Incomplete hardening caused by cooling slower than the steel's critical rate, from weak agitation, hot or contaminated quenchant, a long transfer or an overpacked basket. The surface or core contains non-martensitic products, hardness reads low and scattered, and tempering cannot fix it. The cure is to reharden, usually after normalizing.
Mount shows fine pearlite at the tooth root, that's a slack quench, the basket was packed way too tight.
Also heard as
- slack-quenched
Related terms
Pearlite
A layered mix of ferrite and cementite that forms when austenite cools slowly through the eutectoid range.
Quench severity
How fast a quenchant pulls heat out of steel, usually rated by the Grossmann H value.
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.