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The surface of a high-speed tool steel has been modified by an intense pulsed-ion beam (IPIB) that has an ion energy of 180 keV, an ion current density of 460 A/cm2, and a pulse duration of 65 ns. Transformation of the crystalline structure in the sample surface layer by IPIB-irradiation was observed by a glancing angle X-ray diffraction and a transmission electron microscopy. The second-phase carbides, V4C3, Cr6C, and Fe6C, were dispersed from the irradiated surface layer. A martensitic matrix in the surface layer was converted into an austenitic matrix by ten-pulses-irradiation of the IPIB. After repeated IPIB-irradiation of 100 pulses, a mixed phase of the austenite containing 2.0 wt.% carbon and a cementite was formed in the surface layer. The crystalline size of the sample was reduced from 7 μm for the untreated to 41 nm after 100-pulses-irradiation. The Vickers hardness of the treated surface was Hv=1030 corresponding to 1.2 times of the untreated one. In addition, the friction coefficient of the treated surface was reduced from 1.2 to 0.9, and the wear resistance of the surface was significantly improved.