Production of ( Working and Merits and Demerits)  Bessemer  Open hearth  LD methods  Classification of steel ( properties and uses only)  Mild, Medium and High

15CY104: Material Technology SRM University 2 • What is ? – Iron is a chemical element. It is a strong, hard, heavy gray , – Iron is produced by melting iron ore (mineral compounds in the earth's crust – 5% of the Earth's crust is iron ) and removing impurities.

• What is steel? – Steel is simply a purer form of iron with lower carbon content. – Steel can be produced from molten iron ore with blast of air (BOF), Electric furnace, Bessemer converter.

15CY104: Material Technology SRM University 3 15CY104: Material Technology SRM University 4 15CY104: Material Technology SRM University 5  Production of Steel  Bessemer  Open hearth  LD methods

15CY104: Material Technology SRM University 6 • The Bessemer process was the first inexpensive industrial process for the massproduction of steel from molten prior to the . The key principle is removal of impurities from the iron by oxidation with air being blown through the molten iron.

15CY104: Material Technology SRM University 7 • In this process pig iron is poured into Bessemer converter which is pear shaped and has a steel shell lined with material. It’s pivoted on trunnions so as to facilitate tilting, pouring or charging. • Once the above converter is charged with molten pig iron, a strong thrust of air is blasted across the molten mass for about 20 minutes through nozzles provided at the bottom of the vessel. The process oxidizes all traces of the carbon and present, leaving the converter with pure iron . • After this the blasting of air is stopped and the specified amount of ferro is added to it for the sake of including the recommended content of carbon and manganese to the steel. • The air blasted procedure is again initiated for some time , ensuring perfect mixing of the . • The converter is then tilted so that the molten material can be discharged into the ladles. In the final step the molten alloy is shifted into rectangular moulds where it’s obtained in the form of solid ingots.

15CY104: Material Technology SRM University 8 Chemistry of the Process  During the first stage of the operation, Si and Mn are oxidized

2Fe + O 2  2FeO; H= 128,000 cal. 2FeO + Si  2Fe + SiO 2; H= 70,200 cal. FeO + Mn  2Fe + MnO; H = 26,800 cal.

 SiO 2, MnO and some FeO combine to form the (FeO.SiO 2 & MnO.SiO 2 )  After most of the Mn and Si are gone, the carbon begins to burn FeO + C  Fe + CO

FeO + Fe 3C  4Fe + CO 2CO + O 2  2CO 2 Recarburizing  Carbon in the form of or graphite may be added to the blow metal to have desired carbon content of the finished steel. Deoxidizing  Ferromanganese is added to the blown metal to remove the residual oxygen remaining in the metal FeO + Mn  MnO + Fe 15CY104: Material Technology SRM University 9 • The open hearth process is a batch process and a batch is called a "heat". Heavy , such as building, construction or steel milling scrap is added, together with pig iron from blast furnaces. • This process was known as the SiemensMartin process, and the furnace as an "open hearth" furnace

15CY104: Material Technology SRM University 10 • The specialty of openhearth furnaces is the extreme heat that can be obtained from them due to their regenerative process . The charge of pig iron, steel scrap, iron ore, and flux are together kept in a shallow container with a flame burning above it. The process is initiated inside reverbaratory gasfired regenerative furnaces for greater efficiency. • Regenerators are placed below the furnace and positioned in two pairs. The pairs are heated alternately through the passage of hot gases given out from the furnace in their route to the chimney. This heat is retained by the regenerators and is reversed and given back to the furnace . This heat exchange procedure helps the furnace to maintain high temperatures even with less fuels . • Once the furnace is charged with pig iron, pure oxidizing ores like haematite are added to it from time to time, which helps oxidization and the removal of impurities like silicon, carbon, and manganese in the pig iron. Spiegel is also introduced when the carbon content becomes less than 0.1%, and ferro manganese after the metal is tapped out into the ladle. Ferromanganese becomes important for restoring malleability and also for the iron.

15CY104: Material Technology SRM University 11 Bessemer Process Open Hearth Process It can use comparatively higher phosphatic It can use lower phosphatic pigs of narrower pigs of wider ranges of composition. ranges of composition. Scrap iron cannot be used. Scarp iron can be used. and finishing require 10 to 20 Refining and finishing, are completed within 8 to minutes. 10 hours. Operations depend entirely on eye Operation is guided by laboratory analysis, so it is judgement, so it is very difficult to produce a comparatively possible to produce a uniform uniform product. product. Bessemer process produces an inferior Open hearth steel is of much superior quality quality steel associated with blow holes and containing lesser blowholes and inclusions. inclusions. Carbon is completely eliminated first and so Carbon is partially removed and requires smaller requires large amount of recarburizer and amount of recarburizer and the product is more the product becomes less homogeneous. homogeneous. Low capital investment. High capital investment. Output low (80% of pig used). Output high comparatively. Because of rapidity of the process, the Operation is comparatively easy and finishing up control of different operations is rather to the desired analysis is feasible. difficult and careful working is necessitated.

15CY104: Material Technology SRM University 12  The name LD stands for Linz and Donawitz, these were the two places in Austria where the process was born.  This process is also called as Basic Oxygen Process.  LD process is a refining process which is carried out in a LD vessel(or LD converter/BOF).

