Additional nano SiC reinforced nodular cast iron and preparation method thereof

Abstract

The invention relates to nano SiC reinforced nodular cast iron and a preparation method, and belongs to the technical field of metal composite materials. The preparation method of the reinforced nodular cast iron with additional nano SiC comprises the following steps: mixing iron powder and nano silicon carbide particles, and carrying out ball milling to obtain modified nano silicon carbide particles; pig iron, waste steel, foundry returns and a carburant are weighed and smelted to obtain molten iron; slagging off the molten iron, then adding a spheroidizing agent, modified nano silicon carbide particles and a primary inoculant, and covering with a covering agent for spheroidizing and primary inoculation treatment to obtain molten metal; and casting the molten metal, adding a secondary inoculant along with the flow during casting, and cooling to obtain the metal alloy. Nanometer silicon carbide particles are mixed with iron powder, the nanometer silicon carbide particles are modified through a high-energy ball milling method, and the compatibility of the nanometer silicon carbide particles and molten iron can be improved. And by adding the modified nano silicon carbide particles, the texture, strength and toughness of the nodular cast iron are improved.

Description

Technical Field

[0001] This invention belongs to the field of metal composite materials technology, specifically relating to an externally reinforced nano-SiC ductile iron and its preparation method. Background Technology

[0002] Ductile iron, due to its good casting performance, low price, and combination of the advantages of ordinary cast iron and steel, has become a new type of structural material and is widely used in automobiles, machine tools, wind power, and other fields. With the development of machinery towards higher power, lighter weight, and longer service life, the performance requirements for ductile iron are becoming increasingly stringent. To improve the microstructure and properties of ductile iron, researchers both domestically and internationally have mainly focused on heat treatment processes, composite casting, and alloying. However, heat treatment processes are complex, have long production cycles, and are prone to problems such as high-temperature oxidation and deformation cracking, resulting in high scrap rates and energy consumption. While composite casting processes offer relatively high cost-effectiveness, their casting methods and process parameters need further standardization. Alloying elements have both synergistic and antagonistic effects; while increasing material strength, they inevitably lead to a decrease in plasticity. Therefore, a reasonable design of the types and contents of alloying elements is necessary to achieve good alloying results. Grain refinement is the most effective way to improve the strength and toughness of materials. However, it only plays a role in refining the microstructure of cast iron when the size of the second-phase particles in the molten iron is less than 1 μm, the number is so small that the distance between them is greater than 10 μm, and the interfacial energy between the matrix and the crystalline phase is small. Both added and endogenous second-phase particles can inhibit grain growth and improve material properties. However, the size, number, and distribution of endogenous particles are difficult to control, and their positive effects are difficult to fully realize. The size, amount, and morphology of added particles are easier to control, and the requirements for the purity of the molten iron are not high. Therefore, research on adding particles to molten iron has certain practical significance.

[0003] With the development of casting technology and nanotechnology, nanomaterials have been widely used and researched in the casting field due to their small size effect and unique physicochemical properties. Liu Zhenglu's research found that adding 0.02% nano-TiC ceramic particles to K214 casting alloy can reduce different grain sizes of the alloy by 30-60%, increase tensile strength by 82 MPa, and increase elongation by 22.4%. Zhao Yu's research found that there is an optimal amount of nano-SiO2 particles added to cast ductile iron. When the amount of nano-SiO2 added is 0.50%, the tensile strength reaches a maximum of 471 MPa, and the elongation is a maximum of 26.42%, but the mechanical properties of the ductile iron are still not ideal. Summary of the Invention

[0004] The first objective of this invention is to provide a method for preparing ductile iron reinforced with nano-SiC, which modifies nano-silicon carbide particles by iron powder and adds the modified nano-silicon carbide particles to molten iron. The modified nano-silicon carbide particles are used as a long-lasting inoculant for ductile iron, thereby improving the microstructure, mechanical strength and toughness of ductile iron.

[0005] The second objective of this invention is to provide an externally reinforced nano-SiC ductile iron.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The preparation method of ductile iron reinforced with nano-SiC includes the following steps:

[0008] S1: Modified nano-silicon carbide particles are obtained by ball milling iron powder and nano-silicon carbide particles.

