A high-precision steel ball production process based on multi-station cold upsetting forming

Abstract

The present application belongs to the technical field of cold heading forming of metal parts, and particularly relates to a high-precision steel ball production process based on multi-station cold heading forming. The present application adds appropriate nano needle-shaped nickel molybdenum alloy and metal vanadium particles on the basis of the original high-carbon alloy steel composition, designs a new micro-alloy high-carbon grinding ball steel material, and the steel ball has high hardness, good impact fatigue life and excellent wear resistance. By optimizing the continuous casting electromagnetic stirring process parameters, the low-multiple quality and composition uniformity of the steel ball steel are improved, the heating process, rolling process and heat treatment process are optimized, the grain is refined, the strength and toughness are improved, the impact fatigue life and wear resistance are improved, and the problem of low drop ball life of high-carbon alloy steel ball is solved.

Description

Technical Field

[0001] This invention belongs to the field of cold heading technology for metal parts, and specifically relates to a high-precision steel ball production process based on multi-station cold heading. Background Technology

[0002] Steel balls are core components in bearings, precision instruments, and automotive parts. Their dimensional accuracy, geometric accuracy (sphericity), surface roughness, and material properties directly affect the performance and lifespan of the final product. Traditional steel ball manufacturing processes mainly involve multiple steps, including cold heading, smoothing, heat treatment, hard grinding, preliminary grinding, and final grinding. Among these, cold heading, as the initial step, is crucial for the subsequent machining allowances and final precision.

[0003] Existing cold heading processes mostly employ single-station or double-station cold heading machines, which have the following drawbacks: Dispersed processes: Multiple heating and transfer operations are required, resulting in low production efficiency, high energy consumption, and the risk of damage from repeated clamping. Poor precision consistency: Large deformation in a single forming operation leads to uneven distribution of internal material flow lines, easily causing defects such as cracks and folds, resulting in poor roundness and dimensional consistency of the steel ball blanks. Large machining allowance: Due to the low precision of the blanks, a large grinding allowance must be reserved to ensure a high yield, which not only increases the time and abrasive consumption of subsequent grinding processes but also reduces material utilization. Poor surface quality: Inaccurate control of friction and deformation during forming results in high surface roughness, requiring extensive subsequent machining to compensate. Therefore, there is an urgent need for a process that can produce high-precision, highly consistent steel ball blanks in a single operation to reduce subsequent machining, lower production costs, and improve overall efficiency and product quality.

[0004] Because high-carbon alloy grinding balls do not contain nano-needle-shaped nickel-molybdenum alloy and trace amounts of vanadium, they exhibit coarse and uneven grain size during heating or hot deformation, leading to quality problems such as insufficient impact fatigue life and out-of-roundness during use. Therefore, this invention adds appropriate amounts of nano-needle-shaped nickel-molybdenum alloy and metallic vanadium particles to the original high-carbon alloy steel composition, designing a new micro-alloyed high-carbon grinding ball steel material. The resulting steel balls possess high hardness, good impact fatigue life, and excellent wear resistance. Furthermore, by optimizing the continuous casting electromagnetic stirring process parameters, the low-density mass and compositional uniformity of the steel used for the balls are improved. Optimizing the heating, rolling, and heat treatment processes refines the grain size, increases strength and toughness, and improves impact fatigue life and wear resistance, thus solving the quality problem of low drop life in high-carbon alloy steel balls. Summary of the Invention

[0005] To address the above problems, this invention provides a high-precision steel ball production process based on multi-station cold heading, characterized by the following specific steps:

[0006] S1. Copper nanoneedles were prepared using copper foam as a substrate; they were electrodeposited in a plating solution containing nickel and molybdenum to obtain a nanoneedle-shaped nickel-molybdenum alloy.

[0007] S2. Raw materials such as scrap steel or ferroalloys are initially smelted in an electric arc furnace at a temperature of 3250-3875 °C for 43-87 min; the tapping temperature is controlled at 1780-1820 °C; in a ladle refining furnace, argon gas is introduced for stirring; vanadium nanoparticles are added; the temperature is lowered to 1280-1340 °C, and nano-needle-shaped nickel-molybdenum alloy prepared in S1 is added; stirring is carried out for 53-76 min, and the ladle is placed in a vacuum chamber to allow the gas in the molten steel to escape; the molten steel is continuously cast, cooled, and cut into steel billets of fixed lengths through a continuous casting machine;

[0008] S3. The solidified steel billet from S2 undergoes plastic processing, followed by initial rolling at 1104-1183 ℃ and final rolling at 813-895 ℃; then, it is rolled at 63-86 ℃ min. -1 After cooling the temperature to 688-648 ℃, adjust the cooling rate to 8-10 ℃ / min. -1 ;

[0009] S4. Heat the steel billet prepared in S3 to 754-789 ℃ for post-rolling treatment and spheroidizing annealing;

[0010] S5. Cut the steel treated in S4 into cylindrical blanks, extrude upsetting balls, and extrude the upsetting balls into cup-shaped sleeves; use a conical half-die to extrude the end of the connecting rod into a conical upsetting head, and then use a spherical half-die to extrude it into a spherical head; rotate the workpiece 90° and extrude the spherical head into a flat spherical head, and then extrude symmetrical concave platforms from the two ends of the flat spherical head towards each other, forming through holes; the cold-extruded spherical blanks need to undergo stress-relieving annealing, with a low-temperature tempering temperature of 152-168 ℃ and a holding time of 2.3-3.7 h;

[0011] S6. Remove the ring, two poles and surface oxide layer of the spherical blank prepared in S5, quench at 1035-1058 ℃, temper at 473-485 ℃, and cold treat at -44 ℃.

[0012] S7. Grind the steel ball described in S6 in a closed environment with constant temperature of 23±2℃, constant humidity of 60-65%, and dust-free environment using a 3000-8000 grit resin grinding wheel. Gradually reduce the grinding plate pressure, adjust the spindle speed to 26-34 rpm, and control the grinding efficiency from 2-3 μm / h to 0.75-0.82 μm / h, so that the variation in the diameter of the steel ball is controlled within 0.01-0.25 μm.

[0013] The specific operating steps are as follows:

[0014] S1. Soak copper foam in 1-3 M HCl solution for ultrasonic cleaning for 8-11 min, rinse thoroughly with water, and then soak in isopropanol for another 8-10 min of ultrasonic cleaning; followed by ultrasonic cleaning with water for 8-10 min, drying, and then immersing in 25-28% ammonium fluoride solution for 2-3 min, followed by rinsing to obtain pretreated copper foam; Soak the copper foam in a 3-5 M KOH or NaOH solution containing 0.03-0.21 g of sodium thiosulfate or ammonium thiosulfate in an Ar atmosphere for 40-55 min to obtain copper hydroxide nanoneedles; Electroreduc the copper hydroxide nanoneedles to copper nanoneedles in 2-4 M NaHCO3 electrolyte at a reduction voltage of -1.1 V; Then, using the copper nanoneedles as the working electrode, in a solution containing 0.54-0.68 g nickel nitrate or nickel sulfate, 0.31-0.76 g sodium molybdate or ammonium molybdate, and 0.9-1.3 g... Nanoneedle-shaped nickel-molybdenum alloys can be obtained by electrodeposition in a solution of ethylenediamine (g), 0.43-0.52 g sodium dodecyl sulfate (NDS), 121-130 μL 98% sulfuric acid, and 35-42 mL distilled water for 900-1300 s. The main purpose of this step is to clean the surface of the copper foam of 0.43-0.52 g, ensuring the stability and repeatability of subsequent reactions. Brief immersion in ammonium fluoride makes the surface of the copper foam more hydrophobic, preventing it from contacting KOH or NaOH too quickly in subsequent steps, thus promoting the formation of uniform nanoneedle morphology. Immersion in KOH or NaOH ensures the copper foam is exposed to an OH--rich environment, and the use of sodium thiosulfate or ammonium thiosulfate ensures the rapid formation of the nanoneedle array. This step reduces the copper oxide array structure to a copper array structure, improving its conductivity and facilitating the deposition of the nickel-molybdenum alloy.

