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AssigneeNippon Steel Corporation
InventorsMasafumi Zeze, Takashi Morohoshi, Ryusuke Miura, Shintaro Kusunoki, Yasuhiro Kinari, Masayuki Abe, Hiroshi Sugano, Kenichiro Miyamoto, Masaharu Oka, Yuji Koyama
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A cast steel with excellent workability, characterized in that not less than 60% of the total cross section thereof is occupied by equiaxed crystals, the diameters (mm) of which satisfy the following formula: D<1.2X1/3+0.75, wherein D designates each diameter (mm) of equiaxed crystals in terms of internal structure in which the crystal orientations are identical, and X the distance (mm) from the surface of the cast steel. The cast steel and the steel material obtained by processing the cast steel have very few surface flaws and internal defects.
A method for processing molten steel for making fine the solidification structure of a cast steel, characterized by controlling the total amount of Ca in said molten steel at not more than 0.0010 mass % such that the generation of calcium aluminate is suppressed, and then adding a prescribed amount of Mg to generate high melting point oxides which act as a solidification nuclei when molten steel solidifies and produces a fine-grain structure wherein internal casting defects are suppressed.
A method for processing molten steel for making fine the solidification structure of a cast steel, characterized by carrying out a deoxidation treatment by adding a prescribed amount of Al-containing alloy in said molten steel to generate Al2O3 and then adding a prescribed amount of Mg to form MgO or MgAl2O3 generated by oxidation of Mg on the surface of Al2O3, which acts as solidification nuclei when molten steel solidifies and produces a fine-grain structure wherein internal casting defects are suppressed.
Dependencies are inferred from the claim text.