370MPa Grade Stainless Steel Clad Plate and Its Preparation Method

Abstract

The present invention discloses a 370 MPa grade stainless steel clad plate and a preparation method thereof. The yield strength of the stainless steel clad plate is ≥ 370 MPa, the tensile strength is ≥ 510 MPa, the elongation after fracture is ≥ 20%, and the yield ratio is ≤ 0.85. In the method, gas shielded welding and surfacing, vacuum pumping and sealing are adopted in the preparation of the composite billet; two-stage controlled rolling of rough rolling + finish rolling is adopted. In the rough rolling stage, the starting rolling temperature is ≤ 1030 °C, the finishing rolling temperature is ≥ 990 °C, transverse rolling is carried out first and then longitudinal rolling, and the reduction per pass is ≥ 35 mm in at least one pass during longitudinal rolling; then it is kept warm, and when the surface temperature of the intermediate billet drops below 850 °C, the finish rolling stage starts; the finishing rolling temperature in the finish rolling stage is ≥ 820 °C; the starting cooling temperature is ≥ 750 °C, the cooling rate is 8 - 15 °C / s, and the final cooling temperature is 540 - 560 °C; after straightening and trimming, the clad plate is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material preparation, and relates to a 370MPa grade stainless steel composite plate and a preparation method thereof. Background Art

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

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

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

[0005] The object of the present invention is to provide a 370MPa 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, an embodiment of the present invention provides a method for preparing a 370MPa grade stainless steel composite plate, which comprises the following steps:

[0007] 1) Composite blank preparation

[0008] Prepare two carbon steel billets with a thickness T1, a length L1, and a width W1 as the base materials; and prepare two stainless steel billets with a thickness T2, a length L2, and a width W2 as the clad materials; L2 < L1, W2 < W1; The chemical composition of the carbon steel billet is by mass percentage: C: 0.08 - 0.12%, Si: 0.16 - 0.24%, Mn: 1.36 - 1.44%, P ≤ 0.015%, S ≤ 0.0025%, Cr: 0.11 - 0.19%, Ni: 0.06 - 0.14%, Nb: 0.016 - 0.024%, Ti: 0.011 - 0.019%, Al: 0.030 - 0.040%, and the rest is Fe and unavoidable impurities;

[0009] Surface-treat at least one surface of each of the two base materials and the two clad materials;

[0010] Apply a release agent on one surface of one clad material;

[0011] Form a billet stack in the order of base material, clad material, clad material, base material; wherein, the clad material is placed centered relative to the base material, and the surfaces of the base material and the clad material that are in contact with each other are all the surfaces that have undergone the surface treatment, and the surface coated with the release agent faces the other clad material;

[0012] Prepare four seals with a width W3, W3 = 2T2 - 1 to 2 mm, attach the seals to the four sides of the two clad materials, and perform gas shielded welding between adjacent seals and between the seals and the base material, so that the two base materials and the seals form an integral body to obtain a composite billet base blank;

[0013] Machine a round hole on the seal at the groove on the side of the composite billet base blank, and weld a seamless steel pipe at the round hole;

[0014] Build-up weld the grooves on the four sides of the composite billet base blank;

[0015] Use a vacuum pump to evacuate the composite billet through this seamless steel pipe, with the vacuum degree ≤ 10 -1 Pa, and then hold the pressure for more than 4 h; finally, seal the seamless steel pipe;

[0016] 2) Rolling of the composite billet

[0017] Heat the obtained composite billet, with the heating temperature being 1170 - 1190 °C, the total heating time ≥ 1.2 × tmin / mm, where t is the thickness of the composite billet, and the soaking section holding time is 30 min - 50 min;

[0018] Two-stage controlled rolling with rough rolling + finish rolling is adopted. In the rough rolling stage, the starting rolling temperature ≤ 1030 °C, the finishing rolling temperature ≥ 990 °C. First, transverse rolling is carried out and then longitudinal rolling. When performing longitudinal rolling, the reduction of at least one pass ≥ 35 mm. The total reduction in rough rolling is 40 - 60%, and the rough rolling stage ends when the thickness of the intermediate billet reaches 2.5 - 3.5 times the target thickness of the large composite plate. Then, it waits for temperature reduction, and during this period, water cooling is carried out. When the surface temperature of the intermediate billet drops below 850 °C, the finish rolling stage begins. The finishing rolling temperature in the finish rolling stage ≥ 820 °C, and the total reduction in finish rolling is 55 - 75%, obtaining the large composite plate.

[0019] After rolling is completed, the large composite plate enters the ultra-rapid cooling system for cooling. The starting cooling temperature ≥ 750 °C, the cooling rate is 8 - 15 °C / s, and the final cooling temperature is 540 - 560 °C.

[0020] After the large composite plate leaves the ultra-rapid cooling system, it directly enters the straightening machine for straightening.

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

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

[0023] Perform transverse flattening and cold straightening on the small composite plates to obtain the finished stainless steel composite plate.

[0024] Preferably, the chemical composition of the stainless steel billet is by mass percentage: C ≤ 0.15%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.030%, Ni: 6.0 - 22.0%, Cr: 16.0 - 26.0%, Mo ≤ 3.0%, and the balance is Fe and unavoidable impurities.

[0025] Preferably, the depth of surface scale penetration and the depth of surface pits of the carbon steel billet are both ≤ 0.3 mm, and the flatness ≤ 3 mm / m; the flatness of the stainless steel billet ≤ 2 mm / m.

[0026] Preferably, in the step of "coating a release agent on one surface of a composite material", the release agent used is a coating solution containing silicon oxide and magnesium oxide, and the mass ratio of silicon oxide to magnesium oxide is 3:1. Preferably, the amount of the release agent coated is 20 ymg / m 2 , where y is the thickness ratio of the composite billet to the large composite plate. Preferably, before the step of "assembling the billet in the stacking order of substrate, composite material, composite material, substrate", the composite material coated with the release agent is placed in a trolley furnace for heating and drying. The drying temperature is 340 - 360 °C, and the drying time is 35 - 45 min.

[0027] Preferably, in the step of "coating a release agent on one surface of a composite material", the components of the release agent used are in a mass ratio of: 25-35% silicon nitride, 5-10% thermosetting amino resin, and 55-70% water. Preferably, the thickness of the coated release agent is 0.2-0.5 mm. Preferably, before the step of "assembling blanks in the stacking order of substrate, composite material, composite material, substrate", the composite material coated with the release agent is heated and dried, the drying temperature is 100-250 °C, and the drying time is 20-40 min.

[0028] Preferably, after the step of "assembling blanks in the stacking order of substrate, composite material, composite material, substrate", the stacked four steel blanks are placed as a whole under a four-column hydraulic machine, and the opposite surfaces of the two substrates are pressurized, with the pressure ≥ 500 tons.

[0029] Preferably, the step of "surface-treating 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 scale.

[0030] Preferably, L2 = L1 - L0, W2 = W1 - W0, and the value ranges of L0 and W0 are 90-150 mm respectively;

[0031] In the statement of "the composite material is placed centered relative to the substrate", the distance from the lateral side of the composite material to the corresponding side of the substrate is half of W0, and the distance from the longitudinal side of the composite material to the corresponding side of the substrate is half of L0.

[0032] Preferably, the step of "surface-treating at least one surface of each of the two substrates and the two composite materials" includes:

[0033] grinding and polishing one surface of each composite material to remove surface scale; and,

[0034] According to the complementary relative shape, milling and processing one surface of the two substrates to process the surface 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 gradually changing thickness in the transverse direction, or processing the surface 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 gradually changing thickness in the longitudinal direction.

[0035] Preferably, L2 = L11 - L0, W2 = W11 - W0, and the value ranges of L0 and W0 are 90-150 mm respectively;

[0036] In the statement of "the composite material is placed centered relative to the substrate", the distance from the lateral side of the composite material to the corresponding side of the substrate is half of W0, and the distance from the longitudinal side of the composite material to the corresponding side of the substrate is half of L0.

[0037] Preferably, the step of "surface-treating at least one surface of each of the two base materials and the two composite materials" includes:

[0038] In a manner of relative shape complementarity, mill one surface of the two base materials to process the surface into an irregular concave-convex surface including n planes sequentially connected in the transverse direction, the base material being a non-uniform-thickness blank with non-monotonic thickness change in the transverse direction, the length L12 of the irregular concave-convex surface being L1 and the total width W12 > W1; or, process the surface into an irregular concave-convex surface including n planes sequentially connected in the longitudinal direction, the base material being a non-uniform-thickness blank with non-monotonic thickness change in the longitudinal direction, the total length L12 of the irregular concave-convex surface being > L1 and the width W12 being W1; n ≥ 2;

[0039] Grind and polish one surface of each composite material to remove the surface scale; then bend each composite material to match the corresponding irregular concave-convex surface.

