EP3329022A1

EP3329022A1 - Body component or chassis component of a motor vehicle having improved crash performance, and method for producing same

Info

Publication number: EP3329022A1
Application number: EP16735810.0A
Authority: EP
Inventors: Andreas Frehn; Georg Frost
Original assignee: Benteler Automobiltechnik GmbH
Current assignee: Benteler Automobiltechnik GmbH
Priority date: 2015-07-28
Filing date: 2016-05-12
Publication date: 2018-06-06
Also published as: WO2017016535A1; DE102015112327A9; US20180370578A1; EP3328643B1; CN108472929A; US20180222536A1; CN107922990A; CN108472929B; EP3328643A1; WO2017016536A1; DE102015112327A1

Abstract

The invention relates to a body component or chassis component (1) for a motor vehicle, comprising at least one surface segment (2, 3) composed of a three-layer sheet-metal composite (10) having a central layer (11) and two outer layers (12, 13), which bound the central layer (11) on the outside and which are integrally joined to the central layer face to face, characterized in that the outer layers (12, 13) are composed of a stainless steel alloy having a microstructure selected from the group of ferritic, austenitic, or martensitic microstructure and the central layer (11) is composed of a heat-treatable steel alloy, and the body component or chassis component has a bending angle of greater than 80°, determined in the plate bending test according to VDA 238-100, having an Rp0.2 yield strength of greater than 900 MPa.

Description

Body or chassis component of a motor vehicle with improved crash performance and method for its production

The invention relates to a body or chassis component for a motor vehicle with improved crash performance and to a method for producing a body or chassis component with improved crash performance and corrosion protection.

In the automotive industry, crash-sensitive components are used for the body, which give the vehicle stability and rigidity and absorb crash energy in the event of an accident and provide the occupants with a survival space. Likewise, more components are used in the chassis of a motor vehicle, which in addition to stiffness and dynamic load especially high demands on a defined deformability but also to the economy. One common method is the so-called thermoforming and press hardening of temperable steel grades with the steps of heating for austenitizing, hot working and quench hardening in a press mold. It is customary to provide as a temporary corrosion protection and anti-scaling during heating an aluminum-silicon coating on a heat-treatable steel sheet. This material of the company ArcelorMittal is known under the trade name Usibor for hot forming and widely used. WO 2009 090 555 A1 describes the corresponding material and the coating structure before and after hot forming and press hardening. It will also discuss the heating strategy for the economical production of body parts. A disadvantage of coated hot-forming steels, even more so than uncoated thermoforming steels, is an increased tendency to crack starting from the surface of the component in the press-hardened state, which can be noticeable during a crash in a component failure. The reason for this is the cold deformation acting on the press-hardened component in the event of a crash, as a result of which microcracks already frequently growing on the hard and brittle surface, in particular the aluminum coating alloyed with iron atoms, frequently grow. The same problems are even more pronounced with zinc alloy coated steels for thermoforming.

Based on this, the object of the present invention is accordingly to propose improved bodywork or chassis components for a motor vehicle and their production methods in the crash properties, which nevertheless are inexpensive to manufacture, process and light.

This object is solved objectively by the features of claim 1. Dependent claims 2 to 16 form advantageous developments of the invention.

The object is solved by the method by the features of claim 17. The dependent claims 18 to 21 represent advantageous developments of the method. It is proposed a body or chassis component for a motor vehicle with improved crash performance comprising at least one surface portion of a multi-layer, in particular three-layer sheet metal composite with a central position and two outwardly limiting the center layer outer layers. According to the outer layers are connected flat and cohesively with the central layer. Characteristic is that the outer layers of a stainless steel alloy with a microstructure selected from the group of ferritic, austenitic or martensitic microstructure and the middle layer of a heat treatable, especially hardened steel alloy, and the bodywork or chassis component a bending angle greater than 80 degrees (° ), determined in the platelet bending test according to VDA 238-100: 2010, at a yield strength Rp0.2 of greater than 900 MPa. This allows a maximum of corrosion protection throughout the life of the vehicle, even under rough handling and operating conditions. In addition, the softer outer layer, which is firmly connected to the harder middle layer, causes the tendency for the crack to drop significantly during an intended load in the event of a crash, but also already during a joining or cold-forming operation following the component component. According to the invention, the connection between the outer layers and the middle layer takes place in a planar manner through a material bond such that there are essentially no inclusions or contaminants between the layers, wherein in particular a metallurgical connection is formed. According to the invention, the individual layers are preferably bonded to one another in a material-bonded and metallurgical manner over the entire surface. The starting material used for the invention can be produced, for example, by hot rolling three previously mechanically and / or materially prefixed connected slabs, or a multi-stage cast slab, or an order-welded slab.

As a ferritic stainless steel alloy, it has proved particularly advantageous to use an alloy which, in addition to molten metal-related impurities and iron, comprises the following alloy constituents in percent by weight: Carbon (C): 0.08% to 0.16%

Silicon (Si): 0.5% to 1, 8%

Manganese (Mn): 0.8% to 1, 4%

Chromium (Cr): 13.0% to 22.0%

Aluminum (AI): 0.5% to 1, 5%

Phosphorus (P): maximum 0.06%

Sulfur (S): maximum 0.02%.

