Isothermal quenching nodular cast iron ball and preparation method thereof

Abstract

The application discloses a preparation method of isothermal quenching nodular cast iron grinding ball, which comprises the following steps: pouring molten iron into a ladle containing spheroidizing agent, placing primary inoculant on the surface of the molten iron, performing spheroidizing and inoculating treatment, then adding secondary inoculant, performing secondary inoculating treatment, and then cooling, polishing and sand cleaning to obtain intermediate grinding ball; then heat treatment and tempering to obtain isothermal quenching nodular cast iron grinding ball; wherein the raw material of the molten iron comprises the following components in percentage by weight: C 3.2-3.4%, Si 2.0-2.2%, Mn 0.3-0.4%, Cr 0.8-0.9%, Re 0.04-0.05%, Mg 0.02-0.025%, Nb 0.2-0.25%, P≤0.05%, S≤0.03%, and the balance is Fe. The application further discloses an isothermal quenching nodular cast iron grinding ball. The grinding ball prepared by the application has good impact resistance and is suitable for large ball mills.

Description

Technical Field

[0001] This invention relates to the field of wear-resistant steel ball technology, and in particular to an isothermal quenched ductile iron grinding ball and its preparation method. Background Technology

[0002] To improve powder preparation efficiency, ball mills are trending towards larger sizes. However, this larger size also brings problems such as increased impact wear on the grinding balls, more frequent downtime for ball replacement, and consequently higher production costs. Therefore, improving the impact wear resistance of grinding balls and developing new wear-resistant materials are crucial ways to reduce energy and material consumption in large ball mills.

[0003] Isothermal hardened ductile iron grinding balls containing carbides are a new type of wear-resistant material used in mining enterprises in recent years. This material has excellent wear resistance and has been rapidly adopted in ball mills. However, its application in large ball mills is very limited because the large diameter of these mills results in high impact forces on the grinding media during operation, and conventional isothermal hardened ductile iron grinding balls lack sufficient impact toughness. Therefore, it is necessary to improve the performance of isothermal hardened ductile iron grinding balls. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes an isothermal quenched ductile iron grinding ball and its preparation method. The grinding ball prepared by the present invention has good impact resistance and is suitable for large ball mills.

[0005] This invention proposes a method for preparing isothermal quenched ductile iron grinding balls, comprising the following steps: pouring molten iron into a ladle containing a spheroidizing agent, placing a primary inoculant on the surface of the molten iron for spheroidization and inoculation treatment, then adding a secondary inoculant for secondary inoculation treatment, followed by cooling, grinding, and sand removal to obtain intermediate grinding balls; then heat-treating and tempering to obtain isothermal quenched ductile iron grinding balls.

[0006] The raw materials for molten iron, by weight percentage, include: C 3.2-3.4%, Si 2.0-2.2%, Mn 0.3-0.4%, Cr 0.8-0.9%, Re 0.04-0.05%, Mg 0.02-0.025%, Nb 0.2-0.25%, P≤0.05%, S≤0.03%, with the balance being Fe.

[0007] Preferably, the primary inoculant is 75% ferrosilicon in block form.

[0008] Preferably, the length of the block-shaped 75 ferrosilicon is 15-25 mm and the width is 15-25 mm.

[0009] Preferably, the weight ratio of molten iron to primary inoculant is 100:0.5-0.6.

[0010] Preferably, the spheroidizing agent is FeSiMg6Re2 spheroidizing agent.

[0011] Both the 75% ferrosilicon and FeSiMg6Re2 spheroidizing agents mentioned above are available on the market.

[0012] Preferably, the weight ratio of molten iron to spheroidizing agent is 100:1.2-1.4.

[0013] Preferably, the secondary inoculant is composed of 75% ferrosilicon powder, nano-SiC, and nano-vanadium carbide.

[0014] Preferably, the weight ratio of 75% ferrosilicon powder, nano-SiC, and nano-vanadium carbide is 4:0.6-0.8:0.6-0.8.

