Duplex stainless steel propeller and casting method

Abstract

The invention relates to a casting method for a duplex stainless steel propeller. According to the method, a 3D printing sand mold is adopted to print a propeller sand mold cavity, and modeling is conducted; the method comprises the steps that SAF2507 duplex stainless steel is smelted into molten metal in an intermediate frequency furnace, pure nitrogen is blown into the molten metal for multiple times in the oxidation period and the reduction period of smelting in an AOD furnace, and the treated molten metal is obtained; the treated molten metal is poured into a propeller sand mold cavity; a casting is obtained after the casting is solidified and cooled, and the duplex stainless steel propeller is obtained after the casting is subjected to annealing and solution treatment again; wherein when the molten metal is poured into a propeller sand mold cavity, solidified and formed and then cooled to 800-1000 DEG C, mold dismantling and cleaning need to be carried out. The method is applied to machining and manufacturing of marine propellers made of SAF2507 duplex stainless steel, the manufacturing period is shortened, the manufacturing efficiency is improved, the defects of air holes and inclusions of castings are avoided, and the machining precision and performance of the propeller castings are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of ship propeller processing, and in particular relates to a duplex stainless steel propeller and a casting method. Background Art

[0002] Marine propellers are key components of ship propulsion systems, and their performance is directly related to the ship's navigation efficiency and safety. SAF2507 duplex stainless steel has become an ideal material for manufacturing marine propellers due to its excellent mechanical properties and corrosion resistance. However, the metallurgical structure of SAF2507 material is complex and its fluidity is poor. Especially in the casting process of thin-walled parts, it is prone to molding difficulties, which increases the difficulty of manufacturing. In addition, marine propellers are usually designed with complex geometric shapes, such as the shape of the spiral line and the curvature of the blades. These characteristics put higher requirements on the casting process.

[0003] Although the casting process has certain advantages in material forming, for high-performance materials such as SAF2507 duplex stainless steel, the traditional propeller casting process causes defects such as pores and inclusions in the castings, and there are problems such as low processing accuracy, long manufacturing cycle, and low efficiency, which cannot guarantee the performance and accuracy of the SAF2507 stainless steel propeller. Therefore, the traditional casting method cannot meet its high standards for accuracy and performance.

[0004] In order to overcome the problems in the prior art and improve the manufacturing quality of marine propellers, the present invention proposes a casting processing method for a duplex stainless steel marine propeller. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a duplex stainless steel propeller and a casting method, wherein the method can optimize the casting process in the prior art so that it can be applied to the processing and manufacturing of marine propellers using SAF2507 duplex stainless steel, shortening the production cycle, improving the production efficiency, and preventing the casting from having defects such as pores and inclusions, thereby improving the processing accuracy and performance of the propeller casting.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: The first implementation scheme provided by the present invention is to provide a method for casting a duplex stainless steel propeller. The method uses SAF2507 duplex stainless steel to cast a propeller, and comprises the following steps: The propeller sand mold cavity is printed and shaped using 3D printing sand molds; the 3D printing sand mold is used to achieve one-time accurate printing according to complex geometric shapes, reducing waste and unnecessary post-processing time and saving costs.

[0007] SAF2507 duplex stainless steel is melted into molten metal, and pure nitrogen is blown into the molten metal several times during the oxidation and reduction periods of the melting to obtain the treated molten metal; the purpose of blowing pure nitrogen into the molten metal is to control and optimize the chemical composition of the steel, especially the nitrogen content can improve the strength and corrosion resistance of the steel, help decarburization and refining of the molten steel, remove sulfur and other impurities in the molten steel, reduce oxidation of the molten steel, protect the alloy elements in the molten steel from excessive oxidation, thereby reducing burning. At the same time, the blowing of nitrogen also helps to remove gas and inclusions in the molten steel, improve the purity of the molten steel, reduce casting defects, and thus improve smelting efficiency, shorten smelting time, and reduce production costs.

[0008] The molten metal after the above treatment is poured into the propeller sand mold cavity. When the molten metal is poured into the propeller sand mold cavity and solidified and cooled to 800℃~1000℃, it is necessary to perform box cleaning to reduce the temperature difference of various parts of the propeller blades, thereby reducing the deformation of the propeller blades and ensuring the stability and performance of the casting. After solidification and cooling, the casting is obtained. After the casting is taken out of the propeller sand mold cavity, necessary trimming and cleaning procedures are performed to remove surface defects such as runners, risers, burrs, and oxide scales, so that the casting reaches the required appearance quality; then the propeller casting is taken out of the propeller sand mold cavity, and it is cut, cleaned, trimmed and other process treatments are performed to remove impurities such as oxide scales and residual sand on the surface of the casting, and ensure the requirements of geometric dimensions and surface quality. The casting is annealed and solution treated again to obtain a duplex stainless steel propeller.

