Method for improving graphite structure uniformity of nodular iron casting for wind power casting

Abstract

The invention discloses a method for improving graphite structure uniformity of a nodular iron casting for a wind power casting, and belongs to the technical field of casting. The method for improving the graphite structure uniformity of the nodular iron casting for the wind power casting comprises the following steps: (1) preparing materials: 40-45wt% of pig iron, 30-35wt% of scrap steel and 20-30wt% of foundry returns; (2) pig iron, foundry returns and waste steel are put into a medium-frequency induction furnace to be melted into molten iron, and a carburant, ferrosilicon and a desulfurizing agent are added to conduct component adjustment on the molten iron; (3) a spheroidizing agent, alloy antimony and a nucleating agent are sequentially placed at the bottom of a casting ladle from bottom to top in advance, and molten iron obtained after component adjustment is poured into the casting ladle; (4) the molten iron treated in the step (3) is subjected to slagging-off and then poured into a casting mold, and a stream inoculant is added in the pouring process; and (5) after the pouring is finished, slowly cooling to below 350 DEG C in a casting mold provided with a chilling block, and removing a casting from the casting mold.

Description

Technical Field

[0001] This invention relates to the field of casting technology, specifically to a method for improving the uniformity of graphite structure in ductile iron castings used in wind power castings. Background Technology

[0002] As early as two thousand years ago, my country was already capable of producing cast iron parts with spheroidal graphite characteristics, making it the world's earliest country to master ductile iron manufacturing technology. However, limited by the smelting and control technology at the time, the process conditions were extremely demanding, making it difficult to achieve stable mass production. Therefore, this ancient technology has not survived to the present day. Modern industrial production of ductile iron began in 1943 when American scholar K.D. Millis first successfully prepared cast iron with spheroidal graphite structure using a nickel-magnesium (Ni-Mg) alloy. Its basic process principle is highly similar to today's mainstream spheroidizing treatment methods. Since 1949, with the continuous advancement of spheroidizing and inoculation technologies, the production process of ductile iron has become increasingly mature, achieving rapid development and widespread application globally in the 1950s and 60s.

[0003] In the production process of ductile iron, in addition to common casting defects (such as porosity, sand inclusions, and cold shuts), some unique metallurgical defects are also prone to occur, mainly including slag inclusions, graphite flotation, spheroidization decay, shrinkage cavities, and shrinkage porosity. Among these, shrinkage cavities and shrinkage porosity are particularly prominent, mainly due to the unique solidification characteristics of ductile iron: its eutectic solidification occurs in a "pasty" manner, with a large number of eutectic clusters and random growth directions, resulting in obstructed feeding channels and making it easy to form microscale shrinkage porosity defects between dendrites or at the boundaries of eutectic clusters. Although current engineering practices have widely adopted techniques such as increasing mold stiffness, optimizing pouring temperature, setting risers, or combining chills to effectively suppress the formation of concentrated shrinkage cavities on a macroscopic level and reduce the size and distribution range of shrinkage porosity areas to some extent, large-area and locally concentrated micro-shrinkage porosity structures can still be observed under a metallographic microscope.

[0004] For ordinary ductile iron parts with relatively simple stress states, such micro-defects have limited impact on overall performance. However, in large ductile iron castings used in wind power equipment, especially under harsh service conditions such as low temperature, high load, and alternating stress, micro-shrinkage porosity can not only become a source of fatigue crack initiation but also significantly reduce the material's low-temperature impact toughness and fracture resistance, thereby threatening the safety and reliability of the entire machine. Furthermore, the size, quantity, and uniformity of graphite spheres directly determine the continuity of the matrix structure and the consistency of mechanical properties. Uneven graphite structure can easily lead to localized stress concentration, further exacerbating the harm caused by micro-shrinkage porosity.

[0005] Therefore, there is an urgent need to develop an inoculation treatment technology that can effectively improve the uniformity of graphite structure in ductile iron for wind power castings. This technology can promote the precipitation of fine, dispersed, and uniform graphite spheres while optimizing the feeding behavior during solidification, thereby reducing the tendency of micro-shrinkage porosity from the source and significantly improving the internal quality stability and service safety of the castings. Summary of the Invention

[0006] The purpose of this invention is to provide a method for improving the uniformity of graphite structure in ductile iron castings for wind power applications, thereby solving the technical problems mentioned in the background section.

[0007] The technical solution to achieve the objective of this invention is: This invention provides a method for improving the uniformity of graphite structure in ductile iron castings used in wind power projects, comprising the following steps: (1) Material preparation: 40-45 wt% pig iron, 30-35 wt% scrap steel, 20-30 wt% recycled material; (2) Pig iron, recycled materials and scrap steel are put into a medium frequency induction furnace to melt into molten iron, and carbon raiser, ferrosilicon and desulfurizer are added to adjust the composition of molten iron; (3) Place the spheroidizing agent, TiC nanoparticles, antimony alloy, and inoculant in sequence from bottom to top at the bottom of the ladle before pouring in the molten iron with adjusted composition; (4) After removing the slag from the molten iron treated in step (3), pour it into the mold and add a flow-inoculating agent during the pouring process; (5) After pouring, the casting is slowly cooled to below 350°C in a mold with chills and then removed from the mold.

