Steel and device created therewith for ballistic protection of living things, machinery and equipment, and / or buildings

Abstract

The invention relates to a use of a steel as a material for ballistic protection of living things and / or machinery and equipment and / or buildings, said steel having a tensile strength of > 780 MPa. According to the invention, said steel is a multi-phase steel having a hardness of < 330 HB and consisting of (in wt.%) C: 0.08 to 0.35, Mn: 0.80 to 3.50, Mo: 0.10 to 1.00, optionally one or more of the following elements: N: 0.0020 to 0.0160, S: up to 0.020, Cr: 0.050 to 1.0, P: up to 0.050, Cu: 0.001 to 1.0, Si: 0.05 to 1.5, Al: 0.0030 to 1.0, Ni: 0.03 to 1.50, Nb: 0.005 to 0.150, Ti: 0.005 to 0.150, V: 0.001 to 0.300, B: 0.0005 to 0.0050, and Ca: 0.0005 to 0.0060, the remainder iron and unavoidable impurities, and having a microstructure in which the sum of the volume percentages of the microstructure constituents martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite is at least 30.0 volume percent and in which the remaining microstructure consists of ferrite and pearlite, the volume percentage of the microstructure constituent ferrite in the microstructure being at least 20.0 volume percent. The invention also relates to a device for ballistic protection of living things and / or machinery and equipment and / or buildings, comprising at least one planar component which comprises, at in a region of ballistic protective effect, at least one steel layer made of a steel having a tensile strength of > 780 MPa, said steel being a corresponding multi-phase steel having a hardness of < 330 HB.

Description

[0001] Steel and equipment made from it for ballistic protection of living beings, devices and / or structures

[0002] The invention relates to a steel for use as a material for ballistic protection of living beings, devices and / or structures, which has a tensile strength of more than 780 MPa.

[0003] The invention further relates to a device for the ballistic protection of living beings, devices and / or structures, with at least one flat component, in particular a wall, which has at least one steel layer made of a steel with a tensile strength of more than 780 MPa in at least one area of ​​ballistic protection.

[0004] For such purposes, high-hardness tempering steels with 400 HB to 650 HB (HB: Brinell hardness) or materials with even higher hardness, such as maraging steels or ceramics, are usually used.

[0005] The use of high-hardness materials is based on the experience that high hardness of the material used ensures high ballistic protection. Various studies have shown that devices made of high-hardness materials (HB > 400) exhibit significantly better resistance to failure from projectiles impacting with high kinetic energy compared to devices made of materials with a hardness below 400 HB (T. Demir, M. Übeyli, and RO Yildrim. "Effect of Hardness on the Ballistic Impact Behavior of High-Strength Steels Against 7.62-mm Armor Piercing Projectiles," JMEPEG (2009) 18:145-153).

[0006] The particular advantage of using high-strength, particularly hard steels was seen in their suitability as a cost-effective material for securing protective structures. By manufacturing the walls of the component used for this purpose as a composite material with a steel / glass fiber reinforced plastic / steel layer structure, the protective effect can be increased, while the GRP insert can also prevent the dreaded breakout of hard sheets on the back of the component wall opposite the impact surface.However, the inherently good suitability of high-strength, high-hardness steels of the type described above as a material for ballistic protection brings with it, in addition to the problem of the steel material breaking out and tearing open when projectiles hit with high kinetic energies, the problem that relatively large material thicknesses of 30 mm and more are required in order to reliably achieve the desired protective effect.

[0007] Document DE 102 20476 B9 describes the use of martensitic hot-rolled strip with a tensile strength of more than 800 MPa and a hardness of approximately 340 HB as a cost-effective alternative to conventional materials with a hardness of more than 400 HB. Due to the lower hardness and strength compared to high-hardness steels, martensitic hot-rolled and cold-rolled strip can be formed, for example, by roll forming. However, forming operations such as deep drawing, which place high demands on the material's ductility, are only feasible to a very limited extent with martensitic steels.

[0008] The document DE 102018220 116 A1 describes a flat product consisting of a multi-layer composite with a ballistic layer made of a safety steel with a predominantly martensitic and / or bainitic microstructure, in which martensite, tempered martensite and / or bainite are present with at least 70 area% and up to 30 area% of more ductile phases such as retained austenite and / or ferrite can be present.

