Preparation method of h13 roller for hot-rolled steel ball

Abstract

The application discloses a preparation method of H13 rolling roller for hot-rolled steel ball, which comprises the following steps: S1, molten steel smelting and electroslag remelting; S2, high-temperature diffusion annealing: high-temperature diffusion annealing is conducted on the electroslag steel ingot to eliminate the as-cast dendritic segregation and homogenize the organization composition; S3, multi-directional forging; S4, post-forging heat treatment and spheroidizing annealing; S5, rough machining and flaw detection; S6, vacuum quenching; S7, instant deep cooling treatment; S8, three times of gradient tempering; S9, fine machining and surface treatment. Through multi-directional cross forging, the application solves the problem of rolling roller fracture failure; instant deep cooling treatment within 2 hours after quenching improves the organization stability; through three times of differential gradient tempering, the problem of mismatching between the strength and toughness of the roller body and the roller neck is solved; through rare earth composite slag system electroslag remelting, the purity of the molten steel is improved, and the crack sensitivity is reduced; the whole-process process synergistically improves the service life of the rolling roller and reduces the production cost.

Description

Technical Field

[0001] This invention relates to the field of rolling mill production technology, and in particular to a method for preparing an H13 rolling mill roll for hot-rolled steel balls. Background Technology

[0002] Hot-rolled steel balls are core wear-resistant spare parts for ball mill equipment in industries such as mining, mineral processing, building materials, cement, and thermal power generation. Hot-rolled steel ball rolls are the core and critical components of hot-rolled steel ball production lines, and their service conditions are extremely harsh: during the rolling process, they must withstand alternating thermal shock from steel billets at temperatures above 1000℃, heavy rolling forces of tens of tons, and severe frictional wear between the steel billet and the die, accompanied by frequent impact loads. Therefore, hot-rolled steel ball rolls must simultaneously possess excellent resistance to thermal fatigue cracking, high wear resistance, high impact toughness, and excellent dimensional stability.

[0003] H13 hot work die steel is currently the mainstream material used for hot-rolled steel ball rolls in China. The existing industry-standard and mature production process is as follows: electric arc furnace smelting → LF refining → VD vacuum degassing preparation → electroslag remelting → forging → spheroidizing annealing → rough machining → quenching + tempering → finish machining. This process improves the basic purity of the molten steel through electroslag remelting and is the standard solution for the industrial production of H13 rolls. However, under the high-temperature, heavy-load, alternating service conditions of hot-rolled steel balls, this existing process still has the following inherent technical defects that cannot be overcome.

[0004] First, the existing unidirectional forging process does not fully break down carbides, resulting in banded segregation of ≥3 levels and severe material anisotropy, which can easily lead to early failures such as roll body fracture and roll neck torsion.

[0005] Second, the existing process only adopts the heat treatment scheme of "vacuum quenching + 1-2 conventional overall tempering", without deep cryogenic treatment, or only supplements deep cryogenic treatment after tempering. It cannot effectively eliminate the metastable residual austenite formed during quenching. The residual austenite content in the finished rolls is generally ≥5%, the microstructure is unstable, the rolls have insufficient thermal fatigue resistance, are prone to hot cracks, and the service life is greatly shortened.

[0006] Third, the tempering process cannot achieve differentiated performance control and cannot solve the core contradiction of matching the strength and toughness of the rolls;

[0007] Fourth, the existing electroslag remelting process only uses the conventional CaF2-Al2O3-CaO ternary slag system, which can only achieve basic deoxidation and removal of large inclusions. It cannot modify the fine non-metallic inclusions remaining in the steel, which are very likely to become the core of crack initiation, greatly reducing the thermal fatigue resistance and impact toughness of the rolls and accelerating the early failure of the rolls.

[0008] Therefore, this application provides a method for preparing H13 rolls for hot-rolled steel balls and an H13 roll to meet the requirements. Summary of the Invention

[0009] The purpose of this application is to provide a method for preparing H13 rolls for hot-rolled steel balls and an H13 roll, in order to solve the technical problems mentioned in the background.

[0010] To achieve the above objectives, this application provides the following technical solution: a method for preparing H13 rolls for hot-rolled steel balls, comprising the following steps:

[0011] S1. Steel smelting and electroslag remelting: Electrode rods that meet the composition requirements are prepared by electric arc furnace smelting + LF refining + VD vacuum degassing, and then the electrode rods are electroslag remelted to obtain high-purity electroslag steel ingots.

[0012] S2. High-temperature diffusion annealing: High-temperature diffusion annealing is performed on electroslag steel ingots to eliminate dendritic segregation in the as-cast state and homogenize the microstructure and composition.

[0013] S3. Multi-directional forging: Multi-directional "cross" forging is carried out on the steel ingot after high-temperature diffusion annealing. The three-directional deformation is carried out alternately, the total forging ratio is ≥6, the initial forging temperature is 1150-1180℃, and the final forging temperature is ≥900℃. Carbides are fully broken, and banded segregation and anisotropy are eliminated.

[0014] The multi-directional "cross" forging with alternating triaxial deformation can achieve uniform plastic deformation of steel ingots in the radial, axial and circumferential directions compared with conventional uniaxial elongation. It breaks down network carbides and eutectic carbides from all directions, completely eliminates carbide banding segregation, eliminates material anisotropy, significantly improves transverse impact toughness, and solves the core failure problems of hot rolling roll neck torsion and roll body cracking along banded structure.

[0015] Total forging ratio ≥6: If the forging ratio is <6, the carbides cannot be fully broken up and the banded segregation cannot be eliminated; if the total forging ratio is ≥6, the triaxial deformation can be fully guaranteed, the carbides can be completely broken up and evenly distributed, and the austenite grains can be refined to improve the comprehensive mechanical properties of the material.

[0016] Initial forging temperature 1150-1180℃: The solidus temperature of H13 steel is about 1400℃. Within the range of 1150-1180℃, the steel has the best plasticity and the lowest deformation resistance, which can achieve large deformation forging without cracking. If the initial forging temperature exceeds 1180℃, it will cause the austenite grains to grow excessively and even burn. If the initial forging temperature is below 1150℃, the plasticity of the steel decreases and the deformation resistance increases, making it impossible to achieve large deformation forging.

[0017] Final forging temperature ≥900℃: H13 steel still maintains good plasticity above 900℃. A final forging temperature ≥900℃ can avoid the problems of uneven structure and excessive internal stress caused by forging in the two-phase region.

