Preparation method and application of iron-silicon powder

Abstract

The invention belongs to the technical field of soft magnetic materials, and particularly relates to a preparation method and application of iron-silicon powder. The preparation method of the iron-silicon powder comprises the following steps: melting, atomizing and screening raw materials to obtain atomized iron-silicon powder; pre-cooling the atomized iron-silicon powder, and then carrying out low-temperature grinding, screening and heat treatment to obtain iron-silicon powder; the atomized iron-silicon powder comprises the atomized iron-silicon powder with the particle size larger than or equal to 200 meshes and smaller than or equal to 60 meshes; the pre-cooling temperature and the low-temperature grinding temperature are both-160 DEG C to-90 DEG C. According to the method, the atomized iron-silicon alloy powder is subjected to pre-cooling treatment, the mechanical abrasiveness can be improved, grinding is conducted under the low-temperature condition, the iron-silicon powder has the good grinding effect, the grinding efficiency can be improved, the powder yield is increased, the powder is fine, and meanwhile the oxygen content is lower. In addition, the problems that the atomized iron-silicon powder with the particle size larger than 200 meshes needs to be returned to a furnace, the economic benefit is poor, and the recovery rate is low can be solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of soft magnetic materials, and particularly relates to a preparation method and application of iron-silicon powder. Background Art

[0002] Soft magnetic alloy powder materials mainly include iron-silicon-aluminum alloy powder, iron-silicon alloy powder, iron-nickel-molybdenum alloy powder, iron-nickel alloy powder, iron-silicon-chromium alloy powder, etc. Using the above soft magnetic alloy powder as raw material, through insulation coating, pressing, and sintering, corresponding metal soft magnetic powder cores are formed, such as iron-silicon-aluminum soft magnetic powder cores, iron-silicon soft magnetic powder cores, etc. Since the metal soft magnetic powder core is composed of insulated-coated metal powder particles and has a distributed air gap, the magnetic core has the characteristic of soft saturation. At the same time, because the metal powder particles are insulated-coated, it has lower eddy current loss and can be applied to higher frequencies.

[0003] The metal soft magnetic iron-silicon magnetic core also has a distributed air gap, and the saturation magnetic induction intensity is about 1.6T. The loss of the iron-silicon magnetic powder core is lower than that of iron powder, and it has excellent DC bias performance. The soft saturation characteristic of the iron-silicon magnetic powder core is also significantly better than that of the iron powder core and iron-silicon-aluminum. Iron-silicon materials can be used to manufacture various different shapes and super-large-sized magnetic cores, and due to their excellent DC bias performance, good temperature stability, and high energy storage performance, they are widely used in fields such as switch power output inductors, solar inverters, wind power inverters, power factor correction (PFC) inductance filters, choke inductors, electric vehicle inverters, automotive anti-lock braking (ABS) control systems, automotive generators, and variable frequency air conditioners.

[0004] Soft magnetic iron-silicon alloy powder is the most important raw material for metal soft magnetic iron-silicon magnetic cores. Soft magnetic iron-silicon alloy powder is mainly prepared by atomization processes, especially gas atomization processes, and rarely by mechanical methods. This is because iron-silicon alloy powder has the characteristics of toughness, and it is difficult to break iron-silicon alloy powder by conventional mechanical methods, and the powder yield of the broken iron-silicon alloy powder is extremely low. After the iron-silicon alloy powder is prepared by gas atomization, the powder is uneven in thickness. To ensure that the subsequent prepared metal magnetic powder core has low eddy current loss, it needs to be screened before use. The current mainstream on the market is -200 mesh (particle size less than 200 mesh) iron-silicon alloy powder, that is, the atomized powder needs to be screened through 200 mesh, and the -200 mesh powder can be used as a finished product. For the +200 mesh (particle size greater than 200 mesh) oversize powder, it can only be reheated in a reverberatory furnace for alloying and then re-atomized into iron-silicon powder. The powder material has a relatively high specific surface area. During the process of reheating and melting in an intermediate frequency furnace, the powder material is more likely to be oxidized during the heating process. Especially for the silicon element in the iron-silicon alloy, it will lead to a decrease in the material yield, and the alloy composition fluctuates greatly, making it difficult to accurately control. In addition, after the iron-silicon alloy powder is oxidized, the non-metallic impurities increase and the slag increases, resulting in a decrease in the purity of the molten steel and an increase in the probability of the slag blocking the atomization nozzle during the atomization process, reducing the atomization success rate.

[0005] Some studies have provided a kind of iron-silicon soft magnetic alloy, but it needs to add Ti, rare earth elements, etc. The material cost is high, the alloy composition is complex, and the alloying process is difficult to control. At the same time, multi-stage crushing and multi-stage ball milling are required, the process is complex, and the powder yield of preparing iron-silicon alloy by conventional ball milling method is low, the particle size of the powder is coarse, and the oxygen content is high, which limits its large-scale application.

[0006] Therefore, there is an urgent need to provide a preparation method of iron-silicon powder, and the prepared iron-silicon powder has a high powder yield, a low oxygen content, and a low preparation cost. Summary of the Invention

[0007] The present invention aims to solve one or more technical problems existing in the prior art, and at least provides a beneficial choice or creates conditions. The present invention provides a preparation method of iron-silicon powder, and the prepared iron-silicon powder has a high powder yield, a low oxygen content, and a low preparation cost.

