Method for producing a steel sheet with optimized surface quality

Abstract

The application discloses a preparation method of a steel plate with excellent surface quality. The method comprises the following steps: placing a main slab between two protective slabs, forming a combined slab by welding, heating, rough rolling, finish rolling and cooling the combined slab according to a preset scheme in the range of ①, ② and ③ according to the carbon, silicon and nickel content of the main slab, straightening and separating the slab to obtain a steel plate product. For example, ① C is greater than or equal to 0.25%, the heating temperature is 1160-1200 DEG C, the heating time is (1-1.2) min / m x t, the rough rolling temperature is 960-1030 DEG C, the finish rolling temperature is 840-900 DEG C, the open cooling temperature is greater than or equal to 750 DEG C, the cooling speed is less than or equal to 5 DEG C / s, and the final cooling temperature is greater than or equal to 700 DEG C. The application can obtain a high-Ni / Si / C steel plate product with excellent surface quality, and the surface is free of residual iron oxide scale, foreign matters and indentation, and free of decarburized layer. Meanwhile, two protective plate byproducts can be obtained, and the application has great economic effect.

Description

Technical Field

[0001] This invention belongs to the field of steel material preparation technology, and relates to a method for preparing steel plates, specifically a method for preparing steel plates with optimized surface quality. Background Technology

[0002] As competition in the heavy plate market intensifies, customers are demanding higher quality steel plates. Downstream high-end users, in addition to focusing on performance, also require high-quality surface finishes in their supply technical specifications. This is particularly true in industries such as shipbuilding and construction machinery, where surface quality requirements are extremely stringent. Visible defects caused by oxide scale peeling are not permitted, and pitting or roughness on the entire plate is unacceptable. However, given the current state of steel production, the high temperatures inherent in processes like heating and rolling inevitably result in surface defects of varying natures in the finished products. For example, high-temperature heating causes oxidation and decarburization on the steel plate surface, and some oxide scale is difficult to remove due to its high adhesion, ultimately leading to oxide scale indentation on the finished steel plate surface.

[0003] In particular, surface quality issues are more severe for steel plates with high Si, Ni, or C content. For example, in high-Si steel, the silicon in the steel matrix is ​​easily oxidized. The higher the silicon content, the more easily silicon particles accumulate at the interface between the inner oxide scale and the matrix, resulting in a dense iron oxide layer of Fe2SiO4. This oxide layer has high viscosity and strong adhesion to the matrix, making it impossible to completely remove during high-pressure descaling. It is then pressed into the steel plate during subsequent hot rolling, causing surface quality problems. Similarly, in high-Ni steel, during high-temperature heating, the billet surface develops an oxide scale of FeO, Fe3O4, NiO, Fe2O3, and nickel spinel NiFe2O4 due to oxidation. A Ni-rich layer forms inside this oxide scale, making it difficult to remove the surface oxide scale during rolling, thus affecting the surface quality of the product. For high-C steel, at high temperatures, the steel surface is oxidized, which significantly reduces the carbon content of the surface and forms a decarburized layer. The higher the carbon content and the higher the heating temperature, the easier it is to decarburize. Decarburization has an adverse effect on the surface hardness, wear resistance and fatigue performance of the steel. Summary of the Invention

[0004] In order to solve the problem of poor surface quality (e.g., oxide scale indentation, decarburization, etc.) of existing high-nickel, high-silicon, or high-carbon steel plates, the present invention aims to provide a method for preparing high-nickel silicon-carbon steel plates with optimized surface quality.

[0005] To achieve the above-mentioned objective, one embodiment of the present invention provides a method for preparing a steel plate. The method includes:

[0006] Prepare at least three steel slabs; two of the at least three steel slabs are protective slabs with C≤0.20%, Si≤0.20%, and Ni≤0.50% by mass percentage, and the remainder are main slabs with at least one of C≥0.25%, Si≥0.50%, and Ni≥1.00%.

[0007] The main board blank is placed between two protective board blanks and then welded together to form a composite blank.

[0008] The resulting composite billet is heated in a heating furnace according to a preset scheme;

[0009] After exiting the heating furnace, the composite billet undergoes rough rolling and finish rolling according to a pre-set plan to obtain the composite plate; the thickness of the intermediate billet obtained during rough rolling is 2.5 to 3.5 times the target thickness of the composite plate.

[0010] The resulting composite panel is cooled in an ultra-fast cooling system according to a preset scheme;

[0011] The cooled composite plate is straightened and separated to obtain steel plate products;

[0012] The preset scheme is as follows: when the main plate billet satisfies one of C≥0.25%, Si≥0.50%, and Ni≥1.00%, one of the following ①, ②, and ③ shall be adopted; when the main plate billet satisfies two or more of C≥0.25%, Si≥0.50%, and Ni≥1.00%, the heating temperature, heating duration, and termination cooling temperature shall respectively adopt the larger of the lower limits of two or more of the following ①, ②, and ③; the roughing temperature, finishing temperature, and start cooling temperature shall respectively adopt the smaller of the lower limits of two or more of the following ①, ②, and ③; and the cooling rate shall adopt the smaller of the upper limits of two or more of the following ①, ②, and ③.

[0013] ① The main sheet blank has a carbon content ≥ 0.25%, a heating temperature of 1160~1200℃, a heating time of (1.0~1.2) min / m×t, a rough rolling temperature of 960~1030℃, a finish rolling temperature of 840~900℃, an initial cooling temperature ≥ 750℃, a cooling rate ≤ 5℃ / s, and an initial cooling temperature ≥ 700℃.

[0014] ② The main sheet blank has a Si content ≥ 0.50%, a heating temperature of 1170~1210℃, a heating time of (1.0~1.2) min / m×t, a rough rolling temperature of 970~1040℃, a finish rolling temperature of 820~880℃, an initial cooling temperature ≥ 740℃, a cooling rate ≤ 8℃ / s, and a final cooling temperature ≥ 650℃.

[0015] ③ The main blank has Ni ≥ 1.00%, heating temperature 1190~1230℃, heating time (1.1~1.3) min / m×t, rough rolling temperature 980~1050℃, finish rolling temperature 800~860℃, initial cooling temperature ≥ 730℃, cooling rate 5~12℃ / s, and final cooling temperature ≥ 600℃;

[0016] t represents the thickness of the composite billet.

[0017] As a further improvement to the invention, in the process of "heating the obtained composite billet in a heating furnace according to a preset scheme", the soaking time is 20-40 minutes.

[0018] As a further improvement to the invention, the preparation method further includes:

[0019] After the process of "placing the main plate blank between two protective plate blanks and forming a composite blank by welding", the oxygen in the gap between the two adjacent steel plates is discharged through the exhaust port located on the side of the composite blank, and then the exhaust port is sealed.

[0020] As a further improvement to the invention, in the process of "expelling oxygen in the gap between two stacked adjacent steel plates through an exhaust port located on the side of the composite billet and then sealing the exhaust port", nitrogen or a rare gas is used to expel oxygen from the gap between the two stacked adjacent steel plates.

[0021] As a further improvement to the invention, in the description of "expelling oxygen in the gap between two stacked adjacent steel plates through an exhaust port located on the side of the assembled billet, and then sealing the exhaust port":

[0022] The gap between two adjacent stacked steel plates is connected to at least two exhaust ports. One of the exhaust ports is connected to an air pump to fill the gap between the two adjacent stacked steel plates with nitrogen gas for a first time period. During the first time period, the remaining exhaust ports are opened one by one in sequence.

[0023] As a further improvement to the invention, a steel pipe is welded to the exhaust port of the air pump, and the air pump's inflation pipe is connected to the steel pipe.

[0024] As a further improvement to the invention, the first time period is ≥5 min.

[0025] As a further improvement to the invention, the gap between any two adjacent stacked steel plates has an exhaust port connected to it.