[0009] S2: Weigh pig iron, scrap steel, recycled materials, and carbonizer, and smelt them to obtain molten iron;

[0010] S3: Remove slag from molten iron, then add spheroidizing agent, modified nano-silicon carbide particles, and primary inoculant, and cover with a covering agent to perform spheroidizing and primary inoculation treatment to obtain molten metal;

[0011] S4: The molten metal is poured into the casting process, and a secondary inoculant is added during the pouring. The mixture is then cooled to obtain the final product.

[0012] Furthermore, in S1, the mass ratio of iron powder to nano-silicon carbide particles is 7-9.5:1; and the particle size of the modified nano-silicon carbide particles is 50-60 nm.

[0013] Furthermore, the ball-to-material ratio of the ball mill is 10:1, the rotation speed is 200-250 r / min, and the time is 25-30 h.

[0014] Furthermore, the mass of the spheroidizing agent added is 1.1-1.2% of the mass of the molten iron; the mass of the primary inoculant added is 0.6-0.8% of the mass of the molten iron; the mass of the secondary inoculant added is 0.18-0.22% of the mass of the molten iron; the mass of the modified nano-silicon carbide particles added is 0.10-0.12% of the mass of the molten iron; and the mass of the carburizing agent added is 0.12-0.14% of the mass of the molten iron.

[0015] Furthermore, the spheroidizing agent is FeSiMg8RE3 spheroidizing agent with a particle size of 5-20 mm; the primary inoculant is 75SiFe inoculant with a particle size of 3-15 mm; the secondary inoculant is silicon-calcium inoculant with a particle size of 0.5-1.5 mm; and the covering agent is an anvil.

[0016] Furthermore, the melting temperature described in S2 is 1480-1520℃, and the casting temperature described in S4 is 1450-1490℃.

[0017] The nano-SiC-reinforced ductile iron was prepared using the above-described method for preparing nano-SiC-reinforced ductile iron.

[0018] The beneficial effects of this invention are:

[0019] The present invention involves mixing nano-silicon carbide particles with high-purity iron powder and then modifying the nano-silicon carbide particles using a high-energy ball milling method, which improves the compatibility between the nano-silicon carbide particles and molten iron. The addition of modified nano-silicon carbide particles improves the microstructure, strength, and toughness of ductile iron.

[0020] The added modified nano-silicon carbide particles have a two-dimensional mismatch of 0.5% with graphite, serving as effective nuclei for graphite formation. The two-dimensional mismatch between SiC and SiO2 is 9.41%, allowing SiC to combine with SiO2 to form nuclei for graphite spheroids, thus increasing the number of graphite nuclei. The modified nano-silicon carbide particles can be used as a long-lasting inoculant for ductile iron, increasing the number of graphite nuclei and consequently increasing the number of spheroids, while also refining the microstructure of the ductile iron. Attached Figure Description

[0021] Figure 1 The images show the morphology of silicon carbide nanoparticles, where A is the morphology of silicon carbide nanoparticles before modification and B is the morphology of modified silicon carbide nanoparticles.

[0022] Figure 2 The images are metallographic images of QT1 in Example 1 and QT0 in Comparative Example 1 before and after etching, where A is the metallographic image of QT0 in Comparative Example 1 before etching, B is the metallographic image of QT1 in Example 1 before etching, C is the metallographic image of QT0 in Comparative Example 1 after etching, and D is the metallographic image of QT1 in Example 1 after etching.

[0023] Figure 3 The images show SEM images of pearlite in QT1 of Example 1 and QT0 of Comparative Example 1, where A is the SEM image of pearlite in QT0 of Comparative Example 1 and B is the SEM image of pearlite in QT1 of Example 1.

[0024] Figure 4 The images show the morphology and distribution of inclusions in QT1 of Example 1 and QT0 of Comparative Example 1, where A is the morphology and distribution of inclusions in QT0 of Comparative Example 1 and B is the morphology and distribution of inclusions in QT1 of Example 1.

[0025] Figure 5The images show the tensile fracture surface SEM images of QT1 in Example 1 and QT0 in Comparative Example 1, where A is the tensile fracture surface SEM image of QT0 in Comparative Example 1 and B is the tensile fracture surface SEM image of QT1 in Example 1.

