Preparation method of hot / cold rolled plate of high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel

Abstract

The present invention relates to the technical field of high-chromium and high-molybdenum ferritic stainless steels, and specifically to a method for preparing a hot / cold rolled sheet of high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel. In order to solve the problems in the prior art that the finish rolling temperature in hot rolling is relatively high and it is easy to form alumina particles and large-sized carbon / nitride particles in the method for avoiding the precipitation of brittle phases, a new method for preparing a hot / cold rolled sheet of high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel is provided, which includes the following steps: melting, casting, forging, hot rolling, annealing, pickling, cold rolling, and recrystallization annealing. Through the forging process in this preparation method, the formation of large-sized TiN and Ti / Nb(C,N) particles can be avoided; through the warm rolling process, nano-scale Laves phases are precipitated, and at the same time, a large-deformation structure is formed, obtaining a large number of deformation microstructures such as shear bands and deformation bands, solving the problem of grain coarsening, and improving the plasticity, toughness and corrosion resistance of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of high-chromium and high-molybdenum ferritic stainless steel, and specifically provides a method for preparing hot / cold rolled sheets of high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel. Background Art

[0002] High-chromium and high-molybdenum ferritic stainless steel has good thermal conductivity, low linear expansion coefficient and good formability, and is widely used in fields such as acid making, seawater desalination, petrochemical industry, etc. There is a risk of precipitation of brittle phases such as large σ-phase and χ-phase in high-chromium and high-molybdenum ferritic stainless steel, which is likely to deteriorate the plasticity, toughness and corrosion resistance of the material. In order to avoid the problem of brittle phase precipitation in the prior art, generally, a high hot rolling finishing temperature or alloying addition method is used to avoid or hinder the precipitation of brittle phases.

[0003] In the prior art, such as the technical solution with the patent number 201110363876.9 and the patent name of a high-Cr ferritic stainless steel and its manufacturing method, by controlling the hot rolling finishing temperature at 950-1000°C and subjecting the hot rolled sheet to a solution treatment at a high temperature of 1100°C, the harmful σ-phase and χ-phase precipitation can be completely eliminated. However, its hot rolling finishing temperature is relatively high and the control difficulty is relatively large;

[0004] In the prior art, such as the technical solution with the patent number 202011559796.6 and the patent name of a method for preparing high-chromium and high-molybdenum ferritic stainless steel, the problem of σ-phase brittleness is solved by inducing the precipitation of Laves phase at a relatively high temperature while avoiding the precipitation of σ-phase. However, its hot rolling finishing temperature is 960-1020°C and the control difficulty is also relatively large;

[0005] In the prior art, such as the technical solution with the patent number 202211553095.0 and the patent name of a special super ferritic stainless steel and its preparation method, Al alloying is used to inhibit the precipitation of σ-phase, and solution treatment is used to promote the precipitation of Laves phase to refine the structure and optimize the texture. At the same time, it is also required that the hot rolling finishing temperature ≥850°C, and its control difficulty is also relatively large. In addition, this solution is also extremely likely to cause the formation of alumina particles and coarse carbon / nitride particles in ferritic stainless steel, which instead easily deteriorates the plasticity, toughness and corrosion resistance of the material, seriously restricting the large-scale production and wide application of such products. Summary of the Invention

[0006] In order to solve the problems in the prior art that the method for avoiding brittle phase precipitation has a relatively high hot rolling finishing temperature and is prone to form large-sized carbon / nitride particles and alumina particles, the present invention provides a new method for preparing hot / cold rolled sheets of high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel.

[0007] The present invention is implemented by adopting the following technical solutions:

[0008] Solution 1:

[0009] A method for preparing a hot-rolled plate of high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel comprises the following steps in sequence:

[0010] 1) Melting:

[0011] The weight percentages of the elements in the melting raw materials are as follows: 25.0% ≤ Cr ≤ 30.0%, 0.5% ≤ Mo ≤ 4.5%, 1.0% ≤ Ni ≤ 4.0%, 0.15% ≤ Nb ≤ 0.65%, 0.01% ≤ Ti ≤ 0.35%, 0.5 ≤ Al ≤ 2.5%, Mn ≤ 0.6%, Si ≤ 1.0%, S ≤ 0.005%, P ≤ 0.005%, O ≤ 0.004%, C > 0%, N > 0%, C + N ≤ 0.025%, and it satisfies Cr + 3.3% × Mo ≥ 35%. The remaining are Fe and inevitable impurities. After configuring the raw materials according to the above element ratios, melting is carried out to obtain molten steel;

