WO2008088282A1

WO2008088282A1 - Armour for human body ballistic protection, said armour comprising a duplex stainless steel alloy, and bullet proof vest comprising this armour

Info

Publication number: WO2008088282A1
Application number: PCT/SE2008/050041
Authority: WO
Inventors: Carl Johan Irander; Göran Berglund; Guocai Chai
Original assignee: Sandvik Intellectual Property Ab
Priority date: 2007-01-19
Filing date: 2008-01-15
Publication date: 2008-07-24
Also published as: SE0700142L; SE530848C2

Abstract

The present invention relates to an armour for human body ballistic protection comprising a duplex stainless steel alloy con- taining in weight-%: C max 0.2%, Si 0.05-2.0%, Mn 0.1 -10%, Cr 20-35%, Ni 0.1 -12%, Mo 0-6.0%, W 0-6%, Cu 0-3%, Co 0-5%, N 0.05-0.65%, balance Fe and normal occurring impurities, wherein the ferrite content is 25-75 volume-%, and said duplex stainless steel alloy has a yield point in tension exceeding 1400 MPa.

Description

Jo/hj

Applicant: Sandvik Intellectual Property AB

Armour for human body ballistic protection, said armour comprising a duplex stainless steel alloy, and bullet proof vest comprising this armour.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an armour for human body ballistic protection, and any type of armour used for protecting a human body against bullets fired by a firearm.

An example of such an armour is a ballistic sheet-like panel received in a pocket in a bullet proof vest for covering body organs of vital importance of the carrier of the vest, and this particular application will be discussed further below for illuminating the present invention but for that sake not restricting the cover- age of the invention thereto. Other applications of such an armour is in aeroplanes and cars, in which sheet-like panels may be introduced on selected locations for protecting humans inside the vehicles against bullets fired by a firearm.

It is important that such an armour is able to alone or together with another material layer arranged in front of or behind it both stop the bullet from reaching and penetrating into the body of a said human and by that risking to cause fatal injuries to the person and not cause to much trauma (damage of body tissue) to the person while stopping the bullet.

BACKGROUND OF THE INVENTION AND PRIOR ART

A bullet proof vest having pockets for receiving armour for bal- listic protection in the form of sheet-like panels is known through for example GB 108244. Such contemporary bullet proof vests are made of a low weight material, mostly Kevlar® and Dyneema®, since they have to allow the carrier, which may carry other heavy equipment, to move fast and accurately, since such vests are normally carried by soldiers, police officers, bodyguards and the like. As a consequence of this requirement for enabling proper movability of the carrier of the vest it may not be constructed to be able to stop a bullet from penetrating the vest all over the vest. This is the reason why armours mentioned above in the form of sheet-like panels are introduced into pockets covering body organs of vital importance, such as the heart, of the carrier, since a bullet has there to be stopped even if it has an impact angle being the most unfavourable from said carrier's point of view.

Such armours are then classified with respect to which type of ammunition they are able to stop, such as the Ballistic Standard of the Swedish Police Force, that requires for level 3 protection the armour to stop a round of Para 9.0, FMJ ammunition of type Vanas m/39B at 420 m/s, thus a full metal jacket bullet.

It is known to use such sheet-like panels made of polyethylene, but such panels have to be thick for obtaining the requirement according to some classifications, which negatively influences the way of moving and behaving of the carrier thereof, and in the case of for instance arrangement in cars or aeroplanes negatively influences the appearance of parts of these vehicles.

It is also known to use ceramic (aluminium oxide) sheet-like panels, but they have turned out to have a tendency to be pulverized when hit several times.

Sheet-like panels of carbon steel have also been used and turned out to function well, but the weight thereof may in certain applications be experienced to be a problem. SUMMARY OF THE INVENTION

The object of the present invention is to provide an armour for human body ballistic protection being improved with respect to such armours already known.

This object is according to the invention obtained by providing such an armour for human body ballistic protection, which com- prises a duplex stainless steel alloy containing in weight-%: C max 0.2%, Si 0.05-2.0%, Mn 0.1 -10%, Cr 20-35%, Ni 0.1-12%, Mo 0-6.0%, W 0-6%, Cu 0-3%, Co 0-5%, N 0.05-0.65%, balance Fe and normal occurring impurities, wherein the ferrite content is 25-75 volume-%, and said duplex stainless steel alloy has a yield point in tension exceeding 1400 MPa.

