Production method of high-strength gray cast iron

Abstract

The invention provides a production method of high-strength gray cast iron, which is characterized in that the high-strength gray cast iron is produced by optimizing the element types of the gray cast iron, adopting the theory of passivating graphite by rare earth, magnesium, nitrogen and sulfur elements and adopting rare earth magnesium alloy to synthesize cast iron according to a high silicon-carbon ratio, alloying and proportioning, in-ladle inoculation, furnace-front stream inoculation and instantaneous inoculation processes. According to the preparation method, a single casting sample and an attached casting sample with the tensile strength being 350 MPa or above are prepared, the problems that in a traditional preparation method, a large amount of alloy is added, and poor matrix structures such as supercooled graphite and carbide are likely to appear are effectively solved, the cracking risk of thin-wall parts is eliminated, the preparation process is simple and easy to operate, the carbide content of the prepared high-strength gray cast iron does not exceed 1%, and the service life of the high-strength gray cast iron is prolonged. Bad tissues such as supercooled graphite do not appear, and the produced thin-wall box type castings do not have any casting defects.

Description

Technical Field

[0001] The invention belongs to the technical field of gray cast iron preparation, and in particular relates to a production method of high-strength gray cast iron. Background Art

[0002] A single-cast specimen is a test piece cast separately for experimental use. It can be used to analyze the composition of molten iron and check for inclusions. Its cooling conditions are different from those of the actual workpiece, and its metallographic structure is different. Therefore, it is of little value to use it for mechanical testing. An attached-cast specimen is a test block cavity made on the mold. The test block is cast together with the part to be cast. Its composition is the same as that of the workpiece to be cast, and its cooling conditions are basically the same. It can be used to test mechanical tests. Some destructive tests can be done directly with the test block, such as hardness testing and breaking, to avoid direct testing of the workpiece and causing damage to the workpiece. In the past, HT300 was produced by using low carbon equivalent, high alloying, and flow inoculation methods to achieve a single-cast specimen tensile strength of not less than 300MPa. However, there are few cases where the tensile strength of the attached cast specimen is required to be not less than 300MPa. According to production experience, the tensile strength of the single-cast specimen must be not less than 350MPa, and the tensile strength of the attached cast specimen may reach more than 300MPa. Moreover, more alloys are added, which is prone to undesirable matrix structures such as supercooled graphite and carbides. Thin-walled parts are also at risk of cracking. Therefore, it is necessary to make improvements. Summary of the invention

[0003] The technical problem solved by the present invention is as follows: a production method of high-strength gray cast iron is provided, by optimizing the element types of gray cast iron, adopting the theory of passivating graphite with rare earth, magnesium, nitrogen and sulfur elements, synthesizing cast iron with a high silicon-carbon ratio using rare earth magnesium alloy, alloying ingredients, inoculation in a ladle, in-flow inoculation in front of a furnace and instantaneous inoculation processes to produce high-strength gray cast iron, and preparing single-cast samples and attached-cast samples with a tensile strength of more than 350 MPa, effectively solving the problems of adding more alloys and being prone to undesirable matrix structures such as supercooled graphite and carbide in traditional preparation methods, eliminating the risk of cracking of thin-walled parts, and the preparation process is simple and easy to operate. The carbide content of the prepared high-strength gray cast iron does not exceed 1%, and undesirable structures such as supercooled graphite do not appear, and the produced thin-walled box castings do not have any casting defects.

[0004] The technical solution adopted by the present invention is a production method of high-strength gray cast iron, wherein the high-strength gray cast iron material contains the following elements in mass percentage: C: 2.95% to 3.05%, Si: 1.9% to 2.1%, Mn: 0.8% to 0.89%, P≤0.06%, S: 0.061% to 0.08%, Cu: 0.45% to 0.55%, Ni: 0.2% to 0.3%, Sb: 0.026% to 0.032, Cr: 0.15% to 0.24%, Sn: 0.020% to 0.030%, N: 0.009% to 0.012%, Mg: 0.01% to 0.02%, RE: 0.015% to 0.020%, and the rest is Fe; the specific preparation comprises the following steps:

[0005] 1) Charge: The charge includes 60% to 70% scrap steel, 20% to 30% recycled material and 10% pig iron according to the mass percentage;

