Key Lubrication Concepts to Understand the Role of Flow, Heat Transfer and Solidification for Modelling Defect Formation during Continuous Casting

Abstract

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 quality and improved yield. Accordingly, numerical modelling has become a ubiquitous tool to analyse the formation mechanisms of such defects. However, industrial application of simulations is often hampered by oversimplifications and omissions of important process details such as variations in material properties, specific casting practices or shortcomings regarding fundamental metallurgical concepts. The present manuscript seeks to create awareness on these issues by visiting key notions such as slag infiltration, interfacial resistance and Lubrication Index. This is done from a conceptual point of view based on industrial observations and numerical modelling experiences. The latter allows a re-formulation of outdated concepts and misconceptions regarding the influence of fluid flow, heat transfer and solidification on lubrication and defect formation. Additionally, the manuscript addresses common challenges and constraints that occur during industrial implementation of numerical models such as the lack of high-temperature material data for slags. Finally, the manuscript provides examples of improvements on product quality and process stability that can be achieved through a holistic approach which combines modelling with laboratory tests, experiences from operators and direct plant measurements.KEY WORDS: numerical modelling; Continuous Casting; defects; lubrication; powder consumption.introduced as an alternative to study such issues in a more cost-efficient way than using traditional trial-error tests in the plant. Starting in the late 70's and 80's with the advent of personal computers, the first generation of models managed to predict the overall behaviour of the caster based on empirical data. 5-7) Subsequently, models in the 90's added Computational Fluid Dynamics (CFD) and solidification to casting simulations. [8][9][10] Faster computers and improved codes allowed huge progress regarding multi-phase applications (e.g. bubbles and inclusions) combined with calculations of flow and solidification in the past decade. 11-14)Currently, a wide variety of commercial and in-house codes are available for CC modelling such as PROCAST, COMSOL, TEMPSIMU, CON1D/2D, etc. [15][16][17] Moreover, a recent trend is the development of thermo-mechanical models coupled to flow dynamics for solving the combined problem of flow, solidification and stress-strain during casting. 18,19) Of all these, PHYSICA and THERCAST are two of the most promising approaches; which allow: a) 3D unstructured -mesh, multi-physics model using a combina-

Norton-Hoff model for deformation of growing solid shell of thin slab casting in funnel-shape mold

“…In the continuous casting (CC), the defects are formed and accumulated under the mechanical strain during the casting process and can result in a breakout due to the variation of the alloy properties. The course of the initial solidification in the CC mold, the interaction of the growing shell with the turbulent melt flow and its behavior during a withdrawal are one of the key features for the final product quality in the CC process [2][3][4][5][6].…”

“…The extended reviews on the methodology and practical applications of the numerical modeling of the continuous casting are presented throughout two decades starting from early two-thousands by Thomas [7] and Atkinson [8] and supplemented by recent works by many researchers [2,4,5,[9][10][11].…”

Dynamic Distributions of Mold Flux and Air Gap in Slab Continuous Casting Mold

“…24) However, the distributions of the heat transfer media infilling the shell/mold gap and the 3-D contact behavior between mold and slab were partly or seldom involved which may greatly affect the simulated results in modelling the slab defect formation such as surface cracks and off-corner depression. 25) In order to describe the distribution characteristics of the mold flux films which include the liquid and solid flux film layers, and the formation process of air gap under the complex slab continuous casting conditions, a three dimensional finite element model coupling with an interfacial heat transfer model, in which the dynamic distributions of the mold flux film and air gap were considered, was developed in the present work. Based on these, the shell deformation and the temperature evolution of shell, as well as the non-uniform distributions of mold flux films and air gap formation during a peritectic steel solidifying in 2 200 mm × 300 mm mold were predicted.…”

On Modelling Parasitic Solidification Due to Heat Loss at Submerged Entry Nozzle Region of Continuous Casting Mold

“…Both experimental work and advanced model development have been the topics of recent research [44][45][46][47][48]. Lopez et al [49] addressed slag infiltration, interfacial resistance, and a lubrication index in aiming to re-formulate outdated quality concepts.…”