High-saturation ferrocobalt alloy and low-temperature high-toughness eddy current brake magnetic pole

Abstract

The invention relates to a high-saturation ferrocobalt alloy and a low-temperature high-toughness eddy current braking magnetic pole. The high-saturation iron-cobalt alloy comprises the following components: 16%-18% of Co; 1.4% to 2.2% of Cr; mo: 0 or < = 1.5%; v: 0 or < = 0.4%; and the balance of Fe and inevitable impurity elements. The invention also provides a low-temperature high-toughness eddy current brake magnetic pole which is prepared from the high-saturation iron-cobalt alloy through smelting, forging, heat treatment and machining. According to the high-saturation iron-cobalt alloy and the low-temperature high-toughness eddy current braking magnetic pole prepared from the high-saturation iron-cobalt alloy, the components of the iron-cobalt alloy material are regulated and controlled, so that the magnetic pole prepared from the high-saturation iron-cobalt alloy has high saturation magnetic performance and excellent low-temperature impact toughness.

Description

Technical Field

[0001] This invention relates to a high-saturation iron-cobalt alloy and a low-temperature, high-toughness eddy current braking magnetic pole, belonging to the field of magnetic materials technology. Background Technology

[0002] With the increasing speed of trains and the advancements in electrification and intelligence, the demand for electromagnetic braking technology is becoming increasingly significant. Technologies such as linear eddy current braking, rotating eddy current braking, and magnetic track braking, when used in conjunction with existing electro-pneumatic composite braking systems, can effectively shorten train braking distances and improve operational economy and comfort. Therefore, electromagnetic brakes for trains have always been a research hotspot both domestically and internationally.

[0003] Train eddy current brakes are typically mounted on bogies and must withstand severe vibration and impact loads. Meanwhile, the operating temperature range of trains is generally -25℃ to +40℃ or -40℃ to +50℃. The electromagnet poles are the core components of the eddy current brake; their magnetic properties determine the braking efficiency of the brake. Their mechanical properties must meet the requirements of various load conditions and low-temperature operating environments, especially maintaining good impact toughness at -40℃.

[0004] Based on the above requirements for magnetic and mechanical properties, low-carbon steel is generally used for the magnetic poles of train electromagnetic brakes. However, the utilization of saturated magnetic properties of carbon steel materials has reached its limit, making it impossible to further improve the overall performance of electromagnetic brakes, namely, weight reduction, energy saving, and braking force.

[0005] Iron-cobalt alloys possess excellent high-saturation magnetic properties, making them an effective means to further improve the overall performance of electromagnetic brakes. They can achieve significant weight reduction, energy saving, and increased braking force. However, commonly used iron-cobalt alloys have poor impact toughness, failing to meet the requirement of good impact toughness in low-temperature applications. Currently, domestic and international standards for iron-cobalt alloys, such as GB / T 14986.3-2018 and BS EN 60404-8-6:2017, primarily emphasize the magnetic properties of soft magnetic materials and do not address impact toughness requirements. For example, the 1J21, 1J22, and 1J27 iron-cobalt alloys in GB / T 14986.3 have an elongation after fracture ≤12%, and tests have shown that the room-temperature Charpy impact energy of these alloys is ≤10J, exhibiting typical brittle fracture characteristics.

[0006] Therefore, in order to utilize the high saturation magnetic properties of iron-cobalt alloys, such as the technical solution disclosed in CN115050537A, a combined structural solution is often adopted to solve the problem of insufficient impact toughness of existing iron-cobalt alloys. However, this leads to an increase in the types and number of magnetic pole components, a more complex structure, and a decrease in reliability. Summary of the Invention

[0007] To solve the above-mentioned technical problems, the present invention aims to provide a high-saturation iron-cobalt alloy and a low-temperature high-toughness eddy current braking magnetic pole, wherein the magnetic pole prepared by the alloy can take into account both high saturation magnetic properties and excellent low-temperature impact toughness.