[0018] S4. Post-forging heat treatment and spheroidizing annealing: The forged steel ingot is immediately put into the furnace for post-forging annealing to eliminate forging internal stress and prevent cracking; then isothermal spheroidizing annealing is performed to obtain a uniformly distributed spherical pearlite structure, reduce hardness, and improve machinability.

[0019] S5. Rough machining and flaw detection: Rough machining is performed on the spheroidized annealed billet, leaving a machining allowance of 3mm on each side. Then, ultrasonic flaw detection is performed. After passing the flaw detection, the billet proceeds to the next process.

[0020] Leaving a 3mm machining allowance on one side can ensure that the surface damage layer and decarburized layer from the roughing process are completely removed during subsequent finishing, while avoiding excessive allowance that would increase finishing costs. At the same time, it allows sufficient machining allowance for deformation during subsequent heat treatment, preventing the product from being unable to be machined to the finished size after heat treatment deformation.

[0021] S6. Vacuum quenching: The blank that has passed the flaw detection is subjected to double-chamber vacuum quenching to obtain a uniform martensitic matrix structure. After quenching, it is cooled to room temperature.

[0022] S7. Immediate cryogenic treatment: Within 2 hours after vacuum quenching, the billet is subjected to cryogenic treatment at a temperature of -110℃ to -130℃ and a holding time of 1.5-3 hours to maximize the transformation of residual austenite and stabilize the microstructure.

[0023] Perform within 2 hours after quenching: If the residual austenite of H13 steel remains at room temperature for more than 2 hours after quenching, carbon atoms will segregate, forming Cotillard gas clusters, pinning dislocations, and causing the residual austenite to become thermally stable. Even subsequent deep cooling cannot transform it. Limiting the process to within 2 hours can completely avoid the thermal stabilization of the residual austenite and ensure the maximum effect of deep cooling.

[0024] Cryogenic temperature -110℃~-130℃: The martensitic transformation termination temperature (Mf point) of H13 steel is approximately -100℃. Cryogenic temperatures below the Mf point are necessary to ensure complete transformation of retained austenite. The range of -110℃ to -130℃ completely covers the Mf point, ensuring sufficient transformation of retained austenite. Temperatures below -130℃ will lead to excessive internal stress, resulting in cryogenic cracks and increasing production costs. Temperatures above -110℃ will not reach the Mf point, resulting in insufficient transformation of retained austenite.

[0025] S8. Three-stage gradient tempering: After the billet is heated to room temperature after cryogenic treatment, it is subjected to three-stage gradient tempering. After each tempering, it is oil-cooled to below 100°C and then air-cooled to precipitate dispersed secondary carbides, eliminate internal stress and temper brittleness, and adjust the hardness to the target range.

[0026] Compared to conventional 1-2 tempering, triple gradient tempering can fully eliminate the internal stress generated during quenching and deep cooling, promote the precipitation of dispersed secondary alloy carbides in the martensitic matrix, achieve secondary hardening, eliminate secondary tempering brittleness, and stabilize the microstructure and dimensions. Combined with differentiated tempering of the roll body and roll neck, it can simultaneously achieve high hardness and wear resistance of the roll body and high toughness and torsional resistance of the roll neck.

[0027] After each tempering, oil cooling to below 100℃ and then air cooling are performed: H13 steel has a tempering brittleness range of 300-550℃. After tempering, oil cooling quickly passes through the brittleness range, which can completely avoid secondary tempering brittleness and ensure the toughness of the material. Cooling to below 100℃ and then air cooling can avoid the internal stress caused by air cooling at excessively high temperatures.

[0028] S9. Finishing and Surface Treatment: The tempered billet is finished to the target dimensional accuracy, then surface strengthening treatment is carried out. After passing the dimensional, hardness and metallographic tests, it is packaged and put into storage.

[0029] In a preferred embodiment of this example, in S1, the slag system used for electroslag remelting is as follows by mass percentage: CaF2 68-72%, Al2O3 18-22%, CaO 8-12%. The slag system also contains 0.5-1.0% rare earth composite oxide, which is a mixture of La2O3 and CeO2 in a mass ratio of 1:1.

[0030] The melting rate of electroslag remelting is 8-12 kg / min, the working current is 5000-8000 A, the working voltage is 60-70 V, and the feeding process is to gradually reduce the power by 10% / 5 min × 3 times.

[0031] 0.5-1.0% La2O3-CeO2 composite rare earth oxides: Rare earth elements have extremely strong deoxidation and desulfurization capabilities, which can further reduce the oxygen and sulfur content in steel. At the same time, they can transform sharp-angled hard oxides and sulfide inclusions in steel into spherical rare earth inclusions, significantly reducing the crack sensitivity of inclusions and improving the material's thermal fatigue resistance and impact toughness. If the addition amount is <0.5%, the modification effect is insufficient; if the addition amount is >1.0%, rare earth inclusions will aggregate, which will reduce the material's performance. 0.5-1.0% is the optimal addition range.

[0032] The gradual reduction of power by 10% / 5min × 3 feeding processes can gradually reduce the temperature of the molten pool, achieve sequential solidification of the top of the steel ingot, completely eliminate shrinkage cavities and porosity defects at the top of the steel ingot, and ensure the density of the steel ingot.

[0033] As a preferred embodiment of this example, in S2, the process parameters for high-temperature diffusion annealing are: heating temperature 1200-1250℃, holding time 15-20h, furnace cooling to 800℃ and then air cooling.

[0034] Heating temperature 1200-1250℃: The austenitizing temperature of H13 steel is about 850℃. Above 1200℃, the alloying elements can obtain sufficient diffusion activation energy to achieve full diffusion. The upper limit of 1250℃ can avoid excessive growth of austenite grains, which would cause the steel ingot to overheat and burn, and ensure the plasticity of subsequent forging.

[0035] Holding time 15-20h: If the holding time is less than 15h, the alloying elements cannot diffuse fully and dendrite segregation cannot be completely eliminated; if the holding time exceeds 20h, it will lead to abnormal growth of austenite grains and increase production costs. 15-20h is the optimal range that balances diffusion effect and grain control.

[0036] Furnace cooling to 800℃ followed by air cooling: Furnace cooling to 800℃ can avoid thermal stress caused by a sudden drop in temperature and prevent the steel ingot from cracking. Air cooling below 800℃ will not cause a sudden change in the structure and will improve production efficiency.

[0037] As a preferred embodiment of this example, in S3, the multi-directional "cross" forging adopts a two-upsetting and two-drawing process, with a single-pass upsetting ratio ≥2.5 and a single-pass drawing length ratio ≥3.0;

[0038] The forging heating process is as follows: first, preheat at 600-650℃ for 2 hours, then raise the temperature to 850-900℃ and hold for 1.5 hours, and finally raise the temperature to 1150-1180℃ and hold until the steel ingot is fully heated.

