Sources and scope for this page: ISO 513:2012, covering the definition of material group (p/m/k/n/s/h). No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. How sources, methods and updates are recorded.
Definition
The six groups let insert grades be selected by behaviour rather than by individual alloy: P steel, M stainless, K cast iron, N non-ferrous, S superalloys and titanium, H hardened materials.
Each group is subdivided by hardness and by whether the material is prone to work hardening or abrasion. The system exists because two alloys with the same hardness can machine very differently — and because it lets a tooling catalogue be organised by a handful of groups instead of thousands of grades.
Common misuse
Selecting an insert grade on hardness alone. Group membership matters as much, particularly for stainless and superalloys.