[0008] To achieve the above objectives, the present invention provides a high-saturation iron-cobalt alloy, which is a soft magnetic material of iron-cobalt alloy. The high-saturation iron-cobalt alloy comprises, by mass percentage: Co: 16%-18%; Cr: 1.4%-2.2%; Mo: 0 or ≤1.5%; V: 0 or ≤0.4%; with the remainder being Fe and unavoidable impurity elements.

[0009] According to a specific embodiment of the present invention, the high-saturation iron-cobalt alloy of the present invention may be composed of Co, Cr and Fe, and may further contain Mo and V.

[0010] According to a specific embodiment of the present invention, preferably, the composition of the high-saturation iron-cobalt alloy, by mass percentage, comprises: Co: 16.5%-17.5%; Cr: 1.4%-2.2%; the remainder being Fe and unavoidable impurity elements.

[0011] According to a specific embodiment of the present invention, preferably, the high-saturation iron-cobalt alloy comprises, by mass percentage: Co: 16.5%-17.5%; Cr: 1.4%-2.2%; Mo: 0.5%-1.2%; V: 0 or ≤0.4%; the remainder being Fe and unavoidable impurity elements.

[0012] According to a specific embodiment of the present invention, when containing Mo and excluding V, the composition of the high-saturation iron-cobalt alloy may include: Co: 16.5%-17.5%; Cr: 1.4%-2.2%; Mo: 0.5%-1.2%; with the remainder being Fe and unavoidable impurity elements; more preferably, by mass percentage, the composition of the high-saturation iron-cobalt alloy includes: Co: 16.5%-17.5%; Cr: 1.8%-2.2%; Mo: 0.8%-1.2%; with the remainder being Fe and unavoidable impurity elements.

[0013] According to a specific embodiment of the present invention, when containing Mo and V, the composition of the high-saturation iron-cobalt alloy may include: Co: 16.5%-17.5%; Cr: 1.4%-2.2%; Mo: 0.5-1.2%; V: ≤0.4%; the remainder being Fe and unavoidable impurity elements.

[0014] In the high-saturation iron-cobalt alloy provided by this invention, the content of unavoidable impurity elements is ≤0.3%.

[0015] In this invention, the properties of each element are as follows:

[0016] Cobalt: Cobalt is a major element affecting the microstructure and properties of iron-cobalt soft magnetic alloys. It is a strongly ferromagnetic material with extremely high saturation magnetization, high Curie temperature, and high magnetic permeability, and is hard and brittle. Iron-cobalt alloys exhibit an ordering transformation within a wide cobalt content range of 25%-75%. Existing engineered iron-cobalt soft magnetic alloys all fall within this range, and this ordering transformation severely affects the alloy's impact toughness and tensile ductility. To improve the toughness and ductility of iron-cobalt alloys, the upper limit of the cobalt content should be far from the ordering transformation region. When the cobalt content is reduced to below 18%, the ordering transformation of iron-cobalt alloys can be effectively suppressed, thus improving their impact toughness. However, as the cobalt content decreases, the saturation magnetization of iron-cobalt alloys also decreases. To ensure excellent saturation magnetization, the cobalt content should not be too low. Therefore, a suitable cobalt content is 16%-18%.

[0017] Chromium: The addition of chromium can improve the plasticity of iron-cobalt alloys and significantly reduce their ductile-brittle transition temperature. The effect is more pronounced when the content reaches 1.4% or higher, and the ductile-brittle transition temperature fully meets the requirements for eddy current braking magnetic poles when the content reaches around 2.0%. However, chromium is an antiferromagnetic material, and increasing its content will reduce the magnetic properties of iron-cobalt alloy materials. Therefore, the suitable chromium content is 1.4%-2.2%.

[0018] Molybdenum (Mo): Molybdenum is mainly used to suppress the maximum order of the alloy, significantly refine the grains, and improve the tensile strength of iron-cobalt alloys. Working together with chromium, it can further improve the low-temperature impact toughness and stability of low-iron-cobalt alloys. Since molybdenum is paramagnetic, adding small amounts has little effect on the magnetic properties of iron-cobalt alloys. Therefore, the appropriate molybdenum content is Mo: 0 or ≤1.5%.

