cast strip

Block casting Twin roll casting Twin-belt casting

Tandem mill Hot rolls Molten metal Twin-belt caster Coiler Further processing

Billet for rolling Billet for extrusion . Hot rolling . extrusion . Cold rolling . Forging . Heat treatment . Tube production . Foil production . drawing . Heat treatment Further processing Magnesium

• Lowest density/mass. production for structural purposes, ρ=1,8 gcm-3 • Low melting point, ~650°C • Hexagonal lattice, low formability • The „future’s structural metals” – Low weight, automotive industry • Presently ~35% as Mg-alloys, the rest as alloying for aluminium and steel Technological properties

• Good machinability • Can be cast in faster cycles • Longer service time for cast-dies • High-end cameras, technical appliances, structural parts, airplane and rocket parts Magnesium alloys

. Cast alloys – Alloys with good castability – Mg-Al-Zn cast alloys

. Formable alloys – Al-Zn alloying – Mn alloying – Zr alloying – Zr-Th alloying – Rare earth element alloying – Li alloying Alloys with good castability

• Main alloying: 0.6-0.7% Zr, weldable – Don't: Al, Si, Fe, Mn, Co, Ni, Sb, Sn • Mg-Zr-Zn-RE alloys (Ce) – Complex parts, low eutectic temperature • Mg-Zr-Ag-RE alloys (Nd) – Thermal fatigue resistant up to 200°C • Mg-Zr-Y-RE alloys (Nd) – Good corrosion resistant and mechanical properties Mg-Al-Zn cast alloys

• More cheaper and widely used as the previous group – Susceptible to microporosity (wall thickness, die casting) • Mg-Al dual phase alloys – Precipitation hardenable • Mg-Zn dual phase alloys – Better toughness and corrosion resistance, precipitation hardenable • Mg-Al-Zn-Mn alloys – Enhanced corrosion resistance • Mg-Al-Zn-Si alloys

– Mg2Si precipitations, enhanced creep resistance • Mg-Al-Zn-RE alloys – Ce, La, Nd, Pr, precipitation, better creep resistance • Mg-Al-Zn-Cu alloys – Engines Formable magnesium alloys

• Mg-Al-Zn – Most common, moderate strength, rollable, weldable • Mg-Mn – For electrochemical purposes, cathodic protection of steels • Mg-Zn-Zr – Grain refinement, rollable, forgeable • Mg-Th – Increased heat resistance, radioactive • Mg-RE – Hot formable • Mg-Li – Good formability, excellent weldability Titanium

• Not really light (4,5 gcm-3) • Two allotropic forms – -titanium (hexagonal), producing e.: : Al, O, C, N – -titanium (BCC), producing e.: Mo, V, Nb; Mn, Fe, Cr, Si, Ni, Cu • Good strength/weight ratio • Good corrosion resistance • Biocompatible • Good strength at elevated temperatures • Not good formability and machinability • Strong oxidizing, deoxidizing and carbide forming element Important titanium alloys

• Pure titanium – Grade1…4, according to the solved oxygen • and quasi-α • α + β • β and quasi-β • Schäffler-diagram-like diagram – Mo and Al equivalent Titanium alloys and utilisation

. Corrosion resistant types – Unalloyed and low alloyed (Ti-0.2Pd), moderate strength

. High strength types – Yield stress over 800 MPa, up to 25% alloying, many types, aviation- and cryogen-technique

. Creep- and heat resistant types – Much higher strength than Ni-alloys up to 700°C, excessively expensive Titanium alloys and utilization

• Turbo-jet engines, gas turbines • Chemistry pumps, pipelines heat exchangers • Parts for racing machines • Armors, weapons • Medical tools, implants, prosthesis • Sporting goods • Watch production, optical tools • Architecture Titanium alloys and utilisation Copper

• Heavy metal (8,93 gcm-3), melting point: 1083°C • Good formability, FCC lattice • Soft, low strength

• Good electric and heat conductivity – Alloying spoils it – Most important impurity element: Oxygen, forms Cu2O eutectic at grain boundaries – brittleness

• Corrosion resistant

• Bronze and brass – Tin bronze, lead bronze, aluminium bronze, chrome bronze Copper Industrial coppers

• Copper containing oxygen(>99,9% Cu) – Good electric and heat conductivity – Produced by electrolysis (Cu-ETP) – Formerly fire refining (Cu-FRHC and FRTP (casting))

• Oxygen-free(deoxidized) copper – Deoxidizing with phosphorous – good weldablility – phosphorous spoils the electric conductivity • Cu-DHP: 0.013-0.5% P, Cu-DLP: 0.004-0.012% P

• Oxygen-free, high conductivity copper – Cu-OF: >99.95 Cu, Cu-OFE: >99.99% Cu (electronics) – Deoxidizing fire refinement Low alloyed copper alloys

• Cu-Ag – Minimal Ag alloying. Recrystallization temperature increases from 200 to 300°C, welding and soldering gun parts • Cu-Cd – strength, fatigue limit, creep limit doubled by cold working, spot-welding, toxic, prohibited • Cu-Te – Enhanced machinability and strength, higher recrystallizations temperature, conductivity decreases a little, laser-nozzle • Cu-Cr – 450 MPa strength by precipitation hardening, spot welding electrode, brake, high-performance switches • Cu-Be and Cu-Co-Be – 500 MPa strength by precipitation hardening, keeps this strength up to 300°C, springs, wisher, membrane, nonsparking switches, ¼ conductivity High alloyed copper alloys – Brasses I.

• Main alloy: Zn, 5-45% • The color changes with Zn% from red to yellow • Good castability, cold and hot formability • Deep drawable, machinable • Unalloyed Brass – α-alloy (Zn<33%) as above – α+β alloy (33%

α High alloyed copper alloys – Brasses II.

• Alloyed brass – Pb: spherical shaped grains, better machinability – Sn, Al, Si elements, phase producing elements, enhance the hot workability – Ni, Mn and Fe are α phase producing elements enhance the formability High alloyed copper alloys – Brasses III.

• The brasses have in general good corrosion resistance but over 15% of Zn two problems can appear: – Season cracking: residual stresses (welding), stress-corrosion, moist environment – Dezincing: the Zn is solved into the watery environment (primarily the high Zn-containing -phase). Process can be slowed with As alloying: admiralty copper High alloyed copper alloys – Bronzes I.

