Excellent steel wire rod or bar steel to cold forging property

摘要

The present invention is, cold forging excellent in steel wire rod, there is provided a steel bar. steel wire rod of the present invention, steel bars, there is provided a steel wire rod, bar steel which remains hot rolling with a predetermined chemical component composition, the cross-sectional radius R 0.5 from (mm) to the center the depth d from the surface of 20HV0.2 or high surface area relative to the average hardness HV0.2 in the region (mm) satisfies the expression (1), the steel structure is a ferrite fraction of the surface layer region is the area ratio in the balance martensite at 10% or less, a bainite, and one or more of the steel structure of pearlite, the steel structure from cross-sectional radius R 0.5 (mm) from the center ferrite - pearlite or ferrite - a bainite steel structure, the surface roughness Ra of the circumferential upon removing scale adhered to a surface which is less steel wire rod, bar steel 4 m.