A spheroidal graphite cast iron and a method for producing the same and use thereof

Abstract

The application belongs to the technical field of nodular cast iron, and particularly relates to a novel nodular cast iron and a preparation method and application thereof. The novel nodular cast iron has the following element composition and mass percentage: C 3.75-3.90%, Si 2.00-2.20%, Mn≤0.10%, Mg 0.035-0.055%, RE≤0.008%, P≤0.02%, S≤0.01%, Cu 0.1-2.0%, Mo≤0.02%, Ni 1.0-2.0%, Sn≤0.05%, Ti≤0.01%, V≤0.02%, B≤0.0008%, Sb 0.003-0.007%, Cr≤0.05% and the balance of Fe; and is composed of 45-55% pearlite and 45-55% ferrite. By controlling the element content in the nodular cast iron and combining with an efficient preparation method, the nodular cast iron with a pearlite content of 45-55% and a spheroidization rate of greater than 95% is obtained, and the nodular cast iron exhibits high strength, high plasticity and a relatively high low-temperature impact value.

Description

Technical Field

[0001] This invention belongs to the field of ductile iron technology, specifically relating to a ductile iron, its preparation method, and its application. Background Technology

[0002] Ductile iron is a high-strength cast iron material with comprehensive properties close to those of steel. It possesses excellent comprehensive mechanical properties and machinability, and has been successfully used to cast parts subject to complex stresses and requiring high strength, toughness, and wear resistance. High-strength, high-toughness ductile iron can now replace cast steel in the manufacture of special parts with high-performance requirements. In my country's national standard for ductile iron, the existing material grade QT800-2 is suitable for high-strength components, such as crankshafts and camshafts of diesel engines, lathe spindles, small hydro turbine spindles, and wind turbine planetary carriers, especially the planetary carriers of wind turbine gearboxes. The required tensile strength is 750 MPa, yield strength is above 450 MPa, and elongation is above 2%.

[0003] The planetary carrier is one of the main components of a planetary gear transmission, used to support the planetary gear shafts or bearings. It is the part in the mechanism that bears the largest external torque. The planetary carrier structure needs sufficient strength, high manufacturing precision, and a certain degree of rigidity. In actual production needs, there is an urgent need for a high-strength, high-elongation, and high-low temperature impact value ductile iron material to meet the manufacturing process and performance requirements of wind turbine gearbox planetary carriers, so that ductile iron has good strength while also having high elongation and high and low temperature impact values. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned technical problems by providing a ductile iron with a suitable pearlite content, exhibiting good mechanical properties and low-temperature impact resistance.

[0005] The ductile iron in the technical solution of this invention has the following elemental composition and mass percentage: C 3.75~3.90%, Si 2.00~2.20%, Mn≤0.10%, Mg 0.035~0.055%, RE≤0.008%, P≤0.02%, S≤0.01%, Cu 0.1~2.0%, Mo≤0.02%, Ni 1.0~2.0%, Sn≤0.05%, Ti≤0.01%, V≤0.02%, B≤0.0008%, Sb 0.003~0.007%, Cr≤0.05%, with the balance being Fe.

[0006] Si (silicon) promotes graphitization, improving the strength and hardness of ductile iron. It also significantly influences graphite morphology; higher silicon content promotes the formation of fragmented graphite (in areas with a wall thickness greater than 150 mm), reduces elongation, and while strengthening the ferrite matrix, decreases the low-temperature impact toughness of ductile iron. Excessive Mn (manganese) content reduces plasticity and toughness, and increases the brittle-to-ductile transition temperature. Excessive P (phosphorus) content easily leads to the segregation of phosphorus eutectic at eutectic boundaries, reducing the mechanical properties of ductile iron. Cu (copper) promotes pearlite formation, narrowing the gap between steady-state and metastable eutectic temperatures by lowering the eutectic temperature. When used with Ni (ni) and Sn (sinus), it improves hardenability. Ni refines grains and also narrows the gap between steady-state and metastable eutectic temperatures by lowering the eutectic temperature, reducing the ferrite transition temperature, increasing ferrite strength, and improving the uniformity and hardenability of the microstructure. Sn... Elements can also promote the formation of pearlite. When the content is high, lamellar graphite is formed in the intercellular structure, which reduces the elongation. When the Ti content is too high, intergranular carbides will be formed, and segregation will occur at the boundary of the eutectic, which reduces the elongation and low-temperature impact resistance.

