HIGH-HARDNESS HOT-ROLLED STEEL PLATE HAVING EXCELLENT WELDABILITY, WORKABILITY AND PENETRATION RESISTANCE TO HIGH-SPEED COLLISION AGAINST HIGH HARDNESS MISSILE, AND MANUFACTURING METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a hot-rolled steel plate having penetration resistance to a high-speed collision against a high-hardness missile, weldability and workability.;SOLUTION: The steel plate has a chemical composition comprising 0.22 or more but less than 0.30% C, 0.15 to 0.50% Si, 0.10 or more but less than 0.60% Mn, 0.005% or less P, 0.0020% or less S, 2.5 to 4.5% Ni, 0.20 or more but less than 1.00% Mo, 0.005 to 0.030% Nb, 0.01 to 0.10% Al, 0.006% or less N, optionally one or two elements selected from among 0.10 to 0.80% Cr, 0.01 to 0.20% V, 0.003 to 0.030% Ti and 0.0005 to 0.0030% B, and remaining Fe and unavoidable impurities, while satisfying a PCE value of 0.60% or less. The hot-rolled steel plate has such a composition, has a microstructure that includes a martensitic structure in an amount of 95% or higher by fraction which contains crystal grains of former austenite with an average grain size of 6 μm or less, and has a Brinell hardness of 470 to 560.;COPYRIGHT: (C)2008,JPO&INPIT