Duhamel advises to have two tilting hammers ; one of the weight of one hun dred and fifty pounds, and the other half that weight ; the first for the purpose of forging large works, and the latter small bars for cutlers. He recommends another small hammer of about twelve pounds, for forging bars still smaller, to make gravers, small files, and the like. The steel must not be heated beyond the de gree of cherry-red for forging. The tilt ing hammers should give at least three hundred strokes in a minute.
The cast steel of England is made as follows : a crucible about ten inches high, and seven in diameter, is filled with ends and fragments of the crude steel of the manufactories, and the filings or frag ments of steel works. They add a flux, the component parts of which are usually concealed. It is probable, however, that the success does not much depend upon this flux, which, from the quality of the cast steel itself, may be presumed to be of the nature of a steel cement. This crucible is placed in a wind furnace like that of the founders, but smaller, because intended to contain one pot only. It is likewise surmounted by a cover and chimney, to increase the draught of air. The furnace is entirely filled with coke or charred pit-coal. Five hours are re quired for the perfect fusion of the steel. It is then poured into long square or oc tagonal moulds, each composed of two pieces of cast iron fitted together. The ingots, when taken out of the moulds, have the appearance of cast iron. It is then forged in the same manner as other steel, but with less heat and more pre caution, because more liable to break.
This cast steel is almost twice as dear as other good steel. M. Duhamel says that it is not proper for all kinds of work, particularly those which require much tenacity, as well as hardness, to resist violent blows and strains ; but it is good for razors, knives, and all toys and small work which require an exquisite polish. It does not seem, however, that the tena city of this steel is inferior to that of the best of the other kinds, and its uniformi ty of texture is for many works an invalu able advantage. It is daily more and more used in England, and must necessarily be excluded from many works of considera ble size, on account of the facility with which it is degraded in the fire, and the difficulty of welding it, which cannot be done in the common way. We have been informed, that the faces of anvils and broad hammers for the use of silver smiths and other artists have been made of cast steel, and welded to iron by a particular management, which consisted in substituting between the iron and the steel another kind of steel, in the form of filings, or a thin plate. The steel plate intended for the face was made as hot as could be done with safety, and the iron being at the same time brought to the welding heat, was applied to the steel, and quickly united by hammering.
When we consider the operations by which crude iron's brought into the mal leable state, then converted into steel, and afterwards into a fusible metal, which is not malleable, we may perceive that steel-making is a kind of inversion of the process of refining iron, as practised in the first instance. When the oxide of iron is mixed in the smelting furnace with combustible matter and glass, it will either be completely or partially revived, according to the management of the pro cess. Much of the coal will however be so Znveloped with the vitreous matter as to remain unburned : and the reduced iron, with which it may be in contact, will be in the same situation as forged iron in the cementing pot ; that is to say, it will be in contact with coal at a very elevated temperature, and defended from the air. From the great infusibility of
iron, it may reasonably be concluded, that the reduced metal does not flow into the bottom of the furnace, until the charcoal has converted it into a fusible matter similar to steel, by the same action which takes place in cementation, what ever that action may be. Hence it must follow, that the various specimens of crude or cast iron will differ in their qualities, as well on account ofthe degree of cemen tation they have undergone, as the degree of reduction which has taken place among the metallic parts, which are carried down, and form the whole mass. Since the coal, in the process of cementation, communicates or adds weight' to the iron; and since crude iron, as well as steel, exhibits sparkles, and is more easily burned than other iron; it may therefore be concluded, that, in the process of re fining, that part of the inflammable sub stance which had united with the metal is burned, and leaves the iron much less fu sible than before. Stirring the mass mul tiplies the contacts of the air with the burned substances ; these surfaces of con tact will therefore successively afford thin coats of infusible metal. In this manner it is found, that, if a large piece of crude iron be exposed to heat in a wind furnace, the external part will be deprived of its fusibility during the time requiredto pro duce a strong heat in the whole mass; and the internal part will be melted, and run out, leaving the shell behind. Iron, which is of the consistence of paste, may therefore be considered, like any other paste, as a mixture of a fluid with a solid. It will be easily understood, that the forging will bring the parts of difficult fusion together, and extrude the less re fined and fluid parts ; it will also be evi dent, that this operation is not likely to drive out the whole ofthe fusible matter. When the iron has arrived at that state, wherein the quantity of fibre or tough iron is sufficient to answer the mechani cal purposes to which it is intended to be applied, the artist will consider it as suffi ciently refined ; and the residue offfisible iron contained in the bar answers, in all probability, the valuable purpose of con necting these infusible masses together. Thus we find that forged iron appears as if covered with a varnish, when urged to a white heat ; we find that this varnish is more abundant in and that iron and steel may be respectively welded toge ther by application in this state ; an effect which it would be very difficult to account fbr, in this most infusible of metals, if it were not for such an admixture. But cast steel, steel over cemented, and crude iron, appear to be in the side ofall other metals platina excepted. They cannot be welded, because welding implies a partial fusion ; oran effect similar to the gluing or uniting of solids by the application of a fluid, which afterwards becomes consistent. And as platina possesses this valuable property, It seems reasonable to infer,that it must also consist of two metallic sub stances of different degrees of fusibility; a supposition that appears fo be confirmed by the discoveries of Dr. Wollaston and Mr. Tennant.