[0040] Preferably, L2 = L12 - L0, W2 = W12 - W0, and the value ranges of L0 and W0 are 90 - 150 mm respectively;

[0041] In the step of "placing the composite material centrally relative to the base material", the distance from the side edge of the composite material in the transverse direction to the corresponding side edge of the base material is half of W0, and the distance from the side edge of the composite material in the longitudinal direction to the corresponding side edge of the base material is half of L0.

[0042] Preferably, in the step of "preparing four seals with width W3, W3 = 2W2 - 1 to 2 mm, and attaching the seals to the four side edges of the two composite materials":

[0043] Attach two seals respectively to the two side edges in the transverse direction of the two composite materials, with the length L31 = L2 - 1 to 2 mm;

[0044] Attach the other two seals respectively to the two side edges in the longitudinal direction of the two composite materials, with the length L32 = W2 - 1 to 2 mm;

[0045] The thickness T3 of the four seals is 12 - 15 mm.

[0046] Preferably, in the step of "performing gas shielded welding between adjacent seals and between the seals and the base material", the welding current is 215 - 245 A, the welding voltage is 28 - 32 V, the welding speed is 300 - 360 mm / min, and the interpass temperature during the welding process is controlled at 135 - 165 °C.

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

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

[0049] During the welding process, the interpass temperature is controlled at 135 - 165°C, the welding current is 570 - 630 A, the welding voltage is 28 - 32 V, and the welding speed is 420 - 480 mm / min.

[0050] Preferably, after the step "the large composite plate directly enters a straightening machine for straightening after leaving the ultra - rapid cooling system", the large composite plate after straightening is naturally cooled on a cooling bed. When the surface temperature drops below 200°C, a cold straightening machine is used for cold straightening.

[0051] Preferably, after the step "the large composite plate directly enters a straightening machine for straightening after leaving the ultra - rapid cooling system":

[0052] The large composite plate after straightening is placed between two steel plates at a temperature of T f ~T f + 50°C for stacking cooling. The stacking cooling time is 0.4 min / mm × t0 ± 5 min, where t0 is the thickness of the large composite plate;

[0053] After the stacking cooling is completed, the large composite plate is naturally cooled on a cooling bed;

[0054] T f = 550 + 30[Si] - 20[Mn] + 15[Cr] - 15[Ni] + 10[Mo], where [Si], [Mn], [Mo], [Cr],

[0055] [Ni] is 100 times the mass percentage of each element in the base material.

[0056] To achieve the above - mentioned invention purpose, an embodiment of the present invention provides a 370 MPa - grade stainless - steel composite plate. The composite plate is prepared by the above - mentioned preparation method. The total thickness of the composite plate is 5 - 55 mm, the thickness of the base layer is 4 - 45 mm, the thickness of the clad layer is 1 - 10 mm, and the microstructure is 70 - 85% ferrite + 10 - 20% pearlite + 5 - 10% bainite structure. The yield strength is ≥370 MPa, the tensile strength is ≥510 MPa, the elongation after fracture is ≥20%, and the yield - strength ratio is ≤0.85.

[0057] Preferably, the bonding rate of the composite interface of the composite plate is 100%, and the shear strength is ≥300 MPa.

[0058] Preferably, the impact energy of the composite plate at 0°C is ≥120 J, the impact energy at - 20°C is ≥120 J, and the impact energy at - 40°C is ≥120 J; the composite plate has no cracks after 180° outer bending and no cracks after 180° inner bending; after boiling in a sulfuric acid - copper sulfate solution for 20 h and 180° bending, there are no intergranular corrosion cracks in the clad layer.

[0059] Preferably, the flatness of the composite plate is ≤ 3 mm / m.

[0060] Compared with the prior art, the beneficial effects of the present invention are as follows: The composite plate prepared by the preparation method of the present invention has excellent surface quality, excellent plate shape, excellent interface bonding, etc. For example, there are no obvious surface defects such as pits and side scratches existing in the existing composite plates. For example, the flatness of the composite plate is ≤ 3 mm / m. For another example, the bonding rate of the composite interface of the composite plate is 100%, the shear strength is ≥ 300 MPa, and combined with the design of chemical components, it also has excellent mechanical properties. The total thickness of the composite plate is 5 - 55 mm, the thickness of the base layer is 4 - 45 mm, the thickness of the cladding layer is 1 - 10 mm, the structure is 70 - 85% ferrite + 10 - 20% pearlite + 5 - 10% bainite structure, the yield strength is ≥ 370 MPa, the tensile strength is ≥ 510 MPa, the elongation after fracture is ≥ 20%, and the yield ratio is ≤ 0.85. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] For the convenience of clear display and description, in each drawing of the present invention, the dimensions of some structures or parts are enlarged relative to other structures or parts. Therefore, it is only used to illustrate the basic structure of the subject matter of the present invention.

[0062] Figure 1a is a cross-sectional view of a steel billet of the first embodiment of the billet surface treatment step in the present invention;

[0063] Figure 1b is a transverse cross-sectional view of a steel billet of the second embodiment of the billet surface treatment step in the present invention, wherein the change in the surface shape after surface treatment is indicated by a dotted line;

[0064] Figure 1c is a longitudinal cross-sectional view of a steel billet of the third embodiment of the billet surface treatment step in the present invention, wherein the change in the surface shape after surface treatment is indicated by a dotted line;

[0065] Figure 1d is a transverse cross-sectional view of a steel billet of the fourth embodiment of the billet surface treatment step in the present invention, and the change in the surface shape before (A) and after (B) surface treatment is indicated;

[0066] Figure 1e is a longitudinal cross-sectional view of a steel billet of the fifth embodiment of the billet surface treatment step in the present invention, and the change in the surface shape before (A) and after (B) surface treatment is indicated;

[0067] Figure 2a corresponds to Figure 1a a cross-sectional view of the composite billet;

[0068] Figure 2b corresponds toFigure 1b Schematic cross-sectional view of a composite billet;

[0069] Figure 2c corresponds to Figure 1c Schematic longitudinal-sectional view of a composite billet;

[0070] Figure 2d corresponds to Figure 1d Schematic cross-sectional view of a composite billet;

[0071] Figure 2e corresponds to Figure 1e Schematic longitudinal-sectional view of a composite billet;

[0072] Figure 3a is Figure 2a Schematic cross-sectional view of two composite plates rolled from a composite billet;

[0073] Figure 3b is Figure 2b Schematic cross-sectional view of two composite plates rolled from a composite billet;

[0074] Figure 3c is Figure 2c Schematic longitudinal-sectional view of two composite plates rolled from a composite billet;

[0075] Figure 3d is Figure 2d Schematic cross-sectional view of two composite plates rolled from a composite billet;

[0076] Figure 3e is Figure 2e Schematic longitudinal-sectional view of two composite plates rolled from a composite billet. Detailed implementation manners

[0077] The present invention provides a method for preparing a 370 MPa grade stainless steel composite plate, and a composite plate prepared based on this method.

[0078] Compared with the prior art, such as explosion cladding, non-vacuum preparation of composite blanks, vacuum electron beam welding for blank preparation, etc. mentioned in the background art, the composite plate prepared by the preparation method of the present invention has the advantages of excellent surface quality, good plate shape, excellent interface bonding, etc. For example, there are no obvious surface defects such as pits and side scratches existing in the existing composite plates. For example, the flatness of the composite plate is ≤3mm / m. For another example, the bonding rate of the composite interface of the composite plate is 100%, and 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 cladding layer is 1 - 10mm, the microstructure is 70 - 85% ferrite + 10 - 20% pearlite + 5 - 10% bainite structure, the yield strength is ≥370MPa, the tensile strength is ≥510MPa, the elongation after fracture is ≥20%, and the yield ratio is ≤0.85.

[0079] Specifically, the preparation method includes three general steps: composite blank preparation, composite blank rolling, and composite plate separation and straightening.

[0080] The general steps of the composite blank preparation include the following sub-steps:

[0081] Prepare two carbon steel blanks with thickness T1, length L1, and width W1 as the base materials; and prepare two stainless steel blanks with thickness T2, length L2, and width W2 as the clad materials.

[0082] Surface-treat at least one surface of each of the two base materials and the two clad materials.

[0083] Apply a release agent on one surface of one of the clad materials.

[0084] Form a billet according to the stacking order of base material, clad material, clad material, base material.

[0085] Prepare four seal strips with width W3, where W3 = 2T2 - 1 - 2mm. Stick the seal strips against the four side edges of the two clad materials. Perform gas shielded welding between adjacent seal strips and between the seal strips and the base materials, so that the two base materials and the seal strips form an integral body to obtain a composite blank base blank.

