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Page : 200 - 208
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- 알루미늄 5052 및 6061 합금의 양극산화 표면처리를 통한 발수 특성 및 부식 특성 비교
- Aluminum alloy is used by adding various elements according to the needs of the industry. Aluminum alloys such as 5052 and 6061 are known to possess excellent corrosion resistance by adding Mg. Despite their excellent physical properties, corrosion can occur. To solve this problem, an anodization technique generally can improve corrosion resistance by forming an oxide structure with maximized hydrophobic properties through coatings. In this study, the anodizing technique was used to improve the hydrophobicity of aluminum 5052 and 6061 by creating porous nanostructures on top of the surface. An oxide film was formed by applying anodizing voltages of 20, 40, 60, 80, and 100 V to aluminum alloys followed by immersion in 0.1 M phosphoric acid for 30 minutes to expand oxide pores. Contact angle and corrosion characteristics were different according to the structure after anodization. For the 5052 aluminum, the corrosion potential was improved from -363 mV to -154 mV as the contact angle increased from 116° to 136°. For the 6061 aluminum, the corrosion potential improved from -399 mV to -124 mV when the contact angle increased from 116° to 134°.
- KEYWORDs : Hydrophobic, Anodization, Aluminum, Light Metal, Corrosion
- AUTHORs : 박영주, 정찬영†
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Page : 209 - 220
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- 탄소강 및 해드필드강의 파이프 조관에 따른 침식부식 거동에 대한 비교연구
- Erosion-corrosion behaviors of Hadfield steel under a neutral aqueous environment with fine SiO2 particles were examined and compared with those of conventional carbon steel. A range of electrochemical experiments (potentiodynamic polarization, linear polarization, and impedance), immersion test, and slurry pot test (i.e., erosion-corrosion test) were performed. Results showed that the Hadfield steel composed of austenitic matrix with (Fe,Mn)-based carbide had lower corrosion potential and higher corrosion current density than carbon steel with a typical ferrite/pearlite structure. In addition, pipe forming increased total corrosion rates (i.e., pure corrosion and erosion-enhanced corrosion rates). Nevertheless, the erosion-corrosion rate of Hadfield steel was much smaller. Morphological observation showed that local damage in the form of a crater by erosion-corrosion was more noticeable in carbon steel. The higher resistance of Hadfield steel to erosion-corrosion was attributed to its lower total erosion rates (i.e., pure erosion and corrosion-enhanced erosion rates) highly depending on surface hardness. This study suggests that Hadfield steel with higher resistances to flowing erosion-corrosion in an aqueous environment can be applied widely to various industrial fields.
- KEYWORDs : Hadfield steel, 13% Mn steel, Corrosion, Erosion, Pipe forming
- AUTHORs : 윤덕빈, 박진성, 이상철, 최종교, 황중기, 김성진†
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Page : 221 - 229
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- Zn-Al-Mg 합금도금강판의 도금 층 냉각속도 제어에 따른 미세조직 및 부식거동 분석
- To understand effects of cooling rates of coating layer on microstructures and corrosion behaviors of hot-dip alloy coated steel sheets (Zn-5%Al-2%Mg) in a neutral aqueous condition with chloride ion, a range of experimental and analytical methods were used in this study. Results showed that a faster cooling rate during solidification decreased the fraction of primary Zn, and increased the fraction of Zn-Al phase. In addition, interlamellar spacing became refined under a faster cooling rate. These modifications of the coating structure had higher open circuit potentials (OPC) with smaller anodic and cathodic current densities in the electrochemical
potentiodynamic polarization. Surface analyses after a salt spray test showed that the increase in the Zn-Al phase in the coating formed under a faster cooling rate might have contributed to the formation of simonkolleite (Zn5(OH)8Cl2·H2O) and hydrotalcite (ZnAl2(OH)6Cl2·H2O) with a protective nature on the corroded outer surface, thus delaying the formation of red rust. - KEYWORDs : Hot dip galvanizing, Zn-Mg-Al alloy coatings, Cooling rate, Corrosion, Microstructure
- AUTHORs : 이재원, 김성진†
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Page : 230 - 241
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- 오스테나이트계 중탄소 및 저탄소 스테인리스강의 입계부식 거동 분석
- Austenitic stainless steel has been widely used because of its good corrosion resistance and mechanical properties. However, intergranular corrosion can occur if the alloy is welded or aged. The objective of this study was to determine intergranular corrosion behaviors of austenitic medium carbon (0.05 wt%) and low carbon (0.02 wt%) stainless steel aged at several conditions. Alloys were evaluated according to ASTM A262 Practice A, ISO 12732 DL-EPR (double loop-electrochemical potentiokinetic reactivation) test, and ASTM A262 Practice C. The degree of sensitization and intergranular corrosion rate were obtained. The relationship between the degree of sensitization and the intergranular corrosion rate showed a very large fluctuation. Such behavior might be related to whether two-dimension tests or three-dimension tests were performed. On the other hand, regardless of carbon content of alloys, when the intergranular corrosion rate increased, the degree of sensitization also increased. However, the DL-EPR test showed a higher sensitivity than the Huey test for differentiating the intergranular corrosion property at a low intergranular corrosion rate, while the Huey test had a higher sensitivity than the DL-EPR test for distinguishing the intergranular corrosion property at a high intergranular corrosion rate.
