Tasdiqlayman“Chet tiilar” kafedras imudiri M. B. Ganikhanova

Recovery and Recrystallization.

Recovery. During a cold-working process most of the energy used is dissipated as heat but a small percentage is stored within the distorted lattice

structure of the alloy. That energy is the thermodynamic driving force that tends to return the metal to its original state provided there is sufficient thermal energy to

enable the reactions to occur. Cold forming is done above the yield point in the

work-hardening range, so internal stresses can be built up easily. Evidence of this is the spring back as the work leaves the forming operation, and the war page in any subsequent heat treatment. Even a simple washer might, by virtue of the internal stresses resulting from punching and them flattening, warp severely during heat treating. Recovery is a gradual change in the mechanical properties of an alloy, i.e.,loss in brittleness, or marked increase in toughness brought about by controlling the heat-treating times and temperatures so that there are no appreciable changes in the microstructure. However, recovery does significantly reduce the residual stresses within the distorted lattice structure.

When doubt exists as to whether internal stresses will cause war page, a piece

can be checked by heating it to about 1100 deg. F and then letting it cool. If there are internal stresses, the piece is likely to deform.