CN107900355A - A kind of method that powder warm-rolling prepares high silicon steel thin belt material - Google Patents

Abstract

A method for preparing high-silicon steel thin strips by powder warm rolling. The invention adopts reduced Fe powder and high-purity ferrosilicon powder with a Si content of 50-70% to form Fe-4.5-6.7% Si mixed powder, and the powder The warm-rolled slab is sintered in a vacuum or reducing atmosphere at a temperature range of 1050-1150°C, so that the Fe powder particles are incompletely sintered, and Si and Fe are partially alloyed to form a porous, compressible incompletely alloyed slab. High silicon steel billets. Subsequent cold rolling, incomplete sintering, and finally sintering under vacuum or reducing atmosphere protection in the temperature range of 1255-1330 ° C, with the help of thermal diffusion, the homogeneous alloying of high-silicon steel is achieved, and 4.5-6.7% Si is obtained. High-silicon steel strip with a thickness of 0.1-0.5mm and a density of 7.34-7.44g/ ^cm3 .

Description

A method for preparing high-silicon steel thin strips by powder warm rolling

technical field

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

technical background

The remanence and coercivity of soft magnetic materials are very small, that is, the hysteresis loop is very narrow, which almost coincides with the basic magnetization curve, and is mainly used in the cores of inductance coils, transformers, relays and motors. The maximum magnetic permeability of Fe-Si alloy changes with Si content, and two peaks of maximum magnetic permeability appear around 2% and 6.5% of Si mass percentage (the same below), reaching 10000 and 25000 respectively. The maximum magnetic permeability of Fe-Si alloy has no absolute advantage in soft magnetic materials. For example, the maximum magnetic permeability of permalloy can reach 200,000. However, the production cost of Fe-Si alloy sheet with Si<4.5% is low, so silicon steel sheet is also called electrical steel sheet or silicon steel sheet, which is a very important magnetic material.

When Si>4.5%, Fe-Si alloy will undergo eutectoid decomposition reaction of B ₂ ordered phase below 540°C, forming α-Fe disordered phase and DO ₃ ordered phase, making the alloy brittle and difficult to deform .

For iron-silicon alloys with a Si content between 4.5 and 6.7%, they are generally called high-silicon steels, and high-silicon steels with a silicon content of 6.5% are the most important. The reason is that the magnetostriction coefficient of the Fe-Si alloy grain along the <100> direction decreases with the increase of Si content, and basically disappears at about 6.3%, while the magnetostriction coefficient of the <111> direction decreases with the increase of Si content. Increased, equal to the magnetostriction coefficient in the <100> direction at about 6.1%, making high silicon steel exhibit excellent low iron loss characteristics when working at higher frequencies.

A transformer in normal operation will produce a continuous and uniform "humming" sound. This is due to the fact that when the AC current passes through the transformer winding, a periodically changing alternating magnetic flux is generated in the middle of the iron core, causing the iron core to magnetostrict and vibrate. sound. The sound emitted by a large number of or large iron cores during vibration not only causes energy loss, but also causes noise pollution. Especially in military aerospace fields such as spacecraft, submarines and missiles, Fe-Si alloys play an extremely important role. In the late 1960s, an alloy with a Si content of 6.5% appeared as a transformer material on the Apollo 11 spacecraft, completing the feat of man's first moon landing. It can be seen that high silicon steel is an environmentally friendly soft magnetic material with excellent performance in reducing consumption and noise.

Compared with other alloys, the research and development process of high silicon steel is relatively long. In the late 1920s, A. Schulze firstly found that the iron-silicon alloy with a silicon content of 6.5% has almost zero magnetostriction coefficient. In the 1980s, Professor K.I.Arail and others discovered that high-silicon steel has lower iron loss and higher magnetic permeability in AC dynamic magnetic field than traditional alloys with low Si content. In the following decades, in order to overcome the brittleness of high silicon steel, many attempts have been made in the preparation technology. Such as special rolling method of sheathing or temperature control, rapid solidification method, chemical vapor deposition method (CVD method), plasma chemical vapor deposition method (PCVD method), hot dip infiltration-diffusion annealing method, powder metallurgy method, trace alloy Various methods such as chemical modification.

