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.

An induction-hardened crankshaft is provided that offers an excellent balance of fatigue strength, machinability and quench-cracking resistance. An induction-hardened crankshaft has a chemical composition of, in mass %: 0.30 to 0.60% C; 0.01 to 1.50% Si; 0.4 to 2.0% Mn; 0.01 to 0.50% Cr; 0.001 to 0.06% Al; 0.001 to 0.02% N; up to 0.03% P; 0.005 to 0.20% S; 0.005 to 0.060% Nb; and balance Fe and impurities, the non-induction-hardened portion having a microstructure mainly composed of ferrite-pearlite and having a fraction of ferrite Fα satisfying the expression (1) provided below, the induction-hardened portion having a microstructure mainly composed of martensite or tempered martensite, and having a prior austenite grain diameter not larger than 30 μm,

Fα≥150×[C %]+84   (1), where the C content in mass % in the induction-hardened crankshaft is substituted for [C %].

A bearing ring for a rolling-element bearing or plain bearing has at least one first region that is inductively hardened or is configured to be inductively hardened and at least one second region that is not inductively hardened and is not intended to be inductively hardened, and the at least one second region includes at least one stress-relief recess and/or at least one stress-relief projection.

When a rod-shaped workpiece (W) having an outer peripheral surface with a circular cross section is inductively heated to a quenching temperature while being conveyed at a predetermined velocity along an axial direction of the rod-shaped workpiece (W), the rod-shaped workpiece (W) being currently conveyed is heated to a predetermined temperature equal to or lower than the quenching temperature by a first heating coil (2A), which is electrically connected to a first high-frequency power supply (3) and has a constant output. Then, the rod-shaped workpiece (W) being currently conveyed is heated so as to be maintained at the quenching temperature by a second heating coil (2B), which is electrically connected to a second high-frequency power supply (4) and has a constant output.

There is prepared a formed body constituted of steel and having an outer circumferential surface having an annular groove having a bottom surface to serve as a raceway surface of the bearing ring. In the step of forming a heated region, the formed body is induction heated to form a heated region including the bottom surface of the groove and heated to a temperature of at least an A.sub.1 point. In the cooling step, the whole of the heated region is simultaneously cooled to a temperature of not more than an M.sub.s point. The step of retaining the formed body in a state in which heating is stopped is performed after the step of forming a heated region before the step of cooling. In the step of retaining, dispersion in temperature in the heated region in the circumferential direction is suppressed to not more than 20 C.

An inductor for an induction hardening system includes a heating element for heating a heating zone of a workpiece, and the heating element includes a first induction coil and a second induction coil and a gas escape device disposed between the first induction coil and the second induction coil. The gas escape device is configured to substantially prevent a liquid from a quenching device from reaching the heating zone while the heating zone is being heated by the first and second inductors.

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.

A bearing ring for a rolling-element bearing or plain bearing has at least one first region that is inductively hardened or is configured to be inductively hardened and at least one second region that is not inductively hardened and is not intended to be inductively hardened, and the at least one second region includes at least one stress-relief recess and/or at least one stress-relief projection.

When a plurality of outer rings (R) are sequentially and inductively heated to a target temperature by energizing a heating coil (2) elongated more than each of the plurality of outer rings (R), which are made of steel and retained coaxially by a retaining unit (3), while relatively moving the outer rings (R) and the heating coil (2) in an axial direction, an output of the heating coil (2) is varied in consideration of the number of outer rings (R) present in an opposing region of the heating coil (2).

A linear motion guide device having a long-life slider is provided. The linear motion guide device includes a guide rail, a plurality of rolling elements, and a slider. The material of the slider body 11 is alloy steel containing 0.1 mass % or more and less than 0.3 mass % of C, 0.5 mass % or more and 1.5 mass % or less of Cr, and 0.1 mass % or more and 0.4 mass % or less of Si, with the balance being Fe and inevitable impurities. An amount of retained austenite in a surface layer 14F of a slider-side rolling groove 14 subjected to a carburizing heat treatment is 15 vol % or more and 45 vol % or less. The surface hardness of the slider-side rolling groove 14 is Hv 650 or more.