Effect of Rare Earth on the Micro-Pitting Behavior in Rolling Contact Fatigue of GCr15 Bearing Steel

The service performance of the machine tool bearing is closely related to the tribological behavior of the bearing’s each component. At present, the precision life of precision machine tool bearings is concerned. Micro-pitting is a typical damage on the raceway surface when the bearing precision life expires. Rare earth resources are very rich in our country and widely used in bearing steel. Its inclusion in steel has a role in purifying liquid steel, microalloying and metamorphic inclusions. In this paper, the rolling contact fatigue test between rare earth/common GCr15 bearing steel and Si₃N₄ ceramic ball was carried out by using the ball-type rolling contact fatigue testing machine under the condition of oil lubrication. After different cycles of tests, the distribution, size and depth of the micro-pitting corrosion on the surface of the wear marks of the test bearing steel rod were characterized and analyzed, and the effect of the addition of rare earth on the micro-pitting behavior of GCr15 bearing steel during rolling contact fatigue was discussed. At the same time, in addition to the contact fatigue test of the ball rod, the bench test of the bearing was also carried out, and the micro-pitting corrosion of the bearing ring surface was studied after the test. The results showed that the micro-pitting amount increased with the increase of rolling contact cycles, whether it was rare earth GCr15 bearing steel or common GCr15 bearing steel. The difference was that the micro pittings of rare earth GCr15 bearing steel were not only shallower but also smaller and round, while the micro-pittings of common GCr15 bearing steel were not only deeper but also easier to appear in pieces. Also, the bearing bench test was carried out. The same micro-pitting behavior difference was found between rare earth bearing and common bearing. The effect of rare earth addition on micro-pitting behavior was discussed from the aspect of microstructure and carbide of bearing steel. In the microstructure of ordinary GCr15 bearing steel, mesh carbides and liquid evolution carbides were easy to appear, and there were carbides with uneven distribution and large size. The addition of rare earth made the carbides in GCr15 bearing steel more uniformly distribute in the matrix, effectively reduced the precipitation of liquid precipitation carbides and the appearance of a large number of networks carbides, and thus reduced micro-pitting failure of GCr15 bearing steel in rolling contact fatigue. Finally, using the finite element analysis, the formation mechanism of micro-pitting was discussed. In the process of experiment, the micro convex body contact and the uneven distribution of carbide under the effect of the contact stress leaded to the maximum shear stress concentration. As a result, micro cracks nucleated under the micro convex body and carbide, as the test progressed, the micro cracks extended slowly. When the test was stopped, the micro convex body and carbide fell off and formed micro-pitting.