500MPa Grade Stainless Steel Composite Plate and Its Preparation Method

Abstract

The present invention discloses a 500 MPa grade stainless steel clad plate and a preparation method thereof. The chemical composition of the base layer of the clad plate: 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%, the balance being Fe; the structure of the base layer of the clad plate is bainite + a small amount of ferrite structure, the tensile strength ≥ 630 MPa, the elongation after fracture ≥ 18%, the yield ratio ≤ 0.86, and it has excellent surface quality, plate shape and interface bonding quality.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material preparation, and relates to a 500MPa grade stainless steel composite plate and a preparation method thereof. Background Art

[0002] With the continuous development of science and industry, ordinary alloys or a single metal can hardly meet the requirements of industrial development for the comprehensive performance of materials, and composite plates came into being. Stainless steel composite plates are based on carbon steel or low alloy steel as the base layer and stainless steel as the composite layer. The metallurgical bonding of the composite interface is achieved through methods such as explosive composite and rolling composite, so as to save resources and reduce costs without reducing the use effect (mechanical strength, corrosion resistance, etc.). Stainless steel composite plates are widely used in petrochemical, pressure vessels, power equipment, medical equipment, water conservancy, papermaking, bridges and other industries.

[0003] In recent years, with the increasing requirements for the safety and long life of steel bridges, the rust and corrosion prevention of steel bridge structures has become more and more prominent. If a layer of corrosion-resistant protective material is applied to the surface of the bridge steel to replace the single bridge steel plate, the long-term corrosion prevention goal that cannot be achieved by the spraying process can be achieved. Therefore, stainless steel composite plates have become a more ideal choice.

[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 to control plate shape, 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 500MPa grade stainless steel composite plate and a preparation method thereof, wherein the stainless steel composite plate has excellent surface quality, plate shape and interface bonding quality.

[0006] To achieve the above-mentioned purpose, an embodiment of the present invention provides a method for preparing a 500MPa grade stainless steel composite plate. The chemical composition of the base layer of the composite plate is as follows 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;

[0007] The preparation method comprises the following steps:

[0008] 1) Composite blank preparation

[0009] Prepare two carbon steel billets with a thickness of T1, a length of L1, and a width of W1 as the 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 the facing materials for forming the facing layer of the composite plate; L2 < L1, W2 < W1;

[0010] Surface-treat at least one surface of each of the two base materials and the two facing materials;

[0011] Apply a release agent on one surface of one facing material;

[0012] Form a billet stack in the order of base material, facing material, facing material, base material; wherein, the facing material is placed in the middle relative to the base material, and the surfaces of the base material and the facing 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 facing material;

[0013] Prepare four seals with a width of W3, W3 = 2T2 - (1 - 2) mm, attach the seals to the four side edges of the two facing materials, and perform gas shielded welding between adjacent seals and between the seals and the base materials, so that the two base materials and the seals form an integral body to obtain a composite blank base blank;

[0014] Machine a round hole in the seal at the groove on the side edge of the composite blank base blank, and weld a seamless steel pipe at the round hole;

[0015] Build-up weld the grooves on the four side edges of the composite blank base blank;

[0016] Use a vacuum pump to evacuate the composite blank through the seamless steel pipe, with the vacuum degree ≤ 10 -1 Pa, and then maintain the pressure for more than 4 h; finally, seal the seamless steel pipe;

[0017] 2) Rolling of the composite blank

[0018] Heat the obtained composite blank, with the soaking temperature being 1170 - 1220 °C, and the total heating time ≥ 1.2 × t min / mm, where t is the thickness of the composite blank;

[0019] Adopt two-stage controlled rolling of rough rolling + finish rolling. In the rough rolling stage, the final rolling temperature ≥ 1000 °C, and end the rough rolling stage 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 the temperature, and perform water cooling during this period. 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;

[0020] Cool after rolling to obtain a large plate of the composite plate;

[0021] 3) Separation and straightening of the composite plate

[0022] Cut the four sides of the large composite board to remove the part outside the seal, and the large composite board is separated into two small composite boards, the upper and the lower.

[0023] Horizontally flatten and cold straighten the small composite boards to obtain the finished stainless steel composite board.

[0024] Preferably, in the step of "cooling after rolling", after rolling, the large composite board enters the ultra-fast cooling system for intermittent cooling:

[0025] 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 board passes through the ultra-fast 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 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.

[0026] Preferably, after the intermittent cooling, the large composite board is cooled naturally on the cooling bed to room temperature, and thus the rolling of the composite billet in step 2) is completed and enters step 3) the separation and straightening of the composite board.

[0027] Preferably, in the rolling of the composite billet in step 2):

[0028] When "heating the obtained composite billet", a five-stage heating of preheating, first heating, second heating, third heating and soaking is adopted. 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;

[0029] In the "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 board at the nth pass, and 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 composite board, and the rolling reduction in the (n + 1)th pass ≥ 30 mm; in the whole rough rolling stage, the rolling temperature in the first pass ≥ 1060 °C, the starting rolling temperature of the remaining passes ≤ 1050 °C, and the final rolling temperature ≥ 1000 °C;

[0030] After the rough rolling stage, hold the temperature and perform water cooling during this period. When the surface temperature of the intermediate billet drops below 840 °C, start the finish rolling stage. The starting rolling temperature in the finish rolling stage is 810 °C - 840 °C, and the final rolling temperature is ≥ 780 °C.

[0031] Preferably, in the compound billet rolling of step 2):

[0032] Heat the obtained compound billet, with the soaking temperature being 1200 - 1220 °C, the total heating time being ≥ 1.2 × tmin / mm (where t is the thickness of the compound billet), and the soaking section holding time being 30 min - 50 min;

[0033] Adopt two - stage controlled rolling of rough rolling + finish rolling. In the rough rolling stage, the starting rolling temperature is ≤ 1050 °C, the final rolling temperature is ≥ 1000 °C. First, roll transversely and then longitudinally. When rolling longitudinally, at least one pass has a reduction of ≥ 35 mm. The total rough rolling reduction is 40 - 60%. End the rough rolling stage when the thickness of the intermediate billet is 2.5 - 3.5 times the target thickness of the large plate of the composite plate; then hold the temperature and perform water cooling during this period. When the surface temperature of the intermediate billet drops below 830 °C, start the finish rolling stage; the final rolling temperature in the finish rolling stage is ≥ 800 °C, and the total finish rolling reduction is 55 - 75%;

[0034] After rolling, the large plate of the composite plate enters the ultra - fast cooling system for cooling. The starting cooling temperature is ≥ 730 °C, the cooling rate is 10 - 20 °C / s, and the final cooling temperature is 480 - 500 °C.

[0035] Preferably, in the compound billet rolling of step 2): After the large plate of the composite plate leaves the ultra - fast cooling system, directly enter the straightening machine for straightening. After straightening, the large plate of the composite plate is placed on the cooling bed for natural cooling. When the surface temperature drops below 200 °C, use a cold straightening machine for cold straightening.

[0036] Preferably, in the compound billet rolling of step 2):

[0037] After the large plate of the composite plate leaves the ultra - fast cooling system, directly enter the straightening machine for straightening:

[0038] Place the straightened large plate of the composite plate between two steel plates with a temperature of T f - 150 °C to T f - 50 °C for stacking cooling. The stacking cooling time is 0.4 min / mm × t0 ± 5 min, where t0 is the thickness of the large plate of the composite plate;

[0039] After stacking cooling, place the large plate of the composite plate on the cooling bed for natural cooling;

[0040] T f= 550 + 30[Si] - 20[Mn] + 15[Cr] - 15[Ni] + 10[Mo], where [Si], [Mn], [Mo], [Cr],

[0041] [Ni] is 100 times the mass percentage of each element in the base material.

[0042] Preferably, in the step of "coating a release agent on one surface of a composite material", the release agent used is a coating solution containing silicon oxide and magnesium oxide, where the mass ratio of silicon oxide to magnesium oxide is 3:1; the amount of the release agent coated is 20ymg / m 2 , and y is the thickness ratio of the composite blank to the large plate of the composite board;

[0043] Before the step of "assembling the blanks in the stacking order of base material, composite material, composite material, base material", the composite material coated 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 - 45 min.

[0044] Preferably, in the step of "coating a release agent on one surface of a composite material", the components of the release agent used are by weight: 25 - 35% silicon nitride, 5 - 10% thermosetting amino resin, 55 - 70% water; the thickness of the release agent coated is 0.2 - 0.5 mm;

[0045] Before the step of "assembling the blanks in the stacking order of base material, composite material, composite material, base material", 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 min.

[0046] Preferably, in the step of "performing gas shielded welding between adjacent seals and between the seal and the base material", the welding current is 235 - 265 A, the welding voltage is 25 - 29 V, the welding speed is 300 - 360 mm / min, and the interpass temperature during welding is controlled at 135 - 165°C.

[0047] Preferably, in the step of "performing surfacing on the grooves on the four sides of the composite blank base blank", submerged arc surfacing is used;

[0048] Before welding, the welding flux is baked at 350°C for 2 h and then kept warm at 150°C for 1 h;

[0049] During welding, the interpass temperature is controlled at 135 - 165°C, the welding current is 620 - 680 A, the welding voltage is 28 - 32 V, and the welding speed is 420 - 480 mm / min.

