Crystallography of ferrite-austenite phase transformation induced by nitrogen absorption in Fe-25Cr alloy

The phase transformation from ferrite to austenite induced by solution nitriding was discussed in 25mass%Cr ferritic stainless steel on the basis of crystallographic analysis by EBSP method. In the early stage of solution nitriding, austenite grains containing approximately 1mass% nitrogen nucleated at the material surface, and then they gradually grew into the material with solution nitriding. EBSP measurement for the solution-nitrided specimens revealed that some austenite grains have the crystallographic orientations close to Kurdjumov-Sachs (K-S) relationship with the parent ferrite grain; however, there were a lot of austenite grains with no specific orientation relationship. This suggests that the crystallographic orientation of the product phase is not fixed only by that of the parent phase when it nucleates at specimen surface.