[0026] As a further improvement to the invention, in the description of "expelling oxygen in the gap between two stacked adjacent steel plates through an exhaust port located on the side of the composite billet, and then sealing the exhaust port", polyethylene, polypropylene, polyvinyl chloride or polyethylene terephthalate is used to seal the exhaust port.

[0027] As a further improvement to the invention, in the description of "expelling oxygen in the gap between two stacked adjacent steel plates through an exhaust port located on the side of the composite billet, and then sealing the exhaust port", the gap between the two stacked adjacent steel plates is connected to a plurality of exhaust ports located on the four sides of the composite billet, a portion of which is located on the long side of the four sides of the composite billet and another portion is located on the short side of the four sides of the composite billet.

[0028] As a further improvement to the invention, the "placing the main plate blank between two protective plate blanks and forming a combined blank by welding" includes:

[0029] The main board blank is placed between two protective board blanks to form a stacked blank;

[0030] The joint between any two adjacent steel slabs stacked together is sealed by welding to form a composite slab.

[0031] As a further improvement to the invention, the length L1 and width W1 of the main blank, and the length L2 ≤ L1 and width W2 ≤ W1 of the protective blank;

[0032] In the combined billet, the protective slab is placed in the center relative to the main slab.

[0033] As a further improvement to the invention, L1 = L2 + (40~60) mm, W1 = W2 + (40~60) mm.

[0034] As a further improvement to the invention, the "placing the main plate blank between two protective plate blanks and forming a combined blank by welding" includes:

[0035] The main blank is placed between two protective blanks to form a stacked blank. At at least one pair of sides of the stacked blank, there is a gap between the side of the protective blank and the corresponding side of the main blank.

[0036] The joint between any two adjacent steel slabs stacked together is sealed by welding, and a sloping weld surface is formed in the area of ​​the spacing to form a composite slab.

[0037] As a further improvement to the invention, the "placing the main plate blank between two protective plate blanks and forming a combined blank by welding" includes:

[0038] The main blank is placed between two protective blanks to form a stacked blank. At at least one pair of sides of the stacked blank, the corresponding sides of the two adjacent steel blanks are flush and the joint between them is machined with a V-shaped bevel.

[0039] At the joint between any two adjacent steel slabs stacked together, a sealing weld is performed at the V-shaped bevel to form a composite slab.

[0040] As a further improvement of the invention, the V-shaped bevel has a depth of 20-30 mm and an angle of 55-65°, and is located on either of two adjacent steel slabs or is evenly distributed on both of the two adjacent steel slabs.

[0041] As a further improvement to the invention, in the process of "placing the main blank between two protective blanks and forming a combined blank by welding", a release agent is applied between the contact surfaces of any two adjacent steel blanks.

[0042] As a further improvement of the invention, the number of main board blanks is one and its thickness is greater than the thickness of each of the protective board blanks; or, the number of main board blanks is two or more and the sum of their thicknesses is greater than the thickness of each of the protective board blanks.

[0043] In the process of "straightening and separating the cooled composite plate to obtain the steel plate product", the obtained steel plate product includes a main plate transformed from the main plate blank and a protective plate transformed from the protective plate blank. The thickness of the main plate is ≥6mm, and the thickness of the protective plate is ≤8mm.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] 1) For high-Ni, high-Si, or high-C steel, by placing a high-Ni, high-Si, or high-C main plate billet between two upper and lower protective plate billets to form a composite billet, and then heating, rolling, and cooling the composite billet using the aforementioned preset scheme, high-Ni, high-Si, or high-C steel plate products with excellent surface quality can be obtained. For example, the surface of the main plate is free of residual iron oxide scale, foreign matter, and other indentations, and there is no decarburized layer, which solves the problem of difficulty in guaranteeing the surface quality of high-Ni, high-Si, or high-C steel in the prior art. Furthermore, this method is also easy to produce and does not require vacuum rolling to ensure excellent surface quality.

[0046] 2) While obtaining high-Ni, high-Si, or high-C steel plate products with excellent surface quality, two protective plate by-products transformed from the upper and lower protective slabs can also be obtained, which has great economic benefits. Attached Figure Description

[0047] For clarity of illustration and explanation, certain dimensions of structures or parts in the various figures of this invention are enlarged relative to other structures or parts. Therefore, only the basic structure of the subject matter of this invention is used to illustrate the invention.

[0048] Figure 1 This is a flowchart of the method for preparing the steel plate of the present invention;

[0049] Figure 2a This is a schematic cross-sectional view of the steel slab prepared according to the first embodiment of the present invention;

[0050] Figure 2b This is a top view of the composite blank prepared according to the first embodiment of the present invention;

[0051] Figure 2c This is a view of the composite blank prepared according to the first embodiment of the present invention from the short side.

[0052] Figure 2d This is a view of the composite blank prepared according to the first embodiment of the present invention from the long side.

[0053] Figure 3a This is a cross-sectional schematic diagram of the steel slab prepared according to the second embodiment of the present invention;

[0054] Figure 3b This is a view of the composite blank prepared according to the second embodiment of the present invention from the short side.

[0055] Figure 3c This is a view of the composite blank prepared according to the second embodiment of the present invention from the long side;

[0056] Figure 4a This is a view of the composite blank prepared according to the third embodiment of the present invention from the short side.

[0057] Figure 4b This is a view of the composite blank prepared according to the third embodiment of the present invention from the long side;

[0058] Figure 5a This is a view of the composite blank prepared according to the fourth embodiment of the present invention from the short side.

[0059] Figure 5b This is a view of the composite blank prepared according to the fourth embodiment of the present invention from the long side. Detailed Implementation

[0060] This invention provides a method for preparing steel plates with optimized surface quality, which is used to prepare steel plates with a high content of at least one of the three elements: nickel, silicon, and carbon. The preparation method generally includes three stages: a billet preparation stage, a rolling stage, and a plate separation stage.

[0061] Reference Figure 1 , the combined slab preparation stage includes the following steps:

[0062] Prepare at least three steel slabs; two of the at least three steel slabs are protective slabs with C≤0.20%, Si≤0.20%, and Ni≤0.50% by mass percentage, and the rest are main slabs that meet at least one of C≥0.25%, Si≥0.50%, and Ni≥1.00%;

[0063] Place the main slab between two protective slabs and form a combined slab by welding.

[0064] The rolling stage includes the following steps:

[0065] Heat the obtained combined slab in a heating furnace according to a preset plan;

[0066] After the combined slab exits the heating furnace, it is successively rough-rolled and finish-rolled according to a preset plan to obtain a combined plate; the thickness of the intermediate slab obtained during rough rolling is 2.5 - 3.5 times the target thickness of the combined plate;

[0067] The obtained combined plate is cooled in an ultra-fast cooling system according to a preset plan.

[0068] Among them, the preset plan is as follows: when the main slab meets one of C≥0.25%, Si≥0.50%, and Ni≥1.00%, one of the following ①, ②, and ③ is adopted; when the main slab meets two or more of C≥0.25%, Si≥0.50%, and Ni≥1.00%, the heating temperature, heating duration, and termination cooling temperature respectively adopt the larger lower limit values of two or more of the following ①, ②, and ③, the rough rolling temperature, finish rolling temperature, and start cooling temperature respectively adopt the smaller lower limit values of two or more of the following ①, ②, and ③, and the cooling rate adopts the smaller upper limit value of two or more of the following ①, ②, and ③;

[0069] ① When C≥0.25% of the main slab, the heating temperature is 1160 - 1200°C, the heating duration is (1.0 - 1.2) min / m×t, the rough rolling temperature is 960 - 1030°C, the finish rolling temperature is 840 - 900°C, the start cooling temperature is ≥750°C, the cooling rate is ≤5°C / s, and the termination cooling temperature is ≥700°C,

[0070] ② When Si≥0.50% of the main slab, the heating temperature is 1170 - 1210°C, the heating duration is (1.0 - 1.2) min / m×t, the rough rolling temperature is 970 - 1040°C, the finish rolling temperature is 820 - 880°C, the start cooling temperature is ≥740°C, the cooling rate is ≤8°C / s, and the termination cooling temperature is ≥650°C,

[0071] ③ For the main board blank, Ni ≥ 1.00%, heating temperature is 1190 - 1230 °C, heating duration is (1.1 - 1.3) min / m × t, rough rolling temperature is 980 - 1050 °C, finishing rolling temperature is 800 - 860 °C, starting cooling temperature ≥ 730 °C, cooling rate is 5 - 12 °C / s, and ending cooling temperature ≥ 600 °C.

