Effect of pre-weld heat treatment on the microstructure and mechanical properties of electron beam welded 440C stainless steel joint

The effects of pre-weld heat treatment on microstructure and mechanical properties of electron beam welded 440C stainless steel joint were observed and studied, including annealing as well as quenching and tempering. The characteristics of structure change, joint tension and hardness distribution in the two states are analyzed. The results show that the electron beam weld has a good shape without any microcracks. The microstructure located at the weld consists of martensite and retained austenite, showing a non-equilibrium solidification microstructure, carbon and alloying elements exist in the weld structure in solid solution, and the hardness reaches 398 HV. After quenching and tempering heat treatment before welding, the base metal matrix transforms from ferrite into tempered martensite and retained austenite, and at the same time the carbide part is solid-dissolved into the matrix structure, which increases the matrix structure hardness by 60%. Compared with the annealed state before welding, after electron beam welding, the tensile strength of the welded joint is increased by 20%, and the hardness of the welded heat-affected zone is increased by 35%, but the plastic deformation ability of the joint is reduced, and the fracture occurs in the heat-affected zone.