CN108044100B

CN108044100B - Method for preparing Fe-6.5% Si soft magnetic material thin strip by powder rolling

Info

Publication number: CN108044100B
Application number: CN201711369178.3A
Authority: CN
Inventors: 罗丰华; 赵甲正; 朱警; 李益民; 廖相巍
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2017-12-18
Filing date: 2017-12-18
Publication date: 2020-06-02
Anticipated expiration: 2037-12-18
Also published as: CN108044100A

Abstract

The invention relates to a method for preparing a Fe-6.5% Si soft magnetic material thin strip by powder rolling, which adopts water atomized iron powder and high-purity silicon iron powder with the Si content of 70-80% to form Fe-4.5-6.7% Si mixed powder. And forming a porous plate blank by powder rolling, and sintering the plate blank at 1065-1165 ℃ in a vacuum or reducing atmosphere protection manner to ensure that Fe powder particles are not completely connected, and Si and Fe are partially alloyed to form a porous and incompletely alloyed high-silicon steel blank. Subsequently, the high-silicon steel is subjected to cold rolling for multiple times, incomplete sintering and finally sintering under the protection of vacuum or reducing atmosphere at the temperature of 1265-1335 ℃ to realize homogeneous alloying of the high-silicon steel, so that the high-silicon steel with the thickness of 0.1-0.5 mm and the density of 7.34-7.49 g/cm and containing 4.5-6.7 percent of Si is obtained³High silicon steel strip.

Description

Method for preparing Fe-6.5% Si soft magnetic material thin strip by powder rolling

Technical Field

The invention belongs to the field of preparation and processing of metal materials, and particularly relates to a powder metallurgy sintering and rolling deformation method of a high-performance high-silicon steel soft magnetic strip.

Technical Field

The remanence and coercivity of soft magnetic materials are both very small, i.e. the hysteresis loop is very narrow, it almost coincides with the basic magnetization curve, and it is mainly used in the iron cores of inductors, transformers, relays and motors. The maximum magnetic permeability of the Fe-Si alloy changes with the content of Si, and two peak values of the maximum magnetic permeability are respectively generated near 2% and 6.5% of the mass percent of Si (the same is used hereinafter), and respectively reach 10000 and 25000. The maximum permeability of Fe-Si alloys does not have an absolute advantage in soft magnetic materials, e.g. the maximum permeability of permalloy can reach 200000. However, Fe-Si alloy thin plates with Si < 4.5% are inexpensive to manufacture, and therefore, silicon steel sheets, also called electrical steel sheets or silicon steel sheets, are very important magnetic materials.

And Si>At 4.5%, B will occur in the Fe-Si alloy below 540 deg.C₂the eutectoid decomposition reaction of the ordered phase generates α -Fe disordered phase and DO₃Ordered phases, making the alloy brittle and difficult to deform.

For the Fe-Si alloy with Si content between 4.5-6.7%, it is generally called high silicon steel, and the high silicon steel with Si content of 6.5% is the most important. The reason for this is that the magnetostriction coefficient of the Fe — Si alloy grains in the <100> direction decreases with increasing Si content and substantially disappears at about 6.3%, while the magnetostriction coefficient in the <111> direction increases with increasing Si content and is equal to the magnetostriction coefficient in the <100> direction at about 6.1%, so that the high silicon steel exhibits excellent low iron loss characteristics when operated at higher frequencies.

A constant uniform "humming" sound occurs in a normally operating transformer because alternating current passing through the transformer windings creates a periodically varying alternating magnetic flux in the core causing the core to magnetostriction and vibrate. The sound generated by a large number of or large-sized iron cores during vibration not only causes energy loss, but also causes noise pollution. Particularly, in the field of military aviation such as spacecrafts, submarines, missiles and the like, Fe-Si series alloy plays an extremely important role. At the end of the 60's of the 20 th century, alloys with 6.5% Si content appeared on apollo No. 11 airships as transformer materials, completing the first time of lunar ascent and eminence of mankind. Therefore, the high-silicon steel is an environment-friendly soft magnetic material with excellent performance, consumption reduction and noise reduction.

