CRUCIBLE PROCESS

technique for producing fine or tool steel. The process was invented in Britain about 1740 by Benjamin Huntsman, who heated small pieces of carbon steel in a closed fireclay crucible placed in a coke fire. The temperature he was able to achieve (2,900 F, or 1,600 C) was high enough to permit melting steel for the first time, producing a homogeneous metal of uniform composition that he used to manufacture watch and clock springs. After 1870 the Siemens regenerative gas furnace replaced the coke-fire furnace; it produced even higher temperatures. The Siemens furnace had a number of combustion holes, each holding several crucibles, and heated as many as 100 crucibles at a time. All high-quality tool steel and high-speed steel was long made by the crucible process, but in the 20th century the electric furnace has replaced it in countries in which electric power is cheap.