CNC Material Codes and Their International Equivalents
Search DIN EN, material number, AISI/SAE/ASTM, JIS, BS, SS, AFNOR, UNI and UNE codes in a single table. See the common trade designation, ISO machining group, MC/CMC class, nominal hardness, specific cutting force and confidence level together.
Material comparison tool
Example searches: 42CrMo4, 4140, SCM440, GG25, EN-GJL-250, 316L, Ti-6Al-4V.
| Compare | Common designation | ISO | DIN / EN | W.-Nr. | AISI / ASTM | JIS | MC / CMC | Class hardness | Detail |
|---|
How are material names used internationally?
Technical specifications and certificates most often use the modern EN/DIN designation, while older DIN or AISI names still circulate on the shop floor. For example, S235JR is widely known as “St37”, S355 as “St52”, C45 as “CK45 or 1045”, 42CrMo4 as “4140”, EN-GJL-250 as “GG25”, and EN-GJS-400-15 as “GGG40”.
This page shows both the official/modern code and the name commonly heard in the shop. A “Reference” label means the equivalent is a close match per the catalog cross-reference table; a “High” label means the designation is very widely and confidently used in industry.
What do hardness, kc1 and mc mean?
- HB: Brinell hardness value; common for soft and medium-hardness metal classes.
- HRC: Rockwell C hardness; used for hardened steel and tool steel grades.
- Rm: Tensile strength; given in MPa instead of a hardness value for the titanium rows.
- kc1: Specific cutting force starting value for a 1 mm² chip cross-section. Used to estimate machine power and cutting force.
- mc: Exponent expressing how chip thickness affects specific cutting force.
What is machinability?
Machinability describes how “cooperatively” a material behaves during cutting: how much wear it causes on the cutting edge, how the chip forms, and how much force and power it demands. It is not expressed as a single number; in practice it is established by comparing cutting tests run under the same conditions. “Good machinability” means trouble-free cutting and a reasonable tool life, which is why a low-alloy carbon steel is considered easier to machine than an austenitic stainless steel.
Three main factors determine machinability: the metallurgical/mechanical class of the material (alloying, heat treatment, hardness, forged or cast structure); the cutting-edge geometry (macro and micro); and the cutting-tool material (coated carbide, cermet, ceramic, CBN, PCD). Cutting data, surface skin, inclusions and clamping rigidity also affect the result.
Effect of alloying elements in brief: more carbon raises hardness and wear, while carbon below 0.2% causes smearing and built-up edge; sulphur (S) improves machinability (free-cutting steels); in stainless steels nitrogen (N) and molybdenum (Mo) reduce machinability.
ISO groups P, M, K, N, S and H
P covers steels, M covers stainless steels, K covers cast irons, N covers aluminum and other non-ferrous metals, S covers nickel/cobalt/titanium-base superalloys, and H covers hardened materials. Each group has its own machining character:
| Group | Materials | Chip | kc1 (N/mm²) | Watch out for |
|---|---|---|---|---|
| P | Unalloyed to high-alloy steel, cast steel, ferritic/martensitic stainless | Long, easy to control | 1400–3100 | Smearing chips at low carbon; plastic deformation as hardness rises |
| M | Austenitic and duplex stainless steel | Long, hard to break | 1800–2850 | Heat, built-up edge (BUE), work hardening, notch wear |
| K | Grey (GCI), malleable (MCI), nodular (NCI), CGI, ADI | Short | 790–1350 | SiC and sand inclusions are abrasive; NCI/CGI/ADI are harder to machine; negative inserts, thick Al₂O₃ coating |
| N | Aluminum, copper, brass | Long; easy if alloyed | 350–700 | Pure Al smears → sharp edge, high vc; Si > 12% very abrasive → PCD |
| S | Ni/Co/Fe-base superalloys, titanium | Segmented, difficult | HRSA 2400–3100; Ti 1300–1400 | High force and heat, work hardening, short tool life; ageing condition is decisive |
| H | Steel 45–65 HRC, chilled cast iron 400–600 HB | Short, well formed | 2550–4870 | Very high power; turning with CBN, milling/drilling with carbide up to ~60 HRC |
Tool selection and cutting data should never be based on the ISO letter alone. The material’s subclass, hardness, heat-treatment condition, cast/forged structure, workholding rigidity and the tool manufacturer’s current data must all be considered together.
Frequently asked questions
Is 42CrMo4 the same material as 4140?
They are generally treated as equivalents within the same quenched & tempered steel family. However, chemical tolerance, delivery condition and heat-treatment requirements should be confirmed against the certificate.
What is the modern code for GG25?
The common modern EN designation is EN-GJL-250. It is a gray cast iron grade.
What is the modern code for GGG40?
The common modern EN designation is EN-GJS-400-15. It is known as ductile or spheroidal graphite cast iron.
Is the catalog hardness the actual hardness of my part?
No. The table value is a nominal class reference used for selecting cutting data. Actual hardness is determined by measurement or the material certificate.
Source and scope: Material codes, MC/CMC classes and country equivalents were compiled from a 2015 rotating-tool catalog's “material cross-reference list” and cutting data tables. Common international designations reflect standard EN/DIN usage and general industry terminology. This content is for engineering pre-selection and educational purposes; it does not replace a final technical specification or material certificate.