Properties
Steels for heat treatment - Properties and selection guide

According to NF EN 10052, it corresponds to the following definition.

These ideal conditions are such as to obtain a totally martensitic structure (i.e. without ferrite, pearlite, bainite or residual austenite).

In practice, this hardening capacity depends solely on the carbon content of the steel and, if nitriding or carbonitriding is used, on its nitrogen content. In the absence of any deliberate addition of nitrogen, it is quantitatively defined by the 100% martensite curve in the as-quenched condition shown in figure