Method for heat treating metal parts and apparatus for heat treating metal parts

Abstract

A method for heat treating a metal component (2) includes the steps of: 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 temperature control station (4); and c1) cooling a first region (10) of the component (2) in the temperature control station (4), wherein the temperature of the first region (10) after at least cooling is greater than or equal to the austenite retransformation temperature (T AR ), and step c2) the partial region (12) of the first region (10) of the part (2) cooled in step c1) is cooled by the laser unit (9) in the temperature control station (4) to the AC3 temperature (T AC3 ), d) transferring the component (2) from the temperature control station (4) to a second continuous furnace (5), and e) heat treating the component (2) in the second continuous furnace (5), wherein a first region (10) of the component (2) outside the partial region (12) is heated, and the heating is such that the temperature of the first region (10) of the component (2) outside the partial region (12) remains above the AC3 temperature (T AC3 ), wherein during method steps a) to e), the temperature of the second region (11) of the component (2) is at least temporarily lowered to an AC3 temperature (T AC3 ) will be higher.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for heat treating metal parts, particularly automotive steel parts. [Background technology]

[0002] In particular, in the automotive industry, it is known to selectively harden steel parts by heat treatment. For this purpose, different areas of a steel part, such as a B-pillar, are heat treated differently. This results in different ductility in different areas, which is advantageous for the behavior of such parts in a crash. For example, the hard areas of the B-pillar at seat height can protect the vehicle occupants, while the softer areas above and below the B-pillar can deform and thereby absorb energy.

[0003] A proven method for locally different heat treatments on a part involves first heating the entire part in a first furnace, then subjecting the part to locally different heat treatments in a temperature-controlled station, and then heating the entire part in a second furnace. In the temperature-controlled station, certain areas of the part are cooled, for example by applying a cooling fluid thereto, while the remaining parts of the part maintain approximately their own temperature. This allows for excellent results in many use cases. However, there is an increasing need for temperature distributions that are impossible or difficult to achieve using known methods. This is particularly true for parts that require small, hard regions inside a soft region. It is difficult to exclude these small regions when cooling with a cooling fluid. Similar difficulties generally arise when more than a simple division of the part into soft and hard regions is desired. Summary of the Invention [Means for solving the problem]

[0004] The object of the present invention is to provide a particularly flexible method for locally different heat treatments of metal parts. It is also intended to provide a corresponding device.

[0005] These objects are achieved by the methods and devices set out in the independent claims. The dependent claims specify further advantageous developments. The features presented in the claims and in this specification can be combined with one another in any technically significant manner.

[0006] In accordance with the present invention, a method for heat treating a metal component is provided, the method comprising: 1. A method for heat treating a metal part, comprising: a) heating the entire part in a first continuous furnace; b) transferring the part from the first continuous furnace to a temperature control station; c1) cooling a first region of the part at a temperature control station, the temperature of at least the first region after cooling is less than the austenite retransformation temperature of the component; Steps and c2) heating the part of the first area of ​​the component cooled in step c1) by means of a laser unit in a temperature control station to a temperature higher than the AC3 temperature of the component; d) transferring the part from the temperature control station to a second continuous furnace; e) heat treating the part in a second continuous furnace, a first region of the component outside the subregion is heated, and the heating is performed such that the temperature of the first region of the component outside the subregion remains below the AC3 temperature of the component after the heating; Steps and Including, During method steps a) to e), the temperature of the second region of the component is at least temporarily increased above the AC3 temperature of the component.

[0007] The method can be used to heat treat metal parts. The metal parts are preferably steel parts. The steel is preferably 22MnB5. However, the metal parts do not have to meet the definition of steel. Therefore, the present specification will generally refer to metal parts. For example, automotive parts, particularly B-pillars, can be heat treated. However, the method can also be used for any other desired application.

[0008] The component preferably has a material thickness of at least 0.7 mm, particularly in the range of 1 to 4 mm. Such material thicknesses are suitable for many applications. However, the method described above can also be implemented for components with different material thicknesses. The component material thickness is preferably constant throughout the component. Alternatively, the component can have different material thicknesses in different regions. For example, the component can be a "tailor rolled blank" (TRB), where different localized material thicknesses are achieved by rolling different regions. The component can also be a "tailor welded blank" (TWB), where different localized material thicknesses are achieved by welding multiple metal sheets together. TRB and TWB can also be combined. Furthermore, the method is equally applicable to components with and without coatings. An Al / Si coating is particularly suitable as the coating.

