Fe-Si soft magnetic material with yield strength of 780 MPa and manufacturing method of Fe-Si soft magnetic material

Abstract

The invention discloses a Fe-Si soft magnetic material with yield strength of 780MPa grade, which contains Fe and inevitable impurities, and further contains the following chemical elements in percentage by mass: 3.45-4.5% of Si, 0.35-0.35% of Si, 0.35-0.35% of Cr, 0.35-0.35% of Mo, 0.35-0.35% of Mo, 0.35-0.35% of V 0.5 to 2.0 percent of Ni; 0.5% to 1.2% of Al; and at least one of Mn, Cr and Mo, the total content of which is 0.2-2.0%. The invention further discloses a manufacturing method of the Fe-Si soft magnetic material with the yield strength of 780 MPa. The manufacturing method comprises the following steps: smelting and casting; hot rolling; annealing the hot-rolled plate; cold rolling; annealing a finished product; and coating an insulating coating. The high-power-density driving motor has the performance of ultrahigh strength, high frequency and low loss, and can meet the requirements of high efficiency, miniaturization and high reliability of the high-power-density driving motor.

Description

Technical Field

[0001] This invention relates to a metallic material, and more particularly to an Fe-Si soft magnetic material. Background Technology

[0002] With the rapid development of the all-electric aerospace vehicle industry, the performance requirements for drive motors, one of the core components of the power system, are becoming increasingly stringent. These motors need to withstand a very wide range of ambient temperatures and limited working spaces, placing stringent demands on their efficiency, weight, size, and safety. Taking a typical permanent magnet synchronous drive motor as an example, high speed is one of the important means to increase power density. Under the same power conditions, an increase in rotor speed corresponds to a decrease in torque, which in turn reduces the motor size, resulting in reduced material usage and weight.

[0003] For soft magnetic materials that make up motors, when used as rotors, they need to have sufficiently high strength, and when used as stators, they need to have high frequency and low loss, so as to meet the risk of fracture failure under high speed conditions required by high power density drive motors, while reducing energy loss.

[0004] Chinese patent document CN108044100A, published on May 18, 2018, entitled "A Method for Preparing Fe-6.5%Si Soft Magnetic Material Thin Strips by Powder Rolling," discloses a method for preparing Fe-6.5%Si soft magnetic material thin strips by powder rolling. The method involves mixing water-atomized iron powder and high-purity ferrosilicon powder to obtain a mixed powder of Fe-4.5% to 6.7%Si. This powder is then subjected to powder rolling, debinding and sintering, multiple cold rolling cycles, and multiple intermediate densification sintering cycles to obtain 0.1-0.5mm sheet material. Preferably, further homogenization high-temperature sintering at 1265-1335℃ is required for 1-4 hours, ultimately yielding a density of 7.34-7.49 g / cm³. 3 The patent document describes a Fe-6.5%Si alloy strip. However, the preparation process described is cumbersome and complex, making it unsuitable for large-scale production. Furthermore, it does not disclose the high-frequency iron loss level and mechanical properties of this soft magnetic material. Summary of the Invention

[0005] One of the objectives of this invention is to provide a Fe-Si soft magnetic material with a yield strength of 780MPa. This Fe-Si soft magnetic material with a yield strength of 780MPa is made possible by controlling the material's composition, microstructure, and special grain boundaries, thereby achieving ultra-high strength, high frequency, and low loss performance, which can meet the requirements of high efficiency, miniaturization, and high reliability of high power density drive motors.

[0006] To achieve the above objectives, this invention proposes a Fe-Si soft magnetic material with a yield strength of 780 MPa, which contains Fe and unavoidable impurities, and also contains the following chemical elements in the following mass percentages:

[0007] Si: 3.45%-4.5%; Ni: 0.5%-2.0%; Al: 0.5%-1.2%; and at least one of Mn, Cr, and Mo, with a total mass percentage content of 0.2%-2.0%.

[0008] Furthermore, in the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, the mass percentage content of each chemical element is as follows:

[0009] Si: 3.45%-4.5%; Ni: 0.5%-2.0%; Al: 0.5%-1.2%; at least one of Mn, Cr, and Mo, with a total mass percentage content of 0.2%-2.0%; the balance being Fe and unavoidable impurities.

