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Study on the thermodynamic stability and evolution of inclusions in Al–Ti deoxidized steel

  • Jun Wang , Linzhu Wang EMAIL logo , Xiang Li , Junqi Li , Chaoyi Chen , Changrong Li and Changling Zhuang
Published/Copyright: May 3, 2022
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High Temperature Materials and Processes
From the journal High Temperature Materials and Processes Volume 41 Issue 1

Abstract

To investigate the thermodynamic stability and the evolution process of inclusions in the Al–Ti deoxidized steels, both laboratory experiments and thermodynamic calculations were conducted in the present work. Scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and Al2O3–Ti2O3–TiO2 phase diagrams were used to investigate the composition of oxide inclusions after adding various contents of Al and Ti. The results show that the TiO x content of inclusions increases with the increase in titanium addition in steel ranging from 0.31 to 1.88%, and the typical inclusions are transferred from pure Al2O3 to multi-phase Al–Ti complex inclusions and Al2O3–TiO x complex inclusions with uniform composition. The TiO x content in the inclusions first increased and then decreased with the extension of deoxidation time in the steels with deoxidants of [% Al] = 0.055 and [% Al] = 0.71, and the content of TiO x in the inclusions is highest at 360 s of deoxidation. There is a small amount of pure titanium oxide and liquid Al2O3–TiO x composite inclusions in the steel with deoxidants of [% Al] = 0.13 and [% Ti] = 1.88 at 120 s of deoxidation, and then this part of inclusions gradually turns into the Al2O3-rich phase. The predominance diagrams of the Al–Ti–O–Fe system were obtained based on the classical thermodynamic calculation and FactSage calculation with different databases and products. The calculated results were compared with the experimental data, and the discrepancies on the stable region of oxides in the predominance diagrams were discussed. The evolution and transformation of inclusions during the solidification process were analyzed based on FactSage calculation.

Keywords: inclusions; steel; deoxidize

1 Introduction

Steel as a common and economical structural material is widely used in the construction and manufacturing industry. To improve steel properties and obtain better cleanliness, deoxidation has become a necessary step in the smelting process of high-performance steels, but most of the non-metallic inclusions are generated during the deoxidation process. These inclusions will destroy the continuity of the metal matrix, reduce the physical properties of the steel, and lead to the fracture of the steel. The high melting temperature of these non-metallic inclusions will lead to the clogging of the submerged entry nozzle [1,2,3] which hinders the smooth running of the production. To reduce the adverse effects of these non-metallic inclusions on steel properties, researchers at Nippon Steel proposed the concept of oxide metallurgy [4]. Instead of increasing the smelting cost to further improve the purity of the molten steel, inclusions are controlled to make them practical and to improve the mechanical properties of the steel with grain refinement and acicular ferrite formation. It would promote the nucleation of other inclusions’ precipitation by controlling the size of oxide inclusions.

Titanium is an important alloying element in high-performance steels due to its strong affinity with oxygen [1], and many studies have been done on its deoxidation products [5,6,7,8,9,10,11]. Qi [12] found that the titanium oxides can induce intracrystalline ferrite to refine the grain and improve the effect of steel toughness and strength. Furthermore, titanium can combine with nitrogen in the steel to produce TiN [13,14,15,16], reducing the amount of dissolved N in the steel. Wentrup and Hieber [11] concluded that the titanium deoxidation product depends mainly on the titanium content in the steel by the calculation of the titanium deoxidation equilibrium. Similarly, based on X-ray diffraction (XRD) technique and optical microscopy, Iwai et al. [17] and Hadley and Derge [18] found that the balance of titanium-oxygen in steel mainly depends on the titanium content, and it was concluded that the main inclusions produced during titanium deoxidation are Ti2O3 and Ti3O5.

To reduce costs and improve the performance of steel, aluminum, and titanium, complex deoxidation is often used in production. Thermodynamic analysis of the Fe–Al–Ti–O system is necessary to promote the generation of titanium oxides for grain refinement, and to avoid nozzle clogging by reducing the generation of solid inclusions. Because there are many kinds of Al–Ti complex oxide inclusions in the Fe–Al–Ti–O system in the molten steel, the composition and thermodynamic data of the inclusions are still unclear. Based on the detection of SEM/EDS, Ti2O3, Al2O3, Ti3O5, and Al2TiO5 [12] have been widely recognized as the product in molten steel. Matsuura et al. [19] calculated the phase diagram of the Fe–Al–Ti–O melt, due to lack of exact thermodynamic calculation data, they selected the liquid phase region obtained by Ruby-Meyer et al. [20] using the IRSID slag model calculated on CEQCSI software for supplementation. In conclusion, to improve the effect of non-metallic inclusions on steel properties, thermodynamic information on the relation between aluminum and titanium is very important.

