材料科学与工程基础5(上课)课件.pptx

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1、Chapter 5 Engineering Alloys,1,2021/7/13,Chapter 5 Engineering Alloys12,5.1 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

2、alloy（黑色合金）:based on ironNonferrous alloy（有色合金）:based on the other metals,2,2021/7/13,5.1 IntroductionMetals and all,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

3、 furnace in the liquid state.5.2.2 Typical reaction:Fe2 O3(iron ores 铁矿石)+3CO(coke 焦炭)2Fe+3CO2,3,2021/7/13,5.2 Production of Iron and Ste,Production of Iron and Steel,4,2021/7/13,Production of Iron and Steel42,Properties of pure iron:,low strength and ductilityTensile strength:180 230 MN/m2Yield str

4、ength 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.,5,2021/7/13,Properties of pure iron:low s,5.3 Steel making and processing of major steel products,The majority of steels contain less than 0.5%of carbon.

5、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

6、 are lowered.Molten steel is continuously cast and formed into shapes.,6,2021/7/13,5.3 Steel making and proce,7,2021/7/13,72021/7/13,5.4 The iron iron carbide phase diagram(铁碳合金相图),The components for iron iron carbide phase diagram(Fig.9.6),8,2021/7/13,5.4 The iron iron carbide ph,The components for

7、 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:0,9,2021/7/13,The components for iron iron,Sol

8、id phases in the phase diagram:,*-ferrite:高温铁素体 BCC structure An interstitial solid solution of carbon in iron.It has a greater lattice constant.*-ferrite:铁素体 BCC structureAn interstitial solid solution of carbon in the BCC iron crystal lattice.Carbon is only slightly soluble in ferrite,10,2021/7/13

9、,Solid phases in the phase diag,*-austenite:奥氏体 FCC structure An interstitial solid solution of carbon in iron.*cementite(Fe3 C):渗碳体+Fe3 C:mixture of eutectic reaction ledeburite莱氏体 Liquid(4.3%C)(2.08%C)+Fe3 C(6.67%C)*+Fe3 C:mixture of eutectoid reaction,Pearlite 珠光体(0.8%C)(0.02%C)+Fe3 C(6.67%C),11,

10、2021/7/13,*-austenite:奥氏体 FCC s,Point T C C wt%MeaningA 1538 0 melting T of pure FeB 1495 0.53 Lb for peritectic reactionC 1148 4.30 eutectic point(共晶点)D 1227 6.67 melting T of Fe3 C E 1148 2.08 max.C in-FeG 912 0-Fe-FeH 1495 0.09 max.C in-Fe J 1495 0.17 peritectic point(包晶点)N 1394 0-Fe-FeP 723 0.02

11、 max.C in-Fe S 723 0.8 eutectoid point(共析点)Q 650 0.005 max.C in-Fe,Points in the phase diagram:,12,2021/7/13,Points in the phase diagram:12,Invariant reactions,Peritectic reaction:Liquid(0.53%C)+(0.09%C)(0.17%C)Eutectic reaction:Liquid(4.3%C)austenite(2.08%C)+Fe3C(6.67%C)Eutectoid reaction:Austenite

12、(0.8%C)Ferrite(0.02%C)+Fe3C(6.67%C),14950C,11480C,7230C,0.8%CEutectoid Steel,HypoeutectoidSteel,HypereutectoidSteel,Less than 0.8%,More than 0.8%,13,2021/7/13,Invariant reactions Peritectic,5.5 The cooling process of typical composition in iron-iron carbide phase diagram,1)Eutectoid plain-carbon ste

13、el(共析普通碳素钢):0.8%C,cooled from 750 C Fig.9.7 on page 375 Final phases:Pearlite2)Hypoeutectoid plain-carbon steel(亚共析普通碳素钢):0.4%C,cooled from 900 C Fig.9.9 on page 377 Final phases:+pearlite,14,2021/7/13,5.5 The cooling process of ty,3)Hypereutectoid plain-carbon steel(过共析普通碳素钢)1.2%C,cooled from 950 C

14、 Fig.9.11 on page 379 Final phases:Fe3 C+pearlite,15,2021/7/13,3)Hypereutectoid plain-carbon,Example 1,A 0.80%C eutectoid plain-carbon steel is slowly cooled from 750to a temperature just slighly below 723.Assuming that the austenite is completely transformed to and cementite:Calculate the weight pe

