A crankshaft with improved fatigue strength and machinability is provided. The crankshaft includes a pin and journal, having a chemical composition of, in mass %: 0.40 to 0.60% C; 0.01 to 1.50% Si; 0.4 to 2.0% Mn; 0.01 to 0.50% Cr; 0.20 to 0.50% Al; 0.001 to 0.02% N; up to 0.03% P; 0.005 to 0.20% S; 0.005 to 0.060% Nb; 0 to 0.060% Ti; and balance Fe and impurities, wherein, for each of the pin and journal, the hardness measured at a position at a depth of ? of the diameter from the surface is higher than HV 245, the microstructure at that position is mainly composed of ferrite/pearlite, and the fraction of ferrite is not lower than 16%.

A crankshaft with improved fatigue strength and machinability is provided. The crankshaft includes a pin and journal, having a chemical composition of, in mass %: 0.40 to 0.60% C; 0.01 to 1.50% Si; 0.4 to 2.0% Mn; 0.01 to 0.50% Cr; 0.20 to 0.50% Al; 0.001 to 0.02% N; up to 0.03% P; 0.005 to 0.20% S; 0.005 to 0.060% Nb; 0 to 0.060% Ti; and balance Fe and impurities, wherein, for each of the pin and journal, the hardness measured at a position at a depth of ? of the diameter from the surface is higher than HV 245, the microstructure at that position is mainly composed of ferrite/pearlite, and the fraction of ferrite is not lower than 16%.

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 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 of heat treating a workpiece, the method including projecting a laser beam from a laser source onto said workpiece, so as to produce a laser spot on said workpiece; projecting the laser spot onto different portions of said workpiece; and while projecting the laser spot, repetitively scanning the laser beam in two dimensions so as to produce a two-dimensional equivalent effective laser spot on said workpiece and thereby temper, reduce hardness of, enhance ductility of, and/or reduce brittleness of at least one of the different portions of the workpiece.

A method of heat treating a workpiece, the method including projecting a laser beam from a laser source onto said workpiece, so as to produce a laser spot on said workpiece; projecting the laser spot onto different portions of said workpiece; and while projecting the laser spot, repetitively scanning the laser beam in two dimensions so as to produce a two-dimensional equivalent effective laser spot on said workpiece and thereby temper, reduce hardness of, enhance ductility of, and/or reduce brittleness of at least one of the different portions of the workpiece.

A crankshaft with improved fatigue strength is provided. A crankshaft 10 includes journals 11, pins 12, and fillets 14, each fillet 14 having a residual stress distribution where the residual stresses are compressive residual stresses from the surface down to a depth of at least 300 m, the maximum value of the compressive residual stress being not lower than 1000 MPa, the surface roughness Rz being lower than 3.00 m.

A crankshaft with improved fatigue strength is provided. A crankshaft 10 includes journals 11, pins 12, and fillets 14, each fillet 14 having a residual stress distribution where the residual stresses are compressive residual stresses from the surface down to a depth of at least 300 m, the maximum value of the compressive residual stress being not lower than 1000 MPa, the surface roughness Rz being lower than 3.00 m.

A method for heat treating a crankshaft surface on a crankshaft for a vehicle propulsion system includes heating the crankshaft surface to a first temperature and heating the crankshaft surface to a second temperature that is higher than the first temperature.

A method for heat treating a crankshaft surface on a crankshaft for a vehicle propulsion system includes heating the crankshaft surface to a first temperature and heating the crankshaft surface to a second temperature that is higher than the first temperature.