Formation Conditions of Mg2TiO4 and MgAl2O4 in Ti–Mg–Al Complex Deoxidation of Molten Iron

Abstract

It is important to study the complex deoxidation equilibrium of molten iron in Ti-Mg-Al system from the view point of inclusion control. The equilibrium experiments between molten iron and TiO X -MgO-Al 2 O 3 slag and the thermodynamic calculation on the complex deoxidation are conducted at 1 973 K in the present study. The liquid phase region of TiO X -MgO-Al 2 O 3 system in equilibrium with molten iron is clarified at 1 973 K. The equilibrium compounds which are coexisted with the slag on the liquidus curve in the system are identified to be but the study on this system is very limited, and the phase equilibrium relations have not been clarified yet.In the present study, the liquid phase region of TiO X -MgO-Al 2 O 3 system in equilibrium with molten iron is investigated at 1 973 K. The equilibrium relation between the deoxidation products (Mg 2 TiO 4 or MgAl 2 O 4 ) and the composition of solute elements in steel is investigated, and the conditions that Mg 2 TiO 4 forms instead of MgAl 2 O 4 nor Al 2 O 3 are examined in the complex deoxidation of Ti-Mg-Al system. ExperimentalAn induction furnace was used for the deoxidation of high-purity electrolytic iron. The electrolytic iron in an alumina crucible was preliminary deoxidized in H 2 for over an hour at 1 873 K and was used in the following experiments. The slag was made by mixing the reagent grade of TiO 2 (purity Ͼ99 %), MgO (purity Ͼ99 %) and Al 2 O 3 (purity 99.6 %). The initial slag composition was set to the liquidus region in the TiO 2 -MgO-Al 2 O 3 phase diagram Fact Sage5. 4. 1. The calculated phase diagram for TiO 2 -MgO-Al 2 O 3 system at 1 973 K is described in Fig. 2. The initial slag composition is shown in Table 1 and is also plotted in Fig. 2.Sixteen gram of the deoxidized iron and the reagent grade of TiO 2 , MgO and Al 2 O 3 slag totally weighing 8 g were put in a magnesia or an alumina crucible, and the crucible was inserted in a carbon crucible with a carbon lid. The experiments were carried out by using a multipurpose electric resistance furnace, of which the heating element is carbon. After the sample was set in the furnace, the inner space of the furnace was decompressed to 8 Pa and was switched to an inert atmosphere by introducing an argon gas. By carrying out this operation repeatedly 2 time, the inside of the furnace was kept to be an argon gas atmosphere (0.011 to 0.013 MPa). Then, the sample was heated to 1 973 K according to the heat pattern shown in Fig. 3. The sample was equilibrated in the furnace by being held for 3 h in an argon atmosphere at 1 973 K. The sample was quickly cooled in the furnace by switching off the button of the power supply. After each experiment, metal and slag in the crucible were divided, and the Ti, Mg and Al contents of metal and slag and the O content of metal were analyzed by an inductively coupled plasma emission spectrometry (ICP) and an inert gas impulse infrared absorption spectroscopy, respectively.The compound in equilibrium with metal and slag was identified for each sample as follows: The...

Formation and Thermodynamics of Mg-Al-Ti-O Complex Inclusions in Mg-Al-Ti-Deoxidized Steel

“…The calculated stability diagram of Al Ti Mg O system at 1873 K (1600°C) for [Mg] = 3 ppm is shown in Figure 10(b). Simultaneously, the experimental data in the current work and from the literature [39,41,42] Figure 10(b) is more accurate than Figure 10(a) due to all solid inclusion in Table V considered. Figure 10(b) is in accordance with experimental data points.…”

“…[39,41,42] The shaded areas show the liquid phase region calculated using FactSage 6.4 in similar way to Figure 10(c). Figure 11(a) indicates that no Al 2 TiO 5 and Al 2 O 3 inclusions are stably formed with several ppm of [Al] in the molten steel, and there is the stability region The solidification was relatively rapid during the process of samples quenched using water.…”

“…Therefore, the activity of the oxide products is assumed to unity. By plugging the thermodynamic data and T = 1873 K (1600°C) and fixing the content of oxygen as different value, the relationship between [i] and [j] can be [42] e j i (fij) T i A l M g O Ti 0.048 [57] 0.0037 [58] À91.6 [41] À1.026 [59] Al 0.004 [58] 0.038 [60] À0.13 [57] À1.867 [60] Mg À47.4 [41] À0.12 [57] À0.047 [60] À0.602 [60] O À0.34 [59] À1.105 [60] À0.396 [60] À0.175 [60] c determined from the equilibrium equations. Then, the equilibrium curves of the stable phases in the molten steel at 1873 K (1600°C) can be drawn in phase diagram, which are under different oxygen contents.…”

Evolution of Different Inclusions during Ladle Treatment and Continuous Casting of Stainless Steel

“…Modifications of spinel inclusions by a Ti addition and calcium treatment in liquid steel during the refining process were studied by several researchers. [19][20][21][22][23][24][25][26] The formation condition of MgTi2O4 instead of MgAl 2 O 4 was studied by Ono et al 25,26) However, the Ti will accelerate the Mg dissolution from the refractory and slag which will lead to an easier formation of spinel inclusions. 20) Yang et al 22) pointed out that spinel inclusions would transform to liquid complex inclusions, if the dissolved Ca content in the liquid steel exceeds 1 ppm.…”

Equilibrium Relationship between the Oxide Compounds in MgO–Al2O3–Ti2O3 and Molten Iron at 1 873 K

“…5) A determination of the equilibrium relationship between the oxide compounds in MgO-Al 2 O 3 -Ti 2 O 3 and molten iron is important to avoid Al 2 O 3 or MgO · Al 2 O 3 formation and for inclusion control. However, our previous work 6) is the only study that has reported on this and the equilibrium relationship between the deoxidation products and the composition of the solute elements in molten iron was investigated at 1 973 K. Therefore, in this study we investigated the equilibrium relationship between the oxide compounds in MgO-Al 2 O 3 -Ti 2 O 3 and molten iron at 1 873 K.…”