Disclosed are a case hardened steel which is suitable as a material for producing mechanical structural parts having high rotating bending fatigue strength and impact fatigue strength at a relatively low cost, and a method of producing the same. The case hardening steel has a chemical composition containing, by mass %, C, Si, Mn, P, S, Cr, Mo, B, Ti, N, and O within a range satisfying a predetermined relationship, and Al in at least a predetermined amount in relation to the B, N, and Ti contents, with the balance being Fe and inevitable impurities, wherein √I≤80 is satisfied, where I represents an area in μm.sup.2 of an oxide-based inclusion located at the center of a fish-eye on a fracture surface of the case hardening steel after being subjected to carburizing-quenching and tempering and subsequently to a rotating bending fatigue test.

Disclosed are a case hardened steel which is suitable as a material for producing mechanical structural parts having high rotating bending fatigue strength and impact fatigue strength at a relatively low cost, and a method of producing the same. The case hardening steel has a chemical composition containing, by mass %, C, Si, Mn, P, S, Cr, Mo, B, Ti, N, and O within a range satisfying a predetermined relationship, and Al in at least a predetermined amount in relation to the B, N, and Ti contents, with the balance being Fe and inevitable impurities, wherein √I≤80 is satisfied, where I represents an area in μm.sup.2 of an oxide-based inclusion located at the center of a fish-eye on a fracture surface of the case hardening steel after being subjected to carburizing-quenching and tempering and subsequently to a rotating bending fatigue test.

A gear assembly comprises a plurality of planet gear layshafts that have an outer surface having a plurality of gear surfaces and a surface having one or more bearing surfaces. The one or more bearing surfaces of the surfaces of the planet gear layshafts have a first case hardening depth and a first nitriding hardness depth. The gear surfaces of the outer surface of the planet gear layshafts have a second case hardening depth.

There is provided a steel material that is excellent in machinability, and that provides a high roller-pitting fatigue strength, a high high-cycle bending fatigue strength, and a high low-cycle bending fatigue strength when being subjected to induction hardening to be produced into an induction-hardened component. The steel material according to the present disclosure includes a chemical composition consisting of, in mass %, C: 0.40 to 0.70%, Si: 0.15 to 2.10%, Mn: 0.30 to 1.15%, Cr: 0.01 to less than 0.50%, S: 0.005 to 0.070%, N: 0.0020 to 0.0200%, Ti: 0.0080 to 0.2000%, B: 0.0005 to 0.0050%, Al: 0.005 to 0.100%, and P: less than 0.050%, with the balance being Fe and impurities, and satisfying Formula (1) to Formula (5) described herein, and has a ferrite area fraction of 40% or less and a martensite area fraction of 10% or less.

There is provided a steel material that is excellent in machinability, and that provides a high roller-pitting fatigue strength, a high high-cycle bending fatigue strength, and a high low-cycle bending fatigue strength when being subjected to induction hardening to be produced into an induction-hardened component. The steel material according to the present disclosure includes a chemical composition consisting of, in mass %, C: 0.40 to 0.70%, Si: 0.15 to 2.10%, Mn: 0.30 to 1.15%, Cr: 0.01 to less than 0.50%, S: 0.005 to 0.070%, N: 0.0020 to 0.0200%, Ti: 0.0080 to 0.2000%, B: 0.0005 to 0.0050%, Al: 0.005 to 0.100%, and P: less than 0.050%, with the balance being Fe and impurities, and satisfying Formula (1) to Formula (5) described herein, and has a ferrite area fraction of 40% or less and a martensite area fraction of 10% or less.

A method for producing a machine component excellent in pitting resistance characteristics and toughness includes a carburizing step, performed on a steel material containing 0.13-0.30% C and 0.90-2.00% Cr in mass % and at least one of Si, Mn, Ni, Mo, Nb, V, Ti, B, Al, and N, balance Fe and unavoidable impurities; heating the material to 850-1030° C. to attain carbon concentration in a surface of 0.8-1.5%; cooling the material at an average rate of 5° C./sec or lower from a temperature higher than the A.sub.cm point of a surface layer to a cooling end temperature that is at least 50° C. lower than the A.sub.1 point to cause the surface layer to have a pearlite or bainite structure with dispersion; spheroidizing annealing at a temperature not higher than the A.sub.cm point at the surface layer; heating the material to not higher than the A.sub.cm point at the surface layer; and performing tempering.

A method for producing a machine component excellent in pitting resistance characteristics and toughness includes a carburizing step, performed on a steel material containing 0.13-0.30% C and 0.90-2.00% Cr in mass % and at least one of Si, Mn, Ni, Mo, Nb, V, Ti, B, Al, and N, balance Fe and unavoidable impurities; heating the material to 850-1030° C. to attain carbon concentration in a surface of 0.8-1.5%; cooling the material at an average rate of 5° C./sec or lower from a temperature higher than the A.sub.cm point of a surface layer to a cooling end temperature that is at least 50° C. lower than the A.sub.1 point to cause the surface layer to have a pearlite or bainite structure with dispersion; spheroidizing annealing at a temperature not higher than the A.sub.cm point at the surface layer; heating the material to not higher than the A.sub.cm point at the surface layer; and performing tempering.

The invention relates to a device for water spray quenching that includes (i) a quenching chamber designed and set up to receive metallic workpieces, with a batch of volume V.sub.0 of 0.045 to 3.5 m.sup.3 and (ii) at least one atomizer which is configured to atomize water in air or nitrogen and is fluidically connected to the quenching chamber; in which the at least one atomizer and the device are designed and set up to generate a spray mist with a water content of 2.5 to 40 vol. % and a Sauter mean diameter of 20 to 2000 m and also a spray mist flow through the batch volume V.sub.0 of 0.05 to 25 m.sup.3/s.

The invention relates to a device for water spray quenching that includes (i) a quenching chamber designed and set up to receive metallic workpieces, with a batch of volume V.sub.0 of 0.045 to 3.5 m.sup.3 and (ii) at least one atomizer which is configured to atomize water in air or nitrogen and is fluidically connected to the quenching chamber; in which the at least one atomizer and the device are designed and set up to generate a spray mist with a water content of 2.5 to 40 vol. % and a Sauter mean diameter of 20 to 2000 m and also a spray mist flow through the batch volume V.sub.0 of 0.05 to 25 m.sup.3/s.

Provided is a supporting structure for an induction heating coil and an induction heating device in which a surface of an induction heating coil is not formed of a coating film for insulation that generates a gas, and movement of the induction heating coil when the induction heating coil is energized can be suppressed. A supporting structure 4 of an induction heating device 1 includes a supporting column 20 and a plurality of restricting members 21. The supporting column 20 is disposed at an outer side in a radial direction of winding portions 13 of the induction heating coil 3, and extends in an axial direction S1. The restricting members 21 receive the induction heating coil 3 to restrict movement of the induction heating coil 3 in the axial direction S1 in an insulated state, and are supported by the supporting column 20.