The high intensity which possesses the hydrogen invasion depression effect low-alloy steel

摘要

PROBLEM TO BE SOLVED: To provide steel which has sufficient delayed fracture resistance in spite of its having a high strength of ≥1,350 MPa and is applicable to high strength parts/high strength bolts usable under severe environments, such as the seashore or the coastal region in its vicinity.;SOLUTION: The high-strength low alloy steel has a chemical composition consisting of, by mass, 0.35 to 0.55% C, ≤0.3% Si, ≤0.6% Mn, ≤0.025% P, ≤0.050% S, ≤0.10% Al, 0.5 to 1.5% Cr, 0.7 to 1.5% of (Mo+0.5W), ≤0.005 to 0.05% Nb, 0.005 to 0.20% of (Ti+0.5Zr), 0.15 to 0.3% V and the balance Fe with impurities and further containing, if necessary, either or both of 0.2 to 3% Ni and 0.05 to 1% Cu and/or either or both of ≤0.01% Ca and ≤0.01% Mg. Further, the composition of nonmetallic inclusions of ≥500 nm major axis contained in the steel is constituted so that it satisfies inequality (Ti+Zr)/(Ti+Zr+Mn+Ca+Mg)×100≥30(mass%).;COPYRIGHT: (C)2006,JPO&NCIPI