Hydrogen embrittlement is a permanent loss in ductility caused by introducing hydrogen into a metal fastener in combination with stress. A typical hydrogen embrittlement (HE) failure is a delayed failure and happens after assembly. An HE failure is caused when three requirements are fulfilled. These areas are (1) hydrogen induced, (2) stress applied, and (3) high hardness. Continue reading for more information about each area.
Hydrogen needs to be induced for an HE failure. This is most commonly induced in the electroplating process, but can also be introduced into the material through corrosion of the bolt.
Once stress is applied to a bolt that has a significant amount of hydrogen trapped inside the molecular structure, it is a matter of time when the hydrogen collects in molecular void and that void will grow bigger until the fastener fails.
This is the easiest pillar of an HE failure to control in the HE failure spectrum. Industry standards dictate that anything 320 Vickers Hardness or higher needs stress relief and possible further special attention.
HE failures can be very dangerous because the failure is delayed after installation and is very sudden. Before a bolt with HE is installed, there is not a visual way to identify if HE is present.
Any fastener that meets the hardness criteria need special attention and care to avoid HE failures. Contact us at ProvenProductvity@bossard.com if you have any questions about HE and its causes.