STEEL MANUFACTURE. Iron pomessee qualities which render it applicable to innumerable purposes in the arts ; but there are some uses for which it is not sufficiently hard, and this defect is supplied by converting it into steel.
At Eiseniirzt in Styria the manufacture of steel has been carried on ever since the 8th century, and yet the exact nature of the operation is perhaps even now imperfectly understood. It is generally admitted that steel is an intimate compound of iron and charcoal ; for soft iron contains a considerable portion of charcoal, and it is by no moans clear that the quantity is increased in the process of steel-making. There fore we must conclude that some more intimate union ie effected between them when iron is converted into steel. On this point we shall touch again after describing the manufacture.
Hitherto Swedish and Russian bar-iron have been almost exclusively employed in the manufacture of the hest steel ; the prefercuce 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 obtained mostly from the impure carbonate of iron, called argillaceous iron-ore, or from hematite, which is a peroxide of iron, and both of these are reduced by employing coal, or coke prepared from it.
liar-Steri is made, with few exceptions, from the Swedish and Russian iron, the bars of which are marked hoop 1(1), gl (2), and double bulk (3) ; these are the „best kinds. Iron of lower quality is also used, such as (4), which is a Russian iron, and c and crown (5), d wit/ frown (6), which are Swedish irons. There is a medium quality, namely, tc and crowns (7), b and crown (8); these also are Swedish.
These steel irons are imported almost exclusively by English merchants residing in Hull. The limited quantity of the flue 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.
liar-Sled. The usual operation in large steel-works is first to cut the bar-iron into certain lengths. The closed vessels in which the bars aro heated are usually twelve feet in length, and divided into two cells or troughs, on the bottom of which the workman strews charcoal to the thickness of about an inch. Upon this he places on their flat
side a layer of bars ; then about three-fourths of an inch more of charcoal is added; on this another layer of bars ; and so on till the troughs arc filled. These are then covered with a ferruginous earth coming from the grinding-stones, called wheelswarf, to the thick ness 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 troughs near the centre ; three or four bars are placed in the furnace in such a muner that the ends come through this opening, and after the sixth day one is pulled out. If the iron be then not sufficiently carbonised, the heating is continued 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 bum out. It requires from this period fourteen days' time to cool sufficiently to allow a person to go in and discharge the steel. The cells or troughs must be kept completely airtight; the smallest crack will open when the furnace is hot, and admit the air : this of course frestrates the object of the operation, and any steel which has thus suffered is placed aside to be reconverted. It is of the greatest importauce to give the iron the exact quantity of carbon required and no more. For coach-springs, the iron must vet be con verted to the centre. For common cutlery, sheer steel, and for pur poses where steel has to be welded to itself or to iron, the conversion should be low, and gradually disseminated throughout the whole thickness of the bar. For double slicer steel, the conversion should be somewhat harder than the preceding. For files, and all instruments where resistance or fine cutting edges are required, the conversion should be hard, and the iron fully carbonised throughout the bar.