CN108097967B

CN108097967B - Method for preparing Fe-6.5% Si strip by diffusion sintering and powder extrusion

Info

Publication number: CN108097967B
Application number: CN201711369193.8A
Authority: CN
Inventors: 丁艺; 罗丰华; 周立岩; 卢静; 吴子恺; 贾吉祥
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: CN108097967A

Abstract

A method for preparing Fe-6.5% Si strips through diffusion sintering and powder extrusion comprises the steps of selecting reduced Fe powder and water atomized Fe powder, mixing the reduced Fe powder and the water atomized Fe powder according to the proportion of 4: 6-6: 4, and adding high-purity silicon iron powder with the Si content of 50-70% to form Fe-4.5-6.7% Si mixed powder. Pressing the mixture into a square blank, heating the square blank to 950-1050 ℃ to realize Fe phase austenitization, extruding the square blank by using deformation heat with the extrusion ratio of 8-16, performing vacuum or reducing atmosphere protective sintering at 1060-1160 ℃, performing cold rolling and low-temperature diffusion sintering for multiple times, and finally performing vacuum or reducing atmosphere protective sintering at 1260-1320 ℃ to realize homogeneous alloying of the high-silicon steel to obtain the high-silicon steel with the thickness of 0.1-0.5 mm and the density of more than or equal to 7.41g/cm, wherein the Si content is 4.5-6.7 percent³High silicon steel strip.

Description

Method for preparing Fe-6.5% Si strip by diffusion sintering and powder extrusion

Technical Field

The invention mainly belongs to the field of preparation and processing of metal materials, and particularly relates to a method for powder metallurgy sintering, hot extrusion 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% Si thin strip by high-temperature diffusion sintering and powder extrusion, which aims at the problem that a Fe-Si alloy thin strip with the Si content of 4.5-6.7% is difficult to form, industrial pure Fe powder and high-purity silicon iron powder with the Si content of 50-70% are used as raw materials, a forming agent is added to the raw materials to be molded into an extrusion green body, a powder hot extrusion method is adopted to prepare a plate blank with a certain thickness, the large deformation effect of hot extrusion is utilized to improve the density and refine the structure of the extrusion blank, partial alloying is realized under the action of hot diffusion to form multiphase structures of Si-poor alpha-Fe crystal grains with plastic deformation capability and a brittle high-Si phase, a thin plate is obtained after multi-pass cold rolling-sintering, and finally, the high-temperature diffusion sintering is adopted to obtain a homogeneous single-phase high-silicon steel.

the method is realized by the following technical scheme that two kinds of industrial iron powder of reduced Fe powder and water atomized Fe powder are selected and mixed according to the mass ratio of 4: 6-6: 4 to form an industrial pure Fe powder base raw material, fine high-purity silicon iron powder with the Si content of 50-70% is added as a raw material to form Fe-4.5-6.7% Si mixed powder, the fine high-purity silicon iron powder is adhered to the surface of the iron powder or filled in pores of the iron powder in the mixing process through a proper adhesive and a dispersing agent, the industrial pure Fe powder occupies a larger volume ratio in the mixed powder due to the fact that the fine high-purity silicon iron powder is coarse particles with high compressibility, the plastic deformation capacity of the mixed powder is not reduced remarkably after the high-purity silicon iron powder is added, the mixed powder can be molded into a square blank through die pressing, the square blank is heated to 1050 ℃ to realize austenitization of an Fe phase, the blank is extruded by using deformation heat with the extrusion ratio of 8-16, the powder is extruded into a blank in the temperature range of 1060-1160 ℃, the vacuum or reduction atmosphere protection sintering is carried out, the metallurgical bonding of the Fe powder particles, the Si blank realizes partial alloying of the compact silicon steel, the Si, the subsequent high-alpha-deforming ability with the cold-Si, the high-fragile Si structure, the high-fragile Si diffusion, the multi-fragile structure, the multiThe alloy is processed to obtain the alloy with the thickness of 0.1-0.5 mm and the density of more than or equal to 7.41g/cm and containing 4.5-6.7 percent of Si³High silicon steel strip.