[0010] The design principles of each chemical element in the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention are as follows:

[0011] Si: In the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, Si can be dissolved into the matrix, thereby improving the material strength; at the same time, Si can also increase resistivity and reduce iron loss. To achieve the effects of this invention, the Si content is controlled to be above 3.45%; however, when the mass percentage of Si is too high, the difficulty of cold rolling the strip will increase sharply, and a B2 ordered phase will also form, further deteriorating the processing performance. Therefore, in the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, the mass percentage of Si is controlled between 3.45% and 4.5%.

[0012] Ni: In the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, the addition of Ni element can enhance the material's strength by utilizing the solid solution strengthening effect of Ni atoms. Simultaneously, Ni is a ferromagnetic element, which is beneficial to magnetism and can reduce iron loss. To achieve this effect, the amount of Ni added is above 0.5%. However, when the mass percentage of Ni is too high, the cost becomes excessive. Therefore, in the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, the mass percentage of Ni element is controlled between 0.5% and 2.0%.

[0013] Al: In the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, the role of Al is similar to that of Si, increasing the material resistivity and reducing iron loss. Meanwhile, Al has a smaller impact on cold-rolling processing performance than Si, so it can be added in appropriate amounts. However, if the mass percentage of Al is too high, it will cause sprue blockage during casting, affecting production. Therefore, in the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, the mass percentage of Al is controlled between 0.5% and 1.2%.

[0014] Mn, Cr, and Mo elements, as alloying reinforcing elements, can further improve the strength of the material without degrading its magnetic properties. However, considering manufacturing costs, the amount of Mn, Cr, and Mo added should not be excessive. Therefore, in the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, the total mass percentage of Mn, Cr, and Mo elements is between 0.2% and 2.0%.

[0015] Furthermore, the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention also contains Sn or Sb at a mass percentage of 0.01%-0.5%.

[0016] Sn and Sb: In the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, Sn and Sb are grain boundary segregation elements. Sn and Sb can refine the recrystallization structure and enhance the material strength through grain refinement; furthermore, Sn and Sb segregate at grain boundaries, preventing internal oxidation during strip annealing and improving the material texture, thus enhancing the magnetic properties of the Fe-Si soft magnetic material. Therefore, considering alloy cost, the total mass percentage of Sn or Sb in the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention can be between 0.01% and 0.5%.

[0017] Furthermore, in the unavoidable impurities of the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, C ≤ 0.01%, P ≤ 0.02%, and S ≤ 0.005%.

[0018] In the Fe-Si soft magnetic material with a yield strength of 780MPa described in this invention, C, P and S are all impurity elements in the Fe-Si soft magnetic material. Under the condition that technical conditions permit, in order to obtain steel with better performance and higher quality, the content of impurity elements in the steel should be reduced as much as possible.

[0019] Furthermore, the microstructure of the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention contains equiaxed micrograins, and the average size d of the equiaxed micrograins is 5-30 μm.

[0020] Furthermore, in the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, the area content of the equiaxed micrograin structure is 1%-25%.

[0021] In this invention, the microstructure of the Fe-Si soft magnetic material with a yield strength of 780 MPa is an incompletely recrystallized structure, containing some equiaxed grains with an average size of 5-30 micrometers, occupying an area of ​​1%-25%, and the remainder being a fibrous deformed structure that has not undergone recrystallization. This microstructure characteristic mainly serves two purposes:

[0022] (1) The fiber structure retained in the microstructure contains high-density dislocations. By utilizing the strengthening effect of dislocations, the strength of the material can be improved. Combined with the reasonable design of chemical elements in the composition, the yield strength of the material can exceed 780 MPa.

[0023] (2) The microstructure contains a certain amount of recrystallized equiaxed small grains, which can reduce the high-frequency loss of the material. If the grain size is less than 5 micrometers or the area occupied is less than 1%, the yield strength of the material will be improved, but the iron loss will also increase. If the grain size exceeds 30 micrometers or the area occupied exceeds 25%, the yield strength will be lower than 780 MPa. Although the strength loss can be compensated to some extent by continuing to increase the content of solid solution alloying elements, it will increase the difficulty of strip production and manufacturing, especially the cold rolling process, which is prone to brittle fracture and significantly reduces the yield.

[0024] Furthermore, in the Fe-Si soft magnetic material with a yield strength of 780 MPa described in this invention, its iron loss P 10 / 400 ≤40W / kg, yield strength ≥780MPa.

