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1、18Heattreatmentisatermappliedtoavarietyofproceduresforchangingthecharacteristicsofmetalbyheatingandcooling・Byproperheattreatment,itispossibletoobtaincertaincharacteristicsinmetalsuchashardness,tensilestrength(abilitytoresiststretching),andductility.Theproceduresofheattreatmentofst
2、eelincludehardening,tempering,annealing,andcasehardening.热处理这一术语指的是各种各样通过加热和冷却以改变金属特性的过程。通过适当的热处理，能够使金属获得某些性质，例如：硬度、抗拉强度(抗拉伸能力)和韧性。钢的热处理方法包括淬火、回火、退火和表面硬化。1.Hardening淬火Hardeningisaprocessofheatingandcoolingsteeltoincreaseitshardnessandtensilestrength,toreduceitsductility,andtoobtai
3、nafinegrainstructure.Thesimpleexperimentsdescribedbelowmaybeenlightening・Twoold-fashionedsteelknittingneedles,agasring,abowlofwater,apieceofsandpaperandapairofpliersareneeded.淬火是把钢加热然后冷却以捉高其硬度、抗强度，降低韧性并获得细品粒组织的方法。下面的简单实验可能对人冇所启发。取两根老式的钢制毛衣针，一个煤气炉，一碗水、一块砂纸和一把钳子。Experiment1:实验1：Bend
4、oneneedleslightlytofeelhowtoughandspringyitis.Nowholdtheneedleintheflame,usingthepliers,thebowlofwaterbeingcloseathand・Whenitisbrightred,diptheendoftheneedleasquicklyaspossibleintothewater.Theneedleshouldstillberedhotasitisbeingquenched.Thentrytobendthequenchedend;itishardandbritt
5、leandwillsnapoff.轻轻弯曲一•根毛衣针，试一试它的韧性和弹性，然后用钳子夹住-端放在火上烧，手旁放一碗水。当织针达到红热状态时，将其一端迅速浸入水中(织针在淬火时应当还是红热的)，然后，弯曲淬过火的一端，即可发现它硬而脆，而且会折断。2.Tempering冋火Temperingisdonebyreheatingthemetaltolowormoderatetemperature,followedbyquenchingorbycoolinginair.Itisaprocessthatfollowsthehardeningprocedurean
6、dmakesthemetalashardandtoughaspossibleandremovesthebrittlenessfromahardenedpiece.冋火是把金属再加热到较低或适屮的温度，然后急冷或在空气屮冷却。冋火是在淬火之后采用的使金属尽可能变驶变韧的方法，它能消除淬火工件的脆性。Twoimportantpointsarctobenotedinconnectionwiththequenchingandtemperingofsteel:关于钢的淬火和回火有两个要点需要注意：(1)Togetafullyhardenedstructure,the
7、steelshouldbeheatedtotheappropriatetemperature・Andthenrapidlycooled.Theappropriatetemperaturebeforequenchingdependsonthecarboncontentofthesteelconcerned・(2)Temperingdoesnotrestorethepearliticstructure・Beforethatcanbedone,thesteelhastobeheatedtotheappropriatetemperatureandthenslowl
8、ycooled・回火(1)为了达到完全的硬化组织，必须把钢加热到合
