Abstract: A carburized shaft part having a predetermined composition, a C content at a surface layer part of a mass % of 0.60 to 1.00%, at least one hole at an outer circumferential surface, a total volume ratio of martensite and retained austenite of 97% or more at a structure at a position of a 1 mm depth from the outer circumferential surface in an axial direction of the hole and a position of a 20 ?m depth from the surface of the hole, a maximum retained austenite volume ratio (R1) of 10.0 to 30.0% at a position of a 1 mm depth from the outer circumferential surface in the axial direction of the hole and a range up to a 200 ?m depth from the surface of the hole, and a retained austenite reduction ratio of 20% or more found from R1 and the retained austenite volume ratio (R2) at a position of a 1 mm depth from the outer circumferential surface in the axial direction of the hole and a position of a 20 ?m depth from the surface of the hole by the formula (A): ??=(R1?R)/R1×100.

Abstract: A shaft part excellent in static torsional strength and torsional fatigue strength containing, by mass %, essential elements of C: 0.35 to 0.70%, Si: 0.01 to 0.40%, Mn: 0.5 to 2.6%, P: 0.050% or less, S: 0.005 to 0.020%, Al: 0.010 to 0.050%, N: 0.005 to 0.025%, and O: 0.003% or less, further containing optional elements, having a balance of Fe and impurities, having a chemical composition satisfying formula (1), having at least one hole at an outer circumferential surface, having a volume ratio (R1) of 4 to 20% of retained austenite at a position of a 2 mm depth from the outer circumferential surface, having a volume ratio of retained austenite at a position of a 2 mm depth from the outer circumferential surface in an axial direction of the hole and at a position of a 20 ?m depth from the surface of the hole as R2, and having a reduction rate ?? of 40% or more of retained austenite found by the formula (A): ??=[(R1?R2)/R1]×100: Formula (1): 15.0?25.9C+6.35Mn+2.88Cr+3.09Mo+2.73Ni?27.

Abstract: The steel material for a soft magnetic part according to the present invention has a chemical composition consisting of, in mass %, C: 0.02 to 0.13%, Si: 0.005 to 0.50%, Mn: 0.10 to 0.70%, P: 0.035% or less, S: 0.050% or less, Al: 0.005 to 1.300%, V: 0.02 to 0.50%, and N: 0.003 to 0.030%, with the balance being Fe and impurities. The average grain diameter of ferrite grains in the steel material for a soft magnetic part ranges from 5 to 200 ?m. Further, in the ferrite grains, the number Sv (number/mm2) of precipitates having a circle-equivalent diameter of 30 nm or more satisfies Formula (1): Sv?10V×7.0×106??(1) where the V content (mass %) in the steel material for a soft magnetic part is substituted into V in Formula (1).

Abstract: A shaft part excellent in static torsional strength and torsional fatigue strength containing, by mass %, essential elements of C: 0.35 to 0.70%, Si: 0.01 to 0.40%, Mn: 0.5 to 2.6%, P: 0.050% or less, S: 0.005 to 0.020%, Al: 0.010 to 0.050%, N: 0.005 to 0.025%, and O: 0.003% or less, further containing optional elements, having a balance of Fe and impurities, having a chemical composition satisfying formula (1), having at least one hole at an outer circumferential surface, having a volume ratio (R1) of 4 to 20% of retained austenite at a position of a 2 mm depth from the outer circumferential surface, having a volume ratio of retained austenite at a position of a 2 mm depth from the outer circumferential surface in an axial direction of the hole and at a position of a 20 ?m depth from the surface of the hole as R2, and having a reduction rate ?? of 40% or more of retained austenite found by the formula (A): ??=[(R1?R2)/R1]×100: Formula (1): 15.0?25.9C+6.35Mn+2.88Cr+3.09Mo+2.73Ni?27.

Abstract: A carburized shaft part having a predetermined composition, a C content at a surface layer part of a mass % of 0.60 to 1.00%, at least one hole at an outer circumferential surface, a total volume ratio of martensite and retained austenite of 97% or more at a structure at a position of a 1 mm depth from the outer circumferential surface in an axial direction of the hole and a position of a 20 ?m depth from the surface of the hole, a maximum retained austenite volume ratio (R1) of 10.0 to 30.0% at a position of a 1 mm depth from the outer circumferential surface in the axial direction of the hole and a range up to a 200 ?m depth from the surface of the hole, and a retained austenite reduction ratio of 20% or more found from R1 and the retained austenite volume ratio (R2) at a position of a 1 mm depth from the outer circumferential surface in the axial direction of the hole and a position of a 20 ?m depth from the surface of the hole by the formula (A): ??=(R1?R)/R1×100.

Abstract: The steel material for a soft magnetic part according to the present invention has a chemical composition consisting of, in mass %, C: 0.02 to 0.13%, Si: 0.005 to 0.50%, Mn: 0.10 to 0.70%, P: 0.035% or less, S: 0.050% or less, Al: 0.005 to 1.300%, V: 0.02 to 0.50%, and N: 0.003 to 0.030%, with the balance being Fe and impurities. The average grain diameter of ferrite grains in the steel material for a soft magnetic part ranges from 5 to 200 pun. Further, in the ferrite grains, the number Sv (number/mm2) of precipitates having a circle-equivalent diameter of 30 nm or more satisfies Formula (1): Sv?10V×7.0×106??(1) where the V content (mass %) in the steel material for a soft magnetic part is substituted into V in Formula (1).

Abstract: A carburized component with improved fatigue strength has a base steel containing, by mass %, C: 0.15-0.25%, Si: 0.03-0.50%, Mn: more than 0.60% and not more than 1.5%, P?0.015%, S: 0.006-0.030%, Cr: 0.05-2.0%, Al?0.10%, N?0.03%, and O?0.0020%, and optionally at least one element selected from Mo, Cu, Ni, B, Ti, Nb and V, the balance being Fe and impurities. A surface hardened layer portion satisfies: (a) average carbon concentration in the region from the outermost surface to a point of 0.2 mm depth of 0.35-0.60 mass %, (b) surface roughness Rz?15 ?m, and (c) ?r(0)??800 MPa, ?r(100)??800 MPa, and residual stress intensity index Ir?80000, wherein Ir is calculated by [Ir=?|?r(y)|dy], where y ?m is the depth from the outermost surface and ?r(y) is the residual stress for the points from the outermost surface to a depth of 100 ?m with the range of y from 0 to 100 (?m).

Abstract: A carburized component with improved fatigue strength has a base steel containing, by mass %, C: 0.15-0.25%, Si: 0.03-0.50%, Mn: more than 0.60% and not more than 1.5%, P?0.015%, S: 0.006-0.030%, Cr: 0.05-2.0%, Al?0.10%, N?0.03%, and O?0.0020%, and optionally at least one element selected from Mo, Cu, Ni, B, Ti, Nb and V, the balance being Fe and impurities. A surface hardened layer portion satisfies: (a) average carbon concentration in the region from the outermost surface to a point of 0.2 mm depth of 0.35-0.60 mass %, (b) surface roughness Rz?15 ?m, and (c) ?r(0)?-800 MPa, ?r(100)?-800 MPa, and residual stress intensity index Ir?80000, wherein Ir is calculated by [Ir=?|?r(y)|dy], where y ?m is the depth from the outermost surface and ?r(y) is the residual stress for the points from the outermost surface to a depth of 100 ?m with the range of y from 0 to 100 (?m).