Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/368

352 IRON filings, and silica melted in a wind furnace affords a cast iron con taining 15-16 per cent, of silicon and nearly 3 per cent, carbon ; lime or calcium silicate on the other hand removes silicon from silicious iron when the two are melted together. It is a matter of usual belief that silicon expels sulphur from pig iron ; at any rate the conditions most favourable to production of highly silicious pig are not so favourable to the presence of sulphur, and hence grey silicious pig is much less sulphurized than white pig made from the same materials. According to Riley the greater the percentage of silicon in siliconeisen the smaller is the amount of carbon present, so that when 15 or 20 per cent, of silicon is present the carbon is reduced to a vory small amount. Silicon- Manganeiscn. Silicious spiegeleisen (or manganese silicide, as it is sometimes termed) is prepared by the ordinary blast furnace methods of making rich spiegeleisens by increasing the amount of silica present and using large amounts of fuel. For the purpose of preventing "blowholes" in cast soft steels containing but little carbon, an alloy containing about 8 per cent, of silicon, 14-15 of manganese, and about 1 3 per cent, of carbon, has been extensively used at Terre Noire. The steel thus produced gave the following numbers (Euverte, Bulletin Soc. des Ing. Civ., 1877) : Hard Metal for Projectiles. Very soft Metal. Percentage of carbon 0-550 to 0-635 0-260 to 0-317 silicon 0-405 ,, 0-550 0-260 ,, 0-330 ,, manganese 0-95 1-05 0-41 ,, 0-48 Crude Tempered Crude Tempered Breaking slrain in kilogr. per sq. millim ., Metal, j- 52-2 to 58 Metal. 77-2 to 116 Metal. 46-8 to 56 8 Metal. 56-5 to 67-7 Elongation 1-2 4-0 0-7 6-5 12-8 ,, 148 11-0 ,, 17-5 Chromium-steel, or " Chromcisen," as it may conveniently be termed, is closely allied to manganeisen ; the capabilities of this substance for the most part yet remain undeveloped, but the effect of the chromium is analogous in some respects to that of manganese, in others to that of carbon, communicating a fine close texture with hardness and brittleness when present in any quantity. Chrom- eisens containing 10 per cent, and upwards of chromium have been prepared by crucible operations, and of somewhat less rich ness in the blast furnace from ores containing a notable amount of chrome ironstone ; Sergius Kern obtained a very hard chromeisen containing 74 per cent, of chromium and 25 of iron by heating chrome ironstone and charcoal powder in graphite crucibles. The Tasmanian Iron Company produced from Tasmanian ores a pig containing some 6 or 7 per cent, of chromium and 4 of carbon ; . according to Riley a mixture of this pig with ordinary haematite pig (half and half) would not puddle well, being incapable of weld ing and forming a bloom on account of the thick cinder ; with less chromeisen (one-tenth) the puddling period was prolonged ; a little of the chromium remained unoxidized in the iron without materially affecting its qualities ; at first the ordinary grey pig melted whilst the chromium pig remained unfused. By melting chromium pig containing upwards of 2 per cent, of sulphur with ferro-manganese, the sulphur becomes almost entirely eliminated, the resulting product only containing 035 percent.; on adding it (in a fused state) to blown Bessemer metal a product was obtained not at all resembling good manganiferous Bessemer steel, as it crumbled under the hammer at a red heat. The experience of a Sheffield firm as to the tempering qualities of chromium steel has been very unsatisfactory ; and Boussingault states that he was unable to give to iron any of the useful properties of steel by adding chromium unless carbon were also present ; on the other hand, it has been stated that in America mining tools made of chromium steel have been found to be more durable than any others, the tempering being readily managed. Yet again, R. Brown finds that by adding potassium dichromate to blown Bessemer metal or other varieties of steel a certain amount of chromium is reduced and counteracts the evil effects of phosphorus, steel so made being capable of being bent and twisted cold even though containing as much as 1 per cent, of phosphorus ; thus samples of steel so pre pared gave the following numerical results (Journ. I. and S. Inst., 1879, 355): Percentage of carbon present 0-19 018 0"23 0-30 0-30 0-52 0-41 ,, chromium 0-18 0-20 0-21 0-14 0-16 0-20 0-26 ,, phosphorus .... Tensile "strain (tons