STEEL MANUFACTURE. Iron possesses many qualities which render it applicable to innumerable purposes in the arts ; hut there are some uses for which it is not sufficiently hard, and this defect is supplied by converting it into steel. Steel is an intimate compound of iron and charcoal or carbon. There is car bon in soft iron, but in steel it appears to be in more intimate union with the metal.
Hitherto Swedish and Russian bar-iron have been exclusively employed in the manu facture of the best steel. The preference given to this iron is decided, though from what cause it arises has not been satisfactorily made out. We may however remark, that the foreign iron used is made from magnetic iron ore with charcoal ; while British iron is ob tained mostly from the impure carbonate of iron, or from peroxide of iron, and both of these are reduced by employing coal or coke. Bar•steel is made, with few exceptions, from the Swedish and Russian iron, the bars of which are marked Hoop L, G L, and Double Bullet, which are the best kinds. Iron of lower quality is also used, both Russian and Swedish, each kind having its peculiar mark. These steel irons are imported almost exclu sively by English merchants residing in Hull. The limited quantity of the fine iron allowed to be produced from the mines of Danemora in Sweden accounts in some degree for the high price at which they are sold. The quan tity of iron imported into this country for the manufacture of steel is estimated at 12,000 to 15,000 tons annually, of which at least 0000 come from Sweden.
The usual operation in manufacturing steel is first to cut the bar iron into certain leaving room in the vessels for the expansion of the iron: The closed vessels in which the bars are heated are usually twelve feet in length, and divided into two pots or troughs, on the bottom of which the workman strews charcoal to the thickness of about a' inch, and upon this he places on their fiat side a layer of bars ; then about three fourths of an inch more of charcoal is added, and upon this he places another layer of bars, and so on till the troughs are filled ; these are then covered with a ferruginous earth coming from the Sheffield grinding stones, called wheelswharf, to the thickness of about eight inches. All
the apertures of the furnace are closed with loose bricks and plastered over with fire-clay. The fire is then lighted, and in four days and nights the furnace is at its full heat, at which it is kept for several days, according to the degree of hardness required. In order to be able to test the progress of the carbonisation, a hole is left in one of the pots near the cen tre, and three or four bars are placed in the furnace in such a manner, that the ends come through this opening, and after the sixth day pne is pulled out. If the iron be then not sufficiently carbonised, the heating is con tinued from two to four days longer; a bar is drawn every two days, and when the iron is completely converted, the fire is heaped up with small coal, and the furnace is left to burn out and it requires from this period fourteen days' time to cool sufficiently to allow a per son to go in and discharge the steel. A con verting furnace, as it is called, contains gene rally fifteen tons of iron ; and there are some large enough to hold eighteen to twenty tons. The bar-steel, when discharged from the fur nace, is partially covered with small raised portions of the metal ; and from the resem blance of these to blisters, the steel is called blistered steel. The degree of conversion pro duced depends upon the purpose to which the steel is to be applied: Bar steel as it comes from the converting furnace is used for various purposes without refining. Those parts which are free from flaws and blisters are broken out and ham mered or rolled to the sizes required by the manufacturer for files, edge tools, table knives and forks, coach-springs, and a great variety of common agricultural implements. It is also manufactured into what is called sheer steel, which is more homogeneous, tougher, and capable of receiving a finer edge, than bar steel, which is converted into sheer steel by repeated heating, hammering, and welding.