DE102020103831A1 - Method for producing a steel component and a steel component - Google Patents

Abstract

The invention relates to a method for producing a steel component from a three-layer steel material composite with a core layer 1, which, in addition to Fe and impurities that are unavoidable due to the manufacturing process, consists of C: 0.001 to 0.25%, Mn: 0.1 to 2.5%, S: up to 0.03%, H: up to 0.001%, and with two cover layers 2, 3 connected to the core layer 1 in a materially bonded manner, the side facing a load being referred to as the first cover layer 2 and the side facing away from the load being referred to as the second cover layer 3 , with each of the cover layers 2, 3 each made of a steel which, in addition to Fe and impurities that are unavoidable due to the manufacturing process, consists of C: 0.35 to 0.65%, Mn: 0.1 to 2.5%, S: to 0.03%, H: up to 0.001%, the condition K = Mn [% by weight] + 1000 × B [% by weight] with K = 1 to 6 in the core layer 1 and K = 0.5 to 7 is fulfilled in the cover layers 2, 3, and wherein the steel material composite for hot forming is heated to a temperature above Ac3 and then by hot forming and press hardening z u the steel component is reshaped, the reshaped steel material composite being incompletely hardened, the incompletely hardened structure consisting predominantly of martensite and up to 10% bainite and optionally residual austenite.

Description

The invention relates to a method for producing a steel component according to the features of claim 1 and a steel component produced according to this method according to the features of claim 16.

The safety steels known from the prior art are hardened to hardnesses of 400 HV10 and more for their intended use and accordingly have high strength in conjunction with limited ductility. The high hardness required for a security steel aims at a high penetration resistance against an impacting projectile, whereby the diameter of the projectile expands after the impact, whereby energy is dissipated and the penetration depth is minimized.

The properties that are required to meet the requirements for high hardness and high toughness are contrary and can usually only be provided by material composites. Such material composites, in particular made of different steels, are known in the prior art, for example from the European laid-open specification EP 2 123 447 A1 . A three-layer steel is disclosed, the outer layers (cover layers) of which are made from a hard steel with a hardness of more than 600 HB and which enclose a core layer made of a tougher steel with a hardness of only 300 to 350 HB.

The outer cover layer facing the direction of fire serves to break or deform the impacting projectile. The second, tougher core layer serves to absorb the energy of the bullet and stop the bullet. In addition, any cracks in the first top layer should be stopped. The third layer or second cover layer ultimately serves to prevent the projectile from penetrating or the remains of the projectile from penetrating and to avoid deformation of the component. The hardness of the top layers has meanwhile increased to 700 HV10 and more. The increase in hardness is accompanied by brittleness of the materials, so that when a bullet hits the surface, splinters can flake off the top layers. This can lead to personal injury and at the same time to a local weakening of a ballistic steel component.

Thyssenkrupp Steel Europe offers a three-layer steel TRISECURE 650, which surrounds one relatively soft armor steel layer from two relatively hard armor steel layers. The hardnesses are 650 HB / 450 HB / 650 HB. This three-layer steel, provided in the factory-hard condition, has a very good firing performance against hard core bullets of the .308 Win CBC P80 class. To set the factory-hard state, the steel is first hot-rolled and then quenched in a water quench. Very high cooling rates can be achieved by quenching in a water quench. In the case of low-alloy steels, this ensures that the steel is fully hardened even with thick sheet metal. This three-layer steel can only be used as a plate or edge part in the factory-hard condition. For use as a three-dimensionally shaped component, the material would have to be thermoformed, which means that the hard-working heat treatment condition is lost. During hot forming, cooling in the tool takes place at significantly lower cooling rates than in a water quench, so that with this tool-cooled steel a loss of hardness can be determined compared to the steel cooled in the water quench. A further loss of hardness results from the lacquer being burned in in the oven after cathodic dip painting, which is used for corrosion protection in civil vehicle construction. The loss of hardness in turn leads to a loss of performance of the armor steel.

Against this background, the task is to avoid the above-mentioned disadvantages and to show a method for manufacturing a steel component from a three-layer material composite that, even after hot forming, has a very good firing performance especially for the protection classes VPAM 9 or VPAM 10, in particular the bullet classes. 308 Win CBC P80 and 7.62 x 54 RB 32.

This object is achieved by a method with the features of claim 1. A component with the improved properties is the subject of patent claim 16.

The key to providing an improved three-layer steel material composite, in particular in the form of a steel component for ballistic purposes, lies in a combination of alloys specially designed for this purpose for the cover and core layers as well as a special temperature control that aims to ensure that the formed steel material is only partially hardened, the hardened structure predominantly consisting of martensite and containing up to 10% bainite and optionally austenite as the remainder. The desired goal is achieved by deliberately not fully hardening the top layers in particular. The so-called initial hardness, which can also be referred to as maximum hardness, is not achieved. A structure is set that is 3 - 25%, preferably 5 - 10% below the maximum achievable hardness values, i.e. H. below the initial hardness, remains.

The cover layers advantageously consist of the same alloys. Due to the uniform heat treatments for the two top layers, the two top layers also have the same mechanical properties. The steel component should be constructed symmetrically with regard to the layer composition, because asymmetrical layer compositions have different transformation points due to different alloys, so that different structural states would occur during quenching. This in turn can lead to component distortion, which is a hindrance to hot forming. Ultimately, this in turn means that an asymmetrical layer arrangement or structure distribution is technically difficult to implement in hot-formed components.

• C: 0,001 bis 0,25 %, insbesondere 0,1 bis 0,25 %, vorzugsweise 0,15 bis 0,22 %,
• optional Si: bis 1,2 %, insbesondere 0,03 bis 1,2 %, vorzugsweise 0,1 bis 0,6 %,
• Mn: 0,1 bis 2,5 %, insbesondere 0,1 bis 1,8 %, vorzugsweise 0,6 bis 1,3 %,
• optional P: bis 0,05 %, insbesondere 0,005 bis 0,03 %,
• S: bis 0,03 %, insbesondere bis 0,01 %, vorzugsweise bis 0,005 %, bevorzugt bis 0,003 %,
• optional N: bis 0,02 %, insbesondere 0,001 bis 0,015 %, vorzugsweise 0,002 bis 0,015 %, bevorzugt 0,002 bis 0,010%,
• optional Cr: bis 2,5 %, insbesondere 0,05 bis 2,5 %, vorzugsweise 0,5 bis 1,5 %,
• optional Cu: bis 1,0 %, insbesondere 0,005 bis 0,5 %,
• optional Nb: bis 0,2 %, insbesondere 0,005 bis 0,2 %, vorzugsweise 0,005 bis 0,1 %, bevorzugt 0,005 bis 0,04 %, besonders bevorzugt 0,02 bis 0,04 %,
• optional Ti: bis 0,2 %, insbesondere 0,005 bis 0,2 %, vorzugsweise 0,005 bis 0,1 %, bevorzugt 0,005 bis 0,04 %, besonders bevorzugt 0,02 bis 0,04 %,
• optional V: bis 0,2 %, insbesondere bis 0,1 %, vorzugsweise bis 0,05 %,
• optional W: bis 0,2 %, insbesondere bis 0,1 %, vorzugsweise bis 0,05 %,
• optional Mo: bis 1 %, insbesondere 0,01 bis 1%, vorzugsweise 0,01 bis 0,3 %,
• optional Ni: bis 5,5 %, insbesondere bis 1,0 %, vorzugsweise bis 0,5 %, bevorzugt bis 0,3 %,
• optional B: bis 0,01 %, insbesondere 0,0001 bis 0,007 %, vorzugsweise 0,001 bis 0,007 %,
• optional Sn: bis 0,05 %, insbesondere bis 0,04 %,
• optional As: bis 0,02 %,
• optional Co: bis 0,5 %,
• optional O: bis 0,005 %, insbesondere bis 0,002 %,
• H: bis 0,001 %, insbesondere bis 0,0006 %, vorzugsweise bis 0,0004 %, bevorzugt bis 0,0002
• optional Ca: bis 0,015 %, insbesondere 0,0005 bis 0,015 %, vorzugsweise 0,0005 bis 0,005 %,
• optional Al: bis 1,0 %, insbesondere 0,02 bis 0,6 %, vorzugsweise 0,02 bis 0,3 %,
• optional SEM: bis 0,01 %, insbesondere bis 0,005 % besteht.

According to the invention, a steel material is used for the core layer which, in addition to Fe and impurities that are unavoidable due to the manufacturing process, in% by weight

• C: 0.001 to 0.25%, in particular 0.1 to 0.25%, preferably 0.15 to 0.22%,
• optional Si: up to 1.2%, in particular 0.03 to 1.2%, preferably 0.1 to 0.6%,
• Mn: 0.1 to 2.5%, in particular 0.1 to 1.8%, preferably 0.6 to 1.3%,
• optional P: up to 0.05%, in particular 0.005 to 0.03%,
• S: up to 0.03%, in particular up to 0.01%, preferably up to 0.005%, preferably up to 0.003%,
• optional N: up to 0.02%, in particular 0.001 to 0.015%, preferably 0.002 to 0.015%, preferably 0.002 to 0.010%,
• optional Cr: up to 2.5%, in particular 0.05 to 2.5%, preferably 0.5 to 1.5%,
• optional Cu: up to 1.0%, in particular 0.005 to 0.5%,
• optional Nb: up to 0.2%, in particular 0.005 to 0.2%, preferably 0.005 to 0.1%, preferably 0.005 to 0.04%, particularly preferably 0.02 to 0.04%,
• optional Ti: up to 0.2%, in particular 0.005 to 0.2%, preferably 0.005 to 0.1%, preferably 0.005 to 0.04%, particularly preferably 0.02 to 0.04%,
• optional V: up to 0.2%, in particular up to 0.1%, preferably up to 0.05%,
• optional W: up to 0.2%, in particular up to 0.1%, preferably up to 0.05%,
• optional Mo: up to 1%, in particular 0.01 to 1%, preferably 0.01 to 0.3%,
• optional Ni: up to 5.5%, in particular up to 1.0%, preferably up to 0.5%, preferably up to 0.3%,
• optional B: up to 0.01%, in particular 0.0001 to 0.007%, preferably 0.001 to 0.007%,
• optional Sn: up to 0.05%, in particular up to 0.04%,
• optional As: up to 0.02%,
• optional Co: up to 0.5%,
• optional O: up to 0.005%, in particular up to 0.002%,
• H: up to 0.001%, in particular up to 0.0006%, preferably up to 0.0004%, preferably up to 0.0002
• optional Ca: up to 0.015%, in particular 0.0005 to 0.015%, preferably 0.0005 to 0.005%,
• optional Al: up to 1.0%, in particular 0.02 to 0.6%, preferably 0.02 to 0.3%,
• optional SEM: up to 0.01%, in particular up to 0.005%.

