A method for manufacturing a duplex stainless steel and carbon steel asymmetrically rolled clad plate

Abstract

The present application relates to a kind of asymmetric rolling composite plate of duplex stainless steel and carbon steel, wherein stainless steel is any one of duplex stainless steel.Therein carbon steel is any one of plain carbon steel, low carbon steel, alloy steel.A kind of asymmetric composite blank of duplex stainless steel and carbon steel manufacturing method is as follows:1, blank preparation of raw material.2, stainless steel plate pretreatment.3, blank surface treatment of raw material.4 cleaning.5, blank.6, vacuum chamber electron beam sealing.7, composite blank weld detection.8, composite blank heating.9, composite plate rolling.10, laminar flow cooling.11, no cracking phenomenon in the process of heating and rolling, interface shear strength τ ≥280MPa after hot rolling, interface bonding rate is 100%, and the combination performance is good, the ferrite proportion of duplex steel is 40-60%.

Description

Technical Field

[0001] This invention relates to the field of composite plate manufacturing technology, and in particular to a method for manufacturing a composite plate of duplex stainless steel and carbon steel asymmetric rolling. Background Technology

[0002] Stainless steel + carbon steel composite plate is a layered composite material made by combining a carbon steel base layer and a stainless steel cladding layer through specific processes (such as explosive bonding, rolling bonding, or welding bonding). It combines the characteristics of both materials, achieving higher strength while also possessing excellent corrosion resistance and wear resistance. Furthermore, it significantly reduces the amount of stainless steel used, saving on the consumption of precious metals such as chromium and nickel. It is a new type of material with higher cost-effectiveness, higher efficiency, and low carbon footprint, and has broad application prospects.

[0003] Composite production technologies include various processes such as mechanical composite, explosive composite, and rolling composite. Explosive and rolling composites can directly produce composite steel plates or further produce thinner hot-rolled and cold-rolled composite steel plates / coils. Explosive composite technology is relatively outdated, sensitive to environmental factors, and relatively difficult to produce steel plates ≤8mm thick. Most domestic and international rolled composite materials are made from hot-rolled steel plates, but they share the common drawbacks of low production efficiency and yield, and generally employ symmetrical billet assembly methods of ABA or AB + release agent + BA. However, this results in low yield and small unit weight. Achieving asymmetrical billet assembly and rolling of (A+B) type dissimilar steel grades for composite steel plates has become a research hotspot in recent years.

[0004] Due to differences in material properties, composite rolling of dissimilar steel metals presents significant challenges. Composite rolling involves a complete manufacturing process, from welded billet assembly to asymmetric heating rolling, demanding high quality not only in the welds but also in the rolling process itself. Therefore, this paper proposes a complete manufacturing method for asymmetric composite billet assembly and heating rolling of duplex stainless steel and carbon steel. This method achieves asymmetric assembly of stainless steel and carbon steel billets, preventing cracking during the composite billet heating rolling process and yielding high-performance composite plates.

[0005] Stainless steel composite plate products have broad market prospects, high technical requirements, and high requirements for the integrated control system of production line process and equipment.

[0006] This invention relates to a method for manufacturing a duplex stainless steel and carbon steel asymmetric rolled composite plate. The purpose is also to provide a duplex stainless steel and carbon steel asymmetric composite billet and composite plate, the produced composite plate having excellent bonding performance and corrosion resistance. Summary of the Invention

[0007] The purpose of this invention is to address the above-mentioned problems by providing a method for manufacturing a composite plate of duplex stainless steel and carbon steel asymmetric rolling.