[0009] Preferably, the percentage of N can be controlled to be between 0.14 and 0.35 by blowing pure nitrogen into the molten metal multiple times. Nitrogen can improve the strength and corrosion resistance of duplex stainless steel. Nitrogen can synergize with chromium and molybdenum in steel to enhance the material's resistance to pitting corrosion and stress corrosion cracking. The stirring action of nitrogen makes the nitrogen fully homogenized and alloyed in the molten metal.

[0010] Preferably, the obtained casting must be subjected to a reinforcement treatment before annealing and solution treatment. The deformation of the propeller blades after the reinforcement treatment is controlled to be 2.5mm to 3.5mm. This can effectively release stress without causing insufficient structural strength due to excessive deformation. The reinforcement treatment can improve the deformation problem of the propeller blades at high temperatures.

[0011] Preferably, before the metal liquid is introduced into pure nitrogen, ferrosilicon with a silicon mass percentage of ≤2, ferromanganese with a manganese mass percentage of ≤4, ferrochrome with a chromium mass percentage of 21-27, nickel plate with a nickel mass percentage of 4-9, and ferromolybdenum with a molybdenum mass percentage of 3-5 need to be added to the metal liquid in sequence.

[0012] Ferrosilicon improves the alloy's oxidation resistance and strength, ferromanganese enhances the alloy's strength and hardness, ferrochrome provides the alloy's corrosion resistance, nickel plate increases the alloy's toughness and corrosion resistance, and ferromolybdenum enhances the alloy's strength and heat resistance. Strict control of the addition of these elements is necessary to maintain the balance and stability of the alloy's properties.

[0013] Preferably, the molten metal liquid is poured into the propeller sand mold cavity at 1600℃~1620℃. At this temperature, the defects of pores and inclusions can be reduced, while ensuring the fluidity of the metal liquid, which is conducive to obtaining high-quality castings. The pouring time is controlled to be 10s~20s to ensure that the metal liquid can flow quickly and evenly when filling the propeller sand mold cavity, so as to avoid the metal liquid failing to completely fill the cavity due to the pouring time being too short, or the metal liquid temperature dropping too fast due to the casting time being too long, forming defects such as cold shut, pores and inclusions in the cavity. The metal liquid poured into the propeller sand mold cavity needs to be insulated for 2h~3h to ensure that the temperature gradient of the metal liquid is small during the solidification process, reduce the uneven shrinkage inside the casting, and reduce the risk of deformation and cracks. In addition, the insulation treatment also helps to reduce the cooling rate of the casting, so that the gas and inclusions in the metal liquid have more time to escape, and reduce the defects of pores and inclusions in the casting. By controlling the holding time, the microstructure and mechanical properties of the casting can be optimized and the overall quality of the casting can be improved.

[0014] Preferably, the casting is annealed at 550°C to 650°C to eliminate internal stress, improve the microstructure, reduce hardness, improve its plasticity and toughness, and improve processing performance. Annealing in the temperature range of 550°C to 650°C can effectively eliminate the internal stress of steel castings and welded parts. This temperature range is lower than the recrystallization temperature of steel. After heat preservation and cooling in the air, the brittleness of the material can be reduced and its plasticity and toughness can be improved. In addition, this temperature range also helps to reduce the hardness of the material, making it easier for subsequent processing and molding. After annealing, the casting is solution treated at 1050°C to 1150°C to eliminate the stress caused by hot and cold processing, ensure the full dissolution of the main strengthening phase, and obtain a suitable grain size to ensure the mechanical properties of the alloy. If the temperature of annealing or solution treatment is too high, the material may be overheated and the grains may be coarse, thereby reducing the mechanical properties of the material. If the temperature is too low, it may not be possible to fully eliminate the internal stress or dissolve the strengthening phase, resulting in insufficient improvement in the performance of the material. For solution treatment, if the temperature is too low, a uniform solid solution may not be obtained, which will affect the subsequent performance of the material.

[0015] Preferably, the SAF2507 duplex stainless steel is melted into molten metal at 1600° C. to 1660° C. Melting into molten metal at this temperature can reduce pores and inclusions in the casting and improve the internal quality of the casting.

[0016] Preferably, before casting by the casting method, a casting reduction is selected, and the casting reduction is 2.2%. Open pouring and bottom pouring are adopted during pouring, and open riser shrinkage is supplemented. Such operation can reduce pores and inclusions in the casting and improve the internal quality of the casting.

[0017] Preferably, the particle shape of the sand material in the 3D printing sand mold is round or oval, wherein the particle size D50 of the sand material is 170 μm, and D90 is 280 μm. Appropriate particle size distribution and particle shape can ensure the stability of the sand mold during the printing process, reduce the staggered layer phenomenon caused by uneven sand layers, and improve the mechanical properties, printing quality and reliability of the sand mold.

