EP3347160A1

EP3347160A1 - Method for producing a component structure with improved joint properties, and component structure

Info

Publication number: EP3347160A1
Application number: EP16757839.2A
Authority: EP
Inventors: Stefan Myslowicki; David Pieronek
Original assignee: ThyssenKrupp Steel Europe AG; ThyssenKrupp AG
Current assignee: ThyssenKrupp Steel Europe AG; ThyssenKrupp AG
Priority date: 2015-09-07
Filing date: 2016-08-17
Publication date: 2018-07-18
Also published as: DE102015114989B3; MX2018002812A; US20180243863A1; WO2017042005A1; CN108025404A

Abstract

The invention relates to a method for producing a component structure (101, 201, 301) from a first component (102, 202, 302) and at least one additional component (104, 204, 304). The first component (102, 202, 302) is connected to the additional component (104, 204, 304) by means of a thermal joining process. The aim of the invention is to achieve good crash properties and/or vibration resistance for the lightweight construction with an inexpensive production. This is achieved by a generic method in which the first component (102, 202, 302) is a steel material composite that comprises at least one softer layer (102a, 202a, 302a, 302d) and a more rigid layer (102b, 202b, 202c, 302b, 302c). The softer layer (102a, 202a, 302a, 302d) has a lower material strength and a higher deformability than the more rigid layer (102b, 202b, 202c, 302b, 302c), and the joint zone part which lies in the first component (102, 202, 302) is at least partly formed in the softer layer (102a, 202a, 302a, 302d).

Description

Method for producing a component structure with improved

Joining properties and component structure

The present invention relates to a method for producing a component structure comprising a first component and at least one further component, wherein the first component is connected to the further component by means of a thermal joining method. In addition, the invention relates to a component structure, in particular a

Vehicle structure or a part thereof for a motor vehicle or commercial vehicle.

Methods for joining individual components to a component structure for different materials and material combinations are known from the prior art. In particular, components for motor vehicles today are particularly subject to the light pressure in order to meet the ever-increasing demands for fuel consumption, CO 2 emissions and crash safety while shortage of existing resources and economic conditions, For this reason, a trend for the use of steel with years ever higher strength to record.

For example, hot-formed components are used in the field of automotive and commercial vehicles in order to achieve high geometric component freedom at high speeds

To achieve material strength of over 1500 MPa. This can be the high

Lightweight construction requirements are taken into account.

For example, German Offenlegungsschrift DE 10 2008 022 709 A1 describes the use of a multi-layer roll-laminated material composite in one

Vehicle structure, wherein three layers are made of a steel alloy. In this case, the middle layer should consist of a good formable steel alloy, while the outer layers should consist of a higher or higher strength steel alloy. However, the high material strength often can not be directly translated into an increased structural performance, because the connection technology, such as

Welding process, such as resistance spot welding, is a limiting factor. It has been found that in ultra-high strength steels and hot forged steels with strengths above 1000 MPa after welding, that is, after heat input and subsequent cooling, by tempering effects a softening zone in the environment of the compound (heat affected zone) sets, which has a low strength and at the same time has low ductility and is therefore often used as the starting point for cracks ("crack starters") under crash loading, but this can have far-reaching consequences, since the crack can extend from the connection zone into the component and thus lead to total loss of structural integrity This particularly affects the crash properties and / or

Vibration resistance of the components. Corresponding investigations were carried out as part of the FOSTA research project P806 "Characterization and replacement modeling of the fracture behavior of spot welds on ultra-high-strength steels for crash simulation, taking into account the effect of the compound on the component behavior".

This structural behavior is expected to be strictly avoided. This problem can be counteracted, for example, by the fact that, as part of a partial press hardening, a targeted heat treatment is used to bond

provided component flanges or by a subsequent heat treatment.

Alternatively, it is conceivable to deal constructively with the problem and to design oversized critical areas, ie to provide, for example, wider component flanges or to vary the position of the weld points or their number.