[0009] The object of the invention is therefore to provide a steel material that is sufficiently formable and provides a high level of protection against projectile penetration even with relatively thin material thicknesses. A further sub-objective of the invention is to provide a corresponding device that offers sufficient ballistic protection even with a more complex shape of its flat component.

[0010] The object is achieved according to the invention by a use having the features of independent claim 1 and a device having the features of independent claim 7. Preferred embodiments of the invention are specified in the subclaims, which may each individually or in combination represent an aspect of the invention.

[0011] With regard to the steel for use as a material for ballistic protection of living beings and / or devices and / or structures, which has a tensile strength of more than 780 MPa, this object is achieved by a multi-phase steel with a hardness of less than 330 HB, which consists of (in weight %) C: 0.08 to 0.35 Mn: 0.80 to 3.50, Mo: 0.10 to 1.00, optionally one or more of the following elements: N: 0.0020 to 0.0160, S: up to 0.020, Cr: 0.050 to 1.0, P: up to 0.050, Cu: 0.001 to 1.0, Si: 0.05 to 1.5, Al: 0.0030 to 1.0, Ni: 0.03 to 1.50, Nb: 0.005 to 0.150, Ti: 0.005 to 0.150, V: 0.001 to 0.300, B: 0.0005 to 0.0050 and Ca: 0.0005 to 0.0060, the remainder being iron, including usual steel-accompanying impurities caused by melting, and having a structure in which the sum of the volume fractions of the structural components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite is at least 30,0 volume% and the residual structure consists of ferrite and pearlite, with the volume fraction of the ferrite component in the structure being at least 20.0 volume%. This multi-phase steel is excellently suited for cold-forming into devices for the ballistic protection of living beings, devices and / or structures or their subcomponents. The multi-phase steel has a hardness of less than 300 HB. Furthermore, the multi-phase steel is, in particular, a dual-phase steel. In general, the structure of such a dual-phase steel has, on the one hand, ferrite with more than 30 volume% (> 30 volume% and < 70 volume%) and, on the other hand, martensite and tempered martensite with more than 10 volume% (> 10 volume% and < 70 volume%) as its two main components. To ensure a strength level of > 780 MPa for such a dual-phase steel,the minimum proportion of the harder phases martensite and tempered martensite is set at contents > 30 volume% (> 30 volume% and < 70 volume%), in particular > 50 volume% (> 50 volume% and < 70 volume%).

[0012] Such multi-phase steels, such as dual-phase steels, which consist of a hard and a soft phase, are, according to the literature (for example, C. Lesch, N. Kwiaton, and FB Klose “Advanced High Strength Steels (AHSS) for Automotive Applications - Tailored Properties by Smart Microstructural Adjustments”, steel reserach int. 87 (2017)), better suited for larger forming operations than martensitic steels.

[0013] The basic composition of the steel described here, as well as a possibility for its production as a multiphase steel in the form of a steel sheet, is generally known, for example from document WO 2022 / 207913 A1. In the present invention, a generally known multiphase steel is thus used according to the invention as a material for ballistic protection (e.g., resistance to fire and / or blast).

[0014] The information regarding the proportions (in weight %) of the optional elements N, Cr, Cu, Si, Al, Ni, Nb, Ti, V, B, and Ca in multi-phase steel refers to amounts adjusted by alloying the respective elements. A proportion of one of these elements below the specified proportion represents a level at which the corresponding element is part of the unavoidable impurities.

[0015] In particular, the steel has a carbon equivalent CEV between 0.49 and 0.60, whereby the carbon equivalent CEV is calculated according to the formula CEV = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 from the contents of the corresponding chemical elements C, Mn, Cu, Ni, Cr, Mo and V in % by weight.

