Heat treatment of metal parts
By cooling in the temperature control station and heating the metal parts with a laser unit, the problem of difficulty in establishing temperature distribution in the prior art is solved, flexible and precise heat treatment of the metal parts is achieved, and gradually changing ductility is obtained.
Patent Information
- Application Number
- CN202380079181.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-11-15
- Filing Date
- 2023-11-15
- Publication Date
- 2025-06-24
AI Technical Summary
The prior art is difficult to accurately establish the temperature distribution on metal components with gradually changing ductility, especially when cooling by cooling fluid.
A method is adopted in which the entire component is heated in a first continuous furnace and then transferred to a temperature control station where the temperature by cooling the first area is lower than the austenite inverter temperature and the cooling area is regionally heated using a laser unit to establish a temperature gradient. Subsequently, the components are transferred to a second continuous furnace for further heat treatment.
Flexible and precise heat treatment of metal parts is achieved, and temperature gradients can be established in different regions, thereby obtaining gradual ductility and improving the flexibility and accuracy of heat treatment.
Smart Images
Figure CN120202309A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method and a device for heat-treating metal components, in particular steel components of a motor vehicle. Background Art
[0002] Especially in the automotive industry, it is known to selectively harden steel components by heat treatment. For this purpose, regions of the steel component (e.g., the B-pillar) are heat-treated differently. Accordingly, regions with different ductilities are created, which is advantageous for the collision behavior of these components. For example, the occupants of a motor vehicle can be protected by the hard region of the B-pillar at the seat height, while the soft regions at the upper and lower parts of the B-pillar can absorb energy by deformation.
[0003] A successful method for locally different heat treatment of components has proven to be as follows: First, the entire component is heated in a first furnace, then the component is locally differently heat-treated in a temperature control station, and then the entire component is heated in a second furnace. In the temperature control station, for example, a cooling fluid is applied to a certain region of the component to cool this region, while the rest of the component remains approximately at its temperature. For many application cases, this can achieve excellent results. However, there is an increasing need to obtain temperature distributions that cannot be established or are difficult to establish using known methods. This particularly concerns components with a gradually changing ductility. In particular, in the case of cooling by a cooling fluid, it is difficult to precisely establish a temperature gradient. Summary of the Invention
[0004] The object of the present invention is to provide a method for locally different heat treatment of metal components that is particularly flexibly applicable. The object is also to provide a corresponding device.
[0005] These objects are achieved by the method and the device according to the independent claims. Other advantageous configurations are specified in the dependent claims. The features set forth in the claims and the description can be combined with each other in any technically meaningful way.
[0006] According to the present invention, a method for heat-treating a metal component is provided. The method includes:
[0007] a) Heating the entire component in a first continuous furnace,
[0008] b) Transferring (conveying) the component from the first continuous furnace to a temperature control station,
[0009] c1) In the temperature control station, cooling a first region of the component, the temperature of the first region being at least lower than the austenite inversion temperature of the component after cooling,
[0010] c2) In the temperature control station, a laser unit is used to regionally heat the first region of the component cooled in step c1) such that a temperature gradient is established at least in a first sub-region within the first region;
[0011] d) Transfer the component from the temperature control station to a second continuous furnace;
[0012] e) Heat-treat the component in the second continuous furnace;
[0013] wherein, during method steps a) to e), the temperature of a second region of the component exceeds the AC3 temperature of the component at least temporarily.
[0014] The described method enables the heat treatment of metal components. The metal component is preferably a component made of steel. The steel is preferably 22MnB5. However, the metal component does not have to meet the definition of steel. Therefore, this document will generally refer to metal components. For example, components of a motor vehicle, in particular B-pillars, can be heat-treated by the described method. The described method is particularly suitable for so-called door rings. A door ring is a motor vehicle body component that surrounds a door opening. Therefore, a door ring can be used instead of individual components such as A-pillars and B-pillars and the body roof and floor components between them. Preferably, the component is a door ring. However, the method can also be used for any other application in any desired technical field.
[0015] The material thickness of the component is preferably at least 0.7 mm, particularly in the range of 1 to 4 mm. Such a material thickness is suitable for many applications. However, the described method is also applicable to components with different material thicknesses. The material thickness of the component preferably remains constant over the entire component. Alternatively, the component may also have regionally different material thicknesses. For example, the component may be a "tailor rolled blank (TRB)", in which case locally different material thicknesses are obtained by locally different rolling processes. The component may also be a "tailor welded blank (TWB)", in which case locally different material thicknesses are obtained by welding together multiple metal sheets. A combination of TRB and TWB is also possible. The method is equally applicable to coated and uncoated components. The component is particularly preferably coated with Al / Si.
