874

STEEL.— Open-Hearth Process.

balk of the silicon is oxidised early in the blow,during which period also the carbon is burning toC0 2 , the rise in temperature must be proportionatelygreater during this period than during the latterhalf. This also accords with spectroscopic observa-tions ; for the changes in the flame are remarkablyrapid till towards the middle of the blow, after whichthe heat does not appear to increase greatly. If theblast be continued after the whole of the carbon,silicon, and manganese have been burnt out, theiron is burnt very rapidly, and peroxide of iron isformed, which is carried out of the vessel in densevolumes of brown smoke. This carries off so muchheat that, instead of the temperature of the remain-ing metal rising, it is rapidly decreased, and over-blown metal is rarely fluid enoughto allow of its being cast withoutskulling in the ladle. On the addi-tion of spiegeleisen to such over-blown metal, the combustion of itscarbon, manganese, and silicon, bythe dissolved oxide of iron, takesplace with explosive violence.

We have no means of measuringthe final temperature of the metalwith accuracy, but we know that itis above the melting point of plati-num, which Deville places at about1900° C. A stream of the moltensteel will rapidly fuse wrought iron,and when the pig contains 2 percent, or more silicon, the steel willremain fluid in the ladle for a con-siderable time; thus showing thatthe final temperature is much abovethe melting point of steel. In theforegoing remarks no mention wasmade of manganese, English pigiron rarely containing any quantity.

But on the Continent iron contain-ing up to 4 per cent, manganese isconstantly used ; and from the flu-idity of the steel produced, it appearsthat the combustion of this man-ganese adds considerably to the heatof the bath. But as the calorificpower of manganese is not known, itis needless to consider the subjectfurther.

Open-heaetii Process of Steel-making.—Heathpatented the manufacture of steel by melting scrapiron or its equivalent in a bath of pig iron in areverberatory furnace heated by gas, so long ago as1845; but no really successful results were attained,owing to the impossibility of producing a sufficientlyhigh and equable temperature, until Dr. Siemensperfected his regenerative gas furnace. The applica-bility of this furnace for steel-melting was patent toall; and Messrs. Siemens refer to this use of theirsystem in their patent of 1861. In England, how-ever, Attwood was the first to practically use thefurnace for steel-making, while W. M. Martin inFrance carried success to a higher point, by using a

mixture of pig iron, iron scrap, and iron ore. In1867 Siemens took up the question himself, anderected an experimental furnace at Birmingham .He patented his plan of steel-making, and in a shorttime succeeded in placing the manufacture on apermanent footing. Shortly after the Bandore SiemensSteel Company was started, and four 5-ton furnaceswere erected for carrying on the process on- a com-mercial scale. The absolute necessity of the Siemensregenerative principle to any open hearth system of

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steel-making, has led to the general application ofthe terms “ Siemens ” or “ Siemens-Martin ” steel toall steel made by open-hearth processes.

In 1876 Pernot introduced a modification of theSiemens furnace, in which the bed of the furnace ismade circular, and so arranged that it can be rotatedon an axis which is inclined 5° or 6° from thevertical. Thus, the bed dips to one side, and whilethe fluid metal lies on this side any solid portionsare carried round, exposed to the full heat of theflame, and then dipped at each revolution into thebath. By this means more rapid oxidation takesplace than with the fixed furnace.

The general arrangements of the Siemens steel-