Note: Descriptions are shown in the official language in which they were submitted.
CA 02414305 2005-06-10
MATERIAL WITH HIGH BALLISTIC PROTECTIVE EFFECT
The invention relates to the use of known steel alloys as materials for the
production of articles with high ballistic protective effect.
The ballistic protective effect of articles, in particular of those made of
two-
dimensional material, is generally characterized by their security against a
puncture by
projectiles and fragments when high-energy weapons act upon them. To an
increasing
degree there is a demand for a high protective effect and simultaneously, a
reduced
weight of the article or part and an improved economic efficiency of the
production
thereof.
According to the recognized opinion of those skilled in the art, the
mechanical
data obtained from conventional tensile impact and notched impact tests do not
allow a
direct conclusion with respect to the properties of a material under ballistic
stress.
Nevertheless, in many cases the values of hardness, impact strength and
strength of the
material are used as at least a point of reference for predicting the
penetration resistance
of a protective part. However, ultimately, the "stopped shots" of a sheet
metal part
characterize its ballistic protective effect.
Assuming by way of approximation that the strength, hardness and toughness of
a
material do not change with the speed of the stress, it can be predicted that
the material of
protective parts must have both maximum hardness as well as utmost toughness
in order
to withstand destruction under ballistic bombardment and to exert a breaking
effect on
projectiles. For steels and alloys these properties are opposed with respect
to their
simultaneous maximization so that in terms of stress, in addition to a general
improvement of the same, a good balance of toughness and strength of the
material is
required, in particular upon heat treatment.
Depending upon the desired property profile, carbon steels, low and medium-
alloy steels, high-alloy steels and precipitation hardenable alloys with, if
necessary, an
iron content of less than SS percent by weight have been proposed for products
with
ballistic protective effect, and in many cases a composite structure and/or a
hard layer on
the outer surface of the protective part are recognized as being advantageous.
For example, EP-A-180,805 discloses a steel helmet made of a low-alloy boron
steel, which steel helmet is sandblasted after heat treatment.
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CA 02414305 2005-07-22
An armor plate with a heat-treated microstructure is known from European
Patent
1,052,296, granted December 15, 2004, to ThyssenKrupp Stahl AG, which plate
has a
yield point of > 1100 N/mm2 as well as a hardness of > 400 HB and, with a
carbon
content in percent by weight of 0.15 to 0.2, essentially comprises 1 to 2
percent by
weight chromium (Cr), 0.2 to 0.7 percent by weight molybdenum (Mo), 1.0 to 2.5
percent by weight nickel (Ni), 0.05 to 0.25 percent by weight vanadium (V),
the balance
being iron (Fe).
From EP-A-580,062 there is known a process for the manufacture of thick armor
plates, in which process the above alloy, with an increased content of carbon
and nickel,
is first heated in a slab mold to a temperature of above 1150° C,
allowed to cool in a
forced manner and rolled to the final thickness in the range of 1050 to
900° C, each time
with a high forming degree.
A steel armor plate with improved penetration strength against projectiles is
described in EP-B-731,332. The plate has a plurality of inclusions which are
oriented
essentially parallel to the surface of the plate and are concentrated in a
region comprising
one quarter to three quarters of the thickness of the plate.
EP-B-247,020 discloses an armor plate having a base material of tough steel,
onto
which is applied by cladding at least one hard steel layer that is to face the
impact and is
comprised of 0.6 to 1.0 percent by weight carbon (C), 0.2 to 2.0 percent by
weight silicon
(5i), 0.2 to 2.0 percent by weight manganese (Mn), 0.8 to 2.0 percent by
weight
chromium (Cr), 0.05 to 1.0 percent by weight molybdenum (Mo), 0.05 to 0.35
percent by
weight vanadium (V), the balance being iron (Fe) and steel accompanying
impurities. In
this case, an interlayer of pure nickel or pure iron having a thickness
between 0.1 and
15% of the total plate thickness is arranged between the base material and the
cladding,
which interlayer is connected to the base material and the cladding by roll-
bonding. The
interlayer not only facilitates the cladding of the base material, but also
prevents the
cladding material from flaking off, which cladding material, though heat-
treatable to a
hardness of 55 to 60 HRC, apparently has low toughness as a result.
