CN107971495B

CN107971495B - Method for preparing Fe-6.5% Si soft magnetic material thin strip by powder hot isostatic pressing

Info

Publication number: CN107971495B
Application number: CN201711367251.3A
Authority: CN
Inventors: 罗丰华; 温家飞; 王柏钧; 廖相巍; 李益民; 陈雪阳
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: CN107971495A

Abstract

the invention relates to a method for preparing single-phase Fe-6.5% Si silicon steel by powder hot isostatic pressing, which comprises the steps of forming Fe-4.5-6.7% Si mixed powder by adopting water atomized Fe powder and Fe-70-80% Si high-purity silicon iron powder as raw materials, adding a bonding agent and a dispersing agent, uniformly mixing, adopting a soft iron sheath, carrying out hot isostatic pressing at 1065-1165 ℃ under 100-200 MPa to obtain a uniform and compact, wherein the compact consists of Si-poor α -Fe crystal grains and a brittle high-Si phase, has plastic deformation capacity, and has the compact density of 6.88-7.10 g/cm³. The high-silicon steel is subjected to multiple cold rolling and low-temperature diffusion sintering, the density is increased, the thickness is reduced, the high-silicon steel is finally sintered at the temperature 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 more than or equal to 7.39g/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 hot isostatic pressing

Technical Field

The invention belongs to the field of preparation and processing of metal materials, and particularly relates to a method for powder hot isostatic pressing and rolling deformation of a high-silicon steel thin 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% α soft magnetic material thin strip by powder hot isostatic pressing, aiming at the problem that a Fe-4.5-6.7% α alloy thin strip is difficult to form, water atomized Fe powder is uniformly mixed with high-purity ferrosilicon powder with the α content of 70-80%, a high-density uniform slab is prepared by utilizing the characteristics of high-temperature softening action and uniform pressure of hot isostatic pressing, partial alloying is realized under the action of thermal diffusion, a multiphase structure of α -poor alpha-Fe crystal grains with plastic deformation capacity and a brittle high- α phase is formed, the homogeneous single-phase high- α steel strip is further thinned after multi-pass cold rolling-sintering, and finally, the homogeneous single-phase high- α steel strip is obtained by adopting high-temperature diffusion sintering.

The invention is realized by the following technical scheme: the method comprises the steps of adopting water atomized Fe powder with a nearly spherical shape and taking superfine high-purity silicon iron powder with the Si content of 70-80% as a raw material to form Fe-4.5-6.7% Si mixed powder. Adding a small amount of adhesive and dispersant, uniformly mixing, and then obtaining a uniform and compact blank by adopting a soft iron sheath under the action of 100-200 MPa of hot isostatic pressure within the temperature range of 1065-1165 ℃. The density of the pressed compact reaches 6.88 to 7.10g/cm³under the thermal action and pressure action of hot isostatic pressing, Fe powder particles are metallurgically bonded, and Si element is incompletely diffused to form compact α -Fe crystal grains with poor plastic deformation capability and a multiphase structure of a brittle high-Si phase, the density of a plate blank is increased, the plate thickness is reduced, the alloying degree of Si is also continuously increased through multiple times of cold rolling and low-temperature diffusion sintering, finally, the high-silicon steel is subjected to vacuum or reducing atmosphere protection sintering within the temperature range of 1265-1335 ℃, the homogeneous alloying of the high-silicon steel is realized with the help of the thermal diffusion, and the thickness of 0.1-0.5 mm containing 4.5-6.7 percent of Si is obtained, and the density is more than or equal to 7.39g/cm³High 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, the balance of Si, Mn, P, S and other inevitable impurities, adopting high-purity silicon iron powder with the Si content of 70-80 percent, and the grain diameter of less than or equal to 10 mu m, wherein the main impurities of the silicon iron powder except 70-80 percent of Si 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 extrusion 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 into ferrosilicon powder with the grain size of less than or equal to 10 mu m, and Si phase and FeSi in actual tissues of the ferrosilicon powder₂The phase is finer, which is beneficial to the thermal diffusion homogenization of Si element in the subsequent high-temperature sintering process, and homogeneous Fe-4.5-6.7% Si single-phase alloy is formed. 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, so that the Fe-70-80% Si high-purity silicon iron is favorably adhered to the surface of water atomized 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-Fe with Fe-70-80% still has more Si phase, Si can easily adsorb oxygen, and SiO is formed on the surface of the exposed Si phase₂Therefore, 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 processes of material mixing, hot isostatic pressing and rolling, and used tools also need to be dehydrated and dried in advance.

