Gray cast iron and method for its production and use

Abstract

The present application provides a kind of gray cast iron and its preparation method and application, the gray cast iron includes: C3.30%~3.40%, Si 1.80%~2.10%, Mn 0.60%~1.00%, S 0.060%~0.120%, Cu0.50%~0.80%, Cr 0.15%~0.30%, Ni 0.20%~0.40%, Sn 0.040%~0.080%, N0.0080%~0.0110%, impurity element 0~0.11%, balance is Fe.The gray cast iron is high in tensile strength, high in hardness, little in shrinkage risk, when producing cylinder cover, can give consideration to improve mechanical properties, reduce water leakage rate.

Description

Technical Field

[0001] This invention relates to the manufacture of gray cast iron, and more particularly to a gray cast iron, its preparation method, and its applications. Background Technology

[0002] Gray cast iron refers to cast iron with a metallographic structure containing flake graphite. It possesses excellent casting properties and is widely used in the manufacture of engine cylinder heads and cylinder blocks. In recent years, with the increase in engine combustion pressure, stricter national emission requirements, and the need for lightweight engine design, higher demands have been placed on the mechanical properties of cylinder heads and cylinder blocks.

[0003] Traditional processes for improving the mechanical properties of cylinder heads mainly involve two approaches: alloying with elements such as Mo, V, and Nb; and reducing the carbon equivalent. However, both the Mo, V, and Nb alloying and low carbon equivalent approaches increase the cylinder head's tendency to shrink, leading to casting defects such as shrinkage porosity and shrinkage cavities, which in turn cause cylinder head leaks.

[0004] For example, Chinese patent CN110819883B discloses a cylinder head material and its manufacturing process. The components and their mass percentages in the cylinder head material are as follows: C content 3.15-3.25% (carbon equivalent calculated based on content is approximately: C + 1 / 3Si, i.e., 3.78-3.95), Si content 1.90-2.10%, Cr content 0.25-0.30%, Mo content 0.20-0.25%, Mn content 0.5-0.8%, P content ≤0.06%, S content 0.10-0.12%, Cu content 0.80-1.00%, Sn content 0.08-0.10%, with the balance being Fe. The combined content of Cr and Mo is 0.5%. The alloy cast iron cylinder head manufactured using this method exhibits small differences in tensile strength across different parts, but the shrinkage porosity and leakage rate (water leakage rate) is approximately 4%.

[0005] Therefore, how to reduce the leakage rate while ensuring the mechanical performance of the cylinder head is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The present invention provides a gray cast iron that can significantly reduce the leakage rate of cylinder heads while maintaining the mechanical properties of cylinder heads.

[0007] The present invention also provides a method for preparing gray cast iron, which can reduce the shrinkage tendency of the cylinder head, thereby helping to reduce the leakage rate. At the same time, the method can also take into account the mechanical properties of the cylinder head.

[0008] The present invention further provides a gray cast iron part, which has high strength and hardness, low shrinkage tendency, and excellent mechanical properties and low leakage rate when used as a cylinder head.

[0009] This invention provides a gray cast iron, comprising, by mass percentage: C 3.30%–3.40%, Si 1.80%–2.10%, Mn 0.60%–1.00%, S 0.060%–0.120%, Cu 0.50%–0.80%, Cr 0.15%–0.30%, Ni 0.20%–0.40%, Sn 0.040%–0.080%, N 0.0080%–0.0110%, impurity elements 0–0.11%, and the balance being Fe.

[0010] According to one embodiment of the present invention, the gray cast iron is prepared by a method comprising the following processes:

[0011] Silicon carbide and silicon manganese alloy are added to a portion of the molten iron in the smelting furnace. The remaining iron and a carbonizer are then added to the smelting furnace, followed by the addition of ferrosilicon and a sulfurizer to obtain raw molten iron. Copper and nickel are first added to the bottom of the ladle, and then silicon barium calcium inoculant, ferrochrome, tin granules, ferrochrome nitride, and the raw molten iron are added to the ladle along with the flow to obtain ladle molten iron. The ladle molten iron is then used for casting, and a silicon zirconium inoculant is added during the casting process to obtain gray cast iron.

[0012] The original molten iron comprises, by mass percentage: C 3.30%-3.40%, Si 1.50%-1.70%, Mn 0.60%-1.00%, 0.060%≤S≤0.120%, with the balance being Fe; the amount of the silicon-barium-calcium inoculant added is 0.30%-0.50% of the mass of the molten iron in the ladle, with a particle size of 2mm-8mm; the amount of the silicon-zirconium inoculant added is 0.06%-0.10% of the mass of the molten iron in the ladle, with a particle size of 0.2mm-0.7mm.

[0013] This invention also provides a method for preparing gray cast iron, comprising:

[0014] 1) Smelting: After 30%-40% of the iron is melted, silicon carbide and silicon manganese alloy are added to the molten part of the iron in the smelting furnace. Then, the remaining 60%-70% of the iron and the carbonizing agent are added to the smelting furnace. Subsequently, ferrosilicon and sulfurizing agent are added to obtain the original molten iron.

