Structure and composition of expanded austenite produced by nitrogen plasma immersion ion implantation of stainless steels X6CrNiTi1810 and X2CrNiMoN2253

The structure and phase composition of the modified surface of two differen t stainless steels (austenitic steel X6CrNiTi1810 and austenitic-ferritic s teel X2CrNiMoN2253) after 3 h plasma immersion ion implantation of nitrogen at 400 degrees C were compared using XRD, SEM, TEM and Mossbauer spectrosc opy. Both steels show a surface layer with very similar composition. The ma jor phase found is expanded austenite. Very fine precipitates in the near s urface region are most likely decomposition products (ferrite/martensite an d CrN) of the metastable expanded austenite. The stability of the expanded austenite in the austenitic-ferritic steel is lower and the amount of decom position products is higher under the same treatment conditions. (C) 1999 E lsevier Science S.A. All rights reserved.