Regardless of whether its carbon, stainless, or tool steel, all knife alloys have some (or all) of the following elements in their composition. When a knife’s raw forging is heat-treated, these elements form carbides.
What Are Carbides? How Do They Affect a Knife Blade?
Carbides are microscopic nodules found within a steel. They’re made of the element carbon and other metallic or nonmetallic compounds, which we’ll cover below. Carbides are incredibly hard; about as hard as ceramic. Carbides are formed when a steel is heated to very high temperatures — at least 1,425 degrees (F) or higher — before being quenched and hardened. Different carbides contribute certain properties to a knife’s blade, like edge retention, toughness, corrosion resistance, grain structure, and brittleness.
Hardness and edge retention. Carbon is present in every steel. By definition, steel is formed from iron and carbon. The more carbon present in a steel, the harder it is. Carbon also improves tensile strength and edge retention.
A knife steel is considered high-carbon if its carbon content is 0.5% or greater. Blades with a carbon content of 1.5% or more are not suitable for hard striking. They’re instead designed for absolute sharpness and extensive cutting.
“Super steels” can have as much as 3.3% carbon. Those steels require high amounts of other elements (like Chromium and Vanadium) to reduce brittleness.
Corrosion resistance and carbide formation. Chromium often makes up the bulk of any knife steel’s composition. Like we mentioned above, any stainless blade will have at least 10.5% Chromium. A Chromium content of 13% or more is favored for true stainless performance.
Since Chromium facilitates the formation of carbides, its percentage tends to increase as the presence of other elements in a steel (like Vanadium, Molybdenum, Cobalt, and Manganese) also increases.
Lastly, Chromium reduces the brittleness of steel. So, steels with high carbon content also tend to have high Chromium content. The result is a knife blade that’s incredibly hard, with good edge retention but also good toughness.
Chromium represents 0% to 1.6% of a carbon steel’s composition. It ranges between 0.4% and 13% in tool steels, and 11% to 20% in stainless steels.
Toughness. Molybdeum functions like Chromium: It increases blade toughness and hardenability, and it helps to drive carbide formation of other elements in a steel’s composition.
The average amount of molybdenum present in knife steels ranges from as little as 0.1% to 4%.
Toughness. Nickel aids in the heat-treating process, reducing the risk of a steel distorting or cracking when its quenched. Only small amounts of Nickel are ever used in any knife steel.
It typically contributes 0.1% to 0.5% of a steel’s composition, with H1 steel being an outlier: It contains between 6% and 8% Nickel.
Toughness and wear resistance. Next to Chromium, Vanadium is the most common element found in knife steels. That’s because in addition to improving blade toughness, it contributes to carbide formation between carbon and other elements.
Even more importantly, it helps ensure a knife’s steel produces a very fine grain structure when heated and quenched. Smaller grain structures promote strength and hardness — two properties every knife blade benefits from having more of. High levels of Vanadium contribute to incredibly sharp edges that hold well through extensive cutting.
Premium steels, like S90V, S110V, and M390, have between 3% and 9% Vanadium. Its also present in high amounts (up to 10%) in tool steels, though it’s rarely ever used in carbon steel.
Steel hardness. Cobalt assists with the quenching process. It ensures carbides are formed and distributed properly at high temperatures before rapid cooling, helping to improve the overall Rockwell Hardness obtained in a knife’s steel.
Cobalt is not commonly used, though. It’s typically found in premium steels like S110V, S125V, and N690, which have high amounts of other carbides and often measure 60 to 64 HRC on the Rockwell Scale.
Hardenability, strength, and wear resistance. Manganese helps to stabilize a steel when it’s heated, improving the quenching process. It protects against crackings and fissures from forming during rapid cooling, and it helps promote higher tensile strength.
Too much Manganese will make a blade brittle, so it’s typically used in small amounts — between 0.25% and 1% of composition.
Hardenability and strength. Silicon assists with the forging process, removing oxygen and preventing oxidation while blades are formed under heat. As part of the steel’s final structure, it add strength, like Manganese. Typical silicon contents range between 0.2% and 1%.
Toughness, corrosion resistance, and wear resistance. Niobium is typically used in CPM steels to produce very fine grain structures and high amounts of carbides. S35VN is one of the most popular knife steels on the market today. It uses niobium carbides to enhance edge retention and protect against chipping.
Toughness and wear resistance. Tungsten is one of the hardest elements, and its carbide produces some of the most wicked edges you’ll ever find on a knife. However, since its one of the hardest materials on Earth, it’s difficult to work with. It is rarely used in knife steels, and only in low percentages.
Sandrin Knives says their tungsten carbide blades (like the one found on the Monza Titanium) have a Rockwell Rating as high as 71 HRC. The sharp edges on these knives wear slower than conventional steel by nearly an order of magnitude.
Machinability. Sulfur inclusions make a rough blade easier to cut and machine. It helps to ensure consistent chip formation when the blade is being formed by tooling, helping to produce a uniform edge and honed finish.
Hardness and corrosion resistance. Phosphorus is an uncommon inclusion in steels, since it’s usually considered an undesirable impurity. but when present in small amounts (0.04% to 0.1%), it can improve strength and hardness.
Hardness and corrosion resistance. Nitrogen can replace carbon in a steel’s structure, improving hardness without sacrificing corrosion resistance. However, nitrogen alloys tend to be softer. On average, a nitrogen steel will measure 2 to 5 points lower on the Rockwell C Scale when compared to carbon steels with similar carbide compositions.
Corrosion resistance and hardness. Copper may be used in small amounts to promote corrosion resistance. It can also contribute to hardening.
Now that you have a basic understanding of knife steel elements and carbides, you can better understand which types of steels are best for certain applications.
Check out our guide to knife steel types (complete with carbide composition charts!)
Learn What Else Affects Knife Performance
When it comes to a knife’s performance, steel composition plays just one part of the bigger equation. here are the other important factors you should consider when picking a blade for a specific purpose: