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steel which is naturally the and increases its hardness progressively te
that which requires the least the maximum of heat the steel is formed to caf, and that the best temper for each bear. There will be no difficulty then in kind of steel is that produced by the lowest conceiving, that the best state of steel, redegree of heat suitable to that peculiar lative to any particular use, will be at some kind. Hence, various methods have been precise degree between the softest and proposed to ascertain the degree of heat hardest qualities. Thus for springs, much most advantageous to any particular sample tenacity and moderate hardness are reof steel. They are all reducible to that of quired. For chissels and similar tools,wbich igning one end of a bar to a white leat, operate by a blow, a greater hardness may and plunging it into water. The hardness be admitted. Razors, knives, and such of the several parts may then be ascertained tools as effect the intended purpose by a by examination.
gradual stroke, will be still more valuable It appears that the considerations on the harder they are; but even in these the which the first-mentioned general rule is tenacity mast not be too much diminished, founded, are rather of a complicated na- otherwise the edge will be liable to break. ture. If it be true, as conjectured above, They must all be capable of having the that the hardness of steel depends princi- edge turned or bended on one side in the pally on the intimate combination of its operation of whetting. Files are perhaps carbon; it will follow, that the utmost of all tools such as require the greatest hardhardness any steel is capable of, will be ness; but in these, it is far from being the produced by a degree of heat suficient to utmost the steel is capable of receiving. It effect this purpose, and that any superior is found, that the tenacity of steel is corsidegree will only degrade the quality of the derably increased by continued hammering steel ; and consequently, that the general to a certain point. But the whole effect rule will apply only to heats inferior to of this hammering is taken off by strong this maximum. It may also happen, when ignition. Good steel by hardening at a the mass of water is not considerable, though white heat may be rendered so brittle, that the fact has been doubted, when the quantity it will break full as easily as a stick of the is large, that the heating of the wate., same dimensions, and its texture is then and the production of hydrogen, may so found to be coarse and large grained. As far modify the rate of cooling, as even the subsequent annealing does not restore to render it less sudden than might have the effect of the hammering, nor bring the happened with an inferior degree of igni- grain of the steel to the state it would have tion. Lavoisier has remarked, that the possessed if a lower licat had been used at conversion of iron into the hard brittle first; it is evident, that the most usefel oxide, when water is decomposed, may hardness is produced by that degree of heat, perhaps be of the same nature as the which is just sufficient to effect the purpose. hardening of steel. There is another fact, And accordingly, tools made of cast steel, which is of great consequence, and may per. and intended to sustain a good edge for haps afford the principal ground for Rin- cutting iron and other metals, are not afterman's apparent exception to the general ward annealed, but the ignition is carefully rule concerning the hardening of steel. regulated at first. Annealing onght only to Hardness is that property of bodies by be used where considerable softness is rewhich they resist indentation, and rather quired. break than bend or suffer contusion. It is Iron may be hardened to a certain de. the opposite to softness. Tenacity, which gree by ignition and plunging in water, but is very frequently confounded with hard- this effect is confined to the surface; except, ness, is not the property by which they re- as it very often happens, the iron contains sist indentation, but separation of their veins of steel. These are no small impediparts. It is the opposite to friability or ments to the filing and working this matebrittleness. Now that steel, in common rial. It sometimes likewise may happen, language, is said to be the hardest, which that the iron may have undergone a process upites most eminently the properties of of the nature of case-hardening from the hardness and tenacity. Bat the effect of fuel. We have been informed by a workman, heat and sudden cooling is directly opposite that ignited iron, suddenly plunged into the in these two respects. Soft steel is the most soft leather of a shoe, becomes very hard tenacious, but the least hard. The opera. on its surface, which must arise from an intion of hardening diminishes its tenacity, stantaneous effect of this kind.
The increase of dimensions acquired by of hardness and tenacity will be at a niestrel in hardening is such, that in general dium temperature in each kind of steel. such pieces of work as are finished soft With regard to the first particular, little will not fit their places when hardened. need be said, but that the decomposition Rinman found, that bars of steel six inches of steel in heating will be prevented, and long, six lines wide, and half an inch thick, its surface somewhat improved, if it be were lengthened at least one line after bedded in charcoal, or the cementing comhardening by a whitish red heat, which pound, during the application of the heat. is about one seventieth of the linear dimen- The second and third, namely the quantity sious; and supposing the dilatation to be and suddenness of cooling, require an at. proportional, Guyton Morveau computes tention to the doctrine of Caloric, as exthe bulks to be as 48 to 49. But the cubes plained under that article. The cooling of 72 lines and 73 lines are in proportion will be more sudden and effectual the more nearly as 47 to 50. Various kinds of greater the quantity of heat absorbed in steel at different hardness must no doubt the same time. There are three circum. greatly ditfer in this respect. The specific stances which favour this effect, namely, gravities, as given by Brisson, p. 366, art. a very low temperature of the body to GRAVITY (specific), afford a much less ratio. which the hot steel is applied; that it Rinman found by his experiments on two should be a good conductor of heat; or that different kinds of fine cemented steel, the it shall assume either the fluid or elastic specific gravity of which was 7.991, that one state, which always demand a supply of atter hardening gave only 7.553, and the heat for their maintenance. Thus it is other 7.708. These numbers agree suffi. found, that steel is more effectually hardenciently near with the experiment of the six- ed in cold than in warm water, and at like inch bar. Yet he once found Styrian steel temperatures more effectually in mercury augmented in density by hardening in the than in water. It may also be remarked, ratio of 7.822 to 7.782. Morveau found, that these two fluids cool the steel hy with pieces of steel 28 lines long, that the different energies. The water is partly increase of length by hardening was about converted into vaponr, which carries off the tlie 330th part.
