In-situ SEM study of short fatigue crack propagation behavior in a dissimilar metal welded joint of nuclear power plant

• Published in: Materials & design Vol. 88; pp. 598 - 609
• Main Authors: Shang, Yi-Bo, Shi, Hui-Ji, Wang, Zhao-Xi, Zhang, Guo-Dong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 25.12.2015
• Subjects: Austenitic stainless steels; Crack propagation; Dendritic structure; Dissimilar metal welded joint; Fatigue cracks; Fatigue failure; Heat affected zone; Heat resistant steels; High strength steels; In-situ SEM; Nickel chromium molybdenum steels; Propagation; Scanning electron microscopy; Short fatigue crack propagation; Welded joints; Dissimilar metal welded joint; Short fatigue crack propagation; In-situ SEM
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2015.08.090

In-situ Scanning Electron Microscopy (SEM) fatigue experiments were carried out to study short fatigue crack propagation (FCP) behavior of various regions (weld zone, interface region and heat affected zone (HAZ)) in a domestic dissimilar metal welded joint of nuclear power plant. The local microstructural effect on short fatigue crack initiation and propagation behavior was investigated with its influence on both material fatigue and structure fatigue analyzed. Considering material fatigue, in the weld region, crack grows along δ ferrites when propagating parallel to the dendrite, and deflects or branches along δ ferrite, γ austenite dendrite, δ/γ interface and grain boundaries when propagating perpendicular to the dendrite; in safe ends, the crack grows along slip lines and coalesces with secondary cracks; in A508 HAZ, the crack propagates or branches along martensite transgranularly. In terms of structural fatigue, the crack tends to deflect when propagating across the weld/A508 interface or weld/316L interface with the influence of local microstructure, and the weld/A508 interface region has a resistance to FCP due to its high strength. The fatigue crack propagation rate of each region was compared and analyzed. The fatigue fractography was also characterized under SEM to analyze the crack propagation process. [Display omitted] •Microstructural effect on FCP of DMWJ was investigated with in-situ SEM experiment.•Crack grows along δ ferrites when parallel to dendrite in weld.•Crack branches along δ, γ, δ/γ interface when vertical to dendrite in weld.•Weld/316L interface may have resistance to FCP.•Weld/A508 interface has resistance to FCP due to high strength and martensite.