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Page : 233 - 238
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- ALBC3 합금의 표면 개질을 위한 쇼트피닝 분사거리가 전기화학적 특성에 미치는 영향
- In the case of casting materials or ductile materials for marine equipment, it is common to employ a surface modification for achieving cost reduction and improvement in strength. In particular, aluminium bronze ALBC3 exhibits excellent corrosion resistance, and thus widely used for marine application. However, application of the material under high-velocity seawater flow may induce electrochemical corrosion damage and physical damage such as cavitation erosion, leading to shorter service life of equipment.In this study, surface modification was carried out on ALBC3 alloy for different shot peening stand-off distances, and the physical hardness and electrochemical characteristics before and after modification were investigated. The results in each case showed the hardness increase in comparison with non-peened specimen, and the maximum hardness improvement(50 %) was found in 10 cm of shot-peening stand-off distance. It is observed that the electrochemical characteristics were irrelevant to application of shot peening.
- KEYWORDs : cast materials, surface modification, electrochemical experiment, shot peening, stand-off distance
- AUTHORs : 한민수·현광용·김성종†
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Page : 239 - 244
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- ALBC3 합금의 쇼트피닝 분사거리에 따른 해수 내 캐비테이션 손상 평가
- Marine equipment exposed to harsh environments requires not only excellent corrosion resistance but also improvement of physical characteristics against natural material degradation. With growing interests in ocean energy resources, the higher reliability for marine equipment has become more important in terms of material characteristics. ALBC3 alloy represents excellent corrosion resistance and is widely used in corrosive environments. However, cavitation damage occurs frequently due to its poor durability in high flow rate of marine environment. In this research, shot peening technology was employed as a surface modification with shot peening stand-off distance to mitigate cavitation damage. The effects of shot peening on extent of cavitation damage and weight loss were evaluated for both shot peened and non-peened specimens. The results revealed that the application of shot peeing decreased cavitation damage for all experimental conditions in comparison with the non-peened specimens. The optimum stand-off distance was determined to be 10 cm, since more than 35 % of cavitation damage reduction was observed.
- KEYWORDs : :corrosion resistance, cavitation damage, shot-peening, surface modification, stand-off distance
- AUTHORs : 한민수·장석기·김종신·김성종†
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Page : 245 - 252
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- 이종 알루미늄 합금의 로봇 미그 용접 시 용접재료에 따른 기계적 및 전기화학적 특성 평가
- In this study, mechanical and electrochemical characteristics with welding material in MIG welded with ROBOT for dissimilar Al alloys were investigated using various experiment methods. The MIG welding by ROBOT with ER5183 and ER5556 for the 5456-H116 and 6061-T6 Al alloy were carried out. The hardness of welding zone was lower than that of base metal. In electrochemical experiment, ER5183 welding material presented excellent characteristics. The yield strength and maximum tensile strength in welding with welding material of ER5183 presented lower value than those of ER5556. The elongation and time-to-fracture showed the opposite results.
- KEYWORDs : MIG welding, Al alloy, electrochemical experiment, welding material
- AUTHORs : 김성종†·한민수·우용빈
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Page : 253 - 258
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- 수산화구리가 전착도막의 경화성과 내식성에 미치는 영향
- Effects of copper hydroxide(Ⅱ) on the curing and the corrosion resistance of electrocoating were investigated by MEK rubbing test, electrochemical impedance spectroscopy (EIS) and Thermo-gravimetric analysis (TGA). Curing performance of electrocoating was lowered with increasing the content of copper hydroxide(Ⅱ)
as evidenced by the MEK rub performance which decreased with increasing the content of copper hydroxide(Ⅱ). This indicates copper hydroxide(Ⅱ) affected the blocked isocyanate reaction in the coatings, by the decomposition of copper hydroxide(Ⅱ) to CuO and H2O during reaction of isocyanate with nuclephiles.
