JP7261267B2 - Heat treatment method and heat treatment apparatus - Google Patents

Description

The present invention relates to a method and apparatus for heat treating a steel member, specifically targeting individual regions of the steel member.

In the technical field, high strength, low weight sheet metal members are desired for many applications in various sectors. For example, the automotive industry is trying to reduce vehicle fuel consumption and _CO2 emissions while at the same time improving passenger safety. Accordingly, there is a rapidly growing demand for vehicle body components with a favorable strength-to-weight ratio. Such parts include in particular front pillars, center pillars, door side impact protection beams, sills, frame parts, bumpers, cross members for floor and roof, front and rear side members. In modern automobiles, the body shell with the safety cage is usually constructed from hardened steel sheets with a strength of about 1,500 MPa. Here, Al—Si plated steel sheets are often used. A so-called press hardening process has been developed for producing hardened steel parts. In this process, the steel sheet is first heated to the austenite temperature and then placed in press tools for rapid forming and rapid quenching below the martensite start temperature in water-cooled tools. A hard and strong martensite structure having a strength of about 1,500 MPa is thus produced. However, since such a hardened steel sheet has a low elongation at break, it cannot appropriately convert the kinetic energy of collision into deformation heat.

Therefore, for the automobile industry, on the one hand, the area that tends to be rigid (hereinafter referred to as the first area) and, on the other hand, the area that tends to be ductile (hereinafter referred to as the second area) is one. It would be desirable to be able to produce a body part having multiple sections of varying elongation and strength within a single member. On the one hand, high-strength parts are in principle desirable in order to obtain parts with high mechanical load capacity and low weight. On the other hand, even high-strength parts should be able to have partially soft areas. This can enhance the desirable partial impact deformability. Thus, the kinetic energy of the crash can be dissipated to minimize acceleration forces on passengers and other parts of the vehicle. Modern joining processes also require a softening point that allows joining of the same or dissimilar materials. For example, seams, crimped joints, riveted joints must often be used, requiring deformable areas in the parts.

In this regard, there is also a general demand for manufacturing facilities, where there is no loss of cycle time in press hardening plants, the entire facility can be used largely unrestricted, and can be quickly changed from product to product. be. A robust and economical process is required and the manufacturing facility should require only minimal space. High precision is required for the shape and edging of parts.

In all known methods, the targeted heat treatment of the part is performed in a time-intensive process step, which significantly impacts the cycle time of the entire heat treatment apparatus.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and apparatus for heat treating a steel member specifically directed to individual regions of the steel member, such that regions of differing hardness and ductility are obtained and the effect on the cycle time of the entire heat treatment device is reduced. The object is to specify a heat treatment method and apparatus for minimizing the heat treatment.

According to the invention, this object is achieved by a device having the features of independent claim 1 . Advantageous embodiments of the device result from the dependent claims 2-9.

The steel member is first heated to below the austenite temperature Ac3. The steel member is then transferred to a processing station. Here, the one or more second regions are cooled as quickly as possible within the processing time _tB . In a preferred embodiment of this thermal processing apparatus, the processing stations are provided with positioning devices, by which precise positioning of the individual regions is ensured. In a preferred embodiment of the method described above, the rapid cooling of the second zone or zones is effected by blowing a gaseous fluid, eg air or an inert gas. For this purpose, in a preferred embodiment, the treatment station is equipped with a device for spraying one or more second areas. The device may, for example, comprise one or more nozzles. In a preferred embodiment of the method described above, the spraying of the one or more second regions is for example a gaseous fluid to which water is added in an atomized form. For this purpose, in one preferred embodiment, the device is equipped with one or more spray nozzles. Blowing the water-added gaseous fluid increases heat dissipation from the second region or regions. At the end of the treatment time _tB , the one or more second regions reach the final cooling temperature _θS . This processing time t _B is typically in the range of seconds. In this case, the second zone or zones can even be cooled well below the martensite start temperature M _S . This martensite start temperature M _s is, for example, about 410° C. for the commonly used car body structural steel 22MnB5. In the treatment station, the first region or regions are not specially treated, ie sprayed, heated or cooled by other special means. The one or more first regions cool slowly in the processing station, for example by natural convection. It has proved advantageous to take measures to limit the heat loss of the first zone or zones in the treatment station. Such means include, for example, attaching heat radiation reflectors to portions of one or more of the first regions and/or applying a heat insulating treatment to the surface of the processing station.

