Heat treatment process for soft magnetic stainless steel with high magnetic conductivity and ultralow coercive force

Abstract

The invention relates to a high-permeability ultralow-coercive-force soft magnetic stainless steel heat treatment process which comprises the following steps: in a nitrogen atmosphere, firstly heating a hot-rolled wire rod to 900-950 DEG C at a heating rate of 30-50 DEG C / h, preserving heat for 4-6 hours to obtain a fine grain structure of equiaxial recrystallization ferrite, then cooling to room temperature at a cooling rate of less than or equal to 15 DEG C / h to homogenize the ferrite structure, and finally cooling to room temperature at a cooling rate of less than or equal to 15 DEG C / h to obtain the high-permeability ultralow-coercive-force soft magnetic stainless steel. The soft magnetic stainless steel is obtained. The method has the advantages that the maximum magnetic conductivity of the soft magnetic stainless steel is improved, the coercive force of the soft magnetic stainless steel is reduced, and the plasticity index of the soft magnetic stainless steel is improved.

Description

Technical Field

[0001] The invention relates to the technical field of soft magnetic stainless steel, in particular to a heat treatment process of high magnetic permeability and ultra-low coercivity soft magnetic stainless steel. Background Art

[0002] Soft magnetic materials refer to magnetic materials that can respond quickly to changes in external magnetic fields and achieve high magnetic flux density with low iron loss. Such materials are usually processed into automatic control components such as solenoid valves, and are widely used in the field of electronic components, and the demand continues to grow. Compared with traditional soft magnetic materials such as silicon steel and pure iron, soft magnetic stainless steel has shown great market potential and application prospects due to its excellent magnetic properties and corrosion resistance. At present, high-performance soft magnetic stainless steel mainly relies on imports. It is mainly used in high-frequency solenoid valves and has higher requirements for magnetic properties, including high magnetic permeability, low coercive force and higher saturation magnetic induction intensity. These excellent properties make the solenoid valve more sensitive and rapid to the external magnetic field, and the equipment is more advanced. Therefore, the research and development of high magnetic induction, ultra-low iron loss soft magnetic stainless steel for solenoid valves is not only necessary, but also advanced, which will help to accelerate the realization of import substitution and solve bottleneck problems in key areas.

[0003] The key performance indicators of soft magnetic stainless steel include magnetic properties, corrosion resistance, cutting performance, drawing performance, welding performance, etc., and the soft magnetic stainless steel materials used for high-frequency solenoid valves need to take into account both soft magnetic properties and plasticity. The main factors affecting the soft magnetic properties of ferritic stainless steel are alloy composition and microstructure. For example, the Chinese patent with the authorization announcement number CN115287544B recently applied by the applicant discloses a soft magnetic stainless steel wire rod with excellent welding performance. The stainless steel wire rod includes C≤0.020%, Si: 1.50~1.80%, Mn≤0.50%, Cr: 14.0~15.0%, Ni: ≤0.40%, Mo: 0.20~0.40%, N≤0.020%, P<0.020%, S≤0.010%, Ti: 0. 05~0.10%, Nb: 0.20~0.40%, Al: 0.020~0.030%, and the balance is Fe and inevitable impurities; the manufacturing method comprises the following steps of subjecting the charge to arc furnace smelting, AOD furnace smelting, LF refining furnace refining, die casting, electroslag remelting, rough rolling, high-speed wire mill rolling, solution treatment and pickling in sequence; in the solution treatment step, the hot-rolled wire rod formed by high-temperature rolling above 1050°C is subjected to solution heat treatment in an annular solution furnace, the heat treatment temperature is 850~950°C, and the heat treatment time is controlled to be above 60min.