On the premise of controlling the oxygen content, other 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, and fully and uniformly mixing under the inert protective atmosphere.

(3) Powder hot isostatic pressing:

adopting a soft iron sheath, and performing hot isostatic pressing at 100-200 MPa within the temperature range of 1065-1165 DEG CUnder the action of pressure maintaining for 0.5-2 h, uniform and compact green compact with the density of 6.78-7.10 g/cm is obtained³。

(4) Cold rolling-sintering

The hot isostatic pressing plate is subjected to cold rolling-sintering, the thickness is gradually reduced, the single-pass reduction is less than or equal to 8%, the total reduction rate is 30-50% after multi-pass rolling, the hot isostatic pressing plate is subjected to heat preservation sintering at the temperature of 1065-1165 ℃ in a sintering furnace for 0.5-2 h, the thickness of the plate reaches 0.1-0.5 mm after multiple cold rolling-sintering, and the density of the strip reaches 7.32-7.45 g/cm after the alloying of Si is finished³。

A large amount of deformable Fe phase exists in the blank, and the slab can bear cold rolling deformation. However, the slab also has more high Si phase, and the performance is brittle, so the rolling reduction of each pass cannot be too high, the accumulated total reduction rate reaches 30-50%, and about 8-25 passes are needed.

Some micro-cracks may form due to the presence of hard brittle phases, cold deformation processes. In order to realize pore closure and crack repair, and to realize a certain degree of Si element uniform diffusion. And after the cold rolling deformation is accumulated to a certain degree, re-sintering for 1 time, rolling the hot isostatic pressing plate material with the thickness of 36-54 mm to 0.1-0.5 mm, and re-sintering for about 12-20 times.

The adopted sintering temperature range is the sintering process of the prior powder metallurgy iron-based alloy, and the sintering process is widely verified by practice. The sintering temperature is too low, which is not beneficial to the metallurgical bonding of Fe powder particles and the thermal diffusion of Si element; and if the sintering temperature is too high, Si element can be rapidly diffused, the hardness of crystal grains is too high and the crystal grains are embrittled, and the subsequent rolling deformation is difficult to realize.

Reducing, inert gas shielding or vacuum sintering is adopted. W, Mo, heat-resistant steel, etc. can be used as a supporting plate (or called as a burning boat) during sintering, and ceramic plates of corundum, zirconia, etc. can also be used, but the metal plates have good heat conductivity and are beneficial to uniform sintering.

After sintering, a coarse grain structure containing a second phase is formed. The phase of X-ray diffraction is identified as heterogeneous Fe (Si) phase, several characteristic peaks of body-centered cubic have obvious splitting phenomena, which shows that 2 Fe phases with different Si solid solubility exist, wherein one Fe phase has low Si content and plastic deformation capability.

(5) Full alloying high-temperature sintering

Sintering in vacuum or reductive protective atmosphere at 1265-1335 ℃ for 1-4 h, realizing Si full alloying under the action of thermal diffusion to form single-phase alloy, obtaining homogeneous high-silicon steel, wherein the thickness of the densified and sintered plate is almost unchanged and is 0.1-0.5 mm, and the density is increased to 7.34-7.48 g/cm³。

The high-purity silicon iron powder with the grain diameter less than or equal to 10 mu m in the step (1) is obtained by a high-energy ball milling or impact spinning method.

The low-energy mixer is a conical mixer, a V-shaped mixer or a drum mixer.