heat, and leaves the fluid much less altered The fineness of grain in hard steel, as in temperature than mercury, which acts by exhibited in its fracture, is various, accord. its conductivg property. This last Auid, ing to the quality of the metal, and the not having evaporated in the process, is temper it has received. The barder the found to have acquired a much more ele. steel the coarser the grain. But in like vated temperature by the immersion. Oi' circumstances, fine steel has the closest is found to harden the surface of steel much grain, and is ever the most uniform in its more than its internal part, so that it resists appearance. Workmen avail themselves the file, but is much less easily broken by much of this indication. In general a neat the hammer. This effect arises from its curve lined fracture, and even grey tex. imperfect conducting quality, and the eleture, denote good steel; and the appear valed temperature it demands to be con. ance of threads, cracks, or brilliant specks, verted into the vaporous state; to which denotes the contrary. But the manage. we may also add, that a stratum of coal is ment of the forging and other circumstances formed round the steel from the burned of manufacturing will modify these indica- oil, which still more effectually prevents tions; and the steel that is good for some the transmission of the heat. A remarkpurposes may be less suited to others. able instance of this nature presented itself
The fluid into which ignited steel is to our observation in hardening a small plunged is of great consequence. All the piece of steel two inches long, and a quarfacts seem reducible to these general con.
ter of an inch diameter. At the time of clusions. The hardness will be greater, ignition, the water nearest at hand had 1. The hotter the steel is made, provided been used with suap. The steel made very it be not decomposed: 2. The more cousi- little roise when plunged into the water, derably its tmperature is lowered in the and remained bot for a consitterable time; cooling : 3. The shorter the time of cooling: but when taken out was found to be scarce. and 4. The more favorable the fire or the ly at all hardened. It was covered with cooling material may be to the steel making coally matter; which being cleared ofi, and process. But the most useful combination the process repeated with clean water, it became perfectly hard. The heat in both plates in the usual way, in which state they cases was a low red heat, proper for cast are britule and warped : they then soften steel, which is not intended to be afterwards them by blazing, which consists in smearing annealed. We have very little doubt, but that the plate with oil or grease, and heating it alcohol and the essential oil of tarpentine, till thick vapours are emitted, and burn off which are good conductors of heat and very with a blaze ; and after this they may be volatile, would render steel very hard, if hammered flat; lastly, they blue them on a their mtlammability, and the little necessity hot iron, which renders them stiff and elas. there is for using them, were not an impe. tic without altering their flatness. diment to their application. Various artists The Damascus sword blades have long avail themselves of different substances for been celebrated for their excellence, but it the immersion of ignited steel. Some use is not known how they are made. Mr. 'urine, others water charged with common Stoddart took six small bars of good mal. salt, nitre, or sal animoniac. Tallow and leable iron, and the same number of sheer oil are used for such works as are not re- steel ; laid them alternately on each other; quired to be brittle, though very hard, the welded thein together; forged them into a reason of wbich has just been mentioned; stout Alat plate, which was twisted spirally but tallow differs from oil in the heat which into a cylinder, hammered flat, and again becomes latent for its fusion; and accord- welded; hammered this flat, doubled it ingly, solid callow is an excellent material throughout its length, inserted in the fold a for hardening drills and other small articles. slip of good steel to form the edge, and by It has been found by Reaumur, that saline another welding heat consolidated the liquids produce rather more hardness than whole into one mass. This being forged to common water; and in particular, that
a proper shape, cracked in different places aquafortis possesses this property in an on being cooled in water after heating; but eminent degree, probably from its conduct. Mr. Stoddart conceives, that by using more ing power: the makers of files cover them pieces, repeating the twisting, and "not with the grounds of beer and common salt, quenching in water, the process would which assist their hardening, and keep the succeed. surface from scorifying. The mucilage of Every species of iron is convertible into the beer supplies a coally matter; and the steel by cementation ; but good steel is not fused salt seems not only to form a varnish to be made except from iron of the best in the fire and defend the steel, but may quality, which possesses a certain stiffness also produce cold, by its sudden solution in and bardness as well as malleability. Swe: the water at the time of immersion. Very dish iron, as we have before remarked, is small articles heated in a candle are found the best for this purpose.
