Method for reducing occurrence frequency of abnormal breakage of ball head during tensile test of insulator steel foot

Abstract

The invention relates to a method for reducing the occurrence frequency of abnormal breakage of a ball head during a tensile test of an insulator steel foot in the technical field of steel smelting rolling and forging processing, and aims to solve the problem of high abnormal breakage frequency caused by insufficient whole-process organization genetic control in the prior art. According to the technical scheme, the method is characterized in that 45Mn2 steel with specific components is adopted, and the streamline and the structure of a high-stress area of the ball head are stabilized through cooperative control of key processes such as large-section blank casting and electromagnetic stirring of a continuous casting procedure, cold charging and high-temperature heating, initial forging temperature control, two-time forming forging of the ball head and dispersed cooling after forging. The method is mainly used for manufacturing insulator steel pins for high-voltage and ultra-high-voltage transmission lines, and the abnormal fracture frequency of the ball head is reduced to be smaller than or equal to 2 times per million pieces.

Description

Technical Field

[0001] This invention relates to the technical field of steel smelting, rolling and forging, and in particular to a method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs. Background Technology

[0002] Insulator steel feet are critical load-bearing components in high-voltage and ultra-high-voltage transmission lines, and their reliability directly affects the safe and stable operation of the power grid. Insulator steel foot failures can be categorized into two dimensions: the stage of occurrence and the failure mechanism. These mainly include: failures exposed during the manufacturing and testing stages, such as abnormal fracture during tensile testing, and substandard hardness and metallographic structure; failures during long-term service, such as fatigue fracture, stress corrosion cracking, and overload fracture; and failures related to connection and assembly, such as thread failure, mismatch or wear of ball-and-socket connections.

[0003] Abnormal fractures during tensile tests are closely related to the process control of steel mills and forging plants. This defect causes the actual load-bearing capacity of the steel feet to be far lower than the design value, and the fractures are sudden and insidious, posing a significant safety hazard. Specifically, under extreme weather conditions or uneven loads, individual steel feet may suddenly fracture, causing the entire string of insulators to fall and the conductors to the ground, triggering a major power grid accident; the fallen conductors and insulator strings may also cause personal injury, equipment damage, and secondary disasters; furthermore, as a critical structural component, frequent quality problems will seriously damage the brand reputation of the manufacturing enterprise and disqualify it from entering high-end markets such as ultra-high voltage.

[0004] Currently, most domestic and international companies still primarily focus on the dimensions and routine mechanical property testing of the final forgings when controlling the quality of high-strength steel insulator feet, lacking sufficient understanding of the genetic control of the entire process. This technology aims to overcome the technical barriers of unstable internal quality (especially the flow lines and microstructure in high-stress areas) and large batch-to-batch variations, reducing the frequency of abnormal fractures in the ball heads of insulator steel feet during tensile testing, thereby providing reliable assurance for power grid construction and safe operation. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies, such as insufficient genetic control of the entire process of insulator steel foot structure and unstable internal product quality, which leads to a high frequency of abnormal ball head fracture during tensile testing. This invention provides a method to reduce the frequency of abnormal ball head fracture during tensile testing of insulator steel feet. This method involves rationally selecting the rolling ratio, optimizing the electromagnetic stirring parameters of the crystallizer, adopting a cold-loading and high-temperature heating regime, controlling the initial forging temperature, the distribution of ball head forging deformation, and the post-forging cooling method. This stabilizes the streamlines and microstructure of the high-stress area at the connection between the ball head R-angle and the rod, thereby reducing the frequency of abnormal ball head fracture to ≤2 times per million parts, meeting the stringent reliability requirements of power transmission projects for insulator steel feet.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel feet, wherein the steel feet are made of 45Mn2 steel, and the mass percentage composition of the 45Mn2 steel is:

[0007] C 0.42~0.49%, Si 0.17~0.37%, Mn 1.20~1.80%, P ≤0.030%, S ≤0.030%, Cr≤0.30%, Ni ≤0.30%, Mo ≤0.10%, Cu ≤0.30%, V ≤0.05%, Zr ≤0.05%, balance being Fe and unavoidable impurities;

[0008] The method includes sequential processes of converter smelting, LF refining, RH vacuum treatment, continuous casting, rolling, blanking, forging, and cooling, wherein:

[0009] (1) In the continuous casting process, a continuous casting billet cross section and rolling ratio that can obtain sufficient deformation are adopted; and electromagnetic stirring of the crystallizer is applied to optimize the uniformity of the internal structure of the billet.

