Annealing behaviour of nitrogen-ion-implanted 304 stainless steel

We studied the modification of 304 stainless steel following nitrogen ion implantation. We used grazing incidence X-ray diffraction. Nitride formation is enhanced in specimens containing a significant amount of martensite formed by surface finishing. We report for the first time an increase in surface hardness at depths larger than the implantation depth following annealing of such implanted specimens. This effect correlates with the release of nitrogen from nitrides. The nitrogen appears to diffuse inwards and strengthen the martensite phase