Figure below shows the microstructure of different types of

Figure below shows the microstructure of different types of cast irons. Figure Microstructure of a cast iron What are they? Label the graphite in the microstructure. (Chose from A1 to A8) Based on the Structure, discuss the microstructures, mechanical properties and applications of gray cast iron and ductile cast iron.

Solution

Answer-1

(a) Malleable cast iron

A₁ = Graphite A₂ = Ferrite

(b) White cast iron

A₃ = Pearlite A₄ = Cementite

(c) Gray cast iron

A₅ = Graphite flakes A₆ = Ferrite

(d) Nodular cast iron

A₇ = Graphite nodules A₈ = Ferrite

Answer-2

Gray cast iron has graphitic microstructure and has a chemical composition of 2.5% - 4% carbon and 1% - 3% of Silicon and remaining iron. the size and shape of graphite flakes present in the microstructure of gray cast iron affect the mechanical properties. Tensile strenght and shock resistance Gray cast iron is less than the tensile strenght and shock resistance of steel. Gray cast iron is used in the manufacturing of Engine cylinder blocks, flywheel, gearbox cases etc.

Ductile cast iron is also known as spheroidal graphite cast iron. A very tiny nodules of graphite is found in ductile cast iron which is responsible for the spongy behaviors. Ductile cast iron has a chemical composition of 3% - 4% carbon, 0.4% of Mn and 0.1 of P and 1.0% of Ni. Ductile cast iron have the maximum ductility than other form of cast iron and low hardness. Ductile cast iron is used in the manufacturing of Gears, camshafts and crankshafts.