The research and development process of high silicon steel is relatively lengthy compared to other alloys. The first research of A.Schulze at the end of 20 th 20 years in the 20 th century shows that the iron-silicon alloy with 6.5 percent of silicon content has the characteristic that the magnetostriction coefficient is almost zero. Professor k.i. arail, et al, found that high silicon steel had lower core loss and higher permeability in ac dynamic magnetic fields than conventional low Si content alloys in the 80 s of the 20 th century. Over the next decades, many attempts have been made in the manufacturing technology to overcome the brittleness of high silicon steel. Such as a special rolling method for wrapping or temperature control, a rapid solidification method, a chemical vapor deposition method (CVD method), a plasma chemical vapor deposition method (PCVD method), a hot-dip-diffusion annealing method, a powder metallurgy method, a micro-alloying modification method and the like.

Of which CVD is a more successful example. In 1988, the Japan NKK company adopts CVD technology to produce a non-oriented 6.5% Si steel sheet with the thickness of 0.1-0.5 mm and the width of 400mm for the first time. In the early 90 s of the 20 th century, the first commercial CVD production line capable of realizing continuous siliconizing was developed, and the size of the produced product can reach 0.1-0.3 mm multiplied by 600 mm.

The principle of CVD is: at a specific temperature, a silicon-containing gas (SiCl)₄) Will react with the silicon steel strip to generate Fe-Si compound, and will diffuse into the alloy by the increased furnace temperature, finally the alloy reaches the required content. Although the technology is applied to realize small-scale industrial production, the scale and the yield of the technology can not meet the requirements of the international soft magnetic material market, and the preparation method has the advantages of very complex process, high energy consumption and cost, severe operating environment and incapability of meeting the environmental protection requirements.

High silicon steel is a 'steel artwork', the preparation technology of the high silicon steel is the most advanced steel manufacturing technology from time to time and is a hot spot for development and development. For 6.5% Si high silicon steel, the excellent magnetic properties and the wide application prospect thereof attract a great deal of research and development work of science and technology workers. The development and maturity of the preparation process and the economic and effective production are the key points of the wide commercial application of the 6.5% Si high silicon steel, and are also the key points of research work. Once a simple, economic, effective and mature preparation process is found out, huge economic and social benefits can be generated.

Disclosure of Invention

The invention aims to provide a method for preparing a Fe-6.5% Si soft magnetic material thin strip by powder rolling, aiming at the problem that a Fe-Si alloy thin strip with the content of 4.5-6.7% Si is difficult to form, water atomized iron powder and high-purity silicon iron powder with the content of Si of 70-80% are taken as raw materials, a forming agent is added to form a powder mixture with compressibility, a plate blank with a certain thickness is prepared by the powder rolling method, a porous and non-homogeneous blank is formed after degreasing and sintering, a thin plate is obtained after multi-pass cold rolling and sintering, and finally, a high-temperature diffusion sintering is adopted to obtain a homogeneous high-silicon steel strip.

The invention is realized by the following technical scheme: the method comprises the steps of atomizing iron powder by adopting water in a nearly spherical shape, and forming Fe-4.5-6.7% Si mixed powder by using fine high-purity silicon iron powder with the Si content of 70-80%. By means of suitable bondingThe agent and the dispersing agent adhere the high-purity silicon iron powder to the surface of the water atomized iron powder in the mixing process. Because the water atomization Fe powder is coarse particles with high compressibility and occupies a large volume ratio in the mixed powder, the deformation capacity of the water atomization Fe powder cannot be obviously reduced after the fine high-purity silicon iron powder with the Si content of 70-80% is added, and a porous plate blank can be formed through powder rolling. And (2) carrying out vacuum or reducing atmosphere protection sintering on the powder rolling plate blank at the temperature of 1065-1165 ℃, so that incomplete connection of Fe powder particles is realized, and partial alloying of Si and Fe is realized, thereby forming a porous and compressible incompletely alloyed high-silicon steel blank. And the density of the plate blank is increased, the thickness of the plate is reduced and the alloying degree of Si is continuously improved through multiple cold rolling and incomplete sintering. Finally, vacuum or reducing atmosphere protective sintering is carried out within the temperature range of 1265-1335 ℃, homogeneous alloying of the high-silicon steel is realized with the help of thermal diffusion, and the high-silicon steel with the thickness of 0.1-0.5 mm and the density of 7.34-7.49 g/cm and containing 4.5-6.7 percent of Si is obtained³High silicon steel strip.

