Reassessment of Oxide Stability Diagram in the Fe–Al–Ti–O System

Abstract

Phase equilibria of Fe-Al-Ti-O system is shortly reviewed, in particular for stability of oxide phases in equilibrium with liquid Fe alloy in dilute concentration. This system is relevant to Ultra Low Carbon steel with Ti alloying (Ti-ULC), often causing clogging of Submerged Entry Nozzle (SEN) during continuous casting. In order to predict stable oxides in the Ti-ULC steel, thermodynamic calculation using CALPHAD approach was employed. Previously available thermodynamic calculations were examined, and compared with available experimental data. A slight modification of thermodynamic modeling of previous investigation resulted in noticeable improvement for the prediction of stable phases by thermodynamic calculation. Significance of the present revision of the thermodynamic modeling is discussed in the view of nozzle clogging of Ti-ULC casting.

Kinetics of CO Gas Dissolution into Stirred Liquid Fe at 1823 K and Its Impact on Nozzle Clogging during Continuous Casting

“…10,11) As a result, a liquid oxide composed of Fe t O-Al 2 O 3 -TiO x with solid alumina form at the interface. This was thermodynamically predicted 8,9) and experimentally validated by the present authors. 10,11) A schematic explanation can be seen in Fig.…”

“…10,11) Its consequences on nozzle clogging were discussed in the previous report by the present authors utilizing thermodynamic analysis and experimental trials. [8][9][10][11] A probable cause of nozzle clogging often observed during continuous casting of Ti-ULC steel was proposed also by inspecting a series of plant-used nozzles. 12) From the results obtained in the present study, it is likely that the generation of CO gas needs to be suppressed since the CO gas dissolution can be controlled by its supplying rate from the SEN. Optimizing the nozzle refractory constitution is required to suppress CO gas generation, consequently to suppress reoxidation of the liquid steel and nozzle clogging.…”

“…According to previous studies conducted by the present authors, the clogging during Ti-added ULC (hereafter Ti-ULC) steel casting is partly initiated from an interfacial reaction between CO gas from the nozzle and Ti-ULC steel. [8][9][10][11][12] Since major constituents for normal SENs are Al 2 O 3 , SiO 2 , and C, it could be expected that CO gas is emitted by a carbothermic reaction between SiO 2 and C: 3,13,14) SiO refractory C refractory SiC s CO g G Jmo ..... (2) where Δ°G is the standard Gibbs energy change of the reaction at 1 823 K, calculated by FactPS database of FactSage software. 15) It was also reported that Al 2 O 3 in the refractory can react with the graphite: 16) Al O refractory C refractory Al O g CO g G J In the above carbothermic reactions, CO(g) is a common reaction product.…”

“…....................... (8). where J C represents the molar flux of the diffusing C in a boundary layer of the liquid iron (mol m 2 sec − 1 ); k m the mass transfer coefficient of the C in the liquid (m sec − 1 ), C i C the molar concentration of C at the interface (mol m − 3 ), C b C the molar concentration of C in the bulk (mol m − 3 ), respectively.…”

Oxide Stability Diagram of Liquid Steels – Construction and Utilization

“…As the compositions of two oxidizing components are used as the axes variables, this type of diagram is often used to figure out inclusion phases in liquid steel, which was simultaneously deoxidized by the two components. Most well-known diagrams in literature are due to Si-Mn deoxidation, 1) Si-Al deoxidation, [2][3][4] Mg-Al deoxidation, [5][6][7][8][9][10][11][12][13] Al-Ca deoxidation, 11,[14][15][16] Ti-Al deoxidation, [16][17][18][19][20][21][22][23] etc. A partial list of such diagrams published in literature is shown in Table 1.…”