A method for manufacturing a duplex stainless steel flange

Abstract

This invention relates to the field of stainless steel flange manufacturing technology, specifically a method for manufacturing duplex stainless steel flanges, comprising the following steps: S1, preparing duplex stainless steel ingots; S2, hot forging; S3, solution heat treatment; S4, post-treatment; wherein S1 includes S11, preparing core-shell composite particles; S12, preparing an iron-based master alloy; and S13, smelting and casting. This invention, by constructing Y2O3@Ce@CeO2 three-layer core-shell composite particles and uniformly introducing an iron-based master alloy, produces duplex stainless steel flanges with an impact absorption energy of over 120J at -60℃, meeting the stringent requirements of high salt spray and high chloride ion environments in polar oceans, superior to commercially available super duplex stainless steel 2507. It also solves the technical problems of easy agglomeration of nanoparticles and easy burn-off of rare earth elements.

Description

Technical Field

[0001] This invention relates to the field of stainless steel flange manufacturing technology, specifically a method for manufacturing a duplex stainless steel flange. Background Technology

[0002] Duplex stainless steel flanges combine the excellent toughness of austenitic stainless steel with the high strength and corrosion resistance of ferritic stainless steel, and are widely used in oil and gas transportation, chemical industry, marine engineering and other fields. With the advancement of polar oil and gas resource development, stringent service requirements have been placed on duplex stainless steel flanges for pipeline connections, including extremely low temperatures (-60℃ to -80℃), high salt spray, high chloride ion, and long-term alternating loads.

[0003] Although existing commercially available super duplex stainless steel (such as 2507) has high strength and pitting corrosion resistance, it is prone to ductile-brittle transition in the ultra-low temperature environment of polar oceans, and its low temperature impact toughness drops sharply. The impact energy at -60℃ is generally less than 100J. Flanges are prone to brittle fracture under low temperature impact or alternating loads, which seriously threatens the operational safety of polar pipeline systems.

[0004] In existing technologies, numerous studies have been conducted to improve the low-temperature toughness and corrosion resistance of duplex stainless steel. Chinese invention patent CN113549825B discloses a high-corrosion-resistant super stainless steel for marine engineering equipment and its manufacturing method. By controlling the content of alloying elements such as Cr, Ni, Mo, and N, and combining this with specific heating, rolling, and solution treatment processes, the Charpy impact energy at -60℃ can reach over 150J, and the yield strength can reach over 600MPa, demonstrating excellent comprehensive performance. However, this technical route falls within the category of conventional alloying and has approached the performance ceiling of this approach. Especially under long-term alternating loads at ultra-low temperatures in polar regions, it is difficult to further address the fatigue performance degradation problem that may be caused by insufficient microstructure uniformity.

[0005] Studies have also shown that adding rare earth elements (such as Ce) to duplex stainless steel is an effective way to improve its microstructure and properties. Publication number CN115725902A discloses a resource-saving duplex stainless steel containing the rare earth metal Ce. By adding 0.01%–0.07% Ce, the elongation and impact toughness of the material are improved through its purification of molten steel, modification of inclusions, and microalloying effects. Furthermore, the literature "Influence of Cerium Oxide Content on the Microstructure and Properties of Plasma Arc Cladding of 2205 Duplex Stainless Steel" discloses that adding an appropriate amount of CeO2 can refine the microstructure of the duplex stainless steel cladding layer, improving its mechanical properties and corrosion resistance.

[0006] However, rare earth elements are easily burned off and segregated in molten steel, making it difficult to disperse them evenly; and when nanomaterials are introduced into duplex stainless steel, the nanomaterials tend to agglomerate when added directly, failing to achieve the desired refining and toughening effect; thus, it is difficult to meet the requirements of polar marine engineering for the long-term safe service of flanges. Summary of the Invention

[0007] To solve the above problems, the present invention provides a method for manufacturing duplex stainless steel flanges, comprising the following steps: S1, preparing duplex stainless steel ingots.