[0015] 2) Iron tapping: First, add copper and nickel to the ladle, then add the original molten iron, silicon barium calcium inoculant, ferrochrome, tin granules, and ferrochrome nitride to the ladle to obtain molten iron in the ladle;

[0016] 3) Casting: The molten iron in the ladle is used for casting, and a silicon-zirconium inoculant is added during the casting process for secondary inoculation to obtain the gray cast iron;

[0017] The original molten iron comprises, by mass percentage: C 3.30%-3.40%, Si 1.50%-1.70%, Mn 0.60%-1.00%, 0.060%≤S≤0.120%, with the balance being Fe; the amount of the silicon-barium-calcium inoculant added is 0.30%-0.50% of the mass of the molten iron in the ladle, with a particle size of 2mm-8mm; the amount of the silicon-zirconium inoculant added is 0.06%-0.10% of the mass of the molten iron in the ladle, with a particle size of 0.2mm-0.7mm.

[0018] According to one embodiment of the present invention, the iron material accounts for 30%-40% of the total iron material.

[0019] According to one embodiment of the present invention, the silicon carbide comprises 0.80% to 1.20% of the total iron content; and / or,

[0020] The mass of the manganese-silicon alloy is 0.20%-0.40% of the total iron content.

[0021] According to one embodiment of the present invention, the iron material is a mixture of 65% to 80% scrap steel and 20% to 35% recycled iron;

[0022] And / or, the copper is electrolytic copper;

[0023] And / or, the nickel is electrolytic nickel.

[0024] According to one embodiment of the present invention, in step 1), after obtaining the original molten iron, the molten iron is placed at 1500℃~1520℃ and left to stand for 10min~15min, and then a slag-collecting agent is added for slag removal treatment.

[0025] According to one embodiment of the present invention, the temperature of the molten iron in the ladle is 1400℃~1420℃.

[0026] This invention provides a gray cast iron part, comprising the aforementioned gray cast iron;

[0027] Or, including gray cast iron prepared by the aforementioned preparation method.

[0028] According to one embodiment of the present invention, the gray cast iron part includes at least one of a cylinder block and a cylinder head.

[0029] This invention selects elements with low shrinkage tendency, such as Cu, Cr, Ni, Sn, and N, and rationally designs the chemical composition of gray cast iron. By controlling the C and Si content to increase the carbon equivalent, it ensures that gray cast iron has high strength and hardness when used in cylinder heads, while reducing the leakage rate. Attached Figure Description

[0030] Figure 1 These are graphite metallographic images of the cylinder head prepared in Embodiment 1 of the present invention;

[0031] Figure 2 These are pearlitic metallographic images of the cylinder head prepared in Embodiment 1 of the present invention;

[0032] Figure 3 These are graphite metallographic images of the cylinder head prepared in Comparative Example 4 of this invention.

[0033] Figure 4 These are pearlitic metallographic images of the cylinder head prepared in Comparative Example 4 of this invention;

[0034] Figure 5 These are graphite metallographic images of the cylinder head prepared in Comparative Example 8 of this invention;

[0035] Figure 6 This is a pearlitic metallographic image of the cylinder head prepared in Comparative Example 8 of this invention. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The first aspect of the present invention provides a gray cast iron, comprising, by mass percentage: 3.30%–3.40% C, 1.80%–2.10% Si, 0.60%–1.00% Mn, 0.060%–0.120% S, 0.50%–0.80% Cu, 0.15%–0.30% Cr, 0.20%–0.40% Ni, 0.040%–0.080% Sn, 0.0080%–0.0110% N, 0–0.11% impurity elements, and the balance being Fe.

[0038] Fe is the basic component of gray cast iron, C is the basis of graphite in the metallographic structure of gray cast iron, Si is the element that strongly promotes graphitization, S and Mn can improve the morphology of graphite, and Mn can also promote and stabilize the pearlite in the metallographic structure of gray cast iron, thereby improving the strength of gray cast iron.

[0039] Cu, Cr, and Ni elements can refine graphite, stabilize pearlite, increase the amount of pearlite, and improve the strength of gray cast iron. Sn element also promotes pearlite formation and can refine the pearlite. Ni element can passivate the graphite ends of flake graphite in gray cast iron and refine the interlamellar spacing of pearlite in gray cast iron. Therefore, Cu, Cr, Ni, Sn, and Ni elements are beneficial to reducing the shrinkage tendency of gray cast iron and improving its mechanical properties.

[0040] The aforementioned impurity elements are unavoidably introduced during the preparation of gray cast iron, mainly including P, Ti, Mo, V, and Pb. The content of other impurities is generally less than 0.001% and can be ignored. In specific implementation, this invention further controls P ≤ 0.030%, Ti ≤ 0.030%, Mo ≤ 0.030%, V ≤ 0.010%, and Pb ≤ 0.003%.

[0041] It should be noted that the carbon equivalent is calculated by adding 1 / 3 of the C content to the Si content, and the carbon equivalent of the present invention is specifically 3.9% to 4.1%.

[0042] The inventors discovered that by introducing Cu, Cr, Ni, Sn, and N elements and controlling the content of each element in gray cast iron, the gray cast iron of this invention can possess higher strength and hardness. Simultaneously, by controlling the C and Si element content to increase the carbon equivalent, and by selecting elements such as Cu, Cr, Ni, Sn, and N, which have lower shrinkage tendencies compared to Mo, V, and Nb, the shrinkage tendency of gray cast iron can be reduced, thereby significantly reducing the leakage rate of the cylinder head.

