Effect of aging temperature on phase decomposition and mechanical properties in cast duplex stainless steels

The microstructure and mechanical properties in unaged and thermally aged (at 280°C, 320°C, 360°C, and 400°C to 4300h) CF–3 and CF–8 cast duplex stainless steels (CDSS) are investigated. The unaged CF–8 steel has Cr-rich M23C6 carbides located at the δ–ferrite/γ–austenite heterophase interfaces that were not observed in the CF–3 steel and this corresponds to a difference in mechanical properties. Both unaged steels exhibit incipient spinodal decomposition into Fe-rich α–domains and Cr-rich α’–domains. During aging, spinodal decomposition progresses and the mean wavelength (MW) and mean amplitude (MA) of the compositional fluctuations increase as a function of aging temperature. Additionally, G–phase precipitates form between the spinodal decomposition domains in CF–3 at 360°C and 400°C and in CF–8 at 400°C. The microstructural evolution is correlated to changes in mechanical properties.