• 대한기계학회논문집A
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• 제34권1호
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• pp.103-110
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• 2010

본 연구에서는 프랑스의 RCC-MR A16 절차에 기초하여 Mod.9Cr-1Mo 강(ASME Grade 91) 구조의 크리프-피로 균열 개시 및 성장 평가법을 확장 개발하였다. 현재의 A16 지침은 오스테나이트 스테인리스강에 대해서만 크리프-피로 균열 개시 및 성장 평가법을 제시하고 있지만, 현재 초초임계(USC) 화력발전소는 물론 미래형 원자로 시스템의 구조재료로서 폭넓게 채택되고 있는 Mod.9Cr-1Mo 강에 대한 지침은 제시하지 않고 있다. 본 연구에서는 FMS(페리틱-마르텐사이트강)에 대한 크리프-피로 균열 개시 및 성장 평가법을 제시하고 있고, 구조물에 대한 크리프-피로 균열 거동 평가를 수행하였다. 평가결과는 구조시험을 수행한 결과 얻은 관찰 이미지와 비교하였다.

• Journal of Welding and Joining
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• 제31권1호
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• pp.58-64
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• 2013

The following results were obtained, microstructures and tensile properties in arc brazed joints of DP(dual phase) steel using Cu-5.3wt%Sn insert metal was investigated as function of brazing current. 1) The Fusion Zone was composed of ${\alpha}Fe+{\gamma}Cu$ and Cu23Sn2. The reason for the formation of these solid solutions. Despite, Fe & Cu were impossible to solid solution at room temperature. It's melting & reaction to something of insert metal & Base Metal (DP Steel) by Arc. Brazing Process has faster cooling rate then Cast Process, Supersaturated solid solution at room temperature. 2) The increase Hardness of Fusion Zone was directly proportional to the rise of welding current. Because, ${\alpha}Fe+{\gamma}Cu$ phase (higher hardness than the Cu23Sn2.(104.1Hv < 271.9Hv)) Volume fraction was Growth, due to increasing the amount of base metal melting by High current. 3) The results of tensile shear test by Brazing, All specimens happen to fracture in Fusion Zone. On the other hand, when Brazing Current increasing tend to rise tensile load. but it was very small, about 26-30% of the base metal. 4) The result of fracture analysis, The crack initiate at Triple Point for meet to Upper B.M/Under B.M/Fusion Zone. This Crack propagated to Fusion zone. So ruptured by tensile strength. The Reason to in the fusion zone fracture, Fusion zone by Brazing of hardness (strength) was very lower then the base metal (DP steel). In addition the Fusion Zone's thickness in triple point was thin than the base metal's thickness in triple point.

• 비파괴검사학회지
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• 제23권2호
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• pp.148-155
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• 2003

저방사화 페라이트강인 JLF는 핵융합로의 블랑켓과 같은 열교환기의 재료로써 유용한 재료이다. 이 재료의 광범위한 적용을 위해서는 JLF강과 다른 재료와의 접합기술의 개발이 중요하다. 최근 두 이종재료간의 접합에는 마찰용접이 많이 이용되고 있으며 본 연구에서도 JLF강과 STS304 간의 마찰용접에 의한 용접특성을 평가하였으며 특히 비파괴기법중의 하나인 음향방출 기법을 이용하여 두 이종재료간의 용접특성 및 최적의 용접조건을 평가하였다. 음향방출 파라미터중의 하나인 카운트와 사상수 등이 최적용접조건 및 용접품질을 평가하는데 유효한 파라미터들이었다.

• Journal of Welding and Joining
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• 제27권5호
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• pp.49-54
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• 2009

Recently, a demand of ferritic STS is increasing rapidly in automobile exhaust system. Exhaust manifolds are the part nearest to the engine so that the material is exposed to high temperature exhaust gas. Excellent heat resistant properties, especially high temperature strength, thermal fatigue resistance and high corrosion resistance are necessary for these parts. STS429L contains 15 weight percent of Cr and low Mo, so has good price competitive. And it has excellent high temperature strength and corrosion resistance, so receives attentions as material that applying to exhaust manifold. In tensile test of lap joint welded STS 429L, most of specimens are failed in base metal, but occurs brittle fracture in weld metals at some specimens in the face of good welding conditions. In the process of tensile test, lap joint welded STS429L specimens are transformed locally. The brittle fracture occurs that local transforming area exists in weld metals. But, butt welding specimens made by same materials showed ductile fracture in tensile test and bending test. In this study, suppose the reason of brittle fracture is in the combined local transform and tensile stress, through analysis of bead geometry, evaluate geometrical factor of brittle fracture in lap joint welded STS429L.

• 한국재료학회지
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• 제20권7호
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• pp.356-363
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• 2010

For this paper, we investigated the area specific resistance (ASR) of commercially available ferritic stainless steels with different chemical compositions for use as solid oxide fuel cells (SOFC) interconnect. After 430h of oxidation, the STS446M alloy demonstrated excellent oxidation resistance and low ASR, of approximately 40 $m{\Omega}cm^2$, of the thermally grown oxide scale, compared to those of other stainless steels. The reason for the low ASR is that the contact resistance between the Pt paste and the oxide scale is reduced due to the plate-like shape of the $Cr_2O_3$(s). However, the acceptable ASR level is considered to be below 100 $m{\Omega}cm^2$ after 40,000 h of use. To further improve the electrical conductivity of the thermally grown oxide on stainless steels, the Co layer was deposited on the stainless steel by means of an electroless deposition method; it was then thermally oxidized to obtain the $Co_3O_4$ layer, which is a highly conductive layer. With the increase of the Co coating thickness, the ASR value decreased. For Co deposited STS444 with 2 ${\mu}m$hickness, the measured ASR at $800^{\circ}$ after 300 h oxidation is around 10 $m{\Omega}cm^2$, which is lower than that of the STS446M, which alloy has a lower ASR value than that of the non-coated STS. The reason for this improved high temperature conductivity seems to be that the Mn is efficiently diffused into the coating layer, which diffusion formed the highly conductive (Mn,Co)$_3O_4$ spinel phases and the thickness of the $Cr_2O_3$(S), which is the rate controlling layer of the electrical conductivity in the SOFC environment and is very thin