[0043] In specific implementation, the above-mentioned gray cast iron is prepared by a method including the following process:

[0044] Silicon carbide and silicon manganese alloy are added to a portion of the molten iron in a smelting furnace. The remaining iron and a carbonizer are then added to the smelting furnace, followed by the addition of ferrosilicon and a sulfurizer to obtain raw molten iron. Copper and nickel are added to a ladle, and then silicon barium calcium inoculant, ferrochrome, tin granules, ferrochrome nitride, and the raw molten iron are added to the ladle in a flow-through manner to obtain ladle molten iron. The ladle molten iron is then used for casting, with silicon zirconium inoculant added during the casting process to obtain gray cast iron.

[0045] The original molten iron, by mass percentage, includes: C 3.30%-3.40%, Si 1.5%-1.7%, Mn 0.6%-1.0%, and 0.06%≤S≤0.12%; the amount of silicon-barium-calcium inoculant added is 0.3%-0.5% of the molten iron mass, with a particle size of 2mm-8mm; the amount of silicon-zirconium inoculant added is 0.06%-0.10% of the molten iron mass, with a particle size of 0.2mm-0.7mm.

[0046] This invention does not limit the type of iron material; it can be any conventional iron-containing raw material, as long as the content of each element in the final gray cast iron meets the above requirements.

[0047] This invention does not limit the specific amount of the aforementioned iron material, as long as it ensures that the silicon carbide and manganese silicon alloy can be fully melted.

[0048] The above-mentioned carbon raiser is a graphitized carbon raiser, and its composition, calculated by mass percentage, includes: fixed carbon ≥98%, volatile matter ≤0.8%, ash ≤0.7%, sulfur ≤0.05%, and moisture ≤0.3%. The present invention further limits the particle size of the carbon raiser to 1.0 mm to 5.0 mm.

[0049] The sulfur-increasing agent, calculated by mass percentage, comprises: sulfur ≥ 45%, iron ≥ 45%, and silicon dioxide ≤ 3%. The particle size of the sulfur-increasing agent is 10mm-60mm.

[0050] The process of forming molten iron described above is essentially a process of melting and alloying various elements, including iron, silicon carbide, manganese-silicon alloy, carbonizer, ferrosilicon, and sulfurizer.

[0051] The process of preparing molten iron for casting essentially involves two aspects: firstly, introducing Cu, Cr, Ni, Sn, and N elements into the molten iron and alloying them with the iron; secondly, because Cr has a strong effect on promoting white cast iron structure, it can make gray cast iron difficult to machine. Therefore, this step also involves adding a silicon-barium-calcium inoculant to reduce the tendency for white cast iron formation. Specifically, the addition of the silicon-barium-calcium inoculant can improve the morphology and distribution of graphite, refine the microstructure of gray cast iron (graphite morphology, size, pearlite, and ferrite ratio), thereby reducing the tendency for white cast iron formation.

[0052] The process of preparing gray cast iron using molten iron from a ladle is essentially the process of pouring molten iron from a ladle into a mold to form the product. The inventor can choose a suitable mold based on the desired product shape.

[0053] In this invention, the chemical composition of molten iron is a crucial factor in ensuring the production of gray cast iron. Ensuring that the contents of C, Si, Mn, and S in the molten iron meet the above requirements guarantees that the elemental composition of the final gray cast iron meets the requirements and that alloying between the elements is achieved, thereby ensuring the formation of flake graphite and a high content of pearlite structure.

[0054] Meanwhile, the order in which raw materials are added during the molten iron preparation process has a significant impact on the microstructure of gray cast iron. Specifically, adding silicon carbide to the molten portion of the iron material can increase the number of graphite nuclei, refine the grains, and cause the graphite to be converted into flakes rather than other forms. If silicon carbide is added too early, it is difficult to achieve the above effects and can only be used to adjust the chemical composition; if it is added too late, silicon carbide is difficult to fully integrate into the molten iron material. Therefore, this invention adds silicon carbide to the molten portion of the iron material to fully utilize its effects.

[0055] Before adding the carburizing agent, this invention also adds a manganese-silicon alloy. Furthermore, ferrosilicon and a sulfur-adding agent are added after the carburizing agent. This is because molten iron containing manganese is beneficial for the subsequent melting and absorption of the carburizing agent, while the increased content of silicon and sulfur is detrimental to the melting and absorption of the carburizing agent, thus hindering the formation of flake graphite.

[0056] Furthermore, the order, amount, and particle size of the aforementioned silicon-barium-calcium inoculant and silicon-zirconium inoculant also affect the microstructure of gray cast iron. Adding the silicon-barium-calcium inoculant first, followed by the silicon-zirconium inoculant, ensures a good inoculation effect. Excessive use of the silicon-barium-calcium inoculant leads to over-inoculation, resulting in ferrite in the microstructure, casting hardness below HBW200, poor inoculation, and the appearance of D or E type graphite, or even carbides, in the microstructure. Conversely, excessively large or small particle sizes of the silicon-barium-calcium inoculant result in unstable inoculation. Similarly, the silicon-zirconium inoculant also requires appropriate dosage and particle size. Therefore, the present invention controls the addition amount of silicon barium calcium inoculant to be 0.30% to 0.50% of the mass of molten iron in the ladle, with a particle size of 2 mm to 8 mm; the addition amount of silicon zirconium inoculant is 0.06% to 0.10% of the mass of molten iron in the ladle, with a particle size of 0.2 mm to 0.7 mm.

