Gray cast iron cylinder block and process for producing the same

Abstract

This application discloses a gray cast iron cylinder block and its manufacturing process. The gray cast iron cylinder block, based on mass percentage statistics, includes: C: 3.40%–3.50%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.10%, Cu: 0.60%–0.70%, Sn: 0.05%–0.08%, with the remainder being Fe. By controlling the carbon content at a high level of 3.40% to 3.50%, good graphitization and casting fluidity are ensured. The solid solution strengthening of copper and the pearlite stabilizing effect of tin work synergistically to refine the pearlite lamellar spacing, effectively suppress the formation of ferrite in the central part, avoid the precipitation of brittle phases, balance strength and toughness, and ensure the consistency of the microstructure of the casting from the surface to the center, effectively improving the tensile strength and wear resistance of the cylinder block casting.

Description

Technical Field

[0001] This application relates to the field of casting technology, and in particular to a gray cast iron cylinder block and its manufacturing process. Background Technology

[0002] Marine low-speed diesel engine cylinder blocks, as large, thick-walled castings, typically have wall thicknesses of 180 to 250 mm and weigh up to 27 tons. Their complex service conditions necessitate materials with high strength, high wear resistance, and good microstructure uniformity. Currently, conventional gray cast iron materials and traditional inoculation processes, when used to prepare such large-section castings, often result in problems such as coarse graphite and uneven microstructure in the core and surface of the casting under conventional compositional design, making it difficult to meet the required mechanical properties. Summary of the Invention

[0003] This application aims to at least solve one of the technical problems existing in the prior art. To this end, this application proposes a gray cast iron cylinder block and its manufacturing process, which can improve the tensile strength and wear resistance of the cylinder block and improve the uniformity of the microstructure distribution of the casting.

[0004] In a first aspect, embodiments of this application provide a gray cast iron cylinder block, which, based on a mass percentage statistical analysis, comprises the following components: C: 3.40%–3.50%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.10%, Cu: 0.60%–0.70%, Sn: 0.05%–0.08%, with the remainder being Fe.

[0005] In the gray cast iron cylinder block provided in this application embodiment, the gray cast iron cylinder block includes the following components based on a mass percentage statistical analysis: C: 3.40%–3.45%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.10%, Cu: 0.60%–0.70%, Sn: 0.06%–0.07%, with the remainder being Fe.

[0006] Secondly, this application also provides a manufacturing process for a gray cast iron cylinder block, including the following steps: Step 1: Heat the original molten iron to 1500 to 1520 degrees Celsius for slag removal, and then cool the molten iron after slag removal to 1450 to 1470 degrees Celsius for settling. During the settling process, nitrogen gas is blown into the molten iron for pretreatment to obtain pretreated molten iron. Step 2: Place a pre-prepared inoculant at the bottom of the ladle and cover it with a mixture of electrolytic copper blocks and tin granules. Step 3: Pour 30% of the pretreated molten iron by mass into the ladle to melt the inoculant and the mixture layer inside the ladle; Step 4: Inject the remaining pretreated molten iron into the ladle below the liquid surface along the diversion groove set on the side wall of the ladle to form inoculated molten iron in the ladle; Step 5: Pour the molten iron in the ladle into a metering pouring cup. The metering pouring cup includes a liquid surface heat compensation device, which includes a copper wire mesh bag suspended above the metering pouring cup. The copper wire mesh bag is also filled with a supplementary inoculant. When the molten iron in the ladle fills the metering pouring cup, the copper wire mesh bag is immersed in the molten iron in the ladle to release the supplementary inoculant, thus obtaining the target molten iron. Step Six: Apply negative pressure to the casting mold cavity and pour the target inoculated iron into the casting mold cavity. After solidification, a gray cast iron cylinder is obtained. The gray cast iron cylinder body, based on mass percentage, includes the following components: C: 3.40%–3.50%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.10%, Cu: 0.60%–0.70%, Sn: 0.05%–0.08%, with the remainder being Fe.

[0007] In the production process provided in this application embodiment, the gray cast iron cylinder includes the following components based on a mass percentage statistical analysis: C: 3.40%–3.45%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.10%, Cu: 0.60%–0.70%, Sn: 0.06%–0.07%, with the remainder being Fe.

[0008] In the production process provided in this application embodiment, the raw molten iron in step one includes the following components based on mass percentage: C: 3.50–3.55%, Si: 1.60–1.75%, Mn: 0.9–1.0%, P: 0.020–0.050%, S: 0.08–0.10%, with the remainder being Fe.

[0009] In the production process provided in the embodiments of this application, in step two, the inoculant in the ladle accounts for 0.35% of the total mass of the molten iron, the electrolytic copper block accounts for 0.63 to 0.78% of the total mass of the molten iron, and the tin granules account for 0.065 to 0.077% of the total mass of the molten iron.

[0010] In the production process provided in the embodiments of this application, the inoculant in the package comprises the following components based on mass percentage: Si: 72-75%, Al: 0.5-0.8%, with the remainder being Fe, wherein the particle size of the inoculant in the package is 3 to 8 millimeters.

[0011] In the production process provided in this application embodiment, the chemical composition of the supplemental progesterone is the same as that of the in-package progesterone, and the mass of the supplemental progesterone is less than the mass of the in-package progesterone.

[0012] In the production process provided in this application embodiment, during the process of pouring the target inoculated molten iron into the casting mold cavity: When the cavity filling percentage is less than 10%, the target inoculated molten iron is controlled to flow into the cavity at a first injection rate. When the cavity filling percentage reaches 10% to 85%, the target inoculated molten iron is controlled to fill the cavity at a second injection rate; When the cavity filling percentage is greater than 85% but less than 100%, the target inoculated molten iron is controlled to flow into the cavity at a third injection rate; When the cavity filling percentage reaches 100%, add superheated molten iron accounting for 0.3% to 0.8% of the cavity volume into the cavity; The third injection rate is less than the second injection rate but greater than the first injection rate.

[0013] Thirdly, the embodiments of this application provide a gray cast iron cylinder block, which is prepared using the manufacturing process of gray cast iron cylinder blocks as described in the second aspect embodiment.

[0014] According to the gray cast iron cylinder block and its manufacturing process provided in the embodiments of this application, it has at least the following beneficial effects: by controlling the carbon content at a high level of 3.40% to 3.50%, good graphitization and casting fluidity are ensured. The solid solution strengthening of copper and the pearlite stabilizing effect of tin work together to refine the pearlite lamellar spacing, effectively suppress the formation of ferrite in the central part, avoid the precipitation of brittle phases, balance strength and toughness, ensure the consistency of the microstructure of the casting from the surface to the center, and effectively improve the tensile strength and wear resistance of the cylinder block casting.