[0012] 2) Casting:

[0013] The molten steel obtained in step 1) is poured into a casting blank in the hood. The casting blank is cooled to ≤ 1000 °C in the hood, taken out and slowly cooled to room temperature, and the cooling rate is ≤ 20 °C / h, and then grinding is carried out; (Slow cooling in the furnace reduces the oxidation reaction and avoids the formation of alumina)

[0014] 3) Forging:

[0015] The ground casting blank obtained in step 2) is heated to 1180 - 1280 °C, the heating rate is ≤ 10 °C / min, held for 1 - 4 h, the forging start temperature is ≥ 1120 °C, the forging end temperature is ≥ 960 °C, and it is immediately water-cooled to room temperature after forging. The thickness after forging is 30 - 55 mm;

[0016] 4) Rough rolling:

[0017] The forging blank obtained in step 3) is heated to 1100 - 1200 °C, and after holding for 1 - 4 h, rough rolling is carried out. If the outlet temperature of the rough-rolled plate is lower than 1000 °C, it needs to be reheated to 1100 - 1200 °C and held for 5 min - 40 min to continue rough rolling. If the outlet temperature of the rough-rolled plate is equal to or higher than 1000 °C, there is no need for reheating and holding, and rough rolling continues. Rough rolling is carried out 3 - 10 times, the single-pass reduction rate is ≥ 15%, and the total reduction rate is ≥ 60%. This can reduce the thickness of the raw material, thereby reducing the number of rolling passes in the warm rolling stage and reducing production costs to obtain a rough-rolled plate; (As is well known to those skilled in the art, using the hot continuous rolling process, the outlet temperature of the rough-rolled plate is relatively high, and there is no need for reheating and holding, and it can be directly continued for further rough rolling)

[0018] 5) Warm rolling

[0019] Cool the hot-rolled sheet obtained in step 4) to 650 - 800 °C and perform warm rolling. If the outlet temperature of the hot-rolled sheet is lower than 650 °C, heat it to 650 - 800 °C, hold for 3 - 50 min, continue warm rolling, and repeat the above warm rolling steps until the sheet thickness is ≤ 6.5 mm. After warm rolling, water-cool to room temperature;

[0020] 6) Solution treatment:

[0021] Perform solution treatment on the hot-rolled sheet obtained in step 5), with a heating temperature of 1030 - 1150 °C, a holding time of 1 - 60 min, and then rapidly cool to ≤ 10 °C, with a cooling rate ≥ 10 °C / s. (Solution treatment causes recrystallization behavior in the hot-rolled stainless steel sheet. The precipitation of Laves phase during warm rolling plays a role in pinning grain boundaries and refining grains, large deformation structures, deformation microstructures such as shear bands, increasing deformation energy storage, and promoting recrystallization)

[0022] Principle explanation: The applicant's research found that in high-chromium and high-molybdenum ferritic stainless steel, it is very easy to form coarse Ti / Nb(C,N) and TiN particles, which deteriorate the plasticity, toughness and corrosion resistance of the material. The carbide and nitride reactions of Nb in the steel intersect with the precipitation temperature range of the Laves phase, and there is a competitive and conversion relationship between the two. Through large deformation and temperature control, the formation of coarse Nb carbide and nitride can be avoided, and instead, nano-scale Laves phase is formed, and the nano-scale Laves phase can pin recrystallized grain boundaries and refine grains. In addition, the applicant's research found that the inhibitory effect of the added Al element on the σ phase in high-chromium and molybdenum ferritic stainless steel has a composition upper limit. When the addition of the Al element exceeds 2.0%, its inhibitory effect on the σ phase does not increase, and when the Al element is too high, that is, exceeding 2.5%, it is very easy to form coarse alumina particles, reducing the plasticity, toughness and corrosion resistance of the material. Therefore, controlling the appropriate Al element and the melting process can effectively avoid the formation of alumina particles and coarse carbide and nitride particles.

