A hot rolling and controlled cooling process for improving surface hardness of S45C steel after drawing

Abstract

The present application relates to the technical field of steel metallurgy, and discloses a hot-rolling controlled cooling process for improving the surface hardness of S45C steel after drawing, which comprises S1 heating process, S2 temperature control during rolling process, S3 segmented controlled cooling process after rolling, S4 coiling and heat preservation treatment, and S5 quality inspection and process adjustment, the process improves the uniformity of hot-rolled rod organization, lays a foundation for drawing performance, through the heating process of "1050-1150℃ wide range soaking temperature + 120-200 minutes sufficient time in the furnace", and dynamic adjustment according to the billet specification (small specification takes the upper limit of temperature, large specification takes the lower limit), the composition segregation problem caused by traditional uneven heating is effectively solved, the internal temperature fluctuation of the billet is controlled within ±20℃, the composition homogenization degree is improved by 15%-20%; at the same time, through the optimization of entering the finishing rolling (860-900℃), entering the reducing sizing and the wire drawing temperature according to the specification during the rolling stage, the wire drawing temperature fluctuation is controlled within ±15℃, the austenite grain coarsening is avoided, and the conditions for forming fine and uniform organization after rolling are created.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a hot rolling controlled cooling process for improving the surface hardness of S45C steel after drawing. Background Technology

[0002] In the processing scenario where medium carbon steel (carbon content of about 0.42%-0.48%) is used to produce precision bright rods, the traditional hot rolling process generally suffers from the problems of single cooling control parameters and insufficient heating-rolling coordination. This results in poor uniformity of hot-rolled wire rod structure, large fluctuations in surface hardness and tensile strength, and ultimately leads to the core pain points of insufficient surface hardness and excessive bending of the product after drawing. Specifically, traditional processes have the following key defects: In the traditional hot rolling process, the heating stage often uses a fixed homogenization temperature (mostly concentrated at 1080-1120℃) and a short furnace time (100-140 minutes), without adjusting according to the differences in billet specifications. This easily leads to uneven temperature distribution and insufficient homogenization of composition inside the billet, resulting in localized segregation of the microstructure. In the rolling stage, the control precision of the temperature at the entry into the finishing mill, the entry into the sizing mill, and the wire drawing stage is insufficient (e.g., the wire drawing temperature fluctuates by more than ±30℃), and the temperature range is not optimized for different specifications (8-10mm small specifications, 12mm large specifications), which easily causes coarsening of austenite grains. Especially in the post-rolling cooling stage, traditional processes often adopt the mode of "uniform fan air volume + fixed cooling path", without distinguishing the characteristics of fast heat dissipation for small specifications and slow heat dissipation for large specifications. This results in small specifications of wire rods developing Widmanstätten structure due to excessively rapid cooling, while large specifications of wire rods have low pearlite content (mostly below 50%) and large lamellar spacing due to insufficient cooling.

[0003] The aforementioned problems ultimately result in the tensile strength of hot-rolled wire rods often being below 650MPa, the surface hardness (HRB) in the hot-rolled state being below 80, and the surface hardness after drawing easily dropping below 18HRC. The straightness runout of a 400mm length exceeds 0.12mm, requiring correction through repeated straightening and re-rolling. This not only reduces production efficiency but also increases the defect rate (the defect rate of traditional processes can reach 5%-8%), making it difficult to meet the processing requirements of precision bright rods. Summary of the Invention

[0004] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a hot-rolled controlled cooling process for improving the surface hardness of S45C steel after drawing. This process has advantages such as improving the uniformity of the microstructure of hot-rolled wire rods and laying the foundation for drawing performance, thus solving the problem of poor microstructure uniformity in hot-rolled wire rods.

[0005] (II) Technical Solution To achieve the aforementioned goal of improving the uniformity of the microstructure of hot-rolled wire rod and laying the foundation for its drawing performance, this invention provides the following technical solution: a hot-rolled controlled cooling process for improving the surface hardness of S45C steel after drawing, comprising S1 heating process, S2 temperature control during rolling, S3 segmented controlled cooling process after rolling, S4 coiling and heat preservation treatment, and S5 quality inspection and process adjustment. The S3 segmented controlled cooling process after rolling includes S301 small specification (8-10mm) and S302 large specification (12mm). Among them, S5 quality inspection and process adjustment includes the S501 adjustment mechanism.

