Red Heat Research Articles

The effect of temperature on some of the properties of steel

The results here given are derived from part of a series of experiments, now in progress at the Davy-Faraday Laboratory, on the effect of temperature on the elastic coefficient of solids. The particular case of the variation of the rigidities of iron and steel is of some importance, and I believe that these are the first published measures of this quantity at comparatively high temperatures. The fact that iron and steel change into an allotropic form at a temperature of about 800º C. has long been known, and I think that the first accurate observations of the phenomena which accompany this change were made by me in 1873–74. At that time I had no means of measuring the temperature, but automatic records of the variation of length of iron and steel wires were made while they were cooling from a bright red heat.

Societies and Academies

LONDON. Royal Society, March 1.—A. Mallock: The effect of temperature on some of the properties of steel. The period of torsional vibration and the length of a steel wire were automatically and continuously recorded in terms of time, while the temperature was varied between 15° and 1000° C. The results show (1) that the variation of the rigidity of steel between ordinary temperature and a dull red heat is small (less than 1 per cent.); (2) that above the critical temperature (about 800° C.) the rigidity decreases rapidly; (3) that the temperature coefficient of expansion does not show any marked change as the metal passes through the critical temperature; but (4) that a comparison with the cooling curves of iron and steel proves that the specific heat of the high temperature form of the metal is much less than it is at temperatures below the critical point.—C. H. Lees: Inductively coupled low-resistance circuits. The oscillations in each of two circuits of low resistance coupled by their mutual inductance can be simply expressed in terms of a certain product of capacitance and inductance. The expressions for the currents lead to a simple graphical solution of the problem.—Lord Rayleigh: Studies of iridescent colour, and the structure producing it.—(1) The colours of potassium chlorate crystals. The structure of the iridescent potassium chlorate crystals investigated by Stokes and the late Lord Rayleigh is examined microscopically. The periodic twinned structure inferred by the latter is clearly shown in the photographs taken under the microscope with polarised light. Some crystals have exceedingly complex structure, showing many groups of evenly spaced twin planes and a very complex reflection spectrum. This results from high interference from twinned layers situated a considerable distance apart. Chlorate crystals, giving a silvery reflection, were obtained by Madan, who heated the ordinary colourless crystals to about 250° C. A complex twinned structure is induced, and photographs of the structure of the crystal and of the reflection spectrum show corresponding irregularities in each, resulting from want of flatness in the twin planes. (2) Mother-of-pearl. The results generally confirm those of Brewster and A. H. Pfund. Micro-photographs show the grating structure of a pearl oyster shell and the structure of parallel layers of an “ear” shell. The absorption spectrum of the latter shows that in agreement with the spacing of the layers the reflection is of the second order. (3) The colours of Labrador felspar. The colours seen by reflection arise from two distinct origins:—(a) Specular reflection from tabular inclusions, which show the colours of thin plates and are often 0.2 mm. in dimensions; they are distributed parallel to one of the cleavages. (b) Diffuse reflection from a plane about 15° away from the cleavage mentioned; this is the source of the striking colours observed. When the diffuse reflecting plane is examined microscopically under conditions which ensure that the light only comes from a very thin stratum, it is found that the plane of reflection is patchy. The patches are of irregular outline. The diffuse character of the reflection is accounted for by the small diameter of these reflecting surfaces, regarded as independent optical apertures. Their size (0·005 mm) accounts approximately for the angular diameter of the diffuse image of a point source seen by reflection. The colour of the reflection is not sharply limited to special regions of the spectrum, and can be explained by the interference of streams of light from the two surfaces of each patch. The patches may be fissures in the material, and there is evidence that their thickness is not absolutely uniform. The brightness of the colour is explicable by the large number of reflecting patches adding their effects, without definite phase relation such as would give rise to regular interference.—L. V. King: On the complex anisotropic molecule in relation to the dispersion and scattering of light.

