Patent Application
20240238854
The present disclosure relates to a system for thermomechanical rolling of long semi-finished steel products, and to a method for the production of wire-shaped and/or rod-shaped steel, preferably structural steel, from the long semi-finished steel products, along with a wire-shaped and/or rod-shaped steel product that is preferably obtainable by the method.
Thermomechanical rolling methods, which were originally developed for the production of quality steel, are increasingly also being used for the production of reinforcing steel because, in addition to a significant improvement in the essential properties of structural steel, in particular the ductility properties, a reduction in alloying and operating costs can be achieved at the same time. Ductility properties are crucial here, in particular in earthquake-prone regions, in order to minimize the risk of structural failure of buildings.
In order to be approved as a structural building material, structural steel must meet a set of special technological requirements. These include, above all, specifications for yield strength and tensile strength, ductility, elongation at fracture A, fracture constriction Z, impact energy K, weldability, which is mainly specified as carbon equivalent (Ceq), along with fatigue resistance.
With the thermomechanical methods known from the prior art for the production of wire-shaped and/or rod-shaped structural steel, purely ferritic-pearlitic structures can in principle be achieved over the entire cross-section, such that structural steel products produced in this manner exhibit not only high strength values, but also the required ductility properties. Since the entire cooling process is unstable with respect to the respective target temperatures, the process control frequently results in the abrupt formation of unrecognized, martensitic structures in the edge regions of the wire-shaped and/or rod-shaped structural steel, which have a negative effect with respect to the required ductility properties.
The present disclosure provides a system for the thermomechanical rolling of long semi-finished steel products and a method for the production of wire-shaped and/or rod-shaped steel, in particular structural steel, with which wire-shaped and/or rod-shaped steel, in particular structural steel, can be produced in consistent quality with respect to their structure and mechanical properties.
The system for thermomechanically rolling long semi-finished steel products into a wire-shaped and/or rod-shaped steel comprises a first rolling unit; a second rolling unit, arranged downstream of the first rolling unit in the transporting direction; optionally a first cooling device, arranged between the first and the second rolling units; a first thermomechanical sizing block, arranged downstream of the second rolling unit in the transporting direction; a second cooling device, arranged between the second rolling unit and the first thermomechanical sizing block; a cooling-bed, ring-laying, and/or coil-winding device, arranged downstream of the first thermomechanical sizing block in the transporting direction; a third cooling device, arranged between the first thermomechanical sizing block and the cooling-bed, ring-laying, and/or coil-winding device; and also a structure-sensor device, which is arranged between the first thermomechanical sizing block and the cooling-bed, ring-laying and/or coil-winding device, via which a martensitic structure, in particular a proportion of martensite in percent by area (A.-%), in the thermomechanically rolled long semi-finished steel product or in the steel product wire-shaped and/or rod-shaped steel, as the case may be, can be determined directly in the ongoing process.
In the same manner, the disclosure relates to a method for producing wire-shaped and/or rod-shaped steel from long semi-finished steel products, in particular with a yield strength of at least 300 MPa, preferably with a yield strength of at least 400 MPa, even more preferably with a yield strength of at least 500 MPa, and most preferably with a yield strength of at least 600 MPa, wherein the long semi-finished steel product, optionally heated to a temperature of at least 900° C., preferably to a temperature of at least 950° C., is initially pre-rolled in a first rolling unit and optionally cooled in a subsequent first cooling device; is then re-rolled in a second rolling unit arranged downstream in the transporting direction of the first rolling unit and cooled to a temperature of at least 850° C. in a subsequent second cooling device; is subsequently finish-rolled to the wire-shaped and/or rod-shaped steel in a first thermomechanical sizing block arranged downstream in the transporting direction of the second cooling device, which is cooled to a temperature in the range of 400° ° C. to 850° C. in a third cooling device adjoining the first thermomechanical sizing block; is then fed to a cooling-bed, ring-laying, and/or coil-winding device arranged downstream in the transporting direction of the third cooling device, wherein, by means of a structure-sensor device arranged in a section between the first thermomechanical sizing block and the cooling-bed, ring-laying and/or coil-winding device, any martensitic structure present in the thermomechanically rolled long semi-finished steel product or in the wire-shaped and/or rod-shaped steel is determined directly in the ongoing process.
