Characterization of the surface modification of a Metastable Stainless Steel induced by Ground Polishing

Abstract

Metastable austenitic stainless steels are distinguished by their susceptibility to the Transformation Induced Plasticity (TRIP) effect, where austenite (γ) to martensite (α’- and/or ε) transformation is triggered mechanically. They present an optimal relationship between mechanical and physical properties. Surface modification of TRIP steels, and particulaly an AISI 301LN metastable austenitic stainless steel specimens, was performed in order to study the possibility of enhancing their tribological and mechanical properties, by means of a parametric ground polishing analysis, used as a Surface Mechanical Modification Technique. To the best knowledge of the author, this technique has not been studied yet for this application, according to the performed literature review. Microstructural and mechanical properties are studied with the help of advanced characterisation techniques, e.g. Field-Emission Scanning Electron Microscopy (FESEM), Focus Ion Beam (FIB), etc. Experimental results demonstrate that an increase in grinding abrasion induces phase transformation and nano-structuring of the materials’ subsurface, by generation of compressive residual stresses, which contribute to an increase in the overall hardness of the material, which has been noticeable up to the micro-range. In addition, a qualitative analysis of the tribological images obtained leads to demonstrating an evolution in the surface deformation mechanisms, from shear bands to mechanisms related to the grain boundary rotation, as the grinding treatment intensifies. The path opened by this investigation could allow future studies to focus on a more exhaustive analysis of the benefits produced by this surface modification technique, by studying wear rates, the evolution of the friction coefficient and also the fatigue properties.