Near net shape manufacturing method of metal plate strip containing rare earth

Abstract

The invention discloses a near-net-shape manufacturing method for a rare earth-containing metal plate strip. The near-net-shape manufacturing method comprises the steps of smelting, tundish induction heating, continuous casting, rolling, cooling after rolling and coiling. The metal plate comprises the following chemical components in percentage by weight: 0.01-0.06% of C, less than or equal to 0.15% of Si, less than or equal to 0.85% of Mn, less than or equal to 0.02% of P, less than or equal to 0.005% of S, less than or equal to 0.001% of Als, less than or equal to 0.0050% of Ca, 0.001-0.008% of La or 0.001-0.008% of Ce or 0.001-0.008% of La and Ce, and the balance of Fe and other inevitable impurities. On the basis of the near-net-shape thin-strip continuous casting and rolling technology of the ultra-short process, green low-carbon technologies such as tundish induction heating and online six-roller hot rolling are combined, high-performance products with low carbon emission instead of cold are produced in a full-continuous mode, and obvious innovativeness and advancement are achieved in technology.

Description

Technical Field

[0001] The present invention relates to the technical field of thin strip continuous casting, and in particular to a method for manufacturing a near-net-shape rare earth-containing metal plate strip. Background Art

[0002] Traditional thin strip steel is mostly produced by continuous rolling of ingots with a thickness of 70-200mm through multiple passes. The traditional hot rolling process is: continuous casting + ingot reheating and insulation + rough rolling + finishing rolling + cooling + coiling. That is, first, ingots with a thickness of about 200mm are obtained through continuous casting. After the ingots are reheated and kept warm, rough rolling and finishing rolling are performed to obtain steel strips with a thickness generally greater than 2mm. Finally, the steel strips are laminar cooled and coiled to complete the entire hot rolling production process. If steel strips with a thickness of less than 1.5mm (inclusive) are to be produced, it is relatively difficult and usually the hot-rolled steel strips must be subsequently cold rolled and annealed to complete the process. In addition, the process is long, energy consumption is high, multiple units and equipment are required, and infrastructure costs are high, resulting in high production costs.

[0003] The thin slab continuous casting and rolling process is as follows: continuous casting + soaking and hot rolling + cooling + coiling. The main differences between this process and traditional processes are: the thin slab process significantly reduces the thickness of the cast slab to 50-90mm. Due to its thinness, the cast slab only needs one or two rough rolling passes (for slabs with a thickness of 70-90mm) or no rough rolling (for slabs with a thickness of 50mm). In contrast, the traditional continuous casting process requires repeated rolling passes to reduce the cast slab to the required specifications before finishing rolling. Furthermore, the cast slab does not undergo cooling but directly enters the soaking furnace for soaking and holding, or a small amount of supplementary heating. Therefore, the thin slab process significantly shortens the process flow, reduces energy consumption, reduces investment, and thus reduces production costs. However, the faster cooling rate during continuous casting and rolling of thin slabs leads to increased steel strength and yield ratio, thereby increasing the rolling load. As a result, the thickness specification of the economically produced hot-rolled products cannot be too thin, generally ≥1.5mm, see Chinese patents CN200610123458.1, CN200610035800.2 and CN200710031548.2.

[0004] The recently emerging headless thin slab continuous casting and rolling process (ESP) is an improvement on the semi-headless thin slab continuous casting and rolling process. ESP achieves headless rolling during slab casting, eliminating the need for flame cutting and the heating furnaces used for heat preservation and slab transfer. This significantly reduces the total length of the production line to approximately 190 meters. Slabs cast by the continuous caster range from 90-110 mm thick and 1100-1600 mm wide. The cast slabs pass through an induction heated roller conveyor for heat preservation and heat preservation before undergoing roughing, finishing, layer cooling, and coiling to produce hot-rolled plates. This headless rolling process allows for hot-rolled plates as thin as 0.8 mm, expanding the range of hot-rolled plate specifications. Furthermore, a single production line can produce up to 2.2 million tons per year. This process is rapidly developing and expanding, with several ESP production lines currently in operation worldwide.

