Mechanisms and modelling of fatigue crack growth under combined low and high cycle fatigue loading

► The evolution of microcracks was followed for a 10%-chromium steel. ► Martensite needles promote stage 1 crack growth. ► LCF/HCF interaction accelerates fatigue crack growth compared to pure LCF loading. ► A model based on da/dN ∼ ΔCTOD can describe LCF and LCF/HCF crack growth.