[0008] The inventive concept of the present invention: The preparation method of the iron-silicon powder of the present invention includes the following steps: (1) melting, atomizing, and sieving iron and silicon raw materials to obtain atomized iron-silicon powder; (2) pre-cooling the atomized iron-silicon powder obtained in step (1), then performing low-temperature grinding, then sieving, and heat treatment to obtain iron-silicon powder; the atomized iron-silicon powder includes atomized iron-silicon powder with a particle size greater than 200 mesh and less than or equal to 60 mesh; the temperatures of the pre-cooling and low-temperature grinding are both -160°C to -90°C. By performing pre-cooling modification treatment on the relatively coarse-grained atomized iron-silicon alloy powder after atomization, the characteristics of strong toughness and difficulty in mechanical grinding at normal temperature are changed. At the same time, grinding and powder making are carried out under low-temperature conditions. The iron-silicon powder has a good grinding effect, can be quickly ground fine, improves the mechanical grinding efficiency, increases the powder yield, and at the same time, the material has a better anti-oxidation effect at ultra-low temperature, and the ground iron-silicon powder has a lower oxygen content.

[0009] Therefore, in the first aspect of the present invention, a preparation method of iron-silicon powder is provided.

[0010] Specifically, the preparation method of the iron-silicon powder includes the following steps:

[0011] (1) Melting, atomizing, and sieving iron and silicon raw materials to obtain atomized iron-silicon powder;

[0012] (2) Pre-cooling the atomized iron-silicon powder obtained in step (1), then performing low-temperature grinding, then sieving, and heat treatment to obtain iron-silicon powder;

[0013] The atomized iron-silicon powder includes atomized iron-silicon powder with a particle size greater than 200 mesh and less than or equal to 60 mesh;

[0014] The temperatures of the pre-cooling and cryogenic grinding are both -160 to -90 °C.

[0015] Preferably, the temperatures of the pre-cooling and cryogenic grinding are both -150 to -100 °C.

[0016] Preferably, the raw materials include industrial pure iron and industrial pure silicon.

[0017] Preferably, by mass percentage, the iron and silicon raw materials include 5.3 - 6.7% of industrial pure silicon and 93.3 - 94.7% of industrial pure iron.

[0018] Further preferably, by mass percentage, the iron and silicon raw materials include 5.5 - 6.7% of industrial pure silicon and 93.3 - 94.5% of industrial pure iron.

[0019] Preferably, the industrial pure iron is in rod shape and the industrial pure silicon is in large block shape. This is because using rod-shaped and block-shaped raw materials can reduce alloying burn loss compared with granular pure silicon, improve the purity of the molten steel and reduce non-metallic impurities.

[0020] Preferably, in step (1), the melting temperature is 1550 - 1700 °C.

[0021] Further preferably, in step (1), the melting temperature is 1600 - 1680 °C.

[0022] Preferably, in step (1), the atomization is non-vacuum atomization.

[0023] Preferably, in step (1), during atomization, the temperature of the atomization tundish is 950 - 1250 °C; further preferably, in step (1), during atomization, the temperature of the atomization tundish is 1000 - 1200 °C.

[0024] Preferably, in step (1), the atomization rate is 9 - 16.5 kg / min; further preferably, in step (1), the atomization rate is 10 - 15 kg / min.

[0025] Specifically, the atomization rate represents the flow rate of the molten steel per minute during atomization.

[0026] Preferably, in step (1), the atomization pressure is 2.7 - 5.5 MPa; further preferably, in step (1), the atomization pressure is 3 - 5 MPa.

[0027] Preferably, in step (1), the atomized iron-silicon powder also includes atomized iron-silicon powder with a particle size larger than 60 mesh and atomized iron-silicon powder with a particle size smaller than 200 mesh.

[0028] Preferably, the atomized iron-silicon powder with a particle size larger than 60 mesh (+60 mesh) will undergo the processes of melting, atomization, and screening again.

[0029] Preferably, the atomized iron-silicon powder with a particle size smaller than 200 mesh (-200 mesh) is used normally as conventional atomized iron-silicon powder.

[0030] Specifically, the oversize material retained on the +60 mesh sieve is remelted in the furnace, and the atomized iron-silicon powder with a particle size greater than or equal to 200 mesh and less than or equal to 60 mesh (-60 mesh to +200 mesh) is subjected to low-temperature grinding. This is because the proportion of the oversize material retained on the +60 mesh sieve is very low, and at the same time, the powder is relatively coarse, resulting in less loss during remelting in the furnace and having little impact on the new alloy steel liquid. In addition, by removing the coarser oversize material retained on the +60 mesh sieve and using low-temperature grinding for -60 mesh to +200 mesh, the low-temperature grinding efficiency can be improved, and the fineness and powder yield of the powder can be increased.

[0031] Preferably, in step (2), the pre-cooling time is 4 - 12 min; more preferably, in step (2), the pre-cooling time is 5 - 10 min.

[0032] Preferably, in step (2), the refrigerant for the low-temperature grinding includes liquid nitrogen.

[0033] Specifically, under the protection and cooling of the refrigerant liquid nitrogen, grinding and powder making are carried out. The iron-silicon powder has a good grinding effect and can be quickly ground fine. At the same time, the material has a better anti-oxidation effect, and the ground iron-silicon powder has a lower oxygen content.

[0034] Preferably, in step (2), the low-temperature grinding time is 25 - 65 min; more preferably, in step (2), the low-temperature grinding time is 30 - 60 min.

[0035] Preferably, in step (2), a cryogenic grinding machine is used for the low-temperature grinding.