• 한국표면공학회지
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• 제34권5호
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• pp.465-474
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• 2001

Type 304SS coatings were performed at 200$\square$ onto AISI 1045 carbon steel substrate using unbalanced magnetron sputtering (UBMS) with an austenitic AISI 304 stainless steel (SS) target of 100mm diameter. The total deposition pressure in the active Ar gas was 2$\times$10$^{-3}$ Torr. Coatings were done at various target power densities and bias voltages. Chemical compositions of metallic elements of the coatings were measured by energy dispersive X-rays spectroscopy (EDS). The structure and the morphology of Type 304SS coatings were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Corrosion properties of the coated specimens were examined using electrochemical polarization measurements and electrochemical impedance spectroscopy in a deaerated 3.5% NaCl solution. The porosity rate was obtained from a comparison of the dc polarization resistance of the uncoated and coated substrates. Scratch adhesion testing was used to compare the critical loads for different coatings. XRD results showed that the sputtered films exhibit a ferritic b.c.c. $\alpha$-phase. Potentiodynamic polarization curves indicated that all samples had much higher corrosion potential and better corrosion resistance than the bare steel substrate. The corrosion performance increased with increasing power density and the adhesion was enhanced at the bias voltage of -50V. An improvement in the corrosion resistance can be obtained with a better coating adhesion. Finally, an optimized deposition condition for corrosion protection was found as $40W/cm^2$ and -50V.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.57-60
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• 2008

KEPRI has studied planar type SOFC stacks using anode-supported single cells and kW class co-generation systems for residential power generation. A 1kW class SOFC system consisted of a hot box part, a cold BOP part and a water reservoir. A hot box part contains a SOFC stack made up of 48 single cells and ferritic stainless steel interconnectors, a fuel reformer, a catalytic combustor and heat exchangers. Thermal management and insulation system were especially designed for self-sustainable operation. A cold BOP part was composed of blowers, pumps, a water trap and system control units. When a 1kW class SOFC system was operated at $750^{\circ}C$ with hydrogen after pre-treatment process, the stack power was 1.2kW at 30 A and 1.6kW at 50A. Turning off an electric furnace, the SOFC system was operated using hydrogen and city gas without any external heat source. Under self-sustainable operation conditions, the stack power was about 1.3kW with hydrogen and 1.2kW with city gas respectively. The system also recuperated heat of about 1.1kW by making hot water.

• Corrosion Science and Technology
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• 제2권4호
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• pp.171-177
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• 2003

The electronic properties of the passive film formed on Fe-20Cr ferritic stainless steel in pH 8.5 buffer solution containing 0.05 M EDTA (ethylene diammine tetraacetic acid) were examined by the photocurrent measurements and Mott-Schottky analysis for the film. XPS depth profile for the film demonstrated that Cr content in the outermost layer of the passive film was higher in the solution with EDTA than that in the solution without EDTA, due to selective dissolution of Fe by EDTA. In the solution with EDTA, the passive film showed characteristics of an amorphous or highly disordered n-type semiconductor. The band gap energies of the passive film are estimated to be ~ 3.0 eV, irrespective of film formation potential from 0 to 700 $mV_SCE$ and of presence of EDTA. However, the donor density of the passive film formed in the solution with EDTA is much higher than that formed in the solution without EDTA, due to an increase in oxygen vacancy resulted from the dissolution of Fe-oxide in the outermost layer of the passive film. These results support the proposed model that the passive film formed on Fe-20Cr in pH 8.5 buffer solution mainly consists of Cr-substituted $\gamma$-$Fe_2O_3$.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.303-306
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• 2005

Two composites of five plies of STS/Al/Al/Al/STS and STS/Al/STS/Al/STS were produced by roll-cladding at $350^{\circ}C$ from ferritic stainless steel (STS) and aluminum (Al) sheets. In order to analyze the strain states during roll-cladding, the evolution of textures at different through-thickness positions in the roll-clad composites was investigated. Simulations with the finite element method (FEM) disclosed that a strain state which was similar to that of normal rolling with a high friction between roll surface and Al sample led to the formation of texture gradients in the Al sheets in the STS/Al/Al/Al/STS composite. Differences in the material velocity of STS and Al in the rolling direction gave rise to the formation of the shear texture in the Al sheets in the STS/Al/STS/Al/STS composite.

• 대한기계학회논문집A
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• 제34권1호
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• pp.19-26
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• 2010

본 논문에서는 유한요소 해석을 통해 용접부 중앙에 원주방향균열이 있는 배관에 대한 강도불일치 한계하중 해석 및 파괴역학 해석을 수행하였다. 강도불일치 한계하중식을 제시하기 위해 강도불일치 비, 용접부 폭, 균열 길이 및 배관 반경비에 대한 체계적인 변수 해석을 수행하였으며 참조응력법을 바탕으로 스테인리스강 및 페리틱 강에 대한 J-적분 계산을 수행하였다. 본 연구에서 제시한 강도불일치 한계하중을 사용하여 참조응력을 정의할 때, 보다 정확한 J-적분 결과를 얻을 수 있었다.