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Page : 295 - 307
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- 초고강도급 자동차용 강재 내 ε-carbide (Fe2.4C)가 부식 및 수소확산거동에 미치는 영향
- Effects of ε-carbide (Fe2.4C) on corrosion and hydrogen diffusion behaviors of ultra-strong steel sheets for automotive application were investigated using a number of experimental and analytical methods. Results of this study showed that the type of iron carbide precipitated during tempering treatments conducted at below A1 temperatures had a significant influence on corrosion kinetics. Compared to a steel sample with cementite (Fe3C), a steel sample with ε-carbide (Fe2.4C) showed higher corrosion resistance during a long-term exposure to a neutral aqueous solution. In addition, the diffusion kinetics of hydrogen atoms formed by electrochemical corrosion reactions in the steel matrix with ε-carbide were slower than the steel matrix with cementite because of a comparatively higher binding energy of hydrogen with ε-carbide. These results suggest that designing steels with fine ε-carbide distributed uniformly throughout the matrix can be an effective technical strategy to ensure high resistance to hydrogen embrittlement induced by aqueous corrosion.
- KEYWORDs : Ultra high-strength steel, Tempering, Corrosion, Hydrogen diffusion, Iron carbide
- AUTHORs : 박진성 · 윤덕빈 · 성환구 · 김성진†
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Page : 308 - 314
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- 중성자 조사에 따른 Ni도금피복재에서의 He발생량평가
- Neutron dose level at bottom head of a reactor pressure vessel (RPV) was calculated using reactor vessel neutron transport for a Korean nuclear power plant A. At 34 EFPY with a 40-year (2042) design life after plating repair, irradiation fast neutron effect was 6.6x1015 n/cm2. As helium(He) gas can be generated by Ni only at 1/106 level of 5 × 1021 n/cm2, He generation possibility in the Ni plating layer is very little during 40 years of operation (2042, 34 EFPY). Thermal neutrons can significantly affect the generation of He from Ni metal. At 10 years after a repair, He can be generated at a level of about 0.06 appm, a level that can add general welding repair without any consideration. After 40 years of repair, 9.8 appm of He may be generated. Although this is a rather high value, it is within the range of 0.1 to 10 appm when welding repair can be applied. Clad repair by Ni electroplating technology is expected to greatly improve the operation efficiency by improving the safety and shortening the maintenance period of the nuclear power plant.
- KEYWORDs : Nuclear power plant, Corrosion of RPV steel, Ni plating, Neutron effect, He generation
- AUTHORs : 황성식† · 권준현 · 김동진 · 김성우
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Page : 315 - 323
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- 주조 방식 및 압연에 따른 연축전지용 납 합금 기판의 부식 특성
- In this study, we examined corrosion behaviors of two types of Pb alloys for a lead acid battery comparatively. One containing 6.6 wt% Sn, 36 mg/kg Bi, and 612.4 mg/kg Ca was prepared by twin-roll continuous casting. The other containing 5.2 wt% Sn, 30.5 mg/kg Ag, and 557 mg/kg Ca was made by twinbelt continuous casting. Potentiodynamic polarization tests were performed to evaluate corrosion resistance. Cyclic voltammetry was done to examine oxidation and reduction reactions occurring on the surface of each alloy in 4.8 M H2SO4 solution. Electrochemical test results implied that the Pb alloy prepared with the twin-belt casting method was less stable than that cast with the twin-roll method. Such results might be due to precipitations formed during the casting process. Rolling did not appear to affect the corrosion behavior of the twin-roll samples with Ag < 10 mg/kg, while it reduced the anodic reaction of Ag on the surface of the twin-belt sample with 30.5 mg/kg Ag.