[0004] The existing technical solutions described above have the following drawbacks: Although the increase in alloying elements in the above-mentioned stainless steel wire rod improves the plasticity of the material, it also increases the smelting cost and the difficulty of subsequent process preparation. Moreover, the adjustment of the alloying element content has limited effect on the improvement of magnetic properties. Especially in application scenarios requiring high magnetic permeability and ultra-low coercivity, it is difficult to meet the actual requirements solely by adjusting the alloy composition. In addition, although the above heat treatment process can optimize the microstructure of the material to a certain extent and improve the soft magnetic properties, it is often accompanied by problems such as high energy consumption, low efficiency, and coarse structure, which is not conducive to reducing the industrial production cost and achieving the plasticity index. Therefore, how to ensure excellent magnetic properties of soft magnetic stainless steel materials while taking into account good plasticity and cost-effectiveness has become a technical problem that urgently needs to be solved. In response to this challenge, the present invention proposes an innovative heat treatment process, aiming to achieve the heat treatment of soft magnetic stainless steel with high magnetic permeability and ultra-low coercivity through precise control of heat treatment parameters and optimized design of alloy composition, so as to meet the strict requirements for material properties in high-end application fields such as high-frequency solenoid valves. Summary of the Invention

[0005] The problem to be solved by the present invention is to provide a heat treatment process for soft magnetic stainless steel with high magnetic permeability and ultra-low coercivity in view of the above-mentioned deficiencies in the prior art, which has the advantages of increasing the maximum magnetic permeability of soft magnetic stainless steel, reducing the coercivity of soft magnetic stainless steel, and improving the plasticity index of soft magnetic stainless steel.

[0006] The above object of the present invention is achieved by the following technical solutions: A heat treatment process for soft magnetic stainless steel with high magnetic permeability and ultra-low coercivity, comprising the following steps: In a nitrogen atmosphere, first heat the hot-rolled wire rod at a heating rate of 30 - 50 °C / h to 900 - 950 °C, hold for 4 - 6 h to obtain a fine-grained structure of equiaxed recrystallized ferrite, and then cool to room temperature at a cooling rate of ≤15 °C / h to homogenize the ferrite structure, thereby obtaining soft magnetic stainless steel.

[0007] By adopting the above technical solutions, heat treatment is carried out in a nitrogen protection atmosphere, which can prevent the oxidation of the hot-rolled wire rod at high temperature, thereby protecting its surface structure from the influence of recrystallization. When the annealing temperature is set at 900 - 950 °C, the grain boundaries can be completely merged, ensuring complete recrystallization of the internal structure and reducing the proportion of grain boundaries and precipitates. More preferably, the holding time of the annealing process is maintained at 4 - 6 h, which helps to make the structure of the wire rod more uniform and the grains equiaxed. In addition, by precisely controlling the cooling rate of the wire rod after high-temperature annealing, the homogenization of the internal structure can be achieved, and stress concentration can be effectively reduced, thereby reducing the coercivity and increasing the magnetic permeability. Moreover, by adjusting the gas flow rate of the nitrogen protection atmosphere annealing furnace, it can be ensured that the wire rod is non-oxidized, avoiding problems such as overburning of local structure and overly coarse grains.

[0008] Furthermore, the flow rate of the nitrogen gas ≥ 50 m 3 / h.

[0009] Furthermore, the heating process is carried out in an atmosphere protection annealing furnace.

[0010] Furthermore, the cooling method is air cooling.

[0011] Furthermore, the soft magnetic stainless steel is composed of raw materials with the following weight percentages: C: ≤ 0.03%, Si: 1.50 - 2.00%, Mn: ≤ 1.0%, P: ≤ 0.04%, Cr: 15.50 - 16.50%, Mo: 0.20 - 0.60%, N: ≤ 0.03%, and the balance is Fe and inevitable impurities.

[0012] Furthermore, the soft magnetic stainless steel is composed of raw materials with the following weight percentages: C: 0.015 - 0.020%, Si: 1.53 - 1.58%, Mn: 0.75 - 0.80%, P: 0.023 - 0.025%, Cr: 15.60 - 15.71%, Mo: 0.33 - 0.37%, N: 0.011 - 0.013%, and the balance is Fe and inevitable impurities.