Although previous researchers have done lots of studies on Al–Ti deoxidized steel, the results are somewhat different due to the complexity of the deoxidation products and the lack of thermodynamic parameters. In the present study, by observing the morphology of inclusions and analyzing the composition, the phase of inclusions is determined according to the phase diagram of the Al2O3–TiO2–Ti2O3 ternary system, and the results were put into the image of thermodynamic calculation for verification. The stable composition change in inclusions during cooling is calculated to predict the change in inclusions during the steel production. The result will help predict and control the composition of Al–Ti–O(–N) inclusions in steel and prevention of nozzle clogging. Furthermore, this study will be helpful for future researchers on Al–Ti deoxidized steel.

2 Experimental methods

The raw material of all high-temperature experiments in this study is YT01 industrial pure iron. The chemical composition of the raw material is shown in Table 1. The experiments were carried out in a tubular resistance furnace. Before the steel smelting, the temperature inside the furnace was measured with double platinum-rhodium thermocouples after the empty furnace was heated up to 1,873 K. The temperature correction was carried out after determining the constant temperature zone inside the furnace. Approximately 600 g pure iron (initial oxygen content is around 200 ppm) were placed in an Al2O3 crucible (56 mm diameter and 100 mm height), and then transferred to the furnace. The sample was heated to 1,873 K (1,600℃) under argon atmosphere at a flow rate of 5.0 L·min−1, then the melts were held for 30 min at 1,873 K (1,600℃) to achieve sufficient homogenization. Subsequently, the deoxidizing alloy material aluminum powder and Ti–Fe alloy were packed in an iron foil, and then inserted into the melts, after stirring for 10 s to ensure rapid homogenization of the steel composition. The compositions of the aluminum powder and Fe–Ti alloy are shown in Table 2. The aluminum content is more than 99%, and the titanium content is 71.48%. The addition of the deoxidizer was recorded as 0 min, followed by sampling at 120, 600, 1,800, and 3,900 s. After sampling, the samples were placed in the 5% NaCl solution for rapid cooling.

Table 1

Chemical composition of raw materials (mass percent)

C Si Mn P S Cu Ni
0.0016 0.0033 0.01 0.0053 0.0017 0.0037 0.0038
Table 2

Chemical composition of deoxidizer (mass percent)

Deoxidizer Al Ti Fe Si C Mn O N P
Al powder ≥99 — ≤0.2 ≤0.2 — — — — —
Fe–Ti alloy 5.65 71.48 19.25 0.51 0.32 1.02 1.08 0.64 0.05

The final samples were processed into Φ5 mm × 50 mm rods, the total nitrogen and oxygen levels were measured by the inert gas fusion-infrared absorptiometry technique. The oxygen content in each sample was detected three times to judge the uniformity of total oxygen distribution in the molten steel. Some steel chips were cut out and analyzed by the ICP-AES method for the content of metal elements acid-soluble Al and total Ti. The remaining steel samples were inlaid with epoxy resin, in which the composition and morphology of the inclusions were analyzed by Scanning electron microscope-energy dispersive spectrometer SEM-EDS. According to the amount of aluminum and titanium added to the liquid steel, the samples can be divided into four groups. The composition of main elements in steel after 3,900 s deoxidation of each group is shown in Table 3.

Table 3

Main chemical compositions of steel specimens after deoxidation for 3,900 s

Mark Deoxidizer Sample time (s) T. [O] T. [N] S. [Al] T. [Ti] [Ti]/[Al]
(Mass ppm)
T1 0.33 Ti + 0.5 Al 3,900 79 25 300 3,100 10.33
T2 0.56 Ti + 0.5 Al 3,900 34 33 400 5,300 13.25
T3 0.78 Ti + 0.5 Al 120 160 550 7,100 12.91
600 95 540 6,994 12.95
1,800 90 540 6,996 12.96
3,900 28 30 550 6,999 12.73
T4 2.22 Ti + 0.5 Al 120 121 1,500 22,094 14.73
600 110 1,400 19,995 14.28
1,800 44 1,300 18,998 14.61
3,900 27 23 1,300 18,800 14.46

