Quenching medium and water temperature matching process for avoiding secondary quenching and tempering cracking of medium carbon alloy steel CrMo series steel

Abstract

This invention relates to the field of heat treatment technology for steel materials, and discloses a process for matching quenching medium and outlet water temperature to avoid secondary tempering cracking of medium carbon alloy steel CrMo series steel. The process includes steps S1 (quenching medium selection and proportioning), S2 (workpiece pretreatment), S3 (quenching temperature and holding time matching), S4 (quenching medium parameters and outlet water temperature matching), S5 (subsequent tempering process), and S6 (process monitoring and adjustment). This process achieves a precise balance between hardenability and crack resistance: by adapting 5%-10% PAG quenching fluid and 2%-5% brine to differentiated media according to the workpiece structure (rod diameter), and matching a stirring frequency of 15-28Hz and a graded outlet water temperature of 160-240℃, it ensures a stable hardenability layer depth ≥10mm and controls the secondary tempering cracking scrap rate to ≤1.0%, solving the core pain point of existing processes where "cracking occurs with hardenability and insufficient hardenability leads to crack resistance."

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for steel materials, specifically to a process for matching the quenching medium and outlet water temperature to avoid secondary tempering cracking of medium carbon alloy steel CrMo series steel. Background Technology

[0002] Medium-carbon alloy steels, such as the CrMo series, are widely used in the manufacture of key forgings like heavy-duty vehicle steering knuckles due to their excellent strength and toughness. Their production process requires secondary tempering to meet the requirement of a hardened layer depth ≥10mm. However, current technologies mostly adjust only the type of quenching medium or heating temperature, lacking a coordinated design that matches the quenching medium parameters (concentration, stirring frequency) with the outlet water temperature. While using high-cooling-rate media (such as high-concentration brine) can improve hardenability, it easily leads to secondary tempering cracking due to stress concentration. Using slow-cooling media (such as ordinary oil quenching) can reduce the risk of cracking, but often results in insufficient hardened layer depth. Furthermore, factors such as ineffective elimination of residual stress after forging and lack of precise pretreatment of the medium further exacerbate the contradiction between hardenability and crack resistance, leading to a high scrap rate due to cracking and making it difficult to meet the stringent quality requirements of key components. Summary of the Invention

[0003] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a process for matching the quenching medium and outlet water temperature to avoid secondary tempering cracking in medium carbon alloy steel CrMo series steel. This process has the advantages of precisely balancing hardenability and crack resistance, and solves the problem of insufficient hardenability layer.

[0004] (II) Technical Solution To achieve the aforementioned precise balance between hardenability and crack resistance, this invention provides the following technical solution: a process for matching quenching medium and outlet water temperature to avoid secondary tempering cracking in medium carbon alloy steel CrMo series steel, comprising the steps of S1 quenching medium selection and proportioning, S2 workpiece pretreatment, S3 quenching temperature and holding time matching, S4 quenching medium parameters and outlet water temperature matching, S5 subsequent tempering process, and S6 process monitoring and adjustment. The step of S1 quenching medium selection and proportioning includes S101 medium type adaptation and S102 medium pretreatment. Among them, the S3 quenching temperature and holding time matching step includes S301 quenching heating temperature, S302 holding time and S303 heating rate control. Among them, the S4 quenching medium parameter matching and water outlet temperature matching steps include S401 medium dynamic parameter control and S402 precise water outlet temperature control. The subsequent tempering process steps of S5 include tempering temperature of S501 and tempering holding time of S502.

[0005] Preferably, the S101 media type adaptation is as follows: Select the appropriate medium based on the complexity and size of the workpiece structure, prioritizing systems with low cracking risk: For complex structural workpieces (rod diameter ≥ 80mm): use 5%-10% PAG polymer quenching fluid (material base range 5%-8% optimized and expanded), which has both cooling uniformity and slow cooling characteristics, reducing stress concentration; For simple structural workpieces (rod diameter < 80mm): use 2%-5% brine quenching fluid (optimized concentration range of the material's basic brine system) to improve the cooling rate and ensure hardenability. Precise outlet water temperature control is required. For workpieces requiring high crack resistance: use 10%-15% oil-based quenching medium with a slow cooling rate, suitable for workpieces with residual stress accumulation during secondary tempering.

