STEEL is the name of a well known metal, consist ing of iron combined with carbon, or a carburet of iron. When small pieces of fine malleable iron, surrounded with powdered charcoal, are exposed for eight or ten hours to a strong red heat, the iron is converted into steel, and is then found to have united with the 150th part of its own weight of carbon. The following are the general properties of this important metal : Steel unites with the malleability of bar iron the fusibility of cast iron, and if immersed in a cold fluid when hot, or otherwise suddenly cooled, it becomes intensely hard, sonorous, and elastic,—these proper ties varying according to the heat of the steel, and the temperature of the fluid, or other substance in which it is cooled. In consequence of these proper ties, steel is of great use in the arts for all sorts of cutting instruments, for springs, and even for musical instruments. In general, steel is brittle, resists the file, yields sparks with flint, and retains magnetism for a very long time. The hardness, in virtue of which it possesses these properties, disappears after ignition and slow cooling. At a red heat it is malleable, but less so at a white heat. It is capable of being beat out into thinner plates than iron. It melts at ISO° of Wedgewood. Its specific gravity varies from 7.78 to 7.84. By repeated ignition under exposure to the air and hammering, steel again becomes wrought iron. According to Kirwan, steel may be easily distinguished from iron by letting fall a drop of diluted nitric or muriatic acid on a plate of steel. When washed off after lying a few moments, a black spot is left, whereas on iron with nitric acid the colour of the spot is whitish green. The cause of the black spot is, that a portion of the iron is dissolved, while the carbon is left.
There are three different kinds of steel, which are obtained by three different processes. 1st, Natural steel ;2d, Steel of cementation ; and 3d, Cast:steel.
1. _Natural steel. The natural or native steel of Eis enhartz in Styria, is obtained directly from the ore. The ore used is the Spathose ironstone, consisting of the carbonates of iron, manganese and lime, together with a mixture of clay, which occurs abundantly in the neighbouring hill. The fuel employed is always charcoal, and generally amounts to about one-fifth of the ore in weight. The ore is first converted into cast-iron by repeated meltings, and removals of the scoriae, and the cast-iron thus obtained is purified in the crucible of a refinery previously lined with char coal, particular care being taken that the carbon con tained in the cast iron is not burnt away. When the natural steel is thus sufficiently purified, it is extended under the hammer, and cut into bars which are ex amined by their fracture, and separated into hard steel, soft steel, and steely iron, the last of which is used for pointing ploughshares, and other rough work.
The other two kinds of bars are made up into packets, the hard steel being placed inside, and when drawn into bars at a lower heat than that used for iron, it becomes natural steel.
In this process a portion of the carbon is supposed to combine with the oxygen in the cast iron, and to escape as carbonic acid gas, while the rest of the car bon unites with the pure iron, and forms steel. In quality this steel is inferior to other kinds. It is less homogeneous, and is softer and less frangible. From the cheapness of the process, it brings a lower price.
2. Steel of cementation. The process of forming steel by cementation is performed in two parallel troughs constructed of fire brick, or of an open-grain ed siliceous free stone, unalterable by the fire. These troughs are placed upon a long grate beneath an arch ed vault, surrounded with a cone of masonry. Bars of the best Dannemora or oregrund (Swedish) iron, free of cracks and flaws, are then selected for the purpose of cementation. A layer of coarsely bruised charcoal, capable of passing through a quarter inch riddle, is now laid at the bottom of the cementing troughs, and above this is laid a row of bars of iron, another stra tum of charcoal succeeds, and then bars of iron, and so on till the trough is nearly full, containing about eight tons of iron. The whole is then covered with clay and sand mixed, and rammed as close as possible to exclude the air. The heat of the whole is raised to a glowing red, which is kept up from seven to eleven days,according to the quantity of iron. Through a small hole in each trough a bar is allowed to project, that it may be taken 6ot from time to time to observe the pro gress of the operation. When the trial bars announce the perfection of the process, the fire is extinguished. The bars retain their original shape, but their surface is covered with blisters, as if a gaseous fluid had been confined in different parts of it. Hence it is called Blistered Steel. The bar iron when thus converted into steel is found to have increased in weight from four to twelve oz. per cwt. or on an average 1 part in 224. The first proportion constitutes mild, and the second very hard steel; and if the process had been pushed much farther, the steel would have melted, and in the act of fusion would have taken an additional close of charcoal, so as to bring it to the state of Cast Iron, No. I.