The present inventors have realized that duplex stainless steel alloys with this composition have the physical properties allowing them to be adapted to be very well suited for the demands put on an armour for human body ballistic protection. A sheet- like panel of such a duplex stainless steel alloy having a yield point in tension exceeding 1400 MPa may be given a considerably reduced thickness with respect to known ballistic sheet-like panels of carbon steel, so that a corresponding weight reduction of such a panel is possible without for that sake jeopardizing the proper function thereof. It is of course also possible to make the panel of said duplex stainless steel alloy just as thick and heavy as a former carbon steel panel while obtaining a better ability to stop bullets instead. A high yield point in tension also results in a high energy absorbing capacity resisting deformation of the armour, such as plate, better than a corresponding armour with a lower yield point in tension. This means that the bullet is initially more efficiently deformed which results in a greater area that may absorb energy. A yield point in tension exceeding 1400 MPa for such a duplex stainless steel alloy may be obtained by conventional cold working possibly followed by ageing thereof. The stainless property is also a clear advantage with respect to for instance said carbon steels. Duplex stainless steel alloys which may be prepared for this particular application as armour for human body ballistic protection are for instance those dis- closed in EP 220 141 , EP 708 845, EP 1 259 656 and WO 2006/049572.

According to an embodiment of the invention said duplex stainless steel alloy has a necking in rupture test corresponding to an area contraction exceeding 20%, preferably exceeding 30%. This feature of a said duplex stainless steel alloy is favourable for the ability to stop a bullet while keeping the required thickness of the armour at a low level. The area contraction is defined as (original area-area at rupture)/original area.

According to another embodiment of the invention said duplex stainless steel alloy has a rupture strain exceeding 5%, preferably exceeding 6%. The ductility of a said d uplex s tainless steel alloy makes it well suited for the use in an armour for human body ballistic protection, since it means that the material may be suitably extended before rupture thereof, so that a bullet may be stopped without causing too much trauma to a person carrying a ballistic sheet-like panel of this material close to the body. A high rupture strain value results in a high energy absorbing ca- pacity of the material.

It is pointed out that there may be a slight anisotropy of the duplex stainless steel alloy in the armour according to the present invention and that the limits mentioned for the yield point in ten- sion, area contraction and rupture strain in this disclosure are limits valid f or a pplication of a load t hereto i n all d irections, so that it has to be exceeded in all directions.

According to another embodiment of the invention said duplex stainless s teel alloy i s o ne o f UNS S 32750, UNS S32205, U NS

S32906, UNS S32101 and S3207, in which the latter is an alloy in which C is max 0.05%, Si max 2.0%, Mn max 3.0%, Cr 29- 35%, Ni 4.0-10%, Mo 3.0-5.0% and N 0.45-0.55%, balance Fe, all expressed in weight-%. It has turned out that all these duplex stainless steel alloys are after suitable working very well suited as armour for human body ballistic protection.

According to another embodiment of the invention the content of Ni in said duplex stainless steel alloy is 3-7 weight-%, preferably 4-7 weight-%. It has turned out that such a content of Ni is fa- vourable for obtaining a high yield point in tension improving the ability to stop a bullet of such an armour.

According to another embodiment of the invention the content of Cu in said duplex stainless steel alloy is above 0.2 weight-%. Also such a content of Cu has turned out to have a positive influence upon said yield point in tension.

According to another embodiment of the invention the content of N in said duplex stainless steel alloy is above 0.3 weight-%. This content of N improves the physical properties of the duplex stainless steel alloy.

According to another embodiment of the invention the content of Mn in said duplex stainless steel alloy is max 4 weight-%.

According to another embodiment of the invention said armour is designed as a ballistic sheet-like panel, which is an advantageous design of such an armour. It is pointed out that this panel is normally flat, but it may have any shape adapted to for in- stance the shape of a vehicle or the body of a person.