By introducing the structure-sensor device, via which a martensitic structure that may be present, in particular the proportion of martensite in A.-%, can be continuously determined in the thermomechanically finished-rolled wire-shaped and/or rod-shaped steel, the production process can be made significantly more effective, since the online identification of the martensite structure can be used to directly influence the respective process parameters, for example to the effect that the temperature in the respective cooling devices, the rolling temperature and/or the removal in the respective rolling units can be adjusted.
This results in wire-shaped and/or rod-shaped steel, in particular structural steel, which has an almost constant martensite-free quality with respect to its structure. In addition, in the event of a faulty and/or unfavorable cooling temperature in the respective cooling devices, the scrap rate can be promptly detected and directly corrected via the online sensor system.
Further advantageous embodiments of the invention are indicated in the dependent formulated claims. The features listed individually in the dependent formulated claims can be combined with one another in a technologically useful manner and may define further embodiments of the invention. In addition, the features indicated in the claims are further specified and explained in the description, wherein further preferred embodiments of the invention are shown.
It should be noted that the temperatures stated here represent the average temperatures over the cross-section of the rolling stock and therefore cannot be equated with surface temperatures.
Within the context of the present disclosure, the term “long semi-finished steel products” is understood to mean semi-finished steel products that are suitable for the production of the wire-shaped and/or rod-shaped steel or steel products, in particular structural steel. Such long semi-finished steel products are also called billets and usually have a square or rectangular cross-section.
Within the context of the present disclosure, the term “wire-shaped and/or rod-shaped steel or steel products” is understood to mean steel products, in particular structural steel. These preferably have a round cross-section with a ribbed and/or smooth surface. However, in an alternative embodiment, they can also have a square, a rectangular or a hexagonal cross-section.
Wire-shaped steel products can have a diameter in the range of 4.5 to 29 mm, preferably a diameter in the range of 5.5 to 16 mm, and are fed at the end of the production line to a ring-laying device, in particular a coil layer. The ring-laying device or coil layer forms the wire-shaped steel product into wire coils of a desired size, which are then fanned out on a roller table for homogeneous cooling and subsequently collected as a coil in a coil-forming chamber.
Rod-shaped steel products, on the other hand, can have diameters in the range of 8.0 to 60.0 mm or 6.0 to 50.0 mm. If the long semi-finished steel products are to be processed into rod steel with finished lengths of up to 12 m, the rod-shaped steel products have a diameter in the range of 8.0 to 60.0 mm and are fed to a cooling bed at the end of the production line. If the long semi-finished steel products are to be processed into rod steel that is wound into a coil, the rod-shaped steel products have a diameter in the range of 6.0 to 50 mm, preferably a diameter in the range of 6.0 to 32.0 mm, and are then fed to a coil-winding device at the end of the production line.
The first rolling unit, in which the long steel semi-finished product heated in advance to a temperature of at least 900° C., preferably to a temperature of at least 950° C., is pre-rolled, can be formed from a plurality of housingless rolling mill stands. Advantageously, the first rolling unit comprises at least six, more preferably at least eight, still more preferably at least ten, and most preferably twelve of such housingless rolling mill stands.
A first cooling device can be arranged downstream of the first rolling unit if the temperature of the pre-rolled long steel semi-finished product needs to be regulated. The first cooling device comprises one or two water tanks spaced apart from one another in a first line section between the first and second rolling units.
The pre-rolled long semi-finished steel products are then re-rolled in the second rolling unit. Advantageously, the second rolling unit comprises at least two, more preferably at least four, and most preferably six housingless rolling mill stands.
In addition, or alternatively, the first and/or the second rolling unit can comprise hydraulically adjustable rolling mill stands instead of the housingless rolling mill stands.