[0009] After the heat treatment, the part is preferably press-hardened in a press and hot-formed to some extent. The method preferably further comprises the steps of transferring the part from the second continuous furnace to the press (step f)) and press-hardening the part in the press (step g). In this case, the method is a method for heat treating and press-hardening a part. However, press-hardening of the part does not have to be performed as part of the method. The method may also serve as preparation for a press-hardening operation performed outside the method. In general, the part heat-treated according to the method may undergo further processes, and the result of these and further processes may be, for example, a complete automobile. However, the heat treatment of the part is a defined subsidiary process within this overall process. Therefore, it is preferable to consider the heat treatment separately from the subsequent processes, in particular from the press-hardening.

[0010] In step a), the parts are heated in a first continuous furnace. A furnace is an apparatus inside which a settable temperature is maintained and into which parts can be inserted. Over time, the temperature of the parts gradually approaches the temperature prevailing inside the furnace. Heat is thus transferred to the parts from the gas present in the furnace (which may in particular be air). A continuous furnace is a furnace that allows the parts to move through it, heating them as they pass through it.

[0011] The first continuous furnace is preferably a roller hearth furnace. In the first continuous furnace, the part is preferably heated by a burner, in particular a gas burner. As a result, the part can have a particularly uniformly distributed temperature. The entire part is heated in the first continuous furnace. The part is completely contained within the first continuous furnace. Furthermore, heating with particularly large temperature differences can be achieved using a continuous furnace. The part can be heated, in particular, from room temperature to the AC3 temperature of the part. Such wide-area heating is not possible with many other heating methods, or at least only with disproportionate effort.

[0012] In the case of coated components, the first continuous furnace may serve to diffuse the coating into the remaining material of the component. This is particularly true for Al / Si coatings. In the case of coated components, it is preferred that the component is heated in step a) in such a way that the coating material diffuses into the remaining material of the component. Therefore, it is preferred that the component is heated in step a) to a temperature higher than the temperature at which the coating material diffuses into the remaining material of the component. Preferably, the component is heated in step a) to a temperature higher than the aforementioned temperature for at least 1 minute, in particular for at least 2 minutes. Preferably, the component is heated in step a) to a temperature of at least 700°C, in particular at least 780°C. Satisfactory results have already been obtained at these temperatures. However, to increase the reliability of the process, it is preferred to heat the component to at least 830°C. Preferably, the component is heated in step a) to a temperature higher than 700°C, in particular higher than 780°C or higher than 830°C, for at least 1 minute, in particular for at least 2 minutes. Particularly preferably, in the case of coated components, in step a) the component is heated to a temperature above the AC1 temperature of the component, in particular above the AC3 temperature of the component. Preferably, the temperature of the component in step a) is above the AC1 temperature of the component, in particular above the AC3 temperature of the component, for at least 1 minute, in particular for at least 2 minutes. In this regard, the heating in step a) can be used not only to diffuse the coating, but also to contribute to the deformation of the microstructure.

[0013] Heating in a continuous furnace is particularly in contrast to heating by what is called "direct energization." With direct energization, it would be difficult to heat the part uniformly and sufficiently. With direct energization, the heating rate is more important. Furthermore, direct energization requires contact with the part. In step a) of the method, heating is preferably carried out without contact. This does not exclude that the part is moved through the first continuous furnace by conveying rollers and therefore comes into contact with the conveying rollers. Heating is contactless if the heat input into the part is via gas and / or thermal radiation.

[0014] In step b) of the method, the part is transferred from the first continuous furnace to a temperature control station, preferably by a first transfer device. In the temperature control station, different regions of the part are heat treated differently. Thus, in particular, the method is a method for locally differently heat treating a metal part. However, this need not be mentioned explicitly, since the locally different heat treatment is explicitly defined by steps c1) and c2).

