Influence of carbon content on the microstructure formation of duplex stainless steels Fe-25Cr-5Ni

Abstract

This study evaluated the as-cast microstructure of three alloys based on Fe-25%Cr-5%Ni weight (wt.) composition whose carbon content is 0.02 wt.%, 0.12 wt.%, and 0.37 wt.%, respectively. Thermocalc was applied to predict the possible phases that could be formed during the cooling of each alloy and then the cross-sections of the ingots were characterized. The first alloy, with 0.02 wt.%C, presented a microstructure composed of ferrite and austenite, which was formed through solid-state precipitation. The second alloy, with 0.12 wt.%C, showed a microstructure formed by ferrite, austenite from the peritectic reaction (L + δ → γ) and M₂₃C₆ (M=Fe, Cr) carbide. Finally, the third alloy, with 0.37 wt.%C, exhibited a microstructure formed by dendrites of ferrite and austenite, also formed according to the peritectic reaction (L + δ → γ), with an M₂₃C₆ (M = Fe, Cr) and M₇C₃ (M = Fe, Cr) carbide network in the interdendritic regions.

Keywords:
duplex stainless steels; high carbon; thermocalc; microstructure