[0026] Figure 6 This is a diagram showing the matching relationship between SiO2 and graphite.

[0027] Figure 7 The images show the XRD diffraction patterns of graphite spheres and their cores, where A represents the SiC phase found in the graphite spheres, B represents the XRD diffraction pattern of SiC, C represents the SiC+SiO2 dual phase found in the graphite spheres, and D represents the XRD diffraction pattern of SiC+SiO2. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0029] The carbon raiser used in this invention has a particle size of 3-5 mm; the spheroidizing agent has a particle size of 5-20 mm; the 75SiFe inoculant has a particle size of 3-15 mm and a silicon mass percentage of 75%; the silicon-calcium inoculant has a particle size of 0.5-1.5 mm, a silicon mass percentage of 75%, and a calcium mass percentage of 25%. The iron powder has a purity >99.5%, a particle size of 20 nm, and a density of 7.87 g / cm³. 3 The nano-sized silicon carbide particles have a particle size of 20-30 nm and a density of 3.2-3.25 g / cm³. 3 .

[0030] Example 1

[0031] The preparation method of externally reinforced nano-SiC ductile iron in Example 1 includes the following steps:

[0032] S1: 83.2g of iron powder and 8.8g of nano-silicon carbide particles were mixed and ball-milled using a JX-4G high-performance ball mill to obtain modified nano-silicon carbide particles; the ball-to-material ratio in the ball mill was 10:1, the rotation speed was 220r / min, and the ball milling time was 27h; the particle size of the modified nano-silicon carbide particles was 50-60nm.

[0033] S2: Q12 pig iron, 45 scrap steel, ductile iron remelting material, and 10.4g of carbon raiser were smelted in a KGPS-1250 medium frequency furnace to obtain 8000g of molten iron at a melting temperature of 1500℃. After slag removal, the molten iron was sampled and tested.

[0034] S3: Add 92g of FeSiMg8RE3 spheroidizing agent, 8.8g of modified nano-silicon carbide particles, and 56g of 75SiFe inoculant sequentially from bottom to top in the spheroidizing dam tank, compact it, place the anvil on top of the 75SiFe inoculant, and carry out spheroidization and one-time inoculation to obtain molten metal.

[0035] S4: The molten metal is poured at a temperature of 1460℃. 16g of silicon-calcium inoculant is added during the pouring process. After air cooling in Y-type resin self-hardening sand, the product is obtained. The ductile iron reinforced with nano-SiC from Example 1 is named QT1.

[0036] Comparative Example 1

[0037] The preparation method of the ductile iron in Comparative Example 1 is largely the same as that in Example 1. The difference between Comparative Example 1 and Example 1 is that modified nano-silicon carbide particles were not added in Comparative Example 1. The ductile iron in Comparative Example 1 is named QT0.

[0038] According to GB / T1348-2009 "Ductile Iron Castings", the lower part of the cast Y-shaped test block was machined into a standard tensile specimen (d=10mm, L0=50mm, L...). c Tensile tests were conducted on an HT-2402 universal testing machine at a tensile rate of 0.5 mm / min. Metallographic specimens were prepared from the broken specimen ends and etched with 4% nitric acid alcohol for 30 s. The spheroidization rate and grade were observed and analyzed using a CLYMPVS-DEM metallographic microscope, and the pearlite and ferrite contents were analyzed. The tensile fracture morphology was observed using a JE0L-6360LV scanning electron microscope, and the average lamellar spacing of pearlite was measured. The hardness was tested using an HB-3000B hardness tester. Ar ion etching was performed on the cast specimens using a magnetron sputtering physical deposition system to expose the graphite core. The etching conditions were: voltage 850 V, current 135 mA, and pressure 8.4 Pa. The graphite core morphology was examined using a JE0L-6360LV scanning electron microscope, and phase analysis was performed using a D8 ADVANCE X-ray diffractometer. All experimental results were the average of three tests.