[0015] The first continuous furnace and the temperature control station are separate units, spatially separated from each other. Transferring the parts between the first continuous furnace and the temperature control station facilitates cooling the parts between heating in the first continuous furnace and heat treatment in the temperature control station. In the temperature control station, the parts are cooled as quickly as possible in at least some areas. Rapid cooling can be more efficiently achieved outside the hot first continuous furnace. In this way, cooling can begin already during transfer. In this respect, the physical separation between the first continuous furnace and the temperature control station accelerates processing. This contrasts with solutions in which all method steps are performed in the same equipment, which do not require part transfer. Such solutions typically aim to minimize or completely avoid the labor involved in part transfer. Because the first continuous furnace and the temperature control station have different requirements, the spatial separation between the first continuous furnace and the temperature control station also facilitates manufacturing.

[0016] In step d), the parts are transferred from the temperature control station to a second continuous furnace, preferably by a second transfer device. In step e), the parts are heat treated in the second continuous furnace. For step e), the whole parts are placed in the second continuous furnace.

[0017] The temperature control station and the second continuous furnace are separate units, spatially separated from each other. Transferring the temperature control station and the second continuous furnace facilitates cooling the parts between the heat treatment in the temperature control station and the heat treatment in the second continuous furnace. In this way, the parts can be cooled, particularly partially cooled, during transfer. This shortens the required transfer time within the temperature control station and accelerates processing. This contrasts with solutions in which no part transfer is required and all method steps are performed in the same machine as much as possible. Such solutions typically aim to minimize or completely avoid the labor involved in transferring parts. Because the temperature control station and the second continuous furnace have different requirements, the spatial separation between them also facilitates manufacturing. Therefore, integrating both into a single machine would be correspondingly complex.

[0018] The second continuous furnace is preferably a roller hearth furnace. The entire part is heat-treated, preferably heated, in the second continuous furnace. The part is completely contained in the second continuous furnace. Heat treatment in a continuous furnace is particularly in contrast to heating by what is called "direct energization." Heat treatment in the second continuous furnace serves, in particular, to promote microstructural deformation. Since the part is not directly cooled downstream of the temperature control station, for example in a press, there is sufficient time for the part to form the desired microstructural distribution. In particular, carbon atoms can diffuse into the interior of the part in step e), resulting in the desired change in the part's microstructure. Furthermore, heat treatment in the second continuous furnace reduces thermal stresses in the part, which reduces distortion of the part during the subsequent press hardening operation.

[0019] The method allows for three regions to be heat-treated in different ways. First, a first region and a second region can be distinguished. Furthermore, a partial region of the first region is treated separately from the remainder of the first region. This therefore results in at least a partial region of the first region, the remainder of the first region, and the second region.

[0020] The first region, the sub-region of the first region, and the second region are not necessarily adjacent regions. In particular, the middle part of the B-pillar can form the first region, and the upper and lower parts of the B-pillar together can form the second region. Within the first region, the sub-region may consist of one or more parts. It is preferred, but not necessary, that the part only has the first region and the second region, i.e., no additional regions. This also applies to the sub-region, since it is part of the first region.

[0021] The partial region constitutes a part of the first region. The partial region is smaller than the first region. Therefore, there are parts of the first region that are not part of the partial region.

[0022] The method allows regions of a component to be heat treated differently, thereby affecting the component's microstructural composition locally differently, thereby resulting in locally different ductility. A first region outside the subregion is more ductile than the subregion and the second region. The second region and the subregion of the first region can be given the same or different ductility.

[0023] In step a), the entire part is heated in the first continuous furnace, so that all areas are treated in the same way in step a), and it is therefore not necessary to be able to distinguish between the areas in step a).

[0024] The method has multiple stages and includes, in addition to heating in the first continuous furnace, heat treatment in a temperature control station and heating in the second continuous furnace. Therefore, heating in the first continuous furnace can, in principle, be carried out at any desired temperature. If the part is heated less in the first continuous furnace, the partial region and the second region can be heated more in the subsequent course of the method, and vice versa. In particular, the part can be heated in the first continuous furnace to a temperature higher or lower than the AC3 temperature of the part.

