Depth of a case, measured on a sectioned sample by microhardness traverse, by etched appearance or by chemical analysis. Drawings call out either effective case depth, to a set hardness, or total case depth, to where hardness or carbon matches the core. Typical carburized gear cases are 0.5 to 1.5 mm, nitrided cases 0.1 to 0.6 mm and induction cases 1 to 6 mm.
Customer wants case depth checked at the pitch line, not the tip, so section it through the tooth.
Always ask whether a callout means effective or total case; on the same part the two numbers can differ by a third or more.
Also heard as
- total case depth
- TCD
Do not mix it up with
- Effective case depth: Total case depth runs to where the case ends entirely, while effective case depth stops at the 50 HRC point, so it is always the smaller number.
Related terms
Effective case depth
Depth below the surface where hardness falls to a set value, usually 50 HRC, on a case-hardened part.
Microhardness
Hardness measured with very small loads under a microscope, used for thin cases and individual phases.
Case
The hardened outer layer of a case-hardened part, as opposed to its softer, tougher core.
Carburizing
Diffusing carbon into the surface of low-carbon steel at high heat, then quenching for a hard case.