Anti-cavitation wear-resistant nodular cast iron as well as preparation method and application thereof

Abstract

The invention relates to the technical field of metallurgical manufacturing, in particular to anti-cavitation wear-resistant nodular cast iron and a preparation method and application thereof.The preparation method comprises the following steps that S1, raw materials are smelted and subjected to heat preservation, and molten iron is obtained; s2, a desulfurizing agent is added into the molten iron for molten iron desulfurization treatment, and desulfurized molten iron is obtained; s3, a spheroidizing agent is added into the desulfurized iron liquid, collected slag is covered for a spheroidizing reaction, and spheroidized iron liquid is obtained; s4, a first nucleating agent is added into the spheroidized molten iron, then a second nucleating agent is added along with the flow, and inoculated molten iron is obtained; and S5, the inoculation iron liquid is subjected to pouring, secondary annealing and cooling in sequence, and the anti-cavitation wear-resistant nodular cast iron is obtained. The first nucleating agent is a Zr-Al-Si nucleating agent, and the second nucleating agent is a Ba-Sr-Si nucleating agent. The toughness, wear resistance and cavitation resistance of the nodular cast iron are remarkably improved.

Description

Technical Field

[0001] This application relates to the field of metallurgical manufacturing technology, and in particular to a cavitation-resistant and wear-resistant ductile iron, its preparation method, and its application. Background Technology

[0002] Ductile iron is made by spheroidizing and inoculating to obtain spheroidal graphite, which effectively improves the mechanical properties of cast iron, especially its plasticity and toughness, thus achieving higher strength than carbon steel. It is used as an excellent engineering material to replace carbon steel and alloy steel, and is widely used in important components such as crankshafts, gears, connecting rods, housings, and valves of internal combustion engines.

[0003] However, in high-speed fluid machinery (such as water pumps, turbines, ship propellers, and valves) and under conditions of strong erosion, the surfaces of components are prone to cavitation damage and wear. Cavitation is caused by changes in fluid pressure triggering the collapse of cavitation bubbles, generating microjets and shock waves, leading to fatigue spalling of the material surface; wear further exacerbates material loss. Traditional ductile iron is still insufficient in resisting the combined effects of cavitation and wear, and the graphite phase, carbide morphology, and toughness of ductile iron directly affect its durability. Summary of the Invention

[0004] To address the aforementioned problems, this application provides a cavitation-resistant and wear-resistant ductile iron, its preparation method, and its application.

[0005] This application provides a cavitation-resistant and wear-resistant ductile iron and its preparation method, which adopts the following technical solution: A method for preparing cavitation-resistant and wear-resistant ductile iron includes the following steps: S1: Melting and holding the raw materials to obtain molten iron; S2: Adding a desulfurizing agent to the molten iron for desulfurization treatment to obtain desulfurized molten iron; S3: Adding a spheroidizing agent to the desulfurized molten iron, covering and collecting slag to carry out a spheroidizing reaction to obtain spheroidized molten iron; S4: Adding a first inoculant to the spheroidized molten iron, and then adding a second inoculant in the flow to obtain inoculated molten iron; S5: Casting the inoculated molten iron sequentially, performing secondary annealing, and cooling to obtain cavitation-resistant and wear-resistant ductile iron; the first inoculant is a Zr-Al-Si inoculant, and the second inoculant is a Ba-Sr-Si inoculant.

[0006] By adopting the above technical solution, Zr in the first inoculant preferentially forms high-melting-point thermally stable fine compounds, which serve as highly efficient nucleation cores, significantly increasing the number of graphite nuclei and reducing the size and more uniform distribution of graphite spheres. Since coarse graphite and graphite agglomerates are the micro-regions most prone to cavitation impact and wear crack initiation, the fine and rounded graphite structure formed by Zr-Al-Si inoculation can effectively reduce the stress concentration at the matrix interface, thereby reducing the initial formation of cavitation pits and inhibiting early wear and spalling.

[0007] The second inoculant, with its long-lasting and slow-decaying Ba and Sr elements, can continuously inoculate graphite in the later stages of casting and in complex flow areas, preventing problems such as graphite degradation and localized white cast iron. By being added in-flow, it can stabilize and compensate for the fine graphite structure formed by the first inoculant, ensuring uniform graphite morphology and hardness across all parts of the casting. This avoids cavitation concentration and uneven wear caused by localized hardening or softening zones. Ultimately, without simply increasing hardness, it effectively reduces stress concentration and inhibits crack propagation, thereby significantly improving the material's toughness, wear resistance, and cavitation resistance.

