High temperature dynamics strain hardening behavior in stainless steels and nickel alloys

Primary water stress corrosion cracking (PWSCC) is a major materials challenge for dissimilar metal welds (DMW) in pressurized water reactors. The reliability of structure integrity assessment of DMW is strongly dependent on the reliable determination of the weld residual stress (WRS) field, which is one of the primary driving forces for PWSCC. Recent studies have shown that WRS prediction using today's DMW WRS models strongly depends upon the choice of strain-hardening constitutive model. The commonly used strain hardening models (isotropic, kinematic, and mixed) are all time-independent ones that are inadequate to accounting for the time-dependent (viscous) plastic deformation at the elevated temperatures during welding. Recently, a dynamics strain hardening constitutive model has been proposed and the application of such a model has resulted in improved WRS prediction when compared to the WRS measurement results by contour method and deep-hole drilling method. In this study, the dynamic strain hardening behavior, under uniaxial tensile loading conditions, of several stainless steels and nickel alloys (SS304, Alloy 600, Alloy 82 and Alloy 52) commonly used in pressure vessel nozzle DMW are experimentally determined and compared. The extent of softening due to different duration of high-temperature exposure is studied and its influence on final residual stresses is discussed. An empirical correlation combining both the time and temperature effects on dynamic strain hardening is proposed for weld residual stress modeling.