Evolution of Inclusions with Ce Addition and Ca Treatment in Al-killed Steel during RH Refining Process

Abstract

The evolution of inclusions with Ce addition and Ca treatment in Al-killed steel during RH refining process was investigated through experimental observations and thermodynamic calculations. The results indicated that the typical inclusions before Ce addition are CaO–Al₂O₃ inclusions, which were a liquid state during RH refining. After Ce addition, the typical inclusions was transformed from calcium aluminate inclusion to (Ca–Ce–S–O)+(Ce–Al–Ca–O) complex inclusion. After Ca treatment, the types and morphologies of typical inclusions in steel did not change. Experimental observation and thermodynamic calculations shown that a certain amount of Ca addition can’t affect the formation of Ce-containing inclusion, which may indicate that Ca treatment should not be carried out for rare earth treated steel.

1. Introduction

High-strength low-alloy (HSLA) steel has been widely used in many fields such as buildings, bridges, pressure vessels and pipelines.^1,2) With a increasing requirement of welding performance, higher cleanliness is required in the industrial production of HSLA steel, which is determined by the morphology, size, number and distribution of inclusions. For Al-killed steel, Al₂O₃ and MgO·Al₂O₃ spinel inclusions are commonly observed as deoxidations products. With a high hardness and angular shape, these inclusions usually affect the impact toughness, fatigue properties, fracture toughness of steel,^3,4,5) especially for large-sized inclusions.

In order to avoid the harmful effect of alumina and magnesia alumina spinel inclusions to steel, Ca treatment is commonly used to modify these high-melting-point inclusions. Being modified into a lower melting-point inclusions, these inclusions can be removed more effectively in secondary-refining process, improving the cleanliness of molten steel and avoid clogging during continuous casting.^6,7,8)

Moreover, the effect of rare earth on modifying inclusions has also been studied by many researchers. Wang et al.⁹⁾ indicated that, after Ce addition, MgO·Al₂O₃ inclusions were wrapped by rare earth inclusions to form a ring like shape Ce-riched band around the inclusions, which was useful to improve fatigue and corrosion resistance of spring steel. Ren et al.¹⁰⁾ demonstrated that with the increasing Ce content in ultra-low-carbon aluminum-killed steel, the variation of the inclusion composition was Al₂O₃ → CeAlO₃ → Ce₂O₂S → Ce₂O₂S + CeS. Based on thermodynamic calculations, a prediction model of the inclusion composition was also established. Except to modify these alumina and spinel inclusions to minimize their detriments to steel by Ce treatment, as modification reaction products, rare earth inclusions can even play a benefit role on the welding performance of steel, which was known as ‘oxide metallurgy’.^11,12,13)

Because of the difficulties in the practical application of rare earth, most of the researches on rare earth are based on laboratory experiments, and the effect of Ca is seldom considered on the basis of rare earth condition. However, for Al-killed steel, some enterprises also carry out Ca treatment after rare earth addition in industrial production.¹⁴⁾ Therefore, this work was undertaken to reveal evolution of inclusions after Ce addition and Ca treatment in RH refining process of Al-killed steel. A SEM equipped with and EDS was employed to characterize the inclusions, and thermodynamic calculation was performed to clarify the modification process of oxide inclusions. Through experimental observations and thermodynamic calculations, the evolution mechanism of inclusions after Ce addition and Ca treatment was investigated.

2. Materials and Methods

2.1. Experimental Procedure

The experimental materials were manufactured at Baotou Iron and Steel Co., Ltd. The production process was as follows: basic oxygen furnace (BOF) → ladle furnace (LF) refining → Ruhrstahl-Heraeus (RH) refining → continuous casting.

In this production process, deoxidation was accomplished by adding aluminum after converter tapping. The deep desulfurization and alloy composition adjustments were performed during LF refining. After the LF refining, refining slag was not poured off and the refining ladle was lifted into the RH refining station. During RH refining, Ce–Fe alloy (where the mass fraction of Ce is 10% and the total mass fraction of impurity elements including carbon, sulfur, oxygen and phosphorus is lower than 0.02%) weighted 80 kg was added into 210 t of liquid iron under vacuum treatment. The vacuum cycling was held for 8 min and then 200 m Ca–Si wire was added. After soft-stirring for approximately 15 min, molten steel was cast into a plate by continuous casting. To study the effect of Ce and Ca treatment on inclusions, steel samples were taken from RH refining before Ce addition, after Ce addition and after Ca–Si addition, marked S1, S2 and S3, respectively. Samples S2 and S3 were taken after adding Ce addition and Ca–Si wire for 1.5 min, the time of a complete cycle of molten steel in RH refining.

