ARMOUR
A steel armour comprising between 90% and 50% bainite, the rest being austenite, in which excess carbon remains within the bainitic ferrite at a concentration beyond that consistent with equilibrium; there is also partial partitioning of carbon into the residual austenite. In one embodiment of the invention the bainite comprises in weight percent: carbon 0.6 to 1.1%, silicon 1.5 to 2.0%, manganese 0.5 to 1.8%, nickel up to 3%, chromium 1.0 to 1.5%, molybdenum 0.2 to 0.5%, vanadium 0.1 to 0.2%, balance iron save for incidental impurities. In particular it was noted that excellent properties were obtained if the manganese content is about 1% by weight. By forming the steel as a pearlite sheet the elements (310,410) of the panel can be formed easily by cutting or stamping before final transformation to bainite. Cutting may also occur after final transformation using water- jet or laser cutting. Alternatively hot forging elements is described. The invention notes that such armours may have holes or slots to fragment incoming projectiles.
This invention relates to armour systems and elements therefore and their manufacture. Although intended primarily for vehicles, the invention can be used in other ways, for example, personal body-armour, armouring buildings and vulnerable parts of ships, for example the bridge, to protect them against piracy.
In Patent Citation 0001: WO WO 2006/103431 A (THE SECREATRAY OF STATE FOR DEFENCE). 2006-10-05. an armour panel comprising a layer of ceramic armour elements and spacing means is characterised in that the spacing means comprises a lug on a side of a ceramic armour element arranged to co-operate with an adjacent ceramic armour element. The element of this publication is, in fact, is a three dimensional object having two faces substantially opposed to each other and having at least three sides joining the faces. Alternatively, the two faces may be circular and joined by one side. The spacing means provides substantially uniform spacing for formation of a bond line between sides of adjacent ceramic armour elements in the panel, a bond line being a layer of adhesive is formed between sides of adjacent ceramic armour elements.
An embodiment of WO2006/103431 utilises a hexagonal element shape which incorporates a lug on each side of the hexagonal element. When the ceramic armour element is rotated 60° through the axis of symmetry of the hexagonal transverse cross section of the ceramic armour element, the position of the lugs on the ceramic armour element is substantially the same. The lugs may be an integral part of the element moulded as part of the element. This hexagonal element shape with integral lugs has the advantage that assembly of the ceramic armour elements in the panel is simplified. When a panel is being assembled, elements are configured to tessellate. The hexagonal symmetry of the elements means that elements can be fitted into the array with minimal effort required for proper orientation to ensure tessellation.
The invention of WO2006/103431 has the further advantage that the lugs separate adjacent elements evenly, thus the requirement of an independent spacing means between each element can be dispensed with. The lugs on the element and the spacing provided between elements facilitate in-plane adhesive infusion and allow for adhesive to be distributed evenly between the elements without any voids. The element shape has the advantage that there is no need for the addition of extra material to fill interstitial voids between elements, as for example the small spheres in Patent Citation 0002: US 3523057 B (BUCK). 1970-08-04.
Patent Citation 0003: WO WO 2010/013054 A (THE SECRETARY OF STATE FOR DEFENCE). 2010-02-04.
published after the priority date hereof, describes a carbide free bainite steel which comprises between 90% and 50% bainite, the rest being austenite, in which excess carbon remains within the bainitic ferrite at a concentration beyond that consistent with equilibrium; there is also partial partitioning of carbon into the residual austenite. Such bainite steel has very fine bainite platelets (thickness 100 nm or less). In this specification the expression “Super Bainite Steel” is used for such steel.
It has now been found that the processes described in Super Bainite Steels of PCT Patent Application PCT/GB2009/050947 make for the easy and economic manufacture of armour elements, for example elements of the kind described in WO2006/103431. Furthermore a hardness of 630 Hv and more is obtained readily. The elements can be constructed with thicknesses of about two thirds of the ceramic elements described in WO2006/103431 more cheaply yet giving similar performance.
In this specification the word “element” in relation to armour means a component of the armour. It may, for example, comprise a tile which may or may not be physically linked to another tile, a shaped item or element of the kind described in WO2006/103431, or a sheet forming part of the armour.
In the present invention armour is characterised in that it comprises a plurality of elements of Super Bainite Steel.
Preferably the Super Bainite Steel comprises by weight percent: carbon 0.6% to 1.1%; manganese 0.3% to 1.8%; nickel up to 3%; chromium 0.5% to 1.5%; molybdenum up to 0.5%; vanadium up to 0.2%; sufficient silicon and or aluminium to render the bainite substantially carbide free; with the balance being iron save for incidental impurities.
Such steels can be very hard, 550 HV to 750 HV.
Silicon is preferred to aluminium both on cost grounds and for ease of manufacture, for armour steels aluminium would not, therefore, normally be used. The practical minimum silicon content is 0.5% by weight and it should not exceed 2% by weight. Excess silicon renders the process difficult to control.
