Patent ID: 7575646

Claim:
A heat treated steel wire provided for at least one high strength spring, characterized by: comprising, in mass, C: 0.75% to 0.85%, Si: 1.5% to 2.5%, Mn: 0.5% to 1.0%, Cr: 0.3% to 1.0%, P: not more than 0.015%, S: not more than 0.015%, N: 0.001% to 0.007%, W: 0.05% to 0.3%, and the balance consisting of Fe and unavoidable impurities, wherein a tensile strength of the steel wire is at least 2,000 MPa, wherein spheroidal carbides of the steel wire are composed of mainly cementite observed in a microscopic visual field, the cementite satisfying the area percentage of the spheroidal carbides of at least 0.2 μm in a circle equivalent diameter being not more than 7%, the density of the spheroidal carbides 0.2 μm to 3 μm in circle equivalent diameter being at most 1 piece/me, a density of the spheroidal carbides being over 3 μm in circle equivalent diameter being not more than 0.001 piece/me, wherein a prior austenite grain size number of the steel wire is at least #10, wherein the content of a retained austenite of the steel wire is at most 12 mass %, wherein a maximum diameter of the spheroidal carbides is at most 15 μm, and wherein a maximum diameter of oxides of the steel wire at most 15 μm.