High-n low-ni type duplex stainless steel large deformation hot compression processing method

Abstract

The application relates to a high-N and low-Ni type duplex stainless steel large-deformation hot compression processing method, and belongs to the technical field of stainless steel hot processing. The application comprises the following steps: (1) preparing duplex stainless steel raw materials, smelting high-N and low-Ni type duplex stainless steel, and obtaining a casting blank; (2) pre-forging the casting blank, and water-cooling to obtain a pre-forging plate; (3) pre-rolling the pre-forging plate, and water-cooling to obtain a hot-rolled plate; (4) solid-solution heat-treating the hot-rolled plate, and then water-cooling; (5) homogenizing the structure of the solid-solution treated material, and then carrying out hot compression processing, and water-cooling after hot processing to obtain a finished product. The application adds more N in the duplex stainless steel, increases the replacement amount of N to Ni, increases the strength and corrosion resistance, and achieves the combination of economy and high performance. In view of the deterioration of the high-N to the hot processing performance of the duplex stainless steel, the role of regulating and controlling the hot processing parameters is played, and the problem that the high-N duplex stainless steel is prone to cracking in large-deformation hot processing is solved.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel hot working technology, and relates to a method for hot compression processing of high-N low-Ni duplex stainless steel with large deformation. Background Technology

[0002] Duplex stainless steel is a dual-phase material whose matrix consists of ferrite and austenite in a near 1:1 ratio, with the minimum phase comprising no less than 30%. Duplex stainless steel combines the excellent weldability and toughness of austenitic stainless steel with the superior strength and resistance to chloride stress corrosion of ferritic stainless steel, and is widely used in petroleum, chemical, nuclear power, marine engineering, and energy industries.

[0003] Duplex stainless steel typically includes elements such as Cr, Ni, Mo, and Mn. However, in recent years, the global production of nickel ore has been insufficient, and the price of nickel has continued to rise, once reaching 300,000 yuan / ton. This has resulted in high production costs for duplex stainless steel. Therefore, it is necessary to seek lower-cost alternative elements to alleviate the pressure of Ni consumption and reduce costs.

[0004] Ni's primary role in duplex stainless steel is austenite formation, resulting in a two-phase microstructure. Mn and N, as austenite-forming elements, are commonly used to replace Ni. Increasing the Mn content or adding N to replace Ni can reduce the Ni content in duplex stainless steel, thus alleviating Ni consumption pressure and lowering costs. However, a high Mn content in duplex stainless steel increases the tendency for σ-phase precipitation, negatively impacting product performance. N, on the other hand, is a strong austenite-forming and stabilizing element, with an austenite-forming ability approximately 30 times that of Ni and 60 times that of Mn. Furthermore, N's strong solid solution strengthening effect effectively improves the strength of austenite in duplex stainless steel, with a solid solution strengthening effect approximately 100 times that of Mn. Therefore, using N to replace Ni not only reduces the Mn content but also significantly enhances the mechanical properties and corrosion resistance of duplex stainless steel. Nitrogen (N) can effectively improve the pitting corrosion resistance of duplex stainless steel, increasing its pitting corrosion resistance equivalent by 30 times that of Cr. Conversely, manganese (Mn) reduces the pitting corrosion resistance equivalent; therefore, its addition can compensate for the impact of reduced Ni content on the corrosion resistance of duplex stainless steel. Furthermore, nitrogen can also improve the creep resistance, fatigue resistance, and wear resistance of duplex stainless steel. Therefore, the development of high-N, low-Ni duplex stainless steel is of great significance.

[0005] Poor hot working properties are one of the main reasons limiting the large-scale production and application of duplex stainless steel. During hot working, the significant differences in structure and hardness between the two phases of duplex stainless steel cause them to exhibit different deformation characteristics and softening behaviors, making them prone to cracking. For high-nitrogen duplex stainless steel, on the one hand, the strong solid solution strengthening effect of nitrogen significantly increases the hardness and strength of the austenite phase at high temperatures, further increasing the incoordination of deformation between the two phases and thus increasing the risk of cracking during production; on the other hand, the high nitrogen content promotes the precipitation of hard Cr2N at the phase boundaries, making duplex stainless steel more susceptible to cracking during production.