[0018] The second implementation scheme provided by the present invention is to provide a duplex stainless steel propeller prepared by a duplex stainless steel propeller casting method.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The duplex stainless steel propeller casting method provided by the present invention adopts 3D printing sand mold to print the propeller sand mold cavity, which can improve the production efficiency of the propeller sand mold cavity, reduce the debugging cost of the propeller sand mold cavity, realize the freedom of casting process design, and save the propeller sand mold cavity cost.

[0020] The present invention blows pure nitrogen into the molten metal multiple times during the oxidation period and the reduction period, and the molten metal is stirred by the pure nitrogen gas, so that the nitrogen element is fully homogenized and alloyed in the molten metal. Accompanied by the multiple blowing of pure nitrogen and PMI in the furnace (wherein (PMI is Process, Measurement, and Control Integration, i.e., process, measurement and control integration technology), the amount and pressure of nitrogen added are accurately measured and controlled, and the nitrogen content is accurately controlled, which can effectively reduce the pores and inclusions in the propeller casting, so as to obtain an ideal phase composition and microstructure, and improve the mechanical properties and corrosion resistance of the material. The nitriding treatment significantly improves the hardness, wear resistance and corrosion resistance of the material by forming a layer of hard nitride layer on the metal surface. The formation of these nitrides not only increases the surface hardness, but also generates residual compressive stress on the surface of the material, which helps to improve the fatigue strength and crack resistance of the material. At the same time, the nitriding layer improves the surface roughness, reduces the friction coefficient, and enhances the chemical reaction activity of the material, further improving the adhesion and corrosion resistance.

[0021] The casting is cooled to 800℃~1000℃ before annealing and solution treatment for box cleaning, which reduces the temperature difference between various parts of the propeller blades, helps to achieve uniform distribution of casting temperature, reduce the difference in cooling rate between different parts, thereby reducing internal stress and deformation of propeller blades, and further improves its precision and performance; the casting is annealed and solution treated to eliminate internal stress, improve microstructure, improve corrosion resistance, refine grains and optimize phase composition, further improving its precision and performance. This is because annealing helps to reduce the internal stress generated during casting and cooling and increase dimensional stability; solution treatment dissolves solute atoms in the solvent lattice through rapid cooling, improves the uniformity of the material, reduces grain boundary segregation, and improves the mechanical properties of the material. These heat treatment processes work together to make the casting show better comprehensive performance in subsequent processing and use.

[0022] 2. In the present invention, necessary tie bars are added to the casting before heat treatment, and the wall thickness of the tie bars and components is equal to improve the deformation of the blades at high temperatures. By adding tie bars, the casting can be reinforced and shaped in advance, and its free expansion at high temperatures can be limited, thereby reducing deformation. The use of tie bars can also help disperse and balance these internal stresses, reducing the risk of cracks in the casting due to stress concentration.

[0023] 3. In the present invention, before pure nitrogen is introduced into the molten metal, ferrosilicon, ferromanganese, ferrochrome, nickel plate and ferromolybdenum need to be added to the molten metal in sequence, and the added mass percentage of each element in ferrosilicon, ferromanganese, ferrochrome, nickel plate and ferromolybdenum can be controlled to further improve its accuracy and performance. Ferrosilicon and ferromanganese are commonly used deoxidizers, which can remove oxygen from the molten steel and improve the purity of the steel. Ferrochrome, nickel plate and ferromolybdenum are alloying elements that can adjust the chemical composition of steel and alloy the steel. These elements can improve the mechanical properties and corrosion resistance of steel.

[0024] 4. The casting provided in the present invention needs to be heat-insulated for about 2h to 3h. The molten metal is poured into the required cavity of the propeller at 1600℃~1620℃, and the pouring time is controlled to be 10s to 20s. Controlling at an appropriate smelting temperature can reduce production costs, ensure the quality and fluidity of the molten metal, and reduce the formation of pores and inclusions. The appropriate pouring temperature can ensure that the molten metal has good fluidity, reduce cold shut and insufficient pouring defects during the filling process, and at the same time, a higher pouring temperature can also help reduce the formation of pores. Controlling the pouring speed can ensure that the molten metal fills the mold evenly, avoid turbulence and air or slag retention caused by excessive pouring speed, and reduce porosity and other casting defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the SAF2507 stainless steel propeller casting process of the present invention; Figure 2This is a sample diagram after mechanical property testing of the present invention, wherein Figure 2 a is the sample mosaic image, Figure 2 b is the sample splitting diagram.

