Study of repair welding on microstructure, mechanical properties and corrosion resistance of dissimilar welded joints of SUS304 and Q345B steel

In this study, the influence of repair welding on microstructure evolution, mechanical properties, and corrosion resistance of SUS304-Q345B dissimilar metal active gas arc (MAG) welding plates was investigated via optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), hardness, tensile, fatigue, intergranular corrosion, and electrochemical tests, in which the zero (R0), primary (R1), and secondary repair welding (R2) were performed by MAG welding. The results showed that, after repair welding, the δ-ferrite morphology in the weld evolved from a continuous dendritic shape to a dispersed worm-like structure and the bar ferrite in the heat-affected zone of SUS304 (HAZSUS304) evolved into short bar ferrite. The grain size of the weld was reduced due to the remelting caused by repair welding. The hardness of the weld increased first and then decreased which was related to the decrease of δ-ferrite morphology and grain size of weld. In the tensile test, all specimens were fractured at Q345B base material (BMQ345B), which revealed that repair welding had little effect on the tensile properties. The fatigue limit strength of R1 didn't reduce significantly, while the fracture position of R2 transferred from the SUS304 base material (BMSUS304) to the fusion line of SUS304 (FLSUS304). The corrosion resistance of R1 weld possessed the best corrosion resistance owing to the finer grain size and better δ-ferrite morphology. The results indicated that repair welding was feasible for the repair and reuse of welded joints, and it was of great importance in engineering applications of welded plates.