Improvements in the Manufacture of Armour and similar Protective Plates.
Year: 1897

page_text: Date of Application, 15th Mar., 1897-Accepted, 19th June, 1897
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Armour and similar Protective
Plates.
:
1, JEAN WERTH, of 4, Rue Mogador Prolongée, Paris, France, Technical
Manager of the Works of the Société Anonyme des Hauts-Fourneaux, Forges et
Aciéries de Denain et Anzin, 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 relates to a new method of manufacturing armour and similar
protective plates of high resistance to impact, whereby there can be produced in'
a perfect manner armour and similar protective plates (hereinafter included under
the term armour-plates) of steel of homogeneous chemical composition, the impact-
face of which has a degree of hardness equal to that obtained by cementation and
tempering. This hardness is uniform, not only at the surface but for a depth
proportionate to the total thickness of the plates, and from this depth it diminishes
uniformly towards the opposite face or back.
This method thus enables a gradual decrease in hardness in the total thickness.
of the plate to be obtained, whilst retaining a layer of uniform maximum hardness
of any desired thickness starting from the impact face, and a layer of similarly,
variable thickness of uniform maximum malleability or softness at the opposite"
face or back.
This result is produced by two heating operations on forged or rolled plates, one
at the high temperature of from cherry red to light cherry red for. hardening the
face, and the other at the low temperature of from incipient red heat to dark red
heat for softening the back.
1
Each heating operation is followed merely by an ordinary cooling operation in
air or in ashes.
This mode of treatment is consequently quite different from those at present in
use for hardening by cementation or direct carburization, and by tempering in
liquids of variable cooling action.
:
The hardening to a high degree of plates of homogeneous steel without change
in the chemical composition of the metal by heating to the temperature of from
cherry red to light cherry red with ordinary cooling in air or in ashes, is a result
which is diametrically opposed to the one that is obtained with the various kinds
of forged or rolled steel at present used in the manufacture of armour-plates.
The various kinds of steel employed for the application of our special method
of manufacture of armour-plates are produced in the Martin furnace.
They are specially characterized by the combination, during fusion, with
carburized iron free from sulphur and phosphorus, of a percentage either of nickel..
or cobalt, which may vary according to the desired final hardness from 5 to 15 per
cent.; or of a percentage of manganese varying from 2 to 12 per cent.; or of an
alloy of nickel or cobalt and manganese in the foregoing proportions. The normal
presence in the steel, of silicon, chrome, or tungsten, does not affect the action of
the heat for producing the hardness or the softness in the final treatment of the
armour plates.

page_text: The presence of nickel or cobalt or manganese, or of an alloy of these metals, is
necessary on account of their direct action upon the carbon, the iron, and the other
chemical constituents of the metal, for the purpose of producing the two allotropic
transformations of the constituents of the steel under the influence of heat, the one
transformation producing hardness at the temperatures comprised between cherry
red and light cherry red, and the other transformation producing softness at the
temperatures comprised between incipient redness and dark red, without any change
in the elementary chemical composition.
There is thereby obtained an extremely numerous series of steels of varying
composition, capable of furnishing, notwithstanding the variety of the constituent
elements, physical results which are mutually comparable by the presence of
nickel, cobalt, or manganese and having in common the essential characteristics of
hardening by heating between cherry red and light cherry red, and of softening
by heating between incipient redness and dark red, these two heatings being
followed only by the usual cooling in air or in ashes, in place of the usual processes
of the normal annealing of ordinary steels.
All these special grades of steels can be forged or rolled without difficulty
únder the ordinary conditions of heating at present in use in the manufacture of
armour-plates.
Following on this operation, which is analogous to all forging or rolling
operations, the armour-plates of our manufacture are cooled in the air without risk
of cracks and without special precautions.
After this, ordinary operation the armour-plates are placed in an ordinary cold
furnace and. are heated gently and uniformly throughout their mass at a temperature
of between incipient redness and dark red. For this heating operation, any
annealing-furnaces may be employed in which the temperatures may be adjusted to
dark red.
The dark red heat is produced in plates having the above-mentioned lowest
percentages of the metallic elements necessary for hardening-viz., nickel, cobalt,
and manganese.
Incipient red heat is applied in heating plates having the highest percentages of
the said metallic elements.
The armour-plates when raised to a uniform temperature of between those of
incipient red and dark red are removed from the furnace and are placed upon
trestles in the workshop to cool in the ordinary way in the air.
When cool, the
'plates are machined by the usual means to their respective dimensions.
In this state, the metal of the plates is homogeneous and soft and can be worked
cold in the normal conditions of ordinary steel, having a strength of from 60 to
75 kilogs. per square millimetre.
The characteristics of the physical tests of the improved steels for armour-plates,
after the softening by heating at a low temperature followed by ordinary cooling,
are as follows:-
:
Limit of elasticity from 50 to 80 kilogs. per sq. mm.
Breaking strength 70 100
Elongation (measured on a bar of 100) 25%-15% do.
30
Bending (on flat bar of 10
thickness.
L
on a block having a radius equal to twice the
Absence of brittleness to shock or normal working cold with a tool for cutting
30
Bending (on flat bar of
on a block having
a radius equal to twice the
10

