High-carbon low-alloy wear-resistant forged ball and heat treatment process thereof

Abstract

The heat treatment process comprises the following steps that S1, isothermal spheroidizing annealing is conducted, specifically, the high-carbon low-alloy forged ball which is forged, formed and air-cooled to the room temperature is heated to 750-780 DEG C, and heat preservation is conducted for 1-3 hours; then rapidly cooling to 670-720 DEG C, and preserving heat for 2-4 hours at the temperature of 670-720 DEG C; and finally, cooling to below 500-600 DEG C along with the furnace, and then discharging and air-cooling. S2, quenching is conducted, specifically, the forged balls treated in the step S1 are heated to 770-800 DEG C, heat preservation is conducted for 15-60 min, and then the forged balls are put into quenching oil to be cooled to the room temperature; and S3, tempering is conducted, specifically, the forged balls treated in the step S2 are heated to 170-220 DEG C, heat preservation is conducted for 60-150 min, and then the forged balls are discharged out of the furnace and subjected to air cooling. According to the method, the microscopic structure of the forged ball can be remarkably improved, and the impact toughness is remarkably improved while the high hardness of the forged ball is kept.

Description

Technical Field

[0001] This invention relates to the field of heat treatment of metallic materials and wear-resistant products, specifically to a high-carbon, low-alloy wear-resistant forged ball and its heat treatment process. Background Technology

[0002] Grinding balls are key consumables in grinding operations in industries such as mining, cement, and power, and their performance directly affects production efficiency and cost. With the development of larger grinding equipment, higher requirements are placed on the comprehensive performance of large-sized grinding balls (such as those with a diameter ≥100mm), which need to have high hardness, high wear resistance, and good impact toughness to prevent breakage and failure.

[0003] Currently, high-carbon, low-alloy wear-resistant forged steel balls (such as B2, B3, and B6 steel) are widely used. Although these forged balls are relatively inexpensive, they are prone to cracking and breakage under complex working conditions as their size increases. Their performance largely depends on the heat treatment process. The lamellar pearlite structure obtained by pre-heat treatment in conventional production processes (such as normalizing or ordinary annealing) has a low nucleation rate during the austenitization process in subsequent quenching, making it difficult to obtain extremely fine and uniform austenite grains. This limits the refinement of the final quenched and tempered structure and the improvement of performance, especially the improvement of impact toughness.

[0004] Therefore, developing an optimized heat treatment process for large-sized high-carbon low-alloy forged balls, aiming to refine the microstructure while improving hardness and toughness, has become an urgent problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a high-carbon, low-alloy wear-resistant forged ball and its heat treatment process. By optimizing the pre-heat treatment process, the microstructure of the forged ball is significantly improved, so that while maintaining high hardness, the impact toughness is significantly improved.

[0006] In one aspect of the invention, a heat treatment process for high-carbon, low-alloy wear-resistant forged balls is provided. According to an embodiment of the invention, the method includes the following steps:

[0007] S1. Isothermal spheroidizing annealing: Forged high-carbon low-alloy forged balls that have been air-cooled to room temperature are heated to 750-780℃ and held for 1-3 hours; then rapidly cooled to 670-720℃ and held at this temperature for 2-4 hours; finally, cooled in the furnace to below 500-600℃ and then air-cooled.

[0008] S2. Quenching: Heat the forged balls treated in step S1 to 770-800℃, hold for 15-60 min, and then immerse them in quenching oil to cool to room temperature.

[0009] S3. Tempering: Heat the forged balls treated in step S2 to 170-220℃, hold for 60-150 minutes, and then remove them from the furnace and air cool.

[0010] After isothermal spheroidizing annealing, grain refinement is achieved by controlling the austenitizing temperature and holding time. During the holding process at 670-690℃, a spherical pearlite microstructure is obtained with granular cementite distributed on a fine-grained ferrite matrix. In step S2, controlling the austenitizing temperature and time achieves austenitization while retaining some undissolved carbides, thus obtaining a composite microstructure of acicular martensite + carbides + a small amount of retained austenite during subsequent quenching. After tempering in step S3, a final microstructure of tempered martensite + carbides + a small amount of retained austenite is obtained.