[0006] Preferably, the S102 media pretreatment: Newly prepared media should be ultrasonically stirred for 20-30 minutes (5 minutes for basic materials, with optimization extension) to ensure uniform composition and no sedimentation or stratification. The medium must be filtered to remove impurities before use. The filter screen pore size should be ≤50μm to avoid impurities affecting the uniformity of cooling. Maintain the pH of the medium between 7.5 and 9.0, replenish the medium regularly, and keep the concentration fluctuation ≤ ±1%.

[0007] Preferably, the S2 workpiece pretreatment step includes: Before the second heat treatment, the workpiece is preheated: the temperature is 860-890℃ (870℃ is the optimized range based on the material), and the holding time is 40-80min, which is adjusted according to the maximum cross-sectional size of the workpiece (increase by 10min for every 10mm) to eliminate forging residual stress. After preheating, the furnace is cooled to 300-350℃ before being removed and air-cooled to reduce the temperature difference stress with the quenching medium. Clean the workpiece surface of oxide scale, oil stains and defects to prevent crack initiation.

[0008] Preferably, the S301 quenching heating temperature is 830-880℃ (840-875℃ is optimized and expanded based on the material), with the lower limit (830-850℃) for complex structure workpieces and the upper limit (850-880℃) for simple structure workpieces. S302 heat preservation time: calculated based on the effective thickness of the workpiece, 30 minutes of heat preservation for every 20mm, with a minimum of 30 minutes and a maximum of 90 minutes (30-60 minutes for the basic material, optimized and expanded) to ensure complete austenitization of the core; S303 heating rate control: ≤150℃ / h, to avoid excessively rapid heating leading to thermal stress concentration.

[0009] Preferably, the S401 medium dynamic parameter control: Stirring frequency: 15-28Hz (material base 18-26Hz optimized and expanded), 15-22Hz for complex structure workpieces, 22-28Hz for simple structure workpieces, and adjust cooling uniformity by frequency conversion stirring. Medium temperature: Maintain at 15-40℃ (the range is not clearly defined based on the material, so further optimization is needed). For PAG medium, control at 20-35℃, and for brine medium, control at 15-30℃ to avoid excessively high temperatures that could reduce cooling efficiency.

[0010] Preferably, the S402 outlet water temperature is precisely controlled: 5%-10% PAG medium: For rods with a diameter ≤100mm: outlet water temperature 160-190℃ (material base 180-200℃ optimized and expanded), heat preservation time 10-15min followed by tempering; For rod diameter > 100mm: outlet water temperature 190-220℃, heat preservation time 15-20min, to release residual stress in the core; 2%-5% brine medium: The outlet water temperature is 180-230℃ (the material base temperature is 180-200℃, which is optimized and expanded). After the water comes out, the workpiece should be wrapped with heat insulation cotton immediately to slow down the cooling rate. 10%-15% oily media: The water temperature is 200-240℃, and no additional insulation is required. It can be directly transferred to the tempering process. Water discharge timing judgment: The surface temperature of the workpiece is monitored in real time by an infrared thermometer with a deviation of ≤±5℃, avoiding temperature runaway caused by relying on experience.

[0011] Preferably, the S501 tempering temperature is 620-660℃ (630-655℃ is optimized and expanded based on the material base). It is adjusted according to the end quenching requirements. The lower limit is taken when J30 needs to be ≥40HRC, and the upper limit is taken when it is necessary to reduce the hardness.

[0012] Preferably, the S502 tempering and holding time is 90-180 min (120-160 min for basic materials, optimized and expanded) to ensure full stress release. After holding, it is cooled in the furnace to below 200°C and then air-cooled. After tempering, the workpiece is straightened, and the straightening force is controlled at 30%-40% of the material's yield strength to avoid cracking caused by hard straightening.

[0013] Preferably, the S6 process monitoring and adjustment steps are as follows: For each batch of production, 3-5 samples are selected to test the depth of the hardened layer, the core structure and hardness. If the cracking rate exceeds the standard, the parameters are adjusted immediately. If cracking occurs: prioritize reducing the stirring frequency (±3Hz) or increasing the outlet water temperature (±15℃); if quenching is insufficient, appropriately increase the quenching temperature (±10℃) or decrease the outlet water temperature (±10℃). The correlation between media usage status, quenching parameters and cracking rate is statistically analyzed monthly, and a parameter optimization database is established.

