Carbon (C)
Contributions: Hardness, edge retention.
You'll find carbon in every form of steel. Essentially, it is the element that converts the base metal iron into steel and plays an important role in the hardening process. Typically as the carbon content increases, you get harder steel, higher tensile strength, edge retention and overall wear resistance. Knife steel is often described as "high carbon" if it contains more than 0.5% carbon. However, if the manufacturer goes over the top with too high a carbon content, it can make the steel brittle and also increase its tendency to corrode.
Chromium (Cr)
Contribution: Corrosion resistance.
By adding chromium to steel, it is often possible to improve oxidation and corrosion resistance. To be classified as "stainless steel" there should be at least 13% chromium. Chromium is a key driver of carbide formation, which reduces brittleness but can also adversely affect edge retention. In addition to improving corrosion resistance, chromium also improves hardenability and tensile strength. Every type of steel will corrode if exposed for long periods of time. Also note that too much chromium can reduce toughness.
Molybdenum (Mo)
Contribution: Tenacity.
Molybdenum increases toughness, which reduces the likelihood of chipping. It also allows the steel to maintain its strength at high temperatures, which helps with how easily the blade can be produced in the factory. Like chromium, it is a driver of carbide formation, but is usually used in smaller relative amounts.
Nickel (Ni)
Contribution: Tenacity.
Some manufacturers choose to add a small amount of nickel to increase toughness and strength, especially at low temperatures, which essentially limits deformation and cracking during the quenching stage of heat treatment. Many manufacturers claim it also reduces corrosion, but this is often disputed.
Vanadium (V)
Contributions: toughness, wear resistance.
Vanadium is another element similar to molybdenum that promotes the formation of carbides (the hardest) and adds wear resistance to steel. Perhaps more importantly, vanadium creates very fine grains during the heat treatment of steel, which increases overall toughness. Some ultra-high-quality steels contain relatively high levels of vanadium and have ultra-sharp edges.
Cobalt (Co)
Contribution: Hardness.
Adding very small amounts of cobalt allows for quenching at higher temperatures (i.e. rapid cooling to gain hardness) and tends to increase the influence of other elements in more complex steels. It's not a carbide former per se, but it certainly contributes to overall hardness.
Manganese (Mn)
Contributions: Hardenability, Strength, Wear Resistance.
Yet another key element that contributes to hot working performance is making the tool more stable during the quenching process. Manganese will help increase hardness as well as tensile strength and wear resistance. As with anything that adds hardness, steel with too much manganese can also be too brittle.
Silicon (Si)
Contribution: Hardenability, Strength.
Silicon adds overall strength similar to the effect of manganese, making steel more stable to manufacture. However, the real value of silicon is in deoxidation and degassing to remove oxygen. Oxygen is undesirable in steel production because it can cause porosity or pitting corrosion.
Niobium (Nb)
Contributions: toughness, wear resistance.
Niobium is primarily used to aid in the fine grain structure, which helps improve wear resistance and prevent chipping. Arguably the most famous knife steel that utilizes niobium is CPM-S35VN, which is combined with carbon and introduces niobium carbide to aid in wear resistance and edge cutting. The result is strong edge retention.
Tungsten (W)
Contribution: Wear resistance
Tungsten forms carbides and tends to improve wear resistance. It is often added with chromium or molybdenum for best results.