[0025] In this invention, Fe-Si soft magnetic material with a yield strength of 780 MPa, after annealing, can be directly used as the core rotor of a drive motor. The material does not require stress-relief annealing after lamination. In its annealed state, the material exhibits low high-frequency iron loss P at a frequency of 400 Hz and a maximum magnetic polarization of 1.0 T. 10 / 400 With a strength of ≤40W / kg and a yield strength of ≥780MPa, it can meet the requirements of high-speed rotor operation without breakage, while reducing motor iron loss.

[0026] Another objective of this invention is to provide a method for manufacturing Fe-Si soft magnetic materials with a yield strength of 780 MPa, which can obtain Fe-Si soft magnetic materials with ultra-high strength, high frequency and low loss.

[0027] To achieve the above objectives, the present invention provides a method for manufacturing Fe-Si soft magnetic materials with a yield strength of 780 MPa, comprising the following steps:

[0028] Smelting and casting;

[0029] Hot-rolled;

[0030] Annealing of hot-rolled steel sheet;

[0031] Cold rolling;

[0032] Finished product annealing: The temperature of the soaking zone is 660℃-740℃, and the holding time t in the soaking zone meets the following requirements:

[0033]

[0034] Where d is the average size of the equiaxed micrograin structure in the recrystallized portion of the annealed plate, with the unit parameter being μm; T is the temperature of the soaking zone, with the unit parameter being ℃; and s is the area percentage of the equiaxed micrograin structure, for example, when the area percentage is 25%, the value is 0.25.

[0035] Apply an insulating coating.

[0036] In this invention, to ensure that the strip's grain structure after annealing is an incompletely recrystallized structure, with the average size of the formed equiaxed small grains being 5-30 micrometers and occupying an area between 1% and 25%, two important parameters—the final annealing homogenization temperature and the holding time—need to be strictly controlled. When the homogenization temperature is below 660℃, recrystallization is difficult to occur during annealing, resulting in high-frequency iron loss exceeding 40W / kg; when the homogenization temperature is above 740℃, complete recrystallization occurs, reducing the material's yield strength. The holding time is adjusted based on three factors: the average grain size of the recrystallized portion in the target grain structure, the area occupied, and the annealing temperature, with the maximum value satisfying:

[0037]

[0038] Otherwise, it will result in excessively large grain size or an area exceeding 25%, causing the yield strength to be lower than 780 MPa.

[0039] The Fe-Si soft magnetic material with a yield strength of 780 MPa and its manufacturing method described in this invention have the following advantages and beneficial effects:

[0040] The Fe-Si soft magnetic material with a yield strength of 780MPa described in this invention possesses high strength, high frequency, and low loss properties through material composition design, microstructure, and special grain boundary control, which can meet the requirements of high efficiency, miniaturization, and high reliability of high power density drive motors.

[0041] In some embodiments, the iron loss P of Fe-Si soft magnetic materials with a yield strength of 780 MPa is... 10 / 400 ≤40W / kg, yield strength ≥780MPa. Detailed Implementation

[0042] The following will further explain and illustrate the Fe-Si soft magnetic material with a yield strength of 780MPa and its manufacturing method described in this invention with reference to specific embodiments. However, this explanation and illustration do not constitute an undue limitation on the technical solution of this invention.

[0043] Examples 1-8 and Comparative Examples 1-5

[0044] The Fe-Si soft magnetic materials with a yield strength of 780 MPa in Examples 1-8 of this invention and the comparative materials in Comparative Examples 1-5 were prepared using the following steps:

[0045] (1) Smelting and casting: blast furnace molten iron undergoes molten iron pretreatment, converter smelting, RH refining, and continuous casting and rolling to obtain cast billets.

[0046] (2) Hot rolling: The billet heating temperature can be 1180℃, the holding time is 2h, the final rolling temperature can be 800℃, and finally hot rolled to a thickness of 2.0mm.

[0047] (3) Annealing of hot-rolled plate: In order to fully recrystallize the grain structure of hot-rolled plate, the holding temperature can be 900℃ and the holding time can be 5min.

[0048] (4) Cold rolling: Cold rolling yields a finished product with a thickness of 0.30 mm.

