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

Abstract

A method for heat treating a metal part (2) includes the steps of: a) heating the entire part (2) in a first continuous furnace (3); b) transferring the part (2) from the first continuous furnace (3) to a temperature control station (4); c) cooling at least one first region (10) of the part (2) in the temperature control station (4); d) transferring the part (2) from the temperature control station (4) to a second continuous furnace (5); and e) heat treating the part (2) in the second continuous furnace (5), wherein after step c) is completed, an edge (12) of the first region (10) is at least partially heated by a laser unit (9), and the temperature of the part (2) in a core (15) of the first region (10) surrounded by the edge (12) of the first region (10) is at least equal to the austenite retransformation temperature (T AR ) and after step c), the AC3 temperature (T AC3 ), and during method steps a) to e), the temperature of the second region (11) of the component (2) does not exceed 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 beneficial 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 soft areas above and below the B-pillar can deform and absorb energy. Furthermore, for example, the B-pillar can be selectively softened at the points where it connects to other vehicle body parts. Such soft connection areas are sometimes called soft spots. In the soft spots, the B-pillar can be easily drilled, for example, for rivets or screws.

[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 maintains approximately its own temperature. This approach can achieve excellent results in many use cases. However, known methods lack precision, particularly in the creation of soft spots. This is because the cooling cannot be locally limited, or can be achieved only with difficulty, by means of nozzles or the like. Similar difficulties generally arise when more than simply dividing a part into soft and hard regions is desired. Summary of the Invention [Means for solving the problem]

[0004] The object of the present invention is to provide a method for heat treating metal parts, which allows the formation of soft areas with particularly precise contours. It is also intended to provide a corresponding device.

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

[0006] In accordance with the present invention, a method for heat treating a metal component is provided, the method comprising: 1. A method for heat treating a metal part, comprising: a) heating the entire part in a first continuous furnace; b) transferring the part from the first continuous furnace to a temperature control station; c) cooling at least one first region of the part in a temperature control station; 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, After step c) is completed, an edge of the first region is at least partially heated by a laser unit; the temperature of the component at a core of the first region surrounded by the edge of the first region is at least after cooling in step c) below the austenite retransformation temperature of the component, and does not exceed the AC3 temperature of the component after step c); During method steps a) to e), the temperature of the second region of the component is at least temporarily increased above the AC3 temperature of the component.

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

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

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

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

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

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

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

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

[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 the first region to be contoured particularly precisely, for which purpose the edge of the first region is at least partially heated by a laser unit after step c) has been completed.

[0020] The edge is formed around the remaining portion of the first region, and thus the edge surrounds the remaining portion of the first region. At least partially heating the edge means that at least a portion of the edge is heated, and this portion is formed around the remaining portion of the first region, and thus partially surrounds the remaining portion of the first region. Preferably, the edge of the first region is entirely heated by the laser unit after step c) is completed.

[0021] This allows three regions in particular to be heat treated differently: first, a first region can be distinguished from a second region, and the edge of the first region can be treated separately from the remainder of the first region, i.e., the core of the first region.

[0022] There is at least one first region; that is, there may be only one first region, or there may be multiple first regions. Preferably, there are multiple first regions. The following description will mainly focus on an example where there is only one first region. If there are multiple first regions, the following description applies to all of the first regions.

[0023] The edge of the first region constitutes a two-dimensionally extending portion of the first region. Therefore, the edge of the first region may also be called an edge region. The edge region is a partial region of the first region. In other words, the edge is smaller than the first region. There is also a portion of the first region that is not the edge of the first region. This portion is called the core of the first region. The core of the first region is a two-dimensionally extending region and therefore may also be called the core region of the first region. When there are multiple first regions, each first region has a core and an edge.

[0024] Preferably, but not necessarily, the component has only one first region, or multiple first regions and one (i.e., not multiple) second region, and it is not important whether there is one or multiple second regions.

