Evaluation for Creep Properties of 316FR Weld Metal with Miniature Weld Metal and Full-Thickness Welded Joint Specimens
Hiromichi HONGO, Masayoshi YAMAZAKI, Takashi WATANABE, Masaaki TABUCHI, Tatsuhiko TANABE and Yoshio MONMA
Abstract:In order to examine the distribution of creep properties in a 316FR weld metal, a narrow gap welded joint was prepared from 50mm thick 316FR steel plates by gas tungsten arc welding (GTAW) process using type 316 filler wire, and constant-load creep rupture tests were conducted at 823K in air using full thickness large welded joint specimens and pure weld metal miniature specimens. The latter specimens were taken parallel to the weld line of 316FR weld metal in the welded joint. Specimen sampling locations were the plate surface, the 1/4 and the 1/2 plate thickness positions from the surface. By interrupting the creep test for the full thickness welded joint specimen, we observed the change in creep strain distribution in the weld metal in the thickness direction of the plate. The last layer of weld metal showed considerably larger creep strain than the central layers of the weld metal. Further, the creep strength of weld center is larger than that of the top of the weld. The cause of this difference in the creep strength in the weld metal is that due to large thermal expansion coefficient and small thermal conductivity of austenitic stainless steel strain introduced through thermal histories was larger in the central part than in the vicinity of the surface of the welded joint. Hardness variation in the weld metal and the results of transmission electron microscopic examination revealing dislocation configuration support this speculation. From the results above, it is concluded that the creep properties of weld metal in multi-pass, multi-layer welded joints strongly depend on the location of specimen sampling. Key Words:Creep properties, Weld metal, Welded joint, 316FR, Stainless steel