Analysis on property uniformity of hot-rolled coil of 1 000 MPa grade high strength automobile steel
HAN Yun1, YANG Feng1, QIU Mu-sheng1, ZOU Ying1, HAN Long-shuai1, ZHANG Shi-jie2
1. Research Institute of Technology, Shougang Group Co., Ltd., Beijing 100043, China; 2. Shougang Jingtang United Iron and Steel Co., Ltd., Tangshan 063200, Hebei, China
Abstract:Four industrial tests were carried out to study and improve the property uniformity of hot-rolled coil for a 1 000 MPa grade high strength automobile steel. When the coiling temperature was 620 ℃, the microstructures at different positions of coil varied greatly, and the properties fluctuated significantly. At 10 m from the coil tail, the edge was composed by fine ferrite and martensite, while the middle part was composed by coarse ferrite and pearlite. At 100 m from the coil tail, the edge was composed by fine ferrite, tempered martensite and a small amount of fresh martensite, while the middle part was still composed by coarse ferrite and pearlite. The great difference of microstructure led to the remarkable fluctuation of tensile strength up to 552 MPa. The effect of entering slow cooling pit on microstructure and property uniformity of steel coil was not obvious, but the opposite was true for increasing the coiling temperature. When the coiling temperature was increased to 680 ℃, the organization difference of edge and middle part decreased, and the fluctuation value of tensile strength for entire coil decreased to 146 MPa. After applying the combination of high coiling temperature and edge-masking technology, the fluctuation value of tensile strength was further reduced to 108 MPa, and the uniform performance of coil was further improved.
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