1. Sheet Metal Research Institute, Technology Institute of Shougang Group Co., Ltd., Beijing 100043, China;
2. Beijing Key Laboratory of Green Recyclable Process for Iron and Steel Production, Beijing 100043, China;
3. Manufacturing Department, Beijing Shougang Co., Ltd., Tangshan 064404, Hebei, China
Abstract:In order to develop a 500 MPa grade high ductility square tube steel that meets the requirements of secondary processing,the microstructure,properties,strengthening mechanism and work hardening mechanism of 500 MPa grade high ductility square tube steel were investigated by utilizing optical microscope(OM),scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results show that the microstructures of the two tested steels are composed of ferrite and a small amount of pearlite. Compared with the high C-high Mn-Nb microalloyed test steel,the size of ferrite and pearlite is finer,the size of the second phase precipitates is larger,and the density of dislocation is similar. The mechanical properties of the tested steels are similar before forming,except for the yield ratio of the low C-low Mn-Nb and Ti microalloyed test steel is higher. The low C-low Mn-Nb and Ti microalloyed test steel has a significantly work hardening effect after forming,the yield strength and tensile strength increased by 45 and 26 MPa,respectively,while the elongation decreased by 6.0%. The yield strength and tensile strength of the high C-high Mn-Nb microalloyed test steel increased by 22 MPa and 10 MPa,respectively,and the elongation decreased by 4.0%. The grain refinement strengthening is the most important strengthening modes,the grain refinement strengthening accounts for 52.9%-61.8%,the solid solution strengthening is the second main strengthening mechanism,the solid strengthening accounts for 17.2% to 25.3%,while the precipitation strengthening and dislocation strengthening contributes little to the yield strength. The dislocation strengthening increased to 82 MPa of the low C-low Mn-Nb and Ti microalloyed test steel after forming,which is higher than that of the high C-high Mn-Nb microalloyed test steel. Hence,the high C-high Mn-Nb microalloyed test steel is more suitable for the preparation of high ductility automotive square tube in view of the comprehensive mechanical properties as compared to the other one.
惠亚军, 吴科敏, 许克好, 肖宝亮, 令狐克志, 刘锟. 500 MPa级高延性方管用钢的开发及加工硬化行为[J]. 钢铁, 2020, 55(2): 131-138.
HUI Ya-jun, WU Ke-min, XU Ke-hao, XIAO Bao-liang, LINGHU Ke-zhi, LIU Kun. Development of 500 MPa grade high ductility square tube steel and its work hardening behavior. Iron and Steel, 2020, 55(2): 131-138.
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