[0025] It is advantageous, particularly for energy reasons, to heat the component relatively strongly in the first continuous furnace. This makes it possible to utilize the aforementioned advantages of heating in a continuous furnace over other types of heating, particularly direct current heating. Therefore, preferably, in step a), the component is heated to at least 400°C, particularly at least 600°C. Preferably, in step a), the component is heated to a temperature higher than the AC1 temperature of the component. Preferably, in step a), the component is heated to a temperature at most 400 K lower than the AC3 temperature of the component, particularly at most 200 K lower than the AC3 temperature of the component. Preferably, in step a), the component does not exceed a temperature 200 K higher than the AC3 temperature of the component. For example, in step a), the component may be heated to a temperature in the range of 600-800°C. Alternatively, even higher temperatures, particularly higher than the AC3 temperature of the component, are preferred. Therefore, it is also preferred that in step a), the component is heated to a temperature of at least 900°C, particularly at least 1000°C. For example, in step a) the part may be heated to a temperature in the range of 850-1200°C.

[0026] The component is locally heat-treated differently in a temperature-controlled station downstream of the first continuous furnace. Thus, the first and second regions of the component are first heat-treated differently in the temperature-controlled station. In step c1), the first region is cooled in the temperature-controlled station. This is preferably achieved by supplying 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. This relatively high pressure allows a large amount of compressed air to be delivered to the first region of the component in a very short time, thereby achieving a sufficiently high cooling rate. However, in this processing mode, the method used to cool the first region is usually irrelevant.

[0027] In step c1), the first zone is cooled in such a way that the temperature of the first zone, at least after cooling, is below the austenite retransformation temperature of the component, which in principle makes it possible to achieve high ductility in the first zone.

[0028] When the entire component is heated to a temperature above the AC3 temperature in step a), austenite forms throughout the component. This austenite in the first region is again destroyed by cooling the first region to a temperature below the austenite retransformation temperature of the component in step c1). The austenite retransformation temperature is defined by the austenite destruction when the temperature drops below the austenite retransformation temperature. The austenite retransformation temperature is a material property. The fact that the temperature of the first region, at least after cooling, is below the austenite retransformation temperature of the component does not imply that austenite was previously formed within the component.

[0029] If the entire component is not heated above the AC3 temperature in step a), austenite will not form in this step. However, even in this case, cooling the first region to a temperature below the austenite retransformation temperature of the component in step c1) may contribute to the absence of austenite formation in the first region, even if the component is further heated in the process. If austenite does not form in step a), it is not necessary to reduce the temperature below the austenite retransformation temperature in step c1) to destroy the austenite. Therefore, if the entire component is not heated above the AC3 temperature in step a), it is sufficient to cool the first region in any desired manner in step c1). However, even in this case, it is preferable to reduce the temperature below the austenite retransformation temperature. This is not inferred from the fact that austenite retransformation occurs below this temperature, but simply from the fact that the austenite retransformation temperature is generally significantly lower than the AC3 temperature.

[0030] Preferably, in step c1), the first zone is cooled by at least 100 K, in particular by at least 250 K. After step c1), the temperature of the first zone is preferably in the range of 400-700°C, in particular in the range of 500-600°C.

[0031] Therefore, regardless of the temperature reached in step a), after cooling in step c1), no austenite is present in the first region. If the first region does not (again) exceed the AC3 temperature of the component after cooling in step c1), a ductile microstructure can be obtained in the first region. However, as a result of step c2), a part of the first region exceeds the AC3 temperature. This part of the first region is referred to as a subregion of the first region. In step c2), the subregion is heated by a laser unit in a temperature control station to a temperature higher than the AC3 temperature of the component. This also makes it possible to form austenite in the subregion of the first region.

[0032] It is not important for the function of the method whether the heating in step c2) is performed by a single laser or by multiple lasers, it is provided that the heating in step c2) is performed by a laser unit. The laser unit may have one or multiple lasers. The electronics for powering and controlling at least one laser may be part of the laser unit or may be located outside the laser unit, for example in a control unit of the device for the method.

[0033] Preferably, in step c2) the subregions of the first region are heated by at least 100 K, in particular by at least 250 K. After step c2) the temperature of the subregions of the first region is preferably in the range of 900-1100°C.