The method specifically comprises the following steps:

(1) raw material powder preparation

The method comprises the steps of adopting water atomized iron powder with 100 meshes, wherein Fe in the water atomized iron powder is more than or equal to 99.0 percent, and the balance of Si, Mn, P, S and other inevitable impurities, adopting refined high-purity ferrosilicon powder with the Si content of 70-80 percent, wherein the grain size is less than or equal to 10 mu m, the ferrosilicon powder contains 70-80 percent of Si, the main impurities comprise-0.25 percent of Al, 0.08 percent of Ca and 0.02 percent of C, and the balance of Fe.

The water atomized Fe powder is widely used industrial iron powder, has a nearly spherical shape, has impurity content lower than that of reduced Fe powder, has higher compressibility and fluidity, and is beneficial to uniform flow of powder in the powder rolling process. The low impurity content in the water atomized Fe powder is beneficial to the soft magnetic property of the high silicon steel.

the Fe-70-80% Si high-purity silicon iron has eutectic reaction at 1207 ℃ in the solidification process except primary Si grains, and β -FeSi with a tP3 structure₂And a Si-phase eutectic structure, which is very brittle and can be easily refined by a mechanical crushing process. Crushing Fe-70-80% Si high-purity ferrosilicon to less than or equal to 10 mu mFerrosilicon powder, its Si phase in actual structure, FeSi₂The phase is finer, which is beneficial to the thermal diffusion homogenization of Si element in the subsequent high-temperature sintering process to form homogeneous Fe-6.5% Si single-phase alloy. Meanwhile, 20-30% of Fe in the powder can effectively reduce the oxidation degree of Si, and is beneficial to improving the product quality of high-silicon steel.

Mechanically crushing the Fe-70-80% Si high-purity silicon iron until the grain size is less than or equal to 10 mu m, which is favorable for the Fe-70-80% Si high-purity silicon iron to be adhered to the surface of reduced Fe powder or filled in the pores of the reduced Fe powder, and fine Si and FeSi₂The phases are dispersed in the blank to play a strengthening and toughening role in tissue refinement, so that the toughness of the subsequent blank is improved, and the cracks are not easy to cause in the rolling and densifying process. However, the high-purity Si iron containing Fe-70-80% of Si still has more Si phases, Si can easily adsorb oxygen, and SiO is formed on the surface of the exposed Si phases₂Therefore, inert gas protection is adopted in the processes of preparation, storage and transfer of the Fe-70-80% Si high-purity silicon iron powder, and the subsequent mixing and rolling processes, and used tools also need to be dehydrated and dried in advance.

On the premise of controlling the oxygen content, impurities such as Al, Ca, Mn and the like have little influence on the magnetic performance of the alloy, and the possibility of introducing other alloy elements in the process is also low.

(2) Powder mixing

Weighing water atomized Fe powder and Fe-70-80% Si high-purity silicon iron powder according to the proportion of Fe-4.5-6.7% Si; mixing by adopting a low-energy mixer under inert protective atmosphere, wherein the mixing speed and the mixing time depend on the mixing uniformity, and the work hardening of the Fe powder in the mixing process is reduced as much as possible.

(3) Powder rolling

A two-roller horizontal rolling mill and an inclined feeding trough are adopted, the self weight of the powder and the friction force between the roller and the powder are utilized for feeding, the rolled thickness is 1.0-2.4 mm, the width is 100-240 mm, and the density is 6.0-6.7 g/cm³The powder rolling of (1).

According to the different direction of the strip out of the roller, the powder rolling can be divided into 3 types of vertical, horizontal and inclined, and the feeding mode comprises dead weight feeding, forced feeding, pre-bonding feeding and the like. The width of the blank is related to the width of the feeding trough, and the length of the blank depends on the permission of production conditions and actual needs.

