Development of solidification microstructures in continuously cast billets of boron and resulphurised steel grades

Abstract

The continuous casting process equipped by electromagnetic stirrer has been simulated through thermal model in order to identify the growing velocity of the solid front, the thermal gradient and the undercooling featuring the solidification process. The results of the model obtained after imposing the measured boundary condition allowed to describe the solidification process identifying the thermal gradient of the solid front and its velocity of growth. The main parameters featuring the solidification structure have been measured: primary dendrite arm spacings (PDAS), secondary dendrite arm spacings (SDAS) and the extension of the columnar zone, the columnar equiaxed zone and the equiaxed one. The results obtained by the computational activity and by the experimental trial have been combined to determine the condition for the columnar equiaxic transition, to estimate the nucleation and the constitutional undercooling interesting solid liquid system, the relation among the PDAS, the thermal gradient and the growth velocity of the solid front and to improve the relation between the SDAS and the solidification time through the inclusion of the effects produced by the main alloying elements contained within the steel. The performed analysis has permitted to characterise the solidification process of the studied steels and effects produced on their microstructure by the particular configuration of the continuous casting plant which has been considered.