Grey cast iron, preparation method and application of ferromanganese nitride

Abstract

The present invention provides a gray cast iron, a preparation method and the application of ferromanganese nitride. The preparation method of the gray cast iron comprises the following steps: configuring and melting raw materials to obtain molten iron, wherein, by mass percentage, C in the molten iron is 3.40% - 3.50%, Si is 1.30% - 1.50%, Mn is 0.60% - 0.70%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe; providing a ladle, adding an inoculant to the bottom of the ladle, and then injecting the molten iron into the ladle for inoculation treatment, wherein, based on the mass of the molten iron, the inoculant comprises 0.40% - 0.60% of 75Si-Fe, 0.06% - 0.08% of Sn and 0.2% - 0.4% of ferromanganese nitride; pouring the inoculated molten iron into a mold to obtain gray cast iron. The preparation method of the present invention has a simple process and low cost, and the gray cast iron produced has high strength and hardness.

Description

Technical Field

[0001] The present invention relates to the technical field of gray cast iron, and particularly relates to a gray cast iron, a preparation method thereof, and the application of ferromanganese nitride. Background Art

[0002] As a traditional metal material, gray cast iron has a large proportion in fields such as automobiles and construction machinery, which is mainly related to its good casting formability, low price, excellent corrosion resistance, wear resistance, high hardness, and easy control of casting quality.

[0003] With the development of the modern automotive industry towards lightweight and high-power, the requirements for the thin-wall high-strength performance of gray cast iron materials are getting higher and higher. To improve the strength and hardness of gray cast iron, the existing solution is to add precious metals such as copper, molybdenum, and chromium during preparation to refine the grains. However, the addition of a large amount of copper and molybdenum not only increases the tendency of white mouth but also increases the production cost accordingly, reducing the market competitiveness. Moreover, for some gray cast iron used in brake discs, etc., it is required to have a higher hardness than ordinary gray cast iron and not allow heat treatment, making it difficult for the existing production process to prepare gray cast iron that meets the requirements. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of gray cast iron to solve the problems of low strength and hardness and high production cost of gray cast iron in the prior art.

[0005] To solve the above technical problems, the present application adopts the following technical solutions:

[0006] The present application provides a preparation method of gray cast iron, comprising the following steps:

[0007] Configure and melt raw materials to obtain molten iron. Among them, by mass percentage, C in the molten iron is 3.40%-3.50%, Si is 1.30%-1.50%, Mn is 0.60%-0.70%, P≤0.05%, S is 0.06%-0.12%, Cr is 0.35%-0.45%, Cu is 0.40%-0.50%, Sn is 0.065%-0.07%, and the rest are trace elements and Fe;

[0008] Provide a ladle, add an inoculant to the bottom of the ladle, and then inject the molten iron into the ladle for inoculation treatment. Among them, based on the mass of the molten iron, the inoculant includes 0.40%-0.60% of 75Si-Fe, 0.06%-0.08% of Sn, and 0.2%-0.4% of ferromanganese nitride;

[0009] Pour the inoculated molten iron into a mold to obtain gray cast iron.

[0010] According to some embodiments of the present application, based on the mass of the hot metal, the content of ferromanganese nitride in the inoculant is 0.35%.

[0011] According to some embodiments of the present application, the temperature of the hot metal when injected into the ladle is 1520°C - 1540°C.

[0012] According to some embodiments of the present application, by mass percentage, in the hot metal after inoculation treatment, C is 3.40% - 3.50%, Si is 1.90% - 2.00%, Mn is 0.80% - 1.00%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

[0013] According to some embodiments of the present application, the temperature of the casting and molding is 1380°C - 1420°C, and the casting time for the casting and molding ≤ 8 min.

[0014] According to some embodiments of the present application, during the casting and molding, a pearlite in - stream inoculant accounting for 0.1% - 0.2% of the mass of the hot metal is added along with the flow. Among them, by mass percentage, in the pearlite in - stream inoculant, Si is 65% - 72%, Ca is 0.5% - 2.0%, Sb is 4% - 8%, and the rest is Fe.

[0015] According to some embodiments of the present application, the step of configuring and melting raw materials to obtain hot metal includes: weighing 40% - 50% of scrap steel, 15% - 20% of iron filings, 30% - 45% of return scrap, and 1.6% - 2.0% of carburizer by mass percentage; successively adding the scrap steel, the iron filings, the return scrap, and the carburizer into an electric furnace for melting, and adjusting the composition to obtain the hot metal.

