Effect of Medium Basicity Refining Slag on the Cleanliness of Al-killed Steel

Abstract

Al-killed hot rolled steels are mainly produced with calcium treatment for the purpose either to minimize nozzle clogging in continuous casting or to modify plastic MnS inclusions. There are some negative effects of calcium treatment. In order to solve the problems, the possibility was explored to applying medium basicity refining slag for the production of hot rolled steel without calcium treatment. In this study, effect of medium basicity refining slag on desulphurization and inclusions in Al-killed steel was investigated by thermodynamic calculation and laboratory experiment. Results showed that some medium basicity slags of CaO–Al₂O₃–SiO₂–MgO system, such as basicity of 4 and Al₂O₃ content of 20%, had relatively high a_CaO and low a_Al2O3, as well as satisfactory desulphurization efficiency, which indicated that they had strong desulphurization ability. After reacted with such slags, the surrounding part of most inclusions transformed from MgO–Al₂O₃, which was the main type in master steel, to MgO–Al₂O₃–SiO₂–CaO(–MnO), the shape changes from irregular to near-spherical, and a large number of inclusions go into or near the region with relatively low melting temperature. It indicated that reaction with such slags could lower melting temperature of inclusions. In addition, steel cleanliness was improved. Based on the results, medium basicity slag may be used for production of some Al-killed hot rolled steel in which calcium treatment could be cancelled.

1. Introduction

Al-killed hot rolled steels, mainly used in high building, bridge, mechanical engineering, etc., have high requirement for such properties as strength, toughness, welding property, etc. Sulphur has great influence on these properties, especially in the direction vertical to rolling. So sulphur content in steel should be strictly controlled. Hot rolled steels are usually produced by the following process, hot metal pretreatment – basic oxygen furnace(BOF) steelmaking – ladle furnace(LF) refining – calcium treatment – slab continuous casting. Sometimes vaccum treatment is adopted for degassing or inclusion removal. During the process, Al deoxidation and refining slag with high desulphurization ability are usually used to remove sulphur.^1,2,3) In addition, calcium treatment is used either to minimize the nozzle clogging in continuous casting or to modify plastic MnS inclusions.^4,5,6,7,8)

As regard minimizing nozzle clogging which is one of the main purposes of calcium treatment, many factors have an influence on the effect, such as [Al] and [S] in molten steel, amount and composition of inclusions in steel, re-oxidition, yield of calcium, etc. Both insufficient and excess calcium addition would generate high melting point inclusions, such as partially modified Al₂O₃ or spinel inclusions, as well as CaS, which would decrease the effect of calcium treatment greatly.^{9,10,11,12,13,14)} In addition, calcium treatment has some other problems, including increase of inclusion amount and size, increasing cost, causing air pollution, etc.^15,16) With the improvement of steel cleanliness, other measures should be taken to solve the nozzle clogging rather than calcium treatment. A number of researches^{17,18,19,20,21,22,23,24,25,26,27)} have been done on inclusion modification under the interaction of refractory-slag-metal-inclusion, which indicates that inclusion control can be possible by choosing proper top slag composition and refractory materials. In studies of Wang²⁵⁾ and Yu,²⁶⁾ inclusions with lower melting temperature were achieved through slag-steel reaction by using top slag with high basicity and high Al₂O₃ content. Hu²⁷⁾ carried out contrasting experiments of Al-killed 60Si2MnA spring steel under LF refining with and without calcium treatment. Results showed that refining slag with basicity(B: CaO/SiO₂) of 5.0 had similar effect on controlling inclusions and improving steel cleanness to calcium treatment. In addition to the researches on inclusion modification by multiphase reactions among slag, refractory, metal and inclusion, influence of slag composition on inclusion removal has also been studied.^28,29) In present authors’ previous studies,^30,31) some medium basicity slags have strong desulphurization ability. A decrease of Al₂O₃ content in slag is beneficial for desulphurization ability, decrease of inclusion amount and improvement of steel cleanliness.