[0013] Specifically, the soft magnetic stainless steel for high - frequency solenoid valves is required to have excellent magnetic properties, where the saturation magnetic induction intensity ≥ 1.58 T, the coercive force ≤ 180 A / m, the maximum magnetic permeability ≥ 1800 H / m, and the residual magnetic induction intensity ≤ 0.5 T to meet the high - frequency precise control requirements in the application of the solenoid valve; the functions and design principles of each chemical component in the present invention are elaborated below; Carbon (C) and nitrogen (N): C and N are the main elements forming austenite stainless steel. As soft magnetic stainless steel is ferritic stainless steel, it is necessary to reduce the austenite content in the steel and increase the ferrite content. Therefore, the contents of C and N in the soft magnetic steel need to be controlled. In the present invention, the carbon content is controlled at ≤ 0.03%, and the nitrogen content is controlled at ≤ 0.03%; Silicon (Si): Silicon is a strong deoxidizer, which reduces the oxygen content in the steel and improves the inclusions in the steel. The silicon element can increase the magnetic permeability of the soft magnetic steel and reduce the coercive force; thus, the silicon content in the present invention is controlled at 1.50 - 2.00%; Manganese (Mn): Manganese is an austenite - forming element, and the improvement of magnetic properties by manganese element is limited. Therefore, the manganese content in the present invention is controlled at ≤ 0.40%; Phosphorus (P): Phosphorus is a harmful element in the steel, which causes the steel to be cold - brittle. The phosphorus content in the present invention is controlled at ≤ 0.04%; Chromium (Cr): Chromium is the main element in stainless steel. As the chromium content in stainless steel increases, the pitting potential of stainless steel rises, and its corrosion resistance improves. Excessive chromium will reduce the magnetic permeability. Therefore, the chromium content in this invention is controlled at 15.50 - 16.50%; Molybdenum (Mo): Molybdenum is an important element in austenitic stainless steel. Its main function is to improve the corrosion resistance of stainless steel together with chromium, especially to enhance the resistance to pitting corrosion, crevice corrosion, etc. Therefore, the molybdenum content in this invention is controlled at 0.20 - 0.60%.

[0014] Furthermore, the maximum magnetic permeability of the soft magnetic stainless steel ≥ 2000 H / m, and the coercive force ≤ 100 A / m.

[0015] Even further, the saturation magnetic induction intensity of the soft magnetic stainless steel ≥ 1.60 T, and the remanent magnetic induction intensity ≤ 0.50 T.

[0016] Even further, the tensile strength of the soft magnetic stainless steel is 450 - 500 MPa, the elongation after fracture is 35.0 - 40.0%, and the reduction of area is 65.0 - 70.0%.

[0017] Even further, the grain size of the soft magnetic stainless steel is grade 6.

[0018] In summary, the beneficial technical effects of this invention are as follows: The heat treatment process of this invention can significantly increase the proportion of recrystallized structure of soft magnetic stainless steel and reduce the proportion of grain boundaries by designing the annealing temperature and holding time and introducing a nitrogen protection atmosphere. Such improvement makes it more conducive to domain wall movement during the magnetization process of the material, thus being easy to magnetize and quickly demagnetize. In addition, this process also significantly improves the comprehensive mechanical properties of the material, ensures excellent processing performance, and finally achieves the goal of increasing the maximum magnetic permeability of soft magnetic stainless steel, reducing its coercive force, and improving the plasticity index. Description of the Drawings

[0019] Figure 1 is the hysteresis loop diagram of the soft magnetic stainless steel in Example 1 of this invention.

[0020] Figure 2 is the hysteresis loop diagram of the soft magnetic stainless steel in Comparative Example 1 of this invention.

[0021] Figure 3 is the metallographic structure diagram of the soft magnetic stainless steel in Example 1 of this invention.

