Residual stress-induced crack closure during fatigue crack growth in electron-beam welded 316L stainless steel

Fatigue crack growth rates in welded specimens are difficult to predict and interpret due to weld residual stresses and variations in microstructure complicating data interpretation. In the present work, several notch positions are investigated in electron-beam welded 316L stainless steel compact tension specimens which contain nominally similar residual stress fields. This is done to compare the effect of microstructure and residual stress on fatigue crack growth rates. The microstructure and residual stress states in the welded specimens are first characterised. Fatigue crack growth rate measurements are then performed on the specimens. Three different methods are then compared for correcting for the effect of residual stress induced closure: the compliance offset method, adjusted compliance ratio method, and a proposed method using the residual stress induced stress intensity factor, K r e s . The microstructure in the weld is shown to have little influence on the fatigue crack growth rate, as specimens with the crack initiated in different parts of the weld follow the same fatigue crack growth rate behaviour. When allowed to grow freely, fatigue cracks in specimens with their notches cut from the weld fusion zone boundary and heat affected zone grew away from the fusion zone towards the parent material. The residual stress in the specimens appears to be the dominant factor in the changes observed in fatigue crack growth rates. The proposed K r e s correction method successfully corrects the fatigue crack growth rate behaviour and creates a Paris law fit which is close to that of the parent material once the effect of residual stress is accounted for. • Proposed an improved method to account for residual stress in fatigue crack growth. • Comparison of the proposed method with two commonly used methods. • The effect of residual stress and microstructure on fatigue crack growth rates in EB welded 316L.