The effect of continuous casting conditions on the mechanical properties of low-carbon steel wire rods

Solidification plays a fundamental role in metallurgical processes, such as continuous casting of steel billets, as it greatly influences the final microstructure, in terms of chemical segregation, grains morphology and size. Segregation of solute elements occurs because of their partitioning between the liquid and the growing solid. The liquid interdendritic regions are enriched of solute elements rejected by the growing dendrites. Such segregation cannot be fully mitigated through subsequent hot rolling processes. Common evidence of this undesirable phenomenon is the banded microstructure observed in hot-rolled products, characterized by alternating longitudinal bands of ferrite and pearlite. Normalization can reduce the banded microstructure, but micro-segregation remains difficult to completely homogenize. Therefore, hot-rolled wire rods produced from steel billets solidified under different conditions exhibit varying mechanical properties. In this context, the study presents a comparative analysis of two low-carbon steel billets with similar chemical composition but produced under different casting conditions with two different casting machines. The analysis investigated the differences in macro and micro-structure of the two billets by measuring the secondary dendrite arm spacing (SDAS) and the segregation index. The mechanical properties of wire rods derived from the billets were assessed by tensile tests and micro-hardness Vickers measurements. The microstructures (of billets and wire rods) were analyzed by optical and scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS).