Temperature-controlled Gradient Phase Transformation Strengthening Pattern for Ultra-high-strength Steel
TONG Ying1, GAO Lin2, ZHANG Kaikai2, QUAN Guozheng2, WANG Xuan2, ZHOU Jie2
1 College of Intelligent Manufacturing and Automotive, Chongqing College of Electronic Engineering, Chongqing 401331 2 School of Materials Science and Engineering, Chongqing University, Chongqing 400044
Abstract: The staged variable strength zoning is the prerequisite to satisfy both high strength and high plasticity requirements in the design of automotive lightweight structure. However, the abrupt change of mechanical properties at the junction of different zones has become a tough technical bottleneck. Aiming at seeking the ideal pattern of temperature-controlled gradient phase transformation strengthening for ultra-high strength steel plate, numerical simulation was employed to investigate hot stamping approach capable of achieving the smooth transition of mechanical properties by temperature-controlled gradient phase transformation strengthening. Based on the developed automatic temperature-controlled gradient phase transformation testing platform, a series of gradient temperature-controlled phase transformation hot stamping tests were carried out. Furthermore, the mapping relationship between the tailored gradient cooling conditions and mechanical properties (hardness, tensile strength and elongation at break) of the sheet metal in hot forming process was established. The results showed that temperature-controlled gradient phase transformation strengthening pattern could endow hot forming parts with high-strength and high-plasticity structures, and realize smooth graded microstructure and properties. The increase of die temperature and holding time, and the decrease of initial forming temperature would result in the raise of bainite content, decline of tensile strength and Vickers hardness, and boost of elongation.
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2019, Vol. 33 
