Abstract
Heavy reduction (HR) is a novel technology that could effectively improve the internal porosities and other internal quality problems in continuously cast steel, during which a large reduction deformation is implemented at and after the strand solidification end. In the present paper, non-uniform solidification of the wide-thick slab was calculated with a two-dimensional (2D) heat transfer model. Based on the predicted temperature distribution at the solidification end of the casting strand, a three-dimensional (3D) thermal-mechanical coupled model was developed for investigating the deformation behavior of the internal porosities in wide-thick slab during HR. An Arrhenius-type constitutive model for the studied steel grade was derived based on the measured true stress-strain with single-pass thermosimulation compression experiments and applied to the 3D thermal-mechanical coupled model for improving the calculation accuracy. With the developed 3D thermal-mechanical coupled model, deformation behavior of the two artificial porosities located at the slab center of 1/2 width and 1/8 width during HR was investigated under different condition of HR deformation, HR start position, and HR reduction mode. Based on the calculated porosity closure degree (ηs) and the corresponding equivalent strain (εeq) under different HR conditions, a prediction model that describes the quantitative relationship between ηs and εeq was derived for directly and accurately evaluating the process effect of HR on improving the internal porosities in wide-thick slab.
Highlights
Due to solidification shrinkage and gas entrapment, internal porosity often occurs in casting steel.As one kind of the common internal defects, it seriously influences the mechanical properties of the final products, for example, decreasing the fatigue life and the yield strength, and should be eliminated in the subsequent rolling or forging process.To provide theoretical guide for process design of rolling or forging, many investigations were carried out by previous researchers to clarify the closure mechanism of internal porosity in metal materials during the forging or rolling process
Thermal-mechanical coupled model, deformation behavior of the two artificial porosities located at the slab center of 1/2 width and 1/8 width during Heavy reduction (HR) was investigated under different condition of HR deformation, HR start position, and HR reduction mode
In order to quantitatively describe the overall deformation behavior of each artificial porosity in the 3D thermal-mechanical coupled model and evaluate the process effect of HR on improving the internal porosity, the porosity closure degree was defined based on the porosity axis length before and after HR: 2L x
Summary
Due to solidification shrinkage and gas entrapment, internal porosity often occurs in casting steel. Some theoretical and experimental investigations were carried out recently for studying the improving effect of HR on porosity and other internal defects in continuous casting bloom [28,29], billet [30], or slab [19,20,21], and some new HR technologies were proposed and applied. Based on the predicted heat transfer results by the 2D heat transfer model and the derived constitutive model for the studied steel grade during HR, a 3D thermal-mechanical coupled model, containing two artificial spheroidal porosities, respectively, located the slab center of 1/8 width (P1/8 ) and 1/2 width (P1/2 ), was established With this 3D thermal-mechanical coupled model, the deformation behavior of P1/8 and P1/2 during HR was numerically investigated under different HR conditions, including the HR deformation, HR start position, and HR mode. Based on the predicted porosity deformation results under different HR conditions and the corresponding equivalent strain (εeq ), a prediction model for the porosity closure behavior was derived to describe the quantitative relationship between the porosity closure degree (ηs ) and εeq
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