METHOD FOR PRODUCING METAL BAND MATERIAL WITH DIFFERENT MECHANICAL PROPERTIES ACROSS THE WIDTH OF THE BAND

Abstract

A method for producing metal band material with different mechanic& properties across the width of the band, in which the hand is heated zonally with regard to the width so that zones with a different heating state are temporarily produced and the band is then cooled in, order to produce regions with a different metal structure and thus different mechanical properties, wherein one or more zones that are to be heated are acted on with a heating device, while the other zones are isolated from the heating or are freed of the heating or are actively cooled or else a beat flow, which is introduced into the zones that are not to be heated, is diverted to contact masses that are resting against the zones that are not to be heated.

Claims

1. A method for producing a metal band material with different mechanical properties across a width of the band, comprising: heating the band is zonally with regard to the width to temporarily produce zones with a different heating state by acting on one or more zones with a heating device; while any remaining zones that are not to be heated are isolated from the heating or are free of the heating or are actively cooled, or diverting a heat flow to contact masses that are resting against the remaining zones that are not to be heated; and cooling, the band in order to produce regions with a different metal structure and thus different mechanical properties.

2. The method according to claim 1, wherein the heating of the band from a starting temperature to a target temperature takes place within one pass, between two deflection rollers of a band looping apparatus.

3. The method according to claim 1, wherein the cooling of the band takes place after the zonal heating within one pass of a band looping apparatus.

4. The method according to claim 1, wherein both the heating and the cooling of the band take place within the same pass of a baud looping apparatus.

5. The method according to claim 1, wherein in the region of a zonal heating and re-cooling, the band is guided with rollers, which are embodied as convex or concave depending on thermal expansion-dictated arching of the band.

6. The method according to claim 1, wherein in at least one zone that is to be heated, the band has a difference in tensile strength of at least 30 MPa.

7. The method according to claim 1, wherein in the one or more zones that are to be heated, the band has a difference in tensile strength of at least 5%, of a tensile strength of the untreated region.

8. The method according to claim 1, wherein the one or more zones that is/are to be heated has a respective width of at least 20 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The invention will be explained by way of example below based on the drawings. In the drawings:

[0045] FIG. 1 shows a very schematic view of a first embodiment of a device for zonally heating a metal band;

[0046] FIG. 2 shows a very schematic view of another embodiment of a device for zonally heating a metal band;

[0047] FIG. 3 shows a guide roller for guiding a zonally heated metal band in a first embodiment;

[0048] FIG. 4 shows a guide roller for guiding a zonally heated metal band in another embodiment;

[0049] FIG. 5 shows a very schematic view of an another embodiment of a guide roller for a zonally heated metal hand.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] According to the invention, a metal band 1 and in particular a metal band 1, which is conveyed through a device for heat treating a metal band, is heated in a zonally different way across its width B (FIG. 1). This can also take place in the form of an additional heating after a basic heating has already been carried out (recrystallization).

[0051] This means that across its band width, the metal band has different mechanical properties such as the tensile strength Rm.

[0052] The zone relates to a width section, which, across its entire height (band thickness), has this different property in comparison to the rest of the band. This is particularly true of steel belts with a maximum thickness of 5 mm, particularly preferably 0.5 mm to 3 mm.

[0053] For this different, zonal heating, preferably a band width of at most ⅓ of the total band width is carried out.

[0054] The zone(s), however, can also be divided from one another on the band, i.e. there can also be an untreated width section between 2 heat-treated width sections. The minimum width for the zonal heating can preferably be greater than 100 mm in order to adjust the mechanical properties in a more efficient way.

[0055] The device for heating or heat-treating the metal band, in particular a steel band, can be a so-called continuous annealing system, but can also be any other tempering device in which a steel band is tempered, for example it can also be the tempering device or heat treating device before the steel band undergoes a metallic hot-dip coating (zinc-based or aluminum-based coating) or a after passage through a corresponding hot-dip coating.

