Synergetic effects of thermo-mechanical controlled process and ultrasonic surface rolling processing on mechanical and tribology performances of M50 bearing steel

To meet the stringent performance requirements of the new generation aero-engine bearing material, matrix toughness and surface hardness of M50 steel were synergistically enhanced by thermo-mechanical controlled process (TMCP) and ultrasonic surface rolling processing (USRP). Micro-structure, mechanical and tribology performances of the mechanically treated M50 steel were investigated to clarify structure-properties relationships and strengthening mechanisms by SEM, OM, EBSD, EPMA and TEM analyses. The results show impact toughness of M50 steel is significantly improved by carbide refinement after TMCP (big forging ratio and accelerated cooling). Surface hardness and wear resistance of M50 steel are enhanced by 6.33% and 40.63%, because severe plastic deformation layer (white layer) with high density dislocation and nano-crystalline is formed in the near-surface region after USRP. After the synergetic effects of TMCP and USRP, wear surface of M50 steel with white layer facilitates the generation of low-roughness tribolayer, and the dominant wear mode transitions from adhesive to predominantly abrasive with residual adhesive components.