Effect of Welding Current on Microstructure and Mechanical Properties of Resistance Spot Welded Joint of H1000 and GMW2 Dissimilar Steels

The resistance spot welding of H1000 stainless steel and GMW2 low carbon steel with the thickness of 1.2 mm was carried out to analyze the influence of welding current on the microstructure, mechanical properties and tensile-shear fracture mode of the joint. The results show that with the increase of welding current, the tensile shear force of the joint increases firstly and then decreases gradually.When the welding current is 8.5 kA, the tensile shear force of the joint reaches the maximum value, about 6800 N. When the current reaches or exceeds 9.0 kA, defects such as shrinkage and cracks are formed inside the joint, which seriously affects the quality of the joint. The joint has significant nugget offset phenomenon.Most of the nugget zone is located at the side of H1000 steel, and the microstructure is mostly austenite and a small amount of martensite, and the hardness of the nugget zone is between the two base metals, about 300 HV. The fracture mode of the joint transforms with the increase of the nugget diameter.When the welding current is less than or equal to 6.5 kA, the tensile shear fracture mode of the joint is interfacial fracture, while the current is bigger than or equal to 7.0 kA, the fracture mode of the joint is button fracture.