• 한국해양공학회지
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• 제6권2호
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• pp.85-93
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• 1992

The only hardness of 2nd phase of martensite in dual phase steel which was composed of the martensite and ferrite was changed. Fatigue test was conducted by cantilever type of self-made rotated bending fatigue testing machine. The corrosion fatigue fracture behaviors of dual phase steel were investigated in 3% NaCl solution at $N_f$ = $1.5\times$$10^5$ $N_f$=1.0 $\times$ $10^6$ cycles. The fatigue strength was increased with increasing the hardness of 2nd phase. The size and number of corrsion pits were influenced by the 2nd phase hardness and pits remain constant in size just after they were transited into cracks. The life of crack initiation was effected by stress level. The shape of relation of $\Delta$K and da/dn has smaller scattering in it in 3% NaCl solution than that in air. The higher the 2nd phase hardness is, the higher the corrosion fatigue life becomes. Corrosion fatigue fracture behavior was effected by mechanics in case of $N_f$=1.5$\times$10$^5$$N_f$=1.5$\times$10$^6$ cycles.

• Corrosion Science and Technology
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• 제23권2호
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• pp.166-178
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• 2024

The localized corrosion resistance of UNS N07718 alloy was investigated after solution heat treatment. When the alloy was heat-treated at 1050 ℃ for 2.5 hours, it experienced an increase in average grain diameter, a reduction in grain boundary area, and the dissolution of delta phases along grain boundaries. Additionally, primary metallic nitrides (MN) and metallic carbides (MC), enriched with either Ti or Nb, were identified and exhibited a random distribution within the microstructures. Despite the solution heat treatment, the composition, diameter, and abundance of MNs and MCs remained relatively consistent. The critical pitting temperature (CPT), as determined by the ASTM G48-C immersion test, revealed similar values of 45 ℃ for both treated and untreated alloys. However, a decrease in maximum pit depth and corrosion rate was observed after the solution heat treatment. The microstructural changes that occurred during the heat treatment and their potential implications were discussed to understand the influence of the solution heat treatment.

• 산업기술연구
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• 제22권B호
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• pp.13-20
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• 2002

The purpose of this study is to investigate the effect of acid fog on the rust formation behavior of weathering steel (SMA50) which is used in uncoated bridges. Weathering steel didn't form the passive film under the environment of acid fog(pH5,6), whereas the environment of distilled water formed the protective oxide film. Therefore, the construction of weathering steel under the environment extremely exposed to SOx and NOx which are the main compositions of acid fog is not adequate. Fatigue limits of weathering steel under acid fog environment are remarkably decreased as compared with environment of distilled water. The corrosive constituents in acid fog has piled up the corrosion products on specimen surface and generated the corrosion pits. Because of the high stress concentration arising at this corrosion pit, relatively low fatigue limits were obtained for acid fog specimens.

• 대한기계학회논문집A
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• 제32권1호
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• pp.13-20
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• 2008

The purpose of this study is to investigate the effect of acid fog on the rust formation behavior of weathering steel (SMA50) which is used in un-coated bridges. Weathering steel didn't form the passive film under the environment of acid fog(pH5,6), whereas the environment of distilled water formed the protective oxide film. Therefore, the construction of weathering steel under the environment extremely exposed to SOx and NOx which are the main compositions of acid fog is not adequate. Fatigue limits of weathering steel under acid fog environment are remarkably decreased as compared with environment of distilled water. The corrosive constituents in acid fog has piled up the corrosion products on specimen surface and generated the corrosion pits. Because of the high stress concentration arising at this corrosion pit, relatively low fatigue limits were obtained for acid fog specimens.

• 한국세라믹학회지
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• 제32권11호
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• pp.1301-1307
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• 1995

Pitting corrosion of TiN film deposited on Inconel 600 by plasma assisted chemical vapor deposition (PACVD) was investigated. Cyclic potentiodynamic polarization (CPP) tests were conducted in order to determine the pit nucleation potentials, Enp, of the TiN-deposited sample and the bare Inconel 600 in deaerated NaCl solution at 25, 135 and 20$0^{\circ}C$. The effects of the TiN film thickness, the solution temperature and the Cl- concentration on Enp were studied. Enp of the TiN-deposited sample which had the film thickness above 1${\mu}{\textrm}{m}$ were higher than those of the bare Inconel 600 by 300~600mV at all the solution temperatures, implying the pitting resistance improvement of the TiN film. The morphologies of the pits generated after immersion test were examined with a scaning electron microscopy. The higher was the solution temperature, the more corrosion products, mainly composed of Cr and Ni oxides, were formed.

