共查询到20条相似文献,搜索用时 15 毫秒
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Lejun Zhou Huan Li Wanlin Wang Zhaoyang Wu Jie Yu Senlin Xie 《Metallurgical and Materials Transactions B》2017,48(6):2949-2960
This paper investigates the crystallization behavior of CaO-SiO2- and CaO-Al2O3-based mold fluxes for casting high-aluminum steels using single hot thermocouple technology, developed kinetic models, and scanning electron microscope. The results showed that the crystallization ability of the typical CaO-SiO2-based Flux A (CaO/SiO2 0.62, Al2O3 2 mass pct) is weaker than that of CaO-Al2O3-based Flux B (CaO/SiO2 4.11, Al2O3 31.9 mass pct) because of its higher initial crystallization temperature. The crystallization kinetics of Flux A was “surface nucleation and growth, interface reaction control” in the overall non-isothermal crystallization process, whereas that of Flux B was “constant nucleation rate, 1-dimensional growth, diffusion control, in the primary crystallization stage, and then transformed into constant nucleation rate, 3-dimensional growth, interface reaction control in the secondary crystallization stage.” The energy dispersive spectroscopy results for Flux B suggested that the variations in the crystallization kinetics for Flux B are due to different crystals precipitating in the primary (BaCa2Al8O15) and secondary (CaAl2O4) crystallization periods during the non-isothermal crystallization process. 相似文献
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Shu Qifeng Li Qiangqi Medeiros Samuel Lucas Santos Klug Jeferson Leandro 《Metallurgical and Materials Transactions B》2020,51(3):1169-1180
Metallurgical and Materials Transactions B - It is necessary to study crystallization from glass (devitrification) for non-reactive F-free CaO-Al2O3 based mold fluxes; this is especially important... 相似文献
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The isothermal and non-isothermal experiments were performed to construct the continuous cooling transformation (CCT) and temperature time transformation (TTT) diagrams of four industrial mold fluxes through visual observations in an experimental apparatus based on the single hot thermocouple technique (SHTT). The results of the CCT diagrams indicate that ① the crystallization temperature of mold fluxes lowers as the cooling rate increases, ② the mold fluxes have larger critical cooling rate, higher crystallization temperature, and less onset time of crystallization when the basicity increases or the viscosity decreases, ③ the influences of the melting points of the mold fluxes on their crystallization tendency are not significant. Isothermal tests show that the onset time of crystallization decreases at first, and then increases, and finally represents a "C" shape with increasing isothermal temperature. The TTT diagrams of four industrial mold fluxes were divided into two separate "C" shape regions. The crystal phase of C20A selected was analyzed by X-ray diffraction, which is cuspidine (Ca4 Si2 O7F2 ) over I 100 ℃ and calcium silicon oxide fluoride (Ca2SiO2F2) below 1 100℃. When compared with the TTT diagram, the CCT diagram can provide a more realistic estimate of the critical cooling rate of the mold fluxes. Thus, both the CCT and TTT diagrams can unambiguously describe the crystallization phenomena of the mold fluxes. 相似文献
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Jian Yang Jianqiang Zhang Yasushi Sasaki Oleg Ostrovski Chen Zhang Dexiang Cai Yoshiaki Kashiwaya 《Metallurgical and Materials Transactions B》2018,49(6):3097-3106
The effect of MgO on crystallization and heat transfer of fluoride-free mold fluxes was studied using single/double-hot thermocouple technique (SHTT/DHTT) and infrared emitter technique (IET), respectively. SHTT experiments demonstrated that the increase of MgO concentration promoted the crystallization tendency of mold fluxes. XRD analysis showed that the dominant phases changed from CaSiO3 to CaSiO3/Ca2MgSi2O7/Ca11Si4B2O22, and to Ca2MgSi2O7 as the MgO content was increased. The heat flux across mold flux disks was reduced from 671 to 615 kW/m2 in IET experiments when MgO concentration was increased from 0.9 to 4.9 mass pct. 相似文献
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The time temperature transformation (TTT) diagrams of fluoride free mold fluxes containing TiO2/ZrO2 were constructed through the confocal scanning laser microscope (CSLM) technique. It was found that the crystallization temperature of F free mold fluxes containing TiO2 or ZrO2 increases, while incubation time decreases with increasing basicity. The crystallization tendency increases with the zirconia addition in slag melt, as it may be thought that the addition solubility is limited in molten slag and the solid particles act as heterogeneous nucleation sites. Three types of crystal morphologies were observed, corresponding to different crystallization mechanisms. CaSiO3 and Ca3Si2O7 precipitate in the slag with low basicity, and Ca2SiO4 was formed with increasing basicity. The addition of TiO2 promotes the precipitation of CaTiO3. The logarithm of crystal growth rate increased with increasing isothermal temperature, suggesting that the crystal/melt interface reaction is the controlling step in the present experiment. 相似文献
