Microstructure and Properties of Pulse Tungsten Inert Gas Welded Joint for Different Thickness CR22MnB5/DH1050 Dissimilar High-Strength Steel

The CR22MnB5/DH1050 dissimilar high-strength steel in automotive crash beams was welded by the direct current pulse TIG welding method. The microstructure and mechanical properties of the joints under different post-weld tempering treatments were tested and analyzed. The present results had a certain effect on further improving the performance of high-strength welded joints to use in the auto structure. The result showed that the weld zone (WZ) of the as-weld joint basically consisted of lath martensite. With the increasing tempering temperature, the original lath martensite gradually transformed into tempered martensite and tempered sorbite, and the C-containing solid solution in α-Fe gradually decreases, increasing carbides and grain growth. The WZ had the highest hardness, and a soft zone existed in the heat-affected zone of all steels. After tempering treatments, the microhardness of welded joint decreased, and the hardness decreased obviously after tempering at 550 °C. After tempering at 250 °C, the tensile strength of the joint was reduced (about 7 MPa) compared with the base material (BM), and the elongation was increased by 0.27%. After tempering at 550 °C, the tensile strength of the joint decreased by 166 MPa compared with the BM, while the elongation increased by 4.8%. After tempering at 250 °C, the maximum bending load applied to the joint (516 N) decreased insignificantly compared to the as-weld joint (558 N), while the bending resistance of the specimen (438 N) decreased significantly after the high temperature at 550 °C. In addition, the electrochemical corrosion potential of the welded joint by tempering treatments was positively shifted and the corrosion resistance was improved.