材料科学与工程基础5(上课)课件

Chapter 5 Engineering Alloys,5.1 Introduction,Metals and alloys are the most important engineering materials in industry, which account for about 90% of the worlds production of metals. Because of: Good strength ,Toughness, Ductility, Low cost Major types: Ferrous alloy（黑色合金）: based on iron Nonferrous alloy（有色合金）: based on the other metals,5.2 Production of Iron and Steel,5.2.1 Production of Pig Iron ( 生铁 ) Most pig iron is extracted from iron ores in a large blast furnace ( 高炉 ), and then is usually transferred to steel-making furnace in the liquid state. 5.2.2 Typical reaction: Fe2 O3 ( iron ores 铁矿石 ) + 3CO ( coke 焦炭 ) 2Fe + 3CO2,Production of Iron and Steel,Properties of pure iron:,low strength and ductility Tensile strength: 180 230 MN/m2 Yield strength at 0.2 % offset: 100-170 MN/m2 Hardness( Hb ): 50 80 kgf/mm2 Percent elongation at fracture: 30-50% Therefore, it is rare to use pure iron in industry.,5.3 Steel making and processing of major steel products,The majority of steels contain less than 0.5% of carbon. Most commonly process for converting pig iron into steel is basic process ( 氧气吹顶法 ).,Pig iron and 30% steel crap is fed into refractory furnace to which oxygen lane is inserted. Oxygen reacts with liquid bath to form iron oxide. FeO + C Fe + CO Slag forming fluxes are added. Carbon content and other impurities are lowered. Molten steel is continuously cast and formed into shapes.,5.4 The iron iron carbide phase diagram ( 铁碳合金相图 ),The components for iron iron carbide phase diagram ( Fig. 9.6 ),The components for iron iron carbide phase diagram ( Fig. 9.6 ) * Pure Fe * Fe3 C ( 渗碳体 ): intermetallic compound,up to 6.67 wt% c in the system Basic properties for Fe3 C: High hardness with brittle feature