Iron mold casting method of nodular iron casting, nodular iron casting and wind generating set

Abstract

The invention provides an iron mold casting method of a nodular iron casting, the nodular iron casting and a wind generating set. The iron mold casting method comprises the step that molten iron is poured into a cavity formed by a metal outer mold and a sand core. The nodular iron casting comprises, by mass, 3.6 wt%-3.8 wt% of C, 2.3 wt%-2.6 wt% of Si, smaller than or equal to 0.14 wt% of Mn and 0.20 wt%-0.55 wt% of Ni. According to the iron mold casting method for the nodular iron casting, the comprehensive mechanical property of the nodular iron casting can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of iron mold casting, and particularly to an iron mold casting method for ductile iron castings, a ductile iron casting, and a wind power generating set. Background Art

[0002] With the continuous development of ductile iron technology, ductile iron has gradually replaced cast steel and become a new type of metal material. As a kind of ductile iron, as-cast ferritic ductile iron has been widely used in construction machinery, basic components of injection molding machines, basic components of die-casting machines, and wind power foundations or key components, etc.

[0003] At present, the research on ductile iron for wind power mainly focuses on solving problems such as how to meet the performance requirements of impact energy under low-temperature environments while maintaining the existing strength, and preventing the casting from cracking. However, the existing chemical composition formulations and production process methods cannot ensure that while significantly improving the strength, the low-temperature impact energy meets the indicators. From the research results of the existing technology, improving the strength while ensuring the low-temperature impact energy is a contradiction. Increasing the strength will inevitably affect the low-temperature impact energy. How to solve this difficult problem has become the current research direction.

[0004] In addition, the main shaft of a wind power generating set is used to connect the impeller and the gearbox and bears complex axial loads and radial loads. As the power of wind power generating sets is getting larger and larger, it is necessary to improve the performance of the main shaft. The performance of the main shaft mainly depends on the material of the main shaft and the process of main shaft forming. The existing main shafts have problems that they cannot meet higher performance requirements. Summary of the Invention

[0005] One object of the present invention is to provide an iron mold casting method for ductile iron castings that can improve the comprehensive mechanical properties of ductile iron castings.

[0006] Another object of the present invention is to provide an iron mold casting method for ductile iron castings that can improve the tissue compactness of ductile iron castings and reduce the number of shrinkage cavities and porosity.

[0007] Another object of the present invention is to provide a ductile iron casting (such as the main shaft of a wind power generating set) with improved comprehensive mechanical properties and a wind power generating set.

[0008] According to one aspect of the present invention, there is provided an iron mold casting method for ductile iron castings, the iron mold casting method comprising pouring molten iron into a cavity formed by a metal outer mold and a sand core, and the ductile iron casting comprises, by mass percentage: C 3.6 - 3.8 wt%, Si 2.3 - 2.6 wt%, Mn ≤ 0.14 wt%, Ni 0.20 - 0.55 wt%.

[0009] Optionally, the iron mold casting method further includes: (1) Melting: subjecting a material including pig iron to carbon increasing treatment and melting it into molten iron; (2) Spheroidizing and inoculating: spheroidizing and inoculating the molten iron obtained from step (1); and (3) Pouring: pouring the molten iron obtained from step (2) into the mold cavity, wherein, in step (1) and / or step (2), the preparation method further includes microalloying treatment, and the microalloying treatment includes adding Ni, adding a spheroidizing agent containing Si and an inoculant containing Si in step (2), and adding a stream inoculant containing Si in step (3).

[0010] Optionally, based on the total mass of the molten iron, in step (1), the content of Si included in the material is in the range of 1.4 - 1.6 wt%, in step (2), a spheroidizing agent containing Si and an inoculant containing Si are added such that the content of Si is in the range of 2.25 - 2.45 wt%, and in step (3), a stream inoculant containing Si is added such that the content of Si is in the range of 2.3 - 2.6 wt%.

[0011] Optionally, based on the total mass of the spheroidizing agent, the spheroidizing agent includes 40 - 50 wt% of Si by mass percentage, based on the total mass of the inoculant, the inoculant includes 72 - 78 wt% of Si by mass percentage, and based on the total mass of the stream inoculant, the stream inoculant includes 70 - 80 wt% of Si by mass percentage.

[0012] Optionally, based on the total mass of the inoculant, the inoculant includes by mass percentage: 72 - 78 wt% of Si, 1.0 - 2.0 wt% of Ca, 2.0 - 3.0 wt% of Ba, < 1.5 wt% of Al, and the balance is iron; based on the total mass of the spheroidizing agent, the spheroidizing agent includes by mass percentage: 4.5 - 6 wt% of Mg, 0.15 - 0.3 wt% of RE, 40 - 50 wt% of Si, and the balance is iron; based on the total mass of the stream inoculant, the stream inoculant includes by mass percentage: 70 - 80 wt% of Si, 0.5 - 2.5 wt% of Bi, ≤ 2.0 wt% of Ca, ≤ 2.0 wt% of Al, and the balance is Fe.

[0013] Optionally, in step (2), the addition amount of the inoculant is 0.35 - 0.67 wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.0 - 1.3 wt% of the total mass of the molten iron, and in step (3), the addition amount of the stream inoculant is 0.08 - 0.2 wt% of the total mass of the molten iron.

[0014] Optionally, the inoculant in step (2) includes a primary inoculant and a covering inoculant. Based on the total mass of the primary inoculant, the primary inoculant includes, by mass percentage: 72 - 78 wt% Si, 1.0 - 2.0 wt% Ca, 2.0 - 3.0 wt% Ba, Al < 1.5 wt%, and the balance is iron. Based on the total mass of the covering inoculant, the covering inoculant includes, by mass percentage: 72 - 78 wt% Si, 1.0 - 2.0 wt% Ca, 2.0 - 3.0 wt% Ba, Al < 1.5 wt%, and the balance is iron.

[0015] Optionally, in step (2), the addition amount of the primary inoculant is 0.30 - 0.55 wt% of the total mass of the molten iron, and the addition amount of the covering inoculant is 0.05 - 0.12 wt% of the total mass of the molten iron.

[0016] Optionally, Mg is added in step (2) such that, based on the total mass of the molten iron, the content of Mg is in the range of 0.045 - 0.078 wt%. Based on the total mass of the spheroidizing agent, the spheroidizing agent includes 4.5 - 6 wt% Mg by mass percentage. The addition amount of the spheroidizing agent in step (2) is 1.0 - 1.3 wt% of the total mass of the molten iron. In step (1) and / or step (2), the addition amount of Ni is 0.2 - 0.4 wt% of the total mass of the molten iron. The microalloying treatment in step (1) and / or step (2) includes adding Ni such that the content of Ni is in the range of 0.20 - 0.55 wt% of the total mass of the molten iron. In step (1) and / or step (2), the microalloying treatment also includes adding TiC to the molten iron, and the addition amount of TiC is 0.01 - 0.03 wt% of the total mass of the molten iron.

[0017] Optionally, the pig iron in step (1) is pig iron of grade Q10 or above, and the content of Mn is adjusted in step (1) such that the content of Mn in step (1) is in the range of 0.10 - 0.12 wt% of the total mass of the molten iron.

[0018] Optionally, the wall thickness of the metal outer mold (110) is 100 mm - 200 mm.

[0019] Optionally, before pouring the molten iron into the cavity, the temperature of the cavity is preheated to 50 - 200 °C. In step (4), the pouring temperature of the molten iron is 1330 - 1360 °C, and the pouring speed of the molten iron is 100 - 150 kg / s.

[0020] Optionally, the content of Si is in the range of 2.30 - 2.40 wt%.

[0021] According to another aspect of the present invention, there is provided a ductile iron casting, which is formed by the iron mold casting method as described above.

[0022] Optionally, the wall thickness of the ductile iron casting is greater than or equal to 60 mm.

[0023] Optionally, the ductile iron casting is the main shaft of a wind turbine generator. The main shaft includes a shaft body, a large flange disposed at one axial end of the shaft body, a flared connecting member connecting the shaft body and the large flange, and a small flange disposed at the other axial end of the shaft body. The outer diameter of the shaft body is greater than or equal to 1.0 m.

[0024] According to another aspect of the present invention, there is provided a wind turbine generator including the ductile iron casting as described above.

[0025] According to the permanent mold casting method of the ductile iron casting of the present invention, by controlling the composition of the ductile iron casting and / or the permanent mold casting method, the comprehensive mechanical properties of the ductile iron casting can be improved.

[0026] According to the permanent mold casting method of the ductile iron casting of the present invention, by controlling the composition of the ductile iron casting, the tensile strength of the test block of the ductile iron casting can be greater than 400 MPa, the yield strength can be greater than 280 MPa, and the low-temperature impact energy at -20 °C can be greater than 7 J. Therefore, it can be widely applied to the manufacture of ductile iron castings with high comprehensive performance requirements.

[0027] In addition, according to the permanent mold casting method of the ductile iron casting of the present invention, the comprehensive mechanical properties of each main part of the wind power main shaft can be improved, and high strength (for example, tensile strength and yield strength) can still be ensured while increasing the low-temperature impact energy. Therefore, the permanent mold casting method of the ductile iron casting according to the present invention can be widely applied to large-section castings in wind turbine generators or castings with high comprehensive performance requirements in other fields. Description of the Drawings

[0028] Through the following detailed description in conjunction with the drawings, the above and other objects, features, and advantages of the present invention will become clearer, where: Figure 1 is the main shaft of a wind turbine generator as an example of a ductile iron casting; Figure 2 is Figure 1 the axial sectional view of Figure 3 is a schematic diagram of a permanent mold for preparing a ductile iron casting according to an embodiment of the present invention; Figure 4A and Figure 4B respectively show the graphite morphologies of ductile iron according to a comparative example and an inventive example; Figure 5A and Figure 5BThe tensile fracture morphologies of ductile cast iron according to the comparative example and the inventive example are respectively shown; Figure 6A and Figure 6B The three-dimensional tensile fracture morphologies of ductile cast iron according to the comparative example and the inventive example are respectively shown; and Figure 7A and Figure 7B The impact fracture morphologies of ductile cast iron according to the comparative example and the inventive example are respectively shown. Detailed implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention.

[0031] In addition, unless there are conflicting descriptions, the following-described embodiments may also be combined with each other. In addition, unless otherwise specified, the devices with the same reference numerals in each embodiment have the same structure, and redundant descriptions will no longer be provided.

