Kinetics of gas nitriding process on austenitic stainless steels under dry sliding conditions
摘要
The need is to provide improved performance from stainless steel surface employed under dry sliding environments through thermo chemical surface modification methods. Gas nitriding is employed in austenitic grades like AISI 253SS, AISI 304SS, and AISI 904 L as they are possessed with low wear resistance and poor hardness. Gas nitriding has the potential of overcoming these shortcomings by injecting nitrogen in the surface layer to form an extended austenite structure and enhance tribological qualities. This research is involved with gas-nitriding of all three materials at a fixed temperature of 570 °C, 100 ml/min gas flow rate over a period of 18 h to determine the kinetics of the nitrogen diffusion process and the subsequent variations in the surface characteristics. The experimental data showed that the case depth of 15.0 μm, 19.5 μm, 18.8 μm for AISI 253SS, AISI 304SS, and AISI 904 L, respectively, after 18 h. The hardness of the surface increased significantly and was identified to be 415 HV after gas nitriding from 217 Hv in AISI 253SS, 369 HV after gas nitriding from 129 Hv in AISI 304SS, 381 HV after gas nitriding from 168 Hv in AISI 904 L, which was an indication for a stronger nitrogen-based layer. During the wear test, an average wear volume loss of 4.47 mm³ were obtained for untreated material, 1.25 mm³ for 253SS, 1.70 mm³ for 304SS, 1.30 mm³ for 904 L SS respectively. The results indicate that gas nitriding was a promising technique for increasing the hardness, case depth, wear resistance for stainless steels and surface durability under dry sliding conditions.