Ferrous Metallurgy: Introduction to Steel and Steel making methods, Slides of Metallurgical Engineering

Download Ferrous Metallurgy: Introduction to Steel and Steel making methods and more Slides Metallurgical Engineering in PDF only on Docsity! 1 Ferrous Metallurgy-II (Introduction) لِلنَّاِس َوَمنَاِفُع َشِديدٌ 'ٌس بَْأ فِ,يِه ال'َحِديدَ َوَأَنَزل'نَا [ 25:ا,لحديد ] 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: Bessemer, open hearth, 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 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; 1. Soft or low carbon steels: up to 0.15% 2. Mild steels: 0.15% - 0.35% (generally ~ 0.2%) 3. Medium carbon steels: 0.35% - 0.65% 4. High carbon steels: 0.65%-1.75% Steels and their classifications Plain carbon steels 7 Three subgroups (not strict) • Other alloying elements are also present with carbon • Percentage of total alloying contents; 1. Low alloy steels: up to 5% (generally only a few %) 2. Medium alloy steels: 5% - 10% 3. 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 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. o 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 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 t el 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. 20 Classification of steel making processes Dominant processes (currently in use) LD Convertor 21 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. Classification of steel making processes Dominant processes (currently in use) 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) 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, • Basic 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 O2 means oxygen. Vessel rotation is indicated by arrows.