A tempering heat treatment process for 42CrMo1 steel based on end-quenching value control

Abstract

This invention relates to the field of heat treatment methods and discloses a quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control. The process includes steps 1: pre-quenching and tempering preparation (related end-quenching value preset), 2: quenching treatment (core end-quenching value control step), 3: tempering treatment (stress relief and microstructure stabilization), 4: post-quenching and tempering quality verification (related end-quenching value feedback), and 5: finished product identification and archiving. This process achieves a balance between hardenability and quenching cracking risk, reducing the scrap rate through "precise control of Ti element + synergistic optimization of main alloy composition." It avoids excessive hardenability caused by excessive main alloy composition and refines grains and improves hardenability through Ti element, reducing the quenching cracking rate from 16.8% to below 3%. Out of 925 steering knuckles, only 30 were scrapped due to quenching cracking (cracking rate 3.25%). Furthermore, by reducing the stirring frequency (from 20Hz to 18Hz), the cracking rate in subsequent batches was further reduced to around 1%, completely solving the problem of "hardenability versus cracking." The core contradiction.

Description

Technical Field

[0001] This invention relates to the field of heat treatment methods, specifically to a quenching and tempering heat treatment process for 42CrMo1 steel based on end-quench value control. Background Technology

[0002] As a key forging material bearing heavy loads, the quality of 42CrMo1 steel's quenching and tempering heat treatment (hardenability and microstructure uniformity) directly determines the mechanical properties of the parts. If the hardenability is insufficient, a mixed ferrite and bainite microstructure will appear in the 10mm position of the part's rod (rated above level 5), reducing the load-bearing capacity. If the process is blindly adjusted to improve hardenability (such as excessively high quenching temperature or excessively fast cooling rate), it will cause quenching cracks (184 out of 1094 parts in a certain batch were scrapped after secondary quenching, with a scrap rate of 16.8%).

[0003] Before this process optimization, the quenching and tempering heat treatment of 42CrMo1 steel had the following core technical pain points, resulting in large quality fluctuations: The end quenching value is disconnected from the process parameters: no correlation mechanism has been established between the end quenching value (J15, J30) and the quenching parameters. For example, when the end quenching J30 is only 38HRC, the conventional quenching temperature of 845℃ is still used, resulting in a hardened layer of only 6-7mm (10mm is required); in some furnaces, J30 reaches 44HRC but the cooling intensity is not reduced, which causes edge cracking.

[0004] There is no standardized range for quenching parameters: parameters such as quenching heating rate, holding time, and cooling stirring frequency are adjusted according to the operator's experience. For example, some batches have a heating rate of 150℃ / h (leading to thermal stress concentration), some batches have a holding time of only 120 minutes (not fully austenitized), and the cooling stirring frequency is fixed at 22HZ (not adjusted according to the part size). The quenching layer deviation of parts in the same batch can reach 3-4mm.

[0005] Poor matching of tempering process: The tempering temperature and holding time were not dynamically adjusted according to the hardness after quenching. For example, when the hardness after quenching is 52HRC, tempering at 630℃ is still used, resulting in a hardness of only 26HRC after tempering (the required hardness is 28-32HRC); some batches are only tempered for 120 minutes (stress relief is incomplete), and the parts are deformed in subsequent processing.

[0006] The quality verification process lacked specificity: quality was judged only by surface hardness testing, without verifying the metallographic structure and end-quench values ​​at a depth of 10mm. This resulted in some parts that were "qualified on the surface but insufficiently hardened in the core" flowing downstream and cracking during cold heading. Summary of the Invention

[0007] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a quenching and tempering heat treatment process for 42CrMo1 steel based on end-quench value control. This process has advantages such as balancing hardenability and the risk of quenching cracking, and reducing scrap rate, thus solving the problem of quenching cracking.

[0008] (II) Technical Solution To achieve the above-mentioned balance between hardenability and quenching crack risk, and to reduce the scrap rate, this invention provides the following technical solution: a quenching and tempering heat treatment process for 42CrMo1 steel based on end-quench value control, including step 1: pre-quenching and tempering preparation (related end-quench value preset), step 2: quenching treatment (core end-quench value control link), step 3: tempering treatment (stress relief and microstructure stabilization), step 4: post-quenching and tempering quality verification (related end-quench value feedback), and step 5: finished product identification and archiving. Step 1: pre-quenching and tempering preparation (related end-quench value preset) includes step 1.1 raw material end-quench value verification and step 1.2 part pretreatment and marking. Step 2: Quenching treatment (core end quenching value control) includes step 2.1 segmented heating control (reducing thermal stress), step 2.2 austenitizing and holding, and step 2.3 staged cooling (balancing hardenability and cracking risk). Step 3: Tempering treatment (stress relief and microstructure stabilization) includes step 3.1 tempering temperature matching and step 3.2 tempering holding and cooling; Step 4: Quality verification after tempering (associated end quenching value feedback) includes Step 4.1 Hardness test (preliminary judgment of hardenability), Step 4.2 Metallographic structure analysis (accurate determination of hardenable layer) and Step 4.3 Anomaly handling and recording.

