I disagree with Norma. 70/30 brass does not age or soften with time. The brass can only get softer by the grain size increasing, this only happens at elevated temp. There is no metallurgical mechanism for the grain size to increase at room temp. Never heard of self strain relieving in brass at low temp (I will look into strain relief at low temp). It only gets softer from annealing at temperatures above 750F. Cartridges loaded from WWI have not lost grip on a bullet.
I struggled and bent from side to side to pull the bullet out of my 100 YO 45/70 case.
I know it isn't brass but copper has very similar properties as 70/30 brass as far as work hardening and annealing. Many countries have chosen copper to store nuclear waste since the coppers properties won't change for at least 100,000 years. It's probably annealed copper. If anyone has info to the contrary I would like to see it from some reliable metallurgical research.
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Data from sellers of copper and brass sheet, plate and wire.
Source:
http://www.totalmateria.com/Article25.htm
Stress Relieving (not annealing)
Stress relieving is aimed to reduce or eliminate residual stress, thereby reducing the likelihood that the part will fail by cracking or corrosion fatigue in service. Parts are stress-relieved at temperatures below the normal annealing range that do not cause recrystallization and consequent softening of the metal.
Residual stresses contribute to this type of failure, which is frequently seen in brasses containing 15% zinc or more. Even higher-copper alloys such as aluminum bronzes and silicon bronzes may crack under critical combinations of stress and specific corroding, and all copper alloys are susceptible to more rapid corrosion attack when in the stressed condition.
Stressed phosphor bronzes and copper nickels have comparatively slight tendencies toward stress-corrosion cracking; these alloys are more susceptible to fire cracking, which is cracking caused when stressed metal is heated too rapidly to the annealing temperature. Slow heating provides a measure of stress relief and minimizes non-uniform temperature distributions, which lead to thermal stress.
Using a high stress-relieving temperature for a short time is generally considered best for keeping processing time and cost to a practical minimum, even though there is usually some sacrifice in mechanical properties. Using a lower temperature for a longer time will provide complete stress relief with no decrease in mechanical properties. Actually, the hardness and strength of severely cold worked alloys will increase slightly when low stress-relieving temperatures are used.
SOURCE:
http://www.lfa-wire.com/70-30-brass-wire_c26000.htm
PHYSICAL PROPERTIES
C26000, 70/30 BRASS
Annealing Temperature
800-1400°F
425-750°C
Stress Relief Temperature
(1 hr)
500°F
260°C