[0022] Figure 4 is the metallographic structure diagram of the soft magnetic stainless steel in Comparative Example 1 of this invention. Detailed Description of the Invention

[0023] In order to make the technical means, creative features, achieved purposes and functions of the present invention clearer and easier to understand, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0024] Example 1: A heat treatment process for soft magnetic stainless steel with high magnetic permeability and ultra-low coercivity disclosed by the present invention includes the following steps. In a nitrogen atmosphere, and controlling the nitrogen flow rate to be 60 m 3 / h, first put the hot-rolled wire rod into an atmosphere-protected annealing furnace, heat it to 950 °C at a heating rate of 34 °C / h, hold for 4.5 h to obtain a fine-grained structure of equiaxed recrystallized ferrite, and then cool it to room temperature at a cooling rate of 13 °C / h to homogenize the ferrite structure and obtain soft magnetic stainless steel.

[0025] Among them, the soft magnetic stainless steel is composed of the following raw materials by weight percentage: C: 0.020%, Si: 1.55%, Mn: 0.80%, P: 0.025%, Cr: 15.6%, Mo: 0.33%, N: 0.011%, and the rest are Fe and inevitable impurities.

[0026] After testing, the coercivity of the soft magnetic stainless steel is 89.7 A / m, the maximum magnetic permeability is 2496 H / m, the remanent magnetic induction intensity is 0.4 T, the saturation magnetic induction intensity is 1.63 T, the tensile strength at room temperature is 461 MPa, the elongation after fracture is 37.5%, and the reduction of area is 67%.

[0027] Example 2: A heat treatment process for soft magnetic stainless steel with high magnetic permeability and ultra-low coercivity disclosed by the present invention includes the following steps. In a nitrogen atmosphere, and controlling the nitrogen flow rate to be 58 m 3 / h, first put the hot-rolled wire rod into an atmosphere-protected annealing furnace, heat it to 930 °C at a heating rate of 39 °C / h, hold for 5.0 h to obtain a fine-grained structure of equiaxed recrystallized ferrite, and then cool it to room temperature at a cooling rate of 11 °C / h to homogenize the ferrite structure and obtain soft magnetic stainless steel.

[0028] Among them, the soft magnetic stainless steel is composed of the following raw materials by weight percentage: C: 0.019%, Si: 1.58%, Mn: 0.75%, P: 0.023%, Cr: 15.65%, Mo: 0.36%, N: 0.012%, and the rest are Fe and inevitable impurities.

[0029] After testing, the coercivity of the soft magnetic stainless steel is 92.1 A / m, the maximum magnetic permeability is 2110 H / m, the remanent magnetic induction intensity is 0.43 T, the saturation magnetic induction intensity is 1.62 T, the tensile strength at room temperature is 474 MPa, the elongation after fracture is 36.5%, and the reduction of area is 66%.

[0030] Example 3: A heat treatment process for high permeability and ultra-low coercivity soft magnetic stainless steel disclosed by the present invention includes the following steps. In a nitrogen atmosphere, with the nitrogen flow rate controlled at 56 m 3 / h, first put the hot-rolled wire rod into an atmosphere-protected annealing furnace, heat it to 900 °C at a heating rate of 41 °C / h, hold for 5.8 h to obtain a fine-grained structure of equiaxed recrystallized ferrite, and then cool it to room temperature at a cooling rate of 10 °C / h to homogenize the ferrite structure, thus obtaining the soft magnetic stainless steel.

[0031] Among them, the soft magnetic stainless steel is composed of the following raw materials by weight percentage: C: 0.015%, Si: 1.53%, Mn: 0.77%, P: 0.024%, Cr: 15.71%, Mo: 0.37%, N: 0.013%, and the rest are Fe and inevitable impurities.

[0032] After testing, the coercivity of the soft magnetic stainless steel is 98.3 A / m, the maximum permeability is 2073 H / m, the remanent magnetic induction intensity is 0.45 T, the saturation magnetic induction intensity is 1.6 T, the tensile strength at room temperature is 487 MPa, the elongation after fracture is 35.5%, and the reduction of area is 65.5%.