[0016] After heat treatment, the component is preferably press-hardened in a press and thus hot-formed. The method preferably includes the further steps of transferring the component from the second continuous furnace to the press (step f)) and press-hardening the component in the press (step g)). In this case, the method is a method for heat-treating and press-hardening the component. However, the press-hardening of the component does not have to be carried out as part of the method. The method can also be a preparation for a press-hardening operation carried out outside the method. Generally speaking, the component heat-treated by the method can be subjected to further process steps, and the result together with the further processes can be, for example, a finished motor vehicle. However, the heat treatment of the component is a defined sub-method in such an overall process. Therefore, it is advantageous to consider the heat treatment separately from the subsequent process steps, especially separately from the press-hardening.
[0017] In step a), the entire component is heated in a first continuous furnace. A furnace is understood to be a device inside which a settable temperature can be achieved and into which the component can be introduced. Over time, the temperature of the component gradually approaches the actual (prevailing) temperature inside the furnace. Thus, heat is transferred to the component through the gas (especially air) inside the furnace. A continuous furnace is a furnace through which the component can move and is 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 (especially gas burners). This enables a particularly uniformly distributed temperature to be provided for the component. In the first continuous furnace, the entire component is heated. The component is completely accommodated by the first continuous furnace. In addition, a continuous furnace can be used to obtain heating with a particularly large temperature difference. Using a continuous furnace, in particular, the component can be heated from room temperature to a temperature within its AC3 temperature range. For many other heating methods, such comprehensive heating is not achievable; even if it is possible, it would be too costly.
[0019] In the case of a coated component, the first continuous furnace can also be used to diffuse the coating into the remaining material of the component. This is particularly applicable to Al / Si coatings. In the case of a coated component, preferably, in step a), the component is heated in such a way that the coating material diffuses into the remaining material of the component in step a). Thus, in step a), preferably the component is heated to a temperature higher than the temperature at which the coating material diffuses into the remaining material of the component. Preferably, in step a), the temperature of the component is higher than this temperature for at least 1 minute, particularly even at least 2 minutes. Preferably, in step a), the component is heated to a temperature of at least 700 °C, particularly a temperature of at least 780 °C. Satisfactory results have been obtained at these temperatures. However, for increased process reliability, it is preferably heated to at least 830 °C. Preferably, in step a), the temperature of the component is higher than 700 °C, particularly 780 °C or even 830 °C, for at least 1 minute, particularly even at least 2 minutes. Particularly preferably, in the case of a coated component, in step a), the component is heated to a temperature higher than the AC1 temperature of the component, particularly higher than the AC3 temperature of the component. Preferably, in step a), the temperature of the component is higher than the AC1 temperature of the component, particularly higher than the AC3 temperature of the component, for at least 1 minute, particularly even at least 2 minutes. In this regard, the heating in step a) can not only be used to diffuse the coating, but also already contributes to the transformation of the microstructure.
[0020] Heating in a continuous furnace can in particular be contrasted with so-called "direct electrical heating". This heating method makes it difficult to heat the component evenly and with a sufficient amount of heat. Direct electrical heating focuses more on rapid heating. In addition, in the case of direct electrical heating, contact with the component is required. In step a) of the method, heating is preferably carried out non-contact. This does not exclude the component moving through the first continuous furnace via conveyor rollers and being in contact with the conveyor rollers in this regard. Heating is non-contact when the heat is introduced into the component via gas and / or thermal radiation.
[0021] In step b) of the method, the component is transferred from the first continuous furnace to a temperature control station. This is preferably carried out by a first transfer device. In the temperature control station, different heat treatments are carried out on regions of the component. Thus, in particular, the method described is a method for carrying out locally different heat treatments on a metal component. However, this does not need to be explicitly mentioned as steps c1) and c2) already clearly define the locally different heat treatments.
[0022] The first continuous furnace and the temperature control station are components that are different from each other and spatially separated. The transfer between the first continuous furnace and the temperature control station makes it easier to cool the components between heating in the first continuous furnace and heat treatment in the temperature control station. In the temperature control station, the components are regionally cooled as quickly as possible anyway. Rapid cooling can be carried out more effectively outside the hot first continuous furnace. Therefore, cooling can already start during the transfer. In this regard, the spatial separation of the first continuous furnace from the temperature control station speeds up the method. This is in contrast to solutions where all method steps are carried out in the same device without transferring the components. The aim of such solutions is usually to keep the cost of component transfer low or even avoid such costs. The spatial separation between the first continuous furnace and the temperature control station also makes construction easier because the requirements for the first continuous furnace and for the temperature control station are different.
