Heat treatment is the set of operations of heating, exposure and cooling speed of hard metal alloys with the aim of obtaining desired properties by changing the internal structure. Heat treatment is used either as an intermediate step to improve workability by pressing, cutting, or as the final operation of the technological process, providing a given level of item’s properties.
Total duration of heating metal during the heat treatment consists actually of the heating to the desired temperature time and exposure at this temperature time. The heating time depends on the type of furnace, items dimensions, their placing in the furnace; exposure time depends on the rate of occurrence of phase transformations.
Heating may be accompanied by interaction of metal surface with gas phase and lead to the decarbonization of surface and formation of dross. Decarburization leads to the fact that the surface of the part becomes less durable and loses its hardness.
With heating and cooling of steel phase transformations occur, which are characterized by temperature critical points. Critical points of steel are denoted with the letter A. A1 critical point lies on the PSK line (727 ° C) of the iron-carbon diagram and corresponds to the transformation of pearlite to austenite. A2 critical points lie on the MO line (768 ° C), characterizing the magnetic ferrite transformation. A3 corresponds to GS and SE lines, at which the ferrite and cementite transformation respectively is completed into austenite during heating.
To denote the critical points of the heating and cooling additional indexes are introduced: the letter "c" in the case of heating and the letter "r" in the case of cooling, for example Ac1, Ac3, Ar1, Ar3.
Annealing, hardening, tempering, normalizing - boot window of 350 * 200 * 350 mm
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