PRODUCTION OF HIGH-TOUGHNESS STEEL MATERIAL

摘要

PURPOSE:To enable production of a steel material having excellent toughness with less energy consumption and higher productivity in the case of utilizing the heat retained by a continuous casting billet of a steel in hot rolling said billet by adjusting the content of P in the compsn. of the continuous casting billet to a specific value or below. CONSTITUTION:The compsn. of a steel shifts from a gamma phase to an alpha phase just once during the stage of hot rolling a continuous casting billet in the stage of casting continuously the molten steel, then cutting the continuous casting billet and hot rolling the cut billet by utilizing the heat retained by the same. The amt. of segregation at the grain boundary of P is therefore large and the toughness as material quality is extremely inferior. The content of P in the molten steel is adjusted to <=0.009% in order to prevent such segregation and the billet is hardened after hot rolling so as to pass just once the point at which >=60% of the cross section of the billet is transformed from the gamma phase to the alpha phase during hot rolling. The rolled material having excellent toughness is obtd. with highly economized energy and high productivity by making use of the quantity of the heat that the continuously cast billet itself possesses.