Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/299

 I R O N 283 Name. Tensile strength in kilos per sq. millim. Elongation per cent. Approximate percentage of carbon. General Characters. I Welds, but docs not nr. Extra soft 48 to 50 20 to 25 0-25 to 0-35 -: harden ; used for boiler ( plates, rivets, &amp;lt;fec. f Welds but badly, and ft Soft !- 5G G9 10 20 - ( 0-35 0-45 0-45 0-55 I hardens slightly, but -, not (o any great extent; c. Semi-hard. 1. rails, pistons, &amp;lt;fec. f Hardens well, but ,/ Hard 0-55 ,, 0-65 used for springs, cut- f 1 5 10 -j l&amp;lt;fcc. {Hardens, but does e. Extra hard 1 above 65 not weld; used for fine springs and tools, spin dles, &c. A tensile strength of 1 kilogramme per square millimetre is about equal to 63 tons per square inch, so that on this scale extra soft, soft and semihard, and hard steels have average tensile strengths of about 32, 39, and 55 tons per square inch respectively. Steels of the (a) class can be bent U shape without breaking, and will generally allow the two ends of the U to be hammered together without fracture ; steels of the (c) class break when the angle of bsnd reaches to 130-140; and tho other classes are intermediate between these limits. Hackney has proposed a classification of iron and steel practi cally identical with this &quot;Seraiug scale &quot; ; the main objections to such scales are that, as even the softest completely fused metals are thus designated &quot;steel,&quot; the time-honoured definition of steel as being a substance that can be hardened and tempered is wholly done away with ; and the circumstance that the numerical values ex pressing the ductility and tensile strength are variable with the dimensions of the piece of metal tested ( 43). Much confusion and litigation would be avoided were some name other than &quot;steel&quot; applied to the modern metals of low carbon percentage obtained by fusion processes, and destitute of the power of taking any consider able amount of temper by heating red hot and rapidly cooling. In practically testing a sample of steel, the difference between a specimen that has been prepared by a fusion process and by a process of puddling is usually very mani fest when the specimens are slightly etched by dilute nitric acid or other agent that will gradually attack the metal : the fusion product exhibits a regular more or less granular structure, whilst the other exhibits more or less of a fibroid character. On dissolving the metal in cupric chloride ( 6), a small amount of silicious cinder is left undissolved in the latter case, but practically none with a properly fused steel. The presence of sulphur and phosphorus in true steels in other than the most minute proportions exercises a marked deteriorating effect upon the strength and tenacity of the metal, the former substance rendering the steel more or less brittle when hot (red-short or hot-short), the latter causing it to be liable to crack and break when cold (cold short). The presence of manganese, however, and to some extent of carbon and silicon, modifies the exact amount of effect produced by a given quantity of phosphorus or sulphur ; as a general rule it may be said that a steel con taining 5 per cent, of carbon and upwards, and also con taining more than O l per cent, of sulphur, will be objection ably red-short, and that, if it contain more than O l per cent, of phosphorus, it will be too cold-short for most applications; whilst a much smaller quantity, as little as 03 per cent., renders the steel almost useless for tools and cutting instruments, &c., in which a fine temper is essential. These figures, however, are subject to notable corrections : the presence of manganese to an extent of several times the amount of sulphur present considerably mitigates the evil effect of that substance, whilst, provided the carbon be very low (i.e., that the metal is really not steel at all but only fused iron), much larger quantities of phosphorus than O l per cent, may be present without deteriorating the properties of the substance to so great an extent as would be occasioned by the presence of much smaller quantities of phosphorus simultaneously with several tenths per cent, of carbon. Thus years ago the practical experience acquired at the Terre Noire works proved that good rails could be made from steel containing about 1 per cent, of manganese and as much as 3 per cent, of phosphorus, provided the carbon did not exceed half that amount; subsequently, good serviceable rails have been rolkd not only in England but also in Saxony, Austria, America, and elsewhere, containing 3 to nearly 4 per cent, of phosphorus and about half as much of carbon, or less. These &quot; phosphoric steels &quot; (more correctly &quot; homo geneous irons,&quot; fused irons, or &quot; ingot irons &quot;), however, are wholly unsuitable for all purposes requiring the metal to be tempered, on account of the impossibility of having so much phosphorus present together with more than minute amounts of carbon without producing brittleness and utter inability to be worked. The effect of silicon on the physical qualities of steel is far less marked than that of sulphur and phosphorus. Like that of the latter it is modified by the amount of carbon present : thus Riley has found 2 per cent, of silicon in rails of good quality ; Gautier states that a silicoueisen con taining upwards of 7 per cent, of silicon, but almost desti tute of carbon, could be forged perfectly, whilst a steel containing To per cent, of silicon and slightly less than 2 per cent, of carbon (with 076 of manganese) rolled perfectly and was very strong. The presence of silicon, moreover, conjointly with that of manganese, exerts a remarkable action in diminishing the extrusion of gases from molten steel in the act of solidifying, thereby pro ducing honeycombing ; so that when very soft steels are cast into ingots much sounder masses are obtained by the ordinary casting processes (i.e., not under hydraulic or rich spiegeleisen or ferro-manganese is employed. On the present to the extent of 5 to I O per cent, or thereabouts, both hot and cold shortness are brought about to a greater or lesser extent. Nitrogen has been supposed by many chemists and especi ally by Fremy to be an essential constituent of steel ; and in favour of this view it is to be noticed that in the prepara tion of steel by cementation the addition of nitrogenous organic matter (scraps of leather, horn, ferrocyanide of potassium, &c.) is found to facilitate the conversion of bar iron into blister steel. On the other hand this may be due simply to the formation and absorption of cyanogen, which carbonizes the iron without necessarily communicat ing nitrogen to it. The actual quantity of nitrogen found in steel by various experimenters is always extremely small, 1 whilst it is possible to produce steel from iron free from nitrogen by cementation in pure carbon oxide, or in an atmosphere of coal gas (Macintosh s patent), so that nitrogen is clearly not an essential constituent in these cases. Moreover, nitrogen has been found both in wrought and in cast iron in even larger quantity than in steel, so that the peculiar properties of steel as regards hardening 1 From O Oll to 018 per cent, of nitrogen was found by Bouis in various specimens of malleable iron, cast iron, and steel ; from 007 to 057 per cent, in various steels and wrought irons was found by Boussingault. By heating metallic iron in ammonia gas much more highly nitrogenized substances can be produced, Fremy Laving thus obtained substances containing as much as 9 &quot;8 per cent, of nitrogen. In these and other analogous experiments by others, various methods of analysis were adopted, the most conclusive ones being solution of the metal in pure hydrochloric acid, and determination ot the ammonia freed by the combination of the nascent hydrogen with the nitrogen. Recently A. H. Allen has repeated these experiments, and also made others by passing steam over the red-hot metal, and determining the ammonia produced. The quantity of nitrogen thus obtainable varied from G 0041 per cent, in spiegeleisen to 0172 per cent, in steel made from Dannemora iron.
 * used for tires, axles,
 * does not weld readily ;
 * ting tools, saws drills,
 * -6D 105
 * other powerful pressure) when a little siliciuretted metal is
 * added to the steel just before casting than when ordinary
 * other hand, when carbon and silicon are simultaneously