[0006] Preferably, the S1 heating process; Key parameters: Isostatic temperature: 1050-1150℃ (adjusted flexibly according to billet specifications; upper limit for small specifications, lower limit for large specifications). Furnace time: 120-200 minutes (to ensure uniform internal temperature of the billet and avoid local differences in microstructure). Temperature fluctuation control: ≤±20℃, to prevent uneven heating of steel billets from causing subsequent microstructure segregation.

[0007] Preferably, the temperature is controlled during the S2 rolling process; Key parameters: Finishing rolling temperature: 860-900℃ (to ensure the plasticity of the rolling process and avoid grain coarsening caused by high temperature); Infeed sizing temperature: 840-940℃ (adjusted according to specifications, 840-880℃ for small specifications, 880-940℃ for large specifications). Spinning temperature: 790-870℃ (core parameter, 810-870℃ for small sizes, 790-830℃ for large sizes, to avoid excessive spinning temperature causing coarsening of pearlite). Dimensional accuracy control: ovality ≤ 0.35mm for small sizes (8-10mm) and ovality ≤ 0.45mm for large sizes (12mm), ensuring uniformity in subsequent drawing.

[0008] Preferably, the S301 has a smaller size (8-10mm): Roller conveyor speed: 0.80-0.90 m / s, to ensure uniform cooling; Number of fans to be turned on: 1-5# fans, air volume 40%-75% (dynamically adjusted according to the spinning temperature, the upper limit of air volume is used when the spinning temperature is high); Cooling path: Water tank cooling (water tanks 1-3 are open) → segmented air cooling line to ensure stable cooling rate.

[0009] Preferably, the S302 has a large size (12mm): Roller conveyor speed: 0.70-0.85m / s, extending cooling time; Number of fans in operation: 1-5# fans, air volume 50%-75% (slightly higher than the air volume of smaller fans to compensate for the slow heat dissipation of larger fans); Cooling path: Water tank cooling (water tanks 1-3 are open) → enhanced cooling via air cooling line, airflow of fans 1-2 can be increased to 70%-75%; Cooling rate control: Ensure that the pearlite content of the rolled wire rod is ≥55%, refine the interlamellar spacing, and avoid the formation of Widmanstätten structure.

[0010] Preferably, the S4 winding and heat preservation treatment; Key parameters: Winding temperature: ≥650℃, to avoid stress concentration caused by low-temperature winding; Insulation method: For small sizes (8-10mm), close the insulation cover and allow natural cooling; for large sizes (12mm), partially open the insulation cover (selectively open insulation covers 1-4#) and allow slow cooling. Insulation time: After winding, keep naturally warm for 30-60 minutes until the temperature is uniform before proceeding with subsequent processing.

[0011] Preferably, S5 involves quality inspection and process adjustment; Inspection items and standards: Mechanical properties: tensile strength of hot-rolled wire rod ≥680MPa, yield strength ≥400MPa; Surface hardness: HRB≥85 in hot rolled state, and ≥20HRC after drawing; Tissue examination: The pearlitic structure is uniform, with no obvious Widmanstätten or network cementite.

[0012] Preferably, the S501 adjustment mechanism is as follows: if the tensile strength is lower than the lower limit, increase the fan air volume by 5%-10% or reduce the spinning temperature by 10-20℃; if the hardness fluctuates too much, adjust the furnace time or the number of fans turned on in the cooling path.

[0013] (III) Beneficial Effects Compared with the prior art, the present invention provides a hot rolling controlled cooling process for improving the surface hardness of S45C steel after drawing, which has the following beneficial effects: 1. This hot-rolled controlled cooling process improves the surface hardness of S45C steel after drawing. This process enhances the uniformity of the microstructure of the hot-rolled wire rod, laying the foundation for its drawing performance. It is achieved by employing a wide-range homogenization temperature of 1050-1150℃ + sufficient furnace time of 120-200 minutes. The heating process, dynamically adjusted according to billet specifications (upper temperature limit for small specifications, lower temperature limit for large specifications), effectively solves the problem of compositional segregation caused by uneven heating in traditional methods. The internal temperature fluctuation of the billet is controlled within ±20℃, and the homogenization of composition is improved by 15%-20%. At the same time, the rolling stage is optimized by specification for the pre-finishing rolling (860-900℃), the pre-sizing and reducing (840-880℃ for small specifications, 880-940℃ for large specifications), and the wire drawing temperature (810-870℃ for small specifications, 790-830℃ for large specifications). The wire drawing temperature fluctuation is controlled within ±15℃, avoiding austenite grain coarsening and creating conditions for the formation of a fine and uniform microstructure after rolling.

