HIGH-STRENGTH SPRING STEEL

PROBLEM TO BE SOLVED: To provide a spring steel capable of providing a coil spring, which spring steel combines high strength with good corrosion fatigue property even when a temper treatment conducted after coiling is omitted during working of the spring steel into a coil spring by coiling the spring steel, and further is excellent in low temperature toughness.SOLUTION: There is provided the spring steel which contains C:0.15 to 0.40%, Si:1 to 3.5%, Mn:0.20 to 2.0%, and at least one kind selected from a group consisting of Ti:0.005 to 0.10%, Nb:0.005 to 0.05% and V:0.25%, and further contains Cr:0.05 to 1.20%, P:0.030% or less, S:0.02% or less and the balance iron with inevitable impurities and which has a carbon equivalent Ceqrepresented by the following formula (1) of 0.55 or less. Ceq=[C]+0.108×[Si]-0.067×[Mn]+0.024×[Cr]-0.05×[Ni]+0.074[V] (1) 【課題】ばね用鋼をコイリングしてコイルばねに加工する際に、コイリング後に行う焼入れ後の焼戻し処理を省略しても高強度と良好な腐食疲労特性を両立し、さらに低温靭性にも優れるコイルばねを提供できるばね用鋼を提供する。【解決手段】Ｃ：０．１５〜０．４０％、Ｓｉ：１〜３．５％、Ｍｎ：０．２０〜２．０％を含有するとともに、Ｔｉ：０．００５〜０．１０％、Ｎｂ：０．００５〜０．０５％、およびＶ：０．２５％以下よりなる群から選択される少なくとも１種、Ｃｒ：０．０５〜１．２０％、Ｐ：０．０３０％以下、Ｓ：０．０２％以下を含有し、残部が鉄および不可避不純物からなり、下記式（１）で示される炭素当量Ｃｅｑ1が０．５５以下であるばね用鋼。Ｃｅｑ1＝［Ｃ］＋０．１０８?［Ｓｉ］−０．０６７?［Ｍｎ］＋０．０２４?［Ｃｒ］−０．０５?［Ｎｉ］＋０．０７４［Ｖ］ ・・・（１）【選択図】図１