The method specifically comprises the following steps:

(1) raw material powder preparation

Adopting 100-mesh reduced iron powder, wherein Fe in the reduced Fe powder is more than or equal to 98.5 percent, and the balance is impurities such as Si, Mn, P, S and the like, adopting 100-mesh water atomized iron powder, wherein Fe in the water atomized Fe powder is more than or equal to 99.0 percent, and the balance is impurities such as Si, Mn, P, S and the like. The method comprises the steps of preparing reduced Fe powder and water atomized Fe powder according to the mass ratio of 4: 6-6: 4, mixing the reduced Fe powder and the water atomized Fe powder by adopting a conical mixer, a V-shaped mixer or a drum mixer to form an industrial pure Fe powder base raw material, wherein the mixing time is 2-6 hours, and a small amount of absolute ethyl alcohol can be added according to the ratio of 200-500 ml/ton in the mixing process.

The method comprises the steps of adopting refined high-purity ferrosilicon powder with the Si content of 50-70% and the grain size of less than or equal to 6 microns, wherein the ferrosilicon powder contains 50-70% of Si, and comprises main impurities of-0.24% of Al, 0.07% of Ca and 0.02% of C, and the balance of Fe.

The reduced iron powder is widely used industrial iron powder, has irregular porous appearance, is beneficial to storing and adhering fine silicon powder, is easy to realize mutual engagement of powder in the subsequent powder extrusion process so as to improve the strength of a pressed blank, and is beneficial to the stability of the powder extrusion process. The water atomized Fe powder is also a widely used industrial iron powder, has a nearly spherical shape, has lower impurity content than reduced Fe powder, has higher compressibility and fluidity, is beneficial to the uniform flow of powder in the powder extrusion process, and has low impurity content which is beneficial to the soft magnetic characteristic of high silicon steel. The two kinds of industrial iron powder, namely the reduced Fe powder and the water atomized Fe powder, are mixed according to the proportion of 4: 6-6: 4 to form an industrial pure Fe powder base material, so that the advantages of the two kinds of pure iron powder are brought into play, and the method is a common method for industrially producing iron-based parts.

two eutectic reactions exist in the solidification process of the Fe-50-70% Si high-purity silicon iron, and β -FeSi with a tP3 structure is formed on the Si-rich side at 1207 DEG C₂and a eutectic structure of Si phase, and beta-FeSi with a tP3 structure is formed at 1212 ℃ on the Fe-rich side₂And cP8 knotthe structure of FeSi eutectic crystal, and β -FeSi is also present at 982 ℃ and 937 DEG C₂Decomposition and oC48-FeSi₂Phase formation two solid state phase transition processes. Therefore, Fe-50-70% Si is easy to embrittle in the solidification process after refining, a fine Fe-Si or Si multiphase structure is formed, and the fine Fe-Si or Si multiphase structure is easy to refine through a mechanical crushing process. Crushing the high-purity Si iron containing Fe-50-70% of Si to obtain silicon iron powder with the grain size of less than or equal to 6 mu m, and the Si phase and FeSi in the actual tissue₂The FeSi 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, 30-50% of Fe in the high-purity silicon iron powder can effectively reduce the oxidation degree of Si, and the product quality of the high-purity silicon iron is improved.

Mechanically crushing the Fe-50-70% Si high-purity silicon iron until the grain size is less than or equal to 6 mu m, which is favorable for the Fe-50-70% 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 FeSi phase is dispersed in the blank to play a strengthening and toughening role of tissue refinement, so that the subsequent blank toughness is improved, and cracking is not easily caused in the rolling and densifying process. However, the Fe-50-70% Si high-purity ferrosilicon still contains a small amount of 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-50-70% Si high-purity silicon iron powder and the subsequent processes of material mixing, powder hot extrusion 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 superfine Fe-50-70% Si high-purity silicon iron powder according to the proportion of Fe-4.5-6.7% Si; mixing by adopting a low-energy mixer such as a conical mixer, a V-shaped mixer or a drum 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 extrusion

