High-hardenability automobile bearing alloy steel and manufacturing method thereof

Abstract

The invention belongs to the technical field of alloy steel, and particularly relates to high-hardenability automobile bearing alloy steel and a manufacturing method thereof. The steel comprises the following components in percentage by weight: 0.65 to 0.85 percent of C, 0.50 to 0.70 percent of Si, 1.2 to 1.6 percent of Mn, 1.2 to 1.5 percent of Cr, 0.10 to 0.15 percent of V, 0.01 to 0.03 percent of Nb, 0.010 to 0.030 percent of Ti, less than or equal to 0.025 percent of Ni, 0.020 to 0.040 percent of Mo, 0.02 to 0.03 percent of Al, 0.001 to 0.002 percent of La, 0.002 to 0.003 percent of Ce, less than or equal to 0.005 percent of N, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S and the balance of Fe and inevitable impurities. The high-hardenability automobile bearing alloy steel with excellent performance is finally obtained by optimizing components and improving heating, quenching, annealing and other treatments.

Description

Technical Field

[0001] This invention belongs to the technical field of bearing alloy steel, specifically relating to a high hardenability automotive bearing alloy steel and its manufacturing method. Background Technology

[0002] In the precision gears of industrial civilization, bearings act as the "active joints" of mechanical systems, bearing the transmission of tens of millions of tons of power with millimeter-level precision movements. As a strategic material for manufacturing this core component, the performance of bearing steel directly affects the mechanical performance of all fields, from micro-watch bearings to heavy equipment shafts—the arrangement of its microscopic grains can even rewrite the service life of an entire piece of equipment. In automotive applications, the selection of bearing steel is comparable to the material design of aerospace vehicles. Facing temperatures exceeding 200°C, GPa-level contact stress, and centrifugal forces of tens of thousands of revolutions per minute, automotive bearings need to possess both the "body of steel" and the "toughness of a spring." This special steel, which can maintain dimensional stability even under extreme conditions, is a perfect embodiment of the "combination of rigidity and flexibility" in modern mechanical engineering, while also placing extremely stringent requirements on the manufacturing materials.

[0003] Conventional axle materials use high-strength alloy steel and low-alloy structural steel. While low-alloy structural steel can achieve the desired microstructure and properties through quenching and tempering heat treatment, its low alloy content leads to insufficient hardenability in large-section axles, resulting in uneven microstructure and properties across the cross-section and affecting overall mechanical properties. In contrast, while high-strength alloy steel can meet the performance requirements of small flywheel rotors, its core microstructure and properties cannot be consistent with the surface / near-surface layer when manufacturing large-section flywheel rotors. This results in poor uniformity of cross-sectional properties, making it difficult for the core strength to meet industry safety standards, thus significantly reducing the material's service life and safety.

[0004] Furthermore, traditional solutions to address insufficient hardenability involve adding elements such as Cr, Nb, and B to improve the hardenability of steel. However, simple element adjustments, due to a lack of effective process control, can lead to the formation of BN, resulting in the hardenability improvement not meeting expectations. Moreover, this can easily cause side effects such as uneven grain size, further reducing the performance of bearing alloy steel. Summary of the Invention

[0005] The purpose of this invention is to overcome the technical defects existing in the prior art and provide a high hardenability automotive bearing alloy steel and its manufacturing method, thereby improving the comprehensive performance of the bearing alloy steel by combining component and process optimization.

[0006] To achieve the above objectives, the present invention first provides a high hardenability automotive bearing alloy steel, which is composed of the following components by weight percentage: C: 0.65–0.85%, Si: 0.50–0.70%, Mn: 1.20–1.60%, Cr: 1.2–1.5%, V: 0.10–0.15%, Nb: 0.010–0.030%, Ti: 0.010–0.030%, Ni≤0.025%, Mo: 0.020–0.040%, Al: 0.02–0.030%, La: 0.001–0.002%, Ce: 0.002–0.003%, N≤0.005%, P≤0.015%, S≤0.015%; the balance is Fe and unavoidable impurities.

[0007] All high hardenability automotive bearing alloy steels have good comprehensive mechanical properties with tensile strength of over 950 MPa and room temperature impact energy of over 90 J. They also have uniform and fine austenitic grains with a grain size of 7 to 8. No mixed grains or abnormally coarse grains were observed.