[0009] Preferably, step 1.1 involves verifying the quenching value at the raw material end; Operation procedure: Select 3-5 forgings from each batch, cut end-quenched samples (25-30mm in diameter, 70-130mm in length) from non-critical parts, and conduct end-quenching tests according to GB / T 225 standard to verify whether the end-quenching value of the raw material matches the process requirements. Key parameters: End-quenched J15 hardness 45-57 HRC, J30 hardness 36-47 HRC; if J30 < 36 HRC, mark as "requires enhanced quenching"; if J30 > 47 HRC, mark as "requires weakened cooling". Judgment criteria: Raw materials with end-quenching values ​​outside the range need to have their process parameters formulated separately (if J30 is low, increase the quenching temperature by 5-10℃) and should not be mixed with qualified raw materials for tempering; Step 1.2 Part pretreatment and marking; Operation procedure: Remove oxide scale from the surface of the forging by sandblasting and pickling (pickling time 5-10 minutes, extended from the original 6-9 minutes), visually inspect the surface for cracks and scratches; mark inspection points (10mm from the surface) on key locations on the rod and disc of the part with a marker pen. Key parameters: surface roughness Ra≤1.6μm after pickling, marking point spacing 20-30mm, avoid marking at stress concentration points.

[0010] Preferably, step 2.1 involves segmented temperature control (to reduce thermal stress). Operation procedure: Load the pretreated parts into the quenching furnace and use a "two-stage heating" method: the first stage is to heat from room temperature to 500-550℃ (preheating stage), and the second stage is to heat from 500-550℃ to the target quenching temperature to avoid excessive temperature difference between the inside and outside of the parts, which may cause cracks. Key parameters: Preheating rate: 80-120℃ / h; hold for 30-60 minutes. The quenching heating rate is 50-80℃ / h, and the target quenching temperature is 835-860℃. When J30 < 38HRC, take 845-860℃, and when J30 > 43HRC, take 835-850℃.

[0011] Preferably, step 2.2 involves austenitizing and heat preservation. Operation procedure: After the part is heated to the target temperature, it is kept at a constant temperature to ensure sufficient austenitization. The holding time is calculated based on the maximum thickness of the part (40-60 minutes for every 20mm of thickness). Key parameters: Total holding time 120-180 minutes, furnace temperature recorded every 20 minutes, holding time paused and adjustment made if deviation exceeds ±5℃; the furnace atmosphere during holding time is weakly oxidizing (to avoid decarburization), and the decarburized layer thickness is ≤0.02mm.

[0012] Preferably, step 2.3 involves graded cooling (balancing hardenability and cracking risk). Operation procedure: After the heat preservation is completed, the parts are quickly transferred to the quenching tank (transfer time ≤ 10 seconds). The cooling intensity is adjusted according to the end quenching value: if J30 is low, the cooling is strengthened; if J30 is high, the cooling is weakened. Key parameters: Cooling medium temperature 18-28℃, stirring frequency 20-28HZ (24-28HZ when J30 < 38HRC, 20-24HZ when J30 > 43HRC); Remove from the water when cooled to 80-120℃. Avoid prolonged low-temperature contact (≤5 minutes) to prevent incomplete martensite transformation.

[0013] Preferably, step 3.1 involves tempering and temperature matching; Operation procedure: Immediately load the quenched parts into the tempering furnace (interval ≤ 2 hours to avoid quenching stress accumulation), and raise the temperature to the target tempering temperature according to the principle of "slow heating", with a heating rate of 60-100℃ / h; Key parameters: Target tempering temperature 620-660℃ — 640-660℃ when the hardness after quenching is 50-55HRC, and 620-640℃ when the hardness is 48-50HRC.

[0014] Preferably, step 3.2 involves tempering, heat preservation, and cooling; Operation procedure: After the parts are heated to the tempering temperature, they are kept at a constant temperature to ensure that the internal stress is fully released; after the holding period, the cooling method (water cooling or air cooling) is selected according to the performance requirements of the parts. Key parameters: The holding time is 140-180 minutes, and the furnace temperature is recorded every 30 minutes, with a deviation of ≤±3℃; Water cooling is used when high toughness is required (cooling time to room temperature ≤ 1 hour), and air cooling is used when high stability is required (cooling time to room temperature ≤ 4 hours).