[0036] Specifically, the cryogenic grinding machine uses liquid nitrogen as the cold source. The material to be pulverized is cooled to achieve a brittle and easily pulverized state at low temperature, and then enters the mechanical pulverizer cavity. Through the high-speed rotation of the impeller, the material is subjected to comprehensive actions such as repeated impacts, collisions, shearing, and friction between the material and the blades, tooth discs, and between the materials, to achieve the pulverization effect. Most of the cold air returns to the silo for recycling.

[0037] Preferably, the cryogenic grinding machine includes a silo, a mechanical grinder, an induced draft fan, a cyclone powder collector, a bag dust collector tower, and a liquid nitrogen tank connected in sequence; the liquid outlet at the lower part of the liquid nitrogen tank is provided with two pipelines, which are respectively connected to the silo and the mechanical grinder.

[0038] Specifically, the liquid nitrogen tank can supply liquid nitrogen to both the silo and the mechanical grinder chamber simultaneously.

[0039] Preferably, a pipeline is provided in the gasification chamber above the liquid nitrogen tank and is connected to the silo, which can provide gasified nitrogen for the silo to purge the air in the silo and the mechanical grinder and serve as a protective atmosphere.

[0040] Preferably, the discharge port below the silo is connected to a screw feeder, the outlet of the screw feeder is connected to the inner cavity of the mechanical grinder, the outlet of the mechanical grinder is connected to an induced draft fan, and the rear end of the induced draft fan is connected to a cyclone powder collector.

[0041] Preferably, the outlet pipeline at the upper end of the cyclone powder collector includes three pipelines, one pipeline is connected to the silo, one pipeline is connected to the inner cavity of the mechanical grinder, and one pipeline is connected to the bag dust collection tower, and the rear end of the bag dust collection tower is an air release port.

[0042] Preferably, the outlet pipeline at the upper end of the cyclone powder collector is connected back to the silo and the inner cavity of the mechanical grinder, so that the liquid nitrogen refrigerant forms a closed-loop circulation system, and the refrigerant can be reused repeatedly, saving the usage amount of liquid nitrogen.

[0043] Preferably, a quick-release powder collection tank is connected below the cyclone powder collector, and butterfly valves are provided at both the upper inlet and the lower inlet of the powder collection tank, and the upper inlet is connected to the lower outlet of the cyclone powder collector.

[0044] Preferably, in step (2), the heat treatment is carried out at a holding temperature of 550 - 880 °C and the holding time of the heat treatment is 0.5 - 3.5 h.

[0045] More preferably, in step (2), the heat treatment is carried out at a holding temperature of 600 - 800 °C and the holding time of the heat treatment is 1 - 3 h.

[0046] Preferably, in step (2), a process of batch mixing is further included after the heat treatment.

[0047] The second aspect of the present invention provides an application of the method for preparing the iron-silicon powder as described in the first aspect of the present invention in the field of electronic products or new energy.

[0048] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:

[0049] (1) By performing pre-cooling modification treatment on the relatively coarse-grained atomized iron-silicon alloy powder after atomization, the present invention changes its characteristics of being tough and difficult to mechanically grind at normal temperature. At the same time, grinding and powder making are carried out under low-temperature conditions, and the iron-silicon powder has a good grinding effect, can be quickly ground fine, improves the mechanical grinding efficiency and the powder output rate. At the same time, the material has a better anti-oxidation effect at ultra-low temperature, and the ground iron-silicon powder has a lower oxygen content.

[0050] (2) The present invention only returns the +60 mesh atomized iron silicon powder to the furnace for re-melting and alloying, and performs low-temperature grinding on the -60 mesh to +200 mesh atomized iron silicon powder. The proportion of the +60 mesh sieve oversize is very low, and the powder is also coarse, so the burn loss during the return to the furnace for melting is small, and the impact on the new alloy steel liquid is also small. After removing the large-sized +60 mesh sieve oversize, the -60 mesh to +200 mesh atomized iron silicon powder is subjected to low-temperature grinding, which can also improve the low-temperature grinding efficiency, and improve the powder fineness and powder yield. Therefore, the present invention can solve the problem of poor economic benefits, low recovery rate, and affecting the purity of a new furnace of iron silicon alloy steel liquid caused by the need to return the coarse-grained powder (particle size greater than 200 mesh) of the atomized iron silicon alloy powder to the furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The scanning electron microscope images of the iron silicon powder prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention are shown;

[0052] Figure 2 This is the hysteresis loop diagram of iron silicon powder in Example 1 of the present invention. DETAILED DESCRIPTION

[0053] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0054] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0055] Example 1

[0056] A method for preparing iron-aluminum powder comprises the following steps:

[0057] (1) Industrial pure silicon is prepared according to a percentage of 6.7%wt, and the balance is industrial pure iron; the prepared industrial pure iron and industrial pure silicon are placed in a 200kg non-vacuum medium frequency furnace, the medium frequency power is turned on, the initial power is adjusted to 50kW, the heating time is 20min, and then the power is adjusted to 300kW for about 25min, the material is heated to a molten state, stirred for 3min, covered with a slag-making agent for slag making and slag removal twice, and when the temperature of the molten steel reaches 1620°C, the power is adjusted to 100kW, and steel tapping is performed;

[0058] (2) While the intermediate frequency furnace is heating up, turn on the power supply of the atomizing tundish with a power of 10 kW to heat the atomizing tundish, and heat it to 1100 °C. After the molten steel temperature in the intermediate frequency furnace and the temperature of the atomizing tundish reach the corresponding temperatures, turn on the induced draft fan, set the power ratio to 55%, tilt the intermediate frequency furnace, pour the molten steel into the atomizing tundish with the nozzle already installed, and at the same time turn on the high-pressure nitrogen pressure, adjust the atomizing pressure to 3.5 MPa, control the molten steel flow rate at an atomizing rate of 12 kg / min, and continuously carry out the atomizing operation. The ferrosilicon alloy molten steel is atomized into fine spherical powder particles under the impact, dispersion, and cooling effects of high-pressure nitrogen, enters the cyclone powder collector tower, and obtains the atomized powder.

