材料科学与工程基础5(上课)ppt课件.pptx

Chapter 5 Engineering Alloys5.1 IntroductionMetals and alloys are the most important engineering materials in industry, which account for about 90% of the world’s production of metals.Because of: Good strength ,Toughness, Ductility, Low costMajor types:Ferrous alloy（黑色合金）: based on ironNonferrous alloy（有色合金）: based on the other metals5.2 Production of Iron and Steel5.2.1 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 + 3CO2Production of Iron and SteelProperties of pure iron: low strength and ductilityTensile strength: 180 – 230 MN/m2Yield strength at 0.2 % offset: 100-170 MN/m2Hardness( Hb ): 50 – 80 kgf/mm2Percent 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 systemBasic properties for Fe3 C:High hardness with brittle featureTensile strength: 30 MN/m2Hardness ( Hb ): 800 kgf/mm2Percent elongation at fracture: 0 Solid phases in the phase diagram: * ? - ferrite:高温铁素体 BCC structure An interstitial solid solution of