Component-end quenching synergistic process for hardenability bandwidth control of CrMnMo series gear steel

Abstract

The invention relates to the technical field of steel and iron material processing, and discloses a component-end quenching synergistic process for hardenability bandwidth control of CrMnMo series gear steel. Comprising the steps of S1, component accurate design and regulation, S2, smelting process optimization and component homogenization, S3, continuous casting process control and segregation inhibition, S4, rolling-controlled cooling collaborative process optimization, S5, end quenching test and hardenability accurate calibration and S6, finished product inspection and feedback optimization. And through main alloy element narrow interval design, segregation suppression and end quenching cooperative calibration, the hardenability bandwidth of the gear steel is stably controlled to be smaller than or equal to 4 HRC, the J9 hardness ranges from 36 HRC to 49 HRC, and the J15 hardness ranges from 30 HRC to 44 HRC, the requirement of high-end part machining for hardenability uniformity is completely met, and the machining rejection rate caused by hardenability fluctuation is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of steel material processing technology, specifically to a composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel. Background Technology

[0002] As a core material for critical components in the automotive, wind power, and other fields, the hardenability uniformity of CrMnMo series gear steels directly determines the strength-toughness matching and processing stability of the components. In traditional production processes, the control range of the main alloying elements (C, Mn, Cr, Mo) is wide, resulting in large compositional fluctuations (PPK values ​​of some elements below 1.0). Furthermore, continuous casting processes are prone to problems such as central segregation and excessive banding structures. In addition, the lack of a coordinated calibration mechanism for composition and end-quench testing leads to a hardenability bandwidth often reaching 8-9 HRC, far exceeding the stringent customer requirement of ≤4 HRC. This not only causes excessive deformation during gear machining and increases the risk of heat treatment cracking, but also reduces the service life of components and makes it difficult to meet the requirements of high-end equipment for consistent material performance, becoming a core bottleneck restricting the market competitiveness of this type of gear steel. Summary of the Invention

[0003] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steels. This process has advantages such as precise and controllable hardenability bandwidth and solves problems such as central segregation and excessive banded structure that easily occur during the casting process.

[0004] (II) Technical Solution To achieve the aforementioned goal of precise and controllable hardenability bandwidth, this invention provides the following technical solution: a composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel, comprising S1 precise composition design and control, S2 smelting process optimization and composition homogenization, S3 continuous casting process control and segregation suppression, S4 rolling-controlled cooling synergistic process optimization, S5 end quenching test and precise hardenability calibration, and S6 finished product inspection and feedback optimization. The S1 precise composition design and control includes S101 main alloying element control, S102 harmful element and trace element optimization, and S103 carbon equivalent control. Among them, the S2 smelting process optimization and composition homogenization includes S201 converter smelting, S202 LF refining, S203 VD vacuum treatment and S204 protective casting; Among them, S3 continuous casting process control and segregation suppression includes S301 process parameters, S302 electromagnetic stirring, S303 light reduction process and S304 billet treatment. Among them, the S4 rolling-controlled cooling synergistic process optimization includes S401 heating regime, S402 rolling control and S403 controlled cooling synergy; Among them, the S5 end quenching test and hardenability precision calibration include S501 sample preparation, S502 end quenching test and S503 bandwidth calibration. Among them, S6 finished product inspection and feedback optimization includes S601 composition inspection, S602 microstructure and property inspection and S603 hardenability verification.

[0005] Preferably, the main alloying elements of S101 are controlled as follows: C content 0.17~0.24% (core influence on hardenability benchmark), Mn content 1.00~1.25%, Cr content 1.10~1.35%, Mo content 0.20~0.30%, reducing the impact of composition fluctuations on hardenability through narrow range control; Ni content ≤0.35%, avoiding excessive increase in hardenability leading to bandwidth expansion.

[0006] Preferably, the harmful and trace elements in S102 are optimized as follows: P≤0.020%, S≤0.008%, to reduce the risk of segregation; Al content 0.020~0.045%, N content 0.008~0.014%, controlling the Al / N ratio >2.5, refining the microstructure through AlN pinning grains, and stabilizing hardenability; S103 carbon equivalent control: calculated according to Ceq=C+Si / 10+2Mn / 11+Cr / 5+V / 3, Ceq is controlled at 0.65~0.82% to balance the matching degree of strength, toughness and hardenability.