[0032] Hereinafter, reference will be made to Figures 1 to 3 to describe the permanent mold casting method of ductile cast iron parts, ductile cast iron parts, the main shaft of a wind turbine generator, and a wind turbine generator according to the embodiments of the present invention. Figure 1 is the main shaft of a wind turbine generator as an example of ductile cast iron parts, Figure 2 is Figure 1 the axial sectional view of Figure 3 is a schematic diagram of a permanent mold for preparing ductile cast iron parts according to the embodiments of the present invention. Figure 4A and Figure 4B respectively show the graphite morphologies of ductile cast iron according to the comparative example and the inventive example, Figure 5A and Figure 5B respectively show the tensile fracture morphologies of ductile cast iron according to the comparative example and the inventive example, Figure 6A and Figure 6B respectively show the three-dimensional tensile fracture morphologies of ductile cast iron according to the comparative example and the inventive example, Figure 7A and Figure 7BThe impact fracture morphologies of ductile cast iron according to the comparative example and the inventive example are respectively shown.

[0033] The permanent mold casting method of a ductile cast iron part according to an embodiment of the present invention may include: pouring molten iron into a cavity 130 formed by a metal outer mold 110 and a sand core 120.

[0034] The ductile cast iron part according to an embodiment of the present invention can be formed by permanent mold casting. The ductile cast iron part can be the main shaft of a large-section wind power generation unit, or can also be the planet carrier of the gearbox of a large-section wind power generation unit, etc. In addition, the ductile cast iron part is not limited to the components in the wind power generation field, and can also be other ductile cast iron parts. As an example, the wall thickness of the ductile cast iron part can be greater than or equal to 60 mm.

[0035] For the convenience of description, the permanent mold casting method of the ductile cast iron part will be described in detail below by taking the main shaft of the wind power generation unit as an example.

[0036] As Figure 1 and Figure 2 shown, one end of the main shaft 20 (the left end in Figure 1 ) is used to connect with the impeller of the wind power generation unit, and the other end of the main shaft 20 (the right end in Figure 1 ) is used to connect with the gearbox of the wind power generation unit. The main shaft 20 includes a shaft body 21, a large flange 22 arranged at one end of the main shaft 20, and a trumpet-shaped connecting piece 23 connecting the shaft body 21 and the large flange 22. In addition, the main shaft 20 further includes a small flange 24 arranged at the other end of the main shaft 20. The large flange 22 is arranged at the large radial end of the main shaft 20 and is used to connect with the impeller of the wind power generation unit, and the small flange 24 is arranged at the small radial end of the main shaft 20 and is used to connect with the gearbox of the wind power generation unit. The large flange 22, the trumpet-shaped connecting piece 23 and the small flange 24 are used to connect other rotating parts, and the loads they bear are large and complex, and it is necessary to ensure their comprehensive mechanical properties.

[0037] As Figure 3 shown, the permanent mold 100 may include a metal outer mold 110 and a sand core 120. The internal shape of the metal outer mold 110 may be consistent with the external shape of the main shaft 20. The wall thickness of the metal outer mold 110 can be 100 mm - 200 mm. However, the present invention is not limited thereto. The wall thickness of the metal outer mold 110 can be reasonably set according to the size of the ductile cast iron part. In addition, the wall thickness of each part of the metal outer mold 110 can be the same or different, and the present invention does not make specific restrictions on this.

[0038] The external shape of the inner sand core 120 is consistent with the inner cavity shape of the main shaft 20. According to needs, the metal outer mold 110 and the inner sand core 120 can be divided into multiple sections axially. As an example, the metal outer mold 110 can be divided into at least three sections axially, and the inner sand core 120 can be divided into at least two sections axially to facilitate production and manufacturing.

[0039] According to an embodiment of the present invention, the cavity 130 may include a shaft cavity 131 for forming the shaft body 21, a large flange cavity 132 for forming the large flange 22, a horn cavity 133 for forming the horn-shaped connecting member 23, and a small flange cavity 134 for forming the small flange 24. The above division of the cavity 130 is a functional division and does not represent a physical division of the structure.

[0040] According to an embodiment of the present invention, the molten iron pouring system (not shown) can be a bottom-pouring system or a side-pouring system. The specific structural form of the bottom-pouring system or the side-pouring system is not limited. According to an embodiment of the present invention, the form of the molten iron riser system (not shown) is not specifically limited. For example, it can be a top riser or a side riser.

[0041] According to an embodiment of the present invention, compared with sand casting, since the metal external mold 110 can be reused, cost can be saved. In addition, the surface finish of the ductile iron casting formed by using the metal external mold 110 is high. Furthermore, compared with sand casting, the metal external mold 110 can effectively increase the cooling rate of the molten iron, refine the grains, and improve the tissue compactness, thus being beneficial to improving the comprehensive mechanical properties.

[0042] According to an embodiment of the present invention, the internal sand core 120 can effectively absorb the stress during the solidification of the molten iron, thereby preventing the cracking of the ductile iron casting, which is beneficial to improving the comprehensive mechanical properties.

[0043] Hereinafter, the composition of the ductile iron casting according to an embodiment of the present invention will be described.

[0044] According to the present invention, based on the total mass of the ductile iron casting, the ductile iron casting may include, by mass percentage: C 3.6 - 3.8 wt%, Si 2.3 - 2.6 wt%, Mn ≤ 0.14 wt%, Ni 0.20 - 0.55 wt%. In addition, the matrix of the ductile iron casting according to an embodiment of the present invention can be ferrite.

[0045] The present invention controls the content of each element in the ductile iron casting, especially the content of Si, Mn, and Ni, so as to obtain the technical effects that the tensile strength of the test block of the ductile iron casting specimen is greater than 400 MPa, the yield strength is greater than 280 MPa, and the low-temperature impact energy at -20 °C is greater than 7 J.

[0046] In an embodiment, the ductile iron casting according to an exemplary embodiment of the present invention may further include, by mass percentage: V 0.001-0.01wt%, Ti 0.02-0.03wt%. In another embodiment, the ductile iron casting according to an exemplary embodiment of the present invention may further include, by mass percentage: P ≤0.035wt%, S ≤0.02wt%, Cr ≤0.025wt%, Mg 残 0.035-0.060wt%.

[0047] Specifically, Si can play a role in solid solution strengthening. The principle is to form a solid solution by incorporating a certain solute element into the molten iron to strengthen the metal. The solute atoms incorporated into the solid solution cause lattice distortion. The lattice distortion increases the resistance to dislocation movement, making slip difficult to occur, thereby increasing the strength and hardness of the alloy solid solution. When the concentration of solute atoms in the melt is appropriate, the strength and hardness of the material are significantly improved, but its toughness and plasticity decrease. In the embodiments of the present invention, the Si content can be controlled within the range of 2.3-2.6wt%, preferably within the range of 2.30-2.49wt%, within the range of 2.35-2.49wt%, or within the range of 2.30-2.40wt%, more preferably within the range of 2.39-2.45wt%. If the Si content is outside the range defined in the present invention, the toughness and plasticity of the ductile iron casting will decrease, so the Si content must be strictly controlled.

[0048] Mn is a positive segregation element, which is likely to form alloy carbides at grain boundaries, stabilize pearlite, and inhibit the formation of ferrite. Mn will significantly increase the ductile-brittle transition temperature and reduce the plasticity and toughness of the ductile iron casting. For every 0.1% increase in manganese, the low-temperature brittle transition temperature of the ductile iron casting will increase by 12°C. In order to ensure the low-temperature impact toughness of the ductile iron casting, the Mn content must be strictly controlled. In the embodiments of the present invention, the Mn content can be controlled within the range of less than or equal to 0.14wt%, preferably within the range of 0.10-0.12wt%. If the Mn content is outside the range defined in the present invention, the ductile-brittle transition temperature will increase, which will lead to a decrease in low-temperature impact performance.

[0049] Ni can be infinitely dissolved in ductile iron castings without affecting the graphite morphology and the number of eutectic cells. Nickel in the as-cast state can promote the formation of pearlite and refine pearlite, and has a certain solution strengthening effect on ferrite, which is beneficial to improving the tensile strength of ductile iron castings. However, it will reduce the elongation and low-temperature impact toughness of ductile iron castings. Adding nickel to low-temperature high-toughness ductile iron castings cannot effectively reduce the ductile-brittle transition temperature, and the improvement effect of nickel on the low-temperature impact toughness of materials is not obvious. However, it can improve its tensile strength without reducing the low-temperature impact toughness of the material, thereby making up for the problem of insufficient strength caused by the reduction of silicon content. In the embodiments of the present invention, the content of Ni can be controlled within the range of 0.20-0.55 wt%, preferably within the range of 0.35-0.55 wt%, and more preferably within the range of 0.35-0.45 wt%. If the Ni content is outside the range defined by the present invention, the strength and hardness of ductile iron castings will deteriorate, so the content of Ni should be strictly controlled.

[0050] Excessive contents of Ti and Cr will have adverse effects on the microstructure and properties of ductile iron castings. Both Ti and Cr are very active elements, which are easy to form particles with very high microhardness with C and N. Ti and Cr also have the characteristics of selective crystallization and are easy to enrich at grain boundaries and the last solidified part of the casting during the crystallization process. Excessive contents of Ti and Cr will affect the spheroidization quality, interfere with spheroidization, and cause distortion of graphite shape. Therefore, preferably, the contents of Ti and Cr can be controlled to further improve the properties of ductile iron castings. In the embodiments of the present invention, preferably, the content of Ti can be within the range of 0.02-0.03 wt%, and the content of Cr can be less than or equal to 0.025 wt%.

[0051] S and Mg 残 are the reasons for forming grain boundary inclusions, reducing impact performance, and being one of the reasons for low-temperature impact performance. Therefore, in order to further improve the properties of ductile iron castings, their contents can be controlled within a relatively low range. In addition, Mg can also promote the spheroidization of graphite, making the spheroidization rate of graphite higher and the distribution more uniform. In the embodiments of the present invention, preferably, the content of S can be controlled within the range of less than or equal to 0.02 wt%, and more preferably, less than 0.015 wt%. Preferably, the content of Mg 残 can be controlled within the range of 0.035-0.060 wt%, and more preferably, within the range of 0.040-0.054 wt%.

[0052] P is one of the elements that affect the ductile-brittle transition temperature of ductile iron castings. Therefore, in order to further improve the properties of ductile iron castings, the content of P can be controlled. In the embodiments of the present invention, preferably, the content of P can be controlled within the range of less than or equal to 0.035 wt%.

[0053] In an embodiment of the present invention, the solid solution strengthening of V in ductile iron, the precipitated phases and formed compounds during the solidification process, and the strengthening effect on the matrix can be utilized to further improve the mechanical properties of the ductile iron castings of the present invention. Therefore, preferably, the content of V can be controlled within the range of 0.001-0.01 wt%.