[0015] Preferably, the weight ratio of molten iron to secondary inoculant is 100:0.52-0.56.

[0016] Preferably, the heat treatment procedure is as follows: heat to 910-930℃, hold for 2-2.5h, and then quench isothermally in a salt bath at 240-260℃ for 2-2.5h.

[0017] Preferably, the ductile iron grinding balls are tempered at 200-230℃ for 4-5 hours and then air-cooled to room temperature to obtain isothermal quenched ductile iron grinding balls.

[0018] Preferably, the casting temperature is 1400-1450℃.

[0019] After the above heat treatment, the grinding balls are cooled to 80°C, cleaned, and then tempered.

[0020] The salt bath described above is a mixture of potassium nitrate and sodium nitrate, with a weight ratio of 1:1.

[0021] The present invention also proposes an isothermal quenched ductile iron grinding ball, which is prepared according to the above-described method for preparing isothermal quenched ductile iron grinding balls.

[0022] Beneficial effects:

[0023] This invention places a blocky 75% ferrosilicon inoculant on the surface of molten iron. During spheroidization, it can absorb an appropriate amount of oxygen from the air, promoting the formation of graphite nuclei and working in conjunction with the spheroidizing agent to further promote graphite spheroidization. Then, a suitable ratio of 75% ferrosilicon powder, nano-SiC, and nano-vanadium carbide is used as a secondary inoculant, which can promote heterogeneous nucleation of graphite, increase the number of graphite particles, increase the cooling rate during solidification, inhibit the growth of graphite spheres, and improve the sphericity and uniform distribution of graphite spheres. This achieves the effect of increasing the number of graphite particles and refining and uniformly distributing them, thereby improving impact resistance while maintaining good wear resistance.

[0024] In addition, this invention adjusts the content of Re, Mg, and Nb in molten iron. The combination of these three can transform the network carbides into granular forms during heat treatment, thereby improving the impact toughness of the grinding balls. Furthermore, by selecting an appropriate heat treatment temperature, the carbides in the grinding ball structure are evenly distributed, further improving the impact toughness and hardness of the grinding balls, making them suitable for large ball mills and extending their service life. Detailed Implementation

[0025] The technical solution of the present invention will now be described in detail through specific embodiments.

[0026] Example 1

[0027] A method for preparing isothermally quenched ductile iron grinding balls includes the following steps:

[0028] The molten iron obtained from smelting contains the following raw materials by weight percentage: C 3.2%, Si 2.2%, Mn 0.3%, Cr 0.9%, Re 0.04%, Mg 0.025%, Nb 0.2%, P≤0.05%, S≤0.03%, with the balance being Fe;

[0029] Molten iron is poured into a ladle containing FeSiMg6Re2 spheroidizing agent at 1450℃, and a block of 75 ferrosilicon inoculant with a length of 15mm and a width of 15mm is placed on the surface of the molten iron. Spheroidization and inoculation are carried out for 90s. Then, a secondary inoculant is added and a secondary inoculation is carried out for 60s. After cooling, grinding and sand removal, intermediate grinding balls are obtained.

[0030] The weight ratio of molten iron to primary inoculant is 100:0.6, and the weight ratio of molten iron to spheroidizing agent is 100:1.4.

[0031] The secondary inoculant is composed of 75% ferrosilicon powder, nano-SiC, and nano-vanadium carbide in a weight ratio of 4:0.6:0.6, and the weight ratio of molten iron to the secondary inoculant is 100:0.52.

[0032] Take the intermediate grinding ball, heat it to 910℃, hold it for 2.5h, then isothermally quench it at 240℃ in a salt bath (the salt bath consists of equal weights of potassium nitrate and sodium nitrate) for 2.5h. Then cool the grinding ball down to 80℃, clean it, temper it at 200℃ for 5h, and then air cool it to room temperature to obtain isothermally quenched ductile iron grinding balls.

