Steel wire rod and method of producing same

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,

S< 12 r+ 65  (Expression 1)

RA≧ 100−0.045× TS   (Expression 2)

RA≧ 45  (Expression 3)

0.005≦Al+Ti≦0.1  (Expression 4).

2. A method of producing a steel wire rod, the method comprising:

a casting process to obtain a cast piece consisting of the chemical composition according to claim 1 ;

a heating process of heating the cast piece to a temperature of 1000° C. to 1100° C.;

a hot-rolling process of hot-finish-rolling the cast piece after the heating process by controlling a finishing temperature to be 850° C. to 1000° C. to obtain a hot-rolled steel;

a coiling process of coiling the hot-rolled steel within a temperature range of 780° C. to 840° C.;

a patenting process of directly immersing the hot-rolled steel after the coiling process in a molten salt, which is held at a temperature of 480° C. to 580° C., within 15 seconds after the coiling process; and

a cooling process of cooling the hot-rolled steel after the patenting process to a room temperature to obtain the steel wire rod.