[0015] Preferably, step 4.1 is hardness testing (preliminary assessment of hardenability). Operation procedure: Use a Rockwell hardness tester to test the hardness at the marked points on the part (5mm and 10mm from the surface), test each point 2-3 times and take the average value; at the same time, test the hardness of the end-quenched sample after tempering to verify the matching of process parameters. Key parameters: target hardness 27-33 HRC, hardness deviation at 10mm from surface hardness ≤3 HRC; tempering and post-quenching J30 38-45 HRC (consistent with process target).

[0016] Preferably, step 4.2 is metallographic analysis (accurately determining the hardened layer). Procedure: Take a metallographic sample (5-8mm thick, based on the original 5-8mm) from a part with qualified hardness. After coarse grinding, fine grinding, and polishing, etch it with 2.5-3.5% nitric acid alcohol solution for 5-8 minutes. Observe the structure at 10mm under a 500X microscope. Key parameters: The microstructure at 10mm is tempered sorbite + a small amount of ferrite (ferrite content ≤5%), with a metallographic rating of 3-5; the hardened layer depth is ≥9-12mm, with no bainite microstructure; Step 4.3 Exception handling and logging; Operating procedures: If the hardness is out of tolerance (<27HRC and >33HRC), re-tempering is required (temperature adjustment ±10℃); if the hardened layer is less than 9mm, the end-quench value and quenching parameters must be analyzed for compatibility (if J30 is low, increase the holding time by 10-20 minutes next time). Key parameters: number of re-tempering times ≤ 2 (to avoid grain coarsening), and the abnormal handling record should be linked to the raw material end quenching value and quenching / tempering parameters for easy traceability later.

[0017] Preferably, step 5: finished product identification and archiving; Operational procedures: Mark qualified tempered parts (label furnace number, batch, tempering date, and test results), and store them by category; organize and archive end quenching reports, hardness test records, and metallographic reports, and retain them for ≥3 years; Key parameters: Clear and identifiable markings (resistant to erasure), archived records must include a table showing the correspondence between "end quench value - quenching temperature - tempering hardness" to provide data support for subsequent process optimization.

[0018] (III) Beneficial Effects Compared with the prior art, the present invention provides a quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control, which has the following beneficial effects: 1. This heat treatment process for 42CrMo1 steel based on end-quench value control achieves a balance between hardenability and quenching crack risk, reducing the scrap rate. Through "precise Ti element control + synergistic optimization of main alloy composition" (Ti content controlled at 0.005-0.013%, C 0.39-0.42%, Cr 1.08-1.18%, Mo 0.18-0.23%), it avoids excessive hardenability caused by excessive main alloy content, while refining grain size and improving hardenability through Ti element control. The hardened layer depth compliance rate increased from 75% to 98%: the hardened layer after tempering reached 12-13mm, meeting the requirements of key components; The quenching cracking rate was reduced from 16.8% to below 3%: only 30 out of 925 steering knuckles were scrapped due to quenching cracking (cracking rate 3.25%). Furthermore, by reducing the stirring frequency (from 20Hz to 18Hz), the cracking rate of subsequent batches was further reduced to about 1%, completely resolving the core contradiction between "quenching through and cracking".

[0019] 2. This heat treatment process for 42CrMo1 steel based on end-quench value control improves compositional segregation and enhances the uniformity of molten steel. Through a process of "dynamic matching of continuous casting parameters + RH vacuum treatment strengthening" (crystallizer EMS current 80-220A, end-F-EMS current 150-300A, RH vacuum degree ≤67Pa, holding pressure 15-25min), segregation is significantly improved. The carbon segregation index was controlled between 0.95 and 1.05: the carbon segregation index of the center of the furnace billet was 0.9713, and the statistical segregation degree was 0.034, which is better than the same steel grades in Xining (0.046) and Daye (0.038); Element uniformity improved by 40%: Ti element segregation decreased from 0.004% to ≤0.003%, Cr and Mo element fluctuation range ≤±0.03%, and the hardness deviation between the rod and the disk of the same part at 10mm decreased from 5HRC to 2HRC, avoiding extreme cases of "insufficient local hardening and local cracking".

[0020] 3. This quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control achieves stable end-quenching values, ensuring consistent quenching and tempering quality. It utilizes an "end-quenching value-heat treatment parameter linkage" mechanism (quenching temperature 845-860℃ and stirring frequency 24-28HZ for J30 < 38HRC; quenching temperature 835-850℃ and stirring frequency 20-24HZ for J30 > 43HRC), combined with a "batch-by-batch end-quenching verification" process. The end-quenching value qualification rate increased from 80% to 95%; the hardness of J30 steel produced in more than 20 heats was stable at 37-46HRC, with a fluctuation range of ≤±2HRC. Significantly improved consistency in heat treatment quality: The deviation in the depth of the hardened layer of parts in the same batch was reduced from 3-4mm to 1-2mm. For 700 steering knuckles of 130mm specification steel produced by furnace 25803470, the hardened layer reached 10-11mm, and no part was reworked due to insufficient hardening, thus completely solving the problem of unstable quality caused by fluctuations in end quenching value.

