System and method for producing steel products in the form of wires and / or bars

Abstract

The present application relates to a system (1) and a method for the thermomechanical rolling of long semifinished steel products (2), comprising a first rolling device (5); a second rolling device (7), arranged downstream of the first rolling device (5) in the transporting direction; optionally a first cooling device (6), arranged between the first and second rolling devices (5, 7); a first thermomechanical sizing block (11), arranged downstream of the second rolling device (7) in the transporting direction; a second cooling device (9), arranged between the second rolling device (7) and the first thermomechanical sizing block (11, 11.1); a cooling-bed, ring-laying and / or coil-winding device (16), arranged downstream of the first thermomechanical sizing block (11) in the transporting direction; a third cooling device (14), arranged between the first thermomechanical sizing block (11) and the cooling-bed, ring-laying and / or coil-winding device (16); and also a structure-sensor device (17), which is arranged between the first thermomechanical sizing block (11) and the cooling-bed, ring-laying and / or coil-winding device (16) and can be used for determining directly in the ongoing process a martensitic structure, in particular a proportion of martensite in percent by area (% by area), in the thermomechanically rolled long semifinished steel product or in the steel product (3) in the form of a wire or bar.

Description

[0001] The present invention relates to a system for the thermomechanical rolling of long steel semi-finished products, a method for producing wire and / or rod-shaped steels, preferably structural steels, from the long steel semi-finished products, in particular with a yield strength of at least 300 MPa, preferably with a yield strength of at least 400 MPa, and a wire and / or rod-shaped steel product, which is preferably obtainable according to the method according to the invention.

[0002] Thermomechanical rolling processes, originally developed for the production of high-quality steels, are increasingly being used for the production of reinforcing steel. This is because, in addition to significantly improving the essential properties of structural steel, particularly its ductility, these processes simultaneously reduce alloying and operating costs. Ductility is of crucial importance, especially in earthquake-prone regions, to minimize the risk of structural failure.

[0003] To be approved as a structural material, structural steel must meet several specific technological requirements. These include, in particular, specifications for yield strength and tensile strength, ductility, elongation at break (A), reduction of area (Z), impact strength (K), weldability (mainly expressed as carbon equivalent (Ceq)), and fatigue resistance.

[0004] With the thermomechanical processes known from the prior art for the production of wire and / or bar-shaped structural steels, purely ferritic-pearlitic microstructures can generally be achieved across the entire cross-section, so that structural steel products manufactured in this way 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 often leads to the sudden formation of undetected martensitic microstructures in the surface regions of the wire and / or bar-shaped structural steels, which negatively impacts the required ductility properties.

[0005] For example, EP 0 496 726 A2 discloses a method and a plant for the continuous production of wire wound into rings, in which a continuously cast strand of material is rolled into a wire with a predetermined cross-section and the wire exiting the rolling stand is first rapidly and briefly cooled to a higher temperature than the temperature of the surface layer to form a martensitic or bainitic surface layer and a core zone of the wire material, whereupon the wire is left in a subsequent tempering zone until the quenched surface layer is tempered by the supply of heat, and then a length of wire is gathered into a ring without tension or twist, and the immediately following length of wire is deflected and also gathered into a ring without tension or twist.

[0006] In the publication by M. Albedyhl et al., Stahl & Eisen, "Temperature-controlled rolling of bar steel and wire", Vol. 108 (1988), October 31, No. 22, a thermomechanical rolling process for rolling bar steel is described. For this purpose, the two last finishing stands were arranged at a distance of 25 m from the finishing mill, whereby a temperature reduction before the last two passes was achieved by means of an intermediate cooling section.

[0007] The present invention is therefore based on the objective of providing a system for the thermomechanical rolling of long steel semi-finished products and a method for the production of wire and / or bar-shaped steels, in particular structural steels, with which wire and / or bar-shaped steels, in particular structural steels, can be produced in consistent quality with regard to their microstructure and mechanical properties.

