Thermally Treating a Metallic Component

[0001]The invention relates to a method and an apparatus for thermally treating a metallic component, in particular a steel component for a motor vehicle.

[0002]In particular in the automotive industry, it is known to selectively harden steel components by thermal treatment. To this end, regions of the steel components, which are for example B pillars, are subjected to different thermal treatments. Correspondingly, regions of different ductilities are created, and this is advantageous for the crash behavior of such components. For instance, occupants of a motor vehicle can be protected by a hard region of the B pillar at seat height, while soft regions in the upper and the lower region of the B pillar can absorb energy by deforming.

[0003]Methods that have proven successful for the locally different thermal treatment of components are those in which firstly the entire component is heated in a first furnace, then the component is subjected to locally different thermal treatment in a temperature control station, and then the entire component is heated in a second furnace. In the temperature control station, a region of the component is cooled, for example by applying a cooling fluid to it, and the rest of the parts of the component are kept approximately at its temperature. For many use cases, this makes it possible to achieve excellent results. However, there is an increasing need to obtain temperature distributions which cannot be established, or can be established only with difficulty, using known methods. This relates in particular to components in which the ductility changes gradually. In particular, it is difficult to precisely establish a temperature gradient in the case of cooling by means of cooling fluid.

[0004]An object of the present invention is to present a particularly flexibly applicable method for the locally different thermal treatment of metallic components. The intention is also to present a corresponding apparatus.

[0005]These objects are achieved by the method and the apparatus according to the independent claims. Further advantageous configurations 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 meaningful way.

[0014]The described method makes it possible to thermally treat a metallic component. The metallic component is preferably a component made of steel. The steel is preferably 22MnB5. It is, however, not necessary for the metallic component to satisfy the definition of steel. Therefore, this document will refer in general to a metallic component. For example, a component for a motor vehicle, in particular a B pillar, can be thermally treated by the described method. The described method is particularly suitable for what are known as door rings. A door ring is a motor vehicle bodywork part which surrounds the opening for a door. A door ring can thus be used instead of separate components for the A and the B pillar and also for the bodywork roof and floor parts in between. With preference, the component is a door ring. The method can, however, also be used for any other applications in any desired technical field.

[0015]The component preferably has a material thickness of at least 0.7 mm, in particular in the range of 1 to 4 mm. Such a material thickness is expedient for many use cases. The described method can, however, also be carried out with components of different material thicknesses. The material thickness of the component is preferably constant over the entire component. As an alternative, the component may also have regionally different material thicknesses. For example, the component may be a “tailor rolled blank (TRB)”, in the case of which locally different material thicknesses are obtained by locally different rolling. The component may also be a “tailor welded blank (TWB)”, in the case of which locally different material thicknesses are obtained by welding multiple sheets of metal together. A combination of TRB and TWB is also possible. The method may also equally be applied to components with and without a coating. The component is particularly preferably coated with Al/Si.

[0016]After the thermal treatment, the component is preferably press-hardened in a press and in this respect hot-formed. The method preferably comprises the further steps of transferring the component from the second continuous furnace into the press (step f)) and press-hardening the component in the press (step g)). In that case, the described method is a method for thermally treating and press-hardening a component. It is, however, not necessary to carry out the press-hardening of the component as part of the described method. The described method can also serve as preparation for a press-hardening operation carried out outside the described method. Generally speaking, the component thermally treated by the described method can be subjected to further process steps, the result of which, together with further processes, can be for example a finished motor vehicle. The thermal treatment of the component is, however, a defined sub-method in such an overall process. It is therefore expedient to consider the thermal treatment separately from the subsequent process steps, in particular separately from the press-hardening.

[0017]In step a), the entire component is heated in the first continuous furnace. A furnace is understood to be a device the inside of which can be brought to a settable temperature and into which a component can be introduced. Over time, the temperature of the component gradually approaches the temperature prevailing inside the furnace. The heat is thus transferred to the component by the gas, which in particular can be air, inside the furnace. A continuous furnace is a furnace through which the component can be moved, the component being heated as it passes through the furnace.

