RU2413320C1 - Procedure for production of magnetic soft material - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: there is prepared charge containing 3-7 wt % of silicon powder, powder of ferrophosphorus at amount facilitating contents of phosphorus in charge not more, than 0.5 wt % and powder of iron as base. Produced mixture is compressed, is subjected to at least one operation of annealing at temperature 1100-1300°C with successive cooling and is sintered in atmosphere of nitrogen gas by cyclic method by alternating annealing and cooling till there are obtained required magnetic properties.

EFFECT: produced material possesses high specific electric resistance and low losses for eddy currents at satisfactory coercion force and magnetisation.

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Description

The invention relates to powder metallurgy, and in particular to the production of materials for magnetic cores operating in variable fields of medium frequency.

In powder metallurgy, the positive effect of phosphorus on the magnetic properties of soft magnetic materials based on iron is known. The technology for producing materials of the Fe-P system (A.P. Bolshachenko et al. Development of industrial technology for manufacturing cermet magnetic cores. - Powder metallurgy, 1972, No. 12, p. 38-41), along with other technological parameters, considers the sintering atmosphere: hydrogen and converted gas. It has been established that materials sintered in hydrogen at maximum temperature (1250 ° C) possess the best properties. Of course, such materials will have good properties, but their manufacture requires large material and energy costs. So materials having the best magnetic and mechanical properties were obtained as follows: after mixing the powders of iron and ferrophosphorus, the mixture was pressed and sintered in a hydrogen atmosphere at 900 ° C for 2 hours. After sintering, the samples were pressed again and annealed at a temperature of 1250 ° C for 4 hours in a hydrogen atmosphere. Alternatively, another technological option was proposed in the work: sintering in hydrogen at 1170 ° C for 4 hours. The service characteristics of such material are slightly worse than in the previous technological regime, but much cheaper. For both technologies, there is one significant drawback - hydrogen, as the sintering atmosphere, is expensive and explosive, which requires strict observance of safety precautions.

To replace the expensive sintering atmosphere with a cheaper and safer one, a method for producing soft magnetic material is known, including mixing powders of iron (90-94 wt.%) And ferrophosphorus (6-10 wt.%) With a phosphorus content of 10-13 wt.%, Pressing them and sintering in a nitrogen atmosphere (RF Patent No. 2040810, IPC6 H01F 1/22, B22F 3/12, filing date 1992.08.27, publication date 1995.07.25).

A comparative analysis of the physical properties of materials of the Fe-P system in the concentration range (up to 1.3)% P sintered in hydrogen and nitrogen gas (96-95% N ₂ + 4-5% H ₂ ) showed that the properties of materials sintered in nitrogen gas in the range of phosphorus concentrations of 0.8-1.3% is no worse than sintered in hydrogen under the same conditions.

A known method for producing soft magnetic material, including mixing powders of iron and ferrophosphorus, pressing, sintering the obtained compacts in nitrogen gas by the cyclic method by alternating annealing and cooling (RF Patent No. 2296382, IPC H01F 1/22, B22F 3/12, filing date 20.07.2005 , publication date 03/27/2007 - prototype). Studies of the physical properties of the materials of the Fe-P system after cyclic treatment in a nitrogen gas atmosphere by alternating annealing at a temperature of 1000-1100 ° C and cooling with a furnace showed that the properties of the materials in the concentration region (0.8-1.5)% P sintered in nitrogen gas, improve compared to materials without phosphorus or sintered in hydrogen under the same conditions. It was shown that the electrical resistivity linearly depends on the concentration of phosphorus and is 30-40 · 10 ^-8 Ohm · m at 1.5% phosphorus.

A disadvantage of the known solutions is that the resulting materials can only be used in variable fields up to 50 Hz.

The objective of the presented technical solution is to create a soft magnetic powder material suitable for operation in variable electromagnetic fields of medium frequencies, i.e. more than 50 Hz, due to an increase in electrical resistivity with satisfactory characteristics of magnetization and coercive force.

The technical result of the claimed invention is to increase the electrical resistivity and, as a consequence, reduce eddy current losses, with satisfactory coercive force and magnetization due to the complex alloying of iron with silicon and phosphorus.

The specified technical result is achieved by the fact that in the method of producing a soft magnetic material for the manufacture of medium-frequency AC magnetic circuits, including the preparation of a mixture containing iron and ferrophosphorus powders, pressing and sintering in an atmosphere of nitrogen gas by a cyclic method by alternating annealing and cooling, according to the invention, to a mixture 3-7 wt.% Silicon powder, ferrophosphorus powder is introduced into the mixture in an amount providing a phosphorus content in the mixture of not more than 0.5 wt.%, And before sinter iem material is subjected to at least one annealing operation at a temperature of 1100-1300 ° C, followed by cooling.