[0021] 4. This 42CrMo1 steel quenching and tempering heat treatment process based on end-quenching value control establishes full-process process assurance and achieves quality traceability. It utilizes three major assurance mechanisms: "precise Ti element calculation + MES real-time monitoring + anomaly closed-loop management" (Ti addition amount = (target Ti - initial Ti) × steel quantity / (Ti iron purity × 85%-95% recovery rate), MES generates parameter reports every 10 minutes, and automatically alarms in case of anomalies). Process parameter fluctuation rate reduced by 70%: Ti element addition deviation reduced from ±0.003% to ±0.002%, LF furnace refining temperature fluctuation ≤±5℃; Quality traceability efficiency improved by 80%: The end-quenching report, smelting parameters, and tempering records of each batch of steel are linked to the furnace number. If problems occur later, the root cause can be located within 1 hour. The rectification cycle for similar problems is shortened from 7 days to 2 days, realizing "problems are traceable and rectification can be implemented".

[0022] 5. This quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control is adaptable to multiple parts specifications, expanding the process's applicability. It utilizes a "specification-process parameter matching" model (quenching temperature 840-850℃, stirring frequency 18-22HZ for 110-120mm steel; quenching temperature 835-845℃, stirring frequency 22-24HZ for 130-140mm steel): The hardening penetration rate of various specifications of parts is ≥95%: the hardening penetration of the 110mm specification A458 steering knuckle (25803465 furnace) reaches 9-10mm, and the hardening penetration of the 140mm specification A107 steering knuckle reaches 12-13mm. Parts of different specifications meet the usage requirements. Process adaptability expansion: It can cover steel with a specification of Φ100-150mm, and by adjusting the quenching temperature (835-860℃) and tempering temperature (620-660℃), it can be adapted to different types of forgings such as steering knuckles and ball joints, without the need to develop separate processes for a single specification, thus reducing production complexity. Detailed Implementation

[0023] 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.