[0008] S11. Preparation of core-shell composite particles: Y2O3 nanoparticles were dispersed in anhydrous ethanol, and 0.5-5% (by weight of Y2O3 nanoparticles) of surfactant were added. After ultrasonic oscillation for 1-2 hours, the mixture was filtered and vacuum dried at 60-80℃ for 12-24 hours to obtain Y2O3 nanocores. Using magnetron sputtering with high-purity Ce as the target material, the Y2O3 nanocores were sputtered and coated in a rotating powder container to obtain Y2O3@Ce core-shell particles, which were stored under argon atmosphere for later use. Using atomic layer deposition with Ce(TMHD)4 and H2O as precursors, a CeO2 ceramic shell was deposited on the surface of the Y2O3@Ce core-shell particles to obtain Y2O3@Ce@CeO2 three-layer core-shell composite particles. The composite particles were vacuum dried at 60℃ for 4-6 hours for later use.

[0009] S12. Preparation of iron-based master alloy: The core-shell composite particles obtained in step S11 are initially mixed with iron powder at a mass ratio of (5-15):(85-95). The mixture is ball-milled under argon protection. The ball-milled powder is loaded into a steel sleeve and degassed under vacuum. Then, it is kept at a temperature and pressure in a hot isostatic pressing furnace for 4-8 hours. After cooling with the furnace, the steel sleeve is removed to obtain an iron-based master alloy with uniformly dispersed core-shell composite particles.

[0010] S13. Smelting and Casting: The molten steel obtained from the primary smelting in the electric arc furnace is transferred to a vacuum refining furnace, where industrial pure iron, ferrochrome, electrolytic nickel, ferromolybdenum, chromium nitride, and electrolytic manganese are added for alloying treatment; an iron-based master alloy is added to the molten steel to adjust the content of core-shell composite particles, Cr, Ni, Mo, N, and Mn in the molten steel to the preset range; after refining, it is cast under argon protection to prepare duplex stainless steel ingots.

[0011] The components of duplex stainless steel ingots, by mass percentage, are: Cr 24-26%, Ni 7.8-8.5%, Mo 3.5-4.5%, N 0.3-0.34%, Mn 1.4-1.8%, core-shell composite particles 0.065%-0.22%, C≤0.03%, S≤0.01%, P≤0.02%, with the balance being Fe.

[0012] S2. Hot forging process: Duplex stainless steel ingots are hot forged to obtain flange blanks.

[0013] S3. Solution heat treatment: Solution treatment is performed on the flange blank.

[0014] S4. Post-treatment: The flange blank after solution treatment is pickled to remove scale and then machined to obtain duplex stainless steel flange.

[0015] Preferably, the mass ratio of Y2O3 nanoparticles to anhydrous ethanol is 1:(30-50), and the surfactant is polyethylene glycol.

[0016] Preferably, the ferrite volume fraction of the duplex stainless steel ingot is 35-40%, with austenite as the balance.

[0017] Preferably, in the magnetron sputtering method, the sputtering parameters are: background vacuum ≤ 5 × 10⁻⁶. -4 Pa, Ar pressure 0.2–1 Pa, power density 2–8 W / cm³ 2 The sputtering process is controlled at a temperature of ≤50℃, and the sputtering deposition time is 60 min. The deposition thickness of the Ce shell is 5-10 nm.

[0018] Preferably, in the atomic layer deposition method, the deposition temperature is 250-350℃, Ce(TMHD)4 is the cerium source and H2O is the oxygen source, the deposition is carried out in a pulse-purge cycle mode, the pulse time is 0.5-2s, the purge time is 10-30s, 80 cycles are deposited, and the CeO2 shell thickness is 10-20nm.

[0019] Preferably, in S12, the vacuum degassing temperature is 400-500℃, the hot isostatic pressing temperature is 650-780℃, the pressure is 150-200MPa, the cooling method after hot isostatic pressing is furnace cooling, and the mass ratio of core-shell composite particles to iron powder in S12 is (5-15):(85-95).