[0008] The objective of this invention is achieved as follows: A method for manufacturing a duplex stainless steel and carbon steel asymmetric rolled composite plate, comprising the following steps: Step 1: Raw material preparation for billet assembly: Carbon steel is continuously cast into billets after converter smelting and ladle refining. The thickness of the carbon steel billets is 200-280mm. After the carbon steel billets are produced, they are stacked and stored for cooling for no less than 3 days. One carbon steel billet is placed at the bottom, and the carbon steel billet for composite billet making is placed in the middle of the stack. Two carbon steel billets are placed on the top layer to ensure composite billet making. Carbon steel billets with an unevenness ≤5mm are used as the base material for composite panels. Stainless steel billets are rolled into stainless steel medium plates with a thickness of 10-67mm, used as the cladding material for composite panels. The base and cladding thickness ratio is (3-28):1. Step 2: Pretreatment of stainless steel medium plates: The stainless steel medium plates used for the cladding material of composite panels are first subjected to solution treatment. The solution treatment temperature is controlled at 950-1100℃, and the holding time is controlled at 1.5min / mm. Water cooling is then performed. At room temperature, the solution-treated stainless steel medium plate is then pickled to remove the oxide scale from its surface and passivated. After pickling, it is straightened to ensure that the unevenness of the stainless steel medium plate is ≤7mm. Step 3: Surface treatment of raw materials for billet assembly: ① The surface of the carbon steel billet to be composited is milled on one side to remove surface iron oxide scale, cracks, and slag inclusions, and a metallic color is achieved; ② The surface of the stainless steel medium plate to be composited is ground with an 80-grit flap wheel automatic grinding machine to remove the passivation layer and achieve a metallic color. Color; ③ The carbon steel billet after milling and the stainless steel medium plate after automatic grinding are both ground manually with a 100-120 grit grinding wheel to achieve a surface roughness of Ra2.0-4.0μm; Step 4: Cleaning: First, use compressed air without water vapor to blow away the surface dust or iron dust, then use acetone or volatile alkaline cleaning agent to clean the dust particles that cannot be blown away; Cleaning time should be 3-5 min / m 2 Step 5: Billet Assembly: First, place the carbon steel billet on the lower layer with the ground surface facing up. Then, flip the stainless steel middle plate so that the ground surface of the stainless steel faces down. Hoist it and align it with the lower carbon steel billet. Use a flattening machine to press down the stainless steel middle plate, ensuring that the gap between the composite surfaces is ≤1mm. Spot weld the four sides with a spot weld length of 40-60mm and a spot weld interval of 300-500mm. After assembly, it becomes a composite billet. Press the carbon steel billet on top of the composite billet and send it into the vacuum chamber. Step 6: Vacuum Chamber Electron Beam Sealing: ① Evacuate the vacuum chamber to a vacuum degree of ≤7.5×10 -2Pa; ② Then spot weld the four sides of the composite billet, with an interval of 200-300mm; ③ Position of the electron beam gun: The billet assembly method adopts direct welding of stainless steel medium plate and carbon steel casting billet, and the electron beam gun should be directly facing the center of the weld; ④ Welding sequence is to weld the two long sides first, and then weld the two short sides; ⑤ Sealing process adopts welding beam current of 140-200mA, welding voltage of 65-75KV, and welding speed of 100-150mm / min; Step 7: Composite billet weld inspection: After the composite billet is sealed, first remove the carbon steel casting billet pressing on it, and then inspect the weld for cracks and porosity by ultrasonic testing to ensure that the penetration depth is 35-50mm; Step 8: Composite billet heating: Before the composite billet is heated in the ingot furnace, place a carbon steel pad billet at the bottom, place the composite billet on the pad billet with the stainless steel side facing down, and the length and width of the pad billet should not be less than The composite billet is placed in the middle of the backing billet, pressing down on all four sides to suppress weld deformation. A two-stage heating process is used in the ingot furnace: the furnace is loaded at 500℃-600℃, with the first stage heating rate at 70-90℃ / h, reaching 1000-1100℃ and holding for 4-6 hours; the second stage heating rate is 50-70℃ / h, reaching 1200-1230℃ and holding for 4-6 hours. Step nine: Composite plate rolling: a two-stage rolling process is used. The first stage opening temperature is 1000-1080℃, the second stage opening temperature is ≤930℃, the intermediate thickness is 2-4 times the finished product thickness, and the final rolling temperature is controlled at 830±20℃. Step ten: Laminar flow cooling: ACC laminar flow cooling is used, with the water inlet temperature controlled at 780±20℃ and the final cooling temperature controlled at 600±20℃.

[0009] In step two, the pickling concentration is HNO3: 120-300 g / L, HF: 15-50 g / L, and the pickling speed is 2-8 m / min.

[0010] The beneficial effects of this invention are as follows: Addressing the challenges of assembling and hot rolling duplex stainless steel and carbon steel billets, this invention provides a method for manufacturing asymmetric rolled composite plates of duplex stainless steel and carbon steel. This method has lower costs, improves the success rate of billet rolling, and can obtain high-quality asymmetric rolled composite plates of duplex stainless steel and carbon steel. The composite plates obtained by the above manufacturing method have a shear strength τ of 295-350 MPa, a 100% interfacial bonding rate, good bonding performance, and excellent corrosion resistance. Attached Figure Description

[0011] The present invention will now be further described with reference to the accompanying drawings.

[0012] Figure 1 This is a diagram illustrating the furnace heating method for composite billet ingots according to the present invention. 1-Composite billet base layer carbon steel, 2-Composite billet cladding layer stainless steel, 3-Carbon steel backing billet. Detailed Implementation

[0013] This invention relates to a method for manufacturing an asymmetric rolled composite plate of duplex stainless steel and carbon steel. The stainless steel can be any type of duplex stainless steel, and the carbon steel can be any type of plain carbon steel, low-carbon steel, or alloy steel. The method includes the following steps: preparation of billet raw materials → pretreatment of stainless steel medium plates → surface treatment of billet raw materials → cleaning → billet assembly → vacuum chamber electron beam sealing → composite billet weld inspection → composite billet heating → composite plate rolling → laminar flow cooling.

[0014] The stainless steel used for the cladding layer of the composite plate can be any type of duplex stainless steel, with a thickness of 10-67mm for the stainless steel medium plate. The carbon steel used for the base layer of the composite plate can be any type of ordinary carbon steel, low-carbon steel, or alloy steel, with a thickness of 200-280mm for the carbon steel billet, and the unevenness of the carbon steel billet used for composite billet preparation ≤5mm. The thickness ratio of the base layer to the cladding layer is (3-28):1.

