Effect of Precipitation Behavior and Deformation Twinning Evolution on the Mechanical Properties of 16Cr–25.5Ni–4.2Mo Superaustenitic Stainless Steel Weld Metals

In the study, three 16Cr–25.5Ni–4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%, 0.075 wt%, and 0.045 wt%, were prepared to investigate the microstructural evolution and its effect on mechanical behavior. At a C content of 0.082 wt%, the microstructure of weld metal consisted of austenite, M₆C, and M₂₃C₆, where M₆C was the main carbide. The number and average size of the M₆C carbides significantly decreased as the C content decreased. At a C content of 0.045 wt%, only a very small number of M₆C carbides were observed in the weld metal. For the tensile process, the number of deformation twins increased as the C content decreased, which introduced a stronger dynamic Hall–Petch effect, resulting in only a small decrease in the ultimate tensile strength of the weld metal. Meanwhile, the increase in deformation twins significantly enhanced the elongation of the weld metals. For the impact process, the impact energy increased from 204 to 241 J as the C content decreased. The crack initiation resistance was improved due to the reduction in M₆C carbide, which inhibited cracking at the interface of M₆C/matrix. Additionally, the crack propagation resistance was enhanced due to the increase in deformation twins, which consumed more impact energy.