Thermal treatment of a metallic component

Abstract

Method for thermally treating 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 (11) of the component (2) during the process steps a) to e) at least temporarily exceeds the AC3 temperature (T AC3 ) of the component (2).

Description

The invention relates to a method for the thermal treatment of a metallic component, in particular a steel component for a motor vehicle.In particular in the automobile industry, it is known to specifically cure steel components by thermal treatment. For this purpose, steel components such as, for example, B-pillars are treated differently thermally in some regions. Accordingly, a ductility differing in certain areas arises, which is advantageous for the crash behavior of such components. For example, occupants of a motor vehicle can be protected by a hard region of the B-pillar at the height of the seats, while soft regions in the upper and lower region of the B-pillar absorb energy by deformation.Methods have proven successful for locally different thermal treatment of components, in which first the entire component is heated in a first furnace, the component is subsequently treated locally differently thermally in a temperature control station and the entire component is subsequently heated in a second furnace. In the temperature control station, a region of the component is cooled, for example, by exposure to a cooling fluid, and the remaining part of the component is kept approximately at its temperature. Excellent results can be achieved for many applications. However, there is an increasing need to obtain temperature distributions which cannot be adjusted or can only be adjusted with difficulty using known methods. This relates in particular to components in which more than two regions of different ductility are to be formed. This is particularly relevant with respect to so-called door rings and double door rings. These components cover a comparatively large part of a body, so that there is accordingly frequently the requirement to form more than two regions of different ductility.It is an object of the present invention to provide a particularly flexible method for locally different thermal treatment of metallic components.This object is achieved with the method according to the independent claim. Further advantageous embodiments are specified in the dependent claims. The features shown in the claims and in the description can be combined with one another in any desired, technologically meaningful manner.According to the invention, a method for the thermal treatment of 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 into a temperature control station, c) in the temperature control station, cooling a first soft region of the component and a second soft region of the component with a cooling fluid, 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 lies below the austenite reconversion temperature of the component at least after cooling, d) transferring the component from the temperature control station into 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, the respective temperature of the first soft region and of the second soft region is below the AC3 temperature of the component even after heating, wherein a temperature of a hard region of the component exceeds the AC3 temperature of the component at least temporarily during method steps a) to e).A metallic component can be thermally treated with the method described. The metallic component is preferably a component made of steel. The steel is preferably 22MnB5. However, it is not necessary for the metallic component to meet the definition of steel. Therefore, a metallic component is generally referred to 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 by the method described. However, the method can also be used for any other desired applications.The component preferably has a material thickness of at least 0.7 mm, in particular in the range from 1 to 4 mm. Such a material thickness is useful for many applications. The described method can, however, also be carried out with components of a different material thickness. The material thickness of the component is preferably constant over the entire component. Alternatively, the component can also have a different material thickness in some areas. For example, the component can be a "Tail Rolled Blank (TRB)", in which locally different material thicknesses are obtained by locally different rolling. The component can also be a "tail welded blank (TWB)", in which locally different material thicknesses are obtained by welding a plurality of metal sheets together. A combination of TRB and TWB is also possible. Furthermore, the method can be applied equally to components with and without coating. Particularly preferably, the component is coated with Al / Si. After the thermal treatment, the component is preferably press-hardened in a press and in this respect hot-formed. The method preferably comprises as further steps that the component is transferred from the second continuous furnace into the press (step f)) and is press-hardened in the press (step g)). In this case, the method described is a method for the thermal treatment and press curing of a component. However, it is not necessary for the press curing of the component to be carried out as part of the method described. The method described can also serve as a preparation for press hardening carried out outside the method described. In general, the component thermally treated with the described method can be subjected to further process steps which, together with further processes, can lead, for example, as a result to a finished motor vehicle. However, the thermal treatment of the component is a distinct sub-process in such an overall process. It is therefore expedient to consider the thermal treatment as being separated from the subsequent process steps, in particular also as being separated from the press curing.In step a), the entire component is heated in the first continuous furnace. A furnace is understood to mean a device which is brought in its interior to an adjustable temperature and into which a component can be introduced. Over time, the temperature of the component approaches the temperature prevailing in the interior of the furnace. The heat is thus transferred to the component by the gas located in the furnace, which can be air in particular. A continuous furnace is a furnace through which the component can be moved, wherein the component is heated during the passage of the furnace.