• Corrosion Science and Technology
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• 제14권6호
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• pp.313-324
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• 2015

Austenitic stainless steels have been widely used in many engineering fields because of their high corrosion resistance and good mechanical properties. However, welding or aging treatment may induce intergranular corrosion, stress corrosion cracking, pitting, etc. Since these types of corrosion are closely related to the formation of chromium carbide in grain boundaries, the alloys are controlled using methods such as lowering the carbon content, solution heat treatment, alloying of stabilization elements, and grain boundary engineering. This work focused on the effects of aging and UNSM (Ultrasonic Nano-crystal Surface Modification) on the intergranular corrosion of commercial 316L stainless steel and the results are discussed on the basis of the sensitization by chromium carbide formation and carbon segregation, residual stress, grain refinement, and grain boundary engineering.

• 대한금속재료학회지
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• 제49권10호
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• pp.780-789
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• 2011

The effects of alloyed carbon on the pitting corrosion, the general corrosion, and the passivity behavior of Fe18Cr10Mn0.4NxC (x=0~0.38 wt%) alloys were investigated by various electrochemical methods and XPS analysis. The alloyed carbon increased the general corrosion resistance of the FeCrMnN matrix. Carbon enhanced the corrosion potential, reduced the metal dissolution rate, and accelerated the hydrogen evolution reaction rate in various acidic solutions. In addition, carbon promoted the pitting corrosion resistance of the matrix in a chloride solution. The alloyed carbon in the matrix increased the chromium content in the passive film, and thus the passive film became more protective.

• 한국재료학회:학술대회논문집
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• 한국재료학회 1997년도 한국재료학회 추계학술발표회
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• pp.131-131
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• 1997

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 춘계학술대회
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• pp.77-80
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• 2007

To increase the capacity of hydrogen adsorption, transition metals were adopted as catalyst. The PAN-based CNFs involving transition metal were obtained by electrospinning method and heat treatment. To study the surface of carbon fibers, SEM analysis was conducted. The mass of transition metals were spreaded or covered among CNFs. XRD and EDX analysis were used to confirm transition metals on the surface of carbon fibers. Volumetric method was used for studying the capacity of hydrogen adsorption on the carbon fibers involving transition metals. In this study. vanadium has the best characteristics among chromium, titanium, and copper for hydrogen adsorption.

• 한국재료학회지
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• 제23권5호
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• pp.293-298
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• 2013

In this study, an HP-mod. type(KHR-45A), which is used as a heater tube material in the pyrolysis process, was evaluated for its carburizing properties. It was confirmed from the microstructural observation of the tubes that the volume fraction of carbide increased and that the coarsening of Cr-carbide generated as a degree of carburization increased. The depth of the hardened layer, which is similar to the thickness of the carburized region of each specimen, due to carburization is confirmed by measurement of the micro-Vickers hardness of the cross section tube, which thickness is similar to that of the carburized region of each specimen. Two types of chromium carbides were identified from the EBSD (electron back-scattered diffraction) image and the EDS (energy-dispersive spectroscopy) analysis: Cr-rich $M_{23}C_6$ in the outer region and Cr-rich $M_7C_3$ in the inner region of tubes. The EDS analysis revealed a correlation between the ferromagnetic behavior of the tubes and the chromium depletion in the matrix. The chromium depletion in the austenite matrix is the main cause of the magnetization of the carburized tube. The method used currently for the measurement of the carburization of the tubes is confirmed; carburizing evaluation is useful for magnetic flux density measurement. The volume fraction of the carbide increased as the measuring point moved into the carburized side; this was determined from the calculation of the volume fraction in the cross-section image of the tubes. These results are similar to the trends of carburization measurement when those trends were evaluated by measurement of the magnetic flux density.

• 공업화학
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• 제34권6호
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• pp.596-602
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• 2023

