Motor vehicle component, method for producing same and production device
阅读说明：本技术 机动车构件及其制造方法和生产设备 (Motor vehicle component, method for producing same and production device ) 是由 M·霍尔茨威斯格 M·克特勒 K·布拉克 G·弗罗斯特 A·弗雷恩 于 2019-05-09 设计创作，主要内容包括：本发明涉及一种机动车构件及其制造方法和生产设备,其中,该机动车构件具有大于1800MPa的抗拉强度Rm,其中,将由具有大于等于0.3％(质量)含碳量的、可硬化的含碳的合金钢构成的板坯(3)在直通式加热炉(4)中加热到大于等于AC3的温度,紧接着,将板坯由直通式加热炉(4)取出并且在热成型和加压淬火模具(8)中进行热成型和加压淬火,在直通式加热炉(4)中的炉气氛中测量按体积百分比的含氧量,并且将氮气输送至直通式加热炉(4),其中,氮气的量调节地输送,使得在炉气氛中调节出0.5～15％(体积)的氧含量,并且机动车构件具有大于50°的弯曲角度。(The invention relates to a motor vehicle component, a method for the production thereof and a production plant, wherein the motor vehicle component has a tensile strength Rm of more than 1800MPa, wherein a slab (3) consisting of a hardenable carbon-containing alloy steel having a carbon content of 0.3 mass% or more is heated in a continuous heating furnace (4) to a temperature of AC3 or more, and subsequently the slab is taken out of the continuous heating furnace (4) and is hot-formed and press-quenched in a hot-forming and press-quenching die (8), measuring the oxygen content in volume percent in the furnace atmosphere in the continuous heating furnace (4) and feeding nitrogen to the continuous heating furnace (4), wherein the amount of nitrogen is adjusted such that an oxygen content of 0.5 to 15% by volume is adjusted in the furnace atmosphere and the motor vehicle component has a bending angle of more than 50 °.)
1. A method for producing a motor vehicle component (2) by hot forming and press hardening, which has a tensile strength Rm of more than 1800MPa, wherein a slab (3) consisting of a hardenable carbon-containing alloy steel having a carbon content of 0.3 mass% or more is heated in a continuous heating furnace (4) to a temperature of AC3 or more, and subsequently the slab is taken out of the continuous heating furnace (4) and is hot-formed and press-quenched in a hot-forming and press-quenching die (8), characterized in that the oxygen content in volume percent is measured in the furnace atmosphere in the continuous-flow furnace (4) and nitrogen is fed to the continuous-flow furnace (4), wherein the amount of nitrogen is adjusted such that an oxygen content of 0.5 to 15% by volume is adjusted in the furnace atmosphere and the motor vehicle component has a bending angle of more than 50 °.
2. Method according to claim 1, characterized in that the oxygen content is adjusted between 0.5 and 10% by volume, preferably between 0.5 and 5% by volume and particularly preferably between 0.5 and 3% by volume.
3. Method according to claim 1 or 2, characterized in that the nitrogen has a volume flow rate per hour which is equal to between 2 and 4 times, preferably between 2.5 and 3.5 times and preferably 3 times the furnace volume of the continuous-flow furnace (4).
4. A method according to claims 1 to 3, characterized in that nitrogen is introduced into the continuous heating furnace (4) above the slab (3) to be heated, with reference to the spatial direction.
5. A method according to claims 1 to 4, characterized in that the tailor welded blank is machined and/or that a coating is applied to the formed component in a next machining step.
6. The method according to claims 1 to 5, characterized in that the slab (3) is passed through the continuous-flow furnace (4) over a time of preferably 120 seconds to 10 minutes, preferably 120 seconds to 360 seconds, particularly preferably 160 seconds to 200 seconds and particularly preferably 180 seconds.
7. Method according to claims 1 to 6, characterized in that a temperature between 910 ℃ and 980 ℃, preferably between 930 ℃ and 950 ℃, is generated in the continuous heating furnace (4) and/or the temperature within the continuous heating furnace (4) is preferably more than 5%, in particular more than 10% higher than the AC3 temperature of the steel material.
