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IRON AND STEEL
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See also:IRON AND See also:STEEL .' 1 . See also:Iron, the most abundant and the cheapest of the heavy metals, the strongest and most magnetic of known substances, is perhaps also the most indispensable of all See also:save the See also:air we breathe and the See also:water we drink . For one See also:kind of See also:meat we could substitute another; See also:wool could be replaced by See also:cotton, See also:silk or See also:fur; were our See also:common silicate See also:glass gone, we could probably perfect and cheapen some other of the transparent solids; but even if the See also:earth could be made to yield any substitute for the See also:forty or fifty million tons of iron which we use each See also:year for rails, See also:wire, machinery, and structural purposes of many kinds, we could not replace either the See also:steel of our cutting tools or the iron of our magnets, the basis of all commercial See also:electricity . This usefulness iron owes in See also:part, indeed, to its abundance, through which it has led us in the last few thousands of years to adapt our ways to its; but still in See also:chief part first to the single qualities in which itvery weak; conducting See also:heat and electricity easily, and again offering See also:great resistance to their passage; here See also:welding readily, there incapable of welding; here very infusible, there melting with relative ease . The coincidence that so indispensable a thing should also be so abundant, that an iron-needing See also:man should be set on an iron-cored globe, certainly suggests See also:design . The indispensableness of such abundant things as air, water and See also:light is readily explained by saying that their very abundance has evolved a creature dependent on them . But the indispensable qualities of iron did not shape man's See also:evolution, because its great usefulness did not arise until historic times, or even, as in See also:case of See also:magnetism, until See also:modern times . These See also:variations in the properties of iron are brought about in part by corresponding variations in See also:mechanical and thermal treatment, by which it is influenced profoundly, and in part by variations in the proportions of certain See also:foreign elements which it contains; for, unlike most of the other metals, it is never used in the pure See also:state . Indeed pure iron is a rare curiosity . Foremost among these elements is See also:carbon, which iron inevitably absorbs from the See also:fuel used in extracting it from its ores . Se strong is the effect of carbon that the use to which the See also:metal is put, and indeed its See also:division into its two great classes, the malleable one, comprising steel and wrought iron, with less than 2.20% of carbon, and the unmalleable one, See also:cast iron, with more than this quantity, are based on carbon-content . (See Table I.) Containing very little Carbon (say, Containing an Intermediate Containing much Carbon (say, less than li0.30 ttle %) . C Contaifrom 2.2 to 5 %) . Quantity of Carbon (say, between 0.30 and 2.2 /°) . Slag-bearing or ... WROUGHT IRON . WELD STEEL . " Weld-metal " See also:Series . Puddled and bloomary, or See also:Charcoal- Puddled and See also:blister steel See also:hearth iron belong here. belong here . See also:LOW-CARBON Or MILD STEEL, See also:HALF-HARD and HIGH-CARBON CAST IRON . sometimes called " See also:ingot-iron." STEELS, sometimes called " ingot-steel." Slagless or "Ingot- It may be either See also:Bessemer, open- They may be either Bessemer, Normal cast iron, " washed " metal, Metal " Series. hearth, or crucible steel. open-hearth, and most " malleable cast iron " belong here . or crucible steel . iron also often Malleable cast belongs here . ALLOY STEELS .
