STEEL MATERIAL COMPOSITE WITH INHOMOGENEOUS PROPERTY DISTRIBUTION

Abstract

The present invention relates to a steel material composite, comprising a core layer of a higher-strength or high-strength steel and, integrally bonded to the core layer on one or both sides, an outer layer of ferritic, chemically resistant steel. Corresponding flat steel products are distinguished by favourable properties with respect to their strength, ductility, low sensitivity to hydrogen-induced crack formation and favourable corrosion resistance. The present invention also relates to a method for producing a corresponding steel material composite and to the use of such steel material composites in vehicle structures and in particular in bodywork structures.

Claims

1. A steel material composite, comprising a core layer of a higher-strength or high-strength steel and, integrally bonded to the core layer, an outer layer of ferritic, chemically resistant steel on one or both sides of the core layer, wherein the ferritic, chemically resistant steel contains 0.07% by weight of carbon, 1% by weight of manganese, 12 to 30% by weight of chromium, 7% by weight of molybdenum, 0.05% by weight of in each case phosphorus and sulphur, 0.5% by weight of aluminium, 0.5% by weight of silicon, and 1% by weight of in each case titanium, niobium, vanadium and zirconium, with titanium, niobium, vanadium and zirconium in total making up a proportion of >0.1% by weight, and the remainder being iron and unavoidable impurities.

2. A steel material composite according to claim 1, wherein the ferritic, chemically resistant steel has a tensile strength of <1000 MPa.

3. A steel material composite according to claim 1, wherein the ferritic, chemically resistant steel has a chromium content of 16% by weight.

4. A steel material composite according to claim 1, wherein the higher-strength or high-strength steel has a carbon content of 0.15% by weight.

5. A steel material composite according to claim 1, wherein the carbon content in the region of joining of the higher-strength or high-strength steel and the ferritic, chemically resistant steel has a maximum which is at least 1.2 times, the carbon content of the ferritic, chemically resistant steel.

6. A steel material composite according to claim 1, which has a strength of >1200 MPa on average over the total thickness of the composite.

7. A steel material composite according to claim 1, wherein the steel material composite in addition to the core layer and outer layer includes further coatings, on the respective outer side of the steel material composite.

8. A layer of ferritic, chemically resistant steel with a carbon content of 0.07% by weight, 1% by weight of manganese, 12 to 30% by weight of chromium, 7% by weight of molybdenum, 0.05% by weight of in each case phosphorus and sulphur, 0.5% by weight of aluminium, 0.5% by weight of silicon, and 1% by weight of in each case titanium, niobium, vanadium and zirconium, with titanium, niobium, vanadium and zirconium in total making up a proportion of >0.1% by weight, and the remainder being iron and unavoidable impurities, said layer comprising a plating layer on a higher-strength or high-strength steel layer core for improving the bending properties of the steel material composite.

9. A method for producing a steel material composite according to claim 1, comprising the provision of a higher-strength or high-strength steel as core layer, the laying of a layer of ferritic, chemically resistant steel on one or both sides of the steel of the core layer, and the joining of the steel substrate and layer of ferritic, chemically resistant steel under suitable conditions.

10. A method according to claim 9, characterised in that the joining of the steel of the core layer and layer of ferritic, chemically resistant steel takes place by hot roll cladding.

11. A steel material composite according to claim 1 as a component of a vehicle structure.

12. The component of claim 11, characterised in that the vehicle structure is for a B-pillar, structural components in the power flow, gusset plates, seat rails, components with high strength requirements which are at risk of corrosion, such as chassis, tanks, crash boxes, side members or battery boxes.

13. A steel material composite according to claim 1, wherein the ferritic, chemically resistant steel has a chromium content of 20% by weight.

14. A steel material composite according to claim 1, wherein the higher-strength or high-strength steel has a carbon content of 0.20% by weight.

15. A steel material composite according to claim 1, wherein the higher-strength or high-strength steel has a carbon content of 0.25% by weight.

16. A steel material composite according to claim 1, wherein the carbon content in the region of joining of the higher-strength or high-strength steel and the ferritic, chemically resistant steel has a maximum which is at least 2 times the carbon content of the ferritic, chemically resistant steel.

17. A steel material composite according to claim 1, wherein the steel material composite in addition to the core layer and outer layer includes aluminium-based, zinc-based or paint-based coatings, on the respective outer side of the steel material composite.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 A shows a section through a conventional C-steel/C-steel material composite. The carbon concentration profile of this steel is illustrated in B. A uniformly rising concentration profile is shown which leads to a uniform increase in strength over the cross-section.

[0037] FIG. 2 A shows a section through a chemically resistant steel (ferrite)/C-steel material composite in accordance with the present invention. The carbon profile resulting in this case over the material cross-section B shows the occurrence of a concentration maximum at the boundary layer between the ferritic plating layer and core material. This results in the material next to the core material in the initial state having a further region with a lowered C content (C sink). This region owing to the lower carbon content upon heating to an austenitising temperature in conjunction with press-hardening will attain a lower martensitic hardness than the non-influenced core having a higher carbon content.