Effect of microstructure and temperature on the stress corrosion cracking of two microalloyed pipeline steels in H2S environment for gas transport
Résumé
The stress corrosion cracking resistance of two API X65 microalloyed steels, with different microstructures has been evaluated both at room temperature and at 55 °C, by means of Linear Elastic Fracture Mechanics (LEFM) specimens known as MWOL (Modified WOL specimen), under constant displacement. The material with a ferritic–pearlitic microstructure showed crack tip dissolution, a transgranular crack growth mode and some evidence of Hydrogen Induced Cracking (HIC). At room temperature, besides crack propagation, decohesion between grain boundaries was also observed, as well as some cavitation at the front of the crack tip. The material with martensitic microstructure tested at room temperature showed a mixed transgranular-intergranular crack growth mode, without cavitation at the crack tip front. At 55 °C, the crack growth path observed was transgranular, with cracks longer than those observed at room temperature, indicating that some Hydrogen mechanisms, probably thermally activated, could be present in addition to the anodic dissolution mechanisms.