Preferred ranges of some of the other constituents of the Super Bainite Steel, by weight percent, are: manganese 0.5% to 1.5%; chromium 1.0% to 1.5%; molybdenum to 0.2% to 0.5%; vanadium 0.1% to 0.2%.
By varying the manganese content, it has been found that the processing time can be varied as described in WO2010/013054, the higher the manganese content the longer the processing time. However, from a practical point of view it has been found that a manganese content of about 1% by weight percent provides a sensible compromise, producing a very hard product highly suitable for armour elements. In reality, the manganese content, even if 1% by weight percent is aimed for, will vary between about 0.9% and 1.1% by weight percent, thus in this context of this invention, the word “about” implies a possible variation of + or −10% from the quoted figures.
Super Bainite Steel armours comprising a plurality of elements made with constituents within the preferred ranges have been found to have extremely fine bainite platelets (platelet thickness on average 40 nm or less thick and usually above 20 nm thick) and hardness of 630 HV or greater and are substantially free of blocky austenite.
In one particularly advantageous configuration the elements are maintained in a fretwork construction within the armour by maintaining narrow uncut bridges between adjacent elements. In use the bridges help to maintain the elements in place, but will fail on the impact of an armour piercing round on one of the adjacent elements preventing the spread of the impact effects to adjacent elements. If necessary, the bridges can be made less deep than the elements themselves by partially cutting them through so that the bridges will break preferentially to avoid transmission of shocks from one element to another.
A further advantage of proving weakened bridges is that armour comprising a plurality of elements can be sold to vehicle manufacturers or other end users mounted in large fretted sheets to be broken or cut to the final shape or configuration as required.
Providing holes in the elements has advantages for some applications, as the holes deflect and break up armour piercing rounds, and will lighten an armour panel formed of such elements considerably. These holes can be round or in the form of slots or other suitable shape and formed by stamping, drilling, or laser or water-jet cutting while the steel is in a pearlite form by stamping or by laser or water-jet cutting once the final Super Bainite Steel is formed. If a forging process is used to manufacture elements the holes can be formed during the forging.
An armour panel may comprise a layer of armour elements and bridges means associated with one element in which the bridges join the element to adjacent elements. An element may comprise a three dimensional object having two faces substantially opposed to each other and having at least three sides joining the opposed faces. The bridges provide substantially uniform spacing between elements in which spacing a bond line is formed between sides of adjacent armour elements in the panel. A bond line is a layer of material between sides of adjacent armour elements. In this embodiment the panel may additionally be formed of material other than Super Bainite Steel.
In the embodiment described in the preceding paragraph rectangular or hexagonally shaped elements are convenient. For ease of manufacture with hexagonal elements joined by bridges, it has been found that the bridges are best placed at the angles formed between the lateral sides
The bridges create space for a controlled uniform bond line between the elements, equivalent to the width of the bridges. A bond line formed between the elements limits energy transfer from one element to adjacent elements by providing a means for energy absorption. Known armours do not have bond line achieved by the use of elements with bridges. In this embodiment, because of the reduction in energy transfer between elements, there is a high probability that armour elements in the panel remain intact and adjacent armour elements remain bonded to a backing plate. The shock absorbing properties of a panel made in accordance with this invention has the advantage that a plate or film of synthetic material for shock absorbing does not have to be added separately, as in, for example GB 2149482 A (HARRY) Dec. 6, 1985.
This invention has the further advantage that the bridges ensure that adjacent elements are evenly separated, thus there is no requirement for independent spacing means between each element. The bond line thus formed facilitates in-plane infusion of bond line material and allows it to be distributed evenly between the elements without any voids.
In a further embodiment, the invention the elements are hexagonal incorporating a lug on each side of such hexagonal elements. When the armour element is rotated 60° through the axis of symmetry of the hexagonal transverse cross section of the armour element, the position of the bridges on the armour element is substantially the same. In this form the elements are configured to tessellate. The hexagonal symmetry of the elements means that elements can be fitted into a frame with minimal effort required for proper orientation to ensure tessellation.
A method of manufacture of armour according to the invention includes the steps of:
cooling sufficiently a steel sufficiently quickly to avoid the formation of pearlite from a temperature above its austenitic transition temperature to a temperature above its martensite start temperature but below the bainite start temperature;
holding the steel at a temperature within that range for a sufficiently long period to transform it to Super Bainite Steel;
cutting the steel to form armour comprising a plurality of elements.
The cutting may be by laser or water-jet or other appropriate means.