3 Results

3.1 Particle morphology and composition

Typical inclusions of the four groups of samples are shown in Figure 1. Approximately 40–50 inclusions were counted for each sample, it can be found that the inclusions in T1 and T2 are mainly spherical and irregular alumina inclusions, and there are a small number of two-phase or multi-phase Al–Ti complex inclusions, most of which are Al2O3–TiO x inclusions and TiN bonded with pure alumina inclusions. Figure 1(c) shows the four-phase inclusions, which are pure alumina phase, aluminum-titanium complex inclusions with different titanium oxide contents and TiN, respectively. The inclusions in T3 and T4 include multi-phase Al–Ti complex inclusions and Al2O3–TiO x complex inclusions with uniform composition, most of which have irregular morphology.

Figure 1 Morphology and composition of typical inclusions in Al–Ti deoxidized steel at 3,900 s. (a) Typical Al2O3 inclusions in samples T1; (b) Al2O3-TiOx inclusions in sample T1; (c) Al2O3-TiN-TiOx inclusions in sample T2; (d) Al2O3-TiOx inclusions in sample T2; (e)-(f) Al2O3-TiOx inclusions in sample T3; (g)-(h) Al2O3-TiOx-TiN inclusions in sample T4.
Figure 1

Morphology and composition of typical inclusions in Al–Ti deoxidized steel at 3,900 s. (a) Typical Al2O3 inclusions in samples T1; (b) Al2O3-TiOx inclusions in sample T1; (c) Al2O3-TiN-TiOx inclusions in sample T2; (d) Al2O3-TiOx inclusions in sample T2; (e)-(f) Al2O3-TiOx inclusions in sample T3; (g)-(h) Al2O3-TiOx-TiN inclusions in sample T4.

Surface scanning of typical multi-phase Al–Ti complex inclusions is illustrated in Figure 2, and it indicates that the inclusions’ composition distribution is not uniform. Figure 2(a) consists of three phases, which are black alumina-enriched zone, light gray Al2O3–TiO x -enriched zone, and TiN-enriched zone. Figure 2(b) is also composed of similar three phases, Al2O3–TiO x inclusions are dependent on the Al2O3 inclusions, and the TiN adheres to the Al2O3–TiO x inclusions.

Figure 2 Surface scanning of multiphase Al–Ti complex inclusions. (a) surface scanning of typical Al-Ti-O-N inclusions; (b) surface scanning of typical Al-Ti-O inclusions.
Figure 2

Surface scanning of multiphase Al–Ti complex inclusions. (a) surface scanning of typical Al-Ti-O-N inclusions; (b) surface scanning of typical Al-Ti-O inclusions.

To study the Al2O3–TiO2–Ti2O3 complex inclusions, the phase diagram of Al2O3–TiO2–Ti2O3 at 1,873 K was drawn by thermodynamic software, as shown in Figure 3. It can be seen that the Al2O3–TiO2–Ti2O3 at 1,873 K can be divided into corundum phase, Al4TiO8, Al4TiO5, liquid phase, ilmenite, pseudobrookite, rutile, and TinO2n−1. The main compositions of corundum, ilmenite, pseudobrookite, and liquid composite phases are shown in Table 4. The content of TiO x in the liquid region is in the range of 64–91%. Because of the limitation of the content of elements with atomic number less than 11 analyzed by EDS, the determination of oxygen content in inclusions is not accurate enough, and the type of titanium oxide in inclusions could not be accurately analyzed according to EDS results.

Figure 3 Distribution of inclusion composition in Al–Ti deoxidized steel (the points mean average composition of inclusions in each sample; the color shadow region represents the composition range of inclusions). (a) Average composition of inclusions in four groups of samples at 3,900 s of deoxidation; (b) distribution of inclusions composition in T3 within 1,800 s deoxidation; (c) distribution of inclusions composition in T4 steel during the deoxidation time of 1,800 s.
Figure 3

Distribution of inclusion composition in Al–Ti deoxidized steel (the points mean average composition of inclusions in each sample; the color shadow region represents the composition range of inclusions). (a) Average composition of inclusions in four groups of samples at 3,900 s of deoxidation; (b) distribution of inclusions composition in T3 within 1,800 s deoxidation; (c) distribution of inclusions composition in T4 steel during the deoxidation time of 1,800 s.

