• Journal of the Microelectronics and Packaging Society
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• v.20 no.1
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• pp.39-43
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• 2013

The experiments were carried out in the variation of current density, pH, temperature, and duty cycle to investigate the influence of electroplating parameters on the properties of Ni-Fe invar alloys. When the current density and temperature were changed, the composition of invar alloy was varied, however, duty cycle and pH hardly affected on the composition of electrodeposited alloys. However, as the duty cycle was increased, microstructure was changed and the decrease of hardness was also observed.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.167-176
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• 2001

The effects of heat treatments and testing temperatures on the mechanical properties of Invar materials were investigated through experiments, which call influence the formability in metal forming fields. Annealing temperatures were changed from $900^{\circ}C$ to $1200^{\circ}C$ with an increment of $100^{\circ}C$ under two different furnace atmosphere(vacuum and H$_2$gas). Microstructure and hardness tests were performed for annealed specimens at room temperature(RT) and tensile tests were also performed by changing annealing temperatures as well as testing temperatures from RT to $300^{\circ}C$. The grain size of annealed materials increased with increasing annealing temperature, while micro-hardness distributions showed almost same hardness values regardless of annealing temperatures. Strength ratio (tensile/yield strength), which influences the forming characteristics of sheet metal, remained almost constant for various experimental conditions in case of unannealed specimens. However, it showed increasing tendency with increasing both annealing and testing temperatures, particularly at the testing temperature higher than $200^{\circ}C$. Therefore it can be concluded that press formability of fully-annealed Invar material can be improved by warm forming technique.

• Journal of Welding and Joining
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• v.27 no.5
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• pp.74-80
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• 2009

The membrane of the LNG carriers consists of thin strips of INVAR(Fe-36%Ni) steel plates, and the junction between INVAR strips is fabricated by welding. Thousands of the raised edge joints, regularly spaced, are located around all the side of the tank corner near the transverse bulkhead, and TIG welding is manually made on the top of the raised edges. Since the thickness of all the laminated edge plies is extremely thin and the weld position is under a bad accessibility, highly skilled workers are required to perform welding relatively for a long welding time. An alternative scheme for the corner membrane fabrication is proposed in the study to improve the installation workability and thus productivity. The scheme replaces the welded edges with the preformed corrugation ones. A panel strip with regularly-spaced corrugations is installed at the corner instead of the individual flat strip of which edge is vertically raised to be welded with the adjacent strip. In the study, a series of the evaluation on the corrugated edge members was performed to assess the applicability to the real LNG carrier fabrication. Opening displacement at the raised edge was experimentally examined. Elastic stiffness regressed from the displacement was nearly same in both edge types. Edge displacement and local stresses were calculated under hydrostatic pressure and temperature change due to liquefied cargo. Fatigue test was performed on both corrugated and welded edge specimens consisting of two or five plies of invar strips. Fatigue strength of the corrugated specimens was not less than that of the welded specimens.

• Transactions of Materials Processing
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• v.24 no.1
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• pp.44-51
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• 2015

The current study seeks to examine the effects of V and C additions on the mechanical and low thermal expansion properties of a high strength invar base alloy. The base alloy (Fe-36%Ni-0.9%Co-2.75%Mo-0.7Cr-0.23Mn-0.17Si-0.3%C, wt.%) contains $Mo_2C$ carbides, which form as the main precipitate. In contrast, alloys with additions of 0.4%V+0.3%C (alloy A) or 0.4%V+0.45%C (alloy B) contain $Mo_2C$+[V, Mo]C carbides. The average thermal expansion coefficients of these high strength invar based alloys were measured in the range of $5.16{\sim}5.43{\mu}m/m{\cdot}^{\circ}C$ for temperatures of $15{\sim}230^{\circ}C$. Moreover, alloy B showed lower thermal expansion coefficient than the other alloys in this temperature range. For the mechanical properties, the [V, Mo]C improved hardness and strengths(Y.S. and T.S.) of the high strength invar base alloy. T.S.(tensile strength) and Y.S.(yield strength) of hot forged alloy B specimen were measured at 844.6MPa and 518.0MPa, respectively. The tensile fractography of alloy B exhibited a ductile transgranular fracture mode and voids were initiated between the [V, Mo]C particles and the matrix. Superior properties of high strength and low thermal expansion coefficient can be obtained by [V, Mo]C precipitation in alloy B with the addition of 0.4%V and 0.45%C.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1274-1277
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• 2004

