Nippon Steel Corporation

Other

Takanari Miyaki

Hiroshi Hagiwara

Masayuki Hashimura

Hiroaki Hayashi

Noriyuki Yamada

Ikuo Ochiai

Seiichi Koike

Katsuaki Shiiki

Shoichi Suzuki

Toshio Banno

Shouich Suzuki

The present invention provides a spring steel having both a high strength and a good coiling property after heat treatment, characterized by: containing, in mass, C: 0.4 to 1.2%, Si: 0.9 to 3.0%, Mn: 0.1 to 2.0%, P: 0.015% or less, S: 0.015% or less, Cr: 2.5% or less, and N: 0.001 to 0.015%, with the balance consisting of Fe and unavoidable impurities; and, in the microstructure of the steel after hot rolling, the density of globular cementite carbides 0.2 to 3 &#x3bc;m in circle-equivalent diameter being 0.5 piece/&#x3bc;mor less and the density of globular cementite carbides over 3 &#x3bc;m in circle-equivalent diameter being 0.005 piece/&#x3bc;mor less.

High-strength spring steel wire

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

The present invention provides a spring steel showing a sufficient reduction in area and an impact toughness while the steel has a high strength, in particular a tensile strength as high as at least 1,500 Mpa. A high toughness spring steel according to the present invention comprises, based on mass, 0.45 to 0.85% of C, 0.9 to 2.5% of Si, 0.1 to 1.2% of Mn, 0.1 to 2.0% of Cr, 0.005 to 0.07% of Ti, 0.001 to 0.007% of N, the Ti content being greater than four times the N content in terms of percent by mass, 0.0005 to 0.0060% B, at least one of 0.0005 to 0.01% Mg, 0.0005 to 0.01% La, and 0.0005 to 0.01% Ce, P and S with restrictive contents of less than 0.020% and less than 0.020%, respectively, and the balance of Fe and unavoidable impurities, and selectively contains V, Nb, Ni, Mo and Cu. The percent area of oxides and sulfides is not more than 0.1%.

High toughness spring steel

Steel wire for high-strength springs and method of producing the same

Growing community of inventors

Hokkaido, Japan

Takanari Miyaki