(4) Degreasing and sintering

Placing the powder rolling blank on a support plate coated with MgO micropowder on the surface, placing the support plate in a vacuum degreasing and sintering furnace, adopting a heating rate of 2-5 ℃/min, respectively preserving heat for 2-4 h at 200 ℃ and 400 ℃, then heating to 1065-1165 ℃, preserving heat and sintering for 2-4 h, wherein the density of the sintering blank is 6.1-6.8 g/cm³。

After sintering, a uniform equiaxed crystal structure is formed. The grain size of the matrix is about 70-120 mu m, the grain boundary has pores of about 10-20 mu m, and the subsequent rolling and sintering can be closed. A large number of second phases with the diameter of 1-5 mu m are uniformly distributed in the matrix structure, and the second phases have good interface combination with the matrix structure, namely, no split surface appears. Obviously, the second phases are certain Si-rich phases, and the existence of the Si-rich phases reduces the Si content of the matrix structure, so that the matrix structure has high plastic deformation capacity; meanwhile, the good interface combination and dispersion distribution of the nano-particles and the matrix structure are beneficial to subsequent uniform diffusion.

The sintering temperature is too low to be beneficial to the connection among Fe powder particles and the Si atom diffusion, and the sintering temperature is too high to be easy to realize rolling densification due to the coarse pores generated by the surface diffusion of Fe and Si elements.

The powder-millable billet can be placed in multiple layers during sintering, but the layers must be separated from one another to avoid cracking caused by shrinkage of the slab during sintering. The temperature rise speed is not too fast during sintering, and multi-stage heat preservation can be arranged in the temperature rise process to realize the functions of degassing and degreasing. Or degreasing and sintering under reducing or inert gas protection. W, Mo, heat-resistant steel and the like can be used as a supporting plate (or called as a burning boat) during sintering, and ceramic plates such as corundum, zirconia and the like can also be used, but the metal plates have good heat conductivity and are beneficial to uniform sintering shrinkage.

(5) Cold rolling-sintering densification

The sintered plate blank is subjected to cold rolling and thinning, the single-pass reduction is less than or equal to 8 percent, the sintered plate blank is subjected to multi-pass rolling until the total reduction rate reaches 30-45 percent, and then is sintered for 0.5-2 h at the temperature of 1065-1165 ℃ in a sintering furnace,after multiple cold rolling and sintering, the thickness of the plate reaches 0.1-0.5 mm, and the density reaches 7.33-7.48 g/cm³。

Since the powder blank is porous and a deformable Fe phase is present, the blank can withstand cold rolling deformation. However, the slab also has more high Si phase, so the rolling reduction of each pass cannot be higher than 8%, and 8-20 passes are required when the accumulated total reduction rate reaches 30-45%.

Because a large amount of pores and hard and brittle phases exist, the sintering is carried out at 1065-1165 ℃ under vacuum sintering or reducing protective atmosphere to realize pore closure and crack repair and Si element homogenization diffusion to a certain degree. The temperature rise speed can be fast at 5-10 ℃/min, the temperature can be continuously raised, the heat preservation time is determined according to the plate thickness, and the heat preservation time is 1-2 h when the plate thickness is more than or equal to 1 mm; the thickness of the plate is 0.1-1 mm, and the heat preservation time is reduced to 0.5-1 h. After the accumulated reduction after each sintering reaches 30-45%, the sintering needs to be carried out again for 1 time, namely, the sintering needs to be carried out again for about 4-8 times from 1.0-2.5 mm powder blank rolling to 0.1-0.5 mm. In addition, in order to make the density of the plate material reach 7.2g/cm³(about 95% of the theoretical density) or more, 4 or more times of re-sintering is also required.

The metallographic structure matrix after 2 times of cold rolling-sintering is about 100 mu m of grain structure, and a small amount of fine pores exist. The matrix crystal grains have two different contrasts, which are caused by different Si contents and corrosion difference, and the low-Si crystal grains in the structure are beneficial to processing deformation, so that the manufacture of a thin plate with the thickness of 0.1-0.5 mm is possible.

(6) Homogenizing high-temperature sintering

Finally sintering the silicon plate in vacuum or reducing protective atmosphere at the temperature of 1265-1335 ℃ for 1-4 h, realizing homogenization of Si under the action of thermal diffusion to form single-phase alloy, obtaining homogeneous high-silicon steel, wherein the thickness of the plate after densification and sintering is almost unchanged and is 0.1-0.5 mm, the density is slightly reduced and reaches 7.34-7.49 g/cm³。

High-purity silicon iron powder with the grain diameter less than or equal to 10 is obtained by a high-energy ball milling or impact spinning method.

And (3) the low-energy mixer in the step (2) is a conical mixer, a V-shaped mixer or a drum mixer.