COMPARISON OF HOT AND COLD MODULUS OF RUPTURE FOR SILICA BRICK

Purpose of the Investigation.—(1) To obtain relative values for the cross-breaking strength of silica brick at temperatures encountered in coke oven practice. (2) To correlate the hot modulus of rupture test, if possible, with the cold modulus of rupture, or cold crushing test, either of which is cheaper and more easily conducted. This report gives the method of making the test, difficulties encountered and results obtained. The report shows a comparison of cold crushing, cold modulus of rupture and hot modulus of rupture on a series of silica brick made from special mixes, commercially burned. Conclusions.—The modulus of rupture of a silica brick at 1350°C is approximately one-third the strength at atmospheric temperature. For this series it averaged from 130 to 189 lbs. per square inch. Too rapid or eccentric heating up to red heat may cause such weakening of the structure or bond that the brick will break under very low pressure. Cross-breaking strength decreases as the temperature increases. Hot modulus of rupture test appears to give results, in most respects, comparable to the cold test, and for routine testing it would seem advisable to use the cold test since it can be made in much shorter time.

The Flow of Steels at a Low Red Heat

RECENT developments in chemical engineering have called for the provision of metallic containers capable of withstanding considerable stress at high temperatures and for long periods. The investigation of the mechanical properties of steels and alloys at these temperatures has accordingly become a matter of very direct practical importance. The existing literature of the subject almost invariably consists of graphs, in which tensile test results are plotted against the temperature at which the test was made, care being taken to eliminate the disturbing, but very important, factor of time, by carrying out each test under as nearly the same conditions as possible, the duration of each test being at most a few hours, with an actual loading time of a few minutes. It cannot fairly be claimed that such information gives more than a general indication of the relative ability of different materials to meet the working conditions usually encountered by the exhaust valve of an aeroengine or the retorts, catalyst tubes, etc., of the engineer. Certainly it does not enable a designer to construct a container which can be depended upon to maintain its shape indefinitely, at super-atmospheric temperatures when in a state of stress.

On the velocity of sound in gases at high temperatures, and the ratio of the specific heats

The experiments described in this memoir on the velocity of sound in gases, at temperatures varying from atmospheric to that of a bright red heat, were made with the object of tracing the change in the specific heat of gases with rising temperature, and, if possible, of arriving at formulæ which might be applicable to the extremely high temperatures reached in explosions. The sound method was decided on chiefly for the reasons (1) that the velocity of sound in a heated gas gives a value for the ratio of the two specific heats at the temperature of the experiment, and not as in the method of mixtures at a mean temperature between the highest and lowest point of the heated and cooled gas; and (2) because we had had considerable experience in the use of a chronograph for measuring the rapid movements of flame through gases in long tubes. It is necessary to make it clear at starting that no claim is made that these experiments give more exact determinations of the specific heat of gases than those given previously by experiments over low ranges of temperature; the object has been to obtain by comparative measurements the general gradients of the curves rather than to find the exact value at any definite point.

THE BONDING STRENGTHS OF A NUMBER OF CLAYS BETWEEN NORMAL TEMPERATURE AND RED HEAT

Journal of the American Ceramic SocietyVolume 1, Issue 2 p. 113-133 THE BONDING STRENGTHS OF A NUMBER OF CLAYS BETWEEN NORMAL TEMPERATURE AND RED HEAT C. W. Saxe, C. W. Saxe Norton Co., Worcester, Mass.Search for more papers by this authorO. S. Buckner, O. S. Buckner Norton Co., Worcester, Mass.Search for more papers by this author C. W. Saxe, C. W. Saxe Norton Co., Worcester, Mass.Search for more papers by this authorO. S. Buckner, O. S. Buckner Norton Co., Worcester, Mass.Search for more papers by this author First published: February 1918 https://doi.org/10.1111/j.1151-2916.1918.tb18598.xCitations: 6Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume1, Issue2February 1918Pages 113-133 RelatedInformation

The emission of electricity from various substances at high temperatures

In previous papers an account was given of experiments in which ionisation currents of great magnitude were obtained from carbon at high temperatures. It was remarked that the largest currents appeared to be associated with the expulsion (at about 2000°C.) of impurities, such as silica, alumina and iron, which are always present in commercial carbon. Such a result is perhaps not surprising in view of Wehnelt's work on the alkaline earths and their large electronic emissivity when raised to a white heat, as for example in a Wehnelt cathode. Furthermore, Sir J. J. Thomson showed some years ago that oxides, when raised to a red heat in a crucible, gave out an excess of negative electricity, the most copious streams coming from the oxides of calcium and barium. The currents generated were such as were readily indicated by an electroscope.

