Carburizing behavior and microstructural characteristics of hot-rolled strip at surface sliver defects
PAN Yi-qing1, YIN Sheng2, TIAN Qing-chao1, PEI Xin-hua2, LUO Ke-li3
1. School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China; 2. Research and Development Center, Shanghai Meishan Iron and Steel Co., Ltd., Nanjing 210039, Jiangsu, China; 3. Hot Rolling Plant, Shanghai Meishan Iron and Steel Co., Ltd., Nanjing 210039, Jiangsu, China
Abstract:The formation mechanism of abnormal sliver defects was studied in order to improve the surface quality of SPHC hot-rolled strip. The differences in microstructure,composition and properties between the defects and the matrix were analyzed by optical microscope,scanning electron microscope,energy spectrometer and hardness tester. The results show that the defects are mainly induced by the presence of many slag inclusions in the continuous casting slabs,and these slag inclusions with a high carbon content play a role of "carburizing" on the surrounding matrix during the heating process of the slab,in which the thickness of the carburizing layer can reach 5 727.2 μm. The varied microstructure in strip cross-section is caused by the difference of dynamic recovery and dynamic recrystallization owing to the temperature discrepancy between the surface and core. During the laminar flow cooling period,the intensely distributed fine carbide particles in the carburizing region cause the divorced eutectoid transformation of the supercooled austenite in the surface layer,and the granular cementite precipitates along the grain boundaries.
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