Reference library · ISO material groups
ISO Material Groups Chart
In the ISO 513 system every workpiece material belongs to one of six letter-coded groups: P is steel, M is stainless steel, K is cast iron, N is non-ferrous metals, S is superalloys and titanium, H is hardened steel. Below, 26 material sub-groups across the six colour-coded categories. Each page covers hardness range, tooling guidance, and a direct link into the AI advisor for your specific cutting parameters. Guidance is drawn from standard machining references — verify insert selection on a sample part before production.
| ISO | Material class | Typical hardness | Sub-groups | What decides the tool |
|---|---|---|---|---|
| P | Steel: unalloyed, low-alloy and alloy steels, cast steel | 125–330 HB | 6 | CVD-coated carbide at Vc 200–400 m/min. Positive geometry for finishing, negative for roughing. |
| M | Stainless steel: austenitic, ferritic, martensitic, duplex, PH | 150–330 HB | 4 | Work hardening is the main challenge. Sharp positive geometry, high-pressure coolant 15–20 bar, consistent DOC. |
| K | Cast iron: grey, nodular, compacted graphite, malleable | 120–320 HB | 4 | CVD alumina coatings excel. Dry machining acceptable for grey CI. Abrasive wear is the main failure mode. |
| N | Non-ferrous: aluminium, copper, brass, bronze, plastics | 30–150 HB | 4 | Uncoated or DLC carbide for aluminium. Sharp edges, high positive rake, polished flutes prevent BUE. |
| S | Superalloys and titanium: nickel and cobalt base, Ti alloys | 200–450 HB | 4 | Most difficult ISO group. High-pressure coolant mandatory. Low Vc, consistent DOC, sharp positive geometry. |
| H | Hardened materials: hardened and chilled cast steel, hard cast iron | 45–68 HRC | 4 | CBN/PCBN required above 55 HRC. Dry machining preferred, coolant causes thermal shock. |
The letter is a machinability class, not a specification. Two materials in the same group are cut with the same family of tools and a similar strategy; they are not the same alloy and they do not share a datasheet. The colour coding (blue P, yellow M, red K, green N, orange S, grey H) is the same one printed on insert boxes by every major manufacturer, which is why the letter travels across brands even when the grade codes do not. Each of the 26 sub-groups below has its own page with hardness range and tooling guidance.
ISO P — Steels
ISO P material means steel: unalloyed, low-alloy and alloy steels plus cast steel, roughly 125 to 330 HB across six sub-groups.
CVD-coated carbide at Vc 200–400 m/min. Positive geometry for finishing, negative for roughing.
ISO M — Stainless Steel
ISO M material means stainless steel: austenitic, ferritic, martensitic, duplex and precipitation-hardening grades, four sub-groups.
Work hardening is the main challenge. Sharp positive geometry, high-pressure coolant 15–20 bar, consistent DOC.
ISO K — Cast Iron
ISO K material means cast iron: grey, nodular, compacted graphite and malleable iron, four sub-groups.
CVD alumina coatings excel. Dry machining acceptable for grey CI. Abrasive wear is the main failure mode.
ISO N — Non-Ferrous
ISO N material means non-ferrous metals: aluminium, copper, brass and bronze, plus plastics and composites, four sub-groups.
Uncoated or DLC carbide for aluminium. Sharp edges, high positive rake, polished flutes prevent BUE.
ISO S — Superalloys & Titanium
ISO S material means superalloys and titanium: nickel and cobalt base alloys and titanium alloys, four sub-groups.
Most difficult ISO group. High-pressure coolant mandatory. Low Vc, consistent DOC, sharp positive geometry.
ISO H — Hardened Steel
ISO H material means hardened materials: hardened steel, chilled cast steel and hard cast iron from about 45 to 68 HRC, four sub-groups.
CBN/PCBN required above 55 HRC. Dry machining preferred — coolant causes thermal shock.
What are the ISO material groups?
ISO 513 sorts every workpiece material into six letter-coded application groups: P = steel, M = stainless steel, K = cast iron, N = non-ferrous, S = superalloys & titanium, H = hardened steel. Each group has its own identification colour and its own tooling logic — coating, geometry, speed range and dominant wear mode all change with the letter. This reference splits the six groups into 26 sub-groups with hardness ranges.
What ISO standard group is represented by the letter P?
In ISO 513 the letter P identifies steel. It splits into 7 sub-groups: P01 Low carbon steel, 125–180 HB; P02 Medium carbon steel, 160–220 HB; P10 Alloy steel, 180–280 HB; P20 Alloy steel (heat treated), 200–300 HB; P30 Case-hardened steel, 58–62 HRC surface; P40 Free-cutting steel, 160–230 HB; P50 High-strength steel, 280–350 HB. CVD-coated carbide at Vc 200–400 m/min. Positive geometry for finishing, negative for roughing.
What ISO standard group is represented by the letter M?
In ISO 513 the letter M identifies stainless steel. It splits into 4 sub-groups: M01 Austenitic (304, 316L), 150–220 HB; M10 Duplex stainless, 240–300 HB; M20 Ferritic stainless, 160–220 HB; M30 PH stainless (17-4PH), 28–44 HRC. Work hardening is the main challenge. Sharp positive geometry, high-pressure coolant 15–20 bar, consistent DOC.
What ISO standard group is represented by the letter K?
In ISO 513 the letter K identifies cast iron. It splits into 5 sub-groups: K01 Grey cast iron (soft), 180–220 HB; K10 Grey cast iron (hard), 200–280 HB; K20 Nodular / ductile iron, 170–260 HB; K30 Malleable iron, 150–230 HB; K40 Compacted graphite iron, 160–250 HB. CVD alumina coatings excel. Dry machining acceptable for grey CI. Abrasive wear is the main failure mode.
What ISO standard group is represented by the letter N?
In ISO 513 the letter N identifies non-ferrous. It splits into 4 sub-groups: N01 Aluminium (wrought), ~65 HB; N10 Aluminium alloys (cast), 75–130 HB; N20 Copper / Brass, 80–160 HB; N30 Magnesium alloys, ~60 HB. Uncoated or DLC carbide for aluminium. Sharp edges, high positive rake, polished flutes prevent BUE.
What ISO standard group is represented by the letter S?
In ISO 513 the letter S identifies superalloys & titanium. It splits into 3 sub-groups: S01 Titanium (commercially pure), ~200 HB · 30 HRC; S10 Titanium alloys (Ti-6Al-4V), 320–380 HB; S20 Nickel superalloys (Inconel 718), 280–380 HB. Most difficult ISO group. High-pressure coolant mandatory. Low Vc, consistent DOC, sharp positive geometry.
What ISO standard group is represented by the letter H?
In ISO 513 the letter H identifies hardened steel. It splits into 3 sub-groups: H01 Hardened steel (low), 45–55 HRC; H10 Hardened steel (medium), 55–60 HRC; H20 Hardened steel (high), 60–68 HRC. CBN/PCBN required above 55 HRC. Dry machining preferred — coolant causes thermal shock.
Which standard defines the ISO material groups?
ISO 513. It classifies hard cutting materials for machining and defines the application groups P, M, K, N, S, H together with their identification colours. The letter describes the workpiece material being cut; the number after it (for example P10, K20) narrows the application from finishing towards roughing within that group.
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