Thermally treating a metal component

Abstract

The invention relates to a method for thermally treating a metal component (2), comprising: a) heating the entire component (2) in a first continuous furnace (3), b) transferring the component (2) from the first continuous furnace (3) into a temperature-control station (4), c) in the temperature-control station (4), cooling a first soft region (10) of the component (2) and a second soft region (11) of the component (2) with a cooling fluid, wherein the first soft region (10) and the second soft region (11) are cooled differently, and wherein a temperature of the first soft region (10) and a temperature of the second soft region (11) are below the austenite reversion temperature (TAR) of the component (2) at least after the cooling, d) transferring the component (2) from the temperature-control station (4) into a second continuous furnace (5), e) thermally treating the component (2) in the second continuous furnace (5), wherein the first soft region (10) and the second soft region (11) of the component (2) are heated such that the temperature of the first soft region (10) and the temperature of the second soft region (11) are below the AC3 temperature (TAC3) of the component (2) even after the heating, wherein a temperature of a hard region (11) of the component (2) exceeds the AC3 temperature (TAC3) of the component (2) during method steps a) to e) at least intermittently.

Description

[0001] Thermal treatment of a metallic component

[0002] The invention relates to a method for the thermal treatment of a metallic component, in particular a steel component for a motor vehicle.

[0003] In the automotive industry in particular, it is well known to specifically harden steel components through thermal treatment. For this purpose, steel components such as B-pillars are thermally treated differently in certain areas. This results in different ductility in certain areas, which is advantageous for the crash behavior of such components. For example, vehicle occupants can be protected by a hard section of the B-pillar at seat height, while soft sections in the upper and lower sections of the B-pillar absorb energy through deformation.

[0004] For the locally varied thermal treatment of components, processes have proven successful. In these processes, the entire component is first heated in a first furnace, the component is then subjected to locally varied thermal treatment in a tempering station, and the entire component is finally heated in a second furnace. In the tempering station, one area of ​​the component is cooled, for example by exposure to a cooling fluid, while the rest of the component is kept approximately at its temperature. Excellent results can be achieved in this way for many applications. However, there is a growing need to achieve temperature distributions that cannot be achieved, or are difficult to achieve, using conventional processes. This particularly applies to components in which more than two areas of different ductility are to be formed. This is particularly relevant with regard to so-called door rings and double door rings.These components cover a comparatively large part of a car body, so that there is often a requirement to create more than two areas of different ductility.

[0005] The object of the present invention is to present a particularly flexible method for the locally different thermal treatment of metallic components.

[0006] This object is achieved by the method according to the independent claim. Further advantageous embodiments are specified in the dependent claims. The features presented in the claims and in the description can be combined with one another in any technologically expedient manner.

[0007] According to the invention, a method for thermally treating a metallic component is presented. The method comprises: a) heating the entire component in a first continuous furnace, b) transferring the component from the first continuous furnace to a tempering station, c) cooling a first soft region of the component and a second soft region of the component with a cooling fluid in the tempering station, wherein the first soft region and the second soft region are cooled differently, and wherein a respective temperature of the first soft region and the second soft region is below the austenite retransformation temperature of the component, at least after cooling, d) transferring the component from the tempering station to a second continuous furnace, e) thermally treating the component in the second continuous furnace, wherein the first soft region and the second soft region of the component are heated in such a way thatthat the respective temperature of the first soft region and the second soft region remains below the AC3 temperature of the component even after heating, whereby a temperature of a hard region of the component during process steps a) to e) at least temporarily exceeds the AC3 temperature of the component.

[0008] The described method can be used to thermally treat a metallic component. The metallic component is preferably made of steel. The steel is preferably 22MnB5. However, it is not necessary for the metallic component to meet the definition of steel. Therefore, the term "metallic component" is generally used herein. For example, a component for a motor vehicle, in particular a B-pillar, a door ring, or a double door ring, can be thermally treated using the described method. However, the method can also be used for any other applications.

[0009] The component preferably has a material thickness of at least 0.7 mm, particularly in the range of 1 to 4 mm. Such a material thickness is useful for many applications. However, the described process can also be carried out with components of other material thicknesses. The material thickness of the component is preferably constant across the entire component. Alternatively, the component can also have a material thickness that varies in certain areas. For example, the component can be a "Tailor Rolled Blank (TRB)", in which locally different material thicknesses are obtained through locally different rolling processes. The component can also be a "Tailor Welded Blank (TWB)", in which locally different material thicknesses are obtained by welding several sheets together. A combination of TRB and TWB is also possible. Furthermore, the process can be applied equally to components with and without coating.The component is particularly preferably coated with Al / Si.

[0010] After the thermal treatment, the component is preferably press-hardened in a press and thus hot-formed. The method preferably comprises the further steps of transferring the component from the second continuous furnace to the press (step f)) and press-hardening in the press (step g)). In this case, the described method is a method for the thermal treatment and press-hardening of a component. However, it is not necessary for the press-hardening of the component to be carried out as part of the described method. The described method can also serve as preparation for press-hardening carried out outside of the described method. In general, the component thermally treated with the described method can be subjected to further process steps which, together with other processes, can result in, for example, a finished motor vehicle.However, the thermal treatment of the component is a distinct sub-process within such an overall process. It is therefore useful to consider the thermal treatment separately from the subsequent process steps, especially separately from press hardening.

[0011] In step a), the entire component is heated in the first continuous furnace. A furnace is a device whose interior is heated to an adjustable temperature and into which a component can be inserted. Over time, the temperature of the component approaches the temperature prevailing inside the furnace. The heat is thus transferred from the gas in the furnace, which can in particular be air, to the component. A continuous furnace is a furnace through which the component can be moved, whereby the component is heated as it passes through the furnace.

