METHOD FOR HEAT TREATMENT OF A METAL COMPONENT

Abstract

The invention relates to a method for heat treating a metal component. The invention relates in particular to an application in the partial hardening of optionally pre-coated components made of high-strength manganese-boron steel. With the method, at least one first sub-region of the component is convectively cooled by means of at least one nozzle, which discharges a fluid stream to the first sub-region so that a temperature difference of at least 100 K is set between the at least one first sub-region and at least one second sub-region of the component, wherein the at least one nozzle is operated with a positive pressure of at least 2 bar.

Description

The invention relates to a method for heat treating a metal component. The invention is used, in particular, during the partial hardening of optionally pre-coated components made of a high-strength manganese-boron steel.

To produce safety-relevant vehicle body parts made of sheet steel, it is generally required to harden the sheet steel while or after it is formed into the body part. For this purpose, a heat treatment method referred to as “press hardening” has established itself. In this process, the sheet steel, which is generally provided in the form of a blank, is initially heated in a furnace and thereafter is cooled during the forming operation in a press, whereby it is hardened.

There has been an endeavor for several years now to use press hardening to provide body parts of motor vehicles, such as A and B pillars, side impact protection beams in doors, sills, frame parts, bumpers, transverse beams for the floor and roof, and front and rear longitudinal beams, which have differing strengths in sub-regions, so that the body part can partially fulfill different functions. For example, the center region of a B pillar of a vehicle should have high strength so as to protect the occupants in the event of a side impact. At the same time, the upper and lower end regions of the B pillar should have comparatively low strength, so as to be able to absorb deformation energy during a side impact, while enabling easy connectability to other body parts during the installation of the B pillar.

So as to create such a partially hardened body part, it is necessary for the hardened component to have differing material microstructures or strength properties in the sub-regions. So as to set differing material microstructures or strength properties after hardening, the sheet steel to be hardened may, for example, already be provided with differing sheet sections that are joined to one another or may be partially cooled differently in the press.

As an alternative or in addition, there is the option to subject the sheet steel to be hardened to partially differing heat treatment processes prior to the cooling and forming steps in the press. In this connection, for example, it possible to heat only sub-regions of the sheet steel to be hardened in which a transformation toward harder microstructures, such as martensite, is to be effectuated. This kind of process control, however, generally has the disadvantage that the inward diffusion of a coating, which is usually to be applied to the surface of the sheet steel to protect against scaling, such as an aluminum silicon coating, cannot be efficiently integrated into the heat treatment process. Furthermore, the option exists to carry out the partial heat treatment by way of contact plates, which are designed to partially control the temperature of the sheet steel by way of heat conduction. This, however, requires a certain contact time with the plates, which is usually longer than a (minimum) cycle time achievable by the downstream press. Furthermore, the coordination between a certain contact time and the cycle time at the press generally makes it more difficult to integrate corresponding temperature control stations into a press hardening line on an industrial scale, where production fluctuations during operation are in general unavoidable.

Proceeding from this, it is the object of the present invention to at least partially solve the problems described with regard to the prior art. In particular, a method for heat treating a metal component is to be provided, which allows a partially differing heat treatment of the component to be carried out on an industrial scale, and in particular as efficiently as possible. Moreover, the method, in particular, is to help reduce the influence of the process segment of the heat treatment process located upstream of the press on the cycle time of the overall heat treatment process.

These objects are achieved by the features of the independent claims. Further advantageous embodiments of the solution disclosed herein are described in the dependent claims. It should be noted that the features listed individually in the dependent claims can be combined with one another in any arbitrary, technologically meaningful manner and define further embodiments of the invention. Furthermore, the features described in the claims are specified and explained in greater detail in the description, wherein further preferred embodiments of the invention are presented.

In a method according to the invention for the (partially differing) heat treatment of a metal component, at least one first sub-region of the component (which is more ductile in the fully treated component) is convectively cooled by means of at least one nozzle, which discharges a fluid stream toward the first sub-region, so that a temperature difference of at least 100 K [Kelvin] is set between the at least one first sub-region and at least one second sub-region of the component (which is comparatively harder in the fully treated component), wherein the at least one nozzle is operated at a positive pressure of at least 2 bar.

The disclosed method is used, in particular, for the targeted component zone-specific heat treatment of a (steel) component or for setting different microstructures in a targeted manner in various sub-regions of a steel component. Preferably, the method is used to partially harden optionally pre-coated components made of a (high-strength) manganese-boron steel.

