Inter-metallic observations using a backscattering technique on 25Cr super duplex stainless steel alloy

摘要

The in-service performance of duplex stainless steels can be severely affected by the formation of harmful inter-metallic phases which precipitate in the material over a range of elevated temperatures experienced during welding and heat-treatment operations. In this work the precipitation of inter-metallic phases in 25Cr-07Ni-0.28N super duplex was characterized by both backscattered scanning electron microscopy (BSE) and secondary electron images using more traditional scanning electron microscopy (SEM). The chemical composition of the secondary phases and the ferrite-austenite grain boundaries were analyzed using X-ray diffraction. The chemical analysis showed the enrichment of inter-metallic phases by chrome, nickel and molybdenum where depletion for such elements on the grain boundaries was found. The investigation showed that the super-duplex alloy was highly susceptible to the precipitation of sigma (ó) and chi (÷) phase after 30 minutes heat treatment at 1000°C followed by water quench.