INFLUENCE OF CASTING SPEED ON CENTERLINE POROSITY FORMATION IN CONTINUOUSLY CAST ROUND STEEL BILLETS

During continuous casting of steel, a centerline porosity formation frequently occurs and participates on decrease of internal quality of continuously cast billets. To avoid the centerline porosity formation, a description of casting parameters connection with centerline porosity is necessary. This paper is focused on study of casting speed influence on centerline porosity formation in continuously cast round steel billets through a numerical modelling. Centerline porosity formation is closely related with solidification of billet which can be affected by casting speed change. Usually, in real conditions, the change of casting speed includes a change of cooling conditions both in primary and secondary zone. For determination of influence of technological parameter on observed quantitative parameters of billet, only casting speed was changed during numerical modelling while keeping cooling intensity. With relation of casting speed changes, the attention was paid also on metallurgical length which effects centerline porosity formation. Metallurgical length shortening should lead to reduction of centerline porosity formation. In accordance with literature knowledge, the increasing of fraction solid due to decreasing of casting speed was confirmed. Fraction solid increasing was caused by increase of time which billet spent in cooling zones. Mentioned fact affected positively metallurgical length shortening. Centerline porosity was evaluated by liquid pressure in centerline region of billet. The porosity formation can be assumed at zero liquid pressure in centerline region. It was found out that with decrease of casting speed, the liquid pressure in centerline region increased. Thus, occurrence of centerline porosity decreases with decrease of casting speed.