Super-thick stainless steel clad plate and method for manufacturing the same

Abstract

The present application discloses a kind of extra-thick stainless steel composite plate and its preparation method.In the method, first, the composite blank with the stacking order of base material, composite material, composite material and base material is prepared; then, the obtained composite blank is heated, and the soaking temperature is 1170-1220 DEG C; two-stage controlled rolling of rough rolling+finish rolling is used to obtain the composite plate big plate with thickness ≥54 mm; then, intermittent cooling is carried out: when the composite plate big plate passes through the ultra-fast cooling system, the opening and closing state of 24 groups of cooling headers is controlled according to the mode of opening N groups of cooling headers and then not opening M groups of cooling headers, the cooling water pressure is 0.2 MPa, the cooling speed is 3-15 DEG C / s, the final cooling temperature is 380-450 DEG C, and the roller speed is 0.2-0.4 m / s; wherein N and M are 2, 3 or 4; the composite plate big plate passes through the ultra-fast cooling system once, which completes the intermittent cooling, and then is naturally cooled to room temperature on the cooling bed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of steel material preparation, and relates to a special thick stainless steel composite plate and a preparation method thereof. BACKGROUND

[0002] With the continuous development of science and industry, ordinary alloys or single metals have been difficult to meet the requirements of industrial development on the comprehensive performance of materials, and composite plates have emerged as the times require. The stainless steel composite plate is a base layer of carbon steel or low alloy steel and a composite layer of stainless steel, and the metallurgical combination of the composite interface is realized through explosion compounding, rolling compounding and other methods, so as to save resources and reduce costs on the premise of not reducing the use effect (mechanical strength, corrosion resistance, etc.). The stainless steel composite plate is widely used in petrochemical, pressure vessel, power equipment, medical equipment, water conservancy, papermaking, bridge and other industries.

[0003] With the implementation of the national highway and railway network construction strategy, the bridge manufacturing industry has developed rapidly. The construction of cross-river and cross-sea channels urgently requires the construction of large-span steel bridges. With the increase of the span of steel bridges, the requirements for stainless steel composite plates for bridge structures are also increasing, such as large thickness, good plate shape, excellent bonding performance, high strength and high toughness.

[0004] The existing stainless steel composite plate has problems of poor plate shape and poor uniformity, and the problems of plate shape and uniformity are more serious for special thick steel plates. SUMMARY

[0005] The present application provides a special thick stainless steel composite plate and a preparation method thereof.

[0006] To achieve the above-mentioned purpose of the application, an embodiment of the present application provides a preparation method of a special thick stainless steel composite plate, which comprises three steps of composite blank preparation, composite blank rolling and composite plate separation and straightening performed in sequence.

[0007] In the composite blank preparation step, the prepared composite blank is stacked in the order of base material, composite material, composite material and base material;

[0008] The composite blank rolling step comprises:

[0009] The obtained composite blank is heated, the soaking temperature is 1170-1220℃, and the total heating time is ≥1.2xtmin / mm, t being the thickness of the composite blank;

[0010] The two-stage controlled rolling of rough rolling + finish rolling is adopted, in the rough rolling stage, the finish rolling temperature is ≥1000℃, the rolling is ended when the intermediate blank thickness is 2.5-3.5 times of the target thickness of the clad plate large plate; then the temperature is kept, and the water cooling is carried out during the period, when the surface temperature of the intermediate blank is reduced to below 840℃, the finish rolling stage is started, the finish rolling temperature is ≥780℃, and the clad plate large plate with thickness ≥54mm is obtained;

[0011] After the rolling is ended, the cooling is carried out, and the clad plate large plate enters the ultra-fast cooling system to carry out the intermittent cooling: when the clad plate large plate passes through the ultra-fast cooling system, the opening and closing state of the total 24 groups of cooling headers of the ultra-fast cooling system is controlled according to the mode of opening N groups of cooling headers and then not opening M groups of cooling headers, the cooling water pressure is 0.2MPa, the cooling speed is 3-15℃ / s, the final cooling temperature is 380-450℃, and the roller speed is 0.2-0.4m / s; wherein N is 2, 3 or 4, and M is 2, 3 or 4.

[0012] Preferably, the cooling distance of each group of cooling headers is 1m.

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

[0014] Preferably, in the step of "adopting the two-stage controlled rolling of rough rolling + finish rolling", in the rough rolling stage, the longitudinal rolling is adopted in the first pass, and the rolling reduction is ≥46mm; the transverse rolling is adopted from the second pass, until the clad blank is rolled to the target width of the final clad plate, the rolling reduction of the second pass is ≥25mm; the longitudinal rolling is adopted from the (n+1)th pass, the rough rolling stage is ended when the intermediate blank thickness is 2.5-3.5 times of the target thickness of the clad plate large plate, and the rolling reduction of the (n+1)th pass is ≥30mm.

[0015] Preferably, the rolling temperature of the first pass is ≥1060℃, the open rolling temperature of the remaining passes is ≤1050℃, and the finish rolling temperature is ≥1000℃ in the whole rough rolling stage; after the rough rolling stage, the intermediate blank is allowed to warm up, during which water cooling is performed; when the surface temperature of the intermediate blank is reduced to below 840℃, the finish rolling stage is started, and the open rolling temperature is 810-840℃ and the finish rolling temperature is 780-810℃.

[0016] Preferably, the composite blank preparation step comprises the steps of steel blank preparation, blank surface treatment, application of release agent, blank assembly, sealing and wrapping, gas shielded welding, surfacing, vacuumizing and sealing.

[0017] Preferably, the vacuumizing is performed to a vacuum degree ≤10 -1 Pa, and the pressure is maintained for 4h.

[0018] Preferably, the release agent used comprises, by weight, 25-35% silicon nitride, 5-10% thermosetting amino resin and 55-70% water.

[0019] The thickness of the applied release agent is 0.2-0.5mm.

[0020] Before the blank assembly, the composite blank coated with the release agent is heated and dried at a temperature of 100-250℃ for 20-40min.

[0021] Preferably, the release agent used comprises, by weight, 25-35% silicon nitride, 5-10% thermosetting amino resin and 55-70% water.

[0022] The thickness of the applied release agent is 0.2-0.5mm.