[0023] In step d), the components are transferred from the temperature control station to the second continuous furnace. This is preferably carried out by a second transfer device. In step e), the components are heat treated in the second continuous furnace. For step e), the entire component is accommodated by the second continuous furnace.
[0024] The temperature control station and the second continuous furnace are components that are different from each other and spatially separated. The transfer between the temperature control station and the second continuous furnace makes it easier to cool the components between heat treatment in the temperature control station and in the second continuous furnace. Therefore, the part of the component to be cooled can still be cooled during the transfer. This reduces the necessary residence time in the temperature control station and speeds up the method. This is in contrast to solutions where all method steps are carried out in the same device as much as possible without transferring the components. The aim of such solutions is usually to keep the cost of component transfer low or even avoid such costs. The spatial separation between the temperature control station and the second continuous furnace also makes 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 heat treated, preferably heated. The component is completely accommodated by the second continuous furnace. The heat treatment carried out in the continuous furnace can be contrasted in particular with so-called "direct electric heating". The heat treatment in the second continuous furnace is particularly used 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 sufficient time to establish the required microstructure distribution in the component. In particular, in step e), carbon atoms can diffuse inside the component, so that the microstructure of the component changes as expected. In addition, the heat treatment in the second continuous furnace can be used to reduce the thermal stress in the component. In a subsequent stamping hardening operation, warping of the component can be reduced.
[0026] In particular, the method can perform different heat treatments on three regions. First, a distinction can be made between a first region and a second region. In addition, a first sub-region of the first region is treated separately from the rest of the first region. As a result, there are at least the first sub-region of the first region, the rest of the first region, and the second region. In addition to the first sub-region of the first region, the first region can also have a second sub-region and optionally other sub-regions. In this case, the result is thus the first sub-region of the first region, the second sub-region of the first region, the rest of the first region, and the second region.
[0027] The first region, one or more sub-regions of the first region, and the second region do not have to be contiguous regions. Thus, in particular, the central part of the B-pillar can form the first region, while the upper and lower parts of the B-pillar together form the second region. Within the first region, one or more parts can form the first sub-region. The component preferably but not necessarily has only the first region and the second region, i.e., no other regions. This also applies even if there are one or more sub-regions, since they are part of the first region.
[0028] Each sub-region forms part of the first region. Each sub-region is smaller than the first region. Thus, in particular, there is also a part of the first region that does not belong to the part of the first sub-region.
[0029] The method enables different heat treatments to be performed on the regions of the component. As a result, the composition of the microstructure of the component may be locally differently affected, thereby obtaining locally different ductilities. In particular, a ductility gradient can be established in the first sub-region of the first region. Outside the first sub-region, the first region is preferably more ductile than the second region. In this case, the ductility of the first sub-region can in particular be between the ductility of the rest of the first region and the ductility of the second region. In particular, the ductility of the first sub-region can gradually increase from the ductility of the second region to the ductility of the rest of the first region. In this regard, the first sub-region can be in the form of a transition region. Although transition regions are usually formed when different heat treatments are performed on the regions of a component, the described method can deliberately and precisely establish a transition region.
[0030] The fact that a temperature gradient is established at least in a first sub-region within a first region does not exclude the temperature gradient from extending beyond the first sub-region. Thus, it is even conceivable that the temperature gradient extends over the entire first region. In this case, the first sub-region can be defined as any desired part of the first region. Thus, the fact that a temperature gradient is established at least in a first sub-region within a first region means that the temperature gradient is established over the entire first region, or that the temperature gradient is established in a part of the first region and then this part is referred to as the first sub-region. If a temperature gradient is established over the entire first region, there is no need for a first sub-region that is different from the rest of the first region. This means the same as saying that any desired part of the first region is identified as the first sub-region, even though this part is not distinguishable from the rest of the first region. However, preferably, the temperature gradient is limited to the first sub-region. In this case, the first sub-region is delimited from the rest of the first region. Then, the temperature gradient is established only in the first sub-region within the first region.
[0031] In step a), the entire component is heated in a first continuous furnace. Thus, in step a), all regions are treated in the same way. Thus, in particular, it is not necessary to be able to distinguish these regions already in step a).
