• Title/Summary/Keyword: Grain size of ferrite

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600MPa급과 800MPa급 전용착금속의 미세조직에 따른 수소지연파괴 거동 (Microstructural Effects on Hydrogen Delayed Fracture of 600MPa and 800MPa grade Deposited Weld Metal)

  • 강희재;이태우;윤병현;박서정;장웅성;조경목;강남현
    • 대한금속재료학회지
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    • 제50권1호
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    • pp.52-58
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    • 2012
  • Hydrogen-delayed fracture (HDF) was analyzed from the deposited weld metals of 600-MPa and 800-MPa flux-cored arc (FCA) welding wires, and then from the diffusible hydrogen behavior of the weld zone. Two types of deposited weld metal, that is, rutile weld metal and alkali weld metal, were used for each strength level. Constant loading test (CLT) and thermal desorption spectrometry (TDS) analysis were conducted on the hydrogen pre-charged specimens electrochemically for 72 h. The effects of microstructures such as acicular ferrite, grain-boundary ferrite, and low-temperature-transformation phase on the time-to-failure and amount of diffusible hydrogen were analyzed. The fracture time for hydrogen-purged specimens in the constant loading tests decreased as the grain size of acicular ferrite decreased. The major trapping site for diffusible hydrogen was the grain boundary, as determined by calculating the activation energies for hydrogen detrapping. As the strength was increased and alkali weld metal was used, the resistance to HDF decreased.

복합조직강의 미시조직변화가 피로파괴전파에 미치는 영향 (The Effects of the Microstructural Change of Dual Phase Steel on Fatigue Fracture Propagation)

  • 오세욱;김웅집
    • 한국해양공학회지
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    • 제5권2호
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    • pp.198-198
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    • 1991
  • Not only difference of fatigue crack growth and propagation behavior resulted from the grain size, the hardness ratio and volume fraction in M.E.F. dual phase steel composed of martensite in hard phase and ferrite in soft phase, but also the effects of the plastic constraint were investigated by fracture mechanics and microstructural method. The main results obtained are as follows: 1) The fatigue endurance of M.E.F. steel increases with decreasing the grain size, increasing the ratio of hardness and volume fraction. 2) The initiation of slip and crack occures faster as the stress level goes higher. These phenomena result from the plastic constraint effect of the second phase. 3) The crack propagation rate in the constant stress level is faster as the grain size gets larger, the ratio of hardness lower and volume fraction smaller.

대입열 EH36-TM강의 Tandem EGW 용접부 미세조직 및 기계적 성질 (Mechanical Properties and Microstructures of High Heat Input Welded Tandem EGW Joint in EH36-TM Steel)

  • 정홍철;박영환;안영호;이종봉
    • Journal of Welding and Joining
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    • 제25권1호
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    • pp.57-62
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    • 2007
  • In the coarse grained HAZ of conventional TiN steel, most TiN particles are dissolved and austenite grain growth easily occurrs during high heat input welding. To avoid this difficulty, thermal stability of TiN particles is improved by increasing nitrogen content in EH36-TM steel. Increased thermal stability of TiN particle is helpful for preventing austenite grain growth by the pinning effect. In this study, the mechanical properties and microstructures of high heat input welded Tandem EGW joint in EH36-TM steel with high nitrogen content were investigated. The austenite grain size in simulated HAZ of the steel at $1400^{\circ}C$ was much smaller than that of conventional TiN steel. Even for high heat input welding, the microstructure of coarse grained HAZ consisted of fine ferrite and pearlite and the mechanical properties of the joint were sufficient to meet all the requirements specified in classification rule.

600 MPa급 고강도 일반 및 내진 철근의 미세조직, 경도와 인장 특성 (Microstructure, Hardness and Tensile Properties of 600 MPa-Grade High-Strength and Seismic Resistant Reinforcing Steels)

  • 서하늘;이상인;황병철
    • 한국재료학회지
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    • 제27권9호
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    • pp.477-483
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    • 2017
  • This present study deals with the microstructure and tensile properties of 600 MPa-grade high strength and seismic resistant reinforcing steels. The high strength reinforcing steel (SD 600) was fabricated by Tempcore processing, while the seismic resistant reinforcing steel (SD 600S) was air-cooled after hot-rolling treatment. The microstructure analysis results showed that the SD 600 steel specimen consisted of a tempered martensite and ferrite-pearlite structure after Tempcore processing, while the SD 600S steel specimen had a fully ferrite-pearlite structure. The room-temperature tensile test results indicate that, because of the enhanced solid solution and precipitation strengthening caused by relatively higher contents of C, Mn, Si and V in the SD 600S steel specimen, this specimen, with fully ferrite-pearlite structure, had yield and tensile strengths higher than those of the SD 600 specimen. On the other hand, the hardness of the SD 600 and SD 600S steel specimens changed in different ways according to location, dependent on the microstructure, ferrite grain size, and volume fraction.

