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 degrees 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 Cr(2) N from the nitrogen supersaturated gamma(s) 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 gamma and gamma(s) phases. When gamma and gamma(s) reach the same nitrogen concentration, the precipitation stops even if the transformation of the matrix has not yet been completed.