Production process of nodular cast iron and application of nodular cast iron in wind power casting

Abstract

The invention discloses a production process of nodular cast iron and application of the nodular cast iron in wind power castings, and belongs to the technical field of casting. The production process of the nodular cast iron comprises the following steps: S1, preparing materials: 40-60% of pig iron, 10-20% of foundry returns and 10-30% of waste steel; s2, smelting: jointly smelting the pig iron, the scrap steel and the foundry returns into molten iron; s3, pretreatment is conducted, specifically, components of the molten iron are adjusted, and a nickel source is added; a nodulizer, a covering agent and alloy antimony are placed at the bottom of a casting ladle in advance, the covering agent is laid on the surface of the nodulizer, and then the molten iron adjusted in the step S3 is poured into the casting ladle; s5, pouring is conducted, specifically, the molten iron obtained after spheroidizing inoculation treatment in the step S4 is subjected to slagging-off and then poured into a casting mold, and a stream inoculant is added in the pouring process; s6, cooling: after the pouring is finished, slowly cooling to below 400 DEG C in the casting mold, and removing a casting from the casting mold; and S7, heat treatment, wherein the casting is loaded into an annealing furnace to be subjected to three-stage annealing, and the nodular cast iron is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to a production process of nodular cast iron and its application in wind power castings. BACKGROUND

[0002] With the growing global demand for renewable energy, wind energy as a renewable, pollution-free clean energy, its importance is increasingly prominent. Wind energy not only helps to reduce carbon emissions, but also promotes the transformation of energy consumption structure, as one of the green and environmentally friendly new energy. Countries around the world have increased their attention to wind energy development, making the world's wind power industry develop rapidly.

[0003] However, wind power equipment is usually built on the sea or in the desert and other windy areas, and the climate conditions in these areas are harsh, which puts higher requirements on the nodular cast iron parts used in wind power equipment. Especially considering the wide north-south region in China, the temperature difference is large, and the industry competition intensifies, leading to the trend of light weight and large size of wind turbines, which makes the requirements for wind power castings more and more strict. In order to ensure that the unit can operate stably in an environment of-20℃ or even lower to-40℃, the castings must have excellent yield strength and low-temperature impact toughness.

[0004] Therefore, the standard of GB / T-25390-2024 Wind Power Generation System Wind Turbine Generator Nodular Cast Iron Parts has added material standards such as QT400-18L-1 and -2 to meet the harsh environmental requirements. Among them, QT400-18L nodular cast iron material is a material that has been widely included in the national standard, and its impact requirement is (-20℃); and QT400-18L-1 and -2 need to meet the requirements of the material in tensile properties and impact performance at lower temperatures (such as-30℃ or-40℃), and the impact value needs to be consistent with QT400-18L at (-20℃).

[0005] Compared with ordinary nodular castings, the process of producing low-temperature impact-resistant nodular castings is more complex, which puts higher requirements on the selection of pig iron, scrap steel, nodularizing agent and inoculant, the precise control of chemical composition, especially the adjustment of C and Si content, and the heat treatment process. Therefore, how to improve the yield strength and low-temperature impact resistance has become one of the key problems in current research. SUMMARY

[0006] The purpose of the present application is to provide a production process of nodular cast iron and its application in wind power castings to solve the technical problems mentioned in the background.

[0007] The technical solution to achieve the purpose of the present application is: In a first aspect, the present application provides a production process of nodular cast iron, comprising the following steps: S1. Ingredients: 40~60% pig iron, 10~20% recycled material, 10~30% scrap steel; S2. Smelting: Melting pig iron, scrap steel, and recycled materials together into molten iron; S3. Pretreatment: Adding pretreatment agents and nickel sources to adjust the composition of molten iron; the pretreatment process refers to the process of adding pretreatment agents before spheroidizing to stably control the amount of w(O) and w(S) in molten iron at a low level, providing good conditions for spheroidizing. At the same time, the reaction products of the pretreatment agents can become stable nucleation particles and nucleation cores of graphite in eutectic transformation.

