U.S. patent application number 12/967534 was filed with the patent office on 2012-06-21 for blast resistant, non-magnetic, stainless steel armor.
Invention is credited to Christopher F. Pilliod, Peter T. Thompson.
Application Number | 20120156085 12/967534 |
Document ID | / |
Family ID | 44680916 |
Filed Date | 2012-06-21 |
United States Patent
Application |
20120156085 |
Kind Code |
A1 |
Thompson; Peter T. ; et
al. |
June 21, 2012 |
Blast Resistant, Non-Magnetic, Stainless Steel Armor
Abstract
An article of manufacture formed of an alloy having the
following weight percent composition is described. TABLE-US-00001
Carbon 0.25 max. Manganese 14-20 Silicon up to 2.0 Phosphorus 0.05
max. Sulfur 0.5 max. Chromium 12-22 Nickel 3.5 max. Molybdenum
0.5-4 Copper 2.0 max. Nitrogen 0.2-0.8 Boron 0.06 max. The balance
of the alloy is iron and the usual, inevitable impurities found in
commercial grades of stainless steel alloys. Optionally, the alloy
may contain niobium, titanium, vanadium, zirconium, hafnium, and
tungsten in a combined amount of up to about 0.5%. An intermediate
form of the article is armor plate made from the alloy. In
accordance with another aspect of the present invention, the plate
is shaped to form an armor part that is attached to a larger
structure to provide resistance to an explosion fragments or a
ballistic projectile.
Inventors: |
Thompson; Peter T.; (Sinking
Spring, PA) ; Pilliod; Christopher F.; (Sinking
Spring, PA) |
Family ID: |
44680916 |
Appl. No.: |
12/967534 |
Filed: |
December 14, 2010 |
Current U.S.
Class: |
420/57 ; 148/542;
164/76.1; 420/586.1 |
Current CPC
Class: |
C22C 38/58 20130101;
C22C 38/42 20130101; C22C 38/44 20130101; C22C 38/02 20130101; C22C
38/54 20130101; C21D 8/0273 20130101; F41H 5/045 20130101; C21D
8/0226 20130101; C22C 38/001 20130101; C21D 8/0231 20130101; C21D
6/005 20130101; C21D 8/0205 20130101; C21D 9/42 20130101; C21D
6/002 20130101 |
Class at
Publication: |
420/57 ;
420/586.1; 164/76.1; 148/542 |
International
Class: |
C22C 38/58 20060101
C22C038/58; B22D 25/06 20060101 B22D025/06; C21D 8/02 20060101
C21D008/02; C22C 30/00 20060101 C22C030/00 |
Claims
1. A blast resistant armor article formed of a high strength, high
toughness, stainless steel alloy having the following composition
in weight percent, about TABLE-US-00009 Carbon 0.25 max. Manganese
14-20 Silicon up to 2.0 Phosphorus 0.05 max. Sulfur 0.5 max.
Chromium 12-22 Nickel 3.5 max. Molybdenum 0.5-4 Copper 2.0 max.
Nitrogen 0.2-0.8 Boron 0.06 max.
said alloy optionally containing niobium, titanium, vanadium,
zirconium, hafnium, and tungsten in a combined amount of up to
about 0.5%; and the balance of the alloy is iron and usual
impurities.
2. An armor article as claimed in claim 1 wherein the article
comprises plate made from the alloy.
3. An armor article as claimed in claim 1 wherein the article
comprises plate made from the alloy and said plate is shaped to
form an armor part for attachment to a larger structure to provide
resistance to damage from an explosion blast, an explosion
fragment, or a ballistic projectile.
4. (canceled)
5. An armor article as claimed in claim 1 wherein the alloy
comprises the following elements in weight percent, TABLE-US-00010
Carbon 0.08 max. Manganese 14-19 Silicon 1 max. Phosphorus 0.05
max. Sulfur 0.03 max. Chromium 12-21 Nickel 3.5 max. Molybdenum
0.5-4 Copper 2.0 max. Nitrogen 0.2-0.8 Boron 0.06 max.
6. An armor article as claimed in claim 1 wherein the alloy
comprises the following elements in weight percent, TABLE-US-00011
Carbon 0.05 max. Manganese 15-18 Silicon 1 max. Phosphorus 0.05
max. Sulfur 0.03 max. Chromium 14-19.5 Nickel 2.5 max. Molybdenum
0.75-2.5 Copper 1.5 max. Nitrogen 0.3-0.7 Boron 0.005 max.
