CN112246910A - Method for improving performance uniformity of thermomechanically-rolled steel plate and thermomechanically-rolled steel plate - Google Patents
Method for improving performance uniformity of thermomechanically-rolled steel plate and thermomechanically-rolled steel plate Download PDFInfo
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- CN112246910A CN112246910A CN202010970272.XA CN202010970272A CN112246910A CN 112246910 A CN112246910 A CN 112246910A CN 202010970272 A CN202010970272 A CN 202010970272A CN 112246910 A CN112246910 A CN 112246910A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
- B21C37/02—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of sheets
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
- B21B2001/225—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length by hot-rolling
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Abstract
The invention provides a method for improving the performance uniformity of a thermomechanically rolled steel plate, which belongs to the technical field of thermomechanically rolled medium plates and comprises the following steps: heating the casting blank, then carrying out rough rolling, wherein a low-speed high-reduction process is adopted in the rough rolling stage; the casting blank comprises the following chemical components in percentage by mass: nb: 0.02 to 0.08%, Mn: 1.4-2.0%, and S is less than or equal to 0.0025%; carrying out finish rolling after the rough rolling is finished, wherein the finish rolling process adopts model steel rolling, the rolling pass adopts odd number of passes, the initial rolling temperature is 850-950 ℃, and the rolling speed is 4.0 m/s; pre-straightening the steel plate after finish rolling: after pre-straighteningAccelerated cooling treatment is carried out, a head and tail shielding process is adopted, and the acceleration range is 0.001m/S2‑0.01m/S2. The invention also provides a thermomechanical rolling steel plate with high performance uniformity.
Description
Technical Field
The invention belongs to the technical field of thermomechanically rolled medium plates, and relates to a method for improving the performance uniformity of a thermomechanically rolled steel plate and the thermomechanically rolled steel plate.
Background
With the improvement of the steel rolling equipment level in China and the maturity of the controlled rolling and controlled cooling process, a new generation of thermomechanically rolled high-performance steel plate has lower production cost and good welding performance, gradually replaces a heat treatment state steel plate represented by normalizing and tempering, and is widely applied to the fields of bridges, pipelines, high-rise buildings, ocean engineering and the like. Although the thermomechanical rolling steel plate can fully play the technical means of phase transformation strengthening, precipitation strengthening, dislocation strengthening and the like under the condition of low-carbon equivalent component design, and the steel plate is ensured to have better toughness matching. However, compared with the normalized and tempered steel plate whose performance depends on the single factor of the heat treatment temperature, the thermomechanically rolled steel plate has close relationship between the uniformity of the performance and the uniformity of the temperature, and the temperature difference includes the temperature uniformity of the billet in the heating process, the descaling in the rolling process, the primary descaling, the secondary descaling, the cooling water of the roller body, the temperature uniformity brought in the temperature waiting process, the temperature uniformity in the water cooling process and the like, and the heating, rolling and water cooling processes all have important influence on the performance of the thermomechanically rolled steel plate. On one hand, the uniformity of the performance of the steel plate is poor in appearance of a workpiece due to the deformation nonuniformity of different parts in the machining process, and on the other hand, in the service process of a large-scale steel structure, the steel plate with poor performance uniformity is prone to generating plastic deformation at a position with lower strength and easily generating fracture or fatigue failure under the same stress environment. Therefore, technical development has been carried out for thermomechanically rolled steel sheets to ensure uniformity of properties thereof.