[0018]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 makes it possible to give the component a particularly uniformly distributed temperature. In the first continuous furnace, the entire component is heated. The component is received completely by the first continuous furnace. In addition, a continuous furnace can be used to obtain heating with an especially large temperature difference. With a continuous furnace, a component can be heated in particular from room temperature to a temperature in the region of the AC3 temperature of the component. Such comprehensive heating is not possible, in any case not without excessive outlay, with many other heating methods.

[0019]In the case of a coated component, the first continuous furnace may also serve to diffuse the coating into the rest of the material of the component. This applies in particular for an Al/Si coating. In the case of a coated component, it is preferred if, in step a), the component is heated in such a way that the material of the coating in step a) diffuses into the material of the rest of the component. The component is thus, in step a), preferably heated to a temperature above the temperature at which the material of the coating diffuses into the material of the rest of the component. With preference, the temperature of the component in step a) lies above this temperature for at least 1 min, in particular even at least 2 min. With preference, the component in step a) is heated to a temperature of at least 700° C., in particular at least 780° C. At these temperatures, results which are already satisfactory have been obtained. In order to increase the process reliability, however, heating to at least 830° C. is preferred. With preference, the temperature of the component in step a) lies above a temperature of 700° C., in particular 780° C. or even 830° C., for at least 1 min, in particular even at least 2 min. With particular preference, in the case of a coated component, the component in step a) is heated to a temperature above the AC1 temperature of the component, in particular above the AC3 temperature of the component. With preference, the temperature of the component in step a) lies above the AC1 temperature of the component, in particular above the AC3 temperature of the component, for at least 1 min, in particular even at least 2 min. In this respect, the heating in step a) can be used not only to make the coating diffuse in, but also to already contribute to the transformation of the microstructure.

[0020]Heating in a continuous furnace in particular can be contrasted with heating by what is referred to as “direct energization”. Such heating would only make it possible with difficulty to heat the component uniformly and by a sufficiently high amount. Direct energization is more about the quickness of the heating. In addition, in the case of direct energization, contact with the component is necessary. In step a) of the described method, the heating is preferably done contactlessly. This does not rule out the component being moved through the first continuous furnace by means of transport rollers and in this respect being in contact with the transport rollers. The heating is contactless when heat is introduced into the component via a gas and/or via heat radiation.

[0021]In step b) of the method, the component is transferred from the first continuous furnace into the temperature control station. This is preferably performed by a first transfer device. In the temperature control station, regions of the component are thermally treated differently. In particular, therefore, the described method is a method for locally differently thermally treating metallic components. However, this does not need to be mentioned explicitly, because the locally different thermal treatment is explicitly defined by steps c1) and c2).

[0022]The first continuous furnace and the temperature control station are components that are different from one another and are spatially separate. The transfer between the first continuous furnace and the temperature control station makes it easier to cool the component between being heated in the first continuous furnace and thermally treated in the temperature control station. In the temperature control station, the component is regionally cooled as rapidly as possible in any case. Rapid cooling can be done more efficiently outside the hot first continuous furnace. The cooling can thus start already during the transfer. In this respect, the spatial separation of the first continuous furnace from the temperature control station speeds up the method. This can be contrasted with a solution in which all the method steps are carried out in the same device, without needing to transfer the component. The aim of such solutions is typically to keep the outlay on component transfers low or even avoid it. The spatial separation between the first continuous furnace and the temperature control station also makes the construction easier, because the requirements for the first continuous furnace and for the temperature control station are different.

[0023]In step d), the component is transferred from the temperature control station into a second continuous furnace. This is preferably performed by a second transfer device. In step e), the component is thermally treated in the second continuous furnace. For step e), the entire component is received by the second continuous furnace.

