A high-pressure-torsion apparatus (100), comprising a working axis (102), a first anvil (110), a second anvil (120), and an annular body (130). The annular body (130) comprises a first total-loss convective chiller (140), a second total-loss convective chiller (150), and a heater (160). Each of the first total-loss convective chiller (140) and the second total-loss convective chiller (150) is translatable between the first anvil (110) and the second anvil (120) along the working axis (102), is configured to be thermally convectively coupled with a workpiece (190), and is configured to selectively cool the workpiece (190). The heater (160) is positioned between the first total-loss convective chiller (140) and the second total-loss convective chiller (150) along the working axis (102), is translatable between the first anvil (110) and the second anvil (120) along the working axis (102), and is configured to selectively heat the workpiece (190).

A high-pressure-torsion apparatus (100) comprises a working axis (102), a first anvil (110), a second anvil (120), and an annular body (130). The annular body (130) comprises a first conductive chiller (140), a second conductive chiller (150), and a heater (160). Each of the first conductive chiller (140) and the second conductive chiller (150) is translatable between the first anvil (110) and the second anvil (120) along the working axis (102), is configured to be thermally conductively coupled with a workpiece (190), and is configured to selectively cool the workpiece (190). The heater (160) is positioned between the first conductive chiller (140) and the second conductive chiller (150) along the working axis (102), is translatable between the first anvil (110) and the second anvil (120) along the working axis (102), and is configured to selectively heat the workpiece (190).

A high-pressure-torsion apparatus (100) comprises a working axis (102), a first anvil (110), a second anvil (120), and an annular body (130). The annular body (130) comprises a a first recirculating convective chiller (140), a second recirculating convective chiller (150), and a heater (160). Each of the first recirculating convective chiller (140) and the second recirculating convective chiller (150) is translatable between the first anvil (110) and the second anvil (120) along the working axis (102), is configured to be thermally convectively coupled with a workpiece (190), and is configured to selectively cool the workpiece (190). The heater (160) is positioned between the first recirculating convective chiller (140) and the second recirculating convective chiller (150) along the working axis (102), is translatable between the first anvil (110) and the second anvil (120) along the working axis (102), and is configured to selectively heat the workpiece (190).

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): =(R1R)/R1100.

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): =(R1R)/R1100.

Metal components subject to wear or contact fatigue in a first area, and subject to bending, axial and/or torsional stress loading in a second area comprise a surface hardened, first surface layer in the first area; and a surface compressive-stress treated, second surface layer in the second area. The second surface layer has a material hardness different from, and typically lower than the first surface layer, and induced residual compressive stress to improve fatigue strength. Example components described include a gear, a cog, a pinion, a rack, a splined shaft, a splined coupling, a torquing tool and a nut driving tool. A hybrid manufacturing process is described, including area-selective surface hardening combined with a process to add compressive stress to fatigue failure prone areas.

Metal components subject to wear or contact fatigue in a first area, and subject to bending, axial and/or torsional stress loading in a second area comprise a surface hardened, first surface layer in the first area; and a surface compressive-stress treated, second surface layer in the second area. The second surface layer has a material hardness different from, and typically lower than the first surface layer, and induced residual compressive stress to improve fatigue strength. Example components described include a gear, a cog, a pinion, a rack, a splined shaft, a splined coupling, a torquing tool and a nut driving tool. A hybrid manufacturing process is described, including area-selective surface hardening combined with a process to add compressive stress to fatigue failure prone areas.

A method for manufacturing a shaft body by welding a plurality of shaft members together and forming the shaft body, the method including: a primary tempering step of subjecting a range in at least one of the shaft members, which is in the vicinity of an end of another shaft member side adjacent thereto, to tempering before the shaft members are welded together so that a strength of an end side of a region thereof is lower than a strength at a side which is opposite to the end of the region thereof; a welding step of welding the shaft members together after the primary tempering step; and a secondary tempering step of tempering the vicinity of a weld part between the shaft members after the welding step.

A method for manufacturing a shaft body by welding a plurality of shaft members together and forming the shaft body, the method including: a primary tempering step of subjecting a range in at least one of the shaft members, which is in the vicinity of an end of another shaft member side adjacent thereto, to tempering before the shaft members are welded together so that a strength of an end side of a region thereof is lower than a strength at a side which is opposite to the end of the region thereof; a welding step of welding the shaft members together after the primary tempering step; and a secondary tempering step of tempering the vicinity of a weld part between the shaft members after the welding step.

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.