In a further advantageous embodiment, the long semi-finished steel product finish-rolled in the second rolling unit can be split by forming in the last rolling mill stand in the transporting direction into two individual strands, which can be finish-rolled in the further process in thermomechanical sizing blocks arranged parallel to one another to form the wire-shaped and/or rod-shaped steel products.
In the transporting direction behind the second rolling unit, the second cooling device is arranged in a second line section. Advantageously, the second cooling device comprises at least two, more preferably at least three or four, water tanks, which are spaced apart from one another in the second section of the line, in order to achieve a temperature reduction in the rolling stock prior to the step of thermomechanical rolling.
The first and second line sections are preferably selected in such a manner that the rolling stock is given sufficient time for adequate temperature equalization across the cross-section. The temperature in the rolling stock is equalized by conduction from the core to the surface. In order to achieve as uniform a temperature as possible over the entire cross-section of the rolling stock, it is particularly preferred that a temperature gradient of maximum 100° C., more preferably a temperature gradient of maximum 80° C., even more preferably a temperature gradient of maximum 60° C., and most preferably a temperature gradient of maximum 50° C. is set. The homogenization of the cross-section temperatures can be controlled indirectly between the respective stations by measuring the surface temperatures of the rolled long steel semi-finished product. Corresponding process models can also be used as a supplement.
As such, the first line section between the first and second rolling units advantageously has a length of 40 to 80 m, more preferably a length of 45 to 60 m. Advantageously, the second line section between the second rolling unit and the first thermomechanical rolling block has a length of 100 to 140 m, more preferably a length of 115 to 130 m.
The rolled long semi-finished steel product cooled down to a temperature of at least 850° C. in the second cooling device is then fed to the first thermomechanical sizing block, in which it is finish-rolled to the desired or specified end diameter.
In a particularly advantageous embodiment, it is provided that the rolled long steel semi-finished product is fed to the first thermomechanical sizing block at a temperature in the range of 700° C., preferably at a temperature of at least 730° C., more preferably at a temperature of at least 750° C. still more preferably at a temperature of at least 760° C., and most preferably at a temperature of at least 770° C. However, the temperature of the rolled long semi-finished steel products must not be too high, since otherwise the temperature gradient between the surface and the core temperatures, which is required for the metallurgical recrystallization processes and the associated grain refinement effects, and which is as low as possible, cannot be set. As such, the temperature at which the rolled long steel semi-finished product is fed to the first thermomechanical sizing block is limited to 850° C., preferably to 840° C., more preferably to 820° C., and most preferably to 800° C. Particularly preferably, the rolled long semi-finished steel product is fed to the first thermomechanical sizing block at a temperature of 780° C.
In the thermomechanical sizing block, the highest forming or the highest reduction, as the case may be, takes place, which can preferably be 30 to 80%. The thermomechanical sizing block can be of single-stand, preferably two-stand, more preferably four-stand, even more preferably six-stand, and most preferably eight-stand design.
In a further advantageous embodiment, the system can comprise a second thermomechanical sizing block between the first thermomechanical sizing block and the third cooling device, which can also be of single-stand, preferably two-stand, more preferably four-stand, even more preferably six-stand, and most preferably eight-stand design. In this connection, it is particularly preferably provided that an intermediate cooling device is provided between the two thermomechanical sizing blocks, comprising one or two water tanks that are spaced apart from one another. For example, in a first advantageous embodiment, the first thermomechanical sizing block can be of four-stand design and the second thermomechanical sizing block can be of two-stand design. In a further advantageous embodiment, the first thermomechanical sizing block can, for example, be of four-stand design, and the second thermomechanical sizing block can also be of four-stand design. Any other combination is possible and conceivable with respect to the distribution of the aforementioned stands between the two thermomechanical sizing blocks.
In addition, a thermomechanical sizing block formed in a basic design, for example a six-stand thermomechanical sizing block, could be divided into six single-stand thermomechanical sizing blocks, wherein an intermediate cooling device with at least one water tank is provided between each two of such six single-stand thermomechanical sizing blocks within the entire cascade of, for example, six single-stand thermomechanical sizing blocks.