[0032] The method has a plurality of stages and, in addition to heating in a first continuous furnace, includes heat treatment at a temperature control station and heating in a second continuous furnace. Thus, the heating in the first continuous furnace can in principle be carried out to any desired temperature. If the component is only heated slightly in the first continuous furnace, the component can be heated more in a subsequent process of the method (in particular in a 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] Particularly for energy-related reasons, it is advantageous to heat the component relatively strongly in the first continuous furnace. This enables the above-described advantages of heating in a continuous furnace to be utilized compared to other types of heating, particularly compared to direct electrification. Thus, preferably, the component is heated to at least 400 °C, particularly at least 600 °C, in step a). Preferably, the component is heated to a temperature above the AC1 temperature of the component in step a). Preferably, the component is heated to a temperature that is at most 400 K below the AC3 temperature of the component, particularly at most 200 K below the AC3 temperature of the component, in step a). Preferably, the temperature of the component in step a) does not exceed 200 K above the AC3 temperature of the component. For example, the component can reach a temperature in the range of 600 to 800 °C in step a). As an alternative, higher temperatures are preferred, particularly above the AC3 temperature of the component. Thus, it is also preferred that the component is heated to at least 900 °C, particularly at least 1000 °C, in step a). Preferably, the component can be heated to a temperature in the range of 850 to 1200 °C in step a).
[0034] Due to the temperature control station downstream of the first continuous furnace, the component undergoes locally different heat treatment. For this purpose, in the temperature control station, different heat treatments are first carried out on a first region and a second region of the component. In step c1), the first region is cooled in the temperature control station. This is preferably achieved by applying a cooling fluid, particularly compressed air, to the first region. The pressure of the compressed air is preferably in the range of 2 to 4.5 bar. Due to this relatively high pressure, a large amount of compressed air can be directed to the first region of the component in a very short time, so that a sufficiently high cooling rate can be achieved. However, for the operating mode of the method, it generally does not matter which method is used to cool the first region.
[0035] In step c1), the first region is cooled in such a way that at least after cooling, the temperature of the first region is below the austenite inversion temperature of the component. This can in principle achieve high ductility in the first region.
[0036] If the entire component is heated to a temperature above the AC3 temperature in step a), austenite will form throughout the component. By cooling the first region to below the austenite inversion temperature of the component in step c1), this austenite decomposes again in the first region. The austenite inversion temperature is defined by the fact that once the temperature drops below the austenite inversion temperature, the austenite decomposes. The austenite inversion temperature is a material property. Thus, the fact that the temperature of the first region is below the austenite inversion temperature of the component at least after cooling does not mean that austenite has previously formed in the component.
[0037] If the entire component is not heated to a temperature above the AC3 temperature in step a), austenite will not form in this step. However, cooling the first region below the austenite inversion temperature of the component in step c1) will also cause, in this case, that in the subsequent process of the method, even if the component is subjected to further heating, austenite will not form in the first region. If austenite does not form in step a), there is no need to lower the temperature below the austenite inversion temperature in step c1) to cause the decomposition of austenite. If the entire component is not heated to a temperature above the AC3 temperature in step a), any required cooling of the first region in step c1) is sufficient. However, in this case, it is also advantageous to lower the temperature below the austenite inversion temperature. This does not follow from the fact that austenite inversion occurs below this temperature, but merely from the fact that the austenite inversion temperature is generally significantly lower than the AC3 temperature.
[0038] Preferably, in step c1), the first region is cooled by at least 100 K, in particular at least 250 K. After step c1), the temperature of the first region is preferably in the range of 400 to 700 °C, in particular in the range of 500 to 600 °C.
[0039] Therefore, regardless of the temperature reached in step a), after cooling in step c1), there is no austenite in the first region. As long as the AC3 temperature of the component is not exceeded (again) in the first region after cooling in step c1), a ductile microstructure can be obtained in the first region. However, step c2) involves heating at least a part of the first region. This allows a lower ductility to be obtained in this part. In particular, the AC3 temperature can be exceeded.
[0040] In step c2), the first region is regionally heated by a laser unit in the temperature control station such that a temperature gradient is established at least in the first sub-region. The temperature gradient extends from a first end with a lower temperature to a second end with a higher temperature. Between the first end and the second end, the temperature of the component gradually increases from the lower temperature to the higher temperature. This increase can be linear or non-linear. The lower temperature is preferably below the AC3 temperature, in particular below the austenite inversion temperature. The higher temperature can also be below the AC3 temperature, in particular below the austenite inversion temperature. However, preferably, the higher temperature is above the austenite inversion temperature, even above the AC3 temperature. The higher temperature is preferably in the range of 900 to 1100 °C. The higher temperature is preferably at least 100 K, in particular at least 250 K, higher than the temperature before step c2). Preferably, in step c2), the first sub-region of the first region is thus heated by at least 100 K, in particular 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 lower than the higher temperature. Generally, the greater the difference between the lower temperature and the higher temperature, the stronger the effect of the temperature gradient.
