A method for preparing high-strength, high-toughness, high-corrosion-resistant high-chromium and high-molybdenum ferrite stainless steel

Abstract

The present invention relates to ferritic stainless steel, specifically a method for preparing high-strength, high-toughness, and high-corrosion-resistant high-chromium, high-molybdenum ferritic stainless steel. The purpose is to provide a method for preparing high-strength, high-toughness, and high-corrosion-resistant high-chromium, high-molybdenum ferritic stainless steel. Specifically, the method significantly improves the yield strength, tensile strength, elongation, and corrosion resistance of the high-chromium, high-molybdenum ferritic stainless steel by adding an appropriate amount of Cu, controlling the Si content, and employing Nb monostabilization, along with selecting a suitable production process.

Description

Technical Field

[0001] The invention relates to the technical field of high-chromium and high-molybdenum ferrite stainless steel, and in particular to a method for preparing high-strength, high-toughness, and high-corrosion-resistant high-chromium and high-molybdenum ferrite stainless steel. Background Art

[0002] High-chromium, high-molybdenum ferritic stainless steel, due to its high Cr and Mo content, exhibits excellent comprehensive properties such as high corrosion resistance, high strength, good thermal conductivity, and low expansion. It is primarily used as a low-cost heat exchange material in corrosive environments, such as replacing copper and titanium tubes in the manufacture of XX power plant condensers. XX power plant condensers typically use seawater as circulating cooling water. In a Cl ion environment, pitting corrosion is prone to occur in the condenser tubes, significantly reducing their service life. At the same time, high-chromium, high-molybdenum ferritic stainless steel requires excellent strength and toughness to be processed and formed into complex components in actual production. However, due to the high Cr and Mo content, high-chromium, high-molybdenum ferritic stainless steel is prone to precipitating brittle phases (σ (Fe-Cr-Mo) and χ (Fe36Cr12Mo10)) during the preparation process. These brittle phases significantly deteriorate the material's strength, toughness, and corrosion resistance. Therefore, improving its strength, toughness, and corrosion resistance in Cl ion environments is a current research challenge in this field.

[0003] In order to improve the strength, toughness and corrosion resistance of high-chromium, high-molybdenum ferritic stainless steel, refining the grains and avoiding the precipitation of brittle phases are effective ways to solve this problem. Existing technologies use alloying elements such as Ce, Al, and Cu to inhibit the precipitation of brittle phases to improve the strength, toughness and corrosion resistance of the material, but other problems still exist. For example, publication number CN108220812A discloses a rare earth-containing high-strength and plastic super ferritic stainless steel and a preparation method thereof, which utilizes the solid solution effect and segregated grain boundaries of the rare earth element Ce to achieve the purpose of grain refinement. However, since the expensive rare earth element Ce is added in this invention, its preparation cost is increased; publication number CN11565624A discloses an ultra-super ferritic stainless steel and a preparation method thereof, which adds Al element to inhibit the σ-phase and promote the precipitation of nano-scale Laves phase to achieve the purpose of grain refinement, but the Al element promotes the precipitation of large-sized Nb (C, N) particles, deteriorating the pitting corrosion resistance; publication number CN118703752A discloses a high-strength and plastic copper-containing super ferritic stainless steel and a production process thereof, which optimizes the plasticity and toughness of the super ferritic stainless steel by adding Cu element, but its strength improvement still cannot meet the strength requirements of certain products. At the same time, since Ti is added to stabilize C and N, large-sized TiN particles are precipitated, which reduces the pitting corrosion resistance. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing high-strength, high-toughness, high-corrosion-resistant high-chromium, high-molybdenum ferritic stainless steel, that is, a method for preparing high-strength, high-toughness, high-corrosion-resistant high-chromium, high-molybdenum ferritic stainless steel.

[0005] The present invention is achieved by adopting the following technical solutions:

[0006] Option 1:

[0007] A method for preparing high-strength, high-toughness, high-corrosion-resistant high-chromium, high-molybdenum ferritic stainless steel comprises the following steps in sequence:

[0008] 1) Melting:

[0009] The weight percentages of the elements in the smelting raw materials are as follows: 25%≤Cr≤30.0%, 1.5%≤Mo≤4.5%, 0.5%≤Ni≤4.5%, C≤0.015%, N≤0.015%, 0.10%≤Nb≤0.80%, 0.40%≤Cu≤2.0%, Mn≤0.4%, 0.3%≤Si≤1.5%, S≤0.005%, P≤0.005%, O≤0.02%, and satisfying Cr+3.3×Mo≥35%, Si≥Nb+0.25%, Cu≥2×Nb+0.20%, with the remainder being Fe and unavoidable impurities. The raw materials are configured according to the above element ratios and then smelted to obtain molten steel.

