Definition
A property of steel that describes the depth and uniformity to which it can be hardened by heat treatment. A steel with high hardenability will harden deeper into the material when quenched, while one with low hardenability will harden only near the surface.
Plain English
How deeply and evenly a piece of steel will get hard when it's heated and then cooled quickly. Some steels harden all the way through; others only harden on the outside.
Context Anchor
Seen in aircraft maintenance and materials discussions for heat-treated steel parts such as bolts, shafts, gears, and other load-carrying components.
Derivation
From 'harden' plus '-ability,' meaning the capacity to be hardened. The word describes a steel's potential to accept hardening, not how hard it already is.
Why Pilots Care
Aircraft parts must be made from steels chosen for the right hardenability. A part that needs to be tough all the way through (like a crankshaft) requires high-hardenability steel; getting this wrong leads to part failure.
Intuition Check
Do not read hardenability as the same thing as hardness. Hardness is how hard the metal is now; hardenability is how well it can be hardened during treatment.
Example Sentence 1
The mechanic selected a steel with high hardenability so the heat-treated bolt would be strong throughout, not just on the surface.
Example Sentence 2
Low hardenability in the selected alloy meant only the outer layer became hard while the core remained softer than required.