[0006] Currently, some low-Ni duplex stainless steels are made by replacing Ni with Mn. However, Mn causes the precipitation of the σ phase, which easily becomes a source of cracking failure, reducing tensile properties. A Cr-depleted zone is formed around the σ phase, and the addition of Mn easily leads to the formation of loose and porous MnO in the stainless steel passivation film, resulting in decreased corrosion resistance. Some low-Ni duplex stainless steels also contain added N, but the N content is low, less than 0.3 wt.%, and the improvement in Ni substitution and the strength and corrosion resistance of the duplex stainless steel is not significant. Considering both economic efficiency and performance, it is necessary to further increase the amount of N added to duplex stainless steel.

[0007] Therefore, it is necessary to provide a large deformation hot compression processing method for high-N, low-Ni duplex stainless steel to solve the problem of the deterioration of the hot working properties of duplex stainless steel caused by high N addition. By using a large deformation hot compression processing method to process high-N, low-Ni duplex stainless steel, the hot compression processing parameters can be synergistically controlled to avoid the influence of high N content on the processing of duplex stainless steel, while giving full play to the substitution effect of N on Ni. Summary of the Invention

[0008] To overcome the problems existing in the background technology, the present invention provides a method for hot compression processing of high-N and low-Ni duplex stainless steel with large deformation. By controlling the strain rate and deformation temperature, the thermoplasticity of duplex stainless steel with high N content, low Mn content and low Ni content is improved and the recrystallization structure is regulated during the hot compression processing of high-N and low-Ni duplex stainless steel with large deformation is improved. This solves the problem that the duplex stainless steel is difficult to deform and easy to crack during processing after increasing the N content, and obtains a finished high-N and low-Ni duplex stainless steel with uniform and fine two-phase structure.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0010] The processing method includes the following steps:

[0011] (1) Prepare high-N low-Ni duplex stainless steel raw materials according to the formula, and refine high-N low-Ni duplex stainless steel in a vacuum melting furnace to obtain high-N low-Ni duplex stainless steel billet.

[0012] (2) The high-N low-Ni duplex stainless steel billet obtained in step (1) is pre-forged and then water-cooled to obtain pre-forged plate.

[0013] (3) The pre-forged plate in step (2) is pre-rolled and then water-cooled to obtain a hot-rolled plate;

[0014] (4) Use a box-type resistance furnace to perform solution heat treatment on the hot-rolled plate obtained in step (3), and then water cool it to obtain a solution heat-treated plate.

[0015] (5) The solution heat-treated plate obtained in step (4) is processed to obtain a hot-compressed sample;

[0016] (6) The hot-compressed sample in step (5) is subjected to a homogenization treatment, cooled to the deformation temperature and kept warm, and then subjected to hot compression processing at the deformation temperature to obtain a high-N low-Ni duplex stainless steel product.

[0017] Preferably, the chemical composition of the high-N, low-Ni duplex stainless steel formulation, by mass percentage, is as follows: C: 0.004–0.010%, Si: 0.20–0.22%, Mn: 1.80–2.00%, Cr: 22.00–23.00%, Ni: 1.30–1.40%, Mo: 2.70–2.80%, Cu: 0.09–0.15%, N: 0.50%–0.55%, P: ≤0.008%, S: ≤0.005%, with the balance being Fe and unavoidable impurities.

[0018] Preferably, in step (2), the initial forging temperature of the pre-forging treatment is controlled at 1100-1200℃, the final forging temperature is ≥950℃, and the forging ratio is 3-4.

[0019] Preferably, in step (3), the initial rolling temperature is controlled at 1100-1150℃ and the final rolling temperature is ≥950℃.

[0020] Preferably, in step (4), the solution temperature is 1180-1200℃ and the solution time is 30-40 min.

[0021] Preferably, in step (6), the hot-compressed sample is heated to 1200°C at a heating rate of 5°C / s, held at that temperature for 5 minutes, and then cooled to the deformation temperature (1140–1160°C) at a cooling rate of 10°C / s, held at that temperature for 1 minute, and then cooled at 1140–1160°C at a cooling rate of 0.01–1s. -1 The strain rate is subjected to hot compression processing, and the deformation is 65% to 70%.