[0012] The first continuous furnace is preferably a roller hearth furnace. In the first continuous furnace, the component is preferably heated by burners, in particular gas burners. This allows the component to achieve a particularly evenly distributed temperature. In the first continuous furnace, the entire component is heated. The component is completely absorbed by the first continuous furnace. In addition, a continuous furnace can achieve heating by a particularly large temperature difference. With a continuous furnace, a component can be heated, in particular, from room temperature to a temperature in the range of the component's AC3 temperature. Such extensive heating is not possible with many other heating methods, or at least not without disproportionately great effort.

[0013] In the case of a coated component, the first continuous furnace can also serve to diffuse the coating into the remaining material of the component. This applies in particular to an Al / Si coating. In the case of a coated component, it is preferred that the component is heated in step a) such that the coating material diffuses into the material of the remaining component in step a). The component is therefore preferably heated in step a) to a temperature that is above the temperature at which the coating material diffuses into the material of the remaining component. Preferably, the temperature of the component in step a) is above this temperature for at least 1 minute, in particular even at least 2 minutes. Preferably, the component is heated in step a) to a temperature of at least 700°C, in particular of at least 780°C. Satisfactory results have already been achieved at these temperatures.However, to increase process reliability, heating to at least 830 °C is preferred. Preferably, the temperature of the component in step a) is above a temperature of 700 °C, in particular 780 °C or even 830 °C for at least 1 minute, in particular even at least 2 minutes. In the case of a coated component, the component is particularly preferably heated in step a) to a temperature above the Ad temperature of the component, in particular above the AC3 temperature of the component. Preferably, the temperature of the component in step a) is above the ACI temperature of the component, in particular above the AC3 temperature of the component, for at least 1 minute, in particular even at least 2 minutes. In this respect, the heating in step a) can be used not only to diffuse the coating, but can also already make a contribution to the microstructure transformation.

[0014] Heating in a continuous furnace is particularly in contrast to heating by so-called "direct energization". This would make it difficult to heat the component evenly and to a sufficiently high degree. With direct energization, the speed of heating is more important. In addition, direct energization requires contact with the component. In step a) of the described process, heating is preferably carried out without contact. This does not preclude the component from being moved through the first continuous furnace on transport rollers and thus being in contact with the transport rollers. Heating is considered contactless if the heat is introduced into the component via a gas and / or thermal radiation.

[0015] In step b) of the process, the component is transferred from the first continuous furnace to the tempering station. This is preferably done using a first transfer device. In the tempering station, the component is thermally treated differently in certain areas. For this reason in particular, the described process is a process for the locally different thermal treatment of metallic components. However, this does not need to be explicitly mentioned, since the locally different thermal treatment is explicitly defined by step c).

[0016] The first continuous furnace and the tempering station are separate components that are spatially separated from each other. The transfer between the first continuous furnace and the tempering station facilitates the cooling of the component between heating in the first continuous furnace and thermal treatment in the tempering station. In the tempering station, the component is cooled as quickly as possible in certain areas. Rapid cooling can be achieved more efficiently outside the hot first continuous furnace. This allows cooling to begin during the transfer. In this respect, the spatial separation of the first continuous furnace from the tempering station accelerates the process. This contrasts with a solution in which all process steps are carried out in the same facility without having to transfer the component. Such solutions typically aim to minimize the effort required for component transfers or to avoid them altogether.The spatial separation between the first continuous furnace and the tempering station also simplifies the design because the requirements for the first continuous furnace and the tempering station are different.

[0017] In step d), the component is transferred from the tempering station to a second continuous furnace. This is preferably done using a second transfer device. In step e), the component is thermally treated in the second continuous furnace. For step e), the entire component is removed from the second continuous furnace.

[0018] The tempering station and the second continuous furnace are separate components that are spatially separated from each other. The transfer between the tempering station and the second continuous furnace facilitates the cooling of the component between the thermal treatment in the tempering station and in the second continuous furnace. This allows a part of the component that requires cooling to be cooled during the transfer. This reduces the required residence time in the tempering station and accelerates the process. This contrasts with a solution in which all process steps are carried out in the same facility, if possible, without having to transfer the component. Such solutions typically aim to minimize the effort required for component transfers or to avoid them altogether.The spatial separation between the tempering station and the second continuous furnace also simplifies the design because the requirements for the tempering station and the second continuous furnace are different.

[0019] The second continuous furnace is preferably a roller hearth furnace. In the second continuous furnace, the entire component is thermally treated, preferably heated. The component is completely absorbed by the second continuous furnace. Thermal treatment in a continuous furnace contrasts particularly with heating by so-called "direct energization." Thermal treatment in the second continuous furnace serves, in particular, to promote microstructural transformation. Because the component is not immediately cooled after the tempering station, for example, in a press, sufficient time is provided for the desired microstructural distribution to develop within the component. In particular, in step e), carbon atoms can diffuse within the component, changing the component's microstructure as desired. Furthermore, thermal treatment in the second continuous furnace can serve to reduce thermal stresses in the component.During subsequent press hardening, the distortion of the component can be reduced.

[0020] With the described process, three areas in particular can be thermally treated differently. First, a distinction can be made between a first soft area and a second soft area. In addition, a hard area is created. The component is thermally treated with the described process in such a way that the hard area has lower ductility after press hardening than the two soft areas, and that the two soft areas have different ductilities. Thus, three different ductilities are created in the component. In this respect, the described process is particularly flexible.