In this study, a new idea is put forward that is modifying high melting temperature inclusions to lower melting temperature ones by slag-steel reaction while cancelling calcium treatment. It is well known that both low sulphur content and good castability of molten steel are required for production of Al-killed hot rolled steel. For this purpose, laboratory investigation was carried out with main focus on desulphurization ability and effect on inclusions of medium basicity slag.

2. Methodology

2.1. Thermodynamic Calculations

Activity of CaO (a_CaO) and Al₂O₃ (a_Al2O3) of CaO–Al₂O₃–SiO₂–MgO system slag was calculated by thermodynamic commercial software Thermo-Calc Version TCCR.

The calculated conditions are as follows: temperature (T), 1873 K; pressure (P), 101325 Pa; basicity (B: CaO/SiO₂), 3, 4, 7; Al₂O₃, 15%–35%; MgO, saturated. All compositions in this paper are given in mass percentage unless specially stated.

2.2. Laboratory Experiments

Two groups of experiments are included. One is desulphurization experiment and the other is experiment on non-metallic inclusions, named as De-S Exp. and Inc. Exp., respectively.

Desulphurization experiment was done in Si–Mo heated electrical resistance furnace. 200 g master steel, which was taken from the industrial continuous casting slab, and 40 g slag material, which was mixtures of reagent-grade Al₂O₃, MgO, SiO₂ and dehydrated CaO, were charged together into a MgO crucible (ID, 38 mm; OD, 44 mm; H, 136 mm). Then temperature was raised to 1873 K, which was set as the starting time of slag-steel reaction. At 30 minute of reaction, the melt was stirred with molybdenum wire to achieve better composition uniformity and kinetic condition. After the reaction time reached 90 minutes, the MgO crucible was quickly lifted out and water quenched. Especially stated, FeS reagent was put into the crucible along with the master steel at the beginning of experiment to increase the initial sulfur content of molten steel. When the temperature reached 1873 K, a small amount of Al was added to steel bath to keep low oxygen potential of reaction system. During the whole experiment, 5N purity Ar was infilled for protective atmosphere.

As for the experiment on inclusions, the experimental procedure was similar to the desulphurization experiment except that no FeS and Al were added as well as no stirring was done during the whole reaction. Table 1 shows the chemical compositions of master steel and initial slags which were used in both experiments. Slag No. 2 was adopted in desulphurization experiment and slag No. 1 through No. 4 in inclusion experiments.

Table 1. Chemical compositions of master steel and initial slags, mass%.

Master steel
C	Si	Mn	P	S	Als
0.069	0.018	0.72	0.011	0.0059	0.043
Initial slag
No.	CaO	Al2O3	SiO2	MgO	B
1	51.75	25	17.25	6	3
2	59.2	20	14.8	6	4
3	55.2	25	13.8	6	4
4	51.2	30	12.8	6	4

After high temperature experiments, the chemical compositions of steel and slag samples were analysized. The inclusions in steel samples were detected with an Explorer 4 analyzer (ThermoFisher Scientific), an automatic scanning electron microscope with an energy dispersive spectrometer (EDS). The accelerating voltage used for EDS analysis was 15 kV during the Explorer 4 Analyzer observation. The detailed experimental method was described in the authors’ previous researches.^31,32,33)

3. Results and Discussion

3.1. Desulphurization Ability

3.1.1. a_CaO and a_Al2O3

For Al-killed steel, the main desulphurization reaction in secondary refining is shown as Eq. (1).   

$$3\mathrm{C}\mathrm{a}\mathrm{O}+3\left[\mathrm{S}\right]+2\left[\mathrm{A}\mathrm{l}\right]=3\mathrm{C}\mathrm{a}\mathrm{S}+\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$$(1)