[0014] 2. This hot-rolled controlled cooling process improves the surface hardness of S45C steel after drawing. This process significantly improves the mechanical properties of hot-rolled wire rod and directly ensures the surface hardness after drawing. The segmented controlled cooling process after rolling achieves precise control of the cooling rate through specification-differentiated design: small specifications use "0.80-0.90m / s roller speed + 1-5# fan 40%-75% air volume", and large specifications use "0.70-0.85m / s roller speed + 1-5# fan 50%-75% air volume". The air volume of 1-2# fan is specifically strengthened for large specifications (70%-75%) to ensure that wire rods of different specifications can form a microstructure with pearlite content ≥55% and fine lamellar spacing. Ultimately, the tensile strength of hot-rolled wire rod is stable at ≥680MPa (5%-8% improvement compared to traditional processes), and the surface hardness HRB in the hot-rolled state is ≥85 (6%-10% improvement), providing core support for achieving the performance standards after drawing.

[0015] 3. This hot-rolling controlled-cooling process improves the surface hardness of S45C steel after drawing. This process ensures that the performance of the drawn product meets the standards and reduces the defect rate. Through optimization of parameters throughout the entire process, this process directly solves the problems of insufficient surface hardness and excessive curvature after drawing in traditional processes: the surface hardness of the drawn product is stable at ≥20HRC (far exceeding the requirement of ≥18HRC), and the hardness fluctuation range is reduced to ±1.5HRC (compared to more than ±3HRC in traditional processes); the straightness runout of a 400mm length is strictly controlled to ≤0.10mm, and the straightness qualification rate is increased to more than 98% (compared to only 92%-95% in traditional processes); at the same time, post-rolling cooling avoids Widmanstätten and network cementite defects, improves the uniformity of material stress during drawing, eliminates the need for repeated straightening, and reduces the defect rate to 1%-2%, a decrease of 4-6 percentage points compared to traditional processes.

[0016] 4. This hot-rolled controlled cooling process improves the surface hardness of S45C steel after drawing. This process enhances production stability and reduces process adjustment costs. During the coiling and heat preservation stage, heat preservation methods are designed according to specifications (small specifications are cooled naturally with the heat preservation cover closed, while large specifications are cooled slowly with heat preservation covers #1-4 open selectively), and a natural heat preservation time of 30-60 minutes is set to reduce the temperature difference between the inside and outside of the coil after coiling (the temperature difference is controlled within ≤40℃), avoiding bending deformation caused by stress concentration. At the same time, a dynamic adjustment mechanism of "performance-parameter" is established in the quality inspection process (if the tensile strength is insufficient, the fan air volume is increased by 5%-10% or the wire drawing temperature is reduced by 10-20℃), realizing real-time optimization of process parameters, reducing batch non-conformities caused by parameter deviations, reducing the frequency of process adjustments by 30%-40%, significantly improving production stability, and indirectly reducing the cost of re-rolling and rework.

