Surface zone whose chemistry or structure has been changed to make it harder than the interior, by carburizing, carbonitriding, nitriding, induction or flame hardening. The case carries wear and contact stress while the core supplies toughness. A carburized gear typically has a 58 to 62 HRC case over a core of 30 to 45 HRC, and the case depth is the controlling dimension.
Case is right on at 60 HRC but the core's only 25, so check what steel they actually sent us.
A case is part of the steel itself, not a coating, so it cannot flake off the way plating or paint can.
Also heard as
- hardened case
Related terms
Case depth
Thickness of a hardened surface layer, measured from the surface to a specified hardness or structure.
Carburizing
Diffusing carbon into the surface of low-carbon steel at high heat, then quenching for a hard case.
Induction hardening
Heating only the surface of a steel part with an alternating magnetic field, then quenching for a hard case.
Through hardening
Hardening a steel part so martensite forms across the whole section, not just at the surface.