At what region of a stress-strain curve does strain hardening occur? What does strain hardening do?

Strain Hardening (also known as cold-working, work hardening): Process of making a metal harder and stronger through plastic deformation. When a metal is plastically deformed, dislocations move and additional dislocations are generated. This will result in a decrease in the mobility of the dislocations and a strengthening of the material. Occurs at low (relative) temperature.

Occurs between points C and E on the above stress/strain curve.