And (3) adding cellulose, paraffin micro powder or zinc stearate water-insoluble as a forming agent during mixing in the step (2), wherein the total addition amount of the forming agent is not more than 0.8 percent of the total mass of the mixed powder, adding grease and absolute ethyl alcohol as passivators to passivate Si powder, bond Fe-Si powder and enhance the flowability and the green strength of the powder, and the total addition amount of the passivators is not more than 2 percent of the total mass of the mixed powder.

Sintering at 1065-1165 ℃ in a vacuum sintering or reducing protective atmosphere, continuously heating at 5-10 ℃/min, and keeping the temperature for 1-2 h when the plate thickness is more than or equal to 1 mm; the thickness of the plate is 0.1-1 mm, the heat preservation time is reduced to 0.5-1 h, after the accumulated reduction after each sintering reaches 30-45%, the plate is re-sintered for 1 time, and the plate is rolled to 0.1-0.5 mm from 1.0-2.4 mm of powder blank and needs to be re-sintered for 4-8 times.

The supporting plate in the step (4) adopts W, Mo, corundum or zirconia ceramic burning boat.

The sintered plates can be stacked during high-temperature sintering, but MgO powder must be laid between layers, and W, Mo and a ceramic burning boat can be adopted. However, the plate must be laid flat, and a flat weight can be placed on the plate to prevent deformation in the sintering process.

The magnetic properties of high silicon steel are greatly influenced by the grain size, grain orientation, content of elements such as C and the like in addition to the Si content, and can be controlled by technical means such as wet hydrogen annealing, normalizing treatment and the like.

The method is characterized in that Fe-70-80% Si high-purity powder with the particle size of less than or equal to 10 mu m is added into water atomized Fe powder with good plasticity and large volume proportion to form Fe-4.5-6.7% Si alloy mixture, incomplete alloying sintering is carried out after the powder is rolled into a plate blank, the incomplete sintering of Fe powder particles is realized, partial alloying of Si and Fe is realized, and porous and compressible incompletely alloyed high-silicon steel blank is formed. And subsequently, the uniformity and compactness of the structure are improved through multi-pass cold rolling and sintering, and the homogenization of Si is realized through a high-temperature diffusion process, so that a completely alloyed single-phase high-silicon steel strip is obtained. The methodBy means of process and equipment design, automatic and continuous production of the process is realized, and the product with the thickness of 0.1-0.5 mm and the density of 7.34-7.49 g/cm can be produced in large batch³High silicon steel strip.

Drawings

FIG. 1 is a diagram of a gold phase of a sintered powder rolled compact of example 2 of the present invention;

FIG. 2 is a metallographic picture of a sheet material obtained by 2 cold rolling-sintering processes according to example 3 of the present invention;

FIG. 3 is an XRD diffraction curve of the powder rolled compact of example 3 of the present invention after high temperature sintering.

Detailed Description

The invention is described in further detail below with reference to the figures and the detailed description.

Example 1

Mixing water atomized Fe powder of-100 meshes with Fe-80% Si high-purity powder with the grain size less than or equal to 10 mu m according to the proportion of 91.625:8.375 to form mixed powder of Fe-6.7% Si. During mixing, 0.6 percent of paraffin micro powder and 0.1 percent of engine oil are added. The absolute ethanol was added in an amount of 200 ml/ton. The powders were mixed for 4h using a V blender.

A two-roller horizontal rolling mill and an inclined feeding trough are adopted, powder is fed by using the self weight of the powder and the friction force between the roller and the powder, and a powder rolling plate blank with the width of 2.4mm is rolled out, wherein the width of the plate blank is 100 mm. The density of the green compact was 6.0g/cm³。

And placing the powder rolling blank on a molybdenum plate coated with MgO micropowder on the surface, and placing the molybdenum plate in a vacuum degreasing and sintering furnace. The temperature rise speed is 2 ℃/min, and the temperature is respectively kept at 200 ℃ and 400 ℃ for 4 h. Then the temperature is increased to 1065 ℃ and sintering is carried out for 4 hours under the condition of heat preservation. The density of the sintered compact was 6.1g/cm³。

