Development of Fluoride-free Mold Powders for Peritectic Steel Slab Casting

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1 , pp Development of Fluoride-free Mold Powders for Peritectic Steel Slab Casting Guanghua WEN, 1,2) Seetharaman SRIDHAR, 2) Ping TANG, 1) Xin QI 1) and Yongqing LIU 1) 1) Department of Metallurgy, College of Materials Science and Engineering, Chongqing University, 174 Shazhengjie, Chongqing , P. R. China. 2) Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes, Pittsburgh, PA 15213, U.S.A. (Received on April 2, 2007; accepted on May 21, 2007) In this paper, titanium-bearing blast furnace slags (CaO SiO 2 TiO 2 ) produced at Panzhihua Iron and Steel Company (P. R. China) is used as the base material to develop fluoride-free (F-free) mold powders to improve the heat transfer between the mold and the strand. Effects of the binary basicity (CaO/SiO 2 ), TiO 2, Na 2 O, Li 2 O, MgO, MnO and B 2 O 3 on the melting temperature, viscosity and heat flux of F-free mold powders are investigated. The laboratory results indicate that 1) the melting temperature and the viscosity of the F-free powder decrease, as expected, with increasing the content of Li 2 O, B 2 O 3 and Na 2 O respectively, but the lowest viscosity is achieved with 6.0 mass% TiO 2 ; 2) the heat flux of the F-free slag film with mass% TiO 2 is close to that of a conventional mold slag film with mass% F; 3) the effect of basicity of the F-free powder on the heat flux is the same as the powder bearing fluoride; 4) the heat flux changes significantly with more than 8.0 mass% Na 2 O and about 4.0 mass% MnO, whereas the effects of Li 2 O and B 2 O 3 in the F-free powder on heat flux are not significant. The suitable range of main components of the F-free powder with TiO 2 is proposed for casting peritectic-grade-steel slabs. The industrial trials of peritectic steel casting, using the proposed F-free flux, reveals a good surface quality of the slab, and wellcontrolled heat transfer at the continuous casting mold by the F-free powder with the precipitated crystalline phase being perovskite (CaTiO 3 ) instead of cuspidine in the conventional mold slags that contain fluoride. KEY WORDS: titanium-bearing blast furnace slag; slabs; continuous casting; F-free mold powder; heat transfer; peritectic steel. 1. Introduction Mold powders play an important role in ensuring the surface quality of the products and the process stability of the continuous casting process, especially longitudinal cracking and sticker breakout. In addition, the molten mold powder, in form of a top-covering slag may contribute to refining of the melt from inclusions. Mold powders usually contain the following components: CaO, SiO 2, Na 2 O and CaF 2. Among the chemical compositions of mold powder, the roles of fluorine are to control viscosity, break temperature and crystallization fraction developed in a slag film, which are directly related to both lubrication and heat transfer through the slag that infiltrates between the mold wall and the solidified steel shell. 1) However, the fluorine emissions lead to erosion of plant, acidification of the cooling water and are a potential health and safety hazard. 2) Thus the replacement of fluorine with a more benign constituents in the mold powder is a research area of interest. 3) The melting and viscosity characteristics of the F-free mold powder were investigated in laboratory scale, which indicated that the melting temperature and the viscosity at C of F-free mold powders with B 2 O 3 added in place of F in traditional powders can be controlled in the required range. 4) Industrial trials of the fluoride-free mold powder were carried out at some steel works with the focus on billet and bloom casters. 5) For slab casters, especially those casting peritectic grade steels, there is currently no substitute for fluorine in the mold slag. This is due to that, while mold slag viscosity is the pertinent design parameter for developing mold fluxes for casting billets, for the case slab casting, the heat transfer through the slag also needs to be considered in order to control surface defects. This is because the longitudinal cracking in peritectic carbon ( mass% C) steels results from the 4% mismatch in the thermal shrinkage coefficients for the d and g phases which results in stresses which can only be relieved by cracking. The stresses can be minimized by keeping the shell as thin and as uniform as possible. This is achieved by reducing the heat transfer by maintaining a thick layer of slag film with a significant crystalline fraction inside the mold/strand gap. Owing to the inevitably need of controlled cuspidine crystallization in the slag to control the mold heat flux, the issue of F-free slab mold powders by the substitution of B 2 O 3 is not acceptable. 1) Therefore, the solution to the outstanding problem of the F-free slab mold powders requires the tailoring of a chemistry that simultaneously ISIJ