After that, that is, when the processing time _tB ends, the steel member is transferred to the second furnace. In this second furnace, the entire steel member is heated. This heating can be done, for example, by thermal radiation. Here, the steel member remains in the second furnace for a residence time t ₁₃₀ measured such that the temperature of the first zone or zones rises above the Ac3 temperature. Since the temperature of the second zone or zones after the aforementioned method steps is much lower than the first zone or zones at the beginning of said residence time t ₁₃₀ , the residence time t At the end of ₁₃₀ the Ac3 temperature is never reached. The steel component can then be transferred to a press hardening tool where one or more first regions are fully austenitized while one or more second regions are not austenitized. Thereby, by quenching in the subsequent press hardening treatment, the one or more first regions form a martensitic structure with high strength values. In this way, the second region or regions have not been austenitized at any time and thus will have a ferrite-pearlite structure with low strength values and high ductility after the press hardening step.

According to the invention, the parts are transported after a few seconds in a processing station, which can also be equipped with a positioning device to ensure the correct positioning of each zone, to a second furnace, which is then assigned to the individual zones. It is preferred that no special equipment be provided for various treatments. In one embodiment, only a furnace temperature θ ₄ higher than the austenitizing temperature Ac3, ie, a substantially uniform temperature throughout the furnace interior space, is set. These individual regions can be sharply demarcated and the small temperature difference between these two regions minimizes distortion of the steel member. A slight spreading of the temperature level of this component has a beneficial effect on further processing in the press.

In one embodiment, a continuous heating furnace is preferably provided as the first furnace. Continuous furnaces are particularly suitable for mass production because they typically have a large capacity and can be recharged and operated inexpensively. On the other hand, a batch furnace such as a chamber furnace can also be used as the first furnace.

In one embodiment, the second furnace is preferably a continuously heated furnace.

When both the first furnace and the second furnace are configured as continuous heating furnaces, the residence time required for the one or more first and second zones depends on the setting of the conveying speed and the design of the length of each furnace. By doing so, it can be realized according to the length of the member. In this way, by using a heat treatment device and a pressing machine for subsequent press hardening, it is possible to avoid affecting the cycle time of the entire production line.

In another embodiment, the second furnace is a batch furnace, eg a chamber furnace.

In a preferred embodiment, the processing station includes apparatus for rapidly cooling one or more second regions of the steel member. In one preferred embodiment, the apparatus comprises a nozzle for blowing a gaseous fluid, for example air or an inert gas, such as nitrogen, onto one or more second regions of the steel member. For this purpose, in a preferred embodiment, the device is equipped with one or more spray nozzles. Blowing the water-added gaseous fluid increases heat dissipation from the second region or regions.

In another embodiment, the cooling of the second zone(s) is by thermal conduction, eg by contact with one or more dies having a much lower temperature than the steel member. The mold can be manufactured from a material with sufficient thermal conductivity for this purpose and/or can be cooled directly or indirectly. A combination of cooling methods is also conceivable.

By using the method according to the present invention and the heat treatment apparatus according to the present invention, a steel member having one or more first regions and/or second regions, respectively, which can also be produced in a complex manner, each region can be brought to the required treatment temperature very quickly in a well-matched manner, so that a corresponding temperature profile can be obtained economically.

According to the invention, using the illustrated method and the heat treatment apparatus according to the invention, the number of second regions can be set to almost any number. When performing this method, the second region or regions are not austenitized and will have similar low strength values after pressing as the original strength of the untreated steel component. The shape chosen for the subregions is also freely selectable. For example, punctate or linear regions can be formed, such as large regions. The positions of these regions are also irrelevant. The second region may be completely contained within the first region or located at the end of the steel member. A full surface treatment is also conceivable. A specific orientation of the steel member with respect to the throughput direction is not necessary for the purposes of the method according to the invention for the heat treatment of the steel member, which specifically targets individual regions of the steel member. At the same time, the limit on the number of steel members to be processed is maximized by the press hardening tools and conveyor technology of the heat treatment equipment as a whole. Likewise, it is possible to apply the method of the invention to preformed steel members. Due to the three-dimensionally shaped surfaces of the pre-formed steel members, only opposing faces can be formed, even at high cost of design.