[0008] According to the invention, the problem is solved by a system with the features of claim 1 and a method with the features of claim 8.

[0009] The inventive system for thermomechanical rolling of long steel semi-finished products into wire- and / or rod-shaped steel comprises a first rolling device; a second rolling device arranged downwards in the transport direction of the first rolling device; optionally,a first cooling device arranged between the first and second rolling mills; a first thermomechanical sizing block arranged downwards in the transport direction of the second rolling mill; a second cooling device arranged between the second rolling mill and the first thermomechanical sizing block; a cooling bed, ring forming and / or coil winding device arranged downwards in the transport direction of the first thermomechanical sizing block; a third cooling device arranged between the first thermomechanical sizing block and the cooling bed, ring forming and / or coil winding device; and a microstructure sensor device arranged between the first thermomechanical sizing block and the cooling bed, ring forming and / or coil winding device, by which a martensitic microstructure, in particular a martensite content in areal percent (A%), in the thermomechanically rolled long steel semi-finished product is detected.in the wire and / or rod-shaped steel, which can be directly determined during the ongoing process.

[0010] Similarly, the invention relates to a method for producing wire- and / or rod-shaped steels from long steel semi-finished products with a yield strength of at least 300 MPa, preferably with a yield strength of at least 400 MPa, 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 steel semi-finished product, heated to a temperature of at least 900 °C, preferably to a temperature of at least 950 °C, is first pre-rolled in a first rolling device and optionally cooled in a subsequent first cooling device; then re-rolled in a second rolling device arranged downwards in the transport direction of the first rolling device and cooled to a temperature of at least 850 °C in a subsequent second cooling device;The steel is then finished in a first thermomechanical rolling mill arranged downwards in the transport direction of the second cooling unit, resulting in wire and / or bar-shaped steel. This steel is then cooled to a temperature in the range of 400 °C to 850 °C in a third cooling unit connected to the first thermomechanical rolling mill. It is then fed to a cooling bed, ring forming, and / or coil winding unit arranged downwards in the transport direction of the third cooling unit. A microstructure sensor, located in a section between the first thermomechanical rolling mill and the cooling bed, ring forming, and / or coil winding unit, detects any martensitic microstructure present in the thermomechanically rolled long steel semi-finished product or in the wire and / or bar-shaped steel during the ongoing process.

[0011] By introducing the microstructure sensor device, which allows for the continuous determination of any martensitic microstructure present, in particular the martensite content in A%, in the thermomechanically finished wire and / or bar-shaped steel, the manufacturing process can be made significantly more effective, since the online identification of the martensitic microstructure allows direct influence on the respective process parameters, for example, by adjusting the temperature in the respective cooling devices, the rolling temperature and / or the removal rates in the respective rolling units.

[0012] This process yields wire and / or rod-shaped steels, particularly structural steels, that exhibit a virtually consistent, martensite-free microstructure. Additionally, online sensors allow for the timely detection and immediate correction of scrap rates in the event of faulty and / or unfavorable cooling temperatures in the respective cooling systems.

[0013] Further advantageous embodiments of the invention are specified in the dependent claims. The features listed individually in the dependent claims can be combined in a technologically meaningful manner and can define further embodiments of the invention. Furthermore, the features specified in the claims are specified and explained in more detail in the description, which also presents further preferred embodiments of the invention.

[0014] It should be noted that the temperatures mentioned here represent the average temperatures across the cross-section of the rolled material and therefore cannot be equated with surface temperatures.

[0015] For the purposes of the present invention, the term "long steel semi-finished products" refers to steel semi-finished products suitable for the production of the wire and / or bar-shaped steels or steel products according to the invention, in particular structural steels. Such long steel semi-finished products are also referred to as billets and generally have a square or rectangular cross-section.

[0016] For the purposes of the present invention, the term "wire and / or bar-shaped steels or steel products" refers to steel products, in particular structural steels. These preferably have a round cross-section with a ribbed and / or smooth surface. In an alternative embodiment, however, they can also have a square, rectangular, or hexagonal cross-section.