- KEYWORDs : Lead acid battery, Pb alloy, Corrosion, Rolling
- AUTHORs : 오꽃님 · 이규혁 · 장희진†
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Page : 325 - 334
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- Effect of Solution Temperature on the Cavitation Corrosion Properties of Carbon Steel and its Electrochemical Effect
- In the open system (vessel and pipe), the maximum corrosion rate of carbon steel at ca. 80 oC was obtained due to the decrease of dissolved oxygen by increasing the solution temperature. Effect of temperature on the cavitation damage can be explained through several mechanisms. Moreover, when cavitation occurs on the surface of metal and alloys, whether cavitation is erosion or corrosion is still controversial. This work focused on the effect of solution temperature on the corrosion of carbon steel under cavitation in an open system, Tests were performed using an electrochemical cavitation corrosion tester in 3.5% NaCl solution and the effect of solution temperature of carbon steel was discussed. Cavitation corrosion rate can be increased by cavitation, but when the temperature increases, a dissolved oxygen content reduces at a very
high speed and thus the maximum cavitation corrosion temperature changed from 80 oC to 45 oC. Below the maximum cavitation temperature, the electrochemical effect was more dominant than the mechanical effect by increasing temperature, but over the maximum cavitation temperature, the mechanical effect was more dominant than the electrochemical effect by increasing temperature. - KEYWORDs : Carbon steel, Cavitation Corrosion, Electrochemical Cavitation, Solution Temperature
- AUTHORs : J. M. Jeon, Y. R. Yoo and Y. S. Kim†
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Page : 335 - 346
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- Effect of Solution Temperature on the Cavitation Degradation Properties of Epoxy Coatings for Seawater Piping
- Since epoxy resin coating shows excellent properties in formability, adhesion, and corrosion resistance, they have been extensively used in many industries. However, various types of damages in the epoxy coated tube within a relative short time have been reported due to cavitation erosion, liquid impingement, variation of temperature and pressure. Nevertheless, there has been little research on the effect of temperature on the cavitation degradation of epoxy coatings. Therefore, this work used an ultrasonic cavitation tester to focus on the effect of solution temperature on the cavitation properties of 3 kinds of epoxy coatings in 3.5% NaCl. The cavitation properties were discussed basis on the material properties and environmental
aspects. As the solution temperature increased, even though with large fluctuation, the cavitation
degradation rates of A and B coatings were reduced rapidly, but the rate of C coating was decreased gradually. In addition to the cushioning effect, the reason that the cavitation degradation rate reduced with solution temperature was partly related to the brittle fracture and water absorptivity of the epoxy coatings, and the water density, but was little related to the shape and composition of the compound in the coatings or the phase transition of the epoxy coating. - KEYWORDs : Corrosion, Carbon Steel, Epoxy Coating, Cavitation, Temperature
- AUTHORs : J. M. Jeon, Y. R. Yoo, M. J. Jeong, Y. C. Kim, and Y. S. Kim†
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Page : 347 - 360
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- 고분자 전해질 연료전지 금속 분리판용 금속의 염화물 농도에 따른 전기화학적 특성 연구
- Currently, the demand for eco-friendly energy sources is high, which has prompted research on polymer electrolyte membrane fuel cells. Both aluminum alloys and nickel alloys, which are commonly considered as materials of bipolar plates in fuel cells, oxide layers formed on the metal surface have excellent corrosion resistance. In this research, the electrochemical characteristics of 6061-T6 aluminum alloy and Inconel 600 were investigated with chloride concentrations
in an acid environment that simulated the cathode condition of the PEMFC. After potentiodynamic polarization experiments, Tafel analysis and surface analysis were performed. Inconel 600 presented remarkably good corrosion resistance under all test conditions. The corrosion current density of 6061-T6 aluminum alloy was significantly higher than that of Inconel 600 under all test conditions. Also, 6061-T6 aluminum alloy and Inconel 600 presented uniform corrosion and intergranular corrosion, respectively. The Ni, Cr, and Fe, which are the main chemical
compositions of Inconel 600, are higher than Al in the electromotive force series. And a double oxide film of NiOCr 2O3, which is more stable than Al2O3, is formed. Thus, the corrosion resistance of Inconel 600 is better. - KEYWORDs : PEMFC, Metallic bipolar plate, Metals, NaCl concentration, Electrochemical characteristics
- AUTHORs : 신동호· 김성종†
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Page : 361 - 366
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- 염수 환경에서 Inconel 718의 국부 부식 거동
- Localized corrosion behavior of Ni-based Inconel 718 alloy was investigated by electrochemical anodic polarization techniques in NACE TM 0177 A solution of 5 wt% NaCl + 0.5 wt% acetic acid at room temperature. After the solution heat treated at 1080 oC for 2.5 h, Inconel 718 was age-hardened at 780 oC for 8 h. The microstructure of the alloy surface was investigated by optical microscopic or scanning electron microscopic technique. The austenitic phase with the presence of metal carbides was observed on the surface of Inconel 718. Metal-carbides such as Nb-Mo and Ti-carbide with diameters of approximately 10 and 3 μm, respectively, were formed in Inconel 718. Anodic polarization results revealed that localized corrosion was observed at the interface between austenitic phase of a substrate and metal carbides. Difference in electrochemical property between a metal carbide and an austenitic substrate could provide an initiation site for localized corrosion of Inconel 718 surface.