[0008] Furthermore, the carbon raiser is a high-temperature graphitized carbon raiser with a fixed carbon content of ≥ 99.0% and a particle size of 0.5~5.0 mm.

[0009] Furthermore, the ferrosilicon is 72 ferrosilicon, whose main components are silicon 72.0~75.0%, aluminum ≤1.50%, calcium ≤1.50%, and the remainder is iron, with a particle size of 5.0~100.0 mm.

[0010] Furthermore, the desulfurizing agent consists of lime and calcium carbide, with a particle size of 0.5~5.0 mm.

[0011] Furthermore, the elements and contents of the molten iron composition adjusted in step (2) include: C: 3.35~3.45wt%, Si: 2.50~2.70wt%, Mn: 0.120~0.150wt%, P≤0.035wt%, S≤0.012wt%, and the remainder is iron.

[0012] Furthermore, the spheroidizing agent is selected from rare earth silicon-iron-magnesium alloy. The main components of the rare earth silicon-iron-magnesium alloy include 5.5~6.0wt%Mg, 0.15~0.30wt%Re, 45.0~50.0wt%Si, 0.80~1.50wt%Ca, and the remainder is iron. The amount of spheroidizing agent used is 0.95~1.15wt% based on the weight percentage of the molten iron, and the particle size is 4~28 mm.

[0013] Furthermore, the preparation method of the TiC nanoparticles is as follows: iron powder and titanium carbide are mixed and ball-milled at a mass ratio of 2.5~3.5:5 to obtain TiC nanoparticles. The ball milling speed is 600~800 r / min, the grinding balls are corundum balls, the ball-to-material ratio is 3.6~4:1, and the ball milling time is 3~12 h. The amount of TiC nanoparticles added as a spheroidizing agent is 0.1~0.3 wt% based on the weight percentage of the molten iron.

[0014] Furthermore, the inoculant is a silicon-calcium-barium inoculant whose main components include 70.0~75.0wt% Si, 2.00~3.00wt% Ba, 1.00~2.00wt% Ca, with the remainder being Fe, and a particle size of 3.0~8.0mm; the in-flow inoculant is a sulfur-oxygen inoculant, and the amount of inoculant added is 0.25~0.45wt% based on the weight percentage of the molten iron, the amount of antimony alloy added is 30~50 ppm, and the amount of in-flow inoculant added is 0.11~0.13wt%.

[0015] Furthermore, the chills are placed in molds on both sides of the casting cross-section, with the thickness of the chills on each side being 1 / 3 to 1 / 2 of the casting cross-section thickness.

[0016] Furthermore, in step (5), a pressure of 50-100 MPa is applied during the cooling of the molten iron in the mold.

[0017] By adopting the above technical solution, the present invention has the following beneficial effects: This invention relates to a method for improving the uniformity of graphite microstructure in ductile iron castings used in wind power projects. The method includes key steps such as smelting, composition adjustment, spheroidization inoculation treatment, in-flow inoculation casting, and cooling. Its core lies in the synergistic effect of introducing TiC nanoparticles and optimizing solidification conditions. This not only significantly increases the number of graphite spheres, refines their size, and improves their roundness, but also achieves a highly uniform distribution of graphite microstructure at both the macroscopic and microscopic scales.

[0018] Specifically, during the spheroidization inoculation stage, TiC nanoparticles, prepared by high-energy ball milling of iron powder and titanium carbide particles, are placed at the bottom of the ladle in advance. TiC nanoparticles have high melting point, high stability, and lattice matching degree similar to graphite, and can serve as efficient heterogeneous nucleation nuclei, significantly increasing the number of graphite spheres during the early stage of eutectic solidification of molten iron. The large number of uniformly distributed nucleation points effectively inhibit local graphite coarsening and aggregation, promoting the precipitation of graphite in a fine, round, and dispersed manner, thereby improving the number density and distribution uniformity of graphite spheres.

[0019] Subsequently, during the pouring process, in-flow inoculation was used to further supplement active inoculation elements, maintain good inoculation effect of molten iron, and prevent inoculation decline. At the same time, molten iron was poured into a mold with chills on both sides of the casting cross-section and subjected to high-pressure cooling. The setting of chills accelerated the heat dissipation rate in the casting cross-section, shortened the solidification time, reduced the width of the pasty solidification zone, facilitated the smooth flow of feeding channels, and inhibited the formation of micro shrinkage porosity. High-pressure cooling further promoted the homogenization of the temperature field, reduced local overcooling or overheating areas, and allowed graphite spheres to precipitate synchronously and uniformly on the entire casting cross-section. Attached Figure Description

[0020] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a metallographic image of the center position of a stepped test block with a wall thickness of 200 mm, according to an embodiment of the present invention.