• Main alloying element is tin (Sn), 3-20% • Unalloyed bronzes – 3-20%Sn, except: bell bronze (20-25%) and speculum metal (30-35%) – Industrial bronzes: • Good formability, α bronzes, strength increases with increasing tin-content and cold deformation • Cast α+δ bronzes, properties depends on the hard δ phase (cooling rate!) Cu-Sn phase diagram

α Alloyed bronzes

• Additional alloying elements besides Sn

• Phosphorus bronzes (CuSn8P)

– Cu3P precipitations increases the strength

• Leaded bronzes (CuSn8Pb3Zn6) – Pb do not solve, good machinability, good lubrication properties (up to 30% Pb)

• Zinc bronzes (CuSn5Zn5Pb5) – Zn enhance the castability and formability water pipes and fittings Aluminium bronzes

• Aluminium bronzes (cupro-aluminium) – 4-14% Al resist to seawater, stress corrosion and corrosion-fatigue, high strength – Unalloyed: good formability, one or more phase (strength increases, toughness decreases) – Alloyed: Fe, Ni, Mn alloying • Enhanced corrosion resistance and strength • Ship propellers, turbine blades • Heat exchanger plates and tubes Al-Cu phase diagram Nickel bronzes

• Nickel bronzes (cupro-nickels) – Unlimited solubility between Cu and Ni • Good resistance in high-speed-streaming sea water • Few percent of Mn and Fe can be added • sheets, strips for general purpose, tubes for heat exchangers • Constantan: 40-45% Ni content, conductivity does not changes in wide range of temperature • Nickel silver (alpaca): Cu-Ni-Zn alloy, between brass and cupro-nickels – One-phase alloys with good formability – Hot workable, two-phase alloy with good machinability Ni-Cu phase diagram Other copper alloys

• Silicon bronzes (cupro-silicons) – Good friction properties, strength ans corrosion resistance

– CuSi3Mn, CuSi2Al2,5

• Lead bronzes – Good friction properties, plain bearings

– CuPb8, CuPb15, CuPb20, CuPb30

• Shape memory copper alloys – Reversible martensitic transformation – Cu-Zn-Al, Cu-Zn-Ni alloys Nickel

. Heavy metal, density 8,89 gcm-3 . Melting point 1440°C . FCC lattice . Excellent corrosion, heat and creep resistance . Energy, chemical and oil industry, airplane engines Corrosion resistant nickel alloys

• Unalloyed – chemical industry nickel two subtypes depending on C% – soft, can be strengthened by cold working, toughness decreases but, significant even at low temperatures • Ni-Cu Alloys– Monel – 28-34% Cu, high pressure water, steam and seawater pipes, brass instrument, evaporators • Ni-Cr-Fe and Ni-Mo alloys– Inconel, Hastalloy, Incoloy, Nimonic – Individual corrosion resistance • Ni-Cr-Fe: vitriolic, phosphoric acidic, seawater, chloric • Ni-Mo: hydrochloric, fluor acidic environment • Ni-Cr-Mo: wide corrosion resistance, pitting and crevice corrosion resistance Heat resistant nickel alloys

• Ni-Cr and Ni-Cr-Fe alloys – Excellent strength at high temperatures, creep resistance – Resistance heaters, resist to hot air

• Fe-Ni-Cr alloys – Main component is Fe, not typical Ni alloys – Perform well even in oxidizing, carbonizing and sulphiding environment Creep resistant nickel and cobalt alloys

• High heat and creep resistant super alloys • Developed for improving gas turbines’ efficiency • Up to 10-15 alloying components – C, Cr, Co, Ni, Mo, W, Ti, Al, Nb, Fe, B, Zr, Ta, V, Re, Hf, La, Y Creep resistant nickel and cobalt alloys

• Single crystal turbine blades strengthened by precipitation hardening Special nickel alloys

• Resistance heaters (Ni-20Cr-Si, CuNi45 (Constantan)) • Thermocouples , K type 90Ni-9Cr and 94Ni-AlMn-Fe-Si- Co • Soft magnetic materials, Permalloy • Alloys with low thermal expansion: Invar36, Kovar • Intermetallic alloys • Maraging – X2NiCoMo18-9-5 – Martensitic, precipitation hardenable Special nickel alloys

•Shape memory Ni-Ti alloys Zink

• Heavy metal, density 7,133 gcm-3 • Melting point 906°C • Hexagonal lattice • Base material for corrosion protection: coating – Zinc-carbonate surface layer • 5 purity levels (Z1…Z5) – Z1: 99.995% Zn … Z5: 98.5% Zn • Main impurity elements: Pb (Cd, Fe, Sn, Cu, Al) • Anodic protection • Cu, Ti increases the strength • soft(~100 MPa yield stress, creep starts form 100°C) Zink alloys

• Excellent castablility, numerous casting application – Rapid prototyping (sand mold + machining) – Small series production (die casting) – Large-scale production(pressure die casting) – Surface treating (Hot-dip galvanization)

• Keys, x-ray tube sockets, luxury goods, window lock mechanisms, pin, phone-case, locks etc. Zink alloys

• Zn-Al (eutectic at ~5% Al) • Hypoeutectic, ~4% Al – End of 1930s, Zamak alloy (Zn-Al-Mg-Cu) – Investment casting

• Hypereutectic, 6-12% Al – 1950s: 6-8% Al, Zamak, heat and wear resistance – Tonsul alloy+Mg, jewelry alloys – Ilzro: 12% Al and 1% Cu, gravity casting, larger parts, e.g. office chair leg Zink alloys

• Hypereutectoid alloys – 25-35% Al content – Good strength, up to 400 MPa yield stress – Porous surface – containing lubricant – • Al free Zn-Cu-Ti alloys – Zn-Cu: cast building industry parts, coins, deep draw tools – Zn-Cu-Ti and Zn-Cu-Cr-Ti: large sand-mold cast parts, roof structures, 300 MPa yield stress – Zn-Pb-Cd-Fe: batteries’ case Tin and its alloys

• Corrosion and acid resistant • Alloys for bearings and filler metals (Pb) for soldering • Tin pest – Below 18°C tetragonal  diamond lattice transformation – Allotropic transformation – Volume changes – Inner stresses – The part pulverizes Tin and its alloys

•Tin pest Metals Technology

Forming I. Today’s topic

• Microstructure fundamentals: crystal plasticity, anisotropy • Mechanical fundamentals: stress, strain, strain rate and volume constancy. Equivalent stress and strain • Cold and hot forming, forming limits • Flow stress, flow curve and main variables • Friction. • Forming operations Plastic deformation - lattice defects

Lattice defects and theirs role

Ideal lattice: no defects

Real lattice: defects

. Vacancy, interstitial atom 0D . Dislocation 1D . Grain boundaries 2D . Precipitations 3D Plastic deformation - lattice defects

Plastic deformation

Mechanical properties ~ plastic deformation

. hardness, toughness, yield stress . formability

Mechanism of the plastic deformation:

. Slip of the dislocation (slip plain and slip direction) Plastic deformation - lattice defects

A transmission electron micrograph of a titanium alloy in which the dark lines are dislocations Elastic and plastic deformation

Elastic deformation • after the load is removed, no deformation remains • no rearrangements in the atomic order