[0072] The board splitting stage includes the following steps:

[0073] Straighten and split the cooled combined board to obtain steel plate products.

[0074] The preparation method of the present invention will be introduced in detail below with reference to the accompanying drawings.

[0075] <First Embodiment>

[0076] This embodiment provides a preparation method of steel plates, which includes three stages - combined blank preparation stage, rolling stage, and board splitting stage.

[0077] Specifically, the combined blank preparation stage includes processes such as preparing steel plate blanks, coating release agents, stacking blanks, sealing welding, exhausting oxygen, and sealing.

[0078] Among them, the process of preparing steel plate blanks includes: preparing at least three steel plate blanks.

[0079] See Figure 2a , among all the prepared steel plate blanks, the chemical compositions of two steel plate blanks 12 are C ≤ 0.20%, Si ≤ 0.20%, Ni ≤ 0.50% by mass percentage, and in this application, for the convenience of description and understanding, they are named protection board blanks 12.

[0080] Among all the prepared steel plate blanks, except for the aforementioned two protection board blanks 12, the chemical compositions of the remaining steel plate blanks satisfy at least one of C ≥ 0.25%, Si ≥ 0.50%, Ni ≥ 1.00% by mass percentage, that is, at least one of C, Si, and Ni is within the content range defined here, and in this application, for the convenience of description and understanding, they are named main board blanks 11.

[0081] It can be understood that when C ≥ 0.25% is satisfied, this main board blank 11 can basically be considered as high - carbon steel; when Si ≥ 0.50% is satisfied, this main board blank 11 can basically be considered as high - silicon steel; when Ni ≥ 1.00% is satisfied, this main board blank 11 can basically be considered as high - nickel steel.

[0082] In this embodiment, three steel slabs are prepared, and correspondingly, one main plate blank 11 is prepared. Of course, in other embodiments of the present invention, four or more steel slabs are prepared, and two or more main plate blanks 11 are prepared.

[0083] Preferably, the reference Figure 2b The main board blank 11 has a length L1, width W1, and thickness T1, and the protective board blank 12 has a length L2, width W2, and thickness T2, wherein L2 ≤ L1 and W2 ≤ W1. In this embodiment, L2 < L1 and W2 < W1. Of course, in variant embodiments, L2 < L1 and W2 = W1, or L2 = L1 and W2 < W1, or L2 = L1 and W2 = W1.

[0084] More specifically, L1 = L2 + (40~60) mm, W1 = W2 + (40~60) mm.

[0085] In addition, preferably, the depth of iron oxide scale, pits or foreign objects pressed into the surface of the protective slab 12 is ≤0.3mm, and the unevenness is ≤4mm / m; the depth of iron oxide scale, pits or foreign objects pressed into the surface of the main slab 11 is ≤0.3mm, and the unevenness is ≤2mm / m.

[0086] Furthermore, the process of preparing the steel slab billet also includes grinding the two surfaces and four sides of the prepared steel slab billet.

[0087] Specifically, the two surfaces and four sides of the prepared protective slab 12 are polished using a grinding wheel or belt sander to remove iron oxide scale and other materials until a metallic luster is exposed; the two surfaces and four sides of the prepared main slab 11 are polished using a grinding wheel, belt sander, or milling machine to remove iron oxide scale and other materials until a metallic luster is exposed.

[0088] The process of applying the release agent includes applying a release agent to one of the two surfaces of the protective blank 12. This surface to which the release agent is applied is the contact surface that will face the main blank 11 in the subsequent assembly blank, for example... Figure 2a The surfaces p1 and p2 are marked in the middle.

[0089] Further, the stacking process includes: placing the main blank 11 between two protective blanks 12 to form a stacked blank. Specifically, in this stacked blank, the protective blank 12 is centered relative to the main blank 11. For example, refer to... Figure 2bAs previously described, the dimensions of the protective slab 12 and the main slab 11 satisfy L1=L2+(40~60)mm and W1=W2+(40~60)mm. In this stacked slab, the distance W0 from each long side of the protective slab 12 to the corresponding long side of the main slab 11 is equal, and this distance W0 is half of W2-W1. Similarly, the distance W0 from each short side of the protective slab 12 to the corresponding short side of the main slab 11 is equal, and this distance L0 is half of L2-L1. Of course, in a variation embodiment, if L1=L2 or W1=W2, then at the corresponding pair of sides of the stacked slab, the corresponding pair of sides of the two adjacent steel slabs are flush and the joint between them has a V-shaped bevel (for example, the V-shaped bevel mentioned in the second to fourth embodiments).

[0090] Preferably, the laminated blank is placed under a four-column hydraulic machine and pressurized from above and below the laminated blank, with a pressure ≥100 tons.

[0091] Furthermore, the sealing welding process includes: forming a composite billet through welding. Specifically, it includes: sealing welding two adjacent steel plate billets in any stack to form a composite billet. For example, sealing welding the joint between two adjacent steel plate billets in any stack. Figure 2c and 2d As shown, at the four sides of the stacked blank, there is a gap between the side of the protective blank 12 and the corresponding side of the main blank 11, and a sloping weld surface 13 is formed by welding in the area of ​​the gap.

[0092] As can be understood, based on the previously applied release agent, the contact surfaces of any two adjacent steel slabs in the composite billet are coated with a release agent. For example, Figure 2a The surface p1 of the middle protective slab 12 and the surface p2 of the other protective slab 12 are both coated with a release agent. In the combined slab, both surfaces p1 and p2 face the main slab 11, so that there is a release agent between the upper protective slab 12 and the main slab 11, and there is also a release agent between the lower protective slab 12 and the main slab 11.

[0093] Furthermore, in the sealing welding process, the resulting composite billet has a plurality of vents 14 on its four sides. The gap between any two adjacent stacked steel plates is connected to one or more vents 14. In this embodiment, the gap between two adjacent stacked steel plates is connected to a plurality of vents 14, some of which are located on the long sides of the four sides of the composite billet (e.g., as shown in the figure, there are ≥5 vents 14 on the long sides), and others are located on the short sides of the four sides of the composite billet (e.g., as shown in the figure, there are ≥3 vents 14 on the long sides). Of course, in a variation embodiment, the gap between two adjacent stacked steel plates may also be connected to only one or two vents 14.

[0094] Furthermore, the oxygen removal process includes: removing the oxygen in the gap between two adjacent stacked steel plates through the exhaust port 14 connected thereto.

[0095] Specifically, in this embodiment, nitrogen or a rare gas is used to expel oxygen from the gap between two adjacent stacked steel plates. For example, the gap between two adjacent stacked steel plates is connected to at least two exhaust ports 14. One of the exhaust ports 14 is connected to an air pump to fill the gap between the two adjacent stacked steel plates with nitrogen for a first time period (preferably ≥5 min). During the first time period, the remaining exhaust ports 14 are opened individually in sequence. For example, at the moment the air pump starts filling, only one of the remaining exhaust ports 14 is open, while the rest are closed. After a while, such as after 30 seconds, the air pump continues to fill, while the previously open exhaust port 14 closes, and the previously closed exhaust port 14 opens instead... This continues until the cumulative filling time reaches the first time period (preferably ≥5 min).