The method for improving the performance uniformity of a thermomechanically rolled steel plate in the prior production technology mainly focuses on controlling the final cooling temperature uniformity in the water cooling process, namely improving the cooling uniformity by head and tail shielding and the change of the speed of a water cooling roller way, so as to improve the performance uniformity of the steel plate, and related researches such as an accelerated cooling device and a method for improving the cooling uniformity of the steel plate related to CN 103599950B, a method for improving the control cooling temperature uniformity of a hot rolled steel plate and the like mainly adopt the head and the tail of the steel plate to improve the speed of the roller way and reduce the cooling time of the head and the tail in the water cooling device so as to achieve the purpose of uniform performance of the head and the tail and the middle part of; the method for improving the uniformity of ultra-fast cooling of the rolled medium plate disclosed in the grant publication No. CN 102371283B realizes the uniformity of cooling of the steel plate under the condition of ultra-fast cooling of the rolled medium plate by adopting a head-to-tail shielding control means of adjusting the position of a jet flow collecting pipe, setting a scouring water area on the upper surface of the steel plate, increasing the compensation of the flow of the upper and lower collecting pipes on the heat exchange capacity of the lower surface and removing the speed of a isohexy roller way of residual cooling water on the upper surface; the method for improving the performance uniformity of the hot-rolled steel plate is disclosed in the grant No. CN 107983784B, and is mainly characterized in that ultra-fast cooling is adopted to carry out water cooling on the hot-rolled steel plate, and the sectional water cooling and the sectional head and tail shielding of the steel plate are controlled to eliminate the longitudinal temperature difference of the steel plate, the temperature difference between the head and tail parts and the center part of the steel plate is less than or equal to 20 ℃, the performance of the steel plate is uniform, and the yield strength copper plate difference. The above patent technology focuses on the important influence of the water cooling uniformity on the mechanical properties of the steel plate, but as mentioned above, the composition, heating, rolling process, pre-straightening and cooling bed cooling process of the steel plate all have important influence on the property uniformity of the steel plate, so that a full-flow technology is required to ensure the property uniformity of the whole steel plate.
Disclosure of Invention
The invention provides a method for improving the performance uniformity of a thermomechanically rolled steel plate, aiming at solving the technical problem that the performance uniformity of the conventional thermomechanically rolled steel plate is poor.
The invention also provides a thermomechanical rolling steel plate with high performance uniformity.
The invention is realized by the following technical scheme:
a method of improving uniformity of properties of a thermomechanically rolled steel sheet comprising:
heating the casting blank, then carrying out rough rolling, wherein a low-speed high-reduction process is adopted in the rough rolling stage;
the casting blank comprises the following chemical components in percentage by mass:
Nb：0.02～0.08％，Mn：1.4～2.0％，S≤0.0025％；
carrying out finish rolling after the rough rolling is finished, wherein the finish rolling process adopts model steel rolling, the rolling pass adopts odd number of passes, the initial rolling temperature is 850-950 ℃, and the rolling speed is 3.0-5.0 m/s;
pre-straightening the steel plate after finish rolling:
after pre-straightening, accelerated cooling treatment is carried out, a head-tail shielding process is adopted, and the acceleration range is 0.001m/S2-0.01m/S2。
Wherein the heating temperature of the casting blank is 1180-1220 ℃, and the in-furnace time is 0.9-1.2 min/mm.
Furthermore, the maximum reduction rate of a single pass of the rough rolling process is more than or equal to 15%, the rolling speed is 0.8-1.2 m/s, and the thickness to be heated is 2.0-3.0 times of the target thickness.
Furthermore, in the pre-straightening process, the straightening force is 1500 tons, the inclination amount is 0-10mm, and the roll gap is set within +/-1.0 mm of the target thickness.
Further, after the accelerated cooling treatment is finished, thermal straightening and straightening are carried out for three times, the straightening force is set to be 800-1000 tons, the tilting amount is set to be 0.2-0.3mm, and the roll gap is consistent with the target thickness.
Further, after the thermal straightening is finished, carrying out on-line finishing post-treatment on a steel plate with the thickness specification of less than or equal to 30mm after direct cooling by a cooling bed, wherein the on-line finishing post-treatment specifically comprises on-line flaw detection, trimming, sizing, surface quality inspection and performance sampling; for the steel plate with the thickness of more than 30mm, the cold stacking treatment is adopted, the head and the tail of the steel plate are well covered, and the cold stacking time is more than 24 hours.