Plastic deformation • deformation which remains after load is removed • atomic rearrangements (change of neighbours)

Plastic deformation of crystals does not change the lattice structure. Plastic deformation

Frenkel model (~1920)

2휋푥 휏τ = - shear 퐴 푖 stress x – displacement푎

푎 퐺 휏 Hooke's= law 2휋 G – shear modul Theoretical strength · 102-103 Real strength Plastic deformation

Plastic deformation – slip of dislocations

Slip plane Orowan and Taylor

Deformation of crystals occurs by slip of lattice planes, motion of dislocations Plastic deformation

Plastic deformation – slip of dislocations

Screw dislocation Types of dislocations:

Edge dislocation Plastic deformation

Slip system

Slip system: slip plane + slip direction

Slip system is characterized by: • slip plane normal • slip direction, slip vector (a lattice vector in the slip direction)

often: slip planes are most densely packed lattice planes slip directions are most densely packed lattice directions Plastic deformation

Reaction of dislocations

Meeting of two dislocation: Sum of the their vectors

annihilation Plastic deformation

Cottrel-Lommer junction

Two dislocations combine (two different slip planes), and the plain of the resulting dislocation is not a slip plane.

This immobile dislocation will act as a barrier for other dislocations Deformation of a single crystal

Stress (pressure) 퐹 Driving force for 휎slip =:퐴 Tensile stress leads to resolved shear stress in slip system

휏

No shear stress: slip direction or slip plane normal are perpendicular to the tensile axis

Maximum shear stress: slip plane and slip direction are under 45º to the tensile axis. In single crystals: Slip starts on slip system with highest  active slip system

휏 Deformation of a single crystal

Macroscopic slip in a single crystals Deformation of a single crystal

Slip systems in different lattices

active slip system: Slip starts on slip system with highest

휏 Characteristic slip systems

slip Nr. of slip structure slip planes directions sys. bcc <111> {110} 12 fcc <110> {111} 12 hex <11 0> {0001} 3

2 Deformation of a single crystal

Single and multiple slip

Singe slip: The deformation starts in only one slip system (position of the force F)

Multiple slip: Two or more slip systems are active

4 active slip systems highest stress

fcc lattice eomto fasnl crystal single of a Deformation Stress system operatessystem oneonly slip easy glide stage of dislocations interactionand multiplication stage slip multiplecross and Multiple stage glide climb deformation Deformation of a single crystal

Stage I.

Only one slip system is active. The necessary shear stress for the deformation increases only slightly.

Deformation in macroscopic scale: • A lot of dislocation is necessary. • 1 dislocation causes a displacement of b.

If b = 2·10-8 m then for the displacement of 1 mm:

dislocation are necessary.

There are not so many dislocation in the material at the beginning. How are they generated? Deformation of a single crystal

Frank-Read sources Deformation of a single crystal

Frank-Read sources

Simulation of frank-read source Deformation of a single crystal

Stage II.

More and more dislocations are generated, the shear stress is increasing.

The crystal starts to rotate in a more favorable position: slip occurs on two or more slip system

The dislocations are not evenly distributed. Deformation of a single crystal

Stage II.

Dislocation on two or more slip system.

Cottrel-Lommer junction: (The combination of two dislocations is not on a slip plane.)

1. This immobile dislocation will act as a barrier for other dislocations. 2. For further deformation new slip systems become active. 3. Increase of the shear stress Deformation of a single crystal

Stage III. Cross slip of dislocations.

The dislocation are piled up behind the immobile ones. The stress is high enough for the screw dislocation to bypass the immobile dislocation, and continue on a neighboring slip plane.

Screw dislocations are more mobile, they are not bounded to only one slip plane Deformation of a polycrystalline materials polycrystalline of a Deformation

Stress stage stage stage deformation single crystalsingle polycrystal Deformation of a polycrystalline materials

Polycrystalline material consist differently oriented crystals.

During the deformation the continuity of the body remains. Grain boundaries do not rip apart, rather they remain together during deformation.

Each grain’s shape is formed by the shape of its adjacent neighbors

There are more active slip systems in each grains (min. 5) Slip lines in differently The stress increase is always oriented more intensive in polycrystalline grains materials. polycrystalline specimen of copper Deformation of a polycrystalline materials

Alteration of the grain structure of a polycrystalline metal as a result of plastic deformation.

(a) Before deformation (b) The deformation the grains are equiaxed. has produced elongated grains. Deformation of a polycrystalline materials

Macroscopic and microscopic deformation

The macroscopic The deformation of the deformation (deformation crystal is the sum of the of the body) is the slips on the slip systems average of the crystals’ deformation

휀푎 = 휀푎 F 휀푎 = ℎ푎 푎푖 푖

F Texture of a polycrystalline materials

The texture is the distribution of crystals’ orientations of a polycrystalline material. No texture: the orientations are fully random. Texture: some orientation are more preferred than others weak, moderate or strong texture Almost all produced material have texture, and can have a great influence on material properties.

Origin of the texture: • Deformation texture (sheets, wires) • Texture originates from crystallization, or recrystallization (casting, heat treatment...) • Vapor depositions (PVD, CVD, …)

No texture: isotropic material direction independent prop. Texture: anisotropic material direction dependent prop. Texture of a polycrystalline materials

Evolution of deformation textures

Because of the constrained deformation (neighboring crystals) of a crystal minimum 5 active slip system is necessary. The number of active slip systems depends on the position of the crystal. e.g bcc crystal: 5 - 12 (maximum) The less active slip system is necessary for the deformation the more prefered is the position of the crystal.  Crystallographic slip results in lattice rotations relative to the external axes of a body.

Sheet rolling Texture of a polycrystalline materials

Evolution of recrystallization textures

New crystal structure is growing over the old one. The texture of the new crystal structure depends on

• Original texture • Dislocation structure of the original crystals Volume and surface forces

f External forces acting on volume t and surface .

Volume changes from V0 to V x3 ΔV External forces: ΔA volume and surface forces

x2

1 F F f  lim t x 0  lim 1  V  V A0 A

Volume force desity Surface force desity Stress tensor

Tought experiment: cut the body into two

T t V tni ij j , t σn  n II t1 11 n 1   12 n 2   13 n 3 dA t2 21 n 1   22 n 2   23 n 3 VI

t3 31 n 1   32 n 2   33 n 3

σ – Cauchy stress tensor

11 12 13       σ  21 22 23   31  32  33  Stress tensor

Diagonal elements: normal stress components 11 12 13  Off-diagonal elements: shear stress      σ  21 22 23  components  31  32  33 

 33

 23 13  32 Normal stress is positiv if tension-like  22  31 12  21 Normal stress is negative if compression-like  11 x2

x1 Stress tensor

Equivalent (von Mises) stress

'  3 J2

1 2 2 2 2 2 2 11   22     22   33     11   33  6  12   23   13  2 Stress states

1 0 0   0  0   2  L1  0 0  3  L2

S1 S2 S3

T1 T2 T3 T3 Deformation – true (logarithmic) strain

xX33,

xX22,

xX11,

Materials changes shape during deformation Deformation – true (logarithmic) strain dS – radius of the sphere, dsi – axes of the ellipsoid ds1>ds2>ds3

ds ds ds   ln  ln 1 ,   ln  ln 2 ,   ln  ln 3 1 1 dS 2 2 dS 3 3 dS

1 0 0     0  0   2   0 0 3 

Equivalent strain 2      2     2     2  62  2  2  3 11 22 11 33 22 33 12 13 23 Volume constancy

During large plastic deformation the materials uncompressibility can be assumed. Comparing to the plastic part the elastic deformation can be neglected.