[0033] Example 4: A heat treatment process for high permeability and ultra-low coercivity soft magnetic stainless steel disclosed by the present invention includes the following steps. In a nitrogen atmosphere, with the nitrogen flow rate controlled at 50 m 3 / h, first put the hot-rolled wire rod into an atmosphere-protected annealing furnace, heat it to 900 °C at a heating rate of 30 °C / h, hold for 4.0 h to obtain a fine-grained structure of equiaxed recrystallized ferrite, and then cool it to room temperature at a cooling rate of 5 °C / h to homogenize the ferrite structure, thus obtaining the soft magnetic stainless steel.

[0034] Among them, the soft magnetic stainless steel is composed of the following raw materials by weight percentage: C: 0.010%, Si: 1.50%, Mn: 0.50%, P: 0.020%, Cr: 15.50%, Mo: 0.20%, N: 0.010%, and the rest are Fe and inevitable impurities.

[0035] Example 5: A heat treatment process for high permeability and ultra-low coercivity soft magnetic stainless steel disclosed by the present invention includes the following steps. In a nitrogen atmosphere, with the nitrogen flow rate controlled at 70 m 3 / h, first put the hot-rolled wire rod into an atmosphere-protected annealing furnace, heat it to 950 °C at a heating rate of 50 °C / h, hold for 6.0 h to obtain a fine-grained structure of equiaxed recrystallized ferrite, and then cool it to room temperature at a cooling rate of 15 °C / h to homogenize the ferrite structure, thus obtaining the soft magnetic stainless steel.

[0036] Among them, the soft magnetic stainless steel is composed of raw materials with the following weight percentages: C: 0.030%, Si: 2.00%, Mn: 1.00%, P: 0.040%, Cr: 16.50%, Mo: 0.60%, N: 0.030%, and the rest are Fe and inevitable impurities.

[0037] Comparative Example 1: A heat treatment process for soft magnetic stainless steel with high magnetic permeability and ultra-low coercivity disclosed in the present invention, including the following steps. Without using nitrogen protection, first put the hot-rolled wire rod into an atmosphere protection annealing furnace, heat it to 820 °C at a heating rate of 34 °C / h, hold for 4.0 h to obtain a fine-grained structure of equiaxed recrystallized ferrite, and then cool it to room temperature at a cooling rate of 30 °C / h to homogenize the ferrite structure, thus obtaining the soft magnetic stainless steel.

[0038] Among them, the soft magnetic stainless steel is composed of raw materials with the following weight percentages: C: 0.017%, Si: 1.56%, Mn: 0.78%, P: 0.027%, Cr: 15.77%, Mo: 0.31%, N: 0.020%, and the rest are Fe and inevitable impurities.

[0039] After testing, the coercivity of the soft magnetic stainless steel is 224 A / m, the maximum magnetic permeability is 930 H / m, the remanent magnetic induction intensity is 0.63 T, the saturation magnetic induction intensity is 1.51 T, the tensile strength at room temperature is 521 MPa, the elongation after fracture is 30%, and the reduction of area is 58%.

[0040] The following is through combining Figures 1 to 4 Compare the properties of the soft magnetic stainless steel prepared in Example 1 and Comparative Example 1 of the present invention.