In addition to the above low and medium alloy steels, high-alloy chromium
steel
alloys (CH-A-648,354) and precipitation-hardened or maraging steels (AT-
336,659, DE-
C-19921961, EP-A-1,008,659) have also been proposed for ballistic protection
as an
individual part or in composite structure with a hard outer layer, if
necessary. Although
these types of steels with a high content of alloying elements of up to 50%
can be used
2
CA 02414305 2005-06-10
advantageously as a material for components with highly effective ballistic
protection,
they have the disadvantage of'being very expensive.
In view of the foregoing, it would be desirable to have available materials
from
which products with high ballistic protective effect and a low weight can be
manufactured economically and in ,a simple manner. These products or parts
should have
a high bullet or projectile breaking effect, be made of an iron-based alloy,
and should
have toughness and strength properties that are adjustable by means of heat
treatment,
with maximization of both properties. Moreover, the material should be
suitable for the
production of composites and mufti-layered parts and should also be capable of
being
surface hardened and welded.
The present invention provides an article having a ballistic protective
effect, a
process for making such an article which comprises the provision of an alloy
and the
shaping thereof, and its use in a method of providing ballistic protection.
In the present specification and in the appended claims all concentrations are
based on the total weight of the composition (e.g:; alloy), unless indicated
otherwise.
Moreover, in the context of concentrations, the term "less than" includes 0 %
by weight,
i.e., complete absence. Also, it should be understood that the numerical
values given
herein are approximate values, i.e., are not limited to the exact value
indicated herein.
According to one alternative, the alloy comprises, in percent by weight:
Carbon (C) 0.26 to 0.79;
Silicon (Si) 0.2 to 1.2;
Manganese (Mn) 0.2 to 0.9;
Chromium (Cr) 1.1 to 7.94;
Molybdenum (Mo) 0.56 to 3.49;
Vanadium (V) 0.26 to 1.74;
the balance being iron (Fe) as well as accompanying elements and impurities.
In the
alloy, the total concentration of phosphorus (P) plus sulfur (S) is Iess than
0.025
P + S < 0.025 percent by weight;
the concentration of nickel (Ni) is less than 0.28
Ni < 0.28 percent by weight;
and the total of the grain-boundary active impurity elements arsenic (As),
antimony (Sb),
bismuth (Bi), tin (Sn), zinc (Zn) and boron (B) is less than 0.01 I
As + Sb + Bi + Sn + Zn + B < O.OI 1 percent by weight. .
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In a preferred embodiment according to this alternative, the alloy comprises
one
or more elements have the concentrations, in percent by weight:
Carbon (C) 0.36 to ' 0.64, preferably 0.41 to 0.58;
Silicon (Si) 0.36 to 0.9, preferably 0.41 to 0.68;
Manganese (Mn) 0.36 to 0.7, preferably 0.41 to 0.59;
Chromium (Cr) I .7 to 5.95, preferably 2.61 to 5.2;
Molybdenum (Mo) 1.05 to 2.9, preferably 1.3 to 2:7;
Vanadium (V) 0.36 to I.25, preferably' 0.39 to 0.83:
According to a second alternative, the alloy comprises, in percent by weight:
Carbon (C) 0.3 to 0.6;
Silicon (Si) 0.08 to 0.59;
Manganese (Mn) O.I to 0.6;
Chromium (Cr) 0.9 to 1.5;
Nickel (Ni} 2.4 to 5.5;
the balance being iron (Fe) as well as accompanying elements and impurities.
In the
alloy, the total concentration of phosphorus (P) plus sulfur (S) is less than
0.025
P + S < 0.025 percent by weight;
the concentration of molybdenum (Mo) is less than 0.34 and that of tungsten
(W} is
below 0.29, with the total value of molybdenunn (Mo) plus tungsten (W) divided
by two
not exceeding 0.38
Mo < 0.34 percent by weight;
W < 0.29 percent by weight;
Mo + ~ < 0.38 percent by weight;
and the total of the grain-boundary active impurity elements arsenic (As),
antimony (Sb),
bismuth (Bi), tin (Sn), zinc (Zn) and boron (B) is less than 0.011
As + Sb + Bi + Sn + Zn + B < 0.011 percent by weight.
