한국부식방식학회

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Cu-7Al-2.5Si 합금의 기계적 및 내식특성에 미치는 열처리 효과
Recently, the fuel oil of diesel engines of marine ships has been increasingly changed to heavy oil of low quality as the oil price is getting higher and higher. Therefore, the spiral gear attached at the motor of the oil purifier which plays an important role to purify the heavy oil is also easy to expose at severe environmental condition due to the purification of the heavy oil in higher temperature. Thus, the material of the spiral gear requires a better mechanical strength, wear and corrosion resistance. In this study, the heat treatment(tempering) with various holding time at temperature of 500℃ was carried out to the alloy of Cu-7Al-2.5Si as centrifugal casting, and the properties of both hardness and corrosion resistance with
and without heat treatment were investigated with observation of the microstructure and with electrochemical methods, such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram, and a.c. impedance. in natural seawater solution. The α, β\' and phases were observed in the material in spite of no heat treatment due to quenching effect of a spin mold. However, their phases, that is, β\' and phases decreased gradually with increasing the holding time at a constant temperature of 500 oC. The hardness more or less decreased with heat treatment, however its corrosion resistance was improved with the heat treatment. Furthermore, the longer holding time, the better corrosion resistance.
In addition, when the holding time was 48hrs, its corrosion current density showed the lowest value. The pattern of corroded surface was nearly similar to that of the pitting corrosion, and this morphology was greatly observed in the case of no heat treatment. It is considered that  phase at the grain boundary was
corroded preferentially as an anode. However, the pattern of general corrosion exhibited increasingly due
to decreasing the  phase with heat treatment. Consequently, it is suggested that the corrosion resistance
of Cu-7Al-2.5Si alloy can be improved with the heat treatment as a holding time for 48 hrs at 500 oC.
KEYWORDs : Cu-7Al-2.5Si alloy, purifier, spiral gear, heat treatment, microstructure, corrosion resistanc
AUTHORs : 이성열, 원종필, 박동현, 문경만†, 이명훈, 정진아, 백태실

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몰타르 시험편(W/C:0.4) 내부철근의 분극특성에 미치는 재령년수의 영향
The structures of reinforced concrete has been extensively increased with rapid development of industrial society. Futhermore, these reinforced concretes are easy to expose to severe corrosive environments such as sea water, contaminated water, acid rain and seashore etc.. Thus, corrosion problem of inner steel bar embedded in concrete is very important in terms of safety and economical point of view. In this study, multiple mortar test specimen(W/C:0.4) with six types having different cover thickness each other was prepared and was immerged in seawater solution for five years to evaluate the effect of cover thickness and immersion years to corrosion property of embedded steel bar. And the polarization characteristics of these embedded steel bars was investigated using electrochemical methods such as measuring corrosion potential, cathodic polarization curve, and cyclic voltammogram. At the beginning of immersion, the corrosion potentials exhibited
increasingly nobler values with increasing cover thickness. However, after immersed for 5 years, the thicker cover of thickness, the corrosion potentials shifted in the negative direction, and the relationship between corrosion potential and cover thickness was not in good agreement with each other. Therefore, it is considered
that the thinner cover of thickness, corrosive products deposited on the surface of the embedded steel bar plays the role as a resistance polarization which is resulted in decreasing the corrosion rate as well as shifting the corrosion potential in the positive direction. As a result, it seemed that the evaluation which corrosion possibility of the reinforced steel would be estimated by only measuring the corrosion potential may not be a completely desirable method. Therefore, it is suggested that we should take into account various parameters, including cover thickness, passed aged years as well as corrosion potential for more accurate assessment of corrosion possibility of reinforced steel which is exposed to partially or fully in marine environment for long years.
KEYWORDs : reinforced concrete, corrosion potential, impedance, cover thickness, W/C
AUTHORs : 문경만, 원종필, 박동현, 이성열†, 정진아, 이명훈, 백태실

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방오도료 도막의 마모율과 분극특성의 상관관계에 관한 평가
Recently, anti-fouling paints which does not include the poison components such as tin(Sn), copper(Cu) have been increasingly developed in order to inhibit the environmental contamination of the sea water. Moreover, the wear ratios of these anti-fouling paints are very important problem to prolong their life time in economical
point of view. In this study, five types of anti-fouling paints as self polishing type were investigated on the relationship between their polarization characteristics and wear ratios. It was verified that there was apparently a good relationship between the wear ratio and polarization characteristics, for example, the wear ratio increased
with increasing the impedance ratio, and increased or decreased with the corrosion potential shifting in the negative or positive direction respectively. In addition, the wear ratio decreased with decreasing the corrosion current density. Consequently, it is suggested that we can qualitatively expect the wear ratio by only measuring the
polarization characteristics. Therefore, before the examination of the wear ratio was actually carried out in the field, the evaluation of polarization property in the laboratory may give a available reference data for their developments.
KEYWORDs : anti-fouling paint, self polishing type, polarization characteristics, wear ratio, impedance, corrosion potential
AUTHORs : 정재현, 문경만†, 원종필, 박동현, 김현명, 이명훈, 백태실

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스프링클러 동배관의 공식부식 발생원인
Copper metal is widely used in tubes installed in sprinkler water services because of its excellent corrosion resistance. Copper corrosion is considered to be insignificant in water system and the incident of copper pipeline failure is relatively low. However, pitting corrosion is a major problem with all copper tubes.
In this study, leaked sprinkler copper tubes were collected from three different locations and examined on the causes of pitting corrosion of copper tubes in sprinkler water plumbing systems. Electrochemical tests such as potentiodynamic polarization, as well as surface and chemical analyses were performed. Results
show that pitting corrosion of copper tubes were found as Type I pitting that the carbon film formed on the copper tubes have a harmful effects, causing the pinhole failure in the pipe and resulting in leakage of water. The contermeasures on Type I pitting corrosion of copper tubes were proposed.
KEYWORDs : copper tube, pitting corrosion, potentiodynamic polarization, carbon film, Fe-SEM
AUTHORs : 이재봉†, 정호석

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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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