A production method of 20Cr13 stainless steel wire rod for cold heading bushing

Abstract

The present application belongs to the technical field of stainless steel production, and relates to a production method of 20Cr13 stainless steel wire rod for cold upsetting shaft sleeve. The method is further improved on the basis of the conventional method in the steps of smelting, rolling and annealing. In the smelting process, the elements of the molten steel are adjusted as follows: C: 0.16-0.20%; Si≤0.40; Mn≤0.40%; Cr: 12.0-14.0%; Ni≤0.30%; Cu: 0.10-0.30%. The high-speed rolling mill is used for rolling to obtain the stainless steel wire rod with good surface quality and high dimensional accuracy. Then, the annealing treatment is carried out in the cover annealing furnace to obtain the 20Cr13 stainless steel wire rod for cold upsetting shaft sleeve. Through the comprehensive effect of element control, rolling speed and temperature control and annealing process, the annealing hardness of the finished wire rod is ≤145HBW, the strength is ≤510Mpa, the elongation is ≥35%, and the shrinkage is ≥75%. The finished wire rod has excellent cold working performance, reduces the cracking tendency of the wire rod in cold upsetting, and has a broad market application prospect. The production method is simple to operate and suitable for large-scale industrial application.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel production technology, and particularly relates to stainless steel smelting, rolling and heat treatment technology, specifically to a production method of 20Cr13 stainless steel wire rod for cold heading bushings. Background Technology

[0002] 20Cr13 is a martensitic stainless steel. It possesses high heat-treatable hardness in the quenched state and good cold-working properties in the annealed state, making it commonly used in the manufacture of hardware such as shafts and bushings. Traditional bushing production uses stainless steel round bars as raw material, which are sawn, turned, or cold-headed, resulting in low yield and production efficiency. With the successful development of large-diameter stainless steel coils by various steel mills, new processes can use large-diameter coils as raw material, undergoing annealing, drawing, re-annealing, surface treatment, and continuous cold-heading, significantly improving yield and production efficiency. However, this process places higher demands on the material's cold-working properties and is prone to cold-heading cracking defects.

[0003] Currently, the improvement of the cold working performance of materials is mostly achieved by adjusting the heat treatment process. There are already relevant patents and literature that have studied the strength and hardness of 20Cr13 stainless steel wire rod, in order to improve the cold working performance by reducing the strength and hardness of the material: (1) Patent CN 112280942A discloses an annealing process for martensitic stainless steel 2Cr13 wire, which can achieve a strength of 634-689 MPa and a hardness of 174-204 HB; (2) Patent CN 111304416A discloses a softening annealing method for 20Cr13, which can achieve a minimum hardness of 164-167 HB; (3) Patent CN 109182680A discloses a method for annealing martensitic stainless steel bars and wires for cold heading, which can anneal the hardness of 20Cr13 to 149-162HB. However, its annealing temperature is relatively high, 945-955℃, which can easily cause decarburization. It has strict requirements for production equipment and is not suitable for large-scale production. (4) Literature 1-2 Research on annealing process operation and annealing hardness of Cr13_Wang Gangjian, Special Steel Technology, tried 8 different processes and could anneal the hardness of 20Cr13 to 160-229HB. As can be seen from the above, the existing methods can only reduce the strength to 634Mpa and the hardness to 149HB. The improvement of the cold working performance of the material is still limited. Moreover, adjusting only from the mechanical properties is still limited in reducing defects in the cold working process. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a production method for 20Cr13 stainless steel wire rods used in cold heading bushings. Specifically, the chemical composition, surface quality, and mechanical properties are controlled during the smelting, rolling, and annealing processes, resulting in finished wire rods with good surface quality, high dimensional accuracy, low strength and hardness, and high elongation and shrinkage, thus avoiding cold working defects from multiple aspects. Wire rods produced using this method retain good cold working performance after drawing and can be directly cold-headed without further annealing, improving production efficiency while saving production costs.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A method for producing 20Cr13 stainless steel wire rod for cold heading bushings includes the following steps:

[0007] S1. Smelting: The raw materials are smelted and cast to obtain stainless steel billets with low residual elements; wherein, the elements of the molten steel are adjusted during smelting as follows: C: 0.16~0.20%; Si≤0.40%; Mn≤0.40%; Cr: 12.0~14.0%; Ni≤0.30%; Cu: 0.10~0.30%;

[0008] S2. Rolling and forming: High-speed rolling is used to produce stainless steel wire rods with good surface quality and high dimensional accuracy;

[0009] S3. Annealing: The wire rod obtained in S2 is placed in an atmosphere-protected annealing furnace for annealing treatment to obtain better mechanical properties and obtain 20Cr13 stainless steel wire rod for cold heading bushings.

