Manufacture of Compressed Carbonised Steel, and Armour Plates and other Articles therefrom.
Year: 1895

page_text: Date of Application, 10th Apr., 1895 -Accepted, 22nd June, 1895
COMPLETE SPECIFICATION.
Communicated from abroad by WILLIAM ELLIS CAREY, of Munhall, in the
County of Allegheny and State of Pennsylvania, United States of
America.]
Manufacture of Compressed Carbonised Steel, and Armour Plates and
other Articles therefrom.
1, OLIVER IMRAY, of No. 28 Southampton Buildings, Chancery Lane, in the
County of London, Chartered Patent Agent, 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 :-
My invention relates to the manufacture of a new material, carbonized and
compressed steel, which having the qualities of great strength and toughness,
combined with extreme hardness of surface, is specially adapted to the manufacture
of armour plates and to articles requiring like qualities.
I shall describe the process which I employ for producing compressed carbonized
steel, and in manufacturing armour plates of this material, it being understood
however that these processes are not limited to the production of armour plates
which I shall now set forth by way of illustration.
Armour plates are usually about sixteen feet in length eight feet in width, and
from fourteen to eighteen inches in thickness and are carbonised or hardened on
one side or surface only, the hardness gradually decreasing from the carbonised
surface towards the other side.
My invention, however applies to plates, slabs, ingots or pieces of steel hardened
on both or on all sides and also to articles of dimensions other than those named
above which dimensions I have stated because in describing the process, so as to be
intelligible, it is desirable to indicate the size of the articles to the treatment of
which the temperatures and periods used in the several steps are applicable; these
features of the process being necessarily subject to modification as the larger the
piece of steel treated the greater is the heat and to some extent the time of exposure
to the heat necessary to produce the best results.
By the term "steel plates" I mean pieces of steel of any required shape or size
made by any process of conversion of iron into steel, and whether the steel be or
be not alloyed or mixed with nickel, aluminium or other metal or alloy.
The plate having been made of steel of the desired quality cast as an ingot and
forged or rolled to the desired thickness and surface shape is placed in the
carbonising furnace in a receptacle of refractory material which may be movable
to and from the furnace.
The bottom of this receptacle is covered with a layer of comminuted carbonaceous
material of uniform thickness and so placed as to be in close contact with the
surface of the steel plate to be treated which may be of plane, or curved or irregular
shape. The carbonaceous material may be animal or vegetable charcoal or coke
or a mixture of any or all of those. By placing the steel plate on the carbon the
plate and carbon are brought into close surface contact, and, when two or more
plates are treated, they may be placed one above the other with the surfaces which
are to be carbonised turned towards and in contact with the carbon forming a layer
between two plates. If as is usual in armour plates they are to be carbonised on

page_text: one side only the surface not to be carbonised is covered with some refractory
material; or access of air is otherwise excluded so as to prevent the oxidation of
the carbonaceous matter and of the steel. The furnace used for heating the plates
may be a regenerative gas furnace or any other suitable furnace. The furnace is
heated to a comparatively low heat about 1950° F., (1066° C.) and the temperature
is gradually raised during a period of about ten days until the steel is heated up to
about 2175° F. (119.°C.). The hot gases are then shut off and the furnace is
banked for about a week during which a gradual cooling takes place until the plates
are reduced in temperature to about 1600° F. (870° C.). They are then ready for
the next step in the process, which is compression, for the purpose of compacting
and toughening them.
As, however, it is important to ascertain the condition of the plates as to the
degree of carbonisation and the depth to which it has penetrated, it is preferable
to postpone the compression of the plates until they have been tested. In this case
they are allowed to remain in the furnace until the temperature is reduced to
about 1100° F. (590° C.) so as to avoid air hardening which might occur at a higher
temperature and also to aid in annealing. When thus reduced in temperature the
plates are removed from the furnace and the receptacle in which they were heated
and are allowed to cool gradually in the air to a suitable temperature such
as 100° F. (38° C.) when the faces which were covered with refractory material
are cleaned off, and a few holes being drilled from the carbonised surface, samples
of the metal at different depths are analysed so as to ascertain the depth and
degree of carbonisation.