In a preferred aspect according
to this alternative, the
alloy comprises one or more
elements of the same having
the concentrations, in percent
by weight:
Carbon (C) 0.36 to 0.54, preferably 0.41 to 0.49;
Silicon (Si) 0.11 to 0.39;
Manganese (Mn) 0.18 to 0.49, preferably 0.25 to 0.38;
Chromium (Cr) 1.15 to 1.4;
Nickel (Ni) 2.56 to 4.9, preferably 2.9 to 3.9;
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CA 02414305 2005-06-10
for use as a material, and improved properties can be achieved by these in a
firing test. A
further increase in the property profile is obtained by reducing the sulfur
content to below
0.005 percent by weight.
The process of the invention can further comprise subjecting the alloy to a
technology selected from ladle metallurgy, vacuum treatment, vacuum smelting,
vacuum-
arc remelting, electrosIag remelting (optionally under pressure), powder
metallurgy or
any combination thereof.
In another aspect of the article is subjected to a heat treatment to a
strength of
higher than 1800 N/mm2, e.g., higher than 2000 N/mm2, or even higher than 2100
N/mm2.
The invention further provides an article for providing ballistic protection.
The
article comprises an alloy as set forth above (first and second alternatives),
has a strength
of higher than 1800 NImm2, e.g., higher than 2000 N/mm2 or even higher than
2100
N/mm2, and may have been processed as indicated above. Preferably, the article
has a
toughness at room temperature of higher than SEP 150 J, e.g., higher than SEP
185 J, or
even higher than SEP 245 J. The article can comprise a plate, e.g., a plate
having a
thickness of at least 5 mm.
The invention also provides a method of providing an object (including the
human or animal body) with ballistic protection. According to this method, at
least one of
the surfaces of the object is covered (completely or partially) with a
material comprising
an alloy selected from those indicated above. The alloy and/or the material
may have
been processed as set forth above. Furthermore, the material may show the
strength and
toughness properties indicated.
The advantages achieved with the invention according to the first alternative
as
set forth above essentially can be seen in that limiting the content of the
impurity
elements sulfur and phosphorus to a combined value of less than 0.025 percent
by weight
results in a high toughness of the material, if, as has been found, at the
same time the
total concentration of the additional impurity components arsenic, antimony,
bismuth, tin,
zinc and boron is kept below 0.011 percent by weight. Because nickel in
interaction with
the other alloying elements, in particular molybdenum and vanadium,
surprisingly
increases the danger of a grain-boundary coating, the upper limit of the
nickel content is
less than 0.28 percent by weight. The advantageous properties achieved by the
invention
manifest themselves in a firing test by a high proportion of stopped shots,
and are
CA 02414305 2005-06-10
particularly apparent in parts that have been heat-treated to a strength of
higher than 1900
N/mm2. A still further improvement in the properties of the material is
achieved when the
sulfur content is kept below 0.005 percent by weight.
Excellent results are achieved in a firing test if one or more of the above
elements
are present in the following concentrations, in percent by weight:
Carbon (C) 0.36 to 0.64, preferably0.4I to 0.58;
Silicon (Si) 0.36 to 0.9, preferably0.41 to 0.68;
Manganese (Mn) 0.36 to 0.7, preferably0,4I to 0.59;
Chromium (Cr} 1.7 to 5.95, preferably2.61 to 5.2;
Molybdenum (Mo)1.05 to 2.9, preferably1.3 to 2.7;
Vanadium (V) 0.36 to 1.25, preferably0.39 to 0.83.
When present in the above concentrations, the selected elements, in close
coordination with the other alloying elements, have a positive effect on the
microstructural transformations during heat treatment, i.e., promote an
increase in
hardness without interfering regions at the grain boundaries, and guarantee
the formation
of a largely homogeneous heat-treated microstructure during tempering.
