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

Abstract

The present invention relates to the technical field of high-chromium molybdenum ferritic stainless steel, and specifically to a preparation method of high-chromium molybdenum aluminum-containing ferritic stainless steel. In order to solve the problems that multiple annealings exist in the existing methods for avoiding the precipitation of brittle phases in high-chromium high-molybdenum ferritic stainless steel, resulting in relatively high control risks, long preparation processes, high manufacturing costs, and grain coarsening caused by high-temperature heating, a new preparation method of high-chromium molybdenum aluminum-containing ferritic stainless steel is provided. The preparation method includes melting, ingot casting and grinding, forging and blooming, multi-stand hot continuous rolling or single-stand hot rolling, surface treatment, cold rolling, recrystallization annealing, and cooling. In this preparation method, solution annealing is not required, the grains are fine, no brittle phases are precipitated, and the plastic toughness is good.

Description

Technical Field

[0001] The present invention relates to the technical field of high-chromium molybdenum ferritic stainless steel, and particularly to a preparation method of high-chromium molybdenum aluminum-containing ferritic stainless steel. Background Art

[0002] Super ferritic stainless steel is a nickel-saving high-corrosion-resistant stainless steel, which also has good thermal conductivity, a low linear expansion coefficient, and good formability. It has been successfully used to replace copper and titanium in the manufacture of coastal power plant condensers, and can also replace super austenitic stainless steel and nickel-based alloys in fields such as acid making, seawater desalination, and petrochemical industry. The characteristics of high chromium, high molybdenum, and nickel in super ferritic stainless steel lead to the easy formation of various brittle phases in super ferritic steel, such as σ phase, χ phase, etc. The formation of these brittle phases not only seriously deteriorates the plasticity and toughness of the material, causing material embrittlement (referred to as σ-phase brittleness), but also reduces its corrosion resistance, severely restricting the large-scale production and wide application of such products.

[0003] In order to avoid the precipitation of brittle phases such as σ phase and χ phase in the prior art, multiple annealing and alloying addition methods are generally used to avoid or hinder the precipitation of brittle phases. However, multiple annealing also increases the risk of controlling the precipitation of brittle phases (annealing is divided into solution annealing, recrystallization annealing, etc. To avoid or hinder the precipitation of brittle phases, rapid cooling is required during annealing cooling, and the control of rapid cooling is difficult, requiring the cooperation of multiple aspects such as cooling rate and coolant, with a relatively large control risk). At the same time, it also results in a longer preparation process and higher production costs.

[0004] For example, in the technical solution of a special super ferritic stainless steel and its preparation method with the patent number 202211553095.0 (prior art one), Al alloying is used 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 still needs to be carried out after hot rolling, with multiple annealing times (solution annealing and recrystallization annealing), a relatively large risk of controlling the precipitation of brittle phases, a longer preparation process, and higher manufacturing costs.

[0005] Another example is the technical solution of a high-Cr ferritic stainless steel and its manufacturing method with the patent number 201110363876.9. The hot-rolled plate needs to be solution annealed at a high temperature of 1100°C to completely eliminate the precipitation of harmful σ phase and χ phase, ensuring that the material obtains good room-temperature impact toughness. It has multiple annealing times, a relatively large risk of controlling the precipitation of brittle phases, a longer preparation process, and the problem of grain coarsening caused by high-temperature heating. Summary of the Invention

[0006] In order to solve the problems that multiple annealings exist in the existing methods for avoiding the precipitation of brittle phases in high-chromium and high-molybdenum ferritic stainless steels, resulting in relatively high control risks, long preparation processes, high manufacturing costs, and grain coarsening problems caused by high-temperature heating, a new preparation method for a high-chromium, molybdenum, and aluminum-containing ferritic stainless steel is provided. In this preparation method, solution annealing is not required, the grains are fine, no brittle phases are precipitated, and the plastic toughness is good.

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

[0008] Solution 1:

[0009] A preparation method for a high-chromium, molybdenum, and aluminum-containing ferritic stainless steel sequentially includes the following steps:

[0010] 1) Melting:

[0011] The weight percentages of the elements in the melting raw materials are as follows: 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 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) Die casting and grinding:

[0013] The molten steel obtained in step 1) is poured into a casting blank in a furnace hood. The casting blank is cooled to ≤ 1000 °C in the furnace hood, taken out and slowly cooled to room temperature, and then ground.

[0014] 3) Forging and blooming

[0015] The ground casting blank obtained in step 2) is heated in the furnace to 1180 - 1250 °C at a heating rate of 0.5 - 10 °C / min, the heat preservation time is 1 - 4 h, the forging start temperature is 1100 - 1200 °C, the final forging temperature is ≥ 950 °C, and the forging ratio is 2.0 - 4.0. Subsequently, it is air-cooled to room temperature to obtain a forged blank; (wherein the deformation amount of forging is controlled to ensure that the material is fully deformed during forging, and forging is carried out from multiple directions during the forging process, which can promote the uniform distribution of elements;).