[0007] Preferably, the S201 converter smelting process involves: endpoint control of [C] ≥ 0.06%, [P] ≤ 0.020%, high-pressure blowing frequency ≤ 3 times, and slag-blocking during steel tapping to ensure a slag layer in the ladle ≤ 65 mm, thereby reducing secondary oxidation; S202 LF refining: power-on time ≥20min, total argon blowing time ≥35min, rapid production of high-basicity white slag (basicity ≥3.5), white slag holding time ≥30min, deep deoxidation and desulfurization; during the process, the main alloying elements are finely adjusted in stages, and the deviation is controlled within ±0.02%.

[0008] Preferably, the S203 VD vacuum treatment involves: a vacuum target of ≤0.8 tor (107 Pa), a vacuum holding time of ≥12 min, and soft blowing of argon gas for ≥15 min after rupture of the vacuum to promote the flotation of inclusions and uniform composition; controlling the molten steel [H] ≤2.2 ppm and [O] ≤0.0025%. S204 protective casting: The entire process uses long nozzle argon blowing + nozzle sealing ring for sealing, and the liquid level in the tundish is ≥550mm to avoid secondary contamination of molten steel and resulting in component segregation.

[0009] Preferably, the S301 process parameters are as follows: the superheat of the tundish is controlled at 15~32℃, and the superheat of the continuous casting furnace is ≤30℃; the casting speed is 0.50~0.85m / min, which is dynamically adjusted according to the cross-section of the billet (280×280~350×430mm) to avoid compositional segregation caused by casting speed fluctuations; S302 electromagnetic stirring: The electromagnetic stirring current of the crystallizer is 150~350A and the frequency is 2.0~5.0Hz; the electromagnetic stirring current of the end is 200~600A and the frequency is 5.0~16Hz, which promotes uniform composition and grain refinement and reduces center segregation. S303 light reduction process: Dynamic light reduction is implemented at the end of the solidification of the billet, with a total reduction of 6~12mm, which is completed in 3~4 stages to suppress the segregation of carbon and alloying elements and reduce the risk of hardenability fluctuation. S304 billet treatment: After coming off the production line, the billets are stacked together for slow cooling for ≥24 hours to avoid excessive temperature difference between the inside and outside of the billet, which can cause stress and compositional segregation.

[0010] Preferably, the S401 heating regime is as follows: preheating zone temperature ≤ 850℃, heating zone temperature 1150~1220℃, soaking zone temperature 1180~1210℃; the furnace time is adjusted to 240~450min according to the cross-section of the billet to ensure that the alloying elements are fully dissolved and reduce composition inhomogeneity. S402 rolling control: initial rolling temperature ≥1050℃, final rolling temperature 870~970℃, ensuring a compression ratio ≥5.5; the reduction of the first two passes is not less than 55mm and 50mm respectively, to refine the austenite grains and stabilize the hardenability. S403 controlled cooling synergy: The temperature of the rolled steel billet entering the cooling bed is 700~780℃, and a slow cooling process with close-packed insulation hood is adopted, with a cooling rate of 0.4~1.5℃ / s; the temperature of entering the hood is 620~680℃, and the collection temperature is 380~460℃, so as to avoid uneven microstructure caused by excessively fast or slow cooling rate, thereby expanding the hardenability bandwidth.

[0011] Preferably, the S501 sample preparation involves randomly selecting 3 finished steel pieces from each heat number, preparing φ25mm×100mm samples according to GB / T225, and subjecting them to normalizing treatment at 915~935℃ (holding for 30~60min) to eliminate rolling stress and uneven microstructure. S502 end quenching test: The sample was quenched at 850~870℃ (held for 30min), cooled using a standard end quenching device, and the hardness values ​​at positions 9mm (J9) and 15mm (J15) from the quenched end were measured respectively. S503 Bandwidth Calibration: If the hardenability bandwidth of the same heat number is >4HRC, adjust the main alloying elements (such as Mn, Cr deviation ±0.01~0.02%) or optimize the controlled cooling rate (±0.1~0.2℃ / s) until the bandwidth is ≤4HRC.

[0012] Preferably, the S601 component inspection is performed using GB / T223 and GB / T4336 standards to ensure that the deviations of each element comply with the requirements of GB / T222, and the Al / N ratio is stable at 2.5~3.5; S602 microstructure and properties inspection: Low magnification microstructure is generally loose, with central looseness ≤2.0 grade, and ingot segregation ≤1.5 grade; non-metallic inclusions are graded according to GB / T10561 Method A, with Class A ≤2.5 grade, Class B ≤2.0 grade, Class C ≤1.0 grade, and Class D ≤1.5 grade; austenite grain size ≥6 grade, and banded microstructure ≤2.5 grade.

