JP2010132977A - Extra-thin silicon steel sheet and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an extra-thin silicon steel sheet which is less in the quantity of coarse grains even when being subjected to heat treatment at ≥1,100°C, has high B8/Bs and is suitable to siliconizing treatment, and to provide a manufacturing method therefor,. <P>SOLUTION: This extra-thin silicon steel sheet having 0.03-0.10 mm sheet thickness, is obtained by re-rolling a unidirectional silicon steel secondary recrystallized sheet containing 2-4 mass% of recompression. The peculiarity is that the ratio of the coarse grain exceeding 5 times of the sheet thickness to the maximum width of crystallized grains is ≤15% after applying the heat-treatment under condition of temperature of 1,100°C for 1 minute during the nitrogen atmosphere and B8/Bs is ≥0.85. When this steel sheet is manufactured, on the surface of the unidirectional silicon steel secondary recrystallized sheet before re-rolling, for example, a mechanical-grinding or a chemical-corrosion is applied, and after making an arithmetic means Ra of the surface roughness from 0.6 μm to <3.5 μm, the re-rolling is applied. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ultra-thin silicon steel plate suitable as a material for siliconization of a high silicon steel plate that is effective in reducing the size and loss of a high-frequency power source, and a method for manufacturing the same.

In recent years, power electronics technology has been used not only in large industrial power supplies but also in various fields such as power supplies for home appliances and power supplies for driving hybrid cars. In particular, switching semiconductor devices such as IGBT (Insulated Gate Bipolar Transistor) have been developed remarkably, and their application range tends to be higher and higher capacity.
Conventionally, a dust core obtained by solidifying a silicon steel plate or iron powder has been used for a transformer or a reactor of such a switching power supply. However, these materials have a tendency that when the excitation frequency increases, the iron loss increases rapidly and the heat generation becomes significant. For this reason, recently, iron-based amorphous materials having a low high-frequency iron loss and soft magnetic ferrite mainly composed of iron oxide powder are being studied as iron core materials. However, the amorphous core is expensive and has a large magnetostriction, so noise countermeasures are essential. On the other hand, soft magnetic ferrite has a high specific resistance and is expected to greatly reduce eddy current loss, which is the main cause of iron loss in the high-frequency range. On the other hand, the magnetic flux density is lower than that of iron-based materials. Although it is suitable for a power supply with a small capacity, it is considered unsuitable for a power supply with a relatively large capacity at several kHz where an IGBT is used because the iron core becomes large.

Since silicon steel plates are relatively inexpensive and have high magnetic flux density, they are used not only for commercial use but also for high frequency power supplies of several hundred Hz to several kHz. However, measures to reduce high-frequency iron loss by suppressing eddy current loss, such as reducing the thickness of the plate and increasing the Si content to increase the specific resistance, rather than diverting commercial silicon steel plates directly to high frequencies. Has been adopted.
As a thin plate, an ultra-thin silicon steel plate having a thickness of 0.05 to 0.10 mm containing about 3% Si by weight is currently on the market. This ultra-thin silicon steel sheet has a non-directional, relatively low magnetic flux density that exhibits uniform characteristics within the plate surface, and a high magnetic flux density with a high degree of integration of {110} <001> orientation (Goth orientation). There is a thing. The non-directional one is not fundamentally different from a normal plate thickness manufacturing process in that the final plate thickness of rolling is reduced and primary recrystallization is performed by finish annealing. The one with a higher degree of {110} <001> orientation integration is cold-rolled to the final finished plate thickness as a normal unidirectional silicon steel sheet as a manufacturing process, and this is subjected to primary recrystallization and further secondary recrystallization. And producing a unidirectional silicon steel sheet having a high {110} <001> orientation integration by secondary recrystallization once with a thickness of about 0.3 mm, A method (for example, Patent Documents 2 and 3) in which rolling is performed to obtain a plate thickness of 0.10 mm or less and then primary recrystallization annealing at 700 to 900 ° C. is considered. However, the former method is actually used because the secondary recrystallization becomes unstable and it becomes difficult to obtain a {110} <001> oriented structure when the cold-rolled sheet thickness is 0.10 mm or less. The latter is a method by rerolling the latter secondary recrystallized plate. Further, the ultrathin silicon steel sheet having a high {110} <001> orientation integration obtained in this way has a high magnetic flux density in the rolling direction, and thus is expected to reduce the size of the iron core.

