A rare earth composite inoculant containing gadolinium for use in gray cast iron cylinder blocks

Abstract

This invention discloses a gadolinium-containing rare earth composite inoculant for gray cast iron cylinder blocks. Its chemical composition and mass percentages are as follows: Si: 45-50%, RE: 4-12% (Gd: 20%, other rare earth elements: 80%), Cr: 4-12%, Mn: 3-9%, Ca: 0.5-1.0%, Ba: 2.0-3.0%, Al: 1-2%, Cu: 5%, with the balance being Fe. This inoculant incorporates rare earth elements, chromium, manganese, calcium, barium, and aluminum. On one hand, the RE element purifies the molten iron and inhibits rapid cooling; on the other hand, the interaction of these elements enhances the inoculation ability, promotes the formation of type A graphite, makes the graphite more curved and refined with blunted ends, refines and increases the pearlite content, reduces the pearlite lamellar spacing, and appropriately increases the eutectic cluster content. This improves the strength and stiffness of the gray cast iron, and enhances the cross-sectional sensitivity and machinability of the casting.

Description

Technical Field

[0001] This invention belongs to the field of casting production, and particularly relates to a rare earth composite inoculant containing gadolinium for use in gray cast iron cylinder blocks. Background Technology

[0002] Gray cast iron has a gray fracture surface and a lamellar structure of graphite and pearlite. It has excellent comprehensive engineering properties, such as good casting performance and machinability, good wear resistance, friction reduction and vibration reduction performance, and low price. As a result, it is widely used in the automotive, machine tool and shipbuilding industries, and is particularly suitable for box-type parts. It also occupies a significant share in high-power engines.

[0003] Engine blocks are subjected to significant thermal shock and fatigue during operation, requiring gray cast iron to possess excellent dimensional stability, high tensile strength, and rapid heat dissipation. Inoculation treatment can reduce the tendency for white cast iron to form; increase the pearlite content and refine the pearlite lamellar spacing; reduce coarse flake graphite, making the graphite structure more refined, curved, and blunt at the ends; thereby improving the uniformity of the structure, cross-sectional sensitivity, and machinability, resulting in improved mechanical properties and a significant reduction in casting defects.

[0004] The cylinder block casting process is very complex. In the production of cylinder blocks and cylinder heads, inoculation treatment is a crucial step, but castings still suffer from problems such as shrinkage cavities, porosity, and poor cross-sectional sensitivity. With the increasing performance requirements of gray cast iron cylinder blocks, exploring new inoculants to improve the microstructure and properties of gray cast iron cylinder blocks has always been a research focus. Summary of the Invention

[0005] This invention provides a gadolinium-containing rare-earth composite inoculant for gray cast iron cylinder blocks. It increases the proportion of type A graphite (over 90%), while simultaneously passivating the graphite ends, improving the machinability of gray cast iron castings, reducing the tendency for white cast iron, refining the pearlite structure, and increasing the tensile strength, stiffness, and hardness of gray cast iron castings. This results in high-performance engine cylinder block castings with good sectional sensitivity. Compared to ferrosilicon inoculants, gray cast iron castings produced using this inoculant can achieve a strength of up to 338 MPa, a Brinell hardness of up to 242 HB, and a sectional sensitivity reduced to 25 HB.

[0006] The technical solution of this invention:

[0007] A rare earth composite inoculant containing gadolinium for use in gray cast iron cylinder blocks, wherein the chemical composition and mass percentage of the inoculant are as follows: Si: 45-50%, RE: 4-12% (Gd: 20%, other rare earths: 80%), Cr: 4-12%, Mn: 3-9%, Ca: 0.5-1.0%, Ba: 2.0-3.0%, Al: 1-2%, Cu: 5%, with the balance being Fe.

[0008] Furthermore, the rare earth elements in the inoculant are derived from: metallic gadolinium and rare earth ferrosilicon.

[0009] Furthermore, the gadolinium-containing rare earth composite inoculant for the gray cast iron cylinder block has a particle size of 3-5 mm.

