STEEL. Before the introduction of 'the modern methods of steel making in the middle of the 19th century the name of steel was ap plied only to iron containing a sufficient per centage of carbon to become intensely hard on rapid cooling (quenching) from a red heat or higher temperature. The invention of the Bessemer and Open Hearth processes, however, by which it is possible to produce, in a molten condition, iron containing any proportion of carbon from a trace to 2 per cent or more, made a revision of the nomenclature necessary. The name of steel is now very generally applied to any iron obtained in a liquid state, provided it is malleable, regardless of the percentage of carbon it may contain and regardless, therefore, of whether it possesses or not the property of becoming hard on quenching. All malleable products manufactured by the Bessemer or Open Hearth processes are consequently classi fied as steel although some of them may con tain but a mere trace of carbon and be as soft and as deprived of hardening power as wrought iron. Iron products which are obtained in a molten condition but which are not malleable, owing generally to too high a percentage of car bon, are classified as cast iron. Iron products Which are malleable but obtained in a pasty state are classified as wrought iron. This nomen clature necessarily leaves out of consideration blister steel (also called cemented or converted steel, and 'by the English blister bar) which is obtained by introducing carbon (the cemen tation process) at a high temperature but below the meltingpoint, into bars of wrought iron. Ingot iron (obsolete) was a term applied to steel containing too little carbon to be usefully hardened. Plated bar is blister steel in the form of bars obtained through rolling or forg ing while hot. Shear steel is steel obtained through rolling or forging piles or fagots of plated or blister bars. After one such operation it is known as single-shear steel. The piling and forging of bars of single-shear steel yields double-shear steel. Bessemer, Open Hearth, crucible, electric steels, etc., are steels made re spectively by the Bessemer, Open Hearth, cru cible, electnc, etc., processes. Crucible steel is sometimes called cast steel. All steels, however, are initially cast. Eutectoid steel is steel con taining in the vicinity of 0.90 per cent carbon.
Hypo-eutectoid steel is steel containing less than 0.90 per cent carbon, while hyper-eutectoid steel is steel containing more than 0.90 per cent carbon (see IRON AND STEEL, METALLOGRA PHY or). Acid steel is steel made by Bessemer or Open Hearth processes when an acid (silicious) lining is used. Basic steel is steel made by the same processes when a basic lining is used. Low phosphorus pig iron must be used, for the manufacture of steel by an acid process whereas by a basic process high phosphorus pig iron may be used. Alloy or special steels are steels containing a sufficient percentage of one or more special elements to cause some of its properties to be deeply modified. The alloy ing elements most commonly used are nickel, chromium, tungsten, molybdenum, vanadium, manganese and silicon, hence the names of nickel steel, nickel-chromium steel, manganese steel, etc. By opposition steels which do not contain appreciable quantities of these elements are sometimes termed carbon steels. High speed steel is an alloy steel generally containing large proportions of • tungsten and chromium (sometimes also molybdenum and vanadium) and which after suitable heat treatment is so resistant to wear by abrasion that it can be used as cutting tools under such severe condi tions that the cutting edge of the tool may be heated to a red heat by the heat generated in cutting and still retain its cutting properties. This makes high speed cutting possible, hence the name of the steel.
Iron and carbon are the essential elements of all ordinary (carbon) steels. The carbon con tent may vary from a mere trace (a few hundredths of 1 per cent to some 1.5 per cent). With much larger proportions of carbon the metal ceases to be malleable and is no longer, therefore, classified as steel. Manganese 'is a necessary element of all steels, its introduction in the 'process of manufacture being necessary to obtain good forgeability. It is generally present in amounts varying between 0.1 to 1 per cent. Sulphur and phosphorus are unavoid able impurities. No steel of good quality should contain more than 0.1 per cent of either of these, while high grade steels should con tain much smaller proportions. Silicon is also always unavoidably present, varying in amount between 0.1 per cent or less to some 0.3 or 0.4 per cent.