Transient Evolution of Inclusions during Calcium Modification in Linepipe Steels

摘要

The laboratory experiments of Al_2O_3 inclusions modified by calcium treatment in linepipe steels with the S content of 30 ppm and 310 ppm were performed at 1873 K. Particularly, samples were taken before calcium treatment ( 1 minute before the calcium addition) and at various times (typically 1 minute, 10 minutes and 30 minutes) after calcium treatment to study the transient inclusions evolution during calcium modification. Traditional modification mechanism of Al_2O_3 inclusions is that Al_2O_3 inclusion is directly modified by dissolved calcium or indirectly modified via CaO formed from calcium and oxygen. In the current study, after Ca-Si alloy power addition, CaS outer layer were promptly formed on the angular Al_2O_3 inclusion. With the reaction of the CaS outer layer and the Al_2O_3 core or [O], the Al_2O_3 inclusion was modified to a spherical liquid calcium aluminate. Moreover, the equilibrium curve of Ca-O and Ca-S, the stability diagram of inclusions and equilibrium precipitation of inclusions during solidification in linepipe steels were calculated to study the formation of inclusions.