[0021] The terms "soft region" and "hard region" refer to the ductility after press hardening. Before press hardening, the soft regions generally do not have a higher ductility than the hard region. During the process described herein, the soft regions of the component are therefore those regions of the component that are thermally treated using the process described in such a way that they achieve a higher ductility than the hard region in a subsequent process. For the sake of simplicity, the terms "soft region" and "hard region" are also used herein to refer to the period before press hardening. Alternatively, the first soft region could be referred to as the first region, the second soft region as the second region, and the hard region as the third region.

[0022] The fact that the first and second softening zones are cooled differently in step c) means that there are at least two different softening zones. However, it is also possible and even preferred to have more than two different softening zones, for example, three or four.

[0023] The soft areas can also be referred to as soft zones. The two soft areas have different ductility. This corresponds to the fact that the two soft areas have a different microstructure after press hardening. This can be the case, for example, if after press hardening the first soft area has a bainitic structure and the second soft area a ferritic-pearlitic structure, while the hard area is martensitic. However, it is not necessary that the microstructures of the two soft areas differ so fundamentally. It is also possible that the first soft area and the second soft area each have a mixed microstructure of the same type but different composition after press hardening. In this respect, comparatively minor differences in the ductility of the soft areas can be realized.However, these go beyond mere statistical fluctuations in that the two soft areas are deliberately treated differently in step e).

[0024] The first soft region, the second soft region, and the hard region are not necessarily contiguous regions. Therefore, there may be several spaced-apart subregions that together form the first soft region. The same applies to the second soft region and the hard region. The component preferably, but not necessarily, has only the first soft region, the second soft region, and the hard region. In this case, the component has no further regions.

[0025] In step a), the entire component is heated in the first continuous furnace. All areas are treated equally in step a). Therefore, it is not necessary for the areas to be distinguishable from one another in step a).

[0026] The described process is multi-stage and includes, in addition to heating in the first continuous furnace, thermal treatment in the tempering station and heating in the second continuous furnace. Therefore, heating in the first continuous furnace can, in principle, be carried out to any desired temperature. If the component is only slightly heated in the first continuous furnace, it can be heated more intensively in the hard zone as the process progresses, and vice versa. In particular, heating of the component in the first continuous furnace can be carried out to a temperature above or below the component's AC3 temperature.

[0027] Particularly for energy reasons, it is advantageous to heat the component comparatively strongly in the first continuous furnace. This makes it possible to exploit the previously described advantage of heating in a continuous furnace compared to other heating methods, in particular compared to direct energization. The component is therefore preferably heated in step a) to at least 400 °C, in particular to at least 600 °C. The component is preferably heated in step a) to a temperature above the AC3 temperature of the component. Preferably, the component is heated in step a) to a temperature which is a maximum of 400 K below the AC3 temperature of the component, in particular a maximum of 200 K below the AC3 temperature of the component. Preferably, the component does not exceed a temperature of 200 K above the AC3 temperature of the component in step a). For example, the component can be heated to a temperature in the range 600 to 800 °C in step a).Alternatively, higher temperatures are preferred, in particular those above the AC3 temperature of the component. It is also preferred that the component be heated in step a) to a temperature of at least 900°C, in particular at least 1000°C. For example, the component can be heated in step a) to a temperature in the range of 850 to 1200°C.

[0028] The temperature control station downstream of the first continuous furnace applies locally different thermal treatments to the component. To do this, the first soft zone and the second soft zone of the component are cooled differently in the temperature control station. This is achieved by exposing the first soft zone and the second soft zone to a cooling fluid, in particular compressed air. The first soft zone and the second soft zone can be exposed to the same cooling fluid or to different cooling fluids. For practical reasons, it is preferable to use the same cooling fluid for the first soft zone and the second soft zone. However, the composition of the cooling fluid is not relevant to the functioning of the process. All that matters is the cooling effect. Different cooling fluids can therefore also be used for the two soft zones.

[0029] The first soft zone can be cooled in step c) by continuously directing the cooling fluid to the first soft zone for a first cooling period. During the first cooling period, the cooling fluid is discharged toward the first soft zone at a constant pressure. Alternatively, the first soft zone can be cooled in step c) by directing the cooling fluid to the first soft zone in pulsed fashion for a first cooling period. During the first cooling period, the cooling fluid is discharged toward the first soft zone at a pressure that periodically changes over time. The pressure can temporarily drop to zero, but this is not necessary. Pulsed discharge of the cooling fluid has proven to be particularly efficient.

[0030] The second soft zone can be cooled in step c) by continuously directing the cooling fluid to the second soft zone for a second cooling period. During the second cooling period, the cooling fluid is discharged toward the second soft zone at a constant pressure. Alternatively, the second soft zone can be cooled in step c) by directing the cooling fluid to the second soft zone in pulsed fashion for a second cooling period. During the second cooling period, the cooling fluid is discharged toward the second soft zone at a pressure that periodically changes over time. The pressure can temporarily drop to zero, but this is not required. Pulsed discharge of the cooling fluid has proven to be particularly efficient.

[0031] The first cooling period and the second cooling period are generally independent of each other. The first cooling period and the second cooling period can therefore be of equal or different lengths, can begin at the same or different times, and can end at the same or different times. However, it is preferred that the first cooling period and the second cooling period at least overlap. This reduces the duration of the process. Preferably, the first cooling period and the second cooling period begin at the same time and / or the first cooling period and the second cooling period end at the same time.

