Heat treatment method and heat treatment apparatus

Abstract

The invention relates to a method and an apparatus for the targeted heat treatment of specific component zones of a steel component. A predominantly austenitic structure can be created in the steel component in one or more first regions, from which, by quenching, a majority martensitic microstructure can be created; and in one or more second regions, a majority bainitic microstructure can be created, wherein the steel component is initially heated in a furnace to a temperature above the AC3 temperature, the steel component is subsequently transferred into a treatment station, and can cool down during the transfer, and in the treatment station, the one or more second regions of the steel component are cooled down to a cooling finish temperature ϑ.sub.2 during a treatment time.

Claims

1. A method for the targeted heat treatment of specific component zones of a steel component, wherein a predominantly austenitic structure is created in the steel component in one or more first regions, from which, by quenching, a majority martensitic microstructure is subsequently created, and in one or more second regions, a majority bainitic microstructure is subsequently created, the method comprising: initially heating the steel component in a furnace to a temperature above the AC3 temperature, subsequently transferring the steel component into a treatment station, and cooling down in the treatment station the one or more second regions of the steel component to a cooling finish temperature ϑ.sub.2 during a treatment time t.sub.B, wherein the temperature of the one or more second regions rises during a subsequent dwell time t.sub.150 due to recalescence, without reaching the AC3 temperature.

2. The method according to claim 1, wherein the cooling finish temperature ϑ.sub.2 is selected to be higher than the martensite start temperature M.sub.S.

3. The method according to claim 1, wherein the one or more second regions are cooled by one-sided blowing with a fluid.

4. The method according to claim 1, wherein during the treatment time t.sub.B, no active heating of the second region or regions occurs in the treatment station.

5. The method according to claim 1, wherein during the treatment time t.sub.B, the second region or regions are actively heated in the treatment station.

Description

(1) Further advantages, features and advantageous developments of the invention will become apparent from the dependent claims and the following description of preferred embodiments with reference to the drawings.

(2) In the drawings:

(3) FIG. 1 shows a typical temperature curve for the heat treatment of a steel component, with a first and a second region,

(4) FIG. 2 shows a thermal heat treatment apparatus according to the invention in a plan view, as a schematic drawing,

(5) FIG. 3 shows a further thermal heat treatment apparatus according to the invention, in a plan view, as a schematic drawing,

(6) FIG. 4 shows a further thermal heat treatment apparatus according to the invention, in a plan view, as a schematic drawing.

(7) FIG. 1 is a typical temperature curve for 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 the furnace 110 to a temperature above the AC3 temperature during the dwell time t.sub.110 in the furnace, according to the schematically-drawn temperature profile ϑ.sub.200,110.

(8) Subsequently, the steel component 200 is transferred into the treatment station 150, with a transfer time t.sub.120. The steel component loses heat during this time. In the treatment station, a second region 220 of the steel component 200 is rapidly cooled, wherein the second region 220 quickly loses heat in accordance with the indicated curve ϑ.sub.220,150. The cooling ends after the expiry of the treatment time t.sub.B, which is only a few seconds, depending on the thickness of the steel component 200, the desired material properties, and the size of the second region 220. The second region 220 has now reached the cooling finish temperature ϑ.sub.2 above the martensite start temperature M.sub.S. In this case, the temperature of the first region 210 of the steel component 200 may fall below the AC3 temperature, but this does not necessarily have to occur. On the other hand, the temperature of the second region 220 of the steel component 200 may rise again slightly during the dwell time t.sub.150 due to recalescence, according to the temperature curve ϑ.sub.220,130 shown in the figure, without reaching the AC3 temperature, before continuing to slowly drop.

(9) After the dwell time t.sub.150 of the steel component 200 in the treatment station is finished, it is transferred during the transfer time t.sub.131 into a press-hardening tool 160, where it is transformed and hardened during the dwell time t.sub.160.

(10) FIG. 2 shows a heat treatment apparatus 100 according to the invention, in a 90° arrangement. The heat treatment apparatus 100 has a loading station 101 via which the steel components are fed to the furnace 110. Furthermore, the heat treatment apparatus 100 comprises the treatment station 150. A removal station 131, which is equipped with a positioning device (not shown), is arranged further in the primary flow direction D behind the furnace 110. The primary flow direction at this point bends substantially 90° to allow a press-hardening tool 160 to follow in a press (not shown) in which the steel component 200 is press-hardened. A container 161 into which rejects can be placed is arranged in the axial direction of the furnace 110.

(11) FIG. 3 shows a heat treatment apparatus 100 according to the invention, in a straight arrangement. The heat treatment apparatus 100 has a loading station 101 via which the steel components are fed to the furnace 110. Furthermore, the heat treatment apparatus 100 comprises the treatment station 150. A removal station 131, which is equipped with a positioning device (not shown), is arranged further in the primary flow direction D behind the furnace 110. A press-hardening tool 160 in a press (not shown) in which the steel component 200 is press-hardened follows in the continued, straight primary flow direction. A container 161 into which rejects can be placed is arranged essentially at 90° to the removal station 131.

(12) FIG. 4 shows a further variant of a heat treatment apparatus 100 according to the invention. The heat treatment apparatus 100 again has a loading station 101 via which the steel components are fed to the furnace 110. The furnace 110 is preferably designed in this embodiment as a continuous furnace. Furthermore, the heat treatment apparatus 100 comprises the treatment station 150. The removal device 131 may have, for example, a gripping device (not shown). The removal station 131 removes, for example by means of the gripping device, the steel components 200 from the furnace 110. In contrast to the embodiment shown in FIG. 2, the treatment station 150 is arranged in this case on the furnace 110. This arrangement saves installation floor space. The primary flow direction changes, in this embodiment, the plane in which the steel component 200 is lifted from the removal station after leaving the furnace 110 and placed in the treatment station 150. After expiry of the dwell time t.sub.150 of the steel component 200 in the treatment station 150, the removal station 131 removes the steel component 200 from the treatment station 150 and places it into a press-hardening tool 160 installed in a press. In the embodiment shown, the press is arranged in line with the furnace 110, while a container 161 for rejects is arranged at an angle to the furnace axis. The positions of the press with the tool 160 and container 161 can also be reversed.

(13) The embodiments shown herein are only examples of the present invention and therefore should not be considered as limiting the same. Alternative embodiments contemplated by a person skilled in the art are equally within the scope of protection of the present invention.

LIST OF REFERENCE NUMBERS

(14) 100 heat treatment apparatus 110 furnace 131 removal station 150 treatment station 160 press-hardening tool 161 container 200 steel component 210 first region 220 second region D primary flow direction M.sub.S martensite start temperature t.sub.B treatment time t.sub.110 dwell time in the furnace t.sub.120 transfer time of the steel component into the treatment station t.sub.131 transfer time of the steel component into the press-hardening tool t.sub.150 dwell time in the treatment station t.sub.160 dwell time in the press-hardening tool ϑ.sub.1 microstructure transformation starting temperature ϑ.sub.2 cooldown finish temperature ϑ.sub.3 internal temperature, furnace ϑ.sub.200,110 temperature profile of the steel component in the furnace ϑ.sub.210,150 temperature profile of the first region of the steel component in the treatment station ϑ.sub.220,150 temperature profile of the second region of the steel component in the treatment station ϑ.sub.200,160 temperature profile of the steel component in the press-hardening tool