[0016] According to some embodiments of the present application, the step of adjusting the composition includes:

[0017] Taking the mixture of the melted scrap steel, the iron filings, the return scrap, and the carburizer, and making it into a spectral test block;

[0018] Using a rapid direct - reading spectrometer to detect the elemental composition in the spectral test block, and then adjusting according to the difference between the detected composition and the preset composition of the hot metal;

[0019] When the content of the C element in the spectral test block is higher than the preset composition in the hot metal, adding a corresponding amount of scrap steel;

[0020] When the content of the C element in the spectral test block is lower than the preset composition in the hot metal, adding a corresponding amount of carburizer;

[0021] When the content of Si element in the spectral test block is lower than the preset content in the molten iron, add the corresponding amount of 75Si-Fe;

[0022] When the content of Mn element in the spectral test block is lower than the preset content in the molten iron, add the corresponding amount of 65Mn-Fe;

[0023] When the content of Cr element in the spectral test block is lower than the preset content in the molten iron, add the corresponding amount of ferrochromium.

[0024] This application also proposes a gray cast iron, which is prepared by using the preparation method described in any of the above embodiments.

[0025] This application also proposes the application of ferromanganese nitride in improving the strength and / or hardness of gray cast iron. Among them, ferromanganese nitride is used as an inoculant, and its addition amount is 0.2-0.4% of the mass of the molten iron.

[0026] It can be seen from the above technical solutions that the advantages and positive effects of the present invention are as follows:

[0027] In the preparation method of the gray cast iron of the present invention, ferromanganese nitride is added in the inoculation treatment. The nitrogen element in ferromanganese nitride can inhibit the growth of graphite, make the graphite blunt and bent, and at the same time refine the graphite and grains, thereby reducing the splitting effect of graphite on the matrix, significantly improving the strength and hardness of the gray cast iron. The tensile strength of the obtained gray cast iron reaches more than 240 MPa, and the Brinell hardness reaches more than 200 HB. And ferromanganese nitride has good thermal conductivity, which improves the heat dissipation of the gray cast iron, thereby increasing the service life.

[0028] Furthermore, this application optimizes the addition amount of ferromanganese nitride according to the mass of the molten iron. When the dosage of ferromanganese nitride is between 0.2% and 0.4%, the strength and hardness can be significantly improved, and there will be no tendency to form chilled zone. While improving the mechanical properties of gray cast iron, the production cost is saved.

[0029] The inoculant addition amount of the preparation method of the present invention is small, the cost is low, and the process is simple. The gray cast iron produced by using the preparation method of the gray cast iron of the present invention has high strength and hardness and high quality. Description of the Drawings

[0030] Figure 1 is the flowchart of the preparation method of the gray cast iron in the embodiment of the present invention. Detailed Embodiments

[0031] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments, all of which do not depart from the scope of the present invention, and the descriptions and illustrations therein are for illustrative purposes in nature and are not intended to limit the present invention.

[0032] In this application, unless otherwise specified, the raw materials used are commercially available products well-known in the art.

[0033] The present invention provides a preparation method for gray cast iron. In the process of inoculating molten iron, an inoculant containing ferromanganese nitride is used for inoculation treatment. Ferromanganese nitride can limit the growth space of eutectic graphite, obtain a round, curved, and fine graphite structure, reduce the splitting effect of graphite on the matrix, and thus can greatly improve the tensile strength and hardness of gray cast iron. Ferromanganese nitride has low cost, small addition amount, and will not cause white mouth tendency in gray cast iron. While improving the mechanical properties and heat dissipation performance of gray cast iron, it reduces the production and manufacturing cost. This preparation method has low cost and simple process.

[0034] The following specifically details the principle of the preparation method for this gray cast iron.

[0035] Refer to Figure 1 , and the specific steps are as follows:

[0036] S101. Configure and melt the raw materials to obtain molten iron. Among them, by mass percentage, in the molten iron, C is 3.40% - 3.50%, Si is 1.30% - 1.50%, Mn is 0.60% - 0.70%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

[0037] Specifically, by mass percentage, weigh 40% - 50% of scrap steel, 15% - 20% of iron filings, 30% - 45% of return material, and 1.6% - 2.0% of carburizer; sequentially add the scrap steel, return material, iron filings, and carburizer into an electric furnace for melting, and adjust the composition to obtain molten iron.

