Process for improving cold working performance of 20CrMnTiSH1-H5 steel

Abstract

The invention relates to the technical field of steel cold machining, and discloses a process for improving the cold machining performance of 20CrMnTiSH1-H5 steel, and the process comprises the first step of pretreatment before cold machining, the second step of structure homogenization optimization, the third step of surface lubrication strengthening, the fourth step of staged cold machining implementation, the fifth step of treatment after cold machining and the sixth step of quality control. The surface (Ra is smaller than or equal to 0.8 micron) is deeply purified through mechanical shot blasting and weak acid pickling, the hardness is stabilized at 150-220 HB in combination with spheroidizing annealing, and the machining resistance is effectively reduced; through the combination of homogenization heating and Ti / N microalloying regulation and control (the Ti / N ratio is 2.0-4.5), the composition segregation in the steel is greatly improved, the size of titanium nitride inclusions is smaller than or equal to 12 microns, the grain size is larger than or equal to 7 grades, the percentage elongation after fracture is increased to be larger than or equal to 22%, no crack exists in a 180-degree cold bending test, and the problems of scratching and fracture during cold machining are thoroughly solved.

Description

Technical Field

[0001] This invention relates to the field of cold working technology of steel, specifically to a process for improving the cold working performance of 20CrMnTiSH1~H5 steel. Background Technology

[0002] Cold working is widely used in the forming and processing of high-strength steel parts such as automotive transmission gears and precision shafts. These parts have stringent requirements for the cold working plasticity, dimensional stability, and surface quality of the materials. Existing cold working processes have several technical shortcomings: surface pretreatment only removes oxide scale, failing to thoroughly remove micro-oil stains and minor scratches, and lacks targeted softening treatment, resulting in workpieces with high hardness (often exceeding 230 HB), making them prone to scratches, peeling, and even breakage during cold working; severe component segregation in the steel, with uneven distribution of elements such as C, Mn, and Cr, coupled with excessively large non-metallic inclusions (especially titanium nitride) (often exceeding 15 μm), resulting in coarse grains with poor uniformity (grain size mostly 5-6). The process is characterized by several challenges: Firstly, the lubricant application is often a single coating method, resulting in weak adhesion, easy failure, and a lack of a circulating purification system. This leads to insufficient lubrication during processing, causing mold wear and surface scratches on the workpiece. Secondly, cold working is often a one-time large deformation process without graded treatment or intermediate stress relief, resulting in severe work hardening and residual stress accumulation (often exceeding 200 MPa), which can easily lead to dimensional deformation and cracking. Thirdly, post-processing stress-relief annealing is insufficient, surface cleaning and rust prevention measures are simple, resulting in poor product corrosion resistance and large quality fluctuations during mass production, making it difficult to meet the high precision and high reliability requirements of high-end precision 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 improving the cold working properties of 20CrMnTiSH1~H5 steel. This process has the advantages of significantly improved cold working plasticity and reduced processing difficulty, and solves the problems of scratches, peeling, and even breakage during cold working, as well as severe component segregation in the steel.

[0004] (II) Technical Solution To achieve the aforementioned goal of significantly improving cold working plasticity and reducing processing difficulty, this invention provides the following technical solution: a process for improving the cold working performance of 20CrMnTiSH1~H5 steel, comprising: S1 pre-treatment stage before cold working, S2 microstructure homogenization optimization stage, S3 surface lubrication strengthening stage, S4 graded cold working implementation stage, S5 post-treatment stage after cold working, and S6 quality control stage. The S1 pre-treatment stage before cold working includes S1.1 surface cleaning treatment and S1.2 softening annealing treatment. The S2 microstructure homogenization optimization stage includes S2.1 homogenization heat treatment and S2.2 microalloying control. The S3 surface lubrication enhancement stage includes S3.1 lubricant selection and coating and S3.2 lubricant circulation and purification. The S4 graded cold working implementation stage includes S4.1 roughing process, S4.2 semi-finishing process, S4.3 finishing process and S4.4 intermediate stress relief treatment; The S5 cold working post-treatment stage includes S5.1 stress-relief annealing and S5.2 surface cleaning and rust prevention; The S6 quality control stage includes S6.1 cold working performance testing and S6.2 microstructure and surface quality testing.