[0008] Preferably, in step S1, the alloying elements are added together with the raw materials and participate in the smelting; the percentage of each alloying element added by mass of the raw materials is: nickel 1.5%-2.5%, chromium 0.8%-1.2%, molybdenum 0.3%-0.7%, and boron 0.001%-0.006%; and the boron is added by wetting with phenolic resin, and the amount of phenolic resin added accounts for 0.5%-3.0% of the amount of boron added.

[0009] By adopting the above technical solution, Ni promotes the formation of austenite, thereby improving the toughness of the material; Cr and Mo form carbides to enhance wear resistance; the addition of trace amounts of B helps to refine the grains, so that the material can obtain high wear resistance while maintaining sufficient toughness to resist cavitation impact and prevent brittle spalling.

[0010] After the addition of phenolic resin wetting agent B, a seamless "gas scavenging—carbon layer shield—carbon dissolution optimization" mechanism is implemented during the heating process of molten iron, providing phased synergistic protection. At 400-500℃, the phenolic resin initially decomposes, producing reducing gases such as CO and H2, forming a localized reducing atmosphere around the alloy particles. This removes initial free oxygen, protects easily oxidized elements like boron, and reduces instantaneous oxidation loss. Above 600℃, the material enters the carbonization stabilization stage, transforming into a stable carbonaceous layer. This layer acts as a physical barrier to isolate the molten iron, continuously consuming oxygen and adsorbing impurities, providing sustained protection for the alloy's melting and dissolution. In the spheroidization activation range of 1100-1500℃, the carbon layer dissolves into dissolved carbon, reducing the oxygen and sulfur activity of the molten iron. This ensures sufficient solid solution strengthening of boron and reduces magnesium loss during subsequent spheroidization treatment, improving spheroidization efficiency and stability. This mechanism not only ensures high yield of alloying elements but also optimizes the spheroidization incubation environment, laying the microstructure foundation for the material's excellent cavitation resistance and wear resistance.

[0011] If the amount of phenolic resin added is too low, insufficient reducing gas will lead to the burn-off of easily oxidized elements such as boron, resulting in a reduced yield and difficulty in forming grain boundary strengthening; it will also be difficult to form an effective carbon layer, leading to a decrease in the wear resistance and cavitation resistance of ductile iron. If the amount of phenolic resin added is too high, the large amount of free carbon released by its decomposition will lead to a high carbon equivalent in the molten iron, and the gas generated by excessive decomposition will be difficult to escape completely, easily forming dispersed porosity defects inside the casting; thus reducing the wear resistance and cavitation resistance of the material to a certain extent.

[0012] Preferably, in S2, the desulfurizing agent is a composite desulfurizing agent of CaO-Al2O3-MgO, and the dosage is 1.1%-2.0% of the total mass of the molten iron.

[0013] By adopting the above technical solution, desulfurization is carried out using a CaO-Al2O3-MgO composite desulfurizing agent. Through the synergistic desulfurization effect of CaO and MgO and the structural stabilizing effect of Al2O3, deep desulfurization of molten iron is achieved and sulfur reversion is inhibited. At the same time, the cleanliness of molten iron is improved, providing a low-sulfur, low-oxygen and stable molten iron environment for subsequent spheroidizing and inoculation processes, thereby improving the anti-cavitation and wear resistance of ductile iron.

[0014] If the amount of composite desulfurizing agent added is insufficient, the effective contact between the desulfurizing agent and the sulfur in the molten iron will be insufficient, resulting in an incomplete desulfurization reaction. The residual sulfur in the molten iron may react with the magnesium in the subsequent spheroidizing agent, making it difficult to consume the spheroidizing agent, resulting in poor graphite spheroidization, the appearance of flocculent or flaky graphite, reducing the spheroidization rate and the number of graphite spheroids, and thus affecting the toughness and cavitation resistance of cast iron.

[0015] If the amount of composite desulfurizing agent added is excessive, the excess desulfurizing agent cannot be completely floated to the surface and discharged, and may remain in the molten iron to form secondary inclusions. These inclusions will disrupt the uniform distribution of graphite spheres, thereby causing a decline in the material's mechanical properties and resistance to cavitation and wear.

[0016] Preferably, the composite desulfurizing agent comprises the following components in parts by weight: CaO: 60-65 parts, Al2O3: 25-30 parts, MgO: 10-15 parts.

[0017] By adopting the above technical solution, CaO is used as the main desulfurization component, MgO forms a complementary medium- and low-temperature desulfurization process, and Al2O3 regulates the slag phase characteristics, achieving deep desulfurization of molten iron and inhibiting re-sulfurization, thus significantly improving the cleanliness of molten iron. Simultaneously, the reaction is mild, causing no fluctuations in molten iron temperature, and is compatible with subsequent spheroidizing and inoculation processes, ensuring the quality of graphite spheroidization and the efficiency of alloying element action, ultimately improving the cavitation resistance and wear resistance of ductile iron.