[0013] Preferably, the S603 hardenability verification involves randomly selecting 5% of samples from each batch for end-quenching tests to ensure that J9 hardness is 36~49HRC, J15 hardness is 30~44HRC, and bandwidth is ≤4HRC; a hardenability database is established to provide real-time feedback for adjusting smelting and rolling process parameters.

[0014] (III) Beneficial Effects Compared with the prior art, the present invention provides a composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel, which has the following beneficial effects: 1. The composition-end quenching synergistic process for controlling the hardenability bandwidth of the CrMnMo series gear steel achieves precise and controllable hardenability bandwidth: through narrow range design of main alloying elements, segregation suppression and end quenching synergistic calibration, the hardenability bandwidth of the gear steel is stably controlled at ≤4HRC, J9 hardness 36~49HRC, J15 hardness 30~44HRC, which fully meets the requirements of high-end component processing for hardenability uniformity and greatly reduces the scrap rate caused by hardenability fluctuations.

[0015] 2. The CrMnMo series gear steel utilizes a composition-end quenching synergistic process for hardenability bandwidth control. This process significantly improves the uniformity of composition and microstructure: segregation control throughout the smelting-continuous casting-rolling process, combined with Al / N ratio optimization (2.5~3.5), ensures that non-metallic inclusions in the steel meet the required standards, austenite grain size ≥6, and banded microstructure ≤2.5, effectively reducing processing deformation and heat treatment cracking risks, and improving component assembly accuracy.

[0016] 3. The CrMnMo series gear steel utilizes a composition-end quenching synergistic process with controlled hardenability bandwidth. This process achieves optimized strength and toughness matching: the synergistic regulation of carbon equivalent and alloying elements balances the hardenability and toughness of the material, resulting in a tensile strength of ≥1180MPa and an impact absorption energy of ≥55J for the gear steel. This meets the wear-resistant and impact-resistant requirements of key components and extends the service life of the products.

