Formation of Nano M₂X Particles by a Tempering in High Cr Ferritic/Martensitic Steel

Abstract

The precipitation of nano Cr2N particles in high Cr FM steels has been studied. The nitrogen content of the FM steels was changed to form stable Cr2N particles. Tempering temperature was also changed from 500 oC to 800 oC to study the precipitation behavior of the Cr2N particles with the tempering temperature. The Cr2N particles remained as a stable phase at a higher tempering temperature by increasing the nitrogen content. The shape of these particle was a fine needle type which was very similar to V(C,N) particles. The size of some Cr2N particles was increased as the nitrogen content increased. But these precipitates were not dissolved or largely coarsened during a creep deformation at 600°C. So it seems that they may act as an effective obstacle against a dislocation glide during a creep deformation, thus contribute to an increase of the creep rupture strength in high Cr FM steels.