[0096] Furthermore, preferably, a steel pipe is welded to one of the exhaust ports 14 connected to the air pump, and the air pump's inflation pipe is connected to the steel pipe. The exhaust port 14 is a circular hole with a diameter of approximately 6-12 mm; the outer diameter of the steel pipe is the same as the diameter of the exhaust port 14, its wall thickness is 1.2-2 mm, and its length is 20-30 mm.

[0097] Furthermore, the sealing process includes sealing the exhaust port 14 after the oxygen venting process. Specifically, polyethylene, polypropylene, polyvinyl chloride, or polyethylene terephthalate can be used to seal the exhaust port 14.

[0098] The preparation stage of the composite billet in this embodiment has been described in detail above. Next, the rolling stage of the preparation method will be described in detail.

[0099] The rolling stage includes:

[0100] Heating process – The obtained composite billet is heated in a heating furnace according to a preset plan, specifically the heating temperature and heating time are implemented according to the preset plan;

[0101] Rolling process—After the combined billet exits the heating furnace, it undergoes rough rolling and finish rolling sequentially according to the preset scheme to obtain the combined plate; the thickness of the intermediate billet obtained during rough rolling is 2.5 to 3.5 times the target thickness of the combined plate; specifically, the rough rolling temperature and finish rolling temperature are implemented according to the preset scheme;

[0102] Cooling process – The resulting composite board is cooled in an ultra-fast cooling system according to a preset plan, specifically the start cooling temperature, cooling rate and end cooling temperature are implemented according to the preset plan.

[0103] The preset scheme is as follows: when the main plate billet satisfies one of C≥0.25%, Si≥0.50%, and Ni≥1.00%, one of the following ①, ②, and ③ shall be adopted; when the main plate billet satisfies two or more of C≥0.25%, Si≥0.50%, and Ni≥1.00%, the heating temperature, heating duration, and termination cooling temperature shall respectively adopt the larger of the lower limits of two or more of the following ①, ②, and ③; the roughing temperature, finishing temperature, and start cooling temperature shall respectively adopt the smaller of the lower limits of two or more of the following ①, ②, and ③; and the cooling rate shall adopt the smaller of the upper limits of two or more of the following ①, ②, and ③.

[0104] ① The main sheet blank has a carbon content ≥ 0.25%, a heating temperature of 1160~1200℃, a heating time of (1.0~1.2) min / m×t, a rough rolling temperature of 960~1030℃, a finish rolling temperature of 840~900℃, an initial cooling temperature ≥ 750℃, a cooling rate ≤ 5℃ / s, and an initial cooling temperature ≥ 700℃.

[0105] ② The main sheet blank has a Si content ≥ 0.50%, a heating temperature of 1170~1210℃, a heating time of (1.0~1.2) min / m×t, a rough rolling temperature of 970~1040℃, a finish rolling temperature of 820~880℃, an initial cooling temperature ≥ 740℃, a cooling rate ≤ 8℃ / s, and a final cooling temperature ≥ 650℃.

[0106] ③ The main blank has Ni ≥ 1.00%, heating temperature 1190~1230℃, heating time (1.1~1.3) min / m×t, rough rolling temperature 980~1050℃, finish rolling temperature 800~860℃, initial cooling temperature ≥ 730℃, cooling rate 5~12℃ / s, and final cooling temperature ≥ 600℃;

[0107] t represents the thickness of the composite billet.

[0108] For example, if the main blank 11 has C≥0.25%, Si<0.50%, and Ni<1.00%, meaning it only satisfies C≥0.25%, Si≥0.50%, and Ni≥1.00%, then implementation ① will be adopted accordingly, specifically:

[0109] Heating process—The obtained composite billet is heated in a heating furnace at a heating temperature of 1160~1200℃ for a heating time of (1.0~1.2) min / m×t;

[0110] Rolling process—After exiting the heating furnace, the composite billet is subjected to rough rolling at a temperature of 960~1030℃ and finish rolling at a temperature of 840~900℃ to obtain the composite plate; the thickness of the intermediate billet obtained during rough rolling is 2.5~3.5 times the target thickness of the composite plate;

[0111] Cooling process – The resulting composite board is cooled in an ultra-fast cooling system with a starting cooling temperature ≥750℃, a cooling rate ≤5℃ / s, and a ending cooling temperature ≥700℃.

[0112] The above examples illustrate the case where only C ≥ 0.25%. When only Si ≥ 0.50%, then ② is used, and when only Ni ≥ 1.00%, then ③ is used.

[0113] For example, if the main billet 11 has C≥0.25%, Si<0.50%, and Ni≥1.00%, meaning it only satisfies C≥0.25% and Ni≥1.00%, then the heating temperature, heating duration, and final cooling temperature should respectively use the larger lower limit of range ① (corresponding to C≥0.25%) and ③ (corresponding to Ni≥1.00%). The roughing temperature, finishing temperature, and initial cooling temperature should respectively use the smaller lower limit of range ① (corresponding to C≥0.25%) and ③ (corresponding to Ni≥1.00%). The cooling rate should use the smaller upper limit of range ① (corresponding to C≥0.25%) and ③ (corresponding to Ni≥1.00%). Specifically:

[0114] Heating process—The obtained composite billet is heated in a heating furnace at a heating temperature of 1190~1230℃ and a heating time of (1.1~1.3) min / m×t;

[0115] Rolling process—After exiting the heating furnace, the composite billet is subjected to rough rolling at a temperature of 960~1030℃ and finish rolling at a temperature of 800~860℃ to obtain the composite plate; the thickness of the intermediate billet obtained during rough rolling is 2.5~3.5 times the target thickness of the composite plate;

[0116] Cooling process – The resulting composite board is cooled in an ultra-fast cooling system with a starting cooling temperature ≥730℃, a cooling rate ≤5℃ / s, and a ending cooling temperature ≥700℃.

[0117] The above examples illustrate the case where only C≥0.25% and Ni≥1.00% are satisfied. When only C≥0.25% and Si≥0.50% are satisfied, the heating temperature should be 1170~1210℃, heating time (1.0~1.2) min / m×t, roughing temperature 960~1030℃, finishing temperature 820~880℃, initial cooling temperature ≥740℃, cooling rate ≤5℃ / s, and final cooling temperature ≥700℃ in ① and ② respectively. When only Ni≥1.00% and Si≥0.50% are satisfied, the heating temperature should be 1190~1230℃, heating time (1.1~1.3) min / m×t, roughing temperature 970~1040℃, finishing temperature 800~860℃, initial cooling temperature ≥730℃, cooling rate ≤8℃ / s, and final cooling temperature ≥650℃ in ③ and ② respectively.

[0118] For example, if the main billet 11 has C≥0.25%, Si≥0.50%, and Ni≥1.00%, then the heating temperature, heating time, and final cooling temperature should respectively adopt the larger lower limit of the ranges ①, ②, and ③—heating temperature 1190~1230℃, heating time (1.1~1.3) min / m×t, and final cooling temperature ≥700℃. The roughing temperature, finishing temperature, and initial cooling temperature should respectively adopt the smaller lower limit of the ranges ①, ②, and ③—roughing temperature 960~1030℃, finishing temperature 800~860℃, and initial cooling temperature ≥730℃. The cooling rate should adopt the smaller upper limit of the ranges ①, ②, and ③—cooling rate ≤5℃ / s.

[0119] More preferably, in the heating process, the heat equalization time is 20-40 minutes.

[0120] The rolling stage of this embodiment has been described in detail above. Next, the plate separation stage of the preparation method will be described.

