• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 somma/kms meeting
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• pp.210-210
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• 2003

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 somma/kms meeting
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• pp.270-270
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• 2003

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2007년도 The 1st International Symposium on Advanced Magnetic Materials
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• pp.273.1-273.1
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• 2007

• 한국자기학회지
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• 제24권2호
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• pp.46-50
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• 2014

Sol-gel법을 이용하여 $Fe_3O_4$과 $M_{0.2}Fe_{2.8}O_4$(M =Mn, Ni, Cu) 박막 시료을 만들어 M 치환에 따른 $Fe_3O_4$의 결정구조적 특성 및 양이온 분포를 X-ray diffraction(XRD)과 conversion electron M$\ddot{o}$ssbauer(CEMS) 분광법을 이용하여 조사하였다. CEMS 분광법을 이용하여 Fe 이온의 전하상태와 거동과 초미세 자기적 특성을 분석하였다. $M_{0.2}Fe_{2.8}O_4$(M =Mn, Ni, Cu) 시료들은 $Fe_3O_4$에서와 같이 입방정 스피넬 구조를 나타내었으며, Ni 이온 치환된 시료에서는 격자상수 값이 $Fe_3O_4$에서의 값과 비교하여 감소하였고, Mn 및 Cu 이온 치환된 시료에서는 증가하였다. CEMS 분석 결과 $Mn^{2+}$ 및 $Ni^{2+}$ 이온들은 주로 팔면체 자리를 치환하는 것으로 나타났으며, $Cu^{2+}$ 이온들은 팔면체, 사면체 자리를 모두 치환하는 것으로 나타났다. 부스펙트럼들의 세기비 $A_B/A_A$는 계산값과 측정값에 다소 차이가 있었으며, 이것은 M 치환이 A와 B자리의 Debye 온도에 영향을 주는 것으로 해석된다. B-자리 부스펙트럼의 비교적 큰 선폭값은 M 이온 치환에 기인한 B-자리의 M 이온분포가 초미세자기장에 미치는 분포효과로 나타났다.

• 한국재료학회지
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• 제23권9호
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• pp.525-530
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• 2013

This study investigated the continuous cooling transformation, microstructure, and mechanical properties of highstrength low-alloy steels containing B and Cu. Continuous cooling transformation diagrams under non-deformed and deformed conditions were constructed by means of dilatometry, metallographic methods, and hardness data. Based on the continuous cooling transformation behaviors, six kinds of steel specimens with different B and Cu contents were fabricated by a thermomechanical control process comprising controlled rolling and accelerated cooling. Then, tensile and Charpy impact tests were conducted to examine the correlation of the microstructure with mechanical properties. Deformation in the austenite region promoted the formation of quasi-polygonal ferrite and granular bainite with a significant increase in transformation start temperatures. The mechanical test results indicate that the B-added steel specimens had higher strength and lower upper-shelf energy than the B-free steel specimens without deterioration in low-temperature toughness because their microstructures were mostly composed of lower bainite and lath martensite with a small amount of degenerate upper bainite. On the other hand, the increase of Cu content from 0.5 wt.% to 1.5 wt.% noticeably increased yield and tensile strengths by 100 MPa without loss of ductility, which may be attributed to the enhanced solid solution hardening and precipitation hardening resulting from veryfine Cu precipitates formed during accelerated cooling.

• 열처리공학회지
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• 제8권2호
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• pp.101-112
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• 1995

A study was made to examine the effects of heat-treatment on the microstructures of Cu-bearing HSLA steels. The details of microstructures were studied by using optical microscopy(OM), transmission electron microscopy(TEM) and hardness test. The as-rolled microstructure of HSLA-A consists of ferrite (${\alpha}$) whereas that of HSLA-B consists of needle-shaped phase. The difference in microstructure can be ascribed to the different amount of Ni, Mn, Mo, Cu which affect the hardenability. The austenite grain size is very small up to $1000^{\circ}C$ owing to the Nb-precipitates. As the austenitizing temperature increases above $1000^{\circ}C$, the austenite grain grows rapidly. There are two hardness peaks in the hardness versus temperature curve, at $500^{\circ}C$ and at $675^{\circ}C$ (HSLA-A), $725^{\circ}C$ (HSLA-B). The peak at $500^{\circ}C$ result from the formation of Cu-precipitates and second hardness peak is created due to the formation of M-A constituents. The hardriess decrease in HSLA-B steel with ageing temperature is small because of the higher amounts of Cu than HSLA-A steel. The fine, round ${\varepsilon}$-Cu precipitates grow with ageing temperature and finally transform into rod shape.