Among them, CVD is a more successful example. In 1988, Japan's NKK company used CVD technology to produce non-oriented 6.5% Si steel sheets with a thickness of 0.1-0.5mm and a width of 400mm for the first time. In the early 1990s, the world's first commercial CVD production line capable of continuous silicon infiltration was developed, and the product size can reach 0.1-0.3mm×600mm.

The principle of CVD is: under certain temperature conditions, silicon-containing gas (SiCl ₄ ) will react with silicon steel strip to form Fe-Si compound, and then diffuse into the alloy with the help of elevated furnace temperature, and finally make the alloy reach the required content. Although this technology has been used to achieve small-scale industrial production, its scale and output are far from meeting the needs of the international soft magnetic material market, and this preparation method is very complicated in process, high in energy consumption and cost, and the working environment is not good. It is harsh and cannot meet environmental protection requirements.

High-silicon steel is a "steel art", and its preparation technology is always the most advanced steel manufacturing technology, and it is a hot spot in research and development. For 6.5%Si high-silicon steel, its excellent magnetic properties and broad application prospects attract scientific and technological workers to do a lot of research and development work. The development and maturity of the preparation process and the economical and effective production are the key to the commercialization and wide application of 6.5% Si high-silicon steel, and have always been the focus of research work. Once a simple, economical, effective and mature preparation process is found out, it will produce huge economic and social benefits.

Contents of the invention

The purpose of the present invention is to provide a method for preparing high-silicon steel thin strips by powder warm rolling, aiming at the problem that Fe-Si alloy thin strips with a Si content of 4.5 to 6.7% are difficult to form, the reduced iron powder and Si content are 50 ~ 70% of high-purity ferrosilicon powder is used as raw material, and composite forming agent is added to form a powder mixture suitable for warm rolling deformation, and then a slab of a certain thickness is prepared by powder warm rolling method, and a porous, non-porous slab is formed after degreasing and sintering Homogeneous billets, thin plates are obtained after multi-pass cold rolling-sintering, and finally high-temperature diffusion sintering is used to obtain homogeneous high-silicon steel strips.

The invention is realized through the following technical solutions: using reduced Fe powder with irregular shape and fine high-purity ferrosilicon powder with Si content of 50-70%, to form Fe-4.5-6.7% Si mixed powder. The composite forming agent is used to adhere the high-purity ferrosilicon powder to the surface of the reduced iron powder or to fill the pores of the iron powder during the mixing process. Since the reduced Fe powder is a coarse particle with high compressibility, which occupies a relatively large volume ratio in the mixed powder, adding fine high-purity ferrosilicon powder with a Si content of 50-70% will not significantly reduce its deformability. Taking advantage of the technical advantages of warm rolling forming, powder warm rolling forming is carried out at 125-150°C to prepare slabs with high density and uniform structure distribution. The powder warm-rolled slab is sintered in a vacuum or reducing atmosphere at a temperature range of 1050-1150°C, so that the Fe powder particles are incompletely sintered, and Si and Fe are partially alloyed to form a porous and compressible incomplete alloy. Chemicalized high-silicon steel blanks. After repeated cold rolling and incomplete sintering, the density of the slab increased, the thickness of the slab decreased, and the degree of alloying of Si also continued to increase. Finally, protect and sinter in vacuum or reducing atmosphere in the temperature range of 1255-1330°C, and realize the homogeneous alloying of high-silicon steel with the help of thermal diffusion, and obtain a 0.1-0.5mm thick steel containing 4.5-6.7% Si, and a density of 7.34-7.44g /cm ³ high silicon steel strip.

The inventive method specifically comprises the steps:

(1) Raw material powder preparation

-100 mesh reduced iron powder is used, Fe in the reduced iron powder is ≥ 98.5%, the rest is Si, Mn, P, S and other unavoidable impurities, and the refined high-purity ferrosilicon powder with Si content of 50-70% is used. Particle size ≤ 6μm, this ferrosilicon powder contains 50-70% Si, the main impurities are ~0.24% Al, ~0.07% Ca and ~0.02% C, and the rest is Fe.

