Open hearth process

Kingdom. Adapted to steelmaking, the open-hearth process was the principal method for producing steel throughout the world until 1970. As of this writing (1996), it is stiU used in China and the CIS. 

The mechanism of carbon elimination is similar to those of the earlier open-hearth processes, ie, oxidation of carbon to carbon monoxide and carbon dioxide. The chemical reactions and results are the same in both cases. The progress of the reaction is plotted in Figure 5. 

Martin-. (Zron) Martin, open-hearth, -fluss-eisen, n. open-hearth iron, -fluss-stahl, m. open-hearth steel, -ofen, m. Martin furnace, open-hearth furnace, -ofenschlacke,/. open-hearth slag, -roheisen, n. open-hearth pig (iron). -Stahl, m. Martin steel (open-hearth steel). -stahlofeQ, m. open-hearth steel furnace. -verfahren, n. (Siemens-)Martin process, open-hearth process. 

Acid Open Hearth The original version of the Open Hearth process for steelmaking in which the hearth is made of a silica refractory. The process does not remove phosphoms or sulfur, the acid impurities in the iron, so the raw materials must be relatively free from these. Pioneered by C. W. Siemens and F. M. E. and P. Martin at Sireuil, France, in 1864. 

Basic Open Hearth A version of the Open Hearth process for steelmaking in which the hearth is made from calcined dolomite (calcium and magnesium oxides). The sulfur and phosphorus impurities in the raw materials are converted to basic slag, which is separated from the molten steel. First operated in 1882 at Alexandrovsky, near St. Petersburg, Russia, and at Le Creusot, France. It was the major steelmaking process in the world in the first half of the 20th century. See Thomas. 

Chenot An early steelmaking process. Iron ore was first reduced to sponge iron this was mixed with charcoal, manganese, and resin and compressed into small blocks. These blocks were then melted as in the Crucible process. Invented by A. Chenot in France in 1846 and operated on a small scale in Sheffield in the 1860s, but abandoned after the introduction of the Open Hearth process. 

Pig and ore A colloquial name for the Siemens Open Hearth process. 

Saniter A modification of the Basic Open Hearth process for reducing the sulfur content of the steel product by adding relatively large quantities of limestone and calcium chloride. Invented by E. H. Saniter at the Wigan Coal Iron Company in England in 1892, and used there and in Germany for approximately 20 years until superseded by the use of calcium fluoride as a flux. 

Talbot A semi-continuous steelmaking process which combines the Bessemer and Open Hearth processes. Molten pig iron from a Bessemer converter is poured into an Open Hearth furnace containing fresh ore and lime. Impurities in the pig iron oxidize and enter the slag. The process improves the yield of steel and the throughput of the plant. Introduced by B. Talbot at Pencoed, PA, in 1900 and subsequently adopted in Europe. 

Prior to the Civil War, engineers were pretty well limited to working with only a few materials, such as iron, copper, tin, zinc, brass and bronze and, of course, wood. Steel became more readily available shortly after the Civil War through the wider use of the recently discovered Bessemer and open-hearth processes and the subsequent discovery of alloy steels. And around the turn of the century, aluminum was becoming available in commercial quantities. 

The pig iron is brittle because it contains close to 5 per cent carbon. To turn il into steel, the carbon must be burned out until nnly from. 5 to 1.5 per cent remains. This is done either hy the Bessemer process (named for an Englishman. Henry Bessemer) or by the open-hearth process. The finished steel is molded... 

Historical Open-Hearth Process. For well over a century prior to the I96t)s. ihe open-licarlh process was die principal means for making sieel. As of tlte late If 80s. open-hearth steels had dropped from well over 90% of lolal steel production to less than 10% of steel produclion. The attraction of the basic open-hearth system over many decades was versatility in handling a variety of raw materials required for most grades of steel. Raw material charges could he 100% scrap. 100% hot metal, or scrap and hot metal in all intermediate ratios. 

Electric Iurnace Processes. Electric furnaces have been used for several decades to produce special steels lor which the open-hearth process was not suitable. 

In comparison with the Bessemer process, the open-hearth process has certain important advantages. It provides accurate control of temperature owing to the use of an outside source of heat. The composition of the final product can be predetermined by analysis and thereby controlled. Complete removal of phosphorus is accomplished, and this permits use of low-grade iron ores, which are usually of relatively high phosphorus content. None of these advantages is possessed by the Bessemer process. 

More than three-fourths of the steel produced in this country is produced by the open-hearth process. The uses are innumerable and include practically every commercial application except those in which special alloys must be employed. 

Electric-furnace process. One of the highest grades of steel now produced is made in electric furnaces in which steel from the Bessemer or open-hearth process is subjected to further refining. The steel produced in this relatively new process is characterized by its high density and the absence of occluded gases. The chief advantage of this process is its provision for more precise control of temperature. 

In the open-hearth process the slag may be removed by ladling or tilting, when the phosphorus content of the iron has been reduced from 1 per cent, or over to about 0-2 per cent. This furnishes a high-grade slag. A new slag by means of which the phosphorus content is reduced to about 002 per cent, is of much poorer quality (see Table I.). 

Yaws, C.L. and Hopper, J.R., in Chemical Processing Handbook, Marcel Dekker, New York, 1993, 939. Siemens-Martin A predecessor of the Siemens Open Hearth process. See Open Hearth. Siemens Open Hearth See Open Hearth. 

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