[0032] The cooling fluid preferably has a pressure in the range of 2 to 4.5 bar. This comparatively high pressure allows a large amount of cooling fluid to be directed to the first soft zone and the second soft zone of the component within a very short time, thus achieving a sufficiently high cooling rate. However, the method used to cool the soft zones is generally not important for the functionality of the described process.

[0033] The first soft area and the second soft area can be cooled with the cooling fluid in step c) by directing the cooling fluid onto the soft areas. This can be done on one side or both sides. The first soft area can be cooled in step c) by applying the cooling fluid to the first soft area from below and / or from above. The second soft area can be cooled in step c) by applying the cooling fluid to the second soft area from below and / or from above. A particularly intensive cooling effect can be achieved by combining cooling from below and from above. This is particularly advantageous for thicker components and / or components composed of multiple layers.

[0034] It is preferred, but not necessary, that the first softening zone and the second softening zone are treated equally in that both are cooled only from above, both are cooled only from below, or both are cooled from both above and below.

[0035] For practical reasons, applying cooling fluid to the first soft zone and the second soft zone from above is preferred. This leaves space below the component for a transport device. Applying cooling fluid to the first soft zone and the second soft zone from below is particularly preferred in addition to applying cooling fluid to the first soft zone and the second soft zone from above. The first soft zone and the second soft zone can thus be cooled primarily from above and additionally from below, for example with additional nozzles arranged below the component. Since the additional nozzles are only of secondary importance, they can be designed accordingly small and, for example, arranged below the component in addition to a transport device.

[0036] The first soft zone and the second soft zone are cooled differently in step c). The two soft zones are therefore cooled in different ways and / or with different cooling parameters. The temporal temperature profile of the first soft zone is therefore not identical to the temporal temperature profile of the second soft zone. The two soft zones can therefore have different temperatures at the end of step c) and / or be cooled at different cooling rates in step c).

[0037] The fact that the two soft regions are cooled with different cooling parameters means that in step c) the first soft region is cooled with first cooling parameters and the second soft region is cooled with second cooling parameters, whereby the first cooling parameters are not identical to the second cooling parameters. The cooling parameters can be, for example, a duration of exposure to the cooling fluid (i.e. the first cooling time or the second cooling time), a pressure of the cooling fluid and a temperature of the cooling fluid. In the simplest case, the two soft regions are exposed to cooling fluid for different lengths of time. In this case, the first cooling time and the second cooling time are different lengths. The question of whether the component in a soft region is exposed to the cooling fluid from below and / or from above can also be expressed as a cooling parameter.

[0038] The two soft areas can be cooled differently, for example, by discharging the cooling fluid onto the two soft areas using differently designed nozzles and / or a different number of nozzles. For example, the cooling effect can be influenced by the spray pattern of the nozzles. Different cooling can also be achieved by, for example, only cooling one of the two soft areas from below.

[0039] Cooling with a cooling fluid allows the desired flexibility to be achieved in that the two soft areas in step c) are cooled to different degrees. This would be impossible or very difficult to achieve with other cooling technologies. For example, prior art solutions exist in which cooler areas are maintained by locally shielding a heat source. In this case, it is practically impossible or very difficult to differentiate between different soft areas. Cooling with a cooling fluid, on the other hand, allows for easily fine gradations of any desired degree. If such gradation is achieved, for example, via the cooling duration, the gradation can even be implemented solely via the control system. No hardware intervention is required.

[0040] If the entire component is heated to a temperature above the AC3 temperature in step a), austenite forms throughout the component. Cooling the soft regions below the component's austenite retransformation temperature in step e) causes this austenite to decompose again in the soft regions. The austenite retransformation temperature is defined by the fact that austenite decomposes as soon as the temperature falls below the austenite retransformation temperature. The austenite retransformation temperature is a material property. The fact that the temperature of the soft regions is below the component's austenite retransformation temperature, at least after cooling, does not imply that austenite was previously formed in the component.

[0041] If the entire component is not heated to a temperature above the AC3 temperature in step a), no austenite will form in this step. However, cooling the soft zones in step e) below the austenite re-transformation temperature of the component can help ensure that no austenite is formed in the soft zones during the further course of the process, even if the component is subjected to further heating. If no austenite is formed in step a), the austenite re-transformation temperature in step c) does not have to be undercut for the austenite to decompose. In the event that the entire component is not heated to a temperature above the AC3 temperature in step a), any cooling of the soft zones in step c) is sufficient. Nevertheless, it is still advisable to undercut the austenite re-transformation temperature in this case.

[0042] This does not result from the fact of austenite retransformation below this temperature, but merely from the fact that the austenite retransformation temperature is generally significantly below the AC3 temperature.

[0043] Preferably, the soft regions are each cooled in step c) by at least 100 K, in particular by at least 250 K. The temperature of the soft regions after step c) is preferably in the range from 400 to 700 °C, in particular in the range from 500 to 600 °C. The temperature of the two soft regions after step c) preferably differs by at least 50 K, in particular by at least 100 K.

[0044] Regardless of the temperature reached in step a), no austenite is present in either soft zone after cooling in step c). As long as the AC3 temperature of the component is not (again) exceeded in the soft zones after cooling in step c), a more ductile microstructure can be obtained in the soft zones than in the hard zone.

[0045] In the soft regions, the AC3 temperature of the component is not exceeded in steps d) to e). This prevents austenite from forming in the soft regions. In step e), the soft regions of the component are heated such that the respective temperature of the soft regions remains below the AC3 temperature of the component even after heating. The soft regions are therefore no longer heated above the AC3 temperature of the component after cooling in step c). Preferably, the respective temperature of the soft regions of the component does not exceed the AC3 temperature of the component, at least in steps d) and e). If press hardening is part of the claimed process, the temperature of the soft regions of the component preferably does not exceed the AC3 temperature of the component up to and including press hardening. In this way, a ductile microstructure can be maintained in the soft regions.However, strict attention to ensuring that the AC3 temperature is not exceeded during the specified periods is not required. Austenite is not formed instantaneously. Even if a small amount of austenite forms in one of the component's soft areas, acceptable results can be achieved.