[0016] 4) Multi-stand hot continuous rolling or single-stand hot rolling:

[0017] Multi-stand hot continuous rolling: Heat the forging billet obtained in step 3) and then conduct hot rolling. The heating temperature is 1080 - 1220 °C, the holding time is 10 - 240 min, the starting rolling temperature is ≥1050 °C, the finishing rolling temperature is 650 - 800 °C, the finishing rolling reduction ratio is ≥20%. After hot rolling, rapidly cool to room temperature, and the cooling rate is ≥50 °C / min. Further, during multi-stand hot continuous rolling in step 4), after the forging billet passes through the first stand, it stays for 2 - 30 min, enabling the hot-rolled plate after hot rolling through the first stand to complete recrystallization, refining the structure through recrystallization, simultaneously dissolving elements such as Nb, Cr, and Al precipitated during hot rolling, and controlling the precipitation of a small amount of nanoscale Laves phase.

[0018] Single-stand hot rolling: Heat the forging billet obtained in step 3) multiple times and then conduct hot rolling. The heating temperature for hot rolling after the first heating is 1050 - 1180 °C, the holding time is 10 - 240 min, the starting rolling temperature is ≥1050 °C, the finishing rolling temperature is ≥950 °C, the first reduction ratio is ≥15%. The heating temperature for hot rolling after the last heating is 1030 - 1180 °C, the holding time is 2 - 60 min, the starting rolling temperature is ≥1030 °C, the finishing rolling temperature is 650 - 800 °C, the finishing rolling reduction ratio is ≥20%. After hot rolling, rapidly cool to room temperature, and the cooling rate is ≥50 °C / min, thereby obtaining a hot-rolled plate.

[0019] 5) Cold rolling:

[0020] Conduct multi-pass cold rolling on the hot-rolled plate obtained in step 4) to obtain a cold-rolled plate; (After cold rolling, a large-deformation cold-rolled structure is obtained, increasing the deformation energy storage, providing a nucleation driving force for subsequent recrystallization annealing. At the same time, a large number of microstructures such as shear bands and deformation bands are formed in the deformed structure, providing a sufficient number of nucleation sites for subsequent recrystallization. The nanoscale Laves phase pins the recrystallization grain boundaries, further refining the recrystallized grains)

[0021] 6) Recrystallization annealing:

[0022] Conduct recrystallization annealing on the cold-rolled plate obtained in step 5). The annealing temperature is 980 - 1100 °C, the holding time is 0.5 - 60 min. After recrystallization annealing, rapidly cool to room temperature, and the cooling rate is ≥30 °C / s to form fine recrystallized grains.

[0023] Principle description: In the preparation method of the present invention, in step 1), the brittleness is reduced by designing with low contents of C and N. Adding appropriate amounts of Nb and Ti elements can stabilize C and N, further reducing the contents of dissolved C and N in the matrix. Adding Al element can inhibit the precipitation of σ phase while promoting the precipitation of nanoscale Laves phase, and the nanoscale Laves phase refines the grains. The low oxygen content can avoid the formation of alumina particles; in step 2), the cooling rate is controlled at 5°C / h - 10°C / h. Slow cooling helps to improve the plasticity and toughness of the continuous casting billet and avoid the cracking of the casting. In step 3), the forging billet is slowly heated, and the heating rate is not higher than 10°C / min, which can fully dissolve the segregation elements such as Cr, Mo, Nb, and Al formed in the casting billet and make them uniformly distributed. During the forging process, it is reheated in the furnace to make the alloying elements uniformly distributed, reduce the segregation phenomenon, and the reheated materials are easier to forge, which can improve the forging efficiency and reduce the material loss during forging. At the same time, too high or too low temperature may lead to element segregation, so the final forging temperature is controlled not lower than 950°C to avoid the formation of coarse NbTi(CN) and TiN particles, and at the same time form an appropriate amount of nanoscale Laves phase precipitation to reduce the forging resistance and avoid forging cracks. Step 4) Multi-stand hot continuous rolling: The forging billet is heated to 1080 - 1220°C, exceeding the precipitation temperature range of large-size Laves phase, ensuring the dissolution of large-size Laves phase and at the same time completing recrystallization to obtain equiaxed grains without large-size Laves phase precipitation. Due to the use of hot continuous rolling, the temperature of the hot rolled sheet will not drop significantly after passing through the previous stands. Therefore, the hot rolled sheet can stay for 2 - 30 minutes after passing through the first stand to complete recrystallization, refine the structure through recrystallization, and control the precipitation of a small amount of nanoscale Laves phase. Subsequently, the final rolling temperature is controlled at 600 - 800°C, and large reduction rate cold hot rolling is carried out to obtain a large deformation structure, and at the same time control the formation of uniformly distributed nanoscale Laves phase. Step 4) Single-stand hot rolling: The forging billet is heated to 1050 - 1180°C, exceeding the precipitation temperature range of large-size Laves phase, ensuring the dissolution of large-size Laves phase and at the same time completing recrystallization to obtain equiaxed grains without large-size Laves phase precipitation. After the first hot rolling with a large reduction rate, a large deformation structure is obtained. The last hot rolling is carried out at 1030 - 1180°C to refine the structure through recrystallization and control the precipitation of a small amount of nanoscale Laves phase. Subsequently, the final rolling temperature is controlled at 650 - 800°C. While avoiding the precipitation of σ and χ phases, large reduction rate cold hot rolling is carried out to obtain a large deformation structure, and at the same time control the formation of uniformly distributed nanoscale Laves phase and the formation of a large number of shear bands. Step 5) After cold rolling, a large deformation cold rolled structure is obtained, increasing the deformation energy storage, providing a nucleation driving force for subsequent recrystallization annealing. The nanoscale Laves phase pins the recrystallization grain boundaries, further refining the recrystallized grains. In step 6), the annealing temperature of the cold rolled sheet is 980 - 1100°C, and small recrystallized grains will be formed after rapid cooling to room temperature.Finally, high-chromium molybdenum aluminous ferritic stainless steel is prepared by direct cold rolling without solution treatment.