[0006] 2) Adding order: add 10% pig iron to the bottom of the smelting furnace, then add 1 / 2 of silicon carbide and 1 / 2 of the recarburizer in sequence, then add 30% to 35% of scrap steel, the remaining 1 / 2 of the recarburizer, 30% to 35% of scrap steel and 20% to 30% of the recycled materials in sequence, and finally add the remaining 1 / 2 of the silicon carbide. When the original molten iron in the smelting furnace and the added ingredients are melted evenly and the temperature rises to 1420°C to 1440°C, take samples, and finally use a cast steel sample spoon coated with an alcohol-based coating on the surface to dig out 100mm to 200mm of the molten iron casting spectrum and chemical samples below the molten iron surface;

[0007] 3) Inoculation treatment: A vermicular casting ladle is used to produce vermicular iron by the flushing method. When the molten iron is discharged from the furnace, 0.25% by mass of rare earth magnesium ferrosilicon alloy is added to one side of the bottom of the ladle, and then 0.3% by mass of ferrochrome, 0.025% by mass of pure tin, and 0.1% by mass of calcium barium inoculant are covered layer by layer, and finally 0.08-0.12% by mass of silicon steel sheets are evenly covered on it. The molten iron is flushed into the other side of the ladle. When the molten iron is discharged to 2 / 3, the remaining 1 / 3 of the molten iron is added with 0.4% by mass of antimony-containing inoculant. When casting single casting samples and castings, 0.1% by mass of silicon manganese zirconium inoculant is used to flow into the mold with the molten iron for instantaneous inoculation.

[0008] In the above step 2), the mass percentage of the silicon carbide is 0.85%, and the mass percentage of the recarburizer added each time is 0.7%.

[0009] In the above step 2) and the above step 3), the rare earth content of the rare earth magnesium ferrosilicon alloy is 5.3% to 6.3%, the magnesium content is 4.8% to 5.8%, the silicon content is 44% to 47%, the calcium content is 1.5% to 2.5%, and the remainder is iron.

[0010] In the above step 3), the particle size of the ferrochrome is 5 mm to 10 mm and the chromium content is 60% to 70%.

[0011] In the above step 3), the antimony-containing inoculant composition includes 6.21% by weight of antimony, 68% by weight of silicon, and the remainder is iron; the silicon-manganese-zirconium inoculant composition includes 62%-68% by weight of silicon, 3.0%-4.5% by weight of manganese, and 3.0%-4.5% by weight of zirconium.

[0012] Furthermore, the poured single casting sample is kept warm in the resin sand mold to below 200° C. and boxed and cleaned, and the casting is kept warm in the resin sand mold to below 200° C. and boxed and cleaned.

[0013] Furthermore, when the resin sand mold is used to produce thin-walled box-type castings with a wall thickness ranging from 12 mm to 50 mm, the furnace temperature is 1480°C to 1500°C, and the molten iron pouring temperature is 1380°C to 1400°C.

[0014] The advantages of the present invention compared with the prior art are:

[0015] 1. This technical solution optimizes the element types of gray cast iron, adopts the theory of rare earth, magnesium, nitrogen and sulfur elements to passivate graphite, uses rare earth magnesium alloy to synthesize cast iron with high silicon-carbon ratio, alloys ingredients, and produces high-strength gray cast iron by ladle inoculation, furnace front flow inoculation and instantaneous inoculation processes. Single casting specimens and attached casting specimens with a tensile strength of more than 350MPa are prepared, which effectively solves the problems of traditional preparation methods such as adding too much alloy, prone to the occurrence of undesirable matrix structures such as supercooled graphite and carbide, and eliminates the risk of cracking of thin-walled parts;

[0016] 2. This technical solution adopts rare earth magnesium alloy inoculant in the ladle and antimony-containing inoculant to rush into inoculant after being inoculated out of the furnace, and silicon manganese zirconium instant inoculant, that is, triple inoculant, which can effectively prevent the appearance of supercooled graphite, and can also use rare earth magnesium antimony to passivate graphite, making the graphite tip round, blunt, short and thick, greatly reducing the cutting effect of graphite on the matrix;

[0017] 3. The preparation process of this technical solution is simple and easy to operate. The carbide content of the prepared high-strength gray cast iron does not exceed 1%, and no undesirable structures such as supercooled graphite appear. The produced thin-walled box castings do not have any casting defects. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0019] In this document, the terms "comprises", "comprising" or any other variation thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further limitations. The elements defined by the sentence "comprising a ..." do not exclude the presence of other identical elements in the process, method, article or device comprising the elements.