According to another embodiment of the invention said armour is a plate adapted to be introduced into pockets in bullet proof clothing. This is a suitable design of such an armour, since it may be given a low weight with respect to the energy absorbing ability and by that the ballistic protection ability thereof. It is pointed out that "clothing" is to be interpreted broadly and may also be clothing covering other parts of a body than the chest, such as legs and the head.

According to another embodiment of the invention the armour is a said plate designed to be introduced into a bullet proof vest for covering body organs of vital importance, which is a preferred use of such an armour thanks to the physical properties thereof. Said plate has to together with the vest material be able to stop a bullet and not result in unacceptable trauma, i.e. damage of body tissues thereunder. This may be obtained by stopping the bullet by the plate without penetrating it or by causing such a deformation of the bullet when passing through the plate that the bullet will stay within the vest.

The invention also relates to a use of a duplex stainless steel alloy as defined above as an armour for human body ballistic protection. The advantages of such a use of such a duplex stainless steel alloy thanks to the behaviour thereof when hit by a bullet as well as of the embodiments thereof defined in the dependent use claims appear clearly from the discussion above of the armour according to the present invention.

The invention also relates to a bullet proof vest having one or more pockets and one or more ballistic sheet-like panels intro- ducible into and/or received by these pockets for covering body organs of vital importance of a carrier of the vest, in which at least one ballistic sheet-like panel is made of a duplex stainless steel alloy as defined above. Such a bullet proof vest of a cer- tain material, such a Kevlar® and Dyneema®, having excellent ballistic protection properties while offering a high degree of comfort to the person carrying the vest is provided in this way.

According to an embodiment of the invention said ballistic sheet- like panel is designed to fulfil the Ballistic Standard of the Swedish Police Force, that requires for level 3 protection the armour to stop a round of Para 9.0, FMJ ammunition of type Vanas m/39B at 420 m/s. Said panel may then have a minimum thickness of 1 .0-1 .5 mm, so that the weight thereof may be low even if it covers a considerable area.

BRIEF DESCRIPTION OF THE DRAWING

Fig 1 is a simplified view illustrating the use of an armour for human body ballistic protection according to the present inven- tion in the form of a plate adapted to be introduced into a pocket in a bullet proof vest for covering body organs (the heart region) of vital importance.

DETAILED DESCRIPTION OF THE INVENTION

A high energy absorbing capability with respect to the thickness of a member in the form of an armour for human body ballistic protection is obtained by using a duplex stainless steel alloy according to the invention. The alloy according to the invention contains (in weight-%): C max 0.2% Si 0.05-2.0%

Mn 0.1 -10%

Cr 20-35% Ni 0.1 -12%

Mo 0-6.0%

W 0-6%

Cu 0-3%

Co 0-5% N 0.05-0.65% balance Fe and normal occurring impurities, wherein the ferrite content is 25-75 volume-%, and said duplex stainless steel alloy has a yield point in tension exceeding 1400 MPa.

Carbon (C) has limited solubility in both ferrite and austenite. The limited solubility implies a risk of precipitation of chromium carbides and the content should therefore not exceed 0.2 weight-%.

Silicon (Si) is utilized as desoxidation agent in the steel produc- tion and it increases the flowability during production and welding. However, too high contents of Si lead to precipitation of unwanted intermetallic phase, and the content thereof is limited to 2.0 weight-%.

Manganese (Mn) is added in order to increase the N-solubility in the material. However, it has been shown that Mn only has a limited influence on the N-solubility in the type of alloy in question. Instead there are found other elements with higher influence on the solubility. The content of Mn is limited to 0.1 -10 weight-%.

Chromium (Cr) should have a high content for getting a very good N-solubility in the material. The content should therefore be at least 20 weight-%. However, high contents of Cr increase the risk of intermetallic precipitations and the formation of CrN, for what reason the content of chromium should not exceed 35 weight-%.

Nickel (Ni) is used as austenite stabilizing element and is added in suitable contents in order to obtain the desired content of fer- rite. In order to obtain the desired relationship between the aus- tenitic and the ferritic phase with between 25-75 volume-%, preferably 40-60 volume-%, ferrite, an addition of 0.1-12 weight-

%, preferably 3-7 weight-% and most preferred 4 weight-% nickel is suitable.