[0016] The steel used in the invention has a low to moderately high carbon equivalent (CEV) and a hardness below 330 HB. The hardness of the steel used in the invention is in some cases significantly below the hardness considered in the prior art to be a prerequisite for good suitability as protection against ballistic impacts. Surprisingly, it has now been shown that this known steel withstands ballistic impacts and the locally very limited ballistic loads associated with this impact, with a projectile velocity of > 440 m / s, without cracking.This property, which has not been recognized by experts until now, in combination with its well-known good cold formability, which, however, relates to a larger surface area, means that the multi-phase steel according to the invention is superior to the harder steels recommended in the prior art for the production of ballistic protective structures.

[0017] The good protective effect of the multiphase steel used according to the invention is achieved even at material thicknesses < 4 mm. Furthermore, by ensuring that the steel remains crack-free even under localized deformation loads, the feared problem of fragments bursting off on the side of the material opposite the impact point, which is common with hard materials, does not occur with the multiphase steel according to the invention.

[0018] Preferably, the microstructure of the multi-phase steel comprises, on the one hand, ferrite with a proportion of > 32.0 volume% and < 70.0 volume% and, on the other hand, the sum of the microstructure components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite with a proportion of > 30.0 volume% and < 68.0 volume%. Particularly preferably, the microstructure of the multi-phase steel comprises, on the one hand, ferrite with a proportion of > 35.0 volume% and < 68.0 volume% and, on the other hand, the sum of the microstructure components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite with a proportion of > 32.0 volume% and < 65.0 volume%. The microstructural component pearlite has a volume fraction of < 0.1% (usually 0.0%) of the microstructure. The volume fraction of pearlite is therefore negligible.The ratio of the contents / volume fractions of the two aforementioned "main phases" of the microstructure (ferrite on the one hand, and the sum of the structural components martensite, tempered martensite, retained austenite, M / A phase, upper bainite, and / or lower bainite on the other) is quite balanced and, on average, slightly "ferrite-laden." Such a multiphase steel is well suited for larger forming operations.

[0019] According to a preferred embodiment of the invention, at least one of the elements C, Si, Mn and Mo in the multi-phase steel has the following proportion:

[0020] C: 0.09 to 0.20 wt%,

[0021] Si: 0.25 to 0.65 wt%,

[0022] Mn: 2.00 to 2.55 wt% and

[0023] Mo: 0.20 to 0.35 wt%. These proportions of the chemical elements mentioned provide an optimal combination of protective effect and formability.

[0024] According to a further preferred embodiment of the invention, the multi-phase steel has a yield strength of < 700 MPa and a notch impact energy at -40°C of > 80 J / cm 2 A steel described by such parameters has sufficient toughness.

[0025] Furthermore, the above-mentioned sub-task is achieved by a device for the ballistic protection of living beings, devices and / or structures, with at least one flat component, in particular a wall, which has at least one steel layer made of a steel with a tensile strength > 780 MPa at least in an area of ​​ballistic protection effect, in which this steel is a multi-phase steel with a hardness < 330 HB and consists of (in weight %) C: 0.08 to 0.35 Mn: 0.80 to 3.50, Mo: 0.10 to 1.00, optionally one or more of the following elements:

[0026] N: 0.0020 to 0.0160,

[0027] S: up to 0.020,

[0028] Cr: 0.050 to 1.0,

[0029] P: up to 0.050,

[0030] Cu: 0.001 to 1.0,

[0031] Si: 0.05 to 1.5,

[0032] AI: 0.0030 to 1.0, Ni: 0.03 to 1.50,

[0033] Nb: 0.005 to 0.150,

[0034] Ti: 0.005 to 0.150,

[0035] V: 0.001 to 0.300,

[0036] B: 0.0005 to 0.0050 and

[0037] Approx: 0.0005 to 0.0060,

[0038] The remainder consists of iron, including normal impurities associated with the melting process and has a structure in which the sum of the volume fractions of the structural components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite is at least 30.0 volume% and the remaining structure consists of ferrite and pearlite, whereby the volume fraction of the structural component ferrite in the structure is at least 20.0 volume%.

[0039] The device for the ballistic protection of living beings, devices, and / or structures can serve as a complete protective device in itself (e.g., a helmet or protective vest) or be a component of / a structural element for a larger unit (e.g., structural elements for "armoring" a vehicle). The steel layer made of the multiphase steel described here can also be manufactured in very complex shapes.

