A shaft connecting block type steel production and processing method

Abstract

This application relates to the field of metal pressure processing and special-shaped steel rolling, and particularly to a method for producing shaft link block steel. Addressing the problems of easy bending and difficulty in accurately forming small arcs in existing asymmetric section rolling processes, this application divides multi-pass rolling into a billet stage, a forming stage, and a finishing stage. Asymmetric deformation compensation is introduced in the forming and finishing stages, making the ratio of the reduction on the thick-walled side to the thin-walled side Δh₁ / Δh₂ = 1.05~1.25. In the forming stage, small arcs with a curvature radius R < 5mm are replaced with transition arcs not less than 3 times the finished product radius. The finishing stage provides final constraint forming. The reduction rate per pass decreases in a stepwise manner. This application effectively suppresses workpiece bending, with each pass exit bending degree ≤ 2mm / m, and small arcs are completely filled without defects. Combined with controlled cooling, a uniform microstructure with a ferrite grain size ≥ 7 is obtained, and the uniformity deviation of the carburized layer depth is ≤ 0.1mm. This method is suitable for the production of asymmetric special-shaped section steel made of alloy steel such as 20Cr.

Description

Technical Field

[0001] This application relates to the field of metal pressure processing and special-shaped steel rolling, and in particular to a method for producing and processing shaft link block steel. Background Technology

[0002] Shaft link block steel is a type of shaped steel used in mechanical transmission and connection applications. Its typical cross-section is asymmetrical, usually consisting of at least two circular arc profiles with different radii of curvature and an asymmetrical transition section connecting these arc profiles. This type of steel is often formed by hot rolling cylindrical billets, requiring the finished product to have precise dimensions and good surface quality to meet the requirements of subsequent assembly and heat treatment processes. In current production, an open-pass rolling system including vertical and horizontal rolling passes is often used to continuously roll the heated billet in multiple passes, gradually transforming the circular cross-section into the desired shaped section.

[0003] However, due to the asymmetry of the cross-section of the shaft-connecting block steel, the flow of metal along the width direction during rolling exhibits a significant unevenness: the metal flow on the thin-walled side is better than that on the thick-walled side, which easily leads to bending or twisting of the rolled piece at the exit, affecting the bite and forming accuracy of subsequent passes. Simultaneously, for small arc transition areas with a radius of curvature less than 5mm on the cross-section, direct forming during the roughing stage can easily result in defects such as folding, cracking, or incomplete filling due to localized stress concentration, making it difficult to guarantee the integrity of the final product's contour. Furthermore, an unreasonable distribution of deformation at different rolling stages can cause surface scratches or dimensional deviations during the finishing stage, further reducing yield and dimensional consistency.

[0004] To address the aforementioned issues, a method for producing shaft link block steel is needed. This method can effectively suppress bending caused by cross-sectional asymmetry during multi-pass continuous rolling, ensure precise filling of minute arc contours, and balance roughing efficiency with finishing accuracy through reasonable deformation distribution, thereby stably producing asymmetric profile steel that meets design requirements. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this application provides a method for rolling asymmetric irregular cross-sections of shaft link block steel, which can achieve precise forming of asymmetric micro-arc contours, effectively suppress bending of rolled parts and improve the accuracy of finished cross-section contours.

[0006] This application is achieved through the following technical solution: A method for producing shaft link block steel, used to roll a cylindrical steel billet into shaft link block steel with an asymmetrical irregular cross-section, wherein the asymmetrical irregular cross-section comprises at least two arc profiles with different radii of curvature and an asymmetrical transition segment connecting the arc profiles, characterized by comprising the following steps: Step S1, Billet Heating: The cylindrical steel billet is sent into the heating furnace for heating and heat preservation; Step S2, roll forming: Using an open roll forming system that includes vertical and horizontal roll forming holes, the heated billet is continuously rolled in multiple passes to gradually form the finished product with the asymmetric cross-section. The multi-pass continuous rolling process is divided into three stages: billet preparation, forming, and finishing rolling. The billet-opening stage employs at least one vertical rolling pass to control the widening of the rolled piece and correct the side profile; the forming stage and the finishing stage employ multiple horizontal rolling passes. In the forming and finishing stages, asymmetric deformation compensation is introduced into the pass structure of each pass, such that the single-pass reduction Δh1 on the thick-walled side and the single-pass reduction Δh2 on the thin-walled side satisfy: Δh1 / Δh2 = 1.05~1.25, to compensate for the flow of metal to the thin-walled side caused by the asymmetry of the cross-section; wherein, the definition of the thick-walled side and the thin-walled side is based on the geometric characteristics of the finished cross-section, and the reduction ratio is achieved by adjusting the difference in the pass depth of the corresponding parts in the pass design; The forming stage constrains the large arc profile with a curvature radius R ≥ 10 mm in the cross section through the rough forming pass. For the small arc transition area with a curvature radius R < 5 mm, a transition arc pass with a curvature radius not less than 3 times the curvature radius of the final finished small arc is used for rolling. The finishing rolling stage finally constrains the forming of the small arc and straight transition section with a curvature radius R < 5 mm. The single-pass surface reduction rate of the multi-pass continuous rolling process is distributed in a stepwise manner, wherein the single-pass surface reduction rate of the billet stage and the single-pass surface reduction rate of the forming stage are both greater than the single-pass surface reduction rate of the finishing rolling stage.

