Investigating the impact of weld dilution and local mismatch on the low-cycle fatigue failure of Alloy 182 dissimilar weld transition under intermediate isothermal condition

Abstract

Dissimilar welded joints are the critical region that determines the operation lifetime of pressure vessels under severe cyclic deformation. The failure susceptibility of dissimilar welded joints is attributed to local strength mismatch and heterogeneous microstructures. This study evaluated the isothermal low-cycle fatigue performance of a dissimilar welded joint between nickel-based Alloy 182 and 1.25Cr-0.5Mo steel at 250 °C. During low-cycle fatigue tests, the Alloy 182 weld metal exhibited significant cyclic hardening over the 1.25Cr-0.5Mo steel base metal. The local strain variations in the weld transition were measured using the digital image correlation (DIC) technique to reveal the impact of material strength and hardening mismatch upon the cyclic behavior within the weld transition. Microhardness measurements of as-welded and cyclically deformed weld transition regions were performed to assess the hardening due to cyclic deformation. The WT failures occurred in the weld metal region adjacent to the fusion boundary. In addition, microstructural characterization shows that the crack initiation occurred within the weld dilution region, and the short crack growth was affected by microstructural heterogeneity in the weld metal.