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. As a result, the component can obtain a particularly uniformly distributed temperature. In the first continuous furnace, the entire component is heated. The component is completely accommodated by the first continuous furnace. In addition, heating by a particularly large temperature difference can be achieved with a continuous furnace. A continuous furnace can be used to heat a component, in particular from room temperature, to a temperature in the range of the AC3temperature of the component. Such extensive heating is not possible, or at least not possible without disproportionately great effort, with many other heating methods.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) in such a way that the material of the coating diffuses into the material of the rest of the component in step a). In step a), the component is thus preferably heated to a temperature which is above the temperature at which the material of the coating diffuses into the material of the remaining component. Preferably, the temperature of the component in step a) is at least 1 min, in particular even at least 2 min above this temperature. 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 obtained at these temperatures. In order to increase the process safety, however, heating to at least 830° C. is preferred. Preferably, the temperature of the component in step a) is at least 1 min, in particular even at least 2 min above a temperature of 700° C., in particular of 780° C. or even of 830° C. Particularly preferably, in the case of a coated component, the component is heated in step a) to a temperature above the AC1temperature of the component, in particular above the AC3temperature of the component. Preferably, the temperature of the component in step a) is at least 1 min, in particular even at least 2 min above the AC1temperature of the component, in particular above the AC3temperature of the component. In this respect, the heating in step a) can be used not only for diffusing in the coating, but can already contribute to the structure transformation.The heating in a continuous furnace is in particular in contrast to heating by the so-called "direct energy". It would thus be difficult to heat the component uniformly and by a sufficiently high amount. In direct energization, the speed of heating is rather important. In addition, in the case of direct energization, contact with the component is required. In step a) of the described method, the heating is preferably carried out contactless. This does not exclude that the component with transport rollers is moved through the first continuous furnace and is thus in contact with the transport rollers. The heating is contactless if the heat input into the component takes place via a gas and / or via thermal radiation.In step b) of the method, the component is transferred from the first continuous furnace into the temperature control station. This is preferably done with a first transfer device. In the temperature control station, the component is thermally treated in different regions. In particular, therefore, the method described is a method for the locally different thermal treatment of metallic components. However, this need not be mentioned explicitly, since the locally different thermal treatment is defined explicitly by step c).The first continuous furnace and the temperature control station are components which are different from one another and are spatially separated from one another. The transfer between the first continuous furnace and the temperature control station facilitates the cooling of the component between the heating in the first continuous furnace and the thermal treatment in the temperature control station. In the temperature control station, the component is cooled in any case in regions as quickly as possible. Rapid cooling can be more efficiently performed outside the hot first continuous furnace. Thus, cooling can already begin during the transfer. In this respect, the spatial separation of the first continuous furnace from the temperature control station accelerates the method. This is in contrast to a solution in which all method steps are carried out in the same device without having to transfer the component. Solutions of this type typically have the aim of keeping the outlay for component transfers low or completely avoiding it. The spatial separation between the first continuous furnace and the temperature control station also facilitates the construction because the requirements for the first continuous furnace and for the temperature control station are different.In step d), the component is transferred from the temperature control station into a second continuous furnace. This is preferably done with a second transfer device. In step e), the component is thermally treated in the second continuous furnace. For step e), the entire component is picked up by the second continuous furnace.The temperature control station and the second continuous furnace are components which are different from one another and are spatially separated from one another. The transfer between the temperature control station and the second continuous furnace facilitates the cooling of the component between the thermal treatment in the temperature control station and in the second continuous furnace. Thus, during the transfer, in particular, a part of the component to be cooled can also be cooled. This reduces the required dwell time in the temperature control station and accelerates the process. This is in contrast to a solution in which all method steps are carried out as far as possible in the same device without having to transfer the component. Solutions of this type typically have the aim of keeping the outlay for component transfers low or completely avoiding it. The spatial separation between the temperature control station and the second continuous furnace also facilitates the construction because the requirements for the temperature control station and for the second continuous furnace are different.