Introduction
Gray cast iron is one of the most widely used ferrous alloys for various mechanical components owing to its desirable combination of mechanical efficiency at the low cost. It consists of the combination of pearlite, ferrite and graphite.As an iron-carbon alloy, the distribution of these constituents within the microstructure greatly influence the properties of the material.
Classification of Gray Cast Iron
Gray iron can be classified according to its microstructure, as follows:
• White Iron
It mainly consists of pearlite, predominantly eutectic, with a small amount of cementite. The matrix is nearly 100% pearlite, with a distributed small amount of cementite. This elemental combination affects the physical characteristics of the iron such as its hardness and wear resistance.
• Gray Iron
It consists of a ferritic matrix pock-marked with alternating flakes of flake graphite and globular graphite.The degree of graphitization depends upon the rate of solidification. The slower the process, the more box-like shape the graphite takes compared to the faster rate of solidification where the graphite takes a more spherical shape.
• Malleable Iron
It consists of an interlinked network of large, irregularly shaped globules of cementite, a matrix of ferrite and sometimes pearlite and graphite.The large globules of cementite are formed as a result of an annealing process where the matrix is slowly cooled and a high carbon content, typically above 1%.
• Ductile Iron
It consists of nodular graphite, mainly ferlite and and small or negligible amounts of pearite, together with a cementite constituent. Unlike gray iron and malleable iron, ductile iron contains a substantial content of magnesium (Mg) or cerium (Ce). This element acts as a nodulizer which allows the graphite to take the nodular shape.
Conclusion
Gray cast iron is one of the most widely used ferrous alloys for various mechanical components due to its desirable combination of mechanical efficiency and low costs. It can be classified according to its microstructure: white iron, gray iron, malleable iron, and ductile iron. Each type of gray cast iron exhibits unique physical characteristics and yields different mechanical performances. Gray cast iron, however, is notorious for being prone to cracking and degradation under certain conditions. It is important to understand the different types of gray cast iron and to select the appropriate material for your particular application in order to optimize its usefulness and efficiency.
