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Page : 298 - 304
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- 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†
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Page : 305 - 316
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- 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†
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Page : 317 - 327
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- 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
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Page : 1 - 5
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- The Composition of the Rare Earth Based Conversion Coating Formed on AZ91D Magnesium Alloy
- As structural materials, magnesium (Mg) alloys have been widely used in the fields of aviation, automobiles, optical instruments, and electronic products. There are few studies on the effect of coating conditions on the compositional variation during the formation process of the conversion coatings. Rare-earth based conversion coating on AZ91 magnesium alloy was prepared in ceric sulfate and hydrogen peroxide contained solution. The element composition and valence as well as their distribution in the coating were analyzed with energy dispersive X-ray spectroscopy (EDS), Electron probe micro-analyzer (EPMA), X-ray photoelectron spectroscopy
(XPS). The effect of treating process on the element composition were also studied. It was found that the conversion coating surface consists of Mg, Al, O, Ce, and the weight content of Ce in the coating was affected by the treating solution concentration and immersion time; the Ce element was distributed in the coating non-uniformly and existed in the form of Ce+3 and Ce+4, while the O element existed in
the form of OH-, O2-, H2O. Based on microscopic analysis results, the electrochemical deposition mechanism on the micro-anode and micro-cathode in the process of the coating growth was suggested. - KEYWORDs : magnesium alloy, surface treatment, rare earth, microscopic analysis
- AUTHORs : Menglei Chang, Jianfeng Wu, Dongchu Chen†, and Shulin Ye
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Page : 6 - 11
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- Atmospheric Corrosion of 7B04 Aluminum Alloy in Marine Environments
- Outdoor exposure tests using of 7B04 aluminium alloy samples including plate, tensile and various SCC samples were carried out in Tuandao station, Shandong province (East of China) and Wanning station, Hainan province (South of China). Corrosion characteristics including weight loss, microstructure, tensile strength and SCC susceptibility were investigated. The corrosion rates in Tuandao and Wanning showed high to low and the corrosion rates changed to the following equation of w=atb (b<1). The corrosion of 7B04 aluminium alloy in Wanning was more serious than that in Tuandao. Pitting appeared at early stage of expose test, and it can be changed to general corrosion with test time extension. The 7B04 aluminium alloy of which specimen shapes are forging and thick plate also showed SCC (Stress corrosion cracking) in the marine atmosphere. The higher SCC sensitivity was observed in Wanning station than in Tuandao station. The 7B04 aluminium alloy with a high stress level was more sensitive to SCC. Intergranular and transgranular or a mixed mode of cracking can be observed in different marine exposure.
- KEYWORDs : 7B04 aluminum alloy, atmospheric corrosion, SCC
- AUTHORs : Xiaoyun Zhang†, Ming Liu, Feng Lu, Minghui Liu, Zhihua Sun, and Zhihui Tang
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Page : 12 - 19
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- 수도관 부식에 대한 잔류염소 농도 영향 및 부식제어 방안
- Langelier Index (LI) is used as a tap water corrosiveness index. Residual chlorine in tap water induces corrosion inside water pipes. This study takes a deeper look into the effect of residual chlorine in water pipes. Comparison between tap waters of Y and K water treatment plant (WTP) shows that the LI index of K WTP is lower than that of Y. However, the corrosion rate of Y WTP is higher than that of K WTP. This means that the higher the concentration of residual chlorine in tap water, the higher the corrosion rate of pipe materials. When calcium hydroxide was added to tap water,
the corrosiveness index was improved and thus the corrosion rate reduced. It is possible to increase the disinfection efficiency by increasing the duration of residual chlorine and suppressing the rust generation of water pipes and to supply minerals. A guideline for corrosion control with residual chlorine should be set up. The effects of residual chlorine should be included in the corrosiveness index of tap water. - KEYWORDs : top water, corrosion, LI, Chlorine, calcium hydroxide
- AUTHORs : 한금석†·박주현·박영복·김성재·김현돈·최영준·최인철·홍성호
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Page : 20 - 29
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- CP-Ti 및 Ti-6Al-4V 합금의 전기화학적 특성에 미치는 제조공정의 영향
- Ti and its alloys show the excellent corrosion resistance to chloride environments, but they show less corrosion resistance in HCl, H2SO4, NaOH, H3PO4, and especially HF environments at high temperature and concentration. In this study, we used the commercially pure titanium and Ti-6Al-4V alloy, and evaluated the effect of the manufacturing process on the electrochemical properties. We used commercial
