Choosing a Survival Knife  |  Knife Sharpening  |  Knife Steel Properties  |  Knives and UK Law  |  Knife Terminology

Confused about all those different steel references they give when you're trying to decide on what knife to buy?

Firstly, what is steel? Well, Steel is an alloy of iron, with carbon, which may contribute up to 2.1% of its weight. Various other elements may be added to the steel alloy to affect different properties, the main ones being:

• Strength – This represents the ability to resist deforming when subject to stress and applied forces.
• Hardness - Similar to strength this refers to the ability to avoid any permanent deformations.
• Toughness - The ability to resist damage like cracks or chips when being used in heavy duty applications. This also defines the steel’s ability to flex without breaking. Note that the stronger or harder the steel the less tough it will probably be.
• Wear Resistance – This is the steel’s ability to withstand wear and general abrasion during normal use.
• Corrosion/Rust Resistance - This is the ability to resist corrosion such as rust caused by external element. Note that a high resistance to corrosion does involve a sacrifice in the overall edge performance.
• Initial Sharpness – This is simply how sharp the blade is when first used.
• Edge Retention - Represents how long the blade will retain its sharpness and not require re-sharpening.

"Stainless Steel" is a modern alloy developed in the early 1900’s after metallurgists discovered that chromium-iron alloys displayed superior corrosion resistance to carbon steel alloys. Steels must have at least 10% chromium (see below) in their content to be called Stainless. Below this value, the alloy steels will experience increasing corrosion rates and will begin to rust in wet environments. The chromium forms a protective self-healing oxide film, which is the reason why this group of steels exhibits such corrosion resistance. The ability of the oxide layer to heal itself means that the steel is corrosion resistant, no matter how much of the surface is removed.

Stainless steels may be classified by their crystalline structure into three main types:

Chemical Composition of Knife Steel

The chemical composition of a knife steel must be balanced, not over alloyed and precise. The specification tolerances must be tight in order to secure a high consistent quality in the finished knife. Here is a list of common elements used in knife steel production:

Carbon (C) - The main driver for hardness. Too much carbon however makes it more difficult for the material to produce martensite and thereby deep freezing is necessary to achieve high hardness. The hardness is related to the amount of carbon dissolved in the steel matrix. By tying up chromium into carbides the carbon is indirectly decreasing corrosion resistance.

Chromium (Cr) - The main driver for corrosion resistance. The corrosion resistance achieved is related to the amount of Cr dissolved into the steel matrix and not related to the nominal composition. Cr is also the main driver for carbide formation.

Molybdenum (Mo) - Drives carbide formation and has a small influence on hardness and corrosion resistance in martensitic stainless grades.

Vanadium (V) - A strong carbide former. The vanadium carbides are also very stable and do not dissolve during heat treatment.

Manganese (Mn) - An important element, manganese aids the grain structure, and contributes to hardenability. Also strength and wear resistance. Improves the steel (e.g., deoxidizes) during the steel's manufacturing (hot working and rolling). Present in most cutlery steel except for A2, L-6, and CPM 420V.

Nickel (Ni) - Adds toughness. Present in L-6 and AUS-6 and AUS-8. Nickel is widely believed to play a role in corrosion resistance as well, but this is probably incorrect.

Nitrogen (N) - Hardness driver like carbon but does not have the same negative effect on corrosion resistance. Nitrogen is not commonly used in these applications since it is difficult to achieve significant levels of nitrogen in conventional steel production.

Sulphur (S) - Forms sulphide inclusions which have a negative influence on the initiation of pitting corrosion.

Tungsten (W) - A carbide former, it increases wear resistance. When combined properly with chromium or molybdenum, tungsten will make the steel to be a high-speed steel. The high-speed steel M2 has a high amount of tungsten. The strongest carbide former behind vanadium.

Vanadium (V) - Contributes to wear resistance and hardenability, and as a carbide former (in fact, vanadium carbides are the hardest carbides) it contribute to wear resistance. It also refines the grain of the steel, which contributes to toughness and allows the blade to take a very sharp edge. A number of steels have vanadium, but M2, Vascowear, and CPM T440V and 420V (in order of increasing amounts) have high amounts of vanadium. BG-42's biggest difference with ATS-34 is the addition of vanadium.

Manganese (Mn), Phosphorus (P) and Silicon (Si) - These elements make no significant contributions. The general rule is to keep these as low as possible.

The most important thing to remember is that hardness and corrosion resistance are related to the composition of the matrix after hardening, not the nominal chemical composition of the steel. The excess amounts of these elements will form large primary carbides during casting and will not add to the hardness or corrosion resistance of the finished knife.

Primary carbides will make the knife more brittle and more difficult to sharpen than a fine-grain steel knife at the same hardness. The steels containing large primary carbides will also cause very high tool wear for blanking tools, making them unsuitable for blanking or stamping.