P. Gardin

Visualization of Liquid Metal Two-phase Flows in a Physical Model of the Continuous Casting Process of Steel

We present an experimental study concerned with investigations of the two-phase flow in a mock-up of the continuous casting process of steel. A specific experimental facility was designed and constructed at HZDR for visualizing liquid metal two-phase flows in the mold and the submerged entry nozzle (SEN) by means of X-ray radioscopy. This setup operates with the low melting, eutectic alloy GaInSn as model liquid. The argon gas is injected through the tip of the stopper rod into the liquid metal flow. The system operates continuously under isothermal conditions. First results will be presented here revealing complex flow structures in the SEN widely differing from a homogeneously dispersed bubbly flow. The patterns are mainly dominated by large bubbles and large-area detachments of the liquid metal flow from the inner nozzle wall. Various flow regimes can be distinguished depending on the ratio between the liquid and the gas flow rate. Smaller gas bubbles are produced by strong shear flows near the nozzle ports. The small bubbles are entrained by the submerged jet and mainly entrapped by the lower circulation roll in the mold. Larger bubbles develop by coalescence and ascend toward the free surface.

Toward a Full Simulation of the Basic Oxygen Furnace: Deformation of the Bath Free Surface and Coupled Transfer Processes Associated with the Post-Combustion in the Gas Region

The present article treats different phenomena taking place in a steelmaking converter through the development of two separate models. The first model describes the cavity produced at the free surface of the metal bath by the high-speed impinging oxygen jet. The model is based on a zonal approach, where gas compressibility effects are taken into account only in the high velocity jet region, while elsewhere the gas is treated as incompressible. The volume of fluid (VOF) method is employed to follow the deformation of the bath free surface. Calculations are presented for two- and three-phase systems and compared against experimental data obtained in a cold model experiment presented in the literature. The influence on the size and shape of the cavity of various parameters and models (including the jet inlet boundary conditions, the VOF advection scheme, and the turbulence model) is studied. Next, the model is used to simulate the interaction of a supersonic oxygen jet with the surface of a liquid steel bath in a pilot-scale converter. The second model concentrates on fluid flow, heat transfer, and the post-combustion reaction in the gas phase above the metal bath. The model uses the simple chemical reaction scheme approach to describe the transport of the chemical species and takes into account the consumption of oxygen by the bath and thermal radiative transfer. The model predictions are in reasonable agreement with measurements collected in a laboratory experiment and in a pilot-scale furnace.

Theoretical evaluation of influence of convective heat transfer and original sample size on shell melting time during Ti dissolution in secondary steelmaking

Abstract The dissolution of Ti additions in liquid steel during secondary steelmaking occurs in a two step process. In the first step, a steel shell solidifies around the initial cold addition, whereas in the second step, after this shell has remelted, the Ti dissolves directly in the steel bath. The initial presence of this steel shell modifies the position of dissolution and influences the local concentration and thus the inclusion formation. Further complications arise from the fact that part of the Ti will dissolve while enclosed by the steel shell, altering the alloy composition first released in the ladle and effectively shortening the subsequent free dissolution period. The duration of the steel shell period and the fraction of predissolved Ti have been investigated using a conservative one-dimensional sharp interface model solving the coupled heat and mass transfer in a cylindrical shell/addition composite. The influence of the convection conditions and the original Ti radius was evaluated in a parametric study. A pronounced effect of the convective heat transfer on the shell melting time was found. It is thus concluded that the dissolution behaviour is strongly dependent on the local flow conditions, which is determined by factors such as stirring conditions and addition characteristics.

Experimental Evaluation of the Dissolution Rates of Ti and FeTi70 in Liquid Fe

During secondary steelmaking, improving alloy yield and engineering inclusion content require understanding and quantification of the alloy distribution in the melt. When additions are dropped in the melt, a steel shell solidifies around them. After this shell has melted, the alloy is spread in the melt. The influence of process parameters on the duration of the shell period for Ti and FeTi70 additions has been experimentally evaluated. For Ti, the melt temperature and the initial addition size were varied and for FeTi70, only the melt temperature was varied. By continuously measuring the apparent weight of submerged samples with a load cell, the shell period and the amount of molten alloy within the shell were determined. The shell period increases at lower superheats and for larger sample sizes. For a certain size of Ti additions, the molten content within the shell increases with increasing shell period. The importance of this period, relative to the total dissolution time, increases at lower superheats. All investigated FeTi70 samples may melt completely within the shell. While the shell period lasts longer for FeTi70 than for the corresponding Ti samples, this fast internal melting yields a net reduction in total dissolution time.

Experimental and Numerical Simulation of the Mould Region of a Steel Continuous Caster

A finite volume numerical model was developed to determine the fluid flow patterns and investigate the transient behaviour of the slag/steel (oil/water) interface using a water model configuration. This model includes a Lagrangian representation of argon bubble tracks and their influence on the flowfield (due to buoyancy) and on surface behaviour. In the process of validation between the multi‐phase model and the LDA experimental measurements several explanations are provided for the different observed phenomena and their influence on the Continuous Casting of steel. As a next aim in the project, the heat transfer between slag and steel in an industrial configuration is studied. These multi‐phase interactions involve the melting of the flux powder and the formation of the slag layer.