In the step (3), the blank is processed into a square block with the length, width and thickness of 100-300 mm and 36-54 mm; the three-point bending test of the hot isostatic pressing blank shows plasticity, and the bending strength is 262-459 MPa.

During mixing, cellulose, paraffin micro powder or zinc stearate water-insoluble forming agent is added, the total addition amount of the forming agent is not more than 0.3 percent of the total mass of the mixed powder, meanwhile, grease and absolute ethyl alcohol are added as passivators to play a role in passivating Si powder, bonding Fe-Si powder and enhancing the powder flowability and green strength, and the total addition amount of the passivators is not more than 2 percent of the total mass of the mixed powder.

And (4) adopting a molybdenum plate, a W plate, heat-resistant steel, corundum or zirconia ceramic plate as the supporting plate.

And (6) during high-temperature sintering, superposing and placing sintered plates, paving MgO powder between layers, flatly laying the plates, and placing flat weights on the plates 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 essence of the invention is that the high-purity Si-Fe powder with a certain volume ratio of fine Fe-70-80% Si is added into the water atomized Fe powder with a large volume ratio with good plasticity to form Fe-4.5-6.7% Si mixed powder. By passingHot isostatic pressing achieves high density and high homogeneity. Under the thermal action of hot isostatic pressing, incomplete alloying occurs, and a composite material consisting of plastic Fe grains and a brittle high Si phase is obtained. 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 high-temperature diffusion sintering, so that the high-quality single-phase high-silicon steel strip is obtained. The method realizes automatic and continuous production of the process through process and equipment design, and can realize mass production of the product with the thickness of 0.1-0.5 mm and the density of more than or equal to 7.34g/cm³High silicon steel strip.

Drawings

FIG. 1 is a three point bend plot of a post powder hot isostatic pressing billet of example 1 of the present invention;

FIG. 2 is a metallographic structure diagram after powder HIP-cold rolling-sintering according to example 2 of the present invention;

FIG. 3 is a XRD diffraction pattern after powder HIP-cold rolling-sintering for example 2 of the present invention;

FIG. 4 is a XRD diffraction pattern after powder HIP-COLD ROLLING-HIGH-TEMPERATURE SINTERING for example 4 of the present invention.

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, 0.2% of paraffin micro powder and 0.1% of engine oil are added. The absolute ethanol was added in an amount of 200 ml/ton.

And (3) fully mixing the powder, and then adopting a soft iron sheath to maintain the pressure for 1.5h at the temperature of 1065 ℃ under the action of 200MPa of hot isostatic pressing to obtain a uniform and compact. The jacket was removed by machining and the billet was machined into 36X 100mm squares. The compact density reaches 6.73g/cm³. The three-point bending test showed a bending strength of 262MPa, see FIG. 1, and plasticity.

And (3) cold rolling and sintering the hot isostatic pressing plate, and gradually thinning. The specific reduction-annealing system is as follows: 36mm → 24mm → 17mm → 12mm → 9.5mm → 7.2mm → 5mm → 3.5mm → 2.4mm → 1.6mm → 1.02mm → 1.02mm → 0.71mm → 0.49mm, i.e. by 13 cold rolling and 12 sintering.

After the multi-pass cold rolling is carried out to 30-50%, the plate is subjected to heat preservation sintering for 2 hours at the temperature of 1065 ℃ in a vacuum sintering furnace, the thickness of the plate is reduced to 0.49mm, and the density reaches 7.37g/cm³。

Vacuum sintering at 1335 deg.C for 1h to realize Si full alloying and form single-phase alloy with thickness of 0.5mm and density of 7.39g/cm³And the Si content was 6.7%.

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 0.2 percent of the total amount of the raw materials and engine oil accounting for 0.01 percent of the total amount of the raw materials are added. Anhydrous ethanol was added in an amount of 400 ml/ton.