• C: 0,35 bis 0,65 %, insbesondere 0,40 bis 0,60 %, vorzugsweise 0,40 bis 0,58 %, bevorzugt 0,40 bis 0,55 %,
• optional Si: bis 1,2 %, insbesondere 0,03 bis 1,2 %, vorzugsweise 0,05 bis 0,6 %, besonders bevorzugt 0,10 bis 0,6 %,
• Mn: 0,1 bis 2,5 %, insbesondere 0,1 bis 1,9 %, vorzugsweise 0,6 bis 1,5 %,
• optional P: bis 0,05 %, insbesondere 0,005 bis 0,03 %,
• S: bis 0,03 %, insbesondere bis 0,01 %,
• optional N: bis 0,02 %, insbesondere 0,001 bis 0,015 %,
• optional Cr: bis 3,5 %, insbesondere 0,1 bis 2,5 %, vorzugsweise 0,5 bis 2,0 %, bevorzugt 0,7 bis 2,0 %,
• optional Cu: bis 1,0 %, insbesondere 0,005 bis 0,5 %,
• optional Nb: bis 0,2 %, insbesondere bis 0,1 %, vorzugsweise bis 0,04 %,
• optional Ti: bis 0,2 %, insbesondere bis 0,1 %, vorzugsweise bis 0,04 %,
• optional V: bis 0,8 %, insbesondere 0,04 bis 0,25 %, vorzugsweise 0,06 bis 0,2 %,
• optional W: bis 1,5 %, insbesondere bis 1,3 %, vorzugsweise bis 0,7 %, bevorzugt bis 0,2 %, weiter bevorzugt bis 0,1 %, besonders bevorzugt bis 0,04 %,
• optional Mo: bis 1,5 %, insbesondere bis 0,5 %, vorzugsweise bis 0,3 %,
• optional Ni: bis 5,5 %, insbesondere bis 2,0 %, vorzugsweise bis 1,5 %,
• optional B: bis 0,01 %, insbesondere bis 0,007 %,
• optional Sn: bis 0,05 %, insbesondere bis 0,04 %,
• optional As: bis 0,02 %,
• optional Co: bis 0,5 %,
• optional O: bis 0,005 %, insbesondere bis 0,002 %,
• H: bis 0,001 %, insbesondere bis 0,0006 %, vorzugsweise bis 0,0004 %, bevorzugt bis 0,0002 %,
• optional Ca: bis 0,015 %, insbesondere 0,0005 bis 0,005 %,
• optional AI: bis 2,0 %, insbesondere bis 1,0 %, vorzugsweise bis 0,5 %, bevorzugt bis 0,3 %,
• optional SEM: bis 0,01 %, insbesondere bis 0,005 % besteht.

Furthermore, the two cover layers are firmly bonded to the core layer. The side facing the load is referred to as the first cover layer and the side facing away from the load is referred to as the second cover layer. A load is to be understood as a ballistic load. The two top layers consist of iron and unavoidable impurities in weight percent due to the manufacturing process

• C: 0.35 to 0.65%, in particular 0.40 to 0.60%, preferably 0.40 to 0.58%, preferably 0.40 to 0.55%,
• optional Si: up to 1.2%, in particular 0.03 to 1.2%, preferably 0.05 to 0.6%, particularly preferably 0.10 to 0.6%,
• Mn: 0.1 to 2.5%, in particular 0.1 to 1.9%, preferably 0.6 to 1.5%,
• optional P: up to 0.05%, in particular 0.005 to 0.03%,
• S: up to 0.03%, in particular up to 0.01%,
• optional N: up to 0.02%, in particular 0.001 to 0.015%,
• optional Cr: up to 3.5%, in particular 0.1 to 2.5%, preferably 0.5 to 2.0%, preferably 0.7 to 2.0%,
• optional Cu: up to 1.0%, in particular 0.005 to 0.5%,
• optional Nb: up to 0.2%, in particular up to 0.1%, preferably up to 0.04%,
• optional Ti: up to 0.2%, in particular up to 0.1%, preferably up to 0.04%,
• optional V: up to 0.8%, in particular 0.04 to 0.25%, preferably 0.06 to 0.2%,
• optional W: up to 1.5%, in particular up to 1.3%, preferably up to 0.7%, preferably up to 0.2%, more preferably up to 0.1%, particularly preferably up to 0.04%,
• optional Mo: up to 1.5%, in particular up to 0.5%, preferably up to 0.3%,
• optional Ni: up to 5.5%, in particular up to 2.0%, preferably up to 1.5%,
• optional B: up to 0.01%, in particular up to 0.007%,
• optional Sn: up to 0.05%, in particular up to 0.04%,
• optional As: up to 0.02%,
• optional Co: up to 0.5%,
• optional O: up to 0.005%, in particular up to 0.002%,
• H: up to 0.001%, in particular up to 0.0006%, preferably up to 0.0004%, preferably up to 0.0002%,
• optional Ca: up to 0.015%, in particular 0.0005 to 0.005%,
• optional AI: up to 2.0%, in particular up to 1.0%, preferably up to 0.5%, preferably up to 0.3%,
• optional SEM: up to 0.01%, in particular up to 0.005%.

Due to the interaction of the alloying elements between the individual layers in the steel material composite, a higher toughness can be set in the core layer compared to the cover layers, whereby a high hardness can be set in the cover layers, especially in the hardened, but not maximally hardened state of the safety steel. Said properties can be achieved while minimizing component distortion, in particular by choosing the same or a very similar composition (for example from different melts of the same target composition) for the first and second cover layer.

In the case of the alloy used according to the invention, Mn and preferably, but optionally, B are specifically alloyed. Mn and B normally avoid the formation of bainite by shifting the bainitic transformation towards longer cooling times. In this application, however, this leads to the control of the bainite content in the final structure. For this reason, the composition of the composite material should adhere to a characteristic value K, which is between 1 and 6 in the core layer and between 0.5 and 7 in the top layer. The characteristic value is determined according to the following equation: $$\text{K}=\text{Mn}\left[\text{Weight}.-\%\right]+1000\times \text{B.}\left[\text{Weight}.-\%\right].$$

In the core layer, the characteristic value K is at least 1, in particular at least 2, preferably at least 2.5, particularly preferably at least 2.7 with an upper limit of at most 6, in particular at most 5, preferably at most 4.5 and particularly preferably at maximum. 4.2.

In the outer layers, the lower limit for the characteristic value K is at least 0.5, in particular at least 0.6, preferably at least 0.7, particularly preferably at least 0.8. The upper limit for the parameter K in the outer layers is a maximum of 7, in particular a maximum of 6, preferably a maximum of 5, particularly preferably a maximum of 4.5.

By adhering to this characteristic value, the bainitic transformation is deliberately shifted to longer times in order to avoid excessive bainite formation during the hot forming process.

abgeschätzt werden.The lower limit for preheating in the course of hot forming is at least the Ac3 temperature of the cover layers, in particular at least the Ac3 temperature of the core layer. They are typically heated to between 910 ° C and 960 ° C over a certain holding period. The duration depends on the total thickness of the steel composite and the size of the cut. The duration in minutes can be according to the formula $$\text{Total thickness}\left[\text{mm}\right]\times 2+\left(5-10\text{min}.\right)$$

be estimated.

After forming, the blank is cooled down in such a way that the material of the cover layers is not completely hardened, but mainly martensite, up to 10% bainite and optionally has residual austenite. As a result, the incompletely hardened structure has a hardness that _{remains below the so-called initial hardness HV 0} in the bullet-breaking cover layer. The initial hardness is determined by the following formula A. Latz et al .: Modeling of Hardenability and Tempering of High-Strength Structural Steels. HTM J. Heat Treatm. Mat. 74 (2019) Are defined: $${\text{HV}}_0\left(\text{in HV}10\right)=295+922\times \left(\text{C in wt}.-\%\right).$$

The lower limit for the crack hardness in the bullet-breaking top layer should be at least 600 HV10, in particular at least 620 HV10, preferably at least 650 HV10 and particularly preferably at least 680 HV10, the upper limit being arbitrary, in particular max. 950 HV10, preferably max. 850 HV10, of which particularly preferably a maximum of 820 HV10.

The _{initial hardness HV 0} in the crack-stopping core layer should theoretically have any lower limit. The lower limit is preferably at least 300 HV10, preferably at least 350 HV10, particularly preferably at least 400 HV10, with the upper limit of the crack hardness in the crack-stopping core layer being max. 600 HV10, in particular max. 550 HV10, preferably max. 500 HV10.