[0041] Among them, Figure 1 is the hysteresis loop of the soft magnetic stainless steel prepared in Example 1. It can be seen from Figure 1 that the area formed by the B-H loop is relatively narrow, indicating that it has high magnetic permeability and ultra-low coercivity. The material can reach saturation when the magnetic field strength is 2000 A / m, and can be instantaneously demagnetized when the reverse magnetic field strength is 90 A / m, which can meet the requirements of high-frequency and high-efficiency solenoid valve spools in the market. Figure 2 is the hysteresis loop of the soft magnetic stainless steel prepared in Comparative Example 1. It can be seen from Figure 2 that the area formed by the B-H loop is relatively wide and the curve is relatively flat. The material needs to reach saturation when the magnetic field strength is 5000 A / m, but the saturation magnetic induction intensity is not high. At the same time, it needs to be demagnetized when the reverse magnetic field strength is 224 A / m. The entire magnetization and demagnetization process reacts relatively slowly and cannot meet the requirements of high-frequency solenoid valve spools in the market. Figure 3 is the transverse tissue distribution of the soft magnetic stainless steel prepared in Example 1. It can be seen fromFigure 3 It can be seen that the room-temperature structure of Example 1 is equiaxed grains with a high degree of homogenization. There is no phenomenon of coarse ferrite structure, and the grain boundaries are clear. Its grain size rating is 6, ensuring the stability of the mechanical properties of the material; Figure 4 Figure 4 shows the transverse tissue distribution of the soft magnetic stainless steel prepared in Comparative Example 1. From Figure 4 it can be seen that there are sub-grain structures that have not recrystallized, and the overall grain size rating is 7-8.

[0042] Through the above performance test results, combined with Figures 1 to 4 , it can be found that the high-permeability, ultra-low coercivity soft magnetic stainless steel produced by the present invention has excellent magnetic properties. Among them, the maximum permeability of the finished material is ≥2000, and the coercivity is ≤100 A / m; the saturation magnetic induction intensity of the finished material is ≥1.6 T, and the remanent magnetic induction intensity is ≤0.5 T; it has excellent plasticity at room temperature, with an elongation of 35.0-40.0% and a reduction of area of 65-70%.

[0043] Therefore, the present invention sets heat treatment process parameters, including annealing temperature, heating rate, holding time, and cooling rate, and introduces a nitrogen protection measure to ensure that the material achieves a fully recrystallized and uniformly distributed organizational structure. This significantly improves the magnetic properties and plasticity indexes of the soft magnetic stainless steel. The high-permeability, ultra-low coercivity soft magnetic stainless steel produced by the process of the present invention effectively solves the problems of difficult magnetization and slow disconnection during the application of soft magnetic stainless steel. Such materials are mainly used in the field of high-frequency solenoid valves and have begun to gradually replace imported products.

[0044] Comparative Example 2: A heat treatment process for high-permeability ultra-low coercivity soft magnetic stainless steel disclosed in the present invention, including the following steps. Without using nitrogen protection, first put the hot-rolled wire rod into an atmosphere protection annealing furnace, heat it to 850 °C at a heating rate of 34 °C / h, hold for 4.0 h to obtain a fine-grained structure of equiaxed recrystallized ferrite, and then cool it to room temperature at a cooling rate of 30 °C / h to homogenize the ferrite structure to obtain soft magnetic stainless steel.

[0045] Among them, the soft magnetic stainless steel is composed of the following raw materials by weight percentage: C: 0.019%, Si: 1.55%, Mn: 0.71%, P: 0.026%, Cr: 15.83%, Mo: 0.41%, N: 0.011%, and the rest are Fe and inevitable impurities.

[0046] After testing, the coercivity of the soft magnetic stainless steel is 207 A / m, the maximum permeability is 991 H / m, the remanent magnetic induction intensity is 0.58 T, the saturation magnetic induction intensity is 1.54 T, the tensile strength at room temperature is 503 MPa, the elongation after fracture is 31%, and the reduction of area is 61%.

[0047] Comparative Example 3: A heat treatment process for a soft magnetic stainless steel with high magnetic permeability and ultra-low coercivity disclosed in the present invention, comprising the following steps. Without using nitrogen protection, first put the hot-rolled wire rod into an atmosphere-protected annealing furnace, heat it to 880 °C at a heating rate of 34 °C / h, hold for 4.0 h to obtain a fine-grained structure of equiaxed recrystallized ferrite, and then cool it to room temperature at a cooling rate of 30 °C / h to homogenize the ferrite structure, thus obtaining the soft magnetic stainless steel.