[0007] Furthermore, the aforementioned ductile iron is composed of 45-55% pearlite and 45-55% ferrite.

[0008] When the ferrite content is high, the plasticity is good, but the strength is low. When the pearlite and ferrite content are equal, the chemical composition of ductile iron can be made uniform, so as to obtain excellent comprehensive mechanical properties.

[0009] Furthermore, the spheroidization rate of the above-mentioned ductile iron is greater than 95%, and the number of graphite nodules is 260~290 per mm. 2 .

[0010] The present invention also provides a method for preparing the above-mentioned ductile iron, including raw material smelting, tapping, spheroidizing inoculation, casting, and annealing treatment.

[0011] Furthermore, the raw material smelting involves mixing pure iron, scrap steel, ferrosilicon, silicon carbide, electrolytic copper, ferronickel, and a low-sulfur carbon raiser. After the furnace charge is melted, the temperature is raised to 1500~1550℃, then allowed to stand and the slag is removed.

[0012] Silicon carbide can enhance the nucleation ability of molten iron, ferrosilicon can increase the number of graphite nodules, improve the microstructure, and enhance the mechanical properties of ductile iron. Micro-sulfur carburizing agents can ensure the stability of carbon content in molten iron, help improve the micro-shrinkage porosity of ductile iron, and ensure the elongation of ductile iron.

[0013] Furthermore, the addition amounts of pure iron, scrap steel, electrolytic copper, nickel iron, and micro-sulfur carbon raiser are 55-80 parts, 15-40 parts, 1.0-3.0 parts, 3.0-6.0 parts, and 0.2-0.3 parts, respectively.

[0014] Furthermore, the particle size of scrap steel is 50~500mm.

[0015] Furthermore, the amount of ferrosilicon added is 0.8 to 1.2% of the total mass of pure iron and scrap steel; and / or the amount of silicon carbide added is 0.2 to 0.5% of the total mass of pure iron and scrap steel.

[0016] Furthermore, the particle size of ferrosilicon is 20-50 mm; and / or the particle size of silicon carbide is 1-7 mm.

[0017] Furthermore, during tapping, 0.03~0.05% of graphitizing recarburizing agent by weight of the molten iron is added to the tapping trough, with a particle size of 0.1~0.7mm. The purpose of adding the graphitizing recarburizing agent is to further increase the number of graphite nuclei in the molten iron, increase the number of graphite spheroids in the molten iron, improve the graphite morphology, and help improve the mechanical properties of ductile iron.

[0018] Furthermore, the tapping temperature is 1480~1490℃.

[0019] Furthermore, during the spheroidizing inoculation, 1.0-1.5% of the spheroidizing agent by weight of the molten iron is added sequentially to the ladle. After compaction, 0.1-0.3% of the first inoculant by weight of the molten iron, 0.005-0.008% of antimony by weight of the molten iron, and 0.5-0.9% of scrap steel by weight of the molten iron are added sequentially.

[0020] Furthermore, the rare earth content in the spheroidizing agent is less than 0.12%, the magnesium content is 5.0%-6.5%, and the particle size is 4~32mm.

[0021] Furthermore, the first inoculant is a silicon-calcium-barium inoculant with a particle size of 1-3 mm.

[0022] Furthermore, the particle size of antimony is 1~20mm.

[0023] Furthermore, the particle size of the scrap steel 2 is 5~10mm. Adding scrap steel 2 can ensure the spheroidization effect of molten iron and the magnesium explosion time.

[0024] Furthermore, the spheroidization incubation time is 60-80 seconds.

[0025] Furthermore, a second inoculant of 0.2-0.5% by weight of the molten iron is added during casting.

[0026] Furthermore, the second inoculant is a silicon-aluminum inoculant with a particle size of 0.2~0.7mm.

[0027] Secondary inoculation can not only prevent inoculation decline, but also improve the roundness and number of graphite spheres, thereby enhancing the mechanical properties of ductile iron.

[0028] Furthermore, the pouring temperature is 1380~1390℃.

[0029] Furthermore, during the annealing process, the casting is placed in the furnace at a temperature of less than 150°C, heated to 520~560°C at a rate of less than 100°C / h, held for 3~5 hours, and cooled at a rate of less than or equal to 80°C / h.

