Analysis of lamellar tearing defects in the Z-directional tensile fracture of Q355 hot-rolled thick plates
LIU Xiaofeng1, SHEN Wenjun2, ZHANG Chuangju1, PAN Shisong3, DAI Lin3, CHENG Guoguang2
1. Steelmaking Plant,Chongqing Iron and Steel Co., Ltd.,Chongqing 401258,China; 2. State Key Laboratory of Advanced Metallurgy,University of Science and Technology Beijing, Beijing 100083,China; 3. Manufacturing Management Department,Chongqing Iron and Steel Co., Ltd.,Chongqing 401258,China
Abstract：In order to improve the Z-directional tensile plasticity of Q355 thick plates, the reasons for the formation of Z-directional tensile defects were investigated through tensile fracture morphology observation, inclusions observation and statistics, microstructure observation and solidification structure simulation of continuous casting slab. In addition, the reasons for the appearance of MnS inclusions aggregated in the centre of the plate were further investigated. It is found that the brittle fracture platform of the tensile fracture is covered with MnS inclusions. These MnS only appear in the centre of the plate together with martensite and are accompanied by severe C and Mn segregation. The large amount of aggregated MnS in the centre of the plate create a large area of brittle fracture influence, which results in Z-directional tensile defects in the plate. The root cause of the aggregation of MnS in the centre of the plate is the overdeveloped columnar crystal of the continuous casting slab. The overdeveloped columnar crystals form a severe central segregation, which eventually leads to large aggregates of MnS and martensite together. Avoiding the appearance of overdeveloped columnar crystals and reducing the central segregation of the continuous cast slab is an effective way to improve Z-directional tensile plasticity.
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2023, Vol. 42 