[0010] 2) Forging: The molten steel obtained in step 1) is cast into a billet, which is opened by forging. The billet is slowly heated to 1180-1250°C at a heating rate of 0.5-10°C / min, a forging temperature of 980-1200°C, and a forging ratio of 2-4 to obtain a primary forged sample. The primary forged sample is heated to 1100-1200°C, held at this temperature for 0.2-2 hours, and continuously forged to a thickness of 30-50 mm. The final forging temperature is ≥950°C, and air-cooled after forging to obtain a final forging.

[0011] 3) Rough rolling: The final forging obtained in step 2) is heated to 1050-1180°C at a heating rate of ≥20°C / min, and kept at this temperature for 0.5h-4h before being subjected to multiple passes of rough rolling, with a single pass rough rolling reduction of ≥15% and a total rough rolling reduction of ≥40%;

[0012] 4) Finish rolling

[0013] The rough rolled sheet obtained in step 3) is then subjected to multiple passes of finish rolling, with the final rolling temperature being 600-850°C to obtain a finished rolled sheet;

[0014] 5) Solution treatment:

[0015] The finished rolled plate obtained in step 4) is subjected to solution treatment at a heating temperature of 1010-1150°C for a holding time of 5-120 minutes, followed by immediate rapid cooling at a cooling rate of 50-200°C / s to obtain a hot-rolled solution plate;

[0016] 6) Cold rolling:

[0017] The hot-rolled solid solution plate obtained in step 5) is subjected to multiple cold rolling passes with a cold rolling reduction rate of 50-90% to obtain a cold-rolled plate;

[0018] 7) Recrystallization annealing:

[0019] The cold rolled sheet obtained in step 6) is subjected to recrystallization annealing at a temperature of 980-1100° C. for a holding time of 1-60 min, followed by immediate rapid cooling.

[0020] The alloy components of the present invention function as follows:

[0021] Cr: Cr is the most important alloying element in ferritic stainless steel, significantly affecting its strength, toughness, and corrosion resistance. With the increase of Cr, the strength, toughness, and corrosion resistance of stainless steel are significantly improved. However, high Cr content promotes the precipitation of brittle phases, σ and χ, seriously deteriorating the performance of the stainless steel. Therefore, it is necessary to control the Cr content between 25% and 30%, and adopt appropriate preparation processes to avoid the precipitation of brittle phases.

[0022] Mo: Mo element can improve the corrosion resistance of stainless steel and significantly improve the hardness and mechanical properties of stainless steel. However, Mo will also accelerate the precipitation of brittle phases of σ phase and χ phase, seriously deteriorating the performance of stainless steel. Therefore, the Mo content is limited to between 1.5% and 4.5%, and a suitable preparation process is used to avoid the precipitation of brittle phases.

[0023] Ni: Ni can improve the strength and corrosion resistance of stainless steel, improve its room temperature toughness, and lower its ductility-to-ductility transition temperature. However, Ni is expensive, so the content should be controlled at 0.5% ≤ Ni ≤ 4.5%.

[0024] C, N: C and N are the most harmful elements in stainless steel. Since C and N have very low solubility in ferritic stainless steel and diffuse quickly, they are easy to form Cr 23 Harmful precipitates such as C6 have a detrimental effect on the plasticity, toughness, and corrosion resistance of stainless steel. Therefore, it is necessary to add stabilizing elements to combine with C and N to form carbonitrides. During the preparation process, the C and N contents are strictly controlled. In this invention, the limits are C ≤ 0.015% and N ≤ 0.015%.

[0025] Nb: Nb is a stabilizing element in stainless steel. It combines with C and N to form Nb (C, N) compounds, reducing the precipitation of Cr carbides, further reducing the C and N content in the matrix, and improving intergranular corrosion resistance and formability. At the same time, Nb can also inhibit the precipitation of Cu-rich phase. However, excessive Nb content will precipitate large-sized NbC particles and reduce pitting corrosion resistance. Therefore, the Nb content is controlled to be 0.10%≤Nb≤0.80%.