[0057] The aforementioned copper and nickel can be added at any time to achieve alloying. Specifically, they can be added at any time during the preparation of the original molten iron, or mixed with the prepared original molten iron, or added together with the original molten iron, silicon barium calcium inoculant, etc., into the ladle, or added to the ladle first, and then the original molten iron, silicon barium calcium inoculant, ferrochrome, tin granules, and ferrochrome nitride are added to the ladle. For cost considerations, the present invention preferably adds the above substances after the original molten iron is prepared; furthermore, in order to obtain gray cast iron with different copper and nickel element compositions, the present invention also adds copper and nickel to the ladle first, then adds the original molten iron, and the silicon barium calcium inoculant, ferrochrome, tin granules, and ferrochrome nitride are added to the ladle with the molten iron flow.

[0058] When adding the remaining iron and recarburizing agent to the smelting furnace, this invention further improves the uniformity of the metallographic structure distribution in gray cast iron by adding them in batches, making it easier to obtain flake graphite. At the same time, adding them in batches can also promote the absorption of the recarburizing agent by the molten iron, improve the accuracy of the process, and reduce the cost of raw materials.

[0059] Therefore, by adding the above-mentioned raw materials and controlling the order, amount, and particle size of the raw materials, it is beneficial to obtain flake graphite and increase the content of pearlite, thereby obtaining gray cast iron that meets the technical requirements of the blank.

[0060] It is understandable that when the above-mentioned raw materials are added, the chemical composition of the molten iron and the ladle molten iron is difficult to determine due to various factors such as impurity elements and melting degree within the raw materials. In order to ensure that the obtained molten iron and ladle molten iron meet the above requirements, this invention uses a carbon-sulfur analyzer, a nitrogen-oxygen analyzer, and a direct-reading spectrometer to analyze the chemical composition of the original molten iron and the ladle molten iron.

[0061] It should be noted that, since iron constitutes the majority of the composition, the changes in the C, Mn, and S content are minimal during the process of adding other substances to the original molten iron to form the ladle molten iron. Therefore, this invention directly uses the C, Mn, and S content of the original molten iron as the C, Mn, and S content of the ladle molten iron. Similarly, although a silicon-zirconium inoculant is added during the process of preparing gray cast iron using ladle molten iron, the amount added is extremely small and has virtually no impact on the elemental composition of the ladle molten iron. Therefore, the elemental composition of the ladle molten iron in this invention is consistent with the elemental composition of the gray cast iron.

[0062] A second aspect of the present invention provides a method for preparing gray cast iron, comprising:

[0063] 1) Smelting: Add silicon carbide and silicon manganese alloy to the molten iron in the smelting furnace, then add the remaining iron and carbonizing agent into the smelting furnace, followed by ferrosilicon and sulfurizing agent to obtain the original molten iron;

[0064] 2) Pouring iron: First, add copper and nickel to the ladle, then add silicon barium calcium inoculant, ferrochrome, tin granules, ferrochrome nitride and the original molten iron into the ladle to obtain molten iron in the ladle;

[0065] 3) Casting: Molten iron is cast using a ladle, and a silicon-zirconium inoculant is added during the casting process for secondary inoculation to obtain gray cast iron;

[0066] The original molten iron, by mass percentage, comprises: C 3.30%-3.40%, Si 1.50%-1.70%, Mn 0.60%-1.00%, 0.060%≤S≤0.120%, with the balance being Fe; the amount of silicon-barium-calcium inoculant added is 0.30%-0.50% of the mass of the molten iron in the ladle, with a particle size of 2mm-8mm; the amount of silicon-zirconium inoculant added is 0.06%-0.10% of the mass of the molten iron in the ladle, with a particle size of 0.2mm-0.7mm.

[0067] The present invention does not limit the specific type of the above-mentioned smelting furnace. For example, it can be a medium-frequency induction furnace.

[0068] The gray cast iron prepared by the above method has a metallographic structure in which the graphite type is type A (flaky graphite), the graphite length is grade 4, and the pearlite content is ≥98%, which meets the technical requirements of the casting blank. This gray cast iron also has high tensile strength and hardness, and when used in cylinder heads, the leakage rate can be as low as below 0.8%.

[0069] Through the inventor's research, it was found that by first melting 30%-40% of the iron material, then adding silicon carbide and silicon manganese alloy to the smelting furnace, followed by adding the remaining 60%-70% of the iron material and a carburizing agent, and finally adding ferrosilicon and a sulfurizing agent, the original molten iron is obtained. This process has several advantages: firstly, it facilitates the absorption of the carburizing agent and the formation of flake graphite; secondly, it is understandable that the volume of the iron material is much larger than the volume of the molten iron after smelting, and the smelting furnace used to hold the molten iron is generally too small for the iron material. Therefore, adding a portion of the iron material first also provides convenience in process operation.

[0070] In the specific implementation process, the mass of silicon carbide is 0.80% to 1.20% of the total iron material. Within this range, silicon carbide can fully pretreat the original molten iron, refine the graphite morphology, and thus facilitate the obtaining of uniformly distributed type A graphite.

[0071] Furthermore, in order to control the chemical composition of gray cast iron, the mass of the manganese silicon alloy is 0.20%-0.40% of the iron material.

[0072] In practice, the iron material is a mixture of 65% to 80% scrap steel and 20% to 35% recycled iron, by mass percentage.

[0073] This invention does not limit the specific source of the aforementioned scrap steel, which can be obtained through any channel. In specific implementation, the scrap steel of this invention is obtained from commercial purchases.

[0074] This invention does not limit the specific source of the recycled iron, as long as it can meet the final chemical composition requirements of the gray cast iron parts.

