2017 年 35 巻 1 号 p. 36-44
The aim of this study was to elucidate the grain refinement mechanism in weld metal of type 310S stainless steel by hot-wire GTA welding. Quenched microstructure of weld pool during welding was obtained by liquid-tin and water quenching method. Microstructure evolution of wire during heating was investigated using hot-wire heating device.
The quenched microstructure showed that since the fine grain formed in conjunction with filler wire, the fine grain seemed to be formed depending on the fine grain formation of filler wire. According to the microstructure evolution of wire during heating, recrystallization, grain growth and local melting occurred in the heated wire in accordance with the temperature distribution of the wire. And the fine grain in the weld metal formed by inserting semi-molten state filler wire during feeding. The fine grain formed depending on the local melting phenomena at sub-boundary in the grain of filler wire by hot-wire condition. It was considered that the sub-boundary in the grain at which solute elements should enrich was formed during grain boundary migration in grain growth process, because the filler wire was rapidly heated with a heating rate of more than 1400°C/s. Therefore, the grain refinement phenomenon in weld metal of type 310S stainless steel seemed to be a phenomenon unique to the hot-wire GTA welding.