[0022] By controlling the strain rate and deformation temperature, the strain distribution and recrystallization behavior during hot deformation can be adjusted, thereby improving or enhancing the plasticity and microstructure refinement of high-N, low-Ni duplex stainless steel. High N content intensifies work hardening; reducing the strain rate and increasing the temperature can mitigate this effect, thus reducing the hardness difference between the two phases and preventing cracking during processing. Furthermore, controlling the strain rate and deformation temperature allows for dynamic recrystallization of the two phases in duplex stainless steel, resulting in a uniform and fine two-phase microstructure. This improves both strength and plasticity. Too low a strain rate hinders the critical dislocation conditions for recrystallization, while too high a strain rate leads to work hardening far exceeding recrystallization softening, causing the recrystallized grains to revert to deformed grains. Too low a deformation temperature inhibits recrystallization, while too high a temperature causes grain coarsening. Therefore, it is necessary to rationally control the hot working parameters to achieve optimal recrystallization softening behavior.

[0023] In duplex stainless steel, the two phases exhibit different dynamic recrystallization softening mechanisms, and favorable dynamic recrystallization behavior can be achieved through larger deformation amounts. On one hand, the ferrite phase tends to soften through dynamic recovery during hot deformation, making dynamic recrystallization relatively difficult. However, under large deformation amounts, ferrite accumulates significant distortion energy, which promotes the transformation of ferrite from dynamic recovery to dynamic recrystallization, resulting in refined ferrite grains. On the other hand, although austenite tends to undergo direct dynamic recrystallization, a large deformation amount is required to drive the nucleation and growth process. Lower deformation amounts (<20-30%) are not conducive to the storage of distortion energy, inhibiting the nucleation of dynamic recrystallization. Simultaneously, the harder austenite is unlikely to undergo a relatively complete recrystallization nucleation and growth process. Larger deformation amounts (>40-50%) are beneficial for austenite to obtain uniform and fine grains. Therefore, by controlling a larger deformation amount, dynamic recrystallization of both phases can be promoted, thereby obtaining uniform and fine grains.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention processes high-N, low-Ni duplex stainless steel using a large deformation hot compression processing method, and coordinates the hot compression processing parameters to reduce the property differences between the two phases during the hot compression deformation process, thereby obtaining good recrystallization softening behavior, avoiding cracking of the duplex stainless steel during processing, and obtaining duplex stainless steel with uniform and fine grains.

[0026] 2. This invention reduces the distribution difference of nitrogen (N) between ferrite and austenite in duplex stainless steel by controlling the deformation temperature and avoiding the Cr2N precipitation temperature range, thereby reducing the tendency for Cr2N precipitation. By controlling the strain rate, the incubation time for Cr2N precipitation can be reduced, thus inhibiting Cr2N precipitation.

[0027] 3. In this invention, the minimum Mn content is 1.80% and the maximum N content is 0.55%. The Mn content is about 3.3 times that of N. Therefore, the substitution of Ni by N accounts for about 30%, which fully utilizes the substitution effect of N for Ni. At the same time, the low Mn content can also reduce the tendency of σ phase precipitation, which is beneficial to the performance of duplex stainless steel products.

[0028] 4. This invention promotes the recrystallization of the ferrite phase, which is difficult to recrystallize in duplex stainless steel, through hot compression processing with a large deformation, thereby refining the grain size. Simultaneously, it allows for a greater amount of recrystallized material in both phases, resulting in a uniform and refined two-phase microstructure.

[0029] 5. In the process of processing, the homogenization treatment can be directly cooled to the deformation temperature of hot compression processing, so that the homogenization treatment and hot compression processing have good connection and no further cooling or heating treatment is required, which is beneficial to improving the processing efficiency of duplex stainless steel. Attached Figure Description

[0030] Figure 1 The rheological curves for embodiments and comparative examples of the present invention are shown below, wherein (a) is Embodiment 1 and Comparative Examples 1, 2, and 3; (b) is Embodiment 2 and Comparative Examples 4, 5, and 6; (c) is Embodiment 3 and Comparative Examples 7, 8, and 9; and (d) is Comparative Examples 10-13.

