The influence of S and (Mn/S) on the crack susceptibility of continuous casting steels was studied. It is theoretically demonstrated that there is a critical value of the (Mn/S) ratio, (Mn/S)c, under which a high susceptibility to cracking, during casting or deformation of as‐cast material, is expected. The value of (Mn/S)c increases as the S content of the steel decreases. Based on literature data and results from rolling continuous casting billets the following experimental equation has been found: (Mn/S)c = 1.345 · S−0.7934. A high similarity between this experimental equation and the theoretical one is achieved. A comparison between the equation found and previous expressions from literature was carried out. The MSC index as the ratio between the (Mn/S) ratio of a steel and the corresponding critical one was defined. The MSC index is a useful tool for the analysis of experimental results from literature.

Resumen La instalación de agitadores electromagnéticos en las máquinas de colada continua del acero ha mejorado notablemente la calidad interna del producto colado. En este trabajo se describen los ensayos efectuados con bobinas agitadoras situadas en diferentes lugares en máquinas de colada continua de palanquilla. Se ha puesto de manifiesto que la bobina situada en el molde, al comienzo del proceso de solidificación, es la que produce una mayor modificación de la estructura de solidificación junto con una disminución de la segregación central de la palanquilla. Se ha diseñado una bobina para el molde que permite utilizar altas potencias de agitación sin que el movimiento del acero líqui-do, a la altura del menisco, produzca atrapes de los polvos de colada. Por otro lado, se ha encontrado un método por el que se puede calcular la frecuencia eléctrica óptima de trabajo de la bobina situada en el molde.Palabras clave: Colada continua. Acero. Agitación electromagnética. Calidad central. Segregación central. Electromagnetic stirring in the continuous casting of steel AbstractThe electromagnetic stirring of steel in the machines for the continuous casting process has improved the intemal quality of the cast product. Experimental work with stirrers situated at different positions of continuous casting machines of billets has been carried out. The in-mould stirrer is the one that produces a major modification of the billet intemal structure, and also the biggest decrease of the central segregation. An in-mould electromagnetic coil has been developed which allows the use of high stirring power without producing an undesirable movement of the liquid steel in the meniscus zone, therefore no mould powders entrapments are produced. It has been developed a method for determining the optimum electric frequency of the stirrer.

The influence of carbon content and alloying elements on the central billet quality of continuous casting has been studied. In plain carbon steels the higher central equiaxed zone (CEZ) value (the area, expressed as a percentage, of equiaxed crystals) is obtained for medium carbon content. For lower and higher carbon contents, this value becomes smaller. However, the decrease is more pronounced in the latter situation than in the former and it is associated with a deterioration of the central quality of the billet. A difference in the CEZ behaviour wasfound between plain carbon steel and low alloy steels. This difference can be explained by the modification that alloying elements produce in the percentage of material that transforms from {)-ferrite into austenite during the peritectic reaction.MSTj796

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