Phase Decomposition of Stainless Steel Weldment by Thermal Aging

Abstract

A SUS308 stainless steel weldment of which main phases are ferrite and austenite was aged at 450°C for a time period up to 11000 h in order to investigate the compositional evolution of the ferrite by Mossbauer spectroscopy. Changes in the internal magnetic field of Fe with aging time suggest that the ferrite decomposes by spinodal process finally to produce the Fe-rich α and the Cr-rich α' phase. According to the mean internal magnetic field measurement, the Cr content of the former is about 9 at% Cr which is consistent with a calculated phase diagram. The Cr content of the α' phase is evaluated to be about 83 at% Cr by the isomer shift measurement, which shows a slight deviation from the calculated phase diagram. The phase decomposition is accompanied by an increase in the hardness of ferrite, while that of austenite is remained unchanged.