In this study, we investigated the suppression of the corrosion of cast iron in a copper–cast iron double-layered canister under local corrosion of the copper layer. The cold spray coating technique was used to insert metals with lower galvanic activity than that of copper, such as silver, nickel, and titanium, between the copper and cast iron layers. Electrochemically accelerated corrosion tests were performed on the galvanic specimens in KURT groundwater at a voltage of 1.0 V for a week. The results revealed that copper corrosion was evident in all galvanic specimens of Cu–Ag, Cu–Ni, and Cu–Ti. By contrast, the copper was barely corroded in the Cu–Fe specimens. Therefore, it was concluded that if an inactive galvanic metal is applied to the areas where local corrosion is concerned, such as welding parts, the disposal canister can overcome local or non-uniform corrosion of the copper canister for long periods.

This study aimed to address the limitations of traditional plasma nitriding methods by implementing a short-term plasma oxy-nitriding treatment on the surface of AISI 420 martensitic stainless steel. This treatment involved the sequential formation of nitride and oxide layers, to enhance surface hardness and corrosion resistance, respectively. The process resulted in the formation of a 20 μm-thick nitride layer and a 3 μm-thick oxide layer on the steel surface. Initially, the hardness increased by 2.2 times after nitriding, followed by a subsequent decrease of approximately 31 % after oxidation. While the nitriding process reduced corrosion resistance, the subsequent oxidation process led to the formation of a passive oxide film, effectively resolving this issue. The pitting corrosion of the oxide passive film started at 82.6 mVssc, providing better corrosion resistance characteristics than the nitride layer. Consequently, the trade-off between surface hardness and corrosion resistance in plasma oxy-nitrided AISI 420 martensitic stainless steel is anticipated to be recognized as an innovative and comprehensive surface treatment process for biomedical components.

Attempts to use the molten salt system in various aspects such as MSR or energy storage systems are increasing. However, there are limitations in the molten salt-assisted technique due to the harsh corrosiveness of the molten salt, and a more detailed study on salt-induced corrosion is needed to solve this problem. In this study, corrosion behaviors of 80Ni-20Cr alloy in various salt environments such as eutectic NaCl-MgCl2 with NiCl2, CrCl2, and EuCl3 additives were investigated. Meanwhile, the corrosion acceleration effects of 80Ni-20Cr specimens were analyzed for various ceramic materials such as SiC, Al2O3, SiO2, graphite, and BN, and metallic materials such as Ni-based alloy, Fe-based alloy, and pure metals in a molten salt environment. The experiments were conducted at 973 K for up to 28 days, and after the experiment, the microstructural change of the specimen was analyzed through SEM-EDS, and salt condition was analyzed by ICP-OES.

Spent nuclear fuels in Korea are temporarily stored at the nuclear power plant site and it is expected that will become saturated from 2031. Deep geological disposal in engineered barrier system (EBS) is one of the most important options for disposing spent nuclear fuel. The disposal canister is the first barrier that prevents leakage of nuclides in the spent nuclear fuel to the environment. Therefore, the corrosion behavior of the canister materials are significant factors in determining the overall disposal period. Oxygen-free copper is the most widely used material for disposal canisters, and manufacturing methods include forging, cold spray, and electro-deposition. In this study, corrosion behavior of materials that have the potential to replace oxygen-free copper manufactured using various 3D printing method were analyzed. As a result of electrochemical analysis of various materials such as copper manufactured by the Atmospheric Plasma Spray (APS) process and Inconel 718 manufactured by the Direct Energy Deposition (DED) process, the possibility of replacing oxygen-free copper was confirmed.

In Korea, borated stainless steel (BSS) is used as spent fuel pool (SFP) storage rack to maintain nuclear criticality of spent fuels. As number of nuclear power plants and corresponding number of spent fuels increased, density in SFP storage rack also increased. In this regard, maintain subcriticality of spent nuclear fuels was raised as an issue and BSS was selected as structural material and neutron absorber for high density storage rack. Because it is difficult to replace storage rack, corrosion resistance and neutron absorbency are required for long period. BSS is based on stainless steel 304 and it is specified in the ASTM A887-89 standard depending on the boron concentration from 304B (0.20-0.29% B) to 304B7 (1.75-2.25% B). Due to low solubility of boron in austenitic stainless steel, metallic borides such as (Fe, Cr)2B are formed as secondary phase metallic borides could make Cr depletion near it which could decrease the corrosion resistance of material. In this paper, long-term corrosion behavior of BSS and its oxide microstructures are investigated through accelerated corrosion experiment in simulated SFP condition. Because corrosion rate of austenitic stainless steel is known to be dependent on the Arrhenius equation, a function of temperature, corrosion experiment is conducted by increasing the experimental temperature. Detail microstructural analysis was conducted with scanning electron microscope, transmission electron microscope and energy dispersive spectrometer. After oxidation, hematite structure oxide film is formed and pitting corrosions occur on the surface of specimens. Most of pitting corrosions are found at the substrate surface because corrosion resistance of substrate, which has low Cr content, is relatively low. Also, oxidation reaction of B in the secondary phase has the lowest Gibbs free energy compared to other elements. Furthermore, oxidation of Cr has low Gibbs free energy which means that oxidation of B and Cr could be faster than other elements. Thus, the long-term corrosion might affect to boron content and the neutron absorption ability of the material.