[0025] The method allows regions of the component to be heat treated differently, so that the microstructural composition of the component can be affected differently locally, resulting in locally different ductility. A first region outside the part region is more ductile than the edge of the first region and the second region. The edge of the first region and the second region can be given the same or different ductility, preferably the same ductility.

[0026] In particular, the core of the first region can be in the form of a soft spot, through which the part can be connected to another part, for example, if the part is a B-pillar, to another body part. The first region is thus a soft connection part that makes it easy to drill holes in the part, for example to provide holes for rivets or screws. The first region is preferably circular.

[0027] In step a), the entire part is heated in the first continuous furnace, so that all areas are treated in the same way in step a), and it is therefore not necessary to be able to distinguish between the areas in step a).

[0028] 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. Thus, heating in the first continuous furnace can, in principle, be performed at any desired temperature. If the part is heated less in the first continuous furnace, the edge of the first region and the second region 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.

[0029] 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.

[0030] 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.

[0031] The cooling in step c) does not need to be precise. In particular, during the cooling in step c), the desired soft spots do not need to be clearly distinguished from the surrounding areas. It is sufficient that the portion of the part intended to become a soft spot is cooled in step c). This is the core of the first region, or, if there are multiple first regions, each of the cores of each first region. This can be done, for example, by blowing compressed air onto the portion. However, if the compressed air is directed at a small area of ​​the part, the compressed air will spread over the surface of the part, resulting in some cooling of the part outside the area that is actually to be cooled (e.g., where the soft spot is intended to be formed). Subsequent heating of the edges of the first regions with a laser unit creates the desired, clearly defined contour of the core. The laser unit can completely or partially reverse any unnecessary cooling outside the area of ​​the part that is actually to be cooled.

[0032] The part of the part cooled in step c) is called the first region. This includes parts of the part that were unnecessarily cooled due to insufficient precision. This part constitutes the edge of the first region, which is subsequently reheated by the laser unit. The area that actually needs to be cooled is the part of the first region that is not included in the edge of the first region. This part of the first region is called the core of the first region. The edge of the first region surrounds the core of the first region. The soft spot can be provided by the core of the first region. The fact that the method allows for a well-defined delineation of the first region can be understood to mean that a well-defined core can be formed from the first region by precisely heating the edge of the first region. Similarly, it can be said that the method allows for a well-defined core of the first region to be defined.

[0033] Heat treating by the method increases the ductility of the core of the first region, and the temperature of the component at the core of the first region is below the austenite retransformation temperature of the component, at least after cooling in step c), and does not exceed the AC3 temperature of the component after step c).

[0034] In step a), when the entire component is heated to a temperature above the AC3 temperature, austenite is formed throughout the entire component. In step c), this austenite is again destroyed in the core of the first region by cooling the core of the first region to a temperature below the austenite retransformation temperature of the component. 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 core of the first region, at least after cooling, is below the austenite retransformation temperature of the component does not mean that austenite was previously formed in the component.

[0035] 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 core of the first region to a temperature below the austenite retransformation temperature of the component in step c) may contribute to preventing austenite from forming in the core of the first region, even if the component is further heated in the further course of the method. If austenite is not formed in step a), it is not necessary to reduce the temperature below the austenite retransformation temperature in step c) 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 core of the first region in any desired manner in step c). 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.

[0036] Preferably, in step c) the core of the first region is cooled by at least 100 K, in particular by at least 250 K. After step c), 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.

[0037] Therefore, regardless of the temperature reached in step a), no austenite will be present in the core of the first region after cooling in step c). A ductile microstructure can be obtained in the core of the first region if the core of the first region does not (again) exceed the AC3 temperature of the component after cooling in step c). Therefore, the core of the first region does not exceed the AC3 temperature of the component in steps d) to e). This prevents the formation of austenite in the core of the first region after cooling. In step e), the core of the first region of the component is heated such that the temperature of the core of the first region remains below the AC3 temperature of the component after heating. Therefore, the core of the first region of the component is not heated above the AC3 temperature of the component after cooling in step c).

