• Title/Summary/Keyword: Dynamic Recrystallization

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Analysis of Hot Forming Process with Flow Softening by Dynamic Recrystallization (동적 재결정에 의한 연화를 고려한 열간성험공정 해석)

  • 방원규;이종수;장영원
    • Transactions of Materials Processing
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    • v.10 no.2
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    • pp.137-143
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    • 2001
  • The change of flow stress due to dynamic recrystallization during hot forming process is investigated. A series of mechanical tests has been conducted at various temperatures, and constitutive relations and recrystallization kinetics were formulated from the test results. The effect of dynamic recrystallization to the flow stress was implemented to a commercial FEM code by conditioned remapping of state variables. The datum strain of stress compensation was optimized to minimize the overestimation of forming loads. Suggested datum was formulated as an exclusive function of critical strain for recrystallizalion and validated by mechanical tests and microstructural observations.

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Effect of Deformation on Dynamic Recrystallization of an AZ31 Mg alloy (AZ31 합금의 동적 재결정에 미치는 변형 조건의 영향)

  • Kwon, Yong-Nam;Lee, Y.S.;Lee, J.H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2006.05a
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    • pp.59-62
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    • 2006
  • Mg alloys have drawn a huge attention in the field of transportation and consumer electronics industries since it is the lightest alloy which could be industrially applicable. Most Mg alloy components have been fabricated by casting method. However, there have been a lot of research activities on the wrought alloys and their plastic forming process recently. The deformation behavior of an AZ31 Mg alloy at the elevated temperature was examined firstly to find out the optimum plastic forming range in terms of temperature and strain rate. During high temperature deformation, AZ31 alloy is usually undergone the dynamic recrystallization which influence the deformation behavior in turn. In the present study, the effect of deformation on dynamic recrystallization of an AZ31 alloy was investigated to clarify the relation between the deformation and recrystallization. In an AZ31 alloy system, the dynamic recrystallization was found to occur continuously. Recrystallized grain size was dependent on the stress level.

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A Study on Meta-Dynamic Recrystallization of 304 Stainless Steels (304 스테인레스강의 준동적재결정에 관한 연구)

  • 한형기;조상현;유연철
    • Transactions of Materials Processing
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    • v.10 no.1
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    • pp.42-52
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    • 2001
  • The static softening mechanisms of 304 stainless steel were studied by hot torsion test. The interrupted deformation tests were performed In the range of 900~$1100^{\circ}C$ and 5.0$\times$$10^{-2}$- 5.0$\times$$10^0$/sec. The metadynamic recrystallization (MDRX) could be distinguished from the static recrystallization (SRX). Comparison of the softening kinetics between MDRX and SRX showed that the rate of MDRX was more rapid than that of SRX for the same deformation variables. To the exact prediction of MDRX, the MDRX parameter, which could be simultaneously estimated by the interpass time and Zener-Hollomon parameter, was developed. The time lot 50% MDRX, $t_{0.5} was modeled using the deformation parameters : $t_{0.5} = 1.33\times10^{-11}$ $\.\varepsilon^{-0.41}$ D exp(230.3kJ/mol/RT) and the predicted value was very correspondent with the measurement. It was found that the static parameters such as interpass time can control the dynamic states in the several successive deformation process.

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The Prediction of Dynamic Recrystallization and Grain Size of 304 Stainless Steel during Hot Deformation (304 스테인리스강의 열간동적재결정과 미세조직 예측)

  • 권영표;조종래;이성열;이정환
    • Transactions of Materials Processing
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    • v.10 no.7
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    • pp.573-578
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    • 2001
  • The flow stress of 304 stainless steel during hot forming process were determined by conducting hot compression tests at the range of 1273 K∼1423 K and 0.05 /s∼2.0 /s as these are typical temperature and strain rate in hot forging operation. In this material, Dynamic recrystallization was found to be the major softening mechanism with this conditions as Previous studies. Based on the observed phenomena, a constitutive model of flow stress was assumed as a function of strain, strain rate, temperature. In the constitutive model, the effects of strain hardening and dynamic recrystallization were taken into consideration. A finite element method connected to constitutive model was performed to predict the dynamic recrystallization behaviors and also stress-strain curves in hot compression of 304 stainless steel.

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A Physically Based Dynamic Recrystallization Model for Predicting High Temperature Flow Stress (열간 유동응력 예측을 위한 물리식 기반 동적 재결정 모델)

  • Lee, H.W.;Kang, S.H.;Lee, Y.S.
    • Transactions of Materials Processing
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    • v.22 no.8
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    • pp.450-455
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    • 2013
  • In the current study, a new dynamic recrystallization model for predicting high temperature flow stress is developed based on a physical model and the mean field theory. In the model, the grain aggregate is assumed as a representative volume element to describe dynamic recrystallization. The flow stress and microstructure during dynamic recrystallization were calculated using three sub-models for work hardening, for nucleation and for growth. In the case of work hardening, a single parameter dislocation density model was used to calculate change of dislocation density and stress in the grains. For modeling nucleation, the nucleation criterion developed was based on the grain boundary bulge mechanism and a constant nucleation rate was assumed. Conventional rate theory was used for describing growth. The flow stress behavior of pure copper was investigated using the model and compared with experimental findings. Simulated results by cellular automata were used for validating the model.

