钢铁热处理中英文对照外文翻译文献

中英文对照外文翻译

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Heat Treatment of Steel

Types of Heat Treating Operations Five Operations are detailed in this lesson as the basis of heat treatment. Explanations of these operations follow.

Full annealing Full annealing is the process of softening steel by a heating and cooling cycle, so that it may be bent or cut easily. In annealing, steel is heated above a transformation temperature and cooled very slowly after it has reached a suitable temperature. The distinguishing characteristics of full annealing are: (a) temperature above

the critical temperature and (b) very slow cooling, usually in the furnace.

Normalizing Normalizing is identical with annealing, except that the steel is air cooled; this is much faster than cooling in a furnace. Steel is normalized to refine grain size, make its structure more uniform, or to improve machinability.

Hardening Hardening is carried out y quenching a steel, that is, cooling it rapidly from a temperature above the transformation temperature. Steel is quenched in water or brine for the most rapid cooling, in oil for some alloy steels, and in air for certain higher alloy steels. After steel is quenched, it is usually very hard and brittle; it may even crack if dropped. To make the steel more ductile, it must be tempered.

Tempering Tempering consistes of reheating a quenched steel to a suitable temperature below the transformation temperature for an appropriate time and cooling back to room temperature. How this process makes steel tough will be discussed later.

Stress relieving Stress 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 machining.

This is sometimes called process annealing.

Reasons for Heat Treating Heat treatment of steel is usually intended to accomplish any one of the following objectives:

●Remove stresses induced by cold working or to

remove stresses set up by nonuniform cooling of hot metal

objects;

●Refine the grain structure of hot worked steels

which may have developed coarse grain size;

●Secure the proper grain structure;

●Decrease the hardness and increase the ductility;

●Increase the hardness so as to increase resistance

to wear or to enable the steel to withstand more service

conditions;

●Increase the toughness; that is, to produce a steel

having both a high tensile strength and good ductility,

enabling it to withstand high impact;

●Improve the machinability;

●Improve the electrical properties;

●Change or modify the magnetic properties of steel.

Heat Treatment The hardest condition for any givens steel is obtained by quenching to a fully martensitic structure.