[0054] In the ductile iron castings of the embodiments of the present invention, the content of Si is controlled within the range of 2.3-2.6 wt%, the content of Mn is controlled within the range of less than or equal to 0.14 wt%, the content of Ni is controlled within the range of 0.20-0.55 wt%. More preferably, the content of V is also controlled within the range of 0.001-0.01 wt%, and the content of Ti is also controlled within the range of 0.02-0.03 wt%. Therefore, the ductile iron castings of the embodiments of the present invention can achieve the technical effects that the tensile strength is greater than 400 MPa, the yield strength is greater than 280 MPa, and the low-temperature impact energy at -20 °C is greater than 7 J. The relevant technical effects can refer to that the performance of the castings reaches the relevant indicators, or the effects of the test blocks reach the relevant indicators. The test blocks can be the test blocks prepared according to GB_T 1348-2019 Ductile Iron Castings, or the test blocks that can reflect the performance of the overall castings.

[0055] Therefore, the ductile iron castings of the present invention can be widely used in castings, especially in the castings of wind turbine generators.

[0056] The preparation method of the ductile iron castings according to the embodiments of the present invention may further include the following steps: (1) Melting: Carrying out carbon addition treatment on the materials including pig iron and melting them into molten iron; (2) Nodulizing and inoculating: Nodulizing and inoculating the molten iron obtained from step (1); and (3) Pouring: Pouring the molten iron obtained from step (2) into the cavity 130, and forming ductile iron castings after cooling and solidification, wherein, in step (1) and / or step (2), the preparation method may further include microalloying treatment.

[0057] Specifically, in step (1) and / or step (2), the microalloying treatment may include adding Ni such that the content of Ni is 0.20-0.55 wt% based on the total mass of the molten iron. A nodulizer containing Si and an inoculant containing Si can be added in step (2), and a stream inoculant containing Si can be added in step (3) such that the content of Si is 2.3-2.6 wt% based on the total mass of the molten iron. The materials added to the furnace in step (1) can be adjusted such that the content of Mn is less than or equal to 0.14 wt% based on the total mass of the molten iron.

[0058] In the present invention, the addition amount of additives (such as carburizer, nodulizer, inoculant, etc.) in each step is much less than the total mass of the molten iron in each step. Therefore, for the total mass of the molten iron, the addition amount of additives in each step can be negligible. That is, the total mass of the molten iron in each step in the present invention is basically equal. In other words, the "total mass of the molten iron" in the present invention may refer to the mass of the materials including pig iron melted into molten iron in step (1).

[0059] In addition, according to the embodiments of the present invention, the contents of Si, Mn, and / or Ni can be controlled in different steps to further improve the comprehensive properties of the ductile iron castings (such as improving the tensile strength, yield strength, and low-temperature impact energy).

[0060] The present invention adds Ni through microalloying treatment in step (1) and / or step (2) to control the content of Ni based on the total mass of the molten iron within the range of 0.20 - 0.55 wt%, preferably within the range of 0.35 - 0.55 wt%, and more preferably within the range of 0.35 - 0.45 wt%. Additionally, the present invention controls the content of Si based on the total mass of the molten iron within the range of 1.4 - 1.6 wt% in step (1), adds a nodulizer containing Si and an inoculant containing Si in step (2) to control Si within the range of 2.25 - 2.45 wt% based on the total mass of the molten iron, and adds a stream inoculant containing Si in step (4) to control the content of Si based on the total mass of the molten iron within the range of 2.3 - 2.6 wt%, preferably within the range of 2.35 - 2.49 wt%, and more preferably within the range of 2.39 - 2.45 wt%. Furthermore, the present invention adjusts the content of Mn in step (1) to control the content of Mn based on the total mass of the molten iron to be less than or equal to 0.14 wt%, preferably within the range of 0.10 - 0.12 wt%.

[0061] Specifically, in step (1), materials including pig iron can be added into a melting furnace and heated to melt so that the above materials are melted into molten iron. Pig iron, return scrap, and scrap steel commonly used in the art can be used as long as the content of Si based on the total mass of the molten iron in step (1) is within the range of 1.4 - 1.6 wt% and the content of Mn based on the total mass of the molten iron is less than or equal to 0.14 wt%. For example, the pig iron in the present invention can include pig iron of grade Q10 or above. However, the embodiments of the present invention are not limited thereto.

[0062] In addition, in step (1), if the Si content is less than 1.4 wt%, ferrosilicon with a higher Si content needs to be added. If the Si content is higher than 1.6 wt%, other pig irons with a lower Si content (such as plain carbon steel, but the present invention is not limited thereto) need to be added. In addition, in step (1), the Mn content is preferably controlled within the range of 0.10 - 0.12 wt%. If the Mn content of the hot metal in step (1) is low, ferromanganese can be added to increase the Mn content in the hot metal. However, the embodiments of the present invention are not limited thereto.

[0063] In step (1), the hot metal obtained by smelting can be subjected to carbon addition treatment. Specifically, a carbon additive can be added to the hot metal to perform carbon addition treatment on the hot metal. For example, the temperature of the hot metal can be controlled within the range of 1400 °C - 1450 °C, and a carbon additive can be added to the hot metal to perform carbon addition treatment. In the embodiments of the present invention, in order to reduce the influence of trace elements on ductile iron castings, the carbon content in the carbon additive can be greater than 90 wt% and the sulfur content can be less than 0.05 wt%. Under the teaching of the inventive concept, those skilled in the art can select a suitable carbon additive as long as it meets the foregoing conditions.

[0064] In step (2), the hot metal obtained from step (1) can be subjected to spheroidization, inoculation, and microalloying treatment. Specifically, as an example, first, the inoculant can be laid on one side of the dam in the ladle, second, the spheroidizing agent and the microalloy are laid on the other side of the dam in the ladle and covered with iron filings, and then the carbon addition-treated hot metal is added to the ladle, thereby performing the spheroidization, inoculation, and microalloying treatment process. Alternatively, microalloying treatment can also be performed on the hot metal in step (1).

[0065] In step (3), a stream inoculant is added during the pouring of the hot metal obtained from step (2) to perform stream inoculation.

[0066] In the embodiments of the present invention, based on the total mass of the spheroidizing agent, the spheroidizing agent may include 40 - 50 wt% of Si by mass percentage. Preferably, the spheroidizing agent may include, by mass percentage: 4.5 - 6 wt% of Mg, 0.15 - 0.3 wt% of RE, 40 - 50 wt% of Si, and the balance being iron. However, the embodiments of the present invention are not limited thereto. Based on the total mass of the inoculant, the inoculant may include 75 ± 3 wt% of Si by mass percentage. Preferably, the inoculant may include, by mass percentage: 75 ± 3 wt% of Si, 1.0 - 2.0 wt% of Ca, 2.0 - 3.0 wt% of Ba, Al < 1.5 wt%, and the balance being iron. However, the embodiments of the present invention are not limited thereto. In addition, in step (2), the addition amount of the inoculant may be 0.35 - 0.67 wt% of the total mass of the molten iron, and the addition amount of the spheroidizing agent may be 1.0 - 1.3 wt% of the total mass of the molten iron, so as to control Si within the range of 2.25 - 2.45 wt% based on the total mass of the molten iron in step (2).

[0067] In the embodiments of the present invention, based on the total mass of the in-stream inoculant, the in-stream inoculant may include 70 - 80 wt% of Si by mass percentage. Preferably, the in-stream inoculant may include, by mass percentage: 70 - 80 wt% of Si, 0.5 - 2.5 wt% of Bi, Ca ≤ 2.0 wt%, Al ≤ 2.0 wt%, and the balance being Fe. However, the embodiments of the present invention are not limited thereto. In step (3), the addition amount of the in-stream inoculant may be 0.08 - 0.2 wt% of the total mass of the molten iron, so as to control the content of Si within the range of 2.3 - 2.6 wt% based on the total mass of the molten iron In a preferred embodiment, the inoculant in step (2) may include a primary inoculant and a covering inoculant. In the embodiment, based on the total mass of the primary inoculant, the primary inoculant may include 75 ± 3 wt% of Si by mass percentage. Preferably, the primary inoculant may include, by mass percentage: 75 ± 3 wt% of Si, 1.0 - 2.0 wt% of Ca, 2.0 - 3.0 wt% of Ba, Al < 1.5 wt%, and the balance being iron. In the embodiment, based on the total mass of the covering inoculant, the covering inoculant may include 75 ± 3 wt% of Si by mass percentage. Preferably, the covering inoculant may include, by mass percentage: 75 ± 3 wt% of Si, 1.0 - 2.0 wt% of Ca, 2.0 - 3.0 wt% of Ba, Al < 1.5 wt%, and the balance being iron.

[0068] Specifically, as an example, a primary inoculant can be laid on one side of the dam in the nodulizing ladle, a nodulizer, a microalloy, and a covering inoculant can be laid on the other side, and the nodulizer and the microalloy can be covered with iron filings, and then the molten iron after carbon addition treatment is added into the nodulizing ladle. In the embodiment, the addition amount of the primary inoculant can be 0.30 - 0.55 wt% of the total mass of the molten iron, the addition amount of the nodulizer can be 1.0 - 1.3 wt% of the total mass of the molten iron, the addition amount of the covering inoculant can be 0.05 - 0.12 wt% of the total mass of the molten iron, and the addition amount of the in-stream inoculant can be 0.08 - 0.20 wt% of the total mass of the molten iron. However, the embodiments of the present invention are not limited thereto, as long as the content of Si based on the total mass of the ductile iron casting is within the range of 2.3 - 2.6 wt%. More preferably, as long as the content of Si in step (1) is within the range of 1.4 - 1.6 wt%, the content of Si in step (2) is within the range of 2.25 - 2.45 wt%, and the content of Si in step (3) is within the range of 2.3 - 2.6 wt%.

[0069] In the embodiment, Mg can be added in step (2) such that the content of Mg based on the total mass of the molten iron is within the range of 0.045 - 0.078 wt%. In the embodiment, Mg can be included in the nodulizer. Based on the total mass of the nodulizer, the nodulizer can include 4.5 - 6.5 wt% of Mg by mass percentage, and the addition amount of the nodulizer in step (2) can be 1.0 - 1.3 wt% of the total mass of the molten iron. However, the embodiments of the present invention are not limited thereto.

[0070] In step (1) and / or step (2), the microalloy treatment can include adding Ni to control the content of Ni based on the total mass of the molten iron within the range of 0.20 - 0.55 wt%. Specifically, the addition amount of Ni can be 0.20 - 0.40 wt% of the total mass of the molten iron.

[0071] In another embodiment, in step (1) and / or step (2), the microalloy treatment can further include adding TiC to the molten iron, wherein the addition amount of TiC can be 0.01 - 0.03 wt% of the total mass of the molten iron. In some preferred embodiments, a carrier can be added to TiC, and the carrier is 75 ferrosilicon, and the mixing of TiC and 75 ferrosilicon can make the alloy components evenly distributed at the grain boundaries, playing a role in solution strengthening. Preferably, the mass ratio of TiC to 75 ferrosilicon can be 1:2.

