Knowledge of heat preservation and cooling of steel shot through quenching process

　　The purpose of quenching the steel shot is to obtain a martensite or bainite structure, and then tempering at different temperatures to greatly improve the rigidity, hardness, wear resistance, fatigue strength and toughness of the steel, so as to meet the requirements of various Different requirements for the use of various mechanical parts and tools. The knowledge of heat preservation and cooling in this process is an important part. Next, let's follow the footsteps of steel shot manufacturers to take a look!

　　1. Quenching and heat preservation

　　The quenching holding time is determined by various factors such as the heating method of the steel shot equipment, the size of the parts, the composition of the steel, the amount of furnace loading and the power of the equipment. For overall quenching, the purpose of heat preservation is to make the internal temperature of the steel shot uniform and consistent. For all kinds of quenching, the holding time ultimately depends on obtaining a good quenching heating structure in the area requiring quenching. Heating and holding are an important link that affects the quality of quenching.

　　2. Quenching and cooling

　　To make the high temperature phase in the steel shot - austenite transform into the low temperature metastable phase - martensite during the cooling process, the cooling rate must be greater than the critical cooling rate of the steel. During the cooling process of the steel shot, there is a certain difference in the cooling rate between the surface and the core. If the difference is large enough, it may cause the part greater than the critical cooling rate to transform into martensite, while the core that is less than the critical cooling rate cannot be transformed. The case of martensite formation. In order to ensure that the entire section is transformed into martensite, it is necessary to select a quenching medium with sufficient cooling capacity to ensure that the core of the steel shot has a sufficiently high cooling rate. However, the cooling rate is large, and the internal stress caused by uneven thermal expansion and contraction inside the workpiece may cause deformation or cracking of the workpiece. Therefore, the above two contradictory factors should be considered, and the quenching medium and cooling method should be selected reasonably.