To unintentionally soften a previously hardened and tempered metal component by heating it beyond its original tempering temperature. This usually happens during subsequent manufacturing steps like welding, aggressive grinding, or operating the part in a high-heat environment. The excessive heat over-tempers the martensite, causing a permanent loss of strength and hardness that can only be fixed by completely re-heat treating the part.
Be careful with the torch near that bracket, or you'll untemper the spring and it will bend under load.
Untempering is a common error in post-heat treat machining. A dull grinding wheel can easily generate enough localized heat to drop the surface hardness well below specifications.
Also heard as
- over-temper
Related terms
Grinding burn
Heat damage to a hardened surface from abusive grinding, which softens it or creates brittle rehardened spots.
Soft spot
A small area on a hardened surface that reads lower than the rest, usually from uneven quenching.
Rehard
To harden a part again after it misses hardness, usually after normalizing or annealing it first.