VEHICLE SUSPENSION COIL SPRING AND METHOD FOR MANUFACTURING SAME

摘要

A spring wire (20) with hardness of 50 to 56 HRC is subjected to first and second shot peening processes (S6) (S7) within a warm working temperature range of 150 to 350°C. In the first shot peening process (S6), the first shot of a shot size of 1.0 mm or more is used. In the second shot peening process (S7), the second shot smaller in shot size than the first shot is used. Through these shot peening processes (S6) (S7), compressive residual stress is imparted to the spring wire (20). The spring wire (20) includes a residual stress increase part (T1 residual stress peak part (T3), and residual stress decrease part (T4). In the residual stress decrease part (T4), a part (B) including the compressive residual stress magnitude of which is equivalent to the magnitude of the compressive residual stress at the surface of the spring wire (20) exists at a position at a depth exceeding the permissible pit depth (R max ).