[0033] Example 2

[0034] A method for preparing isothermally quenched ductile iron grinding balls includes the following steps:

[0035] The molten iron obtained from smelting contains the following raw materials by weight percentage: C 3.4%, Si 2.0%, Mn 0.4%, Cr 0.8%, Re 0.05%, Mg 0.02%, Nb 0.25%, P≤0.05%, S≤0.03%, with the balance being Fe;

[0036] Molten iron is poured into a ladle containing FeSiMg6Re2 spheroidizing agent at 1400℃, and a block of 75 ferrosilicon inoculant with a length of 25mm and a width of 25mm is placed on the surface of the molten iron. Spheroidization and inoculation are carried out for 90s. Then, a secondary inoculant is added and secondary inoculation is carried out for 60s. After cooling, grinding and sand removal, intermediate grinding balls are obtained.

[0037] The weight ratio of molten iron to primary inoculant is 100:0.5, and the weight ratio of molten iron to spheroidizing agent is 100:1.2.

[0038] The secondary inoculant is composed of 75% ferrosilicon powder, nano-SiC, and nano-vanadium carbide in a weight ratio of 4:0.8:0.8, and the weight ratio of molten iron to the secondary inoculant is 100:0.56.

[0039] Take the intermediate grinding ball, heat it to 930℃, hold it for 2 hours, then isothermally quench it at 260℃ in a salt bath (the salt bath consists of equal weights of potassium nitrate and sodium nitrate) for 2 hours. Then cool the grinding ball down to 80℃, clean it, temper it at 230℃ for 4 hours, and then air cool it to room temperature to obtain isothermally quenched ductile iron grinding balls.

[0040] Example 3

[0041] A method for preparing isothermally quenched ductile iron grinding balls includes the following steps:

[0042] The molten iron obtained from smelting contains the following raw materials by weight percentage: C 3.3%, Si 2.1%, Mn 0.35%, Cr 0.85%, Re 0.045%, Mg 0.022%, Nb 0.22%, P≤0.05%, S≤0.03%, with the balance being Fe;

[0043] Molten iron is poured into a ladle containing FeSiMg6Re2 spheroidizing agent at 1430℃, and a block of 75 ferrosilicon inoculant with a length of 20mm and a width of 20mm is placed on the surface of the molten iron. Spheroidization and inoculation are carried out for 90s. Then, a secondary inoculant is added and a secondary inoculation is carried out for 60s. After cooling, grinding and sand removal, intermediate grinding balls are obtained.

[0044] The weight ratio of molten iron to primary inoculant is 100:0.55, and the weight ratio of molten iron to spheroidizing agent is 100:1.3.

[0045] The secondary inoculant is composed of 75% ferrosilicon powder, nano-SiC, and nano-vanadium carbide in a weight ratio of 4:0.7:0.7, and the weight ratio of molten iron to the secondary inoculant is 100:0.54.

[0046] Take the intermediate grinding ball, heat it to 920℃, hold it for 2 hours, then isothermally quench it at 250℃ in a salt bath (the salt bath consists of equal weights of potassium nitrate and sodium nitrate) for 2 hours. Then cool the grinding ball down to 80℃, clean it, temper it at 220℃ for 4.5 hours, and then air cool it to room temperature to obtain isothermally quenched ductile iron grinding balls.

[0047] Comparative Example 1

[0048] Replace the blocky 75% ferrosilicon inoculant with 75% ferrosilicon powder, and place it in the ladle together with the FeSiMg6Re2 spheroidizing agent. Then pour the molten iron into the ladle for spheroidizing and inoculation treatment. Then add a secondary inoculant. Other steps are the same as in Example 3.

[0049] Comparative Example 2

[0050] The secondary inoculant is 75% ferrosilicon powder, and the weight ratio of molten iron to secondary inoculant is 100:0.4. Other details are the same as in Example 3.