2 Fig. 1. Images of typical stages during the melting process. lowers viscosity and crystallizes in a manner that results in a desirable control of heat flow through the mold/strand gap. In the current study, the hot metal bearing vanadium and the blast furnace slag bearing titanium (CaO SiO 2 TiO 2 ) from the Vanadic Titanomagnetite are obtained as a result of the blast furnace smelting process at Panzhihua Iron and Steel Company (PanSteel) (P. R. China). The content of TiO 2 in the slag is about mass%. The current annual amount of the blast furnace slag bearing titanium is over 5 Mt at PanSteel. This blast furnace slag bearing titanium consists of bearing titanium minerals with high crystallization tendency, and can therefore, unlike common blast furnace slags, not be extensively recycled through use in cement manufacturing. The titanium in the slag is distributed as different mineral compounds, such as perovskite (CaO TiO 2 ), titanaugite (CaO TiO 2 Al 2 O 3 ) and titanium diopside (Ca 2 (Mg 3,Ti) (Al 2,Ti) 2 (SiO 4 ) 2 O 12 ). Content of TiO 2 in perovskite crystal is 60 mass% of total TiO 2 amount in the slag. 6) Recently, crystallization of CaO SiO 2 TiO 2 synthetic slag with the basicity (CaO/SiO 2 ) of about 0.8 as a candidate for F-free mold flux was conducted by H. Nakada et al. 7) The result indicates that the CaOSiO 2 TO 2 crystallizes rapidly in the slag film, similar to cuspidine in commercial mold fluxes, but the thickness of the crystalline layer was found to be smaller than that of the crystalline layer resulting from cuspidine precipitation. The prescence of Ti in the glassy could result in a change in opacity and therefore radiative properties of the slag layer but this has not been quantified. According to the equilibrium phase diagram of CaO SiO 2 TiO 2 system, 8) the main crystalline phase related to TiO 2 should be perovskite since the basicity of commercial mold powder is approximately 0.8 to 1.4. If the blast furnace slag bearing titanium could be used as a base chemistry for manufacturing mold powders, the cuspidine in the fluxes with fluoride could potentially be replaced by the perovskite in the slag. It may thus be feasible to control the mold heat flux for casting of different steel grades. This would require that the F-free powder with TiO 2 must exhibit similar (i) melting temperature and (ii) viscosity, in addition to (iii) crystallization and resulting thermal conductivity, as those in the F-bearing powder. Therefore, before applying the blast furnace slag bearing titanium to the F-free mold powder, the research on these thermophysical properties is needed. This paper investigates the change of viscosity, melting temperature, and heat flux of the above mentioned slags. 2. Experimental The melting temperature of mold powders was determined using a high temperature microscope. The specimen is heated and monitored for signs of melting. The test consists of heating an agglomerated sample pressed into a cylinder (3 mm in diameter and 3 mm in height) at a controlled rate, and then monitoring the changes in sample dimension. Shapes corresponding to softening, hemisphere and fluidity are specified, their height is original height of 75%, 50% and 25%, respectively (see Fig. 1) and the temperatures at which the samples achieve these shapes are recorded by a computer. The hemisphere temperature is usually defined as the melting temperature of mold fluxes. 9) The high temperature viscosity of liquid mold fluxes was measured with a rotating viscometer. This instrument measures the torque of spindle rotated at fixed speed in a crucible filled with the liquid of 250 g. The crucible was heated from room temperature to C in the MoSi 2 electric furnace, and then maintained isothermally at C for 10 min. The viscosity at C is determined by the averaged value of 20 measurements which were continuously measured. A calibration measurement was carried out at room temperature by using standard oil of known viscosity. It is well known that the heat transfer through the slag film in the mold primarily depends on two parameters of the mold fluxes, namely break temperature as it governs the thickness of the slag film layer and crystallization tendency, but it is very difficult to accurately quantify them. 10) Consequently, an experimental apparatus for simulating copper mold was designed to directly measure the heat flux of the slag film, which is schematically shown in Fig. 2. A quantity of g slag was melted in a graphite crucible which was heated in an induction furnace. The water cooled detector made of