Nippon Steel Sumitomo Metal Corporation

Kouichi Yamazaki

Takashi Fujita

Hiroshi Hagiwara

Tatsuro Ochi

Masayuki Hashimura

Takayuki Kisu

Takanori Miyaki

The present invention provides spring steel used for spring steel wire achieving both high strength and cold coilability and spring steel wire, that is, spring steel containing, by mass %, C: 0.45 to 0.70%, Si: 1.0 to 3.0%, Mn: 0.05 to 2.0%, P: 0.015% or less, S: 0.015% or less, N: 0.0015 to 0.0200%, and t-O: 0.0002 to 0.01 and further limiting Al&#x2264;0.01% and Ti&#x2264;0.003%. Further, it is characterized by satisfying the following regarding the cementite-based spherical carbides present at an observed plane, an occupied area ratio of grains with a circle equivalent diameter of 0.2 &#x3bc;m or more of 7% or less, a density of presence of grains with a circle equivalent diameter of 0.2 to 3 &#x3bc;m of 1/&#x3bc;mor less, and a density of presence of grains with a circle equivalent diameter 3 &#x3bc;m or more of 0.001/&#x3bc;mor less, having an prior austenite grain size number of #10 or higher and a residual austenite of 15 mass % or less, and having an area ratio of poor regions with a small density of presence of cementite-based carbides of a circle equivalent diameter of 2 &#x3bc;m or more of 3% or less.

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Muroran, Japan

Kouichi Yamazaki