Abstract Dissertation deals with the changes in the surface layers of steels 5ChNM (L6), 3Ch2W8F (H21) and 4Ch5MFS (H11) in laser treatment and thermal cycling. Microstructure in melted zone of the three types of steels after laser treatment is documented. A mechanism of it's formation in steels 3Ch2W8F and 4Ch5MFS is established, including crystallization and following transformation: liquid (d-ferrite + liquid) (d-ferrite + austenite) (d-ferrite + martensite + residual austenite). Data of the hardness changes on the surface and in the depth of the laser-hardened layers are given. The hardness of the three types of steels increases in about 220-450 HV5, but the most significant it increases in the steel 5ChNM (L6) - 900 HV5. The dispersal microstructure of the melted zone of steels 3Ch2W8F and 4Ch5MFS after thermal cycling is established while the steel 5ChNM keeps its column morphology. The hardness of the steels 5ChNM and 4Ch5MFS decreases in the first stage of the thermal cycling and becomes equal to this of the basic metal while the hardness of the steel 3Ch2W8F remains higher. Kinetics of the crack growth in the laser-hardened layers of steels 5ChNM and 3Ch2W8F after thermal cycling is investigated. It is established that after laser treatment without melting the crack growth is accelerated while in the regimes with melting the kinetics is different and depends on the forming in thermal cycling microstructure of the surface layer. Methods and nomograms for selection of the technological parameters of the laser treatment are developed and the recommended technological regimes are given. « « « предходна страница             следваща страница » » »