페라이트 기지 구상흑연주철의 플라즈마 질화에 미치는 공정변수의 영향

Effect of Process Parameters on the Plasma Nitriding of Ferritic Ductile Cast Iron

The effect of time, temperature and gas composition on the case thickness, hardness and nitride formation in the surface of ductile cast iron(GCD400) have been studied by micro-pulse plasma technique. Typically, external compound layer and internal diffusion layer which is much thicker than compound layer was observed in the nitride case of ductile cast iron. The relative amount and kind of phases formed in the nitrided case changed with the change of nitriding conditions. Generally, only nitride phases such as γ´(Fe4N), or ε(Fe2-3N) phases were detected in compound layer by XRD analysis. The thickness of compound layer increased with the increase of nitrogen content in the gas composition. The optimum nitriding temperature was 520℃ at which temperature high have nitrided case was obtained. The nitrided case thickened parabolically with nitriding time( t ) and thus, the case depth( d ) fits well with the typical parabolic equation ; d = k t . The material constant k for GCD400 nitrided at 520℃ was 0.04919×103㎛․hr-1/2.