Enhanced wear resistance of high-speed steel by pulsed electron-beam melting

We investigated the structural and phasic transformations occurring in the near-surface layers of pre-quenched high-speed steel subjected to pulsed electron beam melting and their effect on the wear resistance of cutting tools. Melting was induced by a pulsed electron beam depositing at the surface between 3 to 18 J/cm(2). Using electron microscopy and X-ray diffractions it has been revealed that - increasing the beam energy density during deposition - a gradual liquid-phase dissolution of initial globular MC carbide particles occurs in the near-surface layer of thickness up to similar to1 mum. This process is accompanied by the formation of martensite crystals and an increase of residual austenite content. When the carbide particles are completely dissolved, martensitic transformation is suppressed. In this case, a structure is formed consisting predominantly of submicron cells of austenite phase separated by nanosized carbide interlayers. Irradiation of cutting tools (drills and saw blades) in a mode corresponding to an abrupt decrease in the content of M6C particles enhances the wear resistance of the tools. This is associated with the fixation of undissolved particles in the matrix, the formation of residual compressive stresses and of dispersed M3C carbide particles as well as the high content of the metastable austenite phase in the surface layer.