The hardness of the incompletely hardened structure of the bullet-breaking cover layer remains 3 - 25%, preferably 5 - 10% below the maximum values of the above-mentioned initial hardnesses. After the hot forming or press hardening in the top layer, the steel component should preferably have a hardness of 630-900 HV10, preferably 650-850 HV10, particularly preferably 720-800 HV10.

Before the hot forming, the steel material composite should be provided, in particular in the hardened state, preferably in a state hardened to the initial hardness. Although the structural condition is initially destroyed and changed by austenitizing and press hardening, the fine-grained initial structure of the steel composites hardened to initial hardness simplifies the subsequent hot forming and heat treatment and, in particular, enables a high level of toughness to be set on the component.

The desired structure with the aforementioned properties is achieved in particular in that the formed steel component is cooled down more slowly after the hot forming, in particular in the press tool. The cooling rate should be set higher above the martensite start temperature Ms than below the martensite start temperature Ms. In particular in a temperature range between 200 ° C. and 150 ° C., a particularly low cooling rate should be selected. The three-layer steel composite should be cooled relatively quickly down to the martensite temperature. After that, more slowly. When the temperature falls below the martensite start temperature, which is typically around 430 ° C, the structural transformation begins and with further cooling, a large proportion of strength-increasing martensite quickly forms Temperature range between 150 ° C and 250 ° C a self-tempering effect of the three-layer steel composite. This leads to an increase in the toughness of the three-layer steel. Depending on the further process steps, the thermoformed component can be cooled to room temperature, in particular continuously, or else it can be kept at an elevated temperature at up to 200 ° C. initially.

• für eine Gesamtdicke von 2,5 mm ergeben sich die maximalen Abkühlgeschwindigkeiten von:
  • oberhalb Ms: 40 bis 100 K/s
  • unterhalb Ms: 10 bis 40 K/s
• für eine Gesamtdicke von 40 mm ergeben sich die minimalen Abkühlgeschwindigkeiten von:
  • oberhalb Ms: 1 bis 5 K/s
  • unterhalb Ms: 0,1 bis 1 K/s.

The cooling rate depends on the total thickness used (sheet thickness) of the three-layer steel composite. The greater the total thickness, the lower the cooling rate is set. For steel components with wall thicknesses between 2.5 mm and 40 mm, the cooling rates should be within the following limits:

• for a total thickness of 2.5 mm, the maximum cooling speeds are:
  • above Ms: 40 to 100 K / s
  • below Ms: 10 to 40 K / s
• for a total thickness of 40 mm, the minimum cooling speeds are:
  • above Ms: 1 to 5 K / s
  • below Ms: 0.1 to 1 K / s.

As an example, a cooling rate above Ms of 5 to 15 K / s can be specified for a sheet thickness of 8.5 mm and for the temperature range below Ms 1 to 3 K / s.

Optionally, the hot-formed steel component can also be tempered after the hot forming and cooling, for a period of 1 to 50 minutes, in particular for a period of 10 to 30 minutes at temperatures between 150 ° C and 250 ° C. This increases the toughness of the three-layer composite material and in particular of the top layer. In principle, the toughness of the core layer is also increased, but the alloy selected for the core layer has a lower hardness from the outset and already has increased toughness.

In an advantageous further development of the invention, the tempering takes place in a process-economical manner during a paint burn-in after the cathodic dip painting, which is carried out in the said temperature range.

As a result, after tempering, the steel component should preferably have a hardness of the cover layers in a range of 600-880 HV10, preferably 600-820 HV10, particularly preferably 670-750 HV10. Such a hot-formed and press-hardened steel component, which deliberately does not have the maximum possible hardness, but values that are 3 - 25%, particularly preferably 5 - 10% below the maximum, has the very positive property that the top layers are prone to cracking and chipping is greatly reduced. This enables better personal protection and also a lower probability of failure of the component in the event of fire.

According to the invention, the steel components for ballistic purposes are produced by a suitable alloy in combination with cooling rates which are suitable for hot-forming tools. In addition, the temperature control makes use of a self-starting effect and, optionally, subsequent starting is carried out. Particularly suitable thermoformed, ballistically used press-hardened components have hardnesses in the top layers of preferably 630-900 HV10, preferably 650-850 HV10, particularly preferably 720 HV10-800 HV10 and in the press-hard and tempered state preferably 600-880 HV10, preferably 600 - 820 HV10, particularly preferably 670 HV10. In the press-hard state, the hardnesses of the top layer / core layer / top layer are 630/300/630-900/600/900 HV10, preferably 630/350/630 - 850/550/850 HV10, particularly preferably 720/400/720 - 800/500 / 800 HV10 and in the press-hard and tempered state from 600/300/600 - 880/600/880 HV10, preferably 600/350/600 - 820/550/820 HV10, particularly preferably 670/400/670 - 750/500/750 HV10 viewed as particularly cheap. The depth of decarburization in the top layers is advantageously no greater than 75 μm. The decarburization leads to a loss of hardness and thus to a reduction in the bullet-breaking effect. By reducing the depth of decarburization, the result is that the impacting bullet does not dig into the sheet metal.

• Decklage jeweils ≥10 %, bevorzugt jeweils ≥20 %, besonders bevorzugt jeweils ≥25 % und Kernlage: ≥4 %, bevorzugt ≥15 % , besonders bevorzugt ≥35 % der Gesamtdicke, bevorzugt in den Kombination 30 %/40 %/30 % oder 40 %/20 %/40 %,, wobei die angegebenen Dickenanteile produktionsbedingt um jeweils maximal 5 %, insbesondere maximal 3 %, der Gesamtdicke schwanken können.

The steel composite material provided should preferably have the following thickness ratios:

• Cover layer in each case ≥10%, preferably in each case ≥20%, particularly preferably in each case ≥25% and core layer: ≥4%, preferably ≥15%, particularly preferably ≥35% of the total thickness, preferably in the combination of 30% / 40% / 30% or 40% / 20% / 40%, where the specified proportions of thickness can vary depending on the production by a maximum of 5%, in particular a maximum of 3%, of the total thickness.

The steel composite material provided preferably has a total thickness of 2.5 mm, in particular 4 mm, preferably 5 mm, particularly preferably 6 mm and 40 mm, preferably 25 mm, particularly preferably 18 mm.

• C: 0,17 bis 0,22 %,
• Si: 0,2 bis 0,45 %,
• Mn: 0,8 bis 1,1 %,
• P: bis 0,03 %,
• S: bis 0,01 %,
• Cr: 0,6 bis 0,9 %,
• Cu: 0,01 bis 0,05 %,
• Nb: bis 0,04 %,
• Mo: bis 0,3 %,
• N: bis 0,015 %,
• Ti: bis 0,02 %,
• V: bis 0,05 %,
• Ni: bis 1,5 %,
• B: bis 0,007 %,
• H: bis 0,0004 %,
• O: bis 0,002 %,
• Ca: bis 0,005 %,
• AI: 0,02 bis 0,1 %,

besteht, und Decklagen aus jeweils einem Stahl, welche neben Fe und herstellungsbedingt unvermeidbaren Verunreinigungen in Gew.-% aus

• C: 0,45 bis 0,60 %,
• Si: 0,15 bis 0,3 %,
• Mn: 0,70 bis 1,0 %,
• P: bis 0,03 %,
• S: bis 0,01 %,
• Cr: 0,80 bis 1,2 %,
• Cu: bis 0,3 %,
• Nb: bis 0,04 %,
• Mo: bis 0,3 %,
• N: bis 0,015 %,
• Ti: bis 0,02 %,
• V: 0,04 bis 0,25 %,
• Ni: bis 1,5 %,
• B: bis 0,007 %,
• H: bis 0,0004 %,
• O: bis 0,002 %,
• Ca: bis 0,005 %,
• Al: 0,01 bis 0,1 % besteht,

aufweist.The steel material composite used has, in particular, a core layer made of a steel which, in addition to Fe and unavoidable impurities due to the manufacturing process, is made up in% by weight

• C: 0.17 to 0.22%,
• Si: 0.2 to 0.45%,
• Mn: 0.8 to 1.1%,
• P: up to 0.03%,
• S: up to 0.01%,
• Cr: 0.6 to 0.9%,
• Cu: 0.01 to 0.05%,
• Nb: up to 0.04%,
• Mon: up to 0.3%,
• N: up to 0.015%,
• Ti: up to 0.02%,
• V: up to 0.05%,
• Ni: up to 1.5%,
• B: up to 0.007%,
• H: up to 0.0004%,
• O: up to 0.002%,
• Ca: up to 0.005%,
• AI: 0.02 to 0.1%,

consists, and top layers each made of a steel, which in addition to Fe and unavoidable impurities due to the manufacturing process in% by weight

• C: 0.45 to 0.60%,
• Si: 0.15 to 0.3%,
• Mn: 0.70 to 1.0%,
• P: up to 0.03%,
• S: up to 0.01%,
• Cr: 0.80 to 1.2%,
• Cu: up to 0.3%,
• Nb: up to 0.04%,
• Mon: up to 0.3%,
• N: up to 0.015%,
• Ti: up to 0.02%,
• V: 0.04 to 0.25%,
• Ni: up to 1.5%,
• B: up to 0.007%,
• H: up to 0.0004%,
• O: up to 0.002%,
• Ca: up to 0.005%,
• Al: 0.01 to 0.1%,

having.