CaO is the desulphurization agent which reacts with S in steel to remove it, and Al₂O₃ is one of the products of the reaction. Therefore, both a_CaO and a_Al2O3 have a great effect on desulphurization. For secondary refining slag, higher a_CaO and lower a_Al2O3 are preferred for desulphurization.^2,30,34) Figure 1 shows the calculated a_CaO and a_Al2O3 of CaO–Al₂O₃–SiO₂–MgO system slags. With slag basicity increasing and Al₂O₃ content decreasing, the value of a_CaO increases while a_Al2O3 decreases. Y. Ogura¹⁾ studied desulphurization to produce ultra-low sulphur steel and the obtained optimum slag composition was 60%CaO-32%Al₂O₃-8SiO₂. Refining slag with high basicity and high Al₂O₃ content is usually used for production of ultra-low sulphur steel grade.^35,36,37) Therefore, the slag with basicity of 7 was chosen in this work to represent the conventional desulphurization slag. As Fig. 1 shows, the a_CaO of the slags with basicity of 7 as well as Al₂O₃ content of 30% and 35% is 0.760 and 0.462, respectively. Also, a_Al2O3 of such slags is 1.983×10⁻³ and 6.091×10⁻³, respectively. The line A in Fig. 1(a) and line B in Fig. 1(b) are the line whose value is equal to that of a_CaO and a_Al2O3 of the slag with basicity of 7 and Al₂O₃ content of 35%, respectively. The points near or above line A have similar or higher a_CaO than the conventional desulphurization slags. Also, the points near or below line B have similar or lower a_Al2O3 than such slags. Therefore, the slags with the compositions of the points both above line A and below line B or near them have relatively high a_CaO and low a_Al2O3, then it can be inferred from Eq. (1) that these slags may have strong desulphurization ability. For medium basicity slag in this study, these points include B=3, Al₂O₃=15% and 20% as well as B=4, Al₂O₃=15%, 20% and 25%. In previous studies,^2,30,31) a decrease of Al₂O₃ content in slag is beneficial for desulphurization ability. Slags with basicity of 3.5–5.0 and Al₂O₃ content of around 20 wt% has strong desulphurization ability. Considering the future application to industrial production, focus was mainly put on the slags with basicity of 4 as well as Al₂O₃ content of 20% and 25% in this study.

Fig. 1.

Activity of slag components (a) a_CaO, (b) a_Al2O3. (Online version in color.)

3.1.2. Desulphurization Efficiency

Based on the thermodynamic calculation, laboratory desulphurization experiment was carried out by slag-steel reaction. S content was removed to 0.0031% from 0.1% before the reaction. In the authors’ previous studies,³¹⁾ both medium basicity slag (B=4.5, Al₂O₃=20%) and high basicity slag (B=7, Al₂O₃=30%), which stood for the conventional desulphurization slag, were chosen for laboratory scale desulphurization which was done in vacuum induction furnace. The S content was removed to 0.0011% and 0.0015% from the initial 0.0067% and 0.0069%, respectively, which indicated that the medium basicity slag had similar desulphurization efficiency as the conventional desulphurization slag. Figure 2 shows the desulphurization efficiency of both studies. The experimental results agree with the thermodynamic calculation, which indicates that some medium basicity slags have strong desulphurization ability.

Fig. 2.

Desulphurization efficiency of experiments. (Online version in color.)

3.2. Effect on Inclusions

3.2.1. Effect on Composition and Morphology

Based on the desulphurization results, slag No. 1 through No. 4 were chosen to investigate the effect of medium basicity slag on non-metallic inclusions. The chemical compositions of final slags are shown in Table 2.

Table 2. Chemical compositions of final slags, mass%.