7. An armor article as claimed in claim 1 wherein the alloy
comprises the following elements in weight percent, TABLE-US-00012
Carbon 0.035 max. Manganese 16-18 Silicon 0.75 max. Phosphorus 0.05
max. Sulfur 0.03 max. Chromium 16-18 Nickel 1.5 max. Molybdenum
1.0-2.0 Copper 1.0 max. Nitrogen 0.4-0.6 Boron 0.005 max.
8. An improved armor plate formed of a high strength steel alloy,
wherein the improvement comprises the steel alloy consisting
essentially of, about TABLE-US-00013 Carbon 0.25 max. Manganese
14-20 Silicon up to 2.0 Phosphorus 0.05 max. Sulfur 0.5 max.
Chromium 12-22 Nickel 3.5 max. Molybdenum 0.5-4 Copper 2.0 max.
Nitrogen 0.2-0.8 Boron 0.06 max.
said steel alloy optionally containing niobium, titanium, vanadium,
zirconium, hafnium, and tungsten in a combined amount of up to
about 0.5%, and the balance of the alloy is iron and usual
impurities.
9. An improved armor plate as claimed in claim 8 wherein the steel
alloy consists essentially of, in weight percent, about
TABLE-US-00014 Carbon 0.08 max. Manganese 14-19 Silicon 1 max.
Phosphorus 0.05 max. Sulfur 0.03 max. Chromium 12-21 Nickel 3.5
max. Molybdenum 0.5-4 Copper 2.0 max. Nitrogen 0.2-0.8 Boron 0.06
max.
10. An improved armor plate as claimed in claim 8 wherein the steel
alloy consists essentially of, in weight percent, about
TABLE-US-00015 Carbon 0.05 max. Manganese 15-18 Silicon 1 max.
Phosphorus 0.05 max. Sulfur 0.03 max. Chromium 14-19.5 Nickel 2.5
max. Molybdenum 0.75-2.5 Copper 1.5 max. Nitrogen 0.3-0.7 Boron
0.005 max.
11. An improved armor plate as claimed in claim 8 wherein the steel
alloy consists essentially of, in weight percent, about
TABLE-US-00016 Carbon 0.035 max. Manganese 16-18 Silicon 0.75 max.
Phosphorus 0.05 max. Sulfur 0.03 max. Chromium 16-18 Nickel 1.5
max. Molybdenum 1.0-2.0 Copper 1.0 max. Nitrogen 0.4-0.6 Boron
0.005 max.
12. A process for making armor plate comprising the steps of:
melting an alloy having the following weight percent composition,
about TABLE-US-00017 Carbon 0.25 max. Manganese 14-20 Silicon up to
2.0 Phosphorus 0.05 max. Sulfur 0.5 max. Chromium 12-22 Nickel 3.5
max. Molybdenum 0.5-4 Copper 2.0 max. Nitrogen 0.2-0.8 Boron 0.06
max.
said alloy optionally containing niobium, titanium, vanadium,
zirconium, hafnium, and tungsten in a combined amount of up to
about 0.5%, and the balance of the alloy is iron and usual
impurities; casting the alloy into a mold to form an ingot; and
then mechanically working said alloy ingot to form plate.
13. The process claimed in claim 12 wherein the step of
mechanically working the alloy ingot comprises the steps of: hot
working the ingot to form a slab; hot working the slab to form the
plate; and then cooling the as-formed plate at a cooling rate that
is fast enough to avoid substantial sensitization of the alloy; and
wherein the step of hot working the slab is performed such that the
alloy receives a reduction in thickness selected to provide a
combination of strength, hardness, and toughness in said plate
after said cooling step sufficient to resist damage from an
explosion blast, an explosion fragment, or a ballistic projectile,
when tested in accordance with MIL-STD-662F.
14. The process claimed in claim 13 wherein the step of hot working
the slab comprises the steps of: heating the slab to a starting
temperature of about 1500-2000.degree. F.; and then reducing the
thickness of the slab from the starting temperature down to a
finish temperature of about 1100-1400.degree. F.
