Effect of Hydrogen Attack on Fatigue and Fracture Behaviour of Steels

The effect of hydrogen attack caused by exposure to hydrogen atmosphere at different temperatures and time on mechanical properties,fatigue crack growth behavior and fracture mechanism for Chinese made steels 20G,15CrMo and 2.25Cr-IMO were studied.The microstructure after hydrogen attack and the propagation path of fatigue crack have been observed by optical and electrical microscopy.The tensile tests showed that tensile strength and ductility decreased considerably with increasing of hydrogen attack.The COD testing indicated that fracture toughness material.The2.25Cr-IMo steel showed a lower susceptibility to hydrogen attack due to the action of element Cr and Mo,not resulting in a significant change in fatigue crack behaviour.It is suggested that the increase in the threshold K value could be attributed to the crack closure effect caused by the tortuous cracking path.