Reduced iron powder is a widely used industrial iron powder. It has irregular porous morphology, which is conducive to storage and adhesion of fine high-purity ferrosilicon powder, and it is also easy to achieve interlocking of powder in the subsequent powder warm rolling process to improve the pressure. The strength of the billet is conducive to the stability of the powder warm rolling process.

There are two eutectic reactions in the solidification process of Fe-50～70% Si high-purity ferrosilicon. On the Si-rich side at 1207 ° C, β-FeSi ₂ and Si phase eutectic structure with tP3 structure are formed. On the Fe-rich side On one side, β-FeSi ₂ with tP3 structure and FeSi eutectic structure with cP8 structure are formed at 1212°C; at 982°C and 937°C, there are also two solid states, the decomposition of β-FeSi ₂ and the formation of oC48-FeSi _{2 phase} phase change process. Therefore, Fe-50-70% Si is easy to become brittle during the solidification process after refining, forming a fine Fe-Si or Si multi-phase structure, which is easily refined by mechanical crushing process. Fe-50～70%Si high-purity ferrosilicon is crushed to ≤6μm ferrosilicon powder, the Si phase, FeSi ₂ , and FeSi phase in the actual structure are finer, which is conducive to the homogenization of thermal diffusion of Si element during subsequent high-temperature sintering , forming a homogeneous Fe-6.5% Si single-phase alloy. At the same time, 30-50% Fe in the high-purity ferrosilicon powder can effectively reduce the oxidation degree of Si, which is beneficial to improve the product quality of high-silicon steel.

Mechanically crush Fe-50-70% Si high-purity ferrosilicon to particle size ≤ 6 μm, which is conducive to its adhesion on the surface of reduced Fe powder or filling in the pores of reduced Fe powder, and the fine Si, FeSi ₂ , FeSi phase Dispersed in the billet, it plays the role of strengthening and toughening the microstructure, which is conducive to improving the toughness of the subsequent billet, and is not easy to cause cracking during the rolling and densification process. However, Fe-50-70% Si high-purity ferrosilicon still contains a small amount of Si phase, Si is easy to absorb oxygen, and _SiO2 film is formed on the exposed Si phase surface, so in Fe-50-70% Si high-purity ferrosilicon powder Inert gas protection should be used in the process of preparation, storage and transfer, as well as in the subsequent mixing and rolling process, and the tools used must also be dehydrated and dried in advance.

Under the premise of controlling the oxygen content, impurities such as Al, Ca, and Mn have little effect on the magnetic properties of the alloy, and the possibility of introducing other alloy elements in the process is not great.

(2) Powder mixing

According to the proportion of Fe-4.5-6.7% Si, weigh the reduced Fe powder and Fe-50-70% Si high-purity ferrosilicon powder; use a low-energy mixer under an inert protective atmosphere to mix. When mixing, add 0.4-0.6% lubricant of the total amount of powder.

The powder warm rolling process can reduce the internal friction during the powder deformation process, improve the density and density of the powder compact, and the uniformity of the structure, and reduce the friction and wear of the tool and die. Lubricant is the key to the success of the process. The principle of lubricant selection should meet the glass transition temperature of about 120-150 ℃, low friction coefficient and other conditions. There are many commonly used powder temperature deformation forming agents.

(3) Warm powder rolling

Using a two-roller horizontal rolling mill and an inclined feeding trough, using the self-weight of the powder and the friction between the roll and the powder to feed, the rolled thickness is 1.2-2.3mm, the width is 100-200mm, and the density is 6.1-6.5g/cm ³ powder warm rolled slabs. Before rolling, use a powder heating device to heat the mixed powder to 125-150°C, and preheat the roll to the same temperature.

According to the different rolling direction of the strip, the powder warm rolling can be divided into three types: vertical, horizontal and inclined. The feeding methods include self-weight feeding, forced feeding, and pre-adhesive feeding. The width of the blank is related to the width of the feeding trough, and the length of the blank depends on the production conditions and actual needs.

