Whether the quality of the steel shot is related to the blackness of the surface

　　In fact, the more black and brighter the appearance of the steel shot just means that the heat treatment temperature in the production process is too high, resulting in the production of reduced carbon in the steel shot, so that the hardness of the steel shot becomes low, the steel shot is prone to deformation in the process of hitting.

　　Conclusion: The blacker the appearance, the brighter the steel shot, but not necessarily good quality, may be "look useless".

　　The production of steel shot is the need for heat treatment and quenching, so we should pay attention to these aspects of the problem, to ensure the quality of the steel shot, the carbon content of the steel shot determines the hardness and quality of the steel shot, so we should pay attention to this problem.

　　After the steel is heated by quenching, there will be two cooling methods, one is isothermal cooling, that is, isothermal quenching; The second is continuous cooling, that is, ordinary quenching. Isothermal cooling can obtain pearlite, sostenite, trostenite, bainite, etc., as needed, while ordinary quenching is to obtain martensite. All kinds of steel parts, mechanical parts and molds should be used after quenching and tempering. Hardening and hardening during quenching is due to the formation of martensite.

　　There are two basic forms of martensite, one is lath martensite, which is composed of groups of lath under the crystal phase microscope. The other is lamellar martensite, which looks like a bamboo leaf under a crystalline phase microscope. In terms of performance, lath martensite not only has high hardness, but also has good toughness; On the other hand, flake martensite has high hardness but poor toughness. It is typically hard and brittle, so it needs to be tempered at the expense of hardness to improve toughness. Therefore, we hope to get more lath martensite after quenching. In practice, lath martensite is produced after quenching in steels with carbon content less than 0.2%, lath martensite and sheet martensite are formed after quenching in steels with carbon content of 0.2-1.0%, and sheet martensite is almost formed in steels with carbon content higher than 1.0%.

　　Although the carbon content determines the form of the martensite, we can adjust the process to maximize the performance of the workpiece. Low carbon steel and low carbon alloy steel have poor hardenability, so we can obtain almost all the lath martensite by using strong quenching (cold brine), and get a good match of high strength and toughness. Medium carbon (carbon content 0.3%-0.6%) steel or medium carbon alloy steel is widely used steel, its carbon content is between 0.2-1.0%, quenching to form lath martensite and sheet martensite mixed structure, will be heated and quenched at high temperature, can obtain more lath martensite, under the condition of constant hardness, greatly improve the toughness of steel. For high carbon steel parts, in order to obtain more lath martensite, the method of heating and quenching at low temperature and short time can be adopted.

　　It can be seen that the same material, through a more reasonable quenching process, can get more ideal properties.