2.2. Chemical Analysis and Inclusions Observation

Steel powders were machined from each steel sample to analyze Ce, Mg, Ca and Als contents by inductively coupled plasma mass spectrometry (ICP-MS, Thermo Fisher iCAP RQ, USA). Polished rods of 5 mm in diameter and 7 mm in length were created measure the total content of oxygen (T.O) and N content using an oxygen, nitrogen and hydrogen analyzer (HORIBA EMGA-830, Japan). The C and S contents were determined using a carbon and sulfur analyzer (HORIBA EMIA-920V2, Japan). The other element contents were tested using optical emission spectrometer (ThermoFisher ARL-8860, USA). The composition of slag samples was determined using an X-ray fluorescence (XRF) spectrometer (Rigaku ZSX Promus II, Japan). The chemical compositions of the experimental steels are listed in Table 1. The Ca, Mg, Ce, O and S contents of steel samples are shown in Table 2.

Table 1. Chemical compositions of experiment steels (mass%).

C	Si	Mn	Nb	V	Ti	Cr	Mo	Al
0.14	0.29	1.49	0.045	0.042	0.016	0.4	0.244	0.024

Table 2. Ca, Mg, Ce, O and S contents of samples (mass%).

Sample numbers	Ca	Mg	Ce	T.O	S
S1	0.0018	0.0008	<0.0001	0.0028	0.0033
S2	0.0007	0.0004	0.0023	0.0024	0.0032
S3	0.0016	0.0005	0.0023	0.0033	0.0032

To reveal the evolution of inclusions in steel, the steel samples were polished using silicon carbide papers and diamond paste for analyzing inclusion characteristics by scanning electron microscope (SEM, FEI Quanta-250; FEI Corporation, Hillsboro, OR, USA) equipped with an energy dispersive spectrometer (EDS, XFlash 5030; Bruker, Germany). The instrument was operated at an acceleration voltage of 20 kV.

3. Results and Discussion

3.1. Inclusions Before Ce-addition

The element mappings of typical inclusions in sample S1 are shown in Fig. 1. From SEM-EDS determination shown in Figs. 1(a) and 1(b), it can be seen that the typical inclusions in sample S1 is CaO–Al₂O₃–(MgO)+ CaS. The core is calcium aluminates, surrounded by calcium sulfide. As a common deoxidation product in Al-killed steel, Al₂O₃ can be modified to calcium aluminates after Ca addition, with a inclusion transformation path of CaO·6Al₂O₃ → CaO·2Al₂O₃ → CaO·Al₂O₃ → 12CaO·7Al₂O₃.^15,16,17,18)

Fig. 1.

BSE images and element mappings of typical inclusions observed in sample S1: CaO–Al₂O₃–(MgO)+ CaS. (Online version in color.)

More than twenty oxide inclusions in sample S1 were analyzed and collected by EDS scanning, and the composition distribution of these inclusions is drawn in CaO–MgO–Al₂O₃ ternary phase diagram, as shown in Fig. 2. The regions surrounded by the different color lines in the phase diagram corresponding to different melting-temperature regions calculated using FactSage 8.0 (FToxid database). The compositions of oxide inclusions before Ce addition are mostly located in the region below 1873 K, which indicated their liquid state during RH refining.

Fig. 2.

Composition distribution of oxide inclusions in sample S1 in the CaO–MgO–Al₂O₃ phase diagram. (Online version in color.)

3.2. Inclusions After Ce Addition

Element mappings of typical inclusions in sample S2 are shown in Figs. 3 and 4. The typical inclusions after Ce addition were composed of two areas: one area was darker than the steel matrix and the other was lighter. According to the element maps shown in Fig. 3(a), the distribution of S, Ce and Ca was corresponding to the light area, while no accumulation of oxygen was obvious. However, the corresponding EDS spectra shown in Figs. 3(d) and 3(e) indicated that oxygen existed in the white part of the inclusion. Therefore, the white core of the inclusion was identified as Ca–Ce–S–O. In addition, according to the element mappings shown in Fig. 3, it can be seen that the dark area was composed by Ca, Ce, Al and O elements. Thus, the typical inclusions after Ce addition can be identified (Ca–Ce–S–O)+(Ca–Ce–Al–O).