[0059] (3) After atomization is completed, the atomized raw powder is released from the cyclone powder collector tower below the atomizing tower. Place two layers of sieves with 60 mesh and 200 mesh on the screening machine. The screening machine uses a rotary vibrating screen. Put the atomized powder obtained in step (2) into the screening machine for screening, and screen out the atomized ferrosilicon powder with +60 mesh, the atomized ferrosilicon powder with -60 mesh to +200 mesh, and the atomized ferrosilicon powder with -200 mesh. Take the atomized ferrosilicon powder with -60 mesh to +200 mesh for use.

[0060] (4) Put the atomized ferrosilicon powder with -60 mesh to +200 mesh into the hopper of the cryogenic grinder. Open the gaseous valve of the liquid nitrogen tank and the vent valve of the grinder to purge and vent the air inside the grinder system. After 5 minutes, close the valves. Open the liquid outlet below the liquid nitrogen tank, and at the same time introduce nitrogen into the hopper and the inner cavity of the mechanical grinder to pre-cool the ferrosilicon material and the grinder. The pre-cooling temperature is -140 °C, and the pre-cooling time is 10 minutes. Then start the mechanical grinder, control the grinder speed at 4500 Hz, the current at 95 A, open the valve at the outlet below the hopper, open the connected screw feeder, set the feeding frequency to 3 Hz, and gradually send the ferrosilicon powder material into the inner cavity of the mechanical grinder. Open the induced draft fan, control the fan speed at 5000 Hz, and the damper opening degree at 80%. The grinding time is 40 minutes, and the temperature is maintained at -120 °C. After grinding is completed, open the valve below the powder collection tank connected to the cyclone powder collector to release the ground ferrosilicon alloy powder. For the ground powder, screen it with a rotary vibrating screen at 200 mesh, and take the -200 mesh powder for the next process.

[0061] (5) Put the -200 mesh powder obtained by screening in step (4) into the heat treatment furnace. The heat treatment temperature is 700 °C, the heat treatment holding time is 2 h, use nitrogen as the protective atmosphere for protection, and cool it with the furnace. The protective atmosphere is continuously introduced during the cooling process.

[0062] (6) Take out the powder cooled with the furnace, mix it evenly for 25 minutes to obtain the ferrosilicon powder.

[0063] Example 2

[0064] The difference between Example 2 and Example 1 is mainly the adjustment of process parameters.

[0065] Specifically, the preparation method of the iron-silicon powder in Example 2 includes the following steps:

[0066] (1) Charge industrial pure silicon at a percentage of 6.7% wt, and the balance is industrial pure iron; put the prepared industrial pure iron and industrial pure silicon into a 200 kg non-vacuum medium-frequency furnace, turn on the medium-frequency power supply, adjust the initial power to 40 kW, heat for 20 min, then adjust the power to 280 kW for about 25 min, heat the materials to the molten state, stir for 3 min, cover with a slag-making agent to make slag and remove slag twice. When the temperature of the molten steel reaches 1600 °C, adjust the power to 100 kW and carry out steel tapping and atomization;

[0067] (2) While the medium-frequency furnace is heating up, turn on the power supply of the atomizing tundish, with a power of 8 kW, heat the atomizing tundish to a temperature of 1100 °C; after the temperature of the molten steel in the medium-frequency furnace and the temperature of the atomizing tundish reach the corresponding temperatures, turn on the induced draft fan, set the power ratio to 55%, tilt the medium-frequency furnace, pour the molten steel into the atomizing tundish equipped with a nozzle, and at the same time turn on the high-pressure nitrogen pressure, adjust the atomizing pressure to 4 MPa, control the molten steel flow rate at an atomizing rate of 12 kg / min, and continuously carry out atomization operation; the iron-silicon alloy molten steel is atomized into fine spherical powder particles under the impact, dispersion, and cooling effects of high-pressure nitrogen, and enters the cyclone powder collector tower to obtain atomized powder;

[0068] (3) After atomization is completed, the atomized raw powder is discharged from the cyclone powder collector tower below the atomization tower. Place two layers of sieves with 60 mesh and 200 mesh on the screening machine. The screening machine uses a vibrating screen. Put the atomized powder obtained in step (2) into the screening machine for screening to obtain atomized iron-silicon powder with +60 mesh, atomized iron-silicon powder with -60 mesh to +200 mesh, and atomized iron-silicon powder with -200 mesh. Take the atomized iron-silicon powder with -60 mesh to +200 mesh for use;

[0069] (4) Place the atomized iron silicon powder of -60 mesh to +200 mesh into the silo of the cryogenic grinder, open the gas valve of the liquid nitrogen tank and the vent valve of the grinder, purge and vent the air inside the grinder system, and close the valve after 5 minutes; open the liquid outlet below the liquid nitrogen tank, and introduce nitrogen into the silo and the inner cavity of the mechanical grinder at the same time to pre-cool the iron silicon material and the grinder. The pre-cooling temperature is -120°C and the pre-cooling time is 10 minutes; then start the mechanical grinder, control the grinder speed at 4200Hz, the current at 92A, and turn on the grinder. Open the outlet valve below the silo, open the connected screw feeder, set the feeding frequency to 3Hz, and gradually feed the iron-silicon powder material to the inner cavity of the mechanical grinder; turn on the induced draft fan, control the fan speed at 5000Hz, and the damper opening degree to 80%; the grinding time is 50min, and the temperature is maintained at -130℃; after grinding, open the valve below the powder collecting tank connected to the cyclone powder collector to release the ground iron-silicon alloy powder; sieve the ground powder with a 200-mesh rotary vibrating screen, and take the -200-mesh powder to enter the next step;

[0070] (5) placing the -200 mesh powder obtained after sieving in step (4) into a heat treatment furnace at a temperature of 700° C. for a holding time of 2 h, using nitrogen as a protective atmosphere for protection, and cooling with the furnace, with the protective atmosphere continuously introduced during the cooling process;

[0071] (6) Take out the powder cooled in the furnace and mix it evenly for 15 minutes to obtain iron silicon powder.

