01- Introduction.pptx By Sir Rabnawaz Khan Of PIEAS university

Professor of Pakistan institute of applied science and technology

1. Ferrous Metallurgy-II ( Introduction) وَأَنزَلْنَا الْحَدِيدَ فِيهِ بَأْسٌ شَدِيدٌ وَمَنَافِعُ لِلنَّاسِ [ الحديد ‏: 25] And we brought down iron with in in it mighty power, as well as many benefits for mankind [ Al- Hadid : 25] ‏

2. Classification of steel Routes of steel making: Electric arc furnace, top-blown and bottom blown processes, acid and basic processes. Thermodynamics and chemistry of steel making, decarburizing, fluxing and slag forming for removal of impurities in steels. Secondary steel making process, e.g., AOD, VOD, ESR, VAR. Vacuum induction melting, Alloy additions and their control for low alloy steel and stainless steels Ingot casting and continuous casting, Casting defects . Ferrous Metallurgy-II Course Contents

3. Lecture contents Steels and Their Classifications Routes of Steel Making Principles of Steel Making Classification of Steel Making Processes Steel Making Processes Steel Plant Products SAE Steel Grades System ( USA) International Organization for Standardization (ISO )

4. Steels A malleable alloy of iron and one or more other elements such as carbon, chromium, nickel, silicon, vanadium , tungsten, etc. Thousands of steel varieties exists (odd). Different in composition. However, a couple of hundred varieties are predominantly in use. Composition based categories Plain carbon steels: Alloys of iron and carbon only Alloy steels: Alloys of iron and carbon with 1 or more other elements To ensure specific properties such as better mechanical strength , ductility , electrical and magnetic properties, corrosion resistance Specifically added elements are known as alloying additions in the steels Steels and their classifications

5. Impurities in Steels Al, Si, Mn , S, P, O, etc . which are unavoidable and not added Associated with the iron and steel making processes Cannot be eliminated 100% due to high cost of refining processes Tolerable (safe) limits of impurities Sulfur < 0.05% for ordinary steel and for special steel < 0.005% For most high quality steels now the total impurity level acceptable is below 100 ppm and the aim is 45 ppm Steels and their classifications

6. Four types Major and only alloying element is carbon Percentage of carbon in different types; Soft or low carbon steels: up to 0.15% Mild steels: 0.15% - 0.35 % ( generally ~ 0.2%) Medium carbon steels: 0.35% - 0.65 % High carbon steels: 0.65 %-1.75 % Steels and their classifications Plain carbon s teels

7. Three subgroups (not strict) Other alloying elements are also present with carbon Percentage of total alloying contents; Low alloy steels: up to 5% (generally only a few %) Medium alloy steels: 5% - 10% High alloy steels: more than 10%- 1.75 % Process based classification is also sometime used but obsoleted Because many steel making processes can make several types of steels In terms of use , steels are often classified as structural, forging , deep-drawing, rail , flats , and the like . Steels and their classifications Alloy steels

8. Mild steels: economical to produce & therefore relatively cheap Low C steels: difficult to produce & therefore cost goes up with falling carbon below 0.20 - 0.25%. High C steels: cost increases by increasing C content > 0.30% Alloy steels: Costlier than plain carbon steels. Plain C steels: 80 % of the total steel production , and within that %age , the mild steels , being cheap , take the lion’s share and used for construction purposes Flat products are produced from low C steels because of their much better malleability , which enables their easy rolling into thin sections. High C steels: cutting tools because of their associated better hardness . Steels and their classifications Cost comparison of steels

9. Steel is produced from iron ores in a minimum of two stages , Production of iron by reduction smelting in the first stage: e.g. pig-iron if molten and sponge iron or directly reduced iron if solid Subsequent refining to steel in the second stage . Pig-iron: may contain impurities like C, Si, Mn , P, S, etc., which together may add up to 8 wt.% of the iron. Sponge iron may contain the gangue oxides of the iron ore like Al 2 O 3 , SiO 2 , CaO , MgO , etc., as impurities . The actual contents shall depend on the quality of iron ore used to produce sponge iron . Routes of steel making

10. Routes of steel making Four different routs Rout (a) Rout (b) Rout (c) Rout (d)

11. Route (a) is no longer used and is only for historical knowledge . Route(b ) is used for large-scale integrated steel plants of several million metric tons per annum capacity. Route (c) is the alternative developed where coking coal is not available and alternative fuel is available. Route (d) is the process of conversion of scrap into finished steel, which is then carburized in solid state to produce steel . Now much of the steel is produced by route (b) wherein iron ore is reduced by carbon in a vertical shaft furnace to produce molten iron. The produced molten iron is refined using iron ore or oxygen as the oxidizing agent to produce steel in molten condition. Routes of steel making Four different routs