[0010] Preferably, the raw materials used in step S1 are furnace charge with low Mn and Ni content, more preferably Mn ≤ 0.40% and Ni ≤ 0.30%.

[0011] Preferably, in step S1, the elements in the molten steel are required to be C: 0.16-0.20%; Si≤0.40%; Mn≤0.40%; Cr: 12.0-14.0%; Ni≤0.30%; Cu: 0.10-0.30%, and the control requirements for other elements meet the requirements of 20Cr13 in GB / T 4356 stainless steel wire rod.

[0012] Preferably, in step S2, the billet rolling process controls the initial roughing speed to be ≤1.0 m / s and the final rolling speed to be ≤55 m / s; more preferably, the rolling process temperature is controlled at 800~950℃.

[0013] Preferably, in step S2, the depth of defects such as scratches and pits on the surface of the wire rod after rolling is ≤0.10mm, and the wire rod out-of-roundness is ≤0.20mm.

[0014] Preferably, the atmosphere of the atmosphere protection hood in step S3 is at least one of nitrogen and hydrogen.

[0015] Preferably, the annealing process in step S3 includes the setting of heating, holding, controlled cooling and rapid cooling stages. The holding temperature in the holding stage is 880-920℃ and the holding time is ≥8 hours. The cooling rate in the controlled cooling stage is ≤25℃ / h, and rapid cooling is performed after the temperature drops to below 600℃.

[0016] Preferably, the wire rod obtained in step S3 has an annealed hardness ≤145HBW, a strength ≤510Mpa, an elongation ≥35%, a shrinkage ≥75%, and excellent cold working performance.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] (1) By controlling the raw materials and smelting of stainless steel, the content of elements C, Si, Mn and Ni can be reduced, thereby reducing the strengthening effect of the matrix alloy and directly reducing the strength and hardness of the material after annealing. Reducing the austenitic elements (Mn and Ni) will make the annealing process more conducive to the transformation of the microstructure, thus making the strength and hardness after annealing extremely low. Increasing the Cu content can further improve the cold heading performance.

[0019] (2) By controlling the temperature and speed during the rolling process, surface defects can be reduced while dimensional accuracy can be improved, avoiding cold heading defects caused by surface defects and dimensional inconsistencies. At the same time, the amount of drawing in subsequent drawing processes can be reduced, the degree of work hardening can be reduced, and subsequent cold heading processes can be facilitated.

[0020] (3) Through the combined effects of element control, rolling speed and temperature control and annealing process, the finished wire rod has an annealing hardness of ≤145HBW, strength of ≤510Mpa, elongation of ≥35%, shrinkage of ≥75%, and excellent cold working performance.

[0021] (4) By comprehensively controlling the depth of surface defects, improving dimensional accuracy, reducing material hardness and strength, and increasing elongation and shrinkage, the tendency of wire rod to crack during cold heading is reduced. After drawing, it still maintains good cold working performance and can be directly cold heading without re-annealing, which has broad market application prospects. Moreover, the production method is simple to operate and suitable for large-scale industrial applications. Attached Figure Description

[0022] Figure 1 This invention improves the scratch defects on the circular surface of the front disc.

[0023] Figure 2 This invention improves the surface pitting defects of the front wire rod.

[0024] Figure 3This is a diagram showing the improved surface morphology of the wire rod according to the present invention;

[0025] Figure 4 This invention improves the machining cracking of parts caused by surface defects in the front wire rod;

[0026] Figure 5 This invention improves the machining of parts that crack due to the high hardness of the original wire rod;

[0027] Figure 6 This is a drawing of a qualified part after the improvement of this invention. Detailed Implementation

[0028] To facilitate understanding, the technical solutions and implementation methods of the present invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described herein are implemented based on the technical solutions of the present invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of the present invention, not all embodiments. The specific implementation methods described are limited to illustrative purposes and do not limit the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used in the examples are commercially available unless otherwise specified.

[0030] This invention provides a method for producing 20Cr13 stainless steel wire rod for cold heading bushings. Based on conventional manufacturing processes, the chemical composition, surface quality, and mechanical properties of the smelting, rolling, and annealing steps are further adjusted and controlled. This comprehensive adjustment results in a finished wire rod with good surface quality, high dimensional accuracy, low strength and hardness, high elongation and shrinkage, and excellent cold working performance. The main improvements of this invention's production method include the following:

[0031] S1. Smelting: The raw materials are smelted and cast to obtain stainless steel billets with low residual elements; wherein, the elements of the molten steel are adjusted during smelting as follows: C: 0.16~0.20%; Si≤0.40%; Mn≤0.40%; Cr: 12.0~14.0%; Ni≤0.30%; Cu: 0.10~0.30%; and the control requirements of other elements meet the requirements of 20Cr13 in GB / T4356 stainless steel wire rod.