Fig. 3.

BSE images and EDS results of the typical inclusions observed in sample S2. (The EDS spectra shown in (d)–(g) correspond to the points marked in (a)–(c)). (Online version in color.)

Fig. 4.

BSE images and EDS results of the typical inclusions observed in sample S2. (The result of line scanning shown in (b) correspond to the yellow line in (a), and the EDS spectra shown in (c) and (d) correspond to the points marked in (a)). (Online version in color.)

3.3. Inclusions After Ca Treatment

Element mappings of typical inclusions in sample S3 are shown in Fig. 5. From SEM-EDS determination, the typical inclusions after Ca treatment could be determined as (Ca–Ce–O–S)+(Ca–Ce–Al–O) complex inclusion. The white core is composed by Ca, Ce, O and S elements, surrounded by (Ca–Ce–Al–O) inclusion. Compared with the typical inclusions after Ce addition shown in Figs. 3 and 4, the types and morphologies of inclusions after Ca treatment did not change. This result may indicate that Ca can not modify rare earth inclusions, which will be further analyzed in later.

Fig. 5.

BSE images and element mappings of typical inclusions observed in sample S3. (Online version in color.)

According to the proportion of different elements, the composition distribution of Ca–Ce–Al–O inclusions of sample S2 and sample S3 was drawn in CaO–CeO_1.5–AlO_1.5 ternary phase diagram, as shown in Fig. 6. The CaO–CeO_1.5–AlO_1.5 ternary phase diagram is referred to the article of Ryo Kitano et al.¹⁹⁾ The region surrounded by the black line corresponded to the liquid area at 1873 K. It can be seen that the melting-point-temperatures of most (Ca–Ce–Al–O) inclusions were about 1873 K. This result may be explained that, after Ce addition, Ce entered calcium aluminate inclusions. With Ce content in (Ca–Ce–Al–O) inclusion increasing, its melting-point-temperature also increased gradually. Thus, (Ca–Ce–Al–O) inclusion was considered in liquid state in molten steel during RH refining process. In addition, the composition of (Ca–Ce–Al–O) inclusion did not change after Ca treatment. However, due to the lack of related thermodynamic data, the formation analysis of (Ca–Ce–Al–O) was ignored in present study.

Fig. 6.

Composition distribution of Ca–Ce–Al–O inclusion in sample S2 and S3 in the CaO–CeO_1.5–AlO_1.5 ternary phase diagram.

3.4. Equilibrium Thermodynamic Calculation

For the given steel composition of sample S1, the stability diagram of Fe–Ca–Al–Mg–O system at 1873 K was calculated using software FactSage 8.0, as shown in Fig. 7. The Ca and Al contents vary from 0.0001 to 0.0025% and 0.01 to 0.05%, respectively. The calculation results indicated that even the Ca content in the molten steel was 0.0001%, Ca-containing inclusions can be formed. And when the Ca content in the molten steel was increased, the state of inclusions in molten steel could be modified from solid to liquid. For the composition of sample S1, as marked in Fig. 7, liquid calcium aluminates can be formed in molten steel.

Fig. 7.

Stability diagram of Fe–Ca–Al–Mg–O system at 1873 K.

For Al-killed steel, the dissolved oxygen content was limited by the Al–O equilibrium, expressed as following equations.²⁰⁾   

$$2\left[\text{Al}\right]+3\left[\text{O}\right]={\text{Al}}_2{\text{O}}_3$$(1)

  

$$\mathrm{\Delta }{G}^0=-1\mathrm{\hspace{0.17em} }225\mathrm{\hspace{0.17em} }417+393.86T$$(2)

  

$$[\%\mathrm{O}]={\left[{\displaystyle \frac{a_{\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3}\cdot e^{{\displaystyle \frac{\mathrm{\Delta }{G}_1^0}{\mathrm{R}T}}}}{{([\%\mathrm{A}\mathrm{l}]\cdot f_{\mathrm{A}\mathrm{l}})}^2\cdot f_{\mathrm{O}}^3}}\right]}^{{\displaystyle \frac{1}{3}}}$$(3)

