Abstract: A steel for high-strength spring has an Ac3 transformation temperature as an indicator of the decarburization performance, which is calculated by Equation (1) below, is from 859 to 885° C., a maximum hardened diameter DI as an indicator of the hardening performance, which is calculated by Equation (2) below, is from 70 to 238 mm, and a temper hardness HRC as an indicator of the spring performance, which is calculated by Equation (3) below, is from 50 to 55. Ac3=910?203×?{square root over (C)}?15.2Ni+44.7Si+104V+31.5Mo+13.1W??(1) DI=DO×fSi×fMn×fP×fS×fCu×fNi×fCr??(2) HRC=38.99+17.48C+2.55Si?2.28Ni+2.37Cr+8.04Ti??(3) wherein, D0=8.65×?{square root over (C)}, fSi=1+0.64×% Si, fMn=1+4.10×% Mn, fP=1+2.83×% P, fS=1?0.62×% S, fCu=1+0.27×% Cu, fNi=1+0.52×% Ni, and fCr=1+2.33×% Cr.

Abstract: A steel for high-strength spring has an Ac3 transformation temperature as an indicator of the decarburization performance, which is calculated by Equation (1) below, is from 859 to 885° C., a maximum hardened diameter DI as an indicator of the hardening performance, which is calculated by Equation (2) below, is from 70 to 238 mm, and a temper hardness HRC as an indicator of the spring performance, which is calculated by Equation (3) below, is from 50 to 55. Ac3=910?203×?{square root over (C)}?15.2Ni+44.7Si+104V+31.5Mo+13.1W??(1) DI=DO×fSi×fMn×fP×fS×fCu×fNi×fCr??(2) HRC=38.99+17.48C+2.55Si?2.28Ni+2.37Cr+8.04Ti??(3) wherein, D0=8.65×?{square root over (C)}, fSi=1+0.64×% Si, fMn=1+4.10×% Mn, fP=1+2.83×% P, fS=1?0.62×% S, fCu=1+0.27×% Cu, fNi=1+0.52×% Ni, and fCr=1+2.33×% Cr.

Abstract: A spring wire with a hardness of 50 to 56 HRC is subjected to first and second shot peening processes within a warm working temperature range of 150° C. to 350° C. In the first shot peening process, a first shot of a shot size of at least 1.0 mm is used. In the second shot peening process, a second shot smaller in shot size than the first shot is used. Through these shot peening processes, compressive residual stress is imparted to the spring wire. The spring wire includes a residual stress increase part, residual stress peak part, and residual stress decrease part. In the residual stress decrease part, a part including a compressive residual stress magnitude equivalent to the magnitude of the compressive residual stress at a surface of the spring wire exists at a region at a depth exceeding the permissible pit depth.

Abstract: A spring wire with hardness of 50 to 56 HRC is subjected to first and second shot peening processes within a warm working temperature range of 150 to 350° C. In the first shot peening process, the first shot of a shot size of 1.0 mm or more is used. In the second shot peening process, the second shot smaller in shot size than the first shot is used. Through these shot peening processes, compressive residual stress is imparted to the spring wire. The spring wire includes a residual stress increase part, residual stress peak part, and residual stress decrease part. In the residual stress decrease part, a part 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 exists at a position at a depth exceeding the permissible pit depth.

Abstract: The reflection portion of the reflection member is moved along the inner surface in the hole of the pipe from the entrance opening of the hole of the pipe to the exit opening of the hole thereof. In this case, the reflection portion is guided by the guide portion provided at both sides of the reflection portion. The shots, which are projected toward the inner surface in the hole of the pipe, reach the reflection portion through the holes of the guide portion of the entrance side, and they are reflected toward the inner surface in the hole of the pipe. Since the shots can be reflected toward the inner surface inside in the hole of the pipe, the tendency that shots may be moved toward the inner surface outside in the hole of the curved portion can be small.

Abstract: A spring wire with a hardness of 50 to 56 HRC is subjected to first and second shot peening processes within a warm working temperature range of 150 to 350° C. In the first shot peening process, a first shot of a shot size of at least 1.0 mm is used. In the second shot peening process, a second shot smaller in shot size than the first shot is sued. Through these shot peening processes, compressive residual stress is imparted to the spring wire. The spring wire includes a residual stress increase part, residual stress peak part, and residual stress decrease part. In the residual stress decrease part, a part including a compressive residual stress magnitude equivalent to the magnitude of the compressive residual stress at a surface of the spring wire exists at a region at a depth exceeding the permissible pit depth.

Abstract: A spring wire with hardness of 50 to 56 HRC is subjected to first and second shot peening processes within a warm working temperature range of 150 to 350° C. In the first shot peening process, the first shot of a shot size of 1.0 mm or more is used. In the second shot peening process, the second shot smaller in shot size than the first shot is used. Through these shot peening processes, compressive residual stress is imparted to the spring wire. The spring wire includes a residual stress increase part, residual stress peak part, and residual stress decrease part. In the residual stress decrease part, a part 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 exists at a position at a depth exceeding the permissible pit depth.

Abstract: The reflection portion of the reflection member is moved along the inner surface in the hole of the pipe from the entrance opening of the hole of the pipe to the exit opening of the hole thereof. In this case, the reflection portion is guided by the guide portion provided at both sides of the reflection portion. The shots, which are projected toward the inner surface in the hole of the pipe reach the reflection portion through the holes of the guide portion of the entrance side, and they are reflected toward the inner surface in the hole of the pipe. Since the shots can be reflected toward the inner surface inside in the hole of the pipe, the tendency that shots may be moved toward the inner surface outside in the hole of the curved portion can be small.