• C: 0,17 bis 0,22 %,
• Si: 0,2 bis 0,45 %,
• Mn: 0,8 bis 1,1 %,
• P: bis 0,03 %,
• S: bis 0,01 %,
• Cr: 0,6 bis 0,9 %,
• Cu: 0,01 bis 0,05 %,
• Nb: bis 0,04 %,
• Mo: bis 0,3 %,
• N: bis 0,015 %,
• Ti: bis 0,02 %,
• V: bis 0,05 %,
• Ni: bis 1,5 %,
• B: bis 0,007 %,
• H: bis 0,0004 %,
• O: bis 0,002 %,
• Ca: bis 0,005 %,
• Al: 0,02 bis 0,1 %,

besteht, und Decklagen aus jeweils einem Stahl, welcher neben Fe und herstellungsbedingt unvermeidbaren Verunreinigungen in Gew.-% aus

• C: 0,35 bis 0,45 %,
• Si: 0,1 bis 0,3 %,
• Mn: 0,6 bis 1,0 %,
• P: bis 0,03 %,
• S: bis 0,01 %,
• Cr: 0,5 bis 1,0 %,
• Cu: bis 0,3 %,
• Nb: bis 0,04 %,
• Mo: bis 0,3 %,
• N: bis 0,015 %,
• Ti: bis 0,02 %,
• Ni: 0,9 bis 1,3 %,
• B: bis 0,007 %,
• H: bis 0,0004 %,
• O: bis 0,002 %,
• Ca: bis 0,005 %,
• Al: 0,02 bis 0,1 % besteht,

aufweist.Alternatively, a steel material composite is considered to be particularly expedient in which the steel material composite used has a core layer made of a steel which, in addition to Fe and impurities that are unavoidable due to the manufacturing process, is made up in% by weight

• C: 0.17 to 0.22%,
• Si: 0.2 to 0.45%,
• Mn: 0.8 to 1.1%,
• P: up to 0.03%,
• S: up to 0.01%,
• Cr: 0.6 to 0.9%,
• Cu: 0.01 to 0.05%,
• Nb: up to 0.04%,
• Mon: up to 0.3%,
• N: up to 0.015%,
• Ti: up to 0.02%,
• V: up to 0.05%,
• Ni: up to 1.5%,
• B: up to 0.007%,
• H: up to 0.0004%,
• O: up to 0.002%,
• Ca: up to 0.005%,
• Al: 0.02 to 0.1%,

consists, and top layers each made of a steel, which in addition to Fe and unavoidable impurities in weight percent due to the manufacturing process

• C: 0.35 to 0.45%,
• Si: 0.1 to 0.3%,
• Mn: 0.6 to 1.0%,
• P: up to 0.03%,
• S: up to 0.01%,
• Cr: 0.5 to 1.0%,
• Cu: up to 0.3%,
• Nb: up to 0.04%,
• Mon: up to 0.3%,
• N: up to 0.015%,
• Ti: up to 0.02%,
• Ni: 0.9 to 1.3%,
• B: up to 0.007%,
• H: up to 0.0004%,
• O: up to 0.002%,
• Ca: up to 0.005%,
• Al: 0.02 to 0.1%,

having.

The toughness of the individual layers of a multilayer composite is difficult to determine experimentally. If this is desired, the individual layers must be mechanically or thermally separated from one another and tested separately. With a corresponding thickness of the individual layers, the usual destructive test in the notched bar impact test can be used to determine the toughness DIN EN ISO 148-1: 2010 at. In the case of thinner layers, such as the cover layers with a relatively small thickness of the multilayer composite, such a toughness test is hardly technically possible since the specimen that is then too thin could buckle during the test. Therefore, the characteristic of the mean former austenite grain size is used to estimate the toughness properties DIN EN ISO 643: 2012 used. Under the mean former austenite grain size, the according to DIN EN ISO 643: 2012 understood certain mean diameters of the former austenite grain. In the case of non-round austenite grains, the area of the austenite grain is considered and the equivalent diameter is specified so that a round grain with this diameter has the same area. The mean former austenite grain size is preferably determined in the cross section, a cross section being defined in such a way that the rolling direction is orthogonal to the surface viewed in the section and therefore the rolling direction is parallel to the viewing direction. Tests have shown that the material behavior, which is still quite tough despite the high hardness, correlates well with this feature, especially of the outer layers. If a perfect microscopic determination was not possible, the ARPGE software was used and an austenite grain reconstruction based on the EBSD technique was carried out. The method used was first described in the article "Reconstruction of parent grains from EBSD data" by C. Cayron et al. published in 2006, see "Materials Characterization 57", p. 386- 401 . The method was further described in 2007 by C. Cayron: "ARPGE: a computer program to automatically reconstruct the parent grains from electron backscatter diffraction data", published in the Journal of Applied Crystallography, ISSN 0021-8898, pp. 1183-1188 .

According to the invention, the hardened state means that the safety steel is subjected to a heat treatment, the steel material composite being first heated to a temperature which is not lower than the Ac3 temperature of the steel of the cover layers. The cooling takes place after the hot forming in the pressing tool. In a further embodiment of the invention, the multilayer composite can still be left on, that is to say can be converted into the tempered state as a whole. The tempering temperature and duration should be selected so that at least the hardness of the first top layer does not decrease too much. In particular, a reduction in hardness compared to the initial hardness HV ₀ of a maximum of 100 HV10, particularly preferably of a maximum of 70 HV10, is tolerated. The thermoformed component can be used in the hardened state as a component for ballistic purposes.

HV corresponds to the Vickers hardness and is after DIN EN ISO 6507-1: 2005 determined. What is meant by “hardening” and “tempering / tempering” is in the DIN EN ISO 4885: 2017 regulated.

The steel used according to the invention can be provided in the form of a strip, plate or sheet for hot forming. The three-layer steel material composite described above is preferably hardened or tempered in the flat state, since this allows the properties described below to be set in a particularly homogeneous manner.

In the production of the steel sheet used, the flat state of the three-layer steel material composite allows very fast, automated transport of the material composite from an austenitizing unit into a quenching unit, with austenitizing and quenching both continuously on, if the provision for hot forming is to take place in the hardened or quenched and tempered state Bands as well as individual sheets or plates can be done.

• C ist ein festigkeitssteigerndes Legierungselement und trägt mit zunehmendem Gehalt zur Härtesteigerung bei, indem es entweder als interstitielles Atom im Austenit gelöst vorliegt und bei der Abkühlung zur Bildung härteren Martensits beitragen oder mit Fe, Cr, Ti, Nb, V und/oder W Karbide bildet, die einerseits härter als die umgebende Matrix sein können oder diese zumindest so verzerren können, dass die Härte der Matrix steigt. C ist daher mit Gehalten von mindestens 0,001 Gew.-%, insbesondere von mindestens 0,1 Gew.-%, vorzugsweise von mindestens 0,15 Gew.-% vorhanden, um eine gewünschte Härte zu erreichen bzw. einzustellen. Die hier eingestellte Härte gewährleistet, dass auch die Kernlage zur Erhöhung der Beschuss- bzw. Verschleißfestigkeit des Verbundwerkstoffes beiträgt, wenn auch in deutlich geringerem Maße als die Decklagen. Darüber hinaus kann die Kernlage auch ausschließlich auf Zähigkeit ausgelegt sein und hierfür nur wenig Kohlenstoff aufweisen. Da die Kernlage im Wesentlichen zur Erhöhung der Zähigkeit des Stahlwerkstoffverbundes beitragen soll, ist der Gehalt auf maximal 0,25 Gew.-%, insbesondere auf maximal 0,22 Gew.-% beschränkt.

The alloying elements of the steel of the core layer are indicated as follows:

• C is a strength-increasing alloying element and, with increasing content, contributes to the increase in hardness, in that it is either dissolved in the austenite as an interstitial atom and contributes to the formation of harder martensites during cooling or forms carbides with Fe, Cr, Ti, Nb, V and / or W which on the one hand can be harder than the surrounding matrix or can at least distort it in such a way that the hardness of the matrix increases. C is therefore present with contents of at least 0.001% by weight, in particular of at least 0.1% by weight, preferably of at least 0.15% by weight, in order to achieve or set a desired hardness. The hardness set here ensures that the core layer also contributes to increasing the bullet resistance and wear resistance of the composite material, albeit to a significantly lesser extent than the top layers. In addition, the core layer can also be designed exclusively for toughness and for this purpose have only a little carbon. Since the core layer should essentially contribute to increasing the toughness of the steel material composite, the content is limited to a maximum of 0.25% by weight, in particular to a maximum of 0.22% by weight.

Si is an optional alloy element that contributes to solid solution hardening and, depending on its content, can have a positive effect in increasing the hardness, so that a content of at least 0.03% by weight, preferably at least 0.1% by weight, can be present. In the case of lower contents, the effectiveness of Si cannot be clearly demonstrated, but Si does not have a negative effect on the properties of the steel either. If too much silicon is added to the steel, this has a negative impact on weldability, deformability and toughness properties. The alloy element is therefore limited to a maximum of 1.2% by weight, in particular to a maximum of 0.6% by weight, in order to ensure adequate rollability. In addition, Si can be used to deoxidize the steel if the use of Al is to be avoided, for example, in order to prevent undesired binding, e.g. B. to be avoided in the presence of N.

Mn is an alloying element that contributes to hardenability and is used in particular to bind S to MnS, so that it has a content of at least 0.1% by weight, in particular at least 0.6% by weight. Manganese reduces the critical cooling rate, which increases hardenability. The alloying element is to a maximum of 2.5% by weight, in particular to a maximum of 1.8% by weight, in order to ensure adequate weldability and good deformation behavior. In addition, Mn has a strong segregating effect and is therefore preferably limited to a maximum of 1.3% by weight.