크롬 기반 금속유기골격체(MIL-101(Cr))를 제조하고 이들을 활용한 유사화학작용제 diisopropyl methyl phosphonate(DIMP) 흡착 실험을 통해 방독면 정화통이나 보호의 충진물질로서 활용 가능성을 평가하였다. MIL-101(Cr)은 조절인자로 아세트산(MIL-101(Cr)-A)과 수산화나트륨(MIL-101(Cr)-N)을 활용하여 각각 제작하였는데, 아세트산을 조절인자로 사용하였을 때 보다 넓은 비표면적과 높은 DIMP 흡착량을 보였다. MIL-101(Cr)-A는 상대습도 90% 환경에서 10일 동안 노출 시 흡착제 무게 대비 약 160%의 수분을 흡수하여 활성탄 등 다른 흡착제와 비교할 때 흡수율이 높았다. MIL-101(Cr)-A를 상대습도 90% 환경에서 일정기간 노출한 시료에 대한 DIMP 흡착량 실험 결과 24시간 이후에는 노출되지 않았을 때 흡착량의 약 40% 수준으로 감소하였으나, 이 흡착량은 상용 방독면 정화통 충진 활성탄과 비교하였을 때 여전히 높은 흡착량으로 추후 방독면 정화통이나 보호의 충진물질로서 활용가능성이 높은 것으로 판단된다.

• 열처리공학회지
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• 제9권3호
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• pp.169-176
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• 1996

Effect of retained austenite on rolling contact fatigue of nitrocarburized high-carbon chromium bearing steel has been investigated to develop surface-hardened bearing steel with imprved resistance to rolling contact fatigue. Fatigue tests were conducted in elesto-hydrodynamic lubricating conditions at a shaft speed of 5,000rpm, under max, hertzian stress of $492kg/mm^2$. Volume fraction of retained austenite in austenitic nitrocarburized STB2 steel was controlled by tempering at various temperature, $200{\sim}250^{\circ}C$. It was observed using TEM that decomposition of retained austenite during tempering at $250^{\circ}C$ was the highest in quantity, resulted in formation of lower bainite. Rolling contact fatigue life of the specimens with lower bainite, formed by decomposition of retained austenite, was improved in comparison with there of specimens with more amount of retained austenite.

• Corrosion Science and Technology
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• 제22권4호
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• pp.252-256
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• 2023

The galvanostatic polarization technique was used to accelerate corrosion in high chromium cast iron (HCCI) immersed in a simulated slurry solution of 0.1 mol dm^-3 H₂SO₄, 0.05 mol dm^-3 HCl, and 10 wt% SiC. The HCCI contained 27 wt% of Cr and 2.8 wt% of C, and its microstructure mainly comprised austenitic and carbide phases. A two-electrode system using a dense carbon rod and the HCCI sample was employed for the galvanostatic polarization by applying an anodic current for 24 hours. The corrosion rate increased upon applying the anodic current, but the increase was not significant, particularly for current densities higher than 10 µA cm^-2. Following polarization, the corrosion morphology revealed that the anodic current accelerated surface corrosion in the HCCI; however while the depth of the corroded area increased, the increase was not substantial. The propagation behavior of the anodic current and its impact on corrosion were further discussed.

• Carbon letters
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• 제22권
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• pp.60-69
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• 2017

Nitrogen-doped carbon nanosheets with a developed porous structure were prepared from polyurethane foams by hydrothermal carbonization following $ZnCl_2$ chemical activation. Scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, solid state $^{13}C$ nuclear magnetic resonance (NMR) spectra and X-ray photoelectron spectroscopy were used to characterize the nitrogen-doped carbon nanosheet structure and composition. The removal of Cr(VI) by the N-doped carbon nanosheets was investigated. The results showed that the maximum removal capacity for chromium of 188 mg/g was found at pH=2.0 with PHC-Z-3. pH had an important effect on Cr(VI) removal and the optimal pH was 2.0. Moreover, amino groups and carboxyl groups in the nitrogen-doped carbon nanosheet played important roles in Cr(VI) removal, and promoted the reduction of Cr(VI) to Cr(III).

• Carbon letters
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• 제9권1호
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• pp.23-27
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• 2008

The adsorption and reduction of Cr (VI) to Cr (III) by surface modified activated carbon (AC) in an aqueous solution was studied. The effects of surface modifications on the properties of the carbons were investigated by the analysis of specific surface area, carbon surface pH, acid/base surface values and functional groups. In order to understand the Cr(VI) adsorption and reduction ratio from Cr(VI) to Cr(III), the Cr adsorption capacity of AC was also measured and discussed by using inductively coupled plasma and UV spectrophotometer. The modifications bring about substantial variation in the chemical properties whereas the physical properties such as specific surface area, pore volume and pore size distribution nearly were not changed. Total Cr adsorption efficiency of as-received activated carbon (R-AC) and nitric acid treated activated carbon (N1-AC and N2-AC) were recorded on 98.2, 99.7 and 100%. Cr(III) reduction efficiency of R-AC increased largely from 0.4% to 28.3% compared to N1-AC and N2-AC.