The advantage of the ferric stainless steel alloy in combination with a hardenable, ferritic-pearlitic steel alloy of the middle layer is that the composition of the outer layer during the heat treatment with the middle layer forms a particularly homogeneous and durable cohesive connection. Even during structural transformation of the middle layer during thermoforming and press hardening, there is no danger of cracks, spalling or the like of the outer layer.

While chromium ensures heat resistance and thus a scale-free surface during heating and hot forming, the heat treatable steel alloy of the middle layer ensures maximum tensile strength. Furthermore, reference should be made to the content of EN 10088-1 for further usable ferritic stainless steel alloys, with chromium contents of between 10.5% and 30% depending on the variety. To ensure weldability, stabilization additives of less than 0.5% of titanium, niobium or zirconium and limited to 0, 16% carbon content.

With regard to usable austenitic stainless steel alloys, reference is hereby made to grades EN 1.4310 and EN 1.4318. The ductility and elongation at break of austenitic stainless steels is very high both in the low temperature range and in the hot working. The brittle fracture tendency is extremely low. During cold forming and crash, its strength increases by converting metastable austenitic phases into martensite.

With regard to martensitic stainless steel alloys, reference is made, by way of example, to the readily weldable grades EN 1.4313 and EN 1 .4418 as well as supermartensitic steels of the grade EN 1.4415. The latter are at the same time high strength, very tough and have, in addition to molten impurities and iron, a chemical composition expressed in weight percent, comprising:

Carbon (C) max. 0.03%

Chromium (Cr) -13%

Nickel (Ni) 2-6%

Molybdenum (Mo) max. 3%

Nitrogen (N)> 0.005%.

Preferably, the bending angle of the body or chassis component is greater than 95 ° and the yield strength Rp0.2 greater 950 megapascals (MPa).

Particularly preferably, the bending angle is greater than 90 °, in particular greater than 100 °, preferably greater than 1 10 °. In particular, the body or chassis component has a product of bending angle and yield strength Rp0.2 between 90,000 ° MPa (Megapascal degrees) and 180,000 ° MPa, resulting in an optimal performance for the case of a crash without special measures of the process control during or after thermoforming, without danger of cracks or even a component failure.

In order to make maximum use of the lightweight construction potential of the heat-treatable steel alloy, according to the invention, the middle layer of the surface section preferably has an ultra-high-strength microstructure, with at least 80 percent martensite. The tensile strength Rm within the area section with a three-layer composite is greater than 1300 megapascals (MPa).

It is also possible that the middle layer of a surface portion has a structure selected from a group of tempered martensite with a share of at least 80 percent or a mixed structure with at least 70 percent levels of ferrite and perlite and residual martensite, retained austenite and / or bainite.

The percentages of the structural components relate to metallographically easily ascertainable area proportions.

Preferably, the surface portion with the three-layer composite sheet on a total thickness and one of the outer layers has a thickness, wherein the thickness of one of the outer layers at least 3 percent and at most 15 percent, preferably 4 percent to 10 percent of the total thickness of this surface section corresponds. Under total thickness is to be understood the sum of the thicknesses of the two outer layers and the middle layer in the respective surface sections. The total thickness is preferably between 1 and 10 millimeters (mm), in particular between 1, 7 and 3.5 mm. A thicker outer layer hardly brings any advantages under anticorrosive aspects, but significantly reduces the overall strength of the surface section. A thinner outer layer is currently difficult to produce reliably by means of rolling technology and, with regard to the corrosion protection, does not fall below the usual service life of a motor vehicle. In the context of the invention, the opposing outer layers preferably have the same thickness. But it is also possible that different thickness outer layers are formed in at least one surface portion, if this is necessary to be particularly well adapted to different crash or corrosion requirements on the inside and outside, for example, in a hollow body or chassis component.

As a heat treatable steel alloy is particularly suitable a manganese-boron steel such as 16MnB5, but preferably 22MnB5 or alternatively 36MnB5. In particular, recoverable steel alloys having a carbon content greater than or equal to 0.27% by weight may be used, for example MBW 1900. These would be too brittle for direct thermoforming and press hardening. Due to the outer layers, their processing by means of thermoforming and press hardening is also possible in a direct thermoforming process, thus without cold deformation.

Figure 1 shows the mechanical characteristics of tensile strength Rm, yield strength Rp0.2, elongation at break A30 and Figure 2 the bending angle of a body component according to the invention with a center of steel grade 22MnB5 and two outer layers of thickness of 5 percent of the total thickness of a ferritic stainless steel alloy. The ferritic steel alloy used was X10CrAISi18. In comparison, Figures 3 and 4 show the results for a steel component of the trade name Usibor with double-sided aluminum-silicon coating according to the prior art. All components had a thickness of 2 millimeters.

In an improved development of the invention, the body or chassis component on a second surface portion of a three-layer sheet metal composite. In this case, the first surface portion has a first middle layer of ultra-high-strength structure with at least 80 percent martensite, while the second surface portion has a second middle layer with a structure selected from a group of tempered martensite with a share of at least 80 percent or mixed structure with at least 70 percent Proportions of ferrite and perlite and residual amounts of martensite and / or retained austenite and / or bainite. Thus, components can be produced with softer and more ductile surface sections.

