Investigations included remelting and alloying experiments on the X40CrMoV5-1 hot-work steel with the high power diode laser. Tests have been made using the high power diode laser (HPDL) in the technological process of remelting and alloying the surface layer with the tungsten carbides. The surface remelting tests have been carried out for the X40CrMoV5-1 steel disk-shaped specimens, and surface alloying tests with tungsten carbide applied onto the steel in the form of paste. The effect of remelting and alloying parameters, and thickness of paste coatings applied onto the surface of the steel, on structure and properties of its surface layer, as well as on stresses, strains, and also remelting geometry and shape. The influence of alloying process parameters on the structure of substrate material are presented. Guidelines for remelting and alloying with the tungsten carbide of the X40CrMoV5-1 steel surface using the high power diode laser feature the outcome of the investigation aimed at obtaining its optimum mechanical and working properties. Results of test on spectrometer GDOS.