Quote (mrfailure)

I came across a claim during literature review for a failure that "HE failures are ALWAYS intergranular"

With untempered martensite it can be pretty hard to tell by optical metallography. In the practical business of failure analysis I don't think this level of science is essential.
If factors required for EAC are all present - tensile stress, susceptible material, and environment (bad actor + temperature) then it is safe to presume HE mechanism, if other possible mechanisms have been eliminated from consideration.

Certainly 'CrMoV high-strength martensitic steel' and 'fasteners' are among the usual suspects...

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

Thanks IM. Conditions appear to be right. I'm still looking into the environment to confirm HE could be induced. One question I am currently chasing down is whether the hydrogen could have been introduced from the thread lube. SEM/EDS suggests a carbon-based oil or grease containing aluminum and calcium.

The initial fracture may be intergranular, but once it begins to propagate all bets are off.
You see this is SS with CSCC, mixed mode is very common.

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P.E. Metallurgy, consulting work welcomed

I agree with ironic metallurgist: it can be very hard to tell with martensite, especially. Another option is to try ASTM F1624 testing using the actual material. It takes a sub-size specimen and determines the threshold for hydrogen embrittlement.