• 대한금속재료학회지
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• 제46권6호
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• pp.329-337
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• 2008

During the continuous casting of boron-bearing steel, the corner cracks on the slab are formed by deformation with low strain rate and rapid cooling at the unbending temperature within the range of 800- $1000^{\circ}C$. Especially, the rapid cooling in the corner of slab during the continuous casting leads to as corner cracking. Therefore, in this study, the hot tensile tests applied to the different cooling rates were taken into account in order to study the effect of cooling rate on the hot ductility of boron-bearing steel. The results revealed that increasing cooling rate deteriorate the hot ductility of boron- bearing steel. Rapid decreasing of the hot ductility is caused by formation of a film-like ferrite and precipitate at the austenite grain boundaries. The morphology of the precipitates in the boron-bearing steel was monitored by PTA (Particle Tracking Autoradiography) and TEM, we observed MnS and BN compound and their morphology was quite different depending on the cooling rates. When the cooling rate is increased, rodshape MnS and BN precipitates can be formed along the austenite grain boundaries. It can cause that weakening the boundary region and decreasing the hot ductility of boron-bearing steel.

• 한국주조공학회지
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• 제19권6호
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• pp.484-492
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• 1999

The microstructures and mechanical properties of high strength yellow brass, Al bronze and Sn bronze alloys fabricated by gravity die casting and squeeze casting were investigated. A rapid cooling of casting was enhanced by pressure applied during solidification of Cu alloys, the cooling rate of casting was more great for high strength yellow brass alloy than other Cu alloys. Grain size and phases of the squeeze cast products become refined to 1/2 level compared to gravity die castings. Squeeze cast Al bronze and high strength yellow brass has about 10-20% higher yield and tensile strength and slighter decreased or nearly same elongation, compared to gravity die cast ones. Sn bronze has nearly same strength and hardness, but shows increased in elongation, compared to gravity die cast ones.

• 대한기계학회논문집B
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• 제21권10호
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• pp.1245-1253
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• 1997

An Experimental investigation was carried out to examine the heat transfer characteristics of rapid cooling process by Twin-Roll. The experimental results were compared with numerical solutions. The measured temperature showed the about 3 % difference to the calculated results. But the cooling rate estimated by the microstructure interpretation method has much difference to the calculated results.

• 한국산학기술학회논문지
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• 제3권2호
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• pp.136-140
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• 2002

정밀하고 복잡한 형상의 금속 부품을 제작하는데 사용되는 정밀주조법은 왁스형을 만드는 과정을 수작업으로 진행하므로 많은 시간과 비용이 소요되었다. 왁스형 제작공정을 개선하기 위해 쾌속조형기를 이용하는 방법을 제안하였다. SLS 형 쾌속조형기를 이용하여 캐스트폼형을 제작하고 여기에 용융된 왁스를 함침시켜 왁스형을 완성한다. 이 방법을 이용하여 스텐레스 스틸 소재의 금속 주분을 제작하였는데, 시간과 비용이 크게 절감되었으며 정밀도도 향상되었다.

• 대한기계학회논문집B
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• 제25권10호
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• pp.1365-1372
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• 2001

In the planar flow casting(PFC) process, the conditions of the melt puddle between nozzle and rotating wheel affect significantly the quality and dimensional uniformity of the downstream ribbon. For stable puddle formation, the nozzle is placed very close to the quenching wheel, so the surface-tension and wall-adhesion forces have an important effect upon the fluid flow.\`In this study the planar flow casting process has been mode]ed using the VOF method for free surface tracking. The transient puddle formation from the present analysis shows good agreements with the previous experimental results. Furthermore, the variation of melt temperature and the corresponding cooling rate of the melt have been examined. The present results also show how the melt puddle can be farmed on the rotating substrate, how the melt flows within the puddle, and how the changes of the process variables affect the puddle formation and its corresponding fluid flow and heat transfer behavior.

• 한국주조공학회지
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• 제39권2호
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• pp.26-31
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• 2019

In this study, the mechanical characteristics and microstructure of hypereutectic Al-17Si-5Fe extruded alloys prepared by a rapid solidification process (RSP) were investigated. The hypereutectic Al alloy was fabricated by means of RSP and permanent casting. For RSP, the Al alloy melted at $920^{\circ}C$, cooling the specimens at a rate of $10^6^{\circ}C/s$ when the RSP was used, thus allowing the refining of primary Si particles more than when using permanent casting, at a rate of about 91%. We tested an extrusion RSP billet and a permanent-cast billet. Before the hot-extrusion process, heating to $450^{\circ}C$ took place for one hour. The samples were then hotextruded with a condition of extrusion ratio of 27 and a ram speed of 0.5 mm/s. Microstructural analyses of the extruded RSP method and the permanent casting method were carried out with OM and SEM-EDS mapping. The mechanical properties in both cases were evaluated by Vickers micro-hardness, wear resistance and tensile tests. It was found that when hypereutectic Al-17Si-5Fe alloys were fabricated by a rapid solidification method, it becomes possible to refine Si and intermetallic compounds. During the preparation of the hypereutectic Al-17Si-5Fe alloy by the rapid solidification method, the pressure of the melting crucible was low, and at faster drum speeds, smaller grain alloy flakes could be produced. Hot extrusion of the hypereutectic Al-17Si-5Fe alloy during the rapid solidification method required higher pressure levels than hot extrusion of the permanent mold-casted alloy. However, it was possible to produce an extruded material with a better surface than that of the hot extruded material processed by permanent mold casting.

