外文翻譯--金屬熱處理

1、<p><b>　　英文原文</b></p><p>　　HEAT TREATMENT OF METAL</p><p><b>　　Annealing</b></p><p>　　The word anneal has been used before to describe heat-treating pro

2、cesses for softening and regaining ductility in connection with cold working of material. It has a similar meaning when used in connection with the heat treating of allotropic materials. The purpose of full annealing is

3、o decrease hardness, increase ductility, and sometimes improve machinability of high carbon steels that might otherwise be difficult to cut. The treatment is also used to relieve stresses,refine grain size, and pro</p

4、><p>　　Machinability is not always improved by annealing. The word machinability is used to describe several interrelated factors, including the ability of a material to be cut with a good surface finish. Plain

5、 low carbon steels, when fully annealed, are soft and relatively weak , offering little resistance to cutting, but udually having sufficient ductility and toughness that acut chip tends to pull and tear the surface from

6、which it is removed, leaving a comparatively poor quality surface, which resu</p><p>　　The procedure for annealing hypoeutectoid steel is to heat slowly to approximately 60 above the Ac3 line,3 °°

7、to soak for a long enough period that the temperature equalizes throughout the material and homogeneous austenite is formed, and then to allow the steel to cool very slowly by cooling it in the fumace or burying it in li

8、me ot some other insulating material. The slow cooling is easential to the precipitation of the maximum ferrite and the coarsest pearlite to place the steel in its softes</p><p>　　Normalizing</p><

9、p>　　The purpose of normalizing is somewhat similar to that of annealing with the exceptions that the steel is not reduced to its softest condition and the pearlite is left rather fine instead of coarse. Refinement of

10、grain size, relief of internal stresses, and improvement of structural uniformity together with recovery of some ductility provide high toughness qualities in normalized steel. The process is frequently used for improvem

11、ent of machinability and for stress relief to reduce distortion tha</p><p>　　The procedure for normalizing is to austenitize by slowly heating to approximately 80° above the Ao3 or Accm3 temperature fo

12、r hypoeutectoid or hyereutectoid sreels, respectively.</p><p>　　Providing soaking time for the formation of austenite; and cooling slowly in still air, Note that the steels with more carbon than the eutectoi

13、d composition are heated abou the Accm instead of the Ac13 used for annealing. The purpose of normalizing is to attempt to dissolve all the cementite during austenitization to eliminate, as far as possible, the settling

14、of hard, brittle iron carbide in the grain boundaries. The desired decomposition products are smallgrained, fine pearlite with a minimum </p><p>　　Spheroidizing</p><p>　　Minimum hardness and max

15、imum ductility of steel can be produced by a process called spheroidizing, which causes the iron carbide to form in small spheres or nodules in a ferrite matrix. In order to start with small grains that spheroidize more

16、readily, the process is usually performed on normalized steel. Several variations ofprocessing are used, but all require the holding of the steel near the A1 temperature {usually slightly below } for a number of hours to

17、 allow, the iron carbide to form on </p><p>　　The main need for the process is to improve the machinability quality of high carbon steel and to pretreat hardened steel to help produce greater structural unif

18、ormity after quenching. Because of the lengthy treatment time and therefore rather high cost, spheroidizing is not performed nearly as much as annealing or normalizing.</p><p>　　Hardening of Steel </p&

19、gt;<p>　　Most of the heat treatment hardening processes for steel ate based on the production of high percebtages of martensite.The first step,therefore, is that used for most of the other heat-treating processes—

20、treatmentto produce austenite. Hypoeutectoid steels ate heated to approximately 60°above the Ac3 temperature and allowed to soak to obtain temperature uniformity and austenite homogeneity. Hypereutectoid steels ate

21、 soaked at about 60°above the Ac1 temperature,which leaves some iron carbide pres</p><p>　　The second step involves cooling rapidly in an attempt to avoid pearlite transformation by missing the nose of

22、the I—Tcurve.The cooling rate is determined by the temperature and ability of the quenching media to carry heat away from the surface of the material being quenched and by the conduction of heat through the material itse

23、lf.Table 11—1 shows some of the commonly used media and the method of application to remove heat, arranged in order of decreasing cooling ability.</p><p>　　High temperature gradients contribute to high stres

24、ser that cause distortion and cracking, so the quench should only as extreme as is necessary to produce the desired structure. Care must be exercised in quenching that heat is removed uniformly to minimize thermal stress

25、es. For example, a long slender bar should be end-quenched, that is, inserted into the qudenching medium vertically so that the entire section is subjected to temperature change at one time. If a shape of this kind were

26、to be que</p><p>　　Seyeral special types of quench are conducted to minimize quenching stresses and decrease the tendency for distortion and cracking. One of these is called martemoering and consists of quen

27、ching an austenitized steel in a salt at a temperature above that needed for the start of martensite formation (Ms).The steel being quenched is held in this bath until it is of uniform temperature but is removed before t

