Abstract
Austenitic stainless steel of medical grade was subjected to low-temperature thermochemical heat treatment process which forms a distinctive layer on the surface of the material. The distinctive layer is commonly known as `S phase', and resulted due to diffusion of elemental species present in the heat treatment atmosphere. A crosssectional microstructural investigation confirms that the layer thickness increases with the increase of methane (CH4) contents in the carrier gas and the microstructure contain abundance of structural defects like slip bands, stacking faults, twins, and dislocations. Subjected to micro-pillar compression, the ultimate compressive strength of this layer was up to 190% more than that of bulk material which comes in expense of limited strain accommodation of such layer. Consequently, the critically resolved shear stress of the S phase layers were higher than that of the bulk material and microstructural defects contribute up to 83.17 MPa on that. On course of the micro-pillar compression, the S phase layers show catastrophic cleavage type brittle fracture in contract of progressive ductile fracture of the bulk material.