  On the other hand, the method of reducing the high-frequency iron loss by increasing the Si content in steel and lowering the high-frequency iron loss is substantially difficult to roll a thin plate exceeding 4% Si content. A siliconization process is employed in which Si is added using a Si-based gas in the final annealing step after rolling to a thickness of 0.05 to 0.3 mm in the state (for example, Patent Document 4). In particular, 6.5% Si not only reduces high-frequency iron loss, but also has a tremendous effect in reducing noise in the power supply because the magnetostriction is close to zero. In addition, a material having a specific Si concentration gradient in the plate thickness direction that can further reduce the high-frequency iron loss compared to the 6.5% Si steel plate having the same plate thickness has been manufactured (for example, Patent Document 5). Furthermore, the workability of high Si products produced in the siliconization process is important. Therefore, it is necessary to take measures to improve workability such as crystal grain size and grain boundary oxidation so as not to be broken by slit processing, punching processing, bending processing, etc. when producing a transformer / reactor. In Reference 6, the average particle size is defined so that the punching processability is good.

As for the method of increasing the specific resistance by increasing the Si content with respect to the above-described {110} <001> orientation integration degree, in Patent Document 7, it has {110} <001> orientation and B8 / A unidirectional silicon steel sheet with Bs> 1.9 is cold-rolled at a rolling reduction of 60 to 90% to a thickness of 0.15 mm or less, then heat-treated under predetermined conditions to obtain a primary recrystallized structure, and then SiCl ₄ A process is disclosed in which a siliconizing process is performed with a gas, and a magnetic domain refinement process is further performed on the silicon.
Japanese Patent Laid-Open No. 2-77524 JP-A-2-77748 U.S. Pat.No. 2,473,156 Japanese Patent No. 1836404 Japanese Patent No. 3896688 Japanese Patent No. 2998676 Japanese Patent No. 278483

However, the above prior art has the following problems.
For example, it is difficult to make a steel sheet containing Si exceeding 4% in the rolling process into an ultrathin silicon steel sheet with a thickness of 0.10 mm or less. Is about 3% Si. These ultrathin silicon steel sheets are non-oriented and those with a high degree of integration of <001> {110} textures. Both high-frequency iron losses are of the same thickness produced by the siliconization process. It does not reach silicon steel sheets.

  The high silicon steel plate obtained by the siliconization process described in Patent Documents 4 and 5 is mainly a non-oriented silicon steel plate, and the magnetic flux density when this non-oriented silicon steel plate is excited with a magnetizing force of 800 A / m. The ratio of B8 to saturation magnetic flux density Bs (hereinafter referred to as B8 / Bs) is only about 0.7 (corresponding to B8 = 1.42T for 3% Si and B8 = 1.26T for 6.5% Si). There is a strong demand for miniaturization of power supplies in the power electronics market, and there is a demand for significant improvement in characteristics of high silicon steel sheets (for example, miniaturization of iron cores by more than 20% of the current level). The index corresponding to this is B8 / Bs> 0.85 (corresponding to B8> 1.73T at 3% Si and B8> 1.53T at 6.5% Si), and the non-oriented electrical steel sheet is insufficient. In addition, it is extremely difficult to obtain a material with B8 / Bs> 0.85 by repeated cold rolling and annealing without using secondary recrystallization.

  For example, in the method for producing an ultrathin silicon steel sheet disclosed in Patent Document 7, when the siliconizing process is performed at 1000 ° C. or lower, iron chloride (boiling point 1023 ° C.) generated by the siliconizing reaction remains on the steel sheet surface. Since the siliconization speed is significantly reduced and the silicon homogenization diffusion process takes several hours, it is unsuitable for processing on a continuous line as currently performed. In order to perform the siliconizing treatment on the continuous line, it is essential to perform the iron chloride boiling point of 1023 ° C. or higher, more preferably 1100 ° C. or higher, and the Si uniform diffusion treatment at a temperature of 1100 ° C. or higher in a short time.

  As described above, in the field of home appliances and hybrid cars, there is an extremely strong demand for miniaturization, weight reduction, and high efficiency of power supplies, and the characteristics required for iron core materials are becoming stricter year by year. The number of cases where large power supply capacity is used is increasing, but at present, there are few materials that meet these conditions of use, and improvements in characteristics are desired.

  The present invention has been made in view of such circumstances, and provides an ultra-thin silicon steel sheet suitable for siliconization treatment that has few coarse grains and exhibits high B8 / Bs even when heat-treated at 1100 ° C. or higher, and a method for producing the same. The purpose is to do.

