A high-carbon bainite wear-resistant steel ball containing rare earth and a preparation method thereof

Abstract

The application discloses a rare earth-containing high-carbon bainite wear-resistant steel ball steel and a preparation method thereof, and belongs to the technical field of alloy steel metallurgy. The chemical components of the steel are as follows in percentage by mass: C: 0.57-0.70%, Si: 1.32-1.55%, Mn: 0.72-0.90%, Cr: 0.82-0.95%, Mo: 0.02-0.12%, Ti: 0.015-0.040%, B: 0.0010-0.0035%, RE: 0.0005-0.008%, Al: 0.015-0.050%, P: 0.025% or less, S: 0.015% or less, and the balance of Fe and inevitable impurities. The application can obtain a duplex structure with lower bainite being greater than or equal to 80% and hardness being greater than or equal to 42HRC and impact toughness being greater than or equal to 25J / cm without offline isothermal quenching through the synergy between elements. 2 ​

Description

Technical Field

[0001] This invention relates to the field of alloy steel metallurgy, and in particular to a high-carbon bainitic wear-resistant steel ball containing rare earth elements and its preparation method. Background Technology

[0002] Wear-resistant steel balls are the grinding media used in ball mills in industries such as mining, metallurgy, and cement, with huge annual consumption. Their quality directly affects the production efficiency and economic benefits of ore processing enterprises. Currently, developing high-quality, low-consumption wear-resistant steel balls is of significant practical importance.

[0003] Wear-resistant steel balls are made from hot-rolled bars that have undergone hot skew rolling and quenching and tempering. The bars are required to have high surface and core quality, as well as uniformity of composition and structure. Currently, the main quality problems include: (1) poor cleanliness of molten steel with a large number of non-metallic inclusions; (2) poor low-magnification quality of continuously cast steel billets and rolled products, with serious central porosity and shrinkage cavities; (3) severe central segregation of cast billets. Traditional casting grinding balls have a coarse, loose structure and a high breakage rate. Although forging and rolling processes can improve the internal quality, they place higher demands on the metallurgical quality and structural uniformity of raw materials.

[0004] Wear-resistant steel balls are mostly made of high-carbon, high-alloy steel. Current products typically exhibit a microstructure of ferrite and pearlite, resulting in low hardness and insufficient wear resistance. A few studies have attempted to improve wear resistance by obtaining bainitic microstructure through alloying and heat treatment, but these methods largely rely on subsequent heat treatment processes such as offline isothermal quenching. These processes are lengthy, costly, and energy-intensive, and controlling the uniformity and stability of the microstructure is challenging. Therefore, how to directly obtain wear-resistant steel balls with a high degree of hardness and high toughness through composition design and process control under existing rolling production line conditions is a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a rare earth-containing high-carbon bainitic wear-resistant steel ball and its preparation method, thereby solving the above-mentioned problems.

[0006] To achieve the above objectives, the present invention provides a high-carbon bainitic wear-resistant steel ball containing rare earth elements, comprising the following components by mass percentage: C: 0.57~0.70%, Si: 1.32~1.55%, Mn: 0.72~0.90%, Cr: 0.82~0.95%, Mo: 0.02~0.12%, Ti: 0.015~0.040%, B: 0.0010~0.0035%, RE: 0.0005~0.008%, Al: 0.015~0.050%, P≤0.025%, S≤0.015%, with the balance being Fe and unavoidable impurities.

[0007] Preferably, the microstructure of the high-carbon bainitic wear-resistant steel ball has ≥80% lower bainite.

[0008] Preferably, the lower bainite has a high dislocation density lath ferrite matrix, and the lath contains finely oriented ε-carbide precipitates.

[0009] Preferably, the microstructure of the high-carbon bainitic wear-resistant steel ball has 5%~15% fine-grained ferrite, ≤5% retained austenite, and a grain size ≥7.5.

[0010] Preferably, the content of B is 0.0015~0.0030%, and the content of Mo is 0.08~0.12%.

