Preparation method of high-chromium-molybdenum aluminum-containing ferritic stainless steel

Abstract

The invention relates to the technical field of high-chromium-molybdenum ferritic stainless steel, in particular to a preparation method of high-chromium-molybdenum aluminum-containing ferritic stainless steel. In order to solve the problems that in an existing method for avoiding brittle phase precipitation of high-chromium and high-molybdenum ferritic stainless steel, multiple times of annealing exist, so that the control risk of the high-chromium and high-molybdenum ferritic stainless steel is large, the preparation process is long, the manufacturing cost is high, and grain coarsening is caused by high-temperature heating, the novel preparation method of the high-chromium and high-molybdenum aluminum-containing ferritic stainless steel is provided. The preparation method comprises the steps of smelting, die casting and coping, forging cogging, multi-rack hot continuous rolling or single-rack hot rolling, surface treatment, cold rolling, recrystallization annealing and cooling. According to the preparation method, solid solution annealing is not needed, crystal grains are fine, brittle phase precipitation is avoided, and plasticity and toughness are good.

Description

Technical Field

[0001] The invention relates to the technical field of high-chromium-molybdenum ferrite stainless steel, in particular to a preparation method of high-chromium-molybdenum aluminum-containing ferrite stainless steel. Background Art

[0002] Super ferritic stainless steel is a nickel-saving, highly corrosion-resistant stainless steel with good thermal conductivity, low linear expansion coefficient and good formability. It has successfully replaced copper and titanium in the manufacture of coastal power station condensers. It can also replace super austenitic stainless steel and nickel-based alloys in acid production, seawater desalination, petrochemicals and other fields. The high chromium, high molybdenum and nickel-containing composition characteristics of super ferritic stainless steel lead to the easy formation of various brittle phases in super ferritic steel, such as σ phase and χ phase. The formation of these brittle phases not only seriously deteriorates the plastic toughness of the material and causes the material to become brittle (called σ phase brittleness), but also reduces its corrosion resistance, which seriously restricts the large-scale production and wide application of such products.

[0003] In order to avoid the precipitation problem of brittle phases such as σ phase and χ phase, the existing technology generally adopts multiple annealing and alloying addition to avoid or hinder the precipitation of brittle phases, but multiple annealing also increases the risk of controlling the precipitation of brittle phases (annealing is divided into solution annealing, recrystallization annealing, etc. In order to avoid or hinder the precipitation of brittle phases, rapid cooling is required during annealing cooling, and rapid cooling is difficult to control and requires coordination of cooling speed, coolant and other aspects, resulting in greater control risks). At the same time, it also leads to a longer preparation process and higher production costs.

[0004] For example, the prior art, i.e., the technical solution of a super ferritic stainless steel and a preparation method thereof with patent number 202211553095.0, uses Al alloying to inhibit the precipitation of σ phase and promote the precipitation of nano-scale Laves phase. However, in order to avoid the precipitation of large-sized carbides (NbTi / CN) and Laves phase, solution annealing is still required after hot rolling. The number of annealing times is large (solution annealing and recrystallization annealing), the risk of controlling brittle phase precipitation is relatively high, the preparation process is relatively long, and the manufacturing cost is relatively high.

[0005] Another example is the technical solution of a high-Cr ferritic stainless steel and its manufacturing method with patent number 201110363876.9. The hot-rolled plate is subjected to high-temperature 1100°C solution annealing to completely eliminate harmful σ phase and χ phase precipitation, ensuring that the material has good room-temperature impact toughness. The annealing times are many, the risk of brittle phase precipitation control is relatively high, the preparation process is long, and high-temperature heating also brings about the problem of grain coarsening. Summary of the invention

[0006] In order to solve the problems that the existing methods for avoiding the precipitation of brittle phases of high-chromium and high-molybdenum ferritic stainless steels all involve multiple annealing, which leads to greater control risks, longer preparation processes, higher manufacturing costs and grain coarsening caused by high-temperature heating, the present invention provides a new preparation method for high-chromium, molybdenum and aluminum-containing ferritic stainless steel. In the preparation method, no solution annealing is required, the grains are fine, no brittle phase is precipitated, and the plasticity and toughness are good.

[0007] The present invention is achieved by adopting the following technical solutions: Solution 1:

[0008] A method for preparing high chromium-molybdenum aluminum-containing ferritic stainless steel comprises the following steps in sequence: 1) Melting: The weight percentage of each element in the smelting raw material is: 25%≤Cr≤30.0%, 0.5%≤Mo≤4.0%, 1.5%≤Ni≤4.5%, C≤0.015%, N≤0.010%, 0.10%≤Nb≤0.50%, 0.10%≤Ti≤0.25%, 0.50%≤Al≤4.0%, Mn≤0.4%, 0.2%≤Si≤0.7%, S≤0.005%, P≤0.005%, O≤0.004%, and the rest is Fe and unavoidable impurities. After the raw materials are configured according to the above element ratios, they are smelted to obtain molten steel; 2) Die casting and grinding: The molten steel obtained in step 1) is poured into a casting in a furnace hood, the casting is cooled to ≤1000°C in the furnace hood, taken out and slowly cooled to room temperature, and then ground; 3) Forging The ground ingot obtained in step 2) is heated to 1180-1250°C with a furnace, with a heating rate of 0.5-10°C / min, a holding time of 1-4h, a start forging temperature of 1100-1200°C, a final forging temperature of ≥950°C, a forging ratio of 2.0-4.0, and then air-cooled to room temperature to obtain a forged ingot; (wherein the deformation amount of forging is controlled to ensure that the material is fully deformed during the forging process, and the forging process is performed from multiple directions, which can promote the uniform distribution of elements;) 4) Multi-stand hot rolling or single-stand hot rolling: Multi-stand hot rolling: the forging blank obtained in step 3) is heated and then hot rolled, the heating temperature is 1080-1220°C, the holding time is 10-240 min, the starting rolling temperature is ≥1050°C, the final rolling temperature is 650-800°C, the final rolling reduction rate is ≥20%, and the forging blank is quickly cooled to room temperature after hot rolling, and the cooling rate is ≥50°C / min; further, during the multi-stand hot rolling in step 4), the forging blank stays for 2-30 minutes after passing through the first stand, so that the hot-rolled plate after hot rolling in the first stand completes recrystallization, and the structure is refined by recrystallization, and at the same time, the elements such as Nb, Cr, Al precipitated during the hot rolling process can be dissolved, and a small amount of nano-scale Laves phase can be controlled to precipitate.

[0009] Single-stand hot rolling: the forged billet obtained in step 3) is subjected to multiple heating and then hot rolling, the heating temperature of the hot rolling after the first heating is 1050-1180°C, the holding time is 10-240 min, the start rolling temperature is ≥1050°C, the final rolling temperature is ≥950°C, the first reduction rate is ≥15%, the heating temperature of the hot rolling after the last heating is 1030-1180°C, the holding time is 2-60 min, the start rolling temperature is ≥1030°C, the final rolling temperature is 650-800°C, the final rolling reduction rate is ≥20%, and the hot-rolled plate is quickly cooled to room temperature after hot rolling, and the cooling rate is ≥50°C / min, so as to obtain a hot-rolled plate; 5) Cold rolling: The hot-rolled sheet obtained in step 4) is subjected to multiple cold rolling to obtain a cold-rolled sheet; (after cold rolling, a large deformation cold-rolled structure is obtained, which improves the deformation energy storage and provides a nucleation driving force for the subsequent recrystallization annealing. At the same time, a large number of shear bands, deformation bands and other microstructures are formed in the deformed structure to provide sufficient nucleation points for the subsequent recrystallization. The nano-scale Laves phase pins the recrystallization grain boundary and further refines the recrystallized grains) 6) Recrystallization annealing: The cold rolled sheet obtained in step 5) is subjected to recrystallization annealing at a temperature of 980-1100°C for a holding time of 0.5-60 min. After the recrystallization annealing, the sheet is rapidly cooled to room temperature at a cooling rate of ≥30°C / s to form fine recrystallized grains.

[0010] Principle description: In the preparation method of the present invention, step 1) reduces brittleness by adopting low-content C and low-content N design, adding appropriate amounts of Nb and Ti elements can stabilize C and N, further reduce the dissolved C and N content in the matrix, and adding Al elements can inhibit the precipitation of σ phase while promoting the precipitation of nano-scale Laves phase, and the nano-scale Laves phase refines the grains. Low oxygen content can avoid the formation of alumina particles; in step 2), the cooling rate is controlled at 5℃ / h-10℃ / h, and slow cooling helps to improve the plasticity and toughness of the continuous casting billet and avoid cracking of the casting. Step 3) The forging billet is slowly heated, and the heating rate is not higher than 10℃ / min, which can fully dissolve the segregation elements Cr, Mo, Nb, Al, etc. formed in the billet and make them uniformly distributed. The forging process is heated in the furnace to make the alloy elements evenly distributed, reduce segregation, and the heated material is easier to forge, which can improve the efficiency of forging and reduce material loss in the forging process. At the same time, too high or too low temperature may lead to element segregation, so the final forging temperature is controlled not less than 950℃ to avoid the formation of coarse NbTi (CN) and TiN particles, and to form an appropriate amount of nano-scale Laves phase precipitation, reduce forging resistance, reduce forging resistance, and avoid forging cracks. Step 4) Multi-stand hot rolling: The forging billet is heated to 1080-12200℃, exceeding the precipitation temperature range of large-size Laves phase, to ensure the dissolution of large-size Laves phase, and to complete recrystallization at the same time, to obtain equiaxed grains without large-size Laves phase precipitation. Due to the use of hot rolling, the temperature of the hot-rolled plate will not drop significantly after passing through the first few stands, so the hot-rolled plate can stay for 2-30 minutes after passing through the first stand, so that the hot-rolled plate completes recrystallization, refines the structure through recrystallization, and controls the precipitation of a small amount of nano-scale Laves phase. Subsequently, the final rolling temperature is controlled to 600-800℃, and a large reduction rate and low-temperature hot rolling is implemented to obtain a large deformation structure, while controlling the formation of a uniformly distributed nano-scale Laves phase. Step 4) Single-stand hot rolling: Heat the forging billet to 1050-1180℃, exceeding the precipitation temperature range of large-size Laves phase, ensure the dissolution of large-size Laves phase, complete recrystallization at the same time, and obtain equiaxed grains without large-size Laves phase precipitation. After the first large reduction rate hot rolling, a large deformation structure is obtained. The last hot rolling is heated to 1030-1180℃, the structure is refined by recrystallization, and a small amount of nano-scale Laves phase is controlled to precipitate. Subsequently, the final rolling temperature is controlled to be 650-800. While avoiding the precipitation of σ and χ phases, a large reduction rate and low-temperature hot rolling are implemented to obtain a large deformation structure, and at the same time, a uniformly distributed nano-scale Laves phase and a large number of shear bands are controlled to form. Step 5) After cold rolling, a large deformation cold rolling structure is obtained, the deformation energy storage is improved, and the nucleation driving force is provided for the subsequent recrystallization annealing. The nano-scale Laves phase pins the recrystallization grain boundary, further refining the recrystallized grains. In step 6), the cold rolled sheet is annealed at 980-1100°C, and fine recrystallized grains are formed after rapid cooling to room temperature.Finally, the high chromium, molybdenum, aluminum-containing ferritic stainless steel can be produced by direct cold rolling without solid solution.

