Takes the keenest edge of any kitchen steel, and rusts if you let it.
Also called: carbon steel, blue steel, white steel
Measurement
Usually 60 to 64 HRC
The basics
What to know about high-carbon steel
High-carbon steel has little or no chromium, which is exactly why it cuts so well and exactly why it needs looking after. Without chromium the grain can be made finer and the blade harder, usually 60 to 64 HRC. It takes an edge that slices a tomato under its own weight and keeps it for months. Grain here means the size of the crystals in the steel, and finer crystals let the edge come to a thinner, straighter line.
The cost is rust. Water left on the blade will spot it within minutes, and anything acidic, onion, lemon, tomato, will mark it faster. You wipe the blade dry as you cook, not when you finish. Do that and the marks settle into a grey or blue patina, which is stable and protects the steel underneath. Neglected blades pit orange instead, and that pitting does not come off. Force the patina early if you like: wipe the new blade with a cut lemon, then rinse and dry.
Hardness also means brittleness. A carbon blade at 63 HRC will chip on a bone or a frozen edge where a soft stainless blade would just roll. Keep it for board work and let a cheaper knife take the abuse.
Carbon takes a stone quickly because it is not fighting chromium. Ten minutes on a 1000 grit stone restores an edge that a pull-through would only round off. Chips are the failure to watch for, and they start as bright specks along the edge you can see under a lamp. Check for them after any job with bones, hard rinds or a frozen center, and grind them out early while they are still shallow.
How it is made
How high-carbon steel is made
Carbon knife steel is iron and carbon with very little else. The Japanese white and blue steels named on many blades are this. White is near-pure iron and carbon, and blue adds a little tungsten and chromium for wear resistance. Neither has enough chromium to count as stainless.
Because the steel is run hard, the heat treatment is delicate and often done in small batches. Many carbon blades are then laminated, with a hard cutting core forged between two softer stainless outer layers. That gives the fine edge of carbon on the cutting surface while the sides resist rust and absorb shock. It is also where the visible wavy line on some blades comes from.
Best for
When it works well
Cooks who already sharpen, since ten minutes on a stone is the standing price of the edge.
Precise slicing of fish, herbs and vegetables, where a 60 to 64 HRC edge parts food instead of pushing it aside.
Anyone who will dry the blade during cooking rather than after, because water spots bare carbon within minutes.
Dry board work only, with a second knife kept back for bones, frozen food and hard squash.