[0017] Wire-shaped steel products according to the present invention 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 to a coil forming device, in particular a coil forming device, at the end of the production line. The wire-shaped steel product is formed into wire coils of a desired size by the coil forming device or coil forming device, then fanned out on a roller conveyor for homogeneous cooling, and subsequently collected as a coil in a coil forming chamber.

[0018] Rod-shaped steel products, on the other hand, can have a diameter in the range of 8.0 to 60.0 mm or 6.0 to 50.0 mm. If the long steel semi-finished products are to be processed into bar 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 steel semi-finished products are to be processed into bar 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.

[0019] The first rolling mill, in which the long steel semi-finished product, preheated 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 standless rolling stands. Advantageously, the first rolling mill comprises at least six, more preferably at least eight, even more preferably at least ten, and most preferably twelve of these standless rolling stands.

[0020] In the direction of transport, downstream of the first rolling mill, a first cooling unit can be arranged if the temperature of the pre-rolled long steel semi-finished product needs to be regulated. The first cooling unit comprises one or two water tanks, which are spaced apart from each other in a first section of the track between the first and the second rolling mill.

[0021] In the second rolling mill, the pre-rolled long steel semi-finished products are then re-rolled. The second rolling mill advantageously comprises at least two, more preferably at least four, and most preferably six standless rolling stands.

[0022] Additionally or alternatively, the first and / or the second rolling mill can include hydraulically adjustable rolling mills instead of standless rolling stands.

[0023] In another advantageous embodiment, the long steel semi-finished product, which has been finished in the second rolling unit, can be separated into two individual strands by forming in the last rolling stand in the transport direction, which can then be finished rolled into wire and / or rod-shaped steel products in the further process in thermomechanical dimension rolling blocks arranged parallel to each other.

[0024] In the direction of transport, downstream of the second rolling unit, the second cooling unit is arranged in a second section of the track. Advantageously, the second cooling unit comprises at least two, more preferably at least three or four, water tanks spaced apart from each other in the second section of the track to reduce the temperature of the rolled material before the thermomechanical rolling step.

[0025] The first and second sections of the rolling process are preferably selected such that the rolled material has sufficient time for adequate temperature equalization across its cross-section. Temperature equalization within the rolled material occurs through conduction from the core to the surface. To achieve the most uniform temperature possible across the entire cross-section of the rolled material, a temperature gradient of no more than 100 °C, more preferably no more than 80 °C, even more preferably no more than 60 °C, and most preferably no more than 50 °C is preferably applied. The homogenization of the cross-sectional temperatures can be controlled indirectly between the respective stations by measuring the surface temperatures of the rolled long steel semi-finished product. Alternatively, appropriate process models can also be used.

[0026] The first section of track between the first and second rolling mills therefore advantageously has a length of 40 to 80 m, more preferably a length of 45 to 60 m. The second section of track between the second rolling mill and the first thermomechanical rolling block advantageously has a length of 100 to 140 m, more preferably a length of 115 to 130 m.

[0027] The rolled long steel semi-finished product, cooled down to a temperature of at least 850 °C in the second cooling unit, is then fed to the first thermomechanical dimensional rolling mill, in which it is finished-rolled to the desired or specified final diameter.

[0028] In a particularly advantageous embodiment, the rolled long steel semi-finished product is fed to the first thermomechanical dimensional rolling 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, even 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 steel semi-finished products must not be too high, as otherwise the necessary and minimal temperature gradient between surface and core temperature, required for the metallurgical recrystallization processes and the associated grain refinement effects, cannot be achieved.Therefore, the temperature at which the rolled long steel semi-finished product is fed to the first thermomechanical sizing die is limited to 850 °C, preferably to 840 °C, more preferably to 820 °C, and most preferably to 800 °C. It is particularly preferred that the rolled long steel semi-finished product be fed to the first thermomechanical sizing die at a temperature of 780 °C.