[0011] Furthermore, in step 5), surface treatment is performed before cold rolling, that is, pickling or mechanical processing is used to remove the iron oxide scale on the surface of the hot-rolled plate obtained in step 4), and the surface roughness is Ra≤12.8μm to remove the oxide scale on the surface of the hot-rolled plate, thereby improving the surface quality of the hot-rolled plate and making the surface of the hot-rolled plate smooth and flat for subsequent cold rolling.

[0012] Further, in step 3), two forgings are performed during forging. During the first forging, the ground billet obtained in step 2) is heated to 1180-1250°C with the furnace, the heating rate is 0.5-10°C / min, the holding time is 1-4h, the start forging temperature is 1100-1200°C, the final forging temperature is ≥950°C, and the forging ratio is 2.0-4.0. During the second forging, it is heated to 1120-1250°C again, the holding time is 0.2-1h, the start forging temperature is 1100-1200°C, the final forging temperature is ≥960°C, and then air-cooled to room temperature to obtain a forged piece. Two forgings can further refine the grains, and when the billet is thick, it also needs to be forged twice.

[0013] Furthermore, in the single-stand continuous rolling in step 4), the heating temperature of hot rolling after intermediate heating is 1050-1180°C, the holding time is 10-240 min, the start rolling temperature is ≥1050°C, the final rolling temperature is ≥950°C, the reduction rate is ≥15%, and the number of hot rolling after intermediate heating is determined according to the target hot rolling thickness.

[0014] Furthermore, in step 5), the total reduction ratio during cold rolling is ≥ 20%.

[0015] Furthermore, the cooling rate of the slow cooling in step 1) is ≤20°C / h. Option 2:

[0016] A method for preparing high chromium-molybdenum aluminum-containing ferritic stainless steel comprises the following steps in sequence: 1) Melting: The weight percentage of each element in the smelting raw material is: 25%≤Cr≤30.0%, 0.5%≤Mo≤4.0%, 1.5%≤Ni≤4.5%, C≤0.015%, N≤0.010%, 0.10%≤Nb≤0.50%, 0.10%≤Ti≤0.25%, 0.50%≤Al≤4.0%, Mn≤0.4%, 0.2%≤Si≤0.7%, S≤0.005%, P≤0.005%, O≤0.004%, and the rest is Fe and unavoidable impurities. After the raw materials are configured according to the above element ratios, they are smelted to obtain molten steel; 2) Continuous casting and grinding: The molten steel obtained in step 1) is continuously cast into a continuous casting billet, and the continuous casting billet is then slowly cooled to 300°C-500°C at a cooling rate of 4°C / h-10°C / h, and then ground; 3) Multi-stand hot rolling or single-stand hot rolling: Multi-stand hot rolling: the continuous casting billet obtained in step 2) is heated and then hot rolled, the heating temperature is 1080-1220°C, the holding time is 10-240 min, the starting rolling temperature is ≥1050°C, the final rolling temperature is 650-800°C, the final rolling reduction rate is ≥20%, and the hot rolling is followed by rapid cooling to room temperature, with a cooling rate of ≥50°C / min; Single-stand hot rolling: the forged billet obtained in step 3) is subjected to multiple heating and then hot rolling, the heating temperature of the hot rolling after the first heating is 1050-1180°C, the holding time is 10-240 min, the start rolling temperature is ≥1050°C, the final rolling temperature is ≥950°C, the first reduction rate is ≥15%, the heating temperature of the hot rolling after the last heating is 1030-1180°C, the holding time is 2-60 min, the start rolling temperature is ≥1030°C, the final rolling temperature is 650-800°C, the final rolling reduction rate is ≥20%, and the hot rolling is quickly cooled to room temperature after hot rolling, and the cooling rate is ≥50°C / min, so as to obtain a hot-rolled plate, wherein the shear band and nano-scale Laves phase are formed; 4) Cold rolling: The hot-rolled sheet obtained in step 3) is subjected to multiple cold rolling processes to obtain a cold-rolled sheet; 5) Recrystallization annealing: The cold rolled sheet obtained in step 4) is subjected to recrystallization annealing at a temperature of 980-1100°C for a holding time of 0.5-60 min. After the recrystallization annealing, the sheet is rapidly cooled to room temperature at a cooling rate of ≥30°C / s to form fine recrystallized grains.

