Heat treatment method and heat treatment device

Abstract

In one or more first regions of a steel component, a primarily austenitic microstructure can be produced from which a mainly martensitic microstructure can be brought about through a quenching process. In one or more second regions of the component, a mainly ferritic-pearlitic microstructure can be brought about. In one or more third regions, a mainly bainitic microstructure can be brought about. The component is first heated to a temperature below the AC3 temperature in a first furnace, and transferred into a treatment station. The component can be cooled during the transfer. In the treatment station, the first and third regions are brought to a temperature above the austenitization temperature. Only the third regions are cooled to a cooling stop temperature ϑs. The component is transferred into a second furnace, with a temperature lying below the AC3 temperature. There, the temperatures of the three different regions approximate one another.

Claims

1. A method for carrying out targeted heat-treatment of individual zones of a steel component, said method comprising: forming a primarily austenitic structure in a first region of the steel component, wherein the primarily austenitic structure, when quenched, forms a predominantly martensitic structure, forming a predominantly ferritic-pearlitic structure in a second region of the steel component, forming a primarily bainitic structure in a third region of the steel component, heating the steel component in a first furnace to a temperature that is below the AC3 temperature, transferring the steel component to a treatment station, cooling down said component while the component is being transferred, heating the first and third regions in the treatment station to a temperature that is above the AC3 temperature within a dwell time t151, cooling the third region to the cooling stop temperature ϑs, and transferring the steel component to a second furnace in which the steel component remains at a temperature that is below the austenitizing temperature until a sufficiently bainitic structure has been formed in the third region.

2. The method according to claim 1, further comprising supplying heat to the second furnace via thermal radiation.

3. The method according to claim 1, further comprising, within the treatment station, using a high-power laser to heat the first region to a temperature that is above the austenitizing temperature within a dwell time t151.

4. The method according to claim 1, further comprising, within the treatment station, using a high-power laser to heat the third region to a temperature that is above the austenitizing temperature within a dwell time t151.

5. The method according to claim 1, further comprising, within the treatment station, blowing a gaseous fluid against the third region within a dwell time t152 in order to cool them.

6. The method according to claim 5, wherein the gaseous fluid contains water.

7. The method according to claim 1, further comprising, within the treatment station, bringing the third region into contact with a punch within a dwell time t152 in order to cool the third region, the punch having a lower temperature than that of the third region.

8. The method according to claim 1, further comprising maintaining a temperature ϑ4 inside the second furnace to be lower than the AC3 temperature.

9. The method of claim 1, after a sufficiently bainitic structure has been formed in the third region, quenching the steel component.

10. The method of claim 1, after a sufficiently bainitic structure has been formed in the third region, press hardening the steel component.

Description

(1) Additional advantages, features and expedient developments of the invention can be found in the dependent claims and the following description of preferred embodiments on the basis of the drawings, in which:

(2) FIG. 1 shows a typical temperature curve when heat-treating a steel component comprising a first, second and a third region,

(3) FIG. 2 is schematic plan view of a thermal heat-treatment device according to the invention,

(4) FIG. 3 is a schematic plan view of another hermal heat-treatment device according to the invention,

(5) FIG. 4 is a schematic plan view of another hermal heat-treatment device according to the invention,

(6) FIG. 5 is a schematic plan view of another thermal heat-treatment device according to the invention,

(7) FIG. 6 is a schematic plan view of another thermal heat-treatment device according to the invention, and

(8) FIG. 7 is a schematic plan view of another thermal heat-treatment device according to the invention.

(9) FIG. 1 shows a typical temperature curve when heat-treating a steel component 200 comprising a first region 210, a second region 220 and a third region 230 according to the method of the invention. Several of each region can be provided, i.e. a plurality of first regions 210, a plurality of second regions 220 and a plurality of third regions 230 can be provided, it being possible to combine any number of regions. The steel component 200 is heated in the first furnace 110 to a temperature below the AC3 temperature during the dwell time t.sub.110 in accordance with the schematically drawn temperature profile ϑ.sub.200, 110. The steel component 200 is then transferred to the treatment station 150 at a transfer time t.sub.121. In this case, the steel component loses heat. In the treatment station, a first region 210 and a third region 230 of the steel component 200 is rapidly heated to above the austenitising temperature AC3 by means of laser radiation, the second region 220 losing heat in accordance with the profile ϑ.sub.220, 151 or ϑ.sub.220, 152 drawn. This takes place within a few seconds. Immediately thereafter, the third region 230 is rapidly cooled to the desired cooling stop temperature ϑ.sub.s in accordance with the temperature profile ϑ.sub.230, 152 drawn. In this case, the cooling stop temperature ϑ.sub.s between the individual partial surfaces of the third regions 230 can be different if it is desirable for the third regions 230 within one component to have variable material properties. The third region 230 can be rapidly cooled by a gaseous fluid being blown therein, for example.