Furthermore, it can be provided that the second surface portion is a three-layer sheet metal composite, and the first center layer and the second center layer each have a thickness, and the thickness of the first center layer is different from the thickness of the second center layer. A particularly thick surface section can thus be arranged in zones of highest stress and load capacity or where a material reinforcement in the middle of a thinner surface section is required for joining, for example by means of rivet or screw.

The first surface portion may have an overall thickness which differs from the total thickness of the second or further surface portions by at least 10 percent, in particular between 20 and 100 percent.

According to the invention, it can also be provided that the bodywork or chassis component has a second surface section or further surface sections made of a ferritic or martensitic or austenitic, stainless steel alloy. In particular, the surface sections of the bodywork or chassis component can be butt welded to each other. But it is also possible that the bodywork or chassis component has a second surface portion of a ferritic steel alloy, in particular, the surface portions are in turn butt welded together.

Also, the second surface portion or further surface portion may be selected from a low-alloy steel alloy or a multi-phase steel alloy, or a steel alloy having TWIP and / or TRIP properties. Particularly preferably, in the method for producing the chassis or body component of the second surface portion can be heated only to a temperature lower than the AC1 temperature to prevent scaling.

Preferably, the body or chassis component on an edge, wherein the edge is embraced in an end face in the surface portion with three-layer composite sheet at least partially from the outer layer, such that the end face of the central layer is shielded from the environment by the outer layer. As a result, the corrosion resistance is further improved.

Body or chassis components of a motor vehicle according to the invention are particularly from the group door pillar, especially in the form of an A-pillar or center pillar, roof frame, sill, bumper cross member, side member, floor cross member and wishbone, trailing arm, wishbone, stabilizer, twist beam axles, axle, crash box , Door impact beams, tunnels selected for example transmission tunnel. The use as a battery case for a traction battery of an electric or hybrid vehicle is possible.

In the case of a door pillar or a roof frame of the motor vehicle, it is preferable for the second surface section or another surface section with low tensile strength to be arranged in each case in the edge. The edge is ductile in this case and serves for the easier connectivity of connection components, strike plates, local reinforcements or other mechanical processing steps.

The procedural part of the invention is achieved by a method for producing a body or chassis component as described above, with the steps: Provision of a sheet-metal blank comprising at least one surface section of a three-layer sheet metal composite with a middle layer of a heat-treatable steel alloy and one outer layer each bounding the middle layer,

Heating at least the sheet-metal composite, in particular the entire blank to austenitizing temperature,

• Hot forming of the sheet metal blank in an at least partially cooled mold and

At least partially curing the formed sheet metal blank in the press mold or in a subsequent cooling tool stage.

A particular advantage arises in the method when the hot forming and hardening of the sheet metal blank is carried out in or by means of a single press with several tool stages. Alternatively or preferably at the same time it can be provided that the heating and hot forming of the sheet metal blank is carried out in a single press with multiple tool stages. Thus, in each case at least one sheet metal blank is heated, thermoformed and hardened simultaneously in a single press cycle. It is understood that when using servo-driven or mechanical presses an extremely low cycle time and thus a high throughput are possible.

In a further development of the method according to the invention, the heating is carried out within 30 seconds, preferably within 20 seconds, in particular within 10 seconds, which allows a space-saving, low-heat austenitization. Advantageously, the heating is performed in cycles sequentially with the hot forming or the press cycle of a hot forming line. Further preferably, the heating may comprise at least one holding phase. It can be heated without a protective gas atmosphere, since the outer layers have no tendency to mist. An advantage is that a blast treatment of the finished molded component can be omitted before painting or a KTL treatment. When heating the sheet metal plate contact heating is particularly favorable to use, since a high degree of efficiency and low heat losses associated with it as well as the possibility by differently tempered contact plates before thermoforming a first surface portion of the sheet metal blank on more than Austenitisierungstemperatur and a second surface portion less than 700 ° C. This also applies to a tempering stage after heating and upstream of the press mold stage. In particular, the advantage over pre-coated steels results that no alloying must take place beforehand.

According to the invention, it may be provided that a component trimming or a separation, in particular a punching of the component after the hot forming and press hardening, is carried out only on the hardened component. This can then be done by a combined rolling and cutting or pressure cutting, in particular in one of the press tool stage subsequent tool stage of the press, but also outside in a separate operation. In this case, a part of the outer layer is displaced in the edge region in the front side of the separation area or hole edge and at the same time a slug or Verschnittrand is separated. In contrast to aluminum-coated tempering steel, according to the invention, the outer layer of stainless steel alloy protects the central layer against environmental influences, in particular against entry of process-related molecular hydrogen during heating, and prevents the risk of embrittlement of the component caused by introduction of hydrogen. The stainless steel outer layers are not crack-sensitive, unlike coated components. It is therefore very possible to cut these after press hardening in the cold and hard state. In particular, in a press cutting, the lower layer has no significant fraction fraction. The cut edges are essentially free of grades due to the increased ductility of the outer layers. The trimming can also be carried out in a separate cutting tool. In particular, the trimming is carried out completely. This means on final contour. In particular, a crack-free surface is provided. Also, the cutting edge is provided largely free of cracks. They are preferred no cracks or microcracks larger than 10 m are present on the surfaces. A laser cut or complex hot cut can thus be omitted.

