High-silicon steel generally refers to ferrosilicon alloy containing 4.5 wt%-6.7 wt%, and the general high-silicon steel is 6.5%.
Ferrosilicon alloy. 6.5wt% high silicon steel is a soft magnetic alloy with high permeability, low coercivity and low iron loss, 6.5 wt%.
The resistivity p of Si high-silicon steel is 82μω×cm, which is about twice that of 3 wt% Si silicon steel (3 wt% Si silicon steel ρ= 48μω×cm), and the saturation magnetic induction intensity Bs= 1.80T, which is lower than 3 wt%Si silicon steel (Bs=2.03 T) and magnetostrictive coefficient. The magnetic characteristics of high silicon steel are that the high frequency iron loss is obviously reduced, the maximum permeability is improved and the coercivity Ho is low. High silicon steel has excellent soft magnetic properties such as low iron loss, high permeability and low magnetostrictive coefficient, and has broad application prospects in high-performance generators, transformers, relays, especially microelectronic components. However, high silicon steel is brittle at room temperature and has poor processability, so it is difficult to prepare plates and strips by conventional (casting-rolling) process, which seriously affects the wide application of this alloy.
2 status of silicon steel grinding
2. 1 Development Status of High Silicon Steel
1953 Takeshi Tanaka of NKK Iron and Steel Company of Japan adopted cold rolling annealing with large reduction rate, and the carbon content increased by 0. The silicon content decreased by 2. 05%. 94%, aluminum decreased by 0. 02%. In 0. 0062% nitrogen steel plate, {1/kloc-0} < 001> The orientation degree of texture and its magnetism are also improved. Therefore, researchers began to realize that using AlN as an inhibitor, a sheet with higher magnetism than ordinary oriented silicon steel can be prepared by one-time rolling process. Therefore, in 196 1 year, NKK Company began to use A 1N and MnS as inhibitors to prepare high-oriented silicon steel on the basis of importing the patented technology of Armco steel from the United States. It was not until 1964 that NKK successfully trial-produced high magnetic induction oriented silicon steel, which was later named Hi-B steel. However, because the research on this process is still in the primary stage, the magnetic properties of Hi-B steel prepared by NKK are still extremely unstable. At the same time, D. Brown and others also proved that the loss of iron is 6. 5% ferrosilicon single crystal is 0. 2W/ kg, the magnetostriction is about110 of 3% ferrosilicon single crystal, and the magnetic anisotropy is about 1/3. At 1965, DJ. The elongation of 5% ferrosilicon is 65438 0% ~ 2% by tensile test. Subsequently, a tensile test was conducted on a steel plate with 5%Si-Fe added with Ni. The experimental results show that adding nickel can obviously improve the elongation of steel, such as adding 6% nickel to improve the elongation by 9% and adding 7.5% nickel to improve the elongation by 20%. In 1966, T. IShizaka et al. hot rolled 6.5%S i silicon steel at 600℃-750℃ with 70% reduction, and then cold rolled it from 1mm to 0. The thickness after finishing is 3 mm. So far, the magnetic properties of ordinary oriented silicon steel are basically stable, and the iron loss is reduced to zero.
05W/Kg. Therefore, researchers began to study the simplification, economy and operability of 6.5%Si manufacturing process. ?
In 1978, the thickness of 6.5% ferrosilicon thin strip is 0. 03-0. 1 mm was prepared by rapid cooling in Japan by N. Tsuya and k.i.arai. In the same year, Kawasaki Company of Japan adopted this process for trial production, but it has not been mass-produced so far. Subsequently, 6.5% Si-Fe alloy, Sendust alloy and various Fe3S i-based alloys prepared by this process also appeared one after another. 1978, Wang Dong and others in China successfully prepared 6.5%Si-Fe as-cast ultra-thin strip by rapid solidification method. The resistivity of this strip is very high, and the magnetostriction is close to zero. But these are limited to scientific research and applied basic research, and it is difficult to produce them on a large scale by this process. ?
