Stress relief cycle for a steel weldment
Most of a stress-relief cycle is the controlled cool, which is why the process costs two weeks of schedule rather than much money. Enter the section thickness and get the cycle — and a drawing note that leaves a shop nowhere to be vague.
Rates are controlled only above 300 °C — below that the furnace can move freely. Cooling is controlled down to 300 °C, then still air.
Total cycle, charge to cold
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- Heating rate above 300 °C
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- Time to soak temperature
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- Soak time at temperature
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- Cooling rate to 300 °C
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- Furnace cool time
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- Machining allowance to leave
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The drawing note
Copy this onto the drawing. A vague instruction gets vague compliance.
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How this is calculated
Heating and cooling rates follow AWS D1.1: above 300 °C the heating rate shall not exceed 220 °C/h divided by the maximum thickness in inches, need not be less than 56 °C/h, and need not exceed 220 °C/h. Cooling uses 280 °C/h on the same basis, down to 300 °C, after which the part comes out to still air.
Soak time is the widely used one hour per 25 mm of maximum section. The AWS table permits a 15-minute floor on thin material; the two-hour floor is what we normally specify on machine frames, because the cost of the extra hour is trivial against the cost of a base that relaxes in service.
The choice between thermal treatment, vibratory treatment and natural aging — and where the cycle sits relative to rough and finish machining — is set out instress relieving welded machine bases. Relieving after finish machining destroys the geometry you just paid for.
Cite or link this page
Free to quote, reference or link with attribution. The calculation method is stated above so it can be checked rather than taken on trust.