Microstructure of gray iron
Gray iron has an easily recognizable microstructure, with a series of graphite flakes in a silicon-iron matrix.This microstructure is the source of all the qualities of gray iron castings, but it also makes for a brittle material that cannot sustain elongation. When you need deformation or higher loads, ductile iron castings become a better choice.
MICROSTRUCTURE OF GRAY IRON UNDER A 100X MICROSCOPE
Microstructure of ductile iron
The spheroidal microstructure gives the material its ductility. It is obtained my adding magnesium to the laddle.
AN EXAMPLE OF A DUCTILE IRON MICROSTRUCTURE UNDER A 100X MICROSCOPE.
Microstructure of Compacted Graphite Iron casting
CG iron castings obtain better results for thermal fatigue than gray iron in certain applications, mostly when the brittle nature of gray iron becomes an inconvenient. It can often outperform both ductile iron castings and gray iron castings in applications with thermal shock resistance required. Fast cooling ingot mold are a great example of application with such high thermal shock resistance requirement.
MICROSTRUCTURE OF COMPACTED GRAPHITE IRON UNDER A 100X MICROSCOPE