[0039] from Figure 1 It can be seen that the unmodified silicon carbide nanoparticles are approximately spherical in shape, with a particle size between 20-30 nm, and exhibit obvious agglomeration in their natural state. The density of the unmodified silicon carbide nanoparticles is 3.2-3.25 g / cm³. 3 It is far lower than the density of cast iron, which is 7.87 g / cm³. 3Directly adding silicon carbide to molten iron can cause it to float and agglomerate, affecting its grain refinement effect. However, after modification with iron powder, the modified nano-silicon carbide particles bond well with the iron powder through a cold welding effect, resulting in a spherical morphology with an increased particle size of 50-60 nm. It exhibits good dispersibility in its natural state. The modified nano-silicon carbide particles not only avoid agglomeration but also increase particle density, mitigating their floating in molten ductile iron and demonstrating good wettability with the molten iron.

[0040] According to GB9441-2009 "Metallographic Examination of Ductile Iron", the number of graphite spheroids was estimated based on the metallographic images. A representative field of view was selected, and the graphite spheroid morphology and matrix structure of the QT0 and QT1 samples were quantitatively evaluated using JX2000 software. The results are shown in Table 1.

[0041] Table 1 Metallographic test results of QT0 and QT1

[0042] As shown in Table 1, compared with QT0, QT1 has a 7.71% higher spheroidization rate, a 50% higher number of ductile iron particles, and a 50% higher ferrite content. The reduction in ductile iron particle size and the increase in ferrite content are beneficial to improving the strength and toughness of ductile iron.

[0043] from Figure 2 It can be seen that the QT0 sample of Comparative Example 1 has fewer graphite spheroids, uneven distribution, and significant size differences, with a small amount of fragmented graphite present. Some graphite spheroids exhibit cracks and sharp protrusions around their edges. This is because during the smelting process of molten iron, the presence of sulfur and oxygen elements generates sulfur oxide inclusions during the spheroidizing reaction, consuming Mg and RE in the spheroidizing agent. The spheroidizing agent degrades, leading to poor graphite spheroidizing reaction. In contrast, the QT1 sample of Example 1 shows an increased number of graphite spheroids, improved roundness, smaller size, and improved distribution uniformity. This is because the highly dispersed distribution of modified nano-silicon carbide particles in the molten iron can act as non-spontaneous nucleation sites for graphite, increasing both the number of graphite spheroids and the uniformity of graphite distribution. Figure 2 and Figure 3It can be seen that the matrix structure in both QT0 and QT1 samples consists of gray-black pearlite and gray-white ferrite. The pearlite morphology is irregular lamellar, located between the ferrite, while the ferrite morphology is mostly bullseye-shaped, surrounding the graphite spheroids, with a small amount being irregular lamellar. The QT0 sample has a higher pearlite content and a lower ferrite content, with uneven distribution and size. In the QT1 sample, the ferrite content increases, the pearlite content decreases, and the uniformity of distribution and size is significantly improved. This is because the addition of modified nano-silicon carbide particles promotes graphite nucleation, increases the number of spheroids, and increases the latent heat release rate of graphite crystallization, resulting in more heat generated during the solidification process of the molten iron. This reduces the supercooling at the solidification front, slows down the graphite growth rate, reduces the probability of graphite distortion during growth in the molten iron, reduces the size of the spheroids, and improves their roundness. The increased number of graphite spheroids reduces the diffusion distance of carbon atoms, leading to the formation and precipitation of numerous graphite spheroids. This consumes a significant amount of carbon atoms, reducing the carbon atom concentration in the molten iron surrounding the graphite spheroids. This, in turn, increases the carbon atom concentration gradient at the phase interface, accelerating ferrite growth, reducing cementite, and increasing ferrite content. Meanwhile, in the molten iron regions far from the graphite, due to incomplete carbon atom diffusion, pearlite eventually forms. The increased number of graphite spheroids also improves distribution uniformity, dividing pearlite and ferrite into finer grains, thus improving the uniformity of the matrix structure. Therefore, modified nano-silicon carbide particles act as an inoculant in the molten iron smelting process, increasing the number of graphite nuclei, promoting graphite spheroid refinement, improving spheroid roundness, and reducing the probability of graphite distortion.

[0044] Table 2. Main chemical composition of molten iron before and after the addition of modified nano-silicon carbide particles.