[0034] After heating in step c2), the temperature of the sub-regions preferably does not fall below the austenite retransformation temperature of the component until at least step e) is completed. If press quenching is part of the method, the temperature of the sub-regions of the first region preferably falls below the austenite retransformation temperature only in the press. However, it is not necessary to take great care that the temperature of the sub-regions of the first region after step c2) does not fall below the austenite retransformation temperature until step e) is completed. Austenite does not collapse instantly. Acceptable results can be obtained even if austenite is partially collapsed in the sub-regions of the first region before press quenching.

[0035] In step e), the temperature of the sub-region of the first region preferably changes by a maximum of 200 K, in particular by a maximum of 100 K. This can also be referred to as maintaining the temperature while allowing a temperature change within a tolerance range of 200 K or 100 K. For example, in the second continuous oven, the sub-region of the first region can be exposed to a temperature higher than the AC3 temperature of the parts. Depending on the temperature of the sub-region of the first region upon entry into the second oven and the residence time of the parts in the second oven, the sub-region of the first region in the temperature control station can maintain its temperature or be heated, or the cooling of the sub-region of the first region can be slowed down.

[0036] Outside the subregion of the first region, the AC3 temperature of the component is not exceeded in steps c2) to e). This avoids the formation of austenite outside the subregion of the first region. In step e), the first region of the component outside the subregion is heated in such a way that the temperature of the first region outside the subregion remains below the AC3 temperature of the component after heating. Thus, the first region of the component outside the subregion, i.e., the part of the first region that is not part of the subregion, is not heated above the AC3 temperature of the component after cooling in step c1). The temperature of the first region of the component outside the 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 the first region of the component outside the subregion preferably does not exceed the AC3 temperature of the component before or during the press-hardening operation. This makes it possible to obtain a ductile microstructure in the first region outside the subregion. However, great care is not required to avoid exceeding the AC3 temperature during these periods. Austenite does not form instantaneously, and acceptable results can be obtained even if a small amount of austenite forms in the first region of the part outside the partial region.

[0037] In addition to the first region having the subregion, the component has a second region. The method is performed such that during method steps a) to e), the temperature of the second region of the component at least temporarily exceeds the AC3 temperature of the component. This allows austenite to form in the second region. During the press-hardening operation, martensite can form from the austenite, resulting in a relatively low ductility in the second region.

[0038] It is not important at what point the temperature of the second zone exceeds the AC3 temperature of the part. If the entire part is heated to a temperature above the AC3 temperature of the part in step a), this condition is already met in step a). If the second zone is heated to a temperature below the AC3 temperature in step a), the second zone can be heated to a temperature above the AC3 temperature in a temperature control station or a second furnace.

[0039] After heating to a temperature above the AC3 temperature of the part, the temperature of the second zone is preferably not reduced below the austenite retransformation temperature until step e) is completed. In the second zone, the temperature is preferably reduced below the austenite retransformation temperature only in the press. This makes it possible to avoid the collapse of the austenite formed in the second zone before the press quench.

[0040] In steps b) to e), the temperature of the second zone preferably varies by no more than 200 K, particularly no more than 100 K. This can also be described as maintaining the temperature while allowing for a temperature change within a 200 K or 100 K tolerance. For example, the second zone can be exposed to a temperature higher than the AC3 temperature of the part in the temperature control station in steps c1) and c2), or the second zone can be exposed to a temperature higher than the AC3 temperature of the part in the second oven in step e), or both. Depending on the temperature of the second zone upon entry into the temperature control station or the second oven and depending on the residence time of the part in the temperature control station or the second oven, the second zone in the temperature control station can maintain its temperature or be heated, or the cooling of the second zone can be slowed. However, in particular, the second zone can be cooled by exposing it to ambient air in the temperature control station.

[0041] It is possible that the temperature of the second zone in steps a) to e) first rises above the AC3 temperature, then falls below the austenite retransformation temperature, and then rises above the AC3 temperature again. In that case, it is sufficient that, after the second heating above the AC3 temperature, the temperature of the second zone does not fall below the austenite retransformation temperature until step e) is completed. This is included in the expression that, during method steps a) to e), the temperature of the second zone of the component at least temporarily exceeds the AC3 temperature of the component and does not fall below the austenite retransformation temperature of the component.

