Which is the best steel for kitchen knives?
What is steel?
Steel is an alloy. It is basically a combination of iron and carbon and when no other element is present is called plain carbon steel. Usually, today’s steels contain small amounts of various elements such as Silicon, Manganese, and Vanadium that give to the steel different properties. For example, steels that have added chromium over 12-14% are considered corrosion resistant (labeled as “stainless steels” in the market) or steel that contains manganese have increased strength, toughness and hardenability.
Hardness, in general, is a good thing. The harder the blade the better the edge has (edge stability and edge holding). It is preferably measured using the Rockwell scale (HRC) and commercial kitchen knives typically range between 55-60 HRC. Usually handmade kitchen knives are hardened more to the 60-65 HRC range or even higher.
What are the properties of steel?
Strength: The ability to resist applied forces.
Hardness: The ability to resist permanent deformations.
Toughness: The ability to resist prior to fracturing (also resistibility to cracks /chips when used in heavy duty applications). The harder the steel the less tough it is.
Wear Resistance: The ability to resist wear and abrasion.
Corrosion Resistance: The ability to resist corrosion as a result of reaction with external elements.
Edge Retention: The ability to hold an edge without re-sharpening
Hardenability: The ability of a steel to be hardened through the heat-treating process
Steel performance depends on many factors and many of its properties are inversely proportional to each other.
With that said, when an element is added to the recipe- because we want a specific property- we inevitably sacrifice another one and therefore its properties. Subsequently, we have to trade-off some properties and usually this is hardness/strength with toughness. The bet is to find the best recipe for your work, in order to perform specific tasks.
There are some very important elements of the knife making industry that give steel specific properties. Below you will find some of the most important.
Carbon: Increases hardness and strength. Over 0.5% carbon in an alloy is considered “high-carbon”.
Nitrogen: Substitute of Carbon. New technologies use nitrogen in place/ complimentary of carbon to increase hardness.
Chromium: Increases hardenability, corrosion resistance and wear resistance, but in high amounts decreases toughness. Over 12%, a steel is considered “stainless”.
Molybdenum: Increases hardenability, tensile strength, and corrosion resistance.
Nickel: Increases toughness, hardenability and corrosion resistance.
Niobium: Forms very hard but also very small carbides that lead in wear resistance. Keeps the grain small and refines structure.
Vanadium: Increases hardenability and promotes fine grain structure.
Tungsten: Increases wear resistance and is the second strongest carbide* former after vanadium.