Metallurgical investigations on creep rupture mechanisms of dissimilar welded joints between Gr.91 and 304SS

異材溶接継手の界面破断メカニズムにおける冶金学的検討

山下 拓哉  ; 永江 勇二 ; 菊地 浩一*; 山本 賢二*

Yamashita, Takuya; Nagae, Yuji; Kikuchi, Koichi*; Yamamoto, Kenji*

A dissimilar welded joint was adopted to achieve higher thermal efficiency and economy levels in nuclear and thermal power plants. 2 types of dissimilar welded joints which were different heat input during welding to the ferrite steels were manufactured. The dissimilar welded joints were made of following materials; the modified 9Cr-1Mo steel (Gr. 91) for the ferritic steels, the 304 stainless steel for the austenitic steels and the Inconel 600 for the filler metals, Welding methods for the modified 9Cr-1Mo steel were used Plasma Arc Welding and Gas Tungsten Arc Welding (GTAW), respectively. Creep tests were conducted. Specimens by GTAW failed in base metal part and interface between the modified 9Cr-1Mo steel and Inconel 600. Interface failure mechanisms were analyzed from a perspective of metallurgy which were precipitation and growth of type I carbide and formation of oxide layer.