[0015] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures particularly pointed out in the description and the accompanying drawings. Attached Figure Description

[0016] The present application will be further described below with reference to the accompanying drawings and embodiments; Figure 1This is a flowchart of the gray cast iron cylinder block manufacturing process provided in the embodiments of this application; Figure 2 This is a schematic diagram of the structure of the casting mold for the cylinder block of a marine low-speed diesel engine provided in the embodiments of this application; Figure 3 This is a schematic diagram of the casting mold for the cylinder block of a marine low-speed diesel engine provided in an embodiment of this application from another perspective. Figure 4 This is a schematic diagram of the casting mold for the cylinder block of a marine low-speed diesel engine provided in an embodiment of this application, from another perspective. Detailed Implementation

[0017] This section will describe in detail the specific embodiments of this application. Preferred embodiments of this application are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of this application, but they should not be construed as limiting the scope of protection of this application.

[0018] It should be understood that in the description of the embodiments of this application, the use of terms such as "first" and "second" is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of technical features indicated, or implicitly indicating the order of the technical features indicated. "At least one" means one or more, and "more than one" means two or more. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or multiple items.

[0019] Furthermore, unless otherwise explicitly specified and limited, the term "connection / linkage" should be interpreted broadly, for example, it can be a fixed connection or a movable connection, a detachable connection or a non-detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection or a connection that can communicate with each other; it can be a direct connection or an indirect connection through an intermediate medium.

[0020] In the description of the embodiments in this application, the terms "one embodiment / implementation," "another embodiment / implementation," or "some embodiments / implementations," "in the above embodiments / implementations," etc., refer to specific features, structures, materials, or characteristics described in conjunction with embodiments or examples that are included in at least two embodiments or implementations disclosed in this application. In this disclosure, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or implementation. It should be noted that although a logical order is shown in the flowcharts, in some cases, the steps shown or described may be performed in a different order than that shown in the flowcharts.

[0021] Traditional marine low-speed diesel engine cylinder blocks are large, thick-walled castings. Due to conventional composition design, the core and surface of the castings are prone to problems such as coarse graphite and uneven structure, making it difficult to meet the requirements of high strength, high wear resistance and good structural uniformity in terms of mechanical properties.

[0022] To at least solve the technical problems existing in the prior art, this application proposes a gray cast iron cylinder block, which aims to optimize the microstructure of the casting by precisely controlling the components such as carbon, silicon, manganese, phosphorus, sulfur, copper, and tin, thereby improving the comprehensive mechanical properties of large thick-walled castings to meet the high requirements of marine low-speed diesel engine cylinder blocks for high strength, high wear resistance, and uniform microstructure.

[0023] It should be noted that the technical features involved in the various embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0024] For ease of understanding, the following explains some key terms in this embodiment: Gray cast iron refers to cast iron in which carbon exists mainly in the form of flake graphite in a ferrite or pearlite matrix.

[0025] The diesel engine cylinder block is the skeleton component of an internal combustion engine, used to house the piston and cylinder liner, and serving as the mounting base for moving parts such as the crankshaft and connecting rods. It also withstands the high-temperature, high-pressure combustion gas loads generated in the combustion chamber. Due to the enormous size and harsh operating conditions of marine low-speed diesel engine cylinder blocks, which must withstand continuous combustion pressure, thermal fatigue, and mechanical fatigue, the microstructure and performance requirements for the castings from the surface to the core are very high.

[0026] Microstructure refers to the microscopic morphology of the internal metal of a casting after solidification, mainly including two aspects: graphite morphology and matrix structure.

[0027] The embodiments of this application will be further described below with reference to the accompanying drawings.

[0028] In one aspect, the present application provides a gray cast iron cylinder block, and the gray cast iron cylinder block is described below with reference to specific embodiments.

[0029] Example 1 The composition of gray cast iron cylinder blocks is based on mass percentage statistics. The carbon content can be 3.40% to 3.50%, the silicon content can be 1.95% to 2.05%, the manganese content can be 0.90% to 1.00%, the phosphorus content can be 0.020% to 0.050%, the sulfur content can be 0.08% to 0.10%, the copper content can be 0.60% to 0.70%, the tin content can be 0.05% to 0.08%, and the remainder is iron.

[0030] Specifically, the carbon (C) content is controlled within a high range of 3.40% to 3.50%, providing ample carbon source for graphite precipitation while ensuring good fluidity of the molten iron for easy casting. While maintaining good fluidity, the high carbon content provides sufficient carbon supersaturation for subsequent processes, enabling gradient nucleation. For example, when the carbon content is close to 3.50%, the graphitization tendency is higher, contributing to the formation of more graphite phases; when the carbon content is close to 3.40%, the graphitization tendency is relatively lower, but it still improves the matrix strength.

[0031] The silicon (Si) content was controlled between 1.95% and 2.05%. Silicon, acting as a graphitization promoter, effectively facilitates the precipitation of carbon in graphite form within this range and strengthens the matrix through solid solution. The manganese (Mn) content was controlled between 0.90% and 1.00%, and the sulfur (S) content between 0.08% and 0.10%. Manganese stabilizes pearlite and inhibits ferrite formation, thereby improving the material's hardness and wear resistance. Simultaneously, manganese combines with sulfur to form sulfides, mitigating the harmful effects of sulfur. For example, a manganese content of around 1.00% results in stronger pearlite stabilization, while around 0.90% has less impact on molten iron flowability. The manganese-to-sulfur ratio was carefully designed to ensure the formation of sufficient and dispersed manganese sulfide nuclei. Furthermore, the phosphorus (P) content was controlled between 0.020% and 0.050%. Maintaining a low phosphorus content aims to reduce the formation of brittle phosphorus eutectics, thus preserving the material's toughness. For example, the material exhibits minimal toughness loss when the phosphorus content is around 0.020%, and the formation of brittle phases can still be effectively controlled when the content is around 0.050%.

[0032] The copper content is controlled between 0.60% and 0.70%. As an alloying element, copper can strengthen the matrix through solid solution and help refine the pearlite lamellar spacing, thereby improving the strength and wear resistance of the material. Meanwhile, the tin content is controlled between 0.05% and 0.08%. Tin is a strong pearlite stabilizer, effectively promoting pearlite formation and refining its microstructure, especially during the slow cooling process of thick-walled castings, helping to ensure the uniformity of the matrix structure. The designed ratio of copper and tin allows for synergistic effects, simultaneously strengthening the matrix through solid solution, stabilizing pearlite, and refining the pearlite lamellar spacing. This ensures that even in the central region of thicker castings, the pearlite content remains stable at over 98%, with no brittle phase precipitation. The remaining component in the casting is iron. As the matrix metal, iron supports the solid solution and precipitation of the aforementioned alloying elements, forming the main structure of the gray cast iron cylinder block.

[0033] Through precise control and synergistic design of the aforementioned components, the gray cast iron cylinder block prepared in this application effectively solves the problems of coarse graphite and uneven microstructure that occur during the preparation of traditional large, thick-walled castings. The mechanical properties of the gray cast iron cylinder block according to the above embodiments achieve a type A graphite content greater than 92%, a pearlite content greater than 95%, and a carbide-free microstructure. The tensile strength of a single casting test bar reaches 365 to 410 MPa, and the hardness reaches 220 to 260 HBW. The tensile strength of an attached casting test block reaches 265 to 300 MPa, and the hardness reaches 230 to 270 HBW. The hardness of the casting body reaches 220 to 260 HBW. Thus, the core and surface microstructure of the casting are effectively optimized, resulting in a more uniform and fine graphite morphology and pearlite matrix, thereby significantly improving the comprehensive mechanical properties of the material. This enables it to meet the stringent service requirements of marine low-speed diesel engine cylinder blocks for high strength, high wear resistance, and good microstructure uniformity.