15、rcent eutectoid ferrite formed.Calculate the weight percent eutectoid cementite formed.,16,2021/7/13,Example 1 A 0.80%C eutect,Example 2,A 0.4%C hypoeutectoid plain-carbon steel is slowly cooled from 940to a temperature just slightly below 723Calculate the weight percent proeutectoid ferrite present

16、 in the steelCalculate the weight percent eutectoid ferrite and weight percent eutectoid cementite present in the steel,17,2021/7/13,Example 2A 0.4%C hypoeutectoi,Example 3,A hypoeutectoid plain-carbon steel was slow-cooled from the austenitic region to room temperature contains 9.1%eutectoid ferrit

17、e.Assuming no change in structure on cooling from just below the eutectoid temperature to room temperature,What is the carbon content of the steel?,18,2021/7/13,Example 3A hypoeutectoid plain,Problem,A hypereutectoid plain-carbon steel contains 10.7wt%eutectoid Fe3C.What is its average carbon conten

18、t in weight percent?Fig.EP 9.3 P381,19,2021/7/13,ProblemA hypereutectoid plain-,Slow Cooling of Plain Carbon Steel,Eutectoid plain carbon steel:If a sample is heated up to 7500C and held for sufficient time,structure will become homogeneous austenite.,Below eutectoid temperature,layers of ferrite an

19、d cementite are formed.Pearlite.,20,2021/7/13,Slow Cooling of Plain Carbon S,Slow Cooling of Plain Carbon Steel(Cont.),Hypoeutectoid plain carbon steel:If a sample of 0.4%C is heated up to 9000C,it gets austenitized.Further cooling gives rise to and pearlite.,Pearlite,21,2021/7/13,Slow Cooling of Pl

20、ain Carbon S,Slow Cooling of Plain Carbon Steel(Cont.),Hypereutectoid plain carbon steel:If a 1.2%C sample is heated up to 9500C and held for sufficient time,it entirely gets austenitized.Further cooling results results in eutectoid cementite and pearlite.,22,2021/7/13,Slow Cooling of Plain Carbon S

21、,Heat treatment is the way to improve the components and/or structures of metallic materials.*Annealing(退火）*Normalizing(正火)*Quenching(淬火)*Tempering(回火）,5.6 Heat treatment of metallic materials,23,2021/7/13,Heat treatment is the way,Annealing(退火):Definition:金属加热到适当温度保温一段时间，以适当速度冷却到室温的热处理过程。full annea

22、ling(完全退火)process annealing:stress relief(低温退火,去应力退火),24,2021/7/13,242021/7/13,1)full annealing(完全退火)full annealing temperature for hypereutectoid steel:above Accm(+40)temperature Structure:pearlite(珠光体）+cementite（渗碳体）for hypoeutectoid steel:above Acs temperature Structure:pearlite(珠光体）+ferrite（铁素体）

23、purpose:increase of ductility,decrease of hardness and strength,25,2021/7/13,1)full annealing(完全退火)2520,26,2021/7/13,262021/7/13,2)process annealing:stress relief(低温退火,去应力退火)temperature below the eutectoid temperature.Which is often referred to as a stress relief,partially softens cold-worked low-ca

24、rbon steels by relieving internal stresses from cold working.For hypoeutectoid steels with less than 0.3%C below eutectoid temperature,550-650,27,2021/7/13,2)process annealing:stress r,*Normalizing(正火)The steel is heated in the austenitic region and then cooled in still air.ACs(orAccm)+3050 The purp

25、ose of normalizing:To refine the grain structureTo increase the strength of the steelTo reduce compositional segregation in castings or forgings and thus provide a more uniform structure,28,2021/7/13,*Normalizing(正火)282021/7/1,*Quenching(淬火)1.Definition and Destination of quenching Definition:A samp

26、le of a heated metallic materials is rapidly cooled to a settled temperature in water or oil.(加热的钢或合金，在一设定温度保温一段时间，以获得不同要求的高温相，然后快速冷却以获得远离平衡相组织的过程。）,29,2021/7/13,*Quenching(淬火)292021/7/13,For example:plain-carbon steel in the austenitic condition be quenched in waterthe forming of martensite(马氏体):A