[0040] The advantages and embodiments of the invention mentioned in connection with the multi-phase steel according to the invention for use as a material for ballistic protection of living beings and / or devices and / or structures (e.g. for inhibiting ballistic attacks and / or explosions) also apply completely analogously to the device according to the invention for the ballistic protection of living beings, devices and / or structures or their steel layer / steel layers made of corresponding multi-phase steel.

[0041] The flat component is in particular designed in multiple layers, wherein at least one of these layers is formed as a steel layer made of the multi-phase steel according to the invention.

[0042] Preferably, the microstructure of the multi-phase steel comprises, on the one hand, ferrite with a proportion of > 32.0 volume% and < 70.0 volume% and, on the other hand, the sum of the microstructure components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite with a proportion of > 30.0 volume% and < 68.0 volume%. Particularly preferably, the microstructure of the multi-phase steel comprises, on the one hand, ferrite with a proportion of > 35.0 volume% and < 68.0 volume% and, on the other hand, the sum of the microstructure components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite with a proportion of > 32.0 volume% and < 65.0 volume%. The microstructural component pearlite has a volume fraction of < 0.1% (usually 0.0%) of the microstructure. The volume fraction of pearlite is therefore negligible.

[0043] According to a preferred embodiment of the device according to the invention, the flat component has at least one additional layer made of a high-strength tempering steel and / or a maraging steel. This additional layer is, in particular, composed of several individual parts. The flat component can have such a complex overall geometry that—unlike the multi-phase steel according to the invention—a corresponding layer made of high-strength tempering steel or maraging steel cannot be realized "in one piece" or only with very great effort.

[0044] According to a further preferred embodiment of the device according to the invention, it is provided that the flat component has at least one additional layer which is made of a fiber composite material, wherein the fiber composite material is in particular Kevlar and / or aramid.

[0045] An increase in the strength of the steel used can be achieved by increasing the martensite content. This can be achieved, in particular, by adding the element Mn. However, excessively high martensite contents, especially greater than 90% by volume, are detrimental to formability, so the Mn content is limited to 0.80 to 3.50% by weight, especially 2.00 to 2.55% by weight.

[0046] The martensite content can also be increased by the more costly but more effective

[0047] Element Mo can be controlled. The Mo content is therefore limited to 0.10 to 1.00 weight percent, in particular to 0.20 to 0.35 weight percent.

[0048] An alternative increase in strength can be achieved by adding carbon. However, an increased carbon content has a particularly negative impact on weldability, so the steel is limited to a carbon content of 0.08 to 0.35 wt%, preferably 0.09 to 0.20 wt%.

[0049] Silicon and aluminum are essential in the production of steel, particularly to achieve high strength. They also serve to prevent carbide formation during self-tempering. However, to improve the surface quality of the produced steel sheet, the Si content should be limited. If silicon is used, its content is limited to 0.05 to 1.50. Preferably, the silicon content of the steel is limited to 0.25 to 0.65 weight percent.

[0050] The steel according to the invention can be used not only on its own as a material for the production of components for protection against ballistic attacks, but can of course also be advantageously combined with other materials. For example, it may be advantageous to form the flat component or wall produced using the multiphase steel according to the invention in multiple layers, with one or more of these layers being formed by the multiphase steel according to the invention and at least one other layer being made of a different, harder material.

[0051] This harder material can be a tempering steel already used for this purpose in the prior art. These materials typically have hardnesses of 400 HB to 650 HB, but in contrast to the steel used in the invention, they exhibit significantly poorer forming behavior under extremely high loads limited to small impact areas, such as those caused by the impact of a projectile.

[0052] By combining the hard materials with the steel used according to the invention, the high formability of the soft multiphase steel according to the invention is optimally combined with the high hardness of a less easily formable material. A further increase in strength and energy absorption capacity can also be achieved by using the multiphase steel according to the invention together with a fiber composite material such as Kevlar or aramid.

[0053] The invention is explained below using an embodiment.