The volume of the material remains constant during forming:

dS1 dS 2 dS 3 ds 1 ds 2 ds 3  1   2   3  0 div v  0,

 11   22   33  0 Stress-strain relation

The matial deforms plastically when the stress reachs a critical value (yield stress). With the deformation the yield stress changes.

The constitutive law푖푎 푖 describe the stress-strain휎 = 휎

relation. Yieldstress flow curves

휎푖 = 휑,휑, 푇 Plastic strain Stress-strain relation

Mathematical desription of flow curves

flow curves – cold deformation flow curves – hot deformation

Yieldstress Yieldstress

Plastic strain Plastic strain Formability

The matals’ plastic deformation is limited by - plastic instability - damage/crack

Plastic instability: The strain hardening is eliminated locally by a softening effect: chagnes of - geometry - rate of deformation - temperature

Stretching of a plate Does the deformation localize? Formability

Damage, crack: The material can not deform plastically any more: forming limit

The formability is infuenced by the temperature strin rate and the local stress state.

Charachteristation: - Lode-parameter ( ) - stress state index (k) 휇휎

2휎 − 휎 − 휎 휎 + 휎 + 휎 휇휎 = 푘 = 휎 − 휎 휎푖 Formability

Forming limit diagram - sheet

crack safe

Different deformation routes

crack

Formability diagram - bulk strain Failure upsetting torsion tension

Stress state index Friction

Constitutive law for the lubricant

Hydrodynamic friction

Dry friction Boundarylubrication Stribeck diagram

Mixed film lubrication

Fluid-film lubrication Frictions effect on forming processes

Friction leads to unequal deformation distribution. Thus influences the stress state of the workpiece

. Influence on deformation  yield stress . Friction forces leads to increased forming forces and energies. (more work must be done) . Wear of the tools shorten the service time . Worse surface quality

Lubrication Friction – lubricant materials

Role of lubricant material

. Separation of the tools’ and workpiece’s surface . Decreasing the friction forces . Decreasing the wear of the tools . Increasing of the surface quality of the workpiece . Temporarily corrosion protection . Cooling effect Classification of forming processes

. Hot working, warm working, cold working

. Bulk forming, sheet forming

. Primary and component forming Classification - temperature

. Cold working – Temperature < 0.3 * melting point in deg. K – In practice for most engineering metal this means room temperature –Work hardening is dominant

. Hot working – Above the recrystalization temperature – Temperature > 0.5 (or 0.6) * melting point in deg. K – Strain rate sensitivity more important

. Warm working –Temperature between 0.3 and 0.5 of melting point –Flow stresses somewhat less than cold working Classification – workpiece type

Sheet metal forming –Input material: sheet form –Thickness changes very small –Stresses: tensile

Bulk forming –Input material in the form of bars, billets, etc. –Thickness of material usually substantially reduced –Stresses: compressive Classification – primary / component process.

Primary forming processes –Processes predominantly for producing materials for further processing –Examples are rolling, drawing, extrusion, etc.

Component producing processes –Processes for producing component parts –Input materials produced by primary processes –Examples are forging, deep drawing, stretch forming, etc. Range of forming processes

. Free forming –Tool does not contain the desired shape . Two dimensional forming –Point contact between tool and work material –Two relative motions required to produce geometry –Incremental forming processes . One dimensional forming –Line or surface contact with work material –Only one relative motion required to produce geometry . Total forming –Tool contains the desired geometry . Process kinematics within each group differentiates the different processes Range of forming processes

Total forming

One dimensional forming

Two dimensional forming

Free forming Free forming processes One dimensional forming processes One dimensional forming processes Two dimensional forming processes Total forming processes Metals Technology

Forming II. Today’s topic

• Rolling

• Forging

• Extrusion

• Sheet metal forming Rolling techniques Flat rolling

Material’s flow in the rolling gap Flat rolling

Rolling arrangement Flat rolling

Bending of the rolls

Cylindrical rolls Rolls with camber

Hot rolling, recrystallisation Flat rolling - defects

Wavy edges Cracks in the center

Edge cracks Aligatoring Shape (caliber) and ring rolling Thread rolling

Reciprocating flat dies

Roller dies Seamless tubes and pipes by rolling

Cavity formation in a solid round bar

Rotary tubepiercing process Seamless tubes and pipes by rolling different techniques Forging techniques

Cold warm and hot forging depending on the temperature Grain flow control

Open die Closed die

+Simple and inexpensive dies +Relatively good utilization of material; +Small quantity +better properties than open-die forgings -Limited to simple shapes +dimensional accuracy; -low production rate +high production rates; -high degree of skill required +good reproducibility

-High die cost -not economical for small quantities Open die forging - stages

(a) forge hot billet to max diameter

(b) “fuller: tool to mark step-locations

(c) forge right side

(d) reverse part, forge left side

(e) finish (dimension control)

[source:www.scotforge.com] Closed die forging Closed die forging

Forge rolling Closed die forging Closed die forging

Trimming flash from a forged part. Closed die forging – technology sequence

1. Prepare a slug, billet, by shearing, sawing, or cutting. (clean surfaces e-g by shot blasting) 2. For hot forging, heat the workpiece in a furnace and then descale it (wire brush, water jet, or steam) 3. For hot forging: preheat and lubricate the dies For cold forging: lubricate the blank 4. Forge the billet in dies and in the proper sequence. (+ metarial removal (e.g.flash) by trimming, machining, or grinding. 5. Clean the forging and the dimensions 6. Additional operations: straightening, heat treating 7. Machining and grinding to final dimensions and specified tolerances. 8. Inspection: external and internal defects. Forging – grain flow

Quality of forged parts

Surface finish/Dimensional control: Better than casting (typically)