Other objects, advantages, features and applications of the present invention will become apparent from the following description of several embodiments with reference to schematic drawings. All described and / or illustrated features alone or in any meaningful combination form the subject matter of the present invention, also independent of their summary in the claims or their dependency.

Showing:

FIG. 1 a and b) two application examples for body and chassis components according to the invention,

Figure 2 shows a first embodiment of a three-layer sheet metal composite for a surface portion of the body or chassis component according to the invention

Figure 3 shows a body component according to the invention in modified

embodiment,

Figure 4 shows a second embodiment of a three-layer sheet metal composite for a surface portion of the body or chassis component according to the invention

FIG. 5 shows a third embodiment of a three-layer sheet-metal composite for a surface section of the body or chassis component according to the invention,

Figure 6a) and b) two further examples of use for an inventive

Body component, FIG. 7 shows a fourth embodiment of a three-layer sheet-metal composite for a surface section of the body or chassis component according to the invention,

FIG. 8 shows a fifth embodiment of a three-layered sheet metal composite for a surface section of the body or chassis component according to the invention,

9 shows a sixth embodiment of a three-layer sheet-metal composite for a surface section of the body or chassis component according to the invention, FIG.

FIG. 10 shows a body or chassis component according to the invention in a marginal detail;

Figure 1 1 a) a first process sequence for carrying out the production process according to the invention and

Figure 1 b) a modification of the first procedure

FIG. 12 shows an alternative method sequence for carrying out the production method according to the invention,

Figure 3a) and b) an inventive body component in a plan view and in cross section and

FIG. 14 a) and b) result images of a corrosion test for a) according to the invention

Component sample and b) a comparative sample according to the prior art.

FIG. 1 shows two advantageous application examples for a body and chassis component 1 according to the invention, in each case in a plan view and cross-sectional representations.

Figure 1 a) shows a center column 20 for the side structure of a motor vehicle, which is used between sill and roof frame and especially the Overall stability of the vehicle body and the Kollisionsenergieabbau and intrusion protection during a side impact serves.

FIG. 1 b) illustrates a transverse link 30 of a wheel suspension of a motor vehicle chassis.

Both examples are body or chassis components 1 made of sheet metal, which were formed three-dimensionally by means of compression molding. Both the center column 20 and the wishbone 30 comprise at least one surface portion 2 of a three-layer sheet metal composite 10 with, as Figure 2 shows in more detail, a central position 1 1 and two the center layer 1 1 outwardly bounding outer layers 12, 13, wherein the outer layers 12, 13 of a stainless, in particular ferritic steel alloy and the middle layer 1 1 consist of a heat-treatable steel alloy. The tensile strength Rm within the area section 2 with a three-layered sheet metal composite 10 is more than 1300 MPa.

In section B and C is indicated in each case a section, which is shown enlarged in the figure 2 and describes the structure of the three-layer sheet metal composite 10 in more detail.

Figure 2 shows a first embodiment of the three-layer sheet metal composite 10 for a surface portion 2 of the body or chassis component 1 according to the invention in sections in cross section. A central position 1 1 of the surface portion 2 is bounded at its top in the image plane top 7 by an outer layer 12, and limited at its bottom in the center below 8 limited by a further outer layer 13. There is a metallurgical connection between the center layer 1 1 and the outer layers 12, 13, so that a detachment of the outer layers 12, 13 is excluded from the central layer 1 1, the weldability, formability and other mechanical workability, however, are quite easy. The composite sheet 10 has a total thickness D2 and a thickness of the central layer Dm and a thickness Da of the outer layer 12. The outer layers 12, 13 are both the same thickness here.

FIG. 3 shows a body component 1 according to the invention in the form of the center pillar according to FIG. 1 in a modified embodiment. Here, the center pillar 20 'is formed of a first surface portion 2 with a three-layered Sheet metal composite 10 in an upper portion 21 of the center column 20 'and from a second surface portion 3 with a three-layer sheet metal composite 15 in a second portion 22 of the center column. The second portion 22 of the center pillar 20 'extends approximately to just below a door lock connection for a vehicle door (not shown). Between the first surface portion 2 and the second surface portion 3, a weld 40 is formed, wherein both surface portions 2, 3 are joined butting against each other, in particular in front of a three-dimensional molding to the body component 1. In section BB at the level of the weld 40 is indicated the section of Sheet metal composite 10, 5, which is considered in more detail in Figures 4 and 5.

FIG. 4 shows the construction of the sheet-metal composite according to FIG. 3, which has a central layer 16 of a low-alloy steel alloy and outer layers 17, 18 of a ferritic stainless steel alloy in the second surface section 3. About the weld both surface sections 2, 3 are connected together. The outer layers 12, 13 of the first surface portion 2 correspond to the outer layers 17, 18 of the second surface portion 3 as in the case of the sheet metal composite according to Figure 2 here is a metallurgical connection between the central layer 1 1 and the outer layers 12, 13. In addition also the outer layers 17 and 18 metallurgically and permanently firmly connected to the central layer 16. This sheet metal composite has a uniform total thickness D2.

