A method for laser-hardening a shaft for a vehicle includes applying laser light energy in a repeating pattern to a journal surface. The method further includes, responsive to the repeating pattern being applied completely around the shaft, applying laser light energy to the surface in a pattern different than the repeating pattern to form an overlap surface pattern that defines a tapered ramp having a corresponding hardness less than a hardness corresponding to the repeating pattern alone.

A method for laser-hardening a shaft for a vehicle includes applying laser light energy in a repeating pattern to a journal surface. The method further includes, responsive to the repeating pattern being applied completely around the shaft, applying laser light energy to the surface in a pattern different than the repeating pattern to form an overlap surface pattern that defines a tapered ramp having a corresponding hardness less than a hardness corresponding to the repeating pattern alone.

A crankshaft that can be strengthened in a short time without being subjected to wasteful processing, and that can be strengthened over a wide range. The crankshaft includes a crank pin and a fillet portion of a journal pin. Compressive residual stress is applied to a region on the fillet portion, which extends at almost equal distances to both sides in a circumferential direction from a portion in which the greatest bending load is applied, and a processing depth for applying the compressive residual stress is gradually decreased in a circumferential direction from the center position in which the compressive residual stress is greatest.

A crankshaft that can be strengthened in a short time without being subjected to wasteful processing, and that can be strengthened over a wide range. The crankshaft includes a crank pin and a fillet portion of a journal pin. Compressive residual stress is applied to a region on the fillet portion, which extends at almost equal distances to both sides in a circumferential direction from a portion in which the greatest bending load is applied, and a processing depth for applying the compressive residual stress is gradually decreased in a circumferential direction from the center position in which the compressive residual stress is greatest.

A weld joint with an excellent CTOD property is produced with a weld metal, using a steel plate as a base metal. The steel plate has a chemical composition including C: 0.03% to 0.09%, Si: 0.01% to 0.35%, Mn: 1.3% to 2.0%, P: 0.012% or less, S: 0.0035% or less, Al: 0.01% to 0.06%, Ni: less than 0.3%, Mo: less than 0.10%, Nb: 0.005% to 0.023%, Ti: 0.005% to 0.025%, B: less than 0.0003%, N: 0.002% to 0.005%, Ca: 0.0005% to 0.0050%, and O: 0.0030% or less, with the components additionally satisfying a predetermined relationship. The weld metal has a chemical composition including C: 0.040% to 0.090%, Si: 0.1% to 0.8%, Mn: 1.0% to 2.5%, Al: 0.020% or less, Ni: 0.1% to 1.0%, Mo: 0.05% to 0.50%, Ti: 0.005% to 0.050%, and B: 0.0015% or less, the balance being Fe and incidental impurities.

An automotive shaft fillet treating method including laser hardening a green machined fillet surface to a uniform depth d to induce compressive stresses into the surface, the surface extending the entire length l between outer edges of two undercut regions of the fillet, and applying additional compressive stress to the laser hardened surface via fillet rolling such that the uniform depth d is maintained along the entire length l during a subsequent grinding operation.

An automotive shaft fillet treating method including laser hardening a green machined fillet surface to a uniform depth d to induce compressive stresses into the surface, the surface extending the entire length l between outer edges of two undercut regions of the fillet, and applying additional compressive stress to the laser hardened surface via fillet rolling such that the uniform depth d is maintained along the entire length l during a subsequent grinding operation.

A non-heat treated steel for induction hardening contains, in mass %, C: 0.35 to 0.44%, Si: 0.01 to less than 0.30%, Mn: 0.80 to 1.50%, P: 0.030% or less, S: more than 0.010 to 0.095%, Cr: more than 0.10 to 0.30%, V: 0.050 to 0.200%, N: 0.0040 to 0.0200%, O: 0.0024% or less, Cu: 0.05% or less and Ni: 0.05% or less, and for which fn150.0, fn2: 0.70 to 1.00, and fn31.30. In the steel, a ratio of a number of Mn oxides containing oxygen in an amount of 20.0 mass % or more and Mn in an amount of 10.0 mass % or more to the number of oxides is 10.0% or less.

fn1=80C.sup.2+55C+13Si+4.8Mn+30P+30S+1.5Cr

fn2=C+(Si/10)+(Mn/5)(5S/7)+(5Cr/22)+1.65V

fn3=2CSi+2.33Mn+0.26Cr+V1.5Cu1.5Ni

The high-strength steel for steel forgings according to the present invention has a composition that includes, as basic components, C: 0.35 mass % to 0.47 mass %; Si: 0 mass % to 0.4 mass %; Mn: 0.6 mass % to 1.5 mass %; Ni: more than 0 mass % up to 2.0 mass %; Cr: 0.8 mass % to 2.5 mass %; Mo: 0.10 mass % to 0.7 mass %; V: 0.035 mass % to 0.20 mass %; Al: 0.015 mass % to 0.050 mass %; N: 30 ppm to 100 ppm, and O: more than 0 ppm up to 30 ppm, the balance being Fe and inevitable impurities. The metal structure is mainly bainite, martensite or a mixed structure of bainite and martensite. Among cubic B1-type precipitates, the number of coherent precipitates having a diameter equal to or smaller than 30 nm is equal to or smaller than 50/m.sup.2.

A crankshaft with improved seizure resistance is provided. A crankshaft having journals 11 and pins 12 includes a compound layer containing iron and nitrogen on its surface, wherein, in the compound layer, for both the journals 11 and pins 12, the porosity area ratio of the thinner one of a region from the surface to a depth of 3.0 ?m and a region across the total thickness of the compound layer is not higher than 10.0%, and both the journals 11 and pins 12 have such a surface geometry that the arithmetical mean deviation of the primary profile, Pa, is not larger than 0.090 ?m.