[0034] Example 2 The gray cast iron cylinder block, based on mass percentage statistics, includes the following components: C: 3.40%–3.45%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.10%, Cu: 0.60%–0.70%, Sn: 0.06%–0.07%, with the remainder being Fe.

[0035] Specifically, the gray cast iron cylinder block proposed in this application embodiment achieves precise control over its components. Carbon, as the main element in gray cast iron, is limited to a narrower range of 3.40% to 3.45%. Compared to the wide range of carbon content in Embodiment 1, Embodiment 2, by narrowing the upper limit of carbon content, can more effectively suppress the excessive production and coarsening of graphite during the slow cooling process of large, thick-walled castings, ensuring a finer and more uniform distribution of graphite flakes, thereby effectively improving the strength and density of the casting.

[0036] The silicon content ranges from 1.95% to 2.05%. Silicon promotes the precipitation of carbon in the form of graphite and affects the matrix structure. Within this range, sufficient graphitization capability is ensured while avoiding excessive ferrite content leading to reduced strength due to excessive silicon content, or white cast iron tendency due to insufficient silicon content. For example, the silicon content can be adjusted by adding ferrosilicon or silicon-calcium alloy.

[0037] The manganese content ranges from 0.90% to 1.00%, while the sulfur content is controlled between 0.08% and 0.10%. Manganese is a pearlite stabilizing element and also has a desulfurizing effect. Within this range, it can effectively promote pearlite formation, improve matrix strength and hardness, and combine with sulfur to form sulfides, reducing the harmful effects of sulfur. Maintaining a low sulfur content minimizes its negative impact and improves the purity of the casting.

[0038] The phosphorus content ranges from 0.020% to 0.050%. Phosphorus can form a hard and brittle phosphoeutectic in gray cast iron. An appropriate amount of phosphorus can improve the wear resistance of castings, but excessive phosphorus will significantly reduce toughness. Within this range, it is possible to ensure a certain level of wear resistance while avoiding excessive damage to the toughness of the castings.

[0039] The copper content ranges from 0.60% to 0.70%. Copper is a pearlite stabilizing element that refines graphite, improves matrix strength and wear resistance, and enhances the corrosion resistance of castings. Within this range, copper's alloying effect can be fully utilized to improve the overall performance of castings. Meanwhile, the tin content ranges from 0.06% to 0.07%. Tin is also a pearlite stabilizing element and is crucial for the uniformity of the core structure in thick-walled castings. Precisely limiting the tin content within this narrow window ensures sufficient pearlite formation in the core while preventing the formation of brittle tin-rich phases at grain boundaries due to excessive tin content, thus improving both wear resistance and material toughness. For example, the tin content can be precisely controlled by adding pure tin granules or tin-containing alloys.

[0040] The remaining components in the casting are iron, which serves as the base metal, bearing and connecting the aforementioned alloying elements to form the overall structure of gray cast iron.

[0041] The mechanical properties of the gray cast iron cylinder block proposed in the above embodiments can achieve greater than 95% type A graphite, greater than 97% pearlite content, and no carbide in the microstructure. The tensile strength of a single cast test bar reaches 385 to 420 MPa, and the hardness reaches 230 to 260 HBW. The tensile strength of an attached cast test block reaches 275 to 310 MPa, and the hardness reaches 240 to 280 HBW. The hardness of the casting body can reach 230 to 260 HBW. It is evident that this application effectively optimizes the microstructure of the casting by precisely limiting the mass percentage of carbon and tin elements in the gray cast iron cylinder block within a narrower range, combined with the synergistic effect of other alloying elements. Specifically, controlling the carbon content within the range of 3.40% to 3.45% can effectively suppress excessive growth and coarsening of graphite during the solidification process of large-section castings, ensuring a finer and more uniform distribution of graphite flakes, thereby improving the strength and density of the casting. Meanwhile, by limiting the tin content to the range of 0.06% to 0.07%, tin is utilized as a pearlite stabilizing element. This ensures the uniformity of the matrix structure while avoiding the increase of brittle phases due to excessive tin content or insufficient pearlite content due to insufficient tin content. This approach improves wear resistance while maintaining the toughness of the material. This refined composition ratio effectively balances the microstructure evolution of the casting under different cooling rates, solves the problem of inconsistent microstructure properties between the core and surface of large, thick-walled castings, and provides a fundamental compositional guarantee for achieving high-strength, high-wear-resistant marine low-speed diesel engine cylinder blocks, significantly improving the performance stability of castings under complex operating conditions.

[0042] Secondly, this application provides a manufacturing process for a gray cast iron cylinder block. The manufacturing process for the gray cast iron cylinder block is described below with reference to specific embodiments.

[0043] Example 3 like Figure 1 As shown, Figure 1 This is a flowchart of the manufacturing process of the gray cast iron cylinder block provided in the embodiments of this application, which may include the following steps: Step 1: Heat the original molten iron to 1500 to 1520 degrees Celsius for slag removal, and then cool the molten iron after slag removal to 1450 to 1470 degrees Celsius for settling. During the settling process, nitrogen gas is blown into the molten iron for pretreatment to obtain pretreated molten iron. Step 2: Place the pre-prepared inoculant at the bottom of the ladle and cover it with a mixture of electrolytic copper blocks and tin granules. Step 3: Pour 30% of the total mass of pretreated molten iron into the ladle to melt the inoculant and mixture layer inside the ladle; Step 4: Inject the remaining pretreated molten iron into the ladle below the liquid surface along the diversion channel set on the side wall of the ladle to form inoculated molten iron in the ladle; Step 5: Pour the molten iron from the ladle into a metering pouring cup. The metering pouring cup includes a liquid surface heat compensation device, which includes a copper wire mesh bag suspended above the metering pouring cup. The copper wire mesh bag is also filled with a supplementary inoculant. When the molten iron in the ladle fills the metering pouring cup, the copper wire mesh bag is immersed in the molten iron in the ladle to release the supplementary inoculant, thus obtaining the target molten iron. Step Six: Apply negative pressure to the casting mold cavity and pour the target inoculated iron into the casting mold cavity. After solidification, a gray cast iron cylinder is obtained. The gray cast iron cylinder body, based on mass percentage statistics, includes the following components: C: 3.40%~3.50%, Si: 1.95%~2.05%, Mn: 0.90%~1.00%, P: 0.020%~0.050%, S: 0.08%~0.10%, Cu: 0.60%~0.70%, Sn: 0.05%~0.08%, with the remainder being Fe.