[0041] In a part of the first sub-region, austenite can be formed and martensite can be obtained from the austenite by press hardening, while this is not the case in the remaining part of the first sub-region. Between the two, the composition of the microstructure can change gradually.
[0042] For the function of the method, it is not important whether the heating in step c2) is performed by a single laser or by multiple lasers. Therefore, it is stipulated that the heating in step c2) is performed by a laser unit. The laser unit can include one or more lasers. The electronic device for supplying power to and controlling at least one laser can be part of the laser unit or can be arranged outside the laser unit, for example, in the control unit of the device for the method.
[0043] If martensite is to be obtained in a part of the first sub-region, preferably, after the regional heating in step c2), the temperature of this part of the first sub-region does not drop below the austenite inversion temperature of the component, at least until step e) is completed. If press hardening is part of the method, preferably, in the press, the temperature of this part of the first sub-region of the first region first drops below the austenite inversion temperature. However, no special attention needs to be paid to the fact that the temperature of this part of the first sub-region does not drop below the austenite inversion temperature before step e) is completed after step c2). Austenite does not decompose immediately. Acceptable results can also be obtained when part of the austenite in the first sub-region has decomposed before press hardening.
[0044] In step e), the temperature change in the first sub-region of the first region is preferably at most 200 K, in particular at most 100 K. This can also be referred to as maintaining the temperature, where temperature changes within a tolerance of 200 K or 100 K respectively are acceptable. For example, the first sub-region 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 sub-region of the first region when entering the second furnace and depending on the residence time of the component in the second furnace, in the second continuous furnace, the second sub-region of the first region can be maintained at its temperature or heated, or the cooling of the first sub-region of the first region can be slowed down. Due to the local temperature change in the first sub-region, the statements in this paragraph apply to each position in the first sub-region.
[0045] In step e), outside the first sub-region of the first region, the component can be heat-treated in a different manner. Preferably, outside the first sub-region, there is another sub-region of the first region, the temperature of which does not exceed the AC3 temperature of the component in steps c2) to e). This avoids the formation of austenite in this sub-region of the first region. In step e), this part of the first region of the component is heated such that even after heating, the temperature is below the AC3 temperature of the component. Thus, after cooling in step c1), in any case, this part of the first sub-region is no longer heated to a temperature above the AC3 temperature of the component. The temperature of this part of the first sub-region preferably does not exceed the AC3 temperature of the component at least in steps c2) to e). If the press hardening operation is part of the claimed method, the temperature of this part of the first sub-region preferably does not exceed the AC3 temperature of the component before or during the press hardening operation. In this way, a ductile microstructure can be obtained in this part of the first sub-region. However, no special attention needs to be paid to not exceeding the AC3 temperature during these time periods. Austenite does not form immediately. Even if a small amount of austenite forms, acceptable results can be obtained.
[0046] In addition to the first region having the first sub-region, the component also has a second region. The method is implemented 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 enables the formation of austenite in the second region. During the press hardening operation, martensite can be formed therefrom, and thus the second region has a relatively low ductility.
[0047] It does not matter when 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 is heated to a temperature below AC3 in step a), the second region can be heated to a temperature above AC3 in the temperature control station or in the second furnace.
[0048] Preferably, after heating to a temperature above the AC3 temperature of the component, until step e) is completed, the temperature of the second region does not drop below the austenite inversion temperature. Preferably, in the second region, the temperature first drops below the austenite inversion temperature in a press. This makes it possible to avoid the decomposition of austenite formed in the second region before press hardening.
[0049] In steps b) to e), the temperature change in the second region is preferably at most 200 K, in particular at most 100 K. This can also be referred to as maintaining the temperature, where temperature changes within a tolerance range of 200 K or 100 K, respectively, are acceptable. For example, the second region can be exposed to a temperature above the AC3 temperature of the component in a temperature control station in steps c1) and c2), and / or can be exposed to a temperature above the AC3 temperature of the component in a second furnace in step e). Depending on the temperature of the second region when it enters the temperature control station or the second furnace, and depending on the residence time of the component in the temperature control station or in the second furnace, in the temperature control station, the second region can be maintained at its temperature or heated, or the cooling of the second region can be slowed down. However, in particular, the second region can also be cooled in the temperature control station by exposure to ambient air.
[0050] In steps a) to e), the temperature of the second region can first rise above the AC3 temperature, then drop below the austenite inversion temperature, and then rise above the AC3 temperature again. In this case, it is sufficient that as long as after the second heating to a temperature above the AC3 temperature, until step e) is completed, the temperature of the second region does not drop below the austenite inversion temperature. This is included in the following statement: 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 and does not subsequently drop below the austenite inversion temperature of the component.
