Page:The American Cyclopædia (1879) Volume XV.djvu/374

 3G2 STEEL process, and also to the large amount of silicon remaining in the steel. When highly manga- niferous pig is used, the silicon may sink be- low 1 per cent., and the resulting steel is of a much finer quality. Much of the Swedish Bessemer steel, celebrated for its purity and strength, is made from pig iron of this charac- ter. The heavy ingots of Bessemer steel in- tended for rails are either hammered or rolled (bloomed), becoming thereby condensed and elongated, and then cut into lengths suitable for rolling into rails. Blooming is now gen- erally conceded to make the best and most uni- form product. The American blooming train consists of three rolls 30 in. in diameter and 6 ft. in length, which are adjustable in housings by means of steel screws. Ingots 12 in. square are reduced by four grooves and 17 passes to 6 or 7 in. square in four minutes. Special ap- pliances for manipulating these heavy masses of metal by machinery are attached to the rolls and greatly facilitate the operation, which in some cases is nearly automatic. The rail trains are ordinarily three high rolls. (See IRON MAN- UFACTURE.) A 21-inch train for rolling 7-inch ingots into rails in 13 passes is divided into three lengths. The product of a steel rail mill, working on 7-inch blooms, is about 1,000 tons of rails a week. The consolidation of steel usually accomplished by hammering or rolling may also be effected by the application of a heavy steady pressure. This latter method is applicable not only to the forging of masses of steel, but also to the compression of the metal while in the molten state. Bessemer embodied this idea in one of his earlier patents. Origi- nally practised in France, the compression of liquid steel has attained its greatest develop- ment in England, where Sir Joseph Whitworth has an extensive plant for this purpose, which includes four hydraulic presses capable of ex- erting a pressure of 2,000 to 8,000 tons. The pressure usually applied is six tons to the square inch, by which an ingot is reduced one eighth in length. To small castings a pressure of 20 tons to the square inch is sometimes applied. Mild steels treated by this process have shown a tensile strength of 40 tons to the square inch, with an elongation of 30 per cent. A tube of this compressed steel 26 in. long and 7*83 in. in diameter, with a bore of 2-56 in. (being that of a nine-pound field gun), sustained 48 explo- sions of H lb. of powder with the bore closed by a screw plug, the only escape for the gases being through the touch hole, T V in. in diame- ter. The expansion of the bore increases at every explosion, but without rupture. Forg- ing steel by means of hydraulic pressure was first introduced by Ilaswell in Vienna in 1861. Heavy ingots are forged by this method more effectually than by hammering, and smaller articles of irregular or intricate outline, up to 150 Ibs. or more, may be directly formed by pressure of the white-hot metal into moulds. Zd. The Berard Process. The conversion of pig iron into steel or soft iron by means of oxidizing and reducing gases, in this process, is carried out on the hearth of a reverberatory furnace heated by gas. The pig iron is decar- burized by means of air in connection with hydro-carbon gases, which are expected to re- move the sulphur and phosphorus. The result- ing iron is recarburized by the reducing gases. This process has not yet proved a commercial success. 3. Steel from Wrought Iron. The above described processes under the second division of the classification, to which many others of minor importance might be added, all use pig iron as the principal material for the preparation of steel ; and as it is a substance of complex and variable composition, the qual- ity of the steel derived from it will depend on the composition of the pig iron used. In none of the processes using pig iron is there a com- plete elimination of all the substances associ- ated with the iron ; hence only the purer va- rieties can be used where a good product is desired. In the third division wrought iron is the principal material used, and as this may be made in a state of great purity even from moderately pure pig irons, the steel made from it is as a rule superior to that made from pig iron. Wrought iron when imperfectly worked contains considerable cinder, which holds the greater part of the phosphorus originally in the pig iron; and when steel is made from such wrought iron by fusion, the phosphorus enters the steel. 3. The Martin Process. The principle of manufacturing steel by the reaction of wrought iron upon melted pig has long been known. Einmann, Vanaccio, and even Agricola (about 1550) describe processes of this kind. Ke~aumur (1722), Chulut, and Clouet (1778) published experiments in which steel was produced by the simultaneous fusion of cast and wrought iron, or of cast iron and iron oxide. But these experiments, and many others of subsequent date, were successful only so far as the manufacture in crucibles was concerned. It was only in closed ves- sels, heated from without, that the necessary high temperature, combined with exclusion of air, could be maintained. Vitreous fluxes were early used, to protect the surface of the molten metals; and the idea of employing a reverberatory furnace is found in the work of Hassenfratz (1812). Several English and French patents of the early part of this cen- tury show that metallurgists were actively en- gaged with this problem. The most impor- tant historically, though at the time without commercial results, was that of Heath (1845), which indicated the fusion of material in a hearth, the maintenance of an extremely high temperature, and the employment of gase- ous fuel. In a former patent (1839) Heath had claimed the addition of carburet of man- ganese. The oxides of manganese had been previously used in metallurgy ; but the intro- duction of metallic manganese, alloyed with carbon, was an important novelty, which pref- aced the employment by Mushet, Bessemer,