[0024]The temperature control station and the second continuous furnace are components that are different from one another and are spatially separate. The transfer between the temperature control station and the second continuous furnace makes it easier to cool the component between the thermal treatments in the temperature control station and in the second continuous furnace. It is thus also possible still during the transfer to cool in particular a part to be cooled of the component. This reduces the necessary dwell time in the temperature control station and speeds up the method. This can be contrasted with a solution in which all the method steps are carried out as far as possible in the same device, without needing to transfer the component. The aim of such solutions is typically to keep the outlay on component transfers low or even avoid it. The spatial separation between the temperature control station and the second continuous furnace also makes the construction easier, because the requirements for the temperature control station and for the second continuous furnace are different.

[0025]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 received completely by the second continuous furnace. Thermal treatment in a continuous furnace in particular can be contrasted with heating by what is referred to as “direct energization”. The thermal treatment in the second continuous furnace serves in particular to promote the transformation of the microstructure. Since the component is not cooled directly, for example in a press, downstream of the temperature control station, there is enough time for the desired microstructure distribution to be established in the component. In particular, in step e) carbon atoms can diffuse inside the component, as a result of which the microstructure 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 a subsequent presshardening operation, the warping of the component can be reduced as a result.

[0026]The described method makes it possible in particular for three regions to be differently thermally treated. Firstly, a distinction can be made between a first region and a second region. Furthermore, a first subregion of the first region is treated separately from the rest of the first region. The result is therefore at least the first subregion of the first region, the rest of the first region, and the second region. Besides the first subregion of the first region, the first region can also have a second subregion and optionally also further subregions. In that case, the result is therefore the first subregion of the first region, the second subregion of the first region, the rest of the first region, and the second region.

[0027]The first region, the subregion(s) of the first region, and the second region are not necessarily all coherent regions. It is thus possible in particular for a central part of a B pillar to constitute the first region, while an upper and a lower part of the B pillar together constitute the second region. Within the first region, one or more parts may constitute the first subregion. The component preferably, but not necessarily, has only the first region and the second region, i.e. no further regions. This also applies in spite of the one or more subregions, because they are part of the first region.

[0028]The subregion(s) each constitute a part of the first region. The subregion(s) are each smaller than the first region. There is thus in particular also a part of the first region which is not part of the first subregion.

[0029]The described method makes it possible for regions of the component to be differently thermally treated. As a result, the composition of the microstructure of the component can be locally differently influenced, so that locally different ductilities are obtained. In particular, a ductility gradient can be established in the first subregion of the first region. Outside the first subregion, the first region is preferably more ductile than the second region. The ductility of the first subregion can in particular in that case lie between the ductility of the rest of the first region and that of the second region. In particular, the ductility in the first subregion can gradually increase from the ductility of the second region to the ductility of the rest of the first region. The first subregion can in this respect be in the form of a transition region. Although a transition region generally develops when regions of a component are thermally treated differently, the described method makes it possible to establish the transition region deliberately and precisely.

[0030]The fact that a temperature gradient is established at least in a first subregion within the first region does not rule out the temperature gradient extending beyond the first subregion. It is therefore even conceivable for the temperature gradient to extend over the entire first region. The first subregion can in that case be defined as any desired part of the first region. The fact that a temperature gradient is established at least in a first subregion within the first region thus means that the temperature gradient is established throughout the first region or that the temperature gradient is established in a part of the first region-which is then referred to as the first subregion. If the temperature gradient is established throughout the first region, there does not need to be a first subregion which differs from the rest of the first region. This means the same thing as saying that any desired part of the first region is identified as a first subregion, although this part does not differ from the rest of the first region. Preferably, however, the temperature gradient is limited to the first subregion. In that case, the first subregion is delimited from the rest of the first region. A temperature gradient is then established only in the first subregion within the first region.

[0031]In step a), the entire component is heated in the first continuous furnace. All the regions are thus treated in the same way in step a). It is therefore in particular not necessary to be able to make a distinction between the regions already in step a).