Stronger/tougher than cast/machined parts of same material Forging - defects

Temperature controll: temperature decreases → cracks Extrusion processes

Hot and cold extrusion Forward and backward extrusion Extrusion of other shapes Drawing of rod and wire Forward extrusion Extrusion of a seamless tubes

using an internal mandrel

using a spider die Impact extrusion

cold extrusion process Extrusion - defects

Surface Cracking stick-slip - bamboo defect

Pipe (fishtail) defect Internal cracking Drawing

The cross section of a long rod or wire is reduced or changed by pulling it through a draw die. Drawing of pipe Drawing of wire

Multistage wire drawing Sheet metal forming

. Deep Drawing . Shearing . Rubber Forming and . Formability Hydroforming . Bending Sheets, Plates, . Spinning and Tubes . Superplastic Forming . Specialized Forming Processes Shearing Shearing Shearing – fine blanking Shearing – punching and blanking Shearing – Slitting with rotary knives Shearing – Tailor welded blanks

Production of an outer side panel of a car body Formability of metal sheets

Forming limit diagram

crack safe Bending of sheets pipes and tubes

Springback in bending (recovers elastically)

overbending Defects Bending of sheets Bending of pipes, tubes Deep drawing Deep drawing - defects

Flange wrinklingWall wrinkling Cracking Earing Beverage can – production steps Beverage can – production steps Ruber forming

The outer surface of the sheet is protected from damage or scratches: no contact with a hard metal surface during forming. Hydroforming Spinning Spinning

Shear-spinning

Tube-spinning Materials Engineering

Heat treatment Overview

Heat treatment of Steels Structural Steels Phase and Time-Temperature-Transformation diagrams Microstructure and properties Annealing and normalizing Quenching and Tempering Surface treatment processes Tools steels high speed steels Heat treatment of aluminium alloys Annealing Precipitation hardening Fe-Fe3C phase diagram

liquid

mass

mass Effect of C% on properties

Contraction Z

Impact Energy , KV

UTS

Hardness HB, Strength (MPa) Strength HB, Hardness Strain, contraction (%) Imp. E (J) E Imp. (%) contraction Strain,

Carbon %

Structural steels Tool steels Isothermal transformation diagram Continuous cooling transformation diagram CCT Perlitic transformation

Diffision of Cementite carbon atoms Austenite grainboundary Ferrite

Perlite growth Δ Diffusional process direction with nucleation

Δ T high

Δ T low

Austenite % Perlite % Process speed increases with overcooling (ΔT) Time (s) Perlitic transformation

Transformation immediately Transformation more below below the A1 temperature: the A1 temperature: ΔT lower, faster diffusion ΔT higher, slower diffusion

ΔT low, ΔT high, coarse lamellar Fine lamellar structure structure Bainitic transformation

Austenite (stable)

Pelite/bainite boundary Upper bainite

Lower bainite

Time (s)

Ammount of bainite Bainitic transformation

Upper bainite Lower bainite Martensite

Cementite Martensite

Cementite Ferrite Ferrite

Ferrite needles and Fe3C Thin ferrite plates and elongated particles Fe3C particles

The transformations’ speed is controlled by the diffusion (nucleation). Fine structure. Spheroidite

Austenite (stable)

(Ferrite) Spheroidite

(cementite)

Time (s)

After long time, the perlite/bainite’s structure transforms (diffusion).

Fine Fe3C spheres in the ferrite matrix Matrensitic transformation

Martensite phase is produces from the initial austenite phase. Diffusionless transformation, no nucleation, high cooling rates

Austenite (stable)

Martensite needles Austenite Quantity of martensite Matrensitic transformation – Bain model

Lattice parameter

C%

The austenite lattice contains the martensite’s lattice. Connection between the two crystall structures. Matrensitic transformation

MsMsandés Mf hőmérséklettemperatur over the carbonszéntartalom content függése

Needle Martensite Plate& neddle martensite Plate martensite

Ms – Martensite start temperature Mf – Martensite finish temperature Hypo- and hypereutectic steel – isotermal transf.

Austenite (stable) Austenite (stable) Ferrite Cemetite

Time (s) Time (s) Proeutectic ferrite Proeutectic cementite Hypo- and hypereutectoid steel – CCT

Continuous Cooling Transformation (CCT) diagram

Austenite (stable)

Perlitic transformation Begin End Critical cooling rate

Time (s)

(1-2) Quenching: Martensite or Martensite&Bainite&Perlite (3) Normalizing: fine Perlite (4) Annealing: coarse plate perlite Basic heat treatment techniques

. Quenching . Tempering . Quenching + Tempering . Normalizing . Annealing Basic heat treatment techniques

T Quenching 750~950°C, 20~30 min Austenitising and fast cooling A3 (Acm) Austenite →Martensite

time Tempering T tempering below temperature A1 A (A ) Martensite → fine perlite 3 cm 150~600°C , 1.5~2 h Normalizing Austenitising and cooling on air time fine uniform microstructure

Annealing Austenitising and very slow cooling soft and tough state Heat treatment initial temperatures Hypoeutectoid steel – CCT diagram

1- quenching 2- normalizing 3- annealing Hypereutectoid steel – CCT diagram

1- quenching 2- normalizing 3- annealing Tempering

Increase of touhgness and decrease of inner stresses and brittleness (martensite)

T austenite

T tempering

Very fine Fe3C particles embedded in ferrite matrix

martensite Quenching and tempering

austenitizing

Tempering Quen.

The machanical properties can be changes in wide range depending on the tempering temperature Martempering of eutectoid steel

Austenite (stable)

Ttempering

Transform.

Modified quenching technique: lower inner stresses and possibility of cracking Austempering of eutectoid steel

Austenite (stable)

Transform.

Production of Bainite: high strength with relative high toughness Summary of heat treating processes

Austenite

slow Moderate Fast cooling cooling cooling Perlite Bainite Marteniste +Fe C +Fe C layers α 3 No diffusion α 3 plates/needles

tempering Martensite Bainite Tempered Fine perlite marteniste α+very fine Fe3C

Coarse particles strength toughness perlite spheroidite Effect of C% on properties

Quenched state

Annealed state

Non-heat Heat treateble treatable Surface treatment processes

Hard surface and tough core

CVD, PCD coatings (TiN, TiC, etc) HRC

Flame or induction hardening Hardness

Boro- Case hardening nizing Nitriding Depth Flame and induction hardening

For heat treatable steels Surface hardness: 50 to 60 HRC Depth: 0.7 to 6 mm Distortion: little

T Austenitizing and quenching Flame or induction hardening of the surface

A1 tempering low temp. tempering time Nitriding

For nitriding steels Surface hardness: 1100 HV Depth: 0.1 to 0.6 mm Distortion: no

T Austenitizing and quenching

A1

500-550°C

Ttemp. > Tnitr time

tempering nitriding

Finishing here if necessary no finishing after nitriding! Case hardening (carburizing)

For case hardening steels Surface hardness: 50 to 60 HRC Depth: up to 1.5 mm Distortion: yes Low carbon steels Carburizing and hardening the surface

Carburizing T 1h ~ 0.1 mm 900-950°C

A3 core

A3 surface

core surf. time Quenching Tempering Low carbon core High carbon surface Tool steels – high speed steels

1200-1250°C T Cooling in 2 steps

quenching Tempering 2-3x

500-550°C time -70°C Deep cooling Heat treatment of aluminium alloys - annealing

homogenisation

Quenching

softest state! Temperature

time concentration

Initial quenched Precipitation hardening

homogenisation

Quenching (softest state!)

