• Journal of Korea Foundry Society
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• v.25 no.6
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• pp.233-239
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• 2005

Contact material is widely used in the field of electrical parts. Ag-CdO has a good wear resistance and stable contact resistance. We studied a lifetime of Ag-CdO material because of getting better properties of Ag-CdO using Post-oxidation. The experimental procedure were melting using high frequency induction, heat treatment, rolling and internal oxidation. And we experimented on difference process, Post-oxidaion. Then we tested a lifetime and analysed. We obtained the optimizing oxidation temperature was $750^{\circ}C$. Using Pre-oxidation, coarse oxide and depleted oxidation layer existed but finer oxides were existed and depleted oxidation layer was not using Post-oxidation. In Post-oxidation, The density was 10 $g/cm^{3}$, the hardness was Hv 80 and the adhesive strength was 9000N. The specimen of Post-oxidation had better lifetime properties than that of Pre-oxidation. We predicted that the lifetime of Post-oxidation specimen is more longer twice than that of Pre-oxidation one.

• Journal of the Korean Society for Heat Treatment
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• v.14 no.2
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• pp.81-88
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• 2001

The effects of post-oxidation and sulfnitriding treatments on the phase transformation in the nitrided case of tool steels have been studied. Dense and compact $Fe_3O_4$ layer was formed at the outer surface of nitride compound layer by post-oxidation treatment and multi layer of iron sulfide(FeS) was formed in the compound layer by sulfnitriding treatment. The surface hardness decreased because of formation of the soft oxide or sulfide at the nitride surface. Diffusion layer of nitride case was not affected by post-oxidation treatment or sulfnitriding treatment of nitrided alloy tool steels.

• Journal of Korea Foundry Society
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• v.25 no.6
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• pp.226-232
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• 2005

Contact material is widely used in the field of electrical parts. Ag-CdO material has a good wear resistance and stable contact resistance. In order to establish optimizing heat treatment condition, rolling temperature and oxidation process, we studied the microstructure of Ag-CdO material with various conditions. The experimental procedure were melting using high frequency induction, heat treatment, rolling and internal oxidation. And we experimented on difference process, Post-oxidaion. In this study, we obtained the optimizing heat treatment condition was $700^{\circ}C$ for 15 min. and the optimizing rolling temperature was $730^{\circ}C$. In investigation of the microstructure of oxidized material, coarse oxide and depleted oxidation layer existed. The hardness was average Hv 70. When we used Post-oxidation, oxides were finer than prior process and depleted oxidation layer did not exist. The hardness of Post-oxidation material was average Hv 80. And the optimizing rolling temperature was $800^{\circ}C$.

• Korean Journal of Materials Research
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• v.16 no.11
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• pp.681-686
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• 2006

Plasma nitrocarburising and plasma post oxidation were performed to improve the wear and corrosion resistance of S45C and SCM440 steel by a plasma ion nitriding system. Plasma nitrocarburizing was conducted for 3h at $570^{\circ}C$ in the nitrogen, hydrogen and methane atmosphere to produce the ${\varepsilon}-Fe_{2-3}$(N, C) phase. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of $500^{\circ}C$ for 1 hour. The very thin magnetite ($Fe_3O_4$) layer $1-2{\mu}m$ in thickness on top of the $15{\sim}25{\mu}m$ ${\varepsilon}-Fe_{2-3}$(N, C) compound layer was obtained by plasma post oxidation. A salt spray test and electrochemical testing revealed that in the tested 5% NaCl solution, the corrosion characteristics of the nitrocarburized compound layer could be further improved by the application of the superficial magnetite layer. Throttle valve shafts were treated under optimum plasma processing conditions. Accelerated life time test results, using throttle body assembled with shaft treated by plasma nitrocarburising and post oxidation, showed that plasma nitrocarburizing and plasma post oxidation processes could be a viable technology in the very near future which can replace $Cr^{6+}$ plating.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.2
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• pp.90-95
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• 2006

Nitriding or carburizing of carbon steels results in good mechanical properties such as high surface hardness and wear resistance but it has no affection on the corrosion resistance. Corrosion properties of nitriding and carburizing steels could be deteriorated. So, recently, there have been great demand for oxi-nitriding to enhance both mechanical properties and corrosion resistance. In this study, the corrosion resistance of carbon steel, S35C, and free cutting steel, SUM222, are prepared by vacuum nitriding and vacuum post-oxidation were compared with those treated by nitriding. After vacuum post-oxidation, $5{\mu}m$ oxide layer was formed on the nitride layer with $20{\sim}30{\mu}m$ depth. Potentio-dynamic polarization curve in corrosion test showed that the corrosion potential after post oxidation was increased from 200 mV to 800 mV in S35C and from 600 mV to 1200 mV in SUM222. SEM analyses showed that pores was increased and surface roughness became rougher with post oxidation. However, the formation of $Fe_3O_4$ resulted in the enhanced corrosion resistance of steels.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.5
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• pp.298-306
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• 2009

