Heat treatment is a process in which the part looks unchanged from the outside while its inside has changed completely. So the question "was the treatment done correctly?" can only be answered with tests and records. In aerospace, standards such as the AMS 2759 series for steels and AMS 2770 / 2771 for aluminum define these checks.
What is checked?
- Furnace record: Do temperature, time and cooling match the specification? Are the quench delay and quenchant temperature recorded?
- Hardness: The fastest and most common check. The measurement location, the method (HRC, HB, HV) and, if a conversion was made, which table was used must all be recorded.
- Tensile test: Yield strength, tensile strength and elongation, on a specimen from the same lot that went through the same treatment as the part.
- Microstructure: Has the expected structure formed, and is there carbon loss (decarburization) at the surface?
- Conductivity: Used on aluminum together with hardness to verify the treatment.
Related reading: What is a TUS? · What is a SAT? · AMS2759 explained
Common mistakes
- Mixing hardness and strength values in different units
- The test specimen not being in the same furnace load as the part
- Not linking the furnace record to the test report
- Keeping the microstructure image as a screenshot
- The furnace's TUS/SAT interval having expired (our AMS 2750 article)
Which of these is in your records?
Most of these mistakes slip past when records are read one by one by eye, and auditors look for them first. The real question is which one sits in your own records. Upload your test results to NTB SpecPro and quickly see which points may carry risk, the likely reason and a suggestion.
Quick evaluation
The NTB SpecPro heat treat module compares your hardness and tensile results with the relevant AMS standard according to the material and treatment condition. It reads the furnace chart from a photo, reviews the microstructure image and gives suggestions, and prepares the report. Final evaluation stays with the authorized heat treatment personnel.
Prepared by NTB SpecPro process quality engineering; reviewed by an engineer holding the International Welding Engineer (IWE) qualification. Questions: info@ntbspecpro.com
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