[0021] Figure 2 Metallographic image of the center position of a stepped test block with a wall thickness of 200 mm, according to another embodiment of the present invention.

[0022] Figure 3 This is a metallographic image of the center position of a stepped test block with a wall thickness of 270 mm, according to an embodiment of the present invention.

[0023] Figure 4 Metallographic image of the center position of a stepped test block with a wall thickness of 270 mm, according to another embodiment of the present invention. Detailed Implementation

[0024] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0027] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0028] The pig iron is made of high-purity cast iron for ductile iron production. Its main components are: C: 4.0~4.5wt%, Si: 0.40~0.60wt%, Mn≤0.10wt%, P≤0.03wt%, S≤0.01wt%, Ti<0.010wt%, and the remainder is iron.

[0029] The scrap steel is selected from high-quality carbon steel sheets, with the following main components: C≤0.15wt%, Si≤0.40wt%, Mn≤0.30wt%, P≤0.02wt%, S≤0.03wt%, Cr≤0.06wt%, Ti<0.001wt%, and the remainder is iron.

[0030] The recycled material is ferritic ductile iron recycled material. Example

[0031] A method for improving the uniformity of graphite microstructure in ductile iron castings for wind power applications, comprising the following steps: (1) Material preparation: 40-45 wt% pig iron, 30-35 wt% scrap steel, 20-30 wt% recycled material; (2) Pig iron, recycled materials and scrap steel are put into a medium frequency induction furnace to melt into molten iron. The temperature is measured. When the temperature of the molten iron in the furnace reaches 1480℃, a sample is taken for composition analysis. The composition of the molten iron is adjusted by adding carbon raiser, ferrosilicon and desulfurizer. The elements and contents of the adjusted molten iron are as follows: C: 3.35~3.45wt%, Si: 2.50~2.70wt%, Mn: 0.120~0.150wt%, P≤0.035wt%, S≤0.012wt%, and the remainder is iron; (3) Place the spheroidizing agent, TiC nanoparticles, antimony alloy, and inoculant in sequence from bottom to top at the bottom of the dam-type spheroidizing ladle, and pour in the molten iron after the composition adjustment in step (2); a funnel is set at the ladle nozzle of the dam-type spheroidizing ladle; (4) After removing the slag from the molten iron treated in step (3), pour it into the mold. Add a flow-through inoculant during the pouring process. The pouring temperature is 1350℃. (5) After pouring, the casting is slowly cooled to below 350°C at 50~100MPa in a mold equipped with chills, and then removed from the mold.

[0032] The carbon raiser is a high-temperature graphitized carbon raiser with a fixed carbon content of ≥ 99.0% and a particle size of 0.5~5.0 mm.

[0033] The ferrosilicon is 72 ferrosilicon, whose main components are silicon 72.0~75.0%, aluminum ≤1.50%, calcium ≤1.50%, and the remainder is iron, with a particle size of 5.0~100.0 mm.

[0034] The desulfurizing agent consists of lime and calcium carbide, with a particle size of 0.5~5.0 mm.

[0035] The spheroidizing agent is a rare earth silicon-iron-magnesium alloy, whose main components include 5.5~6.0wt%Mg, 0.15~0.30wt%Re, 45.0~50.0wt%Si, 0.80~1.50wt%Ca, with the remainder being iron, and a particle size of 4~28 mm.

[0036] The TiC nanoparticles are prepared as follows: iron powder and titanium carbide are mixed and ball-milled at a mass ratio of 2.5~3.5:5 to obtain TiC nanoparticles. The ball milling speed is 600~800 r / min, the grinding balls are corundum balls, the ball-to-material ratio is 3.6~4:1, and the ball milling time is 3~12 h.

[0037] The inoculant is a silicon-calcium-barium inoculant, whose main components include 70.0~75.0wt% Si, 2.00~3.00wt% Ba, 1.00~2.00wt% Ca, with the remainder being Fe, and a particle size of 3.0~8.0mm. The in-flow inoculant is a sulfur-oxygen inoculant, whose main components are: Si: 74.5wt%, S: 0.71wt%, O: 0.69wt%, Ba: 0.20wt%, Ca: 0.94wt%, Ce: 1.73wt%, with the remainder being iron. Based on the weight percentage of the molten iron, the inoculant addition is 0.25~0.45wt%, the antimony alloy addition is 30~50 ppm, the in-flow inoculant addition is 0.11~0.13wt%, the spheroidizing agent addition is 0.95~1.15wt%, and the spheroidizing agent TiC nanoparticle addition is 0.1~0.3wt%.

