Laser surface treatment of high-speed tool steel (AISI M2)

High-speed tool steel (AISI M2) surface is pre-prepared to form a thin carbon film containing 5% B₄C particles prior to laser treatment process. Morphological and metallurgical changes are examined in the treated layer using electron microscope, energy dispersive spectroscopy, and X-ray diffraction. The microhardness and the residual stress formed at the treated surfaces are measured for samples with and without B₄C particles. It is found that the micro-stresses formed in the neighborhood of B₄C particles at the treated surface contributed to the microhardness enhancement at the surface. This is associated with the mismatch of thermal expansion coefficients between B₄C particles and the base alloy. The nitride phases are formed at the treated surface, which also contribute to the microhardness increase at the surface.