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 accommodated by the second continuous furnace. The thermal treatment in a continuous furnace is in particular in contrast to heating by the so-called "direct energy". The thermal treatment in the second continuous furnace serves in particular to promote the structure transformation. Because the component is not cooled directly after the temperature control station, for example in a press, there is sufficient time for the desired microstructure distribution to be established in the component. In particular, in step e) carbon atoms can diffuse within the component, as a result of which the structure of the component changes as desired. In addition, the 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 thereby be reduced.With the method described, in particular three regions can be thermally treated differently. Firstly, a distinction can be made between a first soft region and a second soft region. Moreover, a hard portion is obtained. The component is thermally treated with the method described such that the hard region after press hardening has a lower ductility than the two soft regions and that the two soft regions have mutually different ductility. Thus, three different ductility are obtained in the component. In this respect, the method described is particularly flexible.The terms "soft region" and "hard region" refer to the ductility after press hardening. Prior to press hardening, the soft regions generally have no higher ductility than the hard region. During the method described herein, the soft regions of the component are therefore the regions of the component which are thermally treated with the method described such that they receive a higher ductility than the hard region in a subsequent process. The terms "soft region" and "hard region" are used herein for the sake of simplicity, but also for the period of time 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.The fact that in step c) the first soft region and the second soft region are cooled differently means that there are at least two different soft regions. However, it is also possible and even preferred for there to be more than two different soft regions, for example three or four.The soft regions can also be referred to as soft zones. The two soft regions have different ductility. This corresponds to the fact that the two soft regions have a different structure composition after press curing. This can be the case, for example, insofar as after the press hardening the first soft region has a bainitic structure and the second soft region has a ferritic-perlite structure, while the hard region is martensitic. However, it is not necessary for the structures of the two soft regions to differ in such a fundamental manner. It is also possible for the first soft region and the second soft region to each have a mixed structure of the same type, but of different composition, after press curing. In this respect, comparatively minor differences in the ductility of the soft regions can be realized. However, these go beyond mere statistical fluctuations in so far that the two soft regions are deliberately treated differently in step c).The first soft region, the second soft region and the hard region are not necessarily respectively contiguous regions. There may thus be a plurality of partial regions arranged at a distance from one another, which together form the first soft region. The same applies to the two soft region and the hard region. The component preferably, but not necessarily, comprises only the first soft region, the second soft region and the hard region. In this case, the component has no further regions.In step a), the entire component is heated in the first continuous furnace. All regions are therefore treated identically in step a). It is therefore not necessary that the regions can be differentiated from one another already in step a).The method described is multistage and comprises not only the heating in the first continuous furnace but also the thermal treatment in the temperature control station and the heating in the second continuous furnace. Therefore, the heating in the first continuous furnace can basically be carried out to any desired temperature. If the component is heated only slightly in the first continuous furnace, the component can be heated all the more in the hard region during the further course of the method, and vice versa. In particular, the heating of the component in the first continuous furnace can take place to a temperature above or below the AC3temperature of the component.Especially for energy reasons, it is advantageous to heat the component comparatively strongly in the first continuous furnace. This makes it possible to utilize the advantage described above of heating in a continuous furnace compared to other heating types, in particular compared to direct energy. Preferably, the component is therefore heated in step a) to at least 400° C., in particular to at least 600° C. Preferably, in step a), the component is heated to a temperature above the AC1temperature of the component. Preferably, in step a), the component is heated to a temperature which is at most 400 K below the AC3temperature of the component, in particular at most 200 K below the AC3temperature of the component. Preferably, in step a), the component does not exceed a temperature of 200 K above the AC3temperature of the component. For example, the component in step a) can be brought to a temperature in the range from 600 to 800° C. Alternatively, higher temperatures are preferred, which are in particular above the AC3temperature of the component. Thus, it is also preferred that the component in step a) is heated to a temperature of at least 900° C., in particular of at least 1000° C. For example, the component in step a) can be heated to a temperature in the range from 850 to 1200° C.By means of the temperature control station downstream of the first continuous furnace, the component is thermally treated locally in different ways. For this purpose, in the temperature control station, first the first soft region and the second soft region of the component are cooled differently. This is done by the first soft region and the second soft region being acted upon by a cooling fluid, in particular by compressed air. The first soft region and the second soft region can be acted upon by the same cooling fluid or by different cooling fluids. For practical reasons, it is preferred that the same cooling fluid be used for the first soft region and the second soft region. The composition of the cooling fluid is, however, not relevant any further for the mode of operation of the method. The only factor which arises is the cooling effect. Therefore, different cooling fluids can also be used for the two soft regions.The first soft region can be cooled in step c) by continuously guiding the cooling fluid to the first soft region for a first cooling time. During the first cooling time, the cooling fluid is discharged with constant pressure in the direction of the first soft region. Alternatively, the first soft region