[0046] In addition to the soft areas, the component also has a hard area. The process is carried out in such a way that the temperature of the hard area of ​​the component exceeds the AC3 temperature of the component at least temporarily during process steps a) to e). This can lead to the formation of austenite in the hard area. During press hardening, martensite can be formed from this, giving the hard area comparatively low ductility.

[0047] It is irrelevant at what point the temperature of the hard zone exceeds the AC3 temperature of the component. If the entire component is heated to a temperature above the AC3 temperature of the component in step a), the aforementioned condition is already met in step a). If the hard zone is heated to below the AC3 temperature in step a), the hard zone can be heated to a temperature above the AC3 temperature in the tempering station or in the second furnace.

[0048] It is preferred that the temperature of the hard region, after heating to a temperature above the AC3 temperature of the component, no longer falls below the austenite retransformation temperature until the completion of step e). Preferably, the temperature in the hard region does not fall below the austenite retransformation temperature until the press is completed. This prevents the austenite formed in the hard region from decomposing before press hardening. In steps b) to e), the temperature of the hard region preferably changes by a maximum of 200 K, in particular by a maximum of 100 K. This can also be referred to as maintaining the temperature, whereby a change in the temperature within a tolerance of 200 K or 100 K is accepted.For example, in step c) in the temperature control station, the hard area can be exposed to a temperature above the AC3 temperature of the component and / or in step e) in the second furnace, it can be exposed to a temperature above the AC3 temperature of the component. Depending on the temperature of the hard area upon entry into the temperature control station or the second furnace and the length of time the component remains in the temperature control station or the second furnace, the hard area can be maintained at its temperature in the temperature control station or heated, or cooling of the hard area can be slowed down. In particular, the hard area can also cool in the temperature control station in ambient air.

[0049] It is possible that the temperature of the hard region in steps a) to e) initially rises above the AC3 temperature, then falls below the austenite retransformation temperature, and then rises above the AC3 temperature again. In this case, it is sufficient that the temperature of the hard region does not fall below the austenite retransformation temperature after the second heating to above the AC3 temperature until the completion of step e). This is encompassed by the formulation that a temperature of the hard region of the component during process steps a) to e) at least temporarily exceeds the AC3 temperature of the component and subsequently does not fall below an austenite retransformation temperature of the component.

[0050] In a preferred embodiment of the method, after cooling, the temperature of the first softening region differs from the temperature of the second softening region, preferably by at least 50 K, in particular by at least 100 K.

[0051] In this embodiment, the soft regions are cooled differently in step c) in such a way that the two soft regions have different temperatures at the end of step c). In a further preferred embodiment of the method, the first soft region and the second soft region are cooled differently in step e) in such a way that the first soft region and the second soft region are exposed to the cooling fluid for different lengths of time.

[0052] The longer the respective soft area of ​​the component is exposed to the cooling fluid, the more this soft area is cooled in step c). The cooling effect can be adjusted accordingly by adjusting the cooling duration. This can be done via the control system without requiring any hardware intervention.

[0053] In a further preferred embodiment of the method, the first soft region and the second soft region are cooled differently in step e) in that the first soft region and the second soft region are subjected to the cooling fluid under different pressures.

[0054] The higher the pressure of the cooling fluid used to cool a soft area, the more effectively this soft area will be cooled in step c). The cooling effect can be adjusted accordingly using the pressure of the cooling fluid. This can be done via the controller without requiring any hardware intervention.

[0055] The two previously described embodiments can be combined. For this purpose, the first soft zone and the second soft zone are cooled differently in step c) in that the first soft zone and the second soft zone are exposed to the cooling fluid for different lengths of time and at different pressures.

[0056] In a further preferred embodiment of the method, the first soft region is completely surrounded by the hard region and / or the second soft region is completely surrounded by the hard region.

[0057] In this embodiment, the component can be considered to be essentially formed by the hard region, with the soft regions formed within the hard region. Such a configuration is desirable for many applications.

[0058] In a further preferred embodiment of the method, the first soft region borders an edge of the component and / or the second soft region borders an edge of the component. In this embodiment, the first soft region and / or the second soft region are located at an edge of the component. Thus, in contrast to the previous embodiment, the first soft region and / or the second soft region are not completely surrounded by the hard region. Such a configuration is desirable for many applications, particularly in the case of a door ring or double door ring as the component.

[0059] A combination of the two above embodiments is also possible. For example, the first soft region can be completely surrounded by the hard region, and the second soft region can be adjacent to an edge of the component.

[0060] In a further preferred embodiment of the method, the tempering station has a heatable heating chamber, wherein the component is received within the heating chamber in step c), wherein the tempering station further comprises a first nozzle box and a second nozzle box, which are each formed at least partially within the heating chamber and which each have at least one nozzle for discharging the cooling fluid, wherein the first soft region of the component is cooled in step c) by discharging the cooling fluid with the at least one nozzle of the first nozzle box, and wherein the second soft region of the component is cooled in step c) by discharging the cooling fluid with the at least one nozzle of the second nozzle box.