[0024] Furthermore, before cold rolling in step 5), surface treatment is carried out first, that is, the scale on the surface of the hot-rolled sheet obtained in step 4) is removed by pickling or machining. The surface roughness Ra≤12.8μm to remove the scale on the surface of the hot-rolled sheet, improve the surface quality of the hot-rolled sheet, and make the surface of the hot-rolled sheet smooth and flat for subsequent cold rolling.

[0025] Furthermore, in step 3), during forging and blooming, two forging operations are carried out. During the first forging, the ground billet obtained in step 2) is heated in the furnace to 1180 - 1250°C at a heating rate of 0.5 - 10°C / min, with a holding time of 1 - 4h, the starting forging temperature is 1100 - 1200°C, the final forging temperature ≥950°C, and the forging ratio is 2.0 - 4.0. During the second forging, it is reheated to 1120 - 1250°C, with a holding time of 0.2 - 1h, the starting forging temperature is 1100 - 1200°C, the final forging temperature ≥960°C, and then air-cooled to room temperature to obtain the forging. Two forging operations can further refine the grains. At the same time, when the billet is relatively thick, two forging operations are also required.

[0026] Furthermore, in the single-stand continuous rolling in step 4), the heating temperature for hot rolling after intermediate heating is 1050 - 1180°C, the holding time is 10 - 240 min, the starting rolling temperature ≥1050°C, the final rolling temperature ≥950°C, the reduction rate ≥15%, and the number of hot rolling operations after intermediate heating is determined according to the target hot-rolled thickness.

[0027] Furthermore, in step 5), the total reduction rate during cold rolling ≥20%.

[0028] Furthermore, in step 1), the cooling rate during slow cooling ≤20°C / h.

[0029] Scheme Two:

[0030] A preparation method of high-chromium molybdenum aluminous ferritic stainless steel, successively including the following steps:

[0031] 1) Melting:

[0032] The weight percentages of each element in the melting raw materials are: 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 are Fe and inevitable impurities. After configuring the raw materials according to the above element ratios, melting is carried out to obtain the molten steel;

[0033] 2) Continuous casting and grinding:

[0034] The molten steel obtained in step 1) is continuously cast into a continuous casting billet, and the continuous casting billet is slowly cooled to 300°C - 500°C at a cooling rate of 4°C / h - 10°C / h, and then ground;

[0035] 3) Multi-stand hot tandem rolling or single-stand hot rolling:

[0036] Multi-stand hot tandem 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 rolling start temperature is ≥1050°C, the final rolling temperature is 650 - 800°C, the final rolling reduction rate is ≥20%, and after hot rolling, it is quickly cooled to room temperature, and the cooling rate is ≥50°C / min;

[0037] Single-stand hot rolling: The forging billet obtained in step 3) is heated multiple times and then hot rolled. The heating temperature for hot rolling after the first heating is 1050 - 1180°C, the holding time is 10 - 240 min, the rolling start temperature is ≥1050°C, the final rolling temperature is ≥950°C, the first reduction rate is ≥15%, the heating temperature for hot rolling after the last heating is 1030 - 1180 °C, the holding time is 2 - 60 min, the rolling start temperature is ≥1030°C, the final rolling temperature is 650 - 800°C, the final rolling reduction rate is ≥20%, and after hot rolling, it is quickly cooled to room temperature, and the cooling rate is ≥50°C / min, thereby obtaining a hot rolled plate with shear bands and nano-scale Laves phase formed;

[0038] 4) Cold rolling:

[0039] The hot rolled plate obtained in step 3) is cold rolled in multiple passes to obtain a cold rolled plate;

[0040] 5) Recrystallization annealing:

[0041] The cold rolled plate obtained in step 4) is subjected to recrystallization annealing. The annealing temperature is 980 - 1100°C, the holding time is 0.5 - 60 min, and after recrystallization annealing, it is quickly cooled to room temperature, and the cooling rate is ≥30°C / s, forming fine recrystallized grains.