And (3) cold rolling and thinning the sintered plate blank, wherein the single-pass reduction is less than or equal to 8%, rolling is carried out for multiple passes until the total reduction rate reaches 30-45%, and then heat preservation and sintering are carried out in a vacuum sintering furnace at 1065 ℃. Continuously heating at the speed of 5 ℃/min, determining the heat preservation time according to the plate thickness, and keeping the heat preservation time for 2h when the plate thickness is more than or equal to 1 mm; the thickness of the plate is 0.1-1 mm, and the heat preservation time is 1 h. The specific reduction-annealing system is as follows: 2.4mm → 1.6mm → 1.02mm → 0.71mm → 0.49mm, namely after 4 times of cold rolling and 3 times of sintering, the thickness of the plate reaches 0.49mm, and the density reaches 7.33g/cm³。

Vacuum sintering the cold rolled strip at 1335 deg.C for 1h to obtain a thickness of about 0.50mm and a density of 7.34g/cm³And the single-phase homogeneous high-silicon steel with the Si content of 6.7 percent.

Example 2

Mixing water atomized Fe powder of-100 meshes with Fe-70% Si high-purity powder with the grain size less than or equal to 10 mu m according to the proportion of 93.57:6.42 to form mixed powder of Fe-4.5% Si. When mixing, zinc stearate accounting for 0.7 percent of the total amount of the raw materials and engine oil accounting for 0.1 percent of the total amount of the raw materials are added. Anhydrous ethanol was added in an amount of 400 ml/ton. The powders were mixed for 6h using a roller mixer.

A two-roller horizontal rolling mill and an inclined feeding trough are adopted, powder is fed by using the self weight of the powder and the friction force between the roller and the powder, and a powder rolling plate blank with the width of 1.0mm is rolled out, wherein the width of the plate blank is 240 mm. The density of the green compact was 6.7g/cm³。

And placing the powder rolling blank on a molybdenum plate coated with MgO micropowder on the surface, and placing the molybdenum plate in a vacuum degreasing and sintering furnace. The temperature is raised at a speed of 5 ℃/min and is respectively kept at 200 ℃ and 400 ℃ for 2 h. Then heating to 1165 ℃ and sintering for 2 h. The density of the sintered compact is 6.8g/cm³。

After sintering, a uniform equiaxed crystal structure is formed, as shown in fig. 1. The grain size of the matrix is about 70-120 mu m, the grain boundary has pores of about 10-20 mu m, and the subsequent rolling and sintering can be closed. A large number of second phases with the diameter of 1-5 mu m are uniformly distributed in the matrix structure, and the second phases have good interface combination with the matrix structure, namely, no split surface appears. Obviously, the second phases are certain Si-rich phases, and the existence of the Si-rich phases reduces the Si content of the matrix structure, so that the matrix structure has high plastic deformation capacity; meanwhile, the good interface combination and dispersion distribution of the nano-particles and the matrix structure are beneficial to subsequent uniform diffusion.

And (3) cold rolling and thinning the sintered plate blank, wherein the single-pass reduction is less than or equal to 8%, rolling is carried out for multiple passes until the total reduction rate reaches 30-45%, and then heat preservation and sintering are carried out in a vacuum sintering furnace at 1165 ℃. Continuously heating at the speed of 10 ℃/min, and keeping the temperature for 1 h.The specific reduction-annealing system is as follows: 1.0mm → 0.65mm → 0.39mm → 0.25mm → 0.17mm → 0.13mm → 0.10mm, namely after 6 times of cold rolling and 5 times of sintering, the thickness of the plate reaches 0.10mm, and the density reaches 7.48g/cm³。

Vacuum sintering the cold rolled strip at 1265 deg.C for 4h to obtain a thickness of about 0.10mm and a density of 7.49g/cm³Single-phase homogeneous high-silicon steel with 4.5% of Si content.

Example 3

Mixing water atomized Fe powder of-100 meshes with Fe-76% Si high-purity powder with the grain size less than or equal to 10 mu m according to the proportion of 91.45:8.55 to form mixed powder of Fe-6.5% Si. During mixing, 0.4% of paraffin micropowder, 0.2% of methylcellulose and 0.1% of engine oil are added. Anhydrous ethanol was added in an amount of 400 ml/ton. The powders were mixed for 6h using a roller mixer.