To use materials in alternating electromagnetic fields with a frequency above 50 Hz, it is necessary to increase the electrical resistivity, since the power losses in a unit volume P during magnetization reversal dI / dt are:

где r - радиус окружности частиц материала, ρ - удельное электросопротивление образца. Из формулы видно, что потери на перемагничивание тем меньше, чем больше удельное электросопротивление. Установлено, что для повышения удельного электросопротивления магнитомягкого материала необходимо легирование железа кремнием. Однако такой материал невозможно спекать в азотном газе, так как из-за растворимости азота в железе и образования нитридов на поверхности частиц кремния значительно повышается коэрцитивная сила. Для блокирования растворимости азота и образования нитридов применяли легирование материала феррофосфором. Исследование служебных характеристик материалов на основе железа, легированного фосфором и кремнием и спеченного в азотном газе ((95-96)% N₂+(5-4)% Н₂), показало, что оптимальным диапазоном концентраций кремния является 3-7 мас.%, а фосфора - не более 0,5 мас.%.

where r is the radius of the circumference of the particles of the material, ρ is the electrical resistivity of the sample. It can be seen from the formula that the magnetization reversal losses are the smaller, the greater the electrical resistivity. It was found that to increase the electrical resistivity of a soft magnetic material, it is necessary to alloy silicon with silicon. However, such a material cannot be sintered in nitrogen gas, since the coercive force significantly increases due to the solubility of nitrogen in iron and the formation of nitrides on the surface of silicon particles. To block the solubility of nitrogen and the formation of nitrides, doping of the material with ferrophosphorus was used. The study of the service characteristics of materials based on iron doped with phosphorus and silicon and sintered in nitrogen gas ((95-96)% N ₂ + (5-4)% H ₂ ) showed that the optimum range of silicon concentrations is 3-7 wt. %, and phosphorus - not more than 0.5 wt.%.

Example 1. A mixture of powders of iron grade ПЖР 3 or ПЖВ 3, ferrophosphorus (phosphorus content 12-15 wt.%) And technical monosilicon grade Kp1 was mixed for 1.5 hours. The percentage of phosphorus in the samples was 0.5 wt.%, and silicon - 7.0 wt.%. Pressing was carried out in a carbide mold with a unilateral load of 600 MPa. After pressing, the samples were sintered at 1300 ° С for 3 h. The results of a comparative analysis of Fe-0.5% P materials with and without silicon are presented in Table 1.

As can be seen from the table, the addition of silicon reduces the coercive force (He) and increases the electrical resistivity (ρ) by more than 5 times.

Example 2. A mixture of powders of iron grade ПЖР 3, ferrophosphorus (phosphorus content 12-15 wt.%) And technical monosilicon grade Kp1 was mixed for 1.5 hours. The percentage of phosphorus in the samples was 0.5 wt.% And 1.0 wt.%, and silicon 7 wt.%. Pressing was carried out in a carbide mold with a unilateral load of 600 MPa. After pressing, the samples were sintered at temperatures of 1100, 1200, and 1300 ° С for 3 h. The results of a comparative analysis of the coercive force of materials sintered at different temperatures with different phosphorus contents are presented in Table 2.

As can be seen from the table, the sintering temperature reduces the coercive force of the powder materials of the Fe-7% Si system with the addition of phosphorus of 0.5-1 wt.%. The minimum coercive force in materials with the addition of 0.5 wt.% R.

Example 3. A mixture of powders of iron, ferrophosphorus (phosphorus content of 12-15 wt.%) And technical monosilicon grade Kp1 was mixed for 1.5 hours. The percentage of phosphorus was 0.5 wt.%, And silicon was varied within 3.0 -7.0 wt.%. The pressing was carried out in a carbide mold with a unilateral load of 700 MPa. After pressing, the samples were sintered at a temperature of 1100 ° С using the cyclic method: annealing for 3 h followed by cooling, followed by another cycle 2 times. After each annealing, the properties of the obtained materials were measured. The results of a comparative analysis of the physical properties of materials sintered by the cyclic method are presented in table 3.

As can be seen from the table, after the first annealing at 1100 ° C, the coercive force of a material with 7.0 wt.% Silicon is less than that without silicon, and the electrical resistivity is more than 5 times higher. Each annealing improves the properties of the soft magnetic material, increasing the electrical resistivity and reducing the coercive force. It was found that the dissolution of silicon or other elements in iron depends on the concentration of the alloying element, on the temperature or duration of annealing. Therefore, the first annealing improved only the properties of the material with 7.0 wt.% Silicon.

