Reasons analysis of edge cracks on 980 MPa level dual- phase steel strip leading to strip- break
LI Run- chang1,ZHANG Huan- yu1,XIA Yin- feng1,ZHANG Liang- liang2
（1. Manufacturing Department, Shougang Jingtang United Iron and Steel Co., Ltd., Tangshan 063200, Hebei, China 2. Sheet Metal Research Institute, Research Institute of Technology, Shougang Group Corporation, Beijing 100043, China）
Abstract：There is a strong possibility that edge cracks may occur in cold rolling process of 980 MPa level dual- phase steel. And the main reason was the formation of bainite phase and the heterogeneous precipitation of carbides, which mainly occurred in the tail of the hot rolled coil. The main reason for the formation of bainite was that the temperature of hot rolled coiling was higher than that of bainite, and the temperature of the edge of the steel coiling was lower. As a result, the edge entered the temperature region of bainite. The reason for the heterogeneous precipitation of carbides was that after the coil rolled off the hot line, the temperature dropped through the ferrite area, ferrite was formed and the carbide was precipitated. At the same time, the cooling speed of the edge was faster, and the carbide can not achieve the homogenization distribution and spheroidization. Cracks may easily occur in the bainite, the ferrite and bainite binding zone, and the carbide segregation zone during cold rolling. In the subsequent production, under the strip tension and shear force by roll surface, cracks extended along the original direction, and the severe case can result in the strip- break. Increasing the hot tail coiling temperature, lining into the slow cooling pit or reducing the coiling temperature can inhibit the three kinds of crack sources, and reduce the formation of edge cracks and the risk of strip- break.
2018, Vol. 28 