Ageing Temperature

time concentration

Natural and artificial ageing

Initial quenched aged Precipitation hardening

heat treating to this state

Coherent connection semicoherent

zones Hardness incoherent

time Material Selection & FEM Overview

• Overview of the material selection’s process

• Material – production method - shape • Finite element method

• Utilization and limitation of FEM

• examples Material selection’s process

1. Translation express design requirements as constraints & objectives 1. Screening eliminate materials that cannot do the job 3. Ranking find the materials that do the job best 4. Other information overview the best solutions

M.F. Ashby, Materials Selection in Mechanical Design, 3rd Ed., Elsevier, 2005 First step

Express design requirements as constraints and objectives

Function: What does the component do? Without to constrain the method of implementation Objectives: What must be minimised or maximised?

Constrains: What basic condition must be fullfilled? What production method must be applied? Free parameters, design variables: Which can be changed? Which are the desired configurations? First step, example

Material for a light and high strength wire

Function: A support the tension load Objective: minimize mass

Constrains: defined length Loading force without damage

Free parameters: Area of the cross section material Second step

Screening: Eliminating unsuitable matarials

metals

Hybrid Ceramics Polymers materials

Glasses Second step

Filtering accouding to the given condition(s) Second step

Filtering accouding to the given condition(s) Second step

Filtering according to the given condition(s) Third step

Ranking: Find the most suitable materials

What if there are more possibilities after screening?

Which one is the best? Third step, example

Overhead transmission cable

Function: transmitting electricity Objective: minimal electric resistance Constrains: length, and cross section are given must not fail under ice and wind minimum tensile strength > 80 MPa Free parameters: material

screening according to strength, and ranking by electric resistance Fourth step

Other auxiliary informations:

overview of the most suitable solutions

- processing technology - costs - batch size - other considerations Material – Process – Shape

The properties of a component are determined by three group factors.

Material

Manufacturing process

Shape Material – Process – Shape

Selection the shape and the material

The property can depend on the shap as well, not only on the material.

- Optimizing the shape to the given, specific load. - The simple geometries are not always advantageous (square cross section, I-beam, tube) - The shape can be constrained by the processing technique - The aim is the optimizing of the shape and the material to the given circumstances Material – Process – Shape

Shape Stiffness increases more than13 times for the same cross secion area Material – Process – Shape

Material

Is it possible to manufacture the shape using every material?

Processing technique

Shaping, Surface treatment , Joining (e.g. welding)

- The shape can be constrained by the processing technique

The material constrains the applicable processing technologies:

- Welding of aluminium and titanium - Machining of ceramics and composites (?) Finite Element Method Finite Element Method

The method approximates the e.g. displacement field in the body with small, finite number volumes (elements). The field is continuous over the elements, and unknown parameters are assigned to finite number of nodes. The required quantities (Stress, strain, tempereture) are determined by the solution of a algebraic equation system. Utilization and limitation of FEM

Mechanical problems Steady stade Linear Thermal problems Electromagnetic problems Tranzient Nonlinear etc… Utilization and limitation of FEM - steps

Definition of the problem

Model building (simplification) defining the problem and element types geometry selection of the material model initial and boundary conditions

Limitations, dangers computational costs, limit of our computers numerical process (approximation, numerical errors, etc.) skill of the user (not competent person) Exapmple – Cooling of an electric circuit

Funktion: Cooling fin Objective: appropriate cooling Constrains: maximal service temperature: 200ºC electric insulator R > 1020 ohm cm good heat conductance > ??? W/m K light: ρ < 3 Mg/m3 Free parameters: Material manufacturing technology

Jeremy Gregory et al. 2005 Exapmple – Cooling of an electric circuit 1. Példa – Elektromos áramkör hűtése

Jeremy Gregory et al. 2005 Materials Engineering Welding 1

1 INTRODUCTION Classifying joining processes

JOINTS

CLOSE ALAKKAL WITH ZÁRÓ FORM CLOSESÚRLÓDÁSSAL BY FRICTION ZÁRÓ JOIN BY MATERIAL

Shaft coupling, clutches, screw ÉkKey,-, csap-, pin and szegecskötés bolt Karimás- és WELDED connections csavaros kötések JOINTS

Tengelyagy-kötések Axis connections Stamped axis-hub connections withSajtolt or without tengelyagy-kötések flexible Rugalmas parts közbenső SOLDERED Elemek a helyzetbiztosításhoz elemekkel Positioning parts JOINT Rugalmas közbenső elemek nélkül Pattintó-Tensioning, feszítő and- és szorítókötésekpressing parts GLUED JOINTS

Historical overview 1

1724: Desaguliers joins lead rods by compression and torsion. 1849: Staite patents joining metals by electric arc. 1866: Thomson patents resistance butt welding. 1887: Benardosz makes spot welding by graphite electrodes. 1895: Goldschmidt designs thermite welding. 1906: Gas welding spreads around the industry. 1908: Kjellberg patents coated electrodes. 1915: Resistance spot welding is used to produce car bodies. 1919: Roberts and von Nuys performs shielding gas tests. Historical overview 2

1929: Dultshevskiy patents the submerged arc welding. 1935: Shielded arc welding experiments at Union Carbide. 1946: Cold pressure welding process has been validated. 1949: Electroslag welding was validated in Paton Institution. 1957: Electron-beam welding has been developed. 1963: Fisrt indutrial robots are put in operation. 1969: Experimental welding operations made in the space. 1995: Friction Stir welding process was developed. Classifying the welding processes

• Based on the source of energy used to create joint • Based on the filler material type • Based on the protection of the weld • Based on the level of mechanizing or automation • Based on the technological parameters.

Most frequently the source of energy is the classifying criterion. Another possible arrangement

HMÉRSÉKLETTEMPERATURE

OlvadásiMelting temperaturehmérséklet

HotMeleg-sajtoló pressure weldinghegesztések pr. Cold Hideg-sajtoló pressure weldinghegesztések pr.