And (3) fully mixing the powder, and keeping the pressure for 0.5h by using a soft iron sheath at the temperature of 1165 ℃ under the action of 100MPa of hot isostatic pressing to obtain a uniform and compact. The jacket was removed by machining and the billet was machined into blocks of 54X 300 mm. The compact density reaches 7.05g/cm³. The bending strength of the three-point bending test reaches 459 MPa.

And (3) cold rolling and sintering the hot isostatic pressing plate, and gradually thinning. The specific reduction-annealing system is as follows: 54mm → 36mm → 36mm → 24mm → 17mm → 12mm → 9.5mm → 7.2mm → 5mm → 3.5mm → 2.4mm → 1.6mm → 1.02mm → 1.02mm → 0.71mm → 0.49mm → 0.39mm → 0.25mm → 0.17mm → 0.13mm → 0.10mm, i.e. 20 cold rollings and 19 sinterings.

After the multi-pass cold rolling is carried out to reach the total reduction rate of 30-50%, the heat preservation sintering is carried out for 0.5h in a hydrogen protection sintering furnace at the temperature of 1165 ℃, the thickness of the plate is reduced to 0.10mm, and the density reaches 7.50g/cm³。

After sintering, a coarse grain structure containing a second phase is formed, see fig. 2. The X-ray diffraction phase is identified as heterogeneous Fe (Si) phase, as seen in figure 3, several characteristic peaks of the body-centered cubic have obvious splitting phenomena, which indicates that 2 Fe phases with different Si solid solubility exist, wherein one Fe phase has low Si content and plastic deformation capability.

Vacuum sintering at 1265 deg.C for 4 hr to realize Si full alloying and form single-phase alloy with thickness of 0.1mm and density of 7.53g/cm³And the Si content was 4.5%.

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, 0.1% of paraffin micropowder, 0.1% of methylcellulose and 0.1% of engine oil are added. Anhydrous ethanol was added in an amount of 400 ml/ton.

And (3) fully mixing the powder, and then adopting a soft iron sheath to maintain the pressure for 0.8h at the temperature of 1120 ℃ and under the action of 160MPa of hot isostatic pressing to obtain a uniform and compact. The covering was removed by machining and the blank was machined into 46X 150mm squares. The green compact density reaches 6.73-7.05 g/cm³. The bending strength of the three-point bending test reaches 289 MPa.

And (3) cold rolling and sintering the hot isostatic pressing plate, and gradually thinning. The specific reduction-annealing system is as follows: 46mm → 36mm → 24mm → 17mm → 12mm → 9.5mm → 7.2mm → 5mm → 3.5mm → 2.4mm → 1.6mm → 1.02mm → 1.02mm → 0.71mm → 0.49mm → 0.39mm → 0.27mm, i.e. 16 cold rolling passes and 15 sintering passes.

After the multi-pass cold rolling is carried out to 30-50% of total deformation, the heat preservation sintering is carried out for 1h in a nitrogen protection sintering furnace at 1120 ℃, the thickness of the plate is reduced to 0.27mm, and the density reaches 7.39g/cm³。

Vacuum sintering at 1320 deg.C for 2h to realize Si full alloying and form single-phase alloy with thickness of 0.27mm and density of 7.42g/cm³The content of Si is 6.5 percent,

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. When mixing, engine oil with the total amount of 0.2 percent of the raw materials is added. Anhydrous ethanol was added in an amount of 400 ml/ton.

And (3) fully mixing the powder, and then adopting a soft iron sheath to maintain the pressure for 1.5h at the temperature of 1160 ℃ and under the action of 150MPa of hot isostatic pressure to obtain a uniform and compact. The jacket was removed by machining and the billet was machined into 52X 200mm squares. The compact density reaches 6.87g/cm³. The bending strength of the three-point bending test reaches 298 MPa.

And (3) cold rolling and sintering the hot isostatic pressing plate, and gradually thinning. The specific reduction-annealing system is as follows: 52mm → 39mm → 26mm → 18mm → 13mm → 10.5mm → 8.2mm → 5mm → 3.2mm → 2.4mm → 2.0mm → 1.3mm → 0.90mm → 0.63 → 0.43mm → 0.32mm → 0.21 mm. I.e. 17 cold rolling passes and 16 sintering passes.