In a particularly advantageous manner, the disclosed method makes it possible to reliably carry out a partially differing heat treatment of a component even on an industrial scale. In particular by cooling the at least one first sub-region of the component by means of at least one nozzle operated at a positive pressure of at least 2 bar, the influence of the process segment of the heat treatment process located upstream of the press on the cycle time of the entire heat treatment process can be reduced. In other words, cooling the at least one first sub-region of the component by means of at least one nozzle operated at a positive pressure of at least 2 bar particularly advantageously allows the at least one first sub-region of the component to be cooled very quickly by at least 100 K, and in particular so quickly that a cooling period is less than or equal to a cycle time of a downstream press hardening tool (press cycle). It is not possible to achieve such short cooling periods, in particular, when using fans, which can be used to generate a (cooling) air stream toward a component surface.

Preferably, a cooling period during which the at least one first sub-region of the component is cooled by way of convection or by means of the nozzle is less than fifteen seconds, in particular less than ten seconds or even less than five seconds, and particularly preferably less than three seconds.

The metal component is preferably a metal blank, a sheet steel or an at least partially preformed semi-finished product. The metal component is preferably made with or of a (hardenable) steel, for example a boron (manganese) steel, such as that with the designation 22 MnB5. It is furthermore preferred that the metal component is provided or pre-coated with a (metal) coating at least to a large degree. For example, the metal coating may be a coating (predominantly) comprising zinc, or a coating (predominantly) comprising aluminum and/or silicon, and in particular what is known as an aluminum/silicon (Al/Si) coating.

The at least one nozzle is preferably disposed in a temperature control station, wherein the temperature control station is particularly preferably located downstream of a first furnace and/or a second furnace. The at least one nozzle, and in particular an outlet of the nozzle, may be oriented toward the first sub-region. Moreover, the at least one nozzle, and in particular an inlet of the nozzle, may be connected to a fluid source. The fluid source may be a tank in which the fluid forming the fluid stream is stored in compressed form. The fluid may be, for example, (compressed) air, nitrogen, water or a mixture thereof, for example.

The fluid is preferably compressed air and/or the fluid stream is preferably a (compressed) air stream. The at least one nozzle is preferably at least one compressed air nozzle. In other words, the at least one nozzle is preferably operated with compressed air. To provide the compressed air, the at least one nozzle, and in particular an inlet of the nozzle, may be connected to at least one compressor. In other words, compressed air having a positive pressure of at least 2 bar can be provided by means of at least one compressor. Furthermore, the compressed air thus provided can be supplied to the at least one nozzle. This may take place prior to, simultaneously with and/or at least partially simultaneously with the cooling by means of the at least one nozzle. If multiple nozzles are provided, these can be connected to a shared compressor. Preferably, the compressor is provided and configured for supplying compressed air having a positive pressure of at least 2 bar to the at least one compressed air nozzle. For this purpose, for example, the compressor can provide a positive (system) pressure of at least 2 bar, which is preferably kept available or stored in a pressure (or compressed air) reservoir. Particularly preferably, an (appropriate) pressure reservoir is disposed in a piping system connecting the compressor to the at least one compressed air nozzle and/or is connected to the piping system between the compressor and the at least one compressed air nozzle. Furthermore, at least one activatable valve, which is actuated, and in particular opened and closed, in keeping with a desired cooling period and/or a desired (compressed air) volume flow, can be disposed between the compressor and the at least one compressed air nozzle. Furthermore, it is advantageously possible to form a preferably activatable valve between the compressor and the at least one compressed air nozzle, by means of which the flow rate of the fluid stream through the nozzle can be adapted, so that the volume flow through the nozzle can be adapted, for example as a function of the operating situation and/or as a function of properties of the component, such as the thickness of the component.

Preferably, the (or each) nozzle is shaped in the manner of a fan nozzle. It is furthermore preferred when multiple nozzles are provided, which particularly preferably are arranged so as to form a nozzle array. In particular, the shape of the nozzle array and/or the arrangement of the multiple nozzles is adapted to the (desired) geometry of the at least one first sub-region of the component.

