| 摘要 |
PURPOSE: To produce a high strength hot rolled steel plate excellent in bendability, weldability, and tensile strength by constituting a hot rolled steel plate, as a steel plate for construction machinery, of a low alloy steel of specific composition. CONSTITUTION: A slab of a steel, which has a composition consisting of, by weight, 0.05-0.15% C, <1.50% Si, 0.70-2.50% Mn, 0.25-1.5% Ni, 0.12-0.30% Ti, 0.0005-0.0030% B, <0.020% P, <0.010% S, 0.010-0.10% sol.Al, <0.0050% N, and the balance Fe, further containing, if necessary, <1.00% Cr, and satisfying C+Si/30+Mn/20+Ni/60+5B <=0.27, is hot-rolled and the resulting hot rolled steel plate is coiled. By adding B and controlling cooling velocity after hot rolling, fine ferrite crystals of <=10μm grain size, TiC of <=10nm, and Fe carbides of <=10/μm grain size are precipitated. By this method, the high strength hot rolled steel plate for construction, excellent in bendability and weldability, having >=95ON/mm<2> tensile strength, and particularly having >=850N/mm<2> proportional limit, can be produced.
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