(4) Degreasing and sintering

The powder compact is placed on a support plate coated with MgO micropowder, and placed in a vacuum degreasing and sintering furnace. Use a heating rate of 2-5°C/min, and keep warm at 200°C and 400°C for 2h-4h respectively. Then heat up to 1050-1150°C for 2-4 hours for sintering. The density of the sintered body is 6.15-6.55g/cm ³ .

After sintering, a uniform equiaxed grain structure is formed, the matrix grains are about 70-100 μm, and there are pores of about 10 μm in the grain boundary, which can be closed by subsequent rolling and sintering. Only a small amount of ~2μm second phase remains in the matrix tissue, which has a good interface with the matrix tissue, that is, there is no split surface. Obviously these second phases are some kind of Si-rich phase, the existence of these Si-rich phases reduces the Si content of the matrix tissue, making the matrix tissue have high plastic deformation ability; at the same time, it has a good interface bonding and dispersion distribution with the matrix tissue It is beneficial to the subsequent homogenization and diffusion.

If the sintering temperature is too low, it is not conducive to the connection between Fe powder particles and the diffusion of Si atoms, while if the sintering temperature is too high, due to the surface diffusion of Fe and Si elements, coarse pores will appear, which will make it difficult to press later, and the rolling densification will be difficult to achieve.

During sintering, the powder warm-rolled billet can be placed in multiple layers, but the layers must be separated to avoid cracking caused by the shrinkage of the slab during sintering. During sintering, the heating rate should not be too fast, and multi-stage heat preservation can be set during the heating process to achieve degassing and degreasing. Reducing or inert gas protection degreasing and sintering can also be used. During sintering, W, Mo, heat-resistant steel, etc. can be used as support plates (or called sintering boats), and ceramic plates such as corundum and zirconia can also be used, but metal plates have good thermal conductivity and are conducive to uniform sintering shrinkage.

(5) Cold rolling - sintering densification

The above-mentioned sintered slab is cold-rolled and thinned, and the reduction in a single pass is ≤8%, and after multi-pass rolling until the total reduction reaches 30-50%, it is re-sintered in a sintering furnace at 1050-1150°C 0.5～2h. After repeated cold rolling and sintering, the thickness of the sheet material reaches 0.1-0.5 mm, and the density reaches 7.33-7.43 g/cm ³ .

Due to the porous structure of the powder billet and the presence of deformable Fe phase, the slab can withstand cold rolling deformation. However, there are also many high-Si phases in the slab, and its performance is relatively brittle, so the reduction in each pass cannot be higher than 8%, and the cumulative total reduction rate reaches 30-50%. It takes about 8-20 passes.

Due to the existence of a large number of pores and hard and brittle phases, when resintering at 1050 ° C to 1150 ° C, it is sintered in a vacuum or reducing protective atmosphere to achieve pore closure and crack repair, as well as a certain degree of homogeneous diffusion of Si elements. At this time, the heating speed can be faster, and the temperature can be continuously raised at 5-10°C/min. The holding time depends on the thickness of the plate. When the plate thickness is ≥ 1mm, the holding time is 1-2h; To 0.5 ~ 1h. After the cumulative reduction after each sintering reaches 30-50%, it needs to be re-sintered once, and it needs about 4-8 times of re-sintering to roll from the powder billet of 1.2-2.3mm to 0.1-0.5mm. In addition, more than 4 times of re-sintering are also required in order to make the density of the board more than 7.2 g/cm ³ (about 95% of the theoretical density).

After two times of cold rolling and sintering, the matrix has a grain structure of about 100 μm, and there are a small amount of fine pores. The matrix grains have two different contrasts. This is due to the difference in corrosion caused by the different Si content. The low Si grains in this structure are conducive to processing deformation, making it possible to manufacture thin plates of 0.1-0.5mm.

(6) Homogenized high temperature sintering

Finally, sinter in vacuum or reducing protective atmosphere for 1-4 hours in the temperature range of 1255-1330°C. Under the action of thermal diffusion, the homogenization of Si is realized, a single-phase alloy is formed, and a homogeneous high-silicon steel is obtained. After densification and sintering, the thickness of the sheet material is almost unchanged, ranging from 0.1 to 0.5 mm, and the density reaches 7.34 to 7.44 g/cm ³ .