[0050] Preferably, the step of "performing surface treatment on at least one surface of each of the two base materials and the two composite materials" includes:

[0051] Grind and polish one surface of each composite material to remove the surface scale; and,

[0052] Milling process one surface of two base materials in a relatively shape-complementary manner, and process the surface into a laterally inclined surface with length L11 = L1 and width W11 > W1, where the base material is a non-uniform thickness blank with a gradually changing thickness in the lateral direction, or process the surface into a longitudinally inclined surface with length L11 > L1 and width W11 = W1, where the base material is a non-uniform thickness blank with a gradually changing thickness in the longitudinal direction.

[0053] Preferably, the step of "surface treatment of at least one surface of two base materials and two composite materials respectively" includes:

[0054] Milling process one surface of two base materials in a relatively shape-complementary manner, and process the surface into an irregular concave-convex surface including n planes connected in sequence in the lateral direction, where the base material is a non-uniform thickness blank with a non-monotonic thickness change in the lateral direction, and the length L12 of the irregular concave-convex surface is L1 and the total width W12 > W1; or, process the surface into an irregular concave-convex surface including n planes connected in sequence in the longitudinal direction, where the base material is a non-uniform thickness blank with a non-monotonic thickness change in the longitudinal direction, and the total length L12 of the irregular concave-convex surface is > L1 and the width W12 = W1; n ≥ 2;

[0055] Grind and polish one surface of each composite material to remove the surface scale; then bend each composite material to match the corresponding irregular concave-convex surface.

[0056] Preferably, in the "composite material is placed centered relative to the base material", the distance from the lateral side of the composite material to the corresponding side of the base material is half of the width difference between the contact surfaces of the composite material and the base material, and the distance from the longitudinal side of the composite material to the corresponding side of the base material is half of the length difference between the contact surfaces of the composite material and the base material.

[0057] To achieve the above invention object, an embodiment of the present invention provides a 500MPa grade stainless steel composite plate, and the composite plate is prepared by using the above preparation method.

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows: The composite plate prepared by the preparation method of the present invention has excellent surface quality, excellent plate shape, excellent interface bonding, etc. For example, there are no obvious surface defects such as pits and side scratches existing in the existing composite plates. For example, the flatness of the composite plate is ≤ 3 mm / m. For another example, the bonding rate of the composite interface of the composite plate is 100%, the shear strength is ≥ 300 MPa, and it also has excellent mechanical properties. The total thickness of the composite plate is 15 - 39 mm, the thickness of the base layer is 12 - 36 mm, the thickness of the cladding layer is 3 mm. The structure of the base layer is bainite + a small amount of ferrite structure, the yield strength is ≥ 500 MPa, the tensile strength is ≥ 630 MPa, the elongation after fracture is ≥ 18%, and the yield ratio is ≤ 0.86. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] For the convenience of clear display and description, in each drawing of the present invention, the sizes of some structures or parts are enlarged relative to other structures or parts. Therefore, it is only used to illustrate the basic structure of the subject matter of the present invention.

[0060] Figure 1a is a schematic cross-sectional view of a steel billet of the first embodiment of the blank surface treatment step in the present invention;

[0061] Figure 1b is a schematic cross-sectional view of a steel billet of the second embodiment of the blank surface treatment step in the present invention, wherein the change in the surface shape after surface treatment is indicated by a dotted line;

[0062] Figure 1c is a schematic longitudinal cross-sectional view of a steel billet of the third embodiment of the blank surface treatment step in the present invention, wherein the change in the surface shape after surface treatment is indicated by a dotted line;

[0063] Figure 1d is a schematic cross-sectional view of a steel billet of the fourth embodiment of the blank surface treatment step in the present invention, and the change in the surface shape before (A) and after (B) surface treatment is indicated;

[0064] Figure 1e is a schematic longitudinal cross-sectional view of a steel billet of the fifth embodiment of the blank surface treatment step in the present invention, and the change in the surface shape before (A) and after (B) surface treatment is indicated;

[0065] Figure 2a corresponds to Figure 1a a schematic cross-sectional view of the composite billet;

[0066] Figure 2b corresponds to Figure 1b a schematic cross-sectional view of the composite billet;

[0067] Figure 2c corresponds toFigure 1c Longitudinal sectional view of the composite blank;

[0068] Figure 2d corresponds to Figure 1d Transverse sectional view of the composite blank;

[0069] Figure 2e corresponds to Figure 1e Longitudinal sectional view of the composite blank;

[0070] Figures 3a - 3e respectively are Figures 2a - 2e Cross-sectional views of two composite plates rolled from the composite blanks;

[0071] Figures 4a - 4f Flow charts of different embodiments of the rolling step of the composite blank of the present invention respectively. Specific embodiments

[0072] The present invention provides a method for preparing a 500 MPa grade stainless steel composite plate and a composite plate prepared based on this method.

[0073] Compared with the prior art, such as explosive cladding, non-vacuum preparation of composite blanks, vacuum electron beam welding for blank preparation, etc. mentioned in the background art, the composite plate prepared by the preparation method of the present invention has advantages such as excellent surface quality, excellent plate shape, excellent interface bonding, etc. For example, there are no obvious surface defects such as pits and side scratches existing in the existing composite plates. For example, the flatness of the composite plate is ≤ 3 mm / m. For another example, the bonding rate of the composite interface of the composite plate is 100%, the shear strength is ≥ 300 MPa, and it also has excellent mechanical properties. The total thickness of the composite plate is 15 - 39 mm, the thickness of the base layer is 12 - 36 mm, the thickness of the clad layer is 3 mm, the structure of the base layer is bainite + a small amount of ferrite structure, the yield strength is ≥ 500 MPa, the tensile strength is ≥ 630 MPa, the elongation after fracture is ≥ 18%, and the yield ratio is ≤ 0.86.

[0074] Specifically, the preparation method includes three general steps: composite blank preparation, composite blank rolling, and composite plate separation and straightening.

[0075] The general steps of the composite blank preparation include the following sub-steps:

[0076] Prepare two carbon steel blanks with thickness T1, length L1, and width W1 as the base materials; and prepare two stainless steel blanks with thickness T2, length L2, and width W2 as the clad materials;

[0077] Perform surface treatment on at least one surface of each of the two base materials and the two clad materials;

[0078] Apply a release agent on one surface of one of the clad materials;

[0079] Stack the base material, the composite material, the composite material, and the base material in this order to form a blank stack.

[0080] Prepare four seal strips with a width of W3, where W3 = 2T2 - (1 - 2) mm. Attach the seal strips to the four side edges of the two composite materials, and perform gas shielded welding between adjacent seal strips and between the seal strips and the base material, so that the two base materials and the seal strips form an integral body, obtaining a composite blank base blank.

[0081] Machine a round hole on the seal strip at the groove on the side edge of the composite blank base blank, and weld a seamless steel pipe at the round hole.

[0082] Perform surfacing welding on the grooves on the four side edges of the composite blank base blank.

[0083] 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.

[0084] Furthermore, the above steps are described in detail as follows.

[0085] The step of "preparing two carbon steel blanks with a length of L1 and a width of W1 as the base material; and preparing two stainless steel blanks with a length of L2 and a width of W2 as the composite material", that is, the blank preparation step.

[0086] Among them, the carbon steel blank used as the base material has a thickness of T1, a length of L1, and a width of W1, which is a rectangular steel blank; similarly, the stainless steel blank used as the composite material has a thickness of T2, a length of L2, and a width of W2, which is also a rectangular steel blank. And, L2 < L1, W2 < W1, and the length and width dimensions of the composite material are smaller than those of the base material.

[0087] As a preferred solution, the stainless steel blank is preferably austenitic stainless steel.

[0088] Furthermore, the chemical composition of the stainless steel blank in mass percentage is: 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 unavoidable impurities. Using the stainless steel blank with this chemical composition can further ensure the performance of the composite plate under the above technical effects, especially the corrosion resistance of the cladding layer. For example, the cladding layer of the obtained composite plate (that is, obtained by rolling the composite material) is boiled in a sulfuric acid - copper sulfate solution for 20 hours and has no intergranular corrosion cracks after being bent 180°.

[0089] It should be noted here that the chemical compositions of the two stainless steel billets can be the same or different. Only one of them can adopt the chemical composition provided by the above preferred solution, or both can adopt or neither can adopt the chemical composition provided by the above preferred solution.

[0090] As a preferred solution, the chemical composition of the carbon steel billet 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. For the carbon steel billet with this chemical composition, combined with the control of each temperature, time, reduction and cooling rate in the above composite billet rolling step, the mechanical properties of the composite plate can be further improved on the basis of the above technical effects, and the toughness can be guaranteed. For example, the impact energy of the composite plate at 0°C ≥ 120J, at -20°C ≥ 120J, at -40°C ≥ 120J; the composite plate has no crack when bent outward 180°, and no crack when bent inward 180°.

[0091] Similar to the description of the above stainless steel plate, the chemical compositions of the two carbon steel billets can be the same or different. Only one of the two carbon steel billets can adopt the chemical composition provided by the above preferred solution, or both can adopt or neither can adopt the chemical composition provided by the above preferred solution.

[0092] As a preferred solution, the penetration depth of the surface scale and the depth of the surface pits of the carbon steel billet are both ≤ 0.3mm, and the flatness is ≤ 3mm / m; the surface of the stainless steel billet has no scratches, and the flatness is ≤ 2mm / m. In this way, it is avoided that the billet enters the production line of the composite plate with obvious surface defects or shape defects.

