Corrugated iron

“ While this carbon or iron-carbide solid solution may and probably does itself confer additional hardness to the steel, its main function is to retard or slow down the change from gamma into beta and alpha iron, which change in carbonless iron and low carbon steels is so insistent and extremely rapid that not even the most severe quenching, as in ice-water or liquid air, can prevent or stop it. ”

“ The iron rapidly melts and saturates itself with carbon. After a few minutes’ heating to a temperature above 4000° C.—a temperature at which the iron melts like wax and volatilises in clouds—the current is stopped and the dazzling fiery crucible is plunged beneath the surface of cold water, where it is held till it sinks below a red heat. As is well known, iron increases in volume at the moment of passing from the liquid to the solid state. The sudden cooling solidifies the outer layer of iron and holds the inner molten mass in a tight grip. ”

“ Cold iron, however, cannot retain in the chemically combined form as much carbon as does molten iron, so, during the solidification and cooling of the alloy, more or less of its carbon was precipitated, i.e., thrown out of solution and from chemical combination with the iron, the amount depending mainly upon the speed of the cooling. ”

“ One has no difficulty in realizing that these flakes, which cut in every direction through the metal, make it structurally weak, especially toward a sudden blow.
No. 1d shows a typical section of wrought iron cut lengthwise of the rolled bar. It will be noted that, as in photomicrograph No. 99b, there are no graphite flakes.
In the process of wrought iron manufacture practically all of the carbon of the original pig iron is burned out, leaving little besides the iron itself and some viscous cinder or slag. ”

“ It is only slightly malleable, except when specially treated, is rigid and has great resistance to crushing, but is more or less brittle and not adapted to tensile strains. Wrought iron is nearly pure iron, and in modern metallurgical processes is usually obtained by removing the carbon and other impurities from cast iron. ”

“ Open-hearth iron is practically pure iron, having no constituents or slag inclusions which materially affect its properties.
2. Wrought iron, for all practical purposes, is pure iron 86except for its content of slag. It is the only one of the iron family which does normally contain slag.
3. Neither open-hearth iron nor wrought iron contains carbon in appreciable quantities.
4. The distinguishing and active element of the steel family is carbon. With increase of carbon the hardness of the alloy increases as does its tensile strength, but the ductility (elongation or stretch) decreases. ”

“ These contend that the so-called beta iron and martensite are only decomposition or transition forms of gamma iron and austenite.
Two or three other theories have been more or less strongly advocated but these also suffer from lack of evidence. The one which perhaps ranks next in number of advocates is the “carbon theory.” Its supporters contend that by quenching, alpha iron is made to hold carbon or iron carbide in solid solution and that it is this solution of carbon or carbide which gives to the steel hardness in proportion to its carbon content. ”

“ Coating with aluminium powder also greatly prolongs the life of an iron sheath. When used in lead baths, the immersed part, if of iron or steel, should be bored from the solid, and left thick at the portion opposite the surface of the lead, where most corrosion occurs. A graphite tube, or one made of a composition containing graphite, is often useful in cases where iron is readily corroded, and can be used to much higher temperatures. ”

“ Wrought iron is softer than cast iron, and, being pure iron, is more liable to be corroded by the action of the atmosphere and products of combustion of the powder; it possesses also considerable ductility. The tensile strength of wrought iron, which under the most favorable circumstances is double that of the best cast iron, depends on the character of the crystalline structure, and the manner of applying the tensile force, or in other words, wrought iron offers the greatest resistance to a force of extension when the structure is fibrous, and the force acts in the direction of the fibres. ”

“ The greater the amount of carbon chemically combined with the iron, the whiter, harder, and more brittle does it become.
The white cast iron is stronger than the grey, but being more brittle it is not so suitable for resisting suddenly applied loads. White iron melts at a lower temperature than grey iron, but after melting it does not flow so well, or is not so liquid as the grey iron. White iron contracts while grey iron expands on solidifying. The grey iron, therefore, makes finer castings than the white. ”

“ During the melting of the charge the heat is kept as high as possible and the molten iron is “puddled,” i. e., stirred, by the “puddler” or his helper with a “rabbler” or iron bar. In order to take out the phosphorus and sulphur, which for best results should be removed before the carbon is eliminated, the heat of the furnace is lowered somewhat as soon as all of the pig has melted, and some iron oxide is mixed into the “bath” of molten iron and cinder. Most of the phosphorus and sulphur are chemically acted upon and pass into the cinder which covers the iron. ”

“ Another constituent which is of great interest scientifically, though not at all commercially, is “austenite.” By quenching very high carbon steels from a very high temperature very suddenly and completely, we can fasten the “austenite” structure, which exists only at temperatures higher than martensite, i.e., austenite is our gamma iron with the carbon of the alloy in solid solution, perhaps as iron carbide, while martensite is thought to be the beta iron solid solution, perhaps with some gamma iron mixed with it. ”

“ That is, as soon as a vessel costing millions of dollars leaves the docks, she enters into active competition for a place on the junk pile."
The greatest improvement that can be imagined in the iron situation will be in the discovery and use of alloys or mixtures of iron with other materials. Steel, the strongest of all forms of iron, is an alloy of iron and carbon, and for various purposes these are further mixed with nickel and silicas. Many other alloys have been discovered within the last few years, and each makes possible new uses for iron requiring greater strength. ”

“ No one knows just when, with increase of carbon, steel ceases to be steel and becomes white cast iron. There is no definite dividing line either in chemical or physical properties. The changes are extremely gradual throughout the scale. Aided by the microscope, modern physical chemistry has disclosed the fact that alloys of iron with carbon “freeze” from molten to solid condition according to two different laws. ”