[0038] The chills are placed in the molds on both sides of the casting cross-section, and the thickness of the chills on each side is 1 / 3 to 1 / 2 of the thickness of the casting cross-section. Example 1

[0039] A method for improving the uniformity of graphite microstructure in ductile iron castings for wind power applications, comprising the following steps: (1) Material preparation: 40-45 wt% pig iron, 30-35 wt% scrap steel, 20-30 wt% recycled material; (2) Pig iron, recycled materials and scrap steel are put into a medium frequency induction furnace to melt into molten iron. The temperature is measured. When the temperature of the molten iron in the furnace reaches 1480℃, a sample is taken for composition analysis. The composition of the molten iron is adjusted by adding carbon raiser, ferrosilicon and desulfurizer. The elements and contents of the adjusted molten iron are: C: 3.45wt%, Si: 2.70wt%, Mn: 0.120~0.150wt%, P≤0.035wt%, S≤0.012wt%, and the remainder is iron. (3) Place the spheroidizing agent, TiC nanoparticles, antimony alloy, and inoculant in sequence from bottom to top at the bottom of the dam-type spheroidizing ladle, and pour in the molten iron after the composition adjustment in step (2); a funnel is set at the ladle nozzle of the dam-type spheroidizing ladle; (4) After removing the slag from the molten iron treated in step (3), pour it into the mold. Add a flow-inoculating agent during the pouring process. The pouring temperature is 1340℃. (5) After pouring, the casting is slowly cooled to below 350°C at 50~100MPa in a mold equipped with chills, and then removed from the mold.

[0040] The carbon raiser is a high-temperature graphitized carbon raiser with a fixed carbon content of ≥ 99.0% and a particle size of 0.5~5.0 mm.

[0041] The ferrosilicon is 72 ferrosilicon, whose main components are silicon 72.0~75.0%, aluminum ≤1.50%, calcium ≤1.50%, and the remainder is iron, with a particle size of 5.0~100.0 mm.

[0042] The desulfurizing agent consists of lime and calcium carbide, with a particle size of 0.5~5.0 mm.

[0043] The spheroidizing agent is a rare earth silicon-iron-magnesium alloy, whose main components include 5.5~6.0wt%Mg, 0.15~0.30wt%Re, 45.0~50.0wt%Si, 0.80~1.50wt%Ca, with the remainder being iron, and a particle size of 4~28 mm.

[0044] The TiC nanoparticles are prepared as follows: iron powder and titanium carbide are mixed and ball-milled at a mass ratio of 2.5~3.5:5 to obtain TiC nanoparticles. The ball milling speed is 600~800 r / min, the grinding balls are corundum balls, the ball-to-material ratio is 3.6~4:1, and the ball milling time is 3~12 h.

[0045] The inoculant is a silicon-calcium-barium inoculant, whose main components include 70.0~75.0wt% Si, 2.00~3.00wt% Ba, 1.00~2.00wt% Ca, with the remainder being Fe, and a particle size of 3.0~8.0mm. The in-flow inoculant is a sulfur-oxygen inoculant, whose main components are: Si: 74.5wt%, S: 0.71wt%, O: 0.69wt%, Ba: 0.20wt%, Ca: 0.94wt%, Ce: 1.73wt%, with the remainder being iron. Based on the weight percentage of the molten iron, the inoculant addition is 0.25wt%, the antimony alloy addition is 30 ppm, the in-flow inoculant addition is 0.11wt%, the spheroidizing agent addition is 0.95wt%, and the spheroidizing agent TiC nanoparticle addition is 0.1wt%.

[0046] The chills are placed in molds on both sides of the casting cross-section, with the thickness of the chills on each side being 1 / 3 of the thickness of the casting cross-section.

[0047] like Figure 1 , 3 Metallographic images of the center positions of the stepped test blocks of ductile iron castings for wind power castings obtained in Example 2, with wall thicknesses of 200 mm and 270 mm. Example 2

[0048] A method for improving the uniformity of graphite microstructure in ductile iron castings for wind power applications, comprising the following steps: (1) Material preparation: 40-45 wt% pig iron, 30-35 wt% scrap steel, 20-30 wt% recycled material; (2) Pig iron, recycled materials and scrap steel are put into a medium frequency induction furnace to melt into molten iron. The temperature is measured. When the temperature of the molten iron in the furnace reaches 1480℃, a sample is taken for composition analysis. The composition of the molten iron is adjusted by adding carbon raiser, ferrosilicon and desulfurizer. The elements and contents of the adjusted molten iron are: C: 3.45wt%, Si: 2.70wt%, Mn: 0.120~0.150wt%, P≤0.035wt%, S≤0.012wt%, and the remainder is iron. (3) Place the spheroidizing agent, TiC nanoparticles, antimony alloy, and inoculant in sequence from bottom to top at the bottom of the dam-type spheroidizing ladle, and pour in the molten iron after the composition adjustment in step (2); a funnel is set at the ladle nozzle of the dam-type spheroidizing ladle; (4) After removing the slag from the molten iron treated in step (3), pour it into the mold. Add a flow-through inoculant during the pouring process. The pouring temperature is 1350℃. (5) After pouring, the casting is slowly cooled to below 350°C at 50~100MPa in a mold equipped with chills, and then removed from the mold.

[0049] The carbon raiser is a high-temperature graphitized carbon raiser with a fixed carbon content of ≥ 99.0% and a particle size of 0.5~5.0 mm.