It also has been found that, in addition to the above-mentioned high purity or
low
content of impurity elements, respectively, of the material used according to
the
invention, the manufacturing technology has an effect on the ballistic
protective effect of
parts made thereof. In other words, the manufacturing technologies Ladle
metallurgy,
vacuum 'treatment, vacuum smelting or vacuum-arc remelting, electroslag
remelting
(optionally under pressure) and powder metallurgy, individually and in any
combination
thereof, can have an improving effect on the ballistic protection provided by
parts
produced in such manner, because the isotropy of the material in particular is
promoted
thereby. In this regard, a heat treatment can produce higher strength values
with
improved material toughness; whereby the product is given a substantially
increased
resistance to puncture by projectiles.
If the material has a strength of higher than 1800 N/mmz, preferably higher
than
2000 N/mm2, in particular above 2100 N/mm2, with a toughness at room
temperature of
higher than SEP 150 J, preferably higher than I85 J, in particular above 245
J, measured
in accordance with SEP 1314 (Stahl Eisen Prufblatt = Steel Iron Testing
Standard), the
maximum penetration resistance or strength, respectively, can be achieved with
low
alloying costs of the products.
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The advantages achieved with the invention according to the second alternative
as
set forth above essentially~can be seen in that, on the one hand, by selecting
the alloying
elements and their respective concentrations, a desired high material strength
can be
achieved by means of a heat treatment: As has been found, a high toughness of
the
material can, on the other hand, be achieved by means of three additional
alloying
measures. By limiting the total concentration of sulfur and phosphorus, which
elements
may interact with respect to a formation of inclusions and embrittlement
caused by the
coating of grain boundaries, at least the prerequisite for high toughness of
the material is
provided. The elements molybdenum and tungsten which per se can have a
strength
increasing effect in alloys, individually and in combination show the tendency
to
concentrate in an embrittling manner at grain boundaries in the material so
that the
above-mentioned limitation of the concentrations thereof has a toughness
promoting
effect. It has also been found that, even in low concentrations, the impurity
elements
arsenic, antimony, bismuth, tin, zinc, and boron cause a steep drop in the
toughness of the
material when high mechanical stresses act on the material abruptly, as in the
case of,
e.g., the bombardment of a part made thereof, which is the reason why the
total
concentration thereof is limited according to the invention. As also mentioned
at the
outset, the mechanical properties of a material as determined by means of
conventional
tests may change substantially when a high-energy weapon acts on the material
so that,
strictly speaking, the penetration resistance to bullets or fragments as well
as the cracking
behavior of protective parts can only be evaluated by means of a firing test.
The alloy
used according to the present invention shows special advantages as a material
for
products with high ballistic protective effect, not only because of the
improved properties
associated therewith, but also for economic reasons. In particular, the total
concentration
of the alloying elements in the alloy is below 8.8 percent by weight, and a
low-distortion
heat treatment can be performed therewith. The material also shows adequate
weldability
for component production, e.g., for armor-plating limousines.
Even further improved properties can be achieved in a bring test if one or
more of
the above elements are present the following concentrations, in percent by
weight:
Carbon (C) 0.36 to 0.54, preferably 0.41 to 0.49;
Silicon (Si) 0.11 to 0.39;
Manganese 0.18 to 0.49, preferably 0.25 to 0.38;
(Mn)
Chromium (Cr)1.15 to 1.4;
Nickel (Ni) 2.9 to 4.9, preferably 2.56 to 3.9.
7
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A further improvement in the property profile is obtained by reducing the
sulfur
content to below 0.005 percent by weight.
The advantageous properties of the material that are achieved according to the
second alternative of the invention are particularly apparent during a
bombardment, if the
parts are heat-treated to strength values of above 1900 N/mm2. One of the
reasons
therefor is that a narrower range of the concentration of a respective
alloying element
which interacts with the other components of the alloy favorably influences
the
transformation and the development of the microstructure of the material
during heat
treatment, whereby the increase in hardness and the tempering behavior are
improved,
resulting in an extensive isotropy with low internal stresses.
The manufacturing technologies ladle metallurgy, vacuum treatment, vacuum
smelting or vacuum arc remelting, electroslag remelting (optionally under
pressure) and
powder metallurgy, individually and in any combination thereof, can have an
improving
effect on the ballistic protection provided by parts produced in such manner,
because the
isotropy of the material in particular is promoted thereby, also with regard
to
microsegregations. In this way, an increase in the toughness of the material
can occur in
all directions even with heat treatment to higher strengths of the material,
and the
resistance to puncture by projectiles can be increased.