Table 4

Main chemical compositions of steel specimens (wt%)

Name of phase Composition of phase
Corundum Mainly Al2O3
Ilmenite Al2O3–Ti2O3
Liquid Al2O3–Ti2O3–TiO2
Pseudobrookite Mainly Ti3O5

In the present study, the content of titanium oxide in inclusions was analyzed by EDS, and the composition of inclusions was speculated by combining with the phase diagram of Al2O3–TiO2–Ti2O3. The points in Figure 3 represent the average composition of inclusions in the corresponding samples, and the color shadow region represents the composition range of inclusions in corresponding samples. Figure 3(a) shows the average composition of inclusions and the range of TiO x content in the four groups of samples at 3,900 s of deoxidation, which shows that the TiO x content of inclusions increases with the increase in titanium addition. At 3,900 s, the stable composition of inclusions in T1, T2, and T3 steel is corundum, which means that the inclusions are mainly solid-phase Al2O3. The inclusions composition in T4 steel is distributed in the corundum region and the Al2O3–TiO x composite inclusions region, including ilmenite region, Al4TiO8, Al4TiO5, and liquid Al2O3–TiO x regions. A small amount of spherical Al2O3–TiO x composite inclusions is detected in T4 steel, indicating that this part of the inclusion’s composition may be in the liquid Al2O3–TiO x region.

Figure 3(b) shows the distribution of inclusions composition in T3 within 1,800 s deoxidation time. The TiO x content in inclusions increases first and then decreases with the extension of deoxidation time. The TiO x in inclusions is highest at 360 s deoxidation. The average TiO x content reaches about 27%, and some inclusions may be in the ilmenite region, Al4TiO8, Al4TiO5, and liquid Al2O3–TiO x region. Figure 3(c) shows the distribution of inclusions composition in T4 steel during the deoxidation time of 1,800 s. The TiO x content of inclusions gradually decreases with the extension of deoxidation time. There is a small amount of pure titanium oxide and liquid Al2O3–TiO x composite inclusions in the steel at 120 s of deoxidation, and then this part of inclusions gradually turns into the Al2O3-rich phase. In general, transient inclusions with high titanium content are produced within 360 s of deoxidation. The composition of these inclusions gradually changed with the extension of the deoxidation time, and the titanium oxide content in the inclusions gradually decreased, which is consistent with the results of Wang et al. [21,22], mainly due to the high titanium content in local molten steel after adding deoxidizer.

The TiO x content in inclusions increases first and then decreases with the extension of the deoxidation time. The TiO x in inclusions is highest at 360 s deoxidation. The TiO x content of inclusions gradually decreases with the extension of deoxidation time. There is a small amount of pure titanium oxide and liquid Al2O3–TiO x composite inclusions in the steel at 120 s of deoxidation, and then this part of inclusions gradually turns into the Al2O3-rich phase.

3.2 Thermodynamic stability of inclusions

To predict the transformation trend of the inclusions in the Fe–Al–Ti–O melt and to determine the stability of the resulting inclusions, the thermodynamic calculation is essential. The predominance diagram of inclusions is of great importance for guiding the actual production to avoid the nozzle clogging and to improve the steel quality.

The predominance diagram of inclusions was calculated based on the Gibbs free energy minimum principle of chemical reactions, and the products present have been identified as Al2O3, TiO, Ti2O3, Ti3O5, and Al2TiO5 according to the experimental results of Cha et al. [23], of which generation reactions are shown in Table 5. The standard Gibbs free energy of generation of the above products at 1,873 K (1,600℃) can be derived from the data in Table 5. The Gibbs free energy expression of the reaction can be calculated according to the Van’t Hoff isothermal equation as shown in equation (1).

(1) Δ G = Δ G θ + R T ln K ,

where R is the gas constant, 8.314, T is the temperature in K, and K is the equilibrium constant, which is related to the activity of the reactants and products. Taking the reaction to produce Ti2O3 as an example, the equilibrium constant can be calculated by K = a [Ti] × a [O]. According to the Gibbs free energy minimum principle, the reaction reaches equilibrium when the free energy no longer changes, i.e., ΔG = 0, and as shown in equation (2)

(2) Δ G θ = − R T ln K .