[0017] 4. The composition-end quenching synergistic process for controlling the hardenability bandwidth of the CrMnMo series gear steel has achieved the following improvements in production efficiency and stability: a hardenability database has been established to provide real-time feedback for process optimization, reducing rework adjustments caused by composition fluctuations and increasing the finished product qualification rate by more than 10%; at the same time, subsequent processing steps have been simplified, production costs have been reduced, and the needs of large-scale production have been met. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] This solution provides a technical approach, specifically a composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel, including the following process: S1 Precise design and control of composition: S101 main alloying element control: C content 0.17~0.24% (core influence on hardenability benchmark), Mn content 1.00~1.25%, Cr content 1.10~1.35%, Mo content 0.20~0.30%, reducing the impact of composition fluctuations on hardenability through narrow range control; Ni content ≤0.35%, avoiding excessive hardenability enhancement leading to bandwidth expansion; S102 harmful element and trace element optimization: P≤0.020%, S≤0.008%, reducing the risk of segregation; Al content 0.020~0.045%, N content 0.008~0.014%, controlling Al / N ratio >2.5, refining the structure through AlN pinning grains, and stabilizing hardenability; S103 carbon equivalent control: calculated according to Ceq=C+Si / 10+2Mn / 11+Cr / 5+V / 3, Ceq is controlled at 0.65~0.82% to balance the matching degree of strength, toughness and hardenability; S2 smelting process optimization and composition homogenization: S201 converter smelting: Endpoint control [C]≥0.06%, [P]≤0.020%, high-strength blowing times≤3 times, slag blocking during tapping to ensure slag layer in ladle ≤65mm, reducing secondary oxidation; S202 LF refining: power-on time ≥20min, total argon blowing time ≥35min, rapid production of high-basicity white slag (basicity ≥3.5), white slag holding time ≥30min, deep deoxidation and desulfurization; during the process, the main alloying elements are finely adjusted in stages, and the deviation is controlled within ±0.02%; S203 VD vacuum treatment: vacuum target ≤0.8tor (107Pa), vacuum holding time ≥12min, soft blowing of argon gas ≥15min after vacuum breaking to promote inclusion flotation and compositional uniformity; control molten steel [H] ≤2.2ppm, [O] ≤0.0025%; S204 protective casting: The entire process adopts long nozzle argon blowing + nozzle sealing ring sealing, and the liquid level in the tundish is ≥550mm to avoid secondary contamination of molten steel and resulting in component segregation; S3 Continuous Casting Process Control and Segregation Suppression: S301 process parameters: The superheat of the tundish is controlled at 15~32℃, and the superheat of the continuous casting furnace is ≤30℃; the casting speed is 0.50~0.85m / min, which is dynamically adjusted according to the cross-section of the billet (280×280~350×430mm) to avoid compositional segregation caused by casting speed fluctuations; S302 electromagnetic stirring: The electromagnetic stirring current of the crystallizer is 150~350A and the frequency is 2.0~5.0Hz; the electromagnetic stirring current of the end is 200~600A and the frequency is 5.0~16Hz, which promotes uniform composition and grain refinement and reduces center segregation. S303 light reduction process: Dynamic light reduction is implemented at the end of the solidification of the billet, with a total reduction of 6~12mm, which is completed in 3~4 stages to suppress the segregation of carbon and alloying elements and reduce the risk of hardenability fluctuation. S304 billet treatment: After coming off the production line, the billets are stacked together for slow cooling. The slow cooling time is ≥24 hours to avoid excessive temperature difference between the inside and outside of the billet, which can cause stress and compositional segregation. S4 rolling - controlled cooling synergistic process optimization: S401 heating regime: preheating zone temperature ≤850℃, heating zone temperature 1150~1220℃, soaking zone temperature 1180~1210℃; furnace time is adjusted to 240~450min according to the cross-section of the billet to ensure full solid solution of alloying elements and reduce composition inhomogeneity. S402 rolling control: initial rolling temperature ≥1050℃, final rolling temperature 870~970℃, ensuring a compression ratio ≥5.5; the reduction of the first two passes is not less than 55mm and 50mm respectively, to refine the austenite grains and stabilize the hardenability. S403 controlled cooling synergy: The temperature of the rolled steel billet entering the cooling bed is 700~780℃, and a slow cooling process with a close-packed heat insulation cover is adopted, with a cooling rate of 0.4~1.5℃ / s; the temperature of entering the cover is 620~680℃, and the collection temperature is 380~460℃, so as to avoid uneven microstructure caused by excessively fast or slow cooling rate, thereby expanding the hardenability bandwidth. S5 end-quench test and precise calibration of hardenability: S501 Sample Preparation: Three finished steel samples were randomly selected from each heat number and prepared according to GB / T225 with a diameter of 25mm and a diameter of 100mm. The samples were then normalized at 915~935℃ (holding temperature for 30~60min) to eliminate rolling stress and uneven microstructure. S502 end quenching test: The sample was quenched at 850~870℃ (held for 30min), cooled using a standard end quenching device, and the hardness values ​​at positions 9mm (J9) and 15mm (J15) from the quenched end were measured respectively. S503 Bandwidth Calibration: If the hardenability bandwidth of the same heat number is >4HRC, adjust the main alloying elements (such as Mn, Cr deviation ±0.01~0.02%) or optimize the controlled cooling rate (±0.1~0.2℃ / s) until the bandwidth is ≤4HRC; S6 Finished Product Inspection and Feedback Optimization: S601 Composition Inspection: The test shall be conducted in accordance with the standards of GB / T223 and GB / T4336 to ensure that the deviation of each element complies with the requirements of GB / T222, and the Al / N ratio is stable at 2.5~3.5; S602 microstructure and properties inspection: Low-magnification microstructure is generally loose, with central looseness ≤2.0 grade, and ingot segregation ≤1.5 grade; non-metallic inclusions are graded according to GB / T10561 Method A: Class A ≤2.5 grade, Class B ≤2.0 grade, Class C ≤1.0 grade, and Class D ≤1.5 grade; austenite grain size ≥6 grade, and banded microstructure ≤2.5 grade; S603 Hardenability Verification: 5% of samples from each batch are randomly selected for end-quenching tests to ensure that J9 hardness is 36~49HRC, J15 hardness is 30~44HRC, and bandwidth is ≤4HRC; establish a hardenability database and provide real-time feedback to adjust smelting and rolling process parameters; Furthermore, this process achieves precise and controllable hardenability bandwidth: through narrow range design of main alloying elements, segregation suppression and end-quench synergistic calibration, the hardenability bandwidth of gear steel is stably controlled at ≤4HRC, J9 hardness 36~49HRC, J15 hardness 30~44HRC, which fully meets the requirements of high-end component processing for hardenability uniformity and significantly reduces the scrap rate caused by hardenability fluctuations. Furthermore, this process achieves a significant improvement in composition and microstructure uniformity: segregation control throughout the entire smelting-continuous casting-rolling process, combined with Al / N ratio optimization (2.5~3.5), ensures that the non-metallic inclusion rating in the steel meets the standards, the austenite grain size is ≥6, and the banded structure is ≤2.5, effectively reducing the risk of processing deformation and heat treatment cracking, and improving the assembly accuracy of components; Furthermore, this process achieves optimized strength and toughness matching: the synergistic regulation of carbon equivalent and alloying elements balances the hardenability and toughness of the material, making the gear steel tensile strength ≥1180MPa and impact absorption energy ≥55J, meeting the wear resistance and impact resistance requirements of key components and extending the service life of the product. Furthermore, this process achieves improved production efficiency and stability: establishing a hardenability database provides real-time feedback to optimize the process, reducing rework adjustments caused by composition fluctuations, and increasing the finished product qualification rate by more than 10%; at the same time, it simplifies subsequent processing steps, reduces production costs, and adapts to the needs of large-scale production.