The second annealing improved the properties of the material alloyed with 3.0 wt% silicon and more, and the third annealing improved the properties of the materials compared with the properties after the second annealing. The number of anneals depends on the balance of economic necessity and the required performance characteristics. As shown in table 3, the percentage of silicon proportionally reduces the coercive force, but it decreases the saturation magnetization Ms (table 4), which negatively affects the service characteristics of the material. Therefore, the content of more than 7.0 wt.% Si in the material is impractical, since already at 8 wt.% Si the saturation magnetization is less than 100 · 10 ⁴ A / m.

A comparative analysis of the properties of materials performed by the claimed technical solution and properties of materials obtained by the technological parameters of the prototype are presented in table 5. A comparative analysis showed that the coercive force of materials with the addition of 3.0-7.0 wt.% Si of the claimed patent is somewhat higher than in the prototype. In this case, the electrical resistivity of the claimed invention is 3-4 times greater than that of the materials of the prototype. Given the economic feasibility of the claimed technical solution has advantages over the prototype.

Thus, the following points can be inferred from the presented tables: 1) alloying the material with silicon significantly increases the electrical resistivity, which makes it promising for operation in variable medium-frequency fields; 2) for sintering materials in nitrogen gas, it is sufficient to alloy them with no more than 0.5 wt.% P; with a higher concentration of phosphorus, the service characteristics of materials deteriorate; 3) an increase in the sintering temperature reduces the coercive force, which is a positive factor, however, the electrical resistance decreases and the energy consumption increases, therefore, the claimed temperature range of 1100-1300 ° C is optimal; 4) the concentration of silicon in the claimed invention should be maintained in the range of 3.0-7.0 wt.%. At a lower concentration, the electrical resistivity is not more than in the prototype, and at a higher concentration, the saturation magnetization becomes less than 100 · 10 ⁴ A / m; 5); the amount of cyclic annealing in nitrogen gas improves all the service properties of the materials.

Table 1. Physical properties of Fe-0.5% P materials after sintering in nitrogen gas with and without silicon % Si γ, g / cm ³ Hc, A / m ρ · 10 ^-8 Ohm · m 0 6.76 244 22 7 5.60 108 one hundred

Table 2. The values of the coercive force of samples of Fe-7% Si with the addition of phosphorus after annealing in nitrogen gas at various temperatures % P Coercive force, A / m at temperature 1100 ° C 1200 ° C 1300 ° C 0.5 159 125 108 one 226 163 140

Table 3. Physical properties of Fe-Si-0.5% P materials annealed by a cyclic method in nitrogen gas % Si Physical properties Density, g / cm ³ Hc, A / m ρ · 10 ^-8 Ohm · m Sintering Sintering Sintering 1 annealing 2 annealing 3 annealing 1 annealing 2 annealing 3 annealing 1 annealing 2 annealing 3 annealing 0 6.76 6.81 6.83 218 164 129 24 23 23 3 6.19 6.27 6.33 244 160 124 33 53 65 four 6.09 6.10 6.16 232 158 121 36 77 82 5 5.84 5.86 6.00 254 152 117 56 94 102 6 5.69 5.79 5.82 236 143 111 61 109 131 7 5.60 5.62 5.68 202 139 BY BY 131 141

Table 4. Saturation magnetization of materials of the Fe-0.5% P-Si system after the third annealing in nitrogen gas ((95-96)% N ₂ + (5-4)% H ₂ ) % Si 0 3 four 5 6 7 8 Ms · 10 ⁴ , A / m 157 132 132 125 117 111 95

Table 5. The results of a comparative analysis of the properties of the materials obtained according to the claimed invention, with the prototype Sintering modes The content of alloying, wt.% Physical properties Atmosphere Temperature and time R Si Hc, A / m p · 10 ^-8 Ohm · m Invention Nitrogen gas 1100 ° C, 3 + 3 h 0.5 3 160 53 5 152 94 7 139 130 Prototype Nitrogen gas 1100 ° C, 2 + 2 h 0.8 - 107 20-29 1,0 - one hundred 24-31 1,5 - 103 30-44 Invention Nitrogen gas 1100 ° C, 3 + 3 + 3 h 0.5 7 110 140 Prototype Nitrogen gas 1100 ° C, 2 + 2 + 4 h one - 95 30 ± 5

Claims (1)

A method of producing soft magnetic material for the manufacture of medium-frequency alternating current magnetic circuits, including the preparation of a mixture containing iron and ferrophosphorus powders, pressing and sintering in an atmosphere of nitrogen gas by a cyclic method by alternating annealing and cooling, characterized in that 3-7 wt. % silicon powder, ferrophosphorus powder is introduced into the mixture in an amount providing a phosphorus content in the mixture of not more than 0.5 wt.%, and before sintering the material is subjected to at least one op radio annealing at a temperature of 1100-1300 ° C, followed by cooling.