Wrought iron and its preparation process and application

Abstract

The application discloses vermicular cast iron and a preparation process and application thereof. The preparation raw materials of the vermicular cast iron include Fe, rare earth-containing vermicularizing agent, rare earth-containing inoculant, and elements such as C, Si, Mn, Cu, Sn and the like. Based on the component collocation of the preparation raw materials, the vermicular cast iron has the characteristics of small hardness fluctuation, good thermal conductivity, good wear resistance and high tensile strength, can better meet the use requirements of high-temperature and high-pressure working conditions, and prolongs the service life; meanwhile, the vermicular cast iron has low manufacturing cost. The application further provides the preparation process and application of the vermicular cast iron.

Description

Technical Field

[0001] This invention relates to the field of cast iron materials technology, and in particular to a vermicular graphite cast iron and its preparation process and application. Background Technology

[0002] Based on the different morphologies of graphite, cast iron can be classified into the following categories: gray cast iron, ductile cast iron, malleable cast iron, and vermicular graphite cast iron. In gray cast iron, graphite is distributed independently in flake-like forms within the matrix, separated from each other; in ductile cast iron, graphite is distributed in spherical forms; in malleable cast iron, graphite is distributed in a clump-like mass; and in vermicular graphite cast iron, graphite is distributed in a vermicular pattern. The microstructures of gray cast iron, ductile cast iron, and vermicular graphite cast iron are as follows: Figures 1-3 As shown. In comparison, gray cast iron contains a large amount of flake graphite, which has a greater cutting effect on the matrix and lower strength and wear resistance; ductile cast iron has higher strength, but poorer thermal conductivity and machinability.

[0003] Currently, gray cast iron or ductile iron are commonly used materials for manufacturing transmission or braking parts such as scroll compressors. The main structure of a scroll compressor is as follows: Figure 4 As shown, it includes a moving scroll plate 110, a stationary scroll plate 120, an upper support 130, a cross slip ring 140, an eccentric crankshaft 150, an air inlet 160, and an exhaust port 170. The working principle is as follows: the motor drives the eccentric crankshaft 150 to rotate. Under the constraint of the upper support 130 and the cross slip ring 140, the moving scroll plate 110 performs a circular translation around the stationary scroll plate 120. The moving scroll plate 110 and the stationary scroll plate 120 mesh to form several crescent-shaped compression chambers. As the circular translation continues, the volume of the compression chambers gradually decreases, and the gas pressure gradually increases. Finally, the high-pressure gas is discharged from the axial hole at the center of the stationary scroll plate 120. Due to the insufficient strength and wear resistance of gray cast iron, the scroll plate is prone to breakage or wear, resulting in a short service life. Similarly, ductile iron, limited by its thermal conductivity and machinability, also has limitations in application.

[0004] Vermicular graphite cast iron possesses comprehensive properties between gray cast iron and ductile iron, making it a potential material for manufacturing components such as scroll plates. However, existing vermicular graphite cast irons suffer from insufficient strength, large hardness fluctuations, and poor thermal conductivity. Their performance in terms of wear resistance and thermal fatigue resistance is also limited, failing to adequately meet the application requirements of high-temperature and high-pressure differential working environments. Therefore, it is necessary to develop a new high-performance cast iron material. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a vermicular graphite cast iron with controllable microstructure and characteristics of small hardness fluctuation, good thermal conductivity, good wear resistance and high tensile strength.

[0006] The present invention also proposes a preparation process for the vermicular graphite cast iron.

[0007] The present invention also proposes the application of the vermicular graphite cast iron.

[0008] Specifically, the first aspect of this invention relates to a vermicular graphite cast iron, which comprises Fe, a rare earth vermicularizing agent, a rare earth inoculant, and the following raw materials by mass percentage:

[0009] C: 3.5% to 3.8%, Si: 1.8% to 2.6%, Mn: 0.2% to 0.5%, Cu: 0.2% to 0.5%, Sn: 0.03% to 0.06%, Cr: 0% to 0.05%, Sb: 0% to 0.01%.

[0010] The vermicular graphite cast iron according to the first aspect of the present invention has at least the following beneficial effects:

[0011] In this embodiment, the combination of raw materials has a significant impact on the microstructure and physical and mechanical properties of vermicular graphite cast iron, wherein:

[0012] Carbon (C) is the basic element for forming graphite. The C content has a significant impact on the microstructure and mechanical properties of cast iron. Controlling the carbon content within a suitable range can adjust the ferrite and graphite content, ensuring strength and hardness.

[0013] The molten iron contains trace amounts of oxygen (O). Si reacts with the O in the molten iron to form silicon dioxide crystals, which act as external nuclei for graphite crystallization and promote graphitization. An appropriate Si content is also beneficial to the morphological stability of vermicular graphite cast iron.

[0014] Mn plays a role in reducing the number of eutectic clusters and stabilizing carbides and austenite. During the eutectoid transformation, Mn plays a role in refining and stabilizing pearlite. However, the Mn content should not be too high to avoid supercooling.

[0015] Cu plays a role in increasing and stabilizing pearlite in the matrix, and an appropriate Cu content is important for ensuring mechanical properties such as strength and elongation.

[0016] Cr is a strong pearlite-promoting element; however, during the solidification process of cast iron, chromium also strongly promotes cementite formation, increasing the tendency of cast iron to develop white cast iron. Therefore, the Cr content should not be too high. By combining Cr and Cu to adjust the pearlite content, it is more beneficial to ensure mechanical properties and wear resistance.

[0017] Sn plays a role in increasing pearlite content, but the Sn content should not be too high to avoid hardness and brittleness.

[0018] Sb can refine graphite, but excessive content can have an adverse effect on the properties of cast iron.

[0019] Rare earth vermicularizing agents and rare earth inoculants can control the morphology of graphite and the microstructure of cast iron, forming a mixed microstructure of pearlite, ferrite and graphite. They can help regulate the vermicularization rate, the proportion of pearlite and the proportion of graphite within a suitable range, improve the uniformity of the microstructure, and thus improve wear resistance and thermal conductivity while ensuring mechanical properties.