[0045] Table 2 shows that the composition of other elements in the ductile iron samples remained basically unchanged before and after the addition of modified nano-silicon carbide particles, but Mg... 残 The content varies considerably. Mg in QT0 残 The content of Mg in QT1 is 0.029%. 残 The content is 0.042%, compared with QT0, Mg 残 The content increased by 44.83%. When Mg 残 When the concentration varies within the range of 0.02%-0.05%, the number of spheroids increases with increasing Mg content. However, when Mg... 残 When the content reaches 0.058% or higher, the number of spheroids decreases sharply, and the graphitization morphology begins to become irregular. Residual Mg in molten iron 残Silicon carbide particles readily adsorb onto the graphite interface, increasing the dynamic undercooling and causing the graphite c-axis growth rate to exceed the a-axis growth rate. This also hinders the diffusion of carbon from the liquid into the graphite, resulting in smaller spherical graphite size, improved roundness, and a lower probability of graphite spheroid distortion. Therefore, adding an appropriate amount of modified nano-silicon carbide particles to the molten ductile iron increases the Mg content in the molten iron. 残 The content can increase the number of graphite spheres, reduce their size and improve their roundness, and reduce the probability of graphite sphere distortion.

[0046] from Figure 4 It can be seen that the inclusions in the QT0 sample are mainly aggregated and distributed in the matrix or at the grain boundaries, i.e. Figure 4 Within the white ellipse in sample A, the morphology is mainly blocky with very distinct edges and corners; a few are ellipsoidal, relatively large in size, and numerous. The size of the inclusions is approximately 7-10 μm, and the average distance between the inclusions is 10.83 μm. In sample QT1, the inclusions are uniformly distributed in the matrix or at grain boundaries, i.e. Figure 4 In section B, marked with a white arrow, the inclusions are mostly ellipsoidal, with a few blocky inclusions. They are small in size and fewer in number, with an average size of 5.2 μm and an average distance between inclusions of 31.67 μm. Sharper shapes, larger sizes, and greater numbers of inclusions severely disrupt the continuity of the matrix structure, significantly impacting the mechanical properties of ductile iron. Inclusions smaller than 10 μm, with a distance much greater than 10 μm between inclusions, relatively rounded shapes, and fewer inclusions have a smaller negative impact on the properties of ductile iron. The addition of modified nano-silicon carbide particles refines the inclusion size, improves the inclusion morphology, reduces the number of inclusions, and increases the uniformity of inclusion distribution, which is beneficial for improving the mechanical properties of ductile iron.

[0047] Table 3. Test results of mechanical properties of QT0 and QT1 specimens

[0048] Table 3 shows that compared with the QT0 sample, the tensile strength of QT1 increased by 14.99%, the hardness increased by 5.67%, and the elongation increased by 73.83%. Figure 2-3 It is evident that both the QT0 and QT1 samples consist of graphite, pearlite, and ferrite. Table 1 shows that the pearlite content in the QT1 sample is lower than that in the QT0 sample. Pearlite has a higher strength than ferrite, while the hardness of the QT1 sample increases rather than decreases. Figure 3It is evident that the interlamellar spacing of pearlite in the QT1 sample is smaller than that in the QT0 sample, with the interlamellar spacing being 12.24% smaller. This suggests that the increased hardness of QT1 is related to the finer pearlite size. Smaller interlamellar spacing results in more phase interfaces between ferrite and cementite, increasing the resistance to dislocation movement and thus the resistance to plastic deformation, thereby increasing hardness. Table 1 shows that the ferrite content in the QT1 sample is higher than that in the QT0 sample. Ferrite exhibits better plasticity and toughness than pearlite, suggesting that the increased elongation of the QT1 sample is related to the increased ferrite content. The number of ductile iron particles and the quantity, morphology, distribution, and size of inclusions also significantly affect the mechanical properties of ductile iron. Compared to the QT0 sample, the QT1 sample shows a significantly increased number of ductile iron particles, improved spheroidization, smaller size, and improved uniformity of distribution. Compared to the QT0 sample, the QT1 sample has a significantly smaller average size of inclusions and a significantly larger average distance between inclusions. The roundness and distribution uniformity are improved, and the cutting effect of ductile iron and inclusions on the matrix is ​​smaller. Under the action of external force, stress concentration is less likely to occur, reducing the probability of crack initiation. The overall mechanical properties are also better, so the strength and toughness of QT1 are improved.

