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스테인리스강의 국부부식 저항성 연구에 미세방울셀의 응용
김성유,김희산,Kim Sung-Yu,Kim Hee-San 한국전기화학회 2006 한국전기화학회지 Vol.9 No.2
마이크로 전기화학 실험법인 비접촉식 미세방울셀이 산 용액에 노출된 저 크롬이 함유된 스테인리스강(STS 316)과 같이 젖음성이 높은 전기화학계에 사용되는데 어려움이 있었다. 음압의 인가, 방울의 크기 제어 그리고 소수성의 개스킷의 사용은 높은 젖음성을 지닌 표면에서 비접촉식 미세방울셀의 적용을 가능하게 하였다. 개선된 미세방울셀의 신뢰성을 확인하고자 3종류의 다른 계-산성염화용액과 고 크롬 페라이트 스테인리스강, 산성염화용액과 STS 316 그리고 중성염화용액과 STS 316-에 대하여 개선된 미세방울셀로 국부부식 연구를 수행하였다. 첫째 산성용액에서 고 크롬강의 양극 분극 결과는 $\alpha/\sigma$ 계면 근처에서 국부부식이 크롬 고갈층에 의한 것임을 보여주었다. 둘째 산성용액에서 STS316의 양극 분극실험이 개선된 미세방울셀에서 성공적으로 수행됨을 확인할 수 있었다. 특히, 미세방울셀에서 얻어진 국부 양극 분극곡선을 통해 STS316의 내식성에 미치는 $\delta$-라이트 영향을 밝힐 수 있었다. 마지막으로 중성염화 용액에서 STS316의 양극 분극곡선은 핏팅 저항성이 $\delta$-페라이트보다 개재물에 의존됨을 보여주었다. Micro-droplet cell with free droplet as a micro-electrochemical technique has been limited to apply to electrochemical systems with high wetting properties such as an acidic solution and low grade stainless steels(Type 316L). By loading negative pressure to a droplet, control of droplet size, and use of hydrophobic gasket, the cell is modified to be allowed to use for electrochemical systems with high wetting properties. For giving the reliability of new cell, studies on local corrosion were conducted for three different systems-an acidic chloride solution and high chromium ferritic stainless steel, the other acidic chloride solution and type 316, and a neutral chloride solution and type 316. stainless steel. Firstly, the modified micro-droplet cell allows the anodic polarization curves in an acidic chloride solution to show the fact that the local corrosion of high chromium stainless steel near the $\alpha/\sigma$ interface is due to the Cr depleted zone. Secondly, the local anodic polarization test of type 316 L in the other acidic chloride solution can be successfully conducted in the cell. Furthermore, the local polarization curves help elucidating the corrosion of type 316 with $\delta-ferrite$ phase. Finally, the polarization curves of type 316 L in a neutral chloride solution indicates that the factor affecting the pitting corrosion resistance was inclusions rather than $\delta-ferrite$.
현영민 ( Young Min Hyun ),김희산 ( Hee San Kim ),김영호 ( Young Ho Kim ),장현정 ( Hyun Jung Jang ),박영복 ( Young Bog Park ),최영준 ( Young June Choi ) 한국부식방식학회(구 한국부식학회) 2012 Corrosion Science and Technology Vol.11 No.2
Factors affecting corrosion of stainless steels such as pH, oxidation and redox potential (ORP), soil resistivity, water content of soil, chloride ion concentration, bacteria activity, and corrosion potential have been investigated using soil analysis, bacterial analysis, surfacial analysis, and analysis of corrosion potentials of several stainless steels buried in 8 sites of Seoul metropolitan for one year. Corrosion potential was affected by occurrance of corrosion as well as bacteria activity but the behavior of corrosion potential with time is different depending on occurrance of corrosion and bacteria activity. The main factor affecting corrosion of stainless steels in soil is level of chloride ion concentration which is also a main factor affecting corrosion of stainless steels in chloride containing drinkable water, Furthermore, guideline of stainless steels in drinkable water is concluded to be applicable to that in soil by the results from surfacial analysis.