[0017] The principle described in this scheme is basically the same as the principle shown in the above scheme one, wherein continuous casting and grinding are equivalent to the die casting and grinding and forging in the above scheme one.

[0018] Furthermore, in step 4), surface treatment is performed before cold rolling, that is, pickling or mechanical processing is used to remove the iron oxide scale on the surface of the hot-rolled plate obtained in step 3), and the surface roughness is Ra≤12.8μm to remove the oxide scale on the surface of the hot-rolled plate, improve the surface quality of the hot-rolled plate, and make the surface of the hot-rolled plate smooth and flat for subsequent cold rolling.

[0019] Furthermore, in the single-stand continuous rolling in step 3), the heating temperature of hot rolling after intermediate heating is 1050-1180°C, the holding time is 10-240 min, the start rolling temperature is ≥1050°C, the final rolling temperature is ≥950°C, the reduction rate is ≥15%, and the number of hot rolling after intermediate heating is determined according to the target hot rolling thickness.

[0020] Furthermore, in step 4), the total reduction ratio during cold rolling is ≥20%.

[0021] The beneficial effects of the present invention are as follows: the preparation method of the present invention can inhibit the formation of intermediate phases such as σ phase and χ phase by adding Al element, and avoid the precipitation of aluminum oxide particles by reducing the content of oxygen element. At the same time, in the forging process of the ingot, the precipitation of large-sized carbides (NbTi / CN) is effectively avoided by adopting slow heating, reheating during the forging process, controlling the forging temperature, forging ratio and other means. Therefore, there is no need for solid solution treatment to dissolve the precipitated phase in the hot-rolled plate. The hot-rolled plate without oxide inclusions, brittle phases and large-sized carbide precipitation can effectively prevent the occurrence of edge cracks and the like during the cold rolling process. Therefore, cold rolling is directly carried out, and finally the preparation of high chromium-molybdenum aluminum-containing ferritic stainless steel is achieved by direct cold rolling without solid solution treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0024] Figure 1 The shear bands and nano-scale Laves phases are formed in the hot-rolled sheet obtained after low-temperature final rolling using a multi-stand hot rolling method; Figure 2 Nanoscale Laves phase formed in hot rolled sheet after low temperature final rolling using multi-stand hot rolling method (high magnification); Figure 3 The recrystallized structure of the recrystallized annealed sheet obtained after low temperature final rolling using a multi-stand hot rolling method; Figure 4 The shear bands and nano-scale Laves phases are formed in the hot-rolled sheet obtained after low-temperature final rolling using a single-stand hot rolling method; Figure 5 Nanoscale Laves phase formed in the hot-rolled sheet obtained after low-temperature final rolling using a single-stand hot rolling method (high magnification); Figure 6 The recrystallized structure of the recrystallized annealed sheet obtained after low temperature final rolling using a single stand hot rolling method. DETAILED DESCRIPTION

[0025] 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 the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0026] In the description, it should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be understood as indicating or implying relative importance. It should be noted that, unless otherwise clearly specified 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 a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two elements. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0027] 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 of the embodiments.

[0028] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. Embodiment 1

[0029] A method for preparing high chromium-molybdenum aluminum-containing ferritic stainless steel comprises the following steps in sequence: 1) Melting: The weight percentage of each element of the smelting raw material is: 25.9% Cr, 3.15% Mo, 1.75% Ni, 0.008% C, 0.004% N, 0.14% Nb, 0.16% Ti, 1.21% Al, 0.27% Mn, 0.24% Si, 0.0024% S, 0.0027% P, 0.0014% O, and the rest is Fe and inevitable impurities. After the raw materials are configured according to the above element ratios, they are smelted to obtain molten steel; 2) Die casting and grinding: The molten steel obtained in step 1) is poured into a casting in a furnace hood, the casting is cooled to 1000° C. in the furnace hood, taken out and slowly cooled to room temperature at a cooling rate of 20° C. / h, and then ground; 3) Forging The ingot obtained in step 2) is forged and forged twice. In the first forging, the ingot obtained in step 2) after grinding is heated to 1200°C with the furnace, the heating rate is 5°C / min, the holding time is 2h, the start forging temperature is 1200°C, the final forging temperature is 950°C, and the forging ratio is 2.0. In the second forging, it is heated to 1200°C again, the holding time is 1h, the start forging temperature is 1100°C, the final forging temperature is 960°C, and then air-cooled to room temperature to obtain a forging; 4) Multi-stand hot rolling The forging blank obtained in step 3) is heated and then hot rolled, with a heating temperature of 1100°C, a holding time of 120 min, a starting rolling temperature of 1100°C, a stay time of 10 min after passing through the first stand, a final rolling temperature of 860°C, a final rolling reduction rate of 22%, a total reduction rate of 82.2%, and rapid cooling to room temperature after hot rolling at a cooling rate of 50°C / min, thereby obtaining a hot rolled plate, such as Figure 1 and Figure 2 As shown, a uniformly distributed nanoscale Laves phase is formed, and a large number of shear bands are formed in the deformed structure to provide sufficient nucleation points for subsequent recrystallization; the hot-rolled steel plate is sampled and then the structure is observed and the tensile properties are tested, and the results are shown in Table 1.