When the material has a strength of higher than 1800 NImm2, preferably higher
. than 2000 N/mm2, in particular above 2100 N/mm2, with a toughness at room
temperature of higher than SEP 150 J, preferably higher than 185 J, in
particular above
245 J, measured in accordance with SEP 1314 ~Stahl Eisen Priifblatt = Steel
Iron Testing
Standard), products and protective components, respectively, with a maximum
penetration resistance can be produced therefrom.
The present invention is further described in the detailed description which
follows, with reference to the noted plurality of drawings by way of non-
limiting
examples of exemplary embodiments of the present invention, in which like
reference
numerals represent similar parts throughout the several views of the drawings,
and
wherein:
Fig. 1 shows the percentage of stopped shots as a function of the thickness of
a plate
made of an alloy used according to the first alternative of the present
invention, a
managing steel and a carbon steel, respectively; and
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Fig. 2 shows the percentage of stopped shots as a function of the thickness of
a plate
made of an alloy used according to the second alternative of the present
invention, a
managing steel and a carbon steel, respectively.
The particulars shown herein are by way of example and for purposes of
illustrative discussion of the embodiments of the present invention only and
are presented
in the cause of providing what is believed to be the most useful and readily
understood
description of the principles and conceptual aspects of the present invention.
In this
regard, no attempt is made to show structural details of the present invention
in more
detail than is necessary for the fundamental understanding of the present
invention, the
description taken with the drawings making apparent to those skilled in the
art how the
several forms of the present invention may be embodied in practice.
The invention according to the first alternative will in the following be
explained
in greater detail, with reference to Examples 1 and 2.
Example 1
A plate made of an ESU (electroslag remelting) block and having a plate
thickness of 6.6 mm and a composition, in percent by weight, of 0.49 carbon
(C), 0.59
silicon (Si), 0.3 manganese (Mn), 0.004 sulfur (S), 0.019 phosphorus (P), 3.23
chromium
(Cr), 1.37 molybdenum (Mo), 0.29 vanadium (V) as well as 0.19 nickel (Ni), the
balance
being iron (Fe) and accompanying elements (arsenic, antimony, bismuth, tin,
zinc and
boron) in a total concentration of 0.008 was heat-treated to a hardness of 56
~ 1 HRC and
subjected to a firing test with 100 rounds, of which 93 shots were stopped. A
plate made
of heat-treated carbon steel was also tested under the same firing conditions,
and stopped
57 shots.
Example 2
A plate made of Cr-Mo-V steel, treated by ladle metallurgy and vacuum degassed
and having a composition, in percent by weight, of 0.45 carbon (C), 0.62
silicon (Si),
0.64 manganese (Mn), 0.016 phosphorus (P), 0.007 sulfur (S), 3.35 chromium
(Cr), 1.62
molybdenum (Mo), and 0.32 vanadium (V) was rolled from a slab ingot to a
thickness of
7.5 mm. Specimens were fabricated from the plate, heat treated with different
technologies and tested. Table 1 shows the heat treatment parameters and the
mechanical
values obtained.
9
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Table 1
SpecimenHardeningTemperingNumberRm Rpp A Notched Hardness
No. Temperature 2 impact
strength
C C N/mm'N/mm' % 3 Mean HRC
A 930 300 I 1941 1441 6.2167 180166 171 55
B 930 300 1 1872 1471 7.684 209160 151 53
C 950 300 I 1975 1576 5.661 201171 144 55
The effect of different heat treatment parameters on the mechanical properties
of
the material is evident from the above results. This clearly suggests an easy
adjustment of
the desired product properties according to the invention.
About 60% more shots were stopped in the firing test by the plate according to
the invention as compared with a plate of heat-treated carbon steel of the
same thickness.
In another test, a comparison was made of plates according to the invention
with plates
made of carbon steel and maraging steel with regard to stopped shots. The
indicated
values (those plotted in Fig. 1 ) represent respective mean values of results
from at least
three shots.
Fig. 1 shows the percentage of stopped shots as a function of the plate
thickness.
