Heating modification of an austenitic steel with high nitrogen content

The micro-structural changes of an austenitic steel with high-nitrogen content have been investigated after heat treatments at 850 ◦C. Micro-chemical composition of heat-induced structures was analyzed using XPS, multipoint AES and photoemission spectro-microscopy. Before the XPS, AES and photoemission spectro-microscopy analyses, the samples were cleaned in situ by Ar ion sputtering. The results show that the discontinuous precipitation of Cr2 N from the nitrogen supersaturated γs phase is accompanied by a net flux of nitrogen toward the transformed zones, thus confirming that the principal force behind boundary migration is the nitrogen concentration gradient between the γ and γs phases. When γ and γs reach the same nitrogen concentration, the precipitation stops even if the transformation of thematrix has not yet been completed.