共查询到20条相似文献,搜索用时 31 毫秒
1.
Wanlin Wang Jie Yu Lejun Zhou Zhaoyang Wu Huan Li 《Metallurgical and Materials Transactions B》2018,49(4):1580-1587
To compensate the negative effect caused by the absorption of chromium oxide inclusions during the casting process of Cr-contained steels, a new mold flux system has been designed and investigated. The melting temperature range of the newly designed mold flux system is from [1124 K to 1395 K (851 °C to 1122 °C)]. The viscosity at 1573 K (1300 °C) and the break temperature increase with the addition of MnO and Cr2O3 but decrease with the addition of B2O3. The crystalline fraction of mold flux decreases from 81 to 42.1 pct with the addition of MnO and Cr2O3, and then further decreases to 25.3 pct with the addition of B2O3; however, it improves from 54.4 to 81.5 pct when the basicity increases. Besides, the heat-transfer ability of mold flux is inverse to the crystallization ratio of the slag. The comprehensive study of the properties for the four designed mold fluxes suggests that the mold flux with 1.15 basicity-3.01 pct B2O3-1.10 pct MnO-2.10 pct Cr2O3 shows the best properties for the continuous casting of Cr-contained steels. 相似文献
2.
Cheng-Bin Shi Myung-Duk Seo Jung-Wook Cho Seon-Hyo Kim 《Metallurgical and Materials Transactions B》2014,45(3):1081-1097
Crystallization behaviors of the newly developed lime-alumina-based mold fluxes for high-aluminum transformation induced plasticity (TRIP) steels casting were experimentally studied, and compared with those of lime-silica-based mold fluxes. The effects of mold flux crystallization characteristics on heat transfer and lubrication performance in casting high-Al TRIP steels were also evaluated. The results show that the crystallization temperatures of lime-alumina-based mold fluxes are much lower than those of lime-silica-based mold fluxes. Increasing B2O3 addition suppresses the crystallization of lime-alumina-based mold fluxes, while Na2O exhibits an opposite effect. In continuous cooling of lime-alumina-based mold fluxes with high B2O3 contents and a CaO/Al2O3 ratio of 3.3, faceted cuspidine precipitates first, followed by needle-like CaO·B2O3 or 9CaO·3B2O3·CaF2. In lime-alumina-based mold flux with low B2O3 content (5.4 mass pct) and a CaO/Al2O3 ratio of 1.2, the formation of fine CaF2 takes place first, followed by blocky interconnected CaO·2Al2O3 as the dominant crystalline phase, and rod-like 2CaO·B2O3 precipitates at lower temperature during continuous cooling of the mold flux. In B2O3-free mold flux, blocky interconnected 3CaO·Al2O3 precipitates after CaF2 and 3CaO·2SiO2 formation, and takes up almost the whole crystalline fraction. The casting trials show that the mold heat transfer rate significantly decreases near the meniscus during the continuous casting using lime-alumina-mold fluxes with higher crystallinity, which brings a great reduction of surface depressions on cast slabs. However, excessive crystallinity of mold flux causes poor lubrication between mold and solidifying steel shell, which induces various defects such as drag marks on cast slab. Among the studied mold fluxes, lime-alumina-based mold fluxes with higher B2O3 contents and a CaO/Al2O3 ratio of 3.3 show comparatively improved performance. 相似文献
3.
Boxun Lu Wanlin Wang Jin Li Huan Zhao Daoyuan Huang 《Metallurgical and Materials Transactions B》2013,44(2):365-377
An investigation was carried out to study the effects of basicity (CaO/Si2O) and B2O3 on the crystallization and heat transfer behaviors of low fluorine mold flux for casting medium carbon steels. The double hot thermocouple technique (DHTT) was employed to study the crystallization behavior of mold flux with a different basicity and B2O3 content, under the simulated thermal gradient as in a real caster. The infrared emitter technique (IET) was also applied for the study of heat transfer behavior of the above mold fluxes. By combining the results of IET and DHTT, this article indicated that the increase of basicity would decrease the general heat transfer rate of mold flux, as it tends to promote crystallization of mold flux apparently, while B2O3 has the opposite function. The combined effects of basicity and B2O3 could be used to adjust the general crystallization and heat transfer properties of low fluorine mold flux for casting medium carbon steels, which would provide an instructive way for the design of Fluorine free mold flux for casting medium carbon steels. 相似文献
4.