[0038] Exemplarily, the electric furnace can be an intermediate frequency induction furnace.

[0039] Among them, the step of adjusting the composition of the molten iron so that the content of each element reaches the preset range specifically includes:

[0040] Take the mixture after melting the scrap steel, iron filings, return material, and carburizer, and make it into a spectral test block;

[0041] Use a rapid direct reading spectrometer to detect the element composition in the spectral test block, and then adjust according to the difference between the detected composition and the preset composition of the molten iron;

[0042] For example, when the content of element C in the spectral test block is higher than the preset content in the molten iron, add the corresponding amount of scrap steel; when the content of element C in the spectral test block is lower than the preset content in the molten iron, add the corresponding amount of carburizer; when the content of element Si in the spectral test block is lower than the preset content in the molten iron, add the corresponding amount of 75Si-Fe. In 75Si-Fe, by mass percentage, Si is 72%-80%, Al≤1%, Ca≤1%, Mn≤0.4%, and the rest is Fe. For every 8 Kg of 75Si-Fe added, the Si content can be increased by 0.1%; when the content of element Mn in the spectral test block is lower than the preset content in the molten iron, add the corresponding amount of 65Mn-Fe. In 65Mn-Fe, by mass percentage, Mn is 65%-72%, C≤7%, Si≤2.5%, and the rest is Fe. For every 9 Kg of 65Mn-Fe added, the Mn content can be increased by 0.1%; when the content of element Cr in the spectral test block is lower than the preset content in the molten iron, add the corresponding amount of ferrochrome. In ferrochrome, by mass percentage, Cr is 60%-65%, C≤9.5%, Si≤3%, and the rest is Fe. For every 10 Kg of ferrochrome added, the Cr can be increased by 0.1%.

[0043] S102. Provide a ladle for molten iron, add an inoculant to the bottom of the ladle for molten iron, and then pour the molten iron into the ladle for molten iron for inoculation treatment. Among them, based on the mass of the molten iron, the inoculant includes 0.40%-0.60% of 75Si-Fe, 0.06%-0.08% of Sn, and 0.2%-0.4% of ferromanganese nitride.

[0044] Specifically, the inside of the ladle for molten iron has an accommodation space. According to the mass of the molten iron, 0.40%-0.60% of 75Si-Fe, 0.06%-0.08% of Sn, and 0.2%-0.4% of ferromanganese nitride, which account for the mass of the molten iron, are added to the bottom of the ladle for molten iron in sequence.

[0045] Raise the temperature of the molten iron to 1520°C - 1540°C, then pour the molten iron into the ladle for molten iron with the above-mentioned inoculant added, and skim the scum on the surface of the molten iron, thus completing the inoculation treatment and enabling pouring.

[0046] Among them, the nitrogen element in ferromanganese nitride can inhibit the growth of graphite, make the graphite blunt and curved, and at the same time refine the graphite and grains, thereby reducing the splitting effect of graphite on the matrix, so that the obtained gray cast iron has a high carbon equivalent and a high silicon equivalent while having significantly improved strength and hardness. And ferromanganese nitride has good thermal conductivity, which improves the heat dissipation of gray cast iron, thereby extending the service life.

[0047] Among them, the addition amount of ferromanganese nitride can be 0.2%, 0.22%, 0.25%, 0.3%, 0.35%, 0.38%, 0.4%, etc. of the mass of the molten iron, and more preferably 0.35%. If the addition amount is less than 0.2%, the passivation effect on graphite is not good, and the mechanical properties of gray cast iron cannot meet the required standards. If the addition amount is greater than 0.4%, the nitrogen content in the molten iron will be too high, and the obtained gray cast iron is likely to form nitrogen pores and be scrapped.

[0048] The present invention conveniently improves the strength and hardness of gray cast iron through ferromanganese nitride with low cost. Moreover, the inoculant in this preparation method also contains elements such as Si, Fe, and Sn. It not only utilizes the inoculation ability of each element itself, but also has a synergistic effect among the elements and between the elements and ferromanganese nitride, enabling the graphite to be small, curved, and most evenly distributed, greatly improving the tensile strength and hardness of gray cast iron, and reducing the tendency of white mouth.

[0049] S103. Pour the inoculated molten iron into a mold to obtain gray cast iron.