[0023] Specifically, the content of C+N elements added in the preparation method of the present invention does not exceed 0.025%, which weakens the formation of coarse Ti / Nb(C,N) and TiN particles, so as to reduce the intergranular corrosion of ferritic stainless steel; adding Ni element can improve the toughness of ferritic stainless steel, and adding Nb and Ti elements are used to further eliminate the adverse effects of C and N; adding 0.5-2.5% of Al element can not only ensure the inhibition of the precipitation of σ phase and χ phase, but also avoid the formation of coarse alumina particles due to excessive Al element, thereby reducing the plasticity and toughness of the material. In addition, vacuum melting can effectively reduce the oxidation reaction during the melting process, and the melting point of Al is relatively low. By controlling the addition sequence, addition temperature and addition content of Al element, other alloy elements can be fully melted and evenly distributed, which is convenient for the rapid mixing of Al element with the molten metal and reduces the generation of alumina; in step 3), slow heating can avoid the generation of cracks due to large internal thermal stress of the material, and at the same time make the elements fully dissolve; adopting a final forging temperature ≥960°C can avoid the segregation of Nb and Ti elements, and further avoid the formation of coarse TiN and Ti / Nb(C,N) particles. At this time, the forging temperature is in the range where the Laves phase is easily precipitated. During forging, a large deformed structure and a large number of shear bands will be generated, providing favorable nucleation sites for the formation of the Laves phase and promoting the precipitation of a large number of beneficial nano-scale Laves phases. The large deformed structure and shear bands generated at this final forging temperature can increase the deformation energy storage, facilitate recrystallization caused by pre-hot rolling holding, and promote the precipitation of the Laves phase. The nano-scale Laves phase plays a role in pinning grain boundaries and refining grains for the recrystallization caused by pre-hot rolling holding; in step 4), heat preservation at 1100~1200°C during hot rolling can cause the forging billet to recrystallize, restore the plasticity of the forging billet, and at the same time make the heating temperature of the forging billet uniform, avoiding cracks caused by uneven temperature during hot rolling, and at the same time dissolving the Laves phase, and not precipitating during the high-temperature hot rolling process; secondary heating and heat preservation can cause recrystallization inside the previous hot-rolled plate, form new fine recrystallized grains, restore the plasticity of the previous hot-rolled plate, and at the same time further dissolve the Laves phase, providing an element guarantee for the precipitation of the Laves phase during the warm rolling process in step 5); in step 5), controlling the warm rolling temperature at 650~800 °C is convenient for the formation of a large deformed structure, obtaining a large number of deformation microstructures such as shear bands, deformation bands, and dislocation cells, increasing the deformation energy storage, and promoting the occurrence of recrystallization during solution treatment; during the warm rolling process, heating and heat preservation can precipitate nano-scale Laves phases, which play a role in pinning grain boundaries and refining grains for the recrystallization occurring during solution treatment. If the warm rolling temperature is too low, the rolling resistance is large and the requirements for the rolling mill are high; in step 6), the solution treatment temperature is 1030~1150°C, which enables the hot-rolled plate to complete recrystallization. Under the combined action of the warm rolling large deformed structure and fine Laves phases, a fine recrystallized structure is formed, and finally a hot-rolled plate of high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel with excellent plasticity, toughness and corrosion resistance is obtained.

[0024] Further, in step 1), vacuum induction furnace melting is adopted. During melting, the melting raw materials except Al are first added to the vacuum induction furnace for melting to form primary molten steel, and then Al is added to the primary molten steel. The temperature of the primary molten steel is 1500 - 1600 °C when adding Al;

[0025] Further, in step 4), the total reduction ratio during rough rolling is ≥60%.

[0026] Further, in step 5), the total reduction ratio during warm rolling is ≥40%.

[0027] Scheme Two:

[0028] A method for preparing a cold-rolled plate of high-chromium high-molybdenum aluminum-containing ferritic stainless steel, successively including the following steps:

[0029] 1) Melting:

[0030] The weight percentages of the elements of the melting raw materials are as follows: 25.0% ≤ Cr ≤ 30.0%, 0.5% ≤ Mo ≤ 4.5%, 1.0% ≤ Ni ≤ 4.0%, 0.15% ≤ Nb ≤ 0.65%, 0.01% ≤ Ti ≤ 0.35%, 0.5 ≤ Al ≤ 2.5%, Mn ≤ 0.6%, Si ≤ 1.0%, S ≤ 0.005%, P ≤ 0.005%, O ≤ 0.004%, C ≤ 0.015%, N ≤ 0.010%, and it satisfies Cr + 3.3% × Mo ≥ 35%. The rest are Fe and unavoidable impurities. After configuring the raw materials according to the above element ratios, melting is carried out to obtain molten steel; Further, in step 1), vacuum induction furnace melting is adopted. During melting, the melting raw materials except Al are first added to the vacuum induction furnace for melting to form primary molten steel, and then Al is added to the primary molten steel. The temperature of the primary molten steel is 1500 - 1600 °C when adding Al;

