HEAT TREATMENT METHOD AND HEAT TREATMENT DEVICE

Abstract

The invention relates to a method and to a device for the heat treatment of a steel component directed specifically at individual zones of the component. In one or more first regions of the steel component a primarily austenitic structure can be set, from which, by quenching, a predominantly martensitic structure can be produced, and in one or more second regions of the steel component there is a predominantly ferritic-pearlitic structure. The steel component is first of all heated in a first furnace to a temperature below the Ac3 temperature, and the steel component is then transferred into a handling station. During the transfer the steel component can cool, and in the handling station, one or more second regions of the steel component are cooled within a residence time t.sub.150 to a final cooling temperature ?.sub.S, and is then transferred to a second furnace, in which heat is delivered to the steel component. The temperature of the one or more second regions increases again during the residence time t.sub.130 to a temperature below the Ac3 temperature, whilst the temperature of the one or more first regions is heated in the same residence time t.sub.130 to a temperature above the Ac3 temperature.

Claims

1. A method for the heat treatment of a steel component directed specifically at individual zones of the component, wherein in one or more first regions of the steel component a primarily austenitic structure can be set, from which, by quenching, a predominantly martensitic structure can be produced, and in one or more second regions a predominantly ferritic-pearlitic structure can be set, the method comprising: first heating the steel component in a first furnace to a temperature below the Ac3 temperature, transferring the steel component to a handling station, wherein the steel component is cooled cool during the transfer, cooling in the handling station the one or more second regions of the steel component within a residence time t.sub.150 to a final cooling temperature ?S, and transferring the steel component to a second furnace, in which heat is delivered to the steel component, wherein the temperature of the one or more second regions increases again during the residence time t.sub.130 to a temperature below the Ac3 temperature, whilst the temperature of the one or more first regions is heated in the same residence time t.sub.130 to a temperature above the Ac3 temperature.

2. The method according to claim 1, wherein heat supply in the second furnace is achieved via thermal radiation.

3. The method according to claim 1, wherein the one or more second regions of the steel component are blown with a gaseous fluid in the handling station within a residence time t.sub.150 for cooling.

4. The method according to claim 3, wherein the gaseous fluid contains water.

5. The method according to claim 1, wherein the cooling of the one or more second regions of the steel component takes place in the handling station within a residence time t.sub.150 via thermal conduction.

6. The method according to claim 5, wherein the one or more second regions of the steel component are brought into contact with a die in the handling station within a residence time t.sub.150 for cooling, wherein the die has a lower temperature than the second region or regions.

7. The method according to claim 1, wherein the internal temperature ?4 in the second furnace is greater than the Ac3 temperature.

8. A heat treatment device, including a first furnace for heating a steel component to a temperature below Ac3 temperature, wherein the heat treatment device further includes a handling station and a second furnace, wherein the handling station includes a device for the rapid cooling of one or more second regions of the steel component and the second furnace includes a device for the introduction of heat, with which at least the first region or first regions of the steel component can be heated to a temperature greater than the Ac3 temperature.

9. The heat treatment device according to claim 8, wherein the device for the rapid cooling of one or more second regions of the steel component has a nozzle for blowing the second region or regions of the steel component with a gaseous fluid.

10. The heat treatment device (100) according to claim 8, wherein the device for the rapid cooling of one or more second regions of the steel component has a nozzle for blowing the second region or regions of the steel component with a gaseous fluid, to which water is added.

11. The heat treatment device according claim 8, wherein the device for the rapid cooling of one or more second regions of the steel component includes dies for contacting the second region or regions of the steel component.

12. The heat treatment device according to claim 11, wherein the die for contacting the one or more second regions of the steel component is executed to be coolable.

13. The heat treatment device according to claim 8, wherein in that the handling station has a positioning device.

14. The heat treatment device according to claim 8, wherein the second furnace is heated to a substantially homogeneous temperature ?4.

15. The heat treatment device according to claim 8, wherein the handling station includes heat reflectors.

16. The heat treatment device according to claim 8, wherein the handling station includes thermally insulated walls.

Description

[0021] Further advantages, special features and expedient developments of the invention result from the subordinate Claims and the following representation of preferred exemplary embodiments with reference to the illustrations.

[0022] Of the illustrations,

[0023] FIG. 1 shows a typical temperature curve in the heat treatment of a steel component with a first and a second region

[0024] FIG. 2 shows a thermal heat treatment device according to the invention in a top view as a schematic drawing

[0025] FIG. 3 shows another thermal heat treatment device according to the invention in a top view as a schematic drawing

[0026] FIG. 4 shows another thermal heat treatment device according to the invention in a top view as a schematic drawing

[0027] FIG. 5 shows another thermal heat treatment device according to the invention in a top view as a schematic drawing

[0028] FIG. 6 shows another thermal heat treatment device according to the invention in a top view as a schematic drawing

[0029] FIG. 7 shows another thermal heat treatment device according to the invention in a top view as a schematic drawing.