[0005] Preferably, the surface cleaning treatment in step S1.1 is as follows: The process employs a combination of mechanical shot blasting and weak acid pickling to thoroughly remove surface oxide scale, rust, and oil stains. Key parameters are: shot blasting pressure 0.2-1.0 MPa, steel shot diameter 0.15-0.8 mm, and cleaning time 2-15 min; acid pickling uses a 3-15% hydrochloric acid solution at a temperature of 25-65℃ for 8-35 min, followed by rinsing with clean water until the pH value reaches 6.0-8.0; drying temperature is 80-120℃, and drying time is 15-40 min. Precautions: During shot blasting, ensure uniform impact across the entire workpiece surface; complex structural parts require targeted treatment of blind holes and grooves; dry promptly after acid pickling to prevent secondary corrosion. S1.2 Softening annealing treatment: Spheroidizing annealing reduces hardness, refines microstructure, and improves cold workability. Key parameters: annealing temperature 650-780℃, heating rate 40-160℃ / h, holding time 3-8h; after holding, use stepped cooling at a rate of 15-60℃ / h, cooling to room temperature after reaching below 350℃. Precautions: Nitrogen gas is introduced for protection during annealing, with a gas flow rate of 0.4-1.8m³. 3 / h, to prevent surface oxidation and decarburization; workpiece stacking spacing ≥15mm to ensure uniform heating.

[0006] Preferably, the S2.1 homogenization heating treatment: To improve compositional segregation in steel and enhance microstructure uniformity, key parameters are: homogenization temperature 1080-1250℃, heating rate 60-140℃ / h, and holding time 2-5h; after holding, cool in the furnace to 800-850℃, then air cool to room temperature. Precautions: strictly control the heating rate to avoid thermal stress-induced cracking; adjust the holding time according to the workpiece cross-sectional dimensions, and appropriately extend the holding time for large cross-section workpieces. S2.2 Microalloying Control: Optimize the Ti and N element ratio to form dispersed carbonitrides and refine the grains. Key parameters: Ti content controlled at 0.03-0.08%, N content controlled at 40-80ppm, Ti / N ratio 2.0-4.5; non-metallic inclusions in the steel: Class A ≤ 2.5, Class B ≤ 2.0, Class C ≤ 1.5, Class D ≤ 1.5; titanium nitride inclusion size ≤ 12μm. Precautions: Ti alloy is added in the later stage of refining to avoid premature oxidation and burn-off; reduce gas content through vacuum degassing: O ≤ 15ppm, H ≤ 2.5ppm.

[0007] Preferably, in step S3.1, the selection and application of the lubricant: A high-adhesion, high-temperature resistant special cold-working lubricant is selected, employing a dual process of "pre-coating + online lubrication." Key parameters: the lubricant is either graphite-based or phosphosaponified, with a viscosity of 40-180 mmHg. 2 / s (40℃); Coating thickness 0.04-0.20mm, pre-lubrication temperature 15-60℃, heat preservation time 10-50min, Precautions: Lubricant needs to be filtered and purified regularly, impurity content ≤0.5%; For complex shaped workpieces, use a combination of dip coating and brush coating to ensure full lubrication coverage; S3.2 Lubricant circulation and purification: To establish a lubricant circulation and filtration system and maintain stable lubrication performance, key parameters are: filtration accuracy ≤20μm, and circulation flow rate 5-15m³ / h. 3 / h; Regularly test the viscosity and pH of the lubricant. The viscosity change should be ≤±20%, and the pH value should be maintained between 7.0 and 9.0. Precautions: Replenish the lubricant in time, with the replenishment amount being 5-10% of the total circulation volume per cycle; Avoid water from mixing with the lubricant, and the water content should be ≤0.8%.

[0008] Preferably, the S4.1 roughing process is as follows: Preliminary diameter reduction and removal of residual surface defects. Key parameters: processing speed 3-18m / min, diameter reduction per pass 1.0-3.0mm; continuous cold drawing or cold rolling, with a pause time of 1-3min between passes to release instantaneous stress. Precautions: after rough machining, the surface roughness Ra≤1.5μm, with no obvious scratches or peeling; if defects occur, return to the pretreatment stage for reprocessing.

