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); b) transferring the component (2) to a temperature control station (4); and c1) cooling a first region (10) of the component (2) at the temperature control station (4), wherein the temperature of the first region (10) after cooling is at least equal to or greater than the austenite retransformation temperature (T AR c2) in a temperature control station (4), heating the first region (10) of the part (2) cooled in step c1) by a laser unit (9), region by region, the heating being performed so as to form a temperature gradient at least in a first partial region (12) within the first region (10); d) transferring the part (2) to a second continuous furnace (5); and e) heat-treating the part (2) in the second continuous furnace (5), wherein during method steps a) to e), the temperature of the second region (11) of the part (2) is at least temporarily lowered to the 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 differentially heat-treating a part involves first heating the entire part in a first furnace, then subjecting the part to locally differential heat treatment 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 remainder of the part remains at approximately its own temperature. This approach can achieve excellent results in many application scenarios. However, there is a growing need for temperature distributions that are impossible or difficult to achieve using known methods. This is particularly true for parts with gradually changing ductility. Creating accurate temperature gradients is difficult, especially when cooling with a cooling fluid. 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: 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, a temperature of at least the first region after said cooling is less than an austenite retransformation temperature of the component; c2) in a temperature control station, heating the first area of ​​the part cooled in step c1) by a laser unit, The heating is performed so as to form a temperature gradient in at least a first subregion within the first region; d) transferring the part from the temperature control station to a second continuous furnace; e) heat treating the part in a second continuous furnace; 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, in particular B-pillars, can be heat treated. The method is particularly suitable for so-called door rings. A door ring is a part of the body of an automobile that surrounds the door opening. Door rings can be used instead of separate parts for the A-pillar and B-pillar, or the parts of the body floor or roof that are located between them. Preferably, the part is a door ring. However, the method can also be applied to any other application in any technical field.

[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 three regions in particular to be heat-treated differently. First, a first region and a second region can be distinguished. Furthermore, a first partial region of the first region is treated separately from the remainder of the first region. This therefore results in at least the first partial region of the first region, the remainder of the first region, and the second region. In addition to the first partial region of the first region, the first region may have a second partial region, or possibly even further partial regions. In this case, the result is the first partial region of the first region, the second partial region of the first region, the remainder of the first region, and the second region.

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

[0021] Each of the one or more partial regions constitutes a part of the first region, and each of the one or more partial regions is smaller than the first region, so that in particular there are also parts of the first region that are not part of the first partial region.

[0022] The method allows regions of the component to be heat-treated differently. As a result, the microstructural composition of the component can be affected differently locally, resulting in locally different ductility. In particular, a ductility gradient can be formed in the first subregion of the first region. Outside the first subregion, the first region is preferably more ductile than the second region. The ductility of the first subregion, in particular, is in this case between the ductility of the remainder of the first region and the ductility of the second region. In particular, the ductility of the first subregion increases gradually from the ductility of the second region to the ductility of the remainder of the first region. The first subregion can in this respect take the form of a transition region. A transition region usually occurs when different regions of the component are heat-treated differently. The method allows the transition region to be formed deliberately and precisely.

[0023] The statement that a temperature gradient is formed in at least a first partial region within the first region does not exclude the temperature gradient extending beyond the first partial region. Therefore, it is conceivable that the temperature gradient extends beyond the entire first region. In such a case, the first partial region may be defined as any desired portion of the first region. The statement that a temperature gradient is formed in at least a first partial region within the first region means that the temperature gradient is formed throughout the entire first region, or that the temperature gradient is formed in a portion of the first region, i.e., a portion referred to as the first partial region. If the temperature gradient is formed throughout the entire first region, there need not be a first partial region that is distinct from the remainder of the first region. This means that any desired portion of the first region is identified as the first partial region, but this desired portion of the first region is not distinct from the remainder of the first region. However, preferably, the temperature gradient is limited to the first region. In this case, the first partial region is limited to the remainder of the first region. The temperature gradient is formed only in the first partial region within the first region.

[0024] In step a), the entire part is heated in the first continuous furnace, so 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).

[0025] 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 a second continuous furnace. Therefore, heating in the first continuous furnace can, in principle, be performed at any desired temperature. In particular, if the part is heated only slightly in the first continuous furnace, the second zone may 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.

[0026] 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.

[0027] 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 c), 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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, step c2) involves heating at least a portion of the first region, which can reduce the ductility of this portion, in particular above the AC3 temperature.