[0032]The described method has multiple stages and also comprises, in addition to the heating in the first continuous furnace, 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 in principle be performed to any desired temperature. If the component is only heated a little in the first continuous furnace, the component can be heated all the more in the further course of the method, in particular in the second region, and vice versa. In particular, the component can be heated in the first continuous furnace to a temperature above or below the AC3 temperature of the component.

[0033]In particular for energy-related reasons, it is advantageous to heat the component relatively strongly in the first continuous furnace. This makes it possible to exploit the above-described advantage of heating in a continuous furnace over other types of heating, in particular over direct energization. With preference, the component in step a) is therefore heated to at least 400° C., in particular at least 600° C. With preference, the component in step a) is heated to a temperature above the AC1 temperature of the component. With preference, the component in step a) is heated to a temperature at most 400 K below the AC3 temperature of the component, in particular at most 200 K below the AC3 temperature of the component. With preference, the component in step a) does not exceed a temperature of 200 K above the AC3 temperature of the component. For example, the component in step a) can to a temperature in the range of 600 to 800° C. As an alternative, higher temperatures that lie in particular above the AC3 temperature of the component are preferred. Thus, it is also preferred if the component in step a) is heated to a temperature of at least 900° C., in particular at least 1000° C. For example, the component in step a) can be heated to a temperature in the range of 850 to 1200° C.

[0034]Owing to the temperature control station downstream of the first continuous furnace, the component is locally differently thermally treated. To this end, in the temperature control station, firstly the first region and the second region of the component are differently thermally treated. The first region is cooled in the temperature control station in step c1). This is preferably done by applying a cooling fluid, in particular compressed air, to the first region. The compressed air preferably has a pressure in the range of 2 to 4.5 bar. Owing to this relatively high pressure, a large quantity of compressed air can be conducted onto the first region of the component within an extremely short time, so that a sufficiently high cooling rate can be achieved. For the mode of operation of the described method, however, it generally does not matter which method is used to cool the first region.

[0035]The first region is cooled in step c1) in such a way that a temperature of the first region at least after the cooling lies below the austenite reversion temperature of the component. This makes it possible to achieve in principle a high ductility in the first region.

[0036]If the entire component in step a) is heated to a temperature above the AC3 temperature, austenite forms in the entire component. By cooling the first region in step c1) below the austenite reversion temperature of the component, this austenite breaks down again in the first region. The austenite reversion temperature is defined by the fact that austenite breaks down once the temperature drops below the austenite reversion temperature. The austenite reversion temperature is a material property. The fact that the temperature of the first region at least after the cooling lies below the austenite reversion temperature of the component thus does not imply that austenite had previously formed in the component.

[0037]If the entire component in step a) is not heated to a temperature above the AC3 temperature, austenite does not form in this step. The cooling of the first region in step c1) below the austenite reversion temperature of the component can, however, in this case also contribute to no austenite being formed in the first region in the further course of the method, even if the component is subjected to further heating. If no austenite is formed in step a), the temperature does not need to drop below the austenite reversion temperature in step c1) in order that the austenite breaks down. If the entire component in step a) is not heated to a temperature above the AC3 temperature, in step c1) any desired cooling of the first region is therefore sufficient. Nevertheless, it is also expedient in that case for the temperature to drop below the austenite reversion temperature. This is not gathered from the fact that austenite reversion happens below this temperature, but merely the fact that the austenite reversion temperature in general lies significantly below the AC3 temperature.

[0038]With preference, in step c1) the first region is cooled by at least 100 K, in particular by at least 250 K. After step c1), the temperature of the first region preferably lies in the range from 400 to 700° C., in particular in the range from 500 to 600° C.

[0039]Irrespective of the temperature reached in step a), after the cooling in step c1) there is therefore no austenite in the first region. Provided the AC3 temperature of the component in the first region is not exceeded (again) after the cooling in step c1), a ductile microstructure can be obtained in the first region. Step c2), however, involves heating at least part of the first region. This makes it possible to obtain a lower ductility in this part. In particular, the AC3 temperature can be exceeded.