M. Dnbamel to be hardened perfectly by suddenly whirl- tried a great:umber of the irons of France, ing them in the cold air; and thin bars or Sweden, and Spain. He found the second plates of steel, such as the magnetic needle to be the best; but he likewise obtained of a compass, acquire a good degree of excellent steel, superior to those of Styria hardness by being ignited, then laid on a and Carinthia, which are the best German plate of cold lead, and suddenly covered with steels, by using certain iron made in France. another plate. These would be uneqnally But this iron was selected without fault; hardened, and bend, if plunged in water. and, in some instances, the loup or piece at
The bluing of steel appears to affect its the smelting furnace was fused and forged elasticity in a manner not easily explained. a second time; a process which, though This operation consists in exposing steel, attended with loss of weight and additional the surface of which has been tirst brighten- expense, he recommends as absolutely ne. ed, to the regulated heat of a plate of metal, cessary for making steel iron from ores of or a charcoal fire, or the fame of a lamp, indifferent quality. The white spathose iron till the surface has acquired a blue colour. ores afforded him the best iron for the pur. Now, if this blue coal be removed by grind pose of cementation; and these also are the ing, the elasticity is completely destroyed, ores which afford the best steel by fusion in and may be restored by bluing the steel Styria, Carinthia, and Tyrol. He informs again. Rubbing with sand or emery-paper, us that the English use no other cement glazing, or burnishing, equally impairs the than mere charcoal
, which he also finds elasticity in proportion as it destroys the perfectly adequate to the purpose ; and, blue coat. Saw-makers first harden their moreover, that the quality of the steel is
not affected by the different kinds of char- nued somewhat beyond the time requisite for
heat and more precaution, because more action may be. Hence it must follow, that liable to break.
the various specimens of crude or cast iron This cast steel is almost twice as dear as will differ in their qualities, as well on acother good steel. M. Duhamel says that count of the degree of cementation they it is not proper for all kinds of work, par- have undergone, as the degree of redaction ticularly those which require much tenacity, which has taken place among the metabc as well as hardness to resist violent blows parts, which are carried down, and form and strains; but it is good for razors, knives, the whole mass. Since the coal, in the and all toys and small work which require process of cementation, communicates or an exquisite polish. It does not seem, how. adds weight to the iron ; and since erude ever, that the tenacity of this steel is inferior iron, as well as steel, exbibits sparkles, and to that of the best of the other kinds, and is more easily burned than other iron; it its uniformity of texture is for many works may therefore be concluded, that in tine an invaluable advantange. It is daily more process of refining, that part of the inflamand more used in England, but must neces- mable substance which had united with the sarily be excluded from many works of con- metal is burned, and leaves the iron much siderable size, on acconnt of the facility less fusible than before. Stirring the mzes with which it is degraded in the fire, and multiplies the contacts of the air with the the difficulty of welding it, which cannot be burned substances; these surfaces of cobdone in the common way. We have been in- tact will therefore successively afford this formed that the faces of anvils and broad coats of infusible metal. In this manner hammers, for the use of silversmiths and
it is found, that, if a large piece of crode other artists, have been made of cast steel, iron be exposed to heat in a wind furmace, and welded to iron by a particular manage the external part will be deprived of its ment, which consisted in substituting be- fusibility during the time required to protween the iron and the steel another kind duce a strong heat in the whole mass; and of steel in the form of filings, or a thin the internal part will be melted, and run plate. The steel plate intended for the out, leaving the shell behind. Iron, włuch face was made as hot as could be done with is of the consistence of paste, may theresafety, and the iron being at the same fore be considered, like any other paste, as time brought to the welding heat, was a mixture of a Anid with a solid. It will applied to the steel, and quickly united by be easily understood, that the forging will hammering
bring the parts of difficult fusion together, When we consider the operations by and extrude the less refined and fluid parts: which crude iron is brought into the mal. it will also be evident, that this operation is leable state, then converted into steel, and not likely to drive out the whole of the afterward into a fusible meial, which is not fusible matter. When the iron bas arrived malleable; we may perceive that steel
at that state, wherein the quantity of fibre making is a kind of inversion of the process or touglı iron is sufficient to answer the meof refining iron, as practised in the first in- chanical purposes to which it is intended stance. When the oxide of iron is mixed to be applied, the artist will consider it as in the smelting furnace with combustible sufficiently refined; and the residue of fu. matter and glass, it will either be complete. sible iron contained in the bar, answers, in ly or partially revived, according to the all probability, the valuable purpose of conmanagement of the process. Much of the vecting these infusible masses together. coal will however be so enveloped with Thus we find that forged iron appears as the vitreous matter as to remain unburned: if covered with a varnish, when urged to a and the reduced iron, with which it may be white heat; we find that this varnish is in contaet, will be in the same situation as
more abundant in steel; and that iron and forged iron in the cementing pot; that is steel may be respectively welded together lo say, it will be in contact with coal at a
by application in this state; an effect which very elevated temperature, and defended it would be very difficult to account for, in from the air. From the great infusibility this most infusible of metals, if it were not of iron, it may reasonably be concluded, for such an aumixture. But cast steel, steel that the reduced metal does not flow into over cemented, and crude iron, appear to the bottom of the surnace, until the char- be in the state of all other metals, platina coal has converted it into a fusible matter excepted. They cannot be welded, because similar to steel, by the same action which welding implies a partial fusion: or an takes place in cenientation, whatever that effect similar to the gluing or uniting of