In any case, these described approaches lead due to the more complex

Manufacturing process (for example, by more complex tools, controls, etc.) or oversizing at extra cost and / or extra weight and thus stand against the goal of cost-effective lightweight construction. Against this background, the object is to provide a generic method and a component structure, in which good crash properties and / or

Resistance to vibration for lightweight construction can be achieved with cost-effective production.

The object is achieved according to a first teaching of the invention in a generic method in that the first component is a steel composite material, which comprises at least a softer layer and a firmer layer, the softer layer having a lower material strength and a higher ductility than the has a firmer position, and wherein the lying in the first component part of the joining zone is at least partially formed in the softer layer.

According to the invention it was recognized that the connection strength and thus

accompanied in particular the crash properties and / or fatigue strength of the component structure can be improved if a steel composite material is used, which is joined so that the joining zone is at least partially formed in the softer layer, which has a higher compared to the firmer layer deformability and bond strength having. It has been shown that the transferable with the component structure forces can increase significantly, if the

Joining zone is at least partially formed in a softer layer, since the cracks usually start from the surface of the facing, joined together materials. In addition, the majority formation of the joining zone in the softer layer avoids the formation of a softening zone in the load-critical region of the joining zone or around the joining zone in comparison to a monolithic solution with the material of the more rigid layer. As a result, forces are at least partially first transferred to the layer with the higher ductility and can then be transferred from there flat to the firmer layer.

A steel composite material is understood as meaning a composite material which has at least one layer, in particular the softer and / or stronger layer, of steel. Preferably, several or all layers of the steel composite material are formed from a steel. The steel composite material can also have more than two layers. In particular, the steel composite material, for example, several (for example, two or three) have softer layers. Also, the steel composite material may have multiple (for example, two or three) firmer layers. In this case, preferably all softer layers have higher ductility than the stronger layers. In particular, in this case, the part of the joining zone lying in the first component can be formed at least partially in at least one of the softer layers. But it is also possible that the joining zone is at least partially formed in a plurality (for example, two) of the softer layers.

The further component may for example be formed as a monolithic component or may also be made of a steel composite material. In particular, the further component can be constructed like the first component. In this respect, the remarks made herein with respect to the first component also apply to the further component.

The fact that the softer layer has lower material strength and higher ductility than the firmer layer means, in particular, that the softer layer has a higher ductility, a higher elongation at break, a lower tensile strength and / or a lower hardness compared to the more rigid layer

hot-worked condition. In addition, the softer layer is preferably characterized by a good weldability and / or sufficient bond strength of

Welding off.

The joining zone is to be understood in particular as meaning the area influenced by the integral connection of the components, for example a weld nugget. The weld nugget is surrounded by a heat affected zone in which the structural properties of the steels have been changed. For steels with strengths above 1000 MPa, in particular hot-formed or press-hardened steels, the critical softening zone forms in the area of the heat-affected zone.

According to one embodiment of the method according to the invention, the outer layer of the first component facing the further component is a softer layer. This can be achieved in a simple manner that the joining zone is at least partially in the softer layer of the first component and also the softer layer can be positioned close to the joining zone. This can result in an effective

Improve the mechanical properties of the component structure. The softer position of the first component, the further component at least partially

(For example, at least in the area to be joined) contact directly.

It is possible that the lying in the first component part of the joining zone

mostly or even exclusively in the softer position. This voltage peaks due to mechanical stress due to the softer layer can be well absorbed. The softening zone in the firmer position is thus in the

Optimal case not critical.

According to a further embodiment of the method according to the invention, the part of the joining zone lying in the first component extends over a plurality of layers of the first component. As a result, an optimum of properties of the joint connection and of the crash performance and / or the vibration resistance can be achieved if the joint zone extends over several (for example over two, three or more) layers.

According to a further embodiment of the method according to the invention, the softer layer consists for example of a deep-drawing steel, IF steel or microalloyed steel and the firmer layer of a high-strength or ultra-high strength steel, in particular a steel with martensite, preferably manganese-boron steel. It has been found that by using a (hot-workable) manganese-boron steel, depending on the alloy composition, a material composite can be represented for a particularly favorable component structure.