[0040]In step c2), the first region is regionally heated by means of a laser unit in the temperature control station in such a way that a temperature gradient is established at least in the first subregion. The temperature gradient extends from a first end with a lower temperature to a second end with an upper temperature. Between the first end and the second end, the temperature of the component gradually increases from the lower temperature to the upper temperature. This increase may be linear or non-linear. The lower temperature is preferably below the AC3 temperature, in particular below the austenite reversion temperature. The upper temperature may also be below the AC3 temperature, in particular below the austenite reversion temperature. However, it is preferable if the upper temperature is above the austenite reversion temperature and even above the AC3 temperature. The upper temperature is preferably in the range of 900 to 1100° C. The upper temperature is preferably at least 100 K, in particular at least 250 K above the temperature before step c2). Preferably, the first subregion of the first region in step c2) is thus heated at least partially by at least 100 K, in particular by at least 250 K. The lower temperature is preferably at least 100 K, in particular at least 200 K or even at least 400 K below the upper temperature. Generally speaking, the effect of the temperature gradient is all the stronger the further apart the lower temperature and the upper temperature are.

[0041]In one part of the first subregion, austenite can be formed, from which martensite can be obtained by the press-hardening, while this is not the case in the rest of the first subregion. In between, the composition of the microstructure can change gradually.

[0042]For the functioning of the described method, it does not matter whether the heating in step c2) is performed by a single laser or by multiple lasers. It is therefore provided that the heating in step c2) is performed by a laser unit. The laser unit may comprise one or more lasers. Electronics for supplying power to and controlling the at least one laser can be part of the laser unit or be provided outside the laser unit, for example in a control unit of an apparatus used for the method.

[0043]If martensite is to be obtained in a part of the first subregion, it is preferred if, after the regional heating in step c2), the temperature of this part of the first subregion does not fall below the austenite reversion temperature of the component any more, at least until step e) is finished. If the press-hardening is part of the described method, the temperature of this part of the first subregion of the first region preferably first falls below the austenite reversion temperature in the press. However, it is not necessary to take meticulous care that the temperature of this part of the first subregion after step c2) does not fall below the austenite reversion temperature any more until step e) is finished. Austenite does not break down instantly. Acceptable results can also be obtained when a part of the austenite in the first subregion has broken down before the press hardening.

[0044]In step e), a temperature of the first subregion of the first region preferably changes by at most 200 K, in particular by at most 100 K. This can also be referred to as holding the temperature, with a change in the temperature within a tolerance of 200 K or 100 K, respectively, being accepted. For example, the first subregion of the first region can be exposed to a temperature above the AC3 temperature of the component in the second continuous furnace. Depending on the temperature of the first subregion of the first region upon entry into the second furnace and depending on the dwell time of the component in the second furnace, in the second continuous furnace the first subregion of the first region can be held at its temperature or heated, or a cooling of the first subregion of the first region can be slowed down. Since the temperature of the first subregion locally varies, the statements in this paragraph hold true for each location in the first subregion.

[0045]Outside the first subregion of the first region, in step e) the component can be thermally treated in different ways. Preferably, outside the first subregion there is a further subregion of the first region in which the temperature does not exceed the AC3 temperature of the component in steps c2) to e). This avoids the formation of austenite in this subregion of the first region. In step e), this part of the first region of the component is heated such that a temperature is below the AC3 temperature of the component even after the heating. This part of the first subregion is thus no longer heated above the AC3 temperature of the component in any case after the cooling in step c1). The temperature of this part of the first subregion preferably does not exceed the AC3 temperature of the component at least in steps c2) to e). If a press-hardening operation is part of the claimed method, the temperature of this part of the first subregion preferably does not exceed the AC3 temperature of the component before or during the press-hardening operation. It is thus possible to obtain a ductile microstructure in this part of the first subregion. However, it is not necessary to take meticulous care that the AC3 temperature is not exceeded in these periods of time. Austenite is not formed instantly. Even if a small amount of austenite forms, acceptable results can be achieved.