[0075] Choosing a mixture of 65%–80% scrap steel and 20%–35% recycled iron as the iron material can solve the problem of high raw material costs caused by the use of large amounts of pig iron in traditional methods, and can ensure the mechanical properties of gray cast iron.

[0076] Furthermore, the copper is electrolytic copper;

[0077] Furthermore, the nickel is electrolytic nickel.

[0078] The aforementioned electrolytic copper and electrolytic nickel have the advantage of high purity. When electrolytic copper and electrolytic nickel are selected as raw materials for copper and nickel respectively, the amount of raw materials used is small, the calculation is convenient, and the cost is low. In addition, the molten iron obtained from the ladle has a low impurity content, which is conducive to obtaining high-quality gray cast iron.

[0079] In step 1) of this invention, after obtaining molten iron, the molten iron is placed at 1500℃~1520℃ and left to stand for 10min~15min, and then a slag-collecting agent is added for slag removal treatment.

[0080] In order to remove insoluble impurities from molten iron, this invention controls the temperature of the molten iron to 1500℃~1520℃ to make the slag float to the surface, and then removes the slag from the molten iron by adding a slag-collecting agent.

[0081] It is understood that the composition and particle size of the slag-collecting agent have a significant impact on the slag-collecting effect. Therefore, this invention selects a slag-collecting agent composed of ≥82% silicon dioxide and aluminum oxide, 1%–4% sodium oxide, 2%–4% potassium oxide, and ≤0.5% moisture for slag removal. The particle size of the slag-collecting agent is 0.15 mm–0.85 mm. This slag-collecting agent can effectively remove slag from molten iron.

[0082] According to one embodiment of the present invention, the temperature of the molten iron in the ladle is 1400℃~1420℃.

[0083] During the casting process, the temperature of the molten iron in the ladle is a crucial factor affecting the quality of gray cast iron. Excessive temperature leads to poor graphite morphology and an increased scrap rate due to shrinkage cavities; conversely, excessively low temperatures easily result in porosity, leading to a high scrap rate in gray cast iron. Therefore, this invention controls the temperature of the molten iron in the ladle to be between 1400℃ and 1420℃.

[0084] A third aspect of the present invention provides a gray cast iron part, comprising the aforementioned gray cast iron;

[0085] Alternatively, it may include gray cast iron prepared by the aforementioned method. The metallographic structure of this gray cast iron part exhibits type A graphite, a flake length of grade 4, and a pearlite content of over 98%, meeting the technical requirements for gray cast iron blanks.

[0086] It is understandable that after casting, the gray cast iron part is at a high temperature and is integral with the mold. Therefore, it is necessary to separate the gray cast iron part from the mold. Specifically, this invention separates the gray cast iron part from the mold by cooling the integral part obtained after casting at room temperature (0-40℃) for more than 4 hours, and then performing a mold-making process when the casting temperature is below 500℃.

[0087] Finally, the parts are cleaned to obtain gray cast iron parts.

[0088] In specific implementation, the gray cast iron part includes at least one of a cylinder block and a cylinder head. When the gray cast iron part is used as the cylinder head, the leakage rate of the cylinder head is reduced to below 0.8%, and when the wall thickness is 20mm to 24mm, the tensile strength is as high as 290MPa or more (corresponding to HT350 material), and the hardness is not less than 200HBW.

[0089] The present invention will now be described in more detail through specific embodiments.

[0090] The embodiments and comparative examples of the present invention are all gray cast iron parts prepared using cylinder heads as an example, and the same casting mold is used.

[0091] Example 1

[0092] 1) Smelting: Prepare a mixture of 70% scrap steel and 30% recycled iron as the iron charge by mass percentage; add 1.0% silicon carbide and 0.26% manganese silicon alloy to the molten iron charge in the medium-frequency induction furnace, then add the remaining iron charge and carbonizer into the furnace, followed by ferrosilicon and sulfurizer to obtain the original molten iron; control the temperature of the molten iron at 1512℃, let it stand for 11 minutes, and add slag remover for slag removal.

[0093] Some of the iron materials account for 35% of the total mass of the iron materials;

[0094] The raw molten iron, by mass percentage, comprises: C 3.33%, Si 1.63%, Mn 0.67%, S 0.080%, P 0.023%, with the balance being Fe;

[0095] 2) Tapping: Add the slag-removed molten iron, silicon barium calcium inoculant, ferrochrome, tin granules, and ferrochrome nitride to a ladle containing copper and nickel to obtain molten iron in a ladle; control the temperature of the molten iron in the ladle to 1406℃;

[0096] The amount of silicon-barium-calcium inoculant added is 0.42% of the mass of the molten iron in the ladle; the particle size is 2mm to 8mm.

[0097] The molten iron in the ladle comprises, by mass percentage: C 3.33%, Si 1.92%, Mn 0.67%, S 0.080%, Cu 0.70%, Cr 0.19%, Ni 0.30%, Sn 0.050%, N 0.0096%, and impurities including P 0.023%, Ti 0.011%, Mo 0.025%, V 0.003%, Pb 0.002%, with the balance being Fe;

[0098] 3) Casting: Molten iron is cast using a ladle. During the casting process, a silicon-zirconium inoculant is added for secondary inoculation to obtain an integral part of the cylinder head and the mold. The amount of silicon-zirconium inoculant added is 0.08% of the mass of the molten iron cast in each mold, and the particle size is 0.2mm-0.7mm.

[0099] 4) Cooling and cleaning: Cool the integrated part at room temperature (15-35)℃ for 5 hours, then clean and clean it to obtain the cylinder head.