[0039] An intermediate annealing process is set up during the forging process, with a process of 900℃×1h. After the furnace is cooled to 650℃, it is heated again for forging.

[0040] The cross forging process of two upsetting and two drawing can achieve upsetting and drawing in two perpendicular directions, ensuring uniform deformation in three directions; the upsetting ratio of a single pass is ≥2.5, which can achieve large axial deformation of the steel ingot and fully break up the axial network of carbides; the drawing ratio of a single pass is ≥3.0, which can achieve large radial deformation and fully break up radial carbide agglomeration. The combination of the two can achieve carbide breaking in all directions and completely eliminate banded segregation.

[0041] Preheating at a low temperature first, then holding at a medium temperature, and finally heating at a high temperature can avoid thermal stress cracking caused by direct high-temperature heating of the steel ingot, while ensuring uniform temperature inside and outside the steel ingot, sufficient heat penetration, uniform deformation during forging, and avoiding insufficient local deformation.

[0042] An intermediate annealing process of 900℃ for 1 hour is set between the two upsetting and two drawing processes. This process can eliminate the internal stress generated by the first forging process, restore the plasticity of the steel, and prevent cracking caused by excessive internal stress during the second forging process. At the same time, it can refine the dynamic recrystallized grains and further improve the uniformity of the microstructure.

[0043] As a preferred embodiment of this example, in S4, the post-forging annealing process is as follows: holding at 650-700℃ for 4-6 hours, then furnace cooling to below 300℃ before exiting the furnace; the isothermal spheroidizing annealing process is as follows: holding at 860-880℃ for 4 hours to complete austenitization, furnace cooling to 740-760℃ at a rate of ≤30℃ / h and holding at 740-760℃ for 6-8 hours for isothermal spheroidization, and then furnace cooling to below 500℃ at a rate of ≤30℃ / h before exiting the furnace.

[0044] Annealing after forging at 650-700℃ for 4-6 hours: 650-700℃ is within the recrystallization temperature range of H13 steel, which can fully eliminate forging internal stress and achieve recrystallization to refine the grains; holding time of 4-6 hours can ensure that the internal stress is completely eliminated, while avoiding grain growth caused by excessive holding time.

[0045] Cool the billet to below 300°C before unloading: Unloading the billet at below 300°C and air cooling can avoid thermal stress caused by excessively high temperatures and prevent the billet from cracking.

[0046] Spheroidizing annealing at 860-880℃ for 4 hours for austenitization: 860-880℃ is above the Ac3 line of H13 steel, which can achieve complete austenitization, dissolve lamellar cementite, and provide a uniform austenite matrix for subsequent isothermal spheroidization; if the temperature is too high, austenite grains will grow, and if the temperature is too low, complete austenitization cannot be achieved, resulting in poor spheroidization effect;

[0047] Isothermal spheroidization after furnace cooling to 740-760℃ and holding for 6-8 hours: This is the optimal nucleation and growth temperature range for spherical cementite. Isothermal spheroidization at this temperature allows dissolved carbides to precipitate uniformly in spherical form, avoiding the formation of platy carbides. Holding for 6-8 hours ensures complete spheroidization and yields uniform spherical pearlite.

[0048] Cooling rate ≤30℃ / h: A cooling rate exceeding 30℃ / h will cause the precipitation of plate-like carbides, making it impossible to achieve the spheroidization effect. A slow cooling rate of ≤30℃ / h can ensure that the carbides are fully spheroidized and avoid the formation of plate-like structures.

[0049] Cooling the furnace to below 500℃ before unloading: The microstructure is completely stable below 500℃, and air cooling after unloading will not cause any changes in the microstructure, while improving production efficiency.

[0050] As a preferred embodiment of this example, in S6, the vacuum quenching adopts a two-stage preheating process: first, it is preheated at 600℃ for 30 minutes and at 850℃ for 30 minutes, and then heated to 1020-1050℃ and held for 1.5-2 hours; the quenching cooling adopts 5-8 bar high-pressure nitrogen gas quenching, or a graded quenching process: holding at 580-620℃ in a salt bath for 15 minutes and then air cooling to room temperature.

[0051] Two-stage preheating process: first, hold at 600℃ for 30 minutes, then hold at 850℃ for 30 minutes. This can avoid the huge thermal stress generated by directly heating the billet to the quenching temperature, prevent the billet from cracking, and at the same time ensure uniform temperature inside and outside the billet, uniform austenitization, and avoid uneven internal and external structure.

[0052] Quenching heating temperature 1020-1050℃: 1020-1050℃ is the optimal quenching temperature range for H13 steel. Within this temperature range, alloy carbides such as Cr, Mo, and V can fully dissolve into austenite, ensuring the degree of martensite alloying after quenching and improving the secondary hardening effect after tempering. If the temperature exceeds 1050℃, it will cause abnormal growth of austenite grains, resulting in coarse martensite after quenching and a significant decrease in toughness. If the temperature is below 1020℃, alloy carbides cannot fully dissolve, resulting in insufficient hardness after quenching and poor secondary hardening effect.

[0053] Holding time 1.5-2h: Insufficient holding time results in uneven austenitization and incomplete dissolution of alloy carbides; excessive holding time leads to austenite grain growth and decreased toughness. 1.5-2h is the optimal range that balances austenitization uniformity and grain size.

[0054] 580-620℃ salt bath graded quenching: can significantly reduce thermal stress and structural stress during the quenching process, avoid quenching cracks, and ensure sufficient martensitic transformation. It is especially suitable for quenching treatment of large-size rolls.

[0055] As a preferred embodiment of this example, in S7, the cryogenic treatment adopts a stepped cryogenic process: first, the billet is cooled to -70~-90℃ at a cooling rate of ≤10℃ / min and held for 1 hour, and then cooled to -110~-130℃ at the same rate and held for 1.5-3 hours.

[0056] After cryogenic treatment, the billet is allowed to naturally warm to room temperature in the air.

[0057] Advantages of stepped cryogenic process: Compared with direct cooling to the final cryogenic temperature, stepped cooling can avoid the huge thermal stress and structural stress caused by sudden temperature drop, prevent the billet from developing cryogenic cracks, and at the same time make the temperature inside and outside the billet uniform, ensuring that the residual austenite in the core is fully transformed and improving the uniformity of the cryogenic effect.

