Parts heat treatment

Abstract

A method for heat treating a part (2), comprising the steps of: a) heating the part (2) in a first continuous furnace (3), the first continuous furnace being divided in a conveying direction (r) of the part (2) into a first section (6) adjacent to the first section and a second section (7) through which the part (2) subsequently passes, the first section (6) and the second section (7) together extending over at least 70% of the first continuous furnace (3) in the conveying direction (r) of the part (2), and the average temperature of the first section (6) being equal to or higher than the AC3 temperature (T AC3 ), and the average temperature of the second area (7) is below the AC3 temperature (T AC3 ), b) transferring the part (2) from the first continuous furnace (3) to a temperature control station (4), and c) heat treating the part (2) in the temperature control station (4), wherein the first region of the part (2) is heated to an AC3 temperature (T AC3 ) to a temperature above the average temperature T 1 and cooling the second region of the part (2). By subjecting the different regions to different heat treatments, the part (2) acquires different ductility in different regions. This is advantageous for automotive B-pillars, for example. The different temperatures (T Z1 , T Z2 ) has the effect that the regions of different ductility are separated from one another in a particularly clear manner.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for heat treating parts, particularly automotive steel parts. [Background technology]

[0002] In particular, in the automotive industry, it is known to selectively harden steel parts by heat treatment. For this purpose, different areas of a steel part, such as a B-pillar, are heat treated differently. This results in different ductility in different areas, which is beneficial for the behavior of such parts in a crash. For example, the hard areas of the B-pillar at seat height can protect the occupant, while the softer areas above and below the B-pillar can deform and thereby absorb energy. Summary of the Invention [Problem to be solved by the invention]

[0003] The object of the present invention is to provide a method for heat treating a part, in which areas of the part can be heat treated in a particularly clear manner so that they are separated from one another, and also to provide a corresponding device. [Means for solving the problem]

[0004] These objects are achieved by the methods and devices set out in the independent claims. The dependent claims specify further advantageous developments. The features presented in the claims and in this specification can be combined with one another in any technically significant manner.

[0005] According to the present invention, there is provided a method of heat treating a component, the method comprising: a) heating the parts in a first continuous furnace, the first continuous furnace being divided in a conveying direction of the parts into a first zone and a second zone adjacent to the first zone through which the parts subsequently pass, the first zone extending over at least 70% of the first continuous furnace in the conveying direction of the parts, the average temperature of the first zone being below the AC3 temperature of the parts, and the average temperature of the second zone being above the AC3 temperature of the parts; b) transferring the part from the first continuous furnace to a temperature control station; c) heat treating the part in a temperature controlled station, exposing a first region of the part to a temperature that is on average above the AC3 temperature of the part, and cooling a second region of the part; Includes:

[0006] The method can be used to heat treat a part. The part is preferably a steel part. The steel is preferably 22MnB5. The method can be used, for example, to heat treat an automotive part, in particular a B-pillar. After the heat treatment, the part is preferably press-hardened in a press and hot-formed to some extent. The method preferably includes a further step in which, after the heat treatment, the part is transferred to a press and press-hardened in the press. In this case, the method is a method for heat treating and press-hardening a part.

[0007] The part preferably has a material thickness of at least 1 mm, in particular a material thickness in the range of 1 to 4 mm. The material thickness of the part is preferably constant throughout the part. Alternatively, the part can have different material thicknesses in different regions. For example, the part can be a "tailor rolled blank" (TRB), where different material thicknesses are obtained locally by rolling different areas. The part can also be a "tailor welded blank" (TWB), where different material thicknesses are obtained locally by welding several metal sheets together. TRB and TWB can also be combined. Furthermore, the method is equally applicable to parts with and without coatings. As coatings, Al / Si coatings are particularly suitable.