Further, the pre-straightening speed is consistent with the speed of a water-cooling roller way for accelerating cooling treatment of the steel plate.
A thermomechanically rolled steel sheet having high uniformity of properties, which is produced by the above-mentioned method for improving uniformity of properties of a thermomechanically rolled steel sheet.
Further, the thermomechanically rolled steel sheet has the following chemical components in percentage by mass:
c: 0.10%, Si: 0.25%, Mn: 1.50%, P: 0.010%, S: 0.0015%, Cr: 0.10%, Nb: 0.03%, Ti: 0.015% and the balance Fe and other unavoidable impurities.
Further, the thermomechanically rolled steel sheet has the following chemical components in percentage by mass:
c: 0.09%, Si: 0.25%, Mn: 1.50%, P: 0.010%, S: 0.0010%, Cr: 0.10%, Nb: 0.03%, Ti: 0.015% and the balance Fe and other unavoidable impurities.
One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
according to the method for improving the performance uniformity of the thermomechanically rolled steel plate, the chemical components of a casting blank are adjusted, the rolling process and the cooling process are changed, the yield strength of the obtained steel plate is not more than 40MPa with the plate difference, the tensile strength is not more than 30MPa with the plate difference, the elongation after fracture is not more than 3.0% with the plate difference, the toughness is not more than 30J with the plate difference, and the steel plate has excellent performance uniformity.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 shows the 1/4-site metallographic structure of a 16mm high-performance uniformity steel plate.
FIG. 2 is a metallurgical structure of 1/4 sites of the thickness of a 50mm high performance uniformity steel plate.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
In order to solve the technical problems, the embodiment of the invention provides the following general ideas:
the invention provides a method for improving the performance uniformity of a thermomechanically rolled steel plate, which comprises the following steps:
(1) heating a casting blank, then carrying out rough rolling, wherein the heating temperature of the casting blank is 1180-1220 ℃, the furnace time is 0.9-1.2 min/mm, a low-speed high reduction process is adopted in the rough rolling stage, the single-pass maximum reduction rate is more than or equal to 15%, the rolling speed is 1.0m/s, and the thickness is 2.0-3.0 times of the target thickness;
the casting blank comprises the following chemical components in percentage by mass: nb: 0.02 to 0.08%, Mn: 1.4-2.0%, S is less than or equal to 0.0025%, and common chemical elements of other steels comprise C, Si, P, Ni, Cr, Cu, Mo, V, Ti and the like, and are designed according to the requirements of the strength and the toughness of the steel plate;
(2) carrying out finish rolling after the rough rolling is finished, wherein the finish rolling process adopts model steel rolling, the rolling pass adopts odd number of passes, the initial rolling temperature is 850-950 ℃, and the rolling speed is 4.0 m/s;
(3) pre-straightening the steel plate after finish rolling, wherein the straightening force is 1500 tons, the inclination amount is 0-10mm, the roll gap is set within +/-1.0 mm of the target thickness, and the pre-straightening speed is consistent with the speed of a water-cooling roller way for accelerating cooling treatment of the steel plate;
(4) after pre-straightening, accelerated cooling treatment is carried out, a head-tail shielding process is adopted, and the acceleration range is 0.001m/S2-0.01m/S2；
(5) And (4) carrying out thermal straightening for three times, wherein the straightening force is set to be 800-1000 tons, the tilting amount is set to be 0.2-0.3mm, and the roll gap is consistent with the target thickness.
(6) Further, after the thermal straightening is finished, the steel plate with the thickness specification of less than or equal to 30mm is subjected to on-line finishing post-treatment after being cooled by a direct cooling bed, and the steel plate with the thickness of more than 30mm is subjected to heap cooling treatment, so that the head and the tail of the steel plate are well covered, and the heap cooling time is more than 24 hours.
