Change over from elastic to permanent deformation during structural transformations

Summary

• 1. Permanent deformation in metals and alloys can arise through a combination of first and second-order plastic deformations. The first involves displacements of large groups of atoms, the second, individual atomic displacements.

• 2. Second-order plastic deformation is increased by factors which increase atomic mobility-increase of temperature, the degree of metastability of the structure, and increase of the time of stressing.

• 3. Second-order plasticity arises in diffusion of atoms, and also in structural diffusional and diffusionless transformations.

• 4. Clamping of parts in fixing jigs at the moment of transformation straightens them, even if the metal is very hard. In particular, for preventing warpage, parts may be clamped in tempering, and also in the martensite transformation.