[0086] Machine a round hole on the seal strip at the groove on the side edge of the composite blank base blank, and weld a seamless steel pipe at the round hole.

[0087] Build up weld the grooves on the four side edges of the composite blank base blank.

[0088] Use a vacuum pump to evacuate the composite blank through this seamless steel pipe, with the vacuum degree ≤10 -1 Pa, and then hold the pressure for more than 4h; finally, seal the seamless steel pipe.

[0089] Furthermore, the above sub-steps are described in detail as follows.

[0090] The step of "preparing two carbon steel billets with length L1 and width W1 as the base material; and preparing two stainless steel billets with length L2 and width W2 as the clad material", that is, the billet preparation step.

[0091] Among them, the carbon steel billet as the base material has a thickness T1, a length L1, and a width W1, that is, a rectangular steel billet; similarly, the stainless steel billet as the clad material has a thickness T2, a length L2, and a width W2, which is also a rectangular steel billet. And, L2 < L1, W2 < W1, and the length and width dimensions of the clad material are smaller than those of the base material.

[0092] The chemical composition of the carbon steel billet is by mass percentage: C: 0.08 - 0.12%, Si: 0.16 - 0.24%, Mn: 1.36 - 1.44%, P ≤ 0.015%, S ≤ 0.0025%, Cr: 0.11 - 0.19%, Ni: 0.06 - 0.14%, Nb: 0.016 - 0.024%, Ti: 0.011 - 0.019%, Al: 0.030 - 0.040%, and the rest is Fe and unavoidable impurities. Using the carbon steel billet with this chemical composition, combined with the control of each temperature, time, reduction, and cooling rate in the composite billet rolling step, the mechanical properties of the composite plate can be further improved under the above technical effects, and the toughness can be ensured. For example, the impact energy of the composite plate at 0°C ≥ 120 J, at -20°C ≥ 120 J, at -40°C ≥ 120 J; the composite plate has no cracks when bent 180° outward and no cracks when bent 180° inward.

[0093] The chemical compositions of the two carbon steel billets can be the same or different. Only one of the two carbon steel billets can adopt the chemical composition provided by the above preferred scheme, or both can adopt or both do not adopt the chemical composition provided by the above preferred scheme.

[0094] As a preferred scheme, the stainless steel billet is preferably austenitic stainless steel.

[0095] Furthermore, the chemical composition of the stainless steel billet is by mass percentage: C ≤ 0.15%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.030%, Ni: 6.0 - 22.0%, Cr: 16.0 - 26.0%, Mo ≤ 3.0%, and the balance is Fe and unavoidable impurities. Using the stainless steel billet with this chemical composition can further ensure the performance of the composite plate, especially the corrosion resistance of the clad layer, under the above technical effects. For example, the clad layer of the obtained composite plate (that is, obtained by rolling the clad material) has no intergranular corrosion cracks after boiling in sulfuric acid - copper sulfate solution for 20 h and bending 180°.

[0096] It should be noted here that the chemical compositions of the two stainless steel billets can be the same or different. Only one of them can adopt the chemical composition provided by the above preferred solution, or both can adopt or neither can adopt the chemical composition provided by the above preferred solution.

[0097] As a preferred solution, the depth of surface scale pressing-in and the depth of surface pits of the carbon steel billet are both ≤ 0.3 mm, and the flatness is ≤ 3 mm / m; the surface of the stainless steel billet has no scratches and the flatness is ≤ 2 mm / m. In this way, it is avoided that the billets enter the production line of the composite plate with obvious surface defects or shape defects.

[0098] Next, regarding the step of "performing surface treatment on at least one surface of each of the two substrates and the two cladding materials", that is, the billet surface treatment step. The present invention provides five preferred embodiments, and the following will introduce these five embodiments respectively.

[0099] <The first embodiment of the billet surface treatment step>

[0100] In this embodiment, one surface of each substrate and each cladding material is ground and polished to remove the surface scale and expose the metallic luster.

[0101] Refer Figure 1a As shown, for example, for the surface p1a of the substrate 11a, a grinding machine, a belt grinder or a milling machine is used for grinding and polishing to remove the surface scale and expose the metallic luster; similarly, for the surface p2a of the prepared substrate 12a, a grinding machine, a belt grinder or a milling machine is used for grinding and polishing to remove the surface scale and expose the metallic luster.

[0102] For the surface p3a of the prepared cladding material 21a, a wire wheel is used for grinding and polishing to remove the surface scale and expose the metallic luster; similarly, for the surface p4a of the prepared cladding material 22a, a wire wheel is used for grinding and polishing to remove the surface scale and expose the metallic luster.

[0103] Combined with the following text, it can be known that when assembling the billets, the surfaces that have undergone surface treatment (grinding and polishing in this embodiment) are used as the surfaces where the substrate and the cladding material are in contact with each other. For example, the surface p1a and the surface p3a are in contact with each other, and the surface p4a and the surface p2a are in contact with each other. In this way, the interface bonding quality can be ensured.

[0104] <The second embodiment of the billet surface treatment step>

[0105] In this embodiment, the same as the foregoing first embodiment, one surface of each cladding material (such as Figure 1b the surfaces p3b and p4b) is ground and polished to remove the surface scale and expose the metallic luster, which will not be elaborated here.

[0106] In this embodiment, different from the foregoing first embodiment, it is the surface treatment of the substrate:

[0107] Refer Figure 1b , the surface p1b of the substrate 11b is milled to process the surface p1b into a surface p1b0, which is a transverse inclined surface with a length L11 = L1 and a width W11 > W1. Correspondingly, the substrate 11b is processed into a non-uniform-thickness blank with a gradually changing thickness in the transverse direction (i.e., the width direction). That is to say, after the substrate 11b is milled, the height gradually increases from one side to the other side in the width direction.

[0108] Similarly, the surface p2b of the substrate 12b is milled to process the surface p2b into a surface p2b0, which is a transverse inclined surface with a length L11 = L1 and a width W11 > W1. Correspondingly, the substrate 12b is processed into a non-uniform-thickness blank with a gradually changing thickness in the transverse direction.

[0109] Among them, when milling the surface p2b of the substrate 12b and the surface p1b of the substrate 11b, it is carried out in a relatively shape-complementary manner, that is, the processed surfaces p2b0 and p1b0 are shape-complementary when facing each other. For example, the transverse inclination angle of the surface p2b0 (e.g., the angle with the original surface p2b) is equal to the transverse inclination angle of the surface p1b0 (e.g., the angle with the original surface p1b), so as to ensure that the upper and lower surfaces of the composite blank are parallel when assembling the blanks later.

[0110] It can be understood that through the above milling process, the surface scale on the surface p1b of the substrate 11b and the surface p2b of the substrate 12b can also be removed, revealing the metallic luster.

[0111] Combined with the following text, it can be seen that when assembling the blanks, by using the surfaces after surface treatment (milling in this embodiment) as the surfaces where the substrate and the composite material are in contact with each other. For example, the surface p1b0 and the surface p3b are in contact with each other, and the surface p4b and the surface p2b0 are in contact with each other. Similarly, it can ensure the interface bonding quality as in the foregoing first embodiment, and this embodiment can further be used to prepare a non-uniform-thickness composite plate with a gradually changing transverse thickness to improve the applicable scenarios and scope of the composite plate.

[0112] <The third embodiment of the blank surface treatment step>

[0113] This embodiment is basically the same as the aforementioned second embodiment (including the surface treatment of surfaces p3c and p4c), except that: the thickness change of the substrate in the transverse direction in the second embodiment is changed to the thickness change of the substrate in the longitudinal direction (i.e., the length direction) in this embodiment. The differences will be introduced below, and for other similarities, refer to the introduction of the second embodiment and will not be elaborated here.

[0114] Refer to Figure 1c , the surface p1c of the substrate 11c is milled to process the surface p1c into a surface p1c0, which is a longitudinal inclined surface with a length L11 > L1 and a width W11 = W1. Correspondingly, the substrate 11c is processed into a non-uniform thickness blank with a thickness change in the longitudinal direction.

[0115] Similarly, the surface p2c of the substrate 12c is milled to process the surface p2c into a surface p2c0, which is a longitudinal inclined surface with a length L11 > L1 and a width W11 = W1. Correspondingly, the substrate 12c is processed into a non-uniform thickness blank with a thickness change in the longitudinal direction.

[0116] Among them, when milling the surface p2c of the substrate 12c and the surface p1c of the substrate 11c, it is carried out in a relatively shape-complementary manner, that is, the processed surfaces p2c0 and p1c0 are shape-complementary when facing each other. For example, the longitudinal inclination angle of the surface p2c0 (such as the angle with the original surface p2c) is equal to the longitudinal inclination angle of the surface p1c0 (such as the angle with the original surface p1c), so as to ensure that the upper and lower surfaces of the composite blank are parallel during subsequent blank assembly.