[0011] Preferably, the Ti content is 0.020~0.035%, and the Ti / N ratio is ≥4.5.

[0012] Preferably, RE is one or more of cerium, lanthanum, and yttrium, or a mixture of rare earth elements with these as the main component.

[0013] Preferably, the Si content is 1.40~1.55%.

[0014] This invention also provides a method for preparing the above-mentioned rare-earth-containing high-carbon bainitic wear-resistant steel ball, comprising the following steps: (1) Smelting: The primary smelting is completed by electric arc furnace or converter, followed by LF ladle refining and VD or VOD vacuum degassing treatment; the oxygen and hydrogen content in the molten steel is controlled throughout the process; The feeding sequence in the LF refining stage is as follows: first, add metallic aluminum for pre-deoxidation until the molten steel reaches the pre-deoxidation target value, then add titanium-iron alloy and control the Ti / N mass ratio to be ≥4.5; After LF refining is completed, it is sent to VD or VOD for vacuum degassing. After the vacuum is broken, the boron-iron alloy is fed in the form of cored wire within 10 minutes. Finally, rare earth elements are added and bottom blowing with argon soft blowing for 8-10 minutes. (2) Continuous casting: control the superheat to 20~30℃ and use end electromagnetic stirring; (3) Rolling: The temperature of the billet soaking section is controlled at 1180~1220℃. After the billet is heated to the target temperature, it is kept in the soaking temperature for ≥2.5h. The final rolling temperature is controlled at 800~850℃.

[0015] (4) Post-rolling controlled cooling: Three-stage control is adopted; (5) Finishing: Perform non-destructive testing.

[0016] Preferably, in step (1), the wire feeding speed of the ferroboron alloy is ≤2m / s; the rare earth elements are added in the form of rare earth ferrosilicon alloy.

[0017] Preferably, in step (1), the oxygen content is controlled to be [O]≤15ppm and the hydrogen content is controlled to be [H]≤1.5ppm; the pre-deoxygenation target value is [O]≤10ppm.

[0018] Preferably, the three-stage control in step (4) is as follows: Pre-cooling section: rapidly cools to 650~700℃; Phase transition section: Cooled to 350~450℃ at a cooling rate of 0.5~2.0℃ / s; Insulation section: Hold at 350~400℃ for 30~60 minutes to complete the isothermal transformation of bainite using residual heat after rolling.

[0019] Preferably, the rapid cooling rate of the precooling section is 5-15℃ / s.

[0020] Therefore, the present invention employs the above-mentioned rare-earth-containing high-carbon bainitic wear-resistant steel ball and its preparation method, which has the following beneficial effects: (1) This invention uses a quaternary synergistic microalloying design of B, Mo, Ti and RE. B segregates grain boundaries to delay the pearlite transformation, Mo expands the bainite formation window, Ti refines grains and fixes free N, and rare earth (RE) spheroidizes inclusions and purifies grain boundaries, so that steel can stably obtain a multiphase structure with ≥80% lower bainite under slow cooling conditions. The comprehensive performance is significantly better than the traditional ferrite + pearlite structure.

[0021] (2) In this invention, the lower bainite has a high dislocation density lath ferrite matrix, and the lath contains finely oriented ε-carbides, which endow the steel with high hardness and good wear resistance. At the same time, the fine-grained ferrite and retained austenite effectively coordinate plasticity and avoid brittle fracture. The hardness is ≥42HRC and the impact toughness is ≥25J / cm. 2 This achieves a good balance between hardness and toughness.

[0022] (3) This invention does not require offline isothermal quenching. Bainite transformation can be completed online through three-stage controlled cooling after rolling, eliminating the need for subsequent quenching and tempering processes. The overall cost per ton of steel is reduced, and the process flow is short and energy consumption is low, which is in line with the development direction of green manufacturing.