[0050] The ferrosilicon is 72 ferrosilicon, whose main components are silicon 72.0~75.0%, aluminum ≤1.50%, calcium ≤1.50%, and the remainder is iron, with a particle size of 5.0~100.0 mm.

[0051] The desulfurizing agent consists of lime and calcium carbide, with a particle size of 0.5~5.0 mm.

[0052] The spheroidizing agent is a rare earth silicon-iron-magnesium alloy, whose main components include 5.5~6.0wt%Mg, 0.15~0.30wt%Re, 45.0~50.0wt%Si, 0.80~1.50wt%Ca, with the remainder being iron, and a particle size of 4~28 mm.

[0053] The TiC nanoparticles are prepared as follows: iron powder and titanium carbide are mixed and ball-milled at a mass ratio of 2.5~3.5:5 to obtain TiC nanoparticles. The ball milling speed is 600~800 r / min, the grinding balls are corundum balls, the ball-to-material ratio is 3.6~4:1, and the ball milling time is 3~12 h.

[0054] The inoculant is a silicon-calcium-barium inoculant, whose main components include 70.0~75.0wt% Si, 2.00~3.00wt% Ba, 1.00~2.00wt% Ca, with the remainder being Fe, and a particle size of 3.0~8.0mm. The in-flow inoculant is a sulfur-oxygen inoculant, whose main components are: Si: 74.5wt%, S: 0.71wt%, O: 0.69wt%, Ba: 0.20wt%, Ca: 0.94wt%, Ce: 1.73wt%, with the remainder being iron. Based on the weight percentage of the molten iron, the inoculant addition is 0.35wt%, the antimony alloy addition is 40 ppm, the in-flow inoculant addition is 0.12wt%, the spheroidizing agent addition is 1.05wt%, and the spheroidizing agent TiC nanoparticle addition is 0.2wt%.

[0055] The chills are placed in molds on both sides of the casting cross-section, with the thickness of the chills on each side being 1 / 2 of the casting cross-section thickness. Example 3

[0056] A method for improving the uniformity of graphite microstructure in ductile iron castings for wind power applications, comprising the following steps: (1) Material preparation: 40-45 wt% pig iron, 30-35 wt% scrap steel, 20-30 wt% recycled material; (2) Pig iron, recycled materials and scrap steel are put into a medium frequency induction furnace to melt into molten iron. The temperature is measured. When the temperature of the molten iron in the furnace reaches 1480℃, a sample is taken for composition analysis. The composition of the molten iron is adjusted by adding carbon raiser, ferrosilicon and desulfurizer. The elements and contents of the adjusted molten iron are: C: 3.45wt%, Si: 2.70wt%, Mn: 0.120~0.150wt%, P≤0.035wt%, S≤0.012wt%, and the remainder is iron. (3) Place the spheroidizing agent, antimony alloy, and inoculant in sequence from bottom to top at the bottom of the dam-type spheroidizing ladle, and pour in the molten iron after the composition adjustment in step (2); a funnel is set at the ladle nozzle of the dam-type spheroidizing ladle; (4) After removing the slag from the molten iron treated in step (3), pour it into the mold. Add a flow-through inoculant during the pouring process. The pouring temperature is 1350℃. (5) After pouring, the casting is slowly cooled to below 350°C at 50~100MPa in a mold equipped with chills, and then removed from the mold.

[0057] The carbon raiser is a high-temperature graphitized carbon raiser with a fixed carbon content of ≥ 99.0% and a particle size of 0.5~5.0 mm.

[0058] The ferrosilicon is 72 ferrosilicon, whose main components are silicon 72.0~75.0%, aluminum ≤1.50%, calcium ≤1.50%, and the remainder is iron, with a particle size of 5.0~100.0 mm.

[0059] The desulfurizing agent consists of lime and calcium carbide, with a particle size of 0.5~5.0 mm.

[0060] The spheroidizing agent is a rare earth silicon-iron-magnesium alloy, whose main components include 5.5~6.0wt%Mg, 0.15~0.30wt%Re, 45.0~50.0wt%Si, 0.80~1.50wt%Ca, with the remainder being iron, and a particle size of 4~28 mm.

[0061] The inoculant is a silicon-calcium-barium inoculant, whose main components include 70.0~75.0wt% Si, 2.00~3.00wt% Ba, 1.00~2.00wt% Ca, with the remainder being Fe, and a particle size of 3.0~8.0mm. The in-flow inoculant is a sulfur-oxygen inoculant, whose main components are: Si: 74.5wt%, S: 0.71wt%, O: 0.69wt%, Ba: 0.20wt%, Ca: 0.94wt%, Ce: 1.73wt%, with the remainder being iron. Based on the weight percentage of the molten iron, the inoculant addition is 0.35wt%, the antimony alloy addition is 40 ppm, the in-flow inoculant addition is 0.12wt%, and the spheroidizing agent addition is 1.05wt%.

