A wire heating system includes an induction heating apparatus having a power supply and an induction coil arranged to heat a wire rod by an induction heating using current supplied from the power supply, and a controller configured to control the current to be supplied to the induction coil based on a feeding speed of the wire rod. The induction heating apparatus has a heating section in which the wire rod is heated by the induction heating using the induction coil, and a soaking section located downstream of the heating section to homogenize the temperature distribution of the induction-heated wire rod. The controller is configured to control the current to be supplied to the induction coil such that a temperature of the wire rod at a downstream end of the soaking section becomes a target temperature.

A method of and an equipment for controlled cooling of one or multiple previously heated, straight, and thick steel wire to a predetermined temperature range between 400 C. and 650 C. Each of the thick steel wires is subjected to a controlled cooling-transformation treatment from austenite to pearlite, which occurs substantially after the wire leaves a forced water cooling length.

An annealing furnace for annealing a strand of steel. The annealing furnace including a first heating apparatus for heating the strand during operation of the annealing furnace. A transport device advances the strand in a direction of transport through the annealing furnace during operation of the annealing furnace. The annealing furnace also includes a first cooling device for cooling the outer surface of the strand with a gas guide in the direction of transport behind the first heater, wherein the gas guide is arranged in such a manner that a gas flows along the outer surface of the strand during operation of the annealing furnace for cooling the strand.

A steel for cold forging has a predetermined chemical composition, satisfies d+310.0 and SA/SB<0.30, includes 1200/mm.sup.2 or more of sulfides having an equivalent circle diameter of 1.0 to 10.0 m in a microstructure, and has an average distance between the sulfides of less than 30.0 m. Here, d is an average value of equivalent circle diameters of sulfides having an equivalent circle diameter of 1.0 m or more, is a standard deviation of the equivalent circle diameters of the sulfides having an equivalent circle diameter of 1.0 m or more, SA is the number of sulfides having an equivalent circle diameter of 1.0 m or more and less than 3.0 m, and SB is the number of the sulfides having an equivalent circle diameter of 1.0 m or more.

The present invention provides a steel material, such as a high-strength spring, that has excellent fatigue properties, and, more specifically, a steel material, such as the high-strength spring, that can improve the fatigue properties in a high-strength region more easily, without increasing an alloy cost. The steel material includes, in percent by mass, C: 0.5 to 1.0%, Si: 1.5 to 2.50%, Mn: 0.5 to 1.50%, P: more than 0% to 0.020% or less, S: more than 0% to 0.020% or less, Cr: more than 0% to 0.2% or less, Al: more than 0% to 0.010% or less, N: more than 0% to 0.0070% or less, and O: more than 0% to 0.0040% or less, and the balance consisting of iron and inevitable impurities, wherein Cr and Si contents satisfy a formula of CrSi0.20, a ratio of tempered martensite in a steel microstructure is 80% or more by area, and a number density of particles of Cr-containing carbide or carbonitride having a circle-equivalent diameter of 50 nm or more in the steel microstructure is 0.10 particles/m.sup.2 or less.

A wire rod according to an aspect of the present invention has a predetermined chemical composition, a solute N is 0.0015% or less, a structure in an area from a surface of the wire rod to a depth of of a diameter of the wire rod in a cross section thereof includes 90.0 area % or more of pearlite, and 0 to 10.0 area % in total of bainite and ferrite, a total amount of martensite and cementite in the area from the surface of the wire rod to the depth of of the diameter of the wire rod is limited to 2.0 area % or less, and the calculated maximum size of TiN-type inclusions in a surface layer area of the wire rod is 50 m or less.

A steel wire for machine structural parts, may include Fe, inevitable impurities, and, by mass: 0.05 to 0.60% C; 0.005 to 0.50% Si; 0.30 to 1.20% Mn; more than 0 to 0.050% P; more than 0 to 0.050% S; 0.001 to 0.10% Al; more than 0 to 1.5% Cr; and more than 0 to 0.02% N. An area of cementite present at ferrite grain boundaries in an area of all cementite of the steel wire may be 32% or more. When a C content (% by mass) of a steel is expressed as [C], an average circular-equivalent diameter of all the cementite is (1.668-2.13 [C]) ?m or more and (1.863-2.13 [C]) ?m or less.

The present invention relates to a ferritic free-cutting stainless steel material having a component composition contains: in terms of mass %, 10.0%?Cr?25.0%, 0.2%?Mn?2.0%, 0.30%?Al?2.50%, 0.02%?Si?0.60%, and 0.10%?S?0.45%, and further two or more selected from the group consisting of: 0.03%?Pb?0.40%, 0.03%?Bi?0.40%, and 0.01%?Te?0.10%, with a balance being Fe and unavoidable impurities. The component composition satisfies: 900([C]+[N])+170[Si]+12[Cr]+30[Mo]+10[Al]?300, and ([Cr]+[Mo]+1.5[Si]+4[Al])/([Ni]+0.5[Mn]+30[C]+30[N])?7. The ferritic free-cutting stainless steel material contains sulfides having a circle equivalent diameter of 1.5 ?m or more, and the sulfides have an average circle equivalent diameter of 3.0 to 15.0 ?m, an average aspect ratio of 2.5 or less, and an area ratio of 0.5 to 2.0%, and the maximum value of Vickers hardness of 170 HV or less.

Disclosed is an iron-nickel alloy having the following composition in percent by weight: 36.5%?Ni?38.5% 0.50%?Mn?1.25% 0.001%?Cu?0.85% 0.040%?C?0.150% 0.10%?Si?0.35%
the remainder being iron and unavoidable impurities resulting from the manufacturing.

The chemical composition of a steel material according to the present embodiment consists of, in mass %, C: 0.50 to 0.80%, Si: 1.20 to 2.90%, Mn: 0.25 to 1.00%, Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, P: 0.020% or less, S: 0.020% or less, N: 0.0100% or less, Mo: 0 to 0.50%, Nb: 0 to 0.050%, W: 0 to 0.60%, Ni: 0 to 0.50%, Co: 0 to 0.30%, B: 0 to 0.0050%, Cu: 0 to 0.050%, Al: 0 to 0.0050%, and Ti: 0 to 0.050%, with the balance being Fe and impurities. In the microstructure of the steel material, an area fraction of pearlite is 90% or more, and in ferrite in the pearlite, a volumetric number density of V-based precipitates having a maximum diameter of 2 to 20 nm is 3000 to 80000 pieces/?m.sup.3.