[0117] It can be understood that through the above milling process, the surface oxide scale on the surface p1c of the substrate 11c and the surface p2c of the substrate 12c can also be removed, revealing the metallic luster.

[0118] <The Fourth Embodiment of the Blank Surface Treatment Step>

[0119] In this embodiment, one surface of each substrate is milled to process the surface into an irregular concave-convex surface including n planes connected in sequence along the transverse direction, and the substrate is a non-uniform thickness blank with a non-monotonic thickness change in the transverse direction, and the length L12 of the irregular surface = L1 and the total width W12 > W1.

[0120] For example, refer to Figure 1d , the surface p1d of the substrate 11d is milled to process the surface p1d from Figure 1d the horizontal surface in (A) into Figure 1dThe irregular concave-convex surface p1d0 shown in (B), which specifically includes n planes connected in sequence along the transverse direction, where n ≥ 2, and is exemplified as 8 planes in the figure. It can be seen from the figure that the 1st, 3rd, 5th, and 7th of these 8 planes in the direction from the left side to the right side of the figure are all transversely inclined surfaces, while the 2nd, 4th, 6th, and 8th are all horizontal planes. Of course, this is only an example, and it can also be implemented with other values of n, or only including transversely inclined surfaces without horizontal planes, etc.

[0121] Refer Figure 1d , through the milling process of the surface p1d, the base material 11d is processed into a non-uniform thickness blank with non-monotonic thickness change in the transverse direction.

[0122] The length L12 of the irregular concave-convex surface p1d0 = L1, that is, it does not change due to the milling process; while the total width W12 of the irregular concave-convex surface p1d0 > W1. It can be understood that this total width W12 is the sum of the widths of the n planes.

[0123] Correspondingly, refer Figure 1d , the surface p2d of the base material 12d is also milled, and the surface p2d is processed from the Figure 1d horizontal surface in (A) into the Figure 1d irregular concave-convex surface p2d0 shown in (B). Among them, when milling the surface p2d of the base material 12d and the surface p1d of the base material 11d, it is carried out in a relatively shape-complementary manner, that is, the processed surface p2d0 and the surface p1d0 are shape-complementary when they face each other.

[0124] According to the relative shape complementarity, this irregular concave-convex surface p2d0 also specifically includes n planes connected in sequence along the transverse direction, and is exemplified as 8 planes in the figure. The length L12 of the irregular concave-convex surface p2d0 = L1, that is, it does not change due to the milling process; while the total width W12 of the irregular concave-convex surface p2d0 > W1. It can be understood that this total width W12 is the sum of the widths of the n planes of the irregular concave-convex surface p2d0.

[0125] Refer Figure 1d , through the milling process of the surface p2d, the base material 12d is processed into a non-uniform thickness blank with non-monotonic thickness change in the transverse direction. Based on the relative shape complementarity of the irregular concave-convex surface p2d0 and the irregular concave-convex surface p1d0, if the milled base materials 12d and 11d are placed opposite to each other, the sum of the thicknesses at each place is constant. Thus, when assembling the blanks subsequently, the upper and lower surfaces of the composite blank are parallel.

[0126] The above introduces the surface treatment of two base materials in this embodiment. Next, the surface treatment of two composite materials will be introduced.

[0127] In this embodiment, for the surface p3d of the prepared composite material 21d, a wire wheel is used for grinding and polishing to remove the surface scale and expose the metallic luster. Similarly, for the surface p4d of the prepared composite material 22d, a wire wheel is used for grinding and polishing to remove the surface scale and expose the metallic luster.

[0128] Furthermore, matching the surface shapes of the base materials 11d and 12d, after removing the surface scale, each composite material in this embodiment is bent so that each composite material matches the corresponding irregular concave-convex surface. For example, for the composite material 21d, it is bent to match the corresponding irregular concave-convex surface p1d0 to facilitate the fitting contact during subsequent blank assembly; for another example, for the composite material 22d, it is bent to match the corresponding irregular concave-convex surface p2d0 to facilitate the fitting contact during subsequent blank assembly.

[0129] The surface treatment of this embodiment can ensure the interface bonding quality as in the aforementioned first embodiment, and can further be used to prepare a non-uniform-thickness composite plate with non-monotonic change in transverse thickness, so as to expand the applicable scenarios and scope of the composite plate, enhance the corrosion resistance compared with the existing steel plates, and avoid frequent welding and dissimilar welding between composite plates of different thicknesses.

[0130] <The Fifth Embodiment of the Blank Surface Treatment Step>

[0131] The difference between this embodiment and the aforementioned fourth embodiment is that: the thickness of the base material in the fourth embodiment changes non-monotonically in the transverse direction, while the thickness of the base material in this embodiment changes non-monotonically in the longitudinal direction.

[0132] For example, referring to Figure 1e , the surface p1e of the base material 11e is milled, and the surface p1e is processed from the horizontal surface in Figure 1e (A) into the irregular concave-convex surface p1e0 shown in Figure 1e (B). The irregular concave-convex surface p1e0 specifically includes n planes connected in sequence along the longitudinal direction, where n≥2, and is exemplified as 8 planes in the figure. It can be seen from the figure that the 1st, 3rd, 5th, and 7th of these 8 planes in the direction from the left to the right of the figure are longitudinally inclined surfaces, while the 2nd, 4th, 6th, and 8th are horizontal planes. Of course, this is only an example, and it can also be implemented with n taking other numbers, or only including longitudinally inclined surfaces without horizontal planes, etc.

[0133] Referring to Figure 1e , through the milling of the surface p1e, the base material 11e is processed into a non-uniform-thickness blank with non-monotonic change in longitudinal thickness.

[0134] The width W12 of the irregular concave-convex surface p1e0 is W1, that is, it does not change due to milling; while 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.

[0135] Correspondingly, refer Figure 1e , the surface p2e of the base material 12e is also milled, and the surface p2e is changed from Figure 1e the horizontal surface in (A) to Figure 1e the irregular concave-convex surface p2e0 shown in (B). Among them, when milling the surface p2e of the base material 12e and the surface p1e of the base material 11e, it is carried out in a complementary relative shape manner, that is, the processed surfaces p2e0 and p1e0 are complementary in shape when they face each other.

[0136] According to the complementary relative shape, the irregular concave-convex surface p2e0 also specifically includes n planes connected in sequence longitudinally, which are exemplified as 8 planes in the figure. The width W12 of the irregular concave-convex surface p2e0 is W1, and the total length L12 is greater than L1.

[0137] Refer Figure 1e , through the milling of the surface p2e, the base material 12e is processed into a non-uniform thickness blank with non-monotonic thickness change in the longitudinal direction. Based on the complementary relative shape of the irregular concave-convex surface p2e0 and the irregular concave-convex surface p1e0, if the milled base materials 12e and 11e are placed opposite to each other, the sum of the thicknesses at each place is constant. Thus, when assembling the blanks later, the upper and lower surfaces of the composite blank are parallel.

[0138] The above introduces the surface treatment of two base materials in this embodiment. Next, the surface treatment of two composite materials will be introduced.

[0139] In this embodiment, for the surface p3e of the prepared composite material 21e, a wire wheel is used for grinding and polishing to remove the surface oxide scale and expose the metallic luster; similarly, for the surface p4e of the prepared composite material 22e, a wire wheel is used for grinding and polishing to remove the surface oxide scale and expose the metallic luster.

[0140] Furthermore, matching the surface shapes of the base materials 11e and 12e, after removing the surface oxide scale, each composite material in this embodiment is bent so that each composite material matches the corresponding irregular concave-convex surface. For example, for the composite material 21e, it is bent to match the corresponding irregular concave-convex surface p1e0 for easy fitting contact during subsequent blank assembly; for another example, for the composite material 22e, it is bent to match the corresponding irregular concave-convex surface p2e0 for easy fitting contact during subsequent blank assembly.

[0141] Similar to the aforementioned fourth embodiment, this embodiment can also improve the application scenarios and scope of the composite plate, enhance the corrosion resistance relative to the existing steel plate, and avoid frequent welding and dissimilar welding between composite plates of different thicknesses.

[0142] The above introduces five preferred implementation methods of the blank surface treatment steps in the composite blank preparation step. Although only one surface 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, other surfaces of each substrate and composite material can be further treated to remove oxide scale. Although this additional treatment to remove 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.

[0143] The other sub-steps of the composite blank preparation step will be introduced below.

[0144] The step of "coating a release agent on one surface of a composite material" is the step of coating the release agent.