page_text: 30
Folding flat
with radius of 60° = 60°.
10
It is to be well understood that these proportions are given only by way of
example and do not limit the invention.
The machined plates are ready for the hardening of the face, which may
penetrate to any desired depth, irrespective of the total depth of the armour-
plates. This result is obtained by raising the face to the desired depth to the
temperature comprised between those of cherry red and light cherry red by heating
the said face uniformly and progressively, whilst sufficiently protecting the back
by cooling with air or water, in order that the temperature of the said back may
not exceed at any place that of red heat which is the temperature corresponding to
well smoking wood-say from 450 to 500° as the maximum. This relatively low
temperature may be observed rapidly at various points of the plate, either by
meaus of the electric pyrometer of Mr. H. Le Châtelier, or by means of metal
strips (tin, lead, zinc, etc.) enabling the rise of temperature at the bulk to be
followed, or by any other suitable means.
The back having been previously softened throughout its mass by the first
heating operation necessary for the machining of the plates, the back can be
easily kept cold in the case of the thick plates by a current of air continued
during the heating of the impact-face to cherry red for hardening.
For this hardening-operating, one or more of the external walls of the heating
furnace may be simply formed by the plates themselves, the back forming the
external surface of the furnace.
The flames, at the outlet from the hearth, are distributed by flues uniformly
distributed over its length and its breadth in the enclosure formed by the plate (or
plates) and the other faces in refractory masonry. The departure of the Hames is
controlled by dampers in such a manner as to obtain in the interior of the furnace,
a uniform temperature, which will be kept at light cherry redness during the time
necessary for the penetration of this temperature to the thickness desirable
according to the thickness of the plates. Heating by producer-gas is preferable
to heating by oil, as regards the facility for regulating the successive temperatures
up to the maximum of light cherry. During the heating, the supply of the gases
is reduced three or four times in order to equilibrate the absorption of the heat by
the plates to be hardened.
For the heating to a definite thickness to cherry red from the impact-face,
metallic baths and particularly lead baths heated to the temperature of light cherry
may, however, be very advantageously employed.
After cleaning the surface of the metallic bath, the plate is immersed, with its
impact-face downwards, to a depth determined by the thickness of the hardening.
The temperature of the metallic bath is kept constant at from cherry red to light
cherry red, this temperature being verified by the pyrometer of Mr. H. Le Châtelier
or by any other suitable means. The upper and non-immersed face is cooled by
a current of air in order to permit the temperature of this face to keep below
dark red.
After verification of the uniformity of the temperature of light cherry red on
the impact face and the penetration to the desirable thickness of the corresponding
heat of between light cherry red and cherry red, with "uniform diminution towards
the back, the plate is taken out of the metallic bath to permit the normal cooling
in the air of the impact-face, the elevation of the temperature above dark red
over the back being prevented, as is the case during the heating. When the

page_text: The soft grades can usefully be employed for the thin armour-plates, the hard
grades being reserved for the belt armour-plates or turret armour-plates of medium
and great thicknesses.
After hardening the impact-surface, as regards the hard grades, the metal
cannot be cut by any tool over the whole thickness transformed by the heating at
high temperature, but the back can be worked normally to the thickness of the
metal softened by the heating at low temperature.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
The hereinbefore described improved method of manufacturing armour and
similar protective plates according to which the impact-face of a plate of homo-
geneous steel of variable composition but containing as molecular and allotropic
elements of transformation by heat nickel, or cobalt, or manganese, or an alloy
of these metals, is hardened to the desirable depth and the back of the said plate
is softened, likewise to the desirable thickness, with regular diminution of hardness

page_text: from the hard portion of the impact-face to the softened portion of the back, the
softening being effected after the forging or rolling of the plate by uniformly
heating it to a temperature between those of incipient red and dark red (or those
of smoking wood and blazing wood), the hardening being likewise effected after the
forging or rolling, but by uniformly heating the portion to be hardened to an
elevated temperature between those of cherry red and light cherry red, the plate
being cooled in an ordinary manner, after each of the two operations, either in the
air or in ashes, and the two operations being either successive or simultaneous
according to the thickness of the plate and terminating its metallurgic treatment
to the exclusion of any cementation or tempering operation such as at present
employed for hardening armour-plates as set forth.
:
F. WISE HOWORTH,
46 Lincoln's Inn Fields, London, W.C., Agent for the Applicant.