• 설비공학논문집
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• 제28권9호
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• pp.350-354
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• 2016

Although fibrous insulations are generally used with resistive insulation type, metallic insulation is proper matter to satisfy low head-loss and equipment life when considering the specific condition, especially for Nuclear power plant. Common insulation is resistance insulation with a low thermal conductivity. but RMI is made of sheet plate with low emissivity and closed air space. Thermal radiation is blocked by stainless steel with low emissivity. Thermal conductivity and thermal convection are blocked by closed air space. This study shows the changes and effects of the heat loss according to shape and method of stacking sheet plates inserted into the insulation and analyzed the most optimized way for thermal insulation performance. The result shows that using sheet plate structure through raised and protruding shape processing was the appropriate model to optimize thermal performance. Additionally, insulating performance of RMI improved by placing the sheet plate in a high temperature region intensively.

• 한국철도학회:학술대회논문집
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• 한국철도학회 1998년도 추계학술대회 논문집
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• pp.560-567
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• 1998

The pitch of spot-weld is a important variable in a view of both production cost and strength of car-body. Various renditions for the selection of pitches have been researched and especially in this paper the buckling analysis is carried out for the 2-sheet pannel structures. The optimal pitch is obtained by optimization program and FEM, which can enhance the buckling strength.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2007년도 추계학술발표논문집
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• pp.337-340
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• 2007

냉간단조금형(Cold Forging Die)의 다이블록(Dieblock)을 제작하는 방법 중의 하나로, 다이블록 제작용 재료를 면가공 하여 다이블록 상면(上面)을 마스터펀치(Master Punch)인 호브(Hob)로 압입(Indentaion) 시켜 절삭가공((Cutting Work)이 아닌 다이호빙(Die Hobbing) 방법으로 임프레션(Impression)을 성형하여 제작하고 있다. 이 방법에 의하여 다이블록의 재료를 합금공구강(Alloy Tool Steel)인 SKD11을 사용하여 제작하고, 스테인리스판(Stainless Sheet Metal)을 제품 재료로 하여 냉간단조가공(Cold Forging Work)을 하였더니 6,000 스트로크(Stroke)에서 금형수명(Die Life)을 다 하였다. 본 논문에서는 다이블록 재료를 고속도공구강(High Speed Tool Steel)인 SKH51로 교체 제작하고, 탄소강(Carbon Steel)인 S45C를 제품 재료로 하여 냉간단조가공을 수행 하였더니 21,000 스트로크에서 금형수명을 다하고 종료 되어 종래의 방법과 비교 검토 하였을 때 350%의 금형수명 연장 효과를 얻게 되었다.

• Corrosion Science and Technology
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• 제16권2호
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• pp.49-58
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• 2017

Many research efforts on the effect of nitrogen on the corrosion resistance of stainless steels have been reported, but little research has been conducted on the effect of nitrogen for the weldment of stainless steels by the seal-weld method. Therefore, this work focused on the determining the corrosion resistance of tube/tube sheet mock-up specimen for sea water condensers, and elucidating the effect of shielding nitrogen gas on its resistance. The pitting corrosion of autogenously welded specimen propagated preferentially along the dendritic structure. Regardless of the percent of shielding nitrogen gas, the analyzed nitrogen contents were very much lower than that of the bulk specimen. This can be arisen because the nitrogen in shielding gas may partly dissolve into the weldment, but simultaneously during the welding process, nitrogen in the alloy may escape into the atmosphere. However, the pitting resistance equivalent number (PREN) of the interdendrite area was higher than that of the dendrite arm, regardless of the shielding gas percent; and the PREN of the interdendrite area was higher than that of the base metal; the PREN of the dendrite arm was lower than that of the base metal because of the formation of (Cr, Mo) rich phases by welding.

• Journal of Welding and Joining
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• 제32권6호
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• pp.64-69
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• 2014

The applications by using fiber laser have increased recently. However, due to high beam quality of fiber laser, it is inappropriate to apply the existing laser welding monitoring technology to the fiber laser welding as it is. On this study, thus, we analyzed emission signal with RMS and FFT for the in-process monitoring during fiber laser welding. 12mm-thick 304L stainless steel sheet was used in fiber laser welding and the result showed as follows: The intensity changes in RMS did not clarify the distinction between full penetration and partial penetration. However, as welding speed increases, specific frequency also increases in regards of frequency analysis by using FFT.

