Origins of Non-metallic Inclusions and their Chemical Development during Ladle Treatment

Abstract

In the present work, steel, slag and refractory samples were taken from the ladle at OVAKO Steel in Hofors, Sweden. The steel samples were analysed in LOM, SEM and OES PDA. The chemical compositions of the inclusions were determined by EDS. According to the morphologies and compositions, the inclusions were classified into 5 different types, namely, (1) type-1, alumina inclusions, (2) type-2, calcium aluminate, (3) type-3, splnel-calclum aluminate, (4) type-4, calcium aluminate surrounded by a CaS shell, and (5) spinel-calcium aluminate surrounded by a CaS shell. Ladle glaze was found to be a major supplier of the inclusions, while the inclusions brought over from EAF could be another important source. The results of OES PDA showed that removal of inclusions took place mostly during the vacuum degassing period.The characteristics of the non-equilibrium decarburization process during the vacuum circulation (RH) refining of molten steel have been considered and analysed. On the basis of the fundamentals of metallurgical reaction engineering and non-equilibrium thermodynamics, as well as the two-fluid model for gas-liquid two-phase flow and a modified k-s model for turbulent flow, a novel three-dimensional mathematical model for the process has been proposed and developed. The details of the model, including the establishment of the governing equations and the especially modified two-equation k-s model, the determination of the appropriate source terms and boundary conditions and others, have been presented. The related parameters of the model have been discussed and determined for the decarburization refining process of molten steel in a 90-t multifunction RH degasser under RH and RH-KTB operating conditions.

Mechanism study on formation and chemical changes of calcium aluminate inclusions containing SiO2in ladle treatment of tool steel

“…On the basis of the standard Gibbs energy for reaction (5), the activities of MgO, Al and O, the Gibbs energy for reaction (5) (5) going to the right hand side. Hence, the formation of spinel phase is inevitable.…”

“…The standard Gibbs energy for reaction (5) can be obtained by the combination of standard Gibbs energies for reactions (6) 15 and (7) …”

Inclusion Evolution during Modification of Alumina Inclusions by Calcium in Liquid Steel and Deformation during Hot Rolling Process

“…1. Because the modification of alumina during LF refining had been fully studied by previous researchers, 4,6,9,10) present work mainly focuses on the transformation of inclusions after LF refining and distribution of inclusions at different step is shown in Fig. 2, where the low melting region surrounded by solid line in the ternary phase diagram was obtained by FactSage 6.2 at 1 873 K. At LF End, inclusions were mainly calcium aluminates and calcium magnesium aluminates, of which a small amount had located into the low melting point area as shown in Fig.…”

Formation and Evolution of Non-Metallic Inclusions during Deoxidation by Al Addition in BOF Crude Steel

“…Smaller, fewer and uniform‐distributed inclusions are advantage for its quality. In order to improve the cleanliness of steel grades, numerous investigations have been carried out to study the control of the inclusions in the past few decades, and most of them focused on the source, their evolution, and the removal of inclusions …”