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

Abstract

A system for the thermomechanical rolling of long semi-finished steel products includes a first rolling unit; a second rolling unit, arranged downstream of the first rolling unit; a first thermomechanical sizing block, arranged downstream of the second rolling unit; 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; a third cooling device, arranged between the first thermomechanical sizing block and the cooling-bed, ring-laying and/or coil-winding device; and a structure-sensor device, which is arranged between the first thermomechanical sizing block and the cooling-bed, ring-laying and/or coil-winding device, and can be used for determining directly in the ongoing process a martensitic structure, in particular a proportion of martensite in percent by area, in the thermomechanically rolled long semi-finished steel product or in the steel product.

Claims

1.-11. (canceled)

12. A system (1) for thermomechanical rolling of long semi-finished steel products (2) into wire-shaped and/or rod-shaped steel (3), comprising: a first rolling unit (5); a second rolling unit (7), arranged downstream of the first rolling unit (5); a first thermomechanical sizing block (11), arranged downstream of the second rolling unit (7); a second cooling device (9), arranged between the second rolling unit (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); 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 a structure-sensor device (17), arranged between the first thermomechanical sizing block (11) and the cooling-bed, ring-laying, and/or coil-winding device (16), wherein the structure-sensor device (17) is configured to directly determine a martensitic structure in the thermomechanically rolled long semi-finished steel product (2) or in the wire-shaped and/or rod-shaped steel (3) during an ongoing process.

13. The system according to claim 12, further comprising: a first cooling device (6), arranged between the first rolling unit (5) and the second rolling unit (7), wherein the structure-sensor device (17) is configured to determine a proportion of martensite in percent by area (A.-%).

14. The system (1) according to claim 12, wherein the structure-sensor device (17) is arranged directly upstream of the cooling-bed, ring-laying, and/or coil-winding device (16), directly upstream of a separating device upstream of the cooling-bed, ring-laying, and/or coil-winding device (16), or downstream of the third cooling device (14).

15. The system (1) according to claim 12, wherein the structure-sensor device (17) comprises an ultrasonic measuring device, an X-ray measuring device, a radar measuring device, and/or an electro-magnetic measuring device.

16. The system (1) according to claim 12, further comprising a second thermomechanical sizing block (11.2) arranged between the first thermomechanical sizing block (11, 11.1) and the third cooling device (14).

17. The system (1) according to claim 16, further comprising an intermediate cooling device (13) arranged between the first thermomechanical sizing block (11, 11.1) and the second thermomechanical sizing block (11.2).

18. The system (1) according to claim 12, wherein the second cooling device (9) and/or the third cooling device (14) comprises at least four water tanks that are arranged spaced apart from one another.

19. The system (1) according to claim 16, wherein the first thermomechanical sizing block (11.1) is of one-, two-, four-, six-, or eight-stand design, and wherein the second thermomechanical sizing block (11.2) is of one-, two-, four-, six-, or eight-stand design.

20. The system (1) according to claim 12, wherein the structure-sensor device (17) is coupled to an open-loop or closed-loop control device for setting a temperature in one or more of the second cooling device (9) and third cooling device (14), a rolling temperature, and/or a rolling speed in one or more of the first rolling unit (5), the second rolling unit (7), and the first thermomechanical sizing block (11).

21. A method for producing wire-shaped and/or rod-shaped steel (3) from a long semi-finished steel product (2) with a yield strength of at least 300 MPa, comprising: heating the long steel semi-finished product (2) to a temperature of at least 900? ? C.; pre-rolling the heated long steel semi-finished product (2) in a first rolling unit (5); re-rolling the long steel semi-finished product (2) in a second rolling unit (7) arranged downstream of the first rolling unit (5); cooling the long steel semi-finished product (2) in an adjoining second cooling device (9) to a temperature of at least 850? C.; subsequently finish-rolling the long steel semi-finished product (2) to the wire-shaped and/or rod-shaped steel in a first thermomechanical sizing block (11, 11.1) arranged downstream of the second cooling device (9); cooling the wire-shaped and/or rod-shaped steel to a temperature in the range of 400? C. to 850? C. in a third cooling device (14) adjoining the first thermomechanical sizing block (11, 11.1); feeding the wire-shaped and/or rod-shaped steel to a cooling bed, ring-laying, and/or coil-winding device (16) arranged downstream of the third cooling device (14); and directly determining, by a structure-sensor device (17) arranged in a section between the first thermomechanical sizing block (11, 11.1) and the cooling bed, ring-laying, and/or coil-winding device (16), any martensitic structure present in the thermomechanically rolled long semi-finished steel product (2) or in the wire-shaped and/or rod-shaped steel (3) in an ongoing process.

