852 STEEL.— Carinthian Process.' Cementation Process.
in the sixteenth century, are all modifications of aprocess of making steel in finery hearths.
The Carinthian Haw Steel Process, which has beenvery elaborately described by Professor Tunner,may be taken as a type of these processes. Thehearth employed is about 8 feet square and 9 inchesdeep. The sides are formed of cast-iron plates, andthe bed of stamped charcoal and ashes about 6 inchesthick. The height of the back plate facing the twyer,and on which the pig iron to be melted lies, isadjustable, so as to be from 2j- to 5 inches abovethe twyer. The twyer is about lj inch diameter,and projects about 4 inches over the plate, pointingdownwards at an angle of 10° to 16°. The pressureof blast is equal to 15 or 16 inches water column.Charcoal is the fuel used. The pig iron is firstrefined by melting it down, and subjecting it moreor less to the action of the blast, by which it isdecarburized and the silicon removed. While thismelting and refining action is going on, the previ-ously-formed crude lumps of steel are heated andworked in the same fire. By the waste of metal inthis operation a good deal of rich cinder is formed,which reacts upon the refined iron lying in thehearth. If the refined iron is still liquid, richhammer slag is poured in. When sufficiently re-fined, the slag is removed, fresh charcoal put in,and the lump of metal raised up among it, so as tobe more under the action of the blast. In this waythe carbon is reduced to a sufficiently low point,and the mass then sinks down into a pasty cake atthe bottom of the hearth. The cinder is then tappedoff, the cake removed, and the adherent, semi-fluidmetal knocked off. The cake is then cut up, andforged under the hammer. The process takes fromfive to six hours.
Production of Steel fromWrought Iron by Cementa-tion. —This mode of makingsteel has been carried onfor 150 years in England,and similar plans have beenfollowed in Sweden, West-phalia , and other countries;but when and by whom thediscovery of the processwas made is not known, itsearly history being involvedin much obscurity. Keau-mur, in 1722, speaks withgreat clearness upon theprocess, and even statesthat his own experimentsshowed, that if a bar ofiron three-sixteenths of aninch thick took six hoursto convert, a bar seven-six-teenths of an inch requiredthirty-six hours to becomeequally carburized, thusshowing that not only wastlie process known, but the mode of action wasbeing studied at this early period.
Eig. 1 is a vertical section of a converting furnace,a, a, are the converting chests; b, fire-place; c,ash-pit; d, d, arched roof; e, e, flues.
The process consists in exposing bars of wroughtiron to the action of a prolonged heat while they arethoroughly embedded in charcoal, protected in sucha way that the charcoal cannot burn. Under thesecircumstances, it is found that the bars take up acertain quantity of carbon, the amount dependingupon the time of exposure and quality of the char-coal, &c. The carburization is found to proceedfrom the surface towards the interior, and as ReaumPrshowed a century and a half ago, it takes severaltimes as long to convert a bar seven-sixteenthsthick as it does to carburize to the same extent oneonly three-sixteenths thick. The mode of operationis as follows:—The bars of iron are placed side byside in a rectangular chest (a, Fig. 1), which is builtup of fire-brick or freestone blocks. These chests areusually about 12 feet long, 3 feet 6 inches wide anddeep, with walls 6 inches thick. They rest upon goodsolid masonry. Charcoal is spread upon the bot-tom, then a layer of bars, then a layer of charcoalabout half an inch thick, then more bars, and soon till the chamber is filled, care being taken toallow for expansion of the bars lengthways and side-ways. A thick layer of charcoal is placed upon thetop, and the whole is covered with a plaster of“wheelswarf,” four or five inches thick. This is themixture of sandstone and steel which is produced bygrinding steel on stones. A moderate heat rendersit plastic, and thus it forms a perfect cover for thechests or “ pots,” and prevents the air from burningthe charcoal. The pots are generally arranged sideby side, with a fire-place beneath them, and fromwhich flues pass up between and at the sides of thepots, so that the flame can thoroughly surroundthem. They are generally placed in pairs, and arecovered by an arched roof, as shown in Fig. 1;and the whole is covered by a cone-shaped chimney.Trial bars are inserted in the chests in such a waythat they can be drawn out and examined from timeto time, to see how the cementation is progressing.When all has been carefully luted up so as to renderthe chests impervious to air, the fire is lighted, andthe chests are kept at a good red heat for severaldays. Usually steel for melting, which must con-tain about 1 per cent, carbon, requires from nine toten days; shear steel, which is less highly carburized,say to f per cent., takes eight days; and spring steel,which requires from ^ to J per cent, carbon, takesabout seven days. When the proper amount ofcarbon has been taken up (judged of from the frac-ture of trial bars), the fire is allowed to burn out, oris withdrawn, and the pots allowed to gradually cooldown. A usual charge for a furnace is from 10 to18 tons of bars. When sufficiently cooled down thebars are taken out, and are found to have increasedin weight from J to 1 per cent, and are frequentlycovered with blisters. Hence the product is knownas “ blister steel.” The cause of these blisters wasfor a long time obscure, but it is now proved beyonddoubt that they only occur in carburizing puddled