[0011] In addition, the heat treatment process for a high-carbon low-alloy wear-resistant forged ball according to the above embodiments of the present invention may also have the following additional technical features:

[0012] In some embodiments of the present invention, in step S1, the high-carbon low-alloy forged ball comprises the following components by weight percentage: 0.74%-0.85% C, 0.15%-0.35% Si, 0.90%-1.05% Mn, 0.88%-0.98% Cr, less than or equal to 0.02% P, 0.025%-0.045% Al, with the remainder being Fe and unavoidable impurities.

[0013] In some embodiments of the present invention, in step S1, the heating rate is 80-150°C / hour.

[0014] In some embodiments of the present invention, in step S2, the heating rate is 80-150°C / hour.

[0015] In some embodiments of the present invention, in step S3, the heating rate is 50-100°C / hour.

[0016] In another aspect of the invention, a high-carbon, low-alloy wear-resistant forged ball obtained by a heat treatment process is proposed.

[0017] In addition, the high-carbon low-alloy wear-resistant forged balls according to the above embodiments of the present invention may also have the following additional technical features:

[0018] In some embodiments of the present invention, the microstructure of the wear-resistant forged ball consists of fine tempered martensite and uniformly distributed carbides. Retaining some undissolved carbides during the quenching process has the following three effects: undissolved carbides, as a hard phase, can significantly improve the wear resistance of the forged ball; the presence of undissolved carbides can reduce the carbon content of the martensitic matrix, reduce the tendency of martensite to crack, and improve impact toughness; undissolved carbides restrict martensite growth during martensite formation, which can reduce martensite grain size and improve strength and toughness.

[0019] In some embodiments of the present invention, the wear-resistant forged ball has a hardness of not less than 60 HRC and an impact toughness of not less than 70 J / cm². The fundamental reason for this is that during the quenching process, some undissolved carbides are controlled, reducing the carbon content of the martensitic matrix and obtaining cryptocrystalline martensite, thereby achieving high impact toughness while maintaining high hardness.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1) This invention employs a specific isothermal spheroidizing annealing process (770℃ → rapid cooling to 680℃ isothermally), replacing traditional normalizing or full annealing, successfully transforming the original lamellar pearlite structure after forging into a uniform, fine granular pearlite structure. This structure provides numerous and uniform nucleation sites for austenite during subsequent quenching heating.

[0022] 2) Due to the high austenite nucleation rate, the martensite structure obtained after quenching in this invention is finer and more uniform, with a more reasonable distribution of retained austenite. This refined microstructure is key to simultaneously improving both hardness and toughness.

[0023] 3) The forged balls processed by this process maintain high hardness (≥60 HRC) while significantly improving impact toughness (≥100 J / cm²), effectively solving the problem of difficulty in balancing hardness and toughness in large-size grinding balls. It is expected to greatly reduce the breakage rate of grinding balls during use and extend their service life.

[0024] 4) The process of this invention is stable and the cost is controllable: The process parameters are clear and the operation is strong. There is no need to add expensive alloying elements or complex equipment. It is easy to implement and promote under existing production conditions and has good prospects for industrial application. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the heat treatment process in Embodiment 1 of the present invention;

[0026] Figure 2 The images show the microstructure of the high-carbon low-alloy wear-resistant forged balls after treatment in Comparative Example 1(a) and Example 1(b) of this invention, as well as metallographic photographs (a1, b1) and scanning electron microscope photographs (a2, b2). Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] like Figure 1 As shown, a heat treatment process for high-carbon, low-alloy wear-resistant forged balls includes the following steps:

[0030] (1) A forged ball sample of Φ140mm B6 steel with a weight percentage of 0.76% C, 0.29% Si, 0.90% Mn, 0.89% Cr, 0.013% P, 0.044% Al, and the remainder being Fe and unavoidable impurities was selected.

[0031] (2) Isothermal spheroidizing annealing: The sample is heated to 770°C at 10°C / min and held for 1 hour; then it is quickly transferred to a furnace at 680°C and held for 3 hours; then it is cooled to 550°C in the furnace and then air-cooled after being removed from the furnace.

