METHOD FOR CONTROLLING SOLIDIFICATION SEGREGATION OF CONTINUOUS CASTING STEEL INGOT

摘要

PURPOSE:To control effectively solidification segregation, more particularly the overlap segregation among trees in the stage of solidification and to obtain a product having good quality in continuous casting of a carbon steel having a specific value or below of C concn. by adding a prescribed ratio of Mo into the molten steel. CONSTITUTION:Mo is added at =2wt% into the carbon steel contg. =0.53wt%C in continuous casting of said carbon steel. The delta phase (=alpha phase) region in the phase diagram of the carbon steel is thereby expanded. In general, the diffusion speed of the impurities or additive element in solid iron is 10-100 times larger in the delta phase than in the alpha phase. The diffusion speed from the segregated part of a high concn. to the low concn. part at the periphery increases correspondingly and the solidification can be decreased when the quantity and presence time of the delta phase increases in the solidification process of the steel. The delta phase region in the dendrite part increases when the alpha stabilizing element such as P is added to the steel. As a result the co-existence region of the delta phase and alpha phase increases and the sepn. of the alpha, gamma (e.g., Mn) stabilizing elements is accelerated, by which the overlap segregation among trees is decreased.