Continuous casting is a mature, sophisticated technological process, used to produce most of the world’s steel, so is worthy of fundamentally-based computational modeling. It involves many interacting phenomena including heat transfer, solidification, multiphase turbulent flow, clogging, electromagnetic effects, complex interfacial behavior, particle entrapment, thermal-mechanical distortion, stress, cracks, segregation, and microstructure formation. Furthermore, these phenomena are transient, three-dimensional, and operate over wide length and time scales. This paper reviews the current state of the art in modeling these phenomena, focusing on practical applications to the formation of defects. It emphasizes model verification and validation of model predictions. The models reviewed range from fast and simple for implementation into online model-based control systems to sophisticated multiphysics simulations that incorporate many coupled phenomena. Both the accomplishments and remaining challenges are discussed.

Review on Modeling and Simulation of Continuous Casting

A coupled three-dimensional model, including Large Eddy Simulation model, Lagrangian Discrete Phase Model and VOF multiphase model was developed to investigate the transient two-phase flow and bubble distribution in continuous casting strand. A two-way coupling model including the effect of the drag force, lift force, virtual mass force and pressure gradient force was adopted.
 The lift force was added via user defined function. A Rosin–Rammler bubble size distribution base on the water model was employed. The results show that the effect of the lift force cannot be ignored during the calculation of the steel and argon gas two-phase flow. Only the bubbles smaller than 2 mm would be brought to near the narrow face. With the increase of the argon flow rate, the transformation of the flow pattern from the double roll to complex flow and single roll was successfully predicted.

Numerical Simulation of Steel and Argon Gas Two-Phase Flow in Continuous Casting Using LES + VOF + DPM Model

Viscosity and structure evolution of CaO–SiO2-based mold fluxes with involvement of CaO–Al2O3-based tundish fluxes

Gas injection through the submerged entry nozzle (SEN) into the continuous casting mold can be an effective approach for preventing SEN clogging and promoting the floatation of the non-metallic inclusions. However, sometimes the exposed slag eyes due to gas injection appear on the top surface of the liquid slag layer, resulting in heat losses, re-oxidation, and nitrogen pickup in the molten steel. An Eulerian multiphase-flow model is developed to predict the argon-steel-slag three-phase flow in a slab continuous casting mold. All the phases are treated based on Eulerian approach. The mathematical model is compared with the industrial observations and the water model experiments. Both of physical and numerical results reproduce the phenomenon of the high gas concentration at the SEN exit port. Most of the argon bubbles stay below the slag layer for quite long time because the slag blocks their floatation. Furthermore, the argon bubbles would gradually gather in a dense plume while escaping through the slag layer. Scattered argon exit spots are found at the top surface of slag layer. Two main locations of the exposed slag eye are found: 1) adjacent to the SEN; 2) at the mold’s mid-section at the position where a concentrated argon plume breaches through the slag layer. The near-SEN exposed eye occurs under any of considered conditions. The one at the mid-section is formed when the meniscus convex reaches a critical level, been dependent on the casting conditions.

Physical and Numerical Modeling of Exposed Slag Eye in Continuous Casting Mold using Euler–Euler Approach

Large Eddy Simulation on the Two-Phase Flow in a Water Model of Continuous Casting Strand with Gas Injection

Recent developments of an advanced numerical model for Continuous Casting of steel unveiled at the previous 2010 CSSCR Conference in Sapporo, Japan are presented. These include coupling of the existing multiphase, heat transfer and solidification model to argon injection for tracking bubble trajectories in the SEN, metal bulk and across the slag bed after passing through the metal surface. Hence, description of a method for adding gas injection in combination with a multiphase model for tracking metal/slag interfaces (Discrete Phase Model + Volume Of Fluid, DPM+VOF) is given. Validation is supported by tests on a revamped Continuous Casting Simulator (CCS-1) based on a low melting point alloy, which can realistically replicate the flow conditions in the caster. Metal-slag-argon flow predictions were compared to observations in the physical model showing good agreement on features such as discharging jets, rolls, standing waves and argon distribution measured through a variety of techniques such as ultrasound, electromagnetic probes and video sequences. Ultimately, the model makes possible the prediction of stable or unstable flows within the mould as a function of different argon flow-rates and bubble sizes. Application to industrial practice is an ongoing task and preliminary results are illustrated. The robustness of the model combined with direct observations in CCS-1 make possible the description of phenomena difficult to observe in the caster (e.g. argon injection and metal flow), but critical for the stability of the process and the quality of cast products.

Recent Developments of a Numerical Model for Continuous Casting of Steel: Model Theory, Setup and Comparison to Physical Modelling with Liquid Metal

Surface defects are recurrent problems during Continuous Casting of steel due to the introduction of new grades that are often difficult to cast, as well as the everlasting pursuit for higher quali ...

Key lubrication concepts to understand the role of flow, heat transfer and solidification for modelling defect formation during continuous casting

This work presents a novel modeling methodology which allows one to predict slag infiltration in a 3D slab model by coupling the slag behavior with the metal flow, heat transfer, oscillation and so 

A novel approach for coupling slag infiltration to metal flow, solidification and mold oscillation on a 3d model for continuous casting of slabs

In recent years, the addition of the slag phase to numerical models of the Continuous Casting (CC) process has opened the door to a whole new range of predictions. These include the estimation of slag infiltration and powder consumption (lubrication), heat transfer and cooling through the cooper mould (solidification) and investigating the effect of operational parameters such as mould oscillation and powder composition on surface quality / defect formation. This work presents 2D and 3D CC models capable of describing the dynamic behaviour of the liquid/solid slag in both the shell mould-gap and bed as well as its effects on heat extraction and shell formation. The present paper also illustrates the application of the model to a variety of casters and the challenges faced during its implementation. The model attained good agreement on the prediction of mould temperatures and shell thicknesses as well as slag film formation and heat flux variations during the casting sequence. The effect of different oscillation strategies (sinusoidal and non-sinusoidal) was explored in order to enhance powder consumption and surface quality. Furthermore, the modelling approach allows one to predict the conditions leading to irregular shell growth and uneven lubrication; these are responsible for defects such as, stickers, cracking and, in the worst case scenario, to breakouts. Possible mechanisms for defect formation are presented together with strategies to enhance process stability and productivity of the CC machine.

https://iopscience.iop.org/article/10.1088/1757-899X/33/1/012013/pdf

Ulf Sjöström

Papers

Recent Developments of a Numerical Model for Continuous Casting of Steel: Model Theory, Setup and Comparison to Physical Modelling with Liquid Metal

Key lubrication concepts to understand the role of flow, heat transfer and solidification for modelling defect formation during continuous casting

A novel approach for coupling slag infiltration to metal flow, solidification and mold oscillation on a 3d model for continuous casting of slabs

Industrial application of a numerical model to simulate lubrication, mould oscillation, solidification and defect formation during continuous casting