glödgning

Glödgning, or annealing, is a heat-treatment process used in metallurgy to alter the properties of metals. In Swedish technical usage, glödgning corresponds to annealing and is employed to soften the material, relieve internal stresses, refine the grain structure, and improve ductility and machinability.

The general method involves heating the material to a specified temperature, holding it for a period, and cooling it under controlled conditions. During heating, the metal’s microstructure reorganizes toward a more stable phase; slow cooling prevents the formation of hard, brittle structures and promotes recrystallization. The cooling rate and atmosphere determine the final structure and properties. The process is typically conducted in furnaces with controlled temperature and, if needed, protective atmospheres to minimize oxidation.

Common variants for steel include full annealing, process annealing, and stress-relief annealing. Full annealing heats above the critical temperature and cools slowly in a furnace to room temperature to yield a soft, ductile metal. Process annealing softens work-hardened material by heating below the recrystallization temperature. Stress-relief annealing reduces residual stresses at lower temperatures. Annealing is also used for non-ferrous metals such as copper and aluminum, often to improve ductility and reduce work hardening.

Considerations include selecting appropriate temperature, soaking time, and cooling path, as well as atmosphere to avoid oxidation and decarburization. Poor control can cause excessive grain growth, reducing toughness, or loss of strength. Safety concerns involve high-temperature equipment, radiant heat, and fumes.

Applications span construction, automotive, electronics, and tooling, where annealed metals are easier to form, weld, or machine. Glödgning is related to other heat treatments such as normalizing and spheroidizing, which employ different cooling paths and microstructures.