[0020] By rationally controlling the C and Si content, and the mass percentages of pearlite-forming elements Mn, Cu, and Sn, and by using rare-earth vermicularizing agents and rare-earth inoculants, the microstructure and uniformity of the entire cast iron matrix can be adjusted. This reduces the range of hardness fluctuations in cast iron, avoids the impact of excessively hard particles on wear resistance and machinability, and lowers manufacturing costs. Controlling the vermicularization rate and graphite ratio within appropriate ranges improves thermal conductivity, reduces boundary friction caused by high-temperature thermal deformation, enhances wear-resistant and friction-reducing properties, and better meets the requirements of high-temperature and high-pressure operating conditions, extending service life. Furthermore, adding appropriate amounts of easily segregating element Sb and carbide-forming element Cr can achieve even better modification effects.

[0021] The vermicular graphite cast iron of the present invention has a tensile strength ≥450MPa, a yield strength ≥335MPa, and a hardness value of HB160~230. Moreover, the hardness fluctuation is small, and the hardness fluctuation range can be as low as below 10HB. The overall mechanical properties, wear resistance and thermal conductivity are significantly improved compared with the existing vermicular graphite cast iron.

[0022] According to some embodiments of the first aspect of the present invention, in the rare earth vermicularizing agent, the rare earth element is selected from Ce, Zr or a combination thereof.

[0023] According to some embodiments of the first aspect of the present invention, the rare earth vermicularizing agent further contains Si, Mg, Ca and Fe.

[0024] According to some embodiments of the first aspect of the present invention, the rare earth vermicularizing agent comprises Fe and the following elements in mass percentage: Mg 4%–6%, Si 43%–47%, Ca 1%–2%, Re 2%–4%, wherein Re is selected from Ce, Zr, or a combination thereof. The balance is Fe, without considering the content of impurity elements.

[0025] According to some embodiments of the first aspect of the present invention, the mass percentage of the rare earth vermicularizing agent is 0.2% to 0.5% based on the total mass of the remaining raw materials other than the rare earth vermicularizing agent and the rare earth inoculant.

[0026] According to some embodiments of the first aspect of the present invention, the rare earth element in the rare earth inoculant is selected from Ce, Zr, or a combination thereof.

[0027] According to some embodiments of the first aspect of the present invention, the rare earth inoculant further contains Si, Ca, Ba and Fe, or the rare earth inoculant further contains Si, Ca, Ba, Al and Fe.

[0028] According to some embodiments of the first aspect of the present invention, the rare earth element in the rare earth-containing inoculant is selected from Ce.

[0029] According to some embodiments of the first aspect of the present invention, the rare earth-containing inoculant comprises Fe and the following elements in mass percentage: Si 70%–80%, Ca 0.75%–2%, Ba 1%–3%, Ce 0.3%–1%, Al 0%–1.5%. The balance is Fe, without considering the content of impurity elements.

[0030] According to some embodiments of the first aspect of the present invention, the rare earth inoculant comprises a rare earth ferrosilicon alloy and a silicon-barium-calcium-iron alloy. The rare earth ferrosilicon alloy comprises Fe and the following elements by mass percentage: Si 70%–76%, Ca 0.75%–1.25%, Al 0.75%–1.25%, Ce 1.5%–2.0%. The silicon-barium-calcium-iron alloy comprises Fe and the following elements by mass percentage: Si 72%–78%, Ca 1.0%–2.0%, Ba 2.0%–3.0%, Al 0%–1.25%. The mass ratio of the rare earth ferrosilicon alloy to the silicon-barium-calcium-iron alloy is 1:1–4. In the rare earth ferrosilicon alloy or the silicon-barium-calcium-iron alloy, the balance is Fe, without considering the content of impurity elements.

[0031] By using two alloys for composite inoculation, the limitations on the amount of inoculant added in traditional vermicular graphite cast iron smelting are relaxed, the limitations of a single inoculant are avoided, the composition of the inoculant is easily adjusted, the internal microstructure and uniformity of the cast iron are guaranteed, and the overall performance of the cast iron is improved.

[0032] According to some embodiments of the first aspect of the present invention, the rare earth ferrosilicon alloy comprises 0.1% to 0.2% of the total mass of the remaining raw materials other than the rare earth vermicularizing agent and the rare earth inoculant, and the silicon barium calcium iron alloy comprises 0.2% to 0.4% of the total mass.

[0033] According to some embodiments of the first aspect of the present invention, the mass percentage of the rare earth inoculant is 0.3% to 0.6% based on the total mass of the remaining raw materials other than the rare earth vermicularizing agent and the rare earth inoculant.

[0034] The choice of inoculant or vermicularizer affects grain refinement. Selecting a suitable inoculant or vermicularizer system can reduce white iron formation and promote graphitization. This is because molten iron contains trace amounts of dissolved O and N, and may also contain associated impurities such as S. These trace elements can combine with elements in rare earth inoculants, improving the inoculation and vermicularization effects. Specifically, Ca, Al, and Ce can form sulfides; Si, Mg, Ca, Al, and Ba can form oxides; Si, Al, Ca, and Ba can form carbides; Si, Al, Zr, and Ce can form nitrides; and Ce can also form intermetallic compounds with Sb and Sn, suppressing the negative effects of trace interfering elements. The resulting sulfides, oxides, carbides, nitrides, and rare earth compounds can all act as crystal nuclei, promoting graphitization and grain refinement, adjusting the matrix morphology and uniformity, preventing cementite formation, and preventing white iron formation.

[0035] By selecting a combination of vermicularizing agents and inoculants and introducing multiple nucleating elements, the amount of rare earth elements can be reduced while ensuring the overall performance of cast iron.

[0036] According to some embodiments of the first aspect of the present invention, the carbon equivalent (CE) value of the vermicular graphite cast iron is 4.3 to 4.6. Controlling the carbon equivalent range can ensure that the carbon equivalent of the molten iron during solidification is close to the eutectic composition, which can achieve near-eutectic solidification. This refines the graphite size, reduces internal shrinkage porosity of the cast iron, and avoids excessive carbon equivalent that would cause graphite floating.