P can be present as an iron companion, which has a strong toughness-reducing effect and is usually one of the undesirable accompanying elements in safety steels. In order to use its strength-increasing effect, it can optionally be added with contents in particular of at least 0.005% by weight. P can due to its low diffusion rate when solidifying the Melt lead to strong segregation. For these reasons, the element is limited to a maximum of 0.05% by weight, in particular to a maximum of 0.03% by weight.

As an undesirable accompanying element in steel, S has a strong tendency to segregate and forms undesirable FeS, which is why it has to be bound by Mn. The S content is therefore restricted to a maximum of 0.03% by weight, in particular to a maximum of 0.01% by weight, preferably to a maximum of 0.005% by weight, preferably to a maximum of 0.003% by weight.

As an optional alloying element, N can have a similar effect to C, because its ability to form nitrides can have a positive effect on strength. In the presence of Al, aluminum nitrides are formed, which improve nucleation and hinder grain growth. In order to develop the effect described above, it can optionally be added in amounts in particular of at least 0.001% by weight. For economic reasons, contents of at least 0.002% by weight are preferred. The content is limited to a maximum of 0.02% by weight. A maximum content of 0.015% by weight, in particular a maximum content of 0.010% by weight, is preferably set in order to avoid the undesired formation of coarse titanium nitrides, which would have a negative effect on the toughness, in the presence of Ti. In addition, when the alloying element boron is used, it is bound by nitrogen if the aluminum or titanium content is not high enough or not available.

As an optional alloying element, depending on its content, Cr can also make a positive contribution to setting the strength, in particular to hardenability, with a content in particular of at least 0.05% by weight. In addition, Cr can be used alone or in combination with other elements as a carbide former. Because of the positive effect on the toughness of the material, in particular on the toughness of the core layer, the Cr content can preferably be set to at least 0.5% by weight. For economic reasons, the alloy element is limited to a maximum of 2.5% by weight, in particular to a maximum of 1.5% by weight, in order to ensure adequate weldability.

Cu as an optional alloying element, with a content in particular of 0.005% by weight to 1.0% by weight, can contribute to an increase in hardness.

Ti, Nb, V and / or W can be added as optional alloying elements individually or in combination for grain refinement; they can also be used to bind N. Above all, however, these elements can be used as micro-alloy elements in order to form strength-increasing carbides, nitrides and / or carbonitrides. To ensure their effectiveness, Ti, Nb, V and / or W can be used with contents of in each case or in total at least 0.005% by weight. In order to achieve a corresponding effect, a content of in total at least 0.010% by weight, particularly preferably at least 0.020% by weight, is added. The sum of the elements can in particular assume a value of a maximum of 0.50% by weight, preferably a maximum of 0.40% by weight, particularly preferably a maximum of 0.15% by weight Provide a Ti content of at least 3.42 * N. In order to be able to achieve a significant increase in strength through precipitation formation, a content of at least 0.02% by weight Ti, in particular at least 0.02% by weight Nb, in particular at least 0.02% by weight V and / or in particular at least 0.02 wt.% W is used, the use of Ti and / or Nb being preferred, since these alloying elements can make a particularly high contribution to grain refinement, which, in addition to increasing strength, can also increase the toughness of the core layer. Nb is to a maximum of 0.2% by weight, in particular to a maximum of 0.1% by weight, preferably to a maximum of 0.04% by weight, Ti is to a maximum of 0.2% by weight, in particular to a maximum of 0 , 1% by weight, preferably to a maximum of 0.04% by weight, V is to a maximum of 0.2% by weight, preferably to a maximum of 0.1% by weight, particularly preferably to a maximum of 0.05% by weight. -% and W is limited to a maximum of 0.2% by weight, preferably to a maximum of 0.1% by weight, particularly preferably to a maximum of 0.05% by weight, since higher contents have a detrimental effect on the material properties, in particular on themselves can have a negative effect on the toughness of the core layer.

Mo can optionally be added to increase strength and improve hardenability. Furthermore, Mo has a positive effect on the toughness properties. Mo can be used as a carbide former to increase the yield strength and improve the toughness. In order to ensure the effectiveness of these effects, a content of at least 0.01% by weight, preferably at least 0.1% by weight, can be added. For reasons of cost, the maximum content is limited to 1% by weight, preferably to 0.3% by weight.

Ni, which can optionally be added up to a maximum of 5.5% by weight, can have a positive effect on the deformability of the material, in particular that of the core layer and, associated therewith, that of the material composite. By reducing the critical cooling rate, nickel also improves hardening and tempering. For reasons of cost, contents of a maximum of 2.5% by weight, preferably of a maximum of 1.5% by weight, preferably of a maximum of 1.0% by weight, particularly preferably of a maximum of 0.5% by weight, are further increased preferably adjusted to a maximum of 0.3% by weight. An effect of the optional alloy element can develop in particular from 0.1% by weight, lower contents can be tolerated and do not significantly influence the material behavior.

As an optional alloying element in atomic form, B can delay the structural transformation to ferrite / bainite and improve hardenability and strength, in particular if N is bound by strong nitride formers such as Al or Nb and can in particular with a content of at least 0.0001% by weight, preferably at least 0.001% by weight. The alloying element is limited to a maximum of 0.01% by weight, in particular to a maximum of 0.007% by weight, since higher contents can have a detrimental effect on the material properties, in particular with regard to the toughness at the grain boundaries.

Sn, As and / or Co are optional alloying elements which, individually or in combination, if they are not specifically added to set special properties, can be counted among the impurities. The contents are limited to a maximum of 0.05% by weight Sn, in particular to a maximum of 0.04% by weight Sn, to a maximum of 0.50% by weight Co and to a maximum of 0.02% by weight As.

O is usually undesirable, but it can also be beneficial in very low levels, especially from 0.0005% by weight, since oxide deposits, especially on the separating layer between the core and top layer, prevent diffusion between the steels that are deliberately differently alloyed, as is the case, for example, in the German Offenlegungsschrift DE 10 2016 204 567 A1 described. The maximum content for oxygen is given as 0.005% by weight, preferably 0.002% by weight.

As the smallest atom, H is very mobile in interstitial spaces in steel and can lead to tears in the core when it cools down from hot rolling, especially in high-strength steels. For technical reasons, the presence of H cannot be completely avoided. H is therefore reduced to a content of a maximum of 0.001% by weight, in particular to a maximum of 0.0006% by weight, preferably to a maximum of 0.0004% by weight, more preferably to a maximum of 0.0002% by weight.

Ca can optionally be added to the melt as a desulfurizing agent and for targeted sulfide influence in contents of up to 0.015% by weight, preferably up to 0.005% by weight, which leads to a changed plasticity of the sulfides during hot rolling. In addition, the addition of calcium preferably also improves the cold forming behavior. The effects described are effective from contents of 0.0005% by weight, which is why this limit can be selected as a minimum when using Ca.

Al in particular contributes to deoxidation, which is why a content of in particular at least 0.02% by weight can optionally be set. The alloy element is limited to a maximum of 1.0% by weight to ensure the best possible castability, in particular to a maximum of 0.6% by weight, preferably to a maximum of 0.3% by weight, in order to avoid undesired precipitations in the material, in particular in To substantially reduce and / or avoid the form of non-metallic oxidic inclusions, which can negatively affect the material properties. For example, the content is set between 0.02 and 0.3% by weight. Al can also be used to bind the nitrogen present in the steel.

If Nb, B and Al, optionally Ca, are present in the core layer within the specified limits, these alloying elements can, among other things, bring about a grain refinement. Grain refinement is a strengthening mechanism in which not only strength but also toughness can be increased. As a result, a sufficiently high toughness and thus a hardness similar to that of other core layers known from the prior art, high momentum and energy absorption as well as a high resistance to crack propagation can be provided in the steel material composite, in particular in the safety steel.

Rare earth metals (SEM) such as cerium, lanthanum, neodymium, praseodymium and others can be added to the core layer of the multilayer composite as optional alloying elements in order to bind S, P and / or O and to reduce or reduce the formation of oxides and / or sulfides and phosphorus segregations at grain boundaries to avoid completely and thus to increase the toughness. In order to achieve a recognizable effect, contents of at least 0.0005% by weight, in particular of at least 0.0015% by weight, are added when using SEM. The SEM content is limited to a maximum of 0.01% by weight in order not to form too many additional precipitates, which can negatively affect the toughness. In particular, for reasons of cost, a maximum of 0.005% by weight of SEM is added.

Optional alloying elements, the content of which in the core layer is below the specified minimum content, are to be seen as impurities, do not influence the material properties or only influence them to a small extent and can therefore be tolerated.

• C ist ein festigkeitssteigerndes Legierungselement und trägt mit zunehmendem Gehalt zur Festigkeitssteigerung bei, so dass ein Gehalt von mindestens 0,35 Gew.-%, insbesondere von mindestens 0,40 Gew.-% vorhanden ist, um die gewünschte Festigkeit bzw. Härte im Stahlwerkstoffverbund zu erreichen bzw. einzustellen. Die maximale Aufhärtbarkeit von Stählen ist bei Abschreckung auf Raumtemperatur bei ca. 0,65 Gew.-% Kohlenstoff erreicht, so dass der Gehalt auf maximal 0,65 Gew.-%, insbesondere auf maximal 0,60 Gew.-%, vorzugsweise auf maximal 0,58 Gew.-%, besonders bevorzugt auf maximal 0,55 Gew.-% beschränkt ist. Die Beschränkung auf die vorgenannten Gehalte beeinflusst die Materialeigenschaften der Decklagen nicht negativ, insbesondere geht eine Kohlenstofferhöhung über die angegebenen Werte hinaus mit einer Sprödigkeitszunahme bzw. Zunahme der Rissanfälligkeit einher. Der weitere Vorteil, den C-Gehalt der Decklagen in den vorgenannten Grenzen einzustellen ist, dass beim Härten ein Restaustenitanteil im Gefüge kontrolliert eingestellt werden kann und vor dem Hintergrund der Schweißbarkeit insbesondere der CEV-Wert (carbon equivalent value) bzw. CET-Wert (carbon equivalent thyssen) gering gehalten werden kann. Die Definition bzw. Berechnung dieser Werte ist auf der Internetseite www.wikipedia.de unter dem Begriff Kohlenstoffäquivalent zu finden.

