Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 235

_Prop., &c._ White; semi-crystalline; insoluble in water and cold alcohol; soluble in 225 parts of cold ether, and freely so in boiling ether. It melts at 130 Fahr. The stearin of commerce is stearic acid.

=STEAROP'TEN.= The name given by Herberger to the concrete portion or camphor of volatile oils. Bizio calls it stereusin.

=STEEL.= This important material may be defined as iron chemically combined with sufficient carbon to give it extreme toughness and hardness without brittleness. According to one of our greatest authorities on metallurgy, steel should contain from 833% to 167% of carbon, these numbers referring respectively to the softest and the hardest varieties.

By some authorities silicon in small quant.i.ties is supposed to be a useful ingredient in steel, and to increase its capacity for being hardened; an opinion dissented from by others, who hold that its presence has a tendency to interfere with the welding of the metal. Faraday and Stodart believed that the addition of small quant.i.ties of chromium and iridium to steel served to improve its quality, and the same has been a.s.serted of tungsten and t.i.tanium; but on these points there is still a divergence of opinion, and no satisfactory decision has yet been arrived at concerning them.

Manganese has also been credited with the property of improving steel, but as it has been found that only a very minute quant.i.ty of the manganese is taken up by the steel, an indirect influence may possibly be exercised by it, viz. its power of uniting with the stage, and of carrying away any prejudicial excess of sulphur and phosphorus with it; and in this manner it may contribute to the increased purity of the metal. The addition of manganese to cast steel const.i.tutes Mr Heath's patent, the chief advantage of which is that blistered steel made from British bar iron can be subst.i.tuted for the much more expensive Swedish and Russian iron, in certain branches of iron manufacture.

"Among the various substances which are frequently present in malleable iron and in cast iron, those which are more prejudicial to the quality of steel are sulphur, phosphorus, and copper. The amount of sulphur in steel of the best quality rarely exceeds 012; within the limit of 1 per cent.

it is considered to render the metal more capable of being welded at a moderate heat, but to make it red short. Phosphorus also renders steel more capable of being welded, and at the same time makes its cold short when it amounts to 1 per cent. The best steel rarely contains so much.

Copper renders steel decidedly red short when present in very small amount, and for this reason iron smelted from ores containing copper pyrites is not suitable for making steel."[195]

[Footnote 195: Payen.]

Within the last few years great attention has been paid to the investigation of the chemistry of steel. The researches of Despretz and Fremy tend to the conclusion that nitrogen exercises a very important influence over the phenomena of 'steeling,' and that carbon plays a less necessary part; while those of Caron and Deville still refer the formation of steel to the chemical combination of iron with carbon. There is no test of the value of steel beyond its elasticity and temper, and the fineness, equality, and smoothness of its grain.

Cast iron, wrought iron, and steel are all combinations of iron and carbon, differing in the amount they contain of the latter element. As cast iron contains a larger and wrought iron a smaller proportion of carbon than steel, it follows that to convert the cast iron into steel, its excess of carbon must be removed; whilst conversely, to make the wrought iron into steel, the requisite amount of carbon must be added to it.

Thus it is that the various processes for the manufacture of steel (with the exception of those which propose to obtain it direct from the ores) are directed to one or other of these ends, viz. the decarburation of cast or pig iron, and the carburation of wrought or malleable iron.

1. In the first, or decarburation method, the oxygen of the air plays an important part. Best carbon is heated with coal or charcoal, in some works on the refining hearth, in others upon the bed of the puddling furnace.

The oxygen burnt off the excess of carbon from the iron and steel is left.

Payen says that when the iron contains slag, the ferrous silicate present in this takes part in the reaction.

The steel obtained by this method is called natural steel. It is afterwards subjected to forging, and being of inferior quality is employed in the manufacture of springs for machinery, railway carriages, wheel tyres, ploughs, and other farming implements.

_The following Table, from 'Payen's Industrial Chemistry' gives the Composition of several kinds of Steel._

+--------------+---------+------+------+------+---------------+ Carbon. +------+--------+ Kind of Steel. Locality. Fe. Mn. Cu. Comb- Graphi- ined. tic. +--------------+---------+------+------+------+------+--------+ Natural Steel Siegen ... ... 379 1698 ... Ditto Solingen ... ... ... 1570 ... Puddled Steel Hartz ... 012 ... 1380 ... Cement Steel English ... ... ... 1807 ... Ditto German ... ... ... 416 080 Cast Steel Sheffield ... ... ... 950 220 Ditto Ditto ... ... ... 1758 Ditto French ... ... ... 65 Sword Steel Damascus ... 070 ... 1089 Ditto Ditto ... trace ... 775 Wootz Indian ... ... ... 1500 Ditto Ditto 98092 ... ... 1333 312 Cast Steel German ... trace 300 1180 Ditto English ... 024 066 1275 Bessemer Steel Dowlais ... 576 025 490 Ditto Sweden ... trace ... 085 Ditto ... ... 179 ... 300 Ditto ... ... 256 ... 700 Ditto ... ... 468 ... 950 Ditto ... ... 355 ... 1050 Wired Barrow- ... 214 ... 200 in-Furness Rail Heads German ... 386 ... 138 Rails ... ... 264 ... 150 Ditto ... ... 638 ... 046 Boiler Plates ... ... 136 ... 250 Ditto ... ... 273 ... 300 +--------------+---------+------+------+------+---------------+