[0031] 2) Casting:

[0032] The molten steel obtained in step 1) is poured into a casting blank in the furnace hood. The casting blank is cooled to ≤1000 °C in the furnace hood, taken out and slowly cooled to room temperature, and the cooling rate is ≤20 °C / h, and then grinding is carried out; (Slow cooling in the furnace reduces the oxidation reaction and avoids the formation of aluminum oxide)

[0033] 3) Forging:

[0034] The ground casting blank obtained in step 2) is heated to 1180 - 1280 °C, the heating rate is ≤10 °C / min, held for 1 - 4 h, the forging start temperature is ≥1120 °C, the forging end temperature is ≥960 °C, and it is immediately water-cooled to room temperature after forging. The thickness after forging is 30 - 55 mm;

[0035] 4) Rough rolling:

[0036] Heat the forged blank obtained in step 3) to 1100 - 1200 °C, hold for 1 - 4 h and then perform rough rolling. If the outlet temperature of the rough rolled plate is lower than 1000 °C, it needs to be reheated to 1100 - 1200 °C for 5 min - 40 min and continue rough rolling. If the outlet temperature of the rough rolled plate is equal to or higher than 1000 °C, there is no need for secondary heating and holding, and continue rough rolling. Rough roll 3 - 10 times, with a single pass reduction rate ≥ 15%, and rough roll until the total reduction rate ≥ 60%, which can reduce the thickness of the raw material, thus reducing the number of rolling passes in the warm rolling stage, lowering the production cost and obtaining a rough rolled plate; (As is well known to those skilled in the art, using the hot continuous rolling process, the outlet temperature of the rough rolled plate is relatively high, and there is no need for secondary heating and holding, and it can be directly continued for further rough rolling)

[0037] 5) Warm rolling

[0038] Cool the rough rolled plate obtained in step 4) to 650 - 800 °C and perform warm rolling. If the outlet temperature of the hot rolled plate is lower than 650 °C, heat it to 650 - 800 °C, hold for 3 - 50 min, and continue warm rolling. Repeat the above warm rolling steps until the plate thickness ≤ 6.5 mm, and then water cool to room temperature after warm rolling;

[0039] 6) Solution treatment:

[0040] Perform solution treatment on the hot rolled plate obtained in step 5), with a heating temperature of 1030 - 1150 °C, a holding time of 1 - 60 min, and then quickly cool to ≤ 10 °C, with a cooling rate ≥ 10 °C / s to obtain a solution treated plate;

[0041] 7) Pickling:

[0042] Pickle the solution treated plate obtained in step 6) with a sulfuric acid mixture;

[0043] 8) Cold rolling:

[0044] Perform cold rolling at room temperature on the pickled solution treated plate obtained in step 7), with a cold rolling reduction rate ≥ 50% to obtain a cold rolled plate;

[0045] 9) Recrystallization annealing:

[0046] Perform recrystallization annealing on the cold rolled plate obtained in step 8), with an annealing temperature of 970 - 1070 °C, a holding time of 0.5 - 120 min, and then immediately cool to room temperature, with the cooling rate controlled at ≥ 50 °C / s.

[0047] Principle description: The principles of steps 1) to 6) in Solution 2 are the same as those in Solution 1. In step 7), pickling is used to remove the oxide scale generated due to solution treatment to prevent affecting the surface quality of the cold-rolled stainless steel sheet. The large cold rolling reduction rate in step 8) makes a large number of cold rolling deformation structures generated inside the material, which can provide nucleation sites for the recrystallization annealing in step 9). In step 9), by controlling the annealing temperature and holding time, fine equiaxed grains are formed.

[0048] Furthermore, in step 1), vacuum induction furnace melting is adopted. During melting, the melting raw materials except Al are first added to the vacuum induction furnace for melting to form primary molten steel, and then Al is added to the primary molten steel. The temperature of the primary molten steel is 1500 - 1600 °C when adding Al.

