自動車外板用極低炭素IF鋼における加工後筋状欠陥の発生機構および熱延前再加熱温度とSb添加の影響

抄録

Streak-shaped defects were infrequently observed on ultra-low carbon IF cold-rolled steel sheets for automotive outer panels after press-forming. The defects occurred due to heterogeneous remaining of elongated grains on the steel surface layer. Elongated grains are hard to recrystallize due to the pinning effect of small precipitates on grain boundaries. These precipitates consist mainly of Ti(NC), TiS and AlN. In order to eliminate the streak defect, lower excess Ti, lower temperature slab reheating and Sb-addition to the steel are efficient. These countermeasures result in a drastic reduction of the defect ratio. This improvement is considered to be obtained due to the reduction of small precipitates of Ti(CN), TiS and AlN in the steel surface layer.