Binbin Jiang Wanlin Wang Il Sohn Juan Wei Lejun Zhou Boxun Lu 《Metallurgical and Materials Transactions B》2014,45(3):1057-1067
The crystallization behavior of a CaO-Al2O3-based slag system with various ZrO2 content (from 1 to 5 wt pct) and CaO/Al2O3 (C/A) ratio (from 0.8 to 1.2) has been studied by using single hot thermocouple technology (SHTT) in this article. The continuous-cooling-transformation (CCT) diagrams and time-temperature-transformation (TTT) diagrams of the above slag system were constructed for the analysis of the varying crystallization behaviors. The results suggested that Al2O3 tended to enhance the slag samples crystallization when the C/A ratio ranged from 0.8 to 1.2, and the critical cooling rate and crystallization temperature increased with the decrease of C/A ratio; meanwhile, the incubation time was also getting shorter with the reduction of C/A ratio. The addition of ZrO2 would enhance the crystallization of slag samples because of the induced heterogeneous nucleation of molten slag. However, the general crystallization was determined by the balance between molten slag viscosity and heterogeneous nucleation, such that Sample 3 (C/A = 1.0, ZrO2 = 3 pct, B2O3 = 10 pct, Li2O = 3 pct [in wt pct]) would demonstrate the strongest crystallization kinetics in a high-temperature zone. The different crystals formed during the tests were also analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). 相似文献
5.
Myung-Duk Seo Cheng-Bin Shi Jung-Wook Cho Seon-Hyo Kim 《Metallurgical and Materials Transactions B》2014,45(5):1874-1886
The effects of basicity (CaO/SiO2), B2O3, and Li2O addition on the crystallization behaviors of lime-silica-based mold fluxes have been investigated by non-isothermal differential scanning calorimetry (DSC), field emission scanning electron microscopy, X-ray diffraction (XRD), and single hot thermocouple technique. It was found that the crystallization temperature of cuspidine increased with increasing the basicity of mold fluxes. The crystallization of wollastonite was suppressed with increasing the mold flux basicity due to the enhancement of cuspidine crystallization. The addition of B2O3 suppresses the crystallization of mold flux. The crystallization temperature of mold flux decreases with Li2O addition. The size of cuspidine increases, while the number of cuspidine decreases with increasing mold flux basicity. The morphology of cuspidine in mold fluxes with lower basicity is largely dendritic. The dendritic cuspidine in mold fluxes is composed of many fine cuspidine crystals. On the contrary, in mold fluxes with higher basicity, the cuspidine crystals are larger in size with mainly faceted morphology. The crystalline phase evolution was also calculated using a thermodynamic database, and compared with the experimental results determined by DSC and XRD. The results of thermodynamic calculation of crystalline phase formation are in accordance with the results determined by DSC and XRD. 相似文献
6.
Lejun Zhou Wanlin Wang Daoyuan Huang Juan Wei Jin Li 《Metallurgical and Materials Transactions B》2012,43(4):925-936
The crystallization processes of mold fluxes for casting low-carbon (LC) and medium-carbon (MC) steels were investigated by using double hot thermocouple technology (DHTT) in this article. The results showed that the glass phase was first formed at the cold side thermocouple (CH-2), when the LC mold flux (mold flux for casting low-carbon steel) was exposed to the temperature gradient of 1773 K (1500 °C) to 1073 K (800 °C); then, the fine crystals were precipitated at the liquid/glass interface and grew toward glass and later on to liquid phase. However, the crystals were directly formed at CH-2 when MC flux (mold flux for casting medium-carbon steel) was under the same thermal gradient. The growth rate of MC flux crystals was much faster than that of LC ones. Scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS) analyses suggested that the crystals formed in LC mold flux were mainly dendritic cuspidine Ca4Si2O7F2, and the crystals formed from the liquid phase were larger than those from the glass. For MC mold flux, the earlier precipitated crystals were large dendritic Ca4Si2O7F2, whereas the later ones were composed of equiaxed Ca2Al2SiO7 crystals. The results of DHTT measurements were consistent with the time-temperature-transformation (TTT) diagrams and X-ray diffraction (XRD) analysis. 相似文献
7.
