Ferritic stainless steel cold heading magnetic material manufacturing method and cold heading part

Abstract

A manufacturing method of a ferritic stainless steel cold heading magnetic material comprises the following steps that a ferritic raw material is provided, the Fe content of the structure of the ferritic raw material is strictly controlled to be not lower than 81%, the structure of the ferritic raw material does not contain A-class and C-class inclusions, B-class inclusions are smaller than or equal to 0.5, and D-class inclusions are smaller than or equal to 1; drawing and annealing the ferrite raw material to obtain an annealed blank; and performance verification is conducted on the electromagnetic performance and the mechanical performance of the annealed blank, if the verification test is qualified, cold heading machining and heat treatment are continuously conducted on the remaining annealed blank to obtain the cold heading magnetic material, otherwise, the annealed blank is prepared again, and performance verification is repeated. According to the method, the ferritic stainless steel magnetic cold heading material with stable magnetic performance and mechanical performance can be prepared in batches to replace a martensitic stainless steel magnetic material with unstable magnetic performance, and the manufactured electromagnetic valve sleeve can effectively improve the performance and reliability of an engine high-pressure oil injector. The invention further provides the cold heading part.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic valves, specifically relating to a method for manufacturing ferritic stainless steel cold-forged magnetic materials and cold-forged parts. Background Technology

[0002] High-pressure fuel injectors are one of the most critical components in the direct injection system of automotive engines. The sensitivity and reliability of the injector directly determine engine performance. Especially with the current market's increasing emphasis on engine economy, more and more automotive engine designs are employing multiple fuel injections to achieve lean combustion, reducing fuel consumption and improving thermal efficiency. This places even higher demands on the performance of high-pressure fuel injectors. During their service life, high-pressure fuel injectors need to operate at high frequencies hundreds of millions of times under high-temperature conditions, and must maintain high motion precision to ensure stable fuel injection. Therefore, the stability of the magnetic and mechanical properties of the various components of their solenoid valves is crucial. Currently, high-pressure fuel injector valve sleeves are generally manufactured using martensitic stainless steel through machining to ensure the mechanical properties of the valve sleeve. However, martensitic stainless steel has relatively low structural stability and may undergo phase transformation during processing, leading to insufficient magnetic stability and affecting the final performance of the solenoid valve. Therefore, providing a method for manufacturing cold-forged materials with stable magnetic properties is of positive significance for improving engine performance and reliability. Summary of the Invention

[0003] The purpose of this invention is to provide a method for manufacturing ferritic stainless steel cold-heading magnetic materials, enabling the mass production of cold-headed parts with stable magnetic properties. This invention also provides a cold-headed part.

[0004] According to an embodiment of the present invention, a method for manufacturing ferritic stainless steel cold-heading magnetic material is provided, the method comprising the following steps:

[0005] a) Provide a ferrite raw material, wherein the ferrite raw material contains, by weight, 0.35%-0.70% Si, 0.55%-0.90% Mn, 16.8%-17.8% Cr, not exceeding 0.02% C, and 12[C]-0.35% Nb, and not exceeding 0.07% N, not exceeding 0.03% P, not exceeding 0.03% Ti, not exceeding 0.40% Cu, not exceeding 0.006% S, not exceeding 0.30% Mo, not exceeding 0.30% Ni, not exceeding 0.02% As, not exceeding 0.01% Sb and 0.025% Sn, with the balance being Fe and the Fe content not less than 81%, wherein [C] is the C content; the ferrite raw material also satisfies the following conditions: the number of Class A inclusions and Class C inclusions is 0, the number of Class B inclusions is ≤0.5, and the number of Class D inclusions is ≤1.

[0006] b) The ferrite raw material is drawn and annealed to obtain an annealed billet; a portion of the annealed billet is taken as a verification material, and the performance of the verification material is verified. The performance verification includes the following steps: a portion of the verification material is subjected to magnetic heat treatment in a vacuum or protective atmosphere and cooled to room temperature; the electromagnetic properties of the verification material after magnetic heat treatment are tested, and the mechanical properties of the verification material without magnetic heat treatment are tested. If the electromagnetic properties of the verification material meet the following conditions: Hc≤200A / m, Jy≥1.28 when H=2000A / m, Jy≥1.36 when H=4000A / m, Jy≥1.49 when H=10000A / m, Jy≥1.58 when H=50000A / m, and resistivity≤0.60μΩm; and the mechanical properties meet the following conditions: tensile strength≤600MPa, elongation≥15%, then it is judged to be qualified; otherwise, the annealed billet is re-prepared and the performance verification is repeated.