[0054] To demonstrate their suitability for the production of components / parts for ballistic protection, a steel A composed according to the invention was melted and cast into slabs. The composition of steel A is given in Table 1. The determined arsenic (As) and tin (Sn) contents, at 0.003 wt.% and 0.002 wt.%, are so low that the arsenic and tin content can be considered unavoidable impurities. The determined nickel (Ni) contents, at 0.029 wt.% and the boron (B) contents, at 0.0002 wt.%, are also within a range where nickel and boron can be considered unavoidable impurities.

[0055] The steel was then processed into an annealed hot strip (hot strip: hot-rolled strip sheet) analogously to the procedure known from document WO 2022 / 207913 A1. The procedure can be outlined as follows: A hot-rolled strip sheet made of steel of the said composition is heat-treated / annealed as a coil (e.g. by so-called batch annealing in a batch annealing plant), whereby it

[0056] (i) is heated to a temperature of more than 750 °C and assumes a temperature above 750 °C for a certain period of time, wherein the heating up to a limit temperature of 750 °C takes place in particular with an average heating rate in the range between 1 K / h and 300 K / h, and then

[0057] (ii) cooling to a temperature below 200 °C, the cooling being carried out between 750 °C and 200 °C at an average cooling rate of between 1 K / h and 300 K / h.

[0058] The typical average heating rate in the temperature range between 100 °C and 750 °C is 30 K / h - 170 K / h, the typical time period in which the strip sheet assumes a temperature above 750 °C is 5 - 15 h, the maximum temperature reached by the strip sheet is typically around 830 °C and the typical average cooling rate in the temperature range between 750 °C and 200 °C is around 20 K / h - 35 K / h.

[0059] The steel from the annealed hot-rolled strip has a resulting microstructure with the following volume fractions: ferrite 55.0 volume%, pearlite 0.0 volume%, and the sum of the microstructure components martensite, tempered martensite, retained austenite, M / A phase, upper bainite, and / or lower bainite: 45.0 volume%. The annealed hot-rolled strip thus obtained was then processed into sheet samples.

[0060] Ballistic tests were conducted on the sheet metal samples produced from steel A. The thickness d, the hardness HB, and the characteristic tensile test values ​​of the sheet metal samples produced from steel A are listed in Table 2. Table 2 also shows the results of ballistic tests and the conditions observed. From these results, a high level of protection against projectile penetration can be deduced, without spalling of the sample material on the side opposite the point of impact.

[0061] It was shown that the sheet metal samples produced from the steel A used according to the invention, with a wall thickness of less than 4 mm and a hardness significantly less than 330 HB (254 HB in the example), are equivalent in terms of ballistic protection to the steel samples known from document DE 102 20476 B9. The multiphase steel according to the invention has a tensile strength (> 800 MPa: 840 MPa in the example) that is quite comparable to the tensile strength of the martensitic steel of these known steel samples. This illustrates that the multiphase steel according to the invention, with comparable protection, is particularly suitable for the production of complex shaped parts / components by cold forming, the shaping of which cannot be easily achieved with the known materials for ballistic protection. Table 1

[0062] Table 2

[0063] *) JSP / FN / SC = Jacketed Soft Point, Flat Nose, Soft Core **) KD BoR, MH = No penetration, dent without crack, multi-hit

Claims

Patent claims 1. Use of a steel as a material for ballistic protection of living beings and / or devices and / or structures, which has a tensile strength > 780 MPa, said steel being a multi-phase steel with a hardness < 330 HB, which consists of (in weight %) C: 0.08 to 0.35 Mn: 0.80 to 3.50, Mo: 0.10 to 1.00, optionally one or more of the following elements: N: 0.0020 to 0.0160, S: to 0.020, Cr: 0.050 to 1.0, P: to 0.050, Cu: 0.001 to 1.0, Si: 0.05 to 1.5, Al: 0.0030 to 1.0, Ni: 0.03 to 1.50, Nb: 0.005 to 0.150, Ti: 0.005 to 0.150, V: 0.001 to 0.300, B: 0.0005 to 0.0050 and Ca: 0.0005 to 0.0060, the remainder being iron and unavoidable impurities, and having a structure in which the sum of the volume fractions of the structural components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite is at least 30.0 volume% and the remaining structure consists of ferrite and pearlite, the volume fraction of the structural component ferrite in the structure being at least 20.0 volume%.

