Corrosion-resistant alloy, its preparation method and application in deep-sea electromagnetic valve group device

Abstract

This invention relates to the field of nickel-based alloys, and more particularly to a corrosion-resistant alloy, its preparation method, and its application in deep-sea solenoid valve assembly equipment. The corrosion-resistant alloy comprises the following raw materials: C, Si, Mn, P, S, Cr, Mo, Nb, Ni, Ti, Al, B, Zr, Ce, and Fe. The preparation method of the corrosion-resistant alloy includes: first, melting the alloy raw materials under vacuum induction and then casting them into ingots; then, electroslag remelting to obtain electroslag ingots; then, forging the electroslag ingots; and then sequentially performing solution treatment, deep cryogenic treatment, staged aging, and plasma electrolytic oxidation. This corrosion-resistant alloy exhibits excellent seawater corrosion resistance, higher pitting potential, alloy antibacterial properties, and high and low temperature toughness, resulting in better overall performance and making it widely applicable in deep-sea solenoid valve assembly equipment.

Description

Technical Field

[0001] This invention relates to the field of nickel-based alloys, and more particularly to a corrosion-resistant alloy, its preparation method, and its application in deep-sea solenoid valve assembly equipment. Background Technology

[0002] Deep-sea solenoid valve assemblies are key actuators for fluid control in deep-sea equipment, primarily used in deep-sea oil and gas extraction, subsea pipeline transportation, underwater robots (ROVs), and marine energy development. In the deep-sea environment, these devices must operate under extreme conditions such as high pressure, strong corrosion, and low temperatures for extended periods, placing extremely high demands on material performance and structural design.

[0003] Specifically, key components in deep-sea solenoid valve assemblies are typically made of corrosion-resistant alloys. The valve body and cover must withstand hydrostatic pressure of at least 30 MPa and continuous corrosion from seawater, while their surface roughness must be controlled to Ra ≤ 0.8 μm to reduce marine organism attachment and slow down bio-corrosion. The valve stem and valve core must possess excellent resistance to seawater erosion and high-pressure hydrogen permeation. The pressure spring must undergo residual stress relief treatment and possess good resistance to hydrogen embrittlement. Connecting bolts must remain stable under long-term pre-tightening and possess resistance to stress corrosion cracking (SCC).

[0004] However, the complexity of the deep-sea environment further exacerbates the challenges to material performance. On the one hand, at depths exceeding 3000 meters, hydrostatic pressure can reach over 30 MPa, easily inducing creep and plastic deformation in materials, thus requiring high yield strength. On the other hand, the approximately 3.5% NaCl concentration in seawater and the continuous penetration of chloride ions make materials susceptible to pitting corrosion, crevice corrosion, and stress corrosion cracking. Simultaneously, the alternating effects of low deep-sea temperatures (approximately 2°C) and high ambient temperatures (up to 150°C) can lead to thermal fatigue and induce microcracks. Furthermore, marine microorganisms form biofilms on the material surface, which can quickly reach significant thicknesses, further aggravating localized corrosion. Under high pressure, the diffusion rate of hydrogen ions increases significantly, making materials more prone to hydrogen embrittlement and stress corrosion cracking.

[0005] Under the aforementioned service environment, the corrosion-resistant alloys used in existing deep-sea solenoid valve assemblies still have many shortcomings. First, these alloys have poor machinability and are prone to significant work hardening during machining, with a hardening index reaching 0.4. This leads to severe tool wear and frequent replacement of specialized tools (such as tungsten carbide coated tools), significantly increasing machining costs. Second, due to the significant work hardening effect, the deformation per pass is limited, increasing the number of machining passes and resulting in low overall machining efficiency. Third, existing materials are poorly designed to resist microbial adhesion and biocontamination, and still pose a high risk of hydrogen embrittlement. Furthermore, in the oxygen-deficient environment of the deep sea, the self-healing ability of the passivation film on the material surface decreases, and the local pitting corrosion rate can reach 0.5 mm / year, seriously affecting the long-term reliability of the equipment.

[0006] Therefore, there is an urgent need to develop a new type of corrosion-resistant alloy and its application scheme suitable for the extreme environment of the deep sea, so as to improve the processing performance and enhance the resistance to microbial adhesion and hydrogen embrittlement while ensuring high strength and corrosion resistance, thereby meeting the requirements for long-term stable operation of deep-sea solenoid valve groups. Summary of the Invention

[0007] This invention provides a corrosion-resistant alloy, its preparation method, and its application in deep-sea solenoid valve assembly equipment. The corrosion-resistant alloy has excellent seawater corrosion resistance, higher pitting potential, alloy antibacterial properties, and high and low temperature toughness, with better overall performance, and can be widely used in deep-sea solenoid valve assembly equipment.

[0008] To address the above problems, the present invention provides the following technical solution: This invention provides a corrosion-resistant alloy comprising the following raw materials in weight percentages: C 0~0.11% and not 0, Si≤0.6% and not 0, Mn≤0.6% and not 0, P 0.006~0.015%, S 0.001~0.015%, Cr 19.5~23.5%, Mo 7.5~10.5%, Nb 3.05~4.25%, Ti≤0.5%, Al≤0.5%, B 0.001~0.01%, Zr 0.01~0.1%, Ce 0.001~0.05%, Fe≤5%, and Ni balance.

