Werkharden

In Dutch metallurgy, werkharden refers to the strengthening of a metal by plastic deformation at ambient temperature. In English-language literature, the same phenomenon is called work hardening or strain hardening. The process increases yield strength and hardness while typically reducing ductility, without changing the metal’s chemical composition.

Mechanism and methods: Werkharden occurs when dislocations multiply and entangle, making further glide more difficult. It is most pronounced during cold work—deformations performed below the material's recrystallization temperature—through operations such as rolling, drawing, bending, and hammering. If the material is subsequently heated above the recrystallization temperature, recovery and recrystallization can reduce or erase the hardening.

Impacts and uses: The resulting higher strength can improve stiffness and load-bearing capacity, as in sheet metal, wires, springs, or fasteners, without alloying. However, reduced ductility and the buildup of residual stresses can be drawbacks. To restore ductility, heat treatments like annealing are used to rearrange or eliminate dislocations and form new grains.

Measurement and context: Quantifying werkharden typically involves hardness testing (Rockwell, Vickers) and tensile testing to determine yield strength and elongation. The degree of hardening depends on material system, amount of deformation, and temperature history.