Steel Production
For more than a century, steel has been the most important metal in industry. By the turn of the twentieth century, steel had replaced its parent metal, iron, as the primary metal for heavy industries such as construction, railroads, and, later, the automobile and airline industries. The invention of Henry Bessemer's converter in 1856 was the true beginning of steel as a commercially viable material.
Steel is a malleable alloy of iron with carbon and other trace elements. It is made by carefully removing excess amounts of carbon from pig iron, which has about four or five percent carbon content, and adding the other trace elements. Carbon steel contains less than one per cent carbon. Steel has been known for about two thousand years. Even earlier, smiths worked meteoric iron, which usually contains a large portion of nickel and resembles stainless steel in its composition. In Sri Lanka, in the seventh to the eleventh centuries, for example, they produced high-quality steel using furnaces that used monsoon winds fan flames for the furnace. These furnaces might have produced the legendary Damascus swords. There is evidence of co-fusion production of steel in Merv (located in Western Asia) in the ninth century.
However, steel was never produced in large quantities until the late 1800s. New methods in the manufacture and use of iron during the 1700s and early 1800s made iron more practical and affordable than ever, which helped keep steel in the background for more than a century. Blast furnaces and rolling mills were producing wrought and cast iron in affordable quantities. Both the Industrial Revolution and the architectural revolution that utilized load-bearing iron frames, were founded on the iron industry.
Bessemer's converter, or pneumatic conversion process, was the first efficient method of removing carbon from pig iron in amounts necessary for mass production of steel. The method applied blasts of cool air directly to the molten iron for rapid carbon burn-off. The same process credited to Bessemer was actually invented about five years earlier by the American William Kelly. Kelly chose to keep his invention secret rather than patent it. Bessemer, unaware of Kelly's work, made the same discovery and gained the commercial recognition by going public with it right away. Later, in 1875, Englishman Sidney Gilchrist Thomas took the Bessemer process further by introducing burned limestone to remove the phosphorus from iron ore. Bessemer had used phosphorous-free ores. Thomas' improvement widened the range of ores suitable for steel production.
Bernard Lauth of Pittsburgh inadvertently discovered cold rolling when a pair of tongs was reshaped after an accidental trip between the rollers. After developing the process, he opened the first cold-rolling mill in 1860. Lauth's method processed the metal by rolling iron and steel at room temperature at high speed. Since hot rolled steel required additional processing, the cold rolled method soon replaced it.
The next improvement to steel production was the open-hearth process. The open hearth used regenerated heat for a more efficiently sustained heat. The process is called the Siemens-Martin Process. Sir Charles William Siemens invented the process in 1856. The following year, Pierre-Émile Martin made improvements in the arrangement of Siemens' heat-capture chambers and also introduced scrap steel to further cheapen the steel production process.
In 1878, Siemens developed an electric arc furnace which produced an iron-melting temperature with an electric current. In 1898, Paul-Louis-Touussaint Heroult (1863-1914) incorporated the electric arc for commercial steel production.
The Siemens-Martin Process surpassed the Bessemer Process as the leading steelmaking process by the beginning of the twentieth century. It remained unchallenged until the 1950s and the development of the basic oxygen process. This process is also known as the L-D process, for Lin-Donawitz, the Austrian town where it was first developed. The basic oxygen process is similar to the Bessemer conversion process except that air is blown in from above instead of below and at supersonic speed. Molten iron is poured into the furnace to melt scrap steel faster. By 1969 the basic oxygen process had become the leading steelmaking process in the United States. In the 1980s, bottom-stirred furnaces were introduced, which reduced the carbon levels in steel, and became industry standards.
Steel is produced in units called ingots which are quenched, or rapidly cooled by dipping them in water or oil. The ingots are then delivered to semi-finishing mills where they are further reduced to blooms (rolled ingots), bars, and billets (short bars). The steel is then sent on to finishing mills where it is shaped to fit its intended use, as plates, sheets, wire, pipe or more specialized shapes. Some of the finished steel is delivered to warehouses or construction sites, while other forms are sent to assembly plants to go into automobiles, washing machines, trains, airplanes and a multitude of other products.
Steel is often alloyed with other metals to combine the qualities of both metals. Metals such as chromium, tungsten, nickel and vanadium are added to increase hardness, resiliency, durability and resistance to heat and corrosion under various conditions. Stainless steel has chromium as its chief alloy. Chromium resists rust and renders the metal more visually attractive.
Steel and its related industries has become central to the economies of many regions. In the United States, production is centered around the Great Lakes and the Ohio River valley. These areas are strategically situated to take advantage of water and rail transportation routes, which allow raw materials to be brought in and finished products to be shipped out. The coal reserves of the Appalachian mountains and central Illinois are near by to provide fuel for the furnaces. Finally, the steel mills require large amounts of water which is provided by the lake or river. Other world steel production areas are Japan, the Ruhr Valley of Germany, central England and the Donetsk Valley of Russia.
International competition has caused a decline in steel production in some areas that were once major industrial centers. Many mills closed during the 1970s due to inefficient employment structures and failure to modernize older plants, causing hardships for many communities in which the mills were once their lifeblood. However, several new methods of steel production were in development in the 1990s. AmericanÕs developed direct steel-making, which reduces steelmaking to a one-step process and eliminates the need for coke. Untreated coal, iron ore and scrap metal are mixed together and injected with oxygen, treated, and purified. The coalÕs function is two-fold. It works as a heat-generating fuel and as a reducing agent. When the molten metal is ready, it is poured into a ladle and further refined into partially finished products like sheets. Direct steel-making cuts costs and also releases fewer toxins into the atmosphere. With such innovations, steel production will remain viable in the United States for the foreseeable future.
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