2. Use according to claim 1, characterized in that the structure of the multi-phase steel comprises, on the one hand, ferrite with a proportion of > 32.0 volume% and < 70.0 volume% and, on the other hand, the sum of the structural components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite with a proportion of > 30.0 volume% and < 68.0 volume%.

3. Use according to claim 1 or 2, characterized in that the structure of the multi-phase steel comprises, on the one hand, ferrite with a proportion of > 35.0 volume% and < 68.0 volume% and, on the other hand, the sum of the structural components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite with a proportion of > 32.0 volume% and < 65.0 volume%.

4. Use according to one of claims 1 to 3, characterized in that at least one of the elements C, Si, Mn and Mo in the multiphase steel has the following proportion: C: 0.09 to 0.20 wt%, Si: 0.25 to 0.65 wt%, Mn: 2.00 to 2.55 wt% and Mo: 0.20 to 0.35 wt%.

5. Use according to one of claims 1 to 4, characterized in that the multiphase steel has a yield strength < 700 MPa and a notched bar impact energy at - 40 °C of > 80 J / cm 2 has.

6. Use according to one of claims 1 to 5, characterized in that the multiphase steel has an elongation at break of > 10%.

7. Device for the ballistic protection of living beings and / or devices and / or structures, with at least one flat component, in particular a wall, which has at least one steel layer made of a steel with a tensile strength > 780 MPa in at least one area of ​​ballistic protection, said steel being a multi-phase steel with a hardness < 330 HB and consisting of (in weight %) C: 0.08 to 0.35 Mn: 0.80 to 3.50, Mo: 0.10 to 1.00, optionally one or more of the following elements: N: 0.0020 to 0.0160, S: to 0.020, Cr: 0.050 to 1.0, P: up to 0.050, Cu: 0.001 to 1.0, Si: 0.05 to 1.5, AI: 0.0030 to 1.0, Ni: 0.03 to 1.50, Nb: 0.005 to 0.150, Ti: 0.005 to 0.150, V: 0.001 to 0.300, B: 0.0005 to 0.0050 and Approx.: 0.0005 to 0.0060, The remainder consists of iron and unavoidable impurities and has a structure in which the sum of the volume fractions of the structural components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite is at least 30.0 volume% and the remaining structure consists of ferrite and pearlite, whereby the volume fraction of the structural component ferrite in the structure is at least 20.0 volume%.

8. Device according to claim 7, characterized in that the structure of the multi-phase steel has, on the one hand, ferrite with a proportion of > 32.0 volume% and < 70.0 volume% and, on the other hand, the sum of the structural components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite with a proportion of > 30.0 volume% and < 68.0 volume%.

9. Device according to claim 7 or 8, characterized in that the structure of the multi-phase steel has, on the one hand, ferrite with a proportion of > 35.0 volume% and < 68.0 volume% and, on the other hand, the sum of the structural components martensite, tempered martensite, retained austenite, M / A phase, upper bainite and / or lower bainite with a proportion of > 32.0 volume% and < 65.0 volume%.

10. Device according to one of claims 7 to 9, characterized in that at least one of the elements C, Si, Mn and Mo in the multi-phase steel has the following proportion: C: 0.09 to 0.20 wt% Si: 0.25 to 0.65 wt% Mn: 2.0 to 2.55 wt% and Mo: 0.20 to 0.35 wt%.

11. Device according to one of claims 7 to 10, characterized in that the multiphase steel has a yield strength < 700 MPa and a notch impact energy at - 40 °C of > 80 J / cm 2 has.

12. Device according to one of claims 7 to 11, characterized in that the multi-phase steel has an elongation at break of > 10%.

13. Device according to one of claims 7 to 12, characterized in that the flat component has, at least in the area of ​​the ballistic protective effect, at least one further layer made of a high-strength heat-treated steel and / or a maraging steel.

14. Device according to one of claims 7 to 13, characterized in that the flat component has, at least in the area of ​​the ballistic protective effect, at least one additional layer made of a fiber composite material, the fiber composite material being in particular Kevlar and / or Aramid.

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