Rolled wire rod
A rolled wire rod wherein the contents of Ti, N, and S (mass %) are respectively [Ti], [N], and [S], and, if [S]≤0.0010, [Ti] is (4.5×[S]+3.4×[N]) or more and (0.008+3.4×[N]) or less, while if [S]≥0.0010, [Ti] is (4.5×[S]+3.4×[N]) or more and (8.0×[S]+3.4×[N]) or less, the internal structure is a mixed structure of ferrite and pearlite with an area ratio of a ferrite fraction of 40% or more, and a mean area of sulfides present in a range from a surface of the wire rod to a depth position D/8 from the surface of the wire rod is 6 μm 2 or less, wherein D represents a diameter, in mm, in a cross-section of the wire rod at a plane including the axis of the wire rod, and a mean aspect ratio of the sulfides is 5 or less.
1. A rolled wire rod comprising, by mass %,
C: 0.20% to less than 0.40%,
Mn: 0.10% to less than 0.40%,
S: less than 0.020%,
P: less than 0.020%,
Cr: 0.70% to 1.60%,
Al: 0.005% to 0.060%,
Ti: 0.010% to 0.080%,
B: 0.0003% to 0.0040%, and
N: 0.0020% to 0.0080% and having
a balance of Fe and impurities, wherein:
the contents of Ti, N, and S (mass %) are respectively [Ti], [N], and [S], and
if [S]≤0.0010, [Ti] is (4.5×[S]+3.4×[N]) or more and (0.008+3.4×[N]) or less, while
if [S]≥0.0010, [Ti] is (4.5×[S]+3.4×[N]) or more and (8.0×[S]+3.4×[N]) or less,
the internal structure is a mixed structure of ferrite and pearlite with an area ratio of a ferrite fraction of 40% or more, and
a mean area of sulfides present in a range from a surface of the wire rod to a depth position D/8 from the surface of the wire rod is 6 μm 2 or less, wherein D represents a diameter, in mm, in a cross-section of the wire rod at a plane including the axis of the wire rod, and a mean aspect ratio of the sulfides is 5 or less.
2. The rolled wire rod according to claim 1 comprising, instead of part of said Fe, by mass %, at least one type of Si: 0% to less than 0.40% and Nb: 0% to 0.050%.
3. The rolled wire rod according to claim 1 comprising, instead of part of said Fe, by mass %, at least one type of Cu: 0.50% or less, Ni: 0.30% or less, Mo: 0.05% or less, and V: 0.05% or less.
4. The rolled wire rod according to claim 1 comprising, instead of part of said Fe, by mass %, at least one type of Zr: 0.05% or less, Ca: 0.005% or less, and Mg: 0.005% or less.
5. The rolled wire rod according to claim 2 comprising, instead of part of said Fe, by mass %, at least one type of Cu: 0.50% or less, Ni: 0.30% or less, Mo: 0.05% or less, and V: 0.05% or less.
6. The rolled wire rod according to claim 2 comprising, instead of part of said Fe, by mass %, at least one type of Zr: 0.05% or less, Ca: 0.005% or less, and Mg: 0.005% or less.
7. The rolled wire rod according to claim 3 comprising, instead of part of said Fe, by mass %, at least one type of Zr: 0.05% or less, Ca: 0.005% or less, and Mg: 0.005% or less.