The high-purity ferrosilicon powder with a particle size of ≤6 μm is obtained by high-energy ball milling or spinning.

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

Step (2) when mixing, add a lubricant with a total powder mass of 0.4% to 0.6%, and add 0.1% glycerin with a total powder mass at the same time. The lubricant is a composite lubricant composed of zinc stearate and vinyl distearate Amide composition, zinc stearate: EBS ratio of 4:6 to 2:8, using absolute ethanol as solvent, adding 400 to 600ml per ton of mixed powder.

The support plate described in step (4) adopts molybdenum plate, W plate, heat-resistant steel, corundum or zirconia ceramic plate.

During high-temperature sintering, sintered plates can be stacked, but MgO powder must be laid between layers, and W, Mo and ceramic firing boats can be used. However, the sheet must be placed flat, and a flat weight can be placed on the sheet to prevent deformation during sintering.

In addition to the Si content, the magnetic properties of high-silicon steel will also have a greater impact on the grain size, grain orientation, and the content of elements such as C, which can be controlled by technical means such as wet hydrogen annealing and normalization treatment.

The essence of the present invention is to form a composite material capable of powder warm rolling by adding Fe-50-70% Si high-purity powder with a particle size of ≤6 μm to the reduced Fe powder with good plasticity and large volume ratio; Roll forming produces a slab with high density and uniform structure distribution; through incomplete sintering, the Fe powder particles are incompletely connected, and Si and Fe are partially alloyed to form a porous, compressible incomplete alloyed High-silicon steel blanks; followed by multi-pass cold rolling and sintering to improve the uniformity and compactness of the structure; and then through the high-temperature diffusion process to achieve Si homogenization, thereby obtaining high-quality high-silicon steel strips. The method realizes process automation and continuous production through process and equipment design, and can mass-produce high-silicon steel strips with a thickness of 0.1-0.5 mm and a density of 7.34-7.44 g/cm ³ .

Description of drawings

Fig. 1 is the metallographic diagram after the sintering of the powder warm rolling billet of embodiment 2 of the present invention;

Fig. 2 is the metallographic diagram of the sheet metal of embodiment 3 of the present invention after 2 times of cold rolling-sintering;

Fig. 3 is an XRD diffraction curve of the powder warm-rolled slab of Example 4 of the present invention after high-temperature sintering.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

Mix -100 mesh reduced Fe powder with Fe-70% Si high-purity powder with a particle size of ≤6 μm in a ratio of 90.43:9.57 to form Fe-6.7% Si mixed powder. When mixing, add a total amount of 0.4% composite lubricant and 0.1% glycerin to reduce the oxidation of the powder during heating, and use absolute ethanol as a solvent, adding in an amount of 500ml/ton. The composite lubricant is composed of zinc stearate and EBS, and the ratio of zinc stearate:EBS is 2:8. The above powders were mixed for 4 h using a V-shaped blender.

The mixed powder is heated to 140°C with a powder heating device, and the roll is preheated to the same temperature. Using a two-roller horizontal rolling mill and an inclined feeding trough, using the powder's own weight and the friction between the roll and the powder to feed, a 2.3mm powder warm-rolled slab is rolled out, and the width of the slab is 100mm. The density of the compact was 6.1 g/cm ³ .

The powder compact is placed on a molybdenum plate coated with MgO micropowder, and placed in a vacuum degreasing and sintering furnace. Adopt a heating rate of 2°C/min, and keep warm at 200°C and 400°C for 4 hours respectively. Then heat up to 1050°C for 4 hours for sintering. The density of the sintered compact was 6.15 g/cm ³ .

The above-mentioned sintered slab is cold-rolled and thinned, and the reduction in a single pass is ≤8%, and after multi-pass rolling until the total reduction rate reaches 30-50%, it is then sintered in a vacuum sintering furnace at 1050°C . The temperature is continuously raised at a rate of 5°C/min, and the holding time is determined by the thickness of the plate. When the plate thickness is ≥1mm, the holding time is 2h; when the plate thickness is 0.1-1mm, the holding time is 1h. The specific pressing-annealing system is: 2.3mm→1.56mm→1.02mm→0.71mm→0.49mm, that is, after 4 times of cold rolling and 3 times of sintering, the thickness of the sheet material reaches 0.50mm, and the density reaches 7.33g/cm ³ .