The cooling preferably takes place by means of a plurality of nozzles, and in particular by means of at least five or even at least ten nozzles, which can be activated individually or in groups and which, in particular, can be supplied with a (certain) fluid volume flow. The nozzles are preferably activated as a function of time. It is furthermore preferred that the nozzles are activated (individually or in groups) in such a way that one or more temperature differences are set deliberately between sub-regions of the component, for example between the at least one first sub-region and the at least one second sub-region. Moreover, the nozzles can be activated (individually or in groups) in such a way that ambient influencing conditions in the temperature control station, which can act on the component upon leaving the temperature control station, can be compensated for. Such a compensation, which in particular shall be understood to mean a prevention, may take place in such a way, for example, that a region of the component located closer to the edge, and in particular a region of the at least one first sub-region located closer to the component edge, is cooled to a lesser degree than a region of the component located further away from the edge, and in particular than a region of the at least one first sub-region of the component located further away from the component edge, so as to take into consideration or even (substantially) compensate for faster cooling of the component in the edge regions thereof, which may possibly take place upon leaving the temperature control station, in particular in the heat exchange with the surrounding area.

As a result of the convective cooling, a temperature difference of at least 100 K, preferably of at least 150 K or even of at least 200 K is set between the at least one first sub-region and at least one second sub-region of the component. After cooling, the component has partially differing (component) temperatures, wherein a temperature difference is set between a first temperature of the at least one first sub-region and a second temperature of the at least one second sub-region of the component. Moreover, it is possible to set several (different) temperature differences between sub-regions of the component. It is possible, for example, to set three or more sub-regions in the component, each having a temperature different from the others. The partially differing temperatures can cause differing microstructures and/or strength properties to be produced in the component, in particular during a possibly following quenching process, such as during a press hardening operation.

The at least one nozzle is operated at a positive pressure of at least 2 bar, preferably of at least 2.5 bar, particularly preferably of at least 3.5 bar or even of at least 5 bar. Preferably, a fluid forming the fluid stream has a positive pressure of at least 2 bar, preferably of at least 2.5 bar, particularly preferably of at least 3.5 bar or even of at least 5 bar, at an inlet of the at least one nozzle, in particular during a cooling period. In other words, this means, in particular, that the positive pressure that is used to operate the at least one nozzle can be measured on an inlet of the at least one nozzle. When the nozzle is connected to a pressure (or compressed air) reservoir, the positive pressure that is used to operate the at least one nozzle will refer in particular to the positive pressure kept available or stored in the pressure reservoir. A positive pressure here shall be understood to mean a pressure that is determined relative to the ambient pressure or atmospheric pressure.

The fluid stream may be accelerated while flowing through the at least one nozzle. Preferably, the fluid stream exits the at least one nozzle with an exit velocity of approximately the sound velocity. It is furthermore preferred that the fluid stream discharged by means of the at least one nozzle applies a blowing pressure of at least 3000 Pa [Pascal] or N/m² [Newton per square meter] onto a surface of the component in the at least one first sub-region of the component. Preferably, the cooling by means of the at least one nozzle sets a cooling rate of at least 100 K/s [Kelvin per second] in the at least one first sub-region of the component.

According to an advantageous embodiment, it is proposed that, prior to cooling, at least the at least one first sub-region of the component is heated by at least 500 K, preferably by at least 600 K or even by at least 800 K. Preferably, prior to cooling, the at least one first sub-region of the component is heated by means of the at least one nozzle in a first furnace and/or by way of radiant heat and/or convection. It is furthermore preferred that the cooling takes place by means of the at least one nozzle in a temperature control station located downstream of a first furnace.

According to an advantageous embodiment, it is proposed that, after cooling, at least the at least one first sub-region of the component is heated by at least 100 K, preferably by at least 150 K or even by at least 200 K. Preferably, after cooling, the at least one first sub-region of the component is heated by means of the at least one nozzle in a second furnace and/or by way of radiant heat and/or convection. It is particularly preferred when the second furnace is located downstream of the temperature control station.

According to a further aspect, a method for the (partially differing) heat treatment of a metal component comprising at least the following steps is disclosed:

• • a) heating the component in a first furnace, in particular by way of radiant heat and/or convection;
  • b) moving the component into a temperature control station;
  • c) convectively (partially) cooling at least one first sub-region of the component in the temperature control station by means of at least one nozzle discharging a fluid stream toward the first sub-region, wherein a temperature difference is set between the at least one first sub-region and at least one second sub-region of the component, and wherein the at least one nozzle is operated at a positive pressure of at least 2 bar.

The indicated sequence of method steps a), b) and c) is derived during a regular process of the method. Individual or multiple of the method steps may be carried out simultaneously, consecutively and/or at least partially simultaneously.