[0046]Besides the first region with the first subregion, the component has the second region. The method is carried out such that a temperature of the second region of the component during method steps a) to e) at least temporarily exceeds the AC3 temperature of the component. This makes it possible to form austenite in the second region. During the press-hardening operation, martensite can be formed therefrom, as a result of which the second region is given a relatively low ductility.

[0047]It does not matter at what time the temperature of the second region exceeds the AC3 temperature of the component. If, in step a), the entire component is heated to a temperature above the AC3 temperature of the component, this condition is already met in step a). If the second region in step a) is heated to lower than the AC3 temperature, the second region can be heated to a temperature above the AC3 temperature in the temperature control station or in the second furnace.

[0048]It is preferred if the temperature of the second region no longer falls below the austenite reversion temperature after the heating to a temperature above the AC3 temperature of the component until step e) is finished. Preferably, in the second region, the temperature first falls below the austenite reversion temperature in the press. This makes it possible to avoid the austenite formed in the second region breaking down before the press-hardening.

[0049]In steps b) to e), a temperature of the second region preferably changes by at most 200 K, in particular by at most 100 K. This can also be referred to as holding the temperature, with a change in the temperature within a tolerance of 200 K or 100 K, respectively, being accepted. For example, the second region in steps c1) and c2) can be exposed to a temperature above the AC3 temperature of the component in the temperature control station and/or in step e) can be exposed to a temperature above the AC3 temperature of the component in the second furnace. Depending on the temperature of the second region upon 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, in the temperature control station the second region can be held at its temperature or heated, or a cooling of the second region can be slowed down. In particular, however, the second region can also be cooled in the temperature control station by exposure to ambient air.

[0050]It is possible for the temperature of the second region in steps a) to e) to firstly rise above the AC3 temperature, then drop below the austenite reversion temperature and then rise above the AC3 temperature again. In that case, it is sufficient if the temperature of the second region no longer falls below the austenite reversion temperature after the second heating to a temperature above the AC3 temperature until step e) is finished. This is included in the wording that a temperature of the second region of the component during method steps a) to e) at least temporarily exceeds the AC3 temperature of the component and then does not fall below an austenite reversion temperature of the component.

[0051]The first subregion can be created particularly precisely owing to the heating by the laser unit. In particular, the subregion may have a finer contour and/or be smaller than would be possible by other methods. Cooling would make it possible to obtain the temperature gradient only with difficulty or would not make it possible at all. In a preferred embodiment of the method, the first region of the component in step c1) is cooled by having cooling fluid applied to it.

[0052]The cooling fluid is preferably compressed air. The cooling fluid is preferably dispensed onto the first region using nozzles. This allows the first region to be cooled easily and in a short period of time. The use of nozzles, however, fundamentally has the disadvantage that the cooling fluid does not allow a precise separation between the cooled and the non-cooled part of the component. The described method circumvents this. Firstly, in step c1), the first region including the first subregion is cooled. At least the first subregion is then regionally heated again by the laser unit, so that the temperature gradient is obtained. The result of this corresponds in principle to a method in which the first subregion is regionally differently cooled. Depending on the desired configuration of the temperature gradient, however, this would not be possible or would be possible only with difficulty by way of cooling with nozzles. By contrast, the described method is easier.

[0053]In a further, preferred embodiment of the method, a temperature of the component in step a) does not exceed the AC3 temperature of the component.

[0054]In this embodiment, the AC3 temperature of the component is first exceeded in the temperature control station or in the second furnace. With preference, the component in step a) is heated to a temperature above the AC1 temperature of the component. In that case, the component in step a) is thus heated to a temperature between the AC1 temperature and the AC3 temperature of the component.

[0055]In a further, preferred embodiment of the method, the entire component in step a) is heated to a temperature above the AC3 temperature of the component.

