INFLUENCE OF SHORT-PULSE LASER RADIATION ON THE SURFACE MICROSTRUCTURES FORMATION AND HARDNESS OF STAINLESS STEEL

The paper deals with the issues related to the technology of short-pulse laser treatment of AISI321 steel. The object of the study is the surface structures formed after short-pulse exposure to a nanosecond laser, as well as their physical and mechanical characteristics. The subject of the study in the work are the processes of formation of periodic surface structures after short-pulse laser exposure. The assumption about correlation of the character of formation of structural transformations in the surface layer of the processed material during the process of laser exposure with low intensity of laser radiation, and traditional heating cooling was formed. It is noted that when the corresponding critical irradiation conditions (irradiation power, heating and cooling rates, strain gradient, etc.) are reached, laser hardening of austenitic steel with hardness increase, i.e. quenching, occurs. It is emphasised that short-pulse laser exposure at low laser powers causes such processes in the surface layer of AISI321 stainless steel, which mainly prevent the deposition of chromium carbide and do not strengthen the material, and the absorbed laser energy is still insufficient to significantly create martensitic structures. It is also emphasised that the repeated short-term superposition of heat spots repeatedly crossing each other results in an increase in the thermal deformation of the material and, as a result, stronger crystal structures such as martensite, carbides and oxides are formed in the surface layer.