• Corrosion Science and Technology
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• 제8권6호
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• pp.209-216
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• 2009

In this study the effect of different surface finishing techniques on the pitting corrosion behaviour of a commercial 304 stainless steel alloy was investigated. Surface finishing methods were divided into two categories, i.e. mechanical and chemical. Mechanical treatment methods include power tooling such as grinding, emery paper brushing, stainless steel wire brushing and stainless steel shot blasting. Chemical treatment methods include chemical passivation (phosphoric acid, citric acid, nitric acid) and electro-cleaning (phosphoric acid and citric acid). Potentiodynamic polarization experiments were carried out in 3.5 wt. % NaCl solution at room temp. (20 $^{\circ}C$). The results showed that chemical treatment methods improved the corrosion resistance of stainless steel 304, measured in terms of pitting potential ($E_{pit}$). Corrosion resistance of the specimens was increased in the order of; electro-cleaning > manual passivation > mechanical cleaning. Surface of electro-cleaned specimens was smoother than rest of the surface treatment methods. Chrome content in chemically treated specimens was higher than in mechanically treated specimens as shown by EDX analysis.

• Journal of Advanced Marine Engineering and Technology
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• 제23권6호
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• pp.761-769
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• 1999

In this paper the effect of aging heat treatment to the Corrosion behavior for the Nimonic 80A superalloy was studied by AC Impedance methods. Tested solution was 3.5% with tempera-ture $25^{\circ}C$ Electro-chemical corrosion test were carried out for the Nimonic 80A super-alloy which solution heat treated at $1080^{\circ}C$ for 8 hours followed by aging heat treated at $650^{\circ}C,\;700^{\circ}C,\;750^{\circ}C\;800^{\circ}C$ and $850^{\circ}C$ with 16hours under vacuum environment. The obtained results were as follows; 1. Base metal and solution-treated materials were exhibited similar corrosion tendency as Ran-dle equivalent cell. The value of passive film resistance was 579 ohms for the base metal and 124,770 ohms for the solutionized metal such a difference was arose by the ${{\gamma}_^'}$ precipitate on the metal surface during heat treatment. 2. The measure value of $R_p$ for heat-treated at $650^{\circ}C,\;700^{\circ}C,\;800^{\circ}C$and $850^{\circ}C$ were 97,943, 93, 111, 26,961, 15,798 and 11,780ohm respectively. Which indicated that the passive film resistance Rp was reduced as aging temperature increased due to the growth of grain size and sensitization at the grain boundary. 3. The similar tendency was exhibited for corrosion behavior of the electro-chemical corrosion polarization method and AC impedance method and confirmed that AC impedance method was useful tool for corrosion research.

• Design & Manufacturing
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• 제13권1호
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• pp.13-18
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• 2019

The size and prospects of the domestic semiconductor equipment market are increasing every year. In the case of various parts used inside semiconductor equipments, high durability such as high strength and abrasion resistance is demanded. Particularly, the gases used in semiconductor production processes are toxic. In order to prevent such toxic gas leakage, a precision processing technique and a surface treatment technique for preventing corrosion are required. Electro-polishing is an electro-chemical method of polishing a metal surface to make it smooth and polished. Electro-polishing is mainly used in the finishing process of metal surface. Unlike mechanical polishing, electro-polishing is used in many fields, such as fine chemical etching equipment, since no damaged layer or burr, fine polishing groove and particles are generated. However, in order to withstand the gas used in the semiconductor equipment, the parts must have high corrosion resistance. However, the surface hardness generally become lowered through electro-polishing. Therefore, in this study, surface hardness were experimentally observed before and after electro-polishing. Then, a method of improving hardness by preparing a nitrided layer by plasma ion nitriding treatment.