[0023] (4) The steel of the present invention has a dense structure, high hardness and good wear resistance. Combined with optimized purity and low magnification structure, the wear coefficient of the wear-resistant steel ball is greatly reduced, which significantly improves production efficiency and economic benefits.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 Metallurgical microscope image of Example 1; Figure 2Metallurgical microscope image of Example 2; Figure 3 Metallurgical microscope image of Example 3; Figure 4 Metallurgical microscope image of Example 4; Figure 5 This is a metallographic microscope image of Example 5. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0027] This invention provides a rare earth-containing high-carbon bainitic wear-resistant steel ball, comprising the following components by mass percentage: C: 0.57~0.70%, Si: 1.32~1.55%, Mn: 0.72~0.90%, Cr: 0.82~0.95%, Mo: 0.02~0.12%, Ti: 0.015~0.040%, B: 0.0010~0.0035%, RE: 0.0005~0.008%, Al: 0.015~0.050%, P≤0.025%, S≤0.015%, with the balance being Fe and unavoidable impurities.

[0028] In a preferred embodiment, the content of B is 0.0015~0.0030%, and the content of Mo is 0.08~0.12%.

[0029] In a preferred embodiment, the Ti content is 0.020~0.035%, and the Ti / N ratio is ≥4.5.

[0030] In a preferred embodiment, RE is one or more of cerium, lanthanum, and yttrium, or a mixture of rare earth elements with these as the main component.

[0031] In a preferred embodiment, the Si content is 1.40~1.55%.

[0032] In this invention, the alloying elements do not act in isolation, but rather form a synergistic effect through a specific timing sequence. Ti combines with free N in the steel to form TiN, fixing the N and preventing the subsequently added B from being consumed by N and becoming ineffective, ensuring that B can segregate on the austenite grain boundaries in a solid solution state. Solid solution B can effectively delay the nucleation of proeutectoid ferrite and pearlite, allowing the supercooled austenite to cross the pearlite transformation zone under slow cooling conditions. Mo further inhibits the pearlite transformation, complementing B. Together, they broaden the cooling rate range for easy bainite formation to 0.5~3.0℃ / s, and can stably obtain bainite structure even under conventional slow cooling conditions. Si hinders cementite precipitation during the bainite transformation process, causing carbon to be oriented in the form of ε-carbides within the ferrite laths, thereby obtaining a lower bainite structure. RE can spheroidize inclusions and purify grain boundaries, compensating for the toughness loss caused by inclusions in high-carbon steel, and ensuring that the impact toughness meets the standard stably.

[0033] The high-carbon bainitic wear-resistant steel ball steel of this invention has a microstructure containing ≥80% lower bainite, 5%~15% fine-grained ferrite, ≤5% retained austenite, and a grain size ≥7.5. The fine-grained ferrite is distributed at the original austenite grain boundaries, which can coordinate plasticity during deformation and prevent brittle fracture; the retained austenite is distributed in a thin film between the bainite laths, further improving toughness.

[0034] This invention provides a method for preparing the above-mentioned rare-earth-containing high-carbon bainitic wear-resistant steel ball, comprising the following steps: (1) Smelting: The primary smelting is carried out by electric arc furnace or converter, followed by LF ladle refining and VD or VOD vacuum degassing treatment. The oxygen and hydrogen content in the molten steel are controlled throughout the process, and the final oxygen content is controlled to be [O]≤15ppm and the hydrogen content is controlled to be [H]≤1.5ppm.

[0035] The feeding sequence and control logic of the LF refining stage are as follows: First, add metallic aluminum for pre-deoxidation until the molten steel reaches the pre-deoxidation target value [O]≤10ppm; then add titanium-iron alloy and control the Ti / N mass ratio ≥4.5 so that the free N in the steel preferentially combines with Ti to form TiN, avoiding the subsequent addition of B being fixed by N and becoming ineffective.

[0036] After LF refining, the wire is fed into a VD or VOD for vacuum degassing. The vacuum degassing time is ≥15 min, and the vacuum degree is ≤67 Pa. Within 10 minutes after vacuum degassing, a boron-iron alloy is fed in as a cored wire to prevent the boron (B) from being oxidized. The feeding speed of the boron-iron alloy is ≤2 m / s. After feeding the boron-iron alloy, rare earth elements are added in the form of a rare earth ferrosilicon alloy after an interval of 2-3 minutes to avoid excessively high local concentrations that could form coarse rare earth borides. Finally, bottom blowing with argon for 8-10 minutes is performed to ensure that the elements are fully and evenly distributed and to promote the flotation and removal of inclusions.