[0031] Figure 2 The microstructure of the sample after solution treatment in Example 1 is shown.

[0032] Figure 3 The microstructures of duplex stainless steel samples from Example 1 and Comparative Examples 1, 2, and 3 of the present invention are shown, wherein (a) is Comparative Example 1; (b) is Comparative Example 2; (c) is Comparative Example 3; and (d) is Example 1.

[0033] Figure 4The microstructures of duplex stainless steel samples from Example 2 and Comparative Examples 4, 5, and 6 of the present invention are shown, wherein (a) is Comparative Example 4; (b) is Comparative Example 5; (c) is Comparative Example 6; and (d) is Example 2.

[0034] Figure 5 The microstructures of duplex stainless steel samples from Example 3 and Comparative Examples 7, 8, and 9 of this invention are shown, wherein (a) is Comparative Example 7; (b) is Comparative Example 8; (c) is Comparative Example 9; and (d) is Example 3.

[0035] Figure 6 The microstructures of duplex stainless steel samples for comparative examples 10-13 of the present invention are shown, wherein (a) is comparative example 10; (b) is comparative example 11; (c) is comparative example 12; and (d) is comparative example 13.

[0036] Figure 7 The images show magnified microstructures of duplex stainless steel samples from Example 2 and Comparative Examples 5, 11, and 13 of the present invention: (a) Comparative Example 5; (b) Example 2; (c) Comparative Example 11; (d) Comparative Example 13.

[0037] Figure 8 The macroscopic morphology of duplex stainless steel samples in the embodiments and comparative examples of the present invention is shown in (a to a3) for Example 1 and Comparative Examples 1-3; (b to b3) for Example 2 and Comparative Examples 4-6; (c to c3) for Example 3 and Comparative Examples 7-9; and (d to d3) for Comparative Examples 10-13. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to specific embodiments.

[0039] The raw material formulations for the embodiments are shown in Table 1.

[0040] Table 1

[0041]

[0042] The processing parameters for duplex stainless steel in the embodiments are shown in Table 2.

[0043] Table 2

[0044]

[0045] The metallographic sample preparation conditions for the embodiments and comparative examples of the present invention are as follows: electrochemical corrosion is carried out in a 10% acetic acid solution with a DC voltage of 3V and a corrosion time of 90s.

[0046] The hardness test conditions for the embodiments and comparative examples of this invention are: magnification 400×, load 245.2mN.

[0047] In the embodiments and comparative examples of this invention, the hot-compression specimens have the following specifications: diameter 8 mm, height 12 mm. The hot-compression specimens are homogenized using Gleeble-3800, and the hot compression is performed in a single pass.

[0048] Example 1

[0049] In this embodiment, the duplex stainless steel formula is prepared according to Table 1, and the parameters during processing are set according to Table 2.

[0050] (1) A 50kg vacuum melting furnace was used to melt high-N low-Ni duplex stainless steel to obtain a billet.

[0051] (2) Weigh the billet and pre-forge it, then water-cool it to obtain the pre-forged plate.

[0052] (3) The pre-forged plate is pre-rolled and then water-cooled to obtain a hot-rolled plate.

[0053] (4) The hot-rolled sheet is subjected to solution heat treatment, and then water-cooled to obtain the solution heat-treated sheet.

[0054] (5) The solution heat-treated plate is processed to obtain a hot-compressed sample.

[0055] (6) The hot-compressed sample is subjected to homogenization treatment and hot compression processing to obtain duplex stainless steel finished product.

[0056] Example 2

[0057] In this embodiment, the duplex stainless steel formulation was prepared according to Table 1, and the processing parameters were set according to Table 2. The duplex stainless steel sample preparation process was the same as in Example 1.

[0058] Example 3

[0059] In this embodiment, the duplex stainless steel formulation was prepared according to Table 1, and the processing parameters were set according to Table 2. The duplex stainless steel sample preparation process was the same as in Example 1.

