AH Age hardening / precipitation hardening
Age hardening / precipitation hardening · Tratamiento térmico · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “17-4PH H1150 · 34-38 HRC” states a age hardening / precipitation hardening requirement.
What controls
Holding at an intermediate temperature, after solution treatment, so that the phases that strengthen the alloy precipitate in a controlled way. It is the treatment that gives the final properties to precipitation-hardening stainless steels, high-strength aluminum alloys and some nickel alloys. The result depends heavily on the combination of temperature and time: the same alloy can end up harder and less tough, or the other way round, depending on the aging condition called out on the drawing.
How to verify
Hardness tester on the specified scale to confirm the condition achieved, with several indentations, and a heat treatment certificate stating temperature, time and designated condition. When the drawing requires mechanical properties, they are demonstrated by tests on specimens treated in the same batch. On close-tolerance parts, it is worth measuring critical dimensions before and after to quantify the dimensional change.
Common mistakes when interpreting it
- Replacing the aging condition designated on the drawing with another “equivalent” one: they are not equivalent, and the properties change.
- Aging without proper prior solution treatment and expecting catalog hardness.
- Machining to final size before aging without allowing for the dimensional change caused by the treatment.
How to get it in the workshop / if it comes out of tolerance
The practical rule is to machine in the solution-treated condition and age at the end, because after aging the part is noticeably harder. Aging also causes a small dimensional change, which on close-fit parts has to be allowed for with stock or with a follow-up inspection. Never improvise the aging condition: the drawing specifies a particular one, and changing it changes the properties.
Hardness below requirement: inadequate solution treatment before aging, or insufficient temperature or time; in many cases it cannot be fixed by re-aging without solution treating again. Hardness above requirement with poor toughness: aging condition too low for what the application needs. Dimensional changes that take the part out of tolerance: anticipate the effect and leave material for a final finishing pass.
Related symbols
Other symbols in Heat treatment
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