[0072] In step (3), an in-stream inoculant is added to the molten iron obtained from step (2) and casting is carried out, and the addition amount of the in-stream inoculant can be 0.1 - 0.2 wt% of the total mass of the molten iron.

[0073] The pouring temperature in step (3) can be 1330 - 1360 °C, and the pouring speed can be 100 - 150 kg / s. Before pouring the molten iron into the cavity 130, the temperature of the cavity 130 can be preheated to 50 - 200 °C. In the embodiment, step (3) further includes slowly cooling the castings after pouring to below 400 °C, where the slow cooling rate can be 10 - 20 °C / min.

[0074] In the present invention, by controlling the contents of Si, Mn, and Ni, more preferably, controlling the contents of Si and Mn in step (1), controlling the content of Ni in step (1) and / or (2), and controlling the content of Si in step (2) and step (3) respectively, ductile iron castings with a tensile strength greater than 400 MPa, a yield strength greater than 280 MPa, and a low-temperature impact energy greater than 7 J at -20 °C can be obtained. Specifically, in step (1), the content of Si is controlled to be 1.4 - 1.6 wt%, and the content of Mn is controlled to be less than or equal to 0.14 wt%. In step (1) and / or step (2), the content of Ni is controlled to be 0.20 - 0.55 wt% by microalloy treatment. In step (2), a spheroidizing agent and an inoculant are added to control the content of Si to be 2.25 - 2.45 wt%. In step (3), a stream inoculant is added to control the content of Si to be 2.3 - 2.6 wt%.

[0075] In the prior art, for small parts (such as wall thickness less than 60 mm), due to good heat dissipation conditions and fast solidification speed, the time for graphite growth is relatively short, the tendency of graphite distortion is small, its structure is easy to control, and the material properties are good. However, for large-section castings (such as wall thickness greater than or equal to 60 mm), its cooling speed is slow, the time for graphite ball growth is long, and this material relies on solid solution strengthening by silicon. With a high silicon content, large-section castings often have abnormal graphite such as fragmented graphite, and the performance also deteriorates sharply. The ductile iron castings prepared by the present invention solve the above problems, have good core structure, and basically no abnormal graphite such as fragmented graphite appears, and are especially suitable for large-section castings.

[0076] In addition, the present invention uses an iron mold casting process including a metal outer mold 110 and a sand core 120 to pour molten iron with the above element content ranges. By improving the cooling speed of the molten iron and the composition of the molten iron, the comprehensive mechanical properties of each key part of large-section castings (such as the main shaft) can be improved.

[0077] Hereinafter, the beneficial effects of the present invention will be more clearly elaborated in combination with the embodiments and comparative examples of the present invention. The preparation methods in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials used are all conventional reagents and materials in the art unless otherwise specified, and can all be obtained through commercial purchase.

[0078] Example 1 (1) A 20T intermediate frequency furnace is adopted. High-temperature graphitized carburizer and pig iron of grade Q10 are charged, and smelting and carburizing treatment are carried out at 1430 °C to obtain molten iron. 75 ferrosilicon is added to adjust the silicon content in the molten iron to 1.48 wt%. Ferromanganese is added to make the manganese content in the molten iron 0.125 wt%. The addition amount of the carburizer is 0.2 wt% of the total mass of the molten iron. The element composition of the carburizer is: carbon greater than 98.5 wt%, sulfur less than 0.05 wt%, ash less than 0.5 wt%, and moisture less than 0.5 wt%. (2) Carry out spheroidizing, inoculating and microalloying treatment on the molten iron after the carburizing treatment in step (1): Lay the inoculant on one side of the dam in a 20T spheroidizing ladle. On the other side of the dam, lay the spheroidizing agent, microalloying Ni from bottom to top in sequence, and then cover the microalloying with cast iron chips with a covering thickness of 6 mm. Add the molten iron into the spheroidizing ladle from the side where the inoculant is laid in the spheroidizing ladle. Among them, the addition amount of the inoculant is 0.54 wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.1 wt% of the total mass of the molten iron; the addition amount of microalloying Ni is 0.46 wt% of the total mass of the molten iron. Among them, the element composition of the inoculant is: Si 75 ± 3 wt%; Ca 1.0 - 2.0 wt%; Ba 2.0 - 3.0 wt%; Al < 1.5 wt%, and the rest is iron. The element composition of the spheroidizing agent is: Si 45.5 wt%, Mg 5.1 wt%, RE 0.243 wt%, Ba 1.31 wt%, Ca 0.94 wt%, and the rest is iron. (3) Pouring: Add in-stream inoculant for in-stream inoculation during the pouring process. The addition amount of the in-stream inoculant is 0.14 wt% of the total mass of the molten iron; after pouring is completed, the casting is slowly cooled in the mold to below 400 °C (the slow cooling rate is 10 °C / min), and the casting is cleaned out of the mold, which is the ductile iron casting.

[0079] The element composition of the in-stream inoculant is: Si 72.09 wt%, Bi 1.23 wt%, Ca 1.32 wt%, Al 1.09 wt%, and the rest is iron.

[0080] The elements of the obtained ductile iron casting include: C 3.71 wt%, Si 2.49 wt%, Mn 0.125 wt%, P 0.025 wt%, S 0.02 wt%, Ni 0.46 wt%, Cr 0.011 wt%, Mg 残 0.04 wt%, and the rest is iron and inevitable impurities.

[0081] Example 2 (1) A 20T intermediate frequency furnace is used. High-temperature graphitized carburizer and pig iron of grade Q10 are charged, and smelting and carburizing treatment are carried out at 1430 °C to obtain molten iron. 75 ferrosilicon is added to adjust the silicon content in the molten iron to 1.47 wt%. Ferromanganese is added to make the manganese content in the molten iron 0.122 wt%. The addition amount of the carburizer is 0.2 wt% of the total mass of the molten iron. The element composition of the carburizer is: carbon greater than 98.5 wt%, sulfur less than 0.05 wt%, ash less than 0.5 wt%, and moisture less than 0.5 wt%. (2) The molten iron after carburizing treatment in step (1) is subjected to spheroidizing, inoculating and microalloying treatment: On one side of the dam in a 20T spheroidizing ladle, the primary inoculant is laid. On the other side of the dam, the spheroidizing agent, covering inoculant, and microalloy Ni are laid in sequence from bottom to top. Then, cast iron chips are used to cover the microalloy, and the covering thickness is 6 mm. The molten iron is added into the spheroidizing ladle from the side where the primary inoculant is laid.

[0082] Among them, the addition amount of the primary inoculant is 0.45 wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.1 wt% of the total mass of the molten iron, the addition amount of the covering inoculant is 0.09 wt% of the total mass of the molten iron; the addition amount of microalloy Ni is 0.46 wt% of the total mass of the molten iron. Among them, the element composition of the primary inoculant is: Si 75 ± 3 wt%; Ca 1.0 - 2.0 wt%; Ba 2.0 - 3.0 wt%; Al < 1.5 wt%, and the rest is iron. The element composition of the spheroidizing agent is: Si 45.5 wt%, Mg 5.1 wt%, RE 0.243 wt%, Ba 1.31 wt%, Ca 0.94 wt%, and the rest is iron. The element composition of the covering inoculant is: Si 73.3 wt%, C 8.0 wt%, Ca 0.45 wt%, Ba 1.94 wt%, Al 0.52 wt%, and the rest is iron. (3) Pouring: During the pouring process, in-mold inoculant is added for in-mold inoculation. The addition amount of the in-mold inoculant is 0.14 wt% of the total mass of the molten iron; after pouring is completed, the casting is slowly cooled in the mold to below 400 °C (the slow cooling rate is 10 °C / min), and the casting is cleaned out of the mold, which is the ductile iron casting.

[0083] The element composition of the in-mold inoculant is: Si 72.09 wt%, Bi 1.23 wt%, Ca 1.32 wt%, Al 1.09 wt%, and the rest is iron.

[0084] The elements of the obtained ductile iron parts include C 3.70wt%, Si 2.47wt%, Mn 0.122wt%, P 0.027wt%, S 0.017wt%, Ni 0.46wt%, Cr 0.009wt%, Mg 残 0.05wt%, and the rest is iron and inevitable impurities.

[0085] Example 3 (1) Use a 20T intermediate frequency furnace, load high-temperature graphitizing carburizer and pig iron of grade Q10, carry out smelting and carburizing treatment at 1430°C to obtain molten iron, add 75 ferrosilicon, and adjust the silicon content in the molten iron to 1.45wt%; add ferromanganese to make the manganese content in the molten iron 0.121wt%; the addition amount of the carburizer is 0.2wt% of the total mass of the molten iron. The element composition of the carburizer is: carbon greater than 98.5wt%, sulfur less than 0.05wt%, ash less than 0.5wt%, and moisture less than 0.5wt%. (2) Carry out spheroidizing, inoculating and microalloying treatment on the molten iron after the carburizing treatment in step (1): Lay the primary inoculant on one side of the dam in a 20T spheroidizing ladle. On the other side of the dam, lay the spheroidizing agent, microalloying Ni, microalloying TiC (the mass ratio of TiC to 75 ferrosilicon is 1:2) and covering inoculant from bottom to top in sequence. Then cover the microalloying and covering inoculant with cast iron chips, and the covering thickness is 6mm. Add the molten iron into the spheroidizing ladle from the side where the primary inoculant is laid. Among them, the addition amount of the primary inoculant is 0.45wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.1wt% of the total mass of the molten iron, the addition amount of the covering inoculant is 0.09wt% of the total mass of the molten iron; the addition amount of microalloying Ni is 0.45wt% of the total mass of the molten iron; the addition amount of microalloying TiC is 0.025wt% of the total mass of the molten iron. Among them, the element composition of the primary inoculant is: Si 75±3wt%; Ca 1.0 - 2.0wt%; Ba 2.0 - 3.0wt%; Al<1.5wt%, and the rest is iron. The element composition of the spheroidizing agent is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron. The element composition of the covering inoculant is: Si 73.3wt%, C 8.0wt%, V 0.16wt%, Ca 0.45wt%, Ba 1.94wt%, Al 0.52wt%, and the rest is iron. (3) Pouring: During the pouring process, in-mold inoculation is carried out by adding in-mold inoculant, and the addition amount of the in-mold inoculant is 0.14wt% of the total mass of the molten iron. After pouring is completed, the casting is slowly cooled in the mold to below 400 °C (the slow cooling rate is 10 °C / min), and the casting is removed from the mold, which is then a ductile iron casting.

[0086] The elemental composition of the in-mold inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0087] The elements of the obtained ductile iron casting include C 3.75wt%, Si 2.45wt%, Mn 0.121wt%, P 0.024wt%, S 0.01wt%, V 0.001wt%, Ni 0.45wt%, Ti 0.021wt%, Cr 0.006wt%, residual Mg 0.04wt%, and the rest is iron and unavoidable impurities.