[0030] Annealing can eliminate casting stress and segregation in ductile iron, ensuring the material's strength while improving its elongation and low-temperature impact value.

[0031] The present invention also provides the application of the above-mentioned ductile iron in the planetary carrier of wind turbine gearbox.

[0032] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) By controlling the content of each element in ductile iron and combining it with an efficient preparation method, ductile iron with a pearlite content of 45-55% and a spheroidization rate of more than 95% is obtained, which exhibits high strength, high plasticity and high low temperature impact value. (2) The original molten iron was pretreated with ferrosilicon and silicon carbide, and the nucleation treatment was improved by graphitizing carbide. Combined with secondary inoculation treatment, the spheroidization rate and elongation of the material were improved, the metallographic structure of the material was improved, and finally ductile iron with high strength, high plasticity and excellent mechanical properties was obtained. (3) Secondary inoculation during the preparation of ductile iron can not only prevent inoculation decline, but also improve the roundness and number of graphite spheres, thereby improving the mechanical properties of ductile iron. (4) Annealing of ductile iron parts can eliminate casting stress and segregation in ductile iron, ensuring the strength of the material while improving its elongation and low-temperature impact value. (5) The ductile iron obtained by this invention has a tensile strength of up to 750 MPa, a yield strength of up to 460 MPa, an elongation of up to 15%, and an average impact value at -20℃ > 7 J. (6) The ductile iron obtained by this invention has good low-temperature impact and other mechanical properties, which can better meet the performance requirements of the material in low-temperature environments. Attached Figure Description

[0033] Figure 1 This is a microstructure diagram of the ductile iron obtained in Example 1 before corrosion. Figure 2 This is a microstructure diagram of the ductile iron obtained in Example 1 after corrosion. Detailed Implementation

[0034] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the specific scope of the present invention. Furthermore, the accompanying drawings used herein are merely for better illustrating the content disclosed in the present invention and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0035] The graphitized recarburizer used in the following examples and comparative examples is 918 Dishougu recarburizer. Example 1

[0036] The preparation method of ductile iron in this embodiment includes the following steps: (1) Mix 65 parts pure iron, 30 parts scrap steel (100 mm particle size), 1.8 parts electrolytic copper, 3.0 parts nickel iron, and 0.2 parts carbon raiser, and add 1.0% ferrosilicon (30 mm particle size) of pure iron and scrap steel and 0.3% silicon carbide (3 mm particle size) of pure iron and scrap steel. After the furnace charge is melted, heat it to 1520℃, let it stand, and remove the slag. (2) Add 0.05% of graphitizing recarburizing agent (0.3mm particle size) by weight of molten iron to the tapping trough, tap the iron at 1485℃, add 1.2% of spheroidizing agent (10mm particle size) by weight of molten iron to the ladle in sequence, tamp it down, and then add 0.2% of silicon-calcium-barium inoculant (5mm particle size), 0.006% of antimony (10mm particle size), and 0.7% of scrap steel (8mm particle size) by weight of molten iron in sequence. After spheroidizing and inoculating for 70s, remove the slag. (3) After the molten iron was allowed to stand for 2 minutes, it was poured at 1390℃. 0.3% of the molten iron mass of silicon-aluminum inoculant (particle size 0.5mm) was added with the flow for secondary inoculation. After cleaning, the casting was placed in the furnace at 130℃, heated to 530℃ at a rate of 80℃ / h and held for 4 hours, and then cooled at a rate of 70℃ / h. The elemental composition and mass percentage of the obtained ductile iron are as follows: C 3.8%, Si 2.0%, Mn 0.10%, Mg 0.04%, RE 0.008%, P 0.02%, S 0.01%, Cu 0.2%, Mo 0.02%, Ni 1.2%, Sn 0.04%, Ti 0.01%, V 0.02%, B 0.0008%, Sb 0.004%, Cr 0.05%, with the balance being Fe; the pearlite content is 51%, and the spheroidization rate is 96%. Example 2