[0015] Stainless steel medium plates used for composite cladding undergo solution treatment at a temperature controlled between 950-1100℃, with a holding time of 1.5 min / mm, followed by water cooling to room temperature. After solution treatment, the stainless steel medium plates are straightened to ensure a flatness ≤7mm.

[0016] The stainless steel medium plate is ground using an 80-mesh flap wheel automatic grinding machine, replacing the milling process, which greatly improves the processing efficiency and the surface roughness Ra4.0-6.0μm.

[0017] The surface roughness of carbon steel billets and stainless steel medium plates after manual milling with 100-120 mesh grinding wheels is Ra2.0-4.0μm.

[0018] The carbon steel billet is placed in the lower layer with the ground surface facing upwards, and the stainless steel medium plate is placed in the upper layer with the ground surface facing downwards. After the billets are aligned, the gap between the composite surfaces is ≤1mm.

[0019] The sealing vacuum degree is ≤7.5×10-2Pa. Spot welding is performed on all four sides of the composite blank, with a spacing of 200-300mm. The electron beam gun is positioned directly in front of the center of the weld. The welding sequence is to weld the two long sides first, then the two short sides. A welding beam current of 140-200mA, a welding voltage of 65-75KV, and a welding speed of 100-150mm / min are used.

[0020] The composite billet is loaded into the ingot furnace at 500℃. A carbon steel support billet is placed at the bottom, and the composite billet is placed on the support billet with the stainless steel side facing down. The length and width of the support billet are not smaller than the composite billet, ensuring that the composite billet is placed in the middle of the support billet and pressing down the four sides. A two-stage heating process is adopted in the ingot furnace. The first stage is a heating rate of 70-90℃ / h, heating to 1050℃ and holding for 4 hours. The second stage is a heating rate of 50-70℃ / h, heating to 1200-1230℃ and holding for 4 hours.

[0021] The composite plate is rolled using differential speed throughout the entire rolling process, with the stainless steel side rolling at a speed 10-15% faster than the carbon steel side. Controlled rolling employs a two-stage rolling process: the first stage starts at a rolling temperature of 1000-1080℃, the second stage starts at a rolling temperature ≤930℃, the intermediate thickness is 2-4 times the finished product thickness, and the final rolling temperature is controlled at 830±20℃.

[0022] ACC laminar flow cooling is adopted, with an inlet water temperature of 780±20℃. In order to quickly pass through the harmful phase precipitation zone, the final cooling temperature is controlled at 600±20℃.

[0023] The composite billet has a melt depth ≥35mm. The asymmetric composite billet of duplex stainless steel and carbon steel is obtained through hot rolling. The interfacial shear strength τ of the stainless steel and carbon steel composite plate is ≥280MPa, the interfacial bonding rate is 100%, and the bonding performance is good. The ferrite phase in the stainless steel cladding layer meets the requirement of 40-60%.

[0024] The technical solution adopted in this invention is as follows: 1. Preparation of raw materials for billet assembly. Carbon steel is continuously cast into billets after converter smelting and ladle refining (LF). The thickness of the carbon steel billets is 200-280mm. After the billets are produced, they are stacked and stored for cooling for no less than 3 days. One billet is placed at the bottom, and the carbon steel billets for composite billet making are placed in the middle of the stack. Two billets are placed at the top, ensuring that the unevenness of the carbon steel billets for composite billet making is ≤5mm. These billets are used as the base material for composite plates. Stainless steel billets (200mm thick) are rolled into stainless steel medium plates with a thickness of 10-67mm. These medium plates are used as the cladding material for composite plates. The base and cladding thickness ratio is (3-28):1.

[0025] 2. Pretreatment of Stainless Steel Medium Plates. First, the stainless steel medium plates used for the cladding of the composite plate undergo solution treatment. The solution treatment temperature is controlled at 950-1100℃, and the holding time is controlled at 1.5 min / mm, followed by water cooling to room temperature. A proper solution treatment process can soften and homogenize the microstructure of duplex stainless steel, improve internal stress, reduce the degree of welding deformation of duplex stainless steel, and effectively reduce the cracking rate during subsequent heating and rolling processes, thus enhancing the composite effect. The solution-treated stainless steel medium plates are then pickled and straightened to ensure that the unevenness of the stainless steel medium plates is ≤7mm.

[0026] 3. Surface Treatment of Raw Materials for Composite Plates. ① The carbon steel billet to be composited is milled on one side to remove surface defects such as iron oxide scale, cracks, and slag inclusions, resulting in a metallic finish. ② The stainless steel to be composited surface is ground using an 80-grit flap wheel automatic grinding machine to remove the passivation layer and achieve a metallic finish. This replaces the stainless steel milling process, significantly improving processing efficiency. ③ Both the milled carbon steel billet and the automatically ground stainless steel medium plate to be composited are manually ground using a 100-120 grit grinding wheel. The surface roughness after treatment reaches Ra2.0-4.0μm, effectively removing surface iron oxide scale and forming a surface hardened layer. This hard and brittle hardened layer facilitates rolling composite and improves the interfacial bonding strength of the composite plate.

