There is provided a steel material that has a high critical working ratio in cold forging and has a high fatigue strength and an excellent hydrogen embrittlement resistance when the steel material is formed into a carburized-steel component. The steel material according to the present embodiment has a chemical composition that contains, in mass %, C: 0.07 to 0.13%, Si: 0.15 to 0.35%, Mn: 0.60 to 0.80%, S: 0.005 to 0.050%, Cr: 1.90 to 2.50%, B: 0.0005 to 0.0100%, Ti: 0.010 to less than 0.050%, Al: 0.010 to 0.100%, Ca: 0.0002% to 0.0030%, N: 0.0080% or less, P: 0.050% or less, and O: 0.0030% or less, with the balance being Fe and impurities, and satisfies Formula (1) to Formula (5) described in the specification.

A sintered material with a composition composed of an iron-based alloy and a structure in which the number of compound particles 0.3 μm or more in size is less than 200 per 100 μm×100 μm unit area in a cross section, wherein the sintered material has a relative density of 93% or more.

A steel for a gear includes, based on a total weight of the steel: C: 0.10-0.30 wt %, Si: 0.60-0.80 wt %, Mn: 0.25-0.75 wt %, Cr: 1.80-2.20 wt %, Ni: 0.50-1.50 wt %, Mo: 0.20-0.40 wt %, Nb: 0.025-0.050 wt %, V: 0.030-0.050 wt %, and a balance of Fe and inevitable impurities, wherein contents of Nb and V satisfy the following <Relationship Formula 1>:

0.055<[Nb]+[V]<0.100  <Relationship Formula 1>, wherein [Nb] represents a content of Nb and [V] represents a content of V.

A steel for a gear includes, based on a total weight of the steel: C: 0.10-0.30 wt %, Si: 0.60-0.80 wt %, Mn: 0.25-0.75 wt %, Cr: 1.80-2.20 wt %, Ni: 0.50-1.50 wt %, Mo: 0.20-0.40 wt %, Nb: 0.025-0.050 wt %, V: 0.030-0.050 wt %, and a balance of Fe and inevitable impurities, wherein contents of Nb and V satisfy the following <Relationship Formula 1>:

0.055<[Nb]+[V]<0.100  <Relationship Formula 1>, wherein [Nb] represents a content of Nb and [V] represents a content of V.

A differential hypoid gear, a pinion gear, and paired hypoid gears formed by a combination thereof are provided. The differential hypoid gear includes a ring-shaped main body and a tooth-forming surface, and has a chemical component composition including C: 0.15-0.30 mass %, Si: 0.55-1.00 mass %, Mn: 0.50-1.20 mass %, Cr: 0.50-1.50 mass %, Al: 0.020-0.080 mass %, B: 0.0005-0.0050 mass %, Ti: 0.01-0.08 mass %, N: 0.0020-0.0100 mass %, Mo: 0.25 mass % or less, and Nb: less than 0.10 mass %, the remainder being Fe and unavoidable impurities. The chemical component composition satisfies Formulae 1 and 2. The differential hypoid gear has a metallographic structure including mainly tempered martensite. A martensite ratio at an inside of a dedendum differs between an end portion of a tooth and a central portion of the tooth within a range of 15% or less. A core hardness of the dedendum at the central portion falls within 350-500 HV.

A charging device for the heat treatment of workpieces being provided with a hub, comprising a charging support, a shaft and at least one auxiliary hub, wherein the workpiece can be vertically supported on the shaft by auxiliary hub(s) precisely fitted into the hub, and the shaft being supported by the charging support as well as use of auxiliary hubs for the dimensionally stable hardening of gear-wheels in vertical position.

A charging device for the heat treatment of workpieces being provided with a hub, comprising a charging support, a shaft and at least one auxiliary hub, wherein the workpiece can be vertically supported on the shaft by auxiliary hub(s) precisely fitted into the hub, and the shaft being supported by the charging support as well as use of auxiliary hubs for the dimensionally stable hardening of gear-wheels in vertical position.

The invention relates to a method for machining a rack and to a rack (1) machined according to said method, for example a steering rack. In said method, the stress pattern that is present after hardening and/or straightening the rack and that has a chaotic internal stress distribution of tensile and compressive stresses is converted into a stress pattern that optimizes the strength and the use of the material and also the diameter of the rack, such that, without altering the structure, at least the region of the gear teeth (2) is pre-stressed, in a functionally combined series of steps of a machining pass, with a deliberately introduced internal compressive stress without tensile stress and with a predominantly uniform stress distribution or stress plane.

The invention relates to a method for machining a rack and to a rack (1) machined according to said method, for example a steering rack. In said method, the stress pattern that is present after hardening and/or straightening the rack and that has a chaotic internal stress distribution of tensile and compressive stresses is converted into a stress pattern that optimizes the strength and the use of the material and also the diameter of the rack, such that, without altering the structure, at least the region of the gear teeth (2) is pre-stressed, in a functionally combined series of steps of a machining pass, with a deliberately introduced internal compressive stress without tensile stress and with a predominantly uniform stress distribution or stress plane.

A method for heat treating a horological component includes the following steps: heating of the component by irradiation, using a laser beam, of at least 80% or at least 90% of the projected surface of the component parallel to the direction of the laser beam, and cooling of the component in a gas stream.