The parameter setting principle of this patent is as follows:
when the steel plate is cooled by water and accelerated cooling is carried out, the head and the tail of the steel plate inevitably generate temperature difference, namely the head of the steel plate firstly enters water cooling equipment to be finally cooled to be high in temperature and the tail of the steel plate to be finally cooled to be low in temperature. Therefore, the present invention adds a sufficient amount of austenite enlarging elements, i.e., Ni and Mn, to the composition design, and lowers the precipitation temperature of the pro-eutectoid ferrite. Specifically, the Mn content is set to be 1.4-2.0%, and meanwhile, in order to avoid the elongation problem caused by central MnS, the S content is controlled to be below 0.0025%; on the other hand, the finish rolling initial rolling temperature of the steel plate is increased in order to ensure that the tail part of the steel plate does not generate the transformation of pro-eutectoid ferrite, the recrystallization zone temperature of the steel plate needs to be increased in order to avoid the rolling of the steel plate in a mixed crystal zone, and the Nb has a good effect of inhibiting the recrystallization of the steel plate, so that the Nb content is set to be 0.02-0.08%.
In the steel plate rolling process, the premise of the uniformity of water cooling of the steel plate is that the steel plate has a stable start-cooling temperature, and the start-cooling temperature is closely related to the start-rolling temperature and the finish-rolling temperature of the steel plate, so the stable start-rolling temperature of the steel plate needs to be ensured in order to ensure the stable start-cooling temperature of the steel plate. Compared with the automatic model steel rolling mode of the steel plate, the steel plate has more stable initial rolling and final rolling temperatures. Therefore, in order to ensure that the steel plate has better performance uniformity, the invention adopts model steel rolling in the rolling process, and the initial rolling temperature is set to be 850-950 ℃ according to the thickness difference of the steel plate. And in order to avoid the temperature drop of the steel plate in the rolling process, the finish rolling speed is set to be 4m/s, in addition, in order to ensure that the rolled steel plate can be quickly fed into the pre-straightening machine, the rolling pass is set to be an odd number, and the temperature drop increase of the empty pass of the rolled steel plate is avoided.
And straightening the rolled steel plate by adopting pre-straightening to ensure the unevenness of the steel plate. The head and the tail of the rolled steel plate are easy to warp due to uneven stress when the head is bitten, and the output plate profile of the rolling mill has the problems of medium waves and edge waves. When the plate shape problem is directly connected to the accelerated cooling device, because the model control of the steel plate is calculated when the steel plate is a plane during cooling, if the surface of the steel plate is arc-shaped, the local heat exchange process between cooling water and the surface of the steel plate is changed, and jet impact heat exchange area, air film heat exchange area and radiation heat exchange area on the surface of the steel plate are changed, the problems that the final cooling temperature of the steel plate is uneven and the final cooling target cannot be hit are caused. Therefore, after the steel plate is straightened by the pre-straightening machine before entering water, the flatness of the steel plate before entering water is improved, conditions are provided for uniform water cooling of the steel plate, and the performance uniformity of the steel plate is effectively improved.
Due to the temperature difference in the longitudinal direction of the steel sheet, the head and tail portions need to be shielded during the water cooling process. Because the head and the tail of the steel plate are in contact with the roller in the rolling processThe temperature of the head and the tail of the steel plate is lower than the middle position of the steel plate due to heat, in order to ensure that the steel plate has the same final cooling temperature after water cooling, the roller way acceleration is needed before the steel plate enters water and leaves the water to reduce the water quantity of the steel plate in the cooling process so as to achieve the purpose of the same final cooling temperature, the actual acceleration is set to be 0.001m/S in combination with the setting of the thickness and the final cooling temperature of the steel plate2-0.01m/S2。
The steel plate after hot straightening has better cold removal uniformity of thin steel plates at the thickness section and the head and the tail of the steel plate, so that an on-line cooling bed cooling and finishing post-treatment process is directly adopted; for thick steel plates, because the steel plates are thick, the head and the tail of the steel plates are easy to generate supercooling, the thickness direction of the steel plates is easy to generate temperature gradient and cooling strength gradient, the surface of the steel plates has tissue gradient to the center, in order to improve the influence of the supercooling of the head and the tail and the tissue gradient of the thickness direction on the performance of the steel plates, the process of quickly inserting the steel plates into slow cooling pits for cold piling is adopted, and the heat treatment of tempering (annealing) is carried out on the supercooling tissues of the head and the tail of the steel plates and the surface of the steel plates by utilizing the core return temperature of the steel plates.