[0049] Furthermore, in step 4), the total reduction rate during rough rolling is ≥ 60%.

[0050] Furthermore, in step 5), the total reduction rate during warm rolling is ≥ 40%.

[0051] The beneficial effects produced by the present invention are as follows: The present invention realizes low-temperature hot rolling finish rolling, which is convenient to control the hot rolling finish rolling temperature. At the same time, it is found and utilized that there is an intersection between the reaction of Nb carbonitrides and the precipitation temperature range of Laves phase. Through large deformation and temperature control, the formation of coarse Nb carbonitrides is avoided, and instead, nanoscale Laves phase is formed. In addition, by controlling the addition of Al content and the addition sequence and addition temperature of Al during melting, the formation of alumina is effectively reduced, thereby further improving the plasticity, toughness and corrosion resistance of the finally produced hot-rolled sheet and cold-rolled sheet. Brief description of the drawings

[0052] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments in line with the present invention and used together with the specification to explain the principles of the present invention.

[0053] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0054] Figure 1 It is the Laves phase diagram precipitated from the forged steel of the present invention;

[0055] Figure 2 It is the hot-rolled state microstructure diagram of the present invention;

[0056] Figure 3 It is the recrystallized microstructure diagram formed after solution treatment of the present invention;

[0057] Figure 4 This is the recrystallized microstructure diagram formed after the cold-rolled state of the present invention is recrystallized.

[0058] Figure 5 This is the corrosion morphology diagram after the present invention is immersed in a 6% FeCl3 + 1% HCl solution (at a temperature of 65 ± 1°C) for 72 hours. Detailed implementation manners

[0059] In order to more clearly understand the above objects, features and advantages of the present invention, the solution of the present invention will be further described below. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0060] In the description, it should be noted that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. It should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific situations.

[0061] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0062] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Embodiment 1

[0063] A preparation method of a high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel cold-rolled plate successively includes the following steps:

[0064] 1) Melting:

[0065] The weight percentages of the elements of the melting raw materials are: 29% Cr, 3.5% Mo, 1.0% Ni, 0.01% C, 0.01% N, 0.20% Nb, 0.01% Ti, 0.5% Mn, 0.6% Si, 0.005% S, 0.005% P, 1.5% Al, 0.004% O, and the rest are Fe and unavoidable impurities. After configuring the raw materials according to the above element ratios, vacuum induction furnace melting is carried out. During melting, the melting raw materials except Al are first added to the vacuum induction furnace for melting to form primary molten steel, and then Al is added to the primary molten steel. When adding Al, the temperature of the primary molten steel is 1600°C to obtain molten steel;

[0066] 2) Casting:

[0067] Pour the molten steel obtained in step 1) into a slab inside the hood. Cool the slab inside the hood to 1000 °C, take it out and slowly cool it to room temperature at a cooling rate of 20 °C / h, and then perform grinding;

[0068] 3) Forging:

[0069] Heat the ground slab obtained in step 2) to 1180 °C at a heating rate of 10 °C / min, hold for 2 h, start forging at 1180 °C, finish forging at 960 °C, immediately water-cool to room temperature after forging, and the thickness after forging is 40 mm to obtain a forged blank, as Figure 1 shown;

[0070] 4) Rough rolling:

[0071] Heat the forged blank obtained in step 3) to 1150 °C, perform rough rolling after holding for 1 h. If the outlet temperature of the rough-rolled plate is lower than 1000 °C, it needs to be reheated to 1150 °C and held for 5 min to continue rough rolling. If the outlet temperature of the rough-rolled plate is equal to or higher than 1000 °C, there is no need to reheat and hold it, and continue rough rolling. The single-pass reduction rate is 15%, and rough roll until the total reduction rate is 70% to obtain a rough-rolled plate;

[0072] 5) Warm rolling

[0073] Cool the rough-rolled plate obtained in step 4) to 800 °C and perform warm rolling. If the outlet temperature of the warm-rolled plate is lower than 650 °C, heat it to 800 °C, hold for 4 min, and continue warm rolling. Repeat the above warm-rolling steps until the plate thickness is 5 mm and the total reduction rate is 50%. Water-cool to room temperature after warm rolling to obtain a warm-rolled plate, as Figure 2 shown;

[0074] 6) Solution treatment:

[0075] Perform solution treatment on the warm-rolled plate obtained in step 5), heat at 1050 °C, hold for 40 min, then quickly cool to 10 °C at a cooling rate of 100 °C / s to obtain a solution-treated plate. This solution-treated plate is the hot-rolled plate of high-chromium high-molybdenum ferritic stainless steel, and its recrystallization microstructure diagram is as Figure 3 shown;

[0076] After sampling the steel plate prepared by the above process, perform microstructure observation and tensile property testing, and the results are shown in Table 1.

