THREE-LAYER HIGH-STRENGTH STEEL OR BALLISTIC STEEL, METHOD FOR PRODUCING A COMPONENT, AND USE THEREOF

Abstract

The invention relates to a three-layer wear-resistant steel or ballistic steel. The invention further relates to a process for producing a component from the wear-resistant steel or ballistic steel and also a corresponding use.

Claims

1. A three-layer wear-resistant steel or ballistic steel comprising a core layer composed of a steel which in the hardened or tempered state has a hardness of >350 HBW and two covering layers which are joined by substance-to-substance bonding to the core layer and are composed of a softer steel, where the covering layers have a hardness which is at least 20% lower than that of the core layer in the hardened or tempered state, wherein the core layer comprises, in addition to Fe and production-related unavoidable impurities, in % by weight, C: from 0.1 to 0.6%, Mn: from 0.1 to 2.5%, S: up to 0.03%, Sn: up to 0.05%, As: up to 0.02%, Co: up to 0.02%, O: up to 0.005%, H: up to 0.001%, and the covering layers comprise, in addition to Fe and production-related unavoidable impurities, in % by weight, C: from 0.001 to 0.15%, S: up to 0.03%, Sn: up to 0.05%, As: up to 0.02%, Co: up to 0.02%, H: up to 0.001%, O: up to 0.005%.

2. The wear-resistant steel or ballistic steel as claimed in claim 1, wherein the covering layers have a thickness of material in the range from 1% to 12%, per side based on the total thickness of material of the wear-resistant steel or ballistic steel.

3. The wear-resistant steel or ballistic steel as claimed in claim 2 wherein the wear-resistant steel or ballistic steel has a metallic anticorrosion coating on one or both sides and/or is provided on one or both sides with an organic coating.

4. The wear-resistant steel or ballistic steel as claimed in claim 2 wherein the wear-resistant steel or ballistic steel has been produced by means of cladding or by means of casting.

5. The wear-resistant steel or ballistic steel of claim 1 wherein the ballistic steel is cold formed.

6. (canceled)

7. A process for producing a component which is to be subjected to high abrasive wear, wherein a wear-resistant steel as claimed in claim 4 is cold formed.

8. (canceled)

9. The wear-resistant steel or ballistic steel of claim 1 wherein the core layer further comprises at least one of N: from 0.003 to 0.01% and Si: from 0.05 to 1.5%.

10. The wear-resistant steel or ballistic steel of claim 1 wherein the core layer further comprises at least one of Al: from 0.01 to 2.0%, Cr: from 0.05 to 1.5%, and B: from 0.0001 to 0.01%.

11. The wear-resistant steel or ballistic steel of claim 1 wherein the core layer further comprises at least one element selected from the group comprising of Nb, Ti, V and W: in total from 0.005 to 0.2%.

12. The wear-resistant steel or ballistic steel of claim 1 wherein the core layer further comprises at least one of Ca: from 0.0015 to 0.015%, and Ni: from 0.1 to 5.0%.

13. The wear-resistant steel or ballistic steel of claim 1 wherein the covering layers further comprise at least one of N: from 0.001 to 0.01%, Si: from 0.03 to 0.7%, Mn: from 0.05 to 2.5%, P: from 0.005 to 0.1%, Mo: from 0.05 to 0.45%, Cr: from 0.1 to 0.75%, Cu: from 0.05 to 0.75%, Ni: from 0.05 to 0.5%, Al: from 0.005 to 0.5%, and B: from 0.0001 to 0.01%.

14. The wear-resistant steel or ballistic steel of claim 1 wherein the covering layers further comprise one or more elements selected from the group consisting of Nb, Ti, V and W: from 0.001 to 0.3%.

15. The wear-resistant steel or ballistic steel of claim 1 wherein the covering layers further comprise Ca: from 0.0015 to 0.015%.

