| 摘要 |
This invention provides a steel wire rod/steel bar having excellent cold forgeability. This steel wire rod/steel bar is provided with a predetermined chemical component composition in the condition immediately after hot rolling, wherein the depth d (mm), from the surface, of a surface layer region having a mean hardness HV0.2 that is at least 20 higher than the mean hardness HV0.2 of the region from the cross-section radius (R)×0.5 (mm) to the center satisfies formula (1); the steel structure of the surface layer region comprises ferrite in a fraction of 10% or less by area ratio, with the balance being made up of one or more types of steel structure from amongst martensite, bainite, and pearlite; the steel structure from the cross-section radius (R)×0.5 (mm) to the center is a ferrite-pearlite or ferrite-bainite steel structure; and the surface roughness (Ra) in the circumferential direction when scales adhering to the surface have been removed is equal to or less than 4 μm. |
