Distinctive features of the effect of laser treatment on the corrosion-fatigue fracture of structural steel

The dependence of the susceptibility of surface-hardened 40KhMFA steel ({sigma}{sub u}=950 MPa, {sigma}{sub 0.2}=780 MPa) to crack initiation and propogation on the mode of laser treatment is studied by the methods of fracture mechanics. The influence of laser treatment on the initiation of a fatigue crack is ambiquous: in air, it results in a substantial increase in the fatigue threshold, while in 3% NaCl solution, the fatigue threshold decreases. The growth rate of short fatigue cracks decreases in both air and corrosive media. The positive effect of laser treatment on the kinetics of crack growth and the threshold SIF becomes more pronounced as the yield limit of the surface layer {sigma}{sub 0.2} increases. The depth of the influence of laser treatment on crack growth is not restricted to the hardened surface layer due to the redistribution of residual stresses. Unlike the base material, short cracks in the surface layer hardened by a laser are characterized by a high degree of crack closure, which proves to be the main factor that provokes an increase in the fatigue crack-growth resistance.