[0009] Preferably, the S4.2 semi-finishing process is as follows: Refine dimensional accuracy and gradually improve machining uniformity. Key parameters: machining speed 5-22m / min, single-pass diameter reduction 0.6-2.0mm; cumulative diameter reduction ≤6.0mm. Avoid over-machining leading to hardening. Precautions: perform online degreasing after every 2-3 passes, and use hot air drying (temperature 70-110℃, time 3-8min); monitor the workpiece temperature in real time, and stop the machine for cooling when it exceeds 90℃.

[0010] Preferably, the S4.3 finishing process is as follows: To ensure the dimensional accuracy and surface quality of cold-worked finished products, key parameters are: processing speed 8-28m / min, single-pass diameter reduction 0.2-1.5mm; die hole surface finish Ra≤0.04μm, dimensional accuracy≤±0.03mm. Precautions: maintain uniform speed during finishing, with speed fluctuation ≤±1.5m / min; check die wear after processing every 30-50 workpieces and polish and repair as needed.

[0011] Preferably, the intermediate stress relief treatment in step S4.4 is as follows: For workpieces that have undergone multiple processing steps, work hardening is eliminated. Key parameters: stress relief temperature 180-320℃, holding time 1.0-3.0h, cooling rate 30-80℃ / h. Precautions: after stress relief treatment, the hardness of the workpiece should be controlled at 150-220HB, and the elongation after fracture should be ≥20%. After treatment, the surface should be lubricated again before proceeding to the next cold working process.

[0012] Preferably, the stress-relief annealing in step S5.1: Completely eliminate residual stress from cold working, stabilize dimensions and performance. Key parameters: annealing temperature 200-350℃, heating rate 50-120℃ / h, holding time 2-4h; after holding, air cool to room temperature, avoid rapid cooling during the cooling process. Precautions: residual stress of the workpiece after annealing ≤150MPa; during batch production, sample 3-5 pieces from each batch to ensure performance consistency. S5.2 Surface cleaning and rust prevention: Remove residual lubricant and impurities from the surface after cold working, and perform rust prevention protection. Key parameters: use low-pressure shot blasting (pressure 0.3-0.9MPa) or alkaline degreasing (concentration 5-12%, temperature 40-70℃, time 10-25min); rust prevention treatment uses rust-preventive oil spraying or passivation, with rust-preventive oil thickness ≥0.02mm and passivation film thickness 0.004-0.018mm. Precautions: after cleaning, the surface roughness Ra≤0.8μm, free of oil stains and rust; packaging should be completed within 24 hours after rust prevention treatment, and the relative humidity of the storage environment should be ≤75%.

[0013] Preferably, the S6.1 cold working performance test includes: Key parameters: Elongation at break after cold working ≥22%, reduction of area ≥50%, no cracks in 180° cold bending test (bending mandrel diameter d = finished product diameter a); hardness uniformity deviation ≤10HB. Note: 5-8 samples should be taken from each batch, covering different processing passes, to comprehensively test the cold working performance. S6.2 Organization and Surface Quality Inspection: Key parameters: Grain size ≥ 7, no Widmanstätten structure, banded structure ≤ 1.5; surface free of cracks, scratches, indentations, and defects, with defect depth ≤ 0.12 mm. Notes: Microstructure is observed using a metallographic microscope, and surface quality is tested using a 10x magnifying glass combined with surface flaw detection; non-conforming products need to be traced back to the previous process, and process parameters need to be optimized.

[0014] (III) Beneficial Effects Compared with the prior art, the present invention provides a process for improving the cold working properties of 20CrMnTiSH1~H5 steel, which has the following beneficial effects: 1. Improved cold working performance technology for 20CrMnTiSH1~H5 steel: This technology significantly enhances cold working plasticity and reduces processing difficulty. The surface is thoroughly cleaned (Ra≤0.8μm) through mechanical shot blasting and weak acid pickling, combined with spheroidizing annealing to stabilize the hardness at 150-220HB, effectively reducing processing resistance. Furthermore, homogenization heating and Ti / N microalloying control (Ti / N ratio 2.0-4.5) significantly improve compositional segregation in the steel, resulting in titanium nitride inclusions ≤12μm in size, grain size ≥7, elongation after fracture ≥22%, and no cracks in the 180° cold bending test, completely solving the problems of scratches and fractures during cold working.

