"Jim Wilkins" writes:

...

Would fatigue cracking in oil be similar enough to cracking in air,
which oxidizes freshly exposed steel?

I think so - very little difference.
Well my instinct says for environment in general that
* negligible difference at high stresses
* possible significant effects at low stresses / huge numbers of
cycles to crack / break
I suspect the difference between in-air and in-oil would be
negligible.

Another thing I must test though.

Rich S