Cheng-Li Wang Weng-Sing Hwang Horng-Huey Ko Chi-Shiung Hsi Kuo-Ming Chang Moo-Chin Wang 《Metallurgical and Materials Transactions A》2014,45(1):250-260
This paper examines the phase transformation and microstructure of Zn2Ti3O8 nanocrystallite powders prepared using the hydrothermal process that includes TiCl4 and Zn(NO3)2·6H2O as the initial materials. Differential thermal analysis, X-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction, nanobeam electron diffraction, and high resolution TEM were utilized to characterize the transition behavior of zinc titanate precursor powders after calcination. Nanocrystalline Zn2Ti3O8 powders with a size range of about 5.0 to 8.0 nm were obtained when the precursor powders were calcined at 773 K (500 °C) for 1 hour. When the zinc titanate precursor powders were calcined at 1073 K (800 °C) for 1 hour, the cubic crystal of Zn2Ti3O8 with a o = 0.8399 ± 0.0003 nm still remained the predominant crystalline phase and the crystallite size increased to 20.0 nm. In addition, ZnTiO3 phase first appeared because of the 13.8 pct of Zn2Ti3O8 decomposition when the zinc titanate precursor powders were calcined at 1073 K (800 °C) for 1 hour. When the zinc titanate precursor powders were calcined at 1073 K (800 °C) for 9 hours, the Zn2Ti3O8 crystallites grew continuously to 80.0 nm and enhanced the crystallinity. When the precursor powders were calcined at 1273 K (1000 °C) for 1 hour, Zn2TiO4 crystallites with a o = 0.8461 ± 0.0002 nm were the predominant crystalline phase. 相似文献
8.
Qiang Wang Min Sun Shengtao Qiu Zhiling Tian Guoling Zhu Longmei Wang Pei Zhao 《Metallurgical and Materials Transactions B》2014,45(2):540-546
The slag-steel equilibrium reaction between the newly developed mold slag ND-MSL and 20Mn23AlV steel has been studied at high temperatures in the laboratory. The crystal morphology, microanalysis, and phase analysis of the original and final ND-MSL slags were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Results show that, in the final ND-MSL slag, the constitution of SiO2 decreased by 0.7 wt pct and Al2O3 increased by 6.46 wt pct, while the melting temperature, viscosity, and crystallization rate increased by 62 K, 0.66 dPa s, and 15 pct, respectively. NaAlSi3O8 and CaAl2Si2O8 were found to be precipitated in the final ND-MSL slag. Both the original and final ND-MSL slags have a small amount of LiF crystal and good glass form. The ND-MSL slag has little change in the composition and properties compared with the two currently used mold slags. 相似文献
9.
Boxun Lu Kun Chen Wanlin Wang Binbin Jiang 《Metallurgical and Materials Transactions B》2014,45(4):1496-1509
With the development of advanced high strength steel (AHSS), a large amount of aluminum was added into steels. The reaction between aluminum in the molten steel and silica based mold flux in the continuous-casting process would tend to cause a series of problems and influence the quality of slabs. To solve the above problems caused by the slag–steel reaction, nonreactive lime-alumina-based mold flux system has been proposed. In this article, the effect of Li2O and Na2O on the crystallization behavior of the lime-alumina-silica-based mold flux has been studied by using the single hot thermocouple technology (SHTT) and double hot thermocouple technology (DHTT). The results indicated that Li2O and Na2O in the above mold flux system play different roles as they behaved in traditional lime-silica based mold flux, which would tend to inhibit general mold flux crystallization by lowering the initial crystallization temperature and increasing incubation time, especially in the high-temperature region. However, when their content exceeds a critical value, the crystallization process of mold fluxes in low temperature zone would be greatly accelerated by the new phase formation of LiAlO2 and Na x Al y Si z O4 crystals, respectively. The crystalline phases precipitated in all samples during the experiments are discussed in the article. 相似文献
10.
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
11.
Wei Yan Weiqing Chen Carsten Lippold Hongcheng Xu 《Metallurgical and Materials Transactions B》2013,44(6):1466-1477
The heat-transfer behavior across mold fluxes for Invar alloy Fe-36Ni would introduce significant influence on the slab surface quality. A study on the heat-transfer property of mold flux film for Invar alloy Fe-36Ni was carried out by an interaction between laboratory simulation and field trial. The study results indicate that great effect on heat transfer across flux film is caused by chemical compositions of mold fluxes. An increase of basicity and CaF2 content suppresses heat transfer across flux film; heat transfer across flux film increases when the Al2O3 content increases from 4 pct to 8 pct but decreases when Al2O3 content is above 8 pct. The crystalline phases of both the conventional mold fluxes and the improved mold fluxes are all cuspidine phases. However, crystallization capability of the improved mold fluxes decreases as the result of the increase of basicity and CaF2 content as well as the decrease of Al2O3 content. The average thickness of flux film taken from mold is about 1.6 mm, and the crystalline fraction is only 21.4 pct. All these promote heat transfer across the flux film. The field trial of the improved mold fluxes shows that the properties of liquid slag are steady during continuous casting; comprehensive heat transfer across flux film meets the needs of continuous casting of Fe-36Ni. Border solidification structures of solidified shell are refined remarkably, and hot cracking gets avoidance eventually. 相似文献
12.