[0088] Example 4 (1) Use a 20T intermediate frequency furnace, load high-temperature graphitizing carburizer and pig iron of grade Q10, carry out melting and carburizing treatment at 1430 °C to obtain molten iron, add 75 ferrosilicon, and adjust the silicon content in the molten iron to 1.15wt%; add ferromanganese to make the manganese content in the molten iron 0.125wt%; the addition amount of the carburizer is 0.2wt% of the total mass of the molten iron. The elemental composition of the carburizer is: carbon greater than 98.5%, sulfur less than 0.05%, ash less than 0.5%, and moisture less than 0.5%. (2) Carry out spheroidizing, inoculating and microalloying treatment on the molten iron after carburizing treatment in step (1): Lay the inoculant on one side of the dam in a 20T spheroidizing ladle. On the other side of the dam, lay the spheroidizing agent, microalloying Ni from bottom to top, and then cover the microalloying with cast iron chips with a covering thickness of 6 mm. Add the molten iron into the spheroidizing ladle from the side where the inoculant is laid in the spheroidizing ladle. Among them, the addition amount of the inoculant is 0.75wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.1wt% of the total mass of the molten iron; the addition amount of microalloying Ni is 0.46wt% of the total mass of the molten iron. Among them, the elemental composition of the inoculant is: Si 75±3%; Ca 1.0 - 2.0%; Ba 2.0 - 3.0%; Al<1.5%, and the rest is iron. The elemental composition of the spheroidizing agent is: Si 45.5%, Mg 5.1%, RE 0.243%, Ba 1.31%, Ca 0.94%, and the rest is iron. (3) Pouring: During pouring, in-stream inoculant is added for in-stream inoculation, and the addition amount of the in-stream inoculant is 0.14 wt% of the total mass of the molten iron. After pouring is completed, the casting is slowly cooled in the mold to below 400 °C (the slow cooling rate is 10 °C / min), and the casting is cleaned out of the mold, which is then a ductile iron casting.

[0089] The elemental composition of the in-stream inoculant is: Si 72.09 wt%, Bi 1.23 wt%, Ca 1.32 wt%, Al 1.09 wt%, and the rest is iron.

[0090] The elements of the obtained ductile iron casting include C 3.71 wt%, Si 2.31 wt%, Mn 0.125 wt%, P 0.025 wt%, S 0.02 wt%, Ni 0.46 wt%, Cr 0.011 wt%, residual Mg 0.05 wt%, and the rest is iron and unavoidable impurities.

[0091] Example 5 (1) Use a 20T intermediate frequency furnace, charge high-temperature graphitizing carburizer and pig iron of Q10 grade, carry out melting and carburizing treatment at 1430 °C to obtain molten iron, add 75 ferrosilicon, and adjust the silicon content in the molten iron to 1.23 wt%; add ferromanganese to make the manganese content in the molten iron 0.13 wt%; the addition amount of the carburizer is 0.2 wt% of the total mass of the molten iron. The elemental composition of the carburizer is: carbon > 98.5%, sulfur < 0.05%, ash < 0.5%, moisture < 0.5%; (2) Carry out spheroidizing, inoculating and microalloying treatment on the molten iron after carburizing treatment in step (1): Lay the inoculant on one side of the dam in a 20T spheroidizing ladle. On the other side of the dam, lay the spheroidizing agent, microalloying Ni from bottom to top in sequence, and then cover the microalloying with cast iron chips, with a covering thickness of 6 mm. Pour the molten iron into the spheroidizing ladle from the side where the inoculant is laid. Among them, the addition amount of the inoculant is 0.54 wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.1 wt% of the total mass of the molten iron; the addition amount of microalloying Ni is 0.46 wt% of the total mass of the molten iron; the addition amount of the carburizer is 0.2 wt% of the total mass of the molten iron; Among them, the elemental composition of the inoculant is: Si 75 ± 3%; Ca 1.0 - 2.0%; Ba 2.0 - 3.0%; Al < 1.5%, and the rest is iron; The elemental composition of the spheroidizing agent is: Si 45.5%, Mg 5.1%, RE 0.243%, Ba 1.31%, Ca 0.94%, and the rest is iron; (3) Pouring: During the pouring process, in-stream inoculant is added for in-stream inoculation. The addition amount of the in-stream inoculant is 0.47 wt% of the total mass of the molten iron. After pouring is completed, the casting is slowly cooled in the mold to below 400 °C (the slow cooling rate is 10 °C / min). The casting is cleaned out of the mold, and it is a ductile iron casting.

[0092] The element composition of the in-stream inoculant is: Si 72.09 wt%, Bi 1.23 wt%, Ca 1.32 wt%, Al 1.09 wt%, and the rest is iron.

[0093] The elements of the obtained ductile iron casting include C 3.71 wt%, Si 2.47 wt%, Mn 0.13 wt%, P 0.024 wt%, S 0.017 wt%, Ni 0.46 wt%, Cr 0.015 wt%, residual Mg 0.048 wt%, and the rest is iron and unavoidable impurities.

[0094] Example 6 (1) Use a 20T intermediate frequency furnace, load high-temperature graphitizing carburizer and pig iron of Q10 grade, carry out melting and carburizing treatment at 1430 °C to obtain molten iron. Add 75 ferrosilicon to adjust the silicon content in the molten iron to 1.44 wt%. Add ferromanganese to make the manganese content in the molten iron 0.125 wt%. The addition amount of the carburizer is 0.2 wt% of the total mass of the molten iron. The element composition of the carburizer is: carbon greater than 98.5 wt%, sulfur less than 0.05 wt%, ash less than 0.5 wt%, and moisture less than 0.5 wt%. (2) Carry out spheroidizing, inoculating and microalloying treatment on the molten iron after the carburizing treatment in step (1): Lay the inoculant on one side of the dam in a 20T spheroidizing ladle. On the other side of the dam, lay the spheroidizing agent, microalloying Ni from bottom to top in sequence, and then cover the microalloying with cast iron chips, with a covering thickness of 6 mm. Pour the molten iron into the spheroidizing ladle from the side where the inoculant is laid. Among them, the addition amount of the inoculant is 0.75 wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.1 wt% of the total mass of the molten iron; the addition amount of microalloying Ni is 0.46 wt% of the total mass of the molten iron. Among them, the element composition of the inoculant is: Si 75 ± 3 wt%; Ca 1.0 - 2.0 wt%; Ba 2.0 - 3.0 wt%; Al < 1.5 wt%, and the rest is iron; The element composition of the spheroidizing agent is: Si 45.5 wt%, Mg 5.1 wt%, RE 0.243 wt%, Ba 1.31 wt%, Ca 0.94 wt%, and the rest is iron; (3) Pouring: During the pouring process, in-stream inoculant is added for in-stream inoculation, and the addition amount of the in-stream inoculant is 0.14 wt% of the total mass of the molten iron. After pouring is completed, the casting is slowly cooled in the mold to below 400 °C (the slow cooling rate is 10 °C / min), and the casting is cleaned out of the mold, which is then a ductile iron casting.

[0095] The elemental composition of the in-stream inoculant is: Si 72.09 wt%, Bi 1.23 wt%, Ca 1.32 wt%, Al 1.09 wt%, and the rest is iron.

[0096] The elements of the obtained ductile iron casting include: C 3.71 wt%, Si 2.60 wt%, Mn 0.125 wt%, P 0.025 wt%, S 0.02 wt%, Ni 0.46 wt%, Cr 0.011 wt%, Mg 残 0.048 wt%, and the rest is iron and inevitable impurities.

[0097] Example 7 (1) Use a 20T intermediate frequency furnace, load high-temperature graphitizing carburizer and pig iron of grade Q10, carry out melting and carburizing treatment at 1430 °C to obtain molten iron, add 75 ferrosilicon, and adjust the silicon content in the molten iron to 1.23 wt%; add ferromanganese to make the manganese content in the molten iron 0.14 wt%; the addition amount of the carburizer is 0.2 wt% of the total mass of the molten iron. The elemental composition of the carburizer is: carbon greater than 98.5 wt%, sulfur less than 0.05 wt%, ash less than 0.5 wt%, and moisture less than 0.5 wt%. (2) Carry out spheroidizing, inoculating and microalloying treatment on the molten iron after the carburizing treatment in step (1): Lay the inoculant on one side of the dam in a 20T spheroidizing ladle. On the other side of the dam, lay the spheroidizing agent, microalloying Ni from bottom to top in sequence, and then cover the microalloying with cast iron chips with a covering thickness of 6 mm. Pour the molten iron into the spheroidizing ladle from the side where the inoculant is laid. Among them, the addition amount of the inoculant is 0.54 wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.1 wt% of the total mass of the molten iron; the addition amount of microalloying Ni is 0.46 wt% of the total mass of the molten iron; Among them, the elemental composition of the inoculant is: Si 75 ± 3 wt%; Ca 1.0 - 2.0 wt%; Ba 2.0 - 3.0 wt%; Al < 1.5 wt%, and the rest is iron; The elemental composition of the spheroidizing agent is: Si 45.5 wt%, Mg 5.1 wt%, RE 0.243 wt%, Ba 1.31 wt%, Ca 0.94 wt%, and the rest is iron; (3) Pouring: During the pouring process, in-mould inoculant is added for in-mould inoculation, and the addition amount of the in-mould inoculant is 0.47 wt% of the total mass of the molten iron. After pouring is completed, the casting is slowly cooled in the mold to below 400 °C (the slow cooling rate is 10 °C / min), and the casting is cleaned out of the mold, which is the ductile iron casting.

[0098] The elemental composition of the in-mould inoculant is: Si 72.09 wt%, Bi 1.23 wt%, Ca 1.32 wt%, Al 1.09 wt%, and the rest is iron.

[0099] The elements of the obtained ductile iron casting include: C 3.71 wt%, Si 2.47 wt%, Mn 0.14 wt%, P 0.025 wt%, S 0.02 wt%, Ni 0.46 wt%, Cr 0.011 wt%, Mg 残 0.048 wt%, and the rest is iron and unavoidable impurities.

[0100] Example 8 Except that the addition amount of the microalloying Ni in Example 2 is adjusted to 0.2 wt% of the total mass of the molten iron, the ductile iron casting is prepared in the same manner as in Example 2.

[0101] The elements of the obtained ductile iron casting include C 3.70 wt%, Si 2.47 wt%, Mn 0.122 wt%, P 0.027 wt%, S 0.017 wt%, Ni 0.20 wt%, Cr 0.009 wt%, Mg 残 0.05 wt%, and the rest is iron and unavoidable impurities.

