There is a wide variety of materials used in the metal cutting and CNC cutting industry, based on the ISO standards, the workpiece materials can be divided into six groups. Each class of metal or alloy is indicated by a code and color. The ISO classification divides the workpiece materials into six categories, mainly based on the dominant physical properties of the different materials. These properties are determined by the alloying elements, heat treatment, etc.
Workpiece material groups are used to help determine the correct cutting tool and starting values for machining conditions in particular applications. The material category can be identified by the letter or color.
P
Steel |
M
Stainless Steel |
K
Cast Iron |
N
Non-ferrous metals |
S
HRSA and Titanium |
H
Hardened Steel |
– P (Steel): the most common material group, ranging from unalloyed to high alloyed material, including steel castings, ferritic and martensitic stainless steels. Machinability is normally good but differs depending on material hardness and content.
– M (Stainless Steel): stainless steel are materials alloyed with a minimum of 12% chromium, other alloys can be nickel and molybdenum. Different conditions such as ferritic, martensitic, austenitic, and austenitic-ferritic, make this a large family. They all expose cutting edges to a great deal of heat, notch wear and built-up-edge.
– K (Cast Iron): cast iron is a short-chipping type of material. Grey cast iron (GCI) and malleable cast iron (MCI) are quite easy to machine, while others including nodular cast irons (NCI), compact cast irons (CGI) and austempered cast irons (ADI) are more difficult. All cast irons contain silicon carbide, which is very abrasive to the cutting edge.
– N (Non-Ferrous): non-ferrous metals are softer types of metals such as aluminum, copper, brass, etc. Aluminum with a silicon content of 13% is very abrasive. Generally, high cutting speeds and long tool life can be expected.
– S (HRSA and Titanium): HRSA refers to heat-resistant superalloys, including a great number of high-alloyed iron, nickel, cobalt, and titanium-based materials. They are sticky, create built-up-edge, work hardening and generate heat. They are difficult to cut and have a short tool life.
– H (Hardened Steel): this group covers steels with a hardness between 45-65 HRC and also chilled cast iron around 400-600 HB. The hardness makes them difficult to machine. The materials generate heat during cutting and are abrasive to cutting edges.
Just dividing the material into six different groups does not provide enough information to select the correct tool and cutting parameters. Therefore, materials can be further subdivided into the following subgroups based on their structure, composition, etc.
Steel is Iron (Fe), with the addition of 0.1 – 2.5 wt. % of Carbon (C). Besides carbon, steel may also contain many other alloying elements up to a total content of around 20%. Pure Iron is very soft. Iron becomes steel by “playing” with the mix and amount of the different alloying elements.
Stainless steels, as their name suggests, are a group of steel alloys with a shiny appearance and good corrosion resistance. The base element (70-80%) is Iron (Fe) with a minimum of 10.5% Chromium; most grades will have additional alloying elements such as nickel (Ni) and molybdenum (Mo).
Cast Iron is a group of Iron- Carbon-Silicone materials with 1.8-4% carbon (C) and 1-3% of Silicon (Si) content. The silicon pushes part of the carbon out of the solution, forming graphite flakes. The material is brittle at room temperature but has a low melting point and thus has excellent castability. Each subgroup contains different alloys at a wide range of hardness. The hardness has a major effect on machinability, and therefore we compare all the subgroups at 230 HB.
Superalloys are a group of materials engineered to have very high strength and superb corrosion resistance. Some of them also preserve these properties at very high temperatures and chemically hostile environments. They are mainly used in jet engines, turbines, oil&gas equipment, and medical implants.
ISO Class | Subgroup | Material |
---|---|---|
P-Steel | P1 | Free Cutting steel and structural steel |
P2 | Carbon steel and low alloy steel | |
P3 | Medium alloy and heat treated steel | |
P4 | High alloy steel | |
P5 | Tool steel | |
P6 | High tensile strength steel | |
H-Hardened Steel | H1 | Hardened steel |
H2 | Hardened bearing steel | |
H3 | Hardened tool steel | |
H4 | Hardened martensitic stainless steel | |
H5 | Hardened white cast iron | |
M-Stainless Steel | M1 | Ferritic stainless steel |
M2 | Austenitic stainless steel(good machinability) | |
M3 | Austenitic stainless steel(medium machinability) | |
M4 | Martensitic stainless steel | |
M5 | PH stainless steel | |
S-Heat resistant super alloy & titanium | S1 | Heat resistant super alloys (good machinability) |
S2 | Heat resistant super alloys (medium machinability) | |
S3 | Heat resistant super alloys(low machinability) | |
S4 | Low alloy titanium(good machinability) | |
S5 | High alloy titanium(medium machinability) | |
K-Cast iron | K1 | Grey cast iran |
K2 | Nodular cast iron | |
K3 | Austenitic cast iron | |
K4 | ADI cast iron | |
N-Non Ferrous | N1 | Aluminum alloys < 12% Si |
N2 | Aluminum alloys > 12%Si | |
N3 | Copper | |
N4 | Bronze and brass | |
N5 | Plastic materials | |
N6 | Fiber and composites |