[0056] In order to be able to perform zonally different tempering of the metal band with a sufficient dividing precision and in particular, in order to be able to carry out tempering in accordance with predetermined zones Z1, Z2, and Z3, a heating device 2 is provided in one or more zones in which a higher temperature of the band 1 is specified (Z2 in FIG. 1). The heating device 2 can be an intrinsically known heating device, in particular it can involve radiant tubes, an electrical heating unit, a flame heating unit, a flame in a jacket radiant tube, or an inductor, This heating device 2 acts on the surface of the band 1.

[0057] In order to avoid heating adjacent zones (Z1 and Z3 in FIG. 1) due to thermal conduction of the sheet from the heated zone (Z2), these regions can be provided with cooling devices 3, which act on the surface of the steel band 1.

[0058] The cooling devices 3 are depicted as blowers in FIG. 1.

[0059] Depending on the cooling power required, the blowers direct a cooling gas flow—which is metered in terms of its quantity, speed, and temperature—onto the surface of the metal band 1. With the regulation of the temperature of the gas flow and/or the quantity of the gas flow and/or the speed of the gas flow, it is possible to establish a desired necessary cooling rate.

[0060] The cooling gas flow applied to the surface is advantageously applied in the region in which heat develops in the heated zone Z2; the cooling gas flow is also advantageously withdrawn again at the end of the heating section in the zone Z2 in order to avoid an overflow of the gas flow into the heating zone Z2.

[0061] Instead of corresponding gas flows and the corresponding device for producing and directing them, the cooling can also take place in a different way, in particular by means of spraying with fluids or through contact with solid objects.

[0062] Particularly with cooling gas flows, but also with heating gas flows, in particular flame treatment, in order to also be able to increase the dividing precision in the region of zones Z1, Z2, and Z3 and particularly in the region of the zonal heating, partition walls or partition curtains 4 can be provided in order to define the respective zones.

[0063] This significantly improves the introduction of heat, but also significantly improves the withdrawal of cooling gas flows or cooling liquid flows. The ends 5 of the respective curtains or partition walls 4 oriented toward the steel band can thus be spaced a short distance away from the steel or metal band 1 and in particular, an arching of the band caused by the heating can be compensated for by changing the length and the walls 4, which means that the distance of the ends 5 from the steel surface 1 is always as uniform as possible.

[0064] Particularly with flowing cooling media or heating media, in the vicinity of the ends 5 of the curtains or walls 4, gas outlet openings can be provided, from which a gas flows, which forms a gas curtain for dividing the atmospheres of the zones Z1, Z2, and Z3. For this purpose, the walls 4 are then correspondingly embodied so that they can absorb a corresponding gas flow and convey it to the ends or end edges 5.

[0065] The ends 6 of the outer walls 4 in this case can extend laterally beyond the steel band and can thus also cover the free edges.

[0066] This arrangement can also be doubled and can act across the width of the band from both sides.

[0067] In another advantageous embodiment (FIG. 2), a zone that is to be heated (Z2 in this case) is acted on with heat by means of a heating device. The heating device 2 can be a heating device that is intrinsically known for such purposes; in particular, it can involve radiant tubes, an electrical heating unit, a flame heating unit, a flame in a jacket radiant tube, some other kind of burner, or an inductor. This heating device 2 acts on the surface of the band 1.

[0068] In this embodiment, the heating device 2 is, for example, an inductor, which can in particular be moved in the direction of arrow 7 toward the surface of the steel band and away from it.

[0069] On the opposite side of the steel band 1, in the zones (Z1 and Z3) that are not supposed to be heated and that are supposed to have a temperature that lies below the temperature in the heated zone Z2, devices 8 are provided, which maintain a constant heat in the zones Z1 and Z3 that are not supposed to be heated or that are supposed to be heated less. This happens by virtue of the fact that in these regions, heat, which has been brought by the heating device 2 into the zone Z2 and is discharged into the zones Z1 and Z3, is introduced into the devices 8 due to thermal conduction and due to a thermal capacity that is as high as possible so that a heat flow from the zone Z2 and/or the heating device 2 that flows into the zones Z1 and Z3 is absorbed by the devices 8.

