Study on the parameters optimization and the microstructure of spot welding joints of 304 stainless steel

Resistance spot welding experiments of 304 stainless steel were performed in this study. Orthogonal test and analysis method were used to carry out the experiments and optimize process parameters based on their effects on tensile shear load and nugget diameter of the spot-welded joint. The microstructure and the defects of spot-welded joints were studied. The highest tensile shear load of joint was 9.529 kN produced at optimum parameters, i.e., electrode force of 3.5 kN, welding current of 6.5 kA, and welding time of eight cycles. Microstructure of the nugget of welded spot joint was columnar dendrite grains which contains austenite and delta-ferrite, and the microstructure of the HAZ region was coarse equiaxed grains of austenite that were induced by different heat inputs. The solidification cracks and shrinkage cavities were observed in resistance spot-welded joints which were produced at higher heat input. These defects seriously reduced the strength of spot-welded joint.