[0007] By adopting the above technical solutions, asymmetric deformation compensation is introduced in the forming and finishing rolling stages, controlling the ratio of the reduction on the thick-walled side to the thin-walled side to be between 1.05 and 1.25. This effectively counteracts the tendency of metal to preferentially flow to the thin-walled side due to cross-sectional asymmetry, suppressing bending or twisting of the rolled piece. Simultaneously, for small arcs, a transition arc with a radius not less than three times the radius of the finished arc is used as a replacement forming method, with final constraint applied in the finishing rolling stage. This prevents small arcs from folding, cracking, or incomplete filling due to stress concentration in the roughing passes. Furthermore, the single-pass reduction rate in the billet and forming stages is designed to be greater than that in the finishing rolling stage, forming a stepped reduction distribution. This ensures sufficient deformation in the early stages to quickly approximate the finished contour while avoiding excessive deformation in the finishing rolling stage that could lead to surface scratches or dimensional deviations. The synergy of these three factors enables shaft-connecting block steel sections containing multiple arcs with different radii of curvature and asymmetric transition sections to stably obtain high-precision cross-sectional contours during continuous rolling.

[0008] Optionally, the reduction ratio Δh1 / Δh2 of the asymmetric deformation compensation is distributed in a decreasing manner among the passes; in the first half of the forming stage, Δh1 / Δh2 = 1.15 to 1.25; in the second half of the forming stage, Δh1 / Δh2 = 1.10 to 1.20; in the finishing rolling stage, Δh1 / Δh2 gradually converges to 1.05 to 1.10; and the curvature of the exit piece of each pass is ≤2mm / m.

[0009] By adopting the above technical solution, the reduction ratio is gradually distributed between each pass, which matches the gradual establishment process of cross-sectional asymmetry: when the asymmetry is not fully formed in the early stage of forming, a larger compensation amount is used to prevent early bending. As the cross-sectional shape approaches the finished product, the compensation amount is gradually reduced to avoid over-compensation causing reverse bending, thereby achieving stable rolling throughout the process and providing a flat material shape foundation for the precise filling of the small arcs in the subsequent finishing rolling. The exit curvature of each pass is controlled within 2mm per meter.

[0010] Optionally, in step S2, the total reduction rate of the entire roll pass is controlled at 70% to 80%; the reduction rate of a single pass in the billet stage is controlled at 11% to 16%; the reduction rate of a single pass in the forming stage is controlled at 12% to 16%; and the reduction rate of a single pass in the finishing stage is controlled at 8% to 10%.

[0011] By adopting the above technical solution, it is ensured that the total deformation is sufficient to refine the grains and eliminate the casting structure. At the same time, a lower reduction rate is used in the finishing rolling stage to control the final dimensional accuracy and surface quality, avoiding work hardening or surface defects in the small arc area caused by excessive finishing rolling deformation. Meanwhile, the decreasing distribution of the ratio with the reduction amount forms a synergistic matching of process parameters, so that the deformation load of each pass is evenly distributed.

[0012] Optionally, a pre-finished hole is used in the penultimate pass of the finishing rolling stage. The pre-finished hole has a finishing rolling allowance of 0.5 to 1.0 mm uniformly reserved on each dimension surface based on the final finished cross-sectional size. The finishing rolling allowance is eliminated in the finished hole of the last pass to finally constrain and form the micro-arc and straight transition section. The surface hardness of the roll surface of the finished hole in the area corresponding to the micro-arc is ≥ HRC55.

