Original Article

Fluid flow, slag entrainment, and composition evolution of slag inclusions during vacuum degassing refining

School of Mechanical and Materials Engineering, North China University of Technology, Beijing 100144, PR China

^* e-mail: zhanglifeng@ncut.edu.cn

Received: 4 June 2024
Accepted: 24 September 2024

Abstract

A multiphase mathematical model was established to study the fluid flow, the open-eye formation, and the residence time of slag inclusions in a bottom argon-blowing ladle. The fluid flow was solved using the Eulerian-Lagrangian multiphase approach, and the interface between different phases was described using the Volume of Fluid (VOF) model. The motion of argon bubbles and slag inclusions was tracked with the method of the discrete phase model (DPM). Moreover, the composition transformation of slag inclusions was predicted by employing a kinetic model based on the coupled reactions model. Numerical results show that the flow of the molten steel and the open-eye of the molten slag were sensitive to the argon blowing rate. The larger argon blowing rate expanded the volume of the plume and the area of the open-eye. Slag droplets were considered to move with the steel to the region away from the open-eye and then entrained into the steel to form slag inclusions as there was barely any downward velocity around the open-eye. Most slag inclusions were able to be removed immediately after the entrainment, while there still were some slag inclusions retaining in the steel for as long as thousands of seconds. The composition of slag inclusions had an apparent transformation due to reactions with the steel. The content of SiO₂ and MgO in slag inclusions had a decrease while that of Al₂O₃ rose remarkably. The variation of SiO₂ content occurred in the early one minute and the MgO content reduced gradually from 7.34wt% to 1.12wt% in 10 min. The composition transformation of slag inclusions was basically completed within 10 min in the current case.