Effect of Grain Refinement on the Elemental Composition and Nanohardness of the Surface Layers in AISI 316L Austenitic Steel Subjected to Ion-Plasma Hardening

Abstract

We study the effect of the grain refinement on the elemental composition and nanohardness of the surface layers in AISI 316L austenitic steel processed by ion-plasma hardening. Ion-plasma hardening of the samples with (1) grain-subgrain (with high dislocation density) and (2) coarse-grained structures causes a surface hardening and formation of the composite layers with a thickness of about 20 μm. The nanohardness and depth profiles of elemental concentration of nitrogen, carbon and oxygen in the ion-plasma hardened layers depends on pretreatment regime of the steel specimens. Cold rolling causes an increase in the grain and subgrain boundaries fraction and dislocation density in steel specimens, provides more intensive accumulation of interstitial atoms in thin surface 5 μm-layer, leads to additional surface hardening and suppress carbon diffusion into depth of the specimens as compared with coarse-grained structure.