Nippon Steel Corporation

Kohichi Yamamoto

Suguru Yoshida

Kazuo Watanabe

Akira Inagaki

Yasushi Takeshima

Naoki Oda

After a predeoxidation treatment of a molten steel comprising as basic ingredients, in terms of % by weight, 0.04 to 0.20% of C, 0.05 to 0.50% of Si, 0.4 to 2.0% of Mn, 0.3 to 0.7% of Mo, 0.003 to 0.015% of N, 0.04 to 0.20% of V and less than 0.005% of Al to regulate [O %] to 0.003 to 0.015% by weight, titanium is added thereto so as to satisfy a requirement represented by the formula: -0.006.ltoreq.[Ti %]-2[O %].ltoreq.0.008 to crystallize a titanium-based oxide in an amount of 20 particles/mm.sup.2 or more, and MnS, TiN and V(C, N) are deposited on the titanium-based oxide to disperse the titanium-based oxide as a composite precipitate in the steel to provide a cast slab, and a high-strength high-toughness shape steel having an excellent fire resistance is provided by a combination of water cooling between rolling passes at the time of rolling with accelerated cooling after the completion of the rolling.

Shape steel material having high strength, high toughness and excellent

A method for producing a steel section by a rolling process including a rough rolling step, an intermediate rolling step and a finishing rolling step. The intermediate rolling step comprises water-cooling the flange portion of the rough-rolled steel section between rolling passes in the intermediate rolling step to cool the surface layer of the flange to a temperature not higher than 750.degree. C., and rolling the flange portion during recuperation of the surface layer of the flange at least one time between the rolling passes with a total draft not less than 20% and at an average rolling temperature not higher than 950.degree. C. and, after the finishing rolling step the outer surface of the flange is cooled at a cooling rate ranging from 0.5.degree. to 10.degree. C./sec depending on the thickness of the flange. Also the carbon equivalent of the steel is controlled. The advantage is that steel sections of various contours and dimensions can be produced from minimized varieties of steel compositions.

Method for producing low carbon equivalent rolled steel shapes by

Process for producing rolled shape steel material having high strength,

A cast strip for an H-shape steel having excellent fire resistance and toughness for use as a structural member for constructions and a shape steel having a flange, such as an I-shape steel, produced by accelerated cooling and controlled rolling of the cast slab, are produced in an in-line manner. After the regulation of the oxygen concentration of a molten steel by a predeoxidation treatment in a steel making process to form a steel having predetermined ingredients, the steel is subjected to final deoxidation with a minor amount of Al to provide a cast slab containing, in a dispersed state, compound oxide precipitate having a capability of forming intragranular ferrite. The stead is then subjected to a treatment comprising a combination of water cooling between rolling passes with accelerated cooling after hot rolling to attain refinement of the structure and a low alloy steel, thereby improving the strength at room temperature and at high temperature and the toughness.

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Sakai, Japan

Kohichi Yamamoto