High temperature processed high Nb X80 steel with excellent heat-affected zone toughness

Abstract

In this letter, the investigation focused on the coarse-grained heat-affected zone (CGHAZ) of a high temperature processed (HTP) high Nb (0.11wt%) X80 steel. The microstructural examination showed that the microstructure of CGHAZ consisted of granular bainite, baintic ferrite and secondary phases such as martensitic–austenitic (M–A) constituent. The comparatively fine austenite grain size was due to both Ti–Nb precipitates and solute Nb. The Charpy V-notch (CVN) testing revealed that the HTP steel exhibited excellent toughness in CGHAZ, which was indicated by the low ductile–brittle transition temperature (DBTT). The improved toughness was ascribed to the combined contribution from the relatively fine prior austenite grain size, fine sub-microstructures and dispersed fine M–A constituent.