[0020] Example 1

[0021] A method for producing high-strength gray cast iron, wherein the high-strength gray cast iron material comprises the following elements in percentage by mass: C: 2.98%, Si: 1.95%, Mn: 0.82%, P: 0.0:3%, S: 0.065%, Cu: 0.48%, Ni: 0.23%, Sb: 0.028, Cr: 0.18%, Sn: 0.023%, N: 0.0095%, Mg: 0.012%, RE: 0.016%, and the rest is Fe;

[0022] The specific preparation includes the following steps:

[0023] 1) Charge: The charge includes 62% scrap steel, 28% recycled material and 10% pig iron by mass percentage;

[0024] 2) Adding order: add 10% pig iron to the bottom of the smelting furnace, then add 0.425% silicon carbide and 0.7% recarburizer by mass in sequence, then add 31% scrap steel, 0.7% recarburizer, 31% scrap steel, 28% recycled materials in sequence, and finally add 0.425% silicon carbide by mass. When the original molten iron in the smelting furnace and the added ingredients are melted evenly and heated to 1420°C, take samples, and finally use a cast steel sample spoon coated with alcohol-based coating on the surface to dig out the molten iron casting spectrum and chemical samples 120mm below the molten iron surface; adding silicon carbide can help increase the number of eutectic groups and obtain fine and evenly distributed A-type graphite. The recarburizer and silicon carbide can form nucleation particles in the original molten iron, which plays a role in pre-treating the molten iron and reducing the tendency of the molten iron to be overcooled. In addition, silicon carbide and the recarburizer contain a certain amount of nitrogen, which can add nitrogen to the molten iron;

[0025] 3) Inoculation treatment: The vermicular casting ladle of vermicular iron is produced by the flushing method. When the molten iron comes out of the furnace, 0.25% by mass of rare earth magnesium ferrosilicon alloy is added to one side of the bottom of the ladle, wherein the rare earth content of the rare earth magnesium ferrosilicon alloy is 5.5%, the magnesium content is 5.0%, the silicon content is 44, the calcium content is 2.5%, and the rest is iron; then 0.3% by mass of ferrochrome, 0.025% of pure tin, and 0.1% of calcium-barium inoculant are covered layer by layer, wherein the particle size of the ferrochrome is 6mm and the chromium content is 63%; finally, 0.3% by mass of ferrochrome is evenly covered on the top. The silicon steel sheet with an iron content of 0.09% is poured into the other side of the ladle. When the iron is discharged to 2 / 3, the remaining 1 / 3 of the iron is added with an antimony-containing inoculant with a mass percentage of 0.4%, wherein the antimony-containing inoculant comprises 6.21% antimony and 68% silicon by weight, and the remainder is iron. When casting single casting samples and castings, a silicon-manganese-zirconium inoculant with a mass percentage of 0.12% is used to flow into the mold with the iron for instantaneous inoculation, wherein the silicon-manganese-zirconium inoculant comprises 64% silicon, 3.6% manganese and 3.2% zirconium by weight.

[0026] Example 2

[0027] A method for producing high-strength gray cast iron, wherein the high-strength gray cast iron material comprises the following elements in percentage by mass: C: 3.00%, Si: 1.98%, Mn: 0.85%, P: 0.04%, S: 0.07%, Cu: 0.50%, Ni: 0.25%, Sb: 0.030%, Cr: 0.20%, Sn: 0.025%, N: 0.0098%, Mg: 0.015%, RE: 0.018%, and the rest is Fe;

[0028] The specific preparation includes the following steps:

[0029] 1) Charge: The charge includes 65% scrap steel, 25% recycled material and 10% pig iron by mass percentage;

[0030] 2) Adding order: add 10% pig iron to the bottom of the smelting furnace, then add 0.425% silicon carbide and 0.7% recarburizer by mass in sequence, then add 32% scrap steel, 0.7% recarburizer by mass, 33% scrap steel and 25% recycled materials in sequence, and finally add 0.425% silicon carbide, and take samples when the original molten iron in the smelting furnace and the added ingredients are melted evenly and heated to 1430°C, and finally use a cast steel sample spoon coated with alcohol-based coating on the surface to dig out the molten iron casting spectrum and chemical samples 150mm below the molten iron surface; adding silicon carbide can help increase the number of eutectic groups and obtain fine and evenly distributed A-type graphite, and the recarburizer and silicon carbide can form nucleation particles in the original molten iron, which plays a role in pre-treating the molten iron and reducing the tendency of the molten iron to be overcooled. In addition, silicon carbide and the recarburizer contain a certain amount of nitrogen, which can add nitrogen to the molten iron;

