Investigation of Surface Integrity Induced by Various Finishing Processes of AISI 52100 Bearing Rings

Abstract

Surface integrity induced by finishing processes significantly affects the functional performance of machined components. In this work, three kinds of finishing processes, i.e., precision hard turning, conventional grinding, and sequential grinding and honing, were used for the finish machining of AISI 52100 bearing steel rings. The surface integrity induced by these finishing processes was studied via SEM investigations and residual stress measurements. To investigate rolling contact fatigue performance, contact fatigue tests were performed on a twin-disc testing machine. As the main results, the SEM observations show that precision hard turning and grinding introduce microstructural alterations. Indeed, in precision hard turning, a fine white layer (<1 μm) is observed on the top surface, followed by a thermally affected zone in the subsurface, and in grinding only, a white layer with 5 μm thickness is observed. However, no microstructural changes are found after sequential grinding and honing processes. White layers induced by precision hard turning and grinding possess compressive residual stresses. Grinding and sequential grinding and honing processes generate similar residual stress distributions, which are maximum and compressive at the machined surface and tensile at the subsurface depth of 15 μm. Precision hard turning generates a “hook”-shaped residual stress profile with maximum compressive value at the subsurface depth and thus contributes as a prenominal factor to the obtainment of the longest fatigue life with respect to other finishing processes. Due to the high quality of surface roughness (Ra = 0.05 μm), honing post grinding improves the fatigue life of bearing rings by 2.6 times in comparison with grinding. Subsurface compressive residual stresses, as well as low surface roughness, are key parameters for extending bearing fatigue life.

Keywords: bearing steel; finishing processes; residual stresses; rolling contact fatigue; surface integrity.

Figure 1

Workflow of the present study.

Figure 2

(a) Bearing ring finished by precision hard turning; (b) sectioned specimen; (c) mounted, polished, and etched specimen.

Figure 3

(a) Setup for the residual stress measurements; (b) residual stress measurement directions; (c) limiting device of X-ray beam with the raceway width.

Figure 4

Twin-disc test machine and schematic representation of the geometry of ring specimens.

Figure 5

Drawing of ring specimens.

Figure 6

Micrographs of AISI 52100 steel after (a) precision hard turning, (b) grinding, and (c) sequential grinding and honing.

Figure 7

Residual stresses in circumferential direction.

Figure 8

Residual stresses in tangential direction.

Figure 9

RCF life vs. finishing processes.

Figure 10

Circumferential residual stresses after different phases.

Figure 11

Tangential residual stresses after different phases.