[0020] Preferably, S2, the hot forging process includes: heating the duplex stainless steel ingot to 700-750℃ at a rate of ≤80℃ / h and holding it for 4-6h; then continuing to heat it to 1150-1180℃ at a rate of ≤100℃ / h, with the holding time calculated at 1.5-2min / mm based on the billet thickness; immediately starting forging after the holding period, with an initial forging temperature of 1100-1180℃ and a final forging temperature of 950-1000℃, ensuring that the single forging pressure is ≥30% and ≤70% during the forging process, and the total forging ratio is ≥4.

[0021] Preferably, S3, solution heat treatment includes: heating the flange blank to 1080~1110℃, and holding it for 2~2.5min / mm based on the flange thickness; after holding, directly water quenching the flange blank to below 100℃, with the flange blank immersing in water for no more than 30s.

[0022] Preferably, in S4, the post-treatment acid washing and descaling uses a mixed acid solution of HNO3-HF, wherein the mass fraction of HNO3 is 15-25% and the mass fraction of HF is 2-6%, the solution temperature is controlled at 30-40℃, and the acid washing time is 10-30 min.

[0023] Preferably, in S4, post-processing machining includes turning the flange sealing surface and machining bolt holes.

[0024] The duplex stainless steel flanges prepared using the above method are applied in polar marine environments.

[0025] As the outermost layer in direct contact with molten steel, the dense CeO2 ceramic shell, approximately 15 nm thick, has a melting point exceeding 2400°C. When added to the reducing molten steel, it does not melt instantly. Trace amounts of carbon and other deoxidizing elements in the steel gradually undergo reduction reactions, generating low-valence cerium oxides and releasing carbon monoxide. This process consumes the CeO2 ceramic shell, providing a crucial buffer time for the inner Ce shell layer. This ensures that the inner layer is exposed only when the composition is homogeneous in the later stages of steel refining, rather than being dispersed or burned off immediately upon addition. During this process, the CeO2 ceramic shell also acts as a physical barrier, preventing the Y2O3 nanonuclei from directly contacting the molten steel and agglomerating.

[0026] When the outermost CeO2 ceramic shell is partially consumed, the inner Ce shell is exposed. The metallic Ce is extremely chemically reactive and quickly dissolves in the molten steel. It reacts with O and S in the molten steel to form rare earth inclusions such as Ce2O3 and Ce2O2S with high melting points. These inclusions float to the slag phase, thereby purifying the molten steel.

[0027] Ce can also utilize the inherent inclusion modification effect of rare earth elements to transform the original harmful inclusions such as strip-shaped MnS and brittle Al2O3 in steel into spherical and fine rare earth composite inclusions, thus eliminating stress concentration sources. At the same time, based on the solid solution strengthening mechanism of rare earth microalloying, trace amounts of Ce dissolve in the matrix, producing lattice distortion and playing a solid solution strengthening role.

[0028] After the CeO2 ceramic shell and Ce shell are consumed in sequence, the Y2O3 nanonuclei are released into the molten steel. At this time, the molten steel has a low impurity content due to the purification effect of Ce, and the Y2O3 nanonuclei are distributed in the molten steel in a dispersed state. In the subsequent solidification and hot working process, they can act as heterogeneous nucleation cores of ferrite, refine the grains, and pin the grain boundaries to inhibit grain growth, thereby improving the low-temperature impact toughness.

[0029] A core-shell composite particle was mixed with iron powder through ball milling, vacuum degassing, and hot isostatic pressing to produce an iron-based master alloy, achieving pre-dispersion of the core-shell particle in the iron matrix. When this master alloy was added to molten steel at the end of refining, the iron matrix rapidly melted, while the core-shell particle, already encapsulated in the iron matrix, avoided direct agglomeration and was thus uniformly dispersed in the molten steel. This method effectively overcomes the segregation and agglomeration problems caused by density differences and high surface energy when traditional rare earth or nanomaterials are directly added.

[0030] The outer CeO2 layer provides slow-release protection, the middle Ce layer plays a purifying and modifying role, and the inner Y2O3 layer achieves dispersion strengthening and grain refinement; the iron-based master alloy ensures spatial uniformity throughout the process. All three are indispensable and together enable the preparation of duplex stainless steel flanges that combine high strength, excellent low-temperature toughness, and high corrosion resistance.

