Precipitation of TiS in Al–Ti Simultaneously Deoxidized Steel

Abstract

Herein, the precipitation of TiS in an Al–Ti simultaneously deoxidized steel is observed, and the results confirm the precipitation of single TiS, two‐layered oxide (Al2O3 or TiOx)–TiS composite, and three‐layered Al2O3–TiOx–TiS composite inclusions in the steel. Thermodynamic calculations reveal that TiS precipitated in the experimental steel during the solidification process when the solid fraction (xs) is 0.880. In addition, the precipitation of TiOx during solidification depends on the equilibrium partition of O. When the O content in steel is very low, TiS rather than TiOx is precipitated. In addition, the enrichment of O in the residual liquid steel results in the precipitation of TiOx during the solidification process. Oxide–TiS is formed by TiS precipitation on the surface of Al2O3 and TiOx precipitation in the liquid steel or at the initial stage of solidification. However, Al2O3–TiS is formed only in preformed solid steel with low oxygen content. The lattice misfit results suggest that it is easier to match TiS to TiO and TiO2, while the misfit of TiS(001)/bcc Fe(100) is 6.06.

Effect of cooling conditions on the size evolution of typical inclusions in the Al-Ti deoxidised steel

“…The precipitating reaction of TiS by [Ti] reacting with [S] is as follows: The concentration product of [Ti] and [S] at the equilibrium state log K’ TiS can be calculated as: The actual concentration product of [Ti] and [S] ( Q TiS ) is calculated as [24]: where T represents the temperature of steel, and represent the actual concentration of Ti and S, respectively.…”

“…Many studies focus on the formation mechanism of inclusions during Al-Ti deoxidation [16][17][18][19][20][21][22][23][24]. Kunisada et al [16].…”

“…Sun et al [22] studied the precipitation mechanism of inclusions formed in Al/Ti-complex deoxidation steel melt. The present authors also investigated the formation mechanism of inclusions of Al/Ti-complex deoxidation by experimental method and first principles method [23, 24]. However, the mechanism of inclusion formation under different cooling rates is a lack.…”

Effects of S Content on Inclusion Formation in the Al and Ti–Mg Complex Deoxidized Steel

“…Lv et al [ 24 ] found that MnS can be changed into TiS at 1623 K in the solidification process. The current authors [ 25 ] observed single TiS, two‐layer Al 2 O 3 –TiS (TiO x –TiS), and three‐layer Al 2 O 3 –TiO x –TiS inclusions in Al–Ti deoxidized low‐carbon steel, the precipitation of TiS is prior to that of MnS when Mn content is equal to Ti content, and a lower‐oxygen content can profit TiS precipitation in solidification process.…”