[0032] (3) Quenching: The sample treated in step (2) is heated to 780°C at 10°C / min, held for 20 min, and then quickly immersed in quenching oil to cool to room temperature after being taken out of the furnace.

[0033] (4) Tempering: The quenched sample is heated to 180°C at 10°C / min, held for 120 min, and then air-cooled after being taken out of the furnace.

[0034] Example 2

[0035] A heat treatment process for high-carbon, low-alloy wear-resistant forged balls includes the following steps:

[0036] (1) A forged ball sample of Φ140mm B6 steel with a weight percentage of 0.76% C, 0.29% Si, 0.90% Mn, 0.89% Cr, 0.013% P, 0.044% Al, and the remainder being Fe and unavoidable impurities was selected.

[0037] (2) Isothermal spheroidizing annealing: The sample was heated to 770°C at 10°C / min and held for 1.5 hours; then it was quickly transferred to a furnace at 680°C and held for 3 hours; then it was cooled to 550°C in the furnace and then removed from the furnace and air-cooled.

[0038] (3) Quenching: The sample treated in step (2) is heated to 780°C at 10°C / min, held for 20 min, and then quickly immersed in quenching oil to cool to room temperature after being taken out of the furnace.

[0039] (4) Tempering: The quenched sample is heated to 180°C at 10°C / min, held for 120 min, and then air-cooled after being taken out of the furnace.

[0040] Example 3

[0041] A heat treatment process for high-carbon, low-alloy wear-resistant forged balls includes the following steps:

[0042] (1) A forged ball sample of Φ140mm B6 steel with a weight percentage of 0.76% C, 0.29% Si, 0.90% Mn, 0.89% Cr, 0.013% P, 0.044% Al, and the remainder being Fe and unavoidable impurities was selected.

[0043] (2) Isothermal spheroidizing annealing: The sample is heated to 770°C at 10°C / min and held for 2 hours; then it is quickly transferred to a furnace at 680°C and held for 3 hours; then it is cooled to 550°C in the furnace and then air-cooled after being removed from the furnace.

[0044] (3) Quenching: The sample treated in step (2) is heated to 780°C at 10°C / min, held for 20 min, and then quickly immersed in quenching oil to cool to room temperature after being taken out of the furnace.

[0045] (4) Tempering: The quenched sample is heated to 180°C at 10°C / min, held for 120 min, and then air-cooled after being taken out of the furnace.

[0046] Example 4

[0047] A heat treatment process for high-carbon, low-alloy wear-resistant forged balls includes the following steps:

[0048] (1) A forged ball sample of Φ140mm B6 steel with a weight percentage of 0.76% C, 0.29% Si, 0.90% Mn, 0.89% Cr, 0.013% P, 0.044% Al, and the remainder being Fe and unavoidable impurities was selected.

[0049] (2) Isothermal spheroidizing annealing: The sample is heated to 770°C at 10°C / min and held for 1.5 hours; then it is quickly transferred to a furnace at 670°C and held for 3 hours; then it is cooled to 550°C in the furnace and then air-cooled.

[0050] (3) Quenching: The sample treated in step (2) is heated to 780°C at 10°C / min, held for 20 min, and then quickly immersed in quenching oil to cool to room temperature after being taken out of the furnace.

[0051] (4) Tempering: The quenched sample is heated to 180°C at 10°C / min, held for 120 min, and then air-cooled after being taken out of the furnace.

[0052] Example 5

[0053] A heat treatment process for high-carbon, low-alloy wear-resistant forged balls includes the following steps:

[0054] (1) A forged ball sample of Φ140mm B6 steel with a weight percentage of 0.76% C, 0.29% Si, 0.90% Mn, 0.89% Cr, 0.013% P, 0.044% Al, and the remainder being Fe and unavoidable impurities was selected.

[0055] (2) Isothermal spheroidizing annealing: The sample is heated to 770°C at 10°C / min and held for 1.5 hours; then it is quickly transferred to a furnace at 690°C and held for 3 hours; then it is cooled to 550°C in the furnace and then air-cooled after being removed from the furnace.

[0056] (3) Quenching: The sample treated in step (2) is heated to 780°C at 10°C / min, held for 20 min, and then quickly immersed in quenching oil to cool to room temperature after being taken out of the furnace.