[0008] Ingredient design: Carbon content control: A medium-to-high carbon range of 0.65% to 0.85% is used to ensure high hardness and wear resistance of the martensitic matrix after quenching. Because carbon (C) can improve the hardenability of steel, it allows the steel to form a high-hardness phase transformation structure during quenching and cooling. When the C content in the steel is too low, the steel cannot obtain sufficient tensile strength and it is difficult to achieve high hardenability. However, the C content in the steel should not be too high either. When the C content is too high, it will increase the proportion of hard phases and reduce the toughness of the steel. Therefore, considering the influence of C content on the performance of steel, a medium-to-high carbon range is selected in the high hardenability and high strength medium-carbon steel described in this invention, and the mass percentage of C is controlled between 0.75% and 0.95%.

[0009] This invention further adjusts the contents of Cr, Mo, and V under conventional alloy steel composition conditions. By controlling the Cr content to 1.20%-1.50%, hardenability is improved and carbide stability is enhanced; by controlling the Mo content to 0.20-0.40%, grain size is reduced and temper brittleness is suppressed; and by controlling the V content to 0.10-0.15%, finer carbides are formed, improving high-temperature wear resistance. In addition, the present invention introduces rare earth elements: lanthanum (La) and cerium (Ce), and controls La to be 0.001~0.002% and Ce to be 0.002~0.003%, thereby purifying the molten steel and improving the uniformity of carbide distribution.

[0010] Finally, phosphorus (P) ≤ 0.015% and sulfur (S) ≤ 0.015% are limited to reduce the impact of non-metallic inclusions on fatigue life.

[0011] This invention also provides a method for manufacturing high hardenability automotive bearing alloy steel, comprising the following steps: The steel is smelted in a converter, electric furnace, or vacuum induction furnace, refined outside the ladle, heated, and then continuously cast. The billet obtained from the continuous casting is then forged and rolled into an axle, air-cooled after forging and rolling, and then heat-treated to obtain high hardenability automotive bearing alloy steel.

[0012] The heating process is as follows: the steel billet is first heated to no higher than 900℃ in the preheating section, then further heated to no higher than 980℃ in the first heating section, held at that temperature, and then further heated to 1000~1250℃ in the second heating section, held at that temperature, and then placed in the soaking section at 1300~1350℃. After holding at that temperature, it is then subjected to subsequent continuous casting or forging. The preferred preheating section temperature is 860~880℃; the first heating section temperature is 950℃~980℃.

[0013] The heat treatment specifically involves first subjecting the forged and rolled steel to quenching heat treatment, followed by a second annealing treatment.

[0014] Before axle forging and rolling: The continuously cast billet obtained from continuous casting is heated to 1200-1280℃, held for 4-6 hours and then taken out of the furnace. The initial rolling temperature is 1100-1150℃, the final rolling temperature is 950-980℃, and after rolling, it is cooled to 200-500℃ on a cooling bed before being taken off the production line.

[0015] The quenching heat treatment temperature is 850-920℃, and the holding time is 90-120 minutes. The cooling method for the quenching heat treatment is water cooling. The specific water cooling method is: using a strong cooling-weak cooling alternation method. The strong cooling method is used to rapidly cool the steel. Due to the heat transfer effect from high to low, the heat in the core of the round steel is gradually transferred to the surface. In order to transfer as much heat in the core of the round steel as possible to the surface and avoid thermal stress caused by a large temperature gradient in the round steel, weak cooling is adopted after strong cooling. This allows more time for heat transfer in the core during the cooling process, ensuring that the steel structure and mechanical properties are more uniform.

