Extremely Low Carbon Steel Plate Excellent in Surface Characteristics, Workability, and Formability and a Method of Producing Extremely Low Carbon Cast Slab

Abstract

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, 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
   −0.021≦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≦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  claim 1  characterized by decarburizing said molten steel by vacuum degassing. 
     
     
         5 . A method of producing an extremely low carbon steel cast slab according to  claim 1  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 . Extremely low carbon steel plate having excellent surface characteristics, workability, and formability 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 . 
     
     
         8 . Extremely low carbon steel plate having excellent surface characteristics, workability, and formability comprised of steel containing C: 0.005 mass % or less, acid soluble Al: 0.005 mass % or less, Cu: 0.01 to 3.0 mass %, and further Nb and B of respectively
   −0.02≦Nb−(93/12)×C≦0.1     −0.0023≦B−(11/14)×C≦0.0045   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 .   
     
     
         9 . Extremely low carbon steel plate having excellent surface characteristics, workability, and formability comprised of steel containing C: 0.005 mass % or less, acid soluble Al: 0.005 mass % or less, Cu: 0.01 to 3.0 mass %, Ni: 0.5×Cu mass % or less, and further Nb and B of respectively
   −0.02≦Nb−(93/12)×C≦0.1     −0.0023≦B−(11/14)×N≦0.0045   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 .   
     
     
         10 . Extremely low carbon steel plate having excellent surface characteristics, workability, and formability 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 at least 40% of the number of oxides present in the steel include at least Si, Mn, and Fe. 
     
     
         11 . Extremely low carbon steel plate having excellent surface characteristics, workability, and formability comprised of steel containing C: 0.005 mass % or less, acid soluble Al: 0.005 mass % or less, Cu: 0.01 to 3.0 mass %, and further Nb and B of respectively
   −0.02≦Nb−(93/12)×C≦0.1     −0.0023≦B−(11/14)×N≦0.0045   characterized in that at least 40% of the number of oxides present in the steel include at least Si, Mn, and Fe.   
     
     
         12 . Extremely low carbon steel plate having excellent surface characteristics, workability, and formability comprised of steel containing C: 0.005 mass % or less, acid soluble Al: 0.005 mass % or less, Cu: 0.01 to 3.0 mass %, Ni: 0.5×Cu mass % or less, and further Nb and B of respectively
   −0.02≦Nb−(93/12)×C≦0.1     −0.0023≦B−(11/14)×C≦0.0045   characterized in that at least 40% of the number of oxides present in the steel include at least Si, Mn, and Fe.   
     
     
         13 . An extremely low carbon steel plate having excellent surface characteristics, workability, and formability according to  claim 10  characterized in that the contents of the at least Si oxides, Mn oxides, and Fe oxides which at least 40% of the number of oxides present in the steel include is 20 mass % or more.