• Journal of the Korean Society of Safety
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• v.21 no.3 s.75
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• pp.8-15
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• 2006

It is no wonder that mechanical structures are accompanied by problems related to corrosion after being exposed to long hours of work. Corrosion of mechanical structures has been the most serious problem in the field of industry. The present study employed a laser beam irradiation test to improve the corrosion resistance of degraded Cr-Mo steel, which was used for more than 60,000 hours. To find the optimum irradiation test condition for the corrosion resistance of degraded Cr-Mo steel, hardness and residual stress measurements, micro-structural observation, and the electrochemical potentiokinetic reactivation (EPR) tests were performed with changes in laser beam test conditions including laser beam output, diameter, and velocity. Thus, the present study indicates that the optimum test condition and absorption energy for a laser beam test need to be determined to enhance corrosion resistance of degraded Cr-Mo steel.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.209-211
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• 2005

Super duplex stainless steels have been used for offshore oil and gas piping systems which are subject to corrosion atmosphere, because they have excellent resistance to Stress Corrosion Cracking (SCC) and Pitting corrosion and high strength/weight ratio. Normally, the welding for duplex stainless steels has been peformed using GTAW with Ar shielding gas. However, in case of using Ar as shielding gas, the corrosion resistance at root weld metal will be deteriorated due to loss of nitrogen from weld deposit during welding. It is wellknown that the corrosion resistance of super duplex stainless can be restored by addition of nitrogen as shielding gas. In this study, we made super duplex welding with using several kinds of shielding and purging gases and investigated the relationship between shielding gas and corrosion resistance. Consequently, it was shown that corrosion resistance of weld deposit can be restored by addition of $N_{2}$ as shielding gas.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.5
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• pp.702-711
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• 1998

The characteristics of corrosion resistance for the surface of medium high carbon steels and low alloy steels utilizing as manufacturing the machinery structures and machining tools and treating by plasma/ion nitriding process have been studied in terms of electrochemical polarization behav-iors including corrosion potential(Ecorr) anodic polarization trends and polarization resistance(Rp) The seven base materials showed a clear passivation behavior for the polarization tests in the ASTM standard solution 1N ${H_2){SO_4}$ Although the treated surface by plasma nitriding for the seven test materials showed a significant increase in hardness the treatment gave a detri-mental effect in corrosion resistance. The various characteristics including corrosion potential polarization curves microstructures corrosion current polarization resistance among non-treat-ed nitriding and/or soft-nitriding treated specimens have been investigated and some of the mechanisms discussed.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.10
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• pp.883-887
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• 2016

This study aims to evaluate the corrosion behavior of a newly developed high-strength steel in marine environments. Metals used in seawater are easily deteriorated because of the presence of corrosive species such as chloride ions in it. Seawater causes much higher corrosion than fresh water. Thus, the corrosion of steel in marine environment has been recognized as a crucial problem in designing structures which cannot be cathodically protected. In this study, the corrosion resistance of a newly developed high-strength steel was evaluated. Four different specimens were tested to confirm the corrosion resistance. The exposure corrosion test was carried out by exposing the specimens to different marine environments such as atmospheric, tidal, splash, and submerged zones for two years. The specimens taken out from each location were cleaned ultrasonically and chemically prior to the evaluation of their corrosion resistance by the weight loss method. Finally, the pitting depth of the specimens was also measured to evaluate their pitting corrosion. The conditions used for the corrosion test were similar to the environmental conditions. The corrosion test results revealed that the corrosion rate and pitting corrosion of the newly developed high-strength steel was lower than that of the other carbon steels.

• Corrosion Science and Technology
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• v.15 no.4
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• pp.166-170
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• 2016

The combined process of porous type anodizing and desiccation treatment was applied to improve wettability of A1050 aluminum alloy. The water contact angles of anodized samples were increaseds considerably with desiccation treatment. However, there was no considerable effect of polishing and anodizing time on water contact angle. The corrosion behavior with the treatments was investigated electrochemically. The corrosion resistance of the samples in 3.5 mass% NaCl solutions increased with higher contact angle. Anodized and desiccated samples showed better corrosion resistance than un-desiccated samples around rest potential region.

• Corrosion Science and Technology
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• v.17 no.3
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• pp.129-137
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• 2018

The resistance to corrosion of additive manufactured (3D printing) Ti-6Al-4V alloys was investigated using micro-electrochemical tests. In terms of corrosion resistance, the acicular martensitic ${\alpha}^{\prime}$ phase in such additive manufactured Ti-6Al-4V was the focus of attention, and its behavior was distinct from that of conventional subtractive manufactured Ti-6Al-4V. To order to identify ${\alpha}^{\prime}$ phase, XRD tests were performed and micro Vickers hardness was measured for different grains (bright and dark grains) in the additive manufactured Ti-6Al-4V alloy. Micro-electrochemical tests were performed to measure corrosion resistance of bright and dark grains in the additive manufactured Ti-6Al-4V alloy with specially designed electrochemical micro-droplet cell. Critical pitting temperature (CPT) measurement was performed to evaluate the resistance to pitting corrosion of additive manufactured Ti-6Al-4V alloys with different volumes of ${\alpha}^{\prime}$ phase and subtractive manufactured Ti-6Al-4V alloy. The dark grains of the laminated Ti-6Al-4V alloy distributed broader than the bright grains measured with low microhardness. The dark grains of the Ti-6Al-4V alloy, which was rich in martensite ${\alpha}^{\prime}$, had lower general corrosion and pitting resistance than bright grains. As the fraction of martensite ${\alpha}^{\prime}$ phase increased, the resistance to the pitting corrosion decreased.

