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.