can be cooled in step c) by the cooling fluid being directed pulsed onto the first soft region for a first cooling time. During the first cooling time, the cooling fluid is discharged in the direction of the first soft region with a pressure which periodically varies over time. The pressure can drop temporarily to zero, which is not necessary, however. The pulsed discharge of the cooling fluid has proven to be particularly efficient.The second soft region can be cooled in step c) by continuously guiding the cooling fluid to the second soft region for a second cooling time. During the second cooling time, the cooling fluid is discharged with constant pressure in the direction of the second soft region. Alternatively, the second soft region can be cooled in step c) by the cooling fluid being directed pulsed onto the second soft region for a second cooling time. During the second cooling time, the cooling fluid is discharged in the direction of the second soft region with a pressure which periodically varies over time. The pressure can drop temporarily to zero, which is not necessary, however. The pulsed discharge of the cooling fluid has proven to be particularly efficient.The first cooling time and the second cooling time are generally independent of each other. The first cooling time and the second cooling time can thus be of the same length or of different lengths, can start at the same or different points in time and can end at the same or different points in time. However, it is preferred that the first cooling time and the second cooling time at least overlap. This reduces the process time. Preferably, the first cooling time and the second cooling time start at the same time and / or the first cooling time and the second cooling time end at the same time.The cooling fluid preferably has a pressure in the range of 2 to 4.5 bar. As a result of this comparatively high pressure, a large quantity of the cooling fluid can be conducted to the first soft region and the second soft region of the component within the shortest time, so that a sufficiently high cooling speed can be achieved. However, the method described generally does not involve the method by which the soft regions are cooled.The first soft region and the second soft region can be cooled with the cooling fluid in step c) by guiding the cooling fluid onto the soft regions. This can be done on one side or on both sides. The first soft region can be cooled in step c) by the cooling fluid being applied to the first soft region from below and / or from above. The second soft region can be cooled in step c) by the cooling fluid being applied to the second soft region from below and / or from above. A combination of cooling from below and from above can achieve a particularly intensive cooling effect. This is particularly advantageous in the case of thicker components and / or in the case of components composed of a plurality of layers.It is preferred, but not necessary, that the first soft region and the second soft region be treated the same insofar as both are cooled only from above, both only from below or both both from above and from below.The application of cooling fluid from above to the first soft region and the second soft region is preferred for practical reasons. Space for a transport device thereby remains below the component. The application of cooling fluid from below to the first soft region and to the second soft region is preferred in particular in addition to the application of cooling fluid from above to the first soft region and to the second soft region. The first soft region and the second soft region can thus be cooled mainly from above and additionally from below, for example with additional nozzles arranged below the component. Since the additional nozzles are of only secondary importance, they can be designed to be correspondingly small and, for example, be arranged below the component in addition to a transport device.The first soft region and the second soft region are cooled differently in step c). The two soft regions are thus cooled in different ways and / or with different cooling parameters. The time profile of the temperature of the first soft region is therefore not identical to the time profile of the temperature of the second soft region. The two soft regions can thus have different temperatures at the end of step c) and / or be cooled at different cooling speeds in step c).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, wherein the first cooling parameters are not identical to the second cooling parameters. The cooling parameters can be, for example, a duration of the application of 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 acted upon with cooling fluid for different lengths. In this case, the first cooling time and the second cooling time are different. The question as to whether the component is acted upon by the cooling fluid from below and / or from above in a soft region can also be expressed as a cooling parameter.The fact that the two soft regions are cooled in different ways can be realized, for example, by discharging the cooling fluid onto the two soft regions with differently configured nozzles and / or with a different number of nozzles. For example, the cooling effect can be influenced via the spray pattern of the nozzles. The different cooling can also be effected by additionally cooling only one of the two soft regions from below, for example.By cooling with a cooling fluid, the desired flexibility can be achieved insofar as the two soft regions are cooled to different extents in step c). With other cooling techniques, this would not be implementable or would only be difficult to implement. For example, solutions are known from the prior art in which cooler regions are obtained by locally shielding a heat source. In this case, it is practically impossible or only possible with difficulty to differentiate between different soft regions. In the cooling with a cooling fluid, however, any desired fine graduations can be easily carried out. If such a gradation is realized, for example, over the cooling period, the gradation can even be realized solely by means of the controller. An intervention in the hardware is not required.If the entire component is heated in step a) to a temperature above the AC3temperature, austenite forms in the entire component. By cooling the soft regions in step c) below the austenite reconversion temperature of the component, this austenite breaks down again in the soft regions. The austenite reconversion temperature is defined in that austenite