[0049] (5) Finished product annealing: The temperature of the soaking zone is 660℃-740℃, and the holding time t in the soaking zone meets the following requirements: Where d is the average size of the equiaxed micrograins in the recrystallized portion of the annealed plate, with units of μm; T is the temperature of the soaking zone, with units of °C; and s is the area percentage of the equiaxed micrograins. The upper limit of the holding time calculated by this formula is listed in Table 2.

[0050] (6) Applying an insulating coating: After the finished product is annealed, an insulating coating is applied to the surface of the material.

[0051] Tables 1-1 and 1-2 list the mass percentage of each chemical element in the Fe-Si soft magnetic materials with a yield strength of 780 MPa in Examples 1-8 of the present invention and the comparative materials in Comparative Examples 1-5.

[0052] Table 1-1. (wt%, balance Fe and unavoidable impurities other than C, P and S)

[0053] serial number Si Ni Al Mn Cr Mo Mn+Cr+Mo Example 1 3.45 2.0 0.70 0.50 - - 0.50 Example 2 3.50 1.5 0.80 0.50 0.2 - 0.70 Example 3 3.60 0.6 1.20 0.20 1.0 - 1.20 Example 4 3.70 1.2 0.50 - 2.0 - 2.00 Example 5 3.80 0.5 0.60 1.20 - 0.2 1.40 Example 6 4.00 0.8 0.80 0.20 0.1 - 0.30 Example 7 4.20 0.7 0.50 0.20 0.5 - 0.70 Example 8 4.50 0.5 0.85 - 0.2 - 0.2 Comparative Example 1 2.00 - 0.50 0.50 - - 0.50 Comparative Example 2 3.50 - - 0.50 - - 0.50 Comparative Example 3 3.60 0.8 1.0 0.20 - - 0.20 Comparative Example 4 4.00 1.0 0.80 0.75 0.5 - 1.25 Comparative Example 5 3.70 0.7 0.60 0.55 - - 0.55

[0054] Table 1-2. (wt%, balance Fe and unavoidable impurities other than C, P and S)

[0055]

[0056]

[0057] Table 2 lists the specific process parameters of the Fe-Si soft magnetic materials with a yield strength of 780 MPa in Examples 1-8 of the present invention and the comparative materials in Comparative Examples 1-5.

[0058] Table 2.

[0059] serial number Temperature T (°C) of the soaking zone Insulation time (s) Upper limit of heat preservation time t(s) Example 1 660 7 7 Example 2 680 10 11 Example 3 680 5 7 Example 4 680 15 19 Example 5 680 20 32 Example 6 700 20 26 Example 7 700 15 20 Example 8 740 15 23 Comparative Example 1 700 10 13 Comparative Example 2 700 10 12 Comparative Example 3 640 20 - Comparative Example 4 750 50 65 Comparative Example 5 680 80 61

[0060] Samples were taken from the Fe-Si soft magnetic materials with a yield strength of 780 MPa obtained in Examples 1-8 and the comparative materials in Comparative Examples 1-5. The average size of the equiaxed micrograin structure, the area content of the equiaxed micrograin structure, and the iron loss P were measured. 10 / 400 The yield strength was tested, and the results are listed in Table 3. The specific testing methods are as follows:

[0061] Iron loss P10 / 400: Based on the square circle method of the standard "GB / T10129-2019 Measurement Method of Medium Frequency Magnetic Properties of Electrical Steel Strips (Sheets)".

[0062] Yield strength performance index test: based on the standard GB / T 228.1-2010 Metallic materials, tensile testing - Part 1: Test method at room temperature.

[0063] Microstructure: Electron backscattering (EBSD) technology was used, referring to the standard GB / T 19501-2013 "General Rules for Electron Backscattering Diffraction Analysis Methods in Microbeam Analysis". 15*20mm samples were randomly cut from finished annealed strips, with the observation surface being an RD*ND cross section. The samples were ground, mechanically polished, and electrolytically polished before observation under a field emission scanning electron microscope equipped with an EBSD testing system. The testing conditions were set to a reference voltage of 20kV, a current of 30μA, and a scanning step of 1μm. Four fields of view were randomly selected for each sample, with a total statistical area of ​​no less than 1,000,000μm. 2 Then, the number of recrystallized grains and their area ratio are calculated.

[0064] Average grain size: The average area of ​​each grain can be calculated by dividing the total area of ​​all recrystallized grains by the number of recrystallized grains, and the equivalent circle diameter can then be calculated.