[0026] Figure 3 Is the metallographic diagram of the present invention; wherein Figure 3 a is a metallographic image magnified 50 times. Figure 3 b is a metallographic image magnified 100 times. DETAILED DESCRIPTION

[0027] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are conventional methods unless otherwise specified.

[0028] The inventors found that SAF2507 duplex stainless steel has excellent mechanical properties and chloride corrosion resistance due to its ultra-low carbon content, good phase ratio and high alloying element content. However, in traditional casting processes, SAF2507 duplex stainless steel castings are prone to defects such as pores and inclusions, which can cause precision and performance problems. Porosity is a common defect in castings, which reduces the effective bearing area of ​​the castings and reduces the strength and toughness of the castings. Porosity may also become a source of stress concentration, increasing the risk of fracture of castings during service. Excessive inclusion content is the main cause of cracks, and has a significant impact on the elongation, cross-sectional shrinkage, fatigue strength, etc. of SAF2507 stainless steel. Inclusions will destroy the continuity of the matrix, reduce the plasticity and toughness of the material, and increase the source of cracks, thereby affecting the overall performance and service life of the castings.

[0029] In view of the above problems, the present invention optimizes and improves the casting process, that is, by controlling the pouring temperature and cooling rate, adopting a special pouring system design, and improving the molding sand and riser system, which can effectively reduce the generation of pores and inclusions, thereby improving the precision and performance of SAF2507 duplex stainless steel castings, shortening the manufacturing cycle, and improving production efficiency.

[0030] Product structure analysis: The SAF2507 super duplex stainless steel propeller developed this time has an overall dimension of Ø621x239, a propeller shaft diameter of 110mm, a hyperbolic wall thickness gradient of the blade, the thinnest part is 1.9mm, and the net weight is 46kg. SAF2507 material has a melting point of 1350℃~1380℃, density: 7.8g / cm³, thermal conductivity: 13.7W / (m·K), linear expansion coefficient: 13.7um / m·℃, ferrite and austenite each account for about 45%~55% in the organization, with high strength and excellent corrosion resistance, but its metallurgical structure and organization are complex, and improper treatment may lead to problems such as intergranular corrosion and brittle fracture; the most important thing is that the material has poor fluidity and it is difficult to form thin walls. Propeller casting requires increasing and adjusting the pouring temperature and pouring speed. A higher pouring temperature can reduce the viscosity of the molten metal and reduce the involvement of gas, while increasing the solubility of gas in the molten metal and reducing the formation of pores. The appropriate pouring speed helps the molten metal to fill the cavity smoothly and reduce the generation of bubbles and inclusions, thereby improving the density and surface quality of the casting.

[0031] Sand mold printing and modeling: 3D printing sand molds are used to print the propeller sand mold cavity and perform modeling. The advantage of this technology is that it can quickly form the cavity required for the part, verify and adjust the process parameters in a timely manner, and shorten the debugging cycle. The forming process of the propeller requires high-precision mold design and manufacturing, and the propeller has a complex geometric shape and is difficult to process. With the help of 3D printing sand casting technology, production efficiency can be improved, debugging costs can be reduced, casting process design can be free, and molds can be saved. The use of 3D printing sand mold technology requires the selection and optimization of sand materials, and the analysis of sand material particle size distribution, particle shape, fluidity and other characteristics can improve the printing quality and reliability of sand molds.

[0032] Casting process formulation: The casting scale is selected as 2.2%, and an open pouring system and bottom pouring are used, with open riser for shrinkage compensation. After the parameters are formulated, the casting process simulation analysis is carried out through modeling to determine the best casting parameters, including pouring temperature, pouring speed, and cooling speed. Controlling the appropriate melting temperature can reduce production costs, ensure the quality and fluidity of the molten metal, and reduce the formation of pores and inclusions. Appropriate pouring temperature can ensure that the molten metal has good fluidity, reduce cold shut and insufficient pouring defects during the filling process, and at the same time, higher pouring temperature can also help reduce the formation of pores. Controlling the pouring speed can ensure that the molten metal fills the mold evenly, avoid turbulence and air or slag retention caused by excessive pouring speed, and reduce porosity and other casting defects.

[0033] Melting and pouring: Smelting is carried out in a medium frequency furnace. After the scrap steel is melted, ferrosilicon with a silicon mass percentage of ≤2, ferromanganese with a manganese mass percentage of ≤4, ferrochrome with a chromium mass percentage of 21~27, nickel plate with a nickel mass percentage of 4~9, and ferromolybdenum with a molybdenum mass percentage of 3~5 are added in sequence for preliminary melting of the metal. When the composition is adjusted to the required composition, it is transferred to the AOD furnace and refined by the AOD argon oxygen decarburization refining furnace. Under standard atmospheric pressure, pure nitrogen is blown into the molten steel liquid many times during the oxidation and reduction periods in the AOD furnace. By blowing pure nitrogen into the metal liquid many times, the N percentage can be controlled at 0.14~0.35. The stirring effect of the gas makes the nitrogen element fully homogenized and alloyed in the steel liquid, effectively reducing the carbon content in the steel liquid and inhibiting the oxidation of chromium. Accompanied by multiple gas blowing and PMI in the furnace, the nitrogen content in the alloy is precisely controlled to obtain the ideal phase composition and microstructure, and improve the mechanical properties and corrosion resistance of the material.

