Effect of shot peening on short crack propagation in 300M steel

The short crack growth behaviour of high strength martensitic 300M steel was studied for as-machined, polished and 2 peening conditions subjected to axial fatigue at 2 stress amplitudes. It was observed that prior austenite grain boundaries acted as barriers to short crack propagation in peened specimens within the peening induced compressive residual stress layer, causing crack decelerations upto 6 grains. Using the da/dN - Delta K trend of the short cracks, fatigue lives of the peened specimens were predicted at both the stress amplitudes. These analytical predictions (which reflect the effect of microstructure and compressive residual stresses) were within 15% of the experimental fatigue lives.