Original, The invention of the process of making crucible steel by Huntsman, near Sheffield, England, in 1740, was a great advance in the art of making steel. He melted bars of cemented steel in small crucibles and thus got ingots of much greater uniformity. In succeeding decades men learned how to melt purer iron with carbonaceous materials and to introduce the requisite amount of manganese for making very high-grade material.
As practiced today, wrought iron, or scraps of good-quality soft steel, are melted in fire-clay or graphite crucibles holding about 100 pounds of metal in furnaces heated by coke or gas. The requisite amounts of carbonaceous alloying ingredients will be dissolved, as the metal liquefies at a necessarily very high temperature, and, after standing for some time to become a perfect liquid, the metal may be deoxidized with a bit of metallic aluminum and then poured carefully into ingot molds.
Fig. 22. Working Ingots at a Crucible Steel Furnace Courtesy of The Cotonial Sreet Company, Pifferburgh, Pennsylogonia.
Fig. 22 shows the men working at such a crucible furnace. Such a furnace is hardly more than a melting hole into which are led the pre-heated gas and air to combine about the crucibles. The furnace is run regeneratively, as will be explained further in the section on Open-Hearth Steel, with the gas supplied by gas-producers. One gets a good idea of the size of the crucibles, of the intense heat, and of the methods of handling the crucibles from this picture.
The manufacture of crucible steel still is carried out on a considerable scale, but, as the process never has overcome the defects of extremely small melts and much hand labor, it has lost relatively, in comparison with the tonnage processes. The process requires much skill, and is even yet being perfected in various details. There still is a strong demand for such material, especially for high-grade alloyed steels with the remarkable properties developed by the use of nickel, manganese, chromium, and tungsten.