In step a), the (entire) component is heated in a first furnace. Preferably, the component is heated homogeneously or uniformly in the first furnace. It is furthermore preferred that the component is heated in the first furnace (exclusively) by way of radiant heat, for example by at least one electrically operated heating element (not making physical or electrical contact with the component), such as a heating loop and/or a heating wire, and/or by at least one (gas-heated) radiant tube. The first furnace can be a continuous furnace or a batch furnace.

In step b), the component is moved, in particular, from the first furnace into a temperature control station. For this purpose, a transport unit may be provided, for example at least comprising a roller table and/or an (industrial) robot. Preferably, the component travels a distance of at least 0.5 m [meters] from the first furnace to the temperature control station. The component may be guided in contact with the ambient area or within a protective atmosphere.

In step c), at least one first sub-region of the component is (actively) cooled in the temperature control station. Preferably, an input of thermal energy into the at least one second sub-region of the component takes place in the temperature control station, simultaneously or at least partially simultaneously with the cooling of the at least one first sub-region of the component. Preferably, the at least one second sub-region of the component is subjected in the temperature control station (exclusively) to heat radiation, which is generated and/or irradiated, for example, by at least one electrically operated or heated heating element, which is disposed in particular in the temperature control station (and does not make contact with the component), such as a heating loop and/or a heating wire, and/or by at least one (gas-heated) radiant tube, which is, in particular, disposed in the temperature control station.

The input of thermal energy into the at least one second sub-region of the component can preferably take place in the temperature control station in such a way that a decrease in the temperature of the at least one second sub-region and/or a cooling rate of the at least one second sub-region is at least reduced while the component remains in the temperature control station. This process control is in particular advantageous when the component was heated in step a) to a temperature above the Ac3 temperature. As an alternative, the input of thermal energy into the at least one second sub-region of the component in the temperature control station may take place in such a way that the at least one second sub-region of the component is heated (considerably), in particular by at least approximately 50 K. This process control is in particular advantageous when the component was heated in step a) to a temperature below the Ac3 temperature, or even below the Ac1 temperature.

According to an advantageous embodiment, it is proposed that the method furthermore comprises at least the following steps:

• • d) moving the component from the temperature control station into a second furnace; and
  • e) heating at least the at least one first sub-region of the component in the second furnace by at least 100 K [Kelvin], in particular by way of radiant heat and/or convection.

In step d), the component is moved from the temperature control station into a second furnace. For this purpose, a transport unit may be provided, for example at least comprising a roller table and/or an (industrial) robot. The component preferably travels a distance of at least 0.5 m from the temperature control station to the second furnace. The component may be guided in contact with the ambient area or within a protective atmosphere. Preferably, the component is transferred directly into the second furnace immediately upon having been removed from the temperature control station. The second furnace can be a continuous furnace or batch furnace.

In step e), at least the at least one first sub-region of the component is heated in the second furnace by at least 100 K, preferably by at least 150 K or even by at least 200 K. In other words, another heating process takes place in the second furnace, wherein at least the previously (actively) cooled at least one first sub-region is heated by at least 100 K. Preferably, at least the at least one first sub-region of the component is heated in the second furnace (exclusively) by way of radiant heat, for example by at least one electrically operated heating element (not making contact with the component), such as a heating loop and/or a heating wire, and/or by at least one (gas-heated) radiant tube. It is furthermore preferred that in step e), in particular simultaneously or at least partially simultaneously with the heating of the at least one first sub-region, the at least one second sub-region of the component is heated in the second furnace by at least 50 K, particularly preferably by at least 70 K or even by at least 100 K, in particular (exclusively) by way of radiant heat. Particularly preferably, the at least one second sub-region of the component is heated in step e) to a temperature above the Ac1 temperature or even above the Ac3 temperature. Alternatively, in step e), in particular simultaneously or at least partially simultaneously with the heating of the at least one first sub-region, a decrease in the temperature of the at least one second sub-region and/or a cooling rate of the at least one second sub-region is at least reduced while the component remains in the second furnace.

In other words, in step e) an input of thermal energy, in particular by way of radiant heat, into the entire component may take place. For example, the second furnace may (for this purpose) include a furnace interior, which in particular is heated (exclusively) by way of radiant heat, in which preferably a substantially uniform inside temperature prevails. The input of thermal energy into the at least one first sub-region of the component in the second furnace preferably takes place in such a way that the temperature of the at least one first sub-region is increased by at least 100 K, preferably by at least 120 K, particularly preferably by at least 150 or even by at least 200 K.