[0037] (2) Continuous casting: The superheat of the molten steel in the tundish is controlled at 20~30℃, and a combination of crystallizer electromagnetic stirring (M-EMS) and end electromagnetic stirring (F-EMS) is adopted. The current intensity of the end electromagnetic stirring is increased by 5%~10% compared with the conventional method to effectively break up columnar crystal bridging and improve center segregation and shrinkage cavities. The cross-sectional size of the billet is 250mm×280mm, and the casting speed is controlled at 0.50~0.65m / min.

[0038] (3) Rolling: The continuously cast billet is heated in a walking beam furnace. The temperature of the soaking zone is controlled at 1180~1220℃. After the billet is heated to the target temperature, it is kept at the soaking temperature for ≥2.5h. The final rolling temperature is controlled at 800~850℃.

[0039] (4) Post-rolling controlled cooling: a three-stage control is adopted. The pre-cooling stage quickly passes through the pearlite nose temperature range to avoid pearlite transformation; the phase transformation stage slowly passes through the bainite transformation zone to allow the transformation to proceed fully; the heat preservation stage uses the residual heat after rolling to complete the isothermal transformation and maximize the bainite transformation.

[0040] Pre-cooling section: rapidly cools to 650~700℃ at a cooling rate of 5~15℃ / s.

[0041] Phase transition section: Cooled to 350~450℃ at a cooling rate of 0.5~2.0℃ / s.

[0042] Insulation section: Hold at 350~400℃ for 30~60 minutes to complete the isothermal transformation of bainite using residual heat after rolling.

[0043] (5) Finishing: After the rolled steel is finished (straightening, chamfering, etc.), non-destructive testing is carried out. Ultrasonic testing is carried out in accordance with GB / T4162-2020 standard, and the qualified level should meet the requirements of B grade or above.

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0045] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following description will be provided in conjunction with the accompanying drawings of the embodiments of the present invention. Figures 1 to 5 The technical solutions of the present invention have been clearly and completely described. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0047] Example 1 This embodiment provides a high-carbon bainitic wear-resistant steel ball containing rare earth elements, comprising the following components by mass percentage: C 0.63%, Si 1.45%, Mn 0.82%, Cr 0.88%, Mo 0.10%, Ti 0.028%, B 0.0022%, RE (cerium-based mixed rare earth) 0.0035%, Al 0.026%, P 0.014%, S 0.006%, with the balance being Fe and unavoidable impurities. The Ti / N mass ratio was measured to be 5.2.

[0048] The preparation method in this embodiment is as follows: Smelting Process: A 110-ton Consteel electric arc furnace was used for primary smelting, followed by LF ladle refining. During the LF refining stage, metallic aluminum was first added for pre-deoxidation until the oxygen activity of the molten steel dropped to 9 ppm; then, ferrotitanium alloy was added, controlling the Ti / N mass ratio to be ≥4.5. After LF refining, the steel was sent to a VD furnace for vacuum degassing, with a vacuum degree ≤67 Pa and a vacuum holding time of 18 min. Within 8 minutes of vacuum breaking, ferroboron alloy was fed in the form of cored wire at a feeding speed of 1.5 m / s; after a 2.5-minute interval following the ferroboron feeding, cerium-based mixed rare earth elements were added in the form of rare earth ferrosilicon alloy; subsequently, bottom blowing with argon was performed for 9 min. Testing revealed that the final steel contained 9 ppm of [O] and 1.2 ppm of [H].

[0049] Continuous casting process: The superheat of molten steel in the tundish is controlled at 24℃. A combination of electromagnetic stirring in the crystallizer and electromagnetic stirring at the end is adopted, with the end electromagnetic stirring current increased by 8% compared to the benchmark. The billet cross-section is 250mm×280mm, and the casting speed is 0.58m / min.