After the multi-pass cold rolling is carried out to 30-50% of total deformation, the heat preservation sintering is carried out for 1h in a hydrogen protection sintering furnace at the temperature of 1150 ℃, the thickness of the plate is reduced to 0.21mm, and the density reaches 7.45g/cm³。

Vacuum sintering at 1300 deg.C for 2h to realize Si full alloying and form single-phase alloy with thickness of 0.21mm and density of 7.41g/cm³And the Si content is 5.8 percent, and the XRD analysis chart of the final plate is shown in figure 4 and is single-phase homogeneous high-silicon steel.

Claims

1. A method for preparing a Fe-6.5% Si soft magnetic material thin strip by powder hot isostatic pressing specifically comprises the following steps:

(1) raw material powder preparation

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

(3) powder hot isostatic pressing:

adopts a soft iron sheath, and the temperature is 100 to 1165 ℃ within the temperature range of 1065 to 1165 DEG CKeeping the pressure for 0.5-2 h under the action of 200MPa of hot isostatic pressure to obtain a uniform and compact with the compact density of 6.78-7.10 g/cm³；

(4) Cold rolling-sintering

The hot isostatic pressing compact is subjected to cold rolling-sintering, gradually thinned, the single-pass reduction is less than or equal to 8%, the hot isostatic pressing compact is subjected to multi-pass rolling until the total reduction rate reaches 30-50%, then the hot isostatic pressing compact is subjected to heat preservation sintering in a sintering furnace at the temperature of 1065-1165 ℃ for 0.5-2 h, and after multiple cold rolling-sintering, the thickness of a plate reaches 0.1-0.5 mm, and the density reaches 7.32-7.45 g/cm³；

(5) Full alloying high-temperature sintering

Sintering the mixture for 1 to 4 hours in vacuum or in a reducing protective atmosphere at the temperature of 1265 to 1335 ℃, realizing Si full alloying under the action of thermal diffusion to form single-phase alloy, obtaining homogeneous Fe-6.5 percent Si soft magnetic material, wherein the thickness of the thin strip after full alloying high-temperature sintering is 0.1 to 0.5mm, and the density is 7.34 to 7.48g/cm³。

2. The process for powder hot isostatic pressing of thin strips of Fe-6.5% Si soft magnetic material according to claim 1, wherein: and (2) obtaining the high-purity ferrosilicon powder with the grain size less than or equal to 10 mu m in the step (1) by a high-energy ball milling or spinning method.

3. The process for powder hot isostatic pressing of thin strips of Fe-6.5% Si soft magnetic material according to claim 1, wherein: the powder is mixed by a low energy mixer which is a conical mixer, a V-shaped mixer or a drum mixer.

4. The process for powder hot isostatic pressing of thin strips of Fe-6.5% Si soft magnetic material according to claim 1, wherein: processing the pressed blank obtained in the step (3) into a square block with the length, the width and the thickness of 100-300 mm and 36-54 mm; the three-point bending test of the hot isostatic pressing compact shows plasticity, and the bending strength is 262-459 MPa.

5. The process for powder hot isostatic pressing of thin strips of Fe-6.5% Si soft magnetic material according to claim 1, wherein: during mixing, cellulose, paraffin micro powder or zinc stearate water-insoluble forming agent is added, the total addition amount of the forming agent is not more than 0.3 percent of the total mass of the mixed powder, grease and absolute ethyl alcohol are added to serve as passivators to passivate high-purity silicon iron powder, bond the powder and enhance the powder flowability and the green strength, and the total addition amount of the passivators is not more than 2 percent of the total mass of the mixed powder.

6. The process for powder hot isostatic pressing of thin strips of Fe-6.5% Si soft magnetic material according to claim 1, wherein: and (5) during the full-alloying high-temperature sintering, superposing the sintered plates, paving MgO powder between layers, flatly laying the plates, and placing a flat plate weight on the plates to prevent deformation in the sintering process.