Abstract: Grain size is an important index to measure the quality of M50 bearing steel.By discussing the effect of annealing process on the grain size of M50 steel,in order to improve the coarse grain size and mixed grain of high temperature bearing steel M50 in the actual production process. The test results show that the grain size of M50 steel is not affected by appropriately increasing the annealing temperature and extending the holding time. It has been verified in actual production that the annealing process is changed from holding heat at 860 ℃ for 5 h to holding heat at 910 ℃ for 8h, which can im- prove the grain size and mixed crystal of M50 steel caused by insufficient uniformity of furnace temperature. In addition, it is verified that when the cooling rate is too fast after annealing and heat preservation, it is easy to cause coarse quenched grain of the finished bearing, which should be paid attention to in the actual production process.

Key words: Grain Size, Mixed Grain, Annealing, Temperature, Time

摘要： 晶粒度大小是衡量M50轴承钢质量的重要指标，通过探讨退火工艺对M50钢晶粒度级别的影响，以期改善实际生产过程中高温轴承钢M50钢材晶粒粗大、混晶问题。试验结果表明，适当提高退火温度、延长保温时间不会对M50钢晶粒度级别造成不利影响。实际生产中进行验证，退火工艺由860℃下保温5 h变更为910℃下保温8 h,可以改善因炉温均匀性差造成的M50钢材晶粒粗大及混晶等问题。另外，验证了当退火保温后的冷却速度过快，容易造成成品轴承淬火晶粒粗大，在实际生产过程中应予以关注。

关键词: 晶粒度, 混晶, 退火, 温度, 时间