A two-roller horizontal rolling mill and an inclined feeding trough are adopted, powder is fed by using the self weight of the powder and the friction force between the roller and the powder, and a powder rolling plate blank with the width of 1.6mm is rolled out, wherein the width of the plate blank is 180 mm. The density of the green compact was 6.15g/cm³。

And placing the powder rolling blank on a corundum plate coated with MgO micro powder on the surface, placing the corundum plate in a hydrogen tube furnace for degreasing and sintering. The temperature is increased at a speed of 3 ℃/min, and the temperature is kept at 200 ℃ for 2h and at 400 ℃ for 3 h. Then heating to 1100 ℃, and sintering for 3h under the condition of heat preservation. The density of the sintered compact was 6.20g/cm³。

And (3) cold-rolling and thinning the sintered plate blank, wherein the single-pass reduction is less than or equal to 8%, rolling for multiple passes until the total reduction rate reaches 30-45%, and then sintering at 1100 ℃ for 1h in a hydrogen tube furnace. The temperature was continuously raised at a rate of 6 ℃/min. The specific reduction-annealing system is as follows: 1.6mm → 1.08mm → 0.70mm → 0.45mm → 0.27mm, namely after 4 times of cold rolling and 3 times of sintering, the thickness of the plate reaches 0.27mm, and the density reaches 7.36g/cm³。

The metallographic structure after 2 times of cold rolling-sintering is shown in fig. 2, the matrix is a grain structure of about 100 μm, and a small amount of fine pores are present. The matrix crystal grains have two different contrasts, which are caused by different Si contents and corrosion difference, and the low-Si crystal grains in the structure are beneficial to processing deformation, so that the manufacture of a thin plate with the thickness of 0.1-0.5 mm is possible.

The cold rolled strip was vacuum sintered at 1300 ℃ for 2 hours to obtain a thickness of about 0.27mm and a density of 7.37g/cm³And 6.5% of Si, and the XRD analysis chart of the final plate is shown in figure 3.

Example 4

Mixing water atomized Fe powder of-100 meshes with Fe-72% Si high-purity powder with the grain size less than or equal to 10 mu m according to the proportion of 91.05:8.95 to form mixed powder of Fe-5.8% Si. During mixing, 0.6 percent of paraffin micro powder and 0.2 percent of engine oil are added. Anhydrous ethanol was added in an amount of 400 ml/ton. The powders were mixed for 3h using a roller mixer.

A two-roller horizontal rolling mill and an inclined feeding trough are adopted, powder is fed by using the self weight of the powder and the friction force between the roller and the powder, and a powder rolling plate blank with the width of 1.96mm is rolled out, wherein the width of the plate blank is 200 mm. The density of the green compact was 6.25g/cm³。

And placing the powder rolling blank on a corundum plate coated with MgO micro powder on the surface, placing the corundum plate in a hydrogen tube furnace for degreasing and sintering. The temperature is increased at a speed of 4 ℃/min, and the temperature is kept at 200 ℃ for 3h and 400 ℃ for 2 h. Then the temperature is increased to 1130 ℃ and the sintering is carried out for 2 h. The density of the sintered compact was 6.30g/cm³。

And (3) cold-rolling and thinning the sintered plate blank, wherein the single-pass reduction is less than or equal to 8%, rolling for multiple passes until the total reduction rate reaches 30-45%, and then sintering for 0.5h at 1130 ℃ in a hydrogen tube furnace. The temperature was continuously raised at a rate of 8 ℃/min. The specific reduction-annealing system is as follows: 1.96mm → 1.3mm → 0.96mm → 0.72mm → 0.46mm → 0.32mm → 0.21mm, namely after 7 times of cold rolling and 6 times of sintering, the thickness of the plate reaches 0.21mm, and the density reaches 7.39g/cm³。

The cold rolled strip was vacuum sintered at 1300 ℃ for 2 hours to obtain a thickness of about 0.22mm and a density of 7.40g/cm³The Si content is 5.8 percent, and the silicon steel is single-phase homogeneous high silicon steel.

