Formation Mechanism of CaS-Bearing Inclusions and the Rolling Deformation in Al-Killed, Low-Alloy Steel with Ca Treatmen
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UM treatment is widely used for inclusion modification in Al-killed steel. It makes the inclusions modify liquid globular calcium aluminates, which are easier to float up and to be absorbed by top slag, thereby improving the cleanness of steel. Although calcium has good modification ability to the inclusion in Al-killed steel, improper calcium treatment will bring adverse effects. Insufficient calcium treatment promotes the inclusion into solid calcium aluminates, which are hard to be removed. For excessive calcium treatment, redundant calcium will react directly with sulfur to form CaS inclusion. At the same time, the dissolved aluminum and sulfur in molten steel will react with CaO in excessive modification of calcium aluminates to form oxide-sulfur duplex inclusion, so that a large number of CaS-bearing inclusions will form after excessive calcium treatment. CaS-bearing inclusions can degrade the castability of steel GUANG XU, Doctoral Candidate, and ZHOUHUA JIANG and YANG LI, Professors, are with the School of Materials and Metallurgy, Northeastern University, 241 Mailbox, No. 3-11, Wenhua Road, Heping District, Shenyang, 110819, P.R. China. Contact e-mail: [email protected] Manuscript submitted March 10, 2016. Article published online May 26, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
on account of its high melting point and lead to erosion of the ladle slide gate as well as refractory nozzles during casting.[1] Several researchers have examined the formation mechanism of oxide-sulfide duplex inclusion and its rolling performance. Ye et al.[2] considered that dissolved aluminum and sulfur can react with CaO in complete or overmodified aluminum inclusion due to its high activity of CaO. Holappa et al.[3] pointed out that CaS and oxide-sulfide duplex inclusion is promoted by enrichment of sulfur in the liquid residual as well as by the decreasing of temperature. Choudary and Ghosh[4] established a thermodynamic model to forecast the formation of oxide-sulfide duplex inclusion generated from the reaction between [Al], [S] and liquid calcium aluminates in Al-killed steel. However, thermodynamic investigations of them only aimed at the Al-S equilibriums of CA, C12A7, and C3A (where A means Al2O3 and C means CaO) for the precipitation of CaS in oxide-sulfide duplex inclusion. The authors of this article thinks that Al-S equilibriums of CA, C12A7, and C3A alone cannot forecast the precipitation of CaS accurately because the aCaO of each calcium aluminate is different and they should not be replaced by the aCaO of CA, C12A7, or C3A. It is worth mentioning that the research about how much CaS can be produced by the reaction between [Al], [S] and (CaO) is scarcely reported in the published literature. Jing Guo et al.[5] found that oxide-sulfide duplex inclusion has good rolling VOLUME 47B, AUGUST 2016—2411
performance. But when CaS in the oxide-sulfide inclusion increases, its rolling performance may become worse. Some CaS-bearing inclusions contain low modification of core that were not researched extensively in their study, s
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