Workpiece Material Guide: What is ISO Material & ISO Material Groups and Classification Chart


To figure out if the tool is right for your CNC machining operation, the material to be processed is critical. For example, the hardness of different materials varies a lot, which requires different cutting tools to cut the workpiece. In this guide, we’ll present the ISO material groups and the workpiece material classification chart.

What is ISO Material

There are 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 (Blue): Steel

M (Yellow): Stainless Steel

K (Red): Cast Iron

N (Green): Non-ferrous metals

S (Orange): HRSA and Titanium

H (Grey): Hardened Steel

ISO Material Groups - Workpiece Material Groups

– 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. 

ISO Material Classification Chart

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.

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