[0013] By adopting the above technical solution, the reserved finishing rolling allowance allows only a thin layer of metal to be removed in the last pass, which is conducive to the accurate replication of the micro-arc and the improvement of surface finish; while the high hardness of the roller surface can resist the high contact stress in the micro-arc area, prevent the arc size distortion caused by the wear of the die, and ensure the consistency of the finished product cross section in mass production.

[0014] Optionally, in step S2, the rolling speed V1 of the finishing rolling stage and the rolling speed V2 of the forming stage satisfy: V1 / V2 = 1.3~1.8, so as to shorten the total time of the finishing rolling stage, make the final rolling temperature ≥880℃, and ensure that the metal in the micro-arc region of the finishing rolling stage is in the fully austenitic region and fully fills the die.

[0015] By adopting the above technical solutions, the finishing rolling speed is increased, the contact heat dissipation time between the workpiece and the rolls and the environment is reduced, and the final rolling temperature is maintained above 880°C in the fully austenitic region. This significantly reduces the deformation resistance and improves the ability of the metal to fill the die, ensuring that small arcs with a curvature radius of less than 5 mm can be completely replicated without producing missing corners or edge collapse.

[0016] Optionally, for round steel billets with a specification of Φ105mm, the multi-pass continuous rolling is set to a total of 11 passes, wherein: the billet opening stage includes the first to second consecutive vertical rolling passes, which sequentially roll the round billet into an elliptical and rectangular billet; the forming stage includes the third to eighth consecutive horizontal rolling passes; the finishing rolling stage includes the ninth to eleventh consecutive horizontal rolling passes; the opening pass system adopts a conjugate pass design, and the sidewall slope of the vertical rolling pass is controlled at 10% to 15%.

[0017] By adopting the above technical solution, the first two vertical rolling passes are widened by lateral constraint control and initially establish an asymmetric profile, the middle six horizontal rolling passes gradually approach the final shape, and the last three horizontal rolling passes complete the finishing. The conjugate roll design ensures the matching accuracy of the upper and lower roll rolls, while the 10% to 15% sidewall slope is beneficial for degrooving and avoids excessive lateral flow. It is a parameter optimized for the cross-sectional characteristics of the shaft link block steel.

[0018] Optionally, in step S1, the steel billet is 20Cr alloy carburizing steel; the heating temperature is set to 1150~1250℃, and the furnace exit temperature is controlled at 1100~1150℃.

[0019] By adopting the above technical solution, the alloying elements are fully dissolved, while avoiding excessively coarse grains, thus providing a uniform austenitic structure for subsequent rolling. The temperature drop between the furnace exit temperature and the final rolling temperature is matched with the aforementioned rolling speed ratio design, ensuring that the final rolling temperature can still be maintained above 880°C during the finishing rolling stage, ensuring that the metal in the small arc area is in a highly ductile state.

[0020] Optionally, it also includes step S3, controlled cooling and post-processing: the rolled steel section from step S2 is subjected to controlled cooling, multi-roll straightening and cutting in sequence; the specific process of controlled cooling is as follows: in the temperature range from the final rolling temperature to 650℃, air cooling is used, and the cooling rate is controlled at 2-5℃ / s to suppress the formation of a continuous network distribution of proeutectoid ferrite along the austenite grain boundaries; below 650℃, slow cooling is adopted, and the cooling rate is ≤1℃ / s to room temperature; the controlled cooling makes the rolled microstructure of the steel section a uniform ferrite and pearlite mixed microstructure with a ferrite grain size ≥7; the multi-roll straightening controls the straightness of the steel section to ≤0.5mm / m.

[0021] By adopting the above technical solution, the rapid cooling of sand at 2 to 5°C can interrupt the continuous distribution of ferrite network, avoid grain boundary weakening, and at the same time avoid the formation of hard and brittle phases such as martensite, thus obtaining a fine-grained and uniformly mixed structure. This structure not only improves the strength and toughness of the steel section, but more importantly, it provides a matrix with uniform composition and structure for subsequent carburizing treatment, so as to fundamentally ensure the uniformity of the carburized layer depth. Multi-roll straightening ensures that the straightness does not exceed 0.5 mm / m.

[0022] Optionally, after step S3, step S4, carburizing and quenching treatment, is further included: the steel section is carburized at 920-940℃, then quenched at 800-820℃, and finally tempered at 180-200℃; wherein, the ferrite grain size ≥7 uniform ferrite and pearlite mixed structure obtained in step S3 makes the uniformity deviation of the carburized layer depth ≤0.1mm.

