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Page : 158 - 168 DOWNLOAD
양성자 조사가 316 스테인리스강의 미세조직과 표면산화 특성에 미치는 영향
Austenitic 316 stainless steel was irradiated with protons accelerated by an energy of 2 MeV at 360 oC, the various defects induced by this proton irradiation were characterized with microscopic equipment. In our observations irradiation defects such as dislocations and micro-voids were clearly revealed. The typical irradiation defects observed differed according to depth, indicating the evolution of irradiation defects follows the characteristics of radiation damage profiles that depend on depth. Surface oxidation tests were conducted under the simulated primary water conditions of a pressurized water reactor (PWR) to understand the role irradiation defects play in surface oxidation behavior and also to investigate the resultant irradiation assisted stress corrosion cracking (IASCC) susceptibility that occurs after exposure to PWR primary water. We found that Cr and Fe became depleted while Ni was enriched at the grain boundary beneath the surface oxidation layer both in the non-irradiated and proton-irradiated specimens. However, the degree of Cr/Fe depletion and Ni enrichment was much higher in the proton-irradiated sample than in the non-irradiated one owing to radiation-induced segregation and the irradiation defects. The microstructural and microchemical changes induced by proton irradiation all appear to significantly increase the susceptibility of austenitic 316 stainless steel to IASCC.
KEYWORDs : Austenitic 316 stainless steel, Proton irradiation, Irradiation Defects, Surface Oxidation, IASCC
AUTHORs : 임연수† · 김동진 · 황성식 · 최민재 · 조성환

Page : 152 - 157 DOWNLOAD
스테인리스 스틸의 표면 산화피막 성장과 내부식성 상관관계
Stainless steel is a metal that does not generate rust. Due to its excellent workability, economic feasibility, and corrosion resistance, it is used in various industrial fields such as ships, piping, nuclear power, and machinery. However, stainless steel is vulnerable to corrosion in harsh environments. To solve this problem, its corrosion resistance could be improved by electrochemically forming an anodized film on its surface. In this study, 316L stainless steel was anodized at room temperature with ethylene glycol-based 0.1 M NH4F and 0.1M H2O electrolyte to adjust the thickness of the oxide film using different anodic oxidation voltages (30 V, 50 V, and 70 V) with time control. The anodic oxidation experiment was performed by increasing the time from 1 hour to 7 hours at 2-hour intervals. Corrosion resistance according to the thickness of the anodic oxide film was observed. Electrochemical corrosion behavior of oxide films was investigated through polarization experiments.
KEYWORDs : Stainless steel, Anodization, Oxide thickness, Nanostructure, Corrosion resistance
AUTHORs : 박영주 · 유진석 · 심성구 · 정찬영†

Page : 143 - 151 DOWNLOAD
쇼트피닝이 회주철의 캐비테이션 침식 저항성에 미치는 영향
In this study, optimal shot peening process conditions were investigated for improving the cavitation erosion resistance of gray cast iron under a marine environment. Shot peening was performed with variables of injection pressure and injection time. The durability was then evaluated through cavitation erosion test which was conducted according to the modified ASTM G-32 standard. The tendency of cavitation erosion damage according to shot peening process condition was investigated through weight loss rate, surface and cross-sectional analysis of the specimen before and after the test. As a result, the shot peening process condition that could minimize cavitation erosion was when the injection pressure was the lowest and when the injection time was the shortest. This was because the flake graphite exposed on the gray cast iron surface could be easily removed under such condition. Therefore, the notch effect can be prevented by surface modification. In addition, the cavitation erosion damage mechanism of gray cast iron was discussed in detail.
KEYWORDs : Gray cast iron, Cavitation erosion, Flake graphite, Shot peening, Marine environment
AUTHORs : 박일초†

Page : 129 - 142 DOWNLOAD
Effects of Inhibitors on Corrosion Resistance of Steel in CaCl2 Solution Based on Response Surface Analysis
Effects of corrosion inhibitors (i.e., sodium nitrite, sodium hexametaphosphate, trimethylamine (TEA), sugar, and urea) on the corrosion resistance of carbon steel in CaCl2 solution were investigated. The test solution was designed with response surface methodology of design of experiments (DOE) in the range of 0 ~ 50 ppm for NaNO2, 0 ~ 200 ppm for (NaPO3)6, 0 ~ 2000 ppm for TEA, 0 ~ 3000 ppm for sugar, 0 ~ 200 ppm for urea with 3 wt% CaCl2. The corrosion potential and the corrosion rate were measured with potentiodynamic polarization tests and analyzed statistically to find main effects of inhibitor concentrations and interactions between them. As a result, hexametaphosphate was the most effective compound in reducing the corrosion rate. Sugar also reduced the corrosion rate significantly possibly because it covered the surface effectively with a high molecular weight. The inhibiting action of sugar was found to be enhanced by adding trimethylamine into the solution. Nevertheless, trimethylamine did not appear to be effective in inhibiting corrosion by itself. However, urea and sodium nitrite showed almost no inhibition on corrosion resistance of steel.
KEYWORDs : Corrosion, Design of Experiment (DOE), Corrosion inhibitor, Steel, Chloride
AUTHORs : Tae-Jun Park and HeeJin Jang†

