Effects of Alloying Elements

•Carbon•The basic metal, iron, is alloyed with carbon to make steel and has the effect of increasing the hardness and strength by heat treatment but the addition of carbon enables a wide range of hardness and strength.

•Manganese•Manganese is added to steel to improve hot working properties and increase strength, toughness and hardenability.

•Molybdenum

           Molybdenum, when added to chromium-nickel austenitic steels, improves resistance to pitting corrosion especially by chlorides and sulphur chemicals.
•When added to low alloy steels, molybdenum improves high temperature strengths and hardness.• When added to chromium steels it greatly diminishes the tendency of steels to decay in service or in heat treatment.

•Titanium•The main use of titanium as an alloying element in steel is for carbide stabilisation.
•It combines with carbon to form titanium carbides, which are quite stable and hard to dissolve in steel, this tends to minimise the occurrence of inter-granular corrosion.

•Phosphorus•Phosphorus is usually added with sulphur to improve machinability in low alloy steels, phosphorus, in small amounts, aids strength and corrosion resistance.• Phosphorus additions are known to increase the tendency to cracking during welding.

•Sulphur•When added in small amounts sulphur improves machinability .

•Silicon•Silicon is used as a deoxidising (killing) agent in the melting of steel, as a result, most steels contain a small percentage of silicon. Silicon contributes to hardening of the ferritic phase in steels and for this reason silicon killed steels are somewhat harder and stiffer than aluminium killed steels.