• 한국재료학회지
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• 제16권8호
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• pp.516-523
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• 2006

In recent years, Magnesium (Mg) and its alloys have become a center of special interest in the automobile industry. Due to their high specific mechanical properties, they offer a significant weight saving potential in modern vehicle constructions. Most Mg alloys show very good machinability and processability, and even the most complicated die-casting parts can be easily produced. The die casting process is a fast production method capable of a high degree of automation for which certain Mg alloys are ideally suited. In this study, step-dies and flowability tests for AM50 were performed by die-casting process according to various combination of casting pressure and plunger velocity. We were discussed to velocity effect of forming conditions followed by results of microstructure, FESEM-EDX, hardness and tensile strength. Experimental results represented that the conditions of complete filling measured die-casting pressure 400 bar, 1st plunger velocity 1.0 m/s and 2nd plunger velocity 6.0 m/s. The increasing of 2nd plunger velocity 4.0 to 7.0 m/s decreased average grain size of $\alpha$ phase and pore. It was due to rapid filling of molten metal, increasing of cooling rate and pressure followed by increased 2nd plunger velocity. The pressure should maintain until complete solidification to make castings of good quality, however, the cracks were appeared at pressure 800bar over.

• 한국주조공학회지
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• 제7권1호
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• pp.45-52
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• 1987

The effects of melting and casting conditions on cast structures of Cu-Sn-Pb alloys were studied. Specimens were prepared at different pouring temperatures of $1100^{\circ}C$ to $1260^{\circ}C$ with use of various kind of molds, green sand mold, $CO_2$ sand mold, shell mold, furan sand mold and metallic mold. (1) The transition of equiaxed to columnar structure greatly influenced by adding elements and mold binders. (2) The change of equiaxed structure according to pouring temperatures were expressed by separation theory. Lower pouring temperature and rapid cooling rate increase hardness and it's further increase was shown in the region of columnar structure. (3) Proper controls of pouring temperature, cooling rate and mold binder were important factors to improve wear properties of Cu-Sn-Pb alloys castings.

• Tribology and Lubricants
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• 제8권1호
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• pp.70-77
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• 1992

Al-Pb-Si bearing alloys were produced by a forced stirring method and a rapid solidification process to study wear properties of bearing alloys. A homogeneous distribution of Pb particles in Al matrix could be obtained by means of the forced stirring and the rapid cooling during the casting. The wear properties of bearing alloys were tested by a pin-on-disc wear tester. The change in microstructure according to the alloy manufacturing variables was observed by the backscattered electron images. Al-Pb and Al-Si binary alloys showed a transition from mild to severe wear. The transition was not found in Al-Pb-Si ternary alloys. It could be concluded that the lubricatioin effect of Pb and the strengthening effect of Si in the ternary alloys enhanced the bearing properties. A Al-25%Pb-13%Si alloy showed the lowest coefficient of friction in this experiment. It indicated that the optimum concentration of alloy was 25% Pb and 13% Si when the forced stirring of melt and water-cooled-copper-mold solidification were adopted.

• Journal of Advanced Marine Engineering and Technology
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• 제15권3호
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• pp.57-65
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• 1991

The quenching of steels by water is one of the important problems in engineering for the applications of heat treatment or continuous casting process, but the fundamental researches by the theoretical approaches have not been satisfactorily improved yet. The very rapid cooling problems by the thermal conduction including the latent heat of phase transformation in steel and the transient boiling heat transfer of water on the surface of the steel covering from $850^{\circ}C$ to $20^{\circ}C$ are the key problems of heat treatment. The present quenching experiments are performed for the cylindrical specimens of carbon steel, S45C of diameters (12-30). Nonlinear transient heat conduction and transient boiling heat transfer problem of water on the surface of specimens is analyzed by the numerical method of inverse heat conduction problem. The conditions for the calculation are that the initial temperature of specimens is $820^{\circ}C$ and the cooling water in bath are $20^{\circ}C$,$40^{\circ}C$,$60^{\circ}C$,$80^{\circ}C$,$95^{\circ}C$ with no agitation.