Research on Microstructure and Properties of MIG and SAW Welds in 310S Heat-Resistant Stainless Steel

Currently, the preparation process for high-temperature rotating shafts made of 310S stainless steel, which possesses excellent high-temperature oxidation resistance and corrosion resistance due to its high chromium and nickel content, using Metal Inert Gas (MIG) welding, still faces issues such as low welding efficiency and the complexity of multi-pass welding procedures. There is a need to find more efficient preparation methods. To enhance processing efficiency, this study innovatively attempts to utilize the more efficient Submerged Arc Welding (SAW) process for preparing the microstructure and properties of 310S stainless steel high-temperature rotating shafts. A comparative study focusing on the microstructure and mechanical properties between MIG and SAW welds was conducted. Microstructural analysis revealed that in MIG welding, due to multi-pass overlapping and repeated heating, dendrites in the weld continuously grow along the boundaries of the previous weld pool, forming a distinct interlocking crystallization structure. In contrast, SAW welding, with its higher heat input, primarily exhibits a columnar grain structure in the weld zone, with more uniform grains and superior isotropy. Both types of welded joints displayed typical solidified microstructures composed of columnar grains and polygonal ferrite. However, the SAW weld showed a more fully recrystallized Heat-Affected Zone (HAZ) with a reduced coarse-grained region. Comparison of mechanical properties showed that the microhardness of the SAW weld (162–227 HV_0.2) was essentially equivalent to that of the MIG weld (171–225 HV_0.2). Importantly, the ultimate tensile strength (573 MPa) and elongation after fracture (24%) of the SAW weld were significantly improved, surpassing those of the MIG weld (556 MPa, 19.4%). Based on the reasonable comparison of microstructures and properties obtained in this study, it is proposed to replace MIG welding with SAW welding. Utilizing continuous high-current wire feeding and submerged combustion under a flux layer enables deep-penetration single-pass welding. This results in a deposition rate several times higher than MIG welding, substantially reducing the number of passes and labor hours, thereby effectively improving production efficiency. This approach is particularly well-suited for large rotating shaft components and can effectively replace the original multi-pass MIG welding method.