Patent ID: 9255306
Filing Date: 2016-02-09
CPC Classification: C21D,C22C

Claim Text:
1. A steel wire rod having a diameter of 5.5 mm to 12.5 mm after finish rolling consisting of, as a chemical composition, by mass %: 0.70% to 1.00% of C; 0.15% to 0.35% of Si; 0.1% to 1.0% of Mn; 0.001% to 0.005% of N; 0.005% to less than 0.050% of Ni; at least one of 0.005% to 0.10% of Al or 0.005% to 0.10% of Ti; at least one of more than 0% to 0.50% of Cr, more than 0% to 0.50% of Co, more than 0% to 0.50% of V, more than 0% to 0.20% of Cu, more than 0% to 0.10% of Nb, more than 0% to 0.20% of Mo, more than 0% to 0.0020% of W, more than 0% to 0.0050% of Rare Earth Metal, more than 0.0005% to 0.0050% of Ca, more than 0.0005% to 0.0050% of Mg, or more than 0.0005% to 0.010% of Zr; and a balance consisting of iron and unavoidable impurities, and as a metallographic structure, by area %, 95% to 100% of a pearlite, wherein, when a distance from a peripheral surface to a center is r in unit of mm, an average pearlite block size at a central portion which is an area from the center to r×0.99 is 1 μm to 25 μm, an average pearlite block size at a surface layer portion which is an area from the peripheral surface to r×0.01 is 1 μm to 20 μm, when a minimum lamellar spacing of the pearlite at the central portion is S in unit of nm, a following Expression 1 is satisfied, wherein the steel wire rod has a tensile strength of 1200 MPa or more, and the tensile strength, TS in unit of MPa, and a reduction of area, RA in unit of %, satisfy a following Expression 2 and a following Expression 3, and amounts expressed in mass % of each element in the chemical composition satisfy a following Expression 4,