PRESSUREER

PRESSURESAJTOLÓ WELDING HEGESZTÉSEK PROCESSES

FUSIONÖMLESZT WELDING HEGESZTÉSEK PROCESSES Creating a weld bead

MATERIAL ENERGY

CLASSIFICATION CLASSIFICATION

BY PHASE BY PRESSURE BY ENERGY

LIQUID SOLID THERMIC OTHER WITHOUT PRESSURE

W. PRESSURE THERMOMECHANIC MECHANIC

8 The role of heating at pressure welding

Y F F (d/dt)2

(d/dt)1 1 2 2 2  egy  1  2   2  3  1  3  eqv 2 T   Y Y eqv  d  Yk f  , , T   dt 

Rp0,2

Heating:  Y decreases  welding time shortens Resistance spot welding

Crystallization under force creates the weld.

Higher joint strength

10 Creating the weld bead – melting processes Creating the weld bead – melting processes

Fusion zone

Fusion zone Base metal solid liquid Base metal Dendritic solidified crystallization Solid-liquid 1. liquid 1. Prefered boundary grain grain growing direction grain grain Prefered growing Fusion zone direction Base metal Hexagonal subgrain cross section solidified solid Fusion zone 1. Base metal liquid grain liquid 1. grain Sub- grain grains Tipical cross grain section Solid-liquid boundary

12 Creating the weld bead – pressure processes

orientationorientationOrientáció difference különbség difference repulsive force repulsive

l attractive force attractive

a a

ConditionConditionA sajtoló of the pressure hegesztésof pressure welding processes: feltétele:welding:

orientation difference ll a a ...... orientationOrientáció difference különbség 0° 0° BASIC MANUAL PROCESSES

14 Manual metal arc welding

15 Roles of the flux covering

• Stabilizing the arc (K, Na, Ca decreases the emission energy and the ionization potential). • Evolving gas (organic matters, for example cellulose (C6H10O5)n and from CaCO3) • Deoxidizing, denitridizing (Mn, Si, Al, V, Ti, etc.) • Alloying (alloys depending on base material, in the form of ferro-alloys as Fe-Si, Fe-Ti, Fe-Cr etc.) • Making up the slag (from rutile, from organic materials, from SiO2 and MnO etc.) • Decrease the cooling speed, metallurgic processes • Increase the melting rate (melting efficiency can reach 220 %). Applications based on the type of flux covering

• Acid flux electrode should be applied when the welding position is simple but the penetration to be reached is high. • Cellulose flux electrode is used for tubes root pass welding (transmission line tubes). • Rutile flux electrode is used for „around the house” type of works and when the expected mechanical properties are at medium level. • Basical electrodes are used for constructions where mechanical properties are important and high. Welding parameters

• Wire diameter: de=1,5 ÷ 6 mm

• Current: I = 30 ÷ 500 A (I = (30÷60) x de, A) • Arc voltage: U = 20 ÷ 50 V (U = 0,04 I + 20, V)

• Welding speed: vweld= 80 ÷ 200 mm/min

• Pull out length: Lpull= 100 ÷ 400 mm. Pull out length means the length of the weld seam that can be made with the efficient length of the electrode. By the pull out length, the cross section of the weld and the heat input (welding speed) can be well controlled.

18 Welding power sources

DC and AC current can be applied produced by: • Welding transformers Welding rectifiers • U power source • Welding generators electric arc

L1  L Characteristics: L (internal regulation)

working point I ΔI

19 Application of manual arc welding

• Widely used in every segment of the industry, because of its simplicity, and low price. Practically there is suitable electrode for every type of material, easy to learn the procedure and does not require high capital investment. • Strongly alloyed steels are welded with flux covered electrodes in 75 % of the cases. • For surface welding most welding materials are available in the form of flux covered electrodes. • Disadvantage is the low melt-off efficiency, the rather strong contribution of the human factor, and it is hard to apply for non-ferrite based metals.

20 Oxyfuel-gas welding

Disso gas pressure bottle Oxygen pressure bottle

Disso gas: Acetylene is dissolved in acetone to enable acetylene pressure up to 30 bar. The pressure bottle is filled with porous material (cement, asbestos, carbon), so the gas can not get concentrated in a small volume. The porous material soaks up the gas-fluid mixture. (In a few cm3 volume – approx. a walnut 16x15x24mm – acetylene is explosively dissociating.)

21 Burning of acetylene

• Primary reaction:

C2H2 O2  2CO  H2 Q

• Secondary reaction (now oxygen is coming from the air): 3 2CO  H  O  2CO  H O  Q 2 2 2 2 2

22 Welding torch and reductor

Gas blowing through the little diameter hole arrives into a bigger volume, this way its pressure decreases. Burning gas and oxygen mixed based on the theory of injector-effect.

23 Welding technique

weldingWeldingHegesztés direction direction irányaweldingWelding Hegesztés direction direction iránya

backwardBalra hegesztés welding forewardJobbra hegesztés welding

Backward welding is applied for thin metal sheets (s ≤ 3 mm), forward welding is used for thicker metal sheets and tubes. In case of forward welding the weld bed is heated, so bigger penetration can be reached. Applied flame types

• Natural flame (for steels and copper) • Oxidizing flame (for welding of brass) • Carburizing flame (for aluminum and its alloys)

Natural Oxidizing Carburizing

25 Application of oxyfuel-gas welding

Welding parameters: • On-site welding, FMCG assembly applications. • dh = 1....10 mm (filler material diameter) • Repairs (for example car chassis). • pC2H2 = 0,1....0,6 bar For FMCG assemblies • pO2 = 2....5 bar • – central heating, water, v = 10....100 mm/min • weld gas piping – other • VC2H2 = 1.....50 l/min procedures are hard to apply. • VO2 = 1.....55 l/min.

26 Oxyfuel-gas cutting

The process: • Preheating for flashing- point temperature • Burning with oxygen • Blowing out the products of combustion to form the gap

27 Oxyfuel-gas cutting conditions

Flash T, ºC • The material must be point capable to burn in oxygen • Flash point temperature must be lower than melting point. 2,1 Limit of ofwell good cuttability cutting • Melting point of the oxide A könnyű lángvághatóság határa must be lower than that of the metal itself. • The combustion product C, % must be a fluid, so it can be 0,8 4,3 flown out to form the gap.

Well cuttable materials: Weldable unalloyed and low alloyed steels. (Alloying materials usually decrease weldability.)