[0024] This invention provides a technical solution, specifically, a quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control. The prerequisites for this process are: Before implementing this process, ensure that all of the following basic conditions are met to avoid process deviations due to missing initial conditions: Raw material requirements: The 42CrMo1 steel forgings to be quenched and tempered must meet the preset range of end quenching values ​​(J15 45-57HRC, J30 36-47HRC), and the surface must be free of scabs and initial folding defects. The dimensional deviation of the parts must be ≤±0.5mm (rod diameter 60-85mm). Equipment status requirements: Quenching furnace: Temperature control accuracy ±5℃, adjustable heating rate range 50-150℃ / h, internal temperature difference ≤8℃; Quenching tank: Temperature control range 18-28℃ (expanded from the original 20-25℃), stirring frequency adjustable 20-28HZ, cooling medium (PAG aqueous solution) concentration 5-8%; Tempering furnace: Temperature control accuracy ±3℃, holding time error ≤±10 minutes; Testing equipment: Rockwell hardness tester with an accuracy of ±0.5HRC, metallographic microscope with a magnification of 50-500X, and end-quenching tester conforming to GB / T 225 standard; Personnel qualification requirements: Operators must be certified and familiar with the end-quench value judgment standard (J15 / J30 hardness range) and the quenching-tempering parameter adjustment logic; Inspection personnel must master the metallographic structure rating method at a depth of 10mm (GB / T 13320). Auxiliary material requirements: The metallographic etching agent should be a 2.5-3.5% nitric acid alcohol solution; the hardness test standard block should have an accuracy of ±0.3 HRC; and the concentration of the cooling medium should be checked periodically (once a week). A quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control includes the following process steps: Step 1: Preparation before quenching and tempering (related to the preset end-quenching value). Step 1.1 Verification of raw material end-quenching values; Operation procedure: Select 3-5 forgings from each batch, cut end-quenched samples (25-30mm in diameter, 70-130mm in length) from non-critical parts, and conduct end-quenching tests according to GB / T 225 standard to verify whether the end-quenching value of the raw material matches the process requirements. Key parameters: End-quenched J15 hardness 45-57 HRC, J30 hardness 36-47 HRC; if J30 < 36 HRC, mark as "requires enhanced quenching"; if J30 > 47 HRC, mark as "requires weakened cooling". Judgment criteria: Raw materials with end-quenching values ​​outside the range need to have their process parameters formulated separately (if J30 is low, increase the quenching temperature by 5-10℃) and should not be mixed with qualified raw materials for tempering; Step 1.2 Part pretreatment and marking; Operation procedure: Remove oxide scale from the surface of the forging by sandblasting and pickling (pickling time 5-10 minutes, extended from the original 6-9 minutes), visually inspect the surface for cracks and scratches; mark inspection points (10mm from the surface) on key locations on the rod and disc of the part with a marker pen. Key parameters: Surface roughness Ra ≤ 1.6μm after pickling; Marking point spacing 20-30mm; Avoid marking at stress concentration points. Step 2: Quenching treatment (core end quenching value control step); Step 2.1 Segmented temperature control (to reduce thermal stress); Operation procedure: Load the pretreated parts into the quenching furnace and use a "two-stage heating" method: the first stage is to heat from room temperature to 500-550℃ (preheating stage), and the second stage is to heat from 500-550℃ to the target quenching temperature to avoid excessive temperature difference between the inside and outside of the parts, which may cause cracks. Key parameters: Preheating rate: 80-120℃ / h; hold for 30-60 minutes. Quenching heating rate is 50-80℃ / h, target quenching temperature is 835-860℃—845-860℃ is taken when J30 < 38HRC, and 835-850℃ is taken when J30 > 43HRC; Step 2.2 Austenitizing insulation; Operation procedure: After the part is heated to the target temperature, it is kept at a constant temperature to ensure sufficient austenitization. The holding time is calculated based on the maximum thickness of the part (40-60 minutes for every 20mm of thickness). Key parameters: Total holding time 120-180 minutes, furnace temperature recorded every 20 minutes, holding time paused and adjustment made if deviation exceeds ±5℃; the furnace atmosphere during holding time is weakly oxidizing (to avoid decarburization), and the decarburized layer thickness ≤0.02mm; Step 2.3 Staged cooling (balancing hardenability and cracking risk); Operation procedure: After the heat preservation is completed, the parts are quickly transferred to the quenching tank (transfer time ≤ 10 seconds). The cooling intensity is adjusted according to the end quenching value: if J30 is low, the cooling is strengthened; if J30 is high, the cooling is weakened. Key parameters: Cooling medium temperature 18-28℃, stirring frequency 20-28HZ (24-28HZ when J30 < 38HRC, 20-24HZ when J30 > 43HRC); Remove from the water when cooled to 80-120℃, avoiding prolonged low-temperature contact (≤5 minutes) to prevent incomplete martensite transformation; Step 3: Tempering treatment (to relieve stress and stabilize the microstructure); Step 3.1 Tempering and temperature matching; Operation procedure: Immediately load the quenched parts into the tempering furnace (interval ≤ 2 hours to avoid quenching stress accumulation), and raise the temperature to the target tempering temperature according to the principle of "slow heating", with a heating rate of 60-100℃ / h; Key parameters: Target tempering temperature 620-660℃ — 640-660℃ when the hardness after quenching is 50-55HRC, and 620-640℃ when the hardness is 48-50HRC; Step 3.2 Tempering, heat preservation, and cooling; Operation procedure: After the parts are heated to the tempering temperature, they are kept at a constant temperature to ensure that the internal stress is fully released; after the holding period, the cooling method (water cooling or air cooling) is selected according to the performance requirements of the parts. Key parameters: The holding time is 140-180 minutes, and the furnace temperature is recorded every 30 minutes, with a deviation of ≤±3℃; Water cooling is used when high toughness is required (cooling time to room temperature ≤ 1 hour), and air cooling is used when high stability is required (cooling time to room temperature ≤ 4 hours). Step 4: Quality verification after heat treatment (feedback of quenching value at associated end). Step 4.1 Hardness test (preliminary assessment of hardenability); Operation procedure: Use a Rockwell hardness tester to test the hardness at the marked points on the part (5mm and 10mm from the surface), test each point 2-3 times and take the average value; at the same time, test the hardness of the end-quenched sample after tempering to verify the matching of process parameters. Key parameters: Target hardness 27-33 HRC, hardness deviation at 10mm from surface hardness ≤3 HRC; tempering and post-quenching J30 38-45 HRC (consistent with process target); Step 4.2 Metallographic analysis (accurately determining the hardened layer); Procedure: Take a metallographic sample (5-8mm thick, based on the original 5-8mm) from a part with qualified hardness. After coarse grinding, fine grinding, and polishing, etch it with 2.5-3.5% nitric acid alcohol solution for 5-8 minutes. Observe the structure at 10mm under a 500X microscope. Key parameters: The microstructure at 10mm is tempered sorbite + a small amount of ferrite (ferrite content ≤5%), with a metallographic rating of 3-5; the hardened layer depth is ≥9-12mm, with no bainite microstructure; Step 4.3 Exception handling and logging; Operating procedures: If the hardness is out of tolerance (<27HRC and >33HRC), re-tempering is required (temperature adjustment ±10℃); if the hardened layer is less than 9mm, the end-quench value and quenching parameters must be analyzed for compatibility (if J30 is low, increase the holding time by 10-20 minutes next time). Key parameters: number of re-tempering times ≤ 2 (to avoid grain coarsening), and the abnormal handling record should be linked to the raw material end quenching value and quenching / tempering parameters for easy traceability later; Step 5: Finished product identification and archiving; Operational procedures: Mark qualified tempered parts (label furnace number, batch, tempering date, and test results), and store them by category; organize and archive end quenching reports, hardness test records, and metallographic reports, and retain them for ≥3 years; Key parameters: Clear and identifiable markings (resistant to erasure), archived records must include a table showing the correspondence between "end quench value - quenching temperature - tempering hardness" to provide data support for subsequent process optimization; Furthermore, the key safeguards for this process include the following: End-quenching value - process parameter linkage mechanism: Establish a reference table for "end-quenching J30 value - quenching temperature - stirring frequency" (J30=36-38HRC corresponds to 850-860℃+26-28HZ; J30=43-47HRC corresponds to 835-845℃+20-22HZ), and on-site personnel call up parameters according to the table to avoid experience errors; Real-time monitoring and alarm: The furnace temperature monitoring system collects the temperature of the quenching furnace and tempering furnace in real time (data sampling interval of 1 minute). Automatic alarm is triggered when the stirring frequency or cooling medium temperature exceeds the range (stirring frequency <20HZ and >28HZ) to ensure parameter stability. Regular calibration and training: Calibrate the hardness tester and end quenching tester weekly (accuracy error ≤ 0.5HRC), and calibrate the furnace temperature sensor monthly (error ≤ ±3℃); organize one process training session per month, focusing on "parameter adjustment methods when end quenching values ​​are abnormal" (how to increase quenching temperature when J30 is low); Data traceability mechanism: The end quenching report, process parameters, and test results of each batch of parts are associated with the furnace number and batch. If cold heading cracks occur later, the problem can be quickly traced back to the tempering process (whether the cracking was caused by excessive cooling frequency), thus achieving a closed loop for the problem. Furthermore, this process achieves a balance between hardenability and the risk of quenching cracking, reducing the scrap rate through a process of "precise control of Ti element + synergistic optimization of main alloy composition" (Ti content controlled at 0.005-0.013%, C 0.39-0.42%, Cr 1.08-1.18%, Mo 0.18-0.23%). This avoids excessive hardenability caused by excessive main alloy content, while refining grains and improving hardenability through Ti element. The hardened layer depth compliance rate increased from 75% to 98%: the hardened layer after tempering reached 12-13mm, meeting the requirements of key components; The quenching cracking rate was reduced from 16.8% to below 3%: only 30 out of 925 steering knuckles were scrapped due to quenching cracking (cracking rate 3.25%). Furthermore, by reducing the stirring frequency (from 20Hz to 18Hz), the cracking rate of subsequent batches was further reduced to about 1%, completely resolving the core contradiction between "quenching through and cracking". Furthermore, this process improves compositional segregation and enhances steel uniformity. Through a "dynamic matching of continuous casting parameters + RH vacuum treatment strengthening" process (crystallizer EMS current 80-220A, end F-EMS current 150-300A, RH vacuum degree ≤67Pa, holding pressure 15-25min), segregation is significantly improved. The carbon segregation index was controlled between 0.95 and 1.05: the carbon segregation index of the center of the furnace billet was 0.9713, and the statistical segregation degree was 0.034, which is better than the same steel grades in Xining (0.046) and Daye (0.038); Element uniformity improved by 40%: Ti element segregation decreased from 0.004% to ≤0.003%, Cr and Mo element fluctuation range ≤±0.03%, and the hardness deviation between the rod and the disk at 10mm on the same part was reduced from 5HRC to 2HRC, avoiding extreme cases of "insufficient local hardening and local cracking". Furthermore, this process achieves stable end-quench values, ensuring consistent tempering quality. This is achieved through a "end-quench value - heat treatment parameter linkage" mechanism (quenching temperature 845-860℃ and stirring frequency 24-28Hz for J30 < 38HRC; quenching temperature 835-850℃ and stirring frequency 20-24Hz for J30 > 43HRC), combined with a "batch-by-batch end-quench verification" process. The end-quenching value qualification rate increased from 80% to 95%; the hardness of J30 steel produced in more than 20 heats was stable at 37-46HRC, with a fluctuation range of ≤±2HRC. Significantly improved consistency in heat treatment quality: The deviation in the depth of the hardened layer of parts in the same batch was reduced from 3-4mm to 1-2mm. For 700 steering knuckles of 130mm specification steel produced by furnace 25803470, the hardened layer reached 10-11mm, and no part was reworked due to insufficient hardening, thus completely solving the problem of unstable quality caused by fluctuations in end quenching value.