The method of improving uniformity of properties of a thermomechanically rolled steel sheet according to the present invention will be described in detail with reference to examples, comparative examples and experimental data.
Example 1
The target thickness of the steel plate is 16mm, and the yield strength of the steel plate is 370 MPa.
The steel plate is designed by the following chemical components in percentage by mass: 0.10% of C, 0.25% of Si, 1.50% of Mn, 0.010% of P, 0.0015% of S, 0.10% of Cr, 0.03% of Nb, 0.015% of Ti, and the balance of Fe and other unavoidable impurities, and common noble elements such as Ni, Cu, V, and Mo are not intentionally added.
The key process steps and parameters of the steel plate thermomechanical rolling are as follows:
(1) heating a casting blank: heating the steel billet at 1180 ℃, selecting a continuous casting billet with the thickness of 200mm, wherein the steel billet is heated in the furnace for 210 min:
(2) controlled rolling: after the billet is taken out of the heating furnace, the billet is descaled in a descaler and then is put in a roughing mill for roughing, the maximum pass reduction rate is 18.0 percent, and after the temperature and the thickness are 48mm, the billet is subjected to swing air cooling between a roughing rolling roller way and a finish rolling roller way; model steel rolling is adopted for finish rolling, when the steel plate is cooled to the model temperature of 880 ℃ in air, automatic steel biting rolling is started, the rolling pass is set to be 7, and the rolling speed is 4.0 m/s;
(3) pre-straightening: straightening the rolled steel plate in a pre-straightening machine, setting a roll gap to be 16.0mm, and setting the straightening speed to be consistent with the speed of an accelerated cooling roller bed;
(4) accelerated cooling: the steel plate is set to be 730 ℃ in the cold starting temperature, 580 ℃ in the final cooling temperature, 20 ℃/S in the cooling speed, and 0.008m/S in the acceleration of the roller way2To ensure temperature uniformity across the plate.
(5) And (3) thermal straightening: straightening is carried out for three times, straightening force is set to be 800 tons, the tilting amount is set to be 0.2mm, and a roll gap is set to be 16 mm.
(6) Cooling and finishing: and (4) putting the steel plate into a cooling bed for air cooling, and performing finishing processes such as online flaw detection, sizing and the like.
The mechanical property test is carried out on the 16mm steel plate, and the head and tail property test is carried out on 294 batches produced, and the statistical data of the mean value of the test results are shown in the following table 1. And (3) carrying out yield strength statistics on the head and the tail of each steel plate, wherein the steel plate with the yield strength fluctuation of less than 40MPa accounts for 97.4%, the steel plate with the tensile strength fluctuation of less than 30MPa accounts for 98.3%, the steel plate with the elongation after fracture accounts for 97.6%, and the impact work head with the low-temperature toughness of-20 ℃ accounts for 99.6% and the impact work head with the low-temperature toughness of-30J accounts for 99.6%.
Mechanical property data of table 116 mm steel plate
| Performance index | Yield strength/MPa | Tensile strength/MPa | Elongation after break/% | Low temperature toughness/J |
| Head part | 462 | 566 | 26.0 | 307 |
| Tail part | 453 | 558 | 26.0 | 307 |
In table 1, the respective mechanical property data are average values.
Example 2
The thickness of the steel plate is 50mm, and the yield strength of the steel plate is 370 MPa.
