“ At once the founding of iron became an important art. It was not long, however, before the fact was established that by further treatment the cast iron would be transformed into wrought iron. To-day the production of cast iron in the blast-furnace is the first step in the manufacture of iron and steel. ”

“ When the highly heated blast enters the furnace the carbon of the fuel burns with the oxygen of the air to form carbon dioxide; this, at the high temperature prevailing in the hearth, is almost immediately dissociated, and the liberated oxygen combines with more carbon to produce carbon monoxide. Carbon monoxide, being a powerful reducing agent, takes oxygen from the ore to produce carbon dioxide. When the iron ore is charged into the furnace it at first suffers no chemical change, but gradually absorbs heat until at a temperature of about 200° C. it begins slowly to lose oxygen. ”

“ In pig-casting machines two endless chains carry a series of pressed-steel molds, which travel at slow speed past a trough terminating in two mouths. The molten iron from the furnace is tapped into a ladle, which is carried by a ladle-car into position to discharge into the double-mouthed trough. As each mold passes it is filled with molten iron. The endless chain of molds as it moves along descends under a tank of water, where the molten metal cools and hardens. ”

“ Uses of Iron and Steel. The uses to which iron and steel are put are so familiar that only brief mention need be made of them. Cast iron is used chiefly in founding or iron-casting, the varieties and purposes of such castings being almost innumerable. ”

“ Cast iron melts at about 1200° C., and when cold is hard and brittle. It is not malleable or ductile, and cannot be tempered. Of the several elements named, carbon and silicon are of value in steel-making, which is the chief purpose for which cast iron is produced at the present time; but sulphur and phosphorus are generally highly objectionable. In using the term cast iron here, the chemical nomenclature has been retained. The foundryman generally gives the name pig iron to the direct product of the blast-furnace, and the term cast iron to the form which pig iron assumes after remelting. ”

“ By a slow process called cementation the carbon penetrates the metal at the rate of about one-eighth inch every twenty- four hours. The process of cementation is carried on in large retorts which handle many tons of bars at one time, so that it will always happen that some parts of the furnace arrive at full heat much sooner than others, and remain longer at that temperature. The consequence is that it is necessary to break all the bars and grade the pieces by fracture according to their degree of carburization. Steel made in this way is commonly known as blister steel. ”

“ The iron made by the ancients, and, indeed, by all peoples up to 1350, when cast iron was first produced in the German blast-furnaces, was wrought iron, and it was produced from the ore in a single operation. ”

“ The physical properties of steel depend upon the chemical composition and method of manufacture, and they vary so greatly, both relatively and absolutely, that no effort will be made to define them here. The mild and soft structural steels for bridges and buildings have tensile strengths of from 60,000 pounds to 70,000 pounds per square inch, with a limit of elasticity of from 30,000 pounds to 40,000 pounds per square inch. The hard steels have a much greater strength. The compressive strength of steel is always greater than the tensile strength. ”

“ In hearths the fuel is burned in direct contact with the iron, and the chief source of oxygen is the atmosphere; in the reverberatory furnace the oxygen is obtained from special oxidizing materials added for the purpose, and the fuel is burned in a chamber separate from, but communicating with, the chamber in which the charge is placed. With this outline of the methods of producing wrought iron from cast iron, attention will be turned to the process which is chiefly employed. ”

“ The general construction is a masonry lining within a steel shell. To keep the hearth cool it is surrounded by a water-jacket. Air is supplied by tuyeres drawing from a circular blast-main. At the top there is a funnel-shaped charging hopper closed by a conical door and suitable exits for the furnace gases. These gases pass down through metal pipes to the stoves for heating the blast. Blast pressure is supplied by blowing engines which draw in cold air and discharge it through the hot-blast stove, whence it passes into the blast-mains and then through the tuyeres into the furnace. ”

“ Cast steel is used for many of the same purposes as cast iron, but more particularly for those purposes where castings of great strength are required. Wrought iron is forged into various shapes for special purposes, and is rolled into bars, plates, beams, rails, and structural shapes. Extra hard steels are used for tools, hard steel for piston-rods and other parts of machines, medium steel for rails and guns, and the mild and soft steels for beams and structural purposes. ”

