A steel according to an aspect of the present invention has a chemical composition within a predetermined range, in which a hardenability index Ceq ranges from greater than 7.5 to smaller than 44.0, an AlN precipitation index I.sub.AlN ranges from greater than 0.00030 to smaller than 0.00110, a metallographic structure includes ferrite ranging from 85 to 100 area %, an average distance between sulfides, which are observed in a cross section parallel to a rolling direction of the steel and have an equivalent circle diameter ranging from 1 m or greater to smaller than 2 m, is shorter than 30.0 m, and a presence density of the sulfides, which are observed in the cross section parallel to the rolling direction of the steel and have an equivalent circle diameter ranging from 1 m or greater to smaller than 2 m, is 300 pieces/mm.sup.2 or more.

A steel according to an aspect of the present invention has a chemical composition within a predetermined range, in which a hardenability index Ceq ranges from greater than 7.5 to smaller than 44.0, an AlN precipitation index I.sub.AlN ranges from greater than 0.00030 to smaller than 0.00110, a metallographic structure includes ferrite ranging from 85 to 100 area %, an average distance between sulfides, which are observed in a cross section parallel to a rolling direction of the steel and have an equivalent circle diameter ranging from 1 m or greater to smaller than 2 m, is shorter than 30.0 m, and a presence density of the sulfides, which are observed in the cross section parallel to the rolling direction of the steel and have an equivalent circle diameter ranging from 1 m or greater to smaller than 2 m, is 300 pieces/mm.sup.2 or more.

A method of hardening a planetary gear shaft includes carbonitriding an outer peripheral surface of the planetary gear shaft and quenching the planetary gear shaft in oil at a temperature between approximately 120 and 150 C. The method also includes quenching the planetary gear shaft in a liquid at a temperature between approximately 70 and 120 C., and tempering the planetary gear shaft. After tempering, the outer peripheral surface of the planetary gear shaft includes a surface hardness of HV 832 or more and with the shaft material maintaining a hardness of at least HV 513 to a depth of at least 0.5 mm. High temperature tempering and induction hardening steps may be added to obtain soft ends of the shaft suitable for a staking operation.

A method of hardening a planetary gear shaft includes carbonitriding an outer peripheral surface of the planetary gear shaft and quenching the planetary gear shaft in oil at a temperature between approximately 120 and 150 C. The method also includes quenching the planetary gear shaft in a liquid at a temperature between approximately 70 and 120 C., and tempering the planetary gear shaft. After tempering, the outer peripheral surface of the planetary gear shaft includes a surface hardness of HV 832 or more and with the shaft material maintaining a hardness of at least HV 513 to a depth of at least 0.5 mm. High temperature tempering and induction hardening steps may be added to obtain soft ends of the shaft suitable for a staking operation.

Provided is a rail vehicle axle having an excellent fatigue limit and notch factor. A rail vehicle axle according to the present embodiment has a chemical composition consisting of, in mass %, C: 0.20 to 0.35%, Si: 0.20 to 0.65%, Mn: 0.40 to 1.20%, P: 0.020% or less, S: 0.020% or less, Sn: 0.07 to 0.40%, N: 0.0200% or less, Cu: 0 to 0.30%, Ni: 0 to 0.30%, Cr: 0 to 0.30%, Mo: 0 to 0.08%, Al: 0 to 0.100%, V: 0 to 0.060%, and Ti: 0 to 0.020%, with the balance being Fe and impurities, and satisfying Formulae (1) and (2):

0.58?C+Si/8+Mn/5+Cu/10+Cr/4+V?0.67(1)

Si+0.9Cr?0.50(2) where, each element symbol in Formulae (1) and (2) is substituted by the content (mass %) of a corresponding element.

Provided is a rail vehicle axle having an excellent fatigue limit and notch factor. A rail vehicle axle according to the present embodiment has a chemical composition consisting of, in mass %, C: 0.20 to 0.35%, Si: 0.20 to 0.65%, Mn: 0.40 to 1.20%, P: 0.020% or less, S: 0.020% or less, Sn: 0.07 to 0.40%, N: 0.0200% or less, Cu: 0 to 0.30%, Ni: 0 to 0.30%, Cr: 0 to 0.30%, Mo: 0 to 0.08%, Al: 0 to 0.100%, V: 0 to 0.060%, and Ti: 0 to 0.020%, with the balance being Fe and impurities, and satisfying Formulae (1) and (2):

0.58?C+Si/8+Mn/5+Cu/10+Cr/4+V?0.67(1)

Si+0.9Cr?0.50(2) where, each element symbol in Formulae (1) and (2) is substituted by the content (mass %) of a corresponding element.

A method of hardening an article of manufacture that includes a body that defines a longitudinal axis made of a material that is capable of being hardened and that is intended for a particular use includes locally heating the material at a first location found on the article along the axis to a first predetermined depth in a direction that is perpendicular to the axis and locally heating the material at a second location found on the article along the axis to a second predetermined depth in a direction that is perpendicular to the axis, wherein the first predetermined depth is different than the second predetermined depth.

A method of hardening an article of manufacture that includes a body that defines a longitudinal axis made of a material that is capable of being hardened and that is intended for a particular use includes locally heating the material at a first location found on the article along the axis to a first predetermined depth in a direction that is perpendicular to the axis and locally heating the material at a second location found on the article along the axis to a second predetermined depth in a direction that is perpendicular to the axis, wherein the first predetermined depth is different than the second predetermined depth.

Provided is a method for manufacturing a magnetostrictive torque sensor shaft mounting a sensor portion of a magnetostrictive torque sensor. The method includes conducting heat treatment on a shaft material including chrome steel or chrome-molybdenum steel by carburizing, quenching and tempering, and conducting shot peening on the shaft material after the heat treatment at least on a position where the sensor portion is to be mounted. The shot peening is conducted by firing shot with a particle size of not less than 0.6 mm and a Rockwell hardness of not less than 60 at a jet pressure of not less than 0.4 MPa for a jet exposure time of not less than 2 minutes.

Multi-chamber furnace for vacuum carburizing and quenching of gears, shafts, rings and similar components has at least two process chambers connected in parallel, with a continuous feeding mechanism for individual workpieces. Those chambersthe first one being a heating chamber, the second being a carburizing chamber and the third one diffusion chamberare configured in a vertical arrangement, placed in a shared vacuum space with gas-tight division, whereas at the ends of each chamber there are incorporated heating chambers with thermal insulation, with a graphite heating system and stepping feeding mechanism incorporated in the core for the purpose of continuous feeding of individual workpieces. At the ends of those chambers the construction incorporates transport chambers featuring loading and unloading systems X-Y enabling cooperation with individual process chambers through thermal and gas-tight doors installed in chamber ends, while external access to the transport chambers is ensured through loading and unloading locks.