345MPa grade stainless steel composite plate and preparation method thereof

Abstract

The present invention discloses a 345MPa grade stainless steel composite plate and its preparation method. In the method, the blanks are assembled in the stacking order of substrate, composite material, composite material, and substrate; a seal is wrapped around the four sides of two composite materials, and gas shielded welding and surfacing are performed; the composite blank is vacuumed through the seamless steel pipe at the seal and then sealed; the resulting composite blank is heated to a temperature of 1150-1170°C; a two-stage controlled rolling process of roughing and finishing is adopted, wherein in the roughing stage, the starting rolling temperature is ≤1020°C and the finishing rolling temperature is ≥980°C, and the horizontal rolling is performed first and then the longitudinal rolling is performed, and at least one pass of the longitudinal rolling has a reduction of ≥35mm; then, the intermediate blank is allowed to warm up, and when the surface temperature of the intermediate blank drops below 860°C, the finishing rolling stage is started; the finishing rolling temperature of the finishing rolling stage is ≥830°C; the starting cooling temperature is ≥760°C, the cooling rate is 6-12°C / s, and the final cooling temperature is 570-590°C; and the composite plate is obtained after straightening and trimming.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material preparation, and relates to a 345MPa grade stainless steel composite plate and a preparation method thereof. Background Art

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

[0003] In recent years, with the increasing demands for safety and longevity of steel bridges, the rust and corrosion protection of steel bridge structures has become increasingly prominent. Covering the steel surface with a corrosion-resistant protective material, replacing a single steel plate, can achieve long-term corrosion protection that cannot be achieved with spray coatings. Therefore, stainless steel composite panels have become an 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 plate shape control, poor interface bonding quality, low yield rate and low production efficiency. Summary of the Invention

[0005] The object of the present invention is to provide a 345MPa 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 object of the invention, one embodiment of the present invention provides a method for preparing a 345MPa grade stainless steel composite plate, which comprises the following steps:

[0007] 1) Composite blank preparation

[0008] Prepare two carbon steel billets with a thickness of T1, a length of L1, and a width of W1 as base materials; and prepare two stainless steel billets with a thickness of T2, a length of L2, and a width of W2 as composite materials; L2 < L1, W2 < W1;

[0009] performing surface treatment on at least one surface of each of the two substrates and the two composite materials;

[0010] Apply a release agent to one surface of a composite material;

[0011] Assembling the blanks in the order of stacking substrate, composite, composite, and substrate; wherein the composite is placed in the center relative to the substrate, the surfaces of the substrate and composite that are in contact with each other are both surfaces that have undergone the surface treatment, and the surface coated with the release agent faces the other composite;

[0012] Prepare four sealing strips with a width of W3, where W3 = 2T2 - 1 to 2 mm, and place the sealing strips against the four sides of the two composite materials. Perform gas shielded welding between adjacent sealing strips and between the sealing strips and the base material, so that the two base materials and the sealing strips form a whole, thereby obtaining a composite blank base material.

[0013] A circular hole is machined on the seal strip at the groove on the side of the composite billet base, and a seamless steel pipe is welded at the circular hole;

[0014] Performing surfacing welding on the grooves on four sides of the composite billet base;

[0015] The composite billet is vacuumed through the seamless steel pipe by a vacuum pump, and the vacuum degree is ≤10 -1 Pa, then maintain the pressure for more than 4 hours; finally, seal the seamless steel pipe;

[0016] 2) Composite billet rolling

[0017] The obtained composite blank is heated at a temperature of 1150-1170° C., the total heating time is ≥1.2×tmin / mm, where t is the thickness of the composite blank, and the holding time in the soaking section is 30-50 min.

[0018] A two-stage controlled rolling process of rough rolling and finishing rolling is adopted. In the rough rolling stage, the starting rolling temperature is ≤1020°C and the final rolling temperature is ≥980°C. Transverse rolling is performed first and then longitudinal rolling. During longitudinal rolling, at least one pass has a reduction of ≥35mm. The total rough rolling reduction is 40-60%. The rough rolling stage is terminated when the intermediate billet thickness is 2.5-3.5 times the target thickness of the composite plate. The intermediate billet is then allowed to warm up and water cooling is performed during the process. When the surface temperature of the intermediate billet drops below 860°C, the finishing rolling stage is started. The final rolling temperature of the finishing rolling stage is ≥830°C, and the total finishing reduction is 55-75% to obtain the composite plate.

[0019] After rolling, the composite plate enters the ultra-fast cooling system for cooling, with the starting cooling temperature ≥760℃, the cooling rate of 6-12℃ / s, and the final cooling temperature of 570-590℃;

[0020] After leaving the ultra-fast cooling system, the composite plate directly enters the straightening machine for straightening;

[0021] 3) Composite plate separation and straightening

[0022] Cut the four sides of the composite board to remove the parts other than the seal, and separate the composite board into two small composite boards;

[0023] The composite plate is flattened horizontally and cold straightened to obtain the finished stainless steel composite plate.

[0024] Preferably, the chemical composition of the stainless steel billet is as follows in percentage by mass: 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 remainder is Fe and unavoidable impurities.

[0025] Preferably, the chemical composition of the carbon steel billet is, in percentage by mass: 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 is Fe and unavoidable impurities.

[0026] Preferably, the surface scale indentation depth and surface pit depth of the carbon steel billet are both ≤0.3 mm, and the unevenness is ≤3 mm / m; the unevenness of the stainless steel billet is ≤2 mm / m.

[0027] Preferably, in the step of "applying a release agent to one surface of a composite material", the release agent used is a coating solution containing silicon oxide and magnesium oxide, wherein the mass ratio of silicon oxide to magnesium oxide is 3:1. Preferably, the amount of the release agent applied is 20 μmg / m 2 , y is the thickness ratio of the composite blank to the composite panel. Preferably, before the step of "assembling the blanks in the order of substrate, composite, composite, and substrate," the release-coated composite is heated and dried in a trolley furnace at a temperature of 340-360°C for 35-45 minutes.

[0028] Preferably, in the step of "applying a release agent to one surface of a composite material," the release agent comprises the following components by mass: 25-35% silicon nitride, 5-10% thermosetting amino resin, and 55-70% water. Preferably, the release agent is applied to a thickness of 0.2-0.5 mm. Preferably, before the step of "assembling the composite material in the order of substrate, composite material, composite material, and substrate," the composite material coated with the release agent is heated and dried at a temperature of 100-250°C for 20-40 minutes.

[0029] Preferably, after the step of "assembling the billets in the order of stacking substrate, composite material, composite material, and substrate", the stacked four billets are placed as a whole under a four-column hydraulic machine, and the opposite surfaces of the two substrates are pressurized at a pressure of ≥500 tons.

[0030] Preferably, the step of "subjecting surface treatment to at least one surface of each of the two substrates and the two composite materials" includes: grinding and polishing one surface of each substrate and each composite material to remove surface oxide scale.

[0031] Preferably, L2=L1-L0, W2=W1-W0, and the value ranges of L0 and W0 are 90-150 mm respectively;

[0032] In the aforementioned “the composite is placed centrally relative to the substrate”, the distance from the lateral side of the composite to the corresponding side of the substrate is half of W0, and the distance from the longitudinal side of the composite to the corresponding side of the substrate is half of L0.

[0033] Preferably, the step of "substituting surface treatment on at least one surface of each of the two substrates and the two composite materials" comprises:

[0034] Grinding and polishing one surface of each composite material to remove surface oxide scale; and,

[0035] In a manner of relative shape complementarity, one surface of the two substrates is milled and ground, and the surface is processed into a transverse inclined surface with a length L11=L1 and a width W11>W1, and the substrate is a non-uniform thickness blank with a thickness gradient in the transverse direction, or the surface is processed into a longitudinal inclined surface with a length L11>L1 and a width W11=W1, and the substrate is a non-uniform thickness blank with a thickness gradient in the longitudinal direction.

[0036] Preferably, L2=L11-L0, W2=W11-W0, and the value ranges of L0 and W0 are 90-150 mm respectively;

[0037] In the aforementioned “the composite is placed centrally relative to the substrate”, the distance from the lateral side of the composite to the corresponding side of the substrate is half of W0, and the distance from the longitudinal side of the composite to the corresponding side of the substrate is half of L0.

[0038] Preferably, the step of "substituting surface treatment on at least one surface of each of the two substrates and the two composite materials" comprises:

[0039] Milling one surface of two substrates in a manner of relative shape complementation to form an irregular concave-convex surface comprising n planes sequentially connected in a transverse direction, wherein the substrate is a non-uniform thickness blank with a non-monotonically varying thickness in the transverse direction, wherein the length L12 of the irregular concave-convex surface is equal to L1 and the total width W12 is greater than W1; or milling the one surface of two substrates into an irregular concave-convex surface comprising n planes sequentially connected in a longitudinal direction, wherein the substrate is a non-uniform thickness blank with a non-monotonically varying thickness in the longitudinal direction, wherein the total length L12 of the irregular concave-convex surface is greater than L1 and the width W12 is equal to W1; n ≥ 2;

[0040] One surface of each composite material is ground and polished to remove surface oxide scale; and then each composite material is bent to match the corresponding irregular concave and convex surface.