[0009] A second aspect of the present invention also provides a method for preparing the above-mentioned corrosion-resistant alloy, comprising the following steps: First, the alloy raw materials are melted by vacuum induction and then cast into ingots. Then, they are electroslag remelted to obtain electroslag ingots. The electroslag ingots are then forged and subjected to solution treatment, deep cryogenic treatment, staged aging and plasma electrolytic oxidation in sequence.

[0010] In some specific embodiments, the vacuum induction melting includes melting, refining and casting processes; During the melting process, the vacuum degree is ≤0.067 Pa; In the refining process, the vacuum degree is ≤1Pa, the temperature is 1620~1660℃, and the time is ≥30min; The temperature during the casting process is 1580~1600℃.

[0011] In some specific embodiments, the protective slag in the electroslag remelting includes a quaternary slag system, which includes CaF2, Al2O3, CaO and MgO; the mass ratio of CaF2, Al2O3, CaO and MgO is 45:25:25:5.

[0012] In some specific embodiments, during the electroslag remelting, in the arc initiation and slag formation stage, the current is gradually increased from 1500A to 5000A, and the slag formation time is ≥40min; in the current increase stage, the current is gradually increased from 5000A to 7500A, taking 25min, and then the electrode is remelted at 7500~8000A for 180~240min; in the feeding stage, the current is gradually decreased to 2000A, and the feeding time is ≥30min.

[0013] In some specific embodiments, the forging process includes multi-stage forging; The multi-fire forging process includes the following steps: (1) Continuously heat up to 600℃ and keep warm for 1 hour; (2) Continuously heat up to 800℃ and keep warm for 1 hour.

[0014] (3) Continuously heat up to the uniform heating temperature for forging, hold for 2~4 hours, and the uniform heating temperature is a constant temperature of 1100~1200℃.

[0015] In some specific embodiments, the solution treatment is carried out at a temperature of 1040~1150℃ for 1~2 hours.

[0016] In some specific embodiments, the cryogenic medium is liquid nitrogen, the temperature is -150 to -196°C, and the holding time is 7.5 to 24.5 hours.

[0017] In some specific embodiments, the conditions for the first stage of the phased aging process are: temperature of 700~740℃, holding time of 6~10h, furnace cooling to 650℃, and cooling rate ≤50℃ / h. In the phased aging process, the conditions for the second phase are: temperature of 630~670℃, heat preservation time of 18~22h, and air cooling to 10~30℃.

[0018] In some specific embodiments, the conditions for plasma electrolytic oxidation are as follows: the electrolyte includes a silicate-phosphate composite electrolyte, the pH of the electrolyte is 10-12, the pulse voltage is 400-600V, and the current density is 12-18A / dm³. 2 The time is 25~65 minutes.

[0019] A third aspect of the present invention also provides an application of the above-mentioned corrosion-resistant alloy in deep-sea solenoid valve assembly equipment.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The corrosion-resistant alloy provided by this invention improves the alloy's oxidation resistance, stress corrosion resistance, hot corrosion resistance, and thermal fatigue resistance by innovating the alloy formula, increasing the content of elements such as chromium, nickel, and molybdenum, and adding appropriate amounts of niobium, boron, zirconium, and cerium. In addition, this invention adds appropriate amounts of boron, zirconium, and cerium to the nickel-based high-temperature alloy to purify grain boundaries, strengthen grain boundaries, and inhibit grain growth.

[0021] (2) The method for preparing corrosion-resistant alloy provided by the present invention innovates the process by step aging to achieve enrichment of Cr / Mo elements at the grain boundary, improve pitting potential, and reduce crack propagation rate under high-voltage alternating load; innovates the design of cryogenic treatment to achieve wear resistance, dimensional stability and low-temperature sealing reliability of electromagnetic valve group; and innovates the design of plasma electrolytic oxidation process to improve surface wear resistance and inhibit marine organism attachment. Attached Figure Description

[0022] The above and other objects, features, and advantages of the invention will be apparent from the following description of preferred embodiments illustrating the gist of the invention and its use, and the accompanying drawings, in which: Figure 1 The electroslag remelting current of the corrosion-resistant alloy of this invention is determined.

[0023] Figure 2 This is the heating process curve for electroslag ingot forging of the corrosion-resistant alloy of the present invention. Detailed Implementation

[0024] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments described below are for illustrative purposes only and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the following embodiments, conditions and methods known in the art can be used for processing.

[0025] This invention provides a corrosion-resistant alloy comprising the following raw materials in weight percentages: C 0~0.11% and not 0, Si≤0.6% and not 0, Mn≤0.6% and not 0, P 0.006~0.015%, S 0.001~0.015%, Cr 19.5~23.5%, Mo 7.5~10.5%, Nb 3.05~4.25%, Ti≤0.5%, Al≤0.5%, B 0.001~0.01%, Zr 0.01~0.1%, Ce 0.001~0.05%, Fe≤5%, and Ni balance.

