Study on Mechanical Properties of Weld Joints of Stainless Steel and Carbon Steel

The engineering application scenarios are becoming more and more complex, and the structure is facing higher requirements in terms of bearing capacity, corrosion resistance and economy. It is difficult for a single metal material to meet all engineering requirements. Stainless steel is a kind of green high-performance material, which is conducive to the realization of the goal of ‘double carbon’ in China, and has good strength and corrosion resistance. Carbon steel is widely used because of its low price, but its corrosion resistance is poor. In order to improve the utilization of materials and save costs, stainless steel and carbon steel are often welded in engineering. At present, due to the different working environment and working medium of the equipment in the nuclear power plant, austenitic stainless steel and carbon steel are usually used for welding; in the building curtain wall, the general outdoor wall panels, connectors, glass curtain wall support system will use stainless steel, while the internal keel and the theme steel truss column will use carbon steel, so there will be a large number of stainless steel and carbon steel welding. However, the current domestic specifications do not support the welding of stainless steel and carbon steel. Due to the different chemical composition and physical properties of the two materials, the welding of stainless steel and carbon steel encounters problems. For example, the difference in melting point causes metal loss, the difference in linear expansion coefficient may lead to cracks in the weld, and the difference in chemical composition causes brittle compounds in the welding process. Since the existing research mainly focuses on the welding of Q235B steel and austenitic stainless steel, there is no systematic study on the common types of stainless steel and carbon steel. The S30408, QN1803, S22053 stainless steel and Q235B, Q355B carbon steel are connected by butt weld. The mechanical properties such as metallographic structure, hardness, strength and fracture morphology of 6 different combinations and 48 stainless steel and carbon steel welded joints were systematically studied through experiments. The results show that there are obvious carburized layer and decarburized layer in the welded joint of stainless steel and carbon steel near the fusion line. The grain size of the heat affected zone increases, and the brittle structure such as martensite appears, so that the hardness of the heat affected zone is greater than that of the metal base metal. The tensile specimens of stainless steel and carbon steel welded joints fractured on the side of carbon steel. The tensile strength was consistent with the tensile strength of the carbon steel base metal. The yield strength was lower than that of the carbon steel base metal, and the elongation was significantly reduced. Due to the formation of decarburized layer, the hardness and toughness near the fusion line of carbon steel decrease, the tensile fractures of stainless steel and carbon steel welded joints show dimples, which are ductile fractures.