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 breakdown of the most common elements in knife steel:

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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.

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.

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.