Strain-controlled out-of-phase thermo-mechanical fatigue tests at 100–500 °C and various strain ranges were conducted on five cast iron grades, including one lamellar, three compacted and one spheroidal graphite iron. Investigations of graphite morphology and matrix characteristics were performed to associate parameters, such as geometrical features of graphite inclusions and the matrix microhardness, to the thermo-mechanical fatigue performance of each grade. From this, thermo-mechanical fatigue life as a function of maximum stress at half-life, is found to decrease consistently with increasing average graphite inclusion length irrespective of the graphite content. In contrast, no evident correlation between the fatigue life and the matrix microhardness is observed.

The effect of adding a superimposed high-frequent strain load, denoted as a high-cycle fatigue strain component, upon a strain-controlled thermo-mechanical fatigue test has been studied on a compacted graphite iron EN-GJV-400 for different thermo-mechanical fatigue cycles and high-cycle fatigue strain ranges. It is demonstrated that the successive application of an high-cycle fatigue load has a consistent effect on the fatigue life, namely the existence of a constant high-cycle fatigue strain range threshold below which the fatigue life is unaffected but severely reduced when above. This effect on the fatigue life is predicted assuming that microstructurally small cracks are propagated and accelerated according to a Paris law incorporating an experimentally estimated crack opening level.

The static and low cycle fatigue properties of four pearlitic grey iron alloys intended for brake discs are investigated. The effect of alloying a base composition with 0.1 wt% and 0.3 wt% niobium is compared to a 0.3 wt% addition of the more conventional alloying element molybdenum. The results show that the static properties remain unaffected for an Nb content of 0.1 wt% while an addition of 0.3 wt% Nb or 0.3 wt% Mo increases the strength compared to the base alloy without Nb and Mo. The fatigue life on the other hand remains more or less unaffected by the alloying, although the stress levels are substantially higher for the compositions with 0.3 wt% Mo or 0.3 wt% Nb. Thus, the experiments show that graphite is very important for the low cycle fatigue life. It is also seen that crack propagation controls more than 90% of the life. Full scale brake dynamometer crack tests also gave a similar fatigue life of the different brake disc alloys independent of the composition.