[0030] FIG. 1 shows a typical temperature curve in the heat treatment of a steel component 200 with a first region 210 and a second region 220 according to the inventive method. The steel component 200 is heated in a first furnace 110 according to the temperature curve ?.sub.200,110 drawn in schematically during the residence time t.sub.110 in the first furnace to a temperature below the Ac3 temperature. The steel component 200 is then transferred with a transfer time t.sub.120 to the handling station 150. The steel component loses heat here. In the handling station a second region 220 of the steel component 200 is cooled quickly, wherein the second region 220 loses heat according to the drawn-in curve ?.sub.220,150. The blowing ends on expiry of the handling time t.sub.B, which is only a few seconds depending on the thickness of the steel component 200 and the size of the second region 220. In a first approximation, the handling time t.sub.B is equal here to the residence time t.sub.150 in the handling station 150. The second region 220 has now reached the final cooling temperature ?.sub.S. At the same time, the temperature of the first region 210 has fallen in the handling station 150 according to the drawn-in temperature curve ?.sub.210,150, wherein the first region 210 is not located in the area of the cooling device. On expiry of the handling time t.sub.B, the steel component 200 is transferred during transfer time t.sub.121 to the second furnace 130, wherein it loses further heat. In the second furnace 130, the temperature of the first region 210 of the steel component 200 changes according to the schematically drawn-in temperature curve ?.sub.210,130 during the residence time t.sub.130, i.e. the temperature of the first region 210 of the steel component 200 is heated to a temperature above the Ac3 temperature. The temperature of the second region 220 of the steel component 200 also rises according to the drawn-in temperature curve ?.sub.220,130 during the residence time t.sub.130 without reaching the Ac3 temperature. The second furnace 130 has no special devices for the different treatment of the various regions 210, 220. Only a furnace temperature ?.sub.4, i.e. a substantially homogeneous temperature ?.sub.4 in the entire interior space of the second furnace 130, is set, which is above the austenitization temperature Ac3. Since the second region or second regions have a much lower temperature than the first region or regions at the beginning of the residence time t.sub.130 in the second furnace 130 and both regions are heated equally in the second furnace 130, at the end of the residence time t.sub.130 they have a likewise different temperature. The residence time t.sub.130 of the steel component 200 in the second furnace 130 is measured so that the first region or the first regions have a temperature at the end of the residence time t.sub.130 that is above the Ac3 temperature, while the second region or second regions have not yet reached the Ac3 temperature at this point.

[0031] The steel component can then be transferred during a transfer time t.sub.131 to a press hardening tool 160, which is installed in a press, which is not shown. During the transfer time t.sub.131 the steel component 200 again loses heat, so that the temperature of the first region or regions can also fall below the Ac3 temperature. This region or these regions are substantially completely austenitized, however, when they leave the second furnace 130, so that due to quenching during a residence time t.sub.160 in the press hardening tool 160 they experience a transformation to a hard martensitic structure.

[0032] Clearly outlined delimitations of the individual regions 210, 220 can be realized between the two regions 210, 220 and due to the small temperature difference the distortion of the steel component 200 is minimized. Small spreads in the temperature level of the steel component 200 have an advantageous effect in the further processing in the press hardening tool 160. The necessary residence time t.sub.130 of the steel component 200 in the second furnace 130 can be realized as a function of the length of the steel component 200 by way of the setting of the conveying speed and the design of the length of the second furnace 130. Influencing of the cycle time of the heat treatment device 100 is minimized thus and can even be avoided entirely.

[0033] FIG. 2 shows a heat treatment device 100 according to the invention in a 90? arrangement. The heat treatment device 100 has a loading station 101, via which steel components are supplied to the first furnace 110. The heat treatment device 100 also has the handling station 150 and the second furnace 130 arranged behind it in the main throughput direction D. Arranged further behind in the main throughput direction D is a removal station 131, which is equipped with a positioning device (not shown). The main throughput direction now bends by substantially 90? to let a press hardening tool 160 in a press (not shown) follow, in which the steel component 200 is press hardened. Arranged in the axial direction of the first furnace 110 and the second furnace 130 is a container 161, into which reject parts can be passed. The first furnace 110 and the second furnace 120 are preferably executed in this arrangement as continuous furnaces, for example roller hearth furnaces.

[0034] FIG. 3 shows a heat treatment device 100 according to the invention in a straight arrangement. The heat treatment device 100 has a loading station 101, via which steel components are supplied to the first furnace 110. The heat treatment device 100 also has the handling station 150 and arranged behind it in the main throughput direction D the second furnace 130. Arranged further behind in the main throughput direction D is a removal station 131, which is equipped with a positioning device (not shown). Also following in the main throughput direction, which continues to be linear, is a press hardening tool 160 in a press (not shown), in which the steel component 200 is press hardened. Arranged substantially at 90? to the removal station 131 is a container 161, into which reject parts can be passed. The first furnace 110 and the second furnace 120 are likewise preferably executed as continuous furnaces, for example roller hearth furnaces, in this arrangement.

