A heat treatment process for improving initial permeability of a permalloy

Abstract

The present application relates to the technical field of heat treatment, in particular to a heat treatment process for improving initial permeability of permalloy. The permalloy is 1J85 iron-nickel alloy sheet, and the heat treatment process comprises the following steps: firstly, controlling the purity of the atmosphere in the electric resistance furnace, then annealing the 1J85 iron-nickel alloy sheet, keeping the annealing temperature at 1175 DEG C for 3.5 hours, then opening the furnace when the temperature is lowered to 600 DEG C, forcibly air cooling for 0.5 hours after the furnace is opened, then opening the furnace when the temperature is lowered to below 300 DEG C, and sorting the sheet as soon as possible after the furnace is opened. The above test shows that the initial permeability of the permalloy sheet can be improved to a certain extent by appropriately increasing the annealing temperature of the permalloy 1J85, appropriately reducing the annealing holding time, selecting the best furnace opening temperature and increasing the cooling speed, ensuring the purity of the atmosphere in the heat treatment furnace, and preventing the uneven stress of the treated permalloy sheet 1J85 i .

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat treatment, in particular to a heat treatment process for improving initial permeability of permalloy. BACKGROUND

[0002] High nickel alloy iron-nickel alloy 1J85 has excellent magnetic properties and good processing performance, 1J85 belongs to high nickel content high permeability material, the initial magnetic permeability u i is greater than 16000. It is widely used in medium and high frequency transformers. Because the performance parameters such as coercive force and magnetic permeability are very sensitive to stress, it is necessary to eliminate or reduce the adverse effects of residual stress on the soft magnetic properties of the alloy through appropriate heat treatment process. From the existing product structure, inductance is the most critical technical index in the customer technical agreement, and the initial magnetic permeability directly determines the size of the inductance.

[0003] In the existing product structure, the iron-nickel alloy hard thin plate with a thickness of 0.20mm is mainly used, which is stamped into EI-shaped iron-nickel alloy sheet, as shown in Figure 1 . Then it is placed in a high vacuum resistance furnace, and through appropriate heat treatment process, the soft iron-nickel alloy sheet meeting the application of medium and high frequency transformer is produced. In the actual production process, sometimes it is found that the initial magnetic permeability of the iron-nickel alloy sheet 1J85 after heat treatment is low, the inductance of the transformer is low, and it is difficult to meet the customer's technical requirements. SUMMARY

[0004] The purpose of the present application is to provide a heat treatment process for improving the initial magnetic permeability of permalloy, which provides an effective method for improving the initial magnetic permeability u i and increasing the inductance of the permalloy 1J85 series plug-in transformer.

[0005] To solve the above technical problems, the present application provides a heat treatment process for improving the initial magnetic permeability of permalloy, the permalloy is 1J85 iron-nickel alloy sheet, and the heat treatment process comprises:

[0006] First, the purity of the atmosphere in the resistance furnace is controlled, then the 1J85 iron-nickel alloy sheet is annealed, the annealing temperature is 1175℃, the temperature is kept for 3.5h, then the furnace is opened when the temperature is reduced to 600℃, after the furnace is opened, forced air cooling is carried out for 0.5h, then the furnace is opened when the temperature is reduced to 300℃, and the sheet is arranged as soon as possible after the furnace is opened (the sheet refers to arranging the 1J85 iron-nickel alloy sheet to prevent mutual extrusion and increase stress).

[0007] Preferably, the heat treatment process further comprises annealing the 1J85 iron-nickel alloy sheet in a vacuum environment, that is, controlling the vacuum degree in the furnace to be less than 6.67Pa.

[0008] Preferably, the temperature is raised to 1175℃ at a rate of 200℃ / h.

[0009] Preferably, the temperature is lowered to 600℃ at a rate of 200℃ / h.

[0010] Preferably, the forced air cooling is achieved by using compressed air and exhaust fan.

[0011] Preferably, the process of controlling the purity of the atmosphere in the furnace includes the following steps: selecting chemically pure alumina before heat treatment, and pre-baking to remove moisture; selecting clean aviation gasoline, thoroughly cleaning the surface of the 1J85 iron-nickel alloy sheet, and placing it in the furnace after drying.

[0012] Preferably, during the process of controlling the purity of the atmosphere in the furnace, the 1J85 iron-nickel alloy sheet is not directly touched by hand.