The thermomechanical sizing blocks are in principle known and marketed by the applicant under the brand name MEERdrive®.
The third cooling device is then arranged in a third line section downstream of the first, optionally second, thermomechanical sizing block, in which the long semi-finished steel products, which have been finish-rolled into wire-shaped and/or rod-shaped steel, are cooled in order to stop further grain growth. The third cooling device comprises at least one, preferably at least two, more preferably at least three, still more preferably at least four, and most preferably at least five water tanks, by means of which the wire-shaped and/or rod-shaped steel are cooled in order, on the one hand, to ensure temperature equalization and, on the other hand, to prevent the formation of hardened structures in the form of martensite or bainite.
Particularly advantageously, the third cooling device comprises two to twelve water tanks, more preferably four to ten water tanks.
The cooling capacity of the respective water tanks of each cooling device can be set in a targeted manner on the basis of the volume flow of the cooling water, the number of active cooling tubes per water tank, the cooling tube diameter and/or the cooling water pressure and, if necessary, the cooling water temperature. The specifications can typically be predetermined by means of specific process models and adjusted by online control.
An exemplary water tank can have a water tank length of 6500 mm and comprise six cooling tubes, in each case 750 mm long. Such a water tank then typically has a maximum cooling water quantity of 230 m3/h and an adjustable cooling water pressure range of 1.5 to 6.0 bar.
The third line section, which extends between the first or second thermomechanical sizing block and the cooling-bed, ring-laying, and/or coil-winding device, is also preferably selected in such a manner that the rolling stock is given sufficient time for adequate temperature equalization across the cross-section. As such, preferably, a temperature gradient of at most 100° C., more preferably a temperature gradient of at most 80° C., still more preferably a temperature gradient of at most 60° ° C., and most preferably a temperature gradient of at most 50° C. is set in the long semi-finished steel product that has been finish-rolled into wire shape and/or rod shape. Advantageously, the third line section therefore has a transport length of 110 to 150 m, more preferably a transport length of 110 to 130 m. In this connection, it has been shown to be particularly preferable that cooling as soon as possible immediately after the last pass, i.e. after the first or second thermomechanical sizing block, is decisive for controlling the recrystallization processes and achieving a high fine grain size, preferably with an average grain diameter of less than 12.0 μm, even more preferably with an average grain diameter of less than 10.0 μm.
Advantageously, it is therefore provided that the wire-shaped and/or rod-shaped steel, which have a temperature in the range of 700° C. to 1100° C. after the last pass, are fed to the third cooling device, in particular to the first water tank of the third cooling device, after a maximum of 300 ms, preferably after a maximum of 200 ms, even more preferably after a maximum of 100 ms, further preferably after a maximum of 90 ms, and most preferably after a maximum of 80 ms.
In order to prevent further grain growth, the wire-shaped and/or rod-shaped steel are cooled to such an extent that a cooling-bed inlet temperature, an inlet temperature into the ring-laying device and/or an inlet temperature into the coil-winding device in the range of 400° ° C. to 850° C. is achieved. A particularly advantageous cooling-bed inlet temperature is 550° C. to 750° C., more preferably 600° C. to 650° ° C. A particularly advantageous inlet temperature into the coil-winding device, on the other hand, is 450° C. to 550° C. A particularly advantageous inlet temperature into the ring-laying device is 600° C. to 750° C.
The structure-sensor device, which is arranged in the third section between the first or second thermomechanical sizing block and the cooling-bed, ring-laying, and/or coil-winding device, can advantageously be arranged in the transporting direction directly upstream of the cooling-bed, ring-laying, and/or coil-winding device, directly upstream of a separating device arranged in the transporting direction upstream of the cooling-bed, ring-laying, and/or coil-winding device, and/or in the transporting direction, optionally directly downstream of the third cooling device, in particular downstream of the last water tank. An arrangement between two water tanks of the plurality of water tanks in the third cooling device is also possible.