[0061] The temperature control device has a heatable heating chamber. How the heating chamber is heated is irrelevant. For example, the heating chamber can be gas-heated and / or electrically heated. For example, the heating chamber can have one or more heating elements. A radiant tube, for example, can be used as a heating element. The component can be thermally treated in the heating chamber. This can be achieved, in particular, by heating part of the component using radiant heat or convection in the heating chamber.

[0062] The heating chamber is preferably designed as a thermally insulated chamber. For this purpose, the heating chamber can be defined by a wall, a floor, and a ceiling. Preferably, thermal insulation is applied to the wall, floor, and / or ceiling. An inlet opening is preferably provided in the wall, through which the component can be introduced into the heating chamber. An outlet opening is preferably provided in the wall, through which the component can be removed from the heating chamber. The inlet opening and the outlet opening can be designed as separate openings. Alternatively, one opening can serve as both an inlet opening and an outlet opening.

[0063] In step c), the component is placed inside the heating chamber. For this purpose, the component can be placed in a treatment position within the heating chamber for thermal treatment. In step c), the component is preferably arranged in the treatment position.

[0064] The temperature control device further comprises a first nozzle box and a second nozzle box, each of which is at least partially formed within the heating chamber. The nozzle boxes each have at least one nozzle. The first soft region of the component is cooled in step c) by discharging the cooling fluid with the at least one nozzle of the first nozzle box. The second soft region of the component is cooled in step c) by discharging the cooling fluid with the at least one nozzle of the second nozzle box.

[0065] The fact that the temperature control device has two nozzle boxes means that the temperature control device has at least two nozzle boxes. However, it is also possible and even preferred for the temperature control device to have more than two nozzle boxes, for example, three or four. In particular, one nozzle box can be provided for each softening zone. However, it is also possible for multiple nozzle boxes to be used for the same thermal treatment and thus jointly create a softening zone. The following description applies to the first nozzle box and the second nozzle box.

[0066] Preferably, a first part of the nozzle box is formed within the heating chamber and a second part of the nozzle box is formed outside the heating chamber. The nozzle box is preferably arranged above the treatment position. The nozzle box can then primarily act on the upper side of the component when the component is arranged in the treatment position. The nozzle box is preferably open on its lower side. The nozzle box is then open on the side facing the component when the component is received in the treatment position. A cooling fluid can be discharged from the nozzle box at the lower open side of the nozzle box in order to act on the component located below the nozzle box in the treatment position. The part of the component located below the nozzle box, referred to herein as the soft region, can thereby be cooled.The position, shape, and size of the soft zone are generally determined by the position, shape, and size of the nozzle box. It is therefore preferable to use component-specific nozzle boxes and / or to arrange the nozzle boxes within the heating chamber in a component-specific manner.

[0067] The nozzle box preferably has an interior space. The at least one nozzle for discharging a cooling fluid toward the treatment position is arranged in the interior space. The at least one nozzle is considered part of the nozzle box. The nozzle box preferably has a plurality of nozzles in the interior space for discharging a cooling fluid toward the treatment position, particularly preferably between 5 and 100 nozzles.

[0068] The at least one nozzle can be used to discharge the cooling fluid, which in step c) acts on the component located in the treatment position. The at least one nozzle is aligned so that the cooling fluid is discharged in the direction of the treatment position. In the simplest case, the at least one nozzle is arranged so that the cooling fluid is discharged downwards. However, the cooling fluid can also reach the component if the nozzle is aligned diagonally downwards, for example. Because the nozzle box is preferably open at the bottom and arranged above the treatment position, the cooling fluid discharged from the at least one nozzle can reach the component.

[0069] With the described design of the tempering device, a particularly sharp separation can be achieved between the soft areas on the one hand and the hard area on the other. This applies first of all to the temperature at which these areas each leave the tempering device. Furthermore, this also applies to the resulting microstructure composition.

[0070] The sharp separation is initially achieved by arranging at least one nozzle in the nozzle box. The nozzle box allows the cooling fluid to be directed precisely to the respective soft area of ​​the component and kept away from the hard area. This basic principle is already known from the prior art. In the past, attempts have also been made to design nozzle boxes so that the resulting separation of the areas is as sharp as possible. The focus was on the transition between the nozzle box and the component. This is naturally the case because it is precisely at this point that the cooling fluid can escape from the nozzle box and enter the hard area. This also cools the edge of the hard area surrounding the respective soft area, creating a transition area between the soft area and the hard area.A preferred embodiment of the invention, however, is based on the realization that not only the transition between the component and the nozzle box is relevant for a sharp separation of the regions. Rather, it was recognized for this preferred embodiment that the discharge of the cooling fluid discharged from the at least one nozzle after it has hit the component also influences how sharply the regions are separated from one another. Therefore, it is preferably provided that the first nozzle box has a fluidic connection to an area surrounding the heating chamber and / or that the second nozzle box has a fluidic connection to an area surrounding the heating chamber. The "and" case is preferred. Via this fluidic connection, the fluid discharged from the at least one nozzle can be discharged from the corresponding nozzle box, particularly after it has come into contact with the respective soft area of ​​the component.This prevents the cooling fluid introduced into the nozzle box from building up pressure in the nozzle box, which would force the cooling fluid out of the nozzle box towards the hard area of ​​the component.

[0071] The fluidic connection can be designed as desired. In order to achieve the desired sharp separation between the areas, it is sufficient for there to be even a small fluidic connection to the environment of the heating chamber. However, the larger the flow cross-section of the fluidic connection, the greater the effect. It is therefore preferred, for example, for the first nozzle box to pass through a ceiling of the heating chamber and be open on an upper side and / or for the second nozzle box to pass through a ceiling of the heating chamber and be open on an upper side. In this case, the entire cross-section of the respective nozzle box is available as a fluidic connection. Particularly preferably, the first nozzle box has a constant cross-section between the lower side and the upper side and / or the second nozzle box has a constant cross-section between the lower side and the upper side.

