recovery stage of annealing, the physical and mechanical properties that suffered changes as a result of cold working tend to recover their original values. For many years, the fact that hardness and other properties could be altered without an apparent change in the microstructure, as signified by recrystallization, was regarded as a mystery. That the various physical and mechanical properties do not recover their values at the same rate is indicative of the complicated nature of the recovery process. Figure 8.6 shows another anisothermal anneal curve corresponding to the energy released on heating cold-worked polycrystalline nickel.3 The peak at point c defines the region of recrystallization. The fraction of the energy released during recovery in this metal is much larger than that in the example of Fig. 8.2. Plotted on the same diagram are curves indicating the change in electrical resistivity and hardness as a function of the annealing temperature. Notice that the resistivity is almost completely recovered before the state of recrystallization. On the other hand, the major change in the hardness occurs simultaneously with recrystallization of the matrix.