[0008] S4. Spheroidizing and inoculation treatment: Place spheroidizing agent, covering agent and antimony alloy at the bottom of the ladle in advance. Spread the covering agent on the surface of the spheroidizing agent. Then pour the molten iron adjusted in step S3 into the ladle. At the same time, add an inoculant once when the volume of molten iron is close to 2 / 3 of the ladle. S5. Pouring: After removing slag from the molten iron after the spheroidizing inoculation treatment in step S4, pour it into the mold. During the pouring process, add a flow-inoculating agent. S6. Cooling: After pouring, slowly cool the casting in the mold to below 400°C, and remove the casting from the mold; S7. Heat treatment: The casting is placed in an annealing furnace for two-stage low-temperature annealing.

[0009] Furthermore, the composition of the ductile iron is as follows: C: 3.75~3.85wt%, Si: 1.95~2.05wt%, Mn: ≤0.15wt%, P: ≤0.035wt%, S: 0.006~0.012wt%, Mg: 0.030~0.045wt%, Sb: 0.003~0.005wt%, B: ≤0.001wt%, Ni: 0.49~0.88wt%, with the remainder being Fe and impurities introduced during the preparation process.

[0010] Carbon is one of the five basic elements in ductile iron and has a significant impact on material properties. Carbon promotes graphitization, reduces the tendency for white iron formation, increases ferrite content, and improves magnesium absorption, thus facilitating the spheroidization, refinement, and rounding of graphite. Furthermore, carbon can slightly lower the brittle transition temperature and increase volume expansion. However, when the carbon content exceeds the eutectic composition, graphite floating can easily occur, affecting casting quality. For ferritic ductile iron, the carbon content mainly affects its mechanical properties by influencing the number, diameter, and roundness of graphite spheres. With increasing carbon content, hardness and tensile strength gradually decrease, and yield strength also slightly decreases. This is mainly due to the increased number of graphite spheres, leading to a reduction in the effective load-bearing area in the metal matrix. However, when the carbon content is high, i.e., the carbon mass fraction exceeds 3.2%, the impact toughness improves. Therefore, this invention controls the carbon content between 3.75 and 3.85 wt% to ensure that the castings have good mechanical and casting properties.

[0011] Silicon is a solid solution strengthening agent for ferrite, and adding silicon can improve tensile strength and yield strength. However, silicon also increases the brittle transition temperature of ductile iron. For every 0.1% increase in Si, the brittle transition temperature rises by 5.5~6.0℃. Therefore, excessive silicon content will affect elongation and impact resistance. This invention controls the silicon content between 1.95~2.05wt% to ensure that the castings have good mechanical and casting properties.

[0012] Manganese can significantly increase the pearlite content in ductile iron, but it is prone to segregation at the eutectic boundaries during solidification, which has an adverse effect on mechanical properties and leads to a decrease in material toughness. In order to make the castings have good mechanical properties, the manganese content of the present invention is controlled at ≤0.15%.

[0013] Phosphorus mainly enters ductile iron along with the metal charge. Although phosphorus has no significant effect on the spheroidization process, it is a harmful element that can dissolve in molten iron and cause severe segregation during solidification, forming phosphorus eutectic with a low melting point. As the wall thickness of the casting increases, the degree of phosphorus segregation becomes more pronounced, and the phosphorus eutectic tends to be distributed at the boundaries of eutectic clusters, thus significantly deteriorating the mechanical properties of the cast iron. In addition, phosphorus also increases the brittle transition temperature of ductile iron. For every 0.01% increase in phosphorus content, the brittle transition temperature rises by about 4.0 to 4.5°C. To ensure that the casting has good comprehensive mechanical properties, the phosphorus content should be reduced as much as possible, and its mass fraction is usually required to be controlled below 0.025%.

[0014] Sulfur is both a harmful and an indispensable element in ductile iron. In order to ensure good spheroidization effect and a large number of graphite spheres, the mass fraction of sulfur is usually controlled between 0.006% and 0.012%.

[0015] Magnesium is a key element necessary for the production of ductile iron, and its content directly affects the morphology of graphite. In thick and large castings, due to the long solidification time, magnesium is easily lost during solidification, leading to a decline in spheroidization effect and the appearance of distorted graphite, which affects the spheroidization quality of graphite. To ensure the acquisition of graphite spheres with good sphericity, the mass fraction of magnesium is usually controlled between 0.030% and 0.045%.

[0016] Boron is a trace element in ductile iron and tends to segregate at grain boundaries. When its content is low, it can promote graphitization, but when its content is high, it will inhibit the graphitization process. For ferritic ductile iron, the presence of boron will significantly reduce the material's low-temperature impact performance. The boron content in the castings of this invention is controlled below 0.001 wt% to avoid adverse effects on its microstructure and properties.