Preparing a square pressed blank by adopting a compression molding method, wherein the density of the pressed blank is 6.41-6.60 g/cm³(ii) a Adopting a square extrusion barrel with an extrusion ratio of 8-16, adopting a hard alloy die, using engine oil and glass powder as a lubricant, heating a die-pressed square blank to 950-1050 ℃ under the protection of nitrogen before extrusion, preserving heat for 2-4 h, preheating the extrusion barrel and the extrusion die at 400-600 ℃ for 1-2 h, performing hot extrusion, wherein the density of the hot extruded blank is 6.86-7.18 g/cm³。

(4) Sintering

And placing the hot extrusion plate on a support plate coated with MgO micropowder on the surface, and placing the support plate in a sintering furnace. Heating to 1060-1160 ℃ at a heating rate of 2-5 ℃/min, and sintering for 2-4 h in a heat preservation manner. The density of the sintered blank is 7.28-7.40 g/cm³. The density is slightly reduced compared to the density of the extruded billet.

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.

Sintering under the protection of reducing and inert gases. 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) Cold rolling-sintering densification

And (3) gradually cold rolling and sintering the sintered plate blank to reduce the thickness, wherein the single-pass reduction is less than or equal to 8%, and after the total reduction rate reaches 30-45% through multi-pass rolling, the sintered plate blank is subjected to heat preservation sintering in a sintering furnace at 1060-1160 ℃ for 0.5-2 h. After multiple cold rolling and sintering, the thickness of the plate reaches 0.1-0.5 mm, and the density reaches 7.40-7.51 g/cm³。

Due to the presence of the deformable Fe phase in the blank, the slab can withstand cold rolling deformation. However, the slab also has more high Si phase and brittle performance, so the rolling reduction of each pass cannot be higher than 8%, the accumulated total reduction rate reaches 30-45%, and about 8-20 passes are needed.

Due to the existence of the hard and brittle phase, the vacuum sintering is carried out again by heat preservation at 1060-1160 ℃ or the sintering is carried out in a reducing protective atmosphere, so that the pore closure and the crack repair generated in the cold rolling process are realized, and the Si element is uniformly diffused to a certain degree. After the accumulated reduction after each sintering reaches 30-45%, re-sintering is needed for 1 time, and the hot-extruded plate with the thickness of 2.5-5.0 mm is rolled to 0.1-0.5 mm, and re-sintering is needed for about 6-10 times.

(6) Homogenizing high-temperature sintering

Sintering the silicon alloy in vacuum or reductive protective atmosphere at 1260-1320 ℃ for 1-4 h, and realizing homogenization of Si under the action of thermal diffusion to form single-phase alloy so as to obtain the homogeneous high-silicon steel. The thickness of the densified and sintered plate is almost unchanged and is 0.1-0.5 mm, and the density is slightly reduced to 7.42-7.46 g/cm³。

And (2) adding anhydrous ethanol according to the proportion of 200-500 ml/ton in the mixing process in the step (1).

The ferrosilicon powder with the grain diameter less than or equal to 6 mu m is obtained by a high-energy ball milling or impact spinning method.

And (3) adding cellulose, paraffin micro powder or a zinc stearate water-insoluble 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-Si iron powder, bond Fe-Si powder and enhance 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.

In the step (3), a square extrusion container with the thickness of 40mm multiplied by 120mm is adopted, an extrusion die is 5-2.5 mm multiplied by 120mm, and the corresponding extrusion ratios are 8-16 respectively; a hard alloy die is adopted, engine oil and glass powder are used as lubricants, a 300-ton press is adopted for hot extrusion, and three-point bending test shows plasticity of 178-340 MPa.

And (4) adopting corundum or zirconia ceramic plates as the supporting plates.