15. The process claimed in claim 12 wherein the step of hot working
the alloy ingot comprises the steps of: hot working the ingot to
form a slab; hot working the slab to form an intermediate thickness
plate; warm working the intermediate thickness plate to provide a
final thickness plate; and then cooling the warm-worked plate;
wherein the step of warm working the intermediate thickness plate
is performed such that the alloy receives a reduction in thickness
selected to provide a combination of strength, hardness, and
toughness in said final thickness plate after said cooling step
sufficient to resist damage from an explosion blast, explosion
fragment, or a ballistic projectile, when tested in accordance with
MIL-STD-662F.
16. The process claimed in claim 15 wherein the step of hot working
the slab to intermediate thickness plate comprises the steps of
heating the slab to a start temperature of about 1700-2200.degree.
F.; reducing the thickness of the slab from the starting
temperature down to a finish temperature of about 1600-1900.degree.
F.; and then cooling the intermediate thickness plate at a cooling
rate that is fast enough to avoid sensitization of the alloy.
17. The process claimed in claim 16 wherein after said cooling
step, the alloy is annealed at about 1600-2350.degree. F.
18. The process claimed in claim 15 wherein the warm working step
is carried out at a temperature of about 800-1200.degree. F.
19. The process claimed in claim 18 wherein after said warm working
step, the final thickness plate is cooled at a cooling rate that is
fast enough to avoid substantial sensitization of the alloy.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to blast resistant articles of
manufacture and in particular to such an armor article made from a
corrosion resistant, non-magnetic, high strength, high toughness
steel alloy and to a process for making the armor article.
[0003] 2. Description of the Related Art
[0004] The use of improvised explosive devices (IED's) and land
mines by military insurgents causes significant destruction of
military equipment and substantial injury and loss of life of
military personnel. Because of such threats, a need has arisen
among armored vehicle manufacturers for new blast-resistant
materials which provide a better combination of strength with
energy absorption capability than the materials currently in use.
Energy absorption capability is related to the toughness of a
material. The toughness of a material has been defined as the
ability to absorb energy and deform plastically before fracturing.
Two known families of materials used for blast resistant armor are
martensitic steels and aluminum alloys. Martensitic steels provide
high strength, but less than desirable energy absorption compared
to aluminum alloys. On the other hand, aluminum alloys provide good
energy absorption, but lower strength than martensitic steels. It
is also desirable for the blast resistant material to be
non-magnetic so that it would provide some protection from mines
that are magnetically triggered.
[0005] Austenitic stainless steel alloys sold under the registered
trademarks "15-15LC" and "15-15HS" are designed for and have been
used exclusively for making components for the oil-drilling
industry, primarily drill collars. The alloys sold under the marks
"15-15LC" and "15-15HS" are described and claimed in U.S. Pat. No.
3,904,401, U.S. Pat. No. 5,094,812, and U.S. Pat. No. 5,308,877,
the entireties of which are incorporated herein by reference.
SUMMARY OF THE INVENTION
[0006] In accordance with a first aspect of this invention there is
provided an article of manufacture formed of an alloy having the
following broad and preferred compositions in weight percent.
TABLE-US-00002 Broad Preferred 1 Preferred 2 Preferred 3 Carbon
0.25 max. 0.08 max. 0.05 max. 0.035 max. Manganese 14-20 14-19
15-18 16-18 Silicon up to 2.0 1 max. 1 max. 0.75 max. Phosphorus
0.05 max. 0.05 max. 0.05 max. 0.05 max. Sulfur 0.5 max. 0.03 max.
0.03 max. 0.03 max. Chromium 12-22 12-21 14-19.5 16-18 Nickel 3.5
max. 3.5 max. 2.5 max. 1.5 max. Molybdenum 0.5-4 0.5-4 0.75-2.5
1.0-2.0 Copper 2.0 max. 2.0 max. 1.5 max. 1.0 max. Nitrogen 0.2-0.8
0.2-0.8 0.3-0.7 0.4-0.6 Boron 0.06 max. 0.06 max. 0.005 max. 0.005
max.
The balance of the alloy is iron and the usual, inevitable
impurities found in commercial grades of stainless steel alloys.
Optionally, the alloy may contain niobium, titanium, vanadium,
zirconium, hafnium, and tungsten in a combined amount of up to
about 0.5%. An intermediate form of the article is plate made from
the alloy. In accordance with another aspect of the present
invention, the plate is shaped to form an armor part that is
attached to a larger structure to provide resistance to an
explosion or a ballistic projectile.
