A Annealing
Annealing · Tratamiento térmico · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Isothermal anneal before rough machining” states a annealing requirement.
What controls
Heating followed by slow, controlled cooling, normally inside the furnace, to leave the material in its softest and most stable condition: it reduces hardness, homogenizes the structure and removes a large part of the internal stresses. It is a preparatory treatment, not a final-result one: it is done to allow good machining, to allow forming, or to erase the thermal history of a worked or welded material. If the drawing calls it out, what can be verified is usually the resulting maximum hardness, not the cycle.
How to verify
Hardness tester to check that hardness dropped to the expected level, which is the practical confirmation that the anneal was done. For demanding materials and parts, metallography on a test coupon to verify the structure obtained, plus the heat treatment certificate with the temperature-time curve. Freedom from stress is not measured directly on the shop floor: it is checked indirectly by how little the part moves during machining.
Common mistakes when interpreting it
- Confusing annealing with stress relief: annealing changes hardness and structure, stress relief aims not to.
- Expecting service properties from an annealed part: it is the softest condition, intended for manufacturing, not for service.
- Finishing to final dimensions before an anneal, which leaves the part soft and possibly with surface decarburization.
How to get it in the workshop / if it comes out of tolerance
An annealed part machines better and moves less, but in soft steels it also smears onto the cutting edge more: lower the speed and use sharp geometries. After annealing, the material is at its minimum hardness, so do not expect wear resistance from it. If the part is to be hardened afterward, annealing is an intermediate stage and final dimensions are reached at the end of the complete cycle.
Hardness still high after annealing: cooling too fast or temperature too low; the cycle must be repeated. If the part keeps moving during machining, the anneal did not remove the stresses or they are being generated by the machining itself: split the roughing and leave light finishing passes. Surface decarburization after annealing in an unprotected atmosphere: leave enough stock to remove it.
Related symbols
Other symbols in Heat treatment
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