Mechanical properties of low-temperature gaseous carburizated layer in 316L stainless steel based on nano-indentation and four-point bending tests

Low-temperature gaseous carburization (LTGC) is an effective method to generate a surface carburized layer with gradient carbon content in austenitic stainless steels. In the present paper, optical microscopy (OM), X-ray diffractometry (XRD), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM) were employed to characterize the surface carburized layer in 316L stainless steel. The gradient mechanical properties of surface carburized layer were investigated by four-point bending and nano-indentation tests. The results show that the mechanical properties of the carburized layer, such as initial yield strength (σ_y), strain hardening exponent (n) and elastic modulus (E), increase with the increase of solid solution carbon atoms and plastic deformation. Because of huge carbon content and plastic deformation, the surface of carburized layer become very brittle and the fracture strain is only about 1.4%. In the paper, we also show that four-point bending test and nano-indentation test are both useful methods to evaluate the mechanical property distribution in a gradient surface layer such as carburized layer.