Microstructure characteristics of duplex stainless steel CMT-P composite welding

By introducing the CMT-P welding method, the welded joints of UNS S32750 super duplex stainless steel with excellent forming quality were successfully prepared. Metallographic microscope, X-ray diffractometer, scanning electron microscope, energy dispersive spectrometer and transmission electron microscope were used to study the microstructure of different regions of the joint. The results showed that the weld, heat-affected zone and base metal structure show significant differences. Compared with the base metal and the weld, the austenite content in the heat-affected zone is the lowest (32.3%), but the austenite content in each micro-zone of the welded joint meets the standard requirement of not less than 30%. Due to the effect of reheating during the welding thermal cycle, intra-grain γ₂ and grain boundary γ₂ with different scales and morphologies are precipitated in the weld root and heat-affected zone, but there is no γ₂ precipitation in the weld filling zone. In addition, short rod-shaped Cr₂N precipitated in the weld root and heat-affected zone, which is mainly distributed in the ferrite grains and grain boundaries. The precipitation of Cr₂N caused the adjacent ferrite matrix to form an obvious Cr-poor zone.