Likewise, the further component or layers thereof may consist of a manganese-boron steel.

According to one embodiment, at least one layer of the first component consists of a deep-drawing steel, an IF steel, a microalloyed steel, a dual-phase steel, a Complex phase steel or a martensite phase steel. According to another

Embodiment consists of at least one layer of the first component made of a steel alloy with good corrosion protection properties. The same applies to embodiments of the further component. Furthermore, the first and / or the further component may have a metallic and / or organic coating on one or both sides.

According to a further embodiment of the method according to the invention, the softer layer in the use state has an elongation at break A ₈₀ of at least 10%, preferably at least 14%, particularly preferably at least 17%. With such elongation at break values, the softer layer has a correspondingly high deformability. It has been found that such minimum breaking elongations of the softer layer positively influence the performance of the component structure after joining. As already stated, the first component can also have further layers for which such properties are advantageous. The condition of use is in particular the hardened state.

The firmer layer preferably has an elongation at break A ₈₀ which is less than the elongation at break of the softer layer. As a result, the strength of the first component can be improved. However, the breaking elongation A ₈₀ is at least 3% of the stronger location, preferably at least 5%.

According to a further embodiment of the method according to the invention, the C content of the softer layer is at most 0.25% by weight, preferably at most 0.15% by weight, particularly preferably at most 0.1% by weight. As a result, the ductility and weldability and bond strength of the softer layer can be kept high, which positively influences the crash performance and / or fatigue strength of the component structure.

For example, the softer layer consists of a steel alloy with the following alloy constituents in% by weight:

C <0.10

Si <0.35 Mn <1.00

P <0.030

s <0.025

AI> 0.06

Nb <0.10

Ti <0.15

Cr <0.2

Cu <0.20

Mo <0.05

N <0.007

Ni <0.20

Remaining iron and unavoidable impurities.

For example, the stronger layer is made of a manganese-boron steel having the following alloy components in% by weight:

c <0.60

Si <0.40

Mn <1.40

P <0.025

s <0.010

AI> 0.06

Ti <0.05

Cr + Mo <0.5

B <0.005

N <0.008

Ni <0.20

Nb <0.005

V <0.02

Sn <0.05

Ca <0.006

As <0.02

Co <0.02 Remaining iron and unavoidable impurities.

The firmer layer consists, for example, of a steel whose C content is at most 0.40% by weight and preferably at most 0.30% by weight. For example, the C content of the firmer layer is higher than that of the softer layer. That is, the C content of the firmer layer is, for example, at least 0.1% by weight, preferably at least 0.15% by weight. As a result, the strength of the component is improved.

According to a further embodiment of the method according to the invention, the softer layer in the use state has a tensile strength R _m of at most 1000 MPa, preferably at most 800 MPa, more preferably at most 600 MPa and / or the firmer layer has a tensile strength R _m of at least 700 MPa in use , preferably at least 900 MPa, more preferably at least 1000 MPa. It has been found that such a maximum limitation of the tensile strength in the softer layer keeps the ductility high and thus improves the joining properties of the first component. At the same time, the strength of the first component can be increased if the firmer layer has the specified minimum tensile strengths.

According to a further embodiment of the method according to the invention, the thermal joining is welding, in particular resistance spot welding, and the joining zone is a weld nugget or a MAG welding zone. Welding is a frequently used method for joining individual components to a structure, especially in the automotive sector. It has been shown that in particular

Welding process as well as MAG welding benefit from the proposed method. However, it is also possible to realize the thermal joining by soldering, for example arc soldering.

According to a further embodiment of the method according to the invention, the starting material for producing the first component is produced by roll-plating, in particular hot-roll plating or by a casting method. In this way, the layers of the first component can be easily connected to each other. Also, a connection of the layers by, for example, a casting process is conceivable. According to a further embodiment of the method according to the invention, the first and / or the second component is hot-formed prior to joining, in particular

press hardened. By hot forming or press hardening of the components particularly lightweight and stable component structures which are suitable for lightweight construction can be provided. Advantageously, it can be dispensed with to make special precautions in the area of the joint connection during press hardening, which is the case

Component forming made simpler and cheaper. It is basically also conceivable that the first and / or second component cold-formed or

semi-hot-formed. Combinations of these forming processes are possible.