[0121] The plate separation stage includes: straightening and separating the cooled composite plates to obtain steel plate products.

[0122] Preferably, the cooled composite plate is first straightened, and then the four sides of the composite plate are cut. After cutting, under the action of the release agent, the two protective plates transformed from the two protective plate blanks 12 and the main plate transformed from the main plate blank 11 are separated. Finally, the plate is flattened and straightened to obtain the steel plate product.

[0123] That is, the steel plate products obtained include a main plate transformed from the main plate blank and a protective plate transformed from the protective plate blank, totaling three steel plate products.

[0124] Preferably, in the steel slab preparation process described above, the number of main slab slabs prepared in this embodiment is one, and its thickness T1 is greater than the thickness T2 of each of the protective slab slabs. Correspondingly, in the three steel plate products obtained, the thickness of the main slab is greater than the thickness of the protective plate. Of course, in a variation embodiment, the number of main slab slabs prepared is two or more, and the sum of the thicknesses of these main slab slabs is greater than the thickness of each of the protective slab slabs.

[0125] More preferably, the motherboard is ≥6mm thick, and the protection board is ≤8mm thick.

[0126] In summary, the preparation method of one embodiment of the present invention has the following beneficial effects:

[0127] 1) For high-Ni, high-Si, or high-C steel, by placing a high-Ni, high-Si, or high-C main plate billet between two upper and lower protective plate billets to form a composite billet, and then heating, rolling, and cooling the composite billet using the aforementioned preset scheme, high-Ni, high-Si, or high-C steel plate products with excellent surface quality can be obtained. For example, the surface of the main plate is free of residual iron oxide scale, foreign matter, and other indentations, and there is no decarburized layer, which solves the problem of difficulty in guaranteeing the surface quality of high-Ni, high-Si, or high-C steel in the prior art. Furthermore, this method is also easy to produce and does not require vacuum rolling to ensure excellent surface quality.

[0128] 2) While obtaining high-Ni, high-Si, or high-C steel plate products with excellent surface quality, two protective plate by-products transformed from the upper and lower protective slabs can also be obtained, which has great economic benefits.

[0129] 3) Preferably, the upper and lower protective slabs are thinner than the middle main slab. Thus, after the preparation method described above, the upper and lower protective slabs can be obtained as thin plate products, which solves the problems of low production efficiency and high rolling difficulty in the prior art for thin plate rolling, and has great economic benefits. Moreover, the thinner protective slabs have very little impact on the temperature, heating rate, deformation penetration and cooling rate of the middle main slab in the heating, rolling and cooling processes. This not only ensures the excellent structure and strong stability of the middle main slab, but also further improves the uniformity of the structure of the main slab and improves the quality of the final main slab.

[0130] 4) Furthermore, preferably, the oxygen removal process can further improve the surface quality of the steel plate, avoid defects such as surface indentation and decarburization, and also ensure the excellent quality of the steel plate's structure and properties. In addition, the material used in the sealing process has a softening temperature generally around 100°C and a melting point less than 300°C, which can simply and quickly seal the steel pipe opening, prevent external air or water vapor from entering the billet interior. At the same time, when the composite billet is heated at high temperature, the plastic melts and decomposes, which will not have an adverse effect on the billet and will not affect the discharge of hot gas during subsequent rolling, avoiding the influence on the surface quality due to internal gas residue.

[0131] <Second Embodiment>

[0132] This embodiment provides a method for preparing a steel plate. The preparation method includes three stages - the combined billet preparation stage, the rolling stage, and the plate splitting stage. The difference from the aforementioned first embodiment is only in the combined billet preparation stage, while the rolling stage and the plate splitting stage are the same as those in the first embodiment. Only the combined billet preparation stage will be introduced below. For the rolling stage and the plate splitting stage, refer to the first embodiment and will not be elaborated here.

[0133] Specifically, in this embodiment, the combined billet preparation stage includes processes such as preparing steel plate billets, coating with an isolating agent, stacking billets, sealing welding, oxygen removal, and sealing.

[0134] Among them, the process of preparing steel plate billets includes: preparing at least three steel plate billets.

[0135] Refer to Figure 3a , among all the prepared steel plate billets, the chemical compositions of two steel plate billets 22 are C≤0.20%, Si≤0.20%, Ni≤0.50% in terms of mass percentage. In this application, for the convenience of description and understanding, they are named protective plate billets 22.

[0136] Among all the prepared steel plate billets, except for the aforementioned two protective plate billets 22, the chemical compositions of the remaining steel plate billets satisfy at least one of C≥0.25%, Si≥0.50%, Ni≥1.00% in terms of mass percentage. In this application, for the convenience of description and understanding, they are named main plate billets 21.

[0137] It can be understood that when C≥0.25%, the main plate billet 21 can basically be considered as high-carbon steel; when Si≥0.50%, the main plate billet 21 can basically be considered as high-silicon steel; when Ni≥1.00%, the main plate billet 21 can basically be considered as high-nickel steel.

[0138] In this embodiment, three steel slabs are prepared, and correspondingly, one main plate blank 21 is prepared. Of course, in other embodiments of the present invention, four or more steel slabs are prepared, and two or more main plate blanks 21 are prepared.

[0139] Preferably, the length L1, width W1, and thickness T1 of the main board blank 21, and the length L2, width W2, and thickness T2 of the protective board blank 22, wherein L2 ≤ L1 and W2 ≤ W1. In this embodiment, L2 = L1 and W2 = W1. Of course, in variant embodiments, L2 < L1 and W2 = W1, or L2 = L1 and W2 < W1, or L2 < L1 and W2 < W1.

[0140] In addition, preferably, the depth of iron oxide scale, pits or foreign objects pressed into the surface of the protective slab 22 is ≤0.3mm, and the unevenness is ≤4mm / m; the depth of iron oxide scale, pits or foreign objects pressed into the surface of the main slab 21 is ≤0.3mm, and the unevenness is ≤2mm / m.

[0141] Furthermore, the process of preparing the steel slab billet also includes grinding the two surfaces and four sides of the prepared steel slab billet.

[0142] Specifically, the two surfaces and four sides of the prepared protective slab 22 are polished using a grinding wheel or belt sander to remove iron oxide scale and other materials until a metallic luster is exposed; the two surfaces and four sides of the prepared main slab 21 are polished using a grinding wheel, belt sander, or milling machine to remove iron oxide scale and other materials until a metallic luster is exposed.

[0143] Furthermore, in this embodiment, the steel slab preparation process further includes: cutting a V-shaped bevel 25 along the side edge on one surface of each protective slab 22, wherein the depth H of the V-shaped bevel 25 is 20~30mm and the angle A is 55~65°. The surface with the V-shaped bevel 25 is the contact surface that needs to face the main slab 21 in the subsequent assembly of the slab, for example... Figure 3a The surfaces p1 and p2 are marked in the middle.

[0144] Furthermore, the process of applying the release agent includes applying the release agent to one surface of each protective blank 22 (specifically, the surface with the V-shaped bevel 25 cut as described above, such as surface p1 and surface p2). This surface with the release agent applied is also the contact surface that needs to face the main blank 21 in the subsequent assembly blank.

[0145] Further, the stacking process includes: placing the main blank 21 between two protective blanks 22 to form a stacked blank. Specifically, in this stacked blank, the protective blank 22 is placed centrally relative to the main blank 21. Based on the foregoing explanation that the dimensions of the protective blank 22 and the main blank 21 satisfy L1=L2 and W1=W2, at the four sides of the stacked blank, the corresponding sides of the two adjacent steel blanks are flush and the joint between them has a V-shaped bevel 25. In a variant embodiment, if L2<L1 or W2<W1, then at the corresponding pair of sides of the stacked blank, there is a gap (e.g., the gap W0 or L0 mentioned in the first embodiment) between the protective blank and the corresponding side of the main blank.

