Chapter 9 | Grinding and Hard Turning Metallurgical Property Relationships
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Published:2022
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Hardened bearing steel component grinding, hard turning, and final finishing operations of raceways are critical to rolling bearing function performance. If grinding or hard turning damage is present the metallurgical integrity is compromised and RCF life reduced. Therefore, hard-machining operations are key aspects of rolling bearing steel technologies. Grinding damage is generally prevented by the use of optimum grinding abrasives, speeds, loads and coolants. Prevention and control of excessive localized heat generation at the hard-machining surface is an essential quality assurance measure. Grinding burns are tested by appropriate methods such as acid etching and visual comparison charts. The test component preparation and acid etchants can vary depending on the bearing steel composition as given in the ISO 14104:2017 standard method. MIL-STD-867C standard describes grinding burn inspection methods for 52100, M50, and 440C bearing steels. Barkhausen noise testing can be used for grinding damage assessment. The white layers formed on hard-turned rolling bearing surfaces need to be minimized and possibly removed by a final lapping operation. It is published that beneficial compressive stresses can be generated in hard-finishing operations. Hard turning metallurgical parameters need precise control methodologies and if too much heat is generated in hard turning, undesired subsurface tensile residual stresses may be present. In common with other metallurgical tests, experience and precision is required in rolling bearing component grinding damage control.