316L 오스테나이트계 스테인리스강의 저온 플라즈마질화처리시 공정변수가 표면경화층 특성에 미치는 영향

Abstract

A systematic investigation was made on the influence of processing parameters such as gas composition and treatment temperature on the surface characteristics of hardened layers of low temperature plasma nitrided 316L Austenitic Stainless Steel. Various nitriding processes were conducted by changing temperature (370°C to 430°C) and changing N2 percentage (10 % to 25 %) for 15 hours in the glow discharge environment of a gas mixture of N2 and H2 in a plasma nitriding system. In this process a constant pressure of 4 Torr was maintained. Increasing nitriding temperature from 370°C to 430°C, increases the thickness of S phase layer and the surface hardness, and also makes an improvement in corrosion resistance, irrespective of nitrogen percent. Moreover increasing nitrogen percent from 10 to 25% at 430°C, increases the surface hardness and the thickness of S phase layer but decreases their corrosion resistance. Therefore, optimized condition was selected as nitriding temperature of 430°C with 10% nitrogen, as at this condition, the treated sample showed better corrosion resistance. Moreover to further increase the thickness of S phase layer and surface hardness without compromising the corrosion behavior, further research was conducted by fixing the N2 content at 10 % with introducing various amount of CH4 content from 0 % to 5 % in the nitriding atmosphere. The best treatment condition was determined as 10% N2 and 5 % CH4 content at 430°C , where the thickness of S phase layer of about 17 ㎛ and a surface hardness of 980 HV0.1 were obtained (before treatment 250 HV0.1 hardness). This specimen also showed better corrosion resistance than specimens treated at different process conditions and the untreated one due to much higher pitting potential.