[0042] The method allows for obtaining a ductile microstructure in a first region outside the subregion, while obtaining a less ductile microstructure in the second region and in the subregion of the first region, respectively.

[0043] By heating with a laser unit, the partial areas can be produced particularly precisely. In particular, the partial areas can have fine contours and / or be smaller than would be possible with other methods. This is particularly in comparison with methods in which the partial areas are removed during the cooling operation. In this respect, the method can be applied particularly flexibly.

[0044] In a preferred embodiment of the method, in step c1), a first region of the component is cooled by applying a cooling fluid to the component.

[0045] The cooling fluid is preferably compressed air. The cooling fluid is preferably spread over the first region using a nozzle. This allows the first region to be cooled easily and in a short time. However, using a nozzle has the fundamental disadvantage that the cooling fluid cannot accurately separate the cooled and uncooled portions of the part. This method avoids this. First, in step c1), the first region, including the subregion, is cooled. Then, the subregion is reheated by the laser unit. As a result, this essentially corresponds to a method that does not cool the subregion. However, depending on the desired contour of the region, this may be impossible or difficult to achieve with nozzle cooling. In contrast, this method is easier.

[0046] In a further preferred embodiment of the method, in step a) the temperature of the component does not exceed the AC3 temperature of the component.

[0047] In this embodiment, the sub-region of the first region and the second region of the component are first heated in a temperature control station or a second furnace to above the AC3 temperature. Preferably, in step a), the component is heated to a temperature above the AC1 temperature of the component. In that case, in step a), the component is heated to a temperature between the AC1 temperature and the AC3 temperature of the component.

[0048] In a further preferred embodiment of the method, in step a) the entire component is heated to a temperature higher than the AC3 temperature of the component.

[0049] In a further preferred embodiment of the method, in step c2) partial regions of the first region of the component are locally heated with different intensities.

[0050] The laser unit allows for particularly precise heating of the subregions. This is not only due to the fact that particularly precise contours of the subregions can be obtained. In the present exemplary embodiment, the subregions can also be heated locally with different intensities. As a result, it is possible to obtain locally different ductility within the subregions.

[0051] Differential local heating of partial areas can be achieved by varying the power of the laser unit.

[0052] In a further preferred embodiment of the method, in step c2), partial areas of the first area of ​​the component are locally heated with different intensities, the heating being carried out in such a way that a temperature gradient is obtained over said partial areas of the first area of ​​the component.

[0053] The locally different heating makes it possible to obtain a temperature gradient over the subregion. After step c2), for example, it is possible to increase the temperature of the subregion from one edge to the opposite edge of the subregion. In this way, precisely defined regions of transition of different ductility can be obtained.

[0054] Basically, it is preferable that regions of different ductility are separated from each other as clearly as possible. Therefore, it is preferable that the transition area between adjacent regions is as small as possible. In contrast, in this embodiment, the temperature gradient can be established precisely. Therefore, the subsequent ductility gradient is not just randomly generated. There are use cases where a precisely established ductility gradient is preferable.

[0055] In a further aspect of the present invention, there is provided an apparatus for heat treating a metal part, the apparatus comprising: a first continuous furnace for heating the entire part; a temperature control station having a cooling device (7) for cooling a first region of the part and a heating device having a laser unit for heating a partial region of the first region of the part; a second continuous furnace for heat treating the parts; a first transfer device for moving the parts from the first continuous furnace to the temperature control station; a second transfer device for moving the parts from the temperature control station to the second continuous furnace; Equipped with.

[0056] The aforementioned special advantages and features of the present method can be applied and transferred to the present apparatus, and vice versa. The present apparatus is preferably designed to operate according to the present method. The present method is preferably carried out using the present apparatus. A first continuous furnace is used in step a), a first transfer device is used in step b), a temperature control station is used in steps c1) and c2), a second transfer device is used in step d), and a second continuous furnace is used in step e).

[0057] The apparatus preferably includes a control device designed to control the apparatus in accordance with the method.

[0058] Additionally, the apparatus preferably includes a press for press-hardening the parts, and a third transfer device for moving the parts from the second continuous furnace to the press.

