A self-lubricating rolling bearing is provided. The chemical compositions in the inner rings and the outer rings of bearing are 3.4-3.7% C, 2.7-2.9% Si, 0.3-0.5% Mn, 0.3-0.5% Cr, ≤0.05% S, ≤0.05% P, 0.03-0.045% Residual Mg, and the remainder Fe. The total percent of the chemical compositions is 100%. The material for the inner and outer rings of the rolling bearing introduced in the invention is austempered ductile iron (ADI). In the microstructure of ADI, the diameter of the graphite nodules is less than 0.02 mm, the number of graphite spheres per square millimeter is more than 400, and the microstructure of the metal matrix in the ADI can be showed clearly only when it is observed on the microscope with a magnification more than 500. Eventually, the self-lubricating rolling bearings are made from the ADI.

A self-lubricating rolling bearing is provided. The chemical compositions in the inner rings and the outer rings of bearing are 3.4-3.7% C, 2.7-2.9% Si, 0.3-0.5% Mn, 0.3-0.5% Cr, ≤0.05% S, ≤0.05% P, 0.03-0.045% Residual Mg, and the remainder Fe. The total percent of the chemical compositions is 100%. The material for the inner and outer rings of the rolling bearing introduced in the invention is austempered ductile iron (ADI). In the microstructure of ADI, the diameter of the graphite nodules is less than 0.02 mm, the number of graphite spheres per square millimeter is more than 400, and the microstructure of the metal matrix in the ADI can be showed clearly only when it is observed on the microscope with a magnification more than 500. Eventually, the self-lubricating rolling bearings are made from the ADI.

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 clad material includes a first layer made of stainless steel and a second layer made of Cu or a Cu alloy and roll-bonded to the first layer. In the clad material, a grain size of the second layer measured by a comparison method of JIS H 0501 is 0.150 mm or less.

A clad material includes a first layer made of stainless steel and a second layer made of Cu or a Cu alloy and roll-bonded to the first layer. In the clad material, a grain size of the second layer measured by a comparison method of JIS H 0501 is 0.150 mm or less.

The present invention provides an annealed steel material having a composition containing, in mass %, 0.28≤C≤0.42, 0.01≤Si≤1.50, 0.20≤Mn≤1.20, 4.80≤Cr≤6.00, 0.80≤Mo≤3.20, 0.40≤V≤1.20, and 0.002≤N≤0.080, with the balance being Fe and unavoidable impurities; in which the annealed steel material has a cross-sectional size of a thickness of 200 mm or more and a width of 250 mm or more, and a hardness of 100 HRB or less; and in which a diameter of a largest ferritic grain observed in a microstructure is 120 μm or less in terms of a perfect circle equivalent, an area ratio of carbides is 3.0% or more and less than 10.5%, and an average particle diameter of the carbides is 0.18 μm or more and 0.29 μm or less.

The present invention provides an annealed steel material having a composition containing, in mass %, 0.28≤C≤0.42, 0.01≤Si≤1.50, 0.20≤Mn≤1.20, 4.80≤Cr≤6.00, 0.80≤Mo≤3.20, 0.40≤V≤1.20, and 0.002≤N≤0.080, with the balance being Fe and unavoidable impurities; in which the annealed steel material has a cross-sectional size of a thickness of 200 mm or more and a width of 250 mm or more, and a hardness of 100 HRB or less; and in which a diameter of a largest ferritic grain observed in a microstructure is 120 μm or less in terms of a perfect circle equivalent, an area ratio of carbides is 3.0% or more and less than 10.5%, and an average particle diameter of the carbides is 0.18 μm or more and 0.29 μm or less.

An example bushing has three portions along its radial direction including an inner portion most proximal to a central hole of the bushing, an outer portion most distal from the center hole, and a core portion between the inner portion and the outer portion. The core portion has a hardness that is less than the hardness of the inner portion or the outer portion of the bushing. The bushing may be formed using high carbon steel, which in some cases may be spheroidal cementite crystal structure. A rough bushing may be formed using the high carbon steel, followed by a direct hardening process, and an induction hardening process on the inner surface most proximal to the central hole of the bushing. The induction hardening on the inner surface may harden the outer portion while tempering the core portion of the bushing.

A tool steel having strength and high impact toughness incudes 0.7 to 0.9 wt % of C, 0.4 to 0.6 wt % of Si, 0.4 to 0.6 wt % of Mn, 7.0 to 9.0 wt % of Cr, 1.5 to 2.5 wt % of Mo, up to 1.0 wt % or less (excluding 0 wt %) of V, 0.01 to 0.06 wt % of Ce, and a remainder of Fe and inevitable impurities, wherein the tool steel has a hardness of 59 to 65 HRC and an impact toughness of 30 to 42 J/cm.sup.2. The tool steel has super-high-strength combined with high impact toughness due to inclusion of Ce, thus reducing primary carbide content in an as-cast state and after solution treatment and tempering.

A tool steel having strength and high impact toughness incudes 0.7 to 0.9 wt % of C, 0.4 to 0.6 wt % of Si, 0.4 to 0.6 wt % of Mn, 7.0 to 9.0 wt % of Cr, 1.5 to 2.5 wt % of Mo, up to 1.0 wt % or less (excluding 0 wt %) of V, 0.01 to 0.06 wt % of Ce, and a remainder of Fe and inevitable impurities, wherein the tool steel has a hardness of 59 to 65 HRC and an impact toughness of 30 to 42 J/cm.sup.2. The tool steel has super-high-strength combined with high impact toughness due to inclusion of Ce, thus reducing primary carbide content in an as-cast state and after solution treatment and tempering.