• 한국수산과학회지
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• 제7권4호
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• pp.234-237
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• 1974

$5\%\;H_2SO_4$ 수용액에 연강재를 침적하여 두고 전압 100mV, 전류 100mA 하에 응력을 부가시킨 상태로 전기화학적인 부식을 시켜 부식으로 인한 질양손실 및 인장응력을 측정해 본 결과 다음과 같은 결과를 얻었다. 1. 부식된 질양척실은 부식시 부가응력이 높을 수록 커지며, 처음부터 천천히 부식질양이 점차 증가하여 어느 일정한 시간(본 실험에는 약 13시간)이 경과한 후에 서로 비례 관계가 성립함을 볼 수 있었다 . 2. 부가응력과 부식으로 인한 응력감소율은 서로 역비례 관계가 성립하며, 항복응력의 감소율과 인장응력의 감소율은 거의 일치하였다. 3. 재료외 불순물이 밀집한 부분이나 결정립계가 부식되어 점차 확대되었다. 4. 외력에 의한 내력(응력)이 산재하거나 가공경화로 사한 공간격자의 변화가 있는 불안전한 조직을 가진 재료는 부식의 응력감소율이 적었다.

• Journal of Welding and Joining
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• 제17권2호
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• pp.76-83
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• 1999

Fracture toughness({TEX}$J_{IC}${/TEX}) on 304 austenitic stainless steel weldments artificially degraded for long period under SCC environments were evaluated to investigate its reliability and environmental characteristics. Electro-chemical polarization tests were previously carried out to evaluate corrosion susceptiblility of weldment, and stress corrosion cracking was tested under various conditions of 3.5wt.% NaCl solution, the temperature of $25^{\circ}$C and $95^{\circ}$C, and oxygen concentration during 3000hours. From the results obtained, it was found that 304 stainless steel weldment was so susceptible under high temperature and high oxygen concentration of 3.5wt.% NaCl solution, and fracture toughness({TEX}$J_{IC}${/TEX}) was also considerably reduced by material degradation.

• Journal of Advanced Marine Engineering and Technology
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• 제22권5호
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• pp.660-669
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• 1998

In this paper the Hardness and Electro-chemical corrosion of the Nimonic 80A superalloy were studied. It aging heat treatments was carried out at $650^{\circ}C$, $700^{\circ}C$, $750^{\circ}C$,$800^{\circ}C$ and $850^{\circ}C$ with different time of 20min , 30min 1hour, 2hours, 4hours, and 16hours additionally 64hours and 128hours at $650^{\circ}C$. The obtained results were as follows; 1. As aging temperature increased the time for the maximum hardness was reduced from 128hours at $650^{\circ}C$ to 30min at $850^{\circ}C$ whereas the highest hardness was reduced from Hv 381 at $650^{\circ}C$ to Hv 321 at $850^{\circ}C$. 2. In the Electro-chemical corrosion test as a function of aging heat treatment time and tem-perature the corrosion potential was reversely proportional to Hardness which indicated the effects of ${\gamma}/{\gamma}'$ coherency of base material and precipitate. 3. Initiation point of the pitting was observed at grain boundary twin boundary and near${\gamma}'$ pre-cipitates. The results of composition analysis by EDS at this point indicated that sulphur originat-ed from 1N $H_2SO_4$ solution was found in depletion at the grain boundaries and the pit which arouse in the near precipitates were lack of Al Ti and Ni which are the main element of ${\gamma}'$ The depletion of such element was cause breakdown of passive film.

• Corrosion Science and Technology
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• 제14권5호
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• pp.213-217
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• 2015

