• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.6
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• pp.477-482
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• 2008

The influence of dislocation substructure of metallic materials on ultrasonic velocity has been experimentally investigated. The test materials of pure Cu, brass (Cu-35Zn), 2.25Cr-1Mo steel, and AISI 316 with different stacking fault energy (SFE) are plastically deformed in order to generate dislocation substructures. The longitudinal wave velocit $(C_L)$ decreases as a function of tensile strain in each material. The $C_L$ of Cu-35Zn and AISI 316 decreases monotonously with tensile strain, but $C_L$ of Cu and 2.25Cr-1Mo steel shows plateau phenomena due to the stable dislocation substructure. The variation of ultrasonic velocity with the extent of dislocation damping and dislocation substructures is discussed.

• New & Renewable Energy
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• v.4 no.1
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• pp.31-36
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• 2008

Stainless steels have been widely considered as metallic bipolar plates, due to their passive surface film, which is good for corrosion resistance. However, the high resistivity of the passive film increases interfacial contact resistance between the bipolar plates and the electrodes. Stainless steels thermal spray coated with a mixture of tungsten carbide and stainless steel powders showed that the coated layer safely combined with the matrix but they suffered many internal defects including voids and cracks. Many cracks were formed in the coated layer and the interface of the matrix and the coated layer during the rolling process. The coated and rolled stainless steels showed lower interfacial contact resistance and corrosion resistance than bare stainless steel because of low resistivity of tungsten carbide and numerous defects, which caused crevice corrosion, in the coated layer.

• Journal of Korean Association for Spatial Structures
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• v.6 no.3 s.21
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• pp.77-86
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• 2006

The stress analysis of cold-formed channel section steel beams under transverse load is presented. The local buckling as well as the lateral buckling effects are included in the analysis. The analytical model is developed based on the thin-walled beam theory, and a one-dimensional finite element model is formulated to solve the analytical model. Numerical results are compared with AISI code. It shows that the proposed model is appropriate for predicting of stress as well as deflection of the cold-formed channel section beam.

• Tribology and Lubricants
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• v.17 no.6
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• pp.459-466
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• 2001

In this study, the effects of oxide layer formed on the contact parts of TiN coated ball and steel disk on friction characteristics in various sliding conditions were investigated. AISI52100 steel ball was used for the substrate of coated ball specimens, which were prepared by depositing TiN coating with 1(m in coating thickness. AISI1045 steel was used for the disk type counter-body. To investigate the effect of oxide layer on the contact parts of two materials, the tests were performed both in air for forming oxide layer on the contact parts and in nitrogen environment to avoid oxidation. From the test results, the frictional characteristic between the two materials was predominated by iron oxide layer that formed on wear tract of counter-body and this layer caused friction transition and high friction. And the adhesive wear occurred from steel disk to TiN coated ball caused the formation of oxide layer on counter parts between the two materials.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.2
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• pp.54-62
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• 2008

This investigation deals with machining AISI 52100 steel using a carbide-coated tool. The machining cutting force and tool tip temperature are measured online while turning using different cutting parameters. The surface roughness is also measured, but off-line after each cut. The obtained data are analyzed and the influence of the cutting parameters on the machining variables is determined in the form of plots. Regression models obtained from the results are tested using additional experimental data.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.1-5
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• 2008

Stainless steels have been widely considered as metallic separators, due to their passive surface film, which is good for corrosion resistance. However, the high resistivity of the passive film increases interfacial contact resistance between the separators and electrodes. Stainless steels thermal spray coated with a mixture of tungsten carbide and stainless steel powders showed that the coated layer safely combined with the matrix but they suffered many internal defects including voids and cracks. Many cracks were formed in the coated layer and the interface of the matrix and the coated layer during the rolling process. The coated and rolled stainless steels showed lower interfacial contact resistance and corrosion resistance than bare stainless steel because of low resistivity of tungsten carbide and numerous defects, which caused crevice corrosion, in the coated layer.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.289-290
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• 2015

In this experiment, nitriding treatment has been performed at $400^{\circ}C$ with various $N_2$ content and with changing processing time on AISI 420 martensitic stainless steel to investigate the expanded martensite layer (${\alpha}^{\prime}_N$ layer) formation behavior. Nitriding was implemented with changing $N_2$ content from 10% to 25% for 15 hrs and processing time was changed from 4hr to 15hr at 25% $N_2$ content. After treatment, the behavior of the ${\alpha}^{\prime}_N$ layer was investigated by optical microscopy, X-ray diffraction, and micro-hardness testing. Potentiodynamic polarization test was also used to evaluate the corrosion resistance of the samples. It was found that the surface hardness and ${\alpha}^{\prime}_N$ layer thickness increases with increasing $N_2$ percentage and processing time. Although their corrosion behaviors are worse than the bare sample.

• Journal of Welding and Joining
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• v.31 no.2
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• pp.49-56
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• 2013

We have investigated traits of clad metals in hot-rolled clad steel plates, sensitization and mechanical properties of STS 316 steel plate and carbon steel(A516). Clad steel plates were butt-weld by SAW+SMAW, and with the time of heat treatment as the variable, heat treatment was conducted at $625^{\circ}C$, for 80, 160, 320, 640, 1280 minutes. As a way to evaluate it, sectioned weldments and external surfaces were investigated to reveal the degree of sensitization by mechanical property, etching and those of EPR test, results were compared with it. In short, the purpose of this study is suggesting some considerations in developing on-site techniques to evaluate the sensitization of stainless steels.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.302-302
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• 2013

본 연구는 이온질화시 self-sputtering에 의한 AISI D2 소재의 표면경화에 대한 연구를 진행하였다. 이를 위해 이온질화시 질소가스와 아르곤 가스를 이용해 이온질화를 수행하였다. 이에 대한 결과는 optical micrograph (OM), scanning electron microscopy (SEM), X-ray diffraction(XRD), transmission electron microscopy (TEM)를 이용해 분석하였다. 실험결과, 소재의 경도는 570 HV에서 약 1470 HV까지 상승하였다. 극표면에 CrN-enriched layer의 형성 및 극표면 아래층에서 질소의 과포된 화합물층을 관찰할 수 있었다. 표면경화는, 극표면에 CrN-enriched layer의 형성과, 아래 N의 과포화에 의한 ${\gamma}$?autenite) phase, 그리고 diffusion layer의 형성에 의한 multi-layer의 형성으로 표면에 강화에 기여한것으로 사료된다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.401-405
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• 2001

The effects of oxide layer formed on TiN coated ball and counter-body have been investigated from the frictional point of view during sliding tests. AISI52100 steel ball was used for the substrate of coated specimens. Two types of coated specimens were prepared by depositing TiN coating with 1 and 4$\mu\textrm{m}$ in coating thickness. AISI1045 steel was used for the disk type counter-body. To investigate the effect of oxide layer on the contact parts of two materials, the tests were performed both in ambient for forming oxide layer on the contact parts and in nitrogen environment to avoid oxidation.