[0007] In accordance with a further aspect of the present
invention, there is provided a process for making armor components
for vehicles and other structures. The process includes the step of
forming plate from an alloy having the following broad and
preferred weight percent compositions.
TABLE-US-00003 Broad Preferred 1 Preferred 2 Preferred 3 Carbon
0.25 max. 0.08 max. 0.05 max. 0.035 max. Manganese 14-20 14-19
15-18 16-18 Silicon up to 2.0 1 max. 1 max. 0.75 max. Phosphorus
0.05 max. 0.05 max. 0.05 max. 0.05 max. Sulfur 0.5 max. 0.03 max.
0.03 max. 0.03 max. Chromium 12-22 12-21 14-19.5 16-18 Nickel 3.5
max. 3.5 max. 2.5 max. 1.5 max. Molybdenum 0.5-4 0.5-4 0.75-2.5
1.0-2.0 Copper 2.0 max. 2.0 max. 1.5 max. 1.0 max. Nitrogen 0.2-0.8
0.2-0.8 0.3-0.7 0.4-0.6 Boron 0.06 max. 0.06 max. 0.005 max. 0.005
max. Iron Balance Balance Balance Balance
The "Balance" includes inevitable impurities found in commercial
grades of stainless steel alloys. Optionally, the alloy may contain
niobium, titanium, vanadium, zirconium, hafnium, and tungsten in a
combined amount of up to about 0.5%. The alloy is hot worked to
plate having a final thickness having a preselected level of
strength and impact toughness. Alternatively, the alloy is hot
worked to plate having an intermediate thickness. The intermediate
thickness plate material is then preferably warm-worked to a final
thickness that provides a preselected level of strength and impact
toughness. The process further includes the step of shaping the
warm-worked plate to form an armor part for a vehicle or other
structure without annealing after the warm working step.
[0008] In accordance with a still further aspect of this invention,
there is provided a method of armoring a vehicle or other structure
to make it blast resistant. The method includes the steps of
forming plate from any of the alloys described above, warm working
the plate without a subsequent anneal, and shaping the plate to
form an armor part for a vehicle or other structure. The method
includes the further step of attaching the armor part to the
vehicle or other structure.
[0009] The foregoing tabulations are provided as convenient
summaries and are not intended thereby to restrict the lower and
upper values of the ranges of the individual elements of the alloy
used in this invention for use solely in combination with each
other or to restrict the various broad and preferred ranges of the
elements for use solely in combination with each other. Thus, one
or more of the broad and preferred ranges can be used with one or
more of the other ranges for the remaining elements. In addition, a
broad or preferred minimum or maximum for an element can be used
with the maximum or minimum for that element from one of the
remaining ranges. Throughout this application, the symbol "%" or
"w/o" or the term "percent" means weight percent or mass percent
unless otherwise indicated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The foregoing summary of the invention and the following
detailed description will be better understood when read in
conjunction with the drawings, wherein:
[0011] FIG. 1 is a graph of Charpy V-notch toughness as a function
of hardness for alloys used in the present invention compared to
the known alloys.
[0012] FIG. 2 is a schematic diagram of a passenger vehicle
equipped with a blast protective armor article in accordance with
the present invention.
[0013] FIG. 3 is a schematic diagram of a .30 Cal armor piercing
projectile.
[0014] FIG. 4 is a schematic diagram of a .50 Cal fragment
simulating projectile.
[0015] FIG. 5 is a graph of .30 Cal APM2 V50 velocity as a function
of the .50 Cal FSP V50 velocity for examples of armor plate made in
accordance with the present invention.
DETAILED DESCRIPTION
[0016] An armor article according to this invention includes a
shaped piece of steel plate. The steel plate is made from a high
strength, corrosion resistant alloy have a weight percent
composition that is within any of the broad or preferred weight
percent ranges described above. The alloy used in the article
according to the present invention provides substantial resistance
to damage from explosions because it provides a unique combination
of very high strength and high toughness. The toughness property is
one measure of damage tolerance for armor material. The toughness
of a material is typically evaluated based on the Charpy V-notch
impact strength (CVN). CVN is determined in accordance with ASTM
Standard Test Specification E 23. The hardness of a material is a
measure of its strength. The harder a material is, the higher its
strength is expected to be. Set forth in FIG. 1 is a graph showing
the CVN of certain alloys as a function of the hardness of the
material.
