NOTICE.

The SOCIETY OF ARTS, established in conformity with the plan of the Massachusetts Institute of Technology, as set forth in the act of incorporation, April, 1861, held its first meeting on April 8, 1862. The objects of the Society are to awaken and maintain an active interest in the practical sciences, and to aid generally in their advancement in connection with arts, agriculture, manufactures, and com

merce.

Regular meetings are held semi-monthly from October to May, inclusive, in the Institute building; and at each meeting communications are presented on some subjects germane to the objects of the Society, as stated above.

The present volume contains the abstracts of the communications made during the year ending October 1, 1887, most of the business portions of the records being omitted.

For the opinions advanced by any of the speakers the Society assumes no responsibility.

BOSTON, June, 1887.

LINUS FAUNCE,

SECRETARY.

PROCEEDINGS OF THE SOCIETY OF ARTS

FOR THE TWENTY-FIFTH YEAR.

MEETING 350.

Steel for Warfare.

BY MR. H. M. HOWE.

The 350th meeting of the SOCIETY OF ARTS was held at the Institute on Thursday, October 14, 1886, at 8 P. M., Prof. T. M. Drown in the chair.

After the reading of the minutes of the previous meeting, and the election of new members, the chairman introduced MR. H. M. Howe, who read a paper on " Steel for Warfare."

Mr. Howe first described what steel was, and showed by diagrams the effect of varying proportions of carbon on certain of the physical properties of iron. The tensile strength increases with the carbon, reaches a maximum, and again declines. The hardness also increases with the carbon, but it does not reach its maximum as soon as the tensile strength does. The property of being rendered alternately hard and malleable by rapid and slow cooling also increases with the carbon, reaches a maximum, and declines. The ductility, however, decreases as the carbon increases; and the melting point of the metal rapidly falls. The region of high ductility is one of great infusibility, and it is only within a few years that these ductile irons could be melted, and consequently the intermingled slag be removed.

The presence or absence of this mechanically intermingled slag marks the only difference between ordinary wrought iron and steels low in carbon. The steel of today offers the engineer an enormous

range of properties, and we have but a crude notion as to what particular degree of carburization, with its corresponding relation between strength and ductility, is best suited for many of the most important

uses.

The speaker next took up some of the more important purposes for which steel is employed in warfare, showing what particular relation between ductility and strength was best suited to each case, and consequently the percentage of carbon the steel should contain. Thus, the shafts of marine engines should be made of a highly ductile steel, to resist the constant bending backwards and forwards consequent upon the distortion of the steamer, and also to resist the shock given by the connecting rod to the crank after the brasses become worn; and we find that shafts are made whose carbon varies from 0.10 per cent to 0.51 per cent. Steel for marine boilers should be very ductile, so as to enable it to be bent and flanged with safety, and to resist the strains caused by the unequal expansion of different parts of the boiler. In some hundreds of cases which have come under Mr. Howe's notice, the highest percentage of carbon in boiler-plate steel, he said, was 0.25, and the lowest 0.07; the average being 0.15 per The plating of the hulls of iron steamers should also be ductile, so that in striking submerged rocks, etc., the steel will be bent in and not broken through, thus enabling the steamer to keep afloat. This steel has about the same degree of carburization and the same properties as that selected for boilers.

cent.

"In the case of great guns," Mr. Howe said, "it is not so clear from a priori considerations what degree of ductility and strength is needed. On the one hand the gun is subjected to something of shock on the explosion of the powder; to resist this shock ductility is needed. But on the other hand great strength is needed to hold in the pressure set up by the explosion. Moreover, while permanent distortion is permissible in the plates of a boiler or of a hull, it could not be tolerated in the least in the tube of a gun, which must retain its shape unaltered. The difficulty of judging of the best composition for gun steel may be recognized in the fact that makers of great intelligence have used steel with 1.18 per cent of carbon, which is hard enough for razors, and with 0.12 per cent, which is soft enough for rivets and horse-nails. Our present experience, which however is not fully ripe, seems to point to an intermediate composition of about 0.33 per cent

of carbon, which is decidedly stronger and less ductile than boilerplate steel, as best suited to great guns.