Page : 118 - 128 DOWNLOAD
A way Analyzing Oxide Layer on an Irradiated CANDU-PHWR Pressure Tube Using an EPMA and X-ray Image Mapping
The oxide layer in samples taken from an irradiated Zr-2.5Nb pressure tube from a CANDU-PHWR reactor was analyzed using electron probe microanalysis (EPMA). The examined tube had been exposed to temperatures ranging from 264 to 306 oC and a neutron fluence of 8.9 × 1021 n/cm2 (E > 1 MeV) for the maximum 10 effective full-power years in a nuclear power plant. Measuring oxide layer thickness generally employs optical microscopy. However, in this study, analysis of the oxide layer from the irradiated pressure tube components was undertaken through X-ray image mapping obtained using EPMA. The oxide layer characteristics were analyzed by X-ray image mapping with 256 × 256 pixels using EPMA. In addition,the slope of the oxide layer was measured for each location. A particular advantage of this study was that backscattered electrons and X-ray image mapping were obtained at a magnification of 9,000 when 20 kV volts and 30 uA of current were applied to radiation-shielded EPMA. The results of this study should usefully contribute to the study of the oxide layer properties of various types of metallic materials irradiated by high radiation in nuclear power plants.
KEYWORDs : Irradiated Zr-2.5Nb, CANDU-PHWR, Pressure tube, Oxide properties, EPMA
AUTHORs : Yang Hong Jung† and Hee Moon Kim

Page : 112 - 117 DOWNLOAD
Enhancement of the Corrosion Resistance of CrN Film Deposited by Inductively Coupled Plasma Magnetron Sputtering
Inductively coupled plasma magnetron sputtering (ICPMS) has the advantage of being able to dramatically improve coating properties by increasing the plasma ionization rate and the ion bombardment effect during deposition. Thus, this paper presents the comparative results of CrN films deposited by direct current magnetron sputtering (dcMS) and ICPMS systems. The structure, microstructure, and mechanical and corrosive properties of the CrN coatings were investigated by X-ray diffractometry, scanning electron microscopy, nanoindentation, and corrosion-resistance measurements. The as-deposited CrN films by ICPMS grew preferentially on a 200 plane compared to dcMS on a 111 plane. As a result, the films deposited by ICPMS had a very compact microstructure with high hardness. The nanoindentation hardness reached 19.8 GPa, and 13.5 GPa by dcMS. The corrosion current density of CrN film prepared by ICPMS was about 9.8 × 10-6 mA/cm2, which was 1/470 of 4.6 × 10-3 mA/cm2, the corrosion current density of CrN film prepared by dcMS.
KEYWORDs : Corrosion resistance, CrN, Films, Inductively coupled plasma, Sputtering
AUTHORs : Sung-Yong Chun and Seong-Jong Kim†

Page : 105 - 111 DOWNLOAD
Three-dimensional Computational Modeling and Simulation of Intergranular Corrosion Propagation of Stainless Steel
In oxidizing nitric acid solutions, stainless steel undergoes intergranular corrosion accompanied by grain dropping and changes in the corrosion rate. For the safe operation of reprocessing plants, this mechanism should be understood. In this study, we constructed a three-dimensional computational model using a cellular automata method to simulate the intergranular corrosion propagation of stainless steel. The computational model was constructed of three types of cells: grain (bulk), grain boundary (GB), and solution cells. Model simulations verified the relationship between surface roughness during corrosion and dispersion of the dissolution rate of the GB. The relationship was investigated by simulation applying a constant dissolution rate and a distributed dissolution rate of the GB cells. The distribution of the dissolution rate of the GB cells was derived from the intergranular corrosion depth obtained by corrosion tests. The constant dissolution rate of the GB was derived from the average dissolution rate. Surface roughness calculated by the distributed dissolution rates of the GBs of the model was greater than the constant dissolution rates of the GBs. The cross-sectional images obtained were comparable to the corrosion test results. These results indicate that the surface roughness during corrosion is associated with the distribution of the corrosion rate.
KEYWORDs : Intergranular corrosion, Stainless steel, Corrosion shape, Computer simulation, Cellular automata method
AUTHORs : T. Igarashi†, A. Komatsu, T. Motooka, F. Ueno, and M. Yamamoto

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