[0041] Preferably, L2=L12-L0, W2=W12-W0, and the value ranges of L0 and W0 are 90-150 mm respectively;

[0042] In the aforementioned “the composite is placed centrally relative to the substrate”, the distance from the lateral side of the composite to the corresponding side of the substrate is half of W0, and the distance from the longitudinal side of the composite to the corresponding side of the substrate is half of L0.

[0043] Preferably, in the step of "preparing four sealing strips of width W3, where W3 = 2W2 - 1 to 2 mm, and attaching the sealing strips to the four sides of the two composite materials":

[0044] The two sealing strips are respectively attached to the two sides of the two composite materials in the horizontal direction, with a length of L31 = L2-1~2mm;

[0045] The other two sealing strips are respectively attached to the longitudinal sides of the two composite materials, with a length of L32 = W2-1 ~ 2mm;

[0046] The thickness T3 of the four seals is 12 to 15 mm.

[0047] Preferably, in the step of "gas shielded welding is performed between adjacent seals and between the seal and the substrate", the welding current is 215-245A, the welding voltage is 28-32V, the welding speed is 300-360mm / min, and the interpass temperature during the welding process is controlled at 135-165°C.

[0048] Preferably, in the step of "surfacing the grooves on the four sides of the composite blank base blank", submerged arc surfacing is used;

[0049] Before welding, the flux was baked at 350°C for 2 h and then kept at 150°C for 1 h;

[0050] During the welding process, the interpass temperature is controlled at 135-165°C, the welding current is 570-630A, the welding voltage is 28-32V, and the welding speed is 420-480mm / min.

[0051] Preferably, after the step of "the large composite plate leaves the ultra-fast cooling system and directly enters the straightening machine for straightening", the straightened large composite plate is naturally cooled on the cooling bed, and when the surface temperature drops below 200°C, a cold straightening machine is used for cold straightening.

[0052] Preferably, after the step of "the large composite plate leaves the ultra-fast cooling system and directly enters the straightening machine for straightening":

[0053] The straightened composite board is placed at a temperature of T f The stack cooling is carried out between two steel plates at +100~150℃, and the stack cooling time is 0.4min / mm×t0±5min, where t0 is the thickness of the composite plate;

[0054] After the stack cooling is completed, the composite board is placed on the cooling bed to cool naturally;

[0055] T f =550+30[Si]-20[Mn]+15[Cr]-15[Ni]+10[Mo], where [Si], [Mn], [Mo], [Cr],

[0056] [Ni] is 100 times the mass percentage of each element in the base material.

[0057] To achieve the above-mentioned purpose of the invention, one embodiment of the present invention provides a 345MPa grade stainless steel composite plate, which is prepared by the preparation method. The total thickness of the composite plate is 5 to 55mm, the thickness of the base layer is 4 to 45mm, the thickness of the composite layer is 1 to 10mm, the structure is ferrite + pearlite structure, the yield strength is ≥345MPa, the tensile strength is ≥490MPa, the elongation after fracture is ≥20%, and the yield strength ratio is ≤0.85.

[0058] Preferably, the composite interface bonding rate of the composite plate is 100%, and the shear strength is ≥300 MPa.

[0059] Preferably, the impact energy of the composite plate at 0°C is ≥120J, the impact energy at -20°C is ≥120J, and the impact energy at -40°C is ≥120J; the composite plate has no cracks when bent outward 180° and no cracks when bent inward 180°; after being boiled in a sulfuric acid-copper sulfate solution for 20 hours and bent 180°, the composite layer has no intergranular corrosion cracks.

[0060] Preferably, the unevenness of the composite plate is ≤3 mm / m.

[0061] 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 the advantages of excellent surface quality, excellent plate shape, and excellent interface bonding. For example, there are no obvious surface defects such as pits and side scratches existing in the existing composite plates. For example, the unevenness of the composite plate is ≤3mm / m, and the composite interface bonding rate of the composite plate is 100%, the shear strength is ≥300MPa, and it also has excellent mechanical properties. The total thickness of the composite plate is 5-55mm, the thickness of the base layer is 4-45mm, the thickness of the composite layer is 1-10mm, the structure is ferrite + pearlite structure, the yield strength is ≥345MPa, the tensile strength is ≥490MPa, the elongation after fracture is ≥20%, and the yield strength ratio is ≤0.85. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] For the sake of clarity in presentation and description, in the various drawings of the present invention, certain dimensions of structures or parts are exaggerated relative to other structures or parts. Therefore, these drawings are only used to illustrate the basic structure of the subject matter of the present invention.

[0063] Figure 1a is a schematic cross-sectional view of a steel billet according to a first embodiment of the billet surface treatment step of the present invention;

[0064] Figure 1b is a schematic transverse cross-sectional view of a steel billet according to a second embodiment of the billet surface treatment step of the present invention, wherein the change in surface shape after the surface treatment is indicated by a dot-dash line;

[0065] Figure 1c FIG1 is a schematic longitudinal cross-sectional view of a steel billet according to a third embodiment of the billet surface treatment step of the present invention, wherein the change in surface shape after the surface treatment is indicated by a dot-dash line;

[0066] Figure 1d is a schematic transverse cross-sectional view of a steel billet according to a fourth embodiment of the billet surface treatment step of the present invention, and illustrates the changes in surface shape before (A) and after (B) the surface treatment;

[0067] Figure 1e is a schematic longitudinal cross-sectional view of a steel billet according to a fifth embodiment of the billet surface treatment step of the present invention, and illustrates the changes in surface shape before (A) and after (B) the surface treatment;

[0068] Figure 2a corresponds to Figure 1a A schematic cross-sectional view of a composite billet;

[0069] Figure 2b corresponds to Figure 1b A schematic transverse cross-sectional view of a composite blank;

[0070] Figure 2c corresponds to Figure 1cA schematic longitudinal cross-sectional view of a composite blank;

[0071] Figure 2d corresponds to Figure 1d A schematic transverse cross-sectional view of a composite blank;

[0072] Figure 2e corresponds to Figure 1e A schematic longitudinal cross-sectional view of a composite blank;

[0073] Figure 3a yes Figure 2a A schematic cross-sectional view of two composite plates rolled from a composite billet;

[0074] Figure 3b yes Figure 2b A schematic transverse cross-sectional view of two composite plates rolled from a composite billet;

[0075] Figure 3c yes Figure 2c A schematic longitudinal cross-sectional view of two composite plates rolled from a composite billet;

[0076] Figure 3d yes Figure 2d A schematic transverse cross-sectional view of two composite plates rolled from a composite billet;

[0077] Figure 3e yes Figure 2e Schematic diagram of the longitudinal section of two composite plates rolled from a composite billet. DETAILED DESCRIPTION

[0078] The present invention provides a method for preparing a 345MPa grade stainless steel composite plate, and a composite plate prepared based on the method.

[0079] Compared with the existing technology, such as the explosive composite, non-vacuum composite blank preparation, vacuum electron beam welding blank making, etc. mentioned in the background technology, the composite plate prepared by the preparation method of the present invention has the advantages of excellent surface quality, excellent plate shape, and excellent interface bonding. For example, there are no obvious surface defects such as pits and side scratches existing in the existing composite plates. For example, the unevenness of the composite plate is ≤3mm / m. For another example, the composite interface bonding rate of the composite plate is 100%, the shear strength is ≥300MPa, and it also has excellent mechanical properties. The total thickness of the composite plate is 5-55mm, the thickness of the base layer is 4-45mm, the thickness of the composite layer is 1-10mm, the structure is ferrite + pearlite structure, the yield strength is ≥345MPa, the tensile strength is ≥490MPa, the elongation after fracture is ≥20%, and the yield strength ratio is ≤0.85.

[0080] Specifically, the preparation method includes three general steps: composite billet preparation, composite billet rolling, and composite plate separation and straightening.

[0081] The overall steps of preparing the composite blank include the following sub-steps:

[0082] Prepare two carbon steel billets with a thickness of T1, a length of L1, and a width of W1 as base materials; and prepare two stainless steel billets with a thickness of T2, a length of L2, and a width of W2 as composite materials;

[0083] performing surface treatment on at least one surface of each of the two substrates and the two composite materials;

[0084] Apply a release agent to one surface of a composite material;

[0085] Assemble the blanks in the order of stacking base material, composite material, composite material and base material;

[0086] Prepare four sealing strips with a width of W3, where W3 = 2T2 - 1 to 2 mm, and place the sealing strips against the four sides of the two composite materials. Perform gas shielded welding between adjacent sealing strips and between the sealing strips and the base material, so that the two base materials and the sealing strips form a whole, thereby obtaining a composite blank base material.

[0087] A circular hole is machined on the seal strip at the groove on the side of the composite billet base, and a seamless steel pipe is welded at the circular hole;

[0088] Performing surfacing welding on the grooves on four sides of the composite billet base;

[0089] The composite billet is vacuumed through the seamless steel pipe by a vacuum pump, and the vacuum degree is ≤10 -1 Pa, then maintain the pressure for more than 4 hours; finally, seal the seamless steel pipe.

