1. The energy of crack nucleation in case-hardened steel 14KhN3MA is practically independent of the regimes of LHT in the range of speeds v=0.1-2.0 m/min. Tempering at 200°C does not affect the energy of crck nucleation. 2. After LHT of case-hardened steel 14KhN3MA with scanning speeds of the laser beam v from 0.1 to 2.0 m/min six zones with different structure form in the fracture of nontempered specimens. With increasing v the zones of the fracture occupied by facets of intercrystalline failure including zones of columnar crystallites become shorter. 3. The size of the laser-affected zone is equal to the thickness of the hardened layer and to the distance between the surface of the specimen and the boundary of the zone of ductile pitted failure. 4. Laser heat treatment with v=0.1-1.0 m/min causes fusion of the surface of the specimen, and that leads to growth of columnar cyrstallites with weakened boundaries in the fused region and to the development of intergranular failure along the boundaries of these crystallites. 5. Tempering at 200°C after LHT with v=0.1-1.0 m/min reduces in the case-hardened case the proportion of fracture taken up by intercrystalline failure and transcrystalline shear while the surface layer of the specimen (up to 0.7 mm thick) retains its high hardness of 600-730 H. 6. Tempering at 600°C, which promotes crack propagation by the pitting mechanism of failure, is accompanied by a substantial decrease of hardness of the surface layer of the specimen to 300-350 H. © 1992 Plenum Publishing Corporation.