[0016] The first annealing treatment is performed at a temperature of 720–800℃, and the holding time is 2–3 hours. The second annealing treatment is performed at a temperature of 630–650℃, and the holding time is 4–5 hours. After the second annealing, the mixture is air-cooled to room temperature. Beneficial effects:

[0017] 1. This invention employs a medium-to-high carbon range of 0.65-0.85% to ensure high hardness and wear resistance of the martensitic matrix after quenching. Furthermore, under conventional alloy steel composition conditions, the contents of Cr, Mo, and V are adjusted. By controlling the Cr content to 1.20-1.50%, hardenability and carbide stability are improved; by controlling the Mo content to 0.20-0.40%, grain size is reduced and temper brittleness is suppressed; by controlling the V content to 0.10-0.15%, finer carbides are formed, improving high-temperature wear resistance. Simultaneously, this invention introduces rare earth elements La and Ce, strictly controlling La to 0.001-0.002% and Ce to 0.002-0.003%, thereby purifying the molten steel and improving the uniformity of carbide distribution.

[0018] 2. This invention uses medium and high carbon elements, combined with Nb, Ti, V and rare earth element composite microalloying technology, which can effectively prevent the growth of austenite grains during the high-temperature carburizing process of gear steel, avoid abnormal growth of austenite grains and mixed grain structure in the steel during the high-temperature vacuum carburizing process, so that the gear meets the grain size under the high-temperature carburizing conditions and shortens the carburizing heat treatment process cycle.

[0019] 3. This invention, based on an overall design, increases the temperature of the soaking zone to 1300~1350℃. Within this temperature range, the compositional and microstructure uniformity of the continuously cast billet is improved during the heating diffusion process. Furthermore, the higher temperature allows for a faster solidification rate of the precipitated phases, thereby increasing the concentration of microalloying elements in the matrix. On the other hand, the increased soaking zone temperature simultaneously raises the final rolling temperature, resulting in more complete austenite recovery and recrystallization after rolling, and a more uniform distribution of precipitated phases.

[0020] 4. The present invention uses quenching (850~920℃) + secondary high temperature annealing heat treatment (720~800℃, 630~650℃) to obtain uniform fine-grained austenitic grains, achieving an excellent match of high strength, high toughness and high hardenability, ultimately giving the automotive bearing alloy steel good impact resistance, fatigue resistance and other service performance as well as good hardenability.

[0021] 5. The bearing alloy steel prepared by this invention has good comprehensive mechanical properties with tensile strength of over 950MPa and room temperature impact energy of over 90J. It also has uniform and fine austenitic grains with a grain size of 7-8. No mixed grains or abnormally coarse grains were observed. The hardenability has been significantly improved, and it has a better strength and toughness match than the comparison steel. Detailed Implementation

[0022] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these embodiments.

[0023] A high hardenability automotive bearing alloy steel, composed of the following components by weight percentage: C: 0.65–0.85%, Si: 0.50–0.70%, Mn: 1.20–1.60%, Cr: 1.2–1.5%, V: 0.10–0.15%, Nb: 0.010–0.030%, Ti: 0.010–0.030%, Ni≤0.025%, Mo: 0.020–0.040%, Al: 0.02–0.030%, La: 0.001–0.002%, Ce: 0.002–0.003%, N≤0.005%, P≤0.015%, S≤0.015%; the balance is Fe and unavoidable impurities.

[0024] Carbon content control: A medium-to-high carbon range of 0.65% to 0.85% is adopted to ensure high hardness and wear resistance of the martensitic matrix after quenching. Because carbon (C) can improve the hardenability of steel, it allows the steel to form a high-hardness phase transformation structure during quenching and cooling. When the C content in the steel is too low, the steel cannot obtain sufficient tensile strength and it is difficult to achieve high hardenability. However, the C content in the steel should not be too high either. When the C content is too high, it will increase the proportion of hard phases and reduce the toughness of the steel. Therefore, considering the influence of C content on the performance of steel, a medium-to-high carbon range is selected in the high hardenability and high strength medium-carbon steel described in this invention, and the mass percentage of C is controlled between 0.75% and 0.95%.

[0025] This invention further adjusts the contents of Cr, Mo, and V under conventional alloy steel composition conditions. By controlling the Cr content to 1.20–1.50%, hardenability is improved and carbide stability is enhanced; by controlling the Mo content to 0.20–0.40%, grain size is reduced and temper brittleness is suppressed; by controlling the V content to 0.10–0.15%, finer carbides are formed, improving high-temperature wear resistance. In addition, the present invention introduces rare earth elements lanthanum (La) and cerium (Ce), and controls La to be 0.001-0.002% and Ce to be 0.002-0.003%, thereby purifying the molten steel and improving the uniformity of carbide distribution. Example 1:

[0026] The chemical composition by mass percentage is as follows: C: 0.65%, Si: 0.60%, Mn: 1.40%, Cr: 1.2%, V: 0.11%, Nb: 0.025%, Ti: 0.015%, Ni: 0.018%, Mo: 0.025%, Al: 0.023%, La: 0.001%, Ce: 0.003%, N: 0.0051%, P: 0.012%, S: 0.013%; the balance is Fe and unavoidable impurities.

