Steel is a metal alloy whose major component is iron, with carbon being the primary alloying material. Carbon acts as a binding agent, locking the otherwise easily-moved iron atoms into a rigid lattice. Varying the amount of carbon and its distribution in the alloy controls the qualities of the resulting steel. With the increased carbon, steel is harder and has a much higher tensile strength than iron, but is also more brittle. One classical definition is that steels are iron-carbon alloys with up to 2.1 percent carbon.Presently there are several classes of steels in which carbon is replaced with other alloying materials, and carbon, if present, is undesired. A more recent definition is that steels are iron-based alloys that can be plastically formed (pounded, rolled, etc.).
1 Iron and steel
Iron, like most metals, is not found in the Earth's crust in a native state. Since the rise of the cyanobacteria and their dumping of oxygen into the atmosphere, iron can be found only in oxide form, typically Fe2O3— the form of iron oxide found as the mineral hematiteHematite ( AE) or haematite ( BE) is the mineral form of Iron (III) oxide, (FeO), one of several iron oxides. The ore sometimes contains slight amounts of titanium. When shaped into ornaments it is often called black diamond. Rouge is a powderized form of. Iron oxide is a soft sandstoneSandstone is an arenaceous sedimentary rock composed mainly of feldspar and quartz and varies in colour (in a similar way to sand), through grey, yellow, red, and white. Since sandstones often form highly visible cliffs and other rock formations, certain-like material with limited uses on its own. Iron is extracted from oreAn ore is a mineral deposit containing a metal or other valuable resource in economically viable concentrations. Usually, it is used in the context of a mineral deposit from which it is economical to extract its metallic component. Ores are mined. Ore bod by removing the oxygen by combining it with a preferred chemical partner such as carbon. This process, known as smeltingChemical reduction or smelting is a form of extractive metallurgy. The main use of smelting is to produce iron and steel. It makes use of a chemical reducing agent such as carbon ( coke, or in earlier times charcoal) to change the oxidation state of the m, was first applied to metals with lower meltingPhysics In physics, melting is the process of heating a solid substance to a point (called melting point) where it turns liquid. An object, which has melted, is molten . Freezing is the opposite of melting. It is the process of turning a liquid to a solid points. CopperCopper is a chemical element in the periodic table that has the symbol Cu and atomic number 29. Notable characteristics Copper is a reddish-coloured metal, with a high electrical and thermal conductivity (among pure metals at room temperature, only silver and tinThe word tin is often used to mean a can, even if it does not contain any tin metal. Tin is a chemical element in the periodic table that has the symbol Sn ( L. Stannum and atomic number 50. This silvery, malleable poor metal that is not easily oxidized i both melt at just over 1000 °CThe degree Celsius (°C) is a unit of temperature named after the Swedish astronomer Anders Celsius ( 1701 1744), who first proposed it in 1742. The Celsius temperature scale was designed so that the freezing point of water is 0 degrees, and the boiling po, temperatures that could be reached with ancient methods that have been in use for at least 6000 years (since the Bronze Age). Since the oxidation rate itself increases rapidly beyond 800 °C, it is important that smelting take place in a fairly oxygen-free environment.
This heap of iron ore pellets will be used in steel production.
Another important part of making quality steel is that the carbon-iron matrix can form into a number of different structures, or allotropes, some stronger than others. In its natural form steel will tend to form the body-centered cubic ferrite form, which is fairly soft. At about 910 °C ferrite will transition to the denser, face-centered cubic austenite phase, in which the carbon has considerably higher solubility but is otherwise structurally similar. While cooling, however, the mixture will take on one of several forms as it attempts to revert to the ferrite phase. One complex structure, known as cementite, forms when the over-saturated carbon precipitates out of the austenite to form a carbon-ferrite mixture. Cementite often forms in regions of higher carbon content while other areas revert to ferrite around it, leading to a patterned layering known as perlite due to its pearl-like microscopic structure, or the similar but unpatterned bainite. Another important allotrope is martensite, a complex mixture of austenite and ferrite with about four to five times the strength of ferrite.
The key to producing strong steel is to lock in the crystal structure in a strong state before it can revert to a softer one while cooling. This is accomplished by quenching the hot metal in water or oil, cooling it so rapidly that the transformation to ferrite or perlite does not have time to take place. However this process also introduces tiny cracks and imperfections into the metal structure, allowing the metal to break along those points. After quenching, the metal is re-heated to a lower temperature and "worked" (via hammering or rolling) to force the cracks to close and produce a much stronger metal. This process is known as tempering , source of the term tempered steel.
Other materials are often added to the iron-carbon mixture to tailor the resulting properties. Nickel in steel adds to the tensile strength, chromium increases the hardness, and vanadium also increases the hardness while reducing the effects of metal fatigue. On the other hand sulfur and phosphorus create gaps in the structure that leads to it being easily broken, so these commonly found elements must be removed from the ore during processing.
Generally the production of steel proceeds in several steps. First the iron is smelted from the ore using a variety of methods, removing impurities in the process. It is then re-processed in order to add the correct amount of carbon and other alloying materials. Finally the mixture is cooled in a way to lock in the required structure, and then worked to remove mechanical defects. In modern steelmaking these processes are often combined, with ore going in one end of the assembly line and finished steel coming out the other.
