• Journal of Welding and Joining
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• 제28권4호
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• pp.73-80
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• 2010

In this work, the effect of welding variables on weldability of gas tungsten arc(GTA) welding was investigated with experimental analysis for a commercial pure(CP) titanium (Grade.1). The GTA welding tests on sheet samples with 0.5mm in thick were carried out at different process variables such as arc length, welding speed and electrode shape. In order to search an optimum arc length with full penetration, bead- on-plate welding before butt-welding were performed with different arc length conditions. From the bead- on-plate welding results, the optimum condition considering arc stability and electrode loss was obtained in the arc length of 0.8mm. Butt-welding tests based on the arc length of 0.8mm were carried out to achieve the optimum conditions of welding speed and electrode shape. Optimum conditions of welding speed and electrode shape were suggested as 10 mm/s and truncated electrode shape, respectively. It was successfully validated by the microstructural observation, tensile tests, micro-hardness tests and formability tests.

• Journal of Animal Science and Technology
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• 제52권1호
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• pp.9-16
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• 2010

본 연구는 지방산합성의 완성에 관여하는 소 FASN (Fatty acid synthase) 유전자내의 g.11280G>A (Silent), g.13125T>C (Exon24-His1390Tyr)와 g.17924G>A (Exon39-Thr2158Ala) 단일염기 변이들이 한우집단 925 두를 대상으로 도체형질과의 연관성 분석, 연관불균형의 정도 및 반수체형의 분석을 위하여 수행하였다. g.11280G>A 변이의 연관성분석에 있어서는 도체중, 등지방두께 및 육량지수에 유의성이 있는 것으로 관찰되었으며 g.17924G>A변이 역시 연관성분석에서 도체중에 유의성이 있는 것으로 나타났다(P<0.05). 하지만 g.13125T>C 변이는 한우집단에서 형질과의 유의적인 연관성을 관찰 할 수 없었다. 또한 g.11280G>A, g.13125T>C와 g.17924G>A 변이들에 대한 연관불균형(Linkage disequilibrium) 분석을 한 결과 g.11280G>A와 g.13125T>C 두변이에 대한 r-square=0.177로 나타났으며 D'=0.568 로 관측되었다. 또한 g.13125T>C와 g.17924G>A 두 변이들은 r-square = 0.207로 나타났으며 D'=0.607로 나타났으며 g.11280G>A와 g.17924G>A 변이들은 r-square = 0.101으로 나타났으며 D'=0.920으로 관찰되었다. 연관불균형 유의수준(r-square>0.1, D'>0.500)에 따라 계산된 반수체형 총 7개중 그 빈도가 0.05 이상인 중요한 반수체형은 4개(-GCG- [0.378], -ATG- [0.301], -GTA- [0.191], -ACG- [0.063])를 선별하여 연관성분석을 실시하였다. FASN 반수체형 1번(-GCG-), 반수체형 2번(-ATG-)와 반수체형 4번 (-ACG-)는 한우집단에서 형질과의 유의적인 연관성을 관찰 할 수 없었으나 FASN 반수체형 3번(-GTA-)은 도체중과 연관성을 보였다(P=0.0327). 염색체상 반수체형 -GTA-.구조를 가지지 않은 동형접합체(0-copies)인 개체의 도체중은 354.70+3.58로 나타났으며, 반수체형 -GTA- 구조를 하나만 가지는 이형접합체(1-copies) 347.63+4.84으로 관찰되었으며 0-copies인 동형접합체보다 현저히 낮은 도체중을 나타내었다. 또한 반수체형 -GTA- 구조를 가지는 동형접합체(2-copies)인 개체는 22두가 나타났으며 도체중은 351.01+4.18로 0-copies 인 동형접합체 보다 낮은 도체중을 나타내었다. 이상의 결과는 소 FASN 유전자내의 g.11280G>A, g. 13125T>C와 g.17924G>A 변이들은 육질 뿐만 아니라 육량에도 관여하는 것으로 사료되며, FASN 유전자내의 g.11280G>A와 g.17924G>A 두 개의 단일염기변이는 한우개량사업소의 씨숫소의 유전자 마커를 통한 도움 선발(marker assisted selection, MAS)에 이용 될 수 있을 것이며 일반농가에서도 송아지 생산을 위한 암소 선발에 활용될 수 있을 것으로 사료된다.

• Journal of Welding and Joining
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• 제30권2호
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• pp.70-75
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• 2012

In this study, effect of nitrogen volume in the shielding gas of Ar-$N_2$ mixing gas on the bead shape, hardness and microstructure of GTA welds of 3mm thick Commercial Pure Ti was investigated. As the nitrogen volume increased, the welding current for full penetration was reduced and hardness in the fusion zone significantly increased compared with that of the base metal, but there is no difference in the hardness of HAZ. Microstructure in the fusion zone with pure Ar gas changed from equiaxed alpha of the base metal to serrated alpha. On the other hand, microstructure using Ar-$N_2$ mixing gas changed to acicular alpha. With the increasing of nitrogen content, the amount of acicular alpha increased and the size of that was fine.