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Crystallization kinetics and the structure of mold fluxes with SiO2 being substituted by 0, 5, and 10 pct TiO2 were studied by differential thermal analysis technique and Raman spectroscopy, respectively, to explore the effect of TiO2 on the crystallization behavior of the slag. Crystallization kinetics analysis shows that the activation energy for crystal growth increases with the increase of TiO2 substitution, implying that TiO2 substitution for SiO2 in mold fluxes produces negative effects on crystal growth and retards the crystallization process. Raman spectral study indicates that TiO2 enters the system mainly in the form of [TiO4] in monomer structure unit, and simultaneously, there appear relatively small amounts of [TiO6] structure unit. The introduction of TiO2 leads to a decrease of the dimer and chain Si-O-Si structure unit (Q1 and Q2). 相似文献
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Lejun Zhou Wanlin Wang Fanjun Ma Jin Li Juan Wei Hiroyuki Matsuura Fumitaka Tsukihashi 《Metallurgical and Materials Transactions B》2012,43(2):354-362
The effect of basicity on the mold fluxes crystallization was investigated in this article. The time-temperature-transformation
(TTT) diagrams and continuous-cooling-transformation (CCT) diagrams of mold fluxes with different basicity were constructed
by using single, hot thermocouple technology (SHTT). The results showed that with the increase of basicity, the incubation
time of isothermal crystallization became shorter, the crystallization temperature was getting higher, and the critical cooling
rate of continuous cooling crystallization became faster. The X-ray diffraction analysis suggested that calcium silicate (CaO·SiO2) was precipitated at the upper part of the TTT diagram and cuspidine (Ca4Si2O7F2) was formed at the lower part, when the basicity of mold fluxes was within 1.0 to 1.2. However, when basicity was 0.8, only
the cuspidine phase was formed. A kinetic study of isothermal crystallization process indicated that the increase of the basicity
tended to enhance the mold flux crystallization, and the crystallization activation energy became smaller. The crystallization
mechanism of cupsidine was changing from one-dimensional growth to three-dimensional growth with a constant number of nuclei,
when the basicity of mold fluxes varied from 0.8 to 1.2. 相似文献
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碱度0.85、CaO-SiO2-Al2O3-MgO-Na2O-CaF2为基本渣系,采用旋转动力学方法研究了TiO2棒的旋转角速度(50~120)r/min,碱度(0.7~1.15),熔渣温度(1300~1480℃),TiO2(0~12%),CaF2(5%~15%)对保护渣吸收TiO2速率的影响。结果表明,分别随温度升高,碱度增加,TiO2含量降低和CaF2含量增加,使TiO2在渣中的溶解速率升高,其中温度和碱度的影响最显著。TiO2溶解的限制性环节是扩散过程,溶解过程的活化能为130.9kJ/mol。 相似文献
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ZHU Chuan-yun HAN Wen-dian LIU Cheng-jun JIANG Mao-fa 《钢铁研究学报(英文版)》2005,12(6):23-26
Moldfluxformsaliquidphaseinfiltratinginto thegapbetweenthemoldandstrand.Thelayerof fluxfilmonthemoldplateisasolidglassylayer,whilethelayerclosesttothestrandremainsliquid andacrystallizationlayerliesbetweenthistwolay ers[1-3].Thecrystallizationtemperatureo… 相似文献
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The crystallization behavior of mold fluxes containing 0-8 mass% TiO 2 was investigated using the single hot thermocouple technique (SHTT)and X-ray diffraction (XRD)to study the possible effects on the coordination of heat transfer control and strand lubrication for casting crack-sensitive peritectic steels.Time-temperature-transforma-tion (TTT)and continuous-cooling-transformation (CCT)curves were plotted using the data obtained from SHTT to characterize the crystallization of the mold fluxes.The results showed that crystallization of the mold fluxes during isothermal and non-isothermal processes was suppressed with TiO 2 addition.From the TTT curves,it could be seen that the incubation and growth time of crystallization increased significantly with TiO 2 addition.The CCT curves showed that the crystallization temperature initially decreased,and then suddenly increased with increasing the TiO 2 content.XRD analysis suggested the presence of cuspidine in the mold fluxes with lower TiO 2 content (< 4 mass%),while both perovskite and cuspidine were detected in the mold fluxes when the TiO 2 content was increased to 8 mass%.In addition,the growth mechanisms of the crystals changed during the isothermal crystallization process from interface-controlled growth to diffusion-controlled growth with increasing the TiO 2 content. 相似文献
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Flores F. Tania M. Rodríguez A. Sergio Ortega C. Félix Castillejos E. A. Humberto 《Metallurgical and Materials Transactions B》2018,49(5):2633-2648
Metallurgical and Materials Transactions B - The rate and extent of formation of crystalline phases in the slag film that develops between the mold and the strand in steel continuous casting... 相似文献