Abstract:
In order to reduce the hardness and improve the plasticity of the connection position of Hot formed steel, the Gaussian laser beam was used to quickly scan the surface of the sample, and the high-temperature tempering principle was used to reduce the strength and hardness of the material, thus successfully softening the material in local areas. The results show that the softening zone structure is tempered sorbite, and the slower the scanning speed, the better the softening effect. At temperature of 800 ℃ and scanning line speed of 2 mm/s, the softening zone hardness is 230 HV, which is 47.92% of the base metal hardness. The tensile strength of the softening zone decreases by 767 MPa, which is 50.53% of the base metal. Its elongation after fracture is 17.36%, which is 188.08% of the base metal. The softened tensile specimen exhibits ductile fracture with a cup-shaped cross-section. After softening, spot welding will not change the hardness of the weld nugget. It can widen the heat-affected zone, avoid the sudden drop and rise of its hardness, improve the stress concentration in the heat-affected zone, prevent the interface fracture of the welding spot, and increase the maximum displacement of the weld spot fracture by 60% after softening. Maximum energy absorption work increased by 10.14%. This study demonstrates the feasibility of laser softening hot-formed steel and has a certain guiding significance for the local softening of hot-stamped automotive parts.