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ISO Cutting Tool Material Groups (P, M, K, N, S, H) Reference

Insert and end mill catalogs sort every grade by six colour coded ISO groups. Knowing which group your workpiece falls in is the first step to choosing a grade, geometry and starting speed. This reference lists common materials with their group.

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Workpiece material	Example designation	ISO group	Catalog colour	Machining note
Low carbon steel	AISI 1018, S235	P	Blue	Gummy, long chips. Use chip breaker geometry.
Free machining steel	AISI 12L14, 11SMn30	P	Blue	Good chip control, high speeds possible.
Medium carbon steel	AISI 1045, C45	P	Blue	General purpose group for coated carbide.
Alloy steel (soft or annealed)	AISI 4140, 42CrMo4	P	Blue	Reduce speed as hardness rises.
Alloy steel (pre-hardened)	4140 at 28-34 HRC	P	Blue	Strong edge and heat resistant coating.
Austenitic stainless steel	AISI 304, 316	M	Yellow	Work hardens. Keep feed up, avoid rubbing.
Precipitation hardening stainless	17-4 PH	M	Yellow	Condition dependent, tougher when aged.
Duplex stainless steel	2205 (UNS S32205)	M	Yellow	High strength, high cutting forces.
Gray cast iron	ASTM A48 Class 30	K	Red	Short chips, abrasive. Often run dry.
Ductile (nodular) cast iron	ASTM A536 65-45-12	K	Red	Tougher than gray iron, coated carbide.
Aluminum alloy (wrought)	6061-T6, 7075-T6	N	Green	Sharp uncoated or PCD edges, high speeds.
Aluminum alloy (high silicon cast)	A390, A356	N	Green	Abrasive silicon, PCD tools extend life.
Copper alloys	C110 copper, C360 brass	N	Green	Brass is easy, pure copper is gummy.
Plastics	Delrin (POM), nylon, PEEK	N	Green	Sharp edges, low heat, avoid melting.
Titanium alloy	Ti-6Al-4V (Grade 5)	S	Orange	Low speed, high coolant, sharp edges.
Nickel based superalloy	Inconel 718, Inconel 625	S	Orange	Work hardens, ceramics at high speed.
Cobalt based alloy	Stellite, Haynes 25	S	Orange	Very abrasive and tough.
Hardened steel	AISI 4340 at 50 HRC	H	Grey	CBN or fine grain carbide.
Hardened tool steel	AISI D2 at 58-62 HRC	H	Grey	CBN inserts, rigid setup, light cuts.

Group assignments follow the ISO 513 style grouping used by major insert catalogs. Individual manufacturers subdivide each group (for example P10 to P50) and may place borderline alloys differently, so confirm in the catalog you buy from.

Material and tooling rules in your ERP

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How to use the reference

Search for your workpiece material or alloy designation, note the ISO group letter, then open the tooling catalog at that group. Grades are labelled with the group letter and a number, where lower numbers favour wear resistance and higher numbers favour toughness. Export the table if you want a reference page in your tooling standard.

What the six groups mean

P is steel, M is stainless steel, K is cast iron, N is non-ferrous metals and plastics, S is heat resistant superalloys and titanium, and H is hardened steel. The colour code is blue, yellow, red, green, orange and grey respectively. The groups reflect how chips form and what tool wear mechanism dominates, not just hardness.

P blue: steel
M yellow: stainless
K red: cast iron
N green: non-ferrous and plastics
S orange: titanium and superalloys
H grey: hardened steel

Using group data in a tooling database

Store the ISO group on every material record in your ERP or tool crib system. That lets a program or a planner filter approved insert grades by material instead of keeping a separate spreadsheet. It also helps when a customer changes the material on a drawing, because the affected tools and cutting data are easy to find.

Common mistakes

Do not assume all stainless steels behave alike, since free machining 303 is easier than 316, and do not use a steel grade on titanium because heat concentrates at the edge. Another common error is treating hardness as the only factor: pre-hardened 4140 at 30 HRC is still a P material, while 50 HRC steel moves to H.

Frequently Asked Questions

What does P M K N S H stand for?

They are the six ISO material groups used by cutting tool makers: P for steel, M for stainless steel, K for cast iron, N for non-ferrous metals, S for heat resistant alloys and titanium, and H for hardened steel.

Which group is aluminum?

Aluminum alloys are in the N group, shown in green. High silicon cast aluminum is abrasive and often needs PCD tooling, while wrought alloys like 6061 and 7075 are machined with sharp, polished carbide.

Which group is Inconel and titanium?

Both belong to the S group, shown in orange. They are machined at much lower cutting speeds than steel because of heat and work hardening, and need rigid setups and plenty of coolant.

Can one insert cut several groups?

Some multi-purpose grades list more than one group, for example P and M, but performance is a compromise. For production work, pick the grade that is rated for your group and operation type.

If material and tooling rules are scattered across spreadsheets, we can show how an ERP-connected assistant could answer which tool to use for a given part and material.

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