Stainless steel for knives | Knife steel - Chemical composition, hardness, properties

Chemical composition of stainless steel and alloys for knives

The chemical composition of knife steel (knife stainless steel) must be balanced, not overalloyed and accurate. The specification tolerance must be tight to ensure high consistent quality of the finished knife.

The most common chemical elements of knife steel:

• Carbon (C): the main factor in hardness. However, too much carbon makes it difficult to produce martensite from the material, so deep freezing is necessary to achieve high hardness. Hardness is related to the amount of carbon dissolved in the steel matrix. By binding chromium into carbides, carbon indirectly reduces corrosion resistance.
• Chromium (Cr): the main factor in corrosion resistance. The achieved corrosion resistance depends on the amount of Cr dissolved in the steel matrix and is not related to the nominal composition. Cr is also a major factor in carbide formation.
• Molybdenum (Mo): promotes carbide formation and has a small effect on the hardness and corrosion resistance of martensitic stainless grades.
• Vanadium (V): strong carbide former. Vanadium carbides are also very stable and do not dissolve during heat treatment.
• Nitrogen (N): A hardness factor like carbon, but does not have the same negative effect on corrosion resistance. Nitrogen is not normally used in these applications because it is difficult to achieve significant levels of nitrogen in traditional steelmaking.
• Sulfur (S): forms sulphide inclusions that adversely affect the initiation of pitting.
• Manganese (Mn), phosphorus (P) and silicon (Si): these elements do not contribute significantly. A general rule of thumb is to keep them as low as possible in the knife steel composition.

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

Primary carbides make the knife more brittle and harder to sharpen than a fine-grained steel knife of the same hardness. Steels containing large primary carbides will also cause very high wear on the stamping tools, making them unsuitable for stamping.

Hardness of stainless steel and alloys for knives

Physical properties of stainless steel for knives, blades