[0059] In a preferred embodiment of the device, the laser unit comprises a VCSEL.

[0060] A "Vertical-Cavity Surface-Emitting Laser" (VCSEL) is a laser diode that emits light perpendicular to its surface. VCSELs are also sometimes called surface emitters. It has been found that in step c2) particularly good results can be achieved using VCSELs.

[0061] The invention will now be explained in more detail with reference to the drawings, which show particularly preferred embodiments, but to which the invention is not limited, and the drawings and the proportions shown therein are only schematic. [Brief explanation of the drawings]

[0062] [Figure 1] 1 shows an apparatus for heat treating metal parts according to the present invention; [Figure 2] FIG. 2 shows a temperature profile that can be produced by the device of FIG. 1 according to the method of the present invention. [Figure 3] 3a-3c show three examples of parts processed by the method shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0063] 1 shows an apparatus 1 for heat treating metal parts 2. The apparatus 1 comprises a first continuous furnace 3, a temperature control station 4 and a second continuous furnace 5, which are arranged in succession in the conveying direction r of the parts 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.

[0064] The temperature control station 4 comprises a cooling device 7 for cooling a first region 10 of the component 2 and a heating device 8 with a laser unit 9 for heating a partial region 12 of the first region 10 of the component 2. The regions 10, 11, 12 of the component 2 are shown in Figure 3. The laser unit 9 may in particular comprise a VCSEL.

[0065] Furthermore, the apparatus 1 comprises a first transfer device 13 for transferring the part 2 from the first continuous furnace 3 to the temperature control station 4, and a second transfer device 14 for transferring the part 2 from the temperature control station 4 to the second continuous furnace 5.

[0066] Figure 2 shows the temperature profile experienced by the part 2 as it moves through the apparatus 1 of Figure 1. Figure 2 is a schematic representation showing a plot of temperature T versus time t in arbitrary units. The part 2 is first heated in a first continuous furnace 3. The residence time of the part 2 in the first continuous furnace 3 is defined as t D1 In this example, the entire part 2 is heated to the AC3 temperature T AC3 Alternatively, the temperature of the part 2 is heated to a temperature higher than the AC3 temperature T AC3 The method may be carried out such that the

[0067] The part 2 is then transferred to the temperature control station 4. The transfer time for this is t T1 During this transfer, part 2 can be cooled.

[0068] residence period t TS During this time, the part 2 remains in the temperature control station 4. During this time, the first region 10 of the part 2 cools, and the temperature of the first region 10 after cooling reaches the austenite retransformation temperature T AR The temperature of the first region 10 is designated T1. After cooling, the previously cooled partial region 12 of the first region 10 of the component 2 is cooled by the laser unit 9 to the AC3 temperature T AC3 The temperature of the partial region 12 of the first region 10 is heated to a temperature higher than T 1A and the temperature of the remaining first region 10 is T 1B It is expressed as:

[0069] The subregion 12 of the first region 10 of the component 2 is maintained at a uniform temperature T 1AHowever, in another way of carrying out the method, it would also be possible to locally heat the sub-regions 12 to different intensities. This would in particular make it possible to create a temperature gradient over the sub-regions 12, which is not shown.

[0070] After the part 2 is heat-treated in the temperature control station 4, it is transferred to the second continuous furnace 5. The transfer time for this is t T2 The part 2 can be cooled during this transfer, but this cooling may vary depending on the area.

[0071] In the second continuous furnace 5, the part 2 is further heat-treated. The residence time of the part 2 in the second continuous furnace 5 is t D2 In the second continuous furnace 5, the first region 10 of the part 2, which is outside the partial region 12, is heated, and this heating is performed to a temperature T 1B However, even after this heating, the AC3 temperature T AC3 It is carried out in such a way that the

[0072] The temperature T2 of the second region 11 of the part 2 is equal to the AC3 temperature T AC3 It will get higher and will never drop below that temperature again until the end of the method presented.

[0073] Figure 3a shows a plan view of a first example of the configuration of a part 2. In this example, the part 2 is a B-pillar for a motor vehicle. A first region 10 and a second region 11 are clearly indicated. Inside the first region 10, a partial region 12 is shown.

