• Proceedings of the KSME Conference
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• 2004.04a
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• pp.78-83
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• 2004

Environmental fatigue crack propagation of CF8M and CF8A steels used in the domestic PWR were investigated on the simulated PWR condition(Temperature: $316^{\circ}C$, Pressure: 15MPa). The test equipment for environmental fatigue(high temperature-high pressure loop, autoclave, load frame, measurement system) were designed. As-received and 60-year aged specimens were used in the test. To compare with environmental fatigue test, another test was performed in the air condition. The fracture surface of specimens were difficult to verify the fracture modes such as striation, intergranular crack and cleavage and so on. As the ferrite content of CF8M is increased, more particles covered fracture surface were peeled.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.296-301
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• 2004

By the purpose to investigate the change of internal stress and mobile dislocation density in creep, the stress relaxation test is carried out in the condition of each strain. Mobile dislocation density increased until it reached minimum creep rate and after that, it decreased and internal stress didn't have the change approximately until it reached minimum creep rate and after that, it decreased. The stress relaxation rate is fast and approached zero after 1.5 seconds after the beginning of the stress relaxation. And the larger the applied stress is, the larger the internal stress is. By the evaluation of mobility of dislocation, the dislocations glide viscously in STS31OJlTB but it is the dislocations glide viscously which N passes by cutting Cr atom rather than typical viscosity movement after calculating mobility of dislocation.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2008.11a
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• pp.31-31
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• 2008

복합 싸이클 시험 모니터링을 통해 NaCl, $CaCl_2$ 제설염 환경에서 11 % Cr, 17 % Cr 페라이트 스테인리스강의 외면부식특성을 조사하고자 하였다. 용액 내 NaCl 및 $CaCl_2$의 농도가 증가함에 따라 용액의 pH가 떨어졌으며, $CaCl_2$의 농도증가에 따른 산성화도가 NaCl에 비해 크게 나타났다. 염수분무-건조-습윤 과정의 반복으로 구성되어 있는 복합싸이클 시험 중 소재의 표면상태 변화를 모니터링 한 결과, 건조 과정 중에 공식이 시작되며, NaCl 환경의 경우엔 습윤과정 중에 $CaCl_2$ 환경의 경우엔 건조 중에 공식성장이 주로 이루어지는 것으로 확인되었다.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.66-67
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• 2006

The master sintering curve (MSC) is derived from densification data over a range of heating rates and temperatures. To improve the accuracy, several modifications were proposed: multi-phase MSC for solid state sintering with phase changes, MSC for liquid phase sintering, and MSC with consideration of grain growth. The developed MSC models were applied to several material systems such as molybdenum, stainless steels, and tungsten heavy alloys (WHA), in order to evaluate the effect of compaction pressure, phase change, grain growth, and composition on densification, to classify regions having different sintering mechanism, and to help engineer design, optimize, and monitor sintering cycles.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.696-697
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• 2006

This paper presents the densification and microstructure evolution of bilayer components made from 316L stainless steel and M2 High speed steel during co-sintering process. The sintering was carried out at temperatures ranging from $1230-1320^{\circ}C$ in a reducing atmosphere. The addition of boron to 316L was examined in order to increase the densification rate and improve the sintering compatibility between the two layers. It was shown that the mismatch strain bettwen the two layers induces biaxial stresses during sintering, influencing the densification rate. The effect of boron addition was also found to be positive as it improves the bonding between the two layers.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.11a
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• pp.65-68
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• 2007

저온 플라즈마 기술을 이용하면 오스테나이트계 스테인리스강의 내식성과 표면경도를 동시에 증가 시킬 수 있다. 여러 가지 처리방법 중 질탄화와 2-step 공정으로 처리한 AISI304L강의 표면을 분석하였다. 처리한 모든 시편의 표면은 expanded austenite(${\gamma}_N$)이 형성되었고, 표면 경도도 모재보다 약 4배 이상 증가 하였다. 저온플라즈마 질탄화 공정의 경우 경화층의 두께가 최대 15 ${\mu}m$밖에 형성되지 않았지만 2-step공정의 경우 질탄화 공정보다 짧은 시간으로 약 2배의 경화층을 얻을 수 있었다. 두 가지 공정 모두 온도와 시간이 증가할수록 경화층의 두께가 두꺼워졌지만, 과도하게 높은 온도와 긴 공정시간은 석출물을 형성 시켰다. 석출물이 형성되지 않은 시편의 경우 내식성이 증가하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.309-310
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• 2012

스테인레스강의 내식성을 향상시키기 위한 고농도 침입형 질화층(S-phase)처리를 하는 논문들이 발표되고 있지만 테스트 시편이 아닌 실제 제품이나 가공품등의 질화 처리 하였을 경우 내식성향상이 아닌 저하되는 것을 볼 수 있다. 스테인레스강의 제품화 과정에서 압연 및 기계가공에서 발생되는 각종 문제, 가공경화로 인한 현상 및 질화 처리후 표면개질의 석출상이나 입계로부터 시작되는 크랙이 내식성을 저감시키는 경향을 살펴보았다. 이러한 경향은 봉재나 두꺼운 소재보다는 가공소재인 판재나 형상이 있는 제품에 더 심하게 나타나는 것을 보여준다. 소재의 관리와 질화 온도 및 여러가지 변수에 의해 최적화 되어 S-phase 질화층을 형성해야 내식특성을 유지 할 수 있다.

• Korean Journal of Metals and Materials
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• v.49 no.10
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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.

• Journal of the Korean institute of surface engineering
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• v.27 no.3
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• pp.123-133
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• 1994

Oxidation behavior of STS 304 and 430, produced by POSCO, Korea, was studied in order to study the surface defects formed during manufacturing processes. Oxidation experiments were carried out in a preheat-ed furnace at 850~$1, 250^{\circ}C$ in air and in a simulated coke oven gas(COG) atmosphere. The reaction products were examined by XRD, SEM and EDX on their surfaces and cross sections. Protective $Cr_2O_3$-primary oxide film was formed initially, but at critical point this film was broken and a duplex scale consisting of $Fe_2O_3$- and Fe$Cr_2O_4$- was formed. It was more severely attacked in a simulated COG atmosphere than in air, and STS 304 was superior to STS 430 in oxidation resistance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1415-1420
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• 2014

Super-critical $CO_2$ ($S-CO_2$) Brayton cycle has been considered to replace the current steam Rankine cycle in Sodium-cooled Fast Reactor (SFR) in order to improve the inherent safety and thermal efficiency. Several austenitic alloys are considered as the structural materials for high temperature $S-CO_2$ environment.. Microstructural change after long-term exposure to high temperature $S-CO_2$ environment could affect to the mechanical properties. In this study, candidate materials (austenitic stainless steels and Alloy 800HT) were exposed to $S-CO_2$ to assess oxidation resistance and the change in tensile properties. Loss of ductility was observed for some austenitic stainless steels even after 250 h exposure. The contribution of $S-CO_2$ environment on such changes was analyzed based on the characterization of the surface oxide and carburization of the materials in which 316H and 800H showed different oxidation behaviors.