[0044] Understandably, this application proposes a production process for gray cast iron cylinder blocks. Specifically, the original molten iron is first heated to 1500-1520 degrees Celsius for slag removal, effectively removing impurities. Subsequently, the slag-removed molten iron is cooled to 1450-1470 degrees Celsius and allowed to stand. During this standing process, nitrogen gas is blown into the molten iron for pretreatment, resulting in pretreated molten iron. The blown nitrogen gas not only acts as a stirrer and purifier, making the molten iron composition more uniform, but also causes some of the dissolved nitrogen to precipitate as fine nitrides during subsequent solidification, serving as heterogeneous nucleation sites for graphite and refining the graphite structure.

[0045] Secondly, a pre-prepared inoculant is placed at the bottom of the ladle, and a mixture of electrolytic copper blocks and tin granules is laid on top of the inoculant. Then, 30% of the total mass of pretreated molten iron is poured into the ladle to melt the inoculant and mixture layer. This low-temperature initial pour creates a localized supercooled zone at the bottom of the ladle, promoting the early precipitation of numerous primary austenite dendrites and fine graphite nuclei, while preferentially dissolving copper and tin elements to form locally high-concentration micro-regions. Next, the remaining pretreated molten iron is injected into the ladle below the liquid surface along the drainage channels set on the side wall of the ladle, forming inoculated molten iron within the ladle. The opposing injection of high-temperature molten iron generates a strong convection effect, uniformly diffusing the locally high-concentration micro-regions to the entire molten iron system, achieving a dynamic transition from localized enrichment to overall uniformity, avoiding problems of uneven alloying elements or burn-off.

[0046] Next, the molten iron inoculated in the ladle is poured into a metering pouring cup, which includes a liquid surface heat compensation device. This device comprises a copper wire mesh bag suspended above the pouring cup, containing supplementary inoculant. When the supplementary inoculated iron fills the pouring cup, the copper wire mesh bag is immersed in the molten iron in the ladle, releasing the supplementary inoculant to obtain the target molten iron. The copper wire mesh bag plays a dual role in this process: firstly, its high thermal conductivity causes localized micro-region supercooling, generating additional nucleation pulses; secondly, the copper mesh itself melts to replenish trace amounts of copper and simultaneously releases supplementary inoculant, forming a dual release of copper and inoculant, effectively compensating for the degradation of the inoculant during the long-flow casting process.

[0047] Finally, negative pressure is applied to the mold cavity, and the target inoculated iron is poured into the mold cavity. After solidification, a gray cast iron cylinder is obtained. The gray cast iron cylinder body, based on mass percentage, comprises the following components: C: 3.40%–3.50%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.010%, Cu: 0.60%–0.70%, Sn: 0.05%–0.08%, with the remainder being Fe. Applying negative pressure enhances the venting capacity within the mold cavity, reduces porosity defects, improves filling capacity, and strengthens the feeding effect, effectively increasing the density of the casting.

[0048] Through the above technical solution, this application breaks through the traditional process of single-stage inoculation and gravity casting. It utilizes a supplementary inoculant placed in a copper wire mesh bag for secondary inoculation, ensuring the nucleation effect throughout the entire casting process. Nitrogen blowing pretreatment integrates purification and microalloying nucleation; the thermal gradient characteristics of the low-temperature first stroke and high-temperature counter-stroke promote the uniform distribution of alloying elements; the liquid surface heat compensation device of the copper wire mesh bag provides secondary inoculation strengthening; and negative pressure casting optimizes the filling and feeding processes. As a result, the core and surface microstructure of the casting are effectively optimized, obtaining a uniform and fine graphite morphology and pearlite matrix, thereby effectively improving the comprehensive mechanical properties of the material and meeting the high requirements of marine low-speed diesel engine cylinder blocks for high strength, high wear resistance, and good microstructure uniformity.

[0049] The solidified gray cast iron cylinder, based on mass percentage statistics, includes the following components: C: 3.40%–3.45%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.010%, Cu: 0.60%–0.70%, Sn: 0.06%–0.07%, with the remainder being Fe.

[0050] The original molten iron contains the following components by mass percentage: C: 3.50%–3.55%, Si: 1.60%–1.75%, Mn: 0.9%–1.0%, P: 0.020%–0.050%, S: 0.08%–0.10%, with the remainder being Fe.

[0051] Specifically, the carbon content is controlled within a relatively high range of 3.50% to 3.55% to provide sufficient carbon source for graphitization, reduce the tendency for white iron formation, and provide a sufficient nucleation basis for subsequent inoculation treatment. The carbon content can be precisely adjusted by calculating the furnace charge ratio or by adding a carburizing agent after melting. The silicon content is set within a relatively low range of 1.60% to 1.75%. Silicon is a strong graphitizing element. Setting a low silicon content in the original molten iron aims to leave sufficient adjustment space for subsequent inoculation treatment in the ladle, avoiding excessive silicon content in the final casting. The silicon content can be controlled by adding alloys such as ferrosilicon. The manganese content is controlled within a range of 0.9% to 1.0%. It has the function of stabilizing pearlite and improving strength and hardness, while also combining with sulfur to form MnS inclusions that affect graphite nucleation. Adding manganese in the original molten iron stage helps it to dissolve fully and uniformly. Phosphorus content is strictly controlled at a low level of 0.020%–0.050% to inhibit the formation of brittle phosphorus eutectic and improve the toughness of castings. Phosphorus content is mainly controlled by selecting low-phosphorus pig iron and scrap steel as raw materials. Sulfur content is set within a specific range of 0.08%–0.10%. MnS inclusions formed by the combination of appropriate amounts of sulfur and manganese can act as heterogeneous nucleation sites for graphite, promoting the formation of type A graphite.

[0052] By precisely pre-defining the chemical composition of the original molten iron as described above, the embodiments of this application effectively solve the problem of uneven microstructure caused by fluctuations in initial composition in traditional processes. Specifically, the relatively high carbon content of 3.50% to 3.55% provides sufficient carbon supersaturation for the subsequent first-stroke stage, ensuring the precipitation of a large number of primary graphite nuclei and laying a microscopic foundation for microstructure refinement; the relatively low silicon content of 1.60% to 1.75% provides precise room for increasing the addition of high-silicon inoculant at the bottom of the ladle, making the silicon content controllable; the combination of 0.9% to 1.0% manganese content and 0.08% to 0.10% sulfur content forms a two-phase heterogeneous nucleation of manganese sulfide and nitride after nitrogen pretreatment, effectively increasing the graphite nucleus density and promoting the formation of uniform A-type graphite in the core of thick-walled castings. In addition, elements such as manganese, phosphorus, and sulfur are precisely adjusted and homogenized during the initial molten iron stage, avoiding the problem of insufficient alloy dissolution caused by the limited processing time in the ladle, thereby effectively improving the consistency of the microstructure from the surface to the core of large, thick-walled castings.

[0053] In the production process of gray cast iron cylinder blocks, in step two, the inoculant in the ladle accounts for 0.35% of the total mass of molten iron, the electrolytic copper block accounts for 0.63% to 0.78% of the total mass of molten iron, and the tin granules account for 0.065% to 0.077% of the total mass of molten iron.