[0029] The highest degree of deformation or reduction, preferably 30 to 80%, takes place in the thermomechanical sizing roll. The thermomechanical sizing roll can be designed with one, preferably two, more preferably four, even more preferably six, and most preferably eight stands.

[0030] In a further advantageous embodiment, the system can include a second thermomechanical rolling mill between the first thermomechanical rolling mill and the third cooling unit. This second rolling mill can also be configured with one, preferably two, more preferably four, even more preferably six, and most preferably eight stands. In this context, it is particularly preferred that an intermediate cooling unit be provided between the two thermomechanical rolling mills, comprising one or two spaced-apart water tanks. For example, in a first advantageous embodiment, the first thermomechanical rolling mill can be configured with four stands and the second thermomechanical rolling mill with two stands.In another advantageous embodiment, the first thermomechanical rolling mill can, for example, have four stands, and the second thermomechanical rolling mill can also have four stands. Any other combination is possible and conceivable with regard to the distribution of the aforementioned stands between the two thermomechanical rolling mills.

[0031] Thus, a thermomechanical dimensional rolling mill designed in a basic configuration, for example a six-stand thermomechanical dimensional rolling mill, could also be divided into six single-stand thermomechanical dimensional rolling mills, whereby within the entire cascade of, for example, six single-stand thermomechanical dimensional rolling mills, an intermediate cooling device with at least one water tank must be provided between each pair of these six single-stand thermomechanical dimensional rolling mills.

[0032] The thermomechanical dimensioning blocks are generally known and are marketed by the applicant under the brand name MEERdrive ®<.

[0033] In the direction of transport, downstream of the first, and optionally second, thermomechanical rolling mill, the third cooling unit is arranged in a third section of the mill. In this unit, the long steel semi-finished products, which have been finished to wire and / or bar form, are cooled to prevent further grain growth. The third cooling unit comprises at least one, preferably at least two, more preferably at least three, even more preferably at least four, and most preferably at least five water tanks. These tanks cool the wire and / or bar form to ensure temperature equalization and to prevent the formation of hardened microstructures in the form of martensite or bainite.

[0034] The third cooling unit particularly advantageously comprises two to twelve water crates, more preferably four to ten water crates.

[0035] The cooling capacity of each water tank in any cooling system can be precisely adjusted based on the cooling water flow rate, the number of active cooling pipes per tank, the cooling pipe diameter and / or the cooling water pressure, and, if applicable, the cooling water temperature. These parameters can typically be predefined using specific process models and adjusted via online control.

[0036] An example water tank might have a length of 6500 mm and include six cooling pipes, each 750 mm long. Such a water tank would then typically have a maximum cooling water flow rate of 230 m³ / h and an adjustable cooling water pressure range of 1.5 to 6.0 bar.

[0037] The third section of the track, which extends between the first or second thermomechanical rolling mill and the cooling bed, ring forming, or coil winding unit, is preferably selected such that the rolled material has sufficient time for adequate temperature equalization across its cross-section. Therefore, a temperature gradient of no more than 100 °C, more preferably a temperature gradient of no more than 80 °C, even more preferably a temperature gradient of no more than 60 °C, and most preferably a temperature gradient of no more than 50 °C is preferably established in the finished long steel semi-finished product rolled into wire and / or bar-shaped steel. Advantageously, the third section of the track thus has a transport length of 110 to 150 m, more preferably a transport length of 110 to 130 m.In this context, it has proven particularly advantageous that cooling that begins as soon as possible immediately after the last pass, i.e., after the first or second thermomechanical die-rolling block, is crucial for controlling the recrystallization processes and for achieving a high fine grain size, preferably with an average grain diameter of less than 12.0 µm, and even more preferably with an average grain diameter of less than 10.0 µm.