[0093] Next, regarding the step of "surface-treating at least one surface of each of the two substrates and the two claddings", that is, the billet surface treatment step. The present invention provides five preferred embodiments, and the following will introduce these five embodiments respectively.

[0094] <The first embodiment of the billet surface treatment step>

[0095] In this embodiment, one surface of each substrate and each cladding is ground and polished to remove the surface scale and expose the metallic luster.

[0096] See Figure 1aAs shown, for example, for the surface p1a of the base material 11a, a grinding wheel, a belt sander or a milling machine is used for grinding and polishing to remove the surface scale and expose the metallic luster. Similarly, for the surface p2a of the prepared base material 12a, a grinding wheel, a belt sander or a milling machine is used for grinding and polishing to remove the surface scale and expose the metallic luster.

[0097] For the surface p3a of the prepared composite material 21a, a wire wheel is used for grinding and polishing to remove the surface scale and expose the metallic luster. Similarly, for the surface p4a of the prepared composite material 22a, a wire wheel is used for grinding and polishing to remove the surface scale and expose the metallic luster.

[0098] As can be seen from the following text, during blank assembly, the surfaces that have undergone surface treatment (grinding and polishing in this embodiment) are used as the surfaces where the base material and the composite material are in contact with each other. For example, the surface p1a and the surface p3a are in contact with each other, and the surface p4a and the surface p2a are in contact with each other. In this way, the interface bonding quality can be ensured.

[0099] <The second embodiment of the blank surface treatment step>

[0100] In this embodiment, the same as the aforementioned first embodiment, one surface of each composite material (for example Figure 1b the surface p3b of the composite material 21b and the surface p4b of the composite material 22b in the text) is ground and polished to remove the surface scale and expose the metallic luster, which will not be elaborated here.

[0101] In this embodiment, different from the aforementioned first embodiment, the surface treatment of the base material is as follows:

[0102] Refer Figure 1b to, the surface p1b of the base material 11b is milled to process the surface p1b into a surface p1b0, which is a transverse inclined surface with a length L11 = L1 and a width W11 > W1. Correspondingly, the base material 11b is processed into a non-uniform thickness blank with a gradually changing thickness in the transverse direction (i.e., the width direction). That is to say, after the base material 11b is milled, the height gradually increases from one side to the other side in the width direction.

[0103] Similarly, the surface p2b of the base material 12b is milled to process the surface p2b into a surface p2b0, which is a transverse inclined surface with a length L11 = L1 and a width W11 > W1. Correspondingly, the base material 12b is processed into a non-uniform thickness blank with a gradually changing thickness in the transverse direction.

[0104] Among them, when milling the surface p2b of the base material 12b and the surface p1b of the base material 11b, it is carried out in a complementary relative shape manner, that is, the processed surfaces p2b0 and p1b0 are complementary in shape when facing each other. For example, the transverse inclination angle of the surface p2b0 (e.g., the included angle with the original surface p2b) is equal to the transverse inclination angle of the surface p1b0 (e.g., the included angle with the original surface p1b), so that the upper and lower surfaces of the composite blank can be ensured to be parallel during subsequent blank assembly.

[0105] It can be understood that through the above milling process, the surface oxide scale on the surface p1b of the base material 11b and the surface p2b of the base material 12b can also be removed, revealing the metallic luster.

[0106] Combined with the following text, during blank assembly, by using the surfaces after surface treatment (milling in this embodiment) as the surfaces where the base material and the composite material contact each other, for example, the surface p1b0 and the surface p3b contact each other, and the surface p4b and the surface p2b0 contact each other. Similarly, the interface bonding quality can be ensured as in the aforementioned first embodiment, and this embodiment can further be used to prepare a non-uniform thickness composite plate with a gradually changing transverse thickness to improve the applicable scenarios and scope of the composite plate.

[0107] <The third embodiment of the blank surface treatment step>

[0108] This embodiment is basically the same as the aforementioned second embodiment (including the surface treatment of the surfaces p3c and p4c), and the only difference is that: the thickness of the base material gradually changes in the transverse direction in the second embodiment, while the thickness of the base material gradually changes in the longitudinal direction (i.e., the length direction) in this embodiment. The differences are introduced below, and the other similarities are referred to the introduction of the second embodiment and will not be elaborated.

[0109] Refer to Figure 1c , the surface p1c of the base material 11c is milled to process the surface p1c into a surface p1c0, which is a longitudinally inclined surface with a length L11 > L1 and a width W11 = W1. Correspondingly, the base material 11c is processed into a non-uniform thickness blank with a gradually changing thickness in the longitudinal direction.

[0110] Similarly, the surface p2c of the base material 12c is milled to process the surface p2c into a surface p2c0, which is a longitudinally inclined surface with a length L11 > L1 and a width W11 = W1. Correspondingly, the base material 12c is processed into a non-uniform thickness blank with a gradually changing thickness in the longitudinal direction.

[0111] Among them, when milling the surface p2c of the base material 12c and the surface p1c of the base material 11c, it is carried out in a manner of complementary relative shapes, that is, the processed surfaces p2c0 and p1c0 are shape-complementary when facing each other. For example, the longitudinal inclination angle of the surface p2c0 (such as the included angle with the original surface p2c) is equal to the longitudinal inclination angle of the surface p1c0 (such as the included angle with the original surface p1c), so that the upper and lower surfaces of the composite blank can be guaranteed to be parallel during subsequent blank assembly.

[0112] It can be understood that through the above milling process, the surface oxide scale on the surface p1c of the base material 11c and the surface p2c of the base material 12c can also be removed, revealing the metallic luster.

[0113] <The fourth implementation mode of the blank surface treatment step>

[0114] In this implementation mode, one surface of each base material is milled, and the said surface is processed into an irregular concave-convex surface including n planes connected in sequence along the transverse direction, and the base material is a non-uniform-thickness blank with non-monotonic thickness change in the transverse direction, and the length L12 of the irregular surface = L1 and the total width W12 > W1.

[0115] For example, refer Figure 1d , when milling the surface p1d of the base material 11d, the surface p1d is processed from Figure 1d the horizontal surface in (A) into Figure 1d the irregular concave-convex surface p1d0 shown in (B). The irregular concave-convex surface p1d0 specifically includes n planes connected in sequence along the transverse direction, where n≥2, and is exemplified as 8 planes in the figure. It can be seen from the figure that the 1st, 3rd, 5th, and 7th of these 8 planes in the direction from the left to the right of the figure are all transverse inclined surfaces, while the 2nd, 4th, 6th, and 8th are all horizontal planes. Of course, this is only an example, and it can also be implemented with other values of n, or only including transverse inclined surfaces without horizontal planes, etc.

[0116] Refer Figure 1d , through the milling process of the surface p1d, the base material 11d is processed into a non-uniform-thickness blank with non-monotonic thickness change in the transverse direction.

[0117] The length L12 of the irregular concave-convex surface p1d0 = L1, that is, it does not change due to the milling process; while the total width W12 of the irregular concave-convex surface p1d0 > W1. It can be understood that the total width W12 is the sum of the widths of n planes.

[0118] Correspondingly, refer Figure 1d , when milling the surface p2d of the base material 12d, the surface p2d is also processed from Figure 1d the horizontal surface in (A) into Figure 1dThe irregular concave-convex surface p2d0 shown in (B). When milling the surfaces p2d of the substrate 12d and p1d of the substrate 11d, it is carried out in a manner of complementary relative shapes, that is, when the processed surfaces p2d0 and p1d0 face each other, they are shape-complementary.

[0119] According to the complementary relative shapes, the irregular concave-convex surface p2d0 specifically also includes n planes connected in sequence along the transverse direction, which are exemplified as 8 planes in the figure. The length L12 of the irregular concave-convex surface p2d0 = L1, that is, it does not change due to the milling process; while the total width W12 of the irregular concave-convex surface p2d0 > W1. It can be understood that the total width W12 is the sum of the widths of the n planes of the irregular concave-convex surface p2d0.

[0120] Refer Figure 1d , through the milling process of the surface p2d, the substrate 12d is processed into a non-uniform thickness blank with non-monotonic thickness change in the transverse direction. Based on the complementary relative shapes of the irregular concave-convex surface p2d0 and the irregular concave-convex surface p1d0, if the milled substrates 12d and 11d are placed opposite to each other, the sum of the thicknesses at each place is constant. Thus, when assembling the blanks subsequently, the upper and lower surfaces of the composite blank are parallel.

[0121] The above introduced the surface treatment of two substrates in this embodiment. Next, the surface treatment of two composite materials will be introduced.

[0122] In this embodiment, for the surface p3d of the prepared composite material 21d, a wire wheel is used for grinding and polishing to remove the surface scale and expose the metallic luster; similarly, for the surface p4d of the prepared composite material 22d, a wire wheel is used for grinding and polishing to remove the surface scale and expose the metallic luster.

[0123] And further, matching the surface shapes of the substrates 11d and 12d, after removing the surface scale, each composite material in this embodiment is also bent so that each composite material matches the corresponding irregular concave-convex surface. For example, for the composite material 21d, it is bent to match the corresponding irregular concave-convex surface p1d0 for easy fitting contact during subsequent blank assembly; for another example, for the composite material 22d, it is bent to match the corresponding irregular concave-convex surface p2d0 for easy fitting contact during subsequent blank assembly.

