外文翻译--金属热处理精选.docVIP

英文原文 HEAT TREATMENT OF METAL Annealing The word anneal has been used before to describe heat-treating processes 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 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 promote uniformity of structure throughout the material. 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 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 which it is removed, leaving a comparatively poor quality surface, which results in a poor machinability rating.1 For such steels annealing may not be the most suitable treatment. The machinability of many of the higher plain carbon and most of the alloy steels can usually be greatly improyed by annealing, as they are often too hard and strong to be easily cut at any but their softest condition.2 The procedure for annealing hypoeutectoid steel is to heat slowly to approximately 60 above the Ac3 line,3 鞍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 lime ot some other insulating materyial. The slow cooling is easential to the precipitation of the maximum ferrite and the coarsest pearlite to place the steel in its softest, most ductile, and least strained condition. Normalizing The purpose