[0102] Example 9 Except that the addition amount of the microalloying Ni in Example 2 is adjusted to 0.55 wt% of the total mass of the molten iron, the ductile iron casting is prepared in the same manner as in Example 2.

[0103] The elements of the obtained ductile iron casting include C 3.70 wt%, Si 2.47 wt%, Mn 0.122 wt%, P 0.027 wt%, S 0.017 wt%, Ni 0.55 wt%, Cr 0.009 wt%, Mg 残 0.05 wt%, and the rest is iron and unavoidable impurities.

[0104] Comparative Example 1 (1) A 20T intermediate frequency furnace is used, high-temperature graphitizing carburant and pig iron of Q10 grade are charged, and melting and carburizing treatment are carried out at 1430 °C to obtain molten iron. The addition amount of the carburant is 0.2 wt% of the total mass of the molten iron. The element composition of the recarburizer is: carbon > 98.5 wt%, sulfur < 0.05 wt%, ash < 0.5 wt%, moisture < 0.5 wt%. (2)Perform nodulizing, inoculating and microalloying treatments on the molten iron after the recarburizing treatment in step (1): Lay the inoculant on one side of the dam in a 20T nodulizing ladle. On the other side of the dam, lay the nodulizer and microalloy Ni in sequence from bottom to top. Then cover the microalloy with cast iron filings, with a covering thickness of 6 mm. Pour the molten iron into the nodulizing ladle from the side where the inoculant is laid. Among them, the addition amount of the inoculant is 0.5 wt% of the total mass of the molten iron, the addition amount of the nodulizer is 1.1 wt% of the total mass of the molten iron; the addition amount of microalloy Ni is 0.45 wt% of the total mass of the molten iron; Among them, the element composition of the inoculant is: Si 75 ± 3 wt%; Ca 1.0 - 2.0 wt%; Ba 2.0 - 3.0 wt%; Al < 1.5 wt%, and the rest is iron; The element composition of the nodulizer is: Si 45.5 wt%, Mg 5.1 wt%, RE 0.243 wt%, Ba 1.31 wt%, Ca 0.94 wt%, and the rest is iron; (3)Pouring: Add in-stream inoculant for in-stream inoculation during the pouring process. The addition amount of the in-stream inoculant is 0.15 wt% of the total mass of the molten iron; after pouring is completed, the casting is slowly cooled in the mold to below 400 °C (the slow cooling rate is 10 °C / min), and the casting is cleaned out of the mold, which is the ductile iron casting.

[0105] The element composition of the in-stream inoculant is: Si 72.09 wt%, Bi 1.23 wt%, Ca 1.32 wt%, Al 1.09 wt%, and the rest is iron.

[0106] The elements of the obtained ductile iron casting include: C 3.75 wt%, Si 2.65 wt%, Mn 0.12 wt%, P 0.024 wt%, S 0.01 wt%, Ni 0.45 wt%, Mg 残 0.04 wt%, and the rest is iron and inevitable impurities.

[0107] Comparative Example 2 (1)Use a 20T intermediate frequency furnace, load high-temperature graphitizing recarburizer and pig iron of Q10 grade, and carry out melting and recarburizing treatment at 1430 °C to obtain molten iron; the addition amount of the recarburizer is 0.2 wt% of the total mass of the molten iron, The element composition of the recarburizer is: carbon > 98.5%, sulfur < 0.05%, ash < 0.5%, moisture < 0.5%; (2)Perform nodulizing, inoculating, and microalloying treatments on the molten iron after the carburizing treatment in step (1): Lay the inoculant on one side of the dam in a 20T nodulizing ladle. On the other side of the dam, lay the nodulizer and microalloy Ni from bottom to top in sequence, and then cover the microalloy with cast iron filings with a covering thickness of 6 mm. Pour the molten iron into the nodulizing ladle from the side where the inoculant is laid; Among them, the addition amount of the inoculant is 0.54 wt% of the total mass of the molten iron, the addition amount of the nodulizer is 1.1 wt% of the total mass of the molten iron; the addition amount of microalloy Ni is 0.46 wt% of the total mass of the molten iron; Among them, the element composition of the inoculant is: Si 75 ± 3 wt%; Ca 1.0 - 2.0 wt%; Ba 2.0 - 3.0 wt%; Al < 1.5 wt%, and the rest is iron; The element composition of the nodulizer is: Si 45.5 wt%, Mg 5.1 wt%, RE 0.243 wt%, Ba 1.31 wt%, Ca 0.94 wt%, and the rest is iron; (3)Pouring: Add in - stream inoculant during the pouring process for in - stream inoculation. The addition amount of the in - stream inoculant is 0.14 wt% of the total mass of the molten iron; after pouring is completed, the casting is slowly cooled in the mold to below 400 °C (the slow cooling rate is 10 °C / min), and the casting is cleaned out of the mold, which is the ductile iron casting.

[0108] The element composition of the in - stream inoculant is: Si 72.09 wt%, Bi 1.23 wt%, Ca 1.32 wt%, Al 1.09 wt%, and the rest is iron.

[0109] The elements of the obtained ductile iron casting include: C 3.75 wt%, Si 2.49 wt%, Mn 0.16 wt%, P 0.024 wt%, S 0.01 wt%, Ni 0.46 wt%, Mg 残 0.04 wt%, and the rest is iron and inevitable impurities.

[0110] Comparative Example 3 (1)Use a 20T intermediate - frequency furnace to load high - temperature graphitizing carburizer and pig iron of grade Q10, and carry out melting and carburizing treatment at 1430 °C to obtain molten iron; the addition amount of the carburizer is 0.2 wt% of the total mass of the molten iron, The element composition of the carburizer is: carbon > 98.5%, sulfur < 0.05%, ash content < 0.5%, moisture content < 0.5%; (2) Carry out nodulizing, inoculating, and microalloying treatments on the molten iron after the carburizing treatment in step (1): Lay the primary inoculant on one side of the dam in a 20T nodulizing ladle. On the other side of the dam, lay the nodulizer, microalloying Ni, microalloying TiC (the mass ratio of TiC to 75% ferrosilicon is 1:2), and the covering inoculant in sequence from bottom to top. Then cover the microalloying and the covering inoculant with cast iron filings, with a covering thickness of 6 mm. Add the molten iron into the nodulizing ladle from the side where the primary inoculant is laid. Among them, the addition amount of the primary inoculant is 0.35 wt% of the total mass of the molten iron, the addition amount of the nodulizer is 1.1 wt% of the total mass of the molten iron, the addition amount of the covering inoculant is 0.09 wt% of the total mass of the molten iron; the addition amount of microalloying Ni is 0.3 wt% of the total mass of the molten iron; the addition amount of microalloying TiC is 0.025 wt% of the total mass of the molten iron; Among them, the elemental composition of the primary inoculant is: Si 75 ± 3 wt%; Ca 1.0 - 2.0 wt%; Ba 2.0 - 3.0 wt%; Al < 1.5 wt%, and the rest is iron; The elemental composition of the nodulizer is: Si 45.5 wt%, Mg 5.1 wt%, RE 0.243 wt%, Ba 1.31 wt%, Ca 0.94 wt%, and the rest is iron; The elemental composition of the covering inoculant is: Si 73.3 wt%, C 8.0 wt%, V 0.16 wt%, Ca 0.45 wt%, Ba 1.94 wt%, Al 0.52 wt%, and the rest is iron; (3) Pouring: Add in - stream inoculant during the pouring process for in - stream inoculation. The addition amount of the in - stream inoculant is 0.13 wt% of the total mass of the molten iron; after pouring is completed, the casting is slowly cooled in the mold to below 400 °C (the slow cooling rate is 10 °C / min). Clean the casting out of the mold, and it is the ductile iron casting.

[0111] The elemental composition of the in - stream inoculant is: Si 72.09 wt%, Bi 1.23 wt%, Ca 1.32 wt%, Al 1.09 wt%, and the rest is iron.

[0112] The elements of the obtained ductile iron casting include C 3.75 wt%, Si 2.23 wt%, Mn 0.13 wt%, P 0.024 wt%, S 0.01 wt%, V 0.001 wt%, Ni 0.46 wt%, Ti 0.021 wt%, Cr 0.006 wt%, Mg 残 0.04 wt%, and the rest is iron and unavoidable impurities.

[0113] Comparative Example 4 (1) Use a 20T intermediate frequency furnace to charge high-temperature graphitized carburizer and pig iron of grade Q10, and carry out melting and carburizing treatment at 1430°C to obtain molten iron; the addition amount of the carburizer is 0.2wt% of the total mass of the molten iron. The elemental composition of the carburizer is: carbon greater than 98.5%, sulfur less than 0.05%, ash less than 0.5%, and moisture less than 0.5%. (2) Carry out spheroidizing, inoculating and microalloying treatment on the molten iron after the carburizing treatment in step (1): Lay the primary inoculant on one side of the dam in a 20T spheroidizing ladle. On the other side of the dam, lay the spheroidizing agent, microalloying Ni, microalloying TiC (the mass ratio of TiC to 75 ferrosilicon is 1:2) and covering inoculant in sequence from bottom to top. Then cover the microalloying and covering inoculant with cast iron chips, and the covering thickness is 6mm. Pour the molten iron into the spheroidizing ladle from the side where the primary inoculant is laid. Among them, the addition amount of the primary inoculant is 0.41wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.1wt% of the total mass of the molten iron, the addition amount of the covering inoculant is 0.09wt% of the total mass of the molten iron; the addition amount of microalloying Ni is 0.6wt% of the total mass of the molten iron; the addition amount of microalloying TiC is 0.025wt% of the total mass of the molten iron. Among them, the elemental composition of the primary inoculant is: Si 75±3wt%; Ca 1.0 - 2.0wt%; Ba 2.0 - 3.0wt%; Al<1.5wt%, and the rest is iron. The elemental composition of the spheroidizing agent is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron. The elemental composition of the covering inoculant is: Si 73.3wt%, C 8.0wt%, V 0.16wt%, Ca 0.45wt%, Ba 1.94wt%, Al 0.52wt%, and the rest is iron. (3) Pouring: Add in-stream inoculant for in-stream inoculation during the pouring process. The addition amount of the in-stream inoculant is 0.13wt% of the total mass of the molten iron; after the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling speed is 10°C / min), and the casting is cleaned out of the mold, which is the ductile iron casting.

[0114] The elemental composition of the in-stream inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0115] The elements of the obtained ductile iron parts include C 3.75wt%, Si 2.33wt%, Mn 0.125wt%, P 0.024wt%, S 0.01wt%, V 0.001wt%, Ni 0.6wt%, Ti 0.021wt%, Cr 0.006wt%, Mg 残 0.04wt%, and the rest is iron and inevitable impurities.