[0008] In step a), the parts are heated in a first continuous furnace. A furnace is a device whose interior is at a settable temperature and into which the parts can be inserted. Over time, the parts reach the temperature prevailing inside the furnace. Heat is therefore transferred to the parts from the gas present in the furnace (which may in particular be air). A continuous furnace is a furnace that allows the parts to move through it, heating them as they pass through it.

[0009] The first continuous furnace is preferably a roller hearth furnace. In the first continuous furnace, the part is preferably heated by a burner, in particular a gas burner. As a result, the part can have a particularly uniformly distributed temperature. In particular, not only a layer on the surface of the part is heated. The entire part is heated in the first continuous furnace. The part is completely contained in the first continuous furnace. Furthermore, the continuous furnace can be used to achieve heating with particularly large temperature differences. The continuous furnace can be used to heat the part, in particular to temperatures ranging from room temperature to the AC3 temperature of the part. Heating over such a wide range is not possible with many other heating methods, or at least only with disproportionate effort.

[0010] Heating in a continuous furnace is particularly in contrast to heating by what is called "direct energization." With direct energization, it would be difficult to heat the part uniformly and sufficiently. With direct energization, the heating rate is more important. Furthermore, direct energization requires contact with the part. In step a) of the method, heating is preferably carried out without contact. This does not exclude that the part is moved through the first continuous furnace by conveying rollers and therefore comes into contact with the conveying rollers. Heating is contactless if the heat input into the part is via gas and / or thermal radiation.

[0011] The first continuous furnace, and the remainder of the apparatus used in the method, will be described with reference to a "part transport direction." This is the direction in which parts are moved by the apparatus and its elements. Thus, the part transport direction is, in particular, the direction in which parts move through the first continuous furnace.

[0012] In the conveying direction defined in this way, the first continuous oven has a first section and a second section. The fact that the first continuous oven is "divided" into these two sections in the conveying direction of the parts means that the first continuous oven has only these two sections in the conveying direction of the parts. Each of these sections preferably extends across the entire first continuous oven in a direction transverse to the conveying direction of the parts.

[0013] Parts first pass through the first section and then through the second section. Therefore, the second section is located downstream of the first section in the conveying direction. The first and second sections are directly adjacent to each other. The first section is adjacent to the inlet of the first continuous oven, and the second section is adjacent to the outlet of the first continuous oven. Parts can enter the first continuous oven through the inlet and leave the first continuous oven through the outlet.

[0014] The average temperature in the first zone is below the AC3 temperature of the part, and the average temperature in the second zone is above the AC3 temperature of the part. In the first continuous furnace, the part is first heated relatively slowly to a temperature below the AC3 temperature and then briefly exposed to a temperature above the AC3 temperature. In the second zone, the part is preferably heated to a temperature above the AC3 temperature. If the part remains in the second zone for a long enough period, the part can reach the set temperature in the second zone.

[0015] It is preferable that the temperatures of the first and second zones are constant. As a result, the parts are heated uniformly in these zones. However, it should be noted that short-term and / or locally limited temperature changes in the first continuous furnace are largely irrelevant to the heating of the parts. This is because the temperature of the parts adapts relatively slowly to the temperature of the first continuous furnace. To take this into account, these zones are defined in each case by their average temperatures. The average temperature of the first zone is below the AC3 temperature, while the average temperature of the second zone is above the AC3 temperature. For example, the first zone is not interrupted by a small temperature range above the AC3 temperature of the parts. The same applies to the second zone. The average temperature should be understood to mean the average temperature to which the parts are exposed in the zone. This is the temperature in the plane of the parts in the first continuous furnace, i.e., in the plane along which the parts are transported through the first continuous furnace. In particular, if the first continuous furnace is gas-fired, locally elevated temperatures in the burner area should be ignored if the burner is located at a distance from the parts.