[0023] By adopting the above technical solution, the fine-grained uniform matrix promotes the uniform diffusion of carbon atoms during the carburizing process, so that the uniformity deviation of the carburized layer depth does not exceed 0.1mm. This solves the problem of uneven carburizing caused by the complex shape of asymmetric irregular cross sections, and provides a highly wear-resistant surface layer and a strong and tough core for shaft connecting block steel.

[0024] Optionally, in the asymmetric cross-section of the steel, the difference in cooling rate in each region due to the difference in wall thickness is homogenized by controlling the cooling rate within the range of 2 to 5℃ / s in step S3, so that the difference in carburized layer depth in each region of the cross-section in step S4 is ≤0.05mm.

[0025] By adopting the above technical solution and selecting a medium cooling rate range of 2 to 5°C per sand, the thin-walled area is prevented from being overcooled, while the thick-walled area is given sufficient undercooling to refine the grains, reduce the microstructure differences between areas with different wall thicknesses, and ultimately ensure that the difference in carburized layer depth does not exceed 0.05 mm, thereby avoiding premature local failure and extending the overall service life.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. This application effectively suppresses bending and torsion during the asymmetric section rolling process by quantitatively designing the asymmetric deformation compensation reduction ratio Δh1 / Δh2=1.05~1.25 and its decreasing distribution among each pass, so that the bending degree of the exit rolled piece of each pass is ≤2mm / m, providing a straight material shape for subsequent finishing rolling; 2. This application adopts a phased arc forming strategy. In the forming stage, a transition arc with a radius not less than 3 times that of the finished arc is used to replace the small arc. In the finishing rolling stage, the final forming is constrained. This completely solves the process problem that small arcs with a curvature radius of less than 5mm are prone to folding, cracking or incomplete filling in the roughing pass, and the integrity rate of the finished product contour is significantly improved. 3. This application uses a stepped decreasing area reduction ratio combined with a finishing rolling speed ratio V1 / V2=1.3~1.8 to achieve a final rolling temperature ≥880℃, ensuring that the metal in the small arc area is in the fully austenitic region, with excellent filling performance, while avoiding surface scratches during finishing rolling, and achieving a finished product surface quality of Ra≤3.2μm; 4. This application obtains a uniform mixed microstructure with ferrite grain size ≥ 7 by controlling the air cooling rate of 2-5℃ / s in the cooling process, which provides a microstructure uniformity guarantee for subsequent carburizing, making the uniformity deviation of carburized layer depth ≤ 0.1mm and the difference in carburized layer depth in different regions of the cross section ≤ 0.05mm, which is significantly better than the conventional hot-rolled state. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the asymmetric irregular cross-sectional shape of the shaft link block steel product in Example 1; Figure 2 This is a schematic diagram of the profile of the first vertical rolling pass in Embodiment 1 of this application; Figure 3 This is a schematic diagram of the profile of the second vertical rolling hole in Embodiment 1 of this application; Figure 4 This is a schematic diagram of the profile of the flat rolling hole in the forming stage and finishing rolling stage described in Embodiment 1 of this application; Figure 5 This is a schematic diagram illustrating the calculation basis for the single-pass reduction Δh1 and Δh2 in this application; Figure 6 This is a curve comparing the exit curvature of the rolled piece in Embodiment 1 and Comparative Example 1 of this application.

[0028] In the figure: 1. Thick-walled side arc section; 2. Thin-walled side arc section; 3. Asymmetrical transition section; 4. Micro-arc transition area; 5. Vertical rolling hole; 6. Horizontal rolling hole; 7. Transition arc hole type; 8. Finished hole type. Detailed Implementation

[0029] The technical solutions of various embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In this application, the definitions of thick-walled side and thin-walled side are clearly defined: in any normal direction of the finished product section, with the centroid of the section or a specific reference line as a reference, the side with a larger local thickness perpendicular to that direction is called the thick-walled side, and the side with a smaller thickness is called the thin-walled side; for the transition section area, its classification is defined by linear interpolation or by taking the thickness of the adjacent arc segment; in addition, in the pass design, the calculation basis for the single-pass reduction Δh1 and Δh2 is: the dimensional difference between the current pass pass profile and the previous pass rolled piece profile in the corresponding thick-walled side and thin-walled side normal directions. Example 1