[0017] The trace element antimony in ductile iron improves graphite morphology, prevents graphite distortion, and increases the number of graphite spheres, thereby significantly improving the mechanical properties of the material. However, antimony is also prone to precipitate at grain boundaries, forming intergranular precipitates. When the antimony content exceeds 0.01%, antimony-rich phases precipitate at the boundaries of eutectic clusters, leading to a decrease in tensile strength and elongation after fracture. With further increases in antimony content, impact toughness also decreases significantly. This invention controls the antimony content between 0.003% and 0.005% to improve performance while avoiding adverse effects.

[0018] Metallic nickel exhibits a weak graphitizing effect in cast iron, effectively promoting graphite spheroidization. Nickel dissolves in the ferrite matrix, providing solid solution strengthening. As nickel content increases, lattice distortion intensifies, leading to a continuous increase in tensile strength. However, as the solid solubility of nickel in ferrite increases, lattice distortion further intensifies. While the ferrite is strengthened, its brittleness also increases, resulting in a decrease in elongation after fracture. When the amount of nickel dissolved in ferrite reaches a certain level, some undecomposed pearlite may appear in the microstructure, further increasing the hardness with increasing nickel content. This invention controls the nickel content at 0.49~0.88 wt%, ensuring that nickel primarily strengthens the casting through fine grains, enhancing tensile strength while maintaining impact toughness.

[0019] Furthermore, the pretreatment agent includes a desulfurizing agent, a carbon raising agent, and a silicon content adjuster; the desulfurizing agent consists of CaO and CaC2 with a particle size <10mm; the carbon raising agent has a fixed carbon content ≥99wt% and a particle size of 0.5~5mm; the silicon content adjuster consists of Si: 72-80wt%, Al ≤1.5wt%, and the remainder being Mn, Cr, P, S, and Ca, with a particle size of 5~100mm.

[0020] Further, based on the weight percentage of the molten iron being poured, the amount of spheroidizing agent is 1.0~1.1wt%, the amount of covering agent is 0.3~0.5wt%, the amount of primary inoculant is 0.2~0.4wt%, the amount of alloy Sb is 0.003~0.005wt%, and the amount of in-flow inoculant is 0.15~0.25wt%.

[0021] Furthermore, the spheroidizing agent is a rare earth silicon-magnesium spheroidizing agent, with the main components being: Mg: 5.0~7.0wt%, Re: 0.10~0.50wt%, Si: 40~50wt%, and the balance being iron; the covering agent is a low-silicon inoculant, with the main components being: Si: 40~60wt%, Ba: 1.5~2.5wt%, Ca: 0.2~1.0wt%, and the balance being iron; the primary inoculant is a silicon-calcium-barium inoculant, with the main components being: Si: 72~78wt%, Ba: 2.0~3.0wt%, Ca: 1.0~2.0wt%, and the balance being iron.

[0022] Furthermore, the in-flow inoculant is a sulfur-oxygen inoculant, with the main components being: Si: 65~80wt%, Ca: 0.5~1.5wt%, and the balance being iron.

[0023] Furthermore, the pouring temperature is 1320~1370℃.

[0024] Furthermore, the specific steps of the three-stage annealing are as follows: heat up to 900-940℃ at a rate of 60-100℃ / h and hold for 1-2 hours, furnace cool to 720-780℃ and hold for 2-4 hours, furnace cool to 680-700℃ and hold for 3-6 hours, continue furnace cooling to 600℃ and then air cool.

[0025] Furthermore, the mold contains chills located at the bottom of the casting.

[0026] In a second aspect, a wind power casting is manufactured using the ductile iron production process described in the first aspect.

[0027] By adopting the above technical solution, the present invention has the following beneficial effects: (1) The present invention is a three-stage heat treatment process including smelting, pretreatment, spheroidizing inoculation, casting, and cooling. The pretreatment involves adding a pretreatment agent and a nickel source to adjust the composition of the molten iron. The oxygen and sulfur content in the molten iron is stably controlled at a low level to provide good conditions for spheroidizing. At the same time, the reaction products of the pretreatment agent can become stable nucleation particles and nucleation cores of graphite in the eutectic transformation, thereby increasing the number of graphite spheres in the molten iron after spheroidizing. The graphite spheres are small in diameter, round in shape, and uniformly dispersed, thereby improving the mechanical properties of the casting, especially the low-temperature toughness. At the same time, the introduction of nickel can effectively enhance the tensile strength of the casting while ensuring that its impact toughness is not reduced.