[0077] Table 1

[0078]

[0079] 7) Pickling:

[0080] Pickle the solution-treated plate obtained in step 6) with a sulfuric acid mixture solution;

[0081] 8) Cold rolling:

[0082] Cold roll the pickled solution-treated plate obtained in step 7) at room temperature with a cold rolling reduction rate of 80% to obtain a cold-rolled plate;

[0083] 9) Recrystallization annealing:

[0084] Perform recrystallization annealing on the cold-rolled plate obtained in step 8) at an annealing temperature of 1030 °C for a holding time of 30 min, then immediately cool to room temperature with a cooling rate controlled at 150 °C / s to obtain a cold-rolled plate of high chromium and high molybdenum ferritic stainless steel. Its recrystallization microstructure diagram is as shown in Figure 4 shown, and its corrosion morphology diagram is as shown in Figure 5 shown.

[0085] After sampling the steel plate prepared by the above process, conduct microstructure observation and tensile property testing, and the results are shown in Table 2.

[0086] Table 2

[0087] Example 2

[0088] A preparation method of a cold-rolled plate of high chromium, high molybdenum and aluminum-containing ferritic stainless steel successively includes the following steps:

[0089] 1) Melting:

[0090] The weight percentages of each element of the melting raw materials are: 27% Cr, 4.0% Mo, 2.0% Ni, 0.005% C, 0.005% N, 0.30% Nb, 0.01% Ti, 0.5% Mn, 0.7% Si, 0.005% S, 0.005% P, 1.5% Al, 0.004% O, and the rest are Fe and unavoidable impurities. After configuring the raw materials according to the above element ratios, conduct vacuum induction furnace melting. During melting, the melting raw materials except Al are first added to the vacuum induction furnace for melting to form primary molten steel, and then Al is added to the primary molten steel. When adding Al, the temperature of the primary molten steel is 1600 °C to obtain molten steel;

[0091] 2) Casting:

[0092] Pour the molten steel obtained in step 1) into a casting blank in the furnace hood. The casting blank is cooled to 950 °C in the furnace hood, taken out and slowly cooled to room temperature at a cooling rate of 10 °C / h, and then ground;

[0093] 3) Forging:

[0094] Heat the ground billet obtained in step 2) to 1150 °C at a heating rate of 7 °C / min, hold for 2 h, start forging at 1150 °C, finish forging at 950 °C, immediately water-cool to room temperature after forging, and the thickness after forging is 45 mm;

[0095] 4) Rough rolling:

[0096] Heat the forged billet obtained in step 3) to 1150 °C, perform rough rolling after holding for 1 h. If the outlet temperature of the rough-rolled plate is lower than 1000 °C, it needs to be reheated to 1150 °C and held for 5 min to continue rough rolling. If the outlet temperature of the rough-rolled plate is equal to or higher than 1000 °C, there is no need for reheating and holding, and continue rough rolling. The single-pass reduction rate is 15%, and rough roll until the total reduction rate is 75% to obtain a rough-rolled plate;

[0097] 5) Warm rolling

[0098] Cool the rough-rolled plate obtained in step 4) to 800 °C and perform warm rolling. If the outlet temperature of the warm-rolled plate is lower than 650 °C, heat it to 800 °C, hold for 4 min, and continue warm rolling. Repeat the above warm rolling steps until the plate thickness is rolled to 5 mm and the total reduction rate is 50%, and water-cool to room temperature after warm rolling;

[0099] 6) Solution treatment:

[0100] Perform solution treatment on the warm-rolled plate obtained in step 5), heat to 1050 °C, hold for 30 min, then quickly cool to 10 °C at a cooling rate of 100 °C / s to obtain a solution-treated plate;

[0101] Make specimens from the steel plate prepared by the above process and conduct microstructure observation and tensile property testing, and the results are shown in Table 3.

