Microstructure Evolution and Wear Resistance Improvement of Ultrasonic Peened M50 Steel via Electromagnetic Shocking

Herein, the effect of electromagnetic shocking treatment (EST) on microstructure evolution and wear resistance of M50 steel treated by ultrasonic shot peening (USP) is investigated. The microstructure observation indicates that the EST promotes the precipitation of nanoscale carbides. The average grain size decreases slightly and the submicron grain layer increases after EST. The low-angle grain boundaries generated by USP will transform into high-angle grain boundaries, thereby refining the grains on the surface during EST. In addition, the surface hardness of USP-M50 steel decreases slightly, accompanied by the reduction of surface residual stress after EST. The wear resistance results indicate that the wear loss of the EST specimens decreases by 15.7% comparedwith the specimens after USP. The improvement of wear resistance induced by EST is attributed to the increased fine precipitations. These precipitations hinder the grinding of abrasive particles into the matrix and connect with wear debris and oxide particles to form well consolidated self-lubricating films to prevent wear losses. The refinement of surface structure is another important reason for the improvement of wear resistance.