[0031] 3) Inoculation treatment: The vermicular casting ladle of vermicular iron is produced by the flushing method. When the molten iron comes out of the furnace, 0.25% by mass of rare earth magnesium ferrosilicon alloy is added to one side of the bottom of the ladle, wherein the rare earth content of the rare earth magnesium ferrosilicon alloy is 5.8%, the magnesium content is 5.2%, the silicon content is 45%, the calcium content is 1.5%, and the rest is iron; then 0.3% by mass of ferrochrome, 0.025% of pure tin, and 0.1% of calcium-barium inoculant are layered on it, wherein the particle size of the ferrochrome is 8mm and the chromium content is 65%; finally, 0.3% by mass of ferrochrome is evenly covered on it. The ratio of silicon steel sheet is 0.1%, and the molten iron is poured into the other side of the ladle. When the molten iron is discharged to 2 / 3, the remaining 1 / 3 of the molten iron is added with 0.4% by weight of antimony-containing inoculant, wherein the antimony-containing inoculant composition includes 6.21% by weight of antimony, 68% by weight of silicon, and the rest is iron; when pouring single casting samples and castings, a 0.13% by weight silicon-manganese-zirconium inoculant is used to flow into the casting mold with the molten iron for instantaneous inoculation, wherein the silicon-manganese-zirconium inoculant composition includes 65% by weight of silicon, 4.0% by weight of manganese, and 3.8% by weight of zirconium;

[0032] Example 3

[0033] A method for producing high-strength gray cast iron, wherein the high-strength gray cast iron material comprises the following elements in percentage by mass: C: 3.02%, Si: 2.1%, Mn: 0.89%, P: 0.05%, S: 0.078%, Cu: 0.52%, Ni: 0.28%, Sb: 0.032%, Cr: 0.22%, Sn: 0.028%, N: 0.010%, Mg: 0.018%, RE: 0.020%, and the rest is Fe;

[0034] The specific preparation includes the following steps:

[0035] 1) Charge: The charge includes 70% scrap steel, 20% recycled material and 10% pig iron by mass percentage;

[0036] 2) Adding order: add 10% pig iron to the bottom of the smelting furnace, then add 0.425% silicon carbide and 0.7% recarburizer by mass in sequence, then add 35% scrap steel, 0.7% recarburizer by mass, 35% scrap steel and 20% recycled materials in sequence, and finally add 0.425% silicon carbide. When the original molten iron in the smelting furnace and the added ingredients are melted evenly and heated to 1440°C, take samples, and finally use a cast steel sample spoon coated with alcohol-based coating on the surface to dig out the molten iron casting spectrum and chemical samples 180mm below the molten iron surface; adding silicon carbide can help increase the number of eutectic groups and obtain fine and evenly distributed A-type graphite. The recarburizer and silicon carbide can form nucleation particles in the original molten iron, which plays a role in pre-treating the molten iron and reducing the tendency of the molten iron to be overcooled. In addition, silicon carbide and the recarburizer contain a certain amount of nitrogen, which can add nitrogen to the molten iron;

[0037] 3) Inoculation treatment: The vermicular casting ladle of vermicular iron is produced by the flushing method. When the molten iron comes out of the furnace, 0.25% by mass of rare earth magnesium ferrosilicon alloy is added to one side of the bottom of the ladle, wherein the rare earth content of the rare earth magnesium ferrosilicon alloy is 6.3%, the magnesium content is 5.8%, the silicon content is 47%, the calcium content is 1.5%, and the rest is iron; then 0.3% by mass of ferrochrome, 0.025% of pure tin, and 0.1% of calcium-barium inoculant are layered on it, wherein the particle size of the ferrochrome is 10mm and the chromium content is 68%; finally, 0.3% by mass of ferrochrome is evenly covered on it. The ratio of silicon steel sheet is 0.12%, and molten iron is poured into the other side of the ladle. When the molten iron is discharged to 2 / 3, the remaining 1 / 3 of the molten iron is added with 0.4% by weight antimony-containing inoculant, wherein the antimony-containing inoculant comprises 6.21% by weight antimony, 68% by weight silicon, and the rest is iron; when pouring single casting samples and castings, a silicon-manganese-zirconium inoculant with a mass percentage of 0.14% is used to flow into the mold with the molten iron for instantaneous inoculation, wherein the silicon-manganese-zirconium inoculant comprises 68% by weight silicon, 4.2% by weight manganese, and 4.5% by weight zirconium.