[0060] Comparative Example 1

[0061] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 1, except that the deformation temperature in this comparative example is 850℃.

[0062] Comparative Example 2

[0063] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 1, except that the deformation temperature in this comparative example is 950℃.

[0064] Comparative Example 3

[0065] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 1, except that the deformation temperature in this comparative example is 1050℃.

[0066] Comparative Example 4

[0067] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 2, except that the deformation temperature in this comparative example is 850℃.

[0068] Comparative Example 5

[0069] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 2, except that the deformation temperature in this comparative example is 950℃.

[0070] Comparative Example 6

[0071] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 2, except that the deformation temperature in this comparative example is 1050℃.

[0072] Comparative Example 7

[0073] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 3, except that the deformation temperature in this comparative example is 850℃.

[0074] Comparative Example 8

[0075] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 3, except that the deformation temperature in this comparative example is 950℃.

[0076] Comparative Example 9

[0077] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 3, except that the deformation temperature in this comparative example is 1050℃.

[0078] Comparative Example 10

[0079] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 1, except that the deformation temperature is 850℃ and the strain rate is 10s. -1 .

[0080] Comparative Example 11

[0081] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 1, except that the deformation temperature is 950℃ and the strain rate is 10s. -1 .

[0082] Comparative Example 12

[0083] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 1, except that the deformation temperature is 1050℃ and the strain rate is 10s. -1 .

[0084] Comparative Example 13

[0085] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 1, except that the deformation temperature is 1150℃ and the strain rate is 10s. -1 .

[0086] Comparative Example 14

[0087] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 1, except that the N content of the duplex stainless steel in this comparative example is 0.6 wt%.

[0088] Comparative Example 15

[0089] In this comparative example, the duplex stainless steel formula and processing parameters are the same as in Example 1, except that the deformation amount in this comparative example is 60%.

[0090] Comparative Example 16

[0091] In this comparative example, the duplex stainless steel formulation and processing parameters are the same as in Example 1, except that the deformation temperature in this comparative example is 1200℃.

[0092] The ferrite and austenite phases in the duplex stainless steel samples of the embodiments and comparative examples of the present invention were tested by micro Vickers hardness values, and the results are shown in Table 3.

[0093] Table 3

[0094]

[0095] As shown in Table 3, in Comparative Examples 1-13, the hardness difference between the ferrite and austenite phases of the duplex stainless steel samples is greater than 100 HV. This indicates that during the processing of duplex stainless steel, the large hardness difference between the two phases and the uneven strain distribution make it very prone to cracking. Figure 8 As shown in (a-a2, b-b2, c-c2, d-d3), in Examples 1-3, the hardness difference between the ferrite and austenite phases of the duplex stainless steel samples is less than 100 HV. The duplex stainless steel will not crack during processing. Figure 8 As shown in (a3, b3, c3). Therefore, when the strain rate is between 0.01 and 1 s... -1 When the deformation temperature is 1150℃, it can be ensured that duplex stainless steel will not crack during processing.

[0096] pass Figure 1 (a) It can be seen that at 0.01s -1 Under hot compression deformation at strain rate, high-N, low-Ni duplex stainless steel is more prone to dynamic recrystallization, and the rheological stress continues to decrease after reaching its peak, resulting in better hot working performance.

[0097] pass Figure 1 (b) It can be seen that when the strain rate is 0.1 s⁻¹ -1 At 850℃, the rheological stress in the second half of the deformation process fluctuated significantly, indicating that it is difficult to perform large deformation hot compression at 850℃. However, as the temperature increases, the rheological stress during the hot compression process decreases steadily, indicating that increasing the deformation temperature is beneficial to the recrystallization softening of the two phases and the hot working process.

[0098] pass Figure 1 (c) It can be seen that at a strain rate of 1s -1 At 850℃, the rheological stress continuously increased with increasing strain, indicating that the increase in strain rate intensified the work hardening process. When the temperature rose to 950–1050℃, the rheological stress decreased slightly after reaching its peak, and then rose again, indicating that increasing the temperature weakened the work hardening effect. At 1150℃, the rheological stress decreased and then tended to stabilize, indicating that at high strain rates, the deformation temperature needs to be increased to obtain a better recrystallization process and a stable hot working process.