Sol-gel 법에 의한 Co-Zn Ferrite 박막의 제호와 자기 특성에 관한 연구 (Fabrication and magnetic properties of Co-Zn ferrite thin films prepared by a sol-gel process)

  • 김철성;안성용;이승화;양계준;류연국
    • 한국자기학회지
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    • 제11권4호
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    • pp.168-172
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    • 2001
  • Sol-gel법을 이용하여 Co$_{0.9}$Zn$_{0.1}$Fe$_2$O$_4$ 박막을 제조하였다. 성장한 박막의 구조 및 자기적 성질에 관하여 x선 회절분석기 (XRD), atomic force microscopy(AFM) 및 Auger electron spectroscopy(AES), 진동시료자화측정기 (VSM)을 이용하였다. Co-Zn 페라이트 박막의 경우, 400 $^{\circ}C$ 이상의 열처리 온도에서 단일상의 spinel 구조만을 가지고 있으며, 아무런 방향성이 없이 성장함을 나타내고 있다. 열처리 온도가 600 $^{\circ}C$ 이하에서 성장된 박막 표면의 거칠기는 3 nm 이하였으며, 형성된 입자의 크기는 약 40nm이하임을 알 수 있었다. 또한, 40$0^{\circ}C$에서 열처리한 경우 기판에서 Si이 Co-Zn 페라이트 박막내로 확산이 거의 나타나지 않았으나, 870 $^{\circ}C$에서 열처리한 경우 계면에서 기판과 박막의 상호 확산을 확인할 수 있었다. 제작한 박막은 외부 자기장의 방향과는 무관한 등방성의 자기적 특성을 보이며, 최대 보자력은 600 $^{\circ}C$에선 열처리한 자성박막이 약 1,900 Oe을 가짐을 알 수 있었다.있었다.

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Ti산화물강의 HAZ인성 및 미세조직에 미치는 용접열 cycle의 영향 (Effect of weld thermal cycle on the HAZ toughness and microstructure of a Ti-oxide bearing steel)

  • 정홍철;한재광;방국수
    • Journal of Welding and Joining
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    • 제14권2호
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    • pp.46-56
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    • 1996
  • HAZ impact toughness of Ti-oxide steel was investigated and compared to that of a conventional Ti-nitride steel. Toughness variations of each steel with weld peak temperatures and cooling rates were interpreted with microstructural transformation characteristics. In contrast to Ti-nitride steel showing continuous decrease in HAZ toughness with peak temperature, Ti-oxide steel showed increase in HAZ toughness above $1400^{\circ}C$ peak temperature. The HAZ microstructure of the Ti-oxide steel is characterized by the formation of intragranular ferrite plate, which was found to start from Ti-oxide particles dispersed in the matrix of the steel. Large austenite grain size above $1400^{\circ}C$ promoted intragranular ferrite plate formation in Ti-oxide steel while little intragranular ferrite plate was formed in Ti-nitride steel because of dissolution of Ti-nitrides. Ti-oxides in the Ti-oxide steel usually contain MnS and have crystal structures of TiO and/or $Ti_2O_3$.

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유기산염 열분해법에 의한 Cu-Ni-Zn 페라이트의 전자파 흡수 특성 (The Electromagnetic Wave Absorption Characteristics of Cu-Ni-Zn Ferrite by Thermal Decomposition of Organic Acid Salt)

  • 정재우;이완재
    • 한국자기학회지
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    • 제5권6호
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    • pp.947-951
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    • 1995
  • 페라이트는 높은 자기적 손실을 이용하여 전자파 흡수체로 사용하고 있다. 전자파 흡수체는 미세조직이 균일하고 미세할수록 흡수특성이 향상된다. 유기산염 열분해법으로 합성한 분말을 사용하여 Cu-Ni-Zn 페라이트를 제조하였다. 복소유전율과 복소투자율은 밀도가 높고, 입자의 크기가 미세할수록 상승하였다. 페라이트의 정합두께는 소결온도가 높을수록 얇아졌다. Cu-Ni-Zn 페라이트의 전자파 흡수능은 정합두께가 6.75 mm 일 때 160 MHz 부터 640 MHz 까지의 주파수에서 20dB 이상의 값이엿다.

