Summary for hydrogen embrittlement Discussion
hydrogen embrittlement is explained here as a permanent loss of ductility in high-strength steels and some other metals after exposure to atomic hydrogen that is not promptly baked out. Maurizio "Mauri" Palluconi asks what evidence is needed to identify it and whether a broken part can show it under a microscope or in a photo. The answer says the condition is usually inferred from circumstantial evidence, especially a brittle fracture, rather than from direct visual proof of hydrogen itself. Common sources include acid treatments and electroplating, both of which can introduce hydrogen at the surface. The reply notes that once the hydrogen has invaded the crystal lattice, later baking will not restore strength. It also mentions that people often fracture notched samples to check for embrittlement, and that the effects are not something you can really see at an atomic level in a broken part.
Q. What is “hydrogen embrittlement” and what evidence is required to identify it. Can a broken part reveal its nature under a microscope? Can it be revealed with a photo?
Maurizio “Mauri” Palluconi
Product Engineer – Rochester, New York, USA
2004
A. If high strength steels (and some other metals) are exposed to atomic hydrogen, and it is not promptly baked out, it invades the crystal lattice and embrittles it. The embrittlement will then be permanent, such that baking a week later or a month later will not restore the strength.
It is common to try to fracture ‘notched samples’ to see if hydrogen embrittlement is present.
Common sources include acid treatments, which by their nature, release hydrogen at the surface of the part, and electroplating processes, which do the same.
I don’t believe that the effects of the hydrogen can be seen on an atomic level; and because the embrittlement can persist even after the hydrogen is gone, I don’t think you can tell that way either. But the way you can tell is through the circumstantial evidence of a brittle fracture, and brittle fracture is observable. This is a plater talking, so more info may come if a metallurgist signs on :-)
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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2004
A. Hydrogen embrittlement has been discussed many times on this site, so please review the archives for more information regarding the definition, mechanism, etc. With regards to microscopic examination, the usual features that are detected during fractography are regions of flat fracture characterized by brittle, intergranular fracture. These regions are often called “rock-candy” fracture due their appearance. Final fracture may still occur in a ductile overload manner when hydrogen embrittlement is involved, so care must be taken to evaluate the entire fracture surface. Scanning Electron Microscopy is best suited for fractography, due to the exceptional depth-of-field resolution compared to light optical microscopy.
Toby Padfield
Automotive module supplier – Michigan
2004