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 μm depth from the surface of the hole as R2, and having a reduction rate Δγ of 40% or more of retained austenite found by the formula (A): Δγ=[(R1−R2)/R1]×100: Formula (1): 15.0≤25.9C+6.35Mn+2.88Cr+3.09Mo+2.73Ni≤27.2 (Notations of elements in formula are contents of the elements)

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 μm depth from the surface of the hole as R2, and having a reduction rate Δγ of 40% or more of retained austenite found by the formula (A): Δγ=[(R1−R2)/R1]×100: Formula (1): 15.0≤25.9C+6.35Mn+2.88Cr+3.09Mo+2.73Ni≤27.2 (Notations of elements in formula are contents of the elements)

A steel alloy is disclosed that provides a unique combination of strength, toughness, and fatigue life. The steel alloy has the following composition in weight percent:

TABLE-US-00001 C about 0.15 to about 0.30 Mn about 1.7 to about 2.3 Si about 0.7 to about 1.1 Cr about 1.85 to about 2.35 Ni about 0.5 to about 0.9 Mo + ½W about 0.1 to about 0.3 Cu about 0.3 to about 0.7 V + 5/9 × Nb about 0.2 to about 0.5
The balance of the alloy is iron, usual impurities, and residual amounts of other elements added during melting for deoxidizing and/or desulfurizing the alloy. A hardened and tempered steel article made from the alloy is also disclosed.

A steel alloy is disclosed that provides a unique combination of strength, toughness, and fatigue life. The steel alloy has the following composition in weight percent:

TABLE-US-00001 C about 0.15 to about 0.30 Mn about 1.7 to about 2.3 Si about 0.7 to about 1.1 Cr about 1.85 to about 2.35 Ni about 0.5 to about 0.9 Mo + ½W about 0.1 to about 0.3 Cu about 0.3 to about 0.7 V + 5/9 × Nb about 0.2 to about 0.5
The balance of the alloy is iron, usual impurities, and residual amounts of other elements added during melting for deoxidizing and/or desulfurizing the alloy. A hardened and tempered steel article made from the alloy is also disclosed.

A method is provided for preventing cracking along the surface at the inner hole of a hollow shaft during water quenching, including: a step of water-quenching the inner hole of the shaft placed horizontally, while the outer circle of the shaft is in a state of air cooling, in which the cooling time of the outer circle is selected to be not lower than its A.sub.r1 temperature so as to induce a compressive stress in the surface layer of the inner hole; and a step of water-quenching the outer circle and the inner hole of the shaft simultaneously, moreover, the quenching intensity of the inner hole is gradually reduced to cause a temperature rise in the surface layer of the inner hole to allow martensite in the surface layer to undergo self-tempering, which prevents the formation of quenching cracks along the surface of the inner hole.

A method is provided for preventing cracking along the surface at the inner hole of a hollow shaft during water quenching, including: a step of water-quenching the inner hole of the shaft placed horizontally, while the outer circle of the shaft is in a state of air cooling, in which the cooling time of the outer circle is selected to be not lower than its A.sub.r1 temperature so as to induce a compressive stress in the surface layer of the inner hole; and a step of water-quenching the outer circle and the inner hole of the shaft simultaneously, moreover, the quenching intensity of the inner hole is gradually reduced to cause a temperature rise in the surface layer of the inner hole to allow martensite in the surface layer to undergo self-tempering, which prevents the formation of quenching cracks along the surface of the inner hole.

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.

A treatment machine comprises a chamber for the treatment of one substrate or a plurality of substrates. A rotatably supported temperature-controlled shaft (30) defines a cylindrical, gas-tight hollow space. A heating arrangement (40, 50) is provided for electrically heating at least a part of the shaft (30) arranged in the chamber. The heating arrangement (40, 50) comprises an accommodation mandrel (40) for accommodating at least one electrical heating element (50), said accommodation mandrel (40) being arranged in a non-rotating manner and extending into the hollow space of the shaft (30). An outer surface of the accommodation mandrel (40) is spaced apart from an inner surface of the shaft (30) by a gap.

A treatment machine comprises a chamber for the treatment of one substrate or a plurality of substrates. A rotatably supported temperature-controlled shaft (30) defines a cylindrical, gas-tight hollow space. A heating arrangement (40, 50) is provided for electrically heating at least a part of the shaft (30) arranged in the chamber. The heating arrangement (40, 50) comprises an accommodation mandrel (40) for accommodating at least one electrical heating element (50), said accommodation mandrel (40) being arranged in a non-rotating manner and extending into the hollow space of the shaft (30). An outer surface of the accommodation mandrel (40) is spaced apart from an inner surface of the shaft (30) by a gap.

A process for reducing film boiling by keeping the quenchant pressure above the vapor pressure of the liquid quenchant, and/or using a controlled quenchant renewal to more uniformly cool the surface of part at the initial moment of contact and apparatuses to conduct the pressure and controlled quenchant renewal are disclosed. It is believed that these processes will improve the heat treating of parts with intricate geometries to provide predictable part distortion. The applicability of the method to gun barrels, tubes, round rings, and hollow axles is explained.