A Closer Look at Iron Smelting or Extractive MetallurgyThe Smelting ProcessHistorical TimelineBloomeryBloomery - 2Bloomery - 3Charcoal and CokeCharcoal to CokeBlast FurnaceBlast Furnace - 2Coke IronThe Pace of TechnologySlide 13http://www.pigiron.org.uk/index.php?nav=furnaceprocessIron and its AlloysProperties and Uses of Iron = f(composition)Effect of Iron Impurities on PropertiesA Closer Look at Iron Smelting or Extractive MetallurgyThe Smelting Process•Early smelting operations in Britain involved a two step process: smelting in a charcoal-burning furnace and then refining in a forge (to reduce non-iron content). •These required considerable capital, raw materials (iron ore, wood to make charcoal – later coal to make coke, limestone) and a transportation system to distribute the products.Historical TimelineDate Technology12th c. BCETools and weapons made from Fe in meteorites by smelting in bloomeries1200 BCEFe + charcoal  wrought iron1st c. BCE Oldest existing blast furnace in China1500 Steel production appeared in Europe1709Fe + coke  cast iron (A. Darby)2008 Top steel producers: China, US, JapanBloomery•A bloomery was the earliest form of a smelter.•Bloomery consists of a heat resistant chimney + pipes at the bottom for air + way to remove product called bloom (reduced iron).•Air is added via natural draft or bellows which required power (e.g. Water power)Bloomery - 2•Process: Heat bloomery by burning charcoal or coke; when hot, add iron ore + more fuel + limestone.•During the process, iron in the ore is reduced as pure iron pieces fall to bottom of chimney and weld together in a spongy mass to form the bloom.Bloomery - 3•The rest of the ore (impurities) form the slag. It also ends up at the bottom of the chimney including becoming embedded in the bloom.•To remove the slag and thus further purify the iron product, the bloom is reheated and then hammered. •The product of this process is called wrought iron.Charcoal and Coke•Charcoal: Residue left when wood (carbohydrate) is heated in absence of oxygen (anerobic) to drive off water and other volatile components. The porous residue is about 85% carbon and burns hotter and cleaner than wood.•Coke: Residue left when coal is heated in absence of oxygen (anerobic) to drive off water and other gases (H2, CH4, CO).Charcoal to Coke•Clow and Clow p 331, diagram on p 336•A process for converting coal to coke was patented in 1627.Blast Furnace•Again the required components are iron ore, fuel (originally charcoal), oxygen or air and a way to recover the product.•Process: Add iron ore and fuel from top and air (the blast) from the bottom resulting in iron reduction occurring continuously throughout the furnace.•Reduced iron and slag fall to the bottom and are recovered.Blast Furnace - 2•The process of using coke instead of charcoal as the fuel was first developed and sustained by Abraham Darby I in Coalbrookedale in 1709. This was a major contributor to the Industrial Revolution.•This furnace originally made cast iron pots, kettles, and later steam engine cylinders. •Later pig iron was produced.Coke Iron•A second blast furnace was built in 1715 where work culminated in 1754 (A. Darby II) successfully producing iron bars from pig iron. This led to a huge expansion of the iron industry.•1768 – first iron rails•1778 – A. Darby III started building the first Ironbridge and completed it in 1780.The Pace of Technology•The transition to coke-based cast iron production from charcoal-based malleable iron production took over 50 years even as forests were depleted, new cast-iron technologies were developed and limitations overcome:–Lack of high quality coal (i.e. low in S)–Lack of high quality coke–Developing more and new sources of power–Resistance to change to new technology•The first Darby furnace was excavated and is on display at Ironbridge.•The following slide shows a modern balst furnace.http://www.pigiron.org.uk/index.php?nav=furnaceprocessIron and its AlloysFe OxidesFe2O3(hematite), Fe3O4(magnetite), FeOPig Fe 3.5%-4.5% C + Si, Mn, P, S impurities. Very brittle (why called “pig” iron?)Cast Fe 2%-4% C + 1%-6% Si + Mn impurities. Produced by heating pig iron to reduce P and S.C Steel 2% C with Mn, S, P and SiWrought Fe< 0.25% C. Very malleableAlloy Steel Low C, but with added Cr, Mb, Ni, WHSLA Microalloyed, high strength, low alloyProperties and Uses of Iron = f(composition)•At least 3 types of pig iron were produced in the early stages of smelting. They differ in % Fe, C, etc–White crude iron: most brittle, not malleable, very hard, bright white crystals when fractured.–Grey crude iron: dark granular fractures, not as hard or brittle, more easily shaped–Black cast-iron: rough fracturesEffect of Iron Impurities on PropertiesC As %C increases, hardness increases, but malleability decreases.S Causes hot iron to be brittle causing cracks  limited integrity, weld failure.Si Leads to gray iron which is less brittle, preferred for casting.P Increases hardness and strength if 0.05% < %P < 0.2%. But > 0.2%, iron becomes brittle and unstable at low T.Al Mainly impacts slag viscosity