Modelling of Solidification Microstructure in Continuously Cast Steel Billets from the Delta Steel Company Using Finite Element Analysis

This study develops a finite element model of solidification microstructure evolution in continuously cast steel billets produced at the Delta Steel Company, Ovwian-Aladja, Delta State, to investigate the relationship between casting parameters and billet internal quality. Continuous casting is the primary route for billet production in Nigeria's steel industry, and microstructural defects including centreline segregation, porosity, and hot tears are linked to process parameter inconsistencies that degrade downstream product properties. A coupled thermal-microstructural model is developed in ABAQUS, incorporating heat transfer analysis with temperature-dependent thermal properties, latent heat evolution, and a columnar-to-equiaxed transition (CET) criterion based on nucleation and growth kinetics. Model inputs include casting speed, mould cooling water flow rate, secondary cooling spray pattern, and superheat, based on operational data collected from Delta Steel Company. The model is validated against thermocouple measurements taken in a trial casting campaign and post-cast billet macro-etch examination. Parametric studies are conducted by varying superheat (15 to 45 degrees Celsius) and casting speed (1.8 to 2.8 m/min). Findings reveal that superheat reduction from 40 to 20 degrees Celsius combined with a casting speed reduction of 0.2 m/min produces a 30 percent increase in equiaxed zone fraction and measurable reduction in centreline segregation index. Keywords: continuous casting, solidification, finite element model, billet, Delta Steel.