“ On the application of heat in furnaces, constructed for the purpose, the charcoal unites with the oxygen of the oxide, reducing it to the metallic state, and escapes in the form of carbonic acid; and the lime, if the ore be argillaceous, unites with the clay, forming a kind of glass, which floats on the melted metal. When the iron is suffered to run into moulds, prepared for its reception, it usually takes the name of pig iron.
Manufacturers distinguish cast iron by its colour and other qualities. The white cast iron is hard and brittle, and can neither be filed, bored, nor bent. ”

“ With such a volume of weakening constituents and particularly with the graphite flakes cutting through and separating the iron grains as the photomicrographs show, can one wonder that cast iron is fragile—more so than steel or wrought iron? ”

“ If the iron has too much or too little carbon it cannot be hardened at all; if there is too little it is very soft and malleable and is called “wrought iron”. If there is too much carbon it is harder than mild steel, but is very brittle indeed ”

“ But since modern methods of manufacturing have been adopted, tons of metal, which would have been classed as iron if judged by the cooling test, are at present known as mild or soft steel.
Steel may properly be defined as an alloy of iron with carbon, the latter not exceeding 1.8 per cent; the materials are completely fused and poured into molds, allowed to cool, and then rolled into shape. In the processes of making wrought iron the materials are only partly fused and are not cast into molds, but are taken out of the furnace in a soft, pasty condition suitable for immediate working. ”

“ An important feature in the process is, that by stopping it at a particular stage, immediately following the boil, before the whole of the carbon has been abstracted by the oxygen, the crude iron will be found to have passed into the condition of cast-steel of ordinary quality. By continuing the process, the metal losing its carbon, it passes from hard to soft steel, thence to steely iron, and last of all to very soft iron ”

“ Not only do we fail to get austenite, which is gamma iron, until we get 1% or more of carbon present and quench from very high to very low temperatures, but we cannot even stop the transition at beta iron, the next lower allotropic variety until we have at least .30% of carbon, and, for serviceable hardening fully .60% of carbon in the steel. ”

“ As the carburets of iron, whether in the form of pig or of steel, may be considered as alloys, if they be presented to other metals, the results must necessarily be different from what occurs when pure iron is exposed to the same substance. The union that may take place in the one instance may not occur in the other. It may often happen, that when the iron is pure, a true chemical combination will occur, while in the other case, no more than a mechanical mixture can be effected. ”

“ The properties of wrought iron are the properties of pure iron. As more and more carbon is introduced into the iron, it combines with the iron and distributes itself throughout the metal in extremely small crystals of cementite, and this brittle, hard substance lends more and more hardness and strength to the steel, at the expense of the original toughness of the iron. As more and more carbon is contained in the alloy—for steel is a true alloy—it begins to appear as graphite, and its properties counteract the remaining brittle cementite. ”

“ The end of all iron is the same. However many may be its metamorphoses while in the service of man it relapses at last into its original state of oxidation. To save a pound of iron from corrosion is then as much a benefit to the world as to produce another pound from the ore. In fact it is of much greater benefit, for it takes four pounds of coal to produce one pound of steel, so whenever a piece of iron is allowed to oxidize it means that four times as much coal must be oxidized in order to replace it. And the beds of coal will be exhausted before the beds of iron ore. ”

“ Some kinds are broken up to be used as foundation for roads; others are granulated by being run into water, and so made into cement. Over in Germany, where the ores are rich in phosphorus, they grind up the linings of the furnace to make phosphatic fertilizers for the farmers.”
“Then,” said Dr. Crandon, “the making of iron involves the use of chemistry, doesn’t it?”
“It certainly does,” answered Mr. Prescott; “from the chemical composition of ores to the finished product. We are learning a great deal just now from the chemists about steel alloys. ”

“ As carbon steel is simply iron which has absorbed not over 2 per cent of carbon (cast iron described above has a supersaturation with its 31⁄2 per cent to 5 per cent of carbon and therefore is entirely different) they were able to make it in small quantities. When hardened by cooling quickly in water, a forged-out blade of this product would cleave without dulling its edge a piece of iron, it is said, or cut cleanly a tuft of silk floss tossed into the air. ”

“ Of the iron-carbon alloys of compositions lying to the right of the line UV, we find the case to be different, for each one of them has more than the 1.7% of carbon which is the maximum amount which “gamma” iron can retain. Now the lowest temperature at which any iron-carbon alloy can exist without freezing is slightly above 2066° F., and there is but one composition—95.7% of iron and 4.3% of carbon—which can survive until this low temperature is reached. ”

“ The reduction of the ores of iron into metallic iron is in principle very simple, because when the oxides of iron are strongly heated with charcoal, hydrogen, carbonic oxide, and other reducing agents, [5] they easily give metallic iron. But the matter is rendered more [322] difficult by the fact that the iron does not melt at the heat developed by the combustion of the charcoal, and therefore it does not separate from those mechanically mixed impurities which are found in the iron ore. ”

“ Another and a more interesting reason is that gray iron melts in a much lower temperature than does thermit steel and consequently has a lower shrinkage. Therefore when the molten thermit, with its terrific heat, cools there is a large shrinkage. Thermit steel being much stronger than gray iron, its shrinking sometimes strains and cracks the iron casting. ”

“ So during ordinary cooling from the molten alloy or the slower cooling of the steel during the annealing process, the martensitic structure breaks down at the recalescent temperature into pearlite and ferrite (soft iron) if the carbon content of the steel is lower than about .90%, or pearlite and the other and very hard constituent, “cementite,” if the steel has more than .90% of carbon. If the carbon content happens to be just .90%, or thereabouts, there is exactly sufficient pearlite to make up the total area of the field shown under the microscope. ”