[0042] The principle described in this solution is basically the same as that shown in the above solution 1, where continuous casting and grinding are equivalent to die casting, grinding, and forging blanking in the above solution 1.

[0043] Further, before step 4) cold rolling, surface treatment is first carried out, that is, pickling or mechanical processing is used to remove the scale on the surface of the hot rolled plate obtained in step 3). The surface roughness Ra ≤ 12.8μm to remove the 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.

[0044] Further, in the single-stand tandem rolling in step 3), the heating temperature for hot rolling after intermediate reheating is 1050 - 1180°C, the holding time is 10 - 240 min, the starting rolling temperature is ≥1050°C, the finishing rolling temperature is ≥950°C, the reduction ratio is ≥15%, and the number of hot rolling passes after intermediate reheating is determined according to the target hot-rolled thickness.

[0045] Further, in step 4), the total reduction ratio during cold rolling is ≥20%.

[0046] 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 alumina particles by reducing the oxygen content. At the same time, during the forging process of the billet, by means of slow heating, reheating during the forging process, controlling the forging temperature, forging ratio, etc., the precipitation of large-sized carbides (NbTi / CN) is effectively avoided. Therefore, there is no need for solution treatment to dissolve the precipitated phases in the hot-rolled sheet. The hot-rolled sheet without oxide inclusions, brittle phases, and the precipitation of large-sized carbides can effectively prevent phenomena such as edge cracking during cold rolling. Therefore, cold rolling can be directly carried out, and finally, high-chromium molybdenum aluminum-containing ferritic stainless steel is prepared by direct cold rolling without solution treatment. Description of the Drawings

[0047] 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 are used together with the specification to explain the principles of the present invention.

[0048] 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.

[0049] Figure 1 Shear bands and nano-scale Laves phases formed in the hot-rolled sheet obtained by multi-stand hot tandem rolling after low-temperature finishing rolling;

[0050] Figure 2 Nano-scale Laves phases (high magnification) formed in the hot-rolled sheet obtained by multi-stand hot tandem rolling after low-temperature finishing rolling;

[0051] Figure 3 Recrystallized structure of the recrystallized annealed sheet obtained by multi-stand hot tandem rolling after low-temperature finishing rolling;

[0052] Figure 4 Shear bands and nano-scale Laves phases formed in the hot-rolled sheet obtained by single-stand hot rolling after low-temperature finishing rolling;

[0053] Figure 5The nano-scale Laves phase (high magnification) formed in the hot-rolled sheet obtained after finish rolling at low temperature using a single-stand hot rolling method;

[0054] Figure 6 The recrystallized structure of the recrystallized annealed sheet obtained after finish rolling at low temperature using a single-stand hot rolling method. Detailed implementation manners

[0055] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the solutions 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.

[0056] 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 elements. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific situations.

[0057] 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 a part of the embodiments of the present invention, rather than all the embodiments.

[0058] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Embodiment 1

[0059] A preparation method of a high-chromium molybdenum aluminum-containing ferritic stainless steel successively includes the following steps:

[0060] 1) Melting:

[0061] The weight percentages of the elements of the melting raw materials are: 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 are Fe and inevitable impurities. After configuring the raw materials according to the above element ratios, melting is carried out to obtain molten steel;

[0062] 2) Die casting and grinding:

[0063] Pour the molten steel obtained in step 1) into a casting blank inside the furnace hood. Cool the casting blank inside the furnace hood to 1000 °C, take it out and slowly cool it to room temperature. The cooling rate of slow cooling is 20 °C / h, and then carry out grinding;

[0064] 3) Forging and blooming

[0065] Carry out forging and blooming on the casting blank obtained in step 2), and forge it in two times. During the first forging, heat the ground casting blank obtained in step 2) to 1200 °C with the furnace, the heating rate is 5 °C / min, the holding time is 2 h, the forging start temperature is 1200 °C, the final forging temperature is 950 °C, and the forging ratio is 2.0. During the second forging, heat it to 1200 °C again, the holding time is 1 h, the forging start temperature is 1100 °C, and the final forging temperature is 960 °C. Then air-cool it to room temperature to obtain a forging;

[0066] 4) Multi-stand hot continuous rolling

[0067] Heat the forging blank obtained in step 3) and then carry out hot rolling. The heating temperature is 1100 °C, the holding time is 120 min, the rolling start temperature is 1100 °C. After passing through the first stand, stay for 10 min, the final rolling temperature is 860 °C, the final rolling reduction ratio is 22%, and the total reduction ratio is 82.2%. After hot rolling, quickly cool it to room temperature, and the cooling rate is 50 °C / min, so as to obtain a hot-rolled plate, as Figure 1 and Figure 2 shown, forming a uniformly distributed nano-scale Laves phase. At the same time, a large number of shear bands are formed in the deformed structure, providing a sufficient number of nucleation sites for subsequent recrystallization; After sampling the hot-rolled steel plate, carry out microstructure observation and tensile property testing, and the results are shown in Table 1.