[0030] Reference Figures 1 to 3 This embodiment provides a method for producing shaft link block steel, used to roll a cylindrical steel billet into a shaft link block steel with an asymmetrical cross-section. The asymmetrical cross-section includes at least two arc profiles with different radii of curvature and an asymmetrical transition section connecting the arc profiles, including the following steps: Step S1, Billet Heating: The cylindrical steel billet is sent into the heating furnace for heating and heat preservation; Step S2, roll forming: Using an open roll forming system that includes vertical and horizontal roll forming, the heated billet is continuously rolled in multiple passes to gradually form a finished product with an asymmetrical cross-section. Multi-pass continuous rolling is divided into three stages: billet preparation, forming, and finishing. The billet preparation stage uses at least one vertical rolling pass to control the width of the rolled piece and correct the side profile. The forming and finishing stages use multiple horizontal rolling passes. In the forming and finishing rolling stages, asymmetric deformation compensation is introduced into the pass structure of each pass, so that the single-pass reduction Δh1 on the thick-walled side and the single-pass reduction Δh2 on the thin-walled side of the cross-section satisfy: Δh1 / Δh2=1.05~1.25, to compensate for the flow of metal to the thin-walled side caused by the asymmetry of the cross-section; wherein, the definition of the thick-walled side and the thin-walled side is based on the geometric characteristics of the finished cross-section, and the reduction ratio is achieved by adjusting the difference in the depth of the corresponding parts in the pass design; In the forming stage, the large circular arc profile with a curvature radius R≥10mm in the cross section is constrained by the rough forming pass. For the small circular arc transition area with a curvature radius R<5mm, a transition circular arc pass with a curvature radius not less than 3 times the curvature radius of the final finished small circular arc is used for rolling. In the finishing rolling stage, the small circular arc and straight transition section with a curvature radius R<5mm are finally constrained and formed. The single-pass surface reduction rate of multi-pass continuous rolling is distributed in a stepwise manner, wherein the single-pass surface reduction rate of the billet stage and the single-pass surface reduction rate of the forming stage are both greater than the single-pass surface reduction rate of the finishing rolling stage.

[0031] Taking a method for producing an asymmetric cross-section shaft link block steel as an example, this method involves rolling a Φ105mm 20Cr alloy carburized steel round billet into a shaft link block steel with an asymmetric cross-section. This asymmetric cross-section comprises two arc profiles with different radii of curvature: a thick-walled arc R1=15mm and a thin-walled arc R2=8mm, and an asymmetric transition section connecting the two arcs, wherein the transition section includes a small arc with a curvature radius R=3mm. The specific steps are as follows: Step S1, billet heating: The cylindrical steel billet is sent into the heating furnace, the heating temperature is set to 1200℃, the holding time is 90min, and the furnace exit temperature is controlled at 1120℃.

[0032] Step S2, Rolling: An open roll pass system including vertical and horizontal roll passes is adopted, with a total of 11 passes. The billet preparation stage includes passes 1 and 2, which are vertical roll passes, rolling the round billet into vertical elliptical and rectangular billets sequentially. The slope of the vertical roll pass sidewall is controlled at 12%. The forming stage includes passes 3 to 8, which are horizontal roll passes, and the finishing stage includes passes 9 to 11, which are horizontal roll passes. The total reduction rate of the entire roll pass is 75%, the reduction rate per pass in the billet preparation stage is 14%, the reduction rate per pass in the forming stage is 13%, and the reduction rate per pass in the finishing stage is 9%. Asymmetric deformation compensation reduction ratio: In the first half of the forming stage, i.e., passes 3-5, Δh1 / Δh2=1.20; in the second half of the forming stage, i.e., passes 6-8, Δh1 / Δh2=1.15; in the finishing stage, i.e., passes 9-11, Δh1 / Δh2=1.08. For the minute arc with radius R=3mm in the finished product, a transition arc with radius R=10mm is used instead during the forming stage (passes 3-8). In the finishing stage, the final constrained forming in the finished hole in pass 11 is R=3mm. Rolling speed: average rolling speed V2=2.5m / s during the forming stage, rolling speed V1=4.0m / s during the finishing stage, V1 / V2=1.6, and the measured final rolling temperature is 895℃. The surface hardness of the corresponding minute arc area on the finished hole roll surface is HRC58.

[0033] Step S3, Controlled Cooling and Post-processing: Immediately after final rolling, controlled cooling is performed. Air cooling is used within the temperature range of 895℃ to 650℃, with a cooling rate controlled at 3.5℃ / s. Below 650℃, slow cooling is adopted at a rate of 0.5℃ / s to room temperature. The resulting rolled microstructure is a uniform mixture of ferrite and pearlite with a ferrite grain size of grade 8. Multi-roll straightening is then performed, achieving a straightness of 0.3 mm / m after straightening.