[0016] The first zone extends over at least 70% of the first continuous furnace in the direction of component transport, preferably over at least 80%. It has been found that it is sufficient for the components to be initially heated relatively slowly and then exposed to temperatures above AC3 for only a short period of time. Accordingly, the first zone is preferably designed to be significantly longer than the second zone. As a result of this heating, a particularly small transition zone is obtained between the regions of different ductility. The regions of different ductility are therefore separated from one another in a particularly clear manner. This is surprising, in that the relationship between the extent of the transition zone and the manner of heating before temperatures above AC3 were established was previously unknown.

[0017] It is sufficient that these zones are separated from one another only by a set temperature. Furthermore, these zones do not have to be different, or the boundary between them need not be recognizable as such. It is also possible for the first and second zones to be defined differently in the first continuous furnace. It is sufficient that both the first and second zones can be allocated while all the conditions set for the first and second zones are met. In this case, it is not a problem if the allocation options change. However, it is preferable that the allocation of these zones is not random. If the temperature profile in the transport direction of the parts has a clearly recognizable jump, it is preferable that the boundary between the zones coincide with this clearly recognizable jump. It is particularly preferable that the temperature of the boundary between the first and second zones is the AC3 temperature of the parts. This is especially true when the boundary between the two zones is located in a temperature abrupt rise from a value below the AC3 temperature of the parts to a value above the AC3 temperature of the parts.

[0018] Furthermore, it is preferred that the temperature be below the AC3 temperature of the part over at least 80% of the area over which the first section extends in the direction of transport of the part. Similarly, it is preferred that the temperature be above the AC3 temperature of the part over at least 80% of the area over which the second section extends in the direction of transport of the part. It is particularly preferred that the temperature be below the AC3 temperature over the entire first section. It is particularly preferred that the temperature be above the AC3 temperature over the entire second section. This also relates to the temperatures to which the parts are exposed in the first continuous furnace.

[0019] The first continuous furnace preferably has a plurality of heating elements, each of which can be individually set to a different temperature. The first and second zones preferably correspond to groups of heating elements. The heating elements can be assigned to the zones by a control device, and in this regard, the assignment does not have to be visible on the heating elements themselves. Only the temperature distribution is significant. By changing the temperature setting of a heating element at the boundary between the first and second zones, the assignment of that heating element can be changed from the first zone to the second zone and vice versa. Generally, by changing the assignment of heating elements at the boundary between the zones, the extent of these zones can be changed. The temperature distribution of the zones can be adjusted by the respective temperature setting of each heating element. All heating elements within a zone are preferably set to the same temperature.

[0020] In step b) of the method, the part is transferred from the first continuous furnace to a temperature control station, where in step c) the part is differentially heat treated in different regions by exposing a first region of the part to a temperature that is on average above the AC3 temperature of the part and cooling a second region of the part.

[0021] The first continuous furnace and the temperature control station are separate units, spatially separated from each other. Transferring the parts between the first continuous furnace and the temperature control station facilitates cooling the parts between heating in the first continuous furnace and heat treatment in the temperature control station. In the temperature control station, the parts are cooled as quickly as possible in at least some areas. Rapid cooling can be more efficiently achieved outside the hot first continuous furnace. In this way, cooling can begin already during transfer. In this respect, the physical separation of the first continuous furnace and the temperature control station accelerates the process. This contrasts with solutions in which all method steps are performed in the same equipment, which does not require part transfer. Such solutions typically aim to minimize or completely avoid the labor involved in part transfer. Because the first continuous furnace and the temperature control station have different requirements, the spatial separation between the first continuous furnace and the temperature control station also facilitates manufacturing. Therefore, integrating both into a single equipment would be quite complex.

[0022] In the temperature control station, the first area is exposed to a temperature above the AC3 temperature of the part. As a result, the first area is preferably heated in the temperature control station. However, depending on the temperature of the first area upon entry into the temperature control station and the duration of the stay in the temperature control station, the temperature control station can maintain the first area at that temperature or delay the cooling of the first area. The first area of ​​the part is preferably exposed to this temperature as long as it is held in a chamber open to the part and maintained at a temperature above the AC3 temperature of the part by the heating device. The heating device is preferably an electric heating device. The heating device can have a heating element, such as a heating loop. Alternatively or additionally, the heating device can include a radiant heating tube heated by a burner, in particular a gas burner.