[0038] Advantageously, it is therefore provided that the wire and / or rod-shaped steels, which after the last cut have a temperature in the range of 700 °C to 1100 °C, are fed to the third cooling device, in particular 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.

[0039] To prevent further grain growth, the wire and / or rod-shaped steels are cooled to such an extent that a cooling bed inlet temperature, an inlet temperature to the coil forming unit, and / or an inlet temperature to the coil winding unit 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 to the coil winding unit, on the other hand, is 450 °C to 550 °C. A particularly advantageous inlet temperature to the coil forming unit is 600 °C to 750 °C.

[0040] The structural sensor device according to the invention, which is arranged in the third section between the first or second thermomechanical dimensional rolling block and the cooling bed, ring forming, or coil winding device, can advantageously be arranged in the transport direction directly upstream of the cooling bed, ring forming, or coil winding device, directly upstream of a separating device arranged upstream of the cooling bed, ring forming, or coil winding device in the transport direction, and / or in the transport direction, optionally directly, downstream of the third cooling device, in particular downstream of the last water tank. An arrangement between two water tanks or the plurality of water tanks in the third cooling device is also possible.

[0041] In an advantageous embodiment, the system comprises a microstructure sensor device according to the invention behind each of the plurality of water tanks arranged within the third cooling unit in the third section of the system. This allows each of the plurality of water tanks to be individually adjustable and the formation of martensitic structures in the specific water tanks to be attributed to them.

[0042] The microstructure sensor device enables the online identification of the martensitic microstructure, in particular the martensite content in A%, in wire and / or bar-shaped steels during the ongoing process. In principle, all techniques known to those skilled in the art at the time of filing can be used as measurement methods. Advantageously, however, the microstructure sensor device is designed to include an ultrasonic measuring device, an X-ray measuring device, a radar measuring device, and / or an electromagnetic measuring device for identifying the unwanted martensite.

[0043] The microstructure sensor device can advantageously be coupled with a control and / or regulation device, via which, if necessary with the help of appropriate algorithms, active interventions can be made in the respective process steps in order to adjust the desired microstructure.

[0044] In a further aspect, the present invention relates to a wire and / or rod-shaped steel product produced according to the inventive method, 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, comprising a martensite content of at most 15.0 A%, preferably a martensite content of at most 10.0 A%, more preferably a martensite content of at most 8.0 A%, even more preferably a martensite content of at most 6.0 A%, and most preferably a martensite content of at most 5.0 A%, wherein the wire and / or rod-shaped steel, in particular structural steel, has the following chemical composition in wt.%: Carbon: 0.04 to 0.35, Silicon: 0.10 to 0.80, Manganese: 0.40 to 1.60, Phosphorus: maximum 0.06, Sulfur: maximum 0.06, Nitrogen: maximum 0.012, as well as residual iron, possibly other accompanying elements, and unavoidable impurities.

[0045] The wire and / or rod-shaped steel may also preferably include the following elements individually and / or in combination (in wt.%): Chrome: maximum 0.40, Molybdenum: maximum 0.20, Nickel: maximum 0.90, Copper: 0.65 to 1.0, Lead: maximum 0.25, Tin: maximum 0.07.

[0046] It is particularly preferred that the wire 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.

[0047] The invention and its technical context 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 stated otherwise, it is also possible to extract partial aspects of the matters explained in the figures and / or examples and combine them with other components and findings from the present description and / or figures. It should be noted in particular that the figures, and especially the depicted proportions, are only schematic. The same reference numerals denote the same objects, so that explanations from other figures may be consulted as needed. The figures show: Fig. 1 a variant embodiment of the system according to the invention, Fig. 2 a temperature profile of a first embodiment of the method according to the invention, Fig. 3a temperature profile of a second embodiment of the method according to the invention, as well as Fig. 4 a temperature profile of a third embodiment of the method according to the invention.