16. The wear-resistant steel or ballistic steel of claim 2 wherein the covering layers have a thickness of material in the range of 2% to 10% per side.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0060] The invention will be illustrated below with the aid of a drawing depicting a working example. The drawing shows

[0061] FIG. 1) a schematic section through a wear-resistant steel or ballistic steel according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0062] The single FIGURE shows a schematic sectional view through a wear-resistant steel or ballistic steel (1) according to the invention. The three-layer wear-resistant steel or ballistic steel (1) according to the invention comprises a core layer (1.1) composed of a steel which in the hardened or tempered state has a hardness of >350 HBW, in particular >400 HBW, preferably >500 HBW, more preferably >550 HBW, particularly preferably >600 HBW, and two covering layers (1.2) composed of a softer steel which are joined by substance-to-substance bonding to the core layer (1.1), where the covering layers (1.2) have a hardness which is at least 20% lower than that of the core layer (1.1) in the hardened or tempered state, with a hardness of <400 HBW, in particular <350 HBW, preferably <300 HBW, particularly preferably <250 HBW, more preferably <200 HBW. The wear-resistant steel or ballistic steel (1) can have a metallic anticorrosion coating (1.3) on both sides.

[0063] The core layer (1.1) consists of, in addition to Fe and production-related unavoidable impurities, in % by weight, C: from 0.1 to 0.6%, optionally N: from 0.003 to 0.01%, optionally Si: from 0.05 to 1.5%, Mn: from 0.1 to 2.5%, optionally Al: from 0.01 to 2.0%, optionally Cr: from 0.05 to 1.5%, optionally B: from 0.0001 to 0.01%, optionally one or more elements selected from the group consisting of Nb, Ti, V and W: in total from 0.005 to 0.2%, optionally Mo: from 0.1 to 1.0%, optionally Cu: from 0.05 to 0.5%, optionally P: from 0.005 to 0.15%, S: up to 0.03%, optionally Ca: from 0.0015 to 0.015%, optionally Ni: from 0.1 to 5.0%, Sn: up to 0.05%, As: up to 0.02%, Co: up to 0.02%, 0: up to 0.005%, H: up to 0.001%.

[0064] The covering layers (1.2) consist of, in addition to Fe and production-related unavoidable impurities, in % by weight, C: from 0.001 to 0.15%, optionally N: from 0.001 to 0.01%, optionally Si: from 0.03 to 0.7%, optionally Mn: from 0.05 to 2.5%, optionally P: from 0.005 to 0.1%, optionally Mo: from 0.05 to 0.45%, optionally Cr: from 0.1 to 0.75%, optionally Cu: from 0.05 to 0.75%, optionally Ni: from 0.05 to 0.5%, optionally Al: from 0.005 to 0.5%, optionally B: from 0.0001 to 0.01%, optionally one or more elements selected from the group consisting of Nb, Ti, V and W: from 0.001 to 0.3%, S: up to 0.03%, optionally Ca: from 0.0015 to 0.015%, Sn: up to 0.05%, As: up to 0.02%, Co: up to 0.02%, H: up to 0.001%, 0: up to 0.005%.

[0065] The thickness of the materials of the covering layers (1.2) can be in the range from 1% to 12%, in particular from 2% to 10%, preferably from 3% to 8%, per side based on the total thickness of materials of the wear-resistant steel or ballistic steel (1).

[0066] A ballistic steel according to the invention and a wear-resistant steel according to the invention were produced from commercial flat steel products by means of hot rolling cladding, each of which had a three-layer materials composite. A microalloyed steel having the designation S315MC or an IF steel having the designation DC05 was in each case used as covering layers and a steel having the designation XAR 500 or XAR 600 was used as core layer for producing the wear-resistant steel and a steel having the designation SECURE500 or SECURE600 or SECURE 650 was used as core layer for producing the ballistic steel. The covering layers each had a thickness of material of 10% per side based on the total thickness of material of the wear-resistant steel; the thicknesses of materials of the covering layers of the ballistic steel, on the other hand, were in each case 5% per side based on the total thickness of material of the ballistic steel. Both the ballistic steel and also the wear-resistant steel were in all indicated variants of the core layer in each case combined with all indicated variants of the covering layer.

[0067] Pieces of sheet which had been cut to size, comprising two covering layers and a core layer arranged in between, were in each case stacked on top of one another and were joined at least in regions along their edges by substance-to-substance bonding, preferably by means of welding, to give a precomposite. The precomposite was brought to a temperature of >1100 C. and hot rolled in a number of steps to give a materials composite having a total thickness of material of 6 mm. The materials composite was subsequently electrolytically coated on both sides with a zinc-based coating having a layer thickness of 20 m in each case. The layer thicknesses can be in the range from 5 to 30 m.