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] Through the above tests, it can be seen that appropriately increasing the annealing temperature of permalloy 1J85, appropriately reducing the annealing holding time, selecting the optimal discharge temperature and increasing the cooling speed, ensuring the purity of the atmosphere in the heat treatment furnace, and preventing uneven stress on the treated permalloy sheet 1J85 can to some extent increase the initial permeability u i of the permalloy sheet, which provides an effective method for increasing the initial permeability u i and increasing the inductance of the permalloy 1J85 series plug-in transformer. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a schematic diagram of the structure of the iron-nickel alloy sheet punched into an EI shape of the prior product. DETAILED DESCRIPTION

[0016] The present application will be further described in detail below in combination with the drawings and specific examples. The advantages and features of the present application will be more apparent according to the following description. It should be noted that the drawings are very simplified and use non-precise proportions, only to facilitate and clarify the purpose of assisting in the description of the embodiments of the present application.

[0017] The main performance indicators of the iron-nickel alloy 1J85 are the initial permeability u i , maximum permeability u m , coercive force H c , and saturation magnetic induction B s . In view of the application of our company's products and the requirements of customers, the initial permeability is the most critical technical indicator, and the inductance value tested by the test instrument HP4275 can directly represent the initial permeability ui The size of the magnetic field.

[0018] The isolation transformer numbered KF9-2036 is a typical medium-high frequency transformer of our company. This product is mainly applied to the signal isolation circuit of oil field logging, and the customer's performance index of inductance is very important. The inductance requirement is: under 10KHZ, 0.25v excitation voltage, inductance L13≥190mH.

[0019] According to the typical heat treatment process KF0.054.152 of iron-nickel soft magnetic alloy of our company, three batches of iron-nickel alloy sheets were heat treated respectively. The actual inductance value is 158mH-172mH (see Table 1), and the inductance index does not meet the drawing requirements. Next, we will start from the heat treatment process to seek ways to improve the initial permeability of iron-nickel alloy sheet and increase the inductance.

[0020] Table 1:

[0021]

[0022] The typical heat treatment process of iron-nickel alloy sheet 1J85 of our company is as follows: in a vacuum environment with a vacuum degree less than 6.67Pa, the temperature is raised to 1150℃ at a rate of 200℃ / h, and then cooled to 400℃ at a rate of 200℃ / h, and then the furnace is opened for air cooling. However, the typical heat treatment process cannot guarantee that the iron-nickel alloy sheet 1J85 after heat treatment meets the performance index. According to the research and analysis, the following schemes are proposed to improve the initial permeability u i of the iron-nickel alloy sheet.

[0023] ① Appropriately increase the annealing temperature to improve the initial permeability u i of the iron-nickel alloy sheet 1J85.

[0024] When the annealing temperature is within 1200℃, with the increase of the annealing temperature, u i and u m values increase, B s value changes little, and H c value decreases. The comprehensive magnetic properties of 1J85 are continuously improved, and when the temperature exceeds 1200℃, the magnetic properties of the alloy begin to deteriorate sharply. Considering that the temperature control of our heat treatment furnace uses a straight-in heat couple, there will be some error in the actual temperature measurement of the iron-nickel alloy sheet heat treatment area inside the furnace. In order to prevent the actual annealing temperature from being greater than 1200℃, the annealing temperature of the test is set to 1175℃, and the others remain unchanged. After heat treatment, the inductance test values of 5 transformers are as follows, see Table 2.

[0025] Table 2:

[0026] Serial number 1 2 3 4 5 Inductance mH 179 182 185 173 178

[0027] From the test values, it can be seen that the inductance of the transformer has increased compared to the previous values, indicating that by appropriately increasing the annealing temperature of the heat treatment, the initial permeability of 1J85 has increased to a certain extent.

[0028] 2. Selecting appropriate holding time to improve the initial permeability u of the iron-nickel alloy sheet 1J85 i :

[0029] The theory believes that the holding time during annealing affects the magnetic properties of 1J85 as follows: as the holding time is prolonged, the u i value slowly decreases, the u m value and the B s value reach the maximum at 4h, and the H c value reaches the minimum at 4h. Considering the above four indicators, it can be considered that the magnetic properties of the alloy are best when the holding time is 4h. Since the margin of other performance indicators of KF9-2036 is large, and the inductance does not meet the customer's requirements, the holding time during annealing is selected to be 3.5h, and the annealing temperature is 1175℃. After heat treatment, the inductance test values of the five transformers are as follows, see Table 3.

[0030] Table 3:

[0031] Serial number 1 2 3 4 5 Inductance mH 193 187 191 201 194

[0032] From the test values, it can be seen that the inductance of the transformer has increased compared to the previous values, indicating that by appropriately increasing the annealing temperature of the heat treatment, the initial permeability of 1J85 has increased to a certain extent.

[0033] 3. Selecting appropriate furnace temperature and cooling rate to improve the initial permeability u of the iron-nickel alloy sheet 1J85 i :

[0034] Since the 1J85 alloy is annealed and cooled below 600℃, there is a process of Ni3Fe ordering, which can improve the magnetic properties of the alloy by controlling the cooling rate in the temperature range of 600-300℃.