[0015] S2. Scrap steel or ferroalloys are initially smelted in an electric arc furnace. The average furnace temperature gradually increases from room temperature, with the arc zone temperature controlled at 3250-3875 °C and the melting time controlled at 43-87 min. Simultaneously, oxygen is continuously blown at an oxygen supply intensity of 27-42 Nm³ / t·h, with a total oxygen supply controlled at 33-47 Nm³ / t per ton of steel; 3-8 kg / t·min (kg / ton of steel·min). Additionally, nitrogen is used as a carrier gas for carbon injection at an intensity of 3.1-7.6 kg / t·min (kg / ton of steel·min), with the carbon injection amount controlled at 2.5-6.4 kg / t (kg / ton of steel) and the gas pressure controlled at 0.42-0.83 MPa. After the initial smelting, the tapping temperature of the electric arc furnace is controlled at 1780-1820 °C. The molten steel is then transferred to a ladle refining furnace, where argon gas is continuously introduced for stirring for 56-88 minutes. For 103-172 min, the temperature drops by 93-118 °C; 0.03-0.08% vanadium nanoparticles are added; stirring continues for 103-172 min, and the temperature is allowed to drop to 1280-1340 °C. Then, 0.24-0.31% of the nano-needle-shaped nickel-molybdenum alloy prepared in step S1 is added; stirring continues in an argon atmosphere for 53-76 min. The ladle is then placed in a vacuum chamber, with the pressure controlled at 56.5-103.4 Pa. This significant reduction in ambient pressure forces gases out of the molten steel. Finally, the molten steel is continuously cast, cooled, and cut into billets of fixed length using a continuous casting machine. In this step, a high-temperature electric arc is used to break down and melt the cold scrap steel. The high temperature ensures good fluidity of the molten steel and slag, facilitating chemical reactions and impurity removal. Strict control of oxygen blowing intensity and supply in this step ensures that the oxygen jet has sufficient kinetic energy to penetrate the foamy slag layer, impact the molten pool, and effectively participate in the reaction. In this step, the oxygen injection not only burns off impurities, but more importantly, it reacts with elements such as carbon and iron in the scrap steel to generate a large amount of chemical heat (C + 1 / 2O2 → CO + Heat). This chemical energy provides 25%-35% of the total energy required in the furnace, greatly accelerating melting. Additionally, carbon powder is injected into the molten pool, reacting with the blown-in oxygen to generate CO bubbles, causing vigorous "carbon boiling." This not only generates chemical heat but also agitates the molten pool, making heat transfer more uniform and avoiding "cold zones." The benefits of introducing vanadium nanoparticles in this step include: Vanadium is a strong carbide and nitride forming element. During the heating (austenitization) and heat treatment of steel, vanadium nanoparticles dissolve. During subsequent cooling or tempering, it precipitates in an extremely fine, dispersed form as nanoscale vanadium carbide or vanadium carbonitride particles. These nanoprecipitates can extremely effectively hinder dislocation movement. This can significantly increase the yield strength and tensile strength of the steel ball, resulting in a higher and more uniform macroscopic hardness.

[0016] S3. The steel billet solidified in step S2 is subjected to plastic processing at 1153-1246 ℃, ensuring sufficient heating time according to the billet size, and ensuring K is 1.4-1.8 min cm. -1 After being removed from the heating furnace, it is rolled at 1104-1183 ℃, and then finished rolling is carried out at 813-895 ℃ to ensure that the deformation is completed in a single austenitic region; then it is rolled at 63-86 ℃ for min. -1 The cooling rate was increased to 688-648 ℃, and after rapid cooling, the cooling rate was adjusted to 8-10 ℃ / min. -1 To prevent excessive internal stress, this step involves controlling the cooling rate through the regions where carbides are most likely to precipitate, thus preventing the formation of network carbides at the austenite grain boundaries. Network carbides are brittle and severely reduce the bearing's toughness and fatigue strength. The purpose of this step is to uniformly heat the cast steel billet to the austenitic temperature range suitable for plastic deformation, ensuring complete austenitization and reducing deformation resistance.

[0017] S4. Heat the steel billet prepared in step S3 to 754-789 ℃ for post-rolling treatment and spheroidizing annealing, and hold for 180-220 min. Then peel or polish the steel to remove the decarburized layer, cracks and other defects on the surface to ensure surface quality. The purpose of this step is to transform the hard and brittle lamellar pearlite in the rolled structure into a soft, easy-to-cut and cold-form spheroid pearlite structure.

[0018] S5. Cut the steel processed in step S4 into cylindrical blanks of a predetermined length, then extrude upsetting balls of the required diameter, and further extrude the upsetting balls into cup-shaped sleeves; then use a conical half-die to extrude the end of the connecting rod into a conical upsetting head, and then use a spherical half-die to extrude it into a spherical head; the ball blank design adopts a shape with a bipolar cone angle (2α) of 95-125° and a ring to reduce deformation stress and material loss; rotate the workpiece 90° and extrude the spherical head into a flat spherical head, then extrude symmetrical concave platforms from the two ends of the flat spherical head towards each other, and finally extrude towards each other to form a through hole; the ball blank after cold upsetting needs to be stress-relieved annealed at a low temperature of 152-168 ℃ and held for 2.3-3.7 h to eliminate the internal stress generated by cold upsetting.

[0019] S6. Remove the ring, polarity, and surface oxide layer from the spherical billet prepared in step S5 to make it basically spherical; quench at 1035-1058 ℃, temper at 473-485 ℃, and cold treat at -44 ℃ for 152-175 min. Then, perform surface strengthening treatment on a steel ball strengthening machine. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth of 0.15-0.32 mm is formed on the surface to improve the distribution of residual compressive stress and enhance the fatigue resistance of the steel balls. The purpose of the cold treatment in this step is to increase the hardness of the steel balls, stabilize the microstructure, and eliminate residual austenite. The purpose of the hard grinding in this step is to correct the roundness and spherical error. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth greater than 0.2 mm is formed on the surface to improve the distribution of residual compressive stress and enhance the fatigue resistance.

[0020] S7. The steel balls obtained in step S6 are precision ground in a closed environment with constant temperature of 23±2℃, constant humidity of 60-65%, and dust-free environment using a 3000-8000 grit resin grinding wheel. The grinding plate pressure is gradually reduced from 19-21 KN to 11-13 KN, the spindle speed is adjusted to 26-34 rpm, and the grinding efficiency is controlled from 2-3 μm / h to 0.75-0.82 μm / h, so that the variation in the diameter of the steel balls is controlled within 0.01-0.25 μm.

[0021] Preferably: In step S1 of the present invention, the foamed copper is ultrasonically cleaned in 2 M HCl solution for 8 min, rinsed with water, and then ultrasonically cleaned in isopropanol for 10 min; then ultrasonically cleaned with water for 8 min, dried, and then soaked in 28% ammonium fluoride solution for 2 min, and rinsed clean to obtain pretreated foamed copper; the foamed copper is then soaked in 5 M KOH solution containing 0.21 g sodium thiosulfate in an Ar atmosphere for 55 min to obtain copper hydroxide nanoneedles; the copper hydroxide nanoneedles are electroreduced to copper nanoneedles in 2 M NaHCO3 electrolyte with a reduction voltage of -1.1 V; then, using the copper nanoneedles as the working electrode, electrodeposition is performed for 900 s in a solution containing 0.68 g nickel nitrate, 0.76 g ammonium molybdate, 0.9 g ethylenediamine, 0.52 g sodium dodecyl sulfate, 121 μL 98% nickel sulfate, and 42 mL distilled water to obtain nanoneedle-shaped nickel-molybdenum alloy.

[0022] Preferably, in step S2 of this invention, scrap steel or ferroalloys are initially smelted in an electric arc furnace. The average temperature inside the furnace gradually increases from room temperature, the temperature in the electric arc zone is controlled at 3875 °C, and the melting time is controlled at 43 min. Simultaneously, oxygen is continuously blown at an oxygen supply intensity of 27 Nm³ / t·h, with the total oxygen supply controlled at 47 Nm³ / t per ton of steel; 3-8 kg / t·min; nitrogen is also used as a carrier gas for carbon injection at a carbon injection intensity of 7.6 kg / t·min, with the carbon injection amount controlled at 6.4 kg / t and the gas pressure controlled at 0.83 MPa. After the initial smelting, the tapping temperature of the electric arc furnace is controlled at 1780 °C. The molten steel is transferred to a ladle refining furnace, and argon gas is continuously introduced for stirring for 88 min, causing the temperature to drop by 93 °C. 0.08% vanadium nanoparticles are added; stirring continues for 103 min, and after the temperature drops to 1280 °C, 0.31% vanadium nanoparticles are added. The nano-needle-shaped nickel-molybdenum alloy prepared in step S1 was stirred for 53 min in an argon atmosphere. Then, the ladle was placed in a vacuum chamber with the pressure controlled at 103.4 Pa. By significantly reducing the ambient pressure, the gas in the molten steel was forced to escape. Finally, the molten steel was continuously cast, cooled, and cut into billets of fixed lengths by a continuous casting machine.

[0023] Preferably, in step S3 of the present invention, the steel billet solidified in step S2 is subjected to plastic processing at 1153 °C, and sufficient heating time is ensured according to the size of the steel billet to ensure that K is 1.8 min cm. -1 Next, after being removed from the heating furnace, it is rolled at 1104 °C, and then finished rolling is carried out at 895 °C to ensure that the deformation is completed within a single austenitic region; then it is rolled at 63 °C for min. -1 The cooling rate was adjusted to reduce the temperature to 648 °C. After rapid cooling, the cooling rate was further adjusted to 8 °C / min. -1 This is to prevent excessive internal stress from being generated.

[0024] Preferably, in step S4 of the present invention, the steel billet prepared in step S3 is heated to 789 °C for post-rolling treatment and spheroidizing annealing, and the holding time is 180 min; then the steel is peeled or polished to remove the decarburized layer, cracks and other defects on the surface to ensure surface quality; the purpose of this step is to transform the hard and brittle lamellar pearlite in the rolled structure into a soft, easily machinable and cold-formable spheroidal pearlite structure.

[0025] Preferably: In step S5 of the present invention, the steel processed in step S4 is cut into cylindrical blanks of a predetermined length, and then an upsetting ball of the required diameter is extruded. The upsetting ball is further extruded into a cup-shaped sleeve. Then, a conical half-die is used to extrude the end of the connecting rod into a conical upsetting head, and then a spherical half-die is used to extrude it into a spherical head. The ball blank is designed with a bipolar cone angle 2α of 95° and a ring shape to reduce deformation stress and material loss. The workpiece is rotated 90° and the spherical head is extruded into a flat spherical head. Then, symmetrical concave platforms are extruded from the two ends of the flat spherical head, and finally, through holes are formed by extrusion. The ball blank after cold upsetting needs to be stress-relieved annealed at a low temperature of 152 ℃ and held for 3.7 h to eliminate the internal stress generated by cold upsetting.