ALLOY CAST IRONS.*
See also:Nickel, See also:manganese, See also:tungsten, and Spiegeleisen, ferro-manganese, and
chrome steels belong here. silico-spiegel belong here
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* The See also:term " Alloy Cast Irons " is not actually in frequent use, not because of any question as to its fitness or meaning, but because the need of such a generic term rarely arises in the See also:industry
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excels, such as its strength, its magnetism, and the See also:property which it alone has of being made at will extremely hard by sudden cooling and soft and extremely pliable by slow cooling; second, to the See also:special combinations of useful properties in which it excels, such as its strength with its ready welding and shaping both hot and See also:cold; and third, to the great variety of its properties
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It is a very See also:Proteus
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It is extremely hard in our files and razors, and extremely soft in our See also:horse-See also:shoe nails, which in some countries the See also: The See also:change from isen to iren in 16th cent. yron) is due to rhotacism, but whether See also:direct from isen or through isern, irern is doubtful . " Steel "• represents the O . Eng. stel or See also:stele (the true See also:form ; only found, however, with spelling See also:style, cf. st yl-ecg, steel-edged ). cognate with Ger . See also:Stahl, Dut. and Dan. slant, &c.; the word is not found outside See also:Teutonic . See also:Skeat (Etym . See also:Diet., 1898) finds the ultimate origin in the Indo-See also:European base sick-, to be See also:firm or still, and compares Lat. stagnunz, See also:standing-water . a I C . 2(' 2 . Nomenclature.—Until about 186o there were only three important classes of iron—wrought iron, steel and cast iron . The essential characteristic of wrought iron was its nearly See also:complete freedom from carbon; that of steel was its moderate carbon-content (say between 0.30 and 2.2 %), which, though great enough to confer the property of being rendered intensely hard and brittle by sudden cooling, yet was not so great but that the metal was malleable when cooled slowly; while that of cast iron was that it contained so much carbon as to be very brittle whether cooled quickly or slowly . This See also:classification was based on carbon-content, or on the properties which it gave . Beyond this, wrought iron, and certain classes of steel which then were important, necessarily contained much slag or " cinder," because they were made by welding together pasty particles of metal in a See also:bath of slag, without subsequent See also:fusion .. But the best class of steel, crucible steel, was freed from slag by fusion in crucibles; hence its name, " cast steel." Between 186o and 187o the invention of the Bessemer and open-hearth processes introduced a new class of iron to-See also:day called " mild " or " low-carbon steel," which lacked the essential property of steel, the hardening See also:power, yet differed from the existing forms of wrought iron in freedom from slag, and from cast iron in being very malleable . Logically it was wrought iron, the essence of which was that it was (r) "iron" as distinguished from steel, and II (2) malleable, i.e. capable of being " wrought." This name did not please those interested in the new product, because existing wrought iron was a low-priced material . Instead of inventing a wholly new name for the wholly new product, they appropriated the name " steel," because this was associated in the public mind with superiority . This they did with the excuse that the new product resembled one class of steel--cast steel—in being See also:free from slag; and, after a See also:period of protest, all acquiesced in calling it " steel," which is now its firmly established name . The old varieties of wrought iron, steel and cast iron preserve their old names; the new class is called steel by See also:main force . As a result, certain varieties, such as blister steel, are called " steel " solely because they have the hardening power, and others, such as low-carbon steel, solely because they are free from slag . But the former lack the essential quality, slaglessness, which makes the latter steel, and the latter lack the essential quality, the hardening power, which makes the former steel . " Steel " has come gradually to stand rather for excellence than for any specific quality . These anomalies, however confusing to the See also:general reader, in fact cause no appreciable trouble to important makers or users of iron and steel, beyond forming an occasional See also:side-issue in litigation . 3 . See also:Definitions.—Wrought iron is slag-bearing malleable iron, containing so little carbon (0.30% or less), or its See also:equivalent, that it does not harden greatly when cooled suddenly . Steel is iron which is malleable at least in some one range of temperature, and also is either (a) cast into an initially malleable See also:mass, or (b) is capable of hardening greatly by sudden cooling, or (c) is both so cast and so capable of hardening . (Tungsten steel and certain classes of manganese steel are malleable only when red-hot.) Normal or carbon steel contains between 0.30 and 2.20% of carbon, enough to make it harden greatly when cooled suddenly, but not enough to prevent it from being usefully malleable when hot . Cast iron is, generically, iron containing so much carbon (2'20% or more) or its equivalent that it is not usefully malleable at any temperature . Specifically, it is cast iron in the form of castings other than pigs, or remelted cast iron suitable for such castings, as distinguished from See also:pig iron, i.e. the molten cast iron as it issues from the blast See also:furnace, or the pigs into which it is cast . Malleable cast iron is iron which has been cast in the See also:condition of cast iron, and made malleable by subsequent treatment without fusion . Alloy steels and cast irons are those which owe their properties chiefly to the presence of one or more elements other than carbon . Ingot iron is slagless steel with less than 0'30% of carbon . Ingot steel is slagless steel containing more than o.3o% of carbon . Weld steel is slag-bearing iron malleable at least at some one temperature, and containing more than 0.30% of carbon . 4 . See also:Historical See also:Sketch.—The iron See also:oxide of which the ores of iron consist would be so easily deoxidized and thus brought to the metallic state by the carbon, i.e. by the glowing coals of any primeval See also:savage's See also:wood See also:fire, and the resulting metallic iron would then differ so strikingly from any See also:object which he had previously seen, that its very See also:early use by our See also:race is only natural . The first observing savage who noticed it among his ashes might easily infer that it resulted from the See also:action of burning wood on certain extremely heavy stones . He could See also:pound it out into many useful shapes .
