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Watchmakers' Hand Book

Part II,
MATERIALS EMPLOYED IN HOROLOGY
Page 2

STEEL

      60. The treatment of steel involves some of the most prolonged and delicate operations in the entire range of horology. If the metal is badly selected and prepared, the working of it will be laborious, difficult and unsatisfactory; the resulting object will be distorted in the hardening, and will not harden uniformly; in short, it will occasion much toil and loss of time, with very little success.

      Let the young watchmaker accustom himself from the first to study the steel that he uses, so that he may be thoroughly cognizant of both its advantages and defects; he will, in the practice of his art, be amply repaid for the brief time spent in making such an examination.

      61. Steel is not an elementary body; it is usually regarded as a carbide of iron, that is to say a combination of carbon and iron. Analysis, however, proves other substances to be usualy present in almost infinitesimal quantities; their remarkable influences on the physicak properties of the metal has not yet been fully investigated, but much attention is being devoted to them at the present day.

      The varieties of steel are very great. What are known as puddled and natural steel are obtained by acting directly on cast iron. Cementation is a very old method of converting bars of malleable or pure iron into steel by enclosing them in charcoal and heating the whole for several days, until the carbon has worked itself into the center of the bars in such quantity as to convert the iron into steel.

      The steel obtained by the above method is very heterogeneous; in other words, the composition is not uniform throughout a given block or bar. One part is highly carbonized, whereas another part, especially towards the center, will not be sufficiently so. The grain, although very fine in one part, will be coarse in another; hard particles of pure cast iron, termed "pins," are to be met with with that resist the action of the graver or the file and give rise to cracks in the hardening, hammering, etc., and portions or sometimes even entire layers that have taken up no carbon whatever. The differences in the density, hardness, malleability, etc., that can be shown to exist at different points in the same bar arise from this cause.

      Such faults can in part be corrected by shearing, an operation which consists in binding together a number of bars in a bundle, raising them to a red heat and beating them with a sledge or steam hammers so as to weld them into one. The bar thus obtained is again heated, folded several times on itself, and again hammered, rolled, etc., when it is termed shear steel. If these operations are performed carefully and without a too great heat, the quality of the steel is much improved; it is more homogeneous and can be worked with greater facility.

      62. The discovery of the earliest method of producing cast steel, thoroughly homogeneous, was made by a watchmaker, B. Huntsman, of York, and metal produced by his method is very highly prized at the present day. Many other methods have been since introduced, amongst which may be mention the Bessemer and the Siemens-Martin processes, and steel is now produced from iron of very varying quality, so that the mark cast steel is now far from being a guarantee of quality. The fusion of shear or cement steel will only secure a marked superiority in its quality under two principal conditions: (1) The metal must be carefully selected, since certain qualities do not intermingle thoroughly. (2) Very great care and skill must be devoted to all the operations, the successive heatings, forging, rolling, etc.

      In short, in the case of steel it is exceptionally true that we must never accept the metal merely on its own recommendation. Whatever maker's mark is selected, the results obtained will never be satisfactory unless the degree of hardness, the elasticity, cohesive force, etc., are such as will suit the metal to the special purpose to which it is to be applied as well as to the working it will have to undergo. Experiment can alone make us fully cognizant of the qualities of a steel.


GENERAL OBSERVATIONS.

      63. All steels, if of good quality to begin with, will deteriorate if subjected too often or too long (according to the character of the metal) to the action of either the fire or the hammer. They will become brittle and incapable of hardening, in the end even reverting to the condition of iron.

      The quality of steel becomes worse as the number of flaws, blackish filaments, more or less carbonaceous veins, and occasional particles of pure iron in its substance are greater; as its surface is cindery, that is to say spotted with the minute black marks which become more prominant after polishing, etc.; as its fracture presents an uneven grain, etc.

      Such a metal is found to vary considerably as regards hardness, elasticity, etc.; not being uniformly affected in the hardening, it becomes difficult to work with the file and almost impossible to form into a perfect cylinder in the lathe.

      Other conditions being equal, these faults are characteristic of natural steel rather than of the two other varieties. At the same time, if well sheared, it becomes very elastic, and has the great advantages of not being deteriorated under the hammer and of being less ready than the other varieties to be converted into iron.

      Rolling, wire-drawing and hammering occasion a molecular re-arrangement; it is necessary, therefore, to anneal the metal from time to time, as otherwise it becomes brittle or cracks.

      There is a certain temperature, corresponding to each variety of steel, which cannot be exceeded without the metal being injuriously affected; this temperature must, then, be previously determined.

      The grain of a piece of steel that has been superheated or burnt is characterixed by brilliant diamond-like particles; the mass loses its beautiful color, and resembles iron more or less according to the degree of heat applied.

      Some few workmen are enabled, by long experience and a very delicate touch, to judge approximately of the quality of a steel from its weight, feel, and resonance. Metal that is of good quality, homogeneous, and very dense, they term full.


SPECIAL OBSERVATIONS.

      64. Natural Steel. In the case of natural steels of low quality, the fracture is usually characterized by uneven grains, a somewhat fibrous nature and a bluish tint. The grain becomes finer and more even and the surface presents more and more the appearance of a piece of coke, as the quality of metal improves. In addition to these distinctive features a natural steel of high quality can be distinguished by the fact of its being more thoroughly hardened and less likely to break when hard.

      In hardening it must be raised to a higher temperature than cement steel; in other words, steel of a low quality must be heated somewhat above bright redness, while the better qualities should be heated to an orange-red, or nearly so (77).

      65. Cement Steel. The cement steel ordinarily met with has a lamellar fracture, the lamellæ varying in form and color from the center towards the circumference. The grain is usually finer and more uniform than that of natural steel, there is seldom any appearance of fibers, veins, or flaws. The color of the fracture is greyish, tending towards blue in the ordinary qualities.

      The better qualities are marked by a closer grain, a more uniform, dull, greyish-white color, exhibiting neither streaks or black spots after hardening, and by the further fact that hardening can be effected at a lower temperature. If of the very best quality, it should not require heating beyond a clear cherry-red; often even a still less degree of heat will suffice.

      66. Cast Steel. Cast steel is the most homogeneous, full, and beautiful of the three classes. Several varieties exist. The fracture of cast steel, as compared with others, is smooth, compact, and of a white-grey color, resembling coke. The grain is fine and very even. The metal must be hardened at a temperature much lower than can be safely applied to other classes of steel, since it is rapidly deteriorated by heat.

      Cast steel is more fusible than ordinary steel, and will fracture with ease under the hammer when heated to a blue tint, so that great care is essential in hammering it.

      The metal should never be heated beyond a dull or cherry-red heat, lest it be burnt.

      The tenacity will be increased by forging at a low temperature or even by cold hammering.

      The fineness in grain, together with its high density, afford an indication that the metal can be rendered very uniformly hard; that very fine cutting edges and the most minute rods can be made of it; and that, after hardening, it can be highly and uniformly polished; in other words, that is does not exhibit spots or streaks differing in color from the mass, as is always the case with natural and cement steels. For most horological purposes (such as making pinions, staffs, pivots, etc.) cast steel is perferable. It is the only kind that can with certainty be highly polished, turned perfectly round, and that does not get distorted in the smoothing. Moreover, when wear does occur it exhibits less irregularity.

      Highly-carbonized shear-steel exhibits a fine, close grain that would make it easily mistaken for cast steel. They can be best distinguished by the application of dilute sulphuric acid. The side of the bar when acted on by this means exhibits lines that indicate the junctions of the several layers constituting shear-steal.

Submitted by: Samuel Kirk (##)

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