[0026] Preferably, in step S6 of the present invention, the ring, two poles and surface oxide layer of the spherical blank prepared in step S5 are removed to make it basically spherical; it is quenched at 1035 ℃, tempered at 473 ℃, and cold treated at -44 ℃ for 175 min. Then, it is surface strengthened on a steel ball strengthening machine. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth of 0.15 mm is formed on the surface, which improves the distribution of residual compressive stress and improves the fatigue resistance of the steel balls.

[0027] Preferably, in step S7 of the present invention, the steel ball obtained in step S6 is precision ground in a closed environment with constant temperature of 23±2℃, constant humidity of 65%, and dust-free environment using a 3000-mesh resin grinding wheel. The grinding plate pressure is gradually reduced from 19KN to 11KN, the spindle speed is adjusted to 34 rpm, and the grinding efficiency is controlled to decrease from 2 μm / h to 0.75 μm / h, so that the variation in the diameter of the steel ball is controlled within 0.25 μm.

[0028] Preferably, the reference electrode used in step S1 of the present invention is an Ag / AgCl electrode.

[0029] Preferably, the reference electrode used in step S1 of the present invention is a saturated calomel electrode.

[0030] Preferably, the carbon used in the carbon injection process of the present invention is anthracite powder or coke powder.

[0031] Preferably, the carbon used in the carbon spraying process of the present invention has a fixed carbon content of 85% and a particle size of less than 1 mm.

[0032] Preferably, the surface strengthening method described in this invention uses an LZJ09-S type steel ball strengthening machine.

[0033] Preferably, the surface strengthening process described in this invention is often performed before or after cold pickling to expose surface defects and facilitate the removal of defective products.

[0034] Preferably, the present invention uses a five-station high-speed precision cold heading machine of model ZSB-105S.

[0035] The beneficial effects of this invention are:

[0036] 1. Microalloying is achieved by adding nano-needle-shaped nickel-molybdenum alloy and metallic vanadium particles. The nickel-molybdenum alloy refines austenite grains, improves hardenability, and enhances the toughness of the matrix; vanadium forms dispersed vanadium carbonitride particles, producing a strong precipitation strengthening effect, significantly improving the strength, wear resistance, and fatigue resistance of the steel. The synergistic effect of these two components allows the steel ball to maintain high hardness while significantly increasing its impact fatigue life.

[0037] 2. By optimizing the electromagnetic stirring parameters in continuous casting, the central porosity and compositional segregation of the steel billet were significantly improved, enhancing the material uniformity from the source and laying the foundation for subsequent processing and performance consistency. Optimized rolling and heat treatment processes further refined the grains, achieving an optimal balance between strength and toughness in the material.

[0038] 3. The steel balls produced by this invention are not only highly precise and hard, but also have a longer impact life than steel balls of the same specifications produced by traditional processes, and improved wear resistance, thus solving the core quality problem of low impact life of high carbon alloy steel balls.

[0039] 4. Combined with multi-station cold heading forming process, it has high material utilization and high production efficiency, making it suitable for large-scale industrial production. Attached Figure Description

[0040] Figure 1 The image shows the XRD pattern of the nano-needle-shaped nickel-molybdenum alloy prepared in Example 1 of this invention.

[0041] Figure 2 This is a TEM image of the nanoneedle-shaped nickel-molybdenum alloy prepared in Example 1 of the present invention.

[0042] Figure 3 This is a SEM image of the copper nanoneedles prepared in Example 2 of the present invention.

[0043] Figure 4 This is a SEM image of the copper nanoneedles prepared in Comparative Example 5 of this invention.

[0044] Figure 5 The images show the XRD patterns of the steel balls prepared in Examples 3 and 4 of this invention. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all 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.

[0046] Example 1

[0047] S1. Soak the copper foam in 1 M HCl solution for 8 min using ultrasonic cleaning, rinse with water, and then soak in isopropanol for another 8 min using ultrasonic cleaning. Next, sonicate with water for 8 min, air dry, and then immerse in a 25% ammonium fluoride solution for 2 min, followed by rinsing to obtain pretreated copper foam. Soak the copper foam in a 3 M KOH solution containing 0.03 g ammonium thiosulfate in an Ar atmosphere for 40 min to obtain copper hydroxide nanoneedles. Electrodegrade the copper hydroxide nanoneedles to copper nanoneedles in 2 M NaHCO3 electrolyte at a reduction voltage of -1.1 V. Then, using the copper nanoneedles as the working electrode, electrodeposit 900 μm of a solution containing 0.54 g nickel nitrate, 0.31 g sodium molybdate, 0.9 g ethylenediamine, 0.43 g sodium dodecyl sulfate, 121 μL 98% sulfuric acid, and 35 mL distilled water. Nanoneedle-shaped nickel-molybdenum alloys can be obtained in this step. The main purpose of this step is to clean the impurities and oil on the surface of the foamed copper, ensuring the stability and repeatability of subsequent reactions. The purpose of briefly soaking in ammonium fluoride is to make the surface of the foamed copper more hydrophobic, ensuring that it does not come into contact with KOH too quickly in subsequent steps, thereby promoting the formation of uniform nanoneedle morphology. Soaking the foamed copper in KOH ensures that it is exposed to an OH- rich environment, and the use of sodium thiosulfate ensures the rapid formation of nanoneedle arrays. This step reduces the copper oxide array structure to a copper array structure, improving its conductivity and facilitating the deposition of nickel-molybdenum alloys.

[0048] S2. Scrap steel or ferroalloys are initially smelted in an electric arc furnace. The average furnace temperature gradually increases from room temperature, with the arc zone temperature controlled at 3250 °C and the melting time controlled at 43 min. Simultaneously, oxygen is continuously purged at an oxygen supply intensity of 27 Nm³ / t·h, with a total oxygen supply controlled at 33 Nm³ / t per ton of steel; 3 kg / t·min (kg / ton steel·min). Additionally, nitrogen is used as the carrier gas for carbon injection at an intensity of 3.1 kg / t·min (kg / ton steel·min), with the carbon injection amount controlled at 2.5 kg / t (kg / ton steel) and the gas pressure controlled at 0.42 MPa. After the initial smelting, the tapping temperature of the electric arc furnace is controlled at 1780 °C. The molten steel is then transferred to a ladle refining furnace, where argon gas is continuously introduced and stirred for 56 min, causing the temperature to drop by 93 °C. 0.03% vanadium nanoparticles are added; stirring continues for 103 minutes. After waiting for the temperature to drop to 1280°C, 0.24% of the nano-needle-shaped nickel-molybdenum alloy prepared in step S1 is added. Stirring continues for 53 minutes in an argon atmosphere. The ladle is then placed in a vacuum chamber with the pressure controlled at 56.5 Pa. This significant reduction in ambient pressure forces the gases in the molten steel to escape. Finally, the molten steel is continuously cast, cooled, and cut into billets of fixed lengths using a continuous casting machine. In this step, a high-temperature electric arc is used to break down and melt the cold scrap steel. The high temperature ensures good fluidity of the molten steel and slag, facilitating chemical reactions and impurity removal. Strict control of the oxygen blowing intensity and supply in this step ensures that the oxygen jet has sufficient kinetic energy to penetrate the foamy slag layer, impact the molten pool, and effectively participate in the reaction. The oxygen injection in this step not only burns off impurities but, more importantly, reacts with carbon, iron, and other elements in the scrap steel to generate a large amount of chemical heat (C + 1 / 2O2 → CO + Heat). This chemical energy provides 25%-35% of the total energy required in the furnace, greatly accelerating melting. Additionally, carbon powder is injected into the molten pool, reacting with the blown-in oxygen to generate CO bubbles, causing vigorous "carbon boiling." This not only generates chemical heat but also agitates the molten pool, making heat transfer more even and avoiding "cold zones."

[0049] S3. The steel billet solidified in step S2 is subjected to plastic processing at 1153 °C, ensuring sufficient heating time based on the billet size, and ensuring K is 1.4 min cm. -1 After being removed from the heating furnace, it is rolled at 1104 °C, followed by final rolling at 813 °C to ensure that the deformation is completed within a single austenitic region; then rolled at 63 °C for a minimum of 1 minute. -1 The cooling rate was increased to 688 °C, and after rapid cooling, the cooling rate was adjusted to 8 °C / min. -1To prevent excessive internal stress, this step involves controlling the cooling rate through the regions where carbides are most likely to precipitate, thus preventing the formation of network carbides at the austenite grain boundaries. Network carbides are brittle and severely reduce the bearing's toughness and fatigue strength. The purpose of this step is to uniformly heat the cast steel billet to the austenitic temperature range suitable for plastic deformation, ensuring complete austenitization and reducing deformation resistance.

[0050] S4. Heat the steel billet prepared in step S3 to 754 ℃ for post-rolling treatment and spheroidizing annealing, and hold for 180 min. Then peel or polish the steel to remove the decarburized layer, cracks and other defects on the surface to ensure surface quality. The purpose of this step is to transform the hard and brittle lamellar pearlite in the rolled structure into a soft, easy-to-cut and cold-form spheroid pearlite structure.

