72 years ago the US Navy did a careful study on the subject. They debunked the then-long-held tradition of storing cast iron "in the weather" and under various conditions to reduce internal stresses in the cast iron piece. Here is a link:
https://apps.dtic.mil/dtic/tr/fulltext/u2/620556.pdf They did show that properly done high_temperature thermal stress relief is effective.
If you are interested in the subject, take a few minutes to read it. Old traditions die hard as you will still hear many advocating for aging castings. Vibratory stress relief has its advocates but is controversial as to whether it works and in what circumstances it might work. From Wiki which has no axe to grind in this matter "
The effectiveness of vibratory stress relief is highly questionable.[SUP]
[4][/SUP]
In general, the strain amplitudes achieved during vibratory stress relief are too low to exceed the critical stress required to activate mechanical relaxation during the induced low amplitude high cycle fatigue excitation of the transducer vibrations. If the strain amplitudes were increased to a level sufficient to cause instability in the residual stresses, fatigue damage would occur.[SUP]
[5][/SUP][SUP]
[6][/SUP]
For most applications, conventional stress relief methodologies should be applied to components that require the reduction of residual stresses.[SUP]
[7]"
[/SUP]You will find a whole bunch of papers purporting to support vibratory stress relief on the Web. But those all trace back to the companies hustling vibratory equipment. None come from independent sources, universities etc.
This seems to be a subject that stirs heated (so to speak) discussion and lots of anecdotes. I listen to the science on the subject.
Denis