22. The method according to claim 21, further comprising: cooling the long semi-finished steel product (2) in a first cooling device (6) adjoining the first rolling unit (5).

23. A wire-shaped and/or rod-shaped steel (3), produced according to the method in accordance with claim 21, wherein the wire-shaped and/or rod-shaped steel (3) has a yield strength of at least 300 MPa and a proportion of martensite of at most 15.0 A.-%.

24. The wire-shaped and/or rod-shaped steel (3) according to claim 23, comprising the following chemical composition in % by weight: TABLE-US-00003 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 a balance being residual iron, further accompanying elements, and unavoidable impurities.

25. The wire-shaped and/or rod-shaped steel (3) according to claim 23, having a carbon equivalent (Ceq) of ?0.60.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG. 1 shows an embodiment of the system for the thermomechanical rolling of long semi-finished steel products into wire-shaped and/or rod-shaped steel.

[0049] FIG. 2 shows a temperature profile of a first embodiment of the method for producing wire-shaped and/or rod-shaped steel from long semi-finished steel products.

[0050] FIG. 3 shows a temperature profile of a second embodiment thereof.

[0051] FIG. 4 shows a temperature profile of a third embodiment thereof.

DETAILED DESCRIPTION

[0052] FIG. 1 shows a schematic block diagram of an embodiment of the system 1 for thermomechanical rolling of long semi-finished steel products 2. Such long semi-finished steel products 2, which are thermomechanically rolled into wire-shaped and/or rod-shaped steel 3 in the system 1, can have a quadrilateral (square) cross-section with dimensions of 165?165 mm. The corresponding finish-rolled wire-shaped and/or rod-shaped steel 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 (rod-shaped steel).

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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 ?m. 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] FIGS. 2 to 4 show three different temperature profiles (average temperatures) 18, 19, 20 of three rod steels 3 of different diameters, which have been produced in accordance with one embodiment of the method in accordance with the disclosure. For this purpose, billets of grade HRB 400 with a quadrilateral (square) cross-section with dimensions of 165?165 mm were thermomechanically rolled, in a system 1, which comprises a reheating furnace 4, a first rolling unit 5 with twelve housingless rolling mill stands (not shown), a first cooling device 6 with two water tanks, a second rolling unit 7 with six housingless rolling mill stands (not shown), a second cooling device 9 with three water tanks, a six-stand sizing block 11, a third cooling device 14 with five water tanks along with a cooling-bed device 16, into rod steel 3 with diameters of 8 mm (FIG. 2), 18 mm (FIG. 3) and 25 mm (FIG. 4).

LIST OF REFERENCE SIGNS

[0067] 1 System [0068] 2 Long semi-finished steel product [0069] 3 Wire-shaped/rod-shaped steel/rod steel [0070] 4 Furnace [0071] 5 First rolling unit [0072] 6 First cooling device [0073] 7 Second rolling unit [0074] 8 First line section [0075] 9 Second cooling device [0076] 10 Second line section [0077] 11 First sizing block [0078] 11.1 First sizing block [0079] 11.2 Second sizing block [0080] 12 Intermediate line section [0081] 13 Intermediate cooling device [0082] 14 Third cooling device [0083] 15 Third line section [0084] 16 Cooling-bed device/coil-winding device/ring-laying device [0085] 17 Structure-sensor device [0086] 18 Temperature profile [0087] 19 Temperature profile [0088] 20 Temperature profile