[0026] The corrosion-resistant alloy of this invention, based on a nickel-based superalloy, improves its oxidation resistance, stress corrosion resistance, hot corrosion resistance, and thermal fatigue resistance by increasing the content of elements such as chromium, nickel, and molybdenum, and adding appropriate amounts of niobium, boron, zirconium, and cerium. In detail: Chromium forms a dense Cr2O3 oxide film, inhibiting the growth of Cl. - Penetrating the oxide film initiates pitting corrosion (PREN value > 45), improving the pitting sites and seawater corrosion resistance of the alloy; nickel can improve the alloy's strength and hardness, enhance its oxidation resistance, increase its high-temperature strength and creep strength, and improve its structural stability; molybdenum and niobium can achieve solid solution strengthening with the matrix, and the γ'' phase pins grain boundaries, inhibiting grain boundary slip and improving the alloy's creep and creep resistance; Nb combines with carbon to form stable carbides (NbC), preventing the formation of chromium-depleted grain boundary regions and eliminating the risk of chloride stress corrosion cracking.

[0027] Furthermore, this invention adds suitable boron, zirconium, and cerium to the nickel-based superalloy to purify and strengthen grain boundaries and inhibit grain growth. Trace amounts of boron will segregate at grain boundaries, inhibiting the coarsening of grain boundary carbides (such as NbC) at high temperatures, delaying grain boundary crack initiation, and improving the alloy's creep life. Boron forms stable borides (NbB2) with niobium, pinning dislocation movement and improving the alloy's creep strength. Boron promotes the enrichment of chromium at grain boundaries, enhancing the continuity of the oxide film (Cr2O3) and increasing the pitting breakdown potential of the alloy in chloride-containing media. Zr preferentially combines with impurities such as sulfur (S) and phosphorus (P) to form high-melting-point ZrS / ZrP compounds (melting point > 1800℃), reducing low-melting-point eutectic at grain boundaries and improving the alloy's high-temperature creep strength. Zr adsorption at grain boundaries inhibits carbide coarsening and improves the alloy's creep performance. Zr promotes the uniform nucleation of the γ' phase (Ni3(Al,Ti)), refining the size of the strengthening phase to 20-80 nm and improving room temperature yield strength. Cerium refines grain size, inhibits grain boundary slip at high temperatures, and increases the stress corrosion cracking threshold stress. Ce atoms agglomerate at grain boundaries, forming CeO2 nanoparticles, pinning dislocations, blocking crack propagation paths, and improving alloy fatigue life. Cerium ions embed into the grain boundaries of the Cr2O3 oxide film, improving oxide film adhesion, promoting the formation of a dense Cr2O3 / Al2O3 mixed oxide film, reducing oxygen diffusion rate, and improving the alloy's oxidation resistance. Cerium forms high-melting-point CeP / CeS compounds (melting point > 2000℃) with impurities such as phosphorus and sulfur, inhibiting intergranular corrosion tendency. Cerium promotes passivation film homogenization and increases breakdown potential. Cerium lowers the nucleation barrier of the γ'' phase (Ni3Nb), refining its size to ≤50 nm and improving room temperature yield strength.

[0028] A second aspect of the present invention also provides a method for preparing the above-mentioned corrosion-resistant alloy, comprising the following steps: First, the alloy raw materials are melted by vacuum induction and then cast into ingots. Then, they are electroslag remelted to obtain electroslag ingots. The electroslag ingots are then forged and subjected to solution treatment, deep cryogenic treatment, staged aging and plasma electrolytic oxidation in sequence.

[0029] In some embodiments, the preparation of the corrosion-resistant alloy specifically includes the following steps: Step 1: Raw material preparation. Specifically, select low-carbon, low-phosphorus, and low-sulfur alloy raw materials, including recycled steel of this grade, metallic chromium, molybdenum bars, niobium bars, electrolytic nickel, pure titanium, pure aluminum, pure iron, crystalline silicon, electrolytic manganese, ferroborone, metallic zirconium, and rare earth Ce. The raw materials should be dry, clean, and free of oil, dirt, and rust. If the raw materials are damp, dry them before use. The drying temperature should be 200~300℃, and the time should be 3~4 hours.

[0030] Step 2, vacuum induction melting, includes charging, vacuuming, melting, refining, and casting processes; (1) Loading process: The loading should be loose at the top and tight at the bottom to prevent "bridging"; Before loading large materials, a layer of fine, lightweight material should be laid at the bottom of the furnace. High-melting-point furnace materials such as electrolytic nickel, metallic chromium, and tungsten bars should be placed in the middle and lower high-temperature zone of the crucible; Pure titanium and pure aluminum are added in the later stage of refining, while ferroboron and metallic zirconium are added 5 minutes before tapping. Rare earth Ce is added to the ladle when 1 / 3 of the steel has been tapped.

[0031] (2) Vacuuming process: turn on the mechanical pump to evacuate the vacuum, with a power of 50-70KW, and record the water temperature and vacuum degree every 20 minutes.

[0032] Turn on the booster pump to raise the oil temperature.