The steel plate is designed by the following chemical components in percentage by mass: 0.09% of C, 0.25% of Si, 1.50% of Mn, 0.010% of P, 0.0010% of S, 0.10% of Cr, 0.03% of Nb, 0.015% of Ti, and the balance of Fe and other unavoidable impurities, and common noble elements such as Ni, Cu, V, and Mo are not intentionally added.
The key process steps and parameters of the steel plate thermomechanical rolling are as follows:
(1) heating a casting blank: heating the steel billet at 1200 ℃, selecting a continuous casting billet with the thickness of 400mm, and keeping the furnace time of the steel billet for 440 min;
(2) controlled rolling: after the billet is taken out of the heating furnace, the billet is descaled in a descaler, and then is subjected to swing air cooling between a rough rolling roller way and a finish rolling roller way if a rough rolling mill is used for rough rolling, the maximum pass reduction rate is 18.0 percent, and the temperature thickness is 130 mm; model steel rolling is adopted for finish rolling, when the steel plate is cooled to the model temperature of 850 ℃ in air, automatic steel biting rolling is started, the rolling pass is set to be 9, and the rolling speed is 4.0 m/s;
(3) pre-straightening: and (4) straightening the rolled steel plate in a pre-straightening machine with the pre-straightening force of 1500 tons. The inclination amount is 2mm, the roll gap is set to be 50.0mm, and the setting of the straightening speed is consistent with the speed of the accelerated cooling roller bed;
(4) the steel plate is set to 760 ℃, the final cooling temperature is set to 500 ℃, the cooling speed is 10 ℃/S, and the roller bed acceleration is set to 0.002m/S2To ensure temperature uniformity across the plate.
(5) And (3) thermal straightening: straightening was performed three times, the straightening force was set to 1000 tons, the amount of tilting was set to 0.3mm, and the roll gap was set to 50 mm.
(6) Cooling and finishing: and (4) quickly unloading the steel plate for cooling, slowly cooling the steel plate in a slow cooling pit, stacking the head and the tail of the steel plate uniformly, and covering the exposed position.
The mechanical property test is carried out on 50mm steel plates, the head and tail property test is carried out on 58 batches produced, the statistical data of the mean value of the test results are shown in the following table 2, and all the mechanical property data in the table are mean values. And (3) carrying out yield strength statistics on the head and the tail of each steel plate, wherein the steel plate with the yield strength fluctuation of less than 40MPa accounts for 97.8%, the steel plate with the tensile strength fluctuation of less than 30MPa accounts for 97.6%, the steel plate with the elongation after fracture accounts for 98.6%, and the impact work with the low temperature toughness of-20 ℃ accounts for 99.7% and the head fluctuation of less than 30J.
TABLE 250 mm Steel plate mechanical Property data
| Performance index | Yield strength/MPa | Tensile strength/MPa | Elongation after break/% | Low temperature toughness/J |
| Head part | 451 | 572 | 28.0 | 300 |
| Tail part | 446 | 563 | 28.0 | 309 |
Comparative example 1
The thickness of the steel plate is 16mm, and the yield strength of the steel plate is 370 MPa.
The steel plate is designed by the following chemical components in percentage by mass: 0.10% of C, 0.25% of Si, 1.50% of Mn, 0.010% of P, 0.0015% of S, 0.10% of Cr, 0.015% of Ti, and the balance of Fe and other inevitable impurities, and a micro-alloying element Nb is not added, and common noble elements such as Ni, Cu, V, and Mo are not intentionally added.