[0072] In a further preferred embodiment of the method, the tempering station has at least one first additional nozzle, wherein the first soft region of the component is cooled in step c) by applying the cooling fluid from the at least one first additional nozzle to the component from below, and / or the tempering station has at least one second additional nozzle, wherein the second soft region of the component is cooled in step c) by applying the cooling fluid from the at least one second additional nozzle to the component from below. The "and" case is preferred.

[0073] The first auxiliary nozzle and the second auxiliary nozzle can be used to cool the component from below. This implies that the first auxiliary nozzle and the second auxiliary nozzle are positioned below the treatment position.

[0074] The fact that the first soft region or the second soft region of the component is cooled in step c) by subjecting the component to the cooling fluid from below from the at least one first additional nozzle means that this application of the cooling fluid contributes at least to cooling the respective soft region. Particularly preferred is the combination of the present embodiment with the previously described embodiment, in which the soft regions are cooled by discharging the cooling fluid with the at least one nozzle of the respective nozzle box. This should also be understood to mean that this application of the cooling fluid contributes at least to cooling the respective soft region. In this combination of embodiments, the two nozzle boxes are preferably arranged above the treatment position. As a result, the component is cooled from both above and below.

[0075] The first additional nozzle and the second additional nozzle can be arranged below the treatment position without a nozzle box. This leaves a comparatively large amount of space below the treatment position for a transport device, in particular for transport rollers. If no nozzle boxes are provided for the first additional nozzle and the second additional nozzle, this can make the desired sharp separation between the areas more difficult. However, this can be accepted. This applies in particular in the preferred case in which the first soft area is cooled to a lesser extent with the at least one first additional nozzle than with the at least one nozzle of the first nozzle box and / or the second soft area is cooled to a lesser extent with the at least one second additional nozzle than with the at least one nozzle of the second nozzle box.Alternatively, it is preferred that the at least one first additional nozzle is arranged in a third nozzle box and / or that the at least one second additional nozzle is arranged in a fourth nozzle box. The third nozzle box and the fourth nozzle box are arranged below the treatment position. It is also possible that, instead of a complete nozzle box for the first additional nozzle and / or for the second additional nozzle, guide plates and / or insulation are arranged below the treatment position, with which the installation space not occupied by a transport device is optimally utilized in order to achieve a sharp separation of the areas even when cooling from below.

[0076] In a further preferred embodiment of the method, the component is a door ring or a double door ring for a motor vehicle.

[0077] The invention is explained in more detail below with reference to the figures. The figures show a particularly preferred embodiment, to which the invention is not limited, however. The figures and the proportions depicted therein are merely schematic. They show:

[0078] Fig. 1 : an arrangement for carrying out a method according to the invention for the thermal treatment of a metallic component,

[0079] Fig. 2: a temperature profile which can be obtained with the arrangement of Fig. 1 by a method according to the invention, and

[0080] Fig. 3a and 3b: two examples of components which have been treated with the method illustrated in Fig. 2.

[0081] Fig. 1 shows an arrangement 1 for the thermal treatment of a metallic component 2. The arrangement 1 comprises a first continuous furnace 3, a tempering station 4, and a second continuous furnace 5, which are arranged one after the other in a transport direction r of the component 2. A control device 6 is particularly configured to control the first continuous furnace 3, the tempering station 4, and the second continuous furnace 5. Furthermore, the arrangement 1 comprises a first transfer device 13 for transferring the component 2 from the first continuous furnace 3 to the tempering station 4 and a second transfer device 14 for transferring the component 2 from the tempering station 4 to the second continuous furnace 5.

[0082] The temperature control station 4 has a heatable heating chamber 7 as well as a first nozzle box 8 and a second nozzle box 9. The nozzle boxes 8, 9 are each formed within the heating chamber 7 and each have a nozzle 15 for discharging a cooling fluid. The two nozzle boxes 8, 9 are formed above a treatment position 18. The nozzles 15 can be used to cool the component 2 from above. A first additional nozzle 16 and a second additional nozzle 17 are arranged below the treatment position 18. These can be used to cool the component 2 from below.

[0083] Fig. 2 shows a temperature profile that occurs in the component 2 when it is moved through the arrangement 1 of Fig. 1. Through this thermal treatment, the component 2 can receive a first soft region 10, a second soft region 11, and a hard region 12, as shown in Figs. 3a and 3b.

[0084] The representation of Fig. 2 is schematic. It shows a plot of temperature T over time t in arbitrary units. The component 2 is first heated in the first continuous furnace 3. The residence time of the component 2 in the first continuous furnace 3 is denoted by t D1 In the example shown, the entire component 2 is heated in the first continuous furnace 3 to a temperature above the AC3 temperature T AC3 of the component 2. Alternatively, the process could be carried out in such a way that the temperature of the component 2 in the first continuous furnace 3 reaches the AC3 temperature T AC3 of component 2.

[0085] Subsequently, component 2 is transferred to the temperature control station 4. The corresponding transfer time is t Ti During this transfer, component 2 can cool down.

[0086] In the tempering station 4, the component 2 remains for a residence time t TS . During the stay t TSThe component 2 is accommodated within the heating chamber 7 of the tempering station 4. Meanwhile, the first soft area 10 of the component 2 is cooled by discharging a cooling fluid through the nozzle 15 of the first nozzle box 8, and the second soft area 11 of the component 2 is cooled by discharging a cooling fluid through the nozzle 15 of the second nozzle box 9.