[0030] Table 1

[0031] 5) Cold rolling: The hot-rolled sheet obtained in step 4) is first subjected to surface treatment, that is, pickling or mechanical processing is used to remove the iron oxide scale on the surface of the hot-rolled sheet obtained in step 4), and then subjected to multiple cold rolling, with a single cold rolling reduction rate of 10% and a total cold rolling reduction rate of 82.1%, thereby obtaining a cold-rolled sheet; 6) Recrystallization annealing: The cold rolled sheet obtained in step 5) is subjected to recrystallization annealing at a temperature of 1030°C and a holding time of 1 min. After recrystallization annealing, it is rapidly cooled to room temperature at a cooling rate of 30°C / s to form fine recrystallized grains, such as Figure 3 The steel plate prepared by the above process was sampled and then the structure observation and tensile property test were carried out. The results are shown in Table 2.

[0032] Table 2 Embodiment 2

[0033] A method for preparing high chromium-molybdenum aluminum-containing ferritic stainless steel comprises the following steps in sequence: 1) Melting: The weight percentage of each element of the smelting raw material is: 24.9% Cr, 3.05% Mo, 1.85% Ni, 0.008% C, 0.004% N, 0.14% Nb, 0.16% Ti, 1.21% Al, 0.27% Mn, 0.24% Si, 0.0024% S, 0.0027% P, 0.0014% O, and the rest is Fe and inevitable impurities. After the raw materials are configured according to the above element ratios, they are smelted to obtain molten steel; 2) Die casting and grinding: The molten steel obtained in step 1) is poured into a casting in a furnace hood, the casting is cooled to 1000° C. in the furnace hood, taken out and slowly cooled to room temperature at a cooling rate of 20° C. / h, and then ground; 3) Forging The ingot obtained in step 2) is forged and forged twice. In the first forging, the ingot obtained in step 2) after grinding is heated to 1200°C with the furnace, the heating rate is 5°C / min, the holding time is 2h, the start forging temperature is 1200°C, the final forging temperature is 950°C, and the forging ratio is 2.0. In the second forging, it is heated to 1200°C again, the holding time is 1h, the start forging temperature is 1200°C, the final forging temperature is 960°C, and then air-cooled to room temperature to obtain a forging; 4) Multi-stand hot rolling The forging billet obtained in step 3) was heated and then hot rolled, with a heating temperature of 1150°C, a holding time of 120 min, a starting rolling temperature of 1100°C, a stay time of 10 min after passing through the first stand, a final rolling temperature of 860°C, a final rolling reduction of 23%, a total reduction of 81.3%, and rapid cooling to room temperature after hot rolling at a cooling rate of 50°C / min; the steel plate after hot rolling was sampled for microstructure observation and tensile property testing, and the results are shown in Table 3.

[0034] Table 3

[0035] 5) Cold rolling: The hot-rolled sheet obtained in step 4) is first subjected to surface treatment, that is, pickling or mechanical processing is used to remove the iron oxide scale on the surface of the hot-rolled sheet obtained in step 4), and then subjected to multiple cold rolling, with a single cold rolling reduction rate of 10% and a total reduction rate of 83.4%, thereby obtaining a cold-rolled sheet; 6) Recrystallization annealing: The cold rolled sheet obtained in step 5) was subjected to recrystallization annealing at a temperature of 1030°C and a holding time of 1 min. After recrystallization annealing, it was rapidly cooled to room temperature at a cooling rate of 30°C / s. The steel sheet prepared by the above process was sampled and then subjected to microstructure observation and tensile property testing. The results are shown in Table 4.

[0036] Table 4

[0037] Embodiment three: A method for preparing high chromium-molybdenum aluminum-containing ferritic stainless steel comprises the following steps in sequence: 1) Melting: The weight percentage of each element of the smelting raw material is: 28.2% Cr, 3.12% Mo, 1.65% Ni, 0.008% C, 0.004% N, 0.14% Nb, 0.16% Ti, 1.21% Al, 0.27% Mn, 0.24% Si, 0.0024% S, 0.0027% P, 0.0014% O, and the rest is Fe and inevitable impurities. After the raw materials are configured according to the above element ratios, they are smelted to obtain molten steel; 2) Continuous casting and grinding: The molten steel obtained in step 1) is continuously cast into a continuous casting billet, and the continuous casting billet is then slowly cooled to 400° C. at a cooling rate of 5° C. / h, and then ground; 3) Multi-stand hot rolling The forging billet obtained in step 2) was heated and then hot rolled, with a heating temperature of 1100°C, a holding time of 120 min, a starting rolling temperature of 1100°C, a stay time of 10 min after passing through the first stand, a final rolling temperature of 860°C, a final rolling reduction of 23.7%, a total reduction of 82.3%, and rapid cooling to room temperature after hot rolling at a cooling rate of 50°C / min; the steel plate after hot rolling was sampled for microstructure observation and tensile property testing, and the results are shown in Table 5.

