AECH 1103 - Topic 6a Iron and Steel (1) PDF

Topic 6 Metal industry: Iron and Steel AECH 1103 Industrial Process Overview  Metals http://www.tolajob.co.za/media/featured/metallurgy.jpg_1434863829.jpg Ferrous - those based on iron...

Topic 6 Metal industry: Iron and Steel AECH 1103 Industrial Process Overview  Metals http://www.tolajob.co.za/media/featured/metallurgy.jpg_1434863829.jpg Ferrous - those based on iron Steels Cast irons Nonferrous - all other metals Aluminum, magnesium, copper, nickel, titanium, zinc, lead, tin, molybdenum, tungsten, gold, silver, platinum, and others Superalloys 2  Where do metals come from? Metals come from rocks in the ground called ore. Hematite, the main iron ore 3 Steel production: from iron ore to functional industrial products 4 https://www.vepica.com/blog/steel-production-from-iron-ore-to-functional-industrial-products  Iron and Steel Production Iron making - iron is reduced from its ores. Steel making – iron is then refined to obtain desired purity and composition (alloying). Steel = an iron-carbon alloy containing from 0.02% to 2.1% carbon Cast iron = an iron-carbon alloy containing from 2.1% to about 4% or 5% carbon Steels and cast irons can also contain other alloying elements besides carbon 5  Iron Ores Required in Iron-making Iron ore is a rock that contains iron combined with oxygen. The principal ore used in the production of iron and steel is hematite (Fe2O3). Other iron ores include magnetite (Fe3O4), siderite (FeCO3), and limonite (Fe2O3-xH2O, where x is typically around 1.5). Iron ores contain from 50% to around 70% iron, depending on grade (hematite is almost 70% iron). Scrap iron and steel are also widely used today as raw materials in iron- and steel making. 6  Other Raw Materials in Iron-making Coke Coke is made from coal. Once mined, the coal is crushed and washed. Supplies heat for chemical reactions and produces carbon monoxide (CO) to reduce iron ore. During this process, by-products are removed, and coke is produced. Hot gases (CO, H2, CO2, H2O, N2, O2, and fuels) Used to burn coke Flux Limestone and dolomite are fluxes. Flux is a term for minerals used to collect impurities during iron and steelmaking. The flux causes a chemical reaction and elements not needed for steelmaking join to form slag. 7  Blast Furnace A refractory-lined chamber with a diameter of about 9 to 11m at its widest and a height of 40m 8 1- Charging the blast furnace 3- Treating the gases The raw iron is blended with other ore from the Hot gases produced in the chemical reactions top of blast furnace raise to the top of the furnace Very hot air is blown through nozzles Gas treating plant to clean the gas Oxygen reacts with the carbon dioxide and pure Carbon monoxide is useful for chemical iron reactions Image result for production of pig iron in blast furnace 2- Separating the iron from the slag The melted iron sinks to the bottom of the furnace The limestone combines with the rock and other impurities in the ore to form a slag which is lighter than the iron and floats on top Drawn off the iron and slag separately from the bottom Casting iron into an alloy called pigs iron 9  THE BLAST FURNACE G IN THE BLAST FURNACE IRON ORE IS REDUCED TO IRON. A THE REACTION IS POSSIBLE BECAUSE C CARBON IS ABOVE IRON IN THE REACTIVITY SERIES D B B E F 10  THE BLAST FURNACE COKE, LIMESTONE AND IRON ORE ARE ADDED AT THE TOP A 11  THE BLAST FURNACE HOT AIR IS BLOWN IN NEAR THE BOTTOM CARBON + OXYGEN CARBON + HEAT DIOXIDE C + O2 CO2 OXYGEN IN THE AIR REACTS WITH CARBON IN THE COKE. THE REACTION IS HIGHLY EXOTHERMIC B B AND GIVES OUT HEAT. 12  THE BLAST FURNACE THE CARBON DIOXIDE PRODUCED REACTS WITH MORE CARBON TO PRODUCE CARBON MONOXIDE C CARBON + CARBON CARBON DIOXIDE MONOXIDE C + CO2 2CO 13  THE BLAST FURNACE THE CARBON MONOXIDE REDUCES THE IRON OXIDE CARBON + IRON CARBON + IRON MONOXIDE OXIDE DIOXIDE 3CO + Fe2O3 3CO2 + 2Fe D REDUCTION INVOLVES REMOVING OXYGEN Using hematite as the starting ore: Fe2O3 + CO → 2FeO + CO2 Final reduction of FeO to iron: FeO + CO → Fe + CO2 14  THE BLAST FURNACE SILICA IN THE IRON ORE IS REMOVED BY REACTING WITH LIME PRODUCED FROM THE THERMAL DECOMPOSITION OF LIMESTONE CaCO3 CaO + CO2 CaO + SiO2 CaSiO3 CALCIUM SILICATE (SLAG) IS PRODUCED E MOLTEN SLAG IS RUN OFF AND COOLED 15  THE BLAST FURNACE MOLTEN IRON RUNS TO THE BOTTOM OF THE FURNACE. IT IS TAKEN OUT (CAST) AT REGULAR INTERVALS CAST IRON - cheap and easily moulded - used for drainpipes, engine blocks F 16 17  Pig Iron Special rail cars bring the Molten Iron away. The liquid iron typically flows into a channel and indentations in a bed of sand. Once it cools, this metal is known as pig iron. Pig iron is raw iron in an ingot form. The name is derived from the time when the iron ran into moulds. A row of moulds was said to resemble a litter of suckling pigs, so the single ingots were referred to as pigs. It is a hard but brittle mix of iron (90% or more) and carbon (typically 4-5%), manganese, sulphur, phosphorus, and silicon (roughly 3% in total). 