[0090] Furthermore, the above steps are described in detail as follows.

[0091] The step of “preparing two carbon steel billets of length L1 and width W1 as base materials; and preparing two stainless steel billets of length L2 and width W2 as composite materials” is also a billet preparation step.

[0092] The carbon steel billet used as the base material has a thickness of T1, a length of L1, and a width of W1, making it a rectangular billet. Similarly, the stainless steel billet used as the composite material has a thickness of T2, a length of L2, and a width of W2, also a rectangular billet. Furthermore, L2 < L1, and W2 < W1, meaning the length and width of the composite material are both smaller than those of the base material.

[0093] As a preferred solution, the stainless steel billet is preferably austenitic stainless steel.

[0094] Furthermore, the chemical composition of the stainless steel billet is, by mass percentage, as follows: C ≤ 0.15%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.030%, Ni: 6.0-22.0%, Cr: 16.0-26.0%, Mo ≤ 3.0%, with the balance being Fe and unavoidable impurities. Using a stainless steel billet with this chemical composition can further ensure the performance of the composite plate, particularly the corrosion resistance of the composite layer, while achieving the aforementioned technical effects. For example, the composite layer of the composite plate (i.e., obtained by rolling the composite material) exhibits no intergranular corrosion cracking after being boiled in a sulfuric acid-copper sulfate solution for 20 hours and then bent 180°.

[0095] It should be noted that the chemical compositions of the two stainless steel billets may be the same or different, and only one of them may adopt the chemical composition provided by the above preferred solution, or both of them may adopt the chemical composition provided by the above preferred solution, or neither of them may adopt the chemical composition provided by the above preferred solution.

[0096] As a preferred embodiment, the chemical composition of the carbon steel billet is as follows by mass percentage: 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 remainder is Fe and unavoidable impurities. Using a carbon steel billet with this chemical composition, combined with the control of the temperature, time, reduction, and cooling rate in the composite billet rolling step, the mechanical properties of the composite plate can be further improved while maintaining the aforementioned technical effects, and the toughness can be ensured. For example, the composite plate has an impact energy of ≥120J at 0°C, ≥120J at -20°C, and ≥120J at -40°C; and the composite plate has no cracks when bent outward 180° and when bent inward 180°.

[0097] Similar to the description of the aforementioned stainless steel plates, the chemical compositions of the two carbon steel billets may be the same or different. Only one of the two carbon steel billets may adopt the chemical composition provided by the above preferred scheme, or both of the two carbon steel billets may adopt the chemical composition provided by the above preferred scheme, or neither of the two carbon steel billets may adopt the chemical composition provided by the above preferred scheme.

[0098] As a preferred solution, the carbon steel billet's surface oxide scale penetration depth and surface pit depth are both ≤0.3mm, and its roughness is ≤3mm / m. The stainless steel billet's surface is scratch-free and its roughness is ≤2mm / m. This prevents billets with significant surface or shape defects from entering the composite panel production line.

[0099] Next, regarding the step of "subjecting a surface treatment to at least one surface of each of the two substrates and the two composite materials," that is, the blank surface treatment step, the present invention provides five preferred embodiments, which are respectively introduced below.

[0100] <First embodiment of the blank surface treatment step>

[0101] In this embodiment, one surface of each substrate and each composite material is ground and polished to remove surface oxide scale and expose metallic luster.

[0102] Ginseng Figure 1a As shown, for example, a grinding wheel machine, a sanding belt machine or a milling machine is used to grind and polish the surface p1a of the substrate 11a to remove the surface oxide scale and reveal the metallic luster; similarly, a grinding wheel machine, a sanding belt machine or a milling machine is used to grind and polish the surface p2a of the prepared substrate 12a to remove the surface oxide scale and reveal the metallic luster.

[0103] The surface p3a of the prepared composite material 21a is ground and polished with a wire wheel to remove the surface oxide scale and reveal the metallic luster. Similarly, the surface p4a of the prepared composite material 22a is ground and polished with a wire wheel to remove the surface oxide scale and reveal the metallic luster.

[0104] As will be seen from the following text, during assembly, the surface that has been surface treated (polished in this embodiment) is used as the surface where the substrate and the composite material are in contact with each other, for example, surface p1a and surface p3a are in contact with each other, and surface p4a and surface p2a are in contact with each other, so that the interface bonding quality can be guaranteed.

[0105] <Second embodiment of the blank surface treatment step>

[0106] In this embodiment, as in the first embodiment, one surface of each composite material (eg Figure 1b The middle surfaces (p3b and p4b) are ground and polished to remove the surface oxide scale and reveal the metallic luster, which will not be described in detail.

[0107] This embodiment differs from the first embodiment in that the surface treatment of the substrate is performed:

[0108] Ginseng Figure 1b , the surface p1b of the substrate 11b is milled to be processed into a surface p1b0, which is a transverse inclined surface with a length L11=L1 and a width W11>W1. Accordingly, the substrate 11b is processed into a non-uniform thickness blank with a gradual thickness change in the transverse direction (i.e., in the width direction). That is, after the substrate 11b is milled, the height of the substrate 11b gradually increases from one side to the other side in the width direction.

[0109] Similarly, the surface p2b of the substrate 12b is milled to form the surface p2b0, which is a transverse inclined surface with a length L11=L1 and a width W11>W1. Accordingly, the substrate 12b is formed into a non-uniform thickness blank with a gradual thickness variation in the transverse direction.

[0110] The milling of surface p2b of substrate 12b and surface p1b of substrate 11b is performed in a manner that complements their relative shapes. This means that the processed surface p2b0 and surface p1b0 are complementary in shape when facing each other. For example, the lateral inclination angle of surface p2b0 (e.g., the angle with the original surface p2b) is equal to the lateral inclination angle of surface p1b0 (e.g., the angle with the original surface p1b). This ensures that the upper and lower surfaces of the composite blank are parallel during subsequent assembly.

[0111] It is understandable that after the above-mentioned milling process, the surface oxide scales on the surface p1b of the substrate 11b and the surface p2b of the substrate 12b can also be removed, revealing the metallic luster.

[0112] As can be seen from the following text, when assembling, by using the surface that has been surface treated (milling in this embodiment) as the surface where the base material and the composite material are in contact with each other, for example, surface p1b0 and surface p3b are in contact with each other, and surface p4b and surface p2b0 are in contact with each other, the interface bonding quality can be ensured as in the aforementioned first embodiment, and this embodiment can also be further used to prepare non-uniform thickness composite plates with a lateral thickness gradient, so as to improve the applicable scenarios and scope of the composite plates.

[0113] <Third Embodiment of Blank Surface Treatment Step>

[0114] This embodiment is essentially the same as the second embodiment described above (including the surface treatments on surfaces p3c and p4c), differing only in that the substrate thickness gradient in the second embodiment is changed to a longitudinal (i.e., lengthwise) gradient in thickness. These differences are described below; other similarities are discussed in the second embodiment and will not be repeated here.

[0115] Ginseng Figure 1c , the surface p1c of the substrate 11c is milled to be processed into a surface p1c0, which is a longitudinal inclined surface with a length L11>L1 and a width W11=W1. Accordingly, the substrate 11c is processed into a non-uniform thickness blank with a gradual thickness change in the longitudinal direction.

[0116] Similarly, the surface p2c of the substrate 12c is milled to form a surface p2c0, which is a longitudinal inclined surface with a length L11>L1 and a width W11=W1. Accordingly, the substrate 12c is formed into a non-uniform thickness blank with a gradual thickness change in the longitudinal direction.

[0117] The milling of surface p2c of substrate 12c and surface p1c of substrate 11c is performed in a manner that complements their relative shapes. This means that the processed surface p2c0 and surface p1c0 are complementary in shape when facing each other. For example, the longitudinal inclination angle of surface p2c0 (e.g., the angle with the original surface p2c) is equal to the longitudinal inclination angle of surface p1c0 (e.g., the angle with the original surface p1c). This ensures that the upper and lower surfaces of the composite blank are parallel during subsequent assembly.

[0118] It is understandable that after the above-mentioned milling process, the surface oxide scales on the surface p1c of the substrate 11c and the surface p2c of the substrate 12c can also be removed, revealing the metallic luster.

[0119] <Fourth embodiment of the blank surface treatment step>

[0120] In this embodiment, one surface of each substrate is milled and ground to form an irregular concave-convex surface comprising n planes connected in sequence along the transverse direction. The substrate is a non-uniform thickness blank with a non-monotonically varying thickness in the transverse direction. The length of the irregular surface is L12=L1 and the total width is W12>W1.

[0121] For example, Figure 1d The surface p1d of the substrate 11d is milled and the surface p1d is changed from Figure 1d The horizontal surface in (A) is processed into Figure 1d The irregular concave-convex surface p1d0 shown in (B) specifically includes n planes connected in sequence along the transverse direction, where n≥2. In the figure, there are 8 planes. It can be seen from the figure that the 1st, 3rd, 5th and 7th planes from the left side to the right side of the figure are all transverse inclined surfaces, while the 2nd, 4th, 6th and 8th planes are all horizontal planes. Of course, this is only an example, and the implementation can also be changed to n taking other numbers, or not including horizontal planes but only including transverse inclined surfaces, etc.