[0048] In Figure 1 Figure 1 shows a schematic block diagram of an embodiment of the inventive system 1 for the thermomechanical rolling of long steel semi-finished products 2. These long steel semi-finished products 2, which are thermomechanically rolled in system 1 to form wire and / or bar-shaped steels 3, can have a square cross-section with dimensions of 165 x 165 mm. The correspondingly finished wire and / or bar-shaped steels 3 can have a diameter in the range of 4.5 to 29 mm (wire-shaped steel) or a diameter in the range of 8.0 to 60.0 mm or 6.0 to 50.0 mm (bar-shaped steel).

[0049] To produce the corresponding wire and / or rod-shaped steels 3, the long steel semi-finished products 2 are first fed into a reheating furnace 4, in which the long steel semi-finished products 2 to be rolled are heated to a temperature of 900 °C to 1000 °C.

[0050] The heated long steel semi-finished products 2 are fed to a first rolling mill 5, where they are pre-rolled in a cascade of twelve standless rolling mills (not shown). A reduction of 20 to 40% per pass is achieved in each rolling mill. The average temperature of the rolled material in the first rolling mill 5 is 900 °C to 1100 °C.

[0051] In the direction of transport, downstream of the first rolling mill 5, a first cooling unit 6 with one or two water tanks can be arranged to regulate the temperature of the pre-rolled long steel semi-finished product 2 before it is fed to a second rolling mill 7. The first cooling unit 6 is located in a first section 8 between the first and second rolling mills 5, 7, which is selected such that the rolled material has sufficient time for adequate temperature equalization between the two rolling operations. The first section 8 can have a length of 45 to 60 m.

[0052] In the second rolling mill 7, the pre-rolled long steel semi-finished products 2 are then re-rolled in a cascade of six standless rolling mills (not shown), achieving a reduction of 20 to 30% per pass in each mill. The average temperature of the rolled material in the second rolling mill 7 is 800 °C to 1000 °C.

[0053] In the direction of transport, downstream of the second rolling mill 7, a second cooling unit 9 is arranged in a second section 10. This unit comprises three spaced-apart water tanks (not shown) to reduce the temperature of the rolled material, which is between 800 °C and 1000 °C, before the subsequent thermomechanical rolling step. The second section 10 is also designed such that, in addition to the temperature reduction, the rolled material has sufficient time for adequate temperature equalization across its cross-section. Therefore, the second section can have a length of 115 m to 130 m.

[0054] The re-rolled and cooled long steel semi-finished product 2, which now has a round and / or oval cross-section, is then fed to a first thermomechanical sizing mill 11 at a temperature in the range of 740 °C to 800 °C and finished-rolled to the desired or specified final diameter, which can be, for example, 8 mm, 18 mm, or 25 mm. For this purpose, the first thermomechanical sizing mill 11 can be configured with six stands in one embodiment, whereby a reduction of approximately 22 to 27% can be achieved per pass in the individual stands.

[0055] In another embodiment, the first thermomechanical sizing roll 11 / 11.1 can be supplemented by a second thermomechanical sizing roll 11.2, which can also be designed with multiple stands. In this embodiment, an intermediate cooling device 13 with at least one water tank (not shown) is provided in an intermediate section 12 formed between the two thermomechanical sizing rolls 11.1, 11.2. This intermediate section 12 also has a specific length of, for example, 30 m, to allow the rolled material sufficient time for adequate temperature equalization across its cross-section.

[0056] In the direction of transport, downstream of the first or second thermomechanical rolling mill 11.1, 11.2, the third cooling unit 14 is arranged in a third section 15. In this unit, the long steel semi-finished products 2, which have been finished into wire and / or bar-shaped steels 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 to prevent further grain growth and the formation of hardened microstructures in the form of martensite or bainite. For this purpose, cooling must begin as soon as possible after the last pass in order to control the recrystallization processes and achieve a high degree of fineness with an average grain diameter in the range of 6.0 to 10.0 µm.To allow the rolled material sufficient time for adequate temperature equalization across its cross-section on its way to the last station, the third section 15 is also chosen to be correspondingly long. This section can, for example, have a length of 110 to 130 m.