[0145] 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 contact 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 isolation agent coating step is to avoid through the isolation agent that the surfaces of the composite materials that are in contact with the substrate during assembly are subsequently bonded in the composite billet rolling step, resulting in difficulty in separation in the end.

[0146] Based on this, one of the two composite materials is selected to be coated with a release agent. If the selected composite material has one surface treated and the other surface not treated in the previous blank surface treatment step, in the release agent coating step, the release agent is coated on the "untreated" surface. If, as mentioned above, the selected composite material has both surfaces treated in the previous blank surface treatment step, in the release agent coating step, the release agent is coated on the surface that is planned to face the other composite material during blank assembly.

[0147] For example, Figure 1a For example, the release agent may be applied on the surface p6a of the composite material 22a or the surface p5a of the composite material 21a.

[0148] Regarding the release agent, two preferred implementation modes are provided here, which are respectively introduced below.

[0149] <First Embodiment of Release Agent>

[0150] In this embodiment, the parting agent is a coating solution containing silicon oxide and magnesium oxide, and the mass ratio of silicon oxide to magnesium oxide is 3:1. The parting agent of this embodiment can achieve a good parting effect and ensure the separation of the subsequent two small composite plates.

[0151] Here, a preparation method of the parting agent is provided as follows: Mix parting agent powder, binder powder and water in a mass ratio of 27:3:70 to obtain a fluid parting agent coating solution. Among them, the parting agent powder is silicon oxide and magnesium oxide, mixed in a mass ratio of 3:1. The binder powder is polyvinyl alcohol and thermosetting phenolic resin, mixed in a mass ratio of 1:1.

[0152] When the parting agent is applied to the surface of the composite material, the amount of the applied parting agent is 20 ymg / m 2 , that is, the weight of the parting agent per unit area of the surface of the composite material is 20 ymg. Among them, y is the ratio of the thickness of the composite blank obtained in the composite blank preparation step to the thickness of the large composite plate formed by subsequent rolling, and this ratio is also called the rolling compression ratio of the composite blank.

[0153] Further, based on this embodiment, after the application of the parting agent is completed and before subsequent blank assembly, the composite material coated with the parting agent is placed in a trolley furnace for heating and drying. The drying temperature is 340 - 360 °C, and the drying time is 35 - 45 min.

[0154] <The second embodiment of the parting agent>

[0155] In this embodiment, the components of the parting agent are in a mass ratio of: 25 - 35% silicon nitride, 5 - 10% thermosetting amino resin, and 55 - 70% water. Compared with the existing parting agent and even compared with the first embodiment of the foregoing parting agent, the parting agent of this embodiment can not only achieve a good parting effect and ensure the separation of the subsequent two small composite plates, but also the active ingredient silicon nitride has strong chemical stability, high temperature resistance and heat shock resistance. The thermosetting amino resin used as the binder can be cured at low temperature, is non-toxic, and can achieve a strong bonding effect with a very small amount. Therefore, as a whole, it has a low price, simple operation, and good parting and adhesion effects.

[0156] Here, a preferred preparation method of the parting agent is provided, including: First, put 5 - 10% silicon nitride (by weight percentage) in a container such as a beaker, and then pour in 15 - 25% water and stir; after the silicon nitride has no granular feeling and no bubbles, pour in 2 - 3% thermosetting amino resin and continue to stir; when it shows a viscous state, continue to pour in the remaining silicon nitride and water, stir for 3 - 5 min and then pour in the remaining thermosetting amino resin; when it is stirred to a viscous state, the parting agent is prepared.

[0157] When applying the release agent on the surface of the composite material, the thickness of the applied release agent is 0.2 - 0.5 mm.

[0158] Further, based on this embodiment, after applying the release agent and before subsequent layup, the composite material coated with the release agent is heated and dried. The drying temperature is 100 - 250 °C, and the drying time is 20 - 40 min.

[0159] Next, after completing the step of applying the release agent, the step of "laying up in the stacking order of substrate, composite material, composite material, substrate" will be introduced.

[0160] This step of "laying up in the stacking order of substrate, composite material, composite material, substrate", that is, the layup step. Among them, in addition to the stacking order of substrate, composite material, composite material, substrate, the following conditions also need to be met:

[0161] 1) The surfaces of the substrate and the composite material in contact with each other are all surfaces that have undergone the surface treatment; for example, in the first embodiment of the blank surface treatment step described above, refer Figure 2a , the surface p2a of the substrate 12a is in contact with the surface p4a of the composite material 22a, and the surface p1a of the substrate 11a is in contact with the surface p3a of the composite material 21a; in the second embodiment of the blank surface treatment step described above, refer Figure 2b , the surface p1b0 is in contact with the surface p3b, and the surface p4b is in contact with the surface p2b0; in the third embodiment of the blank surface treatment step described above, refer Figure 2c , the surface p1c of the substrate 11c is in contact with the surface p3c of the composite material 21c, and the surface p2c of the substrate 12c is in contact with the surface p4c of the composite material 22c; in the fourth embodiment of the blank surface treatment step described above, refer Figure 2d , the irregular concave-convex surface p1d0 is in contact with the surface p3d of the composite material 21d, and the irregular concave-convex surface p2d0 is in contact with the surface p4d of the composite material 22d; in the fifth embodiment of the blank surface treatment step described above, refer Figure 2e , the irregular concave-convex surface p1e0 is in contact with the surface p3e of the composite material 21e, and the irregular concave-convex surface p2e0 is in contact with the surface p4e of the composite material 22e;

[0162] 2) The surface coated with the release agent faces another composite material; for example, refer Figure 2a , one of the surfaces p6a and p5a is coated with the release agent 30a; refer Figure 2b , one of the surfaces p6b and p5b is coated with the release agent 30b; refer Figure 2c , one of the surfaces p6c and p5c is coated with the release agent 30c; referFigure 2d , one of the surfaces p6d and p5d is coated with a release agent 30d; see Figure 2e , one of the surfaces p6e and p5e is coated with a release agent 30e;

[0163] 3) The composite material is placed centered relative to the base material; in this regard, as introduced above, the length and width dimensions of the composite material are both smaller than those of the base material, L2 < L1, W2 < W1. When forming the billet, the distances from the two side edges of the composite material in the transverse direction to the corresponding two side edges of the base material are equal, and the distances from the two side edges of the composite material in the longitudinal direction to the corresponding two side edges of the base material are also equal.

[0164] The following will separately explain the third point here for each of the five implementation manners of the billet surface treatment steps described above. And, in view of the fact that the composite billet is generally symmetrically arranged up and down, only a set of base material + composite material in the composite billet is taken as an example for explanation, such as the upper set.

[0165] For the first implementation manner of the billet surface treatment steps described above, see Figure 2a , the length L1 and width W1 of the surface p1a of the base material 11a, the length L2 and width W2 of the surface p3a of the composite material 21a, L2 = L1 - L0, W2 = W1 - W0, and the preferably value ranges of L0 and W0 are 90 - 150 mm respectively; in the billet forming state, the distance from the side edge of the composite material 21a in the transverse direction (corresponding to the long side of the surface p3a) to the side edge of the base material 11a in the transverse direction (corresponding to the long side of the surface p1a) is half of W0, and the distance from the side edge of the composite material 21a in the longitudinal direction (corresponding to the short side of the surface p3a) to the side edge of the base material 11a in the longitudinal direction (corresponding to the short side of the surface p1a) is half of L0.

[0166] For the second implementation manner of the billet surface treatment steps described above, see Figure 2b , the length L11 and width W11 of the surface p1b0 of the base material 11b, the length L2 and width W2 of the surface p3b of the composite material 21b, L2 = L11 - L0, W2 = W11 - W0, and the preferably value ranges of L0 and W0 are 90 - 150 mm respectively; in the billet forming state, the distance from the side edge of the composite material 21b in the transverse direction (corresponding to the long side of the surface p3b) to the side edge of the base material 11b in the transverse direction (corresponding to the long side of the surface p1b0) is half of W0, and the distance from the side edge of the composite material 21b in the longitudinal direction (corresponding to the short side of the surface p3b) to the side edge of the base material 11b in the longitudinal direction (corresponding to the short side of the surface p1b0) is half of L0.

[0167] For the third implementation manner of the billet surface treatment steps described above, see Figure 2c, for the length L11 and width W11 of the surface p1c0 of the base material 11c, and the length L2 and width W2 of the surface p3c of the composite material 21c, L2 = L11 - L0, W2 = W11 - W0, and the preferably value ranges of L0 and W0 are 90 - 150 mm respectively; in the blank assembly state, the distance from the side edge in the transverse direction of the composite material 21c (corresponding to the long side of the surface p3c) to the side edge in the transverse direction of the base material 11c (corresponding to the long side of the surface p1c0) is half of W0, and the distance from the side edge in the longitudinal direction of the composite material 21c (corresponding to the short side of the surface p3c) to the side edge in the longitudinal direction of the base material 11c (corresponding to the short side of the surface p1c0) is half of L0.