[0023] In the temperature control station, the second region is cooled, preferably by keeping the second region outside the chamber described above. At this location, a cooling fluid, in particular compressed air, is preferably supplied to the second region. The compressed air preferably has a pressure in the range of 2 to 4.5 bar. This relatively high pressure allows a large volume of compressed air to be delivered to the second region of the part in a very short time, thereby achieving a sufficiently high cooling rate.

[0024] Whether and to what extent the temperature of the part is above or below the AC3 temperature of the part has a significant effect on the resulting microstructural composition. Due to the different heat treatment of two regions of the part, these regions can have different microstructural compositions and, in this regard, different ductility. Thus, the first region is harder than the second region. For example, in the case of an automotive B-pillar, crash properties can be tailored.

[0025] The first and second regions are not necessarily adjacent regions. In particular, the middle part of the B-pillar could form the first region, and the upper and lower parts of the B-pillar together could form the second region. Preferably, but not necessarily, the part has only the first and second regions, i.e., no additional regions.

[0026] In a preferred embodiment, the method comprises: d) transferring the part from the temperature control station to a second continuous furnace; e) heat treating the part in a second continuous furnace; Further includes:

[0027] The temperature control station and the second continuous furnace are separate units, spatially separated from each other. Transferring the temperature control station and the second continuous furnace facilitates cooling the part between the heat treatment in the temperature control station and the heat treatment in the second continuous furnace. In this way, the second region of the part can be cooled during transfer. This reduces the required size of the temperature control station and accelerates processing. This contrasts with solutions in which no part transfer is necessary and all method steps are performed in the same equipment as much as possible. Typically, such solutions aim to minimize or completely avoid the labor involved in transferring parts. Because the temperature control station and the second continuous furnace have different requirements, the spatial separation between them also facilitates manufacturing. Therefore, integrating both into a single equipment would be correspondingly complex.

[0028] The second continuous furnace is preferably a roller hearth furnace. The entire part is heat treated in the second continuous furnace. The part is completely contained within the second continuous furnace. Heat treatment in a continuous furnace is particularly in contrast to heating by what is called "direct current."

[0029] The heat treatment in the second continuous furnace gives the part a microstructural composition different from that which would otherwise occur. In this respect, the present embodiment is directed to applications where a corresponding microstructural composition is desirable. It has been found that in particular for these applications, the advantage of obtaining zones that are separated in a particularly clear manner and have different ductility is achieved due to the different temperatures in these zones in the first continuous furnace. This advantage is achieved in a particular way by combining steps a) to e).

[0030] In another preferred embodiment of the method, the average temperature of the first zone of the first continuous furnace is within 10-30 K below the AC3 temperature of the part, or the average temperature of the second zone of the first continuous furnace is within 10-30 K above the AC3 temperature of the part, or both.

[0031] A suitable combination is one in which the average temperature of the first zone of the first continuous furnace is 10 to 30 K lower than the AC3 temperature of the part, and the average temperature of the second zone of the first continuous furnace is 10 to 30 K higher than the AC3 temperature of the part.

[0032] Tests have shown that the aforementioned advantages are particularly achievable at certain temperature values. This is surprising, since deviations of 10-30 K from the AC3 temperature are relatively small. For example, the AC3 temperature of steel 22MnB5 is 846°C. A deviation of 10 K from this is approximately 1%. Nevertheless, it has been observed that this small deviation significantly reduces the size of the transition zone between regions of different ductility.

[0033] In the case of 22MnB5, it is preferable that the temperature of the first zone is on average 814 to 836°C, and the temperature of the second zone is on average 856 to 876°C. It is particularly preferable that the temperature of the first zone is always within the range of 816 to 836°C, and the temperature of the second zone is always within the range of 856 to 876°C.