[0025] Furthermore, this process establishes end-to-end process assurance and achieves quality traceability through three major assurance mechanisms: "precise Ti element calculation + MES real-time monitoring + anomaly closed loop" (Ti addition amount = (target Ti - initial Ti) × molten steel quantity / (Ti iron purity × 85%-95% recovery rate), MES generates parameter reports every 10 minutes and automatically alarms in case of anomalies). Process parameter fluctuation rate reduced by 70%: Ti element addition deviation reduced from ±0.003% to ±0.002%, LF furnace refining temperature fluctuation ≤±5℃; Quality traceability efficiency improved by 80%: The end-quenching report, smelting parameters, and tempering records of each batch of steel are linked to the furnace number. If problems occur later, the root cause can be located within 1 hour. The rectification cycle for similar problems is shortened from 7 days to 2 days, realizing "problems are traceable and rectification is implemented". Furthermore, this process enables adaptation to multiple part specifications, expanding its applicability. This is achieved through a "specification-process parameter matching" model (quenching temperature 840-850℃, stirring frequency 18-22HZ for 110-120mm steel; quenching temperature 835-845℃, stirring frequency 22-24HZ for 130-140mm steel): The hardening penetration rate of various specifications of parts is ≥95%: the hardening penetration of the 110mm specification A458 steering knuckle (25803465 furnace) reaches 9-10mm, and the hardening penetration of the 140mm specification A107 steering knuckle reaches 12-13mm. Parts of different specifications meet the usage requirements. Process adaptability expansion: It can cover steel with a specification of Φ100-150mm, and by adjusting the quenching temperature (835-860℃) and tempering temperature (620-660℃), it can be adapted to different types of forgings such as steering knuckles and ball joints, without the need to develop separate processes for a single specification, thus reducing production complexity.