[0023] Before the blank assembly, the composite blank coated with the release agent is heated and dried at a temperature of 100-250℃ for 20-40min.

[0024] Preferably, the welding speed is 300-360mm / min, and the interpass temperature is controlled to be 135-165℃ during the gas shielded welding.

[0025] Preferably, submerged arc surfacing is used in the surfacing.

[0026] Before the welding, the flux is baked at 350℃ for 2h and then maintained at 150℃ for 1h.

[0027] During the welding, the interpass temperature is controlled to be 135-165℃, and the welding speed is 420-480mm / min.

[0028] Preferably, when the composite plate large plate passes through the ultra-fast cooling system, the first to fourth groups of cooling headers are opened, the fifth to eighth groups of cooling headers are not opened, the ninth to twelfth groups of cooling headers are opened, the thirteenth to sixteenth groups of cooling headers are not opened, the seventeenth to twentieth groups of cooling headers are opened, the twenty-first to twenty-second groups of cooling headers are not opened, and the twenty-third to twenty-fourth groups of cooling headers are opened.

[0029] The composite plate large plate passes through the ultra-fast cooling system once, that is, the intermittent cooling is completed, and then the composite plate large plate is naturally cooled on a cooling bed to room temperature.

[0030] To achieve the above-mentioned purposes, one embodiment of the present application provides a special thick stainless steel composite plate prepared by the preparation method.

[0031] Preferably, the total thickness of the composite plate is greater than or equal to 27 mm, the thickness of the base layer is greater than or equal to 24 mm, the thickness of the composite layer is 1-10 mm, the Vickers hardness difference in the thickness direction of the base layer of the composite plate is less than or equal to 10, the head-to-middle-tail strength difference is less than or equal to 40 MPa, the strength difference at each position of the whole plate is less than or equal to 40 MPa, and the unevenness is less than or equal to 2 mm / m.

[0032] Preferably, the yield strength of the composite plate is greater than or equal to 500 MPa, the tensile strength is greater than or equal to 630 MPa, the elongation after fracture is greater than or equal to 18%, the yield strength ratio is less than or equal to 0.86, the impact energy at 0 ℃ is greater than or equal to 240 J, the impact energy at -20 ℃ is greater than or equal to 200 J, and the impact energy at -40 ℃ is greater than or equal to 150 J.

[0033] Compared with the prior art, the present application has the following beneficial effects: on the one hand, in the whole preparation method, the corrosion resistance and mechanical strength of the stainless steel composite plate are ensured through specific control of the process, so that the corrosion resistance and mechanical properties are prevented from deteriorating during the rolling of the composite blank; on the other hand, the shape control and uniformity control of the special thick plate are realized, and the production difficulty of the existing special thick stainless steel composite plate is overcome; and on the other hand, the material yield rate is high during production, and the production efficiency is high. BRIEF DESCRIPTION OF DRAWINGS

[0034] For the purpose of clear display and illustration, the size of some structures or parts in each figure of the present application is enlarged relative to other structures or parts, and therefore, is only used to illustrate the basic structure of the subject of the present application.

[0035] Figure 1 is a schematic view of the cross section of the steel blank in the present application;

[0036] Figure 2 is a schematic view of the cross section of the composite blank corresponding to Figure 1 ; and

[0037] Fig. 3 is a flow chart of the rolling step of the composite blank in one embodiment of the present application;

[0038] Figure 4is Figure 2 A cross-sectional view of two single-sided stainless steel composite plates prepared by rolling a composite blank. DETAILED DESCRIPTION

[0039] The present application provides a method for preparing single-sided stainless steel composite plates with excellent plate shape, and a composite plate prepared based on the method. Specifically, the method comprises three overall steps of composite blank preparation, composite blank rolling, and composite plate separation and straightening.

[0040] The overall step of composite blank preparation comprises the following sub-steps:

[0041] Two carbon steel blanks with thickness T1, length L1, and width W1 are prepared as base materials, and two stainless steel blanks with thickness T2, length L2, and width W2 are prepared as composite materials;

[0042] The at least one surface of each of the two base materials and the two composite materials is subjected to surface treatment;

[0043] An isolation agent is applied to one surface of one of the composite materials;

[0044] The blanks are assembled in the order of base material, composite material, composite material, and base material;

[0045] Four sealing strips with width W3, W3 = 2T2-1~2 mm, are prepared, and the sealing strips are attached to the four sides of the two composite materials, and gas shield welding is performed between adjacent sealing strips and between the sealing strips and the base materials, so that the two base materials and the sealing strips form an integral whole, obtaining a composite blank base blank;

[0046] A round hole is machined on the sealing strip at the groove of the side edge of the composite blank base blank, and a seamless steel pipe is welded at the round hole;

[0047] The grooves of the four side edges of the composite blank base blank are subjected to surfacing;

[0048] The composite blank is vacuumed through the seamless steel pipe using a vacuum pump, and the vacuum degree is ≤10 -1 Pa, and the vacuum is maintained for 4 hours or more, and finally the seamless steel pipe is subjected to sealing treatment.

[0049] Further, the above sub-steps are described in detail as follows.

[0050] The step of "preparing two carbon steel blanks with length L1 and width W1 as base materials, and preparing two stainless steel blanks with length L2 and width W2 as composite materials" is also a blank preparation step.

[0051] The carbon steel blank as the base material has thickness T1, length L1, and width W1, i.e., it is a rectangular blank. Similarly, the stainless steel blank as the composite material has thickness T2, length L2, and width W2, i.e., it is also a rectangular blank.

[0052] And, L2 < L1, W2 < W1, the length and width dimensions of the composite material are both smaller than the length and width dimensions of the base material. Preferably, L2 = L1 - L0, W2 = W1 - W0, the preferred value ranges of L0 and W0 are 90-150 mm respectively.

[0053] As a preferred solution, the surface oxide skin pressing depth and the surface pit depth of the carbon steel billet are both ≤0.3 mm, the unevenness is ≤3 mm / m; the surface of the stainless steel billet is free of scratches, and the unevenness is ≤2 mm / m. In this way, it is avoided that the steel billet with obvious surface defects or plate shape defects enters the production line of the composite plate.

