Gray iron or grey iron was the original "cast iron". It is relatively easy and inexpensive to make. Compared to the more modern engineered irons, gray iron has a lower tensile strength and lower ductility. In other words, it will fail more easily, and its mode of failure will be sudden fracture (it will not bend). Used for housings where tensile strength is non critical, engine blocks, pump housings, valve bodies, electrical boxes and decorative castings. Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition). ... It has been suggested that this article or section be merged into Strength of materials. ...
Iron is notable for being the final element produced by stellar nucleosynthesis, and thus the heaviest element which does not require a supernova or similarly cataclysmic event for its formation.
A newer variant of greyiron, referred to as 'ductile iron' is specially treated with trace amounts of magnesium to alter the shape of graphite to sheroids, or nodules, vastly increasing the toughness and strength of the material.
A class of non-heme iron proteins is responsible for a wide range of functions within several life forms, such as enzymes methane monooxygenase (oxidizes methane to methanol), ribonucleotide reductase (reduces ribose to deoxyribose; DNA biosynthesis), hemerythrins (oxygen transport and fixation in marine invertebrates) and purple acid phosphatase (hydrolysis of phosphate esters).
It is made by remelting pig iron, often along with substantial quantities of scrap iron and scrap steel, and taking various steps to remove undesirable contaminants such as phosphorus and sulfur, which weaken the material.
White iron is too brittle for most uses, but with good hardness and abrasion resistance and relatively low cost, it finds use in such applications as balls for rolling-element bearings, the wear surfaces (impeller and volute) of slurry pumps and the teeth of a backhoe's digging bucket.
White cast iron can also be made by using a high percentage of chromium in the iron; Cr is a stong carbide-forming element, so at high enough percentages of chrome, the precipitation of graphite out of the iron is suppressed.
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