Study on microstructure and mechanical properties of welded joints of transition welds with different variable cross-section ratios
Q450NQR1 high-strength weathering steel MAG welding 1∶3,1∶4,1∶5 variable cross-sections transition welds welded joints were stretched,bending,room temperature and low temperature-40 ℃ impact and hardness tests,and the fractures of tensile and impact specimens were scanned and metallographic structure was analyzed.The results showed that the tensile properties of the three kinds of variable section welded joints were good,and the tensile performance of 1∶5 variable cross-sections joints was the best.1∶3,1∶4,1∶5 variable section transition welds welded joints had good bending performance.The room temperature impact performance of each variable section joint was good,and the low temperature impact performance was significantly reduced among which the weld of each variable section welded joints,the impact power of the heat-affected zone was almost the same,and it could be seen from the observation of the fracture:the specimens at different temperatures were ductile fractures.The hardness distribution of three different variable cross-sections welded joints was roughly the same,and the hardness value near the bond line of the 1∶5 variable cross-sections welded joint was higher than that of the other two groove joints,and the hardness value met the standard.Due to the thicker weld and slower heat dissipation,the number of ferrite in the joint weld was more than the other two types of variable section.
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