The first and / or second component can be formed, for example, by a pressure forming, tensile forming, tensile pressure forming, bending forming, or shear forming.

According to a further embodiment of the method according to the invention, the first component has an asymmetrical or symmetrical structure of the layers, in particular with regard to the thickness and / or the material of the layers. As a result, the structure of the first component can be optimally adapted to the joining to be performed. For example, the firmer layer or further layers with the same or similar properties can be made correspondingly thin on the side of the first component facing the further component, for example thinner than on the side of the first component facing away from the further component. As a result, a larger part of the softer layer or further layers with the same or similar properties may overlap with the joining zone. However, the structure can also be symmetrical.

The thickness of the first and / or second component is preferably between 0.5 mm and 6 mm, more preferably between 1 mm and 4 mm. The thickness of the softer layer depends in particular on the total number of layers. If, for example, only a softer and a firmer layer are provided, the softer layer can for example make up 10% to 90%, in particular 20% to 80%, preferably 40% to 60%, of the total thickness of the first component. In addition to the motor vehicle are also variants for Commercial vehicles (including trailers), for example, parts of frame structures conceivable that may have much larger component thicknesses.

According to a further embodiment of the method according to the invention, the first component is constructed in two, three, four or more layers. In multilayer structures of the first component, the component properties can be set with increasing number of layers across the thickness of homogeneous. In the case of three-layered or multi-layered structures of the first component, a plurality of layers of the same material as the softer layer and / or the firmer layer are preferably provided. Preferably, the part of the joining zone lying in the first component is largely formed in softer layers.

According to a further embodiment of the method according to the invention is

Component structure, a component of a vehicle, in particular a motor vehicle or utility vehicle, or a part thereof.

For example, the component structure or at least one of the components is a body, a chassis, a chassis or a part thereof. The body is, for example, self-supporting and preferably built predominantly in shell construction. For example, the body is a skeleton body (for example, based on the space-frame design) or a part of a commercial vehicle structure. For example, the

Component structure or at least one of the components of a structural part or a

Exterior skin part of a vehicle. For example, the component structure or at least one of the components is a handlebar, an axle, a crash part, a gusset plate, a

Guide member, a carrier, in particular a side member or a cross member, a

Reinforcing part, a profile, a hollow profile, a spar, a strut, a pillar,

in particular an A-, B-, C- or D-pillar, a frame, a tunnel, a sill, a floor panel, a strut tower, an end wall, a side impact beam, a bumper, a fender, a Radhausbauteil or a sheet metal part, in particular a Door panel, a hood panel or a roof panel or part thereof.

According to a second teaching of the present invention, the above-mentioned object is also achieved by a component structure, in particular a vehicle structure or a Part thereof for a motor vehicle or commercial vehicle, which after a

prepared according to the invention, solved.

The component structure thus has a first component and a further component, which are connected by means of a thermal joining method. Here, the first component is a steel composite material, which comprises at least one softer layer and a firmer layer. The softer layer has a higher ductility than the firmer layer and the part of the joint zone lying in the first component is at least partially formed in the softer layer.

As already explained at the outset, it was recognized that the joining behavior and, consequently, in particular the crash properties and / or vibration resistance of such a component structure can be improved. In this way, namely, the formation of a softening zone serving as a crack starter in load-critical areas of the connection can be reduced or prevented.

With regard to further advantageous embodiments of the component structure, reference is made to the method according to the invention and its advantages. By the method described and its embodiments, the component structure produced therewith is to be disclosed in particular.

The invention will be explained in more detail below with reference to advantageous embodiments in conjunction with the drawings. In the drawing shows:

Fig. La, b in cross-sectional view of a component structure according to the prior art and a sketchy hardness profile;

Fig. 2 in cross-sectional view a first embodiment of a

inventive component structure and a sketchy hardness curve; Fig. 3 in cross-sectional view, a second embodiment

component structure according to the invention; and

Fig. 4 in cross-sectional view, a third embodiment

Component structure according to the invention.