In a still further aspect of the invention a method of manufacturing armour comprises:
initially cooling a steel having comprising by weight percent: carbon 0.6% to 1.1%, manganese 0.3% to 4%, nickel up to 3%, chromium 0.5% to 1.5%, molybdenum up to 0.5%, vanadium up to 0.2%, silicon 0.5% to 2%, and the balance iron save for incidental impurities into a fully pearlite state;
forming the steel into a plurality of elements;
reheating the steel to a fully austenitic state;
cooling sufficiently quickly to avoid the formation of pearlite from a temperature above its austenitic transition temperature to a temperature above its martensite start temperature but below the bainite start temperature;
holding the steel at a temperature within that range for a sufficiently long period to transform it to Super Bainite Steel.
The steel may be reheated into an austenite form and cooled to a pearlite form on one or more occasions prior to forming into a plurality of elements. Likewise it may be annealed in the pearlite form prior to formation of the elements.
In para [0026] elements may be formed by stamping, laser or water-jet cutting, or other suitable cutting means.
If the armour steel is to have holes or slots these can also be formed while the steel is in a pearlite state. Cutting elements, holes and slots is substantially easier and quicker when carried out while the steel is in a pearlite form than when the steel is transformed to its final super bainite condition. The significant advantage of using Super Bainite Steel rather than other hard steels to manufacture armour elements is the possibility of forming an intermediate pearlite condition wherein the steel is much more easily worked than in its final transformed condition.
In another aspect of the invention, a method of manufacture of armour according to the invention includes the step of hot forging billets of steel into armour elements whilst at temperature above its austenitic transition temperature.
In all these processes greatest hardness is achieved if the manganese content of the steel is about 1% by weight. It is to be understood that ‘about’ in this context means +or −10%.
For practical purposes the maximum temperature at which transformation takes place in this invention is 300° C. or less, but preferably it is in the range 190° C. to 260° C.
The invention will now be described in more detail with reference to the accompanying drawings in which:
In
A number of Super Bainite Steel elements are assembled to co-operate as in
A standard panel as described above contains fixing points to fix the panel to the article to be protected. Panels are assembled to include fixing elements (not shown). Fixing elements are essentially modified steel hexagons having the same dimensions as a Super Bainite Steel element, adapted to facilitate a bolt and adapted to enable lugs of adjacent elements to co-operate with the fixing element. Fixing elements are incorporated into the panel at any position, the position being determined prior to assembly of the panels. The panel will normally be mounted such the lower surfaces of the elements during assembly (24 in
Hot forging is an ideal way to produce individual the individual Super Bainite lugged tiles shown in
In
Each element is supported in a fret-like construction by retaining uncut portions between them to form bridges 216. The thickness of the elements may typically be between 6 and 8 mm, but the there is no reason why thicker or thinner elements to suit the particular application should not made. The processing times and parameters to make the Super Bainite Steel are adapted to suit following the principles described below. Stamping or drilling is carried out when the sheet is in a pearlite form as described in
Optionally, the elements may have holes 214 cut through, this again may be done by stamping or drilling when the sheet is in a pearlite form as discussed with reference to
Alternatively the holes 214 may be replaced by slots.
The elements shown in
The armour panels described in
It is preferred that the bainite transformation temperature is 260° C. or less; the transformation temperature must be above the martensite start temperature. However, transformation temperatures up to 300° C. may be used with steels having manganese content towards the lower end of the range specified (below about 0.7% by weight), or with very low carbon content (less than 0.7% by weight). However, it has been found that Super Bainite Steels made in this way have a lower hardness and may be less desirable for the purpose described in this invention.
In
For most applications, it is preferred that the bridges be retained between elements as shown in
Where the elements are of particularly thick plate, say more than 100 mm thick, the final transformation may be carried out by reducing the temperature from the austenite phase to a temperature just above the bainite transformation temperature and holding the plate at that temperature to ensure that it is uniform throughout the plate before lowering the temperature to one below the maximum bainite transformation temperature to allow final transformation to occur. If this is not done there is a risk that the plate will not transform throughout to Super Bainite.
The temperature/time/transformation diagram for Super Bainite steel used for armour according to the invention showing the effect of varying the manganese content is shown in
The final transformation from austenite to bainite is shown for thin plate (typically 6 to 8 mm) thick by curve 2. Here individual plates are air cooled, by separation of the plates; the cooling rate is typically 80° C./min for example. This avoids transformation to pearlite. If necessary the cooling rate should be controlled accordingly. The bainite transition for 0.5% by weight manganese is shown by the line 10, for 1.0% by weight manganese by line 612, and for 1.5% by weight manganese by line 614. Quenching will convert the material to martensite, the martensite start temperatures are shown by lines 620, 622 and 624 for 0.5%, 1.0% and 1.5% by weight manganese respectively. Failure to maintain the transformation temperature within the range indicates by curves 610, 612 or 614 as appropriate for adequate periods may risk partial transformation to martensite. The curves 630 (for 0.5% by weight manganese), 632 (for 1% by weight manganese) and 634 (for 1.5% by weight manganese) indicate transformation to pearlite which is to be avoided in the final transformation stage of the process. The bainite start temperature is the temperature above which bainite will not from. In
As the thickness of the plate increases, the greater the chance of the slower cooling at the centre of the plate allowing a partial pearlite phase to form at the centre and a less homogeneous structure is obtained. This can be avoided by following a cooling curve such as that marked 3, which is for a 1% by weight manganese steel in accordance with invention. In this case the temperature is reduced to one marked 4A just above the bainite transition start temperature 612 and held just above that transition temperature until the temperature within the plate is uniform. At that point (4B) the temperature is reduced to a point 5 within the transformation range and held within that range to allow the transformation to bainite to take place.