[0033] When the vacuum level reaches ≤1000Pa, a Kerroot pump is used to evacuate the vacuum. When the vacuum level reaches ≤1Pa, the power output increases to 120-150KW; When the vacuum level reaches ≤1Pa, open the high vacuum valve; During the melting period, the melting of the furnace charge should be frequently observed to prevent bridging of the charge.

[0034] (3) Melting process: After the vacuum degree is ≤1Pa, the melting period begins; Maintain a vacuum level of ≤0.067 Pa during the melting period; During the melting period, the melting of the furnace charge should be frequently observed to prevent bridging. After the charge is completely melted, the temperature should be measured and samples taken for analysis.

[0035] (4) Refining process: The main tasks during the refining period include: deoxidation, degassing, elemental composition adjustment, and temperature adjustment; Once the vacuum level is ≤1Pa, the refining process begins. After refining for 10-20 minutes, the molten steel is sufficiently deoxidized and degassed, and electrolytic manganese, pure titanium, and pure aluminum can be added from the feed hopper. Before sampling, tilt the crucible back and forth to wash away any splashes on the crucible wall and homogenize the composition of the molten steel before taking a sample for analysis. Based on the composition analysis results of the melt sample, calculate the amount of each metal element to be added, weigh it, and add it to the furnace. 5 minutes after the feeding is completed; Then shake the crucible and turn on the electromagnetic stirrer to even out the composition and temperature of the molten steel; The refining temperature is controlled at 1620-1660℃, and the refining time is ≥30min to ensure the deoxidation and degassing effect of the molten steel.

[0036] To enhance the deoxidation and degassing of molten steel, an appropriate amount of ferroborone, zirconium metal, nickel-magnesium alloy, and rare earth elements can be added from the silo 5 minutes before tapping, and electromagnetic stirring can be turned on. Temperature is measured and samples are taken for analysis. When the temperature and composition meet the process requirements, the corresponding valves are closed, the pump is stopped, the holding pump and holding valve are opened, argon gas is introduced, and the furnace is turned over to tap the steel.

[0037] (5) Casting process: Casting electrode specifications: Φ220mm, quantity: 1 piece. The alloy of this invention has a melting point of about 1360-1380℃, and the casting temperature is controlled at 1580-1600℃. The steel ingot can be demolded after cooling for more than 30 minutes.

[0038] Step 3: Electroslag Remelting Electrode specifications used: Φ220mm; Electroslag ingot shape is determined by production: Φ320mm, Φ360mm, or Φ390mm can be selected. The protective slag adopts a quaternary slag system: 45wt%CaF2+25wt%CaO+25wt%Al2O3+5wt%MgO; The amount of slag is generally 4% of the electrode weight; Before electroslag remelting, the ingot plate (pure iron plate), the starting plate (Benxi Steel gasket), and the arc ignition agent (fluorite titanium dioxide) need to be baked at a temperature of 200~250℃ for a time of more than 2 hours. Before electroslag remelting, the electrode rods and protective slag must be baked at a temperature of 500-600℃ for a time of more than 6 hours. Electroslag remelting includes the following processes: (1) During the arc initiation and slag formation stage, the current is gradually increased from 1500A to 7500~8000A. The slag formation time should be greater than 40 minutes. When the slag pool of the crystallizer is visibly red and the slag has good fluidity, it can be considered that the slag formation is over. The arc initiation and slag formation stage includes the following gradual increase in current: Maintain a current of 1500A for at least 5 minutes; Maintain a current of 2000A for at least 5 minutes. Maintain a current of 2500A for at least 5 minutes; Maintain a current of 3000A for at least 5 minutes; Maintain a current of 3500A for at least 5 minutes; Maintain a current of 4000A for at least 5 minutes; Maintain a current of 4500A for at least 5 minutes; Apply a current of 5000A and maintain it for at least 5 minutes.

[0039] See Figure 1 In this embodiment of the invention, the slag formation time during the arc initiation and slag formation stage is ≥40 min, including 8 current gradients, with each current value maintained for at least 5 minutes.

[0040] (2) Current ramp-up phase: The current is gradually increased from 5000A to 7500A, taking 25 minutes; The current ramp-up phase includes the following gradual current increase process: 5500A current, maintained for 5 minutes; 6000A current, maintained for 5 minutes; 6500A current, maintained for 5 minutes; 7000A current, maintained for 5 minutes; Set the current to 7500A and maintain it for 5 minutes.

[0041] (3) Melting stage: The current is 7500~8000A for 180~240 minutes to remelt the electrode. The voltage is stable. A constant current of 7500~8000A is used to remelt the electrode.

[0042] (4) Compensation stage: Gradually reduce voltage and current, with the current gradually decreasing to 2000A, and the compensation time is no less than 30 minutes.

[0043] (5) Mold cooling: Φ320 ingot ≥40min; Φ360 ingot ≥40min; Φ390 ingot ≥50min; Take one sample for composition analysis from each end of the electroslag ingot, with the sampling location 30-50 mm away from the end of the ingot; Finishing of electroslag ingots: Remove shrinkage cavities at the head of the electroslag ingot and clean defects such as oxide scale, slag inclusions, and impurities from the surface of the electroslag ingot; Step 4: Forging Multi-pass forging is employed, with the deformation in a single pass not exceeding 50% to prevent excessive deformation and cracking defects. (See reference...) Figure 2 Multi-fire forging includes the following processes: (1) Continuously heat up to 600℃ and keep warm for 1 hour; (2) Continuously heat up to 800℃ and keep warm for 1 hour.

