Provided is a high-carbon steel wire rod with excellent wire drawability, containing predetermined chemical components and the balance: Fe and impurities. In a cross-section perpendicular to a longitudinal direction, an area fraction of pearlite is equal to or more than 95% and equal to or less than 100%, an average block size of the pearlite is 10 μm to 30 μm and standard deviation of block size is 20 μm or less, and when Ceq.=C (%)+Si (%)/24+Mn (%)/6, a tensile strength is equal to or more than 760×Ceq.+255 MPa and equal to or less than 760×Ceq.+325 MPa, reduction of area in a tensile test is −65×Ceq.+96(%) or more, and standard deviation of the reduction of area is 6% or less.

Provided is a high-carbon steel wire rod with excellent wire drawability, containing predetermined chemical components and the balance: Fe and impurities. In a cross-section perpendicular to a longitudinal direction, an area fraction of pearlite is equal to or more than 95% and equal to or less than 100%, an average block size of the pearlite is 10 μm to 30 μm and standard deviation of block size is 20 μm or less, and when Ceq.=C (%)+Si (%)/24+Mn (%)/6, a tensile strength is equal to or more than 760×Ceq.+255 MPa and equal to or less than 760×Ceq.+325 MPa, reduction of area in a tensile test is −65×Ceq.+96(%) or more, and standard deviation of the reduction of area is 6% or less.

A core portion of the carbonitrided bearing component includes a chemical composition consisting of, in mass %, C: 0.15 to 0.45%, Si: 0.50% or less, Mn: 0.20 to 0.60%, P: 0.015% or less, S: 0.005% or less, Cr 0.80 to 1.50%, Mo: 0.17 to 0.30%, V: 0.24 to 0.40%, Al: 0.005 to 0.100%, N: 0.0300% or less, O: 0.0015% or less, and the balance being Fe and impurities, and satisfying Formula (1) to Formula (4) described in the embodiment of the present specification. A concentration of C of its surface is, in mass %, 0.70 to 1.20%, a concentration of N of the surface is, in mass %, 0.15 to 0.60%, a Rockwell C-scale hardness HRC of the surface is 58 to 65, and in the core portion, an area ratio of an area of coarse V-based precipitates to a total area of V-based precipitates is 15.0% or less.

A graphite steel available as a material for mechanical parts of industrial machines or automobiles, and more particularly, a steel wire for graphitization heat treatment and a graphite steel and methods of manufacturing the same. The graphite steel includes, in percent by weight (wt %), 0.6 to 0.9% of carbon (C), 2.0 to 2.5% of silicon (Si), 0.1 to 0.6% of manganese (Mn), 0.015% or less of phosphorus (P), 0.03% or less of sulfur (S), 0.01 to 0.05% of aluminum (Al), 0.01 to 0.02% of titanium (Ti), 0.0005 to 0.002% of boron (B), 0.003 to 0.015% of nitrogen (N), 0.005% or less of oxygen (O), and the remainder of iron (Fe) and inevitable impurities, and satisfying Equation (1) below: wherein graphite grains are distributed in a ferrite base as a microstructure and a graphitization rate is 100%, (1) −0.003<[N]−[Ti]/3.43−[B]/0.77<0.003, wherein in Equation (1), [Ti], [N], and [B] are wt % of titanium, nitrogen, and boron, respectively.

A graphite steel available as a material for mechanical parts of industrial machines or automobiles, and more particularly, a steel wire for graphitization heat treatment and a graphite steel and methods of manufacturing the same. The graphite steel includes, in percent by weight (wt %), 0.6 to 0.9% of carbon (C), 2.0 to 2.5% of silicon (Si), 0.1 to 0.6% of manganese (Mn), 0.015% or less of phosphorus (P), 0.03% or less of sulfur (S), 0.01 to 0.05% of aluminum (Al), 0.01 to 0.02% of titanium (Ti), 0.0005 to 0.002% of boron (B), 0.003 to 0.015% of nitrogen (N), 0.005% or less of oxygen (O), and the remainder of iron (Fe) and inevitable impurities, and satisfying Equation (1) below: wherein graphite grains are distributed in a ferrite base as a microstructure and a graphitization rate is 100%, (1) −0.003<[N]−[Ti]/3.43−[B]/0.77<0.003, wherein in Equation (1), [Ti], [N], and [B] are wt % of titanium, nitrogen, and boron, respectively.