(10) No more fluid is blown in once the cooling time t.sub.152 has elapsed, which only lasts for a few seconds depending on the thickness of the steel component 200. The third region 230 has now reached the cooling stop temperature ϑ.sub.s. At the same time, the temperature of the first region 210 and of the second region 220 in the treatment station 150 has also fallen in accordance with the temperature profiled ϑ.sub.210, 152 or ϑ.sub.220, 151, ϑ.sub.220, 152 drawn.

(11) Once the dwell time t.sub.150 in the treatment station 150 has elapsed, the steel component 200 is transferred to the second furnace 130 during the transfer time t.sub.122. In the second furnace 130, the temperature of the first region 210 of the steel component 200 changes during the dwell time t.sub.130 in accordance with the schematically drawn temperature profile ϑ.sub.210, 130. The temperature of the second region 220 of the steel component 200 also behaves in accordance with the temperature profile ϑ.sub.220, 130 drawn during the dwell time t.sub.130, said temperature profiles not reaching the AC3 temperature. The temperature of the third region 230 of the steel component 200 also behaves in accordance with the temperature profile ϑ.sub.230, 130 drawn during the dwell time t.sub.130, without reaching the AC3 temperature.

(12) The second furnace 130 does not comprise any special devices for treating the different regions 210, 220, 230 in different ways. Merely one furnace temperature ϑ.sub.4, i.e. a substantially homogeneous temperature ϑ.sub.4 is set in the overall interior of the second furnace 130, which is below the austenitising temperature AC3.

(13) The steel component can then be transferred during a transfer time t.sub.140 to a press-hardening die 160, which is integrated in a press (not shown).

(14) Clearly contoured boundaries can be formed between the regions 210, 220, 230 and the small temperature difference minimizes warpage of the steel component 200. Small expansions in the temperature level of the steel component 200 have an advantageous effect during further processing in the press-hardening die 160. The necessary dwell time t.sub.130 of the steel component 200 in the second furnace 130 can be set on the basis of the length of the steel component 200 by setting the conveying speed and choosing the length of the second furnace 130. The cycle time of the heat-treatment device 100 is thereby minimally affected, or may not even be affected at all.

(15) FIG. 2 shows a heat-treatment device 100 according to the invention in a 90° arrangement. The heat-treatment device 100 comprises a loading station 101, by means of which steel components are fed to the first furnace 110. Furthermore, the heat-treatment device 100 comprises the treatment station 150 and, arranged downstream thereof in the main direction of flow D, the second furnace 130. Arranged further downstream in the main direction of flow D is a removal station 140, which is provided with a positioning device (not shown). The main direction of flow then deviates by substantially 90° in order to match a press-hardening die 160 in a press (not shown), in which die the steel component 200 is press-hardened. A container 161 is arranged in the axial direction of the first furnace 110 and of the second furnace 130, in which container rejects can be placed. In this arrangement, the first furnace 110 and the second furnace 130 are preferably formed as continuous furnaces, for example roller hearth furnaces.

(16) FIG. 3 shows a straight-line arrangement of a heat-treatment device 100 according to the invention. The heat-treatment device 100 comprises a loading station 101, by means of which steel components are fed to the first furnace 110. Furthermore, the heat-treatment device 100 comprises the treatment station 150 and, arranged downstream thereof in the main direction of flow D, the second furnace 130. Arranged further downstream in the main direction of flow D is a removal station 140, which is provided with a positioning device (not shown). A press-hardening die 160 in a press (not shown), in which the steel component 200 is press-hardened, then follows in the main direction of flow that now continues in a straight line. A container 161 is substantially arranged at 90° to the removal station 131, in which container rejects can be placed. In this arrangement, the first furnace 110 and the second furnace 130 are likewise preferably formed as continuous furnaces, for example roller hearth furnaces.

