A nitrided steel part excellent in pitting resistance and bending fatigue characteristic enabling reduction of size and decrease of weight of parts or enabling demand for high load capacities to be met, using as a material a steel material containing, by mass %, C: 0.05 to 0.25%, Si: 0.05 to 1.5%, Mn: 0.2 to 2.5%, P: 0.025% or less, S: 0.003 to 0.05%, Cr: over 0.5 to 2.0%, Al: 0.01 to 0.05%, and N: 0.003 to 0.025%, having a balance of Fe and impurities, having formed on the steel surface a compound larger of a thickness 3 m or less containing iron, nitrogen, and carbon and a hardened layer formed below the compound layer, and having an effective hardened layer depth of 160 to 410 m.

A method for joining a carburized steel workpiece to a cast iron workpiece is provided that includes tempering a localized area of the carburized steel workpiece, machining the localized area to reduce carbon content, and welding the carburized steel workpiece to the cast iron workpiece at the localized area. The tempering may be performed by induction heating and results in a hardness profile of the localized area of less than 50 HRC.

A method for joining a carburized steel workpiece to a cast iron workpiece is provided that includes tempering a localized area of the carburized steel workpiece, machining the localized area to reduce carbon content, and welding the carburized steel workpiece to the cast iron workpiece at the localized area. The tempering may be performed by induction heating and results in a hardness profile of the localized area of less than 50 HRC.

A gearbox is provided having a housing, a gear having a plurality of teeth operationally configured within the housing, and a laser peening device located within the housing and configured to perform active laser peening on a predetermined surface of the gear while the gear is rotated within the housing. A method of maintaining compressive residual stresses in a gear is provided, the method including operating a gearbox to rotate a gear within the gearbox and laser peening a predetermined surface of the gear with a laser peening device located within the gearbox.

A gearbox is provided having a housing, a gear having a plurality of teeth operationally configured within the housing, and a laser peening device located within the housing and configured to perform active laser peening on a predetermined surface of the gear while the gear is rotated within the housing. A method of maintaining compressive residual stresses in a gear is provided, the method including operating a gearbox to rotate a gear within the gearbox and laser peening a predetermined surface of the gear with a laser peening device located within the gearbox.

A method for predicting a martensitic transformation rate and a method for setting processing conditions capable of improving the accuracy of a prediction of a martensitic transformation rate when a steel material is subjected to deformation processing as well as to heat treatment are provided. A method for predicting a martensitic transformation rate according to an embodiment includes predicting a rate of a transformation to a martensitic phase that appears when a steel material is subjected to deformation processing as well as to heat treatment in which a temperature of the steel material is changed, in which a martensitic transformation rate Vm is calculated by using a prediction formula, the method further including identifying parameters m and n of the prediction formula, and calculating the martensitic transformation rate at a predetermined temperature and a predetermined strain rate by using the prediction formula into which the identified parameters are substituted.

A method for predicting a martensitic transformation rate and a method for setting processing conditions capable of improving the accuracy of a prediction of a martensitic transformation rate when a steel material is subjected to deformation processing as well as to heat treatment are provided. A method for predicting a martensitic transformation rate according to an embodiment includes predicting a rate of a transformation to a martensitic phase that appears when a steel material is subjected to deformation processing as well as to heat treatment in which a temperature of the steel material is changed, in which a martensitic transformation rate Vm is calculated by using a prediction formula, the method further including identifying parameters m and n of the prediction formula, and calculating the martensitic transformation rate at a predetermined temperature and a predetermined strain rate by using the prediction formula into which the identified parameters are substituted.

A sprocket wheel for a bicycle includes a first main surface, which is flat in one or more sections, and a second main surface, which is situated opposite the first main surface. The second main surface is flat in one or more sections and extends parallel to the first main surface in one or more sections. The sprocket wheel also has an outer circumferential surface, which connects the first and the second main surface to one another and on which toothing is provided.

A sprocket wheel for a bicycle includes a first main surface, which is flat in one or more sections, and a second main surface, which is situated opposite the first main surface. The second main surface is flat in one or more sections and extends parallel to the first main surface in one or more sections. The sprocket wheel also has an outer circumferential surface, which connects the first and the second main surface to one another and on which toothing is provided.

A ring gear that, together with a sun gear and a pinion gear that is disposed radially outward of the sun gear and meshes with the sun gear, forms a planetary gear unit, the ring gear includes: a body, internal teeth that are configured to mesh with the pinion gear and that are formed in at least a part of an inner peripheral surface of the body, and external teeth that have a lower hardness than the internal teeth and that are formed in at least a part of an outer peripheral surface of the body, wherein a surface nitrogen concentration in the internal teeth is higher than that in at least tooth surfaces of the external teeth.