[0015] 2. The cold working performance improvement process of the 20CrMnTiSH1~H5 steel achieves dual optimization of machining accuracy and surface quality: adopting a dual process of "pre-coating + online lubrication" and a circulating purification system (filtration accuracy ≤20μm) to ensure full and stable lubrication coverage, reduce mold wear and workpiece surface scratches, and achieve a surface roughness Ra≤0.8μm and dimensional accuracy ≤±0.03mm after finishing; graded cold working (rough-semi-finish-finish) combined with intermediate stress relief treatment avoids excessive work hardening, and the depth of surface defects on the workpiece is ≤0.12mm, significantly improving dimensional stability.

[0016] 3. The cold working performance improvement process of the 20CrMnTiSH1~H5 steel effectively releases residual stress and enhances service reliability: intermediate stress relief treatment (holding at 180-320℃ for 1.0-3.0h) is set during the processing, combined with subsequent stress relief annealing, so that the residual stress of the workpiece is ≤150MPa, which completely solves the hidden dangers of deformation and cracking after cold working; the banded structure is ≤1.5 grade, there is no Widmanstätten structure, and the hardness uniformity deviation is ≤10HB, ensuring that the parts are subjected to uniform stress in subsequent use and are not prone to failure due to stress concentration.

[0017] 4. The cold working performance improvement process of 20CrMnTiSH1~H5 steel achieves consistent quality in batch production: a closed-loop system of "pretreatment - microstructure optimization - lubrication - graded processing - post-treatment - full-dimensional inspection" is constructed. Batch sampling inspection (5-8 pieces per batch) is carried out on key indicators of cold working performance, microstructure, and surface quality. The inclusion level is strictly controlled (Class A ≤ 2.5, Class B ≤ 2.0), which effectively reduces product quality fluctuations, meets the stringent requirements of batch consistency for high-end precision parts, and reduces the scrap rate during processing, thereby improving production efficiency. 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 invention provides a technical solution, specifically, a process for improving the cold working properties of 20CrMnTiSH1~H5 steel, comprising the following process: S1 Pre-treatment stage before cold working: S1.1 Surface Cleaning Treatment: The process employs a combination of mechanical shot blasting and weak acid pickling to thoroughly remove surface oxide scale, rust, and oil stains. Key parameters are: shot blasting pressure 0.2-1.0 MPa, steel shot diameter 0.15-0.8 mm, and cleaning time 2-15 min; acid pickling uses a 3-15% hydrochloric acid solution at a temperature of 25-65℃ for 8-35 min, followed by rinsing with clean water until the pH value reaches 6.0-8.0; drying temperature is 80-120℃, and drying time is 15-40 min. Precautions: During shot blasting, ensure uniform impact across the entire workpiece surface; complex structural parts require targeted treatment of blind holes and grooves; dry promptly after acid pickling to prevent secondary corrosion. S1.2 Softening annealing treatment: Spheroidizing annealing reduces hardness, refines microstructure, and improves cold workability. Key parameters: annealing temperature 650-780℃, heating rate 40-160℃ / h, holding time 3-8h; after holding, use stepped cooling at a rate of 15-60℃ / h, cooling to room temperature after reaching below 350℃. Precautions: Nitrogen gas is introduced for protection during annealing, with a gas flow rate of 0.4-1.8m³. 3 / h, to prevent surface oxidation and decarburization; workpiece stacking spacing ≥15mm to ensure uniform heating; S2 tissue homogenization optimization stage: S2.1 Homogenization heat treatment: To improve compositional segregation in steel and enhance microstructure uniformity, key parameters are: homogenization temperature 1080-1250℃, heating rate 60-140℃ / h, and holding time 2-5h; after holding, cool in the furnace to 800-850℃, then air cool to room temperature. Precautions: strictly control the heating rate to avoid thermal stress-induced cracking; adjust the holding time according to the workpiece cross-sectional dimensions, and appropriately extend