Abstract :
Metallographical (optical, SEM, TEM), microprobe, wear resistance and microhardness investigations of M2 high-speed tool steel surface melted by continuous CO2 (with different power) and Nd:YAG pulsed lasers are described. It became apparent that there was a considerable influence of the laser type, scanning velocity, gas jet atmosphere and the antireflective graphite coating on the melted zone dimensions and its as-resolidified structure. The notable differences between the microstructures of the melted zones were related to the laser type and laser power. In comparison to the uncoated specimens, laser melting of the specimens coated with a colloidal graphite layer resulted in significantly increased dimensions of the laser-affected layer and a coarser as-resolidified structure. Depletion of the Cr, V, Mn and C in the resolidified zone after treatment under oxygen atmosphere was related with the high reaction efficiency of these elements to oxygen. Hardness of the melted zone in the uncoated samples was higher than that of both the graphite-coated samples and the conventionally hardened matrix. The lathe tools treated by the Nd:YAG pulsed-laser radiation showed the longest cutting life-time.