The input of thermal energy into the at least one second sub-region of the component in the second furnace can preferably take place in such a way that a decrease in the temperature of the at least one second sub-region and/or a cooling rate of the at least one second sub-region is at least reduced while the component remains in the second furnace. This process control is in particular advantageous when the component was heated in step a) to a temperature above the Ac3 temperature. As an alternative, the input of thermal energy into the at least one second sub-region of the component in the second furnace can take place in such a way that the at least one second sub-region of the component is at least (considerably) heated, in particular by at least 50 K, particularly preferably by at least 70 K or even by at least 100 K, and/or is heated to a temperature above the Ac1 temperature or even above the Ac3 temperature. This process control is in particular advantageous when the component was heated in step a) to a temperature below the Ac3 temperature, or even below the Ac1 temperature.

According to a further advantageous embodiment, it is proposed that the method furthermore comprises at least the following steps:

• • f) moving the component from the temperature control station or from the second furnace into a press hardening tool; and
  • g) forming and cooling the component in the press hardening tool.

Preferably, the moving in step f) takes place by means of a transport device, for example at least comprising a roller table and/or an (industrial) robot. Preferably, the component travels a distance of at least 0.5 m from the second furnace to the press hardening tool. The component may be guided in contact with the ambient area or within a protective atmosphere. Preferably, the component is transferred directly into the press hardening tool immediately upon having been removed from the second furnace.

According to an advantageous embodiment, it is proposed that the component is heated in step a) to a temperature below the Ac3 temperature, or even below the Ac1 temperature. The Ac1 temperature is the temperature at which the transformation from ferrite to austenite begins when a metal component, and in particular a steel component, is heated.

According to an (alternative) advantageous embodiment, it is proposed that the component is heated in step a) to a temperature above the Ac3 temperature. The Ac3 temperature is the temperature at which the transformation from ferrite to austenite ends or has been (entirely) completed when a metal component, and in particular a steel component, is heated.

According to an advantageous embodiment, it is proposed that the at least one first sub-region is cooled in step c) by way of convection to a temperature below the Ac1 temperature. Preferably, the at least one first sub-region is cooled in step c), in particular by way of convection, to a temperature below 550° C. [° Celsius] (823.15 K), particularly preferably below 500° C. (773.15 K) or even below 450° C. (723.15 K).

The details, features and advantageous embodiments described in connection with the method disclosed first may also be present accordingly with the method disclosed here, and vice versa. In this regard, all the comments provided there to further characterize the features are hereby incorporated by reference.

So as to achieve the described object(s), a method for the (partially differing) heat treatment of a metal component comprising at least the following steps could also be used:

• • a) heating the component in a first furnace, in particular by way of radiant heat and/or convection;
  • b) moving the component into a temperature control station;
  • c) convectively (partially) cooling at least one first sub-region of the component in the temperature control station by means of at least one nozzle discharging a fluid stream toward the first sub-region, wherein a temperature difference is set between the at least one first sub-region and at least one second sub-region of the component, and wherein the at least one nozzle is operated with compressed air.

The details, features and advantageous embodiments described in connection with the methods disclosed first may also be present accordingly with the method disclosed here, and vice versa. In this regard, all the comments provided there to further characterize the features are hereby incorporated by reference.

According to a further aspect, a device for heat treating a metal component is disclosed, comprising at least the following:

• • a first furnace heatable in particular by way of radiant heat and/or convection;
  • a temperature control station located downstream of the first furnace, in which at least one nozzle is disposed or held, which is provided to discharge a fluid for cooling at least one first sub-region of the component and configured, in particular, such that a temperature difference can be set between the at least one first sub-region and at least one second sub-region of the component, wherein the at least one nozzle is preferably provided and configured to be operated at a positive pressure of at least 2 bar.
  • a second furnace located downstream of the temperature control station and heatable, in particular, by way of radiant heat and/or convection, which is provided and configured for heating at least the at least one first sub-region of the component by at least 100 K.

The device may be used to carry out a method disclosed herein. The device is preferably provided and configured for carrying out the method disclosed herein. Preferably, an electronic control unit, which is suitable for carrying out a method disclosed herein and configured therefor, is assigned to the device. Particularly preferably, the control unit comprises at least one program-controlled microprocessor and an electronic memory for this purpose, a control program that is provided and configured for carrying out a method disclosed herein being stored in the memory.

