Predictions of ICHAZ cyclic thermo-mechanical response in GTAW process for 9Cr steels

This work is concerned with the development of a modeling framework to predict the effects of tempered–untempered martensite heterogeneity on the thermomechanical performance of welded material. A physically based viscoplasticity model for the intercritical heat-affected zone (ICHAZ) for 9Cr steels (e.g., P91, P92) is presented in this work, with the ICHAZ represented as a mixture of tempered and untempered martensite. The constitutive model includes dislocation-based Taylor hardening and damage for different material phases. A sequentially coupled thermal–mechanical welding simulation is conducted to predict the volume fraction compositions for the various weld-affected material zones in a cross-weld (CW) specimen. The out-of-phase cyclic thermomechanical (25 °C to 600 °C) performance of notched and plain samples is comparatively assessed for a range of different tempered–untempered martensitic material heterogeneities. It is shown that the heterogeneity in a simulated CW material is highly detrimental to thermal cyclic performance.