[0034] In a further preferred embodiment of the method, the residence time of the parts in the second zone of the first continuous furnace is in the range of 10 to 30 seconds.

[0035] The residence time in the first continuous furnace is preferably in the range of 250-400 seconds. Therefore, the residence time in the second zone is relatively short, in the range of 10-30 seconds. However, testing has shown that such short residence times in the second zone are sufficient for the aforementioned benefits. Longer residence times may also be detrimental to the microstructural composition.

[0036] In a further preferred embodiment of the method, in step c), the cooling of the second region begins with a delay of 0.5 to 15 seconds after completion of step b).

[0037] Cooling does not begin immediately after the part enters the temperature control station. This allows for cooling by free heat dissipation to the environment, resulting in savings in cooling fluids, etc. Cooling that begins after a delay is active cooling. This allows for particularly precise setting of the strength properties of the part. Tests have shown that an excessively long delay is disadvantageous, as it can particularly increase the size of the transition zone between the different ductility zones. Tests have shown that the combination of zonal heating and a relatively short delay in the first continuous furnace described above results in a particularly clear separation between the different ductility zones.

[0038] In a further preferred embodiment of the method, in step c) the first region of the component is exposed to a temperature on average of 170-250 K above the AC3 temperature of the component.

[0039] The temperature control in the temperature control station was also found to affect the extent of the transition region between regions of different ductility. In tests, the transition region became smaller when the temperature for heat treatment of the first region in the temperature control station was relatively high.

[0040] Preferably, in step c) the component is exposed to a temperature that is always above the AC3 temperature of the component by 170-250 K. For 22MnB5, it is preferred that the first region is exposed in step c) to an average temperature in the range 900-1100 °C, in particular to a constant temperature within this range.

[0041] In a further preferred embodiment of the method, in step c) the part remains in the temperature controlled station for a dwell time in the range of 10 to 30 seconds.

[0042] In accordance with a further aspect of the present invention, there is provided an apparatus for heat treating a component, the apparatus comprising: a first continuous furnace divided into a first section and a second section adjacent to and downstream of the first section in a conveying direction of the parts, the first section extending over at least 70% of the first continuous furnace in the conveying direction of the parts; a temperature control station downstream of the first continuous furnace in the direction of component transport; a control device designed to set an average temperature in the first section of the first continuous furnace below the AC3 temperature of the parts and to set an average temperature in the second section of the first continuous furnace above the AC3 temperature of the parts; Equipped with.

[0043] The aforementioned special advantages and design features of the present method can be applied to the present apparatus, and vice versa. The present apparatus is preferably intended and designed to operate according to the present method. The present method is preferably carried out using the present apparatus. The present apparatus preferably has a second continuous furnace arranged downstream of the temperature control station in the conveying direction of the parts.

[0044] The second section of the first continuous furnace is arranged downstream of the first section in the direction of conveyance of the parts, which means that the parts pass through the second section after the first section. The same applies to the temperature control station and the second continuous furnace, which are arranged downstream of the first continuous furnace and the temperature control station, respectively, in the direction of conveyance of the parts.

[0045] The invention will now be explained in more detail with reference to the drawings, which show particularly preferred embodiments, but to which the invention is not limited, and the drawings and the proportions shown therein are only schematic. [Brief explanation of the drawings]

[0046] [Figure 1] 1 shows an apparatus for heat treating a part according to the present invention. [Figure 2] 2 shows the temperature profile produced by the apparatus of FIG. 1 when a method of heat treating a part according to the present invention is carried out; DETAILED DESCRIPTION OF THE INVENTION

[0047] FIG. 1 shows an apparatus 1 for heat treating parts 2. The apparatus 1 comprises a first continuous furnace 3, which has a first section 6 and a second section 7 downstream of the first section 6 in the conveying direction r of the parts 2. The parts 2 therefore pass through the second section 7 later, which is therefore located to the right of the first section 6 in FIG. 1. The first continuous furnace 3 is divided into the first section 6 and the second section 7 in the conveying direction r. That is, the first continuous furnace does not have any further sections in this direction. The first section 6 extends over 70% of the first continuous furnace 3 in the conveying direction r of the parts 2. The first section 6 and the second section 7 extend across the entire first continuous furnace 3 in a direction transverse to the conveying direction r (i.e., in FIG. 1, vertically, perpendicular to the plane of the drawing).

