STEEL PLATE FOR STRUCTURAL USE, EXCELLENT IN BRITTLENESS RESISTANCE/FRACTURE ARREST PROPERTY AFTER PLASTIC DEFORMATION, AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To produce a steel plate for structural use, excellent in brittleness resistance.fracture arrest property after plastic deformation, by subjecting a steel slab having a specific composition consisting of C, Si, Mn, Al, N, and Fe to specific rapid cooling treatment and then to rolling at specific surface later temp. ;SOLUTION: In a steel plate which has a composition consisting of, by weight, 0.04-0.08% C, 0.05-0.5% Si, 0.3-2.0% Mn, 0.005-0.1% Al, ≤20ppm free-N, and the balance Fe with inevitable impurities and further containing, if necessary, prescribed amounts of Ti, Cu, Ni, Nb, V, Mo, and B, the structure in the regions from the surface and the rear surface to the positions each at a depth of at least 10-30% of plate thickness from the surface and the rear surface, respectively, is formed into ferritic structure of ≤5μm grain size (average circle-equivalent diameter) and also the aspect ratio of the texture colony of the same crystal orientation in the surface layer structure is regulated to ≥4. This steel plate can be obtained by starting rolling for a slab of steel with the above chemical composition at a temp. not lower than the Ac₃ point, applying rapid cooling down to a temp. not higher than the Ar₃ point at a rate of ≥1°C/sec through the region of 0.10t₀/t to 0.30t₀/tmm [where t₀ is plate thickness during rolling and (t) is product plate thickness], starting rolling again, and finishing rolling at ≤(Ac₃-50)°C surface layer temp.;COPYRIGHT: (C)1998,JPO