Fatigue strength of newly developed high-strength low alloy TRIP-aided steels with good hardenability

Fatigue strength of newly developed TRIP-aided annealed martensitic steels (TAM steels) with chemical composition of 0.4%C, 1.5%Si, 1.5%Mn, 0-1.0%Cr, 0-0.2%Mo, 0.05%Nb, 0-18ppmB was examined for application of automotive diesel engine common rail. The TAM steels achieved higher fatigue limits than the conventional structural steels. Also, the TAM steels exhibited extremely high notch fatigue limits and low notch-sensitivity, especially in steels with B or without Cr and Mo. This was associated with TRIP effect of a large amount of metastable retained austenite which suppressed the crack initiation and growth due to plastic relaxation and formation of hard martensite resulting from the strain-induced transformation.