[0034] Step S4, Carburizing and Quenching Treatment: Carburizing at 930℃ for 4 hours, followed by oil quenching at 810℃, and finally tempering at 190℃ for 2 hours. The uniformity deviation of the carburized layer depth was found to be 0.07 mm, and the difference in carburized layer depth between different areas of the cross-section was 0.03 mm.

[0035] The implementation principle of this embodiment is as follows: By setting the asymmetric deformation compensation reduction ratio within the optimization window and decreasing it with each pass, the effect of the metal deformation lagging behind the thin-walled side on the thick-walled side is precisely offset, and the rolled piece remains straight at the exit of each pass. Simultaneously, the micro-arcs are pre-formed with a larger radius transition arc to avoid local stress concentration and dead zones in metal flow. During the finishing rolling stage, the excellent filling properties of the high-temperature austenite region brought about by the high-hardness roll surface and high rolling speed are utilized to accurately replicate the micro-arcs. Combined with controlled cooling to obtain a fine-grained, uniform microstructure, the uniformity of carburization is significantly improved. The synergistic effect among the various parameters enables high-precision, high-efficiency rolling of complex asymmetric micro-arc cross-sections. Example 2

[0036] The difference between this embodiment and Embodiment 1 is that the billet specification remains Φ105mm 20Cr steel, but the radius of curvature of the small arc in the finished cross-section is smaller, R=2mm. Correspondingly, the radius of the transition arc used in the forming stage is four times the radius of the finished arc, i.e., R=8mm. The asymmetric deformation compensation reduction ratio is taken as the lower limit value for each stage: Δh1 / Δh2=1.15 in the first half of forming, Δh1 / Δh2=1.10 in the second half of forming, and Δh1 / Δh2=1.05 in the finishing rolling stage. The rolling speed in the finishing rolling stage is V1 / V2=1.8, where V2=2.5m / s, V1=4.5m / s, and the final rolling temperature reaches 912℃. The cooling rate is controlled at the upper limit of 5℃ / s. The carburizing treatment parameters are the same. The test results are as follows: the maximum exit curvature of each pass is 1.5 mm / m; the finished product has a complete and defect-free micro-arc contour; the ferrite grain size is grade 7.5; the uniformity deviation of the carburized layer depth is 0.05 mm; and the difference in carburized layer depth in different areas of the cross section is 0.02 mm. The straightness after straightening is 0.2 mm / m.

[0037] The implementation principle of this embodiment is as follows: when the radius of the finished micro-arc is smaller, a larger transition arc multiple and a higher rolling speed are required to ensure the filling temperature. Simultaneously, a smaller reduction ratio helps avoid overcompensation. A higher cooling rate further refines the grains, resulting in better carburization uniformity. This embodiment verifies that excellent results can still be achieved even at the lower limit of the parameter range in the claims.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that asymmetric deformation compensation was not used; that is, the same reduction was applied to both the thick-walled and thin-walled sides in each pass, i.e., Δh1 / Δh2=1.0. Other parameters, such as total reduction ratio, pass allocation, heating temperature, and cooling process, were identical to Example 1. Results showed that starting from the 4th pass, significant bending occurred at the exit of the rolled piece, with the maximum measured bending reaching 8 mm / m. This caused difficulty in subsequent passes, and some rolled pieces could not enter the next pass due to excessive bending. After barely completing the rolling, the small arc areas in the finished product cross-section showed significant incomplete filling, with a missing corner depth of 0.5 mm, resulting in a scrap rate as high as 35%. The uniformity deviation of the carburized layer depth was 0.25 mm, and the difference between different areas of the cross-section was 0.18 mm.

[0039] The implementation principle of this comparative example is as follows: without asymmetric deformation compensation, the metal flow advantage on the thin-walled side causes the rolled piece to bend towards the thick-walled side. When the bent rolled piece enters the next die, the force is uneven, which further aggravates the uneven deformation, and ultimately causes insufficient filling of the micro-arcs and uneven carburization.

[0040] Comparative Example 2 The difference between this comparative example and Example 1 is that the die design in this example directly follows the finished micro-arc radius R=3mm during the forming stage, without using a transition arc as a substitute; that is, all passes directly approximate R=3mm. All other parameters are the same as in Example 1. Results showed that in the 5th pass, i.e., the middle of the forming stage, visible folding cracks appeared at the edge of the die corresponding to the micro-arc region. After finishing, magnetic particle testing revealed a crack detection rate of up to 80% in the micro-arc region. Simultaneously, due to the premature forming of the micro-arc, excessive work hardening of the metal in this area led to surface micro-cracks even with a small reduction in the subsequent finishing rolling stage. The uniformity deviation of the carburized layer depth in qualified products was 0.12mm, and the cross-sectional difference was 0.09mm.

