Carbonitriding of Case Hardening and Tempering Steels for Bearing Purposes

The performance of large case hardened rolling contact bearings is dependent on the properties of the surface layers of the rolling partners subjected to strain. This is especially true under challenging conditions like poor lubrication and/ or overrolling of particles. Those properties are mainly affected by the chemical composition of the base alloyed steel and the amount and distribution of induced carbon respectively carbon and nitrogen (carbonitriding). For optimization purposes 11 case-hardening or tempering steels were carbonitrided under varying gas compositions towards approximately equal hardening depths. The surface layers were characterized and chosen states of texture were tested for thermal and mechanical stability. Conclusively capability tests for rolling contact beaings were conducted by overroling tests of discs and angular ball bearings under varying overrolling conditions. The best overall test results with regard to production costs were achieved by the carbonitrided air melted steel grade 32MnCrMo6-4-3.

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