[0031] The present invention has at least one of the following technical effects: 1. By constructing Y2O3@Ce@CeO2 three-layer core-shell structure composite particles and uniformly introducing iron-based intermediate alloy, the impact absorption energy of the duplex stainless steel flange prepared by the present invention at -60℃ is basically above 120J, which is better than that of commercial super duplex stainless steel 2507. At the same time, it also solves the technical problems of easy agglomeration of nanoparticles and easy burn-off of rare earth elements.

[0032] 2. The corrosion weight loss of the flange of this invention is as low as 0.42-1.55 g / m. 2 This invention can meet the stringent requirements of high salt spray and high chloride ion environments in polar oceans. Furthermore, the method of this invention can stably control the ferrite volume fraction between 35% and 40%, avoiding the tendency of low-temperature brittleness caused by excessive ferrite, and ensuring the structural stability of the flange under long-term alternating loads.

[0033] 3. Through the layer-by-layer slow-release design of the three-layer core-shell structure, combined with the pre-dispersion effect of the iron-based intermediate alloy, rare earth Ce and Y2O3 nanoparticles are stably and uniformly dispersed in the duplex stainless steel matrix, overcoming the technical difficulties of rare earth burn-off, segregation, and nanoparticle agglomeration in the traditional direct addition method.

[0034] 4. The flange of this invention has a yield strength of 548-605 MPa, which is comparable to existing high-end duplex stainless steel and can meet the load-bearing capacity requirements of polar pipeline connectors. Attached Figure Description

[0035] Figure 1 SEM image of the Y2O3@Ce@CeO2 three-layer core-shell composite particles prepared in Example 1;

[0036] Figure 2 This is a TEM image of the Y2O3@Ce@CeO2 three-layer core-shell composite particles prepared in Example 1. Detailed Implementation

[0037] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for purposes and uses only to illustrate the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to limit the scope of protection of the invention to these embodiments. All equivalent transformations or simple substitutions made based on the substantive content of this application should fall within the scope of protection of this application. For parameter ranges not mentioned, intermediate values ​​are selected. Furthermore, for mass percentages or weight percentages not explicitly stated or mentioned, they generally refer to the final concentration after addition.

[0038] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0039] Example

[0040] Example 1

[0041] S1. Prepare duplex stainless steel ingots.

[0042] Weigh 100g of Y2O3 nanoparticles with an average particle size of 30nm, disperse them in 4000g of anhydrous ethanol, add 2g of polyethylene glycol, and treat with ultrasonic oscillation at 300W for 1.5h. Then, vacuum filter the mixture and vacuum dry the filter cake at 60℃ for 24h to obtain Y2O3 nanocores for later use.

[0043] A Ce-coated Y₂O₃ nanonuclei were deposited using magnetron sputtering. The nanonuclei were placed in a rotating powder container stage, and high-purity Ce was used as the target material. The sputtering parameters were set to a background vacuum of 3 × 10⁻⁶. -4 Pa, high-purity argon gas is introduced to maintain a pressure of 0.5 Pa, sputtering power density is 5 W / cm². 2 The sputtering process was controlled at ≤50℃ and sputtered for 60 min to obtain Y2O3@Ce core-shell particles with an average Ce shell thickness of 8 nm. After sputtering, the powder was taken out in an argon glove box and sealed in an argon-filled container for later use.

[0044] Atomic layer deposition (ALD) was used to coat a CeO2 ceramic shell. Y2O3@Ce core-shell particles were rapidly transferred into the ALD reaction chamber under argon protection. Ce(TMHD)4 was used as the cerium source, H2O as the oxygen source, and high-purity N2 as the carrier and purge gas. The deposition temperature was set at 300℃, and a pulse-purge cycle deposition mode was employed. Within a single cycle, the cerium source pulse was 1 s, followed by 20 s of high-purity N2 purging, a 0.5 s pulse of the oxygen source, and 20 s of high-purity N2 purging. Eighty cycles were performed to obtain Y2O3@Ce@CeO2 three-layer core-shell composite particles with an average CeO2 shell thickness of 15 nm. The composite particles were then vacuum-dried at 60℃ for 5 h for later use.

