Iron

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Most types of steel contain about 1% carbon and 97% iron, with the remaining 2% consisting of trace elements and impurities.

Iron in Steel

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Iron 3D Structure

The first major expansion of iron occurred in the late second and early first millennium BC.

Iron Metallurgy

While iron is the most abundant element on Earth, most of this iron is concentrated in the inner and outer cores.

Earth's Crust

Fe • PDF Entry 00-006-0696

Iron

Iron is an essential element for all forms of life and is non-toxic.

Biology

While iron is the most abundant element on Earth, most of this iron is concentrated in the inner and outer cores. The fraction of iron that is in Earth's crust only amounts to about 5% of the overall mass of the crust and is thus only the fourth most abundant element in that layer (after oxygen, silicon, and aluminium). Most of the iron in the crust is combined with various other elements to form many iron minerals. An important class is the iron oxide minerals such as hematite (Fe2O3), magnetite (Fe3O4), and siderite (FeCO3), which are the major ores of iron. Many igneous rocks also contain the sulfide minerals pyrrhotite and pentlandite. During weathering, iron tends to leach from sulfide deposits as the sulfate and from silicate deposits as the bicarbonate. Both of these are oxidized in aqueous solution and precipitate in even mildly elevated pH as iron(III) oxide.

Development of iron metallurgy Iron is one of the elements undoubtedly known to the ancient world. It has been worked, or wrought, for millennia. However, iron artefacts of great age are much rarer than objects made of gold or silver due to the ease with which iron corrodes. The technology developed slowly, and even after the discovery of smelting it took many centuries for iron to replace bronze as the metal of choice for tools and weapons.

Persia - 300 BC

China - 500 BC

India - 2700 BC

Egypt - 3500 BC

Steel

Cast iron

Wrought iron

Meteoritic iron

Iron is pervasive, but particularly rich sources of dietary iron include red meat, oysters, beans, poultry, fish, leaf vegetables, watercress, tofu, and blackstrap molasses. Bread and breakfast cereals are sometimes specifically fortified with iron. Iron provided by dietary supplements is often found as iron(II) fumarate, although iron(II) sulfate is cheaper and is absorbed equally well. Elemental iron, or reduced iron, despite being absorbed at only one-third to two-thirds the efficiency (relative to iron sulfate), is often added to foods such as breakfast cereals or enriched wheat flour. Iron is most available to the body when chelated to amino acids and is also available for use as a common iron supplement. Glycine, the least expensive amino acid, is most often used to produce iron glycinate supplements. Iron deficiency is the most common nutritional deficiency in the world. When loss of iron is not adequately compensated by adequate dietary iron intake, a state of latent iron deficiency occurs, which over time leads to iron-deficiency anemia if left untreated, which is characterised by an insufficient number of red blood cells and an insufficient amount of hemoglobin. Most cases of iron-deficiency anemia are mild, but if not treated can cause problems like fast or irregular heartbeat, complications during pregnancy, and delayed growth in infants and children.

PDF Entry: 00-006-0696

When smelting raw iron with the goal of producing steel, metalworking companies will also use this opportunity to add carbon. Carbon distinguishes steel from raw iron, resulting in greater strength and durability. As the raw iron turns from solid to liquid, a specific amount of carbon is added. Metalworking companies will also feed limestone into the furnace when producing steel. Both carbon and limestone are essential to the steel-making process. Limestone is used to remove impurities, including flux, by helping the iron separate from the impurities. In the past, producing steel was a painstakingly tedious and difficult — as well as dangerous — process. Thanks to recent advancements in the field of metalworking, though, companies can produce significantly more steel in less time.

Adding Carbon or Limestone

All steel is made using raw iron. As previously mentioned, steel is characterized by the presence of iron and carbon. The ratio of these two elements varies depending on the specific type of steel being made. With that said, most types of steel contain about 1% carbon and 97% iron, with the remaining 2% consisting of trace elements and impurities. The amount of carbon will affect the steel’s physical properties. Generally speaking, the greater the concentration of carbon, the stronger and harder the steel is. With that said, adding too much carbon to steel can make it susceptible to rust and corrosion while also making it difficult to weld and form.

Why Steel Requires Raw Iron