[0050] Rolling process: The continuously cast billet is heated in a walking beam furnace, with a soaking temperature of 1195℃ and a soaking hold of 2.8h; the initial rolling temperature is 1050℃ and the final rolling temperature is 835℃.

[0051] Post-rolling controlled cooling: A three-stage control system is adopted. The pre-cooling stage rapidly cools to 680℃ at a cooling rate of 10℃ / s; the phase transformation stage cools to 390℃ at a cooling rate of 1.2℃ / s; then it is hoisted to the slow cooling pit and held at 380℃ for 45 minutes to complete the isothermal transformation of bainite using the residual heat after rolling.

[0052] Finishing process: After straightening and chamfering, ultrasonic testing is performed according to GB / T 4162-2020 standard to meet the Class B requirement.

[0053] Example 2 This embodiment provides a high-carbon bainitic wear-resistant steel ball containing rare earth elements, comprising the following components by mass percentage: C 0.62%, Si 1.40%, Mn 0.85%, Cr 0.88%, Mo 0.04%, Ti 0.025%, B 0.0030%, RE (lanthanum-based mixed rare earth) 0.0040%, Al 0.028%, P 0.015%, S 0.005%, with the balance being Fe and unavoidable impurities. The Ti / N mass ratio was measured to be 5.0.

[0054] The preparation method in this embodiment is as follows: Smelting Process: Primary smelting was performed using a 110-ton Consteel electric arc furnace, followed by LF ladle refining. During the LF refining stage, metallic aluminum was first added for pre-deoxidation until the oxygen activity of the molten steel dropped to 8 ppm; then, ferrotitanium alloy was added, controlling the Ti / N mass ratio to be ≥4.5. After LF refining, the steel was sent to a VD furnace for vacuum degassing, with a vacuum degree ≤67 Pa and a vacuum holding time of 20 min. Within 6 minutes of vacuum breaking, ferroboron alloy was fed in the form of a cored wire at a feeding speed of 1.8 m / s; after a 2-minute interval following the ferroboron feeding, lanthanum-based mixed rare earth elements were added in the form of a rare earth ferrosilicon alloy; subsequently, bottom blowing with argon was performed for 10 min. Testing revealed that the final steel contained 8 ppm of [O] and 1.1 ppm of [H].

[0055] Continuous casting process: The superheat of the molten steel in the tundish is controlled at 22℃. A combination of electromagnetic stirring in the crystallizer and electromagnetic stirring at the end is adopted, with the end electromagnetic stirring current increased by 6% compared to the benchmark. The billet cross-section is 250mm×280mm, and the casting speed is 0.60m / min.

[0056] Rolling process: The continuously cast billet is heated in a walking beam furnace, with a soaking temperature of 1205℃ and a soaking holding temperature of 2.6h; the initial rolling temperature is 1070℃ and the final rolling temperature is 845℃.

[0057] Post-rolling controlled cooling: A three-stage control system is adopted. The pre-cooling stage rapidly cools to 670℃ at a cooling rate of 12℃ / s; the phase transformation stage cools to 410℃ at a cooling rate of 0.8℃ / s; then it is hoisted to the slow cooling pit and held at 390℃ for 50 minutes to complete the isothermal transformation of bainite using the residual heat after rolling.

[0058] Finishing process: Same as in Example 1.

[0059] Comparative Example 1 This comparative example provides a wear-resistant steel ball containing the following components by mass percentage: C 0.63%, Si 1.25%, Mn 0.80%, Cr 0.88%, Mo 0.10%, Ti 0.028%, B 0.0022%, RE 0.0035%, Al 0.026%, P 0.014%, S 0.006%, with the balance being Fe and unavoidable impurities.

[0060] The difference between the preparation method of this comparative example and that of Example 1 is that: (1) the final rolling temperature is controlled at 765℃; (2) the heat soaking time is less than 1.5h.