The alloying elements of the steel of the top layers are indicated as follows:

• C is a strength-increasing alloying element and, with increasing content, contributes to increasing strength, so that a content of at least 0.35% by weight, in particular at least 0.40% by weight, is present to achieve the desired strength or hardness in the steel material composite to achieve or to discontinue. The maximum hardenability of steels is reached when quenching to room temperature at approx. 0.65 wt.% Carbon, so that the content is preferably at a maximum of 0.65 wt is limited to a maximum of 0.58% by weight, particularly preferably to a maximum of 0.55% by weight. The restriction to the aforementioned contents does not have a negative effect on the material properties of the outer layers; in particular, an increase in carbon above the specified values is associated with an increase in brittleness or an increase in susceptibility to cracking. The further advantage of setting the C content of the top layers within the aforementioned limits is that a residual austenite content in the structure can be set in a controlled manner during hardening and, against the background of weldability, in particular the CEV value (carbon equivalent value) or CET value ( carbon equivalent thyssen) can be kept low. The definition and calculation of these values can be found on the website www.wikipedia.de under the term carbon equivalent.

Si is an optional alloying element that contributes to solid solution hardening and, depending on its content, can have a positive effect in increasing strength, so that a content of at least 0.03% by weight, preferably of at least 0.05% by weight, preferably of at least 0.10% by weight can be present. The alloying element is limited to a maximum of 1.2% by weight, in particular to a maximum of 0.6% by weight, in order to ensure adequate rollability.

Mn is an alloying element that contributes to hardenability and has a positive effect on tensile strength, in particular for setting S to MnS, so that a content of at least 0.1% by weight, in particular at least 0.6% by weight, is present is. The alloy element is limited to a maximum of 2.5% by weight, in particular to a maximum of 1.9% by weight, preferably to a maximum of 1.5% by weight, in order to ensure adequate weldability.

P can be present as an iron companion, which has a strong toughness-reducing effect and is usually one of the undesirable accompanying elements in safety steels. In order to use its strength-increasing effect, it can optionally be added with contents in particular of at least 0.005% by weight. Due to its low diffusion rate, P can lead to severe segregation when the melt solidifies. For these reasons, the element is limited to a maximum of 0.05% by weight, in particular to a maximum of 0.03% by weight.

As an undesirable accompanying element in steel, S has a strong tendency to segregate and forms undesirable FeS, which is why it has to be bound by Mn. The S content is therefore restricted to a maximum of 0.03% by weight, in particular to a maximum of 0.01% by weight.

As an optional alloying element, N can have a similar effect to C, because its ability to form nitrides can have a positive effect on strength. In the presence of Al, aluminum nitrides are formed, which improve nucleation and hinder grain growth. In order to develop the effect described above, it can optionally be added in amounts, in particular at least 0.001% by weight. For economic reasons, contents of at least 0.002% by weight are preferred. The content is limited to a maximum of 0.02% by weight. A maximum content of 0.015% by weight is preferably set in order to avoid the undesired formation of coarse titanium nitrides, which would have a negative effect on the toughness, in the presence of Ti. In addition, if the optional alloying element boron is used, it is bound by nitrogen if the aluminum or titanium content is not high enough or not present.

As an optional alloy element, depending on the content, Cr can also contribute to setting the strength, in particular positively to hardenability, with a content in particular of at least 0.1% by weight. In addition, Cr can be used alone or in combination with other elements as a carbide former. The resulting (growing) carbides can lead to an increase in hardness and can essentially compensate for a heat-related drop in hardness, for example by tempering the hardened steel material composite. Because of the positive effect on the toughness of the material, the Cr content can be set to at least 0.5% by weight, preferably to at least 0.7% by weight. For economic reasons, the alloy element is limited to a maximum of 3.5% by weight, in particular to a maximum of 2.5% by weight, preferably to a maximum of 2.0% by weight, in order to ensure adequate weldability.

Cu as an optional alloying element, with a content in particular of 0.005% by weight to 1.0% by weight, can contribute to an increase in hardness.

Ti, Nb, V and / or W can be added as optional alloying elements individually or in combination for grain refinement. In addition, Ti, Nb and / or V can be used to tie N. Above all, however, these elements can be used as micro-alloy elements in order to form strength-increasing carbides, nitrides and / or carbonitrides. To ensure their effectiveness, Ti, Nb, V and / or W can be used with contents of in each case or in total at least 0.005% by weight, in particular at least 0.01% by weight, particularly preferably at least 0.02% by weight. The sum of the elements can in particular assume a value of a maximum of 0.5% by weight, preferably a maximum of 0.4% by weight, particularly preferably a maximum of 0.15% by weight. For complete binding of N by Ti, the content of Ti would have to be at least 3.42 * N. Nb is to a maximum of 0.2% by weight, in particular to a maximum of 0.1% by weight, preferably to a maximum of 0.04% by weight, Ti is to a maximum of 0.2% by weight, in particular to a maximum of 0 , 1% by weight, preferably to a maximum of 0.04% by weight, since higher contents can have a detrimental effect on the material properties of the outer layers. V can be added in amounts of up to 0.8% by weight, in particular from 0.04 to 0.25% by weight, preferably from 0.06 to 0.20% by weight. In contrast to the Ti or Nb carbides, the V carbides can easily be partially or completely dissolved during austenitizing in the course of the hot forming process, whereby V can be used in dissolved form to reduce or prevent undesired austenite grain growth. At contents of 0.01 to 1.5% by weight, in particular up to 1.3% by weight, preferably up to 0.7% by weight, W can lead to the formation of tungsten carbides and / or serve to form intermetallic phases . The use of W as a micro-alloy element is preferred, for which contents in particular of a maximum of 0.2% by weight, preferably of a maximum of 0.1% by weight, preferably of a maximum of 0.04% by weight, are used.

Mo can optionally be added to increase the strength and improve the hardenability. To ensure the effectiveness of these effects, a content of at least 0.1% by weight is required. Furthermore, Mo has a positive effect on the toughness properties. Mo can be used as a carbide former to increase the yield strength and improve the toughness. For reasons of cost, the maximum content is limited to 1.5% by weight, in particular to 0.5% by weight, preferably to 0.3% by weight.

Ni, which can optionally be added up to a maximum of 5.5% by weight, can have a positive effect on the deformability of the material. By reducing the critical cooling rate, nickel also increases hardening and tempering. For cost reasons, contents of a maximum of 2.0% by weight, preferably a maximum of 1.5% by weight, are set. An effect of the optional alloy element can develop in particular from 0.1% by weight, lower contents can be tolerated and do not significantly influence the material behavior.

As an optional alloying element in atomic form, B can delay the structural transformation to ferrite / bainite and improve hardenability and strength, especially if N is bonded by strong nitride formers such as Al, Nb and / or Ti and can with a content of at least 0.0001 wt .-% to be available. The alloying element is limited to a maximum of 0.01% by weight, in particular to a maximum of 0.007% by weight, since higher contents can have a disadvantageous effect on the material properties, in particular with regard to the ductility at grain boundaries.

Sn, As and / or Co are optional alloying elements which, individually or in combination, if they are not specifically added to set special properties, can be counted among the impurities. The contents are limited to a maximum of 0.05% by weight Sn, in particular to a maximum of 0.04% by weight Sn, to a maximum of 0.50% by weight Co and to a maximum of 0.02% by weight As.

O is usually undesirable, but very small amounts can also be beneficial, since oxide deposits, in particular on the separating layer between the core and top layer, prevent diffusion between the steels that are deliberately differently alloyed, as is the case, for example, in the German Offenlegungsschrift DE 10 2016 204 567 A1 described. The maximum content for oxygen is given as 0.005% by weight, preferably 0.002% by weight.

As the smallest atom, H is very mobile in interstitial spaces in steel and can lead to tears in the core when it cools down from hot rolling, especially in high-strength steels. For technical reasons, the presence of H cannot be completely avoided. H is therefore reduced to a content of a maximum of 0.001% by weight, in particular a maximum of 0.0006% by weight, preferably a maximum of 0.0004% by weight, preferably a maximum of 0.0002% by weight.

Ca can optionally be added to the melt as a desulphurizing agent and for targeted sulphide influence in contents of up to 0.015% by weight, in particular up to 0.005% by weight, which leads to a changed plasticity of the sulphides during hot rolling. In addition, the addition of calcium preferably also improves the cold forming behavior. The effects described are particularly effective from contents of 0.0005% by weight, which is why this limit can be selected as a minimum when using Ca.

In particular, Al can contribute to deoxidation. The alloying element is to be limited to a maximum of 2.0% by weight to ensure the best possible castability, in particular to a maximum of 1.0% by weight, preferably to a maximum of 0.5% by weight, preferably to a maximum of 0.3% by weight. % limited in order to essentially reduce and / or avoid undesired precipitations in the material, in particular in the form of non-metallic oxidic inclusions, which can negatively influence the material properties.

