한국부식방식학회

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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

Page : 288 - 294 DOWNLOAD
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

Page : 280 - 287 DOWNLOAD
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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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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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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