[0020] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel, comprising S1 precise composition design and control, S2 smelting process optimization and composition homogenization, S3 continuous casting process control and segregation suppression, S4 rolling-controlled cooling synergistic process optimization, S5 end quenching test and precise hardenability calibration, and S6 finished product inspection and feedback optimization, characterized in that: The precise design and control of the S1 composition includes S101 main alloying element control, S102 optimization of harmful and trace elements, and S103 carbon equivalent control. Among them, the S2 smelting process optimization and composition homogenization includes S201 converter smelting, S202 LF refining, S203 VD vacuum treatment and S204 protective casting; Among them, S3 continuous casting process control and segregation suppression includes S301 process parameters, S302 electromagnetic stirring, S303 light reduction process and S304 billet treatment. Among them, the S4 rolling-controlled cooling synergistic process optimization includes S401 heating regime, S402 rolling control and S403 controlled cooling synergy; Among them, the S5 end quenching test and hardenability precision calibration include S501 sample preparation, S502 end quenching test and S503 bandwidth calibration. Among them, S6 finished product inspection and feedback optimization includes S601 composition inspection, S602 microstructure and property inspection and S603 hardenability verification.

2. The composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel according to claim 1, characterized in that: The main alloying elements of S101 are controlled as follows: C content 0.17~0.24% (core influence on hardenability benchmark), Mn content 1.00~1.25%, Cr content 1.10~1.35%, Mo content 0.20~0.30%, reducing the impact of composition fluctuations on hardenability through narrow range control; Ni content ≤0.35%, avoiding excessive increase in hardenability leading to bandwidth expansion.

3. The composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel according to claim 1, characterized in that: The S102 is optimized for harmful and trace elements: P≤0.020%, S≤0.008%, to reduce the risk of segregation; Al content 0.020~0.045%, N content 0.008~0.014%, controlling the Al / N ratio >2.5, refining the microstructure through AlN pinning grains, and stabilizing hardenability; S103 carbon equivalent control: calculated according to Ceq=C+Si / 10+2Mn / 11+Cr / 5+V / 3, Ceq is controlled at 0.65~0.82% to balance the matching degree of strength, toughness and hardenability.

4. The composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel according to claim 1, characterized in that: The S201 converter smelting process includes: endpoint control of [C] ≥ 0.06%, [P] ≤ 0.020%, high-pressure blowing frequency ≤ 3 times, and slag-blocking during tapping to ensure a slag layer of ≤ 65 mm in the ladle, thereby reducing secondary oxidation; S202 LF refining: power-on time ≥20min, total argon blowing time ≥35min, rapid production of high-basicity white slag (basicity ≥3.5), white slag holding time ≥30min, deep deoxidation and desulfurization; during the process, the main alloying elements are finely adjusted in stages, and the deviation is controlled within ±0.02%.

