On 2018-08-08 14:48:54
heat treatment of metal materials analysis of common phenomenon of overheating
How can you make a metal material work better? Is, of course, after the metal heat treatment, the material used to improve performance, in order to achieve the requirements of on one hand, many people are in metal heat treatment process can lead to overheating, loss of metal material has been heat treated, if high temperature overheating, not to advance is not good for metal materials, and even this will be material damage, etc.
Heat treatment equipment according to their own understanding of vacuum furnace analysis: metal material heat treatment overheat common phenomenon
1. General overheating: heating temperature is too high or holding time is too long at high temperature, causing austenite grain coarsening is called overheating. The coarse austenite grain will lead to the decrease of steel strength and toughness, the increase of brittle transition temperature, and the increase of deformation and cracking tendency during quenching. And the cause of overheating is the furnace temperature meter out of control or mixing (often do not understand the process). The superheated structure can be re-austenized to refine the grain under normal conditions after annealing, normalizing, or multiple high-temperature tempering.
2, fracture inheritance: steel with overheating structure, after reheating and quenching, although the austenite grain can be refined, but sometimes still appear coarse grain fracture. There are many controversies about the theory of fracture inheritance. It is generally believed that debris such as MNS has been dissolved into austenite and enriched in grain boundary due to high heating temperature, and these inclusions will be precipitated along the grain boundary when cooled, and are prone to fracture along the thick austenite grain boundary when impacted.
3. Inheritance of coarse structure: When steel parts with coarse martensite, Bainite and Weissner structure are re-austenized, their austenite grains are still coarse when they are heated at a slow rate to the conventional quenching temperature or even lower. This phenomenon is called tissue inheritance. To eliminate the heritability of coarse tissue, intermediate annealing or multiple high temperature tempering treatments can be used.