[0019] Vanadium: Vanadium can suppress the formation of ordered phases, similar to the effect of molybdenum. Furthermore, vanadium has a strong affinity for impurity atoms such as carbon, nitrogen, and oxygen, which can purify grain boundary impurities and reduce alloy brittleness. Generally, to minimize the impact of solid solution elements on the magnetic properties of iron-cobalt alloys, the total content of molybdenum and vanadium should be controlled below 2%. Therefore, a suitable vanadium content is ≤0.4%.

[0020] This invention uses Fe-Co-Cr as the alloy composition base and improves the tensile strength and fracture toughness of the material by adding Mo and V elements, and by means of grain refinement, grain boundary purification and suppression of maximum order, resulting in a lower ductile-brittle transition temperature. By controlling the upper limit of Co content, the alloy is kept away from the order transition region, suppressing the generation of ordered phases and reducing the material's notch sensitivity. At the same time, by controlling the lower limit of Co content, the alloy still has high saturation magnetic induction intensity. Under the condition that the eddy current braking magnetic pole of the iron-cobalt alloy has better saturation magnetic induction intensity than low-carbon steel soft magnetic materials, its low-temperature impact toughness is improved, solving the problem of poor impact toughness of existing iron-cobalt alloy soft magnetic materials.

[0021] The present invention also provides a low-temperature, high-toughness eddy current braking magnetic pole, which is made from the above-mentioned high-saturation iron-cobalt alloy through smelting, forging, heat treatment, and machining.

[0022] According to a specific embodiment of the present invention, in the smelting process, the billet can be prepared using the iron-cobalt alloy smelting process commonly used in the art, preferably a vacuum induction melting furnace, and the specific process parameters can be determined according to the existing smelting process.

[0023] According to a specific embodiment of the present invention, the smelted blank should be forged, and the forged shape of the blank should be consistent with the basic structure of the magnetic pole product, with machining allowance remaining. Preferably, the forging includes: heating the smelted blank to 1100℃-1180℃ and holding it at that temperature for 1.5h-3h, and then forging it to obtain the magnetic pole part. During the forging process, the temperature of the blank is preferably maintained above 800℃.

[0024] According to a specific embodiment of the present invention, preferably, the forged magnetic pole parts are air-cooled to room temperature, and the grain size grade of the magnetic pole parts is greater than or equal to grade 8. This can be achieved by controlling the forging ratio.

[0025] According to a specific embodiment of the present invention, preferably, the heat treatment includes quenching and tempering, wherein the grain size grade of the quenched and tempered magnetic pole part is greater than or equal to grade 7. More preferably, the quenching and tempering includes: heating the magnetic pole part to 700-800°C, holding it at that temperature for 2-3 hours, and then quenching it to room temperature; heating the quenched magnetic pole part to 250-350°C for tempering, holding it at that temperature for 3-5 hours, and then air cooling it to room temperature.

[0026] According to a specific embodiment of the present invention, the ductile-brittle transition temperature of the above-mentioned iron-cobalt alloy eddy current braking magnetic pole is at least not higher than -25°C, more preferably below -40°C, and the energy absorbed in the Charpy impact test under the said low temperature environment should be ≥60J.

[0027] According to a specific embodiment of the present invention, the magnetic properties of the above-mentioned iron-cobalt alloy eddy current braking magnetic pole are superior to those of commonly used low-carbon steel soft magnetic materials (low-carbon steel materials as required by GB / T 699), wherein the saturation magnetic induction intensity B under a low field strength of 10kA / m is superior. 10000 It can increase the saturation magnetic polarization intensity J under a high field strength of 1000kA / m by more than 10%. s It can improve by more than 5%.

[0028] According to a specific embodiment of the present invention, the room temperature tensile strength, yield strength and elongation after fracture of the above-mentioned iron-cobalt alloy eddy current braking magnetic pole are not lower than those of commonly used low carbon steel materials.