copper was immersed liquid slag at C, and a solid slag deposition formed on the copper wall. Subsequently, the copper detector was lifted up and the attached solid slag was removed after an immersion time of 120 s. The liquid slag temperature was measured by a pyrometer. The temperatures of inlet and outlet cooling water were recorded simultaneously and exported to a computer. The heat flux through the slag film was calculated based on the temperature difference of water between outlet and inlet against immersion time. The cooling water flow rate was 0.30 m 3 h 1. A correlation of water temperature difference against immersion time can be obtained, as shown in Fig. 3. It can be seen in this figure that there are three significant stages of water temperature variation. When the detector is immersed in the liquid slag at the C, a sudden increase in tem ISIJ 1118

3 Fig. 2. Schematic diagram of the experimental apparatus (left) and solid slag deposition (right) for copper detector. amount of 8.0 mass% Na 2 O, 3.0 mass% Al 2 O 3, 2.0 mass% MgO was used in all the cases to simulate the conditions similar to industrial ones. All the calculated chemical compositions of studied slags including F-free and F containing are listed in Table 1 and Table 2, respectively. Fig. 3. Schematic diagram of the temperature difference with immersion time. perature difference of DT 1 at time t 1, which mainly represents the heat transfer of liquid slag between the copper mold and liquid slag during initial stage of solid slag deposition. Then, as the solid slag film increases in thickness, the temperature difference decreases from DT 1 to DT 2 during the time period from t 1 to t 2. This is attributed to the combined effects of formation of the solid slag film, recrystallization of the glassy slag layer and formation of the gap between the copper mold and the solid slag film. Finally, after the immersion time exceeded t 2, the solid slag film slowly grows, causing the temperature to drop further, albeit at a slow rate. The result of many trials showed that the range of slag film thickness was 1 5 mm, which is close to the one of the slag films removed from the operating continuous casting mold 11) where the immersion time is close to the experimental time t 2, hence the heat flux of solid slag film in mold is defined as the heat flux at this moment. There were 35 specimens of the F-free powders. Their chemical compositions were chosen considering seven parameters, namely basicity (CaO/SiO 2 ) , and contents of TiO mass%, Na 2 O 2 10 mass%, Li 2 O mass%, MgO 3 8 mass%, MnO 2 6 mass% and B 2 O mass%. Each parameter included five different levels. TiO 2 of the specimens came from the blast furnace slag bearing titanium, the other compositions were achieved by adding pure oxides (CaO, SiO 2, MgO, MnO and B 2 O 3 ), Na 2 CO 3 was added as a source of Na 2 O and Li 2 CO 3 as a source of Li 2 O. For comparison of the heat flux developed in the slag film with the F-free powders, 10 specimens of the powders with fluoride were prepared, the basicity and mass% F were mainly considered, and the constant 3. Results and Discussion 3.1. Melting Temperature and Viscosity Figure 4 shows the effects of the melting temperature and viscosity of the F-free powders as functions of binary basicity, TiO 2, Na 2 O, Li 2 O, MgO, MnO and B 2 O 3, respectively. The viscosity was in all cases measured at C. It can be seen that Li 2 O is the strongest constituent for lowering the melting temperature for compositions of Li 2 O 2.5 mass% in the slag, and B 2 O 3 has a strong influence too. Increasing the contents of TiO 2, MgO and CaO/SiO 2 ratio in the slag increases the melting temperature of the F- free slag bearing titanium. The melting temperature decreases with an increase of Na 2 O and MnO but does not change significantly. The effect of chemical composition on the viscosity of a liquid slag is relatively well understood when considering that slag structure depends on the relative amounts of constituents that act as network formers vs. those that act as network breaker. As indicators of the amount of network breakers present, the compositions of Li 2 O, Na 2 O and the CaO/SiO 2 ratio in the F-free powder bearing titanium lower, as expected, the viscosity in different degrees. Li 2 O lowers the viscosity more if Li 2 O 2.0 mass% in the slag. To a lesser degree for MgO contents larger than 4.0 mass%, there is a tendency to lower the viscosity. The influence of MnO on the viscosity is not significant. For B 2 O 3 content between 2.0 and 10.0 mass%, the effect of B 2 O 3 is to lower the viscosity, which indicates that B 2 O 3 is not only a network former, but also an additive to reduce the viscosity. The influence of TiO 2 on the viscosity seems somewhat complex. The viscosity drops with increasing TiO 2 to reach a minimum at 6.0 mass% TiO 2, and subsequently it increases with increasing TiO 2 content. This is because TiO 2 has both acidity and alkalescence. If the TiO 2 content is larger than 6.0 mass%, Ti ions in the slag acts as a network former and thereby increases the viscosity, while for contents lower than 6.0 mass% it acts as a network breaker and decreases the viscosity. This result is not completely consis ISIJ