[0048] The device 1 also comprises a temperature control station 4 downstream of the first continuous furnace 3 in the conveying direction r of the parts 2. Furthermore, the device 1 comprises a second continuous furnace 5, which is arranged downstream of the temperature control station 4 in the conveying direction r of the parts 2. The temperature in the first section 6 of the first continuous furnace 3, the temperature in the second section 7 of the first continuous furnace 3, the temperature in the temperature control station 4 and the temperature in the second continuous furnace 5 can be set via a control device 8, which is indicated by dotted lines. The control device 8 controls, in particular, the AC3 temperature T of the parts 2 in the first section 6 of the first continuous furnace 3. AC3 and in the second section 7 of the first continuous furnace 3, the AC3 temperature T AC3 It is designed to set an average temperature above

[0049] Figure 2 shows the temperature profile experienced by the part 2 as it moves through the apparatus 1 of Figure 1. Figure 2 is a schematic representation showing a plot of temperature T versus time t in arbitrary units. The part 2 is first heated in a first continuous furnace 3. The residence time of the part 2 in the first continuous furnace 3 is defined as t D1 This residence time t D1 is tZ1 The residence time in the first area 6 is represented by t Z2 and a residence time in the second zone 7, represented by the AC3 temperature T AC3 A value T below Z1 In the second area 7, the temperature is always set to the AC3 temperature T AC3 Values ​​greater than T Z2 As a result, the temperature of part 2 initially reaches the value T Z1 At this value, t Z1 It remains saturated until the end of t Z2 During Z2 It is further heated to

[0050] The part 2 is then transferred to the temperature control station 4. The transfer time for this is t T1 During this transfer, part 2 cools down. The temperature of the first region of the part, T A and the temperature T of the second region of the part B This can be achieved, for example, by insulating the different areas separately during transport.

[0051] residence period t TS During this time, part 2 remains in temperature control station 4. During this time, the AC3 temperature T AC3 A value T that always exceeds TS The part 2 is heat treated in the temperature control station 4 by exposing a first region of the part 2 to a temperature that is t V It starts with a delay t V When the part 2 enters the temperature control station 4, i.e., during the period t T1 ends the period t TS Even though the cooling is in progress, the temperature T B This is due to the release of latent heat. This effect is also known as "reluminescence."

[0052] After the part 2 is heat-treated in the temperature control station 4, it is transferred to the second continuous furnace 5. The transfer time for this is t T2 During this transfer, the part 2 cools down, but this cooling may vary from area to area.

[0053] In the second continuous furnace 5, the component 2 is further heat-treated by being heated as a whole. For this purpose, the component 2 is heated to the AC3 temperature T AC3 During the process, the second, lower temperature region of the part 2 is heated more than the first, higher temperature region. The residence time of the part 2 in the second continuous furnace 5 is defined as t D2 It is expressed as:

[0054] Due to the different heat treatments in the different regions, the part 2 obtains different ductility in different regions, which is advantageous for example in B-pillars for automobiles. Z1 , T Z2 This has the effect that the regions of different ductility are separated from one another in a particularly clear manner. [Explanation of symbols]

