Page:The American Cyclopædia (1879) Volume XV.djvu/370

 358 STEEL general the term fine steel is reserved for those products made by fusion of the purest mate- rials in a crucible, and particularly for the cast steel made by fusion of cement steel. Shear steel, produced by welding and rolling cement steel, may also be classed here. In many in- stances two or more reactions or processes for steel making are combined, but in following the above classification the principal feature only of the process is considered. 1. Steel direct from the Ore. The process for obtain- ing wrought or soft iron direct from the ore (see BLOOM ART, and IROX) affords, with some slight modifications of charging and manipula- tion, a product containing sufficient carbon to entitle it to rank among the steels ; but the steel thus produced is always low in carbon, and may be classed with puddled steel. In the Catalan or bloomary forge the circum- stances favoring the production of a steely product are : a slow process, that the reduced iron may have time to absorb carbon ; the protection as far as possible of the mass of plastic metal from the direct action of the blast and from the action of rich iron cin- der ; and also the use of manganif erous ores, since the oxide of manganese, as already ex- plained, does not oxidize carbon readily. The character of the steel produced by the bloom- ary depends on the nature of the ores and the skill of the workmen. The impurities of the ores are more completely eliminated in the direct processes than in the blast furnace process, a gain obtained at the expense of a considerable loss of iron. Titaniferous ores can be successfully worked in the bloomary, and are said to give a superior steel. The product of the bloomary generally lacks uni- formity, a defect which can be remedied by repeated heatings and hammering. The bloom- ary process is rarely used now for the direct production of steel, but the iron made by this process is, on account of its purity, advanta- geously employed for conversion into steel by the cementation process. 2. Steel from Pig Iron. 2a. Puddled Steel. The process of puddling for steel does not differ essentially from that for iron. (See IRON MANUFACTURE.) The operation is stopped before complete de- carburization, or when the desired hardness is attained. The conditions favoring the produc- tion of steel in the puddling furnace are as follows : 1. Pure pig iron is necessary, since the refining is not carried as far as with wrought iron, and also because a less basic cinder is employed. 2. The pig iron should be highly carburized, that it may not come to nature too quickly. 3. It should not contain too little silicon, or the cinder will be too basic or " rich." 4. The presence of manganese is favorable, as it produces a fluid and non-oxidi- zing cinder. 5. The cinder should be "poor" or highly silicious, since rich cinder decarbu- rizes the metal. 6. The process should go on slowly, that it may be the more under control. 7. During the balling the temperature must be reduced as much as possible, and a smoky flame produced, to prevent oxidation. The na- ture of puddled steel has already been consid- ered in the foregoing. It possesses a degree of hardness proportional to the amount of carbon (which rarely exceeds 0'5 per cent.), and a fibrous or welded structure. It has been large- ly used for the heads of rails, being much more readily welded to iron than ordinary cast steel. Puddled steel made from pure pig irons is also much used for melting in crucibles for the pro- duction of fine cast steel. Saltpetre (potas- sium nitrate) has been used for the conversion of pig iron into wrought iron and steel. Its action is both oxidizing and purifying, the former through the large amount of .oxygen of the salt which is readily given off, and the latter through the strong base, potassa, which combines with the silicic and phosphoric acids produced. The apparatus devised by Heaton for the reaction between molten cast iron and saltpetre, for the conversion of poor pig iron into good steel, has been abandoned on account of the expense and uncertainty of the process. 2J. Uchatim Steel. Steel pro- duced by the reaction of pig iron and iron ore may be obtained in the molten condition, if the temperature of production is high enough. This is effected either in a crucible or in a Siemens regenerative furnace. Uchatius steel, named from its inventor, is made by fusing a mixture of granulated pig iron, iron ore, and oxide of manganese in crucibles. Its manu- facture is now confined to Sweden (though originally introduced in Austria), where the pure irons and ores are admirably adapted to the process. At the Siemens works in Lan- dore, Wales, the manufacture in the open hearth is regularly carried on by mixture of pig iron and iron ore. The process differs from that of Uchatius in that the ore is added in successive portions, and that to the decarbu- rized metal spiegeleisen is added, as is usual in the open-hearth processes. Scrap iron is also sometimes added, but its use is not essential to the process. The .charge consists of 5 to 6 tons of Bessemer pig iron and 30 cwt. of pure ore. The product is used principally for rails, and averages 0*40 per cent of carbon. 2c. Bessemer Steel. The Bessemer or pneumatic process consists in the removal of the carbon, silicon, &c., from pig iron by means of a blast of air forced through the molten metal. The reactions involved are in many respects the same as those in the puddling process ; that is to say, the silicon is first oxidized, and the silica thus formed combines with the oxides of iron and manganese (if present) to form a cin- der, and the carbon is subsequently oxidized to carbonic oxide. Owing, however, to the ra- pidity of the process and the large amount of pig iron employed, the heat developed in the oxidation of the silicon, carbon, &c., is suffi- cient to retain the resulting steel or iron in a fluid condition, so that it can be cast directly into moulds. The history of this remarkable