1 a firstly shows a cross-sectional view of a component structure according to the prior art. The component structure 1 comprises a first component 2 and a further component 4. The component 2 is, for example, press-hardened and has a tensile strength of 1500 MPa. The component 2 was with the other component 4 means

Resistance spot welding joined. This creates a weld nugget 6.

1b schematically shows the hardness curve 8 in the region of the weld nugget 6 illustrated in FIG. 1a along the measurement points 9. For this purpose, the hardness was plotted on the axis 10 above the position along the cross section on the axis 12. It can be seen that the component structure 1 has a high hardness far outside the weld nugget 6 (region A) due to the material property of the first component 2 and inside the weld nugget 6 (region B). In the edge region or transition region of the weld nugget 6 (region C), however, a softening zone with a local drop in hardness arises. Crack starters form here, which makes this area under load,

especially at high loads such as in the case of a crash, the starting point for a material failure.

Fig. 2a shows in cross-sectional view a first embodiment of a

Component structure 101 according to the invention, which was produced with an embodiment of the method according to the invention. The component structure 101 comprises a steel composite material as a first component 102 and a further component 104, which were joined by means of resistance spot welding. The first component 102 comprises a softer layer 102a and a firmer layer 102b, wherein the softer layer 102a has a higher deformability than the firmer layer 102b. The softer and firmer layers 102a, 102b are by hot roll plating, for example cohesively connected to each other. The softer layer 102a is here an outer layer of the first component 102 facing the further component 104.

The softer layer 102a is in this case made of the material MBW 500 and has in the operating condition (after austenitizing at 920 ° C and subsequent

Hot working and press hardening) has a yield strength R _{p 0} , 2 of 400 MPa, a

Tensile strength R _m of 550 MPa and an elongation at break A ₈₀ of at least 17%. The firmer layer 102b is made of the material MBW 1500 in this case and has a yield strength R _{p 0} , 2 of 1000 MPa, a tensile strength R _m of 1500 MPa and an elongation at break A ₈₀ of at least 5% in the used state or press-hardened state , The proportions of the softer and firmer layer 102a, 102b here are each about 50% of the thickness of the first component 102. Overall, the first component has approximately one

Tensile strength of 1000 MPa. The further component 104 is in this case

monolithic component made of a steel material. The part of the welding lens 106 located in the first component is in this case formed exclusively in the softer layer 102a.

FIG. 2 b schematically shows the hardness curve 108 in the region of the weld nugget 106 shown in FIG. 2 a along the measurement points 109. For this purpose, the hardness on the axis 110 was again plotted over the position on the axis 112. It can be seen that the component structure far outside the weld nugget 106 (region A) has a lower hardness than inside the weld nugget 106 (region B) due to the higher deformability of the softer layer 102a. However, no softening zone with a local decrease in hardness arises in the edge region of the weld nugget 106.

As a result, crack starters can be avoided or reduced as a starting point for material failure.

Fig. 3 shows in cross-sectional view a second embodiment of a

Component structure 201 according to the invention, which is the one shown in FIG

Embodiment is similar. In contrast to the first component 102 from FIG. 2, the first component 202 has a three-layer structure and has, in addition to those as before

formed layers 202a, 202b in addition to a (second) firmer layer 202c. The location 202c is made of the same material as the stronger layer 202b. The softer layer 202a is formed here on the inside. However, the firmer layer 202c facing the further component 204 is thinner than the firmer layer 202b facing away from the further component 204. Due to this asymmetric structure of the first component 202 with respect to the thicknesses of the layers, the softer layer 202a is again arranged such that the part of the weld nugget 206 located in the first component 202 is partially formed in the softer layer 202a.

