• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.899-904
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• 2011

This This study aims to verify burr formation and to remove the burrs in micro-channel fabrication using micro-machining tools. The machining processes are combined with micro-milling and magnetic abrasive deburring for AISI316 stainless steel. Depending on the micro-milling conditions that are applied, burrs are formed around the side walls. Magnetic abrasive deburring is used to remove these burrs. AISI316 stainless steel is a nonferrous material and its magnetic flux density, which is an important parameter for efficient magnetic abrasive deburring, is low. To enhance this magnetic flux density, we design and build a magnetic array table. The effect of removing burrs is evaluated via SEM and a surface tester.

• Journal of the Korean institute of surface engineering
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• v.46 no.5
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• pp.192-196
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• 2013

Stainless steels (AISI 316L) are carburized by Inductively coupled plasma using $CH_4$ and Ar gas. The ${\gamma}_c$ phase(S-phase) is formed on the surface of stainless steel after carburizing process. The XRD peak of carburized samples is shifted to lower diffracting angle due to lattice expansion. Overall, the thickness of ${\gamma}_c$ phase showed a linear dependence with respect to increasing temperature due to the faster rate of diffusion of carbon. However, at temperatures above 500, the thickness data deviated from the linear trend. It is expected that the deviation was caused from atomic diffusion as well as other reactions that occurred at high temperatures. The interfacial contact resistance (ICR) and corrosion resistance are measured in a simulated proton exchange membrane fuel cell (PEMFC) environment. The ICR value of the carburized samples decreased from 130 $m{\Omega}cm^2$ (AISI 316L) to about 20 $m{\Omega}cm^2$. The sample carburized at 200 showed the best corrosion current density (6 ${\mu}Acm^{-2}$).

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.21-21
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• 2010

AISI 316L 용접금속의 크롬/니켈 당량비에 따른 시그마상의 영향을 알아보기 위하여 응고모드가 다른 3종류의 플럭스 코어드 와이어를 제작하였다. AISI 316L 시편에 FCAW 프로세스를 적용한 용접재를 $650^{\circ}C$, $750^{\circ}C$, $850^{\circ}C$, $950^{\circ}C$에서 각 각 1H, 5H, 24H, 72H동안 열처리하였다. 크롬/니켈 당량비가 높을수록 즉, 크롬의 함량이 높아질수록 $\delta$-페라이트 함량은 증가하였으며, $\delta$-페라이트는 고온에서 시그마상으로 변태되었다. $\delta$-페라이트는 $650^{\circ}C$에서 가장 느리게 분해되었으며 $850^{\circ}C$에서 가장 활발히 분해되었다. 용접부의 특성상 크롬과 니켈 등의 합금원소에 의하여 응고온도범위가 넓어져 $950^{\circ}C$에서도 시그마상이 석출되었으며, 5시간 이상 유지 시 구형으로 존재하였다. 충격시험 시 시그마상에 의해 취약해진 inter-dendrite 를 따라 파면이 형성되었으며, $-100^{\circ}C$이하의 극저온에서는 시그마상의 양과 무관하게 충격흡수에너지는 0에 가까워졌다. 하지만 3%미만의 $\delta$-페라이트를 함유하는 AF모드에서 발생한 DDC와 미량의 시그마상은 충격흡수에너지에 결정적인 영향을 미치지 않았다.

• Proceedings of the Korean Vacuum Society Conference
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• 2008.08a
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• pp.318-318
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• 2008

• Journal of the Korean institute of surface engineering
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• v.42 no.3
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• pp.116-121
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• 2009

The 2-step low temperature plasma processes (the combined carburizing and post-nitriding) offer the increase of both surface hardness and thickness of hardened layer and corrosion resistance than the individually processed low temperature nitriding and low temperature carburizing techniques. The 2-step low temperature plasma processes were carried out for improving both the surface hardness and corrosion resistance of AISI 316L stainless steel. The influence of gas compositions on the surface properties during nitriding step were investigated. The expanded austenite (${\gamma}_N$) was formed on all of the treated surface. The thickness of ${\gamma}_N$ and concentration of N on the surface increased with increasing both nitrogen gas and Ar gas levels in the atmosphere. The thickness of ${\gamma}_N$ increased up to about $20{\mu}m$ and the thickness of entire hardened layer was determined to be about $40{\mu}m$. The surface hardness was independent of nitrogen and Ar gas contents and reached up to about 1200 $HV_{0.1}$ which is about 5 times higher than that of untreated sample (250 $HV_{0.1}$). The corrosion resistance in 2-step low temperature plasma processed austenitic stainless steels was also much enhanced than that in the untreated austenitic stainless steels due to a high concentration of N on the surface.

