AbstractThe influence of tempering temperature, stress ratio, and prior strain on fatigue crack propagation in a low-alloy chain steel has been investigated. At small stress ratios (R=0·1) tempering above 400°C is beneficial, resulting in higher threshold levels and slower growth rates in the initial growth regime. Thereafter, crack growth is independent of tempering temperature, as it is over the entire growth period under a high mean stress (R=0·5). Prior strain produces a slower growth and higher thresholds at R= 0·1. Intergranular fracture is common and is a function of stress intensity range and tempering temperature. It is concluded that residual stress effects, rather than microstructural effects, account for the experimental observations. In particular, the existence of a tensile residual stress during initial growth and a crack closure stress greater than the minimum applied stress level are proposed.MST/672