SEM such as cerium, lanthanum, neodymium, praseodymium and others can be added to the outer layers of the multilayer composite as optional alloying elements in order to bind S, P and / or O and to reduce or even completely reduce the formation of oxides and / or sulfides as well as phosphorus segregations at grain boundaries avoid. This can in particular reduce the risk that particles break out of the cover layers in the event of the security steel being bombarded or the impacting load, which would mean a significant weakening of the material in the event of renewed loading. In order to achieve a recognizable effect, when using SEM, contents of at least 0.0005% by weight, preferably of at least 0.0015% by weight, are added. The SEM content is limited to a maximum of 0.01% by weight in order not to form too many additional precipitates, which can negatively affect the toughness. For reasons of cost, preference is given to adding a maximum of 0.005% by weight of SEM.

Optional alloying elements, the content of which in the top layers is below the specified minimum content, are to be seen as impurities, do not influence the material properties or only influence them to a small extent and can therefore be tolerated.

According to a further embodiment, the security steel is clad by means of cladding, in particular roll cladding, as is the case, for example, in the German patent DE 10 2005 006 606 B3 is described. During hot-roll cladding, diffusion processes take place between the core layer and the outer layers, because in the boundary layer area of the outer layers, a kind of edge decarburization takes place in the outer layers due to the migration of carbon from the outer layers into the core layer, which results in a locally tougher area compared to the remaining area of the outer layers. The diffusion processes also result in an essentially continuous and not a sudden transition in the material properties (hardness / strength) between the core layer and the cover layers. In the warm state, the core layer advantageously has a reduced resistance to deformation compared to the cover layers due to the higher toughness or ductility, so that it is deformed in the direction of the cover layers during hot-roll cladding or hot rolling and thereby in particular production-related defects, for example air inclusions between the layers due to the Rolled joint can close. This is particularly advantageous during later use or use, so that in the event of an impact load, the defects cannot break out.

To set the desired properties, if the steel material composite is to be provided for hot forming in the hardened or tempered state, the steel material composite provided according to the invention is hardened by accelerated cooling. In a preferred embodiment, the accelerated cooling takes place directly after the hot-roll cladding or hot-rolling without prior cooling from the rolling heat. The cooling is ended at a so-called cooling stop temperature, which is below the martensite start temperature Ms of the cover layers, preferably below the martensite finish temperature Mf of the cover layers or at a maximum of 100 ° C above room temperature, in particular at the lower of the two temperatures Mf and room temperature + 100 ° C.

In an alternative, also preferred embodiment, if the steel material composite is to be provided for hot forming in the hardened or tempered state, hardening can also take place as follows: after hot rolling, the material first cools down to temperatures below 500 ° C to avoid undesirable Avoid effects such as grain growth or coarsening of excretions. The cooling can take place either in the coil or as a plate in air or by applying a cooling medium such as. B. water or oil take place. For logistical reasons, cooling to below 100 ° C. is preferred, particularly preferably to a temperature close to room temperature. The steel material composite is then at least partially austenitized and, for this purpose, heated to a temperature of at least Ac1 of the cover layers. Preference is given to complete austenitization and corresponding heating on at least Ac3 of the cover layers. For energetic reasons, the austenitizing temperature is limited to a maximum of 1100 ° C, to avoid undesired austenite grain growth, preferably to a maximum of (Ac3 + 200 ° C) of the steel of the second cover layer, particularly preferably to a maximum of (Ac3 + 100 ° C) of the steel of the second cover layer .

The stated structural proportions in% relate to those in the section, with the exception of the information on the austenite contents, which are usually determined by X-ray diffractometry and are therefore given in% by volume considered area. The mean former austenite grain size is preferably determined using the ARPGE software.

• Die erste Decklage weist durch ihre Härte einen hohen Eindringwiderstand auf und ist geeignet, ein auftreffendes Projektil zu brechen oder in seinem Umfang aufzuweiten.
• Die Kernlage absorbiert bei Beschuss oder Ansprengung durch ihre hohe Zähigkeit die Energie. Wenn durch eine Überbeanspruchung der ersten Decklage darin Risse entstehen, können diese durch den hohen Widerstand der Kernlage gegen Rissausbreitung gestoppt werden, ohne dass es zum Versagen des betroffenen Bauteils kommt. Insbesondere wird die Härtedifferenz zwischen diesen Lagen (Decklage zu Kernlage) auf mindestens 70 HV10, vorzugsweise auf mindestens 100 HV10, bevorzugt auf mindestens 200 HV10, besonders bevorzugt auf mindestens 250 HV10, eingestellt.

When the hot-formed component made of the steel composite material is loaded, the individual layers have the following functions:

• Due to its hardness, the first cover layer has a high penetration resistance and is suitable for breaking an impacting projectile or for expanding its circumference.
• The core layer, due to its high toughness, absorbs the energy in the event of fire or blasting. If cracks occur in the first cover layer as a result of overstressing, these can be stopped by the high resistance of the core layer to the propagation of cracks without causing the component concerned to fail. In particular, the hardness difference between these layers (top layer to core layer) is set to at least 70 HV10, preferably to at least 100 HV10, preferably to at least 200 HV10, particularly preferably to at least 250 HV10.

The second cover layer is required in order to prevent the projectiles or projectile fragments, braked, broken and / or expanded by the previous layers, from completely penetrating the steel material composite in the event of a bullet load. In the event of exposure to bombardment and / or blasting, the second top layer is required to limit the deformation of the steel material composite: while the first top layer can show cracks after normal loads and therefore no longer contributes to the stiffening of the component, this prevents this compared to the core layer significantly increased yield point of the second top layer, too great a permanent plastic deformation.

The steel component produced according to the invention is suitable as safety steel for the production of components for the protection of living beings, objects and devices, in particular buildings or vehicles against ballistic threats or blasting or for protection against high-speed machines with the risk of flying components. The steel component can be used or used individually or as a component in a multi-part protection system. Due to the excellent properties and, in particular, economical production, the said steel components can in particular replace existing concepts, for example ballistic ceramics that are expensive to manufacture. Due to the excellent properties, in particular with regard to hardness and toughness, and associated therewith also a potential weight saving, the steel component according to the invention can also be used for protection against threats in the aviation industry, such as. B. used in airplanes or helicopters. Further areas of application can be: in the space industry, in rocket construction, for the protection of satellites, in the armaments industry in general, in shipbuilding, in particular for the protection of panic rooms or highly sensitive facilities such as the operations center (command post) and bridges, in particular with structurally specified low installation depths.

In the 1 a schematic sectional illustration through a steel component according to the invention is shown. It includes two top layers 2 , 3 and one between the two top layers 2 , 3 firmly bonded core layer 1 from one compared to the top layers 2 , 3 softer steel in the hardened or quenched and tempered condition.

Sheet metal blanks with two top layers were used for production 2 , 3 and a core layer disposed therebetween 1 stacked on top of one another, which at least in some areas along their edges have been connected to one another in a materially bonded manner, preferably by means of welding to form a pre-composite. In the exemplary embodiment considered here, the pre-composite was brought to a temperature of approx. 1100 ° C. and hot-rolled in several steps to form a steel material composite with a total material thickness of 5 mm.

Blanks were separated from the steel composite produced. The blanks, which had a size of 6000 mm × 2000 mm, were brought to the austenitizing temperature, in particular above Ac3, based on the cover layers 2 , 3 , heated and soaked in an oven for approx. 180 min each time and were then used to set the desired hardness in the top layers 2 , 3 quenched (hardening). Before quenching, the blanks were clamped in a cooling unit, a so-called quette, in order to ensure an essentially distortion-free thermal treatment. The deterrent was done by exposure to water. Other deterrent media, such as gases, liquids, emulsions, or suspensions, can also be used. The cooling rates in the top layers 2 , 3 of the steel material composite were checked by previously introduced thermocouples and were> 20 K / s. Due to the process, a homogeneous cooling performance over the entire surface of the material cannot always be achieved in Quetten, since the water is supplied from spray nozzles which can only produce approximately uniform water exposure. Locally uneven cooling performance can lead to undesirable variations in properties, for example in hardness. Process-related inhomogeneous cooling processes can also occur during the phase transformation of the material Tensions on the surface of the previously used monolithic materials lead, on the one hand, for further processing, such as the hot forming according to the invention, because they can lead to a distortion of a component to be produced during further processing, and on the other hand, local In extreme cases, structural differences lead to material damage close to the surface, which can lead to rejects or necessary reworking in the production process, such as grinding out cracks. It has surprisingly been found that irregularities, as they occasionally occurred with the monolithic steels used up to now, could not be found in the safety steels according to the invention.

It was determined that the interplay of the alloying elements between the individual layers in the steel material composite in the core layer 1 one compared to the top layers 2 , 3 higher toughness can be set.

the 2 shows, purely schematically, a temperature profile in the method according to the invention for producing a steel component to form a three-layer steel material composite. First, the steel is heated at a high heating rate to a temperature above Ac3. When a temperature of typically 910 ° C.-960 ° C. has been reached at t1, the temperature is held until time t2. With a sheet thickness of 8 mm, for example, the temperature is maintained for a period of 21 to 31 minutes. The heated blank is hot-formed and then cooled, the cooling being carried out more quickly between t2 and t3, for example at a cooling rate of 5-15 K / s. When the martensite start temperature is reached, which is typically 430 ° C, the cooling rate is reduced to 1 to 3 K / s. The temperature range for tempering, which is typically 150 ° C to 250 ° C, is passed through relatively slowly, so that a self-tempering effect increases the toughness in the material. When the target temperature t4 is reached, cooling is complete. Optionally, the molded component can be tempered again in the temperature range between t5 and t6 in order to increase the toughness. This can be done in a KTL process.