[0062] The chills are placed in molds on both sides of the casting cross-section, with the thickness of the chills on each side being 1 / 2 of the casting cross-section thickness. Example 4

[0063] A method for improving the uniformity of graphite microstructure in ductile iron castings for wind power applications, comprising the following steps: (1) Material preparation: 40-45 wt% pig iron, 30-35 wt% scrap steel, 20-30 wt% recycled material; (2) Pig iron, recycled materials and scrap steel are put into a medium frequency induction furnace to melt into molten iron. The temperature is measured. When the temperature of the molten iron in the furnace reaches 1480℃, a sample is taken for composition analysis. The composition of the molten iron is adjusted by adding carbon raiser, ferrosilicon and desulfurizer. The elements and contents of the adjusted molten iron are: C: 3.45wt%, Si: 2.70wt%, Mn: 0.120~0.150wt%, P≤0.035wt%, S≤0.012wt%, and the remainder is iron. (3) Place the spheroidizing agent, TiC nanoparticles, antimony alloy, and inoculant in sequence from bottom to top at the bottom of the dam-type spheroidizing ladle, and pour in the molten iron after the composition adjustment in step (2); a funnel is set at the ladle nozzle of the dam-type spheroidizing ladle; (4) After removing the slag from the molten iron treated in step (3), pour it into the mold. Add a flow-through inoculant during the pouring process. The pouring temperature is 1350℃. (5) After pouring, the casting is slowly cooled to below 350°C in the mold at 50~100MPa and then removed from the mold.

[0064] The carbon raiser is a high-temperature graphitized carbon raiser with a fixed carbon content of ≥ 99.0% and a particle size of 0.5~5.0 mm.

[0065] The ferrosilicon is 72 ferrosilicon, whose main components are silicon 72.0~75.0%, aluminum ≤1.50%, calcium ≤1.50%, and the remainder is iron, with a particle size of 5.0~100.0 mm.

[0066] The desulfurizing agent consists of lime and calcium carbide, with a particle size of 0.5~5.0 mm.

[0067] The spheroidizing agent is a rare earth silicon-iron-magnesium alloy, whose main components include 5.5~6.0wt%Mg, 0.15~0.30wt%Re, 45.0~50.0wt%Si, 0.80~1.50wt%Ca, with the remainder being iron, and a particle size of 4~28 mm.

[0068] The TiC nanoparticles are prepared as follows: iron powder and titanium carbide are mixed and ball-milled at a mass ratio of 2.5~3.5:5 to obtain TiC nanoparticles. The ball milling speed is 600~800 r / min, the grinding balls are corundum balls, the ball-to-material ratio is 3.6~4:1, and the ball milling time is 3~12 h.

[0069] The inoculant is a silicon-calcium-barium inoculant, whose main components include 70.0~75.0wt% Si, 2.00~3.00wt% Ba, 1.00~2.00wt% Ca, with the remainder being Fe, and a particle size of 3.0~8.0mm. The in-flow inoculant is a sulfur-oxygen inoculant, whose main components are: Si: 74.5wt%, S: 0.71wt%, O: 0.69wt%, Ba: 0.20wt%, Ca: 0.94wt%, Ce: 1.73wt%, with the remainder being iron. Based on the weight percentage of the molten iron, the inoculant addition is 0.35wt%, the antimony alloy addition is 40 ppm, the in-flow inoculant addition is 0.12wt%, the spheroidizing agent addition is 1.05wt%, and the spheroidizing agent TiC nanoparticle addition is 0.2wt%. Example 5

[0070] A method for improving the uniformity of graphite microstructure in ductile iron castings for wind power applications, comprising the following steps: (1) Material preparation: 40-45 wt% pig iron, 30-35 wt% scrap steel, 20-30 wt% recycled material; (2) Pig iron, recycled materials and scrap steel are put into a medium frequency induction furnace to melt into molten iron. The temperature is measured. When the temperature of the molten iron in the furnace reaches 1480℃, a sample is taken for composition analysis. The composition of the molten iron is adjusted by adding carbon raiser, ferrosilicon and desulfurizer. The elements and contents of the adjusted molten iron are: C: 3.45wt%, Si: 2.70wt%, Mn: 0.120~0.150wt%, P≤0.035wt%, S≤0.012wt%, and the remainder is iron. (3) Place the spheroidizing agent, TiC nanoparticles, antimony alloy, and inoculant in sequence from bottom to top at the bottom of the dam-type spheroidizing ladle, and pour in the molten iron after the composition adjustment in step (2); a funnel is set at the ladle nozzle of the dam-type spheroidizing ladle; (4) After removing the slag from the molten iron treated in step (3), pour it into the mold. Add a flow-through inoculant during the pouring process. The pouring temperature is 1350℃. (5) After pouring, the casting is slowly cooled to below 350°C in a mold with chills and then removed from the mold.

[0071] The carbon raiser is a high-temperature graphitized carbon raiser with a fixed carbon content of ≥ 99.0% and a particle size of 0.5~5.0 mm.

