Not sure how it gets "work hardened" Could be when the brass is formed? i don,t know. My case heads, primer pockets don't expand, are not sized, cant see how it can be work hardened when FL sizing?? Unless spring back does it??
Olin Brass had posted this-
"modulus of elasticity- Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI
when WORK HARDENED. Modulus of Elasticity is 16,000,000 PSI. This means to pull a 1.000 inch long strip to 1.001 inch long induces a 16,000 PSI stress.
So if you pull a 1.000 inch strip to 1.005 inch long, you get about 76,000 PSI, which is the max obtainable."
If you anneal the brass neck and shoulder, the case body gets stress relieved when it reaches about 400 degrees. From Gov on 5.56 ammo fired in full auto. 1 less annealing caused separations.