Furthermore, it is preferred that even existing heat treatment facilities are adaptable to the method according to the invention. For this purpose, in the case of a conventional heat treatment apparatus with only one furnace, the treatment station and the second furnace need only be installed behind this. Depending on the configuration of the existing furnace, it may be possible to split this original furnace to form the first and second furnaces.

Further advantages, special features and suitable developments of the invention are indicated by the dependent claims and the following presentation of preferred embodiments with reference to the figures.

FIG. 4 shows a typical temperature curve for heat treatment of a steel member having first and second regions; It is the schematic which looked at the heat processing apparatus which concerns on this invention from the top. It is the schematic which looked at another heat processing apparatus which concerns on this invention from the top. It is the schematic which looked at another heat processing apparatus which concerns on this invention from the top. It is the schematic which looked at another heat processing apparatus which concerns on this invention from the top. It is the schematic which looked at another heat processing apparatus which concerns on this invention from the top. It is the schematic which looked at another heat processing apparatus which concerns on this invention from the top.

FIG. 1 shows a typical temperature curve for heat treatment of a steel member 200 having a first zone 210 and a second zone 220 according to the method of the present invention. This steel member 200 is heated in the first furnace 110 to a temperature below the Ac3 temperature according to the schematically drawn temperature curve θ _200,110 during a residence time t ₁₁₀ in the first furnace 110 . The steel member 200 is then transferred to the processing station 150 during transfer time _t120 , during which the steel member also loses heat. In this processing station, the second region 220 of the steel member 200 is rapidly cooled and this second region 220 loses heat according to the pull-in curve θ _220,150 . Spraying ends at the end of the treatment time t _B , which is only a few seconds depending on the thickness of the steel member 200 and the size of the second region 220 . In a first approximation, at processing station 150, processing time _tB is now equal to residence time _t150 . At this point, the second region 220 reaches the final cooling temperature _θS . At the same time, the temperature of the first region 210 decreases at the processing station 150 according to the pull-in curve θ _210,150 . This first area 210 is not located in the area of the cooling device. At the end of treatment time _tB , steel member 200 is transferred to second furnace 130 during transfer time _t121 where it loses more heat. In this second furnace 130, the temperature of the first region 210 of the steel member 200 changes according to the general draw-in temperature curve θ 210, ₁₃₀ during the residence time t ₁₃₀ , i.e. the temperature of the first region 210 of the steel member 200 The temperature is heated to a temperature above the Ac3 temperature. The temperature of the second region 220 of the steel member 200 also rises according to the draw-in temperature curve θ 220, ₁₃₀ during the residence time t ₁₃₀ without reaching the Ac3 temperature. This second furnace 130 does not have special equipment for the various treatments of the individual zones 210,220. Only the furnace temperature θ ₄ higher than the austenitizing temperature Ac3, ie the temperature θ ₄ which is substantially uniform throughout the inner space of the second furnace 130, is set. The temperature of the second zone or zones is much lower than the first zone or zones at the beginning of the residence time t ₁₃₀ in the second furnace 130, where both zones are Since they are heated similarly, at the end of residence time t ₁₃₀ both will have different temperatures as well. The residence time t ₁₃₀ of the steel member 200 in the second furnace 130 is measured such that the one or more first zones have a temperature above the Ac3 temperature at the end of the residence time t ₁₃₀ , at which point One or more second regions have not yet reached the Ac3 temperature.

The steel member can then be transferred to a press hardening tool 160 installed in a press (not shown) during transfer time _t131 . The steel member 200 likewise loses heat during this transfer time _t131 , and the temperature of said first zone(s) also drops below the Ac3 temperature. However, this or these regions are almost completely austenitized on exiting the second furnace 130 . This causes a transformation to a hard martensite structure by quenching during residence time t ₁₆₀ in press hardening tool 160 .