[0005] A shorter process than thin slab continuous casting and rolling is thin strip continuous casting and rolling. Thin strip continuous casting is a cutting-edge technology in metallurgy and materials research, with a history of over 160 years since Henry Bessemer proposed the idea in 1865 (see US Patent 49053). However, due to the immaturity of related technologies such as manufacturing and control, the technology remained largely stagnant. It wasn't until the mid-20th century that it was realized in the continuous casting and rolling of aluminum, which rekindled its appeal in the steelmaking industry. Its emergence has revolutionized the steel industry, transforming the traditional steel strip production process in the metallurgical industry by integrating continuous casting, rolling, and even heat treatment processes. This allows thin strip blanks to be formed into thin steel strip in a single, online hot rolling process. This significantly simplifies the production process from molten steel to steel strip and shortens the production cycle. With a process line length of only approximately 50 meters, the steel production process is more compact, continuous, efficient, and environmentally friendly. This also reduces equipment investment and significantly lowers production costs, making it a low-carbon, environmentally friendly hot-rolled thin strip production process. Consequently, thin strip continuous casting technology has become a hot topic for development in countries around the world in recent years.

[0006] The typical process flow of the existing twin-roll thin strip continuous casting and rolling technology is as follows: Figure 1As shown in the figure, the molten steel in the ladle 1 is directly poured into a molten pool 7 surrounded by two relatively rotating and rapidly cooling crystallizing rollers 8a, 8b and side sealing devices 6a, 6b through the ladle long nozzle 2, the tundish 3, the submerged nozzle 4 and the distributor 5. The molten steel solidifies on the rotating circumferential surface of the crystallizing rollers 8a, 8b to form a solidified shell and gradually grows, and then forms a 1-5mm thick steel strip 11 at the smallest point (nip point) of the gap between the two casting rollers. The steel strip is guided by the guide plate 9 to the pinch roller 12 and sent to the rolling mill 13 to be rolled into a thin strip, and then transported to the cooling device 14 for cooling via the conveyor roller 15. After the head is cut by the flying shear device 16, the cut head falls into the flying shear pit 18 along the flying shear guide plate 17. The hot rolled strip after the head is cut enters the coiler 19 to be coiled into a coil.

[0007] The strip steel produced by thin strip continuous casting, especially the thin-gauge products with a thickness of less than 1.2mm, can be directly used to replace cold-rolled products (hot instead of cold) as long as the performance allows, which greatly expands the product field of thin strip continuous casting. Since it does not require multiple cold rolling thinning processes, its production cost is lower than that of products produced by the cold rolling process, and its cost performance is more outstanding.

[0008] Rare earth elements (RE), known as "industrial vitamins," are also known as lanthanides. They comprise 15 lanthanides in the third subgroup of Mendeleev's periodic table, with atomic numbers ranging from 57 to 71, along with scandium (Sc) and yttrium (Y), for a total of 17 elements. Rare earth elements are highly unstable and chemically active. Their atomic radius ranges from 0.1641 to 0.2042 nm, approximately 1.5 times that of Fe. They have a large number of electron shells, but a small number of electrons in their outermost shell, which can easily lead to the loss of these electrons and conversion to positive ions. Therefore, rare earth elements can deeply purify molten steel, serving as steel modifiers and important microalloying elements.

[0009] Rare earth elements not only react with harmful elements to form high-melting-point compounds that are dispersed throughout the steel, but also react with various non-metallic elements to form inclusions. By controlling the shape, quantity, size, and distribution of inclusions, the detrimental effects of impurities on steel properties can be reduced, improving the steel's strength, toughness, and corrosion resistance. Adding appropriate amounts of rare earth elements can effectively improve the steel's microstructure and processing properties, refining grain size and strengthening grain boundaries. Steel grades can be categorized by the effects of rare earth elements: "treated steel" and "microalloyed steel." "Treatened steel" refers to steel whose performance requirements are improved primarily by purifying the molten steel and modifying inclusion morphology, while "microalloyed steel" refers to steel whose specific properties are enhanced by utilizing the microalloying effect of rare earth elements.

[0010] However, in the actual continuous casting process, the reaction between rare earth and air, steel slag and refractory materials can lead to problems such as large burnout, low yield, and refractory erosion. The current rare earth addition process generally has problems such as low yield, steel flocs, and surface defects of the ingot, which are difficult to meet actual production needs. The amount and time of rare earth addition, as well as the high-density rare earth deoxidation products that are difficult to remove are also problems that need to be solved at present. To this end, the present invention proposes that the high-density rare earth deoxidation products can be removed by electromagnetic induction heating of the tundish, and at the same time, the special thin strip continuous casting sub-rapid solidification process can greatly improve the solid solubility of rare earth elements in steel, so that the advantageous role of rare earth elements in steel can be fully exerted. Summary of the Invention

[0011] The purpose of the present invention is to provide a method for near-net-shape manufacturing of rare earth-containing metal plates and strips, to achieve "replacing cold with heat" in the fields of most thickness specifications of products, and to use an ultra-short process and fully continuous near-net-shape production method to effectively improve the shortcomings and problems of the original thin strip continuous casting technology in producing low-carbon steel, with the advantages of high production efficiency, energy saving and environmental protection, low CO2 emissions, and reduced costs. Moreover, the products produced by the present invention have good mechanical properties and high surface quality.