[0027] 4. Cleaning. First, use compressed air without moisture to blow away the surface dust or iron dust; then use acetone or a volatile alkaline cleaning agent to clean the dust particles that cannot be blown away.

[0028] 5. Billet Assembly. First, place the carbon steel billet on the lower layer with the ground surface facing up. Then, flip the stainless steel middle plate so that the ground surface of the stainless steel faces down. Hoist it and slowly align it with the lower billet. Use a flattening machine to press down the stainless steel to ensure that the gap between the composite surfaces is ≤1mm. Spot weld the four sides with a spot weld length of 40-60mm and a spot weld interval of 300-500mm. After billet assembly, press the carbon steel billet on top and send it into the vacuum chamber.

[0029] 6. Electron beam sealing in the vacuum chamber. ① Evacuate the vacuum chamber to a vacuum level ≤7.5×10⁻⁶. -2Pa. As the vacuum level increases, the composite effect is enhanced, which is more conducive to slab composite. ② Then spot weld the four sides of the composite billet, with an interval of 200-300mm. ③ Position of the electron beam gun. This billet assembly method involves direct welding of stainless steel and carbon steel. When welding dissimilar metals, the thermocouple effect may generate a magnetic field, causing the electron beam to deflect to the side with the stronger magnetic field, resulting in weld misalignment. Since duplex stainless steel exhibits weak magnetism, and experiments have shown that no offset compensation is needed during the sealing welding process, the electron beam gun should be positioned directly in the center of the weld. This ensures that the weld fusion point is located in the middle of the weld, effectively guaranteeing weld strength. ④ The welding sequence is to weld the two long sides first, then the two short sides. This effectively reduces stress concentration at the sealing weld joint and improves the reliability of the sealing weld joint. In addition, the spot welding combination and fixation of the stainless steel middle plate and the spare carbon steel billet can effectively reduce the degree of stainless steel welding deformation and reduce the generation of microcracks in the weld during the sealing welding process. Under the combined effect of these two factors, welding efficiency can be improved, and the composite billet can maintain the vacuum effectiveness of the bonding surface during subsequent heating and rolling processes, thus enhancing the composite effect. ⑤ Since the cladding layer uses duplex stainless steel, which is sensitive to heat input, excessive heat input can cause grain growth in the weld heat-affected zone, leading to a decrease in its plasticity and toughness. Therefore, targeted control of the sealing welding process is necessary to ensure weld depth while also enhancing weld strength. The sealing welding process uses a welding current of 140-200mA. A lower current results in insufficient heat input and incomplete penetration, while a higher current leads to a decrease in the plasticity and toughness of the weld heat-affected zone. The welding voltage is 65-75KV; too low a voltage will result in insufficient weld penetration, while too high a voltage will cause excessively wide welds. The welding speed is 100-150mm / min; too fast a welding speed will result in incomplete penetration, while too slow a welding speed will cause weld depressions.

[0030] 7. Inspection of composite billet welds. After the composite billet is sealed and welded, the carbon steel casting on top is removed, and then the weld is inspected by ultrasonic testing to ensure that there are no defects such as cracks and porosity, and that the penetration depth is ≥35mm.

[0031] 8. Heating of Composite Billet. Welds are highly sensitive to heating. If the heating rate is too fast, the difference in thermal expansion coefficients between the upper and lower materials, especially the significant difference in thermal deformation between biaxial stainless steel and carbon steel, can easily lead to high stress at the weld, and even weld cracking. Therefore, before heating the composite billet in the ingot furnace, a carbon steel backing billet is placed at the bottom, with the composite billet placed on top, stainless steel side down. The length and width of the backing billet should not be smaller than the composite billet, ensuring that the composite billet is placed in the middle of the backing billet, pressing down on the four sides to suppress weld deformation. Secondly, a two-stage heating process is adopted in the ingot furnace. The furnace is loaded at 500℃. The first stage involves a heating rate of 70-90℃ / h, reaching 1050℃ and holding for 4 hours. The second stage involves a heating rate of 50-70℃ / h, reaching 1200-1230℃ and holding for 4 hours. This reduces the stress on the weld and lowers the weld cracking rate.

[0032] 9. Composite Plate Rolling. Due to the inconsistent deformation of duplex steel and carbon steel, differential speed rolling is used throughout the composite plate rolling process, with the stainless steel side rolling at a speed 10-15% faster than the carbon steel side. Furthermore, to obtain ideal microstructure and properties, a two-stage rolling process is employed. The first stage starts at a rolling temperature of 1000-1080℃, the second stage starts at a rolling temperature ≤930℃, the intermediate thickness is 2-4 times the finished product thickness, and the final rolling temperature is controlled at 830±20℃.

[0033] 10. Laminar flow cooling. ACC laminar flow cooling is adopted, with the inlet water temperature controlled at 780±20℃. To ensure rapid passage through the harmful phase precipitation zone of the biaxial stainless steel, the final cooling temperature is controlled at 600±20℃.

[0034] 11. The composite plate obtained by the above manufacturing method has a rolling success rate of over 95%, an interfacial shear strength τ≥280MPa, an interfacial bonding rate of 100%, good bonding performance, and a ferrite phase ratio of 40-60% in duplex stainless steel.