Around 1980, Russian researchers used the three-rolling process (hot rolling, warm rolling and cold rolling) to prepare high silicon steel, but this process is too complicated and takes a long time to really implement. 1988, Yoshiichi Takada and Masahiro Abe of NKK Company in Japan successfully prepared 6.5%Si high-silicon steel by CVD method. Subsequently, Japanese researchers carried out a lot of experiments and improvements on this process. 1993, NKK officially built a continuous production line with a thickness of 0. 1~0.5mm and a width of 400mm, with a monthly output of 100 tons. Later, with the development of high-frequency electrical components, NKK Company began to develop high-silicon steel plates named JNEX-Core and JNHF-Core after 1995. The successful preparation of these two kinds of silicon steel sheets not only improves the machinability of high silicon steel, but also greatly reduces eddy current loss and noise pollution.
2.2 The representative events of the application 2.2 6.5% Si high-silicon steel are listed as follows:
1) The iron core of high-speed and high-frequency motor made of 0.35mm thick 6.5wt% high-silicon steel sheet in Japan has achieved good energy-saving effect. Compared with the iron core made of ordinary 3.56.5wt% silicon steel, the motor efficiency is significantly improved under sine wave drive and non-sine wave drive, and the iron loss is reduced by 35% and 43% respectively.
2) The United States and the European Union have applied the annular iron core made of 6.5wt% high silicon steel to the inductance filter of the switching power supply of the automobile GPS system;
3) Japan used 6.5wt% silicon steel instead of 3wt% oriented silicon steel in 8kHz welding machine, and the iron core weight was reduced from 7.5kg to 3 kg;
4) Toyota Motor Corporation took the lead in applying 6.5wt% high-silicon steel to the boost converter reactor of Prius, a hybrid vehicle sold all over the world;
5) In Europe, 6.5wt% high silicon steel strip with a thickness of 0.50mm is used as the core of transformer. Under the working environment with a frequency of 50Hz, compared with ordinary 3.5wt% silicon steel, the noise is reduced by 6dB.
6) Compared with the transformer made of Z7H oriented silicon steel, the 30kg analog audio transformer made of NKK 6.5wt% high silicon steel has a working noise reduction of 2 1dB and a working iron loss reduction of about 40% at b =1t.. ?
2.3 The development of domestic silicon steel industry?
The domestic silicon steel industry started behind the leading countries in the world for nearly half a century. It was not until 1952 that Taiyuan Iron and Steel Plant first prepared low-silicon steel with silicon content of about 1%-2%, and put it into production in 1954. At the same time, the Iron and Steel Research Institute and Taiyuan Iron and Steel Plant jointly trial-produced hot-rolled high-silicon steel plates, which increased the silicon content from the original 1%~2% to about 3%~40%, and put into production two years later. From 1960 to 1978, Shanghai Silicon Steel Sheet Factory improved the traditional preparation process of hot rolled silicon steel sheets, and finally established the preparation process of rapid cooling after hot rolling. The quality and output of high silicon steel prepared by this process are further improved, and its magnetism is also higher than that of similar silicon steel prepared by European and American countries in the early stage. ?
1957, the iron and steel research institute produced {1 10} by cold rolling twice, slow heating and rapid annealing.
& lt00 1 & gt； Textured 3% silicon oriented silicon steel. However, due to the limitation of equipment and technical conditions at that time, researchers did not realize the important role of MnS, A 1N and rolling process, and the magnetic properties of silicon steel sheets prepared by this process were always unstable. From 65438 to 0959, TISCO and Angang began to produce high-oriented silicon steel almost at the same time, but the qualified rate and finished product rate were relatively low. From 65438 to 0964, the Iron and Steel Research Institute carried out a series of technological processes, such as continuous furnace annealing, adding separators and furnace annealing under the action of inhibitors, which further enhanced the magnetism and stability of silicon steel. ?