The plates, if they have been cooled for the purpose of testing, have to be
reheated sufficiently for compression up to about 1600° F. (870° C.), but this, of
course, is not necessary for plates removed from the furnace at that temperature.
Before replacing the plates in the furnace to reheat them for compression, I cover
the carbonised surface or surfaces with a coating of about three inches of pulverised
carbonaceous matter, which if desired may be protected with very finely pulverised
dolomite, magnesite, lime or other refractory material spread over the layer of
carbonaceous material.
I have stated the degree of heat at which the plates are to be removed from the
furnace for compression or to which they are to be reheated for that purpose to
be 1600° F. (870° C.) the purpose being to have the plates at as low a heat as will
enable them to be compressed, as hereinafter described, but the heat should not
exceed 2000° F. (1093° C.). This reheating should be done slowly so as to secure
an even heat throughout the plate and should take from ten to twenty hours
according to the size of the plate. The heated plate is then removed to a com-
pressing machine, preferably a hydraulic press, though rolls or a steam hammer
may be employed for the purpose. When a hydraulic press used it is preferred
to have the upper and lower dies as long as the plate of steel is wide and with
comparatively narrow faces about ten or twelve inches broad. If the faces of the
dies were wider, the plate would have to be hotter, in order to secure the desired
degree of compression but a low temperature is desired in order to prevent
decarbonisation of the plate and also to secure the condensing and compacting
effect of the pressure applied instead of a spreading or elongating of the metal
which would be the consequence of the metal were too hot.
When a press is used which is capable of exerting a pressure of about ten
and a half tons to the square inch of surface, an armour plate, of the dimensions
above stated may be readily reduced an inch in thickness by each first stroke of
the upper compressing die. The plate is moved forward between the dies after
each stroke until the entire surface has been acted on. This operation is
repeated moving the plate to and fro until sufficient compression is obtained.
By this means I have reduced a thickness of 17 inches to a thickness of 14 inches
with the effect of giving greatly increased toughness and strength to the steel.
As the object is not to roll out the plate and thus increase its length or width
but to effect an actual compression of the metal, (although a slight increase in

page_text: those dimensions will occur as the plate need not be confined in any way) it is
obviously desirable to subject the metal to great pressure at as low a temperature
as is compatible with obtaining the compression, and reduction of volume desired.
After the plate has thus been toughened and compacted by pressure it is annealed.
For this purpose it is reheated in the furnace for about twelve hours up to about
1350° F. (730° C.) the carbonised surface being protected from oxidation as for
reheating after testing. The heating is then stopped and the plate is left in the
furnace for about eight hours slowly cooling.
When sufficiently cool, after annealing and before tempering, the plate may if
desired be again tested to ascertain whether it is sufficiently carbonised. Also it
is straightened by a forging press or otherwise and is machined to the required
dimensions the necessary allowance being made for contraction during the
subsequent tempering, which is the last step of the process.
For this, the plate is again slowly heated in the furnace to about 1350° F. (730° C.),
the precautions before employed to prevent oxidation of the surface being repeated,
and, after reheating, scale or other matter adhering to the carbonised surface is
carefully removed by wire brooms, or, if necessary, by hand hammering.
The reheated plate is tempered by cold water, which may be conveniently applied
to the plate when laid horizontally on an open framework between a number of
nozzles above and below which spray copious jets of cold water on the plate.
This is continued until the plate is sufficiently cold, at a temperature such
as 100° F. (38° C.).
This completes the process except that, if the plate has become deformed by
the water cooling it is reheated to a low temperature, such as 200° F. (93° C.)
sufficient to permit of having its shape rectified by the hydraulic press or
otherwise, and finally it may be machined or ground by an emery wheel to the
exact size required.