[0051] Due to the heating by the laser unit, the first sub-region can be created particularly precisely. In particular, this sub-region can have a finer contour and / or be smaller than by other methods. Cooling makes it difficult or even impossible to obtain a temperature gradient. In a preferred embodiment of the method, the first region of the component in step c1) is cooled by applying a cooling fluid.
[0052] The cooling fluid is preferably compressed air. The cooling fluid is preferably distributed onto the first region using a nozzle. This enables the first region to be easily cooled in a short time. However, the fundamental disadvantage of using a nozzle is that the cooling fluid does not allow for an exact separation between the cooled and non-cooled parts of the component. The method described avoids this. First, in step c1), the first region including the first sub-region is cooled. Then, the laser unit regionally heats at least the first sub-region again, thereby obtaining a temperature gradient. The result in principle corresponds to a method of regionally different cooling of the first sub-region. However, depending on the required temperature gradient configuration, it is impossible or very difficult to achieve this by nozzle cooling. In contrast, the method described is easier.
[0053] In another preferred embodiment of the method, the temperature of the component in step a) does not exceed the AC3 temperature of the component.
[0054] In this embodiment, first the AC3 temperature of the component is exceeded in a temperature control station or a second furnace. Preferably, in step a), the component is heated to a temperature above the AC1 temperature of the component. In this case, in step a), the component is thus heated to a temperature between the AC1 temperature and the AC3 temperature of the component.
[0055] In another preferred embodiment of the method, in step a), the entire component is heated to a temperature above the AC3 temperature of the component.
[0056] In another preferred embodiment of the method, in step c2), the laser unit regionally heats the first region of the component, such that a second sub-region of the first region outside the first sub-region is heated to a temperature above the AC3 temperature of the component.
[0057] In this embodiment, the component has a first region and a second region, wherein the first region has at least a first sub-region and a second sub-region. At least in the first sub-region of the first region, a temperature gradient is established, thereby enabling a gradually varying ductility to be obtained. The temperature gradient preferably does not extend to the second sub-region. In the second sub-region of the first region and the second region, the AC3 temperature is exceeded, and thus a low ductility is obtained in these two regions. In principle, this can also be achieved by not cooling the second sub-region of the first region in addition to the second region. However, depending on the profile of the required region, it is impossible or very difficult to achieve this by, for example, nozzle cooling. In contrast, the method described is easier and allows for a finer profile.
[0058] Preferably, in step c2), the second sub-region of the first region is heated by at least 100 K, in particular by at least 250 K. After step c2), the temperature of the second sub-region of the first region is preferably in the range from 900 to 1100 °C.
[0059] Preferably, after heating in step c2), the temperature of the second sub-region does not drop below the austenite inversion temperature of the component, at least until the end of step e). If press hardening is part of the method, then preferably, in the press, the temperature of the second sub-region of the first region is first reduced below the austenite inversion temperature. However, no special attention needs to be paid to the fact that the temperature of the second sub-region of the first region does not drop below the austenite inversion temperature before the end of step e). Austenite does not decompose immediately. Acceptable results can also be obtained when part of the austenite in the second sub-region of the first region has decomposed before press hardening.
[0060] In another preferred embodiment of the method, the first sub-region of the first region adjoins the second sub-region of the first region, and / or the second sub-region of the first region adjoins the second region. The "and" case here is preferred.
[0061] If the first sub-region of the first region adjoins the second sub-region of the first region, then preferably, after step c2), the temperature in the first sub-region decreases gradually relative to the temperature of the second sub-region. In this regard, the first sub-region can be in the form of a transition region.
[0062] If the second sub-region of the first region adjoins (or is adjacent to) the second region, then preferably, after step c2), the temperature of the second sub-region of the first region and the second region is the same. In this regard, the second sub-region of the first region can be in the form of a continuation of the second region.
[0063] Another aspect of the invention provides a device for heat-treating a metal component. The device comprises:
[0064] - a first continuous furnace for heating the entire component,
[0065] - a temperature control station having cooling equipment for cooling a first region of the component and heating equipment with a laser unit designed to locally heat the first region of the component such that a temperature gradient is established at least in a first sub-region within the first region,
[0066] - a second continuous furnace for heat-treating the component,
[0067] - A first transfer device for transferring the component from the first continuous furnace to the temperature control station, and
[0068] - A second transfer device for transferring the component from the temperature control station to the second continuous furnace.