[0010] The effective components of the gadolinium-containing rare earth composite inoculant for gray cast iron cylinder blocks of this invention are ferrosilicon, ferrosilicon barium, ferromanganese, ferrochromium, gadolinium metal, rare earth ferrosilicon, and elemental copper. The effective elements are Si, Mn, Cr, Ca, Ba, Gd, La, Ce, Al, and Cu. The beneficial effects of this inoculant are:

[0011] 1. Si: Promotes graphite nucleation, changes the morphology and refinement of graphite, and reduces the tendency for white graphite formation.

[0012] 2. RE: Desulfurization, deoxidation, and molten iron purification. It has certain anti-fading properties, improves graphite morphology, inhibits rapid cooling, and increases and refines austenite dendrites, thus creating conditions for improving the microstructure and properties of cast iron.

[0013] 3. Cr: It can promote the formation of pearlite and refine the interlamellar spacing. Adding an appropriate amount of Cr can improve the wear resistance and heat resistance of gray cast iron. However, excessive chromium will increase the tendency of white cast iron, so the content should not be too high.

[0014] 4. Mn: Lowers the melting point of the inoculant, can form MnS with S in the molten iron to promote graphite nucleation, and can also be dissolved in the matrix and carbides to inhibit the formation of ferrite and promote the formation of pearlite. The content should not be too high.

[0015] 5. Ca, Ba, Al: Trace elements in molten iron, ensuring less waste residue is produced, having a certain deoxidation and desulfurization effect, forming corresponding oxides and sulfides, forming a large number of graphite nuclei, promoting graphite nucleation, and at the same time reducing the tendency of white iron, improving cross-sectional sensitivity and machinability.

[0016] 6. Cu: Reduces the tendency of white cast iron caused by Cr, and can stabilize and refine pearlite, thereby improving strength and corrosion resistance.

[0017] 7. Gd: A rare earth element with a certain degree of magnetism. It has a certain adsorption effect on metal elements in molten iron, which can improve the uniformity of the structure and improve the performance of thin-walled ultra-cooled parts. However, excessive gadolinium will cause element segregation.

[0018] 8. Synergistic effect 1: Mn, Ca, Ba, Gd, La, and Ce can form oxides and sulfides with a lattice mismatch of less than 12% with O and S, such as XS (X is Mn, La, Gd, etc.), XO (X is Ca, Ba, etc.) and X2O3 (X is Si, Al, Gd, La, Ce, etc.), which become the core of graphite, promote graphitization, refine graphite structure, and improve graphite shape.

[0019] 9. Synergistic effect 2: The oxides formed in synergistic effect 1 can form silicates such as CaO.SiO2, CaO.Al2O3.SiO2, BaO.Al2O3.SiO2, etc. The lattice mismatch degree of these silicates with graphite is less than 12%, which can effectively promote graphite nucleation, improve graphite structure, and blunt graphite tips.

[0020] 10. The combined effect of Mn, Cr, and Cu elements strongly promotes the formation of pearlite, refines the interlamellar spacing of pearlite, and improves the strength, hardness, and impact toughness of gray cast iron. Attached Figure Description

[0021] Figure 1 The graphite microstructure morphology of the control group and gray cast iron in Example 3;

[0022] Figure 2 The matrix morphology of gray cast iron in the control group and Example 3 is shown.

[0023] Figure 3 The primary austenitic dendritic structure morphology of gray cast iron in the control group and Example 3;

[0024] Figure 4 The eutectic morphology of gray cast iron in the control group and Example 3 is shown. Detailed Implementation

[0025] The following describes in more detail the gadolinium-containing rare earth composite inoculant for gray cast iron cylinder blocks of the present invention through specific embodiments. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] Example 1:

[0027] A rare earth composite inoculant containing gadolinium for use in gray cast iron cylinder blocks, wherein the mass percentage of elements contained in the inoculant is: Si: 45.0%, RE: 4.0% (Gd: 0.8%, other rare earths: 3.2%), Mn: 3.0%, Cr: 4.0%, Ca: 0.5%, Ba: 2.0%, Al: 1.0%, Cu: 5%, with the balance being Fe.

