PURPOSE: To produce a high strength steel excellent in hydrogen induced cracking resistance and sulfide stress corrosion cracking resistance by preparing a steel of specific composition, in which metallic structure is composed of acicular ferrite phase and C inclusions are specified.
CONSTITUTION: A high strength steel consisting of, by weight, 0.02-0.06% C, 0.03-0.50% Si, 0.5-2.0% Mn, ≤0.02% P, ≤0.005% S, 0.001-0.005% Ca, 0.01-0.05% sol.Al, ≤0.0015% O, further one or ≥2 kinds among ≤0.5% Cu, ≤0.5% Ni, ≤0.5% Cr, and ≤0.5% Mo, and the balance essentially Fe and in which the metallic microstructure of the steel is composed of acicular ferrite and the number of C type inclusions of ≥5μm diameter in the steel is regulated to <10pieces/mm2, is prepared. By this method, the high strength steel, excellent in hydrogen induced cracking resistance and sulfide stress corrosion cracking resistance, can be obtained.
NAGAE MORIYASU
HIRANO OSAMU
SASAKI TAKAHARU