[0044] (3) Continuously heat up to the uniform temperature for forging, hold for 2 to 4 hours, and maintain the uniform temperature at a constant temperature of 1100 to 1200℃.

[0045] (4) Continuous cooling is used for final forging, and the final forging temperature is ≥930℃; when the electroslag ingot is 0.5 tons, the holding time is 2~3 hours; when the electroslag ingot is 1 ton, the holding time is 3~4 hours.

[0046] The holding time for the intermediate billet in the furnace should be ≥1 hour to ensure even and thorough firing and prevent uneven firing on both sides. The forging ratio should be ≥4. The head and tail removal rate of the forged material should be: ≥3% for the head and ≥5% for the tail. Forged materials must be free from defects such as cracks, folds, and peeling. If such defects are present, they can be cleaned by grinding with a grinding wheel. When a larger forging ratio is required (e.g., forging ratio ≥ 10), the upsetting and drawing process can be used 2-3 times.

[0047] Step 5: Solution Treatment During solution treatment, the temperature is 1040~1150℃, the holding time is 1~2h, and after being taken out of the furnace, it is water-cooled with a cooling rate of >200℃ / s; Step Six: Deep Cryogenics In cryogenic treatment, the medium is liquid nitrogen, the temperature is -150~-196℃, and the holding time is 7.5~24.5h; after cryogenic treatment, the temperature is increased in a stepwise manner (≤10℃ / min), and should not be too fast. Step 7: Phased Time Limits The conditions for the first stage are: temperature 700~740℃, holding time 6~10h, furnace cooling to 650℃, cooling rate ≤50℃ / h; the conditions for the second stage are: temperature 630~670℃, holding time 18~22h, air cooling to 10~30℃. Step 8: Plasma Electrolytic Oxidation In plasma electrolytic oxidation, the electrolyte includes a silicate-phosphate composite electrolyte with a pH of 10-12, a pulse voltage of 400-600V, and a current density of 12-18A / dm³. 2 The time is 25~65 minutes.

[0048] A third aspect of the present invention also provides an application of the above-mentioned corrosion-resistant alloy in deep-sea solenoid valve assembly equipment.

[0049] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] The chemical composition design of the corrosion-resistant alloys in Examples 1-13 is shown in Table 1.

[0051] Table 1. Chemical composition design of corrosion-resistant alloys in Examples 1-13

[0052] In the examples, ten implementation schemes (Scheme 1 to Scheme 10) were used to determine the Zr content in the corrosion-resistant alloy, as detailed in the table below:

[0053] In the examples, ten implementation schemes (Scheme 1 to Scheme 10) were used to determine the B content in the corrosion-resistant alloy, as detailed in the table below:

[0054] In the examples, ten implementation schemes (Scheme 1 to Scheme 10) were used to determine the Ce content in the corrosion-resistant alloy, as detailed in the table below:

[0055] The corrosion-resistant alloys in Examples 1-13 were prepared according to the following method: 1. Raw material preparation Low-carbon, low-phosphorus, and low-sulfur alloy raw materials are selected, including recycled materials of this steel grade, metallic chromium, molybdenum bars, niobium bars, electrolytic nickel, pure titanium, pure aluminum, pure iron, crystalline silicon, electrolytic manganese, ferroborone, metallic zirconium, and rare earth Ce. The materials should be kept dry, clean, and free of oil, dirt, and rust. If the raw materials are damp, they should be dried before use at 250℃ for 3 hours. 2. Vacuum induction melting (1) Loading The charging should be done with a loose top and a tight bottom to prevent bridging; before charging large materials, a layer of fine, lightweight material should be laid at the bottom of the furnace. High-melting-point furnace charge such as electrolytic nickel, metallic chromium, and tungsten bars should be placed in the middle and lower high-temperature zone of the crucible; pure titanium and pure aluminum should be added in the later stage of refining; ferroboron and metallic zirconium should be added 5 minutes before tapping; and rare earth Ce should be added to the ladle when 1 / 3 of the steel has been tapped.

[0056] (2) Vacuuming The mechanical pump was turned on to create a vacuum, with a power of 60KW. The water temperature and vacuum level were recorded every 20 minutes.

[0057] Turn on the booster pump to raise the oil temperature.

[0058] When the vacuum level reaches ≤1000Pa, a Kerroot pump is used to evacuate the vacuum. When the vacuum level reaches ≤1Pa, the power output increases to 145KW; When the vacuum level reaches ≤1Pa, open the high vacuum valve; During the melting period, the melting of the furnace charge should be frequently observed to prevent the furnace charge from being damaged.

[0059] (3) Melting Once the vacuum level is ≤1Pa, the melting period begins; Maintain a vacuum level of ≤0.067 Pa during the melting period; During the melting period, the melting of the furnace charge should be frequently observed to prevent bridging; after the charge is melted and cleared, the temperature should be measured and samples taken for analysis.