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 Fe-4.5-6.7% Si mixed powder is formed by adding Fe-50-70% Si high-purity powder with the grain size less than or equal to 6 mu m into industrial pure Fe powder with good plasticity and large volume proportion. And hot extrusion is adopted to obtain a high-density and high-uniformity plate blank. The slab has low Si element alloying degree, the microstructure of the slab consists of a high-plasticity Fe phase and a brittle Si-rich phase, the slab has high cold deformation capacity, the uniformity and compactness of the structure can be 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 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 7.41g/cm³High silicon steel strip.

Drawings

FIG. 1 is a three-point bend plot of the powder extruded billet of example 1 of the present invention;

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

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

FIG. 4 is a XRD diffraction pattern after powder extrusion-cold rolling-high temperature sintering of 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

Preparing reduced Fe powder of-100 meshes and water atomized Fe powder of-100 meshes according to the proportion of 4:6, mixing by adopting a drum mixer to form an industrial pure Fe powder raw material, wherein the mixing time is 2 hours, and adding absolute ethyl alcohol according to the proportion of 200 ml/ton in the mixing process.

Mixing the premixed industrial pure Fe powder and Fe-70% Si high-purity powder with the particle size less than or equal to 6 mu m according to the proportion of 90.43:9.57 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.

The square pressed blank is prepared by adopting a compression molding method, the length and the width of the pressed blank are respectively 120mm and 80mm, the height of the pressed blank is 40mm, the pressed blank is pressed by adopting the pressure with the surface pressure of 600MPa, and the total output pressure of a press is 576 tons. The green density obtained was 6.41g/cm³。

Square extrusion cylinders of 40 × 120mm are used, the extrusion dies are respectively of 5 × 120mm, and the corresponding extrusion ratio is 8. Heating the molded square billet to 950 ℃ under the protection of nitrogen before extrusion, and preserving heat for 4 hours. Preheating the extrusion cylinder and the extrusion die at 600 ℃ and keeping the temperature for 2 hours. The hot extrusion is carried out by adopting a 300 ton press, and the density of the plate blank after the hot extrusion is 6.86g/cm³The three-point bending test shows plasticity, which is shown in figure 1, and the bending strength is 178 MPa.

Heating to 1060 ℃ at a heating rate of 2 ℃/min, and sintering for 2 h. The density of the sintered compact was 7.28g/cm³. After sintering, a coarse grain structure containing a second phase is formed.

And (3) gradually cold rolling and sintering the sintered plate blank to reduce the thickness, wherein the single-pass reduction is less than or equal to 8%, and after the total reduction rate reaches 30-45% through multi-pass rolling, the sintered plate blank is subjected to heat preservation sintering for 2 hours at 1060 ℃ in a sintering furnace. The specific reduction-annealing system is as follows: 5mm → 3.5mm → 2.4mm → 1.6mm → 1.02mm → 0.71mm → 0.49mm, namely after 6 times of cold rolling and 5 times of sintering, the thickness of the plate reaches 0.49mm, and the density reaches 7.40g/cm³。

And finally, sintering the mixture in vacuum at the temperature of 1320 ℃ for 1h, realizing the homogenization of Si under the action of thermal diffusion, forming single-phase alloy, and obtaining the homogeneous high-silicon steel. The thickness of the densified and sintered plate is almost unchanged and is 0.49mm, and the density reaches 7.41g/cm³。

Example 2

Preparing reduced Fe powder of 100 meshes and water atomized Fe powder of 100 meshes according to the proportion of 5:6, mixing by a drum mixer to form an industrial pure Fe powder raw material, wherein the mixing time is 3h, and absolute ethyl alcohol is added according to the proportion of 400 ml/ton in the mixing process.

Mixing the premixed industrial pure Fe powder with Fe-50% Si high-purity powder with the particle size less than or equal to 10 mu m according to the proportion of 91:9 to form Fe-4.5% Si mixed powder. 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.