1974, WISCO purchased Japanese NKK patented technology and reached an agreement. The annual output of1/kloc-0 brand cold-rolled silicon steel is about 68,000 tons, and 198 1 year produces 4%S i high-silicon steel. During the period of 1983, the Institute of Iron Research produced oriented silicon steel with a thickness of 0.20-0.35mm from WISCO, which was produced by a new process of pickling, cold rolling and annealing. The yield is significantly improved and the manufacturing cost is reduced. ?
However, faced with the vigorous development of foreign steel industry, the domestic silicon steel industry has developed very slowly in recent years. Although domestic researchers have also done some corresponding research on 6.5%Si high-silicon steel, the results are few. So far, Baosteel and other leading enterprises in the domestic silicon steel industry have not implemented or even designed a complete process for preparing 6.5%S i high-silicon steel, and it is even more difficult to pre-build a production line for preparing high-silicon steel. Therefore, in order to adapt to the development of the world steel industry and keep up with the development of domestic modernization, the domestic steel industry must have its own relatively perfect process route and production line to prepare for 6. 5%S i high silicon steel, which will also affect the future development direction of domestic electrical steel industry.
Properties of 3 6.5%Si high silicon steel
3. 1 physical properties
3.2 Magnetic characteristics
Silicon steel is a ferritic steel composed of body-centered cubic a-Fe solid solution, and its magnetization characteristics are different in three main crystal directions: [100] direction is easy to magnetize, [1 10] direction is not easy to magnetize, [165438+. Rolling with deformed recrystallization structure produces a large number of silicon steel sheets, resulting in plane texture, and the {1 10} plane of most grains is parallel to the rolling surface, <100 >; The direction is parallel to the rolling direction, and the < 100 > direction is the easy magnetization direction of iron. The hysteresis expansion coefficient of 6.5wt% high silicon steel is lower than other soft magnetic materials, the iron loss is about 1/2, and the hysteresis expansion coefficient is about 1/25 of non-oriented silicon steel. At 400Hz, the iron loss of 6.5wt% high silicon steel is less than that of oriented silicon steel, and the hysteresis expansion coefficient is about116 of oriented silicon steel. There are many factors that affect the magnetic properties of 6.5wt% high silicon steel alloy, such as impurities, microalloying elements, crystal texture, ordered transformation, grain size, internal stress and steel plate thickness. And these factors are also related, so mastering these factors can effectively improve or control the magnetic properties of 6.5wt% high silicon steel.
Brittle mechanism of 3.3-6.5% Si high silicon steel
The brittleness mechanism of 6.5% Si high silicon steel alloy is closely related to intermetallic compounds, and the main source of its brittleness is ordered intermetallic compounds in the alloy. The brittle mechanism of intermetallic compounds is very complicated, which can be divided into three types: intergranular fracture, transgranular fracture and quasi-cleavage fracture. In essence, it can be divided into intrinsic brittleness and environmental brittleness. The main reasons for the inherent brittleness of intermetallic compounds are: insufficient independent slip coefficient of metals, high P-N force, low cleavage stress, difficult cross slip and brittle grain boundaries.
The environmental brittleness of 6.5wt% high silicon steel refers to the phenomenon that the plasticity and toughness of the alloy decrease due to the interaction with the surrounding environment. According to the mechanism of environmental brittleness, Academician Liu Guodong pointed out that considering the following four aspects in alloy design can reduce the environmental brittleness of intermetallic compounds and improve the plasticity of alloys:
1) Sub-stoichiometric composition: control the content of active elements (such as Si in Fe3Si) in intermetallic compounds to make them have lower grain boundary brittleness and environmental brittleness;
2) Role of boron element (B): For intermetallic compounds with low grain boundary strength, proper addition of B element can effectively improve the grain boundary bonding strength, thus reducing the grain boundary damage caused by environmental brittleness and reducing the diffusion of hydrogen atoms along the grain boundary;
3) reducing the possibility of surface reaction: adding appropriate alloying elements can reduce the rate of surface adsorption reaction, and surface pre-oxidation or coating can also effectively reduce environmental brittleness;
4) Improving the microstructure: changing the grain shape and reducing the low-strength large-angle grain boundaries by heat treatment.