[0060] (4) Refining The main tasks during the refining period include: deoxidation, degassing, elemental composition adjustment, and temperature adjustment; Once the vacuum level is ≤1Pa, the refining process begins. After refining for 20 minutes, the molten steel is sufficiently deoxidized and degassed, and electrolytic manganese, pure titanium, and pure aluminum can be added from the feed hopper. Before sampling, tilt the crucible back and forth to wash away any splashes on the crucible wall and homogenize the composition of the molten steel before taking a sample for analysis. Based on the composition analysis results of the melt sample, calculate the amount of each metal element to be added, weigh it, and add it to the furnace. 5 minutes after the feeding is completed; Then shake the crucible and turn on the electromagnetic stirrer to even out the composition and temperature of the molten steel; The refining temperature is controlled at 1650℃ and the refining time is ≥30min to ensure the deoxidation and degassing effect of the molten steel.

[0061] To enhance the deoxidation and degassing of molten steel, an appropriate amount of ferroborone, zirconium metal, nickel-magnesium alloy, and rare earth elements can be added from the silo 5 minutes before tapping, and electromagnetic stirring can be turned on. Temperature is measured and samples are taken for analysis. When the temperature and composition meet the process requirements, the corresponding valves are closed, the pump is stopped, the holding pump and holding valve are opened, argon gas is introduced, and the furnace is turned over to tap the steel.

[0062] (5) Casting Casting electrode specifications: Φ220mm, quantity: 1 piece. The alloy of this invention has a melting point of approximately 1370℃, and the casting temperature is controlled at 1590℃. The steel ingot can be demolded after cooling for more than 30 minutes.

[0063] 3. Electroslag remelting Electrode specifications used: Φ220mm; Electroslag ingot shape is determined by production: Φ320mm, Φ360mm, or Φ390mm can be selected. The protective slag adopts a quaternary slag system: 45wt%CaF2+25wt%CaO+25wt%Al2O3+5wt%MgO; The amount of slag is generally 4% of the electrode weight; Before electroslag remelting, the ingot plate (pure iron plate), the starting plate (Benxi Steel gasket), and the arc ignition agent (fluorite titanium dioxide) need to be baked at a temperature of 200℃ for a time of more than 2 hours. Before electroslag remelting, the electrode rods and protective slag must be baked at a temperature of 500℃ for a time of more than 6 hours. Electroslag remelting includes the following processes: (1) During the arc initiation and slag formation stage, the current is gradually increased from 1500A to 5000A. The slag formation time should be greater than 40 minutes. When the slag pool of the crystallizer is visibly red and the slag has good fluidity, the slag formation can be considered to be over. The arc initiation and slag formation stage includes the following gradual increase in current: 1500A current, maintained for 5 minutes; 2000A current, maintained for 5 minutes; 2500A current, maintained for 5 minutes; 3000A current, maintained for 5 minutes; 3500A current, maintained for 5 minutes; 4000A current, maintained for 5 minutes; 4500A current, maintained for 5 minutes; Set the current to 5000A and maintain it for 5 minutes.

[0064] See Figure 1 In this embodiment of the invention, the arc initiation and slag formation stage lasts for 40 minutes, including 8 current gradients, with each current value maintained for 5 minutes.

[0065] (2) Current ramp-up phase: The current is gradually increased from 5000A to 7500A, taking 25 minutes; The current ramp-up phase includes the following gradual current increase process: 5500A current, maintained for 5 minutes; 6000A current, maintained for 5 minutes; 6500A current, maintained for 5 minutes; 7000A current, maintained for 5 minutes; Set the current to 7500A and maintain it for 5 minutes.

[0066] (3) Melting stage: The electrode is remelted at 7800A for 200 minutes. The voltage is stable. The electrode is remelted using a constant current of 7800A.

[0067] (4) Compensation stage: Gradually reduce voltage and current, with the current gradually decreasing to 2000A, and the compensation time is no less than 30 minutes.

[0068] See Figure 1 In this embodiment of the invention, the compensation stage takes 30 minutes.

[0069] (5) Mold cooling: Φ320 ingot ≥40min; Φ360 ingot ≥40min; Φ390 ingot ≥50min; One sample for composition analysis was taken from each end of the electroslag ingot, with the sampling location 50 mm away from the end of the ingot; Finishing of electroslag ingots: Remove shrinkage cavities at the head of the electroslag ingot and clean defects such as oxide scale, slag inclusions, and impurities from the surface of the electroslag ingot.

[0070] 4. Forging Multi-pass forging is employed, with the deformation in a single pass not exceeding 50% to prevent excessive deformation and cracking defects. (See reference...) Figure 2 Multi-fire forging includes the following processes: (1) Continuously heat up to 600℃ and keep warm for 1 hour; (2) Continuously heat up to 800℃ and keep warm for 1 hour.

[0071] (3) Continuously heat up to the uniform temperature for forging, hold for 4 hours, and the uniform temperature is a constant temperature of 1100~1200℃.

[0072] (4) Continuous cooling is used for final forging, and the final forging temperature is ≥930℃; when the electroslag ingot is 0.5 tons, the holding time is 2~3 hours; when the electroslag ingot is 1 ton, the holding time is 3~4 hours.