The natural steps first of making it intention-ally by putting such stones into his fire, and next of improving his fire by putting it and these stones into a cavity on the See also:weather side of some See also:bank with an opening towards the prevalent See also:wind, would give a See also:simple forge, differing only in See also:size, in lacking forced blast, and in details of construction, from the Catalan forges and bloomaries of to-day
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Moreover, the coals which deoxidized the iron would inevitably carburize some lumps of it, here so far as to turn it into the brittle and relatively useless cast iron, there only far enough to convert it into steel, strong and very useful even in its unhardened state
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Thus it is almost certain that much of the earliest iron was in fact steel
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How soon afterman's See also:discovery, that he could See also:beat iron and steel out while cold into useful shapes, he learned to forge it while hot is hard to conjecture
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The See also:pretty elaborate appliances, See also:tongs or their equivalent, which would be needed to enable him to hold it conveniently while hot, could hardly have been devised till a very much later period; but then he may have been content to forge it inconveniently, because the great ease with which it mashes out when hot, perhaps pushed with a stout stick from the fire to a neighbouring See also:flat See also: Indeed, though iron ores abound in many places which have neither copper nor tin, yet there are but few places which have both copper and tin . It is not improbable that, once bronze became known, it might replace iron in a measure, perhaps even in a very large measure, because it is so fusible that it can be cast directly and easily into many useful shapes . It seems to be much more prominent than iron in the Homeric poems; but they tell us only of one region at one See also:age . Even if a nation here or there should give up the use of iron completely; that all should is neither probable nor shown by the See also:evidence . The See also:absence of iron and the abundance of bronze in the See also:relics of a prehistoric See also:people is a piece of evidence to be accepted with caution, because the great defect of iron, its proneness to See also:rust, would often See also:lead to its complete disappearance, or See also:conversion into an unrecognizable mass, even though tools of bronze originally laid down beside it might remain but little corroded . That the ancients should have discovered an art of hardening bronze is grossly improbable, first because it is not to be hardened by any simple See also:process like the hardening of steel, and second because, if they had, then a large proportion of the See also:ancient bronze tools now known ought to be hard, which is not the case . Because iron would be so easily made by prehistoric and even by primeval man, and would be so useful to him, we are hardly surprised to read in See also:Genesis that Tubal See also:Cain, the See also:sixth in descent from See also:Adam, discovered it; that the Assyrians had knives and saws which, to be effective, must have been of hardened steel, i.e. of iron which had absorbed some carbon from the coals with which it had been made, and had been quenched in water from a red heat; that an iron See also:tool has been. found embedded in the ancient See also:pyramid of Kephron (probably as early as 3500 B.C.); that iron metallurgy had advanced at the See also:time of Tethmosis (Thothmes) III . (about r500 B.C.) so far that See also:bellows were used for forcing the forge fire; that in See also:Homer's time (not later than the 9th See also:century B.c.) the delicate art of hardening and tempering steel was so See also:familiar that the poet used it for a simile, likening the hissing of the stake which Ulysses drove into the See also:eye of See also:Polyphemus to that of the steel which the smith quenches in water, and closing with a reference to the strengthening effect of this quenching; and that at the time of See also:Pliny (A.D . 23–79) the relative value of different See also:baths for hardening was known, and oil preferred for hardening small tools . These instances of the very early use of this metal, intrinsically at once so useful and so likely to disappear by rusting away, tell a See also:story like that of the single See also:foot-See also:print of the savage which the waves See also:left for See also:Robinson Crusoe's warning . Homer's familiarity with the art of tempering could come only after centuries of the wide use of iron . 5 . Three Periods.—The See also:history of iron may for convenience be divided into three periods: a first in which only the direct extraction of wrought iron from the ore was practised; a second which added to this primitive art the extraction of iron in the form of carburized or cast iron, to be used either as such or for conversion into wrought iron; and a third in which the iron worker used a temperature high enough to melt wrought iron, which he then called molten steel . For brevity we may See also:call these the periods of wrought iron, of cast iron, and of molten steel, recognizing that in the second and third the earlier processes continued in use . The first period began in extremely remote prehistoric times; the second in the 14th century; and the third with the invention of the Bessemer process in 1856 . 