[0069] The advantages and features of the method can be applied and transferred to the device, and vice versa. The device is preferably designed to operate according to the method. The method is preferably implemented by the device. The first continuous furnace is used for step a), the first transfer device is used for step b), the temperature control station is used for steps c1) and c2), the second transfer device is used for step d), and the second continuous furnace is used for step e).
[0070] Preferably, the device has a control device designed to control the device according to the method.
[0071] Preferably, the laser unit is also designed to heat a second sub-region in the first region that is outside the first sub-region to a temperature higher than the AC3 temperature of the component.
[0072] Preferably, the device further has a press for stamping and hardening the component and a third transfer device for transferring the component from the second continuous furnace to the press.
[0073] In a preferred embodiment of the device, the laser unit includes a VCSEL.
[0074] A "vertical-cavity surface-emitting laser" (VCSEL) is a laser diode that emits light perpendicular to its surface. A VCSEL can also be referred to as a surface emitter. It has been found that particularly good results can be obtained by using a VCSEL in step c2). Description of the Drawings
[0075] The present invention will be described in more detail below with reference to the drawings. The drawings show particularly preferred exemplary embodiments, however, the present invention is not limited thereto. The drawings and the relative dimensions shown therein are only schematic. In the drawings:
[0076] Figure 1 : shows a device for heat-treating metal components according to the present invention;
[0077] Figure 2 : shows the temperature curve that can be obtained by using the device according to the method of the present invention, and Figure 1 : shows the temperature curve that can be obtained by using the device according to the method of the present invention, and
[0078] Figure 3 : shows the component processed by the method shown in Figure 2 : shows the component processed by the method shown in Detailed Description of the Preferred Embodiments
[0079] Figure 1 Figure 1 shows an apparatus 1 for heat-treating a metal 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 the other in the conveying direction r of the component 2. A control device 6 is specifically designed 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 having a laser unit 9. The laser unit 9 is designed to locally heat a first region 10 of the component 2 such that a temperature gradient is established at least in a first sub-region 12 within the first region 10 and such that the temperature of a second sub-region 15 of the first region 10 outside the first sub-region 12 reaches a temperature higher than the AC3 temperature of the component 2. These regions 10, 11, 12, 15 of the component 2 are shown in Figure 3 FIG. 2. In particular, the laser unit 9 may comprise a VCSEL.
[0081] The apparatus 1 further comprises a first transfer device 13 for transferring the component 2 from the first continuous furnace 3 to the temperature control station 4 and a second transfer device 14 for transferring the component 2 from the temperature control station 4 to the second continuous furnace 5.
[0082] Figure 2 FIG. 3 shows the temperature profile established in the component 2 when the component 2 moves through the Figure 1 apparatus 1. Figure 2 The illustration in FIG. 3 is a schematic view. It shows a graph of temperature T against time t plotted in arbitrary units. The component 2 is first heated in the first continuous furnace 3. The residence time of the component 2 in the first continuous furnace 3 is denoted as t D1 . In the example shown, the entire component 2 is heated in the first continuous furnace 3 to a temperature higher than the AC3 temperature T AC3 of the component 2. As an alternative, the method may be implemented such that the temperature of the component 2 in the first continuous furnace 3 does not exceed the AC3 temperature T AC3 of the component 2.
[0083] Then, the component 2 is transferred to the temperature control station 4. The associated transfer time is denoted as t T1 . During this transfer, the component 2 may cool down.
[0084] The component 2 remains in the temperature control station 4 for a residence time t TS . During this time, the first region 10 of the component 2 is cooled, and after cooling, the temperature of the first region 10 is lower than the austenite inversion temperature T AR。The temperature of the first region 10 is denoted as T1. After cooling, the previously cooled first region 10 of the component 2 is locally heated by the laser unit 9. The second sub-region 15 is heated to a temperature higher than the AC3 temperature T AC3 of the component 2. The temperature of the second sub-region 15 of the first region 10 is denoted as T 1A . The part of the first region 10 that belongs neither to the first sub-region 12 nor to the second sub-region 15 has the temperature T 1B . In the first sub-region 12, a temperature gradient is obtained. It extends from a lower temperature (temperature T 1B ) to a higher temperature (temperature T 1A ). This is indicated by an arrow in Figure 2 .
[0085] After the component 2 has been heat-treated in the temperature control station 4, the component 2 is transferred to the second continuous furnace 5. This transfer time is denoted as t T2 . During this period, the component 2 can also cool down, and this cooling may vary from one region to the next.