12. Routes of steel making Four different routs Route (a) is not shown in this figure

13. Steel making is a process of selective oxidation of impurities i.e ., the reverse of ironmaking . Impurities are oxidized to their respective oxides which are eliminated either as gas (in the case of carbon) or liquid oxide (slag). The exception: Sulfur is reduced Early years: iron ore and mill scale or air used as the oxidizing agents for refining. These are now almost completely replaced by oxygen gas , nearly pure in form. Modern steel making is therefore often referred to as oxygen steel making . Principles of steel making

14. Bessemer Process in UK 1860s Pneumatic process Air for refining Later, open hearth & electric furnaces Hearth processes (due to shallow hearth) Use of iron ore or mill scale as refining agent Use of external energy for the processes Open hearth : Producer gas Electric furnace: electrical energy Classification of steel making processes Process development era for modern steel making Furnace / convertor based classification

15. Classification of steel making processes Process development era for modern steel making Schematic view of Bessemer Convertor and the Process

16. Classification of steel making processes Process development era for modern steel making Schematic view of Open-hearth Furnace

17. Depending upon the impurities to be eliminated, the slag nature has to be adjusted Acidic processes (rarely used) Silica saturated slag & furnace lining is acidic (silica lining) Removal of silicon, manganese and carbon only Basic processes (more common) Removal of phosphorus and sulfur + silicon , manganese and carbon Basic slag & furnace lining (Mixture of different basic oxides) Use of lime or lime stone as flux Classification of steel making processes Slag based classification Modern steel making is carried out in basic lined furnaces or vessels making basic slag , using oxygen as the refining media. This is often called basic oxygen furnace steel making or BOF.

18. Conventional processes Use iron oxide and air for refining Bessemer, open hearth, and the electric furnace processes Modern processes Use only oxygen for refining Recent origin (developed in recent years) Classification of steel making processes Classical versus modern processes Electric furnace process developed into such a technology that it could now compete with other oxygen steel making processes for making almost any variety of steel .

19. Classification of steel making processes Dominant processes (currently in use) Only two basic processes of steel making are now used LD process (Austria) Named for the cities of Linz and Donawitz (now part of Leoben ) More dominantly used and produces the large bulk of steel today Modified BOF ( basic oxygen furnace ) process Uses molten steel Electric furnaces Includes both arc and induction varieties Use scrap and DRI Any new steel plant will adopt only the modern form of BOF process or electric furnace process alone

20. Classification of steel making processes Dominant processes (currently in use) LD Convertor

21. Classification of steel making processes Dominant processes (currently in use) BOF or LD process Pure oxygen at supersonic speed is blown vertically through a lance (with several openings at the tip) onto the surface of molten hot metal Cylindrically-shaped converter with high productivity (Can’t kept idle) Quicker ( 1 hr ) than open hearth furnaces ( 6 – 8 hrs ) process Autothermal process, i.e. self-sufficient in thermal energy (burning of C, Si, P) Real breakthrough came in the late 1970s & early 1980s with the introduction of mixed blowing Combination of top & bottom blowing Bottom blow: thermodynamic equilibrium at the slag-metal interface brought about by limited gas injection from the converter bottom .

22. EAF process Uses steel scrap and DRI Hot metal can also be used Electrical energy is used to meet the thermal requirements Gaseous/solid oxygen sources (like iron ore) oxidize the impurities in hot metal and to adjust composition Classification of steel making processes Dominant processes (currently in use)

23. Prior to the 1850s Molten iron was refined to first produce wrought iron Nearly impurity-free ferrous material, small amount of entrapped slag particles Recarburized in solid state to make steel Recarborizing decreases its melting point to make it melt-able in furnace (till 1700 A.D) Maximum achievable temp was 1450 ° C due to combustion of chemical fuel This was known as blister or cement steel The process is known as the cementation process of steel making . The excellent quality swords , daggers, clock springs , etc., were made 1740 in the UK , the cement steel melted in a crucible and thereby laid the foundation of the crucible process of steel making Steel making processes A brief history