[0018] Preferably, in S3, the spheroidizing agent is a Mg-RE-Ca composite spheroidizing agent, and the amount of the spheroidizing agent added accounts for 1.0%-1.4% of the desulfurized iron liquid.

[0019] By adopting the above technical solution, Mg is the core spheroidizing element; RE can strongly neutralize anti-spheroidizing elements, purify molten iron and refine the structure, significantly improving the purity and toughness of the material; Ca can slow down the reaction, increase the magnesium yield and make the process more stable. The combination of the three ensures that a high spheroidization rate and fine and round graphite matrix structure are obtained under complex working conditions, thereby improving the anti-cavitation and wear resistance of ductile iron.

[0020] If the amount of spheroidizing agent added is insufficient, it is difficult to fully neutralize anti-spheroidizing elements such as sulfur and oxygen in the molten iron, resulting in a decrease in the graphite spheroidization rate, which in turn leads to a decrease in the anti-cavitation and wear resistance of ductile iron. If the amount of spheroidizing agent added is excessive, Mg and RE will form a large number of brittle inclusions in the matrix, becoming the initiation source of cavitation cracks. Excessive spheroidizing elements will also increase the brittleness of the matrix, making the casting prone to brittle fracture under impact load.

[0021] Preferably, the composite spheroidizing agent, based on a total weight of 100 parts, comprises the following components in parts by weight: Mg: 4-8 parts, RE: 1-3 parts, Ca: 0.5-2 parts, with the balance being ferrosilicon and unavoidable impurities.

[0022] By employing the above technical solution, the Mg content ensures sufficient core magnesium element for spheroidization and strong reaction kinetics; RE can deeply purify molten iron, neutralize harmful trace elements, and effectively refine eutectic clusters and graphite spheres, effectively improving the toughness and cavitation resistance of the matrix. An appropriate amount of Ca plays a crucial "slow-release" and "fluxing" role in the reaction; it not only slows down the violent boiling of magnesium, improves magnesium absorption rate and processing stability, but also improves desulfurization and deoxidation effects. At this ratio, the three elements work together in the deeply desulfurized molten iron, thus laying the foundation for subsequent processing and improving the material's toughness and cavitation resistance.

[0023] Preferably, in step S4, the amount of the first inoculant added accounts for 0.2%-0.4% of the mass of the spheroidized iron liquid; the amount of the second inoculant added accounts for 0.05%-0.15% of the mass of the spheroidized iron liquid; the standing reaction time of the first inoculant and the spheroidized iron liquid is 2.0-4.0 min; and the addition of the second inoculant is completed simultaneously with the casting process.

[0024] By adopting the above technical solution, Zr-Al-Si inoculants usually have strong long-term inoculation and grain refinement effects. A standing time of 2-4 minutes allows the inoculant to melt into the molten iron, and active elements such as Zr and Al to fully diffuse, forming a large number of dispersed heterogeneous nucleation cores, which lays the foundation for subsequent graphite precipitation, thereby improving the material's resistance to cavitation and wear.

[0025] If the settling time is too short, the inoculant may not completely dissolve or be unevenly distributed, weakening the inoculant effect; if the settling time is too long, the inoculant effect will decline.

[0026] Ba-Sr-Si inoculant is an instantaneous inoculator, whose main purpose is to reactivate the molten iron at the last moment before pouring. During pouring, the Ba-Sr-Si inoculant is added in tandem with the pouring time, which maximizes the number of nucleation sites at the last moment before solidification, strongly refines the microstructure, resists inoculation fading, and improves the wear resistance and cavitation resistance of ductile iron.

[0027] A type of cavitation-resistant and wear-resistant ductile iron is prepared by a method for preparing cavitation-resistant and wear-resistant ductile iron.

[0028] A fluid mechanical flow-through component, wherein at least the critical friction or cavitation parts are made of cavitation-resistant and wear-resistant ductile iron; the fluid mechanical flow-through component is a valve core, a water pump impeller, a water turbine blade, or a ship propeller.