[0035] The manufacturing method of the aforementioned asymmetric rolled composite plate of duplex stainless steel and carbon steel is characterized by the following: In step 1, during the preparation of raw materials for the composite plate, the stacking cooling process of the carbon steel billet ensures the flatness of the billet, which is beneficial for subsequent welding and assembly. In step 2, during the pretreatment of the stainless steel medium plate, a reasonable solution treatment process can soften and homogenize the structure of the duplex stainless steel, improve internal stress, and reduce the degree of welding deformation of the duplex stainless steel. This effectively reduces the cracking rate and enhances the composite effect during subsequent heating and rolling. In step 3, during the surface treatment of the raw materials for the composite plate, the stainless steel medium plate is ground using an automatic grinding machine, replacing the traditional milling process. This improves processing efficiency and effectively suppresses the plate deformation of stainless steel during milling, resulting in uniform and rapid surface processing that meets the requirements for composite plate assembly. A reasonable surface treatment process can effectively remove the iron oxide scale on the surface and form a surface hardened layer. The hard and brittle hardened layer is beneficial for achieving rolling composite and improving the interfacial bonding strength of the composite plate. In step 6, during vacuum electron beam sealing welding, a reasonable welding sequence can effectively reduce stress concentration at the weld joint and improve the reliability of the weld joint. The spot welding combination of stainless steel medium plate and carbon steel billet, along with the pressing action of the spare billet, effectively reduces the degree of welding deformation in stainless steel and minimizes the generation of microcracks in the weld. Reduced stress concentration and welding deformation not only improve welding efficiency but also ensure the vacuum effectiveness of the bonding surface during subsequent heating and rolling of the composite billet, enhancing the composite effect. A reasonable sealing welding process is not only simple to operate but also highly efficient, effectively guaranteeing the quality of the composite billet sealing weld. During the heating of the composite billet in step 8, a reasonable furnace loading method and heating process effectively reduce stress concentration during weld heating, lowering the weld heating cracking rate. During the rolling of the composite plate in step 9, a reasonable rolling process yields a composite plate with excellent shape and prevents weld cracking caused by inconsistent deformation of the upper and lower surfaces. Reasonable control of rolling temperature and intermediate thickness results in a good microstructure. During laminar cooling in step 10, a reasonable cooling rate and final cooling temperature prevent the precipitation of harmful phases in duplex steel, ensuring the corrosion resistance of the stainless steel surface.

[0036] This invention obtains an asymmetric rolled composite plate of duplex stainless steel and carbon steel through processes such as billet preparation, stainless steel medium plate pretreatment, billet surface treatment, cleaning, billet assembly, vacuum chamber electron beam sealing welding, composite billet weld inspection, composite billet heating, composite plate rolling, and laminar flow cooling.

[0037] The specific embodiments of the present invention are described in detail below with reference to examples, but the specific embodiments of the present invention are not limited to the following examples. Example 1

[0038] The stainless steel used in this embodiment is duplex stainless steel S22053, and the carbon steel used is Q235B. The thickness of the rolled stainless steel cladding layer is 5mm, and the thickness of the carbon steel base layer is 20mm.

[0039] 1. Raw material preparation for billet assembly. Carbon steel is continuously cast into billets after converter smelting and ladle refining (LF). The thickness of the carbon steel billets is 230mm. After the billets come off the production line, they are stacked for cooling. One billet is placed at the bottom, and carbon steel billets for composite billet making are placed in the middle of the stack. Three billets are placed on the top layer. The unevenness of the carbon steel billets for composite billet making is 5mm, and they are used as the base material for the composite plate. Stainless steel billets (200mm thick) are rolled into stainless steel medium plates with a thickness of 58mm, which are used as the cladding material for the composite plate. The base and cladding thickness ratio is 4:1.

[0040] 2. Pretreatment of Stainless Steel Medium Plates. First, the stainless steel medium plates used for the composite cladding are solution-treated. The solution treatment temperature is controlled at 1040-1100℃, and the holding time is controlled at 1.5 min / mm. Then, they are water-cooled to room temperature. Next, the solution-treated stainless steel medium plates are straightened to achieve a flatness of 7 mm.

[0041] 3. Surface Treatment of Raw Materials for Assembly. ① The carbon steel billet to be assembled is milled on one side to remove surface defects such as iron oxide scale, cracks, and slag inclusions, resulting in a metallic color. ② The stainless steel medium plate to be assembled is ground using an automatic grinding machine to remove the passivation layer, resulting in a metallic color. ③ Both the milled carbon steel billet and the ground stainless steel medium plate to be assembled are manually ground using a 100-grit grinding wheel. The surface roughness of the carbon steel after surface treatment is Ra3.8μm, and the surface roughness of the stainless steel after surface treatment is Ra4.0μm.

[0042] 4. Cleaning. First, use compressed air without moisture to blow away the surface dust or iron dust; then use acetone or a volatile alkaline cleaning agent to clean the dust particles that cannot be blown away.