[0051] S5. The steel processed in step S4 is cut into cylindrical blanks of a predetermined length, and then an upsetting ball of the required diameter is extruded. The upsetting ball is further extruded into a cup-shaped sleeve. Then, a conical half-die is used to extrude the end of the connecting rod into a conical upsetting head, and then a spherical half-die is used to extrude it into a spherical head. The ball blank is designed with a bipolar cone angle (2α) of 95° and a ring shape to reduce deformation stress and material loss. The workpiece is rotated 90° and the spherical head is extruded into a flat spherical head. Then, symmetrical concave platforms are extruded from the two ends of the flat spherical head, and finally, through holes are formed by extrusion. The ball blank after cold upsetting needs to be stress-relieved annealed at a low temperature of 152 ℃ and held for 2.3 h to eliminate the internal stress generated by cold upsetting.

[0052] S6. Remove the ring, polarity, and surface oxide layer from the spherical billet prepared in step S5 to make it basically spherical; quench at 1035 ℃, temper at 473 ℃, and cold treat at -44 ℃ for 152 min. Then, perform surface strengthening treatment on a steel ball strengthening machine. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth of 0.15 mm is formed on the surface, which improves the distribution of residual compressive stress and enhances the fatigue resistance of the steel balls. The purpose of the cold treatment in this step is to increase the hardness of the steel balls, stabilize the microstructure, and eliminate residual austenite. The purpose of the hard grinding in this step is to correct the roundness and spherical error. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth greater than 0.2 mm is formed on the surface, which improves the distribution of residual compressive stress and enhances the fatigue resistance.

[0053] S7. The steel ball obtained in step S6 is precision ground in a closed environment with constant temperature of 23±2℃, constant humidity of 60%, and dust-free environment using a 3000-mesh resin grinding wheel. The grinding plate pressure is gradually reduced from 19 KN to 11 KN, the spindle speed is adjusted to 26 rpm, and the grinding efficiency is controlled from 2 μm / h to 0.75 μm / h, so that the variation in the diameter of the steel ball is controlled within 0.01 μm.

[0054] Figure 1 The image shows the XRD pattern of the nano-needle-shaped nickel-molybdenum alloy prepared in Example 1 of this invention. As can be seen from the image, the material corresponds to JCPDS No. 65-5480 card and belongs to the nickel-molybdenum alloy category. Figure 2The image shows a TEM image of the nanoneedle-shaped nickel-molybdenum alloy prepared in Example 1 of this invention. The image reveals that the nanoneedles consist of copper nanoneedles on the inside and a nickel-molybdenum alloy on the outside, with a strong bond between the two. Applying this alloy to the preparation of steel balls in this invention can improve the toughness of the steel balls. The nanoneedle-shaped nickel-molybdenum alloy structure designed in this invention has an extremely high specific surface area. During the solidification of molten steel and subsequent hot working (rolling, heat treatment), these dispersed nanoparticles can effectively pin the grain boundaries, strongly hindering the growth of austenite grains. This is beneficial for obtaining extremely fine and uniform austenite grains. According to the Hall-Petch Relationship formula, the finer the grains, the higher the strength of the material, and the toughness is also improved. This lays the foundation for the steel ball to maintain good toughness even at high hardness, avoiding brittle fracture. Meanwhile, molybdenum (Mo) is a strong carbide-forming element. During heat treatment (especially tempering), molybdenum combines with carbon to form extremely fine, dispersed special carbides. These nanoscale carbides can also strongly hinder dislocation movement. The addition of nano-needle-shaped nickel-molybdenum alloy significantly improves the high-temperature tempering stability, hardness, and wear resistance of steel. This means that steel balls can achieve the same hardness at a higher tempering temperature, thus better eliminating internal stress and improving toughness. Nickel (Ni) and molybdenum (Mo) are both highly effective alloying elements for improving hardenability. They can delay the transformation of austenite to pearlite and bainite. The nano-needle-shaped nickel-molybdenum alloy also ensures the hardness of the ball's core, ensuring that the entire cross-section of the steel ball (especially the core of large steel balls) fully transforms into a high-hardness martensite structure even at slightly slower cooling rates, avoiding performance degradation caused by the formation of soft non-martensite structures in the core. Reduced risk of heat treatment deformation and cracking: Allows the use of gentler quenching cooling media (such as high-speed oil instead of water-based solutions), reducing thermal and structural stresses, thereby lowering the tendency of steel balls to deform and crack during quenching, which is crucial for high-precision products. The primary role of nickel (Ni) is solid solution strengthening and improving matrix toughness. It does not form carbides but dissolves in ferrite, effectively improving the material's impact toughness. The needle-like particle design can more effectively deflect the propagation path of microcracks under load, absorbing more energy and thus delaying the initiation and propagation of fatigue cracks. The synergistic effect of nickel and molybdenum (Ni improves toughness, Mo provides strength) allows the steel ball matrix to achieve ultra-high hardness while significantly improving impact toughness and fatigue strength. This directly translates to longer rolling contact fatigue life and higher drop ball impact life, solving the core problem of traditional high-carbon steel balls being "hard and brittle" and prone to premature failure. The nickel-molybdenum alloy designed in this invention is at the nanoscale; the fine nanoparticles help form a finer and more uniform spherical pearlite structure during spheroidizing annealing.This structure has uniform hardness and good plasticity. When performing multi-station cold heading, the material flows more evenly and the deformation resistance is moderate. This can reduce the risk of cracking during the cold heading process, improve the mold life and the forming qualification rate, and at the same time ensure the uniformity of the structure of the ball blank after cold heading.

[0055] Example 2

[0056] S1. Soak the copper foam in 3 M HCl solution for 11 min using ultrasonic cleaning, rinse with water, and then soak in isopropanol for another 10 min using ultrasonic cleaning. Next, sonicate with water for 10 min, air dry, and then immerse in 28% ammonium fluoride solution for 3 min, followed by rinsing to obtain pretreated copper foam. Soak the copper foam in a 5 M NaOH solution containing 0.21 g ammonium thiosulfate in an Ar atmosphere for 55 min to obtain copper hydroxide nanoneedles. Electrodegrade the copper hydroxide nanoneedles to copper nanoneedles in 4 M NaHCO3 electrolyte at a reduction voltage of -1.1 V. Then, using the copper nanoneedles as the working electrode, electrodeposit for 1300 seconds in a solution containing 0.68 g nickel sulfate, 0.76 g ammonium molybdate, 1.3 g ethylenediamine, 0.52 g sodium dodecyl sulfate, 130 μL 98% sulfuric acid, and 42 mL distilled water. Nanoneedle-shaped nickel-molybdenum alloys can be obtained in this step. The main purpose of this step is to clean the surface of the foamed copper and remove impurities and oil, ensuring the stability and repeatability of subsequent reactions. The brief soaking in ammonium fluoride is to make the surface of the foamed copper more hydrophobic, ensuring that it does not come into contact with NaOH too quickly in subsequent steps, thereby promoting the formation of uniform nanoneedle morphology. Soaking the foamed copper in NaOH ensures that it is exposed to an OH-- rich environment, and the use of ammonium thiosulfate ensures the rapid formation of nanoneedle arrays. This step reduces the copper oxide array structure to a copper array structure, improving its conductivity and facilitating the deposition of nickel-molybdenum alloys.

[0057] S2. Scrap steel or ferroalloys are initially smelted in an electric arc furnace. The average furnace temperature gradually increases from room temperature, with the arc zone temperature controlled at 3875 °C and the melting time controlled at 87 min. Simultaneously, oxygen is continuously purged at an oxygen supply intensity of 42 Nm³ / t·h, with a total oxygen supply controlled at 47 Nm³ / t per ton of steel; 8 kg / t·min (kg / ton steel·min). Additionally, nitrogen is used as the carrier gas for carbon injection at an intensity of 7.6 kg / t·min (kg / ton steel·min), with the carbon injection amount controlled at 6.4 kg / t (kg / ton steel) and the gas pressure controlled at 0.83 MPa. After the initial smelting, the tapping temperature of the electric arc furnace is controlled at 1820 °C. The molten steel is then transferred to a ladle refining furnace, where argon gas is continuously introduced and stirred for 88 min, causing the temperature to drop by 118 °C. 0.08% vanadium nanoparticles are added; stirring continues for 172 min, waiting for the temperature to drop to 340 °C. At °C, 0.31% of the nano-needle-shaped nickel-molybdenum alloy prepared in step S1 is added; stirring continues for 76 min in an argon atmosphere, then the ladle is placed in a vacuum chamber with the pressure controlled at 103.4 Pa. By significantly reducing the ambient pressure, the gas in the molten steel is forced to escape. Finally, the molten steel is continuously cast, cooled, and cut into billets of fixed lengths using a continuous casting machine. In this step, a high-temperature electric arc is used to break down and melt the cold scrap steel. The high temperature ensures that the molten steel and slag have good fluidity, facilitating chemical reactions and impurity removal. Strict control of oxygen blowing intensity and oxygen supply in this step ensures that the oxygen jet has sufficient kinetic energy to penetrate the foam slag layer, impact the molten pool, and effectively participate in the reaction. In this step, the oxygen injection is not only used to burn off impurities, but more importantly, it reacts with elements such as carbon and iron in the scrap steel to produce a large amount of chemical heat (C + 1 / 2O2 → CO + Heat). This chemical energy can provide 35% of the total energy required in the furnace, greatly accelerating melting. Additionally, carbon powder is injected into the molten pool, reacting with the blown-in oxygen to generate CO bubbles, causing vigorous "carbon boiling." This not only generates chemical heat but also agitates the molten pool, making heat transfer more even and avoiding "cold zones."

