Carbide Size in Knife Steel: Why Is It Important and How to Choose the Right Steel?

What are carbides in knife steel?

Carbides are hard microparticles formed when carbon is combined with other elements in the alloy, such as chromium, vanadium, tungsten or molybdenum, during the hardening of steel. These particles are much harder than the steel matrix itself and strongly influence the cutting properties:

Abrasion resistance
Cut quality
Sharpening complexity
Keeping the edge

The more carbides and the harder and more evenly distributed they are, the longer the blade stays sharp. However, coarse carbides can compromise edge stability, especially when sharpening on small stones or at extremely sharp angles.

Value of carbide size

The size of carbides is usually measured in microns (μm). This is a very important parameter because:

Fine carbides (0,5-3 μm) allow a smoother and sharper cut, making it easier to sharpen to a very sharp edge.
Coarser carbides (5-20 μm) offer better wear resistance but can make the cut rougher and make sharpening more difficult.

Modern powder steels allow carbides to be distributed evenly and reduced in size, while maintaining a high particle content and improving the balance of properties.

Table of carbide sizes and properties for knife steels

Steel	Carbide size (μm)	Dominant carbide	Abrasion resistance	Ease of sharpening	Cut quality
Shirogami #1/#2	0,5-2	Fe₃C	Medium	Very good	Excellent
Aogami #1/#2	1-3	Fe₃C, Cr₇C₃	High	Good	Excellent
VG-10	2-5	Cr₇C₃	High	Medium	Good
440C	5-15	Cr₇C₃	High	Medium-Ordinary	Medium
D2	5-20	Cr₇C₃	Very high	Poor	Medium
CPM S30V	1-4	V₄C₃	Very high	Good	Excellent
CPM S35VN	1-4	V₄C₃, NbC	Very high	Good	Excellent
CPM S90V	1-2	V₄C₃	Extremely high	Medium	Excellent
CPM M4	1-3	Mo₂C, V₄C₃	Very high	Medium	Excellent
M390	1-3	V₄C₃, Cr₇C₃	Extremely high	Good	Excellent
ZDP-189	2-4	Cr₇C₃	Very high	Poor	Excellent

What to know when choosing steel?

If quality of cut and ease of sharpening are a priority, fine carbide steels (Shirogami, Aogami, CPM S30V, S35VN) are a good choice.
If long sharpness retention and wear resistance are important, powder steels with a high vanadium or carbon carbide content (CPM S90V, M390, ZDP-189) should be chosen.
D2 and 440C are durable and popular, but the coarser carbides make them more difficult to sharpen and the cut quality is average.
Powder metallurgy steels (CPM series, M390) have a high carbide content, but small size and uniform distribution, and are often considered the state-of-the-art knife material.

Conclusion

The size of the carbide is one of the most important factors in determining the performance of a knife. The smaller the carbides and the more evenly distributed they are, the sharper the knife will be, the better it will cut fine materials, the easier it will be to sharpen and the more pleasant it will be to use.

When choosing a knife or its manufacturing material, it is not only worth looking at the hardness (HRC) or rust resistance, but also at which carbides predominate in the steel, how many there are and what size they are.