It is important that the metal is kept hot particularly during the final stages of working into a finished shape so as to avoid strain hardening the metal by cold rolling. This can sometimes be difficult, particularly with the rolling of long bars of small diameter, because the smaller or thinner the section the faster it looses heat.
Annealing removes the effects of cold work. In a number ofthe testing programs discussed in this paper the samples were annealed before tensile testing. This was done because the mechanical history of some of the specimens was unknown. By first annealing the metal the 'natural' strength and ductility could be determined as opposed to measuring the strength of a strain hardened sample.
Shearing and punching iron strain hardens the area around the cut or hole. "M. Barba showed that cutting out a ring 1/8 inch thick round a punched hole, or annealing the plate, entirely removed the prejudicial effect of punching" (Unwin 1910). Drilling holes for rivets did not strain harden the metal but was slower and more expensive than punching. Kirkaldy found
that punched plates experienced a 50% loss in ductility compared with plates that were drilled. (Kirkaldy 1876).
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