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.

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.

Description

[0065] 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:

[0066] FIG. 1 shows a diagram of a device that can be used to carry out a method according to the invention;

[0067] FIG. 2 shows a detailed view of the device from FIG. 1;

[0068] FIG. 3 shows a time-temperature curve achievable by means of a method according to the invention; and

[0069] FIG. 4 shows a further time-temperature curve achievable by means of a method according to the invention.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 t.sub.1. By way of example, this heating takes place in a first furnace 2 here. Between the points in time t.sub.1 and t.sub.2, 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.

[0075] Between the points in time t.sub.2 and t.sub.3, 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 t.sub.2 and t.sub.3. 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 t.sub.2 and t.sub.3. 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.

[0076] Between the points in time t.sub.3 and t.sub.4, 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.

[0077] The component is heated in the second furnace from the point in time t.sub.4 to the point in time t.sub.5 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.

[0078] Between the points in time t.sub.5 and t.sub.6, 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.

[0079] From the point in time t.sub.6 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.

[0080] 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 t.sub.1. By way of example, this heating takes place in a first furnace here.

[0081] Between the points in time t.sub.1 and t.sub.2, 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 t.sub.2 and t.sub.3, 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 t.sub.2 and t.sub.3. 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 t.sub.2 and t.sub.3. 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.

[0082] Between the points in time t.sub.3 and t.sub.4, 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.

[0083] The component is heated in the second furnace from the point in time t.sub.4 to the point in time t.sub.5 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.

[0084] Between the points in time t.sub.5 and t.sub.6, 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.

[0085] From the point in time t.sub.6 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

[0086] 1 component

[0087] 2 first sub-region

[0088] 3 nozzle

[0089] 4 fluid stream

[0090] 5 temperature difference

[0091] 6 second sub-region

[0092] 7 first furnace

[0093] 8 temperature control station

[0094] 9 second furnace

[0095] 10 press hardening tool

[0096] 11 heating unit

[0097] 12 device

[0098] 13 compressor