[0086] In the second continuous furnace 5, the component 2 will be further heat-treated. The residence time of the component 2 in the second continuous furnace 5 is denoted as t D2 . In the second continuous furnace 5, the first region 10 of the component 2 located outside the first sub-region 12 and the second sub-region 15 is heated in such a way that even after heating, the temperature T 1B of the first region 10 of the component 2 in this region is lower than the AC3 temperature T AC3 of the component 2.
[0087] In the first continuous furnace 3, the temperature T2 of the second region 11 of the component 2 exceeds the AC3 temperature T AC3 of the component 2 and will not drop below this temperature again before the end of the method shown.
[0088] Figure 3 A plan view of the component 2 is shown. In this example, the component 2 is the B-pillar of a motor vehicle. The first region 10 and the second region 11 are visible in the figure. The first sub-region 12 and the second sub-region 15 are shown within the first region 10. The second sub-region 15 consists of two non-contiguous parts. A temperature gradient indicated by an arrow is established in the first sub-region 12. The shapes of the component 2 and the regions 10, 11, 12, 15 shown are exemplary. Figure 2 The method in
[0089] List of reference numerals
[0090] 1 Device
[0091] 2 Component
[0092] 3 First continuous furnace
[0093] 4 Temperature control station
[0094] 5 Second continuous furnace
[0095] 6 Control equipment
[0096] 7 Cooling equipment
[0097] 8 Heating equipment
[0098] 9 Laser unit
[0099] 10 First area
[0100] 11 Second area
[0101] 12 First sub - area
[0102] 13 First transfer equipment
[0103] 14 Second transfer equipment
[0104] 15 Second sub - area
[0105] T Temperature
[0106] T AC3 AC3 temperature of the component
[0107] T AR Austenite inversion temperature of the component
[0108] T1 Temperature of the first area of the component
[0109] T 1A Temperature of the sub - area of the first area of the component
[0110] T 1B Temperature of the rest of the first area of the component
[0111] T2 Temperature of the second area of the component
[0112] t Time
[0113] t D1 Residence time in the first continuous furnace
[0114] t T1 Duration of transfer from the first continuous furnace to the temperature control station
[0115] t TS Residence time in the temperature control station
[0116] tT2 Duration of transfer from the temperature control station to the second continuous furnace
[0117] t D2 Residence time in the second continuous furnace
[0118] Conveyor direction of the r component
Claims
1. A method for heat-treating a metal component (2), characterized in that, 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), c1) In the temperature control station (4), cool a first region (10) of the component (2), the temperature of the first region (11) being at least below the austenite inversion temperature (T AR ) of the component (2) after the cooling. c2) in the temperature control station (4), regionally heating a first region (10) of the component (2) that was cooled in step c1) by means of a laser unit (9) such that a temperature gradient is established at least in a first sub-region (12) within the first region (10); d) transferring the component (2) from the temperature control station (4) into a second continuous furnace (5), e) heat-treating the component (2) in the second continuous furnace (5), Wherein, during method steps a) to e), the temperature of the second region (11) of the component (2) exceeds at least temporarily the AC3 temperature (T AC3 ) of the component (2).
2. The method according to claim 1, wherein In step c1), the first region (10) of the component (2) is cooled by applying a cooling fluid to the first region (10).
3. The method according to any one of the preceding claims, characterized in that, In step a), the temperature of the component (2) does not exceed the AC3 temperature (T AC3 ) of the component.
4. The method according to any one of claims 1 and 2, characterized in that In step a), the entire component (2) is heated to a temperature higher than the AC3 temperature (T AC3 ) of the component (2).
5. The method according to any one of the preceding claims, characterized in that, In step c2), the first region (10) of the component (2) is regionally heated by means of the laser unit (9), such that a second sub-region (15) of the first region (10) outside the first sub-region (12) is heated to a temperature above the AC3 temperature (T AC3 ) of the component (2).
6. The method according to claim 5, wherein The first sub-region (12) of the first region (10) adjoins a second sub-region (15) of the first region (12), and / or wherein the second sub-region (15) of the first region (10) adjoins a second region (11).
7. An apparatus (1) for heat-treating a metallic component (2), characterized in that, Comprising: - a first continuous furnace (3) for heating the entire component (2), - a temperature control station (4) having a cooling device (7) for cooling a first region (10) of the component (2) and a heating device (8) with a laser unit (9) which is designed to regionally heat the first region (10) of the component (2) such that a temperature gradient is established at least in a first sub-region (12) within the first region (10); - a second continuous furnace (5) for heat-treating the component (2), - 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).
8. The device (1) according to claim 7, characterized in that, The laser unit (9) comprises a VCSEL.