STEEL, a very hard and fusible kind of iron.
Stahl, Cramer, and all good chemists, justly consider steel as an improved iron, which is possessed of a larger quantity of inflammable principle, so necessary to all metals, and which really contains fewer heterogeneous, and more metallic, parts than an equal bulk of iron. We shall be convinced of this truth by a description and explanation of the methods of converting iron into steel, and by examining the characteristic properties of steel.
Steel may be made by fusion or by cementation. The first method is used to convert iron into steel immediately from the ore. All ores of iron are not used indifferently for this purpose; because some of these, which are therefore called ores of steel, are much fitter than others to furnish good steel; and the steel extracted from them is called natural steel (A).
The other method of making steel consists in choosing the best forged iron, or that which is most malleable, whether it be hot or cold; and impregnating this iron with a larger portion of inflammable principle, by cementation alone, without fusion.
To understand well these methods of making steel, we must attend to two essential properties of iron. The first is, that of all metals it is the most difficultly fusible; and that therefore, although, in the smelting of its ores, its fusion be much assisted by the sulphureous parts of the ore itself; yet, as these parts are always expelled as much as is possible, iron never enters into so thin and perfect a fusion as the other metals.
The second property of iron to which we ought to attend is, that the earth of this metal is capable of
combining with the inflammable principle, and of being metallised without fusion.
These things being premised, it happens, in consequence of the former property, that, in the first fusion of ores of iron, we obtained only a hard and brittle iron, both from the sulphureous parts from which this iron is not entirely disengaged, and from the presence of a greater or less quantity of earthy matters, which are either unmetallic; or which, if they be ferruginous, have not been metallised, from want of immediate contact with the phlogiston of the fuel.
We may easily perceive that these earthy parts, unmetallic or not metallised, cannot be entirely separated from the perfect iron, because the fusion is not sufficiently thin for that purpose: but in proportion as the iron is deprived of sulphur, its fusion becomes more and more difficult, and we are obliged to have recourse to another expedient than fusion to disengage it from its earthy parts, which in the first smelting remain intercepted betwixt the metallic parts. This expedient is the forge. The impure iron intended to be rendered malleable is to be heated red-hot, and struck by a very heavy hammer.
This percussion, that iron softened by heat sustains, presses strongly, and folds or welds together the metallic parts, which alone are capable of uniting together; and obliges the unmetallic parts, which are incapable of uniting with the metal, to separate. By this operation these unmetallic parts are pressed between the parts of the iron, and driven by degrees to the surface of the metal, from which they are detached in form of dust and scales. This treatment, which is a kind of kneading of the iron, is to be repeated till it has acquired the proper degree of purity and ductility.
The operations by which steel is to be extracted from its ores are essentially the same as those employed for iron; but they differ from them in being much more exact; that an iron still purer, more filled with phlogiston,
(A) Steel is made sometimes directly from the ore, but more frequently from crude or cast iron. These methods of making steel are not known in England; but are practised in Sweden and other parts of Europe. The process for making steel from cast-iron is thus described by Swedenborgius, as it is performed in Dalecarlia.
The ore from which the crude iron to be converted into steel is obtained is of a good kind. It is black, friable, and composed of many small grains; and it produces very tough iron. The conversion into steel is made upon a forge-hearth, something smaller than common. The sides and bottom are made of cast-iron. The tuyere is placed, with very little inclination, on one of the side-plates. The breadth of the fire-place is 14 inches; its length is greater. The lower part of the tuyere is six one half inches above the bottom. In the interior part of the fire-place, there is an oblong opening for the flowing of the superfluous scoria. The workmen first put scoria on the bottom, then charcoal and powder of charcoal, and upon these the cast-iron run or cut into small pieces. They cover the iron with more charcoal, and excite the fire. When the pieces of iron are of a red-white, and before they begin to melt, they stop the bellows, and carry the mass under a large hammer, where they break it into pieces of three or four pounds each. The pieces are again brought to the hearth, and laid within reach of the workman, who plunges some of them into the fire, and covers them with coal. The bellows are made to blow slowly till the iron is liquified. Then the fire is increased; and when the fusion has been long enough continued, the scoria are allowed to flow out; and at that time the iron hardens. The workman adds more of the pieces of crude iron, which he treats in the same manner, and so on a third and a fourth time, till he obtains a mass of steel of about a hundred pounds, which is generally done in about four hours. This mass is raised and carried to the hammer, where it is forged, and cut into four pieces, which are further beat into square bars four or five feet long. When the steel is thus forged, it is thrown into water, that it may be easily broken; for it is yet crude and coarse-grained. The steel is now carried to another hearth similar to the former, and there broken in pieces. These pieces are laid regularly in the fire-place, first two parallel, upon which seven or eight others are placed across, then a third row across the second, in such a manner that there is space left between those of the same row. The whole is then covered with charcoal, and the fire is excited. In about half or three quarters of an hour the pieces are made hot enough, and are then taken from the fire, one by one, to the hammer, to be forged into little bars from half a foot to two feet long, and while hot, are thrown into water to be hardened. Of these pieces 16 or 20 are put together so as to make a bundle, which is heated and welded, and afterwards forged into bars four inches thick, which are then broken into pieces of convenient length for use.