[0010] (2) Before rolling, the continuous casting billet is cold-charged into the furnace (after cooling the continuous casting billet to room temperature, it is cold-charged into the heating furnace). During the rolling heating process, the heating temperature and time are controlled to achieve full homogenization of the billet structure and composition.

[0011] (3) When forging the ball head, control the initial forging temperature to maintain the plasticity of the material and prevent uneven deformation;

[0012] (4) The ball head is formed by two-stage forging, and the deformation distribution is controlled. Lubricant is used in the final forming to ensure smooth filling of the metal flow lines and avoid turbulence.

[0013] (5) Dispersed cooling is performed on the forged steel foot to prevent the precipitation of abnormal structures.

[0014] To be further specific, in the above technical solution, in step (1), the cross-section of the continuously cast billet is 225mm×270mm, the diameter of the finished product after rolling is φ28mm, and the rolling ratio is 98.7. This process prioritizes the use of billets with larger cross-sections to ensure a sufficient forging ratio, which is conducive to breaking the original structure.

[0015] To further specify, in the above technical solution, in step (1), the current of the electromagnetic stirring of the crystallizer is 340-380A and the frequency is 7-10Hz. In this process, an appropriate electromagnetic stirring current of the crystallizer is selected so that the molten steel can obtain sufficient stirring flow rate and kinetic energy to promote the uniformity of the solidification structure and temperature of the molten steel in the action area; a medium-to-high-end working frequency is selected to adjust the magnetic field penetration depth so that the center of the magnetic field acts on the 1 / 5 cross-sectional width of the billet. This area corresponds to the R angle of the finished insulator steel foot after forging and the high stress concentration area of ​​the rod.

[0016] To further specify, in the above technical solution, in step (2), the heating temperature of the second heating section and the homogenization section of the rolling heating is 1190~1240℃, and the total heating time is 160~260min. This process adopts cold charging process, which increases the time for component diffusion during the cooling and heating process of the billet, and with the long-term high-temperature heating, ensures that the structure and composition are further homogenized.

[0017] To further specify, in the above technical solution, in step (3), the initial forging temperature of the ball head forging is 990 to 1100°C. This process requires controlling the initial forging temperature between 990 and 1100°C. In this range, the 45Mn2 steel material has good plasticity. Forging deformation at this time can prevent strong shear strain from being generated inside the metal, which would cause the flow direction of the structure to be distorted. At the same time, the plasticity of the 45Mn2 steel material does not fluctuate much in this range, which can weaken the uneven internal and external deformation that may be caused by the temperature difference between the core and the surface of the billet.

[0018] To further specify, in the above technical solution, in step (4), the initial forging ratio of the two forming processes is 1.9 to 2.4, the total forging ratio is ≥3.5, and the lubricant is a graphite-based lubricant. In this process, the deformation at the ball head R-angle and rod connection of the insulator steel foot is complex. If the single hammer blow is too large, it will force the metal to undergo violent lateral flow and shearing, disrupting the flow lines. A reasonable allocation of the two forging ratios ensures smooth metal filling and avoids turbulence.

[0019] To further specify, in the above technical solution, in step (5), the forged steel feet are sequentially cooled on the cooling roller conveyor, with the ends not touching. After the ball head temperature drops below 500℃, they fall into the collection box. This process ensures that the forged insulator steel feet are dispersed on the roller conveyor and cooled uniformly to below 500℃ at a relatively fast speed, preventing the formation of continuous abnormal strips and the precipitation of proeutectoid ferrite along the deformation zone.

[0020] To be further specific, in the above technical solution, the current of the electromagnetic stirring of the crystallizer is 360A and the frequency is 8Hz.

[0021] To be further specific, in the above technical solution, the initial forging ratio is 2.3 and the total forging ratio is 4.1.

[0022] To be further specific, in the above technical solution, the initial forging temperature is 1060℃.

[0023] The beneficial effects of this invention are as follows: Compared with existing technologies, the process method provided by this invention effectively stabilizes the streamlines and microstructure of the high-stress area at the connection between the ball head R-angle and the rod by rationally controlling the rolling ratio, optimizing the current and frequency of the electromagnetic stirring in the crystallizer during steelmaking, adopting a cold charging and high-temperature heating regime in the rolling stage, and controlling the initial forging temperature, rationally distributing the ball head forging deformation, and optimizing the post-forging cooling method in the forging stage. Ultimately, this reduces the frequency of abnormal ball head fracture in the insulator steel foot during tensile testing to ≤2 times / million parts, significantly improving product reliability. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The streamlines of the high-stress area at the connection between the ball head R angle of the insulator steel foot and the rod are shown in the embodiment.

