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Open-hearth Cast Steel

This steel is produced on a large scale and is so called to distinguish it from steel made by the Bessemer process, by puddling, or from blister-steel melted in the crucible.

Heath, in 1845, patented his invention of producing cast steel by dissolving malleable scrap in molten cast iron by a process independent of crucibles, by melting pig iron in a cupola, and running this into the bed of a steel-making furnace, into the upper part of which the malleable iron was introduced in bars, that they might be heated by the waste heat and gradually pushed forward so as to dissolve in the molten pig, with the formation of steel. Siemens said this method would have been successful had the regenerative principle been known to Heath, whereby he could have obtained the requisite intensity of heat and absence of cutting draught essential to the proper combination together, by fusion, of the wrought and carbonized iron without oxidation. Substantially, with the addition of the use of a regenerative furnace and improved working details, it is one of the forms of steel-making now known as the Siemens or Siemens-Martin processes. By employing the open-hearth and steel-melting regenerative furnace in the processes of steel-making, the highest possible temperatures are attainable, and the evil effects of a cutting flame and strong draught are obviated.

The Siemens or ore process of producing steel consists in melting hematite or other pig iron free from sulphur and phosphorus, and then adding in small quantities at a time an equally pure ore until a sample, taken out from time to time, does not harden on plunging into water while red-hot. To the fused iron spiegeleisen, etc., is then added. Another method consists of a combination of the Martin and the ore process; the pig and scrap, etc., being fused together, and the decarbonization being then effected, not through oxidation by the gases alone, but by that together with ore added to the mass. The Pernot furnace for steel-making is simply a Siemens-Martin furnace with a rotating bed, the hearth being a saucer-shaped cavity supported by an iron frame, mounted on a nearly vertical axis, and running on wheels upon a rail or guide, supported on a stout bogie. The bed is rotated by means of gearwheels. The charges of pig iron and scrap are well heated before being placed on the hearth, which, when it is made to revolve at from 2 to 4 revolutions per minute, causes the different pieces to keep constantly changing their position; and this, coupled with the fact that one half of the bed is being alternately brought under the full action of the flame as the charge slips down at each revolution, brings about a very rapid fusion of the mass. See REGENERATIVE FURNACE.