Effect of Re-normalizing and Re-tempering on Inter-critical Heat Affected Zone(S) of P91B Steel

Abstract

The novel perspective of this paper was to restore the grain boundary (GB) hardening effect in inter-critical heat affected zone (ICHAZ) of boron modified P91 steel (P91B). To achieve this, samples of the base metal (BM) of P91B steel were thermally simulated by Gleeble followed by post-weld heat treatment (PWHT) and were further re-normalized and re-tempered. With such heat treatment, four different ICHAZ(s) were reproduced. These ICHAZ(s) were subjected to impression creep testing. As impression creep testing brings local deformation, the suitable characterization technique was electron back scatter diffraction (EBSD) for in-depth investigations of microstructural deformation. High creep deformation was observed for simulated ICHAZ followed by PWHT-ICHAZ due to GB softening. Whereas, the least deformation was observed for re-normalized and re-tempered ICHAZ(s) restoring GB hardening. In this respect, type IV cracking was avoided by re-normalizing and re-tempering in P91B steel. This phenomenon was further correlated with the impression creep curves of each ICHAZ with BM.