Claims

1. A method for preparing Fe-6.5% Si soft magnetic material thin strip by powder rolling is characterized by comprising the following steps:

(1) raw material powder preparation

Adopting water atomized iron powder with 100 meshes, wherein Fe in the water atomized iron powder is more than or equal to 99.0 percent, the balance of Si, Mn, P, S and other inevitable impurities, adopting high-purity ferrosilicon powder with the Si content of 70-80 percent, the grain size of the high-purity ferrosilicon powder is less than or equal to 10 mu m, the main impurities are-0.25 percent of Al, 0.08 percent of Ca and 0.02 percent of C, and the balance of Fe;

(2) powder mixing

Weighing water atomized Fe powder and Fe-70-80% Si high-purity silicon iron powder according to the proportion of Fe-6.5% Si; mixing by adopting a low-energy mixer under inert protective atmosphere;

(3) powder rolling

A two-roller horizontal rolling mill and an inclined feeding trough are adopted, the self weight of the powder and the friction force between the roller and the powder are utilized for feeding, the rolled thickness is 1.0-2.4 mm, the width is 100-240 mm, and the density is 6.0-6.7 g/cm³The powder rolling of (4);

(4) degreasing and sintering

Placing the powder rolling blank on a support plate coated with MgO micropowder on the surface, placing the support plate in a vacuum degreasing and sintering furnace, adopting a heating rate of 2-5 ℃/min, respectively preserving heat for 2-4 h at 200 ℃ and 400 ℃, then heating to 1065-1165 ℃, preserving heat and sintering for 2-4 h, wherein the density of the sintered plate blank is 6.1-6.8 g/cm³；

(5) Cold rolling-sintering densification

Cold rolling and thinning the sintered plate blank, wherein the single-pass reduction is less than or equal to 8%, rolling in multiple passes until the total reduction rate reaches 30-45%, sintering in a sintering furnace at 1065-1165 ℃ for 0.5-2 h, and after cold rolling and sintering for multiple times, the thickness of the plate reaches 0.1-0.5 mm, and the density reaches 7.33-7.48 g/cm³；

(6) Homogenizing high-temperature sintering

Sintering at 1265-1335 ℃ in vacuum or reducing protective atmosphere for 1-4 h, realizing homogenization of Si under the action of thermal diffusion to form single-phase alloy, obtaining a homogeneous thin strip, wherein the thickness of the thin strip after the homogenization and high-temperature sintering is 0.1-0.5 mm, and the density reaches 7.34-7.49 g/cm³。

2. The method for producing thin strips of Fe-6.5% Si soft magnetic material by powder rolling according to claim 1, characterized in that: and obtaining the high-purity ferrosilicon powder with the particle size of less than or equal to 10 mu m by a high-energy ball milling or rotary impacting method.

3. The method for producing thin strips of Fe-6.5% Si soft magnetic material by powder rolling according to claim 1, characterized in that: and (3) the low-energy mixer in the step (2) is a conical mixer, a V-shaped mixer or a drum mixer.

4. The method for producing thin strips of Fe-6.5% Si soft magnetic material by powder rolling according to claim 1, characterized in that: and (3) adding cellulose, paraffin micro powder or zinc stearate water-insoluble as a forming agent during mixing in the step (2), wherein the total addition amount of the forming agent is not more than 0.8 percent of the total mass of the mixed powder, adding grease and absolute ethyl alcohol as passivators to passivate high-purity silicon iron powder, bond the powder and enhance the powder flowability and the green compact strength, and the total addition amount of the passivators is not more than 2 percent of the total mass of the mixed powder.

5. The method for producing thin strips of Fe-6.5% Si soft magnetic material by powder rolling according to claim 1, characterized in that: sintering at 1065-1165 ℃ in a vacuum sintering or reducing protective atmosphere, continuously heating at 5-10 ℃/min, and keeping the temperature for 1-2 h when the plate thickness is more than or equal to 1 mm; the thickness of the plate is 0.1-1 mm, the heat preservation time is reduced to 0.5-1 h, after the accumulated reduction after each sintering reaches 30-45%, the plate is re-sintered for 1 time, and the plate blank with the thickness of 1.0-2.4 mm is rolled to 0.1-0.5 mm, and needs to be re-sintered for 4-8 times.

6. The method for producing thin strips of Fe-6.5% Si soft magnetic material by powder rolling according to claim 1, characterized in that: and (3) superposing and placing the sintered plates during uniform high-temperature sintering, and paving MgO powder between layers.

7. The method for producing thin strips of Fe-6.5% Si soft magnetic material by powder rolling according to claim 1, characterized in that: the supporting plate in the step (4) is made of W, Mo, corundum or zirconia ceramic materials.