[0100] The cylinder head prepared in this embodiment has a carbon equivalent of 3.97%.

[0101] Example 2

[0102] The difference between this embodiment and Embodiment 1 is that the amount of silicon-barium-calcium inoculant added is 0.6% of the mass of the molten iron in the ladle, with C 3.32%, Si 1.89%, Mn 0.69%, S 0.085%, Cu 0.72%, Cr 0.18%, Ni 0.28%, Sn 0.052%, N 0.0099%, and impurities including P 0.022%, Ti 0.012%, Mo 0.022%, V 0.003%, Pb 0.002%, with the balance being Fe.

[0103] Example 3

[0104] The difference between this embodiment and Embodiment 1 is that the amount of silicon-zirconium inoculant added is 0% of the mass of the molten iron in the ladle, with C 3.34%, Si 1.90%, Mn 0.66%, S 0.083%, Cu 0.71%, Cr 0.20%, Ni 0.31%, Sn 0.052%, N 0.0095%, and impurities including P 0.025%, Ti 0.014%, Mo 0.023%, V 0.003%, Pb 0.002%, with the balance being Fe.

[0105] Example 4

[0106] The difference between this embodiment and Embodiment 1 is that the temperature of the molten iron in the ladle is 1445℃, and the molten iron in the ladle comprises, by mass percentage: C 3.32%, Si 1.93%, Mn 0.72%, S 0.087%, Cu 0.73%, Cr 0.20%, Ni 0.29%, Sn 0.055%, N 0.0093%, and among the impurity elements, P 0.024%, Ti 0.011%, Mo 0.021%, V 0.004%, Pb 0.002%, with the balance being Fe.

[0107] Example 5

[0108] 1) Smelting: Prepare a mixture of 75% scrap steel and 25% recycled iron as the iron charge by mass percentage; add 0.9% silicon carbide and 0.28% manganese silicon alloy to the molten iron charge in the medium-frequency induction furnace, then add the remaining iron charge and carbonizer into the furnace, followed by ferrosilicon and sulfurizer to obtain the raw molten iron; control the temperature of the raw molten iron at 1516℃, let it stand for 12 minutes, and add slag remover for slag removal.

[0109] Some of the iron materials account for 32% of the total iron material mass;

[0110] The original molten iron, by mass percentage, comprises: C 3.35%, Si 1.62%, Mn 0.72%, S 0.089%, P 0.021%, with the balance being Fe;

[0111] 2) Tapping: Add the slag-removed molten iron, silicon barium calcium inoculant, ferrochrome, tin granules, and ferrochrome nitride to a ladle containing copper and nickel to obtain molten iron in a ladle; control the temperature of the molten iron in the ladle at 1416℃;

[0112] The amount of silicon-barium-calcium inoculant added is 0.38% of the mass of the molten iron in the ladle; the particle size is 2mm to 8mm.

[0113] The molten iron in the ladle comprises, by mass percentage: C 3.35%, Si 1.89%, Mn 0.72%, S 0.089%, Cu 0.76%, Cr 0.18%, Ni 0.32%, Sn 0.053%, N 0.0096%, and impurities including P 0.021%, Ti 0.010%, Mo 0.021%, V 0.004%, Pb 0.002%, with the balance being Fe.

[0114] 3) Casting: Molten iron is cast using a ladle. During the casting process, a silicon-zirconium inoculant is added for secondary inoculation to obtain an integral part of the cylinder head and the mold. The amount of silicon-zirconium inoculant added is 0.076% of the mass of the molten iron in the ladle, and the particle size is 0.2mm to 0.7mm.

[0115] 4) Cooling and cleaning: Cool the integrated part at room temperature (15-35)℃ for 4.5 hours, then clean and clean it to obtain the cylinder head.

[0116] The cylinder head prepared in this embodiment has a carbon equivalent of 3.98%.

[0117] Comparative Example 1

[0118] The difference between this comparative example and Example 1 is that the amount of ferrochrome nitride added is controlled to regulate the nitrogen content, while other conditions remain unchanged, so that the molten iron in the ladle contains, by mass percentage: C 3.34%, Si 1.86%, Mn 0.71%, S 0.082%, Cu 0.68%, Cr 0.25%, Ni 0.29%, Sn 0.078%, N 0.0138%, and impurities including P 0.022%, Ti 0.011%, Mo 0.024%, V 0.003%, Pb 0.002%, with the balance being Fe.

[0119] The carbon equivalent of the cylinder head in this comparative example is 3.96%.

[0120] Comparative Example 2

[0121] The difference between this comparative example and Example 1 is that the amount of ferrochrome nitride added is controlled to regulate the nitrogen content, while other conditions remain unchanged. The molten iron in the ladle comprises, by mass percentage: C 3.33%, Si 1.92%, Mn 0.67%, S 0.083%, Cu 0.69%, Cr 0.22%, Ni 0.30%, Sn 0.052%, N 0.0046%, and impurities including P 0.026%, Ti 0.010%, Mo 0.022%, V 0.004%, Pb 0.002%, with the balance being Fe. The carbon equivalent of the cylinder head in this comparative example is 3.97%.

[0122] Comparative Example 3

[0123] The difference between this comparative example and Example 1 is that the amount of tin granules added is controlled to regulate the Sn content, while other conditions remain unchanged. The molten iron in the ladle contains, by mass percentage: C 3.33%, Si 1.92%, Mn 0.67%, S 0.085%, Cu 0.70%, Cr 0.19%, Ni 0.30%, Sn 0.135%, N 0.0096%, and impurities including P 0.019%, Ti 0.011%, Mo 0.025%, V 0.003%, Pb 0.002%, with the balance being Fe.

