オーステナイト系ステンレス溶接金属の微視組織と低温時効硬化挙動に及ぼす溶接条件ならびに化学組成の影響

抄録

Low temperature thermal age-hardening behavior of type 309 and type 316 stainless steel weld metals have been investigated. The effects of chemical composition and welding conditions on these metals have been also discussed based on nano-indentation testing and transmission electron microscope (TEM) observation using the samples aged up to 12000h at 275, 310, 335 and 475°C. Type 309 weld showed the primary ferrite solidification mode (FA mode) morphology, where the majority of δ-ferrite morphology was vermicular-δ. Type 316 weld showed mainly vermicular-δ and some globular-δ which corresponds to primary austenite solidification mode (AF mode). After aging up to 12000h at 275°C, ferrite hardness of the two types of weld metals did not change. For aging up to 8000h at 335°C, hardness of vermicular-δ of the both weld metals were increased with aging time. Hardness of globular-δ(AF mode) increased and reached maximum hardness at aging time for 2000h ,then decreased after aging for 4000h at 335°C. These results suggest that the solidification mode can affect the age-hardening behavior of weld metals. The correlation between age-hardening behavior and nanostructure in δ-phase will be discussed.