The steel material for a carburized bearing part according to the present invention contains, by mass %, C: 0.25 to 0.45%, Si: 0.15 to 0.45%, Mn: 0.40 to 1.50%, P: 0.015% or less, S: 0.005% or less, Cr: 0.60 to 2.00%, Mo: 0.10 to 0.35%, V: 0.20 to 0.40%, Al: 0.005 to 0.100%, Ca: 0.0002 to 0.0010%, N: 0.0300% or less and O: 0.0015% or less, with the balance being Fe and impurities, and satisfies Formulae (1) to (3).
1.20<0.4Cr+0.4Mo+4.5V<2.75  (1)
A1/A2>0.50  (2)
2.7C+0.4Si+Mn+0.45Ni+0.8Cr+Mo+V>2.55  (3)
Formula (2) shows an area fraction of sulfides containing Ca in an amount of 1 mol % or more among sulfides having an equivalent circular diameter of 1 μm or more.

An inner ring or and outer ring for a roller bearing includes: 0.30-0.45 wt. % carbon, 0.1-0.7 wt. % silicon, 0.6-0.9 wt. % manganese, 0.9-1.2 wt. % chromium, 0.15-0.7 wt. % molybdenum, 0-2.0 wt. % nickel, 0-0.02 wt. % phosphorus, and 0-0.02 wt. % sulfur, the balance being iron and unavoidable impurities. The microstructure of the steel composition contains bainite, and a carbonitrided case layer is provided on a surface of the inner ring or outer ring.

An inner ring or and outer ring for a roller bearing includes: 0.30-0.45 wt. % carbon, 0.1-0.7 wt. % silicon, 0.6-0.9 wt. % manganese, 0.9-1.2 wt. % chromium, 0.15-0.7 wt. % molybdenum, 0-2.0 wt. % nickel, 0-0.02 wt. % phosphorus, and 0 -0.02 wt. % sulfur, the balance being iron and unavoidable impurities. The microstructure of the steel composition contains bainite, and a carbonitrided case layer is provided on a surface of the inner ring or outer ring.

A guiding member, having a body provided with a bore for mounting a mobile element is presented. The body consists of a metallic material. The bore has a surface layer treated against jamming over a diffusion depth of less than or equal to 0.6 mm. The surface layer has a hardness of greater than or equal to 500 Hv1 over a depth of between 5 and 50 μm.

The present invention provides a steel material which is excellent in both of the strength (particularly, fatigue strength) and the manufacturability (particularly, bending straightening properties), and thus can be used as an automobile component such as a crankshaft by being formed into a product shape, being subjected to a high strength treatment such as a nitrocarburizing treatment, and then being subjected to the bending straightening.

Method for producing a ball stud with a joint ball and a shank, wherein the shank includes at least a neck region adjoining the joint ball and a fastening section opposite the joint ball, characterized by the steps: a) plastically shaping a semi-finished ball stud product; b) mechanically machining the semi-finished ball stud product; c) rolling the surface of the joint ball; d) thermochemically hardening the surface of the semi-finished ball stud product; e) removing the surface-hardened layer at least in the neck region and/or the fastening section; f) oxidizing the semi-finished ball stud product; g) polishing the joint ball.

In the tapered roller bearing, at least any one of an outer ring, an inner ring, and a plurality of tapered rollers includes a nitrogen enriched layer. An oil retaining hole is provided in a larger annular portion of a cage. A value of a ratio R/R.sub.BASE is not smaller than 0.75 and not greater than 0.87 where R represents a set radius of curvature of a larger end face of the tapered roller and R.sub.BASE represents a distance from a point which is an apex of a cone angle of the tapered roller to a larger flange surface of the inner ring. A ratio R.sub.process/R is than not lower 0.5 where R.sub.process represents an actual radius of curvature after grinding of the larger end face of the tapered roller and R represents a set radius of curvature.

A tapered roller bearing includes an inner ring having a tapered raceway surface and a large-collar surface on a large-diameter side of the raceway surface, and tapered rollers. Each of the rollers has a large end surface guided by the large-collar surface. When R represents a set curvature radius of the large end surface and R.sub.BASE represents a base curvature radius from a vertex of a cone angle of each of the tapered rollers to the large-collar surface, the base curvature radius R.sub.BASE is 100 mm or less, and a ratio R/R.sub.BASE of the set curvature radius R to the base curvature radius R.sub.BASE is set to 0.90 or less. When R.sub.ACTUAL represents an actual curvature radius of the large end surface of each of the tapered rollers, a ratio R.sub.ACTUAL/R of the actual curvature radius R.sub.ACTUAL to the set curvature radius R exceeds 0.5.

A method for manufacturing a bearing ring of a rolling bearing includes a series of steps of cutting out an annular member from a material, forming a surface-hardened layer on the annular member, quenching and tempering the annular member, and polishing inner and outer diameter surfaces of the annular member. The method includes, after the quenching, rapidly cooling the ring member such that the ring member has a surface temperature of 50° C. or lower to form a bearing ring intermediate member, and after the tempering, polishing inner and outer diameter surfaces of the bearing ring intermediate member.

A bearing part is composed of a steel, and includes a quench-hardened layer in a surface of the bearing part. The quench-hardened layer includes a plurality of martensite crystal grains. A ratio of a total area of the plurality of martensite crystal grains in the quench-hardened layer is more than or equal to 70%. The plurality of martensite crystal grains are classified into a first group and a second group. A minimum value of crystal grain sizes of the martensite crystal grains belonging to the first group is larger than a maximum value of crystal grain sizes of the martensite crystal grains belonging to the second group.