[0034] Cooling and solidification: According to the shape of the casting and the material properties, a temperature gradient is generated inside and outside the blade during the cooling process of the propeller. The temperature changes in different parts vary greatly, which will produce thermal stress and cause the shape of the blade to change. In this regard, the hot stripping box fast cooling method is adopted to minimize the temperature difference between various parts of the blade, thereby reducing blade deformation.

[0035] Demolding and cleaning: The casting is cooled to 800℃~1000℃ and then boxed and cleaned to avoid defects and ensure the stability and performance of the casting. It is taken out of the molding sand and necessary trimming and cleaning procedures are carried out. Surface defects such as runners, risers, burrs, oxide scales, etc. are removed to ensure that the casting meets the required appearance quality.

[0036] Cleaning and trimming: The propeller casting is taken out of the mold and subjected to processes such as cutting, cleaning and trimming to remove impurities such as oxide scale and residual sand on the surface of the casting and ensure the requirements for geometric dimensions and surface quality.

[0037] Heat treatment: Before heat treatment, necessary tie bars are added, and the wall thickness of tie bars and components is equal, which can improve the deformation of blades under high temperature. The results show that the deformation of blades is 2.5mm to 3.5mm after the tie bars are flattened. According to the heat treatment process requirements of SAF2507 stainless steel, the propeller castings are annealed and solution treated to improve their organization and performance.

[0038] The casting process of the SAF2507 stainless steel marine propeller disclosed in the present invention is described in detail below by way of specific embodiments.

[0039] Example 1 like Figure 1 As shown, a hot pressing method for a marine propeller of this embodiment comprises the following specific steps: S1. Use 3D printing sand mold manufacturing technology to manufacture casting molds; the use of 3D printing sand mold technology requires the selection and optimization of sand materials, and the analysis of sand material particle size distribution, particle shape, fluidity and other characteristics can improve the printing quality and reliability of sand molds; S2. Propeller manufacturing using casting technology; S201. The casting reduction is selected as 2.2%. An open pouring system, bottom pouring, and open riser are used to compensate for shrinkage. After the parameters are formulated, the casting process simulation analysis is carried out through modeling to determine the optimal casting parameters. The molten metal is controlled to be discharged from the furnace at 1600℃ and poured at 1600℃. The pouring time is controlled to be 10s.

[0040] S202, adopt medium frequency furnace smelting, after scrap steel is melted, add ferrosilicon, ferromanganese, ferrochrome, nickel plate, ferromolybdenum in turn, control the mass percentage of each element, among which Si≤2, Mn≤4, Cr is 21~27, Ni is 4~9, Mo is 3~5, and after the composition is adjusted to the required composition, transfer to AOD furnace, refine through AOD argon oxygen decarburization refining furnace, blow pure nitrogen into molten steel liquid many times during oxidation and reduction period in AOD furnace, blow pure nitrogen into molten metal liquid many times, and the percentage of N can be controlled at 0.14 by blowing pure nitrogen into molten metal many times, and the nitrogen element is fully homogenized and alloyed in molten steel through the stirring effect of gas. Accompanied by multiple blowing and PMI in furnace, the nitrogen content can be precisely controlled to obtain the ideal phase composition and microstructure, and improve the mechanical properties and corrosion resistance of the material.

[0041] S203. According to the casting shape and material properties, the method of hot stripping box rapid cooling is adopted to minimize the temperature difference of various parts of the blade, thereby reducing blade deformation.

[0042] The casting process proposed in this disclosure has the following advantages and characteristics: (1) Precise scale control: By selecting a casting scale of 2.2%, the dimensional accuracy of the propeller can be ensured during the manufacturing process, which is crucial to ensuring its performance in actual applications.

[0043] (2) Optimize casting quality: The open pouring system and bottom pouring design help the metal liquid to flow smoothly, reduce the generation of bubbles and inclusions, and thus improve the internal quality of the casting. The use of open riser shrinkage can effectively compensate for the shrinkage of the metal during solidification, reduce shrinkage cavities and shrinkage defects, and improve the integrity of the casting.