[0055] 1 device 2 parts 3. No. 1 Continuous Furnace 4. Temperature Control Station 5. No. 2 continuous furnace 6 1st area 7 Second area 8 Control Equipment T temperature T AC3 AC3 temperature of the part T Z1 Temperature in Zone 1 T Z2 Temperature in the second zone T TS Temperature of the second zone in the temperature control station T A Temperature of the first area of ​​the part T B Temperature of the second area of ​​the part t time tD1 Residence time in the first continuous furnace t Z1 Residence time in the first section of the first continuous furnace t Z2 Residence time in the second section of the first continuous furnace t T1 Duration of transfer from the first continuous furnace to the temperature control station t TS Residence time in the temperature control station t V Delayed cooling of the second area of ​​the part t T2 Duration of transfer from the temperature control station to the second continuous furnace t D2 Residence time in the second continuous furnace r Part transport direction

Claims

1. A method for heat treating a steel part (2), comprising the steps of: a) heating the steel part (2) in a first continuous furnace (3), The first continuous furnace is divided into a first zone (6) and a second zone (7) adjacent to the first zone and through which the steel parts (2) pass later in a conveying direction (r) of the steel parts (2), the first zone (6) extends over at least 70% of the length of the first continuous furnace (3) in the conveying direction (r) of the steel parts (2); The average temperature of the first zone (6) is the AC3 temperature (T ＡＣ３ ) below The average temperature of the second zone (7) is the AC3 temperature (T ＡＣ３ ) and The average temperature is the average temperature to which the steel part (2) is exposed. Steps and b) transferring said steel parts (2) from said first continuous furnace (3) to a temperature control station (4); c) heat treating said steel part (2) in said temperature control station (4), The first region of the steel part (2) is heated to the AC3 temperature (T ＡＣ３ ) to a temperature above 100°C on average and cooling the second region of the steel part (2); A method comprising:

2. 10. The method of claim 1, d) transferring said steel parts (2) from said temperature control station (4) to a second continuous furnace (5); e) heat treating the steel part (2) in the second continuous furnace (5); The method further comprises:

3. 3. The method according to claim 1, wherein The average temperature of the first zone (6) of the first continuous furnace (3) is equal to or greater than the AC3 temperature (T ＡＣ３ ) within the range of 10 to 30K, or The average temperature of the second zone (7) of the first continuous furnace (3) is equal to or greater than the AC3 temperature (T ＡＣ３ ) in the range of 10 to 30K, or It's both. method.

4. The method according to any one of claims 1 to 3, The residence time (t) of the steel parts (2) in the second zone (7) of the first continuous furnace (3) Ｚ２ ) is in the range of 10 to 30 seconds, method.

5. The method according to any one of claims 1 to 4, In step c), the cooling of the second region of the steel part (2) is delayed (t ) for 0.5 to 15 seconds after the completion of step b). Ｖ ) to start method.

6. The method according to any one of claims 1 to 5, In step c), the first region of the steel part (2) is heated to the AC3 temperature (T ＡＣ３ ) are exposed to temperatures on average 170-250K higher than method.

7. The method according to any one of claims 1 to 6, In step c), the steel part (2) is placed in the temperature control station (4) for a dwell time (t) ranging from 10 to 30 seconds. ＴＳ )stay, method.

8. An apparatus (1) for heat treating steel parts (2), comprising: A first continuous furnace (3), The first continuous furnace (3) is divided into a first section (6) and a second section (7) adjacent to the first section and downstream of the first section in the conveying direction (r) of the steel parts (2), a first continuous furnace (3), the first zone (6) extending over at least 70% of the length of the first continuous furnace (3) in the conveying direction (r) of the steel parts (2); a temperature control station (4) downstream of the first continuous furnace (3) in the conveying direction (r) of the steel parts (2); A control device (8), In the first zone (6) of the first continuous furnace (3), the AC3 temperature (T ＡＣ３ ) and In the second zone (7) of the first continuous furnace (3), the AC3 temperature (T ＡＣ３ ) and is designed to set an average temperature above The average temperature is the average temperature to which the steel part (2) is exposed, The temperature in the temperature control station (4) can be set via the control device (8). An apparatus comprising:

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