[0014] (III) Beneficial Effects Compared with the prior art, the present invention provides a process for matching the quenching medium and outlet water temperature to avoid secondary tempering cracking in medium carbon alloy steel CrMo series steel, which has the following beneficial effects: 1. This process avoids secondary tempering cracking in medium-carbon alloy steel CrMo series steel by matching the quenching medium and the outlet water temperature. This process achieves a precise balance between hardenability and crack resistance: by adapting the quenching medium to the workpiece structure (rod diameter) with 5%-10% PAG quenching fluid and 2%-5% brine, and matching the stirring frequency of 15-28Hz and the graded outlet water temperature of 160-240℃, it ensures that the hardened layer depth is stable at ≥10mm, and controls the scrap rate of secondary tempering cracking to ≤1.0%, thus solving the core pain point of the existing process of "cracking when hardened and insufficient hardenability when cracking is prevented".

[0015] 2. This process, which avoids secondary tempering cracking in medium carbon alloy steel CrMo series steel, uses a matching quenching medium and outlet water temperature to improve performance stability: preheating at 860-890℃ eliminates forging residual stress, followed by graded heating and precise holding at 830-880℃, and tempering at 620-660℃. This ensures that key end-quenching indicators are stabilized at J15: 45-57HRC and J30: 37-48HRC, with a core microstructure rating of ≤4 and minimal hardness fluctuation, meeting the performance consistency requirements of critical components.

[0016] 3. This process avoids secondary tempering cracking of medium-carbon alloy steel CrMo series steel by matching the quenching medium with the outlet water temperature. This process reduces process risks and costs: medium pretreatment (ultrasonic stirring, filtration and impurity removal) and real-time temperature monitoring (infrared temperature measurement deviation ≤ ±5℃) reduce batch quality problems caused by uneven medium and temperature runaway; the graded and adaptable process design does not require additional equipment and can be directly connected to existing production lines, reducing modification and operating costs.