24. 1860 Henry Bessemer in UK : blowing cold air through molten iron Producing steel, finally in molten condition . Concurrently Robert Mushet : developed deoxidation of molten steel Used low Mn containing ferro-manganese to produce steel ingots This is considered to be the beginning of modern steel making Molten iron is processed, to produce molten steel, Which can produce sound steel ingots for subsequent rolling into desired products. 1878 Thomas in Germany: modified into Basic Bessemer process Usable to remove P & S (also known as the Thomas process of steel making) Steel making processes A brief history

25. 1861 William & Fredrick in Germany and Emile & Pierre Martin in France: used the heat regeneration principle to raise furnace temperature to 1600 °C To melt steel scrap , refine the melt and produce steel in molten condition known as the open-hearth process of steel making Used until World War-II and even a few decades thereafter. Replaced by the faster, economical and better-quality producing oxygen steel making processes. 1900~ Paul Heroult : electric arc furnace Ferranti: induction furnace For melting steel scrap Steel making processes A brief history

26. 1950 LD, Kaldo and the Rotor processes of steel making Using pure oxygen as a refining agent: beginning of modern oxygen steel making The top blowing process is known as LD process in Europe , Basic oxygen steel making (BOS) in the UK , B asic oxygen furnace (BOF ) process in the United States , and in Far East countries . It is known as the basic oxygen process (BOP) in U.S. Steel . Later, bottom blown oxygen processes were developed LD process was modified to blow lime powder with oxygen Steel making processes A brief history Latest in the field is modified LD process: combination of bottom gas blowing and top-blowing of oxygen known as bath agitated processes, BAP

27. Steel making processes A brief history Illustration of underlying principles of major steel making processes. Shows the direction of charge materials, oxygen and products. The abbreviations S , I , and F mean scrap, molten iron and flux , P means products and O 2 means oxygen. Vessel rotation is indicated by arrows .

28. I-sections, channels, angles, plates, rails, sheets, axles, and wheels for railways , merchant products like rounds, hexagons, squares, strips, galvanized sheets , tin plates, wire rods, and so on. Steel plant products Structural shapes HSS: Hollow structural section Sheets Tubes Bars Wire rods

29. Railroad & axles Steel plant supply directly to railways Semis Semi-finished steel products of steel making plant Processed further in engineering industries before their actual use Integrated steel plant (Routes b & c ) Liquid steel is casted into ingots or CCM (continuous casting machine) products Subsequently rolled in several types of mills to produce semis Mini steel plant ( Route d ) More common, use scrap & produce billets using CCM Steel plant products Product and plant types

30. Steel plant products: CCM products

31. SAE designation Type 1xxx Carbon steels 2xxx Nickel steels 3xxx Nickel-chromium steels 4xxx Molybdenum steels 5xxx Chromium steels 6xxx Chromium-vanadium steels 7xxx Tungsten steels 8xxx Nickel-chromium-molybdenum steels 9xxx Silicon-manganese steels SAE steel grades Major classifications of steel Further study: https :// en.wikipedia.org/wiki/SAE_steel_grades

32. Series Type 100 austenitic general purpose stainless steel 200 austenitic chromium-nickel-manganese alloys 300 austenitic chromium-nickel alloys 400 ferritic and martensitic chromium alloys 500 heat-resisting chromium alloys 600 proprietary alloys 900 austenitic chromium-molybdenum alloys SAE steel grades Stainless steel Further study: https :// en.wikipedia.org/wiki/SAE_steel_grades

33. 201 —Austenitic SS that is hardenable through cold working 301 —Highly ductile, for formed products. Also hardens rapidly during mechanical working. Good weldability . 304 —The most common grade; The classic 18/8 (18% chromium, 8% nickel) stainless steel . 316 —The second most common grade (after 304); Food (cutlery) and  surgical stainless steel  uses. Addition of molybdenum prevents specific forms of corrosion (pitting). It is also known as marine grade stainless steel due to its increased resistance to chloride corrosion compared to type 304. 316 is often used for building  nuclear reprocessing plants . Stainless Steel Grades Austenitic chromium- nickel alloys

34. 405 —Ferritic for welding applications 408 —Heat-resistant ; poor corrosion resistance Its higher grade is 439, used for catalytic converter exhaust sections . Increased chromium for improved high temperature corrosion/oxidation resistance. 409 —Cheapest type; used for  automobile exhausts; ferritic 410 —Martensitic (high-strength iron/chromium). Wear-resistant , but less corrosion-resistant . 440 —Cutlery steel, with more C , Edge retention when heat-treated . Hardest stainless steels. Due to its toughness and relatively low cost, most display-only and replica swords or knives are made of 440 stainless . Stainless Steel Grades Ferritic and martensitic chromium alloys