decomposes as soon as the austenite reconversion temperature is undershot. The austenite reconversion temperature is a material property. The fact that the temperature of the soft regions is below the austenite reconversion temperature of the component at least after cooling therefore does not imply that austenite has previously been formed in the component.If the entire component is not heated to a temperature above the AC3temperature in step a), no austenite forms in this step. The cooling of the soft regions in step c) below the austenite reconversion temperature of the component can, however, contribute in this case to the fact that no austenite is formed in the soft regions even in the further course of the method, even if the component is subjected to a further heating. If no austenite is formed in step a), the austenite reconversion temperature in step c) does not have to be fallen below in order for the austenite to decompose. In the case that the entire component is not heated to a temperature above the AC3temperature in step a), therefore, arbitrary cooling of the soft regions is sufficient in step c). Nevertheless, it is also expedient in the case of falling below the austenite reconversion temperature. This arises not from the austenite reconversion circumstance below this temperature, but only from the austenite reconversion temperature generally being significantly below the AC3temperature.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 each case in the range from 400 to 700° C., in particular in each case in the range from 500 to 600° C. The temperature of the two soft regions differs after step c) preferably by at least 50 K, in particular by at least 100 K.Regardless of the temperature reached in step a), no austenite is thus present in both soft regions after cooling in step c). If the AC3temperature of the component is not (again) exceeded in the soft regions after cooling in step c), a more ductile microstructure can be obtained in the soft regions than in the hard region.In the soft regions, the AC3temperature 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 in such a way that a respective temperature of the soft regions is below the AC3temperature of the component even after the heating. The soft regions are therefore in any case no longer heated above the AC3temperature of the component after the cooling in step c). Preferably, the respective temperature of the soft regions of the component does not exceed the AC3temperature of the component at least in steps d) and e). If press curing is part of the claimed method, the temperature of the soft regions of the component preferably does not exceed the AC3temperature of the component up to and including press curing. A ductile structure can thus be obtained in the soft regions. However, it is not necessary to ensure strictly that the AC3 temperature is not exceeded in the stated periods. Austenite is not formed instantaneously. Acceptable results can also be achieved when a small amount of austenite is formed in one of the soft regions of the component.In addition to the soft regions, the component has the hard region. The method is carried out in such a way that a temperature of the hard region of the component during method steps a) to e) at least temporarily exceeds the AC3temperature of the component. As a result, austenite can be formed in the hard region. Martensite can be formed therefrom during press hardening, as a result of which the hard region receives a comparatively low ductility.It is immaterial at what time the temperature of the hard region exceeds the AC3temperature of the component. If the entire component is heated to a temperature above the AC3temperature of the component in step a), the stated condition is already fulfilled in step a). If the hard region is heated in step a) to less than the AC3temperature, the hard region can be heated in the temperature control station or in the second furnace to a temperature above the AC3temperature.It is preferred that the temperature of the hard region no longer falls below the austenite reconversion temperature after heating to a temperature above the AC3temperature of the component until the completion of step e). Preferably, in the hard region, the austenite reconversion temperature is not reached until in the press. This makes it possible to prevent the austenite formed in the hard region from breaking down before press hardening.In steps b) to e), a 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 a holding of the temperature, wherein a change in the temperature within a tolerance of 200 K or 100 K is accepted. For example, the hard region can be exposed in step c) in the temperature control station to a temperature above the AC3temperature of the component and / or in step e) in the second furnace to a temperature above the AC3temperature of the component. Depending on the temperature of the hard region on entry into the temperature control station or into the second furnace and depending on the dwell time of the component in the temperature control station or in the second furnace, the hard region can be kept at its temperature or heated in the temperature control station or cooling of the hard region can be slowed down. In particular, the hard region can also cool down in ambient air in the temperature control station.It is possible that the temperature of the hard region in steps a) to e) first rises above the AC3temperature, then falls below the austenite reconversion temperature and then rises again above the AC3temperature. In this case, it is sufficient that the temperature of the hard region after the second heating to above the AC3temperature until the completion of step e) no longer falls below the austenite reconversion temperature. This is encompassed by the formulation that a temperature of the hard region of the component during method steps a) to e) at least temporarily exceeds the AC3temperature of the component and subsequently does not fall below an austenite reconversion temperature of the component.In a preferred embodiment of the method, after cooling, the temperature of the first soft region differs from the temperature of the second soft region, preferably by at least 50 K, in particular by at least 100 K.In this embodiment, the soft regions are cooled differently in step c) in so far 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 c) insofar as the cooling fluid is applied to the first soft region and the second soft region for different lengths of time.The longer the respective soft region of the component is exposed