[0099] pass Figure 1 (d) It can be seen that when large deformation hot compression is performed at high strain rate, the rheological curve tends to be stable after reaching the peak, indicating that recrystallization is suppressed at excessively high strain rate and softening is mainly dynamic recovery.

[0100] pass Figure 2 It can be seen that a good two-phase equilibrium structure can be obtained after solution treatment.

[0101] pass Figure 3 , Figure 4 and Figure 7 As can be seen from (a) and (b), at 0.01 and 0.1s -1 At strain rates of 850–950℃, the austenite, after deformation, exhibits a long, blocky deformed structure, with partial dynamic recrystallization forming a small number of fine grains; the ferrite undergoes relatively good dynamic recrystallization, forming fine grains. When the temperature rises to 1050℃, the nucleation and growth of austenite dynamic recrystallization develop favorably, increasing the number of fine recrystallized grains, but still containing a small number of deformed grains; the ferrite recrystallized grains grow, reaching a growth rate of 0.01 s-1. -1 Under these conditions, there is sufficient growth time, compared to 0.1s. -1The grains are coarser. Under deformation conditions of 1150℃, austenite underwent good recrystallization, resulting in fine and uniform grains; the recrystallization degree of ferrite was even higher at high temperatures, 0.01s. -1 Under these conditions, the grains further coarsen, while 0.1s -1 Under these conditions, the deformation time is relatively short, resulting in relatively uniform and fine grains. The results show that at lower strain rates, large deformation can induce a good recrystallization process in ferrite, and increasing the temperature promotes grain growth, with higher grain growth at lower strain rates. However, austenite undergoes partial recrystallization and softening at low strain rates and low temperatures, requiring further increases in deformation temperature to achieve more complete recrystallization.

[0102] pass Figure 5 It can be seen that in 1s -1 At the specified strain rate, at 850℃, austenite undergoes block deformation, while most ferrite undergoes dynamic recrystallization to form small grains. As the temperature increases to 950–1050℃, some austenite undergoes recrystallization nucleation, but the deformation remains significant, while ferrite further undergoes dynamic recrystallization, forming dense, fine grains. At a high temperature of 1150℃, most austenite undergoes dynamic recrystallization, and the recrystallized ferrite grains grow to a certain extent, forming fine, uniform equiaxed grains. The results indicate that at higher strain rates, large deformations induce a good dynamic recrystallization process in ferrite, but the grains become finer, and uniform, fine equiaxed grains can be obtained at high temperatures. Austenite work hardening intensifies, requiring higher deformation temperatures to achieve good recrystallization softening.

[0103] pass Figure 6 and Figure 7 (c) and (d) show that at 10s -1 At strain rates of 850–950℃, austenite primarily exists as a blocky deformed structure, while ferrite undergoes dynamic recrystallization to form very fine grains. Upon deformation at 1050–1150℃, austenite forms a small amount of fine recrystallized grains, but the deformed structure remains dominant; ferrite, at faster deformation rates, only grows slightly, forming fine equiaxed grains. The results indicate that at high strain rates, ferrite can still undergo a good dynamic recrystallization process, but the time for merging and growth is limited, resulting in excessively fine grains; while austenite undergoes severe work hardening and is difficult to recrystallize even at higher temperatures.

[0104] A comparison of Example 1 and Comparative Example 14 shows that increasing the nitrogen content significantly improves the hardness of austenite, while having a smaller impact on the hardness of ferrite due to its low solid solution content. Therefore, increasing the nitrogen content in duplex stainless steel exacerbates the strength difference between the two phases, leading to uneven deformation and softening during the deformation process. Furthermore, because nitrogen has a very good effect on improving the hardness of austenite, even a small increase in nitrogen content can easily result in an excessively large hardness difference between the two phases (104.1), causing cracking of the duplex stainless steel during processing.