Exp. No.	CaO	Al2O3	SiO2	MgO	FeO+MnO	S	B
1	49.32	23.79	17.45	8.64	0.71	0.05	2.83
2	56.07	19.33	15.35	7.23	0.7	0.038	3.65
3	51.54	24.29	13.52	9.19	0.76	0.033	3.81
4	48.8	28.53	13.61	8.56	0.69	0.032	3.59

Inclusions in master steel were detected. As shown in Fig. 3, most inclusions are Al₂O₃–MgO–MnS system, in which the components Al₂O₃ and MnS share the majority of inclusions’ compositions. The inclusions are inhomogeneous with dark gray oxide of Al₂O₃–MgO attached by light gray MnS. The shape of oxide inclusions is irregular with angular boundaries. The formation of MnS with temperature decreasing was calculated by FactSage 7.3 for the composition of master steel, as shown in Fig. 4. It can be seen that MnS begins to increase sharply at 1373 K. Therefore, it can be inferred that the component of MnS observed in the inclusions formed during the solidification of steel samples. That is, only oxide inclusions of Al₂O₃–MgO system exist in steel at 1873 K.

Fig. 3.

Typical inclusions in master steel. (Online version in color.)

Fig. 4.

Formation curve of MnS with temperature. (Online version in color.)

After slag-steel reaction, most inclusions in steel changed, as shown in Fig. 5. The inclusions are complex with dark gray MgO–Al₂O₃ in the center and black MgO–Al₂O₃–SiO₂–CaO(–MnO) on the surrounding region. The shape of inclusions is near-spherical with smooth boundaries. Figure 6 shows the mapping of typical inclusions after slag-steel reaction. It can be easily seen that the inner MgO–Al₂O₃ system is surrounded by MgO–Al₂O₃–SiO₂–CaO(–MnO) system. Although the inner part is irregular, the surrounding is near-spherical.

Fig. 5.

Typical inclusions after slag-steel reaction. (Online version in color.)

Fig. 6.

Mapping of typical inclusions after slag-steel reaction. (Online version in color.)

By automatic scanning of Explorer 4 analyzer, chemical compositions and some parameters of inclusions were obtained. The parameters, DMAX, DMIN and DAVE represent the length of maximum and minimum axis of the two-dimension observed inclusion, as well as diameter of the equivalent circle of the inclusion, respectively. AREA and PERIMETER represent the area and perimeter of the inclusion, respectively. ASPECT is the ratio of DMAX to DMIN, as shown in formula (2). The schematic of the parameters obtained by Explorer 4 Analyzer is shown in Fig. 7.   

$$\mathrm{A}\mathrm{S}\mathrm{P}\mathrm{E}\mathrm{C}\mathrm{T}=\mathrm{D}\mathrm{M}\mathrm{A}\mathrm{X}/\mathrm{D}\mathrm{M}\mathrm{I}\mathrm{N}$$(2)

Define Spherical degree as follow.   

$$\mathrm{S}\mathrm{p}\mathrm{h}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{c}\mathrm{a}\mathrm{l}\mathrm{d}\mathrm{e}\mathrm{g}\mathrm{r}\mathrm{e}\mathrm{e}=\mathrm{A}\mathrm{V}\mathrm{G}\left[\mathrm{A}\mathrm{B}\mathrm{S}\left(\mathrm{P}\mathrm{E}\mathrm{R}\mathrm{I}\mathrm{M}\mathrm{E}\mathrm{T}\mathrm{E}\mathrm{R}-\pi *\mathrm{D}\mathrm{A}\mathrm{V}\mathrm{E}\right)\right]$$(3)

Where, AVG and ABS mean taking the average and absolute value, respectively.

Fig. 7.

Schematic of parameters obtained by Explorer 4 Analyzer. (Online version in color.)

Therefore, both the parameter “ASPECT” and “Spherical degree” represent the degree which the inclusions are close to spherical shape. The values of “ASPECT” and “Spherical degree” of a sphere are 1 and 0, respectively.

