Microstructural evolution and thermal fatigue resistance of grey cast iron

In the present work, thermal fatigue in grey cast iron has been investigated by means of a numerical and an experimental approach. Temperature gradients were generated within the material by means of a testing rig specifically designed for the experiments. The temperature gradients were responsible for the formation of severe stress fields that led to the failure of the specimens after a fairly low number of cycles. Crack growth was monitored during the tests, and the microstructure and hardness of samples were analysed after failure and compared with those of untested alloy. The repeated thermal cycles at peak temperatures of 600, 700, and 800 degrees C led to important microstructural alterations of cast iron and to a drop in material hardness. The pearlite lamellae lost their original shape and became more fragmented. Oxygen-rich regions surrounding the graphite flakes were produced by microgalvanic corrosion mechanism.