[0051] Comparative Example 3

[0052] The secondary inoculant is composed of nano-SiC and nano-vanadium carbide in a weight ratio of 0.7:0.7, and the weight ratio of molten iron to the secondary inoculant is 100:0.14. Other aspects are the same as in Example 3.

[0053] Comparative Example 4

[0054] The molten iron does not contain Re or Mg, and the rest is the same as in Example 3.

[0055] Comparative Example 5

[0056] The molten iron does not contain Nb, and other aspects are the same as in Example 3.

[0057] The performance of the grinding balls (all with a diameter of 100 mm) obtained in Examples 1-3 and Comparative Examples 1-5 was tested, and the results are shown in Table 1.

[0058] The grinding balls (all with a diameter of 100 mm) obtained from Examples 1-3 and Comparative Examples 1-5 were used in a ball mill with a diameter of φ3.8×7.5 m to perform iron ore ball milling and to calculate the service life.

[0059] Table 1 Test Results

[0060]

[0061] As can be seen from the table above, the isothermal quenched ductile iron grinding balls prepared by this invention have good impact resistance while maintaining high hardness, and also have a high graphitization content, small graphite balls, and long service life.

[0062] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing isothermally quenched ductile iron grinding balls, characterized in that, The process includes the following steps: molten iron is poured into a ladle containing a spheroidizing agent, and an inoculant is placed on the surface of the molten iron for spheroidizing and inoculation treatment. Then, a second inoculant is added for a second inoculation treatment. The ball is then cooled, polished, and cleaned to obtain an intermediate grinding ball. Finally, the ball is heat-treated and tempered to obtain an isothermal quenched ductile iron grinding ball. The raw materials for molten iron, by weight percentage, include: C 3.2-3.4%, Si 2.0-2.2%, Mn 0.3-0.4%, Cr 0.8-0.9%, Re 0.04-0.05%, Mg 0.02-0.025%, Nb 0.2-0.25%, P≤0.05%, S≤0.03%, with the balance being Fe; The inoculant is 75% ferrosilicon in block form; The secondary inoculant is composed of 75% ferrosilicon powder, nano-SiC, and nano-vanadium carbide. The weight ratio of 75% ferrosilicon powder, nano-SiC, and nano-vanadium carbide is 4:0.6-0.8:0.6-0.

8. The heat treatment procedure is as follows: heat to 910-930℃, hold for 2-2.5h, and then quench isothermally in a salt bath at 240-260℃ for 2-2.5h. Temper at 200-230℃ for 4-5 hours, then air cool to room temperature to obtain isothermal quenched ductile iron grinding balls.

2. The method for preparing isothermal quenched ductile iron grinding balls according to claim 1, characterized in that, The length and width of the block-shaped 75 ferrosilicon are 15-25mm.

3. The method for preparing isothermal quenched ductile iron grinding balls according to claim 1 or 2, characterized in that, The weight ratio of molten iron to primary inoculant is 100:0.5-0.

6.

4. The method for preparing isothermal quenched ductile iron grinding balls according to claim 1 or 2, characterized in that, The spheroidizing agent is FeSiMg6Re2 spheroidizing agent.

5. The method for preparing isothermal quenched ductile iron grinding balls according to claim 1 or 2, characterized in that, The weight ratio of molten iron to spheroidizing agent is 100:1.2-1.

4.

6. The method for preparing isothermal quenched ductile iron grinding balls according to claim 1 or 2, characterized in that, The weight ratio of molten iron to secondary inoculant is 100:0.52-0.

56.

7. The method for preparing isothermal quenched ductile iron grinding balls according to claim 1 or 2, characterized in that, The casting temperature is 1400-1450℃.

8. An isothermal quenched ductile iron grinding ball, characterized in that, The isothermal quenched ductile iron grinding balls are prepared according to the preparation method of any one of claims 1-7.

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