Preparation method of 4 6.5%Si high-silicon steel sheet
Due to the brittleness of 6.5 wt% high silicon steel alloy at room temperature, it is difficult to prepare thin plates by traditional cold rolling method. With the development of preparation technology, the production technology mainly includes the following four aspects: (1) deposition diffusion technology; (2) Rapid condensation technology; (3) Powder calendering technology; (4) Rolling process, etc. The development and perfection of preparation technology and whether it can be produced economically and efficiently are the keys to the commercial application of 6.5wt% high silicon steel. Rolling method has been a hot research topic because of its advantages of economy, high efficiency and easy popularization.
4. 1 deposition diffusion technology
4. 1. 1 chemical vapor deposition process (CVD method)
CVD method is one of the most outstanding and mature technologies for preparing 6.5wt% high silicon steel sheet at present, and its process is divided into three parts: (1) silicon steel sheet containing about 3. 1 wt% Si is produced by ordinary rolling method; (2) The high-temperature chemical reaction between the silicon steel sheet surface and silicide (SiCI4) makes the silicon steel sheet surface rich in Si; (3) Long-time diffusion annealing at 1 100℃ is carried out on the thin plate, so that the silicon on the surface diffuses towards the center, and a silicon steel sheet with a total silicon content of 6.5wt% is generated.
? The core of CVD technology is to heat the silicon steel sheet containing about 3. 1 wt% Si to1200℃ under the protection of non-oxidizing atmosphere (SiCl45%-35%, N2 or rare gas) for reaction. Fe3Si is deposited on the surface of the silicon steel sheet and pyrolyzed into active Si atoms.
Although CVD technology has successfully prepared 6.5wt% high silicon steel thin strip, there are still the following problems:
(1) Deposition and siliconizing are both carried out at high temperature (up to 1320℃), which requires high equipment and consumes a lot of energy.
(SiCl4 _ 4 corrodes silicon steel sheet to form fe3si deposit, which leads to corrosion pits on its surface, and subsequent leveling is complicated;
(3) When the deposited Fe3Si diffuses, Kirkendall cavity will be formed, and the Si concentration distribution after deposition will be uneven, which will lead to the decline of the yield of subsequent processes;
(4) FeCl2 _ 2 _ 2 is produced, which not only pollutes the environment, but also causes iron loss;
(5) At present, 6.5wt% high silicon steel is non-oriented silicon steel.
4. 1.2 electron beam physical vapor deposition process (EB-PVD method)
Electron beam physical vapor deposition (EB-PVD) is an advanced process, which can prepare large-size and adjustable-thickness plates that are difficult to prepare by traditional rolling process. Its principle includes three aspects: (1) electron beam is focused on the ingot of evaporation source by magnetic field or electric field to melt the material; (2) In the vacuum and low pressure environment, the evaporation source gasifies above the molten pool, and the gas phase atoms move linearly from the surface of the molten pool to the surface of the substrate to form a deposition layer; (3) cooling after deposition, and stripping the deposited layer to obtain a plate; The process flow chart for preparing 6.5 wt% high silicon steel is shown in Figure 2.
6.5wt% high-silicon steel is prepared by EB-PVD method, which has the advantages of accurate control of deposit thickness and good process repeatability, avoiding oxidation and pollution between substrate and coating, and is beneficial to environmental protection; Its disadvantages are expensive equipment, high preparation cost and difficult industrial production.
4. 1.3 electrodeposition process of dissolved salt
The process flow chart of preparing 6.5wt% high silicon steel by molten salt electrodeposition is shown in Figure 3, and its working principle can be roughly divided into four points: (1) molten salt systems of LiF, NaF, KF×2h2o and Na2SiF6 are selected; (2) Na _ 2SiF6 is completely melted and evenly mixed above 750℃, with Si content.