- KEYWORDs : Stainless steel, Intergranular Corrosion, Degree of sensitization, Carbon segregation, Chromium depletion
- AUTHORs : 원석연, 김규빈, 유영란, 최승헌, 김영식†
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Page : 243 - 249
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- Failure Analysis of Stress Reliever in Heat-Transport Pipe of District Heating System
- The objective of the present study was to perform failure analysis of double-layered bellow (expansion joint), a core part of stress reliever, used to relieve axial stresses induced by thermal expansion of heattransport pipes in a district heating system. The bellow underwent tensile or compressive stresses due to its structure in terms of position. A leaked position sufferred a fatigue with a tensile component for decades. A cracked bellow contained a higher fraction of martensitic phase because of manufacturing and usage histories, which induced more brittleness on the component. Inclusions in the inner layer of the bellow acted as a site of stress concentration, from which cracks initiated and then propagated along the hoop direction from the inner surface of the inner layer under fatigue loading conditions. As the crack reached critical thickness, the crack propagated
to the outer surface at a higher rate, resulting in leakage of the stress reliever. - KEYWORDs : District heating, Heat-transport pipe, Stress reliever, Crack
- AUTHORs : Jeongmin Cho, Hobyung Chae, Heesan Kim, Jung-Gu Kim, Woo Cheol Kim, and Soo Yeol Lee†
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Page : 250 - 257
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- Synthesis and Electrochemical Properties of FexNbS2/C Composites as an Anode Material for Li Secondary Batteries
- Transition metal sulfide materials have emerged as a new anode material for Li secondary batteries owing to their high capacity and rate capability facilitated by fast Li-ion transport through the layered structure. Among these materials, niobium disulfide (NbS2) has attracted much attention with its high electrical conductivity and high theoretical capacity (683 mAh g?1). In this study, we propose a facile synthesis of Fex-NbS2/C composite via simple ball milling and heat treatment. The starting materials of FeS and Nb were reacted in the first milling step and transformed into an Fe-Nb-S composite. In the second milling step, activated carbon was incorporated and the sulfide was crystallized into FexNbS2 by heat treatment. The prepared materials were characterized by X-ray diffraction, electron spectroscopies, and X-ray photoelectron spectroscopy. The electrochemical test results reveal that the synthesized FexNbS2/C composite electrode demonstrates a high reversible capacity of more than 600 mAh g?1, stable cycling stability, and excellent rate performance for Li-ion battery anodes.
- KEYWORDs : Transition metal dichalcogenide, Niobium sulfide, Composite, Li battery, Electrochemical properties
- AUTHORs : Yunjung Kim and Jae-Hun Kim†
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Page : 258 - 272
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- Atmospheric Corrosion Behavior of Weathering Steel Exposed to the Outdoors for 10 Years in Korea
- Steel structures exposed to the outdoors experienced several types of corrosion, which may reduce their thickness. Since atmospheric corrosion can induce economic losses, it is important to consider the atmospheric corrosion behavior of a variety of metals and alloys. This work performed outdoor exposure tests for 10 years at 14 areas in Korea and calculated the atmospheric corrosion rate of weathering steel. This paper discussed the atmospheric corrosion behavior of weathering steel based on various corrosion factors. The average corrosion rates in coastal, industrial, urban, and rural areas were found to range from (2.83 to 4.23) μm/y, (2.99 to 4.23) μm/y, (1.72 to 3.14) μm/y, and (1.57 to 2.85) μm/y respectively. It should be noted that the maximum corrosion rate was about 6.0 times greater than the average corrosion rate. Regardless of the exposure sites, the color differences were increased, but the glossiness was reduced and there was no relationship between the corrosion rate and environmental factors and the glossiness.
