Creep Deformation Behavior of Weld Metal and Heat Affected Zone on 316FR Steel Thick Plate Welded Joint
Hongo Hiromichi; Yamazaki Masayoshi; Watanabe Takashi; Kinugawa Junichi; Tanabe Tatsuhiko; Monma Yoshio; Nakazawa Takanori
Abstract:Using hot rolled 316FR stainless plate (50mm thick) and 16Cr 8Ni 2Mo filler wire, a narrow gap welded joint was prepared by GTAW (gas tungsten arc welding) process. In addition to conventional round bar specimens of base metals and weld metal, full thickness joint specimens were prepared for creep test. Creep tests were conducted at 550 deg. in order to examine creep deformation and rupture behavior in the weld metal of the welded joint. Creep strain distribution on the surface of the joint specimen was measured by moire interferometry. In the welded joint, creep strength of the weld metal zone apart from the surface was larger than that in the vicinity of the surface due to repeating heat cycles during welding. Creep strain and creep rate within the HAZ adjacent to the weld metal zone were smaller than those within the base metal zone. Creep rate of the weld zone in the welded joint was smaller than that of the weld metal specimen due to the restraint of the hardened HAZ adjacent to the zone. The full thickness welded joint specimens showed longer lives than weld metal specimens, though the lives of the latter was shorter than those of the base metal (undermatching). In the full thickness welded joint specimen, crack started from the last pass layer of the weld metal zone and fracture occurred at the zone. From the results mentioned above, in order to evaluate the creep properties of the welded joint correctly, it is necessary to conduct the creep test using the full thickness welded joint specimen which includes the weakest zones of the weld metal, the front and back sides of the plate. Key Words:316FR stainless steel, 16Cr-8Ni-2Mo weld metal, welding joint, creep strain distribution, creep rupture behavior, fracture location