giston, and better disengaged from its earthy parts, may be obtained.
To succeed in this intention, much smaller quantities must be fused at once than when iron is to be extracted from its ore. Pieces of the first fusion are to be put into crucibles filled and covered with charcoal, and exposed to a violent heat excited by strong bellows. These pieces are to be well fused, and kept in fusion a longer or shorter time, according to the nature of the ore; after which they are to be forged, as iron is; but always in much smaller pieces, and till they are become perfectly ductile both when hot and when cold. Nothing then remains but to temper the steel, of which we shall presently speak.
In these operations, which are to be several times repeated, the iron that is changed into steel must evidently be much better purified, and furnished with a much greater quantity of inflammable principle, than in the smeltings and fusions of large quantities of iron. As the masses of metal are small in these operations for the procuring of steel, and as they are surrounded with a much larger proportion of charcoal, the fusion is not only more complete, by which the separation of the earthy unmetallic parts is much promoted; but also a greater number of ferruginous parts are well metallised; and as all these parts of iron are in more intimate contact with the charcoal, which is capable of supplying them with inflammable principle, they receive the whole quantity of this principle with which they can unite.
The same observation may be applied to the operation of the forge practised upon smaller masses; for the heterogeneous parts are much more easily and copiously pressed out of small masses than great.
This exact purification of iron, by which it is converted into steel, must evidently be attended with considerable loss, or diminution, from the separation of all its heterogeneous parts. This diminution amounts to nearly one half of the weight of the iron. This great loss does not proceed altogether from the separation of heterogeneous parts; for in all the operations used for this separation, some part of the metal is always destroyed and burnt, although all possible precautions are taken to diminish this inconvenience, by securing the melted or red-hot metal from the contact of external air as much as is possible.
Artificial steel is made without fusion from iron ready forged. The chief point to be attended to in the making of the best artificial steel, is to choose the iron which is most perfect and most malleable either when it is hot or cold; which quality always shows that the iron is well purified. It is first to be forged into plates or bars, rather small than large, according to the works for which it is intended; and it is then to be cemented with matters capable of giving to it much inflammable principle. The matters which compose this cement vary according to the uses of different manufacturers. They are all good, provided they contain no sulphur, or vitriolic acid, which might form sulphur during the operation; because sulphur, having much affinity with iron, would certainly unite with this metal, would entirely or partly fuse it, and would, by reducing it to a mineral or pyritous state, give to it qualities very different from those which good steel ought to have.
The matters which enter into the composition of the cement for steel, are the coals of animal or vegetable substances, mixed with ashes, calcined bones, and other matters of this kind. Mr Cramer proposes these two following receipts of cements for steel, which appear to be very good.
Take one part of powder of charcoal, half a part of wood-ashes, and mix them very well together. Or,
Take two parts of charcoal, moderately pulverised: one part of bones, horns, hair or skins of animals, burnt in close vessels to blackness, and powdered; half a part of wood-ashes; and mix them well together.
When steel is to be made, the bars of iron are to be placed vertically in a cylindrical crucible, which ought to be three inches higher than the bars, and into which a stratum of the cement of about the thickness of a finger has been previously put and pressed down. The bars ought to be about an inch distant from each other, and from the sides of the crucible. The interstices and crucible are then to be filled with cement, so that the bars shall be covered with about the thickness of two inches at least. The crucible, previously covered with a lid which fits it exactly, and which must be carefully luted with clay mixed with sand, is to be placed in a furnace where an equal fire is to be kept, so that the crucible shall be red-hot during eight or ten hours: the iron will then be found to be converted into steel, which will be so much better as the iron employed was of a better quality: it then only requires to be tempered.