Molybdenum (Mo) is an active element improving corrosion resistance in chloride environments. The Mo-content should here lie in the range of 0-6.0 weight-%. Tungsten (W) increases mainly the resistance to pitting corrosion. But the addition of too high contents of tungsten in combination with that the Cr-contents as well as Mo-contents are high, means that the risk of intermetallic precipitations increases. The W-content in the present invention should lie in the range of 0- 6.0 weight-%.

Copper (Cu) may be added in order to improve the general corrosion resistance as well as the structure stability and the pos- sibility to obtain a high yield point in tension. The Cu-content should be max 3.0 weight-%.

Cobalt (Co) has properties that are intermediate between those of iron and nickel. Therefore, a minor replacement of these ele- ments with Co, or the use of Co-containing raw materials (Ni scrap metal usually contains some Co, in some cases in quantities greater than 10%) will not result in any major change in properties. The addition of Co should be limited to 5.0 weight-%.

Nitrogen (N) is a very active element, which increases the corrosion resistance, the structural stability as well as the strength of the material. At high contents of N the risk of precipitation of chromium nitrides increases, especially when simultaneously the chromium content is high. The N-content should therefore be limited to max 0.65 weight-% and is preferably above 0.3 weight-%.

The content of ferrite is important in order to obtain good mechanical properties and corrosion properties. From a mechanical properties point of view a content of ferrite between 25-75 vol- ume-% is desirable in order to obtain good such properties. Furthermore, high contents of ferrite imply that the impact strength at low temperatures as well as the resistance to hydrogen- induced brittleness risks deteriorating. The content of ferrite is therefore 25-75 volume-%, preferably 40-60 volume-%. DESCRIPTION OF PREFERRED EMBODIMENTS

An experimental duplex stainless steel alloy according to the standard UNS S32750, which means a content in weight-% of C max 0.03, Si max 0.8, Mn max 1.2, Cr 24-26, Ni 6-8, Mo 3-5, N 0.24-0.32 and Cu max 0.5, balance Fe, was prepared and subjected to cold working and ageing for obtaining a yield point in tension or yield strength of 1455 MPa in the cold rolling direction and 1482 MPa in the direction transversal thereto.

A plate of a thickness of 1.3 mm was thus obtained and introduced into a bullet proof vest and three shots were fired by a 9 mm Lugar at a distance of 5 metres. The results of the tests are presented in Table 1 .

Table 1

s = bullet stopped

Accordingly, such a thin plate would be enough for together with the vest efficiently stop a bullet fired by a firearm of this type at a short distance. This is due to the high yield point in tension (yield strength) in combination with the area contraction and ductility of the duplex stainless steel alloy used for the armour.

A possible application of an armour for human body ballistic protection according to the present invention is schematically illustrated in Fig 1 , in which a ballistic sheet-like panel in the form of a plate 1 , as the one tested above, is introduced into a pocket 2 of a bullet proof vest 3 for covering body organs of vital importance, here the heart region. Such a vest may of course have a plurality of such pockets, and plates 1 may be introduced into certain of these before fulfilling particularly risky tasks, or they may always be there.

Other duplex stainless steel alloys according to the invention for such a use are the following:

UNS S32205: (in weight-%) C max 0.03, Si max 1.0, Mn max 2.0, Cr 22-23, Ni 4.5-6.5, Mo 3.0-3.5 and N 0.14-0.20.

UNS S32906: (in weight-%) C max 0.03, Si max 0.8, Mn 0.8-1.5, Cr 28-30, Ni 5.8-7.5, Mo 1.5-2.6, N 0.3-0.4 and Cu 0.8.

UNS S32101 : (in weight-%) C max 0.04, Mn 4-6, Si max 1 , Ni 1.35-1.70, Cr 21-22, Mo 0.1 -0.8, N 0.20-0.25 and Cu 0.1 -0.8.

S 3207: (in weight-%) C max 0.05, Si max 2.0, Mn max 3.0, Cr 29-35, Ni 4.0-10, Mo 3.0-5.0 and N 0.45-0.55.

All these alloys contain balance Fe and normally occurring impurities, wherein the ferrite content is 25-75 volume-%, and they have been worked to have a yield point in tension exceeding 1400 MPa in all directions.