[0028] (2) Through the synergistic effect of high-temperature decomposition of carbides, medium-temperature regulation of matrix structure and low-temperature stress relief, this invention not only achieves the homogenization of the structure and reduces grain boundary segregation, but also effectively eliminates the influence of brittle phases, thereby significantly improving the low-temperature impact performance of the material.

[0029] (3) The ductile iron produced by the production process of the present invention meets the requirements of QT400-18L-1 / 2 in GB / T 25390 standard: tensile strength Rm≥360MPa, yield strength Rp0.2≥220MPa, elongation A≥12%; and meets the requirements of low temperature -30℃ / -40℃ (kv2) in GB / T 25390 standard: individual values ​​of three samples ≥7J, average value ≥10J. Detailed Implementation

[0030] To better understand the above technical solution, the following will provide a detailed explanation of the technical solution in conjunction with specific implementation methods.

[0031] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0032] The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0033] The pig iron used is Q10 cast iron for ductile iron, with the following composition: C: 4.0~4.5 wt%, Si: 0.50~0.90wt%, Mn: ≤0.15wt%, P: ≤0.04wt%, S: ≤0.02wt%, B: ≤0.001wt%, and harmful alloying elements ≤0.10wt%.

[0034] The scrap steel selected is high-quality scrap steel flakes with the following composition: C≤0.15wt%, Si≤0.40wt%, Mn≤0.30wt%, P≤0.02wt%, S≤0.03wt%, Cr≤0.06wt%, Ti<0.03wt%, B≤0.001wt%.

[0035] The recycled material is ferritic ductile iron recycled material.

[0036] The nickel source is electrolytic nickel containing nickel.

[0037] The spheroidizing agent is a rare earth silicon-magnesium spheroidizing agent, with the following main components: Mg: 5.0~7.0wt%, Re: 0.10~0.50wt%, Si: 40~50wt%, and the balance being iron; The covering agent is a low-silicon inoculant with the following main components: Si: 40~60wt%, Ba: 1.5~2.5wt%, Ca: 0.2~1.0wt%, and the balance being iron. The primary inoculant is a silicon-calcium-barium inoculant, with the following main components: Si: 72~78wt%, Ba: 2.0~3.0wt%, Ca: 1.0~2.0wt%, and the balance being iron.

[0038] The in-flow inoculant is a sulfur-oxygen inoculant, with the main components being: Si: 65~80wt%, Ca: 0.5~1.5wt%, and the balance being iron.

[0039] The molten iron covering agent is composed of perlite, with SiO2 ≥ 72% and a particle size of 1-3 mm.

[0040] The desulfurizing agent consists of CaO and CaC2, with a particle size of <10mm.

[0041] The carbon raiser has a fixed carbon content of ≥99wt% and a particle size of 0.5~5mm.

[0042] The silicon content adjuster consists of Si: 72-80wt%, Al≤1.5wt%, with the remainder being Mn, Cr, P, S, and Ca, and a particle size of 5~100mm. Example 1

[0043] A manufacturing process for ductile iron includes the following steps: S1. Ingredients: 40~60% pig iron, 10~20% recycled material, 10~30% scrap steel; S2. Smelting: Melting pig iron, scrap steel, and recycled materials together into molten iron; S3. Pretreatment: Add pretreatment agent and nickel source to adjust the composition of molten iron; S4. Spheroidizing and inoculation treatment: Place spheroidizing agent, covering agent and antimony alloy at the bottom of the ladle in advance. Spread the covering agent on the surface of the spheroidizing agent. Then pour the molten iron adjusted in step S3 into the ladle. At the same time, add an inoculant once when the volume of molten iron is close to 2 / 3 of the ladle. S5. Pouring: After the spheroidizing and inoculation treatment in step S4, the molten iron is sprinkled with molten iron covering agent and slag is removed before being poured into the mold. During the pouring process, inoculant is added. S6. Cooling: After pouring, the molten iron is slowly cooled to below 400°C in the mold and the casting is removed from the mold. S7. Heat treatment: The casting is placed in an annealing furnace for two-stage low-temperature annealing.

