| Thin slab-direct hot rolling, called mini-mill process, is expected as a future process for production of low carbon steel sheets. However, there are several problems to be solved in the processing, one of which is edge cracking in low carbon steel sheet. To prevent the edge cracks of low carbon steel sheet, an isothermal preheat treatment was adopted before roughing in the mini-mill process. From the metallurgical viewpoint, the effect of Mn/S ratio on the edge cracks of low carbon steel sheet was investigated as well. It was found that edge cracking of low carbon steels contained 0.4% Mn or higher could prevented with isothermal preheat treatment at 1150℃ for 5 minutes before roughing. Reducing S content below 0.01%, 0.3% of Mn is enough to prevent edge cracks with isothermal preheat treatment at 1150℃ for 3 minutes before roughing. A concept of edge crack index is proposed for more accurate estimation of the total amount of edge cracking as a function of Mn/S ratio in this study. |
|