These individual regions 210 , 220 can be sharply demarcated between these two regions 210 , 220 and the small temperature difference minimizes distortion of the steel member 200 . The slightly spread out temperature level of the steel member 200 has a beneficial effect on further processing in the press hardening tool 160 . The required residence time t ₁₃₀ of the steel member 200 in the second furnace 130 can be realized according to the length of the steel member 200 by setting the conveying speed and designing the length of the second furnace 130 . In this way, the effect on the cycle time of thermal processing apparatus 100 is minimized and can even be avoided entirely.

FIG. 2 is a diagram showing the heat treatment apparatus 100 according to the present invention in a 90 degree arrangement. This heat treatment apparatus 100 comprises a loading station 101 through which a first furnace 110 is supplied with steel components. In the heat treatment apparatus 100, a treatment station 150 and a second furnace 130 are arranged in the main throughput direction D behind it. Further behind it in the main throughput direction D is arranged a removal station 131 with a positioning device (not shown). The main throughput direction D is then bent at approximately 90 degrees to be followed by a press hardening tool 160 in a press (not shown) that press hardens the steel member 200 . In the axial direction of the first furnace 110 and the second furnace 130 are arranged containers 161 into which defective parts are sent. The first furnace 110 and the second furnace 130 are preferably arranged in this manner as a continuously heated furnace, eg, a roller hearth furnace.

FIG. 3 is a diagram showing a heat treatment apparatus 100 according to the present invention in a linear arrangement. This heat treatment apparatus 100 comprises a loading station 101 through which a first furnace 110 is supplied with steel parts. The heat treatment apparatus 100 also comprises a treatment station 150 behind which in the main throughput direction D a second furnace 130 is arranged. Further behind it in the main throughput direction D is arranged a removal station 131 with a positioning device (not shown). A press hardening tool 160 in a press (not shown) for press hardening the steel member 200 is then subsequently arranged in the main throughput direction D, which continues to extend linearly. A container 161 is then placed at approximately 90 degrees to the removal station 131 into which the defective parts are fed. The first furnace 110 and the second furnace 130 are likewise preferably arranged in this manner as continuous heating furnaces, eg, roller hearth furnaces.

FIG. 4 is a diagram showing another modification of the heat treatment apparatus 100 according to the present invention. Again, the heat treatment apparatus 100 comprises a loading station 101 through which a first furnace 110 is supplied with steel components. This first furnace 110 is preferably formed as a continuous heating furnace in this embodiment as well. The thermal processor 100 also includes a processing station 150 , which in this embodiment is combined with the removal station 131 . This removal station 131 may also comprise, for example, a gripper device (not shown). The removal station 131 performs removal of the steel member 200 from the first furnace 110, for example by means of its gripper device. A heat treatment, including a cooling treatment, of one or more second zones 220 is performed, and the one or more steel members 200 are transferred into a second furnace 130 positioned at approximately 90 degrees to the axis of the first furnace 110. thrown in. This second furnace 130 is preferably provided in this embodiment as a chamber furnace, for example with several chambers. When the residence time t ₁₃₀ of the steel member 200 in the second furnace 130 expires, the steel member 200 is removed from the second furnace 130 via a removal station 131 and transferred to an opposite press (not shown). It is loaded into the integrated press hardening tool 160 . The removal station 131 may be equipped with a positioning device (not shown) for this purpose. Axially to the first furnace 110, behind the removal station 131, a container 161 is arranged into which defective parts can be fed. In this example, the main throughput direction D exhibits a deflection of approximately 90 degrees. In this embodiment, a second positioning system for processing station 150 is not required. Moreover, this embodiment is advantageous, for example, in the case where sufficient space is not secured in the axial direction of the first furnace 110 in the manufacturing hall. In this embodiment as well, the second region 220 of the steel member 200 can be cooled between the removing station 131 and the second furnace 130, so the stationary processing station 150 is not required. For example, a cooling device, eg a blow nozzle, can be integrated into the gripper device. Removal device 131 manages the transfer of steel member 200 from first furnace 110 to second furnace 130 and further to press hardening tool 160 or vessel 161 .

In this embodiment, as can also be seen from FIG. 5, the positions of the press hardening tool 160 and the container 161 can be interchanged. In this example, the main throughput direction D exhibits two deflections of approximately 90 degrees.

