Steel product for induction hardening, induction-hardened member using the same, and methods producing them

A method for manufacturing an induction hardened member comprising the step of:

• hot working a steel consisting of C:
• 0.35-0.7%, Si:
• 0.30-1.1%, Mn:
• 0.2-2.0%, Al:
• 0.005-0.25%, Ti:
• 0.005-0.1%, Mo:
• 0.05-0.6%, B:
• 0.0003-0.006%, S:
• 0.06% or less, P:
• 0.02% or less, Cr:
• 0.2% or less, by mass, and a balance of Fe and inevitable impurities;
• cooling the hot worked steel at a cooling rate of at least 0.2° C./s, thereby manufacturing a steel product having a structure of bainite and/or martensite, the total volume fraction of bainite and martensite being 10% or more;
• subjecting the steel product to induction hardening at least once, wherein the heating temperature of the final induction hardening is 800-950° C.,
• wherein the thickness of a hardened layer formed on the surface of the steel product by induction hardening is 2 mm or more, and the prior austenite grain size of the hardened layer is 8 μm or less through the thickness of the hardened layer.