[0102] Table 3

[0103]

[0104] 7) Pickling:

[0105] Pickle the solution-treated plate obtained in step 6) with a sulfuric acid mixture;

[0106] 8) Cold rolling:

[0107] Perform cold rolling at room temperature on the pickled solution-treated plate obtained in step 7) with a cold rolling reduction rate of 80% to obtain a cold-rolled plate;

[0108] 9) Recrystallization annealing:

[0109] Perform recrystallization annealing on the cold-rolled plate obtained in step 8), the annealing temperature is 1050 °C, hold for 5 min, then immediately cool to room temperature, and control the cooling rate at 150 °C / s.

[0110] The steel plates prepared by the above process were sampled and subjected to microstructure observation and tensile property testing, and the results are shown in Table 4.

[0111] Table 4

[0112]

[0113] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Although the foregoing embodiments have been described in detail, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered by the protection scope of the claims.

Claims

1. A preparation method of a hot-rolled plate of high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel, characterized in that, comprising the following steps in sequence: 1) Melting: The weight percentages of the elements in the melting raw materials are as follows: 25.0% ≤ Cr ≤ 30.0%, 0.5% ≤ Mo ≤ 4.5%, 1.0% ≤ Ni ≤ 4.0%, 0.15% ≤ Nb ≤ 0.65%, 0.01% ≤ Ti ≤ 0.35%, 0.5 ≤ Al ≤ 2.5%, Mn ≤ 0.6%, Si ≤ 1.0%, S ≤ 0.005%, P ≤ 0.005%, O ≤ 0.004%, C > 0%, N > 0%, C + N ≤ 0.025%, and it satisfies Cr + 3.3% × Mo ≥ 35%. The remaining is Fe and inevitable impurities. After configuring the raw materials according to the above element ratios, melting is carried out to obtain molten steel; 2) Casting: Pour the molten steel obtained in step 1) into a billet in the furnace hood. The billet is cooled in the furnace hood to ≤ 1000 °C, taken out and slowly cooled to room temperature with a cooling rate ≤ 20 °C / h, and then grinding is carried out; 3) Forging: Heat the ground billet obtained in step 2) to 1180 - 1280 °C with a heating rate ≤ 10 °C / min, hold for 1 - 4 h, the forging start temperature ≥ 1120 °C, the forging end temperature ≥ 960 °C, and immediately water-cool to room temperature after forging. The thickness after forging and pressing is 30 - 55 mm; 4) Rough rolling: Heat the forged billet obtained in step 3) to 1100 - 1200 °C, carry out rough rolling after holding for 1 - 4 h. If the outlet temperature of the rough rolled plate is lower than 1000 °C, it needs to be reheated to 1100 - 1200 °C and held for 5 min - 40 min to continue rough rolling. If the outlet temperature of the rough rolled plate is equal to or higher than 1000 °C, there is no need to reheate and hold it, and continue rough rolling. Rough roll 3 - 10 times, the single-pass reduction rate ≥ 15%, and rough roll to a total reduction rate ≥ 60%, which can reduce the thickness of the raw material, thereby reducing the number of rolling passes in the warm rolling stage and reducing production costs to obtain a rough rolled plate; 5) Warm rolling Cool the rough rolled plate obtained in step 4) to 650 - 800 °C and carry out warm rolling. If the outlet temperature of the hot rolled plate is lower than 650 °C, heat it to 650 - 800 °C, hold for 3 - 50 min, and continue warm rolling. Repeat the above warm rolling steps until the plate thickness ≤ 6.5 mm, and water-cool to room temperature after warm rolling; 6) Solution treatment: Carry out solution treatment on the hot rolled plate obtained in step 5), with a heating temperature of 1030 - 1150 °C and a holding time of 30 - 60 min, and then quickly cool to ≤ 10 °C with a cooling rate ≥ 10 °C / s.

2. The preparation method of a high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel hot-rolled sheet according to claim 1, characterized in that, In step 1), vacuum induction furnace melting is adopted. During melting, the melting raw materials except Al are first added to the vacuum induction furnace for melting to form primary molten steel, and then Al is added to the primary molten steel. The temperature of the primary molten steel is 1500 - 1600 °C when adding Al.

3. The preparation method of a high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel hot-rolled sheet according to claim 2, characterized in that, In step 4), the total reduction rate during rough rolling ≥ 60%.

4. The preparation method of a high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel hot-rolled sheet according to claim 3, characterized in that, In step 5), the total reduction rate during warm rolling ≥ 40%.