[0124] The carbon equivalent of the cylinder head in this comparative example is 3.97%.

[0125] Comparative Example 4

[0126] The difference between this comparative example and Example 1 is that the amount of tin granules added is controlled to regulate the Sn content, while other conditions remain unchanged. The molten iron in the ladle contains, by mass percentage: C 3.31%, Si 1.90%, Mn 0.67%, S 0.08%, Cu 0.75%, Cr 0.23%, Ni 0.35%, Sn 0.009%, N 0.0087%, and impurities including P 0.024%, Ti 0.010%, Mo 0.019%, V 0.003%, Pb 0.002%, with the balance being Fe.

[0127] The carbon equivalent of the cylinder head in this comparative example is 3.94%.

[0128] Comparative Example 5

[0129] The difference between this comparative example and Example 1 is that the amount of ferrochrome added is controlled to regulate the Cr content, while the other conditions remain unchanged. The molten iron in the ladle contains, by mass percentage: C 3.33%, Si 1.93%, Mn 0.68%, S 0.088%, Cu 0.70%, Cr 0.39%, Ni 0.28%, Sn 0.062%, N 0.0086%, and impurities including P 0.023%, Ti 0.009%, Mo 0.020%, V 0.003%, Pb 0.002%, with the balance being Fe.

[0130] The carbon equivalent of the cylinder head in this comparative example is 3.97%.

[0131] Comparative Example 6

[0132] The difference between this comparative example and Example 1 is that the amount of ferrochrome added is controlled to regulate the Cr content, while the other conditions remain unchanged. The molten iron in the ladle contains, by mass percentage: C 3.35%, Si 1.96%, Mn 0.71%, S 0.078%, Cu 0.65%, Cr 0.08%, Ni 0.32%, Sn 0.063%, N 0.0092%, and impurities including P 0.025%, Ti 0.010%, Mo 0.023%, V 0.004%, Pb 0.002%, with the balance being Fe.

[0133] The carbon equivalent of the cylinder head in this comparative example is 4.00%.

[0134] Comparative Example 7

[0135] The difference between this comparative example and Example 1 is that the amount of ferrosilicon and carburizer added is controlled to regulate the content of C and Si elements. The molten iron in the ladle contains, by mass percentage: C 3.15%, Si 1.76%, Mn 0.68%, S 0.081%, Cu 0.67%, Cr 0.22%, Ni 0.31%, Sn 0.059%, N 0.0091%, and impurities including P 0.022%, Ti 0.011%, Mo 0.021%, V 0.003%, Pb 0.002%, with the balance being Fe.

[0136] The carbon equivalent of the cylinder head in this comparative example is 3.74%.

[0137] Comparative Example 8

[0138] The difference between this comparative example and Example 1 is that the amount of ferrosilicon and carburizer added is controlled to regulate the content of C and Si elements. The molten iron in the ladle contains, by mass percentage: C 3.45%, Si 2.16%, Mn 0.72%, S 0.083%, Cu 0.77%, Cr 0.26%, Ni 0.31%, Sn 0.069%, N 0.0096%, and impurities including P 0.026%, Ti 0.010%, Mo 0.019%, V 0.004%, Pb 0.002%, with the balance being Fe.

[0139] The carbon equivalent of the cylinder head in this comparative example is 4.17%.

[0140] Experimental Example 1

[0141] Metallographic analysis was performed on the cylinder heads prepared in the embodiments and comparative examples of this invention. The results are shown in the figure. Figures 1 to 6 Since the graphite and pearlite metallographic images of Examples 2-5, Comparative Examples 1-3, Comparative Examples 5 and 7 are essentially the same as those of Example 1, this invention only lists the graphite and pearlite metallographic images of Example 1 as representative of this type of cylinder head; for the same reason, the graphite and pearlite metallographic images of Comparative Example 4 are used as representative of a type of cylinder head metallographic images of Comparative Examples 4 and 6, and Comparative Example 8 is used as a separate type of gray cast iron.

[0142] Figure 1 , Figure 3 , Figure 5 These are graphite metallographic images of Embodiment 1, Comparative Example 4, and Comparative Example 8 of the present invention, respectively. Figure 2 , Figure 4 , Figure 6 These are pearlitic metallographic images of Embodiment 1, Comparative Example 4, and Comparative Example 8 of the present invention.

[0143] according to Figure 1 and Figure 2 It can be seen that the cylinder heads prepared in Examples 1, 2-5, Comparative Examples 1-3, Comparative Examples 5 and 7 can achieve graphite type A, graphite flake length grade 4, and pearlite content greater than 98%, which meets the technical requirements of gray cast iron blanks.

[0144] according to Figure 3 and Figure 4 It can be seen that the cylinder heads prepared in Comparative Examples 4 and 6 can achieve graphite type A and graphite flake length grade 4, but the pearlite content is less than 98%, which does not meet the technical requirements of gray cast iron blanks.

[0145] according to Figure 5 and Figure 6 It can be seen that the cylinder head prepared in Comparative Example 8 can reach type A graphite, but the graphite flake length is less than grade 4 and the pearlite content is greater than 98%, which does not meet the technical requirements of gray cast iron blanks.