According to a further advantageous embodiment, it is proposed that at least the first furnace or the second furnace is a continuous furnace or a batch furnace. Preferably, the first furnace is a continuous furnace, and in particular a roller hearth furnace. The second furnace is particularly preferably a continuous furnace, and in particular a roller hearth furnace, or a batch furnace, and in particular a multi-level batch furnace comprising at least two chambers disposed on top of one another. The second furnace preferably includes a furnace interior, which in particular is heatable (exclusively) by way of radiant heat, in which preferably a substantially uniform inside temperature can be set. In particular when the second furnace is designed as a multi-level batch furnace, multiple such furnace interiors may be present corresponding to the number of chambers.

Preferably, (exclusively) radiant heat sources are disposed in the first furnace and/or in the second furnace. It is particularly preferred when at least one electrically operated heating element (not making contact with the component), such as at least one electrically operated heating loop and/or at least one electrically operated heating wire, is disposed in a furnace interior of the first furnace and/or in a furnace interior of the second furnace. As an alternative or in addition, at least one, in particular gas-heated, radiant tube may be disposed in the furnace interior of the first furnace and/or the furnace interior of the second furnace. Preferably, multiple radiant tube gas burners or radiant tubes into each of which at least one gas burner burns are disposed in the furnace interior of the first furnace and/or the furnace interior of the second furnace. It is particularly advantageous when the inner region of the radiant tubes into which the gas burners burn is atmospherically separated from the furnace interior, so that no combustion gases or exhaust gases can reach the furnace interior, and thus influence the furnace atmosphere. Such a system is also referred to as “indirect gas heating.”

At least one nozzle, which is provided and configured for discharging a fluid, is disposed or held in the temperature control station. The at least one nozzle can be operated at a positive pressure of at least 2 bar. The device can furthermore comprise at least one compressor, which is preferably assigned to the temperature control station, in particular for providing the positive pressure. The compressor can be (fluidically) connected to the at least one nozzle, and in particular to an inlet of the nozzle. Preferably, the device comprises at least one pressure (or compressed air) reservoir, which is provided and configured for keeping pressure provided by means of the compressor available or storing this pressure. The pressure reservoir is preferably assigned to the temperature control station. It is furthermore preferred when the pressure reservoir is disposed in a piping system connecting the compressor to the at least one compressed air nozzle and/or is connected to the piping system between the compressor and the at least one compressed air nozzle. The compressor is preferably provided and configured for providing the fluid forming the fluid stream at a positive pressure of at least 2 bar. The compressor is preferably a reciprocating compressor, a rotary compressor, in particular a screw-type compressor, or a turbo compressor, which particularly preferably is designed with a plurality of rotatably drivable blades (of at least one rotor) and a plurality of fixed blades (of at least one stator).

As an alternative or in addition, a source for a pressurized fluid, which can be connected to the at least one nozzle, may be provided instead of or in addition to a compressor. This is preferably a source in which a liquefied gas is vaporized, for example by way of an appropriate heat exchanger which causes the liquefied gas (such as liquefied nitrogen) to vaporize, for example under ambient air. The vaporized gas can then preferably be supplied to a compressor for increasing the pressure, if the gas pressure at the outlet of the source should be too low.

Preferably, (moreover) at least one heating unit is disposed in the temperature control station. The heating unit is preferably provided and configured for inputting thermal energy into the at least one second sub-region of the component. Particularly preferably, the heating unit is disposed and/or oriented in the temperature control station in such a way that the input of thermal energy into the at least one second sub-region of the component can be carried out simultaneously, or at least partially simultaneously, with the cooling of the at least one first sub-region of the component by means of the at least one nozzle. Preferably, the heating unit (exclusively) comprises at least one radiant heat source. Particularly preferably, the at least one radiant heat source is designed with at least one electrically operated heating element (not making contact with the component), such as at least one electrically operated heating loop and/or at least one electrically operated heating wire. As an alternative or in addition, at least one gas-heated radiant tube can be provided as the radiant heat source.

Furthermore, the device can comprise a press hardening tool, which is located downstream of the second furnace. The press hardening tool is, in particular, provided and configured for simultaneously, or at least partially simultaneously, forming and (at least partially) quenching the component.

The details, features and advantageous embodiments described in connection with the methods may also be present accordingly with the device disclosed herein, and vice versa. In this regard, all the comments provided there to further characterize the features are hereby incorporated by reference.

According to a further aspect, a use of at least one nozzle operated at a positive pressure of at least 2 bar for convectively cooling at least one first sub-region of a metal component is proposed, wherein the nozzle is used in such a way that a temperature difference of at least 100 K is set between the at least one first sub-region and at least one second sub-region of the component.

