Shape steel material having high strength, high toughness and excellent fire resistance and process for producing rolled shape steel of said material

Abstract From the Canadian patent

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 ~ Ti% - 2 O% ~ 0.008 to crystallize a titanium-based oxide in an amount of 20 particles/mm2 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 …