[0054] In the casting process, the inoculant used in the ladle primarily promotes graphite nucleation and refines graphite morphology, thereby improving the mechanical properties of the casting. The amount of inoculant added directly affects the inoculation effect; too little may lead to insufficient inoculation and coarse graphite, while too much may result in inoculation degradation or uneven graphite distribution. Besides the precisely controlled 0.35% ratio in this embodiment, in other applications, the amount of inoculant added can be adjusted within the range of 0.2% to 0.6% based on the molten iron composition, pouring temperature, casting wall thickness, and the required graphite morphology and mechanical properties. For example, for thin-walled castings or castings with low strength requirements, the inoculant ratio can be appropriately reduced; while for castings requiring higher strength and finer graphite, a higher ratio may be needed. Furthermore, the type of inoculant (such as ferrosilicon-based, barium-based, strontium-based, etc.) and particle size also affect the effective addition amount.

[0055] Electrolytic copper blocks, as an alloying element additive, primarily strengthen the matrix structure of gray cast iron, improve its strength and wear resistance, and promote pearlite formation, refining the pearlite lamellars. The amount of graphite added needs precise control to avoid excessive copper content leading to segregation or reduced casting toughness. Besides the precisely controlled ratio of 0.63% to 0.78% in this embodiment, in other gray cast iron production processes, the amount of electrolytic copper added is typically determined based on the performance requirements of the target casting and the target copper content in the final product, generally ranging from 0.5% to 1.0%. For example, for parts requiring higher wear resistance, the copper content can be closer to the upper limit; for parts requiring higher toughness, it can be closer to the lower limit. Furthermore, copper can also be added in the form of copper alloy blocks or copper shavings.

[0056] Tin granules, as a pearlite stabilizing element, can increase pearlite content and refine pearlite microstructure, thereby improving the strength, hardness, and wear resistance of castings, especially the uniformity of the core microstructure in large, thick-walled castings. However, excessive tin content may lead to grain boundary segregation, forming brittle phases and affecting the toughness of the material. Besides the precisely controlled proportion of 0.065% to 0.077% in this embodiment, in other gray cast iron production, the amount of tin added is usually determined based on the casting wall thickness, cooling rate, and required pearlite content, generally within the range of 0.03% to 0.1%. For example, for thin-walled castings, the amount of tin added can be appropriately reduced; for large, thick-walled castings, to ensure the pearlite content in the core, it needs to be more precisely controlled within a higher but not excessive range. Tin can also be added in the form of tin-iron alloys or pure tin ingots.

[0057] Specifically, the inoculant in the ladle is set to 0.35% of the total mass of the molten iron, which is precisely matched with the process parameters of the pretreated molten iron, which accounts for 30% of the total mass of the molten iron in the subsequent step three, for the low-temperature first spur. This ensures that an appropriate amount of primary graphite nuclei are formed at the bottom of the molten iron ladle, providing a stable foundation for the uniform nucleation of graphite. This effectively avoids the problem of coarse structure caused by insufficient inoculation and provides a suitable initial nucleus density for the uniform dispersion of nuclei in the subsequent high-temperature spur, thereby achieving gradient nucleation and making the graphite nucleation density on the surface and in the core of the thick-walled casting highly consistent.

[0058] Meanwhile, by controlling the proportion of electrolytic copper blocks between 0.63% and 0.78%, and in synergy with the copper wire mesh liquid surface heat compensation device in step five, a continuous alloying path is formed, consisting of bottom pre-positioning, gradient injection homogenization, and liquid surface heat compensation replenishment. This ensures that copper elements are always in a state of controlled release, uniform diffusion, and precise replenishment throughout the entire casting process, resulting in a highly uniform copper distribution, effectively strengthening the matrix structure, and improving the strength and wear resistance of the material.

[0059] Furthermore, limiting the tin content to a narrow range of 0.065% to 0.077% utilizes tin's properties of promoting pearlite formation and refining grains, which, combined with the directional solidification characteristics under negative pressure casting, further optimizes the microstructure of the casting. This precise tin content ensures that even in the core region of large, thick-walled castings with a wall thickness of up to 250 mm, the pearlite content remains consistently above 98%, and the proportion of type A graphite exceeds 95%. This solves the problem of coarsening in the core structure of large gray cast iron castings and avoids the grain boundary segregation and brittleness caused by excessive tin content.

[0060] In summary, the embodiments of this application can solve the performance instability caused by fluctuations in the amount of alloying elements added. Through the synergistic effect of each component and the precise coupling with subsequent process steps, the overall mechanical properties, microstructure uniformity, robustness and repeatability of gray cast iron cylinder blocks under complex working conditions are effectively improved.

[0061] The inoculant in the package comprises the following components by weight percentage: Si: 72%–75%, Al: 0.5%–0.8%, with the remainder being Fe, wherein the particle size of the inoculant in the package is 3 to 8 millimeters.

[0062] Silicon is a key element affecting the morphology and quantity of graphite precipitation in gray cast iron. The silicon content in the inoculant is limited to the range of 72% to 75% to provide sufficient nucleation sites for the molten iron and promote the uniform refinement of graphite. Specifically, the silicon content range can be achieved by selecting high-purity ferrosilicon alloys and precisely controlling the alloy ratio and smelting process, or by using a composite formulation of multiple silicon-based alloys.

[0063] In addition to its deoxidizing function, aluminum plays a crucial role in inoculants by combining with nitrogen in molten iron to form AlN compounds. These compounds act as heterogeneous nucleation sites, effectively enhancing graphite nucleation efficiency. By precisely adding a specific proportion of aluminum alloy or pure aluminum during inoculant production, the aluminum content can be controlled within the range of 0.5% to 0.8%. The particle size of the inoculant affects its dissolution rate and distribution uniformity in molten iron; therefore, controlling the particle size to 3 to 8 millimeters ensures that the inoculant's dissolution rate matches subsequent processes.

[0064] This embodiment limits the chemical composition and particle size range of the inoculant within the ladle, using a silicon content of 72% to 75% with an addition of 0.35%, ensuring the final silicon content falls precisely within the target window of 1.95% to 2.05%. An aluminum content of 0.5% to 0.8%, combined with nitrogen introduced through nitrogen pretreatment, forms AlN dual-phase nucleation cores, increasing the number of nucleation cores. A particle size of 3 to 8 mm, coupled with the timing of a small initial inoculation with molten iron and a large secondary counter-inoculation with molten iron, results in slow-release nucleation during the low-temperature initial inoculation stage and explosive, uniform release during the high-temperature counter-inoculation stage. These parameters work together to precisely control graphite nucleation throughout the entire process from the bottom of the ladle to the metering cup, ensuring a high degree of consistency between the core and surface graphite structure of large, thick-walled castings and resolving the problem of uneven microstructure. Simultaneously, the precise quantification of the inoculant composition and particle size effectively eliminates performance fluctuations caused by batch variations and particle size variations in traditional processes, significantly improving process repeatability and product consistency.

[0065] It should be noted that the supplementary inoculant and the inoculant used in the package have the same chemical composition. In other words, both use materials with the same elemental composition and proportion, so that the graphite cores formed by the two inoculation processes, namely in the package inoculation and supplementary inoculation, are consistent in terms of crystal characteristics, nucleation supercooling and growth mode. This avoids uneven graphite morphology or abnormal growth due to different core properties.