[0057] (4) Tempering: The quenched sample is heated to 180°C at 10°C / min, held for 120 min, and then air-cooled after being taken out of the furnace.

[0058] Comparative Example 1

[0059] A heat treatment process for high carbon low alloy wear-resistant forged balls, which differs from Example 1 only in that step (2) isothermal spheroidizing annealing is not performed.

[0060] The hardness and impact toughness of the high-carbon low-alloy wear-resistant forged balls prepared in Example 1 and Comparative Example 1 were tested according to national standards. The performance test results are shown in the table below:

[0061] Table 1. Performance test results of high-carbon low-alloy wear-resistant forged balls prepared in Examples 1-5 and Comparative Example 1.

[0062] Test results show that, under the same hardness, the impact toughness of the forged balls treated with the process of Example 1 is increased by approximately 38% compared to the process of Comparative Example 1, resulting in a significant improvement in overall mechanical properties. This indicates that the heat treatment process provided by this invention can effectively optimize the microstructure of high-carbon low-alloy wear-resistant forged balls, achieving a good match between hardness and impact toughness. It is particularly suitable for the production of large-size wear-resistant forged balls and has significant industrial application value.

[0063] Appendix Figure 2The images show the microstructure of the high-carbon low-alloy wear-resistant forged balls after treatment in Comparative Example 1(a) and Example 1(b) of this invention, with metallographic photographs (a1, b1) and scanning electron microscope (SEM) images (a2, b2). The microstructure of Comparative Example 1 is mainly acicular tempered martensite, which is relatively coarse, with some coarse martensite lamellae penetrating the grains clearly visible. In Example 1, the martensite lamellae are significantly refined, and there are undissolved carbides of uneven size. The carbides in the spherical pearlite dissolve slowly during quenching and heating, hindering austenite grain growth, and also hindering the growth of martensite lamellae during cooling, ultimately resulting in a composite microstructure of fine-grained martensite + spherical carbides.

[0064] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A heat treatment process for high carbon low alloy wear resistant forged ball, characterized by, The method comprises the following steps: S1, isothermal spheroidizing annealing: a high-carbon low-alloy forged ball which is forged and air-cooled to room temperature is heated to 750-780 ℃ and held for 1-3 hours, then rapidly cooled to 670-720 ℃ and held for 2-4 hours at this temperature, and finally furnace-cooled to below 500-600 ℃ and then air-cooled after being taken out of the furnace; S2, quenching: the forged ball treated in step S1 is heated to 770-800 ℃ and held for 15-60 minutes, and then cooled to room temperature by being put into quenching oil; S3, tempering: the forged ball treated in step S2 is heated to 170-220 ℃ and held for 60-150 minutes, and then air-cooled after being taken out of the furnace.

2. The heat treatment process of high carbon low alloy wear resistant forged ball as claimed in claim 1 wherein, In step S1, the high-carbon low-alloy forged ball comprises the following components by weight percentage: 0.74%-0.85% of C, 0.15%-0.35% of Si, 0.90%-1.05% of Mn, 0.88%-0.98% of Cr, less than or equal to 0.02% of P, 0.025%-0.045% of Al, and the rest of Fe and inevitable impurities.

3. The heat treatment process of high carbon low alloy wear resistant forged ball as claimed in claim 1 wherein: In step S1, the heating rate is 80-150 ℃ / h.

4. The heat treatment process of high carbon low alloy wear resistant forged ball as claimed in claim 1 wherein: In step S2, the heating rate is 80-150 ℃ / h.

5. The heat treatment process of high carbon low alloy wear resistant forged ball as claimed in claim 1 wherein: In step S3, the heating rate is 50-100 ℃ / h.

6. A high-carbon low-alloy wear-resistant forged ball obtained by the heat treatment process according to any one of claims 1-5.

7. A high-carbon low-alloy wear-resistant forged ball according to claim 6, characterized in that: The microstructure of the wear-resistant forged ball is fine tempered martensite and uniformly distributed carbides.

8. A high-carbon low-alloy wear-resistant forged ball according to claim 6, characterized in that: The hardness of the wear-resistant forged ball is not less than 60 HRC, and the impact toughness is not less than 70 J / cm².

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