[0044] The pretreatment agent includes a desulfurizing agent, a carbon raising agent, and a silicon content adjuster; the desulfurizing agent consists of CaO and CaC2 with a particle size <10mm; the carbon raising agent has a fixed carbon content ≥99wt% and a particle size of 0.5~5mm; the silicon content adjuster consists of Si: 72-80wt%, Al ≤1.5wt%, and the remainder being Mn, Cr, P, S, and Ca, with a particle size of 5~100mm.

[0045] The amount of spheroidizing agent is 1.0~1.1wt%, the amount of covering agent is 0.3~0.5wt%, the amount of primary inoculant is 0.2~0.4wt%, the amount of alloy Sb is 0.003~0.005wt%, and the amount of in-flow inoculant is 0.15~0.25wt%, calculated by weight percentage of molten iron.

[0046] The pouring temperature is 1320℃.

[0047] The specific steps of the three-stage annealing are as follows: heat up to 920℃ at a rate of 60~100℃ / h and hold for 1.5h, furnace cool to 740℃ and hold for 4h, furnace cool to 700℃ and hold for 6h, continue furnace cooling to 600℃ and then air cool.

[0048] The mold contains a chill, which is located at the bottom of the casting; the thickness of the chill is 2 / 3 of the thickness of the casting.

[0049] Table 1 below shows the main components, nodularity grade, and graphite nodule size grade of the ductile iron prepared in Example 1: Table 1 Example 2

[0050] A manufacturing process for ductile iron includes the following steps: S1. Ingredients: 40~60% pig iron, 10~20% recycled material, 10~30% scrap steel; S2. Smelting: Melting pig iron, scrap steel, and recycled materials together into molten iron; S3. Pretreatment: Add pretreatment agent and nickel source to adjust the composition of molten iron; S4. Spheroidizing and inoculation treatment: Place spheroidizing agent, covering agent and antimony alloy at the bottom of the ladle in advance. Spread the covering agent on the surface of the spheroidizing agent. Then pour the molten iron adjusted in step S3 into the ladle. At the same time, add an inoculant once when the volume of molten iron is close to 2 / 3 of the ladle. S5. Pouring: After the spheroidizing and inoculation treatment in step S4, the molten iron is sprinkled with molten iron covering agent and slag is removed before being poured into the mold. During the pouring process, inoculant is added. S6. Cooling: After pouring, the molten iron is slowly cooled to below 400°C in the mold and the casting is removed from the mold. S7. Heat treatment: The casting is placed in an annealing furnace for two-stage low-temperature annealing.

[0051] The pretreatment agent includes a desulfurizing agent, a carbon raising agent, and a silicon content adjuster; the desulfurizing agent consists of CaO and CaC2 with a particle size <10mm; the carbon raising agent has a fixed carbon content ≥99wt% and a particle size of 0.5~5mm; the silicon content adjuster consists of Si: 72-80wt%, Al ≤1.5wt%, and the remainder being Mn, Cr, P, S, and Ca, with a particle size of 5~100mm.

[0052] The amount of spheroidizing agent is 1.0~1.1wt%, the amount of covering agent is 0.3~0.5wt%, the amount of primary inoculant is 0.2~0.4wt%, the amount of alloy Sb is 0.003~0.005wt%, and the amount of in-flow inoculant is 0.15~0.25wt%, calculated by weight percentage of molten iron.

[0053] The pouring temperature is 1350℃.

[0054] The specific steps of the three-stage annealing are as follows: heat up to 920℃ at a rate of 60~100℃ / h and hold for 1 hour, furnace cool to 780℃ and hold for 3 hours, furnace cool to 700℃ and hold for 3 hours, continue furnace cooling to 600℃ and then air cool.

[0055] The mold contains a chill, which is located at the bottom of the casting; the thickness of the chill is 2 / 3 of the thickness of the casting.