Corrosion cells that simulates engineering barrier system have been stored in an aerobic KURT environment for 10 years, which were recovered and dismantled in 2021. The test specimens were compressed copper (Com. Cu), Cold spray copper (CSC Cu), Ti Gr.2, STS 304, and Cast nodular iron. The specimens were buffered by compact Ca-type Gyeongju bentonite (KJ-I) and compact Na-type Wyoming bentonite. And the corrosion cells were exposed to KURT groundwater at 30°C for about 10 years (3,675 days). As a result of the long-term experiment in aerobic environment, it was confirmed that Na-bentonite is more advantageous for inhibiting corrosion than Ca-bentonite. The corrosion thickness of the most specimens in Ca bentonite was slightly lower than in Na bentonite until the initial 500 days, but after 10 years, the corrosion thickness of copper and cast iron specimens in Na bentonite was clearly lower. The corrosion thickness of the copper specimen in Na bentonite was very low about 0.5 um in both Com. Cu and CSC Cu. Moreover, the corrosion thickness in Ca bentonite was very high about 4 um for Com. Cu and 6 um for CSC Cu. In the case of cast iron, the corrosion thickness in Na bentonite was about 13 um, and 15 um in Ca bentonite. The common feature of copper and cast iron specimens in Ca bentonite, which showed a high corrosion thickness, is the forming of a white mineral deposition layer on the specimen surface, which was presumed to be some kind of feldspar. On the other hand, it was found that the STS304 and Ti specimens were hardly corroded even after 10 years. In conclusion, when a white mineral deposition layer was formed on the specimen surface, the corrosion thickness always increased sharply than before, and thus it was estimated that the generation of the mineral deposition layer cause the increase of bentonite permeability, and rather the weakening of existing passive corrosion film.

Microbiologically Influenced Corrosion (MIC) occurring in underground buried pipes of API 5L X65 steel was investigated. MIC is a corrosion phenomenon caused by microorganisms in soil; it affects steel materials in wet atmosphere. The microstructure and mechanical properties resulting from MIC were analyzed by OM, SEM/EDS, and mapping. Corrosion of pipe cross section was composed of ① surface film, ② iron oxide, and ③ surface/internal microbial corrosive by-product similar to surface corrosion pattern. The surface film is an area where concentrations of C/O components are on average 65 %/ 16 %; the main components of Fe Oxide were measured and found to be 48Fe-42O. The MIC area is divided into surface and inner areas, where high concentrations of N of 6 %/5 % are detected, respectively, in addition to the C/O component. The high concentration of C/O components observed on pipe surfaces and cross sections is considered to be MIC due to the various bacteria present. It is assumed that this is related to the heat-shrinkable sheet, which is a corrosion-resistant coating layer that becomes the MIC by-product component. The MIC generated on the pipe surface and cross section is inferred to have a high concentration of N components. High concentrations of N components occur frequently on surface and inner regions; these regions were investigated and Na/Mg/Ca basic substances were found to have accumulated as well. Therefore, it is presumed that the corrosion of buried pipes is due to the MIC of the NRB (nitrate reducing bacteria) reaction in the soil.