Recently, household electronic industries require environmentally-friendly and highly functional steels in order to enhance the quality of human life. Customers especially require both excellent corrosion and abrasion resistant anti-fingerprint steels for digital TV panels. Thus POSCO has developed new functional electro-galvanized steels, which have double coated layers with organic-inorganic composites on the zinc surface of the steel for usage as the bottom chassis panel of TVs. The inorganic solution for the bottom layer consists of inorganic phosphate, magnesium, and zirconium compounds with a small amount of epoxy binder, and affords both improved adhesion properties by chemical conversion reactions and corrosion resistance due to a self-healing effect. The composite solution for the top layer was prepared by fine dispersion of organic-inorganic ingredients that consist of a urethane modified polyacrylate polymer, hardener, silica sol and a titanium complex inhibitor in aqueous media. Both composite solutions were coated on the steel surface by using a roll coater and then cured through an induction furnace in the electro-galvanizing line. New anti-fingerprint steel was evaluated for quality performance through such procedures as the salt spray test for corrosion resistance, tribological test for abrasion resistance, and conductivity test for surface electric conductance regarding to both types of polymer resin and coating weight of composite solution. New composite coated anti-fingerprint steels afford both better corrosion resistance and abrasion properties compared to conventional anti-fingerprint steel that mainly consists of acrylate polymers. Detailed discussions of both composite solutions and experimental results suggest that urethane modifications of acrylate polymers of composite solutions play a key role in enhanced quality performances.

• Corrosion Science and Technology
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• 제14권5호
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• pp.207-212
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• 2015

The purpose of this research was to synthesize fluorine modified waterborne polyurethane dispersion (F-WPU) by soap-free (internal emulsifier) emulsion polymerization techniques, to prepare coating solution based on fluorine modified waterborne polyurethane dispersion (F-WPU) and to compare the chemical and thermo-mechanical properties on the electrogalvanized steel sheet. Environmentally friendly F-WPU was prepared with a fluorinated polyol containing 60 wt% of fluorine. There are various ways of combining a wide variety of fluorinated polyols and diisocyanate to exhibit novel properties of waterborne polyurethane dispersion. Components of coating solution were largely divided into 4 kinds i.e., F-WPU, acrylic emulsion, silane coupling agent, and colloidal silicate. F-WPU coating solution on the electro-galvanized steel sheet showed excellent properties of corrosion resistance, alkali resistance and heat resistance, as compared to other coating solutions using a general waterborne resin. The F-WPU coating solution's reliable effects are possibly due to the fluorine atoms incorporated even in a small amount of F-WPU.

• 한국표면공학회지
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• 제37권4호
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• pp.200-207
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• 2004

Molybdate chemical conversion coating layer formed on EGI has been studied in view of corrosion resistance, surface morphologies, and phases formed. It was found that coating layer consists of$ MoO_3$, $MoO_2$, Mo oxides having lower valences than 4 and ZnO. It is interesting to note that the coating layer formed at high Mo concentration (30 g/l) in the temperature range of $40-60^{\circ}C$ exhibited relatively high corrosion resistance, although thickness of coating layer is nearly identical with those formed under the other conditions. It was believed that an increase of driving force due to high Mo concentration plays an important role in the formation of corrosion-resistant coating layer, probably due to tile formation of dense coating layer.

• Journal of Advanced Marine Engineering and Technology
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• 제24권6호
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• pp.70-77
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• 2000

In this paper, the effect of solution and age heat treatment to the corrosion behavior for the Ti-6Al-4V alloy were studied by cyclic polarization methods. Ti-6Al-4V was solution heat treated at $1,066^{\circ}C$ and $966^{\circ}C$ for 5 hours, and followed by age heat treated at $650^{\circ}C$, $600^{\circ}C$ and $550^{\circ}C$ with 1, 2, 4, 8 and 16 hours under vacuum environment. Test solution was 3.5% NaCl with temperature $25^{\circ}C$. The obtained results were as follows: 1. Base metal was exhibited higher electrical charge than that of solution and aged material. With decrease of solution-treatment temperature from 1066 to $966^{\circ}C$, the electrical charge was increased due to softening of micro structure. 2. The corrosion resistance of specimen that solution treated at $966^{\circ}C$ for 5 hours and age heat treated at 650, 660 and $550^{\circ}C$ were increased with increase of aging time to 4, 8 and 16 hours respectively, and then decreased. 3. In case of 316L stainless steel, measured charge and corrosion potential was 0.0627 coulomb and -614 mV respectively. Corrosion resistance of Ti-6Al-4V was higher than that of 316L.