The cast steel is comparatively a recent in vention ; but it is gradually superseding the use of bar and sheer steel, on account of the equality of its temper, and the superior qua lity as well as beauty of the articles which are made of it. The process adopted is that of taking bar steel converted to a certain degree of hardness, and breaking it into pieces of about a pound each ; a crucible charged with these is placed in a melting-furnace, similar to those which are used by brass founders. The furnaces are 20 inches long by 16 inches wide, and 3 feet deep. The most intense heat is kept up for two or three hours, coke being used as fuel. When the furnace requires feeding, the workman takes the opportunity of lifting the lid of each crucible and judging how long the charge of each will be before it is completely melted. All the crucibles are usually ready about the same time. They are taken out of the furnace, and the liquid steel is poured into ingots of the shape and size required. This is considered, we believe, the most fearful process which British manufac tures present, in respect to the fierce heat to which the workmen are exposed : the steel is in a perfectly liquid state in the crucibles. The crucibles are immediately returned into the furnace ; and when the contents of all have been poured into the moulds, the crucibles are again charged. They are used three times, and then rejected as useless. The ingots are taken to the forge tilt or rolling mill, and hammered into bars or rolled into sheets as may be required. The celebrated TVootz, or Indian steel, is cast steel ; but it is frequently so imperfect as to resemble cast iron rather than cast steel. It is however made of iron obtained, as the Swedish is, from the magnetic ore. Wootz is made by the natives from mal leable iron, packed in small bits with wood in crucibles, which are then covered with some green leaves and clay : about two dozen of these crucibles are packed in one furnace ; they are covered with fuel, and a blast given for about two hours and a half, which termi nates the operation. When the crucibles are cold, they are broken, and small cakes of steel are obtained in the form in which it is brought to England.
Steel is of a lighter gray colour than iron, so characteristic as to be described as a steel gray. It is susceptible of receiving a very high polish, and this is greater as the grain is finer. Steel is about eight times as heavy as water. When steel is heated to redness and slowly cooled, itis scarcely harder than iron ; but by very rapid cooling it becomes hard, and so brittle as to be readily broken. The fracture
of steel is usually fine grained; in ductility and malleability it is much inferior to iron, but exceeds it greatly in elasticity and sono rousness. It may be subjected to a full red heat, or 2786° Fehr., without melting, and is therefore less fusible than cast iron, but much more so than wrought iron. Pieces of steel which have not been cast may be readily welded together or with iron : hut after cast ing the operation is- more difficult. Steel does not acquire magnetic polarity so readily as iron, but retains it much longer ; by exposure however to a moderate degree of heat this power is lost.
In order to give to steel the different degrees of hardness required for the various purposes to which it is applied, it is subjected to the process of what is called Tempering. It is found that the higher the temperature to which it is raised, and the more sudden the cooling, the greater, is the hardness produced. The steel is usually immersed in a bath of mer cury or of oil, having a temperature varying from to 000°. Captain hater found that or the heat of boiling water, was the exact point at which the knife edges attached to a pendulum were properly tempered. Case hardening is the operation by which articles made of Dialleable iron or cast iron are super ficially converted into steel by heating them with charcoal in a crucible.
With respect to the composition of steel and the nature of the admixture requisite to constitute it, differences of opinion have long existed, and the question even now is consi dered . r some as hardly decided, carbon is indispensably necessary to its for. mation, and whether certain substances or metals, especially silicon, may not give rise it. All steel contains a little silicon and phorus as well as carbon. Mr. Faraday ant Mr. Stodart published in the ' Phil. Trans.' for 1822 a valuable' series of experiments on alloys of steel, from which it appears that by combining steel with other metals its quality is improved. A very minute addition was found sufficient to produce a good effect : thus one 500th of silver gave an alloy harder than cast steel ; one 100th of nickel gave a very hard alloy, susceptible of a fine polish : alloys of rhodium and platinum were also formed; and these, with the alloys of iridium, osmium, and palladium, formed the most valuable com pounds.