A quick introduction to grey iron castings

A type of cast iron, the name of grey iron is derived not only from the basic elemental composition of the material, but also from the coloring of fractured surfaces of the metal. This method is commonly used to distinguish between iron alloys though the molecular structure is also very different. Even within the category of grey casting there are several different types, such as ductile valve casting and spheroidal graphite cast iron, based on molecular composition and internal structure. Even minor differences lead to considerable variation of the many desirable features of grey iron such as low melting point, resistance to deformation and wear, energy dissipation and thermal conductivity.

Making up 5% of the Earth's crust and 35% of its total mass, iron is the most copious element on the planet. Rarely found in pure form, however, iron oxides or iron ores must be mined and processed to produce grey iron. Metalworkers achieve this through the use of a special type of blast furnace known as a cupola or an electric induction furnace. Though several standardized grading systems are available, the general composition of grey cast iron gear is 95% iron by weight with an additional 2.1 to 4% being carbon and 1 to 3% silicon. Manganese and other impurities are also commonly found in or added to molten iron as needed for the diminishing or enhancement of specific properties or casting manufacturers. Sulfur, for example, is commonly introduced to the molten metal in order to increase hardness which is otherwise low in most cast iron components. Specific to grey cast iron is a high amount of silicone which is responsible for the production of graphite when the alloyed materials are heated. The deflection of this graphitic microstructure is what gives the metal its grey appearance. Though most often in flake form, ductile cast iron production slows down the growth of graphite and allows the carbon to separate as spheroidal graphite particles instead. Both the timing and temperature play important roles in the structural disposition of grey iron castings.

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