[0049] Figure 5SEM images of the tensile fracture surfaces of QT0 and QT1 specimens are shown. The tensile fracture surface of the QT0 specimen is relatively flat and smooth, with numerous cleavage steps or river-like patterns visible. The river-like patterns formed by the convergence of cleavage steps occupy most of the fracture surface. There are few dimples on the cleavage surfaces, and distorted graphite can be observed in some local locations. The pits left by the detached graphite are relatively smooth, indicating low adhesion between the graphite spheres and the matrix. There are obvious aggregated fragmented graphite clusters on the fracture surface, with obvious fracture cracks on the fragmented graphite clusters. There are no obvious tear ridges around the graphite, exhibiting brittle fracture characteristics. The tensile fracture surface of the QT1 specimen is relatively rough, with obvious micro-dimples on the cleavage surfaces and a significant reduction in river-like patterns. Graphite is relatively evenly distributed on the fracture surface, leaving deep dimples after detachment. A small number of graphite spheres exhibit tearing. Most of the graphite dimples contain graphite spheres, and obvious tear ridges are observed around the dimples and spheres. Numerous micro-dimples are present on the tear ridges, indicating that the tensile specimen possesses a certain degree of plasticity, exhibiting brittle-ductile fracture characteristics. The QT0 specimen contains fewer spheroidal graphite particles, which are unevenly distributed and vary greatly in size. A small amount of fragmented graphite is present, and some graphite spheres show cracking and sharp protrusions around their periphery. Inclusions are aggregated in the matrix or at grain boundaries. The inclusions are mainly blocky in morphology, with very sharp edges, large size, numerous particles, and small spacing. The strong cutting effect of distorted graphite and fragmented graphite on the matrix leads to stress concentration at the sharp corners of graphite and inclusions under tensile force, which initiates cracks. These cracks easily propagate and connect, leading to fracture and making the matrix structure more prone to cleavage. In the QT1 sample, the number of spherical inks increased, the roundness improved, the size decreased, and the distribution uniformity improved.

[0050] The two-dimensional lattice mismatch between SiO2 and the primary γ-Fe phase of ductile iron is 2.90%, and the characteristic parameter of empirical electron theory is 1.759, which creates conditions for SiO2 to act as a heterogeneous nucleation core for γ-Fe. SiO2 has a melting point of 1600-1700℃, higher than the eutectic temperature of ductile iron (1154℃), and its molar Gibbs free energy is relatively large, allowing it to exist relatively stably in molten iron, thus possessing one of the conditions for serving as a graphite nucleation substrate. To analyze the effectiveness of SiO2 as a graphite nucleation core, the two-dimensional lattice mismatch between SiO2 and graphite was calculated according to Bramfitt's formula for calculating the two-dimensional lattice mismatch. The formula for calculating the two-dimensional lattice mismatch is:

[0051] ;

[0052] [uvw]s is a low-index direction on the substrate crystal plane, [uvw]n is a low-index direction on the nucleation phase crystal plane, d[uvw]s is the interatomic spacing along the [uvw]s direction, d[uvw]n is the interatomic spacing along the [uvw]n direction, and θ is the angle between [uvw]s and [uvw]n.

[0053] SiO2 has a hexagonal crystal system with a = 4.801 and c = 5.317, and its closest packing plane is the

[110] plane. Graphite also has a hexagonal crystal system with lattice constants a = b = 0.2461 nm and c = 0.6708 nm, and its closest packing plane is the

[0001] plane. The matching relationship between SiO2 and graphite is as follows: Figure 6 As shown in Table 4, the small hollow circle represents SiO2 and the large solid circle represents graphite. The calculation results are shown in Table 4. As can be seen from Table 4, the two-dimensional lattice mismatch degree δ between the closest-packed

[110] crystal plane of SiO2 and the closest-packed

[0001] crystal plane of graphite is 15.40% > 12%. Therefore, SiO2 is an ineffective nucleation core for graphite.

