• Journal of Welding and Joining
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• 제17권5호
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• pp.89-96
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• 1999

The base metal and weld metal of alloy designed austenitic stainless steels were electrochemically tested in artificial sea water. Pitting resistance of 14 different stainless steels was evaluated by measuring pitting potential. The effect of alloy element to pitting potential was evaluated by changing chromium, nickel, sulfur content. The site of pitting initiation was observed by optical microscope. As a result of electrochemical test, pitting resistance of weld metal was higher than base metal, and rapidly cooled weld metal has higher pitting potential than slowly cooled weld metal. In case of primary δ-ferrite solidification, pitting potential was increased, but residual δ-ferrite was detrimental to pitting resistance. Chromium was more effective to pitting resistance than nickel, and sulfur was very detrimental element to pitting resistance.

• 한국표면공학회지
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• 제40권5호
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• pp.234-240
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• 2007

As a reactor coolant pump (RCP) is operated in the nuclear power system for a long time, so its surface is continuously contaminated by radioactive scales. In order to maintain for RCP internals, a special chemical decontamination process should be used to reduce the radiation from the RCP surface. In this study, applicable possibility in chemical decontamination for RCP was investigated for the various stainless steels. The stainless steel (STS) 304 showed the best electrochemical properties for corrosion resistance and the lowest weight loss ratio in chemical decontamination process model 3-1 than other materials. However, the pitting corrosion was generated in both STS 415 and STS 431 with the increasing numbers of cycle. The intergranular corrosion in STS 415 was sporadically observed. The sizes of their pitting corrosion were also increased with increasing cycle numbers.

• 열처리공학회지
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• 제17권1호
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• pp.29-35
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• 2004

The effect of low tempering in a temperature range of $150{\sim}400^{\circ}C$ on corrosion resistance in 420J2 stainless steel austenitized at $1000^{\circ}C$ was investigated by the application of salt spray test, electrochemical pitting test in 3.5% NaCl solution and DL-EPR test for intergranular corrosion in 0.5M $H_2SO_4$+0.01M KSCN solution. In salt spray test, good corrosion resistance was obtained in a tempering temperature range of $150{\sim}250^{\circ}C$. Pitting potential was increased to the tempering temperature of $250^{\circ}C$, but decreased with the increase of temperature up to $400^{\circ}C$ And it was thought that the degradation of pitting corrosion resistance showed at the tempering temperature of around $400^{\circ}C$ was due to the precipitation of $Cr_7C_3$ of $M_7C_3$ type. The degree of sensitization showed increasing tendency with the increase of tempering temperature, and also Cr depletion phenomena were observed in the vicinity of grain boundary.

• Journal of Welding and Joining
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• 제13권3호
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• pp.89-95
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• 1995

Effect of boron on corrosion resistance of Type 304 stainless steel has been studied. Boron tends to segregate at the grain boundaries during cooling after solution treatment, and so boron treated steel usually exhibits a ditch structure under the 10% oxalic acid test. However, it was found that the addition of 25 ppm boron in Type 304 steel has no effect on the general and pitting corrosion resistance while it has a little effect on the intergranular corrosion resistance.

• Corrosion Science and Technology
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• 제3권5호
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• pp.187-193
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• 2004

We have investigated the differences between the general corrosion and microbiologically influenced corrosion (MIC) of steels in terms of electrochemical behavior and surface phenomena. Corrosion potential of steels in the absence of SRB (sulfate-reducing bacteria) shifted to a low level and was maintained throughout the experimental period (40 days). The potential in the presence of SRB, however, shifted to a noble level after 20 days' incubation, indicating the growth of SRB biofilms on the test metal specimens and a formation of corrosion products. In addition, the color of medium inoculated with SRB changed from gray to black. The color change appeared to be caused by the formation of pyrites (FeS) as a corrosion product while no significant color change was observed in the medium without SRB inoculation. Moreover, corrosion rates of various steels tested for MIC were higher than those in the absence of SRB. This is probably because SRB were associated with the increasing corrosion rates through increasing cathodic reactions which caused reduction of sulfate to sulfide as well as formation of an oxygen concentration cell. The pitting corrosions were also observed in the SRB-inoculated medium.

• 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.

• 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.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.267-272
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• 2002

Pitting corrosion is a very common occurrence in marine structures. Therefore, the 3-D finite element analysis is carried out to determine the stress intensity factors at the pit depth and also at the surface of the pit. The pits are modeled as a part of sphere, based on the pit depth and the pit diameter as specified by the Ship Structural Committee. The pit depth and pit diameter are function of the percentage of pitting that the plate is subjected to. A dog-bone shaped specimen is subjected to different intensities of pitting and the stress intensity factors are determined under axial tensile loads.

• Corrosion Science and Technology
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• 제20권2호
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• pp.85-93
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• 2021

The corrosion damage of materials in marine environment mainly occurs by Cl^- ions due to the breakdown of passive films. Additionally, various characteristics in seawater such as salinity, temperature, immersion time, flow rate, and biological activity also affect corrosion characteristics. In this study, the corrosion characteristics of stainless steels (STS 304 and STS 316L) and anodized aluminum alloys (AA 3003 and AA 6063) were evaluated with seawater temperature parameters. A potentiodynamic polarization experiment was conducted in a potential range of -0.25 V to 2.0 V at open circuit potential (OCP). Corrosion current density and corrosion potential were obtained through the Tafel extrapolation method to analyze changes in corrosion rate due to temperature. Corrosion behavior was evaluated by measuring weight loss before/after the experiment and also observing surface morphology through a scanning electronic microscope (SEM) and 3D microscopy. Weight loss, maximum damage depth and pitting damage increased as seawater temperature increased, and furthermore, the tendency of higher corrosion current density with an increase of temperature attributed to an increase in corrosion rate. There was lower pitting damage and lower corrosion current density for anodized aluminum alloys than for stainless steels as the temperature increased.

• 동력기계공학회지
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• 제19권6호
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• pp.75-81
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• 2015

A deposited metal specimen of ER2594 which is a super duplex steel welding wire used to investigate the effect of sigma(${\sigma}$) phase on electrochemical corrosion characteristics was prepared by gas tungsten arc welding. Aging treatment was conducted for the specimen at the temperature range of $700^{\circ}C$ to $900^{\circ}C$ for 5 to 300 minutes after annealing at $1050^{\circ}C$. Corrosion current density has decreased a little with an increase of aging time over 60 minutes at $700^{\circ}C$ to $900^{\circ}C$ and the uniform corrosion of deposited metal had more influence on the precipitation of ferrite than the precipitation of sigma phase. Therefore, the precipitation of sigma phase did not have much effect on the uniform corrosion. Pitting potential representing pitting corrosion has shown decreasing tendency as the precipitation of sigma phase increased. The degree of sensitization representing intergranular corrosion has shown increasing tendency as the precipitation of sigma phase increased at $700^{\circ}C$ to $800^{\circ}C$, while it has decreased at $900^{\circ}C$ for 60 to 300 minutes.