[0037] According to some embodiments of the first aspect of the present invention, the mass percentage of C is 3.7% to 3.8%.

[0038] According to some embodiments of the first aspect of the present invention, the mass percentage of Si is 1.8% to 2.2%.

[0039] According to some embodiments of the first aspect of the present invention, the mass percentage of Mn is 0.25% to 0.4%.

[0040] According to some embodiments of the first aspect of the present invention, the mass percentage of Cu is 0.3% to 0.4%.

[0041] According to some embodiments of the first aspect of the present invention, the mass percentage of Sn is 0.04% to 0.06%.

[0042] According to some embodiments of the first aspect of the present invention, the mass percentage of Cr is 0.02% to 0.04%.

[0043] According to some embodiments of the first aspect of the present invention, the mass percentage of Sb does not exceed 0.001%.

[0044] According to some embodiments of the first aspect of the present invention, the raw materials for preparing vermicular graphite cast iron also include impurity elements. Common associated impurity elements include P and S, which are generally harmful impurity elements, but trace amounts of phosphorus can increase the fluidity of molten iron. The S content can be controlled below 0.01%, and the P content can be controlled below 0.02%.

[0045] According to some embodiments of the first aspect of the present invention, the vermicular graphite cast iron has a vermicularization rate of 50% to 80%, as tested according to GB / T 26656-2023.

[0046] Graphite itself has a certain self-lubricating effect. The ends of vermicular graphite are rounded and blunt, shorter and thicker than those of flake graphite, resulting in less cutting effect on the matrix and making it less prone to matrix crack propagation. Given a fixed matrix microstructure ratio, carbon equivalent, and graphite ratio, the lower the vermicularization rate, the higher the strength or hardness, and the more wear-resistant the graphite.

[0047] Controlling the creep rate within a suitable range is crucial for achieving a better balance between thermal conductivity, thermal fatigue resistance, and mechanical properties. When the creep rate in vermicular graphite cast iron is less than 50%, it reduces thermal conductivity and thermal fatigue resistance, negatively impacting wear resistance, especially at high temperatures. When the creep rate exceeds 80%, the thermal conductivity and thermal fatigue resistance of vermicular iron tend to stabilize, but excessively high creep rates increase the cutting effect on the matrix, affecting strength and toughness.

[0048] According to some embodiments of the first aspect of the present invention, the vermicular graphite cast iron has a vermicularization rate of 55% to 75%.

[0049] According to some embodiments of the first aspect of the present invention, the pearlite content of the vermicular graphite cast iron is 50% to 80%, as tested according to GB / T 26656-2023. Within this content range, it is beneficial to obtain a microstructure with high dispersion and uniform distribution, improving hardness uniformity and wear resistance. When the pearlite content is below 50%, the wear resistance decreases significantly, and when the pearlite content is above 80%, it poses a great challenge to machining.

[0050] According to some embodiments of the first aspect of the present invention, the pearlite content of the vermicular graphite cast iron is 50% to 60%.

[0051] According to some embodiments of the first aspect of the present invention, the pearlite content of the vermicular graphite cast iron is 55% to 60%.

[0052] According to some embodiments of the first aspect of the present invention, the graphite content of the vermicular graphite cast iron is 10% to 15%. The graphite content range directly affects lubricity, wear resistance, and thermal conductivity: if the graphite content is too low, it affects thermal conductivity and is not conducive to lubrication and resistance to adhesive wear; if the graphite content is too high, it will lead to low surface strength and reduced wear resistance.

[0053] According to some embodiments of the first aspect of the present invention, the graphite content of the vermicular graphite cast iron is 11% to 13%.

[0054] According to some embodiments of the first aspect of the present invention, the vermicular graphite cast iron has a tensile strength ≥450MPa and a yield strength ≥335MPa, and the test standard is GB / T 228.1-2021.

[0055] According to some embodiments of the first aspect of the present invention, the Brinell hardness value HB of the vermicular graphite cast iron is 160 to 230.

[0056] According to some embodiments of the first aspect of the present invention, the Brinell hardness value HB of the vermicular graphite cast iron fluctuates by ≤10. By adjusting the microstructure morphology and distribution uniformity of the matrix, the hard phase is dispersed as uniformly as possible in the matrix structure, thereby reducing the hardness fluctuation range.

[0057] The second aspect of this invention relates to a process for preparing the vermicular graphite cast iron, comprising the following steps:

[0058] After smelting the raw materials other than those containing rare earth vermicularizing agents and rare earth inoculants, vermicularizing agents are added for vermicularizing treatment, and then rare earth inoculants are added for inoculation treatment. The resulting molten iron is poured out and cast to obtain the vermicular graphite cast iron.

[0059] The preparation process of vermicular graphite cast iron according to the second aspect of the present invention has at least the following beneficial effects:

[0060] After the raw materials are smelted, vermicularization and inoculation treatments are carried out before the molten metal is poured. This allows for more precise control of the amount and dispersion of vermicularizing and inoculating agents, resulting in more uniform vermicularization and inoculation effects, and ensuring the morphology and precipitation of graphite, as well as the internal microstructure and uniformity of vermicular graphite cast iron.

[0061] A common inoculation process for industrially producing vermicular graphite cast iron is the simultaneous use of ladle inoculation and in-flow inoculation. Ladle inoculation involves adding some inoculant when pouring molten iron into a ladle, while in-flow inoculation involves adding some inoculant during the casting process. This two-stage inoculation treatment can eliminate casting defects. In comparison, this embodiment uses a single-stage inoculation process, completing the inoculation operation before ladle pouring. This reduces the requirements for equipment and process control, making it easier to achieve industrialized production and lowering production costs.

[0062] The vermicular graphite cast iron prepared in this embodiment has a uniform mixed structure of pearlite, ferrite and graphite, and the vermicularization rate, pearlite ratio and graphite ratio range can be easily controlled to reduce the hardness fluctuation range. While improving wear resistance and thermal conductivity, it ensures excellent mechanical properties.

