A steel for darburized gear having softening resistance, consisting essentially of, in weight percentages, 0.18 to 0.25% C, 0.45 to 1.00% Si, 0.40 to 0.70% Mn, 0.30 to 0.70% Ni, 1.00 to 1.50% Cr, 0.30 to 0.70% Mo, up to 0.50% Cu, 0.015 to 0.030% A1, 0.03 to 0.30% V, 0.010 to 0.030% Nb, up to 0.0015% O, 0.0100 to 0.0200% N and the balance consisting of Fe and inevitable impurity elements, wherein quenching at 820.degree. C. or higher after carburization does not cause any ferrite to be formed in a hardened structure of the core part of the carburized steel, and wherein, while tempering is generally performed at 160.degree. to 180.degree. C. after the quenching, reheating at any of temperatures inclusive of the tempering temperature and up to 300.degree. C. does not cause the hardness of a carburized case of the carburized steel to decrease by HV 50 or more from the one after the carburization, quenching and tempering.
This invention aims at providing a carburizing bearing steel which can provide excellent rolling fatigue characteristics by providing a long life carburizing bearing steel comprising, in terms of percent by weight, 0.1 to 0.35% of C, 0.3 to 2.0% of Mn, 0.001 to 0.03% of S, 0.4 to 1.5% of Cr, 0.01 to 0.07% of Al, 0.003 to 0.015% of N, 0.0005 to 0.03% of T.Mg, "0.35 to 1.70% of Si" or "0.05 to 1.70% of Si and 0.30 to 1.20% of Mo", a specific amount of at least one member consisting of Ni and V, and not more than 0.025% of P, and not more than 0.0050% of Ti and not more than 0.0020% of T.O, wherein a number ratio of Mg type oxides contained in the steel is at least 0.8.
An annular support ring 32 is fitted onto the outer periphery of each trunnion 22. This support ring 32 and the roller 34 are unitized via a plurality of needle rollers 36 to constitute a roller assembly capable of relative rotations therebetween. In longitudinal section, each trunnion 22 has an outer periphery of straight shape, parallel to the axis of the trunnion 22. In cross section, the trunnion 22 has a generally ellipse shape with the major axis orthogonal to the axis of the joint. The inner periphery of each support ring 32 is arcuate and convex in section. This combines with the general elliptic cross sections of the trunnions 22 and the provision of predetermined clearances between the trunnions 22 and the support rings 32, to allow the support rings 32 to move along the axial directions of the trunnions 22 as well as make tilting movements with respect to the trunnions 22.