[0012] To achieve the above object, the technical solution of the present invention is:

[0013] A method for manufacturing a near-net-shape rare earth-containing metal strip comprises the following steps:

[0014] 1) Smelting

[0015] The chemical composition is smelted according to the following composition, and its weight percentage is: C: 0.01-0.06%, Si≤0.15%, Mn≤0.85%, P≤0.02%, S≤0.005%, Als≤0.001%, Ca≤0.0050%, La: 0.001-0.008% or Ce: 0.001-0.008% or La+Ce:

[0016] 0.001~0.008%, the balance includes Fe and other unavoidable impurities;

[0017] 2) Induction heating of tundish

[0018] The qualified molten steel is poured into the tundish through the ladle, and the tundish is equipped with an electromagnetic induction heating device;

[0019] 3) Continuous casting

[0020] The continuous casting adopts twin-roll thin strip casting. Molten steel is injected from the tundish into the distributor and evenly distributed into the molten pool formed by the two crystallization rollers. A cast strip with a thickness of 1.5 to 3 mm is formed at the smallest gap between the two crystallization rollers. The diameter of the crystallization rollers is 500 to 1500 mm. The crystallization rollers are internally cooled by water. The casting speed of the casting machine is 50 to 150 m / min.

[0021] After the casting strip leaves the crystallization roller, the casting strip temperature is between 1400 and 1480°C and directly enters the lower closed chamber, where non-oxidizing gas is passed through and the oxygen concentration in the lower closed chamber is controlled at

[0022] <5%; the temperature of the casting strip at the outlet of the lower closed chamber is 1100~1300℃;

[0023] 4) Rolling

[0024] After the cast strip passes through the pinch rollers in the lower closed chamber, it enters the online six-high rolling mill for rolling in a closed environment. The starting rolling temperature is 1000-1250℃, the rolling reduction ratio ranges from 15% to 80%, the thickness of the steel strip after rolling is 0.3-2.5mm, and the rolling outlet temperature is 850-1100℃.

[0025] 5) Cooling after rolling

[0026] The strip steel after online hot rolling is cooled by gas atomization cooling at a cooling rate of 20-100℃ / s.

[0027] 6) Coiling

[0028] After the steel strip is sheared to remove the poor quality head, it is directly coiled into a coil; the coiling temperature is 550-650℃.

[0029] The metal plate strip finally obtained by the present invention has a yield strength of 350-380 MPa, a tensile strength of 450-480 MPa, and an elongation of ≥30%.

[0030] Preferably, the remainder of the molten steel composition in step 1) is Fe and other unavoidable impurities.

[0031] Preferably, the smelting in step 1) is carried out in an electric furnace or a converter, or the smelting is then carried out in a refining LF furnace, a VD / VOD furnace or a RH furnace.

[0032] Preferably, the non-oxidizing gas in the lower sealed chamber in step 3) is N2, Ar or CO2 obtained by sublimation of dry ice.

[0033] Preferably, step 4) rolling adopts lubrication rolling, and the iron oxide scale of the strip steel after rolling is evenly distributed and relatively thin. By controlling the oxygen concentration in the lower closed chamber, the thickness of the iron oxide scale is controlled to be 3-10um, preferably 3-6um.

[0034] Preferably, the air-water ratio of the atomization cooling in step 5) is 15:1 to 10:1, the air pressure is 0.5 to 0.8 MPa, and the water pressure is 1.0 to 1.5 MPa.

[0035] Preferably, the coiling in step 6) is performed using a carousel coiler or a double-coil down coiler.

[0036] In the chemical composition design of the low carbon steel of the present invention:

[0037] C: C is the most economical and fundamental strengthening element in steel, increasing the strength of steel through solid solution strengthening and precipitation strengthening. For conventional slab continuous casting, casting in the peritectic reaction zone is prone to surface cracks on the slab, and in severe cases, steel leakage accidents may occur. The same is true for thin strip continuous casting. Casting the strip in the peritectic reaction zone is prone to surface cracks, and in severe cases, the strip may break. Therefore, thin strip continuous casting of Fe-C alloys also needs to avoid the peritectic reaction zone, so the C content range used in the present invention is 0.01-0.06%.