[0043] 5. Billet Assembly. First, place the carbon steel billet on the lower layer with the ground surface facing up. Then, flip the stainless steel middle plate along with the spare carbon steel billet so that the ground stainless steel surface faces down. Hoist it and slowly align it with the lower layer billet, with a 0.9mm gap between the composite surfaces. After assembly, the upper pressure billet is sent into the vacuum chamber.

[0044] 6. Electron beam sealing in the vacuum chamber. ① Evacuate the vacuum chamber to a vacuum level of 6.5 × 10⁻⁶. -2 Pa. ② Spot weld the four sides of the composite blank at 200mm intervals. ③ Position the electron beam gun directly in front of the center of the weld. ④ Weld the two long sides first, then the two short sides. ⑤ Use a welding beam current of 185mA, a welding voltage of 70KV, and a welding speed of 120mm / min.

[0045] 7. Inspection of composite billet welds. After the composite billet is sealed, the spare carbon steel casting billet and stainless steel are separated and removed at the spot welding position. Then, the weld is inspected by ultrasonic testing to ensure there are no defects such as cracks or porosity, and the penetration depth is 45mm.

[0046] 8. Heating of composite billets. The composite billets are heated in the ingot furnace at a rate of 80℃ / h in the first stage, and held at 1050℃ for 4 hours. In the second stage, the heating rate is 70℃ / h, and the temperature is raised to 1230℃ and held for 4 hours.

[0047] 9. Composite plate rolling. The composite plate rolling process is set with a differential speed of 15% throughout. The first stage rolling temperature is 1050℃, the second stage rolling temperature is 925℃, the intermediate thickness is 75mm, and the final rolling temperature is 830℃.

[0048] 10. Laminar flow cooling. Inlet water temperature is 780℃, and final cooling temperature is 600℃.

[0049] 11. The composite billet showed no cracking during heating and rolling. The interfacial shear strength after hot rolling was 305 MPa, the interfacial bonding rate was 100%, the bonding performance was good, and the proportion of duplex ferrite phase was 52%. Example 2

[0050] The stainless steel used in this embodiment is duplex stainless steel S25073, and the carbon steel used is Q355B. The thickness of the rolled stainless steel cladding layer is 1mm, and the thickness of the carbon steel base layer is 28mm.

[0051] 1. Raw material preparation for billet assembly. Carbon steel is continuously cast into billets after converter smelting and ladle refining (LF). The thickness of the carbon steel billets is 280mm. After the billets come off the production line, they are stacked for cooling. One billet is placed at the bottom, and carbon steel billets for composite billet making are placed in the middle of the stack. Three billets are placed on the top layer. The unevenness of the carbon steel billets for composite billet making is 3mm, and they are used as the base material for the composite plate. Stainless steel billets (200mm thick) are rolled into stainless steel medium plates with a thickness of 10mm, which are used as the cladding material for the composite plate. The base and cladding thickness ratio is 28:1.

[0052] 2. Pretreatment of Stainless Steel Medium Plates. First, the stainless steel medium plates used for the composite cladding are solution-treated. The solution treatment temperature is controlled at 1050-1100℃, and the holding time is controlled at 1.5 min / mm. Then, they are water-cooled to room temperature. Next, the solution-treated stainless steel medium plates are straightened to achieve a flatness of 6 mm.

[0053] 3. Surface Treatment of Raw Materials for Assembly. ① The carbon steel billet to be assembled is milled on one side to remove surface defects such as iron oxide scale, cracks, and slag inclusions, achieving a metallic finish. ② The stainless steel to be assembled surface is ground using an automatic grinding machine to remove the passivation layer and achieve a metallic finish. ③ Both the milled carbon steel billet and the ground stainless steel medium plate to be assembled are ground using a manual grinding machine with a 120-grit grinding wheel. The surface roughness of the carbon steel after surface treatment is Ra3.2μm, and the surface roughness of the stainless steel after surface treatment is Ra3.6μm.

[0054] 4. Cleaning. First, use compressed air without moisture to blow away the surface dust or iron dust; then use acetone or a volatile alkaline cleaning agent to clean the dust particles that cannot be blown away.

[0055] 5. Billet Assembly. First, place the carbon steel billet on the lower layer with the ground surface facing up. Then, flip the stainless steel middle plate along with the spare carbon steel billet so that the ground stainless steel surface faces down. Hoist it and slowly align it with the lower layer billet, with a 1.0mm gap between the composite surfaces. After assembly, the upper pressure billet is sent into the vacuum chamber.

[0056] 6. Electron beam sealing in the vacuum chamber. ① Evacuate the vacuum chamber to a vacuum level of 7.5 × 10⁻⁶. -2 Pa. ② Spot weld the four sides of the composite blank at intervals of 240mm. ③ Position the electron beam gun directly at the center of the weld. ④ Weld the two long sides first, then the two short sides. ⑤ Use a welding beam current of 160mA, a welding voltage of 65KV, and a welding speed of 120mm / min.

[0057] 7. Inspection of composite billet welds. After the composite billet is sealed, the spare carbon steel casting billet and stainless steel are separated and removed at the spot welding position. Then, the weld is inspected by ultrasonic testing to ensure there are no defects such as cracks or porosity, and the penetration depth is 35mm.

