Formation of delta-ferrite and its effect on impact toughness of GTAW weld metals in a 12 wt-% Cr steel

Abstract

This research focused on the formation of the δ-phase and the corresponding effect on the impact toughness in a GTAW weld metal of a 12%Cr F/M steel. Two kinds of δ-phase were identified: one located at the prior austenitic grain boundaries (PAGBs) (called δ_PAGB) and the other was in the inter-dendritic region (called δ_inter). The δ_inter implied that the peritectic transition that occurred at the final stage of solidification in the DSC test, was suppressed in the welding process. A preheating treatment at 95°C decreased optimally the δ-phase fraction and thereby decrease the ductile-brittle transition temperature (DBTT). However, excessive preheating at higher temperatures enhanced the fraction of the δ_inter by promoting the micro-segregation and thus increased the DBTT.