Effects of temperature cycling and nitrogen on the stability of microstructures in austenitic stainless steels

The influence of temperature cycling from room temperature to 77 K on nitrogen-alloyed austenitic stainless steels, Fe24Mn13Cr0.4N, Fe24Mn18Cr3Ni0.6N, Fe1Mn19Cr8Ni0.2N and Fe17Mn14Cr1Ni0.4N, has been studied by optical microscopy and scanning electronic microscopy (SEM). Results show that the phase transformation from austenite to ε martensite takes place due to the temperature cycling and stress concentration, whereas nitrogen can stabilize the austenitic microstructures greatly. Finally, the mechanism of the phase transformation and the structure of ε martensite are discussed in detail.