[0050] Specifically, pour the inoculated molten iron into a pouring ladle, with a pouring temperature of 1380°C - 1420°C and a pouring time ≤ 8 min. After molding, gray cast iron is obtained.

[0051] During pouring and molding, add a pearlite in-stream inoculant accounting for 0.1% - 0.2% of the mass of the molten iron. Among them, by mass percentage, Si in the pearlite in-stream inoculant is 65% - 72%, Ca is 0.5% - 2.0%, Sb is 4% - 8%, and the rest is Fe.

[0052] Among them, the nitrogen in ferromanganese nitride can also refine pearlite, reduce the pearlite lamellae, and further achieve the purpose of improving the strength and hardness of gray cast iron.

[0053] The inventor of the present application has prepared gray cast iron with relatively high strength and hardness by strictly designing the process conditions of each step in this preparation method.

[0054] Furthermore, the present application proposes the application of ferromanganese nitride in improving the strength and / or hardness of gray cast iron. Among them, when used as an inoculant, ferromanganese nitride can improve the strength and hardness of gray cast iron by making the graphite round, curved, and / or refined.

[0055] Among them, the addition amount of ferromanganese nitride is 0.2% - 0.4% of the mass of the molten iron.

[0056] In order to introduce the preparation method of the gray cast iron provided by the embodiments of the present invention more clearly and in detail, the following will be described in combination with specific embodiments.

[0057] Example 1

[0058] Weigh 40% of scrap steel, 20% of iron filings, 38% of return scrap, and 2% of recarburizer by mass percentage.

[0059] Add scrap steel, iron filings, return scrap, and recarburizer to an electric furnace in sequence for melting, and adjust the composition to obtain molten iron; wherein, by mass percentage, C in the molten iron is 3.40% - 3.50%, Si is 1.30% - 1.50%, Mn is 0.60% - 0.70%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

[0060] Weigh 0.40% of 75Si - Fe, 0.08% of Sn, and 0.2% of ferromanganese nitride according to the mass ratio to the molten iron, and add 75Si - Fe, Sn, and ferromanganese nitride to the bottom of the molten iron ladle in sequence.

[0061] Raise the temperature of the molten iron to 1520 °C, and then pour the molten iron into the above - mentioned molten iron ladle.

[0062] By mass percentage, in the inoculated molten iron, C is 3.40% - 3.50%, Si is 1.90% - 2.00%, Mn is 0.80% - 1.00%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

[0063] Pour the inoculated molten iron into a pouring ladle, carry out pouring and forming. The pouring temperature is 1380 °C, the pouring time is 8 minutes, and add pearlite in - stream inoculant accounting for 0.1% of the mass of the molten iron during pouring. After forming, gray cast iron is obtained.

[0064] Example 2

[0065] Weigh 50% of scrap steel, 15% of iron filings, 33.4% of return scrap, and 1.6% of recarburizer by mass percentage.

[0066] Add scrap steel, iron filings, return scrap, and recarburizer to an electric furnace in sequence for melting, and adjust the composition to obtain molten iron; wherein, by mass percentage, C in the molten iron is 3.40% - 3.50%, Si is 1.30% - 1.50%, Mn is 0.60% - 0.70%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

[0067] Weigh 0.60% of 75Si-Fe, 0.06% of Sn, and 0.3% of ferromanganese nitride according to the mass ratio to the hot metal, and add 75Si-Fe, Sn, and ferromanganese nitride to the bottom of the hot metal ladle in sequence.

[0068] Raise the temperature of the hot metal to 1540 °C, and then pour the hot metal into the above-mentioned hot metal ladle.

[0069] In terms of mass percentage, in the hot metal after inoculation treatment, C is 3.40% - 3.50%, Si is 1.90% - 2.00%, Mn is 0.80% - 1.00%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

[0070] Pour the inoculated hot metal into the pouring ladle, cast it into shape, with a pouring temperature of 1390 °C and a pouring time of 8 minutes, and add 0.2% of pearlite in-stream inoculant by mass of the hot metal during pouring. After shaping, gray cast iron is obtained.

[0071] Example 3

[0072] Weigh 40% of scrap steel, 18% of iron filings, 40% of return scrap, and 2% of carburizer according to mass percentage.