[0035] According to the typical heat treatment process of our company's iron-nickel alloy sheet 1J85, the temperature at which the sheet is taken out of the furnace is selected to be 400°C, which should miss the best temperature point of Ni3Fe ordering inside the iron-nickel alloy sheet, and the temperature at which the sheet is taken out of the furnace is selected to be 600°C in the following test. The typical process of our company requires that the iron-nickel alloy sheet after being taken out of the furnace is cooled by natural air cooling, but the cooling speed is greatly affected by the environmental temperature and has great uncertainty. In the following test stage, forced air cooling by compressed air and exhaust fan is adopted to accelerate the cooling for 0.5h, and the temperature is reduced to below 300°C before the furnace is opened. The annealing temperature is 1175°C, and the holding time during annealing is 3.5h. After heat treatment, the inductance test values of 5 transformers are as follows, see Table 4.

[0036] Table 4:

[0037]

[0038]

[0039] From the test values, it can be seen that the inductance of the transformer is further increased, which fully meets the inductance index required by the customer.

[0040] (4) Other factors affecting the initial permeability u of iron-nickel alloy 1J85 i

[0041] Since the atmosphere in the furnace at high temperature can affect the initial permeability of the iron-nickel alloy sheet after heat treatment, it is necessary to ensure the purity of the atmosphere in the furnace as much as possible during heat treatment, so chemical pure alumina is selected before heat treatment and pre-baking is performed to remove moisture; clean aviation gasoline is selected when the iron-nickel alloy sheet is washed after being punched, the surface of the iron-nickel alloy sheet is fully washed and dried, and then the sheet is placed in the furnace, which avoids directly touching the iron-nickel alloy sheet by hand.

[0042] The iron-nickel alloy sheet after heat treatment is very sensitive to stress. Therefore, the sheet should be sorted as soon as possible after being taken out of the furnace to prevent the irregular overlapping of the iron-nickel alloy sheet and the resulting uneven stress from causing a large decrease in the initial permeability.

[0043] Verification of the effect of process change:

[0044] In order to verify the effectiveness of the changed heat treatment process of the iron-nickel alloy sheet 1J85, after sufficient preparation and elimination of other factors affecting the initial permeability ui of 1J85, three batches of iron-nickel alloy sheet 1J85 are treated according to the following process: annealing temperature 1175°C, holding time 3.5h, the furnace is opened at 600°C, and then forced air cooling is performed for 0.5h before the sheet is taken out of the furnace when the temperature is reduced to below 300°C. The test data are as follows, see Table 5.

[0045] Table 5:

[0046] ​

[0047] From the test data of the verification test, it can be seen that the pieces according to the modified heat treatment process of the iron-nickel alloy piece 1J85 meet the index requirements.

[0048] The above description is only a description of the preferred embodiments of the present application, and is not any limitation on the scope of the present application. Any modification or modification made by a person skilled in the art according to the above disclosure is within the protection scope of the claims.

Claims

1. A heat treatment process for increasing the initial permeability of a permalloy, characterized in that, The powder metallurgy is a 1J85 iron-nickel alloy sheet, the heat treatment process comprises the following steps: firstly, controlling the purity of the furnace atmosphere of the electric resistance furnace, then annealing the 1J85 iron-nickel alloy sheet, keeping the annealing temperature at 1175 DEG C for 3.5 hours, then opening the furnace when the temperature is lowered to 600 DEG C, forcibly air cooling for 0.5 hours after the furnace is opened, then opening the furnace when the temperature is lowered to 300 DEG C, and quickly sorting the sheets after the furnace is opened to prevent mutual extrusion and stress increase; controlling the temperature rising rate to be 200 DEG C / h, and then rising the temperature to 1175 DEG C, and controlling the temperature lowering rate to be 200 DEG C / h, and then lowering the temperature to 600 DEG C; the specific steps of controlling the purity of the furnace atmosphere are as follows: selecting chemically pure alumina before heat treatment, and pre-baking and dehumidifying treatment; selecting clean aviation gasoline, fully cleaning the surface oil stains of the 1J85 iron-nickel alloy sheet, and then drying and placing in the furnace.

2. The heat treatment process for improving the initial magnetic permeability of permalloy as described in claim 1, characterized in that, The heat treatment process further comprises: annealing the 1J85 iron-nickel alloy sheet in a vacuum environment, i.e. controlling the vacuum degree in the furnace to be less than 6.67 Pa.

3. The heat treatment process for improving initial permeability of a permalloy as claimed in claim 1 wherein, The forcibly air cooling mode is the combination of compressed air and exhaust fan.

4. The heat treatment process for improving initial permeability of a permalloy as claimed in claim 1 wherein, In the process of controlling the purity of the furnace atmosphere, the 1J85 iron-nickel alloy sheet is avoided to be directly touched by hand.

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