• 한국재료학회지
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• 제6권12호
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• pp.1221-1232
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• 1996

용접부 인성을 향상시키기 위해 Ti 산화물을 첨가한 Ti 산화물강에 대하여 용접시 최고가 열온도와 냉각속도의 변화가 용접열영향부의 미세조직에 미치는 영향을 조사하였다. 용접열영향부의 인성향상에 기여하는 acicular ferrite는 140$0^{\circ}C$ 이상의 최고가열온도와 $\Delta$t800-500가 40초보다 빠른 냉각속도에서 활발해 생성되었다. 오스테나이트 결정립내에서 개재물로부터 핵생성된 일차 acicular ferite의 생성량은 전체 aicular ferrite의 약 20% 정도로 적었으며 대부분의 acicular ferrite는 일차 acicular ferrite로부터 생성된 이차 acicular ferrite인 것으로 나타났다. 이차 acicular ferrite는 plate사이에 Fe3C층이 존재하는 것으로 보아 확산기구에 의해 생성되는 것으로 생각된다. 개재물은 TiO, TiO2, TiN, MnS, AI2O3 MnO(galaxite)등으로 구성된 복합상이었으며 개재물이 일차 acicular ferrite의 핵생성 site로 작용하기 위해서는 약 1$\mu\textrm{m}$이상의 크기가 효과적인 것으로 나타났다. Ti 산화물과 TiN는 직접적인 acicular ferrite의 핵생성 site로 작용하기보다는 MnS, galaxite 등의 석출 site로 작용하여 개재물의 크기를 증가시킴으로써 acicular ferrite의 생성을 촉진시키는 것으로 생각된다.

• 한국재료학회지
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• 제10권3호
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• pp.223-226
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• 2000

산소 결핍 페라이트 (oxygen deficient ferrites, ODF) $MeFe_2O_{4-\delta}$는 약 $300^{\circ}C$의 낮은 온도에서 $CO_2$를 C와 $O_2$로 분해한다. 본 연구에서는 $(Ni_x,\;Zn_{1-x}Fe_2_4$ 초미세 페라이트 분말을 수열합성법으로 제조하여 $CO_2$ 분해특성을 살펴보았다. 제조된 페라이트는 XRD 분석 결과, 페라이트의 전형적인 스피넬 구조를 보여주고 있으며, ICP-AES, EDS 정량분석에 의하여 초기 혼합 조성비와 거의 동일한 조성비로 합성되었음을 알 수 있었다. 제조된 (Ni, Zn)-ferrites 분말의 BET 비표면적은 약 $110\textrm{mg}^2$/g$ 이상의 큰 값으로 나타났으며, 입자크기는 약 5~10nm로 매우 작았다. 산소결핍 페라이트 $(Ni_x,\;Zn_{1-x})Fe_2O_{4-{$\delta}}$의 $CO_2$ 분해 효율은 조성에 따라 큰 차이를 보이지 않았으며 3원계 (Ni, Zn)-ferrite가 Ni-ferrite보다 더 높았다.

• Journal of Welding and Joining
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• 제33권4호
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• pp.37-43
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• 2015

Characteristics of dissimilar metal welds between STS 316L and carbon steel ASTM A516 Gr.70 made with GTAW have been evaluated in terms of microstructure, ferrite content, chemical analysis, hardness and corrosion resistance. Three heat inputs of 9.00, 11.25, 13.00kJ/cm were employed to make joints of dissimilar metals with ER309 wire. Based on microstructural examination, the amount of vermicular type of ${\delta}$-ferrite was increased with increasing heat input due to the increase of Creq/Nieq in the second layer of welds. Based on the EDX analysis of weld metals, Cr and Ni content in the 2nd layer increased while those content in the first layer of welds decreased with heat inputs. Cellular solidification mode in the 1st layer and dendritic solidification mode in the 2nd layer due to different cooling rates were prevailed, respectively. Heat affected zone which formed hard microstructure showed higher hardness than the weld metal. The salt spray test of dissimilar metals weld joints showed that the carbon steel surfaces only corroded. The weight loss rate due to corrosion increased up to 100hours but it decreased above 100 hours. There was little difference in the weight loss caused by corrosion regardless of heat inputs.

• Journal of Welding and Joining
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• 제32권2호
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• pp.29-36
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• 2014

Recently, in order to enhance the function and usefulness of products, cladding of dissimilar materials that maximizes the performance of the material is being widely used in all areas of industry as an important process. Clad steel plate, produced by cladding stainless steel plate, an anticorrosive material, on carbon steel plate, is being used to produce pressure vessels. Stainless steel plate has good corrosion resistance, and carbon steel plate has good rigidity and strength; clad steel can satisfy all of these qualities at once. This study aims to find the ${\delta}$-ferrite behavior, mechanical properties, structure change, integrity and reliability of clad steel weld on hot rolled steel plates. For this purpose, multi-layer welding, repair welding and post weld heat treatment were implemented according to welding procedure specifications (WPS). In order to observe the mechanical properties and toughness of clad steel weld zone, post weld heat treatment was carried out according to ASME Sec. VIII Div.1 UW-40 procedure for post weld heat treatment. With heat treatment at $625^{\circ}C$, the hold time was used as the process variable, increased by intervals that were doubled each time, from 80 to 1,280 min. The structure of weld part was typical cast structure; localized primary austenite areas appeared near central vermicular ferrite and fusion line. The heat affected zone showed rough austenite structure created by the weld heat input. Due to annealing effects of heat treatment, the mechanical properties (tensile strength, hardness, impact value) of the heat affected area tended to decrease. From the results of this study, it is possible to conclude the integrity of clad steel welds is not affected much in field welding, repair welding, multi-layer welding, post weld heat treatment, etc.