[0063] According to some embodiments of the second aspect of the present invention, the smelting temperature is 1450–1500°C. Controlling the smelting temperature helps to improve the purity of the molten iron and eliminate the heritability of graphite, so that fine, uniform graphite morphology can be obtained after inoculation treatment.

[0064] According to some embodiments of the second aspect of the present invention, the temperature of the vermicularization treatment is 1500–1550°C.

[0065] According to some embodiments of the second aspect of the present invention, the vermicomposting process takes 20 to 40 seconds.

[0066] According to some embodiments of the second aspect of the present invention, the temperature of the incubation treatment is 1500-1550°C.

[0067] According to some embodiments of the second aspect of the present invention, the incubation treatment time is 20 to 40 seconds.

[0068] If the temperature of the vermicularization or inoculation treatment is too low, the vermicularizing agent or inoculant will not dissolve easily; if the temperature is too high, it may increase burn-off. Controlling the treatment time during the vermicularization or inoculation stage ensures that the vermicularizing agent or inoculant dissolves in the molten iron after melting and forms a certain concentration difference at the microscopic level. This allows the molten iron to form sufficient crystal nuclei during the later cooling and solidification process, thus better controlling the microstructure of vermicular graphite cast iron.

[0069] According to some embodiments of the second aspect of the present invention, the temperature at which the molten iron is poured is 1500–1550°C.

[0070] According to some embodiments of the second aspect of the present invention, the casting time does not exceed 15 minutes to avoid affecting the fluidity of the molten iron and to ensure the casting quality.

[0071] According to some embodiments of the second aspect of the present invention, the unpacking time after casting is ≥75 minutes, so as to better control the matrix structure and improve the overall performance such as hardness.

[0072] According to some embodiments of the second aspect of the present invention, the molten iron after smelting and / or the molten iron before casting is subjected to compositional analysis. The compositional analysis is used to determine whether the actual composition of the molten iron obtained after the corresponding process meets the elemental ratio range (i.e., target elemental composition) of the raw materials in the aforementioned embodiments of vermicular graphite cast iron, and to replenish materials as needed based on the analysis results to ensure that the composition of the molten iron matches the feeding ratio.

[0073] According to some embodiments of the second aspect of the present invention, the component analysis is performed using a silicon carbide analyzer and a spectrophotometer. The silicon carbide analyzer is used to detect the carbon content of the corresponding molten iron, and the spectrophotometer is used to detect the contents of Si, Mn, P, S, Cu, Sn, and Cr in the corresponding molten iron.

[0074] According to some embodiments of the second aspect of the present invention, slag removal is performed after the component analysis.

[0075] According to some embodiments of the second aspect of the present invention, the raw materials for preparation can be selected from scrap steel and recycled materials to achieve resource reuse.

[0076] The third aspect of the present invention relates to the application of the above-mentioned vermicular graphite cast iron in the manufacture of transmission components or braking components.

[0077] Because the vermicular graphite cast iron has excellent physical and mechanical properties, thermal conductivity and wear resistance, it is easy to produce industrially, which improves the overall performance of transmission or braking components made of the vermicular graphite cast iron, helps to increase service life and reduce production costs.

[0078] According to some embodiments of the third aspect of the present invention, the transmission component is selected from an automatic scroll plate, a stationary scroll plate, a scroll compressor, an engine block, an engine cylinder head, or an engine.

[0079] According to some embodiments of the third aspect of the present invention, the braking component is selected from a brake disc or a brake device.

[0080] The fourth aspect of the present invention relates to a scroll compressor, the scroll compressor comprising a moving scroll disk and a stationary scroll disk, the moving scroll disk and / or the stationary scroll disk being made of vermicular graphite cast iron.

[0081] Given that the overall performance of the vermicular graphite cast iron in the embodiments of the present invention is significantly improved, the overall performance of the moving scroll or stationary scroll is enhanced, which gives the scroll compressor significant advantages in terms of service life and production cost.

[0082] A fifth aspect of the present invention relates to a refrigeration apparatus, wherein the refrigeration apparatus is provided with the scroll compressor.

[0083] Scroll compressors are characterized by high efficiency, quiet operation, stable operation, and a wide compression ratio range. They are widely used in household and commercial refrigeration systems such as air conditioners, freezers, and cold storage facilities, meeting the compression requirements of different types of refrigeration equipment. Given the performance advantages of scroll compressors, refrigeration equipment equipped with them also offers significant advantages in terms of service life and production costs.

[0084] According to some embodiments of the fifth aspect of the present invention, the refrigeration device is selected from an air conditioner, a freezer, or a cold storage.

[0085] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0086] Figure 1 It is the metallographic structure of existing gray cast iron.

[0087] Figure 2 It is the metallographic structure of existing ductile iron.

[0088] Figure 3 It is the metallographic structure of existing vermicular graphite cast iron.

[0089] Figure 4 This is a schematic diagram of a scroll compressor.

[0090] Figure 5 This is the metallographic structure of Example 1.

[0091] Figure 6 This is the metallographic structure of Example 2.

[0092] Figure 7 This is the metallographic structure of Example 3.

[0093] Figure 8 This is the metallographic structure of Comparative Example 1.

[0094] Figure 9 This is a diagram showing the dimensions of the test block for hardness testing. Detailed Implementation

[0095] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0096] A first aspect of this invention relates to a vermicular graphite cast iron, comprising Fe, a rare earth vermicularizing agent, a rare earth inoculant, and the following raw materials in weight percentages:

[0097] C: 3.5% to 3.8%, Si: 1.8% to 2.6%, Mn: 0.2% to 0.5%, Cu: 0.2% to 0.5%, Sn: 0.03% to 0.06%, Cr: 0% to 0.05%, Sb: 0% to 0.01%.

[0098] Carbon (C) content significantly affects the microstructure and mechanical properties of cast iron. Controlling the carbon content within a suitable range can regulate ferrite and graphite content, ensuring strength and hardness. Si promotes graphitization, and appropriate Si content also contributes to the morphological stability of vermicular graphite cast iron. Mn reduces the number of eutectic clusters, stabilizes carbides, and refines and stabilizes pearlite; however, Mn content should not be too high to avoid overcooling. Cu increases and stabilizes pearlite in the matrix; appropriate Cu content helps ensure mechanical properties such as strength and elongation. Cr is a strong pearlite-promoting element; by combining Cr and Cu, adjusting the pearlite content further enhances mechanical properties and wear resistance. Sn increases pearlite, while Sb refines graphite; both should not be excessively high to avoid adverse effects on cast iron properties.

