Patent ID: 6764528
Filing Date: 2004-07-20
Classification: C21C,C22C

Abstract:
A method of producing a high nitrogen, ultra low carbon steel of preparing a rolling material for use in ultra low carbon steel sheets at: C&lE;0.0060 mass %, characterized byapplying primary decarburization refining to molten iron from a blast furnace and controlling composition in the molten steel after the primary decarburization refining into a range satisfying the following relation (1), then, conducting secondary decarburization refining to a ultra low carbon concentration region at: C&lE;0.0050 mass % so as to satisfy the following relation (2) in a vacuum degassing facility, subsequently applying deoxidation by Al so as to provide: Al&gE;0.005 mass % after deoxidation and controlling the composition such that the Al concentration and the N concentration satisfy the following relation (3), and the N concentration satisfies N: 0.0050 to 0.0250 mass %, and the following relation (4) or N&gE;0.0120 mass %, and successively casting the composition-controlled molten steel continuously: Note:[mass % N]âˆ’0.15[mass % C]&gE;0.0060â€ƒâ€ƒ(1) &Dgr;N/&Dgr;C&lE;0.15â€ƒâ€ƒ(2) in which&Dgr;N: reduction amount of the N concentration in steel in secondary decarburization refining (mass %) &Dgr;C: reduction amount of the C concentration in steel in secondary decarburization refining (mass %) [mass % Al]Â·[mass % N]&lE;0.0004â€ƒâ€ƒ(3) [mass % N]&gE;0.0030+14/27[mass % Al]+14/93[mass % Nb]+14/11[mass % B]+14/48[mass % Ti]â€ƒâ€ƒ(4), providing that[mass % Nb]=0 in steel not containing Nb [mass % B]=0 in steel not containing B [mass % Ti]=0 in steel not containing Ti.