the holding time for large cross-section workpieces. S2.2 Microalloying Control: Optimize the Ti and N element ratio to form dispersed carbonitrides and refine the grains. Key parameters: Ti content controlled at 0.03-0.08%, N content controlled at 40-80ppm, Ti / N ratio 2.0-4.5; non-metallic inclusions in the steel: Class A ≤ 2.5, Class B ≤ 2.0, Class C ≤ 1.5, Class D ≤ 1.5; titanium nitride inclusion size ≤ 12μm. Precautions: Ti alloy is added in the later stage of refining to avoid premature oxidation and burn-off; reduce gas content through vacuum degassing: O ≤ 15ppm, H ≤ 2.5ppm. S3 Surface Lubrication Enhancement Stage: S3.1 Lubricant Selection and Application: A high-adhesion, high-temperature resistant special cold-working lubricant is selected, employing a dual process of "pre-coating + online lubrication." Key parameters: the lubricant is either graphite-based or phosphosaponified, with a viscosity of 40-180 mmHg. 2 / s (40℃); Coating thickness 0.04-0.20mm, pre-lubrication temperature 15-60℃, heat preservation time 10-50min, Precautions: Lubricant needs to be filtered and purified regularly, impurity content ≤0.5%; For complex shaped workpieces, use a combination of dip coating and brush coating to ensure full lubrication coverage; S3.2 Lubricant circulation and purification: To establish a lubricant circulation and filtration system and maintain stable lubrication performance, key parameters are: filtration accuracy ≤20μm, and circulation flow rate 5-15m³ / h. 3 / h; Regularly test the lubricant viscosity and pH; viscosity change ≤ ±20%, pH value maintained between 7.0 and 9.0. Precautions: Replenish with new lubricant promptly, the replenishment amount is 5-10% of the total circulation volume per cycle; avoid water contamination of the lubricant, water content ≤ 0.8%; S4 graded cold working implementation phase: S4.1 Rough machining process: Preliminary diameter reduction and removal of residual surface defects. Key parameters: processing speed 3-18m / min, diameter reduction per pass 1.0-3.0mm; continuous cold drawing or cold rolling, with a pause time of 1-3min between passes to release instantaneous stress. Precautions: after rough machining, the surface roughness Ra≤1.5μm, with no obvious scratches or peeling; if defects occur, return to the pretreatment stage for reprocessing. S4.2 Semi-finishing process: Refine dimensional accuracy and gradually improve machining uniformity. Key parameters: machining speed 5-22m / min, single-pass diameter reduction 0.6-2.0mm; cumulative diameter reduction ≤6.0mm. Avoid over-machining leading to hardening. Precautions: perform online degreasing after every 2-3 passes, and use hot air drying (temperature 70-110℃, time 3-8min); monitor the workpiece temperature in real time, and stop the machine for cooling when it exceeds 90℃. S4.3 Finishing process: To ensure the dimensional accuracy and surface quality of cold-worked finished products, key parameters are: processing speed 8-28 m / min, single-pass diameter reduction 0.2-1.5 mm; die hole surface finish Ra≤0.04 μm, dimensional accuracy≤±0.03 mm. Precautions: maintain a uniform speed during finishing, with speed fluctuation ≤±1.5 m / min; check die wear after every 30-50 workpieces processed and polish and repair as needed. S4.4 Intermediate stress relief treatment: For workpieces that have undergone multiple processing steps, the key parameters for stress relief are: stress relief temperature 180-320℃, holding time 1.0-3.0h, and cooling rate 30-80℃ / h. Precautions include: after stress relief treatment, the workpiece hardness should be controlled at 150-220HB, and the elongation after fracture should be ≥20%. After treatment, the surface should be re-lubricated before proceeding to the next cold working process. S5 cold working post-processing stage: S5.1 Stress-relief annealing: Completely eliminate residual stress from cold working, stabilize dimensions and performance. Key parameters: annealing temperature 200-350℃, heating rate 50-120℃ / h, holding time 2-4h; after holding, air cool to room temperature, avoid rapid cooling during the cooling process. Precautions: residual stress of the workpiece after annealing ≤150MPa; during batch production, sample 3-5 pieces from each batch to ensure performance consistency. S5.2 Surface cleaning