[0045] The prepared composite particles were observed using scanning electron microscopy and transmission electron microscopy, and the results are as follows: Figure 1 and Figure 2 As shown, the prepared Y2O3@Ce@CeO2 composite particles exhibit a relatively uniform spherical or near-spherical morphology, with particle sizes ranging from 30 to 60 nm, which is basically consistent with the initial Y2O3 nanoparticle size (30 nm) and the total thickness of the subsequent coating layer (approximately 23 nm). The particle surfaces are smooth and intact, without obvious damage or detachment, and the particles are well dispersed, with no obvious large-sized agglomerates observed, indicating that the magnetron sputtering and atomic layer deposition processes did not disrupt the particle dispersion.

[0046] Depend on Figure 2 The TEM images clearly reveal a three-layer core-shell structure: the darker central region is the Y₂O₃ nanocore; the middle, lighter-colored continuous layer is the Ce metal shell, approximately 8 nm thick, consistent with the magnetron sputtering parameters; and the outermost, lightest dense layer is the CeO₂ ceramic shell, approximately 15 nm thick, matching the expected thickness after 80 cycles of atomic layer deposition. The interfaces between the layers are continuous, clear, and free of delamination or porosity defects, indicating that both magnetron sputtering and atomic layer deposition achieved uniform and complete coating. This lays a reliable material foundation for subsequent preparation of iron-based master alloys and for achieving rare earth slow release, molten steel purification, inclusion modification, and nano-dispersion strengthening in duplex stainless steel.

[0047] S12. Preparation of iron-based master alloy: Weigh 150g of core-shell composite particles and 850g of iron powder, and mix them in a V-type mixer for 30 minutes to obtain a mixed powder with a total weight of 1000g and a mass ratio of 15:85. Place the mixed powder in a planetary ball mill and ball mill it under argon protection. The ball-to-powder ratio is 15:1, the speed is 200 rpm, and the ball milling time is 4 hours. The ball-milled powder is loaded into a steel sleeve, vibrated, and vacuum degassed at 450℃ until the vacuum degree inside the sleeve is ≤1×10-2Pa. Then, it is sealed and welded. The sealed sleeve is placed in a hot isostatic pressing furnace and held at 720℃ and 170MPa for 6 hours. After cooling with the furnace, the steel sleeve is removed to obtain an iron-based master alloy with uniformly dispersed core-shell composite particles.

[0048] S13. Smelting and Casting: The molten steel obtained from the electric arc furnace primary refining is transferred to a vacuum refining furnace. According to the target composition, 2289.6 kg of industrial pure iron, 1775.38 kg of ferrochrome, 407.91 kg of electrolytic nickel, 333.33 kg of ferromolybdenum, 160 kg of chromium nitride, and 80.81 kg of electrolytic manganese are added sequentially for alloying treatment. At the end of refining, 50 kg of iron-based master alloy is added to the molten steel to adjust the content of core-shell composite particles, Cr, Ni, Mo, and N in the molten steel to the preset range. After refining, the steel is cast under argon protection to prepare duplex stainless steel ingots. The components of the duplex stainless steel ingots, by mass percentage, are: Cr 25%, Ni 8.15%, Mo 4%, N 0.32%, Mn 1.6%, core-shell composite particles 0.15%, C≤0.03%, S≤0.01%, P≤0.02%, with the balance being Fe.

[0049] In ferrochrome, chromium accounts for 65% by mass, with the balance being iron; in ferromolybdenum, molybdenum accounts for 60% by mass, with the balance being iron; and in chromium nitride, chromium accounts for 60% by mass, nitrogen accounts for 10% by mass, with the balance being iron.

[0050] S2. Hot forging process: The duplex stainless steel ingot is heated to 730℃ at a rate of 60℃ / h and held for 5h; then the temperature is increased to 1160℃ at a rate of 80℃ / h, and the holding time is calculated at 2min / mm based on the thickness of the billet; forging begins immediately after the holding time is completed, with an initial forging temperature of 1150℃ and a final forging temperature of 970℃. During the forging process, the single pressing amount is guaranteed to be 40-60%, and the total forging ratio is 4.

