WANG Zhonglei, SHI Zhen, ZHOU Hao, NI Jinshang, PENG Weifeng
Aiming at the problems of cold cracking, heat affected zone softening,toughness decreasing, and residual stress in the welding of high-strength steel for automobiles, the Q960E automobiles high-strength steel has been taken as the research object, the laser composite welding test method has been used to study the effects of different heat treatment parameters such as preheating temperature, quenching temperature, and tempering temperature on the microstructure and mechanical properties of the welded joint. The research results indicate that the welded joint of Q960E high-strength steel consists of a welding base material, a weld seam, a fusion zone, an overheated zone, and a normalized zone, at preheating temperature of 100 ℃, quenching temperature of 900 ℃, and tempering temperature of 400 ℃, the base material is tempered martensite, the weld seam is fine bainite, the fusion zone is fine bainite and coarse martensite, the overheated zone is coarse bainite, and the normalized zone is a recrystallized crystal composed of bainite and martensite. As the quenching temperature increases, the tensile strength and yield strength of the welded joint show a trend of first increasing and then decreasing, and the elongation at break shows a trend of first decreasing and then increasing. As the tempering temperature increases, the tensile strength and yield strength of the welded joint show a gradually decreasing trend, while the elongation at break shows a gradually increasing trend. When the preheating temperature is 100 ℃, the quenching temperature is 900 ℃, and the tempering temperature is 400 ℃, the tensile strength of the welded joint is 1 150 MPa, the yield strength is 1 075 MPa, and the elongation at break is 10.56%, the comprehensive performance is superior, and it is the best heat treatment processes for Q960E automotive high-strength steel.