[0058] S3. The steel billet solidified in step S2 is subjected to plastic processing at 1246 °C, ensuring sufficient heating time according to the billet size, and ensuring K is 1.8 min cm. -1 Next, after being removed from the heating furnace, rolling was carried out at 1183 °C, followed by final rolling at 895 °C to ensure that the deformation was completed within a single austenitic region; then, rolling was continued at 86 °C for a minimum of 1 minute. -1 The cooling rate was increased to 648 °C, and after rapid cooling, the cooling rate was adjusted to 10 °C / min. -1To prevent excessive internal stress, this step involves controlling the cooling rate through the regions where carbides are most likely to precipitate, thus preventing the formation of network carbides at the austenite grain boundaries. Network carbides are brittle and severely reduce the bearing's toughness and fatigue strength. The purpose of this step is to uniformly heat the cast steel billet to the austenitic temperature range suitable for plastic deformation, ensuring complete austenitization and reducing deformation resistance.

[0059] S4. Heat the steel billet prepared in step S3 to 754-789 ℃ for post-rolling treatment and spheroidizing annealing, and hold for 220 min. Then peel or polish the steel to remove the decarburized layer, cracks and other defects on the surface to ensure surface quality. The purpose of this step is to transform the hard and brittle lamellar pearlite in the rolled structure into a soft, easy-to-cut and cold-form spheroid pearlite structure.

[0060] S5. The steel processed in step S4 is cut into cylindrical blanks of a predetermined length, and then an upsetting ball of the required diameter is extruded. The upsetting ball is further extruded into a cup-shaped sleeve. Then, a conical half-die is used to extrude the end of the connecting rod into a conical upsetting head, and then a spherical half-die is used to extrude it into a spherical head. The ball blank is designed with a bipolar cone angle (2α) of 125° and a ring shape to reduce deformation stress and material loss. The workpiece is rotated 90° and the spherical head is extruded into a flat spherical head. Then, symmetrical concave platforms are extruded from the two ends of the flat spherical head, and finally, through holes are formed by extrusion. The ball blank after cold upsetting needs to be stress-relieved annealed at a low temperature of 168 ℃ and held for 3.7 h to eliminate the internal stress generated by cold upsetting.

[0061] S6. Remove the ring, polarity, and surface oxide layer from the spherical billet prepared in step S5 to make it basically spherical; quench at 1058 ℃, temper at 485 ℃, and cold treat at -44 ℃ for 175 min. Then, perform surface strengthening treatment on a steel ball strengthening machine. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth of 0.32 mm is formed on the surface, which improves the distribution of residual compressive stress and enhances the fatigue resistance of the steel balls. The purpose of the cold treatment in this step is to increase the hardness of the steel balls, stabilize the microstructure, and eliminate residual austenite. The purpose of the hard grinding in this step is to correct the roundness and spherical error. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth greater than 0.2 mm is formed on the surface, which improves the distribution of residual compressive stress and enhances the fatigue resistance.

[0062] S7. The steel ball obtained in step S6 is precision ground in a closed environment with constant temperature of 23±2℃, constant humidity of 65%, and dust-free environment using an 8000-mesh resin grinding wheel. The grinding plate pressure is gradually reduced from 21 KN to 13 KN, the spindle speed is adjusted to 34 rpm, and the grinding efficiency is controlled to decrease from 3 μm / h to 0.82 μm / h, so that the variation in the diameter of the steel ball is controlled within 0.25 μm.

[0063] Comparative Example 1: Except for step S1, in which 0.68 g of nickel sulfate was not added, all other steps were the same as in Example 2.

[0064] Comparative Example 2: Except for step S1, in which 0.76 g of ammonium molybdate was not added, all other steps were the same as in Example 2.

[0065] Comparative Example 3: Except for step S2, in which 0.08% vanadium nanoparticles were not added, all other steps were the same as in Example 2.

[0066] Comparative Example 4: Except for step S2, which does not include 0.31% of the nano-needle-shaped nickel-molybdenum alloy prepared in step S1, all other steps are the same as in Example 2.

[0067] Table 1. Hardness of the central region of the steel ball

[0068]

[0069] Figure 3This is a SEM image of the copper nanoneedles prepared in Example 2 of the present invention. It can be clearly seen that the overall morphology of the copper nanoneedles prepared in this invention is a uniform array structure, which facilitates the bonding between the nickel-molybdenum alloy and the array, and leverages the advantages of the nanoneedle shape. Hardness test: A cubic sample with dimensions of 10mm*10mm*10mm was extracted from the center of the steel ball. The sample was tested five times, and the average value was used to characterize the hardness of the central region of the steel ball. Table 1 shows the hardness of the central region of the steel balls prepared in Comparative Examples 1-4 and Example 2 of the present invention. Table 1 shows that the hardness value of the steel ball prepared in Example 2 of the present invention is 61.5 HRC, which is higher than that of the steel balls prepared in Comparative Examples 1-3. This indicates that the addition of vanadium nanoparticles and nanoneedle-shaped nickel-molybdenum alloy during the steel ball production process of the present invention has the synergistic benefit of improving the hardness of the steel ball. This synergistic effect gives the steel ball excellent toughness, derived from fine grain strengthening and nickel solid solution toughening. The ultra-long fatigue life, derived from the uniform microstructure, fine grains, and tough matrix, can effectively inhibit crack initiation and propagation. The exceptional performance consistency is attributed to the extreme uniformity provided by the nanoparticles. The combination of vanadium nanoparticles and nanoneedle-shaped nickel-molybdenum alloy represents a perfect blend of rigidity and flexibility. Vanadium provides exceptional hardness, strength, and wear resistance. Nickel-molybdenum offers excellent toughness, hardenability, and impact-resistant bonding. The nanoneedle morphology ensures their uniform integration and efficient function. This synergistic design fundamentally resolves the inherent contradiction between high hardness and high toughness in steel balls at the most basic materials science level, resulting in higher-quality steel balls.

[0070] Example 3

[0071] S1. Soak the copper foam in 2 M HCl solution for 9 min using ultrasonic cleaning, rinse with water, and then soak in isopropanol for another 9 min using ultrasonic cleaning. Next, sonicate with water for 9 min, air dry, and then immerse in 28% ammonium fluoride solution for 3 min, rinsing thoroughly to obtain pretreated copper foam. Immerse the copper foam in a 4 M KOH solution containing 0.11 g ammonium thiosulfate in an Ar atmosphere for 45 min to obtain copper hydroxide nanoneedles. Electrodegrade the copper hydroxide nanoneedles to copper nanoneedles in 3 M NaHCO3 electrolyte at a reduction voltage of -1.1 V. Then, using the copper nanoneedles as the working electrode, electrodeposit for 1100 μL in a solution containing 0.58 g nickel sulfate, 0.56 g sodium molybdate, 1.1 g ethylenediamine, 0.48 g sodium dodecyl sulfate, 125 μL 98% sulfuric acid, and 39 mL distilled water. Nanoneedle-shaped nickel-molybdenum alloys can be obtained in this step. The main purpose of this step is to clean the impurities and oil on the surface of the foamed copper, ensuring the stability and repeatability of subsequent reactions. The purpose of briefly soaking in ammonium fluoride is to make the surface of the foamed copper more hydrophobic, ensuring that it does not come into contact with KOH too quickly in subsequent steps, thereby promoting the formation of uniform nanoneedle morphology. Soaking the foamed copper in KOH ensures that it is exposed to an OH- rich environment. The use of sodium thiosulfate or ammonium thiosulfate ensures the rapid formation of nanoneedle arrays. This step reduces the copper oxide array structure to a copper array structure, improving its conductivity and facilitating the deposition of nickel-molybdenum alloys.

[0072] S2. Scrap steel or ferroalloys are initially smelted in an electric arc furnace. The average furnace temperature gradually increases from room temperature, with the arc zone temperature controlled at 3650 °C and the melting time controlled at 67 min. Simultaneously, oxygen is continuously blown at an oxygen supply intensity of 32 Nm³ / t·h, with a total oxygen supply controlled at 45 Nm³ / t per ton of steel; 6 kg / t·min (kg / ton steel·min). Additionally, nitrogen is used as the carrier gas for carbon injection at an intensity of 4.6 kg / t·min (kg / ton steel·min), with the carbon injection amount controlled at 4.4 kg / t (kg / ton steel) and the gas pressure controlled at 0.73 MPa. After the initial smelting, the tapping temperature of the electric arc furnace is controlled at 1790 °C. The molten steel is then transferred to a ladle refining furnace, where argon gas is continuously introduced and stirred for 78 min, causing the temperature to drop by 108 °C. 0.05% vanadium nanoparticles are added; stirring continues for 142 min, waiting for the temperature to drop to 1330 °C. At °C, 0.28% of the nano-needle-shaped nickel-molybdenum alloy prepared in step S1 is added; stirring continues for 66 min in an argon atmosphere, then the ladle is placed in a vacuum chamber with the pressure controlled at 93.4 Pa. By significantly reducing the ambient pressure, the gas in the molten steel is forced to escape. Finally, the molten steel is continuously cast, cooled, and cut into billets of fixed lengths using a continuous casting machine. In this step, a high-temperature electric arc is used to break down and melt the cold scrap steel. The high temperature ensures that the molten steel and slag have good fluidity, facilitating chemical reactions and impurity removal. Strict control of oxygen blowing intensity and oxygen supply in this step ensures that the oxygen jet has sufficient kinetic energy to penetrate the foam slag layer, impact the molten pool, and effectively participate in the reaction. In this step, the oxygen injection is not only used to burn off impurities, but more importantly, it reacts with carbon, iron, and other elements in the scrap steel to produce a large amount of chemical heat (C + 1 / 2O2 → CO + Heat). This chemical energy can provide 25%-35% of the total energy required in the furnace, greatly accelerating melting. Additionally, carbon powder is injected into the molten pool, reacting with the blown-in oxygen to generate CO bubbles, causing vigorous "carbon boiling." This not only generates chemical heat but also agitates the molten pool, making heat transfer more even and avoiding "cold zones."