[0058] The advantage of limiting the cooling rate to ≤10℃ / min is that too fast a cooling rate will lead to an excessive temperature difference between the inside and outside of the billet, generating huge thermal stress and easily causing cracks; a slow cooling rate of ≤10℃ / min can ensure uniform temperature inside and outside of the billet, controllable internal stress, and avoid deep cryogenic cracks.

[0059] The benefits of holding at -70~-90℃ for 1 hour: Holding at this temperature range can make the temperature inside and outside of the billet uniform, while achieving the pre-transformation of some residual austenite, reducing the structural stress in the final cryogenic stage, and avoiding cracking.

[0060] In a preferred embodiment of this invention, in step S8, the three-stage gradient tempering employs a differentiated tempering process for the roll body and the roll neck, with the following specific parameters:

[0061] First tempering: Both the roll body and the roll neck are held at 590-610℃ for 2 hours to eliminate quenching and deep cryogenic internal stress and stabilize the matrix structure.

[0062] Second tempering: The working area of ​​the roll body is kept at 580-600℃ for 2 hours, and the hardness is adjusted to 50-60HRC; the drive area of ​​the roll neck is kept at 630-650℃ for 2 hours, and the hardness is adjusted to 40-45HRC.

[0063] Third tempering: The working area of ​​the roll body is kept at 570-590℃ for 2 hours to eliminate the brittleness caused by secondary tempering; the drive area of ​​the roll neck is kept at 620-640℃ for 2 hours to further stabilize the microstructure.

[0064] The benefits of using a uniform first tempering temperature of 590-610℃ and holding it for 2 hours: The internal stress of the billet after quenching and deep cooling is extremely high. Using a uniform medium-high temperature for the first tempering can fully eliminate the internal stress generated by quenching and deep cooling, causing the martensitic matrix to decompose, precipitating fine carbides, stabilizing the matrix structure, and avoiding cracking due to excessive internal stress during subsequent differentiated tempering.

[0065] Benefits of differentiated temperature limits for the second tempering: Holding at 580-600℃ for 2 hours in the working zone of the roll body: This falls within the peak temperature range of secondary hardening for H13 steel, promoting the dispersion and precipitation of Mo and V alloy carbides, achieving secondary hardening, and adjusting the hardness to 50-60 HRC, ensuring the wear resistance and thermal fatigue resistance of the roll body. Holding at 630-650℃ for 2 hours in the drive zone of the roll neck: This temperature is higher than the secondary hardening temperature, allowing for sufficient tempering of martensite, reducing the hardness to 40-45 HRC, obtaining extremely high impact toughness and plasticity, and ensuring the torsional fracture resistance of the roll neck.

[0066] The benefits of a differentiated tempering temperature limit for the third tempering: Based on the second tempering, tempering at a temperature slightly lowered by 10°C can further eliminate the internal stress generated by the first two temperings, completely eliminate the brittleness caused by secondary tempering, and at the same time make the microstructure completely stable, ensuring that the dimensions and performance of the rolls do not change during service; tempering the roll neck at a slightly lower temperature can prevent further decrease in hardness and ensure the matching of toughness and strength.

[0067] In a preferred embodiment of this example, in S9, the diameter tolerance of the finished roll is ±0.05mm, the coaxiality is ≤0.03mm, and the surface roughness Ra is ≤0.8μm.

[0068] The surface strengthening treatment is any one of laser quenching, gas nitriding, or arc spraying. After laser quenching, the hardened layer depth on the roller surface is 2-3 mm, and the hardness is 58-62 HRC. The gas nitriding process involves holding at 520℃ for 20 hours, with a nitriding layer depth of 0.15-0.25 mm and a surface hardness ≥900 HV.

[0069] An H13 roll for hot-rolled steel balls, wherein the chemical composition of the H13 roll, by mass percentage, is: C 0.32-0.45%, Si 0.80-1.20%, Mn 0.20-0.50%, Cr 4.75-5.50%, Mo 1.10-1.75%, V 0.80-1.20%, P ≤0.020%, S ≤0.010%; the non-metallic inclusions A / B / C / D of the H13 roll are all ≤1.0 grade, and the carbide banded segregation is ≤2 grade.

[0070] In summary, the technical effects and advantages of this invention are as follows:

[0071] This invention utilizes a multi-directional cross forging process to control carbide banding segregation to within level 2, eliminating material anisotropy and solving the problem of roll fracture failure. Through immediate deep cryogenic treatment within 2 hours after quenching, the residual austenite content is controlled to within 1%, overcoming industry technical biases and improving microstructural stability. Three differentiated gradient tempering processes address the industry pain point of mismatched strength and toughness between the roll body and neck. Rare earth composite slag electroslag remelting improves the purity of the molten steel and reduces crack sensitivity. The synergistic effect of the entire process results in a roll service life more than 60% longer than existing processes, significantly reducing production costs and yielding substantial economic benefits. Attached Figure Description

[0072] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0073] Figure 1 The graph shows the measured chemical composition values ​​of H13 steel for each embodiment and comparative example;

[0074] Figure 2 A comparison chart showing the purity and microstructure uniformity of steel ingots in each embodiment and comparative example;

[0075] Figure 3 Comparison diagrams of metallographic structure and hardness indices between the embodiments and comparative examples;

[0076] Figure 4 This is a comparison chart of the room temperature mechanical properties of each embodiment and the comparative example.

[0077] Figure 5 A comparison chart of the thermal fatigue performance of each embodiment and the comparative example.

[0078] Figure 6 The graph shows a comparison of the actual industrial service life of each embodiment and the comparative example. Detailed Implementation

[0079] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0080] The following are the measured chemical composition values ​​of H13 steel in the examples and comparative examples: Figure 1 As shown;

[0081] Example 1

[0082] This embodiment prepares an H13 roll for rolling steel balls of conventional φ30-60mm size according to the preparation method described in claims 1-9. The specific steps are as follows:

[0083] S1. Steelmaking and Electroslag Remelting: A 50t electric arc furnace is used for smelting, according to... Figure 1 The ingredients of Example 1 were prepared by LF refining and VD vacuum degassing to prepare φ200mm electrode rods. The electrode rods were then subjected to electroslag remelting. The slag system, by mass percentage, was: CaF2 70%, Al2O3 20%, CaO 9%, and La2O3 and -CeO2 composite rare earth oxides 1% (mass ratio 1:1). The electroslag remelting process parameters were: melting rate 10kg / min, working current 6500A, working voltage 65V, and feeding was carried out by gradually reducing the power by 10% / 5min × 3 times to obtain φ500mm electroslag steel ingots.

[0084] S2. High-temperature diffusion annealing: The electroslag steel ingot is fed into a bogie furnace, heated to 1220℃ and held for 18 hours. After furnace cooling to 800℃, it is taken out of the furnace and air-cooled to eliminate dendritic segregation in the as-cast state.

