What do P, M, K, N, S and H stand for?

P is steel, including ferritic and martensitic stainless steel; M is austenitic and duplex stainless steel; K is cast iron; N is non-ferrous metals such as aluminium and copper; S is heat-resistant superalloys and titanium; H is hardened steel and hardened or chilled cast iron.

What does the number in P20 or M30 mean?

P20 or M30 is an ISO 513 application group, not a grade name. It places a grade's area of use on a scale inside the group: lower numbers favour wear resistance and higher speeds, higher numbers favour toughness, higher feeds and interrupted cuts. Most grades cover a band, such as P15 to P35.

Which ISO group is stainless steel in?

ISO 513 places austenitic and duplex stainless steels in group M, and ferritic and martensitic stainless steels in group P. Hardened martensitic stainless steel may need tooling recommended for hardened materials.

Can one insert grade cover several groups?

Yes. Many grades are listed for two or three groups, for example steel and stainless steel. The grade's best range is usually in one group, so tell the supplier which material you cut most.

Guide

ISO material groups P, M, K, N, S and H, and what they mean for insert grades

Insert grades are chosen by the material you cut. ISO 513 sorts workpiece materials into six groups, each with a letter and a colour that appear on insert boxes and in catalogues. Knowing the group of your material is the first step to the right grade and chipbreaker.

The six groups

Group	Colour	Materials	How they machine
P	Blue	Steel and cast steel, unalloyed to high-alloyed, including ferritic and martensitic stainless steel	The largest group. Long chips; chip control comes from the chipbreaker and the feed.
M	Yellow	Austenitic and austenitic-ferritic (duplex) stainless steel, including cast grades	High cutting forces, built-up edge, heat and work-hardened surfaces are common.
K	Red	Cast iron: grey, nodular (ductile) and compacted graphite iron	Short chips; abrasive, so wear resistance matters.
N	Green	Non-ferrous metals: aluminium, copper, brass and similar	Mostly soft and prone to sticking, so sharp, positive edges suit them; high-silicon aluminium is abrasive.
S	Brown	Heat-resistant superalloys (nickel, cobalt and iron based) and titanium	Sticky, work-hardening and hot in the cut; usually low cutting speeds.
H	Grey	Hardened steel (in practice about 45–65 HRC) and hardened or chilled cast iron	Very hard; high cutting forces and heat at the edge.

The colours are the ones ISO 513 assigns. They are printed on insert boxes and in catalogues, so a buyer can see at a glance which materials a grade is meant for.

Reading application groups such as P20 or M30

P20 or M30 is not a grade name. It is an ISO 513 application group, which places a grade’s area of use on a scale inside the material group: P01 to P50 for steel, M01 to M40 and K01 to K40, and N01 to N30, S01 to S30 and H01 to H30. A higher number means a tougher grade for higher feeds and less stable conditions; a lower number means a harder, more wear-resistant grade for higher speeds.

Taking group P as an example, roughly:

Low numbers (P01–P15): finishing, high cutting speeds, stable conditions, light feeds.
Middle numbers (P20–P30): general machining.
High numbers (P35–P50): roughing, interrupted cuts, lower speeds and less stable conditions.

A real grade usually covers a band rather than one number, for example P15–P35, and many grades are listed for two or three groups. Each maker uses its own grade names. Two grades listed for the same band are meant for broadly similar work, but they are not equivalent: substrate, coating and edge preparation still differ.

Where stainless steel sits

ISO 513 puts austenitic stainless steels such as 304 and 316, and duplex grades such as 2205, in group M: they work-harden, form built-up edge and are hard on inserts. Ferritic and martensitic stainless steels such as 430 and 410 are in group P; annealed, they machine much like low-alloyed steel. Hardened martensitic stainless steel may need tooling chosen for its hardness. See choosing carbide inserts for stainless steel.

What to tell a supplier

To get the right grade and chipbreaker, give the material, not just the group:

the material standard or name, for example 42CrMo4, 304, GG25 or 6061;
its hardness, if it is heat-treated;
the operation: roughing, finishing, facing, profiling; continuous or interrupted cut;
the insert designation you use now, if any, and what goes wrong with it.

We match grade and coating to these details with each quotation. You can look up an insert code first with the insert designation decoder, or browse the ISO sizes we make.

Questions

What do P, M, K, N, S and H stand for?: P is steel, including ferritic and martensitic stainless steel; M is austenitic and duplex stainless steel; K is cast iron; N is non-ferrous metals such as aluminium and copper; S is heat-resistant superalloys and titanium; H is hardened steel and hardened or chilled cast iron.
What does the number in P20 or M30 mean?: P20 or M30 is an ISO 513 application group, not a grade name. It places a grade's area of use on a scale inside the group: lower numbers favour wear resistance and higher speeds, higher numbers favour toughness, higher feeds and interrupted cuts. Most grades cover a band, such as P15 to P35.
Which ISO group is stainless steel in?: ISO 513 places austenitic and duplex stainless steels in group M, and ferritic and martensitic stainless steels in group P. Hardened martensitic stainless steel may need tooling recommended for hardened materials.
Can one insert grade cover several groups?: Yes. Many grades are listed for two or three groups, for example steel and stainless steel. The grade's best range is usually in one group, so tell the supplier which material you cut most.

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