[0017] 4. This process avoids secondary tempering cracking in medium-carbon alloy steel CrMo series steel by matching the quenching medium with the outlet water temperature. This process enhances process adaptability and controllability: differentiated solutions are designed for different scenarios such as complex structures, simple structures, and high crack resistance requirements. Combined with the dynamic adjustment mechanism of "adjusting stirring / outlet water temperature for cracking and adjusting heating temperature for insufficient quenching", it can flexibly adapt to the production of workpieces of different specifications. Furthermore, monthly parameter statistics and database establishment further improve process stability and replicability. 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 process for matching the quenching medium and outlet water temperature to avoid secondary tempering cracking in medium-carbon alloy steel CrMo series steel, comprising the following steps: S1 Quenching medium selection and proportioning steps: S101 Media Type Adaptation: Select the appropriate medium based on the complexity and size of the workpiece structure, prioritizing systems with low cracking risk: For complex structural workpieces (rod diameter ≥ 80mm): use 5%-10% PAG polymer quenching fluid (material base range 5%-8% optimized and expanded), which has both cooling uniformity and slow cooling characteristics, reducing stress concentration; For simple structural workpieces (rod diameter < 80mm): use 2%-5% brine quenching fluid (optimized concentration range of the material's basic brine system) to improve the cooling rate and ensure hardenability. Precise outlet water temperature control is required. For workpieces requiring high crack resistance: use 10%-15% oil-based quenching medium with a slow cooling rate, suitable for workpieces with residual stress accumulation during secondary tempering; S102 Media Pretreatment: Newly prepared media should be ultrasonically stirred for 20-30 minutes (5 minutes for basic materials, with optimization extension) to ensure uniform composition and no sedimentation or stratification. The medium must be filtered to remove impurities before use. The filter screen pore size should be ≤50μm to avoid impurities affecting the uniformity of cooling. Maintain the pH of the medium between 7.5 and 9.0, replenish with fresh medium regularly, and keep the concentration fluctuation ≤ ±1%; S2 workpiece pretreatment steps: Before the second heat treatment, the workpiece is preheated: the temperature is 860-890℃ (870℃ is the optimized range based on the material), and the holding time is 40-80min, which is adjusted according to the maximum cross-sectional size of the workpiece (increase by 10min for every 10mm) to eliminate forging residual stress. After preheating, the furnace is cooled to 300-350℃ before being removed and air-cooled to reduce the temperature difference stress with the quenching medium. Clean the workpiece surface of oxide scale, oil stains and defects to prevent crack initiation; Steps for matching S3 quenching temperature and holding time: S301 quenching heating temperature: 830-880℃ (material base 840-875℃ optimized and expanded), take the lower limit (830-850℃) for complex structure workpieces, and take the upper limit (850-880℃) for simple structure workpieces. S302 heat preservation time: calculated based on the effective thickness of the workpiece, 30 minutes of heat preservation for every 20mm, with a minimum of 30 minutes and a maximum of 90 minutes (30-60 minutes for the basic material, optimized and expanded) to ensure complete austenitization of the core; S303 heating rate control: ≤150℃ / h, to avoid excessively rapid heating and thermal stress concentration; Steps for matching S4 quenching medium parameters with outlet water temperature: S401 Media Dynamic Parameter Control: Stirring frequency: 15-28Hz (material base 18-26Hz optimized and expanded), 15-22Hz for complex structure workpieces, 22-28Hz for simple structure workpieces, and adjust cooling uniformity by frequency conversion stirring. Medium temperature: Maintain at 15-40℃ (the range is not clearly defined by the material basis and needs to be supplemented and optimized), PAG medium control at 20-35℃, brine medium control at 15-30℃, to avoid excessive temperature and reduced cooling efficiency; S402 provides precise control of outlet water temperature: 5%-10% PAG medium: For rods with a diameter ≤100mm: outlet water temperature 160-190℃ (material base 180-200℃ optimized and expanded), heat preservation time 10-15min followed by tempering; For rod diameter > 100mm: outlet water temperature 190-220℃, heat preservation time 15-20min, to release residual stress in the core; 2%-5% brine medium: The outlet water temperature is 180-230℃ (the material base temperature is 180-200℃, which is optimized and expanded). After the water comes out, the workpiece should be wrapped with heat insulation cotton immediately to slow down the cooling rate. 10%-15% oily media: The water temperature is 200-240℃, and no additional insulation is required. It can be directly transferred to the tempering process. Water discharge timing judgment: The surface temperature of the workpiece is monitored in real time by an infrared thermometer, with a deviation of ≤±5℃, to avoid temperature runaway caused by relying on experience judgment; S5 subsequent tempering process steps: S501 tempering temperature: 620-660℃ (material base 630-655℃ optimized and expanded), adjusted according to end quenching requirements. When J30 needs ≥40HRC, take the lower limit; when it needs to reduce hardness, take the upper limit. S502 tempering holding time: 90-180min (120-160min for basic materials, optimized and expanded), to ensure full stress release. After holding, cool with the furnace to below 200℃ and then air cool. After tempering, the workpiece is straightened, and the straightening force is controlled at 30%-40% of the material's yield strength to avoid cracking caused by hard straightening. S6 Process Monitoring and Adjustment Steps: For each batch of production, 3-5 samples are selected to test the depth of the hardened layer, the core structure and hardness. If the cracking rate exceeds the standard, the parameters are adjusted immediately. If cracking occurs: prioritize reducing the stirring frequency (±3Hz) or increasing the outlet water temperature (±15℃); if quenching is insufficient, appropriately increase the quenching temperature (±10℃) or decrease the outlet water temperature (±10℃). Monthly statistics are compiled on the correlation between media usage status, quenching parameters, and cracking rate to establish a parameter optimization database; Process objectives: By selecting quenching media, optimizing parameters, and precisely matching the outlet water temperature, the scrap rate of secondary tempering cracking is controlled to ≤1.0%, ensuring that the quenching depth is ≥10mm, the key end quenching indicators are stable at J15: 45-57HRC, J30: 37-48HRC, and the core structure rating is ≤4, taking into account both hardenability and crack resistance. Furthermore, this process achieves a precise balance between hardenability and crack resistance: by adapting 5%-10% PAG quenching fluid and 2%-5% brine to differentiated media according to the workpiece structure (rod diameter), and matching a stirring frequency of 15-28Hz and a graded water outlet temperature of 160-240℃, it ensures that the hardened layer depth is stable at ≥10mm, while controlling the secondary tempering cracking scrap rate to ≤1.0%, thus solving the core pain point of the existing process of "cracking when hardened and insufficient hardenability when cracking is not possible"; Furthermore, this process improves performance stability: preheating at 860-890℃ eliminates forging residual stress, graded heating and precise holding at 830-880℃, combined with tempering at 620-660℃, stabilizes key end-quenching indicators at J15: 45-57HRC and J30: 37-48HRC, core microstructure rating ≤ 4, and hardness fluctuation is small, meeting the performance consistency requirements of key components; Furthermore, this process reduces process risks and costs: media pretreatment (ultrasonic stirring, filtration and impurity removal) and real-time temperature monitoring (infrared temperature measurement deviation ≤ ±5℃) reduce batch quality problems caused by media inhomogeneity and temperature runaway; the graded and adaptable process design does not require additional equipment and can be directly connected to existing production lines, reducing modification and operating costs. Furthermore, this process enhances process adaptability and controllability: differentiated solutions are designed for different scenarios such as complex structures, simple structures, and high crack resistance requirements. Combined with a dynamic adjustment mechanism of "adjusting stirring / water outlet temperature when cracking occurs and adjusting heating temperature when quenching is insufficient", it can flexibly adapt to the production of workpieces of different specifications. In addition, monthly parameter statistics and database establishment further improve process stability and replicability.