[0124] The surface treatment of this embodiment can ensure the interface bonding quality as in the aforementioned first embodiment, and can further be used to prepare a non-uniform thickness composite plate with non-monotonic thickness change in the transverse direction, so as to expand the applicable scenarios and scope of the composite plate, enhance the corrosion resistance compared with the existing steel plates, and avoid frequent welding and dissimilar welding between composite plates with different thicknesses.

[0125] <The Fifth Embodiment of the Blank Surface Treatment Step>

[0126] The difference between this embodiment and the aforementioned fourth embodiment is that the thickness of the substrate in the fourth embodiment changes non-monotonically in the transverse direction, while in this embodiment, the thickness of the substrate changes non-monotonically in the longitudinal direction.

[0127] For example, referring to Figure 1e , the surface p1e of the substrate 11e is milled, and the surface p1e is processed from the Figure 1e horizontal surface in (A) into the Figure 1e irregular concave-convex surface p1e0 shown in (B). The irregular concave-convex surface p1e0 specifically includes n planes connected in sequence along the longitudinal direction, where n≥2, and is exemplified as 8 planes in the figure. It can be seen from the figure that the 1st, 3rd, 5th, and 7th of these 8 planes in the direction from the left side to the right side of the figure are longitudinally inclined surfaces, while the 2nd, 4th, 6th, and 8th are horizontal surfaces. Of course, this is only an example, and it can also be implemented with n taking other numbers, or only including longitudinally inclined surfaces without horizontal surfaces, etc.

[0128] Referring to Figure 1e , through the milling of the surface p1e, the substrate 11e is processed into a non-uniform-thickness blank with non-monotonic thickness change in the longitudinal direction.

[0129] The width W12 of the irregular concave-convex surface p1e0 = W1, that is, it does not change due to the milling process; while the total length L12 of the irregular concave-convex surface p1e0 > L1. It can be understood that the total length L12 is the sum of the lengths of n planes.

[0130] Correspondingly, referring to Figure 1e , the surface p2e of the substrate 12e is also milled, and the surface p2e is processed from the Figure 1e horizontal surface in (A) into the Figure 1e irregular concave-convex surface p2e0 shown in (B). Among them, when milling the surface p2e of the substrate 12e and the surface p1e of the substrate 11e, it is carried out in a relatively shape-complementary manner, that is, the processed surface p2e0 and surface p1e0 are shape-complementary when they face each other.

[0131] According to the relative shape complementarity, the irregular concave-convex surface p2e0 also specifically includes n planes connected in sequence along the longitudinal direction, and is exemplified as 8 planes in the figure. The width W12 of the irregular concave-convex surface p2e0 = W1, and the total length L12 > L1.

[0132] Referring to Figure 1e, through the milling process on the surface p2e, the substrate 12e is processed into an unequal-thickness blank with a non-monotonic change in thickness longitudinally. Based on the relative shape complementarity of the irregular concave-convex surface p2e0 and the irregular concave-convex surface p1e0, if the milled substrates 12e and 11e are placed opposite to each other, the sum of the thicknesses at each place of the two is constant. Thus, when assembling the blanks subsequently, the upper and lower surfaces of the composite blank are parallel.

[0133] The above introduced the surface treatment of the two substrates in this embodiment. Next, the surface treatment of the two composite materials will be introduced.

[0134] In this embodiment, for the surface p3e of the prepared composite material 21e, a wire brush wheel is used for grinding and polishing to remove the surface scale and expose the metallic luster; similarly, for the surface p4e of the prepared composite material 22e, a wire brush wheel is used for grinding and polishing to remove the surface scale and expose the metallic luster.

[0135] And further, matching the surface shapes of the substrates 11e and 12e, after removing the surface scale, each composite material in this embodiment is bent so that each composite material matches the corresponding irregular concave-convex surface. For example, for the composite material 21e, it is bent to match the corresponding irregular concave-convex surface p1e0 to facilitate the fitting contact during subsequent blank assembly; for another example, for the composite material 22e, it is bent to match the corresponding irregular concave-convex surface p2e0 to facilitate the fitting contact during subsequent blank assembly.

[0136] The same as the aforementioned fourth embodiment, this embodiment can also improve the applicable scenarios and scope of the composite board, enhance the corrosion resistance compared with the existing steel plates, and avoid frequent welding and dissimilar welding between composite boards of different thicknesses.

[0137] The above introduced five preferred embodiments of the surface treatment of the blank in the composite blank preparation steps. Although only one surface of each of the substrate and the composite material is described for surface treatment, it should be noted that regardless of which of the above five embodiments, the other surfaces of each substrate and composite material can be further treated to remove the scale. Although this additional scale removal treatment is not necessary to achieve the technical effects of the present invention, it may be more optimal; for example, in addition to removing the scale from the surface of the substrate facing the side where the composite material is located, the surface of the substrate facing away from the side where the composite material is located (i.e., the surface of the composite board) can also be treated to remove the scale.

[0138] Next, the other sub-steps of the composite blank preparation step will be continued to be introduced.

[0139] The step of "coating a release agent on one surface of a composite material", that is, the step of coating the release agent.

[0140] Among them, as can be seen from the foregoing, in the previous blank surface treatment step, surface treatments such as grinding and polishing are performed on the surface of the composite material that will come into contact with the base material during blank assembly to ensure the interfacial bonding quality of the composite board; the purpose of this step of applying the release agent is to avoid, through the release agent, the surfaces of the composite materials that come into contact with each other during blank assembly from bonding during the subsequent composite blank rolling step, making it difficult to separate them finally.

[0141] Based on this, select any one of the two composite materials to apply the release agent. If, in the previous blank surface treatment step, one surface of the selected composite material has undergone surface treatment while the other has not, then in this step of applying the release agent, the release agent is applied to the surface that "has not undergone surface treatment". And if, as mentioned above, both surfaces of the selected composite material have undergone surface treatment in the previous blank surface treatment step, then in this step of applying the release agent, the release agent is applied to the surface that is planned to face the other composite material during blank assembly.

[0142] For example, taking Figure 1a as an example, the release agent can be applied to the surface p6a of the composite material 22a or the surface p5a of the composite material 21a.

[0143] Regarding the release agent, two preferred implementation methods are provided here and will be introduced separately below.

[0144] <The first implementation method of the release agent>

[0145] In this implementation method, 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 implementation method can achieve a good release effect and ensure the separation of the subsequent two small composite boards.

[0146] Here, a preparation method of the release agent is provided, which is: mixing the release agent powder, binder powder and water in a mass ratio of 27:3:70 to obtain a fluid release agent coating solution. Among them, the release agent powder is silicon oxide and magnesium oxide, mixed in a mass ratio of 3:1. The binder powder is polyvinyl alcohol and thermosetting phenolic resin, mixed in a mass ratio of 1:1.

[0147] When using the release agent to apply it on the surface of the composite material, the amount of the release agent applied is 20ymg / m 2 , that is, the weight of the release agent per unit area of the surface of the composite material is 20ymg. Among them, 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 rolled subsequently, and this ratio is also called the composite blank rolling compression ratio.

[0148] Further, based on this embodiment, after the release agent is applied and before subsequent blank assembly, the composite material coated 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 - 45 min.

[0149] <The second embodiment of the release agent>

[0150] 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 with the existing release agent, and even compared with the first embodiment of the foregoing release agent, the release agent of this embodiment can not only achieve a good isolation effect and ensure the separation of the subsequent two small composite boards, but also the active ingredient silicon nitride has strong chemical stability, high temperature resistance, and heat shock resistance. 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 very small amount. Therefore, as a whole, it has a low price, simple operation, and good isolation and adhesion effects.

[0151] 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, and 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 - 5 min, and then pour in the remaining thermosetting amino resin; when it is stirred to a viscous state, the release agent is prepared.

[0152] When using the release agent and applying it on the surface of the composite material, the thickness of the applied release agent is 0.2 - 0.5 mm.

[0153] Further, based on this embodiment, after the release agent is applied 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 min.

[0154] Next, after the step of applying the release agent is completed, the step of "assembling the blanks in the stacking order of substrate, composite material, composite material, substrate" is introduced.