[0074] Figure 3b shows a plan view of a second example of the configuration of the component 2. In contrast to Figure 3a, the partial area 12 is made up of two discontinuous parts.

[0075] Figure 3c shows a plan view of a third example of the configuration of the component 2. In contrast to Figure 3a, the second region 11 and the partial region 12 of the first region 10 each consist of two parts.

[0076] The illustrated shapes of the part 2 and the regions 10, 11, 12 are exemplary. The method according to Fig. 2 makes it possible to process parts of any desired geometry. The method is particularly versatile with regard to the configuration of the partial region 12. [Explanation of symbols]

[0077] 1 device 2 parts 3. No. 1 Continuous Furnace 4. Temperature Control Station 5. No. 2 continuous furnace 6 Control equipment 7 Cooling device 8 Heating device 9 Laser unit 10 First area 11 Second area 12 subregion 13 First Transfer Device 14 Second Transfer Device T temperature T AC3 AC3 temperature of the part T AR Austenite retransformation temperature of the component T1: Temperature of the first region of the part T 1A Temperature of a subregion of the first region of the part T 1B The temperature of the first area of ​​the rest of the part T2: Temperature of the second region of the part t time t D1 Residence time in the first continuous furnace t T1 Transfer period from the first continuous furnace to the temperature control station t TS Residence time at the temperature control station t T2 Transfer period from the temperature control station to the second continuous furnace t D2 Residence time in the second continuous furnace r Part transport direction

Claims

1. A method for heat treating a metal part (2), comprising the steps of: a) heating the entire part (2) in a first continuous furnace (3); b) transferring said parts (2) from said first continuous furnace (3) to a temperature control station (4); c1) cooling a first area (10) of the part (2) in the temperature control station (4), The temperature of the first region (10) at least after the cooling is at least equal to the austenite retransformation temperature (T AR ) lower, Steps and c2) the partial area (12) of the first area (10) of the part (2) cooled in step c1) is heated to an AC3 temperature (T AC3 ) to a temperature greater than d) transferring said parts (2) from said temperature control station (4) to a second continuous furnace (5); e) heat treating the component (2) in the second continuous furnace (5), The first region (10) of the component (2) outside the partial region (12) is heated, and the heating is performed so that the temperature of the first region (10) of the component (2) outside the partial region (12) does not exceed the AC3 temperature (T AC3 ) is lower than Steps and Including, During the method steps a) to e), the temperature of the second region (11) of the component (2) is at least temporarily at the AC3 temperature (T AC3 ) becomes higher, method.

2. 10. The method of claim 1, In step c1), the first region (10) of the component (2) is cooled by applying a cooling fluid to the component (2). method.

3. 3. The method of claim 1 or 2, In step a), the temperature of the part (2) is determined by the AC3 temperature (T AC3 ) not exceeding method.

4. 3. The method of claim 1 or 2, In step a), the entire part (2) is heated to the AC3 temperature (T AC3 ) is heated to a temperature higher than method.

5. 5. The method according to any one of claims 1 to 4, In step c2), the partial regions (12) of the first region (10) of the component (2) are locally heated with different intensities. method.

6. 6. The method according to any one of claims 1 to 5, In step c2), the partial area (12) of the first area (10) of the component (2) is locally heated with different intensities, the heating is carried out in such a way that a temperature gradient is obtained over the partial area (12) of the first area (10) of the component (2), method.

7. An apparatus (1) for heat treating a metal part (2), comprising: a first continuous furnace (3) for heating the entire part (2); A temperature control station (4), a cooling device (7) for cooling the first region (10) of the component (2); and a heating device (8) having a laser unit (9) for heating a partial region (12) of the first region (10) of the component (2), a temperature control station (4); a second continuous furnace (5) for heat treating said parts (2); a first transfer device (13) for transferring the parts (2) from the first continuous furnace (3) to the temperature control station (4); a second transfer device (14) for transferring the part (2) from the temperature control station (4) to the second continuous furnace (5); Equipped with Device (1).

8. 8. A device (1) according to claim 7, The laser unit (9) comprises a VCSEL; Device (1).

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