“ Briefly described, each stove consists of an outer shell of steel plates lined with fire-brick to form a vertical cylinder with a dome-shaped top. A circular flue extends from the bottom to the top of the stove, and the remainder of the space is filled with special-shaped fire-bricks which form a honeycombed or cellular filling. Hot gases from the furnace are discharged into the bottom of the vertical flue, where they meet the air-inlet and combination takes place. The burning gases pass up the flue and thence down through the cellular filling to an outlet leading into the chimney. ”

“ The next step is to tap the furnace and draw off, first the molten slag, and then the molten metal. Generally the slag is run to waste, but sometimes it is preserved and submitted to treatment which permits its utilization. Some of these uses are road metal, railway ballast, slag bricks, slag wool, and hydraulic cement. Bricks are made by casting the molten slag in molds. To produce slag wool the molten slag is blown by a jet of steam, which produces small globules, to each of which is attached a long thin filament. ”

“ Hardness is the capacity to resist indentation; weldability is the property which permits two or more separate fragments to be welded together; ductility is the property which renders the metal capable of being drawn out into rods or wire; malleability is the property which permits the metal to be hammered or pressed into different shapes; elasticity is the property which gives the metal power to return to its original form after distortion ”

“ Structurally the furnace consists of cast-iron plates and firebrick. In operation the combustion of the fuel takes place on the grate-bars, and the hot gases and flames rise to the roof and are beaten back or reverberated upon the charge as they move toward the flue. Generally two men work at a furnace. ”

“ All the carbon content of Bessemer steel has, therefore, to be supplied by the recarburizer, and absolutely perfect homogeneity of product can be secured only by absolutely perfect mixing of the molten metal and the recarburizer. ”

“ Magnetic concentration consists in passing naturally fine ores, or ores made fine by crushing, through so-called separators, in which the ore is drawn from the non-ferrous gangue by means of magnetized drums or other mechanism. Weathering consists in stacking the ore in heaps to remove shale and sulphur, which crumble or wash away under the action of the elements. Calcination consists in treating the ores to drive off volatile matters, usually water, carbon dioxide, sulphur, and carbonaceous matter, or to oxidize the ore. ”

“ This double process is expensive, and a cheaper and more common method of making crucible steel is to place powdered charcoal and crude bar iron in the crucible, the iron absorbing the carbon very rapidly in the molten state. This practice is almost universal in America. Sometimes pig iron and wrought iron are melted together, and in Sweden crucible steel is produced from pig iron and iron ore. Both blister steel and crucible steel belong to the general class known as high-carbon steel. Such steel can be made regularly in open-hearth furnaces ”

“ The material hoist is a necessary adjunct to the modern blast-furnace, where hundreds of tons of coke, ore, and limestone have to be raised daily 100 feet or more to the charging hopper. These hoists are operated by hydraulic, pneumatic, or steam power, and in general consist of an elevator cage or corresponding apparatus on which the material cars may be raised and lowered. ”

“ The cooling is continued by sprays of water as the molds ascend from the water and move on toward the tail sheaves, where the pigs are discharged onto cars. The casting machine of one of the most recent American blast-furnace plants has a chain travel of 20 feet per minute, the molds are spaced 1 foot apart on the chains, and the machine delivers 20 pigs per minute averaging in weight 110 pounds each. ”

“ Sometimes the molds are set in a row around the perimeter of a circular pit, and the ladle is swung around in a circle by the crane to fill one mold after another; but more often, in American practice, the molds are mounted on little platform cars which are hauled past the ladle and filled one at a time, the same cars taking the filled molds to the rolling-mill, where they are stripped from the ingots. ”

“ Pig iron contains varying quantities of carbon, and to burn away just enough would necessitate a different length of the blowing for each charge of iron, thus introducing complications difficult to handle. ”

“ As the temperature rises and the materials descend in the furnace the reduction becomes more rapid until at 600° C. it is very rapid. At this temperature also the limestone decomposes, forming quicklime and liberating carbon dioxide, part of which takes up carbon from the fuel-producing carbon monoxide. ”

“ A common roof covers the two chambers. This roof is horizontal over the grate-bars, but curves downward as it extends backward until at the flue-entrance it descends below the level of the charge. There are two doors at the side, one for feeding the fire and the other to give access to the charge. ”