Carbide Grades For Machining

Carbide Grades is a general term in metallurgy referring to sintered WC material used for various applications such as Nozzles, Dies, Rollers, Crush Rolls, and Cutting Tools. It is classified by ISO code ranging from K01 to K40.  However, in the machining jargon, the term “Carbide Grade”, or simply “Grade” refers to the combination of sintered tungsten carbide, coating, and other treatments of a cutting tool. Two cutting tools that are made of the exact same carbide material, but have a different coating or post-treatment are designated by a different grade.

This post provides all the information you need about carbide grades alongside practical examples and Smart Online Calculators.

How to find grades in the tooling catalogs?

Although there is no formal international standard, most suppliers use charts that describe grades’ recommended working envelopes based on their “Application Range” as expressed in a three-character letter-number combination, such as P05-P20. To use the catalogs efficiently, you should have a deep understanding of this coding. Therefore we prepared a complete guide for understanding Application Range in Machining

Assuming you read the guide, head to the supplier’s catalog with the following information:

• The raw material you need to machine. (Steel, Aluminium, etc.)
• Machining application (Milling, Turning, etc.)
• Your application “Stability” as defined in the above-mentioned guide.
• Is your application more suitable for CVD or PVD-coated grades? (Learn more in this guide about coatings )

An easier way is to use our CARBIDE GRADES FINDER which will filter for you all the grades from the main carbide suppliers.

How to find the right grade for your application?

One of the most critical factors in improving performance in a machining application is choosing the most suitable carbide grade. The first step to making the right choice is defining your application correctly by listing the following factors:

• Raw material. (Steel, Stainless, etc.)
• Basic application. (Milling, Turning, etc.)
• What is the maximum cutting speed (SFM) you plan to run?
• Rate your clamping stability on a scale between 1 and 3. (1 – Firm workpiece clamping and short tool overhang, 3 – Poor overall stability)
• Rate the conditions of your workpiece on a scale between 1 and 3. (1 – Smooth and continues, 3 – Heavy interrupted cut)

Enter the above data into our online GRADE WIZARD and get the best grade from each brand for your application.

How to find equivalent grades from other brands?

One of the most common tasks related to carbide grades is finding equivalents. Any cutting tools engineer or machinist faced the situation of using a particular grade, and when he needs to re-order, it is out of stock, or the distributor had bumped up the price.
To find equivalents from another brand that will be as close as possible, you need to obtain the following data about the grade you want to replace:

• What is the hardness?
• Is it CVD or PVD coating?
• What is the coating thickness?
• What is the primary application it is designed for?

With this information at hand, you can contact other suppliers or browse catalogs and try to find the best match.

An easier way is to use our GRADE CONVERTER, which will list for you the closest alternative from the major suppliers.

How to compare two carbide grades?

Machining professionals frequently face the question: “What is the difference between grades A and B?”
A common reason can be, for example, this scenario:

You tested grades A and B. With Grade A, you get early wear, but you get micro breakages on the cutting edge with grade B. You need to find Grade C that will have properties somewhere in the middle.

Instead of “breaking your head”, use our GRADE COMPARING TOOL, which will show you the difference between a pair of grades.

Carbide Grades Glossary

Substrate of Carbide Gardes

The substrate is the material of the bare cutting insert before coating and post-treatment. It is composed of 80-95% of WC.   WC (also referred to as Wolfram) is a combination of tungsten (W) and carbon (C) refactored together. To give the substrate the desired properties, the manufacturers add various alloying elements. The main alloying element is 5-15% of cobalt (Co), which increases the substrate’s toughness (More cobalt=more toughness, Less cobalt=more hardness). The primary property of interest to the machinist is the hardness of the substrate. Very hard substrates have a hardness of 1800 HV and provide excellent wear resistance but are very brittle and can work only in very stable conditions. Very tough substrates have a hardness of about 1300 HV. They can operate only at lower cutting speeds, will wear out faster, but have much better resistance to interrupted cuts and unfavorable conditions. The right balance between hardness and toughness is critical for achieving a longer tool-life and higher productivity in each application.

Substrate Hardness Selection Guide

Coating of Carbide Grades

Most carbide inserts and solid carbide tools are coated with a thin layer of 3 to 20 microns (0.0001-0.0007″). The coating is typically composed of a series of sub-layers composed of mostly titanium nitride, aluminum oxide, and titanium carbon nitride. This thin layer directly enhances the performance of the inserts by increasing their hardness and insulating the heat generated from the cut to the substrate.

Main Coating Technologies:

CVD (Chemical Vapor Deposition) –

As its name suggests, in this process, the coating forms a chemical bond with the substrate. Therefore, the adhesion to the substrate is very strong. With CVD, it is possible to create a thick coating of 5 to 25 microns. Due to its thicker layer, CVD provides excellent heat insulation and enables achieving higher cutting speeds compared with PVD. The downside is more sensitivity to cracks and fractures.

PVD (Physical Vapor Deposition) –

In the PVD process, the coating layer is spattered on the substrate and does not form a chemical bond with it. Therefore, the adhesion is lower, but the process induces compressive residual stress that improves the overall toughness of the carbide insert. PVD is good for creating thin coatings between 1 to 8 microns. PVD-coated inserts need to operate at lower cutting speeds when compared with CVD. However, they are tougher, have a smoother surface (less friction), and can also be applied on sharper edges (small honing and ground inserts).

As a machinist, you need to understand when to prefer a thinner or thicker coating layer and when to prefer a CVD or a PVD insert.

Post Treatment

All coatings have flaws in their surface uniformity caused by coating droplets and non-uniform grain size. Most modern grades add a post-treatment after the coating process. This treatment is usually sandblasting or tumbling, aiming to smoothen the final coating layer, thus reducing the friction and, as a result, also the generated heat.

Carbide Grades Designations

Although there is no formal standard, most of the major carbide inserts suppliers follow the following guidelines for their Carbide Grades designation:

• BB – Brand: Each brand uses a different 2-letter combination as a prefix. (Some brands have several prefixes associated with them). Iscar uses “IC“, Sandvik uses “GC“, and Kennametal “KC“, and so on. Examples: IC808, GC4315, KCU25.
• SS – Coating Series (Family): For example, Sandvik grades GC4305, GC4315, and GC4325 share the same 43 series coating. In this example, “43” is a family of thick CVD-coated grades for steel.
• HH – Hardness Level: The last two digits, in most cases, reflect the hardness level. A smaller number will usually mean a harder substrate. For example, GC4305, GC4315, GC4325, and GC4335 have the same coating. GC4305 is the hardest in the series, and GC4335 is the toughest (Least hard) in the series. While it is not a 100% rule (because the carbide suppliers don’t always follow these guidelines), It is still beneficial to be familiar with this system.