This making of cast-steel is a remarkable operation. The heat of the furnaces is believed to be higher than any other known in English manufactures. The ingots weigh from about 40 to 200 lbs. each, according to the purposes to which they are to be applied. No less than four to five tons of coke are needed for smelting one ton of steel.
The tilting of steel is a process of hammering, mostly for cast-steel. The steel is heated to a certain temperature, and hammered all over for a considerable time ; this closes the pores, and renders the metal as close and compact as possible. The steel for the best articles is both cast and tilted. Case-harden leg is an operation whereby articles made of malleable iron or cast-iron are superficially converted into steel by heating them with charcoal in a crucible.
Relations of Steel to Iron.—The steel manufacture is just now iu a transitionary state ; several new processes of a highly curious nature have been introduced by Heath, Clay, Bessemer, Uchatins, and others, not fully successful, perhaps, but significant of the future. Most of these depend on a study of the relations between iron and steel, in a way which we shall briefly describe.
With respect to the composition of steel and the nature of the mixture necessary to constitute it, differences of opinion have long existed. The question even now is considered by some as hardly decided, whether carbon is indispensably necessary to its formation, and whether certain substances or metals, especially silicon, may not give rise to it ; and it is generally admitted that phosphorus is always present. Berzelius mentions iron containing manganese as particularly eligible, and yet analyses show that this metal is not present in steel in most cases. An experiment performed by Mr. Pepya in 1815, seems not only to prove the necessity of carbon, but also that the diamond is capable of producing the same effect. In order to get rid of the objec tion that the carbonaceous matter of a common fire might supply carbon when iron and diamond were heated by means of it, he placed diamond-powder in a piece of pure soft iron wire ; and having properly secured it, he heated it by means of voltaic electricity : after a few minutes' heating, the diamond had disappeared, and the interior surface of the iron was converted into perfect blistered steel, which, being heated to redness and plunged into cold water, became so hard as to resist the file and scratch glass. Some years since a method was dis
covered by 3lackintoeh of converting iron into steel by means of the carbon of carburetted hydrogen gas. Gay Lussac found that during fusion steel loses much silicon and a little carbon. Braude has found that when the carbon has fallen short of one per cent., the steel was deficient in hardness ; and when it has exceeded this proportion, the dies have split or not stood their work. He states, at the same time, that minute quantities of other bodies appear to influence the quality of steel ; and that unless it contain phosphorus it cannot be depended on for the manufacture of dies in coining. Dr. Thomson examined some cast-steel furnished him by Mr. Buttray, a steel-maker near Glasgow. The general result of his trials gave him a composition which approaches 20 atoms of iron + 1 atom of carbon ; and this he thinks likely to be the constitution of cast-steel, an opinion corrobo rated by the fact above stated by Mr. Braude. Mr. Faraday and 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 addi tion was found sufficient to produce a good effect : thus one 500th of silver gave an alloy harder than cast-steel ; one I00th of nickel gave a very hard alley, 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 compounds.
Mr. Dinka, in a paper read before the Society of Arts in 1857, on the nature and properties of steel, described the experiments which had led him to the following conclusions : That the substances whose appli cation to pure iron convert it into steel, all contain carbon and nitro gen ; or that nitrogen has access to the air during the process. That carbon alone added or applied to pure iron, does net produte steel ; and that neither does nitrogen alone produce it. That it is essential for both carbon and nitrogen to be present. That both exist substantially in steel after its conversion. That such presence is the real cause of the distinctive physical properties of steel from those of iron. That presumptively, though not demonstratively, the form of combination is that of a triple alloy of iron, carbon, and nitrogen.