In an advantageous embodiment, the system comprises a respective structure-sensor device downstream of each of the plurality of water tanks arranged within the third cooling device in the third line section. Thereby, each of the plurality of water tanks can be individually set and the formation of martensitic structures can be allocated to the specific water tanks.
The structure-sensor device can be used to identify the martensitic structure, in particular a proportion of martensite in A.-%, in the wire-shaped and/or rod-shaped steel online in the ongoing process. In principle, all techniques known to the person skilled in the art at the time of application can be used as measuring methods. Advantageously, however, it is provided that the structure-sensor device comprises an ultrasonic measuring device, an X-ray measuring device, a radar measuring device and/or an electro-magnetic measuring device for identifying the undesirable martensite.
The structure-sensor device can advantageously be coupled with an open-loop or closed-loop control device via which, optionally with the aid of corresponding algorithms, active interventions can be made in the respective process steps in order to set the desired structure.
In a further aspect, the present disclosure further relates to a wire-shaped and/or rod-shaped steel product, preferably produced by the described process, in particular having a yield strength of at least 300 MPa, more preferably a yield strength of at least 400 MPa, even more preferably a yield strength of at least 500 MPa, and most preferably a yield strength of at least 600 MPa, having a proportion of martensite of at most 15.0 A.-%, preferably a proportion of martensite of at most 10.0 A.-%, more preferably a proportion of martensite of at most 8.0 A.-%, still more preferably a proportion of martensite of at most 6.0 A.-%, and most preferably a proportion of martensite of at most 5.0 A.-%.
Preferably, the wire-shaped and/or rod-shaped steel, in particular structural steel, has the following chemical composition in % by weight:
As further accompanying elements, the wire-shaped and/or rod-shaped steel can preferably comprise the following elements individually and/or in combination (in % by weight):
It is particularly preferred that the wire-shaped and/or rod-shaped steel, in particular structural steel, has a carbon equivalent (Ceq) of ≤0.60, more preferably a carbon equivalent (Ceq) of ≤0.50.
The invention and the technical environment are explained in more detail below with reference to figures and examples. It should be noted that the invention is not intended to be limited by the exemplary embodiments shown. In particular, unless explicitly shown otherwise, it is also possible to extract partial aspects of the facts explained in the figures and/or examples and combine them with other components and findings from the present description and/or figures. In particular, it should be noted that the figures and in particular the size relationships shown are only schematic. Identical reference signs designate identical objects, such that explanations from other figures can be used as a supplement if necessary.
To produce the corresponding wire-shaped and/or rod-shaped steel 3, the long semi-finished steel products 2 are initially fed to a reheating furnace 4, in which the long semi-finished steel products 2 to be rolled are heated to a temperature of 900° C. to 1000° C.
The long semi-finished steel products 2 that are then heated are fed to a first rolling unit 5, in which they are pre-rolled in a cascade of twelve housingless rolling mill stands (not shown). Thereby, a reduction of 20 to 40% per pass is achieved in the respective rolling mill stand. The average temperature of the rolling stock in the first rolling unit 5 is 900° C. to 1100° C.
A first cooling device 6 with one or two water tanks can be arranged downstream of the first rolling unit 5 in the transporting direction in order to be able to readjust the temperature of the pre-rolled long steel semi-finished product 2 before it is fed to a second rolling unit 7. The first cooling device 6 is arranged in a first line section 8 between the first and second rolling units 5, 7, which is selected in such a manner that the rolling stock has sufficient time for adequate temperature equalization between the two rolling processes. The first line section 8 can have a length of 45 to 60 m.
In the second rolling unit 7, the pre-rolled long semi-finished steel products 2 are then re-rolled in a cascade of six rolling housingless mill stands (not shown), wherein a reduction of 20 to 30% per pass is achieved in the respective rolling mill stand. The average temperature of the rolling stock in the second rolling unit 7 is 800° C. to 1000° C.