[0051] S3. Solution heat treatment: When the surface temperature of the flange blank is below 300℃, it is put into the furnace and heated to 1100℃ at a rate of 90℃ / h. The holding time is calculated based on the flange thickness at 2min / mm. After the holding time is completed, the flange blank is directly water quenched to below 100℃. The immersion time of the flange blank in water shall not exceed 30s.

[0052] S4. Post-treatment: At 35℃, the flange blank after solution treatment is pickled for 20 minutes to remove scale using HNO3-HF mixed acid solution. After that, the flange sealing surface is machined and bolt holes are machined on the flange blank to obtain a super duplex stainless steel flange. The mass fraction of HNO3 in the HNO3-HF mixed acid solution is 20%, the mass fraction of HF is 5%, and the balance is deionized water.

[0053] It should be noted that, due to the large amount of alloy required for the preparation of duplex stainless steel flanges, the demand for iron-based master alloys with uniformly dispersed core-shell composite particles is also large, and they need to be prepared in batches and multiple times.

[0054] Example 2

[0055] The difference from Example 1 is that the mass percentage of the core-shell composite particles is 0.065%.

[0056] Example 3

[0057] The difference from Example 1 is that the mass percentage of the core-shell composite particles is 0.22%.

[0058] Example 4

[0059] The difference from Example 1 is that the mass percentage of Cr is 26%, the mass percentage of Mo is 4.5%, the mass percentage of N is 0.34%, and the mass percentage of Mn is 1.8%.

[0060] Example 5

[0061] The difference from Example 1 is that the solution heat treatment temperature is 1080°C, while the other steps are the same as in Example 1.

[0062] Example 6

[0063] The difference from Example 1 is that the solution heat treatment temperature is 1110°C, while the other steps are the same as in Example 1.

[0064] Example 7

[0065] The difference from Example 1 is that the average thickness of the Ce shell is 5 nm, and the remaining steps are the same as in Example 1.

[0066] Example 8

[0067] The difference from Example 1 is that the CeO2 shell thickness is 20nm, and the remaining steps are the same as in Example 1.

[0068] Comparative Example

[0069] Comparative Example 1

[0070] The difference from Example 1 is that no surfactant is added when the Y2O3 nanoparticles are dispersed in anhydrous ethanol.

[0071] Comparative Example 2

[0072] The difference from Example 1 is that CeO2 ceramic shell deposition is not performed when preparing core-shell composite particles, while the other steps are the same as in Example 1.

[0073] Comparative Example 3

[0074] The difference from Example 1 is that when preparing core-shell composite particles in S11, Ce shell sputtering coating is not performed, and the remaining steps are the same as in Example 1.

[0075] Comparative Example 4

[0076] The difference from Example 1 is that the Y2O3 nanoparticles and rare earth Ce powder are not sputtered and coated, but are dispersed into the iron powder by mixing to obtain an iron-based intermediate alloy.

[0077] Comparative Example 5

[0078] The difference from Example 1 is that only Y2O3 nanoparticles are dispersed in the iron-based master alloy, and the amount of Y2O3 nanoparticles added is equal to the amount of core-shell composite particles added.

[0079] Comparative Example 6

[0080] The difference from Example 1 is that only rare earth Ce powder is dispersed in the iron-based master alloy, and the amount of rare earth Ce powder added is equal to the amount of core-shell composite particles added.

[0081] Comparative Example 7

[0082] The difference from Example 1 is that no core-shell composite particles are added.

[0083] Performance testing

[0084] The duplex stainless steel flanges prepared in Examples 1-8 and Comparative Examples 1-7 were subjected to low-temperature impact toughness testing, pitting corrosion resistance testing, metallographic analysis, and yield strength testing.

[0085] Low-temperature impact toughness test: Charpy V-notch impact test was conducted at -60℃ according to GB / T229 standard to determine the impact absorption energy of duplex stainless steel flange.

[0086] Pitting resistance test: According to ASTM G48 Method A standard, a 24-hour pitting test was conducted in 6% FeCl3 solution at 22°C, and the corrosion weight loss per unit area was calculated.

