【正文】 n ,but not very plex is also possible to produce special sections such as railway wagon wheels by rolling individual pieces. 輥軋輥軋是在兩根旋轉(zhuǎn)輥之間對(duì)金屬施加壓力使其橫截面積減少的一種工藝。2. 因?yàn)榧庸び不脑?，最大變形量也?huì)受到限制，任何后續(xù)的變形都需經(jīng)過(guò)退火。3. 能獲得良好的尺寸精確性。而且，冷加工不會(huì)有表面脫碳的可能性。Cold working advantages1. Cold working increases the strength and hardness of the material due to strain hardening which would be beneficial in some gives some parative values for t he properties obtained after hot working and cold ,there is no possibility of decarburization of the surface..2. Since the working is due in the cold tate,no oxide would form on the surface and conseque ntly,good surface finish obtained.3. Better dimensional accuracy is achieved.4 It is far easier to handle cold parts and also is economical for smaller size. 冷加工益處1. 由于加工硬化的原因，冷加工將會(huì)增加材料的強(qiáng)度和硬度，這在某些方面是有利的。3. 由于金屬內(nèi)熱擴(kuò)散的原因，控制工件的溫度是很困難的，所以在熱加工中很難獲得精確的尺寸。2. 高溫下，金屬表面比例將會(huì)增大，這樣將會(huì)導(dǎo)致最后得到的表面質(zhì)量很差。4. 熱加工中，晶粒的繼續(xù)改良是有可能的，如果溫度和加工率得到適當(dāng)?shù)目刂?，將?huì)獲得優(yōu)良的晶粒尺寸和良好的機(jī)械性能。即使脆性材料也可以進(jìn)行熱加工。HOT Working Advantages1. As the material is above the recrystallization temperature,any amount of workingcan be imparted since there is no strainhardening taking place.2. At a high temperature,the material would have higher amount of ductility andtherefore there is no limit on the amount of hot working that can be done on a brittle material can be hot worked.3. Since the shear stress gets reduced at higher temperatures,hot working requiresmuch less force to achieve the necessary deformation.熱加工益處1. 當(dāng)材料溫度在再結(jié)晶溫度以上時(shí)，加工量的多少都是可以的，因?yàn)檫@時(shí)候沒(méi)有加工硬化的產(chǎn)生。一般情況下，這都不是我們想要的。但是，熱加工的最后溫度比再結(jié)晶溫度高太多的話，如C,晶粒的尺寸就開(kāi)始增大并且最后會(huì)得到粗大的晶粒尺寸。加熱之后，由于再結(jié)晶作用，當(dāng)金屬加工的時(shí)，晶粒尺寸就會(huì)減小。如A中的一個(gè)簡(jiǎn)單加熱過(guò)程，當(dāng)溫度超過(guò)再結(jié)晶溫度后，晶粒就開(kāi)始長(zhǎng)大。同樣，鋼也是一樣的，鋼的再結(jié)晶溫度達(dá)到1000攝氏度，因此，在這溫度以下的加工都是冷加工。In hot working, the process may be carried above the recrystallization temperature with or without actual example,for lead and tin,the recrystallization temperature is below the room temperature and hence working of these metals at room temperature is always hot for steels,the recrystallization temperature is of the order of 1000℃,and therefore working below that temperature is still cold working only.在熱加工中，在加熱或者不加熱的實(shí)際條件下再結(jié)晶可能在再結(jié)晶溫度以上發(fā)生。再結(jié)晶溫度取決于材料已經(jīng)改變的冷加工量。再結(jié)晶溫度是由美國(guó)金屬學(xué)會(huì)這樣定義的“在一定的時(shí)間段內(nèi)，冷加工金屬完成再結(jié)晶時(shí)的最小溫度”。再結(jié)晶破壞了由機(jī)械作用構(gòu)成的原有晶體結(jié)構(gòu)，并且產(chǎn)生了無(wú)應(yīng)變的新的晶體。Those processes , working above the recrystallization temperature, are termed hotworking processes whereas those below are termed coldworking processes在這些加工工藝中，加熱溫度在再結(jié)晶溫度以上的叫做熱加工，在再結(jié)晶溫度以下的叫做冷加工。 Hot Working and Cold WorkingThe metalworking processes are traditionally divided into hot working and coldworking processes. The division is on the basis of the amount of heating applied to the metal before applying the mechanical force. 冷加工和熱加工傳統(tǒng)的金屬加工工藝分為熱加工和冷加工。The wastage of material in metalworking processes is either negligible or very small, and the production rate is in general very high .these two factors give rise to the economy in production材料的浪費(fèi)在金屬加工過(guò)程中是很少的，甚至可以忽略不計(jì)，并且其生產(chǎn)率一般來(lái)說(shuō)是非常高的。