AMS 2759/11
Stress Relief of Steel Parts
Stress relief of carbon, low-alloy, tool, martensitic, precipitation-hardening and austenitic corrosion-resistant steel parts after machining, forming, welding or straightening, without changing the prior heat-treated properties.
What AMS 2759/11 specifies
AMS 2759/11 gives the temperatures, times and cooling for stress relieving steel parts between or after manufacturing operations without altering the strength set by earlier hardening, tempering or ageing. For hardened and tempered carbon and low-alloy steels the stress-relief temperature is held below the last tempering temperature by the margin in the table so hardness is not reduced; annealed or normalized material is stress relieved around 1000–1250 °F (540–675 °C); precipitation-hardening stainless is treated below its ageing temperature; austenitic grades receive either a low stress relief below the 800–1500 °F (425–815 °C) sensitization range or a full anneal; tool steels follow their tempering temperature. Time at temperature scales with section thickness, heating and cooling are slow enough to avoid new thermal gradients (furnace cooling for heavy sections), and atmosphere control is required when the surface will not be machined afterwards. Hardness is checked afterwards to confirm nothing was lost.
Tests and the drawing call-out
Tests the document imposes
- Hardness per ASTM E18 or ASTM E10 before and after stress relief to confirm no change
- Furnace chart review: heating rate, time at temperature, cooling rate; pyrometry per AMS 2750
- Dimensional inspection after stress relief on distortion-critical parts
- Surface condition (scale, discoloration) when processed in air
How to cite it
Drawing call-out
STRESS RELIEVE PER AMS 2759/11 AFTER ROUGH MACHINING, <TEMPERATURE> °F MAX (BELOW TEMPER), <HOURS> H; HARDNESS <RANGE> HRC TO REMAINAngle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to AMS 2759/11
| Treatment | Role | Cost |
|---|---|---|
Stress relief reduces residual stress from welding, machining, forming, casting, or additive manufacture without intentionally changing the bulk microstructure. | Governing | $ |
AMS 2759/11 — frequently asked
Will stress relief lower my hardness?
Not if the temperature stays below the last tempering temperature by the margin the sheet requires; the heat treater reads the temper from the certification and sets the stress relief accordingly. If the temper temperature is unknown, the part must be hardness tested before and after and a low, conservative temperature used.
How long should the part hold?
Typically 1 h minimum plus about 1 h per inch (25 mm) of section, long enough for creep to relax the peak stresses; holding longer gives little further relief, going hotter gives much more. Heavy weldments are furnace cooled to about 600 °F (315 °C) before air cooling so new thermal stress is not built in.
When should stress relief be scheduled?
After rough machining and before finish machining on parts that remove a lot of material or must hold tolerances tighter than about ±0.05 mm; after welding; after cold straightening; and, for high-strength steel, after any straightening as AMS 2759/2 requires. Doing it after finish machining moves the part.
Can austenitic stainless be stress relieved?
Yes, two ways: a low treatment near 750–800 °F (400–425 °C) that relieves part of the stress while staying out of the 800–1500 °F sensitization range, or a full anneal above 1850 °F (1010 °C) that relieves everything but scales and distorts the part. Unstabilized 304 and 316 must not be held in the intermediate range.
AMS 2759/11 is copyrighted by SAE International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