[0038] In addition to at least one first region having a core and an edge, the component has a second region. The method is performed such that during method steps a) to e), the temperature of the second region of the component at least temporarily exceeds the AC3 temperature of the component. This allows austenite to form in the second region. During the press-hardening operation, martensite can form from the austenite, resulting in a relatively low ductility in the second region.

[0039] 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.

[0040] 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.

[0041] 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 also means that the temperature is maintained within a temperature tolerance of 200 K or 100 K. 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 step c), 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.

[0042] 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.

[0043] The method makes it possible to obtain a ductile microstructure in the core of the first region, while obtaining a less ductile microstructure in the second region.

[0044] Thanks to the heating by the laser unit, the core of the first region can be produced particularly precisely. In particular, the core of the first region can have a fine contour and / or can be smaller than would be possible with other methods. In this respect, the method is particularly flexible in its application.

[0045] There are fewer requirements for the heat treatment of the edge of the first region. The edge is part of the first region and therefore, by definition, is cooled in step c). However, in contrast to the core of the first edge, it is not important to what temperature it is cooled to. In particular, the edge of the first region may be the part of the part that is cooled only in step c) due to inaccurate cooling. At present, there is no accurate information available about the temperature to which this part of the part is cooled. The method must take into account the inaccurate cooling of the edge of the first region during cooling.

[0046] Furthermore, it is essential that the core of the first zone does not exceed the AC3 temperature of the part after step c), although this may occur at the edges of the first zone. As a result of heating the edges of the first zone with the laser unit, it is preferable that the AC3 temperature is exceeded at the edges of the first zone. This allows austenite to form at the edges of the first zone. In this way, the edges of the first zone can be made less ductile, just like the second zone.

[0047] In an ideal case, the edge of the first region will have a similar microstructure to the second region. Therefore, it is preferred that the edge of the first region has the same temperature as the second region as a result of heating by the laser unit. Preferably, after heating by the laser unit, the edge of the first region and the second region have the same temperature until the method is complete. In this regard, the edge of the first region is treated like the second region.

[0048] However, the method can be advantageously used even when deviations from the ideal case are encountered. By heating the edge of the first region at all, the edge of the first region is differentiated from the core of the first region. By applying any desired heating to the edge of the first region, the core of the first region can be clearly defined. By heating the edge of the first region at all, the effects of undesired cooling due to insufficient cooling accuracy in step c) are counteracted. Therefore, minimal heating of the edge of the first region is not necessary, much less heating the edge of the first region precisely to the temperature of the second region. However, the more the edge of the first region is heated by the laser unit, the more clearly the core of the first region is differentiated from the surrounding region. This is true as long as the edge of the first region does not exceed the AC3 temperature.

[0049] It has proven advantageous if the laser unit heats the edge of the first region by at least 100 K, in particular by at least 250 K. The temperature of the edge of the first region after heating is preferably in the range of 900-1100°C.

[0050] After the edge of the first region is heated by the laser unit, the temperature of the edge of the first region preferably does not fall below the austenite retransformation temperature of the part until at least step e) is completed. If press quenching is part of the method, the temperature of the edge of the first region preferably falls below the austenite retransformation temperature only in the press. However, it is not necessary to take great care to ensure that the temperature of the edge of the first region after the edge of the first region is heated by the laser unit does not fall below the austenite retransformation temperature until step e) is completed. Austenite does not collapse instantly. Good results can be obtained even if austenite is partially collapsed at the edge of the first region before press quenching. Acceptable results can be obtained whether no austenite forms at the edge of the first region before press quenching or if austenite is completely collapsed before press quenching.