5 shows an alternative embodiment of the surface sections 2, 3 of the center pillar 20 'from FIG. 3. Here, the second surface section 3 has a single homogeneous layer of a ferritic stainless steel alloy. The outer layers 12, 13 of the first surface portion 2 correspond in terms of the material of the steel alloy of the second surface portion 3. As in the sheet metal composite according to Figure 2, there is also a metallurgical connection between the central layer 1 1 and the outer layers 12, 13. The two surface sections 2, 3rd are already welded together before shaping the bodywork or chassis component 1 and then together deformable. The second surface portion 3 is arranged in the vehicle in the so-called dry area, thus outside of corrosion prone areas. The second surface section 3 with Stainless, ferritic steel alloy is preferably heated below 700 ° C during heating of the sheet metal plate, so that a scale formation does not occur in this section.

According to the invention, in addition to a B-pillar, another body or chassis component can have, in addition to a three-layer sheet metal composite in a first surface section, a ductile, particularly corrosion-stressed second surface section made of a stainless steel alloy.

FIG. 6a shows a body component 1 according to the invention in the form of the center pillar according to FIGS. 1 and 3 in a modified embodiment. Here, the center pillar 20 "is formed from a first surface portion 2 with a three-layer sheet metal composite 10 in an upper portion 21 of the center column 20" and from a second surface portion 3 with a three-layer sheet metal composite 15 in a second portion 22 of the center column. The second subregion 22 of the center pillar 20 "extends approximately to just below a door lock connection for a vehicle door (not shown) .A transition region 41 is formed between the first surface section and the second surface section 3, wherein both surface sections 2, 3 in the individual layers each have the same material are formed in one piece or are welded analogously to the embodiment according to Figures 3 and 4. In the latter case, the transition region 41 of the weld can correspond in terms of their location.

The second surface portion 3 has in its central position 16, shown in Figure 7 to 9, a higher ductility and lower tensile strength than in the first surface portion 2, which counteracts a delayed cracking and associated problems in a side impact and a targeted deformation, in the case of Center column 20 "in a safe for the occupants area of the vehicle seat allowed.

In contrast to FIG. 6a, FIG. 6b shows a center pillar 20 '' with a second surface section 3 which, in addition to the second section 22, also extends to a part of the edges 42 of the first, in the image plane upper portion of the center pillar 20 ''. Furthermore, the center pillar 20 "'has a plurality of attachment points 43 for attachment to a vehicle sill Surface portion 3 in the second portion 22 extends a further surface portion 4, which in turn has a higher strength and less ductility compared to the second surface portion 3. Between the two surface portions 2, 3, a further transition region 41 is formed.

In section B-B, the section is indicated, which is considered in more detail in Figures 7 and 9.

7 shows a layer structure of the alternative embodiments according to the center pillar 20 "and 20" 'of Figure 6. The first surface portion 2 has the central position 1 1, which is bounded by two outer layers 12 and 13 up and down. The first surface portion 2 has a first center layer 1 1 of ultra high-strength structure with at least 80 percent martensite, which was adjusted by thermoforming and press hardening a heat treatable steel alloy, the tensile strength within the first surface portion with three-layer composite sheet is greater than 1300 MPa. The body or chassis component 1 in the form of the center column 20 "or 20" 'has a second surface portion 3 of a three-layer sheet metal composite 15, wherein the second surface portion has a second center layer 16 with a structure selected from a group of tempered martensite a proportion of at least 80 percent or mixed structure with at least 70 percent shares of ferrite and perlite and residual amounts of martensite and / or retained austenite and / or bainite. With respect to the material, the surface sections 2, 3 correspond to each other in the individual layers, wherein the outer layers 12, 13, 17, 18 each consist of a ferritic stainless steel alloy.

A transition region 41 in the middle position between the first and the second center layer has a width B1 which is between 10 mm and 150 mm, but preferably below 50 mm, since there is a mechanically difficult to determine and inhomogeneous state in the transition region 41. Of course, this layer structure of the described center column 20 ", 20"'also listed on other body and chassis components as in claim 15, transferable, where a targeted load-oriented component design is expedient. FIG. 8 shows a layer structure of an alternative embodiment of the invention. As before, this is a section to illustrate the relevant component properties in cross section.

A first surface portion 2 has the central position 1 1, which is bounded by two outer layers 12 and 13 up and down. The first surface portion 2 has a first middle layer of ultra-high-strength structure with at least 80 percent martensite, wherein the tensile strength within the first surface portion 2 with three-layer sheet metal composite 10 is greater than 1300 MPa. The body or chassis component 1 has a second surface section 3 made of the same material of the same three-layer sheet metal composite 15, the second surface section 3 having a second center layer 16 with approximately the same metallic microstructure. With respect to the material, the surface portions correspond to each other in the individual layers, wherein the outer layers 12, 13, 17, 18 each consist of a ferritic stainless steel alloy. It is also possible that the thickness jump is formed only on one side, for example on the top, the opposite bottom, however, is flat. This facilitates a later hot working, since a better tool contact is made. It also results in a flat welding level.

