Ask Paul: What Is Carbon Steel?

Slicing through some ambiguous terminology

Published June 23, 2021.

Steel, like pastry, comes in many different varieties, all of them excellent in one way or another, but none of them suited to every occasion.

One cook tells me how he loves his carbon-steel chef’s knife. He’s happy to put up with the demands of caring for it--washing and thoroughly drying the blade after each use, and anointing it with special oil--because its stiff, tough blade stays sharp through months of daily use, with barely a touch of the honing rod. He’s careful not to chip the brittle material, though, and brings out a stainless knife instead for hacking through hard foods.

Another cook’s experience is strangely different. She used to swear by stainless-steel knives until she started sharpening her own, and found that the carbon-steel ones were much easier to bring to a fiercely keen edge, even though they require frequent sharpening in order to keep that edge. She also appreciates that the blade has more flex than the rigid, brittle stainless types.

So is carbon steel harder than stainless steel? Softer? Easier to sharpen? Harder to sharpen? More durable? Less brittle? Hmm. . .

This contradictory muddle comes from a case of category confusion, where one term, “carbon steel,” is widely used to refer to two different things: A) any variety of steel containing a particularly high proportion of carbon, more properly called “high-carbon steel;” or B) any variety of steel that’s not stainless. 

Stepping back for a second: Steel is an alloy, a metal made by mixing together different ingredients. It’s mostly iron, but the proportions of other ingredients vary: a certain percentage of carbon, and several optional other elements mixed in to give it mechanical properties that it wouldn’t otherwise have. If a steel doesn’t contain a noteworthy amount of other elements besides iron and carbon, it’s categorized as “plain carbon steel.” If it does have additions like silicon, nickel, chromium, molybdenum, and so forth, it’s called an “alloy steel.” (Although every steel is an alloy by definition, so that’s not a great term either.)

Stainless steels are low-maintenance alloy steels that resist (not prevent) rust due to a large percentage of chromium (over 11 percent). This forms a thin layer of chromium oxide on the surface of the tool, which prevents oxygen from reaching the rest of the metal and causing corrosion. 

The greater the amount of carbon in a steel, meanwhile, the stronger the steel can be. Typically, if it’s more than 0.5 percent carbon, it qualifies as high-carbon steel.

You may notice that we’re heading for an apparent contradiction here: Wouldn’t it be possible for a steel to contain over 11 percent chromium AND over 0.5 percent carbon, thereby making it both stainless and high-carbon? It sure is possible, and indeed one of the most popular knife steels, called VG-10, is just that, a hard, shiny beast that clocks in at 15 percent chromium, 1 percent carbon, and a sprinkling of vanadium and cobalt.

There’s an entire smartphone app dedicated to cataloguing the varieties of knife steels, because steel is complicated. Like food, its properties depend not only on its component ingredients, but also how they’re treated, with heat, pressure, chilling, marinating. 

Saying that a metal is “high-carbon steel” indicates that it’s hard, making for a durable cutting edge. Calling it “carbon steel” is ambiguous; it may refer to what the steel is, or to what it is not. 

Ask Paul Adams, senior science research editor, about culinary ambiguities, terms of art, and useful distinctions:


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