• 제목/요약/키워드: Transformation Heat

검색결과 584건 처리시간 0.026초

Effect of Phase Stability on the Microstructure Development of α-SiAlON Ceramics

  • Kim, Joosun;Lee, Hae-Weon;Chen, I-Wei
    • 한국분말재료학회지
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    • 제10권2호
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    • pp.118-122
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    • 2003
  • Alpha-SiAlON ceramics having various compositions and modifying cations were investigated with respect to their phase stability, transformation kinetics. and resulting microstructures. Each composition was heat treated at 150$0^{\circ}C$ for 1h and measured the $\alpha$-SiAlON transformation. The phase-boundary composition in the single-phase $\alpha$-SiAlON region showed sluggish transformation from $\alpha$-$Si_3N_4$ to $\alpha$-SiAlON compared to the phase-center composition in the diagram. Using the different rare earth modifying cations, dependence of transformation kinetics on the phase stability in a fixed composition was also explained. By changing size of the stable u-phase region with exchanging cations, systematic change in transformation was observed. Transformation rate of $\alpha$-SiAlON at low temperature has an important role on controlling the final microstructure. Less transformation gives more chances to develop elongated grain in the microstructure.

고온용 NITINOL 형상기억합금의 열적/기계적 특성 평가 (Thermo-mechanical Characteristics of High Temperature NITINOL Shape Memory Alloy)

  • 윤성호
    • 한국정밀공학회지
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    • 제19권10호
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    • pp.52-59
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    • 2002
  • The thermo-mechanical characteristics of high temperature NITINOL shape memory alloy were evaluated using DSC with small samples and DMA with three-point bending specimens. The shape memory alloy of 54.4Ni/45.5Ti wt.% was used so that the phase transformation temperatures were in the range of 50~11$0^{\circ}C$. Two types of sample were tested in the experiments corresponding to as-received and annealed conditions. Simple beam bending theory was used to calculate the dynamic moduli of the shape memory alloy. According to the results, a large discrepancy in transformation temperatures was found between DSC and DMA techniques. Annealing treatment was found to suppress the R-phase transformation during cooling and the secondary plateau in the austenite transformation. Such a heat treatment was also significantly influenced to raise the transformation temperatures and the moduli of the shape memory alloy.

Discrete Group Method for Nonlinear Heat Equation

  • Darania, Parviz;Ebadian, Ali
    • Kyungpook Mathematical Journal
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    • 제46권3호
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    • pp.329-336
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    • 2006
  • In the category of the group theoretic methods using invertible discrete group transformation, we give a useful relation between Emden-Fowler equations and nonlinear heat equation. In this paper, by means of appropriate transformations of discrete group analysis, the nonlinear hate equation transformed into the class of the Emden-Fowler equations. This approach shows that, under the group action, the solution of reference equation can be transformed into the solution of the transformed equation.

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Al-Si 도금된 보론강과 Zn 도금된 DP강 TWB 레이저 용접부내의 Al-편석부 미세조직에 미치는 핫스탬핑 열처리의 영향 (Effect of Hot-stamping Heat Treatment on the Microstructure of Al-Segregated Zone in TWB Laser Joints of Al-Si-coated Boron Steel and Zn-coated DP Steel)

  • 정병훈;공종판;강정윤
    • 대한금속재료학회지
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    • 제50권6호
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    • pp.455-462
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    • 2012
  • Al-Si coated boron steel and Zn coated DP steel plates were laser-welded to manufacture a Tailor Welded Blank (TWB) for a car body frame. Hot-stamping heat treatment ($900^{\circ}C$, 5 min) was applied to the TWB weld, and the microstructural change and transformation mechanism were investigated in the Al-rich area near the bond line of the Al-Si coated steel side. There was Al-rich area with a single phase, $Fe_3(Al,Si)$, which was transformed to ${\alpha}-Fe$ (Ferrite) after the heat treatment. It could be explained that the $Fe_3(Al,Si)$ phase was transformed to ${\alpha}-Fe$ during heat treatment at $900^{\circ}C$ for 5 min and the resultant ${\alpha}-Fe$ phase was not transformed by rapid cooling. Before the heat treatment, the microstructures around the $Fe_3(Al,Si)$ phase consisted of martensite, bainite and ${\alpha}-Fe$ while they were transformed to martensite and ${\delta}-Fe$ after the heat treatment. Due to the heat treatment, Al was diffused to the $Fe_3(Al,Si)$ and this resulted in an increase of Al content to 0.7 wt% around the Al-rich area. If the weld was held at $900^{\circ}C$ for 5 min it was transformed to a mixture of austenite (${\gamma}$) and ${\delta}-Fe$, and only ${\gamma}$ was transformed to the martensite by water cooling while the ${\delta}-Fe$ was remained unchanged.