[0026] Figure 2 The streamlines of the high-stress area at the ball head radius of the insulator's steel foot and the connection point of the rod are shown in the comparative example.

[0027] Figure 3 The structure of the high-stress area at the connection between the ball head R angle of the insulator steel foot and the rod in the embodiment is shown.

[0028] Figure 4 This is a comparative example showing the microstructure of the high-stress area at the ball head radius of the insulator's steel foot and the connection point of the rod. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This section illustrates the comprehensive control effect of the method of the present invention through examples and comparative examples, combined with the smelting, rolling and forging process of insulator steel feet.

[0031] The present invention will be further described in detail below with reference to the embodiments.

[0032] Example 1

[0033] (1) The continuous casting process uses a 225mm×270mm cross-section billet, the finished product specification is φ28 mm, and the rolling ratio is 98.7; the electromagnetic stirring parameters of the continuous casting crystallizer are current 360 A and frequency 8 Hz;

[0034] (2) Before rolling, the continuously cast billet is cold-charged into the furnace. The temperature of the second heating section and the soaking section of the rolling is controlled at 1200-1230℃, and the total heating time is 240 min.

[0035] (3) The initial forging temperature of the ball head is controlled at 1060 ℃;

[0036] (4) The ball head is forged using a two-stage forming process. The first forging ratio is 2.3, the total forging ratio is 4.1, and graphite-based lubricant is used in the final forging.

[0037] (5) After forging, the steel feet are sequentially cooled in the cooling roller conveyor, with the first and last ones not connected. After the ball head temperature is ≤500 ℃, they fall into the collection box.

[0038] Example 2

[0039] The only difference between Example 2 and Example 1 is that the electromagnetic stirring current of the continuous casting crystallizer in step (1) is 340A, while the other process parameters and operations are the same as in Example 1.

[0040] Example 3

[0041] The only difference between Example 3 and Example 1 is that the electromagnetic stirring frequency of the continuous casting crystallizer in step (1) is 10Hz, while the other process parameters and operations are the same as in Example 1.

[0042] Example 4

[0043] The only difference between Example 4 and Example 1 is that the temperature of the rolling heating section and the soaking section in step (2) is controlled at 1190-1220 ℃, while the other process parameters and operations are the same as in Example 1.

[0044] Example 5

[0045] The only difference between Example 5 and Example 1 is that the initial forging temperature of the ball head in step (3) is controlled at 995 ℃, while the other process parameters and operations are the same as in Example 1.

[0046] Example 6

[0047] The only difference between Example 6 and Example 1 is that the initial forging ratio in step (4) is 1.9 and the total forging ratio is 4.1. The remaining process parameters and operations are the same as in Example 1.

[0048] Comparative Example 1

[0049] The difference between Comparative Example 1 and Example 1 is that the cross-section of the continuous casting billet in step (1) is changed to 160mm×160mm, the finished product specification is still φ28 mm, the rolling ratio is 41.6, and the other process parameters and operations are the same as in Example 1.

[0050] Comparative Example 2

[0051] The difference between Comparative Example 2 and Example 1 is that the electromagnetic stirring current of the continuous casting crystallizer in step (1) is changed to 300A, while the other process parameters and operations are the same as in Example 1.

[0052] Comparative Example 3

[0053] The difference between Comparative Example 3 and Example 1 is that the electromagnetic stirring frequency of the continuous casting crystallizer in step (1) is changed to 5Hz, while the other process parameters and operations are the same as in Example 1.

[0054] Comparative Example 4

[0055] The difference between Comparative Example 4 and Example 1 is that the electromagnetic stirring frequency of the continuous casting crystallizer in step (1) is changed to 12Hz, while the other process parameters and operations are the same as in Example 1.

[0056] Comparative Example 5

[0057] The difference between Comparative Example 5 and Example 1 is that the temperature control of the rolling heating section and the soaking section in step (2) is changed to 1150-1180 ℃, while the other process parameters and operations are the same as in Example 1.

[0058] Comparative Example 6

[0059] The difference between Comparative Example 6 and Example 1 is that the initial forging temperature of the ball head in step (3) is changed to 960 ℃, while the other process parameters and operations are the same as in Example 1.

[0060] Comparative Example 7

[0061] The difference between Comparative Example 7 and Example 1 is that the ball forging in step (4) is changed to a one-time forming process with a forging ratio of 4.1. The remaining process parameters and operations are the same as in Example 1.

[0062] Comparative Example 8

[0063] The difference between Comparative Example 8 and Example 1 is that the ball forging in step (4) is still a two-stage process, but the first forging ratio is changed to 2.7, the total forging ratio is still 4.1, and the other process parameters and operations are the same as in Example 1.