본 논문은 철계-형상기억합금(Fe-SMA)의 부식특성을 평가하기 위한 실험적 연구이다. 연구를 수행하기 위해 동전위 분극실험을 통해 Fe-SMA의 부식성능을 평가하였다. 시편을 3전극 플렛셀에 설치 후 전위차계를 이용하여 –200mV∼1000mV 구간의 전위를 2mV/s으 속도로 측정하였다. 기준전극 및 상대전극으로 각각 SCE 기준전극과 백금 와이어를 이용하였다. 동전위 분극곡선 및 타펠 피팅을 이용하여 부식전위 및 부식전류밀도를 측정하였다. Fe-SMA의 부식특성을 직관적으로 확인하기 위해 SD400 철근을 비교군으로 설정하였다. 염화물 환경에서 Fe-SMA의 부식성능을 확인하기 위해 3.5wt% 농도의 NaCl 용액에서 실험을 실시하였으며, 콘크리트 환경에서 Fe-SMA의 부식성능을 확인하기 위해 CaO를 이용하여 수용액의 pH를 13으로 조절하였다. 실험결과 Fe-SMA는 SD400 대비 모든 조건에서 우수한 내부식성이 나타났다. Fe-SMA의 콘크리트 환경에서 내부식성은 우수한 것으로 나타났다. 하지만 Fe-SMA가 염화물에 노출되면 부식저항이 급격히 감소되는 것으로 나타났다. 따라서 염화물에 직접적으로 노출되는 환경에서 Fe-SMA를 사용할 경우 부식을 방지하기 위한 적절한 조치가 필요할 것으로 사료된다.

Martensitic stainless steel is commonly used in the medical implant instrument. The alloy has drawbacks in terms of strength and wear properties when applied to instruments with sharp parts. 440C STS alloy, with improved durability, is an alternative to replace 420 J2 STS. In the present study, the carbide precipitation, and mechanical and corrosion properties of STS 440C alloy are studied as a function of different heat treatments. The STS 440C alloy is first austenitized at different temperatures; this is immediately followed by oil quenching and sub-zero treatment. After sub-zero treatment, the alloy is tempered at low temperatures. The microstructures of the heat treated STS 440C alloy consist of martensite and retained austenite and carbides. Using EDX and SADP with a TEM, the precipitated carbides are identified as a Cr23C6 carbide with a size of 1 to 2 μm. The hardness of STS 440C alloy is improved by austenitization at 1,100 oC with sub-zero treatment and tempering at 200 oC. The values of Ecorr and Icorr for STS 440C increase with austenitization temperature. Results can be explained by the dissolution of Cr-carbide and the increase in the retained austenite. Sub-zero treatment followed by tempering shows a little difference in the properties of potentiodynamic polarizations.

The corrosion behavior of Hastelloy C-276 was investigated to identify its applicability for carbon-anode-based oxide reduction (OR), in which Cl2 and O2 are simultaneously evolved at the anode. Under a 30 mL·min-1 Cl2 + 170 mL·min-1 Ar flow, the corrosion rate was less than 1 g·m-2·h-1 up to 500℃, whereas the rate increased exponentially from 500 to 700℃. The effects of the Cl2-O2 composition on the corrosion rate at flow rates of 30 mL·min-1 Cl2, 20 mL·min-1 Cl2 + 10 mL·min-1 O2, and 10 mL·min-1 Cl2 + 20 mL·min-1 O2 with a constant 170 mL·min-1 Ar flow rate at 600℃ was analyzed. Based on the data from an 8 h reaction, the fastest corrosion rate was observed for the 20 mL·min-1 Cl2 + 10 mL·min-1 O2 case, followed by 30 mL·min-1 Cl2 and 10 mL·min-1 Cl2 + 20 mL·min-1 O2. The effects of the chlorine flow rate on the corrosion rate were negligible within the 5–30 mL·min-1 range. A surface morphology analysis revealed the formation of vertical scratches in specimens that reacted under the Cl2-O2 mixed gas condition.

The corrosion behavior of the Inconel X-750 alloy was investigated for its potential application under a Cl2-O2 mixed gas flow in an Ar atmosphere. The corrosion rate was found to be negligible at temperatures up to 400℃ under a flow rate of 30 mL·min-1 Cl2 + 170 mL·min-1 Ar, whereas an exponential increase was observed in the corrosion rate at temperatures greater than 500℃. The suppression of the corrosion reaction due to the presence of O2 was verified experimentally at flow rates of 30 mL·min-1 Cl2 (4.96 g·m-2·h-1), 20 mL·min-1 Cl2 + 10 mL·min-1 O2 (2.02 g·m-2·h-1), and 10 mL·min-1 Cl2 + 20 mL·min-1 O2 (1.34 g·m-2·h-1) under a constant Ar flow rate of 170 mL·min-1 at 600℃ for 8 h. The surface morphology analysis results revealed that porous surfaces with tunnel-type holes were produced under the Cl2-O2 mixed-gas condition. Furthermore, the effects of the Cl2 flow rate on the corrosion rate were investigated, indicating that its impact was negligible within the range of 5–30 mL·min-1 Cl2 at 600℃.