• 한국세라믹학회지
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• 제31권12호
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• pp.1491-1500
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• 1994

Nonstoichiometry($\delta$) and the phase stability region of a ferrite spinel (Mg0.29Fe0.71)3-$\delta$O4 have been investigated by a coulometric titration method as a function of temperature(T) and oxygen partial pressure(Po2). It has been found that the spinel is thermodynamically stable in the ranges -8.0$\leq$log(PO2/atm)$\leq$-2.4, -7.0$\leq$log(PO2/atm)$\leq$-1.7 respectvely at 100$0^{\circ}C$. The nonstoichiometry extends over the ranges of -0.004$\leq$$\delta$$\leq$0.007, -0.008$\leq$$\delta$$\leq$0.006, -0.033$\leq$$\delta$$\leq$0.004 at 100$0^{\circ}C$, 120$0^{\circ}C$, respectvely. The observed PO2-dependence of $\delta$ suggests that the majority ionic defects are cation interstitials in the low PO2 region and cation vacancies in the high PO2 region.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2001년도 춘계학술발표회요약집
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• pp.294-294
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• 2001

• 한국세라믹학회지
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• 제19권3호
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• pp.223-228
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• 1982

For the preparation of ferroxidure BaO.5.5 $Fe_2O_3$ with high coercive force, the green and calcined coprecipitates, which were obtained by neutralizing the mixed salt solution $FeCl_2-BaCl_2$ and $FeCl_3-BaCl_2$ with alkali solution $NaOH-Na_2CO_3$, were investigated about the thermal reaction, crystal growth, and the magnetic properties of the sintered specimens. The very single-domain crystallites of Ba-ferrite with high coercive force are formed from the coprecipitate of amorphous $Fe(OH)_3$ and amorphous $BaCO_3$ at lower temperature than that of subnucleus crystalline $\delta$-FeOOH and amorphous $BaCO_3$.

• 한국표면공학회지
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• 제21권4호
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• pp.176-182
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• 1988

Effects of Cr, Ni and W on the anodic polarization behavior were investigated for Fe-Cr-Ni-W alloys in deaerated 1N HCI solution. Surface films formed on the polarization were analysed using AES, SEM and EDAX. A higerconcentration of tungten was found in the surface oxide film compared to the matrix. It played an importanet role on incresing the stability of the passive film. The presence of an adequate amount of Cr was essential to increase the pitting resistance of the alloys in acid chloride media. Under 12 wt%cr,alloys containing 6wt%W did not exhidit any passivity at all. The main role of Ni was to control the microstructure rather than to modify the corrosion resistance. In 23 cr-14Ni-^W alloy, the duplex microstructure of ferrite($\delta$-phase) in an austenic matrix was developed. The reson why proferred pitting appeared in austenite and ferrite/austenite interface was that ferrite had more amount of Cr and W than austenite.

• 한국세라믹학회지
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• 제35권8호
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• pp.836-842
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• 1998

In this experiment well-know additives for Mn-Zn ferrites CaO and {{{{ { SiO}_{2 } }} were added at various content and their effects on microstructures and magnetic properties with sintering atmosphere were examined. By adding up to 0.04wt% {{{{ { SiO}_{2 } }} and and 0.06wt% CaO the sintered density was increased and then decreased gra-dually. Higher sintered density and initial permeability were observed by adding both CaO and {{{{ { SiO}_{2 } }} than by adding CaO or {{{{ { SiO}_{2 } }} alone. Without any additives initial permeability and tan$\delta$/${\mu}$ decreased at 1000kHz as oxidation degree(${\gamma}$) increased.

• 전기화학회지
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• 제9권2호
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• pp.70-76
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• 2006

마이크로 전기화학 실험법인 비접촉식 미세방울셀이 산 용액에 노출된 저 크롬이 함유된 스테인리스강(STS 316)과 같이 젖음성이 높은 전기화학계에 사용되는데 어려움이 있었다. 음압의 인가, 방울의 크기 제어 그리고 소수성의 개스킷의 사용은 높은 젖음성을 지닌 표면에서 비접촉식 미세방울셀의 적용을 가능하게 하였다. 개선된 미세방울셀의 신뢰성을 확인하고자 3종류의 다른 계-산성염화용액과 고 크롬 페라이트 스테인리스강, 산성염화용액과 STS 316 그리고 중성염화용액과 STS 316-에 대하여 개선된 미세방울셀로 국부부식 연구를 수행하였다. 첫째 산성용액에서 고 크롬강의 양극 분극 결과는 $\alpha/\sigma$ 계면 근처에서 국부부식이 크롬 고갈층에 의한 것임을 보여주었다. 둘째 산성용액에서 STS316의 양극 분극실험이 개선된 미세방울셀에서 성공적으로 수행됨을 확인할 수 있었다. 특히, 미세방울셀에서 얻어진 국부 양극 분극곡선을 통해 STS316의 내식성에 미치는 $\delta$-라이트 영향을 밝힐 수 있었다. 마지막으로 중성염화 용액에서 STS316의 양극 분극곡선은 핏팅 저항성이 $\delta$-페라이트보다 개재물에 의존됨을 보여주었다.