In
Claims
1. Armour comprising a plurality of elements of a carbide free bainite steel which comprises between 90% and 50% bainite, the rest being austenite, in which excess carbon remains within the bainitic ferrite at a concentration beyond that consistent with equilibrium.
2. Armour according to claim 1 wherein the bainite steel comprises by weight percent: carbon 0.6% to 1.1%; manganese 0.3% to 4%; nickel up to 3%; chromium 0.5% to 1.5%; molybdenum up to 0.5%; vanadium up to 0.2%, silicon in the range about 0.5% by weight to about 2% by weight and the balance iron save for incidental impurities.
3.-9. (canceled)
10. Armour according claim 1 wherein one or more elements has one or more holes therethrough.
11. Armour according to claim 10 wherein the holes comprise slots.
12. Armour according to claim 1 additionally comprising one or more bridges between adjacent elements.
13. Armour according to claim 12 wherein the sides of elements are uniformly spaced apart and a bond line is formed between the sides of the adjacent armour elements.
14. Armour according to claim 12 wherein the bridges are at corners formed between adjacent sides of elements.
15. Armour according to claim 12 wherein the elements comprise a fret like structure.
16. Armour according to claim 12 wherein the elements are hexagonal.
17. Armour according to claim 1 wherein an element has a lug on a side said lug separating said side from the side of an adjacent element.
18. Armour as claimed in claim 1 wherein the elements have a lug on each of their sides.
19. Armour as claimed in claim 18 wherein the lugs on each side of a first element are entirely on one hand (left or right) of the sides of the first element, the lugs on adjacent sides of a second element are entirely on the opposing hand of the sides of said second element when compared to the first element.
20. Armour as claimed in claim 19 wherein the lugs on each side of a first element are entirely on one hand of the sides of the said first element, the lugs on the sides of an adjacent second element are entirely on the opposing hand of the sides of said second element when compared to the first element and when the first element is rotated 60° about an axis of symmetry the position of the lugs on said first element in relation to the second element is substantially the same.
21. Armour according to claim 1 wherein an elastomeric material encapsulates the elements.
22. Armour according to claim 21 wherein a bond line between adjacent elements is filled, at least in part, with recycled material from vehicle tyres.
23. Armour according to claim 1 wherein individual elements are disposed between two layers.
24. (canceled)
25. A method of manufacture of armour including the steps of forming austenite steel comprising carbon 0.6% to 1.1%; manganese 0.3% to 4%; nickel up to 3%; chromium 0.5% to 1.5%; molybdenum up to 0.5%; vanadium up to 0.2%; sufficient silicon and or aluminium to render the bainite substantially carbide free; and the balance iron save for incidental impurities, cooling the steel sufficiently quickly to avoid the formation of pearlite to a temperature above its martensite start temperature but below the bainite start temperature and holding the steel with that temperature range for up to a week and a transforming step wherein the steel is transformed to a carbide free bainite steel which comprises between 90% and 50% bainite, the rest being austenite, in which excess carbon remains within the bainitic ferrite at a concentration beyond that consistent with equilibrium.
26. (canceled)
27. A method of manufacture of armour according to claim 25 wherein it additionally includes the step of forming a sheet of pearlite steel prior to the transforming step and cutting said pearlite sheet to form armour elements.
28. A method of manufacture of armour according to claim 27 wherein it includes the step of forming bridges between the elements.
29. A method of manufacture of armour according to claim 28 wherein it additionally includes the step of rendering said bridges more ductile than the elements.
30. (canceled)
31. A method of manufacture of an armour according to claim 27 wherein it additionally includes the step of the formation of one or more holes or slots in one or a plurality of elements.
32. A method of manufacture of an armour according to claim 25 wherein armour elements are hot forged when the steel is austenitic.
Type: Application
Filed: Aug 20, 2010
Publication Date: Jun 14, 2012
Inventors: Andrew G. Baxter (Salisbury), Peter Brown (Salisbury)
Application Number: 13/391,031
International Classification: F41H 5/02 (20060101); C21D 8/00 (20060101);