6 . First Period.—We can picture to ourselves how in the first period the savage smith, step by step, bettered his See also:control over his fire, at once his source of heat and his deoxidizing See also:agent . Not See also:con-See also:tent to let it See also:burn by natural See also:draught, he would See also:blow it with his own breath, would expose it to the prevalent wind, would urge it with a See also:fan, and would devise the first crude valveless bellows, perhaps the pigskin already familiar as a water-See also:bottle, of which the psalmist says: " I am become as a bottle in the See also:smoke." To drive the air out of this skin by pressing on it, or even by walking on it, would be easy; to fill it again with air by pulling its sides apart with his fingers would be so irksome that he would soon learn to distend it by means of strings . If his bellows had only a single opening, that through which they delivered the blast upon the fire, then in inflating them he would draw back into them the hot air and ashes from the fire . To prevent this he might make a second or suction hole, and thus he would have a, veritable See also:engine, perhaps one of the very earliest of all . While inflating the bellows he would leave the suction See also:port open and See also:close the See also:discharge port with a pinch of his See also:finger; and while blowing the air against the fire he would leave the discharge port open and pinch together the sides of the suction port . The next important step seems to have been taken in the 4th century when some forgotten See also:Watt devised valves for the bellows . But in spite of the activity of the iron manufacture in many of the See also:Roman provinces, especially See also:England, See also:France, See also:Spain, See also:Carinthia and near the See also:Rhine, the little forges in which iron was extracted from the ore remained, until the 14th century, very crude and wasteful of labour, fuel, and iron itself : indeed probably not very different from those of a thousand years before . Where iron ore was found, the See also:local smith, the Waldschmied, converted it with the charcoal of the surrounding See also:forest into the wrought iron which he worked up . Many farmers had their own little forges or smithies to See also:supply the iron for their tools . The fuel, wood or charcoal, which served both to heat and to deoxidize the ore, has so strong a carburizing action that it would turn some of the resultant metal into " natural steel," which differs from wrought iron only in containing so much carbon that it is relatively hard and brittle in its natural state, and that it becomes intensely hard when quenched from a red heat in water . Moreover, this same carburizing action of the fuel would at times go so far as to turn part of the metal into a true cast iron, so brittle that it could not be worked at all . In time the smith learnt how to convert this unwelcome product into wrought iron by remelting it in the forge, exposing it to the blast in such a way as to burn out most of its carbon . 7 . Second Period.—With the second period began, in the 14th century, the See also:gradual displacement of the direct extraction of wrought iron from the ore by the intentional and See also:regular use of this indirect method of first carburizing the metal and thus turning it into cast iron, and then converting it into wrought iron by remelting it in the forge . This displacement has been going on ever since, and it is not quite complete even to-day . It is of the familiar type of the re-placing of the simple but wasteful by the complex and economical, and it was begun unintentionally in the See also:attempt to save fuel and labour, by increasing the size and especially the height of the forge, and by See also:driving the bellows by means of water-power . Indeed it was the use of water-power that gave the smith pressure strong enough to force his blast up through a longer See also:column of ore and fuel, and thus enabled him to increase the height of his forge, enlarge the See also:scale of his operations, and in turn save fuel and labour . And it was the lengthen-See also:ing of the forge, and the length and intimacy of contact between ore and fuel to which it led, that carburized the metal and turned it into cast iron . This is so fusible that it melted, and, See also:running together into a single molten mass, freed itself mechanically from the " See also:gangue," as the foreign minerals with which the ore is mixed are called . Finally, the improvement in the quality of the iron which resulted from thus completely freeing it from the gangue turned out to be a great and unexpected merit of the indirect process, probably the merit which enabled it, in spite of its complexity, to drive out the direct process .
