Influence of various constituents or elements in Steel.

The properties of steel are dependent primarily on the carbon content and to a large extent upon silicon, manganese, Sulphur and Phosphorus. Therefore, an understanding of the effect of each of the chemical elements on the properties of steel is necessary in the selection of steel for definite purposes.

Carbon Increases strength, elasticity (determined by yield point) and hardness, and lowers the ductility (characterized by elongation) and Impact strength. An Important fact is that 0.3 per cent carbon , the steel can be hardened by heating and quenching in water or oil.

Silicon in the finished steel usually ranges from 0.05 to 0.30 per cent. Silicon is put in carbon steels to prevent them from becoming porous. It acts as a very good deoxidizer and removes the gases and oxides, prevents blowholes, and thereby makes the steel tougher and harder. 

Manganese also serves as a valuable deoxidizing and purifying agent. Manganese also combines with Sulphur and thereby decreases the harmful effect of this element remaining in the steel. When uses in ordinary low carbon steels, manganese makes the metal ductile and of good bending qualities. The manganese content of carbon steel is usually less than 1.00 per cent and commonly ranges from 0.30 to 1.00 per cent.

Sulphur occurs in steel either as iron-sulphide or as manganese sulphide. Iron sulphide, because of its low melting point, produces red - shortness, i.e, increased brittleness at elevated temperatures, whilst manganese sulphide does not affect so much. Therefore, manganese sulphide is less objectionable in steel than iron sulphide. The presence of a substantial amount of Sulphur ( Sulphur Inclusion ) in steel unfavorably affects other properties of steel, e.g., tensile strength, yield point, fatigue limit , etc., and decreases its corrosion resistance.

Phosphorous imparts cold-shortness, i.e., high brittleness at normal and especially low temperatures. It increases the tensile strength but at the same type reduces the impact strength and the ductility. At a phosphorous content of slightly over 0.2 per cent the impact strength has a zero value. The embrittlement effect of phosphorus increases with an increase in the carbon content of steel. The sum of carbon and phosphorus usually does not exceed 0.25 per cent. Tool steels of the best quality do not contain more than 0.2 per cent.

The content of  Sulphur and Phosphorous is strictly limited because of their harmful effect on quality of the steel.