Aluminium (Al) is added to steel as a deoxidizer. Added to control grain size aluminium can control austenite grain growth in reheated steels.
Carbon (C) is the most important element in the majority of steel, affecting hardness and strength by heat treatment. The ductility and weldability decreases with increasing carbon content.
Cobalt (Co) can be used up to 10% content in some high speed steels. It becomes radioactive when exposed to nuclear radiation therefore for radioactive applications it must not be present in steel.
Copper (Cu) can be present in stainless steels for precipitation hardening properties. Used in "weathering" steels.
Chromium (Cr) is added to steel to increase corrosion and oxidation resistance. It also increases hardenability and combined with high carbon improves wear and abrasion resistance
Manganese (Mn) contributes to strength and hardness with variable carbon content. It is an austenite forming element in some steels and has a significant effect on hardenability.
Molybdenum (Mo) is added to nickel chrome alloy steels to improve strength and hardness and also in chromium nickel austenitic steels it improves corrosion resistance. Molybdenum is used in some high speed steel grades.
Nickel (Ni) is an important element which increases hardenability, tensile and impact values of steels. Added to high chromium stainless steels in amounts of over 8% it produces austenitic structures which gives high temperature strengths and resistance to oxidation and corrosion.
Niobium (Nb) stabilises carbon in the same way as titanium and strengthens steels for high temperature service.
Nitrogen (N) is added to stainless steel to improve the austenitic stability with increased yield strength.
Phosphorous (P) is normally controlled to low levels but higher phosphorous can be used to improve machineability.
Silicon (Si) is a principal deoxidiser in steel, used in silicon manganese, corrosion and heat resisting steels.
Sulphur (S) is often added to improve machineability, but does decrease ductility and notch impact toughness.
Tungsten (W) is a major element in high speed and some tool steels. In the heat treated condition it retains hardness at elevated temperatures and is particularly useful for cutting tools.
Vanadium (V) helps improve fatigue stress and wear resistance when used with other alloying elements.
Zirconium (Zr) can be added to high strength low alloy steels, affecting inclusion improvement, giving toughness and ductility in bending modes.