Fig. 4 shows in cross-sectional view a third embodiment of a

Component structure 302 according to the invention, which is the one shown in FIG

Embodiment is similar. In contrast to the first component 202 from FIG. 3, the first component 302 has a five-layered construction and, in addition to the previously formed layers 302a, 302b, 302c, additionally has two further softer outer layers 302d, 302e. The softer layers 302d, 302e are made of the same material as the softer layer 302a and thus are more deformable than the stronger layers 302b, 302c. Again, the layers are constructed asymmetrically in thickness, in particular, the firmer layer 302c is thinner than the firmer layer 302b. This in turn ensures that the softer layers 302a, 302d are arranged such that as large a part of the part of the weld nugget 306 located in the first component 302 is formed in two of the three softer layers 302a, 302d.

Claims

P a n t a n s p r e c h e

1) A method for producing a component structure (101, 201, 301) from a first component (102, 202, 302) and at least one further component (104, 204, 304),

- wherein the first component (102, 202, 302) is connected to the further component (104, 204, 304) by means of a thermal joining method,

- wherein the first component (102, 202, 302) is a steel composite material which comprises at least one softer layer (102a, 202a, 302a, 302d) and at least one firmer layer (102b, 202b, 202c, 302b, 302c),

- Wherein the softer layer (102a, 202a, 302a, 302d) a smaller

Material strength and a higher ductility than the firmer layer (102b, 202b, 202c, 302b, 302c), and

- Wherein in the first component (102, 202, 302) lying part of the joining zone

at least partially in the softer layer (102a, 202a, 302a, 302d) is formed.

2. The method according to claim 1,

wherein the outer layer of the first component facing the further component (104, 204, 304) is a softer layer (102a, 302d).

3. The method according to claim 1 or 2,

wherein the part of the joining zone lying in the first component (102, 202, 302) extends over a plurality of layers of the first component (102, 202, 302).

4. The method according to any one of claims 1 to 3,

the softer layer (102a, 202a, 302a, 302d) of a deep-drawing steel, IF steel or microalloyed steel and the stronger layer (102b, 202b, 202c, 302b, 302c) of a high-strength or ultra high-strength steel, in particular a steel with a martensite structure , preferably consists of a manganese-boron steel.

5. The method according to any one of claims 1 to 4,

wherein the softer layer (102a, 202a, 302a, 302d) in the use state has an elongation at break A ₈₀ of at least 10%, preferably at least 14%, particularly preferably at least 17%.

6. The method according to any one of claims 1 to 5,

wherein the C content of the softer layer (102a, 202a, 302a, 302d) is at most 0.25% by weight, preferably at most 0.15% by weight, particularly preferably at most 0.1% by weight.

7. The method according to any one of claims 1 to 6,

wherein the softer layer (102a, 202a, 302a, 302d) in the use state has a tensile strength R _m of at most 1000 MPa, preferably at most 800 MPa, particularly preferably at most 600 MPa, and / or the firmer layer (102b, 202b, 202c, 302b, 302c) in the use state has a tensile strength R _m of at least 700 MPa, preferably at least 900 MPa, particularly preferably at least 1000 MPa.

8. The method according to any one of claims 1 to 7,

wherein the thermal joining is a welding, in particular a

Resistance spot welding is and the joining zone is a weld nugget or a MAG weld.

9. The method according to any one of claims 1 to 8,

wherein the starting material for producing the first component (102, 202, 302) is produced by roll-plating, in particular hot-roll plating or by a casting process.

10. The method according to any one of claims 1 to 9,

wherein the first and / or the further component (102, 202, 302, 104, 204, 304) is hot-formed prior to the joining, in particular press-hardened.

11. The method according to any one of claims 1 to 10,

wherein the first component (102, 202, 302) is an asymmetric or

has symmetrical structure of the layers, in particular with regard to the thickness and / or the material of the layers.

12. The method according to any one of claims 1 to 11,

wherein the first component (102, 202, 302) is constructed in two, three, four or more layers.

13. The method according to any one of claims 1 to 12,

wherein the component structure (101, 201, 301) is a component of a vehicle, in particular a motor vehicle or utility vehicle, or a part thereof.

14. Component structure, in particular a vehicle structure or a part thereof for a motor vehicle or commercial vehicle, produced by a method according to claims 1 to 13.