【文章內(nèi)容簡介】 and will respond to the heat treatment in a more uniform cold deformation, steel has a tendency to harden in deformed areas, making it more difficult to bend and liable to deforming and annealing operations are performed on most manufactured steel annealingFull annealing, where steel is heated 50 to 100C above the third transformation temperature for hypoeutectoid steels, and above the lowest transformation temperature for hypereutectoid steels, and slow cooled, makes the steel much easier to cut, as well as full annealing, cooling must take place very slowly so that a coarse pearlite is cooling is not essential forprocess annealing, since any cooling rate from temperatures below the lowest transformation temperature will result in the same microstructure and annealingProcess annealing consists of heating steel to a temperature just below the lowest transformation temperature for a short makes the steel easier to heat treatment is monly applied in the sheet and wire industries, and the temperatures generally used are from 550 to The twostage heat treating process of quenching and tempering is designed to produce high strength steel capable of resisting shock and deformation without the other hand, the annealing process is intended to make steel easier to deform or manufacturing steel products, machining and severe bending operations are often tempered steel may not cut or bend very easi1y and annealing is often effect of tempering may be il1ustrated as the head of a hammer were quenched to a fully martensitic structure, it probably would crack after the first few during manufacture of the hammer imparts shock resistance with only a slight decrease in is acplished by heating a quenched part to some point below the transformation temperature, and holding it at this temperature for an hour or more, depending on its steels are tempered between 205176。C and 595176。 higher temperatures are employed, toughness or shock resistance of the steel is increased, but the hardness and strength is the ability of a metal to change shape before it quenched martensite is hard but not ductile。in fact, it is very is needed to impart ductility to the martensite, usually at a small sacrifice in addition, tempering greatly increases the resistance of martensite to shock TreatmentThe hardest condition for any given steel is obtained by quenching to a fully martensitic hardness is directly related to strength, a steel posed of 100% martensite is at its strongest possible , strength is not the only property that must be considered in the application of steel may be equally or modify the magnetic properties of the electrical properties。Improve the machinability。Increase the toughness。that is, to produce a steel having both a high tensile strength and good ductility, enabling it to withstand high impact。Increase the hardness so as to increase resistance to wear or to enable the steel to withstand more service conditions。Decrease the hardness and increase the ductility。Secure the proper grain structure。Refine the grain structure of hot worked steels which may have developed coarse grain size。