8. Method according to claims 1 to 7, characterized in that an alloy steel is used which, in addition to iron and impurities resulting from the smelting, has the following alloying elements in mass percent:
9. An automotive component (2) manufactured by hot forming and press quenching from a slab of hardenable steel alloy having a carbon content of 0.3% by mass or more, in particular an automotive component manufactured by a method having the features of claim 1, characterized in that the automotive component (2) has a tensile strength Rm of more than 1800MPa, in particular more than 1900MPa and preferably more than 2000MPa, and the automotive component has a surface decarburized layer (10, 11) on the surface (5, 2), said surface decarburized layer having a layer thickness of 10 to 70 μm, preferably 20 to 40 μm, and the automotive component has a bending angle of more than 50 °, preferably more than 60 °.
10. Automotive component (2) according to claim 9, characterised in that the stratification from the surface decarburized layer (10, 11) to the non-surface decarburized layer is characterised in that the carbon content in the surface decarburized layer (10, 11) is lower than 50% of the carbon content of the intermediate layer (9) of the automotive component (2).
11. A production plant for manufacturing a motor vehicle component (2) having a tensile strength Rm of more than 1800MPa and having a bending angle of more than 50 °, preferably for carrying out the method according to any one of claims 1 to 10, comprising a continuous heating furnace (4) in which a slab (3) consisting of a hardenable carbon-containing alloy steel having a carbon content of 0.3% by mass or more can be heated to a temperature of AC3 or more, and a hot forming and press quenching mould (8) arranged downstream of the continuous heating furnace, the slab taken out of the continuous heating furnace (4) being hot-formable and press-quenched in the hot forming and press-quenching mould (8), characterized in that the production plant comprises nitrogen gas conveying means, by which nitrogen gas can be conveyed to the continuous heating furnace (4), and regulating means, the amount of nitrogen to be fed can be adjusted by means of an adjusting device, so that an oxygen content of 0.5 to 15% by volume can be adjusted in the furnace atmosphere in the continuous-flow furnace (4).
Technical Field
The invention relates to a method and a production plant for producing a motor vehicle component by hot forming and press hardening. The invention also relates to a motor vehicle component produced by hot forming and press hardening. More particularly, the invention relates to a method and a production plant for manufacturing motor vehicle components from extremely high-strength steel alloys with ductile properties, and to such motor vehicle components.
Background
It is known from the prior art to manufacture motor vehicle components from hardenable steel alloys. For this purpose, hot forming and press quenching are used. Here, the slab of hardenable steel alloy is heated to a temperature of at least AC 3. The AC3 temperature is also called the austenitizing temperature and is greater than 800 ℃ depending on the steel alloy used.
If the slab is fully austenitized, the slab has a high degree of formability. In order to produce motor vehicle components from a sheet blank by forming in a thermoforming process.
During and after the forming, the slab or the formed component is cooled rapidly in such a way that the austenitized material is transformed into a hardened material structure. This is a martensitic material structure. In the hardened material structure, a ferrite, pearlite or bainite fraction may also be present. The above process is also called press quenching.
From the prior art, it is known in recent years to produce motor vehicle components having a tensile strength Rm of more than 1000MPa, in particular more than 1200MPa and preferably also more than 1500 MPa.
If a component with a still higher tensile strength, in particular over 1700MPa and preferably over 1800MPa, is now produced, the component has only a small ductility. A bending angle of about 30 ° is obtained on the component. In the event of an accident, it may happen that other components fixed to the component, for example by welding, are brittle and/or broken.
Disclosure of Invention
The object of the invention is therefore to produce a component having extremely high strength and material properties, but also having high ductility, wherein the process costs for producing the component are low and in particular the existing plant technology can be used.
The object is achieved according to the invention by a method for producing a motor vehicle component having a tensile strength Rm of more than 1800MPa by hot forming and press hardening, wherein a slab consisting of a hardenable carbon-containing alloy steel having a carbon content of more than or equal to 0.3% by mass is heated in a continuous heating furnace to a temperature of more than or equal to AC3, and subsequently the slab is removed from the continuous heating furnace and hot formed and press hardened in a hot forming and press hardening mould, wherein the oxygen content is measured in volume percent in a furnace atmosphere in the continuous heating furnace and nitrogen is supplied to the continuous heating furnace, wherein the amount of nitrogen is supplied in a regulated manner such that an oxygen content of 0.5 to 15% by volume is regulated in the furnace atmosphere and the motor vehicle component has a bending angle of more than 50 °.