Where $a_{\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3}$ is the activity of Al₂O₃, which was determined by the Al₂O₃ content in oxide inclusions. Therefore, more than twenty oxide inclusions in sample S1 were collected by SEM and its compositions were determined by EDS. Based on its average compositions, the activities of Al₂O₃, MgO and CaO in oxide inclusions at 1873 K were calculated using software FactSage 8.0 (FToxid database) and determined as 0.10221, 0.26121 and 0.04285, respectively. f_Al and f_O are the activity coefficients of dissolved aluminum and oxygen, respectively, and can be expressed by following formula:   

$$log{f}_i=\sum \left(e_i^j[\text{\%}j]+r_i^j{[\text{\%}j]}^2\right)$$(4)

Where $e_i^j$ and $r_i^j$ are the first- and second-order interaction parameters, respectively. Related first- and second order interaction parameters used in this calculation has been listed in Table 3.

Table 3. First-order interaction coefficients in this study.

	C	Si	Mn	S	Ti	Al	O	N	Ce	Mg	Ca
O	−0.45	−0.131	−0.021	−0.133	−0.6	−3.9	−0.2	0.057	−0.57	−280	−271
S	0.111	0.063	−0.026	−0.028	0.072	0.035	−0.27	0.01	−1.88	−1.82	−110
Mg	−0.24	−0.088	–	−1.38	−0.51	−0.12	−430	–	–	0	–
Al	0.091	0.056	0.035	0.03	–	0.045	−6.6	−0.058	−0.43	−0.3	−0.047
Ce	−0.43	–	–	−8.39	–	−2.25	−5.03	−6.612	−0.0039	–	–
Ca	−0.34	−0.096	−0.0156	−125	–	−0.072	−2500	–	–	–	−0.002

The available second-order interaction parameters at 1873 K are as follows: $r_{\mathrm{A}\mathrm{l}}^C$=−0.004,²⁴⁾ $r_{\mathrm{A}\mathrm{l}}^{\mathrm{S}\mathrm{i}}$=−0.0006,²⁵⁾ $r_{\mathrm{A}\mathrm{l}}^{\mathrm{A}\mathrm{l}}$=−0.001,²⁵⁾ $r_O^{\mathrm{A}\mathrm{l}}$=−0.01.²⁶⁾ Thus, the dissolved oxygen content before Ce addition in sample S1 at 1873 K was calculated as 5.33 ppm.

Due to a unique electronic layer structure, rare earth elements are remarkably efficient in modifying inclusions or combining with dissolve oxygen and sulfur.²³⁾ As reaction products, CeAlO₃, Ce₂O₂S and Ce₂O₃ are commonly formed and observed in molten steel. The reaction formula and related standard Gibbs free energies of Ce-containing inclusions formation are listed in Table 4.

Table 4. Possible reactions in steel and its standard Gibbs free energy.

Reaction equations in molten steel	ΔG0 (J/mol)	Equations No.
[Ce] + [Al] + 3[O] = CeAlO3	-1366460 + 364T	(5)
[Ce] + 3/2[O] = 1/2Ce2O3	-715560 + 180T	(6)
[Ce] + [O] + 1/2[S] = 1/2Ce2O2S	-676795 + 166T	(7)
[Ce] + CaO⋅Al2O3 = CeAlO3 + [Al] + CaO	-168984 - 12.48T	(8)
[Ce] + 1/2CaO⋅Al2O3 = Ce2O3 + [Al] + 1/2CaO	-116822 - 8.24T	(9)
[Ce] + 1/2[S] + 1/2CaO⋅Al2O3 = 1/2Ce2O2S + [Al] + 1/2[O] + 1/2CaO	-78057 - 22.24T	(10)

The Gibbs free energy of Eqs. (5), (6), (7), (8), (9), (10) were calculated, as shown in Fig. 8. According to the calculation results, it can be seen that the Gibbs free energy of Eq. (8) is smallest after adding Ce. This result indicated that, adding Ce–Fe alloy in the studied steel, Ce would modified CaO–Al₂O₃ inclusions firstly.

Fig. 8.

Gibbs free energy of various reactions in liquid steel at 1873 K. (Online version in color.)

