한국부식방식학회

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Page : 317 - 327 DOWNLOAD
초고강도 자동차용 강의 환원정전류인가에 따른 산화 거동 변화 연구
The change in the oxidation behavior of three types of B-added ultrahigh strength martensitic steels containing Ti and Nb induced by applying constant cathodic current was investigated. In a 3% NaCl+0.3% NH4SCN solution, the overall polarization behavior of the three alloys was similar, and degradation of the oxide film was observed in the three alloys after applying constant cathodic current. A significant increase in the anodic current density was observed in the Nb-added alloy, while it was diminished in the Ti-added alloy. Both Ti and Nb alloying decreased the hydrogen overpotential by forming NbC and TiC particles. In addition, the thickest oxide film was formed on the Ti-added alloy, but the addition of Nb decreased the film thickness. Therefore, it was concluded that the remarkable increase in the anodic current density of Nb-added alloy induced by applying constant cathodic current density was attributed to the formation of the thinnest oxide film less protective to hydrogen absorption, and the addition of Ti effectively blocked the hydrogen absorption by forming TiC particles and a relatively thick oxide film.
KEYWORDs : ultrahigh strength martensitic steel, Nb, Ti, hydrogen overpotential, oxide layer formation
AUTHORs : 하헌영†·김혜진·문준오·이태호·조효행·이창근·유병길·양원석

Page : 305 - 316 DOWNLOAD
이음매 없는 304L 스테인리스강관의 부식특성에 미치는 열처리의 영향
Austenitic stainless steels have been widely used for various systems of nuclear power plants. Among these stainless steels, small pipes with diameter less than 14 inch have been produced in the form of seamless pipe. Annealing and cooling process during the manufacturing process can affect corrosion properties of seamless stainless steels. Therefore, 12 inch-diameter of as-received 304L stainless steel pipe was annealed and aged in this study. Intergranular corrosion resistance was evaluated by ASTM A262 Practice A, C, and E methods. The degree of sensitization was determined using a DL-EPR test. U-bend method in an autoclave was used to evaluate the SCC resistance in 0.01 M Na2S4O6 or 40% NaOH solution at 340 °C. As-received specimen showed relatively high degree of sensitization and intergranular corrosion rate. Carbon segregation was also observed near grain boundaries. Annealing treatment could give the dissolution of
segregated carbon into the matrix. Aging treatment could induce segregation of carbon and finally form carbides. Microstructural analysis confirmed that high intergranular corrosion rate of the as-received seamless pipe was due to micro-galvanic corrosion between carbon segregation and grains.
KEYWORDs : seamless 304L stainless steel pipe, heat treatment, carbon segregation, intergranular corrosion, micro-galvanic corrosion
AUTHORs : 김기태·엄상빈·김영식†

Page : 298 - 304 DOWNLOAD
전기화학 임피던스 분석을 통한 자동차용 코일스프링 강의 부식 평가
Coil spring steels from the automobile suspension part after field exposure for 10 years and those after anti-corrosion validation test in proving ground of 5,000 ~ 10,000 km were examined for corrosion damages. Partial loss of paint, accumulation of corrosion product, and cracking of paint and superficial material were observed. The surface and subsurface region of spring steels had compressive residual stress and high hardness by shot peening. The surface hardness values of the specimens were 620 ~ 670 Hv. They were 60 ~ 80 Hv higher than those of the samples taken from the middle part of the spring. The maximum compressive
stress was -916 ~ -1208 MPa measured at depth of about 100 μm. Electrochemical impedance spectroscopy showed that the resistances of charge transfer and the paint layer of the spring steels ranged from several tens to millions Ω∙cm2. The resistance of the field samples was much higher than that of the proving ground
samples used in this study, implying that the proving ground test condition would be more corrosive than the field environment.
KEYWORDs : corrosion, automotive steel, painted steel, coil spring, electrochemical impedance spectroscopy
AUTHORs : 이규혁·박중현·안승호·서지원·장희진†