[0044] (3) Precise control of composition: The combination of medium frequency furnace melting and AOD furnace refining can accurately control the composition of molten steel, especially the nitrogen content, which is crucial to obtaining the ideal phase composition and microstructure. Blowing pure nitrogen into the AOD furnace not only helps to homogenize nitrogen, but also promotes the uniform distribution of alloying elements and improves the overall performance of the material.

[0045] (4) Ensure material properties: The use of hot stripping box rapid cooling can effectively control the cooling rate of the casting, reduce the temperature gradient, and thus reduce the risk of blade deformation and cracking.

[0046] After completing the above casting process, the following steps are performed: S3. After the casting is completed, the casting is demoulded, cleaned and heat treated; S301. Demolding: The casting is cooled to about 800℃ and then boxed and cleaned to avoid defects and ensure the stability and performance of the casting.

[0047] S302. Cleaning: Take it out of the molding sand and carry out necessary trimming and cleaning procedures. Remove surface defects such as runners, risers, burrs, oxide scales, etc., so that the castings can achieve the required appearance quality.

[0048] S303.Finishing: Remove the propeller casting from the mold and perform cutting, cleaning and trimming processes to remove impurities such as scale and residual sand on the surface of the casting and ensure that the geometric dimensions and surface quality requirements are met.

[0049] S304. Heat treatment: Add necessary tie rods. After the tie rods are leveled, the blade deformation is about 2.5mm. The casting is annealed and solution treated.

[0050] S4. Complete the acceptance work and obtain the finished product; use non-destructive testing, chemical analysis, metallographic microscope and other methods to conduct strict quality inspection and performance testing on the propeller castings to ensure that they meet the relevant standards and technical requirements.

[0051] Example 2 like Figure 1 As shown, a hot pressing method for a marine propeller of this embodiment comprises the following specific steps: S1. Use 3D printing sand mold manufacturing technology to manufacture casting molds; the use of 3D printing sand mold technology requires the selection and optimization of sand materials, and the analysis of sand material particle size distribution, particle shape, fluidity and other characteristics can improve the printing quality and reliability of sand molds; S2. Propeller manufacturing using casting technology; S201. The casting reduction is selected as 2.2%. An open pouring system, bottom pouring, and open riser are used to compensate for shrinkage. After the parameters are formulated, the casting process simulation analysis is carried out through modeling to determine the optimal casting parameters. The molten metal is controlled to be discharged from the furnace at 1650℃ and poured at 1600℃. The pouring time is controlled to be 15s.

[0052] S202, adopt medium frequency furnace smelting, after scrap steel is melted, add ferrosilicon, ferromanganese, ferrochrome, nickel plate, ferromolybdenum in turn, control the mass percentage of each element, among which Si≤2, Mn≤4, Cr is 21~27, Ni is 4~9, Mo is 3~5, and after the composition is adjusted to the required composition, transfer to AOD furnace, refine through AOD argon oxygen decarburization refining furnace, blow pure nitrogen into molten steel liquid many times during oxidation and reduction period in AOD furnace, blow pure nitrogen into molten metal liquid many times, and the percentage of N can be controlled at 0.30 by blowing pure nitrogen into molten metal many times, and the nitrogen element is fully homogenized and alloyed in molten steel through the stirring effect of gas. Accompanied by multiple blowing and PMI in furnace, the nitrogen content can be precisely controlled to obtain the ideal phase composition and microstructure, and improve the mechanical properties and corrosion resistance of the material.

[0053] S203. According to the casting shape and material properties, the method of hot stripping box rapid cooling is adopted to minimize the temperature difference of various parts of the blade, thereby reducing blade deformation.

[0054] After completing the above casting process, the following steps are performed: S3. After the casting is completed, the casting is demoulded, cleaned and heat treated; S301. Demolding: The casting is cooled to about 900℃ and then boxed and cleaned to avoid defects and ensure the stability and performance of the casting.

[0055] S302. Cleaning: Take it out of the molding sand and carry out necessary trimming and cleaning procedures. Remove surface defects such as runners, risers, burrs, oxide scales, etc., so that the castings can achieve the required appearance quality.

[0056] S303.Finishing: Remove the propeller casting from the mold and perform cutting, cleaning and trimming processes to remove impurities such as scale and residual sand on the surface of the casting and ensure that the geometric dimensions and surface quality requirements are met.

[0057] S304. Heat treatment: Add necessary tie rods. After the tie rods are leveled, the blade deformation is about 3.0 mm. The casting is annealed and solution treated.

[0058] S4. Complete the acceptance work and obtain the finished product; use non-destructive testing, chemical analysis, metallographic microscope and other methods to conduct strict quality inspection and performance testing on the propeller castings to ensure that they meet the relevant standards and technical requirements.

