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Extremely low carbon steel plate excellent in surface characteristics, workability, and formability and a method of producing extremely low carbon cast slab
Inactive Publication Date: 2012-10-18
NIPPON STEEL & SUMITOMO METAL CORP
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[0008]Considering these problems, the present invention has as its object to provide extremely low carbon steel plate reliably preventing surface defects and superior in workability and formability by finely dispersing oxides at the time of solidification without forming almost any inclusions in the molten steel and a method of production of the same.
[0024]According to the present invention, oxides can be made to finely precipitate in the molten steel at the time of solidification without causing formation of almost any inclusions, so it is possible to reliably prevent surface defects and fix the C and N in the steel plate and possible to control the texture of the hot rolled steel plate, so it is possible to produce a thin-gauge steel plate excellent in workability and formability.
Problems solved by technology
However, with the method of removing alumina-based inclusions as described in Japanese Patent Publication (A) No. 5-104219 and Japanese Patent Publication (A) No. 63-149057, it is extremely difficult to reduce the alumina-based inclusions formed in a large amount in extremely low carbon molten steel, to an extent not forming surface defects.
Further, with the Mg deoxidation not forming any alumina-based inclusions at all such as described in Japanese Patent Publication (A) No. 5-302112, the vapor pressure of the Mg is high and the yield to molten steel is extremely low, so deoxidizing molten steel with a high concentration of dissolved oxygen such as with extremely low carbon steel by just Mg requires a large amount of Mg.
Considering the production costs, the process cannot be said to be practical.
Method used
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example 1
[0085]300 t of molten steel with a C concentration of 0.0019 mass % was produced by refining at a converter and treatment at a rotary flow type vacuum degassing apparatus.
[0086]To the molten steel, alloys of Cu, Nb, and B were added, without adding Al, to give 0.011 mass % Si, 0.16 mass % Mn, 0.014 mass % Nb, 0.003 mass % B, 0.07 mass % Cu, 0.0016 mass % N, 0.043 mass % dissolved oxygen, and 0.001 mass % or less acid soluble Al.
[0087]This molten steel was cast into a slab of a thickness of 250 mm and a width of 1800 mm by continuous casting. The cast slab was cut into 8500 mm lengths for use as coil units.
[0088]The thus obtained slab was hot rolled and cold rolled by ordinary methods to finally obtain a coil of cold rolled steel plate of 0.7 mm thickness and a width of 1800 mm. The quality was visually examined on an inspection line after cold rolling and the number of surface defects formed per coil was evaluated.
[0089]As a result, no surface defects were formed and no cracking due...
example 2
[0091]300 t of molten steel with a C concentration of 0.003 mass % was produced by refining at a converter and treatment at a rotary flow type vacuum degassing apparatus.
[0092]To the molten steel, alloys of Cu, Nb, B, and Ni were added, without adding Al, to give 0.01 mass % Si, 0.15 mass % Mn, 0.035 mass % Nb, 0.005 mass % B, 1.8 mass % Cu, 0.5 mass % Ni, 0.0025 mass % N, 0.004 mass % Ti, 0.015 mass % dissolved oxygen, and 0.001 mass % acid soluble Al.
[0093]This molten steel was cast to a slab of a thickness of 250 mm and a width of 1800 mm using a continuous castingmachine with an in-mold electromagnetic stirring device while electromagnetically stirring the molten metal by an average flow rate of 50 cm / s at the meniscus. The cast slab was cut into 8500 mm lengths for use as coil units.
[0094]The thus obtained slab was hot rolled and cold rolled by ordinary methods to finally obtain a coil of cold rolled steel plate of 0.7 mm thickness and a width of 1800 mm. The quality of the sl...
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Abstract
A method of producing an extremely low carbon steel cast slab characterized by castingmolten 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 / cm2 to 1,000,000 particles / cm2.
Description
TECHNICAL FIELD[0001]The present invention relates to extremely low carbon steel plate excellent in surface characteristics, workability, and formability and a method of producing extremely low carbon cast slab.BACKGROUND ART[0002]Molten steel refined in a converter or vacuum treatment vessel contains a large amount of dissolved oxygen. This excess oxygen is generally removed by Al which is a strong deoxidizing element with a strong affinity with oxygen. However, Al forms alumina-based inclusions by deoxidation. These aggregate and form coarse alumina clusters.[0003]The alumina clusters become the cause of the formation of surface defects during steel plate production and greatly deteriorate the quality of the thin-gauge steel plate. In particular, in extremely low carbon molten steel, which is a material for thin-gauge steel plate having a low carbon concentration and high concentration of dissolved oxygen after refining, the amount of the alumina clusters is extremely large and th...
Claims
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Application Information
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