EXTREMELY LOW CARBON STEEL PLATE EXCELLENT IN SURFACE CHARACTERISTICS, WORKABILITY, AND FORMABILITY AND A METHOD OF PRODUCING EXTREMELY LOW CARBON CAST SLAB
A method of producing an extremely low carbon steel cast slab characterized by casting molten steel obtained by reducing the carbon concentration of the molten steel to 0.005 mass % or less, then adding Cu, Nb, and B to the molten steel, furthermore, and adjusting the concentration of dissolved oxygen in the molten steel to 0.01 mass % to 0.06 mass % and extremely low carbon steel plate comprised of steel containing C: 0.005 mass % or less, acid soluble Al: 0.005 mass % or less, and further Cu, Nb, and B, characterized in that the steel has fine oxides of a diameter of 0.5 μm to 30 μm dispersed in it in an amount of 1000 particles/cm 2 to 1,000,000 particles/cm 2 .
1 . A method of producing an extremely low carbon steel cast slab characterized by casting molten steel obtained by reducing the carbon concentration of the molten steel to 0.005 mass % or less, then adding Cu, Nb, and B to the molten steel without adding Al, furthermore, and adjusting the concentration of dissolved oxygen in the molten steel to 0.01 mass % to 0.06 mass %.
2 . A method of producing an extremely low carbon steel cast slab characterized by casting molten steel obtained by reducing the carbon concentration of the molten steel to 0.005 mass % or less, then adding Cu, Nb, and B to the molten steel to make the molten steel include Cu by 0.01 to 3.0 mass % and Nb and B by respectively
−0.02≦Nb-(93/12)×C≦0.1
−0.0023≦B-(11/14)×N≦0.0045
and further adjusting the concentration of dissolved oxygen in the molten steel to 0.01 mass % to 0.06 mass %.
3 . A method of producing an extremely low carbon steel cast slab characterized by casting molten steel obtained by reducing the carbon concentration of the molten steel to 0.005 mass % or less, adding Cu, Ni, Nb, and B to the molten steel to make the molten steel include Cu by 0.01 to 3.0 mass %, Ni by 0.5×Cu concentration or less, and Nb and B by respectively
−0.02≦Nb-(93/12)×C≦0.1
−0.0023≦B-(11/14)×N≦0.0045
and further adjusting the concentration of dissolved oxygen in the molten steel to 0.01 mass % to 0.06 mass %.
4 . A method of producing an extremely low carbon steel cast slab according to any one of claims 1 to 3 characterized by decarburizing said molten steel by vacuum degassing.
5 . A method of producing an extremely low carbon steel cast slab according to any one of claims 1 to 3 characterized by casting said molten steel by casting it while electromagnetically stirring it.
6 . A method of producing an extremely low carbon steel cast slab according to claim 5 characterized by casting said molten steel by casting it while electromagnetically stirring it to make the molten steel at the meniscus position swirl by an average flow rate of 40 cm/s to 100 cm/s.
7 - 13 . (canceled)