[0085] S3. Multi-directional forging: The steel ingot is subjected to two upsetting and two drawing multi-directional "cross" forging. Heating regime: preheat at 650℃ for 2 hours, hold at 880℃ for 1.5 hours, raise to 1160℃ and hold until the steel ingot is fully heated; in the first heat, the ingot is upset to 1 / 3 of its original height with an upsetting ratio of 3.0, and then drawn back to its original size with a drawing ratio of 3.0; intermediate annealing at 900℃ for 1 hour, followed by furnace cooling to 650℃; in the second heat, the ingot is upset along the cross direction with an upsetting ratio of 2.8, and then drawn back to the size of the roll blank with a drawing ratio of 3.2, for a total forging ratio of 8.5; the initial forging temperature is 1160℃, the final forging temperature is 920℃, and the ingot is immediately placed in the furnace after forging.

[0086] S4. Post-forging heat treatment and spheroidizing annealing: Post-forging annealing process: hold at 680℃ for 5h, furnace cool to 280℃ and remove from the furnace; Isothermal spheroidizing annealing process: hold at 870℃ for 4h to complete austenitization, furnace cool to 750℃ at a rate of 25℃ / h and hold for 7h for isothermal spheroidization, then furnace cool to 480℃ at a rate of 25℃ / h and remove from the furnace to obtain a uniform spherical pearlite structure with a hardness of 220HB.

[0087] S5. Rough machining and flaw detection: Rough machining is performed on the spheroidized annealed billet, with a machining allowance of 3mm on each side, and the surface roughness Ra≤6.3μm; Ultrasonic flaw detection is performed according to GB / T6402-2008, with a single defect ≤Φ3mm, no continuous defects, and the flaw detection is qualified.

[0088] S6. Vacuum quenching: A double-chamber vacuum quenching furnace is used, with two-stage preheating: 600℃×30min and 850℃×30min, then heated to 1030℃ and held for 1.8h, followed by 6bar high-pressure nitrogen quenching and cooling to room temperature.

[0089] S7. Immediate cryogenic treatment: Within 1.5 hours after vacuum quenching, the billet is sent into a cryogenic furnace and a stepped cryogenic process is adopted: the temperature is reduced to -80℃ at a rate of 8℃ / min, held for 1 hour, and then reduced to -120℃ at the same rate and held for 2 hours; after the holding is completed, the billet is allowed to naturally warm up to room temperature in the air.

[0090] S8. Three-stage gradient tempering: Differentiated tempering processes are adopted for the roll body and roll neck. After each tempering, the roll body is oil-cooled to 80℃ and then air-cooled. First tempering: The roll body and roll neck are both held at 600℃ for 2 hours to eliminate quenching and deep cryogenic internal stress and stabilize the matrix structure. Second tempering: The working area of ​​the roll body is held at 590℃ for 2 hours to adjust the hardness to 55-58HRC. The transmission area of ​​the roll neck is held at 640℃ for 2 hours to adjust the hardness to 42-44HRC. Third tempering: The working area of ​​the roll body is held at 580℃ for 2 hours to eliminate the brittleness caused by secondary tempering. The transmission area of ​​the roll neck is held at 630℃ for 2 hours to further stabilize the structure.

[0091] S9. Finishing and Surface Treatment: The tempered billet is finished to the finished size, with a diameter tolerance of ±0.05mm, coaxiality ≤0.03mm, and roll surface roughness Ra≤0.4μm; the roll hole shape is laser hardened to a hardened layer depth of 2.5mm and a hardness of 60-62HRC; after passing the size, hardness, and metallographic tests, it is packaged and stored.

[0092] Example 2

[0093] This embodiment prepares an H13 roll for rolling steel balls with a width of φ20-100mm according to the preparation method described in claims 1-9, using the lower limit of the parameter range in the claims. The specific steps are as follows:

[0094] S1. Steelmaking and Electroslag Remelting: A 30t electric arc furnace is used for smelting, according to... Figure 1 The ingredients of Example 2 were prepared into electrode rods by LF refining and VD vacuum degassing. The electroslag remelting slag system was as follows by mass percentage: CaF2 68%, Al2O3 22%, CaO 9.5%, and La2O3-CeO2 composite rare earth oxides 0.5%. The electroslag remelting process parameters were: melting rate 8 kg / min, working current 5000 A, working voltage 60 V, and the feeding process was the same as in Example 1, resulting in an electroslag steel ingot with a diameter of φ450 mm.

[0095] S2. High-temperature diffusion annealing: The electroslag steel ingot is fed into the bogie furnace, heated to 1200℃ and held for 20 hours, then cooled to 800℃ and air-cooled.

[0096] S3. Multi-directional forging: The steel ingot is subjected to two upsetting and two drawing multi-directional "cross" forging. Heating regime: preheat at 600℃ for 2 hours, hold at 850℃ for 1.5 hours, raise to 1150℃ and hold until the steel ingot is fully heated; the first upsetting ratio is 2.5 and the drawing ratio is 3.0; intermediate annealing is 900℃×1 hour and furnace cooling is 650℃; the second upsetting is carried out along the cross direction, with an upsetting ratio of 2.5, a drawing ratio of 3.0, and a total forging ratio of 6.0; the initial forging temperature is 1150℃ and the final forging temperature is 900℃. The steel ingot is immediately put into the furnace after forging.

[0097] S4. Post-forging heat treatment and spheroidizing annealing: Post-forging annealing process: hold at 650℃ for 6 hours, furnace cool to 260℃ and remove from the furnace; Isothermal spheroidizing annealing process: hold at 860℃ for 4 hours to complete austenitization, furnace cool to 740℃ at a rate of 30℃ / h and hold for 8 hours for isothermal spheroidization, then furnace cool to 470℃ at a rate of 30℃ / h and remove from the furnace, with a hardness of 210HB.

[0098] S5. Rough machining and flaw detection: Same as in Example 1, flaw detection is qualified.

[0099] S6. Vacuum quenching: A double-chamber vacuum quenching furnace is used, with two-stage preheating: 600℃×30min and 850℃×30min. The temperature is raised to 1020℃ and held for 2 hours. High-pressure nitrogen gas quenching at 5 bar is used, followed by cooling to room temperature.

[0100] S7. Immediate cryogenic treatment: Within 2 hours after vacuum quenching, the billet is sent into a cryogenic furnace and a stepped cryogenic process is adopted: the temperature is reduced to -70℃ at a rate of 10℃ / min, held for 1 hour, and then reduced to -110℃ at the same rate and held for 3 hours; after the holding is completed, the temperature is naturally restored to room temperature.