[0061] Comparative Example 2 This comparative example provides a steel for wear-resistant steel balls, which has the same components and component contents as in Example 2.

[0062] The difference between the preparation method of this comparative example and that of Example 2 is: (1) the cooling rate of the phase change section is 3.5℃ / s; (2) the temperature of the heat preservation section is 470℃.

[0063] Comparative Example 3 This comparative example provides a wear-resistant steel ball containing the following components by mass percentage: C 0.63%, Si 1.20%, Mn 0.80%, Cr 0.88%, Mo 0.02%, Ti 0.015%, B 0.0005%, RE 0.0002%, Al 0.026%, P 0.014%, S 0.006%, with the balance being Fe and unavoidable impurities.

[0064] The difference between the preparation method of this comparative example and that of Example 1 is that: after rolling, it was not subjected to three-stage controlled cooling, but was directly placed into a slow cooling pit for natural cooling.

[0065] Metallurgical microscope images of Examples 1-2 and Comparative Examples 1-3 are as follows: Figure 1-5 As shown, the results are as follows: Figure 1 The middle bainite content is approximately 87%, fine-grained ferrite approximately 9%, and retained austenite approximately 4%; the grain size is grade 7.5. The lower bainite has a high dislocation density lath ferrite matrix, with finely oriented ε-carbide precipitates within the laths.

[0066] Figure 2 The lower bainite content is approximately 83%, fine-grained ferrite approximately 12%, and retained austenite approximately 5%; the grain size is grade 7.5. The lower bainite has a high dislocation density lath ferrite matrix, and the laths contain oriented fine ε-carbide precipitates.

[0067] Figure 3 The grains are fine and fragmented, without obvious long lath-like or needle-like outlines, and the structure is a mixture of tempered martensite, granular bainite, or pearlite + martensite.

[0068] Figure 4 It contains coarse needle-like grains, consisting of granular bainite plus a small amount of tempered martensite.

[0069] Figure 5 It contains small, disordered, blocky structures, with carbides randomly and diffusely distributed without uniform orientation, forming a fine, fragmented tempered structure.

[0070] Therefore, the microstructures of Examples 1-2 are mainly composed of slender, oriented lath-shaped lower bainite, with oriented fine ε-carbide precipitates inside the laths, accompanied by a small amount of fine-grained ferrite and retained austenite, with a grain size ≥7.5. This indicates that by using the composition design and three-stage controlled cooling process of this invention, a multiphase microstructure dominated by slender, oriented lath lower bainite can be stably obtained on a conventional rolling production line.

[0071] In Comparative Example 1, the low final rolling temperature resulted in insufficient recrystallization of austenite, leading to fine and mixed grains. Insufficient homogenization and holding time further prevented adequate boron (B) dissolution, causing a large amount of B to precipitate as BN and fail. The low Si content further weakened the ability to suppress carbide precipitation. Therefore, B could not delay the pearlite transformation, and the undercooled austenite did not undergo a complete isothermal bainite transformation during cooling, ultimately forming tempered martensite or a mixture of pearlite and martensite.

[0072] In Comparative Example 2, the excessively rapid cooling rate of the phase transformation section caused austenite to quickly cross the bainite region and enter the martensitic transformation range; the excessively high holding temperature caused the transformation to occur at a higher temperature, which enhanced the diffusion ability of carbon atoms, and the precipitates tended to precipitate between laths rather than oriented within the laths, forming upper bainite or granular bainite; the low Mo content resulted in insufficient synergistic and complementary effects with B, narrowing the bainite transformation window and reducing the process tolerance space.

[0073] In Comparative Example 3, the B content was far below the effective level, the pearlite transformation was not effectively delayed, and the supercooled austenite completed the pearlite transformation in the higher temperature range and could not enter the bainite region; the Si and RE contents were insufficient, the cementite precipitation was not suppressed, and the inclusions cut the matrix in an irregular shape; without three-stage controlled cooling, the austenite stayed in the high temperature region for a long time, and it was impossible to obtain a regular lath structure through bainite transformation.