[0057] Depending on the design variant, the rod-shaped steels 3 are then fed to a cooling bed device 16 with a cooling bed inlet temperature of 550 °C to 750 °C, to a coil winding device 16 with an inlet temperature of 600 °C to 750 °C, or to a coil winding device 16 with a coil winding temperature of 450 °C to 550 °C.

[0058] Since the entire cooling process is unstable with respect to the respective target temperatures, and thus a sudden formation of martensitic microstructures can occur during the process, the system 1 also includes a microstructure sensor device 17, which is arranged in the third section 15.

[0059] The microstructure sensor device 17 can be used to identify the formation of a martensitic microstructure, in particular a martensite content in A%, in the wire and / or rod-shaped steels 3 online during the ongoing process.

[0060] To identify the unwanted martensite, the microstructure sensor device 17 may, for example, include an ultrasonic measuring device, an X-ray measuring device, a radar measuring device and / or an electromagnetic measuring device.

[0061] The dashed arrows indicate possible positions for the structure sensor device 17 in the third section 15. For example, it can be positioned in the transport direction upstream of the third cooling unit 14 or immediately upstream of the cooling bed, ring laying, or coil winding unit 16. It can also be positioned between the water tanks of the majority of the water tanks in the third cooling unit 14 or in the intermediate section 12.

[0062] In the Figures 2 to 4Three different temperature profiles (average temperatures) 18, 19, 20 of three bar steels 3 with different diameters are shown, which were produced according to an embodiment of the process according to the invention. For this purpose, billets of grade HRB 400 with a square cross-section measuring 165 x 165 mm were thermomechanically rolled into bar steel 3 with diameters of 8 mm ( ) in a plant 1, which comprises a reheating furnace 4, a first rolling mill 5 with twelve standless rolling stands (not shown), a first cooling unit 6 with two water tanks, a second rolling mill 7 with six standless rolling stands (not shown), a second cooling unit 9 with three water tanks, a six-stand sizing mill 11, a third cooling unit 14 with five water tanks and a cooling bed unit 16. Fig. 2 ), 18 mm ( Fig. 3 ) and 25 mm ( Fig. 4 ) rolled. Reference symbol list

[0063] 1 Plant 2 Long steel semi-finished product 3 Wire-shaped / bar-shaped steel / bar steel 4 Furnace 5 First rolling mill 6 First cooling unit 7 Second rolling mill 8 First section of track 9 Second cooling unit 10 Second section of track 11 First sizing block 11.1 First sizing block 11.2 Second sizing block 12 Intermediate section of track 13 Intermediate cooling unit 14 Third cooling unit 15 Third section of track 16 Cooling bed / Coil winding unit / Ring laying unit 17 Microstructure sensor unit 18 Temperature profile 19 Temperature profile 20 Temperature profile

Claims

1. Plant (1) for thermomechanical rolling of elongate steel semi-finished products (2) to form wire-shaped and / or rod-shaped steels (3), comprising a first rolling device (5); a second rolling device (7) arranged downstream of the first rolling device (5) in transport direction; optionally a first cooling device (6) arranged between the first and second rolling devices (5, 7); a first thermomechanical sizing rolling block (11) arranged downstream of the second rolling device (7) in transport direction; a second cooling device (9) arranged between the second rolling device (7) and the first thermomechanical sizing rolling block (11, 11.1); a cooling bed device, ring laying device and / or coil winding device (16) arranged downstream of the first thermomechanical sizing rolling block (11) in transport direction; a third cooling device (14) arranged between the first thermomechanical sizing rolling block (11) and the cooling bed device, ring laying device and / or coil winding device (16); and a structure sensor device (17) which is arranged between the first thermomechanical sizing rolling block (11) and the cooling bed device, ring laying device and / or coil winding device (16) and by way of which a martensitic structure, particularly a martensite proportion in area percent (A.-%), is directly determinable in the thermomechanical rolled elongate steel semi-finished product (2) or in the wire-shaped and / or rod-shaped steel (3) while the process ongoing.

