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1、7.1 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
2、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. 7.1 塑性变形本质塑性变形是超过弹性变形范围之后的一种永久变形。通常，金属采用塑性变形加工是因为可以通过其获得良好的机械性能。金属所需要的变形可以只通过施加大量的机械力或者通过加热金属并且施加少量的应力来获得。 . The deformation of metals, which is caused by the disp
3、lacement 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 of metallurgy. On the macroscopic scale, when plastic , deformation occurs the metal appears to flow in the solid state along s
4、pecific 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 vi
5、sible lines are called fibre flow lines, some representative specimens of which are presented in fig 7.1 金属的变形是由原子排列引起的，这种排列是由被称作滑移和孪生过程中的一种或者两者共同作用造成的。微观的变形方式可以从冶金学课本中找到。在微观范围内，当塑性变形产生的时候，在固体内部金属的流动倾向于特定的方向，这个方向取决于加工类型和应力方向。在金属流动方向上金属晶体或者晶粒将会延长。通过显微镜观察抛光和蚀刻后的表面，可以看到这种金属的流动方式。这些可见的线条叫做纤维流线。 Since th
6、e 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 .s
7、ince it is possible sible to control these flow lines in any specific direction by careful manipulation of the applied forces as shown in Fig. 7.1, it is possible to achieve optimum mechanical properties. The metal, of course, would be weak along the flow lines.因为晶粒在流动方向上被拉长了，这样他们就更能够抵抗作用于其上的应力。因此，在
8、被称为锻造产品的机械加工零件的金属流动方向上会获得优良的强度。这是因为，只要小心谨慎地控制应力，就能让纤维流线朝着任何一个方向流动并且获得最佳的机械性能。当然，金属在沿着纤维线的方向也会变得疲软。 the wastage of material in metal-working 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 材料的浪费在金属
9、加工过程中是很少的，甚至可以忽略不计，并且其生产率一般来说是非常高的。这两个因素使其在生产上更为经济。 7.1.1 Hot Working and Cold Workingthe metal-working processes are traditionally divided into hot -working and cold-working processes. the division is on the basis of the amount of heating applied to the metal before applying the mechanical force.7.
10、1.1 冷加工和热加工传统的金属加工工艺分为热加工和冷加工。这种区分是基于机械应力施加前金属的受热程度。 Those processes , working above the recrystallization temperature, are termed hot-working processes whereas those below are termed cold-working processes 在这些加工工艺中，加热温度在再结晶温度以上的叫做热加工，在再结晶温度以下的叫做冷加工。 Under the action of heat and force when the atoms
11、 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 strain-free are formed, the grains, in fact ,start nucleating at the poin
12、ts of severest deformation. Recrystallzation temperature as defined by the American Society of Metals is “ the approximate minimum temperature at which complete recrystallization of a coldworked metal occurs within a specified time ”. 在加热和应力的作用下，当原子达到某一更高能量的等级的时候，新的晶粒就开始形成的过程叫做再结晶。再结晶破坏了由机械作用构成的原有晶体
13、结构，并且产生了无应变的新的晶体。事实上，新的晶粒是在严重变形的时候开始形核的。再结晶温度是由美国金属学会这样定义的“在一定的时间段内，冷加工金属完成再结晶时的最小温度”。 The recrystallization temperature generally varies between one-third to half the melting point of most of the metals. Typical values of recrystallisation temperatures are given in table 7.1,the recrystallization t
14、emperature also depends on the amount of cold work a material has already received. the higher the cold work the lower would the recrystallization temperature as shown in Fig 7.2 大多数的金属再结晶温度一般在金属熔点的三分之一到二分之一内。表7.1给出了具有代表性的再结晶温度值。再结晶温度取决于材料已经改变的冷加工量。冷加工量越高，再结晶温度越低，如图7.2所示。 In hot working, the process
15、 may be carried above the recrystallization temperature with or without actual heating.For 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 working.Similarly for steels,the recrystallization temperature is of the order of 1000,and therefore working below that temperature is still cold working only.在热加工中，在加热或者不加热的实际条件下再结晶可能在再结晶温度以上发生。例如，铅和锡，它们的再结晶温度都在室温以下，所以室温下的加工都属于热加工。同样，钢也是一样的，钢的再结晶温度达到1000摄氏度，因此，在这温度以下的加工都是冷加工。 In hot working.,the temperature at which the worki