[0074] Rockwell hardness (HRC) was tested according to GB / T 230.1 standard. Five test points were taken for each sample and the average value was taken. The results are shown in Table 1.

[0075] Table 1 Hardness test results

[0076] The hardness range of the cross-sections in Examples 1-2 is ≤1.0 HRC, indicating that the steel of the present invention has good uniformity in hardness throughout the cross-section. This is because the lower bainite structure can be fully and uniformly formed in all parts of the steel cross-section, and the distribution of fine-grained ferrite and retained austenite is also relatively uniform, with no localized agglomeration. In Comparative Example 1, due to the excessively low final rolling temperature, the austenite did not recrystallize sufficiently, resulting in fine and mixed grains, and thus the lowest hardness and the worst uniformity.

[0077] The room temperature Charpy V-notch impact test (AkU) was conducted according to GB / T 229 standard. Three parallel specimens were taken from each group and the average value was taken. The results are shown in Table 2.

[0078] Table 2 Impact toughness test results

[0079] The impact toughness of Examples 1-2 is ≥27.0 J / cm. 2 The results are significantly superior to those of Comparative Examples 1-3. The finely oriented ε-carbides within the lower bainitic laths effectively hinder dislocation movement, improving strength without significantly impairing plasticity. The residual austenite film between the laths absorbs energy and blunts crack tips during crack propagation, while the fine-grained ferrite at grain boundaries coordinates local stress concentration through plastic deformation. These three factors together constitute a multi-level toughness regulation mechanism, preventing rapid transgranular crack propagation. Comparative Examples 1-3, due to their microstructure deviating from the target lower bainitic structure, exhibit significantly reduced impact toughness. In particular, although Comparative Example 2 has a similar hardness to the examples, its impact toughness is only about 2 / 3 of that of the examples, indicating that relying solely on hardness enhancement without reasonable microstructure control cannot achieve a good balance between strength and toughness.

[0080] The finished bars were subjected to ultrasonic testing according to GB / T 4162-2022 standard, and the results are shown in Table 3.

[0081] Table 3. Results of Ultrasonic Testing

[0082] Ultrasonic testing of Examples 1-2 and Comparative Examples 1-3 all met the Class B requirements of GB / T 4162-2022 standard. This indicates that the smelting process of the present invention can effectively control the gas and inclusion content in steel, resulting in good internal density of the cast billet and no defects exceeding the standard.

[0083] Wet abrasive wear tests were conducted according to JB / T 7501 standard. The test conditions were: rubber wheel speed 200 r / min, load 130 N, slurry concentration 750 g water + 1500 g quartz sand (particle size 40~70 mesh), and wear time 5 min. The relative wear resistance (wear amount of standard sample / wear amount of test sample) was calculated based on the wear amount of a standard sample (F+P state conventional wear-resistant steel) under the same test conditions. The results are shown in Table 4.

[0084] Table 4 Results of abrasive wear test

[0085] The relative wear resistance of Examples 1 and 2 were 1.55 and 1.49, respectively, which is about 49%-55% higher than that of conventional F+P state wear-resistant steel. During abrasive wear, the high dislocation density increases the strength of the matrix against micro-cutting, making it difficult for abrasive grains to penetrate. The oriented ε-carbides, as hard particles, can effectively hinder the scratching and ploughing action of abrasive grains. At the same time, their fine and dispersed distribution avoids the tendency of coarse carbides to peel off at the wear interface. The synergy of these two factors significantly reduces material loss.