• Journal of Ocean Engineering and Technology
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• v.25 no.6
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• pp.60-65
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• 2011

A low temperature plasma carburizing process was performed on AISI 316L austenitic stainless steel to achieve an enhancement of the surface hardness without degradation of its corrosion resistance. Attempts were made to investigate the influence of the processing temperatures on the surface hardened layer during low temperature plasma carburizing in order to obtain the optimum processing conditions. The expanded austenite (${\gamma}_c$) phase, which contains a high saturation of carbon (S phase), was formed on all of the treated surfaces. Precipitates of chromium carbides were detected in the hardened layer (C-enriched layer) only for the specimen treated at $550^{\circ}C$. The hardened layer thickness of ${\gamma}_c$ increased up to about $65{\mu}m$ with increasing treatment temperature. The surface hardness reached about 900 $HK_{0.05}$, which is about 4 times higher than that of the untreated sample (250 $HK_{0.05}$). A minor loss in corrosion resistance was observed for the specimens treated at temperatures of $300^{\circ}C{\sim}450^{\circ}C$ compared with untreated austenitic stainless steel. In particular, the precipitation of chromium carbides at $550^{\circ}C$ led to a significant decrease in the corrosion resistance. A diamond-like carbon (DLC) film coating was applied to improve the wear and friction properties of the S phase layer. The DLC film showed a low and stable friction coefficient value of about 0.1 compared with that of the carburized surface (about 0.45). The hardness and corrosion resistance of the S phase layer were further improved by the application of such a DLC film.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.4
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• pp.42-50
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• 1995

To study the effect of welding methods on the Stress Corrosion Cracking (SCC) behavior of welded AISI type 316L and 304 austenitic stainless steel, the Slow Strain Rate Technique(SSRT) has been adopted in the boiling 45 wt% $MgCl_2$ solution. The results are as follows. 1) Welded sections are more susceptible than base metal in SCC, and the rank of SCC, and the rasistance in welding method is TIG, MIG, $CO_2$ and ARC. 2) The Ultimate tensile strength(UTS) and the strain of both base metal and welded joint are reduced as decreasing extension rate. 3) The SCC resistance of 316L base metal and welded sections are superior than that of 304. 4) The tendency of pitting and the SCC suseptibility are agreed well, and the SCC site is welded deposit section in 316L whereas HAZ in 304.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.666-670
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• 2001

To improve the corrosion resistance of separator wet-seal area which is the barrier of commercialization of molten carbonate fuel cell(MCFC), Ni/Y/Al coating layer was fabricated by Ni electroplating and Y, Al e-beam PVD on AISI 316L stainless steel. NiAlY alloy coating layer was formed by heat treatment in reduction atmosphere at $800^{\circ}C$ for 5hr. Immersion test in molten carbonate salt at $650^{\circ}C$ was performed on as- received AISI 316L stainless steel and NiAlY coated specimen. According to cross sectional SEM/EDS observations, corrosion resistance of separator wet-seal area was improved by formation of dense oxide layers of Al and Y.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.56-56
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• 2009

AISI 316L 스테인리스강에 새롭게 디자인한 서로 다른 3가지 응고모드를 가진 와이어로 FCAW(Flux Cored Arc Welding)을 하였다. 각각의 3가지 와이어는 Pseudobinary phase diagram에 따라 AF, FA, F모드를 가졌다. 미세조직은 $Cr_{eq}/Ni_{eq}$이 증가할수록 델타 페라이트 함량이 증가하였으며, 초정 상의 경우 초정 오스테나이트에서 초정 페라이트로 변태하였고, 연성저하균열의 민감도가 감소하였다. 연성저하균열은 이동결정립계의 형상에 따라 좌우되며, 미량의 페라이트를 함유한 오스테나이트에서는 페라이트가 핀(Pin) 역할을 제대로 하지 못하여 직선형태의 이동 결정립계 따라 입계 미끄러짐의 메커니즘을 통해 전파되었으며, 곡선형태의 이동 결정립계에서는 델타 페라이트가 핀 역할을 하여 역할을 하여 구속 상태에서 응력집중을 막고 응력을 분산시켜 균열이 전파되는 것을 방해하여 균열이 발생되지 않았다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.11a
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• pp.155-156
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• 2007

AISI316L강에 저온 프라즈마 침탄과 저온 프라즈마 질화를 연속적으로 실시하여 표면경도와 내식성을 동시에 증가시키는 처리법에서 질화처리 시 처리시간 및 온도에 따른 표면특성변화를 조사하였다. 모든 시편의 표면에 N에 의해 확장된 오스테나이트(${\gamma}_N$)가 형성되었으며, 형성된 ${\gamma}_N$로 인하여 표면경도가 약 $3{\sim}4$배 증가하였다. 처리시간과 온도가 증가함에 따라 ${\gamma}_N$층의 두께와 표면의 N농도가 증가 하였다. 표면처리한 모든 시편은 표면의 N의 영향으로 내식성이 증가 하였다.