[0070] The devices 8 in this case can, for example, be solid objects, which rest against the sheet metal band 1 from beneath, in particular cooling elements made of suitable alloys such as an amco alloy; it is also possible for a cooling liquid to flow through these cooling elements. In addition, the devices 8 can also be embodied as cooling rollers 8, which rotate along with the steel sheet band 1 and in this way, on the one hand, absorb the heat and on the other hand, are able to possible dissipate it to suitable cooling devices on the underside.

[0071] In this instance, it is advantageous that there is a very high dividing precision between the zone Z2 to be heated and the zones with a low temperature Z1 and Z3.

[0072] If it is not the central zone Z2 that is heated, but rather one or both of the edge zones, then the arrangement is modified in a corresponding way.

[0073] In order to differently embody the mechanical properties of the steel sheet band or metal band 1 in accordance with the zones, it is necessary, after a corresponding heat treatment, to cool these regions with corresponding cooling rates, thus producing a desired metal structure that possesses a corresponding hardness, ductility, tensile strength, or flexural strength.

[0074] There are already sufficient solutions known from the prior art for zonal cooling of such sheet metal bands.

[0075] A zonal heating of steel sheet bands, however, inevitably results in the fact that the thermal expansion state of the steel sheet band also changes zonally.

[0076] Non-homogeneous temperature distributions in steel sheet bands are to be feared because they result in corresponding occurrences of waviness, and fluttering of the band.

[0077] According to the invention, these occurrences of waviness can be compensated for—particularly after the zonal heating and before the zonal cooling—by providing corresponding; guides, the band can be stabilized, and band flutter can thus be counteracted, without suppressing the waviness by means of pressure with smooth rollers, which can result in cracks in the edge regions of the steel sheet band 1.

[0078] Consequently, a heating in zone Z1 (FIG. 3) causes a thermal expansion to take place there, which results in the fact that the band lines up in an edge region 9. This is taken, into account by the fact that a guide roller 10 assumes this waviness from the basic shape and correspondingly, is likewise embodied as curved. A corresponding roller (not shown can be provided on the top side of the band.

[0079] In FIGS. 3 to 5, the steel belt 1 is respectively shown spaced apart from the roller 10 in order to illustrate the layers; in practice, the steel band naturally must rest against the roller.

[0080] By contrast, if the other edge zone Z3 is acted on with heat (FIG. 4), then the edge region 9 there bends so that in this case, an arching at the edges occurs, which is compensated for by means of a correspondingly shaped roller 10 in a manner that corresponds to FIG. 3.

[0081] If a middle region, i.e. a zone Z2, is acted on with heat, then an arching of the entire steel band 1 occurs so that a convex roller 10 according to FIG. 5 is used; a second roller, which is embodied as concave in accordance with the convexity of the roller 10 (not shown), can be provided in order for the band to be guided above and below. A roller 10 according to FIG. 5, which is embodied as raised or convex, can also be used if zones Z1 and Z3 are acted on with heat, in which case, the convexity in the region of zone Z2 is then somewhat flatter.

[0082] In order to achieve the heating state or in order not to influence the heating state of the respective steel band 1, the rollers 10 can be composed of a material that retains the heat if need be after a start-up phase and keeps an outflow of heat to a minimum. In particular, the rollers 10 can be composed of a ceramic material or of a steel material with a ceramic coating; they can also be provided with a heating medium that flows through them.

[0083] The different rollers 10 for reacting to a different number of heated zones Z1, Z2, and Z3 or different positions thereof can be positioned in revolver stand fashion in the corresponding device for continuous heating or heat-treatment so that these rollers can be pivoted from an idle position into a working position and can be immobilized there, while the previous roller is pivoted out of the working position and into the idle position.

[0084] According to the invention, these convex or formed guide rollers for wavy bands can be positioned after a heating device 2 and before a cooling device (not shown) in order to support the wavy band and also to control the waviness as needed and to act on the band in corresponding fashion.

[0085] This requires that this heating device and the cooling device be situated between the deflection rollers of a corresponding loop-forming system. If the waviness extends across a deflection roller of such a system, then according to the invention, the deflection roller that deflects the still-wavy band, is also embodied as correspondingly convex.

EXAMPLE

[0086] The invention will be explained below based on an example.