The object is also achieved by a motor vehicle component produced by hot forming and press quenching a slab consisting of a hardenable steel alloy having a carbon content of 0.3% by mass or more, in particular a motor vehicle component produced by the method according to the invention, wherein the motor vehicle component has a tensile strength Rm of more than 1800MPa, in particular more than 1900MPa and preferably more than 2000MPa, and the motor vehicle component has a surface decarburized layer on the surface, which layer has a layer thickness of 10 to 70 μm, preferably 20 to 40 μm, and the motor vehicle component has a bending angle of more than 50 °, preferably more than 60 °.
The object is also solved by a production plant for producing motor vehicle components having a tensile strength Rm of more than 1800MPa and having a bending angle of more than 50 °, preferably for carrying out the method according to the invention, comprising a continuous heating furnace in which a slab consisting of a hardenable carbon-containing alloy steel having a carbon content of more than or equal to 0.3% by mass can be heated to a temperature of more than or equal to AC3, and a hot forming and press quenching die arranged downstream of the continuous heating furnace, in which the slab taken out of the continuous heating furnace can be hot formed and press quenched in the hot forming and press quenching die, wherein the production plant comprises nitrogen gas conveying means by which nitrogen gas can be conveyed to the continuous heating furnace, and adjusting means by which the amount of conveyed nitrogen gas can be adjusted, so that the oxygen content of 0.5-15% (volume) can be adjusted in the furnace atmosphere in the straight-through heating furnace.
The method according to the invention for producing a motor vehicle component uses a hot forming and press hardening process. For this purpose, the slab, which consists of a hardenable carbon-containing steel alloy, is heated at least partially, in particular completely, to a temperature above the AC3 temperature. The carbon content is 0.3% by mass or more. But the carbon content should not be more than 1% by mass. The slab to be heated is heated in a continuous furnace. The heated slab is removed from the continuous heating furnace and transferred to a hot forming and press hardening die. The hot forming process and the press quenching process are performed in the hot forming and press quenching die.
In this case, very high-strength steel alloys are used, with which it is possible to provide motor vehicle components having a tensile strength Rm of at least 1800MPa after the end of the press quenching process.
in order to provide the motor vehicle components (also referred to as components) with very high strength properties with a high degree of ductility, in particular with a bending angle of more than 50 °, preferably more than 60 °, surface decarburization is carried out during heating in a continuous-flow furnace. The bending angle is obtained in particular in a plate bending test according to the VDA238-100 standard.
The furnace atmosphere in the flow-through furnace was set to be controlled by feeding ambient air and nitrogen gas of industrial purity. In a flow-through furnace, the oxygen content in the furnace atmosphere was measured in volume percent. According to the invention, the oxygen content in the furnace atmosphere is adjusted to between 0.5 and 15% by volume, preferably between 0.5 and 10% by volume, in particular between 0.5 and 5% by volume and particularly preferably between 0.5 and 3% by volume. The oxygen content is adjusted by adjusting the nitrogen volume flow in the furnace atmosphere.
According to the invention, it has been found that it is therefore possible to perform a surface decarburization on the slab to be heated, so that carbon atoms are combined with oxygen in the corresponding surface layer of the slab to be heated. By decarburizing the respective surfaces, the component subsequently produced by hot forming and press quenching has a high ductility. Also the formation of scale on the surface is substantially avoided.
The ambient air can be supplied by introducing air from the outside into the interior of the furnace. It is preferred that the air or oxygen in the internal chamber of the furnace comes from the immediate environment of the once-through furnace.
In this context, it has advantageously been found according to the invention that by adjusting the surface decarburized layers on both sides of the component, which layers have a layer thickness of 10 to 70 μm, preferably between 10 to 50 μm and preferably 20 to 40 μm, it is possible to produce motor vehicle components having a tensile strength Rm of more than 1800MPa and a bending angle of more than 50 °, in particular more than 60 °.
It is also possible to carry out the method according to the invention on existing production plants by adding nitrogen feed and a regulating method for regulating the oxygen content in the furnace atmosphere to existing continuous furnaces.