[0038] Si: In the present invention, the addition of Si serves as a deoxidizer, improving steel purity. Si also expands the range of ferrite formation, facilitating ferrite rolling. However, excessive Si content can easily lead to the formation of "red scale" defects on the steel sheet after rolling, increasing strength while decreasing elongation. Since the present invention aims for lower strength and higher elongation, a high Si content is not necessary. Therefore, the Si content employed in the present invention is ≤0.15%.

[0039] Mn: Mn is one of the cheapest alloying elements. It improves the hardenability of steel and has a considerable solid solubility in steel. It increases steel's strength through solid solution strengthening while having little effect on its plasticity and toughness. It is the most important strengthening element for increasing steel's strength and also acts as a deoxidizer. However, excessive Mn content can degrade weldability and the toughness of the weld heat-affected zone. Therefore, the Mn content used in this invention is ≤0.85%.

[0040] P: High P contents tend to segregate at grain boundaries, increasing the steel's cold brittleness, impairing weldability, reducing plasticity, and deteriorating cold bending properties. In the thin strip continuous casting process, the cast strip solidifies and cools at extremely rapid rates, effectively suppressing P segregation, thereby effectively avoiding P's disadvantages and fully utilizing its advantages. Therefore, in the present invention, a higher P content than that used in traditional production processes is employed, while the P content is appropriately relaxed. Dephosphorization is eliminated from the steelmaking process. In actual operation, no dephosphorization process is required, nor is additional phosphorus addition. The P content is limited to ≤0.02%.

[0041] S: S is typically a harmful element in steel, causing hot brittleness and reducing its ductility and toughness. S easily forms MnS in steel. The amount and form of sulfides in steel directly affect the formability of the steel sheet. Therefore, S must be below 0.005%. The amount and form of inclusions significantly impact the deep-drawability of steel sheets. In particular, stripe-shaped sulfide inclusions can easily cause cracking during deformation. Therefore, in the present invention, S is controlled as an impurity element, with a content range of ≤ 0.005%.

[0042] Als: To control inclusions in steel, the present invention requires that Al cannot be used for deoxidation. In the use of refractory materials, the additional introduction of Al should also be avoided as much as possible, and the content of acid-soluble aluminum Als should be strictly controlled: <0.001%.

[0043] Ca: It can change the morphology of sulfides in steel, transforming long MnS inclusions into spherical CaS inclusions, improving the plasticity and toughness of the steel plate, and helping to improve the formability of the steel plate. The present invention controls Ca to less than 0.0050%.

[0044] La / Ce: The role of rare earth in steel is mainly reflected in the following aspects:

[0045] ① Purification: Rare earth elements are relatively active metals that can reduce the amount of impurities in steel, effectively purifying molten steel during the steelmaking process. Rare earth elements readily react with non-metallic elements in steel, such as oxygen, sulfur, and carbon, to form inclusions, which are then removed from the molten steel, reducing the concentration of these harmful elements in the steel and their segregation at grain boundaries. The melting point of these rare earth inclusions formed after modification of molten steel containing rare earth elements is generally higher than that of the matrix, and their density is similar to that of the molten steel. The high melting point of rare earth elements allows them to maintain a high concentration in the molten steel. These inclusions are spherical or elliptical in shape and are removed from the molten steel after appropriate sedation, thus purifying the molten steel. Furthermore, rare earth elements readily form compounds with harmful metallic elements, such as phosphorus, tin, sb, and lead, with higher melting points, which are then removed from the molten steel, reducing the adverse effects of other harmful elements with lower melting points, such as phosphorus, tin, sb, and lead. The deoxidizing ability of rare earth elements is comparable to that of calcium, but stronger than that of magnesium, aluminum, and titanium. Their desulfurization ability is second only to calcium. In pure steel, sulfur and phosphorus segregate significantly at grain boundaries, but this segregation decreases with the addition of La or Ce. In steels containing 0.0049% La and 0.0054% Ce, respectively, energy dispersive spectroscopy (EDS) detected no sulfur or phosphorus grains at the grain boundaries. Rare earth elements reduce the precipitation of sulfur and phosphorus at grain boundaries, alleviating the brittleness caused by these elements and thereby increasing grain boundary strength.