[0038] In the above embodiment, the cast single cast sample is kept warm at below 200°C in the resin sand mold and boxed and cleaned, and the casting is kept warm at below 200°C in the resin sand mold and boxed and cleaned; specifically, the furnace temperature of the resin sand mold when producing thin-walled box-type castings with a wall thickness range of 12mm to 50mm is 1480°C to 1500°C, and the molten iron pouring temperature is 1380°C to 1400°C.

[0039] In this scheme, C and Si mainly play the role of graphitization, especially carbon mainly exists in gray iron in the form of flake graphite, which is the main component of gray iron matrix. Flake graphite plays an important role in the physical properties of gray iron such as shock absorption and thermal conductivity; Si mainly plays the role of graphitization to prevent white cast iron; Mn: the main alloying element in gray iron, mainly plays the role of forming pearlite, it generally reacts with S to produce MnS, prevents the formation of FeS and thus avoids hot cracks in castings, in addition, MnS has a certain inoculation effect, but excessive Mn will produce carbides at the intergranular position, therefore, the amount of Mn is controlled at 0.8% to 0.89%; P: has no obvious beneficial effect on conventional gray cast iron, and too high a content will produce phosphorus eutectic and cause cold cracking of castings, which is not suitable for this invention. The content of thin-walled parts in the casting should be controlled within 0.06%; S: promotes the inoculation of gray cast iron; Cu: can increase and refine pearlite in gray cast iron, has a certain graphitization ability to reduce white cast iron, and obtains the entire pearlite matrix together with Cr; Ni: weak pearlite formation effect, can refine graphite and pearlite, improve the density and toughness of castings, and make the hardness of different cross sections uniform; Sb: the ability to promote pearlite formation is twice that of Sn and 100 times that of Cu; Sn: increases pearlite and eliminates ferrite; N: can promote the refinement of pearlite in gray cast iron, passivate graphite flakes, and reduce the cutting effect of graphite on the matrix; Mg and RE: both passivate graphite in gray cast iron, reduce graphite length, and reduce the cutting effect of graphite on the matrix;

[0040] The chemical composition of the original molten iron in the smelting furnace is as follows:

[0041]

[0042] Among them, rare earth magnesium alloy is used to inoculate molten iron. On the one hand, rare earth and magnesium have a passivating effect on graphite flakes, making the tip of the graphite flakes rounded, preventing graphite from growing in the length direction, shortening the graphite and increasing its curvature. On the other hand, magnesium can consume excess sulfur in the molten iron to form magnesium sulfide particles, which can play a role in heterogeneous nucleation and promote inoculation. Calcium-barium inoculant: has a long-term inoculation effect, prevents inoculation decline, reduces casting chill, inhibits carbide formation, and improves the processing performance of castings. The Sb-containing inoculant has the same inoculation effect as the general inoculation, which can reduce chill. In addition, antimony can be added to the molten iron to effectively reduce the negative effects of antimony, such as the production of carbides. Silicon-manganese-zirconium inoculant: manganese And zirconium elements can promote the formation of pearlite, improve material strength, as an instantaneous inoculant, can prevent inoculation decay; RE is a group of elements contained in rare earth magnesium alloys, N mainly comes from scrap steel, recarburizer, silicon carbide and other raw and auxiliary materials; according to current research, Sb, N, Mg, RE in gray cast iron can passivate graphite tips, reduce graphite length, increase graphite sheet thickness and curvature, effectively reduce the graphite on the matrix cutting effect, reduce the risk of casting cracking, among which Sb and N increase and refine pearlite, increase the matrix pearlite content and reduce the spacing between pearlite sheets can effectively improve the gray cast iron matrix strength and hardness, the passivation of graphite and the increase in matrix strength can effectively improve the tensile strength of gray iron.

[0043] The high-strength gray cast iron produced by this technical solution has a carbon equivalent of about 3.7 and a silicon-carbon ratio of about 0.65%. After testing, the tensile strength of the φ30 single-cast specimen and the attached cast specimen is above 350MPa, the fine-flaky pearlite matrix, the carbide does not exceed 1%, and no undesirable structures such as supercooled graphite appear. The produced thin-walled box-type castings do not have any casting defects.

