Processing map approach for surface defect prediction in the hot bar rolling

Since the surface defect frequently encountered in the hot bar rolling of steel can easily lead to a fatal manufacturing defect during the secondary cold forging process of bar stocks, it is necessary to minimize such a defect on the surface of hot rolled bars. In order to predict the instability of the material in the hot bar rolling at roughing mill stage, processing maps based on two approaches available in the literature were obtained by carrying out hot compression tests for two different steels at various temperatures and strain rates and used in the present investigation. The surface quality was examined by using optical microscopy of the cross-section of the hot compressed specimen up to 60% reduction in height. The efficiency of power dissipation was investigated in terms of strain rates and temperatures to correlate with the surface quality. According to the present investigation, both processing maps investigated were not reliable in recapturing the surface defect formation observed in the steel industry. Thus, it was found out that new processing map is required for better prediction.