Helical compression spring and method for manufacturing same

A compression coil spring, comprising a steel wire material consisting of 0.45 to 0.80 weight % of C, 0.15 to 2.50 weight % of Si, 0.3 to 1.0 weight % of Mn and iron and inevitable impurities as the remainder, and having a circle equivalent diameter of 1.5 mm to 3 mm,

• wherein an internal hardness at a freely selected cross section of the wire material is in a range of 570 to 700 Hv,
• a C-condensed layer that exceeds an average concentration of C contained in the steel wire material exists at surface layer part, and
• in an approximate maximum principal stress direction generated when the coil spring is compressed and a compressive load is loaded on an inner diameter side of the coil spring, an unloaded compressive residual stress at a depth of 0.15 mm and 0.3 mm from surface of the wire material is not less than 300 MPa and not less than 50 MPa, respectively.

A compression coil spring, comprising a steel wire material comprising 0.45 to 0.80 weight % of C, 0.15 to 2.50 weight % of Si, 0.3 to 1.0 weight % of Mn, 0.005 to 1.34 weight % of at least one of Cr, B, Ni, Ti, Cu, Nb, V, Mo, and W, and iron and inevitable impurities as the remainder, and having a circle equivalent diameter of 2.5 mm to 10 mm,

• wherein an internal hardness at a freely selected cross section of the wire material is in a range of 570 to 700 Hv,
• a C-condensed layer that exceeds an average concentration of C contained in the steel wire material exists at surface layer part, and
• in an approximate maximum principal stress direction generated when the coil spring is compressed and a compressive load is loaded on an inner diameter side of the coil spring, when defining a depth from a surface of the wire material at which a value of an unloaded compressive residual stress is zero as a crossing point, and when defining a value of an integral from the surface to the crossing point in a residual stress distribution curve having a vertical axis of residual stress and a horizontal axis of wire radius as I−σR, the I−σR is not less than 160 MPa·mm.

A compression coil spring, comprising a steel wire material comprising 0.45 to 0.80 weight % of C, 0.15 to 2.50 weight % of Si, 0.3 to 1.0 weight % of Mn, 0.5 to 2.0 weight % of Cr, and iron and inevitable impurities as the remainder, and having a circle equivalent diameter of 2.5 mm to 10 mm,

• wherein an internal hardness at a freely selected cross section of the wire material is in a range of 570 to 700 Hv,
• a C-condensed layer that exceeds an average concentration of C contained in the steel wire material exists at surface layer part, and
• in an approximate maximum principal stress direction generated when the coil spring is compressed and a compressive load is loaded on an inner diameter side of the coil spring, when defining a depth from a surface of the wire material at which value of an unloaded compressive residual stress is zero as a crossing point, and when defining a value of an integral from the surface to the crossing point in a residual stress distribution curve having a vertical axis of residual stress and a horizontal axis of wire radius as L−σz, the L−σz is not less than 160 MPa·mm.

A compression coil spring, comprising a steel wire material comprising 0.45 to 0.80 weight % of C, 0.15 to 2.50 weight % of Si, 0.3 to 1.0 weight % of Mn, 0.005 to 1.34 weight % of at least one of Cr, B, Ni, Ti, Cu, Nb, V, Mo, and W, and iron and inevitable impurities as the remainder, and having a circle equivalent diameter of 1.5 mm to 3 mm,

• wherein an internal hardness at a freely selected cross section of the wire material is in a range of 570 to 700 Hv,
• a C-condensed layer that exceeds an average concentration of C contained in the steel wire material exists at surface layer part, and
• in an approximate maximum principal stress direction generated when the coil spring is compressed and a compressive load is loaded on an inner diameter side of the coil spring, when defining a depth from a surface of the wire material at which a value of an unloaded compressive residual stress is zero as a crossing point, and when defining value of an integral from the surface to the crossing point in a residual stress distribution curve having a vertical axis of residual stress and a horizontal axis of wire radius as I−σR, the I−σR is not less than 130 MPa·mm.

A compression coil spring, comprising a steel wire material comprising 0.45 to 0.80 weight % of C, 0.15 to 2.50 weight % of Si, 0.3 to 1.0 weight % of Mn, 0.5 to 2.0 weight % of Cr, and iron and inevitable impurities as the remainder, and having a circle equivalent diameter of 1.5 mm to 3 mm,

• wherein an internal hardness at a freely selected cross section of the wire material is in a range of 570 to 700 Hv,
• a C-condensed layer that exceeds an average concentration of C contained in the steel wire material exists at surface layer part, and
• in an approximate maximum principal stress direction generated when the coil spring is compressed and a compressive load is loaded on an inner diameter side of the coil spring, when defining a depth from a surface of the wire material at which a value of an unloaded compressive residual stress is zero as a crossing point, and when defining a value of an integral from the surface to the crossing point in a residual stress distribution curve having a vertical axis of residual stress and a horizontal axis of wire radius as I−σR, the L−σR is not less than 130 MPa·mm.