A compression coil spring includes a steel wire material containing, hereinafter in weight %, 0.5 to 0.7% of C, 1.2 to 3.0% of Si, 0.3 to 1.2% of Mn, 0.5 to 1.9% of Cr and 0.05 to 0.5% of V as necessary components, one or more kinds selected from not more than 1.5% of Ni, not more than 1.5% of Mo and not more than 0.5% of W as freely selected components, and iron and inevitable impurities as the remainder; the C-condensed layer which exceeds the average concentration of C contained in the steel wire material exists at a surface layer part, and the thickness of the C-condensed layer is within 0.01 to 0.05 mm along the entire circumference of the steel wire material.

A compression coil spring includes a steel wire material containing, hereinafter in weight %, 0.5 to 0.7% of C, 1.2 to 3.0% of Si, 0.3 to 1.2% of Mn, 0.5 to 1.9% of Cr and 0.05 to 0.5% of V as necessary components, one or more kinds selected from not more than 1.5% of Ni, not more than 1.5% of Mo and not more than 0.5% of W as freely selected components, and iron and inevitable impurities as the remainder; the C-condensed layer which exceeds the average concentration of C contained in the steel wire material exists at a surface layer part, and the thickness of the C-condensed layer is within 0.01 to 0.05 mm along the entire circumference of the steel wire material.

Spring steel includes: as a chemical composition, by mass %, C: 0.40% to 0.60%, Si: 0.90% to 2.50%, Mn: 0.20% to 1.20%, Cr: 0.15% to 2.00%, Ni: 0.10% to 1.00%, Ti: 0.030% to 0.100%, B: 0.0010% to 0.0060%, N: 0.0010% to 0.0070%, Cu: 0% to 0.50%, Mo: 0% to 1.00%, V: 0% to 0.50%, Nb: 0% to 0.10%, P: limited to less than 0.020%, S: limited to less than 0.020%, Al: limited to less than 0.050%, and a remainder including Fe and impurities, in a case where [Ti] represents a Ti content and [N] represents a N content by mass %, the chemical composition satisfies ([Ti]3.43[N])>0.03, and a total number density of a Ti carbide and a Ti carbonitride having a diameter of 5 nm to 100 nm is more than 50 piece/m.sup.3.

Spring steel includes: as a chemical composition, by mass %, C: 0.40% to 0.60%, Si: 0.90% to 2.50%, Mn: 0.20% to 1.20%, Cr: 0.15% to 2.00%, Ni: 0.10% to 1.00%, Ti: 0.030% to 0.100%, B: 0.0010% to 0.0060%, N: 0.0010% to 0.0070%, Cu: 0% to 0.50%, Mo: 0% to 1.00%, V: 0% to 0.50%, Nb: 0% to 0.10%, P: limited to less than 0.020%, S: limited to less than 0.020%, Al: limited to less than 0.050%, and a remainder including Fe and impurities, in a case where [Ti] represents a Ti content and [N] represents a N content by mass %, the chemical composition satisfies ([Ti]3.43[N])>0.03, and a total number density of a Ti carbide and a Ti carbonitride having a diameter of 5 nm to 100 nm is more than 50 piece/m.sup.3.

Disclosed are a device and method for detecting heating treatment temperatures of double steel wires. The temperature detection device includes a double wires coiling machine, two heating mechanisms for respectively heating two steel wires, and two temperature detection mechanisms for respectively detecting temperatures of the two steel wires in real time, and a controller electrically connected to the two heating mechanisms and the double-wire spring coiling machine respectively.

Disclosed are a device and method for detecting heating treatment temperatures of double steel wires. The temperature detection device includes a double wires coiling machine, two heating mechanisms for respectively heating two steel wires, and two temperature detection mechanisms for respectively detecting temperatures of the two steel wires in real time, and a controller electrically connected to the two heating mechanisms and the double-wire spring coiling machine respectively.

A process for producing a spring or torsion bar from a steel wire by hot forming may involve providing a steel wire; thermomechanically forming the steel wire; cooling the steel wire thermomechanically; cutting the steel wire to length to give rods; heating the rods; hot forming the rods; and tempering the rods to give a spring or torsion bar, comprising quenching the rods to give a spring or torsion bar to a first cooling temperature, reheating the spring or torsion bar to a first annealing temperature, and cooling the spring or rod to a second cooling temperature. Further, in some examples, the cooling of the steel wire may be cooled to a temperature below a minimum recrystallization temperature such that at least a partly ferritic-pearlitic structure is established in the steel wire.

A process for producing a spring or torsion bar from a steel wire by hot forming may involve providing a steel wire; thermomechanically forming the steel wire; cooling the steel wire thermomechanically; cutting the steel wire to length to give rods; heating the rods; hot forming the rods; and tempering the rods to give a spring or torsion bar, comprising quenching the rods to give a spring or torsion bar to a first cooling temperature, reheating the spring or torsion bar to a first annealing temperature, and cooling the spring or rod to a second cooling temperature. Further, in some examples, the cooling of the steel wire may be cooled to a temperature below a minimum recrystallization temperature such that at least a partly ferritic-pearlitic structure is established in the steel wire.

An ultra-high-strength spring steel for an engine valve spring steel comprises, by weight: 0.5-0.7% of carbon (C), 1.3-2.3% of silicon (Si), 0.6-1.2% of manganese (Mn), 0.6-1.2% of chrome (Cr), 0.1-0.5% of molybdenum (Mo), 0.05-0.8% of nickel (Ni), 0.05-0.5% of vanadium (V), 0.05-0.5% of niobium (Nb), 0.05-0.3% of titanium (Ti), 0.001-0.01% of boron (B), 0.01-0.52% of tungsten (W), 0.3% or less (0% exclusive) of copper (Cu), 0.3% or less (0% exclusive) of aluminum (Al), 0.03% or less (0% exclusive) of nitrogen (N), 0.003% or less (0% exclusive) of oxygen (O), and a remainder of Fe and other inevitable impurities, based on 100% by weight of the ultra-high-strength spring steel.

The present invention relates to a ferritic stainless steel according to the present invention, containing, in mass %: 0.001%C0.020%, 0.05%Si0.50%, 0.1%Mn1.0%, 15.0%Cr25.0%, Mo<0.50%, 0.50%W5.00%, and 0.01%Nb0.50%, with a balance being Fe and unavoidable impurities, having a content (coarse Laves phase ratio) of coarse Laves phase having a diameter of 0.50 m or more being 0.1% or less, and having an average grain size being 30 m or more and 200 m or less.