A transition region 44 between the first and the second surface portion 2, 3 has a width B2 which is between 50 millimeters (mm) and 250 mm, but preferably below 200 mm, since the coupling is difficult with other components in uneven sections. It can be seen that the total thickness D3 of the sheet metal composite 15 in the second surface portion 3 is greater than the total thickness D2 of the sheet metal composite 10 in the first surface portion 2, wherein the ratios of the thickness of the layers to each other within a composite sheet do not change.

Of course, it is possible that the bodywork or chassis component 1 comprises further surface sections, which adjoin the second surface section and allow a further increase in the total thickness and thus a strengthening of the load-compatible construction. It should also be noted that the different thickness is preferably already present in the three-dimensional component geometry before the press forming. Finally, FIG. 9 shows an alternative embodiment and a combination of the embodiments of FIGS. 7 and 8. A first surface section 2 of total thickness D2 from a middle layer 11 and two outer layers 12 and 13 passes over a transition region 44 of width B2 into a second surface section 3 of the total thickness D3, wherein the second surface portion 3 in turn has a central layer 16 with a thickness Dm3 and two outer layers 17 and 18, and the central layer 16 has an ultra-high-strength structure with at least 80 percent martensite. The middle layer 1 1 of the first surface section 2, however, has a ductile structure selected from a group of tempered martensite with a share of at least 80 percent and a mixed structure with at least 70 percent shares of ferrite and perlite and residual amounts of martensite and / or retained austenite and / or bainite. Evident is also a transition region 41 of the width B1, which is formed only over part of the width B2 of the transition region 44. The transition region 41, which is undefined in terms of its mechanical properties and its microstructure composition, is accordingly smaller than the transition region 44 characterized by its thickness discontinuity. The result is a body or chassis component 1 with a very good load-bearing design potential with regard to a targeted deformation process, energy absorption capability and good coupling by welding, gluing , Rivets and / or screws to the vehicle body or other attachments.

FIG. 10 shows a detail of the cross-section of a body or chassis component 1 according to the invention with a three-layered sheet metal composite 10 with a rim 42. The edge 42 is at least partially encompassed by an outer layer 12 in its face 9 in the surface section 2 with dreilagigem sheet metal composite 10, such that the end face 9 of the central layer 1 1 of the edge 42 from the environment U by the outer layer 12 and the outer layer 13 shielded is. The outer layers limit as in the preceding embodiments, the central layer 1 1 on top in the image plane top 7 and on the underside located in the middle bottom 8. This can for example be accomplished such that when trimming the sheet metal composite 10 before or after the press molding a Separation with combined or subsequent rolling of the Outer layer 12 of the edge 42 in the direction of the other outer layer 13 takes place under material displacement from the upper side 7 via the end face 9 of the edge 42.

1 a shows a press 50 for carrying out the procedural part of the invention for the production of body or chassis components 1. First, one or more sheet metal blanks 5 are provided, which comprise at least one surface section of a three-layer sheet metal composite with a middle layer of a heat-treatable steel alloy and two the central layer outwardly bound outer layers include. Subsequently, the heating of the sheet metal composite takes place at least in sections on Austenitisierungstemperatur in the press 50 by contact heating 51 by at least one heatable contact plate 56. The contact plate 56 touched during the heating of the outer layers of the metal laminate of the sheet metal blank, wherein at least a surface portion of the sheet metal plate heated in the shortest time austenitizing becomes. This is the recrystallization temperature of the middle layer of the sheet metal composite with heat-treatable steel alloy to enable the subsequent hardening. Subsequently, a transfer of the hot metal sheet takes place in an at least partially cooled mold 52 and the hot forming of the metal sheet 5 is carried out therein. The sheet metal plate 5 is also already cooled slightly. If a previously homogeneously austenitized sheet metal blank 5 is formed in a partially heated die 52, a reduced cooling rate can optionally be effected in a second area section, so that the critical cooling rate for martensitic transformation of the structure in this second area section is excluded.

Subsequently, a transfer of the press-formed sheet metal blank into a subsequent cooling tool stage 53, where the shaped sheet metal blank is at least partially cured. After a further transfer to a third tool stage 54, the final cooling to approximately ambient temperature, but at least a complete hardening of at least the first surface section takes place.

Instead of three cooled tool stages 52, 53, 54 as in Figure 1 1a) can also be provided to dispense with the last cooling tool stage 54 and already in the first cooling tool stage 53 to complete the curing of a surface section. However, this is only possible to a limited extent with larger overall thicknesses of the sheet metal blank 5 or with a particularly high cycle time of the press 50. This is illustrated by means of the press 50 'in FIG. 11 b).

By means of the press mold 52 or the first cooling tool stage 53, a trimming and perforation of the shaped but still uncured component (not shown) can also take place. Decisive advantage of the method according to the invention is that scaling or oxidation during heating and hot forming are excluded by the outer layers of ferritic or austenitic or martensitic stainless steel alloy and so a complex coating, final cleaning of the surface, surface defects and a Schutzgasumhausung the press or contact heating is avoided.

