연주 Bloom의 표면 품질개선에 관한 연구

최회진(Hoi Jin Choi),송치복(Chi Bok Song),임정규(Jeoung Kiu Im),서영식(Young Sik Seo),박현균(Hyun Gyoon Park) 대한금속재료학회 1999 大韓金屬學會會報 Vol.12 No.3

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초대형 구조물용 고강도 강선 및 강봉 개발

정진영 ( Jin Young Jung ),임승호 ( Sung Ho Lim ),박덕영 ( Deok Young Ban ),김현진 ( Hyun Jin Kim ),이덕락 ( Duk Lak Lee ),박상덕 ( Sang Duk Park ),최회진 ( Hoi Jin Choi ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 재료마당 Vol.19 No.4

가스분무한 Al-8wt.%Fe 합금분말의 급속응고과정에 대한 수치해석

김성균,최회진,나형용 ( Seong Gyoon Kim,Hoi Jin Choi,Hyung Yong Ra ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.5

N/A A numerical analysis on the microstructural evolutions of microcellular and cellular α -aluminum phase in the gas-atomized Al-8wt. pct droplets was represented. The 2-dimensional non-Newtonian heat transfer and the dendritic growth theory in the undercooled melt were combined under the assumptions of a point nucleation on droplet surface and the macroscopically smooth solid-liquid interface enveloping the cell tips. It reproduced the main characteristic features of the reported microstructures quite well. It predicted a considerable volume fraction of segregation-free region in a droplet smaller than l0㎛ if an initial undercooling larger than 100K is given. The volume fractions of the microcellular region(g_A) and the sum of the microcellular and cellular region(g_a) were predicted as functions of the heat transfer coefficient, h and initial undercooling, ΔT. It was shown that g_A and g_a, in the typical gas-atomization processes with h=0.1-1.0W/㎠K, are dominated by ΔT and h, respectively, but for h larger than 4.0W/㎠K, a fully microcellular structure can be obtained irrespective of the initial undercooling.

Marforming 處理한 Fe-30% Ni-0.24%C Martensite의 Tempering 擧動

金學信,金炳日,崔會珍 전북대학교 공업기술연구소 1985 工學硏究 Vol.16 No.-

The tempering behavior of marformed martensite in Fe-30% Ni -0.24%C alloy was examined by means of hardness, yield strength, ultimate tensile strength, optical microscopy and transmission electron microsco-py. The results obtained in this work are as follows ; (1) The morphology of virgin martensite at room temperature was plate martensite of transformation twin in Fe-30% Ni-0.24%C alloy. (2) The strength of Fe-30% Ni-0.24%C alloy by marforming treatment was increased due to the work hardening induced from the dislocation density increased during deformation, the formation of dislocation atmosphere induced from interaction between dislocation cell produced during deformation and solute car-bon and the stress concentration induced from crossing of twins. (3) The optical microstructures of marformed martensite tempered below 200℃ was not noticed obvious differents but aboce 300℃, precipitates of carbide were promoted as deformation degree is greater. (4) From tempered structure of virgin martensite the carbide was precipitated in the twin boundary, while the carbide from marformed martensite was precipitated in the twin boundary, cell-like structure and grain boundary of martensite plate in marformed martensite. (5) Virgin martensite and marformed martensite were attained the highest hardness, yield strength and ultimate tensile strength on tempering at 100℃ andd above 100℃, marformed martensite showed a greater softening resistance on tempering because of the effect to degress the precipitation of ε-carbide induced from interaction between interstitial carbon atom and dense dislocation and dispersion strengthening effect precipitated in dense dislocation

열교환법에 의한 실리콘 단결정 성장

김성균,나형용,김동익,최회진 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.2

The effects of cooling rate of heater, melt weight, seed direction, base materials of crucible and purity of silicon were investigated in the experiment of the silicon single-crystal(diameter 7㎝) growth by Heat Exchanger Method in this paper. Silicon single-crystal which purity was electronic-grade could be grown at the cooling rate lower than 0.8℃/min when the seed with $lt;100$gt; direction was used and twins in parallel with the radial direction were formed at the cooling rate higher than 0.2℃/min when the seed with $lt;111$gt; direction was used. But, in any case, some polycrystal formation at the low edge part of the crystal could not been avoided. When the alumina with low thermal conductivity instead of graphite with high thermal conductivity was used as the base material of crucible, the trend of the poly-crystal formation at the low edge part of the crystal could be diminished. Especially, Silicon single-crystal which purity was metallurgical-grade could be grown at the cooling rate lower than 0.2℃/min when the seed with $lt;100$gt; direction was used.