The inventors have made various studies in order to solve the above problems. Hereinafter, the contents of the examination that triggered the invention will be described.
In general, when a {110} <001> highly-integrated unidirectional silicon steel secondary recrystallized plate is re-rolled and heat treated, {110} <001> highly-integrated primary Although the crystal structure is obtained and shows high B8, when annealed at higher temperatures, the crystal grains greatly deviated from the {110} <001> orientation eroded the surrounding primary recrystallized grains to become coarse grains, and B8 significantly decreased. Is well known ((1) CGDunn: Acta Met., 1 (1953), 163, (2) Arai et al., The Metallurgical Society of Japan 31, 5 (1992), 429)
Therefore, in order to investigate this phenomenon in detail, a unidirectional silicon steel secondary recrystallized plate with a plate thickness of 0.30 mm and B8 / Bs = 1.92 was rerolled to a plate thickness of 0.085 mm in a 100% N ₂ non-oxidizing atmosphere. After heating at 1000 ° C. to 1200 ° C. for 2 minutes at a heating rate equivalent to continuous annealing (20 ° C./s), the surface macrostructure and magnetic flux density B8 were evaluated. The macro structure is observed by picking up the steel plate surface with a solution containing hydrochloric acid and then taking a photograph. The magnetic flux density B8 is set to a sample with a 30 mm width x 100 mm length on a single plate magnetometer and is 800 A / m. It was measured as the magnetic flux density when magnetized up to.
The obtained results are shown in FIG. In the present invention, coarse grains having a maximum crystal width of 5 or more times the plate thickness are regarded as abnormal grains different from the normal primary recrystallized grains, and the area ratio of the coarse grains to the entire crystal plate surface is defined as coarse grains. From Fig. 1 defined as the ratio, when the heat treatment temperature is 1050 ° C or less, coarse particles are hardly observed, and B8 shows a value of around 1.80T, whereas when the heat treatment temperature is 1100 ° C or more, the plate thickness is 5 It can be seen that a large number of coarse grains having a size of double to several tens of times are generated, and B8 is greatly reduced to about 1.55T.
Such a tendency was similarly observed when heat treatment was performed in 100% H ₂ and in a N ₂ + H ₂ mixed atmosphere.
Next, orientation analysis was performed on the coarse particles by EBSP and X-ray pole figures. As a result, it was found that the coarse grains had an orientation greatly deviated from {110} <001>. And although this experiment is a heat treatment for a short time on the premise of continuous annealing, it is considered that the same phenomenon as that described in the above cited reference occurs.

  When there are many coarse grains, there is a concern about deterioration of product processability when a silicon steel sheet containing 6.5% Si is subjected to a siliconization treatment. In Patent Document 6, for example, when the plate thickness is 0.10 mm, the average particle size is defined to be less than 253 μm in order to avoid deterioration of workability. However, this is premised on a non-directional primary recrystallized structure having a relatively uniform particle size distribution, and a structure in which coarse grains of 5 to tens of times the plate thickness are mixed is excluded. is there. In fact, in a commercially available 6.5% silicon steel sheet having a thickness of 0.10 mm, most of the crystal grains are in the range of 100 to 200 μm, and there are almost no coarse grains exceeding 5 times the thickness.

  Next, the samples heat-treated at 1050 ° C. and 1100 ° C. as described above were subjected to silicification / diffusion treatment at 1050 ° C. for about 30 minutes using a lab apparatus to reduce the Si amount to 6.5%, It was wound around a rod and observed for cracks. In addition, the surface macrostructure was also observed for the sample after siliconization in the same manner as described above to obtain the coarse particle ratio. The obtained results are shown in Table 1.

  From Table 1, samples with a coarse grain ratio of about 10% (samples heat-treated at 1050 ° C) can be wound up to a round bar diameter of 4mmφ without cracks, whereas samples with a coarse grain ratio of about 40% (heat treated at 1100 ° C) In the sample), cracks were observed at a round bar diameter of 10 mmφ, and when the round bar diameter was 8 mmφ, the sample broke before winding. Note that the structure did not change significantly before and after the siliconization treatment. From this result, it can be seen that reducing the coarse grain ratio is effective in preventing the deterioration of workability of the high silicon steel sheet.

  On the other hand, as apparent from FIG. 1, the {110} <001> orientation accumulation degree decreases as the coarse grains increase. Since heat treatment at 1100 ° C or higher reduces B8 / Bs to the level of non-oriented silicon steel, there is no point in using a re-rolled plate of a unidirectional silicon steel secondary recrystallized plate as a material for siliconization. Become.

From the above, the ultra-thin silicon steel sheet obtained by re-rolling the unidirectional silicon steel secondary recrystallized sheet is a continuous siliconized line that is heat-treated for about 1 to 30 minutes at a temperature of 1100 ° C or higher as it is. It turns out that it is unsuitable as a material. And, in order to produce ultrathin high silicon steel sheet with high {110} <001> orientation integration degree by continuous siliconization line, there are few coarse grains and high B8 / Bs even when heat-treated at 1100 ° C or higher. It is essential to develop an ultrathin silicon steel sheet suitable for siliconization treatment.
Therefore, in the present invention, as a material for siliconization of a high silicon steel plate that is effective in reducing the size and loss of a high-frequency power source, workability deteriorates even if heat treatment is performed at 1100 ° C. for about 1 to 30 minutes. We focused on obtaining ultra-thin silicon steel sheets with few coarse grains and high B8 / Bs suitable for continuous siliconization process.