[0051] This is because heating the edge of the first region at all offsets the undesirable cooling effect caused by insufficient cooling accuracy in step c). If laser heating is performed before step e), the edge of the first region is already formed in step e). In this case, it is not important whether and how much the temperature of the edge of the first region changes in step e). In step e), the temperature of the edge of the first region preferably changes by a maximum of 200 K, particularly by a maximum of 100 K. This can also be said to be maintaining the temperature while allowing a temperature change within a 200 K or 100 K tolerance range. For example, in the second continuous furnace, the edge of the first region can be exposed to a temperature higher than the AC3 temperature of the part. Depending on the temperature of the edge of the first region upon entering the second furnace and the residence time of the part in the second furnace, the edge of the first region in the temperature control station can maintain its temperature or be heated, or the cooling of the edge of the first region can be slowed down.

[0052] Whether the heating of the edge of the first region is performed by a single laser or by multiple lasers is not important for the function of the method. Therefore, it is provided that the heating is performed by a laser unit. The laser unit may have one or multiple lasers. Electronics for powering and controlling at least one laser may be part of the laser unit or may be provided outside the laser unit, for example in a control unit of the apparatus for the method.

[0053] In a preferred embodiment of the method, in step c1), a first region of the component is cooled by applying a cooling fluid to the component.

[0054] The cooling fluid is preferably compressed air. The cooling fluid is preferably spread over the first region using a nozzle. This allows the first region to be cooled easily and in a short time. However, using a nozzle has the fundamental disadvantage that the cooling fluid cannot accurately separate the cooled and uncooled portions of the part. This method avoids this. First, in step c), the first region, including the edge, is cooled. Then, the edge is reheated by the laser unit. As a result, this essentially corresponds to a method in which the edge of the first region is not cooled. However, depending on the desired contour of the region, this may be impossible or difficult to achieve with nozzle cooling. In contrast, this method is easier.

[0055] 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.

[0056] In this embodiment, the second region of the component, and possibly the edge of the first region, is first heated in a temperature control station or second furnace to a temperature above the AC3 temperature. Preferably, in step a), the component is heated to a temperature above the AC1 temperature of the component. In that case, in step a), the component is heated to a temperature between the AC1 and AC3 temperatures of the component.

[0057] 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.

[0058] In a further preferred embodiment of the method, at least partially heating the edge of the first region is performed in step c) or after step e).

[0059] If the edge of the first region is heated in step c), the laser unit is part of the temperature control station. This is advantageous in that the temperature control station provides a relatively large space for the laser unit. Furthermore, it has been found to be advantageous to directly heat the edge of the first region by the laser unit after cooling in step c). In this case, unwanted cooling of the edge of the first region is counteracted particularly quickly. Therefore, there is little time for undesired changes in the microstructure to occur.

[0060] Alternatively, in this embodiment, the edge of the first region may be heated after step e). In this case, the laser unit is downstream of the second continuous furnace. This has the advantage that the laser unit can be relatively easily located outside the second continuous furnace, as opposed to being located, for example, inside the second continuous furnace. Furthermore, the laser unit does not need to be configured for use inside a furnace. If the laser unit is located outside the second continuous furnace, maintenance is also easier. Heating the edge of the first region by the laser unit after step e) has the advantage that the time during which the clear contour obtained in the core of the first region can be lost due to heat conduction within the part is relatively short. This advantage can be realized particularly when the part is press-hardened after step e).

[0061] Both heating options, heating in step c) and heating after step e), have their advantages. It is also conceivable to heat the edge of the first region in step c) with a first laser unit and after step e) with a second laser unit. This solution is more complex but combines the advantages of both options.

[0062] Alternatively to the two options of this embodiment, the edge of the first region can be heated at different times during the method, in particular between steps c) and d), during step d), between steps d) and e), during step e), etc. In these cases, the aforementioned advantages of heating in step c) and heating after step e) are not obtained, but the purpose of heating to define the first region is still achieved.

[0063] 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 at least one first region of the part; a second continuous furnace for heat treating the parts; a first transfer device for moving the parts from the first continuous furnace to the temperature control station; a second transfer device for moving the parts from the temperature control station to the second continuous furnace; a laser unit for at least partially heating an edge of the first region of the part that has been cooled in the temperature control station; Equipped with.

[0064] 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 step c), a second transfer device is used in step d), and a second continuous furnace is used in step e).

