Finite Element Analysis on Inclusion Migration during Hot-Rolling Process of Ultralow Carbon Steel

Abstract

Slivers on the surface of rolled plates, which are serious defects for interstitial-free (IF) steel, occur mainly as a result of inclusions in continuous casting (CC) slabs. It is, therefore, important to study inclusions in CC slabs in terms of their migration towards the surface during hot rolling. To investigate inclusion migration during the hot rolling of ultralow carbon steel, a 3D numerical model was constructed using the finite element method. The positions of the inclusions in the surface layer of an IF steel slab (50 mm) were tracked during hot rolling using a node-tracking method. Furthermore, the study analyzed the effects of scarfing on inclusion migration during hot rolling and inclusion distribution in a hot-rolled plate. During the hot-rolling process, inclusions in the wide faces of the intermediate slab gradually migrated to the surface of the intermediate slab. Owing to a thickness reduction, accumulation areas of inclusions were finally generated at the edge of the hot-rolled plate; these areas may lead to sliver defects. The scarfing of the slab did not affect the distribution of inclusions in the hot-rolled plate; however, it may have reduced the inclusion content in the outermost layers of the hot-rolled plate. The inclusions were mainly located within 1 mm underneath the hot-rolled plate. Moreover, the inclusions near the inner arc of the CC slab were concentrated within 1.5 mm of the upper plate surface. Using galvanostatic electrolysis, the number of large inclusions in samples prepared from a hot-rolled plate obtained from a plant was measured. The measurements agreed well with the numerical model predictions, which validated the FE model in the current work.