• 한국재료학회지
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• 제26권4호
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• pp.200-206
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• 2016

This study was carried out to investigate the effect of W substitution on the precipitation behavior of ${\chi}$ and ${\sigma}$ phases in super duplex stainless steel. The ${\chi}$ phase was precipitated at the interface of ferrite / austenite phases and inside the ferrite phase at the initial stage of aging. With an increase in the aging time, the volume fraction of the ${\chi}$ phase increased, and then decreased with the transformation from the ${\chi}$ phase to the ${\sigma}$ phase. The ${\sigma}$ phase was precipitated later than the ${\chi}$ phase, and the volume fraction of x phase increased with the increase in the aging time. The ferrite phase was decomposed into the new austenite (${\gamma}2$) and ${\sigma}$ phases by aging treatment. The decomposition of the ferrite phase into the ${\gamma}2$ and ${\sigma}$ phases was retarded by W substitution for Mo. The volume fraction of the ${\chi}$ phase increased and that of the ${\sigma}$ phase decreased due to W substitution. The ${\chi}$ and ${\sigma}$ phases were intermetallic compounds, which had lower nickel concentration, and higher chromium, molybdenum, and tungsten concentrations. The ${\chi}$ phase has higher molybdenum and tungsten concentrations than those of the ${\sigma}$ phase. The amounts of chromium and nickel in the ${\chi}$ and ${\sigma}$ phases did not change, but these phases have higher concentrations of molybdenum and tungsten due to W substitution for Mo.

• Journal of Advanced Marine Engineering and Technology
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• 제27권6호
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• pp.704-713
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• 2003

The effect of partial substitution of tungsten for molybdenum on the microstructure and corrosion resistance in 22Cr-5Ni-3Mo duplex stainless steel(DSS) aging heat treated in a temperature range of 600~$1000^{\circ}C$ has been investigated. Electrochemical tests were carried out for the evaluation of corrosion resistance. Aging treatment had hardly influenced the general corrosion resistance. With the increase of aging time, the pitting corrosion resistance of the DSS had decreased, After aging for 2min at 700~$900^{\circ}C$, the pitting potential of the 3Mo steel decreased remarkably, while that of the W-substituted steel hardly changed. During aging. the intermetallic $\sigma$ and secondary austenite ($\gamma_2$) phases were precipitated. and the pitting corrosion and intergranular corrosion resistance were significantly decreased after aging at 700~$750^{\circ}C$ for 10 h, which could be caused by the $\gamma_2$ formation. The ${\gamma}$$_2$ phase could affect the depletion of molybdenum and chromium in the $\gamma_2/\alpha and \gamma_2/\sigma$ boundaries.

• Elastomers and Composites
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• 제56권1호
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• pp.6-11
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• 2021

In order to develop an ultra-high-density elastomeric material for substitution of steel dynamic dampers, a new curing system and technique for high-loading of the filler were examined in this study. Mechanochemical modification of chloroprene rubber (MAH-g-CR) using an internal mixer was carried out with maleic anhydride (MAH) as a reactive monomer. The optimum amount of MAH was 10 phr and the efficient grafting of MAH on CR could be achieved at a mixing temperature of 100℃. After preparing MAH-g-CR, 50 mol% epoxidized natural rubber (ENR 50) was blended with MAH-g-CR to develop a "self-curable rubber blend system" via reaction between the functional groups of the elastomeric matrices without the curing agent and additives. The content of ENR 50 was fixed at 30 wt.% throughout evaluation of the curing behavior of the MAH-g-CR/ENR blend. Tungsten powder was added to the MAH-g-CR/ENR matrix up to 60 vol.% to obtain ultra-high-density, and the maximum density obtained was 7.57 g/㎤. Stable ts2 (scorch time) and t90 (90% cure time) could be obtained even when tungsten powder was incorporated up to 60 vol.%. In addition, the tensile strength and damping properties of MAH-g-CR/ENR containing 60 vol.% of tungsten were better than those of CR containing 60 vol.% of tungsten.

• Corrosion Science and Technology
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• 제5권6호
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• pp.189-195
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• 2006

Effects of tungsten (W) on the precipitation kinetics of secondary phases and the associated resistance to pitting corrosion of 25%Cr duplex stainless steels were investigated through microstructural and electrochemical noise analyses. With the partial substitution of W for Mo in duplex stainless steel, the potential and current noises of the alloy were significantly decreased in chloride solution due to retardation of the ${\sigma}$ phase precipitation. The preferential precipitation of the $\chi$ phase in the W-containing alloy during the early period of aging contributed to retarding the precipitation of the $\sigma$ phase by depleting W and Mo along grain boundaries. In addition, the retardation of the nucleation and growth of the $\sigma$ phase in the W-containing alloy appears to be attributed to the inherently low diffusivity of W compared with that of Mo.

• 한국해양공학회지
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• 제23권6호
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• pp.87-92
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• 2009

The effect of aging on the precipitation of the $\sigma$ phase and the corrosion resistance in tungsten substituted super duplex stainless steels was investigated. The volume fraction of the $\sigma$ phase and the current density increased with aging at temperatures up to $750^{\circ}C$ and then decreased. With an increase in aging time, the volume fraction of the $\sigma$ phase and the current density also increased. The $\sigma$ phase hardly influenced the corrosion resistance. With the substitution of tungsten for molybdenum in super duplex stainless steel, the volume fraction of the $\sigma$ phase and the current density decreased remarkably.