P. Palai P. P. Sahoo Arghya Dey T. K. Roy V. V. Mahashabde 《Metallurgical and Materials Transactions B》2013,44(5):1185-1189
The alumina pickup in a range of mold fluxes used for continuous casting of aluminum (Al)-killed ultralow carbon, low carbon, and peritectic steel have been measured. The Al2O3 pickup in slag varies approximately from 7 to 12 pct and depends on the slag basicity. Significantly higher Al2O3 pickup reported in basic slags and polynomial relationship exists between them. The effect of chemical composition on microstructure evolution and Al2O3 partitioning during crystallization was identified in all three types of mold slags. The microsegregation of Al2O3 inclusions in the constituent phase of CaO-SiO2-Al2O3 based slag film is presented. Constitutional segregation of Al2O3 inclusion in slag was found to affect the Al2O3 pickup phenomena during continuous casting. Segregation of alkalis like Na and K was also observed in an Si-rich interdendritic matrix, whereas F was retained in the dendrites of all the slags studied. The Al2O3 inclusion partitioning and interdendritic segregation in the mold slag is studied with metallographic evidence. 相似文献
13.
Sung Suk Jung Gi Hyun Kim Il Sohn 《Transactions of the Indian Institute of Metals》2013,66(5-6):577-585
The effect of Al2O3 on the crystallization and viscosity of calcium-silicate based fluxes with Na2O and Li2O additions used for continuous casting mold fluxes have been studied using the confocal laser scanning microscope and the rotating spindle rheometer. Al2O3 additions lowered the crystallization temperature of the flux and several crystalline phases for fluxes with high concentrations of SiO2 forms depending on the cooling rate. High Al2O3 containing fluxes formed relatively few crystalline phases and were not highly dependent on the cooling rate. At slow cooling rates of 25 K/min for 10 and 20 wt% Al2O3 containing samples, SEM images revealed dendrites formed within the crystalline phases. At faster cooling rates the dendrite formation is inhibited and a spherical morphology could be observed. The substitution of SiO2 with Al2O3 content modified the dominant silicate network into complex alumino-silicates. This increased the viscosity of the melt. FTIR and Raman analysis showed increased amounts of symmetric Al–O0 stretching with higher Al2O3. With higher CaO/(SiO2 + Al2O3), the symmetric Al–O0 stretching and the Si–O–Al seems to decrease. 相似文献
14.
Lejun Zhou Huan Li Wanlin Wang Dan Xiao Lei Zhang Jie Yu 《Metallurgical and Materials Transactions B》2018,49(5):2232-2240
The effect of Li2O content on the behavior of melting, crystallization, and molten structure for CaO-Al2O3-based mold fluxes was investigated in this article, through use of single hot thermocouple technology (SHTT), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray diffraction (XRD). The SHTT results showed that the melting temperature range of the designed mold fluxes decreases and the crystallization of mold fluxes is inhibited first and then becomes enhanced when the Li2O content increases from 1 to 6 mass pct. The FTIR and Raman spectroscopy results suggested that Li2O could release O2? ions to break the complex Al-O-Al structural unit into Al-O? structure. Meanwhile, Li2O could also stabilize the structural unit of Si-O-Al by link aluminate and Q 0 Si structure through providing Li+ ions to merge into the network and compensate for the charges between Al3+ and Si4+. Besides, the XRD results indicated that the precipitation of LiAlO2 in molten slag would enhance the crystallization behavior of mold flux when Li2O content is over 4.5 mass pct. 相似文献
15.
Huan Zhao Wanlin Wang Lejun Zhou Boxun Lu Youn-Bae Kang 《Metallurgical and Materials Transactions B》2014,45(4):1510-1519
An investigation was carried out to study the effect of MnO on crystallization, melting, and heat transfer of lime-alumina-based mold flux used for high Al-TRIP steel casting, through applying the infrared emitter technique (IET) and the double hot thermocouple technique (DHTT). The results of IET tests showed that MnO could improve the general heat transfer rate through promoting the melting and inhibiting the crystallization of mold flux; meanwhile the radiative heat flux was being attenuated. DHTT experiments indicated that the crystallization fraction, melting temperature of mold flux decreased with the addition of MnO. The results of this study can further elucidate the properties of the CaO-Al2O3 slag system and reinforce the basis for the application of lime-alumina system mold fluxes for casting high Al steels. 相似文献
16.