Gas nitriding and post oxidation were performed on stainless steels and SACM 645 steel. With increasing gas nitriding time, the increasing rate of nitrided layer was most rapid on SACM 645 steel and the nitriding depth of nitrided layer was most narrow on STS 304 steel among three steels. Corrosion resistance was increased with post oxidation on stainless steels and with increasing time the effect of corrosion resistance was decreased to compare with relatively short gas nitriding time. An improvement effect of corrosion resistance was consisted of predominantly on austenitic stainless steel by post oxidation after gas nitriding among three steels and it was relatively less influenced on martensitic stainless steel.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.243-246
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• 1999

We studied the MOSFET characteristics and the hot-carrier reliability with the sidewall spacer composition and the post gate oxidation thickness in 0.20${\mu}{\textrm}{m}$ gate length transistor. The MOSFET with NO(Nitride＋Oxide) sidewall spacer exhibits the large degradation of hot-carrier lifetime because there is no buffering oxide against nitride stress. When the post gate oxidation is skipped, the hot-carrier lifetime is improved, but GIDL (Gate Induced Drain Leakage) current is also increased.

• Journal of Korean Society of Water and Wastewater
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• v.31 no.4
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• pp.273-279
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• 2017

Optimal processes to remove chromaticity at E water treatment plant(WTP) mainly caused by algae of E lake in Jeju island were investigated based on lab-tests of chlorine and ozone oxidation. 42.9% of chromaticity of filtered water was removed by chlorine oxidation under pH 7.0~8.0, dose of 1.0 mg/L with contact time of 30~60 min. On the other hand, chromaticity removal was 71.4% when post-ozone dose of 0.9~1.9 mg/L and pH 9.0, while it was increased to 86.7% under post-ozone dose of 3.1~7.3 mg/L and pH 9.0. However, there was no significant chromaticity removal efficiency increase when ozone doses were higher than 5.0 mg/L regardless of feeding point(i.e., pre-ozonation and post-ozonation) and pHs(i.e., 7.0 and 9.0.) under the experimental conditions. Based on the results, chlorine oxidation using existing chlorination facilities at the WTP is recommended for lower chromaticity while ozone oxidation is recommended for higher chromaticity by installing new ozone feeding facilities.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.5
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• pp.207-214
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• 2024

This study examines the effects of post-oxidation treatment on the microstructure and corrosion resistance of GC250 cast iron. The nitriding process was conducted at 570℃ for 180 minutes with a fixed nitriding potential (Kn) of 1.5, followed by post-oxidation at 450℃, 500℃, and 550℃ for 120 minutes. The post-oxidized specimens showed increased surface hardness and case depth compared to the nitrided specimens, with a maximum surface hardness of approximately 890 HV0.1. The oxidation process increased the thickness of the nitrided layer by more than 3 ㎛, with the oxide layer thickness reaching up to 2.5㎛ as the oxidation temperature increased. XRD analysis identified the presence of ε-phase, γ'-phase, and Fe₃O⁴ phase on the surface. Polarization tests revealed that the specimen treated at the highest oxidation temperature had a corrosion current density of 20.26 ㎂/cm² and a corrosion potential of -0.22V, indicating enhanced corrosion resistance compared to the nitrided specimen. This improvement is attributed to the formation and increased thickness of the oxide layer, which enhances corrosion resistance. In conclusion, the oxide layer formed through post-oxidation treatment significantly improves the corrosion resistance of GC250 cast iron, with the effect becoming more pronounced at higher oxidation temperatures.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.1
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• pp.9-20
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• 1999

The effect of post oxidation, water-quenched after holding in air for 5~420 seconds or cooling or furnace cooling, on corrosion resistance and phase formation characteristics of the surface layer of SM20C and SM45C carbon steels after gas nirtrocarbursing in the $NH_3-5%CO_2-N_2$ gas atmosphere at $580^{\circ}C$ for 3hours is studied. The compound layers of two steels consist of ${\varepsilon}-Fe_{2-3}N$, ${\gamma}^{\prime}-Fe_4N$ and $Fe_3O_4$, phases, however, the quantity of ${\gamma}^{\prime}-Fe_4N$ phase increases for the furnace cooled specimen compared to that of air cooling specimen. With increasing $NH_3$ content in the gas mixture and also increasing the keeping time in the air after gas nitrocarburising, the ${\varepsilon}-Fe_{2-3}N$ phase of compound layer increases, while the decreased current density recognizing the improvement of corrosion resistance are shown. the passive current density of SM45C steel is lower than that of SM20C steel at the same nitrocarburising conditions.