[0056] Table 2 below shows the main components, nodularity grade, and graphite nodule size grade of the ductile iron obtained in Example 2: Table 2 Example 3

[0057] A manufacturing process for ductile iron includes the following steps: S1. Ingredients: 40~60% pig iron, 10~20% recycled material, 10~30% scrap steel; S2. Smelting: Melting pig iron, scrap steel, and recycled materials together into molten iron; S3. Pretreatment: Add pretreatment agent and nickel source to adjust the composition of molten iron; S4. Spheroidizing and inoculation treatment: Place spheroidizing agent, covering agent and antimony alloy at the bottom of the ladle in advance. Spread the covering agent on the surface of the spheroidizing agent. Then pour the molten iron adjusted in step S3 into the ladle. At the same time, add an inoculant once when the volume of molten iron is close to 2 / 3 of the ladle. S5. Pouring: After the spheroidizing and inoculation treatment in step S4, the molten iron is sprinkled with molten iron covering agent and slag is removed before being poured into the mold. During the pouring process, inoculant is added. S6. Cooling: After pouring, the molten iron is slowly cooled to below 400°C in the mold and the casting is removed from the mold. S7. Heat treatment: The casting is placed in an annealing furnace for two-stage low-temperature annealing.

[0058] The pretreatment agent includes a desulfurizing agent, a carbon raising agent, and a silicon content adjuster; the desulfurizing agent consists of CaO and CaC2 with a particle size <10mm; the carbon raising agent has a fixed carbon content ≥99wt% and a particle size of 0.5~5mm; the silicon content adjuster consists of Si: 72-80wt%, Al ≤1.5wt%, and the remainder being Mn, Cr, P, S, and Ca, with a particle size of 5~100mm.

[0059] The amount of spheroidizing agent is 1.0~1.1wt%, the amount of covering agent is 0.3~0.5wt%, the amount of primary inoculant is 0.2~0.4wt%, the amount of alloy Sb is 0.003~0.005wt%, and the amount of in-flow inoculant is 0.15~0.25wt%, calculated by weight percentage of molten iron.

[0060] The pouring temperature is 1350℃.

[0061] The specific steps of the three-stage annealing are as follows: heat up to 920℃ at a rate of 60~100℃ / h and hold for 2 hours, then furnace cool to 740℃ and hold for 2 hours, then furnace cool to 680℃ and hold for 5 hours, then continue furnace cooling to 600℃ and air cooling.

[0062] The mold contains a chill, which is located at the bottom of the casting; the thickness of the chill is 2 / 3 of the thickness of the casting.

[0063] Table 3 below shows the main components, nodularity grade, and graphite nodule size grade of the ductile iron obtained in Example 3: Table 3

[0064] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not add a nickel source during the pretreatment stage.

[0065] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 did not undergo a three-stage annealing heat treatment.

[0066] The difference between Comparative Example 3 and Example 1 is that the heat treatment steps of Comparative Example 3 are as follows: the temperature is raised to 920°C at a rate of 60~100°C / h and held for 4 hours, then furnace cooled to 740°C and held for 4 hours, and then furnace cooled to 600°C and air cooled.

[0067] Table 4 below shows the main components, nodularity grade, and graphite nodule size grade of the ductile iron obtained in Comparative Examples 1-3: Table 4

[0068] Table 5 below shows the mechanical properties of the ductile iron specimens obtained in Examples 1-3 and Comparative Examples 1-3: Table 5

[0069] Note: T200 is a ductile iron test block with length * width * thickness = 1000mm * 400mm * 200mm; T150 is a ductile iron test block with length * width * thickness = 600mm * 300mm * 150mm; T95 is a ductile iron test block with length * width * thickness = 600mm * 150mm * 95mm.

[0070] As can be seen from the data in Tables 1-3 and 5, the mechanical properties of the cast test blocks in Examples 1-3 all meet the requirements of the standard for tensile strength Rm≥360MPa, yield strength Rp0.2≥220MPa, and elongation A≥12%. With the decrease of C content, the yield strength of the cast test blocks of the same wall thickness shows a decreasing trend. In terms of low-temperature impact, only the three different wall thicknesses with high C content can all meet the standard requirement that the average impact energy is greater than 10J. The impact energy test of the largest wall thickness is unqualified when the C content is low. The C content of 3.78wt% in Example 1 is the best composition choice in terms of comprehensive mechanical properties. It can not only meet the customer's requirements for various aspects of casting performance, but also make it more conducive to the self-feeding of the casting to obtain a sound casting.

[0071] As can be seen from the data in Tables 1, 4 and 5: When nickel powder was added and three-stage annealing was carried out during the pretreatment of ductile iron test blocks prepared in Examples 1 to 3, the mechanical properties of the resulting cast test blocks were more in line with the requirements of tensile strength Rm≥360MPa, yield strength Rp0.2≥220MPa, and elongation A≥12% in the standard. At the same time, they also met the requirements of low temperature (-30℃ / -40℃) (kv2) in GB / T 25390 standard: individual values ​​of the three samples ≥7J, and average values ​​≥10J.