Provided are a non-quenched and tempered wire rod having excellent drawability and impact toughness suitable for materials for automobiles or mechanical parts and a method of manufacturing the same. According to an embodiment of the present disclosure, the non-quenched and tempered wire rod includes, in percent by weight (wt %), 0.05 to 0.35% of carbon (C), 0.05 to 0.5% of silicon (Si), 0.5 to 2.0% of manganese (Mn), 1.0% or less of chromium (Cr), 0.03% or less of phosphorus (P), 0.03% or less of sulfur (S), 0.01 to 0.07% of soluble aluminum (sol.Al), 0.01% or less of nitrogen (N), at least one of 0.1% or less of niobium (Nb), 0.5% or less of vanadium (V), and 0.1% or less of titanium (Ti), and the remainder of iron (Fe) and inevitable impurities, and includes a ferrite-pearlite layered structure, as a microstructure, in a rolling direction.

Provided are a non-quenched and tempered wire rod having excellent drawability and impact toughness suitable for materials for automobiles or mechanical parts and a method of manufacturing the same. According to an embodiment of the present disclosure, the non-quenched and tempered wire rod includes, in percent by weight (wt %), 0.05 to 0.35% of carbon (C), 0.05 to 0.5% of silicon (Si), 0.5 to 2.0% of manganese (Mn), 1.0% or less of chromium (Cr), 0.03% or less of phosphorus (P), 0.03% or less of sulfur (S), 0.01 to 0.07% of soluble aluminum (sol.Al), 0.01% or less of nitrogen (N), at least one of 0.1% or less of niobium (Nb), 0.5% or less of vanadium (V), and 0.1% or less of titanium (Ti), and the remainder of iron (Fe) and inevitable impurities, and includes a ferrite-pearlite layered structure, as a microstructure, in a rolling direction.

The present disclosure relates to a steel wire rod enabling the omission of softening heat treatment and a method of manufacturing same. An embodiment of the present disclosure provides a steel wire rod enabling the omission of softening heat treatment and a method of manufacturing same, the steel wire rod comprising, in weight %, 0.2-0.45% of C, 0.02-0.4% of Si, 0.3-1.5% of Mn, 0.01-1.5% of Cr, 0.02-0.05% of Al, 0.01-0.5% of Mo, 0.01% or less of N, and the balance Fe and other unavoidable impurities, wherein the microstructure of the steel wire rod is a composite structure of proeutectoid ferrite+perlite as a main phase; the steel wire rod contains 10 area % or less (including 0%) of at least one of bainite or martensite; and the average colony size of the perlite is 5 μm or less.

This hot-rolled wire rod includes, as a chemical composition, by mass %: C: 0.90% to 1.10%; Si: 0.50% to 0.80%; Mn: 0.10% to 0.70%; Cr: 0.10% to 0.40%; P: 0.020% or less; S: 0.015% or less; N: 0.0060% or less; O: 0.0040% or less; and a remainder consisting of Fe and impurities, in which Formulas (1) and (2) are satisfied by mass %, the structure of the hot-rolled wire rod consists of pearlite in an area ratio of 95.0% or more and a remainder, and TS, which is a tensile strength in unit of MPa, and TS*, which is determined from the C content, the Si content, and the Cr content, satisfy Formula (3),

0.50≤[Si]+[Cr]≤0.90  (1)

0.40≤[Cr]+[Mn]≤0.80  (2)

−50<TS−TS*<50  (3) where the TS* is calculated by Formula (3′),

TS*=1000×[C]+100×[Si]+125×[Cr]+150  (3′).

This hot-rolled wire rod includes, as a chemical composition, by mass %: C: 0.90% to 1.10%; Si: 0.50% to 0.80%; Mn: 0.10% to 0.70%; Cr: 0.10% to 0.40%; P: 0.020% or less; S: 0.015% or less; N: 0.0060% or less; O: 0.0040% or less; and a remainder consisting of Fe and impurities, in which Formulas (1) and (2) are satisfied by mass %, the structure of the hot-rolled wire rod consists of pearlite in an area ratio of 95.0% or more and a remainder, and TS, which is a tensile strength in unit of MPa, and TS*, which is determined from the C content, the Si content, and the Cr content, satisfy Formula (3),

0.50≤[Si]+[Cr]≤0.90  (1)

0.40≤[Cr]+[Mn]≤0.80  (2)

−50<TS−TS*<50  (3) where the TS* is calculated by Formula (3′),

TS*=1000×[C]+100×[Si]+125×[Cr]+150  (3′).