Figure 8 shows the spherical degree of inclusions before and after slag-steel reaction. For master steel, the average values of “ASPECT” and “Spherical degree” of inclusions are 1.55 and 1.14, respectively. After slag-steel reaction, for exp. No. 1 through No. 4, the “ASPECT” is 1.16, 1.16, 1.18, 1.17, respectively, with the average of 1.17. The “Spherical degree” is 0.16, 0.11, 0.18, 0.16, respectively, with the average of 0.15. After slag-steel reaction, the inclusions transform from irregular to near-spherical, in addition, the “ASPECT” and “Spherical degree” decrease close to 1 and 0, respectively. That is, the degree which the inclusions are close to spherical shape increase after reacted with the medium basicity slags. It can be inferred that the inclusions in molten steel, or at least the surrounding parts of inclusions, are in liquid state.

Fig. 8.

Spherical degree of inclusions before and after slag-steel reaction. (Online version in color.)

3.2.2. Effect on Melting Temperature

After reacted with medium basicity slags, most inclusions are inhomogeneous, of which the inner part remains MgO–Al₂O₃ system while the surrounding part transforms to MgO–Al₂O₃–SiO₂–CaO(–MnO) system. Select no less than 10 inclusions randomly for each experimental sample and detect the compositions of both inner and surrounding part manually. With respect to the surrounding compositions, the contents of CaO and MnO of inclusions are relatively lower with the average of 10% and 4%, respectively, compared with the components MgO, Al₂O₃ and SiO₂. In addition, the fluctuation of both contents is smaller. Therefore, the compositions of surrounding part of inclusions are plotted into MgO-Al₂O₃-SiO₂-10%CaO-4%MnO phase diagram, and those in master steel are plotted into MgO–Al₂O₃–SiO₂ diagram, as shown in Fig. 9. The liquid regions at 1773 K, 1873 K and 1973 K of both MgO-Al₂O₃-SiO₂-10%CaO-4%MnO and MgO–Al₂O₃–SiO₂ system were calculated by FactSage 7.3 and also plotted in phase diagram. It can be easily seen that, for master steel, few inclusions are in the liquid region of no higher than 1873 K. After the slag-steel reaction, a large number of inclusions go into or near the liquid region of 1873 K. The results show that the melting temperature of most inclusions in steel has been lowered by the reaction between medium basicity slag and molten steel. Park³⁸⁾ investigated the effect of CaO/Al₂O₃ (=C/A) ratio of the ladle slag on non-metallic inclusions in Al-killed steel. When C/A ratio is in the range of 1.5–2.5, liquid inclusions are easily formed. In present study, the C/A ratio of final slag is in the range of 1.7–2.9, a large number of inclusions enter the liquid zone of 1873 K or nearby region after the reaction with medium basicity slags, which is agreement with the results of Park.

Fig. 9.

Composition distribution of inclusions before (a) and after (b) slag-steel reaction. (Online version in color.)

3.3. Effect on Steel Cleanliness

Figure 10 shows the total oxygen content (T.O) of steel samples before and after slag-steel reaction. T.O content of master steel is 16×10⁻⁶, while decreases after slag-steel reaction with the average value of 9×10⁻⁶.

Fig. 10.

T.O of steel samples.

The statistic information of inclusions was obtained by an Explorer 4 analyzer. The area of each sample of no less than 25 mm² was detected. For master steel, the number of detected inclusions is 333, and for Exp. No. 1–No. 4, the number is 151, 98, 123, and 167, respectively. Define “Area ratio” and “Number density” of inclusions as follows.   

$$\begin{array}{l}\mathrm{A}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}=\mathrm{A}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{o}\mathrm{f}\mathrm{i}\mathrm{n}\mathrm{c}\mathrm{l}\mathrm{u}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}/\\ \hspace{1em}\hspace{1em}\hspace{1em}\hspace{1em}\hspace{1em}\hspace{0.5em}\mathrm{d}\mathrm{e}\mathrm{t}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{e}\mathrm{d}\mathrm{a}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{o}\mathrm{f}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{e}\mathrm{l}\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}\end{array}$$(4)