[0068] Plates were parted from the materials composites produced. In addition to the materials composites, monolithic plates of each of the designations indicated were also produced from the same melt as the core layers. Here, the thicknesses of material in the case of the ballistic steels were 5.4 mm, which corresponded to the core layer thickness of the ballistic steels according to the invention. In the case of the wear-resistant steels, monolithic plates having a thickness of material of 4.8 mm corresponding to the core layer thickness of the wear-resistant steels according to the invention, were in each case produced. The monolithic plates were each provided as reference.

[0069] All plates, which had a size of 6000 mm1200 mm, were heated to the austenitizing temperature, in particular above Acs based on the core layer, in a furnace for in each case about 180 minutes and heated through and were subsequently quenched in order to set the desired hardness in the core layer. Before quenching, the plates were clamped in a cooling apparatus, known as a quencher, in order to ensure an essentially distortion-free thermal treatment. Quenching was carried out by contact with water. Other liquid media for quenching can likewise be used. The cooling rates in the core of the materials composite were monitored by means of thermocouples introduced beforehand and were >20 K/s. Due to the process, a cooling power which is homogeneous over the entire surface of the material cannot always be achieved in quenchers since the water is supplied from spray nozzles which can produce only an approximately uniform supply of water. Locally nonuniform cooling powers can lead to undesirable property variations, for example in the hardness. Inhomogeneous cooling profiles due to the process can also lead, in the phase transformation of the material, to stresses at the surface of the monolithic materials used hitherto, which stresses are firstly undesirable for further processing since they can lead to distortion on a component to be produced during further processing, and secondly local microstructural differences can in the extreme case lead to damage to the material close to the surface, which in the production process can lead to rejects or unavoidable after-working, for example to grind out incipient cracks. It has surprisingly been found that irregularities as occur every now and again in the case of the monolithic steels used hitherto could not be found in the case of the wear-resistant steels and ballistic steels of the invention. One explanation for this could be that the soft covering layers which have very good thermal conductivity have a homogenizing effect in respect of heat removal, effectively provide a type of heat buffer or intermediate buffer, but it is at the same time ensured that the removal of heat is sufficiently high for a hardened microstructure to be able to be formed in the core layers despite the covering layer. The covering layers which perform no function in respect of the application or use therefore also lead, owing to the homogenization of the removal of heat from the core layer, to uniform hardness in the core layer and, cited therewith, to an increase in process reliability.

[0070] The core layers of the ballistic steel of the invention and of the wear-resistant steel of the invention had a microstructure composed predominantly of martensite and/or bainite, in particular mainly martensite. In the case of the covering layer S315MC, a mixed microstructure with proportions of ferrite, bainite and some martensite has been formed in the covering layers. In the case of the covering layer DC05, an essentially ferritic microstructure with small proportions of bainite and/or martensite was observed, which is attributed to carbon diffusion from the core layer. The monolithic reference steels had properties comparable to those of the corresponding core layers having the same composition.

[0071] In a bending test carried out in accordance with the publication Sicherheitssthle SECURE. Verarbeitungsempfehlungen. Of ThyssenKrupp Steel AG, 08/2008 edition, the plates were bent perpendicular to the former rolling direction. The critical bending radius r in the case of the monolithic ballistic steel SECURE 500 with the cladding material DC05 was found to be about 30 mm. Tighter bending radii led to incipient cracks at the surface in the bent region. The critical bending radius r in the case of the monolithic wear-resistant steel XAR 500 with the cladding material DC05 was found to be about 23.5 mm. Tighter bending radii also led to incipient cracks at the surface in the bent region in the case of the monolithic wear-resistant steel. In the case of the ballistic steel according to the invention, bending radii down to about 27 mm were possible without discernible incipient cracks. In the case of the wear-resistant steel according to the invention, bending radii down to about 21 mm could be implemented without problems. The possibility of implementing a smaller bending radius is greater in the case of the wear-resistant steel according to the invention compared to the ballistic steel according to the invention, which is attributed to the slightly greater thickness of material of the covering layers. A reduction in the critical bending radius in the case of wear-resistant steels and ballistic steels of the invention compared to monolithic reference steels having the same properties is associated with a slight increase in weight.

[0072] The invention is not restricted to the working example depicted in the drawing or to the information given in the general description. Rather, the wear-resistant steel or ballistic steel according to the invention can also be produced from a tailored product, for example a tailored blank and/or tailored rolled blank.