[0046] ② Inclusion Modification: The modification effect of rare earth elements on inclusions in steel is primarily manifested in two aspects: deformation and modification. These two effects exist simultaneously and reinforce each other. The deformation effect refers to the ability of rare earth elements to change the shape, size, and distribution of existing inclusions in steel, reducing their detrimental effects on the mechanical properties of the matrix. The modification effect refers to the way rare earth elements influence the formation reaction of inclusions, altering their composition, structure, and type, thereby improving the overall performance of the steel. By changing the properties, morphology, structure, and location of inclusions in the ingot, the performance of the steel grade is improved, ultimately enhancing its quality. After deoxidation and desulfurization, rare earth elements modify the Al2O3, MnS, and AlN in the molten steel, regenerating small, nearly elliptical aluminum oxide and manganese sulfide inclusions, as well as complex modified inclusions with Al2O3, MnS, and other inclusions as cores, surrounded by rare earth elements. Adding an appropriate amount of rare earth elements during the smelting process can transform irregularly shaped harmful inclusions in the molten steel into spindles, spheres, or equiaxed shapes, distributing them in a fine, dispersed manner throughout the molten steel. This reduces the tendency for grain boundary cracks to form and propagate, and reduces stress concentration. During the smelting process, effectively controlling the RE / S ratio to achieve perfect globalization of sulfides avoids processing stresses generated during steel processing and cooling, significantly improving the steel's impact toughness, fatigue resistance, and weldability.

[0047] ③ Microalloying: As the demand for steel functionality continues to increase, the addition of rare earth elements (REs) to steel will play a more focused role in microalloying. Rare earth atoms are approximately 0.5 times larger than iron atoms, and their solubility in molten steel is very low. Their dissolution into the metal causes lattice distortion, leading to solid solution strengthening and increased steel strength. Rare earth atoms utilize a vacancy diffusion mechanism to occupy lattice cross-sections, forming substitutional solid solutions within the crystal. Rare earth atoms tend to segregate at grain boundaries and interact with low-melting-point detrimental elements such as P, C, and N. This reduces grain boundary energy and the driving force for grain growth, enhancing grain boundary strength and impact resistance. They also influence the diffusion, nucleation, and growth of other elements at grain boundaries, causing changes in the grain boundary structure and composition, ultimately altering the steel's microstructure and properties. This is the microalloying effect of REs. The degree of strengthening and toughening achieved by microalloying is determined by factors such as the RE's presence in the steel, its solubility, its interaction with other solute elements, and its effects on the steel's surface and microstructure.

[0048] ④ Grain Refining Effect: Rare earth compounds, as tiny solid particles, can provide heterogeneous nucleation sites during the solidification process of molten steel. They accumulate at crystallization interfaces, inhibiting grain growth and reducing the degree of undercooling in the molten steel, thereby significantly refining the grains. The addition of rare earths to high-sulfur cast steel can expand the equiaxed crystal region, shrink the columnar crystal region, and increase the equiaxed crystal fraction. The addition of rare earths to low-sulfur cast steel can refine the secondary dendrite spacing. The size of the secondary dendrite spacing influences microstructural segregation, inclusions, and porosity, thus affecting mechanical properties. Rare earth atoms can replace iron atoms in cementite, rather than existing as carbides. However, due to their large atomic radius and high distortion energy, rare earth atoms are primarily distributed at the cementite-ferrite interface and segregate at grain boundaries. Increasing rare earth content significantly reduces austenite grain size. In conventional processes, when the rare earth metal content exceeds 0.005%, the austenite grain size can be controlled at around 10 μm. Further increases in rare earth content do not significantly change the austenite grain size. However, in the strip casting and sub-rapid solidification process, the tendency of rare earths to dissolve in steel increases, so their content can be appropriately increased. This maximizes the benefits of rare earths in steel. The present invention raises the upper limit of the La / Ce / La+Ce content to 0.008%, bringing the range to 0.001 to 0.008%.

[0049] In the manufacturing method of the present invention:

[0050] The tundish is equipped with an electromagnetic induction heating device. The induction heating of the tundish can effectively stabilize or increase the temperature of the molten steel in the tundish, and can also make the inclusions float up, thereby effectively removing high-density rare earth deoxidation products.

[0051] The continuous casting adopts double-roll thin strip continuous casting. After the casting strip comes out of the crystallization roller, it directly enters the lower closed chamber. The lower closed chamber is filled with non-oxidizing cooling gas, which can not only achieve anti-oxidation protection for the strip, but also cool the strip. The oxygen concentration in the lower closed chamber is controlled at <5%.

[0052] After passing through pinch rollers in the lower enclosed chamber, the cast strip enters the enclosed six-high rolling mill for rolling. Lubricated rolling improves the strip's surface quality and reduces wear on the rolls. The strip's oxide scale is evenly distributed and relatively thin, with a thickness of 3-10 μm, preferably 3-6 μm.

[0053] Reasons for choosing six-high rolling mill:

[0054] The online rolling mills configured in the existing thin-strip continuous casting and rolling production lines in various countries around the world are all four-roll mills, which can achieve a maximum reduction rate of no more than 50% in a single pass.