[0007] c) The annealed billet that has passed performance verification is subjected to cold heading to obtain a cold-headed billet;

[0008] d) Heat the cold heading billet to 800℃-820℃ under vacuum conditions and hold for 1h-1.5h, then cool it to below 450℃ at a rate of not less than 250-1000℃ / h, and finally air cool it to room temperature.

[0009] The magnetic properties of ferritic finished products are highly sensitive to the processing. Using conventional processing techniques can lead to significant fluctuations in the magnetic properties, failing to meet the design standards for solenoid valve sleeves. Strict control over the composition and impurity content of raw materials ensures the stability of the material's microstructure and composition. Performance verification of annealed billets is conducted to pre-verify their magnetic potential, eliminating random fluctuations in finished product performance and preventing batch scrap. Annealed billets that pass performance verification undergo cold heading and heat treatment. The cold-headed magnetic material forms a uniform and stable microstructure, ensuring that the final product's performance meets design requirements.

[0010] Furthermore, in some embodiments, the ferritic raw material is configured as electroslag remelted wire rod. The electroslag remelting process helps reduce impurity elements and inclusions in the raw material.

[0011] Furthermore, in some embodiments, in step a), C+N < 0.05%. C and N elements have an adverse effect on magnetic properties, and further controlling C+N below 0.05% helps to improve magnetic properties; furthermore, limiting the N content can improve cold heading performance and avoid cracking.

[0012] Furthermore, in some embodiments, step b) involves one to three drawing and annealing processes, wherein the area reduction rate of the final drawing pass is 8%-10%. Strict control over the drawing area reduction rate helps to adjust and control the grain size.

[0013] Furthermore, in some embodiments, step b) involves three drawing and annealing processes, wherein the area reduction rate of the first two drawing processes is 15%-35%.

[0014] Furthermore, in some embodiments, the protective atmosphere in step b) includes a nitrogen atmosphere, a hydrogen atmosphere, or an argon atmosphere; the vacuum condition in step d) is 10... -4 mbar-1mbar. A protective atmosphere is used to prevent oxidation of stainless steel; 10 - 4 A vacuum condition of mbar-1mbar is beneficial in preventing the loss of Cr element through volatilization.

[0015] Furthermore, in some embodiments, in step c), two to four cold upsetting processes are performed, with the total upsetting rate not exceeding 80%, and the upsetting rate of each cold upsetting process being 5%-50%.

[0016] Another embodiment of the present invention provides a cold-forged part, which is manufactured by cold forging using ferritic stainless steel. The ferritic stainless steel contains, by weight, 0.35%-0.70% Si, 0.55%-0.90% Mn, 16.8%-17.8% Cr, not more than 0.02% C, and 12[C]-0.35% Nb, as well as not more than 0.07% N, not more than 0.03% P, and not more than 0. The ferritic stainless steel contains 0.03% Ti, no more than 0.40% Cu, no more than 0.006% S, no more than 0.30% Mo, no more than 0.30% Ni, no more than 0.02% As, no more than 0.01% Sb and 0.025% Sn, with the balance being Fe and the Fe content being no less than 81%, wherein [C] is the C content; the ferritic stainless steel also satisfies the following conditions: the amount of Class A inclusions and Class C inclusions is 0, the amount of Class B inclusions is ≤0.5, and the amount of Class D inclusions is ≤1. The cold-forged part includes a rod body and a flange portion disposed at one end of the rod body; the outer peripheral grain size of the flange portion is grade 6-12; the outer peripheral grain size at the connection between the rod body and the flange portion is ≥ grade 6; the outer peripheral grain size of the rod body is ≥ grade 4; the grain size of the surface at the axial center of the cold-forged part is ≥ grade 4; the surface hardness of the cold-forged part is ≥ 120 HV; the flange portion also forms a welded connection area, the grain size of the welded connection area being grade 6-12. The coercivity of the cold-forged part is 140 A / m-240 A / m.