28、here is time for formation of bainite to start.Completion of the cooling in air then causes </p><p>　　A similar process performed at a slightly higher temperature is called austempering.In this case the stee

29、l is held at the bath temperature for a longer period,and the result of the formation of bainite.The bainite structure is not as hard as the martensite that could be formed from the same composition,but in addition to re

30、ducing the thermal shock to which the steel would be subjected under normal hardening procedures,it is unnecessary to perform any further treatment to develop good impact resi</p><p><b>　　Tempering<

31、/b></p><p>　　A third step usually required to condition a hardened steel for swevice is tempering,or as it is sometimes referred to,drawing. With the exception of austempered steel,which is frequently use

32、d in the as—hardened condition,most steel are not serviceable “as quenched”.The drastic cooling to produce martensite causes the steel to be very hard and to contain both macroscopic internal stresses with the result tha

33、t the material this little ductility and extreme brittleness. Reduction pg these faults i</p><p>　　The magnitude of the structural changes and the change of properties caused bytempering depend upon the temp

34、erature to which the steel is reheated. The higher the temperature, the greater the effect, so the choice of temperature will generally depend on willingness to sacrifice hardenss and strength to gain ductility and tough

35、ness. Reheating to below 100°has little noticeable effect on hardened plain carbon steel. Between 100°and 200°,there is evidence of some structural changes. Above 200°marke</p><p>　　In co

36、mmercial tempering the temperature range of 250—425°C is usually avoided because of an unexplained embrittlement,or loss of ductility, that often occurs with steels tempered in this range of 425—600°C,particula

37、rly when cooled slowly from or through this range of temperature.when high temperature remperature tempering is necessary for these steels,they are usually headed to above600 ºC and quenched for rapid cooling. Quenc

38、hes from this temperature, of course ,do not cause hardening because a</p><p><b>　　附錄B</b></p><p><b>　　漢語翻譯</b></p><p><b>　　金屬熱處理</b></p>

39、<p><b>　　一 退火</b></p><p>　　在前面描述冷拔加工材料的軟化并重新獲得塑性的熱處理方法時，就已使用退火這個詞。當(dāng)用于同素異晶材料的熱處理時，該詞具有相似的意義。完全退火的目的是降低塑性，有時也提高高碳鋼的切削加工性能，否則這種鋼很難加工。這種熱處理方法也用于減少應(yīng)力，細化晶粒，提高整個材料的結(jié)構(gòu)均勻性。</p><p>　　退火不

40、總是能提高切削加工性，切削加工性一詞用來描述幾個相關(guān)因素，包括材料切削時獲得好的表面光潔度（即較小的表面粗糙度值）的能力。當(dāng)完全退火時普通低碳鋼硬度較低，強度較小，對切削的阻力較小，但通常由于塑性和韌性太大以至切削力開工件表面時會劃傷表面，工件表面質(zhì)量比較差，導(dǎo)致較差的切削加工性。對這類鋼，退火可能不是最適合的處理方法。許多高碳鋼和大多數(shù)合金鋼加工性通常可經(jīng)退火大大改善，因為除在最軟條件下，它們的硬度和強度太高而不易加工。</p&

41、gt;<p>　　亞共析鋼的退火方法是將鋼緩慢加熱到Ac3線以上大約60°C，保溫一段時間，使整個材料溫度相同，形成均勻奧氏體，然后歲爐或埋在石灰或其他絕緣材料中緩慢冷卻。要析出粗大鐵素體和珠光體，使鋼處于最軟最韌和應(yīng)變最小的狀態(tài)，必須緩慢冷卻。</p><p><b>　　二 正火</b></p><p>　　正火的目的多少類似于退火，但鋼

42、不是最軟狀態(tài)且珠光體是細勻而不粗大。鋼的正火能細化晶粒，釋放內(nèi)應(yīng)力，改善結(jié)構(gòu)均勻性同時恢復(fù)一些塑性，得到高的韌性。這種方法經(jīng)常用于改進切削加工性，減少應(yīng)力，減少因部分切削加工或時效產(chǎn)生的變形。</p><p>　　正火的方法是將亞析鋼或過共析鋼分別緩慢加熱到Ac3線或Accm線上約80°C，保溫一段時間以便形成奧氏體，并靜止空氣中緩冷。要注意，含碳量超過共析成分的鋼要加熱到Accm線以上，而不是退火時的

43、Ac1線以上。正火的目的是在奧氏體化過程中試圖溶解所有滲碳體，從而經(jīng)可能減少晶界上的脆硬鐵碳化合物，從而得到小晶粒的細珠光體最小自由鐵素體和自由滲碳體。</p><p><b>　　三 球化退火</b></p><p>　　通過球化退火可使鋼得到最小的硬度和最大的塑性，它可使鐵碳化合物以小球狀分布在鐵素體基體上，為了使小顆粒球化更容易，通常對正火鋼進行球化退火。球化