Spectroscopic observations : lithium and cœsium

The present communication deals with a further study of the absorption spectra of the vapours of lithium and cœsium. These spectra were investigated, and the results communicated at the beginning of last year to the Royal Society. The present account deals with an extension of the principal series lines for the two metals, and a more detailed examination of the expression of the wave-lengths by a formula, as well as an investigation of the broadening effect in a pair of lines with increase of density of the vapour of cæsium. We shall deal first of all with the lithium spectrum. As has been remarked before, lithium vapour presents some difficulties, because of the high temperature required and the action of the vapour in this condition on the material of the containing vessel, but this difficulty can be surmounted by the use of a double steel tube and a large quantity of lithium. With the tube at a bright red heat, a dense enough vapour is produced to show in transmitted light a large number of the principal series lines ; the number that can be observed depends, I am convinced, only on the resolving power of the spectrograph used to investigate them. With the instrument at my disposal, I have been able to measure 41 of these lines, and I think in this case the resolution has been pushed as far as practicable, the last few lines being separated by only about 0·2 Ångström unit. Fig. 1, Plate 9, shows the absorption lines up to No. 25. The finer lines after this do not appear in the reproduction.

The absorption spectra of lithium and cæsium

In a paper communicated to the Royal Society in February, 1910, I gave the results of measurements of absorption lines for the three alkali metals, potassium, rubidium, and cæsium. Up to that time I had not been able to obtain the corresponding spectrum for lithium vapour. This was owing to the fact that lithium vaporises at a considerably higher temperature than the other alkali metals, and at the high temperatures required for a sufficient density of vapour the lithium attacks the material of all tubes which I was able to use. Steel, brass, platinum, glass, silica, carbon are all attacked, and no satisfactory photographs could be obtained. Recently, however, by using a relatively large quantity of lithium in a steel tube sufficient vapour was obtained to give an absorption spectrum showing 27 lines of the principal series. The method was the same as that described in the paper referred to, with the exception that a second steel tube was placed in the outer steel absorption tube. This was simply for the protection of the outer tube, which would probably collapse after being acted on by lithium vapour at the bright red heat to which it was raised. The source of light used was the cadmium spark, as the limit of the series is so much further in the ultraviolet than in the case of the other alkali metals. The following table gives the wave-lengths and oscillation frequencies for the complete series of lithium lines. (See Table I opposite.)

Historical Note on Recalescence

IN his recent presidential address to the Iron and Steel Institute, Prof. Sir W. Roberts-Austen stated (NATURE, NO. 1541, p. 43): “To Gore, and to Barrett, we owe the investigation of the nature of a fact which had long been well known to smiths, that iron on cooling from a bright red heat suddenly emits a glow.”

The Gases in Rocks

It has been known for a long time from microscopic studies that some minerals inclose minute cavities which contain both liquid and gaseous matter. For a much shorter period it has been known that various igneous rocks, when exposed to red heat in a vacuum, evolve several times their volume of gas, and that this gas is of quite variable composition. Since these gases occur in proportions entirely different from those of the constituents of the air, it has not seemed probable that they were derived directly from our present atmosphere, unless the rocks manifest some power of selective absorption not now understood. The apparent difficulties involved in this conception have suggested that some earlier atmosphere was rich in those gases. This involves a hypothesis relative to the changes through which the atmosphere has passed, and leads on to a theory of its origin and that of the earth itself. An alternative hypothesis regards these gases, not as the products absorbed by a molten earth from its surrounding gaseous envelope, but as entrapped in the body of the earth during its supposed accretion, and hence as a source from which accessions to our present atmosphere might be derived. A study of the gases in the rocks has seemed, therefore, to give promise of results of some value to atmospheric problems and, perhaps, to those of cosmogony. Because of this, it has appeared advisable to determine more widely the range and the distribution of these gases, their relations to other geologic phenomena, and the states in which the gases, or gas-producing substances, exist in the rocks.