[0058] 8. Heating of composite billets. The composite billets are heated in the ingot furnace at a rate of 90℃ / h in the first stage, and held at 1050℃ for 4 hours. In the second stage, the heating rate is 60℃ / h, and the temperature is raised to 1210℃ and held for 4 hours.

[0059] 9. Composite plate rolling. The composite plate rolling process is set with a differential speed of 13% throughout. The first stage rolling temperature is 1080℃, the second stage rolling temperature is 930℃, the intermediate thickness is 87mm, and the final rolling temperature is 810℃.

[0060] 10. Laminar flow cooling. Inlet water temperature is 760℃, and final cooling temperature is 580℃.

[0061] 11. The composite billet did not crack during subsequent heating and rolling. The interfacial shear strength after hot rolling was 310 MPa, the interfacial bonding rate was 100%, the bonding performance was good, and the proportion of duplex ferrite was 55%. Example 3

[0062] The stainless steel used in this embodiment is duplex stainless steel S23043, and the carbon steel used is Q345R.

[0063] The rolled stainless steel cladding is 2mm thick, and the carbon steel base layer is 12mm thick.

[0064] 1. Raw material preparation for billet assembly. Carbon steel is continuously cast into billets after converter smelting and ladle refining (LF). The thickness of the carbon steel billets is 230mm. After the billets come off the production line, they are stacked for cooling. One billet is placed at the bottom, and carbon steel billets for composite billet making are placed in the middle of the stack. Three billets are placed on the top layer. The unevenness of the carbon steel billets for composite billet making is 4mm, and they are used as the base material for the composite plate. Stainless steel billets (200mm thick) are rolled into stainless steel medium plates with a thickness of 38mm, which are used as the cladding material for the composite plate. The base and cladding thickness ratio is 6:1.

[0065] 2. Pretreatment of Stainless Steel Medium Plates. First, the stainless steel medium plates used for the composite cladding are solution-treated. The solution treatment temperature is controlled at 950-1050℃, and the holding time is controlled at 1.5 min / mm. Then, they are water-cooled to room temperature. Next, the solution-treated stainless steel medium plates are straightened to achieve a flatness of 5 mm.

[0066] 3. Surface Treatment of Raw Materials for Assembly. ① The carbon steel billet to be assembled is milled on one side to remove surface defects such as iron oxide scale, cracks, and slag inclusions, achieving a metallic finish. ② The stainless steel to be assembled surface is ground using an automatic grinding machine to remove the passivation layer and achieve a metallic finish. ③ Both the milled carbon steel billet and the ground stainless steel medium plate to be assembled are ground using a manual grinding machine with a 120-grit grinding wheel. The surface roughness of the carbon steel after surface treatment is Ra2.5μm, and the surface roughness of the stainless steel after surface treatment is Ra3.0μm.

[0067] 4. Cleaning. First, use compressed air without moisture to blow away the surface dust or iron dust; then use acetone or a volatile alkaline cleaning agent to clean the dust particles that cannot be blown away.

[0068] 5. Billet Assembly. First, place the carbon steel billet on the lower layer with the ground surface facing up. Then, flip the stainless steel middle plate along with the spare carbon steel billet so that the ground stainless steel surface faces down. Hoist it and slowly align it with the lower layer billet, with a 0.9mm gap between the composite surfaces. After assembly, the upper pressure billet is sent into the vacuum chamber.

[0069] 6. Electron beam sealing in the vacuum chamber. ① Evacuate the vacuum chamber to a vacuum level of 4.0 × 10⁻⁶. -2 Pa. ② Spot weld the four sides of the composite blank at 300mm intervals. ③ Position the electron beam gun directly in front of the center of the weld. ④ Weld the two long sides first, then the two short sides. ⑤ Use a welding beam current of 200mA, a welding voltage of 75KV, and a welding speed of 140mm / min.

[0070] 7. Inspection of composite billet welds. After the composite billet is sealed, the spare carbon steel casting billet and stainless steel are separated and removed at the spot welding position. Then, the weld is inspected by ultrasonic testing to ensure there are no defects such as cracks or porosity, and the penetration depth is 45mm.

[0071] 8. Heating of composite billets. The composite billets are heated in the ingot furnace at a rate of 70℃ / h in the first stage, and held at 1050℃ for 4 hours. In the second stage, the heating rate is 50℃ / h, and the temperature is raised to 1230℃ and held for 4 hours.

[0072] 9. Composite Plate Rolling. The composite plate rolling process is set with a differential speed of 12% throughout. The first stage rolling temperature is 1050℃, the second stage rolling temperature is 930℃, the intermediate thickness is 56mm, and the final rolling temperature is 850℃.

[0073] 10. Laminar flow cooling. The inlet water temperature is 800℃, and the final cooling temperature is 610℃.

[0074] 11. The composite billet showed no cracking during heating and rolling. The interfacial shear strength after hot rolling was 342 MPa, the interfacial bonding rate was 100%, the bonding performance was good, and the proportion of duplex ferrite was 45%.