The above cold-rolled strip was vacuum sintered at 1330° C. for 1 hour to obtain a single-phase homogeneous high-silicon steel with a thickness of about 0.50 mm, a density of 7.34 g/cm ³ , and a Si content of 6.7%.

Example 2

Mix -100 mesh reduced Fe powder with Fe-50% Si high-purity powder with a particle size of ≤10 μm in a ratio of 91:9 to form Fe-4.5% Si mixed powder. When mixing, add a total amount of 0.5% composite lubricant, and 0.1% glycerin to reduce the oxidation of the powder heating process, using absolute ethanol as a solvent, adding according to the amount of 500ml/ton. The composite lubricant is composed of zinc stearate and EBS, and the ratio of zinc stearate:EBS is 4:6. The above powders were mixed for 6 h using a drum mixer.

The mixed powder is heated to 125°C with a powder heating device, and the roll is preheated to the same temperature. Using a two-roller horizontal rolling mill and an inclined feeding trough, the powder is fed by the weight of the powder and the friction between the roll and the powder, and a 1.2mm powder warm-rolled slab is rolled out, and the width of the slab is 200mm. The density of the compact was 6.5 g/cm ³ .

The powder compact is placed on a molybdenum plate coated with MgO micropowder, and placed in a vacuum degreasing and sintering furnace. Adopt a heating rate of 5°C/min, and keep warm at 200°C and 400°C for 2h respectively. Then heat up to 1150°C for sintering with heat preservation for 2h. The density of the sintered compact was 6.55 g/cm ³ .

After sintering, a uniform equiaxed grain structure is formed, as shown in Figure 1. The matrix grains are about 70-100 μm, and there are pores of about 10 μm in the grain boundary, which can be closed by subsequent rolling and sintering. Only a small amount of ~2μm second phase remains in the matrix tissue, which has a good interface with the matrix tissue, that is, there is no split surface. Obviously these second phases are some kind of Si-rich phase, the existence of these Si-rich phases reduces the Si content of the matrix tissue, making the matrix tissue have high plastic deformation ability; at the same time, it has a good interface bonding and dispersion distribution with the matrix tissue It is beneficial to the subsequent homogenization and diffusion.

The above-mentioned sintered slab is cold-rolled and thinned, and the reduction in a single pass is ≤8%, and after multi-pass rolling until the total reduction reaches 30-50%, it is then sintered in a vacuum sintering furnace at 1150°C . The temperature was continuously raised at a rate of 10°C/min, and the holding time was 1h. The specific pressing-annealing system is: 1.2mm→0.75mm→0.49mm→0.32mm→0.19mm→0.14mm→0.10mm, that is, after 6 times of cold rolling and 5 times of sintering, the thickness of the sheet reaches 0.10mm, and the density It reaches 7.43g/cm ³ .

The above cold-rolled strip was vacuum sintered at 1255° C. for 4 hours to obtain a single-phase homogeneous high-silicon steel with a thickness of about 0.10 mm, a density of 7.44 g/cm ³ , and a Si content of 4.5%.

Example 3

Mix -100 mesh reduced Fe powder with Fe-60% Si high-purity powder with a particle size of ≤6 μm at a ratio of 89.17:10.83 to form Fe-6.5% Si mixed powder. When mixing, add a total amount of 0.6% compound lubricant and 0.1% glycerin to reduce the oxidation of the powder during heating, use absolute ethanol as a solvent, and add according to the amount of 500ml/ton. The composite lubricant is composed of zinc stearate and EBS, and the ratio of zinc stearate:EBS is 3:7. The above powders were mixed for 6 h using a drum mixer.

The mixed powder is heated to 125°C with a powder heating device, and the roll is preheated to the same temperature. Using a two-roller horizontal rolling mill and an inclined feeding trough, using the powder's own weight and the friction between the roll and the powder to feed, a 1.6mm powder warm-rolled slab is rolled out, and the width of the slab is 160mm. The density of the compact was 6.16 g/cm ³ .

