Strain Hardening

Strain hardening

Strain hardening = Cold working = Work Hardening

• All names for the same thing.

Action and affect

• Material is stressed into the plastic region, and then tension released.

• The yield strength has become higher, the next time the material is stressed it will take more stress to bring it into the plastic region.

• The ductility is decreased and the hardness is increased.

Why?

• The plastic deformation causes more dislocations to form, and gives energy to existing dislocations to move around. This allows pinning to occur, which increases the strength of the material.

Negatives of Strain Hardening

• When described as work hardening, it is often referring to the hardening of a component due to stresses while in use or manufacture.

• This hardening can occur at much lower stresses than the yield strength, which means the microstructure can change without any large sudden stress.

• If repeated cyclically, this can cause fatigue. Fatigue is dangerous as a fatigued material can fail at much lower stresses than expected.

Notable cases affected

• While manufacturing a part, the tooling can stress the material, causing it to harden. This then means that the usually harder tool is less effective and could break.