A drive shaft includes a first annular wall and a second annular wall joined together via a friction-welded portion. The first annular wall and the second annular wall have outer diameters of 30 to 50 mm and wall thicknesses of 3 to 5 mm. A burr created at the friction-welded portion has a connection radius of greater than or equal to 0.5 mm, a base radius of greater than or equal to 0.5 mm, a burr base angle of less than or equal to 40°, and a burr slope length of 0.2 to 5 mm.

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 link component (150) with an oil hole (150E) is attached to a crankshaft (106) of an internal combustion engine (E), and the oil hole (150E) allows communication from an outside to the crankshaft (106) side. The oil hole (150E) has an inclined surface (150F) along an opening rim on the crankshaft (106) side. A surface other than the oil hole (150E) has a carbon concentration of 0.5 wt % or more. The inclined surface (150F) has a carbon concentration within a range of 0.7 wt % or more and 0.9 wt % or less. Production cost is suppressed, and at the same time, damage is prevented by increasing resistance of the oil-hole part on which stress is liable to concentrate.

A fastening structure (105) includes a pair of fastening members (105A) joined to each other, which is coupled with a bolt. The fastening member (105) is made of steel. A surface other than joint surfaces (Sa) has a Rockwell hardness of 50 HRC or more. The joint surfaces (Sa) have a Rockwell hardness of 30 HRC or more and less than 50 HRC. The joint surfaces (Sa) have an arithmetic mean roughness (Ra) of 0.2 m or more and 0.5 m or less. Production cost is suppressed, and at the same time, bending fatigue strength is secured and secondary damage due to abrasion powder generated by fretting is prevented.

A method for manufacturing a crankshaft for an internal combustion engine with a plurality of journals having a hardened case with a first microstructure. The crankshaft is comprised of a steel comprising between about 0.3 wt % and 0.77 wt % Carbon. The first microstructure of the hardened case of the journals comprises between about 15% and 30% ferrite and a balance of martensite and the resultant subsurface residual stress between 310 MPa and 620 MPa.

A steel according to one aspect of the present invention has a chemical composition containing, by unit mass %, C: 0.25 to 0.55%, Si: 0.20 to 1.30%, Mn: 0.50 to 1.50%, P: 0.010 to 0.200%, S: 0.010 to 0.100%, Cr: 0 to 1.20%, V: 0.25 to 0.40%, Ti: 0.010 to 0.070%, Mo: 0 to 0.15%, N: 0.0010 to 0.0060%, Al: 0 to 0.200%, Ca: 0 to 0.005%, Zr: 0 to 0.005%, Mg: 0 to 0.005%, Bi: 0 to 0.0050%, Pb: 0 to 0.50%, Nb: 0 to 0.05%, Cu: 0 to 0.05%, and Ni: 0 to 0.05%, with the balance being Fe and impurities, wherein 0.002<Ti3.4N<0.050 is satisfied.

A method for manufacturing a crankshaft for an internal combustion engine with a plurality of journals having a hardened case with a first microstructure. The crankshaft is comprised of a steel comprising between about 0.3 wt % and 0.77 wt % Carbon. The first microstructure of the hardened case of the journals comprises between about 15% and 30% ferrite and a balance of martensite and the resultant subsurface residual stress between 310 MPa and 620 MPa.

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 steel material is heated and punched while tension is applied to the steel material (2) in at least one direction along a surface of the steel material between first and second portions of the steel material distant from each other with forming unit posed therebetween. The tension is applied to increase a distance between the first and second portions of the steel material by a length corresponding to an amount by which the distance between the first and second portions of the steel material thermally expands as the steel material is heated to the temperature in the step of heating and punching. The forming unit includes a first die for punching the steel material and a second die facing the first die, the first die or the second die having a forming surface having a concave curved surface.

The invention relates to a method for producing a rolling bearing ring featuring an improved robustness against the formation of white etching cracks (WEC), wherein the rolling bearing component, which is made of a hypo-eutectoid heat-treated steel containing C in an amount of 0.4-0.55% and Cr in an amount of 0.5-2.0% in order to form a hardened boundary layer, is inductively heated, then quenched and subsequently tempered.