[0055] In order to achieve a larger single-pass reduction rate (>50%) and better plate shape, the present invention first selects a six-roll mill. The six-roll mill has the characteristics of a cold rolling mill. Since the cast strip obtained by continuous casting of thin strips is relatively thin and has a large width-to-thickness ratio, it has some characteristics of cold-rolled strips. Therefore, it is relatively easy to use a six-roll mill to roll the cast strip online, and a strip product with thinner thickness and better plate shape can be obtained.

[0056] Ultra-thin strip containing rare earth elements produced by continuous strip casting can achieve a high compression ratio after entering a six-roll mill at a high reduction rate. This allows for dynamic recrystallization of the material's internal microstructure at higher rolling temperatures. During dynamic recrystallization, the rare earth elements effectively inhibit the growth of recrystallized grains and refine the grains, thereby increasing strength. Using a traditional four-roll mill, the insufficient compression ratio results in incomplete dynamic recrystallization, hindering the full effect of the rare earth element addition. Furthermore, incomplete recrystallization can easily lead to the formation of mixed crystals within the material, affecting performance uniformity.

[0057] After the above manufacturing process, the final product has mechanical properties of 350-380MPa yield strength, 450-480MPa tensile strength, and elongation ≥30%. The products produced by this invention have excellent mechanical properties and high surface quality, and can achieve "hot instead of cold" in most thickness specifications. It is a green and low-carbon product. This ultra-short process, fully continuous, near-net-shape production method can effectively improve the shortcomings and problems of the original thin strip continuous casting technology for producing low-carbon steel, and has the advantages of high production efficiency, energy conservation and environmental protection, low CO2 emissions, and reduced costs.

[0058] The differences and improvements of the present invention over the prior art are as follows:

[0059] In the thin strip continuous casting and rolling technology, the related technology described in the present invention has not been proposed or publicly reported, and no similar industrialized units are sold on the market.

[0060] The online rolling mills configured in the existing thin-strip continuous casting and rolling production lines are all four-roll mills, which can achieve a maximum reduction rate of no more than 50% in a single pass.

[0061] The present invention selects a six-roll mill for the first time in the thin strip continuous casting and rolling process, which meets the requirements of matching the thin strip continuous casting process. The six-roll mill has the characteristics of a cold rolling mill, and the working roll diameter can be smaller, and a larger single-pass reduction rate (>50%) can be achieved. Since the thickness of the cast strip obtained by thin strip continuous casting is relatively thin, the width-to-thickness ratio is large, and it has some characteristics of cold-rolled plate and strip, it is relatively easy to use a six-roll mill to carry out online rolling of the cast strip, and a strip product with thinner thickness and better plate shape can be obtained.

[0062] Therefore, the present invention is based on the ultra-short process of near-net-shape thin strip continuous casting and rolling technology, combined with green and low-carbon technologies such as tundish induction heating and online six-roll hot rolling, to continuously produce high-performance "heat instead of cold" products with low carbon emissions, which is obviously innovative and advanced in technology.

[0063] Beneficial effects of the present invention:

[0064] (1) The present invention can significantly improve the solid solubility tendency of rare earth in steel in the thin strip continuous casting sub-rapid solidification process, and the rare earth content can be appropriately increased, thereby maximizing the advantageous effect of rare earth in steel and effectively improving the performance of steel.

[0065] (2) The present invention utilizes the tundish induction heating technology to effectively stabilize or increase the temperature of the molten steel in the tundish, and can also make inclusions float, thereby effectively removing high-density rare earth deoxidation products. At the same time, the special thin-strip continuous casting sub-rapid solidification process greatly increases the solid solubility of rare earth elements in steel, thereby giving full play to the advantageous role of rare earth elements in steel.

[0066] (3) The present invention selects a six-roll mill for the first time in the thin strip continuous casting and rolling process, which meets the requirements of matching the thin strip continuous casting process. The six-roll mill has the characteristics of a cold rolling mill. Since the thickness of the cast strip obtained by thin strip continuous casting is relatively thin, the width-to-thickness ratio is large, and it has some characteristics of cold-rolled plate and strip, it is relatively easy to use a six-roll mill to roll the cast strip online, and the process requirements of a larger reduction rate (>50%) in a single pass can be achieved, thereby obtaining a strip product with thinner thickness and better plate shape. The ultra-thin specification hot-rolled strip obtained by this method can be as thin as 0.3mm, realizing the "replacing cold with heat" in the field of most thickness specification products, which is a green and low-carbon product.