[0073] The holding time for the intermediate billet in the furnace should be ≥1 hour to ensure even and thorough firing and prevent uneven firing on both sides. The forging ratio should be ≥4. The head and tail removal rate of the forged material should be: ≥3% for the head and ≥5% for the tail. Forged materials must be free from defects such as cracks, folds, and peeling. If such defects are present, they can be cleaned by grinding with a grinding wheel. When a larger forging ratio is required (e.g., forging ratio ≥ 10), a two-stage upsetting and drawing process can be used.

[0074] In this embodiment, ten implementation schemes (Scheme 1 to Scheme 10) are used to determine the forging heating temperature and holding time in the corrosion-resistant alloy. The specific details are shown in the table below:

[0075] 5. Solid solution During solution treatment, the temperature is 1040~1150℃, the holding time is 1~2h, and after being taken out of the furnace, it is water-cooled with a cooling rate of >200℃ / s.

[0076] In this embodiment, eight implementation schemes (Scheme 1 to Scheme 10) are used to determine the solution heat treatment temperature and time for the corrosion-resistant alloy electroslag remelting ingot. The specific details are shown in the table below:

[0077] 6. Cryogenic In cryogenic treatment, the medium is liquid nitrogen, the temperature is -196℃, and the holding time is 20 hours. After cryogenic treatment, the temperature is increased in a stepwise manner (≤10℃ / min), and should not be too fast. 7. Phased timeframe The conditions for the first stage are: temperature 720℃, holding time 8h, furnace cooling to 650℃, cooling rate ≤50℃ / h; the conditions for the second stage are: temperature 650℃, holding time 20h, air cooling to 20℃. 8. Plasma electrolytic oxidation In plasma electrolytic oxidation, the electrolyte includes a silicate-phosphate composite electrolyte with a pH of 11, a pulse voltage of 500V, and a current density of 16A / dm³. 2 The time is 55 minutes.

[0078] 9. Inspection, packaging, and warehousing Comparative Example 1 The previous generation alloy consisted of the following components by mass percentage: C≦0.025%, Si≦1.05%, Mn≦2.05%, Cr:21.5-23.5%, Ni:4.0-7.0%, Mo:2.5-4.0%, N:0.13-0.21%, Fe: balance.

[0079] The preparation method of the aforementioned previous generation alloy includes the following steps: Raw material preparation → Electric furnace primary refining → AOD refining → Casting → Forging → Solution treatment → Machining → Inspection and warehousing.

[0080] Electric furnace primary smelting: Clean, low-impurity alloys such as ferronickel, ferrochrome, and ferromolybdenum, as well as scrap steel, are selected. The primary smelting temperature must reach above 1500℃. In terms of composition control, key alloying elements such as Cr and Mo are controlled at the upper-middle limits to offset losses in subsequent processes. AOD refining: Molten steel is added to the AOD furnace at a temperature ≥1550℃. A mixture of N2 and O2 gas is blown in for decarburization and heating, with an O2 / N2 ratio ranging from 4:1 to 0.5:1. Deep deoxidation is achieved using a composite process of "adding aluminum particles inside the AOD furnace + adding aluminum powder to the slag surface".

[0081] Casting: The casting temperature is usually between 1550-1600℃.

[0082] Forging: The initial forging temperature is controlled at 1100-1180℃, and the final forging temperature is not lower than 950℃. The initial heating of the steel ingot can be set at 1150-1220℃, and the deformation per forging is controlled at 30-50%. The upsetting deformation is 30-40%, and the elongation deformation is 35-45%. After forging, the steel ingot should be rapidly cooled (such as by water cooling or forced air cooling) to below 500℃ immediately.

[0083] Solution treatment: The solution treatment temperature is usually between 1020-1100℃, and the holding time is controlled at 1.2-1.4×D minutes (D is the outer diameter of the workpiece, in mm). Rapid water cooling is used to ensure that the cooling rate is not less than 35℃ / s.

[0084] Performance testing The following performance tests were performed on the corrosion-resistant alloy of the present invention and the previous generation alloy of Comparative Example 1.

[0085] (1) The pitting potentials of the corrosion-resistant alloy of the present invention and the previous generation alloy of Comparative Example 1 are shown in the table below:

[0086] It is evident that the corrosion-resistant alloy used in the deep-sea solenoid valve assembly of this invention exhibits a significantly improved pitting potential compared to the previous generation alloy.

[0087] (2) The low-temperature toughness at -50℃ of the corrosion-resistant alloy of the present invention and the previous generation alloy of Comparative Example 1 are shown in the table below:

[0088] Compared with the previous generation alloy, the corrosion-resistant alloy for deep-sea solenoid valve assembly equipment of this invention has significantly improved low-temperature toughness at -50℃.

[0089] (3) The 300MPa creep life of the corrosion-resistant alloy of the present invention and the previous generation alloy of Comparative Example 1 are shown in the table below:

[0090] Compared with the previous generation alloy, the corrosion-resistant alloy for deep-sea solenoid valve assembly equipment of this invention has a significantly improved creep life of 300MPa.