[0059] Example 3 like Figure 1 As shown, a hot pressing method for a marine propeller of this embodiment comprises the following specific steps: S1. Use 3D printing sand mold manufacturing technology to manufacture casting molds; the use of 3D printing sand mold technology requires the selection and optimization of sand materials, and the analysis of sand material particle size distribution, particle shape, fluidity and other characteristics can improve the printing quality and reliability of sand molds; S2. Propeller manufacturing using casting technology; S201. The casting reduction is selected as 2.2%. An open pouring system, bottom pouring, and open riser are used to compensate for shrinkage. After the parameters are formulated, the casting process simulation analysis is carried out through modeling to determine the optimal casting parameters. The molten metal is controlled to be discharged from the furnace at 1660℃ and poured at 1620℃. The pouring time is controlled to be 20s.

[0060] S202, adopt medium frequency furnace smelting, after scrap steel is melted, add ferrosilicon, ferromanganese, ferrochrome, nickel plate, ferromolybdenum in turn, control the mass percentage of each element, among which Si≤2, Mn≤4, Cr is 21~27, Ni is 4~9, Mo is 3~5, and after the composition is adjusted to the required composition, transfer to AOD furnace, refine through AOD argon oxygen decarburization refining furnace, blow pure nitrogen into molten steel liquid many times during oxidation and reduction period in AOD furnace, blow pure nitrogen into molten metal liquid many times, and the percentage of N can be controlled at 0.35 by blowing pure nitrogen into molten metal many times, and the nitrogen element is fully homogenized and alloyed in molten steel through the stirring effect of gas. Accompanied by multiple blowing and PMI in furnace, the nitrogen content can be precisely controlled to obtain ideal phase composition and microstructure, and improve the mechanical properties and corrosion resistance of materials.

[0061] S203. According to the casting shape and material properties, the method of hot stripping box rapid cooling is adopted to minimize the temperature difference of various parts of the blade, thereby reducing blade deformation.

[0062] After completing the above casting process, the following steps are performed: S3. After the casting is completed, the casting is demoulded, cleaned and heat treated; S301. Demolding: The casting is cooled to about 1000℃ and then boxed and cleaned to avoid defects and ensure the stability and performance of the casting.

[0063] S302. Cleaning: Take it out of the molding sand and carry out necessary trimming and cleaning procedures. Remove surface defects such as runners, risers, burrs, oxide scales, etc., so that the castings can achieve the required appearance quality.

[0064] S303.Finishing: Remove the propeller casting from the mold and perform cutting, cleaning and trimming processes to remove impurities such as scale and residual sand on the surface of the casting and ensure that the geometric dimensions and surface quality requirements are met.

[0065] S304. Heat treatment: Add necessary tie rods. After the tie rods are leveled, the blade deformation is about 3.5mm. The casting is annealed and solution treated.

[0066] S4. Complete the acceptance work and obtain the finished product; use non-destructive testing, chemical analysis, metallographic microscope and other methods to conduct strict quality inspection and performance testing on the propeller castings to ensure that they meet the relevant standards and technical requirements.

[0067] The above-mentioned Examples 1 to 3 can all prepare duplex stainless steel propellers. One of the examples, namely Example 1, is now selected for inspection and testing.

[0068] Inspection and testing: SAF2507 stainless steel castings are strictly inspected and tested for quality by mechanical property testing, chemical analysis, metallographic microscopy and other methods to ensure that they meet relevant standards and technical requirements.

[0069] (0) Mechanical properties testing The prepared propeller casting was tested for mechanical properties. Figure 2 In Figure 2 a and Figure 2 As shown in b.

[0070] Table 1 is the mechanical properties test table of SAF2507 stainless steel castings.

[0071] Table 1 Mechanical properties test The above test results show that the SAF2507 stainless steel obtained by this casting process has high tensile strength, which means that SAF2507 stainless steel is less likely to break when subjected to external forces, that is, it has higher strength and durability; the specified plastic extension strength is high, which means that SAF2507 stainless steel can withstand greater stress before permanent deformation begins, that is, it has a better elastic limit. This shows that the high reliability of SAF2507 stainless steel reduces the risk of breakage or failure, thereby improving the safety and stability of the overall structure.

[0072] (2) Chemical analysis and testing Table 2 is the chemical analysis test table of SAF2507 stainless steel castings, where Table 2 (a) is the multi-element content percentage test report; Table 2 (b) is the oxygen, nitrogen and hydrogen element content ppm test report.