[0027] The high hardenability automotive bearing alloy steel is obtained by smelting in a converter, electric furnace or vacuum induction furnace, refining outside the ladle, heating and continuous casting, and then forging and rolling the billet into an axle. After forging and rolling, the billet is air-cooled and heat-treated.

[0028] After ladle refining, the heating process is as follows: the billet is first heated to 880°C in the preheating section, then heated to 960°C in the first heating section, held at that temperature, and then heated to 1180°C in the second heating section. After holding at that temperature, it enters the soaking section, where the temperature is 1320°C. After holding at that temperature, it is then continuously cast.

[0029] Before axle forging and rolling: the continuous casting billet is heated to 1230℃, held for 4 hours and then taken out of the furnace. The initial rolling temperature is 1120℃, the final rolling temperature is 980℃, and after rolling, it is cooled to 300℃ on a cooling bed and then taken off the production line.

[0030] The heat treatment specifically involves first subjecting the forged and rolled steel to quenching heat treatment, followed by a second annealing treatment to obtain high hardenability automotive bearing alloy steel.

[0031] The quenching heat treatment temperature is 880℃, and the quenching heat treatment holding time is 90min; wherein the quenching cooling method is water cooling (using a strong cooling-weak cooling alternation method).

[0032] The temperature of the first annealing treatment was 750℃, and the holding time of the annealing treatment was 2 hours. The second annealing treatment was performed at a temperature of 650°C, and the holding time for the annealing treatment was 4 hours.

[0033] After secondary annealing, the product is air-cooled to room temperature, finished, tested, and then stored. Example 2:

[0034] The chemical composition by mass percentage is as follows: C: 0.70%, Si: 0.60%, Mn: 1.40%, Cr: 1.25%, V: 0.12%, Nb: 0.025%, Ti: 0.010%, Ni: 0.018%, Mo: 0.025%, Al: 0.023%, La: 0.002%, Ce: 0.002%, N: 0.0041%, P: 0.012%, S: 0.011%; the balance is Fe and unavoidable impurities.

[0035] The high hardenability automotive bearing alloy steel is obtained by smelting in a converter, electric furnace or vacuum induction furnace, refining outside the ladle, heating and continuous casting, and then forging and rolling the billet into an axle. After forging and rolling, the billet is air-cooled and heat-treated.

[0036] After ladle refining, the heating process is as follows: the billet is first heated to 880°C in the preheating section, then heated to 960°C in the first heating section, held at that temperature, and then heated to 1180°C in the second heating section. After holding at that temperature, it enters the soaking section, where the temperature is 1320°C. After holding at that temperature, it is then continuously cast.

[0037] Before axle forging and rolling: the continuous casting billet is heated to 1230℃, held for 4 hours and then taken out of the furnace. The initial rolling temperature is 1120℃, the final rolling temperature is 980℃, and after rolling, it is cooled to 300℃ on a cooling bed and then taken off the production line.

[0038] The heat treatment specifically involves first subjecting the forged and rolled steel to quenching heat treatment, followed by a second annealing treatment to obtain high hardenability automotive bearing alloy steel.

[0039] The quenching heat treatment temperature is 900℃, and the holding time of the quenching heat treatment is 90min; wherein the cooling method of the quenching treatment is water cooling (using a strong cooling-weak cooling alternation method).

[0040] The temperature of the first annealing treatment was 780℃, and the holding time of the annealing treatment was 2 hours. The second annealing treatment was performed at a temperature of 650°C, and the holding time for the annealing treatment was 4 hours.

