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Chemical Composition of Cast Iron in China


If you remember waking up to hash browns sizzling in a heavy black pan on your grandmother's stove, or have ever enjoyed tender bits of meat and gravy out of an old-fashioned Dutch oven, chances are good that you have enjoyed the benefits of cast iron. Cast iron is a hard, albeit, brittle iron alloy commonly used to make cookware. In times past, it was also used in architecture to make gutters, drainpipes and decorations. It is still used today to construct manhole covers. Most cast irons are composed of six primary elements.

Iron is the primary element in cast iron and is responsible for its hard composition and great weight. Hematite and magnetite are common iron ores, and are heated together with coke, a carbon-based substance, and limestone to produce the chemical reaction that separates the iron from the ore. Gray, ductile, compacted graphite, malleable and white iron alloys are used to make varieties of cast iron, each with unique properties.

Carbon is the second most abundant element in cast iron, and is largely what differentiates cast iron from steel. Steel is also an iron-carbon alloy, but contains less than 2 percent carbon, while cast iron contains 2 percent to 4 percent. This abundance of carbon lowers the boiling point of the alloy, which is part of what makes this alloy good for making castings.

Silicon is a natural component of all cast irons, but is especially prevalent in certain types of high-alloy cast irons. When additional silicon is added, the resulting alloy is called high-silicon (Silal) cast iron. While normal cast iron can have silicon concentrations up to three percent, high-silicon irons are from five to 18 percent silicon, and exhibit a greater resistance to heat and acid corrosion.

Manganese, Sulfur and Phosphorous
Manganese, sulfur and phosphorous also occur in cast iron in small concentrations. Manganese is a metal harder than iron and contributes to the strength of alloy. It reacts with sulfur to create a compound that causes iron to form graphite, which arranges in different configurations to give different types of cast iron different properties. Phosphorous, like carbon, lowers the melting point of the alloy and helps to make it highly fluid when liquefied.

Other Elements
Small amounts of other elements affect how cast iron behaves. For example, adding chromium and nickle creates high-alloy cast irons, which are more resistant to heat, corrosion and wear. Bismuth and tellurium aid in the production of malleable iron, and trace amounts of magnesium cause the graphite in the iron to form into spheres, which creates ductile iron.





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