FIG. 12 shows a press 50 "for an alternative implementation of the procedural part of the invention for the production of body or chassis components 1. First, one or more sheet metal blanks 5 are provided which comprise at least a first surface section of a three-day sheet metal composite with a middle layer of a heat-treatable steel alloy Subsequently, the heating of the sheet metal composite takes place in sections at Austenitisierungstemperatur in the press 50 "by contact heating 51 between at least one heatable contact plate 56. The two contact plates 56 shown here touches during heating the outer layers of the sheet metal composite of the sheet metal blank (not shown), wherein one or all surface portions of the sheet metal blank are heated in a very short time. Subsequently, a transfer of the so-heated sheet metal plate takes place in a tempering 55, so that either the homogeneously heated metal sheet 5 is cooled down from an austenitizing temperature in a second surface portion to less than 700 ° C, or a surface portion is from less than 700 ° C to at least Austenitisierungstemperatur heated. The tempering stage may in turn have contact plates for heating and / or cooling, which are set by burners, inductors or resistance heating to the required temperature. The sections of differently tempered sheet metal blank is introduced into a cooled die mold stage 52 and hot-forming the sheet metal blank is performed therein. The sheet metal plate 5 is also already cooled slightly. Subsequently, a transfer of the press-formed sheet metal blank into a subsequent cooling tool stage 53, where the shaped sheet metal plate is at least partially cured, while a second surface portion is not cured. By means of the die 52 can also be a trimming and the perforation of the molded but still uncured component (not shown).

FIG. 13 a) shows a further embodiment of the invention in the form of a cross-sectionally round body component 1 made of a sheet-metal plate or a sheet-metal strip in a plan view. This is an A-pillar 25 with a curved in the image plane lower portion 22 and a straight wider in cross section upper portion 21st FIGS. 13b) to 13d) show various cross-sectional geometries that can be used for the A-pillar of FIG. 13a). In each case a weld 23 closes the formed as a hollow profile member 1 in a rim 42, 42 ', which extends in the axial direction of the component 1.

In FIG. 13b), the component 1 has two edges 42 ', which contact each other in parallel and are coupled in a material-locking manner by the weld seam 23. The edge represents a two-walled flange.

It can be seen in FIG. 13c) that a rim 42 with its end face 9 is designed to make contact with a side face of a second edge 42 'and is joined in a material-bonded manner to a weld seam 23. The edge 42 'represents a single-walled flange.

As can be seen in FIG. 13d), two edges 42 abut one another with their respective end faces 9, so that a flange-free component results. The forming takes place by roll forming or UO-forms and subsequent hydroforming and quench hardening. The cross-sectional configuration according to FIG. 13d) can also be applied to many chassis components such as torsion-beam axles, transverse links. Figure 14a) shows the result of a corrosion test after 48 hours in Salzsprühebenversuchuch for a press-hardened steel sheet made of Usibor material. A corrosion progress can be recognized over the surface of the component and in the edges.

In contrast, Figure 14b) shows the result of a corrosion test after 1000 hours for press-hardened steel sheet according to the invention. You can see a strong corrosion progress only in the edges.

REFERENCE CHARACTERS:

1 - Body or chassis component

2 - first surface section

3 - second surface section

4- area section

5- sheet metal board

7- Top to 11

8- Bottom to 11

9 - face to 11

10- sheet composite

11 - middle position to 0

12- outside would be 10

13 - outer layer to 10

15-sheet composite

16- funds would be 15

17- outer layer to 15

18- outer layer to 15

20- center column

20 '- center column

20 "center column

20 "'center column

21 - upper section

22 - second subarea

23 - weld

24 - A-pillar

30 - Wishbone

40- weld

41 - Transition area

42 - edge

43 connection point

44- Transition area

50- press 50 '- Press

50 "- press

51 - contact heating

52 - Press forming tool

53 - Cooling tool stage

54 - Cooling tool stage

55 - tempering stage 56 - contact plate

D2 - total thickness to 10

D3 - total thickness to 15

Da - thickness of the outer layer

Dm - thickness of the middle layer

Dm2 - thickness to 1 1

Dm3 - thickness to 16

B1 - width to 41

B2 - width to 44

U environment

Claims

claims

1. body or chassis component (1) for a motor vehicle, comprising at least one surface portion (2, 3) of a three-layer sheet metal composite (10) having a central position (11) and two the center layer (11) outwardly bounding outer layers (12, 13 ), which are connected to the central layer (11) surface and cohesively characterized in that the outer layers (12, 13) of a stainless steel alloy having a structure selected from the group of ferritic, austenitic or martensitic structure and the central layer (11) consist of a heat treatable steel alloy, and the bodywork or chassis component has a bending angle greater than 80 °, determined in the platelet bending test according to VDA 238-100: 2010, with a yield strength Rp0.2 of greater than 900 MPa.

2. body or chassis component (1) according to claim 1, characterized in that the body or chassis component (1) has a second surface portion (3).

3. body or chassis component (1) according to one of claims 1 or 2, characterized in that the bending angle greater than 95 ° and the yield strength Rp0,2 greater 950 MPa.

4. body or chassis component (1) according to one of claims 1 to 3, characterized in that the bending angle is greater than 90 °, in particular greater than 100 °, preferably greater than 110 °.

