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.sub.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.sub.I) of a region on the inner side relative to the surface layer satisfies the formula [1.10<Hv.sub.S/Hv.sub.I1.15]. 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.

A method for manufacturing a high-strength steel bar can include the steps of: reheating a steel slab at a temperature ranging from 1000 C. to 1100 C., the steel slab including a certain amount of carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), chromium (Cr), copper (Cu), nickel (Ni), molybdenum (Mo), aluminum (Al), vanadium (V), nitrogen (N), antimony (Sb), tin (Sn), and iron (Fe) and other inevitable impurities, The method can further include finish hot-rolling the reheated steel slab at a temperature of 850 C. to 1000 C., and cooling the hot-rolled steel to a martensite transformation start temperature (Ms ( C.)) through a tempcore process.

Provided is a wire rod for a concrete reinforcing steel fiber, a steel fiber, and a manufacturing method therefor. According to one disclosed embodiment of a wire rod for a concrete reinforcing steel fiber, the wire rod comprises, by weight, C: 0.01 to 0.04%, Si: 0.07 to 0.3%, Mn: 1.0 to 2.0%, P: 0.1 to 0.3% and the balance of Fe and other unavoidable impurities, wherein, when the radius of the wire rod is r, in a region from the center of a cross section perpendicular of the longitudinal direction to 0.95*r, the area fraction of ferrite is 90% or more, and the remainder comprises pearlite, wherein the average grain size of the ferrite may be 30 m or less and the colony size of the pearlite may be 10 m or less.

Provided is a wire rod for a concrete reinforcing steel fiber, a steel fiber, and a manufacturing method therefor. According to one disclosed embodiment of a wire rod for a concrete reinforcing steel fiber, the wire rod comprises, by weight, C: 0.01 to 0.04%, Si: 0.07 to 0.3%, Mn: 1.0 to 2.0%, P: 0.1 to 0.3% and the balance of Fe and other unavoidable impurities, wherein, when the radius of the wire rod is r, in a region from the center of a cross section perpendicular of the longitudinal direction to 0.95*r, the area fraction of ferrite is 90% or more, and the remainder comprises pearlite, wherein the average grain size of the ferrite may be 30 m or less and the colony size of the pearlite may be 10 m or less.

A high manganese content deformed reinforcing bar having an austenite single phase microstructure has excellent bending workability. A deformed reinforcing bar includes a chemical composition containing, in mass %, C: 0.7% or more and 1.2% or less, Si: 1.0% or less, Mn: 9% or more and 15% or less, Cr: 1.0% or less, P: 0.03% or less, and S: 0.05% or less, the balance consisting of Fe and inevitable impurities; and a microstructure comprising an austenite single phase. The ratio of the difference between the maximum and minimum hardness at a periphery of a cross-section perpendicular to the longitudinal direction with respect to a central average hardness is 15% or less. Two or more ribs extend in the longitudinal direction at equal intervals in a cross-sectional circumferential direction. The ratio of the difference between the maximum and minimum width of the ribs to the minimum width is 50% or less.

A high manganese content deformed reinforcing bar having an austenite single phase microstructure has excellent bending workability. A deformed reinforcing bar includes a chemical composition containing, in mass %, C: 0.7% or more and 1.2% or less, Si: 1.0% or less, Mn: 9% or more and 15% or less, Cr: 1.0% or less, P: 0.03% or less, and S: 0.05% or less, the balance consisting of Fe and inevitable impurities; and a microstructure comprising an austenite single phase. The ratio of the difference between the maximum and minimum hardness at a periphery of a cross-section perpendicular to the longitudinal direction with respect to a central average hardness is 15% or less. Two or more ribs extend in the longitudinal direction at equal intervals in a cross-sectional circumferential direction. The ratio of the difference between the maximum and minimum width of the ribs to the minimum width is 50% or less.

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.sub.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.sub.I) of a region on the inner side relative to the surface layer satisfies the formula [1.10<Hv.sub.S/Hv.sub.I1.15]. 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.

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.sub.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.sub.I) of a region on the inner side relative to the surface layer satisfies the formula [1.10<Hv.sub.S/Hv.sub.I1.15]. 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.

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.sub.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.sub.I) of a region on the inner side relative to the surface layer satisfies the formula [1.10<Hv.sub.S/Hv.sub.I1.15]. An average carbon concentration in a region from the surface to a depth of 10 m (outermost layer region) of the steel wire is 0.8 times or less a carbon concentration of the steel wire. 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.

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.sub.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.sub.I) of a region on the inner side relative to the surface layer satisfies the formula [1.10<Hv.sub.S/Hv.sub.I1.15]. An average carbon concentration in a region from the surface to a depth of 10 m (outermost layer region) of the steel wire is 0.8 times or less a carbon concentration of the steel wire. 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.