per ) square inch) f 0-514 40-5 0-560 40-0 0-759 00-3 0-90 43-6 0-95 44-4 1-16 6-0 1-39 4-5 Percentage ultimate exten- ) sion 4-61 24-0 5-7 19-35 8-19 Tungsten-steels have been often brought forward as possessing valu able properties, but do not appear to have been largely manufactured in England. On the Continent they have attracted more attention thus Biermann of Hanover has prepared ferro-tungsten containing from 20 to 50 per cent, of tungsten and a few parts per cent of manganese with the object of using the composition in the same way as ferro-manganese, i.e., intermixing it with larger amounts decarbonized iron so as to obtain a tungsteniferous steel of known composition. Griiner states that the hardness of steel is increased by addition of tungsten almost indefinitely, but that when more than 2 or 3 per cent, is present the metal becomes brittle from extreme hardness ; for lathe tools steel up to 8 per cent, tungsten may be used provided they be submitted only to a mild oil temper ing, for with water they would fly to pieces ; thus a hook tool used in a steel tire shop of the West of France Railway Company contained Tungsten 7-98 per cent. Carbon 1-40 Silicon 0-22 In the manufacture of such steels the tungsten is introduced either as a triple manganese alloy (prepared on a Siemens hearth or in the blast furnace like ferro-manganese) or as crude fritted metallic tungsten obtained by reducing wolfram with a mixture of coal and tar, &c. Levallois has patented in France the use of ternary nickel- tungsten-iron alloys containing No. 1. No. 2; No. 3. Iron 93 95-0 97-0 6 5 4-5 2-5 Nickel 0-5 5 0-5 100-0 100-0 100-0 They are said to be very hard, but can be worked like ordinary cast steel ; they are prepared by putting the tungsten and nickel into a small soft iron tube together with a little ilux (composed of 9 parts boric anhydride and 8 each of calcined quartz and washed calcium carbonate), and placing the tube in the midst of the rest of the iron in a crucible, the surface being covered with some of the flux. When melted up, the whole is poured into moulds in the usual way. Manganese Bronze. By melting fcrro-manganese and copper together, or preferably mixing the two metals separately fused, all traces of oxide disseminated through the copper are removed by the agency of the readily oxidizable manganese, and a close-grained tough alloy results, capable of very many useful applications. The percentage of iron in the alloys usually prepared, however, being but small, the description of these products more properly belongs to the metallurgy of copper and manganese. IX. PHYSICAL QUALITIES OF IKON AND STEEL IN THEIR PRACTICAL RELATIONSHIPS. 42. Hardening, Tempering, and Annealing of Steel. It has been already stated ( 3) that the characteristic property of steel as distinguished from malleable iron is that when heated red hot and suddenly cooled (by plung ing into cold water, oil, mercury, &c.) it becomes hardened to a greater or lesser extent, and rendered more or less brittle and also elastic ; when the steel thus hardened is heated red hot and cooled slowly, on the other hand, it loses this acquired hardness and becomes soft and malleable again j this inverse process is strictly termed " softening " or " annealing." The generic phrase " tempering" is usually applied to mean a combination of the hardening and anneal ing processes practically applied to all steel goods in order to give such a degree of hardness as will best fit them for resisting wear and tear, conjoined with the minimum possible of brittleness, this being effected by first harden ing them by heating to a red heat and suddenly cooling, and then heating up again to a somewhat lower tempera ture and allowing to cool slowly. According to the tem perature to which the hardened steel has been heated before annealing, so is the diminution in the hardness effected by the process ; and the particular resultant combination of hardness with toughness and elasticity is spoken of as the " temper " of the steel. Occasionally, however, this latter phrase is applied in somewhat different senses ; thus steeds of different carbon percentages are sometimes said to differ in temper irrespective of whether they have actually been hardened and annealed or not ; the term " tempering capacity " or " hardening capacity " would better express the idea. Sometimes again, especially amongst " practical " men and workmen, the phrase " to temper a tool " is under stood as signifying simply to harden it ; whilst on the other