High-strength PC steel wire
This invention provides a high-strength PC steel wire having a chemical composition containing, in mass %, C: 0.90 to 1.10%, Si: 0.80 to 1.50%, Mn: 0.30 to 0.70%, P: 0.030% or less, S: 0.030% or less, Al: 0.010 to 0.070%, N: 0.0010 to 0.010%, Cr: 0 to 0.50%, V: 0 to 0.10%, B: 0 to 0.005%, Ni: 0 to 1.0%, Cu: 0 to 0.50%, and the balance: Fe and impurities. A ratio between the Vickers hardness (Hv S ) at a location (surface layer) that is 0.1D [D: diameter of steel wire] from the surface of the steel wire and the Vickers hardness (Hv I ) of a region on the inner side relative to the surface layer satisfies the formula [1.10<Hv S /Hv I ≤1.15]. The steel micro-structure in the region from the surface of the steel wire to 0.01D (outermost layer region) consists of, in area %, a pearlite structure: less than 80%, and the balance: a ferrite structure and/or a bainitic structure. The steel micro-structure in the region on the inner side relative to the outermost layer region contains, in area %, a pearlite structure: 95% or more. The tensile strength of the steel wire is 2000 to 2400 MPa. The method of producing this high-strength PC steel wire is simple, and the high-strength PC steel wire is excellent in delayed fracture resistance characteristics.
1. A PC steel wire, having a chemical composition containing, in mass %,
C: 0.90 to 1.10%,
Si: 0.80 to 1.50%,
Mn: 0.30 to 0.70%,
P: 0.030% or less,
S: 0.030% or less,
Al: 0.010 to 0.070%,
N: 0.0010 to 0.010%,
Cr: 0 to 0.50%,
V: 0 to 0.10%,
B: 0 to 0.005%,
Ni: 0 to 1.0%,
Cu: 0 to 0.50%, and
the balance: Fe and impurities;
wherein:
when a diameter of the steel wire is represented by D, a ratio between a Vickers hardness at a location 0.1D from a surface of the steel wire and a Vickers hardness of a region on an inner side relative to the location 0.1D from the surface of the steel wire satisfies formula (i) below,
a steel micro-structure in a region from the surface to a depth of 0.01 D of the steel wire comprises, in area %:
pearlite structure: less than 80%, and
the balance: a ferrite structure, a bainitic structure, or a ferrite structure and a bainitic structure;
a steel micro-structure in a region on an inner side relative to the region from the surface to a depth of 0.01 D of the steel wire comprises, in area %:
pearlite structure: 95% or more; and
a tensile strength is 2000 to 2400 MPa;
1.10< Hv S /Hv I ≤1.15 (i)
where, the meaning of each symbol in the formula (i) is as follows:
Hv S : Vickers hardness of the location 0.1D from the surface of the steel wire;
Hv I : Vickers hardness of the region on the inner side relative to the location 0.1D from the surface of the steel wire.
2. The PC steel wire according to claim 1 , wherein the chemical composition contains, in mass %, at least one element selected from
Cr: 0.05 to 0.50%,
V: 0.01 to 0.10%, and
B: 0.0001 to 0.005%.
3. The PC steel wire according to claim 1 , wherein the chemical composition contains, in mass %, at least one element selected from
Ni: 0.1 to 1.0%, and
Cu: 0.05 to 0.50%.
4. The PC steel wire according to claim 2 , wherein the chemical composition contains, in mass %, at least one element selected from
Ni: 0.1 to 1.0%, and
Cu: 0.05 to 0.50%.