[0017] Furthermore, in some embodiments, the cold-forged part is manufactured using the ferritic stainless steel cold-forging magnetic material manufacturing method provided in any of the foregoing embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic cross-sectional view of a component in one embodiment;

[0019] Figure 2 This is a flowchart of a cold heading magnetic material manufacturing method in one embodiment;

[0020] Figure 3 The magnetic permeability curves are for a pair of ferritic stainless steel samples in proportion.

[0021] Figure 4 The magnetic permeability curve of a ferritic stainless steel sample in one embodiment is shown.

[0022] Meaning of reference numerals in the attached drawings: 1-valve sleeve; 11-stem body; 12-flange part; 13-recessed hole; 14-transition boss; 101-detection point; 102-detection point; 103-detection point; 104-detection point; 105-detection point; 106-detection point; 107-detection point.

[0023] The purpose of the above-described drawings is to provide a detailed description of the present invention so that those skilled in the art can understand the technical concept of the invention, and is not intended to limit the invention. For the sake of brevity, the above-described drawings only schematically depict the structures related to the technical features of the present invention, and do not depict the complete structure and all details strictly according to actual scale. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0025] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive, independent, or alternative embodiments. Those skilled in the art will understand that the embodiments described herein can be combined with other embodiments without structural conflict. In the description herein, terms such as "first," "second," etc., are used only to distinguish different objects and should not be construed as indicating relative importance or limiting the number, specific order, or hierarchy of the described technical features. In the description herein, "a plurality of" means at least two.

[0026] In automotive engine direct injection systems, high-pressure injectors consist of a valve sleeve with a centrally drilled hole, through which a valve ball with a valve stem is inserted. The valve sleeve is welded to the valve seat. During operation, the valve stem drives the valve ball in a reciprocating motion to control the opening and closing of the injection port. The valve sleeve withstands the impact force generated by the reciprocating motion of the valve stem and also needs to conduct a magnetic circuit to drive the valve stem. Therefore, the valve sleeve needs to possess good magnetic properties (coercivity and magnetic polarization; for soft magnetic materials, magnetic polarization is approximately equal to magnetic induction) to accurately drive the valve stem, and also requires high mechanical properties. Currently, the common manufacturing process involves machining metal bars, which helps ensure the mechanical properties of the valve sleeve. Currently, valve sleeves are mainly manufactured from machined martensitic stainless steel blanks. However, martensitic materials have insufficient magnetic stability; if a phase transition occurs during manufacturing, it will lead to significant fluctuations in magnetic properties, which is detrimental to the stability of the part's performance. Furthermore, machining has low material utilization and results in significant material waste during manufacturing. Compared to martensitic materials, ferritic stainless steel exhibits better structural stability, maintaining long-term stability of its mechanical and magnetic properties during service, thus showing greater application potential. However, the magnetic properties of ferritic stainless steel are highly susceptible to influences from composition, microstructure, and processing methods. Under existing conventional processing techniques, the magnetic properties of soft magnetic materials made from ferritic stainless steel are difficult to control effectively. Significant differences in magnetic properties can occur between different batches of parts, and even between different parts within the same batch, leading to manufacturing difficulties for ferritic stainless steel valve sleeves. To address these issues, embodiments of the present invention provide a method for manufacturing ferritic stainless steel cold-forging magnetic materials, which can improve the stability of the magnetic properties of ferritic stainless steel valve sleeves and enable large-scale production of ferritic stainless steel solenoid valve sleeves.

[0027] The process of this method is as follows: Figure 2 As shown, it includes the following steps:

[0028] First, a ferrite raw material is provided, the composition of which, by weight, contains 0.35%-0.70% Si, 0.55%-0.90% Mn, 16.8%-17.8% Cr, not exceeding 0.02% C, and 12[C]-0.35% Nb, as well as not exceeding 0.07% N, not exceeding 0.03% P, not exceeding 0.03% Ti, not exceeding 0.40% Cu, not exceeding 0.006% S, not exceeding 0.30% Mo, not exceeding 0.30% Ni, not exceeding 0.02% As, not exceeding 0.01% Sb and 0.025% Sn, with the balance being Fe and the Fe content not less than 81%, wherein [C] refers to the C content. Fe, as a matrix element, has a significant impact on the overall magnetic properties of the material. The total Fe content needs to be ensured to be above 81%, with a preferred embodiment controlled at no less than 81.2%. C and N, on the other hand, negatively affect magnetic properties and their contents need to be limited. In a preferred embodiment, C+N is further limited to below 0.05%, and N content is controlled to below 0.03% to facilitate subsequent cold heading. Meanwhile, Mn, Si, and Cr are beneficial for improving material strength but negatively affect magnetic properties. The contents of Mn, Si, and Cr need to be controlled to ensure a basic Fe content, guaranteeing the magnetic saturation strength Js and magnetic properties under low magnetic fields. Nb can combine with C to achieve grain refinement; therefore, it should be at least 12 times the C content to create a competitive advantage against other carbides and reduce the formation of other carbides that are detrimental to the mechanical and magnetic properties of the microstructure.

[0029] In a preferred embodiment, the Fe contents of the two prototype samples were 81.3% and 81.08%, respectively, and their magnetic polarization Jy at 50000 A / m was measured to be 1.611 and 1.630, respectively. In the comparative example, the Jy of the sample with an Fe content of 80.1% at 50000 A / m was 1.576.

[0030] Since the magnetic properties of ferrite are significantly affected by impurities in the microstructure, it is necessary to control the impurity content according to the GB / T 10561-2023 standard to achieve Class A inclusions and Class C inclusions of 0, Class B inclusions ≤0.5, and Class D inclusions ≤1.

[0031] In a comparative example, the number of both type B and type D inclusions in the ferritic stainless steel sample was 1. Figure 3 As shown, the measured permeability curve exhibits a distinct sawtooth pattern (Barkhausen jump) at the peak region A, and Jy is 1.246 at H = 2000 A / m. In the preferred embodiment, the permeability curve of the sample satisfying the following conditions is shown in the figure. (The original text also includes a table showing the permeability curves for inclusions and inclusions, but the context is unclear.) Figure 4As shown, the sawtooth pattern at the peak B region is significantly improved, the maximum permeability reaches about 1.7 times that of the comparative example, and the Jy at H = 2000 A / m is 1.298, which is a significant improvement.

[0032] To meet the purity requirements of ferrite raw materials, in the preferred embodiment, electroslag remelted wire rod steel is used as the ferrite raw material.

[0033] Next, the ferrite raw material is drawn and annealed to obtain an annealed billet. Drawing and annealing are used to adjust the microstructure and grain size of the annealed billet to ensure the stability of magnetic properties during subsequent cold heading. In a preferred embodiment, the annealing and drawing process is performed one to three times, with the area reduction rate of the final drawing step controlled at 8%-10%. In a further preferred embodiment, a total of three drawing and annealing steps are performed. The first drawing reduces the ferrite raw material from Φ14.5mm to Φ12.5mm, with an area reduction rate of 25.68%. After complete annealing, the second drawing reduces the area to Φ11.1mm, with an area reduction rate of 21.15%. After further annealing, the third drawing reduces the area to Φ10.6mm, with an area reduction rate of 8.81%, and then annealing again to obtain the annealed billet. Extensive trial production has shown that controlling the area reduction rate of the final drawing step at 8%-10% helps to obtain more stable mechanical and magnetic properties.

[0034] Because the magnetic properties of ferritic stainless steel are very sensitive to the raw material composition and processing, it is necessary to conduct performance verification by sampling of annealed billets to determine whether the batch of annealed billets has the potential to meet the design requirements for magnetic properties.

[0035] The specific process of performance verification is as follows:

[0036] A portion of the annealed billets was used as verification materials, and the mechanical properties of some of these materials were directly measured to determine whether they met the requirements of tensile strength ≤ 600 MPa and elongation ≥ 15%. If the verification materials met the above conditions, they were deemed to have qualified mechanical properties.