[0099] Rare earth vermicularizing agents and rare earth inoculants can control the morphology of graphite and the microstructure of cast iron, forming a mixed microstructure of pearlite, ferrite and graphite. They can help regulate the vermicularization rate, the proportion of pearlite and the proportion of graphite within a suitable range, improve the uniformity of the microstructure, and thus improve wear resistance and thermal conductivity while ensuring mechanical properties.

[0100] By rationally controlling the C and Si content, and the mass percentages of pearlite-forming elements Mn, Cu, and Sn, and by using rare-earth vermicularizing agents and rare-earth inoculants, the microstructure and uniformity of the entire cast iron matrix can be adjusted, reducing the range of hardness fluctuations, improving wear resistance, thermal conductivity, and machinability, and lowering manufacturing costs. Furthermore, adding appropriate amounts of easily segregating element Sb and carbide-forming element Cr can achieve even better modification effects.

[0101] This vermicular graphite cast iron has a tensile strength ≥450MPa, a yield strength ≥335MPa, and a hardness value of HB160~230. The hardness fluctuation range can be as low as below 10HB. Its overall physical and mechanical properties are significantly better than those of existing vermicular graphite cast iron.

[0102] In some embodiments, the rare earth elements in the rare earth vermicularizing agent are selected from Ce, Zr, or combinations thereof.

[0103] In some embodiments, the rare earth vermicularizing agent also contains Si, Mg, Ca, and Fe.

[0104] In some embodiments, the rare earth vermicularizing agent comprises Fe and the following elements by mass percentage: Mg 4%–6%, Si 43%–47%, Ca 1%–2%, Re 2%–4%, wherein Re is selected from Ce, Zr, or a combination thereof. It is understood that the balance is Fe, without considering the content of impurity elements.

[0105] In some embodiments, the mass percentage of rare earth vermicularizing agent is 0.2% to 0.5% based on the total mass of the remaining raw materials excluding rare earth vermicularizing agent and rare earth inoculant.

[0106] In some embodiments, the rare earth element in the rare earth inoculant is selected from Ce, Zr, or a combination thereof.

[0107] In some embodiments, the rare earth inoculant further contains Si, Ca, Ba and Fe, or the rare earth inoculant further contains Si, Ca, Ba, Al and Fe.

[0108] In some embodiments, the rare earth element in the rare earth inoculant is selected from Ce.

[0109] In some embodiments, the rare earth inoculant comprises Fe and the following elements by mass percentage: Si 70%–80%, Ca 0.75%–2%, Ba 1%–3%, Ce 0.3%–1%, Al 0%–1.5%. It is understood that the balance is Fe, without considering the content of impurity elements.

[0110] In some embodiments, the rare earth inoculant includes rare earth ferrosilicon alloy and silicon-barium-calcium-iron alloy. The rare earth ferrosilicon alloy comprises Fe and the following elements by mass percentage: Si 70%–76%, Ca 0.75%–1.25%, Al 0.75%–1.25%, Ce 1.5%–2.0%; the silicon-barium-calcium-iron alloy comprises Fe and the following elements by mass percentage: Si 72%–78%, Ca 1.0%–2.0%, Ba 2.0%–3.0%, Al 0%–1.25%, and the mass ratio of the rare earth ferrosilicon alloy to the silicon-barium-calcium-iron alloy is 1:1–4. It is understood that in the rare earth ferrosilicon alloy or silicon-barium-calcium-iron alloy, the balance is Fe, without considering the content of impurity elements.

[0111] Using a combination of two alloys allows for adjustment of the inoculant composition, ensuring the microstructure and uniformity of the cast iron and improving its overall performance.

[0112] In one implementation method, the mass ratio of rare earth silicon-iron alloy to silicon-barium-calcium-iron alloy is 1:2 to 3.

[0113] In some embodiments, the mass percentage of rare earth ferrosilicon alloy is 0.1% to 0.2% and the mass percentage of silicon-barium-calcium-iron alloy is 0.2% to 0.4% based on the total mass of the remaining raw materials excluding rare earth vermicularizing agents and rare earth inoculants.

[0114] In some embodiments, the mass percentage of rare earth inoculant is 0.3% to 0.6% based on the total mass of the remaining raw materials excluding rare earth vermicularizing agents and rare earth inoculants.

[0115] In some embodiments, the carbon equivalent (CE) value of vermicular graphite cast iron is 4.3 to 4.6.

[0116] Based on the influence of each element on the actual carbon content at the eutectic point, the amounts of these elements are converted into increases or decreases in carbon content, i.e., carbon equivalent, expressed as CE value (%). The formula for calculating carbon equivalent is: CE% = C% + 1 / 3(Si+P)% + 1 / 6Mn% + 1 / 5Cr% + 1 / 15Cu, with the unit being mass percentage (%).

[0117] Controlling the carbon equivalent range ensures that the carbon equivalent of molten iron during solidification is close to the eutectic composition, enabling near-eutectic solidification. This refines the graphite size, reduces internal shrinkage porosity in cast iron, and prevents excessive carbon equivalent from causing graphite floating.

[0118] In some embodiments, the mass percentage of C is 3.7% to 3.8%.

[0119] In some embodiments, the mass percentage of Si is 1.8% to 2.2%.

[0120] In some embodiments, the mass percentage of Mn is 0.25% to 0.4%.

[0121] In some embodiments, the mass percentage of Cu is 0.3% to 0.4%.

[0122] In some embodiments, the mass percentage of Sn is 0.04% to 0.06%.

[0123] In some embodiments, the mass percentage of Cr is 0.02% to 0.04%.

[0124] In some embodiments, the mass percentage of Sb does not exceed 0.001%.

[0125] In some embodiments, the raw materials for preparing vermicular graphite cast iron also include impurity elements, such as P and S, wherein the content of S can be controlled below 0.01% and the content of P can be controlled below 0.02%.

