Stainless steel composite plate with excellent flatness and its preparation method

Abstract

The present invention discloses a stainless steel composite plate with excellent flatness and a preparation method thereof. The obtained composite billet is heated and rolled, and after rolling, it is cooled. The large composite plate enters an ultra-fast cooling system for intermittent cooling: The ultra-fast cooling system has 24 groups of cooling headers arranged along the roller table, and the cooling distance of each group of cooling headers is 1 m. When the large composite plate passes through the ultra-fast cooling system, the opening and closing states of all 24 groups of cooling headers are controlled in the manner of opening N groups of cooling headers first and then not opening M groups of cooling headers. The cooling water pressure is 0.2 MPa, the cooling rate is 3 to 15 °C / s, and the final cooling temperature is 380 to 450 °C; where N takes values of 2, 3, or 4, and M takes values of 2, 3, or 4.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material preparation, and relates to a stainless steel composite plate with excellent plate shape and a preparation method thereof. Background Art

[0002] With the continuous development of science and industry, ordinary alloys or single metals have become difficult to meet the comprehensive performance requirements of industrial development. This has led to the emergence of composite plates. Stainless steel composite plates are based on carbon steel or low-alloy steel as the base layer and stainless steel as the cladding layer. Through methods such as explosive lamination and rolling lamination, the metallurgical bonding of the composite interface is achieved. This achieves the goal of saving resources and reducing costs without compromising the performance (mechanical strength, corrosion resistance, etc.). Stainless steel composite plates are widely used in industries such as petrochemicals, pressure vessels, power equipment, medical equipment, water conservancy, papermaking, and bridges.

[0003] The construction of cross-river and cross-sea passages urgently requires the construction of long-span steel bridges. As the span of steel bridges increases, the requirements for stainless steel composite plates used in bridge structures are also becoming higher and higher, such as large thickness, good plate shape, excellent bonding properties, high strength, and high toughness.

[0004] Existing stainless steel composite plates are made by explosive composite, non-vacuum composite blank preparation, vacuum electron beam welding and other methods. They have problems such as poor surface quality, difficult plate shape control, poor interface bonding quality, low yield rate and low production efficiency. Summary of the Invention

[0005] The object of the present invention is to provide a stainless steel composite plate with excellent plate shape and a preparation method thereof.

[0006] To achieve the above-mentioned object of the invention, one embodiment of the present invention provides a method for preparing a stainless steel composite plate with excellent plate shape, which comprises three steps of preparing a composite billet, rolling the composite billet, and separating and straightening the composite plate.

[0007] In the composite blank preparation step, the chemical composition of the base material of the composite blank is as follows, in percentage by mass: C: 0.03-0.16%, Si: 0.11-0.29%, Mn: 1.31-1.54%, P≤0.018%, S≤0.0030%, Cr: 0.06-0.29%, Ni≤0.24%, Cu≤0.24%, Mo≤0.24%, Nb: 0.011-0.034%, Ti: 0.011-0.019%, Al: 0.030-0.040%, and the balance is Fe and unavoidable impurities;

[0008] The composite billet rolling step comprises:

[0009] Heat the obtained composite blank, with the soaking temperature being 1170 - 1220°C, and the total heating time ≥ 1.2×tmin / mm, where t is the thickness of the composite blank;

[0010] Adopt two-stage controlled rolling of rough rolling + finish rolling. In the rough rolling stage, the final rolling temperature ≥ 1000°C, and the rough rolling stage ends when the thickness of the intermediate blank is 2.5 - 3.5 times the target thickness of the large plate of the composite plate; then wait for temperature, and during this period, water cooling is carried out. When the surface temperature of the intermediate blank drops below 840°C, start the finish rolling stage, and the final rolling temperature in the finish rolling stage ≥ 780°C;

[0011] After rolling, cooling is carried out. The large plate of the composite plate enters the ultra-rapid cooling system for intermittent cooling: The ultra-rapid cooling system has 24 groups of cooling headers arranged along the roller table, and the cooling distance of each group of cooling headers is 1m. When the large plate of the composite plate passes through the ultra-rapid cooling system, the opening and closing states of all 24 groups of cooling headers are controlled in the way of opening N groups of cooling headers first and then not opening M groups of cooling headers. The cooling water pressure is 0.2MPa, the cooling rate is 3 - 15°C / s, and the final cooling temperature is 380 - 450°C; where N takes the value of 2, 3 or 4, and M takes the value of 2, 3 or 4.

[0012] Preferably, the roller table speed of the ultra-rapid cooling system is 0.4 - 0.9m / s.

[0013] Preferably, in the step of "heating the obtained composite blank", five-stage heating of preheating, first heating, second heating, third heating and soaking is adopted. The preheating temperature ≤ 850°C, and the residence time is (0.45 - 0.55)tmin / mm. The first heating temperature is 1030 - 1090°C, and the residence time is (0.35 - 0.45)t min / mm. The second heating temperature is 1100 - 1160°C, and the residence time is (0.25 - 0.35)t min / mm. The third heating temperature is 1140 - 1180°C, and the residence time is (0.15 - 0.25)t min / mm. The soaking temperature is 1170 - 1210°C, and the residence time is (0.10 - 0.20)tmin / mm.

[0014] Preferably, in the step of "adopting two-stage controlled rolling of rough rolling + finish rolling", in the rough rolling stage, in the first pass, longitudinal rolling is adopted, and the rolling reduction is ≥ 46 mm; in the second pass, transverse rolling is started and continued until the composite blank is rolled to the target width of the final composite plate in the nth pass, and the rolling reduction in the second pass is ≥ 25 mm; in the (n + 1)th pass, longitudinal rolling is started and the rough rolling stage ends when the thickness of the intermediate blank is 2.5 to 3.5 times the target thickness of the large plate of the composite plate, and the rolling reduction in the (n + 1)th pass is ≥ 30 mm; throughout the rough rolling stage, the rolling temperature in the first pass is ≥ 1060 °C, the starting rolling temperature of the remaining passes is ≤ 1050 °C, and the finishing rolling temperature is ≥ 1000 °C; after the rough rolling stage, the temperature is held, and water cooling is carried out during this period. When the surface temperature of the intermediate blank drops below 840 °C, the finish rolling stage starts, and the starting rolling temperature of the finish rolling stage is 810 °C to 840 °C, and the finishing rolling temperature is 780 to 810 °C.

[0015] Preferably, in the step of "heating the obtained composite blank",

[0016] The obtained composite blank is heated, the soaking temperature is 1200 to 1220 °C, the total heating time is ≥ 1.2 × tmin / mm, where t is the thickness of the composite blank, and the soaking section holding time is 30 min to 50 min;

[0017] Two-stage controlled rolling of rough rolling + finish rolling is adopted. In the rough rolling stage, the starting rolling temperature is ≤ 1050 °C, the finishing rolling temperature is ≥ 1000 °C, transverse rolling is carried out first and then longitudinal rolling, and the rolling reduction in at least one pass during longitudinal rolling is ≥ 35 mm. The total rough rolling reduction is 40 to 60%, and the rough rolling stage ends when the thickness of the intermediate blank is 2.5 to 3.5 times the target thickness of the large plate of the composite plate; then the temperature is held, and water cooling is carried out during this period. When the surface temperature of the intermediate blank drops below 830 °C, the finish rolling stage starts; the finishing rolling temperature in the finish rolling stage is ≥ 800 °C, and the total finish rolling reduction is 55 to 75%.