[0029] In summary, this application includes at least one of the following beneficial technical effects: This application employs a Zr-Al-Si and Ba-Sr-Si composite inoculation process: the former uses Zr elements to form high-melting-point fine compounds, which act as efficient nucleation cores, refine graphite spheres and distribute them evenly, reduce stress concentration at the matrix interface, and reduce the initiation of cavitation pits and wear spalling; the latter uses Ba and Sr elements with long inoculation time and slow decay, which can be added in the flow and continue to act in the later stage of casting and in complex parts, stabilize the refined graphite structure, ensure the uniformity of casting performance, and ultimately significantly improve the toughness, wear resistance and cavitation resistance of ductile iron without simply increasing hardness; This application achieves phased synergistic protection through a "gas purging - carbon layer shield - carbon dissolution optimization" linkage mechanism after the addition of phenolic resin wetting B. The first stage decomposes reducing gases to remove free oxygen, the second stage forms a carbon layer to isolate molten iron, and the third stage dissolves the carbon layer to reduce the oxygen and sulfur activity of molten iron, ensuring the recovery rate of alloying elements, optimizing the spheroidization inoculation environment, and laying the microstructure basis for the material's anti-cavitation and wear resistance. This application employs a CaO-Al2O3-MgO composite desulfurizing agent for desulfurization treatment. Through the synergistic desulfurization effect of CaO and MgO and the structural stabilizing effect of Al2O3, deep desulfurization of molten iron is achieved and sulfur reversion is inhibited. At the same time, the cleanliness of molten iron is improved, providing a low-sulfur, low-oxygen and stable molten iron environment for subsequent spheroidizing and inoculation processes. This improves the uniformity of the microstructure and the anti-cavitation and wear resistance of ductile iron. Detailed Implementation

[0031] The raw materials in this application include the following: Phenolic resin: Commercially available product with CAS number 9003-54-3 is used; Pig iron: Pig iron from Lingshou County Taizhen Mineral Products Processing Plant; Scrap steel: The scrap steel used is from Ningbo Development Zone Andrew Precision Casting Co., Ltd., and the scrap steel meets the technical requirements of "Recycled Steel Raw Materials" (GB / T39733-2024); Carbon raiser: Carbon raiser from Beijing Jingang Supply Chain Management Co., Ltd. is used; FeSi75 ferrosilicon inoculant: FeSi75 ferrosilicon inoculant customized by Beijing Jingang Supply Chain Management Co., Ltd. FeSiBa inoculant: FeSiBa ferrosilicon inoculant customized by Beijing Jingang Supply Chain Management Co., Ltd. Perlite slag: Perlite slag produced by Qingyuan New Building Materials Factory in Pingqiao District, Xinyang City.

[0032] Preparation Example 1 The preparation method of the composite desulfurizing agent includes the following steps: A1. Using aluminum hydroxide as raw material, it is placed in a high-temperature calcining kiln at a calcination temperature of 1500℃ and held for 2.5 hours. After calcination, the product is crushed and ground to obtain calcined alumina powder. Natural magnesite is used as raw material. After crushing, it is fed into a light-calcining kiln and calcined at 800℃ for 1.5 hours to obtain light-calcined magnesium oxide powder. Weigh out 62 kg of quicklime powder, 28 kg of calcined alumina powder, and 10 kg of lightly calcined magnesium oxide powder; grind the raw materials to 100-200 mesh to ensure uniform particle size and obtain pretreated powder; A2. Place the three pretreated powders into a conical double-helix mixer, set the speed to 25 r / min, mix for 18 min, add 4% water glass as a binder, and stir until it becomes plastic; put it into a hemispherical mold (mold cavity diameter is 15 mm, cavity depth is 8 mm), apply 18 MPa pressure to press it into a spherical blank with a diameter of 15 mm, hold the pressure for 2.5 min, and obtain the blank; A3. Place the billet into a rotary kiln, heat it to 1050℃ and hold it for 2.5 hours for calcination. After cooling in the kiln, crush it and sieve it to a particle size of 8~12mm to obtain the composite desulfurizing agent CaO-Al2O3-MgO.

[0033] Preparation Example 2 The preparation method of the composite spheroidizing agent includes the following steps: B1. Weigh 6 kg of magnesium, 2 kg of Ce-La rare earth alloy, 1.2 kg of calcium, and 90.8 kg of ferrosilicon, crush them to a particle size of 35 mm, and obtain the pretreated raw materials; B2. The pretreated ferrosilicon, Ce-La rare earth alloy, calcium, and magnesium are sequentially added to a vacuum induction melting furnace for melting. The temperature is raised to 800℃ and held for 35 minutes until completely melted and mixed. After casting, crushing and sieving, Mg-RE-Ca composite spheroidizing agent with a particle size of 1-5mm can be obtained.