[0066] Furthermore, the mass of the supplementary inoculant is less than that of the inoculant already in the ladle. For example, the amount of supplementary inoculant can be controlled between 10% and 40% of the inoculant already in the ladle to achieve a refined inoculation effect. Alternatively, the dosage of supplementary inoculant can be dynamically adjusted based on the size of the metering cup, the temperature of the molten iron, or the wall thickness of the casting, but it should always remain smaller than the amount of inoculant already in the ladle. The purpose of this setting is to position supplementary inoculation as a local enhancement and compensation for the inoculation effect already in the ladle, rather than letting it dominate the inoculation process. By controlling the dosage of supplementary inoculant, it is possible to avoid excessive addition leading to coarse graphite, undercooling of the microstructure, or abnormal graphite morphology. At the same time, it can provide sufficient nucleation sites at the end of pouring or in specific areas to compensate for inoculation decline.

[0067] Therefore, this embodiment achieves precise control over the entire inoculation process by limiting the consistency and mass ratio of the supplementary inoculant and the inoculant in the ladle, combined with the copper wire mesh bag in the liquid surface heat compensation device. Consistent composition ensures the uniformity of the inoculation core properties introduced at different pouring stages, resulting in more coordinated microstructure growth and guaranteeing the stability of the graphitized cores. By constraining the mass ratio, the role of secondary inoculation as an auxiliary method is clearly defined. This differentiated design prevents microstructure overcooling or abnormal graphite morphology caused by excessive inoculant at the end of pouring. Thus, when supplementary inoculation is performed in the quantitative pouring cup, it can precisely compensate for inoculation decline during the molten iron flow process. Especially in thin-walled areas of the casting, the instantaneous overcooling generated when the copper wire mesh bag is immersed in the molten iron can supplement a high-density pulse nucleation, reducing the core density difference between thick and thin walls. Ultimately, through this gradient nucleation chain design with a large-scale uniform background and local high-density pulses, the graphite nucleation is kept within the optimal density range throughout the entire casting process. This improves the microstructure consistency between the core and surface of large, thick-walled castings, optimizes the flexibility of the process, and thus ensures the overall microstructure uniformity of the casting while also optimizing its mechanical properties.

[0068] In the process of pouring the target inoculated molten iron into the casting mold cavity, the injection rate is controlled in stages and end-of-life feeding is performed. Specifically, based on the cavity filling percentage, it is divided into the following four stages: initial filling stage, middle filling stage, final filling stage, and end-of-life feeding stage.

[0069] When the percentage of molten iron filling the mold cavity is less than 10%, it is in the initial stage of filling, and the molten iron is in contact with the bottom and sidewalls of the cavity for the first time. The goal is to control the molten iron to flow in at the lowest possible injection rate, allowing it to spread smoothly in a laminar flow state under the combined influence of gravity and the negative pressure in the mold cavity (-0.03MPa to -0.05MPa), avoiding impact, splashing, or air entrapment. The injection rate can be controlled by limiting the initial opening of the pouring plug or by slowly tilting the pouring ladle. The negative pressure environment at this stage allows even a very low injection rate to drive the molten iron to successfully fill the bottom of the cavity, which is impossible to achieve with gravity pouring alone.

[0070] When the molten iron fills 10% to 85% of the mold cavity, it is in the mid-filling stage. This indicates that the bottom of the cavity has been covered by molten iron, and it is necessary to quickly complete the filling of most of the cavity to reduce the temperature drop of the molten iron during the pouring process and maintain good fluidity. Therefore, a second injection rate is used for molten iron filling, and this second injection rate is set to the maximum flow rate. Under negative pressure, the flow resistance of the gas in the cavity to the molten iron is effectively reduced, making the filling smoother and more efficient at this rate. The second injection rate can be achieved by quickly raising the pouring plug or increasing the tilt angle of the pouring ladle, or it can be automatically switched according to a preset flow rate curve.

[0071] When the molten iron fills 85% but less than 100% of the mold cavity, it is in the final stage of filling. This indicates that the remaining gas space in the mold cavity is very small, and the final filling needs to be completed smoothly to prevent gas from being trapped inside the casting and forming porosity due to excessive flow rate, or turbulent molten iron from scouring the mold wall. Therefore, a third injection rate is used for molten iron filling. The third injection rate is numerically between the first and second injection rates, that is, the third injection rate is less than the second injection rate and greater than the first injection rate. This rate can be achieved by gradually narrowing the pouring plug or by combining it with flow sensor closed-loop control.

[0072] When the molten iron has completely filled the mold cavity, superheated molten iron, accounting for 0.3% to 0.8% of the cavity volume, can be added. This amount of replenishment is not arbitrarily set, but rather a preferred range that precisely matches the volume shrinkage rate of gray cast iron during solidification, approximately 1% to 3%, and the graphitization expansion effect. If the added molten iron is less than 0.3%, the replenishment is insufficient, and shrinkage porosity cannot be eliminated; if it is more than 0.8%, the superheated molten iron may damage the already solidified surface layer or cause component segregation. Replenishment can be achieved by using an independently heated, precisely metered replenishment device, which is injected immediately after the main pouring is completed.

[0073] Therefore, precise segmented rate control and end-feeding treatment of the pouring process of the target inoculated molten iron achieve accurate regulation of the casting filling dynamics. In the initial stage of filling, a first injection rate smoothly introduces molten iron, effectively avoiding violent impacts on the bottom of the cavity and reducing gas entrapment. In the middle stage of filling, a higher second injection rate quickly fills most of the cavity, preventing premature cooling of the molten iron and ensuring good fluidity. In the final stage of filling, a third injection rate smoothly completes the final filling of the cavity, avoiding turbulence caused by excessive flow rate, ensuring the integrity of the casting surface, and facilitating the smooth discharge of gas from the cavity. Finally, after the cavity is completely filled, superheated molten iron is added. Utilizing the high fluidity and thermal compensation effect of the superheated molten iron, shrinkage cavities and porosity problems generated during solidification shrinkage are effectively alleviated, thereby improving the internal density and microstructure uniformity of large, thick-walled castings.

[0074] The segmented injection rate control is matched with the environment of applying negative pressure to the casting mold cavity. Under negative pressure, the extremely slow first injection rate ensures that the molten iron fills the mold smoothly under the dual forces of gravity and negative pressure suction, avoiding impact and air entrapment. The faster second injection rate, under the action of negative pressure, reduces the flow resistance of gas in the cavity to the molten iron, resulting in higher filling efficiency and less temperature drop of the molten iron. The slower third injection rate, combined with the continuous venting under negative pressure, allows the gas to be discharged smoothly, effectively preventing the formation of porosity. In addition, during the feeding stage, the pressure difference between the negative pressure environment and the internal shrinkage negative pressure actively draws the superheated molten iron from the riser or gate into the shrinkage porosity area, achieving active forced feeding. The synergistic effect of negative pressure, segmented rate control, and precise feeding allows the graphitization expansion effect of gray cast iron itself to work in tandem with the externally added superheated molten iron, forming a dual densification of graphite expansion and external feeding. This eliminates porosity and shrinkage defects in large, thick-walled castings, achieves consistency between the surface and core structure of the casting, and improves the overall quality and mechanical properties of the gray cast iron cylinder block.

