Examination on dry sliding wear behavior of AISI 304 stainless steel treated with salt bath nitriding process

Abstract

The wear behaviour of AISI 304 stainless steel was investigated at consistent load under salt bath nitriding. In this salt bath nitriding process, the work pieces are drenched into the liquid shower, the nitride salts contained in it diffuses into the surface of the steel and forms Fe3N compounds. Then the specimens were immersed in salt bath furnace for nitriding at 570 °C for different timing parameters like salt-bath nitride1 (SN1) 60 min, salt-bath nitride2 (SN2) 120 min and salt-bath nitride3 (SN3) 180 min so that the nitrogen diffuses into the steel surface and then it is air cooled. After heat treatment wear test was done to find out the wear loss in the material. The pin of 40 mm length and 12 mm diameter was held on rotating disc of 150 mm diameter. The wear test for all specimens was conducted under the normal loads of 20 N and 30 N respectively. Metallographic tests like optical microscopic results, SEM is done to specimens for comparing physical characteristics before and after heat treatments. To compare the mechanical characteristics of the heat treated specimens before and after heat treatments they are subjected to pin on disc experiment and Vickers hardness test to determine wear resistance and hardness of the material. From SEM analysis, it was observed that a white layer is formed called “S-Phase” an expanded austenite layer formed on the salt bath specimen nitrided for (120 min, 180 min). It was concluded that nitride distribution increases with increase in nitriding time. The hardness of salt bath nitride3 (180 min) was found to be 835 HV.