What does work hardening do

Cold forming

Cold forming refers to the forming of metals at a temperature well below the recrystallization temperature.

The dislocation density in the metal, which increases during plastic deformation, leads to an increased probability that dislocations will meet during their movement and thus mutually hinder their movement. Correspondingly, greater stress is necessary for further deformation, which is noticeable in an increase in the yield strength and hardness. This behavior is also known as work hardening.

The increased dislocation density also leads to an increase in the energy stored in the crystal. So if you bring a work-hardened metal long enough into a temperature range in which the lattice defects can heal, the strength of the metal decreases again through recrystallization.

Work hardening is particularly pronounced with copper. Wholesalers often sell copper tubing as hard or soft. The fitter can locally soften the hard pipes again by heating them with the gas flame. They solidify again when they are bent.

Comparisons of hot and cold forming

Hot forming

  • Working temperature above the recrystallization temperature
  • Great formability of the materials
  • Low forming forces
  • Little change in strength and elongation at break on the formed material

Cold forming

  • Working temperature below the recrystallization temperature
  • Close dimensional tolerances are possible
  • No scaling of the surface
  • Increase in strength and decrease in ductility, d. H. Elongation at break (work hardening)
  • Ductile fabrics are easy to cold form, such as B. by deep drawing, bending or stretching.

By cold forming, the structure of the material used is affected in such a way that, for. B. the welding processing of this component can no longer be ensured. Soft annealing can restore the weldability by reducing dislocations.

See also