To provide a leaf spring material having improved mechanical property by using radio-frequency heating, and to provide its manufacturing method for manufacturing the same in a stable manner.
The leaf spring material is formed of an approximately strip steel plate 10 having a first face 11 and a second face 12. It includes a hardened layer 11a formed near the first face in an induction hardened structure having higher average hardness than a base material structure 12a near the second face 12, and a compression residual stress layer having a thickness near the first face at least not smaller than a thickness d of the hardened layer 11a. This characteristic structure is obtained by stress induction hardening with predetermined tensile stress or more given thereto.
ONO YOSHIKI
TAKAHASHI FUMIO
EBASHI HIRONORI
KIKUCHI SAKAE
HORIKIRI KK
Go Ogoshi
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