[0054] Next, regarding the step of "surface treatment of the respective at least one surface of the two base materials and the two composite materials", namely, the billet surface treatment step.

[0055] In this embodiment, one surface of each base material and each composite material is polished to remove the surface oxide skin and expose the metal luster. For example, as shown in the figure, for the surface p1a of the base material 11a, a grinding machine, a sanding machine or a milling machine is used for polishing to remove the surface oxide skin and expose the metal luster; similarly, for the surface p2a of the prepared base material 12a, a grinding machine, a sanding machine or a milling machine is used for polishing to remove the surface oxide skin and expose the metal luster. Figure 1

[0056] For the surface p3a of the prepared composite material 21a, a steel wire wheel is used for polishing to remove the surface oxide skin and expose the metal luster; similarly, for the surface p4a of the prepared composite material 22a, a steel wire wheel is used for polishing to remove the surface oxide skin and expose the metal luster.

[0057] As will be known later, by using the surface treated (polished in this embodiment) surface as the surface of the base material and the composite material that contact each other when assembling the billet, for example, the surface p1a and the surface p3a contact each other, and the surface p4a and the surface p2a contact each other, the interface bonding quality can be guaranteed.

[0058] Next, the other sub-steps of the composite billet preparation step will be further introduced.

[0059] The step of "applying a release agent on one surface of a composite material", namely, the release agent application step.

[0060] ​In combination with the foregoing, the surface treatment step of the previous blank is to perform grinding and polishing on the surface of the composite material which will contact the base material when the blank is assembled, so as to ensure the interface bonding quality of the composite board. The purpose of the coating of the separating agent is to avoid the bonding between the surfaces of the composite materials which contact each other when the blank is assembled, so as to make the two composite boards difficult to separate.

[0061] Based on this, the separating agent is coated on one of the two composite materials. If one surface of the selected composite material has been treated in the previous surface treatment step of the blank, and the other surface has not been treated, the separating agent is coated on the surface which has not been treated. If both surfaces of the selected composite material have been treated in the previous surface treatment step of the blank, the separating agent is coated on the surface which is planned to face the other composite material when the blank is assembled.

[0062] For example, the separating agent can be coated on the surface p6a of the composite material 22a or the surface p5a of the composite material 21a. Figure 1

[0063] As to the separating agent, two preferred embodiments are provided as follows.

[0064] <First embodiment of the separating agent>

[0065] In this embodiment, the separating agent is a coating liquid containing silicon oxide and magnesium oxide, and the mass ratio of silicon oxide to magnesium oxide is 3:1. The separating agent of this embodiment can achieve good separation effect and ensure the separation of the two composite boards.

[0066] When the separating agent is coated on the surface of the composite material, the amount of the separating agent is 20 ymg / m 2 That is, the weight of the separating agent per unit area on the surface of the composite material is 20 ymg. Wherein, y is the ratio of the thickness of the composite blank prepared in the composite blank preparation step to the thickness of the composite board prepared by subsequent rolling, which is also called the rolling compression ratio of the composite blank.

[0067] Further, based on this embodiment, after the coating of the separating agent is completed and before the subsequent assembly of the blank, the composite material coated with the separating agent is placed in a trolley furnace for heating and drying, and the drying temperature is 340-360°C, and the drying time is 35-45 min.

[0068] <Second embodiment of the separating agent>

[0069] ​In this embodiment, the components of the release agent are in a weight ratio of 25-35% silicon nitride, 5-10% thermosetting amino resin, and 55-70% water. Compared to the prior art release agent, and even compared to the first embodiment of the aforementioned release agent, the release agent of this embodiment not only achieves a good release effect and ensures the separation of the two subsequent composite panels, but also has strong chemical stability and is resistant to high temperature and thermal shock. The thermosetting amino resin used as the adhesive can be cured at low temperatures and is non-toxic, and a small amount of the adhesive can achieve strong adhesion, so the overall price is low, the operation is simple, and the release and adhesion effects are good.

[0070] Here, a preferred preparation method of the release agent is provided, which includes: first, placing 5-10% silicon nitride (by weight) in a beaker or other container, then pouring in 15-25% water and stirring; after the silicon nitride has no particles and no bubbles, pouring in 2-3% thermosetting amino resin and continuing to stir; when a viscous state is reached, the remaining silicon nitride and water are poured in, and after stirring for 3-5 minutes, the remaining thermosetting amino resin is poured in; when a viscous state is reached, the release agent is prepared.

[0071] When the release agent is used to brush the surface of the composite material, the thickness of the brushed release agent is 0.2-0.5 mm.

[0072] Further, based on this embodiment, after the brushing of the release agent is completed and before the subsequent assembly, the composite material brushed with the release agent is heated and dried, with a drying temperature of 100-250°C and a drying time of 20-40 minutes.

[0073] Next, after the step of brushing the release agent is completed, the step of "assembling according to the stacking order of the base material, the composite material, the composite material, and the base material" is introduced.

[0074] This step of "assembling according to the stacking order of the base material, the composite material, the composite material, and the base material" is also the assembly step. In addition to the stacking order of the base material, the composite material, the composite material, and the base material, the following conditions must also be met:

[0075] 1) The surfaces of the base material and the composite material that are in contact with each other are both surfaces that have been treated; for example, referring to Figure 2 the surface p2a of the base material 12a and the surface p4a of the composite material 22a are in contact with each other, and the surface p1a of the base material 11a and the surface p3a of the composite material 21a are in contact with each other;

[0076] 2) The surface brushed with the release agent faces the other composite material; for example, referring to Figure 2 one of the surface p6a and the surface p5a is coated with the release agent 30a;

[0077] 3) The composite material is placed in the middle relative to the base material; for this, given that the composite blank is roughly symmetrical in up and down, only one set of base material + composite material in the composite blank is taken as an example, such as the upper set, see Figure 2 In the group blank state, the distance from the lateral side of the composite material 21a (corresponding to the long side of the surface p3a) to the lateral side of the base material 11a (corresponding to the long side of the surface p1a) in the transverse direction is half of W0, and the distance from the lateral side of the composite material 21a (corresponding to the short side of the surface p3a) to the lateral side of the base material 11a (corresponding to the short side of the surface p1a) in the longitudinal direction is half of L0, as described above, L0 and W0 are respectively 90-150 mm, that is, the distance from the lateral side of the composite material 21a to the lateral side of the base material 11a is in the range of 45-75 mm.