[0038] Table 5

[0039] 4) Cold rolling: The hot-rolled sheet obtained in step 3) is first subjected to surface treatment, that is, pickling or mechanical processing is used to remove the iron oxide scale on the surface of the hot-rolled sheet obtained in step 4), and then subjected to multiple cold rolling, with a single cold rolling reduction rate of 10% and a total reduction rate of 81.1%, thereby obtaining a cold-rolled sheet; 5) Recrystallization annealing: The cold rolled sheet obtained in step 4) was subjected to recrystallization annealing at a temperature of 1030°C and a holding time of 1 min. After recrystallization annealing, it was rapidly cooled to room temperature at a cooling rate of 30°C / s. The steel sheet prepared by the above process was sampled and then subjected to microstructure observation and tensile property testing. The results are shown in Table 6.

[0040] Table 6

[0041] Embodiment 4: A method for preparing high chromium-molybdenum aluminum-containing ferritic stainless steel comprises the following steps in sequence: 1) Melting: The weight percentage of each element of the smelting raw material is: 27.2% Cr, 2.05% Mo, 1.68% Ni, 0.005% C, 0.004% N, 0.13% Nb, 0.16% Ti, 0.99% Al, 0.25% Mn, 0.22% Si, 0.0022% S, 0.0017% P, 0.0024% O, and the rest is Fe and inevitable impurities. After the raw materials are configured according to the above element ratios, they are smelted to obtain molten steel; 2) Continuous casting and grinding: The molten steel obtained in step 1) is continuously cast into a continuous casting billet, and the continuous casting billet is then slowly cooled to 400° C. at a cooling rate of 5° C. / h, and then ground; 3) Single stand hot rolling: The forging billet obtained in step 3) is subjected to multiple heating and then hot rolling. The heating temperature of the hot rolling after the first heating is 1100°C, the holding time is 60 min, the start rolling temperature is 1100°C, the final rolling temperature is 950°C, the first reduction rate is 25%, the heating temperature of the hot rolling after the intermediate heating is 1180°C, the holding time is 10-240 min, the start rolling temperature is 1150°C, the final rolling temperature is 1000°C, the intermediate reduction rate is 20%, and the number of hot rolling after the intermediate heating is determined according to the target hot rolling thickness. The heating temperature of the hot rolling after the last heating is 1100°C, the holding time is 45 min, the start rolling temperature is 1200°C, the final rolling temperature is 650°C, the final rolling reduction rate is 33.5%, the total reduction rate is 82.2%, and the hot rolling is quickly cooled to room temperature after hot rolling at a cooling rate of 50°C / min, thereby obtaining a hot-rolled plate, which forms a uniformly distributed nano-scale Laves phase, and a large number of shear bands are formed in the deformed structure to provide sufficient nucleation particles for subsequent recrystallization, such as Figure 4 and 5 shown.

[0042] The hot rolled steel plates were sampled and then subjected to microstructure observation and tensile property testing. The results are shown in Table 7.

[0043] Table 7

[0044] 4) Cold rolling: The hot-rolled sheet obtained in step 3) is first subjected to surface treatment, that is, pickling or mechanical processing is used to remove the iron oxide scale on the surface of the hot-rolled sheet obtained in step 4), and then subjected to multiple cold rolling, with a single cold rolling reduction rate of 6.2% and a total cold rolling reduction rate of 82.2%, thereby obtaining a cold-rolled sheet; 5) Recrystallization annealing: The cold rolled sheet obtained in step 4) is subjected to recrystallization annealing at a temperature of 1030°C for 31 minutes. After recrystallization annealing, it is rapidly cooled to room temperature at a cooling rate of 30°C / s. The recrystallized grains formed are as follows: Figure 6The steel plate prepared by the above process was sampled and then the structure observation and tensile property test were carried out. The results are shown in Table 8.

