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.
*carbide: A compound of carbon and another element.
Steel acquires its properties (see above) through heat treatment. It is a procedure where it is heated in high temperature (called austenitizing temperature) where it changes its structure and then it is quenched in a medium (oil/water/air) in order to “lock” and keep that structure. The new phase of the steel (which is now called martensite) gives us the desired properties of the steel , hardness, strength etc. Then it is tempered (re-heated into lower temperatures) to release stresses and define hardness according to our needs. Depending the type of steel, a cryo treatment also can be used -as an extra step – to extract even more hardness.
The procedure may sound easy but, it is one of the most crucial steps in the knifemaking process. It requires knowledge of metallurgy, proper equipment and experience.
How to choose a Kitchen Knife
When you searching for your a knife, ask the following questions and consider:
What task do you want to perform? light tasks? (vegetables, boneless proteins etc)?
Do you want something that gets the job done no matter what?
Find the need/tasks you want to cover and then find the best geometry that suits you.
What is the best blade and handle geometry for you?
Is the knife thin enough behind the edge?
What grind type (convex, hollow, flat, “S” , combined) does it have?
Type of Steel and Heat Treatment
Choose the steel based on your preference. High wear resistance? Something stainless? or something that can easily sharpen? Check and find the optimal balance between hardness, toughness, sharpening ease, resistibility to rust and wear resistance . Plus, look a steel that has the ability to take fine edges/low degrees and support that edge without serious deformations for the task needed.
Attention! It doesn’t mean that if you buy an excellent steel with all the above abilities that it would perform amazingly. Appropriate heat treatment for each different steel is essential nowadays! Electronically controlled clins, salt baths and cryo treatments with liquid nitrogen are some prerequisites for proper heat treatment. Please also note that, every steel has different optimal hardness and a higher hardness is only indicative. Higher hardness is not always better than a lower one!
Brands and Types of Kitchen Knife Steels
Below you will find some information about few popular kitchen knife steels available in the market, in order to know where to look and what to expect. The list focuses in stainless carbide steels mainly and it does not cover, by any means, the variety of the kitchen knife steels available.