The expansion of iron and steel metallurgy was the dominant feature of nineteenth-century industry. The Industrial Revolution had introduced crucible steel, coke-burning blast furnaces, and the preheating of blast air. The harnessing of the steam engine to the blowers and the introduction of Neilson's "stoves" greatly increased the size and output of the blast furnace, but they had little effect on its fundamental processes. No further improvement was added to the blastfurnace process, which seemed nearly perfect, until in very recent years it was found to yield more and cheaper pig iron of a better quality when worked under pressure.

The combination of blast furnace and puddling process produced nearly 75 per cent of Britain's iron in the form of wrought iron in 1830, 20 per cent of which was exported. The rest was mainly cast iron. Steel remained a special product produced in small lots, its price being about five times that of wrought iron. In 1850 England produced three million tons of pig iron and only 40,000 tons of steel. Unfortunately, both wrought iron and cast iron had serious disadvantages as construction materials. The problem of producing steel on a larger scale became acute around 1850.

We owe the process for the mass production of steel from crude pig iron to two inventors working independently. In 1862 William Kelly installed his "steel converter" at the Cambria Iron Works in Pennsylvania, but he had been anticipated by Sir Henry Bessemer in 1856. The latter, a professional inventor during the Crimean War, had directed his attention to the making of guns, having been attracted by a prize of money offered by Napoleon III. Realizing that he needed more and better steel than could be produced locally, he made numerous experiments and discovered that a blast of air introduced in a vessel containing molten crude iron will first oxidize the impurities present, and that this rapid oxidation will heat the mass still further. Thus a molten wrought iron or steel remains in the vessel, which is called a converter. By adding the proper minerals, the oxidized impurities were slagged and the molten wrought iron or steel produced could be cast. These converters, of course, had to be properly protected by a refractory lining, which in the early converters consisted of siliceous materials.

The first converters were used in France in 1858, and the process was taken up very quickly. Within a few years the converters were able to produce 20 tons of steel in 25 minutes from one loading of pig iron, and this increased output made larger and stronger castings available.

Bessemer and Kelly came to an understanding about their patents, but it took many more years of experimenting to perfect the method. The American, Holley, finally made the process continuous by using two converters alternately. Since about 1910, however, the Bessemer process has largely yielded to the Siemens-Martin open-hearth process (described below), which was invented about 1860 by William Siemens and first used commercially by Martin in England. Through the Bessemer process and its later competitor, the amount of wrought iron produced declined both in England and in America, and with it the use of the puddling process. At the present time, the output of Bessemer steel in the United States is less than 7 per cent of that produced in the open-hearth furnace. This is mainly due to the fact that better steel can be made by the latter process from low-grade ores.

The Bessemer process is known as the "acid process" because of the acidic nature of the lining of the converter. This limits the use of the process to the conversion of iron ores and pig iron of low phosphorus and sulfur content. The difficulty was that such ores are relatively rare and the larger part of the iron ores available in northwestern Europe have a high phosphorus content, at least above one tenth of one per cent.

Producing from ores containing phosphorus did not prove to be an insoluble problem. Thomas, a clerk, and Gilchrist, a chemist, in 1877 hit on the happy idea of lining the converter with basic materials, such as dolomite. These achieved what the siliceous bricks could not--they absorbed the phosphates formed by the blast air in the converter and bound the sulfurous compounds to slag. This "basic Bessemer process" was a boon to the French and Germans working the phosphoric iron ores of Lorraine (a bone of contention in every war between these countries) and to Belgium and Luxemburg, where they are outcrops and strata of the same nature. The process materially contributed to the rise of German steel production.

As the Bessemer plants went into production, they marketed a "mild steel," the properties of which lay between those of wrought iron and the "hard" blister steel produced in crucibles by the older processes. This mild steel proved an ideal material for rails, boiler plate, bars, structural steel for ships, houses, and reinforced concrete structures, and for sheet metal, such as that gradually demanded by the rising canning industry.

Much research was therefore devoted to some modification of the puddling process that would convert pig iron into mild steel and keep it liquid until ready for casting. A second problem that soon grew important was the use of scrap iron as a base material. It seemed impossible to melt scrap iron in a reverberatory furnace. William Siemens and his brother Ernest von Siemens had pointed out that it might be possible to heat such furnaces to the correct temperature with gas and air preheated in turn by the flue gases escaping from the furnace. Le Chatelier tried this method successfully on steel, and together with the Siemens brothers took out patents in 1856 and 1863.

The correct lining to be applied to these open-hearth furnaces at first still presented some difficulties. Martin and Le Chatelier solved them by producing high-class siliceous bricks which made the Siemens-Martin process completely successful. The first open-hearth furnace was built in the United States in 1873. Today the "basic" modification of the process accounts for nearly 91 per cent of all the steel produced. Five per cent of the total production is converter steel, and four per cent is electric-oven steel. In 1879 the open-hearth process was adapted to the conversion of scrap iron containing phosphorus and sulfur, when Pourcel and Valrand used such basic materials as dolomite and magnesite for the lining of the hearth.

These different processes for the mass production of steel solved many industrial problems. Between 1856 and 1870 the price of steel dropped 50 per cent and its production increased six-fold. Already by 1860 steel plates were in general use for boilers, allowing far higher steam pressures to be used. A steel rail outlasted twenty iron rails. In 1863 the first steel ship and the first steel locomotive were produced. As steel became established as the most commonly used form of iron, different compositional types were recognized.

This progress in metallurgy, as we have pointed out, became possible only through the close contact between science and metallurgy. Sorby, experimenting along the lines laid down by Reaumur and Breant, founded the science of metallography, which studies the crystalline structure of metals and alloys to determine their properties. His researches of 1857 were perfected when the microscope was introduced into metallography in 1864. Austen, Osmond, and Le Chatelier were among those who perfected research in this field in order to guide and improve metallurgical operations. It materially assisted the study of the thermal properties of metals, in which Tschernoff, Heyn, Baur, and the other scientists mentioned above cooperated.

Toward the end of the nineteenth century this led to important advances, such as the development of alloy steels for specialized applications--tungsten steel (Mushet, 1845), chromium steel (Brustlein, 1878), nickel steel (Marbeau, 1883), manganese steel (Hadfield, 1882), and vanadium steel (about 1914). Many of these metals were soon being produced in appreciable quantities and no longer were the laboratory freaks they had been for nearly a century.

Temperature control of these processes became all-important. First, this control was achieved by means of the little siliceous cones of different melting temperatures that had been developed by Wedgewood for pottery manufacture about 1750. When Le Chatelier introduced the thermoelectric pyrometer in 1891, temperature control became far more scientific. The prophecies contained in Faraday's articles in the Philosophical Transactions of 1822 were now fulfilled. Alloys became even more important than the original metals themselves.

A successful competitor of the old crucible-steel process was born when electricity became available in large quantities. This phase began when Clerc in 1879 constructed the first successful electric furnace, using the heat of the electric arc to melt steel and scrap. Many inventors (Heroult and Cowles among others) improved this electric furnace between 1887 and 1890. The experiments of Henri Moissan after 1892 have contributed to the efficiency of this furnace.

A new and intriguing type of electric furnace, the induction furnace, became possible through the work of Northrup in 1916 and Ribaut in 1920. In this furnace the iron or steel is heated by the eddy currents set up within the metal itself as a result of the rapidly changing magnetic fields produced by the flow of alternating current in the external electrical coils. The metal then acts as the core of a transformer, the electric coils surrounding the metal acting as the secondary. This means of heating the metal internally without having it come in contact with the current itself, or with gases or flames, is very important for melting precious metals and various alloy steels. . .