급속응고에서의 밴드조직

김성균,나형용,김동익,최회진 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.2

The microstructural evolutions during the transition between the supersaturated solid solution and the solutal dendrite in rapid solidification were qualitatively examined using the model of banded structure formation proposed by Carrard et al., It was shown that the positive average temperature gradient at solid-liquid interface is a necessary condition for the banded structure formation, and the banded structure can not be formed during rapid undercooled solidification. Also, it was shown that the banded structure is hardly anticipated in melt-spun aluminum alloy and, on the other hand, it can be formed at the free surface side of the melt-spun Ag-Cu alloy ribbons. These predictions are in good agreement with the reported experimental results on banded structure formation.

열교환법에 의한 실리콘 단결정 성장과정의 수치해석

김성균,나형용,김동익,최회진 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.11

Numerical simulations including the fluid flow, conduction and radiation heat transfer have been performed using the geometry of real furnace for the single-crystal growth by heat exchanger method. The finite difference method based on the control volume approach and SIMPLE algorithm were used to solve the momentum and energy equations. Almost all parts of the furnace including the heater, insulating materials and crucible were considered in the calculation domain and the latent heat was accounted by an iterative heat evolution method. Silicon with low thermal conductivity was selected as a model material in order to compare the results with the previous report on the copper single-crystal growth. The effects of cooling rate of the heater, crucible material, crucible shape and melt weight on single-crystal growth were investigated together with the role of natural convection in melt. The optimum process conditions such as the critical cooling rate and the critical ratio of the height to the radius of crystal for the silicon single-crystal growth by heat exchanger method were determined. According to the simulations, among many parameters crucible shape was a dominant processing parameter to control single crystal growth when a thermal conductivity of the specimen was low. The lower the thermal conductivity of base material of crucible was then that of the specimen, the less the region of poly crystal formed at the edge of the crystal was.

열교환법에 의한 구리단결정 성장

김성균,나형용,김동익,최회진 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.5

The effects of cooling velocity, melt weight and purity of copper were reported on copper single-crystal growth by Heat Exchanger Method in this paper. Copper single-crystals could be grown at the cooling velocity lower than 1℃/min. Higher purity(99.995wt%) of copper single crystal less than 7㎝ height(radius 3.5㎝) was grown when the cooling velocity was 0.34℃/min. and the height less than 3.5㎝(radius 3.5㎝) was grown with the plane front of solid-liquid interface and of semi-ellipse, and the free surface of single crystal was solidified in the end. However in the lower purity(99.93wt%) of copper, it should be solidified with plane front at the initial stage, and cell, dendrite formed finally at the cooling velocity lower than 0.5℃/min. The significant segregation were caused when the solid-liquid interface was changed from plane front to cell structure.

열교환법에 의한 구리단결정 성장과정의 수치해석

김성균,나형용,김동익,최회진 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.12

Numerical simulation for copper single crystal growth by a heat exchanger method has been performed including the effects of fluid flow, conduction and radiation heat transfer using the actual geometry of growing furnace. The finite difference method based on a control volume approach and SIMPLE algorithm were used to solve the momentum and energy equations. Almost all parts of the furnace including heater, insulating materials and crucible were considered in the calculation domain and the latent heat was also accounted by an iterative heat evolution method. The effects of cooling rate of heater and crucible position and melt weight were investigated together with the role of natural convection in melt. The optimum process conditions for single crystal growth were determined. The calculated results of critical cooling rate, solidification time and the critical ratio of the height to the radius of crystal were found to be in a good agreement with the experimental results.