[0101] S8. Three-stage gradient tempering: Differentiated tempering process is adopted for the roll body and roll neck. After each tempering, the roll body is oil-cooled to 90℃ and then air-cooled: First tempering: The roll body and roll neck are both held at 590℃ for 2 hours; Second tempering: The working area of ​​the roll body is held at 580℃ for 2 hours, and the hardness is adjusted to 50-53HRC; The transmission area of ​​the roll neck is held at 630℃ for 2 hours, and the hardness is adjusted to 43-45HRC; Third tempering: The working area of ​​the roll body is held at 570℃ for 2 hours; The transmission area of ​​the roll neck is held at 620℃ for 2 hours.

[0102] S9. Finishing and Surface Treatment: Finished to the finished size, with a roller surface roughness Ra≤0.8μm; gas nitriding treatment is adopted, and the temperature is kept at 520℃ for 20h, with a nitriding layer depth of 0.15mm and a surface hardness of 920HV; after passing the inspection, it is put into storage.

[0103] Example 3

[0104] This embodiment prepares an H13 roll for rolling large-diameter steel balls with a diameter of φ80-120mm according to the preparation method described in claims 1-9, using the upper limit of the parameter range in the claims. The specific steps are as follows:

[0105] S1. Steelmaking and Electroslag Remelting: Smelting is carried out using an 80t electric arc furnace, according to... Figure 1The ingredients of Example 3 were prepared into electrode rods by LF refining and VD vacuum degassing. The electroslag remelting slag system was as follows by mass percentage: CaF2 72%, Al2O3 18%, CaO 9.5%, and La2O3-CeO2 composite rare earth oxides 0.5%. The electroslag remelting process parameters were: melting rate 12 kg / min, working current 8000 A, working voltage 70 V, and feeding process was the same as in Example 1, resulting in φ600 mm electroslag steel ingots.

[0106] S2. High-temperature diffusion annealing: The electroslag steel ingot is fed into the bogie furnace, heated to 1250℃ and held for 15 hours, then cooled to 800℃ and air-cooled.

[0107] S3. Multi-directional forging: The steel ingot is subjected to two upsetting and two drawing multi-directional "cross" forging. Heating regime: preheat at 650℃ for 2 hours, hold at 900℃ for 1.5 hours, raise to 1180℃ and hold until the steel ingot is fully heated; the first upsetting ratio is 2.6 and the drawing ratio is 3.2; intermediate annealing is performed at 900℃ for 1 hour, and furnace cooling is performed to 650℃; the second upsetting is performed along the cross direction, with an upsetting ratio of 2.6, a drawing ratio of 3.2, and a total forging ratio of 7.5; the initial forging temperature is 1180℃ and the final forging temperature is 930℃. The steel ingot is immediately placed in the furnace after forging.

[0108] S4. Post-forging heat treatment and spheroidizing annealing: Post-forging annealing process: hold at 700℃ for 4 hours, furnace cool to 290℃ and remove from the furnace; Isothermal spheroidizing annealing process: hold at 880℃ for 4 hours to complete austenitization, furnace cool to 760℃ at a rate of 28℃ / h and hold for 6 hours for isothermal spheroidization, then furnace cool to 490℃ at a rate of 28℃ / h and remove from the furnace, with a hardness of 225HB.

[0109] S5. Rough machining and flaw detection: Same as in Example 1, flaw detection is qualified.

[0110] S6. Vacuum quenching: A double-chamber vacuum quenching furnace is used, with two-stage preheating: 600℃×30min and 850℃×30min, then heating to 1050℃ and holding for 1.5h. A graded quenching process is adopted: holding in a 620℃ salt bath for 15min and then air cooling to room temperature.

[0111] S7. Immediate cryogenic treatment: Within 1 hour after vacuum quenching, the billet is sent into a cryogenic furnace and a stepped cryogenic process is adopted: the temperature is reduced to -90℃ at a rate of 9℃ / min, held for 1 hour, and then reduced to -130℃ at the same rate and held for 1.5 hours; after the holding is completed, the temperature is naturally restored to room temperature.

[0112] S8. Three-stage gradient tempering: Differentiated tempering process is adopted for the roll body and roll neck. After each tempering, the roll body is oil-cooled to 85℃ and then air-cooled: First tempering: The roll body and roll neck are both held at 610℃ for 2 hours; Second tempering: The working area of ​​the roll body is held at 600℃ for 2 hours, and the hardness is adjusted to 57-60HRC; The transmission area of ​​the roll neck is held at 650℃ for 2 hours, and the hardness is adjusted to 40-42HRC; Third tempering: The working area of ​​the roll body is held at 590℃ for 2 hours; The transmission area of ​​the roll neck is held at 640℃ for 2 hours.

[0113] S9. Finishing and Surface Treatment: Finishing to the finished size, with a roller surface roughness Ra≤0.8μm; using arc spraying to apply a Cr3C2-NiCr coating with a thickness of 0.1mm; after passing inspection, it is put into storage.

[0114] Comparative Example 1

[0115] This comparative example uses the existing general process route described in the background art to prepare H13 rolls. It uses the exact same chemical composition as Example 1. The specific process is as follows: electric arc furnace smelting + LF refining + VD vacuum degassing + electroslag remelting (conventional ternary slag system, no rare earth addition) → unidirectional elongation forging (total forging ratio 4, final forging temperature 900℃) → post-forging annealing + spheroidizing annealing → rough machining + ultrasonic flaw detection → vacuum quenching (same as Example 1) → two overall temperings (590℃×2h×2 times) → finish machining → finished product. There is no high-temperature diffusion annealing, no multi-directional cross forging, no deep cryogenic treatment, and no differentiated gradient tempering.

[0116] Comparative Example 2

[0117] The only difference between this comparative example and Example 1 is that the cryogenic treatment is performed 24 hours after quenching (which exceeds the "within 2 hours after quenching" range defined in claim 1), while the other process parameters are exactly the same as in Example 1.

[0118] Comparative Example 3

[0119] The only difference between this comparative example and Example 1 is that unidirectional axial elongation forging is used instead of multidirectional "cross" forging, with a total forging ratio of 4. The remaining process parameters are exactly the same as those in Example 1.

[0120] Comparative Example 4

[0121] The only difference between this comparative example and Example 1 is that three overall uniform tempering processes (590℃×2h×3 times) are used instead of the differentiated gradient tempering of the roll body and roll neck. All other process parameters are exactly the same as those in Example 1.

