Disclosed are a wire rod for a steel fiber having a strength of 1,500 MPa or more without performing LP heat treatment during a wire drawing process, a steel fiber and, a method for manufacturing the same. The wire rod for a high-strength steel fiber according to the present disclosure includes, in percent by weight (wt %), 0.01 to 0.03% of C, 0.05 to 0.15% of Si, 1.0 to 2.0% of Mn, 0.05 to 0.15% of P, 0.005% or less (excluding 0) of Al, 0.01% or less (excluding 0) of N, 0.03% or less (excluding 0) of S, 0.02 to 0.08% of Sn, and the remainder of Fe and inevitable impurities, wherein a microstructure is single-phase ferrite.

Systems and methods disclosed herein relate to the manufacture of metallic material with a thermal expansion coefficient in a predetermined range, comprising: deforming, a metallic material comprising a first phase and a first thermal expansion coefficient. In response to the deformation, at least some of the first phase is transformed into a second phase, wherein the second phase comprises martensite, and orienting the metallic material in at least one predetermined orientation, wherein the metallic material, subsequent to deformation, comprises a second thermal expansion coefficient, wherein the second thermal expansion coefficient is within a predetermined range, and wherein the thermal expansion is in at least one predetermined direction. In some embodiments, the metallic material comprises the second phase and is thermo-mechanically deformed to orient the grains in at least one direction.

A valve spring which has an excellent fatigue limit is provided. A chemical composition of the valve spring according to the present embodiment contains, in mass %, C: 0.50 to 0.80%, Si: 1.20 to less than 2.50%, Mn: 0.25 to 1.00%, P: 0.020% or less. S: 0.020% or less: Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, Ca: 0.0001 to 0.0050%, and N: 0.0100% or less, with the balance being Fe and impurities. In the valve spring, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/μm.sup.3, and a numerical proportion of Ca sulfides with respect to a total number of oxide-based inclusions and sulfide-based inclusions is 0.20% or less.

The present invention discloses a wire rod for an ultrahigh-strength steel cord and a manufacturing method thereof. The manufacturing method includes: smelting molten steel where inclusions in sizes ≥5 μm are at a number density ≤0.5/mm.sup.2 and sizes of inclusions are ≤30 μm; casting the molten steel into an ingot blank with a center carbon segregation value of 0.92-1.08; cogging the ingot blank into an intermediate blank with a center carbon segregation value of 0.95-1.05; rolling the intermediate blank into a wire rod; and performing temperature control cooling on the wire rod to obtain a wire rod with high purity, high homogeneity and tensile strength ≤1,150 MPa. The wire rod may be used for an ultrahigh-strength steel cord with single tensile strength ≥3,600 MPa.

A steel wire which has excellent cold coiling workability, and which has an excellent fatigue limit when made into a spring is provided. A chemical composition of the steel wire according to the present, embodiment containing, in mass %, C: 0.50 to 0.80%, Si: 1.20 to less than 2.50%, Mn: 0.25 to 1.00%, P: 0.020% or less, S: 0.020% or less, Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, and N: 0.0100% or less, with the balance being Fe and impurities. In the steel wire, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/μm.sup.3.

A damper spring which has an excellent fatigue limit is provided. A chemical composition of the damper spring according to the present embodiment contains in mass %, C: 0.50 to 0.80%, Si: 1.20 to less than 2.50%, Mn: 0.25 to 1.00%, P: 0.020% or less, S: 0.020% or less, Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, and N: 0.0100% or less, with the balance being Fe and impurities. In the damper spring, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/m3.

An aspect of the present invention is to provide high-strength ultra-thick steel with excellent cryogenic strain aging impact toughness at the center thereof, and a method for manufacturing same. An embodiment of the present invention provides high-strength ultra-thick steel with excellent cryogenic strain aging impact toughness at the center thereof, and a method for manufacturing same, the steel comprising, by wt %, 0.02-0.06% of C, 1.8-2.2% of Mn, 0.7-1.1% of Ni, 0.2-0.5% of Mo, 0.005-0.03% of Nb, 0.005-0.018% of Ti, 80 ppm or less of P, 20 ppm or less of S, and the remainder of Fe and other evitable impurities, wherein the average grain size of grains having a high boundary angle of 15 degrees or greater is 15 μm or less as measured in a range of ⅜t-⅝t in the thickness (t) direction by EBSD.

A wire for gas-shielded arc welding includes, based on a total mass of the wire C: 0.01 mass % or more and 0.10 mass % or less, Si: 0.05 mass % or more and 0.55 mass % or less, Mn: 1.60 mass % or more and 2.40 mass % or less, Ti: 0.05 mass % or more and 0.25 mass % or less, Cu: 0.30 mass % or less, Al: 0.10 mass % or less, P: 0.025 mass % or less, and S: 0.010 mass % or less with the remainder being Fe and inevitable impurities. In addition, the following relationship is satisfied: 0.1≤[Ti]/[Si]≤3.0, where [Si] is the content of Si (mass %) based on the total mass of the wire and [Ti] is the content of Ti (mass %) based on the total mass of the wire.

Provided is a free-cutting steel that, despites not containing Pb, has machinability by cutting higher than or equal to that of a low carbon sulfur-lead composite free-cutting steel. A free-cutting steel comprises: a chemical composition that contains, in mass %, C: less than 0.09%, Mn: 0.50% to 1.50%, S: 0.250% to 0.600%, O: more than 0.010% and 0.050% or less, and Cr: 0.50% to 1.50%, with a balance consisting of Fe and inevitable impurities, and in which a A value defined by the following formula (1) is 6.0 to 18.0, and a steel microstructure in which at least 500 particles/mm.sup.2 of sulfide of less than 1 μm in equivalent circle diameter and at least 2000 particles/mm.sup.2 of sulfide of 1 μm to 5 μm in equivalent circle diameter are distributed.

Provided is a steel reinforcement including an amount of 0.07 to 0.43 wt % of carbon (C), an amount of 0.5 to 2.0 wt % of manganese (Mn), an amount of 0.05 to 0.5 wt % of silicon (Si), an amount greater than 0 and less than or equal to 0.5 wt % of chromium (Cr), an amount greater than 0 and less than or equal to 4.5 wt % of copper (Cu), an amount greater than 0 and less than or equal to 0.003 wt % of boron (B), an amount greater than 0 and less than or equal to 0.25 wt % of vanadium (V), an amount greater than 0 and less than or equal to 0.012 wt % of nitrogen (N), an amount greater than 0 and less than or equal to 0.03 wt % of phosphorus (P), an amount greater than 0 and less than or equal to 0.03 wt % of sulfur (S), an amount of 0.01 to 0.5 wt % of the sum of one or more of nickel (Ni), niobium (Nb) and titanium (Ti), the balance of iron (Fe), and other inevitable impurities. A final microstructure includes ferrite, bainite, pearlite, retained austenite, and precipitates comprising copper.