- KEYWORDs : Inconel, Corrosion, Passivity, Pitting, Carbide
- AUTHORs : 이준섭† · 이예진 · 권순일 · 신정호 · 이재현
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Page : 367 - 372
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- 산성 용액에서 고크롬 주철의 전면 부식 거동
- The effect of carbon addition on the general corrosion behavior of high-chromium cast iron (HCCI) was
studied by a scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) or electron
back-scattered diffraction (EBSD), or electrochemical polarization techniques in 0.1 mol dm-3 H2SO4 +
0.05 mol dm-3 HCl at room temperature. The addition of 2.1-2.8 wt% carbon to HCCI increased the fraction
of eutectic austenite and eutectic carbide phases, while that of HCCI decreased the fraction of the primary
austenitic phase. Potentiostatic polarization of the HCCI at -0.35 VSSCE or 0.0 VSSCE resulted in
preferential general corrosion of the primary austenitic or eutectic austenitic phases, respectively. The
decrease in corrosion current density and the shift in noble corrosion potential direction with increasing
carbon content in the HCCI indicated that the fraction and the chemical composition of austenitic (primary
and eutectic) and carbide phases were strongly related to the general corrosion behavior of the HCCI. - KEYWORDs : High Chromium Cast Iron, Corrosion, Acidic Solution 1. 서론 고크롬 주철은
- AUTHORs : 이준섭† · 이준형 · 오준석 · 이재현
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Page : 373 - 383
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- Cr 첨가가 고망간강의 중성 수용액 환경 내 유동가속부식 거동에 미치는 영향
- The effect of Cr addition to high Mn steel on flow-accelerated corrosion (FAC) behavior in a neutral aqueous environment was evaluated. For comparison, two types of conventional ferritic steels (API X70 steel and 9% Ni steel) were used. A range of experiments (electrochemical polarization and impedance tests, weight loss measurement, and metallographic observation of corrosion scale) were conducted. This study showed that high Mn steel with 3% Cr exhibited the highest resistance to FAC presumably due to the formation of a bi-layer scale structure composed of an inner Cr enriched Fe oxide and an outer Mn substituted partially with Fe oxide on the surface. Although the high Mn steels had the lowest corrosion resistance at the initial corrosion stage due to rapid dissolution kinetics of Mn elements on their surface, the kinetics of inner scale (i.e. Cr enriched Fe oxide) formation on Cr-bearing high Mn steel was faster in dynamic flowing condition compared to stagnant condition. On the other hand, the corrosion scales formed
on API X70 and 9% Ni steels did not provide sufficient anti-corrosion function during the prolonged exposure to dynamic flowing conditions. - KEYWORDs : High Mn steel, Cr, Flow-accelerated corrosion, Corrosion scale, Electrochemical corrosion
- AUTHORs : 정영재 · 박진성 · 방혜린 · 이순기 · 최종교 · 김성진†
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Page : 384 - 390
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- 용융 알루미늄 도금된 절탄기 강재 튜브의 고상입자 침식 특성
- In this paper, durability evaluation and surface damage mechanism were investigated through solid particle erosion (SPE) test after applying hot-dip aluminizing (HDA) technology for the purpose of maintenance of marine economizer tube. Damaged surface shape was analyzed using SEM and 3D microscope. Compositional changes and microstructure of the HDA layer were analyzed through EDS and XRD. Durability was evaluated by analyzing weight loss and surface damage depth after SPE. HDA was confirmed to have a two-layer structure of Al and Al5Fe2. HDA+HT was made into a single alloy layer of Al5Fe2 by diffusion treatment. In the microstructure of HDA+HT, void and crack defect were induced during the crystal phase transformation process. The SPE damage mechanism depends on material properties. Plastic deformation occurred in the substrate and HDA due to ductility, whereas weight loss due to brittleness occurred significantly in HDA+HT. As a result, the substrate and HDA showed better SPE resistance than HDA+HT.
- KEYWORDs : Solid particle erosion, Hot-dip aluminizing, Durability, Damage mechanism
- AUTHORs : 박일초 · 한민수†
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