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가스 질화침탄처리한 탄소강의 화합물층 성장 및 부식특성에 미치는 CO2함량의 영향
김영희 ( Y. H. Kim ),김석동 ( S. D. Kim ),윤희재 ( H. J. Yoon ) 한국열처리공학회 2002 熱處理工學會誌 Vol.15 No.5
N/A This study has been performed to investigate the effect of CO_2 content on the growth characteristics of the compound layer, porous layer and corrosion characteristics of carbon steels after gaseous nitrocarburizing in 70%NH_3-CO_2-N_2 at 580℃ for 2.5 hrs. The results obtained from the experiment were the thickness of the compound and porous layers increased with increasing CO_2 contents. At the same fixed gas composition the thickness of the compound and porous layer increased with increasing carbon content of the specimens. X-ray diffraction analysis showed that compound layer was mainly consisted of ε-Fe_2-3(N,C) and γ`-Fe_4N as the increased with CO_2 contents in atmosphere, compound layer was chiefly consisted of ε-Fe_2-3(N,C) phase. With increasing CO_2 content and total flow rate in gaseous nitrocarburizing, the amount of ε-Fe_2-3(N,C) phase in the compound layer was increased. The current density of passivity decreased with increasing CO_2 content due to the development of porous layer at the out most surface of ε-Fe_2-3(N,C).
김영희 ( Y. H. Kim ),윤희재 ( H. J. Yoon ) 한국열처리공학회 2003 熱處理工學會誌 Vol.16 No.2
N/A We investigate the phase formation in the compound layer of cast irons during the gaseous nitrocarburising of four different cast irons, that contain different types of graphites in the shape and size. We examine the change in the surface roughness with the nitrocarburising time. The observation of cross-sectional microstructure and X-ray diffraction analysis indicate that the compound layer consists of single ε-Fe_2-3(N,C) phase and that its thickness increase in a parabolic manner with the treatment time. The surface roughness parameters, Rz and Ra increase with increasing treatment time. In other words, the roughness parameters increase as the thickness of compound layer increases. The parameters also depend on the shape and size of graphite in the individual cast irons.
가스 질화침탄처리된 강에서 화합물층의 현미경조직에 미치는 냉각속도의 영향
김영희,윤희재 동아대학교 생산기술연구소 2002 生産技術硏究所硏究論文集 Vol.7 No.2
This study has been performed to investigate the effect of cooling rate from nitrocarburising temperature on the microstructure of compound layer after gaseous nitrocarburising in 60%NH_3―5%CO_2―35%N_2 at 580℃ for 3hrs. Gaseous nitrocarburising of SM20C and SM45C steels produced a dual phase e-Fe_2-3(N,C) + ¡¢-Fe_4N in compound layer. On alloy steels such as SCM420 and SCM440, the e-Fe_2-3(N,C) Phase was essentially formed within compound layer. The result obtained from the experiment shows that the thickness of the compound layer increased with a decrease of cooling rate. It has been demonstrated in plain carbon and alloy steels that the e-Fe_2-3(N,C) Phase Produced within the compound layer by the gaseous nitrocarburising process was partially transformed into ¡¢ -Fe_4N phase during the slow cooling. The transformation is facilitated by decreasing nitrogen and carbon concentration in the steel. The amount of ¡¢ -Fe_4N phase produced from the slow cooling decreased from surface to substrate in the steel. Reduction of amount of carbon in the steel facilitated the e-Fe_2-3(N,C) → ¡¢ -Fe_4N transformation. Fast cooling favours the retention of the e-Fe_2-3(N,C) Phase at room temperature.