+--------------+-----+-------+-----+----------+ Kind of Steel. Si. S. P. Authority. +--------------+-----+-------+-----+----------+ Natural Steel 038 ... ... Karsten. Ditto 020 ... ... Lampadius. Puddled Steel 006 (at12) trace Brauns. Cement Steel 100 ... ... Berthier. Ditto ... ... ... Bromeis. Cast Steel ... ... ... Ditto. Ditto ... ... ... Karsten. Ditto 040 ... ... ... Sword Steel ... (Ni07 Wo01) ... Ditto ... (Ni21 ... Co trace Wo trace) Wootz 600 ... ... ... Ditto 045 (as 037) ... Henry. Cast Steel 330 (Ni 12) 020 ... Ditto 213 (as007) ... ... Bessemer Steel 009 003 036 ... Ditto 008 trace 025 Brusewitz. Ditto 044 do. 033 Ditto. Ditto 032 do. ... Ditto. Ditto 047 do. 032 Ditto. Ditto 067 do. ... Ditto. Wired 179 030 026 Ditto. Rail Heads 306 040 034 Ditto. Rails 091 025 032 Ditto. Ditto 634 045 093 Ditto. Boiler Plates 016 010 ... Ditto. Ditto 056 040 041 Ditto. +--------------+-----+-------+-----+----------+

Krupp's cast steel, manufactured at Essen, near Cologne, is a natural steel, being made on the bed of a puddling furnace. It is obtained from haemat.i.te and spathic ore, c.o.ke being used for the smelting. The proportion of carbon in Krupp's steel is about 12 per cent. When required for ordnance it is fused with a little bar iron in pots, each of which holds 30 lbs. It sometimes happens that in the manufacture of a huge gun or cannon the contents of as many as 1200 of these pots are required. When this is the case the pots are emptied of their molten contents simultaneously into a channel leading to the cast, 400 well-drilled men being required to carry out the operation.

It is very essential that castings of such magnitude should be allowed to cool very gradually. They are therefore enveloped in hot cinders for two or three months, after which they are ready for the forging.

2. _The carburation method._ This is generally effected by the process known as 'cementation,' which is carried out as follows:--Two chests, made of fire-brick or stone, one narrow end of each of which is shown in the accompanying plate, are so fixed in a dome-shaped furnace, so that the flames from the hearth beneath can effectually play around them.

The process renders it necessary that the temperature of the furnace should be steadily maintained for some days; and this is achieved by surrounding the furnace with a conical wall of brick-work, as shown in the cut. The chests are usually about 10 or 12 feet in length, 3 feet in height, and 3 feet in depth. A layer of charcoal of a fineness to pa.s.s through a sieve of a 1/4 inch mesh, or of soot, is placed on the bottom of each chest, and upon this the bars of wrought iron which are intended for conversion into steel. The bars inside must be of iron of the best quality, and generally about 3 inches broad and 3/4 of an inch thick. When arranged regularly a little distance apart, the interstices between them are filled up with charcoal, with which they are then covered to a depth of about an inch. Similar layers of bars, similarly arranged, succeed to this first one, until the chests are filled.

They are then covered in to a depth of 6 inches with a luting of damp clay or sand. Each chest when thus filled contains from 5 to 6 tons of iron.

One of the bars projects through an opening at the end of the chest, to facilitate an inspection of it from time to time by a workman, so that he may be enabled to judge of the progress of the operation. The materials of which the chests are composed render it important that the temperature of the furnace should be carefully and gradually increased, as a too sudden accession of heat would lead to the splitting of the chests. The temperature necessary to effect the carburation of the iron has been found to be that required for the melting of copper, viz. 1996 Fahr. When this temperature is reached it is maintained for eight or ten days, or even longer, the period depending upon the thickness of the iron, and the degree of hardness it is desired it shall possess. Six or eight days are sufficient to yield steel of a moderate degree of hardness. At the end of the requisite time the fire is gradually put out, and the chests as gradually cooled, a process which occupies about another ten days.

[Ill.u.s.tration]

The effect of the treatment to which the iron bars have been subjected has been, in the first place, to entirely alter their interior structure; for if they are broken asunder at any part, instead of showing the fibrous arrangement observable in bar iron, they present a closely granular one.

