Modelling of void healing in hot rolling due to recrystallization

Abstract

Porosities, introduced into the material during continuous casting can impair the mechanical properties and performance of semi-finished material as well as final products. Healing of these porosities through closure and bonding of voids with subsequent dissolution of the interface in further hot working can reduce this detrimental effect. While large deformations under compressive stresses as well as high temperatures are beneficial for void healing, not all regions in the workpiece experience the same conditions. Gradients of these metrics in normal direction and over time create regions of varying probability for void healing. Knowledge on the process conditions and the void shapes in the respective regions is essential to predict void healing successfully and to produce a sound product, especially if the process window is limited. In the present work, a multiscale modelling approach is utilized to predict void closure and recrystallization along the normal direction in the roll gap. A practical void healing criterion is developed by combining these two mechanisms and then used to classify a typical workpiece in normal direction according to the likelihood of void healing. Optimal void healing conditions are found at a relative height of 80% while the center region (50%) of the workpiece exhibits the least favorable conditions for void healing.