The details, features and advantageous embodiments described above in connection with the methods and/or the device may also be present accordingly with the use disclosed herein, and vice versa. In this regard, all the comments provided there to further characterize the features are hereby incorporated by reference.

The invention and the technical environment will be described in more detail hereafter based on the figures. It should be noted that the invention shall not be limited by the shown exemplary embodiments. In particular, it is also possible, unless explicitly described otherwise, to extract partial aspects of the subject matter described in the figures, and to combine these with other components and/or findings from other figures and/or the present description. In the schematic drawings:

FIG. 1 shows a diagram of a device that can be used to carry out a method according to the invention;

FIG. 2 shows a detailed view of the device from FIG. 1;

FIG. 3 shows a time-temperature curve achievable by means of a method according to the invention; and

FIG. 4 shows a further time-temperature curve achievable by means of a method according to the invention.

FIG. 1 schematically shows a device 12 for heat treating a metal component 1, which can be used to carry out a method according to the invention. The device 12 comprises a first furnace 7, a temperature control station 8, a second furnace 9, and a press hardening tool 11. The device 12 represents a hot forming line for press hardening here.

The temperature control station 8 is located (directly) downstream of the first furnace 7, so that a component 1 to be treated by means of the device 12 can be transferred directly into the temperature control station 8 upon leaving the first furnace 7. Furthermore, the second furnace 9 is located (directly) downstream of the temperature control station 8, and the press hardening tool 11 is located (directly) downstream of the second furnace 9.

FIG. 2 schematically shows a detailed view of the device from FIG. 1. FIG. 2 shows the temperature control station 8 of the device from FIG. 1 in more detail. A nozzle 3, which discharges a fluid stream 4 toward a first sub-region 2 of the component so as to (actively) cool this first sub-region 2 by way of convection, is disposed in the temperature control station 8. By way of example, the nozzle 3 is operated at a positive pressure of 5 bar. For this purpose, the nozzle is connected on the inlet side to a compressor 13. Moreover, a heating unit 11, which is provided and configured for inputting thermal energy into a second sub-region 6 of the component 1, is disposed in the temperature control station 8. For this purpose, the heating unit 11 is designed as an electrically operated heating wire, for example.

FIG. 3 schematically shows a time-temperature curve achievable by means of a method according to the invention. The temperature T of the metal component is, or the temperatures T of the at least one first sub-region and of the at least one second sub-region of the component are, plotted against the time t.

According to the time-temperature curve shown in FIG. 3, the metal component 1 is first uniformly heated to a temperature below the Ac1 temperature up until the point in time t₁. By way of example, this heating takes place in a first furnace 2 here. Between the points in time t₁ and t₂, the metal component is transferred from the first furnace into a temperature control station. The component temperature may decrease slightly during this process, for example due to heat emission to the surrounding area.

Between the points in time t₂ and t₃, at least one first sub-region of the component is (actively) cooled in the temperature control station. This is illustrated in FIG. 3 based on the bottom time-temperature curve between the points in time t₂ and t₃. At the same time, at least one second sub-region of the component is (slightly) heated in the temperature control station. This is illustrated in FIG. 3 based on the top time-temperature curve between the points in time t₂ and t₃. In this way, a temperature difference 5 is set in the temperature control station between the at least one first sub-region and at least one second sub-region of the component.

Between the points in time t₃ and t₄, the component is transferred from the temperature control station into a second furnace different from the first furnace. The partially differing temperatures set in the temperature control station may decrease slightly during this process, for example due to heat emission to the surrounding area.

The component is heated in the second furnace from the point in time t₄ to the point in time t₅ in such a way that the temperature of the at least one first sub-region of the component is increased by at least 150 K. Furthermore, the heating in the second furnace takes place in such a way that, at the same time, the temperature of the at least one second sub-region of the component is brought to a temperature above the Ac3 temperature.

Between the points in time t₅ and t₆, the component is transferred from the second furnace into a press hardening tool. The partially differing temperatures set in the second furnace may decrease slightly during this process, for example due to heat emission to the surrounding area.

From the point in time t₆ until the end of the process, the (entire) component is quenched in the press hardening tool. It is possible for a martensitic microstructure to be produced at least partially or even predominantly in the at least one second sub-region of the component, which has comparatively high strength and comparatively low ductility. Essentially no transformation has taken place in the at least one first sub-region of the component since the at least one first sub-region of the component has not exceeded the Ac1 temperature at any point during the process, so that a predominantly ferritic microstructure remains in the at least one first sub-region of the component, which has comparatively low strength and comparatively high ductility.