Here, the stability of stainless steel 316 (SS-316) was investigated to identify its applicability in the oxide reduction process, as a component in related equipment, to produce a complicated gas mixture composed of O2 and Cl2 under an argon (Ar) atmosphere. The effects of the mixed gas composition were investigated at flow rates of 30 mL/min O2, 20 mL/min O2 + 10 mL/min Cl2, 10 mL/min O2 + 20 mL/ min Cl2, and 30 mL/min Cl2, each at 600℃, during a constant argon flow rate of 170 mL/min. It was found that the corrosion of SS-316 by the chlorine gas was suppressed by the presence of oxygen, while the reaction proceeded linearly with the reaction time regardless of gas composition. Surface observation results revealed an uneven surface with circular pits in the samples that were fed mixed gases. Thermodynamic calculations proposed the combination of Fe and Ni chlorination reactions as an explanation for this pit formation phenomenon. An exponential increase in the corrosion rate was observed with an increase in the reaction temperature in a range of 300 ~ 600℃ under a flow of 30 mL/min Cl2 + 170 mL/min Ar.

Evaluation of the durability and stability of materials used in power plants is of great importance because parts or components for turbines, heat exchangers and compressors are often exposed to extreme environments such as high temperature and pressure. In this work, high-temperature corrosion behavior of 316 L stainless steel in a carbon dioxide environment was studied to examine the applicability of a material for a supercritical carbon dioxide Brayton cycle as the next generation power plant system. The specimens were exposed in a high-purity carbon dioxide environment at temperatures ranging from 500 to 800 oC during 1000 hours. The features of the corroded products were examined by optical microscope and scanning electron microscope, and the chemical compound was determined by x-ray photoelectron spectroscopy. The results show that while the 316 L stainless steel had good corrosion resistance in the range of 500-700 oC in the carbon dioxide environment, the corrosion resistance at 800 oC was very poor due to chipping the corroded products off, which resulted in a considerable loss in weight.

ber reinforced polymer (FRP) reinforcing bars for concrete structure have been extensively investigated and a number of FRP bars are commercially available. However, major shortcoming of the existing FRP bars is low elastic modulus compared to conventional steel bars. Because of these reasons, FRP Hybrid Bar which have the concept of material hybridization(synthetic resins, deformed bar, glass fiber etc) for concrete structures have been developed. One of main features of this bar is corrosion resistance and this is important to confirm this anti-corrosion capacity of FRP Hybrid Bar. In this study, galvanic corrosion current behavior of 3 types of specimens, including two types of FRP Hybrid Bars and one conventional steel rebar, was investigated under the 0%, 1.5%, 3% and 6% salt water ratio condition. The result of this study can be used to evaluate the applicability of FRP Hybrid Bar to concrete structures.

To overcome shortcomings of fiber reinforced polymer (FRP), a hybridized FRP rebar was developed by the authors. This hybrid bar herein called “FRP Hybrid Bar” was fabricated by adopting advantages from two different materials, including glass fiber reinforced polymer (GFRP). Corrosion resistant characteristics of FRP Hybrid Bar were evaluated and the test results were explained in this paper. The use of the alternative reinforcement could allow concrete structures to extend life-span, to save maintenance and repair costs, etc. if the FRP Hybrid Bar was applied to RC structures located in a very corrosive environment, such as marina or harbor areas.

티타늄은 표면에 형성되는 보호성 부동태 피막 때문에 일반부식과 해수에서 내식성이 강하지만 염산, 황산, 인산 등의 산에서는 보호성 산화물 피막이 파괴된다고 알려져 있다. 본 연구에서는 Ti에 Al 및 V등을 첨가한 α+β계에 대하여 1066℃와 966℃에서 5시간 용체화 열처리를 실시하고, 이 시편을 550℃, 600℃, 및 650℃에서 각각 1시간, 4시간, 8시간 및 16시간 시효열처리한 후 마이크로비커스 경도를 측정하고, 이 시편을 1N H₂SO₄ 용액에서 전기화학적 분극법으로 부식을 계측하였으며, 분극을 마친 시편의 표면을 현미경 조직사진으로 부식상태를 검토하였다. 시험 결과 용체화열처리한 시편이 모재와 시효열처리한 시편보다 높은 내식성을 나타내며. 용체화 온도가 높고 시간이 길어질수록 내식성은 증가하였다.