[0072] The ferrosilicon is 72 ferrosilicon, whose main components are silicon 72.0~75.0%, aluminum ≤1.50%, calcium ≤1.50%, and the remainder is iron, with a particle size of 5.0~100.0 mm.

[0073] The desulfurizing agent consists of lime and calcium carbide, with a particle size of 0.5~5.0 mm.

[0074] The spheroidizing agent is a rare earth silicon-iron-magnesium alloy, whose main components include 5.5~6.0wt%Mg, 0.15~0.30wt%Re, 45.0~50.0wt%Si, 0.80~1.50wt%Ca, with the remainder being iron, and a particle size of 4~28 mm.

[0075] The TiC nanoparticles are prepared as follows: iron powder and titanium carbide are mixed and ball-milled at a mass ratio of 2.5~3.5:5 to obtain TiC nanoparticles. The ball milling speed is 600~800 r / min, the grinding balls are corundum balls, the ball-to-material ratio is 3.6~4:1, and the ball milling time is 3~12 h.

[0076] The inoculant is a silicon-calcium-barium inoculant, whose main components include 70.0~75.0wt% Si, 2.00~3.00wt% Ba, 1.00~2.00wt% Ca, with the remainder being Fe, and a particle size of 3.0~8.0mm. The in-flow inoculant is a sulfur-oxygen inoculant, whose main components are: Si: 74.5wt%, S: 0.71wt%, O: 0.69wt%, Ba: 0.20wt%, Ca: 0.94wt%, Ce: 1.73wt%, with the remainder being iron. Based on the weight percentage of the molten iron, the inoculant addition is 0.35wt%, the antimony alloy addition is 40 ppm, the in-flow inoculant addition is 0.12wt%, the spheroidizing agent addition is 1.05wt%, and the spheroidizing agent TiC nanoparticle addition is 0.2wt%.

[0077] The chills are placed in molds on both sides of the casting cross-section, with the thickness of the chills on each side being 1 / 2 of the casting cross-section thickness. Comparative Example

[0078] A method for improving the uniformity of graphite microstructure in ductile iron castings for wind power applications, comprising the following steps: (1) Material preparation: 40-45 wt% pig iron, 30-35 wt% scrap steel, 20-30 wt% recycled material; (2) Pig iron, recycled materials and scrap steel are put into a medium frequency induction furnace to melt into molten iron. The temperature is measured. When the temperature of the molten iron in the furnace reaches 1480℃, a sample is taken for composition analysis. The composition of the molten iron is adjusted by adding carbon raiser, ferrosilicon and desulfurizer. The elements and contents of the adjusted molten iron are as follows: C: 3.45wt%, Si: 2.70wt%, Mn: 0.120~0.150wt%, P≤0.035wt%, S≤0.012wt%, and the remainder is iron. (3) Place the spheroidizing agent, antimony alloy, and inoculant in sequence from bottom to top at the bottom of the dam-type spheroidizing ladle, and pour in the molten iron after the composition adjustment in step (2); there is no dam-type spheroidizing ladle nozzle; (4) After removing the slag from the molten iron treated in step (3), pour it into the mold. Add a flow-through inoculant during the pouring process. The pouring temperature is 1350℃. (5) After pouring, the casting is slowly cooled to below 350°C in the mold and then removed from the mold.

[0079] The carbon raiser is a high-temperature graphitized carbon raiser with a fixed carbon content of ≥ 99.0% and a particle size of 0.5~5.0 mm.

[0080] The ferrosilicon is 72 ferrosilicon, whose main components are silicon 72.0~75.0%, aluminum ≤1.50%, calcium ≤1.50%, and the remainder is iron, with a particle size of 5.0~100.0 mm.

[0081] The desulfurizing agent consists of lime and calcium carbide, with a particle size of 0.5~5.0 mm.

[0082] The spheroidizing agent is a rare earth silicon-iron-magnesium alloy, whose main components include 5.5~6.0wt%Mg, 0.15~0.30wt%Re, 45.0~50.0wt%Si, 0.80~1.50wt%Ca, with the remainder being iron, and a particle size of 4~28 mm.

[0083] The inoculant is a silicon-calcium-barium inoculant, whose main components include 70.0~75.0wt% Si, 2.00~3.00wt% Ba, 1.00~2.00wt% Ca, with the remainder being Fe, and a particle size of 3.0~8.0mm. The in-flow inoculant is a sulfur-oxygen inoculant, whose main components are: Si: 74.5wt%, S: 0.71wt%, O: 0.69wt%, Ba: 0.20wt%, Ca: 0.94wt%, Ce: 1.73wt%, with the remainder being iron. Based on the weight percentage of the molten iron, the inoculant addition is 0.35wt%, the antimony alloy addition is 40 ppm, the in-flow inoculant addition is 0.12wt%, and the spheroidizing agent addition is 1.05wt%.