[0017] The 15-15 LC Alloy and the 15-15 HS Alloy are alloys whose
weight percent compositions are within the scope of the alloys used
in the present invention as described in the Broad and Preferred
ranges set forth above. Referring to FIG. 1, it is clear that the
alloys used in the present invention provide significantly greater
impact toughness than very high strength steels such as AISI 4340
and AISI 4130 which have variants that are currently used for armor
applications. It is also seen from FIG. 1, that the 15-15 LC alloy
and the 15-15 HS alloy provide high strength in the unannealed
condition that is at least as good as the very high strength alloys
AISI 4340 and AISI 4130. The combinations of hardness and toughness
illustrated in FIG. 1 for the 15-15 LC alloy and for the 15-15 HS
alloy are clearly superior to the combinations of those properties
demonstrated for the AISI 4340 and AISI 4130 alloys. Moreover, the
15-15 LC alloy is nonmagnetic and so cannot set off a magnetically
activated land mine or IED.
[0018] The alloys used in an article according to this invention
are readily prepared by means of conventional, well-known
techniques including powder metallurgy. Cast and wrought forms of
the alloys are initially melted by electric arc melting (ARC)
preferably followed by argon-oxygen decarburization (AOD) and cast
as an electrode or as an ingot. In addition, the electrodes of this
alloy may be further refined by electroslag remelting (ESR). After
final melting is complete, the ingot is preferably homogenized and
then formed into plate of a desired thickness. In this regard, the
ARC or ESR ingot is initially hot worked to form an elongated slab.
The slab is then further processed in either of two ways. In a
first process, the slab is hot worked, preferably by rolling,
pressing, or forging the slab until a plate having a desired
thickness is obtained. The final thickness is selected such that
the alloy receives a reduction in thickness (RIT) that is
sufficient to provide a desired combination of strength, hardness,
and toughness in the alloy plate. In the first process, the slab is
preferably hot rolled to plate from a temperature of about
1500.degree. F.-2000.degree. F. (about 816.degree. C.-1093.degree.
C.) down to a finish temperature of about 1100.degree.
F.-1400.degree. F. (about 593.degree. C.-760.degree. C.).
Preferably, the plate is rapidly cooled from the finish temperature
such as by quenching with water or oil. The cooling should be
conducted quickly after completion of the hot rolling to avoid
further sensitization of the alloy. However, the inventors have
determined that some sensitization of the alloy may be beneficial
to the ballistic properties of the armor applications. The hot
rolling step can be conducted in one or more passes with reheating
as necessary if the finish temperature is reached before the
desired thickness is obtained.
[0019] In the second process, the slab is hot worked, again
preferably by rolling, pressing, or forging the slab to an
elongated plate having an intermediate thickness. The hot working
step is preferably conducted from a start temperature of about
1700.degree. F.-2200.degree. F. (about 927.degree. C.-1204.degree.
C.) down to a finish temperature of about 1600.degree.
F.-1900.degree. F. (about 871.degree. C.-1038.degree. C.).
Preferably, the intermediate thickness plate is rapidly cooled as
above, preferably within minutes after completion of the hot
rolling step in order to avoid sensitization of the alloy. The
intermediate thickness plate material is preferably annealed at
about 1600.degree. F.-2350.degree. F. (about 871.degree.
C.-1288.degree. C.) for about 30 minutes per inch of thickness and
then water cooled to room temperature. The annealed intermediate
plate is then warm-worked, again preferably by rolling, pressing,
or forging, at a temperature of about 800.degree. F.-1200.degree.
F. (about 427.degree. C.-649.degree. C.) to an RIT that is
sufficient to provide the desired combination of strength and
toughness in the as-worked material. The warm-worked plate is
quenched, as in water, but is not subsequently annealed. The amount
of warm working applied to the alloy, i.e., the percent RIT, is
selected based on the level of hardness and strength to be provided
by the armor article. The greater the RIT is, the greater will be
the strength and toughness of the alloy plate. It is anticipated
that the plate material produced in accordance with this invention
will provide a Brinell hardness (BHN) of about 275-400.
