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Basic steel is produced in furnaces lined with low pH refractories. Steel is mostly iron with added alloying materials like carbon, manganese, chromium, and tungsten. The Bessemer process was used to remove impurities from molten iron, while the LD process uses pure oxygen. Basic refractories are more effective at removing impurities than acid refractories.
Base steel refers to steel produced in a furnace lined with a basic, rather than acidic, substance. The vast majority of steel produced in industrial societies is made this way. Insulating the furnace structure from furnace heat is a central challenge in steelmaking. Removing impurities from iron mixes is another challenge in steelmaking. Since the 1950s, modern methods have been used to insulate kiln walls with low pH or low acid substances.
Steel is mostly iron, but contains a small amount of other elements in the mix. This is desired because it can improve the material properties of the substance, namely the hardness. Carbon is the most common element added to steel, but manganese, chromium and tungsten are also used. These additions to the base iron are called alloying materials. Steel is much stronger than pure aluminum or iron alone, but it has to be manufactured in particular ways.
During the Second Industrial Revolution, the Bessemer process for mass steel production was discovered and widely applied. The major innovation in the process was the ability to remove impurities from molten iron by blowing air into it. Excess silicon, manganese and carbon are oxidized by the air and can therefore leach out of the substance.
To prevent the furnace structure from melting during steelmaking, which can involve very high temperatures, the container is lined with a refractory material. Refractories are substances that retain their physical properties at temperatures above 1,000 degrees Fahrenheit (537.77 degrees Celsius). Low pH refractories are used in basic steelmaking. In the Bessemer process, the mineral dolomite was a common low pH refractory used to line the container during the production of the base steel.
In 1952, a new steelmaking procedure known as the Linz-Donawitz process, or LD, was developed. Instead of using the Bessemer technique of blowing air through the molten iron, pure oxygen is used instead. Increased oxidation of iron allows for more effective removal of impurities. Modern furnaces can convert 350 tons of iron into steel in less than 40 minutes. The basic steelmaking LD process also produces less air pollution than the Bessemer process.
Basic refractories allow the removal of sulfur and phosphorus impurities more effectively than acid refractories. Once the oxygen is blown through the iron, the impurities exit as a gas or form a slag that floats to the surface. Oxidized carbon escapes as carbon monoxide or carbon dioxide. Other impurities form new compounds which separate from the mixture, leaving the base steel.
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