1. School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China; 2. Henan Xinjinhui Stainless Steel Industry Co., Ltd., Xuchang 461000, Henan, China
Abstract:The frequently observed surface peeling defects on the hot and cold-rolled plate of a kind of nickel-saving austenitic stainless steel have an extremely influence on the qualification rate of the final products. The macroscopic morphology, microstructure and element composition of the peeling defects were observed and analyzed by means of metallographic microscope, scanning electron microscope and electron backscattered diffraction, respectively, to explore the cause of peeling defects. The results show that there are obviously embedded Cr and Mn metal oxides on the surface and longitudinal section of peeling defects of the hot-rolled plate, and their chemical composition is highly consistent with their common iron oxide scales. In addition, the residual ferrite structure is found in the longitudinal section of the peeling defect of the hot-rolled plate by EBSD scanning. The thermoplastic difference between ferrite and the matrix austenite phase during rolling might lead to local micro-cracks and oxide embedding, which grows into the oxidative peeling defect frequently observed on the hot-rolled plate. The peeling defect of cold-rolled plate comes from the hidden defect of hot-rolled plate. The abnormal composition of the peeling defect of the cold-rolled plate is basically consistent with the exogenous inclusion such as tundish covering flux and mold protective flux, which is involved into the liquid steel during the casting process and could mostly be exposed during the final cold rolling process. The latter could be defined as inclusions induced peeling defects, which appears as linear peeling and spalling peeling. Through the improvement of continuous casting tundish and submerged nozzle process, the proportion of peeling defects on the surface of this kind of stainless steel rolled sheets could be effectively reduced.
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