5. body or chassis component (1) according to one of claims 1 to 4, characterized in that the product of bending angle and yield strength Rp0,2 between 90,000 ° MPa and 180,000 ° MPa.

6. body or chassis component (1) according to one of the preceding claims, characterized in that the central position (11) of a surface portion (2, 3) has a structure, with at least 80 percent Martensite, and the tensile strength Rm within the area section (2, 3) is greater than 1300 MPa.

7. body or chassis component (1) according to one of the preceding claims, characterized in that the central layer (11, 16) of a surface portion (2, 3) has a structure of tempered martensite with a share of at least 80 percent or a mixed structure with at least 70 percent shares of ferrite and perlite and residual amounts of martensite and / or retained austenite and / or bainite.

8. bodywork or chassis component (1) according to claim 2 to 7, characterized in that the second surface portion (3) is a three-layer sheet metal composite (15), with a second center layer (16) having a structure selected from a group of mixed structure with at least 80 percent shares of ferrite and pearlite or mixed structure with at least 70 percent shares of ferrite and perlite and residual amounts of martensite and / or retained austenite and / or bainite.

9. body or chassis component (1) according to one of claims 1 to 8, characterized in that a surface portion (2, 3) with the three-layer sheet metal composite (10, 15) has a total thickness (D2, D3), and one of the outer layers (12, 13, 17, 18) has a thickness (Da) of at least 3 percent (%) and at most 15 percent (%) of the total thickness (D2, D3), preferably 4 percent (%) to 10 percent (%) of the total thickness (D2, D3) of this surface portion (2, 3).

10. body or chassis component according to one of claims 2 to 8, characterized in that the second surface portion (3) is a three-layer sheet metal composite (15), and the first center layer (11) and the second center layer (16) each have a thickness ( Dm2, Dm3), and the thickness (Dm2) of the first center ply (11) is different from the thickness (Dm3) of the second center ply (16).

11. body or chassis component (1) according to at least one of claims 2 to 10, characterized in that the surface portions (2, 3) are butt welded together adjacent to each other.

12. body or chassis component (1) according to one of claims 2 to 8, characterized in that the bodywork or chassis component (1) has a second surface portion (3) made of a stainless steel alloy, and the surface portions (2, 3) with each other butt-welded to each other.

13. body or chassis component (1) according to one of claims 2 to 12, characterized in that the sheet metal composite (10) in the first surface portion (2) has a total thickness (D2) and the sheet metal composite (15) in the second surface portion (3) Have total thickness (D3), wherein the total thicknesses (D2, D3) differ from each other by at least 10 percent, in particular between 20 and 100 percent.

14, body or chassis component (1) according to at least one of the preceding claims, characterized in that the body or chassis component (1) has an edge (42), and the edge (42) in an end face (9) in the surface portion ( 2, 3) with three-layered sheet metal composite (10, 15) at least partially surrounded by an outer layer (11, 12, 17,18), such that the end face (9) of the central layer (11, 16) of the environment (U) is shielded by the outer layer (11, 12, 17, 18).

15, body or chassis component (1) according to at least one of the preceding claims, characterized in that the bodywork or chassis component (1) a door pillar, in particular a center pillar (20) or a roof frame, sill, bumper cross member, side member, floor cross member, wishbone (30), trailing arm, stabilizer, torsion beam or axle of the motor vehicle.

16 body or chassis component (1) according to at least one of the preceding claims, ad d u rch ge ke n nze i ch n et that the bodywork or chassis component (1) a door pillar (20, 20 ', 20 ", 20 '') or a roof frame with each one edge (42), wherein the second surface portion (3) is at least partially disposed in the edge (42).

17. A method for producing a body or chassis component (1) having the features of at least claim 1, characterized by

Providing a metal sheet (5), comprising at least one surface portion (2) of a three-layer sheet metal composite (10) with a central layer (11) made of a heat-treatable steel alloy and each one of the central layer (11) limiting outer layer (12, 13) of a stainless steel alloy,

Heating at least the sheet-metal composite (10) to austenitizing temperature,

• Hot forming of the sheet metal plate (5) in an at least partially cooled press mold (52) and

At least partially curing the shaped sheet metal blank (5) in the press mold (52) or in a subsequent cooling tool stage (53, 54).

18. The method according to claim 17, characterized in that the hot forming and hardening of the sheet metal blank (5) in or by means of a single press (50, 50 ', 50 ", 50"') with a plurality of tool stages (52, 53, 54) performed becomes.

19. The method according to claim 17, characterized in that the heating and hot forming and optionally hardening of the sheet metal blank (5) in a single press (50, 50 ', 50 ", 50"') with a plurality of tool stages (51, 52, 53, 54, 55) is performed.

20. The method according to any one of claims 17 to 19, characterized in that the heating within 30 seconds, preferably within 20 seconds, in particular within 10 Seconds is performed and / or the heating is carried out without a protective gas atmosphere.

Method according to one of claims 17 to 20, characterized in that a component trimming or punching after hot forming and curing, in particular in a subsequent tool stage (53, 54) of the press (50, 50 ', 50 ") is performed, is preferred a component trimming and / or punching performed after press hardening.

22. The method according to any one of claims 17 to 21, characterized in that the heating is carried out by contact heating.