Role of the V-Notch Location in the Impact Toughness of 9 Pct Cr-CrMoV Dissimilar Welded Joints
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DISSIMILAR welded joints have been gradually used in novel steam turbines with their higher thermal efficiency.[1–5] It is reported that dissimilar welded joints are necessary for various components/systems operating in different service conditions; thus appropriate materials with different mechanical properties are required for these types of joints.[6] Compared with other welding techniques, such as the gas tungsten arc welding (GTAW) or the tungsten inert gas (TIG) welding technique, the narrow gap submerged arc welding (NG-SAW) method is widely applied in dissimilar welded joints due to its high welding efficiency and lower cost.[7] It has been proven that welded joints manufactured by the NG-SAW method could satisfy the requirements of the mechanical properties such as creep and fatigue performance.[8,9] However, the mechanical properties of dissimilar welded joints, e.g., the hardness, tensile strength, and fracture toughness,[10–14] are significantly affected by their heterogeneous structure.[15–18]
KAI DING, BINGGE ZHAO, XIAOHONG LI, YUANHENG ZHANG, TAO WEI, GUANZHI WU, and YULAI GAO are with the Center for Advanced Solidification Technology (CAST), School of Materials Science and Engineering, Shanghai University, Shanghai 200444, P.R. China. Contact e-mail: [email protected] XIN HUO and MANJIE FAN are with the Shanghai Electric Power Generation Equipment Co., Ltd, Shanghai Turbine Plant, Shanghai 200240, P.R. China. Manuscript submitted July 26, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Wang et al.[19] found that the microstructure of base metal of CrMoV steel (CrMoV-BM), WM and 9 pct Cr-BM was granular bainite, tempered martensite and lath martensite, respectively. Shao et al.[20] found that the microstructure of the coarse grain zone (CGZ) was tempered martensite, while granular bainite was the main structure for the BM of NiCrMoV steel. Thus, it is necessary to understand the microstructure evolution of dissimilar welded joints during welding.[21,22] In particular, carbon-enriched and carbon-depleted zones were observed in 9 pct Cr-CrMoV dissimilar welded joints due to the Cr discrepancy between the WM and 9 pct Cr-BM.[23] Kulkarni et al.[24] deemed that carbon migration from low Cr to high Cr steels was one of the major issues in the welding of dissimilar Cr-Mo steels. Alexandrov et al.[9] argued that carbon migration was expected during the post weld heat treatment. Undoubtedly, such a composition discrepancy could deteriorate the mechanical properties of a joint.[25] For example, Laha et al.[26] found that the failure of P22/P91 dissimilar welded joints occurred in the carbon-depleted zone. In the case of 9 pct Cr-CrMoV dissimilar welded joints, Wu et al.[27] concluded that the carbon-depleted zone was responsible for their high-cycle fatigue (HCF) properties. Guo et al.[28] investigated the relationship between the microstructure and the fracture toughness of 9 pct Cr-CrMoV dissimilar welded joints and found that the fine tempered martensite in the heat-affected zone of CrMoV steel (CrMoV-HAZ) poss
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