[0037] The preparation method of ductile iron in this embodiment includes the following steps: (1) Mix 70 parts pure iron, 25 parts scrap steel (100 mm particle size), 1.2 parts electrolytic copper, 3.5 parts nickel iron, and 0.3 parts carbon raiser, and add 0.9% ferrosilicon (30 mm particle size) of pure iron and scrap steel by mass and 0.4% silicon carbide (3 mm particle size) of pure iron and scrap steel by mass. After the furnace charge is melted, heat it to 1520℃, let it stand, and remove the slag. (2) Add 0.04% of graphitizing recarburizing agent (0.3mm particle size) by weight of molten iron to the tapping trough, tap the iron at 1485℃, add 1.3% of spheroidizing agent (10mm particle size) by weight of molten iron to the ladle in sequence, tamp it down, and then add 0.25% of silicon-calcium-barium inoculant (5mm particle size), 0.007% of antimony (10mm particle size), and 0.8% of scrap steel (8mm particle size) by weight of molten iron in sequence. After spheroidizing and inoculating for 65s, remove the slag. (3) After the molten iron was allowed to stand for 2 minutes, it was poured at 1390℃. 0.4% of the molten iron mass of silicon-aluminum inoculant (particle size 0.5mm) was added with the flow for secondary inoculation. After cleaning, the casting was placed in the furnace at 130℃. The temperature was increased to 540℃ at a rate of 80℃ / h and held for 4 hours. The temperature was then decreased at a rate of 70℃ / h. The elemental composition and mass percentage of the obtained ductile iron were as follows: C 3.85%, Si 2.1%, Mn 0.08%, Mg 0.04%, RE 0.006%, P 0.02%, S 0.01%, Cu 0.3%, Mo 0.015%, Ni 1.5%, Sn 0.04%, Ti 0.01%, V 0.015%, B 0.0070%, Sb 0.005%, Cr 0.04%, with the balance being Fe. The pearlite content was 50%, and the spheroidization rate was 97%. Example 3

[0038] The preparation method of ductile iron in this embodiment includes the following steps: (1) Mix 72.8 parts pure iron, 20 parts scrap steel (100 mm particle size), 2.0 parts electrolytic copper, 5.0 parts nickel iron, and 0.2 parts carbon raiser, and add 1.1% ferrosilicon (30 mm particle size) by mass of pure iron and scrap steel and 0.2% silicon carbide (3 mm particle size) by mass of pure iron and scrap steel. After the furnace charge is melted, heat it to 1520℃, let it stand, and remove the slag. (2) Add 0.05% of graphitizing recarburizing agent (0.3mm particle size) by weight of molten iron to the tapping trough, tap the iron at 1485℃, add 1.4% of spheroidizing agent (10mm particle size) by weight of molten iron to the ladle in sequence, tamp it down, and then add 0.15% of silicon-calcium-barium inoculant (5mm particle size), 0.006% of antimony (10mm particle size), and 0.65% of scrap steel (8mm particle size) by weight of molten iron in sequence. After spheroidizing and inoculating for 75s, remove the slag. (3) After the molten iron was allowed to stand for 2 minutes, it was poured at 1390℃. 0.35% of the molten iron mass of silicon-aluminum inoculant (0.5mm particle size) was added with the flow for secondary inoculation. After cleaning, the casting was placed in the furnace at 130℃. The temperature was increased to 550℃ at a rate of 80℃ / h and held for 4 hours. The temperature was then decreased at a rate of 70℃ / h. The elemental composition and mass percentage of the obtained ductile iron were as follows: C 3.8%, Si 2.2%, Mn 0.09%, Mg 0.05%, RE 0.006%, P 0.015%, S 0.01%, Cu 1.0%, Mo 0.02%, Ni 1.8%, Sn 0.03%, Ti 0.01%, V 0.02%, B 0.0008%, Sb 0.006%, Cr 0.05%, with the balance being Fe. The pearlite content was 52%, and the spheroidization rate was 96%. Example 4

[0039] The difference between this embodiment and embodiment 1 is only that step (1) involves mixing 65 parts of pure iron, 30 parts of scrap steel (100mm particle size), 1.8 parts of electrolytic copper, 3.0 parts of nickel iron, and 0.2 parts of carbon raiser, and adding 1.0% ferrosilicon (30mm particle size) by mass of pure iron and scrap steel and 0.1% silicon carbide (3mm particle size) by mass of pure iron and scrap steel. After the furnace charge is melted, the temperature is raised to 1520℃, and the furnace is allowed to stand and the slag is removed. Example 5