[0026] Cu: Cu can enhance the corrosion resistance of stainless steel and improve its mechanical and formability. However, adding too little Cu will not significantly strengthen it. Excessive Cu will cause copper-rich phase precipitation, which in turn reduces the performance of the stainless steel. Therefore, it is necessary to control the Cu content to 0.40% ≤ Cu ≤ 2.0%, and adopt appropriate preparation processes to avoid the precipitation of Cu-rich phases.

[0027] Mn, Si: Si element can promote and stabilize fine Laves phase and improve the corrosion resistance and oxidation resistance of stainless steel. It is usually used as a deoxidizer together with Mn element in the smelting process. Therefore, the present invention controls Mn≤0.4%, 0.3%≤Si≤1.5%.

[0028] P, S: P and S elements exist in stainless steel as unavoidable harmful impurity elements and need to be strictly controlled within an extremely low range during the smelting process. The present invention limits S to ≤ 0.005% and P to ≤ 0.005%.

[0029] Principle description: The preparation method of the present invention stabilizes C and N impurity elements, reduces the C and N content in the matrix, avoids the precipitation of Cr carbides, inhibits the precipitation of Cu-rich phase, and ensures the precipitation of nano-scale Laves phase; adding Cu inhibits the precipitation of σ-phase and χ-phase, and promotes the precipitation of nano-scale Laves phase. Based on this, low-temperature hot rolling can be achieved, and the deformation structure can be retained in the hot-rolled plate to improve the deformation energy storage. The addition of Cu element reduces the stacking fault energy of the material, improves the deformation resistance through solid solution strengthening, retains more dislocations during hot rolling, forms a large number of shear bands and deformation bands, and further provides deformation storage. The Cu element can be used to strengthen the material by solid solution. At the same time, Cu adheres to the surface in a Cl ion environment to inhibit the anodic reaction and improve the pitting corrosion resistance. If the Cu content is too high, a Cu-rich phase will precipitate and the stainless steel will become brittle. If the Cu content is too low, the corrosion resistance cannot be effectively improved. The Cu content is controlled at 0.4-2.0%. A certain amount of Si element is added to the steel. The Si element dissolves into the Laves phase, increases the Laves phase precipitation temperature, promotes and stabilizes the formation of nano-scale Laves phase, and forms a Si-containing passivation film on the surface of the stainless steel, thereby improving the corrosion resistance. In addition, the addition of Si element improves the strength of the material through solid solution strengthening.

[0030] In the specific preparation method, step 2) the forging blank is slowly heated up, with a heating rate of no more than 0.5-10 ℃ / min, which can make the elements uniform and avoid the segregation of elements such as Cr, Nb, and Cu. If the forging temperature is too high, it will lead to coarse grains. If the forging temperature is too low, the forging deformation resistance is too large and the plasticity is poor, making forging difficult. If the final forging temperature is too low, the forging deformation resistance is too large and cracks are easy to appear. Secondary heating in the middle of forging ensures that a fine grain structure is obtained. The forging is heated in step 3) to obtain a high-temperature steel plate, which further dissolves the Cr, Cu, Nb, and Si elements segregated at the interface. Through rough rolling with a large reduction rate, a large number of shear bands and deformation bands are formed (see Figure 1 ), improve deformation energy storage, and provide nucleation particles for subsequent Laves phase precipitation; further perform step 4) finishing rolling, the final rolling temperature is 600-850℃, and low-temperature finishing rolling forms a large deformation structure in the steel plate, improves deformation energy storage, and the deformation structure provides particles for the heterogeneous nucleation of Laves phase, and promotes the diffusion of Si elements into the Laves phase, controls and optimizes the size and content of the Laves phase, and provides appropriate Laves phase for subsequent solid solution recrystallization and grain refinement; step 5) after solution treatment (heating temperature 1010-1150℃, holding time 5-120min), the solid solution process promotes the dissolution and uniform distribution of segregated Cu and Si elements, and completes the recrystallization of the deformation structure in the solid solution plate, and uses the nano-scale Laves phase particles formed in the finishing rolling process to pin the recrystallized grain boundaries to refine the grains, while avoiding the precipitation of σ phase and χ phase (see Figure 2 、 Figure 3 ), improve plastic toughness and prevent cold rolling edge cracking; the hot rolled solid solution plate obtained in step 5) is subjected to step 6) high reduction rate cold rolling, the cold rolling reduction rate is 50-90%, the high reduction rate cold rolling obtains a large deformation structure, improves deformation energy storage, and a large number of shear bands, deformation bands, dislocation cells and other microstructures provide nucleation points for recrystallization in the subsequent annealing process; finally, step 9) recrystallization annealing is carried out, the annealing temperature is 980-1100℃, the holding time is 1-60min, the solid solution Cu element is used to stabilize the nano-scale Laves phase and the formed nano-scale Laves phase is used to pin the grain boundaries, so that the deformed grains are recrystallized into fine equiaxed grains (see Figure 4 ), while no brittle phase precipitation occurs, improving the material's toughness and corrosion resistance. The retention of nanoscale Laves phases in the recrystallized structure further enhances strength through precipitation strengthening. Furthermore, the absence of Ti in the steel prevents the precipitation of TiN particles, reducing the likelihood of pitting corrosion initiation and further improving pitting resistance.