[0122] Comparative Example 5

[0123] The only difference between this comparative example and Example 1 is that no cryogenic treatment is performed; all other process parameters are exactly the same as in Example 1.

[0124] Performance Testing and Comparative Analysis: The H13 rolls prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to systematic performance testing according to relevant national standards. The test results are shown in [Figure Number]. Figures 2-6 All tests were conducted at room temperature, with sampling taken at half the radius of the roll body.

[0125] A comparison table of the purity and microstructure uniformity of steel ingots in each embodiment and comparative example is shown below. Figure 2 As shown, from Figure 2 It can be known that:

[0126] I. The oxygen and hydrogen contents of Examples 1-3 of this invention are much lower than those of Comparative Example 1 of the existing process, and the non-metallic inclusions are all ≤0.5 grade, proving that rare earth composite slag electroslag remelting can significantly improve the purity of molten steel and reduce the sensitivity of inclusion cracks.

[0127] 2. The carbide banding segregation in Examples 1-3 is ≤2, while the carbide banding segregation in Comparative Examples 1 and 3, which are made by unidirectional forging, is 3. This proves that multi-directional "cross" forging can fully break up carbides and eliminate banding segregation, thus verifying the core effect of the process.

[0128] Third, the purity indices of the other comparative examples 2, 4, and 5 are consistent with those of Example 1, proving that the adjustment of other process parameters does not affect the purity of the molten steel, and the purity is determined only by the electroslag remelting process.

[0129] A comparison table of metallographic structures and hardness indices of each embodiment and comparative example is shown below. Figure 3 As shown, from Figure 3 It can be known that:

[0130] I. The residual austenite content in Examples 1-3 of this invention is ≤1%, while the residual austenite content in Comparative Examples 1 and 5 without cryogenic treatment is ≥5.8%, and the residual austenite content in Comparative Example 2, which was cryogenically treated 24 hours after quenching, is 4.5%. This proves that "instantaneous cryogenic treatment within 2 hours after quenching" can maximize the transformation of residual austenite, overcome the time bias of the prior art, and is the core to achieve ultra-high microstructure stability.

[0131] II. Examples 1-3 achieved differentiated hardness matching between the roll body and the roll neck, while the comparative examples 1 and 4, which were tempered as a whole, had the same hardness between the roll body and the roll neck, and could not take into account both wear resistance and torsional resistance. This proves that differentiated gradient tempering can completely solve the industry pain point of matching strength and toughness.

[0132] Third, the residual stress in Examples 1-3 is all beneficial compressive stress, while the residual stress in Comparative Example 1 of the existing process is harmful tensile stress, which proves that the heat treatment process of the present invention can significantly reduce internal stress and reduce the risk of crack initiation.

[0133] The table below compares the room temperature mechanical properties of each embodiment with those of the comparative example. Figure 4 As shown, from Figure 4 It can be known that:

[0134] I. The transverse impact toughness of Examples 1-3 of the present invention is ≥23J / cm², and the transverse / longitudinal impact toughness ratio is ≥88.5%, while the transverse impact toughness of Comparative Examples 1 and 3, which use unidirectional forging, is ≤7J / cm², and the transverse / longitudinal ratio is ≤46.7%. This proves that multi-directional "cross" forging can completely eliminate material anisotropy, greatly improve transverse toughness, and solve the failure problem of roll neck torsion breakage from the root.

[0135] 2. The fracture toughness of Examples 1-3 is improved by more than 50% compared with the existing process Comparative Example 1, which proves that the whole process of the present invention can significantly improve the crack propagation resistance of the roll and extend its service life.

[0136] Third, the transverse / longitudinal impact toughness ratios of the remaining comparative examples 2, 4, and 5 are consistent with those of Example 1, proving that the anisotropy of the material is determined solely by the forging process and is unrelated to the heat treatment process.

[0137] A comparison table of the thermal fatigue performance of each embodiment and the comparative example is shown below. Figure 5 As shown, from Figure 5 It can be known that:

[0138] I. In Examples 1-3 of the present invention, no macroscopic cracks were found after 1000 cycles of hot and cold, while in Comparative Example 1 of the existing process, microcracks appeared after 500 cycles and macroscopic cracks appeared after 1000 cycles. This proves that the process of the present invention can improve the thermal fatigue resistance of the roll by more than 100%.

[0139] Second, the thermal fatigue performance of Comparative Examples 2 and 5 was significantly lower than that of Example 1, proving that "instant deep cryogenic treatment within 2 hours after quenching" reduces the content of residual austenite and is the core factor in improving thermal fatigue resistance.

[0140] Third, the thermal fatigue performance of Comparative Example 3 was significantly lower than that of Example 1, proving that carbide banding segregation would greatly reduce the thermal fatigue resistance of the material. Multi-directional forging to refine carbides is an important basis for improving thermal fatigue performance.

[0141] A comparison table of the actual industrial service life of each embodiment and the comparative example is shown below. Figure 6 As shown, from Figure 6 From this, we can know that:

[0142] I. The single-pair rolling output of the present invention in Examples 1-3 is ≥11,000 tons, which is more than 57% higher than that of the existing process in Comparative Example 1, and the cost per ton of steel ball roll is reduced by more than 40%, which has significant economic benefits.

[0143] Second, the failure modes of Examples 1-3 are all normal wear of the roll profile, without early fracture or thermal cracking failure, while all comparative examples show early failure, proving that the whole process of the present invention can completely solve the core failure problem of existing rolls.

[0144] Third, the service life of each comparative example is significantly lower than that of Example 1, proving that the three core processes of the present invention—multi-directional cross forging, instant cryogenic treatment, and differentiated gradient tempering—all have a significant effect on improving the service life of the rolls, and the absence of any one of these processes will lead to a significant decrease in performance.

