HOT-FORGED PRODUCTS EXCELLENT IN FATIGUE STRENGTH, PROCESS FOR PRODUCTION THEREOF, AND MACHINE STRUCTURAL PART

摘要

PROBLEM TO BE SOLVED: To provide hot-forged products obtained by suitably controlling the structure in a hot-forging step, which are improved in the fatigue strength, that is a factor required for withstanding high stress caused by the weight reduction and/or compactification of hot-forged products obtained by conventional processes and which exhibit excellent machinability in the machining conducted after hot forging not only in the portions not requiring high fatigue strength but also in the other portions and can be therefore easily finished.

SOLUTION: The hot forged product has a hardened portion introduced by partial cooling after hot forging and a nonhardened portion, wherein Vickers hardness (V1) of the hardened portion and Vickers hardness (V2) of the nonhardened portion satisfy the relationship: (V1-V2)/V2=0.1 to 0.8.

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