[0155] This step of "assembling the blanks in the stacking order of substrate, composite material, composite material, substrate" is also 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:

[0156] 1) The surfaces of the substrate and the composite material in contact with each other are all surfaces that have undergone the surface treatment; for example, in the first embodiment of the blank surface treatment step described above, refer Figure 2a, 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; in the second embodiment of the blank surface treatment step described above, refer to Figure 2b , the surface p1b0 and the surface p3b are in contact with each other, and the surface p4b and the surface p2b0 are in contact with each other; in the third embodiment of the blank surface treatment step described above, refer to Figure 2c , the surface p1c of the base material 11c and the surface p3c of the composite material 21c are in contact with each other, and the surface p2c of the base material 12c and the surface p4c of the composite material 22c are in contact with each other; in the fourth embodiment of the blank surface treatment step described above, refer to Figure 2d , the irregular uneven surface p1d0 and the surface p3d of the composite material 21d are in contact with each other, and the irregular uneven surface p2d0 and the surface p4d of the composite material 22d are in contact with each other; in the fifth embodiment of the blank surface treatment step described above, refer to Figure 2e , the irregular uneven surface p1e0 and the surface p3e of the composite material 21e are in contact with each other, and the irregular uneven surface p2e0 and the surface p4e of the composite material 22e are in contact with each other;

[0157] 2) The surface coated with the release agent faces another composite material; for example, refer to Figure 2a , one of the surfaces p6a and p5a is coated with the release agent 30a; refer to Figure 2b , one of the surfaces p6b and p5b is coated with the release agent 30b; refer to Figure 2c , one of the surfaces p6c and p5c is coated with the release agent 30c; refer to Figure 2d , one of the surfaces p6d and p5d is coated with the release agent 30d; refer to Figure 2e , one of the surfaces p6e and p5e is coated with the release agent 30e;

[0158] 3) The composite material is placed centered relative to the base material; in this regard, it was introduced above that both the length and width dimensions of the composite material are smaller than those of the base material, L2 < L1, W2 < W1. When assembling the blank, the distances from the two lateral sides of the composite material to the corresponding two lateral sides of the base material are equal, and the distances from the two longitudinal sides of the composite material to the corresponding two longitudinal sides of the base material are also equal.

[0159] Next, the third point here will be described separately for the five embodiments of the blank surface treatment step described above. And, in view of the fact that the composite blank is generally symmetrically arranged up and down, only one set of base material + composite material in the composite blank will be taken as an example for illustration, such as the upper set.

[0160] For the first embodiment of the blank surface treatment step described above, refer to Figure 2a, the length L1 and width W1 of the surface p1a of the base material 11a, the length L2 and width W2 of the surface p3a of the composite material 21a, L2 = L1 - L0, W2 = W1 - W0, and the preferably value ranges of L0 and W0 are 90 to 150 mm respectively; in the blank forming 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) is half of W0, and the distance from the longitudinal side of the composite material 21a (corresponding to the short side of the surface p3a) to the longitudinal side of the base material 11a (corresponding to the short side of the surface p1a) is half of L0.

[0161] For the second implementation manner of the blank surface treatment step described above, refer Figure 2b , the length L11 and width W11 of the surface p1b0 of the base material 11b, the length L2 and width W2 of the surface p3b of the composite material 21b, L2 = L11 - L0, W2 = W11 - W0, and the preferably value ranges of L0 and W0 are 90 to 150 mm respectively; in the blank forming state, the distance from the lateral side of the composite material 21b (corresponding to the long side of the surface p3b) to the lateral side of the base material 11b (corresponding to the long side of the surface p1b0) is half of W0, and the distance from the longitudinal side of the composite material 21b (corresponding to the short side of the surface p3b) to the longitudinal side of the base material 11b (corresponding to the short side of the surface p1b0) is half of L0.

[0162] For the third implementation manner of the blank surface treatment step described above, refer Figure 2c , the length L11 and width W11 of the surface p1c0 of the base material 11c, the length L2 and width W2 of the surface p3c of the composite material 21c, L2 = L11 - L0, W2 = W11 - W0, and the preferably value ranges of L0 and W0 are 90 to 150 mm respectively; in the blank forming state, the distance from the lateral side of the composite material 21c (corresponding to the long side of the surface p3c) to the lateral side of the base material 11c (corresponding to the long side of the surface p1c0) is half of W0, and the distance from the longitudinal side of the composite material 21c (corresponding to the short side of the surface p3c) to the longitudinal side of the base material 11c (corresponding to the short side of the surface p1c0) is half of L0.

[0163] For the fourth implementation manner of the blank surface treatment step described above, refer Figure 2d, the length L12 and width W12 of the irregular uneven surface p1d0 of the base material 11d, the length L2 and width W2 of the surface p3d of the composite material 21d, L2 = L12 - L0, W2 = W12 - W0, and the preferably value ranges of L0 and W0 are 90 - 150 mm respectively; in the billet forming state, the distance from the lateral side of the composite material 21d (corresponding to the long side of the surface p3d) to the lateral side of the base material 11d (corresponding to the long side of the irregular uneven surface p1d0) is half of W0, and the distance from the longitudinal side of the composite material 21d (corresponding to the short side of the surface p3d) to the longitudinal side of the base material 11d (corresponding to the short side of the irregular uneven surface p1d0) is half of L0.

[0164] For the fifth implementation manner of the billet surface treatment step described above, refer Figure 2e , the length L12 and width W12 of the irregular uneven surface p1e0 of the base material 11e, the length L2 and width W2 of the surface p3e of the composite material 21e, L2 = L12 - L0, W2 = W12 - W0, and the preferably value ranges of L0 and W0 are 90 - 150 mm respectively; in the billet forming state, the distance from the lateral side of the composite material 21e (corresponding to the long side of the surface p3e) to the lateral side of the base material 11e (corresponding to the long side of the irregular uneven surface p1e0) is half of W0, and the distance from the longitudinal side of the composite material 21e (corresponding to the short side of the surface p3e) to the longitudinal side of the base material 11e (corresponding to the short side of the irregular uneven surface p1e0) is half of L0.

[0165] The above introduction of the billet forming step is as follows. In a preferred implementation manner, after implementing the billet forming step, the stacked four billets 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, and the pressure ≥ 500 tons. Thus, the adjacent billets can be in closer contact.

[0166] Furthermore, in the step of "preparing four seals with width W3, attaching the seals to the four side edges of the two composite materials, and performing gas shielded welding between adjacent seals and between the seals and the base materials, so that the two base materials and the seals form an integral body to obtain a composite billet base billet", based on the setting of the seals, the four stacked billets are connected to form an integral composite billet base billet. Specifically, the composite billet base billet is formed as follows: two base materials form the upper and lower surfaces, two composite materials are located in the middle, and four seals form four side frames surrounding the two composite materials and connecting the two base materials. Here, Figures 2a - 2e , the seals are respectively labeled as 40a, 40b, 40c, 40d and 40e.

[0167] The width W3 of the seal strip is 2T2 - (1 - 2) mm, that is, the width of the seal strip is slightly smaller than the sum of the thicknesses of the two composite materials by 1 - 2 mm. The seal strip with this width is used to wrap the upper and lower composite materials simultaneously to improve the wrapping effect.

[0168] Furthermore, among the four seal strips, two seal strips are respectively attached to the two lateral sides of the two composite materials, and the length L31 = L2 - (1 - 2) mm; the other two seal strips are respectively attached to the two longitudinal sides of the two composite materials, and the length L32 = W2 - (1 - 2) mm.

[0169] Preferably, the thickness T3 of the seal strip is 12 - 15 mm.

[0170] Regarding the forming method of each seal strip, 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 seal strips with different lengths. For example, the seal strips at the two longitudinal sides of the two composite materials in the fourth implementation manner of the blank surface treatment step described above, and the seal strips at the two lateral sides of the two composite materials in the fifth implementation manner of the blank surface treatment step described above.

[0171] Furthermore, the seal strip uses the same steel type as the base material. Preferably, the material of the seal strip is the same as that of the base material, and its chemical composition in mass percentage is: C: 0.12 - 0.16%, Si: 0.21 - 0.29%, Mn: 1.31 - 1.39%, P ≤ 0.018%, S ≤ 0.0030%, Cr: 0.06 - 0.14%, Nb: 0.011 - 0.019%, Ti: 0.011 - 0.019%, Al: 0.030 - 0.040%, and the rest are Fe and unavoidable impurities.

[0172] As a preferred implementation manner, in this step, before performing gas shielded welding between adjacent seal strips and between the seal strip and the base material, the seal strip is preheated using a hot air gun or electric heating cotton, etc., and the preheating temperature is 120 - 200 °C. The two ends and two sides of each seal strip 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 strip can be beveled first.

[0173] Furthermore, as a preferred implementation manner, in the step of "performing gas shielded welding between adjacent seal strips and between the seal strip and the base material", the welding current is 235 - 265 A, the welding voltage is 25 - 29 V, the welding speed is 300 - 360 mm / min, and the interpass temperature during the welding process is controlled at 135 - 165 °C.

[0174] Optionally, in the gas shielded arc welding, the welding wire is GMR-65, the diameter of the welding wire is 1.2 mm, and the shielding gas is 75-80% Ar + 20-25% CO2 by volume percentage.

[0175] Next, for the step of "processing a round hole on the seal at the groove on the side of the composite blank base blank and welding a seamless steel pipe at the round hole", the groove mentioned above is the groove formed between 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 the subsequent evacuation of the inside of the composite blank.

[0176] 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 blank base blank, but it is not limited thereto.

[0177] 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.

[0178] Next, for the step of "performing submerged arc surfacing on the grooves on the four sides of the composite blank base blank", submerged arc surfacing is specifically adopted. Optionally, the submerged arc welding wire is GWR-WEF3, the submerged arc welding flux is GXL-105Q, and the diameter of the welding wire is 4.0 mm. It can be understood that outside the four-sided frame formed by the seal, a four-sided frame-shaped filling layer is formed through the surfacing of this step. See Figures 2a - 2e , where the filling layers formed by the surfacing are respectively marked as 50a, 50b, 50c, 50d and 50e.