[0031] Furthermore, before step 6) cold rolling, the hot rolled solid solution plate after the solid solution treatment in step 5) needs to be pickled to remove the surface oxide scale, so as to improve the overall quality of the final product.

[0032] Furthermore, after step 3) rough rolling, the obtained rough rolled plate is heated to 1050-1150° C. and heated again to facilitate recrystallization and grain refinement, while preventing the rough rolled plate from losing too much temperature, which would make it difficult to control the subsequent finishing rolling temperature.

[0033] Furthermore, the cooling rate of the rapid cooling in step 7) is 50-200°C / s.

[0034] Option 2:

[0035] A method for preparing high-strength, high-toughness, high-corrosion-resistant high-chromium, high-molybdenum ferritic stainless steel comprises the following steps in sequence:

[0036] 1) Melting:

[0037] The weight percentages of the elements in the smelting raw materials are as follows: 25%≤Cr≤30.0%, 1.5%≤Mo≤4.5%, 0.5%≤Ni≤4.5%, C≤0.015%, N≤0.015%, 0.10%≤Nb≤0.80%, 0.40%≤Cu≤2.0%, Mn≤0.4%, 0.3%≤Si≤1.5%, S≤0.005%, P≤0.005%, O≤0.02%, and satisfying Cr+3.3×Mo≥35%, Si≥Nb+0.25%, Cu≥2×Nb+0.20%, with the remainder being Fe and unavoidable impurities. The raw materials are configured according to the above element ratios and then smelted to obtain molten steel.

[0038] 2) Continuous casting:

[0039] Continuously casting the molten steel obtained in step 1) into a continuous casting billet, rapidly cooling the continuous casting billet to ≤650°C, then slowly cooling it to 250-400°C at a cooling rate of ≤20°C / h, and grinding it to obtain a casting (controlling the cooling rate to ≤20°C / h; slow cooling helps to improve the plasticity and toughness of the continuous casting billet and avoid cracking of the casting);

[0040] 3) Rough rolling:

[0041] The casting obtained in step 2) is heated to 1180-1280°C at a heating rate of 0.5-10°C / min, and is kept warm for 0.5-4h before being subjected to multiple rough rolling passes, with a single pass reduction of 15-20%, a total reduction of 60-80%, and a rough rolling time of ≤5min to obtain a rough rolled plate (the casting is heated to 1180-1280°C at a heating rate of 0.5-10°C, which can homogenize the elements and avoid segregation of elements such as Cr, Nb, and Cu; the rough rolling time is ≤5min to avoid excessive temperature drop and ensure the subsequent finishing rolling temperature;

[0042] 4) Finish rolling

[0043] The rough rolled sheet obtained in step 3) is then subjected to multiple passes of finish rolling, with the final rolling temperature being 600-850°C to obtain a finished rolled sheet;

[0044] 5) Solution treatment:

[0045] The finished rolled plate obtained in step 4) is subjected to solution treatment at a heating temperature of 1010-1200°C for a holding time of 5-120 minutes, followed by immediate rapid cooling at a cooling rate of 50-200°C / s to obtain a solution plate;

[0046] 6) Cold rolling:

[0047] The solid solution plate obtained in step 5) is subjected to multiple cold rolling passes with a cold rolling reduction rate of 50-90% to obtain a cold rolled plate;

[0048] 7) Recrystallization annealing:

[0049] The cold rolled sheet obtained in step 6) is subjected to recrystallization annealing at a temperature of 980-1100° C. for a holding time of 1-60 min, followed by immediate rapid cooling.