Starting from a sheet thickness of 6 mm upwards, the proportion of shots
stopped by a
plate produced according to the present invention and a plate produced from a
maraging
steel is virtually the same under the same bombardment conditions. With regard
to
economic efficiency, it should be noted that in the material according to the
invention,
the concentration of alloying elements is about 6%, whereas it is 41.5% in the
maraging
steel (comparison material), which makes the latter material substantially
more expensive
than the former.
The invention according to the second alternative will be explained in greater
detail with reference to Examples 3 and 4.
Example 3
A plate having a thickness of 6.8 mm was rolled from a slab ingot made of a
vacuum treated steel having a composition, in percent by weight, of 0.5 carbon
(C), 0.32
silicon (Si), 0.45 manganese (Mn), 0.017 phosphorus (P), 0.006 sulfur (S),
1.25
chromium (Cr), 0.18 molybdenum (Mo), 0.21 tungsten (W), and 3.97 nickel (Ni),
the
total concentration of arsenic, antimony, bismuth, tin, and boron being equal
to 0.0085.
CA 02414305 2005-06-10
This rolling stock was tested mechanically after the application of different
heat
treatment technologies. The results of the corresponding tests are summarized
in Table 2.
Table 2
SpecimenHardeningTemperingNumberRm Rpo,2 A Notched Hardness
No. Temperature impact
- - strength
_
o C o C N/mmzN/mmz % J Mean HRC
AA 840 120 1 2229 1207 6.1225 245228 232 55.5
BB 870 120 1 2227 1133 8.6220 245218 227 50
CC 840 120 I 2282 1306 5.595 233173 167 57
'The firing test showed that the plate with the specimen designation AA had a
shot
stopping capability of 95; whereas a heat treated-plate made of carbon steel
of the same
thickness withstood only 56 of 100 bombardments from shots.
Example 4
A plate having a thickness of 7.5 mm was manufactured from steel treated by
ladle metallurgy and having a composition, in percent by weight, of 0.52
carbon (C), 0.12
silicon (Si), 0.22 manganese (Mn), 0.014 phosphorus (P), 0.003 sulfur (S),
I.42
chromium (Cr), O.I 1 molybdenum (Mo), 0.09 tungsten (W), and 0.004 (As + Sb +
Bi +
Sn + Zn + B). The steel had subsequently been subjected to electroslag
remelting. Heat
treatment to a hardness of 57 HRC, afforded, at a hardening temperature of
880° C and
with air cooling after tempering at 200° C, a yield point of the
material of Rm = 2265
N/mm2, with an average notched impact strength of 202 J. In the firing test a
68.7%
higher number of stopped shots was recorded as colilpared to a plate made of
heat-treated
carbon steel under otherwise identical conditions.
In one of the other tests, a comparison was made by means of a firing test
with
plates according to the present invention and plates made of carbon steel and
maraging
steel, each heat-treated to the maximum values. Fig. 2 shows the percentage of
stopped
shots as a function of the plate thickness. Starting at a plate thickness of 5
mm up to a
thickness of IO mm, the shots stopped by the maraging steel and those stopped
by the
steel according to the invention were proportionally essentially the same,
with slight
advantages for the material according to the invention in the plate thickness
range of
above 6 mm.
It can be seen from the above results that the use of a material according to
the
invention has, one the one hand, a clearly higher ballistic protective effect
compared with
11
CA 02414305 2005-06-10
a material made of carbon steel under the same product form and stress
conditions and,
on the other hand, has a substantially lower proportion of alloying elements
than a
managing steel and, thus, shows economic advantages in the production thereof.
It is noted that the foregoing examples have been provided, merely for the
purpose
of explanation and are in no way to be construed as limiting of the present
invention.
While the present invention has been described with reference to an exemplary
embodiment, it is understood that the words which have been used herein are
words of
description and illustration, rather than words of limitation. Changes may be
made,
within the purview of the appended claims, as presently stated. and as
amended, without
departing from the scope and spirit of the present invention in its aspects.
Although the
present invention has been described herein with reference to particular
means, materials
and embodiments, the present invention is not intended to be limited to the
particulars
disclosed herein; rather, the present invention extends to all functionally
equivalent
structures, methods and uses, such as are within the scope of the appended
claims.
12