FIG. 4 schematically shows a further time-temperature curve achievable by means of a method according to the invention. Initially, the metal component is uniformly heated to a temperature above the Ac3 temperature up until the point in time t₁. By way of example, this heating takes place in a first furnace here.

Between the points in time t₁ and t₂, the metal component is transferred from the first furnace into a temperature control station. The component temperature may decrease slightly during this process. Between the points in time t₂ and t₃, at least one first sub-region of the component is (actively) cooled in the temperature control station. This is illustrated in FIG. 4 based on the bottom time-temperature curve between the points in time t₂ and t₃. At the same time, the temperature of at least one second sub-region of the component may decrease slightly in the temperature control station. This is illustrated in FIG. 4 based on the top time-temperature curve between the points in time t₂ and t₃. This (passive) decrease in temperature in the at least one second sub-region of the component has a considerably lesser cooling rate than the simultaneous (active) cooling of the at least one first sub-region of the component. It is apparent from FIG. 4 that a temperature difference 5 is set between the at least one first sub-region and at least one second sub-region of the component in the temperature control station.

Between the points in time t₃ and t₄, the component is transferred from the temperature control station into a second furnace different from the first furnace. The partially differing temperatures set in the temperature control station may decrease slightly during this process.

The component is heated in the second furnace from the point in time t₄ to the point in time t₅ in such a way that the temperature of the at least one first sub-region of the component is increased by at least 150 K. Moreover, the heating in the second furnace takes place in such a way that, at the same time, a cooling rate of the at least one second sub-region of the component is reduced compared to a cooling rate during heat emission to the surrounding area.

Between the points in time t₅ and t₆, the component is transferred from the second furnace into a press hardening tool. The partially differing temperatures set in the second furnace may decrease slightly during this process, for example due to heat emission to the surrounding area.

From the point in time t₆ until the end of the process, the (entire) component is quenched in the press hardening tool. It is possible for a martensitic microstructure to be produced at least partially or even predominantly in the at least one second sub-region of the component, which has comparatively high strength and comparatively low ductility. It is possible for a bainitic microstructure to be produced at least partially or even predominantly in the at least one first sub-region of the component, which has comparatively low strength and comparatively high ductility.

LIST OF REFERENCE NUMERALS

1 component

2 first sub-region

3 nozzle

4 fluid stream

5 temperature difference

6 second sub-region

7 first furnace

8 temperature control station

9 second furnace

10 press hardening tool

11 heating unit

12 device

13 compressor

Claims

1. A method for heat treating a metal component, wherein the method comprising: convectively cooling at least one first sub-region of the component by means of at least one nozzle discharging a fluid stream toward the first sub-region, so that a temperature difference of at least 100 K is set between the at least one first sub-region and at least one second sub-region of the component, the at least one nozzle being operated at a positive pressure of at least 2 bar.

2. The method according to claim 1, further comprising, prior to cooling, heating at least the at least one first sub-region of the component by at least 500 K.

3. The method according to claim 1, further comprising, after cooling, heating at least the at least one first sub-region of the component by at least 100 K.

4. A method for heat treating a metal component, comprising at least the following steps:

a) heating the component in a first furnace;

b) moving the component into a temperature control station;

c) convectively cooling at least one first sub-region of the component in the temperature control station by means of at least one nozzle discharging a fluid stream toward the first sub-region, wherein a temperature difference is set between the at least one first sub-region and at least one second sub-region of the component, and wherein the at least one nozzle is operated at a positive pressure of at least 2 bar.

5. The method according to claim 4, the method furthermore further comprising at least the following steps:

d) moving the component from the temperature control station into a second furnace; and

e) heating at least the at least one first sub-region of the component in the second furnace by at least 100 K.

6. The method according to claim 4, further comprising at least the following steps:

f) moving the component from the temperature control station or from the second furnace into a press hardening tool; and

g) forming and cooling the component in the press hardening tool.

7. The method according to claim 4, wherein the component is heated in step a) to a temperature below the Ac3 temperature.

8. The method according to claim 4, wherein the component is heated in step a) to a temperature above the Ac3 temperature.

9. The method according to claim 4, wherein the at least one first sub-region is cooled in step c) by way of convection to a temperature below the Ac1 temperature.

10. Use of at least one nozzle operated at a positive pressure of at least 2 bar for convectively cooling at least one first sub-region of a metal component so that a temperature difference of at least 100 K is set between the at least one first sub-region and at least one second sub-region of the component.