[0067] (4) The present invention is directed to the ultra-thin cast strip containing rare earth elements produced by continuous strip casting. After entering a six-roll mill, a large reduction ratio can be achieved for the cast strip under the action of a large reduction ratio. At a high rolling temperature, dynamic recrystallization of the microstructure inside the material is easily achieved. During dynamic recrystallization, the rare earth elements can effectively inhibit the growth of recrystallized grains and effectively refine the grains, thereby achieving the effect of improving strength. If a traditional four-roll mill is used, the compression ratio is insufficient, resulting in incomplete dynamic recrystallization, and the effect of adding rare earth elements cannot be fully exerted. At the same time, incomplete recrystallization easily leads to the formation of mixed crystals inside the material, affecting the uniformity of performance.

[0068] (5) The present invention adopts an ultra-short process, fully continuous, near-net-shape production method, eliminating many complex intermediate steps in traditional process production. The production line has the advantages of small footprint, simplicity and efficiency, high production efficiency, energy saving and environmental protection; the product has low carbon emissions, low energy consumption, low cost, and excellent performance, and is a low-carbon, green and environmentally friendly product. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 This is a typical process flow diagram of the existing twin-roll thin strip continuous casting and rolling technology;

[0070] Figure 2 Schematic diagram of the process layout of the method of the present invention. DETAILED DESCRIPTION

[0071] The present invention will be further described below with reference to the following examples and drawings, but these examples are by no means limiting of the present invention. Any changes made by those skilled in the art in the art in light of this specification will fall within the scope of the claims.

[0072] See also Figure 2 The method for manufacturing a near-net-shape rare earth-containing metal plate and strip according to the present invention comprises the following steps: molten steel conforming to the chemical composition design of the present invention is poured directly into a molten pool 7 surrounded by two relatively rotating and rapidly cooling crystallizing rollers 8a, 8b and side sealing plate devices 6a, 6b through a ladle 1, a tundish 3, an immersion nozzle 4 and a distributor 5; the molten steel solidifies on the rotating circumferential surfaces of the crystallizing rollers 8a, 8b, and forms a solidified shell that gradually grows to form a cast strip 11 with a thickness of 1.5 to 3 mm at the minimum gap between the two crystallizing rollers (nip point); the crystallization diameter of the present invention is between 500 and 1500 mm, and the interior is cooled by water; the casting speed of the casting machine ranges from 50 to 150 m / min depending on the thickness of the cast strip.

[0073] After the cast strip 11 exits the crystallization rollers 8a and 8b, the cast strip temperature is between 1400°C and 1480°C, and the cast strip directly enters the lower closed chamber 10. The lower closed chamber 10 is filled with non-oxidizing gas to protect the strip. The oxygen concentration in the lower closed chamber 10 is controlled to be less than 5%. The lower closed chamber 10 provides anti-oxidation protection for the cast strip 11 until the rolling mill entrance. The temperature of the cast strip 11 at the exit of the lower closed chamber 10 is between 1100°C and 1250°C. The cast strip 11 is then sent to the online six-high rolling mill 13' via the swinging guide plate 9 and the pinch rollers 12 for rolling. The starting rolling temperature is between 1000°C and 1250°C, the rolling reduction rate is between 15% and 80%, the thickness of the steel strip after rolling is between 0.3 and 2.5 mm, and the rolling exit temperature is between 850°C and 1100°C. Lubricated rolling is used, and the oxide scale of the rolled strip is evenly distributed, with an oxide scale thickness of 3 to 10 μm.

[0074] After hot rolling, the strip is conveyed via conveyor rollers 15 to a cooling unit 14 for post-rolling cooling. Gas atomization is used at a cooling rate of 20-100°C / s. The gas-to-water ratio for gas atomization is 15:1-10:1, the gas pressure is 0.5-0.8 MPa, and the water pressure is 1.0-1.5 MPa. The strip passes through a flying shear 16 to remove any poor-quality ends. The cut ends fall along a flying shear guide 17 into a flying shear pit 18. The cut strip then enters a coiler 19 for coiling. The coiling temperature is controlled at 550-650°C.

[0075] The chemical composition of the embodiment of the present invention is shown in Table 1, with the remainder including Fe and other unavoidable impurities. The manufacturing process parameters of the embodiment of the present invention are shown in Table 2, and the properties of the final product are shown in Table 3.

[0076] After the above manufacturing process, the mechanical properties of the final product are a yield strength of 350-380 MPa, a tensile strength of 450-500 MPa, and an elongation of ≥30%.