In order to further investigate the inclusion evolution, FactSage 8.0 with the FSstel, FactPA and FToxid databases was used to analyze the equilibrium thermodynamic calculation in the present work. Figure 9 shows equilibrium precipitation of inclusions of sample S2 from 873 K to 1873 K. In RH refining process, CeAlO₃ was firstly formed after Ce–Fe alloy addition at 1873 K. As cooling process promoted, CaAl₄O₇, CaMg₂Al₁₆O₂₇ and CaS gradually precipitated. When the temperature is cooled to 1423 K, rare earth inclusions transformed from CeAlO₃ to Ce₂O₂S, as the amount of CaS decreased and CaMg₂Al₁₆O₂₇ increased, which can be expressed as Eq. (11). CaO and Al₂O₃, as the reaction products, entered CaMg₂Al₁₆O₂₇ inclusions. As cooling to 1343 K, Ce₂O₂S transformed to Ce₂S₃ inclusion, and the amount of CaS furtherly decreased and CaMg₂Al₁₆O₂₇ increased, expressed as Eq. (12). The transformation mechanism of rare earth inclusion during solidification has also been observed and analyzed by Ren.³²⁾   

$$2\mathrm{C}\mathrm{e}\mathrm{A}\mathrm{l}{\mathrm{O}}_3+\mathrm{C}\mathrm{a}\mathrm{S}=\mathrm{C}{\mathrm{e}}_2{\mathrm{O}}_2\mathrm{S}+\mathrm{C}\mathrm{a}\mathrm{O}+\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$$(11)

  

$$\mathrm{C}{\mathrm{e}}_2{\mathrm{O}}_2\mathrm{S}+2\mathrm{C}\mathrm{a}\mathrm{S}=\mathrm{C}{\mathrm{e}}_2{\mathrm{S}}_3+2\mathrm{C}\mathrm{a}\mathrm{O}$$(12)

Fig. 9.

Equilibrium precipitation of inclusions in sample S2 from 873 K o 1873 K. (Online version in color.)

Figure 10 presents equilibrium precipitation of inclusions in sample S3 from 873 K to 1873 K, based on a higher Ca content as 0.0016%. Combing the chemical compositions listed in Table 2, the Ca content was raised from 0.0007% to 0.0016% after Ca treatment. At 1873 K, CeAlO₃ was first formed in molten steel. With temperature decreased, CaS and CaMg₂Al₁₆O₂₇ gradually precipitated. Keep cooling, CeAlO₃ inclusion transformed to Ce₂O₂S and furtherly transformed to Ce₂S₃ inclusion. Comparing with sample S2, more amount of CaS were precipitated and less MnS formed, as the types and amounts of Ce-containing inclusions did not change. The inclusions transformation process with a higher Ca content is basically same as that of sample S2.

Fig. 10.

Equilibrium precipitation of inclusions in sample S3 from 873 K o 1873 K. (Online version in color.)

Figure 11 shows the stability diagram of Fe–Ca–Ce–Al–Mg–O–S system at 1873 K calculated using software FactSage 8.0. The Al, Mg and S contents used in this calculation are based on the composition of sample S3. In addition, the oxygen content for calculation is dissolved oxygen content, which is determined as 0.0005%. The Ce and Ca contents vary from 0.0001 to 0.0050% and 0.0001 to 0.0020% as ordinate and abscissa, respectively. It can be seen that after Ce and Ca treatment, the formation region of rare earth inclusions did not be affected by Ca content, but determined by Ce content. These results may indicate that Ca can not modify Ce-containing inclusions.

Fig. 11.

Stability diagram of Fe–Ca–Ce–Al–Mg–O–S system at 1873 K.

3.5. Formation and Evolution Mechanism of Inclusions

Based on the experimental results and thermodynamic analysis, the evolution mechanism of inclusions after Ce addition and Ca treatment was illustrated in Fig. 12. Before Ce addition, due to a high Ca content, the typical inclusions in molten steel stayed in liquid state. After Ce addition, Ce reacted with CaO–Al₂O₃ firstly. As reaction products, CeAlO₃ was solid in molten steel, thus easily wrapped by liquid Ca–Ce–Al–O inclusions due to the effect of surface tension. A certain amount of Ca addition can not influence the formation of CeAlO₃ inclusion, but only affected the precipitation of CaS and MnS. During solidification process, CeAlO₃ inclusions gradually transformed to Ca–Ce–O–S inclusion.

