STEEL PLATE WITH HIGH TOUGHNESS AND HIGH STRENGTH FOR BOLTING SPLICE PLATE, EASY OF CUTTING AND BOLTHOLE PUNCHING, AND SPLICE PLATE USING THIS STEEL PLATE

摘要

PROBLEM TO BE SOLVED: To shorten the time required to carry out cutting, bolthole punching, and surface grooving by regulating the hardness of a steel plate with high toughness and high strength for bolting splice plate, having a composition containing specific amounts of C, Si Mn, Al, and S, so that it is higher in the surface layer part and lower in the central part. ;SOLUTION: A steel, having a chemical composition consisting of, by weight, 0.12-0.50% C, 0.03-2.0% Si, 0.25-2.5% Mn, 0.002-0.10% Al, 0.003-0.10% S, and the balance Fe with inevitable impurities, is used. The Vickers hardness, in the part between a position at a depth of ≥0.2mm in a plate-thickness direction from the surface, on one side or both sides, of a steel material, such as steel plate and shape steel, with the above composition and a position at a depth equivalent to 30% of the plate thickness, is regulated to ≥360. Further, the Vickers hardness in the plate thickness central part is regulated to ≤300. By this method, the steel plate of 4-25mm plate thickness, easy of cutting and bolthole punching, can be obtained. Hardening of the surface of the steel plate is carried out, e.g. by applying heating from the surface by furnace heating, high-frequency induction heating, etc., and rapidly heating the surface layer part to a temp. not lower than the Ac₁ point and the central part to a temp. not higher than the Ac₁ point, respectively, and performing hardening without delay.;COPYRIGHT: (C)1998,JPO