G phase and ferrite in a high Si austenitic stainless steel during 510 C aging

Except the excellent oxidation and corrosion resistance at elevated temperatures, the high temperature microstructure stability of high Si austenitic stainless steels is also of attention. In this work, the microstructure and the corresponding mechanical properties evolutions of a high Si austenitic stainless steel during long-term aging at 510 degrees C were investigated. The results showed that Si has promoted the formation of a multi-phase, composed by G phase and ferrite. It is revealed that G phase precipitates at grain boundaries prior to ferrite and it is because G phase formation has changed the composition in the surrounding austenite that ferrite was induced. Such ferrite is proved to be responsible for the dramatically decreased impact toughness during aging, since the impact toughness could be rejuvenated by only reducing the ferrite content through high temperature annealing.