27、interstitial solid solution(间隙固溶体)of carbon in BCC iron.Metastable phase consisting of supersaturated solid solution of C in BCC or BCT iron.Caused by rapid cooling of austenitic steel into room temperature(quenching).,Ms temperature of martensite start.Mf temperature of martensite finish.,30,2021/7

28、/13,For example:plain-carbon ste,Microstructure of Fe C Martensites,Lath martensite（板条状马氏体）:Less than 0.6%C and consists of domains of lathe of different orientation.Plate martensite（片状马氏体）:More than 1.0%C and have fine structure of parallel twins.,Lath type,Plate type,31,2021/7/13,Microstructure of

29、 Fe C Marte,Lath Martensite 板条状,Plate Martensite 片状(或针状),32,2021/7/13,Lath MartensitePlate Martensit,Martensite(Cont.),Transfer to martensite is diffusionless.No change of relative position of carbon atoms after transformation.Strength and hardness increases with carbon content.Strength is due to hi

30、gh dislocation concentration and interstitial solid solution strengthening.,FCC,BCC,BCT,33,2021/7/13,Martensite(Cont.)Transfer t,2.Mechanism of quenching(Three steps)A:Surrounded by vapor(形成蒸汽膜包围)B:boiling to form core(沸腾成核)C:liquid cooling(液体冷却阶段)3.Quenching medium of quenching(淬火介质)(1)Water(2)Salt

31、 solution:NaCl CaCl2(3)Basic water(碱水):5%-10%NaOH(4)Oil（常规，快速，等温）(5)Polymeric solution(高聚物溶液)PVA（聚乙烯醇），PVP（聚乙烯吡咯烷酮，PAG(环氧乙烷和环氧丙烷的共聚物),34,2021/7/13,2.Mechanism of quenching(Thr,4.Methods of quenching(1)single stage quenching 单液淬火(2)double quenching 双液淬火(Ms-oil)(3)interrupted quenching 分级淬火(4)isotherm

32、al quenching 等温淬火(5)localized quench hardening局部淬火,35,2021/7/13,4.Methods of quenching 352021/,Martempering(marquenching)（马氏体等温淬火）Is a modified quenching procedure used for steels to minimize distortion and cracking that may develop during uneven cooling of heat-treated material.,36,2021/7/13,Martem

33、pering(marquenching)（马氏,Process of Martempering:,(1)Austenitizing the steel(2)Quenching it in hot oil or molten salt at temperature just slightly below the Ms temperature Holding the steel in quenching medium until the temperature is uniform throughout and stopping this isothermal treatment before t

34、he austenite-to bainite（贝氏体）transformation begin(4)Cooling at moderate rate to room temperature,37,2021/7/13,Process of Martempering:(1)A,Pearlite珠光体,lower Bainite下贝氏体,upper Bainite上贝氏体,38,2021/7/13,Pearlitelower Bainiteupper Bai,Advantages of Martempering,The martempered steel has high impact energ

35、y values.,Austempering（奥氏体等温淬火）Is an isothermal heat treatment which produces a bainite（贝氏体）structure in some plain-carbon steels.Increasing the toughness and ductility.,39,2021/7/13,Advantages of MartemperingThe,Process of Austempering:,(1)Austenitizing the steel(2)Quenched in a molten salt bath(ab

36、ove the Ms temperature)(3)held isothermally(austenite-to bainite)(4)Cool to room temperature in air,40,2021/7/13,Process of Austempering:(1),Advantages and disadvanges of Austempering,Advantages(1)Improve ductility and impact resistance(2)Decrease distortion of quenched materialsDisadvantagesThe nee

37、d for special molten salt bath(2)The process can be used for only a limited number of steels.,41,2021/7/13,Advantages and disadvanges of,Isothermal decomposition of Austenite.,Several samples are first austenitized above eutectoid temperature and rapidly cooled in salt bath at a desired temperature,

38、after various time intervals,and then quenched in water at room tremperature.,Repeat procedureat progressivelowertemperatures,42,2021/7/13,Isothermal decomposition of Au,43,2021/7/13,432021/7/13,IT Diagrams for Noneutectoid Steels,S curves of IT diagrams of noneutectoid steel is shifted to left.Not