[0072] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A production process for ductile iron, characterized by the following steps: include: S1. Ingredients: 40~60% pig iron, 10~20% recycled material, 10~30% scrap steel; S2. Smelting: Melting pig iron, scrap steel, and recycled materials together into molten iron; S3. Pretreatment: Add pretreatment agent and nickel source to adjust the composition of molten iron; S4. Spheroidizing and inoculation treatment: Place spheroidizing agent, covering agent and antimony alloy at the bottom of the ladle in advance. Spread the covering agent on the surface of the spheroidizing agent. Then pour the molten iron adjusted in step S3 into the ladle. At the same time, add an inoculant once when the volume of molten iron is close to 2 / 3 of the ladle. S5. Pouring: After removing slag from the molten iron after the spheroidizing inoculation treatment in step S4, pour it into the mold. During the pouring process, add a flow-inoculating agent. S6. Cooling: After pouring, slowly cool the casting in the mold to below 400°C, and remove the casting from the mold; S7. Heat treatment: The casting is placed in an annealing furnace for three-stage annealing.

2. The production process of ductile iron according to claim 1, characterized in that, The composition of the ductile iron is as follows: C: 3.75~3.85wt%, Si: 1.95~2.05wt%, Mn: ≤0.15wt%, P: ≤0.035wt%, S: 0.006~0.012wt%, Mg: 0.030~0.045wt%, Sb: 0.003~0.005wt%, B: ≤0.001wt%, Ni: 0.49~0.88wt%, with the remainder being Fe and impurities introduced during the preparation process.

3. The production process of ductile iron according to claim 1, characterized in that, The pretreatment agent includes a desulfurizing agent, a carbon raising agent, and a silicon content adjuster; the desulfurizing agent consists of CaO and CaC2 with a particle size <10mm; the carbon raising agent has a fixed carbon content ≥99wt% and a particle size of 0.5~5mm; the silicon content adjuster consists of Si: 72-80wt%, Al ≤1.5wt%, and the remainder being Mn, Cr, P, S, and Ca, with a particle size of 5~100mm.

4. The production process of ductile iron according to claim 1, characterized in that, The amount of spheroidizing agent is 1.0~1.1wt%, the amount of covering agent is 0.3~0.5wt%, the amount of primary inoculant is 0.2~0.4wt%, the amount of alloy Sb is 0.003~0.005wt%, and the amount of in-flow inoculant is 0.15~0.25wt%, calculated by weight percentage of molten iron.

5. The production process of ductile iron according to claim 4, characterized in that, The spheroidizing agent is a rare earth silicon-magnesium spheroidizing agent, with the main components being: Mg: 5.0~7.0wt%, Re: 0.10~0.50wt%, Si: 40~50wt%, and the balance being iron; the covering agent is a low-silicon inoculant, with the main components being: Si: 40~60wt%, Ba: 1.5~2.5wt%, Ca: 0.2~1.0wt%, and the balance being iron; the primary inoculant is a silicon-calcium-barium inoculant, with the main components being: Si: 72~78wt%, Ba: 2.0~3.0wt%, Ca: 1.0~2.0wt%, and the balance being iron.

6. The production process of ductile iron according to claim 1, characterized in that, The in-flow inoculant is a sulfur-oxygen inoculant, with the following main components: Si: 65~80wt%, Ca: 0.5~1.5wt%, and the balance being iron.

7. The production process of ductile iron according to claim 1, characterized in that, The pouring temperature is 1320~1370℃.

8. The production process of ductile iron according to claim 1, characterized in that, The specific steps of the three-stage annealing are as follows: heat up to 900-940℃ at a rate of 60-100℃ / h and hold for 1-2 hours, then furnace cool to 720-780℃ and hold for 2-4 hours, then furnace cool to 680-700℃ and hold for 3-6 hours, then continue furnace cooling to 600℃ and air cooling.

9. The production process of ductile iron according to claim 1, characterized in that, The mold contains chills, which are located at the bottom of the casting.

10. A wind power casting, characterized in that, The wind power casting is produced by the ductile iron production process described in any one of claims 1 to 9.

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