The activity relationships among [Al], [Ti], and [O] in equilibrium state can be obtained by the above calculation of all the product formation reactions in Table 5. At the same time, the activity coefficients of [Al], [Ti], [O] in liquid steel are calculated by the first-order Wagner model, and the interaction coefficients used are shown in Table 6. After substitution, the concentration relationships of each reaction in an equilibrium state can be obtained. According to the above relationship, the phase diagram of the Fe–Al–Ti–O melt at 1,873 K with Ti and Al mass fraction as variables at 1,873 K is drawn by using MATLAB under the condition of changing the oxygen content (ppm), as shown in Figure 4. It is obvious that the transformation of different titanium oxides is almost independent of aluminum content. With the increase in titanium content, the transformation order of titanium oxides is Ti3O5 → Ti2O3 → TiO. The stable region of Al–Ti composite oxides is located when the content of Al is 0.02% (weight percent) and the content of Ti is below 0.5% (weight percent), and this condition is generated simultaneously with Ti3O5 and Al2O3.

Table 5

Gibbs free energies of the reactions used in the present work

Reaction Δ G θ [J·mol−1] Refs.
2[Al] + [O] = Al2O3(s) −867,300 + 222.5 T [19]
[Ti] + [O] = TiO(s) −360,250 + 130.8 T [12]
2[Ti] + 3[O] = Ti2O3(s) −822,100 + 247.8 T [24]
3[Ti] + 5[O] = Ti3O5(s) −1,307,000 + 381.8 T [24]
2[Al] + 5[O] + 2[Al] = Al2TiO5(s) −1,435,000 + 400.5 T [24,25,26]
Table 6

The interaction parameters of Fe–Al–Ti–O system at 1,873 K (1,600°C) [28]

e i j （j → ） Al Ti O
Al 0.043 0.004 −1.980
Ti 0.0037 0.0493 −1.026
O −1.17 −0.340 −0.174
Figure 4 Based on the classical thermodynamics, the inclusion predominance diagram of Fe–Al–Ti–O system at 1,873 K is calculated by MATLAB. The number beside the thin line is the oxygen content of the corresponding stable boundary, in mass ppm.
Figure 4

Based on the classical thermodynamics, the inclusion predominance diagram of Fe–Al–Ti–O system at 1,873 K is calculated by MATLAB. The number beside the thin line is the oxygen content of the corresponding stable boundary, in mass ppm.

To compare with the results of classical thermodynamic calculations, the predominance diagram of the inclusions in the Al–Ti–O–Fe equilibrium system at 1,873 K was plotted by FactSage 7.2, as shown in Figure 5(a) and (b). The differences between the equilibrium products of the two plots were mainly due to the differences in the selected databases and products. Pure substance database was used, and the selected products were pure substances in Figure 5(a). FToxide database was used in the calculation of Figure 5(b) and the selected products are corundum, liquid oxide phase, ilmenite phase, pseudobrookite phase, and Rutile phase. There are some discrepancies in the liquid oxide region and the boundary line of titanium oxides for these three diagrams. The Al–Ti–O compound region in Figure 5(a) is larger than that in Figures 4 and 5(b). The stability region of Ti2O3 in Figure 5(b) is larger and that of Al2O3 is larger in Figure 4.

Figure 5 Calculated inclusion stability diagrams in the Al–Ti–Fe–O system at 1,873 K (1,600℃) by FactSage 7.2: (a) using FactPS database and (b) using FTOxide database.
Figure 5

Calculated inclusion stability diagrams in the Al–Ti–Fe–O system at 1,873 K (1,600℃) by FactSage 7.2: (a) using FactPS database and (b) using FTOxide database.

The composition points of the experimental melts in Table 3 are marked on three graphs by hollow circles as shown in Figures 4 and 5. The hollow circles are in the Al2O3 stable region in Figure 4, while in the liquid oxide region in Figure 5(a), and in the lime (Ti2O3-rich) region in Figure 5(b). According to the observation and analysis of the current experimental results, it is known that the compositions of inclusions are Al2O3 in T1 and T2 samples and are Al2O3–TiO x inclusions in T3 and T4 samples, which indicate that the calculated results in Figure 4 are more consistent with current experimental results in the alumina stable region. The inaccuracy of thermodynamic on Al2O3–TiO x inclusions in Figure 4 may be due to the lack of thermodynamic data of liquid Al–Ti–O composite products. To further verify the accuracy of the predominance diagrams, the components of the melts and inclusions were obtained from the experiments of Wang et al. [21,22,27,28], Wang et al. [29], Matsuura et al. [19], Zhang et al. [30], and Ono and Ibuta [31] and were investigated and shown in Figures 4–6. They all have a good agreement with Figure 4 in the alumina stable region, indicating that the calculation based on classical thermodynamics is more accurate in the thermodynamic stable region of Al2O3 than that based on FactSage 7.2. The green square representing Ti2O3 based on experiments of Ono et al. is located in the thermodynamic stable region of Ti2O3 for Figure 5b, but in the boundary line of Ti3O5 and Al2O3–TiO x for Figures 4 and 5a, respectively, indicating that the calculated stable region of Ti2O3 based on FactSage with FToxide database is more reliable.