[0040] The difference between this embodiment and embodiment 1 is only in step (1) mixing 65 parts pure iron, 30 parts scrap steel (100mm particle size), 1.8 parts electrolytic copper, 3.0 parts nickel iron, and 0.2 parts carbon raiser, and adding 1.0% ferrosilicon (30mm particle size) by mass of pure iron and scrap steel and 0.6% silicon carbide (3mm particle size) by mass of pure iron and scrap steel. After the furnace charge is melted, the temperature is raised to 1520℃, and the furnace is allowed to stand and the slag is removed. Example 6

[0041] The difference between this embodiment and embodiment 1 is only that step (1) involves mixing 65 parts of pure iron, 30 parts of scrap steel (100mm particle size), 1.8 parts of electrolytic copper, 3.0 parts of nickel iron, and 0.2 parts of carbon raiser, and adding 1.0% ferrosilicon (30mm particle size) by mass of pure iron and scrap steel and 0.3% silicon carbide (0.5mm particle size) by mass of pure iron and scrap steel. After the furnace charge is melted, the temperature is raised to 1520℃, and the furnace is allowed to stand and the slag is removed. Example 7

[0042] The difference between this embodiment and embodiment 1 is only that step (1) involves mixing 65 parts of pure iron, 30 parts of scrap steel (100mm particle size), 1.8 parts of electrolytic copper, 3.0 parts of nickel iron, and 0.2 parts of carbon raiser, and adding 1.0% ferrosilicon (30mm particle size) by mass of pure iron and scrap steel and 0.3% silicon carbide (8mm particle size) by mass of pure iron and scrap steel. After the furnace charge is melted, the temperature is raised to 1520℃, and the furnace is allowed to stand and the slag is removed. Example 8

[0043] The difference between this embodiment and embodiment 1 is only that step (1) involves mixing 65 parts of pure iron, 30 parts of scrap steel (100mm particle size), 1.8 parts of electrolytic copper, 3.0 parts of nickel iron, and 0.2 parts of carbon raiser, and adding 0.5% ferrosilicon (30mm particle size) by mass of pure iron and scrap steel and 0.3% silicon carbide (3mm particle size) by mass of pure iron and scrap steel. After the furnace charge is melted, the temperature is raised to 1520℃, and the furnace is allowed to stand still and the slag is removed. Example 9

[0044] The difference between this embodiment and embodiment 1 is only that step (1) involves mixing 65 parts of pure iron, 30 parts of scrap steel (100mm particle size), 1.8 parts of electrolytic copper, 3.0 parts of nickel iron, and 0.2 parts of carbon raiser, and adding 1.5% ferrosilicon (30mm particle size) by mass of pure iron and scrap steel and 0.3% silicon carbide (3mm particle size) by mass of pure iron and scrap steel. After the furnace charge is melted, the temperature is raised to 1520℃, and the furnace is allowed to stand and the slag is removed. Example 10

[0045] The difference between this embodiment and embodiment 1 is only that step (1) involves mixing 65 parts of pure iron, 30 parts of scrap steel (100mm particle size), 1.8 parts of electrolytic copper, 3.0 parts of nickel iron, and 0.2 parts of carbon raiser, and adding 1.0% ferrosilicon (10mm particle size) by mass of pure iron and scrap steel and 0.3% silicon carbide (3mm particle size) by mass of pure iron and scrap steel. After the furnace charge is melted, the temperature is raised to 1520℃, and the furnace is allowed to stand and the slag is removed. Example 11

[0046] The difference between this embodiment and embodiment 1 is only that step (1) involves mixing 65 parts of pure iron, 30 parts of scrap steel (100mm particle size), 1.8 parts of electrolytic copper, 3.0 parts of nickel iron, and 0.2 parts of carbon raiser, and adding 1.0% ferrosilicon (60mm particle size) by mass of pure iron and scrap steel and 0.3% silicon carbide (3mm particle size) by mass of pure iron and scrap steel. After the furnace charge is melted, the temperature is raised to 1520℃, and the furnace is allowed to stand and the slag is removed. Example 12

[0047] The difference between this embodiment and embodiment 1 is only that in step (2), 0.01% of graphitizing carburizing agent (0.3 mm particle size) by weight of molten iron is added to the molten iron trough, molten iron is tapped at 1485℃, and 1.2% of spheroidizing agent (10 mm particle size) by weight of molten iron is added to the molten iron ladle in sequence. After compaction, 0.2% of silicon-calcium-barium inoculant (5 mm particle size), 0.006% of antimony (10 mm particle size), and 0.7% of scrap steel (8 mm particle size) by weight of molten iron are added in sequence. After spheroidizing and inoculating for 70 seconds, slag is removed. Example 13