[0018] Preferably, after intermittent cooling, the large plate of the composite plate is cooled naturally on the cooling bed to room temperature, and thus the rolling step of the composite blank is completed and the composite plate separation and straightening step is entered.

[0019] Preferably, after intermittent cooling, the large plate of the composite plate directly enters the straightening machine for straightening. After straightening, the large plate of the composite plate is cooled naturally on the cooling bed. When the surface temperature drops below 200 °C, cold straightening is carried out using a cold straightening machine.

[0020] Preferably, after intermittent cooling, the large plate of the composite plate directly enters the straightening machine for straightening;

[0021] Place the straightened large plate of the composite plate at a temperature of T fStack cooling is carried out between two steel plates at 100 to 150 °C, and the stack cooling time is 0.4 min / mm × t0 ± 5 min, where t0 is the thickness of the large plate of the composite plate;

[0022] After the stack cooling is completed, the large plate of the composite plate is placed on the cooling bed and naturally cooled to room temperature;

[0023] T f = 550 + 30[Si] - 20[Mn] + 15[Cr] - 15[Ni] + 10[Mo], where [Si], [Mn], [Mo], [Cr],

[0024] [Ni] is 100 times the mass percentage of each element in the base material.

[0025] Preferably, the steps for preparing the composite billet specifically include:

[0026] Prepare two carbon steel billets with thickness T1, length L1, and width W1 as the base materials for forming the base layer of the composite plate; and prepare two stainless steel billets with thickness T2, length L2, and width W2 as the cladding materials for forming the cladding layer of the composite plate; L2 < L1, W2 < W1;

[0027] Surface-treat at least one surface of each of the two base materials and the two cladding materials;

[0028] Apply a release agent on one surface of one cladding material;

[0029] Form a billet according to the stacking order of base material, cladding material, cladding material, base material; wherein, the cladding material is placed in the middle relative to the base material, and the surfaces of the base material and the cladding material that are in contact with each other are all the surfaces that have undergone the surface treatment, and the surface coated with the release agent faces the other cladding material;

[0030] Prepare four seals with width W3, W3 = 2T2 - 1 to 2 mm, and attach the seals to the four sides of the two cladding materials. Gas shielded welding is carried out between adjacent seals and between the seals and the base material, so that the two base materials and the seals form an integral body to obtain a basic billet of the composite billet;

[0031] Drill a round hole in the seal at the groove on the side of the basic billet of the composite billet, and weld a seamless steel pipe at the round hole;

[0032] Carry out surfacing welding on the grooves on the four sides of the basic billet of the composite billet;

[0033] Use a vacuum pump to evacuate the composite billet through this seamless steel pipe, and the vacuum degree ≤ 10 -1 Pa, and then maintain the pressure for more than 4 h; finally, seal the seamless steel pipe.

[0034] Preferably, the chemical composition of the substrate of the composite blank is, in percentage by mass: C: 0.03-0.07%, Si: 0.11-0.19%, Mn: 1.46-1.54%, P≤0.010%, S≤0.0015%, Cr: 0.21-0.29%, Ni: 0.16-0.24%, Cu: 0.16-0.24%, Mo: 0.16-0.24%, Nb: 0.026-0.034%, Ti: 0.011-0.019%, Al: 0.030-0.040%, and the rest is Fe and unavoidable impurities.

[0035] To achieve the above-mentioned object of the invention, one embodiment of the present invention provides a stainless steel composite plate with excellent plate shape, and the composite plate is prepared by the above-mentioned preparation method.

[0036] Preferably, the total thickness of the composite plate is ≥19 mm, the thickness of the base layer is ≥16 mm, the thickness of the composite layer is 1 to 10 mm, the Vickers hardness difference of the base layer in the thickness direction of the composite plate is ≤10, the strength difference between the head, middle and tail is ≤40 MPa, the strength difference of the entire plate is ≤40 MPa, and the unevenness is ≤2 mm / m.

[0037] Preferably, the yield strength of the composite plate is ≥345MPa, the tensile strength is ≥490MPa, the elongation after fracture is ≥18%, and the yield strength ratio is ≤0.85; the composite interface bonding rate is 100%, the shear strength is ≥300MPa; the impact energy at 0℃ is ≥120J, the impact energy at -20℃ is ≥120J, and the impact energy at -40℃ is ≥120J.

[0038] Preferably, the composite plate has a yield strength of ≥500 MPa, a tensile strength of ≥630 MPa, an elongation at break of ≥18%, a yield strength ratio of ≤0.86, an impact energy of ≥240 J at 0°C, an impact energy of ≥200 J at -20°C, and an impact energy of ≥150 J at -40°C.

[0039] Compared with the existing technology, the beneficial effects of the present invention are: on the one hand, in the entire preparation method, through the specific control of the process, the corrosion resistance and mechanical strength of the stainless steel composite plate are guaranteed, and the degradation of the corrosion resistance and mechanical properties during the rolling process of the composite billet is avoided; on the other hand, the problems of the existing stainless steel composite plate thick plate such as difficult plate shape control, poor surface quality, and low production efficiency are solved, meeting the construction needs of steel bridge projects; on the other hand, the yield rate and production efficiency are high during the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] For the sake of clarity in presentation and description, in the various drawings of the present invention, certain dimensions of structures or parts are exaggerated relative to other structures or parts. Therefore, these drawings are only used to illustrate the basic structure of the subject matter of the present invention.

[0041] Figure 1It is a schematic cross-sectional view of the steel billet in the present invention;

[0042] Figure 2 It corresponds to Figure 1 Schematic cross-sectional view of the composite billet;

[0043] Figure 3 It is Figure 2 Schematic cross-sectional view of two single-sided stainless steel composite plates rolled from the composite billet;

[0044] Figure 4a It is a schematic flow chart of the first implementation mode of the composite billet rolling step of the present invention;

[0045] Figure 4b It is a schematic flow chart of the second implementation mode of the composite billet rolling step of the present invention;

[0046] Figure 4c It is a schematic flow chart of the third implementation mode of the composite billet rolling step of the present invention;

[0047] Figure 4d It is a schematic flow chart of the fifth implementation mode of the composite billet rolling step of the present invention;

[0048] Figure 4e It is a schematic flow chart of the fourth implementation mode of the composite billet rolling step of the present invention;

[0049] Figure 4f It is a schematic flow chart of the sixth implementation mode of the composite billet rolling step of the present invention. Specific embodiments

[0050] The present invention provides a method for preparing a single-sided stainless steel composite plate with excellent flatness, and a composite plate prepared based on this method. Specifically, the preparation method includes three general steps: composite billet preparation, composite billet rolling, and composite plate separation and straightening.