[0072] Example 3

[0073] The difference between Example 3 and Example 1 is mainly the adjustment of process parameters.

[0074] Specifically, the method for preparing the iron silicon powder in Example 3 comprises the following steps:

[0075] (1) Industrial pure silicon is prepared according to a percentage of 5.7%wt, and the remainder is industrial pure iron; the prepared industrial pure iron and industrial pure silicon are placed in a 200kg non-vacuum medium frequency furnace, the medium frequency power is turned on, the initial power is adjusted to 45kW, the heating time is 20min, and then the power is adjusted to 250kW for about 30min, the material is heated to a molten state, stirred for 3min, covered with a slag-making agent for slag-making and slag-removing twice, and when the temperature of the molten steel reaches 1650°C, the power is adjusted to 90kW, and steel tapping is atomized;

[0076] (2) While the intermediate frequency furnace is heating up, turn on the power supply of the atomizing tundish with a power of 11 kW to heat the atomizing tundish, and heat it to 1150 °C. After the molten steel temperature in the intermediate frequency furnace and the atomizing tundish temperature reach the corresponding temperatures, turn on the induced draft fan with a power ratio set at 55%, tilt the intermediate frequency furnace, and pour the molten steel into the atomizing tundish with a nozzle already installed. At the same time, turn on the high-pressure nitrogen gas pressure, adjust the atomizing pressure to 4.2 MPa, control the molten steel flow rate at an atomizing rate of 12 kg / min, and continuously carry out the atomizing operation. The ferrosilicon alloy molten steel is atomized into fine spherical powder particles under the impact, dispersion, and cooling effects of high-pressure nitrogen gas and enters the cyclone powder collector to obtain the atomized powder.

[0077] (3) After atomization is completed, the atomized raw powder is released from the cyclone powder collector below the atomizing tower. Place two layers of sieves with 60 mesh and 200 mesh on the screening machine. The screening machine uses a rotary vibrating screen. Put the atomized powder obtained in step (2) into the screening machine for screening to obtain atomized ferrosilicon powder with +60 mesh, atomized ferrosilicon powder with -60 mesh to +200 mesh, and atomized ferrosilicon powder with -200 mesh. Take the atomized ferrosilicon powder with -60 mesh to +200 mesh for use.

[0078] (4) Put the atomized ferrosilicon powder with -60 mesh to +200 mesh into the hopper of the cryogenic grinder. Open the gas valve of the liquid nitrogen tank and the vent valve of the grinder to purge and vent the air inside the grinder system. After 5 minutes, close the valves. Open the liquid outlet below the liquid nitrogen tank, and at the same time, introduce nitrogen gas into the hopper and the inner cavity of the mechanical grinder to pre-cool the ferrosilicon material and the grinder. The pre-cooling temperature is -130 °C, and the pre-cooling time is 10 minutes. Then turn on the mechanical grinder, control the grinder speed at 4800 Hz, the current at 98 A, open the valve at the outlet below the hopper, open the connected screw feeder, set the feeding frequency at 3 Hz, and gradually send the ferrosilicon powder material into the inner cavity of the mechanical grinder. Turn on the induced draft fan, control the fan speed at 4500 Hz, and the damper opening at 80%. The grinding time is 40 minutes, and the temperature is maintained at -110 °C. After grinding is completed, open the valve below the powder collection tank connected to the cyclone powder collector to release the ground ferrosilicon alloy powder. Screen the ground powder with a rotary vibrating screen at 200 mesh, and take the -200 mesh powder for the next process.

[0079] (5) Put the -200 mesh powder obtained by screening in step (4) into the heat treatment furnace. The heat treatment temperature is 700 °C, the heat treatment holding time is 2 hours, use nitrogen gas as the protective atmosphere for protection, and cool it with the furnace. The protective atmosphere is continuously introduced during the cooling process.

[0080] (6) Take out the powder cooled with the furnace, mix it evenly for 30 minutes to obtain the ferrosilicon powder.

[0081] Comparative Example 1

[0082] The difference between Comparative Example 1 and Example 1 is only that in Comparative Example 1, the atomized iron-silicon powder with a particle size of -60 mesh to +200 mesh was not pre-cooled, and ordinary ball milling was used instead of low-temperature grinding, and the others were the same as in Example 1.

[0083] Specifically, the preparation method of the iron-silicon powder in Comparative Example 1 includes the following steps:

[0084] (1) Charge industrial pure silicon at a percentage of 6.7% wt, and the balance is industrial pure iron; put the prepared industrial pure iron and industrial pure silicon into a 200 kg-class non-vacuum intermediate frequency furnace, turn on the intermediate frequency power supply, adjust the initial power to 50 kW, heat for 20 min, then adjust the power to 300 kW for about 25 min, heat the materials to the molten state, stir for 3 min, cover with a slag-making agent to make slag and remove slag twice. When the temperature of the molten steel reaches 1620 °C, adjust the power to 100 kW and perform tapping and atomization.