[0056]In a further, preferred embodiment of the method, in step c2), the first region of the component is regionally heated by means of the laser unit in such a way that a second subregion, which is outside the first subregion, of the first region is brought to a temperature above the AC3 temperature of the component.

[0057]In the present embodiment, the component has a first region and a second region, the first region having at least a first subregion and a second subregion. At least in the first subregion of the first region, a temperature gradient is established such that a gradually variable ductility can be obtained. The temperature gradient preferably does not extend into the second subregion. In the second subregion of the first region and in the second region, the AC3 temperature is exceeded, and therefore a low ductility is obtained in these two regions. This could in principle also be achieved in that, besides the second region, the second subregion of the first region is also not cooled. Depending on the desired contour of the regions, however, this would not be possible or would be possible only with difficulty by way of cooling for example with nozzles. By contrast, the described method is easier and allows finer contours.

[0058]Preferably, the second subregion of the first region in step c2) is heated by at least 100 K, in particular by at least 250 K. The temperature of the second subregion of the first region after step c2) is preferably in the range of 900 to 1100° C.

[0059]It is preferred if, after the heating in step c2), the temperature of the second subregion does not fall below the austenite reversion temperature of the component any more, at least until step e) is finished. If the press-hardening is part of the described method, the temperature of the second subregion of the first region preferably first falls below the austenite reversion temperature in the press. However, it is not necessary to take meticulous care that the temperature of the second subregion of the first region after step c2) does not fall below the austenite reversion temperature any more until step e) is finished. Austenite does not break down instantly. Acceptable results can also be obtained when a part of the austenite in the second subregion of the first region has broken down before the press hardening.

[0060]In a further, preferred embodiment of the method, the first subregion of the first region adjoins the second subregion of the first region and/or the second subregion of the first region adjoins the second region. The “and” case here is preferred.

[0061]If the first subregion of the first region adjoins the second subregion of the first region, it is preferred if, after step c2), the temperature in the first subregion gradually decreases from the temperature of the second subregion. In this respect, the first subregion may be in the form of a transition region.

[0062]If the second subregion of the first region adjoins the second region, it is preferred if the second subregion of the first region and the second region have the same temperature after step c2). In this respect, the second subregion of the first region may be in the form of a continuation of the second region.

[0069]The described advantages and features of the method can be applied and transferred to the apparatus, and vice versa. The apparatus is preferably designed for being operated according to the method. The method is preferably carried out with the apparatus. The first continuous furnace serves step a), the first transfer device serves step b), the temperature control station serves steps c1) and c2), the second transfer device serves step d), and the second continuous furnace serves step e).

[0070]The apparatus preferably has a control device designed to control the apparatus according to the described method.

[0071]The laser unit is preferably also designed to bring a second subregion, which is outside the first subregion, of the first region to a temperature above the AC3 temperature of the component.

[0072]The apparatus preferably also has a press for press-hardening the component and a third transfer device for transferring the component from the second continuous furnace into the press.

[0073]In a preferred embodiment of the apparatus, the laser unit comprises a VCSEL.

[0074]A “vertical-cavity surface-emitting laser” (VCSEL) is a laser diode which emits light perpendicularly in relation to its surface. A VCSEL can also be referred to as a surface emitter. It has been found that, in step c2), a VCSEL can be used to achieve particularly good results.

[0075]The invention will be explained in greater detail below with reference to the figures. The figures show a particularly preferred exemplary embodiment, to which, however, the invention is not restricted. The figures and the relative sizes shown therein are only schematic. In the figures:

[0076]FIG. 1: shows an apparatus according to the invention for thermally treating a metallic component,

[0077]FIG. 2: shows a temperature profile that can be obtained with the apparatus from FIG. 1 by a method according to the invention, and

[0078]FIG. 3: shows a component that has been treated with the method depicted in FIG. 2.

[0079]FIG. 1 shows an apparatus 1 for thermally treating a metallic component 2. The apparatus 1 comprises a first continuous furnace 3, a temperature control station 4 and a second continuous furnace 5, which are arranged one after another in a transporting direction r of the component 2. A control device 6 is designed in particular to control the first continuous furnace 3, the temperature control station 4 and the second continuous furnace 5.