[0034] Preparation Example 3 The preparation method of the first progesterone includes the following steps: C1. Weigh 12 kg of sponge zirconium powder, 6 kg of electrolytic aluminum powder, and 82 kg of industrial silicon powder. Put the three powders into a planetary ball mill, use anhydrous ethanol as the medium, zirconium oxide as the grinding balls, the ball-to-material ratio is 3:1, the rotation speed is 250 r / min, and after ball milling for 2.5 h, dry at 80℃ to obtain dried powder. C2. The dried powder is loaded into a cylindrical mold (mold cavity diameter 20mm, height 30mm), and a pressure of 250MPa is applied to press it into a cylindrical blank. The pressure is held for 3 minutes to obtain the blank. C3. Place the billet into an atmosphere sintering furnace, heat it to 1150℃ under an argon atmosphere, hold it at that temperature for 5 hours for sintering, and then cool it with the furnace before crushing and sieving it to a particle size of 0.5~3mm to obtain the first inoculant Zr-Al-Si.

[0035] Preparation Example 4 The preparation method of the second progesterone includes the following steps: D1. Weigh 86 kg of silicon blocks, 10 kg of barium blocks, and 4 kg of strontium blocks; crush them to a particle size of 30-50 mm to obtain the pretreated raw materials; D2. The pretreated silicon block, barium block, and strontium block are sequentially added to a vacuum intermediate frequency melting furnace for melting, and the furnace is evacuated to a vacuum level of 3×10⁻⁶. -2 Pa, heat to 1500℃, hold for 25 minutes to ensure that the raw materials are completely melted and uniformly mixed to obtain molten alloy liquid; D3. The molten alloy liquid is introduced into a high-speed copper roller at 3500 r / min for rapid cooling into a thin strip. After crushing, it is sieved to a particle size of 0.2~1 mm to obtain the second inoculant Ba-Sr-Si.

[0036] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0037] Example 1 A cavitation-resistant and wear-resistant ductile iron includes the following steps: S1: Add 350kg of pig iron, 150kg of scrap steel and 50kg of carbon raiser as raw materials to a medium frequency induction furnace for smelting, heat to 1520℃ and hold, stir thoroughly and hold for 10 minutes to obtain molten iron; S2: Transfer 500 kg of the molten iron into a pretreatment package, add 7.5 kg of CaO-Al2O3-MgO composite desulfurizing agent obtained from Preparation Example 1, stir with argon gas for 3 min, remove slag, and obtain 490 kg of desulfurized molten iron. S3: Transfer 490 kg of desulfurized molten iron into a dam-type ladle, add 5.9 kg of Mg-RE-Ca composite spheroidizing agent obtained from Preparation Example 2, cover with 0.5 kg of perlite slag, control the spheroidizing reaction time to 2.5 min, remove the floating slag after the reaction, and obtain 490 kg of spheroidized molten iron. S4: Add 1.5 kg of Zr-Al-Si inoculant obtained from Preparation Example 3 to the spheroidized iron melt, let it stand for 3 min, and then add 0.5 kg of Ba-Sr-Si inoculant obtained from Preparation Example 4 during the casting process to obtain the inoculated iron melt; S5: The inoculated iron molten metal is poured into the resin sand mold of the water pump impeller at 1390±10℃ to obtain the water pump impeller casting; the water pump impeller casting is subjected to a second annealing heat treatment: first, the temperature is raised to 920℃ and held for 2 hours, then furnace cooled to 750℃; then the temperature is raised to 880℃ and held for 1.5 hours, then furnace cooled to 500℃ and air cooled; finally, the anti-cavitation wear-resistant ball ink pump impeller casting is obtained.

[0038] Comparative Examples 1-3 Comparative Example 1 was prepared using the same method as in Example 1, but with Zr-Al-Si inoculant replaced by FeSi75 ferrosilicon inoculant and Ba-Sr-Si inoculant replaced by FeSiBa inoculant, while all other conditions remained unchanged.

[0039] Comparative Example 2 was prepared using the same method as in Example 1, but only Zr-Al-Si inoculation was used, without in-flow inoculation, and all other conditions remained unchanged.

[0040] Comparative Example 3 was prepared using the same method as in Example 1, but only Ba-Sr-Si inoculation was used, without long-term inoculation, and all other conditions remained unchanged.

[0041] The following performance tests were conducted on the anti-cavitation and wear-resistant ductile iron of Example 1 and Comparative Examples 1-3. The test results are shown in Table 1.

[0042] Performance testing: (1) Impact toughness The test was conducted in accordance with GB / T229-2020, Charpy pendulum impact test method for metallic materials, and the specimens were unnotched specimens.