[0048] The difference between this embodiment and embodiment 1 is only that in step (2), 0.1% of graphitizing recarburizing agent (0.3 mm particle size) by weight of molten iron is added to the iron tapping trough, and molten iron is tapped at 1485°C. In the molten iron ladle, 1.2% of spheroidizing agent (10 mm particle size) by weight of molten iron is added in sequence. After compaction, 0.2% of silicon-calcium-barium inoculant (5 mm particle size), 0.006% of antimony (10 mm particle size), and 0.7% of scrap steel (8 mm particle size) by weight of molten iron are added in sequence. After spheroidizing and inoculating for 70 seconds, slag is removed. Comparative Example 1

[0049] (1) Mix 70 parts of ordinary iron, 28.5 parts of ordinary scrap steel I (particle size 100mm), 0.5 parts of electrolytic copper, and 0.1 parts of carbon raiser, and add the mass of ordinary iron and ordinary scrap steel I and 0.9% of ferrosilicon (particle size 100mm). After the furnace charge melts, heat it to 1480℃, let it stand, and remove the slag; (2) Cool it down to 1485℃ and tap the iron. Add 1.2% of the mass of molten iron spheroidizing agent (particle size 10mm) to the molten iron ladle in sequence. After compacting, add 0.4% of the mass of molten iron silicon calcium barium inoculant (particle size 5mm) and 0.7% of the mass of molten iron scrap steel II (particle size 8mm) in sequence. After spheroidizing and inoculating for 70s, remove the slag; (3) After the molten iron is left to stand for 2 minutes, it is poured at 1390℃. 0.15% of the mass of the molten iron is added with the flow to carry out secondary inoculation. The pearlite content of the resulting ductile iron is 32%. Comparative Example 2

[0050] (1) Mix 70 parts of ordinary iron, 30 parts of ordinary scrap steel (100mm particle size), 0.7 parts of electrolytic copper, 0.5 parts of manganese, and 0.1 parts of carbon raiser, and add the mass of ordinary iron and ordinary scrap steel and 0.7% of ferrosilicon (100mm particle size). After the furnace charge melts, heat it to 1480℃, let it stand, and remove the slag. (2) Add 0.05% of the mass of the molten iron to the tapping trough of the molten iron, and tap the iron at 1485℃. Add 1.2% of the mass of the molten iron, and add 10mm of the spheroidizing agent to the ladle in sequence. After compaction, add 0.3% of the mass of the molten iron, and add 5mm of the mass of the silicon-calcium-barium inoculant, 10mm of the mass of the molten iron, 10mm of the mass of the molten iron, 10mm of the mass of the molten iron, 10mm of the mass of the molten iron, 8mm of the mass of the molten iron, and 8mm of the mass of the molten iron scrap steel. After spheroidizing and inoculating for 70s, remove the slag. (3) After the molten iron has been left to stand for 2 minutes, it is poured at 1390℃. 0.3% of the mass of the molten iron is added with the flow to carry out secondary inoculation, so that the pearlite content of the ductile iron is 65%.

[0051] The mechanical properties of the ductile iron obtained in the above embodiments and comparative examples were tested, and the test results are shown in Table 1.

[0052] Table 1 Test data of mechanical properties of ductile iron .

