The Dependence of ☌-Phase Formation in Fe-Cr-Mn Alloys on Cold Work, Aging, and Alloy Composition

Abstract

High manganese and high chromium steels are attractive as low activation materials for fusion reactors. The microstructural stability of Cr-Mn steels during long term service at around 873 K, however, is not yet fully understood. This study is aimed toward the study of changes in microstructure and mechanical properties of Fe-(12 to 16%)Cr-(10 to 30%)Mn alloys during aging in the temperature range from 773 K to 973 K for up to 3.6 Ms(1000 hrs). As a solution treated at 1373 K for 3.6 ks, a microstructure of α′ + ε + γ is observed in the 15%Mn alloy, ε + γ in 20 to 25%Mn alloys and γ in the 30%Mn alloy, σphase formation is not observed in Fe-12%Cr-Mn alloys except at 30%Mn after aging at 873 K for 3.6 Ms. However, straining by rolling (50%in reduction at room temperature) prior to aging accelerates cr-phase formation. All of the strained Fe-12%Cr-Mn alloys form σphase during aging. In the case of 16%Cr alloys, σphase formation occurs more easily. There are three kinds of mechanisms for σphase formation depending on the manganese content, and increase in manganese content accelerates σ-phase formation. These results suggest that the effect of manganese on σ-phase formation is different from the result shown in the Fe-Cr-Mn alloy diagram published by Schafmeister and Ergang.