We may observe, that in this operation the iron suffers no diminution of weight, and no scoria appear upon its surface, as Mr Cramer remarks. By the sole addition, therefore, of a new quantity of phlogiston, the iron acquires the quality of steel. Thus, if this iron contained some parts of martial earth which was not metallised, by the cementation they are metallised, and the iron or steel are thereby improved: but if the iron contained some earthy unmetallic parts, they are not separated by this operation, because the metal has not been fused: and as the best forged iron which is usually sold, is never so well purified from these extraneous matters, as that which is converted into steel in the great works for procuring steel from the ore of iron; hence, in general, artificial steel made by cementation is not so perfect as that made by fusion.
We may observe, that, in the cementation above described, the iron combines with a part of the phlogiston of the cement, without fusion; which effect proceeds from a peculiar property of the earth of iron, by which it is capable of combining with the inflammable principle, and of being metallised without fusion, which is, nevertheless, necessary for the reduction of all other metallic earths.
The steel which has received only the above-mentioned preparations differs from iron in its colour, which is more dark and brown; in its grain, which is finer and closer; in possessing a greater ductility, flexibility, and softness; but the great difference of steel from iron, which renders it more valuable for many purposes and arts, is the extreme hardness it acquires by being tempered.
This operation is very simple. It consists in making steel red-hot, and then in plunging it suddenly in cold water. In an instant all the qualities of this steel
are changed by this tempering; so that from being very ductile and soft, it becomes so hard and so stiff, that it is no longer capable of being cut by the file; but is itself capable of cutting or piercing very hard bodies: that it does not yield to the hammer; but may be sooner broken in pieces like a flint, than be extended. It is sonorous, brittle, very elastic, and capable of acquiring the most lively and most beautiful polish, as we see in finely-wrought toys of steel.
The use of this metal is very extensive for numberless convenient and necessary utensils of all sorts, of which without it we should absolutely be deprived: but what renders its use still more general is, that we can diversify at pleasure its hardness and ductility, by varying the temper. The hotter the steel is when tempered, and the colder the water into which it is plunged, the greater hardness it acquires; but, at the same time, it becomes so much more brittle. This very hard temper is necessary for certain tools designed to cut very hard bodies. On the contrary, the less hot the steel is when tempered, and the hotter the water in which it is tempered, the less hard it becomes, and also the greater ductility it retains; and hence many tools may be made of it fit for cutting bodies moderately hard, which tools are less liable to have their points broken or their edges notched, than if they were made of a harder steel.
No other general rule can be given for the tempering of steel than that we have mentioned. The proper degree of heat is always relative to the use to which the tools to be made of this steel are to be applied.
Another very convenient property of steel is, that after it has been tempered, it may be again untempered and softened to any degree that we think proper; for which purpose we have only to heat it more or less, and to let it cool slowly. By this method we may soften the hardest-tempered steel.
As the temper is a very essential point with regard to steel, and that the best is in general that which gives the greatest hardness, and destroys the least of the ductility of the metal, various substances are used into which steel to be tempered is plunged. Such are fuel, oil, urine; water impregnated with soot, with sal ammoniac, or with other salts. These particular methods are the bases of many secrets in different manufactures; their advantages cannot be ascertained without a very accurate and continued examination. Very interesting researches remain to be made on this subject.
Steel is usually sold tempered, because, in many manufactures of it, the custom is to temper it as soon as it is made, probably that the purchasers of it may be the better able to judge of its quality. When this steel is to be used, it must be untempered, that it may be extended, filed, and receive the form intended to be given to it; after which each workman tempers it again in his manner. But we also find amongst merchants English steel in small bars, which is not tempered, and which is very good.
Well-polished plates of steel, put on a gentle fire of charcoal, acquire different colours on their surface, and pass successively through several shades, as they become hotter, in the following order: white, yellow, orange, purple, violet, and lastly blue, which disap-
pears and leaves a water-colour, if the steel has been heated too much or too long. These different shades mark the degree of heat or of annealing applied to different tools or utensils. The most generally used shade is the blue, such as that given to steel-springs.
One of the most important properties of steel is the magnetic quality, which it is capable of acquiring much better than iron. Good mariners compasses cannot be made without needles of steel.