Finally, as to armor plate. There are several kinds employed. Chilled cast-iron armor, such as Gruson's, is intensely hard, but as intensely brittle; hence it requires enormous thickness, with corresponding enormous weight, to resist successfully the impact of a great projectile. For land fortifications probably nothing can compare with these plates, but they are manifestly unsuited for the armor of war vessels.

Wrought-iron armor has so much less resisting power than steel of equal weight and thickness that it may be considered as out of the race.

Steel plates are of two kinds,-solid steel plates, which are homogeneous, and compound steel-faced plates with a hard steel face and a back of tough wrought iron or soft steel welded to the face. The armor plate must be hard enough to stop the projectile, and tough enough not to be shattered by its blow. The combination of hardness and toughness the compound steel-faced plate attempts to attain by the simple and promising expedient of welding a steel face so hard that the projectile cannot enter it to a backing so tough that the blow cannot shatter it. For such a face we apparently need great strength and hardness. In twelve recent instances the highest carbon which I find is 0.97 per cent, the lowest is 0.56 per cent, and the average is 0.70 per cent. In solid steel armor we need much greater ductility. The famous solid armor made by Schneider of Le Creusôt, has 0.43 per cent of carbon. This composition gives about the highest combination of strength and ductility.

When put to direct competitive test, the steel-faced plate has not shown as much resisting power as the solid steel plate. While in some trials at St. Petersburg the steel-faced plate came out rather better than its competitor, in the famous Spezia trials, as well as in those at Copenhagen, the solid steel showed by far the greater resisting power. The resisting power of the steel-faced plate may possibly be greatly increased, however, by altering the relative thickness of the steel and iron (at present about one-third of the thickness is of steel), by varying the ductility and hardness of its components, etc. There is one source of weakness, however, which is not likely to be removed. A plane of weakness, along which separation readily takes place, occurs at the junction of the steel and iron, even though they be actu

ally welded together. In the compound plate the soft, tough back tends to bulge under the impact, while the hard, inflexible front refuses to bend and is flaked off.

There is one set of conditions where wrought iron may be of use. The wrought-iron turret of the Huascar, in the Chilian-Peruvian war, is reported to have been perforated by several 9-inch shots. The turret of the Huascar could be rotated after having been perforated, but had it been of steel it is altogether conceivable that the force of the blow might have distorted and jammed it so as to prevent its subsequent rotation. Now, though it is a terrible thing to have a shell perforate a turret and explode within it, it would be preferable to having the turret jammed, as this would completely disable the vessel.

In the manufacture of steel any degree of strength that is desired can be obtained by selecting a proper composition. But we obtain strength only at the sacrifice of ductility. Let us now consider certain methods by which strength may be increased without corresponding loss of ductility.

The first of these is by forging, which may be effected by the rolls, the hammer, or the hydraulic press.

But why do we forge steel? First, because molten steel contains a large amount of gas. Now, gases are in general vastly less soluble in solids than in liquids; hence, when the steel solidifies, a large amount of gas is given off. As the steel passes through an intermediate pasty condition before complete solidification sets in, the gases liberated are unable to escape and are imprisoned in the steel in the form of bubbles or blow-holes. In the second place, when the mass solidifies, the exterior cooling first becomes rigid, while the interior is still greatly expanded by heat. As the interior subsequently contracts it becomes unable to completely fill the rigid exterior, and contraction cavities arise. The first, and in my opinion chief, benefit from forging is that it closes these gas bubbles and contraction cavities, and to a certain extent welds their sides together, and gives the continuity which they had prevented.

A second benefit from forging arises from the kneading or working of the metal. We find that by forging masses of steel which are initially completely solid and free from blow-holes both ductility and tensile strength are increased, and we attribute this effect directly to