[0085] (2) While the intermediate frequency furnace is heating up, turn on the atomization tundish power supply with a power of 10 kW to heat the atomization tundish to a temperature of 1100 °C; when the temperature of the molten steel in the intermediate frequency furnace and the temperature of the atomization tundish reach the corresponding temperatures, turn on the induced draft fan with a power ratio set to 55%, tilt the intermediate frequency furnace, pour the molten steel into the atomization tundish equipped with a nozzle, and at the same time turn on the high-pressure nitrogen pressure, adjust the atomization pressure to 3.5 MPa, and control the molten steel flow rate at an atomization rate of 12 kg / min, and continuously perform atomization operations; the iron-silicon alloy molten steel is atomized into fine spherical powder particles under the impact, dispersion, and cooling effects of high-pressure nitrogen, and enters the cyclone powder collector to obtain atomized powder.

[0086] (3) After atomization is completed, the atomized raw powder is discharged from the cyclone powder collector below the atomization tower. Place two layers of sieves with 60 mesh and 200 mesh on the screening machine. The screening machine uses a vibrating screen. Put the atomized powder obtained in step (2) into the screening machine for screening to obtain atomized iron-silicon powder with a particle size of +60 mesh, atomized iron-silicon powder with a particle size of -60 mesh to +200 mesh, and atomized iron-silicon powder with a particle size of -200 mesh. Take the atomized iron-silicon powder with a particle size of -60 mesh to +200 mesh for use.

[0087] (4) Put the atomized iron-silicon powder with a particle size of -60 mesh to +200 mesh into a ball mill, add ball milling balls, and the ball-to-material ratio during ball milling is 6:1. Close the lid of the ball mill feed inlet, turn on the vacuum pump to evacuate, then fill with nitrogen for nitrogen protection. Turn on the ball mill power supply, set the ball milling rotation speed frequency to 40 Hz, and ball mill for 5 h; after ball milling is completed, open the ball mill feed inlet and discharge the ball-milled material; screen the ball-milled powder through a 200-mesh vibrating screen and take the powder with a particle size of -200 mesh.

[0088] (5) placing the -200 mesh powder obtained after sieving in step (4) into a heat treatment furnace at a temperature of 700° C. for a holding time of 2 h, using nitrogen as a protective atmosphere for protection, and cooling with the furnace, with the protective atmosphere continuously introduced during the cooling process;

[0089] (6) Take out the powder cooled in the furnace and mix it evenly for 25 minutes to obtain iron silicon powder.

[0090] Comparative Example 2

[0091] The only difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, the atomized iron silicon powder of -60 mesh to +200 mesh is immersed in liquid nitrogen for precooling, the precooling temperature is -140°C, the precooling time is 50 minutes, and then ground at room temperature. The rest is the same as Example 1.

[0092] Specifically, the preparation method of iron silicon powder in comparative example 2 comprises the following steps:

[0093] (1) Industrial pure silicon is prepared according to a percentage of 6.7%wt, and the balance is industrial pure iron; the prepared industrial pure iron and industrial pure silicon are placed in a 200kg non-vacuum medium frequency furnace, the medium frequency power is turned on, the initial power is adjusted to 50kW, the heating time is 20min, and then the power is adjusted to 300kW for about 25min, the material is heated to a molten state, stirred for 3min, covered with a slag-making agent for slag making and slag removal twice, and when the temperature of the molten steel reaches 1620°C, the power is adjusted to 100kW, and steel tapping is performed;

[0094] (2) While the medium frequency furnace is heating up, the power supply of the atomizing tundish is turned on with a power of 10 kW, and the atomizing tundish is heated to 1100° C.; after the temperature of the molten steel in the medium frequency furnace and the temperature of the atomizing tundish reach the corresponding temperature, the induced draft fan is turned on with a power ratio set to 55%, the medium frequency furnace is tilted, and the molten steel is poured into the atomizing tundish with the nozzle installed, and the high-pressure nitrogen pressure is turned on at the same time, and the atomizing pressure is adjusted to 3.5 MPa. The flow rate of the molten steel is controlled at an atomizing rate of 12 kg / min, and the atomizing operation is continued; the iron-silicon alloy steel liquid is atomized into fine spherical powder particles under the impact, dispersion and cooling action of the high-pressure nitrogen, and enters the cyclone powder collecting tower to obtain atomized powder;

[0095] (3) After atomization is completed, the cyclone powder collecting tower below the atomization tower releases the atomized raw powder, and two layers of 60 mesh and 200 mesh screens are placed on the screening machine. The screening machine adopts a rotary vibrating screen, and the atomized powder obtained in step (2) is placed in the screening machine for screening to obtain +60 mesh atomized iron silicon powder, -60 mesh to +200 mesh atomized iron silicon powder, and -200 mesh atomized iron silicon powder. The -60 mesh to +200 mesh atomized iron silicon powder is taken for standby use;

[0096] (4) Put the atomized iron-silicon powder with a particle size of -60 mesh to +200 mesh obtained in step (3) into liquid nitrogen and soak it for 50 minutes at an immersion temperature of -120°C. Then put the atomized iron-silicon powder with a particle size of -60 mesh to +200 mesh after liquid nitrogen immersion into the feed bin of the grinding machine. Open the gas valve of the liquid nitrogen tank and the vent valve of the grinding machine to purge and vent the air inside the grinding machine system, and carry out nitrogen protection. After 5 minutes, close the valves. Start the mechanical grinding machine, control the grinding machine speed at 4500 Hz, the current at 95 A. Open the valve at the discharge port below the feed bin, turn on the connected screw feeder, set the feeding frequency at 3 Hz, and gradually send the iron-silicon powder material into the inner cavity of the mechanical grinding machine. Turn on the induced draft fan, control the fan speed at 5000 Hz, and the damper opening at 80%. The grinding time is 40 minutes at room temperature. After grinding, open the valve at the bottom of the powder collection tank connected to the cyclone powder collector to discharge the ground iron-silicon alloy powder. Screen the ground powder with a 200-mesh vibrating screen, and take the powder with a particle size of -200 mesh for the next process.

