Patent Application
20210396494
This invention relates generally to armor plate for military and civilian vehicles, and in particular to an armor plate article that is consists of two or more layers of different steel alloys and also to a method of making the layered armor plate.
Armor plate must be hard enough to reliably shatter the hard steel cores of armor-piercing (AP) projectiles and must also have enough toughness to resist plate cracking in order to effectively defeat a high energy AP projectile. The steel core of an AP projectile typically has a hardness of at least about 60 HRC. Therefore, the armor plate must have at least about the same hardness in order to be able to shatter the projectile on contact. The level of fracture toughness that is required to resist plate cracking varies with plate thickness and the type of projectile, but a generally accepted rule of thumb calls for a plane strain fracture toughness (Klc) of at least about 50 ksi√in. There is no known steel alloy that is able to achieve that combination of hardness and fracture toughness.
Armor plate is known that consists of two layers made from different alloys that are bonded together. However, the known plate products leave something to be desired with respect to the combination of hardness and toughness that is required to effectively thwart a high energy AP projectile such as a 30 caliber or 50 caliber AP projectile. Accordingly, there is a need for an armor plate that provides not only a very high hardness of at least about 60 HRC, but also a fracture toughness of at least about 50 ksi√in.
The need for effective armor plate described above is resolved to a large degree by a composite armor plate product in accordance with a first aspect of the present invention. The composite armor plate includes a first layer made from an ultra-high hardness, high strength alloy that is bonded to a second layer made from a high fracture toughness alloy that also may have high strength. The composite armor plate according to the present provides a gradient of strength, hardness, and toughness.
According to a first embodiment, the armor plate according to the present invention comprises a first steel layer made from a first steel alloy having the following composition in weight percent,
and the balance is iron and impurities, said impurities including not more than about 0.003% phosphorus, not more than about 0.0010% sulfur, not more than about 0.0010% oxygen, and not more than about 0.0010% nitrogen, and a second steel layer made from a second steel alloy having the following composition in weight percent,
and the balance is iron and impurities. The first steel layer has a first planar surface that is bonded to a first planar surface of the second steel layer to form a composite armor plate.
In accordance with a second aspect of the present invention there is provided a gradient armor plate that has 3 or 4 steel layers. The gradient armor plate according to this aspect of the invention includes a first layer made from an ultra-high strength alloy, a second layer made from a high strength, high fracture toughness alloy, and one or more intermediate steel layers located between the first and second layers and that is(are) characterized by a combination(s) of strength and fracture toughness that is(are) intermediate the strength and toughness properties of the first and second steel layers. The steel layers in this embodiment are selected to provide a gradient of the properties ranging from the highest hardness and strength in the first layer to the highest fracture toughness in the second layer.
According to an embodiment of the second aspect of the present invention, the armor plate comprises a first steel layer made from a first steel alloy having the following composition in weight percent,
and the balance is iron and impurities, said impurities including not more than about 0.003% phosphorus, not more than about 0.0010% sulfur, not more than about 0.0010% oxygen, and not more than about 0.0010% nitrogen, a second steel layer made from a second steel alloy having the following composition in weight percent,
and the balance is iron and impurities, and a third steel layer made from a third steel alloy having the following composition in weight percent.
The third steel layer is positioned between the first steel layer and the second steel layer. The first steel layer has a first planar surface that is bonded to a first planar surface of the third steel layer and the second steel layer has a first planar surface that is bonded to a second planar surface of the third steel layer.
According to a second embodiment of the second aspect of the present invention, the armor plate comprises a first steel layer made from a first steel alloy having the following composition in weight percent,
and the balance is iron and impurities, said impurities including not more than about 0.003% phosphorus, not more than about 0.0010% sulfur, not more than about 0.0010% oxygen, and not more than about 0.0010% nitrogen, a second steel layer made from a second steel alloy having the following composition in weight percent,
and the balance is iron and impurities, a third steel layer made from a third steel alloy having the following composition in weight percent,
and the balance is iron and impurities, and a fourth steel layer made from a fourth steel alloy having the following composition in weight percent,
and the balance is iron and impurities. The third steel layer is positioned between the first steel layer and the fourth steel layer and the fourth steel layer is positioned between the second steel layer and the third steel layer. The first steel layer has a first planar surface that is bonded to a first planar surface of the third steel layer, the fourth steel layer has a first planar surface that is bonded to a second planar surface of the third steel layer, and the second steel layer has a first planar surface that is bonded to a second planar surface of the fourth steel layer.