[0091] (4) The leakage rates of the corrosion-resistant alloy of the present invention and the previous generation alloy of Comparative Example 1 are shown in the table below:

[0092] Compared with the previous generation of alloys, the corrosion-resistant alloy used in the deep-sea solenoid valve assembly equipment of this invention has a significantly improved leakage rate.

[0093] (5) The corrosion-resistant alloy of the present invention and the previous generation alloy of Comparative Example 1 have 10 7 The high-cycle fatigue limit for the next cycle is shown in the table below.

[0094] Compared with the previous generation alloy, the corrosion-resistant alloy used in the deep-sea solenoid valve assembly equipment of this invention has a 10% improvement. 7 The high-cycle fatigue limit is significantly improved in the next cycle.

[0095] (6) The annual seawater corrosion rates of the corrosion-resistant alloy of the present invention and the previous generation alloy of Comparative Example 1 are shown in the table below:

[0096] Compared with the previous generation of alloys, the corrosion-resistant alloy for deep-sea solenoid valve assembly equipment of this invention has a significantly improved annual seawater corrosion rate.

[0097] (7) The deformation of the corrosion-resistant alloy of the present invention and the previous generation alloy of Comparative Example 1 under 15000psi pressure is shown in the table below:

[0098] Compared with the previous generation alloy, the corrosion-resistant alloy for deep-sea solenoid valve assembly equipment of this invention has a significant improvement in deformation under 15000psi pressure.

[0099] Although preferred embodiments of the invention have been shown and described, it is conceivable that those skilled in the art can devise various modifications to the invention within the spirit and scope of the appended claims.

Claims

1. A corrosion-resistant alloy, characterized in that, Raw materials including the following percentages by mass: C 0~0.11% and not 0, Si≤0.6% and not 0, Mn≤0.6% and not 0, P 0.006~0.015%, S 0.001~0.015%, Cr 19.5~23.5%, Mo 7.5~10.5%, Nb 3.05~4.25%, Ti≤0.5%, Al≤0.5%, B 0.001~0.01%, Zr 0.01~0.1%, Ce 0.001~0.05%, Fe≤5%, and Ni balance.

2. A method for preparing the corrosion-resistant alloy according to claim 1, characterized in that, Includes the following steps: First, the alloy raw materials are melted by vacuum induction and then cast into ingots. Then, they are electroslag remelted to obtain electroslag ingots. The electroslag ingots are then forged and subjected to solution treatment, deep cryogenic treatment, staged aging and plasma electrolytic oxidation in sequence.

3. The method for preparing the corrosion-resistant alloy according to claim 2, characterized in that, The vacuum induction melting process includes melting, refining and casting steps; During the melting process, the vacuum degree is ≤0.067 Pa; In the refining process, the vacuum degree is ≤1Pa, the temperature is 1620~1660℃, and the time is ≥30min; The temperature during the casting process is 1580~1600℃.

4. The method for preparing the corrosion-resistant alloy according to claim 2, characterized in that, In the electroslag remelting process, the protective slag includes a quaternary slag system, which comprises CaF2, Al2O3, CaO, and MgO; the mass ratio of CaF2, Al2O3, CaO, and MgO is 45:25:25:

5. In the electroslag remelting process, during the arc initiation and slag formation stage, the current is gradually increased from 1500A to 5000A, and the slag formation time is ≥40min; during the current increase stage, the current is gradually increased from 5000A to 7500A, taking 25min, and then the electrode is remelted at 7500~8000A for 180~240min; during the feeding stage, the current is gradually decreased to 2000A, and the feeding time is ≥30min.

5. The method for preparing the corrosion-resistant alloy according to claim 2, characterized in that, The forging process includes multi-stage forging. The multi-fire forging Includes the following processes: (1) Continuously heat up to 600℃ and keep warm for 1 hour; (2) Continuously heat up to 800℃ and keep warm for 1 hour. (3) Continuously heat up to the uniform heating temperature for forging, hold for 2~4 hours, and the uniform heating temperature is a constant temperature of 1100~1200℃.

6. The method for preparing the corrosion-resistant alloy according to claim 2, characterized in that, The solution treatment is carried out at a temperature of 1040~1150℃ for 1~2 hours.

7. The method for preparing the corrosion-resistant alloy according to claim 2, characterized in that, In the cryogenic process, the medium is liquid nitrogen, the temperature is -150~-196℃, and the holding time is 7.5~24.5h.

8. The method for preparing the corrosion-resistant alloy according to claim 2, characterized in that, In the phased aging process, the conditions for the first phase are: temperature of 700~740℃, holding time of 6~10h, furnace cooling to 650℃, and cooling rate ≤50℃ / h. In the phased aging process, the conditions for the second phase are: temperature of 630~670℃, heat preservation time of 18~22h, and air cooling to 10~30℃.

9. The method for preparing the corrosion-resistant alloy according to claim 2, characterized in that, The conditions for plasma electrolytic oxidation are as follows: the electrolyte includes a silicate-phosphate composite electrolyte, the pH of the electrolyte is 10-12, the pulse voltage is 400-600V, and the current density is 12-18A / dm³. 2 The time is 25~65 minutes.

10. The application of the corrosion-resistant alloy of claim 1 in deep-sea solenoid valve assembly equipment.

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