Improvements in the Manufacture of Armour Plates.
Year: 1891

page_text: Date of Application, 29th Sept., 1891-Accepted, 21st Nov., 1891
COMPLETE SPECIFICATION.
[Communicated from abroad by HAYWARD AUGUSTUS HARVEY, of 455, Main
Street, Orange, New Jersey, United States of America, Mechanical
Engineer.]
Improvements in the Manufacture of Armour Plates.
I, HENRY HARRIS LAKE, of the firm of Haseltine, Lake & Co., Patent Agents,
45 Southampton Buildings, in the County of Middlesex, do hereby declare
the nature of this invention and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement :-
This invention embraces a method of facilitating the transformation of homo-
geneous low steel armour plates into plates which present upon the side intended to
receive the impact of projectiles a stratum of tenacious steel of heterogeneous
crystalline structure highly and uniformly carburized and excessively hard upon its
exposed surface and less and less carburized and gradually diminishing in hardness
as the depth from said surface increases.
The required transformation is effected by enclosing the low steel plate between
a mass of non-carbonaceous granular material on one side and a mass of granular
carbonaceous material packed firmly against the other side in a compartment
erected within the heating chamber of a suitable furnace and in then raising the
heat of said heating chamber and maintaining it at a temperature above the melting
point of cast iron for a period of time sufficient to effect the desired increase in the
tenacity of the steel and the super-carburization to the desired extent and depth of
the side of the plate against which the granular carbonaceous material is being
constantly pressed. The plate is subsequently removed from the furnace and
chilled by immersion in a cold bath or otherwise, as hereinafter set forth, whereby
its super-carburized side is hardened.
The heat to which the plate is subjected during the described treatment is so
intense that the plate would be melted but for the granular materials surrounding
it by which all parts of it are protected from the air.
The continuous, firm compression of the carbonaceous material against the plate
during the entire treatment secures the perfect contact of the carbonaceous material
with all portions of the adjacent side of the plate, and promotes the rapid and
uniform super-carburization thereof.
The product of the described treatment, except in respect of its crystalline
structure, is a homogeneous armour plate of highly tenaceous steel, which upon the
side intended to receive the impact of projectiles, presents a stratum of prescribed
thickness which is decrementally carburized and consequently has an ununiform
crystalline structure and is excessively hard at its exposed surface and gradually
diminishes in hardness as the distance inward from its exposed surface increases.
The differences in granulation or crystalline structure are those which are
respectively incident to the different percentages of carbon present at different
depths beneath the surface. The said product is herein designated as a
decrementally hardened armour plate because the hardening process is the final step
in its production, and because decremental hardening is dependent upon previous
decremental carburization and involves the presence in the finished product of a
heterogeneous crystalline structure which increases its resistance to cleavage.
The treatment is analogous to that described in Letters Patent of the United
States No. 376,194, issued to H. A. Harvey, January 10th 1888.
As modified for the present purpose, the process is conducted as follows:
The armour plate having been formed of the desired size and shape from a
comparatively low steel, such as Bessemer steel or open-hearth steel, containing
say 0-10 to 0.35 per cent. of carbon, is laid preferably flatwise upon a bed of finely