Remove stresses induced by cold working or to remove stresses set up by nonuniform cooling of hot metal objects。Reasons for Heat TreatingHeat treatment of steel is usually intended to acplish any one of the following objectives:Stress relievingStress relieving is the heating of steel to a temperature below the transformation temperature, as in tempering, but is done primarily to relieve internal stress and thus prevent distortion or cracking during is sometimes called process Tempering consists of reheating a quenched steel to a suitable temperature below the transformation temperature for an appropriate time and cooling back to room this process makes steel tough will be discussed Hardening is carried out by quenching a steel, that is, cooling it rapidly from a temperature above the transformation is quenched in water or brine for the most rapid cooling, in oil for some alloy steels, and in air for certain higher alloy steel is quenched, it is usually very hard and brittle。it may even crack if make the steel more ductile, it must be is identical with annealing, except that the steel is air cooled。this is much faster than cooling in a is normalized to refine grain size, make its structure more uniform, or to improve annealingFull annealing is the process of softening steel by a heating and cooling cycle, so that it may be bent or cut annealing, steel is heated above a transformation temperature and cooled very slowly after it has reached a suitable distinguishing characteristics of full annealing are:(a)temperature above the critical temperature and(b)very slow cooling, usually in the 鋼的熱處理各種不同的熱處理操作 本單元介紹了五種熱處理的基本方法。這些方法介紹如下。完全退火完全退火是對(duì)鋼進(jìn)行反復(fù)的加熱和冷卻使鋼軟化的過程，這樣就容易彎曲和切割。在退火中，使鋼加熱到轉(zhuǎn)變溫度以上的一個(gè)適宜溫度后緩慢地冷卻。完全退火的突出的特點(diǎn)是：（a）溫度高于臨界溫度（b）緩慢冷卻，通常是爐冷。正火正火和退火相同，除了鋼是被空冷的；這比在爐中冷卻得更快。鋼的正火是為了改善晶粒大小，使它的結(jié)構(gòu)更加均勻，或者是提高機(jī)械性能。淬火淬火就是通過冷浸鋼，那就是使鋼從轉(zhuǎn)變溫度以上的一個(gè)溫度快速冷卻。為了最快的冷卻，鋼被冷浸在水中或是鹽水里，合金鋼的是在油里，某些更高合金鋼的要在空氣中冷卻。當(dāng)鋼被淬火之后，它通常是硬和易碎的；甚至落地會(huì)破碎，為了使鋼更有韌性，它必須被回火?；鼗鸹鼗鹗侵钢匦录訜嵋呀?jīng)被淬火的鋼到轉(zhuǎn)變溫度以下的一個(gè)適當(dāng)溫度一段時(shí)間后再冷卻到室溫。至于該過程怎樣使鋼變得有韌性，我們將在以后討論。去應(yīng)力是指加熱鋼到轉(zhuǎn)變溫度以下的適宜溫度，正如回火一樣，但這樣做是為了減少內(nèi)應(yīng)力從而避免在加工過程中的變形和破裂。這有時(shí)也被稱作退火過程。熱處理的原因鋼的熱處理通常是為了達(dá)到以下的任一目的：消除冷卻過程中產(chǎn)生的內(nèi)應(yīng)力和高溫金屬物體因冷卻不均勻而產(chǎn)生的應(yīng)力。改善熱處理鋼可能產(chǎn)生的粗糙晶粒的晶粒結(jié)構(gòu)。得到適當(dāng)?shù)木Я＝Y(jié)構(gòu)降低硬度，提到塑性。增加硬度，以提高到鋼的抗耐磨性和加強(qiáng)鋼使之能承受更多的使用條件。增加韌性，這就是使鋼同時(shí)擁有高的拉伸強(qiáng)度和好的延展性，使它能承受高的撞擊。提高切削性能提高導(dǎo)電性。改變或修正鋼的磁性。熱處理任何一種鋼通過淬火而獲得完全的馬氏體是最難的。由于硬度直接關(guān)系到強(qiáng)度，一種鋼由100%的馬氏體組成是其處于最高強(qiáng)度的可能條件。但是，在鋼的應(yīng)用部分里，強(qiáng)度不是唯一的必需考慮的性能。延展性同樣重要?；鼗鹧诱剐允墙饘僭谄屏亚案淖冃螤畹哪芰?。淬火馬氏體很硬但不能延展，事實(shí)上它是非常碎的。回火是用來使馬氏體獲得可延展性，通常強(qiáng)度會(huì)降低一些。另外，回火大大增加馬氏體抵抗沖擊負(fù)荷的能力?；鼗鸬挠绊懪e例說明如下:如果一個(gè)錘頭被淬火到完全馬氏體結(jié)構(gòu)，它可能在前幾次敲擊就會(huì)破碎?；鼗鹪阱N頭的制造中能增加抗敲擊能力，而硬度只有一點(diǎn)點(diǎn)的下降?；鼗疬^程是這樣達(dá)到的：把淬火后的部分加熱到轉(zhuǎn)變溫度的某點(diǎn)，然后維持這溫度一個(gè)小時(shí)或更多，這要根據(jù)部件的大小判斷。大多的鋼是被加熱到205176。C到595176。C，更高的溫度，鋼的韌性和抗敲擊能力會(huì)增加，但硬度和強(qiáng)度會(huì)下降。退火淬火和回火兩個(gè)熱處理過程來生產(chǎn)高強(qiáng)度的鋼以便抵抗沖擊和變形而不受破壞。另一方面，退火過程的目的是為了使鋼更容易變形和機(jī)器加工。在鋼產(chǎn)品的制造中，機(jī)器加工和嚴(yán)格的彎曲操作經(jīng)常被運(yùn)用到。即使回火鋼也不會(huì)被經(jīng)意的切割和彎曲，退火就常常是不可缺少的。退火過程退火過程就是加熱