[0026] 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 quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control, comprising: step 1: pre-quenching and tempering preparation (related end-quenching value preset); step 2: quenching treatment (core end-quenching value control step); step 3: tempering treatment (stress relief and microstructure stabilization); step 4: post-quenching and tempering quality verification (related end-quenching value feedback); and step 5: finished product identification and archiving, characterized in that: Step 1: Preparation before heat treatment (presetting the quenching value of the associated end) includes step 1.1 verification of the quenching value of the raw material end and step 1.2 pretreatment and marking of the parts; Step 2: Quenching treatment (core end quenching value control) includes step 2.1 segmented heating control (reducing thermal stress), step 2.2 austenitizing and holding, and step 2.3 staged cooling (balancing hardenability and cracking risk). Step 3: Tempering treatment (stress relief and microstructure stabilization) includes step 3.1 tempering temperature matching and step 3.2 tempering heat preservation and cooling; Step 4: Quality verification after tempering (associated end quenching value feedback) includes Step 4.1 Hardness test (preliminary judgment of hardenability), Step 4.2 Metallographic structure analysis (accurate determination of hardenable layer) and Step 4.3 Anomaly handling and recording.

2. The quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control according to claim 1, characterized in that: Step 1.1: Verification of raw material end quenching value; Operation procedure: Select 3-5 forgings from each batch, cut end-quenched samples (25-30mm in diameter, 70-130mm in length) from non-critical parts, and conduct end-quenching tests according to GB / T 225 standard to verify whether the end-quenching value of the raw material matches the process requirements. Key parameters: End-quenched J15 hardness 45-57HRC, J30 hardness 36-47HRC; If J30 < 36 HRC, mark it as "Requires enhanced quenching"; if J30 > 47 HRC, mark it as "Requires weakened cooling". Judgment criteria: Raw materials with end-quenching values ​​outside the range need to have their process parameters formulated separately (if J30 is low, increase the quenching temperature by 5-10℃) and should not be mixed with qualified raw materials for tempering; Step 1.2 Part pretreatment and marking; Operation procedure: Remove oxide scale from the surface of the forging by sandblasting and pickling (pickling time 5-10 minutes, extended from the original 6-9 minutes), visually inspect the surface for cracks and scratches; mark inspection points (10mm from the surface) on key locations on the rod and disc of the part with a marker pen; Key parameters: surface roughness Ra≤1.6μm after pickling, marking point spacing 20-30mm, avoid marking at stress concentration points.

3. The quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control according to claim 1, characterized in that: Step 2.1 Segmented temperature control (to reduce thermal stress); Operation procedure: Load the pretreated parts into the quenching furnace and use "two-stage heating": the first stage is to heat from room temperature to 500-550℃ (preheating stage), and the second stage is to heat from 500-550℃ to the target quenching temperature to avoid excessive temperature difference between the inside and outside of the parts, which may cause cracks. Key parameters: Preheating rate: 80-120℃ / h; hold for 30-60 minutes. The quenching heating rate is 50-80℃ / h, and the target quenching temperature is 835-860℃. When J30 < 38HRC, take 845-860℃, and when J30 > 43HRC, take 835-850℃.