• 한국해양공학회지
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• 제27권2호
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• pp.75-79
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• 2013

This study was carried out to investigate the precipitation behavior of the ${\chi}$ phase and the impact toughness of 25%Cr-7%Ni-2%Mo-4%W super duplex stainless steel. The ${\chi}$ phase was precipitated in the early stage of aging, and with the increasing aging time. However, after reaching a maximum value, the number decreased as a result of the gradual transformation of the ${\chi}$ phase into the ${\sigma}$-phase. It was proved that the ${\chi}$ phase was an intermetallic compound, which represented a lower nickel concentration, higher chromium and molybdenum concentrations, and very higher tungsten concentration compared to the matrix phases. It also showed higher molybdenum and tungsten concentrations than the ${\sigma}$ phase. The decomposition of the ferrite phase into the ${\gamma}_2$ and ${\sigma}$ phases was retarded by W substitution for Mo. Thus, the number of ${\chi}$ phases increased. The impact value was decreased by the substitution of W for Mo. The impact toughness rapidly decreased with time when the ${\chi}$ phase began to precipitate in the initial stage of aging. The impact toughness was, therefore, greatly influenced for the precipitation of the ${\chi}$ phase.

• 비파괴검사학회지
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• 제24권1호
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• pp.29-37
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• 2004

22Cr-5Ni 2상 스테인리스강의 합금원소 중 몰리브덴(Mo) 원소를 텅스텐(W)으로 치환하여 크리프거동에 미치는 영향을 조사하였다. 그리프시험은 $600^{\circ}C$와 $650^{\circ}C$의 온도에서 실시하였다. $650^{\circ}C$ 크리프 시에는 취약한 금속간화합물인 ${\sigma}$상이 석출하였으며 이것은 크리프수명을 급격히 감소시키는 역할을 하였다. Mo에 대한 W원소의 치환은 일반적으로 ${\sigma}$상의 석출을 지연시킨다고 알려져 있으나, 2wt.%까지 W 치환을 실시한 본 연구범위에서는 크리프 수명 및 최소 크리프속도에 뚜렷한 영향을 미치지 못하였다. 크리프손상의 정도를 평가하기 위하여 크리프시편에 대한 초음파검사를 실시하였다 크리프온도 $600^{\circ}C$에서는 크리프시편의 수명이 증가함에 따라 음속이 비례적으로 증가하였으나 $650^{\circ}C$에서는 반대로 감소하였다.

• 대한화학회지
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• 제34권1호
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• pp.85-90
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• 1990

Tetrakis(picolinato)tungsten(IV) 착물에 과량의 methylpicolinic acid를 가하여, 무극성 용액에서 얼마나 inert한지를 60 ~ 120$^{\circ}C$ 및 키실렌의 환류조건에서 분광학적 방법을 관찰하였다. 산소접촉 여부에 무관하게 90$^{\circ}C$에서 2일간은 inert하였으나 산소접촉하에서는 존재하는 리간드농도 제곱에 역비례하는 속도상수를 보이며 급격히 산화되며 리간드를 잃었다. Ar기체하에서 sealing한 시료는 반응속도상수 [k($sec^{-1}$)] = $8.8{\times} 10^{-7}$를 보이며 50일까지 반응속도론적으로 안정하였다. 배위된 질소의 인접 양성자($H_6$)의 화학적 이동은 없었으나 리간드를 잃음에 따라 intensity가 감소하였으며 새로운 유리리간드의 $H_6$ peak가 생성됨을 확인하여 치환반응은 일어나지 않고 착물이 산화되며 리간드를 잃고 있음을 확인하였다.

• 한국군사과학기술학회지
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• 제14권2호
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• pp.264-270
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• 2011

This paper focuses on possibility to design and fabrication new combination of bullet core to substitute current toxic material of heavy metal such as lead by environment-friendly ones. The core is designed as dual structure to manipulate the core center of gravity easily by combining materials, which of basis is tungsten of low cost and easily acquired. Those combinations are W-M series such as W-Cu, W-Sn, W-Cu-Sn, and W-Cu-Ni to target the density of lead, $11.34g/cm^3$ through powder-metallurgy. Out of four, combination of W-Cu-Ni shows the highest compression density of 96% and is confirmed as the most suitable substitution for lead due to the excellent property of matter and sintering. All combination samples is simulated on the PRODAS software for designing and structure analysis by adjusting the center of gravity of dual core samples forward and backward. The simulations confirm the similarity of current bullet core with respect to properties of mass, aero dynamics, and flying stability.

• 한국분말재료학회지
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• 제15권3호
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• pp.239-243
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• 2008

Ni-W(1-5 at.%) alloy rods were made by powder metallurgy process including powder mixing, compacting and subsequent sintering. Ni and W powder of appropriate compositions were mixed by a ball milling and isostatically pressed in a rubber mold into a rod. The compacted rods were sintered at $1000^{\circ}C-1150^{\circ}C$ at a reduced atmosphere for densification. The lattice parameters of Ni-W alloys were estimated by a high resolution neutron powder diffractometer. All sintered rods were found to have a face centered cubic structure without any impurity phase, but the diffraction peak locations were linearly shifted with increasing W content. The lattice parameter of a pure Ni rod was $3.5238{\AA}$ which is consistent with the value reported in JCPDS data. The lattice parameter of N-W alloy rods increased by $0.004{\AA}$ for 1 atomic % of W, which indicates the formation of a Ni-W solid solution due to the substitution of nickel atoms by tungsten atoms of larger size.