The square pressed blank is prepared by adopting a compression molding method, the length and the width of the pressed blank are respectively 120mm and 80mm, the height of the pressed blank is 40mm, the pressed blank is pressed by adopting the pressure with the surface pressure of 600MPa, and the total output pressure of a press is 576 tons. The green compact obtained had a density of 6.60g/cm³。

A square extrusion cylinder of 40X 120mm was used, the die was 2.5X 120mm, corresponding to an extrusion ratio of 16. Heating the die-pressing square billet to 1050 ℃ under the protection of nitrogen before extrusion, and preserving heat for 2 hours. Preheating the extrusion cylinder and the extrusion die at 600 ℃ and keeping the temperature for 2 hours. The hot extrusion is carried out by adopting a 300 ton press, and the density of the plate blank after the hot extrusion is 7.18g/cm³The three-point bending test shows plasticity, and the bending strength is 340 MPa.

Heating to 1160 ℃ at the heating rate of 2 ℃/min, and sintering for 2 h. The density of the sintered compact was 7.40g/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.

And (3) gradually cold rolling and sintering the sintered plate blank to reduce the thickness, wherein the single-pass reduction is less than or equal to 8%, and after the total reduction rate reaches 30-45% through multi-pass rolling, carrying out heat preservation and sintering in a sintering furnace at 1160 ℃ for 0.5 h. After multiple cold rolling and sintering, the thickness of the plate reaches 0.1mm, and the density reaches 7.43g/cm³. The specific cold rolling-sintering system is as follows: 2.5mm → 1.85mm → 1.39mm → 1.15mm → 0.89mm → 0.65mm → 0.39mm → 0.25mm → 0.17mm→ 0.13mm → 0.10mm, i.e. after 10 times of cold rolling and 9 times of sintering, the thickness of the plate reaches 0.10mm and the density reaches 7.51g/cm³。

Finally, vacuum sintering is carried out for 4 hours at the temperature of 1260 ℃, and single-phase homogeneous high silicon steel with the Si content of 4.5 percent is formed, the thickness is 0.1mm, and the density reaches 7.52g/cm³。

Example 3

Preparing reduced Fe powder of-100 meshes and water atomized Fe powder of-100 meshes according to the proportion of 6:4, mixing by adopting a drum mixer to form an industrial pure Fe powder raw material, wherein the mixing time is 4h, and adding absolute ethyl alcohol according to the proportion of 500 ml/ton in the mixing process.

Mixing the premixed industrial pure Fe powder and Fe-60% Si high-purity powder with the particle size less than or equal to 6 mu m according to the proportion of 89.17:10.83 to form Fe-6.5% Si mixed powder. 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.

The square pressed blank is prepared by adopting a compression molding method, the length and the width of the pressed blank are respectively 120mm and 80mm, the height of the pressed blank is 40mm, the pressed blank is pressed by adopting the pressure with the surface pressure of 600MPa, and the total output pressure of a press is 576 tons. The green density obtained was 6.44g/cm³。

A square extrusion cylinder of 40X 120mm was used, the die was 4X 120mm, and the extrusion ratio was 10. Heating the die-pressed square billet to 1000 ℃ under the protection of nitrogen before extrusion, and preserving heat for 3 hours. Preheating the extrusion cylinder and the extrusion die at 600 ℃ and keeping the temperature for 2 hours. The hot extrusion is carried out by adopting a 300 ton press, and the density of the plate blank after the hot extrusion is 6.89g/cm³The flexural strength was 210 MPa.

Heating to 1150 ℃ at a heating rate of 3 ℃/min, and sintering for 2 h. The density of the sintered compact was 7.30g/cm³。

The sintered plate blank is gradually cold rolled-sintered to be thinned, and the specific cold rolling-sintering system is as follows: 4.0mm → 2.8mm → 2.0mm → 1.40mm → 1.08mm → 0.70mm → 0.45mm → 0.27mm, namely after 7 times of cold rolling and 6 times of sintering, the thickness of the plate reaches 0.27mm, and the density reaches 7.41g/cm³。

Vacuum sintering the cold rolled strip at 1280 deg.C for 2h to obtain a product with a thickness of about 0.27mm and a density of 7.42g/cm³And the single-phase homogeneous high-silicon steel with the Si content of 6.5 percent.

