Stress Annealing of Cold Drawn Steel Profile?

Stress Relief Annealing

Stress relief annealing is a heat treatment process used to reduce residual stresses in a material, typically steel. The process involves heating the steel component to a temperature below its critical transformation point, holding it for a specific duration (soaking), and then cooling it slowly in a controlled manner.

1.Principle of Operation

The principle behind stress relief annealing is based on atomic mobility. At elevated temperatures, the atoms within the metal’s crystal lattice gain enough energy to move more freely. This increased mobility allows the locked-in elastic strains, which manifest as residual stresses, to be relieved through plastic deformation at a microscopic level. The result is a more stable, stress-relieved microstructure. 

2.Typical Process Parameters

A common stress relief annealing process for cold drawn profile involves heating the material to a temperature range of 500–650°C (930–1200°F). This sub-critical temperature is high enough to activate stress relief but low enough to prevent significant changes in the material’s microstructure, thereby preserving its original strength and hardness. 

3.Key Process Stages

Heating: The component is heated uniformly to the target temperature. The heating rate must be carefully controlled; heating too quickly can create thermal gradients, leading to new, unwanted stresses.

Soaking: Once the target temperature is reached, the component is held for a predetermined time. This “soak” is critical as it allows the temperature to equalize throughout the material and provides sufficient time for the atoms to move and stresses to dissipate.

Cooling: After the soak period, the component is cooled slowly to room temperature. This controlled cooling (often furnace cooling) is essential to prevent the reintroduction of thermal stresses that would occur from a rapid, uneven cool-down.