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Effect of aging on microstructure, mechanical properties and fracture behavior of high temperature welded joint of 9cr-1.5mo-1co-vnbn martensitic steel

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Document pages: 14 pages

Abstract: In this paper, the effects of long-term aging on impact toughness, creep fracture behavior and hardness of 9cr-1.5mo-1co-vnbn (CB2) steel weldment, as well as its relationship with microstructure and fracture characteristics, were studied. The weldment was studied under post weld heat treatment and after isothermal exposure at 625 ° C for 10000 and 30000 hours. The evolution of microstructure was studied by analytical scanning and transmission electron microscopy. Charpy V-notch impact toughness test shall be conducted for all heat treatment states. The notch positions are located in different welding areas, such as weld metal (WM), heat affected zone (HAZ) and base metal (BM). Due to severe welding induced microstructure degradation, the overheated HAZ region showed the lowest impact toughness. The creep test was carried out at a temperature of 625 ° Cress range between 80 and 120 MPa. At the highest applied stress, creep fracture occurred in WM, whereas at lower stresses the failure position shifted towards fusion zone at WM HAZ interface. The hardness profiles experienced significant scattering due to weld microstructural heterogeneity. The major fracture mechanisms involved transgranular quasi cleavage and intergranular creep cracking in impact and creep loading conditions, respectively.

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