Mechanical Investigation on Interface Failure Mechanisms of Dissimilar Welded Joints

Abstract

2 types of dissimilar welded joints (DWJ), Mod.9Cr-1Mo steel / Alloy 600 / SUS304, which were differential heat input during welding to the ferrite steels were manufactured in this study. Welding methods for Mod.9Cr-Mo steel were used Plasma Arc Welding (PAW) and GTAW, respectively. Constitutions of the heat affected zone (HAZ) formed in Mod.9Cr-1Mo steel were different in PAW and GTAW. The coarse grain HAZ (CGHAZ) was formed in Mod.9Cr-1Mo steel adjacent to Alloy 600 in the dissimilar welded joint by PAW (PAW_DWJ). In contrast, the fine grain HAZ (FGHAZ) was formed in Mod.9Cr-1Mo steel adjacent to Alloy 600 in the dissimilar welded joint by GTAW (GTAW_DWJ). Specimens were sampled from Mod.9Cr-1Mo steel / Alloy 600 part. Creep tests were conducted at 550°C. In creep tests, a GTAW_DWJ failed at the interface, the PAW_DWJs failed at Mod.9Cr-1Mo steel part i.e. not at the interface. Therefore, the Speckle Image Correlation Analysis (SPICA) and the Finite Element Method (FEM) in specimens were carried out to analyze the deformation behavior of the HAZ to focus on mechanical factors of the interface failure mechanisms. SPICA revealed that the concentration of strain in the PAW_DWJ was issued the width of CGHAZ away from interface. The analysis combined with FEM results suggests that slow creep strain rate of CGHAZ formed adjacent to Alloy 600, the difference in creep strain rate between Mod.9Cr-1Mo steel and Alloy 600 was able to be mitigated. As a result, a noticeable shear stress causing interface failure wasn’t issued in the PAW_DWJ.