Transparent silver and other metallic films

It is well known that when thin leaves of gold or silver are mounted upon glass and heated to a temperature which is well below a red heat, a remarkable change of properties takes place, whereby the continuity of the metallic film is destroyed. The result is that white light is now freely transmitted, reflection is correspondingly diminished, while the electric resistivity is enormously increased. A simple method of illustrating this extraordinary change is to mount a sheet of silver leaf between two clean lantern plates, clip them lightly together by means of wire paper fasteners or other suitable means, and then heat gradually to a temperature of not more than 500°C. This can be done con­veniently by placing the plates on a thin fire-brick in a cold gas muffle, and then raising the temperature to the desired point. The gas should now be turned off, and the glass plates allowed to cool slowly, so as to avoid cracking. They can then be bound with strips like an ordinary lantern plate, and a permanent example of transparent silver is obtained. It will be found that such a plate transmits the light of the electric lantern almost as readily as ordinary glass, and does not produce any change of colour. The great trans­parency of the film may be shown by placing the plate upon printing or writing, and photographing the characters through the plate. Every detail of the characters can be reproduced with remarkable clearness. At first sight it is perhaps difficult to conceive that so distinct an impression could be obtained through what was originally a perfectly opaque sheet of silver, and which has only been once heated to a moderate temperature.

Kaolinization and other changes in West of England rocks

The behaviour of a mass of molten but cooling igneous rock under moderate pressure may be compared to that of liquid cupelled silver, which at a certain temperature can no longer retain the oxygen, many times its volume, that it has occluded. Thus, during the submarine eruption off the island of Pantelleria in 1891, blocks of lava that swam for a while on the surface of the sea exploded with violence. Chilling by contact with sea-water had occasioned exactly what Lowthian Bell observed to happen on the sudden cooling of masses of slag by contact with water. There was a discharge within the set outer envelope, at something near a red heat, of previously dissolved water and gases, converting the floating ejectamenta into a species of bombs.

IV. On the discharge of negative electricity from hot calcium and from lime

The discharge of electricity from hot metals has been the subject of a great number of researches by different authors. The metal chiefly used in these experiments has been platinum, on account of its high melting-point, its stability in air, and the ease with which it can he obtained in a state of purity. In the present experiments calcium was chosen for investigation because of its strong electropositive character. Since this implies a great attraction for positive electricity, it would be expected that the negative corpuscles would escape more readily from calcium than from platinum. It should, therefore, be possible to obtain a measurable “negative leak” from calcium at a much lower temperature than from platinum or other less electropositive metal. The first method of experimenting employed consisted in measuring the saturation current from an electrically heated calcium wire to a surrounding electrode, both being placed in a vacuum, but it was found to be impossible to get a clean surface of calcium in this way, for the metal combines with the oxygen, nitrogen, and water vapour in the air, and becomes more or less covered with a coating of calcium compounds before the apparatus can be fitted up. Another difficulty was soon discovered. When the wire was heated to above a dull red heat, the vapour pressure of the metal was sufficient for it to volatilize and condense on the colder walls of the tube. Thus the wire got thinner at its hottest point, and, consequently, the temperature there rose, and the sublimation increased, until in a few seconds the wire had broken through.

Societies and Academies

Societies and Academies

The elastic properties of steel at high temperatures

Hitherto, investigations into the elastic properties of metals have been confined to comparatively low temperatures. Gray, Dunlop, and Blyth have measured the modulus of rigidity and Young’s modulus for wires up to temperatures of 100° C., and found that both these quantities decrease as the temperature rises. Martens determined the influence of heat on the strength of iron up to temperatures of 600° C., but his experiments were the ordinary tensile tests carried to rupture, and though he also found a substantial diminution of Young’s modulus with rise of temperature, he did not go into the point fully, being mainly concerned with breaking stress and elongation. In the experiments here described the elastic properties of steel and iron have been investigated at higher temperatures, ranging up to 800° C., and for stresses greatly below that required to rupture the material. We have found that as the temperature rises the stress-strain relations undergo a remarkable change, which may best be expressed by saying that what is variously called the “time-effect,” or “elastische nachwirkung,” or “creeping,” increases greatly with the temperature. Steel, at high temperatures, behaves like indiarubber or glass; if it is stressed for a time, and the stress removed, it does not at once recover, but after the immediate elastic recovery there is a slow contraction perceptible for many minutes. Such “creeping” can be detected at ordinary temperatures, but at a red heat it attains a different order of magnitude, becoming (in its total amount) a substantial fraction of the whole deformation.

On changes in elastic properties produced by the sudden cooling or ‘quenching’ of metals

It is well known that when steel is quenched from a red heat, its elastic properties suffer a profound change, the material becoming extremely hard and brittle. It is also known that quenched steel, when tested under tension, exhibits no distinct yield-point, Hooke’s law is departed from quite gradually until abrupt fracture occurs at a high stress.