[0065] Table 3 lists the performance test results of the Fe-Si soft magnetic materials with a yield strength of 780 MPa in Examples 1-8 of the present invention and the comparative materials in Comparative Examples 1-5.

[0066] Table 3.

[0067]

[0068] As can be seen from Table 3 above, in Examples 1-8 of the present invention, the key parameters such as alloy chemical composition control, holding temperature and time during the finished product annealing process are all within the design range of the present invention, thus obtaining the iron loss P of the finished Fe-Si alloy strip before stress-relief annealing. 10 / 400 All values ​​are less than 40 W / kg, and the yield strength is greater than or equal to 780 MPa, which meets the requirement that the rotor core does not break or fail at high speed.

[0069] In contrast, although the manufacturing process and finished product annealing process of Comparative Examples 1 and 2 are within the scope of this invention, their chemical composition is not within the scope of this invention, and their finished product high-frequency iron loss or yield strength is not within the scope of this invention.

[0070] Furthermore, although the chemical composition of Comparative Example 3 is within the scope of this invention, its homogenization temperature was too low during the annealing process, and recrystallization did not occur. Although the yield strength reached 835 MPa, it resulted in an increased iron loss, exceeding 40 W / kg.

[0071] In Comparative Examples 4 and 5, although the chemical composition is within the scope of this invention, the homogenization temperature is too high or the holding time is too long during the annealing process of the finished product, resulting in the area content of equiaxed small grain structure of the strip exceeding 25%, the dislocation strengthening effect is weakened, and the yield strength of the finished material is low.

[0072] It should be noted that the scope of protection of the prior art in this invention is not limited to the embodiments given in this application. All prior art that does not contradict the solution of this invention, including but not limited to prior patent documents, prior publications, prior public uses, etc., can be included in the scope of protection of this invention.

[0073] Furthermore, the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0074] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A Fe-Si soft magnetic material with a yield strength of 780 MPa, containing Fe and unavoidable impurities, characterized in that, It also contains the following chemical elements in the following percentages by mass: Si: 3.45%-4.5%; Ni: 0.5%-2.0%; Al: 0.5%-1.2%; and at least one of Mn, Cr, and Mo, with a total mass percentage of 0.2%-2.0%.

2. The Fe-Si soft magnetic material with a yield strength of 780 MPa as described in claim 1, characterized in that, Its mass percentage content of each chemical element is as follows: Si: 3.45%-4.5%; Ni: 0.5%-2.0%; Al: 0.5%-1.2%; and at least one of Mn, Cr, and Mo, with a total mass percentage of 0.2%-2.0%; the balance being Fe and unavoidable impurities.

3. The Fe-Si soft magnetic material with a yield strength of 780 MPa as described in claim 1 or 2, characterized in that, It also contains Sn or Sb at a mass percentage of 0.01%-0.5%.

4. The Fe-Si soft magnetic material with a yield strength of 780 MPa as described in claim 1 or 2, characterized in that, Among the unavoidable impurities, C ≤ 0.01%, P ≤ 0.02%, and S ≤ 0.005%.

5. The Fe-Si soft magnetic material with a yield strength of 780 MPa as described in claim 1 or 2, characterized in that, Its microstructure contains equiaxed micrograins, and the average size d of the equiaxed micrograins is 5-30 μm.

6. The Fe-Si soft magnetic material with a yield strength of 780 MPa as described in claim 1 or 2, characterized in that, The area content of the equiaxed micrograin structure is 1%-25%.

7. The Fe-Si soft magnetic material with a yield strength of 780 MPa as described in claim 1 or 2, characterized in that, Its iron loss P 10 / 400 ≤40W / kg, yield strength ≥780MPa.

8. A method for manufacturing Fe-Si soft magnetic material with a yield strength of 780 MPa as described in any one of claims 1-7, characterized in that, Including the following steps: Smelting and casting; Hot-rolled; Annealing of hot-rolled steel sheet; Cold rolling; Finished product annealing: The temperature of the soaking zone is 660℃-740℃, and the holding time t in the soaking zone meets the following requirements: Wherein, the average size of the equiaxed micrograin structure in the recrystallized portion of the d-annealed plate is expressed in μm; T is the temperature of the soaking zone, expressed in °C; and s is the area percentage of the equiaxed micrograin structure. Apply an insulating coating.

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