A role of initial microstructure in characteristics of the surface layers produced by ion-plasma treatment in CrNiMo austenitic stainless steel

A study on elemental composition, phase composition, microstructure, nanohardness and fracture micromechanisms of the surface layers obtained by ion-plasma treatment of a stable CrNiMo austenitic stainless steel with different initial microstructures has been carried out. In cold-rolled specimens, containing a high dislocation density and deformation-induced low- and high-angle boundaries and possessing structural elements of 330 nm in size, interstitial concentration (carbon and nitrogen) is much higher than that for cold-rolled and annealed specimens with a similar size of structural elements. After ion-plasma treatment, a surface nanohardness of the pre-deformed specimens is higher by 8 GPa than one for specimens annealed after cold rolling. Deformation-assisted microstructure accumulates carbon more likely than nitrogen under ion-plasma treatment. These results provide experimental support for decisive role of high dislocation density and deformation-assisted well-developed microstructure in accumulation and bulk diffusion of interstitials under ion-plasma treatment of steel.