한국부식방식학회

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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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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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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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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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Atmospheric Corrosion Behavior of Carbon Steel by the Outdoor Exposure Test for 10 Years in Korea
Steel was exposed in an atmospheric environment, and atmospheric environmental factors that include chloride, humidity, SO2, NO2 etc. induced the corrosion of steel. Corrosivity categories classified by SO2 and chloride deposition rate were low, but those classified by TOW were high in the Korean Peninsula, and on these environmental categories, the corrosivity of atmospheres classified by corrosion rate in carbon steel was low medium, C2-C3, and medium, C3 for zinc, copper, and aluminum. This work performed the outdoor exposure test for 10 years at 14 areas in Korea and calculated the atmospheric corrosion rate of carbon steel. The atmospheric corrosion behavior of carbon steel is discussed based on the various corrosion factors. When the corrosion product forms on carbon steel by atmospheric corrosion, cracks may also be formed, and through these cracks, the environmental factors can penetrate into the interior of the product, detach some of the corrosion products and finally corrode locally. Thus, the maximum corrosion rate was about 7.3 times greater than the average corrosion rate. The color difference and glossiness of carbon steel by the 10 year-outdoor exposure tests are discussed based on the corrosion rate and the environmental factors.
KEYWORDs : Carbon steel, Atmospheric corrosion, Corrosion rate, Color difference, Glossiness
AUTHORs : Y. R. Yoo, S. H. Choi, Y. S. Kim†

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Evaluation of the Inhibitive Performance of Cyperus Conglomeratus Leaves Extract as a Green Corrosion Inhibitor on Mild Steel XC70 in Acid Medium
The performance and inhibitory action of the aqueous extract of Cyperus Conglomeratus\\\\\\\'s leaves against corrosion of XC70 steel in a 1M HCl acid medium are studied by the determination of the weight loss, the potentiodynamic polarization curves analysis, and electrochemical impedance measurements (electrochemical techniques). The corrosion inhibitory efficiency of XC70 steel increases with the increasing concentration of the green inhibitor, however, the corrosion rate of the steel decreases. Weight loss measurements show that the maximum percentage corrosion inhibition efficiency is approximately 61.86 %, while the analysis of the mixed character polarization curves shows that the inhibitor could achieve an inhibition efficiency of 86.96%. The electrochemical impedance study confirmed that the value of the charge transfer resistance (Rct) increases and the value of the double layer capacity (Cdl) decreases with increasing concentration of the aqueous extract of Cyperus Conglomeratus\\\\\\\'s leaves, thus increasing the inhibition efficiency. The study showed that this aqueous extract acts by adsorption on the metal surface; this adsorption follows the Langmuir isotherm. This research work showed that Cyperus Conglomeratus leaves extract acts as an effective and eco-friendly inhibitor on mild steel in an acid medium.
KEYWORDs : Cyperus Conglomeratus, Green inhibitor, Weight losses, Electrochemical techniques
AUTHORs : Guessoum Belkis†, Hadj Seyd Abdelkader, Rahim Oumelkheir

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