What is not a purpose of annealing heat treatment?

The purpose of annealing heat treatment is primarily focused on enhancing the material's properties through controlled heating and cooling processes. Annealing typically aims to alter the microstructure of a material to alleviate internal stresses, refine grain structure, and improve ductility and toughness, among other benefits.

When considering the function of hardening as achieved through processes like quenching, this is distinctly different from the goals of annealing. The letting down of the material’s hardness via annealing is intentional, allowing for easier workability and forming. The process may soften the material rather than significantly harden it. Therefore, the objective of annealing is not to harden the material significantly but rather to produce a more favorable microstructure and mechanical attributes suited for further processing or use.

The other choices relate directly to annealing's purposes: facilitating cold working by softening the metal, producing a desired microstructure through controlled heat treatment, and achieving desired mechanical properties by tailoring the material's characteristics to meet specific requirements. Thus, the concept of hardening contradicts the fundamental aims of annealing.