The Shear steel, which derives its name from the accidental circumstance of the shears for dressing woollen cloth being usually forged from it, is made by bind ing into a bundle, with a slender steel rod, four parallel bars of blistered steel, previously broken into lengths of about 18 inches, including a fifth of double length, whose projecting end may serve as a handle. This faggot, as it is called, is then heated in the forge-hearth to a good welding-heat, being sprinkled over with sand to form a protecting film of iron slag, carried forthwith to the tilt, and notched down on both sides to unite all the bars together, and close up every internal flaw or fissure. The mass being again heated, and the binding rings knocked off, it is drawn out into a uni form rod of the size required. Manufac turers of cutlery are in the habit of pur chasing the blistered bars at the conver sion furnaces, and sending them to tilt mills to have them drawn out to the pro-• per size, which is done at regular prices to the trade •, from 5 to 8 per cent. dis count being allowed on the rude bars for waste in the tilting. The metal is ren dered so compact by the welding and hammering, as to become susceptible of a much finer polish than blistered steel can take ; while the uniformity of its body, tenacity, and malleability, are at the same time much increased • by which properties it becomes well adapted for making table knives and powerful springs, such as those of gun-locks. The steel is also softened down by this process, pro bably from the expulsion of a portion of its carbon during the welding and subse quent heats ; and if these be frequently or awkwardly applied, it may pass back into common iron.
Cast steel is made by melting, in the best fire-clay crucibles, blistered steel, broken down into small pieces of conve nient size for packing ; and as some car bon is always dissipated in the fusion, a somewhat highly converted steel is used for this purpose. The furnace is a square prismatic cavity, lined with fire-bricks, 12 inches in each side, and 24 deep, with a flue immediately under the cover, 8} inches by 6, for conducting the smoke into an adjoining chimney of considera ble height. In some establishments a dozen such furnaces are constructed in one or two ranges, their tops being on a level with the floor of the laboratory, as in brass foundries, for enabling the u ork men more conveniently to inspect, and lift out, the crucibles with tongs. The ash-pits terminate in a subterraneous passage, which supplies the grate with a current of cool air, and serves for emp tying out the ashes. The crucible stands, of course, on a sole-piece of baked fire clay ; and its mouth is closed with a well-fitted lid. Sometimes a little bottle glass, or blast,furnace slag, is put into the crucible, above the steel-pieces, to form a vitreous coating, that may tho roughly exclude tic air from oxidizing the metal. The fuel employed in the cast-steel furnace is a dense coke, oril liant and sonorous, broken into pieces about the size of an egg, one good charge of which is sufficient. The tongs are
furnished at the fire end with a pair of concave jaws, for embracing the curva ture of the crucible, and lifting it out whenever the fusion is complete. The lid is then removed, the slag or scoria3 cleared away, and the liquid metal pour ed into cast-iron octagonal or rectangular moulds, during which it throws out bril liant scintillations.
Cast steel works much harder under the hammer than shear-steel, and will not, in its usual state, bear much more than a cherry-red heat without becoming brittle ; nor can it bear the fatigue inci dent to the welding operation. It may, however, be firmly welded to iron. through the intervention of a thin film of vitreous boracic acid, at a moderate degree of ig nition. Cast steel, indeed, made from a less earburetted bar steel, would be sus ceptible of welding and hammering at a higher temperature ; but it would require a very high heat for its preparation in the crucible.
Iron may be very elegantly plated with cast steel, by pouring the liquid metal from the crucible into a mould contain ing a bar of iron polished on one face. In this circumstance the adhesion is so perfect as to admit of the two metals being rolled out together ; and in this way the chisels of planes and other tools may be made, at a moderate rate and of excellent quality, the cutting-edge being formed in the steel side. Such instru ments combine the toughness of iron with the hardness of steel.
For correcting the too high carboniza tion of steel, or of equalizing the too highly converted exterior of a bar with the softer steel of the interior, the metal requires merely to be imbedded, at a ce menting heat, in oxide of iron or manga nese ; the oxygen of which soon ab stracts the injurious excess of carbon, so that the outer layers may be even con verted into soft iron, while the axis con tinues steely ; because the decarbonizing advances far more rapidly than the car bonizing.
To preserve steel from rust, Stodart's method is to wash with the ethereal so lution of gold, or with mnriate of platina. In this way, the breadths of polished steel in grates, fenders, &c., are pre served ; and either may be purchased of chemists, or furnishing ironmongers.
Steel heated a little above the degree necessary to temper it, becomes soft, by that very operation of tempering, and this process, for nealing it, is much su perior to the ordinary methods. The process in no way deteriorates the steel, and abridges the operation.
The steel-hardening, alluded to pre Vionsly, is a very important process, in connection with stecl-engraving and die sinking. The subject 33 engraved on soft cast-steel, and then is hardened by placing it in a cast-iron pot, surrounded with animal charcoal. It is then exposed to intense heat of coke in an air-furnace, and afterwards placed in a vessel of cold water, renewed by a current. It is then used to make a puncheon-die on other soft steel, to be hardened, and this is a inatrix for others, by which coin may be struck.