[0073] Add scrap steel, iron filings, return scrap, and carburizer to the electric furnace in sequence to melt, and adjust the composition to obtain hot metal; among them, in terms of mass percentage, in the hot metal, C is 3.40% - 3.50%, Si is 1.30% - 1.50%, Mn is 0.60% - 0.70%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

[0074] Weigh 0.40% of 75Si-Fe, 0.08% of Sn, and 0.35% of ferromanganese nitride according to the mass ratio to the hot metal, and add 75Si-Fe, Sn, and ferromanganese nitride to the bottom of the hot metal ladle in sequence.

[0075] Raise the temperature of the hot metal to 1520 °C, and then pour the hot metal into the above-mentioned hot metal ladle.

[0076] In terms of mass percentage, in the molten iron after inoculation treatment, C is 3.40% - 3.50%, Si is 1.90% - 2.00%, Mn is 0.80% - 1.00%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

[0077] Pour the inoculated molten iron into a pouring ladle, and carry out casting to form. The casting temperature is 1380 °C, and the casting time is 8 minutes. And during casting, add pearlite in-stream inoculant accounting for 0.1% of the mass of the molten iron along with the flow. After forming, gray cast iron is obtained.

[0078] Example 4

[0079] Weigh 42% of scrap steel, 15% of iron filings, 41.2% of return scrap, and 1.8% of carburizer according to mass percentage.

[0080] Add scrap steel, iron filings, return scrap, and carburizer into an electric furnace in sequence for melting, and adjust the composition to obtain molten iron; among them, in terms of mass percentage, in the molten iron, C is 3.40% - 3.50%, Si is 1.30% - 1.50%, Mn is 0.60% - 0.70%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

[0081] Weigh 0.50% of 75Si-Fe, 0.07% of Sn, and 0.4% of ferromanganese nitride according to the mass ratio to the molten iron, and add 75Si-Fe, Sn, and ferromanganese nitride into the bottom of the molten iron ladle in sequence.

[0082] Raise the temperature of the molten iron to 1530 °C, and then pour the molten iron into the above-mentioned molten iron ladle.

[0083] In terms of mass percentage, in the molten iron after inoculation treatment, C is 3.40% - 3.50%, Si is 1.90% - 2.00%, Mn is 0.80% - 1.00%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

[0084] Pour the inoculated molten iron into a pouring ladle, and carry out casting to form. The casting temperature is 1420 °C, and the casting time is 6 minutes. And during casting, add pearlite in-stream inoculant accounting for 0.2% of the mass of the molten iron along with the flow. After forming, gray cast iron is obtained.

[0085] Comparative Example 1

[0086] Prepare gray cast iron according to the method described in Example 1, except that the addition amount of ferromanganese nitride is 0.1% of the mass of the molten iron.

[0087] Comparative Example 2

[0088] Prepare gray cast iron according to the method described in Example 1, except that the addition amount of ferromanganese nitride is 0.5% of the mass of the molten iron.

[0089] Comparative Example 3

[0090] Prepare gray cast iron according to the method described in Example 1, except that ferromanganese nitride is not added during the inoculation treatment.

[0091] Compare the properties of the gray cast iron in Examples 1-4 and Comparative Examples 1-3, as shown in the following table:

[0092]

[0093]

[0094] As can be seen from the above table, the tensile strength and hardness of the gray cast iron prepared in Examples 1-4 are significantly improved compared with those in Comparative Example 1 and Comparative Example 3. It can be seen that the improvement of the tensile strength and hardness of the gray cast iron is positively correlated with the addition amount of ferromanganese nitride. However, in combination with Comparative Example 2, although relatively excellent tensile strength and hardness are obtained when the addition amount of ferromanganese nitride is 0.5%, by observing the morphology of the prepared gray cast iron, it is found that a large number of crack-like nitride holes are formed on the surface of the gray cast iron, resulting in batch scrapping of the castings. Therefore, the preferred addition amount of ferromanganese nitride is 0.2% to 0.4% of the mass of the molten iron.

[0095] As can be seen from the above technical solutions, the advantages and positive effects of the present invention are as follows:

[0096] In the preparation method of the gray cast iron of the present invention, ferromanganese nitride is added during the inoculation treatment. The nitrogen element in ferromanganese nitride can inhibit the growth of graphite, make the graphite blunt and bent, and at the same time refine the graphite and grains, thereby reducing the splitting effect of graphite on the matrix and significantly improving the strength and hardness of the gray cast iron. The obtained gray cast iron has a high carbon equivalent and a high silicon equivalent, its tensile strength reaches more than 240 MPa, and its Brinell hardness reaches more than 200 HB. And ferromanganese nitride has good thermal conductivity, which improves the heat dissipation of the gray cast iron, thereby extending the service life.