[0146] Preferably, the laminated blank is placed under a four-column hydraulic machine and pressurized from above and below the laminated blank, with a pressure ≥100 tons.

[0147] Furthermore, the sealing welding process includes: forming a composite billet through welding. Specifically, it includes: sealing welding two adjacent steel plate billets in any stack to form a composite billet. For example, sealing welding the joint between two adjacent steel plate billets in any stack. Figure 3b and Figure 3c As shown, on the four sides of the stacked billet, the corresponding sides of two adjacent steel billets are flush and the joint between them has a V-shaped bevel 25. A sealing weld is performed at the V-shaped bevel 25 to form a welded layer 23.

[0148] As can be understood, based on the previously applied release agent, the contact surfaces of any two adjacent steel slabs in the composite billet are coated with a release agent. For example, Figure 3a The surface p1 of the middle protective slab 22 and the surface p2 of the other protective slab 22 are both coated with a release agent. In the combined slab, both surfaces p1 and p2 face the main slab 21, so that there is a release agent between the upper protective slab 22 and the main slab 21, and there is also a release agent between the lower protective slab 22 and the main slab 21.

[0149] Furthermore, in the sealing welding process, the resulting composite billet has a plurality of vents 24 on its four sides. The gap between any two adjacent stacked steel plates is connected to one or more vents 24. In this embodiment, the gap between two adjacent stacked steel plates is connected to a plurality of vents 24, some of which are located on the long sides of the four sides of the composite billet (e.g., as shown in the figure, there are ≥5 vents 24 on the long sides), and others are located on the short sides of the four sides of the composite billet (e.g., as shown in the figure, there are ≥3 vents 24 on the long sides). Of course, in a variation embodiment, the gap between two adjacent stacked steel plates may also be connected to only one or two vents 24.

[0150] Further, the oxygen exhausting process includes exhausting the oxygen in the gap between two adjacent stacked steel plates through the exhaust port 24 communicating therewith.

[0151] Specifically, in this embodiment, the oxygen in the gap between two adjacent stacked steel plates is exhausted by filling nitrogen or noble gas. For example, the gap between two adjacent stacked steel plates is connected to at least two exhaust ports 24. One of the exhaust ports 24 is connected to an air pump to fill nitrogen into the gap between two adjacent stacked steel plates and last for a first period (preferably ≥ 5 min). During this first period, the remaining exhaust ports 24 are sequentially and separately opened from beginning to end. For example, at the moment when the air pump starts to fill gas, only one of the remaining exhaust ports 24 is open and the others are sealed; after a while, such as after 30 seconds, the air pump still keeps filling gas, the previously open exhaust port 24 is sealed, and another previously sealed exhaust port 24 is opened...; thus, until the cumulative filling duration reaches the first period (preferably ≥ 5 min).

[0152] Furthermore, preferably, a steel pipe is welded to one of the exhaust ports 24 connected to the air pump, and the gas filling pipe of the air pump is对接 with the steel pipe. Regarding the exhaust port 24, it is a round hole with a diameter of about 6 - 12 mm; the outer diameter of the steel pipe is the same as the diameter of the exhaust port 24, its wall thickness is 1.2 - 2 mm, and its length is 20 - 30 mm.

[0153] Further, the sealing process includes sealing the exhaust port 24 after the oxygen exhausting process. Specifically, the exhaust port 24 can be sealed with polyethylene, polypropylene, polyvinyl chloride or polyethylene terephthalate.

[0154] <Third Embodiment>

[0155] This embodiment provides a preparation method of steel plates. This preparation method includes three stages - the combined billet preparation stage, the rolling stage, and the plate splitting stage. The difference from the aforementioned first embodiment is only in the combined billet preparation stage, and the rolling stage and the plate splitting stage are the same as those in the aforementioned first embodiment. Moreover, the difference from the aforementioned second embodiment is only in the setting position of the V-shaped groove. Only this difference will be introduced below, and the rest will not be elaborated.

[0156] Specifically, in this embodiment, the combined billet preparation stage includes processes such as preparing steel billets, coating with release agent, stacking billets, sealing and welding, exhausting oxygen, and sealing.

[0157] Among them, the process of preparing steel billets includes preparing at least three steel billets.

[0158] See Figure 4a And Figure 4bIn all the prepared steel slabs, the chemical composition of the two steel slabs 32, by mass percentage, is C≤0.20%, Si≤0.20%, and Ni≤0.50%, which is referred to as protective slab 32 in this application for ease of description and understanding.

[0159] Of all the prepared steel slabs, except for the two protective slabs 32 mentioned above, the chemical composition of the remaining steel slabs, by mass percentage, satisfies at least one of the following: C≥0.25%, Si≥0.50%, Ni≥1.00%. In this application, for ease of description and understanding, it is named main slab 31.

[0160] In this embodiment, three steel slabs are prepared, and correspondingly, one main plate blank 31 is prepared. Of course, in other embodiments of the present invention, four or more steel slabs are prepared, and two or more main plate blanks 31 are prepared.

[0161] Preferably, the length L1, width W1, and thickness T1 of the main board blank 31, and the length L2, width W2, and thickness T2 of the protective board blank 32, wherein L2 ≤ L1 and W2 ≤ W1. In this embodiment, L2 = L1 and W2 = W1. Of course, in variant embodiments, L2 < L1 and W2 = W1, or L2 = L1 and W2 < W1, or L2 < L1 and W2 < W1.

[0162] In addition, preferably, the depth of iron oxide scale, pits or foreign objects pressed into the surface of the protective slab 32 is ≤0.3mm, and the unevenness is ≤4mm / m; the depth of iron oxide scale, pits or foreign objects pressed into the surface of the main slab 31 is ≤0.3mm, and the unevenness is ≤2mm / m.

[0163] Furthermore, the process of preparing the steel slab billet also includes grinding the two surfaces and four sides of the prepared steel slab billet.

[0164] Specifically, the two surfaces and four sides of the prepared protective slab 32 are polished using a grinding wheel or belt sander to remove iron oxide scale and other materials until a metallic luster is exposed; the two surfaces and four sides of the prepared main slab 31 are polished using a grinding wheel, belt sander, or milling machine to remove iron oxide scale and other materials until a metallic luster is exposed.

[0165] Furthermore, in this embodiment, the process of preparing the steel slab billet further includes: cutting V-shaped bevels 35 along the side edges on the upper and lower surfaces of the main plate billet 31, wherein the depth H of the V-shaped bevel 35 is 20~30mm and the angle A is 55~65°.

[0166] Furthermore, the release agent coating process includes coating one surface of each protective blank 32 with a release agent. This surface coated with the release agent is the contact surface that will face the main blank 31 in subsequent assembly blanks.

[0167] Further, the stacking process includes placing the main blank 31 between two protective blanks 32 to form a stacked blank. Specifically, in this stacked blank, the protective blank 32 is placed centrally relative to the main blank 31. Based on the foregoing explanation that the dimensions of the protective blank 32 and the main blank 31 satisfy L1=L2 and W1=W2, at the four sides of the stacked blank, the corresponding sides of the two adjacent steel blanks are flush and the joint between them has a V-shaped bevel 35. In a variant embodiment, if L2<L1 or W2<W1, then at the corresponding pair of sides of the stacked blank, there is a gap (e.g., the gap W0 or L0 mentioned in the first embodiment) between the protective blank and the corresponding side of the main blank.

[0168] Preferably, the laminated blank is placed under a four-column hydraulic machine and pressurized from above and below the laminated blank, with a pressure ≥100 tons.

