Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water. Like other group 8 elements, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Consequently, radioactive nickel is the last element to be produced before the violent collapse of a supernova scatters precursor radionuclide of iron into space. Its abundance in rocky planets like Earth is due to its abundant production by fusion in high-mass stars, where the production of nickel-56 (which decays to the most common isotope of iron) is the last nuclear fusion reaction that is exothermic. It is the fourth most common element in the Earth's crust. It is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is a metal in the first transition series. Iron is a chemical element with the symbol Fe (from Latin: ferrum) and atomic number 26. Passivation only occurs if the proportion of chromium is high enough and oxygen is present. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and blocks corrosion from spreading into the metal's internal structure, and due to the similar size of the steel and oxide ions they bond very strongly and remain attached to the surface. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide, and due to the greater volume of the iron oxide this tends to flake and fall away. Unprotected carbon steel rusts readily when exposed to air and moisture. Stainless steel differs from carbon steel by the amount of chromium present. Stainless steel is used where both the properties of steel and corrosion resistance are required. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel does not readily corrode, rust or stain with water as ordinary steel does, but despite the name it is not fully stain-proof, most notably under low-oxygen, high-salinity, or poor-circulation environments. In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is a steel alloy with a minimum of 10.5% chromium content by mass. In recent times, EAF steelmaking technology has evolved closer to oxygen steelmaking as more chemical energy is introduced into the process. Oxygen steelmaking is fuelled predominantly by the exothermic nature of the reactions inside the vessel where as in EAF steelmaking, electrical energy is used to melt the solid scrap and/or DRI materials. There are two major processes for making steel, namely basic oxygen steelmaking which has liquid pig-iron from the blast furnace and scrap steel as the main feed materials, and electric arc furnace (EAF) steelmaking which uses scrap steel or direct reduced iron (DRI) as the main feed materials. Limiting dissolved gases such as nitrogen and oxygen, and entrained impurities (termed "inclusions") in the steel is also important to ensure the quality of the products cast from the liquid steel. In steelmaking, impurities such as nitrogen, silicon, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce different grades of steel. Steelmaking is the process for producing steel from iron and ferrous scrap.
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