A study of transient ladle reactions involving aluminum, titanium and oxygen in molten iron

It is the aim of this project to investigate whether the existence of Ti-containing inclusions can be the results of transient conditions, which can be caused by (i) local and temporary variation of the Ti/Al, (ii) fluctuations in melt temperature and (iii) changes in O availability. The approach undertaken in this study is to simulate transient conditions for the Fe-Al-Ti-O melts and sample the melts as a function of time during a time period that is of relevance to industrial ladle processing.;The most pertinent results are summarized below: (1) Firstly, Al killing without Ti addition was carried out as a control experiment. Immediately after Al killing, the O content of the melt decreased to 30 ppm within 1 minute, and remained at this level for the remainder of the experiment. It was (2) was made 2 minutes after Al addition such that the final melt chemistry had a Ti/Al ratio close to 1. The melt chemistry, after Ti addition, was such that Al2O3 was the only stable inclusion. With time the inclusion chemistry shifted back towards the thermodynamically stable Al2O3 but the change in morphology remained. The samples can be categorized as Ti > Fe-70%Ti > Fe-30%Ti, in terms of the amount of Ti containing inclusions produced during the transient stage. (3) Elevating temperature to 1973 K promoted the reaction between Ti and Al2O 3 inclusions and enhanced the yield of Ti-containing inclusions, especially those in the chemistry close to Al2TiOs. Extending the time interval between Al and Ti additions (from 2 to 5 minutes) did not significantly alter the behavior described in (2). (4) When the Ti/Al ratio in the melt was designed to be 1/4 with the only thermodynamic stable oxide being Al2O 3, the results showed that transient Ti-containing oxides did form but were accompanied by little/no shape change and produced transient stage inclusions with less Ti contents compared with the Ti/Al=1 case. (5) De-oxidation results at Ti/Al=1/2 with the only thermodynamic stable oxide being Al2O 3 showed that transient Ti-containing oxides also existed temporarily after Ti addition, and with time, the predominant inclusion found was Al 2O3. (6) Maintaining the final Ti/Al=1 yet splitting Ti addition into either two batches (Ti/A1=1/2+1/2) or four batches (Ti/A1=1/4+1/4+1/4+1/4) resulted in little difference from the single step addition in terms of composition and morphology. (7) When the Ti/Al ratio in the melt was further increased to the Al2TiOs stable phase region (Ti/Al=15), the inclusion population evolved from spherical-dominant ones to irregular ones. (8) When the Ti/Al ratio in the melt was increased such that Ti3O5 is the thermodynamically stable inclusion (Ti/Al=75), the inclusions evolved after Ti addition towards TiOx inclusions, and this was accompanied by a shape change from spherical to irregular. (9) Finally, de-oxidation experiment only with Ti killing (Ti/Al=infinity) was implemented, and the results showed that the formation of Ti2O could also be possible without the participation of Al2O3. (Abstract shortened by UMI.)...