[0078] The above describes the group blank step, in a preferred embodiment, after the group blank step is implemented, the four stacked steel blanks are placed as a whole under a four-column hydraulic machine, and the opposite surfaces of the two base materials (that is, the upper surface of the upper base material and the lower surface of the lower base material) are pressurized, the pressure is ≥500 tons. Thus, the contact between adjacent steel blanks can be made more closely.

[0079] Further, in the step of "preparing four sealing strips with a width W3, and attaching the sealing strips to the four lateral sides of the two composite materials, and performing gas shield 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, and a composite blank base blank is obtained", based on the arrangement of the sealing strips, the four stacked steel blanks form a composite blank base blank. Specifically, see Figure 2 The composite blank base blank is: the two base materials 11a and 12a form the upper and lower surfaces, the two composite materials 21a and 22a are located in the middle, and the four sealing strips 40a surround the two composite materials 21a and 22a in a four-sided frame and connect the two base materials 11a and 12a.

[0080] The width W3 of the sealing strip is 2T2-1-2 mm, that is, the width of the sealing strip is slightly smaller than the sum of the thicknesses of the two composite materials by 1-2 mm. The sealing strip with this width wraps the upper and lower two composite materials, improving the wrapping effect.

[0081] Furthermore, among the four sealing strips, two sealing strips are attached to the two lateral sides of the two composite materials in the transverse direction, and the length L31 is L2-1-2 mm; the other two sealing strips are attached to the two lateral sides of the two composite materials in the longitudinal direction, and the length L32 is W2-1-2 mm.

[0082] Preferably, the thickness T3 of the sealing strip is 12-15 mm.

[0083] As to the forming mode of each sealing strip, it can be directly cut out on a steel plate according to the thickness T3, the width W3 and the length L31 or L32 without welding, or it can be spliced by welding from multiple sealing strips with different lengths.

[0084] As a preferred embodiment, before the gas shield welding between the adjacent sealing strips and between the sealing strip and the base material, the two ends and the two sides of each sealing strip can be polished to remove the surface oxide skin and improve the welding effect, and / or the two ends and the two sides of each sealing strip can be beveled.

[0085] Further, as a preferred embodiment, in the step of "carrying out gas shield welding between the adjacent sealing strips and between the sealing strip and the base material", the welding speed is 300-360 mm / min, and the interpass temperature is controlled to be 135-165°C during the welding process.

[0086] Next, for the step of "processing a round hole on the sealing strip at the groove of the side edge of the composite blank, and welding a seamless steel pipe at the round hole", the groove is formed outside the sealing strip between the two base materials; in this step, the round hole is processed to weld the seamless steel pipe, so as to facilitate subsequent vacuumizing of the composite blank.

[0087] As a preferred mode, the round hole is processed in the middle of the short edge (i.e. the side edge in the longitudinal direction) of the composite blank blank, but it is not limited thereto.

[0088] As a preferred mode, 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.

[0089] Next, for the step of "carrying out surfacing on the grooves of the four side edges of the composite blank blank", submerged arc surfacing is adopted. It can be understood that, outside the four-edge frame formed by the sealing strips, a filling layer 50a in the form of a four-edge frame is formed by the butt welding in this step, as shown in Figure 2 .

[0090] As a preferred mode, before welding, the flux is baked at 350°C for 2h, and then kept at 150°C for 1h; and during the welding process, the interpass temperature is controlled to be 135-165°C, and the welding speed is 420-480 mm / min. In this way, the submerged arc surfacing technology, combined with the previous sealing strip wrapping and gas shield welding, collectively realizes the stable connection of the four steel blanks, ensures the connection strength, avoids the cracking abnormality in the subsequent composite blank rolling step, and further improves the interface bonding effect on the basis of realizing the quality advantages of the composite plate as described above.

[0091] In addition, during the welding process, before each welding operation, it is necessary to clean the weld bead to keep it clean; after welding, insulation cotton should be used to cover it for insulation.

[0092] Next, the step involves using a vacuum pump to evacuate the composite billet through the seamless steel pipe, achieving a vacuum level of [missing information].

[0093] ≤10 -1 In the process of "holding pressure for more than 4 hours after reaching Pa, and finally sealing the seamless steel pipe", the suction port of the vacuum pump is connected to the seamless steel pipe, and the seamless steel pipe is connected to the space inside the composite billet (such as the surface gap between the composite and the base material, the surface gap between the composites, the end face gap between the composite and the seal, etc.) to expel the air in the space until the vacuum degree is ≤10. -1 The pressure is maintained at 4 Pa, and a vacuum level can be guaranteed by holding the pressure for more than 4 hours. This avoids air in the space from causing surface oxidation at the composite interface during subsequent composite billet rolling, thus ensuring the bonding quality of the composite interface.

[0094] Furthermore, in this step, the seamless steel pipe is sealed, which can be carried out in a manner that is currently feasible in the steel industry, such as heating and flattening the seamless steel pipe with a flame gun to achieve sealing.

[0095] The above details the overall steps for preparing the composite billet. Specific steps such as surface treatment, vacuuming, welding, and sealing lay the foundation for excellent interfacial bonding and surface quality in subsequent rolling of the composite billet. The use of a release agent further facilitates the smooth separation of the two composite plates.

[0096] As mentioned above, the preparation method of the present invention further includes a composite billet rolling step following the overall composite billet preparation step. The present invention provides four embodiments of the composite billet rolling step, which are described in detail below.

[0097] <First Implementation Method of Composite Billet Rolling Step>

[0098] In this embodiment, the reference Figure 3a The composite billet rolling process includes the following sub-steps:

[0099] The obtained composite billet is heated to a homogenization temperature of 1170~1220℃, preferably 1200~1220℃, and the total heating time is ≥1.2×t min / mm, where t is the thickness of the composite billet. The holding time in the homogenization section is 30min~50min.

