Patent ID: 9476112
Filing Date: 2016-10-25
CPC Classification: C21D,C22C

Claim Text:
1. A steel wire rod or steel bar as hot-rolled, having excellent cold forgeability, comprising: by mass %, as a chemical composition, C: 0.1 to 0.6%, Si: 0.7% to 1.5%, Mn: 0.05 to 2.5%, Al: 0.015 to 0.3%, N: 0.0040 to 0.0150%, P: limited to 0.035% or less, and S: limited to 0.025% or less, and a balance consisting of iron and unavoidable impurities, wherein a depth of d (mm) from a surface of a surface layer region with 20 HV 0.2 or more higher, relative to HV 0.2 that is an average hardness in a region where a depth from the surface is from sectional radius R×0.5 (mm) to a center satisfies the following formula (1); a steel structure of the surface layer region has a ferrite fraction of 10% or less by area ratio, with a balance being one or two or more of martensite, bainite and pearlite; the steel structure where the depth from the surface is from the sectional radius R×0.5 (mm) to the center is ferrite-pearlite or ferrite-bainite; and a surface roughness Ra in the circumferential direction when scales adhering to the surface have been removed is 4 μm or less,