김동우 ( Dong Woo Kim ),김희산 ( Hee San Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.6
Co-application of organic coating and cathodic protection has not provided enough durability to low-alloyed steels inseawater ballast tank (SBT) environments. An attempt has made to study the effect of alloy elements (Al, Cr, Cu, Mo, Ni, Si, W) on general and localized corrosion resistance of steels as basic research to develop new low-allowed steels resistive to corrosion in SBT environments. For this study, we measured the corrosion rate by the weigh loss method after periodic immersion in synthetic seawater at 60 ℃, evaluated the localized corrosion resistance by an immersion test in concentrated chloride solution with the critical pH depending on the alloy element (Fe, Cr, Al, Ni), determined the permeability of chloride ion across the rust layer by measuring the membrane potential, and finally, we analyzed the rust layer by EPMA mapping and compared the result with the E-pH diagram calculated in the study. The immersion test of up to 55 days in the synthetic seawater showed that chromium, aluminium, and nickel are beneficial but the other elements are detrimental to corrosion resistance. Among the beneficial elements, chromium and aluminium effectively decreased the corrosion rate of the steels during the initial immersion, while nickel effectively decreased the corrosion rate in a longer than 30-day immersion. The low corrosion rate of Cr- or Al-alloyed steel inthe initial period was due to the formation of Cr2FeO4 or Al2FeO4, respectively -the predicted oxide in the E-pH diagram- which is known as a more protective oxide than Fe3O4. The increased corrosion rate of Cr-alloyed steels with alonger than 30-day exposure was due to low localized corrosion resistance, which is explained bythe effect of the alloying element on a critical pH. In the meantime, the low corrosion rate of Ni-alloyed steel with a longer than 30-day exposure wasdue to an Ni enriched layer containing Fe2NiO4, the predicted oxide in the E-pH diagram. Finally, the measurement of the membrane potential depending on the alloying element showed that a lower permeability of chloride ion does not always result in higher corrosion resistance in seawater.
11 wt% 크롬이 함유된 Ti 첨가 페라이트스테인리스강의 입계부식에 미치는 규소의 영향
현영민 ( Young Min Hyun ),김희산 ( Hee San Kim ) 한국부식방식학회(구 한국부식학회) 2013 Corrosion Science and Technology Vol.12 No.6
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.
논문 : 머플러용 스테인리스강의 내식성에 미치는 열적 산화의 영향
김동우 ( Dong Woo Kim ),김희산 ( Hee San Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 2008 대한금속·재료학회지 Vol.46 No.10
Reduction of NOx in emission gas, improvement of engine efficiency, and extension of warranty period has made demands for developing materials more corrosively resistant to the inner-muffler environments or predicting the lifetime of materials used in muffler more precisely. The corrosion inside muffler has been explained with condensate corrosion mainly though thermal oxidation experiences prior to condensate corrosion. Hence, the aim of this study is to describe how the thermal oxidation affects the corrosion of stainless steel exposed to the inner-muffler environments. Auger electron spectroscopy and electrochemical tests were employed to analyze oxide scale and to evaluate corrosion resistance, respectively. Thermal oxidation has different role of condensate corrosion depending on the temperature: inhibiting condensate corrosion below 380℃ and enhancing condensate corrosion above 380℃. The low temperature oxidation causes to form compact oxide layer functioning a barrier for penetrating condensate into a matrix. Although though thermal oxidation caused chromium-depleted layer between oxide layer and matrix, the enhancement of the condensate corrosion in high temperature oxidation resulted from corrosion-induced crevice formed by oxide scale rather than corrosion in chromium-depleted layer. It was proved by aids of anodic polarization tests and measurements of pitting corrosion potentials. By the study, the role of high temperature oxidation layer affecting the condensate corrosion of stainless steels used as muffler materials was well understood.
Fe와 galvanic couPle된 알루미늄의 내식성에 미치는 마그네슘의 영향
현영민 ( Young Min Hyun ),김희산 ( Hee San Kim ) 한국부식방식학회(구 한국부식학회) 2013 Corrosion Science and Technology Vol.12 No.1
Effects of magnesium and pH on corrosion of aluminum galvanically coupled to iron have studied by using potentio-dynamic and static tests for polarization curves, Mott-Schottky test for analysis of semiconductor property, and GD-AES and XPS for film analysis. Pitting potential was sensitive to magnesium as an alloying element but not to pH. while passive current was sensitive to pH but not to magnesium. It was explained with, instead of point defect model (PDM). surface charge model describing that the ingression of chloride depends on the state of surface charge and passive film at film/solution interface is affected by p11. In addition, galvanic current of aluminum electrically coupled to iron was not affected by magnesium in pH 8.4, 0.2M citrate solution but was increased by magnesium at the solution of p1-I 9.1. The galvanic current at pH 9.1 increased with time at the initial stage and after the exposure of about 200 minute. decreased and stabilized. The behavior of the galvanic current was related with the concentration of magnesium at the surface, It agreed with the depletion of magnesium at the oxide surface by using glow discharge atomic emission spectroscopy (GD-AES). In addition, pitting potential of pure aluminum was reduced in neutral p11 solution where chloride ion maybe are competitively adsorbed on pure aluminum. It was confirmed by the exponential decrease of pitting potential with log of [Cl] around 0.025 M of [Ci] and linear decrease of the pitting potential. From the above results, unlike magnesium, alloying elements with higher electron negativity, lowering isoelectric point (ISE), are recommended to be added to improve pitting corrosion resistance of aluminum and its alloys in neutral solutions as well as their galvanic corrosion resistance in weakly basic solutions.