[0116] Comparative Example 5 (1) Use a 20T intermediate frequency furnace, load high-temperature graphitizing carburizer and pig iron of Q10 grade, carry out smelting and carburizing treatment at 1430°C to obtain molten iron; the addition amount of the carburizer is 0.2wt% of the total mass of the molten iron, The element composition of the carburizer is: carbon greater than 98.5wt%, sulfur less than 0.05wt%, ash less than 0.5wt%, moisture less than 0.5wt%; (2) Carry out spheroidizing, inoculating and microalloying treatment on the molten iron after the carburizing treatment in step (1): Lay the primary inoculant on one side of the dam in a 20T spheroidizing ladle. On the other side of the dam, lay the spheroidizing agent, microalloying Ni, microalloying TiC (the mass ratio of TiC to 75 ferrosilicon is 1:2) and the covering inoculant from bottom to top in sequence. Then cover the microalloying and the covering inoculant with cast iron chips, and the covering thickness is 6mm. Pour the molten iron into the spheroidizing ladle from the side where the primary inoculant is laid; Among them, the addition amount of the primary inoculant is 0.45wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.1wt% of the total mass of the molten iron; the addition amount of microalloying Ni is 0.15wt% of the total mass of the molten iron; Among them, the element composition of the inoculant is: Si 75±3wt%; Ca 1.0 - 2.0wt%; Ba 2.0 - 3.0wt%; Al<1.5wt%, and the rest is iron; The element composition of the spheroidizing agent is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron; (3) Pouring: Add in-stream inoculant for in-stream inoculation during the pouring process. The addition amount of the in-stream inoculant is 0.14wt% of the total mass of the molten iron; after pouring is completed, the casting is slowly cooled to below 400°C in the mold (the slow cooling rate is 10°C / min), and the casting is cleaned out of the mold, which is the ductile iron part.

[0117] The element composition of the in-stream inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0118] The elements of the obtained ductile iron parts include: C 3.75 wt%, Si 2.45 wt%, Mn 0.121 wt%, P 0.024 wt%, S 0.01 wt%, Ni 0.15 wt%, Mg 残 0.04 wt%, and the rest is iron and inevitable impurities.

[0119] 1. Testing of test blocks of ductile iron castings The molten iron prepared according to the above-described examples and comparative examples was cast into test blocks of ductile iron castings. The dimensions of the ductile iron test blocks were designed according to the GB / T 1348-2019 standard, and the thickness of the ductile iron test blocks was 70 mm to compare the effects of different molten iron compositions on the properties of ductile iron castings.

[0120] (1). Performance evaluation of test blocks of ductile iron castings Samples were taken from the cast ductile iron castings according to the following testing methods to test the tensile strength, yield strength, and low impact energy.

[0121] A. Tensile strength was detected according to the method specified in GB / T 228.1; B. Yield strength was detected according to the method specified in GB / T 228.1; C. -20°C low-temperature impact toughness was detected according to the method specified in GB / T 229.

[0122] The main element compositions and specific test results of the ductile iron castings in the examples and comparative examples are shown in Table 1 below. The three performance requirements for the ductile iron casting test blocks are tensile strength > 400 MPa, yield strength > 280 MPa, and -20°C low impact energy > 7 J.

[0123] The main element compositions of ductile iron were detected using EDS. The instrument used in this experiment was the German Zeiss SUPRA 55 field emission scanning electron microscope used in conjunction with an energy spectrometer.

[0124] Table 1

[0125] From the experimental data in Table 1 above, it can be seen that the contents of Si, Mn, and Ni in the test blocks of ductile iron in Examples 1-9 were in the ranges of 2.3-2.6 wt%, ≤ 0.14 wt%, and 0.20-0.55 wt% respectively. Therefore, the tensile strength of the test blocks of ductile iron in Examples 1-9 was greater than 400 MPa, the yield strength was greater than 280 MPa, and the low-temperature impact energy at -20°C was greater than 7 J.

[0126] In Comparative Example 1, the Si content of the ductile iron exceeds 2.6 wt%, so the low-temperature impact energy of the ductile iron in Comparative Example 1 at -20 °C is less than 7 J.

[0127] In Comparative Example 2, the Mn content of the ductile iron exceeds 0.14 wt%, so the low-temperature impact energy of the ductile iron in Comparative Example 2 at -20 °C is less than 7 J.

[0128] In Comparative Example 3, the Si content of the ductile iron is less than 2.3 wt%, so the yield strength of the ductile iron in Comparative Example 3 is less than 280 MPa.

[0129] In Comparative Example 4, the Ni content of the ductile iron is greater than 0.55 wt%, so the low-temperature impact energy of the ductile iron in Comparative Example 4 at -20 °C is less than 7 J.

[0130] In Comparative Example 5, the Ni content of the ductile iron is less than 0.20 wt%, so the tensile strength of the ductile iron in Comparative Example 5 is less than 410 MPa, and the yield strength is less than 280 MPa.

[0131] In the preparation processes of Examples 1 to 3, in step (1), the Si content was controlled to be 1.4 - 1.6 wt%, and the Mn content was controlled to be less than or equal to 0.14 wt%. In step (2), the Ni content was controlled to be 0.20 - 0.55 wt% by microalloying treatment, and a spheroidizing agent and an inoculant were added to control the Si content to be 2.25 - 2.45 wt%. In step (3), a stream inoculant was added to control the Si content to be 2.3 - 2.6 wt%.

[0132] In the preparation process of Example 4, the Si content in step (1) was 1.15 wt%, and the Si content was not controlled within the range of 1.4 - 1.6 wt%. The Si content in step (2) was 2.21 wt%, and the Si content was not controlled within the range of 2.25 - 2.45 wt%.

[0133] In the preparation process of Example 5, the Si content in step (1) was 1.23 wt%, and the Si content was not controlled within the range of 1.4 - 1.6 wt%. The Si content in step (2) was 2.13 wt%, and the Si content was not controlled within the range of 2.25 - 2.45 wt%.

[0134] As can be seen from Table 1 above, compared with Examples 4 and 5, the ductile iron of Examples 1 to 3 can achieve more excellent technical effects in terms of tensile strength, yield strength, and / or low-temperature impact energy at -20 °C.

[0135] (2). Metallography of test blocks of ductile iron castings 2.1 Scanning Electron Microscope Test The scanning electron microscope used in this test is the Zeiss SUPRA 55 field emission scanning electron microscope from Germany. Its principle is to use secondary electron signals to form images to observe the surface morphology of samples. The adjustment range is 20V - 30KV, the adjustment step is continuously adjustable every 10V, and the magnification is 12X - 1,000,000X. The scanning electron microscope is mainly used to observe the tensile fracture morphology, the surface morphology of wear-resistant specimens, and the thermal fatigue crack morphology.

[0136] 2.2 Three-dimensional Video Electron Microscope Test In this test, a Keyence-1000E three-dimensional video electron microscope was used to detect and analyze the tensile and wear specimens. According to the taken photos, the concavity and convexity of the specimen surface were observed, and the average scratch depth of the worn surface was calculated.

[0137] 2.3 Test Results (1) Graphite Morphology Figure 4A To compare the graphite morphology of the ductile iron in Comparative Example 1, Figure 4B is the graphite morphology of the ductile iron in Example 1. It can be seen that, compared with Figure 4A , Figure 4B the spheroidization rate of the graphite is higher and the distribution is more uniform.

[0138] (2) Tensile Fracture Morphology Figure 5A is the tensile fracture morphology of the ductile iron in Comparative Example 1, Figure 5B is the tensile fracture morphology of the ductile iron in Example 1. It can be seen from Figure 5B that macroscopically, the undulation degree of the whole section is not large. The surface morphology of the tensile fracture of the original specimen shows an uneven state, and some graphite balls fall off or break during the tensile test, resulting in holes on the section surface, indicating that the bonding ability between the graphite balls and the matrix is relatively weak. It can be seen from Figure 5B that compared with the original specimen, macroscopically, in terms of the overall flatness of the section, the roughness and undulation degree of the specimen section increase, making it more three-dimensional and having a stronger sense of hierarchy; microscopically, in the tensile fracture morphology of the specimen, the separation of graphite balls from the matrix is significantly reduced, the number of complete graphite balls in the specimen increases, and the dispersion is more uniform. In addition, Figure 5A in the original specimen of Figure 5BAmong them, by comparing the fracture morphology of the specimen, the number of tearing ridges on the fracture surface significantly increases, the distribution of dimples on the ridges is more uniform and dense, the tearing ridges show a bright white color, and each tearing ridge is interconnected to form a network-like closed structure that encloses the graphite balls within it.

[0139] (3) Three-dimensional morphology of tensile fracture Figure 6A To compare the three-dimensional morphology of the tensile fracture of the ductile iron in Example 1, Figure 6B is the three-dimensional morphology of the tensile fracture of the ductile iron in Example 1. From Figure 6A and Figure 6B it can be seen that the concavity and convexity differences in the three-dimensional morphology of the fracture surfaces of the two specimens are relatively large. Among them, Figure 6A the maximum protrusion height of the tensile fracture of the specimen is 596.4 μm, Figure 6B and the maximum protrusion height of the tensile fracture is 687.3 μm, increasing the value of the maximum height difference of the tensile fracture by 15.24%; Judging from the test results, the toughness of the tensile fracture of the ductile iron in Example 1 has been improved.

[0140] (4) Impact fracture morphology Figure 7A is the impact fracture morphology of the ductile iron in Comparative Example 1, Figure 7B is the impact fracture morphology of the ductile iron in Example 1. From Figure 7A it can be seen that the number of tearing ridges on the impact specimen fracture is not large, but the size is relatively large. A certain number of large dimples are formed around the tearing ridges, and a dimple band is formed in some parts. At the same time, cleavage planes exist in some parts of the fracture surface. This phenomenon indicates that during the fracture process of the impact specimen, quasi-cleavage fracture occurs, belonging to mixed fracture. From Figure 7B it can be seen that the number of dimples in its fracture is significantly more than that of the Figure 7A specimen, the length of the tearing ridges becomes significantly shorter and thinner, and the degree of curvature increases. Under the action of impact stress, adjacent dimples can be connected to form a fracture with a certain directionality.

[0141] The tensile strength of the ductile iron according to the embodiment of the present invention is greater than 400 MPa, the yield strength is greater than 280 MPa, and the low-temperature impact energy at -20 °C is greater than 7 J, and it can be applied to large-section castings in wind turbine generators.

[0142] 2. Testing of large-section ductile iron castings In order to test whether the molten iron according to the embodiment of the present invention can also meet the performance requirements of the corresponding castings when poured into large-section ductile iron castings, the following tests are carried out.

[0143] The molten iron prepared according to Example 1 and Comparative Example 1 described above was cast into a main shaft by permanent mold casting and ordinary sand casting respectively. The wall thickness of the metal external mold is 200 mm, and ordinary sand casting refers to sand casting without the chilling of chill iron.