[0100] The two-stage controlled rolling of rough rolling + finish rolling is adopted, in the rough rolling stage, the starting rolling temperature is ≤1050℃, the final rolling temperature is ≥1000℃, the rolling is first transversely and then longitudinally, at least one pass of longitudinal rolling has a reduction of ≥35mm, the total reduction of rough rolling is 40-60%, the rough rolling is ended when the intermediate billet thickness is 2.5-3.5 times of the target thickness of the clad plate large plate; then the intermediate billet is warmed up, and water cooling is carried out during the warming up, when the surface temperature of the intermediate billet is reduced to ≤840℃, preferably ≤830℃, the finish rolling stage is started; the final rolling temperature of the finish rolling stage is ≥780℃, preferably ≥800℃, the total reduction of finish rolling is 55-75%, and the clad plate large plate with a thickness of ≥54mm is obtained;

[0101] After the rolling is ended, the clad plate large plate is cooled, and then is intermittently cooled in the ultra-fast cooling system: when the clad plate large plate passes through the ultra-fast cooling system, the opening and closing states of all the 24 groups of cooling headers are controlled according to the mode of opening N groups of cooling headers and then not opening M groups of cooling headers, the cooling water pressure is 0.2MPa, the cooling speed is 3-15℃ / s, the final cooling temperature is 380-450℃, the roller way speed of the ultra-fast cooling system is 0.2-0.4m / s; wherein N is 2, 3 or 4, and M is 2, 3 or 4; the clad plate large plate passes through the ultra-fast cooling system once, and the intermittent cooling is completed.

[0102] After the intermittent cooling is completed, the clad plate large plate is naturally cooled to room temperature on the cooling bed, and thus the step 2) of rolling the clad billet is completed, and the step 3) of separating and straightening the clad plate is entered.

[0103] Compared to existing technologies, this embodiment employs an intermittent cooling method. As the composite panel passes through the ultra-fast cooling system, it alternates between opening and closing the cooling manifolds. This causes each part of the composite panel to cool, then glow red, then cool again, then glow red again… in a continuous cycle until the composite panel leaves the ultra-fast cooling system. During this cooling-glow-reddening cycle, the carbon steel substrate continuously undergoes phase transformation and self-tempering effects, with the phase transformation reaction gradually penetrating towards the core until the entire carbon steel substrate has completed the phase transformation. This intermittent cooling process differs from conventional reciprocating cooling. In reciprocating cooling, the re-heating and self-tempering occur after the surface or near-surface layer has completed its phase transformation, resulting in a significant temperature difference or cooling rate between the surface and the core, leading to substantial differences in microstructure and mechanical properties. In contrast, the intermittent cooling process in this embodiment involves some parts of the composite board being cooled while others are undergoing re-heating / self-tempering simultaneously. Furthermore, each part of the composite board alternates between cooling and re-heating / self-tempering over time, minimizing differences in temperature, cooling rate, microstructure, and properties between the surface and core. For example, the resulting composite board exhibits a Vickers hardness difference ≤10 in the thickness direction of the base layer, a strength difference ≤40 MPa between the head, middle, and tail, and a strength difference ≤40 MPa across the entire board. Moreover, intermittent cooling further improves the shape of the composite board, resulting in low unevenness. Even without straightening after cooling and directly cooled on a cooling bed, an excellent shape can still be achieved.

[0104] Preferably, the cooling distance of each set of cooling manifolds is 1m. That is, when one set of cooling manifolds is turned on, it can cool a roughly 1m length of the composite panel on the roller conveyor.

[0105] When the composite panel passes through the ultra-fast cooling system, the cooling manifolds of groups 1 to 4 are turned on, groups 5 to 8 are turned off, groups 9 to 12 are turned on, groups 13 to 16 are turned off, groups 17 to 20 are turned on, groups 21 to 22 are turned off, and groups 23 to 24 are turned on.

[0106] <Second Implementation Method of Composite Billet Rolling Step>

[0107] This implementation method, see Figure 3b The composite billet rolling process includes the following sub-steps:

[0108] The five-stage heating is adopted, including preheating, first heating, second heating, third heating and soaking, the preheating temperature is less than or equal to 850℃, the residence time is (0.45-0.55)t min / mm, the first heating temperature is 1030-1090℃, the residence time is (0.35-0.45)t min / mm, the second heating temperature is 1100-1160℃, the residence time is (0.25-0.35)t min / mm, the third heating temperature is 1140-1180℃, the residence time is (0.15-0.25)t min / mm, and the soaking temperature is 1170-1210℃, the residence time is (0.10-0.20)t min / mm;

[0109] The two-stage controlled rolling is adopted, including rough rolling and finish rolling, in the rough rolling stage, the first pass is longitudinal rolling, the rolling reduction is greater than or equal to 46mm; the second pass is transverse rolling, until the target width of the composite plate is reached in the n pass, the rolling reduction of the second pass is greater than or equal to 25mm; the n+1 pass is longitudinal rolling, until the thickness of the intermediate blank is 2.5-3.5 times of the target thickness of the composite plate, the rolling reduction of the n+1 pass is greater than or equal to 30mm; in the whole rough rolling stage, the rolling temperature of the first pass is greater than or equal to 1060℃, the opening rolling temperature of the remaining passes is less than or equal to 1050℃, and the finish rolling temperature is greater than or equal to 1000℃; after the rough rolling stage, the intermediate blank is cooled by spraying water, and when the surface temperature of the intermediate blank is less than or equal to 840℃, the finish rolling stage starts, the opening rolling temperature is 810-840℃, and the finish rolling temperature is 780-810℃, so as to obtain the composite plate with a thickness greater than or equal to 54mm;

[0110] After the rolling is completed, the composite plate is cooled, and the composite plate enters the ultra-fast cooling system for intermittent cooling; when the composite plate passes through the ultra-fast cooling system, the opening and closing states of all 24 groups of cooling headers are controlled according to the mode of opening N groups of cooling headers and then not opening M groups of cooling headers, the cooling water pressure is 0.2MPa, the cooling speed is 3-15℃ / s, the final cooling temperature is 380-450℃, and the roller speed of the ultra-fast cooling system is 0.2-0.4m / s; wherein N is 2, 3 or 4, and M is 2, 3 or 4; the composite plate passes through the ultra-fast cooling system once, that is, the intermittent cooling is completed;

[0111] After the intermittent cooling is completed, the composite plate is naturally cooled on the cooling bed to room temperature, and thus the step 2) of rolling the composite blank is completed and the step 3) of separating and straightening the composite plate is entered.