[0045] Table 8

[0046] Embodiment five: A method for preparing high chromium-molybdenum aluminum-containing ferritic stainless steel comprises the following steps in sequence: 1) Melting: The weight percentage of each element of the smelting raw material is: 27.6% Cr, 2.44% Mo, 1.82% Ni, 0.006% C, 0.004% N, 0.11% Nb, 0.14% Ti, 1.01% Al, 0.24% Mn, 0.22% Si, 0.0022% S, 0.0017% P, 0.0024% O, and the rest is Fe and inevitable impurities. After the raw materials are configured according to the above element ratios, they are smelted to obtain molten steel; 2) Die casting and grinding: The molten steel obtained in step 1) is poured into a casting in a furnace hood, the casting is cooled to 1000° C. in the furnace hood, taken out and slowly cooled to room temperature at a cooling rate of 20° C. / h, and then ground; 3) Forging The ingot obtained in step 2) is forged and forged twice. In the first forging, the ingot obtained in step 2) after grinding is heated to 1200°C with the furnace, the heating rate is 5°C / min, the holding time is 2h, the start forging temperature is 1150°C, the final forging temperature is 950°C, and the forging ratio is 1.94. In the second forging, it is heated to 1150°C again, the holding time is 1h, the start forging temperature is 1200°C, the final forging temperature is 960°C, and then air-cooled to room temperature to obtain a forging; 4) Single stand hot rolling: The forging billet obtained in step 3) is subjected to multiple heating and hot rolling. The heating temperature of the hot rolling after the first heating is 1200°C, the holding time is 60 min, the start rolling temperature is 1300°C, the final rolling temperature is 950°C, the first reduction rate is 25%, the heating temperature of the hot rolling after the intermediate heating is 1200°C, the holding time is 60 min, the start rolling temperature is 300°C, the final rolling temperature is 950°C, the intermediate reduction rate is 25%, and the number of hot rolling after the intermediate heating is determined according to the target hot rolling thickness. The heating temperature of the hot rolling after the last heating is 1030°C, the holding time is 10 min, the start rolling temperature is 1200°C, the final rolling temperature is 850°C, the final rolling reduction rate is 38.2%, the total reduction rate is 82.2%, and the hot rolling is quickly cooled to room temperature at a cooling rate of 50°C / min to obtain a hot rolled plate. The steel plate after hot rolling is sampled and then the microstructure observation and tensile property test are performed. The results are shown in Table 9 Table 9

[0047] 5) Cold rolling: The hot-rolled sheet obtained in step 4) is first subjected to surface treatment, that is, pickling or mechanical processing is used to remove the iron oxide scale on the surface of the hot-rolled sheet obtained in step 4), and then subjected to multiple cold rolling, with a single cold rolling reduction rate of 5.8% and a total reduction rate of 81.9%, thereby obtaining a cold-rolled sheet; 6) Recrystallization annealing: The cold rolled sheet obtained in step 5) was subjected to recrystallization annealing at a temperature of 1030°C and a holding time of 3 minutes. After recrystallization annealing, it was rapidly cooled to room temperature at a cooling rate of 30°C / s. The steel sheet prepared by the above process was sampled and then subjected to microstructure observation and tensile property testing. The results are shown in Table 10.

[0048] Table 10

[0049] The above is only a specific implementation of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions are given with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions 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 method for preparing high chromium-molybdenum aluminum-containing ferritic stainless steel, characterized in that: The steps are as follows: 1) Melting: The weight percentage of each element in the smelting raw materials is: 25%≤Cr≤30.0%, 0.5%≤Mo≤4.0%, 1.5%≤Ni≤4.5%, C≤0.015%, N≤0.010%, 0.10%≤Nb≤0.50%, 0.10%≤Ti≤0.25%, 0.50%≤Al≤4.0%, Mn≤0.4%, 0.2%≤Si≤0.7%, S≤0.005%, P≤0.005%, O≤0.004%, and the rest is Fe and unavoidable impurities. After the raw materials are configured according to the above element ratios, they are melted to obtain molten steel; 2) Die casting and grinding: The molten steel obtained in step 1) is poured into a casting in a furnace hood, the casting is cooled to ≤1000°C in the furnace hood, taken out and slowly cooled to room temperature, and then ground; 3) Forging blank: The ground ingot obtained in step 2) is heated to 1180-1250°C with a furnace, with a heating rate of 0.5-10°C / min, a holding time of 1-4h, a start forging temperature of 1100-1200°C, a final forging temperature of ≥950°C, a forging ratio of 2.0-4.0, and then air-cooled to room temperature to obtain a forging ingot; 4) Multi-stand hot rolling or single-stand hot rolling: Multi-stand hot rolling: the forging billet obtained in step 3) is heated and then hot rolled, the heating temperature is 1080-1220°C, the holding time is 10-240 min, the starting rolling temperature is ≥1050°C, the final rolling temperature is 650-800°C, the final rolling reduction rate is ≥20%, and the hot rolling is followed by rapid cooling to room temperature, with a cooling rate of ≥50°C / min; Single-stand hot rolling: the forged billet obtained in step 3) is subjected to multiple heating and then hot rolling, the heating temperature of the hot rolling after the first heating is 1050-1180°C, the holding time is 10-240 min, the start rolling temperature is ≥1050°C, the final rolling temperature is ≥950°C, the first reduction rate is ≥15%, the heating temperature of the hot rolling after the last heating is 1030-1180°C, the holding time is 2-60 min, the start rolling temperature is ≥1030°C, the final rolling temperature is 650-800°C, the final rolling reduction rate is ≥20%, and the hot-rolled plate is quickly cooled to room temperature after hot rolling, and the cooling rate is ≥50°C / min, so as to obtain a hot-rolled plate; 5) Cold rolling: The hot-rolled sheet obtained in step 4) is subjected to multiple cold rolling processes to obtain a cold-rolled sheet; 6) Recrystallization annealing: The cold rolled sheet obtained in step 5) is subjected to recrystallization annealing at a temperature of 980-1100°C for a holding time of 0.5-60 min. After the recrystallization annealing, the sheet is rapidly cooled to room temperature at a cooling rate of ≥30°C / s.

