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FC-25계 회주철의 Boro-Nitriding 복합 표면처리에 따른 표면특성과 고온산화거동에 관한 연구
허인창,손근수,윤재홍,조동율,박봉규,김현수,김인수 대한금속재료학회 2005 대한금속·재료학회지 Vol.43 No.2
Surface properties and oxidation behavior were studied for FC-25 gray cast iron (GCI), ion nitrided CCI (N CCI), powder boronized CCI (B GCI) and powder boronized N CCI (B-N GCI). A boride (Fe2B and FeB) layer with a tooth shape was formed by boronizing GCI at 650℃. The thickness and hardness of the layer were proportional to boronizing temperature and time. The hardness was decreased as the depth of the boronized layer increased. The activation energy for boride formation was about 74 kJ/mol. The thickness of the graphite layer formed by boronizing was increased by increasing temperature and time. A silicon layer insoluble to borides accumulated beneath the boride layer. The major phases were Fe4N, Fe3N and FeN in the nitride layer formed by ion nitriding. The thickness and hardness of the layer increased with increasing nitriding temperature and time under the Fe4N decomposition temperature of 680℃. The hardness was maximum at the surface and decreased with increasing nitrided depth on B-N GCI at 700℃, above the Fe4N decomposition temperature. Hardness of B-N GCI at the layer depth of 10 μm was 1000 Hv, which was lower than that of the B GCI at the same condition. Also the layer thickness was 50 gm; 10 μm deeper than that of B GCI. The reason was that the nitrogen gas given off by the decomposition made the layer porous and facilitated the diffusion of oxygen and other reactants. The samples were oxidated at 800℃ for 48hrs under atmospheric air. Oxidation rate was in decreasing order of N GCI, GCI, B GCI and B-N GCI. Oxidation rates were greatly influenced by the diffusion of nitrogen gas formed by Fe4N decomposition over the decomposition temperature of 680℃ and the oxidation barrier of the less corrosive boride layer. (Received October 29, 2004)
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FC-25계 회주철의 이온질화처리에 따른 표면특성과 고온산화거동에 관한 연구
허인창,손근수,윤재홍,조동율,박봉규,김현수,김인수 대한금속재료학회 2005 대한금속·재료학회지 Vol.43 No.4
Surface properties and high temperature oxidation behavior were investigated for FC-25 Gray Cast Iron(GCI) and the ion nitrided GCI(N-GCI). The GCI was pre-cleaned to improve hardness to the optimum pre-sputtering parameters with an Ar/H₂ ratio of 1/2, working pressure of 3 torr, working temperature of 550℃ and working time of 1hour. The optimum nitriding conditions for the maximum hardness of 560575 Hv were an N₂/H₂ ratio of 3/1, working pressure of 3 torr, and working temperature of 575℃. The thickness of graphite in the GCI was increased by increasing the working temperature from 525℃ to 595℃ for the nitriding time of 6-18hrs. XRD patterns showed FeO and Fe₂O₃ peaks for both the oxidized N-GCI and GCI at temperatures of 600℃ and 800℃ under atmospheric environment for both 24 and 60hours. At 800℃, above the Fe4N decomposition temperature of 680℃, the oxidation rate of N-GCI was greater than that of the GCI. The most abundant nitride, Fe4N, was decomposed and the nitrogen gas given off by the decomposition made the protective film porous by degassing through the film. But at 600℃, below the decomposition temperature, the degree of oxidation of N-GCI was lower than that of the GCI because the nitride film worked as protective barrier for oxidation. (Received October 29, 2004)
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Boro-Nitriding 처리한 FC-25계 편상흑연주철의 표면특성에 관한 연구
허인창,손근수,윤재홍,조동율,박봉규,김현수,김인수 국립7개대학공동논문집간행위원회 2004 공업기술연구 Vol.4 No.-
Surface properties and oxidation behaviors were studied for FC-25 gray cast iron (GCI), plasma nitrided FC-25 GCI (P-N GCI), powder boronized FC-25 GCI (B GCI) and powder boronized N GCI (B-N GCI). A boride (Fe2B, FeB) layer with a tooth shape was formed by boronizing GCI at temperatures of about 650℃. The thickness and hardness of the layers were proportional to the boronizing temperature and time. The hardness was decreased by increasing boronizing depth. The activation energy for boride formation was 73.8kJ/mol. The thickness of the graphite layer formed by boronizing was increased by the temperature and time. A silicon layer insoluble in borides was accumulated under the boride layer. The major phases were Fe4N, Fe3N and FeN in a nitride layer formed by plasma. The thickness and hardness of the layer were increased with nitriding temperatures and time under the Fe4N decomposition temperature of 680℃. The hardness was maximum at the surface and decreased with nitrided depth on B-N GCI at 700℃, above the decomposition temperature of the Fe4N. Hardness of B-N GCI at the layer depth of 10 ㎛ was ≒1000Hv, which was lower than ≒1500Hv of the B GCI at the same condition. Also the layer thickness was 50 ㎛; deeper than that of B GCI by 10 ㎛ The reasons were that the nitrogen given off by the decomposition made the layer porous and facilitated the diffusion of oxygen and other reactants. The samples were oxidated at 800℃ for 48hrs under atmospheric air. Oxidation rate was in decreasing order of N GCI, GCI, B GCI and G-N GCI. Oxidation rates were greatly influenced by the diffusion of nitrogen formed by Fe4N decomposition over the decomposition temperature of 680℃ and by the oxidation barrier of the less corrosive boride layer.
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허인창,손근수,윤재홍,조동율,박봉규,김현수,김인수 국립7개대학공동논문집간행위원회 2004 공업기술연구 Vol.4 No.-
Surface properties and high temperature oxidation behaviors were investigated for FC-25 Gray Cast Iron(GCI) and the plasma nitrided FC-25 GCI(N GCI). The optimum nitriding conditions for the maximum hardness of 560∼575Hv were N2 /H2 ratio of 3/1, working pressure of 3 torr, and working temperature of 575℃ for 6~18hrs. The thickness of graphite in the GCI was increased by increasing the working temperature from 525℃ to 595℃ for the nitriding time of up to 18hrs. The thickness of nitride was increased with increasing working time. The relationship was d=kt^(1/2), the Arrhenius plot for InK vs 1/T showed that the activation energy for the nitride formation was 107.6kJ/mol for the temperature range of 798oK to 868oK (525℃ to 595℃). XRD showed FeO, Fe₂O₃peaks for both the oxidized N GCI and GCI at temperatures of 600℃ and 800℃ at atmospheric environment for both 24hrs and 60hrs. At 800℃, above the Fe4N decomposition temperature of 680℃, the oxidation rate of N GCI was greater than that of GCI. The most abundant nitride of Fe₄N was decomposed and nitrogen gas given off by the decomposition, resulted in the protective film porous by degassing through the film. But at 600℃, below the decomposition temperature, the degree of oxidation of N GCI was lower than that of GCI because the nitride film worked as protective barrier for oxidation.
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