[0169] Furthermore, the sealing welding process includes: forming a composite billet through welding. Specifically, it includes: sealing welding two adjacent steel plate billets in any stack to form a composite billet. For example, sealing welding the joint between two adjacent steel plate billets in any stack. Figure 4a and Figure 4b As shown, on the four sides of the stacked billet, the corresponding sides of two adjacent steel billets are flush and the joint between them has a V-shaped bevel 35. A sealing weld is performed at the V-shaped bevel 35 to form a welded layer 33.

[0170] Furthermore, in the sealing welding process, the resulting composite billet has a plurality of vents 34 on its four sides. The gap between any two adjacent stacked steel plates is connected to one or more vents 34. In this embodiment, the gap between two adjacent stacked steel plates is connected to a plurality of vents 34, some of which are located on the long sides of the four sides of the composite billet (e.g., as shown in the figure, there are ≥5 vents 34 on the long sides), and others are located on the short sides of the four sides of the composite billet (e.g., as shown in the figure, there are ≥3 vents 34 on the long sides). Of course, in a variation embodiment, the gap between two adjacent stacked steel plates may also be connected to only one or two vents 34.

[0171] Furthermore, the oxygen removal and sealing processes in this embodiment are the same as those in the second embodiment above, and will not be described again here.

[0172] <Fourth Implementation Method>

[0173] This embodiment provides a method for preparing a steel plate. The preparation method includes three stages: combined blank preparation stage, rolling stage, and plate splitting stage. The difference from the aforementioned first embodiment is only in the combined blank preparation stage, while the rolling stage and the plate splitting stage are the same as those in the first embodiment. Moreover, the difference from the second and third embodiments is only in the setting position of the V-shaped groove. Only this difference will be introduced below, and the rest will not be elaborated.

[0174] Specifically, in this embodiment, the combined blank preparation stage includes processes such as preparing steel plate blanks, coating release agents, stacking blanks, sealing welding, exhausting oxygen, and sealing the mouth.

[0175] Among them, the process of preparing steel plate blanks includes: preparing at least three steel plate blanks.

[0176] Refer to Figure 5a and Figure 5b , among all the prepared steel plate blanks, the chemical compositions of two steel plate blanks 42 are C≤0.20%, Si≤0.20%, Ni≤0.50% by mass percentage. In this application, for the convenience of description and understanding, they are named protective plate blanks 42.

[0177] Among all the prepared steel plate blanks, except for the aforementioned two protective plate blanks 32, the chemical compositions of the remaining steel plate blanks satisfy at least one of C≥0.25%, Si≥0.50%, Ni≥1.00% by mass percentage. In this application, for the convenience of description and understanding, they are named main plate blanks 41.

[0178] In this embodiment, the number of prepared steel plate blanks is three. Correspondingly, the number of the main plate blanks 31 is one. Of course, in other embodiments of the present invention, the number of prepared steel plate blanks is four or more, and the number of the main plate blanks 31 is two or more.

[0179] Preferably, for the length L1, width W1, and thickness T1 of the main plate blank 41, and the length L2, width W2, and thickness T2 of the protective plate blank 42, where L2≤L1 and W2≤W1. In this embodiment, L2 = L1 and W2 = W1. Of course, in variant embodiments, it can also be L2<L1 and W2 = W1, or it can also be L2 = L1 and W2<W1, or L2<L1 and W2<W1.

[0180] In addition, preferably, the depth of surface scale, pits, or foreign object indentations, etc. of the protective plate blank 42 is ≤0.3mm, and the flatness is ≤4mm / m; the depth of surface scale, pits, or foreign object indentations, etc. of the main plate blank 41 is ≤0.3mm, and the flatness is ≤2mm / m.

[0181] Furthermore, the process of preparing the steel slab billet also includes grinding the two surfaces and four sides of the prepared steel slab billet.

[0182] Specifically, the two surfaces and four sides of the prepared protective slab blank 42 are polished using a grinding wheel or belt sander to remove iron oxide scale and other materials until a metallic luster is exposed; the two surfaces and four sides of the prepared main slab blank 41 are polished using a grinding wheel, belt sander, or milling machine to remove iron oxide scale and other materials until a metallic luster is exposed.

[0183] Furthermore, in this embodiment, the process of preparing the steel slab billet further includes: cutting a first bevel along the side of the upper and lower surfaces of the main slab billet 41, and cutting a second bevel along the side of one surface of each protective slab billet 42. The depth H of the first bevel and the second bevel are the same and are both 20~30mm. The sum A of the angles of the first bevel and the second bevel is 55~65°. Preferably, the angles of the first bevel and the second bevel are the same.

[0184] Furthermore, the release agent coating process includes coating one surface of each protective blank 42 with a release agent. This surface coated with the release agent is the contact surface that will face the main blank 41 in subsequent assembly blanks.

[0185] Further, the stacking process includes: placing the main blank 41 between two protective blanks 42 to form a stacked blank. Specifically, in this stacked blank, the protective blank 42 is placed centrally relative to the main blank 41. Based on the previous explanation that the dimensions of the protective blank 42 and the main blank 41 satisfy L1=L2 and W1=W2, at the four sides of the stacked blank, the corresponding sides of the two adjacent steel blanks are flush, and the joint between them has a V-shaped bevel 45 formed by the merging of the first bevel and the second bevel. In a variant embodiment, if L2<L1 or W2<W1, then at the corresponding pair of sides of the stacked blank, there is a gap (e.g., the gap W0 or L0 mentioned in the first embodiment) between the protective blank and the corresponding side of the main blank.

[0186] Preferably, the laminated blank is placed under a four-column hydraulic machine and pressurized from above and below the laminated blank, with a pressure ≥100 tons.

[0187] Furthermore, the sealing welding process includes: forming a composite billet through welding. For example, sealing welding is performed on the joint between any two adjacent stacked steel plate billets to form a composite billet. Figure 4a and Figure 4b As shown, at the V-shaped bevel 45 at the joint of the corresponding side of two adjacent steel plates on the four sides of the stacked billet, a sealing weld is performed to form a welded layer 43.

[0188] Furthermore, in the sealing welding process, the resulting composite billet has a plurality of vents 44 on its four sides. The gap between any two adjacent stacked steel plates is connected to one or more vents 44. In this embodiment, the gap between two adjacent stacked steel plates is connected to a plurality of vents 44, some of which are located on the long sides of the four sides of the composite billet (e.g., as shown in the figure, there are ≥5 vents 44 on the long sides), and others are located on the short sides of the four sides of the composite billet (e.g., as shown in the figure, there are ≥3 vents 44 on the long sides). Of course, in a variation embodiment, the gap between two adjacent stacked steel plates may also be connected to only one or two vents 44.

[0189] Furthermore, the oxygen removal and sealing processes in this embodiment are the same as those in the second embodiment above, and will not be described again here.

[0190] In summary, the preparation method of the present invention has the following beneficial effects:

[0191] 1) For high-Ni, high-Si, or high-C steel, by placing a high-Ni, high-Si, or high-C main plate billet between two upper and lower protective plate billets to form a composite billet, and then heating, rolling, and cooling the composite billet using the aforementioned preset scheme, high-Ni, high-Si, or high-C steel plate products with excellent surface quality can be obtained. For example, the surface of the main plate is free of residual iron oxide scale, foreign matter, and other indentations, and there is no decarburized layer, which solves the problem of difficulty in guaranteeing the surface quality of high-Ni, high-Si, or high-C steel in the prior art. Furthermore, this method is also easy to produce and does not require vacuum rolling to ensure excellent surface quality.

[0192] 2) While obtaining high-Ni, high-Si, or high-C steel plate products with excellent surface quality, two protective plate by-products transformed from the upper and lower protective slabs can also be obtained, which has great economic benefits.

