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 a-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 degrees C. After tempering at 250 degrees 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 degrees 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 degrees 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 degrees C. In addition, the electrochemical corrosion potential of the welded joint by tempering treatments was positively shifted and the corrosion resistance was improved.