5. A preparation method of a cold-rolled plate of high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel, characterized in that, comprising the following steps in sequence: 1) Melting: The weight percentages of the elements in the smelting raw materials are as follows: 25.0% ≤ Cr ≤ 30.0%, 0.5% ≤ Mo ≤ 4.5%, 1.0% ≤ Ni ≤ 4.0%, 0.15% ≤ Nb ≤ 0.65%, 0.01% ≤ Ti ≤ 0.35%, 0.5 ≤ Al ≤ 2.5%, Mn ≤ 0.6%, Si ≤ 1.0%, S ≤ 0.005%, P ≤ 0.005%, O ≤ 0.004%, C ≤ 0.015%, N ≤ 0.010%, and it satisfies Cr + 3.3% × Mo ≥ 35%. The remaining are Fe and inevitable impurities. After preparing the raw materials according to the above element ratios, smelting is carried out to obtain molten steel; 2) Casting: Pour the molten steel obtained in step 1) into a billet in the hood. The billet is cooled to ≤ 1000 °C in the hood, taken out and slowly cooled to room temperature, with a cooling rate ≤ 20 °C / h, and then grinding is carried out; 3) Forging: Heat the ground billet obtained in step 2) to 1180 - 1280 °C, with a heating rate ≤ 10 °C / min, hold for 1 - 4 h, the forging start temperature ≥ 1120 °C, the forging end temperature ≥ 960 °C, and immediately water-cool to room temperature after forging. The thickness after forging and pressing is 30 - 45 mm; 4) Rough rolling: Heat the forged billet obtained in step 3) to 1100 - 1200 °C, hold for 1 - 4 h and then carry out rough rolling. If the outlet temperature of the rough rolled plate is lower than 1000 °C, it needs to be reheated to 1100 - 1200 °C and held for 5 min - 40 min to continue rough rolling. If the outlet temperature of the rough rolled plate is equal to or higher than 1000 °C, there is no need to reheat and hold it, and continue rough rolling. Rough roll 3 - 10 times, with a single pass reduction rate ≥ 15%, and the total reduction rate ≥ 60% in rough rolling, which can reduce the thickness of the raw material, thereby reducing the number of rolling passes in the warm rolling stage and reducing production costs to obtain a rough rolled plate; 5) Warm rolling Cool the rough rolled plate obtained in step 4) to 650 - 800 °C and carry out warm rolling. If the outlet temperature of the hot rolled plate is lower than 650 °C, heat it to 650 - 800 °C, hold for 3 - 50 min, and continue warm rolling. Repeat the above warm rolling steps until the plate thickness ≤ 6.5 mm, and water-cool to room temperature after warm rolling; 6) Solution treatment: Carry out solution treatment on the hot rolled plate obtained in step 5), with a heating temperature of 1030 - 1150 °C, a holding time of 30 - 60 min, and then quickly cool to ≤ 10 °C, with a cooling rate ≥ 10 °C / s, to obtain a solution-treated plate; 7) Pickling: Pickle the solution-treated plate obtained in step 6) with a sulfuric acid mixture; 8) Cold rolling: Carry out cold rolling at room temperature on the pickled solution-treated plate obtained in step 7), with a cold rolling reduction rate ≥ 50%, to obtain a cold rolled plate; 9) Recrystallization annealing: Carry out recrystallization annealing on the cold rolled plate obtained in step 8), with an annealing temperature of 970 - 1070 °C, a holding time of 0.5 - 5 min, and then immediately cool to room temperature, with the cooling rate controlled at ≥ 50 °C / s.

6. The preparation method of a high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel cold-rolled sheet according to claim 5, characterized in that, In step 1), vacuum induction furnace melting is adopted. During melting, the melting raw materials except Al are first added to the vacuum induction furnace for melting to form primary molten steel, and then Al is added to the primary molten steel. The temperature of the primary molten steel is 1500 - 1600 °C when adding Al.

7. The preparation method of a high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel cold-rolled sheet according to claim 6, characterized in that, In step 4), the total reduction ratio during rough rolling is ≥60%.

8. The preparation method of a high-chromium, high-molybdenum and aluminum-containing ferritic stainless steel cold-rolled sheet according to claim 7, characterized in that, In step 5), the total reduction ratio during warm rolling is ≥40%.

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