• Journal of Welding and Joining
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• 제11권2호
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• pp.53-61
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• 1993

One of the most interesting and promising steel groups considered for the rocket motor case, aircraft and aerospace component is the maraging(martensitic plus aging) nickel steel, developed by International Nickel Company in 1960. This material attains a very high strength with good fracture toughness by simple heat treatments which do not involve a quenching. Full strength can be obtained by "maraging" at 480.deg. for 3 hours for the 18% Ni maraging steel. The effect of heat treatments was considered on the residual stress field of 18% Ni maraging steel weldments. In experiments, various heat treatments such as stress relieve heat treatment, aging and solution heat treatment were carried out of the GTA weldments and the residual stresses were measured by using the hole drilling method. Whereas the conventional pattern of residual stress shows the stresses to be maximum along the weld centerline with tensile stress extending into the heat affected zone, the pattern in maraging steels shows the centerline stress to be compressive. After welding, a series of aging, solution heat treatment and solution heat treatment plus aging treatment were carried out and the residual stresses were measured to reveal that these heat treatments almost completely remove the welding residual stresses.

• 한국재료학회지
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• 제6권9호
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• pp.905-918
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• 1996

초전도 마그네트 구조용 부재로 최근 개발된 오스테나이트계 스테인레스강 JN1 모재, GTA 용접부 및 열처리재에 대한 기계적 성질을 조사하기 위해 실온(293K)에서 극저온(4K)까지의 온도에서 소형펀치(Small Punch)시험을 실시하였다. GTA 용접부의 용융선 근방의 극저온 기계적 성질은 모재와 용접금속에 비해 크게 저하하였다. 4K에서 실험된 용융선 시험편으로 얻어진 하중-변위곡선상에서 부하의 초기 단계에 보통의 서레이션과 다른 pop-in이 관찰되었고, 이때 시험편 표면의 용융선 근처에서 약 0.1-1mm 정도의 크랙이 발생하였다. 열처리재의 기계적 성질은 열처리 시간과 온도의 증가 또는 시험온도의 저하에 따라 크게 저하되었다. 위의 결과에 기초하여 본 연구에서 실시한 소형 시험편을 사용하는 SP 시험법은 극저온에서 JN1 강의 모재와 열처리재뿐 만 아니라 GTA 용접부의 기계적 성질을 평가할 수 있는 유용한 시험법이었다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.38-38
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• 2009

36 percent nickel-iron alloy possesses a useful combination of low thermal expansion, moderately high strength and good toughness at temperatures down to that of liquid helium, $-269^{\circ}C$. These propeties coupled with good weldability and desirable physical properties make this alloy attractive for many cryogenic applications such as the cargo containment system in Liquefied Natural Gas carriers and pipes for low temperature. Generally, welding method of the 36% nickel-iron is applied with the manual and autogeneous GTAW. Lately white spots have been observed on the some autogeneous GTA welds of them. But the white spot formation have not been studied yet. This paper covers the analysis results of the white spots formation as changing welding variables.

• Journal of Welding and Joining
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• 제28권3호
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• pp.73-78
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• 2010

The purpose of this study is to develop the control technology of the welding distortion caused by Auto NG-GTA(Narrow Gap-GTA) welding process at the STS 304 multi-pass butt weldment. Heat input model for Auto NG-GTA welding process was established and verified by measuring temperature change and molten pool shape at the bead-on-plate weldment. With the heat input model developed, the effect of tension load on the welding distortion at the STS 304 multi-pass butt weldment was evaluated using the thermo-elasto-plastic FE analysis. In accordance with FEA results, the angular distortion and transverse shrinkage sharply decreased with an increase in tension load. This result indicated that tensioning method was an effective countermeasure against the welding distortion of the STS 304 multi-pass butt weldment.

• Journal of Welding and Joining
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• 제16권3호
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• pp.111-120
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• 1998

To predict and evaluate metallurgical and mechanical behavior of th welds, it is essential to understand solidification behavior and microstructural evolution experienced in the welds, neither of which follows the equilibrium phase diagram because of rapid heating and cooling conditions. Metallurgical phenomena in austenitic stainless steel fusion welds, types 304, 309S, 316L, 321 and 304N, were investigated in this study. Autogenous GTA welding was performed on weld coupons, and primary solidification mode and phase distribution were investigated from the welds. Varestraint test was employed to evaluate solidification cracking susceptibilities of the alloys. GTA weld fusion zones in type 304, 321 and 304N stainless steels experienced primary ferrite solidification while those in type 309S primary austenite solidification. Type 316L exhibited a mixed type of primary ferrite and primary austenite solidification. The primary solidification mode strongly depended on $Cr_{eq}/Ni_{eq}$ ratio. In terms of solidification cracking susceptibility, type 309S that solidified as primary austenite exhibited high cracking susceptibility while the alloys experienced primary ferrite solidification showed low cracking susceptibility. The relative ranking in solidification cracking susceptibility was type 304=type 304N < type 321 < type 316L < type 309S.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1991년도 특별강연 및 추계학술발표 개요집
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• pp.55-59
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• 1991

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1995년도 특별강연 및 추계학술발표 개요집
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• pp.160-161
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• 1995