최근 에너지 소비구조의 선진화에 따라 전력수요는 매년 10%이상 증가하고 있지만 철탑부지확보 및 환경 문제 둥에 의해 신규 송전선의 건설은 점차 어려워지고 있다. 이에 대한 대책으로 철탑의 교체 없이 송전선의 전류용량간 증가시키는 방안이 우선적으로 고려되어 적용되고 있다. 이미 국내에서도 기존 송전선인 ACSR 전선을 중용량 저이도의 특성을 가진 STACIR/AW(Super Thermal-resistant Aluminum alloy Conductors, aluminum-clad Invar-Reinforced)송전선으로 교체하여 전력 수송량을 증가시키고 있다. STACIR/AW전선은 도체의 내열성을 향상시켜 연속허용온도$(210^{\circ}C)$를 높임으로 전류용량을 증가시키고, ACSR에 사용되는 강심재료인 고탄소강선을 선팽창계수가 낮은 인바강선(INVAR)으로 대체함으로 고온환경에 따른 이도증가를 방지하고 있다. 그러나 STACIR/AW 송전선은 ACSR 송전선에 비하여 연속허용온도가 높고 경간의 거리가 멀기 때문에 열화에 의한 피로특성의 변화 가능성이 높다. 따라서 본 연구에서는 증용량저이도전선의 강심소재인 INVAR/AW강선을 소정의 온도에서 경년 열화하고, 열화시간에 따른 강도와 피로특성의 변화를 조사하여, STACIR/AW전선의 안정적 운전을 위한 재료물성적 관리인자를 도출하고자 하였다.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1346-1348
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• 2001

Generally, Invar alloy shows very low thermal expansion characteristics, lower than $2{\times}10^{-6}$/K approximately. To apply Fe-Ni-Co-C Invar alloy as a core material for large ampacity transmission line we studied the effects of magnetic properties on coefficient of thermal expansion. The coefficient of thermal expansion(CTE) suddenly decreases with addition of a little carbon(0.08%), increases with the increasing carbon and has a constant value at the composition over than 1.0%C. The trend of Curie temperature change with carbon is similar with that of CTE. Therefore, the CTE has a linear relationship with Curie temperature. However, the CTE linearly decreases with the ratio of saturation magnetization and Curie temperature(${\sigma}_s/T_c$).

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.891-893
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• 1999

Invar alloys have characteristics with very low thermal expansion coefficient and low tensile strength. The mechanical properties of invar alloy have to being improved to apply for structural materials, especially for core of transmission line in electrical field. It is necessary low thermal expansion and high strength core material to transmit increased current capacity. In this paper, we investigated effect of Mo addition affected to thermal and mechanical properties and microstructure in Fe-Ni-Co ternary system.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1599-1601
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• 2000

To study invar alloy as a core material for large ampacity over-head transmission line which have high strength and low thermal expansion coefficient simultaneously, thermal expansion coefficient, physical properties and hardness of Fe-Ni-Co-xC alloy have been studied. It is necessary that invar alloy possess low thermal expansion coefficient and high strength for increased capacity over-head transmission line. In this paper we tried to find out the effect of carbon addition related with mechanical and physical properties. It was found that the thermal expansion coefficient and hardness were increased with carbon addition for whole composition range but the saturation magnetization was decreased except for the range of 0.1$\sim$0.4%C.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.547-550
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• 2008

Precipitation characteristics of the Fe-36Ni based high strength Invar alloy for power transmission wire was investigated in this study. High strength can be obtained in this alloy through precipitation hardening and strain hardening by cold working. $FactSage{(R)}$ in this study, revealing that equilibrium phases which can be formed are two kind of MC-type precipitates and MoC carbide. The latter stoichiometric carbide was expected to be formed at relatively lower temperature $770^{\circ}C$. High strength above 1000MPa and 40% of elongation were obtained at room temperature in both cases.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.214-215
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• 2000

레이저로 발생시킨 플라즈마의 분광학적인 분석은 유용한 분석기술로 평가되고 있다. 이러한 플라즈마를 발생시키는데 있어서 Q-switched 레이저를 많이 사용되고 되고 있으나, Q-switch된 레이저로 발생시킨 플라즈마 복사광의 특성은 주변 분위기에 의해 매우 큰 영향을 받는다. 특히 대기압인 공기분위기에서 레이저로 발생된 플라즈마의 분광특성은 강하고 연속적인 background가 포함되고, 자체적으로 흡수되고, 넓게 퍼진 분광선들이 생성된다. 이는 레이저 발생 플라즈마를 통해 성분을 분석할 경우에 적합하지 않다. (중략)