• Journal of the Korean Society for Heat Treatment
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• v.20 no.4
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• pp.195-202
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• 2007

Corrosion resistance and torque of M10 bolt coated with Magni 565 were investigated. Corrosion protection mechanism were also studied with the microstructure of coating film. The bolts with the optimum conditions showed around $10{\mu}m$ layer thickness, a great corrosion resistance in salt spray test and a proper torque in torque/tension test. But torque coefficient k increased with the number of bolting and clamping force of M10 bolt showed significantly lower than that of specified value 28.3kN. It was thought that the repeated bolting made the coating film peel off and powdery. The sample coated with optimum coating conditions showed more higher polarization resistance and corrosion potential than the specimens of top and base coat only. The base coating film was composed of lamellar zinc flakes, which provides a large sacrificial cathodic protection. Meanwhile, the top coating film was composed of organic aluminium pigments layer, which provides barrier protection to the corrosion circumstances.

• Journal of Technologic Dentistry
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• v.28 no.1
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• pp.61-66
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• 2006

Titanium alloys have been used for dental materials due to it's very good biocompatibility. Ti-6Al-4V alloy instead of pure titanium is being widely used as biomaterials has some characteristics such as high fatigue strength, tensile strength and corrosion resistance. But it has been reported recently that the vanadium element expresses cytotoxicity and carcinogenicity and the aluminium element is related with dementia of Alzheimer type and neurotoxicity. The Ti-Nb alloys has designed and examined corrosion resistance. Ti-3wt.%Nb($\alpha$type), Ti-20wt.%Nb(${\alpha}+{\beta}$type) and Ti-40wt.%Nb($\beta$type) alloys were melted by vacuum arc furnace. The corrosion resistance of Ti alloys was evaluated by potentiodynamic polarization test in the solution of 0.9% NaCl and 5% HCl. The results can be summarized as follows: 1) For the corrosion test in the solution of 0.9% NaCl and 5% HCl, the corrosion behaviour of Ti-Nb alloys was similar to ASTM grade 2 CP Ti. 2) The corrosion resistance of Ti-20Nb alloy was better than that of CP-Ti, Ti-3Nb, Ti-40Nb alloy in 0.9% NaCl and 5% HCl, solutions.

• Journal of Technologic Dentistry
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• v.30 no.2
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• pp.9-16
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• 2008

The surface microstructural changes, mechanical properties and corrosion resistance of Ti-Pd alloys for dental biomaterials have been investigated. Ti, Ti-Pd alloys were melted in arc furnace and the corrosion resistance of Ti-Pd alloys was evaluated by anodic polarization test. The surface microstructural changes and mechanical properties of Ti-Pd alloys were analysed by scanning electron microscope and Vickers micro-hardness tester. The vickers hardnees of pure Ti improved by addition of Pd but Ti-25Pd alloy showed decreasing compared with Ti-15Pd. And anodic polarization and potentiostatic test were conducted in 5% HCl to quantify the resistance to corrosion with the addition of Pd, There was no significant difference in corrosion resistance between pure Ti, Ti-5Pd and Ti-15Pd alloy. However, Ti-25Pd alloy showed decreasing compared with pure Ti in corrosion resistance. From these results, it was concluded that newly formulated Ti-15Pd experimental alloy have adequate hardness and high corrosion resistance, and this alloy is promising candidate for a successful dental casting alloy.

• Corrosion Science and Technology
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• v.2 no.2
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• pp.75-81
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• 2003

Chromium, molybdenum. and nitrogen are very important alloying elements in stainless steels and its effect was approved in pitting resistance equivalent (PRE) equations and many experimental results. However, Cr can improve the corrosion resistance, but facilitate the formation of sigma phase. Also. Mo has the same effect in stainless steels. If Cr and Mo are added at high amount to increase the corrosion resistance of stainless steel, corrosion resistance in annealed alloys can be improved, but in case of welding or aging heat treatment. its resistance will be drastically decreased. In this work, increasing Cr and N contents but decreasing Mo than the commercial alloys made the experimental alloys. Typical alloys are 25Cr-4.5Mo-0.43N alloy, 27Cr-4.7Mo-0.4N alloy, 27Cr-5.3Mo-0.25N alloy, 32Cr-2.6Mo-0.36N alloy. After annealing and aging heat treatment, microstructures, anodic polarization test, and pitting corrosion test were performed. Annealed alloys showed $100^{\circ}C$ of CPT and aged alloys showed the different tendency depending upon Cr and Mo contents(SFI)