page_text: powdered dry clay or sand, deposited upon the bottom of a fire brick cell or
compartment erected within the heating chamber of a suitable furnace.
The plate may be so embedded that its upper surface is in the same plane with
the upper surface of those portions of the bed of clay or sand which adjoin the sides
and ends of the plate, or the plate may, if desired, be allowed to project to a greater
or less distance above the surface of the clay or sand..
In either case, the treating compartment is then partially filled up with granular
carbonaceous material which having been rammed down upon the plate, is covered
with a stratum of sand upon which there is laid a covering of heavy fire bricks.
The furnace is then raised to an intense heat which is kept up for such period of
time as may be required for the apsorption by the metal adjoining the upper
surface of the plate of, say, an additional one per eent. more or less of carbon, or
in other words the quantity of carbon, in addition to that originally present, which
may be necessary to enable the said metal to acquire the capacity of hardening to
the desired degree. The temperature of the heating chamber outside of the
treating compartment is brought up to a height equal to or above that required to
melt cast iron, and is kept up for a greater or less length of time according to the
depth of the stratum of steel which it is intended to charge with an excess of
carbon. This period, however, will of course vary according to the efficiency of
the furnace.
The degrees of efficiency possessed by different furnaces can only be satisfactorily
ascertained by actual trial. When ascertained, the reproduction of given results
merely requires the re-establishment of the conditions as to time and temperature
under which said results have been previously observed to be obtained. This
involves merely the maintenance of the furnace at a heat sufficient to melt cast iron
for the period which by previous observation has been ascertained to be the period
required for adding to the tenacity of the steel and for the super-carburization of
the plate to the prescribed extent and depth. For example, a plate, say ten and
one-half inches in thickness composed of a comparatively low steel containing,
say, 0.35 per cent. of carbon, may be charged with additional quantities of carbon
gradually varying in amount from, say, one-tenth of one per cent. at a depth of three
inches beneath the surface of the exposed side of the plate to one per cent. at the
surface thereof, by a continuance of the treatment for a period of, say, one
hundred and twenty hours after the furnace has been raised to the required
temperature.
The statement that the heat at which the furnace is maintained is sufficient to
melt cast iron, is to be regarded as approximate merely; the more intense the heat
the better, and while it will of course be understood that the longer the treatment
is continued the greater will be the depth to which the carbon penetrates beneath
the surface against which the carbonaceous material is packed, it is also to be
remarked that the penetration of the carbon is greatly facilitated by the continuous,
firm compression of the carbonaceous material against the plate. As a general
rule, the thicker the armour plate, the greater will be the permissible depth of
super-carburization. A ten and a half-inch plate and a depth of super-carburization
of three inches are herein referred to merely for the purpose of illustration.
After the conclusion of the carburizing treatment, the plate is taken out of the
furnace, and without removal of the carbonaceous material from its surface is
allowed to cool down to the proper temperature for chilling.
During the cooling operation, the carbonaceous material protects the hot super-
carburized surface from the air, and thus provents the formation of scale, which if
present would interfere with the subsequent hardening of the metal beneath it.
The carbonaceous material, however, may without injurious consequences be
temporarily removed from and quickly replaced upon small portions of the super-
carburized surface for the purpose of exposing them for observation.. When it is
seen that the super-carburized surface is so far cooled down as to have a dull
cherry red color the carbonaceous material is quickly removed, and the plate is
then chilled by being sprayed with torrents of cold fluid, or by being submerged and

page_text: kept in motion until cold in a large body of cooling fluid, as for example, a more
or less rapidly running stream or river of fresh water, or a tidal current of
salt water.
The exercise of this precaution insures the subsequent uniform hardening of the
super-carburized surface of the plate.
The accompanying drawings symbolically illustrating a furnace suitable for the
described treatment, and mechanical appliances for handling the plate and for
facilitating the chilling operation, are as follows:
Figure 1 is a top view of a furnace provided with a removable cover, erected
upon the bank of a river or other body of water in suitable proximity to a crane
and to a car track extending down the bank along the bottom of the stream or
body of water; showing a car upon which the treated plate is deposited by means
of the crane; a windlass chain connected with the car, and an engine for operating
the windlass, and thereby controlling the movements of the car up and down the
inclined track.
Figure 2 is a side elevation partly in section of the plant represented in
Figure 1.
Figure 3 is a transverse vertical section of the furnace showing the armoni plate
and the cell or compartment containing the bodies of material in which the armour
plate is enclosed.
Figure 4 is a transverse section of a portion of an armour plate shaded to
symbolically represent variable degrees of super-carburization at different depths
beneath the surface upon the side intended for exposure to the impact of
projectiles.
Figure 5 is an elevation of a treating furnace illustrating a mode of arranging
the track so that the armour plate can be taken out of one end of the furnace
directly on to the car upon which it is supported during the chilling operation.
Figure 6 illustrates a provision for chilling the plate by spraying it with torrents
of cooling fluid, and shows a stationary platform extending from one end of the
furnace to a position beneath the spraying tank.
The drawings represent a furnace, A, which may be provided with a movable
cover, A¹, as symbolically represented in Figures 1, 2 and 3, or which may be
constructed with reference to having one or both of its end walls removed to
facilitate the removal of the plate in a horizontal direction, as illustrated in
Figure 6.
Within the heating chamber, A³, of the furnace, is the treating cell or com-
partment, B, which is preferably provided at the bottom with a series, b, of parallel
rails which are imbedded in a stratum of sand, C, of the same height as the rails, and
are intended for the support of the armour plate D. The space around the ends
and sides of the armour plate is also filled with sand, C¹, nearly or quite to the top
of the plate.
A stratum of granular carbonaceous material, E, rising to a height of, say,
eight inches above the upper surface of the plate, D, is tightly rammed down on to
the top of the plate, and is surmounted by a stratum of, say, two inches of sand, F,
covered by a layer, G, of heavy fire brick.
The stratum of sand, F, and the layer of fire brick, G, not only protect the
carbonaceous material from the fire, but serve to weight the carbonaceous material
down upon the plate.
The treating compartment, B, is heated by the flames and hot products of
combustion from the fire chamber, H, which are led upward through the flues, H',
and directed inward over the top of the treating compartment and finally discharged
into the chimney or smoke stack H*.
In Figure 1, the furnace is represented as erected upon the sloping bank, I, of a
river or body of water, J, in suitable proximity to a crane, K, and a car track, L,
extending down the bank and along the bottom of the body of water, J. When
the carburizing treatment is completed, if the furnace shown in Figure 1 is
employed, the cover A¹, is removed, the fire is drawn and the furnace allowed to