[0068] Table 1

[0069]

[0070] 5) Cold rolling:

[0071] First, carry out surface treatment on the hot-rolled plate obtained in step 4), that is, remove the scale on the surface of the hot-rolled plate obtained in step 4) by pickling or machining, and then carry out multi-pass cold rolling. The reduction ratio of a single pass of cold rolling is 10%, and the total reduction ratio is 82.1%, so as to obtain a cold-rolled plate;

[0072] 6) Recrystallization annealing:

[0073] Carry out recrystallization annealing on the cold-rolled plate obtained in step 5). The annealing temperature is 1030 °C, the holding time is 1 min, and after recrystallization annealing, quickly cool it to room temperature, and the cooling rate is 30 °C / s, forming fine recrystallized grains, as Figure 3 shown. After sampling the steel plate prepared by the above process, carry out microstructure observation and tensile property testing, and the results are shown in Table 2.

[0074] Table 2

[0075] Example 2

[0076] A preparation method of high-chromium molybdenum aluminous ferritic stainless steel, successively including the following steps:

[0077] 1) Melting:

[0078] The weight percentages of the elements in the melting raw materials are: 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 are Fe and inevitable impurities. After preparing the raw materials according to the above element ratios, melting is carried out to obtain molten steel;

[0079] 2) Die casting and grinding:

[0080] 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. The cooling rate of slow cooling is 20 °C / h, and then grinding is carried out;

[0081] 3) Forging and blooming

[0082] The casting blank obtained in step 2) is subjected to forging and blooming, and forging is carried out in two times. During the first forging, the ground casting blank obtained in step 2) is heated to 1200 °C with the furnace, the heating rate is 5 °C / min, the holding time is 2 h, the starting forging temperature is 1200 °C, the final forging temperature is 950 °C, and the forging ratio is 2.0. During the second forging, it is heated to 1200 °C again, the holding time is 1 h, the starting forging temperature is 1200 °C, the final forging temperature is 960 °C, and then it is air-cooled to room temperature to obtain a forging;

[0083] 4) Multi-stand hot continuous rolling

[0084] The forging blank obtained in step 3) is heated and then hot-rolled. The heating temperature is 1150 °C, the holding time is 120 min, the starting rolling temperature is 1100 °C, it stays for 10 min after passing through the first stand, the final rolling temperature is 860 °C, the final rolling reduction rate is 23%, the total reduction rate is 81.3%, and after hot rolling, it is quickly cooled to room temperature, and the cooling rate is 50 °C / min; After sampling the hot-rolled steel plate, microstructure observation and tensile property testing are carried out, and the results are shown in Table 3.

[0085] Table 3

[0086]

[0087] 5) Cold rolling:

[0088] The hot-rolled sheet obtained in step 4) is first subjected to surface treatment, that is, the scale on the surface of the hot-rolled sheet obtained in step 4) is removed by pickling or machining, and then multi-pass cold rolling is carried out. The reduction rate per pass of cold rolling is 10%, and the total reduction rate is 83.4% to obtain a cold-rolled sheet;

[0089] 6) Recrystallization annealing:

[0090] The cold-rolled sheet obtained in step 5) is subjected to recrystallization annealing. The annealing temperature is 1030 °C, the holding time is 1 min, and it is rapidly cooled to room temperature after recrystallization annealing, and the cooling rate is 30 °C / s. After the steel sheet prepared by the above process is sampled, microstructure observation and tensile property testing are carried out, and the results are shown in Table 4.

[0091] Table 4

[0092]

[0093] Example 3:

[0094] A preparation method of high-chromium molybdenum aluminum-containing ferritic stainless steel successively includes the following steps:

[0095] 1) Melting:

[0096] The weight percentages of the elements of the melting raw materials are: 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 are Fe and inevitable impurities. After the raw materials are configured according to the above element ratios, melting is carried out to obtain molten steel;

[0097] 2) Continuous casting and grinding:

[0098] The molten steel obtained in step 1) is continuously cast into a continuous casting billet, and the continuous casting billet is slowly cooled to 400 °C at a cooling rate of 5 °C / h, and then grinding is carried out;

[0099] 3) Multi-stand hot tandem rolling

[0100] The forging billet obtained in step 2) is heated and then hot-rolled. The heating temperature is 1100 °C, the holding time is 120 min, the starting rolling temperature is 1100 °C, it stays for 10 min after passing through the first stand, the final rolling temperature is 860 °C, the final rolling reduction rate is 23.7%, and the total reduction rate is 82.3%. After hot rolling, it is rapidly cooled to room temperature, and the cooling rate is 50 °C / min; After the hot-rolled steel sheet is sampled, microstructure observation and tensile property testing are carried out, and the results are shown in Table 5.