[0029] According to a specific embodiment of the present invention, the above-mentioned iron-cobalt alloy material can be prepared by vacuum induction furnace smelting, and the iron-cobalt alloy magnetic poles should have good machinability and can be subjected to conventional forging, machining and heat treatment.

[0030] According to a specific embodiment of the present invention, the top surface of the above-mentioned iron-cobalt alloy magnetic pole can be machined with connecting threaded holes as required. The connection through these threaded holes alone can withstand the three types of vibration and impact conditions of high-speed trains, avoiding complex combined connection structures.

[0031] The high-saturation iron-cobalt alloy and the low-temperature, high-toughness eddy current braking magnetic pole prepared from it provided by this invention, through the control of the iron-cobalt alloy material composition and the adoption of corresponding processing technology, enable the magnetic pole prepared from this alloy to achieve both high saturation magnetic properties and excellent low-temperature impact toughness. The eddy current magnetic pole made using the iron-cobalt alloy provided by this invention can ensure better comprehensive mechanical properties while maintaining high saturation magnetic properties, and maintain high impact toughness at lower temperatures. This can largely prevent brittle fracture of the product under low-temperature and severe vibration operating environments, ensuring safety in use. Replacing existing low-carbon steel eddy current braking magnetic poles can significantly improve the braking power density and braking mass density of eddy current braking electromagnets, giving them better overall performance. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the magnetic pole structure. Detailed Implementation

[0033] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0034] The structures of the magnetic poles involved in the following embodiments are as follows: Figure 1 As shown. The top surface 1 of the magnetic pole is provided with a first threaded hole 11 and a second threaded hole 12.

[0035] The iron-cobalt alloys given in the following embodiments and Comparative Example 1 were all obtained by smelting in the vacuum induction furnace provided by the present invention, and their composition and content are shown in Table 1; the corresponding magnetic poles were made by forging, heat treatment and machining processes:

[0036] The bar stock is forged at an initial forging temperature of 1160℃ and a final forging temperature of 820℃ into a structure similar to magnetic poles (e.g. Figure 1 (as shown), then air-cooled to room temperature;

[0037] The forged magnetic pole blank is heated to 760℃ and held for 2.5 hours, and then quenched to room temperature, preferably by oil quenching.

[0038] The quenched magnetic pole blank is heated to 320℃ and held for 4 hours, then air-cooled to room temperature.

[0039] The heat-treated magnetic pole blanks are machined to remove excess material down to the finished magnetic pole dimensions.

[0040] Comparative Example 2 uses eddy current braking magnetic poles made of 10 steel with mechanical properties meeting the requirements of GB / T 699-2015, which is currently the most commonly used material for eddy current braking magnetic poles. The iron-cobalt alloy of this invention should have tensile strength and yield strength no less than Comparative Example 2, and its magnetic properties should be superior to those of Comparative Example 2.

[0041] Table 1. Composition and content (mass percentage, %) of the iron-cobalt alloy magnetic poles in each embodiment and comparative example.

[0042]

[0043] Experimental Example 1

[0044] This experiment tested the mechanical properties of the magnetic poles in Examples 1-4 and Comparative Examples 1-2. The specific process and results are as follows:

[0045] Standard tensile and impact specimens were taken from the middle of the magnetic pole. According to GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test at room temperature" and GB / T 229-2020 "Metallic materials - Charpy pendulum impact test", the mechanical properties of the iron-cobalt alloy magnetic poles made in Examples 1-4 and Comparative Example 1 at room temperature and the impact energy at -25℃, -40℃ and -50℃ were determined, as shown in Table 2.

[0046] Table 2 Mechanical properties of the magnetic poles in each embodiment and comparative example

[0047]

[0048] Among them, impact energy A kU2 The values ​​are impact energy at room temperature (20℃), impact energy at -25℃, impact energy at -40℃, and impact energy at -50℃, respectively.