[0087] Metallographic analysis: According to the metallographic determination method of GB / T 13305-2024, the 500x image analysis method of metallographic microscope was used. Under the composition and process of this invention, the ferrite volume fraction is stable at 35-40%, which is a result that can be repeatedly verified in the field.

[0088] Yield strength: The yield strength of the flange is determined at room temperature in accordance with GB / T228.1 standard.

[0089] Table 1. Performance test results of Examples 1-8 and Comparative Examples 1-7

[0090]

[0091] All the above performance data are average values ​​measured according to the corresponding standards. The arithmetic mean of three parallel samples is taken for each example / comparative example.

[0092] As shown in Table 1, through comparative examples 1-3, it can be seen that as the amount of core-shell composite particles added increases from 0.065% to 0.22%, the impact energy at -60℃ increases from 124J to 148J, showing a positive correlation. Comparative example 7 is a control example without any core-shell composite particles added, and its impact energy at -60℃ is only 102J, which is significantly lower than that of the examples, indicating that the core-shell composite particles of the present invention play a key role in improving low-temperature toughness.

[0093] The corrosion weight loss in Examples 1-4 was 0.42–1.02 g / m³. 2 The value was significantly lower than that of comparative examples 1-7, indicating that the optimized alloy composition and core-shell particles have a synergistic effect.

[0094] Comparison of Comparative Example 1 and Example 1 shows that the addition of surfactant is a key step in ensuring the uniform dispersion of Y2O3 nanocores.

[0095] By comparing Comparative Example 2 with Example 1, it can be seen that the slow-release protection of the outer CeO2 ceramic shell is the key to preventing premature burn-off of rare earth Ce and ensuring the subsequent toughening effect.

[0096] By comparing Comparative Example 3 with Example 1, it can be seen that the purification of molten steel and the role of rare earth Ce in metamorphic inclusions are indispensable steps in obtaining excellent comprehensive performance.

[0097] Comparative Example 4 exhibits an impact energy of only 62 J at -60℃ and a corrosion weight loss of 3.82 g / m³. 2 This is far inferior to Example 1, proving that simple physical mixing alone cannot achieve uniform dispersion of rare earth elements and effective introduction of nanoparticles.

[0098] The impact energy of Comparative Example 5 (with only Y2O3 added) was 58J, and that of Comparative Example 6 (with only Ce added) was 70J, both significantly lower than that of Example 1 (138J). This indicates that adding Y2O3 or Ce alone cannot achieve the effect of using them together, proving that the Y2O3 nanocore and Ce shell complement each other functionally and are indispensable.

[0099] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0100] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for manufacturing a duplex stainless steel flange, characterized in that, Includes the following steps: S1. Preparation of duplex stainless steel ingots; S11. Preparation of core-shell composite particles: Y2O3 nanoparticles were dispersed in anhydrous ethanol, and 0.5-5% (by weight of Y2O3 nanoparticles) of surfactant were added. After ultrasonic oscillation for 1-2 hours, the mixture was filtered and vacuum dried at 60-80℃ for 12-24 hours to obtain Y2O3 nanocores. Using magnetron sputtering with high-purity Ce as the target material, the Y2O3 nanocores were sputtered and coated in a rotating powder container to obtain Y2O3@Ce core-shell particles, which were stored under argon atmosphere for later use. Using atomic layer deposition with Ce(TMHD)4 and H2O as precursors, a CeO2 ceramic shell was deposited on the surface of the Y2O3@Ce core-shell particles to obtain Y2O3@Ce@CeO2 three-layer core-shell composite particles. The composite particles were vacuum dried at 60℃ for 4-6 hours for later use. S12. Preparation of iron-based master alloy: The core-shell composite particles obtained in step S11 are initially mixed with iron powder at a mass ratio of (5-15):(85-95). The mixture is ball-milled under argon protection. The ball-milled powder is loaded into a steel sleeve, degassed under vacuum, and then kept at a temperature and pressure in a hot isostatic pressing furnace for 4-8 hours. After cooling with the furnace, the steel sleeve is removed to obtain an iron-based master alloy with uniformly dispersed core-shell composite particles. S13. Smelting and Casting: The molten steel obtained from the primary smelting in the electric arc furnace is transferred to a vacuum refining furnace, where industrial pure iron, ferrochrome, electrolytic nickel, ferromolybdenum, chromium nitride, and electrolytic manganese are added for alloying treatment; an iron-based master alloy is added to the molten steel to adjust the content of core-shell composite particles, Cr, Ni, Mo, N, and Mn to the preset range; after refining, the steel is cast under argon protection to prepare duplex stainless steel ingots. The components of duplex stainless steel ingots, by mass percentage, are: Cr 24-26%, Ni 7.8-8.5%, Mo 3.5-4.5%, N 0.3-0.34%, Mn 1.4-1.8%, core-shell composite particles 0.065%-0.22%, C≤0.03%, S≤0.01%, P≤0.02%, with the balance being Fe; S2. Hot forging process: Duplex stainless steel ingots are hot forged to obtain flange blanks; S3. Solution heat treatment: Solution treatment of the flange blank; S4. Post-treatment: The flange blank after solution treatment is pickled to remove scale and then machined to obtain duplex stainless steel flange.