VI. The fracture of metals under repeated alternations of stress

It is well known that metals will break down under repeated application, and especially under repeated reversal, of stresses greatly less than those that have to he applied when the “ultimate strength” of the material is tested in the ordinary way. The researches of Wöhler have shown, for example, that iron capable of bearing about 20 tons per sq. inch of steady load will break when it is exposed to some millions of reversals of a stress of 8 or 9 tons per sq. inch, alternately in compression and extension. When the alternating stress is increased a smaller number of reversals suffices to produce rupture. On the other hand, examples such as are furnished in the balance-spring of a watch, or in a railway axle, show that very many million repetitions may be applied with impunity, provided the limit of greatest stress be kept sufficiently low. The mild steel axle of a railway carriage is exposed to many million reversals of a stress which, in some cases, approaches as high a value as 5 tons on the sq. inch, apparently with perfect impunity, for it seems probable that in the rare instances where fracture of such axles has occurred an explanation is to be found in the gradual spreading of a crack from an origin supplied by an air-bubble or other primitive defect in the material. But Wöhler’s researches, which have been confirmed by other observers, give evidence that a stress not very much greater than this, and far below not only the ultimate strength but even the “yield-point” of the metal, will produce what is called “fatigue” and bring about fracture when reversal of the stress is repeated many times. The purpose of this paper is to describe experiments in which the microscope has been applied to study the nature of the process of fatigue by which breakdown occurs under repeated reversals of stress. The experiments have been made during the past year in the Engineering Laboratory at Cambridge. The metal chosen for experiment was Swedish iron, of high and very uniform quality. It had the further advantage for our purpose of possessing a clearly defined and fairly large crystalline structure, well adapted when polished and etched to exhibit the characteristic lines known as “sliplines” or “slip-bands,” which appear in ordinary testing when any portion of the material has passed its limit of elasticity under strain. We used the metal in the form of rods with a rectangular section, the dimensions being approximately 0·3 inch by 0·1 inch, and to make the structure as uniform as possible these were in all cases annealed by being kept for about two hours at a dull red heat, while enclosed in a tube filled with lime, in a muffle furnace. One of the surfaces of each rod was polished and etched, and the rod was subjected to reversals of stress by bending, so that the polished surface was alternately extended and compressed. This was done, as in Wöhler's original experiments, by making the rod project from a revolving shaft with a load on the projecting end. As the process went on the rod was from time to time examined under the microscope, and in several cases photographs of the same crystals weie taken at each stage to record the progressive effect of repeated reversals of stress.

I. On the tempering of iron hardened by overstrain

It is well known that iron hardened by overstrain—for example, by permanent stretching—may have its original properties restored again by annealing, that is, by heating it above a definite high temperature and allowing it to cool slowly. Experiments to be described in this paper, however, show that if iron hardened by overstrain be raised to any temperature above about 300°C., it may be partially softened in a manner analogous to the ordinary tempering or “letting down” of steel which has been hardened by quenching from a red heat. This tempering from a condition of hardness induced by overstrain, unlike ordinary tempering, is applicable not only to steel but also to wrought iron, and possibly to other materials which can be hardened by overstrain and softened by annealing. The experiments about to be described were all carried out on rods of iron or steel about ⅜ths of an inch in diameter and 11 inches long, the elastic condition of the material being in all cases determined by means of tension tests. The straining and testing were performed by means of the 50-ton single-lever hydraulic testing machine of the Cambridge Engineering Laboratory, and the small strains of extension were measured by an extensometer of Professor Ewing’s design, which gave the extension on a 4-inch length of the specimen to the 1/100000th of an inch. This instrument, which is shown attached to a specimen in the following illustration, is of a design slightly modified from that of the larger extensometer fully described by Professor Ewing in a paper “On Measurements of Small Strains in the Testing of Materials and Structures.”

Aluminium and its Uses

THE number of metals available in large quantities for industrial purposes is so very small, that the successful introduction of a new one must be of the greatest interest. The affinity of aluminium for oxygen much exceeds that of iron at a red heat. Iron oxide is reduced by carbon at that temperature, while alumina cannot be reduced in this way except in the electric arc. And thus,. though the ores of aluminium are more widely distributed even than those of iron, yet the former metal remained for long unknown, and until lately was comparatively rare.