[0065] The apparatus preferably includes a control device designed to control the apparatus in accordance with the method.

[0066] 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.

[0067] In a preferred embodiment of the device, the laser unit comprises a VCSEL.

[0068] 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.

[0069] 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]

[0070] [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. [Figure 4] FIG. 4 is an enlarged view of a first region of FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0071] 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.

[0072] The temperature control station 4 includes 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 an edge 12 of the first region 10 of the component 2. The regions 10, 11, 12, and 15 of the component 2 are shown in Figure 3. The laser unit 9 may include, among other things, a VCSEL.

[0073] 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.

[0074] 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

[0075] 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.

[0076] residence period t TS During this time, the part 2 remains in the temperature control station 4. During this time, the first region 10 of the part 2 cools, and the temperature of the first region 10 after cooling reaches the austenite retransformation temperature T AR The temperature of the first region 10 is denoted by T. After cooling, the edge 12 of the previously cooled first region 10 of the part 2 is cooled by the laser unit 9 to the AC3 temperature T AC3 The temperature of the edge 12 of the first region 10 is heated to a temperature higher than T 1A and the temperature of the core 15 of the first region 10 is T 1B It is expressed as:

[0077] The edge 12 of the first region 10 of the component 2 is at a uniform temperature T 1A 2 shows a schematic representation of this. In particular, the edge 12 of the first region 10 may have a locally different temperature. For example, after cooling, the temperature of the edge 12 of the first region 10 may increase radially from the inside to the outside, as may the core 15 of the first region 10.

[0078] 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 tT2 The part 2 can be cooled during this transfer, but this cooling may vary depending on the area.

[0079] 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 core 15 of the first region 10 of the part 2 is heated, and this heating is performed to raise the temperature T 1B However, even after this heating, the AC3 temperature T AC3 It is done in such a way that it becomes lower.

[0080] 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.

[0081] 3 shows a plan view of an example of the configuration of the part 2. In this example, the part 2 is a B-pillar for an automobile. A plurality of circular first regions 10 and second regions 11 are clearly shown.

[0082] Figure 4 is an enlarged view of a detail of Figure 3, showing one of the first regions 10. The edge 12 and core 15 of the first region 10 are depicted.

[0083] The illustrated shapes of the part 2 and the regions 10, 11, 12, 15 are exemplary. The method according to Fig. 2 makes it possible to process parts of any desired geometry. [Explanation of symbols]

[0084] 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 Edge 13 First Transfer Device 14 Second Transfer Device 15 Core of the First Region 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 at the edge of the first region of the part T 1B Core temperature of the first region of the part T2: Temperature of the second region of the part t time t D1 Residence time in the first continuous furnace t T1 Transfer period from the first continuous furnace to the temperature control station t TS Residence time at the temperature control station t T2 Transfer period from the temperature control station to the second continuous furnace t D2 Residence time in the second continuous furnace r Part transport direction

Claims

1. A method for heat treating a metal part (2), comprising the steps of: a) heating the entire part (2) in a first continuous furnace (3); b) transferring said parts (2) from said first continuous furnace (3) to a temperature control station (4); c) cooling at least one first area (10) of said component (2) in said temperature control station (4); 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, After step c) is completed, the edge (12) of the first region is at least partially heated by a laser unit (9), The temperature of the component (2) at the core (15) of the first region (10) surrounded by the edge (12) of the first region (10) is After the cooling in at least step c), the austenite retransformation temperature (T ＡＲ ) and after step c), the AC3 temperature (T AC3 ) and 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, At least partially heating the edge (12) of the first region (10) is performed in step c) or after step e). method.

6. 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) having a cooling device (7) for cooling at least one first region (10) of said component (2); 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); a laser unit (9) for at least partially heating the edge (12) of the first region (10) of the part (2) cooled in the temperature control station (4); Equipped with Device (1).

7. 7. A device (1) according to claim 6, The laser unit (9) comprises a VCSEL; Apparatus (1).

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