Figure 6 Phase diagram of inclusions during cooling: (a) sample T1, (b) sample T2, (c) sample T3, and (d) sample T4.
Figure 6

Phase diagram of inclusions during cooling: (a) sample T1, (b) sample T2, (c) sample T3, and (d) sample T4.

3.3 Mechanism of inclusions evolution

To investigate the evolution of inclusions during the solidification process, the mass fraction and types of inclusions in four groups of samples are plotted with temperature using FactSage 7.2, as shown in Figure 6, and it indicates that the transformation order of the four groups of sample components is as follows:

T 1 : Al 2 O 3 ( –Ti 2 O 3 ) → Al 2 O 3 + TiN , T 2 : Al 2 O 3 ( –Ti 2 O 3 ) → Al 2 O 3 + TiN , T 3 : Ti 2 O 3 – Al 2 O 3 – TiO 2 → Al 2 O 3 → Al 2 O 3 + TiN , T 4 : Ti 2 O 3 – Al 2 O 3 – TiO 2 → Al 2 O 3 → Al 2 O 3 + TiN

The inclusions with compositions of TiN and corundum precipitate in four samples T1, T2, T3, and T4 after deoxygenation at 3,900 s during the cooling process, and the TiN content of the T1 and T2 sample is lower than T3 and T4. The corundum phase formed first in T1 and T2 samples before they cooled. TiN began to form when the temperature reaches about 1,520℃. When the temperature drops below 1,400℃, the composition change of inclusions is no longer obvious. Most of the corundum phase is Al2O3, and its content increases slightly at the initial stage of cooling. There are mainly liquid oxide inclusions composed of Ti2O3, Al2O3, and TiO2 in T3 and T4 samples before they cooled, and then they disappear at about 1,580°C. The analysis of this result shows that the initial inclusions of T1 and T2 after deoxidation at 3,900 s have only corundum phase as the stable composition at 1,600°C, and TiN begins to precipitate at about 1,500°C during cooling, which is consistent with the SEM/EDS observation. The stable inclusions of T3 and T4 samples after 3,900 s at 1,600°C are liquid phases, and it will gradually disappear during cooling, and the stable phase changes to corundum phase and TiN, this result is similar to the result of the experiment conducted by Pan et al. [32].

4 Conclusion

The inclusions in the steel with complex deoxidation of Al–Ti at 1,600℃ were investigated by experiments and thermodynamic calculations. The main conclusions are as follows:

  1. With the increase of titanium content in steel from 0.31% to 1.88%, the content of TiOx in inclusions is also increasing, which is transformed from typical spherical Al2O3 inclusions to irregular Al2O3–TiOx complex inclusions. Liquid Al2O3–TiO x inclusions may form in the steels within the case with deoxidants of [% Al] = 0.13 and [% Ti] = 1.88.

  2. The effect of holding time on the inclusion compositions has been studied. The TiO x content in the inclusions first increased and then decreased with the extension of deoxidation time in the steels with deoxidants of [% Al] = 0.055 and [% Al] = 0.71, and the content of TiO x in the inclusions is highest at 360 s of deoxidation. There is a small amount of pure titanium oxide and liquid Al2O3–TiO x composite inclusions in the steels with deoxidants of [% Al] = 0.13 and [% Ti] = 1.88 at 120 s of deoxidation, and then this part of inclusions gradually turns into the Al2O3-rich phase.

  3. The predominance diagrams of the Al–Ti–O–Fe system were obtained based on classical thermodynamic calculation and FactSage calculation with different databases and products. There are some discrepancies in the liquid oxide region and the boundary line of titanium oxides for different calculated methods. Experimental results indicate that the calculation of Al–Ti–O–Fe predominance diagrams based on classical thermodynamics is more accurate in the thermodynamic stable region of Al2O3, but more reliable in that of Ti2O3 based on FactSage with FToxide database.