[0073] S3. The steel billet solidified in step S2 is subjected to plastic processing at 1166 ℃, ensuring sufficient heating time according to the billet size, and ensuring K is 1.6 min cm. -1 After being removed from the heating furnace, it is rolled at 1153 °C, followed by final rolling at 845 °C to ensure that the deformation is completed within a single austenitic region; then rolled at 69 °C for a minimum of 1 minute. -1 The cooling rate was adjusted to reduce the temperature to 668 °C. After rapid cooling, the cooling rate was further adjusted to 9 °C / min. -1To prevent excessive internal stress, this step involves controlling the cooling rate through the regions where carbides are most likely to precipitate, thus preventing the formation of network carbides at the austenite grain boundaries. Network carbides are brittle and severely reduce the bearing's toughness and fatigue strength. The purpose of this step is to uniformly heat the cast steel billet to the austenitic temperature range suitable for plastic deformation, ensuring complete austenitization and reducing deformation resistance.

[0074] S4. Heat the steel billet prepared in step S3 to 759 ℃ for post-rolling treatment and spheroidizing annealing, and hold for 190 min. Then peel or polish the steel to remove the decarburized layer, cracks and other defects on the surface to ensure surface quality. The purpose of this step is to transform the hard and brittle lamellar pearlite in the rolled structure into a soft, easy-to-cut and cold-form spheroid pearlite structure.

[0075] S5. The steel processed in step S4 is cut into cylindrical blanks of a predetermined length, and then an upsetting ball of the required diameter is extruded. The upsetting ball is further extruded into a cup-shaped sleeve. Then, a conical half-die is used to extrude the end of the connecting rod into a conical upsetting head, and then a spherical half-die is used to extrude it into a spherical head. The ball blank is designed with a bipolar cone angle (2α) of 115° and a ring shape to reduce deformation stress and material loss. The workpiece is rotated 90° and the spherical head is extruded into a flat spherical head. Then, symmetrical concave platforms are extruded from the two ends of the flat spherical head, and finally, through holes are formed by extrusion. The ball blank after cold upsetting needs to be stress-relieved annealed at a low temperature of 158 ℃ and held for 2.7 h to eliminate the internal stress generated by cold upsetting.

[0076] S6. Remove the ring, polarity, and surface oxide layer from the spherical billet prepared in step S5 to make it basically spherical; quench at 1048 ℃, temper at 478 ℃, and cold treat at -44 ℃ for 165 min. Then, perform surface strengthening treatment on a steel ball strengthening machine. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth of 0.19 mm is formed on the surface, which improves the distribution of residual compressive stress and enhances the fatigue resistance of the steel balls. The purpose of the cold treatment in this step is to increase the hardness of the steel balls, stabilize the microstructure, and eliminate residual austenite. The purpose of the hard grinding in this step is to correct the roundness and spherical error. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth greater than 0.2 mm is formed on the surface, which improves the distribution of residual compressive stress and enhances the fatigue resistance.

[0077] S7. The steel ball obtained in step S6 is precision ground in a closed environment with constant temperature of 23±2℃, constant humidity of 63%, and dust-free environment using a 5000-mesh resin grinding wheel. The grinding plate pressure is gradually reduced from 20 KN to 12 KN, the spindle speed is adjusted to 29 rpm, and the grinding efficiency is controlled to decrease from 3 μm / h to 0.78 μm / h, so that the variation in the diameter of the steel ball is controlled within 0.15 μm.

[0078] Comparative Example 5: Except for step S1, in which 1.1 g of ethylenediamine and 0.48 g of sodium dodecyl sulfate were not added, all other steps were the same as in Example 3.

[0079] Figure 4 This is a SEM image of the copper nanoneedles prepared in Comparative Example 5 of this invention. The image shows that the copper nanoneedles prepared without ethylenediamine and sodium dodecyl sulfate are relatively coarse and prone to cross-linking, making it difficult to electrodeposit nickel-molybdenum alloy on them. In this invention, ethylenediamine (EDA) guides the crystals to grow into uniform needle-like structures in an OH--rich environment through chemical adsorption and complexation. Sodium dodecyl sulfate (SDS) prevents the agglomeration of the generated nanoneedles through physical adsorption and steric hindrance, and also assists in morphology control. The combination of these two agents successfully achieves precise control over the morphology, size, and stability of the copper nanoneedles.

[0080] Example 4

[0081] S1. Soak the copper foam in 1 M HCl solution for 10 min using ultrasonic cleaning, rinse with water, and then soak in isopropanol for another 9 min using ultrasonic cleaning. Next, sonicate with water for 10 min, air dry, and then immerse in a 26% ammonium fluoride solution for 2 min, followed by rinsing to obtain pretreated copper foam. Soak the copper foam in a 3 M NaOH solution containing 0.18 g of sodium thiosulfate in an Ar atmosphere for 45 min to obtain copper hydroxide nanoneedles. Electrodegrade the copper hydroxide nanoneedles to copper nanoneedles in a 3 M NaHCO3 electrolyte solution at a reduction voltage of -1.1 V. Then, using the copper nanoneedles as the working electrode, electrodeposit for 1200 μL in a solution containing 0.58 g nickel nitrate, 0.31-0.76 g sodium molybdate, 0.9 g ethylenediamine, 0.48 g sodium dodecyl sulfate, 127 μL 98% sulfuric acid, and 39 mL distilled water. Nanoneedle-shaped nickel-molybdenum alloys can be obtained in this step. The main purpose of this step is to clean the impurities and oil on the surface of the foamed copper, ensuring the stability and repeatability of subsequent reactions. The purpose of briefly soaking in ammonium fluoride is to make the surface of the foamed copper more hydrophobic, ensuring that it does not come into contact with NaOH too quickly in subsequent steps, thereby promoting the formation of uniform nanoneedle morphology. Soaking the foamed copper in NaOH ensures that it is exposed to an OH- rich environment, and the use of sodium thiosulfate ensures the rapid formation of nanoneedle arrays. This step reduces the copper oxide array structure to a copper array structure, improving its conductivity and facilitating the deposition of nickel-molybdenum alloy.

[0082] S2. Scrap steel or ferroalloys are initially smelted in an electric arc furnace. The average furnace temperature gradually increases from room temperature, with the arc zone temperature controlled at 3375 °C and the melting time controlled at 46 min. Simultaneously, oxygen is continuously blown at an oxygen supply intensity of 29 Nm³ / t·h, with a total oxygen supply controlled at 39 Nm³ / t per ton of steel; 7 kg / t·min (kg / ton steel·min). Additionally, nitrogen is used as the carrier gas for carbon injection at a carbon injection intensity of 5.6 kg / t·min (kg / ton steel·min), with the carbon injection amount controlled at 5.3 kg / t (kg / ton steel) and the gas pressure controlled at 0.55 MPa. After the initial smelting, the tapping temperature of the electric arc furnace is controlled at 1798 °C. The molten steel is then transferred to a ladle refining furnace, where argon gas is continuously introduced and stirred for 78 min, causing the temperature to drop by 98 °C. 0.04% vanadium nanoparticles are added; stirring continues for 152 min, waiting for the temperature to drop to 1298 °C. At °C, 0.28% of the nano-needle-shaped nickel-molybdenum alloy prepared in step S1 is added; stirring continues for 66 min in an argon atmosphere, then the ladle is placed in a vacuum chamber with the pressure controlled at 101.4 Pa. By significantly reducing the ambient pressure, the gas in the molten steel is forced to escape. Finally, the molten steel is continuously cast, cooled, and cut into billets of fixed lengths using a continuous casting machine. In this step, a high-temperature electric arc is used to break down and melt the cold scrap steel. The high temperature ensures that the molten steel and slag have good fluidity, facilitating chemical reactions and impurity removal. Strict control of oxygen blowing intensity and oxygen supply in this step ensures that the oxygen jet has sufficient kinetic energy to penetrate the foam slag layer, impact the molten pool, and effectively participate in the reaction. In this step, the oxygen injection is not only used to burn off impurities, but more importantly, it reacts with elements such as carbon and iron in the scrap steel to produce a large amount of chemical heat (C + 1 / 2O2 → CO + Heat). This chemical energy provides 31% of the total energy required in the furnace, greatly accelerating melting. Additionally, carbon powder is injected into the molten pool, reacting with the blown-in oxygen to generate CO bubbles, causing vigorous "carbon boiling." This not only generates chemical heat but also agitates the molten pool, making heat transfer more even and avoiding "cold zones."

[0083] S3. The steel billet solidified in step S2 is subjected to plastic processing at 1166 ℃, ensuring sufficient heating time according to the billet size, and ensuring K is 1.6 min cm. -1 Next, after being removed from the heating furnace, it is rolled at 1163 °C, and then finished rolling is carried out at 865 °C to ensure that the deformation is completed within a single austenitic region; then it is rolled at 69 °C for min. -1 The cooling rate was increased to 658 °C, and after rapid cooling, the cooling rate was adjusted to 9 °C / min. -1To prevent excessive internal stress, this step involves controlling the cooling rate through the regions where carbides are most likely to precipitate, thus preventing the formation of network carbides at the austenite grain boundaries. Network carbides are brittle and severely reduce the bearing's toughness and fatigue strength. The purpose of this step is to uniformly heat the cast steel billet to the austenitic temperature range suitable for plastic deformation, ensuring complete austenitization and reducing deformation resistance.