From what has been said, we may judge that steel is much better purified iron than any other, impregnated with a larger quantity of inflammable principle, and hardened by the temper. Some celebrated natural philosophers, but who were not chemists, have advanced, that steel was only iron which still retained something of its mineral nature, and that its state was intermediate betwixt that of cast-iron and soft forged iron. But this opinion is manifestly erroneous. They have been deceived by the hardness and brittleness of cast-iron, which are nearly as great as in steel. But these qualities proceed from a remaining part of the mineralising substances, which leave it a pyritous character, very different from that of true steel; since this can only be hardened by the temper, and since in the preparation of it all sulphureous matter must be carefully avoided. The mistake of these authors proceeded from their ignorance of the inflammable principle, the properties of which have been so well explained by the illustrious Stahl, and from their being led into an error by the old chemists, who perpetually confounded phlogiston, or the the purest and simplest inflammable principle of all bodies, with sulphur, with sulphureous matters, and with most other inflammable compounds.
Steel may be unmade, or reduced to the state of iron, by a management similar to that by which it is made, that is, by cementation. But the cement used for this purpose must be composed of substances entirely free from inflammable matter, and rather capable of absorbing it, as calcareous earth and quicklime are. By a cementation then with these matters, continued during eight or ten hours, steel is reduced to the state of iron.
Stahl considers it as an undecided question, whether steel be more fusible than iron, and says, that the workmen cannot decide it from the violence of fire necessary to melt either of them. He believed, with reason, that this question might be decided by melting these metals in the focus of a burning speculum. Mr Macquer says, that by this method he found steel much more fusible than iron. This greater fusibility of steel can be only attributed to the greater quantity of phlogiston united with it, as phlogiston is in general the cause of the fusibility of metals.
By conversion of iron into steel, this metal acquires a closer, more compact, and finer grained texture, greater hardness, elasticity, tenacity, density, sonority, and disposition to receive the magnetic property; and, as some say, an increase of weight. It is also rendered less liable to rust by exposure to air; and less liable to emit sparks when heated. The colours or irises which steel acquires by exposure to heat, and which are marks by which workmen know when any acquired heat is given, are not peculiar to steel and iron, but may also be produced by the same means on all
other calcineable metals. These colours proceed from a calcination gradually advancing on that part of the metals which is exposed to air. And as the particles of metals in their different degrees of calcination are possibly of different sizes, so they must acquire (according to Sir Isaac Newton's theory, which shows that the colours of bodies depend on the size of their integrant parts) different reflective powers, and exhibit changes of colours.
Steel may be made by fusion from the ore, or by cementation of forged iron with inflammable matters. Anciently, steel is said to have been made by immersing forged iron during some time in melted crude iron. Forged iron may also be changed into steel, as Wallerius affirms, by immersing in melted scoria; or by fusion with black flux, glass-gall, or borax; or by strewing sea-salt upon heated iron, and extinguishing it in dung.
Various opinions are formed concerning the cause of the difference between iron and steel. The most general opinion attributes this difference to the presence of a larger quantity of phlogiston in the latter than in the former. Some authors, attending chiefly to the method of conversion by fusion, consider that operation only as a purification of the iron from earthy and heterogeneous particles, and steel merely as a more pure and perfect iron. Others, observing some similitude in the texture of steel to certain kinds of cast-iron, and the hardness of both these, without attending to their essential differences, have imagined that the state of steel was intermediate betwixt that of cast and that of forged iron. Lastly, some metallurgists maintain, that the conversion of iron into steel is effected, not by absorption of phlogiston, but by expulsion of sulphureous or acid particles. To support this opinion, they observe, 1. That steel is less disposed than iron to rust; the cause of rust being, as they think, an acid contained in iron. 2. That steel emits fewer sparks under the hammer than iron, which sparks are found to be most frequent in iron abounding with sulphur, as in red-short iron. 3. That iron may be converted into steel by cementation with alkaline salts, capable of attracting the acid and sulphur. 4. That in the preparation of steel by fusion, the metal is rather exposed to a dissipation of its inflammable parts and burnt, than further phlogisticated; and that this operation is accordingly called by workmen the burning of steel.
In the preparation of steel by fusion, probably much of the earthy matters contained in the iron may be separated, and any contained acid or sulphur may be burnt or dissipated. But the conversion of steel into iron by cementation with absorbent earths, in which operation no acid or sulphur can be absorbed by the metal, shows that the difference between iron and steel does not consist in the presence of an acid or of sulphur in the iron, but rather in the presence of some substance in the steel, which the inflammable cementing substance can give to it, and of which absorbent earths can deprive it. This substance has been generally believed to be phlogiston: by the addition of which the metal acquires a new texture, together with the hardness, elasticity, and other peculiar properties of steel.
The affinities and medicinal virtues of steel are the same as those of iron. See IRON.
Salt of STEEL. See CHEMISTRY, n° 146.
STEEL-Yard. See BALANCE.