[0084] like Figure 2 ,4 Metallographic images of the center positions of the stepped test blocks of ductile iron castings for wind power castings obtained in Example 2, with wall thicknesses of 200 mm and 270 mm. Example of effect

[0085] Table 1 below shows the results of spheroidization grade, graphite nodule size grade, and nodule ratio of the ductile iron prepared in Examples 1-5 and the comparative examples: Table 1

[0086] Table 1 shows that the ductile iron in Examples 1 and 2 has the highest spheroidization grade, graphite spheroid size grade, and spheroidization rate.

[0087] The difference between Example 3 and Example 2 is that titanium carbide nanoparticles were not introduced; the difference between Example 4 and Example 2 is that cold plate cooling was not performed; the difference between Example 5 and Example 2 is that high-pressure cooling was not performed; the comparative example is the conventional preparation process of ductile iron. Compared with Example 2, Examples 3-5 and the comparative example have the highest spheroidization grade, graphite spheroid size grade, and spheroidization rate of ductile iron.

[0088] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the uniformity of graphite structure in ductile iron castings for wind power applications, characterized in that the steps include... include: (1) Material preparation: 40-45 wt% pig iron, 30-35 wt% scrap steel, 20-30 wt% recycled material; (2) Pig iron, recycled materials and scrap steel are put into a medium frequency induction furnace to melt into molten iron, and carbon raiser, ferrosilicon and desulfurizer are added to adjust the composition of molten iron; (3) Place the spheroidizing agent, TiC nanoparticles, antimony alloy, and inoculant in sequence from bottom to top at the bottom of the ladle before pouring in the molten iron with adjusted composition; (4) After removing the slag from the molten iron treated in step (3), pour it into the mold and add a flow-inoculating agent during the pouring process; (5) After pouring, the casting is slowly cooled to below 350°C in a mold with chills and then removed from the mold.

2. The method for improving the uniformity of graphite structure in ductile iron castings for wind power applications according to claim 1, characterized in that, The carbon raiser is a high-temperature graphitized carbon raiser with a fixed carbon content of ≥ 99.0% and a particle size of 0.5~5.0 mm.

3. The method for improving the uniformity of graphite structure in ductile iron castings for wind power applications according to claim 1, characterized in that, The ferrosilicon is 72 ferrosilicon, whose main components are silicon 72.0~75.0%, aluminum ≤1.50%, calcium ≤1.50%, and the remainder is iron, with a particle size of 5.0~100.0 mm.

4. The method for improving the uniformity of graphite structure in ductile iron castings for wind power applications according to claim 1, characterized in that, The desulfurizing agent consists of lime and calcium carbide, with a particle size of 0.5~5.0 mm.

5. The method for improving the uniformity of graphite structure in ductile iron castings for wind power applications according to claim 1, characterized in that, The elements and contents of the molten iron after the adjustment in step (2) include: C: 3.35~3.45wt%, Si: 2.50~2.70wt%, Mn: 0.120~0.150wt%, P≤0.035wt%, S≤0.012wt%, and the remainder is iron.

6. The method for improving the uniformity of graphite structure in ductile iron castings for wind power applications according to claim 1, characterized in that, The spheroidizing agent is a rare earth silicon-iron-magnesium alloy, whose main components include 5.5~6.0wt%Mg, 0.15~0.30wt%Re, 45.0~50.0wt%Si, 0.80~1.50wt%Ca, and the remainder is iron; the amount of spheroidizing agent used is 0.95~1.15wt% based on the weight percentage of the molten iron, and the particle size is 4~28 mm.

7. The method for improving the uniformity of graphite structure in ductile iron castings for wind power applications according to claim 1, characterized in that, The TiC nanoparticles are prepared as follows: iron powder and titanium carbide are mixed and ball-milled at a mass ratio of 2.5~3.5:5 to obtain TiC nanoparticles. The ball milling speed is 600~800 r / min, corundum balls are used for milling, the ball-to-material ratio is 3.6~4:1, and the ball milling time is 3~12 h. The amount of TiC nanoparticles added as a spheroidizing agent is 0.1~0.3 wt% based on the weight percentage of the molten iron.

8. The method for improving the uniformity of graphite structure in ductile iron castings for wind power applications according to claim 1, characterized in that, The inoculant is a silicon-calcium-barium inoculant, whose main components include 70.0~75.0wt% Si, 2.00~3.00wt% Ba, 1.00~2.00wt% Ca, and the remainder being Fe, with a particle size of 3.0~8.0mm. The in-flow inoculant is a sulfur-oxygen inoculant, and the amount added is 0.25~0.45wt% of the weight percentage of the molten iron, the amount of antimony alloy added is 30~50 ppm, and the amount of in-flow inoculant added is 0.11~0.13wt%.

9. The method for improving the uniformity of graphite structure in ductile iron castings for wind power applications according to claim 1, characterized in that, The chills are placed in the molds on both sides of the casting cross-section, and the thickness of the chills on each side is 1 / 3 to 1 / 2 of the thickness of the casting cross-section.

10. The method for improving the uniformity of graphite structure in ductile iron castings for wind power applications according to claim 1, characterized in that, In step (5), a pressure of 50-100 MPa is applied during the cooling of the molten iron in the mold.

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