[0075] The following example will provide a more detailed explanation of the above technical solution: When manufacturing large gray cast iron cylinder blocks for marine low-speed diesel engines, the wall thickness typically reaches 180 to 250 mm, and the operating conditions are complex, placing stringent requirements on the material's strength, wear resistance, and microstructure uniformity. Traditional gray cast iron materials, when used to prepare such thick-walled castings, are prone to problems such as coarse graphite and uneven microstructure in the core and surface of the casting, making it difficult to meet design standards for mechanical properties.

[0076] To address the aforementioned technical problems, this embodiment employs a gray cast iron cylinder block with a specific composition. The chemical composition of this cylinder block, based on mass percentage statistics, specifically includes: carbon (C) 3.45%, silicon (Si) 2.00%, manganese (Mn) 0.95%, phosphorus (P) 0.035%, sulfur (S) 0.009%, copper (Cu) 0.65%, tin (Sn) 0.065%, with the remainder being iron (Fe).

[0077] The elements in this specific component work synergistically to improve the performance of the gray cast iron cylinder block. Specifically: First, the carbon content is controlled within the range of 3.40% to 3.50%, for example, 3.45%, to ensure that the molten iron has good fluidity, which is beneficial for filling large and complex castings, while avoiding excessively coarse graphite due to excessive carbon content.

[0078] Secondly, the silicon content is controlled within the range of 1.95% to 2.05%, for example, 2.00%. As a strong graphitizing element, its precise content ensures that graphitization can be fully achieved even in thick-section castings, effectively inhibiting the formation of white iron structure and promoting the generation of fine, uniformly distributed graphite flakes, thereby improving the machinability and wear resistance of the castings.

[0079] Secondly, controlling the manganese content within the range of 0.90% to 1.00%, such as 0.95%, helps stabilize the pearlite matrix and refine the pearlite structure, thereby improving the strength and hardness of the matrix and enhancing the overall mechanical properties and wear resistance of the cylinder block.

[0080] The phosphorus content is controlled in a low range of 0.020% to 0.050%, for example, 0.035%. The resulting phosphorus eutectic can be finely distributed in the matrix, which improves the wear resistance of the cylinder block without significantly reducing the toughness of the material.

[0081] The sulfur content was controlled at an extremely low level of 0.008% to 0.010%, for example, 0.009%, which reduced the adverse effects of sulfur on graphite morphology, reduced the tendency for white cast iron, and improved the effect of inoculation treatment.

[0082] The copper content is controlled within the range of 0.60% to 0.70%, for example, 0.65%. As a pearlite stabilizer and a mild graphitizing element, it promotes the formation of fine pearlite and helps to homogenize the microstructure. It also reduces the tendency for ferrite to appear in the core of thick cross-section castings, thereby improving strength and wear resistance.

[0083] The tin content is controlled within the range of 0.05% to 0.8%, for example, 0.065%. Even trace amounts of tin are a powerful pearlite stabilizer, which can significantly refine pearlite and effectively inhibit the formation of ferrite. Especially in the thick core area of ​​the casting, it can ensure that the entire cylinder block cross-section has a uniform pearlite matrix and mechanical properties from the surface to the core, solving the problem of uneven core structure in traditional castings.

[0084] Through the precise control of the chemical composition described above, this gray cast iron cylinder block, even when facing the solidification characteristics of large, thick-walled castings, can form fine, uniformly distributed graphite flakes and a dense pearlite matrix during the casting process. Compared with gray cast iron designed with conventional compositions, the gray cast iron cylinder block of this embodiment maintains good microstructure uniformity in both the core and surface, effectively avoiding problems such as coarse graphite and uneven microstructure, thus meeting the stringent requirements of marine low-speed diesel engines for high strength, high wear resistance, and good microstructure uniformity. This compositional design, combined with subsequent production processes such as molten iron pretreatment, ladle inoculant and copper-tin mixture coating, step-by-step molten iron injection, supplementary inoculation in the metering cup, and negative pressure pouring and segmented injection rate control, collectively ensures the superior performance of the product.

[0085] Thirdly, this application proposes a gray cast iron cylinder block for use in marine low-speed diesel engines, which is prepared using the manufacturing process of the gray cast iron cylinder block described in the second aspect embodiment above.

[0086] Reference Figure 2 , 3 and 4, Figure 2 This is a schematic diagram of the structure of the casting mold for the cylinder block of a marine low-speed diesel engine provided in an embodiment of this application. Figure 3 This is a schematic diagram of the casting mold for the cylinder block of a marine low-speed diesel engine provided in an embodiment of this application from another perspective. Figure 4 This is a schematic diagram of the casting mold for a marine low-speed diesel engine cylinder block provided in this application embodiment, from another perspective. As shown in the figure, this is a casting mold 200 for a four-cylinder marine low-speed diesel engine cylinder block, which is generally elongated. The wall thickness of the cylinder block is between 180 and 250 mm, and the entire casting weighs approximately 27 tons, making it a typical large, thick-walled casting. Castings of this size experience slow cooling in the central part during solidification, easily leading to problems such as coarse graphite and a loose microstructure. Furthermore, as shown in the figure, each of the four cylinder block units 210 has an arched combustion chamber 220, where the red pipe is the pouring channel 230, through which molten iron flows.

[0087] In one specific embodiment, the production process solution provided in the second aspect embodiment described above is adopted.

[0088] In terms of chemical composition, the carbon content is controlled at 3.40% to 3.45%, the silicon content at 1.95% to 2.05%, the copper content at 0.60% to 0.70%, and the tin content at 0.06% to 0.07%. In terms of process, it includes nitrogen pretreatment, pre-placing the inoculant at the bottom of the molten iron ladle and injecting it in a gradient, using a liquid surface thermal compensation device for secondary inoculation, and segmented casting and feeding under negative pressure.

[0089] The carbon content is set within this range to ensure sufficient carbon supersaturation in the initial pour of the molten iron to precipitate primary graphite nuclei, laying a foundation for subsequent gradient nucleation. The copper and tin ratio is matched with the process path of pre-placed inoculant at the bottom of the ladle, gradient injection, and copper mesh replenishment, forming a continuous alloying chain that ensures uniform distribution of copper and tin throughout the casting. Because the cylinder block wall thickness reaches 250 mm, core solidification is slow, graphite tends to be coarse, and pearlite may be insufficient. Therefore, nitrogen pretreatment is used to form fine nitride particles in the molten iron, which, together with manganese and sulfur to form manganese sulfide, constitute a biphase heterogeneous nucleation core, increasing the graphite nucleus density. Then, by pre-placing an inoculant at the bottom of the ladle, a portion of the molten iron is added during the initial pour to create nuclei at the bottom. The remaining molten iron is then used to flush out the nuclei, evenly dispersing them throughout the entire molten iron. This ensures that even in a 250 mm thick core, a stable microstructure of over 95% type A graphite and over 98% pearlite can be obtained.