[0193] 3) Preferably, the upper and lower protective slabs are thinner than the middle main slab. Thus, after the preparation method described above, the upper and lower protective slabs can be obtained as thin plate products, which solves the problems of low production efficiency and high rolling difficulty in the prior art for thin plate rolling, and has great economic benefits. Moreover, the thinner protective slabs have very little impact on the temperature, heating rate, deformation penetration and cooling rate of the middle main slab in the heating, rolling and cooling processes. This not only ensures the excellent structure and strong stability of the middle main slab, but also further improves the uniformity of the structure of the main slab and improves the quality of the final main slab.

[0194] 4) Furthermore, the preferred oxygen removal process can further improve the surface quality of the steel plate, avoid defects such as surface pressing and decarburization, and also ensure the excellent structure and performance of the steel plate. In addition, the material used in the sealing process has a softening temperature of around 100℃ and a melting point of less than 300℃, which can easily and quickly seal the steel pipe opening to prevent external air or water vapor from entering the billet. At the same time, when the composite billet is heated at high temperature, the plastic melts and decomposes, which will not have an adverse effect on the billet, and will not affect the discharge of hot gas during subsequent rolling, thus avoiding the impact on surface quality due to residual internal gas.

[0195] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of producing a steel sheet, characterized by, The method comprises: preparing at least three steel slab blanks; two of the at least three steel slab blanks are protective slab blanks with C≤0.20%, Si≤0.20%, and Ni≤0.50% in terms of mass percentage, and the rest are main slab blanks satisfying at least one of C≥0.25%, Si≥0.50%, and Ni≥1.00%; placing the main slab blanks between the two protective slab blanks and forming a combined blank by welding; discharging oxygen in a gap between the two adjacent steel slabs through exhaust ports located at the side edges of the combined blank, and then sealing the exhaust ports; the exhaust ports are sealed by polyethylene, polypropylene, polyvinyl chloride, or polyethylene terephthalate; the gap between the two adjacent steel slabs is connected to at least two exhaust ports, one of the exhaust ports is connected to a gas filling pump to fill nitrogen into the gap between the two adjacent steel slabs for a first time period, and during the first time period, the remaining exhaust ports are sequentially and individually opened from beginning to end, wherein the first time period is ≥5 min; heating the obtained combined blank in a heating furnace according to a preset scheme; after the combined blank leaves the heating furnace, rough rolling and finish rolling are sequentially performed on the combined blank according to a preset scheme to obtain a combined plate; the thickness of the intermediate blank obtained during rough rolling is 2.5-3.5 times the target thickness of the combined plate; cooling the obtained combined plate in an ultra-fast cooling system according to a preset scheme; straightening and dividing the cooled combined plate to obtain a steel plate product; wherein, when the main slab blank satisfies one of C≥0.25%, Si≥0.50%, and Ni≥1.00%, one of ①, ②, and ③ is used; when the main slab blank satisfies two or more of C≥0.25%, Si≥0.50%, and Ni≥1.00%, the lower limit of the larger value of the range of the heating temperature, the heating time, and the termination cooling temperature is the larger value of the lower limits of the ranges of two or more of ①, ②, and ③, the lower limit of the smaller value of the range of the rough rolling temperature, the finish rolling temperature, and the start cooling temperature is the smaller value of the lower limits of the ranges of two or more of ①, ②, and ③, and the upper limit of the smaller value of the range of the cooling speed is the smaller value of the upper limits of the ranges of two or more of ①, ②, and ③; ①C≥0.25% of the main slab blank, heating temperature 1160-1200℃, heating time (1.0-1.2) min / m×t, rough rolling temperature 960-1030℃, finish rolling temperature 840-900℃, start cooling temperature ≥750℃, cooling speed ≤5℃ / s, and termination cooling temperature ≥700℃, ②Si≥0.50% of the main slab blank, heating temperature 1170-1210℃, heating time (1.0-1.2) min / m×t, rough rolling temperature 970-1040℃, finish rolling temperature 820-880℃, start cooling temperature ≥740℃, cooling speed ≤8℃ / s, and termination cooling temperature ≥650℃, ③The main slab has Ni≥1.00%, the heating temperature is 1190-1230℃, the heating time is (1.1-1.3)min / m×t, the rough rolling temperature is 980-1050℃, the finish rolling temperature is 800-860℃, the starting cooling temperature is ≥730℃, the cooling speed is 5-12℃ / s, and the final cooling temperature is ≥600℃; t is the thickness of the combined slab.

2. The method of producing a steel sheet according to claim 1, characterized by, In the process of heating the combined slab in the heating furnace according to the preset scheme, the soaking time is 20-40min.

3. The method of producing a steel sheet according to claim 1, characterized by, A steel pipe is welded at the exhaust port of the communication inflation pump, and the inflation pipe of the inflation pump is connected with the steel pipe.

4. The method of producing a steel sheet according to claim 1, characterized by, The gap between any two adjacent stacked steel plates is connected with an exhaust port.

5. The method of producing a steel sheet according to claim 1, characterized by, In the process of discharging the oxygen in the gap between the two adjacent stacked steel plates through the exhaust port at the side of the combined slab and then sealing the exhaust port, the gap between the two adjacent stacked steel plates is connected with a plurality of exhaust ports at the four sides of the combined slab, and a part of the plurality of exhaust ports is located at the long side of the four sides of the combined slab and the other part is located at the short side of the four sides of the combined slab.

6. The method of producing a steel sheet according to claim 1, characterized by, The process of placing the main slab between two protection slabs and forming a combined slab by welding comprises: The main slab is placed between two protection slabs to form a stacked slab; The joint between any two adjacent stacked steel slabs is sealed and welded to form a combined slab.

7. The method of producing a steel sheet according to claim 6, characterized by, The length L1 and the width W1 of the main slab, and the length L2≤L1 and the width W2≤W1 of the protection slab; In the combined slab, the protection slab is placed centrally relative to the main slab.

8. The method of producing a steel sheet according to claim 7, characterized by, L1=L2+(40-60)mm, and W1=W2+(40-60)mm.

9. The method of producing a steel sheet according to claim 7, characterized by, The process of placing the main slab between two protection slabs and forming a combined slab by welding comprises: The main slab is placed between two protection slabs to form a stacked slab, and at least one pair of side edges of the stacked slab, the side edge of the protection slab has a spacing to the corresponding side edge of the main slab; The joint between any two adjacent stacked steel slabs is sealed and welded, and a bevel welding surface is formed in the area of the spacing by welding to form a combined slab.

10. The method of producing a steel sheet according to claim 7, characterized by, The process of placing the main slab between two protection slabs and forming a combined slab by welding comprises: The main slab is placed between two protection slabs to form a stacked slab, and at least one pair of side edges of the stacked slab, the side edge of the protection slab has a spacing to the corresponding side edge of the main slab; The joint between any two adjacent stacked steel slabs is sealed and welded at the V-shaped groove to form a combined slab.

11. The method of producing a steel sheet according to claim 10, characterized by, The depth of the V-shaped groove is 20-30mm, and the angle is 55-65°, which is located on any one of the two adjacent stacked steel slabs or evenly distributed on both of the two adjacent stacked steel slabs.

12. The method of producing a steel sheet according to claim 1, characterized by, In the process of placing the main slab between two protection slabs and forming a combined slab by welding, an isolation agent is coated between the contact surfaces of any two adjacent steel slabs.

13. The method of producing a steel sheet according to claim 1, characterized by, The number of the main slab is one and the thickness is greater than the thickness of each of the protection slabs; or the number of the main slab is more than two and the sum of the thicknesses is greater than the thickness of each of the protection slabs; In the "straightening and dividing the combined slab after cooling to obtain the steel plate products", the steel plate products include the main plate transformed from the main slab and the protection plate transformed from the protection slab, the thickness of the main plate is greater than or equal to 6mm, and the thickness of the protection plate is less than or equal to 8mm.

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