The Corrosion and Wear Behaviour of low-temperature carburised AISI 316L Austenitic Stainless Steel

The effect of a low temperature carburizing (LTC) treatment on both the corrosion and dry sliding tribological behaviour of AISI 316L is here reported and discussed. The treatment significantly enhances the surface hardness of the steel, due to the formation of the carbon-supersaturated S-phase, without carbide precipitation. Consequently, the wear behaviour (evaluated in dry sliding conditions against different countermaterials) improves, due to the increased resistance of the treated surface to plastic deformation, as well as to the decreased tendency towards adhesion of the mating surfaces. The corrosion behaviour was tested through electrochemical measurements (Ecorr, Rp and polarisation curves) performed in different aggressive environments: 0.5 M H2SO4, chloride-containing electrolytes (35 g/L NaCl and 2.5vol.% HCl), 3vol.% CH3COOH solution and neutral solution of 2.5vol.% Oxonia (oxidising solution used for sanitization in the food industry). The results show that corrosion resistance is significantly improved in both chloride environments, where the formation of a C-rich surface layer ennobles the treated steel. However, at very high anodic potentials, the surface layer is locally penetrated, generating pitting corrosion. Conversely, in acetic acid and in the strongly oxidizing Oxonia solutions the treated steel showed comparable (in acetic acid) or worse (in Oxonia) behaviour than the untreated AISI 316L. In sulphuric acid the treated steel didn’t passivate, but it corroded at a limiting current density much lower that the critical current density for AISI 316L passivation. Therefore, the LTC treatment led to an improvement in the wear behavior (particularly when carried out on the countermaterial), combined with an increased corrosion resistance in chloride environments and with a comparable or partially worsened corrosion behaviour in other environments.