  4. The evolution and transformation of inclusions during the solidification process was analyzed based on FactSage calculation, evolution sequence of inclusions during cooling of samples T1 and T2 is Al2O3(–Ti2O3) → Al2O3 + TiN, and the evolution order of samples T3 and T4 is Ti2O3–Al2O3–TiO2(liquid) → Al2O3(solid) → Al2O3 + TiN(solid). It can be found that there are no liquid inclusions in T1 and T2 samples. There are mainly liquid oxide inclusions composed of Ti2O3, Al2O3, and TiO2 in T3 and T4 samples before cooling and they disappear at about 1,580°C. TiN precipitates at about 1,500°C during the cooling process.

Acknowledgment

The authors gratefully acknowledge the fundamental support from the National Natural Science Foundation of China and the science and technology planning project of Guizhou.

  1. Funding information: This research is supported by the National Science Foundation of China (No. 52064011 and 51804086) and is supported by the science and technology planning project of Guizhou (No. Qian Ke He Ji Chu-ZK [2021]258 and Qian Ke He Zhi Cheng [2021]342), and the research program for talented scholars of the Guizhou Institute of Technology with grant No. XJGC20190962.

  2. Author contributions: Jun Wang: write, data analyses; Linzhu Wang: experiment; Xiang Li: characterization test; Junqi Li: supervisor; Chaoyi Chen: supervisor; Changrong Li: reviewed；Changling Zhuang: methodology.

  3. Conflict of interest: The authors state no conflict of interest.

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Received: 2021-10-09
Accepted: 2021-12-07
Published Online: 2022-05-03

© 2022 Jun Wang et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/htmp-2022-0015
Keywords for this article
inclusions; steel; deoxidize
Creative Commons
BY 4.0

Articles in the same Issue

  1. Research Articles
  2. Numerical and experimental research on solidification of T2 copper alloy during the twin-roll casting
  3. Discrete probability model-based method for recognition of multicomponent combustible gas explosion hazard sources
  4. Dephosphorization kinetics of high-P-containing reduced iron produced from oolitic hematite ore
  5. In-phase thermomechanical fatigue studies on P92 steel with different hold time
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  8. Development of a huge hybrid 3D-printer based on fused deposition modeling (FDM) incorporated with computer numerical control (CNC) machining for industrial applications
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  11. Carbothermal reduction of red mud for iron extraction and sodium removal
  12. Reduction swelling mechanism of hematite fluxed briquettes
  13. Effect of in situ observation of cooling rates on acicular ferrite nucleation
  14. Corrosion behavior of WC–Co coating by plasma transferred arc on EH40 steel in low-temperature
  15. Study on the thermodynamic stability and evolution of inclusions in Al–Ti deoxidized steel
  16. Application on oxidation behavior of metallic copper in fire investigation
  17. Microstructural study of concrete performance after exposure to elevated temperatures via considering C–S–H nanostructure changes
  18. Prediction model of interfacial heat transfer coefficient changing with time and ingot diameter
  19. Design, fabrication, and testing of CVI-SiC/SiC turbine blisk under different load spectrums at elevated temperature
  20. Promoting of metallurgical bonding by ultrasonic insert process in steel–aluminum bimetallic castings
  21. Pre-reduction of carbon-containing pellets of high chromium vanadium–titanium magnetite at different temperatures
  22. Optimization of alkali metals discharge performance of blast furnace slag and its extreme value model
  23. Smelting high purity 55SiCr automobile suspension spring steel with different refractories
  24. Investigation into the thermal stability of a novel hot-work die steel 5CrNiMoVNb
  25. Residual stress relaxation considering microstructure evolution in heat treatment of metallic thin-walled part
  26. Experiments of Ti6Al4V manufactured by low-speed wire cut electrical discharge machining and electrical parameters optimization
  27. Effect of chloride ion concentration on stress corrosion cracking and electrochemical corrosion of high manganese steel
  28. Prediction of oxygen-blowing volume in BOF steelmaking process based on BP neural network and incremental learning
  29. Effect of annealing temperature on the structure and properties of FeCoCrNiMo high-entropy alloy
  30. Study on physical properties of Al2O3-based slags used for the self-propagating high-temperature synthesis (SHS) – metallurgy method
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  41. An investigation on as-cast microstructure and homogenization of nickel base superalloy René 65
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  64. Effect of microstructure on tribocorrosion of FH36 low-temperature steels
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