[0041] After secondary annealing, the product is air-cooled to room temperature, finished, tested, and then stored. Example 3:

[0042] The chemical composition by mass percentage is as follows: C: 0.75%, Si: 0.60%, Mn: 1.40%, Cr: 1.3%, V: 0.15%, Nb: 0.025%, Ti: 0.015%, Ni: 0.020%, Mo: 0.025%, Al: 0.023%, La: 0.002%, Ce: 0.003%, N: 0.004%, P: 0.012%, S: 0.013%; the balance is Fe and unavoidable impurities.

[0043] The high hardenability automotive bearing alloy steel is obtained by smelting in a converter, electric furnace or vacuum induction furnace, refining outside the ladle, heating and continuous casting, and then forging and rolling the billet into an axle. After forging and rolling, the billet is air-cooled and heat-treated.

[0044] After ladle refining, the heating process is as follows: the billet is first heated to 880°C in the preheating section, then heated to 960°C in the first heating section, held at that temperature, and then heated to 1180°C in the second heating section. After holding at that temperature, it enters the soaking section, where the temperature is 1320°C. After holding at that temperature, it is then continuously cast.

[0045] Before axle forging and rolling: the continuous casting billet is heated to 1230℃, held for 4 hours and then taken out of the furnace. The initial rolling temperature is 1120℃, the final rolling temperature is 980℃, and after rolling, it is cooled to 300℃ on a cooling bed and then taken off the production line.

[0046] The heat treatment specifically involves first subjecting the forged and rolled steel to quenching heat treatment, followed by a second annealing treatment to obtain high hardenability automotive bearing alloy steel.

[0047] The quenching heat treatment temperature is 900℃, and the holding time of the quenching heat treatment is 100min; wherein the cooling method of the quenching treatment is water cooling (using a strong cooling-weak cooling alternation method).

[0048] The temperature of the first annealing treatment was 750℃, and the holding time of the annealing treatment was 2 hours. The second annealing treatment was performed at a temperature of 650°C, and the holding time for the annealing treatment was 4 hours.

[0049] After secondary annealing, the product is air-cooled to room temperature, finished, tested, and then stored. Example 4:

[0050] The chemical composition by mass percentage is as follows: C: 0.80%, Si: 0.65%, Mn: 1.40%, Cr: 1.25%, V: 0.11%, Nb: 0.025%, Ti: 0.015%, Ni: 0.018%, Mo: 0.025%, Al: 0.023%, La: 0.002%, Ce: 0.003%, N: 0.0045%, P: 0.012%, S: 0.013%; the balance is Fe and unavoidable impurities.

[0051] The high hardenability automotive bearing alloy steel is obtained by smelting in a converter, electric furnace or vacuum induction furnace, refining outside the ladle, heating and continuous casting, and then forging and rolling the billet into an axle. After forging and rolling, the billet is air-cooled and heat-treated.

[0052] After ladle refining, the heating process is as follows: the billet is first heated to 880°C in the preheating section, then heated to 960°C in the first heating section, held at that temperature, and then heated to 1180°C in the second heating section. After holding at that temperature, it enters the soaking section, where the temperature is 1300°C. After holding at that temperature, it is then continuously cast.

[0053] Before axle forging and rolling: the continuous casting billet is heated to 1230℃, held for 4 hours and then taken out of the furnace. The initial rolling temperature is 1120℃, the final rolling temperature is 980℃, and after rolling, it is cooled to 300℃ on a cooling bed and then taken off the production line.

[0054] The heat treatment specifically involves first subjecting the forged and rolled steel to quenching heat treatment, followed by a second annealing treatment to obtain high hardenability automotive bearing alloy steel.

[0055] The quenching heat treatment temperature is 880℃, and the quenching heat treatment holding time is 90min; wherein the quenching cooling method is water cooling (using a strong cooling-weak cooling alternation method).

[0056] The temperature of the first annealing treatment was 750℃, and the holding time of the annealing treatment was 2 hours. The second annealing treatment was performed at a temperature of 650°C, and the holding time for the annealing treatment was 4 hours.

[0057] After secondary annealing, the product is air-cooled to room temperature, finished, tested, and then stored. Comparative Example 1:

[0058] The chemical composition by mass percentage is as follows: C: 0.45%, Si: 0.60%, Mn: 1.40%, Cr: 0.8%, V: 0.11%, Nb: 0.025%, Ni: 0.018%, Mo: 0.025%, Al: 0.023%, N: 0.005%, P: 0.012%, S: 0.013%; the balance is Fe and unavoidable impurities.