[0043] (2) Abrasion resistance Wear tests were conducted on the composite liner using the following method: An MLG-130 dry abrasive rubber wheel testing machine was used to simulate the working conditions. The rolling abrasive wear environment consists of linear contact friction pairs and the irregular action of loose abrasive particles on the worn material, primarily causing plastic deformation and fatigue wear. Furthermore, the abrasive wear may lead to changes in the material's microstructure. The changes in wear before and after wear were statistically compared to determine the sample's wear weight loss. The specific parameters of the testing machine are as follows: maximum load 130 N, rubber wheel rotation direction: clockwise, rubber wheel speed 100 r / min, rubber wheel diameter 228.6 mm, rubber wheel hardness 60 HD, sample size 57 × 25.5 × 12 mm. 3 The pre-wear rate is 1000 rpm to eliminate the influence of surface stress.

[0044] (3) Cavitation test The test was conducted according to the vibration cavitation test method in GB / T6383-2024, and the solution was a simulated seawater solution.

[0045] Table 1. Performance test results of anti-cavitation and wear-resistant ductile iron in Examples 1 and Comparative Examples 1-3

[0046] Referring to Table 1, comparing Example 1 and Comparative Examples 1-3, it can be seen that in Example 1, a Zr-Al-Si first inoculant was first added to the spheroidized iron melt, followed by a Ba-Sr-Si second inoculant added in the flow. This composite inoculation process is key to obtaining ductile iron with high toughness and excellent cavitation resistance and wear resistance. Its function is to significantly refine and improve the morphology of graphite spheres and increase their number, thereby optimizing the material's microstructure. Using ordinary FeSi75 and FeSiBa inoculants, all properties decreased, demonstrating that the special inoculants containing Zr, Al, Ba, and Sr in this invention have unique advantages in promoting graphite nucleation and refining the microstructure, but none can achieve the synergistic effect of composite inoculation.

[0047] Example 2-3 In Example 2, based on the preparation method of Example 1, 10 kg of nickel, 8.3 kg of chromium, 4.2 kg of ferromolybdenum and 75 g of boron were added together with the raw materials and smelted in S1, while the other conditions remained unchanged.

[0048] In Example 3, based on the preparation method of Example 2, 1.1 kg of phenolic resin was melted at 60-70°C, and 75 g of boron powder was added in three batches while stirring. After cooling and pulverizing, boron coated with phenolic resin was obtained. The boron coated with phenolic resin was added along with nickel, chromium, and ferromolybdenum and smelted together, while the other conditions remained unchanged.

[0049] The anti-cavitation and wear-resistant ductile iron of Examples 2-3 were subjected to the following performance test, and the test results are shown in Table 2.

[0050] Table 2 Performance Test Results of Anti-Cavitation and Wear-Resistant Ductile Iron in Examples 1-3

[0051] Referring to Table 2, comparing Examples 1-3, it can be seen that Example 3 has the best overall performance. Because it adds a multi-element alloy of nickel, chromium, molybdenum and boron and the boron is coated with phenolic resin, the alloying elements diffuse evenly, so that the material can obtain high wear resistance while maintaining sufficient toughness to resist cavitation impact and prevent brittle spalling. In Example 2, the boron is not coated and is easy to oxidize, resulting in uneven distribution, which leads to a decrease in impact toughness and fails to fully exert the strengthening effect.

[0052] Examples 4-8 Example 4 is based on the preparation method of Example 1, but the CaO-Al2O3-MgO composite desulfurizer is replaced with an equal amount of CaC2-CaO, and the other conditions remain unchanged. The specific adjustments are shown in Table 3.

[0053] Examples 4-8 are based on the preparation method of Example 1, but the amount of composite desulfurizing agent added is adjusted, as shown in Table 3.

[0054] The anti-cavitation and wear-resistant ductile irons of Examples 4-8 were subjected to the above performance tests, and the test results are shown in Table 3.

[0055] Table 3 Performance test results for desulfurizer dosage in Examples 1 and 4-8

[0056] Referring to Table 3, a comparison of Examples 1 and 4-8 shows that the performance of ductile iron is optimal when the amount of desulfurizing agent added is 5.5-10.0 kg. This is because this dosage range can achieve a precise balance between desulfurization effect and molten iron purity: on the one hand, the desulfurizing agent in this range can fully contact and react with sulfur in the molten iron, effectively reducing the residual sulfur content and avoiding ineffective reaction between residual sulfur and magnesium in the spheroidizing agent, ensuring that the spheroidizing agent plays an efficient role and promoting the uniform and dense formation of graphite spheres; on the other hand, the desulfurizing agent at this dosage can fully float and be discharged after reaction, without incomplete desulfurization due to insufficient dosage or secondary inclusions due to excessive dosage, thus laying the foundation for the formation of excellent matrix structure in ductile iron, and ultimately enabling the material to achieve a better level of mechanical properties and anti-cavitation and wear resistance.

