Stress Relief vs. Heat Treat

Welcome to the first installment of common misconceptions about spring products.  Through the years I have come across many people that use these terms interchangeably, and that is not good from a technical standpoint.  Let me explain.

Stress Relief:

Stress relief is a common practice in the spring industry to relieve the stress from pre-tempered materials.  A time and temperature formula for the different types of materials will relieve the internal buildup of bending and forming or coiling of the material.  Stress relief is something that is not necessarily called out on drawings, but it is common practice in the industry.  If you can imagine a coil spring’s outer diameter stretches, and the inner diameter will compress.  Heat equalizes that stress.  Also, in coil springs the heat applied will increase or decrease (open or close) the outer diameter.

Here is a short list of pre-tempered common spring materials.

Material OD (open/closes) Temp (F) Time
Music Wire Closes 500° F 30 Min
Oil Tempered Closes 500° F- 600° F 30 Min
Hard Drawn Closes 550° F 20 Min
302 Stainless Opens 600° F- 650° F 30 Min
316 Stainless Does not move 600° F 1 Hour
17-7 Stainless Opens a Little 900° F 1 Hour
Chrome Silicon Closes 800° F 30 Min
Chrome Vanadium Closes 800° F 30 Min
Beryllium Copper Closes 600° F 30 Min – 2 Hours
Valve Oil Tempered Closes 600° F Min until blue on ends

 

Don’t let this chart Stress you out!  Let the Apex Spring experts determine the best material for your applications, and we will figure out the best solution for material selection and stress relief.

The next installment will be on Heat Treatment of Annealed materials.  Thanks for reading and I look forward to talking to you again.

Tom Little, Sales and Engineering Manager

Apex Spring & Stamping

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