[0050] Furthermore, before step 6) cold rolling, the hot rolled solid solution plate after the solid solution treatment in step 5) needs to be pickled to remove the surface oxide scale, so as to improve the overall quality of the final product.

[0051] Furthermore, the cooling rate of the rapid cooling in step 7) is 50-200°C / s.

[0052] The application principle of Option 2 is the same as that of Option 1. The only difference is that Option 1 is forging and Option 2 is continuous casting. These are two means of processing molten steel.

[0053] The beneficial effects of the present invention are as follows: The present invention provides a high-strength, high-toughness, high-corrosion-resistant high-chromium, high-molybdenum copper-containing ferritic stainless steel and its preparation method. By adding an appropriate amount of Cu to the high-chromium, high-molybdenum ferritic stainless steel, controlling the Si content, and employing Nb monostabilization and selecting an appropriate production process, the precipitation of σ and χ brittle phases is suppressed, the precipitation of nanoscale Laves phases is promoted, and the precipitation of Cu-rich phases is avoided. Low-temperature hot rolling is achieved, the deformed structure is retained in the hot-rolled plate, deformation energy storage is increased, and the formation of a sufficient amount of fine Laves phase is promoted. Simultaneously, the dissolved Cu and Si elements are used to stabilize the nanoscale Laves phase, pinning grain boundaries and promoting recrystallization grain refinement. Combined with the solid solution strengthening effects of Cu and Si, the strength and toughness of the stainless steel are improved. The addition of appropriate Nb as a stabilizing element and the omission of Ti prevent the precipitation of TiN particles, reducing the possibility of pitting corrosion initiation. Furthermore, the Cu and Si elements are solid-dissolved in the matrix, and Cu adheres to the surface to suppress anodic reactions and the Si-containing passivation film formed on the stainless steel surface, thereby improving pitting corrosion resistance in a Cl ion environment. The high-strength, high-toughness, high-corrosion-resistant high-chromium and high-molybdenum ferritic stainless steel of the present invention has a yield strength of 560-660 MPa, a tensile strength of 670-770 MPa, an elongation after fracture of 23-27%, and a corrosion rate of 0.0008-0.0066 mm / a after immersion in 6% FeCl3+1% HCl solution (temperature of 65±1°C) for 216 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0055] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0056] Figure 1 Schematic diagram of the shear band microstructure formed after hot rolling in Examples 1-6;

[0057] Figure 2 Schematic diagram of the nanoscale Laves phase precipitated after solution treatment in Examples 1-6;

[0058] Figure 3 Schematic diagram of the recrystallized structure after solution treatment in Example 1-6;

[0059] Figure 4 Schematic diagram of the recrystallized structure after recrystallization annealing in Example 1-6;

[0060] Figure 5Schematic diagram of large TiN particles precipitated in Comparative Example 1;

[0061] Figure 6 Schematic diagram of large-sized NbC particles precipitated in Comparative Example 2;

[0062] Figure 7 This is the corrosion morphology of Example 1-6 after immersion in 6% FeCl3+1% HCl solution (temperature 65±1°C) for 216 hours;

[0063] Figure 8 This is the corrosion morphology of Comparative Example 1 after immersion in 6% FeCl3 + 1% HCl solution (temperature 65±1°C) for 72 hours;

[0064] Figure 9 This is the corrosion morphology of comparative example 2 after immersion in 6% FeCl3+1% HCl solution (temperature 65±1℃) for 72h.

[0065] Among them, the shear band microstructure formed after hot rolling, the nanoscale Laves phase precipitated after solution treatment, the recrystallized structure after solution treatment, and the corrosion morphology after immersion for 72 hours in Examples 1-6 are basically the same, so they are replaced by one figure in this application. DETAILED DESCRIPTION

[0066] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0067] In the description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance. It should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood broadly. For example, they can refer to fixed connections, removable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms based on specific circumstances.

[0068] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0069] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0070] The chemical compositions of the examples and comparative examples of the present invention are shown in Table 1. Examples 1-6 all employed Nb monostabilization and added a certain amount of Cu to control the Si content. Comparative Examples 1-2 all employed Nb and Ti dual stabilization, with a certain amount of Al added in Comparative Example 2. Specific preparation process parameters are shown in Table 2.

