Iron is a metal as well as a chemical element. As an element it is represented by the symbol Fe and atomic number 26, belonging to group 8 and period 4. As a chemical element its placing on the periodic table classifies it as a transitional metal. Iron together with its alloys is the most widely used metal and the most abundant ferromagnetic materials in daily use. The metal appears lustrous and silver-grey in color but forms a brown coating of rust (ferric oxide) when exposed to air as a result of oxidation. Single crystals of iron in pure form are generally soft but they will strengthen when small amounts of impurities, for instance carbon, are added. When iron is alloyed with other metals and carbon in small amounts produces steel, which can be more than a thousand times harder than iron. Among all iron meteorites and in planetary metal cores like earth, iron forms the most abundant metal as well as in the core of red giants. In its pure form iron is a metal but because it readily oxidizes when exposed to moisture and oxygen, it is rarely found in its pure form above earth surfaces. Pure metal iron can be extracted from its ores such as iron ore hematite by removing oxygen at high temperature in a process known as chemical reduction.
Cast iron is a term that commonly refers to grey iron. Generally, cast iron is a blanket term identifying a large group of ferrous alloys that solidify with eutectic. In order to identify an alloy, the color of its fractured surface is used to know which alloy it is. For instance, white cast iron is named so because of its white fractured surface, which is brought by its carbide impurities that allow cracks to go straight through. Grey cast iron as well is named so because of its grey surface when fractured, brought about due to the deflection of passing crack by graphitic flakes, which, as the material breaks, initiate countless new cracks. Iron makes up the biggest percentage by weight of the alloy material, while carbon and silicon make up the main alloying elements. By weight, cast irons contain 2.1 to 4 percent carbon. Cast iron is usually brittle with the exception of malleable cast irons. Cast irons are now popular engineering materials with a wide range of applications because of their low melting point, good machinability, resistance to wear and deformation, and good fluidity. Cast iron is also resistant to oxidation effects of rusting.
Iron is a pure metal, existing as a single element whereas cast iron is alloyed iron which is iron alloyed with elements such as carbon or silicon.
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