44、退火可用幾種不同的方法，但所有的方法都需要在A1 線溫度附近（通常略低）保溫很長時間，使鐵碳化合物形成更穩(wěn)定能級較低的小圓球。</p><p>　　球化退火的方法的主要目的是改進高碳鋼的切削加工性，并對脆硬鋼進行熱處理，使其淬火后結(jié)構(gòu)更均勻。因為熱處理時間長，因此成本高，球化退火不如退火或正火常用。</p><p><b>　　四 鋼的硬化</b></p>

45、;<p>　　鋼的大多數(shù)熱處理硬化方法是基于產(chǎn)生高比例的馬氏體。因此，第一步用的是大多數(shù)其它熱處理方法—產(chǎn)生奧氏體。亞共析鋼加熱到Ac3溫度以上大約是60°C，進行保溫，使溫度均布，奧氏體均勻。過共析鋼在Ac1線溫度以上大約60°C保溫，鋼中仍殘留部分鐵碳化合物。</p><p>　　第二步是快速冷卻，力圖避免在等溫曲線鼻部產(chǎn)生珠光體轉(zhuǎn)變。冷卻速度取決于溫度和淬火時淬火介質(zhì)從鋼表

46、面帶走熱量的能力以及鋼本身傳熱的能力。</p><p>　　高的溫度階梯產(chǎn)生高應(yīng)力，會引起變形和開裂，所以淬火只有在特定結(jié)構(gòu)時才使用。淬火時必須小心，使熱量均勻擴散以減少熱應(yīng)力。比如一個細長棒需端部淬火，即將它垂直插入冷卻介質(zhì)中，這樣整個截面同時產(chǎn)生溫度變化。如果這種形狀的工件的某一邊比另一邊早降溫，尺寸變化很可能引起很高的應(yīng)力，產(chǎn)生塑性流動和永久變形。</p><p>　　用幾種特殊的淬

47、火方法可減少淬火應(yīng)力，減少變形開裂傾向。一種稱為分級淬火，其方法是：將奧氏體鋼放入溫度高于馬氏體轉(zhuǎn)變起始溫度（Ms）的鹽浴中，放置一定的時間直到溫度均勻，再開始形成貝氏體之前取出，然后放在空氣中冷卻，產(chǎn)生與從高溫開始淬火時同樣硬的馬氏體，而導(dǎo)致開裂和翹曲的高的熱應(yīng)力或淬火應(yīng)力已經(jīng)被消除。</p><p>　　在略高一點的溫度下的類似方法稱為等溫淬火，這是將鋼放在鹽浴中，保持很長時間，等溫處理的結(jié)果是形成貝氏體。貝

48、氏體結(jié)構(gòu)不如在同樣成分時形成的馬氏體硬，但除了減少鋼在正常淬火時受到熱沖擊外，不需要進一步處理，就可以獲得在高硬度時好的沖擊韌性。</p><p><b>　　五 回火</b></p><p>　　調(diào)整脆硬鋼以便使用的第三步通常是回火。除了等溫淬火鋼通常在淬火狀態(tài)下使用外，大多數(shù)鋼都不能在淬火狀態(tài)下使用。為了產(chǎn)生馬氏體而采取的激冷使鋼很硬，產(chǎn)生宏觀內(nèi)應(yīng)力和微觀內(nèi)應(yīng)力

49、，使材料的塑性很低，脆性極大。為減少這種危害，可通過將鋼加熱到A1線（低溫轉(zhuǎn)變）以下某一溫度。淬火鋼回火時產(chǎn)生的結(jié)構(gòu)是時間和溫度的函數(shù)，其中溫度是最重要的。必須要強調(diào)，回火不是硬化方法，而是剛好相反?；鼗痄撌菍⒔?jīng)熱處理硬化的鋼，通過回火時的再加熱，來釋放應(yīng)力軟化和提高塑性。</p><p>　　回火引起的結(jié)構(gòu)變化和性能改變?nèi)Q于鋼重新加熱的溫度。溫度越高，效果越大，所以溫度的選擇通常取決于犧牲硬度和強度換取塑性和

50、韌性的程度。重新加熱到100°C以下，對淬火普碳鋼影響不大，在100°C到200°C之間，結(jié)構(gòu)會發(fā)生某些改變，在200°C以上，結(jié)構(gòu)和性能顯著變化，在緊靠著A1溫度以下的長時間加熱會產(chǎn)生與球化退火過程類似的球化結(jié)構(gòu)。</p><p>　　在工業(yè)上，通常要避免在250°C到425°C范圍內(nèi)回火，因為這個范圍內(nèi)回火的鋼經(jīng)常會產(chǎn)生無法解釋的脆性或塑性喪失現(xiàn)象。