正火和回火在钢热处理中的区别是什么?
Difference between normalizing and tempering in steel heat treatment
The purpose of normalizing is similar to complete annealing for hypoeutectoid steel, but due to the rapid cooling rate of double annealing, the number of pearlite in the steel after normalizing is slightly more than that of annealing, and the thickness of the sheet is thin. The strength and hardness are higher than those of annealing. For hypereutectoid steels, normalizing is only to eliminate reticulated cementite and improve the mechanical properties of the steel. Tempering is mainly to eliminate stress, stabilize the structure and size of steel parts, and achieve the required performance of parts. For large-section parts: It has the following effects-and it is very important:
1) For parts such as motor shafts, press containers, etc. (the material is generally carbon steel or low alloy structural steel), normalizing + high temperature tempering is the final heat treatment. Therefore, timely tempering after normalization can effectively stabilize the organization And size to further eliminate the internal stress of the workpiece, which has a significant effect on improving the comprehensive mechanical properties;
2) For large-scale forgings, high-temperature tempering in time after normalizing (usually adding a subcooling in the middle) can not only achieve the purpose described above, but also play an important role in hydrogen diffusion, especially for high hardenability steel (Hydrogen is a factor that produces white spots), and large white forgings are generally scrapped if white spots are generated inside. Therefore, normalizing + high temperature tempering of important parts (or special materials) is very necessary. When materials with good hardenability are normalized, high temperature tempering is required, because after normalizing, materials with good hardenability have higher hardness, such as:20铬2 ni4 18 cr2ni4w等等。需要高温回火。主要钢种:T2 T11 T12 T22 T23 T91 2Cr13、15 crmo, 15 crmog,12 cr1movG, R102 T92
锅炉用钢需要正常化和回火。回火主要是使结构稳定，使其具有一定的高温耐久性、蠕变强度和高温高压下的耐久性。其实，在国外，正常化后的淬炼是很常见的事情。相反，正常化后不回火是一种特殊情况。在中国，为了降低生产成本，一半的性能没有在正常化条件下进行调质。
下一个:40Cr钢的淬火和回火