[0041] The implementation principle of this comparative example is as follows: the small arc is directly formed with the final radius in the roughing stage. Local stress concentration and non-coordinated metal flow lead to folding cracks, and premature hardening makes it difficult to repair defects in subsequent deformation.

[0042] Performance Comparison Performance indicators Example 1 Example 2 Comparative Example 1 Comparative Example 2 Maximum curvature at the exit of each track (mm / m) 1.2 1.5 8.0 2.8 Minor arc defect rate in finished products (%) 0.5 0.3 35 80 Ferrite grain size (grade) 8 7.5 6 7 Uniformity deviation of carburized layer depth (mm) 0.07 0.05 0.25 0.12 Difference in carburized layer depth across cross section (mm) 0.03 0.02 0.18 0.09 Straightness of finished product (mm / m) 0.3 0.2 1.2 0.8 Final rolling temperature (°C) 895 912 860 882 Example 3

[0043] This application also discloses a shaft link block steel product produced by the method described in Embodiment 1 above. (Refer to...) Figure 1The asymmetric cross-section of this product has the following characteristics: a 15mm radius of curvature on the thick-walled side and an 8mm radius of curvature on the thin-walled side, with a small arc of 3mm radius of curvature in the transition section. The rolled microstructure is a uniform mixture of ferrite and pearlite with a ferrite grain size of grade 8, without banded segregation; the proeutectoid ferrite is distributed in isolated blocks rather than a continuous network. After subsequent carburizing, quenching, and tempering, the surface carburized layer depth is 0.8mm, with a hardness of HRC60-62, and the core hardness is HRC32-35. The range of carburized layer depth across the entire cross-section does not exceed 0.07mm. The straightness of the product is ≤0.3mm / m, the surface roughness Ra≤3.2μm, and the small arc contour is intact, without folds, cracks, or other surface defects. This product is used in heavy machinery shaft connecting blocks, and its fatigue life under alternating loads is approximately 30% higher than that of products of the same specifications produced by conventional processes.

[0044] The implementation principle of this application embodiment is as follows: the fine-grained uniform structure obtained by the preceding rolling and controlled cooling processes provides an ideal matrix for subsequent heat treatment, making the carburized layer uniform and the core toughness and plasticity good; at the same time, the precise micro-arc contour reduces the stress concentration factor, thereby significantly improving the fatigue performance of the product.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of this application.

Claims

1. A method for producing shaft link block steel, used to roll a cylindrical steel billet into shaft link block steel with an asymmetrical irregular cross-section, wherein the asymmetrical irregular cross-section comprises at least two arc profiles with different radii of curvature and an asymmetrical transition section connecting the arc profiles, characterized in that, Includes the following steps: Step S1, Billet Heating: The cylindrical steel billet is sent into the heating furnace for heating and heat preservation; Step S2, roll forming: Using an open roll forming system that includes vertical and horizontal roll forming holes, the heated billet is continuously rolled in multiple passes to gradually form the finished product with the asymmetric cross-section. The multi-pass continuous rolling process is divided into a billet stage, a forming stage, and a finishing stage. The billet stage uses at least one vertical rolling pass to control the width of the rolled piece and correct the side profile. The forming stage and the finishing stage use multiple horizontal rolling passes. In the forming and finishing stages, asymmetric deformation compensation is introduced into the pass structure of each pass, such that the single-pass reduction Δh1 on the thick-walled side and the single-pass reduction Δh2 on the thin-walled side satisfy: Δh1 / Δh2 = 1.05~1.25, to compensate for the flow of metal to the thin-walled side caused by the asymmetry of the cross-section; wherein, the definition of the thick-walled side and the thin-walled side is based on the geometric characteristics of the finished cross-section, and the reduction ratio is achieved by adjusting the difference in the pass depth of the corresponding parts in the pass design; The forming stage constrains the large arc profile with a curvature radius R ≥ 10 mm in the cross section through the rough forming pass. For the small arc transition area with a curvature radius R < 5 mm, a transition arc pass with a curvature radius not less than 3 times the curvature radius of the final finished small arc is used for rolling. The finishing rolling stage finally constrains the forming of the small arc and straight transition section with a curvature radius R < 5 mm. The single-pass surface reduction rate of the multi-pass continuous rolling process is distributed in a stepwise manner, wherein the single-pass surface reduction rate of the billet stage and the single-pass surface reduction rate of the forming stage are both greater than the single-pass surface reduction rate of the finishing rolling stage.