page_text: cool off, preparatory to the removal of the superincumbent materials from the
plate, D, and the lifting of the plate, D, by means of the crane out of the treating
compartment and its deposit upon the car, M.
The track, L, is so inclined that the car when freed to the influence of gravity
will run down into the water, and a greater or less distance along the submerged
portion, L¹ of the track. The car is hauled up the inclined portion, L³, of the
track by means of a windlass chain, N, fastened to the shore end of the car, M,
and wound around the drum of the windlass, O, which is operated by the
engine, O¹.
The chilling of the plate is effected by alternately hauling the car up the
inclined portion, L³, of the track, and allowing it to run backward by its own
gravity.
In dealing with a heavy plate, it will usually be found more convenient to
construct the furnace with reference to the removal of one or both of its end walls
to facilitate the removal of the plate from the treating furnace by sliding it in a
horizontal path on to a car, as indicated in Figure 5, or on to a platform, P, which
is on a level with the top of the rails, b, at the bottom of the treating compartment,
as indicated in Figure 6.
The plate having been thus deposited upon the car, the latter can be run down
into the water, as already described, or can be run under a spraying tank, Q; or
the platform, P, may be prolonged sufficiently to reach from the end of the furnace
to a position beneath the spraying tank, as illustrated in Figure 6.
The spraying tank has a perforated bottom, q, which is elevated, say, ten feet
above the platform on which the plate is supported. The tank is supplied with
water or other liquid, by a service pipe or pipes, Q', of sufficient capacity to supply a
quantity greater than the quantity discharged by the apertures in bottom, q, thereof.
After the carbonaceous material has been removed from the top of the plate, and
when the plate having been placed beneath the spraying tank has so far cooled
down as to have a dull red color, the tank is supplied with the cooling fluid which
is discharged therefrom in jets from the perforated bottom directly upon the plate.
With a furnace of the character shown in the drawings, a period of about forty-
eight hours will be required to bring up the heat to the required point, and such
heat will be required to be kept up about one hundred and twenty hours. A further
period of four or five hours will ordinarily be required after the fire has been drawn
to remove the plate from the furnace and have it cool down to the desired dull red
color. The spraying operation will be required to be continuously kept up for a
period of about four hours in order to effect and preserve the chilling of the super-
carburized surface until remainder of the plate has become completely cool.
A plate of ten and a half inches in thickness thus treated will be found to be
excessively hardened upon its super-carburized surface and at the same time to be
remarkably tenacious, so that a hardened projectile of, say, six inches diameter
weighing one hundred pounds, fired at it with a striking velocity of 2000 feet
per second will be shivered to fragments without deeply penetrating the plate.
The extreme point of the projectile, which may slightly penetrate the plate, will
be found to be welded thereto by the great heat resulting from the sudden stoppage
of the projectile in its flight.
Owing to the great tenacity and the heterogeneous crystalline structure of the
super-carburized and hardened stratum, its tough backing and the entire homo-
geneity of the plate from one surface to the other, there will be no cracking off of
the hardened exterior stratum, and no complete piercing of the plate by the
projectile. In these particulars, the plate will be found to differ in a marked
degree from all armour plates heretofore known.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed as communicated to me by my
foreign correspondent, I declare that what I claim is :-
First. The herein described method of producing a decrementally hardened

page_text: tenacious armour plate which consists in enclosing a low steel plate between a mass
of non-carbonaceous material on one side and a mass of granular carbonaceous
material firmly packed upon the other side, contained in a compartment formed
within the heating chamber of a suitable furnace and in maintaining the said
heating chamber for a predetermined period of time at a temperature above the
melting point of cast iron, and in subsequently chilling said plate, whereby a
stratum of steel of prescribed thickness upon the side of the plate against which
said carbonaceous material has been pressed, is made to acquire a heterogeneous
crystalline structure and a condition of excessive hardness upon its exposed surface,
and a condition of gradually diminishing hardness as the depth from said surface
increases.
Second. As a product of the herein described process the decrementally hardened
steel armour plate herein described consisting of a plate of tenacious steci presenting
upon the side intended for receiving the impact of projectiles a stratum of
prescribed thickness, of ununiform crystalline structure uniformly and highly super-
carburized and excessively hard at its exposed surface, and less and less carburized
and gradually diminishing in hardness as the depth from said surface increases.
Deted this 20th day of September 1891.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.