The advantages of this process are: because there is no water in the system, the potential of oxygen obtained by electrodeposition of dissolved salt at anode potential is corrected, and the potential of oxygen obtained at cathode potential is more negative; The disadvantage is that dissolved salt electrolysis makes the electrolyte solution easy to volatilize and oxidize, which consumes a lot of electricity.
4.2 Rapid condensation technology
4.2. 1 rapid solidification preparation process
In recent years, rapid solidification technology has developed rapidly in the field of metal material preparation and processing. The preparation of 6.5wt% high silicon steel thin strip by rapid solidification technology has achieved certain results and showed great development prospects. The schematic diagram of its production equipment is shown in Figure 4. The rapid solidification method for producing 6.5wt% high-silicon steel sheet has three main advantages: ① fine grain structure of the alloy, ② simple manufacturing process, ③ avoiding the inherent brittleness of 6.5wt% high-silicon steel; The main disadvantages are narrow application range of process parameters, easy belt breakage in production, difficult control, poor shape quality and low yield.
4.2. 1 spray forming preparation process
Spray forming is a new material preparation technology involving powder metallurgy, metal atomization, rapid cooling and non-equilibrium solidification. Its principle is to deposit liquid metal droplets atomized by gas on a receiver and directly make products with certain shapes. Using industrial pure iron and industrial pure silicon as raw materials, 6.5wt% high silicon steel was prepared by spray forming technology, and the schematic diagram of its equipment is shown in Figure 5. Its advantages are that the brittle zone in the rolling process of high silicon steel is avoided, and thinner strip can be obtained; The disadvantage is that the prepared high silicon steel has low density, limited alloy width and thickness, and it is difficult to control the uniformity of the material in the thickness direction.
4.3 Powder calendering technology
Powder calendering is a method of feeding powder between a pair of rotating rollers through a funnel to compact it into a continuous strip; There are three main problems: ① Iron powder and silicon powder in raw materials are easy to be oxidized, which affects the subsequent sintering; (2) The raw material particles are fine and the surface area is large, which leads to poor dispersity among particles, and it is difficult to uniformly mix and sinter the green body with uneven density; ③ After turning L, the thickness deviation is large, and it is difficult to accurately control the shape.
4.4 Rolling method
Rolling methods include cold rolling method and special rolling method (including temperature control rolling method and cladding rolling method). High silicon oriented silicon steel was prepared by rolling method, that is, high silicon steel plate with strong Goes texture was prepared by inhibitor and secondary recrystallization in the same way as 3%Si oriented silicon steel.
A lot of research shows that iron loss can be reduced by changing the grain size and weaving groove of high silicon steel sheet and controlling the orderly mobility of high silicon steel through different heat treatment processes. Up to now, there is no report on mass production of oriented high silicon steel and production equipment by rolling method. The technology of preparing oriented high silicon steel by rolling method is only mentioned in patents, which is far from industrialization promotion and needs further exploration and practice.
5 Conclusion and prospect
6.5wt% high-silicon steel has excellent soft magnetic properties such as near-zero magnetostrictive coefficient, large permeability, low coercivity and low iron loss, which has obvious advantages in reducing energy consumption and noise pollution of high-frequency electrical appliances. However, the remarkable low-temperature brittleness of the alloy itself seriously affects the wide application of this material. The brittle nature and plastic deformation mechanism of 6.5wt% high silicon steel are expounded, and the defects in the preparation and forming process of the alloy are actively avoided and effectively controlled. Therefore, it is a key problem to develop a short process and high efficiency preparation and processing method to realize the industrialized production of 6.5wt% high silicon steel.
In recent years, with the development of high-entropy alloys, research shows that reasonable design of high-entropy alloys can not only improve the strength of materials, but also improve the plasticity of materials. Combining the preparation of high-silicon steel with the characteristics of high-entropy alloy can reasonably avoid the low-temperature brittleness of high-silicon steel, and then successfully prepare high-silicon steel.
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