Abstract: The 20CrH special steel bar produced by a special steel factory,after warm forging to make inner star wheel by the downstream user,the mixed crystal phenomenon was found after carburizing heat treatment at 9655 ℃×6 h.Using light microscope observation and design of heat treatment test for verification,the results show that the uneven temperature of forging deformation and the low temperature of holding after forging lead to the abnormal growth of local austenite grains in the subsequent carburizing process and the formation of mixed grains. The temperature preservation of the inner star wheel after warm forging is increased from 710 ℃ to 900℃,which can effectively avoid crystal mixing and provides guidance for the process design of warm forging of similar special steel parts.

Key words: Mixed Crystal, Warm Forging, Metallographic Structure, Carburizing, Inner Star Wheel

摘要： 特钢厂生产的20CrH特殊钢棒材，下游用户温锻制作内星轮后，经965℃×6 h渗碳热处理后发现混晶现象。采用光学显微镜观察并设计热处理试验验证，结果表明：锻造变形温度不均及锻后保温温度偏低，导致在后续渗碳过程中局部奥氏体晶粒出现异常长大而产生混晶。将内星轮温锻后保温温度由710℃提高至900℃,能有效改善混晶现象，为同类特殊钢零部件温锻的工艺设计提供指导。

关键词: 混晶, 温锻, 金相组织, 渗碳, 内星齿轮