When the installation space of the heat treatment equipment is limited, a heat treatment equipment shown in FIG. 6 is proposed in which the second furnace 130 is moved to the second level above the first furnace 110 compared to the embodiment shown in FIG. be. In this embodiment as well, the second region 220 of the steel member 200 can be cooled between the removing station 131 and the second furnace 130, so the stationary processing station 150 is not required. Similarly, it is preferred to provide the first furnace 110 as a continuous heating furnace and the second furnace 130 as a chamber furnace, possibly with several chambers.

Finally, a final embodiment of the heat treatment apparatus of the invention is shown schematically in FIG. Compared to the embodiment shown in FIG. 6, the positions of press hardening tool 160 and container 161 have been interchanged.

The examples presented herein are merely illustrative of the present invention and should not be understood as limiting. Other embodiments considered by persons skilled in the art shall likewise fall within the protection scope of the present invention.

100 heat treatment apparatus 110 first furnace 130 second furnace 131 removal station 135 removal station 150 treatment station 152 point infrared radiator 153 heating panel 160 press hardening tool 161 container 200 steel member 210 first zone 220 second zone D main throughput direction Ms Martensite start temperature t _B treatment time t ₁₁₀ Residence time in first furnace t ₁₂₀ Transfer time of steel parts to treatment station t ₁₂₁ Transfer time of steel parts to second furnace t ₁₃₀ Residence time in second furnace t ₁₃₁ Steel member transfer time to press hardening tool t Residence time at ₁₅₀ treatment station t Residence time at ₁₆₀ press hardening tool θ _S Final cooling temperature θ ₃ Internal temperature of first furnace θ ₄ Internal temperature of second furnace θ _{200, 110} Temperature curve θ _{210, 150} of the steel member in the first furnace θ 210, 150 Temperature curve θ _{210, 150} of the first region of the metal member in the processing station Temperature curve θ _{210, 130} of the second region of the steel member in the processing station Temperature curve θ _{220, 130} of the first region of the steel member in the furnace Temperature curve θ 200, ₁₆₀ of the second region of the steel member in the second furnace Temperature curve of the steel member in the press hardening tool

Claims (7)

A heat treatment apparatus (100) comprising a first furnace (110) for heating a steel member (200) to a temperature below the Ac3 temperature, for heat treating individual regions of the steel member (200) in a desired manner,
The heat treatment apparatus (100) further comprises a treatment station (150) and a second furnace (130),
said steel member (200) is transferable from said first furnace (110) to said processing station (150);
said steel member (200) is transferable from said processing station (150) to said second furnace (130);
said processing station (150) comprising a device for cooling one or more second regions (220) of said steel member (200);
The device for cooling one or more second regions (220) of the steel member (200) comprises a nozzle for blowing a gaseous fluid onto one or more second regions (220) of the steel member (200). equipped with
Said second furnace (130) is equipped with a device for introducing heat and is heated to a uniform temperature θ ₄ , thereby heating at least one or more first regions (210) of said steel member (200) to said can be heated to a temperature above the Ac3 temperature,
A heat treatment apparatus (100) characterized by: The apparatus for cooling one or more of the second regions (220) of the steel member (200) comprises adding water to one or more of the second regions (220) of the steel member (200). having a nozzle for spraying a gaseous fluid,
The thermal processing apparatus (100) of claim 1 , characterized in that: The device for cooling one or more of the second regions (220) of the steel member (200) includes a mold contacting one or more of the second regions (220) of the steel member (200). is equipped with
A heat treatment apparatus (100) according to claim 1 or 2 , characterized in that: The mold that contacts one or more of the second regions (220) of the steel member (200) is configured to be cooled,
The thermal processing apparatus (100) according to claim 3 , characterized in that: said processing station (150) comprises a positioning device;
A heat treatment apparatus (100) according to any one of claims 1 to 4 , characterized in that: the processing station (150) comprises a heat reflector;
A heat treatment apparatus (100) according to any one of claims 1 to 5 , characterized in that: The processing station (150) has an insulating wall,
The thermal processing apparatus (100) according to any one of claims 1 to 6 , characterized in that:

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