• 열처리공학회지
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• 제9권1호
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• pp.19-26
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• 1996

Melt-quenching of steels leads to various metallographic effects such as refinement of grain size, extension of the solid solubility of carbon and alloying elements, and is expected to improve the mechanical properties of conventional steels. Furthermore, this technique is a useful method for producing sheet directly from liquid state. And it will lend itself to development as a continuous cast process which offers significant savings in energy and product costs. The purpose of this study is to present the microstructures of melt-quenched austenitic stainless steels. As the results of this study, the morphology of melt-quenched microstructure show that the roll contact area is columnar structure, and the free surface area is dendrite structure. As the line speed increases, the ratio of $d_{colunnar}/d_{total}$ increases from 0.12 to 0.60, but the ribbon thickness decreases from $150{\mu}m$ to $30{\mu}m$.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.209-214
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• 1995

This paper describes that the effects of punch speed and temperatures of the die and the blank holder on the drawability are examined. Up to now, multi-stage of dies sets have been used generally at room temperature in deep drawing of rectangular shaped components. But using local heating, it is shown that one stage of die set was capable of deep drawing and the drawability was increased and sheet thickness of component was drawn somewhat uniformly. Rectangular deep drawing experiments on two kinds of stainless steel STS316L, STS430 of 1.0 mm thickness have been conducted using local heating. The limiting drawing height can be increased by heating the die and the blank holder up to 100 .deg. C at STS316L. Commercial lubricants hadn't an effect on drawability in rectangular deep drawing, but vinyl and teflon film had an effect on it.

• Corrosion Science and Technology
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• 제13권2호
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• pp.70-80
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• 2014

Duplex stainless steels with nearly equal fraction of the ferrite(${\alpha}$) phase and austenite(${\gamma}$) phase have been increasingly used for various applications such as power plants, desalination facilities due to their high resistance to corrosion, good weldability, and excellent mechanical properties. Hyper duplex stainless steel (HDSS) is defined as the future duplex stainless steel with a pitting resistance equivalent (PRE=wt.%Cr+3.3(wt.%Mo+0.5wt.%W)+30wt.%N) of above 50. However, when HDSS is welded with gas tungsten arc (GTA), incorporation of nitrogen in the Ar shielding gas are very important because the volume fraction of ${\alpha}$-phase and ${\gamma}$-phase is changed and harmful secondary phases can be formed in the welded zone. In other words, the balance of corrosion resistance between two phases and reduction of $Cr_2N$ are the key points of this study. The primary results of this study are as follows. The addition of $N_2$ to the Ar shielding gas provides phase balance under weld-cooling conditions and increases the transformation temperature of the ${\alpha}$-phase to ${\gamma}$-phase, increasing the fraction of ${\gamma}$-phase as well as decreasing the precipitation of $Cr_2N$. In the anodic polarization test, the addition of nitrogen gas in the Ar shielding gas improved values of the electrochemical parameters, compared to the Pure Ar. Also, in the erosion-corrosion test, the HDSS welded with shielding gas containing $N_2$ decreased the weight loss, compared to HDSS welded with the Ar pure gas. This result showed the resistance of erosion-corrosion was increased due to increasing the fraction of ${\gamma}$-phase and the stability of passive film according to the addition $N_2$ gas to the Ar shielding gas. As a result, the addition of nitrogen gas to the shielding gas improved the resistance of erosion-corrosion.

• 한국농공학회논문집
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• 제59권5호
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• pp.73-81
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• 2017

The improved movable weir supplements the advantages and disadvantages of the rubber weir and the conduction gate. It consists of a stainless steel gate, air bags, and a steel clamping plate. The stainless steel gate is the main body of the weir, and the inflatable rubber sheet serves to support the steel gate. The steel clamping plate is typically in direct continuous contact with water, but this leads to corrosion issues that can reduce the life of the entire movable weir. In this study, a panel-type glass-fiber-reinforced polymer (GFRP) clamping plate was designed and fabricated. The test results showed that the flexural load of the panel-type GFRP composite clamping plate was over twice that of the wings type GFRP clamping plate. The lowest moisture absorption value was obtained upon exposure to tap water, and exposure to other solutions showed similar values. Additionally, flexural load testing after exposure to an accelerated environment found the lowest residual loads of 80.51 % and 78.50 % at 50 and 100 days, respectively, for exposure to a $CaCl_2$ solution, while exposure to other environments showed residual failure loads of over 80 % at both 50 and 100 days.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1115-1120
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• 2003

The recent tendency in the automobile industries is toward light weighting vehicle body to improve the problems by environmental pollution as well as improving fuel cost. The effective way to reduce the weight of vehicle body seems to be application of new materials for body structure and such trend is remarkable. Among the various materials for vehicle body, stainless steel sheet (for example, 301L and 304L), TRIP steel and cold rolled steel sheets are under the interests. However, in order to guarantee reliability of new material and to establish the long life design criteria of body structure, it is important and require condition to assess spot weldability of them and fatigue strength of spot welded lap joints which were fabricated under optimized spot welding condition. And, recently, a new issue in the design of the spot welded structure is to predict economically fatigue design criterion without additional fatigue tests. In general, for fatigue design of the spot-welded thin sheet structure, additional fatigue tests according to the welding condition, material, joint type, and fatigue loading condition are generally required. This indicates that much cost and time for it should be consumed. Therefore, in this paper, the maximum stresses at nugget edge of spot weld were calculated through nonlinear finite element analysis first. And next, obtained the ${\Delta}P-N_{f}$ relation through the actual fatigue tests on spot welded lap joints of similar and dissimilar high strength steel sheets. And then, the ${\Delta}P-N_{f}$ relation was rearranged in the ${\Delta}{\sigma}-N_{f}$ relation. From this ${\Delta}{\sigma}-N_{f}$ relation, developed the fatigue design technology for spot welded lap joints of them welded using the optimized welding conditions.