[0051] The general steps of the composite billet preparation include the following sub-steps:

[0052] Prepare two carbon steel billets with thickness T1, length L1, and width W1 as the base materials; and prepare two stainless steel billets with thickness T2, length L2, and width W2 as the clad materials;

[0053] Surface-treat at least one surface of each of the two base materials and the two clad materials;

[0054] Apply a release agent on one surface of one clad material;

[0055] Stack the billets in the order of base material, clad material, clad material, base material;

[0056] Prepare four seals with a width W3, where W3 = 2T2 - 1 to 2 mm. Attach the seals to the four side edges of the two composite materials. Perform gas shielded welding between adjacent seals and between the seals and the base material, so that the two base materials and the seals form an integral body, obtaining a composite blank base blank;

[0057] Process a round hole on the seal at the groove on the side of the composite blank base blank, and weld a seamless steel pipe at the round hole;

[0058] Perform surfacing welding on the grooves on the four side edges of the composite blank base blank;

[0059] Use a vacuum pump to evacuate the composite blank through this seamless steel pipe, with a vacuum degree ≤ 10 -1 Pa, and then maintain the pressure for more than 4 hours; finally, seal the seamless steel pipe.

[0060] Furthermore, the above steps are described in detail as follows.

[0061] The step "Prepare two carbon steel blanks with a length L1 and a width W1 as the base materials; and prepare two stainless steel blanks with a length L2 and a width W2 as the composite materials", that is, the blank preparation step.

[0062] Among them, the carbon steel blank used as the base material has a thickness T1, a length L1, and a width W1, which is a rectangular steel blank; similarly, the stainless steel blank used as the composite material has a thickness T2, a length L2, and a width W2, which is also a rectangular steel blank.

[0063] And, L2 < L1, W2 < W1, and the length and width dimensions of the composite material are both smaller than those of the base material. Preferably, L2 = L1 - L0, W2 = W1 - W0, and the preferred value ranges of L0 and W0 are 90 to 150 mm respectively.

[0064] As a preferred solution, the surface scale pressing depth and the surface pit depth of the carbon steel blank are both ≤ 0.3 mm, and the unevenness is ≤ 3 mm / m; the surface of the stainless steel blank has no scratches, and the unevenness is ≤ 2 mm / m. In this way, it is avoided that the steel blanks enter the production line of the composite board with obvious surface defects or sheet shape defects.

[0065] Next, regarding the step "Perform surface treatment on at least one surface of each of the two base materials and the two composite materials", that is, the blank surface treatment step.

[0066] In this embodiment, grind and polish one surface of each base material and each composite material to remove the surface scale and expose the metallic luster. Refer Figure 1As shown, for example, a grinding wheel machine, a sanding belt machine or a milling machine is used to grind and polish the surface p1a of the substrate 11a to remove the surface oxide scale and reveal the metallic luster; similarly, a grinding wheel machine, a sanding belt machine or a milling machine is used to grind and polish the surface p2a of the prepared substrate 12a to remove the surface oxide scale and reveal the metallic luster.

[0067] The surface p3a of the prepared composite material 21a is ground and polished with a wire wheel to remove the surface oxide scale and reveal the metallic luster. Similarly, the surface p4a of the prepared composite material 22a is ground and polished with a wire wheel to remove the surface oxide scale and reveal the metallic luster.

[0068] As will be seen from the following text, during assembly, the surface that has been surface treated (polished in this embodiment) is used as the surface where the substrate and the composite material are in contact with each other, for example, surface p1a and surface p3a are in contact with each other, and surface p4a and surface p2a are in contact with each other, so that the interface bonding quality can be guaranteed.

[0069] The following will continue to introduce the other sub-steps of the composite blank preparation step.

[0070] The step of "applying a release agent on one surface of a composite material" is also a step of applying a release agent.

[0071] Among them, combined with the above, it can be seen that in the previous billet surface treatment step, the surface of the composite material that will be in contact with the substrate during assembly is subjected to surface treatment such as grinding and polishing in order to ensure the interface bonding quality of the composite plate; and the purpose of the release agent coating step is to avoid the contact between the surfaces of the composite materials and the composite materials during assembly, which will be subsequently bonded during the composite billet rolling step and ultimately difficult to separate.

[0072] Based on this, a release agent is applied to one of the two composite materials. If one surface of the selected composite material has been surface treated and the other has not been surface treated during the previous blank surface treatment step, the release agent is applied to the "untreated" surface during this release agent application step. If, as mentioned above, both surfaces of the selected composite material have been surface treated during the previous blank surface treatment step, the release agent is applied to the surface that is intended to face the other composite material during blank assembly.

[0073] For example, Figure 1 For example, a release agent may be applied on the surface p6a of the composite material 22a or the surface p5a of the composite material 21a.

[0074] Regarding the release agent, two preferred implementations are provided here, which are introduced below respectively.

[0075] <The First Embodiment of the Release Agent>

[0076] In this embodiment, the release agent is a coating solution containing silicon oxide and magnesium oxide, and the mass ratio of silicon oxide to magnesium oxide is 3:1. The release agent of this embodiment can achieve a good release effect and ensure the separation of the two subsequent small composite boards.

[0077] When using the release agent to brush on the surface of the composite material, the amount of the release agent brushed is 20ymg / m 2 , that is, the weight of the release agent per unit area of the surface of the composite material is 20ymg. Here, y is the ratio of the thickness of the composite blank obtained in the composite blank preparation step to the thickness of the large composite board formed by subsequent rolling, and this ratio is also called the rolling compression ratio of the composite blank.

[0078] Furthermore, based on this embodiment, after the release agent is brushed and before the subsequent blank assembly, the composite material brushed with the release agent is placed in a trolley furnace for heating and drying. The drying temperature is 340 - 360°C, and the drying time is 35 - 45min.

[0079] <The Second Embodiment of the Release Agent>

[0080] In this embodiment, the components of the release agent are in the following weight ratio: 25 - 35% silicon nitride, 5 - 10% thermosetting amino resin, and 55 - 70% water. Compared with the existing release agents, and even compared with the first embodiment of the aforementioned release agent, the release agent of this embodiment can not only achieve a good release effect and ensure the separation of the two subsequent small composite boards, but also the chemical stability of the active ingredient silicon nitride is strong, it is resistant to high temperature and heat shock. The thermosetting amino resin as the binder can be cured at low temperature, is non-toxic, and can achieve a strong bonding effect with a small amount. Therefore, as a whole, it has a low price, simple operation, and good release and adhesion effects.

[0081] Here, a preferred preparation method of the release agent is provided, including: first put 5 - 10% silicon nitride (by weight percentage) in a container such as a beaker, then pour in 15 - 25% water and stir; after the silicon nitride has no granular feeling and no bubbles, pour in 2 - 3% thermosetting amino resin and continue to stir; when it shows a viscous state, continue to pour in the remaining silicon nitride and water, stir for 3 - 5min and then pour in the remaining thermosetting amino resin; when it is stirred to a viscous state, the release agent is prepared.

[0082] When using the release agent to brush on the surface of the composite material, the thickness of the release agent brushed is 0.2 - 0.5mm.

[0083] Furthermore, based on this embodiment, after applying the release agent and before subsequent blank assembly, the composite material coated with the release agent is heated and dried. The drying temperature is 100-250°C, and the drying time is 20-40 minutes.