[0059] The high hardenability automotive bearing alloy steel is obtained by smelting in a converter, electric furnace or vacuum induction furnace, refining outside the ladle, heating and continuous casting, and then forging and rolling the billet into an axle. After forging and rolling, the billet is air-cooled and heat-treated.

[0060] After ladle refining, the heating process is as follows: the billet is first heated to 880°C in the preheating section, then heated to 960°C in the first heating section, held at that temperature, and then heated to 1180°C in the second heating section. After holding at that temperature, it enters the soaking section, where the temperature is 1320°C. After holding at that temperature, it is then continuously cast.

[0061] Before axle forging and rolling: the continuous casting billet is heated to 1230℃, held for 4 hours and then taken out of the furnace. The initial rolling temperature is 1120℃, the final rolling temperature is 980℃, and after rolling, it is cooled to 300℃ on a cooling bed and then taken off the production line.

[0062] The heat treatment specifically involves first subjecting the forged and rolled steel to quenching heat treatment, followed by a second annealing treatment to obtain high hardenability automotive bearing alloy steel.

[0063] The quenching heat treatment temperature is 880℃, and the quenching heat treatment holding time is 90min; wherein the quenching cooling method is water cooling (using a strong cooling-weak cooling alternation method).

[0064] The temperature of the first annealing treatment was 750℃, and the holding time of the annealing treatment was 2 hours. The second annealing treatment was performed at a temperature of 650°C, and the holding time for the annealing treatment was 4 hours.

[0065] After secondary annealing, the product is air-cooled to room temperature, finished, tested, and then stored. Comparative Example 2:

[0066] The chemical composition by mass percentage is as follows: C: 0.75%, Si: 0.60%, Mn: 1.40%, Cr: 1.3%, V: 0.011%, Nb: 0.025%, Ti: 0.015%, Ni: 0.018%, Mo: 0.025%, Al: 0.023%, La: 0.002%, Ce: 0.003%, N≤0.005%, P: 0.012%, S: 0.013%; the balance is Fe and unavoidable impurities.

[0067] The high hardenability automotive bearing alloy steel is obtained by smelting in a converter, electric furnace or vacuum induction furnace, refining outside the ladle, heating and continuous casting, and then forging and rolling the billet into an axle. After forging and rolling, the billet is air-cooled and heat-treated.

[0068] After ladle refining, the heating process is as follows: the billet is first heated to 880°C in the preheating section, then heated to 920°C in the first heating section, held at that temperature, and then heated to 1120°C in the second heating section. After holding at that temperature, it enters the soaking section, where the temperature is 1200°C. After holding at that temperature, it is then continuously cast.

[0069] Before axle forging and rolling: the continuous casting billet is heated to 1200℃, held for 4 hours and then taken out of the furnace. The initial rolling temperature is 1120℃, the final rolling temperature is 980℃, and after rolling, it is cooled to 300℃ on a cooling bed and then taken off the production line.

[0070] The heat treatment specifically involves first subjecting the forged and rolled steel to quenching heat treatment, followed by annealing treatment, to obtain automotive bearing alloy steel.

[0071] The quenching heat treatment temperature is 880℃, and the holding time of the quenching heat treatment is 90min; the cooling method of the quenching treatment is water cooling; the annealing temperature is 650℃, and the holding time of the annealing treatment is 6h; after annealing, the material is air-cooled to room temperature, finished, inspected, and then put into storage.

[0072] According to the chemical composition range designed in this invention, automotive bearing alloy steel was produced. The properties of the round steel bars of each embodiment and comparative example after quenching and annealing heat treatment were described. The inventors took samples of the finished round steel bars of Examples 1-4 and the comparative round steel bars of Comparative Examples 1-2 after quenching and tempering heat treatment, and prepared specimens according to GB / T 2975. Tensile tests and impact tests were conducted according to GB / T228.1 and GB / T229, respectively, to obtain the mechanical properties of the steel bars of each embodiment and comparative example after quenching and annealing heat treatment. The relevant mechanical property test results are listed in Table 1 below.

