Abstract
The paper reviews the macroscopic work hardening behaviour in the different stages of the deformation curve. While for stages II and III the storage of dislocations caused by multislip and their additional annihilation either via cross slip (low temperatures) or climb (high temperatures) are widely accepted, stages IV and V have found different explanations. These are critically discussed in the light of experimental results presently available. The importance of this discussion is increased since it has become clear that the strengthening behaviour of nanocrystalline metals produced by severe plastic deformation is governed by stage IV - strengthening mechanisms.

Key words
hardening behaviour, nanocrystalline metals, strengthening behaviour

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