[0035] FIG. 4 shows another variant of a heat treatment device 100 according to the invention. Once again the heat treatment device 100 has a loading station 101, via which steel components are supplied to the first furnace 110. The first furnace 110 is again preferably formed as a continuous furnace in this implementation. The heat treatment device 100 also has the handling station 150, which is combined in this embodiment with a removal station 131. The removal station 131 can have a gripper device (not shown), for example. The removal station 131 removes the steel components 200 from the first furnace 110 by means of the gripper device, for example. The heat treatment with the cooling of the second region or second regions 220 is carried out and the steel component or steel components 200 are placed into a second furnace 130 arranged substantially at 90? to the axis of the first furnace 110. This second furnace 130 is preferably provided in this embodiment as a chamber furnace, for example with several chambers. On expiry of the residence time t.sub.130 of the steel components 200 in the second furnace 130, the steel components 200 are removed from the second furnace 130 via the removal station 131 and placed into a press hardening tool 160 integrated into a press (not shown) lying opposite. The removal station 131 can have a positioning device (not shown) for this. Arranged in the axial direction of the first furnace 110 behind the removal station 131 is a container 161, into which reject parts can be passed. The main throughput direction D in this embodiment describes a deflection of substantially 90?. No second positioning system for the handling station 150 is necessary in this embodiment. Moreover, this embodiment is advantageous if insufficient space is available in an axial direction of the first furnace 110 in a production hall, for example. The cooling of the second regions 220 of the steel component 200 can also take place in this embodiment between removal station 131 and second furnace 130, so that no fixed handling station 150 is required. For example, a cooling device, for example a blowing nozzle, can be integrated into the gripper device. The removal device 131 takes care of the transfer of the steel component 200 from the first furnace 110 to the second furnace 130 and to the press hardening tool 160 or the container 161.

[0036] In this embodiment also the position of press hardening tool 160 and container 161 can be exchanged, as is to be seen in FIG. 5. The main throughput direction D in this embodiment describes two deflections of substantially 90?.

[0037] If the space for setting up the heat treatment device is limited, a heat treatment device according to FIG. 6 is suggested: compared with the embodiment shown in FIG. 4 the second furnace 130 is moved to a second level above the first furnace 110. In this embodiment also the cooling of the second regions 220 of the steel component 200 can likewise take place between removal station 131 and second furnace 130, so that no fixed handling station 150 is required. It is again advantageous to to execute the first furnace 110 as a continuous furnace and the second furnace 120 as a chamber furnace, possibly with several chambers.

[0038] Finally, a last embodiment of the inventive heat treatment device is shown schematically in FIG. 7. Compared with the embodiment shown in FIG. 6, the positions of press hardening tool 160 and container 161 are exchanged.

[0039] The embodiments shown here only represent examples of the present invention and may not therefore be understood in a restrictive manner. Alternative embodiments taken into consideration by the person skilled in the art are likewise covered by the scope of protection of the present invention.

REFERENCE SIGN LIST

[0040] 100 Heat treatment device [0041] 110 First furnace [0042] 130 Second furnace [0043] 131 Removal station [0044] 135 Removal station [0045] 150 Handling station [0046] 152 Punctiform infrared radiator [0047] 153 Heating panel [0048] 160 Press hardening tool [0049] 161 Container [0050] 200 Steel component [0051] 210 First region [0052] 220 Second region [0053] D Main throughput direction [0054] M.sub.S Martensite start temperature [0055] t.sub.B Handling time [0056] t.sub.110 Residence time in first furnace [0057] t.sub.120 Transfer time steel component to handling station [0058] t.sub.121 Transfer time steel component to second furnace [0059] t.sub.130 Residence time in second furnace [0060] t.sub.131 Transfer time steel component to press hardening tool [0061] t.sub.150 Residence time in handling station [0062] t.sub.160 Residence time in press hardening tool [0063] ?.sub.S Final cooling temperature [0064] ?.sub.3 Internal temperature of first furnace [0065] ?.sub.4 Internal temperature of second furnace [0066] ?.sub.200,110 Temperature curve of steel component in first furnace [0067] ?.sub.210,150 Temperature curve of first region of metal component in handling station [0068] ?.sub.220,150 Temperature curve of second region of steel component in handling station [0069] ?.sub.210,130 Temperature curve of first region of steel component in second furnace [0070] ?.sub.220,130 Temperature curve of second region of steel component in second furnace [0071] ?.sub.200,160 Temperature curve of steel component in press hardening tool