  

$$\begin{array}{l}\mathrm{N}\mathrm{u}\mathrm{m}\mathrm{b}\mathrm{e}\mathrm{r}\mathrm{d}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{y}=\mathrm{N}\mathrm{u}\mathrm{m}\mathrm{b}\mathrm{e}\mathrm{r}\mathrm{o}\mathrm{f}\mathrm{i}\mathrm{n}\mathrm{c}\mathrm{l}\mathrm{u}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}/\\ \hspace{1em}\hspace{1em}\hspace{1em}\hspace{1em}\hspace{1em}\hspace{1em}\hspace{1em}\hspace{1em}\mathrm{d}\mathrm{e}\mathrm{t}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{e}\mathrm{d}\mathrm{a}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{o}\mathrm{f}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{e}\mathrm{l}\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}\end{array}$$(5)

Figure 11 gives the inclusion amount of steel samples before and after slag-steel reaction. For master steel, the “Area ratio” and “Number density” of inclusions are 67.43 μm²/mm² and 8.92 mm⁻², respectively. After slag-steel reaction, both “Area ratio” and “Number density” decrease, with the average value of 15.95 μm²/mm² and 5.10 mm⁻², respectively.

Fig. 11.

Inclusion amount of steel samples.

Compared with master steel, both T.O content and inclusion amount of steel samples decrease. It indicates that steel cleanliness is improved after reacted with medium basicity slags.

3.4. Discussion on Applying Medium Basicity Slag for Hot Rolled Steel

For the production of Al-killed hot rolled steel, both low S content and smooth continuous casting should be satisfied. That is, the substitute for calcium treatment needs to accomplish the above purpose. Based on the research results, whether medium basicity slag can be used for the production of hot rolled steel without calcium treatment is discussed as follows.

In regard to desulphurization ability, some medium basicity slags of CaO–Al₂O₃–SiO₂–MgO system, such as, basicity of 4 and Al₂O₃ content of 20% or 25%, have relatively high a_CaO and low a_Al2O3 which is favorable for desulphurization, as well as satisfactory desulphurization efficiency. So, some medium basicity slags of CaO–Al₂O₃–SiO₂–MgO system have strong desulphurization ability.

As regard the effect on inclusions, after slag-steel reaction with such medium basicity slags, the compositions of surrounding part of most oxide inclusions transform from initial MgO–Al₂O₃ to MgO–Al₂O₃–SiO₂–CaO(–MnO), and the shape of inclusions changes from irregular to near-spherical. Both “ASPECT” and “Spherical degree” of inclusions decrease close to 1 and 0, respectively, which indicates that the spherical degree of inclusions increases. Accordingly, lots of inclusions go into or near the liquid region of relative low temperature from high melting temperature region initially. In addition, both T.O content and inclusion amount of steel samples decrease. Steel cleanliness is improved.

Based on the results obtained in laboratory experiments, a trial of one casting sequence including five heats was carried out in industrial production. The sulphur content at the end of LF refining was removed to less than 20×10⁻⁶, which met the requirement of the steel grade, although the desulphurization degree was a little lower than that of the process with calcium treatment. Most oxide inclusions were Al₂O₃–CaO–MgO system with quite a little amount of SiO₂. The inclusion type was different from that with calcium treatment which was mainly Al₂O₃–CaO–CaS. However, the continuous castability under the new process was good.

In summary, with the improvement of steel cleanliness, medium basicity slag may be used for production of some Al-killed hot rolled steel in which calcium treatment could be cancelled.

4. Conclusions

With steel cleanliness increasing, a new idea is put foreward to improving continuous castability of Al-killed hot rolled steel by slag-steel reaction rather than calcium treatment. For this purpose, laboratory experiments were carried out to investigate the effect of medium basicity slag on hot rolled steel. The main conclusions are summarized as follows.

(1) Some medium basicity slags, such as, B=4, Al₂O₃=20%, have relatively high a_CaO and low a_Al2O3, as well as satisfactory desulphurization efficiency, which indicates that they have strong desulphurization ability.