2. The method for producing and processing shaft link block steel according to claim 1, characterized in that, The reduction ratio Δh1 / Δh2 of the asymmetric deformation compensation decreases in each pass. In the first half of the forming stage, Δh1 / Δh2 = 1.15 to 1.25; In the latter half of the forming stage, Δh1 / Δh2 = 1.10 to 1.20; During the finishing rolling stage, Δh1 / Δh2 gradually converges to 1.05–1.10; Furthermore, the curvature of the exit rolled piece in each pass is ≤2mm / m.

3. The method for producing and processing shaft link block steel according to claim 1, characterized in that, In step S2, the total reduction rate of the entire roll pass is controlled at 70% to 80%; the reduction rate of a single pass in the billet stage is controlled at 11% to 16%; the reduction rate of a single pass in the forming stage is controlled at 12% to 16%; and the reduction rate of a single pass in the finishing stage is controlled at 8% to 10%.

4. The method for producing and processing shaft link block steel according to claim 1, characterized in that, In the penultimate pass of the finishing rolling stage, a pre-finished hole is used. Based on the final finished cross-sectional dimensions, a finishing rolling allowance of 0.5 to 1.0 mm is uniformly reserved on each dimension surface of the pre-finished hole. This finishing rolling allowance is eliminated in the finished hole of the last pass to finally constrain and form the micro-arc and straight transition section. The surface hardness of the roll surface of the finished hole in the area corresponding to the micro-arc is ≥ HRC55.

5. The method for producing and processing shaft link block steel according to claim 1, characterized in that, In step S2, the rolling speed V1 in the finishing rolling stage and the rolling speed V2 in the forming stage satisfy: V1 / V2 = 1.3~1.8, so as to shorten the total time of the finishing rolling stage, make the final rolling temperature ≥880℃, and ensure that the metal in the small arc region of the finishing rolling stage is in the fully austenitic region and fully fills the die.

6. The method for producing and processing shaft link block steel according to claim 1, characterized in that, For round steel billets with a specification of Φ105mm, the multi-pass continuous rolling process is set to a total of 11 passes, wherein: the billet opening stage includes the first to second consecutive vertical rolling passes, which sequentially roll the round billet into an elliptical and rectangular billet; the forming stage includes the third to eighth consecutive horizontal rolling passes; the finishing rolling stage includes the ninth to eleventh consecutive horizontal rolling passes; the opening pass system adopts a conjugate pass design, and the sidewall slope of the vertical rolling pass is controlled at 10% to 15%.

7. The method for producing and processing shaft link block steel according to claim 1, characterized in that, In step S1, the steel billet is 20Cr alloy carburizing steel; the heating temperature is set to 1150-1250℃, and the furnace exit temperature is controlled at 1100-1150℃.

8. The method for producing and processing shaft link block steel according to claim 7, characterized in that, It also includes step S3, controlled cooling and post-processing: the steel section rolled in step S2 is subjected to controlled cooling, multi-roll straightening and cutting in sequence; The specific process of controlled cooling is as follows: within the temperature range from the final rolling temperature to 650℃, air cooling is used, and the cooling rate is controlled at 2 to 5℃ / s to suppress the formation of a continuous network distribution of proeutectoid ferrite along the austenite grain boundaries; below 650℃, slow cooling is adopted, and the cooling rate is ≤1℃ / s to room temperature; The controlled cooling process results in a rolled microstructure of the steel profile consisting of a uniform mixture of ferrite and pearlite with a ferrite grain size ≥ 7. The straightness of the multi-roller straightening control steel is ≤0.5mm / m.

9. The method for producing and processing shaft link block steel according to claim 8, characterized in that, Following step S3, the process further includes step S4, carburizing and quenching treatment: The steel section is carburized at 920–940℃, then quenched at 800–820℃, and finally tempered at 180–200℃. The ferrite and pearlite mixed structure with a ferrite grain size ≥ 7 obtained in step S3 ensures that the uniformity deviation of the carburized layer depth is ≤ 0.1 mm.

10. The method for producing and processing shaft link block steel according to claim 9, characterized in that, In the asymmetric irregular cross section of the steel, the difference in cooling rate in each region caused by the difference in wall thickness is homogenized by controlling the cooling rate within the range of 2 to 5℃ / s in step S3, so that the difference in carburized layer depth in each region of the cross section in step S4 is ≤0.05mm.

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