• 한국표면공학회지
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• 제32권3호
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• pp.393-400
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• 1999

The surface characteristics of nitrogen ion implanted iron aluminides were investigated using various electrochemical methods in $H_2$$SO_4$+KSCN and HCl solutions. Nitrogen ion implantation was performed with doses of $3.0$\times$10^{17}$ /ions/$\textrm{cm}^2$ at an energy of 150keV. Nitrogen ion implanted iron aluminides increased the corrosion potential and significantly decreased grain boundary activation, the active current density, and passive current density. Nitrogen implanted iron aluminides with Mo increased the corrosion, pitting potential, repassivation potential and │$E_{pit}$-$E_{corr}$│ value. Whereas, implanted iron aluminides containing boron reduced the pitting and repassivation potential in comparison with nitrogen implanted iron aluminides with Cr and Mo.o.

• 대한기계학회논문집
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• 제11권6호
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• pp.867-876
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• 1987

본 연구에서는 보통강재인 SS 41 강을 열처리하여 얻은 M.E.F.복합조직강의 모상입경변화와 3.5% NaCl수용액의 pH변화 조건하에서 반복굽힘피로실험을 하여 부식 피로파괴에 미치는 영향에 대해 고찰하였다.

• 상하수도학회지
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• 제20권5호
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• pp.737-745
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• 2006

The goal of this study is to present an external pit corrosion rate($p_{ecr}$) model with considering both the age of pipe and the soil characteristics. The correlation of nonlinear exponential model among conventional empirical models was a little higher than other empirical models in the prediction of $p_{ecr}$ according to the age of pipe. However, there has been a limit to predict Peer with the model by using only a pipe age since installation as a variable. The soil analysis results from sixty nine samples showed that all of the samples were non corrosive in the assessment of ANSI/AWWA scoring system. The correlation of soil corrosion factors and $p_{ecr}$ was also low. The application result of linear and nonlinear regression models that soil characteristics only showed a low correlation with $p_{ecr}$ Proposed nonlinear regression model in this study, with considering both the age of pipe and the soil characteristics, showed a little higher correlation ($R^2=0.46$) than conventional model.

• 한국표면공학회지
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• 제38권6호
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• pp.241-247
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• 2005

Effects of Al and Cr alloying elements on the corrosion behavior of Fe-Al-Cr alloy system was investigated using potentiodynamic and cyclic potentiodynamic polarization tests(CPPT) in the $H_2SO_4$ and HCI solutions. The corrosion morphologies in Fe-Al-Cr alloy were analysed by utilizing scanning electron microscopy(SEM) and EDX. It was found that the corrosion potential of Fe-20Cr-20Al was highest whereas the critical anodic current density and passive current density were lower than that of the other alloys in 0.1 M $H_2SO_4$ solution. The second anodic peak at 1000 mV disappeared in the case of alloys containing high Al and low Cr contents. Pitting potential increased with increasing Cr content and repassivation potential decreased with decreasing Al content in 0.1 M HCI solution. Fe-Al-Cr alloy containing high Al and Cr contents showed remarkably improved pitting resistance against $Cl^-$ attack from pit morphologies.

• Corrosion Science and Technology
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• 제10권2호
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• pp.60-64
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• 2011

Lean duplex stainless steels have been developed in Korea for the purpose of being used in the seawater systems of industry. There are also many important seawater systems in nuclear power plants. These systems supply seawater to cooling water condenser tubes, heat exchanger tubes, related pipes and chlorine injection systems. The flow velocity of some part of seawater systems in nuclear power plants is high and damages of components from corrosion are severe. The considered lean duplex stainless steels are STS329LD (20.3Cr-2.2Ni-1.4Mo) and STS329J3L (22.4Cr-5.7Ni-3Mo) and PRENs of them are 29.4 and 37.3 respectively. Physical, mechanical and micro-structural properties of them are evaluated, and electrochemical corrosion resistance is measured quantitatively in NaCl solution. Critical Pitting Temperatures (CPT)s are measured on these alloys and pit depths are evaluated using laser microscope. Long period field tests on these alloys are now being performed, and some results are going to be presented in the following study.