[0064] Comparative Example 9

[0065] The difference between Comparative Example 9 and Example 1 is that the cooling method after forging in step (5) is changed to "windproof stacking cooling after ball forging", while the other process parameters and operations are the same as in Example 1.

[0066] The frequency of abnormal ball head fracture during tensile testing of the insulator steel feet prepared in Examples 1-6 and Comparative Examples 1-9 is shown in Table 1.

[0067] Table 1. Frequency of abnormal ball head fracture during tensile testing of insulator steel legs prepared in Examples 1-6 and Comparative Examples 1-9

[0068] Example The streamlines of the high-stress area connecting the ball head radius and the shaft. Organization of high-stress zone at ball head radius and shaft connection Frequency of abnormal ball head fracture in tensile tests per million parts Example 1 Parallel to the rolling direction uniform 0 Example 2 Parallel to the rolling direction uniform 1 Example 3 Parallel to the rolling direction uniform 0 Example 4 Parallel to the rolling direction uniform 0 Example 5 Parallel to the rolling direction uniform 1 Example 6 Parallel to the rolling direction uniform 0 Comparative Example 1 Local chaos Local abnormalities 4 Comparative Example 2 Local chaos Local abnormalities 5 Comparative Example 3 confusion abnormal 16 Comparative Example 4 confusion abnormal 13 Comparative Example 5 Local chaos Local abnormalities 3 Comparative Example 6 confusion abnormal 9 Comparative Example 7 confusion abnormal 21 Comparative Example 8 Local chaos Local abnormalities 4 Comparative Example 9 Local chaos Local abnormalities 6

[0069] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs, characterized in that, The steel foot is made of 45Mn2 steel, and the mass percentage composition of the 45Mn2 steel is: C 0.42~0.49%, Si 0.17~0.37%, Mn 1.20~1.80%, P ≤0.030%, S ≤0.030%, Cr ≤0.30%, Ni ≤0.30%, Mo ≤0.10%, Cu ≤0.30%, V ≤0.05%, Zr ≤0.05%, balance being Fe and unavoidable impurities; The method includes sequential processes of converter smelting, LF refining, RH vacuum treatment, continuous casting, rolling, blanking, forging, and cooling, wherein: (1) In the continuous casting process, a continuous casting billet cross section and rolling ratio that can obtain sufficient deformation are adopted; and electromagnetic stirring of the crystallizer is applied to optimize the uniformity of the internal structure of the billet. (2) Before rolling, the continuously cast billet is cold-charged into the furnace; during the rolling heating process, the heating temperature and time are controlled to achieve full homogenization of the billet structure and composition; (3) When forging the ball head, control the initial forging temperature to maintain the plasticity of the material and prevent uneven deformation; (4) The ball head is formed by two-stage forging, and the deformation distribution is controlled. Lubricant is used in the final forming to ensure smooth filling of the metal flow lines. (5) Dispersed cooling is performed on the forged steel foot to prevent the precipitation of abnormal structures.

2. The method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs according to claim 1, characterized in that: In step (1), the cross-section of the continuously cast billet is 225mm×270mm, and the diameter of the finished product after rolling is φ28mm, with a rolling ratio of 98.

7.

3. The method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs according to claim 1, characterized in that: In step (1), the current of the electromagnetic stirring of the crystallizer is 340-380A and the frequency is 7-10Hz.

4. The method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs according to claim 1, characterized in that: In step (2), the heating temperature of the second heating section and the soaking section of the rolling heating is 1190-1240℃, and the total heating time is 160-260min.

5. The method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs according to claim 1, characterized in that: In step (3), the initial forging temperature of the ball head forging is 990-1100℃.

6. The method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs according to claim 1, characterized in that: In step (4), the initial forging ratio of the two forming processes is 1.9 to 2.4, the total forging ratio is ≥3.5, and the lubricant is a graphite-based lubricant.

7. The method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs according to claim 1, characterized in that: In step (5), the forged steel feet are cooled sequentially on the cooling roller conveyor, with the ends not connected. After the ball head temperature drops below 500°C, they fall into the collection box.

8. The method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs according to claim 3, characterized in that: The current of the electromagnetic stirring in the crystallizer is 360A and the frequency is 8Hz.

9. A method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs according to claim 6, characterized in that: The initial forging ratio is 2.3, and the total forging ratio is 4.

1.

10. A method for reducing the frequency of abnormal ball head fracture during tensile testing of insulator steel legs according to claim 5, characterized in that: The initial forging temperature is 1060℃.

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