• Title/Summary/Keyword: Dynamic Recrystallization

Search Result 170, Processing Time 0.023 seconds

Effect of Micro-Alloying Elements on Recrystallization Behavior of Carbon Steels at Different Strain Rates (변형률 속도에 따른 탄소강의 재결정 거동에 미치는 미량 합금 원소의 영향)

  • Lee, Sang-In;Lim, Hyeon-Seok;Hwang, Byoungchul
    • Korean Journal of Materials Research
    • /
    • v.26 no.10
    • /
    • pp.535-541
    • /
    • 2016
  • The present study deals with the effects of micro-alloying elements such as Ni, V, and Ti on the recrystallization behavior of carbon steels at different strain rates. Eight steel specimens were fabricated by varying the chemical composition and reheating temperature; then, a high-temperature compressive deformation test was conducted in order to investigate the relationship of the microstructure and the recrystallization behavior. The specimens containing micro-alloying elements had smaller prior austenite grain sizes than those of the other specimens, presumably due to the pinning effect of the formation of carbonitrides and AlN precipitates at the austenite grain boundaries. The high-temperature compressive deformation test results indicate that dynamic recrystallization behavior was suppressed in the specimens with micro-alloying elements, particularly at increased strain rate, because of the pinning effect of precipitates, grain boundary dragging and lattice misfit effects of solute atoms, although the strength increased with increasing strain rate.

Study on the Relationship between Plastic Deformation and Crystal Grain Change in Warm Forging (온간단조에서의 소성변형과 결정입자 변화와의 관계)

  • Je, Jin-Su;Kim, Jae-Hun
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.20 no.2
    • /
    • pp.461-472
    • /
    • 1996
  • The relationship between plastic deformation and crystal grain change in warm forging processes of SM10C carbon steel is studied. If the carbon steel is deformed at warm forging temperature(about recrystallization range), material properties are changed due to microstructural chanre of the crystal grain and cementite of the internal part. Some experimental values are investigated in terms of the elliptic degree of cementite, the grain size of cementite and ferrite grain size. When plastic deformation proceeds, the elliptic degree of cementite becomes larger and the grain size of cementite particle becomes small. In addition, the size of ferrite grain becomes fines by recrystallization. The elliptic degree of cementite has a considerable effect on formability. The distribution of effective strain in the forging was calculated by the rigid visco-plastic FEM analysis. The effective strain distribution obtained from the FEM simulation is compared with the experimental result, At the level of effective strain 0.3, dynamic recovery and dynamic recrystallization begin and at the level of over 2.5, the organization of material has better internal structure that is suitable for the following cold forming.

Isotropy Control of 7075 Al Wrought Alloy by Thixoextrusion (반용융 압출에 의한 A7075 합금의 등방성 제어)

  • Yoon, Young-Ok;Kim, Shae-K.
    • Journal of Korea Foundry Society
    • /
    • v.30 no.6
    • /
    • pp.210-216
    • /
    • 2010
  • The aim of this study is to characterize a thixoextruded 7075 Al wrought alloy bar in terms of its isotropic behavior through the optical microscope, mechanical test and electron back scattered diffraction. It is also discussed of the extrudability improvement for 7075 Al wrought alloy by thixoextrusion, with emphasis on controlling thixoextrusion parameters. Hot extrusion shows that the maximum extrusion pressure depends on their characteristics in terms of flow stress and hot workability. In the contrary, thixoextrusion demonstrates that the maximum extrusion pressure is almost uniform regardless of the experimental parameters, such as initial ram speed, die bearing length and thixoextrusion temperature. The hot extruded microstructures become elongated to extrusion direction, while the thixoextruded microstructures are isotropic and homogeneously distributed due to the existence of liquid phase between solid grains during the process. The grain refinement due to dynamic recrystallization during thixoextrusion has been also occurred. Subsequent recrystallization would lead to the strengthening of mechanical properties, as observed in the study. The important point is that the values of tensile, yield strength and elongation of the thixoextruded bar without plastic deformation are similar to those of the hot extruded bar with severe plastic deformation.

High Temperature Deformation Behavior of SiCp/2124Al Metal Matrix Composites

  • Tian, Y.Z.;Cha, Seung I.;Hong, Soon H.
    • Proceedings of the Korean Society For Composite Materials Conference
    • /
    • 2002.05a
    • /
    • pp.69-72
    • /
    • 2002
  • The high temperature deformation behavior of SiCp/2124Al composite and 2124Al alloy was investigated by hot compression test in a temperature ranged $400~475^{\circ}C$ over a strain rate ranged $10^{-3}~1s^{-1}$. The billets of 2124Al alloy and SiCp/2124Al composite were fabricated by vacuum hot pressing process. The stress-strain curve during high temperature deformation exhibited a peak stress, and then the flow stress decreased gradually into a steady state stress with increasing the strain. It was found that the flow-softening behavior was attributed to the dynamic recovery, local dynamic recrystallization and dynamic precipitation during the deformation. The precipitation phases were identified as S' and S by TEM diffraction pattern. Base on the TEM inspection, the relationship between the Z-H parameter and subgrain size was found based on the experiment data. The dependence of flow stress on temperature and strain rate could be formulated well by a hyperbolic-sinusoidal relationship using the Zener-Hollomon parameter.

