METAL STRESS RELIEVING: An Essential Process for Optimizing Part Performance

Stress relieving is a heat treatment technique commonly employed across various industries. This umbrella term encompasses a wide range of processes but at its core, aims to address the internal stresses present in metal parts.

Understanding the Basics:

Nature of the Process:

  • Nature of the Process: Metal stress relieving typically involves heating a part to a temperature where its yield strength drops significantly. At this point, internal stresses have the freedom to alleviate.
  • Temperature Significance: Optimal results are achieved when parts are exposed to higher temperatures for longer durations. This ensures lower internal stresses. Yet, these temperatures must always be below the threshold at which the metal’s phase changes, especially in steel.
  • Diverse Material Treatment: This process caters to a plethora of materials from plastics, steel, to non-ferrous metals like aluminum and copper alloys. Non-ferrous materials require relatively lower temperatures, such as 200°F for plastics and 900°F for copper alloys.
  • Steel and Iron Treatment: When focusing on steel and iron, typical stress relieving temperatures span from 1000°F to 1300°F. The treatment is always conducted below the temperature range where the austenite phase starts to appear. For minimal internal stresses, temperatures near 1300°F are optimal, a process known as sub-critical annealing due to its proximity to the austenite formation point.
  • Surface Considerations: Using open fire furnaces for metal stress relieving can lead to surface oxidation, ranging from mere discoloration at lower temperatures to a fine scale at sub-critical temperatures. If a pristine surface finish is desired, oxidation can be prevented by employing a nitrogen atmosphere or opting for vacuum stress relieving. These processes’ costs differ significantly, making early communication crucial before settling on industrial heat-treating services.

Recommendations and Key Points from ThermTech:

  • Minimal Distortion: Stress relieving typically causes little to no distortion. However, long slender components or heavily cold-worked plates may require special attention.
  • Post-Process Operations: Operations like shot blasting after stress relieving introduce compressive stresses on the material surface, potentially causing distortion.
  • Material Specific Considerations: Cast materials with low ductility or designs incorporating stress risers can have heightened cracking risks during the heating phase of stress relief. Such materials may demand a slower heating rate to the target temperature.

In essence, stress relieving, whether applied to steel, aluminum, or any other material, provides essential benefits. These range from reduced internal stresses, improved mechanical properties, enhanced surface finishes, and prolonged service life. By understanding the nuances of this process and tailoring it to specific part requirements, industries can ensure optimized performance and longevity of their components.

ThermTech—Experts in Austempering Stampings, Machined Parts, and Investment Castings

ThermTech, Inc. offers both small and large batch capabilities for austempering steel and iron investment castings. Between our neutral salt bath furnaces and our larger austempering furnaces, we have the capabilities to austemper a wide variety of stamping, machined components, and investment castings. We have run austempering on alloys from 1060 through 4340 to ductile iron machined parts.

Our dedicated team works with you to ensure we meet your specifications. Count on our decades of experience with hardening, tempering, surface heat treatments, vacuum treatments, and annealing. To learn more about our services, please contact us today.

Learn more about austempering and how ThermTech can serve you by watching these videos.

Request a free quote online or call us at 800-752-6917. You can also contact us online for all your austempering and heat treating needs.

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ThermTech’s quality policy is ZERO DEFECTS for all customer products and in all quality management system activities. Through our efforts to continually improve the quality of the work we offer, we’ve been recognized as being able to meet the rigorous quality standards required by several of our major customers. ThermTech is certified for ISO 9001 and AS9100 in both Metal Heat Treat and Metal Finishing.