The key process steps and parameters of the steel plate thermomechanical rolling are as follows:
(1) heating a casting blank: heating the steel billet at 1180 ℃, and selecting a continuous casting billet with the thickness of 200mm, wherein the steel billet is in the furnace for 210 min;
(2) controlled rolling: after the billet is taken out of the heating furnace, the billet is descaled in a descaler and then is put in a roughing mill for roughing, the maximum pass reduction rate is 18.0 percent, and after the temperature and the thickness are 48mm, the billet is subjected to swing air cooling between a roughing rolling roller way and a finish rolling roller way; model steel rolling is adopted for finish rolling, when the steel plate is cooled to the model temperature of 850 ℃ in air, automatic steel biting rolling is started, the rolling pass is set to be 7, and the rolling speed is 4.0 m/s;
(3) pre-straightening: straightening the rolled steel plate in a pre-straightening machine, setting the roll gap to be 16.0mm, and setting the straightening speed to be consistent with the speed of an accelerated cooling roller bed;
(4) Accelerated cooling: the steel plate is set to 710 ℃ at the start cooling temperature, 550 ℃ at the final cooling temperature, 20 ℃/S at the cooling speed, and 0.008m/S at the roller way acceleration2To ensure temperature uniformity across the plate.
(5) And (3) thermal straightening: straightening is carried out for three times, straightening force is set to be 800 tons, the tilting amount is set to be 0.2mm, and a roll gap is set to be 16 mm.
Cooling and finishing: and (4) putting the steel plate into a cooling bed for air cooling, and performing finishing processes such as online flaw detection, sizing and the like.
The mechanical properties of the 16mm steel plate were examined, and the test results are shown in the following table.
Mechanical property data of 316 mm steel plate
| Performance index | Yield strength/MPa | Tensile strength/MPa | Elongation after break/% | Low temperature toughness/J |
| Head part | 409 | 596 | 23.0 | 157 |
| Tail part | 381 | 531 | 24.0 | 124 |
Comparative example 2
The thickness of the steel plate is 16mm, and the yield strength of the steel plate is 370 MPa.
The steel plate is designed by the following chemical components in percentage by mass: 0.10% of C, 0.25% of Si, 1.50% of Mn, 0.010% of P, 0.0015% of S, 0.10% of Cr, 0.03% of Nb, 0.015% of Ti, and the balance of Fe and other unavoidable impurities, and common noble elements such as Ni, Cu, V, and Mo are not intentionally added.
The key process steps and parameters of the steel plate thermomechanical rolling are as follows:
(1) heating a casting blank: heating the steel billet at 1180 ℃, and selecting a continuous casting billet with the thickness of 200mm, wherein the steel billet is in the furnace for 210 min;
(2) controlled rolling: after the billet is taken out of the heating furnace, the billet is descaled in a descaler and then is put in a roughing mill for roughing, the maximum pass reduction rate is 18.0 percent, and after the temperature and the thickness are 48mm, the billet is subjected to swing air cooling between a roughing rolling roller way and a finish rolling roller way; model steel rolling is adopted for finish rolling, when the steel plate is cooled to the model temperature of 880 ℃ in air, automatic steel biting rolling is started, the rolling pass is set to be 7, and the rolling speed is 4.0 m/s;
(3) pre-straightening: straightening the rolled steel plate in a pre-straightening machine, setting a roll gap to be 16.0mm, and setting the straightening speed to be consistent with the speed of an accelerated cooling roller bed;
(4) accelerated cooling: the steel plate is set to be 730 ℃ in cold starting temperature, 580 ℃ in final cooling temperature, 20 ℃/s in cooling speed and the acceleration of the roller bed is not set.
(5) And (3) thermal straightening: straightening is carried out for three times, straightening force is set to be 800 tons, the tilting amount is set to be 0.2mm, and a roll gap is set to be 16 mm.
(6) Cooling and finishing: and (4) putting the steel plate into a cooling bed for air cooling, and performing finishing processes such as online flaw detection, sizing and the like.
The mechanical properties of the 16mm steel plate were tested, and the test results are shown in Table 4 below.