Once-through furnaces are usually operated with gas burners in the lance. The combustion process itself is carried out separately from the oxygen content of the furnace atmosphere. Alternatively, the injection pipe can be designed in a resistance heating manner.
It is also particularly preferred that the volume flow of nitrogen introduced into the continuous heating furnace can have a value per hour, for example in m 3, which is preferably between 2 and 4 times, preferably between 2.5 and 3.5 times, and particularly preferably equal to 3 times the furnace volume of the continuous heating furnace.
It has also proven advantageous to introduce nitrogen into the continuous-flow furnace above the slab to be heated, with reference to the spatial direction. Thus, a convective behavior of nitrogen is generated in the flow-through furnace, so that no further thorough mixing of the furnace atmosphere is required.
By the method according to the invention, a splice plate (tailed blank) can preferably be produced. The splice bar is in particular a rolled slab. But also tailor-made molded panels (tailor-made for blank) or tailor-made welded panels (tailor-made welded blank) can be manufactured. Likewise, slabs with a constant wall thickness can of course also be processed.
In addition, it is likewise possible by the method according to the invention to carry out additional coatings on the component being produced. In particular, this relates to a subsequently applied corrosion protection coating, for example a cathodic electrocoating or a zinc diffusion coating.
It has also proven advantageous for the slab to be passed through the continuous heating furnace over a time of from 120 seconds to 10 minutes, in particular from 120 seconds to 400 seconds, particularly preferably from 160 seconds to 200 seconds, and in particular approximately 180 seconds.
It is also provided that a temperature of between 910 ℃ and 980 ℃, in particular a temperature of 930 ℃ to 960 ℃, is produced in the continuous heating furnace itself.
Alternatively or additionally, the temperature in the continuous heating furnace can be set at least 5%, preferably at least 10%, in particular at least 11%, preferably at least 12%, higher than the AC3 temperature of the steel alloy used. However, the furnace temperature should not exceed 30%, particularly preferably not more than 20%, of the AC3 temperature of the steel material used.
Within the scope of the present invention, it has proven to be particularly advantageous to use alloy steels which, in addition to iron and impurities resulting from the smelting, have the following alloying elements in mass percent:
C (carbon)
0.3～0.4
Preference is given to
0.32～0.38
si (silicon)
0.15～1
Preference is given to
0.2～0.5
Mn (manganese)
0.5～2
Preference is given to
0.8～1.5
P (phosphorus)
Maximum 0.05
Preference is given to
Maximum 0.02
s (Sulfur)
Maximum 0.01
Preference is given to
Maximum 0.005
N (Nitrogen)
Maximum 0.01
Preference is given to
Maximum 0.005
Cr (chromium)
0.05～1
Preference is given to
0.1～0.5
Ni (Nickel)
Maximum 0.3
Preference is given to
Maximum 0.1
Cu (copper)
Maximum 0.1
Preference is given to
Maximum 0.05
Mo (molybdenum))
Maximum 0.5
Preference is given to
Maximum 0.3
Al (aluminium)
Maximum 0.1
Preference is given to
Maximum 0.06
Nb (niobium)
0.02～0.1
Preference is given to
0.02～0.06
V (vanadium)
maximum 0.06
Preference is given to
Maximum 0.05
Ti (titanium)
Maximum 0.1
Preference is given to
Maximum 0.01
B (boron)
0.001～0.01
Preference is given to
0.001～0.005
The carbon content here leads to strength/hardness in the produced component. Silicon brings a transition delay and promotes tempering stability. Manganese also brings about a transition delay by the austenite stabilization. Chromium also imparts transition delay and oxidation resistance. Boron also causes a delay in the transition. Niobium produces a fine grained nature in the material structure.
Within the scope of the invention, the method can thus preferably be carried out with the steel alloys described in the tables. The method can, however, also be carried out with other carbon-containing steel alloys, in particular with a carbon content of more than 0.3% by mass. The motor vehicle components described below can likewise be produced from the abovementioned steel alloys. But the carbon content should not exceed 1% by mass.
The invention further relates to a motor vehicle component which is produced from a sheet metal blank by hot forming and press hardening. The slab itself is made of a hardenable alloy steel. In particular, a motor vehicle component is produced according to the method of the invention described above.
