GB491781A - Improvements in or relating to the production of anti-friction bearing members of hardened steel - Google Patents

Abstract

In the production of an anti-friction bearing member of hardened steel, the member or part of it is after a heat-treatment to produce in the finished member a Brinell hardness of at least 600, subjected to a temperature lower than indoor temperature, e.g. below 0 DEG C., for a period of time to ensure that macro-stresses of the character of tensile stresses in directions parallel to the surface, are, when the temperature of the cooled member is subsequently raised to 100-300 DEG C., preferably 200-250 DEG C., either eliminated or rendered very small at that part of the member stressed by the load during use. Before or after the member is subjected to the low temperature, it may be allowed to remain in contact with a surrounding fluid at atmospheric temperature for a period of time in excess of that required to enable the member to assume atmospheric temperature. The member may be cooled to a temperature of -50 DEG C. or to a temperature between 50 and -100 DEG C. and the temperature may be allowed to fall continuously from the hardening temperature or in stages. The member may be subjected during cooling to vibration, produced for example by the action of a periodically varying electromagnetic field produced by an electromagnetic oscillation circuit or by the application of pressure thereto in order to effect a desired modification of the macro-stresses. When treating a plurality of members, a member after cooling may be reheated to an intermediate temperature by immersion in a medium for cooling other members to that temperature. In an example, a member made of steel containing 1 per cent of carbon, 1 of chromium and 1 of manganese is quenched from 800-900 DEG C., preferably 850 DEG C., to indoor temperature in oil and then cooled in a suitable liquid, e.g. alcohol to -20 to -40 DEG C. The member is then transferred to another bath, e.g. of solid carbon dioxide, at -78 DEG C., transferred to the first bath and then reheated to an intermediate cooling temperature. The member is then heated to a temperature above 150 DEG C., preferably 200-250 DEG C. If desired, the cooling may take place in stages to temperatures of -25, -50, -75 and 100 DEG C. after hardening.