[0105] A comparison of Example 1 and Comparative Example 15 shows that the hardness of austenite with 70% deformation is higher than that with 60% deformation, indicating that 70% deformation is more conducive to dynamic recrystallization of austenite and grain refinement. The hardness of ferrite, however, does not change significantly, indicating that ferrite recrystallization is relatively complete in the later stages of deformation. Figure 1 (a) The rheological curve of Example 1 shows a decrease in rheological stress, indicating that increasing the amount of deformation under the conditions of Example 1 is beneficial to recrystallization and refinement of the microstructure.

[0106] A comparison of Example 1 and Comparative Example 16 shows that the high temperature of 1200℃ strongly promotes dynamic recrystallization and grain boundary migration, which causes the recrystallized grains to grow and coarsen further at a lower strain rate, resulting in a significant reduction in the hardness of both phases in duplex stainless steel.

[0107] In summary, to avoid cracking during the processing of duplex stainless steel and to obtain duplex stainless steel with good performance, it is necessary to coordinate and control the strain rate and deformation temperature within a certain range and combine them with a large deformation amount. Therefore, by processing high-N and low-Ni duplex stainless steel using the method of this invention, the negative impact of high N content on the hot working performance of duplex stainless steel can be improved, the tendency of the processed product to crack and fail can be reduced, and high-N and low-Ni duplex stainless steel with uniform and fine two-phase structure can be obtained.

[0108] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for hot compression processing of high-N, low-Ni duplex stainless steel with large deformation, characterized in that: By controlling the strain rate and deformation temperature, cracking during the processing of high-N, low-Ni, and low-Mn duplex stainless steel is avoided. The chemical composition of the high-N, low-Ni duplex stainless steel formulation, by mass percentage, is as follows: C: 0.004~0.010%, Si: 0.20~0.22%, Mn: 1.80~2.00%, Cr: 22.00~23.00%, Ni: 1.30~1.40%, Mo: 2.70~2.80%, Cu: 0.09~0.15%, N: 0.50%~0.55%, P: ≤0.008%, S: ≤0.005%, with the balance being Fe and unavoidable impurities. The processing method includes the following steps: (1) Prepare high-N low-Ni duplex stainless steel raw materials according to the formula, and refine high-N low-Ni duplex stainless steel in a vacuum melting furnace to obtain high-N low-Ni duplex stainless steel billet; (2) The high-N low-Ni duplex stainless steel billet obtained in step (1) is pre-forged and then water-cooled to obtain pre-forged plate. (3) The pre-forged plate in step (2) is pre-rolled, and then water-cooled to obtain a hot-rolled plate; (4) The hot-rolled plate obtained in step (3) is subjected to solution heat treatment using a box-type resistance furnace, and then water-cooled to obtain a solution-heat treated plate. (5) The solution heat-treated plate obtained in step (4) is processed to obtain a hot-compressed sample; (6) The hot-compressed sample in step (5) is subjected to tissue homogenization treatment to obtain the sample at the deformation temperature, and then hot compression processing is performed immediately to obtain high-N low-Ni duplex stainless steel finished product. In step (6), the hot-compressed sample is heated to 1200℃ at a heating rate of 5℃ / s, held at that temperature for 5 min, and then cooled to the deformation temperature (1140~1160℃) at a cooling rate of 10℃ / s, held at that temperature for 1 min, and then cooled at 1140~1160℃ at a cooling rate of 0.01~1s. -1 The strain rate is subjected to hot compression processing, and the deformation is 65%~70%.

2. The method for hot compression processing of high-N, low-Ni duplex stainless steel with large deformation according to claim 1, characterized in that: In step (2), the initial forging temperature of the pre-forging treatment is controlled at 1100~1200℃, the final forging temperature is ≥950℃, and the forging ratio is 3~4.

3. The method for hot compression processing of high-N, low-Ni duplex stainless steel with large deformation according to claim 1, characterized in that: In step (3), the initial rolling temperature is controlled at 1100~1150℃, and the final rolling temperature is ≥950℃.

4. The method for hot compression processing of high-N, low-Ni duplex stainless steel with large deformation according to claim 1, characterized in that: In step (4), the solution temperature is 1180~1200℃ and the solution time is 30-40min.

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