[0084] Next, after the step of applying the release agent is completed, the step of "assembling blanks in the stacking order of substrate, composite material, composite material, substrate" is introduced.

[0085] This step of "assembling blanks in the stacking order of substrate, composite material, composite material, substrate", that is, the blank assembly step. Among them, in addition to the stacking order of substrate, composite material, composite material, substrate, the following conditions also need to be met:

[0086] 1) The surfaces where the substrate and the composite material contact each other are all surfaces that have undergone the surface treatment; for example, refer to Figure 2 , the surface p2a of the substrate 12a and the surface p4a of the composite material 22a contact each other, and the surface p1a of the substrate 11a and the surface p3a of the composite material 21a contact each other;

[0087] 2) The surface coated with the release agent faces another composite material; for example, refer to Figure 2 , one of the surfaces p6a and p5a is coated with the release agent 30a;

[0088] 3) The composite material is placed centered relative to the substrate; in this regard, considering that the composite blank is roughly symmetrically arranged up and down, only one set of substrate + composite material in the composite blank is taken as an example for illustration. For example, in the upper set, refer to Figure 2 , in the blank assembly state, the distance from the lateral side of the composite material 21a (the long side corresponding to the surface p3a) to the lateral side of the substrate 11a (the long side corresponding to the surface p1a) is half of W0, and the distance from the longitudinal side of the composite material 21a (the short side corresponding to the surface p3a) to the longitudinal side of the substrate 11a (the short side corresponding to the surface p1a) is half of L0. As described above, L0 and W0 are 90-150 mm respectively, that is, the distance range from the side of the composite material 21a to the side of the substrate 11a is 45-75 mm.

[0089] The above introduces the blank assembly step. In a preferred embodiment, after implementing the blank assembly step, the stacked four steel blanks are placed as a whole under a four-column hydraulic machine, and the opposite surfaces of the two substrates (that is, the upper surface of the upper substrate and the lower surface of the lower substrate) are pressurized, and the pressure ≥ 500 tons. Thus, the contact between adjacent steel blanks can be made closer.

[0090] Further, in the step of "preparing four seals with width W3, attaching the seals to the four sides of two composite materials, and performing gas shielded welding between adjacent seals and between the seals and the base material, so that the two base materials and the seals form a whole to obtain a composite blank", based on the setting of the seals, the four steel billets stacked together are connected to form a whole composite blank. Specifically, referring to Figure 2 , the composite blank is formed by: two base materials 11a and 12a form the upper and lower surfaces, two composite materials 21a and 22a are located in the middle, and four seals 40a form a four-sided frame around the two composite materials 21a and 22a and connect the two base materials 11a and 12a.

[0091] The width W3 of the seal is 2T2 - 1 to 2 mm, that is, the width of the seal is slightly smaller than the sum of the thicknesses of the two composite materials by 1 to 2 mm. Using seals with this width to wrap the upper and lower two composite materials simultaneously improves the wrapping effect.

[0092] Furthermore, among the four seals, two seals are respectively attached to the two lateral sides of the two composite materials in the transverse direction, and the length L31 = L2 - 1 to 2 mm; the other two seals are respectively attached to the two lateral sides of the two composite materials in the longitudinal direction, and the length L32 = W2 - 1 to 2 mm.

[0093] Preferably, the thickness T3 of the seal is 12 to 15 mm.

[0094] Regarding the forming method of each seal, it can either be directly cut out on a steel plate according to the thickness T3, width W3, length L31 or L32 without welding, or be spliced by welding multiple seals with different lengths.

[0095] As a preferred embodiment, in this step, before performing gas shielded welding between adjacent seals and between the seals and the base material, the two ends and two sides of each seal can be ground and polished first to remove the surface oxide scale and improve the welding effect; and / or, the two ends and two sides of each seal can be grooved first.

[0096] Further, as a preferred embodiment, in the step of "performing gas shielded welding between adjacent seals and between the seals and the base material", the welding speed is 300 to 360 mm / min, and the interpass temperature during the welding process is controlled at 135 to 165 °C.

[0097] Next, for the step of "processing a round hole on the seal at the groove on the side of the composite blank and welding a seamless steel pipe at the round hole", the groove mentioned above is formed between the two base materials and outside the seal; in this step, a round hole is processed to weld the seamless steel pipe, so as to facilitate subsequent vacuum pumping inside the composite.

[0098] As a preferred method, the round hole is processed in the middle of the short side (i.e., the side on the longitudinal direction) of the composite billet base billet, but it is not limited thereto.

[0099] As a preferred method, the diameter of the round hole is 8 - 12 mm; correspondingly, the outer diameter of the seamless steel pipe is consistent with the diameter of the round hole, which is 8 - 12 mm, the wall thickness is 1.2 - 2 mm, and the length is 200 - 400 mm.

[0100] Next, for the step of "surfacing the grooves on the four sides of the composite billet base billet", submerged arc surfacing is specifically adopted. It can be understood that outside the four - frame formed by the seal strips, a four - frame - shaped filling layer 50a is formed through the surfacing of this step. Refer to Figure 2 .

[0101] As a preferred method, before welding, the welding flux is baked at 350 °C for 2 h and then kept at 150 °C for 1 h; during the welding process, the inter - pass temperature is controlled at 135 - 165 °C, and the welding speed is 420 - 480 mm / min. In this way, this submerged arc surfacing technology, combined with the previous seal strip wrapping and gas shielded welding, jointly realizes the stable connection of the four steel billets, ensures the connection strength, avoids abnormal cracking in the subsequent composite billet rolling step, and further improves the interface bonding effect on the basis of realizing the quality advantages of the composite plate described above.

[0102] In addition, during the welding process, before each welding operation, the attachments on the weld bead need to be cleaned to keep the weld bead clean; after welding, it is covered with insulating cotton for heat preservation.

[0103] Next, for the step of "using a vacuum pump to evacuate the composite billet through this seamless steel pipe, with the vacuum degree

[0104] ≤10 -1 Pa, and then maintaining the pressure for more than 4 h; finally, sealing the seamless steel pipe", the suction port of the vacuum pump is docked with the seamless steel pipe, and the seamless steel pipe is connected to the space inside the composite billet (such as the surface - to - surface gap between the composite material and the base material, the surface - to - surface gap between the composite materials, the end - face gap between the composite material and the seal strip, etc.) to discharge the air in this space until the vacuum degree ≤10 -1 Pa, and maintaining the pressure for more than 4 h can ensure the vacuum degree. In this way, it can avoid the air in this space from causing surface oxidation at the composite interface during the subsequent rolling of the composite billet, and thus ensure the bonding quality of the composite interface.

[0105] Furthermore, in this step, the sealing treatment of the seamless steel pipe can be implemented in an existing feasible manner in the steel industry, such as heating and squeezing the seamless steel pipe with a flame gun to achieve sealing.

[0106] As described above, the overall steps of preparing the composite blank are described in detail. Through specific settings such as surface treatment, vacuum pumping, welding, and sealing, it lays a foundation for the composite blank to obtain excellent interfacial bonding quality and surface quality in subsequent rolling; and the setting of the release agent is more conducive to the smooth separation of the two composite small plates.

