９Ｃｒフェライト系耐熱鋼用溶接金属の高温強度特性に及ぼすＷの影響

Abstract

GTA weld metals containing 0.58 mass%W, 1.01 mass%W, 1.47 mass%W and 1.68 mass%W have been prepared, and effects of W on the microstructure, precipitation behaviors, tensile strength and creep rupture strength of the weld metals were studied.X-ray diffraction analyses on extracted residues of the weld metals after PWHT at 1013 K for 2 h revealed the formation of M23C6 and MX type carbo-nitrides. Laves phase precipitated in the weld metals during creep rupture test or aging at 873 K. The addition of W enhanced the precipitation of Laves phase. The chemical analyses of extracted residues showed that the amount of dissolved W in matrix of weld metals after PWHT increased with W content in weld metals. The addition of W improved the tensile strength of weld metals at 293 K and 873 K. The results of chemical analysis suggested that this improvement in the tensile strength was attributable to the solid-solution hardening by W. The creep rupture strength of weld metals at 873 K and 973 K also improved by adding W to weld metals. However, there was little difference between the rupture life of 1.47 mass%W weld metal and that of 1.68 mass%W weld metal longer than roughly 5000 h - 10000 h at 873 K. These results suggest that there is an optimum W content that is most effective in to improving the creep rupture strength. Results of the chemical analyses of residues of aged weld metals suggested that the precipitation of Laves phase was enhanced by the stress or strain during the creep rupture test.