There are loads of steels used to make knife blades; nearly 70 are in common use. Knife steels are classified as carbon or stainless steels. But what does that mean, exactly? Which one’s better? Is one better, overall? Let’s see.
What is Carbon Steel?
Carbon steel is an alloy formed by combining iron and carbon. It contains between 0.05% and 2.1% carbon (C) by weight. The American Iron and Steel Institute (AISI) also says carbon steel must not contain more than 0.4% copper, 1.65% manganese, and 0.6% silicon. Carbon steel must also contain less than 10.5% chromium.
In knife blades, carbon is the most important element: It forms iron carbides and combines with other elements in the steel — like vanadium, molybdenum, manganese, and others — to produce additional carbides. Carbides are tiny, incredibly hard nodules that give a steel its hardness. Carbides are primarily responsible for giving a blade its ability to hold an edge and cut well.
Which Carbon Steels Are Used in Knives?
Carbon steel is further categorized as mild steel (0.05% to 0.25% C) and high-carbon steel (0.6% to 1.5% C).
Mild steel cannot produce a hard-wearing blade, so only high- and ultra high-carbon steels are used to make knife blades. Those steels include the 10xx series carbon steels, and a few others:
Of all the carbon steels, 1095 is the most commonly used blade steel. It contains the most carbon of the 10 series alloys (0.9% to 1.03%), and produces the most carbides for good cutting performance.
Is Tool Steel Considered Carbon Steel?
In most cases, yes. Tool steels are much harder than standard carbon steel because they include higher percentages of carbon and other carbide-producing elements, primarily vanadium, chromium, cobalt, and nickel.
Some tool steels used in knifemaking, like CPM-10V, K390, and CPM-15V, contain 2.45% to 3.4% carbon. Most tool steels meet the definition of carbon steel: They contain less than 0.4% copper, 1.65% manganese, 0.6% silicon, and less than 10.5% chromium.
But the most popular tool steel used in knifemaking, D2 steel, is not a carbon steel. Because of its composition, it is considered a tool steel and a stainless steel.
What is Stainless Steel?
Stainless steel is an alloy formed by combining iron, carbon, and chromium. It contains at least 10.5% chromium (Cr) by weight. Some stainless steels contain up to 20% chromium. Chromium is the element that makes stainless steel rust- and corrosion-resistant. This element forms a thin layer of chrome oxide. This oxide layer prevents oxygen from penetrating deeper into the steel and causing corrosion.
The Chromium in stainless steel also binds with carbon to form chrome carbides. These carbides are orders of magnitude harder than the iron carbides formed in carbon steel. These further enhances a stainless steel blade’s ability to hold an edge longer than a carbon steel.
What Makes a Better Knife: Carbon or Stainless Steel?
Carbon steels are softer and contain fewer carbides. Carbon steel blades are tougher and more flexible, but they suffer softer cutting edges that dull more quickly.
Stainless steels are harder and contain more carbides. Stainless blades are more weaker, but they provide harder, longer-wearing cutting edges.
It’s a myth that carbon steel blades are superior because they’re sharper. This is false. This myth is perpetuated because, generally, carbon blades are easier to sharpen. But any stainless blade can be made as sharp (or even sharper) than a carbon steel blade.
It simply takes longer to sharpen a stainless knife. That’s because the harder and more plentiful carbides found in stainless are more difficult to hone. But, with quality whetstones (like diamond stones), sharpening a stainless knife is easy.
Once sharpened, most stainless steel knives will hold an edge longer than standard carbon steel knives. The chrome carbides found along a stainless blade’s cutting edge will resist wear longer than the iron carbides that make up the bulk of a carbon steel blade’s composition.
But there are exotic, ultra-high-carbon tool steels that also contain high amounts of vanadium and tungsten to maximize edge retention. These steels (like CPM-15V, Rex 86, and Rex 121) beat the longest-wearing stainless knife steel, S125V, in edge retention testing.
However, these tool steels are incredibly expensive and brittle. Blades made from these alloys are prone to chipping and cracking if they’re not used gently. They’re more difficult to sharpen than stainless, too.
Although carbon tool steel technically wins the edge retention category, it is far more practical to invest in a stainless blade that’s tougher, more affordable, and easier to maintain.
Winner: Carbon (technically)
It is true that carbon steel is stronger than stainless steel. However, most stainless steels provide more than enough toughness for any knife blade to resist chipping, cracking, or breaking. Even large fixed blade intended for heavy cutting and striking are most often made from stainless steel.
Stainless alloys are still flexible and strong enough for such tasks. Only in forging a long blade, like a machete or sword, does it become necessary to use carbon steel.
Winner: Carbon (technically, again)
Carbon steels can be treated with certain coatings or oxide layers (like bluing) that reduce corrosion. But no carbon steel will resist corrosion better than any stainless steel. When the chromium in stainless steel is exposed to open air, it immediately forms a protective oxide layer. Carbon steel does not contain elements capable of forming such layers, leaving the blade open to corrosion from oxygen and moisture.
Stainless steel can generally obtain hardness ratings than carbon steel — exotic tool steels notwithstanding. That’s because Chromium is the hardest metal known to man. It’s important to note, however, that a harder blade isn’t necessarily better.
Higher hardness makes for a weaker blade, and a more brittle cutting edge. Because stainless steels contain more carbides than most carbon steels, they can be hardened to lower hardness ratings and still produce superior cutting edges.
In Our Guide to Edge Retention, we observed that higher hardness can actually lower a steel’s ability to hold an edge.
So, Is One Steel Better Overall?
With the above facts in mind, I wholly believe stainless steel is a superior alloy for the practical knife user. It makes little sense to buy a blade made from an exotic, expensive, brittle tool steel merely to boast about edge retention — especially when tougher, more affordable stainless steels like S30V and 14C28N provide excellent edge retention, too. And although carbon steel is stronger, stainless steel is strong enough for even large blades subjected to abuse.