[0097] The preparation method of the present invention has a small addition amount of inoculant, low cost, and simple process. The gray cast iron produced by using the preparation method of the gray cast iron of the present invention has high strength and hardness and high quality.

[0098] While the invention has been described with reference to several exemplary embodiments, it is to be understood that the terms used are descriptive and exemplary rather than restrictive. Since the invention can be embodied in many forms without departing from the spirit or essential characteristics thereof, it should be understood that the above-described embodiments are not limited to any of the foregoing details, but rather should be broadly construed within the spirit and scope defined by the appended claims, and accordingly all variations and modifications that fall within the scope of the claims or their equivalents are to be covered by the appended claims.

Claims

1. A method for preparing gray cast iron, characterized in that, It includes the following steps: Configure and smelt raw materials to obtain molten iron. By mass percentage, in the molten iron, C is 3.40% - 3.50%, Si is 1.30% - 1.50%, Mn is 0.60% - 0.70%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe; Provide a ladle for molten iron, add an inoculant to the bottom of the ladle for molten iron, and then pour the molten iron into the ladle for inoculation treatment. By the mass of the molten iron, the inoculant includes 0.40% - 0.60% of 75Si-Fe, 0.06% - 0.08% of Sn, and 0.2% - 0.4% of ferromanganese nitride; Pour the inoculated molten iron into a mold to obtain gray cast iron; Among them, when pouring and molding, add 0.1% - 0.2% of pearlite in-stream inoculant by the mass of the molten iron. By mass percentage, in the pearlite in-stream inoculant, Si is 65% - 72%, Ca is 0.5% - 2.0%, Sb is 4% - 8%, and the rest is Fe.

2. The preparation method according to claim 1, characterized in that, By the mass of the molten iron, the content of ferromanganese nitride in the inoculant is 0.35%.

3. The preparation method according to claim 1, characterized in that, The temperature when the molten iron is poured into the ladle for molten iron is 1520°C - 1540°C.

4. The preparation method according to claim 1, characterized in that, By mass percentage, in the inoculated molten iron, C is 3.40% - 3.50%, Si is 1.90% - 2.00%, Mn is 0.80% - 1.00%, P ≤ 0.05%, S is 0.06% - 0.12%, Cr is 0.35% - 0.45%, Cu is 0.40% - 0.50%, Sn is 0.065% - 0.07%, and the rest are trace elements and Fe.

5. The preparation method according to claim 1, characterized in that, The temperature of pouring and molding is 1380°C - 1420°C, and the pouring time of pouring and molding ≤ 8 min.

6. The preparation method according to claim 1, characterized in that, The step of configuring and smelting raw materials to obtain molten iron includes: Weigh 40% - 50% of scrap steel, 15% - 20% of iron filings, 30% - 45% of return scrap, and 1.6% - 2.0% of carburizer by mass percentage; Add the scrap steel, iron filings, return scrap, and carburizer into an electric furnace in sequence to melt, and adjust the composition to obtain the molten iron.

7. The preparation method according to claim 6, characterized in that, The step of adjusting the composition includes: Take the mixture of the melted scrap steel, iron filings, return scrap, and carburizer, and make it into a spectral test block; Use a rapid direct-reading spectrometer to detect the elemental composition in the spectral test block, and then adjust according to the difference between the detected composition and the preset composition of the molten iron; When the content of C element in the spectral test block is higher than the preset composition in the molten iron, add the corresponding amount of scrap steel; When the content of C element in the spectral test block is lower than the preset composition in the molten iron, add the corresponding amount of carburizer; When the content of Si element in the spectral test block is lower than the preset composition in the molten iron, add the corresponding amount of 75Si-Fe; When the content of Mn element in the spectral test block is lower than the preset content in the hot metal, add a corresponding amount of 65Mn-Fe; When the content of Cr element in the spectral test block is lower than the preset content in the hot metal, add a corresponding amount of ferrochrome.

8. A gray cast iron, characterized in that, It is prepared by using the preparation method described in any one of claims 1 to 7.

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