[0107] As described above, the preparation method of the present invention further includes the overall rolling step of the composite blank after the overall preparation step of the composite blank. The present invention provides four implementation manners of the rolling step of the composite blank, which are introduced in detail below.

[0108] <The first implementation manner of the rolling step of the composite blank>

[0109] In this implementation manner, refer to Figure 4a , the rolling step of the composite blank includes the following sub-steps:

[0110] Heat the obtained composite blank, the soaking temperature is 1200 - 1220 °C, the total heating time ≥ 1.2 × tmin / mm, where t is the thickness of the composite blank, and the soaking section holding time is 30 min - 50 min;

[0111] Adopt two-stage controlled rolling of rough rolling + finish rolling. In the rough rolling stage, the starting rolling temperature ≤ 1050 °C, the finishing rolling temperature ≥ 1000 °C, first roll transversely and then longitudinally. When rolling longitudinally, the reduction of at least one pass ≥ 35 mm, the total rough rolling reduction is 40 - 60%, and the rough rolling stage ends when the thickness of the intermediate blank reaches 2.5 - 3.5 times the target thickness of the large plate of the composite plate; then wait for the temperature, and water cooling is carried out during this period. When the surface temperature of the intermediate blank drops below 830 °C, the finish rolling stage starts; the finishing rolling temperature in the finish rolling stage ≥ 800 °C, and the total finish rolling reduction is 55 - 75%;

[0112] After rolling, the composite plate enters the ultra-fast cooling system for intermittent cooling: the ultra-fast cooling system has 24 groups of cooling manifolds arranged along the roller, and the cooling distance of each group of cooling manifolds is 1m. When the composite plate passes through the ultra-fast cooling system, the opening and closing states of all 24 groups of cooling manifolds are controlled by opening N groups of cooling manifolds and then not opening M groups of cooling manifolds. The cooling water pressure is 0.2MPa, the cooling rate is 3-15℃ / s, the final cooling temperature is 380-450℃, and the roller speed of the ultra-fast cooling system is 0.4 ~0.9m / s, preferably 0.4~0.6m / s; wherein N is 2, 3 or 4, and M is 2, 3 or 4; for example, when a large composite plate passes through the ultra-fast cooling system, the system is controlled in such a manner that 4 groups of cooling manifolds are opened at a time and then 3 groups of cooling manifolds are closed, that is, the 1st to 4th groups of cooling manifolds are opened, the 5th to 7th groups of cooling manifolds are closed, the 8th to 11th groups of cooling manifolds are opened, the 12th to 14th groups of cooling manifolds are closed, the 15th to 18th groups of cooling manifolds are opened, the 19th to 21st groups of cooling manifolds are closed, and the 22nd to 24th groups of cooling manifolds are opened;

[0113] After the composite plate leaves the ultra-fast cooling system, the cooling bed on the composite plate is naturally cooled to room temperature, thus completing step 2) composite billet rolling and entering step 3) composite plate separation and straightening.

[0114] Compared to the prior art, this embodiment utilizes the aforementioned intermittent cooling method. As the composite plate passes through the ultra-rapid cooling system, it alternates between opening and closing the cooling manifolds. This way, every part of the composite plate cools, then returns to a red state, then cools, then returns to a red state again, and so on, until the composite plate leaves the ultra-rapid cooling system. During this cooling-returning cycle, the carbon steel substrate undergoes a continuous phase transformation and self-tempering effect, with the phase transformation reaction gradually permeating toward the core until the entire carbon steel substrate has undergone a phase transformation. This intermittent cooling process differs from conventional reciprocating cooling. In reciprocating cooling, the annealing and self-tempering occur after the surface or near-surface phase transition has completed, resulting in significant temperature differences or cooling rates between the surface and core, and consequently, significant differences in microstructure and mechanical properties. In contrast, the intermittent cooling process of this embodiment allows for simultaneous cooling of some areas of the composite panel and annealing / self-tempering of others. Furthermore, each area of the composite panel alternates between cooling and annealing over time, minimizing differences in temperature, cooling rate, microstructure, and mechanical properties between the surface and core. For example, the resulting composite panel exhibits a Vickers hardness difference of ≤10 across the thickness of the base layer, a head-to-tail strength difference of ≤40 MPa, and a strength difference of ≤40 MPa across the entire panel. Furthermore, intermittent cooling further improves the composite panel's shape, resulting in reduced unevenness. Even after cooling, excellent panel shape can be achieved by direct cooling on a cooling bed without straightening.

[0115] The second implementation mode of the composite billet rolling step

[0116] In this implementation mode, refer to Figure 4b , the composite billet rolling step includes the following sub-steps:

[0117] Adopt five-stage heating of preheating, first heating, second heating, third heating and soaking. The preheating temperature ≤ 850 °C, the residence time is (0.45 - 0.55)t min / mm, the first heating temperature is 1030 - 1090 °C, the residence time is (0.35 - 0.45)t min / mm, the second heating temperature is 1100 - 1160 °C, the residence time is (0.25 - 0.35)t min / mm, the third heating temperature is 1140 - 1180 °C, the residence time is (0.15 - 0.25)t min / mm, the soaking temperature is 1170 - 1210 °C, and the residence time is (0.10 - 0.20)t min / mm;

[0118] Adopt two-stage controlled rolling of rough rolling + finish rolling. In the rough rolling stage, in the first pass, longitudinal rolling is adopted, and the rolling reduction ≥ 46 mm; starting from the second pass, transverse rolling is adopted until the composite billet is rolled to the target width of the final composite plate in the nth pass. The rolling reduction in the second pass ≥ 25 mm; starting from the (n + 1)th pass, longitudinal rolling is adopted, and the rough rolling stage ends when the thickness of the intermediate billet reaches 2.5 - 3.5 times the target thickness of the large plate of the composite plate. The rolling reduction in the (n + 1)th pass ≥ 30 mm; throughout the rough rolling stage, the rolling temperature in the first pass ≥ 1060 °C, the starting rolling temperature of the remaining passes ≤ 1050 °C, and the finishing rolling temperature ≥ 1000 °C; after the rough rolling stage, wait for the temperature, and water cooling is carried out during this period. When the surface temperature of the intermediate billet drops below 840 °C, the finish rolling stage starts. The starting rolling temperature of the finish rolling stage is 810 °C - 840 °C, and the finishing rolling temperature is 780 - 810 °C;

[0119] After rolling, cooling is carried out. The large plate of the composite plate enters the ultra-rapid cooling system for intermittent cooling: The ultra-rapid cooling system has 24 groups of cooling headers arranged along the roller table. The cooling distance of each group of cooling headers is 1 m. When the large plate of the composite plate passes through the ultra-rapid cooling system, the opening and closing states of all 24 groups of cooling headers are controlled in the way of opening N groups of cooling headers first and then not opening M groups of cooling headers. The cooling water pressure is 0.2 MPa, the cooling speed is 3 - 15 °C / s, the final cooling temperature is 380 - 450 °C, and the roller table speed of the ultra-rapid cooling system is 0.4 - 0.9 m / s; where N takes the value of 2, 3 or 4, and M takes the value of 2, 3 or 4;

[0120] After the large-sized composite slab leaves the ultra-rapid cooling system, the large-sized composite slab is naturally cooled to room temperature on the cooling bed, and thus the rolling of the composite billet in step 2) is completed and step 3) of separating and straightening the composite slab is entered.