and rust prevention: Remove residual lubricant and impurities from the surface after cold working, and perform rust prevention protection. Key parameters: use low-pressure shot blasting (pressure 0.3-0.9MPa) or alkaline degreasing (concentration 5-12%, temperature 40-70℃, time 10-25min); rust prevention treatment uses rust-preventive oil spraying or passivation, with rust-preventive oil thickness ≥0.02mm and passivation film thickness 0.004-0.018mm. Precautions: after cleaning, the surface roughness Ra≤0.8μm, free of oil stains and rust; packaging should be completed within 24 hours after rust prevention treatment, and the relative humidity of the storage environment should be ≤75%. S6 Quality Control Phase: S6.1 Cold working performance test: Key parameters: Elongation at break after cold working ≥22%, reduction of area ≥50%, no cracks in 180° cold bending test (bending mandrel diameter d = finished product diameter a); hardness uniformity deviation ≤10HB. Note: 5-8 samples should be taken from each batch, covering different processing passes, to comprehensively test the cold working performance. S6.2 Organization and Surface Quality Inspection: Key parameters: Grain size ≥ 7, no Widmanstätten structure, banded structure ≤ 1.5; surface free of cracks, scratches, indentations, and defects, with defect depth ≤ 0.12 mm. Notes: Microstructure is observed using a metallographic microscope, and surface quality is inspected using a 10x magnifying glass combined with surface flaw detection; non-conforming products must be traced back to the previous process, and process parameters optimized. Furthermore, this process significantly improves cold working plasticity and reduces processing difficulty: Deep surface purification (Ra≤0.8μm) through "mechanical shot blasting + weak acid pickling," combined with spheroidizing annealing to stabilize hardness at 150-220HB, effectively reduces processing resistance; combined with homogenization heating and Ti / N microalloying control (Ti / N ratio 2.0-4.5), compositional segregation in the steel is greatly improved, titanium nitride inclusion size ≤12μm, grain size ≥7, elongation after fracture increased to ≥22%, and no cracks were observed in the 180° cold bending test, completely solving the problems of scratches and fractures during cold working; Furthermore, this process achieves dual optimization of machining accuracy and surface quality: It employs a dual process of "pre-coating + online lubrication," coupled with a circulating purification system (filtration accuracy ≤20μm), ensuring full and stable lubrication coverage, reducing mold wear and workpiece surface scratches. After finishing, the surface roughness Ra ≤0.8μm and dimensional accuracy ≤±0.03mm are achieved. Graded cold working (rough-semi-finish-finish) combined with intermediate stress relief treatment avoids excessive work hardening, resulting in workpiece surface defect depth ≤0.12mm and significantly improved dimensional stability. Furthermore, this process effectively releases residual stress and enhances service reliability: intermediate stress relief treatment (holding at 180-320℃ for 1.0-3.0h) is set during the processing, combined with subsequent stress relief annealing, so that the residual stress of the workpiece is ≤150MPa, completely solving the hidden dangers of deformation and cracking after cold working; the banded structure is ≤1.5 grade, there is no Widmanstätten structure, and the hardness uniformity deviation is ≤10HB, ensuring that the parts are subjected to uniform stress in subsequent use and are not prone to failure due to stress concentration; Furthermore, this process ensures consistent quality in mass production: it constructs a closed-loop system of "pretreatment - microstructure optimization - lubrication - graded processing - post-treatment - full-dimensional inspection," and conducts batch sampling inspections (5-8 pieces per batch) on key indicators such as cold working performance, microstructure, and surface quality. It strictly controls the level of inclusions (Class A ≤ 2.5, Class B ≤ 2.0), effectively reducing product quality fluctuations, meeting the stringent requirements of high-end precision parts for batch consistency, while reducing scrap rates during processing and improving production efficiency.

