Nippon Steel Corporation

Shouich Suzuki

Hiroshi Hagiwara

Masayuki Hashimura

Noriyuki Yamada

Seiichi Koike

Hiroaki Hayashi

Takanari Miyaki

Katsuaki Shiiki

The present invention provides a steel wire, for springs excellent in coiling property while having a high strength, as a heat treated steel wire for high strength springs, 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; having a tensile strength of not less than 2,000 MPa; spheroidal carbides, composed of mainly cementite, observed in a microscopic visual field satisfying the area percentage of the spheroidal carbides not less than 0.2 &#x3bc;m in circle equivalent diameter being not more than 7%, the density of the spheroidal carbides 0.2 to 3 &#x3bc;m in circle equivalent diameter being not more than 1 piece/&#x3bc;m, and the density of the spheroidal carbides over 3 &#x3bc;m in circle equivalent diameter being not more than 0.001 piece/&#x3bc;m; the prior austenite grain size number being #10 or larger; the content of the retained austenite being not more than 12 mass %; the maximum diameter of carbides being not more than 15 &#x3bc;m; and the maximum diameter of oxides being not more than 15 &#x3bc;m.

Heat-treated steel wire for high strength spring

Growing community of inventors

Chiyoda-ku, Japan

Shouich Suzuki