Fig. 12.

The evolution mechanism of inclusions in the present study. (Online version in color.)

4. Conclusions

In the current study, the evolution mechanism of oxide inclusions after Ce addition and Ca treatment in Al-killed steel was investigated based on the experimental determination and thermodynamic calculations. The following conclusions are obtained:

(1) For the studied steel, the typical inclusions before Ce addition are CaO–Al₂O₃ inclusions. These calcium aluminate inclusions are a liquid state during RH refining.

(2) After Ce addition, the typical inclusions was transformed from calcium aluminate inclusion to (Ca–Ce–S–O)+(Ce–Al–Ca–O) complex inclusion. After Ca treatment, the types and morphologies of typical inclusions in steel did not change.

(3) Experimental observation and thermodynamic calculations may indicate that Ca can not modify rare earth inclusions. Therefore, it is necessary to consider whether Ca treatment should be carried out after rare earth treatment in industrial production. Of course, it should be noted that much more work need to be done in future to examine this conclusion, like the effect of treatment process (single Ce addition, Ce+Ca treatment) on nozzle clogging in continuous casting production, mechanical properties of plates, the effect of different addition amounts of Ce and Ca on inclusion evolution, etc.

Acknowledgement

The authors are grateful for the financial support of the National Natural Science Foundation of China (No. 52074026) and the State Key Laboratory of Advanced Metallurgy (Grant No. 41619003 and 41618020).