[0073] Mechanical property data are shown in Table 1 below.

[0074] Table 1 Mechanical property data

[0075] Hardenability data are shown in Table 2 below.

[0076] Table 2 Hardenability

[0077] The steels prepared by this invention all have good comprehensive mechanical properties with tensile strength of over 950 MPa and room temperature impact energy of over 90 J. They also have uniform and fine austenitic grains with a grain size of 7-8. No mixed grains or abnormally coarse grains were observed. The hardenability is significantly improved, and the steels have a better strength and toughness match than the comparison steels.

[0078] In contrast, the comparative steel of Comparative Example 1 exhibited mixed grain phenomenon (level 1), where 6 (1) indicates an average grain size of level 6, while local coarsening occurred at level 1. Correspondingly, Comparative Example 2, after process adjustment, showed abnormal austenite grain growth (level 1), where 5.5 (1) indicates an average grain size of level 5.5, while local coarsening occurred at level 1.

[0079] Compared to the comparative steels of Comparative Examples 1-2, the alloy steel described in this invention, through reasonable chemical composition design and optimized process, has higher hardenability, finer grain size, and higher strength.

[0080] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A high hardenability automotive bearing alloy steel, characterized in that, Composed of the following ingredients by weight percentage composition: C: 0.65–0.85%, Si: 0.50–0.70%, Mn: 1.20–1.60%, Cr: 1.2–1.5%, V: 0.10–0.15%, Nb: 0.010–0.030%, Ti: 0.010–0.030%, Ni≤0.025%, Mo: 0.020–0.040%, Al: 0.02–0.030%, La: 0.001–0.002%, Ce: 0.002–0.003%, N≤0.005%, P≤0.015%, S≤0.015%; balance Fe and unavoidable impurities.

2. The high hardenability automotive bearing alloy steel according to claim 1, characterized in that, The alloy steel used for the vehicle bearing has a tensile strength of over 950 MPa and an impact energy of over 90 J at room temperature, and it has uniform and fine austenitic grains with a grain size of 7 to 8.

3. The method for manufacturing high hardenability automotive bearing alloy steel according to claim 1, characterized in that, Includes the following steps: The steel is smelted in a converter, electric furnace or vacuum induction furnace, refined outside the ladle, heated and then continuously cast. The billet obtained by continuous casting is then forged and rolled into an axle, air-cooled after forging and rolling, and then heat-treated to obtain high hardenability automotive bearing alloy steel. Heating operation: The steel billet is first heated to no higher than 900°C in the preheating section, and then heated to no higher than 980°C in the first heating section. After holding at this temperature, it is heated to 1000~1250°C in the second heating section. After holding at this temperature, it enters the soaking section, where the temperature is 1300~1350°C. After holding at this temperature, it is then subjected to continuous casting or forging. The heat treatment specifically involves first subjecting the forged and rolled steel to quenching heat treatment, followed by a second annealing treatment.

4. The method for manufacturing high hardenability automotive bearing alloy steel according to claim 3, characterized in that, Before axle forging and rolling: The continuously cast billet obtained from continuous casting is heated to 1200-1280℃, held for 4-6 hours and then taken out of the furnace. The initial rolling temperature is 1100-1150℃, the final rolling temperature is 950-980℃, and after rolling, it is cooled to 200-500℃ on a cooling bed before being taken off the production line.

5. The method for manufacturing high hardenability automotive bearing alloy steel according to claim 3, characterized in that, The quenching heat treatment temperature is 850–920℃, and the holding time of the quenching heat treatment is 90–120 min.

6. The method for manufacturing high hardenability automotive bearing alloy steel according to claim 5, characterized in that, The cooling method for quenching is water cooling; specifically, the water cooling method is an alternating strong cooling and weak cooling method.

7. The method for manufacturing high hardenability automotive bearing alloy steel according to claim 3, characterized in that, The temperature of the first annealing treatment is 720-800℃, and the holding time of the annealing treatment is 2-3 hours.

8. The method for manufacturing high hardenability automotive bearing alloy steel according to claim 3, characterized in that, The temperature for the second annealing treatment is 630-650℃, and the holding time for the annealing treatment is 4-5 hours.

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