Example 4

Preparing reduced Fe powder of-100 meshes and water atomized Fe powder of-100 meshes according to the proportion of 5:5, mixing by adopting a drum mixer to form an industrial pure Fe powder raw material, wherein the mixing time is 6h, and adding absolute ethyl alcohol according to the proportion of 500 ml/ton in the mixing process.

Mixing the premixed industrial pure Fe powder and Fe-62% Si high-purity powder with the grain size less than or equal to 10 mu m according to the proportion of 90.64:9.36 to form Fe-5.8% Si mixed powder. 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.

The square pressed blank is prepared by adopting a compression molding method, the length and the width of the pressed blank are respectively 120mm and 80mm, the height of the pressed blank is 40mm, the pressed blank is pressed by adopting the pressure with the surface pressure of 600MPa, and the total output pressure of a press is 576 tons. The green density obtained was 6.46g/cm³。

Square extrusion cylinders of 40 × 120mm are used, the extrusion dies are 3.2 × 120mm respectively, and the corresponding extrusion ratio is 12.5. Heating the die-pressing square billet to 1020 ℃ under the protection of nitrogen before extrusion, and preserving heat for 4 hours. Preheating the extrusion cylinder and the extrusion die at 600 ℃ and keeping the temperature for 2 hours. The hot extrusion is carried out by adopting a 300-ton press, and the density of the plate blank after the hot extrusion is 6.90g/cm³The flexural strength was 223 MPa.

Heating to 1120 ℃ at a heating rate of 4 ℃/min, and carrying out heat preservation sintering for 2 h. The density of the sintered compact was 7.29g/cm³。

And (3) gradually cold rolling and sintering the sintered plate blank to reduce the thickness, wherein the single-pass reduction is less than or equal to 8%, and after the total reduction rate reaches 30-45% through multi-pass rolling, the sintered plate blank is subjected to heat preservation sintering for 1h at 1120 ℃ in a sintering furnace. After multiple cold rolling and sintering, the thickness of the plate reaches 0.22mm, and the density reaches 7.43g/cm³. The specific cold rolling-sintering system is as follows: 3.2mm → 2.4mm → 2.0mm → 1.3mm → 0.96mm → 0.72mm → 0.46mm → 0.32mm → 0.21mm, that is, after 9 times of cold rolling and 8 times of sintering, the thickness of the plate reaches 0.21mm, density of 7.42g/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 7.43g/cm³And the Si content is 5.8 percent, and the XRD analysis chart of the final plate is shown in figure 3 and is single-phase homogeneous high-silicon steel.

Claims

1. A method for preparing Fe-6.5% Si strip by diffusion sintering and powder extrusion is characterized by comprising the following steps:

(1) raw material powder preparation

Adopting 100-mesh reduced iron powder, wherein Fe in the reduced Fe powder is more than or equal to 98.5 percent, and the balance of Si, Mn, P, S and other inevitable impurities, adopting 100-mesh water atomized iron powder, wherein Fe in the water atomized Fe powder is more than or equal to 99.0 percent, and the balance of Si, Mn, P, S and other inevitable impurities, preparing the reduced Fe powder and the water atomized Fe powder according to the mass ratio of 4: 6-6: 4, and mixing by adopting a conical mixer, a V-shaped mixer or a drum mixer to form an industrial pure Fe powder basic raw material for 2-6 h;

adopting refined high-purity silicon iron powder with the Si content of 50-70%, wherein the grain size is less than or equal to 6 mu m, the main impurities of the high-purity silicon iron powder are-0.24% of Al, -0.07% of Ca and-0.02% of C, and the balance is Fe;

(2) powder mixing

Weighing an industrial pure Fe powder base raw material and Fe-50-70% Si high-purity silicon iron powder according to the proportion of Fe-6.5% Si; mixing by adopting a conical mixer, a V-shaped mixer or a drum mixer under inert protective atmosphere;

