Study of microstructure and properties of TP304/SS400 dissimilar welding joints under three processes

The joining of dissimilar materials of TP304 austenitic stainless steel and SS400 mild steel was performed using flux-cored arc welding (FCAW), shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) methods. The microstructure and mechanical properties of welding joints of TP304 and SS400 were investigated by scanning electron microscopy (SEM) and multi-tests, such as micro-hardness test, tensile test, bend test and impact toughness test. The results indicate that the microstructure in weld metal zone is a mixture of δ-ferrite and austenite, but the content and morphology of δ-ferrite are significantly different. Both the vermicular δ-ferrite in FCAW welds and the acicular δ-ferrite in GTAW welds can improve the toughness effectively, but the impact absorbing energy in SMAW welds decreases for skeletal distribution of δ-ferrite. The impact fracture changed from ductile features to brittle features with the decrease of impact absorbed energy. The mechanical properties of welded joints were excellent and the micro hardness is relatively stable.