[0020] After the plate material is formed, it is cut into parts
which are shaped by bending operations, for example. The shaped
parts are then machined as necessary and attached to a vehicle or
other object by any known technique such as by welding or with
fasteners such as bolts, screws, or rivets. Armor articles made in
accordance the present invention, exhibit an outstanding
combination of properties including very high strength and
toughness, good corrosion resistance, and good non-magnetic
behavior. It is contemplated that armor articles made in accordance
with this invention can be used in or on a wide variety of vehicles
and other objects for which blast resistance/tolerance is needed.
Military vehicles such as tanks, trucks, personnel carriers,
aircraft, ships, and submarines are all suitable candidates for
receiving armor articles made according to the invention. In
addition, civilian security vehicles would also benefit from the
use of armor articles according to the invention. Shown in FIG. 2
is an arrangement for an armored vehicle made in accordance with
the present invention. The vehicle includes a passenger compartment
that is supported on a floor. An armor substructure made in
accordance with the present invention is mounted beneath the
vehicle floor. The armor substructure provides a blast resistant
barrier to protect the passenger compartment from the effects of an
exploding IED or mine. Buildings and architectural features such as
doors can also be fitted with armor articles in accordance with
this invention. It is also contemplated that the armor articles of
this invention can be used in luggage, storage containers and
containment trashcans for nuclear waste and other types of
hazardous waste that may be transported on public roads or rail
lines.
WORKING EXAMPLES
[0021] In order to demonstrate the process and product of the
present invention, two heats were melted and processed into plate.
The plate material was then tested to determine the relevant
mechanical properties, ballistic tolerance, and blast resistance of
the as-processed material. The weight percent compositions of the
two heats are set forth in Table 1 below.
TABLE-US-00004 TABLE 1 Element Heat 1 Heat 2 C 0.035 0.027 Mn 17.99
18.41 Si 0.36 0.37 P 0.022 0.028 S 0.001 <0.001 Cr 17.66 18.56
Ni 0.94 1.97 Mo 0.77 0.74 Cu 0.06 0.06 N 0.52 0.57 B 0.0019
0.0024
The balance of each heat is iron and usual impurities. Heat 1 was
ARC-AOD melted whereas Heat 2 was ARC-ESR melted.
Example 1
[0022] The objective of this example was to produce plate material
in accordance with the first process described above. Material from
the ingot of Heat 1 and from the ingot of Heat 2 was hot worked to
provide slabs 2.58 inches (6.55 cm) thick. The slab formed from
Heat 1 was heated to a temperature of 1650.degree. F. (899.degree.
C.) and hot rolled to 0.55 inch (13.97 mm) thick plate. The slab
formed from Heat 2 was heated to a temperature of 1650.degree. F.
(899.degree. C.) and hot rolled to 0.53 inch (13.5 mm) thick plate.
For both heats, the plate material was quenched with water within
about 10 minutes of the last rolling pass. Longitudinal and
transverse samples for hardness, tensile, and toughness testing
were cut from the plates and machined to form standard size test
specimens. The results of room temperature hardness, tensile, and
Charpy V-notch toughness testing are shown in Tables 2A and 2B
below including the Brinell hardness number (BHN), the 0.2% offset
yield strength (YS) and ultimate tensile strength (UTS) in ksi, the
percent elongation (% El.), the percent reduction in area (% R.A.),
and the Charpy V-notch impact strength in foot-pounds (ft-lbs). The
value for BHN is the average of five (5) different readings. The
CVN values are presented as the average of four (4) tests.
TABLE-US-00005 TABLE 2A Longitudinal BHN Y.S. U.T.S. % El. % R.A.
CVN Heat 1 339 142.3 157.6 34 60 38.3 Heat 2 353 149.9 165.2 34 63
62.7
TABLE-US-00006 TABLE 2B Transverse BHN Y.S. U.T.S. % El. % R.A. CVN
Heat 1 339 130.7 151.3 34 63 43.5 Heat 2 353 143 160.4 31 60
40.7
Example 2
[0023] The objective of this example was to produce plate material
using the two-step process described above. Additional material
from the ingot of Heat 2 was hot worked to provide slabs nominally
5 inches (12.7 cm) thick. The slabs were then hot rolled to
intermediate thicknesses. A first slab was hot rolled from a start
temperature of about 2100.degree. F. (1149.degree. C.) to an
intermediate thickness of about 0.72 inches (18.3 mm). A second
slab was rolled from a start temperature of about 2100.degree. F.