[0084] S4. Heat the steel billet prepared in step S3 to 779 ℃ for post-rolling treatment and spheroidizing annealing, and hold for 192 min. Then peel or polish the steel to remove the decarburized layer, cracks and other defects on the surface to ensure surface quality. The purpose of this step is to transform the hard and brittle lamellar pearlite in the rolled structure into a soft, easy-to-cut and cold-form spheroid pearlite structure.

[0085] S5. The steel processed in step S4 is cut into cylindrical blanks of a predetermined length, and then an upsetting ball of the required diameter is extruded. The upsetting ball is further extruded into a cup-shaped sleeve. Then, a conical half-die is used to extrude the end of the connecting rod into a conical upsetting head, and then a spherical half-die is used to extrude it into a spherical head. The ball blank is designed with a bipolar cone angle (2α) of 105° and a ring shape to reduce deformation stress and material loss. The workpiece is rotated 90° and the spherical head is extruded into a flat spherical head. Then, symmetrical concave platforms are extruded from the two ends of the flat spherical head, and finally, through holes are formed by extrusion. The ball blank after cold upsetting needs to be stress-relieved annealed at a low temperature of 158 ℃ and held for 2.8 h to eliminate the internal stress generated by cold upsetting.

[0086] S6. Remove the ring, polarity, and surface oxide layer from the spherical blank prepared in step S5 to make it basically spherical; quench at 1048 ℃, temper at 479 ℃, and cold treat at -44 ℃ for 165 min. Then, perform surface strengthening treatment on a steel ball strengthening machine. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth of 0.18 mm is formed on the surface, which improves the distribution of residual compressive stress and enhances the fatigue resistance of the steel balls. The purpose of the cold treatment in this step is to increase the hardness of the steel balls, stabilize the microstructure, and eliminate residual austenite. The purpose of the hard grinding in this step is to correct the roundness and spherical error. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth greater than 0.2 mm is formed on the surface, which improves the distribution of residual compressive stress and enhances the fatigue resistance.

[0087] S7. The steel ball obtained in step S6 is precision ground in a closed environment with constant temperature of 23±2℃, constant humidity of 63%, and dust-free environment using a 6000-mesh resin grinding wheel. The grinding plate pressure is gradually reduced from 20 KN to 13 KN, the spindle speed is adjusted to 32 rpm, and the grinding efficiency is controlled to decrease from 3 μm / h to 0.79 μm / h, so that the variation in the diameter of the steel ball is controlled within 0.15 μm.

[0088] Comparative Example 6: Except for the nanoparticles without vanadium in step S2, all other steps are the same as in Example 4.

[0089] Comparative Example 7: Except for step S2, which does not include the nano-needle-shaped nickel-molybdenum alloy prepared in step S1, all other steps are the same as in Example 4.

[0090] Figure 5 The XRD patterns of the steel balls prepared in Examples 3 and 4 of this invention are shown. They indicate that the steel balls have no other impurity peaks and their crystalline phase is relatively pure. Impact toughness test: The impact specimens used in this invention were all vertically machined from the center of each steel ball to prepare unnotched specimens. A metal pendulum was used to test the impact energy of the specimens. Table 2 shows the impact energy and volumetric hardness of the steel balls obtained from Examples 4 and Comparative Examples 6 and 7 of this invention. The comparison shows that the steel balls prepared in this invention have the best mechanical properties.

[0091] Table 2. Impact toughness and volumetric hardness

[0092]

[0093] 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 high-precision steel ball production process based on multi-station cold heading, characterized in that, The specific steps include: S1. Soaking the copper foam in 1-3 M HCl solution for 8-11 min with ultrasonic cleaning, rinsing with water, and then soaking in isopropanol for another 8-10 min with ultrasonic cleaning; then soaking in water for another 8-10 min with ultrasonic cleaning, drying, and then immersing in 25-28% ammonium fluoride solution for 2-3 min, followed by rinsing to obtain pretreated copper foam; immersing the copper foam in 3-5 M KOH or NaOH solution containing 0.03-0.21 g of sodium thiosulfate or ammonium thiosulfate in an Ar atmosphere for 40-55 min to obtain copper hydroxide nanoneedles; electroreducing the copper hydroxide nanoneedles to copper nanoneedles in 2-4 M NaHCO3 electrolyte at a reduction voltage of -1.1 V; then using the copper nanoneedles as the working electrode, in a solution containing 0.54-0.68 g of nickel nitrate or nickel sulfate, 0.31-0.76 g of sodium molybdate or ammonium molybdate, and 0.9-1.3 g of sodium thiosulfate, sodium thiosulfate, and ammonium thiosulfate... Nano-needle nickel-molybdenum alloy can be obtained by electrodeposition for 900-1300 s in a solution of g ethylenediamine, 0.43-0.52 g sodium dodecyl sulfate, 121-130 μL 98% sulfuric acid, and 35-42 mL distilled water; S2, raw materials such as scrap steel or ferroalloys are initially smelted in an electric arc furnace at a temperature of 3250-3875°C for 43-87 min; the tapping temperature is controlled at 1780-1820 °C; in a ladle refining furnace, argon gas is introduced for stirring; vanadium nanoparticles are added; the temperature is lowered to 1280-1340 °C, and the nano-needle nickel-molybdenum alloy prepared in S1 is added; stirring is carried out for 53-76 min, and the ladle is placed in a vacuum chamber to allow the gas in the molten steel to escape; the molten steel is continuously cast, cooled, and cut into steel billets of fixed lengths through a continuous casting machine; S3, the steel billets solidified in S2 are plastically processed at 1104-1183 The initial rolling process is carried out at 813-895 ℃, followed by final rolling at 63-86 ℃ for a minimum of 100 min. -1 After cooling the temperature to 688-648 ℃, adjust the cooling rate to 8-10 ℃ / min. -1 S4. Heat the steel billet prepared in S3 to 754-789 ℃ for post-rolling treatment and spheroidizing annealing; S5. Cut the steel treated in S4 into cylindrical billets, extrude upsetting balls, and extrude the upsetting balls into cup-shaped tube sleeves; use a conical half-die to extrude the end of the connecting rod into a conical upsetting head, and then use a spherical half-die to extrude it into a spherical head; rotate the workpiece 90° and extrude the spherical head into a flat spherical head, and then extrude symmetrical concave platforms from the two ends of the flat spherical head towards each other, forming through holes; the cold-upsetting spherical billet needs to be stress-relieved annealed at a low-temperature tempering temperature of 152-168 ℃ for 2.3-3.7 h; S6. Remove the ring, two poles and surface oxide layer of the spherical billet prepared in S5, quench at 1035-1058 ℃, temper at 473-485 ℃, and anneal at -44 ℃. Cold treatment; S7, Grind the steel ball described in S6 in a closed environment with constant temperature of 23±2℃, constant humidity of 60-65%, and dust-free environment using a 3000-8000 grit resin grinding wheel. Gradually reduce the grinding plate pressure, adjust the spindle speed to 26-34 rpm, and control the grinding efficiency from 2-3 μm / h to 0.75-0.82 μm / h, so that the variation in the diameter of the steel ball is controlled within 0.01-0.25 μm.