[0032] The furnace charge preferably uses low Mn and Ni content, with Mn ≤ 0.40% and Ni ≤ 0.30%.

[0033] S2. Rolling and forming: High-speed rolling is used to produce stainless steel wire rods with good surface quality and high dimensional accuracy; the depth of surface defects such as scratches and pits after rolling is ≤0.10mm, and the out-of-roundness of the wire rod is ≤0.20mm;

[0034] The preferred rolling process control is to have an initial rolling speed of ≤1.0 m / s and a final rolling speed of ≤55 m / s, and the preferred rolling process temperature is to be controlled between 800 and 950℃.

[0035] S3. Annealing: The wire rod obtained in S2 is placed in an atmosphere-protected annealing furnace for annealing treatment to obtain better mechanical properties and obtain 20Cr13 stainless steel wire rod for cold heading bushings.

[0036] The atmosphere of the atmosphere protection hood is preferably at least one of nitrogen and hydrogen;

[0037] The annealing process includes the setting of heating, holding, controlled cooling and rapid cooling stages. The holding temperature in the holding stage is preferably 880-920℃ and the holding time is preferably ≥8 hours. The cooling rate in the controlled cooling stage is ≤25℃ / h. After cooling to below 600℃, rapid cooling is performed.

[0038] The wire rod obtained by this invention has an annealed hardness of ≤145HBW, a strength of ≤510Mpa, an elongation of ≥35%, a shrinkage of ≥75%, and excellent cold working performance.

[0039] Examples 1-8

[0040] A method for producing 20Cr13 stainless steel wire rod for cold heading bushings includes the following steps:

[0041] (1) The smelting process uses stainless steel raw materials with low Mn and low Ni content. The process is carried out by electric furnace + AOD + LF smelting to obtain molten steel with low residual elements. The stainless steel billet is then produced by continuous casting. The main chemical elements in the example are shown in Table 1.

[0042] Reducing the content of elements C, Si, Mn, and Ni diminishes the strengthening effect of the matrix alloy, directly lowering the strength and hardness of the material after annealing. Reducing the content of austenitic elements (Mn and Ni) promotes microstructure transformation during annealing, resulting in extremely low post-annealing strength and hardness. Increasing the Cu content can improve cold heading performance.

[0043] A comparative example was also set up, and the main chemical elements of Comparative Example 1 are shown in Table 1.

[0044] Table 1. Mass percentage of major chemical elements and harmful elements in the examples and comparative examples.

[0045] (2) The billet is heated using a continuous step heating method, with the temperature controlled at 1080–1130℃ during the soaking stage. It is rolled using a transverse high-speed wire rod mill, with low rolling speed and low temperature throughout the rolling process. During the billet rolling process, the initial roughing speed is controlled to ≤1.0 m / s, the final rolling speed to ≤20 m / s, and the rolling temperature to be controlled at 800–950℃. The depth of surface defects such as scratches and pits on the finished product is ≤0.10 mm. The out-of-roundness is ≤0.20 mm.

[0046] Table 2 Process parameters for the examples and comparative examples

[0047] Example Batch number Initial rolling / m / s Final rolling / m / s Temperature / °C Example 1 221103AE08-01 0.8 18 850 Example 2 220629AE04-03 0.8 18 862 Example 3 221205AE06-01 0.8 18 860 Example 4 221205AE08-01 0.8 18 855 Example 5 221205AE10-01 0.8 18 860 Example 6 221205BE05-01 0.8 18 866 Example 7 221205BE06-01 0.8 18 856 Example 8 221205BE08-01 0.8 18 855 Comparative Example 1 190101B09E-01 1.2 20 960 Comparative Example 2 180905B10E-03X 1.2 22 978 Comparative Example 3 191113B01E-01K 1.2 25 990

[0048] Using low-temperature and low-speed rolling can reduce process scratches and surface defects, while improving dimensional accuracy. It also allows for finer carbides formed during rolling, facilitating control of mechanical properties during subsequent annealing. Figure 1 The images show scratch defects on the surface of the wire rods in Comparative Examples 1 and 3. As can be seen from the images, there are obvious scratch defects on the surface of the wire rods. Figure 2 The image shows a pitting defect on the surface of the wire rod in Comparative Example 2. It can be seen from the image that there are obvious pitting defects on the surface of the wire rod, which lead to breakage during subsequent drawing processes. Figure 3 The image shows the surface morphology of the improved wire rod in Example 1. As can be seen from the image, the surface quality is good and the dimensional accuracy is high. The specific dimensional accuracy and defect depth of the examples and comparative examples are shown in Table 3 below.

