HISTORICAL NOTE

Containing more than 5% of alloying metals, "high-alloy" steels usually have Steel and Steel Alloys special properties such as resistance to corrosion and oxidation, or high luster. By the mid-1800s, wrought iron and ently developed by William Kelly in Such steels are used in cutting tools, jet- cast iron were the most commonly used Kentucky in the United States. Kelly engine parts, tableware, chemical equip- materials for technology and industry. received an American patent for his ment, and cooking utensils. Though wrought and cast iron were process in 1857, while Bessemer had The first patented steel alloy—tung- stronger than other metals, neither was received an English patent a year earlier. sten added to tool steels—was patented strong or versatile enough for the many Shortly after the introduction of the in 1861. By 1870, chromium-steel alloys, new structures, machines, or tools re- Bessemer process, German-born English used in tool-making and construction, quired for the world's growing industrial metallurgists William and Friedrich Sie- had begun to appear in France, England, base. mens developed a regenerative-heating and the United States. Patented in 1883 in It had been known for centuries that process, the "open hearth" process, England, Sir Robert Hadfield's excep- alloying iron with small amounts of car- which preheated air through the furnace tionally tough steel alloy made with 1.2% bon (between 0.3 and 1%) made the before blowing it back into the combus- carbon and 12.5% manganese, saw wide- resulting metal—steel—very hard and tion chamber, thereby greatly increasing spread use in excavating equipment, rail- strong, if the metal were cooled rapidly the temperature. From 1857 to 1865, the road tires, and railroad crossings; Had- from a high temperature by, for example, Siemens brothers used their furnace to field also developed silicon-steel alloys quenching in water. Steel was recognized fuse pig iron and iron ore; the oxygen in which, after 1900, were put into wide- as a superior metal for weapons and iron ore burns away the excess carbon in spread use in electrical machinery. tools that needed to be strong, resilient, pig iron, resulting in a far superior alloy. In the late 1880s, nickel steels were and capable of retaining a keen cutting Concurrently, in France, Emile and used by France, the United States, and edge. Unfortunately, until the mid-19th Pierre Martin found that they could make England as an extremely tough metal for century, making steel was a costly and steel by melting wrought-iron scrap with armor plate, projectiles, and gun barrels. time-consuming process. As described in a good grade of pig iron in a regenerative By 1891, France had improved its armor last month's Historical Note, early efforts furnace similar to that developed by plate by adding chromium to the alloy. included a cementation process (sealing Siemens. When combined, the resulting At the turn of the century, the invention wrought iron with charcoal in clay con- Siemens-Martin process uses both ore of the automobile also created a huge tainers and then heating it for days), a and scrap with pig iron in an open-hearth demand for specific alloys for body con- layering process (heating alternating lay- furnace. struction, crankshafts, gears, and springs. ers of high- and low-carbon iron, then Unfortunately, these processes did Another important alloy with superior working the mass together), and a cru- nothing to eliminate the troublesome resistance to corrosion, stainless steel, cible process (melting layered or cement- phosphorous content in iron—which is was developed in 1912 in Great Britain. ed steel in a crucible to increase the especially prevalent in English ores. In Containing over 5% chromium, stainless homogeneity of the metal). In the mid- 1879, English inventors Sidney Thomas steels were first used in cutlery. In the 1800s, two new methods—the Bessemer and Percy Gilchrist discovered that lining same year, Germany introduced im- process and the open-hearth process— the hearth with a basic slag, such as lime, proved stainless steel with chromium- revolutionized steelmaking and made would eliminate nearly all phosphorus nickel additives. steel available in sufficient quantities for and sulfur contaminants in the steel. Steel is the most widely used of all an explosion in industrialization, bridge These developments, all occurring within metals—in everything from' high-rise building, and railroad construction. a decade or two of one another, opened building construction to automobiles, The first major breakthrough occurred the door to an enormous boom in indus- from household appliances to flatware. in England in 1856, when Henry Bes- trialization in the late 19th century. Over the last 40 years, the steel industry semer worked on improving metal cast Steels have been created in thousands has undergone rapid change with the for cannon. Knowing that impurities are of different chemical compositions with emergence of such new technologies as removed from iron by oxidation, he real- extremely versatile material properties. the development of continuous casting ized that the necessary oxygen could Steels such as tungsten-carbide alloy and the use of computerized controls for come from the air itself if he blasted air steels can be made hard enough that only blast furnaces, hot strip mills, and other through molten pig iron. When Bessemer a diamond can scratch them, or—in the production units. tried this idea, he found that it not only case of some low-carbon steels—soft The steel industry in some countries removed the impurities (such as carbon, enough to bend easily by hand. Other has suffered, however, through contin- silicon, and manganese), but also heated elements added to steel can create alloys ued reliance on outdated manufacturing the metal to a much higher temperature, with such special properties as superior methods. Alternative materials, such as rather than cooling and hardening it, as strength, durability, hardness, or corro- plastics, ceramics, and ceramic-metal he had expected. The extra heat came sion resistance. composites, have replaced components from energy released by the oxidation of Low-alloy, or "mild," steels contain a traditionally made of steel. But new steel the impurities. combined total of less than 5% of such alloys continue to be developed to meet Such a high temperature can be main- metal additives as nickel, chromium, specific technological needs such as tained long enough to burn away all con- molybdenum, titanium, vanadium, tung- space construction, defense, and high- taminants, leaving pure molten iron to sten, or niobium. Mild steels are excep- speed transportation. tionally strong and are used in machine which carbon and other alloying ele- KEVIN J. ANDERSON ments can be reintroduced to forge the parts, structural girders for bridges and best steel. The same idea was independ- buildings, and aircraft landing gear.

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