[0179] As a preferred method, before welding, the welding flux is baked at 350 °C for 2 h and then kept warm at 150 °C for 1 h; during the welding process, the interpass temperature is controlled at 135-165 °C, the welding current is 620-680 A, the welding voltage is 28-32 V, and the welding speed is 420-480 mm / min. In this way, this submerged arc surfacing technology, combined with the previous seal wrapping and gas shielded arc welding, jointly realizes the stable connection of the four steel blanks, ensures the connection strength, avoids abnormal cracking in the subsequent rolling step of the composite blank, and further improves the interface bonding effect on the basis of realizing the quality advantages of the composite plate described above.

[0180] In addition, during the welding process, before each welding construction, the attachments on the weld bead need to be cleaned to keep the weld bead clean; after welding, it is covered with heat preservation cotton for heat preservation.

[0181] Next, for the step of "using a vacuum pump to evacuate the composite blank through this seamless steel pipe, the vacuum degree

[0182] ≤10 -1After Pa, hold the pressure for more than 4 hours; finally, seal the seamless steel pipe." In this process, connect the suction port of the vacuum pump to the seamless steel pipe, and the seamless steel pipe is connected to the space inside the composite blank (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, etc.) to exhaust the air in this space until the vacuum degree ≤ 10 -1 Pa, and holding the pressure for more than 4 hours can ensure the vacuum degree. In this way, the air in this space can be avoided from causing surface oxidation at the composite interface during the subsequent rolling of the composite blank, thereby ensuring the bonding quality of the composite interface.

[0183] Furthermore, in this step, the seamless steel pipe can be sealed by existing feasible methods in the steel industry. For example, heat the seamless steel pipe with a flame gun and flatten it to achieve sealing.

[0184] The above has described the total steps of preparing the composite blank in detail. As mentioned above, the preparation method of the present invention further includes the total steps of rolling the composite blank after the total steps of preparing the composite blank. Specifically, the total steps of rolling the composite blank include the following sub-steps:

[0185] Heat the obtained composite blank, with the soaking temperature being 1170 - 1220 °C, and the total heating time ≥ 1.2 × t min / mm, where t is the thickness of the composite blank;

[0186] Adopt two-stage controlled rolling of rough rolling + finish rolling. In the rough rolling stage, the final rolling temperature ≥ 1000 °C, and end the rough rolling stage when the thickness of the intermediate billet reaches 2.5 - 3.5 times the target thickness of the large plate of the composite plate; then wait for the temperature, and during this period, carry out water cooling. When the surface temperature of the intermediate billet drops below 840 °C, start the finish rolling stage, and the final rolling temperature in the finish rolling stage ≥ 780 °C;

[0187] Cool after rolling to obtain the large plate of the composite plate.

[0188] In the total steps of rolling the composite blank, by controlling parameters such as the heating temperature, heating duration, holding duration, various temperatures during rolling, reduction, temperature during cooling, and cooling rate, not only can it be ensured that the structure of the base layer of the finally obtained composite plate is bainite + a small amount of ferrite structure, and it has excellent mechanical properties, including yield strength ≥ 500 MPa, tensile strength ≥ 630 MPa, elongation after fracture ≥ 18%, yield ratio ≤ 0.86, but also excellent surface quality, plate shape, and interface bonding quality can be obtained. Especially in combination with the chemical composition of the carbon steel plate described above, it achieves a significant further improvement in mechanical properties.

[0189] As a further improvement to the above general steps of compound billet rolling, the present invention provides four specific embodiments of the general steps of compound billet rolling, and any of these four embodiments can be combined with any embodiment of the previous compound billet preparation steps and the subsequent compound plate separation and straightening steps.

[0190] <The first embodiment of the compound billet rolling step>

[0191] In this embodiment, referring Figure 4a , the compound billet rolling step specifically includes the following sub-steps:

[0192] Heat the obtained compound billet, with the soaking temperature being 1200 - 1220°C, the total heating time ≥ 1.2 × tmin / mm (where t is the thickness of the compound billet), and the soaking section holding time being 30 - 50 minutes;

[0193] 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 per pass in at least one pass ≥ 35 mm, the total rough rolling reduction being 40 - 60%, and end the rough rolling stage when the thickness of the intermediate billet reaches 2.5 - 3.5 times the target thickness of the large plate of the compound plate; then wait for temperature, and during this period, carry out water cooling. When the surface temperature of the intermediate billet drops below 830°C, start the finish rolling stage; the finishing rolling temperature in the finish rolling stage ≥ 800°C, and the total finish rolling reduction being 55 - 75%;

[0194] After rolling, the large plate of the compound plate enters the ultra-fast cooling system for cooling, with the starting cooling temperature ≥ 730°C, the cooling rate being 10 - 20°C / s, and the final cooling temperature being 480 - 500°C; after the large plate of the compound plate leaves the ultra-fast cooling system, directly enter the straightening machine for straightening 1 - 3 passes, and after straightening, go to the cooling bed for natural cooling. When the surface temperature drops below 200°C, use the cold straightening machine for cold straightening.

[0195] <The second embodiment of the compound billet rolling step>

[0196] This embodiment is the same as the first embodiment of the above compound billet rolling step in sub-steps such as heating and two-stage controlled rolling, and the difference lies only in: cooling and subsequent steps.

[0197] Specifically, in this embodiment, referring Figure 4b , the large plate of the compound plate undergoes intermittent cooling on the ultra-fast cooling system as follows:

[0198] 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 large composite plate passes through the ultra-fast cooling system, the opening and closing states of all 24 groups of cooling manifolds are controlled in a manner of opening N groups of cooling manifolds and then not opening M groups of cooling manifolds. The cooling water pressure is 0.2MPa, the cooling speed is 3-15°C / s, and the final cooling temperature is 380-450°C.

[0199] For example, when a large composite panel passes through the ultra-fast cooling system, it is controlled in a manner of opening 4 groups of cooling manifolds at a time and then closing 3 groups of cooling manifolds, 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.

[0200] Compared with the prior art, this embodiment adopts the intermittent cooling method. When the composite plate passes through the ultra-fast cooling system, it moves in the alternating opening and closing of the cooling manifold. In this way, each part of the composite plate will be cooled, turned red, cooled, turned red... and so on, until the composite plate leaves the ultra-fast cooling system. In the cooling-turning red cycle of the composite plate, the carbon steel substrate continuously undergoes phase change and self-tempering effect, and the phase change reaction gradually penetrates into the core until the entire carbon steel substrate completes the phase change. The intermittent cooling process is different from the conventional reciprocating cooling. The reciprocating cooling reddening and self-tempering occur after the surface or near-surface has completed the phase change. The temperature difference or cooling rate between the surface and the core is quite different, and the organization and mechanical properties are also quite different. The intermittent cooling process of this embodiment is that at the same time, some parts of the composite plate are in a cooling state and some parts are in a reddening / self-tempering state. Moreover, each part of the composite plate is alternately cooled and reddened / self-tempered over time, so that the temperature, cooling rate, organization, performance, etc. of the surface and the core of the plate are relatively small. For example, the Vickers hardness difference of the base layer of the final composite plate in the thickness direction is ≤10, the head-middle-tail strength difference is ≤40MPa, and the strength difference of the whole plate is ≤40MPa. Furthermore, the plate shape of the composite plate can be further improved, that is, the unevenness is low.

[0201] In this embodiment, 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.

[0202] <Third Embodiment of Composite Billet Rolling Step>

[0203] In this embodiment, Figure 4c, the specific steps of rolling the composite billet include the following sub-steps:

[0204] Adopt five-stage heating of preheating, first heating, second heating, third heating and soaking. The preheating temperature is ≤850°C, and the residence time is (0.45 - 0.55)t min / 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)t min / mm;

[0205] Adopt two-stage controlled rolling of rough rolling + finish rolling. In the rough rolling stage, the first pass uses longitudinal rolling, and the rolling reduction is ≥46mm; starting from the second pass, transverse rolling is used until the composite billet is rolled to the target width of the final composite plate at the nth pass. The rolling reduction of the second pass is ≥25mm; starting from the (n + 1)th pass, longitudinal rolling is used, 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 of the (n + 1)th pass is ≥30mm; throughout 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, and the finishing rolling temperature is ≥1000°C; after the rough rolling stage, wait for the temperature, and during this period, water cooling is carried out. 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°C - 810°C;

[0206] Adopt an ultra-fast cooling system for intermittent cooling. The specific process of intermittent cooling is the same as the second implementation mode of the aforementioned composite billet rolling steps, and will not be elaborated here;

[0207] After the large plate of the composite plate leaves the ultra-fast cooling system, the large plate of the composite plate is naturally cooled to room temperature on the cooling bed. Thus, the rolling of the composite billet in step 2) is completed and enters step 3) composite plate separation and straightening.

[0208] In summary, the difference between this implementation mode and the second implementation mode of the aforementioned composite billet rolling steps lies in the two processes of heating and rolling.

[0209] Among them, the heating process of this implementation mode can better control the heating rate of the composite billet in each section, ensure uniform heating of the billet, avoid cracking and air leakage of the composite billet due to the difference in thermal properties of the substrate and clad material of the composite billet, and thus can ensure the interface bonding effect.