[0097] (5) Put the sieved powder with a particle size of -200 mesh obtained in step (4) into a heat treatment furnace. The heat treatment temperature is 700°C, and the heat treatment holding time is 2 hours. Use nitrogen as the protective atmosphere for protection and cool it in the furnace. The protective atmosphere is continuously introduced during the cooling process.

[0098] (6) Take out the powder cooled in the furnace, mix it evenly for 25 minutes to obtain iron-silicon powder.

[0099] Performance testing

[0100] 1. Scanning electron microscopy observation

[0101] Perform scanning electron microscopy analysis on the iron-silicon powders prepared in Example 1, Comparative Example 1, and Comparative Example 2, as Figure 1 shown. Among them, Figure 1 Figures (a) and (b) in Figure 1 are the scanning electron micrographs of the iron-silicon powder in Example 1 at different magnifications, and

[0102] Figures (c) and (d) in Figure 1 are the scanning electron micrographs of the iron-silicon powders in Comparative Example 1 and Comparative Example 2, respectively.

[0103] It can be seen from Figure 1 that the iron-silicon powder in Example 1 is effectively broken into irregular shapes, which will increase the powder yield. However, the iron-silicon powder in Comparative Example 1 is more flattened into a cake shape and cannot be effectively broken, which will result in a lower powder yield than that in Example 1. In addition, compared with Example 1, the particles in Comparative Example 2 are significantly coarser, indicating low grinding efficiency and low powder yield.

[0103] 2. Powder yield, particle size distribution, apparent density, and oxygen content testing

[0104] (1) The powder yield of the ground powders in Examples 1-3 and Comparative Examples 1-2 was tested. The specific method was as follows: The powders (each with a weight of m1) obtained after grinding in steps (4) of Examples 1-3 and Comparative Examples 1-2 were placed on a vibrating screen with a mesh size of 200, and the weight of the powder passing through the 200-mesh screen was weighed and recorded as m2. The powder yield was calculated as m2 / m1 × 100%.

[0105] (2) A flapper sieve was used to test the particle size distribution of the iron-silicon powders after blending in Examples 1-3 and Comparative Examples 1-2. The test method was as follows:

[0106] The flapper sieve was composed of multiple layers of sieves with mesh sizes of 100, 150, 200, 250, 300, 350, and 400 stacked on top of each other. The blended iron-silicon powder, with a weight recorded as n1, was placed on the topmost sieve, screened, and the weight of the powder on each sieve layer was measured. Assuming the weight of the powder on the 200-mesh sieve was n2, then the proportion of the powder with a particle size greater than 200 mesh and less than 150 mesh (-150 mesh to +200 mesh) was n2 / n1 × 100%.

[0107] (3) An oxygen-nitrogen-hydrogen tester ONH-3000 produced by Beijing National Research Institute of Metrology & Metallurgy was used to test the oxygen content of the iron-silicon powders after blending in Examples 1-3 and Comparative Examples 1-2. The specific method was as follows: The iron-silicon powder was placed in a crucible, and under the protection of an inert atmosphere, the sample was melted by pulse heating. Since the crucible contained carbon, the carbon reacted with oxygen to form CO2, and the content of the generated CO2 was measured by infrared absorption method, and then the oxygen content in the iron-silicon powder was calculated.

[0108] The 200-mesh powder yield of the powders after grinding in Examples 1-3 and Comparative Examples 1-2, the particle size distribution and oxygen content of the iron-silicon powders after blending in Examples 1-3 and Comparative Examples 1-2, and the laser particle size and loose bulk density of the iron-silicon powders after blending in Example 1 are shown in Table 1.

[0109] Table 1: Test results of 200-mesh powder yield, particle size distribution (by weight percentage), oxygen content, laser particle size, and loose bulk density

[0110]

[0111]

[0112] In Table 1, "-" indicates not tested.

[0113] Note: For the powder that has been sieved to 200 mesh after grinding, when sieving again through 200 mesh, a small part of the powder will remain on the sieve because the sieve is not completely uniform and the particles are irregular. For example, when sieving for the first time, the particles are vertical to the sieve and can pass through the sieve, while when conducting the percussion sieve test for the second time, the particles are horizontal and cannot pass through the sieve. Therefore, there is a small part of the particle size distribution of -150 to +200 mesh in Examples 1-3 in Table 1.

[0114] As can be seen from Table 1, when producing iron-silicon powder by the preparation method of the present invention, the powder yield of 200 mesh after grinding is relatively high, and the proportion of the iron-silicon powder with a particle size of -400 mesh after batch mixing is very large, accounting for 72.9%. Followed by -350 to +400 mesh, accounting for 14.1%, indicating that the iron-silicon powder prepared by the present invention is relatively fine and has a low oxygen content at the same time.