[0033] In step c2), the first region is heated zone by zone by a laser unit in a temperature control station in such a way that a temperature gradient is formed in at least the first partial region. The temperature gradient extends from a first end at a lower temperature to a second end at a higher temperature. Between the first and second ends, the temperature of the part gradually increases from the lower temperature to the higher temperature. This increase may be linear or nonlinear. The lower temperature is preferably lower than the AC3 temperature, in particular lower than the austenite retransformation temperature. The higher temperature may be lower than the AC3 temperature, in particular lower than the austenite retransformation temperature. However, the higher temperature is preferably higher than the austenite retransformation temperature and higher than the AC3 temperature. The higher temperature is preferably in the range of 900-1000°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 partial region of the first region is at least partially heated by at least 100 K, in particular at least 250 K. The low temperature is preferably at least 100 K lower than the high temperature, in particular at least 200 K, or even at least 400 K. Generally, the effect of a temperature gradient is greater the greater the difference between the low and high temperatures.

[0034] Austenite may form in a portion of the first partial region, from which martensite can be obtained by press-hardening, but this does not apply to the remainder of the first partial region, and the microstructure may change gradually between them.

[0035] 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.

[0036] If martensite can form in part of the first sub-region, it is preferred that after the heating in step c2) zone by zone, the temperature of this part of the first sub-region no longer falls below the austenite retransformation temperature of the part until at least step e) is completed. If press quenching is part of the method, it is preferred that the temperature of this part of the first sub-region of the first region falls below the austenite retransformation temperature only in the press. However, it is not necessary to take great care that the temperature of this part of the first sub-region after step c2) no longer falls below the austenite retransformation temperature until step e) is completed. Austenite does not collapse instantly. Acceptable results can also be obtained if a portion of the austenite collapses in the first sub-region before press quenching.

[0037] In step e), the temperature of the first partial zone of the first zone preferably changes by a maximum of 200 K, in particular by a maximum of 100 K. This can also be described 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 furnace, the first partial zone of the first zone can be exposed to a temperature higher than the AC3 temperature of the parts. Depending on the temperature of the first partial zone of the first zone upon entry into the second furnace and depending on the residence time of the parts in the second furnace, the first partial zone of the first zone in the second continuous furnace can maintain its temperature or be heated, or the cooling of the first partial zone of the first zone can be slowed down. Since the temperature of the first partial zone varies locally, the statements in this paragraph apply to each location of the first partial zone.

[0038] Outside the first sub-region of the first region, the component can be heat-treated differently in step e). Preferably, outside the first sub-region, there is a further sub-region of the first region, in which the temperature does not exceed the AC3 temperature of the component in steps c2) to e). This avoids the formation of austenite in this sub-region of the first region. In step e), this portion of the first region of the component is heated in such a way that the temperature remains below the AC3 temperature of the component after heating. Thus, this portion of the first region is not heated above the AC3 temperature of the component after cooling in step c1). The temperature of this portion of the first sub-region of the component preferably does not exceed the AC3 temperature of the component, at least in steps c2) to e). If a press-hardening operation is part of the claimed method, the temperature of this portion of the first sub-region 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 this portion of the first sub-region. However, extreme caution is not required to avoid exceeding the AC3 temperature during these periods. Austenite does not form instantaneously. Acceptable results can be obtained even if a small amount of austenite is formed.

[0039] In addition to the first region having the first subregion, the component has a second region. The method is performed such that the temperature of the second region of the component at least temporarily exceeds the AC3 temperature of the component during method steps a) to e). 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] Heating by the laser unit allows the first partial region to be produced particularly precisely. In particular, the partial region may have a fine contour and / or may be smaller than would be possible with other methods. Cooling would make it difficult or impossible to achieve a temperature gradient, if at all. In a preferred embodiment of the method, in step c1) the 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 disadvantage. First, in step c1), the first region, including the first partial region, is cooled. Then, the laser unit reheats at least the first partial region in different regions, thereby creating a temperature gradient. This essentially corresponds to a method of cooling the first partial region differently in different regions. However, depending on the desired configuration of the temperature gradient, 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 AC3 temperature of the part is first exceeded in the temperature control station or second furnace. Preferably, in step a), the part is heated to a temperature higher than the AC1 temperature of the part. In that case, in step a), the part is heated to a temperature between the AC1 and AC3 temperatures of the part.

[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), the first region of the component is heated area by area by the laser unit, the heating being carried out in such a way that a second partial region of the first region, which is outside the first partial region, has a temperature higher than the AC3 temperature of the component.

[0050] In this embodiment, the part has a first region and a second region, the first region comprising at least a first subregion and a second subregion. A temperature gradient is formed in at least the first subregion of the first region, resulting in gradually varying ductility. The temperature gradient preferably does not extend into the second region. The AC3 temperature is exceeded in the second subregion of the first region and in the second subregion, resulting in low ductility in these two regions. This could essentially be achieved by cooling the second subregion of the first region in addition to the second region. However, depending on the desired contour of the region, this may be impossible or difficult to achieve with nozzle cooling, for example. In contrast, the present method is easier and can accommodate finer contours.

[0051] Preferably, in step c2), the second partial region of the first region is heated by at least 100 K, in particular by at least 250 K. The temperature of the second partial region of the first region after step c2) is preferably in the range of 900-1000°C.