2. Plant (1) according to claim 1, wherein the structure sensor device (17) is arranged directly in front of the cooling bed device, ring laying device and / or coil winding device (16) in transport direction, directly in front of a separating device arranged in front of the cooling bed device, ring laying device or coil winding device (16) in transport direction and / or behind, optionally directly, the third cooling device (14) in transport direction.

3. Plant (1) according to claim 1 or 2, wherein the structure sensor device (17) comprises an ultrasonic measuring device, an X-ray measuring device, a radar beam measuring device and / or an electromagnetic measuring device.

4. Plant (1) according to any one of the preceding claims, further comprising a second thermomechanical sizing rolling block (11.2), which is arranged between the first thermomechanical sizing rolling block (11, 11.1) and the third cooling device (14), optionally with an intermediate cooling device (13) arranged between the two sizing rolling blocks (11.1, 11.2).

5. Plant (1) according to any one of the preceding claims, wherein the second and / or third cooling device (9, 14) comprises or comprise at least two water tanks, preferably at least three water tanks, even more preferably at least four water tanks, which are respectively arranged at a spacing from one another.

6. Plant (1) according to any one of the preceding claims, wherein each of the thermomechanical sizing rolling blocks (11.1, 11.2) is configured with one, two, four, six and / or eight stands.

7. Plant (1) according to any one of the preceding claims, wherein the structure sensor device (17) is coupled with a controlling and / or regulating device for setting the temperature in the cooling devices (6, 9, 13, 14), the rolling temperature and / or the rolling speed in the respective rolling units (5, 7, 11.1, 11.2) of the plant (1).

8. Method of producing wire-shaped and / or rod-shaped steels (3) from elongate steel semi-finished products (2) with yield strength of at least 300 MPa, preferably with a yield strength of at least 400 MPa, wherein initially the elongate steel semi-finished product (2) heated to a temperature of at least 900° C is rough-rolled in a first rolling device (5) and optionally cooled in a first cooling device (6) following thereon; then skin-rolled in a second rolling device (7), which is arranged downstream of the first rolling device (5) in transport direction, as well as cooled to a temperature of at least 850° C in a second cooling device (9) following thereon; subsequently finish-rolled in a first thermomechanical sizing rolling block (11, 11.1), which is arranged downstream of the second cooling device (9) in transport direction, to form the wire-shaped and / or rod-shaped steel (3), which is cooled to a temperature in the range of 400° C to 850° C in a third cooling device (14) following the first thermomechanical sizing rolling block (11, 11.1); then fed to a cooling bed device, ring laying device and / or coil winding device (16) arranged downstream of the third cooling device (14) in transport direction, wherein by means of a structure sensor device (17), which is arranged in a section between the first thermomechanical sizing rolling block (11, 11.1) and the cooling bed device, ring laying device and / or coil winding device (16), any martensitic structure which may be present in the thermomechanically rolled elongate steel semi-finished product (2) or in the wire-shaped and / or rod-shaped steel (3) is directly determined while the process is ongoing.

9. Wire-shaped and / or rod-shaped steel (3) produced in accordance with a method according to claim 8, with a yield strength of at least 300 MPa, preferably with a yield strength of at least 400 MPa, having a martensite proportion of at most 15.0 A.-%, wherein the wire-shaped and / or rod-shaped steel (3) has the following chemical composition in weight %: carbon:0.04 to 0.35silicon:0.10 to 0.80manganese:0.40 to 1.60phosphorus:maximum 0.06sulphur:maximum 0.06nitrogen:maximum 0.012 remainder iron, optionally further companion elements as well as unavoidable impurities.

10. Wire-shaped and / or rod-shaped steel (3) according to claim 9, comprising a carbon equivalent (Ceq) of ≤ 0.60.

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