[0122] Ginseng Figure 1d By milling the surface p1d, the base material 11d is processed into a non-uniform thickness blank whose thickness in the transverse direction does not change monotonically.

[0123] The length L12 of the irregular concave-convex surface p1d0 is L1, which means that it does not change due to milling. The total width W12 of the irregular concave-convex surface p1d0 is greater than W1. It can be understood that the total width W12 is the sum of the widths of n planes.

[0124] Correspondingly, Figure 1d The surface p2d of the substrate 12d is also milled to change the surface p2d from Figure 1d The horizontal surface in (A) is processed into Figure 1d (B) shows the irregular concave-convex surface p2d0. When the surface p2d of the substrate 12d and the surface p1d of the substrate 11d are milled, they are milled in a manner that their relative shapes complement each other, that is, the machined surface p2d0 and the surface p1d0 are complementary in shape when facing each other.

[0125] Based on the principle of relative shape complementarity, the irregular concave-convex surface p2d0 also specifically comprises n planar faces sequentially connected in the transverse direction, eight in the example shown. The length L12 of the irregular concave-convex surface p2d0 is equal to L1, indicating that it remains unchanged due to milling. The total width W12 of the irregular concave-convex surface p2d0 is greater than W1. It can be understood that the total width W12 is the sum of the widths of the n planar faces of the irregular concave-convex surface p2d0.

[0126] Ginseng Figure 1d By milling surface p2d, substrate 12d is processed into a non-uniform thickness blank with a non-monotonically varying thickness in the transverse direction. Due to the complementary shapes of irregular concave-convex surface p2d0 and irregular concave-convex surface p1d0, if milled substrates 12d and 11d are placed opposite each other, the sum of their thicknesses remains constant. This ensures that the upper and lower surfaces of the composite blank are parallel during subsequent assembly.

[0127] The above describes the surface treatment of the two substrates in this embodiment. The following describes the surface treatment of the two composite materials.

[0128] In this embodiment, the surface p3d of the prepared composite material 21d is ground and polished with a wire wheel to remove the surface oxide scale and reveal the metallic luster; similarly, the surface p4d of the prepared composite material 22d is ground and polished with a wire wheel to remove the surface oxide scale and reveal the metallic luster.

[0129] Furthermore, to match the surface shape of substrates 11d and 12d, after removing the surface oxide scale, this embodiment also bends each composite material to match the corresponding irregular concave-convex surface. For example, composite material 21d is bent to match the corresponding irregular concave-convex surface p1d0, facilitating contact during subsequent assembly. For another example, composite material 22d is bent to match the corresponding irregular concave-convex surface p2d0, facilitating contact during subsequent assembly.

[0130] The surface treatment of this embodiment can ensure the interface bonding quality as in the aforementioned first embodiment, and can also be further used to prepare non-uniform thickness composite plates with non-monotonically varying transverse thicknesses, so as to improve the applicable scenarios and scope of the composite plates, enhance the corrosion resistance compared to existing steel plates, and avoid frequent welding and dissimilar welding between composite plates of different thicknesses.

[0131] <Fifth Embodiment of the Blank Surface Treatment Step>

[0132] The difference between this embodiment and the aforementioned fourth embodiment is that the thickness of the substrate in the transverse direction in the fourth embodiment is changed to the thickness of the substrate in the longitudinal direction in this embodiment.

[0133] For example, Figure 1e The surface p1e of the substrate 11e is milled and ground. Figure 1e The horizontal surface in (A) is processed into Figure 1e The irregular concave-convex surface p1e0 shown in (B) specifically includes n planes connected in sequence along the longitudinal direction, where n≥2. In the figure, there are 8 planes. It can be seen from the figure that the 1st, 3rd, 5th and 7th planes from the left side to the right side of the figure are all longitudinal inclined surfaces, while the 2nd, 4th, 6th and 8th planes are all horizontal planes. Of course, this is only an example, and it can also be implemented in a variable manner such that n takes other numbers, or does not include horizontal planes but only includes longitudinal inclined surfaces, etc.

[0134] Ginseng Figure 1e By milling the surface p1e, the base material 11e is processed into a non-uniform thickness blank with a non-monotonically varying thickness in the longitudinal direction.

[0135] The width W12 of the irregular concave-convex surface p1e0 is equal to W1, which means it has not changed due to milling. The total length L12 of the irregular concave-convex surface p1e0 is greater than L1. It can be understood that the total length L12 is the sum of the lengths of n planes.

[0136] Correspondingly, Figure 1e The surface p2e of the substrate 12e is also milled to change the surface p2e from Figure 1eThe horizontal surface in (A) is processed into Figure 1e (B) shows the irregular concave-convex surface p2e0. When the surface p2e of the substrate 12e and the surface p1e of the substrate 11e are milled, they are processed in a manner that their relative shapes are complementary, that is, the processed surface p2e0 and the surface p1e0 are complementary in shape when facing each other.

[0137] According to the relative shape complementarity, the irregular concave-convex surface p2e0 also specifically includes n planes connected in sequence along the longitudinal direction, exemplified as 8 planes in the figure. The width W12 of the irregular concave-convex surface p2e0 is equal to W1, and the total length L12 is greater than L1.

[0138] Ginseng Figure 1e By milling surface p2e, substrate 12e is processed into a non-uniform thickness blank with a non-monotonically varying thickness in the longitudinal direction. Due to the complementary shapes of irregular concave-convex surface p2e0 and irregular concave-convex surface p1e0, if the milled substrates 12e and 11e are placed opposite each other, the sum of their thicknesses remains constant. This ensures that the upper and lower surfaces of the composite blank are parallel during subsequent assembly.

[0139] The above describes the surface treatment of the two substrates in this embodiment. The following describes the surface treatment of the two composite materials.

[0140] In this embodiment, the surface p3e of the prepared composite material 21e is ground and polished with a wire wheel to remove the surface oxide scale and reveal the metallic luster; similarly, the surface p4e of the prepared composite material 22e is ground and polished with a wire wheel to remove the surface oxide scale and reveal the metallic luster.

[0141] Furthermore, to match the surface shape of substrates 11e and 12e, after removing the surface oxide scale, this embodiment also bends each composite material to match the corresponding irregular concave-convex surface. For example, composite material 21e is bent to match the corresponding irregular concave-convex surface p1e0, facilitating contact during subsequent assembly. For another example, composite material 22e is bent to match the corresponding irregular concave-convex surface p2e0, facilitating contact during subsequent assembly.

[0142] Similar to the aforementioned fourth embodiment, this embodiment can also improve the applicable scenarios and scope of the composite plate, enhance the corrosion resistance compared to the existing steel plate, and avoid frequent welding and dissimilar welding between composite plates of different thicknesses.

[0143] The above introduces five preferred implementation methods of the blank surface treatment steps in the composite blank preparation step. Although only one surface of each of the substrate and the composite material is treated, it should be noted that no matter which of the above five implementation methods is used, the other surfaces of each substrate and composite material can be further treated to remove the oxide scale. Although this additional treatment to remove the oxide scale is not necessary to achieve the technical effect of the present invention, it may be better; for example, in addition to descaling the surface of the substrate facing the composite material, the surface of the substrate facing away from the composite material (i.e., the surface of the composite plate) can also be descaled.

[0144] The following will continue to introduce the other sub-steps of the composite blank preparation step.

[0145] The step of "applying a release agent on one surface of a composite material" is also a step of applying a release agent.

[0146] Among them, combined with the above, it can be seen that in the previous billet surface treatment step, the surface of the composite material that will be in contact with the substrate during assembly is subjected to surface treatment such as grinding and polishing in order to ensure the interface bonding quality of the composite plate; and the purpose of the release agent coating step is to avoid the contact between the surfaces of the composite materials and the composite materials during assembly, which will be subsequently bonded during the composite billet rolling step and ultimately difficult to separate.

[0147] Based on this, a release agent is applied to one of the two composite materials. If one surface of the selected composite material has been surface treated and the other has not been surface treated during the previous blank surface treatment step, the release agent is applied to the "untreated" surface during this release agent application step. If, as mentioned above, both surfaces of the selected composite material have been surface treated during the previous blank surface treatment step, the release agent is applied to the surface that is intended to face the other composite material during blank assembly.

[0148] For example, Figure 1a For example, a release agent may be applied on the surface p6a of the composite material 22a or the surface p5a of the composite material 21a.

[0149] Regarding the release agent, two preferred implementations are provided here, which are introduced below respectively.

[0150] <First embodiment of the release agent>

[0151] In this embodiment, the release agent is a coating liquid containing silicon oxide and magnesium oxide, wherein the mass ratio of silicon oxide to magnesium oxide is 3: 1. The release agent of this embodiment can achieve a good isolation effect, ensuring the subsequent separation of the two composite board plates.

[0152] A method for preparing the release agent is provided, comprising mixing release agent powder, binder powder, and water in a mass ratio of 27:3:70 to obtain a fluid release agent coating solution. The release agent powder comprises silicon oxide and magnesium oxide, mixed in a mass ratio of 3:1. The binder powder comprises polyvinyl alcohol and thermosetting phenolic resin, mixed in a mass ratio of 1:1.