[0126] In some embodiments, the vermicular graphite cast iron has a vermicular rate of 50% to 80%, tested according to GB / T 26656-2023. Controlling the vermicular rate within a suitable range better balances thermal conductivity, thermal fatigue resistance, and mechanical properties.

[0127] In some embodiments, the vermicular graphite cast iron has a vermicularization rate of 55% to 75%.

[0128] In some embodiments, the pearlite content of vermicular graphite cast iron is 50%–80%, as tested according to GB / T 26656-2023. Within this content range, it is beneficial to obtain a microstructure with high dispersion and uniform distribution, improving hardness uniformity and wear resistance. However, when the pearlite content exceeds 80%, it will bring great difficulty to machining.

[0129] In some embodiments, the pearlite content of vermicular graphite cast iron is 50% to 60%.

[0130] In some embodiments, the pearlite content of vermicular graphite cast iron is 55% to 60%.

[0131] In some embodiments, the graphite content of vermicular graphite cast iron is 10% to 15%.

[0132] In some embodiments, the graphite content of vermicular graphite cast iron is 11% to 13%.

[0133] The graphite percentage can be calculated based on the area percentage of graphite within the field of view, referring to the test method for creep rate in GB / T 26656-2023.

[0134] In some embodiments, the tensile strength of vermicular graphite cast iron is ≥450MPa, the yield strength is ≥335MPa, and the test standard is GB / T 228.1-2021.

[0135] In some embodiments, the Brinell hardness value (HB) of vermicular graphite cast iron is 160 to 230.

[0136] In some embodiments, the Brinell hardness value HB of vermicular graphite cast iron fluctuates by ≤10.

[0137] The second aspect of this invention relates to a process for preparing vermicular graphite cast iron, comprising the following steps:

[0138] After smelting the raw materials other than those containing rare earth vermicularizing agents and rare earth inoculants, vermicularizing agents are added for vermicularizing treatment, and then rare earth inoculants are added for inoculation treatment. The resulting molten iron is poured out and cast to obtain vermicular graphite cast iron.

[0139] After melting the raw materials, vermicularization and inoculation treatments are performed before pouring. This allows for more precise control over the amount and dispersion of vermicularizing and inoculating agents, resulting in more uniform vermicularization and inoculation effects. This ensures the morphology and precipitation of graphite, as well as the uniformity of the internal microstructure of the vermicular graphite cast iron. Adding the inoculating agent in the same process segment and completing the inoculation operation before pouring reduces the requirements for equipment and process control, facilitating industrial production and lowering production costs. The resulting vermicular graphite cast iron possesses a uniform mixed structure of pearlite, ferrite, and graphite. The vermicularization rate, pearlite percentage, and graphite percentage ranges are easily controlled, reducing hardness fluctuations and improving wear resistance and thermal conductivity while maintaining excellent mechanical properties.

[0140] In some embodiments, the smelting temperature is 1450–1500°C. Controlling the smelting temperature helps to improve the purity of the molten iron and eliminate the heritability of graphite, so that fine and uniform graphite morphology can be obtained after inoculation treatment.

[0141] In some embodiments, the temperature of the vermicularization treatment is 1500–1550°C.

[0142] In some embodiments, the creeping process takes 20 to 40 seconds.

[0143] In some embodiments, the incubation temperature is 1500–1550°C.

[0144] In some embodiments, the incubation process takes 20 to 40 seconds.

[0145] In some embodiments, the temperature at which the molten iron is poured is 1500–1550°C.

[0146] In some embodiments, the casting time does not exceed 15 minutes. Excessive casting time can affect the fluidity of the molten iron, thereby impacting the casting quality.

[0147] In some embodiments, the unpacking time after casting is ≥75 minutes to better control the matrix structure and improve overall performance such as hardness.

[0148] In some embodiments, compositional analysis is performed on the molten iron after smelting and / or the molten iron before casting.

[0149] In some embodiments, component analysis is performed using a silicon carbide analyzer and a spectrophotometer.

[0150] In some embodiments, slag removal is performed after component analysis.

[0151] In some embodiments, the raw materials for preparation can be selected from scrap steel and recycled materials to achieve resource reuse.

[0152] Specifically, the mass percentage of scrap steel can be controlled between 40% and 60%, and the mass percentage of recycled material can be controlled between 40% and 60%. Based on the target elemental composition, it is easy to select the appropriate type of scrap steel and recycled material and their respective proportions.

[0153] The third aspect of the present invention relates to the application of the above-mentioned vermicular graphite cast iron in the manufacture of transmission components or braking components.

[0154] Transmission components, for example, may specifically be a moving scroll, a stationary scroll, or a scroll compressor comprising at least one of these, or an engine block, an engine cylinder head, or an engine comprising at least one of these. Braking components, for example, are selected from brake discs or brake systems comprising them.

[0155] Because vermicular graphite cast iron has excellent physical and mechanical properties, thermal conductivity and wear resistance, it is easy to produce industrially. This improves the overall performance of transmission or braking components made of vermicular graphite cast iron, which helps to increase service life and reduce production costs.

[0156] The fourth aspect of the present invention relates to a scroll compressor, which includes a moving scroll disk and a stationary scroll disk, wherein the moving scroll disk and / or the stationary scroll disk are made of vermicular graphite cast iron.

[0157] Given that the overall performance of the vermicular graphite cast iron in the embodiments of the present invention is significantly improved, the overall performance of the moving scroll or stationary scroll is enhanced, and the scroll compressor equipped with the moving scroll or stationary scroll also has significant advantages in terms of service life and production cost.

[0158] The fifth aspect of the present invention relates to a refrigeration apparatus, which is equipped with a scroll compressor.

[0159] Given the performance advantages of scroll compressors, refrigeration equipment equipped with scroll compressors also has significant advantages in terms of service life and production cost.

[0160] The present invention will now be described in detail through specific embodiments. The relevant raw materials are described below:

[0161] Vermicularizing agent, Elken The specific composition, by mass percentage, is as follows: Mg 4%–6%, Si 43%–47%, Ca 1%–2%, Re 2%–4%, where Re includes Ce and Zr, and the balance is Fe.