[0121] That is, the difference between this embodiment and the first embodiment of the foregoing composite billet rolling step lies in the two processes of heating and rolling.

[0122] Compared with the prior art, this embodiment also adopts intermittent cooling, and correspondingly has the beneficial effects brought by the intermittent cooling process, which can be referred to the introduction of the first embodiment of the composite billet rolling step in the previous text. Further, compared with the prior art, in the heating process of this embodiment, the heating rate of the composite billet in each section can be better controlled to ensure uniform heating of the billet, avoid cracking and air leakage of the composite billet due to the difference in thermal properties of the base material and the clad material of the composite billet, and thus ensure the interface bonding effect. Moreover, in the rolling process of this embodiment, the rough rolling adopts the method of longitudinal rolling first, then transverse rolling, and then longitudinal rolling, which can ensure the realization of large reduction rolling, effectively penetrate the core of the composite billet, promote the deformation of the core, and ensure the bonding rate of the composite interface; when waiting for the temperature, an immediate cooling device is used for cooling to reduce the waiting time, improve the rolling efficiency, and at the same time, avoid the grain growth of the carbon steel base material due to too long waiting time; the temperature control in the finishing rolling stage can refine the grains and ensure that the thick composite slab has good low-temperature impact toughness.

[0123] <The Third Embodiment of the Composite Billet Rolling Step>

[0124] This embodiment is the same as the first embodiment of the foregoing composite billet rolling step in sub-steps such as heating, two-stage controlled rolling, and cooling, and the difference is only in the steps after the large-sized composite slab leaves the ultra-rapid cooling system.

[0125] In the first embodiment of the foregoing composite billet rolling step, after the large-sized composite slab leaves the ultra-rapid cooling system, the large-sized composite slab is naturally cooled to room temperature on the cooling bed; different from this, in this embodiment, referring to Figure 4c , after the large-sized composite slab leaves the ultra-rapid cooling system, the large-sized composite slab directly enters the straightening machine for straightening, and the straightened large-sized composite slab is naturally cooled on the cooling bed. When the surface temperature drops below 200 °C, a cold straightening machine is used for cold straightening. This can further improve the plate shape.

[0126] Similarly, for the second embodiment of the foregoing composite billet rolling step, it can also be changed to that after the large-sized composite slab leaves the ultra-rapid cooling system, the large-sized composite slab directly enters the straightening machine for straightening, and the straightened large-sized composite slab is naturally cooled on the cooling bed. When the surface temperature drops below 200 °C, a cold straightening machine is used for cold straightening, and thus as the fifth embodiment of the composite billet rolling step, referring to Figure 4d .

[0127] <The fourth implementation of the composite billet rolling step>

[0128] This implementation is the same as the first implementation of the aforementioned composite billet rolling step in sub-steps such as heating, two-stage controlled rolling, and cooling. The only difference lies in the steps after the large composite plate leaves the ultra-rapid cooling system.

[0129] In the first implementation of the aforementioned composite billet rolling step, after the large composite plate leaves the ultra-rapid cooling system, the large composite plate is naturally cooled to room temperature on the cooling bed. Different from this, in this implementation, after the large composite plate leaves the ultra-rapid cooling system, it directly enters the straightening machine for 1 to 3 passes of straightening. Different from the first implementation of the aforementioned composite billet rolling step, in this implementation, Figure 4e , after that, the large composite plate is placed between two steel plates at a temperature of T f +100 - 150 °C for stacking cooling. The stacking cooling time is 0.4 min / mm × t0 ± 5 min, where t0 is the thickness of the large composite plate. Thus, within this stacking cooling time, the large composite plate can slowly cool down and can be clamped by the steel plates to maintain the uniformity of the core and surface temperatures. After the stacking cooling is completed, the large composite plate is naturally cooled on the cooling bed. Among them,

[0130] T f = 550 + 30[Si] - 20[Mn] + 15[Cr] - 15[Ni] + 10[Mo], where [Si], [Mn], [Mo], [Cr], and [Ni] are 100 times the mass percentages of the respective elements in the base material. In this preferred implementation, the stacking cooling, especially the temperatures of the two steel plates during stacking cooling and the stacking cooling time, can further improve the structure, performance, and shape of the finally obtained composite plate compared to the first implementation.

[0131] Similarly, for the second implementation of the aforementioned composite billet rolling step, it can also be changed to that after the large composite plate leaves the ultra-rapid cooling system, the large composite plate directly enters the straightening machine for straightening, and then performs stacking cooling as described above. After the stacking cooling is completed, the large composite plate is naturally cooled on the cooling bed. Thus, as the sixth implementation of the composite billet rolling step, Figure 4f .

[0132] As described above, the total steps of the composite billet rolling have been described in detail. As mentioned before, the preparation method of the present invention also includes the total step of composite plate separation and straightening. Specifically, the total step of the composite plate separation and straightening includes the following sub-steps:

[0133] For the large composite plate obtained from the previous total steps of compound billet rolling, use a plasma cutting machine to cut its four sides to remove the parts outside the seal, and the large composite plate is separated into two small composite plates, one on top and the other at the bottom.

[0134] Perform horizontal flattening and cold straightening on the small composite plates to obtain the finished stainless steel composite plate.

[0135] Among them, regarding the parts outside the seal in the step of "cutting its four sides to remove the parts outside the seal", that is, after the previous compound billet rolling step, the edge parts on the large composite plate transformed from the seal and the filling layer in the compound billet mentioned above. In this way, removing this part reveals the stainless steel cladding layer, and without the connection effect of this part, the large composite plate is separated into two small composite plates, one on top and the other at the bottom. See Figure 3 , corresponding to the five implementation manners of the blank surface treatment step described above Figure 3 respectively show the cross-sectional shapes of the corresponding two small composite plates (that is, the final single-sided stainless steel composite plate).

[0136] Each small composite plate is composed of a cladding layer and a base layer. The cladding layer is obtained by rolling the original composite material, and the base layer is obtained by rolling the original base material. In view of this, in Figure 3 the original label of the original composite material is still marked on the cladding layer, and the original label of the original base material is still marked on the base layer.

[0137] Furthermore, the single-sided stainless steel composite plate obtained by the preparation method of the present invention.

[0138] The cladding layer is preferably austenitic stainless steel, and its chemical composition is in mass percentage: C≤0.15%, Si≤1.00%, Mn≤2.00%, P≤0.045%, S≤0.030%, Ni: 6.0 - 22.0%, Cr: 16.0 - 26.0%, Mo≤3.0%, and the balance is Fe and inevitable impurities. Using this chemical composition can further ensure the performance of the composite plate, especially the corrosion resistance of the cladding layer, under the above-mentioned technical effects. For example, after the cladding layer is boiled in a sulfuric acid - copper sulfate solution for 20 h and bent at 180°, there are no intergranular corrosion cracks.