- KEYWORDs : Weathering steel, Atmospheric corrosion, Corrosion rate, Color difference, Glossiness
- AUTHORs : Y. R. Yoo, S. H. Choi, and Y. S. Kim†
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Page : 273 - 281
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- Effect of Cu Addition on the Properties of Duplex Stainless Steels
- The effect of addition of Cu on the localized corrosion performance of aged duplex stainless steel in chloride media has yet to be explained in a consistent manner, and there is some controversy in the literature regarding the composition of stainless steel and the experimental conditions (pH, temperature, chloride concentration, etc.) used. In this work, the effect of the addition of Cu on the microstructure, hardness, and corrosion resistance of duplex stainless steel in an acidic chloride or high concentration sulfuric acid solutions was investigated for annealed and aged alloys. The Cu addition of annealed duplex stainless steel strengthened the alloy and reduced the ferrite contents of the alloy, and it also increased the polarization behavior in chloride or sulfuric solutions, except for the case of a high potential in acidic chloride solution. However, the Cu addition of aged duplex stainless steel reduced the formation of harmful phases such as sigma and kai and increased the polarization behavior in acidic chloride or sulfuric solutions up to 0.8 wt% of the Cu content, after which it slightly decreased at 0.8 wt% Cu or more.
- KEYWORDs : Duplex stainless steel, Copper, Sigma phase, Hardness, Corrosion
- AUTHORs : D. Hwangbo, Y. R. Yoo, S. H. Choi, S. J. Choi, and Y. S. Kim†
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Page : 282 - 289
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- 알루미늄 1050 합금의 양극산화 시간에 따른 산화피막 성장 거동 및 부식 손상 연구
- Aluminum 1000 series alloy, a pure aluminum with excellent workability and weldability, is mainly used in the ship field. Aluminum alloy can combine with oxygen in the atmosphere and form a natural oxide film with high corrosion resistance. However, its corrosion resistance and durability are decreased when it is exposed to a harsh environment for a long period of time. For solving this problem, a porous oxide film can be formed on the surface using an anodizing treatment method, a typical surface technique among various methods. In this study, aluminum 1050 alloy was anodized for 2 minutes, 6 minutes, and 10 minutes. The structure and shape of the oxide film were then analyzed to determine the corrosion resistance according to the thickness of the oxide film that changed depending on working condition using 15 wt% NaCl. After it was immersed in NaCl solution for 1, 5, and 10 days, corrosion damage was observed. Results confirmed that the thickness of the oxide film increased as the anodization time became longer. The depth of surface damage due to corrosion became deeper when the film was immersed in the 15 wt% NaCl solution for a longer period of time.
- KEYWORDs : Corrosion resistance, Aluminum alloy, Anodization time, Thickness, Porous oxide film
- AUTHORs : 최예지 · 정찬영†
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Page : 290 - 299
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- 양극산화 방법을 이용한 기능성 알루미늄 3003 합금의 표면 특성 및 부식 거동 연구
- Anodizing is an electrochemical surface treatment method conferring corrosion resistance and durability by forming a thick anodization film on the metal surface. Aluminum has a long service life and high thermal conductivity and formability, as well as excellent corrosion resistance. Aluminum 3003 alloy has improved formability, strength, and corrosion resistance due to the addition of a small amount of manganese. However, corrosion occurs in seawater and environments polluted with corrosion-inducing substances, which reduce corrosion resistance. Therefore, it is necessary to artificially form a thick anodized film to improve corrosion resistance. In this study, the anodization treatment time was 4 minutes, and voltages of 10 V, 20 V, 30 V, 40 V, 50 V, 60 V, 70 V, 80 V, 90 V, and 100 V were applied. The thickness and pore size of the oxide film increased according to the applied voltage. A barrier film was formed under voltage conditions from 10 V to 50 V, and a porous film was formed under voltage conditions from 60 V to 100 V. After anodizing, coating was applied. Wettability and corrosion resistance were observed before and after coating according to the surface shape and thickness of the oxide film.
- KEYWORDs : Anodization, Aluminum alloy, Hydrophilicity, Hydrophobicity, Corrosion resistance
- AUTHORs : 김지수 · 정찬영†
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