[0017] 5. This hot-rolling controlled-cooling process improves the surface hardness of S45C steel after drawing. This process is suitable for multi-specification production, enhancing the versatility of the process. This process designs heating temperature, rolling temperature, and post-rolling cooling parameters separately for 8-10mm small specifications and 12mm large specifications (the upper limit of the wire drawing temperature for small specifications is 40℃ higher than that for large specifications, and the lower limit of the fan air volume for large specifications is 10% higher than that for small specifications). It not only adapts to the heat dissipation characteristics of different specifications, but also meets the production needs of multiple specifications on the same production line. There is no need to frequently change equipment parameters, and the production switching efficiency is improved by 25%-30%. It is suitable for multi-specification processing scenarios of precision bright rods, enhancing the versatility and practicality of the process. 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 solution, specifically a hot rolling controlled cooling process to improve the surface hardness of S45C steel after drawing, including the following process: S1 heating process; Process objective: To ensure the uniformity of steel billet composition, laying the microstructure foundation for subsequent rolling and controlled cooling; Key parameters: Isostatic temperature: 1050-1150℃ (adjusted flexibly according to billet specifications; upper limit for small specifications, lower limit for large specifications). Furnace time: 120-200 minutes (to ensure uniform internal temperature of the billet and avoid local differences in microstructure). Temperature fluctuation control: ≤±20℃, to prevent uneven heating of the billet from causing subsequent microstructure segregation; Temperature control during S2 rolling process; Process objective: To control the rolling temperature, avoid excessively large austenite grains, and create conditions for controlled cooling after rolling to form a fine pearlite structure; Key parameters: Finishing rolling temperature: 860-900℃ (to ensure the plasticity of the rolling process and avoid grain coarsening caused by high temperature); Infeed sizing temperature: 840-940℃ (adjusted according to specifications, 840-880℃ for small specifications, 880-940℃ for large specifications). Spinning temperature: 790-870℃ (core parameter, 810-870℃ for small sizes, 790-830℃ for large sizes, to avoid excessive spinning temperature causing coarsening of pearlite). Dimensional accuracy control: ovality ≤ 0.35mm for small sizes (8-10mm) and ovality ≤ 0.45mm for large sizes (12mm), ensuring uniformity in subsequent drawing; S3 post-rolling segmented controlled cooling process; Process objective: To improve the tensile strength and surface hardness of wire rod by precisely controlling the cooling process to adjust the pearlite content and lamellar spacing is the core process step; Key parameters (set according to specification differences): S301 Small Size (8-10mm): Roller conveyor speed: 0.80-0.90 m / s, to ensure uniform cooling; Number of fans to be turned on: 1-5# fans, air volume 40%-75% (dynamically adjusted according to the spinning temperature, the upper limit of air volume is used when the spinning temperature is high); Cooling path: Water tank cooling (water tanks 1-3 are open) → segmented air cooling line to ensure stable cooling rate; S302 Large Size (12mm): Roller conveyor speed: 0.70-0.85m / s, extending cooling time; Number of fans in operation: 1-5# fans, air volume 50%-75% (slightly higher than the air volume of smaller fans to compensate for the slow heat dissipation of larger fans); Cooling path: Water tank cooling (water tanks 1-3 are open) → enhanced cooling via air cooling line, airflow of fans 1-2 can be increased to 70%-75%; Cooling rate control: Ensure that the pearlite content of the rolled wire rod is ≥55%, refine the lamellar spacing, and avoid the formation of Widmanstätten structure; S4 winding and insulation treatment; Process objective: To reduce the temperature difference between the inside and outside of the coil after winding, prevent uneven surface and core structure, and reduce hardness fluctuation after drawing; Key parameters: Winding temperature: ≥650℃, to avoid stress concentration caused by low-temperature winding; Insulation method: For small sizes (8-10mm), close the insulation cover and allow natural cooling; for large sizes (12mm), partially open the insulation cover (selectively open insulation covers 1-4#) and allow slow cooling. Insulation time: After winding, keep naturally warm for 30-60 minutes until the temperature is uniform before proceeding with subsequent processing; S5 Quality Inspection and Process Adjustment; Process objective: To monitor wire rod performance in real time and dynamically optimize process parameters; Inspection items and standards: Mechanical properties: tensile strength of hot-rolled wire rod ≥680MPa, yield strength ≥400MPa; Surface hardness: HRB≥85 in hot rolled state, and ≥20HRC after drawing; Tissue examination: The pearlitic structure is uniform, with no obvious Widmanstätten or network cementite; S501 Adjustment Mechanism: If the tensile strength is below the lower limit, increase the fan air volume by 5%-10% or decrease the wire drawing temperature