Formation Mechanism of Inclusions in Steel by Ti-Al Deoxidation and Their Physicochemical Properties

研究了Al_2O_3-SiO_2-TiO_x氧化物体系的热力学性质，这对于利用炼钢过程中形成的非金属夹杂物控制钢的形态具有重要意义。Al_2O_3和TiO_x的溶解度分别为28%和50%，且随着SiO_2含量的增加，Ti^&lt；4+&gt；/Ti^&lt；3+&gt；的比例增大，说明Ti2+-lt；4+&gt；和Ti^-lt；3+&gt；用Fe-C-Si合金平衡氧化物熔体，根据合金中的最终硅含量和硅的活度系数确定SiO_2的活度。另一方面，采用Knudsen胞腔渗出法测定了Al、Si、AlO和SiO在Al-Si-Ti合金平衡的熔体中Al_2O_3和SiO_2的活度，测定了Al_2O_3和SiO_2的活度。SiO_3的测定值与化学平衡法的测定值吻合较好，TiO_x的测定值也是用Toop法得到的。这些结果表明，SiO_2对Al_2O_3的亲和力与TiO_3的亲和力几乎相同。本研究结果定量地为探讨夹杂物的形成机理提供了驱动力。此外，还可以从结果中评估与各种氧化物夹杂物的成分相平衡的钢的成分，从而导致脱氧过程控制的优化。

Thermodynamic properties of the Al_2O_3-SiO_2-TiOx oxide system, which are important for the morphology control of steel using non-metallic inclusions formed during steelmaking processes, have been investigated.Firstly, phase relations for the Al_2O_3-SiO_2-TiOx system at 1873 K were clarified. Solubilities of Al_2O_3 and TiOx were found to be 28 mass% and 50 mass%, respectively, and the ratio of Ti^<4+>/ Ti^<3+> increased with increase in SiO_2 content of the oxide, which indicated that both Ti^<4+> and Ti^<3+> behaved as network formers also from the results of Raman spectroscopy of the quenched samples.Secondly, the activity of each constituent was measured. Oxide melts were equilibrated with Fe-C-Si alloys and the activity of SiO_2 was determined from the final Si content and activity coefficient of Si in the alloy. On the other hand, Knudsen cell effusion method was employed for the activity of Al_2O_3 From the vapor pressures of Al, Si, AlO and SiO for the molten oxide equilibrated with Al-Si-Ti alloy, the activities of Al_2O_3 and SiO_2 were determined. The obtained value of SiOs agreed well with that by chemical equilibration technique, and that of TiOx was also derived by Toop's method. These values demonstrated that the affinity of Si0_2 for Al_2O_3 was almost the same as that of TiOx.The findings drawn in the present research quantitatively provide the driving force necessary in discussing the mechanism of inclusion formation. Also, the composition of steel equilibrated with various compositions of oxide inclusions can be assessed from the results, which leads to an optimization in deoxidation process control.