[0090] The casting mold 200 has multiple gating channels 230, allowing molten iron to flow from the pouring cup 240 to various corners of the mold. However, as shown in the figure, the long distance of the gating channels 230 results in a long pouring time, causing the inoculant to easily degrade. Therefore, a copper wire mesh bag containing replenished inoculant is placed inside the pouring cup 240. When the molten iron fills the pouring cup 240, the inoculant is released, and nucleation occurs again during the pouring process. This ensures the nucleation capability of the molten iron as it flows to the end of the mold cavity.

[0091] Secondly, cylinder bodies vary in thickness. During conventional casting, the flow and solidification speed of molten iron differs at different thicknesses, easily leading to air entrapment and shrinkage porosity. Therefore, negative pressure is applied to the casting mold 200. This negative pressure allows for smoother venting of the cavity and enhances the feeding effect of graphitization expansion. The segmented filling speed is controlled by using the lowest speed in the initial stage to allow the molten iron to spread smoothly and avoid impact and air entrapment. The highest speed is used in the middle stage for rapid filling to reduce the temperature drop of the molten iron. In the final stage, a medium speed is used in conjunction with negative pressure venting to complete the filling smoothly. This ensures that the molten iron is evenly distributed regardless of the wall thickness and also guarantees a more uniform temperature field in the cavity, avoiding local overheating or undercooling. Because the internal shrinkage generates negative pressure during the solidification of the casting, combined with the external negative pressure environment to form a pressure difference, a small amount of molten iron is actively drawn into the shrinkage porosity area when feeding is added after the casting is fully filled. This perfectly matches the volume shrinkage during the solidification of gray cast iron, eliminating shrinkage porosity and gas holes, and achieving a casting density of over 99.5%.

[0092] Therefore, the resulting gray cast iron cylinder blocks exhibit a highly uniform microstructure from surface to core. The tensile strength of single-cast test bars ranges from 385 to 420 MPa, with a hardness of 255 to 300 HBW. The tensile strength of attached-cast test blocks ranges from 275 to 310 MPa, with a hardness of 240 to 280 HBW. The hardness of the casting itself reaches 230 to 260 HBW. This approach solves the long-standing problem of coarse microstructure and poor performance in large, thick-walled castings. Furthermore, by replacing more expensive elements like nickel and chromium with copper and tin, and by using recycled iron balls, costs are well controlled. Achieving the target microstructure stably within a wider process window increases the yield from 70% to 80% in conventional processes to over 95%, balancing high performance and low cost.

[0093] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application 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 this application.

Claims

1. A gray cast iron cylinder block, characterized in that, The gray cast iron cylinder block, based on a weight percentage statistical analysis, comprises the following components: C: 3.40%–3.50%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.10%, Cu: 0.60%–0.70%, Sn: 0.05%–0.08%, with the remainder being Fe.

2. The gray cast iron cylinder block according to claim 1, characterized in that, The gray cast iron cylinder block, based on a mass percentage statistical analysis, comprises the following components: C: 3.40%–3.45%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.10%, Cu: 0.60%–0.70%, Sn: 0.06%–0.07%, with the remainder being Fe.

3. The manufacturing process of gray cast iron cylinder blocks, characterized in that, Includes the following steps: Step 1: Heat the original molten iron to 1500 to 1520 degrees Celsius for slag removal, and then cool the molten iron after slag removal to 1450 to 1470 degrees Celsius for settling. During the settling process, nitrogen gas is blown into the molten iron for pretreatment to obtain pretreated molten iron. Step 2: Place a pre-prepared inoculant at the bottom of the ladle and cover it with a mixture of electrolytic copper blocks and tin granules. Step 3: Pour 30% of the pretreated molten iron by mass into the ladle to melt the inoculant and the mixture layer inside the ladle; Step 4: Inject the remaining pretreated molten iron into the ladle below the liquid surface along the diversion groove set on the side wall of the ladle to form inoculated molten iron in the ladle; Step 5: Pour the molten iron in the ladle into a metering pouring cup. The metering pouring cup includes a liquid surface heat compensation device, which includes a copper wire mesh bag suspended above the metering pouring cup. The copper wire mesh bag is also filled with a supplementary inoculant. When the molten iron in the ladle fills the metering pouring cup, the copper wire mesh bag is immersed in the molten iron in the ladle to release the supplementary inoculant, thus obtaining the target molten iron. Step Six: Apply negative pressure to the casting mold cavity and pour the target inoculated iron into the casting mold cavity. After solidification, a gray cast iron cylinder is obtained. The gray cast iron cylinder body, based on mass percentage, includes the following components: C: 3.40%–3.50%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.10%, Cu: 0.60%–0.70%, Sn: 0.05%–0.08%, with the remainder being Fe.

4. The production process according to claim 3, characterized in that, The gray cast iron cylinder, based on a percentage by mass, comprises the following components: C: 3.40%–3.45%, Si: 1.95%–2.05%, Mn: 0.90%–1.00%, P: 0.020%–0.050%, S: 0.08%–0.10%, Cu: 0.60%–0.70%, Sn: 0.06%–0.07%, with the remainder being Fe.

5. The production process according to claim 3, characterized in that, The original molten iron mentioned in step one includes the following components based on mass percentage: C: 3.50–3.55%, Si: 1.60–1.75%, Mn: 0.9–1.0%, P: 0.020–0.050%, S: 0.08–0.10%, with the remainder being Fe.

6. The production process according to claim 3, characterized in that, In step two, the inoculant in the ladle accounts for 0.35% of the total mass of the molten iron, the electrolytic copper block accounts for 0.63-0.78% of the total mass of the molten iron, and the tin granules account for 0.065-0.077% of the total mass of the molten iron.

7. The production process according to claim 6, characterized in that, The inoculant in the package comprises the following components by weight percentage: Si: 72-75%, Al: 0.5-0.8%, with the remainder being Fe, wherein the particle size of the inoculant in the package is 3 to 8 millimeters.

8. The production process according to claim 7, characterized in that, The chemical composition of the supplemental progesterone is the same as that of the progesterone in the package, and the mass of the supplemental progesterone is less than the mass of the progesterone in the package.

9. The production process according to claim 3, characterized in that, During the process of pouring the target inoculated molten iron into the casting mold cavity: When the cavity filling percentage is less than 10%, the target inoculated molten iron is controlled to flow into the cavity at a first injection rate. When the cavity filling percentage reaches 10% to 85%, the target inoculated molten iron is controlled to fill the cavity at a second injection rate; When the cavity filling percentage is greater than 85% but less than 100%, the target inoculated molten iron is controlled to flow into the cavity at a third injection rate; When the cavity filling percentage reaches 100%, add superheated molten iron accounting for 0.3% to 0.8% of the cavity volume into the cavity; The third injection rate is less than the second injection rate but greater than the first injection rate.

10. A gray cast iron cylinder block, characterized in that, It is used in marine low-speed diesel engines and is prepared using the manufacturing process of gray cast iron cylinder blocks as described in any one of claims 3 to 9.

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