[0153] When the release agent is applied to the surface of the composite material, the amount of the release agent applied is 20 μg / m 2 , that is, the weight of the release agent per unit area of ​​the composite surface is 20 μmg. Wherein, y is the ratio of the thickness of the composite billet prepared in the composite billet preparation step to the thickness of the composite plate subsequently rolled, which is also known as the composite billet rolling reduction ratio.

[0154] Furthermore, based on this embodiment, after the release agent is applied and before subsequent assembly, the composite material coated with the release agent is placed in a trolley furnace for heating and drying at a temperature of 340-360° C. for 35-45 minutes.

[0155] <Second embodiment of the release agent>

[0156] In this embodiment, the release agent comprises, by mass, 25-35% silicon nitride, 5-10% thermosetting amino resin, and 55-70% water. Compared to existing release agents, and even compared to the first embodiment of the release agent described above, this release agent not only achieves excellent isolation, ensuring the subsequent separation of the two composite board panels, but also boasts strong chemical stability and high-temperature and thermal shock resistance from the active ingredient, silicon nitride. The thermosetting amino resin, serving as the binder, cures at low temperatures, is non-toxic, and achieves strong bonding with minimal usage. Consequently, the release agent is inexpensive, simple to operate, and offers excellent isolation and adhesion properties.

[0157] Here, a preferred preparation method of the release agent is provided, comprising: first placing 5-10% silicon nitride (by weight percentage) in a container such as a beaker, then pouring in 15-25% water and stirring; after the silicon nitride has no granularity and no bubbles, pouring in 2-3% of a thermosetting amino resin and continuing to stir; when it becomes viscous, continue to pour in the remaining silicon nitride and water, stir for 3-5 minutes, and then pour in the remaining thermosetting amino resin; when it is stirred until it becomes viscous, the release agent is prepared.

[0158] When the release agent is applied on the surface of the composite material, the thickness of the release agent applied is 0.2 to 0.5 mm.

[0159] Furthermore, based on this embodiment, after the release agent is applied and before subsequent assembly, the composite material coated with the release agent is heated and dried at a temperature of 100 to 250° C. for 20 to 40 minutes.

[0160] Next, after completing the release agent application step, the step of "assembling the blanks in the stacking order of substrate, composite material, composite material, and substrate" is introduced.

[0161] This step of "assembling the blanks in the order of substrate, composite, composite, and substrate" is also the blank assembly step. In addition to the stacking order of substrate, composite, composite, and substrate, the following conditions must also be met:

[0162] 1) The surfaces of the substrate and the composite material that are in contact with each other are both surfaces that have undergone the surface treatment; for example, in the first embodiment of the blank surface treatment step described above, Figure 2a , the surface p2a of the substrate 12a and the surface p4a of the composite material 22a are in contact with each other, and the surface p1a of the substrate 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, Figure 2b , surface p1b0 and surface p3b are in contact with each other, and surface p4b and surface p2b0 are in contact with each other; in the third embodiment of the blank surface treatment step described above, Figure 2c , the surface p1c of the substrate 11c and the surface p3c of the composite material 21c are in contact with each other, and the surface p2c of the substrate 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, Figure 2d , the irregular concave-convex surface p1d0 and the surface p3d of the composite material 21d are in contact with each other, and the irregular concave-convex 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, Figure 2e , the irregular concave-convex surface p1e0 and the surface p3e of the composite material 21e are in contact with each other, and the irregular concave-convex surface p2e0 and the surface p4e of the composite material 22e are in contact with each other;

[0163] 2) The surface coated with the release agent faces the other composite material; for example, Figure 2a , one of the surfaces p6a and p5a is coated with a release agent 30a; Figure 2b , one of the surfaces p6b and p5b is coated with a release agent 30b; Figure 2c , one of the surfaces p6c ​​and p5c is coated with a release agent 30c; Figure 2d , one of the surface p6d and the surface p5d is coated with a release agent 30d; Figure 2e, one of the surface p6e and the surface p5e is coated with a release agent 30e;

[0164] 3) The composite material is placed in the center relative to the substrate; in this regard, the previous article introduced that the length and width of the composite material are smaller than the length and width of the substrate, L2<L1, W2<W1. When assembling, the distances from the two sides of the composite material in the horizontal direction to the corresponding two sides of the substrate are equal, and the distances from the two sides of the composite material in the longitudinal direction to the corresponding two sides of the substrate are also equal.

[0165] The following describes the three points respectively for the five embodiments of the blank surface treatment steps described above. Furthermore, since the composite blank is generally symmetrically arranged vertically, only one set of substrate + composite material in the composite blank is used as an example for description, such as the set above.

[0166] 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 substrate 11a, the length L2 and width W2 of the surface p3a of the composite 21a, L2 = L1-L0, W2 = W1-W0, and the preferred value ranges of L0 and W0 are 90-150 mm respectively; in the assembled state, the distance from the transverse side of the composite 21a (corresponding to the long side of the surface p3a) to the transverse side of the substrate 11a (corresponding to the long side of the surface p1a) is half of W0, and the distance from the longitudinal side of the composite 21a (corresponding to the short side of the surface p3a) to the longitudinal side of the substrate 11a (corresponding to the short side of the surface p1a) is half of L0.

[0167] For the second embodiment of the blank surface treatment step described above, refer to Figure 2b , the length L11 and width W11 of the surface p1b0 of the substrate 11b, the length L2 and width W2 of the surface p3b of the composite 21b, L2 = L11-L0, W2 = W11-W0, and the preferred value ranges of L0 and W0 are 90-150 mm respectively; in the assembled state, the distance from the transverse side of the composite 21b (corresponding to the long side of the surface p3b) to the transverse side of the substrate 11b (corresponding to the long side of the surface p1b0) is half of W0, and the distance from the longitudinal side of the composite 21b (corresponding to the short side of the surface p3b) to the longitudinal side of the substrate 11b (corresponding to the short side of the surface p1b0) is half of L0.

[0168] For the third embodiment of the blank surface treatment step described above, refer to Figure 2c, the length L11 and width W11 of the surface p1c0 of the substrate 11c, the length L2 and width W2 of the surface p3c of the composite 21c, L2 = L11-L0, W2 = W11-W0, and the preferred value ranges of L0 and W0 are 90-150 mm respectively; in the assembled state, the distance from the transverse side of the composite 21c (corresponding to the long side of the surface p3c) to the transverse side of the substrate 11c (corresponding to the long side of the surface p1c0) is half of W0, and the distance from the longitudinal side of the composite 21c (corresponding to the short side of the surface p3c) to the longitudinal side of the substrate 11c (corresponding to the short side of the surface p1c0) is half of L0.

[0169] Regarding the fourth embodiment of the blank surface treatment step described above, Figure 2d The length L12 and width W12 of the irregular concave-convex surface p1d0 of the substrate 11d, the length L2 and width W2 of the surface p3d of the composite 21d, L2 = L12 - L0, W2 = W12 - W0, and the preferred value ranges of L0 and W0 are 90 to 150 mm, respectively; in the assembled state, the distance from the transverse side of the composite 21d (corresponding to the long side of the surface p3d) to the transverse side of the substrate 11d (corresponding to the long side of the irregular concave-convex surface p1d0) is half of W0, and the distance from the longitudinal side of the composite 21d (corresponding to the short side of the surface p3d) to the longitudinal side of the substrate 11d (corresponding to the short side of the irregular concave-convex surface p1d0) is half of L0.

[0170] For the fifth embodiment of the blank surface treatment step described above, refer to Figure 2e , the length L12 and width W12 of the irregular concave-convex surface p1e0 of the substrate 11e, the length L2 and width W2 of the surface p3e of the composite 21e, L2 = L12 - L0, W2 = W12 - W0, and the preferred value ranges of L0 and W0 are 90 to 150 mm, respectively; in the assembled state, the distance from the transverse side of the composite 21e (corresponding to the long side of the surface p3e) to the transverse side of the substrate 11e (corresponding to the long side of the irregular concave-convex surface p1e0) is half of W0, and the distance from the longitudinal side of the composite 21e (corresponding to the short side of the surface p3e) to the longitudinal side of the substrate 11e (corresponding to the short side of the irregular concave-convex surface p1e0) is half of L0.

[0171] The above describes the assembly step. In a preferred embodiment, after the assembly step, the four stacked billets are placed in a four-column hydraulic press. The opposing surfaces of the two substrates (i.e., the upper surface of the upper substrate and the lower surface of the lower substrate) are pressurized to a pressure of 500 tons or more. This ensures closer contact between adjacent billets.

[0172] Furthermore, in the step "preparing four sealing strips of width W3, placing the sealing strips against the four sides of the two composite materials, and performing gas shielded welding between adjacent sealing strips and between the sealing strips and the base material, so that the two base materials and the sealing strips form a whole, thereby obtaining a composite blank base blank", based on the arrangement of the sealing strips, the four stacked steel blanks are connected to form a composite blank base blank as a whole. Specifically, the composite blank base blank is: two base materials constitute the upper and lower surfaces, two composite materials are located in the middle, and four sealing strips form four frames surrounding the two composite materials and connecting the two base materials. Here, Figures 2a to 2e In the embodiment, the seals are respectively designated as 40a, 40b, 40c, 40d and 40e.