Page : 294 - 297 DOWNLOAD
수치해석에 의한 LNG 저장탱크용 강관파일 전기방식 설계 최적화 연구
For the longer service life of steel pile, cathodic protection is selected sometimes at corrosive environment. The cathodic protection design improvement was investigated in this study. The current demand for cathodic protection was calculated from the potentiostatic current monitoring of the steel specimen in the deaerated soil samples. In this study, the current distribution was studied using the Boundary Element Method (BEM) and the Finite Element Method (FEM) numerical analysis methods. The optimum layout of the anode was developed and confirmed by numerical analysis. Under the conventional design of the anode, the length of the anode hole is same as the pile length. We found that, at the bottom end of the pile, the current density is too high. When the anode hole length was 80% of the pile length, the current consumption at the end was reduced. The construction cost of anode hole drilling was decreased about 20%, as compared to the conventional design. Furthermore, the life of the anode materials could be extended by reducing
the current consumption at the end section. Using this approach, the construction cost was reduced significantly without any under-protection area on the steel piles.
KEYWORDs : steel pile, cathodic protection, BEM, numerical analysis, design
AUTHORs : 김영근†· 송홍석

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The Specific Case Analysis of Biomineralization Induced by Sulfate Reducing Bacteria
The effects of sulfate reducing bacteria (SRB) on the corrosion and scaling of the Q235 carbon steel has been investigated in the simulated sewage water and oil field gathering pipelines production water, using scanning electron microscopy (SEM), energy dispersive x-ray spectrometry (EDS), and three-dimensional stereoscopic microscope. Results indicated that the concentration of SRB reached the maximum value on the ninth day in simulated sewage water with a large amount of scaling on the surface of specimen. In oil field gathering pipelines, a large amount of scaling and mineralization of mineral salts and thick deposition of extracellular polymeric substance (EPS) layers were also observed on the surface of specimen. The thickness of biofilm was about 245 μm within 30 days. After adding microbicides, the thickness of corrosion products film was only up to 48 - 106 μm within 30 days, suggesting that SRB could induce biomineralization. Under-deposit corrosion morphology was uniform in the absence of microbicides while local corrosion was
observed in the presence of microbicides.
KEYWORDs : SRB, biomineralization, EPS, biofilm, corrosion
AUTHORs : Hongwei Liu, Shuang Qin, Chaoyang Fu, Fei Xiao, Deli Wang, Xia Han, Tianli Wang, and Hongfang Liu†

Page : 278 - 284 DOWNLOAD
The Effect of Heat Input and Shielding Gas Composition on Corrosion Resistance of TIG Weld Metal of New Lean Duplex Stainless Steel S82441
The effects of TIG welding and post-treatment procedures on the microstructure and the pitting corrosion resistance of welded lean duplex stainless steel S82441 were investigated. Autogenous TIG welding was used with different amounts of heat input and shielding gases such as Ar, and mixtures of Ar-N2 and Ar-He. The addition of 5% to 15% of nitrogen to argon practically did not affect the level of the pitting corrosion resistance. However, the application of gas mixtures (50% Ar + 50% He) resulted in a significant decrease in pitting corrosion resistance. We found that increased current (200 A and 250 A) led to lower values of CPT of welds compared with welds obtained with 50 A, 100 A and 150 A. In addition, the removal of the weld surface layer (0.2 ~ 0.3 mm thickness) in most cases not only resulted in a significant increase in resistance to the pitting corrosion but also post-treatment of weld, implying that corrosion resistance depended on factors such as surface roughness or the presence of undesirable oxides.
KEYWORDs : lean duplex stainless steel, TIG, pitting corrosion, shielding gas, heat input
AUTHORs : J. Niagaj† and Z. Brytan

Page : 273 - 277 DOWNLOAD
Effect of Tropical Atmosphere on Corrosion of Different Metals
Atmospheric corrosion is clearly the most noticeable of all corrosion processes. A tremendous amount of economic losses are caused by atmospheric corrosion. Thus, it is imperative to know the level of atmosphere’s aggressiveness or in other words “corrosivity”, before designing or planning any corrosion prevention strategy.
In Singapore, corrosivity values were not recorded earlier though the process of measurement and recording was prevalent in other countries. With an aim of filling this gap, three test sites were setup at three locations in Singapore to represent marine, industrial and urban atmospheres or their mixtures. Subsequently, corrosivity
readings were measured and recorded according to ISO 9223:2012 for the first time in Singapore. Salient atmospheric constituents or parameters like time of wetness (TOW), Cl-, SO2, NO2, O3, and HNO3 were measured at all sites over a period of time to categorize corrosivity of particular atmosphere. The effect of the atmosphere on corrosion of steel, Cu, Al, and Zn has also been investigated and quantified. “Estimated” and “determined” corrosivities were quantified and compared according to ISO 9223 standard. The study data along with final corrosivity measurements will be presented and discussed in the present work.
KEYWORDs : atmospheric exposure, corrosivity, Singapore, atmospheric constituents
AUTHORs : Sudesh Wijesinghe† and Tan Zixi

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