28

Semi-automated and automated welding processes

To be automated: • Electric arc regulation to keep the arc length • Consumable electrode feeding • Movements needed to form the bead Main movement (along the bead) Side movements (alternating, circling)

Semi-automation: the movements are not automated. Application of robots and NC-control. Shielding gas welding processes

• Argon gas shielded tungsten electrode arc welding • Consumable electrode arc welding processes CO2 gas shielded welding Mixed protective gas arc welding Argon gas consumable electrode arc welding Flux wire arc welding • Plasma welding, plasma cutting

These are semi-automated processes. Argon shielding gas tungsten electrode arc welding (GTAW)

Fine drop transfer at TIG process. Applying impulse welding

tcicle = tbase + timp

timp current

tbase time

Impulse welding enables well controlled heat input. GTAW - welding applications

• Non ferrous- and light metals, high alloyed steels (tool repairs and pile up welding, corrosion resistant steels). Cylindrical welded seams on tubes, also for root pass at unalloyed and low- alloyed steels. • Application constraint: – Small melt-off efficiency • Needs highly qualified personnel with practice. • Cannot ensure proper gas shielding at windy places. Gas Shielded Metal Arc Welding (GMAW) processes

CO2 – welding, Mixture gas arc welding (MAG), Inert shielding gas arc welding (MIG), Flux cored arc welding (FCAW) Gas shielded metal arc welding

Wire electrode

Wire drum

Current connection Wire feeder

Nozzle +

Power source -

Materials are melted together with the arc between the electrode and the workpiece under gas or gas mixture shielding. Internal control of gas shielded welding processes

L L ív ív2 L ív1

SwingingA fémfürdő movelengésének of the következménye weld bead az >>>ívhossz change változása in arc length

L

+ = L ív - I

I IInom I Balance: vforw = vmelt-off 1 névl. 2 Egyensúly: v elő. = v leolv. vmelt-off = fv(I)

v = f ( I ) Arc length increases Arc length decreases leolv. Ívhossz nő: I I I I 1 névl. Ívhossz csökken: 2 névl. I1 < Inominal I2 > Inominal

vmelt-off < v forw vmelt-off > v forw v v v v leolv. elő. leolv. elő. Application – Gas shielded arc welding processes

• CO2 – welding - Unalloyed and low alloyed mass steel construction - TTKV = 0 ºC • Mixture shielding gas arc welding - Mass steel construction TTKV = - 20 ºC - Robot supported operations • Flux cored wire - Mass steel construction TTKV = - 60 ºC - High alloyed steels, surfacing • MIG - welding - Non-ferrous and light metals - High alloyed steels, surfacing PLASMA WELDING, CUTTING

• Plasma: Ionized and dissociated gas state of material in a thermodynamic balance.

• Plasma can be developed on high temperatures. It has high energy level, suitable for welding, cutting and other thermal manufacturing processes. Developing plasma

High frequency discharge between the electrode and the inner side of the pistol gives the first charge carriers. Plasma develops between the electrode and the work piece (plasma arc). Plasma beam (flame) develops between the tungsten electrode and the inner side of the pistol and the gas blows the plasma out. Plasma welding

Plasma welding results deeply penetrated welded seam. Can be applied for all materials where the GTAW can, but the plasma is stretchable, stable and works at very low current values too. (I ≤ 50 A, micro plasma welding) Submerged arc welding

Fusion welding, the arc is between the consumable wire electrode and the work piece, under shielding powder named flux. Submerged arc welding characteristics

High melting rate, horizontal or close to horizontal arrangements because of the flux. Suitable for both joint and hardfacing welding. Fully mechanized or automated process. Submerged arc welding is economical

If: • Long straight or slightly curved seams are welded (guide is applied when curve). • L ≥ 2 m (welded seam length) • s ≥ 5 mm (metal sheet thickness)

Cylindrical welded seams can be made by rotating device. Submerged arc welding parameters

• de = 1,2....12 mm

• Iarc = 130....5000 A

• Uarc = 20....60 V

• vweld = 100....5000 mm/min

• Lpowder = 10 de, mm. Welding power sources

DC and AC current can be applied produced by: • Welding transformers • Welding rectifiers Welding generators U power source • electric arc L  L Characteristics: 1 external regulation ΔU L by the wire feeding velocity using ΔU working point I Application areas

• Mass steel construction • Unalloyed and low alloyed steels, high alloyed steels • Big layer thickness structures • Long straight or slightly curved welded seams • Horizontal or turn to horizontal arrangements can be welded • One sided „I” weld – up to 10 mm • Two sided „I” weld – up to 20 mm Electroslag welding

The heat is generated by the electric resistance between the electrode(s) and the melted slag (Joule heat). It is not an arc welding method, just at the beginning. Applications

• Mass steel construction, machine industry, ship industry • Welding high thickness metal sheets • Welding Barrels’ longitudinal seam • Unalloyed, low alloyed and also high alloyed steels • Aluminum and alloys • Coated wire electrode with guiding is the most common • Greatest thickness was 2 m. Resistance heating

• The Joule heat is generated by the current running through the work pieces (direct heating) and this heat is proportional with the resistance (R) and the current (I):

th Q   RI 2dt 0

• The second option is to apply induced current, called indirect heating. Resistance welding: advantages and applications 1

• Workpiece dimensions between wide limitations: – Overlapping plates: s = 0,005 … 30 mm – Butt welded rods: D = 0,01 … 350 mm – Crossing rods: D = 0,01 … 80 mm • Almost every material can be welded • The welding process is fully mechanized, well controllable and can be automated. Resistance welding: advantages and applications 2.

• Welding quality is high and stable • Heat affected zone is small, so the microstructure change and remaining deformation is negligible • High productivity • Material and energy saving is an additional advantage. Resistance welding - disadvantages

• Expensive welding equipment • Equipment calibration, setting and maintenance needs highly qualified personnel • Big amount of scrap when settings are incorrect • Problem with the mechanical characteristics in some cases. Butt resistance welding

The current flows through the work pieces. Butt resistance welding

The current running through the rods heats up the connecting surfaces (in certain versions the surfaces melt), when the required temperature is reached, the work pieces are more compressed. Plastic deformation is creating the joint (melted materials are pressed into the flash). Resistance spot welding

The electric circle is closed in the channel between the electrodes. Melting happens between the sheets, then the solidification under force creates the lens form weld. Process of creating a welded spot

a b c d e f The top electrode approaches the work piece (a), electrodes are pressed to the work piece, (b) after the preset time the current flows, the material starts to melt in a lens shaped volume (c). The melted volume is increasing (d), if the current is on for too long time, the melted material can be spattered (e), after the proper time and post keeping the top electrode moves away (f). Simple working order

F I

t tes th tu

Pressing the electrodes onto the work piece (F), presetting time (tes) has passed, the current (I) is turned on, after the welding time has expired (th) the pressure is kept for the post keeping time (tu). Main welding parameters are I, F, th , the pre and post keeping times are supporting parameters. Resistance seam welding

Continuous spot weldings are carried out between disc electrodes (e). Once the spots overlaps each other a seam is made, with no overlapping a row of spots is created. F

e

welding direction

work piece overlapping e F Foil seam welding

Disc electrode Foil

Disc electrode

Foil Disc electrode high-frequency upset welding

disc electrodes

electrical insulation

tube to be welded

The edges to join are not melted. Seam with no defect can only be welded if the melting point of the oxides is lower than that of the base material. Therefore only carbon steels with less than 0,3 % C can be welded. The wall thickness is max. 3 mm, because the deformation is limited.