Analysis Of Centreline Segregation ( Cls ) Essay - 2348 Words

1. Introduction The World Steel Association reported this year that nearly 1.6 billion tonnes of steel was continuously cast (CC) in 2014, which accounted for 96% of the world’s overall steel output [WOR15]. In light of the prolific use of continuous casting, it is necessary to address and innovate upon the issues inherent to the process. Centreline segregation (CLS) has been touted as one of the most notorious defects in CC steel for over 30 years, especially where finely-tuned alloys are concerned (i.e. microalloyed steels) [AYA84]. CLS, in short, describes the appearance of higher concentrations of alloying elements at the center of a CC piece of steel as compared to the nominal composition. All elements are susceptible to CLS, though some, such as Sulphur, Phosphorous, Carbon, and Manganese have a much higher propensity to segregate [IRV93]. Conceptually, CLS is quite a simple phenomenon; solute elements, which in this case consist of alloying elements (e.g. Manganese and Carbon) or impur ities (e.g. Sulphur and Phosphorous) are more soluble in liquid phases than solid phases of similar temperatures; this is known as solute rejection. The difference in solubility causes the solute atoms to be pushed away from solidification fronts within the steel. For CC steel, solidification begins on the outer surface of the structure being cast, leading to solidification fronts that move from the outside surface of the steel to the inside. The outside-to-inside movement of the