The present paper is an investigation into how the Al2O3/SiO2 ratio in the compositions of mold slags influences the crystallization behavior of molten slags. The experimental work is based upon observing the crystallization events through a Confocal Scanning Laser Microscope equipped with a hot‐stage. The study is motivated by the variation in crystallization that might occur in mold slags due to the pickup of alumina during continuous casting of high Al containing TRIP steels. The crystallization temperature was found to increase with increasing Al2O3/SiO2 ratio, and the crystal morphology was dependent upon the chemical composition and isothermal temperature. The crystallization path was complex, with CaF2 found to precipitate first, and followed by a second precipitation event. In this second event, the precipitated phase depended on the chemical composition of mold slag and changed from cuspidine to gehlenite as the mass ratio of Al2O3/SiO2 was increased beyond 0.65, and finally Al2O3 was observed when the alumina content was 30wt.% (corresponding to a mass ratio of = 1.42). 相似文献
17.
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
18.
This study investigated the interfacial reaction kinetics and related phenomena between CaO-SiO2-MgO-Al2O3 flux and Fe-xMn-yAl (x = 10 and 20 mass pct, y = 1, 3, and 6 mass pct) steel, which simulates transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) steels at 1873 K (1600 °C). It also examines the effect of changes in the composition of the steel and slag phases on the interfacial reaction rate and the reaction mechanisms. The content of Al and Si in the 1 mass pct Al-containing steel was found to change rapidly within the first 15 minutes of the reaction, but then it remained relatively constant. The content of Al and Si in the 3 to 6 mass pct Al-containing steels, in contrast, changed continuously throughout the entire reaction time. In addition, the content of Mn in the 1 mass pct Al-containing steels initially decreased with increasing time, but the content did not change in the 3 to 6 mass pct Al-containing steels. Furthermore, the mass transfer coefficient of Al, k Al, in the 1 mass pct Al-containing systems was significantly higher than that in other systems; i.e., the k Al can be arranged such that 1 mass pct Al systems >> 3 mass pct Al systems ≥ 6 mass pct Al systems. The compositions of the final slags were close to the saturation lines of the [Mg,Mn]Al2O4 and MgAl2O4 spinels when the slags reacted with 1 mass pct Al and 3 to 6 mass pct Al-containing steels, respectively. These results, which show the effect of Al content on the reaction phenomena, can be explained by the significant increase in the apparent viscosity of the slags that reacted with the 3 to 6 mass pct Al-containing steels. This reaction was likely caused by the precipitation of solid compounds such as MgAl2O4 spinel and CaAl4O7 grossite at locally alumina-enriched areas in the slag phase. This analysis is in good accordance with the combination of Higbie’s surface renewal model and the Eyring equation. 相似文献
19.
Xu Cheng Chen Yuan Nick Green Paul Withey 《Metallurgical and Materials Transactions A》2013,44(2):888-898
The investment casting process is an economic production method for engineering components in TiAl-based alloys and offers the benefits of a near net-shaped component with a good surface finish. An investigation was undertaken to develop three new face coat systems based on yttria, but with better sintering properties. These face coat systems were mainly based on an yttria-alumina-zirconia system (Y2O3-0.5 wt pct Al2O3-0.5 wt pct ZrO2), an yttria-fluoride system (Y2O3-0.15 wt pct YF3), and an yttria-boride system (Y2O3-0.15 wt pct B2O3). After sintering, the chemical inertness of the face coat was first tested and analyzed using a sessile drop test through the metal wetting behavioral change for each face coat surface. Then, the interactions between the shell and metal were studied by centrifugal investment casting TiAl bars. Although the sintering aids in yttria can decrease the chemical inertness of the face coat, the thickness of the interaction layer in the casting was less than 10 μm; therefore, these face coats still can be possible face coat materials for investment casting TiAl alloys. 相似文献
20.
Christian Thales Mutale Alan W. Cramb Thomas Claudon 《Metallurgical and Materials Transactions B》2005,36(3):417-418
In this work, isothermal crystallization of a synthetic slag containing 46 wt pct CaO, 46 wt pct SiO2, 6 wt pct Al2O3, and 2 wt pct Na2O has been investigated by means of double hot thermocouple technique (DHTT). The effect of Na2O content on crystallization time was confirmed. Two different types of calcium silicate crystals were observed. Calcium di-silicate
forms at temperatures above 1150 °C and calcium tri-silicate precipitate at temperatures below 1050 °C. A mixture of the two
types of calcium silicate has been observed between the two temperatures. The tendency of crystals to become richer in calcium
at low temperatures that has also been observed in previous published works has been confirmed. No effect of the cooling rate
on crystallization start time was confirmed in the range of cooling rates applied in this investigation. 相似文献