[0044] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations within the meaning and scope of the equivalent elements of the claims be included in the invention. Any marking in a claim should not be considered as limiting the claim to which it relates.

[0045] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for producing high-strength grey cast iron, characterized in that: The high-strength gray cast iron material contains the following elements in percentage by mass: C: 2.95% to 3.05%, Si: 1.9% to 2.1%, Mn: 0.8% to 0.89%, P≤0.06%, S: 0.061% to 0.08%, Cu: 0.45% to 0.55%, Ni: 0.2% to 0.3%, Sb: 0.026% to 0.032%, Cr: 0.15% to 0.24%, Sn: 0.020% to 0.030%, N: 0.009% to 0.012%, Mg: 0.01% to 0.02%, RE: 0.015% to 0.020%, and the rest is Fe; The specific preparation includes the following steps: 1) Charge: The charge includes 60% to 70% scrap steel, 20% to 30% recycled material and 10% pig iron according to the mass percentage; 2) Adding order: add 10% pig iron to the bottom of the smelting furnace, then add 1 / 2 of silicon carbide and 1 / 2 of the recarburizer in sequence, then add 30% to 35% of scrap steel, the remaining 1 / 2 of the recarburizer, 30% to 35% of scrap steel and 20% to 30% of the recycled materials in sequence, and finally add the remaining 1 / 2 of the silicon carbide. When the original molten iron in the smelting furnace and the added ingredients are melted evenly and the temperature rises to 1420°C to 1440°C, take samples, and finally use a cast steel sample spoon coated with an alcohol-based coating on the surface to dig out 100mm to 200mm of the molten iron casting spectrum and chemical samples below the molten iron surface; 3) Inoculation treatment: A vermicular casting ladle is used to produce vermicular iron by the flushing method. When the molten iron is discharged from the furnace, 0.25% by mass of rare earth magnesium ferrosilicon alloy is added to one side of the bottom of the ladle, and then 0.3% by mass of ferrochrome, 0.025% by mass of pure tin, and 0.1% by mass of calcium barium inoculant are covered layer by layer, and finally 0.08-0.12% by mass of silicon steel sheets are evenly covered on it. The molten iron is flushed into the other side of the ladle. When the molten iron is discharged to 2 / 3, the remaining 1 / 3 of the molten iron is added with 0.4% by mass of antimony-containing inoculant. When casting single casting samples and castings, 0.1% by mass of silicon manganese zirconium inoculant is used to flow into the mold with the molten iron for instantaneous inoculation.

2. The method for producing high-strength grey cast iron according to claim 1, characterized in that: In the above step 2), the mass percentage of the silicon carbide is 0.85%, and the mass percentage of the recarburizer added each time is 0.7%.

3. The method for producing high-strength grey cast iron according to claim 1, characterized in that: In the above step 2) and the above step 3), the rare earth content of the rare earth magnesium ferrosilicon alloy is 5.3% to 6.3%, the magnesium content is 4.8% to 5.8%, the silicon content is 44% to 47%, the calcium content is 1.5% to 2.5%, and the remainder is iron.

4. The method for producing high-strength grey cast iron according to claim 1, characterized in that: In the above step 3), the particle size of the ferrochrome is 5 mm to 10 mm and the chromium content is 60% to 70%.

5. The method for producing high-strength grey cast iron according to claim 1, characterized in that: In the above step 3), the antimony-containing inoculant composition includes 6.21% by weight of antimony, 68% by weight of silicon, and the remainder is iron; the silicon-manganese-zirconium inoculant composition includes 62%-68% by weight of silicon, 3.0%-4.5% by weight of manganese, and 3.0%-4.5% by weight of zirconium.

6. The method for producing high-strength grey cast iron according to any one of claims 1 to 5, characterized in that: The poured single casting sample is kept warm in the resin sand mold to below 200° C. and then boxed and cleaned, and the casting is kept warm in the resin sand mold to below 200° C. and then boxed and cleaned.

7. The method for producing high-strength grey cast iron according to claim 6, characterized in that: When the resin sand mold is used to produce thin-walled box-type castings with a wall thickness ranging from 12mm to 50mm, the furnace temperature is 1480°C to 1500°C, and the molten iron pouring temperature is 1380°C to 1400°C.

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