[0052] After heating in step c2), the temperature of the second partial region is preferably not allowed to fall below the austenite retransformation temperature of the component until at least step e) is completed. If press-hardening is part of the method, the temperature of the second partial region of the first region is preferably only allowed to fall below the austenite retransformation temperature in the press. However, it is not necessary to take great care that the temperature of the second partial region of the first region after step c2) is not allowed to fall below the austenite retransformation temperature until step e) is completed. Austenite does not collapse instantly. Acceptable results can also be obtained if a portion of the austenite collapses in the second partial region of the first region before press-hardening.

[0053] In a further preferred embodiment of the method, the first sub-region of the first region is adjacent to the second sub-region of the first region, or the second sub-region of the first region is adjacent to the second region, or both. "Both" is preferred.

[0054] If a first partial region of the first region adjoins a second partial region of the first region, it is preferred that after step c2) the temperature of the first partial region is gradually reduced from the temperature of the second partial region, in this respect the first partial region may be in the form of a transition region.

[0055] If the second partial region of the first region is adjacent to the second region, it is preferred that after step c2) the second partial region of the first region and the second region are at the same temperature. In this regard, the second partial region of the first region may be in the form of a contiguous region with the second region.

[0056] 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 for cooling a first region of the component, and a heating device having a laser unit configured to heat the first region of the component in a zone-by-zone manner, the heating being performed in such a way that a temperature gradient is formed in at least a first partial region within the first region; 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.

[0057] 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).

[0058] The apparatus preferably includes a control device designed to control the apparatus in accordance with the method.

[0059] The laser unit is preferably further configured to bring a second sub-region of the first region, which is outside the first sub-region, to a temperature higher than the AC3 temperature of the component.

[0060] 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.

[0061] In a preferred embodiment of the device, the laser unit comprises a VCSEL.

[0062] 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.

[0063] 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]

[0064] [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] 3 shows an example of a part processed by the method shown in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0065] 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.

[0066] 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 laser unit 9 is configured to heat the first region 10 of the component 2 in a region-by-region manner, such that a temperature gradient is formed in at least the first partial region 12 within the first region 10, and such that a second partial region 15 of the first region 10, located outside the first partial region 12, has a temperature higher than the AC3 temperature of the component 2. The regions 10, 11, 12, 15 of the component 2 are shown in Figure 3. The laser unit 9 may in particular comprise a VCSEL.

[0067] 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.

[0068] 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

[0069] 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.

[0070] 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 ARThe temperature of the first region 10 is designated T1. After cooling, the previously cooled first region 10 of the component 2 is heated zone by zone by the laser unit 9. The second partial region 15 is heated to the AC3 temperature T AC3 The temperature of the second partial region 15 of the first region 10 is higher than T 1A The part of the first region 10 that does not belong to the first partial region 12 and the second partial region 15 has a temperature T 1B A temperature gradient is obtained in the first partial region 12. The temperature gradient is determined by the temperature T 1B from the higher temperature T 1A This is indicated by the arrow in Figure 2.

[0071] 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.

[0072] 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 first partial region 12 and the second partial region 15, 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

[0073] 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.

[0074] FIG. 3a shows a plan view of a component 2. In this example, the component 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 first partial region 12 and a second partial region 15 are shown. The second partial region 15 is made up of two discontinuous parts. A temperature gradient, indicated by the arrows, is formed in the first partial region 12. The illustrated shapes of the component 2 and the regions 10, 11, 12, 15 are exemplary. The method according to FIG. 2 makes it possible to process components of any desired geometry. This method is particularly versatile with regard to the configuration of the first partial region 12 and the second partial region 15. [Explanation of symbols]

[0075] 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 First subregion 13 First Transfer Device 14 Second transfer device 15 Second subregion 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 tTS 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) in the temperature control station (4), heating the first area (10) of the part (2) cooled in step c1) by a laser unit (9), The heating is performed so as to form a temperature gradient at least in a first partial region (12) within the first region (10). Steps and d) transferring said parts (2) from said temperature control station (4) to a second continuous furnace (5); e) heat treating said parts (2) in said second continuous furnace (5); 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 first region (10) of the component (2) is heated region by region by the laser unit (9), The heating is performed so that a second partial area (15) of the first area (10), which is outside the first partial area (12), reaches the AC3 temperature (T AC3 ) in a manner that the temperature is higher than method.

6. 6. The method of claim 5, the first partial region (12) of the first region (10) is adjacent to the second partial region (15) of the first region (10), or the second partial region (15) of the first region (10) is adjacent to the second region (11), or It's both. 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) configured to heat the first region (10) of the component (2) region by region, The heating is performed by a heating device (8) so that a temperature gradient is formed at least in a first partial region (12) within the first region (10). 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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