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가스아토마이징된 Zl87.3misch metal8.3Ni4.4 분말의 냉각속도와 수지상 가지 가격에 관한 고찰
김지훈(Ji Hun Kim),예병준(Byung Joon Ye),김영환(Young Hawn Kim) 한국주조공학회 1999 한국주조공학회지 Vol.19 No.1
N/A The present work is an attempt to evaluate the relationship between dendrite arm spacing and average cooling rate in gasatomized Al_(87.3)misch metal_(8.3)Ni_(4.4) powder by means of the following methods. One is calculation of heat transfer coefficient and average cooling rate, which are derived from estimated particle velocity during gas-atomization. The other is measurement of secondary dendrite arm spacing, which are observed on the particle surface. Then, we make experimental equation for this relationship in case of permanent mold casting and compare it with similar equation in case of rapidly solidified powder. Both average cooling rates and solidification rates are considered to represent the variance of dendrite arm spacings in two types soidification route. Even though there is a considerable difference in each average cooling rate, the dendrite arm spacing values are similar in two cases; particle diameter, 100㎛, and casting width, 2.05㎜. It is because that each solidification route has similar solidification rate. (Received October 7, 1998)
과공정 Al-Si 합금의 초정 Si 미세화에 미치는 냉각속도와 P 첨가량의 영향
한상봉,김지훈,류봉선,박원욱,예병준 ( Sang Bong Hahn,Ji Hun Kim,Bong Sun You,Won Wook Park,Byung Joon Ye ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.4
N/A It is well known that the coarse primary Si in hypereutectic Al-Si alloys deteriorate castability, machinability, and mechanical properties. So, many treatment has been tried to refine the primary Si increasing cooling rate and adding refinement agent. Therefore, the purpose of our work was the observation of the effect on the refinement of primary Si and the analysis of the trend to apply to the casting process by changing the amount of P addition and the cooling rate while fixing the temperature at 750℃ of P addition and the type of AlCuP. In the condition of amount of P addition was fixed, primary Si was finer as cooling rate increased but in case of cooling rate was fixed, the effect of refinement was resisted as incersed the amount of P addition. At a relatively slow cooling rate of 22℃/sec, refinement was governed by the amount of P addition rather than cooling rate. At elevated cooling rate of 51℃/sec and 99℃/sec, the undercooling due to faster cooling rate promoted nucleation of primary Si rather than P addition more significantly.
강의 연속주조시 Mold Oscillation에 따른 Meniscus 초기 응고 해석
박태호 ( Park Tae Ho ),김지훈 ( Kim Ji Hun ),최주 ( Choe Ju ),예병준 ( Ye Byeong Jun ) 한국주조공학회 2003 한국주조공학회지 Vol.23 No.6
N/A Numerical models on the formation of oscillation marks have been developed for the decrement of casting surface defects. However it has not yet been reported that the effect of mold oscillation on the solidification of meniscus shell. The present study on the formation of meniscus shell has been conducted by coupling analysis of heat transfer in the mold and fluid flow in the flux caused by the mold oscillation. Finite element method was employed to solve the conservation equation associated with appropriate boundary conditions. Initial solidification started from the curved meniscus and proceeded along the meniscus shape. Solidification of the steel shell at the meniscus was proceeded under the iteration of solidification delay of the shell tip on the positive strip time and rapid solidification on the negative strip time.
강의 연속주조시 Mold Oscillation에 따른 Flux층 내의 동적 압력변화 해석
박태호 ( Park Tae Ho ),김지훈 ( Kim Ji Hun ),최주 ( Choe Ju ),예병준 ( Ye Byeong Jun ) 한국주조공학회 2004 한국주조공학회지 Vol.24 No.1
N/A The pressure of the mold flux acting on the meniscus shell was investigated through the coupling analysis of heat transfer in the mold and fluid flow in the flux caused by the mold oscillation. Finite element method was employed to solve the conservation equation associated with appropriate boundary conditions. As reported by previous workers. the axial pressure is positive on the negative strip time and negative on the positive strip time. A maximum pressure is predicted toward the top of the meniscus shell which has the thin shell arid a maxirnuni value is in proportion to the relative mold oscillation velocity. The relative mold oscillation velocity was changed by the effect of meniscus level fluctuation. Therefore the pressure of the mold flux acting o n the menisctis shell was different each cycle ofthe mold oscillation due to the irregularity of relative mold oscillation velocity
연속주조된 강재 슬래브 표면의 Oscillation Mark 형성에 관한 평가
박태호 ( Park Tae Ho ),김지훈 ( Kim Ji Hun ),최주 ( Choe Ju ),예병준 ( Ye Byeong Jun ) 한국주조공학회 2003 한국주조공학회지 Vol.23 No.5
N/A In early solidification during the continuous casting of steel slabs, the formation of oscillation marks on the surface of slabs was mainly affected by carbon contents and casting conditions. The control of oscillation mark is required for the HCR(Hot Charged Rolling) process because the deep oscillation marks seriously deteriorate the surface qualities of steel slabs. The metallographic study has revealed that the oscillation mark can be classified principally according to the presence or absence of a small `subsurface hook` and the depth of the oscillation marks in the subsurface structure at the basis of individual oscillation marks. The subsurface hook of oscillation marks was either straight or curved. When the amount of overflow was small and the subsurface hook was formed in the top of oscillation marks, the subsurface hook was straight and the oscillation mark was shallow. The oscillation marks without subsurface hook have small early solidification shell and were formed wide. The actual negative strip time(t_(N)) was changed by the effect of meniscus level fluctuation Therefore irregular early solidification shell and oscillation mark were formed.