Stress Relieving - Purpose, Process, Applications

Stress relieving (or stress relief annealing) is a steel heat-treatment that reduces internal stresses caused by welding, casting, heating, or plastic deformation. Unlike normalizing, full annealing, or recrystallization annealing, stress relieving does not affect the microstructure. Steel products in the stress-relieved condition are designated with the additional symbol +SR.

Steel Stress Relieving Process

Stress relief annealing involves heating the workpiece to a temperature below the A_C1 point (typically below 650°C), holding it at that temperature, and then cooling it slowly.

The temperature and duration of stress relief depend on the material type and the source of the internal stress. Examples:

• Casting stress in cast steel is relieved at ~650°C
• Hot work stress: 600–650°C
• Welding stress: 500–600°C
• Thermal stress: 450–500°C
• Cold work stress: 400–450°C
• Stabilizing: below 150°C
• Seasoning: at room temperature (more below)

Cold-worked steel is typically stress-relieved at lower temperatures than hot-worked steel to keep the strength introduced by the cold working.

Stress Relief Annealing of Tool Steel – Examples

Stress relieve temperature for tool steel grades:

• 1.1620 / U7A: 600–700°C
• AISI 02 / 90MnCrV8 / 1.2842: 600–680°C
• WWS1 / X30WCrV5-3 / 1.2567: 600–700°C
• 1.2631 / X50CrMoW9-1-1: 650°C
• 50NiCr13 / 1.2721: 610–650°C

No Structural Changes

Stress relieving reduces internal stresses through very small plastic deformations within the material, without significant changes to its microstructure.

Special Types of Stress Relief

• Stabilizing stress relief annealing is performed at temperatures up to 150°C. It ensures dimensional stability and partially reduces residual stresses.
• Natural stress relief (seasoning) occurs at room temperature over time. This process can take anywhere from several months to several years.