15CY104: Material Technology SRM University 13 15CY104: Material Technology SRM University 14  LD converter is a welded construction of nonageing steel plates (8mm), the height of the vessel varies from 710m.

 L.D converter has a basic lining of bricks (permanent lining) and bricks (working lining).

 Oxygen lance (810m & 2025cm dia) is made of concentric steel tubes and the tip of the lance is made with Copper.

15CY104: Material Technology SRM University 15 1. Charging

2. Blowing

3. Sampling

4. Tapping

5. Slag off

15CY104: Material Technology SRM University 16 i) Scrap:  Home scrap generated in the plant is charged.  It acts as a coolant & utilizes the excess heat energy generated during refining.  LD process can take upto 25% of the metal charge as scrap.

15CY104: Material Technology SRM University 17 ii) Hot Metal (7590%): The analysis of iron required to use in LD process as follows: C → 4.10 4.30%

Si → 0.50 – 0.85%

Mn → 0.50 – 0.80%

S → 0.02 – 0.03%

P → 0.10 – 0.25%

15CY104: Material Technology SRM University 18 iii) Fluxes:  Lime (95% CaO) and dolomite (58%CaO, 39%MgO) are the two primary fluxes. iv) Coolants:  , scrap, iron ore, and sponge iron are all potential coolants that can be added to a heat that has been overblown and is excessively hot. v) Oxygen:

 99.5% of pure oxygen is used as refining agent.

15CY104: Material Technology SRM University 19  After charging, the vessel is rotated to vertical position, lance is lowered to

blowing position and O2 is turned on.

 Oxygen blows at a pressure of 911 atmos. which increases temperature (1600 0C) and burns off impurities.

 The blow continues for nearly 1525 minutes.  Oxygen consumption: 5060 Nm3/t of steel.

15CY104: Material Technology SRM University 20 • Slag and metal samples are taken out for analysis.

• Temperature of the bath is measured by immersion of thermocouple.

15CY104: Material Technology SRM University 21 • If the analysis & tapping temperature are in the required range, then the molten steel is tapped in the laddle. • Deoxidizers and alloying additions are made in the laddle. • Taptotap time is 40 – 50 min.

15CY104: Material Technology SRM University 22 • Deoxidation is the final process in which dissolved oxygen in the steel is removed. • The deoxidizers i.e. Al, FeSi and FeMn are added to the steel, which combines with dissolved oxygen and forms their .

FeO + Al Fe + Al 2O3

FeO + FeSi Fe + SiO 2 FeO + FeMn Fe + MnO

15CY104: Material Technology SRM University 23 • After tapping steel into the ladle, and turning the vessel upside down and tapping the remaining slag into the "slag pot“.

15CY104: Material Technology SRM University 24 1. [Fe] + [O] → (FeO)

2. [C] + [O] → {CO}

3. [Si] + 2 [O] → (SiO 2) 4. [Mn] + [O] → (MnO)

5. 2[P] + 5[O] → (P 2O5) 6. [FeS/MnS] + (CaO) → (CaS) + (FeO/MnO)

15CY104: Material Technology SRM University 25 15CY104: Material Technology SRM University 26  LD process is about ten times faster than the open hearth process.

 Instead of air pure oxygen is used, this eliminates the harmful effects of .

 It produces steel with low S & P content from raw materials of ordinary quality.

 It does not use an external source of heat or fuel.

 Pure oxygen blow helps adjusting to desired lower level of C, Mn, S, Si and P content of iron

15CY104: Material Technology SRM University 27  The major disadvantage of LD process is that the charge must include a considerable quantity of molten pig, thus limiting the amount of scrap that can be used.

 Steel wastage due to splashes by oxygen lancing is more.

 Insufficient depth of penetration of O2, leads to thermal gradient in the bath.

15CY104: Material Technology SRM University 28 Low/mild 0.04-0.30%c Carbon steel Medium 0.3-0.60% High 0.6-1.50% steel Low alloy up to 5%

Medium alloy up to 5- 10% Alloy steel High alloy up to 10%

15CY104: Material Technology SRM University 29 Carbon steels are ironcarbon alloys containing up to 2.06% of carbon, up to 1.65% of manganese, up to 0.5% of silicon and sulfur and as impurities. Carbon content in carbon steel determines its strength and ductility . The higher carbon content, the higher steel strength and the lower its ductility. According to the steels classification there are following groups of carbon steels:  Low carbon steels (C < 0.25%)  Medium carbon steels (C =0.25% to 0.55%)  High carbon steels (C > 0.55%)  Tool carbon steels (C>0.8%)

15CY104: Material Technology SRM University 30 Low carbon steels (C < 0.25%)  Properties : good formability and weldability , low strength, low cost.  Applications : deep drawing parts, chain, pipe, wire, nails, some machine parts.

Medium carbon steels (C =0.25% to 0.55%)  Properties : good toughness and ductility, relatively good strength, may be hardened by  Applications : rolls, axles, screws, cylinders, crankshafts, heat treated machine parts.

15CY104: Material Technology SRM University 31 High carbon steels (C > 0.55%) Properties : high strength, hardness and wear resistance, moderate ductility. Applications : rolling mills , rope wire, screw drivers, hammers, wrenches, band saws.

Tool carbon steels (C>0.8%) – subgroup of high carbon steels Properties : very high strength, hardness and wear resistance, poor weldability low ductility. Applications : punches, shear blades, springs, milling cutters, knives, razors.

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