Claims

1. Armour for human body ballistic protection, characterized in that it comprises a duplex stainless steel alloy containing in weight-%:

C max 0.2%

Si 0.05-2.0%

Mn 0.1 -10%

Cr 20-35% Ni 0.1 -12%

Mo 0-6.0%

W 0-6%

Cu 0-3%

Co 0-5% N 0.05-0.65% balance Fe and normal occurring impurities, wherein the ferrite content is 25-75 volume-%, and that said duplex stainless steel alloy has a yield point in tension exceeding

1400 MPa.

2. Armour according to claim 1 , characterized in that said duplex stainless steel alloy has a necking in rupture test corresponding to an area contraction exceeding 20%, preferably exceeding 30%.

3. Armour according to claim 1 or 2, characterized in that said duplex stainless steel alloy has a rupture strain exceeding 5%, preferably exceeding 6%.

4. Armour according to any of the preceding claims, characterized in that the content of Ni in said duplex stainless steel alloy is 3-7 weight-%, preferably 4-7 weight-%.

5. Armour according to any of the preceding claims, charac- terized in that said duplex stainless steel alloy is one of

UNS S32750, UNS S32205, UNS S32906, UNS S32101 and S3207, in which the latter is an alloy in which C is max 0.05%, Si max 2.0%, Mn max 3.0%, Cr 29-35%, Ni 4.0-10%, Mo 3.0-5.0% and N 0.45-0.55%, all expressed in weight-%, balance Fe.

6. Armour according to any of the preceding claims, characterized in that the content of Cu in said duplex stainless steel alloy is above 0.2 weight-%.

7. Armour according to any of the preceding claims, characterized in that the content of N in said duplex stainless steel alloy is above 0.3 weight-%.

8. Armour according to any of the preceding claims, charac- terized in that the content of Mn in said duplex stainless steel alloy is max 4 weight-%.

9. Armour according to any of the preceding claims, characterized in that it is designed as a ballistic sheet-like panel.

10. Armour according to claim 9, characterized in that it is a plate adapted to be introduced into pockets in bullet proof clothing.

1 1. Armour according to claim 10, characterized in that it is designed to be introduced into a bullet proof vest for covering body organs of vital importance.

12. Use of a duplex stainless steel alloy containing in weight-%: C max 0.2%, Si 0.05-2.0%, Mn 0.1-10%, Cr 20-35%, Ni 0.1-

12%, Mo 0-6.0%, W 0-6%, Cu 0-3%, Co 0-5%, N 0.05-

0.65%, balance Fe and normal occurring impurities, wherein the ferrite content is 25-75 volume-%, and said duplex stainless steel alloy has a yield point in tension exceeding 1400 MPa, as an armour for human body ballistic protection.

13. Use according to claim 12, wherein said armour is a ballistic sheet-like panel.

14. Use according to claim 13, wherein said panel is designed to be introduced into a pocket in clothing, such as a bullet proof vest.

15. Use according to claim 14, wherein said panel is used for covering body organs of vital importance of a person by be- ing introduced into a pocket of a said bullet proof vest.

16. Use according to claim 12, wherein said armour is arranged in a vehicle for ballistic protection of humans in said vehicle.

17. A bullet proof vest having one or more pockets and one or more ballistic sheet-like panels introducible into and/or received by these pockets for covering body organs of vital importance of a carrier of the vest, characterized in that said at least one ballistic sheet-like panel is made of a duplex stainless steel alloy as defined in any of claims 1 -8.

18. A bullet proof vest according to claim 17, characterized in that said ballistic sheet-like panel is designed to fulfil the Ballistic Standard of the Swedish Police Force, that requires for level 3 protection the armour to stop a round of Para 9.0, FMJ ammunition of type Vanas m/39B at 420 m/s.

19. A bullet proof vest according to claim 18, characterized in that said panel has a minimum thickness of 1 .0-1 .5 mm.

20. A bullet proof vest having one or more pockets adapted to receive at least one ballistic sheet-like panel for protecting body organs of vital importance of a carrier of the vest, the improvement consisting of the vest comprising at least one said panel made of a duplex stainless steel alloy as defined in any of claims 1 -8.