(2) After slag-steel reaction with such slags, most oxide inclusions transform from MgO–Al₂O₃ system to complex with the surrounding part of MgO–Al₂O₃–SiO₂–CaO(–MnO), and the shape changes from irregular to near-spherical. Accordingly, lots of high melting point inclusions are modified to relatively low melting point ones. In addition, steel cleanliness is improved.

(3) With the improvement of steel cleanliness, medium basicity slag may be used for production of some Al-killed hot rolled steel in which calcium treatment could be cancelled.

Acknowledgments

The authors are grateful for the financial support from Qian’an iron and steel company, Shougang Co. Ltd. and National Key R&D Program of China (2017YFB0304000 & 2017YFB0304001). The authors express their appreciation to anonymous reviewers for their fruitful comments.

References

• 1)   Y.  Ogura,  Y.  Kikuchi,  T.  Hasegawa,  K.  Matsuo,  K.  Taguchi and  M.  Hanmyo: Tetsu-to-Hagané, 72 (1986), 1309 (in Japanese).
• 2)   N.  Bannenberg,  B.  Bergmann and  H.  Gaye: Steel Res., 63 (1992), 431.
• 3)   P.  Yan,  S.  Huang,  J.  Van Dyck,  M.  Guo and  B.  Blanpain: ISIJ Int., 54 (2014), 72.
• 4)   P. B. P.  Leão,  J. L.  Klug,  C. A. R.  Carneiro,  H.  Caldas and  W. V.  Bielefeldt: Steel Res. Int., 90 (2019), 1900151. https://doi.org/10.1002/srin.201900151
• 5)   X.  Li,  N.  Wang,  M.  Chen and  R.  Zeng: ISIJ Int., 60 (2020), 2446. https://doi.org/10.2355/isijinternational.ISIJINT-2020-237
• 6)   D.  Janke,  Z.  Ma,  P.  Valentin and  A.  Heinen: ISIJ Int., 40 (2000), 31. https://doi.org/10.2355/isijinternational.40.31
• 7)   Y.  Tabatabaei,  K. S.  Coley,  G. A.  Irons and  S.  Sun: Metall. Mater. Trans. B, 49 (2018), 2022.
• 8)   C.  Liu,  Y.  Kacar,  B.  Webler and  P. C.  Pistorius: Metall. Mater. Trans. B, 52 (2021), 2837.
• 9)   N.  Verma,  P.  Pistorius,  R.  Fruehan,  M.  Potter,  M.  Lind and  S.  Story: Metall. Mater. Trans. B, 42 (2011), 720.
• 10)   Y.  Higuchi,  M.  Numata,  S.  Fukagawa and  K.  Shinme: ISIJ Int., 36 (1996), S151.
• 11)   Y.  Liu,  L.  Zhang,  Y.  Zhang,  H.  Duan,  Y.  Ren and  W.  Yang: Metall. Mater. Trans. B, 49 (2018), 610.
• 12)   J.  Xu,  F.  Huang and  X.  Wang: Metall. Mater. Trans. B, 47 (2016), 1217.
• 13)   W. V.  Bielefeldt and  A. C. F.  Vilela: Steel Res. Int., 86 (2015), 375.
• 14)   V.  Gollapalli,  M. B. V.  Rao,  P. S.  Karamched,  C. R.  Borra,  G. G.  Roy and  P.  Srirangam: Ironmaking Steelmaking, 46 (2019), 663.
• 15)   W.  Yang,  L.  Zhang,  X.  Wang,  Y.  Ren,  X.  Liu and  Q.  Shan: ISIJ Int., 53 (2013), 1401.
