Nhk Spring Co., Ltd.

Nissan Motor Company Limited

Kabushiki Kaisha Kobe Seiko Sho

Shinko Wire Company, Ltd.

Naoki Terakado

Noritoshi Takamura

Makoto Abe

Nobuhiko Ibaraki

Sumie Suda

Tadayoshi Fujiwara

Satoru Tendo

Kaoru Hatayama

Tetsuo Jinbo

Tsuyoshi Kuriki

Tetsuyuki Taniguchi

A steel wire has tempered martensite, comprises, as essential components, by mass, C: 0.53 to 0.68%; Si: 1.2 to 2.5%; Mn: 0.2 to 1.5%; Cr: 1.4 to 2.5%; Al: 0.05% or less; further comprises, as a selective component, Ni: 0.4% or less; V: 0.4% or less; Mo: 0.05 to 0.5%; or Nb: 0.05 to 0.5%; and further comprises remainder essentially consisting of Fe and inevitable impurities, wherein the grain size number of prior austenite is 11.0 or larger, and the proof stress ratio (&#x3c3;/&#x3c3;), namely, a ratio of 0.2% proof stress (&#x3c3;) to tensile strength (&#x3c3;) is 0.85 or lower. Satisfying the above requirements makes it possible to produce a steel wire for high-strength spring excellent both in workability (cold workability), and in sag resistance and fatigue properties.

Steel wire for high strength spring excellent in workability and high strength

A high strength spring is made of steel of which composition consists of 0.6 to 0.7 wt % of C, 1.2 to 1.6 wt % of Si, 0.5 to 0.8 wt % of Mn, 0.5 to 0.8 wt % of Cr, 0.05 to 0.2 wt % in total of one or more than one of V, Mo, Nb and Ta and the balance of Fe and inevitable impurities. The steel is limited in particle size of non-metallic inclusions in such a way that the maximum particle size of the non-metallic inclusions is equal to or smaller than 15 .mu.m. The spring is applied at a portion adjacent the outer surface thereof with a residual compression stress in such a way that the maximum of the residual compression stress ranges from 85 to 110 Kgf/mm.sup.2. The spring is further process so as to have such a surface roughness that is equal to or smaller than 15 .mu.m.

High strength spring and its process of manufacturing

Growing community of inventors

Nagano, Japan

Naoki Terakado