Analysis of laser-nitrided stainless steel via nuclear methods

Laser nitriding of iron and other metals is governed by the complicated int erplay of the laser-plasma-liquid surface interactions which lead to a supe rposition of several mechanisms. This article reports on the influence of t he nitrogen gas pressure on the nitriding process for stainless steel. The effects of the nitrogen gas pressure on the nitrogen depth profiles and the phase formation are revealed by resonant nuclear reaction analysis, Mossba uer spectroscopy, and X-ray diffraction. We found that the surface nitrogen concentration reaches 10 at. % with a mean value of about 7.5 at. % in the first 150 nm. There seems to be a pressure window between 0.1 and 0.7 MPa for the most efficient treatment. In the surface layer, an additional gamma -Fe(N) phase can be distinguished from the original gamma-phase of the stai nless steel.