[0112] That is, the embodiment is different from the first embodiment of the step of rolling the composite blank in the heating and rolling processes.

[0113] Compared with the prior art, the present embodiment also adopts intermittent cooling, and accordingly has the beneficial effects brought by the intermittent cooling process. Please refer to the first embodiment of the composite blank rolling step described above. Further, compared with the prior art, the heating process of the present embodiment can better control the temperature rising rate of the composite blank in each section, ensure uniform heating of the blank, and avoid cracking and gas leakage of the composite blank due to the difference in thermal properties of the base material and the composite material, thereby ensuring the interface bonding effect. Furthermore, in the rolling process of the present embodiment, the rough rolling adopts the mode of longitudinal rolling, transverse rolling, and longitudinal rolling again, which can ensure the realization of large reduction rolling, so that the core of the composite blank is effectively penetrated, the core deformation is promoted, and the bonding rate of the composite interface is ensured; the instant cooling device is used for cooling when the temperature is stable, which reduces the temperature stabilization time and improves the rolling efficiency, and at the same time, avoids the grain growth of the carbon steel base material due to the long temperature stabilization time; the temperature control in the finishing rolling stage can refine the grains and ensure that the thick composite plate has good low-temperature impact toughness.

[0114] <Third embodiment of the composite blank rolling step>

[0115] The present embodiment is the same as the first embodiment of the composite blank rolling step described above in the heating, two-stage controlled rolling, and cooling steps, and the difference is only in the steps after the composite plate leaves the ultra-fast cooling system.

[0116] In the first embodiment of the composite blank rolling step described above, after the composite plate leaves the ultra-fast cooling system, the composite plate is naturally cooled to room temperature on the cooling bed; unlike this, in the present embodiment, the composite plate directly enters the straightening machine for straightening after leaving the ultra-fast cooling system, and the straightened composite plate is naturally cooled on the cooling bed. When the surface temperature is reduced to below 200°C, cold straightening is performed by using a cold straightening machine. In this way, the plate shape can be further improved. Figure 3c

[0117] Similarly, the second embodiment of the composite blank rolling step described above can also be changed to directly enter the straightening machine for straightening after the composite plate leaves the ultra-fast cooling system, and the straightened composite plate is naturally cooled on the cooling bed. When the surface temperature is reduced to below 200°C, cold straightening is performed by using a cold straightening machine. Thus, as the fifth embodiment of the composite blank rolling step, please refer to Figure 3d .

[0118] <Fourth embodiment of the composite blank rolling step>

[0119] The present embodiment is the same as the first embodiment of the composite blank rolling step described above in the heating, two-stage controlled rolling, and cooling steps, and the difference is only in the steps after the composite plate leaves the ultra-fast cooling system. ​

[0120] In the first embodiment of the preceding composite blank rolling step, the composite slab is naturally cooled to room temperature on a cooling bed after leaving the ultra-fast cooling system; in this embodiment, however, the composite slab is directly fed into a straightening machine for 1-3 passes of straightening after leaving the ultra-fast cooling system. Unlike the first embodiment of the preceding composite blank rolling step, in this embodiment, the composite slab is cooled to a temperature T Figure 3e After that, the composite slab is placed between two steel plates with a temperature of T f +100-150°C for stack cooling, with a stack cooling time of 0.4 min / mmxt0±5 min, t0 being the thickness of the composite slab, so that the composite slab can be slowly cooled and clamped by the steel plates to maintain the uniformity of the core-surface temperature within the stack cooling time; after the stack cooling, the composite slab is naturally cooled on a cooling bed. In this embodiment,

[0121] 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 base material. In this preferred embodiment, the stack cooling, especially the temperature of the two steel plates and the stack cooling time, can further improve the microstructure, performance and shape of the final composite plate compared to the first embodiment.

[0122] Similarly, the second embodiment of the preceding composite blank rolling step can also be changed so that the composite slab is directly fed into a straightening machine for straightening after leaving the ultra-fast cooling system, and then the stack cooling is performed as described above, and after the stack cooling, the composite slab is naturally cooled on a cooling bed, thereby serving as a sixth embodiment of the composite blank rolling step, as shown in FIG. 6. Figure 3f .

[0123] The total step of the composite blank rolling is described in detail above. As described above, the preparation method of the present application also includes a total step of composite plate separation and straightening. Specifically, the total step of composite plate separation and straightening includes the following sub-steps:

[0124] The composite slab obtained from the preceding total step of composite blank rolling is cut on four sides by a plasma cutting machine to remove the part outside the seal, and the composite slab is separated into two upper and lower composite small plates;

[0125] The composite small plates are transversely flattened and cold straightened to obtain a finished stainless steel composite plate.

[0126] In the step of cutting the four sides of the composite slab to remove the part outside the seal, the part outside the seal is the edge part on the composite slab large plate which is converted from the seal and the filler layer in the composite blank mentioned above after the previous composite blank rolling step. Thus, this part is removed to expose the stainless steel clad layer, and without the connecting effect of this part, the composite slab large plate is separated into two composite slab small plates. Referring to Figure 4 Corresponding to the five embodiments of the blank surface treatment step described above, Figure 4 The cross-sectional shape of the corresponding two composite slab small plates (i.e. the final single-sided stainless steel clad plate) is shown respectively.

[0127] Each composite slab small plate is composed of a clad layer and a base layer, the clad layer is obtained from the original clad material through rolling, and the base layer is obtained from the original base material through rolling. Therefore, in Figure 4 the original clad material is still marked with the original clad material mark, and the base layer is still marked with the original base material mark.

[0128] Further, the single-sided stainless steel clad plate prepared by the preparation method of the present application.

[0129] The clad layer is preferably austenitic stainless steel, and the chemical composition is as follows: 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. With this chemical composition, the performance of the composite plate can be further ensured under the above technical effects, especially the corrosion resistance of the clad layer, for example, the clad layer is boiled in sulfuric acid-copper sulfate solution for 20h, and after 180° bending, there is no intergranular corrosion crack.

[0130] The base layer is carbon steel, and the chemical composition is as follows: 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.