[0028] Example 2:

[0029] A rare earth composite inoculant containing gadolinium for use in gray cast iron cylinder blocks, wherein the mass percentage of elements contained in the inoculant is: Si: 47.5%, RE: 8.0% (Gd: 1.6%, other rare earths: 6.4%), Mn: 6.0%, Cr: 8.0%, Ca: 0.75%, Ba: 2.5%, Al: 1.5%, Cu: 5%, with the balance being Fe.

[0030] Example 3:

[0031] A rare earth composite inoculant containing gadolinium for use in gray cast iron cylinder blocks, wherein the mass percentage of the elements contained in the inoculant is: Si: 47.5%, RE: 8% (Gd: 1.6%, other rare earths: 6.4%), Mn: 6.0%, Cr: 8.0%, Ca: 1.2%, Ba: 3.0%, Al: 1.0%, Cu: 5%, with the balance being Fe.

[0032] Application Cases

[0033] The gadolinium-containing rare earth composite inoculants used for gray cast iron cylinder blocks in Examples 1-3 all exhibited good inoculation capabilities. In Example 3, the elemental proportions of the inoculant were as follows: Si: 47.50%, RE: 8% (Gd: 1.6%, other rare earths: 6.4%), Mn: 6.0%, Cr: 8.0%, Ca: 1.2%, Ba: 3.0%, Al: 1.0%, Cu: 5%, with the balance being Fe. The inoculant particle size was 3-5 mm, and the best inoculation effect was achieved when the amount added was 0.4% of the mass of the molten iron.

[0034] As in Example 3, the specific implementation process is as follows: a certain proportion of gray cast iron raw materials are smelted in a medium-frequency induction furnace. In order to ensure the fluidity of the molten iron and reduce the heritability of the raw material's structure, the temperature of the molten iron is heated to 1520-1550℃ and held for 10 minutes. The converter temperature is 1420-1450℃. Then, inoculation is carried out in the ladle. The molten iron treated with 75% ferrosilicon inoculant is set as the control group. The smelting and casting temperatures of the control group are consistent with those of the example.

[0035] After the molten iron has fully inoculated, it is poured into the furnace at 1390-1410℃. The resin sand sample was cooled. Before casting, a small amount of molten iron was taken to prepare a white cast iron sample, and its composition was determined using a direct-reading spectrometer. The chemical composition is shown in Table 1 below.

[0036] Table 1 Chemical composition (wt.%) of gray cast iron samples

[0037]

[0038] As in Example 3, the components of the gray cast iron met the design requirements. The performance and properties of the gray cast iron were tested, and the test results are shown in Table 2 below. As can be seen from Table 2, the gray cast iron inoculated with the inoculant in Example 3 has higher performance than the gray cast iron inoculated with 75% ferrosilicon. Specifically, the tensile strength increased by 11.92%, the Brinell hardness increased by 15.24%, and the maximum hardness difference at the cross section decreased to 25 HB.

[0039] Table 2 Mechanical properties of gray cast iron specimens

[0040]

[0041] like Figure 1 As shown, Figure 1 (a) is the graphite structure of gray cast iron in the control group. Figure 1 (b) The graphite microstructure of gray cast iron in Example 3 is shown. In the control group, the graphite in the gray cast iron sample consisted of type A graphite and a small amount of type D graphite, with type A graphite accounting for approximately 90% and the graphite length grade being approximately 3-4. Compared with the control group, the proportion of type A graphite in the gray cast iron sample of Example 3 increased to approximately 95%, and the graphite length was grade 4. The graphite was more curved, and the ends were significantly blunted. Therefore, this rare earth composite inoculation can significantly improve the morphology of graphite because the RE and Mn elements in the optimized inoculator can react with O and S to generate oxides and sulfides. At the same time, the Gd element can adsorb metal ions, increasing the nucleation of graphite, promoting the formation of type A graphite, and making the graphite more curved, finer, and with blunted ends.