[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 improving the cold working properties of 20CrMnTiSH1~H5 steel, comprising: S1 pretreatment stage before cold working, S2 microstructure homogenization optimization stage, S3 surface lubrication strengthening stage, S4 graded cold working implementation stage, S5 post-cold working treatment stage, and S6 quality control stage, characterized in that: The S1 pretreatment stage before cold working includes S1.1 surface cleaning treatment and S1.2 softening annealing treatment; The S2 microstructure homogenization optimization stage includes S2.1 homogenization heat treatment and S2.2 microalloying control. The S3 surface lubrication enhancement stage includes S3.1 lubricant selection and coating and S3.2 lubricant circulation and purification. The S4 graded cold working implementation stage includes S4.1 roughing process, S4.2 semi-finishing process, S4.3 finishing process and S4.4 intermediate stress relief treatment; The S5 cold working post-treatment stage includes S5.1 stress-relief annealing and S5.2 surface cleaning and rust prevention; The S6 quality control stage includes S6.1 cold working performance testing and S6.2 microstructure and surface quality testing.

2. The process for improving the cold working properties of 20CrMnTiSH1~H5 steel according to claim 1, characterized in that: The surface cleaning treatment in step S1.1: The process employs a combination of mechanical shot blasting and weak acid pickling to thoroughly remove surface oxide scale, rust, and oil stains. Key parameters are: shot blasting pressure 0.2-1.0 MPa, steel shot diameter 0.15-0.8 mm, and cleaning time 2-15 min; acid pickling uses a 3-15% hydrochloric acid solution at a temperature of 25-65℃ for 8-35 min, followed by rinsing with clean water until the pH value reaches 6.0-8.0; drying temperature is 80-120℃, and drying time is 15-40 min. Precautions: During shot blasting, ensure uniform impact across the entire surface of the workpiece; complex structural parts require targeted treatment of blind holes and grooves; dry promptly after acid pickling to prevent secondary corrosion. S1.2 Softening annealing treatment: Spheroidizing annealing reduces hardness, refines microstructure, and improves cold workability. Key parameters: annealing temperature 650-780℃, heating rate 40-160℃ / h, holding time 3-8h; after holding, use stepped cooling at a rate of 15-60℃ / h, cooling to room temperature after reaching below 350℃. Precautions: Nitrogen gas is introduced for protection during annealing, with a gas flow rate of 0.4-1.8m³. 3 / h, to prevent surface oxidation and decarburization; workpiece stacking spacing ≥15mm to ensure uniform heating.

3. The process for improving the cold working properties of 20CrMnTiSH1~H5 steel according to claim 1, characterized in that: The S2.1 homogenization heating treatment: To improve compositional segregation in steel and enhance microstructure uniformity, key parameters are: homogenization temperature 1080-1250℃, heating rate 60-140℃ / h, and holding time 2-5h; after holding, cool in the furnace to 800-850℃, then air cool to room temperature. Precautions: strictly control the heating rate to avoid thermal stress-induced cracking; adjust the holding time according to the workpiece cross-sectional dimensions, and appropriately extend the holding time for large cross-section workpieces. S2.2 Microalloying Control: Optimize the Ti and N element ratio to form dispersed carbonitrides and refine the grains. Key parameters: Ti content controlled at 0.03-0.08%, N content controlled at 40-80ppm, Ti / N ratio 2.0-4.5; non-metallic inclusions in the steel: Class A ≤ 2.5, Class B ≤ 2.0, Class C ≤ 1.5, Class D ≤ 1.5; titanium nitride inclusion size ≤ 12μm. Precautions: Ti alloy is added in the later stage of refining to avoid premature oxidation and burn-off; reduce gas content through vacuum degassing: O ≤ 15ppm, H ≤ 2.5ppm.

4. The process for improving the cold working properties of 20CrMnTiSH1~H5 steel according to claim 1, characterized in that: S3.1 Lubricant selection and application: A high-adhesion, high-temperature resistant special cold-working lubricant is selected, employing a dual process of "pre-coating + online lubrication." Key parameters: the lubricant is either graphite-based or phosphosaponified, with a viscosity of 40-180 mmHg. 2 / s (40℃); Coating thickness 0.04-0.20mm, pre-lubrication temperature 15-60℃, heat preservation time 10-50min, Precautions: Lubricant needs to be filtered and purified regularly, impurity content ≤0.5%; For complex shaped workpieces, use a combination of dip coating and brush coating to ensure full lubrication coverage; S3.2 Lubricant circulation and purification: To establish a lubricant circulation and filtration system and maintain stable lubrication performance, key parameters are: filtration accuracy ≤20μm, and circulation flow rate 5-15m³ / h. 3 / h; Regularly test the lubricant viscosity and pH, with viscosity change ≤±20% and pH value maintained between 7.0 and 9.

0. Precautions: Replenish with new lubricant in a timely manner, with the replenishment amount being 5-10% of the total circulation volume per cycle; Avoid water contamination in the lubricant, with a water content ≤0.8%.