[0048] Among them, the soft magnetic stainless steel is composed of the following raw materials by weight percentage: C: 0.021%, Si: 1.57%, Mn: 0.88%, P: 0.024%, Cr: 15.73%, Mo: 0.39%, N: 0.022%, and the rest are Fe and inevitable impurities.

[0049] After testing, the coercivity of the soft magnetic stainless steel is 175 A / m, the maximum magnetic permeability is 1317 H / m, the remanent magnetic induction intensity is 0.53 T, the saturation magnetic induction intensity is 1.56 T, the tensile strength at room temperature is 496 MPa, the elongation after fracture is 33%, and the reduction of area is 63%.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A heat treatment process for a soft magnetic stainless steel with high magnetic permeability and ultra-low coercivity, characterized in that: It includes the following steps. In a nitrogen atmosphere, first heat the hot-rolled wire rod at a heating rate of 30 - 50 °C / h to 900 - 950 °C, hold for 4 - 6 h to obtain a fine-grained structure of equiaxed recrystallized ferrite, and then cool to room temperature at a cooling rate of ≤15 °C / h to homogenize the ferrite structure, thus obtaining a soft magnetic stainless steel.

2. The heat treatment process of a high magnetic permeability and ultra-low coercivity soft magnetic stainless steel according to claim 1, characterized in that: The flow rate of the nitrogen gas ≥ 50 m 3 / h.

3. A heat treatment process for a high magnetic permeability and ultra-low coercivity soft magnetic stainless steel according to claim 1, characterized in that: The heating process is carried out in an atmosphere protection annealing furnace.

4. A heat treatment process for a high magnetic permeability and ultra-low coercivity soft magnetic stainless steel according to claim 1, characterized in that: The cooling method is air cooling.

5. A heat treatment process for a high magnetic permeability and ultra-low coercivity soft magnetic stainless steel according to claim 1, characterized in that: The soft magnetic stainless steel is composed of the following raw materials by weight percentage: C: ≤0.03%, Si: 1.50 - 2.00%, Mn: ≤1.0%, P: ≤0.04%, Cr: 15.50 - 16.50%, Mo: 0.20 - 0.60%, N: ≤0.03%, and the rest are Fe and unavoidable impurities.

6. A heat treatment process for a soft magnetic stainless steel with high magnetic permeability and ultra-low coercivity according to claim 5, characterized in that: The soft magnetic stainless steel is composed of the following raw materials by weight percentage: C: 0.015 - 0.020%, Si: 1.53 - 1.58%, Mn: 0.75 - 0.80%, P: 0.023 - 0.025%, Cr: 15.60 - 15.71%, Mo: 0.33 - 0.37%, N: 0.011 - 0.013%, and the rest are Fe and unavoidable impurities.

7. A heat treatment process for a high magnetic permeability and ultra-low coercivity soft magnetic stainless steel according to claim 1, characterized in that: The maximum magnetic permeability of the soft magnetic stainless steel is ≥2000 H / m, and the coercive force is ≤100 A / m.

8. A heat treatment process for a soft magnetic stainless steel with high magnetic permeability and ultra-low coercivity according to claim 7, characterized in that: The saturation magnetic induction intensity of the soft magnetic stainless steel is ≥1.60 T, and the remanent magnetic induction intensity is ≤0.50 T.

9. A heat treatment process for a high magnetic permeability and ultra-low coercivity soft magnetic stainless steel according to claim 7, characterized in that: The tensile strength of the soft magnetic stainless steel is 450 - 500 MPa, the elongation after fracture is 35.0 - 40.0%, and the reduction of area is 65.0 - 70.0%.

10. A heat treatment process for a high magnetic permeability and ultra-low coercivity soft magnetic stainless steel according to claim 7, characterized in that: The grain size of the soft magnetic stainless steel is grade 6.

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