by 10-20℃; if the hardness fluctuates too much, adjust the furnace time or the number of fans turned on in the cooling path. Furthermore, this process improves the uniformity of the microstructure of hot-rolled wire rod, laying the foundation for drawing performance. By adopting a heating process of "wide-range homogenization temperature of 1050-1150℃ + sufficient furnace time of 120-200 minutes", and dynamically adjusting according to the billet specifications (using the upper limit of the temperature for small specifications and the lower limit for large specifications), the problem of compositional segregation caused by uneven heating in traditional methods is effectively solved. The internal temperature fluctuation of the billet is controlled within ±20℃, and the degree of compositional homogenization is improved by 15%-20%. At the same time, in the rolling stage, by optimizing the pre-finishing rolling (860-900℃), pre-sizing (840-880℃ for small specifications and 880-940℃ for large specifications), and wire drawing temperature (810-870℃ for small specifications and 790-830℃ for large specifications), the wire drawing temperature fluctuation is controlled within ±15℃, avoiding austenite grain coarsening and creating conditions for the formation of a fine and uniform microstructure after rolling. Furthermore, this process significantly improves the mechanical properties of hot-rolled wire rod, directly ensuring the surface hardness after drawing. The segmented controlled cooling process after rolling achieves precise control of the cooling rate through specification-differentiated design: small specifications use "0.80-0.90m / s roller speed + 1-5# fan 40%-75% air volume", and large specifications use "0.70-0.85m / s roller speed + 1-5# fan 50%-75% air volume", with targeted enhancement of the air volume of 1-2# fan (70%-75%) for large specifications. This ensures that wire rods of different specifications can form a microstructure with pearlite content ≥55% and fine lamellar spacing, ultimately making the tensile strength of hot-rolled wire rod stable ≥680MPa (5%-8% higher than traditional process) and the surface hardness HRB in the hot-rolled state ≥85 (6%-10% higher), providing core support for achieving performance standards after drawing. Furthermore, this process ensures that the performance of the drawn product meets the standards and reduces the defect rate. Through optimization of parameters throughout the entire process, this process directly solves the problems of insufficient surface hardness and excessive curvature after drawing in traditional processes: the surface hardness of the drawn product is stable at ≥20HRC (far exceeding the requirement of ≥18HRC), and the hardness fluctuation range is reduced to ±1.5HRC (compared to fluctuations of over ±3HRC in traditional processes); the straightness runout of a 400mm length is strictly controlled to ≤0.10mm, and the straightness qualification rate is increased to over 98% (compared to only 92%-95% in traditional processes); at the same time, post-rolling cooling avoids Widmanstätten and network cementite defects, improves the uniformity of material stress during drawing, eliminates the need for repeated straightening, and reduces the defect rate to 1%-2%, a decrease of 4-6 percentage points compared to traditional processes; Furthermore, this process improves production stability and reduces process adjustment costs. During the coiling and insulation stage, insulation methods are designed according to specifications (small specifications are cooled naturally with the insulation cover closed, while large specifications are cooled slowly with insulation covers #1-4 selectively opened), and a natural insulation time of 30-60 minutes is set to reduce the temperature difference between the inside and outside of the coil after coiling (the temperature difference is controlled within ≤40℃), avoiding bending deformation caused by stress concentration. At the same time, a dynamic adjustment mechanism of "performance-parameter" is established in the quality inspection process (if the tensile strength is insufficient, the fan air volume is increased by 5%-10% or the coiling temperature is reduced by 10-20℃), realizing real-time optimization of process parameters, reducing batch non-conformities caused by parameter deviations, reducing the frequency of process adjustments by 30%-40%, significantly improving production stability, and indirectly reducing the cost of re-rolling and rework. Furthermore, this process is adaptable to multi-specification production, enhancing its versatility. The process is designed with separate heating, rolling, and post-rolling cooling parameters for 8-10mm small specifications and 12mm large specifications (the upper limit of the coiling temperature for small specifications is 40℃ higher than that for large specifications, and the lower limit of the fan airflow for large specifications is 10% higher than that for small specifications). This adapts to the heat dissipation characteristics of different specifications and meets the production needs of multiple specifications on the same production line, eliminating the need for frequent changes in equipment parameters and improving production switching efficiency by 25%-30%. It is suitable for multi-specification processing scenarios of precision bright rods, enhancing the versatility and practicality of the process.

