The influence of loading rate on hydrogen induced cracking of microalloyed steels

Since the degradation effect due to environment on the cracking of materials depends on time, the loading rate has an important influence on the parameters that characterise its behaviour. This work analyses the effect of loading rate on the resistance to hydrogen induced cracking (HIC) of two microalloyed steels, E690 and E500. Monotonic loading tests were performed on precracked CT samples using a slow strain rate machine. Tests were done under constant displacement rate varying from 4.1 × 10-7 m/s to 8.2 × 10-10 m/s on the two steels that were cathodically charged with hydrogen at different current densities (1, 5 and 10 mA/cm2) to obtain different hydrogen concentration levels inside the material. Based on an analytical study, the initiation conditions for cracking as well as the crack propagation rates were determined in each case, and analysed as a function of KI. An extensive fractographic SEM study has been performed to help in the analysis of the different zones of behaviour obtained as an effect of loading rate, for each material and environmental condition used.