STEELS, ALLOY. It is almost as hard to draw a clear line of demarcation between "alloy steels" and "steels," as it is be tween "steel" and "iron." Diverse definitions have been set up legally for customs purposes, and commercially for statistical but more especially for pricing purposes. As may be seen in the arti cle IRON AND STEEL, iron is produced from its ores by commercial processes that leave a number of impurities, either alloyed with it or included as insoluble non-metallic particles. (A brief definition of an alloying element or compound is one that is more or less soluble in the major metal and which participates in physical or chemical reactions with changing temperatures and thus modifies the properties.) Carbon (in the chemical compound iron carbide, "cementite," is the principal alloying element in iron, pro portionately increasing its strength and hardness, especially after a correct heat treatment. Only a little iron carbide (carbon) is needed to convert iron into a hardenable steel, so a metallog rapher's definition of carbon steel might well be "a malleable alloy of iron and iron carbide" ("malleable" being inserted to dis tinguish plain carbon steel from cast iron, which is a non-malleable alloy of the same substances). The article IRON AND STEEL also explains the necessity for the presence of fractional percentages of the alloying metals manganese and silicon in commercial plain carbon steels, and it is difficult to say, as these incidental elements increase, just where a carbon steel stops and a manganese alloy steel (or more briefly, a "manganese steel") and a silicon steel start. Likewise "alloy steel practice" consists of far more than adding alloying metals to the liquid steel. The raw material is selected for a low content of deleterious impurities, the furnace practice is extended to include a careful refining period, additions are made to control the grain size (which, in turn, controls the toughness), all surface defects are cut out of ingots or billets—to mention some of the major differences. It may be said, then, that an "alloy steel is a carefully made steel with sufficient alloying metals added to it to modify usefully the properties of a plain car bon steel." The amount of alloy added is no distinction, it may range from very low (0.1o% vanadium) to very high (18% chromium or more).
The earliest alloy steels used those alloys then available; since the World War very useful steels have been developed with alloy ing metals that were formerly unavailable, even rarities. Chromi
um alloy steels were made commercially into hard grinding equip ment by the American, Baur, in 1865. They made their debut into structures in the main arch members of the Eads bridge across the Mississippi river at St. Louis (U.S.A.) ; they now enter many steels for machine parts, and the high chromium steels are corrosion and oxidation resistant (see RUSTLESS STEEL). Nickel, now the other most common constituent of alloy steels, was first incorporated in steels by the Frenchman, Marabeau ; the proper ties were described in 1889 by the Scot, James Riley. Nickel steel was adopted by the American Navy for armour-plate in 1891 ; it is said that the first application in the mass production industries was some armour-plate rolled into small bars for bicycle chains. Tungsten is the essential element in the air-hardening tool steel of the Englishman, Mushet (1871), the precursor of modern high speed tools. It is also used in magnets and in steels for high tern perature, high pressure service. (Molybdenum, its chemical cousin, was unavailable until large American deposits began pro ducing in Colorado about 1918. In addition to being a substitute for tungsten, it is now a most important element, in fractional percentages, in engineering alloy steels.) Manganese formed the first high alloy steel, i o% being added by the Englishman, Had field, in 1882 to form a very tough steel of unique properties, largely used in places like steam-shovel dipper teeth that must resist tremendous battering. Low manganese steels are the product of 1920-30, and are being substituted in many uses for the more expensive chromium and nickel steels. Silicon steels, especially useful for electrical transformers and other equipment, were devised in 1889 by Hadfield. Vanadium and chromium-vana dium steels were investigated in England by Arnold and J. Kent Smith at the turn of the century ; the latter, at Canton, Ohio, U.S.A., in 1907 made the first alloy steel by the open-hearth process for the Ford Motor Co., and this company pioneered the use of alloy steels in mass production. Copper, used in fractional percentage for atmospheric corrosion resistance, is a pre-World War product.