List of reference symbols

1

Core situation

2

upper cover layer

3

lower top layer

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 2123447 A1 [0003]
• DE 102016204567 A1 [0052, 0072]
• DE 102005006606 B3 [0078]

Non-patent literature cited

• A. Latz et al .: Modeling of Hardenability and Tempering of High-Strength Structural Steels. HTM J. Heat Treatm. Mat. 74 (2019) [0018]
• DIN EN ISO 148-1: 2010 [0034]
• DIN EN ISO 643: 2012 [0034]
• C. Cayron et al. published in 2006, see "Materials Characterization 57", pp. 386-401 [0034]
• DIN EN ISO 6507-1: 2005 [0036]
• DIN EN ISO 4885: 2017 [0036]

Claims (16)

Process for the production of a steel component from a three-layer steel material composite with a core layer (1), which, in addition to Fe and impurities that are unavoidable as a result of the production process, in% by weight C: 0.001 to 0.25%, optional Si: up to 1.2%, Mn: 0.1 to 2.5%, optional P: up to 0.05%, S: up to 0.03%, optional N: up to 0.02%, optional Cr: up to 2.5%, optional Cu: up to 0.5%, optional Nb: up to 0.2%, optional Ti: up to 0.2%, optional V: up to 0.2%, optional W: up to 0.2%, optional Mon: up to 1%, optional Ni: up to 5.5%, optional B: up to 0.01, optional Sn: up to 0.05%, optional As: up to 0.02%, optional Co: up to 0.5%, optional O: up to 0.005%, H: up to 0.001%, optional Ca: up to 0.015%, optional Al: up to 1.0%, optional SEM: up to 0.01%, and with two top layers (2, 3) connected to the core layer (1) in a materially bonded manner, the side facing a load being referred to as the first top layer (2) and the side facing away from the load being referred to as the second top layer (3), each of the top layers (2, 3) each made of a steel which, in addition to Fe and impurities that are unavoidable due to the manufacturing process, in% by weight C: 0.35 to 0.65%, optional Si: up to 1.2%, Mn: 0.1 to 2.5%, optional P: up to 0.05%, S: up to 0.03%, optional N: up to 0.02%, optional Cr: up to 3.5%, optional Cu: up to 0.5%, optional Nb: up to 0.2%, optional Ti: up to 0.2%, optional V: up to 0.8%, optional W: up to 1.5%, optional Mon: up to 1.5%, optional Ni: up to 5.5%, optional B: up to 0.01%, optional Sn: up to 0.05%, optional As: up to 0.02%, optional Co: up to 0.02%, optional O: up to 0.005%, H: up to 0.001%, optional Ca: up to 0.015%, optional AI: up to 2.0%, optional SEM: pass up to 0.01%, where the condition K = Mn [% by weight] + 1000 x B [% by weight] with K = 1 to 6 in the core layer (1) and K = 0.5 to 7 in the outer layers (2, 3) is fulfilled, and wherein the steel material composite is heated for hot forming to a temperature above Ac3 and then formed into the steel component by hot forming and press hardening, the formed steel material composite being incompletely hardened, the incompletely hardened structure of the cover layers (2, 3) predominantly made of martensite and consists of up to 10% bainite and optionally retained austenite. Procedure according to Claim 1 , characterized in that the incompletely hardened structure is set to a hardness of 3% to 25%, in particular 5% to 10% below the maximum hardness for the material of the cover layers (2, 3), the maximum hardness for the cover layers ( 2, 3) min. 600 HV10, in particular min. 620 HV10, preferably min. 650 HV10, particularly preferably min. 680 HV10 and max. 950 HV, preferably max. 850 HV10, particularly preferably max. 820 HV10 and for the core layer ( 1) is at least 300 HV10, preferably at least 350 HV10, particularly preferably at least 400 HV and max. 600 HV10, in particular a maximum of 550 HV10, preferably a maximum of 500 HV10. Procedure according to Claim 1 or 2 , characterized in that the steel component is set to a hardness of 650-900 HV10, preferably 650-850 HV10, particularly preferably 720-800 HV10, in the cover layers (2, 3) after the hot forming and press hardening. Method according to one of the Claims 1 until 3 , characterized in that the steel material composite is provided in the hardened or quenched and tempered state before hot forming. Method according to one of the Claims 1 until 4th , characterized in that the formed steel component is cooled down slowly after the hot forming, the cooling rate being set higher above the martensite start temperature Ms than below the martensite start temperature Ms, in particular than in a temperature range between 150 ° C and 250 ° C. Procedure according to Claim 5 , characterized in that the cooling rate is reduced with increasing total thickness of the steel component and moves for steel components with wall thicknesses between 2.5 mm and 40 mm within the following limits: for a total thickness of 2.5 mm: above Ms: 40 to 100 K / s below Ms: 10 to 40 K / s for a total thickness of 40mm above Ms: 1 to 5 K / s below Ms: 0.1 to 1 K / s. Method according to one of the Claims 1 until 6th , characterized in that the steel component is cooled and, after cooling, is tempered for a period of 1 to 50 minutes, in particular 10 to 30 minutes, at a temperature between 150 ° C and 250 ° C. Procedure according to Claim 7 , characterized in that the steel component is cathodically dip-coated, the tempering taking place during the lacquer baking after the dip-coating. Procedure according to Claim 7 or 8th , characterized in that the steel component after tempering is set to a hardness of the cover layers (2, 3) in a range of 600-880 HV10, preferably 600-820 HV10, particularly preferably 670-750 HV10. Method according to one of the Claims 1 until 9 , characterized in that the hardnesses of the top layer (2) / core layer (1) / top layer (3) are adjusted to 750/420/750 HV10 to 800/450/800 HV10 after press hardening. Method according to one of the Claims 7 until 10 , characterized in that the hardnesses of the top layer (2) / core layer (1) / top layer (3) are adjusted to 700/420/700 HV10 to 750/450/750 HV10 after press hardening and tempering. Method according to one of the Claims 1 until 11 , characterized in that the steel composite material provided has the following thickness ratios: top layer (2, 3) in each case ≥10%, preferably in each case ≥20%, particularly preferably in each case ≥25% and core layer (1): ≥4%, preferably ≥15%, particularly preferably ≥35% of the total thickness, preferably in the combination of 30% / 40% / 30% or 40% / 20% / 40%, the specified thickness proportions depending on the production by a maximum of 5%, in particular a maximum of 3%, of the total thickness of the steel composite material can fluctuate. Method according to one of the Claims 1 until 12th , characterized in that the steel composite material provided has a total thickness of ≥ 2.5 mm, in particular ≥ 4 mm, preferably ≥ 5 mm, particularly preferably ≥ 6 mm and ≤ 40 mm, preferably ≤ 25 mm, particularly preferably ≤ 18 mm. Method according to one of the Claims 1 until 13th , characterized in that the steel material composite used has a core layer (1) made of a steel which, in addition to Fe and unavoidable impurities due to the manufacturing process, consists of C: 0.17 to 0.22%, Si: 0.2 to 0.45% by weight %, Mn: 0.8 to 1.1%, P: up to 0.03%, S: up to 0.01%, Cr: 0.6 to 0.9%, Cu: 0.01 to 0.05% , Nb: up to 0.04%, Mo: up to 0.3%, N: up to 0.015%, Ti: up to 0.02%, V: up to 0.05%, Ni: up to 1.5%, B: up to 0.007%, H: up to 0.0004%, O: up to 0.002%, Ca: up to 0.005%, Al: 0.02 to 0.1%, and cover layers (2, 3) each consist of a steel, which in addition to Fe and production-related unavoidable impurities in% by weight from C: 0.45 to 0.60%, Si: 0.15 to 0.3%, Mn: 0.70 to 1.0%, P: up to 0.03%, S. : up to 0.01%, Cr: 0.80 to 1.2%, Cu: up to 0.3%, Nb: up to 0.04%, Mo: up to 0.3%, N: up to 0.015%, Ti: up to 0.02%, V: 0.04 to 0.25%, Ni: up to 1.5%, B: up to 0.007%, H: up to 0.0004%, O: up to 0.002%, Ca: up to 0.005% , Al: 0.01 to 0.1%. Method according to one of the Claims 1 until 13th , characterized in that the steel material composite used has a core layer (1) made of a steel which, in addition to Fe and unavoidable impurities due to the manufacturing process, consists of C: 0.17 to 0.22%, Si: 0.2 to 0.45% by weight %, Mn: 0.8 to 1.1%, P: up to 0.03%, S: up to 0.01%, Cr: 0.6 to 0.9%, Cu: 0.01 to 0.05% , Nb: up to 0.04%, Mo: up to 0.3%, N: up to 0.015%, Ti: up to 0.02%, V: up to 0.05%, Ni: up to 1.5%, B: up to 0.007%, H: up to 0.0004%, O: up to 0.002%, Ca: up to 0.005%, Al: 0.02 to 0.1%, and cover layers (2, 3) each consist of a steel, which is next to Fe and impurities unavoidable due to the manufacturing process in% by weight of C: 0.35 to 0.45%, Si: 0.1 to 0.3%, Mn: 0.6 to 1.0%, P: up to 0.03 %, S: up to 0.01%, Cr: 0.5 to 1.0%, Cu: up to 0.3%, Nb: up to 0.04%, Mo: up to 0.3%, N: up to 0.015% , Ti: up to 0.02%, Ni: 0.9 to 1.3%, B: up to 0.007%, H: up to 0.0004%, O: up to 0.002%, Ca: up to 0.005%, Al: 0, 02 to 0.1%. Steel component for ballistic use, characterized in that it is according to one of the Claims 1 until 15th is made.

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