[0162] Inoculant: Rare earth silicon-iron alloy, Elken The specific composition, by mass percentage, meets the following requirements: Si 70%–76%, Ca 0.75%–1.25%, Al 0.75%–1.25%, Ce 1.5%–2.0%, with the balance being iron; silicon-barium-calcium-iron alloy, Elken. The specific composition by mass percentage is: Si 72%–78%, Ca 1.0%–2.0%, Ba 2.0%–3.0%, Al 0%–1.25%, with the balance being iron.

[0163] Unless otherwise specified, all raw materials used are commercially available.

[0164] Example 1

[0165] This embodiment prepares a vermicular graphite cast iron, including the following preparation steps:

[0166] S1. Melting Material: Scrap steel and recycled materials are added into the medium-frequency induction furnace in a certain proportion. The total elemental composition of the scrap steel and recycled materials meets the elemental composition shown in Table 1 (or target value, in addition to the elements shown in Table 1, the remaining main element is Fe). The furnace temperature is raised to 1450-1500℃ for smelting, so that it is melted into molten iron. The carbon content of the molten iron is detected by a carbon silicon analyzer, and the contents of Si, Mn, P, S, Cu, Sn, and Cr are detected by a spectrophotometer. According to the difference between the measured value and the target value, alloying materials are added to adjust the relevant elemental composition to meet the elemental composition of Table 1.

[0167] S2. Vernix treatment: Stabilize the temperature of the molten iron at 1525℃, add the vernix agent to the heated molten iron using a wire feeding process, and carry out vernix treatment. The amount of vernix agent is 0.4% of the mass of the molten iron, and the vernix treatment time is 30s.

[0168] S3. Inoculation treatment: At constant temperature, silicon-barium-calcium-iron alloy and rare earth silicon-iron alloy are added sequentially to the molten iron ladle for inoculation treatment. The treatment time is 25 seconds. The amount of silicon-barium-calcium-iron alloy is 0.35% of the mass of molten iron, and the amount of rare earth silicon-iron alloy is 0.15% of the mass of molten iron.

[0169] S4. Casting: Transfer the molten iron ladle to the furnace for tapping, controlling the tapping temperature at 1525℃. Pour the molten iron from the ladle into a transfer ladle. Before casting, take a sample of the molten iron for composition analysis to ensure that the composition meets the element ratio requirements in Table 1. Casting is completed within 12 minutes. The ladle is opened 80 minutes after casting to obtain vermicular graphite cast iron.

[0170] Example 2

[0171] This embodiment prepared a vermicular graphite cast iron, which differs from Example 1 in that:

[0172] (1) The main elemental composition of vermicular graphite cast iron is different, and the specific differences are shown in Table 1.

[0173] (2) In step S4, the unpacking time is extended from 80 min to 100 min.

[0174] Example 3

[0175] This embodiment prepared a vermicular graphite cast iron, which differs from Example 1 in that:

[0176] (1) The main elemental composition of vermicular graphite cast iron is different, and the specific differences are shown in Table 1.

[0177] (2) In step S4, the unpacking time is extended from 80 min to 110 min.

[0178] Comparative Example 1

[0179] The main elemental composition of standard RuT450 vermicular graphite cast iron is shown in Table 1.

[0180] Table 1

[0181]

[0182] Test case

[0183] The metallographic structure and physical and mechanical properties of the vermicular graphite cast iron prepared in Examples 1-3 and Comparative Example 1 were tested. Metallographic images are shown below. Figures 5-8 , respectively, represent Examples 1 to 3 and Comparative Example 1. Performance indicators are shown in Table 2.

[0184] Test sample:

[0185] The testing method is as follows:

[0186] (1) Metallographic structure: Detected using a metallographic microscope, brand: Leica, model: DM6000M, magnification: 200X.

[0187] (2) Mechanical properties: National standard GB / T 228.1-2021 "Metallic materials, tensile testing - Part 1: Test method at room temperature", test instrument: universal tensile testing machine, brand: MTS, model: BHTMS-002.

[0188] (3) Hardness: Tested using a Brinell hardness tester. Test sample: 1) Specimen: Cylindrical, dimensions as shown in the figure. Figure 9 As shown, three parallel tests were performed on the measurement surface, and the average value was taken; 2) Part: Moving scroll plate, used to test the hardness fluctuation range. Seven test points were evenly selected on the part, and the distribution range of hardness values ​​was recorded.

[0189] (4) Thermal conductivity: National standard GB / T3651-2008 "Method for measuring thermal conductivity of metals at high temperature".

[0190] (5) Wear resistance: The wear was tested using a conventional friction tester with a force of 100N and a rotation speed of 500rpm. The wear amount was recorded after 20 minutes.

[0191] Table 2

[0192]

[0193]

[0194] The test results show that in the vermicular graphite cast iron of Examples 1-3 of this invention, the graphite morphology has changed significantly, the vermicularization rate is significantly higher, and the graphite proportion and pearlite content are also higher, with better uniformity in graphite and microstructure distribution. The overall physical and mechanical properties of this vermicular graphite cast iron are improved to a certain extent, achieving a tensile strength ≥450 N / mm². 2 Yield strength ≥ 335 N / mm 2 The performance requirements include elongation ≤6% and hardness range of HB170~230, with small hardness fluctuation range not exceeding 10HB, and significantly improved wear resistance and thermal conductivity.

[0195] In comparison, Example 3 had a higher graphite content but a lower vermiformity, indicating that Example 3 contained more non-vermiform graphite. Figure 7 It is evident that the cast iron in Example 3 contains more spheroidal graphite structures, which have less cutting effect on the matrix, thus exhibiting higher strength, hardness, and toughness. The hardness fluctuation range of Example 3 is comparable to other examples, but Example 3 has a higher overall hardness and higher wear resistance. However, the increased spheroidal graphite content in Example 3 is detrimental to improving thermal conductivity. It can be seen that different matrix microstructure morphologies have a significant impact on the properties of cast iron. The difference in matrix structure in Example 3 may be related to the longer unpacking time, which affects the growth morphology of the matrix structure, or it may be related to the different combinations of elements such as Cu, resulting in differences in the induced nucleation effect on the matrix structure.