A second cooling device 9 is arranged in a second line section 10 downstream of the second rolling unit 7, which in the present case comprises three spaced-apart water tanks (not shown), in order to reduce the temperature of the 800° C. to 1000° C. hot rolling stock before the subsequent step of thermomechanical rolling. The second line section 10 is also selected in such a manner that, in addition to the temperature reduction, the rolling stock is given sufficient time for adequate temperature equalization over its cross-section. As such, the second line section can be 115 m to 130 m long.
The re-rolled and cooled long semi-finished steel product 2, which by now has a round and/or oval cross-section, is then fed to a first thermomechanical sizing block 11 at a temperature in the range of 740° ° C. to 800° C. and finish-rolled to the desired or specified, as the case may be, end diameter, which can be 8 mm, 18 mm or 25 mm, for example. In one embodiment, the first thermomechanical sizing block 11 can be designed with six stands, wherein a reduction of approximately 22 to 27% can be achieved per pass in the individual stands.
In a further embodiment, the first thermomechanical sizing block 11/11.1 can be supplemented by a second thermomechanical sizing block 11.2, which can also be of multi-stand design. In this embodiment, an intermediate cooling device 13 with at least one water tank (not shown) is provided in an intermediate line section 12 formed between the two thermomechanical sizing blocks 11.1, 11.2. This intermediate line section 12 also has a specific length of 30 m, for example, in order to allow the rolling stock sufficient time for adequate temperature equalization over its cross-section.
The third cooling device 14 is then arranged in the transporting direction in a third line section 15 downstream of the first or second thermomechanical sizing block 11.1, 11.2. In this, the long semi-finished steel products 2, which have been finish-rolled into wire-shaped and/or rod-shaped steel 3 and have a temperature of 700° C. to 1050° C., are cooled by a cascade of four or five water tanks spaced one behind the other, in order to prevent further grain growth and the formation of hardened structures in the form of martensite or bainite. For this purpose, cooling immediately after the last pass, which should be as short as possible, is necessary to control the recrystallization processes and to achieve a high fine grain size with an average grain diameter in the range of 6.0 to 10.0 μm. In order to allow the rolling stock sufficient time for sufficient temperature equalization over its cross-section on the way to the last station, the third line section 15 is also selected to be correspondingly long. This can have a length of 110 to 130 m, for example.
Depending on the embodiment, the rod-shaped steel 3 is then fed at a cooling-bed inlet temperature of 550° C. to 750° C. to a cooling-bed device 16, at an inlet temperature of 600° ° C. to 750° ° C. to a coil layer 16, or at a coil winding temperature of 450° ° C. to 550° ° C. to a coil-winding device 16.
Since the entire cooling process is unstable with respect to the respective target temperatures, and thus an abrupt formation of martensitic structures can occur in the course of process control, the system 1 also comprises a structure-sensor device 17 arranged in the third line section 15.
Via the structure-sensor device 17, the formation of a martensitic structure, in particular a proportion of martensite in A.-%, in the wire-shaped and/or rod-shaped steel 3 can be identified online in the ongoing process.
To identify the undesirable martensite, the structure-sensing device 17 can comprise, for example, an ultrasonic sensing device, an X-ray sensing device, a radar sensing device and/or an electro-magnetic sensing device.
Via the dashed arrows, possible positionings of the structure-sensor device 17 in the third line section 15 are shown. For example, this can be arranged upstream of the third cooling device 14 in the transporting direction or immediately upstream of the cooling-bed, ring-laying, and/or coil-winding device 16. An arrangement between the water tanks of the plurality of water tanks in the third cooling device 14 or in the intermediate line section 12 is also possible.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 205 429.3 | May 2021 | DE | national |
This application is a national stage application, filed under 35 U.S.C. § 371, of International Patent Application PCT/EP2022/058212, filed on Mar. 29, 2022, which claims the benefit of German Patent Application DE 10 2021 205 429.3 filed on May 28, 2021.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/058212 | 3/29/2022 | WO |