In the second place, chemical a.n.a.lyses demonstrate that the iron has combined with about 1 per cent. of carbon, and that this combination has not only taken place on the surface of the bar, but has extended throughout its whole substance. It is because of this perfect impregnation of the iron by the solid carbon that the process by which it has thus been converted into steel is called 'cementation.'

Two suggestions have been offered in explanation of the blistered surface presented by the steel. One of these, the theory of Mr T. H. Henry, is that part of the carbon in penetrating into the body of the bar iron had combined with the small quant.i.ty of sulphur present in the iron, and that the bisulphide of carbon thus formed becoming vaporised by the elevated temperature, in escaping through the soft surface of the metal, has caused its blistered condition. The second conjecture is that the blebs have arisen from the extrication of carbonic oxide, which had been formed in the bar by the union of the carbon with the small quant.i.ty of oxide of iron or slag accidentally remaining in it.

Graham has shown that soft iron has the power of absorbing or occluding at a low red heat 415 times its volume of carbolic oxide, which the metal, when it becomes cold, retains, but which it parts with when subjected to a temperature such as that which prevailed in the cementation box. This fact seems to offer a reasonable confirmation of the reaction it has been surmised takes place during the cementation process, and which is supposed to be as follows:

The small quant.i.ty of atmospheric oxygen remaining in the chest unites with the carbon to form carbonic oxide. This carbonic oxide gives up half its carbon to the iron (which thereby becomes converted into steel), and in doing so changes to carbonic acid, which becomes reduced to carbonic oxide by the absorption of more carbon from the charcoal, which carbon the carbonic oxide again transfers to the iron.

The above reaction may not improbably occur throughout the substance of the bar. By some chemists, cyanogen compounds are supposed to be present in the cementation powder, and the cyanogen contained in these is supposed to be the carrier of the carbon to the iron.

"The blistered steel obtained by this process is, as would be expected, far from uniform, either in composition or texture; some portions of the bar contain more carbon than others, and the interior contains numerous cavities. In order to improve its quality it is subjected to a process of f.a.gotting similar to that employed in the case of bar iron; the bars of blistered steel, being cut into short lengths are made up into bundles, which are raised to a welding heat, and placed under a tilt hammer weighing about 2 cwt., which strikes 200 or 300 blows in a minute; in this way, the several bars are consolidated into one compound bar, which is then extended under the hammer till of the required dimensions.

"The bars, before being hammered, are sprinkled with sand, which combines with the oxide of iron upon the surface, and forms a vitreous layer which protects the bar from oxidation. The steel which has been thus hammered is much denser and more uniform in composition; its tenacity, malleability, and ductibility are greatly increased, and it is fitted for the manufacture of shears, files, and other tools. It is commonly known as shear steel. Double shear steel is obtained by breaking the tilted bars in two, and welding these into a compound bar. The best variety of steel, however, which is perfectly h.o.m.ogeneous in composition, is that known as cast steel, to obtain which about 30 lbs. of blistered steel are broken into fragments, and fused in a fire-clay or plumbago crucible, heated in a wind furnace, the surface of the metal being protected from oxidation by a little gla.s.s melted upon it. The fused steel is cast into ingots, several crucibles being emptied simultaneously into the same mould. Cast steel is far superior in density and hardness to shear steel, but, since it is exceedingly brittle at a red heat, great care is necessary in forging it.

It has been found that, in addition to 100 parts of the cast steel, of one part of a mixture of charcoal and oxide of manganese, produces a very fine grained steel, which admits of being cast on to a bar of wrought iron in the ingot mould, so that the tenacity of the latter may compensate for the brittleness of the steel; when the compound bar is forged, the wrought iron forming the back of the implement, and the steel its cutting edge."[196]

[Footnote 196: Bloxam's 'Chemistry Inorganic and Organic.']

Another distinct method from the cementation one, by which the carburation of iron is affected, is that in which sc.r.a.p or malleable iron is mixed with pig or cast iron, this latter being fused with the sc.r.a.p iron in quant.i.ty sufficient to afford such an amount of carbon as is necessary to convert the mixture into steel. Steel made by this operation is entirely h.o.m.ogeneous, the tilting process which precedes the casting of the steel obtained by cementation is therefore unnecessary. The pig iron is placed on the bed (made of refractory sand) of one of Siemens' regenerative furnaces, heated by gaseous fuel. The temperature in this furnace is so intense that the pig iron becomes perfectly liquid, and, when in this condition, the sc.r.a.p iron, which has been previously heated to redness in an adjoining refractory furnace, is added, it becomes dissolved by it.

Iron may also be carburetted by heating wrought iron bars in carburetted hydrogen. This process, however, is seldom had recourse to.