[0037] The remaining verification material undergoes magnetic heat treatment. It is heated in a vacuum or protective atmosphere such as argon, hydrogen, or nitrogen until fully demagnetized, then cooled to below 500°C at a rate not exceeding 200°C / h. It is then removed from the furnace and further air-cooled to room temperature. The electromagnetic properties of the magnetically heat-treated verification material are measured. The test standards are: resistivity ≤ 0.6 μΩm, coercivity Hc ≤ 200 A / m, Jy ≥ 1.28 when H = 2000 A / m, Jy ≥ 1.36 when H = 4000 A / m, Jy ≥ 1.49 when H = 10000 A / m, and Jy ≥ 1.58 when H = 50000 A / m. Verification materials meeting these conditions are deemed to have qualified electromagnetic properties.

[0038] If one or more of the mechanical or electromagnetic properties of the material fail the verification, the processing parameters need to be adjusted and the annealed billet needs to be prepared again. The reasons for the failure of the annealed billet performance verification may include random non-uniformity of the composition in the raw material, performance fluctuations caused by trace impurities, or occasional non-uniformity of the structure or accidental introduction of impurities during drawing and annealing.

[0039] For verification materials that meet both mechanical and electromagnetic property requirements, the remaining annealed blanks are cold-headed to obtain the following: Figure 1 The cold heading blank shown is a rod 11 and a flange 12. The flange 12 is connected to one end of the rod 11 and is used to connect to the upstream oil passage after subsequent processing. The other end of the rod 11 is used to install the fuel injector. A transition boss 14 is formed at the connection between the rod 11 and the flange 12. A recess 13 is provided in the center of the flange 12. The recess 13 is used for subsequent drilling guidance and to accommodate other parts of the high-pressure fuel injector. In a preferred embodiment, the cold heading process is completed in two to four passes, with the total upsetting ratio (the ratio of the height reduction after upsetting to the original height) not exceeding 80%, and the upsetting ratio of each pass being 5%-50%. In a preferred embodiment, the upsetting process is completed in four stages: the first stage has an upsetting ratio of 23.4%, resulting in a variable diameter bar; the second stage has an upsetting ratio of 29.1% (45.6% relative to the raw material generatrix), forming the vertical surface of the transition boss 14 relative to the bar body 11; the third stage has an upsetting ratio of 45% (70.3% relative to the raw material generatrix), forming the vertical surface of the flange portion 12 relative to the transition boss 14; and the fourth stage has an upsetting ratio of 8.3% (72.8% relative to the raw material generatrix), achieving the cold-headed billet formation. In other embodiments, the cold-headed billet can also be processed into other shapes, such as cylindrical billets, disc-shaped billets, etc., to suit different application requirements.

[0040] The cold-heading billet is heat-treated to obtain magnetic cold-headed parts. The heat treatment conditions are as follows: a vacuum condition is provided, for example, a vacuum heat treatment furnace is used. First, the temperature is raised to 680°C at a rate of 225°C / h-700°C / h and held for 1 hour. Then, the temperature is raised to 800°C-820°C at a rate of 75°C / h-300°C / h and held for 1 hour-1.5 hours. Finally, the temperature is lowered to 450°C at a rate of 250-1000°C / h. After removal, the parts are air-cooled. For example, the cooling rate can be set to 500°C / h. In a preferred embodiment, the vacuum condition is set to 10... -4 Nitrogen gas at mbar-1mbar. Experiments have shown that the overall coercivity of magnetic cold-forged parts is significantly related to the cooling rate, requiring precise control of the cooling rate to ensure rapid cooling.

[0041] The magnetic cold-forged parts that have undergone heat treatment are inspected and tested to complete the manufacturing process.