[0071] Table 1 Chemical composition of high chromium and high molybdenum ferritic stainless steel of various embodiments of the present invention and comparative examples

[0072]

[0073] Table 2 Main parameters of the preparation process of high chromium and high molybdenum ferritic stainless steel in various embodiments of the present invention and comparative examples

[0074]

[0075] The pitting corrosion test of ferric chloride solution was based on ASTM G48-11 Standard Method for Testing Stainless Steel and Its Alloys for Pitting and Crevice Corrosion Resistance Using Ferric Chloride Solution. The samples were immersed in 6% FeCl3 + 1% HCl solution at 65 ± 1 °C for 216 h and in Comparative Example 1-2 for 72 h. The results are shown in Table 3. It can be seen from Table 3 that the corrosion resistance of the samples in the Cl ion environment is significantly higher than that of the samples in Comparative Example 1-2. At the same time, due to the addition of Ti element in Comparative Example 1, large TiN particles were precipitated (see Table 3). Figure 5 , black particles are TiN particles), in comparative example 2, Al element promotes the precipitation of large-sized NbC particles (see Figure 6 , the white rod-shaped particles are NbC particles), its pitting corrosion resistance is greatly deteriorated, and pitting pits appear in both Comparative Example 1 and Comparative Example 2. Figure 8 and 9 As shown, in Examples 1-6, no pitting phenomenon is observed. Figure 7 As shown, its anti-pitting effect is significant; in addition, it can be seen from Table 3 that the yield strength and tensile strength of Examples 1-6 of the present invention are greatly improved compared with Comparative Examples 1-2, and the elongation after fracture is not reduced;

[0076] Table 3 Properties of high chromium and high molybdenum ferritic stainless steel in various embodiments of the present invention and comparative examples

[0077] Serial number Yield strength / MPa Tensile strength / MPa Elongation after break / % Corrosion rate / (mm / a) Example 1 685 770 23 0.0066 Example 2 580 685 26 0.0033 Example 3 660 750 24 0.0008 Example 4 600 700 27 0.0041 Example 5 595 705 27 0.0016 Example 6 560 670 25 0.0024 Comparative Example 1 520 655 24 0.213 Comparative Example 2 500 650 25 23.484

[0078] The above description is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions have been made with reference to the aforementioned embodiments, those skilled in the art should understand that they may still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents; and such modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments, and they should all be included in the scope of protection of the claims.

Claims

1. A method for preparing high-strength, high-toughness, high-corrosion-resistant high-chromium and high-molybdenum ferritic stainless steel, characterized in that: The following steps are included in sequence: 1) Melting: The weight percentage of each element in the smelting raw materials is: 25%≤Cr≤30.0%, 1.5%≤Mo≤4.5%, 0.5%≤Ni≤4.5%, C≤0.015%, N≤0.015%, 0.10%≤Nb≤0.80%, 0.40%≤Cu≤2.0%, Mn≤0.4%, 0.3%≤Si≤1.5%, S≤0.005%, P≤0.005%, O≤0.02%, and Cr+3.3×Mo≥35%, Si≥Nb+0.25%, Cu≥2×Nb+0.20%, and the remainder is Fe and unavoidable impurities. After the raw materials are prepared according to the above element ratios, they are melted to obtain molten steel; 2) Forging: The molten steel obtained in step 1) is cast into a billet, which is opened by forging. The billet is slowly heated to 1180-1250°C at a heating rate of 0.5-10°C / min, a forging temperature of 980-1200°C, and a forging ratio of 2-4 to obtain a primary forged sample. The primary forged sample is heated to 1100-1200°C, held at this temperature for 0.2-2 hours, and continuously forged to a thickness of 30-50 mm. The final forging temperature is ≥950°C, and air-cooled after forging to obtain a final forging. 3) Rough rolling: The final forging obtained in step 2) is heated to 1050-1180°C at a heating rate of ≥20°C / min, and kept at this temperature for 0.5h-4h before being subjected to multiple passes of rough rolling, with a single pass rough rolling reduction of ≥15% and a total rough rolling reduction of ≥40%; 4) Finish rolling The rough rolled sheet obtained in step 3) is then subjected to multiple passes of finish rolling, with the final rolling temperature being 600-850°C to obtain a finished rolled sheet; 5) Solution treatment: The finished rolled plate obtained in step 4) is subjected to solution treatment at a heating temperature of 1010-1150°C for a holding time of 5-120 minutes, followed by immediate rapid cooling at a cooling rate of 50-200°C / s to obtain a hot-rolled solution plate; 6) Cold rolling: The hot-rolled solid solution plate obtained in step 5) is subjected to multiple cold rolling passes with a cold rolling reduction rate of 50-90% to obtain a cold-rolled plate; 7) Recrystallization annealing: The cold rolled sheet obtained in step 6) is subjected to recrystallization annealing at a temperature of 980-1100° C. for a holding time of 1-60 min, followed by immediate rapid cooling.