TABLE 416 mm Steel plate mechanical Property data
| Performance index | Yield strength/MPa | Tensile strength/MPa | Elongation after break/% | Low temperature toughness/J |
| Head part | 460 | 561 | 26.0 | 307 |
| Tail part | 437 | 538 | 29.0 | 217 |
As can be seen from tables 1-4, the steel plates prepared in examples 1 and 2 have high uniformity of performance, and the steel plates prepared in comparative examples 1 and 2 have different chemical component designs and accelerated cooling processes from those of the invention, so that the obtained steel plates have large differences of mechanical properties at the head and the tail and low uniformity of performance.
Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. A method of improving uniformity of properties of a thermomechanically rolled steel sheet, comprising:
heating the casting blank, then carrying out rough rolling, wherein a low-speed high-reduction process is adopted in the rough rolling stage;
the casting blank comprises the following chemical components in percentage by mass:
Nb：0.02～0.08％，Mn：1.4～2.0％，S≤0.0025％；
carrying out finish rolling after the rough rolling is finished, wherein the finish rolling process adopts model steel rolling, the rolling pass adopts odd number of passes, the initial rolling temperature is 850-950 ℃, and the rolling speed is 3.0-5.0 m/s;
pre-straightening the steel plate after finish rolling:
after pre-straightening, accelerated cooling treatment is carried out, a head-tail shielding process is adopted, and the acceleration range is 0.001m/S2-0.01m/S2。
2. The method for improving the uniformity of the properties of a thermomechanically rolled steel sheet according to claim 1, wherein the billet is heated at 1180-1220 ℃ for 0.9-1.2 min/mm.
3. The method for improving the performance uniformity of the thermomechanically rolled steel plate according to claim 1, wherein the maximum reduction rate of a single pass of the rough rolling process is not less than 15%, the rolling speed is 0.8-1.2 m/s, and the thickness to be heated is 2.0-3.0 times of the target thickness.
4. The method of claim 1, wherein the pre-straightening process is performed with a straightening force of 1500 tons, a tilting amount of 0-10mm, and a roll gap set within a target thickness ± 1.0 mm.
5. The method as claimed in claim 1, wherein the thermal straightening and straightening are performed three times after the accelerated cooling treatment, the straightening force is set to 800-1000 tons, the tilting amount is set to 0.2-0.3mm, and the roll gap is consistent with the target thickness.
6. The method for improving the performance uniformity of the thermomechanically rolled steel plate according to claim 5, characterized in that after the hot straightening is finished, the steel plate with the thickness specification of less than or equal to 30mm is subjected to on-line finishing post-treatment after being cooled by a direct cooling bed, and the steel plate with the thickness of more than 30mm is subjected to heap cooling treatment, so that the head and the tail of the steel plate are well covered, and the heap cooling time is more than 24 hours.
7. The method for improving the uniformity of the properties of a thermomechanically rolled steel sheet according to claim 5, wherein the pre-straightening speed is in accordance with the speed of a water-cooled roller table for accelerated cooling of the steel sheet.
8. A thermomechanically rolled steel sheet having high uniformity of properties, wherein the thermomechanically rolled steel sheet is produced by the method of any one of claims 1 to 7 for improving the uniformity of properties of the thermomechanically rolled steel sheet.
9. The thermomechanically rolled steel sheet having high uniformity of properties according to claim 8, wherein said thermomechanically rolled steel sheet has a chemical composition, in terms of mass fraction, of:
c: 0.10%, Si: 0.25%, Mn: 1.50%, P: 0.010%, S: 0.0015%, Cr: 0.10%, Nb: 0.03%, Ti: 0.015% and the balance Fe and other unavoidable impurities.
10. The thermomechanically rolled steel sheet having high uniformity of properties according to claim 8, wherein said thermomechanically rolled steel sheet has a chemical composition, in terms of mass fraction, of:
c: 0.09%, Si: 0.25%, Mn: 1.50%, P: 0.010%, S: 0.0010%, Cr: 0.10%, Nb: 0.03%, Ti: 0.015% and the balance Fe and other unavoidable impurities.
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