[0101] Table 5

[0102]

[0103] 4) Cold rolling:

[0104] The hot-rolled sheet obtained in step 3) is first subjected to surface treatment, that is, pickling or machining is used to remove the scale on the surface of the hot-rolled sheet obtained in step 4), and then multi-pass cold rolling is carried out. The reduction rate per pass of cold rolling is 10%, and the total reduction rate is 81.1%, so as to obtain a cold-rolled sheet;

[0105] 5) Recrystallization annealing:

[0106] The cold-rolled sheet obtained in step 4) is subjected to recrystallization annealing. The annealing temperature is 1030 °C, the holding time is 1 min, and after recrystallization annealing, it is quickly cooled to room temperature, and the cooling rate is 30 °C / s. After the steel sheet prepared by the above process is sampled, microstructure observation and tensile property testing are carried out, and the results are shown in Table 6.

[0107] Table 6

[0108]

[0109] Example 4:

[0110] A preparation method of high-chromium molybdenum aluminum-containing ferritic stainless steel successively includes the following steps:

[0111] 1) Melting:

[0112] The weight percentages of the elements of the melting raw materials are: 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 are Fe and inevitable impurities. After the raw materials are configured according to the above element ratios, melting is carried out to obtain molten steel;

[0113] 2) Continuous casting and grinding:

[0114] The molten steel obtained in step 1) is continuously cast into a continuous casting billet, and the continuous casting billet is slowly cooled to 400 °C at a cooling rate of 5 °C / h, and then grinding is carried out;

[0115] 3) Single-stand hot rolling:

[0116] The forged blank obtained in step 3) is hot-rolled after being heated multiple times. The heating temperature for hot-rolling after the first heating is 1100 °C, the holding time is 60 min, the starting rolling temperature is 1100 °C, the final rolling temperature is 950 °C, the reduction rate for the first pass is 25%. The heating temperature for hot-rolling after the intermediate heating is 1180 °C, the holding time is 10 - 240 min, the starting rolling temperature is 1150 °C, the final rolling temperature is 1000 °C, the intermediate reduction rate is 20%, and the number of hot-rolling passes after the intermediate heating is determined according to the target hot-rolled thickness. The heating temperature for hot-rolling after the last heating is 1100 °C, the holding time is 45 min, the starting rolling temperature is 1200 °C, the final rolling temperature is 650 °C, the final reduction rate is 33.5%, and the total reduction rate is 82.2%. After hot-rolling, it is rapidly cooled to room temperature at a cooling rate of 50 °C / min, thereby obtaining a hot-rolled plate, which forms a uniformly distributed nano-scale Laves phase, and at the same time, a large number of shear bands are formed in the deformed structure to provide a sufficient number of nucleation sites for subsequent recrystallization, such as Figure 4 and 5 shown.

[0117] The hot-rolled steel plate is sampled and then subjected to microstructure observation and tensile property testing, and the results are shown in Table 7.

[0118] Table 7

[0119]

[0120] 4) Cold rolling:

[0121] The hot-rolled plate obtained in step 3) is first surface-treated, that is, the scale on the surface of the hot-rolled plate obtained in step 4) is removed by pickling or machining, and then multi-pass cold rolling is carried out. The reduction rate for a single cold rolling pass is 6.2%, and the total reduction rate is 82.2%, thereby obtaining a cold-rolled plate;

[0122] 5) Recrystallization annealing:

[0123] The cold-rolled plate obtained in step 4) is subjected to recrystallization annealing. The annealing temperature is 1030 °C, the holding time is 31 min, and after recrystallization annealing, it is rapidly cooled to room temperature at a cooling rate of 30 °C / s. The recrystallized grains formed are as Figure 6 shown. The steel plate prepared by the above process is sampled and then subjected to microstructure observation and tensile property testing, and the results are shown in Table 8.

