Improving the erosion–corrosion resistance of AISI 316 austenitic stainless steel by low-temperature plasma surface alloying with N and C

Abstract

The erosion–corrosion behaviour of low-temperature plasma surface alloyed AISI 316 austenitic stainless steel has been compared with untreated material using a newly developed slurry pot erosion–corrosion apparatus containing a slurry comprising 20 wt.% silica sand and 3.5%NaCl at 40 °C. The total erosion–corrosion wastage, the mechanical erosion under cathodic protection and the electrochemical corrosion were measured directly. Based on the data obtained the synergistic effect of erosion and corrosion was calculated. Post-test examination was conducted to identify material degradation mechanisms involved. It has been shown that the erosion–corrosion resistance of AISI 316 austenitic stainless steel can be effectively improved by low-temperature plasma alloying with carbon (carburising) and nitrogen (nitriding) by 50% and 70%, respectively. The degradation process of the untreated steel is dominated by erosion whilst that of the low-temperature plasma carburised material is by an erosion–corrosion mechanism and that of low-temperature plasma nitrided AISI 316 mainly by corrosion–erosion. The synergy between erosion and corrosion can be ranked from low to high in the order: untreated (1.7%), plasma carburised (30.0%) and plasma nitrided (69.4%) material.