[0077] The ultra-thin cast strip containing rare earths produced by thin strip continuous casting, after entering the six-roll rolling mill, can achieve a large compression ratio of the cast strip under the action of a large reduction rate. At a higher rolling temperature, dynamic recrystallization of the internal microstructure of the material is easy to achieve. At the same time as dynamic recrystallization, rare earth elements can effectively inhibit the growth of recrystallized grains and effectively refine the grains, thereby achieving the effect of improving strength.

[0078] The products produced using this method have excellent mechanical properties and high surface quality, enabling the "hot-to-cold" approach across most thickness specifications, making them green and low-carbon products. This ultra-short, fully continuous, near-net-shape production method effectively overcomes the shortcomings and issues of conventional thin-strip continuous casting technology for producing low-carbon steel, offering advantages such as high production efficiency, energy conservation and environmental protection, low CO2 emissions, and reduced costs.

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Claims

1. A method for producing a near-net-shape rare earth-containing metal strip, characterized in that: The steps include: 1) Smelting Smelted according to the following chemical composition, the weight percentage of which is: C: 0.01-0.06%, Si≤0.15%, Mn≤0.85%, P≤0.02%, S≤0.005%, Als≤0.001%, Ca≤0.0050%, La: 0.001-0.008% or Ce: 0.001-0.008% or La+Ce: 0.001-0.008%, the balance including Fe and other unavoidable impurities; 2) Induction heating of tundish The qualified molten steel is poured into the tundish through the ladle, and the tundish is equipped with an electromagnetic induction heating device; 3) Continuous casting The continuous casting adopts twin-roll thin strip casting. Molten steel is injected from the tundish into the distributor and evenly distributed into the molten pool formed by the two crystallization rollers. A cast strip with a thickness of 1.5 to 3 mm is formed at the smallest gap between the two crystallization rollers. The diameter of the crystallization rollers is 500 to 1500 mm. The crystallization rollers are internally cooled by water. The casting speed of the casting machine is 50 to 150 m / min. After the casting strip leaves the crystallization roller, the casting strip temperature is between 1400 and 1480°C and directly enters the lower closed chamber. Non-oxidizing gas is passed through the lower closed chamber, and the oxygen concentration in the lower closed chamber is controlled at <5%. The temperature of the casting strip at the outlet of the lower closed chamber is between 1100 and 1300°C. 4) Rolling After the cast strip passes through the pinch rollers in the lower closed chamber, it enters the online six-high rolling mill for rolling in a closed environment. The starting rolling temperature is 1000-1250℃, the rolling reduction ratio ranges from 15% to 80%, the thickness of the steel strip after rolling is 0.3-2.5mm, and the rolling outlet temperature is 850-1100℃. 5) Cooling after rolling The strip steel after online hot rolling is cooled by gas atomization cooling at a cooling rate of 20-100℃ / s. 6) Coiling After the steel strip is sheared to remove the poor quality head, it is directly coiled into a coil; the coiling temperature is 550-650℃.

2. The method for producing a near-net-shape rare earth-containing metal sheet and strip according to claim 1, wherein: The yield strength of the metal plate and strip finally obtained is 350-380 MPa, the tensile strength is 450-480 MPa, and the elongation is ≥30%.

3. The method for producing a near-net-shape rare earth-containing metal sheet and strip according to claim 1, wherein: Step 1) The balance in the molten steel composition is Fe and other inevitable impurities.

4. The method for producing a near-net-shape rare earth-containing metal sheet and strip according to claim 1 or 3, wherein: Step 1) Smelting is carried out in an electric furnace or a converter, or the smelting is carried out in a refining LF furnace, a VD / VOD furnace or a RH furnace.

5. The method for producing a near-net-shape rare earth-containing metal sheet and strip according to claim 1, wherein: Step 3) The non-oxidizing gas in the lower sealed chamber is N2, Ar or CO2 obtained by sublimation of dry ice.

6. The method for producing a near-net shape rare earth-containing metal sheet and strip according to claim 1, wherein: Step 4) rolling adopts lubrication rolling, and the thickness of the iron oxide scale is controlled to be 3 to 10 μm.

7. The method for producing a near-net shape rare earth-containing metal sheet and strip according to claim 6, wherein: In step 4), the thickness of the iron oxide scale is controlled to be 3 to 6 μm.

8. The method for producing a near-net shape rare earth-containing metal sheet and strip according to claim 1, wherein: In step 5), the air-water ratio of the atomization cooling is 15:1 to 10:1, the air pressure is 0.5 to 0.8 MPa, and the water pressure is 1.0 to 1.5 MPa.

9. The method for producing a near-net shape of a rare earth-containing metal sheet and strip according to claim 1, wherein: Step 6) Coiling is performed using a Carousel coiler or a double-coil down coiler.

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