• Corrosion Science and Technology
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• v.20 no.5
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• pp.266-280
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• 2021

Since 2020, the International Maritime Organization (IMO) has updated regulations on the sulfur content to be less than 0.5% in exhaust gas emitted from ships. Accordingly, the exhaust gas post-treatment device for ships, which is SOx/NOx reduction technology, was introduced. However, the exhaust gas post-treatment device is suffering corrosion because of the harsh corrosive environment formed by sulfate and chlorine oxide through the desulfurization process. In this investigation, cyclic potentiodynamic polarization (CPDP) experiment for UNS S31603 and UNS N08367 was performed in a green death solution that simulates the environment of a desulfurization device. The corrosion rate of UNS S31603 at the highest temperature was about 3 times higher than that of UNS N83067. Also, electron microscope scan revealed corrosion type UNS N83067 presents intergranular corrosion tendency. On the other hand, UNS S31603 was observed as general corrosion. The α values of UNS N08367 at 30 ℃ and 60 ℃ were higher than those of UNS S31603, thus UNS N08367 is considered to have a higher local damage tendency. Whereas, since the α value of UNS S31603 at 90 ℃ is larger than that of UNS N08367, UNS S31603 is considered to have a higher local damage trend.

• Journal of Surface Science and Engineering
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• v.54 no.4
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• pp.194-199
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• 2021

In this study, rebar corrosion detection sensor was fabricated using multi-walled carbon nanotubes (MWCNTs). MWCNTs were pre-treated in the acid electrolytes to attach the carboxylic acid to the surface of MWCNTs. The fabricated sensor was attached on the surface of rebar and it detected the corrosion of steel using LCR meter with variation of capacitance. The surface morphology and electrical properties were characterized using scanning electron microscope (SEM) and electrical test equipment, respectively. To verify the corrosion detection characteristics, comparison experiment using plastic bar was performed. Moreover, mechanism of corrosion detection sensor was discussed.

• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.997-1002
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• 2022

Oxyapatite[Ca₂Nd₈(SiO₄)₆O₂] glass-ceramics have been suggested as wasteforms for the immobilisation of rare-earth radioactive nuclides because of their high waste-loading capability and good chemical durability. In particular, a partitioning effect is predicted to contribute to an enhancement of corrosion resistance in glass-ceramics compared with that of conjugate glasses of the same composition. Because rare-earths are inherently insoluble nuclides, detection of changes in corrosion behavior between glass-ceramics and conjugate glasses under normal conditions is not easy. In this study, therefore, we revealed the partitioning effect by exposing glass-ceramics and glasses to solution of pH 2, 7 and 10 at 90 ℃ for 20 d. In addition, we proposed the corrosion mechanism for oxyapatite glass-ceramics under various corrosion conditions. Especially, the glassy phase dissolved first, followed by the oxyapatite phase during pH 7 corrosion.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.56-65
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• 2022

The electrochemical corrosion properties of austenitic AISI 304 steel subjected to a long-term-aging heat treatment were investigated. AISI 304 steel was aged at 700 ℃ for up to 10,000 h. The variation in the microstructure of the aged specimens was observed by optical microscopy and scanning electron microscopy. Electrochemical polarization experiments were performed to obtain the corrosion current density (Icorr) and corrosion potential (Ecorr). Analyses indicated that the metastable intermetallic carbide M₂₃C₆ formed near the γ/γ grain boundary and coarsened with increasing aging time; meanwhile, the δ-ferrite decomposed into the σ phase and into M₂₃C₆ carbide. As the aging time increased, the current density increased, but the corrosion potential of the austenitic specimen remained high (at least 0.04 ㎛/cm²). Because intergranular carbide was absent, the austenitic annealed specimen exhibited the highest pitting resistance. Consequently, the corrosion resistance of austenitic AISI 304 steel decreased as the aging heat treatment time increased.

• Corrosion Science and Technology
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• v.23 no.3
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• pp.235-245
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• 2024

DLC coatings have been widely applied in industrial fields that require high corrosion resistance due to their excellent mechanical characteristics and chemical stability. In this research, effects of DLC coating thickness and defects on corrosion resistance were investigated for application of metallic bipolar plates in polymer membrane electrolyte fuel cells (PEMFCs). Results revealed that a DLC coating thickness of 0.7 ㎛ could lead to a defect size reduction of about 75.9% compared to that of 0.3 ㎛.As a result of potentiodynamic polarization experiments, the current density under a potential of 0.6 V was measured to be less than 1 ㎂/cm²,which was an excellent value. Inparticular, the delamination ratio and the decrease rate of maximum pitting depth were up to 84.8% and 63.3%, respectively, with an increase in the DLC coating thickness. These results demonstrate that DLC coating thickness and defects are factors that can affect corrosion resistance of DLC coating and its substrate.