In accordance with a further aspect of the invention, there is provided a method of making multi-layer armor plate as described above. The method according to a first embodiment of this aspect of the invention includes the steps of melting a first steel alloy having the following composition in weight percent:
and the balance is iron and impurities, said impurities including not more than about 0.003% phosphorus, not more than about 0.0010% sulfur, not more than about 0.0010% oxygen, and not more than about 0.0010% nitrogen and casting the first steel alloy into a first ingot and then forming the first ingot into a first billet having a planar surface. The method also includes the steps of melting a second steel alloy having the following composition in weight percent:
and the balance is iron and impurities and casting the second steel alloy to form a second ingot and then forming the second ingot into a second billet having a planar surface. The method further includes the steps of stacking the first and second billets such that the planar surface of the first billet contacts the planar surface of the second billet, bonding the first and second billets across their respective planar surfaces to form a composite billet, hot working the composite billet to form a composite plate having a preselected thickness and having a first layer and a second layer, and then heat treating the composite plate under conditions of time and temperature selected to obtain a first preselected combination of strength and toughness in the first layer and a second preselected combination of strength and toughness in the second layer.
Here and throughout this application the term “percent” or the symbol “%” means percent by weight or percent by mass. The term “face” means a planar surface of a plate or billet form of a steel alloy. The term “SBE” stands for “small but effective amount”.
The composition tables set forth above and in the detailed description are provided as convenient summaries of the alloys used in the present invention. They are not intended to restrict the lower and upper values of the ranges of the individual elements in each table for use in combination with each other, or to restrict the ranges of the elements for use solely in combination with each other. Thus, one or more of the element ranges of the broad composition in a table can be used with one or more of the other ranges for the remaining elements in a preferred composition in the same table. In addition, a minimum or maximum for an element of one preferred embodiment in a table can be used with the maximum or minimum for that element from another preferred embodiment in the same table.
The foregoing summary as well as the following detailed description will be better understood when read in view of the drawings wherein,
Referring now to
The balance of the alloy is iron and the usual impurities found in commercial grades of alloys intended for similar service or use. The levels of such elements are controlled to avoid adversely affecting the desired combination of strength, ductility, and toughness. More specifically, phosphorous is restricted to not more than about 0.003% because of its embrittling effect on the alloy. Sulfur, although inevitably present, is restricted to not more than about 0.0010%, because sulfur adversely affects the toughness provided by the alloy. Oxygen is restricted to not more than about 0.0010% and preferably is kept as low as possible. Similarly, nitrogen is restricted to not more than about 0.0010% and is also preferably kept as low as possible in the alloy. The alloy set forth in Table 1 is disclosed in U.S. Nonprovisional patent application Ser. No. 16/857,413, filed on Apr. 24, 2020, the entirety of which is incorporated herein by reference.
The second layer 30 is made from a steel alloy having the weight percent composition set forth in Table 2 below.
SBE-0.01
1SBE means small but effective amount.
The balance of the alloy is iron and usual impurities. The alloy set forth in Table 2 is disclosed in U.S. Pat. No. 5,268,044, the entirety of which is incorporated herein by reference. As described therein, effective amounts of cerium and lanthanum are present when the ratio Ce/S in the alloy is at least 2.
Referring now to
The balance of the alloy is iron and usual impurities. The alloy set forth in Table 3 is disclosed in U.S. Pat. No. 5,866,066, the entirety of which is incorporated herein by reference.
The balance of the alloy is iron and usual impurities. The alloy set forth in Table 4 is disclosed in US Patent Application Publication 2007/0113931A1, the entirety of which is incorporated herein by reference.
