Gray Iron

Gray Iron Gray iron (also called grey iron) is a type of cast iron that has a graphitic microstructure. It is named after the grey color of the fracture it forms, which is due to the presence of graphite. It is the most common cast iron and the most widely used cast material. Gray iron is one of the oldest cast ferrous products. In spite of competition from newer materials and their energetic promotion, gray iron is still used for those applications where its properties have proved it to be the most suitable material available. MacKenziein his 1944 Howe memorial lecture referred to gray cast iron as ‘steel plus graphite’. Although this simple definition still applies, the properties of gray iron are affected by the amount of graphite present as well as the shape, size, and distribution of the graphite flakes. Composition and effect of composition on properties  Gray iron is commercially produced over a wide range of compositions. The range of compositions which one may find in gray iron castings is given below. Carbon (C) – 2.75 % to 4.00 % Silicon (Si) – 0.75 % to 3.00 % Manganese (Mn) – 0.25 % to 1.50 % Sulfur (S) – 0.02 % to 0.20 % Phosphorus (P) – 0.02 % to 0.75 % One or more of the alloying elements namely molybdenum, copper, nickel, vanadium, titanium, tin, antimony, and chromium may be present in varying amounts. Nitrogen is generally present in the range of 20 to 92 ppm. Si is important for the gray iron since it is a graphite stabilizing element in cast iron, which means it helps the iron to produce graphite instead of iron carbides. Another factor affecting graphitization is the solidification rate. The slower is the rate, the greater is the tendency for graphite...