[0131] Preferably, the base layer has the following chemical composition in 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 Fe and inevitable impurities. With this chemical composition, in combination with the control of the temperature, time, reduction, and cooling speed in the composite blank rolling step, the mechanical properties of the composite plate can be further improved, and the toughness can be ensured, in the case of the aforementioned technical effects.

[0132] Further, the base layer of the composite plate has a bainite + a small amount of ferrite structure, the composite plate has excellent mechanical properties, high impact toughness, excellent corrosion resistance, and good interface bonding quality, plate shape, and surface quality, and in addition, has high uniformity.

[0133] Specifically, the total thickness of the composite plate is ≥27 mm, the thickness of the base layer is ≥24 mm, and the thickness of the clad layer is 1-10 mm.

[0134] The unevenness of the composite plate is ≤3 mm / m, and even more preferably, the unevenness is ≤2 mm / m.

[0135] The yield strength of the composite plate is ≥345 MPa, the tensile strength is ≥490 MPa, the elongation after fracture is ≥18%, and the yield strength ratio is ≤0.86. Even more preferably, the yield strength of the composite plate is ≥500 MPa, and the tensile strength is ≥630 MPa.

[0136] The composite interface bonding rate of the composite plate is 100%, the shear strength is ≥300 MPa, the 0°C impact energy is ≥120 J, the -20°C impact energy is ≥120 J, and the -40°C impact energy is ≥120 J. Even more preferably, the 0°C impact energy of the composite plate is ≥240 J, the -20°C impact energy is ≥200 J, and the -40°C impact energy is ≥150 J.

[0137] The Vickers hardness difference in the thickness direction of the base layer of the composite plate is ≤10, the head-to-middle-tail strength difference is ≤40 MPa, and the strength difference at each part of the whole plate is ≤40 MPa.

[0138] In addition, the composite plate has no cracks after being bent outward by 180°, and has no cracks after being bent inward by 180°. In the corrosion resistance test, the clad layer is sensitized at 650°C for 2 h, then boiled in a sulfuric acid-copper sulfate solution for 20 h, and after being bent by 180°, has no intergranular corrosion cracks.

[0139] Compared with the prior art, the present application has the following advantages: on the one hand, the corrosion resistance and mechanical strength of the stainless steel composite plate are ensured by specific control of the process in the whole preparation method, so that the corrosion resistance and mechanical properties are not deteriorated during the composite blank rolling process; on the other hand, the shape control and uniformity control of the special thick plate are realized, and the production difficulty of the existing special thick stainless steel composite plate is overcome; and on the other hand, the material yield is high and the production efficiency is high.

[0140] The detailed description listed above is only a specific description of the feasible embodiments of the present application, and is not used to limit the protection scope of the present application. Equivalent embodiments or changes made without departing from the spirit of the present application should be included in the protection scope of the present application.

[0141] The beneficial effects of the present application are further illustrated by the following examples, which are only a part of the numerous changeable embodiments of the present application, but not all.

[0142] In these examples, Q500q steel is selected as the base material, and the chemical composition is 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%, and Al: 0.037% by mass percentage. 316L stainless steel is selected as the composite material, and the chemical composition is as follows: C: 0.020%, Si: 0.52%, Mn: 1.36%, P: 0.033%, S: 0.003%, Ni: 10.20%, Mo: 2.10%, and Cr: 16.20% by mass percentage.

[0143] Here, each example is prepared according to the embodiments provided by the present application to obtain a composite blank with a thickness of 378 mm and a constant base material thickness. The composite blank is rolled into a composite plate large plate with a thickness of 54 mm according to the embodiments provided by the present application, and the composite plate large plate is subjected to the composite plate separation and straightening step according to the present application, to obtain a single-sided stainless steel composite plate product with a total thickness of 27 mm, a base layer thickness of 24 mm, and a composite layer thickness of 3 mm.

[0144] Among them, the composite blank rolling steps adopted by each example are as follows: example 1 adopts the first embodiment of the composite blank rolling step as shown in the figure, example 2 adopts the fourth embodiment of the composite blank rolling step as shown in the figure, example 3 adopts the third embodiment of the composite blank rolling step as shown in the figure, and example 4 adopts the second embodiment of the composite blank rolling step as shown in the figure. Figure 3a Figure 3e Figure 3c Figure 3b ​​​The second embodiment of the composite blank rolling step shown is employed in Example 5 Figure 3f The sixth embodiment of the composite blank rolling step shown is employed in Example 6 Figure 3d The fifth embodiment of the composite blank rolling step shown.

[0145] Further, the composite sheets of each example were sampled and tested, and the interfacial bonding rate of each example was 100%, the inner bend 180° was qualified (no cracks), the outer bend 180° was qualified (no cracks), and after being boiled in a sulfuric acid-copper sulfate solution for 20 h, the composite layer had no intergranular corrosion cracks after being bent 180°. In addition, the results of other performance tests are shown in Tables 1 and 2.

[0146] Table 1

[0147]

[0148] Table 2

[0149]

Claims

1. A method for preparing an extra-thick stainless steel composite plate, characterized in that, It comprises three steps of composite blank preparation, composite blank rolling and composite plate separation straightening in sequence; In the composite blank preparation step, a composite blank with the stacking sequence of base material, composite material, composite material and base material is prepared; and a release agent is applied on the side of one composite material facing the other composite material, the release agent comprising, by weight percentage, 25-35% of silicon nitride, 5-10% of thermosetting amino resin and 55-70% of water; The thickness of the release agent is 0.2-0.5mm; Before the blank assembly, the composite material coated with the release agent is heated and dried, the drying temperature being 100-250℃ and the drying time being 20-40min; The composite blank rolling step comprises: The obtained composite blank is heated, the soaking temperature being 1170-1220℃ and the total heating time being ≥1.2xt min / mm, t being the thickness of the composite blank; The two-stage controlled rolling of rough rolling+fine rolling is adopted, in the rough rolling stage, the finish rolling temperature is ≥1000℃, the rough rolling stage is ended when the intermediate blank thickness is 2.5-3.5 times of the target thickness of the composite plate large plate; then the intermediate blank is allowed to cool down, during which water cooling is performed, when the surface temperature of the intermediate blank is reduced to below 840℃, the fine rolling stage is started, the finish rolling temperature of the fine rolling stage is ≥780℃, and the composite plate large plate with a thickness ≥54mm is obtained; After the rolling is ended, the composite plate large plate is subjected to intermittent cooling in the ultra-fast cooling system: when the composite plate large plate passes through the ultra-fast cooling system, the opening and closing states of all 24 groups of cooling headers of the ultra-fast cooling system are controlled according to the mode of opening N groups of cooling headers and then not opening M groups of cooling headers, the cooling water pressure is 0.2MPa, the cooling speed is 3-15℃ / s, the final cooling temperature is 380-450℃, and the roller speed is 0.2-0.4m / s; wherein N is 2, 3 or 4, and M is 2, 3 or 4.

