STEEL. As has been noted, steel was manu factured at a very early date in the history of civilization. Prior to 1,956. however. it was produeed in comparatively small amounts, and its use was restricted to the production of cut lery and tools. In 1456 Henry Bessemer made known the process for making steel in large quantities which revolutionized the iron trade of the world. This was followed try the inven tions of Siemens, Martin, and Thomas, which gave a further impetus to steel manufacture, and widely extended the use of that material. At present steel is made by the cementation proc ess, by the crucible process, by the acid Bes semer process, by the basic Bessemer process, by the acid open-hearth process, and by the basic open-hearth process. • In the following para graphs each of these processes will be described in outline.
Cement steel is made by placing a bar of soft, pure wrought iron in fine charcoal and exposing it to yellow heat. 1;y a slow process called cementation the carbon penetrates the metal at the rate of about one-eighth inch every twenty four hours. The process of cementation is car ried un in large retorts which handle many tons of bars at one time, so that it will always happen that some parts of the furnace arrive at full heat much sooner than others, and remain longer at that temperature. The consequence is that it is
necessary to break all the bars and grade the pieces by fracture according to their degree of carburization. Steel made in this way is com monly known as blister steel. Its use is limited by the fact that it always contains seams or pits of slag, which are present in the wrought iron. To avoid this trouble cement steel may be melted in a crucible out of contact with the air, and, being thus free from the slag, can be east into ingots and hammered or rolled into any desired shape. This double process is expen sive, and a cheaper and more common method of making crucible steel is to place powdered charcoal and crude bar iron in the crucible, the iron absorbing the carbon very rapidly in the molten state. This practice is almost universal in America. Sometimes pig iron and wrought iron are melted together, and in Sweden crucible steel is produced from pig iron and iron ore. Both blister steel and crucible steel belong to the general class known as high-carbon steel. Such steel can be made regularly in open-hearth fur naces; but so far this method, though cheaper, has not replaced the older methods. Blister and crucible steel are chiefly used for high-class edged tools, springs, etc.