용접공정에서 발생하는 변태 소성 구성방정식의 수치적 구현에 관한 연구 (Numerical implementation of a constitutive equation of transformation plasticity in welding)

  • 김주완;임세영;김현규;최강혁
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 춘계학술대회
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    • pp.1154-1158
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    • 2003
  • Finite element analysis of welding processes, which entail phase evolution, heat transfer and deformations, is considered in this paper. Attention focuses on numerical implementation of the thermo-elastic-plastic constitutive equation proposed by Leblond in consideration of the transformation plasticity. Based upon the multiplicative decomposition of deformation gradient, hyperelastic formulation is employed for efficient numerical integration, and the algorithmic consistent moduli for elastic-plastic deformations including transformation plasticity are obtained in the closed form. The convergence behavior of the present implementation is demonstrated via a couple of numerical examples.

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열간압연 고강도강의 온도 및 재질제어 (Temperature and Property Control of High Strength Steel in Hot Strip Mills)

  • 박철재
    • 한국생산제조학회지
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    • 제20권6호
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    • pp.817-823
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    • 2011
  • This paper proposes a cooling stop temperature control(CST) and a phase transformation control(PTR) which aim at obtaining the uniform temperature and quality along the longitudinal direction of the high strength steel on the run-out table(ROT) process. The problems of the temperature control are analyzed for the conventional steel and the new control concepts are derived from a time-temperature transformation(TTT) diagram. The proposed control technologies are verified from the simulation results under the temperature prediction model by the heat transfer governing equation, and the temperature estimation simulator. It is shown through the field test of the hot strip mills that the phase transformation ratio of the high strength steel is considerably improved by the proposed temperature controls.

지르코니아 용사코팅의 상변화에 따른 마멸특성 (Wear characteristics of plasma sprayed yttria-stabilized zirconia coating as phase transformation)

  • 박찬;채영훈;김석삼
    • 한국윤활학회:학술대회논문집
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    • 한국윤활학회 2001년도 제34회 추계학술대회 개최
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    • pp.322-330
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    • 2001
  • The plasma-sprayed 8%Y$_2$O$_3$-Zirconia coating was studied to know the relationship between phase transformation and wear properties after several heat treatment. Wear tests were carried out with ball on disk on 50N, 70N, 90N. The specimen in this study was cast iron and tests were performed on room temperature. The transformation of phase and residual stress was measured by x-ray diffraction method(XRD) and worn surface were observed by SEM.

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열간압연 ROT에서 고강도강의 CSTC 개발 (CSTC of High Strength Steel for ROT Process in Hot Strip Mills)

  • 박철재
    • 제어로봇시스템학회논문지
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    • 제14권2호
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    • pp.191-196
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    • 2008
  • This paper proposes a cooling stop temperature control(CSTC) concept which aims at obtaining the uniform temperature and quality of the material along the longitudinal and lateral direction of the strip. The CSTC is designed using the experimental CCT(Continuous Cooling Transformation), TTT(Time Temperature Transformation) curves and the temperature control model by the heat transfer governing equation, and the temperature control simulator. The cooling pattern and the rolling speed can be solved by the CSTC. It is shown through the field test of the hot strip mill of POSCO that the phase transformation ratio of the high carbon steel is considerably improved by the proposed temperature control.

60 kgf/$\textrm{mm}^2$급 자동차용 변태유기소성강화강 Zn-Ni 전기도금 특성 연구 (Characteristics of Zn-Ni Electrodeposition of 60 kgf/$\textrm{mm}^2$ Grade Transformation Induced Plastic Steel Sheets for Automotive Body)

  • 김동환;김병일;전유택;정연수
    • 한국표면공학회지
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    • 제37권5호
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    • pp.263-272
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    • 2004
  • High strength steels such as transformation induced plastic steel, dual phase and solid solution Hardening have been developed and continuously improved due to the intensified needs in the automotive industry. But silicon and manganese in transformation induced plastic steels were known to exhibit harmful effects on galvannealing reaction by oxide film formed during heat treatment. Therefore, in this work, the applicability of Zn-Ni electrodeposition instead of hot dip galvannealed coating to transformation induced plastic steels was evaluated and optimum electroplating condition was investigated. Based on these investigations optimized electroplating conditions were proposed and Zn-Ni electrogalvanized steel sheet was produced by EGL (electrogalvanized line). Its perfomance properties for automotive steel was evaluated.

Grain Refinement and Phase Transformation of Friction Welded Carbon Steel and Copper Joints

  • Lee, W.B.;Lee, C.Y.;Yeon, Y.M.;Kim, K.K.;Jung, S.B
    • International Journal of Korean Welding Society
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    • 제3권2호
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    • pp.46-52
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    • 2003
  • The refinement of microstructure and phase transformation near the interface of pure copper/carbon steel dissimilar metals joints with various friction welding parameters have been studied in this paper. The microstructure of copper and carbon steel joints were changed to be a finer grain compared to those of the base metals due to the frictional heat and plastic deformation. The microstructure of copper side experienced wide range of deformed region from the weld interface and divided into very fine equaxied grains and elongated grains. Especially, the microstructures near the interface on carbon steel were transformed from ferrite and pearlite dual structure to fine ferrite, grain boundary pearlite and martensite due to the welding thermal cycle and rapid cooling rate after welding. These microstructures were varied with each friction welding parameters. The recrystallization on copper side is reason for softening in copper side and martensite transformation could explain the remarkable hardening region in carbon steel side.

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