• 16)   M.  Jiang,  Z.  Hou,  E.  Yang and  X.  Wang: Proc. 2018 China Symp. on Sustainable Steelmaking Technology (CSST2018), (Tianjin), China Machine Press, Beijing, (2018), 570.
• 17)   H.  Suito and  R.  Inoue: ISIJ Int., 36 (1996), 528.
• 18)   T.  Yoshioka,  K.  Nakahata,  T.  Kawamura and  Y.  Ohba: ISIJ Int., 56 (2016), 1973.
• 19)   B. A.  Webler and  P. C.  Pistorius: Metall. Mater. Trans. B, 51 (2020), 2437.
• 20)   J. H.  Shin and  J. H.  Park: Metall. Mater. Trans. B, 48 (2017), 2820.
• 21)   J.  Björklund,  M.  Andersson and  P.  Jönsson: Ironmaking Steelmaking, 34 (2007), 312.
• 22)   J.  Xu,  K.  Wang,  Y.  Wang,  Z.  Qu,  X.  Tu and  X.  Meng: Ironmaking Steelmaking, 48 (2021), 127.
• 23)   H.  Mu,  T.  Zhang,  R. J.  Fruehan and  B. A.  Webler: Metall. Mater. Trans. B, 49 (2018), 1665.
• 24)   Y.  Ji,  C.  Liu,  Y.  Lu,  H.  Yu,  F.  Huang and  X.  Wang: Metall. Mater. Trans. B, 49 (2018), 3127.
• 25)   X.  Wang,  B.  Chen,  M.  Jiang and  W.  Wang: Proc. 4th Int. Cong. on the Science and Technology of Steelmaking, (Gifu), ISIJ, Tokyo, (2008), 13, CD-ROM.
• 26)   H.  Yu,  X.  Wang,  J.  Zhang,  H.  Li and  W.  Wang: J. Iron Steel Res. Int., 18 (2011), 6.
• 27)   Y.  Hu,  W.  Chen,  H.  Han and  R.  Bai: Ironmaking Steelmaking, 44 (2017), 28.
• 28)   K.  Sasai: ISIJ Int., 60 (2020), 409.
• 29)   D.  You,  C.  Bernhard,  A.  Mayerhofer and  S. K.  Michelic: ISIJ Int., (2021), (Advance Publication). https://doi.org/10.2355/isijinternational.ISIJINT-2021-213
• 30)   H.  Yu,  X.  Wang,  M.  Wang and  W.  Wang: Int. J. Miner. Metall. Mater., 21 (2014), 1160.
• 31)   H.  Yu,  J.  Xu,  J.  Zhang and  X.  Wang: Ironmaking Steelmaking, 43 (2016), 607. https://doi.org/10.1080/03019233.2016.1139858
• 32)   H.  Yu,  D.  Yang,  M.  Li and  N.  Zhang: Steel Res. Int., 91 (2020), 2000143. https://doi.org/10.1002/srin.202000143
• 33)   H.  Yu,  D.  Yang,  M.  Li and  M.  Pan: Metall. Res. Technol., 116 (2019), 620. https://doi.org/10.1051/metal/2019050
• 34)   M.  Hayashi,  N.  Sano and  P.  Fredriksson: ISIJ Int., 44 (2004), 1783.
• 35)   D.  Yang,  X.  Wang,  G.  Yang,  P.  Wei and  J.  He: Steel Res. Int., 85 (2014), 1517. https://doi.org/10.1002/srin.201300393
• 36)   Q.  Li,  X.  Wang,  H.  Li,  F.  Huang,  J.  Yang and  W.  Wang: J. Iron Steel Res. Int., S1 (2011), 563.
• 37)   X.  Wang,  X.  Li,  Q.  Li,  F.  Huang,  H.  Li and  J.  Yang: Steel Res. Int., 85 (2014), 155. https://doi.org/10.1002/srin.201300044
• 38)   J. H.  Shin,  G. H.  Park,  C. H.  Chang,  H. G.  Kim and  J. H.  Park: Proc. 11th Int. Conf. on Molten Slags, Fluxes and Salts, (Virtual), KIM, Seoul, (2021), EA20191128-1261, https://smart.molten2020.org, (accessed 2021-02-21).