ABSTRACT
The nitriding rate of a high chromium, high manganese austenitic steel has been found to exhibit abnormal behaviour similar to that of austenitic stainless steels, i.e. a sudden decrease of the rate at about 870 K; marked acceleration between 670 and 870 K; a discontinuity at about 670 K; and formation of a nitrogen supersaturated nitrided layer below 670 K. These results require a new explanation, since previous theories address the abnormalities in austenitic stainless steels only. Accelerated nitriding is discussed with reference to the free energy of formation of chromium nitrides (Cr2N and CrN) on a T − ΔG° diagram. The sudden decrease of the rate is attributed to the termination of accelerated nitriding.