[0168] For the fourth implementation manner of the blank surface treatment step described above, refer Figure 2d , for the length L12 and width W12 of the irregular concave-convex surface p1d0 of the base material 11d, and the length L2 and width W2 of the surface p3d of the composite material 21d, L2 = L12 - L0, W2 = W12 - W0, and the preferably value ranges of L0 and W0 are 90 - 150 mm respectively; in the blank assembly state, the distance from the side edge in the transverse direction of the composite material 21d (corresponding to the long side of the surface p3d) to the side edge in the transverse direction of the base material 11d (corresponding to the long side of the irregular concave-convex surface p1d0) is half of W0, and the distance from the side edge in the longitudinal direction of the composite material 21d (corresponding to the short side of the surface p3d) to the side edge in the longitudinal direction of the base material 11d (corresponding to the short side of the irregular concave-convex surface p1d0) is half of L0.

[0169] For the fifth implementation manner of the blank surface treatment step described above, refer Figure 2e , for the length L12 and width W12 of the irregular concave-convex surface p1e0 of the base material 11e, and the length L2 and width W2 of the surface p3e of the composite material 21e, L2 = L12 - L0, W2 = W12 - W0, and the preferably value ranges of L0 and W0 are 90 - 150 mm respectively; in the blank assembly state, the distance from the side edge in the transverse direction of the composite material 21e (corresponding to the long side of the surface p3e) to the side edge in the transverse direction of the base material 11e (corresponding to the long side of the irregular concave-convex surface p1e0) is half of W0, and the distance from the side edge in the longitudinal direction of the composite material 21e (corresponding to the short side of the surface p3e) to the side edge in the longitudinal direction of the base material 11e (corresponding to the short side of the irregular concave-convex surface p1e0) is half of L0.

[0170] The above introduced the blank assembly step. In a preferred implementation manner, after implementing the blank assembly step, the stacked four steel billets are placed as a whole under a four-column hydraulic machine, and the opposite surfaces of the two base materials (that is, the upper surface of the upper base material and the lower surface of the lower base material) are pressurized, and the pressure ≥ 500 tons. Thus, the contact between adjacent steel billets can be made closer.

[0171] Further, in the step of "preparing four seals with a width of W3, attaching the seals to the four side edges of the two composite materials, and performing gas shielded welding between adjacent seals and between the seals and the base material, so that the two base materials and the seals form an integral body to obtain a composite blank base blank", based on the setting of the seals, the four steel blanks stacked together are connected to form an integral composite blank base blank. Specifically, the composite blank base blank is formed as follows: two base materials form the upper and lower surfaces, two composite materials are located in the middle, and four seals are arranged as four side frames surrounding the two composite materials on all sides and connecting the two base materials. Here, Figure 2a - 2e Among them, the seals are respectively labeled as 40a, 40b, 40c, 40d, and 40e.

[0172] The width W3 of the seal is 2T2 - 1 to 2 mm, that is, the width of the seal is slightly smaller than the sum of the thicknesses of the two composite materials by 1 to 2 mm. Seals with this width are used to wrap the upper and lower two composite materials simultaneously, improving the wrapping effect.

[0173] Furthermore, among the four seals, two seals are respectively attached to the two lateral side edges of the two composite materials, and the length L31 = L2 - 1 to 2 mm; the other two seals are respectively attached to the two longitudinal side edges of the two composite materials, and the length L32 = W2 - 1 to 2 mm.

[0174] Preferably, the thickness T3 of the seal is 12 to 15 mm.

[0175] Regarding the forming method of each seal, it can either be directly cut out on a steel plate according to the thickness T3, width W3, length L31, or L32 without welding, or be spliced by welding multiple seals with different lengths. For example, the seals at the two longitudinal side edges of the two composite materials in the fourth embodiment of the above-mentioned blank surface treatment step, and the seals at the two lateral side edges of the two composite materials in the fifth embodiment of the above-mentioned blank surface treatment step.

[0176] Further, the seal uses the same steel type as the base material. Preferably, the material of the seal is the same as that of the base material, and its chemical composition in mass percentage is: C: 0.08 - 0.12%, Si: 0.16 - 0.24%, Mn: 1.36 - 1.44%, P ≤ 0.015%, S ≤ 0.0025%, Cr: 0.11 - 0.19%, Ni: 0.06 - 0.14%, Nb: 0.016 - 0.024%, Ti: 0.011 - 0.019%, Al: 0.030 - 0.040%, and the rest is Fe and inevitable impurities.

[0177] As a preferred embodiment, in this step, before performing gas shielded welding between adjacent seals and between the seal and the base material, the two ends and two sides of each seal can be ground and polished first to remove the surface oxide scale and improve the welding effect; and / or, the two ends and two sides of each seal can be beveled first.

[0178] Further, as a preferred embodiment, in the step of "performing gas shielded welding between adjacent seals and between the seal and the base material", the welding current is 215 - 245 A, the welding voltage is 28 - 32 V, the welding speed is 300 - 360 mm / min, and the interpass temperature during the welding process is controlled at 135 - 165 °C.

[0179] Optionally, in the gas shielded welding, the welding wire is ER50-6, the wire diameter is 1.2 mm, and the shielding gas is 75 - 80% Ar + 20 - 25% CO by volume 2 .

[0180] Next, for the step of "processing a round hole on the seal at the groove on the side of the composite blank base blank and welding a seamless steel pipe at the round hole", the groove mentioned herein is the groove formed between two base materials and outside the seal; in this step, a round hole is processed for welding the seamless steel pipe to facilitate subsequent vacuum pumping of the inside of the composite blank.

[0181] As a preferred method, the round hole is processed in the middle of the short side (i.e., the side on the longitudinal direction) of the composite blank base blank, but it is not limited thereto.

[0182] As a preferred method, the diameter of the round hole is 8 - 12 mm; correspondingly, the outer diameter of the seamless steel pipe is consistent with the diameter of the round hole, which is 8 - 12 mm, the wall thickness is 1.2 - 2 mm, and the length is 200 - 400 mm.

[0183] Next, for the step of "performing submerged arc surfacing on the grooves on the four sides of the composite blank base blank", submerged arc surfacing is specifically used. Optionally, the submerged arc welding wire is GWL-H08MN2E, the submerged arc welding flux is GXL-101Q, and the wire diameter is 4.0 mm. It can be understood that outside the four-sided frame formed by the seals, a four-sided frame-shaped filling layer is formed through the surfacing of this step. See Figure 2a - 2e , where the filling layers formed by the surfacing are respectively labeled as 50a, 50b, 50c, 50d, and 50e.

[0184] As a preferred method, before welding, the welding flux is baked at 350°C for 2 hours and then kept warm at 150°C for 1 hour. During welding, the interpass temperature is controlled at 135 - 165°C, the welding current is 570 - 630 A, the welding voltage is 28 - 32 V, and the welding speed is 420 - 480 mm / min. In this way, this submerged arc surfacing technology, combined with the previous seal wrapping and gas shielded welding, jointly realizes the stable connection of the four steel billets, ensures the connection strength, avoids abnormal cracking in the subsequent composite billet rolling step, and further improves the interface bonding effect on the basis of realizing the quality advantages of the composite plate described above.

[0185] In addition, during welding, before each welding operation, the attachments on the weld bead need to be cleaned to keep the weld bead clean; after welding, heat preservation is carried out by covering with heat preservation cotton.

[0186] Next, in the step "using a vacuum pump to evacuate the composite billet through this seamless steel pipe, with the vacuum degree

[0187] ≤10 -1 Pa, and then maintaining the pressure for more than 4 hours; finally, sealing the seamless steel pipe", the suction port of the vacuum pump is connected to the seamless steel pipe, and the seamless steel pipe is connected to the space inside the composite billet (such as the surface gap between the composite 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 discharge the air in this space until the vacuum degree ≤10 -1 Pa, and maintaining the pressure for more than 4 hours can ensure the vacuum degree. In this way, the air in this space can be avoided from causing surface oxidation at the composite interface during the subsequent rolling of the composite billet, thereby ensuring the bonding quality of the composite interface.

[0188] Furthermore, in this step, the sealing treatment of the seamless steel pipe can be implemented by existing feasible methods in the steel industry. For example, the seamless steel pipe is heated with a flame gun and flattened to achieve sealing.

