Optimizing wear resistance of M50 bearing steel via primary carbide subdivision

Optimizing wear resistance and extending service life of M50 bearing steel have attracted significant attention in manufacturing aero-engine bearings. This study achieves enhanced wear resistance in M50 bearing steel using surface mechanical rolling treatment (SMRT). Microstructure observations reveal that a gradient nanostructured surface layer of ∼700 μm in thickness is generated. The SMRT processing subdivides the primary carbides in the near-surface layer, significantly reducing their size and inter-carbide spacing (from ∼44.7 μm to ∼38.2 μm), while increasing their area fraction from ∼3.6% to 11.0%. Dry-sliding wear tests show that the wear resistance of the SMRT samples is significantly enhanced. Under a load of 110 N and sliding for 9000 cycles, the wear volume of the SMRT sample is reduced by ∼54% compared with the as-received (AR) sample. Further analyses suggest that carbide subdivision plays a more significant role than enhanced microhardness and compressive residual stress in the surface layer in the optimized wear resistance of the SMRT samples. This is mostly due to that the refined carbides, with a reduced inter-carbide spacing and an elevated area fraction in the plane paralleling to the sample surface, resist abrasive wear during the initial sliding stage and reduce brittle spalling during the subsequent sliding stage. Moreover, the gradient nanostructured surface layer plays a supporting role in mitigating stress concentration at the carbide/matrix interface when the subdivided carbides are subjected to direct contact loading.