Three phenomena of heating temperature in heat treatment

Metal parts are processed by heat treatment to change the surface structure or internal chemical composition of metal steel, so as to improve the comprehensive mechanical properties of metal steel, so that it has higher processing efficiency and higher economic value.

Three phenomena of heating temperature in heat treatment

1 usually overheated:

If the heating temperature of heat treatment is too high or the holding time is too long at high temperature, the austenite grain coarsening is called overheating. The coarse austenite grain will lead to the decrease of the strength resistance, the change of brittleness temperature and the tendency of deformation and cracking when quenching is added. The reason for overheating is that the furnace temperature is out of control or mixed with materials (often without understanding the technology attack). After annealing, normalizing or repeated high temperature tempering, the grains can be refined by ab initio austenitizing under normal conditions.

2 fracture inheritance:

For the steel with overheated arrangement, the austenite grains can be refined after the heat treatment from the beginning, but sometimes the fracture still appears coarse granular. There are many theoretical controversies on the occurrence of fracture heredity. It is generally believed that MNS and other impurities were once dissolved into austenite and enriched in the crystal interface due to high heating temperature, and these inclusions will separate along the crystal interface when cooling, and will crack along the coarse austenite grain boundary when impacted.

3. Inheritance of rough arrangement:

The austenite grains of the steel with the arrangement of coarse martensite, bainite and widmansite are still coarse when it is heated to the conventional quenching temperature at a slow speed or even lower when it is austenitized from the beginning. This phenomenon is called arrangement heredity. In order to eliminate the heredity of coarse arrangement, central annealing or repeated high temperature tempering can be used.