In the manufacture of Bessemer steel both the carburation and decarburation processes are practised. From 1 to 5 tons of pig or cast iron in a molten state are run from a contiguous blast, cupola, or reverberatory furnace, with an apparatus known as a converter, which is previously heated up to redness by means of c.o.ke. The converter is figured under two aspects in the annexed engraving.

This vessel, which is generally made of boiler plates of sheet iron, has an inside lining, consisting of a siliceous fireproof material, and is perforated at the bottom with a number of concentric little openings, which are the orifices of as many little tubes or tuyeres, that lead into an outside main tube, as shown in the plate. By means of these tubes condensed air is forced into the ma.s.s of melted metal, which is soon thrown into violent commotion, and sends out a shower of ignited sparks.

The oxide of iron formed at the same time being set into active movement by the incoming blast of air, is brought into intimate contact with every particle of the carbon and silicon contained in the cast iron, and converts the former into carbonic oxide, which burns with its characteristic flame at the mouth of the converter, and the silica into silicic acid, which enters into the slag, and floats, in the form of foam, on the top of the heavier molten iron.

[Ill.u.s.tration]

The removal of the carbon (which is known by the discontinuance of the carbonic oxide flame) being thus accomplished, the iron has next to be submitted to the carburetting operation. This is performed by running into the liquid iron in the converter such a quant.i.ty of molten pig or cast iron as contains the required proportion of carbon.

The pig iron used for this purpose generally contains, in addition to a large amount of carbon, a very perceptible quant.i.ty of manganese. The converter (as shown in the plate) is then by means of the trunnion tilted, so that its contents can be run into a ladle and transferred to the necessary moulds. The time of conversion occupies from ten to twenty minutes.

By Bessemer's process the sulphur present in the pig iron is almost entirely eliminated; the greater part of the silicon is also separated, together with the carbon, and almost in the same proportion; but the phosphorus is not removed, and, owing to the oxidation of some iron, the amount is actually greater in the finished steel than in the pig iron.[197]

[Footnote 197: Payen's 'Industrial Chemistry,' edited by B. H. Paul, Ph.D.]

Bessemer's steel is in large demand, and is excellently suited for rails for railroads, cannon, boiler plates, armour plates, and similar heavy material, for the manufacture of which it has largely supplanted wrought iron, but not at all adapted for the manufacture of knives, razors, lancets, or similar instruments, in which a sharp or keen edge is desirable.

The Bessemer process, which is largely adopted by the manufacturers of steel throughout Europe and America, has proved a source of princely income to its inventor, who obtains a bounty of a shilling on every ton of steel made by it. In Europe alone in 1859 5-1/2 million cwts. Seventy per cent. of this quant.i.ty was the produce of British industry.

Latterly, attempts have been made to obtain steel direct from the ores.

The efforts made in this direction have been greatly stimulated by the invention of the regenerating furnace of Siemens. In these furnaces, in which an intense temperature is obtained by means of the combustion of inflammable gases (chiefly consisting of carbonic oxide, hydrogen, and carburetted hydrogen), the ore after (in one process) being melted in hoppers by means of the burning gases, runs down, and is gradually dissolved in some melted pig iron placed on the hearth of the furnace.

When this latter has been sufficiently diluted with the decarbonised iron the operation is complete.

_Properties of Steel._ The effects of temperature upon steel are remarkable, and a knowledge of them has proved of great practical utility in the manufacture of the various steel-ware articles that are so indispensable to our every-day wants and needs. If forged and soft steel is heated, and then suddenly cooled, it becomes hard, the hardness varying with the temperature and the rapidity with which this has been reduced.

The higher the temperature and the more rapidly it is cooled, the greater will be its hardness. Steel, which has been heated until white-hot, and then suddenly plunged into a bath of cold mercury, acquires a hardness nearly equalling that of the diamond. That, however, which the steel gains in hardness, it loses in pliancy and elasticity, besides becoming so brittle as to be of no possible use.

Soft steel, which has been made hard by heating it to redness, and by subsequent sudden immersion in cold water, may be reconverted into soft steel by again heating it to redness and allowing it to cool suddenly. By stopping short, however, of heating it to redness, its hardness may be proportionally modified.

Hence steel articles, varying as much in the qualities of hardness and elasticity as a lancet and watch-spring, are made either by 'heating down'

hard steel to requisite temperature and allowing it to cool, or by 'heating up' soft steel to the necessary point and also letting it gradually cool. When steel is so treated it is said to be _tempered_ or _annealed_. If polished steel be heated over a flame to a temperature of 430 F. its surface becomes of a very pale yellow colour; the colour pa.s.ses through different shades of yellow and blue with each successive increase of temperature, until when raised to 600 F. it becomes blackish blue.