2. The manufacturing method of a duplex stainless steel flange according to claim 1, characterized in that: The mass ratio of Y2O3 nanoparticles to anhydrous ethanol is 1:(30-50), and polyethylene glycol is selected as the surfactant.

3. The manufacturing method of a duplex stainless steel flange according to claim 1, characterized in that: The duplex stainless steel ingot has a ferrite volume fraction of 35-40% and the balance is austenite.

4. The manufacturing method of a duplex stainless steel flange according to claim 1, characterized in that: The sputtering parameters in the magnetron sputtering method are as follows: base vacuum ≤ 5 × 10 -4 Pa, Ar pressure 0.2-1 Pa, power density 2-8 W / cm 2 and the sputtering process temperature control ≤ 50℃.

5. The manufacturing method of a duplex stainless steel flange according to claim 1, characterized in that: In the atomic layer deposition method, the deposition temperature is 250–350℃, Ce(TMHD)4 is the cerium source and H2O is the oxygen source, and the deposition is carried out in a pulse-purge cycle mode with a pulse time of 0.5–2s and a purge time of 10–30s.

6. The manufacturing method of a duplex stainless steel flange according to claim 1, characterized in that: In S12, the vacuum degassing temperature is 400-500℃, the hot isostatic pressing temperature is 650-780℃, the pressure is 150-200MPa, and the cooling method after hot isostatic pressing is furnace cooling. In S12, the mass ratio of core-shell composite particles to iron powder is (5-15):(85-95).

7. A method for manufacturing a duplex stainless steel flange according to claim 1, characterized in that: S2. Hot forging process includes: heating duplex stainless steel ingots to 700-750℃ at a rate of ≤80℃ / h and holding for 4-6h; then continuing to heat to 1150-1180℃ at a rate of ≤100℃ / h, with holding time calculated at 1.5-2min / mm based on the billet thickness; forging begins immediately after holding, with an initial forging temperature of 1100-1180℃ and a final forging temperature of 950-1000℃. During forging, the single forging pressure is guaranteed to be ≥30% and ≤70%, and the total forging ratio is ≥4.

8. A method for manufacturing a duplex stainless steel flange according to claim 1, characterized in that: S3. Solution heat treatment includes: heating the flange blank to 1080~1110℃, and holding time calculated according to flange thickness at 2~2.5min / mm; after holding, directly water quenching the flange blank to below 100℃, and the immersion time of the flange blank in water shall not exceed 30s.

9. A method for manufacturing a duplex stainless steel flange according to claim 1, characterized in that: S4. In the post-treatment, acid washing and descaling are performed using a mixed acid solution of HNO3-HF, wherein the mass fraction of HNO3 is 15-25% and the mass fraction of HF is 2-6%. The solution temperature is controlled at 30-40℃ and the acid washing time is 10-30 min.

10. A method for manufacturing a duplex stainless steel flange according to claim 1, characterized in that: S4. Post-processing machining includes turning the flange sealing surface and machining bolt holes.

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