5. The process for improving the cold working properties of 20CrMnTiSH1~H5 steel according to claim 1, characterized in that: The S4.1 roughing process: Preliminary diameter reduction and removal of residual surface defects. Key parameters: processing speed 3-18m / min, single-pass diameter reduction 1.0-3.0mm; continuous cold drawing or cold rolling, pause time between passes 1-3min to release instantaneous stress. Precautions: after rough machining, surface roughness Ra≤1.5μm, no obvious scratches or peeling. If defects are found, return to the preprocessing stage for reprocessing.

6. The process for improving the cold working properties of 20CrMnTiSH1~H5 steel according to claim 1, characterized in that: The S4.2 semi-finishing process: Refine dimensional accuracy and gradually improve machining uniformity. Key parameters: machining speed 5-22m / min, single-pass diameter reduction 0.6-2.0mm; cumulative diameter reduction ≤6.0mm. Avoid over-machining leading to hardening. Precautions: perform online degreasing after every 2-3 passes, and use hot air drying (temperature 70-110℃, time 3-8min); monitor the workpiece temperature in real time, and stop the machine for cooling when it exceeds 90℃.

7. The process for improving the cold working properties of 20CrMnTiSH1~H5 steel according to claim 1, characterized in that: The S4.3 finishing process: To ensure the dimensional accuracy and surface quality of cold-worked finished products, key parameters are: processing speed 8-28m / min, single-pass diameter reduction 0.2-1.5mm; die hole surface finish Ra≤0.04μm, dimensional accuracy≤±0.03mm. Precautions: maintain uniform speed during finishing, with speed fluctuation ≤±1.5m / min; check die wear after processing every 30-50 workpieces and polish and repair as needed.

8. The process for improving the cold working properties of 20CrMnTiSH1~H5 steel according to claim 1, characterized in that: The intermediate stress relief treatment in S4.4: For workpieces that have undergone multiple processing steps, work hardening is eliminated. Key parameters: stress relief temperature 180-320℃, holding time 1.0-3.0h, cooling rate 30-80℃ / h. Precautions: after stress relief treatment, the hardness of the workpiece should be controlled at 150-220HB, and the elongation after fracture should be ≥20%. After treatment, the surface should be lubricated again before proceeding to the next cold working process.

9. The process for improving the cold working properties of 20CrMnTiSH1~H5 steel according to claim 1, characterized in that: The stress-relief annealing described in S5.1: Completely eliminate residual stress from cold working, stabilize dimensions and performance. Key parameters: annealing temperature 200-350℃, heating rate 50-120℃ / h, holding time 2-4h; after holding, air cool to room temperature, avoid rapid cooling during the cooling process. Precautions: residual stress of the workpiece after annealing ≤150MPa; during batch production, sample 3-5 pieces from each batch to ensure performance consistency. S5.2 Surface cleaning and rust prevention: Remove residual lubricant and impurities from the surface after cold working, and perform rust prevention protection. Key parameters: use low-pressure shot blasting (pressure 0.3-0.9MPa) or alkaline degreasing (concentration 5-12%, temperature 40-70℃, time 10-25min); rust prevention treatment uses rust-preventive oil spraying or passivation, with rust-preventive oil thickness ≥0.02mm and passivation film thickness 0.004-0.018mm. Precautions: after cleaning, the surface roughness Ra≤0.8μm, free of oil stains and rust; packaging should be completed within 24 hours after rust prevention treatment, and the relative humidity of the storage environment should be ≤75%.

10. The process for improving the cold working properties of 20CrMnTiSH1~H5 steel according to claim 1, characterized in that: The S6.1 cold working performance test: Key parameters: Elongation at break after cold working ≥22%, reduction of area ≥50%, no cracks in 180° cold bending test (bending mandrel diameter d = finished product diameter a); hardness uniformity deviation ≤10HB. Note: 5-8 samples should be taken from each batch, covering different processing passes, to comprehensively test the cold working performance. S6.2 Organization and Surface Quality Inspection: Key parameters: Grain size ≥ 7, no Widmanstätten structure, banded structure ≤ 1.5; surface free of cracks, scratches, indentations, and defects, with defect depth ≤ 0.12 mm. Notes: Microstructure is observed using a metallographic microscope, and surface quality is tested using a 10x magnifying glass combined with surface flaw detection; non-conforming products need to be traced back to the previous process, and process parameters need to be optimized.