[0054] Table 4 Calculation results of two-dimensional mismatch degree

[0055] The two-dimensional lattice mismatch degree between SiC and graphite, and between SiC and SiO2 was calculated. SiC is a close-packed hexagonal crystal system with lattice constants a = 0.308 nm and c = 0.5027 nm, and its closest-packed plane is the

[100] plane. The two-dimensional lattice mismatch degree between SiC and graphite is δ = 0.5% < 6%, which is an excellent nucleation core for graphite. It can significantly reduce the interfacial energy during graphite crystallization and promote graphite self-nucleation. The δ = 9.41% < 12% between SiO2 and SiC is a moderately effective nucleation core for SiC. Therefore, SiC can induce SiO2 to co-form a nucleation core for graphite, thereby increasing the graphite nucleation rate, increasing the number of spheroids, reducing the size of spheroids, and improving the roundness and distribution uniformity, thus playing a grain-refining strengthening role in ductile iron.

[0056] Modified nano-silicon carbide particles have a melting point of 2730℃, far exceeding the smelting temperature of molten iron (1480-1520℃). They cannot melt in molten iron but instead dissolve in it via the reaction SiC + Fe = FeSi + C. The carbon replaced by Fe from SiC is highly reactive, exhibiting zero mismatch with the two-dimensional lattice of graphite, resulting in superior inoculation effects. The melting reaction of SiC is an endothermic process, which reduces the diffusion rate of C and the supercooling of the molten iron, refining the microstructure of ductile iron. Therefore, the addition of nano-silicon carbide particles can serve as an ideal long-lasting inoculant for ductile iron, effectively hindering the degradation of spheroidizing agents, 75SiFe inoculants, and calcium silicate inoculants, thus affecting the production quality of ductile iron.

[0057] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the content of the present invention's specification shall also be included within the scope of protection of the present invention.

Claims

1. A method for preparing ductile iron reinforced with nano-SiC, characterized in that, Includes the following steps: S1: Modified nano-silicon carbide particles are obtained by ball milling iron powder and nano-silicon carbide particles. S2: Weigh pig iron, scrap steel, recycled materials, and carbonizer, and smelt them to obtain molten iron; S3: Remove slag from molten iron, then add spheroidizing agent, modified nano-silicon carbide particles, and primary inoculant, and cover with a covering agent to perform spheroidizing and primary inoculation treatment to obtain molten metal; S4: The molten metal is poured into the casting process, and a secondary inoculant is added during the pouring. The mixture is then cooled to obtain the final product.

2. The method for preparing externally reinforced ductile iron with nano-SiC according to claim 1, characterized in that, The mass ratio of iron powder to nano-silicon carbide particles in S1 is 7-9.5:1; the particle size of the modified nano-silicon carbide particles is 50-60 nm.

3. The method for preparing externally reinforced ductile iron with nano-SiC according to claim 1, characterized in that, The ball mill has a ball-to-material ratio of 10:1, a rotation speed of 200-250 r / min, and a time of 25-30 h.

4. The method for preparing externally reinforced ductile iron with nano-SiC according to claim 1, characterized in that, The mass of the spheroidizing agent added is 1.1-1.2% of the mass of the molten iron; the mass of the primary inoculant added is 0.6-0.8% of the mass of the molten iron; the mass of the secondary inoculant added is 0.18-0.22% of the mass of the molten iron; the mass of the modified nano-silicon carbide particles added is 0.10-0.12% of the mass of the molten iron; and the mass of the carburizing agent added is 0.12-0.14% of the mass of the molten iron.

5. The method for preparing externally reinforced ductile iron with nano-SiC according to claim 1, characterized in that, The spheroidizing agent is FeSiMg8RE3 spheroidizing agent with a particle size of 5-20 mm; the primary inoculant is 75SiFe inoculant with a particle size of 3-15 mm; the secondary inoculant is silicon-calcium inoculant with a particle size of 0.5-1.5 mm; and the covering agent is an anvil.

6. The method for preparing externally reinforced ductile iron with nano-SiC according to claim 1, characterized in that, The melting temperature described in S2 is 1480-1520℃, and the casting temperature described in S4 is 1450-1490℃.

7. Ductile iron reinforced with nano-SiC, characterized in that... It was prepared by the method for preparing externally reinforced ductile iron with nano-SiC as described in any one of claims 1-6.

Images