[0080]The temperature control station 4 has a cooling device 7 for cooling a first region 10 of the component 2 and a heating device 8 which has a laser unit 9. The laser unit 9 is designed to regionally heat the first region 10 of the component 2 in such a way that a temperature gradient is established at least in a first subregion 12 within the first region 10 and that a second subregion 15, which is outside the first subregion 12, of the first region 10 is brought to a temperature above the AC3 temperature of the component 2. The regions 10, 11, 12, 15 of the component 2 are depicted in FIG. 3. The laser unit 9 may in particular comprise a VCSEL.

[0081]The apparatus 1 also 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.

[0082]FIG. 2 shows a temperature profile established in the component 2 when it is moved through the apparatus 1 from FIG. 1. The illustration in FIG. 2 is schematic. It shows the temperature T plotted against time t in arbitrary units. The component 2 is firstly heated in the first continuous furnace 3. The dwell time of the component 2 in the first continuous furnace 3 is denoted t_D1. In the example shown, the entire component 2 is heated to a temperature above the AC3 temperature T_AC3 of the component 2 in the first continuous furnace 3. As an alternative, the method could be carried out such that the temperature of the component 2 does not exceed the AC3 temperature T_AC3 of the component 2 in the first continuous furnace 3.

[0083]Then, the component 2 is transferred into the temperature control station 4. The associated transfer time is denoted t_T1. During this transfer, the component 2 can cool down.

[0084]The component 2 remains in the temperature control station 4 for a dwell time t_TS. Within this time, a first region 10 of the component 2 is cooled, a temperature of the first region 10 after the cooling lying below the austenite reversion temperature T_AR of the component 2. The temperature of the first region 10 is denoted T₁. After the cooling, the previously cooled first region 10 of the component 2 is regionally heated by the laser unit 9. The second subregion 15 is heated to a temperature above the AC3 temperature T_AC3 of the component 2. The temperature of the second subregion 15 of the first region 10 is denoted T_1A. That part of the first region 10 that belongs neither to the first subregion 12 nor to the second subregion 15 has a temperature T_1B. In the first subregion 12, a temperature gradient is obtained. It extends from a lower temperature, the temperature T_1B, to an upper temperature, the temperature T_1A. This is indicated in FIG. 2 by arrows.

[0085]After the component 2 has been thermally treated in the temperature control station 4, the component 2 is transferred into the second continuous furnace 5. The transfer time for this is denoted t_T2. During this time, the component 2 can also cool down, and this cooling can be different from one region to the next.

[0086]In the second continuous furnace 5, the component 2 is thermally treated further. The dwell time of the component 2 in the second continuous furnace 5 is denoted t_D2. In the second continuous furnace 5, the first region 10 of the component 2, outside the first subregion 12 and the second subregion 15, is heated in such a way that the temperature T_1B of the first region 10 of the component 2 in this region is below the AC3 temperature T_AC3 of the component 2 even after the heating.

[0087]A temperature T₂ of the second region 11 of the component 2 exceeds the AC3 temperature T_AC3 of the component 2 in the first continuous furnace 3 and does not fall below that temperature again until the end of the method shown.

[0088]FIG. 3 shows a plan view of the component 2. In this example, the component 2 is a B pillar for a motor vehicle. The first region 10 and the second region 11 are evident. The first subregion 12 and the second subregion 15 are depicted within the first region 10. The second subregion 15 is composed of two non-coherent parts. A temperature gradient, indicated by arrows, is established in the first subregion 12. The shape shown of the component 2 and of the regions 10, 11, 12, 15 is exemplary. The method from FIG. 2 makes it possible to treat components of any desired geometry. The method is especially flexible in particular with regard to the configuration of the first subregion 12 and of the second subregion 15.

LIST OF REFERENCE SIGNS