The powder slab is placed on a corundum plate coated with MgO micropowder, and placed in a hydrogen tube furnace for degreasing and sintering. A heating rate of 3°C/min was adopted, and the temperature was kept at 200°C for 2h and at 400°C for 3h. Then heat up to 1120°C for 3 hours for sintering. The density of the sintered compact was 6.2 g/cm ³ .

The above-mentioned sintered slab is cold-rolled and thinned, and the reduction in a single pass is ≤ 8%, and after multi-pass rolling until the total reduction reaches 30-50%, it is then kept in a hydrogen tube furnace at 1120°C Sinter for 1h. The temperature was continuously raised at a rate of 6°C/min. The specific pressing-annealing system is: 1.6mm→1.08mm→0.70mm→0.45mm→0.27mm, that is, after 4 times of cold rolling and 3 times of sintering, the thickness of the sheet material reaches 0.27mm, and the density reaches 7.37g/cm ³ .

The metallographic structure after two times of cold rolling and sintering is shown in Figure 2. The matrix is a grain structure of about 100 μm, with a small amount of fine pores. The matrix grains have two different contrasts. This is due to the difference in corrosion caused by the different Si content. The low Si grains in this structure are conducive to processing deformation, making it possible to manufacture thin plates of 0.1-0.5 mm.

The above cold-rolled strip was vacuum sintered at 1300° C. for 2 hours to obtain a single-phase homogeneous high-silicon steel with a thickness of about 0.27 mm, a density of 7.38 g/cm ³ , and a Si content of 6.5%.

Example 4

Mix -100 mesh reduced Fe powder with Fe-62% Si high-purity powder with a particle size of ≤10 μm in a ratio of 90.64:9.36 to form Fe-5.8% Si mixed powder. When mixing, add a total amount of 0.6% compound lubricant and 0.1% glycerin to reduce the oxidation of the powder during heating, use absolute ethanol as a solvent, and add according to the amount of 500ml/ton. The composite lubricant is composed of zinc stearate and EBS, and the ratio of zinc stearate:EBS is 3:7. The above powders were mixed for 3 h using a drum mixer.

The mixed powder is heated to 150°C with a powder heating device, and the roll is preheated to the same temperature. Using a two-roller horizontal rolling mill and an inclined feeding trough, using the powder's own weight and the friction between the roll and the powder to feed, a 2.0mm powder warm-rolled slab is rolled out, and the width of the slab is 120mm. The density of the compact was 6.2 g/cm ³ .

The powder slab is placed on a corundum plate coated with MgO micropowder, and placed in a hydrogen tube furnace for degreasing and sintering. A heating rate of 4°C/min was adopted, and the temperature was kept at 200°C for 3h and at 400°C for 2h. Then heat up to 1130°C for sintering with heat preservation for 2h. The density of the sintered body was 6.26g/cm ³ .

The above-mentioned sintered slab is cold-rolled and thinned, and the reduction in a single pass is ≤ 8%, and after multi-pass rolling until the total reduction reaches 30-50%, it is then kept in a hydrogen tube furnace at 1130°C Sinter for 0.5h. The temperature was continuously raised at a rate of 8°C/min. The specific pressing-annealing system is: 2.0mm→1.3mm→0.96mm→0.72mm→0.46mm→0.32mm→0.21mm, that is, after 7 times of cold rolling and 6 times of sintering, the thickness of the sheet reaches 0.21mm, and the density It reaches 7.38g/cm ³ .

The above cold-rolled strip was vacuum sintered at 1285°C for 2 hours to obtain a thickness of about 0.22mm, a density of 7.39g/cm ³ , and a Si content of 5.8%. Silicon steel.