[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 hot-rolled controlled cooling process for improving the surface hardness of S45C steel after drawing, comprising S1 heating process, S2 temperature control during rolling, S3 segmented controlled cooling process after rolling, S4 coiling and heat preservation treatment, and S5 quality inspection and process adjustment, characterized in that: The S3 post-rolling segmented controlled cooling process includes S301 small size (8-10mm) and S302 large size (12mm). Among them, S5 quality inspection and process adjustment includes the S501 adjustment mechanism.

2. The hot rolling controlled cooling process for improving the surface hardness of S45C steel after drawing, as described in claim 1, is characterized in that: The S1 heating process; Key parameters: Isostatic temperature: 1050-1150℃ (adjusted flexibly according to billet specifications; upper limit for small specifications, lower limit for large specifications). Furnace time: 120-200 minutes (to ensure uniform internal temperature of the billet and avoid local differences in microstructure). Temperature fluctuation control: ≤±20℃, to prevent uneven heating of steel billets from causing subsequent microstructure segregation.

3. The hot rolling controlled cooling process for improving the surface hardness of S45C steel after drawing, as described in claim 1, is characterized in that: Temperature control during the S2 rolling process; Key parameters: Finishing rolling temperature: 860-900℃ (to ensure the plasticity of the rolling process and avoid grain coarsening caused by high temperature); Infeed sizing temperature: 840-940℃ (adjusted according to specifications, 840-880℃ for small specifications, 880-940℃ for large specifications). Spinning temperature: 790-870℃ (core parameter, 810-870℃ for small sizes, 790-830℃ for large sizes, to avoid excessive spinning temperature causing coarsening of pearlite). Dimensional accuracy control: ovality ≤ 0.35mm for small sizes (8-10mm) and ovality ≤ 0.45mm for large sizes (12mm), ensuring uniformity in subsequent drawing.

4. The hot rolling controlled cooling process for improving the surface hardness of S45C steel after drawing, as described in claim 1, is characterized in that: The S301 small size (8-10mm): Roller conveyor speed: 0.80-0.90 m / s, to ensure uniform cooling; Number of fans to be turned on: 1-5# fans, air volume 40%-75% (dynamically adjusted according to the spinning temperature, the upper limit of air volume is used when the spinning temperature is high); Cooling path: Water tank cooling (water tanks 1-3 are open) → segmented air cooling line to ensure stable cooling rate.

5. The hot rolling controlled cooling process for improving the surface hardness of S45C steel after drawing, as described in claim 1, is characterized in that: The S302 large size (12mm): Roller conveyor speed: 0.70-0.85m / s, extending cooling time; Number of fans in operation: 1-5# fans, air volume 50%-75% (slightly higher than the air volume of smaller fans to compensate for the slow heat dissipation of larger fans); Cooling path: Water tank cooling (water tanks 1-3 are open) → enhanced cooling via air cooling line, airflow of fans 1-2 can be increased to 70%-75%; Cooling rate control: Ensure that the pearlite content of the rolled wire rod is ≥55%, refine the interlamellar spacing, and avoid the formation of Widmanstätten structure.

6. The hot rolling controlled cooling process for improving the surface hardness of S45C steel after drawing, as described in claim 1, is characterized in that: The S4 winding and heat preservation treatment; Key parameters: Winding temperature: ≥650℃, to avoid stress concentration caused by low-temperature winding; Insulation method: For small sizes (8-10mm), close the insulation cover and allow natural cooling; for large sizes (12mm), partially open the insulation cover (selectively open insulation covers 1-4#) and allow slow cooling. Insulation time: After winding, keep naturally warm for 30-60 minutes until the temperature is uniform before proceeding with subsequent processing.

7. The hot rolling controlled cooling process for improving the surface hardness of S45C steel after drawing, as described in claim 1, is characterized in that: The S5 quality inspection and process adjustment; Inspection items and standards: Mechanical properties: tensile strength of hot-rolled wire rod ≥680MPa, yield strength ≥400MPa; Surface hardness: HRB≥85 in hot rolled state, and ≥20HRC after drawing; Tissue examination: The pearlitic structure is uniform, with no obvious Widmanstätten or network cementite.

8. The hot rolling controlled cooling process for improving the surface hardness of S45C steel after drawing, as described in claim 1, is characterized in that: The S501 adjustment mechanism is as follows: if the tensile strength is lower than the lower limit, increase the fan air volume by 5%-10% or decrease the spinning temperature by 10-20℃; if the hardness fluctuates too much, adjust the furnace time or the number of fans turned on in the cooling path.