[0087] The first soft zone 10 and the second soft zone 11 are cooled differently. This is the case in the example shown in Fig. 2 in that after cooling, the temperature T W1 of the first soft area 10 from the temperature T W2 of the second soft area 11. The temperature T W1 of the first soft area 10 and the temperature T w2 of the second soft area 11 are below the austenite retransformation temperature T after cooling AR of component 2.

[0088] After the thermal treatment of the component 2 in the tempering station 4, the component 2 is transferred to the second continuous furnace 5. The transfer time for this is t T2 Component 2 can also cool down, which can vary depending on the area.

[0089] In the second continuous furnace 5, the component 2 is further thermally treated. The residence time of the component 2 in the second continuous furnace 5 is t D2 designated.

[0090] The temperature T H of the hard area 12 of the component 2 exceeds the AC3 temperature T in the first continuous furnace 3 AC3 of component 2 and does not fall below this temperature again until the end of the process shown.

[0091] Fig. 3a shows a first example of the design of component 2 in a top view. In this example, component 2 is a double door ring for a motor vehicle. The first soft area 10, the second soft area 11, and the hard area 12 can be seen. The arrangement of the soft areas 10, 11 is merely exemplary and schematic.

[0092] Fig. 3b shows a second example of the design of component 2 in a top view. In this example, component 2 is a B-pillar for a motor vehicle. The first soft area 10, the second soft area 11, and the hard area 12 can also be seen here. The arrangement of the soft areas 10, 11 is also merely exemplary and schematic. List of reference symbols

[0093] 1 arrangement

[0094] 2 component

[0095] 3 first continuous furnace

[0096] 4 Tempering station

[0097] 5 second continuous furnace

[0098] 6 Control device

[0099] 7 Heating chamber

[0100] 8 first nozzle box

[0101] 9 second nozzle box

[0102] 10 first soft area

[0103] 11 second soft area

[0104] 12 Hard area

[0105] 13 first transfer facility

[0106] 14 second transfer facility

[0107] 15 nozzle

[0108] 16 first additional nozzle

[0109] 17 second additional nozzle

[0110] 18 Treatment position

[0111] T Temperature

[0112] T A C3 AC3 temperature of the component

[0113] T AR Austenite retransformation temperature of the component

[0114] T W1 Temperature of the first soft area of ​​the component

[0115] T W2 Temperature of the second soft area of ​​the component

[0116] T HTemperature of the hard area of ​​the component t Time t D1 Residence time in the first continuous furnace t T1 Transfer time from the first continuous furnace to the tempering station t TS Residence time in the temperature control station t T2 Transfer time from the tempering station to the second continuous furnace t D2 Residence time in the second continuous furnace r Transport direction of the component

Claims

Claims 1. A method for the thermal treatment of a metallic component (2), comprising: a) heating the entire component (2) in a first continuous furnace (3), b) transferring the component (2) from the first continuous furnace (3) to a tempering station (4), c) in the tempering station (4) cooling a first soft region (10) of the component (2) and a second soft region (11) of the component (2) with a cooling fluid, wherein the first soft region (10) and the second soft region (11) are cooled differently, and wherein a respective temperature of the first soft region (10) and the second soft region (11) is below the austenite retransformation temperature (T AR) of the component (2), d) transferring the component (2) from the tempering station (4) into a second continuous furnace (5), e) thermally treating the component (2) in the second continuous furnace (5), wherein the first soft region (10) and the second soft region (11) of the component (2) are heated in such a way that the respective temperature of the first soft region (10) and the second soft region (11) remains below the AC3 temperature (T AC3 ) of the component (2), wherein a temperature of a hard region (12) of the component (2) during the process steps a) to e) at least temporarily exceeds the AC3 temperature (T AC3 ) of the component (2).

2. The method according to claim 1, wherein after cooling the temperature of the first soft region (10) differs from the temperature of the second soft region (11).

3. Method according to one of the preceding claims, wherein the first soft region (10) and the second soft region (11) are cooled differently in step e) in that the first soft region (10) and the second soft region (11) are exposed to the cooling fluid for different lengths of time.

4. Method according to one of the preceding claims, wherein the first soft region (10) and the second soft region (11) are cooled differently in step e) in that the first soft region (10) and the second soft region (11) are subjected to the cooling fluid under different pressures.

5. The method according to any one of the preceding claims, wherein the tempering station (4) has a heatable heating chamber (7), wherein the component (2) is received within the heating chamber (7) in step c), wherein the tempering station (4) further has a first nozzle box (8) and a second nozzle box (9), which are each formed at least partially within the heating chamber (7) and which each have at least one nozzle (15) for discharging the cooling fluid, wherein the first soft region (10) of the component (2) is cooled in step c) by discharging the cooling fluid with the at least one nozzle (15) of the first nozzle box (8), and wherein the second soft region (11) of the component (2) is cooled in step c) by discharging the cooling fluid with the at least one nozzle (15) of the second nozzle box (9).

6. Method according to one of the preceding claims, wherein the tempering station (4) has at least one first additional nozzle (16), and wherein the first soft region (10) of the component (2) is cooled in step e) by the component (2) being subjected to the cooling fluid from the at least one first additional nozzle (16) from below, and / or wherein the tempering station (4) has at least one second additional nozzle (17), and wherein the second soft region (11) of the component (2) is cooled in step c) by the component (2) being subjected to the cooling fluid from the at least one second additional nozzle (17) from below.

7. Method according to one of the preceding claims, wherein the component (2) is a door ring or a double door ring for a motor vehicle.

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