(17) FIG. 4 shows another variant of a heat-treatment device 100 according to the invention. The heat-treatment device 100 again comprises a loading station 101, by means of which steel components are fed to the first furnace 110. In this embodiment, the first furnace 110 is again preferably formed as a continuous furnace. Furthermore, the heat-treatment device 100 comprises the treatment station 150, which is combined with a removal station 131 in this embodiment. The removal station 140 can comprise a gripping device (not shown), for example. In the removal station 140, the steel components 200 are removed from the first furnace 110 by means of the gripping device, for example. The second region or second regions 220 and/or the third region or third regions 230 is/are heat-treated and the steel component or the steel components 200 is/are loaded in a second furnace 130 that is arranged at substantially 90° to the axis of the first furnace 110. In this embodiment, this second furnace 130 is preferably provided as a chamber furnace, for example comprising a plurality of chambers. Once the dwell time t.sub.130 of the steel components 200 in the second furnace 130 has elapsed, the steel components 200 are removed from the second furnace 130 via the removal station 140 and placed in an opposite press-hardening die 160 that is integrated in a press (not shown). For this purpose, the removal station 140 can comprise a positioning apparatus (not shown). With respect to the main direction of flow D, a container 161 is arranged downstream of the removal station 140 in the axial direction of the first furnace 110, in which container rejects can be placed. In this embodiment, the main direction of flow D describes a substantially 90° deflection. In this embodiment, a second positioning system for the treatment station 150 is not required. Furthermore, this embodiment is advantageous when there is not enough space available in the axial direction of the first furnace 110, for example in a production hall. In this embodiment, the first region or first regions 210 and the third region or third regions 230 of the steel component 200 can also be heat-treated between the removal station 140 and the second furnace 130 so that a stationary treatment station 150 is not required. For example, the treatment station 150 can be integrated in the gripping device. The removal station 140 ensures that the steel component 200 is transferred from the first furnace 110 to the second furnace 130 and to the press-hardening die 160 or to the container 161.

(18) In this embodiment, too, the press-hardening die 160 and the container 161 can switch positions, as can be seen in FIG. 5. In this embodiment, the main direction of flow D describes two substantially 90° deflections.

(19) If the space in which the heat-treatment device is to be placed is restricted, a heat-treatment device according to FIG. 6 is advantageous: in comparison with the embodiment shown in FIG. 4, the second furnace 130 is moved to a second plane above the first furnace 110. In this embodiment, too, the first region or first regions 210 and the third region or third regions 230 of the steel component 200 can likewise be treated between the removal station 140 and the second furnace 130, so that a stationary treatment station 150 is not required. Once again it is advantageous for the first furnace 110 to be formed as a continuous furnace and for the second furnace 130 to be formed as a chamber furnace, possibly comprising a plurality of chambers.

(20) Lastly, FIG. 7 is a schematic view of a final embodiment of the heat-treatment device according to the invention. In comparison with the embodiment shown in FIG. 6, the press-hardening die 160 and the container 161 have switched positions.

(21) The embodiments shown here only represent examples of the present invention and should therefore not be taken to be limiting. Alternative embodiments that a person skilled in the art would take into consideration are likewise covered by the scope of protection of the present invention.

LIST OF REFERENCE SIGNS

(22) 100 heat-treatment device 101 loading station 110 first furnace 130 second furnace 140 removal station 150 treatment station 151 high-power laser 152 cooling apparatus 160 press-hardening die 161 container 200 steel component 210 first region 220 second region 230 third region D main direction of flow t.sub.110 dwell time in the first furnace t.sub.121 transfer time of the steel component to the treatment station t.sub.122 transfer time of the steel component to the second furnace t.sub.130 dwell time in the second furnace t.sub.140 transfer time of the steel component to the press-hardening die t.sub.150 dwell time in the treatment station t.sub.151 heating-up time in the treatment station t.sub.152 cooling time in the treatment station t.sub.160 dwell time in the press-hardening die ϑ.sub.s cooling stop temperature ϑ.sub.3 temperature inside the first furnace ϑ.sub.4 temperature inside the second furnace ϑ.sub.200, 110 temperature profile of the steel component in the first furnace ϑ.sub.210, 151 temperature profile of the first region of the steel component in the treatment station during heating ϑ.sub.220, 151 temperature profile of the second region of the steel component in the treatment station ϑ.sub.220, 152 temperature profile of the second region of the steel component in the treatment station ϑ.sub.230, 152 temperature profile of the third region of the steel component in the treatment station during cooling ϑ.sub.210, 130 temperature profile of the first region of the steel component in the second furnace ϑ.sub.220, 130 temperature profile of the second region of the steel component in the second furnace ϑ.sub.230, 130 temperature profile of the third region of the steel component in the second furnace ϑ.sub.200, 160 temperature profile of the steel component in the press-hardening die