products of rolled and forged materials, and made additive manufactured materials by DMT (Directed Metal Tooling) method. We annealed each specimen at 760oC for one hour and then air cooled. We performed anodic polarization test, AC impedance measurement, and Mott-Schottky plot to evaluate the electrochemical properties. Despite of the difference of its microstructure of CP-Ti and Ti-6Al-4V alloys by the manufacturing process, the anodic polarization behavior was similar in 20% sulfuric
acid. However, the addition of 0.1% hydrofluoric acid degraded the electrochemical properties. Among three kinds of the manufacturing process, the electrochemical properties of additive manufactured CP-Ti, and Ti-6Al-4V alloys were the lowest. It is noted that the test materials showed a Warburg impedance in HF acid environments. - KEYWORDs : commercially pure Ti, Ti-6Al-4V, additive manufactured, polarization
- AUTHORs : 김기태·조현우·장현영·김영식†
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Page : 30 - 36
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- 마그네슘 합금의 방청을 위한 하이브리드 졸-겔 코팅제의 개발
- The high rate of corrosion of magnesium alloys makes it limited for industrial applications. Therefore, surface treatment is required to enhance their corrosion resistance. In our study, a chemical conversion coating for protecting the corrosion of the magnesium alloy, AZ31B, was prepared by using a phosphate-permanganate
solution. The chemical conversion coating had a limited protection ability due to defects arising from cracks and pores in the coating layer. The sol-gel coating was prepared by using trimethoxymethylsilane (MTMS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) as precursors, and aluminum acetyl acetonate as a ring opening agent. The corrosion protection properties of sol-gel and conversion coatings in 0.35wt% NaCl solution were measured by the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization
test. The EIS results indicated that the resistance of the chemical conversion coating with the sol-gel coating was significantly improved through the sol-gel sealed phosphate-permanganate conversion coating. The results of the potentiodynamic polarization test revealed that the sol-gel coating decreased the corrosion current density (Icorr). The SEM image showed that the sol-gel coating sealed conversion coating and improved corrosion protection. - KEYWORDs : conversion coating, sol-gel coating, corrosion protection, EIS, Potentiodynamic polarization test
- AUTHORs : 이동욱·김영훈·문명준†
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Page : 37 - 44
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- Correlation between Carbon Steel Corrosion and Atmospheric Factors in Taiwan
- Taiwan has a typical marine climate featuring perennial high-temperature and dampness. This climate, together with the emission of various industrial corrosive waste gases in recent years, contributes a lot to the corrosion of metal materials. In this study, samples of carbon steel exposed to various atmospheres in Taiwan were analyzed to investigate the impacts of atmospheric factors on carbon steel corrosion.
Carbon steel samples were collected from 87 experimental stations between 2009 and 2012. Statistical analysis was employed to investigate the correlations between the carbon steel corrosion situations and the atmospheric factors such as concentrations of sulfur dioxide or chloride, exposure time, rainfall, etc. The results indicate that for samples from industrial areas, the sulfur dioxide concentration and
exposure time during fall and winter are significantly correlated to the condition of the carbon steel corrosion. However, for samples from coastal zones, the significant correlated factors are chloride concentration and wetting time during winter. The results of this study are useful for the development of carbon steel corrosion prediction models. - KEYWORDs : Atmospheric corrosion, Environment factors, Carbon steel, Correlation analysis
- AUTHORs : C. M. Lo, L. H. Tsai, C. W. Hu, and M. D. Lin†
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Page : 45 - 53
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- Surface Protection Obtained by Anodic Oxidation of New Ti-Ta-Zr Alloy
- A new 80Ti-15Ta-5Zr wt% alloy surface was protected by anodic oxidation in phosphoric acid solution. The protective oxide layer (TiO2, ZrO2 and Ta suboxides and thickness of 15.5 nm) incorporated PO4 3- ions from the solution, according to high resolution XPS spectra. The AFM analysis determined a high roughness with SEM detected pores (20 - 50 nm). The electrochemical studies of bare and anodically oxidized Ti-15Ta-5Zr alloy in Carter-Brugirard saliva of different pH values and saliva with 0.05M NaF, pointed to a nobler surface for the protected alloy, with a thicker electrodeposited oxide layer acting as a barrier against aggressive ions. The oxidized alloy significantly decreased corrosion current densities and total quantity of ions released into the oral environment in comparison with the bare one, at higher polarisation resistance and protective capacity of the electrodeposited layer. The impedance data revealed a bi-layered oxidation film formed by: a dense, compact, barrier layer in contact with the metallic substrate, decreasing the potential gradient across the metal/oxide layer/solution interface, reducing the anodic dissolution and a more permissive, porous layer in contact with the electrolyte. The open circuit potential for protected alloy shifted to nobler values, with thickening of the oxidation
film signifying long-term protection. - KEYWORDs : Ti-15Ta-5Zr alloy, Carter-brugirard saliva, Electrochemical behaviour, AFM, SEM
- AUTHORs : C. Vasilescu†, S. I. Drob, J. M. Calderon Moreno, P. Drob, M. Popa, and E. Vasilescu
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