[0057] Examples 9-10 Examples 9-10 are based on the preparation method of Example 1, but the dosage of each component of the composite desulfurizing agent is adjusted, as shown in Table 4.

[0058] The anti-cavitation and wear-resistant ductile iron of Examples 9-10 were subjected to the above performance test, and the test results are shown in Table 4.

[0059] Table 4. Raw material list and performance test table for the composite desulfurizers in Examples 1 and 9-10.

[0060] Referring to Table 4, a comparison of Examples 1 and 9-10 shows that when the CaO content in the composite desulfurizing agent is 60-65 kg, the Al2O3 content is 25-30 kg, and the MgO content is 10-15 kg, the prepared ductile iron can possess good spheroidization effect, mechanical properties, and anti-cavitation and wear-resistant properties. Among these, the composition ratio of Example 1 is optimal. Under this ratio, CaO acts as the main desulfurization component, undertaking the core desulfurization function; MgO forms a complementary effect for medium- and low-temperature desulfurization; and Al2O3 regulates the fluidity and stability of the slag phase. The three components work synergistically to achieve deep desulfurization of the molten iron and effectively inhibit re-sulfurization, significantly improving the cleanliness of the molten iron. At the same time, the desulfurization reaction under this composition ratio is mild and will not cause large fluctuations in the temperature of the molten iron. It can be well adapted to the subsequent spheroidization and inoculation processes, ensuring the quality of graphite spheroidization and the efficiency of alloying elements, ultimately achieving the optimal balance of anti-cavitation and wear-resistant properties, mechanical properties, and batch stability of ductile iron.

[0061] Examples 11-14 Examples 11-14 are based on the preparation method of Example 1, but the amount of spheroidizing agent added is adjusted, as shown in Table 5.

[0062] The anti-cavitation and wear-resistant ductile irons of Examples 1 and 11-14 were subjected to the above performance test, and the test results are shown in Table 5.

[0063] Table 5 Performance test results for the amount of spheroidizing agent added in Examples 1 and 11-14

[0064] Referring to Table 5, a comparison of Examples 1 and 11-14 shows that as the amount of spheroidizing agent increases, the toughness of ductile iron gradually decreases, while its cavitation resistance and wear resistance improve. Considering the trends of both properties, the optimal amount of spheroidizing agent is between 4.9% and 6.9% of the molten iron mass, with 5.9% being the optimal value. Within this range, sufficient spheroidization and cavitation resistance can be ensured, while controlling the formation of brittle inclusions and avoiding excessive reduction in toughness. If the amount added is too low, the residual Mg content in the molten iron is insufficient, failing to effectively neutralize anti-spheroidizing elements such as sulfur and oxygen, leading to a decrease in graphite spheroidization rate and reduced cavitation resistance and wear resistance. Conversely, if excessive amounts are added, excess Mg and RE easily form brittle inclusions, becoming the origin of cavitation cracks, while also increasing the brittleness of the matrix, making the casting prone to fracture under impact.

[0065] Examples 15-18 Examples 15-18 are based on the preparation method of Example 1, with adjustments made to the amount of each component of the spheroidizing agent, as shown in Table 6.

[0066] The anti-cavitation and wear-resistant ductile irons of Examples 15-18 were subjected to the above performance tests, and the test results are shown in Table 6.

[0067] Table 6 Performance test results of spheroidizing agent by weight in Examples 1 and 15-18.

[0068] Referring to Table 6, a comparison of Examples 1 and 15-18 shows that when the spheroidizing agent contains 4-8 kg of Mg, 1-3 kg of RE, and 0.5-2 kg of MgO, the prepared ductile iron exhibits both good toughness and cavitation resistance. The composition ratio in Example 1 is optimal because the high magnesium content ensures sufficient spheroidizing kinetics, sufficient rare earth elements refine the microstructure and purify the molten iron, and an appropriate amount of calcium acts as a slow-release and fluxing agent. The synergistic effect of these three elements stabilizes the residual magnesium and rare earth elements within the optimal range, laying the foundation for obtaining excellent spheroidized microstructure and comprehensive properties, thus achieving optimal toughness and cavitation resistance in the material.

[0069] Examples 19-22 Examples 19-22 are based on the preparation method of Example 1, with adjustments made to the amount of the first and second inoculants added, as well as the standing reaction time of the first inoculant and the spheroidized iron liquid. The specific adjustments are shown in Table 7.