[0049] Table 3. Dimensional accuracy and defect depth of the embodiments and comparative examples

[0050] (3) The wire rod is annealed in a nitrogen-protected annealing furnace. The annealing process consists of heating, holding, controlled cooling and rapid cooling stages. The holding temperature in the holding stage is 880-920℃ and the holding time is ≥8 hours. The cooling rate in the cooling stage is ≤25℃ / h. After cooling to below 600℃, the cooling hood is replaced for rapid cooling.

[0051] Table 4. Process parameters for the examples and comparative examples

[0052]

[0053]

[0054] Nitrogen-protected annealing can reduce the degree of oxidation and decarburization on the surface of the wire rod. High-temperature and long-time annealing can give the wire rod lower strength and hardness, and higher elongation and shrinkage. The properties of 20Cr13 stainless steel wire rod produced using this method are shown in Table 5.

[0055] Table 5. Productivity and mechanical performance test results of finished wire rods from the examples and comparative examples.

[0056]

[0057] Test case

[0058] The subsequent cold heading process was carried out using Example 1 and Comparative Example 1. The process involved drawing Φ28mm wire rod to Φ27.3mm and continuously cold heading it into a bushing with a maximum outer diameter of Φ50mm. After cold heading, the surface was machined, heat-treated, and assembled.

[0059] Comparative Example 1: The processed parts are shown below. Figure 4 and Figure 5 It can be seen that surface defects and high hardness of wire rod easily lead to obvious cracking of processed parts, making further processing impossible and resulting in a product qualification rate of less than 50%; while the parts processed in Embodiment 1 of this invention show... Figure 6 The processing of parts has been significantly improved, and the product qualification rate has reached 95%, which is a significant improvement compared with the comparison ratio.

[0060] 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 method for producing 20Cr13 stainless steel wire rod for cold heading bushings, characterized in that, Includes the following steps: (1) Smelting: The raw materials are smelted and cast to obtain stainless steel billets with low residual elements; wherein, the elements of the molten steel are adjusted during smelting as follows: C: 0.16~0.20%; Si≤0.40%; Mn≤0.40%; Cr: 12.0~14.0%; Ni≤0.30%; Cu: 0.10~0.30%; (2) Rolling and forming: Stainless steel wire rod is produced by high-speed rolling mill; the initial rolling speed of the billet is controlled to be ≤1.0m / s and the final rolling speed is controlled to be ≤55m / s. The rolling temperature is controlled at 800~950℃. The surface defect depth of the wire rod after rolling is ≤0.10mm and the wire rod non-roundness is ≤0.20mm. (3) Annealing: The wire rod obtained from S2 is placed in an atmosphere-protected annealing furnace for annealing treatment to obtain 20Cr13 stainless steel wire rod for cold heading bushings; the annealing process includes heating, holding, controlled cooling and rapid cooling stages. The holding temperature in the holding stage is 880~920℃ and the holding time is ≥8 hours. The cooling rate in the controlled cooling stage is ≤25℃ / h. After cooling to below 600℃, rapid cooling is performed; the annealed wire rod has an annealed hardness ≤145HBW, a strength ≤510Mpa, an elongation ≥35%, and a shrinkage ≥75%.

2. The method for producing 20Cr13 stainless steel wire rod for cold heading bushings according to claim 1, characterized in that, In step (1), the raw materials used are furnace charge with low Mn and low Ni elements.

3. The method for producing 20Cr13 stainless steel wire rod for cold heading bushings according to claim 1, characterized in that, In step (1), the elemental requirements for molten steel are: C: 0.16-0.20%; Si ≤ 0.40%; Mn ≤ 0.40%; Cr: 12.0-14.0%; Ni ≤ 0.30%; Cu: 0.10-0.30%. The control requirements for other elements shall meet the requirements of 20Cr13 in GB / T 4356 stainless steel wire rod.

4. The method for producing 20Cr13 stainless steel wire rod for cold heading bushings according to claim 1, characterized in that, The atmosphere of the protective atmosphere in step (3) is at least one of nitrogen and hydrogen.

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