HOT-WORKING MATERIAL, COMPONENT AND USE

Abstract

The invention relates to a hot-forming material composed of a three-layer composite material, comprising a core layer of a hardenable steel which in the press-hardened state has a tensile strength >1600 MPa and/or a hardness >490 HV10, more particularly a tensile strength >1700 MPa and/or a hardness >520 HV10, and two outer layers bonded substance-to-substance with the core layer and composed of a soft steel which has a tensile strength corresponding at most to one quarter of the tensile strength of the core layer in the press-hardened state, and provided on one or both sides with an anticorrosion coating, more particularly an aluminum-based coating. The invention further relates to a component and also to a corresponding use.

Claims

1. A hot-forming material composed of a three-layer composite material, comprising a core layer of a hardenable steel which in the press-hardened state has at least one of a tensile strength >1600 MPa and a hardness >490 HV10, and two outer layers bonded substance-to-substance with the core layer and composed of a soft steel which has a tensile strength corresponding at most to one quarter of the tensile strength of the core layer in the press-hardened state, and provided on at least one side or both sidcs with an anticorrosion coating.

2. The hot-forming material as claimed in claim 1, wherein the core layer, besides Fe and unavoidable production-related impurities, in wt %, consists of C: 0.27-0.8%, Si: up to 0.5%, Mn: up to 2.0%, P: up to 0.06%, S: up to 0.05%, Al: up to 0.2%, Cr+Mo: up to 1.0%, Cu: up to 0.2%, N: up to 0.01%, Nb+Ti: up to 0.2%, Ni: up to 0.5%, V: up to 0.2%, B: up to 0.01%, As: up to 0.02%, Ca: up to 0.01%, Co: up to 0.02%, and Sn: up to 0.05%.

3. The hot-forming material as claimed in claim 1, wherein the outer layers, besides Fe and unavoidable production-related impurities, in wt %, consist of: C: up to 0.06%, Si: up to 0.6%, Mn: up to 1.0%, P: up to 0.1%, S: up to 0.06%, Al: up to 0.2%, Cr+Mo: up to 0.5%, Cu: up to 0.3%, N: up to 0.01%, Ni: up to 0.3%, Nb+Ti: up to 0.25%, V: up to 0.05%, B: up to 0.01%, Sn: up to 0.05%, Ca: up to 0.01%, and Co: up to 0.02%.

4. The hot-forming material as claimed in claim 1 wherein the core layer has a C content between 0.30-0.75 wt %.

5. The hot-forming material as claimed in claim 1 wherein the outer layers each have a thickness of material of between 0.5% and 20%, based on the total thickness of the hot-forming material.

6. The hot-forming material as claimed in claim 1 wherein the composite material has been produced by means of one of cladding or by means of casting.

7. The hot-forming material as claimed in claim 1 wherein the ratio of the C content of the core layer to the C content of the outer layer is >4, more particularly >5, preferably >6, very preferably >7.

8. The hot-forming material as claimed in claim 1 wherein the hot-forming material satisfies the following relationship in relation to the difference of the bending angle (BW) determined in a VDA 238-100 three-point bending test, in the condition with and without anticorrosion coating: $.Math..Math.\mathrm{BW}<17.Math.*F,\mathrm{where}.Math..Math.F=\frac{\mathrm{tensile}.Math..Math.\mathrm{strength}.Math..Math.\left(\mathrm{core}.Math..Math.\mathrm{layer}\right)}{1500.Math..Math.\mathrm{MPa}}.Math..Math.\mathrm{as}.Math..Math.\mathrm{dimensionless}.Math..Math.\mathrm{strength}.Math..Math.\mathrm{relation}.$

9. The hot-forming material as claimed in claim 1 wherein hot-forming material is part of a tailored product.

10. The hot-forming material of claim 1 wherein the hot forming material is formed by means of press hardening.

11. canceled

12. The hot-forming material of claim 1 wherein the core layer has at least one of a tensile strength >1700 MPa and a hardness >520 HV10.

13. The hot forming material of claim 1 wherein the anti-corrosion coating comprises an aluminum-based coating.

14. The hot forming material of claim 4 wherein the core layer has a C content of between 0.51-0.60 wt %

15. The hot forming material of claim 5 wherein the outer layers each have a thickness of material between 1% and 10%.

16. The hot forming material of claim 7 wherein the ratio of the C content of the core layer to the C content of the outer layer is >7.

17. The hot forming material of claim 9 wherein the hot-forming material is part of one of a tailored welded blank and a tailored rolled bank.

Description

[0072] The present invention is elucidated in more detail below, with reference to a figure and examples.

[0073] FIG. 1 shows results ascertained in a VDA 238-100 plate bending test on a variety of samples.

EXAMPLES

[0074] From commercial flat steel products, by means of hot roll cladding, hot-forming materials were produced, comprising a three-layer composite material. Steels used as outer layers D1-D3 were those specified in table 1, and steels used as core layers K1-K6 were those specified in table 2. The listed tensile strengths in tables 1 and 2 relate to the press-hard state. In all, 24 different hot-forming materials (I-1 to IV-6) were brought together; see table 3. In the case of 18 of the hot-forming materials (I-1 to III-6), the outer layers each had a thickness of material of 10% per side, based on the total thickness of the hot-forming material, whereas for the hot-forming materials (IV-1 to IV-6), the thicknesses of material of the outer layers were only in each case 5% per side, based on the total thickness of the hot-forming material.

