STEEL, MANUFACTURE OF CRUCI BLE. Crucible steel is so called because the ingredients from which it is made are melted in crucibles or pots. The name to day is almost synonymous with "tool steel"— meaning a steel containing at least one half per cent of carbon, which will, there fore harden materially when plunged at a bright red heat into water or oil. Steel of lower carbon than this may be made in crucibles for especial purposes when hardness is not the chief quality desired. For example, steel cast ings are frequently made of crucible steel. The quantity actually so used in this country is only a few thousand tons per annum.
The practice of hardening steel is of great antiquity and is referred to by the early Roman and Greek writers. The ancient Egyptians heated iron, in some cases possibly of meteoric origin, in the forge until, by long contact with the fuel, it absorbed enough carbon to considerable surface hardening when quenched. The difference between oil and water hardening is referred to by Lucretius who says: *The finest tools are tempered in oil, which gives a more durable hardness thah that imparted by water.• The fact that iron heated in contact with carbon absorbs some of that element, which renders it harder, seems have been known for many centuries and prior to Huntsman's invention, in 1740, all steel for tools was made by the process of cementation. Especially in Austria and England the art and industry of converting pure wrought iron into cement- or blister-bar flourished, by which, as French says : steel was obtained which had uncertain per centages of carbon, higher on the outside than on the inside, and varying in hardness from one end to the other, according as the bar came in contact in the converting furnace, with more or less of the carburizing material, or a higher or lower degree of heat.* It was to overcome this lack of uniformity that so-called *single' and *double-shear' were made, but. Huntsman conceived the idea of melting the cemented-bar in crucibles, thus rendering it absolutely homo geneous and of uniform carbon contents throughout the mass. As first carried out, the melted steel was allowed to cool in the crucible, which was then broken away and the resulting mass was used as an ingot. About a century ago Mushet patented the production of steel made in the crucible by melting together soft bar iron and a certain amount of carbonaceous matter. This process did not amount to much until 1839, when Heath patented the use of man ganese as an essential addition to crucible steel.
In America the Mushet-Heath process of melt ing together in crucibles soft bar-iron, with or without a certain percentage of steel scrap, charcoal and oxide of manganese, spiegeleisen or ferromanganese is more generally employed than the original Huntsman process of melting cemented or blister-bar. It has been said of Huntsman's invention that,—*The invention of cast-steel was second in importance to no pre vious event in the world's history, unless it may have been the invention of printing.' Hunts man's process was rapidly adopted and at the time of his death there were several firms melt ing steel, and possibly 500 individuals and firms making files, edge-tools, etc., in Sheffield,— famous for its since Chaucer's day. Among these names appeared Spencer, Jessop, Sanderson, Parkin, Turner, Hobson and Rogers and these same names appear to-day in con nection with both English and American cru cible steel works.
The Materials.— The base used for cruci ble steel is usually wrought iron. England, Ger many and America draw on Sweden for the more expensive grades, and by many it is be lieved that Swedish materials possess some mysterious virtues not afforded by other irons, regardless of what the results of chemical analysis show. The Swedish irons are all made from charcoal pig iron and are refined by the Lancashire or Walloon processes. Some have claimed that these irons contain traces of vana dium and that to this they owe their virtue. They usually contain small amounts of manga nese, while ordinary puddled irons are nearly free from this element. To the writer this seems more important than a possible trace of vanadium. A careful investigation of products made from Swedish and American irons of the some analysis has revealed no differ ence in the quality of the product, chemically, physically or by practical test in tools of divers sorts. Certain it is that rarely does Sheffield tool steel show as great purity as regards sul phur and phosphorus as is seen in the product of American mills. In America, while Swedish iron is still used to some extent, it has been replaced by selected open hearth bar and by the purer product of the puddling furnace. This com monly carries less than one-hundredth of 1 per cent of sulphur and phosphorus, and also contains much less copper than the Swedish irons.