Control of the dendritic structure of the initial frozen shell in continuous casting

The industrial trials performed by SIDENOR I+D in this project aimed to find a mould geometry that improves the quality of the as cast product, validating the numerical models developed to describe the solidification of the steel inside the continuous casting mould. The mould geometries considered were: - CONVENTIONAL GEOMETRY: ' 185 mm sq. ' 800 mm length. ' 10 mm corner radius. ' No face bulging. - NEW GEOMETRY I: ' 185 mm sq. ' 800 mm length. ' 40 mm corner radius. ' 3 mm face bulging. - NEW GEOMETRY II: ' 185 mm sq. ' 800 mm length. ' 40 mm corner radius. ' 5 mm face bulging. The moulds with these geometries were tested in real production conditions to study the influence of the geometry both in the billets and in the rolled product. The conventional mould shape was assessed by means of an statistical survey of billet and rolled products defects in order to have a quality reference for the trials with the new mould geometries. An strong influence between the network cracks and the presence of molybdenum was found. Another observation was that a large number of the defects at the surface of the rolled bars have their origin in the as-cast billet (72% with Mo, 88% without Mo). Experimental ingots as first approximation to the possible results obtained in continuous casting were cast. After the acid etching the solidification structure was studied. Total absence of off-corner cracks and depressions near the corners, no matter the geometry, and the same solidification structure for all the geometries within each quality group was found. With regard to the hot ductility of the off-corner area, high scattering for each steel grade no matter the geometry.