Phase transformations of the duplex stainless steel UNS S31803 under non-isothermal conditions

Abstract

Precipitation of the intermetallic phases embrittles duplex stainless steels. Currently, most studies in this subject simulated aging phenomena by first holding the material at different isothermal conditions and then, quenching down under high cooling rates to investigate the subsequent microstructures and mechanical properties. In this work, specimens of the duplex stainless steel UNS S31803 were submitted to cooling cycles at controlled rates under non-isothermal conditions. The volume fraction of sigma and chi formed was less than 1%. The value was lower than that assumed by the Sieurin and Sandstrom model. We relate this to the initial DSS morphology, with austenite islands in a ferritic matrix. Here, the number of nucleation sites for the deleterious phases is smaller than the lamellar microstructure of ferrite and austenite usually found in duplex stainless steels.