[0075] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for manufacturing a duplex stainless steel and carbon steel asymmetric rolled composite plate, characterized in that: Includes the following steps: Step 1: Raw material preparation for billet assembly: Carbon steel is continuously cast into billets after being smelted in a converter and refined in a ladle. The thickness of the carbon steel billets is 200-280mm. After the carbon steel billets come off the production line, they are stacked and stored for cooling for no less than 3 days. One carbon steel billet is placed at the bottom, and the carbon steel billet for composite billet making is placed in the middle of the stack. Two carbon steel billets are placed at the top, ensuring that the flatness of the carbon steel billet for composite billet making is ≤5mm. It is used as the base material for composite plates. Stainless steel billets are rolled into stainless steel medium plates with a thickness of 10-67mm. They are used as the cladding material for composite plates. The thickness ratio of the base layer to the cladding layer is (3-28):

1. Step 2: Pretreatment of stainless steel medium plate: First, the stainless steel medium plate used for the composite plate cladding is solution treated. The solution treatment temperature is controlled at 950-1100℃, and the holding time is controlled at 1.5min / mm. After water cooling to room temperature, the solution treated stainless steel medium plate is pickled to remove the oxide scale on the surface of the stainless steel medium plate and passivated. After pickling, it is straightened to make the unevenness of the stainless steel medium plate ≤7mm. Step 3: Surface treatment of raw materials for assembly: ① The carbon steel billet to be assembled is milled on one side to remove surface iron oxide scale, cracks, and slag inclusions, and the surface is processed to produce a metallic color; ② The stainless steel medium plate to be assembled is ground with an 80-mesh flap wheel automatic grinding machine to remove the passivation layer and produce a metallic color; ③ The carbon steel billet after milling and the stainless steel medium plate to be assembled are both ground with a manual grinding machine using a 100-120 mesh grinding wheel, and the surface roughness after surface treatment reaches Ra2.0-4.0μm; Step 4: Cleaning: First, use dry compressed air to blow away surface dust or iron dust. Then, use acetone or a volatile alkaline cleaning agent to clean any remaining dust particles that cannot be blown away. Cleaning time should be 3-5 minutes per minute. 2 ; Step 5: Billet Assembly: First, place the carbon steel billet on the lower layer with the ground surface facing up. Then, flip the stainless steel middle plate so that the ground surface of the stainless steel faces down. Hoist it and align it with the lower carbon steel billet. Use a flattening machine to press down the stainless steel middle plate to ensure that the gap between the composite surfaces is ≤1mm. Spot weld the four sides with a spot weld length of 40-60mm and a spot weld interval of 300-500mm. After assembly, it becomes a composite billet. Press the carbon steel billet on the composite billet and send it into the vacuum chamber. Step Six: Electron Beam Sealing in Vacuum Chamber: ① Evacuate the vacuum chamber to a vacuum level ≤7.5×10⁻⁶ -2 Pa; ② Then spot weld the four sides of the composite billet, with an interval of 200-300mm; ③ Position of the electron beam gun: The billet assembly method adopts direct welding of stainless steel medium plate and carbon steel cast billet, and the electron beam gun should be directly facing the center of the weld; ④ Welding sequence is to weld the two long sides first, and then weld the two short sides; ⑤ The sealing welding process adopts a welding beam current of 140-200mA, a welding voltage of 65-75KV, and a welding speed of 100-150mm / min; Step 7: Inspection of composite billet welds: After the composite billet has been sealed and welded, the carbon steel billet pressing on it is removed, and then the weld is inspected by ultrasonic testing to ensure that there are no cracks or pores, and that the penetration depth is 35-50mm. Step 8: Composite Billet Heating: Before heating the composite billet in the ingot furnace, place a carbon steel pad billet at the bottom, and place the composite billet on the pad billet with the stainless steel side facing down. The length and width of the pad billet should not be smaller than the composite billet, ensuring that the composite billet is placed in the middle of the pad billet, pressing down the four sides to suppress weld deformation. Next, a two-stage heating process is adopted in the ingot furnace. The furnace is loaded at a furnace temperature of 500℃-600℃. The first stage heating rate is 70-90℃ / h, and the temperature is raised to 1000-1100℃ and held for 4-6 hours. The second stage heating rate is 50-70℃ / h, and the temperature is raised to 1200-1230℃ and held for 4-6 hours. Step 9: Composite plate rolling: The entire process of composite plate rolling adopts differential speed rolling. The rolling speed of stainless steel surface is 10-15% faster than that of carbon steel surface. Two-stage rolling is adopted. The first stage rolling temperature is 1000-1080℃, the second stage rolling temperature is ≤930℃, the intermediate thickness is 2-4 times the finished product thickness, and the final rolling temperature is controlled at 830±20℃. Step 10: Laminar flow cooling: ACC laminar flow cooling is adopted, with the inlet water temperature controlled at 780±20℃ and the final cooling temperature controlled at 600±20℃.

2. The method for manufacturing a duplex stainless steel and carbon steel asymmetric rolled composite plate according to claim 1, characterized in that: In step two, the pickling concentration is HNO3: 120-300 g / L, HF: 15-50 g / L, and the pickling speed is 2-8 m / min.

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