질화처리가 316L 스테인리스강의 미세조직과 경도에 미치는 영향

Abstract

316L stainless steel is a type of austenitic stainless steels which has great corrosion resistance and manufacturability. By significantly reducing the amount of C in a stainless steel, the intergranular corrosion has decreased; and by adding more than 2% of Mo to the stainless steel, it has obtained better oxidation resistance. However, 316L stainless steel has low strength and hardness value. In order to improve these values in austenitic structure at room temperature, salt bath nitriding was conducted. Due to the relatively low temperature of the heat treatment in salt bath nitriding, not only the grain growth did not occur. Also it ensured excellent corrosion resistance. Salt bath nitrided sample has four layers: an oxidized layer, a nitrided layer, an interface between the nitrided layer and a base metal, and the base metal in order from the surface. The thickness of the nitrided layer changes depending on the time and temperature treated during nitriding process, and the thickness makes differences in the distribution of hardness. Ultimately, the distribution of during the nitriding process. Nitrogen gets soluted in the iron depending on the concentration of the penetrated nitrogen. Nitrided steel is known to form face-centered cubic(Fe4N), Hexagonal cubic(Fe3N), or Orthorhomic(Fe2N). Depending on the structure that substance forms, the distribution of hardness changes. Nitride is a precipitation which contains high concentration of Mn. Si3N4, which was not know till now, has formed through salt bath nitriding. Therefore, in this study, in order to have both corrosion resistance and wear resistance at the surface of 316L autenitic stainless steel, we stuied micrographs, hardness distribution, phase transition and alloy element concentration distribution of nitride.