[0146] Experimental Example 2

[0147] The cylinder heads obtained in the examples and comparative examples were tested for tensile strength, hardness, and leakage rate. The results are shown in Table 1. The wall thickness of the sampling area for tensile strength testing was 23.2 mm. The wall thickness leakage rate test was conducted by introducing compressed air into the water chamber of 1000 finished cylinder heads at pressures ranging from 400 kPa to 600 kPa for 60 seconds; the gas leakage was not to exceed 10 cm³. 3 / min, the leakage rate is obtained by dividing the number of leaking cylinder heads by the total number of cylinder heads tested.

[0148] Table 1

[0149]

[0150]

[0151] As shown in Table 1, the cylinder heads of Embodiments 1-5 of the present invention all have excellent mechanical properties and low leakage rates, while Comparative Examples 1-8 cannot simultaneously achieve both mechanical properties and leakage rates. Therefore, it can be seen that controlling the content of N, Sn, Cr, C and Si elements in gray cast iron within the scope of this application can effectively solve the problem of the inability to simultaneously achieve both cylinder head leakage rate and mechanical properties.

[0152] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention have been clearly and completely described above in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

Claims

1. A type of gray cast iron, characterized in that, The composition, by mass percentage, includes: C 3.30%~3.40%, Si 1.80%~2.10%, Mn 0.60%~1.00%, S 0.060%~0.120%, Cu 0.50%~0.80%, Cr 0.15%~0.30%, Ni 0.20%~0.40%, Sn 0.040%~0.080%, N 0.0080%~0.0110%, impurity elements 0~0.11%, and the balance being Fe. The gray cast iron has a carbon equivalent (CE) of 3.9% to 4.1%, where CE = C + 1 / 3 Si; and the impurity elements are P ≤ 0.030%, Ti ≤ 0.030%, Mo ≤ 0.030%, V ≤ 0.010%, and Pb ≤ 0.003%; the gray cast iron is prepared by a method comprising the following process: Silicon carbide and silicon manganese alloy are added to a portion of the molten iron in a smelting furnace. The remaining iron and a carbonizing agent are then added to the smelting furnace, followed by the addition of ferrosilicon and a sulfurizing agent to obtain raw molten iron. Copper and nickel are added to a ladle, and silicon barium calcium inoculant, ferrochrome, tin granules, ferrochrome nitride, and the raw molten iron are added to the ladle in a flow-through manner to obtain ladle molten iron. The ladle molten iron is then used for casting, with silicon zirconium inoculant added during the casting process to obtain gray cast iron. The original molten iron comprises, by mass percentage: C 3.30%-3.40%, Si 1.50%-1.70%, Mn 0.60%-1.00%, 0.060%≤S≤0.120%, with the balance being Fe; the amount of the silicon-barium-calcium inoculant added is 0.30%~0.50% of the mass of the molten iron in the ladle, with a particle size of 2mm~8mm; the amount of the silicon-zirconium in-flow inoculant added is 0.06%~0.10% of the mass of the molten iron in the ladle, with a particle size of 0.2mm~0.7mm.

2. A method for preparing gray cast iron according to claim 1, characterized in that, include: 1) Smelting: Silicon carbide and silicon manganese alloy are added to the molten iron in the smelting furnace, and the remaining iron and carbonizing agent are added to the smelting furnace. Then ferrosilicon and sulfurizing agent are added to obtain the original molten iron. 2) Iron tapping: First, copper and nickel are added to the ladle, and then silicon barium calcium inoculant, ferrochrome, tin granules, ferrochrome nitride and the original molten iron are added to the ladle along with the flow to obtain ladle molten iron; 3) Casting: The molten iron in the ladle is used for casting, and a silicon-zirconium inoculant is added during the casting process for secondary inoculation to obtain the gray cast iron; The original molten iron comprises, by mass percentage: C 3.30%-3.40%, Si 1.50%-1.70%, Mn 0.60%-1.00%, 0.060%≤S≤0.120%, with the balance being Fe; the amount of the silicon-barium-calcium inoculant added is 0.30%~0.50% of the mass of the molten iron in the ladle, with a particle size of 2mm~8mm; the amount of the silicon-zirconium inoculant added is 0.06%~0.10% of the mass of the molten iron in the ladle, with a particle size of 0.2mm~0.7mm.

3. The preparation method according to claim 2, characterized in that, The iron material mentioned above accounts for 30%-40% of the total iron material.

4. The preparation method according to claim 2, characterized in that, The silicon carbide constitutes 0.80% to 1.20% of the total iron content; and / or, The mass of the manganese-silicon alloy is 0.20%-0.40% of the total iron content.

5. The preparation method according to any one of claims 2-4, characterized in that, The iron material is a mixture of 65% to 80% scrap steel and 20% to 35% recycled iron; And / or, the copper is electrolytic copper; And / or, the nickel is electrolytic nickel.

6. The preparation method according to any one of claims 2-4, characterized in that, In step 1), after obtaining the raw molten iron, the raw molten iron is placed at 1500℃~1520℃ and left to stand for 10min~15min, and then a slag-collecting agent is added for slag removal treatment.

7. The preparation method according to any one of claims 2-4, characterized in that, The temperature of the molten iron poured into the ladle is 1400℃~1420℃.

8. A gray cast iron part, characterized in that, Including the gray cast iron as described in claim 1; Or, including gray cast iron prepared by the preparation method according to any one of claims 2-7.

9. The gray cast iron part according to claim 8, characterized in that, The gray cast iron parts include at least one of a cylinder block and a cylinder head.

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