[0210] In the rolling process of this embodiment, in rough rolling, longitudinal rolling is first carried out, then transverse rolling, and then longitudinal rolling again, which can ensure the realization of large reduction rolling, effectively penetrate the core of the composite billet, promote core deformation, and ensure the bonding rate of the composite interface; during the waiting temperature period, an immediate cooling device is used for cooling, reducing the waiting temperature time, improving the rolling efficiency, and at the same time, avoiding excessive waiting temperature time and the growth of carbon steel base material grains; the temperature control in the finish rolling stage can refine the grains and ensure that the thick composite plate has good low-temperature impact toughness. For example, the impact energy at 0 °C of the finally obtained composite plate is ≥240 J, the impact energy at -20 °C is ≥200 J, and the impact energy at -40 °C is ≥150 J.

[0211] Of course, since this embodiment also adopts intermittent cooling, it correspondingly has the beneficial effects brought by the intermittent cooling process, and reference can be made to the introduction of the second embodiment of the composite billet rolling step in the previous text.

[0212] <The fourth embodiment of the composite billet rolling step>

[0213] This embodiment refers to Figure 4d and is the same as the first embodiment of the foregoing composite billet rolling step in steps such as heating, two-stage controlled rolling, and cooling, with the difference only lying in the steps after the large composite plate leaves the ultra-rapid cooling system.

[0214] Specifically, after the large composite plate leaves the ultra-rapid cooling system, it directly enters the straightening machine for straightening 1 to 3 passes. Different from the first embodiment of the foregoing composite billet rolling step, in this embodiment, afterwards, the large composite plate is placed between two steel plates with a temperature of T f -150 °C to T f -50 °C for stacking and cooling. The stacking and cooling time is 0.4 min / mm × t0 ± 5 min, where t0 is the thickness of the large composite plate, so that the large composite plate can slowly cool down during this stacking and cooling time and can be clamped by the steel plates to maintain the temperature uniformity of the core and surface; after the stacking and cooling is completed, the large composite plate is placed on the cooling bed for natural cooling. Among them,

[0215] 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 embodiment, the stacking and cooling, especially the temperature of the two steel plates during stacking and cooling and the stacking and cooling time, can further improve the microstructure, properties, and plate shape of the finally obtained composite plate compared with the first embodiment.

[0216] As described above, this embodiment is a variant implementation of the "steps after the large composite plate leaves the ultra-rapid cooling system" in the first embodiment of the foregoing composite billet rolling steps. Similarly, the "steps after the large composite plate leaves the ultra-rapid cooling system" in the second and third embodiments of the foregoing composite billet rolling steps can also be varied to the technology provided in this embodiment (including straightening, stacking cooling, and natural cooling on the cooling bed). For example, refer to Figure 4e , 4f which respectively illustrate the fifth and sixth embodiments, so as to further improve the microstructure, properties, and shape of the composite plate.

[0217] The above has described in detail the overall steps of the composite billet rolling. As mentioned before, the preparation method of the present invention further includes the overall steps of composite plate separation and straightening. Specifically, the overall steps of the composite plate separation and straightening include the following sub-steps:

[0218] For the large composite plate obtained from the overall steps of the previous composite billet rolling, use a plasma cutting machine to cut its four sides to remove the part outside the seal, and the large composite plate is separated into two small composite plates, the upper and lower ones;

[0219] Perform transverse flattening and cold straightening on the small composite plates to obtain the finished stainless steel composite plate.

[0220] Among them, the part outside the seal in the step of "cutting its four sides to remove the part outside the seal" is the edge part on the large composite plate transformed from the seal and the filling layer in the composite billet mentioned above after the previous composite billet rolling step. In this way, this part is removed to expose the stainless steel clad layer, and in the absence of the connection effect of this part, the large composite plate is separated into two small composite plates, the upper and lower ones. Refer to Figures 3a - 3e , corresponding to the five embodiments of the billet surface treatment step described above, Figures 3a - 3e which respectively show the cross-sectional shapes of the corresponding two small composite plates (i.e., the final composite plates).

[0221] Each small composite plate is composed of a clad layer and a base layer. The clad layer is obtained by rolling the original clad material, and the base layer is obtained by rolling the original base material. In view of this, in Figures 3a - 3e the original clad material label is still marked on the clad layer, and the original base material label is still marked on the base layer.

[0222] Furthermore, for the composite plate obtained by the preparation method of the present invention, the microstructure of the base layer is bainite + a small amount of ferrite structure, with excellent mechanical properties, good interface bonding quality, shape, and surface quality, and strong impact toughness and excellent corrosion resistance.

[0223] In a preferred embodiment, the total thickness of the composite board is 15-39 mm, the thickness of the base layer is 12-36 mm, and the thickness of the composite layer is 3 mm.

[0224] In a preferred embodiment, the yield strength is ≥500 MPa, the tensile strength is ≥630 MPa, the elongation after fracture is ≥18%, and the yield strength ratio is ≤0.86.

[0225] In a preferred embodiment, the Vickers hardness difference of the base layer of the composite board in the thickness direction is ≤10, the head-middle-tail strength difference is ≤40MPa, and the strength difference of the entire board is ≤40MPa.

[0226] In a preferred embodiment, the composite interface bonding rate of the composite plate is 100%, and the shear strength is ≥300 MPa.

[0227] In a preferred embodiment, the composite board has an impact energy of ≥120 J at 0°C, ≥120 J at -20°C, and ≥120 J at -40°C. Even more preferably, the composite board has an impact energy of ≥240 J at 0°C, ≥200 J at -20°C, and ≥150 J at -40°C.

[0228] In a preferred embodiment, the composite plate has no cracks when bent outwards 180° and has no cracks when bent inwards 180°.

[0229] In a preferred embodiment, the composite plate is boiled in a sulfuric acid-copper sulfate solution for 20 hours and bent 180 degrees, and the composite layer has no intergranular corrosion cracks.

[0230] In a preferred embodiment, the unevenness of the composite plate is ≤3 mm / m, and even better, the unevenness of the composite plate thickness is ≤2 mm / m.

[0231] 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. All 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.

[0232] 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 numerous variations of the present invention, but not all of them.

[0233] In these examples, the steel grade Q500q was selected as the base material, and its chemical composition in mass percentage was: C: 0.05%, Si: 0.15%, Mn: 1.5%, P: 0.010%, S: 0.0015%, Cr: 0.25%, Ni: 0.20%, Cu: 0.20%, Mo: 0.20%, Nb: 0.030%, Ti: 0.015%, Al: 0.035%; the 316 stainless steel was selected as the clad material, and its chemical composition in mass percentage was: C: 0.020%, Si: 0.52%, Mn: 1.36%, P: 0.033%, S: 0.003%, Ni: 10.20%, Mo: 2.10%, Cr: 16.20%.

[0234] Here, each example was prepared into a composite billet with a thickness of 266 mm according to the implementation manner provided by the present invention. Among them, the base material thickness type of some examples was "constant thickness", corresponding to the first implementation manner of the blank surface treatment step, while the base material thickness type of another part of the examples was "variable thickness", corresponding to any one of the second to fifth implementation manners of the blank surface treatment step.

[0235] Further, each example was respectively implemented according to Figure 4a the first implementation manner of the composite billet rolling step shown, Figure 4b the second implementation manner of the composite billet rolling step shown, Figure 4c the third implementation manner of the composite billet rolling step shown, Figure 4d the fourth implementation manner of the composite billet rolling step shown, Figure 4b the fifth implementation manner of the composite billet rolling step shown, Figure 4c the sixth implementation manner of the composite billet rolling step shown. Composite plates with a thickness of 38 mm and a clad layer thickness of 3 mm were obtained. Among them: for the single-sided stainless steel composite plate made of the composite billet with a "constant thickness" base material, its thickness was 19 mm and the base layer thickness was 16 mm; while for the single-sided stainless steel composite plate made of the composite billet with a "variable thickness" base material, its thickness was in the range of 15 - 23 mm, and the base layer thickness was in the range of 12 - 20 mm, which was the thickness range from the minimum thickness to the maximum thickness.

[0236] And samples were taken from and tested on the composite plates of these examples, and it was found that:

[0237] 1) The bonding rate of the composite interface was 100%;

[0238] 2) The inside bend of 180° was qualified (no cracks), and the outside bend of 180° was qualified (no cracks);

[0239] 3) After boiling in sulfuric acid - copper sulfate solution for 20 h and 180° bending, there were no intergranular corrosion cracks in the clad layer;

[0240] 4) Yield strength ≥560MPa, tensile strength ≥670MPa, elongation after fracture ≥24% or even

[0241] 26%, yield strength ratio ≤ 0.84;

[0242] 5) Shear strength ≥ 450MPa, for Figure 4c and Figure 4e In the embodiment shown in the figure, the shear strength even reaches 490 MPa.

[0243] 6) Impact energy ≥120J at 0℃, ≥120J at -20℃, ≥120J at -40℃; Figure 4c and Figure 4e The embodiment of "heating 2" (i.e., the five-stage heating disclosed herein) and "rolling 2" (i.e., the longitudinal, transverse, and longitudinal rolling method disclosed herein) shown in the embodiment has an impact energy of ≥240J at 0°C, ≥200J at -20°C, and ≥150J at -40°C;

[0244] 7) Unevenness ≤ 3 mm / m, while for the embodiment using the "intermittent cooling" technology, the unevenness is within 2 mm / m, and for the embodiment using "intermittent cooling" and "pile cooling" at the same time

[0245] In the embodiment of the technology, the unevenness can be reduced to less than 1mm / m;

[0246] 8) In addition, for the embodiments using "intermittent cooling" and "pile cooling" technology at the same time, the measured uniformity is very good. For example, the Vickers hardness difference in the thickness direction of the base layer is ≤10, the strength difference between the head, the middle and the tail is ≤40MPa, and the strength difference at all parts of the whole plate is ≤40MPa.

