| 摘要 |
Surface layer of the shaft is hardened by induction hardening carbon steel and by forming a two-phase structure of ferrite and martensite in the core. The carbon steel comprises (in weight %) 0.35-0.70 C, 0.4-2.0 Si, 0.3-1.5 Mn, at most 0.025 S, at most 0.092 P, 0.01-0.1 Al, 0.001-0.004 B and 0.002-0.008 N, as base components, and Fe and impurities the remainder. The carbon steel also contains 0.3-1.0 weight % Ni and/or at most 0.2 weight % Mo added to it. The difference between the maximum and minimum value of the hardness of the surface is controlled to be not more than 200 HV. The harness of the core is controlled to be 25-45 HRC. The residual compression stress in the surface is controlled to be at least 60 kgf/mm<2>, and is preferably obtained by hammering so that it does not fall below 90/ kgf/mm<2>. Independent claims are given for universal joints. A universal joint comprises an external element comprising a number of guide grooves formed on the internal circumference, an internal element comprising a number of guide grooves formed on the external surface, torque transmission balls located in a number of ball tracks starting from guide grooves of the external element and the guide grooves of the of the internal element, and a cage for maintaining the torque transmission balls. The external element is made of carbon steel that has been surface hardened by induction hardening and has a two-phase structure of ferrite and martensite in its core. |