Thus we have here one of these cases common in the evolution both of nature and of art, in which a change, made for a specific purpose, has a wholly unforeseen See also:advantage in another direction, so important as to outweigh that for which it was made and to determine the path of future development
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With this method of making molten cast iron in the hands of a people already familiar with bronze See also:founding, iron founding, i.e. the casting of the molten cast iron into shapes which were useful in spite of its brittleness, naturally followed
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Thus ornamental iron castings were made in See also:Sussex in the 14th century, and in the 16th cannons weighing three tons each were cast
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The indirect process once established, the gradual increase in the height and See also:diameter of the high furnace, which has lasted till our own days, naturally went on and See also:developed the gigantic blast furnaces of the See also:present time, still called " high furnaces " in See also:French and See also:German
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The impetus which the indirect process and the See also:acceleration of See also:civilization in the 15th and 16th centuries gave to the iron industry was so great that the demands of the iron masters for fuel made serious inroads on the forests, and in 1558 an See also:act of See also:Queen See also:
B
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See also:Neilson's invention in 1828 of heating the blast, which increased the See also:production and lessened the fuel-See also:consumption of the furnace wonder-fully
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Very soon after this, in 1832, the See also:work of heating the blast was done by means of the See also:waste gases, at Wasseralfingen in See also:Bavaria
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Meanwhile See also:
Third Period.—The third period has for its great distinction the invention of the Bessemer and open-hearth processes, which are like Huntsman's crucible process in that their essence is their freeing wrought iron and low carbon steel from mechanically entangled cinder, by developing the hitherto unattainable temperature, rising to above 1500° C., needed for melting these relatively infusible See also:pro-ducts
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These processes are incalculably more important than Huntsman's, both because they are incomparably cheaper, and because their products are far more >pneflil than his
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Thus the distinctive work of thr.Liseccind, and, third periods is freein
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the metal from mechanical impurities by fusion
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The second period, by converting the metal into the fusible cast iron and melting this, for the first time removed the gangue of the ore; the third period by giving a temperature high enough to melt the most infusible forms of iron, liberated the slag formed in deriving them from cast iron
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In 1856 Bessemer not only invented his extraordinary process of making the heat developed by the rapid oxidation of the impurities in pig iron raise the temperature above the exalted melting-point of the resultant purified steel, but also made it widely known that this steel was a very valuable substance
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Knowing this, and having in the See also:Siemens regenerative See also:gas furnace an See also:independent means of generating this temperature, the See also:
In 1888 F
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Osmond showed that the wonderful changes which thermal treatment andthe presence of certain foreign elements cause were due to See also:allotropy, and from these and like teachings have come a rapid growth of the use of the so-called " alloy steels " in which, thanks to special See also:composition and treatment, the iron exists in one or more of its remarkable allotropic states
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These include the austenitic or See also:gamma non-magnetic manganese steel, already patented by See also:Robert Hadfield in I:;t33, the first important known substance which combined great IUSlleableness with great hardness, and the martensitic or beta " high See also:speed tool steel " of See also: |