  • PDF

Prediction of the Behavior of Dynamic Recrystallization in Inconel 718 (Inconel 718의 열간단조시 동적 재결정 거동 예측)

  • 최민식;강범수;염종택;박노광
    • Proceedings of the Korean Society for Technology of Plasticity Conference
    • /
    • 1997.10a
    • /
    • pp.220-223
    • /
    • 1997
  • This paper presents the prediction of microstructure of Inconel 718 disk forgings. The experiments are carried out to examine the recrystallization ratio and grain growth in the forgings. In the experiments, cylindrical billets are forged by two operations with variations of forging temperature and reduction ratio of deformation. Also the finite element program, developed here for the prediction, is used for the analysis, and the results are compared with the experimental ones. It is noted that the comparison appears in sound agreement.

  • PDF

Prediction of microstructural evloution in hot forging of steel by finite element method (유한요소법에 의한 열간단조공정에서 강의 미세조직변화 예측)

  • 장용순;고대철;최재찬
    • Proceedings of the Korean Society of Precision Engineering Conference
    • /
    • 1995.10a
    • /
    • pp.219-222
    • /
    • 1995
  • The objective of this study is to demonstrate the ability of a computer simulation of microstructural evolution in hot forging of C-Mn steels. The finite element method is applied to the prediction of the microstructural evolution, and it should be coupled with heat transfer analysis to consider the change of thermomechanical properties during the deformation. In this study, Yada's recrystallization model and rigid-thermoviscoplastic finite element method were employed in order to analyze microstructural evolution during hot forging process. To show the validity and effectveness of the proposed method, the experiment of hot compression process was accomplished and the results of experiment were compared with those of simulation. Consequently, this approach shows a good agreement with experimental results.

  • PDF

Prediction of AGS Distribution and Analysis of Rescrystallization Behavior in 3-roll Mill (3-롤 압연 오스테나이트 결정립도 분포 예측 및 재결정 거동 분석)

  • 권혁철;김수영;임용택;이영석;우종수
    • Proceedings of the Korean Society for Technology of Plasticity Conference
    • /
    • 2002.05a
    • /
    • pp.169-172
    • /
    • 2002
  • Recently, the application of 3-roll mill is increasing, because of its flexibility in spread control and stand arrangements due to its compact size. But deformation characteristics and microstructural change in the process is not well known. In this study, austenite grain size (AGS) predictions were made by isothermal FE analyses and a microstructure model available in the literature. From this study, the effect of draught on the AGS characteristics was analyzed based on the divided zones of two major recrystallization behaviors.

  • PDF

Assessment of Grain Size Distribution in Direct Age Processed Alloy 718 (직접시효 처리된 Alloy 718의 결정립분포 해석)

  • Park N. K.;Kim J. H.;Eum C. Y.;Lee C. S.;Yeom J. T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
    • /
    • 2005.05a
    • /
    • pp.291-294
    • /
    • 2005
  • The microstructure evolution of Alloy 718 during the direct age(DA) process was predicted using the recrystallization model and finite element analysis. The DA process of Alloy 718 was performed in two-step forging using capsulated cylindrical billets of 122mm in diameter and 180mm in height. In order to evaluate the microstructural change during the forging, a dynamic recrystallization model of Alloy 718 was implemented onto the user-subroutine of the commercial FEM code. The prediction of microstructure evolution in DA processed Alloy 718 pancake was compared with experimental results.

  • PDF

Comparison of Conventional Hot Forging and Thixoforging of Al 7075 Alloy According to Microstructures, Formability and Hardness (Al 7075합금의 열간단조와 반응고 단조에 있어서 조직, 성형성 및 경도 특성 비교)

  • Lee, Sang-Yong;Jeon, Jae-Il;Lee, Jeong-Hwan;Lee, Yeong-Seon;Sin, Pyeong-U
    • Transactions of Materials Processing
    • /
    • v.7 no.6
    • /
    • pp.620-630
    • /
    • 1998
  • Conventional hot forging and thixoforging of Al 7075 alloy have been compared with respect to microstructures, formability and hardness. Two distinctive temperature-strain rate ranges for hot forging of Al 7075 alloy were observed from the results of simple compression tests with strain rates of 10-3∼101 sec-1 in the temperatures between $250^{\circ}C$ and $500^{\circ}C.$ In the dynamic recovery range (low temperature-high strain rate range) multi-stage forging was necessary to form a complex shape part due to the lack of formability. In the high temperature-low strain rate range, in which dynamic recrystallization takes place a complex shaped park could be formed by single-stage forging. About 50% cold working in the SIMA process was necessary to get a fine and homogeneous microstructures. Microstructural study suggest that thixoforged Al 7075 part has fine grains and homogeneous microstructures. Its hardness number is almost same to that of conventional hot forged part after aging treatment.

  • PDF