Nodularity Measurement

Carbon in the form of graphite is often used as an additive in the production of cast iron, amounting to 2 to 4 percent by weight or 6 to 10 percent by volume in typical castings. The microstructure of graphite within cast iron significantly affects the mechanical properties of the casting. When graphite takes the form of thin flakes the result is flake cast iron, which is hard and brittle. When graphite arranges itself as spherical nodules the result is ductile cast iron, which is softer and more malleable than flake cast iron. The relative high strength and toughness of ductile cast iron provides advantages in many structural applications including automotive crankshafts, pistons and cylinder heads.

Both flake cast and ductile cast iron are made by mixing carbon, silicon, and other additives into molten iron. Part of the mixing of elements is often done in the final mould. If the mixing is non-uniform or the casting process is not optimal, it is possible to make a casting with nodularity variations or with inclusions of flake cast iron present in the ductile cast iron. Since the type of result will significantly change the mechanical properties of the metal, foundries should check the uniformity of ductile cast iron. It is important to ensure that the distribution of graphite in the die casting is uniform and also that the graphite inclusions are present in the correct form: nodules rather than flakes.

STEMart uses various methods to check the uniformity and form of the graphite in the die casting.

Test Methods

• Microscopic examination
• Voltage check
• Tensile strength test
• Ultrasonic test

For more information about our nodularity measurement service, please contact us.