[0173] The width of the seal is W3 = 2T2 - 1-2 mm, which means that the width of the seal is slightly smaller than the sum of the thicknesses of the two composite materials by 1-2 mm. Using a seal of this width to simultaneously wrap the upper and lower composite materials improves the wrapping effect.

[0174] Furthermore, among the four seals, two seals are respectively attached to the two side edges of the two composite materials in the horizontal direction, with a length L31 = L2-1 ~ 2mm; the other two seals are respectively attached to the two side edges of the two composite materials in the longitudinal direction, with a length L32 = W2-1 ~ 2mm.

[0175] Preferably, the thickness T3 of the seal is 12-15 mm.

[0176] Each seal strip can be formed by directly cutting it from a steel plate according to the thickness T3, width W3, and length L31 or L32 without welding, or it can be formed by welding multiple seal strips of different lengths together, for example, the seal strips at the longitudinal side edges of the two composite materials in the fourth embodiment of the blank surface treatment step described above, and the seal strips at the transverse side edges of the two composite materials in the fifth embodiment of the blank surface treatment step described above.

[0177] Furthermore, the seal is made of the same steel grade as the base material. Preferably, the material of the seal is the same as that of the base material, and its chemical composition is as follows by mass percentage: 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 is Fe and unavoidable impurities.

[0178] As a preferred embodiment, in this step, before performing gas shielded welding between adjacent seals or between a seal and a substrate, both ends and both sides of each seal may be ground and polished to remove surface oxide scale and improve welding effect; and / or, both ends and both sides of each seal may be grooved first.

[0179] Furthermore, as a preferred embodiment, in the step of "gas shielded welding is performed between adjacent seals and between the seals and the substrate", the welding current is 215-245A, the welding voltage is 28-32V, the welding speed is 300-360mm / min, and the interpass temperature during the welding process is controlled at 135-165°C.

[0180] Alternatively, in gas shielded welding, the welding wire is ER50-6, the welding wire diameter is 1.2 mm, and the shielding gas is 75-80% Ar+20-25% CO2 in volume percentage.

[0181] Next, for the step of "machining a circular hole on the seal at the groove on the side of the composite blank base, and welding a seamless steel pipe at the circular hole", the groove described therein is a groove formed between the two base materials and outside the seal; in this step, a circular hole is machined to weld the seamless steel pipe to facilitate subsequent vacuuming of the inside of the composite blank.

[0182] As a preferred embodiment, the circular hole is processed in the middle of the short side (ie, the side in the longitudinal direction) of the composite blank base blank, but the present invention is not limited thereto.

[0183] As a preferred embodiment, the diameter of the circular hole is 8 to 12 mm; accordingly, the outer diameter of the seamless steel pipe is consistent with the diameter of the circular hole, which is 8 to 12 mm, the wall thickness is 1.2 to 2 mm, and the length is 200 to 400 mm.

[0184] Next, for the step of "surfacing the grooves on the four sides of the composite blank base blank", submerged arc surfacing is specifically used. Optionally, the submerged arc welding wire is GWL-H08MN2E, the submerged arc welding flux is GXL-101Q, and the wire diameter is 4.0mm. It can be understood that outside the four frames formed by the seal, a filling layer in the shape of a four-frame is formed by the butt welding in this step, see Figures 2a to 2e , wherein the filling layers formed by surfacing are marked as 50a, 50b, 50c, 50d and 50e respectively.

[0185] As a preferred method, before welding, the flux is baked at 350°C for 2 hours and then held at 150°C for 1 hour. During the welding process, the interpass temperature is controlled at 135-165°C, the welding current is 570-630A, the welding voltage is 28-32V, and the welding speed is 420-480mm / min. In this way, this submerged arc cladding technology, combined with the previous sealing and gas shielded welding, achieves a stable connection between the four steel billets, ensuring the connection strength and preventing cracking during the subsequent composite billet rolling step. Furthermore, on top of achieving the quality advantages of the composite plate mentioned above, it can further enhance the interface bonding effect.

[0186] In addition, during the welding process, before each welding operation, the weld attachments need to be cleaned to keep the weld clean; after welding, the weld is covered with thermal insulation cotton for insulation.

[0187] Next, the step of "using a vacuum pump to evacuate the composite billet through the seamless steel pipe, the vacuum degree

[0188] ≤10 -1 Pa, then maintain the pressure for more than 4 hours; finally, seal the seamless steel pipe. Connect the air inlet of the vacuum pump to the seamless steel pipe, and connect the seamless steel pipe to the space inside the composite blank (such as the surface gap between the composite material and the base material, the surface gap between the composite materials, the end face gap between the composite material and the seal, etc.) to exhaust the air in the space until the vacuum degree is ≤10 -1 Pa, and maintaining the pressure for more than 4 hours can ensure the vacuum degree. In this way, the air in the space can be prevented from causing surface oxidation at the composite interface during subsequent composite billet rolling, thereby ensuring the quality of composite interface bonding.

[0189] Furthermore, in this step, the seamless steel pipe is sealed by a method currently available in the steel industry, such as heating and flattening the seamless steel pipe with a flame gun to achieve sealing.

[0190] The above describes in detail the overall steps of preparing the composite billet. As mentioned above, the preparation method of the present invention also includes the overall step of rolling the composite billet after the overall step of preparing the composite billet. Specifically, the overall step of rolling the composite billet includes the following sub-steps:

[0191] The obtained composite blank is heated at a temperature of 1150-1170° C., the total heating time is ≥1.2×tmin / mm, where t is the thickness of the composite blank, and the holding time in the soaking section is 30-50 min.

[0192] A two-stage controlled rolling process of rough rolling and finishing rolling is adopted. In the rough rolling stage, the starting rolling temperature is ≤1020°C and the final rolling temperature is ≥980°C. Transverse rolling is performed first and then longitudinal rolling. During longitudinal rolling, at least one pass has a reduction of ≥35mm. The total rough rolling reduction is 40-60%. The rough rolling stage is terminated when the intermediate billet thickness is 2.5-3.5 times the target thickness of the composite plate. The intermediate billet is then allowed to warm up and water cooling is performed during the process. When the surface temperature of the intermediate billet drops below 860°C, the finishing rolling stage is started. The final rolling temperature of the finishing rolling stage is ≥830°C, and the total finishing reduction is 55-75% to obtain the composite plate.

[0193] After rolling, the composite plate enters the ultra-fast cooling system for cooling, with the starting cooling temperature ≥760℃, the cooling rate of 6-12℃ / s, and the final cooling temperature of 570-590℃;

[0194] After leaving the ultra-fast cooling system, the large composite plate directly enters the straightening machine for straightening.

[0195] During the composite billet rolling process, control of parameters such as the heating temperature, heating time, holding time, various rolling temperatures, reduction, cooling temperature, and cooling rate ensures that the resulting composite plate has a ferrite + pearlite structure and excellent mechanical properties, including yield strength ≥345 MPa, tensile strength ≥490 MPa, elongation after fracture ≥20%, and yield strength ratio ≤0.85. Furthermore, excellent surface quality, plate shape, and interface bonding quality are achieved. In particular, when combined with the chemical composition of the carbon steel plate described above, this significantly further improves mechanical properties.

[0196] Furthermore, in the overall steps of rolling the composite billet, the step of "the large composite plate directly enters the straightening machine for straightening after leaving the ultra-rapid cooling system" is warm straightening. After the large composite plate leaves the ultra-rapid cooling system at a final cooling temperature of 570-590°C, it is directly straightened at a temperature basically the same as or slightly lower than the final cooling temperature to ensure that the large composite plate is straight.

[0197] In a preferred embodiment of the composite sheet rolling process, after 1 to 3 passes of warm straightening, the composite sheet is naturally cooled on a cooling bed. When the surface temperature drops below 200°C, cold straightening is performed in a cold leveler. This improves the shape of the resulting composite sheet.

[0198] As another preferred embodiment of the composite billet rolling process, after performing the warm straightening for 1 to 3 times, the composite plate is placed at a temperature of T f The stack cooling is carried out between two steel plates at +100~150℃, and the stack cooling time is 0.4min / mm×t0±5min, where t0 is the thickness of the composite plate. In this way, the composite plate can be cooled slowly during the stack cooling time and can be clamped by the steel plates to maintain the uniformity of the core and surface temperature. After the stack cooling is completed, the composite plate is cooled naturally on the cooling bed.

[0199] T f =550+30[Si]-20[Mn]+15[Cr]-15[Ni]+10[Mo], where [Si], [Mn], [Mo], [Cr], and [Ni] are 100 times the mass percentage of the respective elements in the base material. In this preferred embodiment, stack cooling, particularly the temperature and duration of the two steel plates during stack cooling, can further significantly improve the microstructure, performance, and shape of the resulting composite plate.

