HELICAL COMPRESSION SPRING AND METHOD FOR MANUFACTURING SAME

摘要

Provided are: a highly-durable helical compression spring that is produced using inexpensive wire rod by eliminating tensile residual stress caused by coiling, and forming a carbon concentrated layer on the surface of the wire rod to impart an appropriate compressive residual stress distribution; and a method for manufacturing the helical compression spring. The helical compression spring is characterized by: using steel wire rod containing, in wt%, 0.45 to 0.80% carbon, 0.15 to 2.50% silicon, and 0.3 to 1.0% manganese, with the remainder comprising iron and unavoidable impurities, said steel wire rod having an equivalent circle diameter of 2.5 mm to 10 mm; having an internal hardness of 570 to 700 HV in an arbitrarily-defined cross section of the wire rod; having a carbon concentrated layer in which the carbon exceeds the average concentration of carbon contained in the steel wire rod in the surface layer; and having an unloaded compressive residual stress greater than or equal to 200 MPa on the inner diameter side of the coil spring at a depth of 0.2 mm from the surface of the wire rod in substantially the direction of maximum principal stress when a compressive load is applied to the spring; and an unloaded compressive residual stress greater than or equal to 60 MPa at a depth of 0.4 mm from the surface.