Surface modification of high-speed tool steel by repeated irradiations of intense pulsed ion beam

Surface modification of a high-speed tool steel (SKH51) has been performed by irradiation of the proton intense pulsed ion beam (IPIB) with the ion en ergy of 180 keV, the ion current density of 460 A/cm(2), and pulse duration of 65 ns. By 1-pulse irradiation of the IPIB, the second phase carbides su ch as VC, Fe6C, and Cr6C are dispersed from the irradiated surface, and the average grain size decreases to 240 nm corresponding to approximately 1/30 of the untreated one. Repeated irradiations of the IPIB result in the redu ction in grain size and conversion of an alpha -Fe structure to a gamma -Fe one. The SKH51 treated by 10-pulses irradiation has a single phase of gamm a -Fe, and the grain size is reduced to approximately 1/170 of that of the untreated one. In addition, the 10-pulses-irradiated surface has an improve d wear resistance.