[0139] The base layer is carbon steel, and its chemical composition is in mass percentage: C: 0.03 - 0.16%, Si: 0.11 - 0.29%, Mn: 1.31 - 1.54%, P≤0.018%, S≤0.0030%, Cr: 0.06 - 0.29%, Ni≤0.24%, Cu≤0.24%, Mo≤0.24%, Nb: 0.011 - 0.034%, Ti: 0.011 - 0.019%, Al: 0.030 - 0.040%, and the balance is Fe and inevitable impurities.

[0140] Preferably, the chemical composition of the base layer is, by mass percentage, as follows: C: 0.03-0.07%, Si: 0.11-0.19%, Mn: 1.46-1.54%, P≤0.010%, S≤0.0015%, Cr: 0.21-0.29%, Ni: 0.16-0.24%, Cu: 0.16-0.24%, Mo: 0.16-0.24%, Nb: 0.026-0.034%, Ti: 0.011-0.019%, Al: 0.030-0.040%, with the remainder being Fe and unavoidable impurities. This chemical composition, combined with the control of the temperature, time, reduction, and cooling rate during the composite billet rolling step, can further improve the mechanical properties of the composite plate while ensuring toughness while maintaining the aforementioned technical effects.

[0141] Furthermore, the base structure of the composite plate is bainite + a small amount of ferrite structure. The composite plate has excellent mechanical properties, strong impact toughness, excellent corrosion resistance, good interface bonding quality, plate shape and surface quality, and high uniformity.

[0142] Specifically, the total thickness of the composite board is ≥19 mm, the thickness of the base layer is ≥16 mm, and the thickness of the composite layer is 1-10 mm.

[0143] The unevenness of the composite plate is ≤3 mm / m, or even ≤2 mm / m.

[0144] The composite plate has a yield strength of 345 MPa or greater, a tensile strength of 490 MPa or greater, an elongation after fracture of 18% or greater, and a yield strength ratio of 0.85 or less. Furthermore, the composite plate has a yield strength of 500 MPa or greater, and a tensile strength of 630 MPa or greater.

[0145] The composite panel has a composite interface bonding rate of 100%, a shear strength of ≥300 MPa, and impact energy of ≥120 J at 0°C, ≥120 J at -20°C, and ≥120 J at -40°C. Furthermore, the composite panel has an impact energy of ≥240 J at 0°C, ≥200 J at -20°C, and ≥150 J at -40°C.

[0146] The Vickers hardness difference of the base layer of the composite board in the thickness direction is ≤10, the strength difference between the head, middle and tail is ≤40MPa, and the strength difference at all parts of the whole board is ≤40MPa.

[0147] In addition, the composite plate showed no cracks when bent outwards 180 degrees and no cracks when bent inwards 180 degrees. In corrosion resistance tests, the composite layer was sensitized at 650°C for 2 hours, then boiled in a sulfuric acid-copper sulfate solution for 20 hours, and then cold-bent at 180 degrees, showing no intergranular corrosion cracks.

[0148] To sum up, compared with the existing technology, the present invention, on the one hand, ensures the corrosion resistance and mechanical strength of the stainless steel composite plate through specific control of the process in the entire preparation method, and avoids the degradation of the corrosion resistance and mechanical properties during the rolling process of the composite billet; on the other hand, solves the problems of difficult plate shape control, poor surface quality, and low production efficiency of existing stainless steel composite plates, and meets the construction needs of steel bridge projects; on the other hand, the production process has a high yield rate and high production efficiency.

[0149] The detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

[0150] The beneficial effects of the present invention are further illustrated below through a plurality of embodiments. Of course, these embodiments are only a part of the many variations of the present invention, but not all of them.

[0151] In these embodiments, Q500q steel is selected as the base material, and its chemical composition is calculated by mass percentage as follows: C: 0.06%, Si: 0.17%, Mn: 1.52%, P: 0.010%, S: 0.0014%, Cr: 0.24%, Ni: 0.21%, Cu: 0.22%, Mo: 0.19%, Nb: 0.031%, Ti: 0.016%, Al: 0.037%; 316L stainless steel is selected as the composite material, and its chemical composition is calculated by mass percentage as follows: C: 0.020%, Si: 0.52%, Mn: 1.36%, P: 0.033%, S: 0.003%, Ni: 10.20%, Mo: 2.10%, Cr: 16.20%.

[0152] In each example, a composite billet with a thickness of 322 mm and a constant base thickness was prepared according to the embodiments of the present invention. The composite billet was then rolled into a 46 mm thick composite plate according to the embodiments of the present invention. The composite plate was then subjected to the composite plate separation and straightening steps described in the present invention, resulting in a finished single-sided stainless steel composite plate with a total thickness of 23 mm, a base layer thickness of 20 mm, and a composite layer thickness of 3 mm.

[0153] The composite billet rolling steps used in each embodiment are as follows: Figure 4a The first embodiment of the composite billet rolling step shown in Example 2 adopts Figure 4e The fourth embodiment of the composite billet rolling step shown in Example 3 adopts Figure 4c The third embodiment of the composite billet rolling step shown in Example 4 adopts Figure 4bThe second implementation of the composite billet rolling step shown. Example 5 uses Figure 4f The sixth implementation of the composite billet rolling step shown. Example 6 uses Figure 4d The fifth implementation of the composite billet rolling step shown.

[0154] Furthermore, samples of the composite plates of each example were taken and tested. The interface bonding rate of each example was 100%, the inner bend of 180° was qualified (without cracks), the outer bend of 180° was qualified (without cracks), and after boiling in sulfuric acid - copper sulfate solution for 20 h and undergoing a 180° bend, there were no intergranular corrosion cracks in the cladding layer. In addition, the results of other performance tests are shown in Tables 1 and 2.

[0155] Table 1

[0156]

[0157] Table 2

[0158]

[0159]

