Thermal fatigue resistance of the laser alloyed 32CrMoV12-28 hot work tool steel

This paper presents the results of laser treatment influence on structure and properties of the surface layer of the 32CrMoV12-28 hot work tool steel, using the High Power Diode Laser (HPDL) for alloying and remelting with diverse ceramic carbide powders with a granulation about 10 µm. Laser remelting and alloying as a laser treatment process can be used for hardening of hot work tool steel surface layer, that cannot be hardened so effectively by any traditional hardening method (austenisation and annealing). As examples for that treatment is alloying of steels with carbide-forming elements as niobium and vanadium. In this work structure changes as well as hardness and roughness are investigated, also phases occurred in the surface layer were determined. During this laser treatment of hot work tool steel, due to the short interaction time between the laser beam and the treated material, carbides are unable to be dissolved to saturate austenite sufficiently with carbon and alloying elements. For this reason technique of laser surface melting can find many practical applications, as a method of formation of rapidly resolidified surface layers possessing many advantageous properties. Special attention was devoted to monitoring of the layer morphology, the particle occurred and the remelted zone thickness. The remelted layers which were formed on the surface of the investigated hot work steel were examined metallographically (light microscope) and analyzed using a hardness and microhardness testing, X-ray diffraction, EDS microanalysis, electron scanning microscope. The goal of this work was also to determine technically and technological conditions for remelting of surface layer with HPDL laser, as well as the thermal fatigue resistance for the surface layer.