2. The method of claim 1, wherein the stainless steel clad plate is prepared by the steps of: preparing a stainless steel plate having a thickness of 50 mm or more; and cold rolling the stainless steel plate to a thickness of 20 mm or less. The cooling distance of each group of cooling headers is 1m.

3. The method of claim 1, wherein the stainless steel clad plate is prepared by the steps of: 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 is ≤850℃, the residence time is (0.45-0.55) t min / mm, the first heating temperature is 1030-1090℃, the residence time is (0.35-0.45) t min / mm, the second heating temperature is 1100-1160℃, the residence time is (0.25-0.35) t min / mm, the third heating temperature is 1140-1180℃, the residence time is (0.15-0.25) t min / mm, and the soaking temperature is 1170-1210℃, the residence time is (0.10-0.20) t min / mm.

4. The method of claim 1, wherein the stainless steel clad plate is prepared by the steps of: preparing a stainless steel plate having a thickness of 50 mm or more; and cold rolling the stainless steel plate to a thickness of 20 mm or less. In the step of two-stage controlled rolling of rough rolling + finish rolling, in the rough rolling stage, longitudinal rolling is adopted in the first pass, and the rolling reduction is ≥ 46 mm; transverse rolling is adopted from the second pass, and the rolling reduction is ≥ 25 mm; longitudinal rolling is adopted from the (n+1)th pass, and the rolling is stopped when the intermediate blank thickness is 2.5-3.5 times the target thickness of the composite plate, and the rolling reduction is ≥ 30 mm.

5. The method of claim 4, wherein the stainless steel clad plate is prepared by the steps of: preparing a stainless steel plate having a thickness of 50 mm or more; and cold rolling the stainless steel plate to a thickness of 20 mm or less. In the whole rough rolling stage, the rolling temperature of the first pass is ≥ 1060℃, the opening rolling temperature of the remaining passes is ≤ 1050℃, and the finish rolling temperature is ≥ 1000℃; after the rough rolling stage, the temperature is waited, and water cooling is performed during the waiting, and when the surface temperature of the intermediate blank is reduced to below 840℃, the finish rolling stage starts, and the opening rolling temperature is 810-840℃, and the finish rolling temperature is 780-810℃.

6. The method of claim 1, wherein the stainless steel clad plate is prepared by the steps of: preparing a stainless steel plate having a thickness of 50 mm or more; and cold rolling the stainless steel plate to a thickness of 20 mm or less. The composite blank preparation step includes steel blank preparation, blank surface treatment, brushing of separating agent, blank assembly, sealing and wrapping, gas shield welding, surfacing, vacuum extraction, and sealing; In the formula, the vacuum degree of the vacuumizing is ≤10 -1 Pa, pressure maintaining for 4 h.

7. The method of claim 6, wherein the stainless steel clad plate is prepared by the steps of: preparing a stainless steel plate having a thickness of 50 mm or more; and cold rolling the stainless steel plate to a thickness of 20 mm or less. In the gas shield welding, the welding speed is 300-360 mm / min, and the interpass temperature is controlled to be 135-165℃ during the welding process.

8. The method of claim 6, wherein the stainless steel clad plate is prepared by the steps of: preparing a stainless steel plate having a thickness of 50 mm or more; and cold rolling the stainless steel plate to a thickness of 20 mm or less. Submerged arc surfacing is adopted in the surfacing; Before welding, the welding agent is baked at 350℃ for 2 h, and then is kept at 150℃ for 1 h; During the welding process, the interpass temperature is controlled to be 135-165℃, and the welding speed is 420-480 mm / min.

9. The method of claim 1, wherein the stainless steel clad plate is prepared by the steps of: preparing a stainless steel plate having a thickness of 50 mm or more; and cold rolling the stainless steel plate to a thickness of 20 mm or less. When the composite plate large plate passes through the ultra-fast cooling system, the first to fourth groups of cooling headers are opened, the fifth to eighth groups of cooling headers are not opened, the ninth to twelfth groups of cooling headers are opened, the thirteenth to sixteenth groups of cooling headers are not opened, the seventeenth to twentieth groups of cooling headers are opened, the twenty-first to twenty-second groups of cooling headers are not opened, and the twenty-third to twenty-fourth groups of cooling headers are opened; The composite plate large plate passes through the ultra-fast cooling system once, that is, the intermittent cooling is completed, and then the composite plate large plate is naturally cooled on the cooling bed to room temperature.

10. A super-thick stainless steel clad plate, characterized by, The composite plate is prepared by the preparation method in any one of claims 1-9.

11. The extra thick stainless steel clad plate according to claim 10, characterized by The total thickness of the composite plate is ≥ 27 mm, the thickness of the base layer is ≥ 24 mm, the thickness of the composite layer is 1-10 mm, the Vickers hardness difference in the thickness direction of the base layer of the composite plate is ≤ 10, the head-to-middle-to-tail strength difference is ≤ 40 MPa, the strength difference at different positions of the whole plate is ≤ 40 MPa, and the unevenness is ≤ 2 mm / m.

12. The extra thick stainless steel clad plate according to claim 10, wherein The yield strength of the composite plate is ≥ 500 MPa, the tensile strength is ≥ 630 MPa, the elongation after fracture is ≥ 18%, the yield strength ratio is ≤ 0.86, the 0℃ impact energy is ≥ 240 J, the -20℃ impact energy is ≥ 200 J, and the -40℃ impact energy is ≥ 150 J.

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