Abstract: A method of producing a high nitrogen, ultra low carbon steel suitable to rolling material for use in cold rolled steel sheets having excellent age hardening property by an age hardening treatment after forming by working, with no defects in slabs or steel sheets, reliably, at a reduced cost and with a high productivity is proposed. The method for producing a rolling material for use in ultra low carbon steel sheets at: C≦0.0050 mass % comprises; applying primary decarburization refining to molten iron from a blast furnace, then controlling the composition in the molten steel after primary decarburization refining to a range satisfying the following relation: [mass % N]−0.15[mass % C]≧0.0060,  subsequently conducting secondary decarburization refining to a ultra low carbon concentration region while suppressing denitridation using a vacuum degassing facility, then conducting deoxidation by Al and, further, controlling the composition.

Abstract: A method of producing a high nitrogen, ultra low carbon steel suitable to rolling material for use in cold rolled steel sheets having excellent age hardening property by an age hardening treatment after forming by working, with no defects in slabs or steel sheets, reliably, at a reduced cost and with a high productivity is proposed.

Abstract: An apparatus for removing non-metallic foreign matter in a molten steel includes a tundish and a coil device. The tundish is an intermediate container receiving the molten steel from a ladle and feeding a purified molten steel by removing the non-metallic foreign matter in the molten steel. For removing the non-metallic foreign matter, the tundish has a swirl flow bath and a floatation bath. In the circumference of the swirl flow bath of the tundish, a coil device is arranged for flowing the molten steel in the swirl flow bath in swirl fashion. The tundish and the coil device are formed separately and constructed for relative movement to each other. The molten steel in the swirl flow bath of the tundish is flown in swirl fashion in the horizontal direction by a magnetic field generated by the coil device. At this time, the molten steel forms a parabolic concaved surface.

Abstract: A method and apparatus is provided for stabilizing the molten metal surface in a mold. The invention is used to improve the quality of the casting slab by modifying a controlling parameter according to the detected slab drawing speed and the actual nozzle flowing characteristics calculated by the measured molten metal surface level and the nozzle opening degree.