Claims

1. A method for preparing a stainless steel composite plate with excellent plate shape, characterized in that: The method comprises three steps of preparing a composite billet, rolling the composite billet and separating and straightening the composite plate in sequence to obtain a composite plate; In the composite blank preparation step, the chemical composition of the base material of the composite blank is as follows, by mass percentage: C: 0.03-0.16%, Si: 0.11-0.29%, Mn: 1.31-1.54%, P≤0.018%, S≤0.0030%, Cr: 0.06-0.29%, Ni≤0.24%, Cu≤0.24%, Mo≤0.24%, Nb: 0.011-0.034%, Ti: 0.011-0.019%, Al: 0.030-0.040%, and the balance is Fe and unavoidable impurities; The composite billet rolling step comprises: The obtained composite blank is heated at a soaking temperature of 1170-1220°C for a total heating time ≥ 1.2 × t min / mm, where t is the thickness of the composite blank. A two-stage controlled rolling process of rough rolling + finishing rolling is adopted to obtain a large composite plate; wherein, in the rough rolling stage, the rolling temperature of the first pass is ≥1060°C, the starting rolling temperature of the remaining passes is ≤1050°C, the final rolling temperature is ≥1000°C, the first pass adopts longitudinal rolling, and the rolling reduction is ≥46mm; transverse rolling is adopted from the second pass until the composite billet is rolled to the target width of the composite plate by the nth pass, and the rolling reduction of the second pass is ≥25mm; the rolling reduction of the n+1th pass is ≥30mm, and longitudinal rolling is adopted from the n+1th pass. The rough rolling stage is terminated when the thickness of the intermediate billet is 2.5~3.5 times the target thickness of the large composite plate; then the intermediate billet is kept warm and water cooling is carried out during the period. When the surface temperature of the intermediate billet drops below 840°C, the finishing rolling stage begins. The starting rolling temperature of the finishing rolling stage is 810°C~840°C and the finishing rolling temperature is 780~810°C; After rolling, the composite plate enters the ultra-fast cooling system for intermittent cooling: the ultra-fast cooling system has 24 groups of cooling manifolds arranged along the roller table, and the cooling distance of each group of cooling manifolds is 1m. When the composite plate passes through the ultra-fast cooling system, the opening and closing states of all 24 groups of cooling manifolds are controlled by opening N groups of cooling manifolds and then not opening M groups of cooling manifolds. The cooling water pressure is 0.2MPa, the cooling rate is 3~15℃ / s, and the final cooling temperature is 380~450℃; where N is 2, 3 or 4, and M is 2, 3 or 4.

2. The method for preparing a stainless steel composite plate with excellent plate shape according to claim 1, characterized in that: The roller speed of the ultra-fast cooling system is 0.4-0.9 m / s.

3. The method for preparing a stainless steel composite plate with excellent plate shape according to claim 1, wherein: In the step of "heating the obtained composite blank", a five-stage heating method of preheating, first heating, second heating, third heating and soaking is adopted, the preheating temperature is ≤850°C, the residence time is (0.45~0.55) t min / mm, the first heating temperature is 1030~1090°C, the residence time is (0.35~0.45) t min / mm, the second heating temperature is 1100~1160°C, the residence time is (0.25~0.35) t min / mm, the third heating temperature is 1140~1180°C, the residence time is (0.15~0.25) t min / mm, the soaking temperature is 1170~1210°C, and the residence time is (0.10~0.20) t min / mm.

4. The method for preparing a stainless steel composite plate with excellent plate shape according to claim 1, characterized in that: After intermittent cooling, the cooling bed on the composite plate is naturally cooled to room temperature, thus completing the composite billet rolling step and entering the composite plate separation and straightening step.

5. The method for preparing a stainless steel composite plate with excellent plate shape according to claim 1, characterized in that: The composite billet rolling step further comprises: After intermittent cooling, the large composite plate directly enters the straightening machine for straightening. The straightened large composite plate is naturally cooled on the cooling bed. When the surface temperature drops below 200℃, a cold straightening machine is used for cold straightening.

6. The method for preparing a stainless steel composite plate with excellent plate shape according to claim 1, characterized in that: The composite billet rolling step further comprises: After intermittent cooling, the composite plate slab directly enters the straightening machine for straightening; The straightened composite board is placed at a temperature of T f The stack cooling is carried out between two steel plates at +100~150℃, and the stack cooling time is 0.4min / mm×t0±5min, where t0 is the thickness of the composite plate; After the stack cooling is completed, the cooling bed on the composite board is naturally cooled to room temperature; T f =550+30[Si]-20[Mn]+15[Cr]-15[Ni]+10[Mo], where [Si], [Mn], [Mo], [Cr], and [Ni] are 100 times the mass percentage of each element in the substrate.

7. The method for preparing a stainless steel composite plate with excellent plate shape according to claim 1, characterized in that: The composite blank preparation steps specifically include: Prepare two carbon steel billets with a thickness of T1, a length of L1, and a width of W1 as base materials for forming the base layer of the composite plate; and prepare two stainless steel billets with a thickness of T2, a length of L2, and a width of W2 as composite materials for forming the cladding layer of the composite plate; L2 < L1, W2 < W1; performing surface treatment on at least one surface of each of the two substrates and the two composite materials; Apply a release agent to one surface of a composite material; Assembling the blanks in the order of stacking substrate, composite, composite, and substrate; wherein the composite is placed in the center relative to the substrate, the surfaces of the substrate and composite that are in contact with each other are both surfaces that have undergone the surface treatment, and the surface coated with the release agent faces the other composite; Prepare four sealing strips with a width of W3 (W3 = 2T2 - 1 ~ 2mm), place the sealing strips against the four sides of the two composite materials, and perform gas shielded welding between adjacent sealing strips and between the sealing strips and the base material, so that the two base materials and the sealing strips form a whole, thereby obtaining a composite blank base material; A circular hole is machined on the seal strip at the groove on the side of the composite billet base, and a seamless steel pipe is welded at the circular hole; Performing surfacing welding on the grooves on four sides of the composite billet base; The composite billet is vacuumed through the seamless steel pipe by a vacuum pump, and the vacuum degree is ≤10 -1 Pa, then maintain the pressure for more than 4 hours; finally, seal the seamless steel pipe.

8. The method for preparing a stainless steel composite plate with excellent plate shape according to claim 1, characterized in that: The chemical composition of the base material of the composite blank is, by mass percentage, C: 0.03~0.07%, Si: 0.11~0.19%, Mn: 1.46~1.54%, P≤0.010%, S≤0.0015%, Cr: 0.21~0.29%, Ni: 0.16~0.24%, Cu: 0.16~0.24%, Mo: 0.16~0.24%, Nb: 0.026~0.034%, Ti: 0.011~0.019%, Al: 0.030~0.040%, and the rest is Fe and unavoidable impurities.

9. A stainless steel composite plate with excellent plate shape, characterized in that: The composite plate is prepared by the preparation method according to any one of claims 1 to 8.

10. The stainless steel composite plate with excellent plate shape according to claim 9, characterized in that: The total thickness of the composite plate is ≥19 mm, the thickness of the base layer is ≥16 mm, the thickness of the composite layer is 1-10 mm, the Vickers hardness difference of the base layer in the thickness direction of the composite plate is ≤10, the strength difference between the head, middle and tail is ≤40 MPa, the strength difference of the entire plate is ≤40 MPa, and the unevenness is ≤2 mm / m.

11. The stainless steel composite plate with excellent plate shape according to claim 9, characterized in that: The yield strength of the composite plate is ≥345MPa, the tensile strength is ≥490MPa, the elongation after fracture is ≥18%, and the yield strength ratio is ≤0.85; the composite interface bonding rate is 100%, the shear strength is ≥300MPa; the impact energy at 0°C is ≥120J, the impact energy at -20°C is ≥120J, and the impact energy at -40°C is ≥120J.

12. The stainless steel composite plate with excellent plate shape according to claim 9, characterized in that: The composite plate has a yield strength of ≥500 MPa, a tensile strength of ≥630 MPa, an elongation after fracture of ≥18%, a yield strength ratio of ≤0.86, an impact energy of ≥240 J at 0°C, an impact energy of ≥200 J at -20°C, and an impact energy of ≥150 J at -40°C.

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