The alloys described in Tables 3 and 4 are designed to provide combinations of hardness, strength, and toughness that are intermediate the properties of the alloys described in Tables 1 and 2. In this manner, the three-layer embodiment of the armor plate shown in
Referring now to
An advantage of using only the alloys set forth in Tables 1-4 able to make the composite armor is that they are from the same alloying family and are heat treated similarly. Thus, the alloys are solution treated, quenched, refrigerated, and aged. The preferred solution treatment temperatures for each alloy are slightly different, but all of the alloys can be aged at about 900° F. The preferred heat treatment for each combination of steel layers would be selected to provide the highest hardness for the first outer layer.
Shown in
The gradient armor plate according to the invention can be produced by mechanically bonding two or more layers together. This can be achieved by forming billets from the ingots of each alloy to be included in the gradient armor plate as described above, grinding the planar surfaces of the billets to clean the surfaces (Steps 18 and 28.) and then stacking the billets with the ground surfaces in contact with each other. (Step 30.) It may be preferable to anneal the billets of each alloy prior to the surface grinding and cleaning step. (Steps 17 and 27.) The stacked billets can then be encased in a mild steel can (Step 32) and then hot isostatically pressed (HIP'd) to thermomechanically bond the billets together across their respective contacting planar surfaces (Step 34). The composite billet can then be hot rolled on a plate mill to form an elongated plate product having a desired thickness. (Step 36.) The plate is preferably cut into panels. (Step 37.) The mild steel can forms a cladding on the composite billet and plate during HIP′g and hot rolling. The cladding is removed from the plate panels, preferably by a grinding process. (Step 38.) The composite plate panels are then heat treated as described more fully below to develop the combinations of strength, hardness, and toughness that are needed for the armor application. (Step 40.) It will be appreciated by those skilled in the art that the process illustrated in
As an alternative to the process shown in
Heat treating to obtain the desired combination of properties in the gradient armor preferably proceeds as follows. The gradient armor plate is austenitized by heating it at about 1550° F.-1900° F. for about 1 hour plus about 5 minutes per inch of thickness and then quenching. The quench rate is preferably rapid enough to cool the alloy from the austenizing temperature to about 150° F. in not more than about 2 hours. The preferred quenching technique will depend on the thickness of the gradient armor plate. However, the hardenability of the alloys is good enough to permit air cooling, vermiculite cooling, or inert gas quenching in a vacuum furnace, as well as oil quenching. As an alternative, it is possible to austenitize the gradient armor plate using a two-step process in which the plate is first heated at about 1850-1900° F. for the time described above, cooled to room temperature, then heated at about 1750-1850° F. for a similar time, and then air cooled. After the austenitizing treatment, the armor plate is preferably cold treated as by deep chilling at about −100° F. for about 0.5-1 hour and then warmed in air.
Age hardening of the alloys used in the armor plate is preferably conducted by heating the gradient armor plate at about 850°−950° F. for up to about 8 hours, preferably at least about 6 or 7 hours, followed by cooling in air. To maximize the strength and toughness properties provided by the alloy, a double aging technique can be used. For example, instead of using a single aging treatment, the aging treatment can be performed with two, separate aging treatments at the aging temperature described above for about 3.5 to 4 hours each. When the two-step aging treatment is used, the armor plate is deep chilled as described above after the first aging step. The cold treatment step between aging steps ensures maximum transformation of any reverted austenite to martensite. If desired, a second cold treatment step can be performed after the second aging step.
Another advantage of the gradient armor plate of this invention is that because the four alloys are from the same alloy family, the same metallurgical phases would be present in each alloy layer and the phase transformation temperatures will be similar. The alloys used in the gradient armor plate according to the invention have a ductile Fe—Ni lath martensite structure in the matrix which is hardened by the precipitation of M2C carbides. In addition, the coefficients of thermal expansion of the alloy should also be similar, so there would be a lower likelihood of the steel layers delaminating.
The terms and expressions which are employed in this specification are used as terms of description and not of limitation. There is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. It is recognized that various modifications are possible within the invention described and claimed herein.
This application claims the benefit of Provisional Patent Application No. 63/040,616 filed Jun. 18, 2020, the entirety of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63040616 | Jun 2020 | US |