[0196] Based on the metallographic images and physical and mechanical property data of Comparative Example 1 and Examples 1-3, it can be found that the existing RuT450 vermicular graphite cast iron of Comparative Example 1 has a low vermicularization rate, low graphite ratio, and low pearlite content, and its microstructure distribution is uneven. Due to the differences in graphite morphology, graphite ratio, and microstructure, the thermal conductivity of Comparative Example 1 is significantly reduced, and the hardness fluctuation range is larger. This results in uneven internal temperature distribution under heating and other working conditions, and the increased internal temperature difference increases thermal stress. Combined with the low strength and uneven hardness of the cast iron itself, this leads to significantly insufficient wear resistance, and a significantly increased wear under the same test conditions. It is understandable that because the vermicular graphite cast iron prepared in Comparative Example 1 has insufficient performance, it is more prone to cracking under stress or heating conditions, and its thermal fatigue resistance is significantly lower than that of the vermicular graphite cast iron of Examples 1-3 of this invention.

[0197] Because the vermicular graphite cast iron of the present invention possesses advantages such as high strength, high hardness, high wear resistance, high thermal conductivity, and small hardness fluctuation, it can be used to manufacture transmission or braking components with high mechanical strength requirements, such as the core component scroll plate of a compressor, engine block, or engine cylinder head, thereby improving the service life of the component or the parts or equipment equipped with it. At the same time, the vermicular graphite cast iron of the present invention is easy to industrialize, which can reduce the production cost of components or equipment using vermicular graphite cast iron, demonstrating significant application advantages.

[0198] As one embodiment, the components or equipment may specifically be a scroll compressor or engine, or a household or commercial refrigeration device such as an air conditioner, freezer, or cold storage.

[0199] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A compacted graphite cast iron, characterized by, The preparation raw materials of the vermicular cast iron include a rare earth-containing vermiculizing agent, a rare earth-containing inoculant and elements of the following components, and the components of the vermicular cast iron satisfy: C: 3.5%~3.8%, Si: 1.8%~2.6%, Mn: 0.2%~0.5%, Cu: 0.2%~0.5%, Sn: 0.03%~0.06%, Cr: 0.02%~0.05%, Sb: not more than 0.001%, the balance being Fe and impurity elements; The rare earth-containing vermiculizing agent includes Fe and the following elements in percentage by mass: Mg 4%~6%, Si 43%~47%, Ca 1%~2%, Re 2%~4%; wherein Re is selected from Ce, Zr or a combination thereof; The rare earth-containing inoculant includes a rare earth ferrosilicon alloy and a silicon barium calcium ferroalloy, the rare earth ferrosilicon alloy includes Fe and the following elements in percentage by mass: Si 70%~76%, Ca 0.75%~1.25%, Al 0.75%~1.25%, Ce 1.5%~2.0%; the silicon barium calcium ferroalloy includes Fe and the following elements in percentage by mass: Si 72%~78%, Ca 1.0%~2.0%, Ba 2.0%~3.0%, Al 0%~1.25%, the mass ratio of the rare earth ferrosilicon alloy and the silicon barium calcium ferroalloy is 1:1~4; The percentage by mass of the rare earth ferrosilicon alloy is 0.1%~0.2%, the percentage by mass of the silicon barium calcium ferroalloy is 0.2%~0.4%, and the percentage by mass of the rare earth-containing vermiculizing agent is 0.2%~0.5%, based on the total mass of the remaining preparation raw materials excluding the rare earth-containing vermiculizing agent and the rare earth-containing inoculant.

2. The compacted graphite iron according to claim 1, characterized in that, The carbon equivalent C.E. value of the vermicular cast iron is 4.3~4.6; and / or, the vermiculization rate of the vermicular cast iron is 50%~80%; and / or, the pearlite content of the vermicular cast iron is 50%~80%; and / or, the graphite proportion of the vermicular cast iron is 10%~15%.

3. The compacted graphite iron according to claim 1, characterized in that, The tensile strength of the vermicular cast iron is ≥450MPa, and the yield strength is ≥335MPa, the test standard is GB / T 228.1-2021; and / or, the Brinell hardness value HB of the vermicular cast iron is 160~230, and the fluctuation range of the hardness value HB is ≤10.

4. The process for producing compacted vermicular cast iron according to any one of claims 1 to 3, characterized in that, The method includes the following steps: after the preparation raw materials excluding the rare earth-containing vermiculizing agent and the rare earth-containing inoculant are melted, the rare earth-containing vermiculizing agent is added for vermiculization treatment, the rare earth-containing inoculant is added for inoculation treatment, the obtained molten iron is tapped, and the vermicular cast iron is obtained by casting.

5. The manufacturing process according to claim 4, characterized in that, The temperature of the melting is 1450~1500℃; and / or, the temperature of the vermiculization treatment is 1500~1550℃, and the time of the vermiculization treatment is 20~40s; and / or, the temperature of the inoculation treatment is 1500~1550℃, and the time of the inoculation treatment is 20~40s; and / or, the temperature of the molten iron tapping is 1500~1550℃; and / or, the time of the casting is not more than 15min; And / or, the opening box time after the casting is completed is ≥75min.

6. The production process according to claim 4 or 5, characterized in that, It also comprises the step of performing a composition analysis of the molten iron after the melting and / or of the molten iron before the casting, followed by slag removal after the composition analysis.

7. Use of the compacted graphite iron according to any one of claims 1 to 3 for the production of a transmission or braking component.

8. A scroll compressor characterized by, The scroll compressor comprises a moving scroll and a stationary scroll, the moving scroll and / or the stationary scroll being made of compacted graphite iron according to any one of claims 1 to 3.

9. A refrigeration apparatus characterized by comprising: The refrigeration device is provided with a scroll compressor according to claim 8.

10. The refrigeration appliance of claim 9, wherein, The refrigeration device is selected from an air conditioner, a refrigerator or a freezer.

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