한국주조공학회

Cold-forged products that are utilized to carburize steel often experience abnormal grain growth during high-temperature carburizing processes due to uneven levels of residual stress that form within the metal during plastic deformation. This abnormal grain growth is a primary cause of both quality degradation and productivity loss during a carburizing heat treatment. In this study, a NSR (normalizing & stress relief) heat treatment is proposed as a pre-treatment before cold forging to control abnormal grain growth more effectively. The effect of this treatment was analyzed using the thermodynamic simulation program Thermo-Calc. The results showed that compared to the conventional SA (spheroidized annealing) heat treatment, the NSR treatment resulted in a twofold increase in the volume fraction of Nb precipitates, with abnormal grain growth effectively controlled due to the grain pinning effect. Notably, the critical temperature for abnormal grain formation increased by 50℃ in the 80% compressed sample.

Normalizing, Stress relieving, Abnormal grain growth, Cold forging and Carburizing.