to the cooling fluid, the more strongly this soft region is cooled in step c). The cooling effect can be adjusted accordingly over the cooling duration. This can be done by the controller without any intervention in the hardware being required.In a further preferred embodiment of the method, the first soft region and the second soft region are cooled differently in step c) insofar as the first soft region and the second soft region are acted upon by the cooling fluid under different pressures.The higher the pressure of the cooling fluid used to cool a soft region, the more that soft region is cooled in step c). The cooling effect can be adjusted accordingly by means of the pressure of the cooling fluid. This can be done by the controller without any intervention in the hardware being required.The two embodiments described above can be combined with each other. For this purpose, the first soft region and the second soft region are cooled differently in step c) to the extent that the cooling fluid under different pressures is applied to the first soft region and the second soft region for different lengths of time.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.In this embodiment, the component can be understood as being basically formed by the hard region, wherein the soft regions are formed within the hard region. Such a configuration is desirable for many applications.In a further preferred embodiment of the method, the first soft region adjoins an edge of the component and / or the second soft region adjoins an edge of the component.In this embodiment, the first soft region and / or the second soft region lie on an edge of the component. The first soft region or the second soft region are thus not completely surrounded by the hard region, in contrast to the preceding embodiment. Such a configuration is desired for many applications, in particular in the case of a door ring or double door ring as the component.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 adjoin an edge of the component.In a further preferred embodiment of the method, the temperature control station has a heatable heating chamber, wherein the component is accommodated within the heating chamber in step c), wherein the temperature control station further has 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.The temperature control device has a heatable heating chamber. How the heating chamber is heated is unimportant. For example, the heating chamber can be gas-heated and / or electrically heated. For example, the heating chamber may include one or more heating element(s). A radiation tube, for example, can be considered as the heating element. In the heating chamber, the component can be thermally treated. This can be effected in particular by heating a part of the component by means of radiant heat or convectively in the heating chamber.The heating chamber is preferably formed as a thermally insulated chamber. For this purpose, the heating chamber can be bounded by a wall, a floor and a ceiling. Preferably, a respective thermal insulation is applied to the wall, the floor and / or the ceiling. In the wall, an inlet opening is preferably provided, via which the component can be introduced into the heating chamber. In the wall, an outlet opening is preferably provided, via which the component can be discharged from the heating chamber. The inlet opening and the outlet opening can be formed as openings which are separate from one another. Alternatively, an opening can serve both as an inlet opening and as an outlet opening.The component is accommodated within the heating chamber in step c). For this purpose, the component for thermal treatment can be accommodated in a treatment position within the heating chamber. In step c), the component is preferably arranged in the treatment position.The temperature control device further comprises a first nozzle box and a second nozzle box, which are each formed at least partially 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.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 soft region. However, it is also possible for a plurality of nozzle boxes to be used for the same thermal treatment and to this extent to jointly produce a soft region. The following description applies to the first nozzle box and the second nozzle box, respectively.Preferably, a first part of the nozzle box is formed inside 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 be used to act primarily on the upper side of the component when the component is arranged in the treatment position. The nozzle box is preferably open at its lower side. The nozzle box is then open on its side facing the component when the component is accommodated in the treatment position. At the lower open side of the nozzle box, a cooling fluid can be discharged from 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 soft region, can thereby be cooled. The position, shape and size of the soft region thus usually result from the position, shape and size of the nozzle box. It is therefore preferred that component-specific nozzle boxes are used and / or that the nozzle boxes are arranged component-specifically within the heating chamber.The nozzle box preferably has an interior. The at least one nozzle for discharging a cooling fluid in the direction of the treatment position is arranged in the interior space. The at least one nozzle is understood herein as part of the nozzle box. The nozzle box preferably has a plurality of nozzles in the interior for discharging a cooling fluid in the direction of the treatment position, particularly preferably between 5 and 100 nozzles.The cooling fluid can be discharged with the at least one nozzle, which cooling fluid acts on the component located in the treatment position in step c). The at least one nozzle is correspondingly oriented such that the cooling fluid is discharged in the direction of the treatment position. In the simplest case, the at least one nozzle is arranged such that the cooling fluid is discharged downward. However, the cooling fluid can also reach the component if the nozzle is oriented obliquely downward, for example. Because the nozzle box is preferably open at the bottom and is arranged above the treatment position, the cooling fluid discharged from the at least one nozzle can reach the component.With the described configuration of the temperature control device, a particularly sharp separation between the soft regions on the one hand and the hard region on the other hand can be achieved. This applies first to the temperature which these regions