[0042] Another embodiment of the present invention provides a cold-forged part, the structure of which is as follows: Figure 1 As shown, the cold-forged part is a valve sleeve 1 made of ferritic stainless steel through cold forging. The ferritic stainless steel comprises, by weight, 0.35%-0.70% Si, 0.55%-0.90% Mn, 16.8%-17.8% Cr, not exceeding 0.02% C, and 12[C]-0.35% Nb, as well as not exceeding 0.07% N, not exceeding 0.03% P, not exceeding 0.03% Ti, not exceeding 0.40% Cu, not exceeding 0.006% S, not exceeding 0.30% Mo, not exceeding 0.30% Ni, not exceeding 0.02% As, not exceeding 0.01% Sb and 0.025% Sn, with the balance being Fe and the Fe content not less than 81%, wherein [C] represents the C content; the ferritic stainless steel also satisfies the following requirements: 0% of Class A and Class C inclusions, ≤0.5% of Class B inclusions, and ≤1% of Class D inclusions. The cold-forged part includes a rod 11 and a flange 12. Its grain size and hardness are measured through the following test points: test points 103 and 104 are located on the outer peripheral surface of the rod 11; test point 102 is located on the outer peripheral surface of the transition boss 14 at the connection between the rod 11 and the flange 12; test point 105 is located on the outer peripheral surface of the flange 12; test point 106 is located at the center of the recess 13; and test point 107 is located at the center of the end of the rod 11. The valve sleeve 1 needs to be welded to the isolation ring that can block the magnetic circuit through the flange 12, so test point 101 is also set in the welding area. The test points of the magnetic cold-forged part should meet the following requirements: hardness ≥ 120 HV; grain size of test points 101 and 105 is between 6 and 12; grain size of test point 102 is ≥ 6; and grain size of test points 103, 104, 106, and 107 is ≥ 4. The coercivity of cold-forged parts should be 140A / m-240A / m.

[0043] In a preferred embodiment, the results measured using the ferritic stainless steel cold-heading magnetic material manufacturing method provided in the foregoing embodiments are as follows: Test point 101: grain size 8.5, hardness 145 HV; Test point 102: grain size 8.5, hardness 148 HV; Test point 103: grain size 10, hardness 151 HV; Test point 104: grain size 11, hardness 150 HV; Test point 105: grain size 9, hardness 154 HV; Test point 106: grain size 9, hardness 148 HV; Test point 107: grain size 9, hardness 154 HV; coercivity is 180 A / m. All meet the above testing standards.

[0044] If the magnetic cold-headed parts do not meet the above standards during acceptance testing, the process parameters in steps b)-d) need to be re-inspected and adjusted based on the confirmation that the ferrite raw material is qualified, to check for any out-of-tolerance process parameters. For magnetic cold-headed parts with unqualified coercivity, if the coercivity is too high, the grain size of the annealed billet should be increased by adjusting the drawing annealing process in step b); if the coercivity is too low, the grain size of the annealed billet should be reduced.

[0045] The magnetic cold-forged parts are machined to obtain the finished valve sleeve. The coercivity of the finished valve sleeve can be controlled at the level of 200A / m-340A / m, which meets the design requirements of the high-pressure fuel injection valve.

[0046] The method for manufacturing ferritic stainless steel cold-forged magnetic materials provided in the above embodiments enables the mass production of ferritic stainless steel cold-forged magnetic materials with stable mechanical and magnetic properties. The process is highly standardized and stable. The ferritic stainless steel solenoid valve sleeves manufactured using the cold-forged parts provided in the above embodiments have high reliability and can be used to replace martensitic stainless steel valve sleeves, further improving the sensitivity and reliability of high-pressure injectors. Simultaneously, using the cold-forging process to manufacture valve sleeves effectively reduces machining losses. Machining a valve sleeve using cutting processes requires approximately 122g of material, while cold-forged parts only require approximately 29g, saving 93g of material and effectively reducing manufacturing costs.