Quantitative Analysis of Hot Forming with Stress Compensation to Dynamic Recrystallization (고온성형중 동적재결정에 의한 하중감소의 정략적 해석)

  • 장영원
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1999.03b
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    • pp.203-206
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    • 1999
  • The shift of flow behavior due to dynamic recrystallization during hot forming process is investigated, A series of load relaxation and compression tests has been conducted at various temperatures Constitutive relations and recrystallization behaviors were formulated from the mechanical test results, The consideration of dynamic recrystallization during a specific forming process was implemented to commercial FEM package by conditioned remeshing and remapping of state variables. Improvement of Load-Stroke prediction was validated by comparison with experimental results.

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A Study on the Prediction of Grain Size Distribution in Hot Forging of Waspaloy Turbine Disc (Waspaloy 터빈디스크의 열간 단조시 결정립분포 해석에 관한 연구)

  • Yeom, Jong-Taek;Lee, Chong-Soo;Kim, Jeoung-Han;Lee, Dong-Geun;Park, Nho-Kwang
    • Journal of the Korea Institute of Military Science and Technology
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    • v.9 no.2 s.25
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    • pp.70-76
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    • 2006
  • The microstructure evolution during a hot forging of Waspaloy was investigated using the recrystallization model and FEM simulation. In order to obtain an uniform microstructure, hot forging was carried out by two step. The change of grain size during hot forging has a deep connection with dynamic recrystallization behavior. Avrami-type constitutive equation for the dynamic recrystallization was implemented into an user subroutine of 2D FE simulator. The evolution of grain structure in the two-step forging of Waspaloy was simulated using the 2D FEM user-subroutine. The detailed variation of microstructures due to dynamic recrystallization could effectively be predicted at various locations in a forged pancake.

Flow Softening Behavior during the High Temperature Deformation of AZ31 Mg alloy (AZ31 Mg 합금의 고온 변형 시의 동적 연화 현상)

  • Lee, Byoung-Ho;Reddy, N.S.;Yeom, Jong-Teak;Lee, Chong-Soo
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2006.05a
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    • pp.70-73
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    • 2006
  • In the present study, the flow-softening behavior occurring during high temperature deformation of AZ31 Mg alloy was investigated. Flow softening of AZ31 Mg alloy was attributed to (1) thermal softening by deformation heating and (2) microstructural softening by dynamic recrystallization. Artificial neural networks method was used to derive the accurate amounts of thermal softening by deformation heating. A series of mechanical tests (High temperature compression and load relaxation tests) was conducted at various temperatures ($250^{\circ}C{\sim}500^{\circ}C$) and strain rates ($10^{-4}/s{\sim}100/s$) to formulate the recrystallization kinetics and grain size relation. The effect of DRX kinetics on microstructure evolution (fraction of recrystallization) was evaluated by the unified SRX/DRX (static recrystallization/dynamic recrystallization) approaches

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Deformation Behavior and Dynamic Recrystallization of Torsion-Tested Alloy 718 (Alloy718의 비틀림변형과 동적재결정)

  • Park, N.K.;Kim, C.H.;Kim, N.Y;Lee, D.G.;Yeom, J.T.
    • Transactions of Materials Processing
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    • v.15 no.8 s.89
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    • pp.591-596
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    • 2006
  • Torsion testing was employed to investigate the deformation and recrystallization behavior of coarse-grained Alloy 718, and the results are compared with the compression testing results. Mechanical testing was conducted on bulk Alloy718 samples within the temperature ranges, $1000^{\circ}C{\sim}1100^{\circ}C$. The strain gradient formed in the torsion specimens resulted in a recrystallization behavior which varied along the radial direction from the center to the surface. The flow curves based on effective stress and effective strain as obtained by Fields and Backofen's isotropic deformation theory and the dynamic recrystallization within the compression tested samples and torsion tested samples are different. The different deformation and recrystallization behavior can be rationalized by the fact that the deformation in the coarse-grained torsion specimens is not uniform and thus the strain gradient within the specimens cannot be analytically predicted by FE simulation. Thus, the extent of recrystallization cannot be properly predicted by the established recrystallization equations based on compression tests.

Assessment of Grain Size Distribution in a Hammer-Forged Alloy 718 Disk (해머 단조된 Alloy 718 디스크의 결정립 분포 해석)

  • 염종택;박노광
    • Transactions of Materials Processing
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    • v.6 no.3
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    • pp.250-256
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    • 1997
  • Hammer forging was employed for Alloy 718 disk. The change in grain size during hot forging depends very much on dynamic recrystallization. The final grain size depends especially on the critical strain$($\varepsilon$_C)$/TEX> for dynamic recrystallization and Zener-Holloman parameter(Z). In this study, the critical strain$($\varepsilon$_C)$, the strain for 50 pct. recrystallization$($\varepsilon$_{0.5})$ and fraction of dynamic recrystallization(Xdyn) were measured by compression tests. FE simulation was also carried out ot predict the evolution of microstructure. The strain, strain rate and temperature distribution predicted by forging simulation can be effectively used to predict the distribution of grain sizes in the forged workpiece. The present model predictions showed an excellent agreement with the microstructural evolution of hammer-forged Alloy 718 disks.

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