[0087] A band steel with the following composition (all values in percent by weight)

[0088] C=0.21

[0089] Mn=1.3

[0090] Si=0.3

[0091] Cr=0.3

[0092] Ti=0.03

[0093] B=0.0025

[0094] remainder=iron and melting-related impurities has a fully martensitic structure and is to be processed in a profiling system.

[0095] In order to achieve an easier formability in the region of the profiling, this band is zonally heated and cooled again, as a result of which, the band is annealed in the zone that has been heated and cooled again and is cooled in such a way that it becomes more ductile in this region.

[0096] To this end, the band is guided through a heating device according to the invention; the band first leaves a guide roller in loop-former, is then zonally subjected to inductive heating and subsequently cooled.

[0097] The band travels through a pass, i.e. two deflection rollers, for 20 meters at a speed of 2 m/s, i.e. in 10 seconds; in this case, the band is heated from 20° C. to 370° C. and is then cooled again.

[0098] After the exit from the pass in the corresponding zone, the tensile strength has decreased by 200 MPa.

[0099] The steel band has a thickness of 2 mm and consequently, this reduction in the tensile strength will be present across the entire band thickness.

[0100] The method according to the invention can also be used for other steel alloys, see the sample compositions in Table 1.

TABLE-US-00001 TABLE 1 Analysis C Si Mn Cr Ni Mo P V A 0.2 0.3 1.3 0.3 0.02 0.002 0.006 0.002 B 0.3 0.3 1.3 0.3 0.02 0.002 0.006 0.002 C 0.2 0.3 2 0.3 0.02 0.002 0.006 0.002 D 0.3 0.3 2 0.3 0.02 0.002 0.006 0.002 E 0.3 0.3 2 0.3 0.02 0.2 0.006 0.002 All values are expressed in percent by weight. Remainder melting-related impurities.

TABLE-US-00002 TABLE 2 Annealing temperature/Rm 350° C. 400° C. 450° C. 500° C. A 1400 1370 1320 1230 B 1580 1540 1480 1370 C 1450 1430 1390 1330 D 1620 1580 1520 1420 E 1650 1620 1580 1520 All values are expressed in MPa.

[0101] For the alloys A through E from Table 1, Table 2 shows the respective tensile strength at an annealing temperature (in the band) of 350° C. to 500° C.,

[0102] In this case, it is clear that by varying the annealing temperature by even 50° C. significant changes occur in the mechanical property, in this case, the tensile strength.

[0103] In the example of alloy E, for example, at an annealing temperature of 350° C., a tensile strength of 1550 MPa is achieved.

[0104] If a zonal width region of for example 250 mm of the right band region is heated with induction to the 500° C. annealing temperature, then in this band region, a tensile strength of 1520 MPa, i.e. a reduction of 130 MPa, can be achieved.

[0105] Naturally, it is also conceivable tot only a certain section to experience this annealing temperature and for the rest of the band to not be annealed.

[0106] Another exemplary embodiment is the intentional annealing, of three narrow strips of 20 mm each in order to enable a selective deformation of the component produced from the band (usual band width approx. 1800 mm) for the sake of improved energy absorption in the event of a crash.

[0107] In this case, induction coils are used to anneal each of the narrow regions across the entire band thickness. The heating and cooling take place within one band pass.

[0108] With the invention, it is advantageous that a method for zonally heating steel sheet bands is created with which the bands, even other metallic bands, can be effectively and reproducible zonally heated and quenched with high dividing precision and can be embodied with zonally different mechanical properties, where a high zonal dividing precision is achieved.

[0109] This invention can advantageously be used not only with three zones, but also with a larger or smaller number of zones with different heating states and mechanical properties.

[0110] The invention relates to a method in which in at least one zone that is to be heated, the hand has a difference in the tensile strength of at least 30 MPa and in particular 50 MPa.

[0111] The invention also relates to a method in which in the one or more zones to be heated, the band has a difference in the tensile strength of at least 5%, in particular 10%, of the tensile strength of the untreated region.

[0112] The invention also relates to a method in which the one or more zones to be heated has/have a width of at least 20 mm.