[0049] Table 2 shows that, at room temperature, the elongation after fracture of the magnetic pole of Comparative Example 1 is 37.5%, and the Charpy impact energy is 78-104.5 J, indicating that its ductility and toughness are far superior to those of the commonly used iron-cobalt alloys described in GB / T 14986.3. However, at low temperatures of -25℃ and below, the magnetic pole of Comparative Example 1 exhibits brittle fracture due to impact, especially below -40℃, showing typical brittle fracture characteristics. This indicates that after reducing the Co content to below 18%, the room temperature ductility and toughness increase significantly, but the low-temperature impact toughness still cannot meet the requirements of the application environment of eddy current braking magnetic poles.

[0050] Compared with Comparative Example 1, the magnetic poles of Examples 1-4 have higher tensile strength and low-temperature ductility. Specifically, the magnetic pole of Example 1 exhibits good low-temperature impact toughness at -25°C, but begins to show brittle fracture at -40°C and below. The magnetic poles of Examples 2-4 still have good low-temperature impact toughness at -50°C, with an impact energy ≥72J.

[0051] Therefore, by controlling the elemental composition and proportion in the iron-cobalt alloy, compared with the commonly used iron-cobalt alloy 1J27 and Comparative Example 1, Example 1 provided by the present invention can meet the low-temperature impact toughness requirement of -25℃, and Examples 2-4 can meet the low-temperature impact toughness requirement of -50℃. Furthermore, the tensile strength and yield strength of the materials in Examples 1-4 of the present invention are not lower than those of the low-carbon steel material of Comparative Example 2, which is currently commonly used in eddy current braking magnetic poles.

[0052] Experimental Example 2

[0053] This experimental example tests the magnetic properties of Examples 1-4 and Comparative Examples 1-2. The specific process and results are as follows:

[0054] A sample of soft magnetic material with DC magnetic properties was taken from the middle of the magnetic pole. Under room temperature conditions, the low-field saturation magnetic induction and high-field saturation magnetic polarization of Examples 1-4 and Comparative Examples 1-2 were measured by a DC magnetic measuring device and a VSM vibrating sample magnetometer according to GB / T 13012-2008 Measurement Method of DC Magnetic Properties of Soft Magnetic Materials and JY / T 0591.1-2020 General Rules for Physical Property Measurement System Part 1: DC Magnetic Test, as shown in Table 3.

[0055] Table 3 Magnetic properties of the magnetic poles in each embodiment and comparative example

[0056]

[0057] As shown in Table 3, compared to the iron-cobalt alloy magnetic poles of Comparative Example 1, the low-field saturation magnetic induction and high-field saturation magnetic polarization of each embodiment decreased slightly with the increase of the content of elements such as chromium and molybdenum, but still maintained the characteristics of high saturation magnetic induction. Compared to the low-carbon steel magnetic poles of Comparative Example 2, the saturation magnetic induction of the iron-cobalt alloys in Examples 1-4 increased by more than 10.80%, and the saturation magnetic polarization increased by more than 6.34%.

[0058] For ferromagnetic materials, it is extremely difficult to increase the saturation magnetic induction or saturation magnetic polarization intensity. Even a slight increase in this parameter can lead to a sharp increase in the working efficiency of eddy current braking electromagnets, such as braking power density or braking mass density. Therefore, the iron-cobalt alloy magnetic poles of Examples 1-4 are of great significance for the technological breakthrough of electromagnetic braking devices for high-speed trains.

[0059] Experimental Example 3

[0060] This test example utilizes the iron-cobalt alloy magnetic poles from Example 1, and conducts vibration and shock tests on a random vibration and shock test bench according to the Class 3 installation level requirements in GB / T 21563-2018. The specific results and process are as follows:

[0061] Test Condition 1: Connect to a special tooling through the threaded hole on the top surface of the magnetic pole, and conduct a simulated long-life vibration test in the vertical, horizontal and longitudinal directions according to the vibration level of the simulated Class 3 axle installation. The acceleration proportional coefficient is 7.83, the test frequency is 10-500Hz, and the test time in each direction is 5h.

[0062] Test Condition 2: Following the connection method described in Test Condition 1, three types of axle installation impact tests were conducted in the vertical, horizontal, and longitudinal directions, with a peak acceleration of 1000 m / s² in each direction. 2 The nominal duration is 6ms.