[0042] like Figure 2 As shown, Figure 2 (a, b) represent the matrix structure of gray cast iron in the control group. Figure 2 (c, d) show the microstructure of the gray cast iron matrix in Example 3. The experimental results indicate that the matrix of the gray cast iron samples consisted entirely of pearlite and a small amount of ferrite. Example 3 gray cast iron exhibited a higher pearlite content (over 98%), smaller interlamellar gaps, and a finer overall microstructure. This is because the addition of Mn, Cr, and Cu elements in the inoculant promotes carbide formation, which in turn promotes pearlite formation. Simultaneously, Mn elements counteract the effect of sulfur hindering graphitization, reducing coarse lamellar pearlite and further refining the pearlite microstructure. Furthermore, the rare earth element Gd in the inoculant allows for a more uniform element distribution, resulting in a more uniform microstructure, improved strength of the gray cast iron, and enhanced cross-sectional sensitivity and machinability.

[0043] like Figure 3 As shown, Figure 3 (a) shows the morphology of primary austenitic dendrite structure in gray cast iron of the control group. Figure 3(b) shows the morphology of the primary austenite dendrite structure in gray cast iron of Example 3. Compared with the control group, the primary austenite dendrites in Example 3 have smaller spacing, more numerous dendrites, a larger austenite dendrite area ratio, and a more uniform distribution, while also possessing a certain network structure. This is because the Mn and Cr elements in the inoculant can hinder the growth of austenite grains and reduce the austenite formation rate, making the spatial network structure of austenite dendrites more complex. This reduces the dendrite spacing, refines the secondary dendrites, increases the resistance to fracture, and improves the tensile strength and hardness of gray cast iron.

[0044] like Figure 4 As shown, Figure 4 (a) shows the eutectic structure of gray cast iron in the control group. Figure 4 (b) shows the eutectic microstructure of gray cast iron in Example 3. The control group gray cast iron had fewer and larger eutectic clusters, while the gray cast iron in Example 3 showed a significant increase in the number of eutectic clusters, smaller sizes, and a more uniform distribution. This is because the primary austenite dendrite spacing in Example 3 is small, and the eutectic clusters are spatially restricted during growth, thus refining the eutectic microstructure. This results in a more uniform microstructure, improved strength, and enhanced cross-sectional sensitivity and machinability of the gray cast iron.

[0045] This invention is not limited to the preferred embodiments described above. Anyone can derive other products in various forms under the guidance of this invention. However, regardless of any changes in shape or structure, any technical solution that is the same as or similar to this application should fall within the protection scope of this invention.

Claims

1. A rare earth composite inoculant containing gadolinium for use in gray cast iron cylinder blocks, characterized in that: The inoculant composition, by mass percentage, is as follows: Si: 45-50%, RE: 4-12%, Cr: 4-12%, Mn: 3-9%, Ca: 0.5-1.0%, Ba: 2.0-3.0%, Al: 1-2%, Cu: 5%, with the balance being Fe; the rare earth elements in the rare earth composite inoculant include Gd, Ce, and La, with Gd accounting for 20% of the total mass of rare earth elements.

2. The gadolinium-containing rare earth composite inoculant for gray cast iron cylinder blocks according to claim 1, characterized in that: The mass percentage of Si in the rare earth composite inoculant is 47-48%.

3. The gadolinium-containing rare earth composite inoculant for gray cast iron cylinder blocks according to claim 1, characterized in that: The mass percentage of RE in the rare earth composite inoculant is 7-9%.

4. The gadolinium-containing rare earth composite inoculant for gray cast iron cylinder blocks according to claim 1, characterized in that, The mass percentage of Cr in the rare earth composite inoculant is 6-7%.

5. The gadolinium-containing rare earth composite inoculant for gray cast iron cylinder blocks according to claim 1, characterized in that: The mass percentage of Mn in the rare earth composite inoculant is 5-7%.

6. The gadolinium-containing rare earth composite inoculant for gray cast iron cylinder blocks according to any one of claims 2-5, characterized in that: The rare earth composite inoculant contains, by mass percentage: Ca: 0.5-0.8%, Ba: 2.0-2.5%, Al: 1.0-1.5%, and Cu: 5%.

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