這是因?yàn)?，只要小心?jǐn)慎地控制應(yīng)力，就能讓纖維流線朝著任何一個(gè)方向流動(dòng)并且獲得最佳的機(jī)械性能。Since the grains are elongated in the direction of flow, whey would be able to offer more resistance to stresses acting across them . As a result, the mechanically worked metals called wrought products would be able to achieve better mechanical strength in specific orientation ,that of the flow direction .since it is possible sible to control these flow lines in any specific direction by careful manipulation of the applied forces as shown in Fig. , it is possible to achieve optimum mechanical properties. The metal, of course, would be weak along the flow lines.因?yàn)榫ЯＴ诹鲃?dòng)方向上被拉長(zhǎng)了，這樣他們就更能夠抵抗作用于其上的應(yīng)力。通過(guò)顯微鏡觀察拋光和蝕刻后的表面，可以看到這種金屬的流動(dòng)方式。在微觀范圍內(nèi)，當(dāng)塑性變形產(chǎn)生的時(shí)候，在固體內(nèi)部金屬的流動(dòng)傾向于特定的方向，這個(gè)方向取決于加工類型和應(yīng)力方向。 metallurgy. On the macroscopic scale, when plastic , deformation occurs the metal appears to flow in the solid state along specific directions, which are depedent on the type of processing and the direction of applied force. The crystals or grains of the metal are elongated in the direction of metal flow. This flow of metal can be seen under microscope after polishing and suitable etching of the mental surface . These visible lines are called fibre flow lines, some representative specimens of which are presented in fig 金屬的變形是由原子排列引起的，這種排列是由被稱作滑移和孿生過(guò)程中的一種或者兩者共同作用造成的。金屬所需要的變形可以只通過(guò)施加大量的機(jī)械力或者通過(guò)加熱金屬并且施加少量的應(yīng)力來(lái)獲得。 NATURE OF PLASTIC DEFORMATIONPlastic deformation is the deformation which is permanent and beyond the elastic rang of the material of ten , metals are worked by pfastic deformation because of the beneficial effect that is imparted to the mechanical properties by it. The necessary deformation in a metal can be achieved by application of large amount of mechanical force only or by heating the metal and then applying a small force. 塑性變形本質(zhì)塑性變形是超過(guò)彈性變形范圍之后的一種永久變形。通常，金屬采用塑性變形加工是因?yàn)榭梢酝ㄟ^(guò)其獲得良好的機(jī)械性能。The deformation of metals, which is caused by the displacement of the atoms is achieved by one or both of the processes called slip and twinning. The details of the microscopic deformation methods can be found in the textbooks of39。微觀的變形方式可以從冶金學(xué)課本中找到。在金屬流動(dòng)方向上金屬晶體或者晶粒將會(huì)延長(zhǎng)。這些可見(jiàn)的線條叫做纖維流線。因此，在被稱為鍛造產(chǎn)品的機(jī)械加工零件的金屬流動(dòng)方向上會(huì)獲得優(yōu)良的強(qiáng)度。當(dāng)然，金屬在沿著纖維線的方向也會(huì)變得疲軟。這兩個(gè)因素使其在生產(chǎn)上更為經(jīng)濟(jì)。這種區(qū)分是基于機(jī)械應(yīng)力施加前金屬的受熱程度。Under the action of heat and force when the atoms reach a certain higher energy level, the new crystals start forming which is termed as recrystallization . Recrystallization destroys the old grain structure deformed by mechanical working and entirely new crystals, which are strainfree are formed, the grains, in fact ,start nucleating at the points of severest deformation. Recrystallzation temperature as defined by the American Society of Metals is “ the approximate minimum temperature at which plete recrystallization of a coldworked metal occurs within a specified time ”.在加熱和應(yīng)力的作用下，當(dāng)原子達(dá)到某一更高能量的等級(jí)的時(shí)候，新的晶粒就開(kāi)始形成的過(guò)程叫做再結(jié)晶。事實(shí)上，新的晶粒是在嚴(yán)重變形的時(shí)候開(kāi)始形核的。The recrystallization temperature generally varies between onethird to half the melting poi