[0124] Table 8

[0125]

[0126] Example 5:

[0127] A preparation method of a high-chromium molybdenum aluminum-containing ferritic stainless steel, which successively includes the following steps:

[0128] 1) Melting:

[0129] The weight percentages of the elements in the smelting raw materials are as follows: 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 are Fe and inevitable impurities. After preparing the raw materials according to the above element ratios, smelting is carried out to obtain molten steel;

[0130] 2) Ingot casting and grinding:

[0131] The molten steel obtained in step 1) is cast into a billet in the hood. The billet is cooled to 1000 °C in the hood, taken out and slowly cooled to room temperature at a cooling rate of 20 °C / h, and then ground;

[0132] 3) Forging and blooming

[0133] The billet obtained in step 2) is forged and bloomed, and forged in two times. During the first forging, the ground billet obtained in step 2) is heated to 1200 °C with the furnace, the heating rate is 5 °C / min, the holding time is 2 h, the starting forging temperature is 1150 °C, the final forging temperature is 950 °C, and the forging ratio is 1.94. During the second forging, it is heated to 1150 °C again, the holding time is 1 h, the starting forging temperature is 1200 °C, and the final forging temperature is 960 °C. Then it is air-cooled to room temperature to obtain a forging;

[0134] 4) Single-stand hot rolling:

[0135] The forging billet obtained in step 3) is hot-rolled after being heated multiple times. The heating temperature for hot rolling after the first heating is 1200 °C, the holding time is 60 min, the starting rolling temperature is 1300 °C, the final rolling temperature is 950 °C, the first reduction ratio is 25%. The heating temperature for hot rolling after the intermediate heating is 1200 °C, the holding time is 60 min, the starting rolling temperature is 300 °C, the final rolling temperature is 950 °C, the intermediate reduction ratio is 25%, and the number of hot rolling after the intermediate heating is determined according to the target hot-rolled thickness. The heating temperature for hot rolling after the last heating is 1030 °C, the holding time is 10 min, the starting rolling temperature is 1200 °C, the final rolling temperature is 850 °C, the final rolling reduction ratio is 38.2%, and the total reduction ratio is 82.2%. After hot rolling, it is quickly cooled to room temperature at a cooling rate of 50 °C / min to obtain a hot-rolled plate; After sampling the hot-rolled steel plate, microstructure observation and tensile property testing are carried out, and the results are shown in Table 9

[0136] Table 9

[0137]

[0138] 5) Cold rolling:

[0139] The hot-rolled sheet obtained in step 4) is first subjected to surface treatment, that is, pickling or machining is used to remove the scale on the surface of the hot-rolled sheet obtained in step 4), and then multi-pass cold rolling is carried out. The reduction rate per pass of cold rolling is 5.8%, and the total reduction rate is 81.9% to obtain a cold-rolled sheet;

[0140] 6) Recrystallization annealing:

[0141] The cold-rolled sheet obtained in step 5) is subjected to recrystallization annealing. The annealing temperature is 1030 °C, and the holding time is 3 min. After recrystallization annealing, it is quickly cooled to room temperature, and the cooling rate is 30 °C / s. The steel sheet prepared by the above process is sampled and then subjected to microstructure observation and tensile property testing, and the results are shown in Table 10.

[0142] Table 10

[0143]

[0144] The above are only specific embodiments of the present invention, which enable those skilled in the art to understand or implement the present invention. Although the above 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 above embodiments, or perform equivalent replacements for some or all of the technical features; 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 above embodiments, and they should all be covered by the protection scope of the claims.

Claims

1. A preparation method of high-chromium molybdenum aluminum-containing ferritic stainless steel, characterized in that, It successively includes the following steps: 1) Melting: The weight percentages of the elements in the melting raw materials are as follows: 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 are Fe and unavoidable impurities. After configuring the raw materials according to the above element ratios, melting is carried out to obtain molten steel; 2) Die casting and grinding: The molten steel obtained in step 1) is poured 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, and then ground; 3) Forging and blooming: The ground billet obtained in step 2) is heated in the furnace to 1180 - 1250 °C at a heating rate of 0.5 - 10 °C / min, with a holding time of 1 - 4 h. The forging start temperature is 1100 - 1200 °C, the final forging temperature is ≥ 950 °C, and the forging ratio is 2.0 - 4.

0. Subsequently, it is air-cooled to room temperature to obtain a forged billet; 4) Multi-stand hot continuous rolling or single-stand hot rolling: Multi-stand hot continuous rolling: The forged 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 rolling start temperature is ≥ 1050 °C, the final rolling temperature is 650 - 800 °C, the final rolling reduction rate is ≥ 20%, and after hot rolling, it is quickly cooled to room temperature with a cooling rate of ≥ 50 °C / min; Single-stand hot rolling: The forged billet obtained in step 3) is heated multiple times and then hot-rolled. The heating temperature for hot rolling after the first heating is 1050 - 1180 °C, the holding time is 10 - 240 min, the rolling start temperature is ≥ 1050 °C, the final rolling temperature is ≥ 950 °C, the reduction rate for the first time is ≥ 15%. The heating temperature for hot rolling after the last heating is 1030 - 1180 °C, the holding time is 2 - 60 min, the rolling start temperature is ≥ 1030 °C, the final rolling temperature is 650 - 800 °C, the final rolling reduction rate is ≥ 20%, and after hot rolling, it is quickly cooled to room temperature with a cooling rate of ≥ 50 °C / min, thereby obtaining a hot-rolled sheet; 5) Cold rolling: The hot-rolled sheet obtained in step 4) is cold-rolled in multiple passes to obtain a cold-rolled sheet; 6) Recrystallization annealing: The cold-rolled sheet obtained in step 5) is subjected to recrystallization annealing. The annealing temperature is 980 - 1100 °C, the holding time is 0.5 - 60 min, and after recrystallization annealing, it is quickly cooled to room temperature with a cooling rate of ≥ 30 °C / s.