[0189] The above has described in detail the total steps of preparing the composite billet. As described above, the preparation method of the present invention further includes the total steps of rolling the composite billet after the total steps of preparing the composite billet. Specifically, the total steps of rolling the composite billet include the following sub-steps:

[0190] Heat the obtained composite billet, with the heating temperature being 1170 - 1190°C, the total heating time ≥1.2×t min / mm, where t is the thickness of the composite billet, and the soaking time in the soaking section is 30 min - 50 min;

[0191] Two-stage controlled rolling of rough rolling + finish rolling is adopted. In the rough rolling stage, the starting rolling temperature ≤ 1030 °C, the finishing rolling temperature ≥ 990 °C. First, transverse rolling is carried out and then longitudinal rolling. When longitudinally rolling, the reduction per pass of at least one pass ≥ 35 mm, the total reduction of rough rolling is 40 - 60%, and the rough rolling stage ends when the thickness of the intermediate billet is 2.5 - 3.5 times the target thickness of the large plate of the composite plate; then it is held at temperature, and water cooling is carried out during this period. When the surface temperature of the intermediate billet drops below 850 °C, the finish rolling stage begins; the finishing rolling temperature of the finish rolling stage ≥ 820 °C, the total reduction of finish rolling is 55 - 75%, and the large plate of the composite plate is obtained.

[0192] After rolling is completed, the large plate of the composite plate enters the ultra-fast cooling system for cooling. The starting cooling temperature ≥ 750 °C, the cooling rate is 8 - 15 °C / s, and the final cooling temperature is 540 - 560 °C.

[0193] After the large plate of the composite plate leaves the ultra-fast cooling system, it directly enters the straightening machine for straightening.

[0194] In the total steps of rolling the composite billet, by controlling parameters such as the heating temperature, heating duration, holding duration, various temperatures during rolling, reduction, temperature during cooling, and cooling rate, not only can it be ensured that the structure of the finally obtained composite plate is 70 - 85% ferrite + 10 - 20% pearlite + 5 - 10% bainite structure, but also it has excellent mechanical properties, including yield strength ≥ 370 MPa, tensile strength ≥ 510 MPa, elongation after fracture ≥ 20%, yield ratio ≤ 0.85, and excellent surface quality, plate shape, and interface bonding quality can also be obtained. Especially in combination with the chemical composition of the carbon steel plate described above, a significant further improvement in mechanical properties is achieved.

[0195] Furthermore, in the total steps of rolling the composite billet, for the step "After the large plate of the composite plate leaves the ultra-fast cooling system, it directly enters the straightening machine for straightening", this straightening is warm straightening. After the large plate of the composite plate leaves the ultra-fast cooling system at the final cooling temperature of 540 - 560 °C, it is directly straightened at a temperature basically the same as or slightly lower than the final cooling temperature to ensure the flatness of the large plate of the composite plate.

[0196] As a preferred implementation manner of the total steps of rolling the composite billet, after 1 - 3 passes of the above-mentioned warm straightening, the large plate of the composite plate is placed on the cooling bed for natural cooling. When the surface temperature drops below 200 °C, cold straightening is carried out using a cold straightening machine. In this way, the plate shape of the finally obtained composite plate can be improved.

[0197] And as another preferred implementation manner of the total steps of rolling the composite billet, after 1 - 3 passes of the above-mentioned warm straightening, the large plate of the composite plate is placed at a temperature of T f ~T fStack cooling is carried out between two steel plates at +50°C, and the stack cooling time is 0.4 min / mm × t0 ± 5 min, where t0 is the thickness of the large plate of the composite plate. Thus, within this stack cooling time, the large plate of the composite plate can slowly cool down and can be clamped by the steel plates to maintain the temperature uniformity between the core and the surface. After the stack cooling is completed, the large plate of the composite plate is placed on the cooling bed and naturally cooled. Among them,

[0198] T f = 550 + 30[Si] - 20[Mn] + 15[Cr] - 15[Ni] + 10[Mo], where [Si], [Mn], [Mo], [Cr], and [Ni] are 100 times the mass percentages of the respective elements in the base material. In this preferred embodiment, the stack cooling, especially the temperatures of the two steel plates during stack cooling and the stack cooling time, can further greatly improve the microstructure, properties, and plate shape of the finally obtained composite plate.

[0199] Above, the total steps of rolling the composite billet have been described in detail. As mentioned before, the preparation method of the present invention also includes the total steps of separating and straightening the composite plate. Specifically, the total steps of separating and straightening the composite plate include the following sub-steps:

[0200] For the large plate of the composite plate obtained from the previous total steps of rolling the composite billet, a plasma cutting machine is used to cut its four sides to remove the part outside the seal strip, and the large plate of the composite plate is separated into two small composite plates, the upper and lower ones;

[0201] The small composite plates are transversely flattened and cold straightened to obtain the finished stainless steel composite plate.

[0202] Among them, for the part outside the seal strip in the step of "cutting its four sides to remove the part outside the seal strip", that is, after the previous step of rolling the composite billet, it is the edge part on the large plate of the composite plate transformed from the seal strip and the filling layer in the composite billet mentioned above. In this way, this part is removed to expose the stainless steel clad layer, and in the absence of the connection effect of this part, the large plate of the composite plate is separated into two small composite plates, the upper and lower ones. See Figure 3a - 3e , corresponding to the five embodiments of the blank surface treatment step described above, Figure 3a - 3e respectively show the cross-sectional shapes of the corresponding two small composite plates (i.e., the final composite plate).

[0203] Each small composite plate is composed of a clad layer and a base layer. The clad layer is obtained by rolling the original clad material, and the base layer is obtained by rolling the original base material. In view of this, in Figure 3a - 3e the original label of the clad material is still marked for the clad layer, and the original label of the base material is still marked for the base layer.

[0204] The detailed description listed above is only a specific description of the feasible implementation manners of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent implementation manners or modifications made without departing from the technical spirit of the present invention shall be included within the protection scope of the present invention.

[0205] The beneficial effects of the present invention will be further illustrated by means of multiple embodiments. Of course, these embodiments are only a part, rather than all, of the numerous variant embodiments included in the present invention.

[0206] In these embodiments, the steel grades / chemical compositions of the composite materials and the base materials selected are shown in Table 1 respectively.

[0207] Table 1

[0208]

[0209]

[0210] Herein, for each embodiment, a composite blank is prepared according to the implementation manners provided by the present invention. The base materials, composite materials, composite blank thicknesses, and composite blank types used are shown in Table 2 respectively. Among them, the base material thickness type of "constant thickness" corresponds to the first implementation manner of the blank surface treatment step, while the base material thickness type of "variable thickness" corresponds to any one of the second to fifth implementation manners of the blank surface treatment step.

[0211] Table 2

[0212] Base material Composite material Total thickness of composite blank, mm Base material thickness type Example 1 Q370q 316L 322 Constant thickness Example 2 Q370q 316L 322 Variable thickness Example 3 Q370q 316L 322 Constant thickness Example 4 Q370q 316L 322 Variable thickness Example 5 Q370R 304L 252 Constant thickness Example 6 Q370R 304L 252 Variable thickness Example 7 Q370R 304L 252 Constant thickness Example 8 Q370R 304L 252 Variable thickness

[0213] Furthermore, for each embodiment, the composite blank rolling step provided by an implementation manner of the present invention is implemented. The specific parameters in the composite blank rolling are shown in Table 3. Among them, in the column of the stacking and cooling temperature in Table 3, "-" indicates that the implementation is carried out in the manner of "the straightened composite plate large plate is placed on the cooling bed and cooled naturally, and when the surface temperature drops below 200 °C, cold straightening is carried out using a cold straightening machine" as described above, while if a number is shown in the column of the stacking and cooling temperature, it indicates that the implementation is carried out in the manner of "placing the straightened composite plate large plate between two steel plates at a temperature of T f ~T f + 50 °C for stacking and cooling".

[0214] Table 3

[0215]

[0216] Furthermore, for the total thickness of the large composite board prepared in each embodiment and the thickness of the small composite board (i.e., the finished composite board), please refer to Table 4. Among them, the composite blanks corresponding to Embodiments 2, 4, 6, and 8 are base materials with variable thicknesses, and the corresponding composite board thickness and base layer thickness are both within a thickness range (i.e., the minimum thickness to the maximum thickness), rather than fixed values.

[0217] Table 4

[0218] Furthermore, samples of the composite boards in each embodiment were taken and tested. The interfacial bonding rate of each embodiment was 100%, the inner bend of 180° was qualified (no cracks), the outer bend of 180° was qualified (no cracks), and after boiling in a sulfuric acid - copper sulfate solution for 20 h and then bending at 180°, there were no intergranular corrosion cracks in the cladding layer. In addition, the results of other performance tests are shown in Table 5.