(1149.degree. C.) to an intermediate thickness of about 0.905
inches (23 mm). A third slab was rolled from a start temperature of
about 2100.degree. F. (1149.degree. C.) to an intermediate
thickness of about 1.25 inches (31.75 mm). A fourth slab was rolled
from a start temperature of about 2100.degree. F. (1149.degree. C.)
to an intermediate thickness of about 2.55 inches (6.48 cm). The
intermediate forms were rapidly cooled with water within about 5
minutes of completion of the last rolling pass on each intermediate
slab. After the intermediate hot rolling, the slabs were annealed
at a temperature of about 1832.degree. F. (1000.degree. C.) for
about 30 minutes per inch of thickness and then water cooled.
[0024] The annealed intermediate forms were then warm worked from a
start temperature of about 800.degree. F. to about 1200.degree. F.
(426.7.degree. C. to 649.degree. C.) to impart RIT's ranging from
about 15% to about 85%. More specifically, the 0.72-inch (18.3 mm)
thick slab was warm worked from a temperature of about 1100.degree.
F. (593.degree. C.) to a thickness of about 0.55 inches (13.97 mm)
representing an RIT of about 24%. The 0.905-inch (23 mm) thick slab
was warm worked from a temperature of about 1100.degree. F.
(593.degree. C.) to a thickness of about 0.55 inches (13.97 mm)
representing an RIT of about 41%. The 1.25-inch (31.75 mm) thick
slab was warm worked from a temperature of about 1100.degree. F.
(593.degree. C.) to a thickness of about 0.55 inches (13.97 mm)
representing an RIT of about 56%. The 2.55-inch (6.48 cm) thick
slab was warm worked from a temperature of about 1100.degree. F.
(593.degree. C.) to a thickness of about 0.55 inches (13.97 mm)
representing an RIT of about 78%. The hot rolled plates were cooled
in air.
[0025] Longitudinal and transverse samples for hardness, tensile,
and toughness testing were cut from the plates and machined to form
standard size test specimens. The results of room temperature
hardness, tensile, and Charpy V-notch toughness testing are shown
in Tables 3A and 3B below including the Brinell hardness number
(BHN), the 0.2% offset yield strength (YS) and the ultimate tensile
strength (UTS) in ksi, the percent elongation (% El.), and the
Charpy V-notch impact strength in foot-pounds (ft-lbs). The value
for BI-IN is the average of five (5) different readings. The CVN
values are presented as the average of three (3) tests.
TABLE-US-00007 TABLE 3A Longitudinal RIT BHN Y.S. U.T.S. % El. CVN
24% 351 125.7 160.1 38 131 41% 373 146.7 176.2 33 120.3 56% 406
167.9 188.4 28 48.7 78% 419 165 198.1 27 18
TABLE-US-00008 TABLE 3B Transverse RIT BHN Y.S. U.T.S. % El. CVN
24% 351 149.4 164.3 39 42.3 41% 373 143.8 175.6 33 33.0 56% 406
152.3 185.3 29 27.3 78% 419 163 195.9 27 16.7
[0026] The combination of hardness, strength, and toughness
provided by an armor article made in accordance with the present
invention makes the armor highly resistant to both armor piercing
projectiles and blast fragments such as from IED's. Specimens of
the armor plate produced in the examples were tested to determine
the V50 velocity for both armor piercing rounds (.30 cal APM2) and
fragment simulating projectiles (FSP) fired normal to the plane of
the armor tested in accordance with MIL-STD-662F. The V50 velocity
is defined as the projectile velocity at which 50% of projectiles
impacting the armor will defeat the armor such as by penetration. A
typical APM2 round used for the ballistic testing is shown in FIG.
3. A typical FSP projectile used for the blast resistance testing
is shown in FIG. 4. The combination of .50 Cal FSP V50 and .30 Cal
APM2 V50 provided by 0.55-inch thick armor plate samples prepared
in accordance with the present invention is shown in FIG. 5. The
data points are for samples having different combinations of
melting technique, annealing temperature, and percent RIT as
described above. Data points near the upper right hand corner of
the graph represent the best combination of APM2 and FSP V50
velocities.
[0027] It will be recognized by those skilled in the art that
changes or modifications may be made to the above-described
embodiments without departing from the broad inventive concepts of
the invention. It is understood, therefore, that the invention is
not limited to the particular embodiments that are described, but
is intended to cover all modifications and changes within the scope
and spirit of the invention as described above and set forth in the
appended claims.
* * * * *