work hardening (was string break)

[Ron Nossaman]

>The phenomenon of work-hardening is critical to achieving tensile pickup 
>for non-modern music wire - thinner gauges are stronger than thicker 
>by a significant amount. The severity of drawing since the final 
>annealing is responsible for the amount of tensile pickup. To answer the 
>question - although it is not really any aid to *understanding* work 
>hardening - at the atomic level cold working metal is supposed to split 
>the crystalline structure into sub-grains or crystallites. These are not 
>removed by heating until the annealing temperature is reached and the 
>metal re-crystallizes. 
>
>Stephen

Yep, something very like that. I've also read that it elongates the
crystalline structure and increases the contact area between individual
crystals. In effect, increasing the perimeter to volume ratio of individual
crystals in the matrix. I was just hoping someone had better details.

Thanks,   
 Ron