Abstract: Addressing the chronic problem of poor toughness of conventional non-quenched and tempered steel tubes, technological measures are taken to improve both strength and toughness of the tube, including adding micro-alloying elements into medium carbon-manganese steel and properly controlling of rolling and cooling processes in order to segregate strengthened and fine grains. As a result, the properties of the said tube is close to or even equal to the level of the quenched and tempered tube, having satisfied the requirement that large-sized non-quenched and tempered oil casing has to be in possession of adequate toughness corresponding to its high strength.