Corrosion resistance of coatings also decreased with the content of copper hydroxide. This reflects the higher barrier property in coatings with higher curing performance. - KEYWORDs : cataphoretic coating, copper hydroxide, curing performance, rub test, corrosion resistance,
- AUTHORs : 양원석†·황운석
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Page : 265 - 273
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- 11 wt% 크롬이 함유된 Ti 첨가 페라이트스테인리스강의 입계부식에 미치는 규소의 영향
- Ti-stabilized 11 wt% Cr ferritic stainless steels (FSSs) for automotive exhaust systems have been experienced intergranular corrosion (IC) in some heat-affected zone (HAZ). The effects of sensitizing heat-treatment and silicon on IC were studied. Time-Temperature-Sensitization (TTS) curves showed that sensitization to
IC was observed at the steels heat-treated at the temperature lower than 650oC and that silicon improved IC resistance. The sensitization was explained by chromium depletion theory, where chromium is depleted by precipitation of chromium carbide during sensitizing heat-treatment. It was confirmed with the results from the analysis of precipitates as well as the thermodynamical prediction of stable phases. In addition, the role of silicon on IC was explained with the stabilization of grain boundary. In other words, silicon promoted the formation of the grain boundaries with low energy where precipitation was suppressed and consequently, the formation of Cr-depleted zone was retarded. The effect of silicon on the formation of
grain boundaries with low energy was proved by the analysis of coincidence site lattice (CSL) grain boundary, which is a typical grain boundary with low energy. - KEYWORDs : intergranular corrosion, coincidence site lattice (CSL), grain boundary energy, silicon, EBSD
- AUTHORs : 현 영 민·김 희 산†
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Page : 274 - 279
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- 150℃에서 원전 2차측 배관재료의 Cr함량에 따른 유체가속부식 특성
- Flow accelerated corrosion (FAC) of the carbon steel piping in nuclear power plants (NPPs) has been major
issue in nuclear industry. During the FAC, a protective oxide layer on carbon steel dissolves into flowing
water leading to a thinning of the oxide layer and accelerating corrosion of base material. As a result,
severe failures may occur in the piping and equipment of NPPs. Effect of alloying elements on FAC of
pipe materials was studied with rotating cylinder FAC test facility at 150℃ and at flow velocity of 4m/s.
The facility is equipped with on line monitoring of pH, conductivity, dissolved oxygen(DO) and temperature.
Test solution was the demineralized water, and DO concentration was less than 1 ppb. Surface appearance of A 106 Gr. B which is used widely in secondary pipe in NPPs showed orange peel appearance, typical appearance of FAC. The materials with Cr content higher than 0.17wt.% showed pit. The pit is thought to early degradation mode of FAC. The corrosion product within the pit was enriched with Cr, Mo, Cu, Ni and S. But S was not detected in SA336 F22V with 2.25wt.% Cr. The enrichment of Cr and Mo seemed to be related with low, solubility of Cr and Mo compared to Fe. Measured FAC rate was compared with Ducreaux’s relationship and showed slightly lower FAC rate than Ducreaux’s relationship. - KEYWORDs : flow accelerated corrosion, pit, corrosion product, steel, pipe
- AUTHORs : 박 태 준·김 홍 표†
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Page : 280 - 287
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- 유동가속부식에 영향을 미치는 수화학 인자 : pH, 용존산소, 하이드라진
- Flow accelerated corrosion(FAC) of the carbon steel piping in pressurized water reactors(PWRs) has been major issue in nuclear industry. Severe accident at Surry Unit 2 in 1986 initiated the worldwide interest in this area. Major parameters influencing FAC are material composition, microstructure, water chemistry,