Claims (7)

1. A method for preparing high-silicon steel thin strips by powder warm rolling, is characterized in that comprising the steps of: (1) Raw material powder preparation -100 mesh reduced iron powder is used, Fe in the reduced iron powder is ≥ 98.5%, and the rest is Si, Mn, P, S and other unavoidable impurities. High-purity ferrosilicon powder with Si content of 50-70% is used. ≤6μm, the main impurities are ~0.24% Al, ~0.07% Ca and ~0.02% C, and the rest is Fe; (2) Powder mixing According to the ratio of Fe-4.5-6.7% Si, weigh the reduced Fe powder and Fe-50-70% Si high-purity ferrosilicon powder; use a low-energy mixer to mix them under an inert protective atmosphere, and the total amount added during mixing is 0.4- 0.6% lubricant; (3) Warm powder rolling Using a two-roller horizontal rolling mill and an inclined feeding trough, using the self-weight of the powder and the friction between the roll and the powder to feed, the rolled thickness is 1.2-2.3mm, the width is 100-200mm, and the density is 6.1-6.5g/cm ³ powder warm rolled slabs. Before rolling, use a powder heating device to heat the mixed powder to 125-150°C, and preheat the roll to the same temperature; (4) Degreasing and sintering Place the powder slab on a support plate coated with MgO micropowder on the surface, place it in a vacuum degreasing and sintering furnace, adopt a heating rate of 2-5°C/min, and keep warm at 200°C and 400°C for 2h-4h respectively. Then heat up to 1050-1150°C for 2-4 hours for sintering, and the density of the sintered compact is 6.15-6.55g/cm ³ ; (5) Cold rolling - sintering densification The above-mentioned sintered slab is cold-rolled and thinned, and the reduction in a single pass is ≤8%, and after multi-pass rolling until the total reduction reaches 30-50%, it is then kept in a sintering furnace at 1050-1150°C Sintering for 0.5～2h, after multiple times of cold rolling and sintering, the thickness of the sheet reaches 0.1～0.5mm, and the density reaches 7.33～7.43g/cm ³ ; (6) Homogenized high temperature sintering Sintering in vacuum or reducing protective atmosphere in the temperature range of 1255-1330°C for 1-4 hours, under the action of thermal diffusion, the homogenization of Si is realized, a single-phase alloy is formed, and homogeneous high-silicon steel is obtained, and the density of the sheet after sintering is densified. The thickness is 0.1-0.5mm, and the density reaches 7.34-7.44g/cm ³ . 2. A method for preparing high-silicon steel strips by warm powder rolling as claimed in claim 1, characterized in that: the high-purity ferrosilicon powder with a particle size of ≤6 μm is obtained by high-energy ball milling or punching. 3. A method for preparing high-silicon steel strips by warm powder rolling as claimed in claim 1, characterized in that: the low-energy mixer is a cone mixer, a V-shaped mixer or a drum Mixer. 4. A method for preparing high-silicon steel thin strips by powder warm rolling as claimed in claim 1, characterized in that: when mixing in step (2), add a lubricant with a total mass of 0.4 to 0.6%, and a total mass of 0.1% % glycerol, the lubricant is a composite lubricant, composed of zinc stearate and vinyl bis stearamide, zinc stearate: EBS is 4:6～2:8, using absolute ethanol as solvent, Add in an amount of 400-600ml per ton of mixed powder. 5. A kind of method for preparing high-silicon steel thin strip by powder warm rolling as claimed in claim 1, characterized in that: vacuum sintering or reducing protective atmosphere sintering is adopted when step (5) is sintered again after cold rolling, and the heating rate is At 5-10°C/min, the temperature is continuously raised, and the holding time is determined according to the thickness of the plate. When the plate thickness is ≥1mm, the holding time is 1-2h; when the plate thickness is 0.1-1mm, the holding time is reduced to 0.5-1h; after each sintering After the cumulative reduction reaches 30-50%, it needs to be re-sintered once, and it needs to be re-sintered 4-8 times when it is rolled from a powder billet of 1.2-2.3mm to 0.1-0.5mm. 6. The method for preparing high-silicon steel thin strips by powder warm rolling as claimed in claim 1, characterized in that: the support plate described in step (4) adopts molybdenum plate, W plate, heat-resistant steel, corundum or Zirconia ceramic plate. 7. A kind of method for preparing high-silicon steel thin strip by powder warm rolling as claimed in claim 1, characterized in that: during high-temperature sintering, the sintered sheets are stacked, MgO powder is laid between the layers, and the sheets are placed flatly. Place a flat weight on the sheet to prevent deformation during sintering.