The high hardness hot rolling steel sheet and its production mannered null mass which are superior in weldability, processability and resistance high-speed collision

摘要

PROBLEM TO BE SOLVED: To provide a high hardness hot rolled steel sheet for a structural member having excellent weldability, workability and resistance to penetration by high speed impact, and to provide a production method therefor.;SOLUTION: The steel has a composition comprising 0.22 to 0.30% C, 0.03 to 0.5% Si, 0.10 to 0.60% Mn, ≤0.005% P, ≤0.002% S, 0.15 to 1.0% Mo, 0.01 to 0.10% Nb, 0.003 to 0.05% Ti and 0.0005 to 0.003% B, and the balance Fe with inevitable impurities, wherein PCE value (=C+Si/30+Mn/12+Ni/50+Cr/15+Mo/6+V/8+25P+30S+15B) is ≤0.55%, and the steel is characterized in that the steel has a microstructure in which the fraction of a martensitic structure in which the average grain diameter of old austenite is ≤20 μm is ≥95%, and that the steel has a Brinell hardness of ≥470.;COPYRIGHT: (C)2008,JPO&INPIT