and hydrodynamics. Qualitative behaviors of FAC have been well understood but quantitative data about FAC have not been published for proprietary reason. In order to minimize the FAC in PWRs, the optimal method is to control water chemistry factors. Chemistry factors influencing FAC such as pH, corrosion potential, and hydrazine contents were reviewed in this paper. FAC rate decreased with pH up to 10 because magnetite solubility decreased with pH. Corrosion potential is generally controlled dissolved oxygen (DO) and hydrazine in secondary water. DO increased corrosion potential. FAC rate decreased with DO by stabilizing magnetite at low DO concentration or by formation of hematite at high DO concentration. Even though
hydrazine is generally used to remove DO, hydrazine itself thermally decomposed to ammonia, nitrogen, and hydrogen raising pH. Hydrazine could react with iron and increased FAC rate. Effect of hydrazine on FAC is rather complex and should be careful in FAC analysis. FAC could be managed by adequate combination of pH, corrosion potential, and hydrazine. - KEYWORDs : flow accelerated corrosion, nuclear power plant, water chemistry factors, pH, corrosion potential,
- AUTHORs : 이 은 희·김 경 모·김 홍 표†
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Page : 288 - 294
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- 표면전류분석을 이용한 전착도막의 표면 균질성 평가
- When the automotive body enters an electrocoating tank while applying an electric current, its steel surface is exposed to a very low induced current. Consequently, surface defects of coating may arise if the steel surface has lack of electric uniformity due to local defects such as local oxide. In this study, we investigated
the preceding assessment methods to evaluate steel susceptibility of the low induced current during electrocoating before mass production. Prior to general electrocoating, we applied low constant voltage such as 3V or low constant current densities such as 0.35㎃/㎠ and 0.50㎃/㎠. In result, we confirmed that such methods were efficient for assessing steel susceptibility of low induce current during electrocoating. - KEYWORDs : cataphoretic electrocoat, coating defect, surface defect analysis, current analysis, contact angle
- AUTHORs : 양 원 석†·이 창 용·정 유 동·문 만 빈·황 운 석
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Page : 295 - 303
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- Silane계 유무기 하이브리드 적용 합금도금강판 내식성 향상 코팅 기술 개발
- Silane surface treatments have been developed as an alternative for toxic and carcinogenic chromate-based treatments for years. It is consistently observed that ultra-thin films offer excellent corrosion protection as well as paint adhesion to metals. The silane performance is comparable to, or in some cases better than, that of chromate layers. Based on the tetra-ethylorthosilicate(TEOS) and methlyl trieethoxysilane(MTES), inorganic sol was synthesized and formed hybrid networks with SiO2 nano particle and polypropylene glycol(PPG) on Zn alloyed steel surface. According to SST results, addition of 10nm and 50nm SiO2 nanoparticle in synthesized solution improved anti-corrosion property by its shear stress relaxation effect during curing process. Also, SST results were shown that anti-corrosive property was affected by the amounts of organic compounds.
- KEYWORDs : Zn alloy coated steel, hybrid coating, anti-corrosive, temporary corrosion protection
- AUTHORs : 박종원†· 이경황·박병규·홍신협
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Page : 1 - 5
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- Effect of Cr, Mo and W on the Microstructure of Al Hot Dipped Carbon Steels
- A low carbon steel, Fe-2.25%Cr steel (ASTM T22), and Fe-2.25%Cr-1.6%W steel (ASTM T23) were aluminized by hot dipping into molten Al baths. After hot-dipping, a thin Al-rich topcoat and a thick alloy layer formed on the surface. The topcoat consisted primarily of a thin Al layer that contained a small amount of Fe, whereas the alloy layer consisted of Al-Fe intermetallics such as Al5Fe2 and AlFe. Cr, Mo, and W in T22 and T23 steels reduced the thickness of the topcoat and the alloy layer, and flattened the reaction front of the aluminized layer, when compared to the low carbon steel.
- KEYWORDs : hot-dip aluminizing, low carbon steel, T22, T23
- AUTHORs : Trinh Van Trung, Min Jung Kim, Soon Yong Park, Poonam Yadav, Muhammad Ali Abro, and Dong Bok Lee†
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