Surface modification of 40CrNiMo7 steel with high current pulsed electron beam treatment

Abstract

High current pulsed electron beam (HCPEB) treatment was conducted on 40CrNiMo7 steel with accelerating voltage 27kV, energy density 3J/cm2, pulse duration 2.5μs and 1–50 pulses. The evolutions of surface microstructure were investigated by using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) techniques. It was found that the carbides in the surface remelted layer of depth ∼4μm were dissolved gradually along with the increasing number of HCPEB pulses. Eventually, the surface microstructure of 40CrNiMo7 steel was transformed to a complex structure composed of very refined ∼150nm austenite as the main part and a little quantity of martensite phases. After 15 pulses of HCPEB treatment, the surface microhardness was doubled to 553HV, and the wear rate decreased to one third of the initial state correspondingly.