[0075] Here, in each case, cut-to-size sheets with two outer layers and a core layer in between them were stacked on top of one another, these sheets, at least in regions along their edges, being bonded substance-to-substance to one another, preferably by means of welding, to form a preliminary assembly. The preliminary assembly was brought to a temperature >1200 C. and in a number of steps was hot-rolled to form a composition material with a total thickness of 3 mm, and processed further into cold strip at 1.5 mm. The composite material or, respectively, the hot-forming material was coated on both sides with an aluminum-based coating, an AlSi coating having a coat thickness in each case of 20 m. The coat thicknesses can be between 5 and 30 m.

[0076] Blanks were divided out of the hot-forming materials produced (I-1 to IV-6). As well as the hot-forming materials, six AlSi-coated steels and six uncoated steels were also provided as reference, corresponding to the compositions in table 2, namely core layers without outer layers, with a thickness of 1.5 mm. The blanks and also the coated and uncoated monolithic steels were heated to austenitization temperature, more particularly above Acs (based on the core layer), in an oven for around 6 minutes each, and were heated through, and were subsequently subjected to hot forming and cooling in a cooled mold, in each case to form identical components. The cooling rates were >30 K/s. The core layers over the thickness were composed substantially entirely of martensite; in the transition region to the outer layer, there may additionally be ferrite and/or bainite present. In the outer layers, a mixed structure with fractions of ferrite, bainite, andpartiallymartensite had been established.

[0077] Samples were cut from the press-hardened components, and were subjected to a VDA 238-100 plate bending test. The results are brought together in FIG. 1. FIG. 1 shows a diagram in which the total tensile strength in [MPa] is plotted on the x-axis and the difference in bending angle in [ ] relative to the uncoated samples is plotted on the y-axis. It is apparent that the monolithic, press-hardened samples of core materials with increasing strength, coated with an aluminum-based coating (AlSi), exhibit the greatest bending angle difference in comparison to the uncoated references. The values for the press-hardened samples obtained from the hot-forming materials of the invention are uniformly below the monolithic, press-hardened samples from core materials. Embodiments I-1 to I-6 have a bending angle difference which is too high, too similar to the monolithic hot-forming materials likewise represented, since the outer layer of embodiments I-1 to I-6 has a C content >=0.07 wt %. Owing to the thermal exposure, there is diffusion here of C from the core layer in the direction of the outer layer, and the effect of the soft outer layer is reduced. In the case of embodiments II-1 and IV-6, conversely, the C content of the outer layers is lower than in the case of embodiments I-1 to I-6, so creating a greater potential for carburization in the sense of a buffer. As a result, a lower bending angle difference is established. The C content in the outer layer is not more than 0.06 wt %, more particularly not more than 0.05 wt %. The following relationship allows hot-forming materials of the invention (see inventive region in FIG. 1) to be delimited from noninventive embodiments:

[00002]$.Math..Math.\mathrm{BW}<17.Math.*F,\mathrm{where}.Math..Math.F=\frac{\mathrm{tensile}.Math..Math.\mathrm{strength}.Math..Math.\left(\mathrm{core}.Math..Math.\mathrm{layer}\right)}{1500.Math..Math.\mathrm{MPa}}.$

[0078] The invention is not limited to the exemplary embodiments shown or to the embodiments in the general description. Instead, the hot-working material of the invention may also be part of a tailored product, in the form, for example, of part of a tailored welding blank and/or tailored rolled blank.

TABLE-US-00001 TABLE 1 C Si Mn P S Al Cr Nb Ti B Rm [MPa] D3 0.003 0.02 0.13 0.01 0.012 0.0325 0.05 0.005 0.007 0.0004 306 D2 0.0375 0.04 0.25 0.015 0.015 0.04 0.06 0.004 0.004 0.0006 319 D1 0.07 0.205 0.8 0.02 0.006 0.04 0.075 0.02 0.004 458

TABLE-US-00002 TABLE 2 C Si Mn P S Al Cr N N Ti V B Ca Rm [MPa] K1 0.35 0.25 1.3 0.01 0.0015 0.035 0.14 0.0015 0.0325 0.0028 1911 K2 0.42 0.225 1.3 0.02 0.003 0.035 0.35 0.003 0.0275 0.003 0.00 3 2093 K3 0.45 0.07 0.62 0.01 0.004 0.04 0.22 0.002 0.026 0.003 2304 K4 0.48 0.22 1.2 0.01 0.002 0.03 0.24 0.002 0.03 0.0032 0.002 2400 K5 0.53 0.23 1.19 0.01 0.003 0.03 0.58 0.2 0.002 0.025 0.02 0.003 2518 K6 0.61 0.39 1.5 0.01 0.003 0.04 0.73 0.0025 0.03 0.0035 0.002 2731 indicates data missing or illegible when filed

TABLE-US-00003 TABLE 3 Proportion Embodiment Core layer Proportion Outer layer (per side) I-1 K1 80% D1 10% I-2 K2 I-3 K3 I-4 K4 I-5 K5 I-6 K6 II-1 K1 D2 II-2 K2 II-3 K3 II-4 K4 II-5 K5 II-6 K6 III-1 K1 D3 III-2 K2 III-3 K3 III-4 K4 III-5 K5 III-6 K6 IV-1 K1 90% D3 5% IV-2 K2 IV-3 K3 IV-4 K4 IV-5 K5 IV-6 K6