References

• 1)   G.  Liang,  S.  Yang,  H.  Wu and  X.  Liu: Rare Met., 32 (2013), 129. https://doi.org/10.1007/s12598-013-0036-y
• 2)   M.  Jiang,  Y.  Yu,  H.  Li,  X.  Ren and  S.  Wang: High Temp. Mater. Process., 36 (2017), 145. https://doi.org/10.1515/htmp-2015-0183
• 3)   X.  Li,  Z.  Jiang,  X.  Geng,  M.  Chen and  L.  Peng: ISIJ Int., 59 (2019), 1552. https://doi.org/10.2355/isijinternational.ISIJINT-2019-094
• 4)   H.  Wang,  J.  Li,  C.  Shi and  J.  Li: Ironmaking Steelmaking, 44 (2017), 128. https://doi.org/10.1080/03019233.2016.1165498
• 5)   J.  Park and  H.  Todoroki: ISIJ Int., 50 (2010), 1333. https://doi.org/10.2355/isijinternational.50.1333
• 6)   H.  Wang,  J.  Li,  C.  Shi,  Y.  Qi and  Y.  Dai: ISIJ Int., 59 (2019), 828. https://doi.org/10.2355/isijinternational.ISIJINT-2018-537
• 7)   C.  Shi,  W.  Yu,  H.  Wang,  J.  Li and  M.  Jiang: Metall. Mater. Trans. B, 48 (2017), 146. https://doi.org/10.1007/s11663-016-0771-1
• 8)   Y.  Tabatabaei,  K.  Coley,  G.  Irons and  S.  Sun: Metall. Mater. Trans. B, 49 (2018), 375. https://doi.org/10.1007/s11663-017-1120-8
• 9)   L.  Wang,  Y.  Liu,  Q.  Wang and  K.  Chou: ISIJ Int., 55 (2015), 970. https://doi.org/10.2355/isijinternational.55.970
• 10)   Q.  Ren and  L.  Zhang: Metall. Mater. Trans. B, 51 (2020), 589. https://doi.org/10.1007/s11663-020-01779-y
• 11)   M.  Song,  Y.  Xie,  B.  Song,  Z.  Xue,  N.  Nie,  C. L.  Hu and  R. S.  Xu: High Temp. Mater. Process., 38 (2019), 362. https://doi.org/10.1515/htmp-2017-0175
• 12)   G.  Thewlis: Mater. Sci. Technol., 22 (2006), 153. https://doi.org/10.1179/026708306X81432
• 13)   Y.  Cao,  X.  Wan,  Y.  Hou,  C.  Niu,  Y.  Liu and  G.  Li: Steel Res. Int., 90 (2019), 1900084. https://doi.org/10.1002/srin.201900084
• 14)   R.  Chu,  Y.  Fan,  Z.  Li,  J.  Liu,  N.  Yin and  N.  Hao: Metals, 8 (2018), 240. https://doi.org/10.3390/met8040240
• 15)   S.  Yang,  Q.  Wang,  L.  Zhang,  J.  Li and  K.  Peaslee: Metall. Mater. Trans. B, 43 (2012), 731. https://doi.org/10.1007/s11663-012-9663-1
• 16)   S.  Yang,  J.  Li,  Z.  Wang,  J.  Li and  L.  Lin: Int. J. Miner. Metall. Mater., 18 (2011), 18. https://doi.org/10.1007/s12613-011-0394-0
• 17)   W.  Yang,  L.  Zhang,  X.  Wang,  Y.  Ren,  X.  Liu and  Q.  Shan: ISIJ Int., 53 (2013), 1401. https://doi.org/10.2355/isijinternational.53.1401
• 18)   N.  Verma,  P.  Pistorius,  R.  Fruehan,  M.  Potter,  M.  Lind and  S.  Story: Metall. Mater. Trans. B, 42 (2011), 720. https://doi.org/10.1007/s11663-011-9517-2
• 19)   R.  Kitano,  M.  Ishii,  M.  Uo and  K.  Morita: ISIJ Int., 56 (2016), 1893. https://doi.org/10.2355/isijinternational.ISIJINT-2016-201
• 20)   D.  Zhao,  H.  Li,  Y.  Cui and  J.  Yang: ISIJ Int., 56 (2016), 1181. https://doi.org/10.2355/isijinternational.ISIJINT-2016-123
• 21)   H.  Itoh,  M.  Hino and  S.  Ban-Ya: Metall. Mater. Trans. B, 28 (1997), 953. https://doi.org/10.1007/s11663-997-0023-5
• 22)   M.  Jiang,  X.  Wang,  B.  Chen and  W.  Wang: ISIJ Int., 48 (2008), 885. https://doi.org/10.2355/isijinternational.48.885
• 23)   Y.  Li,  C.  Liu,  T.  Zhang,  M.  Jiang and  C.  Peng: Metall. Mater. Trans. B, 48 (2017), 956. https://doi.org/10.1007/s11663-016-0873-9
• 24)   H.  Ohta and  H.  Suito: Metall. Mater. Trans. B, 27 (1996), 943. https://doi.org/10.1007/s11663-996-0008-9
• 25)   X.  Shi,  S.  Duan,  W.  Yang,  M.  Mao,  H.  Guo and  J.  Guo: Metall. Mater. Trans. B, 50 (2019), 3072. https://doi.org/10.1007/s11663-019-01685-y
• 26)   H.  Itoh,  M.  Hino and  S.  Ban-Ya: Tetsu-to-Hagané, 83 (1997), 773 (in Japanese). https://doi.org/10.2355/tetsutohagane1955.83.12_773
• 27)   H.  Itoh,  M.  Hino and  S.  Ban-Ya: Tetsu-to-Hagané, 83 (1997), 695 (in Japanese). https://doi.org/10.2355/tetsutohagane1955.83.11_695
• 28)   K.  Nagata,  J.  Tanabe and  K.  Goto: Tetsu-to-Hagané, 75 (1989), 2023 (in Japanese). https://doi.org/10.2355/tetsutohagane1955.75.11_2023
• 29)   W.  Wilson,  L.  Heaslip and  I.  Sommerville: JOM, 37 (1985), 36. https://doi.org/10.1007/BF03258638
• 30)   S.  Gao,  M.  Wang,  J.  Guo,  H.  Wang,  J.  Zhi and  Y.  Bao: Steel Res. Int., 90 (2019), 1900194. https://doi.org/10.1002/srin.201900194
• 31)   Y.  Ren,  L.  Zhang,  W.  Yang and  H.  Duan: Metall. Mater. Trans. B, 45 (2014), 2057. https://doi.org/10.1007/s11663-014-0121-0
• 32)   Q.  Ren,  L.  Zhang,  Y.  Liu,  L.  Cui and  W.  Yang: J. Mater. Res. Technol., 9 (2020), 8197. https://doi.org/10.1016/j.jmrt.2020.05.077