4 Table 1. Chemical compositions of studied F-free slag specimens (mass%). Table 2. Chemical compositions of studied F-containing slag specimens (mass%). tent with reported results on the effect of TiO 2 on the viscosity of F-containing mold fluxes at C, 12) which indicates that the minimum in viscosity occurs at 10.0 mass% TiO 2. In the F-free powder with TiO 2, the sequence of the main factors lowering the melting temperature is Li 2 O B 2 O 3 Na 2 O, and the sequence for the viscosity is Li 2 O B 2 O 3 Na 2 O. Therefore, Li 2 O and B 2 O 3 additions in the F-free powder can replace CaF 2 without compromising the lowering of both the melting temperature and the viscosity Effect of TiO 2 on the Heat Flux It is well known that the heat flux decreases with increasing fluorine content due to enhanced crystallinity of the slag film. It is therefore important to determine what effect TiO 2 replacement of F has on the heat flux through the slag film. Figure 5 shows how the heat flux (measured according to the experimental setup described in Fig. 2) varies with TiO 2 content. The heat flux varies from 0.44 to 0.34 MW m 2 as the increase of TiO 2 content from 1.0 to 6.0 mass%, which is similar to the effect of F from 2.0 to 10.0 mass% in the conventional powder on the heat flux from 0.48 to 0.37 MW m 2. When TiO 2 content is larger than 6.0 mass%, there is a tendency to increase the heat flux. This change in behavior at TiO 2 contents above 6.0 mass% on the heat flux is consistent with the change 2007 ISIJ 1120

5 Fig. 4. Effect of a variety of components on melting temperature and the viscosity of F-free powders. Fig. 5. The influence of TiO 2 in the F-free powder and F in the F-bearing powder on the heat flux. observed on the viscosity (see Fig. 4(b)). If the changes due to that TiO 2 become a network former, above 6.0 mass% this would be expected to increase the phonon contribution to thermal conductivity in the melt which is consistent with the experimental observations. On the other hand, increased polymerization and viscosity should not promote crystallization, which would increase heat transfer. The effect on crystallization needs to be studied independently before the nature of TiO 2 on heat flux can be further elucidated. The change of the heat flux for the F-free powder with TiO 2 and the conventional powder is 20.4% and 22.9%, respectively. Thus it proves that TiO 2 in the F-free powder can be used to replace F in the conventional powder for controlling heat transfer between the mold and the shell Effect of Basicity on the Heat Flux It can be seen in Fig. 6 that the heat flux for the F-free powder with TiO 2 decreases from 0.49 to 0.35 MW m 2 with the increasing of basicity from 0.6 to 1.2 (especially, when the range of basicity is 0.9 to 1.1, there is a significant change of the heat flux), and the heat flux for the F- bearing powder varies from 0.48 to 0.35 MW m 2 with the ISIJ

6 Fig. 6. The effect of basicity on the heat flux (left: F-free powder with TiO 2, right: F-bearing powder). Fig. 7. The effect of individual components of F-free powder on the heat flux. Table 3. Main components of the F-free powder casting peritectic steel for slab (mass%). increasing of basicity from 0.8 to 1.4, when the basicity is larger than 1.4, the heat flux increases a little as well, which implies why the maximum binary basicity is about 1.4 for actual selection of mild cooling F-bearing mold powder. The control range of the heat flux for the F-free powder with TiO 2 and the F-bearing powder is 28.6% and 27.1%, respectively. Therefore, it is clear that the effect of the basicity on the heat flux is the same whether the F-free powder with TiO 2 or the conventional powder with fluoride is used. These are consistent with the expected trend that the high basicity powder with more network breakers has both the higher break temperature and the crystallization ratio Effect of Other Components on the Heat Flux Figure 7 shows the effect of individual components in the F-free powder with TiO 2 on the heat flux, which is Na 2 O, Li 2 O, MgO, MnO and B 2 O 3, respectively. The heat flux changes significantly with more than 8.0 mass% Na 2 O and about 4.0 mass% MnO. The effects of Li 2 O, B 2 O 3 and MgO in the F-free powder on heat flux are not