[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 process for matching quenching medium and outlet water temperature to avoid secondary tempering cracking in medium carbon alloy steel CrMo series steel, comprising the steps of S1 quenching medium selection and proportioning, S2 workpiece pretreatment, S3 matching quenching temperature and holding time, S4 matching quenching medium parameters and outlet water temperature, S5 subsequent tempering process, and S6 process monitoring and adjustment, characterized in that: The S1 quenching medium selection and proportioning steps include S101 medium type adaptation and S102 medium pretreatment; Among them, the S3 quenching temperature and holding time matching step includes S301 quenching heating temperature, S302 holding time and S303 heating rate control. Among them, the S4 quenching medium parameter matching and water outlet temperature matching steps include S401 medium dynamic parameter control and S402 precise water outlet temperature control. The subsequent tempering process steps of S5 include tempering temperature of S501 and tempering holding time of S502.

2. The quenching medium and outlet water temperature matching process for avoiding secondary tempering cracking of medium carbon alloy steel CrMo series steel according to claim 1, characterized in that: The S101 media type adaptation: Select the appropriate medium based on the complexity and size of the workpiece structure, prioritizing systems with low cracking risk: For complex structural workpieces (rod diameter ≥ 80mm): use 5%-10% PAG polymer quenching fluid (material base range 5%-8% optimized and expanded), which has both cooling uniformity and slow cooling characteristics, reducing stress concentration; For simple structural workpieces (rod diameter < 80mm): use 2%-5% brine quenching fluid (optimized concentration range of the material's basic brine system) to improve the cooling rate and ensure hardenability. Precise outlet water temperature control is required. For workpieces requiring high crack resistance: use 10%-15% oil-based quenching medium with a slow cooling rate, suitable for workpieces with residual stress accumulation during secondary tempering.

3. The quenching medium and outlet water temperature matching process for avoiding secondary tempering cracking of medium carbon alloy steel CrMo series steel according to claim 1, characterized in that: The S102 media pretreatment: Newly prepared media should be ultrasonically stirred for 20-30 minutes (5 minutes for basic materials, with optimization extension) to ensure uniform composition and no sedimentation or stratification. The medium must be filtered to remove impurities before use. The filter screen pore size should be ≤50μm to avoid impurities affecting the uniformity of cooling. Maintain the pH of the medium between 7.5 and 9.0, replenish the medium regularly, and keep the concentration fluctuation ≤ ±1%.

4. The quenching medium and outlet water temperature matching process for avoiding secondary tempering cracking of medium carbon alloy steel CrMo series steel according to claim 1, characterized in that: The S2 workpiece pretreatment step: Before the second heat treatment, the workpiece is preheated: the temperature is 860-890℃ (870℃ is the optimized range based on the material), and the holding time is 40-80min, which is adjusted according to the maximum cross-sectional size of the workpiece (increase by 10min for every 10mm) to eliminate forging residual stress. After preheating, the furnace is cooled to 300-350℃ before being removed and air-cooled to reduce the temperature difference stress with the quenching medium. Clean the workpiece surface of oxide scale, oil stains and defects to prevent crack initiation.