[0073] Table 2 (a) Multi-element content percentage test report Table 2 (b) Oxygen, nitrogen and hydrogen content ppm test report Chemical composition analysis shows that oxygen and nitrogen exist in SAF2507 stainless steel samples at the ppm level, with higher nitrogen content, which may enhance hardness but may also increase brittleness. The hydrogen content is extremely low and has little effect on performance. The contents of carbon, silicon, manganese, phosphorus, sulfur, chromium, molybdenum, nickel, copper, vanadium and nitrogen are expressed in percentages, and these elements together determine the mechanical properties, corrosion resistance, machinability and heat resistance of the metal. High contents of chromium and molybdenum improve corrosion resistance and heat resistance, while manganese and nickel enhance strength and toughness. Phosphorus and sulfur may be beneficial at low levels, and the contents of carbon and nitrogen have a positive effect on hardness and strength. It shows that SAF2507 stainless steel has good strength and toughness.

[0074] (3) Metallographic testing like Figure 3 middle Figure 3 a and Figure 3 The metallographic examination of b shows that the material has a dual-phase structure of ferrite and austenite. This structure combines the high strength of ferrite and the high toughness of austenite, so that the material has excellent plasticity and corrosion resistance while maintaining good strength. In addition, the macroscopic grain size of the material is M-8.5, indicating that the grain size is small and the strength and toughness of the material are relatively good. At the same time, small grains can hinder the expansion of cracks, thereby improving the fracture toughness of the material. In addition, small grains can also improve the corrosion resistance and wear resistance of the material.

[0075] This method has been innovatively improved on the basis of the traditional casting process. By precisely controlling the key parameters such as temperature and speed in the casting process, combined with 3D printing sand mold technology and advanced melting and refining processes, the casting process of the propeller has been optimized. This not only improves the processing accuracy and production efficiency of the product, but also ensures the high-performance use requirements of the propeller in harsh marine environments, meeting the high standards of the modern shipbuilding industry for marine propellers.

[0076] In summary, the SAF2507 stainless steel castings obtained by this casting process not only have good strength and toughness, but also have excellent corrosion resistance and corrosion resistance.

[0077] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for casting a duplex stainless steel propeller, wherein the method uses SAF2507 duplex stainless steel to cast a propeller, characterized in that: The steps include: Use 3D printing sand mold to print the propeller sand mold cavity and perform modeling; SAF2507 duplex stainless steel is melted into molten metal, and pure nitrogen is blown into the molten metal multiple times during the oxidation period and the reduction period of the smelting to obtain a treated molten metal; The treated molten metal is poured into the propeller sand mold cavity; after solidification and cooling, a casting is obtained, and the casting is annealed and solution treated again to obtain a duplex stainless steel propeller; When the molten metal is poured into the propeller sand mold cavity and solidified and cooled to 800℃~1000℃, it needs to be boxed and cleaned.

2. A duplex stainless steel propeller casting method as claimed in claim 1, characterized in that: By blowing pure nitrogen into the molten metal multiple times, the N percentage can be controlled at 0.14~0.

35.

3. A duplex stainless steel propeller casting method as claimed in claim 1, characterized in that: The obtained casting must be subjected to a reinforcement treatment before annealing and solution treatment, and the deformation of the propeller blade after the reinforcement treatment is controlled to be 2.5 mm to 3.5 mm.

4. A duplex stainless steel propeller casting method as claimed in claim 1, characterized in that: Before pure nitrogen is introduced into the molten metal, ferrosilicon with a silicon mass percentage of ≤2, ferromanganese with a manganese mass percentage of ≤4, ferrochrome with a chromium mass percentage of 21-27, nickel plate with a nickel mass percentage of 4-9, and ferromolybdenum with a molybdenum mass percentage of 3-5 need to be added into the molten metal in sequence.

5. A duplex stainless steel propeller casting method as claimed in claim 1, characterized in that: The molten metal liquid is poured into the propeller sand mold cavity at 1600℃~1620℃, and the pouring time is controlled to be 10s~20s. The metal liquid after being poured into the propeller sand mold cavity needs to be kept warm for 2h~3h.

6. A duplex stainless steel propeller casting method as claimed in claim 1, characterized in that: The casting is annealed at 550°C~650°C, and after annealing, the casting is solution treated at 1050°C~1150°C.

7. A duplex stainless steel propeller casting method as claimed in claim 1, characterized in that: SAF2507 duplex stainless steel is melted into molten metal at 1600℃~1660℃.

8. A duplex stainless steel propeller casting method as claimed in claim 1, characterized in that: Before casting by the casting method, a casting reduction is selected, which is 2.2%. Open pouring and bottom pouring are used during pouring, and open risers are used to compensate for shrinkage.

9. A duplex stainless steel propeller casting method as claimed in claim 1, characterized in that: The particle shape of the sand material in the 3D printing sand mold is round or oval, wherein the particle size D50 of the sand material is 170 μm and D90 is 280 μm.

10. A duplex stainless steel propeller produced by the duplex stainless steel propeller casting method according to any one of claims 1 to 9.

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