Claims

1. A preparation method of a 500MPa grade stainless steel composite plate, characterized in that, The chemical composition of the base layer of the composite plate is as follows 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 balance is Fe and unavoidable impurities; The preparation method includes the following steps: 1) Composite blank preparation Prepare two carbon steel blanks 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 blanks 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; Perform surface treatment on at least one surface of each of the two base materials and the two cladding materials; Apply a release agent on one surface of one cladding material; Stack the blanks in the 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; Prepare four seals with width W3, W3 = 2T2 - (1 - 2) mm, attach the seals to the four side edges of the two cladding materials, and 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 to obtain a composite blank base blank; Machine a round hole on the seal at the groove on the side edge of the composite blank base blank, and weld a seamless steel pipe at the round hole; Perform surfacing welding on the grooves on the four side edges of the composite blank base blank; Use a vacuum pump to evacuate the composite billet through this seamless steel pipe, with the vacuum degree ≤ 10 -1 Pa, and then maintain the pressure for more than 4 hours; finally, seal the seamless steel pipe; 2) Composite blank rolling Heat the obtained composite blank, and adopt a 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, the residence time is (0.10 - 0.20) t min / mm, and the total heating time ≥ 1.2 × t min / mm, where t is the thickness of the composite blank; Two-stage controlled rolling of rough rolling + finish rolling is adopted. 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 finishing rolling temperature is ≥1000°C, longitudinal rolling is adopted in the first pass, and the rolling reduction is ≥46mm; transverse rolling starts from the second pass 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 ≥25mm; longitudinal rolling starts from the (n + 1)th pass and ends the rough rolling stage when the thickness of the intermediate blank reaches 2.5 - 3.5 times the target thickness of the large composite plate, and the rolling reduction in the (n + 1)th pass is ≥30mm; then it waits for temperature, 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. The starting rolling temperature in the finish rolling stage is 810°C - 840°C, and the finishing rolling temperature is ≥780°C; After rolling, cooling is carried out to obtain the large composite plate; 3) Separation and straightening of the composite plate Cut the four sides of the large composite plate to remove the part outside the seal, and the large composite plate is separated into two small composite plates, the upper and the lower; The small composite plates are transversely flattened and cold straightened to obtain the finished stainless steel composite plate.

2. The preparation method of the 500 MPa grade stainless steel composite plate according to claim 1, wherein, In the step "Cooling is carried out after rolling", after rolling, the large composite plate enters the 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 1m. 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 way of turning on N groups of cooling headers first and then not turning on M groups of cooling headers. The cooling water pressure is 0.2MPa, the cooling speed is 3 - 15°C / s, and the final cooling temperature is 380 - 450°C; where N takes values of 2, 3 or 4, and M takes values of 2, 3 or 4.

3. The preparation method of the 500 MPa grade stainless steel composite plate according to claim 2, wherein, After intermittent cooling, the large composite plate is naturally cooled to room temperature on the cooling bed, and thus the step 2) of composite blank rolling is completed and enters step 3) of separation and straightening of the composite plate.

4. The preparation method of the 500 MPa grade stainless steel composite plate according to claim 2, wherein, In the step 2) of composite blank rolling: After the large composite plate leaves the ultra-fast cooling system, it directly enters the straightening machine for straightening: Place the straightened large composite plate between two steel plates at a temperature of T f -150 °C to T f -50 °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; After stacking cooling, the large composite plate is naturally cooled on the cooling bed; T f = 550 + 30[Si] - 20[Mn] + 15[Cr] - 15[Ni] + 10[Mo], where [Si], [Mn], [Mo], [Cr], [Ni] is 100 times the mass percentage of each element in the base material.

5. The preparation method of the 500 MPa grade stainless steel clad plate according to claim 1, characterized in that, In the step of "coating a release agent on one surface of a composite material", the release agent used is a coating solution containing silicon oxide and magnesium oxide, where the mass ratio of silicon oxide to magnesium oxide is 3:1; the amount of the release agent coated is 20ymg / m 2 , and y is the thickness ratio of the composite blank to the large composite board; Before the step "Grouping the blanks in the stacking order of base material, clad material, clad material, base material", the clad material coated 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.

6. The preparation method of the 500MPa grade stainless steel clad plate according to claim 1, characterized in that, In the step "Coating the release agent on one surface of a clad material", the components of the used release agent are in a weight ratio of: 25 - 35% silicon nitride, 5 - 10% thermosetting amino resin, 55 - 70% water; the thickness of the coated release agent is 0.2 - 0.5mm; Before the step "Grouping the blanks in the stacking order of base material, clad material, clad material, base material", the clad material coated with the release agent is heated and dried. The drying temperature is 100 - 250°C, and the drying time is 20 - 40min.

7. The preparation method of the 500 MPa grade stainless steel composite plate according to claim 1, characterized in that, In the step of "performing gas shielded welding between adjacent seals and between the seal and the base material", the welding current is 235 - 265 A, the welding voltage is 25 - 29 V, the welding speed is 300 - 360 mm / min, and the interpass temperature during the welding process is controlled at 135 - 165 °C.

8. The preparation method of the 500 MPa grade stainless steel clad plate according to claim 1, wherein In the step of "performing surfacing on the grooves on the four sides of the composite base blank", submerged arc surfacing is adopted; Before welding, the welding flux is baked at 350 °C for 2 h and then kept warm at 150 °C for 1 h; During the welding process, the interpass temperature is controlled at 135 - 165 °C, the welding current is 620 - 680 A, the welding voltage is 28 - 32 V, and the welding speed is 420 - 480 mm / min.

9. The preparation method of the 500MPa grade stainless steel clad plate according to claim 1, characterized in that, The step of "performing surface treatment on at least one surface of each of the two base materials and the two composite materials" includes: Grinding and polishing one surface of each composite material to remove the surface scale; and, In a relatively shape - complementary manner, milling and grinding one surface of the two base materials to process the surface into a transverse inclined surface with length L11 = L1 and width W11 > W1, and the base material is a non - uniform - thickness blank with a gradually changing thickness in the transverse direction, or processing the surface into a longitudinal inclined surface with length L11 > L1 and width W11 = W1, and the base material is a non - uniform - thickness blank with a gradually changing thickness in the longitudinal direction.

10. The preparation method of the 500MPa grade stainless steel composite plate according to claim 1, characterized in that, The step of "performing surface treatment on at least one surface of each of the two base materials and the two composite materials" includes: In a relatively shape - complementary manner, milling and grinding one surface of the two base materials to process the surface into an irregular concave - convex surface composed of n planes connected in sequence along the transverse direction, and the base material is a non - uniform - thickness blank with a non - monotonic thickness change in the transverse direction, and the length L12 of the irregular concave - convex surface is L1 and the total width W12 > W1; or processing the surface into an irregular concave - convex surface composed of n planes connected in sequence along the longitudinal direction, and the base material is a non - uniform - thickness blank with a non - monotonic thickness change in the longitudinal direction, and the total length L12 of the irregular concave - convex surface is > L1 and the width W12 = W1; n ≥ 2; Grinding and polishing one surface of each composite material to remove the surface scale; and then bending each composite material to match the corresponding irregular concave - convex surface.

11. The preparation method of the 500 MPa grade stainless steel clad plate according to claim 9 or 10, characterized in that, In the step of "placing the composite material centered relative to the base material", the distance from the lateral side of the composite material to the corresponding side of the base material is half of the width difference between the contact surfaces of the composite material and the base material, and the distance from the longitudinal side of the composite material to the corresponding side of the base material is half of the length difference between the contact surfaces of the composite material and the base material.

12. A 500 MPa grade stainless steel clad plate, characterized in that, The composite plate is prepared by the preparation method described in any one of claims 1 to 11. Its base layer has a bainite + ferrite structure, the yield strength ≥ 500 MPa, the tensile strength ≥ 630 MPa, the elongation after fracture ≥ 18%, and the yield - strength ratio ≤ 0.

86.

13. The 500 MPa grade stainless steel clad plate according to claim 12, wherein, The bonding rate of the composite interface of the composite plate is 100%, and the shear strength ≥ 300 MPa.

14. The 500 MPa grade stainless steel clad plate according to claim 13, characterized in that, The impact energy of the composite plate at 0 °C ≥ 120 J, at - 20 °C ≥ 120 J, and at - 40 °C ≥ 120 J; The total thickness of the composite board is 15-39 mm, the thickness of the base layer is 12-36 mm, the thickness of the composite layer is 3 mm, and the unevenness of the composite board is ≤3 mm / m.

15. The 500 MPa grade stainless steel clad plate according to claim 14, characterized in that, The impact energy of the composite plate at 0°C is ≥240J, the impact energy at -20°C is ≥200J, and the impact energy at -40°C is ≥150J; The Vickers hardness difference of the base layer of the composite plate in the thickness direction is ≤10, the strength difference of the head, middle and tail is ≤40MPa, the strength difference of the whole plate is ≤40MPa, and the unevenness of the composite plate thickness is ≤2mm / m.

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