Tempering (metallurgy)

Tempering is a heat treatment in which a material is selectively heated in order to affect its properties, particularly to reduce stresses. Industrially, the annealing in the processing of steel, aluminum and other nonferrous metals and alloys as well as in the manufacture of glass used.

Method in steel processing

After curing, or welding of steel, the workpiece may be annealed by heating at temperatures below the transformation point A1 ( 723 ° C). In this case, internal stresses are relieved. Tempering is a process of heat treatment.

Usually annealing is applied after curing. Hardened steel is the softer, the higher you anlässt him. Here, the hardness and the toughness decreases increases. By oxidation of the surface, annealing colors that can be used to assess the tempering temperature form. The two most important parameters of the annealing are the annealing temperature and the annealing time. The heating and cooling also affects the tempering effect. In practice, the most common cause temperatures range between 300 ° C and 550 ° C; which tempering duration can last from minutes to hours. The annealing temperatures and annealing durations are interchangeable. Tempering with short duration and high temperature has the same effect as a long-lasting starting with correspondingly low temperature. This interchangeability is described by the Hollomon - Jaffe parameter. Formally correspond to the Larson-Miller parameter which describes creep. There is the possibility of the use of residual heat for tempering ( utilization of residual heat after quenching from the austenitizing temperature remaining desired workpiece residual core temperature) or the complete Neuerwärmung to tempering temperature. The annealing takes place in special tempering which caused by air circulation rapid heating of the workpieces and the feature extraction for a resulting oil vapors. Annealing can also be done in a salt bath ( nitric or Nitriersalzbad ) or in a slightly heated curing oven.

Embrittlement

In connection with the tempering embrittlement two are observed:

Not steel -related procedures

In the further processing of ingots and slugs of aluminum and its alloys as well as from other industrially important non-ferrous metals as well as for die forging is the tempering to the optimum temperature for rolling, drawing and pressing operations, an elaborate technique also order and recrystallization of the to processed material includes.

In the manufacture of glassware, the annealing is used to reduce the cooling or by means of the forming process of glass present in the material stresses. The glassware is thereby heated to the extent that it is soft yet again, but the internal stresses can be compensated. Then the temperature is lowered slowly and slowly cooled to the glass below a critical point. Then it could be rapidly cooled. Does not happen this treatment, the glass breaks or shatters spontaneously at relatively fast temperature shocks.