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다결정 Mg-페라이트의 기공율, 입경, 포화 자화 및 이방성 자기장이 강자성 공명 특성에 미치는 영향 연구 (The study on effects of porosity grain size, magnetization and anisotropy field on the properties of ferromagnetic resonance)

  • 김진호;주승기;최덕균
    • 전자공학회논문지A
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    • 제32A권1호
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    • pp.97-102
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    • 1995
  • The ferromagnetic resonance properties of Mg ferrites which have various porosity grain size, and saturation magnetization are measured at one frequency. This allows a determination of the anisotropy field(Ha). The saturation magnetization multiplied by porosity is the resonance magnetic field. As the saturation magnetization increases, the linewidth decerases due to decrement of magnetic inhomogenity in sample. the porosity is a major factor broadening the linewidth for Mg ferrite when porosity is more thatn 6%, and the anisotropy field is dominant when porosity is less than 6%.

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전기방사법에 의한 NiZn 페라이트 나노섬유의 제조 및 특성 연구 (Preparation and Characterization of NiZn-Ferrite Nanofibers Fabricated by Electrospinning Process)

  • 주용휘;남중희;조정호;전명표;김병익;고태경
    • 한국세라믹학회지
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    • 제46권1호
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    • pp.74-80
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    • 2009
  • Electrospinning process is the useful and unique method to produce nanofibers from metal precursor and polymer solution by controlled viscosity. In this study, the NiZn ferrite nanofibers were prepared by electrospinning with a aqueous metal salts/polymer solution that contained polyvinyl pyrrolidone and Fe (III) chloride, Ni (II) acetate tetrahydrate and zinc acetate dihydrate in N,N-dimethylformamide. The applied electric field and spurting rate for spinning conditions were 10 kV, 2 ml/h, respectively. The obtained fibers were treated at $250^{\circ}C$ for 1 h to remove the polymer. Finally, the NiZn ferrite fibers were calcined at $600^{\circ}C$ for 3 h and annealed at $900{\sim}1200^{\circ}C$ in air. By tuning the viscosity of batch solution before electrospinning, we were able to control the microstructure of NiZn ferrite fiber in the range of $150{\sim}500\;nm$ at 770 cP. The primary particle size in $600^{\circ}C$ calcined ferrite fiber was about 10 nm. The properties of those NiZn ferrite fibers were determined from X-ray diffraction analysis, electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, thermal analysis, and magnetic measurement.

첨가제 변화에 따른 Ni0.8Zn0.2Fe2O2 의 미세구조와 자기적 특성 (The Effects of Additives on Microstructure and Magnetic Properties of Ni0.8Zn0.2Fe2O2)

  • 오영우;이선학;이해연;김현식
    • 한국전기전자재료학회논문지
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    • 제15권5호
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    • pp.406-411
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    • 2002
  • Ni-Zn ferrite is required to have predominant and stable characteristics in the range of high frequency for the power line communication, so that microstructures and magnetic properties such as power loss and initial permeability in $Ni_{0.8}Zn_{0.2}Fe_2O_4$ were investigated in terms of variable $Bi_2O_3,CaO$ and $V_2O_5$ contents. $Bi_2O_3$ and $V_2O_5$ liquid phase created during sintering process promoted sintering and grain growth but much of the closed pore existed in the grains. The grain size of the specimens with $V_2O_5$ of over 0.5 wt% decreased as the result of "pinning effect"and the resonance frequency increased with CaO of 0.3we%. The high initial permeability of 81.52%, resonance frequency of 17.05 MHz and low power loss of 17,858 kW/$\textrm{m}^3$ were obtained from the samples with $Bi_2O_3$ of 0.5, CaO of 0.3, and $V_2O_5$ of 0.7 wt%.