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77 AlloyAlloy SteelsSteels CLASSIFICATION OF

Low High Alloy low med carbon high carbon <0.25wt%C 0.25-0.6wt%C 0.6-1.4wt%C

heat austentitic Name plain HSLA plain plain tool treatable stainless Cr,V Cr, Ni Cr, V, Additions none none none Cr, Ni, Mo Ni, Mo Mo Mo, W Example 1010 4310 1040 4340 1095 4190 304 0 + + ++ ++ +++ 0 TS - 0 + ++ + ++ 0 EL + + 0 - - -- ++ Uses auto bridges crank pistons wear drills high T struc. towers shafts gears applic. saws applic. sheet press. bolts wear dies turbines vessels hammers applic. furnaces blades V. corros. resistant increasing strength, cost, decreasing ductility 3 SME 1613 : 2007 Introduction

Alloy steels differ from carbon steels in that they have compositions that extend beyond the limits set for carbon steels.

As a general guide, alloy will have:- content >1.65% content >0.5% Copper content >0.6%

•Type of alloy steels:- 1. Tool steels 2. High speed steels 3. High strength low alloy steels (HSLA) 4. Maraging steels

SME 1613 : Materials Science 2007 Tool Steels

• Used in manufacturing processes as well as for machining . • Able to withstand high specific loads • Stable at elevated temperatures (200 oC) • Composition: high carbon: 0.6-1.4 %wt C and others elements : (Cr) , (V), (W), and (Mo) to form

•Six types of tool steels 1. High speed, 2. Hot work, 3. Cold work, 4. Shock resisting, 5. Special purpose and 6. Water hardening Effects of Alloying Elements on Tool Steel Properties

• Carbon (C) : increases hardness slightly and wear resistance. • Manganese (Mn): small amounts reduce brittleness and improve forgeability. Larger amounts of manganese improve hardenability, permit oil , and reduce quenching deformation. • Silicon (Si): Improves strength, toughness, and shock resistance. • Tungsten (W) : Improves hardness - used in high-speed tool steel. • Vanadium (V) : Refines carbide structure and improves forgeability, also improving hardness and wear resistance. • Molybdenum (Mo) : Improves deep hardening, toughness, and in larger amounts, "hot hardness". Used in high speed tool steel because it's cheaper than tungsten. • Chromium (Cr) : Improves hardenability, wear resistance and toughness. • Nickel (Ni) : Improves toughness and wear resistance to a lesser degree.

SME 1613 : Materials Science 2007 Heat Treatment

• Heated to temperature prior to quenching

• Tempered to form

• Never allow cooling to room temperature after quenching as this will lead to cracking. • The tool steel must be transferred to the furnace whilst still warm - about 50-80°C. During multiple tempering operations tool steels may be allowed to cool to room temperature between tempers .

• Residual stresses need to be removed prior to heat treatment and it is recommended that a stress relief heat treatment at 500-550°C be carried out allowing the tooling to cool to room temperature after stress relief

SME 1613 : Materials Science 2007 Normalizing &

• The normalising : cycle involves heating slowly and carefully to the normalising temperature for that particular steel, holding at temperature sufficient to allow homogenisation to occur and then air cooling to room temperature.

• The full annealing : process involves heating the steel slowly and uniformly to a temperature above the upper critical transformation point and holding until complete austenitisation and homogenisation occurs. Cooling after heating is carefully controlled at a particular rate as recommended by the steel manufacturer for the grade of tool steel involved.

• Cooling at this specified cooling rate is continued down to 550°C when the steel may be removed from the furnace and air cooled to room temperature.

SME 1613 : Materials Science 2007 Properties of tool steels & Applications

• wear resistant • capable of holding sharp cutting edge • very hard

Applications • wood working tools • concrete drills • cutting tools • drawing dies • embossing dies and etc

SME 1613 : Materials Science 2007 SME 1613 : Materials Science 2007 TYPICAL APPLICATIONS

AISI Compositions Applications NUMBER

M1 0.85C, 3.75Cr, 0.3Ni, 8.7Mo Drills, saws, lathe, 1.75W and 1.2 V and planer tools

A2 1.0C, 5.5Cr, 0.3Ni, 1.15Mo and Punches and dies 0.35 V (No tungsten)

D2 1.5C, 12Cr, 0.3Ni, 0.95Mo and Cutlery and drawing 1.1 V (No tungsten) dies

W1 1.1C, 0.15Cr , 0.2Ni, 0.1Mo. 015W Woodworking tools and 0.1 V

SME 1613 : Materials Science 2007 High Speed Steel (HSS)

• Capable of cutting at a much higher rate (high speed) than carbon tool steel

• Used to cut other metals/alloys

• continues to cut and retain its hardness even when the point of the tool is heated to a low red temperature.

Composition • Tungsten is the major alloying element • Also combined with molybdenum, vanadium and cobalt in varying amounts.

SME 1613 : Materials Science 2007 High Speed Steel (HSS) Mechanical Properties

1. High attainable hardness • Minimum attainable hardness of High-Rupturing Capacity (HRC) • Typical cutting tools may be HRC 64/68, depending on grade & application. • High carbon, along with elements to promote strong secondary hardness (W, Mo), are common to all high speed steels for this purpose

2. High hardness at elevated temperatures (600 oC) • This involves both red hardness (the ability to stay hard at elevated temperature during cutting) and temper resistance (the ability to resist permanent softening over time due to high temperature exposure). • The W and/or Mo contents of high speed steels promote these properties, and cobalt enhances it further when needed.

SME 1613 : Materials Science 2007 High Speed Steel (HSS)

3. High wear resistance • To promote edge retention during cutting. • Constant abrasion wears away tool surfaces. • The high volumes of wear-resistant in high speed steel microstructures aids in resisting this abrasion.

4. Sufficient impact toughness • To handle interrupted cutting applications, to avoid chipping during cutting, and to avoid breakage in fragile tools. • High speed steels are notably tougher than carbide or ceramic materials. • CPM (Crucible Powder Metallurgy)-produced high speed steels offer the ultimate in impact resistance for cutting tools.

SME 1613 : Materials Science 2007 Influence of alloying elements on the properties

SME 1613 : Materials Science 2007 Microstructure of HSS

Fine grain structure at 1000x showing uniform dispersal of carbides. Sample was austenitized at 2240°F and triple tempered at 1025°F to a hardness of HRC 70.

SME 1613 : Materials Science 2007 High Speed Steel: Applications

Turning, planning tools of all types, broaches and hobs, taps, twist drills, economical high speed steel grade, drills, reamers, milling tools, wood working tools, cold work tools, tool bits

SME 1613 : Materials Science 2007 SME 1613 : Materials Science 2007 SME 1613 : Materials Science 2007