anneal

Annealing is a heat treatment used to alter a material’s properties by heating it to a defined temperature, holding for a period, and cooling at a controlled rate. The aim is to soften hard materials, relieve internal stresses, improve ductility, and refine the microstructure to enhance machinability and formability. The exact temperatures and times depend on the material and the desired outcome.

In metals, annealing typically reduces hardness and increases ductility. Full annealing of steel involves heating above the critical temperature and then cooling slowly in a furnace to produce a soft, uniform structure. Process annealing softens work-hardened metals by heating below the full annealing range. Stress-relief annealing targets residual stresses with limited change to microstructure. Overheating can cause grain growth, while rapid cooling can reintroduce hardness or introduce new stresses.

In glass, annealing relieves thermal stresses induced during forming. Glass is heated to a temperature near its annealing point, held briefly, and cooled slowly to room temperature. This minimizes warping and cracking. In polymers, annealing can increase crystallinity and dimensional stability by heating to a temperature below melting and allowing molecular chains to reorganize before cooling.

In electronics and optics, annealing is used to repair crystal damage and activate dopants in semiconductor materials. Overall, annealing is chosen when increased ductility or stress relief is required, and it contrasts with tempering, which is used to increase toughness after hardening.