• Corrosion Science and Technology
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• v.23 no.4
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• pp.296-301
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• 2024

Steels have excellent mechanical properties and weldability. They are also economically producible. Thus, they are widely applied in various industries. However, they have a disadvantage in that rust can occur after a certain period of time. To compensate for this, Zn, which has excellent sacrificial corrosion resistance, can be coated on steels. With global zinc consumption increasing at the current rate, depletion is expected in the near future. Recently, POSCO has developed innovative Al-Zn-Si alloy coated steel sheets with better corrosion resistance than Zn coating. In this study, corrosion resistance, weldability, friction characteristics, and so on were evaluated compared to GI steel sheets to evaluate their applicability to automotive steel sheets. It showed excellent corrosion resistance even at a lower coating weight compared to GI steel sheet. It was also excellent in terms of galling and welding LME. Its spot welding life, electrodeposition coating, and bendability were equally excellent. This is presumed to be related to the formation of the Al-Zn-Si alloy phase at the interface of the coating layer.

• Journal of Power System Engineering
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• v.14 no.2
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• pp.71-77
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• 2010

This paper was studied on microstructure, mechanical properties and corrosion characteristics of 316L stainless steel pipe welds was fabricated by orbital welding process. S-Ar specimen was fabricated by using Ar purge gas and S-$N_2$ specimen was fabricated by using $N_2$ purge gas. Ferrite was not detected in weld metal of S-$N_2$ specimen but the order of 0.13 Ferrite number(FN) was detected in weld metal of S-Ar specimen. Oxygen and Nitrogen concentration of S-$N_2$ specimen was higher than S-Ar specimen on HAZ and inner bead. The welds microstructural characteristics of S-Ar and S-$N_2$ specimens are similar. The microvickers hardness values of S-Ar and S-$N_2$ specimens welds were similar and average values of each regions were in the range of 174~194. The microstructures of S-Ar and S-$N_2$ weld metal were full austenite by primary austenite solidification. The Solidification structures of S-Ar and S-$N_2$ weld metal were formed directional dendrite toward bead center. The potentiodynamic polarization curve of STS 316L pipe welds exhibited typical active, passive, transpassive behaviour. Corrosion current density$(I_{corr.})$ and corrosion rate values of S-Ar specimen in 0.1M HCl solution were $0.95{\mu}A/cm^2$ and $0.31{\mu}A$/year respectively. The values of S-$N_2$ specimen were $1.4{\mu}A/cm^2$ and $0.45{\mu}m$/year.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.4
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• pp.200-207
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• 2006

In addition to the basic properties of the base and top coating agents, corrosion resistance of non-chrome magni 565 coating and characteristics of coating film when coated to steel substrate were studied. The system had a good wettability at room temperature. Moreover, both the contact angle and surface tension were affected little by the viscosity of coating agent and surface roughness of the steel substrate. And the samples coated with optimal conditions showed a great corrosion resistance in salt spray test with 1500 hours or longer of initial appearance time of rust. The coating film was composed of overlapping layer of zinc and aluminium flakes, and the thickness of base coat increased with an increase of base coat viscosity. Based on the C-F peaks of 1,1-Difluoroethaen homo-polymer, it was thought that the base coat was an inorganic polymer bond layer. Meanwhile, the top coat showed C-F peaks of polytetrafluoroethylene with C-H peaks of phenol in FT-IR analysis. From the lower weight loss of base coat in TG analysis, it was thought that cross linking density of base coat was larger than that of top coat. It was thought that the small exothermic reactions observed in DSC curves were due to the thermosetting resins contained in the coating agents. Compared to the non-coated specimen, the coated sample showed more higher polarization resistance and corrosion potential with lower corrosion current density.

• Journal of Advanced Navigation Technology
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• v.9 no.2
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• pp.131-139
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• 2005

On this study, I constructed the reflective acoustic signal detecting system using 15MHz acoustic transducer. The most difficult problems discriminating the characteristics of the metal substance are the discriminating the corrosion state and seeking hidden defects by using none destructive testing. For solving these problems, at first, theoretic analysis has been proceeded on the acoustic V(z) characteristics which is very important on discriminating the material characteristics. For application the V(z) theory to discriminating corrosion state, the 100 and 500 won metal coins which are issued on the different years are used as the test samples. The experimental results showed the distinct differences among the coin's acoustic signals accorded to its issued years. I catched the common regulation by analysing the acquisited acoustic signals and convinced this technique to be very useful on corrosion discrimination of the metal substances by none destructive testing and also can be used to inspect on the aeronautical materials for safety navigation.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.1
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• pp.66-72
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• 2000

In these days, with development of industry, the use of machines and structures like ships, airplanes, bridges, power plants, and structure for construction has increased and these machines and structures are used in various corrosive environment. Especially, in case of STS 304, which is material for every kind of machine and chemical plant, it makes many problems related with corrosion and as a result of this, there are happening tremendous economic loss. Therefor, in this study, the test for polarization characteristics was carried out to study characteristics of crevice corrosion of STS 304 which is austenitic stainless steel, in NaCl environment.The main results obtained are as follows :1) Part of crevice is corroded, neighboring outside surface of crevice is passivation. 2) In polarization behavior, corrosion potential of STS 304 become more noble as the concentration of NaCl solution increased by 3.5% but the concentration increased over 3.5% that of STS 3.4 become less noble. 3) The current density under corrosion potential was high drained as concentration of NaCl solution increased by 3.5% but the concentration increased over 3.5%, the current density was low drained.