(3) powder extrusion

Preparing a square pressed blank by adopting a compression molding method, wherein the density of the pressed blank is 6.41-6.60 g/cm³(ii) a Adopting a square extrusion barrel with an extrusion ratio of 8-16, adopting a hard alloy die, using engine oil and glass powder as a lubricant, heating a die-pressed square blank to 950-1050 ℃ under the protection of nitrogen before extrusion, preserving heat for 2-4 h, preheating the extrusion barrel and the extrusion die at 400-600 ℃ for 1-2 h, performing hot extrusion, wherein the density of the hot extruded blank is 6.86-7.18 g/cm³；

(4) Sintering

Placing the hot extruded slabPlacing the support plate on a support plate coated with MgO micropowder on the surface, placing the support plate in a sintering furnace, heating to 1060-1160 ℃ at a heating rate of 2-5 ℃/min, and carrying out heat preservation sintering for 2-4 h, wherein the density of a sintered plate blank is 7.28-7.40 g/cm³；

(5) Cold rolling-sintering densification:

gradually cold rolling and sintering the sintered plate blank to reduce the thickness, wherein the single-pass reduction is less than or equal to 8 percent, the plate blank is subjected to multi-pass rolling until the total reduction rate reaches 30-45 percent, then the plate blank is subjected to heat preservation sintering at 1060-1160 ℃ in a sintering furnace for 0.5-2 h, and after multiple cold rolling and sintering, the thickness of the plate blank reaches 0.1-0.5 mm, and the density reaches 7.40-7.51 g/cm³；

(6) And (3) homogenizing and high-temperature sintering:

sintering the plate material in vacuum or reducing protective atmosphere at 1260-1320 ℃ for 1-4 h, homogenizing Si under the action of thermal diffusion to form single-phase alloy, obtaining a homogenized Fe-6.5% Si strip, wherein the thickness of the strip after homogenizing high-temperature sintering is 0.1-0.5 mm, and the density reaches 7.41-7.52 g/cm³。

2. The method of diffusion sintering and powder extrusion of Fe-6.5% Si strip as claimed in claim 1 wherein: and (2) adding anhydrous ethanol according to the proportion of 200-500 ml/ton in the mixing process in the step (1).

3. The method of diffusion sintering and powder extrusion of Fe-6.5% Si strip as claimed in claim 2 wherein: the high-purity silicon iron powder with the grain size less than or equal to 6 mu m is obtained by a high-energy ball milling or impact spinning method.

4. The method of diffusion sintering and powder extrusion of Fe-6.5% Si strip as claimed in claim 2 wherein: and (3) adding cellulose, paraffin micro powder or zinc stearate water-insoluble forming agent when mixing in the step (2), wherein the total adding 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 adding amount of the passivators is not more than 2 percent of the total mass of the mixed powder.

5. The method of diffusion sintering and powder extrusion of Fe-6.5% Si strip as claimed in claim 1 wherein: in the step (3), a square extrusion container of 40mm multiplied by 120mm is adopted, an extrusion die is 5-2.5 mm multiplied by 120mm, and the corresponding extrusion ratio is 8-16; and (3) carrying out hot extrusion by adopting a 300-ton press, wherein the three-point bending test of the hot extruded plate blank shows plasticity, and the bending strength is 178-340 MPa.

6. The method of diffusion sintering and powder extrusion of Fe-6.5% Si strip as claimed in claim 1 wherein: and (4) adopting a molybdenum plate, a W plate, a heat-resistant steel plate, a corundum plate or a zirconia ceramic plate as the supporting plate.

7. The method of diffusion sintering and powder extrusion of Fe-6.5% Si strip as claimed in claim 1 wherein: and (6) during high-temperature sintering, plates are stacked, MgO powder is laid between layers, the plates are laid flatly, and flat plate weights are placed on the plates to prevent deformation in the sintering process.