[0086] Comparative Examples 1-3, due to their microstructure deviating from the target lower bainite, exhibited relative wear resistance of only 1.07-1.22. Comparative Example 2, with its predominantly tempered martensite microstructure, while exhibiting high hardness, suffered from non-directional and unevenly distributed carbides, leading to easy flaking of hard particles during wear and resulting in minimal improvement in wear resistance. Comparative Examples 1 and 3, dominated by a mixture of pearlite and martensite and finely fragmented tempered martensite respectively, showed weak carbide strengthening and low matrix hardness, with wear resistance approaching that of the conventional F+P state. These results indicate that increased hardness does not necessarily lead to a significant improvement in wear resistance; only a lower bainite structure with specific morphology and microstructure scale can achieve a significant improvement in wear resistance.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A rare-earth-containing high-carbon bainitic wear-resistant steel ball, characterized in that, It contains the following components by mass percentage: C: 0.57~0.70%, Si: 1.32~1.55%, Mn: 0.72~0.90%, Cr: 0.82~0.95%, Mo: 0.02~0.12%, Ti: 0.015~0.040%, B: 0.0010~0.0035%, RE: 0.0005~0.008%, Al: 0.015~0.050%, P≤0.025%, S≤0.015%, with the balance being Fe and unavoidable impurities.

2. The rare-earth-containing high-carbon bainitic wear-resistant steel ball according to claim 1, characterized in that, The microstructure of high-carbon bainitic wear-resistant steel balls contains ≥80% lower bainite.

3. The rare-earth-containing high-carbon bainitic wear-resistant steel ball according to claim 1, characterized in that, The content of B is 0.0015~0.0030%, and the content of Mo is 0.08~0.12%.

4. The rare-earth-containing high-carbon bainitic wear-resistant steel ball according to claim 1, characterized in that, The Ti content is 0.020~0.035%, and the Ti / N ratio is ≥4.

5.

5. The rare-earth-containing high-carbon bainitic wear-resistant steel ball according to claim 1, characterized in that, RE can be one or more of cerium, lanthanum, and yttrium.

6. A method for preparing rare-earth-containing high-carbon bainitic wear-resistant steel balls as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Smelting: The primary smelting is completed by electric arc furnace or converter, followed by LF ladle refining and VD or VOD vacuum degassing treatment; the oxygen and hydrogen content in the molten steel is controlled throughout the process; The feeding sequence in the refining stage of LF steel ladle is as follows: first, add metallic aluminum for pre-deoxidation until the molten steel reaches the pre-deoxidation target value, then add titanium-iron alloy and control the Ti / N mass ratio to be ≥4.5; After the LF ladle refining is completed, it is sent to VD or VOD for vacuum degassing. After the vacuum is broken, the boron-iron alloy is fed in the form of cored wire within 10 minutes. Finally, rare earth elements are added and bottom blowing with argon soft blowing for 8-10 minutes. (2) Continuous casting: control the superheat to 20~30℃ and use end electromagnetic stirring; (3) Rolling: The temperature of the hot-soaking section of the billet is controlled at 1180~1220℃. After the billet is heated to the target temperature, it is kept hot for ≥2.5h. The final rolling temperature is controlled at 800~850℃. (4) Post-rolling controlled cooling: Three-stage control is adopted; (5) Finishing: Perform non-destructive testing.

7. The method for preparing a rare-earth-containing high-carbon bainitic wear-resistant steel ball according to claim 6, characterized in that, In step (1), the wire feeding speed of the ferroboron alloy is ≤2m / s; rare earth elements are added in the form of rare earth ferrosilicon alloy.

8. The method for preparing a rare-earth-containing high-carbon bainitic wear-resistant steel ball according to claim 6, characterized in that, In step (1), the oxygen content is controlled to be [O]≤15ppm and the hydrogen content is controlled to be [H]≤1.5ppm; the pre-deoxygenation target value is [O]≤10ppm.

9. The method for preparing a rare-earth-containing high-carbon bainitic wear-resistant steel ball according to claim 6, characterized in that, The three-stage control in step (4) is as follows: Pre-cooling section: rapidly cools to 650~700℃; Phase transition section: Cooled to 350~450℃ at a cooling rate of 0.5~2.0℃ / s; Insulation section: Hold at 350~400℃ for 30~60 minutes to complete the isothermal transformation of bainite using residual heat after rolling.

10. The method for preparing a rare-earth-containing high-carbon bainitic wear-resistant steel ball according to claim 9, characterized in that, The rapid cooling rate of the pre-cooling section is 5-15℃ / s.

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