[0053] from Figure 1 It can be seen that the ductile iron obtained in Example 1 has a graphite sphere count of 276 per mm. 2 The graphite spheres have good sphericity, a sphericity rate of 96%, and no defects in the metallographic structure. Figure 2It can be seen that the pearlite content is 51% and the ferrite content is 49%. The ductile iron obtained in Examples 1-3 has high strength, high plasticity, and a relatively high low-temperature impact value. In Example 4, the amount of silicon carbide added during the preparation of ductile iron was small, resulting in poor nucleation ability of the molten iron, fewer graphite spheroids, and poor mechanical properties. In Example 5, the amount of silicon carbide added during the preparation of ductile iron was large, leading to excessive nucleation ability in the molten iron, causing graphite to float and significantly reducing the mechanical properties of the resulting ductile iron. In Example 6, the silicon carbide added during the preparation of ductile iron had too small a particle size, resulting in a fast melting rate and iron... In Example 7, the addition of excessively large silicon carbide particles during ductile iron preparation resulted in slow melting speed, low absorption rate of nucleating material in the molten iron, fewer nuclei, and fewer graphite spheroids, leading to poor mechanical properties of the resulting ductile iron. In Example 8, the addition of a small amount of ferrosilicon during ductile iron preparation increased the pearlite content in the molten iron, resulting in high strength, low elongation, and poor machinability. In Example 9, the addition of a large amount of ferrosilicon during ductile iron preparation reduced the pearlite content in the molten iron. In Example 10, the addition of ferrosilicon with too small a particle size during the preparation of ductile iron resulted in rapid melting, rapid silicon loss, and increased pearlite content in the molten iron, leading to high strength but low elongation. In Example 11, the addition of ferrosilicon with too large a particle size during the preparation of ductile iron resulted in slow melting, high silicon absorption, and increased pearlite content in the molten iron, leading to high strength but low elongation. In Example 12, the addition of a small amount of graphitizing carburizing agent during the preparation of ductile iron resulted in fewer graphite spheroids in the molten iron, resulting in lower mechanical properties. In Example 13, the amount of graphitizing carburizing agent added during the preparation of ductile iron was relatively large, which easily led to the formation of primary graphite in the molten iron, resulting in graphite floating and poor mechanical properties of the ductile iron. In Comparative Example 1, ordinary iron was used instead of pure iron, and no nickel-iron, silicon carbide, antimony, or terzogranitin carburizing agent was added, and no annealing treatment was performed. The resulting ductile iron had a pearlite content of less than 40% and poor mechanical strength. In Comparative Example 2, ordinary iron was used instead of pure iron, and no nickel-iron or silicon carbide was added, but manganese and tin were added. No annealing treatment was performed. The resulting ductile iron had a pearlite content of more than 60%, poor elongation, and increased processing difficulty.

[0054] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the spirit of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A type of ductile iron, characterized in that, The preparation method of the ductile iron includes raw material smelting, tapping, spheroidizing inoculation, casting, and annealing. The raw material smelting involves mixing 55-80 parts pure iron, 15-40 parts scrap steel, ferrosilicon, silicon carbide, 1.0-3.0 parts electrolytic copper, 3.0-6.0 parts ferronickel, and 0.2-0.3 parts micro-sulfur carbon raiser. After the furnace charge melts, the temperature is raised to 1500-1550℃, then allowed to stand and the slag is removed. The amount of ferrosilicon added is 0.8-1.2% of the total mass of pure iron and scrap steel, and the amount of silicon carbide added is 0.2-0.5% of the total mass of pure iron and scrap steel. Graphitized recarburizing agent is added to the tapping trough during tapping; During spheroidizing inoculation, 1.0-1.5% of the spheroidizing agent by weight of molten iron is added sequentially to the ladle. After compaction, 0.1-0.3% of the first inoculant by weight of molten iron, 0.005-0.008% of antimony by weight of molten iron, and 0.5-0.9% of scrap steel by weight of molten iron are added sequentially. The first inoculant is a silicon-calcium-barium inoculant. During casting, 0.2-0.5% of a second inoculant by weight of the molten iron is added; the second inoculant is a silicon-aluminum inoculant. During annealing, the casting is placed in the furnace at a temperature of less than 150°C, heated to 520~560°C at a rate of less than 100°C / h, held for 3~5h, and cooled at a rate of less than or equal to 80°C / h. The elemental composition and mass percentage of the ductile iron are as follows: C 3.75~3.90%, Si 2.00~2.20%, Mn≤0.10%, Mg 0.035~0.055%, RE≤0.008%, P≤0.02%, S≤0.01%, Cu 0.1~2.0%, Mo≤0.02%, Ni 1.2~2.0%, Sn≤0.05%, Ti≤0.01%, V≤0.02%, B≤0.0008%, Sb 0.003~0.007%, Cr≤0.05%, with the balance being Fe; the ductile iron is composed of 50~52% pearlite and 48~50% ferrite.

2. The ductile iron according to claim 1, characterized in that, The particle size of ferrosilicon is 20~50mm; and / or the particle size of silicon carbide is 1~7mm.

3. The ductile iron according to claim 1, characterized in that, When tapping iron, add 0.03~0.05% of graphitized carburizing agent by weight of molten iron to the tapping trough, with a particle size of 0.1~0.7mm.

4. The application of ductile iron as described in claim 1 in the planetary carrier of a wind turbine gearbox.

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