significant. The effect of Na 2 O content on the heat flux may be that too much Na 2 O in the slag makes the break temperature lower. When MnO content is about 4.0 mass%, there is a large change of the heat flux which is similar to the one of TiO 2 on the heat flux at about 6.0 mass% in Fig. 5. It is surprising that Li 2 O, B 2 O 3 and MgO have no obvious influence on the heat flux. Although the break temperature and crystallization tendency are related to the amount of network formers and network breakers, the relationship between chemical composition/break temperature and crystalline content is more complex. Indeed, each component of the powder may influence the crystallization by controlling the nature of the crystalline phases and by interacting with other components as well. 13) 4. Plant Trials According to the results above, the range of main components of F-free powder for peritectic steel slab casting was proposed in Table 3. Two types of F-free mold powders, 1# and 2#, were made. The F-free mold powders were used at 2# slab caster of Steelmaking Plant of Chongqing Iron & Steel Co. The steel grades in the trial were the peritectic steel grades, which were classified as two types, namely plain steel (A, B, Q234B and 20 g (AR)) and low alloy steel (A32, Q295A and Q345A, which contain high Mn content), and their chemical compositions were shown in Table 4. The parameters of the CC slab caster and corresponding cast steel grades were shown in Table 5. The physical and chemical properties of two F-free mold powders were de ISIJ 1122

7 Table 4. Classification and chemical compositions for cast steel grades. Table 5. Slab caster conditions and cast steel grades. Table 6. Physical and chemical parameters of F-free mold powder. Table 7. The result used the F-free powders in mold. tailed in Table 6. The reagents are made up of Na 2 O, Li 2 O and B 2 O 3 in Table 6, Tm, h C, Tc and h represent the hemisphere point temperature, the viscosity at C, the crystallization temperature, and the crystallization fraction of the F-free mold powders, respectively. The crystallization temperature of the slag is determined by the method of Differential Thermal Analysis (DTA), and the crystallization fraction of the slag is evaluated through visual observations in an experimental apparatus based on the single hot thermocouple technique (SHTT). 14) In addition, the heat fluxes of two F-free mold powders and two F-bearing mold powders used were measured. The heat flux through the slag film is MW m 2 for 1# F-free mold powder and MW m 2 for 2# F-free mold powder, and the corresponding value for 1# and 2# F-bearing mold powders is MW m 2 and s MW m 2, respectively. The measured heat flux can be transformed into the integral heat flux of mold based on the following relation 15) q int k Vc q...(1) Where Vc represents casting speed in m min 1, q int and q represent the calculated integral heat flux at a certain casting speed and measured heat flux in MW m 2, respectively, and k is a coefficient related to casting speed. Its regression formula for slab caster is as follow: k Vc Vc Vc (2) For mm 2 section at casting speed of 1.4 m min 1, the integral heat flux value is MW m 2 for 1# F-free mold powder and MW m 2 for 1# F- bearing mold powder; for mm 2 section at casting speed of 0.75 m min 1, the integral heat flux value is MW m 2 for 2# F-free mold powder and MW m 2 for 2# F-bearing mold powder. The results show that the heat flux value of the F-free mold powder developed is close to that of the corresponding F-bearing mold powder used. The results from the industrial trials are listed in Table 7. The F-free mold powders were uniformly melted in the mold, and there were no stick phenomenon, also no formation of lumps and thick slag rims in the mold. No breakout accidents occurred during the trials of 446 continuous casting heats. The consumption of the F-free mold powders was kg/tonne steel. The temperature difference of the cooling water between inlet and outlet in the slab mold was in the normal range of C. The morphology of the slag film taken from plant mold for 1# powder is shown in Fig. 8. The slag film contains two layers: a glassy zone close to the steel shell and a crystalline zone in contact with the mold copper. The apparent bar or cross shaped crystals were shown to be perovskite crystals when analyzed by X-ray diffraction (XRD), and the crystalline fraction of the slag film is about 42% by the determination of image analysis. The morphology of the F-containing slag film with the crystalline fraction of 39% corresponding to the F-free powder is shown in Fig. 9, the left crystalline ISIJ