[0115] In Comparative Example 1, the atomized iron-silicon powder of -60 mesh to +200 mesh was not pre-cooled, and ordinary ball milling was used to replace low-temperature grinding, resulting in a significantly lower powder yield of 200 mesh after grinding than that in Example 1. And the proportion of the iron-silicon powder with a particle size of -200 to +250 mesh after batch mixing is extremely large, accounting for 65.6%, while the proportions of -350 to +400 mesh and -400 mesh are very small, being 0.5% and 0.1% respectively, indicating that the iron-silicon powder in Comparative Example 1 is relatively coarse and it is difficult to prepare fine powder (almost no -400 mesh powder). In addition, the oxygen content of the iron-silicon powder after batch mixing in Comparative Example 1 is significantly higher than that in Example 1.

[0116] In Comparative Example 2, the atomized iron-silicon powder of -60 mesh to +200 mesh was soaked in liquid nitrogen for 10 min and then ground at room temperature, resulting in a significantly lower powder yield of 200 mesh after grinding than that in Example 1. And the particle size proportions of the iron-silicon powder after batch mixing that are relatively large are -200 to +250 mesh, -250 to +300 mesh, and -400 mesh, being 21.1%, 24.4%, and 27.0% respectively. Although the powder in Comparative Example 2 is finer than that in Comparative Example 1, it is still significantly lower than that in Example 1. In addition, the oxygen content of the iron-silicon powder after batch mixing in Comparative Example 2 is significantly higher than that in Example 1.

[0117] 3. Magnetic property test

[0118] The magnetic properties of the iron-silicon powder after batch mixing of Examples 1-3 were tested. The test instrument was a vibrating sample magnetometer (VSM) of Lakeshore 7400-S in the United States, and the hysteresis loop of the iron-silicon-aluminum sample was obtained. The remanence Br and coercivity data Hc were obtained on the test instrument. By dividing the magnetization intensity data on the instrument by the weight of the tested powder, the specific saturation magnetization intensity σs was obtained.

[0119] The magnetic property results of the iron-silicon powder after batch mixing of Examples 1-3 are shown in Table 2. The hysteresis loop diagram of the iron-silicon powder in Example 1 is as Figure 2As shown in the figure, among which, Figure 2 Figure (a) in Figure 2 is the hysteresis loop diagram of the iron-silicon powder in Example 1. The abscissa Field (Oe) represents the magnetic field strength, and Moment (emu) represents the magnetization intensity. Figure 2 Figure (b) in Figure 2 is an enlarged view of the area within the box in Figure (a). The abscissa H (Oe) represents the magnetic field strength, and Moment (emu) represents the magnetization intensity.

[0120] Table 2: Magnetic properties of the iron-silicon powder after combining batches of Examples 1 - 3

[0121]

[0122] From Table 2 and Figure 2 it can be seen that the iron-silicon powder prepared by the present invention has a high specific saturation magnetization intensity, very low remanence and coercivity.

[0123] In summary, the present invention conducts pre-cooling modification treatment on the relatively coarse-grained atomized iron-silicon alloy powder after atomization, changing its characteristics of being tough and difficult to mechanically grind at room temperature. At the same time, grinding and powder making are carried out under low-temperature conditions, which has a good grinding effect, can improve the mechanical grinding efficiency, increase the powder yield, and the powder is finer. At the same time, the iron-silicon powder has a better anti-oxidation effect and lower oxygen content at ultra-low temperature. At the same time, the present invention can also solve the problems that the powder with a particle size larger than 200 mesh of the atomized iron-silicon powder needs to be remelted, with poor economic benefits and low recovery rate.

[0124] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. 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 essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an iron-silicon powder, characterized in that, It includes the following steps: (1) Melting, atomizing, and screening iron and silicon raw materials to obtain atomized iron-silicon powder; (2) Pre-cooling the atomized iron-silicon powder obtained in step (1), then performing cryogenic grinding, screening, and heat treatment to obtain the iron-silicon powder; The atomized iron-silicon powder includes atomized iron-silicon powder with a particle size greater than or equal to 60 mesh and less than or equal to 200 mesh; The temperatures of both the pre-cooling and cryogenic grinding are -160 to -90 °C.

2. The preparation method according to claim 1, wherein The iron and silicon raw materials include industrial pure iron and industrial pure silicon.

3. The preparation method according to claim 2, characterized in that, By mass percentage, the iron and silicon raw materials include 5.3 - 6.7% of industrial pure silicon and 93.3 - 94.7% of industrial pure iron.

4. The preparation method according to claim 1, wherein In step (1), the melting temperature is 1550 - 1700 °C.

5. The preparation method according to claim 1, characterized in that, In step (1), during atomization, the temperature of the atomization tundish is 950 - 1250 °C; and / or, the atomization rate is 9 - 16.5 kg / min.

6. The preparation method according to claim 1, characterized in that, In step (1), the atomized iron-silicon powder also includes atomized iron-silicon powder with a particle size greater than 60 mesh and atomized iron-silicon powder with a particle size less than 200 mesh.

7. The preparation method according to claim 6, characterized in that, The atomized iron-silicon powder with a particle size greater than 60 mesh will be subjected to the processes of melting, atomizing, and screening again.

8. The preparation method according to claim 1, characterized in that, In step (2), the pre-cooling time is 4 - 12 min; and / or, the refrigerant for cryogenic grinding includes liquid nitrogen; and / or, the cryogenic grinding time is 25 - 65 min.

9. The preparation method according to claim 1, wherein, In step (2), the heat treatment holding temperature is 550 - 880 °C, the heat treatment holding time is 0.5 - 3.5 h; and / or, a batching process is also included after the heat treatment.

10. Application of the preparation method according to any one of claims 1 - 9 in the field of electronic products or new energy.

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