5. The composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel according to claim 1, characterized in that: The S203 VD vacuum treatment: vacuum target ≤0.8tor (107Pa), vacuum holding time ≥12min, soft blowing of argon gas ≥15min after vacuum breaking to promote inclusion flotation and compositional uniformity; control molten steel [H] ≤2.2ppm, [O] ≤0.0025%; S204 protective casting: The entire process uses long nozzle argon blowing + nozzle sealing ring for sealing, and the liquid level in the tundish is ≥550mm to avoid secondary contamination of molten steel and resulting in component segregation.

6. The composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel according to claim 1, characterized in that: The S301 process parameters are as follows: the superheat of the tundish is controlled at 15~32℃, and the superheat of the continuous casting furnace is ≤30℃; the casting speed is 0.50~0.85m / min, which is dynamically adjusted according to the cross-section of the billet (280×280~350×430mm) to avoid compositional segregation caused by casting speed fluctuations. S302 electromagnetic stirring: The electromagnetic stirring current of the crystallizer is 150~350A and the frequency is 2.0~5.0Hz; the electromagnetic stirring current of the end is 200~600A and the frequency is 5.0~16Hz, which promotes uniform composition and grain refinement and reduces center segregation. S303 light reduction process: Dynamic light reduction is implemented at the end of the solidification of the billet, with a total reduction of 6~12mm, which is completed in 3~4 stages to suppress the segregation of carbon and alloying elements and reduce the risk of hardenability fluctuation. S304 billet treatment: After coming off the production line, the billets are stacked together for slow cooling for ≥24 hours to avoid excessive temperature difference between the inside and outside of the billet, which can cause stress and compositional segregation.

7. The composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel according to claim 1, characterized in that: The S401 heating regime is as follows: preheating zone temperature ≤850℃, heating zone temperature 1150~1220℃, soaking zone temperature 1180~1210℃; the furnace time is adjusted to 240~450min according to the cross-section of the billet to ensure that the alloying elements are fully dissolved and reduce composition inhomogeneity. S402 rolling control: initial rolling temperature ≥1050℃, final rolling temperature 870~970℃, ensuring a compression ratio ≥5.5; the reduction of the first two passes is not less than 55mm and 50mm respectively, to refine the austenite grains and stabilize the hardenability. S403 controlled cooling synergy: The temperature of the rolled steel billet entering the cooling bed is 700~780℃, and a slow cooling process with close-packed insulation hood is adopted, with a cooling rate of 0.4~1.5℃ / s; the temperature of entering the hood is 620~680℃, and the collection temperature is 380~460℃, so as to avoid uneven microstructure caused by excessively fast or slow cooling rate, thereby expanding the hardenability bandwidth.

8. The composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel according to claim 1, characterized in that: The S501 sample preparation: Three finished steel pieces were randomly selected from each heat number, and φ25mm×100mm samples were prepared according to GB / T225. The samples were then normalized at 915~935℃ (holding temperature for 30~60min) to eliminate rolling stress and uneven microstructure. S502 end quenching test: The sample was quenched at 850~870℃ (held for 30min), cooled using a standard end quenching device, and the hardness values ​​at positions 9mm (J9) and 15mm (J15) from the quenched end were measured respectively. S503 Bandwidth Calibration: If the hardenability bandwidth of the same heat number is >4HRC, adjust the main alloying elements (such as Mn, Cr with a deviation of ±0.01~0.02%) or optimize the controlled cooling rate (±0.1~0.2℃ / s) until the bandwidth is ≤4HRC.

9. The composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel according to claim 1, characterized in that: The S601 component inspection: GB / T223 and GB / T4336 standards are used for testing to ensure that the deviations of each element comply with GB / T222, and the Al / N ratio is stable at 2.5~3.5; S602 microstructure and properties inspection: Low magnification microstructure is generally loose, with central looseness ≤2.0 grade, and ingot segregation ≤1.5 grade; non-metallic inclusions are graded according to GB / T10561 Method A, with Class A ≤2.5 grade, Class B ≤2.0 grade, Class C ≤1.0 grade, and Class D ≤1.5 grade; austenite grain size ≥6 grade, and banded microstructure ≤2.5 grade.

10. The composition-end quenching synergistic process for controlling the hardenability bandwidth of CrMnMo series gear steel according to claim 1, characterized in that: The S603 hardenability verification: 5% of the samples in each batch are randomly selected for end quenching test to ensure that the hardness of J9 is 36~49HRC, the hardness of J15 is 30~44HRC, and the bandwidth is ≤4HRC; establish a hardenability database and provide real-time feedback to adjust the smelting and rolling process parameters.