[0219] Table 5

[0220]

Claims

1. A preparation method of a 370 MPa grade stainless steel composite plate, characterized in that, it comprises the following steps: 1) Composite billet preparation Prepare two carbon steel billets with thickness T1, length L1 and width W1 as the base materials; and prepare two stainless steel billets with thickness T2, length L2 and width W2 as the clad materials; L2 < L1, W2 < W1; The chemical composition of the carbon steel billet is by mass percentage: C: 0.08 - 0.12%, Si: 0.16 - 0.24%, Mn: 1.36 - 1.44%, P ≤ 0.015%, S ≤ 0.0025%, Cr: 0.11 - 0.19%, Ni: 0.06 - 0.14%, Nb: 0.016 - 0.024%, Ti: 0.011 - 0.019%, Al: 0.030 - 0.040%, the rest is Fe and inevitable impurities; The chemical composition of the stainless steel billet is by mass percentage: C ≤ 0.15%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.030%, Ni: 6.0 - 22.0%, Cr: 16.0 - 26.0%, Mo ≤ 3.0%, the balance is Fe and inevitable impurities; Perform surface treatment on at least one surface of each of the two base materials and the two clad materials; Apply a release agent on one surface of one clad material; Form a billet according to the stacking order of base material, clad material, clad material, base material; wherein, the clad material is placed in the middle relative to the base material, and the surfaces of the base material and the clad material in contact with each other are all surfaces that have undergone the surface treatment, and the surface coated with the release agent faces the other clad material; Prepare four seals with width W3, W3 = 2T2 - 1 to 2 mm, attach the seals to the four sides of the two clad materials, and perform gas shielded welding between adjacent seals and between the seals and the base material, so that the two base materials and the seals form an integral body to obtain a composite billet base billet; Machine a round hole on the seal at the groove on the side of the composite billet base billet, and weld a seamless steel pipe at the round hole; Perform surfacing on the grooves on the four sides of the composite billet base billet; A vacuum pump is used to evacuate the composite billet through this seamless steel pipe, and the vacuum degree ≤ 10 -1 Pa. After that, keep the pressure for more than 4 hours; finally, seal the seamless steel pipe; 2) Composite billet rolling Heat the obtained composite billet, the heating temperature is 1170 - 1190 °C, the total heating time ≥ 1.2 × tmin / mm, t is the thickness of the composite billet, and the soaking section holding time is 30 min - 50 min; Adopt two-stage controlled rolling of rough rolling + finish rolling. In the rough rolling stage, the starting rolling temperature ≤ 1030 °C, the finishing rolling temperature ≥ 990 °C, first roll transversely and then longitudinally. When rolling longitudinally, at least one pass reduction ≥ 35 mm, the total rough rolling reduction is 40 - 60%, and the rough rolling stage ends when the intermediate billet thickness reaches 2.5 - 3.5 times the target thickness of the large plate of the composite plate; then wait for the temperature, during which water cooling is carried out. When the surface temperature of the intermediate billet drops below 850 °C, the finish rolling stage starts; the finishing rolling temperature in the finish rolling stage ≥ 820 °C, and the total finish rolling reduction is 55 - 75% to obtain the large plate of the composite plate. After rolling, the large composite plate enters the ultra-rapid cooling system for cooling. The starting cooling temperature is ≥750°C, the cooling rate is 8 - 15°C / s, and the final cooling temperature is 540 - 560°C; After the large composite plate leaves the ultra-rapid cooling system, it directly enters the straightening machine for straightening; 3) Separate straightening of the composite plate Cut the four sides of the large composite plate to remove the part outside the seal, and the large composite plate is separated into two small composite plates, the upper and the lower; Perform transverse flattening and cold straightening on the small composite plates to obtain the finished stainless steel composite plate.

2. The method for preparing a 370 MPa grade stainless steel composite plate according to claim 1, characterized in that, the surface oxide scale penetration depth and the surface pit depth of the carbon steel billet are both ≤0.3 mm, and the flatness is ≤3 mm / m; the flatness of the stainless steel billet is ≤2 mm / m.

3. The method for preparing a 370 MPa grade stainless steel composite plate according to claim 1, characterized in that, in the step of "coating a release agent on one surface of a piece of clad material", the composition of the release agent used is by mass ratio: 25 - 35% of silicon nitride, 5 - 10% of thermosetting amino resin, 55 - 70% of water; the thickness of the coated release agent is 0.2 - 0.5 mm; before the step of "stacking the base material, clad material, clad material, and base material in this order", the clad material coated with the release agent is heated and dried, the drying temperature is 100 - 250°C, and the drying time is 20 - 40 min.

4. The method for preparing a 370 MPa grade stainless steel composite plate according to claim 1, characterized in that, the step of "performing surface treatment on at least one surface of each of the two base materials and the two clad materials" includes: grinding and polishing one surface of each base material and each clad material to remove the surface oxide scale.

5. The method for preparing a 370 MPa grade stainless steel composite plate according to claim 1, characterized in that, the step of "performing surface treatment on at least one surface of each of the two base materials and the two clad materials" includes: grinding and polishing one surface of each clad material to remove the surface oxide scale; and, in a manner of complementary relative shapes, milling and processing one surface of the two base materials, processing the surface into a transverse inclined surface with length L11 = L1 and width W11 > W1, and the base material is a non-uniform thickness blank with a gradually changing thickness in the transverse direction, or processing the surface into a longitudinal inclined surface with length L11 > L1 and width W11 = W1, and the base material is a non-uniform thickness blank with a gradually changing thickness in the longitudinal direction.

6. The method for preparing a 370 MPa grade stainless steel composite plate according to claim 1, characterized in that, the step of "performing surface treatment on at least one surface of each of the two base materials and the two clad materials" includes: One surface of two base materials is milled in a manner of relative shape complementarity to process the surface into an irregular concave-convex surface including n planes connected in sequence transversely, and the base material is an unequal-thickness blank with non-monotonic thickness change in the transverse direction, where the length L12 of the irregular concave-convex surface is L1 and the total width W12 > W1; or, the surface is processed into an irregular concave-convex surface including n planes connected in sequence longitudinally, and the base material is an unequal-thickness blank with non-monotonic thickness change in the longitudinal direction, where the total length L12 of the irregular concave-convex surface is > L1 and the width W12 = W1; n ≥ 2; One surface of each composite material is ground and polished to remove the surface scale; then each composite material is bent to match the corresponding irregular concave-convex surface.

7. The preparation method of the 370 MPa grade stainless steel composite plate according to any one of claims 4 to 6, characterized in that, In the "the composite material is placed centered relative to the base material", the distance from the side edge of the composite material in the transverse direction to the corresponding side edge of the base material is half of the width difference of the contact surface between the composite material and the base material, and the distance from the side edge of the composite material in the longitudinal direction to the corresponding side edge of the base material is half of the length difference of the contact surface between the composite material and the base material.

8. The preparation method of the 370 MPa grade stainless steel composite plate according to claim 1, characterized in that, In the step "gas shielded welding is carried out between adjacent seals and between the seal and the base material", the welding current is 215 - 245 A, the welding voltage is 28 - 32 V, the welding speed is 300 - 360 mm / min, and the interpass temperature is controlled at 135 - 165 °C during the welding process.

9. The preparation method of the 370 MPa grade stainless steel composite plate according to claim 1, characterized in that, In the step "surfacing is carried out on the grooves on the four sides of the composite blank base blank", submerged arc surfacing is adopted; Before welding, the welding flux is baked at 350 °C for 2 h and then kept warm at 150 °C for 1 h; During the welding process, the interpass temperature is controlled at 135 - 165 °C, the welding current is 570 - 630 A, the welding voltage is 28 - 32 V, and the welding speed is 420 - 480 mm / min.

10. The preparation method of the 370 MPa grade stainless steel composite plate according to claim 1, characterized in that, After the step "the large composite plate enters the straightening machine for straightening directly after leaving the ultra-rapid cooling system": Place the straightened large composite plate between two steel plates at a temperature of T f ~T f + 50 °C for stacking cooling. The stacking cooling time is 0.4 min / mm × t0 ± 5 min, where t0 is the thickness of the large composite plate; After the stacking cooling is completed, the large composite plate is placed on the cooling bed and cooled naturally; 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.

11. A 370 MPa grade stainless steel composite plate, characterized in that, The composite plate is prepared by using the preparation method according to any one of claims 1 to 10, and the structure of the composite plate is 70 - 85% ferrite + 10 - 20% pearlite + 5 - 10% bainite structure, the yield strength ≥ 370 MPa, the tensile strength ≥ 510 MPa, the elongation after fracture ≥ 20%, and the yield ratio ≤ 0.

85.

12. The 370 MPa grade stainless steel composite plate according to claim 11, characterized in that, The bonding rate of the composite interface of the composite plate is 100%, and the shear strength is ≥300 MPa; the flatness of the composite plate is ≤3 mm / m.

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