[0063] After the test, the appearance of the magnetic poles of Example 1 was inspected. The test results showed that the magnetic poles of Example 1 could withstand the vibration and impact conditions of the installation of high-speed trains in Class 3. The magnetic pole connection threads and the surface of the parts were intact, without cracks, deformation or other mechanical damage, which met the requirements for the use of eddy current braking electromagnets.

[0064] Test Example 4

[0065] This experimental example utilizes the iron-cobalt alloy magnetic poles from Example 1 and the low-carbon steel magnetic poles from Comparative Example 2. Based on the eddy current braking electromagnet performance testing device (high-speed train eddy current braking performance testing device and method described in CN105181361A), the braking force, power consumption, and weight of the electromagnets were compared under the same excitation current. The test results are shown in Table 4.

[0066] Table 4. Performance of eddy current braking electromagnets for typical embodiments and comparative examples.

[0067]

[0068] As shown in Table 4, compared with the low-carbon steel magnetic pole of Comparative Example 2, the excitation efficiency of the iron-cobalt alloy magnetic pole of Example 1 is significantly improved. Under the same excitation current, it achieves the comprehensive improvement effect of weight reduction, energy consumption reduction and braking performance improvement, that is, the braking power density and braking mass density indicators are improved.

Claims

1. A highly saturated iron-cobalt alloy, wherein, The composition of this highly saturated iron-cobalt alloy, by mass percentage, comprises: Co: 16%-18%; Cr: 1.4%-2.2%; Mo: 0 or ≤1.5%; V: 0 or ≤0.4%; the remainder is Fe and unavoidable impurity elements.

2. The high-saturation iron-cobalt alloy according to claim 1, wherein, The composition of this highly saturated iron-cobalt alloy, by mass percentage, comprises: Co: 16.5%-17.5%; Cr: 1.4%-2.2%; the remainder is Fe and unavoidable impurity elements.

3. The high-saturation iron-cobalt alloy according to claim 1, wherein, The composition of this highly saturated iron-cobalt alloy, by mass percentage, comprises: Co: 16.5%-17.5%; Cr: 1.4%-2.2%; Mo: 0.5%-1.2%; V: 0 or ≤0.4%; the remainder is Fe and unavoidable impurity elements.

4. The high-saturation iron-cobalt alloy according to claim 3, wherein, The composition of this highly saturated iron-cobalt alloy, by mass percentage, comprises: Co: 16.5%-17.5%; Cr: 1.8%-2.2%; Mo: 0.8%-1.2%; the remainder is Fe and unavoidable impurity elements.

5. A low-temperature, high-toughness eddy current braking magnetic pole, which is made from the high-saturation iron-cobalt alloy described in any one of claims 1-4 through smelting, forging, heat treatment, and machining.

6. The low-temperature, high-toughness eddy current braking magnetic pole according to claim 5, wherein, The forging process includes: The blank obtained from smelting is heated to 1100℃-1180℃ and held for 1.5h-3h, and then forged to obtain magnetic pole parts.

7. The low-temperature, high-toughness eddy current braking magnetic pole according to claim 6, wherein, During the forging process, the temperature of the blank is maintained above 800°C.

8. The low-temperature, high-toughness eddy current braking magnetic pole according to claim 5, wherein, After forging, the magnetic pole parts are air-cooled to room temperature, and the grain size grade of the magnetic pole parts is greater than or equal to grade 8.

9. The low-temperature, high-toughness eddy current braking magnetic pole according to claim 5, wherein, The heat treatment includes quenching and tempering, and the grain size grade of the magnetic pole parts after quenching and tempering is greater than or equal to grade 7.

10. The low-temperature, high-toughness eddy current braking magnetic pole according to claim 9, wherein, The heat treatment includes: heating the magnetic pole parts to 700-800℃, holding them at that temperature for 2-3 hours, and then quenching them to room temperature; The quenched magnetic pole parts are heated to 250-350℃ for tempering, held at that temperature for 3-5 hours, and then air-cooled to room temperature.

Images