5. The quenching medium and outlet water temperature matching process for avoiding secondary tempering cracking of medium carbon alloy steel CrMo series steel according to claim 1, characterized in that: The S301 quenching heating temperature is 830-880℃ (840-875℃ is the basic material temperature, which is optimized and expanded). For complex structure workpieces, the lower limit (830-850℃) is used, and for simple structure workpieces, the upper limit (850-880℃) is used. S302 heat preservation time: calculated based on the effective thickness of the workpiece, 30 minutes of heat preservation for every 20mm, with a minimum of 30 minutes and a maximum of 90 minutes (30-60 minutes for the basic material, optimized and expanded) to ensure complete austenitization of the core; S303 heating rate control: ≤150℃ / h, to avoid excessively rapid heating leading to thermal stress concentration.

6. The quenching medium and outlet water temperature matching process for avoiding secondary tempering cracking of medium carbon alloy steel CrMo series steel according to claim 1, characterized in that: The S401 medium dynamic parameter control: Stirring frequency: 15-28Hz (material base 18-26Hz optimized and expanded), 15-22Hz for complex structure workpieces, 22-28Hz for simple structure workpieces, and adjust cooling uniformity by frequency conversion stirring. Medium temperature: Maintain at 15-40℃ (the range is not clearly defined based on the material, so further optimization is needed). For PAG medium, control at 20-35℃, and for brine medium, control at 15-30℃ to avoid excessively high temperatures that could reduce cooling efficiency.

7. The quenching medium and outlet water temperature matching process for avoiding secondary tempering cracking of medium carbon alloy steel CrMo series steel according to claim 1, characterized in that: The S402 outlet water temperature is precisely controlled: 5%-10% PAG medium: For rods with a diameter ≤100mm: outlet water temperature 160-190℃ (material base 180-200℃ optimized and expanded), heat preservation time 10-15min followed by tempering; For rod diameter > 100mm: outlet water temperature 190-220℃, heat preservation time 15-20min, to release residual stress in the core; 2%-5% brine medium: The outlet water temperature is 180-230℃ (the material base temperature is 180-200℃, which is optimized and expanded). After the water comes out, the workpiece should be wrapped with heat insulation cotton immediately to slow down the cooling rate. 10%-15% oily media: The water temperature is 200-240℃, and no additional insulation is required. It can be directly transferred to the tempering process. Water discharge timing judgment: The surface temperature of the workpiece is monitored in real time by an infrared thermometer with a deviation of ≤±5℃, avoiding temperature runaway caused by relying on experience.

8. The quenching medium and outlet water temperature matching process for avoiding secondary tempering cracking of medium carbon alloy steel CrMo series steel according to claim 1, characterized in that: The S501 tempering temperature is 620-660℃ (630-655℃ is the basic material temperature range, which is optimized and expanded). The temperature is adjusted according to the end quenching requirements. When J30 needs to be ≥40HRC, the lower limit is taken; when the hardness needs to be reduced, the upper limit is taken.

9. The quenching medium and outlet water temperature matching process for avoiding secondary tempering cracking of medium carbon alloy steel CrMo series steel according to claim 1, characterized in that: The S502 tempering and holding time is 90-180 min (120-160 min for basic materials, optimized and expanded) to ensure full stress release. After holding, it is cooled with the furnace to below 200℃ and then air-cooled. After tempering, the workpiece is straightened, and the straightening force is controlled at 30%-40% of the material's yield strength to avoid cracking caused by hard straightening.

10. The quenching medium and outlet water temperature matching process for avoiding secondary tempering cracking of medium carbon alloy steel CrMo series steel according to claim 1, characterized in that: The S6 process monitoring and adjustment steps are as follows: For each batch of production, 3-5 samples are selected to test the depth of the hardened layer, the core structure and hardness. If the cracking rate exceeds the standard, the parameters are adjusted immediately. If cracking occurs: prioritize reducing the stirring frequency (±3Hz) or increasing the outlet water temperature (±15℃); if quenching is insufficient, appropriately increase the quenching temperature (±10℃) or decrease the outlet water temperature (±10℃). The correlation between media usage status, quenching parameters and cracking rate is statistically analyzed monthly, and a parameter optimization database is established.