Three phenomena of heat treatment temperature

- May 18, 2017 -

1 General overheating: Heat treatment heating temperature is too high or heat preservation time is too long, resulting in austenite grain coarsening called overheating. Coarse austenite grains can lead to lower strength and toughness of steels, high brittle transition temperature, and increase in deformation and cracking tendency of quenching. The cause of overheating is the temperature meter out of control or mixture (often not understand the process of occurrence). Overheating tissue can be annealed, positive or many times after high temperature tempering, under normal conditions of austenite to refine the grain. 2 Fracture inheritance: Heat treatment has overheated microstructure of steel, after reheating quenching, although can make austenite grain refinement, but sometimes still appear coarse granular fracture. The theory of fracture heredity is more controversial, generally believed that the heating temperature is too high and so that the MNS and other debris dissolved into the austenite and enriched the crystal interface, while cooling these inclusions will also along the crystal interface precipitation, vulnerable to the impact of coarse austenite grain boundaries fracture. 3 Gross tissue inheritance: there are coarse martensite, bainite, the Weimar microstructure of the steel pieces of re-austenite, to slow heating to the conventional quenching temperature, even lower, its austenite grain is still coarse, this phenomenon is known as tissue hereditary. To eliminate the hereditary of coarse tissues, intermediate annealing or multiple high-temperature tempering can be used.

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