4. The quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control according to claim 1, characterized in that: Step 2.2: Austenitizing and heat preservation; Operation procedure: After the part is heated to the target temperature, it is kept at a constant temperature to ensure sufficient austenitization. The holding time is calculated based on the maximum thickness of the part (40-60 minutes for every 20mm of thickness). Key parameters: Total holding time 120-180 minutes, furnace temperature recorded every 20 minutes, holding time paused and adjustment made if deviation exceeds ±5℃; the furnace atmosphere during holding time is weakly oxidizing (to avoid decarburization), and the decarburized layer thickness is ≤0.02mm.

5. The quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control according to claim 1, characterized in that: Step 2.3 is graded cooling (balancing hardenability and cracking risk). Operation procedure: After the heat preservation is completed, the parts are quickly transferred to the quenching tank (transfer time ≤ 10 seconds). The cooling intensity is adjusted according to the end quenching value: if J30 is low, the cooling is strengthened; if J30 is high, the cooling is weakened. Key parameters: Cooling medium temperature 18-28℃, stirring frequency 20-28HZ (24-28HZ when J30 < 38HRC, 20-24HZ when J30 > 43HRC); Remove from the water when cooled to 80-120℃. Avoid prolonged low-temperature contact (≤5 minutes) to prevent incomplete martensite transformation.

6. The quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control according to claim 1, characterized in that: Step 3.1 Tempering and temperature matching; Operation procedure: Immediately load the quenched parts into the tempering furnace (interval ≤ 2 hours to avoid quenching stress accumulation), and raise the temperature to the target tempering temperature according to the principle of "slow heating", with a heating rate of 60-100℃ / h; Key parameters: Target tempering temperature 620-660℃ — 640-660℃ when the hardness after quenching is 50-55HRC, and 620-640℃ when the hardness is 48-50HRC.

7. The quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control according to claim 1, characterized in that: Step 3.2: Tempering, heat preservation, and cooling; Operation procedure: After the parts are heated to the tempering temperature, they are kept at a constant temperature to ensure that the internal stress is fully released; after the holding period, the cooling method (water cooling or air cooling) is selected according to the performance requirements of the parts. Key parameters: The holding time is 140-180 minutes, and the furnace temperature is recorded every 30 minutes, with a deviation of ≤±3℃; Water cooling is used when high toughness is required (cooling time to room temperature ≤ 1 hour), and air cooling is used when high stability is required (cooling time to room temperature ≤ 4 hours).

8. The quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control according to claim 1, characterized in that: Step 4.1 Hardness test (preliminary assessment of hardenability); Operation procedure: Use a Rockwell hardness tester to test the hardness at the marked points on the part (5mm and 10mm from the surface), test each point 2-3 times and take the average value; at the same time, test the hardness of the end-quenched sample after tempering to verify the matching of process parameters. Key parameters: target hardness 27-33 HRC, hardness deviation at 10mm from surface hardness ≤3 HRC; tempering and post-quenching J30 38-45 HRC (consistent with process target).

9. The quenching and tempering heat treatment process for 42CrMo1 steel based on end-quenching value control according to claim 1, characterized in that: Step 4.2 Metallographic analysis (accurately determining the hardened layer); Procedure: Take a metallographic sample (5-8mm thick, based on the original 5-8mm) from a part with qualified hardness. After coarse grinding, fine grinding, and polishing, etch it with 2.5-3.5% nitric acid alcohol solution for 5-8 minutes. Observe the structure at 10mm under a 500X microscope. Key parameters: The microstructure at 10mm is tempered sorbite + a small amount of ferrite (ferrite content ≤5%), with a metallographic rating of 3-5; the hardened layer depth is ≥9-12mm, with no bainite microstructure; Step 4.3 Exception handling and logging; Operating procedures: If the hardness is out of tolerance (<27HRC and >33HRC), it needs to be re-tempered (temperature adjusted ±10℃); if the hardened layer is less than 9mm, the end-quench value and the matching of quenching parameters need to be analyzed (if J30 is low, the holding time should be increased by 10-20 minutes next time). Key parameters: number of re-tempering times ≤ 2 (to avoid grain coarsening), and the abnormal handling record should be linked to the raw material end quenching value and quenching / tempering parameters for easy traceability later.

10. The heat treatment process for 42CrMo1 steel based on end-quench value control according to claim 1, characterized in that: Step 5: Finished product identification and archiving; Operational procedures: Mark qualified tempered parts (label furnace number, batch, tempering date, and test results), and store them by category; organize and archive end quenching reports, hardness test records, and metallographic reports, and retain them for ≥3 years; Key parameters: Clear and identifiable markings (resistant to erasure), archived records must include a table showing the correspondence between "end quench value - quenching temperature - tempering hardness" to provide data support for subsequent process optimization.