2. The method for preparing high chromium, molybdenum, aluminum-containing ferritic stainless steel according to claim 1, characterized in that: Step 5) Surface treatment is performed before cold rolling.

3. The method for preparing high chromium, molybdenum, aluminum-containing ferritic stainless steel according to claim 2, characterized in that: In step 3), two forgings are performed during forging. During the first forging, the ground ingot obtained in step 2) is heated to 1180-1250°C with the furnace, the heating rate is 0.5-10°C / min, the holding time is 1-4h, the start forging temperature is 1100-1200°C, the final forging temperature is ≥950°C, and the forging ratio is 2.0-4.

0. During the second forging, it is heated to 1120-1250°C again, the holding time is 0.2-1h, the start forging temperature is 1100-1200°C, the final forging temperature is ≥960°C, and then air-cooled to room temperature to obtain a forging.

4. The method for preparing high chromium, molybdenum, aluminum-containing ferritic stainless steel according to claim 3, characterized in that: In the single-stand continuous rolling in step 4), the heating temperature of hot rolling after intermediate heating is 1050-1180°C, the holding time is 10-240 min, the starting rolling temperature is ≥1050°C, the final rolling temperature is ≥950°C, the reduction rate is ≥15%, and the number of hot rolling after intermediate heating is determined according to the target hot rolling thickness.

5. The method for preparing high chromium, molybdenum, aluminum-containing ferritic stainless steel according to claim 4, characterized in that: The total reduction rate during cold rolling in step 5) is ≥20%.

6. The method for preparing high chromium, molybdenum, aluminum-containing ferritic stainless steel according to claim 5, characterized in that: The cooling rate of the slow cooling in step 1) is ≤20°C / h.

7. A method for preparing high chromium-molybdenum aluminum-containing ferritic stainless steel, characterized in that: The steps are as follows: 1) Melting: The weight percentage of each element in the smelting raw materials is: 25%≤Cr≤30.0%, 0.5%≤Mo≤4.0%, 1.5%≤Ni≤4.5%, C≤0.015%, N≤0.010%, 0.10%≤Nb≤0.50%, 0.10%≤Ti≤0.25%, 0.50%≤Al≤4.0%, Mn≤0.4%, 0.2%≤Si≤0.7%, S≤0.005%, P≤0.005%, O≤0.004%, and the rest is Fe and unavoidable impurities. After the raw materials are configured according to the above element ratios, they are melted to obtain molten steel; 2) Continuous casting and grinding: The molten steel obtained in step 1) is continuously cast into a continuous casting billet, and the continuous casting billet is then slowly cooled to 300°C-500°C at a cooling rate of 4°C / h-10°C / h, and then ground; 3) Multi-stand hot rolling or single-stand hot rolling: Multi-stand hot rolling: the continuous casting billet obtained in step 2) is heated and then hot rolled, the heating temperature is 1080-1220°C, the holding time is 10-240 min, the starting rolling temperature is ≥1050°C, the final rolling temperature is 650-800°C, the final rolling reduction rate is ≥20%, and the hot rolling is followed by rapid cooling to room temperature, with a cooling rate of ≥50°C / min; Single-stand hot rolling: the forged billet obtained in step 3) is subjected to multiple heating and then hot rolling, the heating temperature of the hot rolling after the first heating is 1050-1180°C, the holding time is 10-240 min, the start rolling temperature is ≥1050°C, the final rolling temperature is ≥950°C, the first reduction rate is ≥15%, the heating temperature of the hot rolling after the last heating is 1030-1180°C, the holding time is 2-60 min, the start rolling temperature is ≥1030°C, the final rolling temperature is 650-800°C, the final rolling reduction rate is ≥20%, and the hot-rolled plate is quickly cooled to room temperature after hot rolling, and the cooling rate is ≥50°C / min, so as to obtain a hot-rolled plate; 4) Cold rolling: The hot-rolled sheet obtained in step 3) is subjected to multiple cold rolling processes to obtain a cold-rolled sheet; 5) Recrystallization annealing: The cold rolled sheet obtained in step 4) is subjected to recrystallization annealing at a temperature of 980-1100°C for a holding time of 0.5-60 min. After the recrystallization annealing, the sheet is rapidly cooled to room temperature at a cooling rate of ≥30°C / s.

8. The method for preparing high chromium, molybdenum, aluminum-containing ferritic stainless steel according to claim 7, characterized in that: Step 4) Surface treatment is performed before cold rolling.

9. The method for preparing high chromium, molybdenum, aluminum-containing ferritic stainless steel according to claim 8, characterized in that: In the single-stand continuous rolling in step 3), the heating temperature of hot rolling after intermediate heating is 1050-1180°C, the holding time is 10-240 min, the starting rolling temperature is ≥1050°C, the final rolling temperature is ≥950°C, the reduction rate is ≥15%, and the number of hot rolling after intermediate heating is determined according to the target hot rolling thickness.

10. The method for preparing high chromium, molybdenum, aluminum-containing ferritic stainless steel according to claim 9, characterized in that: The total reduction rate during cold rolling in step 4) is ≥20%.

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