have in each case after leaving the temperature control device. Furthermore, this also applies to the structure composition resulting therefrom.The sharp separation is initially achieved by the at least one nozzle being arranged in the nozzle box. The cooling fluid can be directed through the nozzle box in a targeted manner onto the respective soft region of the component and kept away from the hard region of the component. This basic principle is already known from the prior art. In the past, attempts have also been made to configure nozzle boxes such that the separation of the regions achieved thereby is as sharp as possible. In this case, the transition between the nozzle box and the component has been focused on. This is also naturally forced up because at exactly this point the cooling fluid can emerge from the nozzle box and reach the hard region. As a result, the edge of the hard region surrounding the respective soft region is also cooled, as a result of which a transition region is formed between the soft region and the hard region. A preferred embodiment of the invention is, however, based on the finding that not only is the transition between component and nozzle box 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 has an influence on how sharply the regions are separated from one another. It is therefore preferably provided that the first nozzle box has a fluidic connection to a surroundings of the heating chamber and / or that the second nozzle box has a fluidic connection to a surroundings of the heating chamber. The "and" case is preferred. By means of this fluidic connection, the fluid discharged from the at least one nozzle can be discharged from the corresponding nozzle box, in particular after it has come into contact with the respective soft region of the component. This prevents the cooling fluid introduced into the nozzle box from building up in the nozzle box a pressure which drives the cooling fluid out of the nozzle box in the direction of the hard region of the component.The fluidic connection can be configured as desired. In order to obtain the desired sharp separation between the regions, it is already sufficient that there is also only 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, that the first nozzle box passes through a ceiling of the heating chamber and is open on an upper side and / or that the second nozzle box passes through a ceiling of the heating chamber and is 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.In a further preferred embodiment of the method, the temperature control station has at least one first additional nozzle, wherein the first soft region of the component is cooled in step c) by the cooling fluid from the at least one first additional nozzle being applied to the component from below, and / or the temperature control station has at least one second additional nozzle, wherein the second soft region of the component is cooled in step c) by the cooling fluid from the at least one second additional nozzle being applied to the component from below. The "and" case is preferred.The first auxiliary nozzle and the second auxiliary nozzle may be used to cool the component from below. This implies that the first additional nozzle or the second additional nozzle are arranged below the treatment position.The fact that the first soft region or the second soft region of the component is cooled in step c) by the component being acted upon from below with the cooling fluid from the at least one first additional nozzle means that this action upon with the cooling fluid contributes at least to the cooling of the respective soft region. The combination of the present embodiment with the previously described embodiment is particularly preferred, in which the soft regions are cooled by the cooling fluid being discharged with the at least one nozzle of the respective nozzle box. This is also to be understood such that this application of the cooling fluid contributes at least to cooling the respective soft region. Preferably, the two nozzle boxes in this combination of the embodiments are arranged above the treatment position. As a result, the component is cooled both from above and from below.The first additional nozzle and the second additional nozzle can be arranged below the treatment position without a nozzle box. As a result, a comparatively large amount of space remains 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 may make the desired sharp separation between the regions more difficult. However, this can be accepted. This applies in particular in the preferred case in which the first soft region is cooled to a lesser extent by the at least one first additional nozzle than by the at least one nozzle of the first nozzle box and / or the second soft region is cooled to a lesser extent by the at least one second additional nozzle than by 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 insulations 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 regions even during the cooling from below.In a further preferred embodiment of the method, the component is a door ring or a dual door ring for a motor vehicle.The invention is explained in more detail below with reference to the figures. The figures show a particularly preferred exemplary embodiment, to which the invention is, however, not limited. The figures and the size relationships illustrated therein are only schematic. The following are shown: FIG. 1 shows an arrangement for carrying out a method according to the invention for the thermal treatment of a metallic component, FIG. 2 : a temperature profile which can be obtained with the arrangement from FIG. 1 by a method according to the invention, and FIGS. 3 aand 3 b : two examples of components which have been treated with the method illustrated in FIG. 2.