| 摘要 |
Bending deformation exceeding a yield stress is applied by winding a material for a coil spring on a mandrel at a temperature at which spring-back occurs. Coiling is performed simultaneously with the application of the bending deformation, and the load is removed after the coiling. This spring includes an outside surface region (W3) having a compressive residual stress and a compressive stress reduction region (W4) in which the compressive residual stress is reduced from the outside surface region (W3) toward the center of the material. A stress change portion (P1) at which a change from the compressive residual stress to a tensile residual stress occurs exists between the outside surface region (W3) and the center of the material. The spring further includes a tensile stress peak portion (P2), tensile stress reduction region (W5), and inside surface region (W6). The inside surface region (W6) has the tensile or compressive residual stress having an absolute value smaller than that of the outside surface region (W3). |
