COMPRESSION COIL SPRING AND MANUFACTURING METHOD THEREFOR

To provide a compression coil spring having high durability and high sag resistance, and capable of avoiding fretting fatigue, and a manufacturing method therefor.SOLUTION: There is provided a compression coil spring using a steel wire containing, by mass%, C of 0.5 to 0.7%, Si of 1.2 to 3.0%, Mn of 0.3 to 1.2%, Cr of 0.5 to 1.9%, V of 0.05 to 0.5%, and one or more kind of Ni of 1.5% or less, Mo of 1.5% or less, and W of 0.5% or less as optional component, and the balance consisting of iron with inevitable impurities. It has internal hardness on any transverse section of the steel wire is 570 to 700 HV, a nitrided layer on a surface layer part, a C concentrated layer having over C concentration contained in the steel wire just blow the nitrided layer, total thickness of a surface treatment layer including the nitrided layer and the C concentrated layer of 0.02 to 0.15 mm, thickness of the nitrided layer of 0.01 to 0.05 mm and a part with hardness of 780 HV or more in the nitrided layer.SELECTED DRAWING: None 【課題】高耐久性かつ高耐へたり性であり、かつフレッティング疲労を回避することができる圧縮コイルばねおよびその製造方法を提供する。【解決手段】重量％で、Ｃを０．５〜０．７％、Ｓｉを１．２〜３．０％、Ｍｎを０．３〜１．２％、Ｃｒを０．５〜１．９％、Ｖを０．０５〜０．５％含むと共に、任意成分としてＮｉを１．５％以下，Ｍｏを１．５％以下、Ｗを０．５％以下のうち１種または２種以上を含み、残部が鉄および不可避不純物からなる鋼線材を用いた圧縮コイルばねである。鋼線材の任意横断面における内部硬さが５７０〜７００ＨＶであり、表層部に窒化層を有し、かつ窒化層直下に鋼線材に含まれるＣの平均濃度を超えるＣ濃化層を有し、窒化層とＣ濃化層を合わせた表面処理層の合計厚さが０．０２〜０．１５ｍｍであり、前記窒化層の厚さが０．０１〜０．０５ｍｍであり、かつ前記窒化層に、７８０ＨＶ以上の硬さの部分を有する。【選択図】なし