8 Fig. 8. Morphology (left) and XRD result (right) of the slag film taken from plant mold for 1# powder. Fig. 9. Morphology of the slag film taken from plant mold for F-containing powder. Fig. 10. The cast slabs of the mm 2 slab (left) and of mm 2 slab (right) using F-free mold powders. Fig. 11. The surface quality of the mm 2 slab (left) and of mm 2 slab (right) using mold powders bearing fluoride (1) and F-free mold powders (2). side (mold side) is composed of cuspidine crystals. It is noteworthy that when comparing Figs. 8 and 9, the thickness of the crystalline layers are roughly similar. The surface quality of the continuous casting slab produced using the F-free mold powders is shown in Fig. 10. It is reasonably good, but some degree of longitudinal cracking does appear to exist. Nevertheless, F-free mold powders produce smaller surface crack indexes, defined as a ratio of the crack length to the slab length, than mold powders bearing fluoride (Fig. 11). By switching the mold powders bearing fluoride to the F-free mold powders, for mm 2 slabs, the surface crack index of the plain steel 2007 ISIJ 1124

9 decreased from 4.5 to 1.6%, the surface crack index of low alloy steel decreased from 2.3 to 0.8%; and for mm 2 slabs, the surface crack index of the plain steel decreased from 6.5 to 2.1%. It appears thus that the use of the F-free mold powders proposed in this study consistently result in improved slab surface quality compared to those obtained when using conventional mold powders bearing fluoride. These F-free mold powders can therefore be considered as less hazardous alternatives in the continuous casting process. 5. Conclusions Titanium-bearing blast furnace slags (CaO SiO 2 TiO 2 ) were used as a base material to develop F-free mold powders and their properties and performance were evaluated through labortoary experiments and plant trials. The conclusions are as follows: (1) The laboratory results show that 1) the melting temperature and the viscosity of the F-free powder decrease with increasing contents of Li 2 O, B 2 O 3 and Na 2 O, respectively, and the lowest viscosity is achieved with 6.0 mass% TiO 2 ; 2) the heat flux of the F-free slag film with mass% TiO 2 is close to that of the slag film with mass% F; 3) the effect of basicity of the F-free powder on the heat flux is the same as the powder bearing fluoride; 4) the heat flux changes significantly with more than 8.0 mass% Na 2 O and about 4.0 mass% MnO, and the effects of Li 2 O and B 2 O 3 in the F-free slag on heat flux are not significant. (2) The suitable range of main components of the F- free powder with TiO 2 is proposed for casting peritectic steel grades (slabs), namely basicity (CaO/SiO 2 ) , TiO mass%, Na 2 O mass%, Li 2 O mass%, MnO mass% and B 2 O mass%. (3) The industrial trial indicates that the F-free powder can effectively control mold heat transfer through the perovskite precipitated in the infiltrated slag layer instead of the cuspidine in fluoride-bearing powder. As a result it produces better slab surface quality than fluoride-bearing powders in terms of crack index. Acknowledgements The authors wish to express their gratitude to the National Natural Science Foundation and Shanghai Baosteel (China) (Grant No.: ) for funding the current study. The special efforts of Henan Xixia Protective Materials Group and Steelmaking Works at Chongqing Iron & Steel Co., to make and use the F-free mold powders in industrial trials, are also greatly appreciated. REFERENCES 1) A. Fox, K. Mills, D. Lever, C. Bezerra, C. Valadares, I. Unamuno, J. Laraudogoitia and J. Gisby: ISIJ Int., 45 (2005), No. 7, ) Alexander and I. Zaiter: Steel Res., 65 (1994), No. 9, ) S. Choi, D. Lee, D. Shin, S. Choi, J. Cho and J. Park: J. Non-Cryst. Solids, (2004), ) W. Han, S. Qiu and G. Zhu: Research on Iron & Steel, (2003), No. 2, 53. 5) B. Harris, A. Normanton, G. Abbel, B. Barber, I. Baillie, R. Koldewijn, A. Chown, S. Riaz, S. Higson, B. Patrick, T. Peeters, A. Smith, H. Visser and J. Kromhout: Ironmaking Steelmaking, 33 (2006), No. 1, 5. 6) N. Fu, Y. Zhang and Z. Sui: Min. Metall. Eng., 17 (1997), No. 4, 36. 7) H. Nakada and K. Nagata: ISIJ Int., 46 (2006), No. 3, ) R. Devries, R. Roy and E. Osborn: J. Am. Ceram. Soc., 38 (1955), No. 5, ) C. Pinheiro, I. Samarasekera and J. Brimacombe: Iron Steelmaker, 22 (1995), No. 3, ) K. Mills and A. Fox: ISIJ Int., 43 (2003), No. 10, ) M. Fonseca and O. Afrange: Proc. of 5th Int. Conf. on Molten Slags, Fluxes and Salts, ISS, Warrendale, PA, (1997), ) T. Mukongo, P. Pistorius and A. Garbers-Craig: Ironmaking Steelmaking, 31 (2004), No. 2, ) Y. Vermeulen, E. Divry and M. Rigaud: Can. Metall. Q., 43 (2004), No. 4, ) B. Jia, J. Shi and G. Wen: J. Iron Steel Res., 18 (2006), No. 2, ) G. Wen, P. Tang and X. Qi: Research Report on Fluoride-free Mold Powder Based on Blast Furnace Slag with Titanium, Chongqing University, Chongqing, (2006), ISIJ