[0070] The anti-cavitation and wear-resistant ductile irons of Examples 19-22 were subjected to the above performance tests, and the test results are shown in Table 1.

[0071] Table 7 Performance Test Table of First and Second Inoculants Added and Standing Reaction Time in Examples 1 and 19-22

[0072] Referring to Table 7, comparing Examples 1 and 19-22, it can be seen that when the amount of the first inoculant added is 1.0-2.0, the amount of the second inoculant added is 0.25-0.73, and the reaction standing time of the first inoculant is 2.0-4.0 min, the prepared ductile iron can have both good anti-cavitation and wear-resistant properties. Among them, Example 1 is the best. The appropriate amount of Zr-Al-Si inoculant can be completely melted and uniformly diffused within a sufficient standing time, thereby forming a dispersed and stable heterogeneous nucleation core in the molten iron, laying the foundation for the uniformity and refinement of the overall structure of the casting. At the same time, the addition of an appropriate amount of Ba-Sr-Si for in-flow instantaneous inoculation can activate the nucleation potential before solidification, effectively inhibit inoculation decline, maximize the number of nucleation cores, strongly refine the structure, and resist inoculation decline, thus making the cavitation wear resistance of ductile iron reach the best balance and the best comprehensive performance.

[0073] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing anti-cavitation and wear-resistant ductile iron, characterized in that, Includes the following steps: S1: Melt the raw materials and keep them at a constant temperature to obtain molten iron; S2: Add a desulfurizing agent to the molten iron to perform desulfurization treatment and obtain desulfurized molten iron; S3: Add a spheroidizing agent to the desulfurized molten iron, cover the slag and carry out the spheroidizing reaction to obtain spheroidized molten iron; S4: Add the first inoculant to the spheroidized iron melt, and then add the second inoculant in the flow to obtain the inoculated iron melt; S5: The inoculated molten iron is poured and annealed twice in sequence, and then cooled to obtain anti-cavitation wear-resistant ductile iron; The first inoculant is a Zr-Al-Si inoculant, and the second inoculant is a Ba-Sr-Si inoculant.

2. The method for preparing anti-cavitation wear-resistant ductile iron according to claim 1, characterized in that, In S1, alloying elements are added along with the raw materials and participate in the smelting process; the percentage of each alloying element by mass of the raw materials is as follows: nickel 1.5%-2.5%, chromium 0.8%-1.2%, molybdenum 0.3%-0.7%, and boron 0.001%-0.006%; and the boron is added by wetting with phenolic resin, and the amount of phenolic resin added accounts for 0.5%-3.0% of the boron added.

3. The method for preparing anti-cavitation and wear-resistant ductile iron according to claim 1, characterized in that, In S2, the desulfurizing agent is a composite desulfurizing agent of CaO-Al2O3-MgO, and the dosage is 1.1%-2.0% of the total mass of the molten iron.

4. The method for preparing anti-cavitation wear-resistant ductile iron according to claim 3, characterized in that, The composite desulfurizing agent comprises the following components in parts by weight: CaO: 60-65 parts, Al2O3: 25-30 parts, MgO: 10-15 parts.

5. The method for preparing anti-cavitation wear-resistant ductile iron according to claim 1, characterized in that, In S3, the spheroidizing agent is a Mg-RE-Ca composite spheroidizing agent, and the amount of the spheroidizing agent added accounts for 1.0%-1.4% of the desulfurized iron liquid.

6. The method for preparing anti-cavitation wear-resistant ductile iron according to claim 5, characterized in that, The composite spheroidizing agent, based on a total weight of 100 parts, comprises the following components in parts by weight: Mg: 4-8 parts, RE: 1-3 parts, Ca: 0.5-2 parts, with the balance being ferrosilicon and unavoidable impurities.

7. The method for preparing anti-cavitation wear-resistant ductile iron according to claim 1, characterized in that, In S4, the amount of the first inoculant added accounts for 0.2%-0.4% of the mass of the spheroidized iron liquid; the amount of the second inoculant added accounts for 0.05%-0.15% of the mass of the spheroidized iron liquid; the standing reaction time of the first inoculant is 2.0-4.0 min; the addition of the second inoculant is completed simultaneously with the casting process.

8. A type of cavitation-resistant and wear-resistant ductile iron, characterized in that, It is prepared by the method for preparing anti-cavitation wear-resistant ductile iron according to any one of claims 1-7.

9. A fluid mechanical flow-through component, characterized in that, At least the critical friction or cavitation parts are made of the cavitation-resistant and wear-resistant ductile iron as described in claim 8; the fluid machinery flow-through parts are valve cores, water pump impellers, water turbine blades or ship propellers.

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