• Corrosion Science and Technology
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• 제21권4호
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• pp.273-281
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• 2022

The effect of addition of Cu on the localized corrosion performance of aged duplex stainless steel in chloride media has yet to be explained in a consistent manner, and there is some controversy in the literature regarding the composition of stainless steel and the experimental conditions (pH, temperature, chloride concentration, etc.) used. In this work, the effect of the addition of Cu on the microstructure, hardness, and corrosion resistance of duplex stainless steel in an acidic chloride or high concentration sulfuric acid solutions was investigated for annealed and aged alloys. The Cu addition of annealed duplex stainless steel strengthened the alloy and reduced the ferrite contents of the alloy, and it also increased the polarization behavior in chloride or sulfuric solutions, except for the case of a high potential in acidic chloride solution. However, the Cu addition of aged duplex stainless steel reduced the formation of harmful phases such as sigma and kai and increased the polarization behavior in acidic chloride or sulfuric solutions up to 0.8 wt% of the Cu content, after which it slightly decreased at 0.8 wt% Cu or more.

• 소성∙가공
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• 제15권2호
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• pp.118-125
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• 2006

API steel is used for line-pipe to transport the oil and natural gas. As the recent trends in the development of API steel are towards the use of larger diameter and thicker plate, many researches have been studied to achieve higher strength, higher toughness and lower yield ratio in API steel. However, the strength of API steel after pipe forming is changed depending on the competition of the Bauschinger effect and work hardening which are affected by the strain history during pipe forming process. So, the purpose of this study is to investigate the influence of microstructure on the Bauschinger effect for API steel. To change the microstructure of API steel we have changed the hot rolling condition and the amounts of V and Cu addition. The compression-tensile test and the microstructure observation by OM and TEM were conducted to investigate the yield strength drop and the correlation between the Bauschinger effect and microstructure of API steel. The experimental results show that the increase of polygonal ferrites volume fraction increases the Baushcinger effect due to the back stress which comes from the increase of mobile dislocation density at polygonal ferrite interior during the compressive deformation. The hot rolling condition was more effective on the Bauschinger effect in API steel than the small amount of V and Cu addition.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.365-368
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• 2000

We have studies on the Microstructures and densities as a function of forming pressures and the magnetic properties of the specimens with additive Bi$_2$O$_3$ that sintered at 95$0^{\circ}C$ for 4.5 hours for synthesizing optimal Ni-Cu-Zn ferrite. Green density rose generally as Forming pressure increased from 1.7 ton/cm$^2$to 2.5 ton/cm$^2$and Cold Isostatic Pressure(CIP) method was more effective than Die Pressure(DP) method to high green density. Forming pressure had no influence on apparent density but on the other hand Bi$_2$O$_3$contents were strongly dominant to appaernt density than forming pressure. Bi$_2$O$_3$liquid phases created during sintering process promoted sintering and grain growth so that apparent density, grain size and permeability increased compared to that of the specimens which were sintered with non-additive Bi$_2$O$_3$.

• 한국자기학회지
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• 제5권2호
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• pp.123-127
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• 1995

Copper ferrite $CuFe_{2}O_{4}$를 화학적인 방법을 사용한 미세입자 상태에서 시료를 제조한 후 이에 대한 결정학적 및 자기적 성질을 X-선 회절, $M\"{o}ssbauer$ 분광법 등을 사용하여 연구하였다. 결정구조는 서냉하여 제조한 결과 tetragonal phase spinel 구조로서 결정 상수는 $a=8.26{\pm}0.05{\AA},\;c=8.75{{\pm}}0.05{\AA}$로 측정되 었다. 실내 온도에서 부터 Curie 온도 이상까지 여러 온도범위에서 $M\"{o}ssbauer$ spectrum 을 측정, 분석한 결과 $Cu_{2+}$는 저온에서 spinel 구조의 8면체 자리에 위치하여 Jahn-Teller 효과를 나타내고, 이에 따라 630K 근방에서 결정구조상의 변화가 일어나고 있음을 알았다. Curie 온도는 690K로 세라믹 방법으로 제조한 시료에 비해 낮은 것으로 나타났다.