The motor vehicle component is characterized in that the motor vehicle component has a tensile strength Rm of more than 1800MPa, in particular more than 1900MPa, preferably more than 2000 MPa. The tensile strength should in particular not exceed 2500 MPa.
In addition, automotive components have high ductility. This ductility is characterized by a bending angle of more than 50 °, in particular more than 60 °, in the motor vehicle component. Typically automotive components have a thickness of between 0.7mm and 3.5 mm. A surface-decarburized layer is preferably formed on each surface of the motor vehicle component, said surface-decarburized layer having a layer thickness of 10 to 70 μm, preferably 20 to 40 μm.
The layer boundary from the surface decarburized layer to the non-surface decarburized layer is characterized in that the carbon content in the surface decarburized layer is at most 50% relative to the core layer, i.e. the intermediate layer, of the manufactured automotive component. This means that, starting from the surface, the surface decarburized layer ends at a point at which the carbon content in the direction of the interior of the motor vehicle component is more than 50% of the carbon content of the intermediate layer of the motor vehicle component. These explanations are also valid for the above-mentioned manufacturing method.
Drawings
The invention is explained further by the following explanation and described by means of the schematic figures, which should be used for a simple understanding of the invention. Wherein:
Figure 1 shows a schematic flow diagram of a method for manufacturing a motor vehicle component,
FIG. 2 shows a motor vehicle component manufactured according to the invention in the form of a B-pillar, and
Fig. 3 shows a cross-sectional view of a motor vehicle component according to the invention.
Detailed Description
Reference numerals or symbols are used in the respective drawings even though repetitive explanation is omitted for the sake of simplicity.
Fig. 1 shows a thermoforming line according to the invention for producing motor vehicle components by thermoforming and press-hardening.
The slab 3 is initially introduced into the continuous furnace 4, ambient air U is supplied to the continuous furnace 4 in order to set the furnace atmosphere in the continuous furnace 4, in addition, nitrogen N 2 of technical purity is supplied to the continuous furnace 4, the quantity of nitrogen N 2 of technical purity supplied is set in accordance with, in particular, the percentage by volume of oxygen measured in the furnace atmosphere, for example, a plurality of measurement points can be provided in the continuous furnace 3, which measure the percentage by volume of oxygen, from which measurement points an average value can then be formed, the slab 5 thus heated having a decarburized layer on each surface 6, 7, the heated slab 5 is then transferred into a hot-forming and pressure-hardening mold 8 and is subjected to hot-forming and pressure-hardening there, and the finished motor vehicle component 2 is removed from the hot-forming and pressure-hardening mold 8 and is supplied to further processing.
Fig. 2 shows a motor vehicle component 2 in a perspective view. This is, for example, a motor vehicle pillar, in particular a B-pillar of a motor vehicle. However, other motor vehicle components 2, in particular motor vehicle structural components, can be produced by the method according to the invention. These further motor vehicle components 2 are components of the motor vehicle body, such as, for example, longitudinal members, transverse members, roof supports, door sills or the like.
Fig. 3 shows a cross-sectional view of the manufactured motor vehicle component 2 according to section line III of fig. 2. The motor vehicle component 2 has a wall thickness W. The surface decarburized layers 10, 11 extend from each surface 6, 7 of the automotive component 2 up to the intermediate layer 9 (or also referred to as core layer). The surface decarburized layers 10, 11 have a layer thickness 12. The layer thickness 12 is particularly preferably 20 to 40 μm. The layer boundary 13 from the surface decarburized layers 10, 11 to the material not decarburized on the surface is characterized in that the carbon content in the surface decarburized layers is 50% of the carbon content of the intermediate layer 9. If the carbon content of the surfaces 6, 7 of the manufactured motor vehicle component exceeds 50%, it is therefore no longer possible within the scope of the invention to speak of a surface decarburized layer.
Another advantage of the present invention is that the manufactured hot formed and press quenched automotive component or slab oxidizes to a negligible degree during heating.
List of reference numerals
1 thermoforming production line
2 Motor vehicle component
3 slab
4 straight-through heating furnace
5 heated slabs
6 surface of
7 surface of
8 hot forming and pressure quenching die
9 middle layer
10 surface decarburized layer
11 surface decarburized layer
12 layers thick
U ambient air
N 2 Nitrogen
Wall thickness of W
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