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Hot Thermocouple법을 이용한 몰드플럭스의 결정화거동 평가
조중욱,김성연 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.3
A SHTT (single hot thermocouple technique) has been applied to measure crystallizing temperature and crystallizing rate of molten mold fluxes. It was possible to measure the crystallizing temperature and crystallizing rate of the commercial mold flux using a SHTT reliably, while the crystallizing temperature from DTA and the breaking temperature showed poor reliability. In SHTT, crystallizing temperature was measured at the continuous cooling speed of 100 K/min, and crystallizing initiation time at 1050℃. The crystallizing initiation time generally decreased for the mold flux of higher crystallizing temperature, and there is good interrelationship (R²=0.9588) between two. It is concluded that the SHTT should be considered as the method of quantifying the crystallization behaviors during continuous casting of steel.
강의 연속주조시 몰드플럭스의 응고수축이 몰드 내 열전달에 미치는 영향
趙重郁 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.3
Solidification contraction during crystallization of molten mold fluxes has been observed in a laboratory scale mold. Mold fluxes with larger contraction show smaller mold heat flux in thin slab caster. This implies that thermal resistance at mold/mold flux interface arises from the solidification and crystallization of the flux film. Also, the effect of chemical composition on the solidification contraction has been clarified using synthetic mold fluxes of 1.25∼1.45 basicity, 8∼12 mass % Na_2O, 7∼11 mass % F, 2∼6 mass % Al_2O_3, 1.5∼4.5 mass % MgO. Larger basicity and Na_2O/F ratio yield larger contraction. Especially, mold flux of 12% Na_2O and 7% F shows larger contraction than that of 8% Na_2O and 11% F. Microphotograph analysis shows that the crystallization of sodium fluoride dicalcium silicate (NaF.2CaO.SiO_2) is the main reason for the increase of solidification contraction.
실리케이트 유리의 전열물성 및 윤활기능 최적화 및 몰드플럭스로의 활용
조중욱 한국세라믹학회 2022 세라미스트 Vol.25 No.3
Development of the advanced mold flux is always mandatory to enhance both the quality and productivity of continuous casting of steels. Especially, the increasing demands for high alloy steels production and high speed casting reveals serious contradiction between two principal functions of mold flux: lubrication and controlling heat transfer. In order to overcome this problematic needs, some innovative research activities are being carried out. MAE (Mixed Alkali Effect) has been examined in alumino-borosilicate-based mold system to stabilize alkali cation and aluminum association, which enables chemically stable glassy mold flux film during casting of high alloy steels. Non-Newtonian mold fluxes could be developed by addition of Si3N4 or SiC due to the increase of stiffness of polymeric structure, which would be beneficial to satisfy the contradictory requirements of viscosity at mold top surface and mold wall. Some innovative ideas for controlling mold heat transfer without deteriorating the lubrication have been examined by dispersion of nano-size metallic particles and by modification of prenucleation motif. All these trials are closely related with glass science and engineering. Therefore, it should be highly beneficial to enhance the collaborative research activities between glass and metallurgy society for further development of advanced functional mold flux systems.
윤대우,조중욱,김선효 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.3
Controlling the heat transfer rate from solidifying shell to copper mold is one of the important role of mold flux film during continuous casting of steels. It is highly desirable to regulate the thermal resistance of mold flux film not to exceed the critical quantity of mold heat transfer rate to prevent cast steel products from surface defects. In order to examine the effect of thermal radiation on the overall heat transfer rate through slag film in the continuous casting mold, the absorption coefficient has been investigated for various mold fluxes using a UV and an FT-IR spectrometer, followed by numerical calculations based on gray gas assumption. It is estimated that the heat transfer rate will decrease in 2-4% by addition of 3.2 mass% NiO into the conventional mold flux system with basicity (CaO/SiO2) of 1.07. As the increase of absorption coefficients will not be harmful to any casting performances such as friction in a casting mold, it is highly recommended to enhance the thermal radiative absorption behavior of mold slag film by optimizing the chemistry of mold fluxes, especially in the wavelength range of 1 to 3 μm at which the emitted energy intensity from steel shell will be maximized.
김선효,전찬욱,조중욱 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.9
The nitrogen reaction between steel and slag was studied by using CaO-Al₂O₃-TiO₂ slag system which has good ability for denitrogenization. The experimentally determined activity of Al₂O₃ increases with increasing TiO₂ content. The nitride capactiy, C_N to quantify the equilibrium nitrogen solubility in the slag increases with increasing TiO₂ content, but decreases with increasing slag basicity. The nitrogen reaction between CaO(BaO)-Al₂O₃-TiO₂ slag and steel may be interpreted by the Network model describing the behavior of oxygen and nitrogen ions in slag. The effect of the addition of BaO for replacing CaO on the nitride capacity was found to be very sensitive to the oxygen potentials. The nitrogen distribution ratio between CaO(BaO)-Al₂O,-TiO₂ slag and 304 stainless steel increased with decreasing Cr content and increasing temperature. Based on the results, the equilibrium nitrogen content in 304 stainless steel can be estimated when the denitrogenization is carried out using the slag investigated.
Numerical Modeling and Analysis of the Thermal Behavior of Copper Molds in Continuous Casting
고은이,이경우,박중길,조중욱,신호정 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.2
In this study, we establish a 3-D numerical analysis model to analyze the thermal behavior and to obtain the detailed heat transfer coefficient of a copper mold in a continuous casting system. This heat transfer coefficient changes according to variations in the mold geometry or cooling system. For increased flow speeds of the cooling water, the heat transfer coefficient also increases, but the rate of increase for the coefficient diminishes at higher flow speeds. As the thickness of the mold between the melt and the cooling water slots increases, the mold’s heat transfer coefficient decreases. However, the uniformity of the heat transfer coefficient improves with greater thickness. The effect of distance between cooling water slots on the mold’s heat transfer coefficient is also observed. Calculations show that greater distances between cooling water slots decrease the heat transfer coefficient.
심상철 ( Sang Chul Shim ),조중욱 ( Jung Wook Cho ),황상택 ( Sang Taek Hwang ),김광천 ( Kwang Chun Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 2008 대한금속·재료학회지 Vol.46 No.10
The behavior of hydrogen in the steel making process was investigated. The relation between the composition of ladle slag and hydrogen concentration in molten steel was considered. The hydrogen distribution ratio between ladle slag and molten steel was increased with increasing basicity of the slag; it was about 20 when the basicity of slag was 15. Hydroxyl capacity measured from the hydrogen distribution ratio between slag and the molten steel was comparatively corresponding to the value of hydroxyl capacity measured by the equilibrium reaction of slag and H2O gas. However, it is considerably different from the value calculated by regular solution model. The influence of hydrogen on a sticking type breakout is considered. The effect of hydrogen and H2O gas on the crystallization behavior of mold powder was investigated by DHTT(Dual hot thermocouple technique). As a result, it was proved that mold powder could be crystallized by H2O gas in the atmosphere. Therefore, it is concluded that H2O gas in the atmosphere can be a possible cause of the sticking type breakout that occasionally occurs in the continuous casting process.