Microstructure and Mechanical Properties of Active Gas Arc Welding between 304 Austenitic Stainless Steel and Q235B Low Carbon Steel

In the present study, metal active gas arc welding was carried out for dissimilar welding of 304 austenitic stainless steel and Q235B low carbon steel. The microstructure of the joints was investigated by using scanning electron microscopy, optical microscopy, and electron backscattered diffraction. Microhardness and tensile test results were utilized to characterize the mechanical behavior of the joints. The tensile fracture mechanism of the welded joints was explored by examining their solidification and crystallization modes. The results indicate that the weld zones of the two base metals are affected by heat input and cooling, which results in coarse grain sizes and low microhardness values. The heat-affected zones contain complex microstructure, including Widmanstatten structure, ferrite, and pearlite. Energy-dispersive spectroscopy analysis shows an obvious elemental transition zone at the fusion line on the Q235B side of a joint. The microhardness is lowest at the weld seam of a joint and highest at the fusion line on the carbon steel side due to martensitic structure. The solidification and crystallization modes of the welded joints are discussed and combined with the analysis of microstructure and mechanical properties. The results show that due to the difference in the thermal conductivities of the two base metals, a grain boundary convergence zone forms in the weld center after solidification and crystallization of the weld metal, resulting in fracture at the weld center in tensile testing.