[0144] The preheating temperature of the cavity for permanent mold casting is 100 °C, the pouring temperature is 1330 - 1360 °C, and the pouring speed of the molten iron is 100 - 150 kg / s. The pouring temperature for sand casting is 1330 - 1360 °C, and the pouring speed of the molten iron is 100 - 150 kg / s.

[0145] The dimensions of the main shaft are as follows: the outer diameter of the shaft body 21 is 1500 mm, the outer diameter of the large flange is 2500 mm, and the outer diameter of the small flange is 1500 mm.

[0146] Samples were taken from the shaft body, large flange, and small flange of the cast main shaft according to the following testing methods to test the tensile strength, yield strength, and low impact energy.

[0147] (1) Tensile strength was detected according to the method specified in GB / T 228.1; (2) Yield strength was detected according to the method specified in GB / T 228.1; (3) The low-temperature impact toughness at -20 °C was detected according to the method specified in GB / T 229.

[0148] Table 2

[0149] As shown in Table 2, Example 10 is the main shaft cast from the molten iron of Example 1 by permanent mold casting, Comparative Example 6 is the main shaft cast from the molten iron of Example 1 by ordinary sand casting, Comparative Example 7 is the main shaft cast from the molten iron of Comparative Example 1 by permanent mold casting, and Comparative Example 8 is the main shaft cast from the molten iron of Comparative Example 1 by ordinary sand casting.

[0150] Compared with Comparative Example 6, the comprehensive mechanical properties of the shaft body, large flange, and small flange of the main shaft in Example 10 were significantly improved, indicating that the tensile strength, yield strength, and low-temperature impact energy of each part of the main shaft cast from the molten iron of the permanent mold casting of the present invention and Example 1 of the present invention have been improved.

[0151] In addition, although the tensile strength and yield strength of Comparative Example 7 are relatively high, its low-temperature impact energy is significantly reduced, and it is impossible to simultaneously improve the tensile strength, yield strength, and low-temperature impact energy of all parts of the main shaft. In addition, the tensile strength, yield strength, and low-temperature impact energy of all parts of the main shaft of Comparative Example 8 have not been improved. That is to say, regardless of whether the molten iron prepared according to Comparative Example 1 is poured by ordinary sand casting or iron mold casting, the comprehensive performance of the shaft body, large flange, and small flange of the main shaft is relatively low.

[0152] Therefore, when manufacturing large-section ductile iron castings with high performance requirements for each part (for example, large-section fan main shafts), by using the iron mold casting method provided by the present invention to pour the molten iron composition provided by the present invention, the comprehensive performance requirements of each part of the large-section ductile iron casting (for example, the main shaft) can be met.

[0153] According to an embodiment of the present invention, a ductile iron casting formed by the above iron mold casting method can also be provided. The ductile iron casting can be a large-section casting, for example, the wall thickness is greater than or equal to 60 mm.

[0154] The ductile iron casting can be the main shaft 20 as described above. According to another embodiment of the present invention, a wind power generation unit including the main shaft 20 can also be provided.

[0155] According to the iron mold casting method of the ductile iron casting of the present invention, by controlling the composition of the ductile iron casting and / or the iron mold casting method, the comprehensive mechanical properties of the ductile iron casting can be improved.

[0156] According to the iron mold casting method of the ductile iron casting of the present invention, by controlling the composition of the ductile iron casting, the tensile strength of the test block of the ductile iron casting can be greater than 400 MPa, the yield strength can be greater than 280 MPa, and the low-temperature impact energy at -20°C can be greater than 7 J. Therefore, it can be widely applied to the manufacture of ductile iron castings with high comprehensive performance requirements.

[0157] In addition, according to the iron mold casting method of the ductile iron casting of the present invention, by using the iron mold casting method provided by the present invention to pour the molten iron composition provided by the present invention, the comprehensive performance requirements of each part of the ductile iron casting can be met. Therefore, the iron mold casting method of the ductile iron casting of the present invention can be widely applied to large-section castings in wind power generation units or castings with high comprehensive performance requirements in other fields.

[0158] Although the exemplary embodiments of the present invention have been specifically described with reference to their exemplary embodiments, those skilled in the art should understand that various changes in form and detail can be made without departing from the spirit and scope of the present invention defined by the claims.

Claims

1. A method for casting ductile iron castings in an iron mold, characterized in that, The ductile iron casting method includes pouring molten iron into a cavity (130) formed by a metal outer mold (110) and a sand core (120). The ductile iron casting, by mass percentage, includes: C 3.6 - 3.8wt%, Si 2.3 - 2.6wt%, Mn ≤0.14wt%, Ni 0.20 - 0.55wt%.

2. The iron mold casting method of the ductile iron casting according to claim 1, characterized in that, The ductile iron casting method further includes: (1) Melting: subjecting a material including pig iron to carbon addition treatment and melting it into molten iron; (2) Spheroidizing and inoculating: spheroidizing and inoculating the molten iron obtained from step (1); and (3) Pouring: pouring the molten iron obtained from step (2) into the cavity (130), wherein, in step (1) and / or step (2), the preparation method further includes microalloying treatment, and the microalloying treatment includes adding Ni, adding a spheroidizing agent containing Si and an inoculant containing Si in step (2) and adding a stream inoculant containing Si in step (3).

3. The iron mold casting method of the ductile iron casting according to claim 2, characterized in that, Based on the total mass of the molten iron, in step (1), the content of Si included in the material is in the range of 1.4 - 1.6wt%, in step (2), adding a spheroidizing agent containing Si and an inoculant containing Si such that the content of Si is in the range of 2.25 - 2.45wt%, and in step (3), adding a stream inoculant containing Si such that the content of Si is in the range of 2.3 - 2.6wt%.

4. The ductile iron casting method of the ductile iron casting according to claim 2, wherein based on the total mass of the spheroidizing agent, the spheroidizing agent, by mass percentage, includes 40 - 50wt% of Si, based on the total mass of the inoculant, the inoculant, by mass percentage, includes 72 - 78wt% of Si, based on the total mass of the stream inoculant, the stream inoculant, by mass percentage, includes 70 - 80wt% of Si.

5. The ductile iron casting method of the ductile iron casting according to claim 4, wherein based on the total mass of the inoculant, the inoculant, by mass percentage, includes: Si 72 - 78wt%, Ca 1.0 - 2.0wt%, Ba 2.0 - 3.0wt%, Al < 1.5wt%, and the balance is iron, based on the total mass of the spheroidizing agent, the spheroidizing agent, by mass percentage, includes: Mg 4.5 - 6wt%, RE 0.15 - 0.3wt%, Si 40 - 50wt%, and the balance is iron, based on the total mass of the stream inoculant, the stream inoculant, by mass percentage, includes: Si 70 - 80wt%, Bi 0.5 - 2.5wt%, Ca ≤2.0wt%, Al ≤2.0wt%, and the balance is Fe.

6. The ductile iron casting method of the ductile iron casting according to claim 4, wherein in step (2), the addition amount of the inoculant is 0.35 - 0.67wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.0 - 1.3wt% of the total mass of the molten iron, in step (3), the addition amount of the stream inoculant is 0.08 - 0.2wt% of the total mass of the molten iron.

7. The iron mold casting method of the ductile iron casting according to claim 6, characterized in that, The inoculant in step (2) includes a primary inoculant and a covering inoculant. Based on the total mass of the primary inoculant, the primary inoculant includes, by mass percentage: 72 - 78 wt% Si, 1.0 - 2.0 wt% Ca, 2.0 - 3.0 wt% Ba, Al < 1.5 wt%, and the balance is iron. Based on the total mass of the covering inoculant, the covering inoculant includes, by mass percentage: 72 - 78 wt% Si, 1.0 - 2.0 wt% Ca, 2.0 - 3.0 wt% Ba, Al < 1.5 wt%, and the balance is iron.

8. The iron mold casting method of the ductile iron casting according to claim 7, characterized in that, In step (2), The addition amount of the primary inoculant is 0.30 - 0.55 wt% of the total mass of the molten iron. The addition amount of the covering inoculant is 0.05 - 0.12 wt% of the total mass of the molten iron.

9. The method for casting ductile iron castings in an iron mold according to claim 2, characterized in that Mg is added in step (2) such that, based on the total mass of the molten iron, the content of Mg is in the range of 0.045 - 0.078 wt%. Based on the total mass of the spheroidizing agent, the spheroidizing agent includes 4.5 - 6 wt% Mg by mass percentage, and the addition amount of the spheroidizing agent in step (2) is 1.0 - 1.3 wt% of the total mass of the molten iron. In step (1) and / or step (2), the addition amount of Ni is 0.2 - 0.4 wt% of the total mass of the molten iron. The microalloying treatment in step (1) and / or step (2) includes adding Ni such that the content of Ni is in the range of 0.20 - 0.55 wt% of the total mass of the molten iron. In step (1) and / or step (2), the microalloying treatment further includes adding TiC to the molten iron, and the addition amount of TiC is 0.01 - 0.03 wt% of the total mass of the molten iron.

10. The method for casting ductile iron castings in an iron mold according to claim 1, characterized in that, The pig iron in step (1) is pig iron of grade Q10 or above. In step (1), the content of Mn is adjusted so that the content of Mn in step (1) is in the range of 0.10 - 0.12 wt% of the total mass of the molten iron.

11. The iron mold casting method of the ductile iron casting according to claim 1, characterized in that, The wall thickness of the metal external mold (110) is 100 mm - 200 mm.

12. The iron mold casting method of the ductile iron casting according to claim 2, characterized in that, Before pouring the molten iron into the cavity (130), the temperature of the cavity (130) is preheated to 50 - 200 °C. In step (4), the pouring temperature of the molten iron is 1330 - 1360 °C, and the pouring speed of the molten iron is 100 - 150 kg / s.

13. The method for casting ductile iron castings in an iron mold according to claim 1, characterized in that, The content of Si is in the range of 2.30 - 2.40 wt%.

14. A ductile iron casting, characterized in that, The ductile iron casting is formed by the iron mold casting method according to any one of claims 1 to 13.

15. The ductile iron casting according to claim 14, wherein, The wall thickness of the ductile iron casting is greater than or equal to 60 mm.

16. The ductile iron casting according to claim 14, wherein The ductile iron casting is the main shaft (20) of a wind power generating set. The main shaft (20) includes a shaft body (21), a large flange (22) provided at one axial end of the shaft body (21), a trumpet-shaped connecting member (23) connecting the shaft body (21) and the large flange (22), and a small flange (24) provided at the other axial end of the shaft body (21). The outer diameter of the shaft body (21) is greater than or equal to 1.0 m.

17. A wind power generating set, characterized in that, The wind turbine generator set includes a ductile iron casting according to any one of claims 14 to 16.

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