In describing my process I have stated the temperatures which I have found it
advisable to use in the various steps, but I do not confine myself to the exact
temperatures mentioned. It is important to conduct the various steps in which heat
is applied, at as low temperatures as are consistent with successful operation, and
in all cases below the melting point of cast iron. It may not be necessary in all
cases to observe the exact order of operation or to perform all the steps described,
as for example, it is not necessary to allow the plates to cool and then to reheat
them before subjecting to compression, although it is desirable previously to test
the carbonisation, for which purpose the plates should be cold enough to handle,
and would then require reheating.
I have referred to the protecting of the plates, while being reheated, with a
coating of carbonaceous matter, and a superimposed layer of finely comminuted
refractory substance. This is specially important where nickel steel, (by which
mean steel to which nickel in any proportion has been added) is being treated
for carbonisation, or in any case where nickel steel requires to be subjected to
heat, owing to the excessive scaling, or surface oxidation to which nickel steel is
subject.
1 carefully remove any scabs or loose scale from the nickel-steel before reheating
it, and cover its carbonised surface with a layer from two to four inches thick of
dry carbonaceous matter, such as coke dust or charcoal; I then cover this layer
with dolomite ground very fine, to a depth of about two inches. When subjected
to heat, the dolomite forms a hard and nearly impervious crust, practically
excluding air from access to the carbon and thus preventing its rapid combustion.
Such air as may penetrate the dolomite crust is so small in amount that it is
taken up by the carbon, forming carbonic oxide gas and does not attack the
heated steel. The thickness of the carbonaceous and refractory layers may be
varied somewhat according to circumstances, but by supplying a sufficient coating
of carbon to the nickel-steel and protecting it by the layer of dolomite carefully
applied, the rapid combustion of the carbon and the scaling of the steel may be
prevented.

page_text: Instead of dolomite, finely pulverised magnesite lime or other refractory material,
which will form a cake or crust when highly heated, may be employed.
Having now particularly described and ascertained the nature of my said' inven-
tion and in what manner the same is to be performed I declare that what I
claim is
1. The herein described process for manufacturing compressed carbonised steel
that is to say, carbonising the plate, slab or other article of steel by applying to
the surface to be carbonised comminuted carbonaceous matters, protected from.
oxidation, and heating gradually, cooling to a temperature sufficient for compression
but below that suited for the ordinary elongation and reduction as by rolling;
then compressing the steel at this temperature and finally annealing and tempering,
substantially in the manner and for the purpose described.
2. The herein described process for manufacturing armour plates of compressed
carbonised steel, consisting of the following steps, Carbonising the plate, by
covering the surface to be hardened, with comminuted carbonaceous matter
placed in close surface contact with the plate, protecting the plate and the
carbonaceous matter from access of air, gradually heating during about ten days,
to about 2175° F. (1200° C.) then gradually cooling down to about 1600° F. (870° C.),
compressing the plate at that temperature so as to compact the metal and reduce
its volume, then annealing the plate by reheating (the carbonised surface being
protected from oxidation) and slowly cooling it, and after straightening, testing
and machining the plate to the shape required, tempering it by slowly reheating in
a furnace to about 1350° F. (730°C.) and then cooling, substantially as and for
the purpose described.
3. In treating plates, slabs, or other articles of steel carbonised by heating while
in surface contact with carbonaceous matter to about 2175° F. (1200° C.) gradually
cooling, and when sufficiently cold, testing the extent of carbonization, then
reheating to about 1600° F. (870° C.) and at about that temperature, compressing,
and then annealing and tempering, substantially as and for the purpose
described.
4. The berein described process for condensing and compacting steel by com-
pression, the steel being heated to a degree sufficient to permit of such
compression but below that ordinarily used for rolling out or elongating,
substantially as described.
5: In reheating plates or articles of steel, protecting them from scaling or
burning of the carbon by placing on the surface a layer of pulverised carbonaceous
material, covered with a protective coating of pulverised dolomite or equivalent
refractory material, substantially as and for the purpose described.
6. Compressed carbonised steel manufactured substantially as herein described.
Dated this 10th day of April 1895
ABEL & IMRAY,
Agents for Applicant.