[0200] The above describes in detail the overall steps of rolling the composite billet. As mentioned above, the preparation method of the present invention also includes the overall step of separating and straightening the composite plate. Specifically, the overall step of separating and straightening the composite plate includes the following sub-steps:

[0201] The composite plate obtained in the above composite billet rolling process is cut on its four sides by a plasma cutting machine to remove the portion other than the seal, and the composite plate is separated into two composite plate sheets, one above the other.

[0202] The composite plate is flattened horizontally and cold straightened to obtain the finished stainless steel composite plate.

[0203] The portion outside the seal in the step of "cutting the four sides to remove the portion outside the seal" refers to the edge portion of the composite plate that is transformed from the seal and the filling layer in the composite plate mentioned above after the composite plate rolling step. In this way, this portion is removed to expose the stainless steel cladding. Without the connecting function of this portion, the composite plate is separated into two small composite plates, one above the other. Figures 3a to 3e , corresponding to the five implementation methods of the blank surface treatment steps described above, Figures 3a to 3e The cross-sectional shapes of the two corresponding composite plate sheets (ie, the final composite plate) are shown respectively.

[0204] Each composite board is composed of a composite layer and a base layer. The composite layer is obtained by rolling the original composite material, and the base layer is obtained by rolling the original base material. In view of this, Figures 3a to 3e The composite layer is still marked with the grade of the original composite material, and the base layer is still marked with the grade of the original base material.

[0205] Furthermore, the composite plate obtained by the preparation method of the present invention has a ferrite + pearlite structure, excellent mechanical properties, good interface bonding quality, plate shape and surface quality, strong impact toughness and excellent corrosion resistance.

[0206] In a preferred embodiment, the total thickness of the composite board is 5 to 55 mm, the thickness of the base layer is 4 to 45 mm, and the thickness of the composite layer is 1 to 10 mm.

[0207] In a preferred embodiment, the yield strength is ≥345 MPa, the tensile strength is ≥490 MPa, the elongation after fracture is ≥20%, and the yield strength ratio is ≤0.85. These values ​​are obtained by sampling in accordance with GB / T 2975 - Steel and Steel Products - "Sampling Location and Preparation of Specimens for Mechanical Properties Tests," and by conducting tensile tests in accordance with GB / T 6396 - "Test Methods for Mechanical and Processing Properties of Composite Steel Plates" and GB / T 228.1 - "Tension Tests on Metallic Materials - Part 1: Room Temperature Test Methods."

[0208] In a preferred embodiment, the composite plate has a composite interface bonding rate of 100% and a shear strength of ≥300 MPa. These values ​​are measured by tensile testing in accordance with GB / T 6396-Test Methods for Mechanical and Process Properties of Composite Steel Plates.

[0209] In a preferred embodiment, the composite plate has an impact energy of ≥120 J at 0°C, ≥120 J at -20°C, and ≥120 J at -40°C. These values ​​are measured by sampling in accordance with GB / T 2975 - Steel and Steel Products - "Sampling Location and Specimen Preparation for Mechanical Properties Tests," and by testing in accordance with GB / T 6396 - "Test Methods for Mechanical and Processing Properties of Composite Steel Plates" and GB / T 229 - "Charpy Pendulum Impact Test Method for Metallic Materials."

[0210] In a preferred embodiment, the composite plate exhibits no cracks during an outward bend of 180° and no cracks during an inward bend of 180°. These data were obtained by sampling in accordance with GB / T 2975 - Steel and Steel Products - "Sampling Location and Specimen Preparation for Mechanical Properties Tests" and testing in accordance with GB / T 6396 - "Test Methods for Mechanical and Processing Properties of Composite Steel Plates."

[0211] In a preferred embodiment, after boiling the composite plate in a sulfuric acid-copper sulfate solution for 20 hours and bending it 180°, the composite layer exhibited no intergranular corrosion cracking. These data were obtained by sampling in accordance with GB / T 6396, "Test Methods for Mechanical and Processing Properties of Composite Steel Plates," and testing in accordance with GB / T 4334, "Corrosion of Metals and Alloys—Test Methods for Intergranular Corrosion of Austenitic and Ferritic-Austenitic (Duplex) Stainless Steels."

[0212] In a preferred embodiment, the unevenness of the composite plate is ≤3 mm / m. These data are measured by testing in accordance with GB / T709- "Dimensions, Shape, Weight and Permissible Deviations of Hot-rolled Steel Sheets and Strips".

[0213] The detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

[0214] The beneficial effects of the present invention are further illustrated below through a plurality of embodiments. Of course, these embodiments are only a part of the many variations of the present invention, but not all of them.

[0215] In these embodiments, the steel types and chemical compositions of the selected composite materials and base materials are shown in Table 1, respectively.

[0216] Table 1

[0217]

[0218]

[0219] Here, composite blanks were prepared in various examples according to the embodiments provided by the present invention. The substrates, composite materials, composite blank thicknesses, and composite blank types used are shown in Table 2. The substrate thickness type of "constant thickness" corresponds to the first embodiment of the blank surface treatment step, while the substrate thickness type of "variable thickness" corresponds to any of the second to fifth embodiments of the blank surface treatment step.

[0220] Table 2

[0221] substrate Composites Total thickness of composite billet, mm Substrate thickness type Example 1 Q345q 316L 266 Constant thickness Example 2 Q345q 316L 266 Variable thickness Example 3 Q345q 316L 266 Constant thickness Example 4 Q345q 316L 266 Variable thickness Example 5 Q345R 304L 308 Constant thickness Example 6 Q345R 304L 308 Variable thickness Example 7 Q345R 304L 308 Constant thickness Example 8 Q345R 304L 308 Variable thickness

[0222] Furthermore, for each embodiment, the composite billet rolling steps provided in one embodiment of the present invention were implemented, and the specific parameters in the composite billet rolling are shown in Table 3. Among them, in the stack cooling temperature column of Table 3, "-" indicates that the implementation is carried out in accordance with the aforementioned method of "naturally cooling the straightened composite plate on a cooling bed, and when the surface temperature drops below 200°C, cold straightening is carried out using a cold straightener", while the numbers shown in the stack cooling temperature column indicate that the implementation is carried out in accordance with the aforementioned method of "placing the straightened composite plate on a cooling bed at a temperature of T f It is implemented by "stack cooling" between two steel plates at +100-150℃.

[0223] Table 3

[0224]

[0225] Furthermore, the total thickness of the composite panels prepared in each embodiment, as well as the thickness of the composite panel (i.e., the finished composite panel), are shown in Table 4. The composite blanks corresponding to Examples 2, 4, 6, and 8 are substrates with variable thickness, and the corresponding composite panel thicknesses and base layer thicknesses are within a thickness range (i.e., minimum thickness to maximum thickness), rather than fixed values.

[0226] Table 4

[0227]

[0228] Furthermore, using the sampling and testing standards disclosed above, samples of the composite panels from various examples were sampled and tested. All examples demonstrated a 100% interfacial bonding rate, a passing 180° inward bend (no cracks), and a passing 180° outward bend (no cracks). Furthermore, after being boiled in a sulfuric acid-copper sulfate solution for 20 hours and then bent 180°, the composite layer showed no intergranular corrosion cracks. Other performance test results are shown in Table 5.

[0229] Table 5

[0230]

[0231]

Claims

1. A method for preparing a 345MPa grade stainless steel composite plate, characterized in that: The following steps are involved: 1) Composite blank preparation Prepare two carbon steel billets with a thickness of T1, a length of L1, and a width of W1 as base materials; and prepare two stainless steel billets with a thickness of T2, a length of L2, and a width of W2 as composite materials; L2<L1,W2<W1; performing surface treatment on at least one surface of each of the two substrates and the two composite materials; Apply a release agent to one surface of a composite material; Assembling the blanks in the order of stacking substrate, composite, composite, and substrate; wherein the composite is placed in the center relative to the substrate, the surfaces of the substrate and composite that are in contact with each other are both surfaces that have undergone the surface treatment, and the surface coated with the release agent faces the other composite; Prepare four sealing strips with a width of W3, where W3 = 2T2 - 1 to 2 mm, and place the sealing strips against the four sides of the two composite materials. Perform gas shielded welding between adjacent sealing strips and between the sealing strips and the base material, so that the two base materials and the sealing strips form a whole, thereby obtaining a composite blank base material. A circular hole is machined on the seal strip at the groove on the side of the composite billet base, and a seamless steel pipe is welded at the circular hole; The grooves on the four sides of the composite billet base are surfacing welded by submerged arc welding; before welding, the flux is baked at 350°C for 2 hours and then kept at 150°C for 1 hour; during welding, the interpass temperature is controlled at 135-165°C, the welding current is 570-630A, the welding voltage is 28-32V, and the welding speed is 420-480mm / min; The composite billet is vacuumed through the seamless steel pipe by a vacuum pump, and the vacuum degree is ≤10 -1 Pa, then maintain the pressure for more than 4 hours; finally, seal the seamless steel pipe; 2) Composite billet rolling The obtained composite blank is heated at a temperature of 1150-1170° C., the total heating time is ≥1.2×tmin / mm, where t is the thickness of the composite blank, and the holding time in the soaking section is 30-50 min. The two-stage controlled rolling process of rough rolling + finishing rolling is adopted. In the rough rolling stage, the starting rolling temperature is ≤1020℃, the finishing rolling temperature is ≥980℃, the horizontal rolling is carried out first and then the longitudinal rolling. During the longitudinal rolling, at least one pass of the reduction is ≥ 35mm, the total rough rolling reduction is 40-60%, and the rough rolling stage is ended when the thickness of the intermediate bar is 2.5-3.5 times the target thickness of the composite plate; then the intermediate bar is kept warm, and water cooling is carried out during the process. When the surface temperature of the intermediate bar drops below 860℃, the finishing rolling stage begins; the final rolling temperature of the finishing rolling stage is ≥830℃, and the total finishing rolling reduction is 55-75%, thereby obtaining the composite plate; After rolling, the composite plate enters the ultra-fast cooling system for cooling, with the starting cooling temperature ≥760℃, the cooling rate of 6-12℃ / s, and the final cooling temperature of 570-590℃; After leaving the ultra-fast cooling system, the composite plate directly enters the straightening machine for straightening; 3) Composite plate separation and straightening Cut the four sides of the composite board to remove the parts other than the seal, and separate the composite board into two small composite boards; The composite plate is flattened horizontally and cold straightened to obtain the finished stainless steel composite plate.

2. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, characterized in that: The chemical composition of the stainless steel billet is as follows in percentage by mass: 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.

3. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, wherein: The chemical composition of the carbon steel billet is, by mass percentage, as follows: 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 is Fe and unavoidable impurities.

4. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, wherein: The surface oxide scale indentation depth and surface pit depth of the carbon steel billet are both ≤0.3mm, and the unevenness is ≤3mm / m; the unevenness of the stainless steel billet is ≤2mm / m.

5. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, characterized in that: In the step of "applying a release agent on one surface of a composite material", the release agent used is a coating solution containing silicon oxide and magnesium oxide, wherein the mass ratio of silicon oxide to magnesium oxide is 3:

1.

6. The method for preparing a 345MPa grade stainless steel composite plate according to claim 5, characterized in that: The amount of the release agent applied is 20 μg / m 2 , y is the thickness ratio of the composite blank to the composite plate.

7. The method for preparing a 345MPa grade stainless steel composite plate according to claim 5, characterized in that: Before the step of "assembling the blanks in the order of stacking the substrate, the composite material, the composite material, and the substrate", the composite material coated with the release agent is placed in a trolley furnace for heating and drying at a temperature of 340 to 360°C for 35 to 45 minutes.

8. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, characterized in that: In the step of "applying a release agent to one surface of a composite material", the components of the release agent used are as follows: 25-35% silicon nitride, 5-10% thermosetting amino resin, and 55-70% water in a mass ratio.

9. The method for preparing a 345MPa grade stainless steel composite plate according to claim 8, characterized in that: The thickness of the release agent is 0.2 to 0.5 mm.

10. The method for preparing a 345MPa grade stainless steel composite plate according to claim 8, characterized in that: Before the step of "assembling the blanks in the order of stacking the substrate, the composite material, the composite material, and the substrate", the composite material coated with the release agent is heated and dried at a temperature of 100 to 250°C for 20 to 40 minutes.

11. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, characterized in that: After the step of "assembling the billets in the order of stacking substrate, composite, composite, and substrate", the four stacked billets are placed as a whole under a four-column hydraulic machine, and the opposing surfaces of the two substrates are pressurized to a pressure of ≥500 tons.

12. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, characterized in that: The step of "subjecting surface treatment to at least one surface of each of the two substrates and the two composites" includes: grinding and polishing one surface of each substrate and each composite to remove surface oxide scale.

13. The method for preparing a 345MPa grade stainless steel composite plate according to claim 12, characterized in that: L2=L1-L0, W2=W1-W0, L0 and W0 range from 90 to 150 mm respectively; In the aforementioned “the composite is placed centrally relative to the substrate”, the distance from the lateral side of the composite to the corresponding side of the substrate is half of W0, and the distance from the longitudinal side of the composite to the corresponding side of the substrate is half of L0.

14. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, characterized in that: The step of "substituting a surface treatment on at least one surface of each of the two substrates and the two composite materials" includes: Grinding and polishing one surface of each composite material to remove surface oxide scale; and, In a manner of relative shape complementarity, one surface of the two substrates is milled and ground, and the surface is processed into a transverse inclined surface with a length L11=L1 and a width W11>W1, and the substrate is a non-uniform thickness blank with a thickness gradient in the transverse direction, or the surface is processed into a longitudinal inclined surface with a length L11>L1 and a width W11=W1, and the substrate is a non-uniform thickness blank with a thickness gradient in the longitudinal direction.

15. The method for preparing a 345MPa grade stainless steel composite plate according to claim 14, characterized in that: L2=L11-L0, W2=W11-W0, L0 and W0 range from 90 to 150 mm respectively; In the aforementioned “the composite is placed centrally relative to the substrate”, the distance from the lateral side of the composite to the corresponding side of the substrate is half of W0, and the distance from the longitudinal side of the composite to the corresponding side of the substrate is half of L0.

16. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, characterized in that: The step of "substituting a surface treatment on at least one surface of each of the two substrates and the two composite materials" includes: Milling one surface of two substrates in a manner of relative shape complementation to form an irregular concave-convex surface comprising n planes sequentially connected in a transverse direction, wherein the substrate is a non-uniform thickness blank with a non-monotonically varying thickness in the transverse direction, wherein the length L12 of the irregular concave-convex surface is equal to L1 and the total width W12 is greater than W1; or milling the one surface of two substrates into an irregular concave-convex surface comprising n planes sequentially connected in a longitudinal direction, wherein the substrate is a non-uniform thickness blank with a non-monotonically varying thickness in the longitudinal direction, wherein the total length L12 of the irregular concave-convex surface is greater than L1 and the width W12 is equal to W1; n ≥ 2; One surface of each composite material is ground and polished to remove surface oxide scale; and then each composite material is bent to match the corresponding irregular concave and convex surface.

17. The method for preparing a 345MPa grade stainless steel composite plate according to claim 16, characterized in that: L2=L12-L0,W2=W12-W0,L0 and W0 range from 90 to 150mm respectively; In the aforementioned “the composite is placed centrally relative to the substrate”, the distance from the lateral side of the composite to the corresponding side of the substrate is half of W0, and the distance from the longitudinal side of the composite to the corresponding side of the substrate is half of L0.

18. The method for preparing a 345 MPa grade stainless steel composite plate according to claim 13, 15 or 17, wherein: In the step "Prepare four seals of width W3, where W3 = 2W2 - 1-2 mm, and affix the seals to the four sides of the two composite materials": The two seals are respectively attached to the two sides of the two composite materials in the horizontal direction, with a length of L31 = L2-1~2mm; The other two sealing strips are respectively attached to the longitudinal sides of the two composite materials, with a length of L32 = W2-1 ~ 2mm; The thickness T3 of the four seals is 12 to 15 mm.

19. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, characterized in that: In the step "gas shielded welding is performed between adjacent seals and between the seal and the base material", the welding current is 215-245A, the welding voltage is 28-32V, the welding speed is 300-360mm / min, and the interpass temperature during the welding process is controlled at 135-165°C.

20. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, characterized in that: After the step "the large composite plate leaves the ultra-fast cooling system and directly enters the straightening machine for straightening", the straightened large composite plate is naturally cooled on the cooling bed. When the surface temperature drops below 200℃, a cold straightening machine is used for cold straightening.

21. The method for preparing a 345MPa grade stainless steel composite plate according to claim 1, characterized in that: After the step "After leaving the ultra-fast cooling system, the composite board slab directly enters the straightening machine for straightening": The straightened composite board is placed at a temperature of T f The stack cooling is carried out between two steel plates at +100~150℃, and the stack cooling time is 0.4min / mm×t0±5min, where t0 is the thickness of the composite plate; After the stack cooling is completed, the composite board is cooled naturally 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.

22. A 345MPa grade stainless steel composite plate, characterized in that: The composite plate is prepared by the preparation method described in any one of claims 1 to 21. The total thickness of the composite plate is 5 to 55 mm, the thickness of the base layer is 4 to 45 mm, the thickness of the composite layer is 1 to 10 mm, the structure is ferrite + pearlite structure, the yield strength is ≥345 MPa, the tensile strength is ≥490 MPa, the elongation after fracture is ≥20%, and the yield strength ratio is ≤0.

85.

23. The 345MPa grade stainless steel composite plate according to claim 22, characterized in that: The composite interface bonding rate of the composite plate is 100%, and the shear strength is ≥300 MPa.

24. The 345MPa grade stainless steel composite plate according to claim 22, characterized in that: The composite plate has an impact energy of ≥120J at 0°C, an impact energy of ≥120J at -20°C, and an impact energy of ≥120J at -40°C; the composite plate has no cracks when bent outwards 180°, and no cracks when bent inwards 180°; and after being boiled in a sulfuric acid-copper sulfate solution for 20 hours and bent 180°, the composite layer has no intergranular corrosion cracks.

25. The 345MPa grade stainless steel composite plate according to claim 22, characterized in that: The unevenness of the composite plate is ≤3 mm / m.

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