[0145] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an H13 roll for hot-rolled steel balls, characterized in that: Includes the following steps: S1. Steel smelting and electroslag remelting: Electrode rods that meet the composition requirements are prepared by electric arc furnace smelting + LF refining + VD vacuum degassing, and then the electrode rods are electroslag remelted to obtain high-purity electroslag steel ingots. S2. High-temperature diffusion annealing: High-temperature diffusion annealing is performed on electroslag steel ingots to eliminate dendritic segregation in the as-cast state and homogenize the microstructure and composition. S3. Multi-directional forging: Multi-directional "cross" forging is carried out on the steel ingot after high-temperature diffusion annealing. The three-directional deformation is carried out alternately, the total forging ratio is ≥6, the initial forging temperature is 1150-1180℃, and the final forging temperature is ≥900℃. Carbides are fully broken, and banded segregation and anisotropy are eliminated. S4. Post-forging heat treatment and spheroidizing annealing: The forged steel ingot is immediately put into the furnace for post-forging annealing to eliminate forging internal stress and prevent cracking; then isothermal spheroidizing annealing is performed to obtain a uniformly distributed spherical pearlite structure, reduce hardness, and improve machinability. S5. Rough machining and flaw detection: Rough machining is performed on the spheroidized annealed billet, leaving a machining allowance of 3mm on each side. Then, ultrasonic flaw detection is performed. After passing the flaw detection, the billet proceeds to the next process. S6. Vacuum quenching: The blank that has passed the flaw detection is subjected to double-chamber vacuum quenching to obtain a uniform martensitic matrix structure. After quenching, it is cooled to room temperature. S7. Immediate cryogenic treatment: Within 2 hours after vacuum quenching, the billet is subjected to cryogenic treatment at a temperature of -110℃ to -130℃ and a holding time of 1.5-3 hours to maximize the transformation of residual austenite and stabilize the microstructure. S8. Three-stage gradient tempering: After the billet is heated to room temperature after cryogenic treatment, it is subjected to three-stage gradient tempering. After each tempering, it is oil-cooled to below 100°C and then air-cooled to precipitate dispersed secondary carbides, eliminate internal stress and temper brittleness, and adjust the hardness to the target range. S9. Finishing and Surface Treatment: The tempered billet is finished to the target dimensional accuracy, then surface strengthening treatment is carried out. After passing the dimensional, hardness and metallographic tests, it is packaged and put into storage.

2. The method for preparing an H13 roll for hot-rolled steel balls according to claim 1, characterized in that: In S1, the slag system used for electroslag remelting is as follows by mass percentage: CaF2 68-72%, Al2O3 18-22%, CaO 8-12%. The slag system also contains 0.5-1.0% rare earth composite oxide, which is a mixture of La2O3 and CeO2 in a mass ratio of 1:

1. The melting rate of electroslag remelting is 8-12 kg / min, the working current is 5000-8000 A, the working voltage is 60-70 V, and the feeding process is to gradually reduce the power by 10% / 5 min × 3 times.

3. The method for preparing an H13 roll for hot-rolled steel balls according to claim 1, characterized in that: In S2, the process parameters for high-temperature diffusion annealing are: heating temperature 1200-1250℃, holding time 15-20h, furnace cooling to 800℃ and then air cooling.

4. The method for preparing an H13 roll for hot-rolled steel balls according to claim 1, characterized in that: In S3, the multi-directional "cross" forging adopts a two-upsetting and two-drawing process, with a single-pass upsetting ratio ≥2.5 and a single-pass drawing length ratio ≥3.0; The forging heating process is as follows: first, preheat at 600-650℃ for 2 hours, then raise the temperature to 850-900℃ and hold for 1.5 hours, and finally raise the temperature to 1150-1180℃ and hold until the steel ingot is fully heated. An intermediate annealing process is set up during the forging process, with a process of 900℃×1h. After the furnace is cooled to 650℃, it is heated again for forging.

5. The method for preparing an H13 roll for hot-rolled steel balls according to claim 1, characterized in that: In S4, the post-forging annealing process is as follows: holding at 650-700℃ for 4-6 hours, furnace cooling to below 300℃ and then unloading from the furnace; the isothermal spheroidizing annealing process is as follows: holding at 860-880℃ for 4 hours to complete austenitization, furnace cooling at a rate of ≤30℃ / h to 740-760℃ for 6-8 hours to perform isothermal spheroidization, and then furnace cooling at a rate of ≤30℃ / h to below 500℃ and then unloading from the furnace.

6. The method for preparing an H13 roll for hot-rolled steel balls according to claim 1, characterized in that: In S6, the vacuum quenching adopts a two-stage preheating process: first, it is preheated at 600℃ for 30 minutes and at 850℃ for 30 minutes, and then heated to 1020-1050℃ and held for 1.5-2 hours; the quenching and cooling adopts 5-8 bar high-pressure nitrogen gas quenching, or a graded quenching process: holding at 580-620℃ in a salt bath for 15 minutes and then air cooling to room temperature.

7. The method for preparing an H13 roll for hot-rolled steel balls according to claim 1, characterized in that: In S7, the cryogenic treatment adopts a stepped cryogenic process: first, the billet is cooled to -70~-90℃ at a cooling rate of ≤10℃ / min and held for 1 hour, and then cooled to -110~-130℃ at the same rate and held for 1.5-3 hours. After cryogenic treatment, the billet is allowed to naturally warm to room temperature in the air.

8. The method for preparing an H13 roll for hot-rolled steel balls according to claim 1, characterized in that: In S8, the three-gradient tempering adopts a differentiated tempering process for the roll body and the roll neck, with the following specific parameters: First tempering: Both the roll body and the roll neck are held at 590-610℃ for 2 hours to eliminate quenching and deep cryogenic internal stress and stabilize the matrix structure. Second tempering: The working area of ​​the roll body is kept at 580-600℃ for 2 hours, and the hardness is adjusted to 50-60HRC; the drive area of ​​the roll neck is kept at 630-650℃ for 2 hours, and the hardness is adjusted to 40-45HRC. Third tempering: The working area of ​​the roll body is kept at 570-590℃ for 2 hours to eliminate the brittleness caused by secondary tempering; the drive area of ​​the roll neck is kept at 620-640℃ for 2 hours to further stabilize the microstructure.

9. The method for preparing an H13 roll for hot-rolled steel balls according to claim 1, characterized in that: In S9, the diameter tolerance of the finished roll is ±0.05mm, the coaxiality is ≤0.03mm, and the surface roughness Ra is ≤0.8μm; The surface strengthening treatment is any one of laser quenching, gas nitriding, or arc spraying. After laser quenching, the hardened layer depth on the roller surface is 2-3 mm, and the hardness is 58-62 HRC. The gas nitriding process involves holding at 520℃ for 20 hours, with a nitriding layer depth of 0.15-0.25 mm and a surface hardness ≥900 HV.

10. An H13 roll for hot-rolled steel balls, manufactured by any one of the preparation methods of claims 1-9, characterized in that: The chemical composition of the H13 roll, by mass percentage, is as follows: C 0.32-0.45%, Si 0.80-1.20%, Mn 0.20-0.50%, Cr 4.75-5.50%, Mo 1.10-1.75%, V 0.80-1.20%, P ≤0.020%, and S ≤0.010%; the non-metallic inclusions A / B / C / D of the H13 roll are all ≤1.0 grade, and the carbide banding segregation is ≤2 grade.

Images