[TheForge] Spring steel (and other) breaking in mild acid

[Andrew Vida]

On 8/26/2011 3:08 PM, xlch58 at swbell.net wrote:

> Springs often are conditioned during manufacture so that they have
> residual compressive stresses so that their fatigue limit is raised.
> Bearings also have residual stress added in manufacturing as well.

AKA work hardening... similar to autofrettage in artillery barrels where 
the ends are plugged and hydraulic pressure is applied such that the 
material is taken to some small percentage past its elastic limit. 
Dramatically increased service life of the bore.  In the old days it was 
done with a swage that would be drawn through the bore on a mandrel to 
the same result.

The difference in result, however, is that with hydraulics, the bore can 
be rifled before autofrettage whereas the other method had to be done on 
a smooth bore that would be rifled afterward.  This, of course, 
complicated manufacture and raised wear on the rifling cutters.