2. The method for preparing a high-toughness, high-corrosion-resistant high-chromium and high-molybdenum ferritic stainless steel according to claim 1, characterized in that: Before step 6) cold rolling, the hot rolled solid solution plate after the solid solution treatment in step 5) needs to be pickled.

3. The method for preparing high-toughness, high-corrosion-resistant high-chromium and high-molybdenum ferritic stainless steel according to claim 2, characterized in that: After step 3) rough rolling and before step 4) finish rolling, the obtained rough rolled sheet is heated to 1050-1150°C.

4. The method for preparing high-toughness, high-corrosion-resistant high-chromium and high-molybdenum ferritic stainless steel according to claim 3, characterized in that: The cooling rate of the rapid cooling in step 7) is 50-200°C / s.

5. A method for preparing high-strength, high-toughness, high-corrosion-resistant high-chromium and high-molybdenum ferritic stainless steel, characterized in that: The following steps are included in sequence: 1) Melting: The weight percentages of the elements in the smelting raw materials are as follows: 25%≤Cr≤30.0%, 1.5%≤Mo≤4.5%, 0.5%≤Ni≤4.5%, C≤0.015%, N≤0.015%, 0.10%≤Nb≤0.80%, 0.40%≤Cu≤2.0%, Mn≤0.4%, 0.3%≤Si≤1.5%, S≤0.005%, P≤0.005%, O≤0.02%, and satisfying Cr+3.3×Mo≥35%, Si≥Nb+0.25%, Cu≥2×Nb+0.20%, with the remainder being Fe and unavoidable impurities. The raw materials are configured according to the above element ratios and then smelted to obtain molten steel. 2) Continuous casting: Continuously casting the molten steel obtained in step 1) into a continuous casting billet, rapidly cooling the continuous casting billet to ≤650°C, then slowly cooling it to 250-400°C at a cooling rate of ≤20°C / h, and grinding it to obtain a casting; 3) Rough rolling: The casting obtained in step 2) is heated to 1180-1280°C at a heating rate of 0.5-10°C / min, and is kept warm for 0.5-4h before being subjected to multiple rough rolling passes with a single-pass reduction rate of 15-20%, a total reduction rate of 60-80%, and a rough rolling time of ≤5min, thereby obtaining a rough-rolled plate; the ingot is heated to 1180-1280°C at a heating rate of 0.5-10°C, which can homogenize the elements and avoid segregation of elements such as Cr, Nb, and Cu; the rough rolling time is ≤5min to avoid excessive temperature drop and ensure the subsequent finishing rolling temperature; 4) Finish rolling The rough rolled sheet obtained in step 3) is then subjected to multiple passes of finish rolling, with the final rolling temperature being 600-850°C to obtain a finished rolled sheet; 5) Solution treatment: The finished rolled plate obtained in step 4) is subjected to solution treatment at a heating temperature of 1010-1200°C for a holding time of 5-120 minutes, followed by immediate rapid cooling at a cooling rate of 50-200°C / s to obtain a solution plate; 6) Cold rolling: The solid solution plate obtained in step 5) is subjected to multiple cold rolling passes with a cold rolling reduction rate of 50-90% to obtain a cold rolled plate; 7) Recrystallization annealing: The cold rolled sheet obtained in step 6) is subjected to recrystallization annealing at a temperature of 980-1100° C. for a holding time of 1-60 min, followed by immediate rapid cooling.

6. The method for preparing high-toughness, high-corrosion-resistant high-chromium and high-molybdenum ferritic stainless steel according to claim 5, characterized in that: Before step 6) cold rolling, the solution plate after the solution treatment in step 5) needs to be pickled.

7. The method for preparing high-toughness, high-corrosion-resistant high-chromium and high-molybdenum ferritic stainless steel according to claim 6, characterized in that: The cooling rate of the rapid cooling in step 7) is 50-200°C / s.

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