Hydrogen-induced cracking, mechanism

Cracking mechanisms in which corrosion is implicated include stress corrosion cracking, corrosion fatigue, hydrogen-induced cracking and liquid metal embrittlement. Purely mechanical forms of cracking such as brittle failure are not considered here. 

Hydrogen-induced cracking (HlC) is most commonly encountered in steels but other metals are susceptible, as shown in Table 53.3. The presence of hydrogen atoms in a metal degrades some of its mechanical properties, especially its ductility, leading in some cases to embrittlement. 

Strength, particularly where the material will be subjected to fatigue loading or is susceptible to degrading mechanisms such as hydrogen-induced cracking ... 

P. Jones, T. Hetu. A Case Study of Hydrogen Induced Cracking Failure - Investigation, Remedial Action and Maintenance. NACE International, Calgary Section, One Day Seminar on Failure Mechanisms, Calgary, Alberta, Canada, 1998-04-07. 

As a topic for research, hydrogen-induced cracking has perhaps received more attention than any other similar phenomenon but the precise mechanism of embrittlement is still not fully understood in terms of chemical and metallurgical reactions, which could be confirmed by direct experiment. Nonetheless, the conditions which collectively result in hydrogen cracking can be recognised and may be stated simply as sufficient hydrogen and sufficient stress in a susceptible microstructure at a temperature usually below 150°C. ... 

The mechanisms of intergranular See may also comprise anodic dissolution in slip bands after fracture in passivating films and/or hydrogen-induced cracking, as the case is for transgranular crack formation. 

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