18  To create a ton of pig Iron We start with 2 tons of ore, 1 ton of coke and ½ ton of limestone The fire consumes 5 tons of air The temperature reaches almost 1600 degrees C at the core of the blast furnace! 19  Wrought Iron Pig iron contains 4 percent to 5 percent carbon and is so hard and brittle that it is almost useless. Therefore, We can i. melt it, mix it with slag and hammer it to eliminate most of the carbon (down to 0.3 percent) and create wrought iron. ii. create steel. Wrought iron is the stuff a blacksmith works with to create tools, horseshoes and so on. When you heat wrought iron, it is malleable, bendable, weldable and very easy to work with. 20  Steel Steel is an alloy mainly composed carbon and iron. It has a consistent concentration of carbon throughout (0.5 percent to 1.5 percent). Impurities like silica, phosphorous and sulphur weaken steel tremendously, so they must be eliminated. The advantage of steel over iron is greatly improved strength, so it is used in buildings, infrastructure, tools, ships, trains, cars, bicycles, machines, electrical appliances, furniture, and weapons. Sometimes to enhance the steel’s properties, other elements are added like: Manganese, Chromium, Tungsten, Vanadium and Nickel Example: Stainless steels, which are resistant to corrosion and oxidation, typically need an additional 11% chromium. 21 Pig Iron vs Steel 22  Production Process of Steel Raw inputs of iron ore, coke, and lime are 1. Iron Making melted in a blast furnace Molten steel from Basic oxygen furnace 2. Steel Making (BOF) or Electric furnace routes are treated to adjust steel composition Steel is formed into shapes by hot rolling 3. Steel Forming and different shaping techniques 4. Manufacturing Finalized for desired properties 5. Fabrication 6. Finishing 23  Basic Oxygen Furnace (BOF) Accounts for  70% of steel production in U.S Adaptation of the Bessemer converter Bessemer process used air blown up through the molten pig iron to burn off impurities BOF uses pure oxygen Typical BOF vessel is  5 m (16 ft) inside diameter and can process 150 to 200 tons per heat Entire cycle time (tap-to-tap time) takes  45 min Basic oxygen furnace showing BOF vessel during processing of a heat 24 BOF sequence : (1) charging of scrap and (2) pig iron, (3) blowing, (4) tapping the molten steel, (5) pouring off the slag 25 26  Electric Arc Furnace Accounts for  30% of steel production in U.S. Scrap iron and scrap steel are primary raw materials Capacities commonly range between 25 and 100 tons per heat Complete melting requires about 2 hr; tap-to-tap time is 4 hr Usually associated with production of alloy steels, tool steels, and stainless steels Noted for better quality steel but higher cost per ton, compared to BOF 27  An electrical furnace in which the thermal effect of an electric arc is used to smelt metals and other materials. Arc furnaces are classified according to their method of heating as direct and indirect furnaces and furnaces with a submerged arc. Electric arc furnace for steelmaking 28  Casting Processes in Steel-making Steels produced by BOF or electric furnace are solidified for subsequent processing either as cast ingots or by continuous casting 1. Casting of ingots – a discrete production process 2. Continuous casting – a semi-continuous process 29  Casting of Ingots Steel ingots = discrete castings weighing from less than one ton up to  300 tons (entire heat) Molds made of high carbon iron, tapered at top or bottom for removal of solid casting The mold is placed on a platform called a stool A big-end-down ingot mold typical of type After solidification the mold is lifted, used in steelmaking leaving the casting on the stool 30  Continuous Casting Continuous casting is widely applied in aluminum and copper production, but its most noteworthy application is in steel- making. Dramatic productivity increases over ingot casting, which is a discrete process. For ingot casting, 10-12 hr may be required for casting to solidify. Continuous casting reduces solidification time by an order of magnitude. 31  Videos IRON -- PRODUCT OF THE BLAST FURNACE https://www.youtube.com/watch?v=PwHmpAlkk7s How steel is produced https://www.youtube.com/watch?v=YZjgUyDSq40 Iron and Steel https://www.youtube.com/watch?v=xAVCY0WE8uM 32