[0047] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent substitution of the components and method steps involved, as well as combination of implementation methods in different embodiments without causing structural or principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A method for manufacturing ferritic stainless steel cold-forged magnetic material, characterized in that, Includes the following steps: a) Provide a ferrite raw material, wherein the ferrite raw material contains, by weight, 0.35%-0.70% Si, 0.55%-0.90% Mn, 16.8%-17.8% Cr, not exceeding 0.02% C, and 12[C]-0.35% Nb, and not exceeding 0.07% N, not exceeding 0.03% P, not exceeding 0.03% Ti, not exceeding 0.40% Cu, not exceeding 0.006% S, not exceeding 0.30% Mo, not exceeding 0.30% Ni, not exceeding 0.02% As, not exceeding 0.01% Sb and 0.025% Sn, with the balance being Fe and the Fe content not less than 81%, wherein [C] is the C content; the ferrite raw material also satisfies the following conditions: the number of Class A inclusions and Class C inclusions is 0, the number of Class B inclusions is ≤0.5, and the number of Class D inclusions is ≤1. b) The ferrite raw material is drawn and annealed to obtain an annealed billet; A portion of the annealed billet was taken as verification material, and the performance of the verification material was verified. The performance verification included the following steps: A portion of the verification material was subjected to magnetic heat treatment in a vacuum or protective atmosphere and then cooled to room temperature; Electromagnetic performance tests were performed on the verification material after magnetic heat treatment, and mechanical performance tests were performed on the verification material without magnetic heat treatment. If the electromagnetic performance of the verification material meets the following requirements: Hc ≤ 200 A / m, Jy ≥ 1.28 when H = 2000 A / m, Jy ≥ 1.36 when H = 4000 A / m, Jy ≥ 1.49 when H = 10000 A / m, Jy ≥ 1.58 when H = 50000 A / m, and resistivity ≤ 0.60 μΩm; and the mechanical performance meets the following requirements: tensile strength ≤ 600 MPa, elongation ≥ 15%, then the material is deemed qualified. Otherwise, the annealed billet is prepared again and the performance verification is repeated; c) The annealed billet that has passed performance verification is subjected to cold heading to obtain a cold-headed billet; d) Heat the cold heading billet to 800℃-820℃ under vacuum conditions and hold for 1h-1.5h, then cool it to below 450℃ at a rate of not less than 250-1000℃ / h, and finally air cool it to room temperature.

2. The method for manufacturing ferritic stainless steel cold-heading magnetic material according to claim 1, characterized in that, The ferritic raw material is configured as electroslag remelted wire rod steel.

3. The method for manufacturing ferritic stainless steel cold-forged magnetic material according to claim 1 or 2, characterized in that, In step a), C+N<0.05%.

4. The method for manufacturing ferritic stainless steel cold-forged magnetic materials according to claim 1 or 2, characterized in that, In step b), one to three drawing and annealing processes are performed, with the final drawing process having a reduction in surface area of ​​8%-10%.

5. The method for manufacturing ferritic stainless steel cold-heading magnetic material according to claim 4, characterized in that, In step b), three drawing and annealing processes are performed, with the area reduction rate of the first two drawing processes being 15%-35%.

6. The method for manufacturing ferritic stainless steel cold-forging magnetic material according to claim 1 or 2, characterized in that, The protective atmosphere in step b) includes a nitrogen atmosphere, a hydrogen atmosphere, or an argon atmosphere; the vacuum condition in step d) is 10. -4 mbar-1mbar.

7. The method for manufacturing ferritic stainless steel cold-heading magnetic material according to claim 1 or 2, characterized in that, In step c), two to four cold heading processes are performed, with the total upsetting rate not exceeding 80%, and the upsetting rate of each cold heading process being 5%-50%.

8. A cold-forged part, characterized in that, The cold-forged parts are manufactured from ferritic stainless steel by cold forging. The ferritic stainless steel, by weight, contains 0.35%-0.70% Si, 0.55%-0.90% Mn, 16.8%-17.8% Cr, not exceeding 0.02% C, and 12[C]-0.35% Nb, as well as not exceeding 0.07% N, not exceeding 0.03% P, not exceeding 0.03% Ti, and not exceeding The ferritic stainless steel contains 0.40% Cu, not more than 0.006% S, not more than 0.30% Mo, not more than 0.30% Ni, not more than 0.02% As, not more than 0.01% Sb, and 0.025% Sn, with the balance being Fe and the Fe content not less than 81%, wherein [C] represents the C content; the ferritic stainless steel also satisfies the following conditions: Class A inclusions and Class C inclusions are 0, Class B inclusions are ≤0.5, and Class D inclusions are ≤1. The cold-forged part includes a rod body and a flange portion disposed at one end of the rod body; The grain size on the outer periphery of the flange is grade 6-12. The outer peripheral grain size at the connection point between the rod and the flange is ≥6 grade; The outer peripheral grain size of the rod is ≥4 grade; The grain size of the surface at the shaft center of the cold-forged part is ≥4 grade; The surface hardness of the cold-forged part is ≥120HV; The flange portion also has a welded connection area, the grain size of which is 6-12. The coercivity of the cold-forged part is 140A / m-240A / m.

9. The cold-forged part according to claim 8, characterized in that, The cold-forged part is manufactured using the ferritic stainless steel cold-forging magnetic material manufacturing method as described in any one of claims 1 to 7.

Images