Expansion of fatigue cracks in laser - hardened 40H steel

Results of fatigue investigations and analyze of fracture crack expansion in 40H steel after different methods of heat treatment: quenching and tempering, induction hardening , laser hardening are presented in the paper. Test of strength fatigue were realized by two twice bend in rotary motion. They gave designation influence of laser hardening (and especially distribution of laser hardened tracks) on fatigue destruction of the investigation material. Presented research of fracture topography with use of scanning and microscopy gave information about hearth and character of cracks initiations and mechanisms and occurrences with accompany destruction advances of fatigue material. (author)