2. The high-precision steel ball production process based on multi-station cold heading as described in claim 1, characterized in that, The specific steps are as follows: S1. Soak copper foam in 1-3 M HCl solution for ultrasonic cleaning for 8-11 min, rinse thoroughly with water, and then soak in isopropanol for another 8-10 min of ultrasonic cleaning; followed by ultrasonic cleaning with water for 8-10 min, drying, and then immersing in 25-28% ammonium fluoride solution for 2-3 min, followed by rinsing to obtain pretreated copper foam; Soak the copper foam in a 3-5 M KOH or NaOH solution containing 0.03-0.21 g of sodium thiosulfate or ammonium thiosulfate in an Ar atmosphere for 40-55 min to obtain copper hydroxide nanoneedles; Electroreduc the copper hydroxide nanoneedles to copper nanoneedles in 2-4 M NaHCO3 electrolyte at a reduction voltage of -1.1V; Then, using the copper nanoneedles as the working electrode, in an electrolyte containing 0.54-0.68 g nickel nitrate or nickel sulfate, 0.31-0.76 g sodium molybdate or ammonium molybdate, and 0.9-1.3 g... Nano-needle-shaped nickel-molybdenum alloys can be obtained by electrodeposition in a solution of g ethylenediamine, 0.43-0.52 g sodium dodecyl sulfate, 121-130 μL 98% sulfuric acid and 35-42 mL distilled water for 900-1300 s. S2. Scrap steel or ferroalloys are initially smelted in an electric arc furnace. The average furnace temperature gradually increases from room temperature, with the arc zone temperature controlled at 3250-3875 °C and the melting time controlled at 43-87 min. Simultaneously, oxygen is continuously blown at an oxygen supply intensity of 27-42 Nm³ / t·h, with a total oxygen supply controlled at 33-47 Nm³ / t per ton of steel; 3-8 kg / t·min. Additionally, nitrogen is used as a carrier gas for carbon injection at a carbon injection intensity of 3.1-7.6 kg / t·min, with the carbon injection amount controlled at 2.5-6.4 kg / t and the gas pressure controlled at 0.42-0.83 MPa. After the initial smelting, the tapping temperature of the electric arc furnace is controlled at 1780-1820 °C. The molten steel is then transferred to a ladle refining furnace, where argon gas is continuously introduced and stirred for 56-88 min, causing the temperature to drop by 93-118 °C. 0.03-0.08... Vanadium nanoparticles were added; stirring was continued for 103-172 min, and the temperature was lowered to 1280-1340 °C. 0.24-0.31% of the nano-needle-shaped nickel-molybdenum alloy prepared in step S1 was added; stirring was continued in an argon atmosphere for 53-76 min, and then the ladle was placed in a vacuum chamber with the pressure controlled at 56.5-103.4 Pa. By significantly reducing the ambient pressure, the gas in the molten steel was forced to escape; finally, the molten steel was continuously cast, cooled, and cut into billets of fixed lengths using a continuous casting machine. S3. The steel billet solidified in step S2 is subjected to plastic processing at 1153-1246 ℃, ensuring sufficient heating time according to the billet size, and ensuring K is 1.4-1.8 min cm. -1 After being removed from the heating furnace, it is rolled at 1104-1183 ℃, and then finished rolling is carried out at 813-895 ℃ to ensure that the deformation is completed within a single austenitic region; then it is rolled at 63-86 ℃ for min. -1 The cooling rate was set to reduce the temperature to 688-648 ℃, and after rapid cooling, the cooling rate was adjusted to 8-10 ℃ / min. -1 This is to prevent excessive internal stress from being generated; S4. Heat the steel billet prepared in step S3 to 754-789 ℃ for post-rolling treatment and spheroidizing annealing, and hold for 180-220 min. Then peel or polish the steel to remove the decarburized layer, cracks and other defects on the surface to ensure surface quality. S5. The steel processed in step S4 is cut into cylindrical blanks of a predetermined length, and then an upsetting ball of the required diameter is extruded. The upsetting ball is further extruded into a cup-shaped sleeve. Then, a conical half-die is used to extrude the end of the connecting rod into a conical upsetting head, and then a spherical half-die is used to extrude it into a spherical head. The ball blank is designed with a bipolar cone angle 2α of 95-125° and a ring shape to reduce deformation stress and material loss. The workpiece is rotated 90° and the spherical head is extruded into a flat spherical head. Then, symmetrical concave platforms are extruded from the two ends of the flat spherical head, and finally, through holes are formed by extrusion. The ball blank after cold upsetting needs to be stress-relieved annealed at a low temperature of 152-168 ℃ and held for 2.3-3.7 h to eliminate the internal stress generated by cold upsetting. S6. Remove the ring, two poles and surface oxide layer of the ball blank prepared in step S5 to make it basically spherical; quench at 1035-1058℃, temper at 473-485℃, and cold treat at -44℃ for 152-175 min. Then, perform surface strengthening treatment on a steel ball strengthening machine. Through the autonomous drop impact and mutual impact of steel balls, a strengthening layer with a depth of 0.15-0.32mm is formed on the surface to improve the distribution of residual compressive stress and improve the fatigue resistance of the steel ball. S7. The steel balls obtained in step S6 are precision ground in a closed environment with constant temperature of 23±2℃, constant humidity of 60-65%, and dust-free environment using a 3000-8000 grit resin grinding wheel. The grinding plate pressure is gradually reduced from 19-21KN to 11-13KN, the spindle speed is adjusted to 26-34 rpm, and the grinding efficiency is controlled from 2-3μm / h to 0.75-0.82μm / h, so that the variation in the diameter of the steel balls is controlled within 0.01-0.25μm.

3. A high-precision steel ball production process based on multi-station cold heading as described in claim 1 or 2, characterized in that, The specific operation steps are as follows: In step S1, the foamed copper is ultrasonically cleaned in 2 M HCl solution for 8 min, rinsed with water, and then ultrasonically cleaned in isopropanol for 10 min; it is then ultrasonically cleaned with water for 8 min, dried, and then soaked in 28% ammonium fluoride solution for 2 min, and rinsed clean to obtain pretreated foamed copper; the foamed copper is then soaked in 5 M KOH solution containing 0.21 g sodium thiosulfate in an Ar atmosphere for 55 min to obtain copper hydroxide nanoneedles; the copper hydroxide nanoneedles are electroreduced to copper nanoneedles in 2 M NaHCO3 electrolyte with a reduction voltage of -1.1 V; then, using the copper nanoneedles as the working electrode, electrodeposition is performed for 900 s in a solution containing 0.68 g nickel nitrate, 0.76 g ammonium molybdate, 0.9 g ethylenediamine, 0.52 g sodium dodecyl sulfate, 121 μL 98% sulfuric acid, and 42 mL distilled water to obtain nanoneedle-shaped nickel-molybdenum alloy.

4. A high-precision steel ball production process based on multi-station cold heading as described in claim 1 or 2, characterized in that, The specific operating steps are as follows: In step S2, scrap steel or ferroalloys are initially smelted in an electric arc furnace. The average temperature inside the furnace gradually increases from room temperature, and the temperature in the electric arc zone is controlled at 3875 °C. The melting time is controlled at 43 min, while oxygen is continuously blown at an oxygen supply intensity of 27 Nm³ / t·h, with the total oxygen supply controlled at 47 Nm³ / t per ton of steel; 3-8 kg / t·min; in addition, nitrogen is used as a carrier gas for carbon injection at a carbon injection intensity of 7.6 kg / t·min, with the carbon injection amount controlled at 6.4 kg / t and the gas pressure controlled at 0.83 MPa; after the initial smelting, the tapping temperature of the electric arc furnace is controlled at 1780 °C; the molten steel is transferred to a ladle refining furnace, and argon gas is continuously introduced for stirring for 88 min, with the temperature dropping by 93 °C; 0.08% vanadium nanoparticles are added; stirring continues for 103 min, and after the temperature drops to 1280 °C, 0.31% vanadium nanoparticles are added. The nano-needle-shaped nickel-molybdenum alloy prepared in step S1 was stirred for 53 min in an argon atmosphere. Then, the ladle was placed in a vacuum chamber with the pressure controlled at 103.4 Pa. By significantly reducing the ambient pressure, the gas in the molten steel was forced to escape. Finally, the molten steel was continuously cast, cooled, and cut into billets of fixed lengths by a continuous casting machine.

5. A high-precision steel ball production process based on multi-station cold heading as described in claim 1 or 2, characterized in that, The specific operation steps are as follows: In step S3, the steel billet solidified in step S2 is plastically processed at 1153 °C, ensuring sufficient heating time according to the billet size, and ensuring K is 1.8 min cm. -1 Next, after being removed from the heating furnace, it is rolled at 1104 °C, and then finished rolling is carried out at 895 °C to ensure that the deformation is completed within a single austenitic region; then it is rolled at 63 °C for min. -1 The cooling rate was adjusted to bring the temperature down to 648 °C. After rapid cooling, the cooling rate was further adjusted to 8 °C / min. -1 This is to prevent excessive internal stress from being generated.

6. A high-precision steel ball production process based on multi-station cold heading as described in claim 1 or 2, characterized in that, The specific operation steps are as follows: In step S4, the steel billet prepared in step S3 is heated to 789 ℃ for post-rolling treatment and spheroidizing annealing, and the holding time is 180 min; then the steel is peeled or polished to remove the decarburized layer, cracks and other defects on the surface to ensure surface quality; the purpose of this step is to transform the hard and brittle lamellar pearlite in the rolled structure into a soft, easy-to-cut and cold-form spheroid pearlite structure.

7. A high-precision steel ball production process based on multi-station cold heading as described in claim 1 or 2, characterized in that, The specific operation steps are as follows: In step S5, the steel processed in step S4 is cut into cylindrical blanks of a predetermined length, and then an upsetting ball of the required diameter is extruded. The upsetting ball is further extruded into a cup-shaped sleeve. Then, a conical half-die is used to extrude the end of the connecting rod into a conical upsetting head, and then a spherical half-die is used to extrude it into a spherical head. The ball blank is designed with a bipolar cone angle 2α of 95° and a ring shape to reduce deformation stress and material loss. The workpiece is rotated 90° and the spherical head is extruded into a flat spherical head. Then, symmetrical concave platforms are extruded from the two ends of the flat spherical head, and finally, through holes are formed by extrusion. The ball blank after cold upsetting needs to be stress-relieved annealed at a low temperature of 152 ℃ and held for 3.7 h to eliminate the internal stress generated by cold upsetting.

8. A high-precision steel ball production process based on multi-station cold heading as described in claim 1 or 2, characterized in that, The specific operation steps are as follows: In step S6, the ring, two poles and surface oxide layer of the ball blank prepared in step S5 are removed to make it basically spherical; quenching is performed at 1035 ℃, tempering is performed at 473 ℃, and cold treatment is performed at -44 ℃ for 175 min. Then, surface strengthening treatment is performed on the steel ball strengthening machine. Through the autonomous drop impact and mutual impact of the steel balls, a strengthening layer with a depth of 0.15 mm is formed on the surface, which improves the distribution of residual compressive stress and improves the fatigue resistance of the steel balls.

9. A high-precision steel ball production process based on multi-station cold heading as described in claim 1 or 2, characterized in that, The specific operation steps are as follows: In step S7, the steel ball obtained in step S6 is precision ground in a closed environment with constant temperature of 23±2℃, constant humidity of 65%, and dust-free environment using a 3000-mesh resin grinding wheel. The grinding plate pressure is gradually reduced from 19KN to 11KN, the spindle speed is adjusted to 34 rpm, and the grinding efficiency is controlled to decrease from 2 μm / h to 0.75 μm / h, so that the variation in the diameter of the steel ball is controlled within 0.25 μm.

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