2. The preparation method of a high-chromium molybdenum aluminum-containing ferritic stainless steel according to claim 1, characterized in that, Surface treatment is carried out before cold rolling in step 5).

3. The preparation method of a high-chromium molybdenum aluminum-containing ferritic stainless steel according to claim 2, characterized in that, In step 3), forging and cogging are carried out twice. During the first forging, the ground billet obtained in step 2) is heated in the furnace to 1180 - 1250 °C at a heating rate of 0.5 - 10 °C / min, with a holding time of 1 - 4 h, an initial forging temperature of 1100 - 1200 °C, a final forging temperature ≥ 950 °C, and a forging ratio of 2.0 - 4.

0. During the second forging, it is reheated to 1120 - 1250 °C, with a holding time of 0.2 - 1 h, an initial forging temperature of 1100 - 1200 °C, and a final forging temperature ≥ 960 °C. Subsequently, it is air-cooled to room temperature to obtain a forgings.

4. The preparation method of a 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 for hot rolling after intermediate heating is 1050 - 1180 °C, the holding time is 10 - 240 min, the rolling start temperature ≥ 1050 °C, the rolling end temperature ≥ 950 °C, the reduction rate ≥ 15%, and the number of hot rolling passes after intermediate heating is determined according to the target hot-rolled thickness.

5. The preparation method of a high-chromium molybdenum aluminum-containing ferritic stainless steel according to claim 4, characterized in that, In step 5), the total reduction rate during cold rolling ≥ 20%.

6. The preparation method of a high-chromium molybdenum aluminum-containing ferritic stainless steel according to claim 5, characterized in that, In step 2), the cooling rate during slow cooling ≤ 20 °C / h.

7. A method for preparing a high-chromium molybdenum aluminum-containing ferritic stainless steel, characterized in that, It successively includes the following steps: 1) Melting: The weight percentages of each element in the melting raw materials are: 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 are Fe and inevitable impurities. After configuring the raw materials according to the above element ratios, melting is carried out 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 slowly cooled to 300 - 500 °C at a cooling rate of 4 °C / h - 10 °C / h, and then grinding is carried out. 3) Multi-stand hot continuous rolling or single-stand hot rolling: Multi-stand hot continuous 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 rolling start temperature ≥ 1050 °C, the rolling end temperature is 650 - 800 °C, the final rolling reduction rate ≥ 20%. After hot rolling, it is rapidly cooled to room temperature, and the cooling rate ≥ 50 °C / min. Single-stand hot rolling: The forged billet obtained in step 3) is hot-rolled after being heated multiple times. The heating temperature for hot rolling after the first heating is 1050 - 1180 °C, the holding time is 10 - 240 min, the rolling start temperature ≥ 1050 °C, the rolling end temperature ≥ 950 °C, the first reduction rate ≥ 15%. The heating temperature for hot rolling after the last heating is 1030 - 1180 °C, the holding time is 2 - 60 min, the rolling start temperature ≥ 1030 °C, the rolling end temperature is 650 - 800 °C, the final rolling reduction rate ≥ 20%. After hot rolling, it is rapidly cooled to room temperature, and the cooling rate ≥ 50 °C / min, thereby obtaining a hot-rolled sheet. 4) Cold rolling: The hot-rolled sheet obtained in step 3) is cold-rolled in multiple passes to obtain a cold-rolled sheet. 5) Recrystallization annealing: The cold-rolled sheet obtained in step 4) is subjected to recrystallization annealing at an annealing temperature of 980 - 1100 °C for a holding time of 0.5 - 60 min, and then rapidly cooled to room temperature after recrystallization annealing, with a cooling rate ≥ 30 °C / s.

8. The preparation method of a high-chromium molybdenum aluminum-containing ferritic stainless steel according to claim 7, characterized in that, Before step 4) cold rolling, surface treatment is carried out first.

9. The preparation method of a 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 for hot rolling after intermediate heating is 1050 - 1180 °C, the holding time is 10 - 240 min, the rolling start temperature ≥ 1050 °C, the final rolling temperature ≥ 950 °C, the reduction ratio ≥ 15%, and the number of hot rolling passes after intermediate heating is determined according to the target hot-rolled thickness.

10. The preparation method of a high-chromium molybdenum aluminum-containing ferritic stainless steel according to claim 9, characterized in that, In step 4), the total reduction ratio during cold rolling ≥ 20%.

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