Microstructure and Mechanical Properties of Laser Welded Joint of High Strength Steel QP980
TIAN Fei1, LIN Hongtao1, JIANG Haitao2
1 Technology Center, Hunan Hualing Lianyuan Iron & Steel Co., LTD, Loudi 417009, China 2 National Engineering Research Center for Advanced Rolling Technology, University of Science and Technology Beijing, Beijing 100083, China
Abstract: In order to solve the welding problems such as component segregation, hardening embrittlement and hydrogen-induced cracking of high strength steel QP980 in automobile lightweight application, the laser welding of QP980 steel was studied, and the welding test of 1.2mm thick QP980 steel was carried out. The microstructure and mechanical properties of the welds were evaluated. It was found that the joints with full penetration and well-formed surface could be obtained under the selected welding parameters. The cross section of the laser welding joints shows hourglass shape, and the joints can be divided into the fusion zone (FZ), the coarse-grained heat affected zone (CGHAZ), the fine-grained heat affected zone (FGHAZ), the intercritical heat affected zone (ICHAZ), the subcritical heat affected zone (SCHAZ) and the BM. The hardness of the FZ and some HAZ of the joints under different welding process parameters are higher than the BM. The highest hardness is in the FGHAZ and there is a softening zone at both sides of the weld. With the increase of heat input, the width of the FZ and the HAZ becomes larger, and the softening zone is further away from the weld center. Under different welding process parameters, the tensile strength of the joints can reach the strength of the BM, the yield strength is higher than the BM, and the elongation of the joints is lower than the BM, it indicated that the joints with good performance have been obtained under the selected welding process parameters.
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2021, Vol. 35 
