Stress Relieving & Normalising: Benefits & Materials

Stress Relieving
Stress relieving reduces internal stresses in ferrous and non-ferrous alloys caused by manufacturing processes like machining, welding, or cold rolling. Without it, materials may distort during further processing or suffer from issues like stress corrosion cracking. It does not significantly alter material properties and is performed at relatively low temperatures.

  • Carbon/Alloy Steel Stress Relieving:
    • 150–200°C: Relieves peak stresses without reducing hardness (e.g., case-hardened components).
    • 600–680°C: Achieves near-complete stress relief (e.g., post-welding or machining).
  • Non-Ferrous Alloys: Performed at temperatures tailored to the alloy type and condition, below ageing temperatures for age-hardened alloys.
  • Austenitic Stainless Steels: Treated below 480°C or above 900°C to avoid reducing corrosion resistance.

Normalising
Normalising improves material consistency, softens, hardens, or stress relieves depending on the initial condition. It refines non-uniform structures from casting, forging, or rolling to enhance machinability, formability, and mechanical properties.

  • Performed at 830–950°C, followed by air cooling.
  • Used for steels requiring dimensional stability after shaping or preparation for hardening.
  • Not suitable for stainless steels or steels that harden significantly during air cooling.

Benefits of Stress Relieving and Normalising

  • Enhance machinability and formability.
  • Prevent distortion or cracking in service.
  • Prepare materials for subsequent hardening or carburising with minimal distortion.
  • Improve resistance to corrosive environments.

Applications and Limitations

Applicable Materials:

  • Stress relieving: All commercial alloys.
  • Normalising: Limited to suitable engineering steels.

Limitations:

  • Final stress-relief treatments must preserve mechanical properties.
  • Some stainless steels require rapid cooling to prevent stress reintroduction.
  • Large or complex parts may require custom supports to avoid distortion during high-temperature treatments.

Potential Issues:

  • Air treatments may cause scaling or discoloration, requiring post-treatment cleaning.
  • Protective atmospheres or media may be needed for certain applications.
  • Thin or heavy components risk sagging or distortion at high temperatures.

Specification Guidelines

Provide the following details to your heat treater:

  1. Process Requirements: Stress relief, normalising, or annealing; indicate if bright treatment is necessary.
  2. Material Details: Type, grade, standards, and any prior treatments.
  3. Mechanical Properties: Hardness range or tensile strength from relevant standards.
  4. Testing Needs: Specify hardness, tensile, or sample locations.
  5. Certifications: List required reports or data.
  6. Additional Services: Straightening, cleaning, or non-destructive testing.

By providing precise specifications, you ensure effective heat treatment tailored to your component’s requirements.