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 temperature control 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 configured in particular to control the first continuous furnace 3, the temperature control 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 into the temperature control station 4 and a second transfer device 14 for transferring the component 2 from the temperature control station 4 into the second continuous furnace 5.The temperature control station 4 has a heatable heating chamber 7 and a first nozzle box 8 and a second nozzle box 9. The two nozzle boxes 8, 9 are formed above a treatment position 18. The component 2 can be cooled from above by means of the nozzles 15. Below the treatment position 18, a first additional nozzle 16 and a second additional nozzle 17 are arranged. With these, the component 2 can be cooled from below.FIG. 2 shows a temperature profile which is established in the component 2 when it is moved through the arrangement 1 from FIG. 1. As shown in FIGS. 3 aand 3 b, the component 2 can be provided with a first soft region 10, a second soft region 11 and a hard region 12 by this thermal treatment.The illustration of FIG. 2 is schematic. Shown is a plot of temperature T versus time t in arbitrary units. The component 2 is first heated in the first continuous furnace 3. The dwell 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 AC3temperature T AC3 of the component 2. Alternatively, the method could be carried out in such a way that the temperature of the component 2 in the first continuous furnace 3 does not exceed the AC3temperature T AC3 of the component 2.The component 2 is then transferred into the temperature control station 4. The associated transfer time is denoted by t T1. During this transfer, the component 2 can cool.In the temperature control station 4, the component 2 remains for a dwell time t TS. During the dwell time t TS the component 2 is accommodated within the heating chamber 7 of the temperature control station 4. Meanwhile, the first soft region 10 of the component 2 is cooled by discharging a cooling fluid with the nozzle 15 of the first nozzle box 8, and the second soft region 11 of the component 2 is cooled by discharging a cooling fluid with the nozzle 15 of the second nozzle box 9.The first soft region 10 and the second soft region 11 are cooled differently in this case. This is the case in the example of FIG. 2 insofar as, after cooling, the temperature T W1 of the first soft region 10 differs from the temperature T W2 of the second soft region 11. The temperature T W1 of the first soft region 10 and the temperature T W2 of the second soft region 11 after cooling are below the austenite reconversion temperature T AR of the component 2.After the thermal treatment of the component 2 in the temperature control station 4, the component 2 is transferred into the second continuous furnace 5. The transfer time therefor is denoted by t T2. In this case, too, the component 2 can cool, which can be different depending on the region.In the second continuous furnace 5, the component 2 is further thermally treated. The dwell time of the component 2 in the second continuous furnace 5 is denoted by t D2.The temperature T H of the hard region 12 of the component 2 exceeds the AC3temperature T AC3 of the component 2 in the first continuous furnace 3 and does not fall below this temperature again until the end of the method shown.FIG. 3 ashows a first example of the configuration of the component 2 in a plan view. In this example, the component 2 is a double door ring for a motor vehicle. The first soft region 10, the second soft region 11 and the hard region 12 can be seen.FIG. 3 bshows a second example of the configuration of the component 2 in a plan view. In this example, the component 2 is a B-pillar for a motor vehicle. Here too, the first soft region 10, the second soft region 11 and the hard region 12 can be seen.List of reference characters1 Arrangement 2 Component 3 First continuous furnace 4 Temperature control station 5 Second continuous furnace 6 Control device 7 Heating chamber 8 First nozzle box 9 Second nozzle box 10 First soft region 11 Second soft region 12 Hard region 13 First transfer device 14 Second transfer device 15 Nozzle 16 First additional nozzle 17 Second additional nozzle 18 Treatment position T Temperature T AC3 AC3Temperature of the component T AR Austenite reconversion temperature of the component T W1 Temperature of the first soft region of the component T W2 Temperature of the second soft region of the component T H Temperature of the hard region of the component t Time t D1 Residence time in the first continuous furnace t T1 transfer duration from the first continuous furnace to the temperature control station t TS dwell time in the temperature control station t T2 transfer duration from the temperature control station to the second continuous furnace t D2 dwell time in the second continuous furnace r transport direction of the component

Claims

Method for thermally treating 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) 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 respective temperature of the first soft region (10) and the second soft region (11) lies below the austenite reconversion temperature (T AR) 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 in such a way that the respective temperature of the first soft region (10) and of the second soft region (11) is below the AC3temperature (T AC3) of the component (2) even after the heating, wherein a temperature of a hard region (12) of the component (2) exceeds the AC3temperature (T AC3) of the component (2) at least temporarily during the method steps a) to e).The method of claim 1, wherein after cooling, the temperature of the first soft region (10) is different from the temperature of the second soft region (11).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 c) insofar as the first soft region (10) and the second soft region (11) are acted upon with the cooling fluid for different lengths of time.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 c) insofar as the first soft region (10) and the second soft region (11) are acted upon by the cooling fluid under different pressures.Method according to one of the preceding claims, wherein the temperature control station (4) has a heatable heating chamber (7), wherein the component (2) is accommodated within the heating chamber (7) in step c), wherein the temperature control station (4) furthermore has a first nozzle box (8) and a second nozzle box (9), which are each at least partially formed 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 the cooling fluid being discharged 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 the cooling fluid being discharged with the at least one nozzle (15) of the second nozzle box (9).Method according to one of the preceding claims, wherein the temperature control 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 c) by the component (2) being acted upon from below by the cooling fluid from the at least one first additional nozzle (16), and / or wherein the temperature control 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 acted upon from below by the cooling fluid from the at least one second additional nozzle (17).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.

Images