39、possible to quench from austenitic region to produce entirely martensite.Additional transformation line indicates start and formation of proeutectoid ferrite.,44,2021/7/13,IT Diagrams for Noneutectoid S,Continuous Cooling-Transformation Diagram,In continuous cooling transformation from martensite to

40、 pearlite takes place at a range of temperature.Start and finish lines shifted to longer time.No transformation below 4500C.,45,2021/7/13,Continuous Cooling-Transformat,*Tempering(回火):heating a steel at a temperature below the eutectoid point temperature（AC1）for a certain time and then lower it to r

41、oom temperature to make it softer and more ductile.the effect of tempering temperature on the shape of the carbide(200-700 cementitie)200-300 rodlike 400-700 spherical-like P396 Fig.9.30 Fig.9.31 the effect of tempering temperature on the hardness of plain-carbon steel Fig.9.32,46,2021/7/13,*Temperi

42、ng(回火):462021/7/13,Effects of Tempering,Hardness decreases as temperature increases above 2000C This is due to diffusion of carbon atoms from interstitial sites to iron carbide precipitates.,47,2021/7/13,Effects of Tempering Hardness,5.7 The classification of iron iron carbide alloy materials,*Major

43、 types on the basis of C concentration in metals:Iron:C 2.08 wt%Steel:C 2.08 wt%*Major types of steel:1)On C contents:low carbon steel:C 0.25 wt%medium carbon steel:0.25 wt%0.6 wt%,48,2021/7/13,5.7 The classification of iron,2)On quality:plain-carbon steel:S 0.055 wt%(普通碳素钢)P 0.045 wt%high quality s

44、teel:S 0.04 wt%(优质碳素钢)P 0.04wt%super high quality steel:S 0.03 wt%(高级优质碳素钢)P 0.035 wt%In addition to C,steel also contains S,P,Si,Mn trace elements.S,P:disadvantages in steel Si,Mn in steel will improve its strength and hardness),49,2021/7/13,2)On quality:492021/7/13,3)On application:Carbon structur

45、e steel(碳素结构钢)e.g.45Mn:C=0.45 wt%,Mn wt 0.8%Carbon tool steel(碳素工具钢)e.g.T8:C=0.8 wt%碳素工具钢 T8A:C=0.8 wt%高级优质碳素工具钢 4)On steel-making method:open-hearth furnace steel(平炉钢)basic oxygen furnace steel(转炉钢),50,2021/7/13,3)On application:502021/7/13,5)Classification of plain-carbon steels in USA by a four d

46、igit AISI-SAE code AISI:American Iron and Steel Institute SAE:Society for Automotive EngineersFor example:1030:a plain-carbon steel with 0.3 wt%of CMedium carbon steels:1020 1040High carbon steels:1060 1095,51,2021/7/13,5)Classification of plain-car,Plain carbon steelsTypical mechanical properties a

47、nd applications of various kinds of plain carbon steels.The limitations of plain carbon steels in engineering applications:1.cant strengthened beyond about 690 MPa 2.They are not deep-hardenable 3.has low corrosion and oxidation resistance 4.Rapid quenching can obtain a fully martensitic structure,h

48、owever,it leads to possible distortion and crack 5.Has poor impact resisitance at low temperature,52,2021/7/13,Plain carbon steels522021/7/,6)Classification of alloy steels in USA Low alloy steels:containing 1 to 4%of alloying elements Alloy steels:may contain up to 50%of alloying elements.,53,2021/

49、7/13,6)Classification of alloy ste,5.7.1 Low Alloy Steels and Alloy Steels,Manganese steels:锰钢Chromium steels:铬钢Chromium molybdenum steels:铬钼钢Nickel molybdenum steels:镍钼钢Nickel chromium-molybdenum steels:镍铬钼钢 Ni:1.83 wt%,Ni:0.55 wt%Table 9.4 on page 394 Table 9.6 on page 402,54,2021/7/13,5.7.1 Low A

50、lloy Steels and A,Classification of Alloy Steels,First two digits:Principle alloying element.Last two digits:%of carbon.,55,2021/7/13,Classification of Alloy Steels,Distribution of Alloying Elements,Distribution depends upon compound and carbide forming tendency of each element.,56,2021/7/13,Distrib