From the results so far, generally, the higher the degree of integration of {110} <001> unidirectional silicon steel secondary recrystallized plates, the higher the annealing after rerolling, the grains with different orientations undergo secondary recrystallization and become coarse grains. It was found that it tends to form. On the other hand, if the unidirectional silicon steel secondary recrystallized plate with a low {110} <001> integration degree is re-rolled, it is thought that coarse grains are less likely to be generated even when high-temperature annealing is performed.
Therefore, samples with different B8 were cut out from the raw material, and these were re-rolled at a reduction rate of 71% and subjected to finish annealing, and the coarse grain ratio and B8 were investigated. The results obtained are shown in Table 2. The coarse particle ratio and B8 were measured by the same method as described above.

  From Table 2, when the part of B8 / Bs = 0.79-0.84 was re-rolled, coarse grains were not recognized even when annealed at 1100-1200 ° C. as expected. However, B8 stayed at a low overall value of 1.50 to 1.66 T (0.73 to 0.83 for B8 / Bs). On the other hand, the re-rolled part of B8 / Bs = 0.91 with the same material shows high B8 with almost no coarse particles up to 1050 ° C as before, but a lot of coarse particles are generated at 1100 ° C or higher and B8 is greatly increased. Declined.

  From the above, when rerolling a plate with a low {110} <001> integration degree, B8 / Bs ≧ 0.85 cannot be achieved after finish annealing, and a plate with a high {110} <001> integration degree In the case of re-rolling, coarse grains are generated during high-temperature annealing at 1100 ° C. or higher, and B8 also decreases.

Therefore, the inventors have intensively studied and found that the roughness of the steel sheet subjected to re-rolling affects the coarse grains after annealing. The details of the experiments that lead the way are shown below.
A unidirectional silicon steel secondary recrystallized plate having a thickness of 0.29 mm and B8 / Bs = 0.93 was used as a material. When the surface roughness was measured with the coating removed by pickling, the arithmetic average Ra was 0.37 μm. This was polished with various emery papers to produce samples with different surface roughness. Next, it was cold-rolled at a reduction rate of 71%, heated at a heating rate of 18 ° C./sec and annealed at 1150 ° C. for 2 minutes, and then the surface macrostructure and B8 were evaluated by the same method as described above.
As a result, in the sample with an arithmetic average Ra of surface roughness before re-rolling of less than 0.6, coarse particles appear prominently, and B8 is also a low value, whereas in samples with an arithmetic average Ra of 0.6 μm or more, the coarse particle ratio It was found that B8 also showed a high value of 1.78T. However, when Ra was 3.7 μm, B8 after annealing was as low as 1.67 T, though almost no coarse grains were observed. The surface roughness after re-rolling was about 0.2 to 0.3 μm regardless of Ra before re-rolling, and no clear difference was observed. From this experimental result, it is considered that the surface roughness before rerolling has a great influence on the recrystallization behavior after rerolling and high temperature finish annealing.

Next, in order to investigate the relationship between the structure and workability of the 6.5% silicon steel plate by siliconizing, the above-mentioned samples with different surface roughnesses were re-rolled to a plate thickness of 0.080 mm. A 6.5% Si steel sheet was fabricated by heating to 1150 ° C at a temperature rate of 16 ° C / s and performing a silicon-soaking / diffusion treatment for 8 minutes using SiCl ₄ gas. A sample treated with the same thermal history in N ₂ without using SiCl ₄ gas was also prepared. When the structures of these samples were observed and compared in the same manner as described above, almost no difference was observed.
Furthermore, the bendability was evaluated by winding the siliconized sample around a small-diameter round bar. The results obtained are shown in Table 3.

From Table 3, it was found that when the coarse particle ratio was 15% or less, it was wound around a round bar having a diameter of 4 mmφ, whereas when the coarse particle ratio exceeded 15%, many cracks occurred during winding. When the round bar is wound around a round bar having a diameter of 4 mm, the plate is an area where the plate is plastically deformed, but it is not preferable in terms of product workability to break at a larger diameter. Therefore, the coarse grain ratio should be 15% or less for the siliconized material.
FIG. 2 summarizes the relationship between the surface roughness Ra before rerolling and the coarse grain ratio and B8 / Bs when annealed at 1150 ° C. for 2 minutes after rerolling to 0.080 mm.

From the above, although the details of the effect of surface roughness before rerolling on the recrystallization behavior of the plate obtained by rerolling the unidirectional silicon steel secondary recrystallized plate are not clear, the observation results show that I think so.
When the cross-sectional structure immediately after re-rolling is etched and observed with an optical microscope, in the sample with a large surface roughness, the traces of twins that appear to have originated from surface irregularities are compared in almost all crystal grains. Evenly. On the other hand, in the sample having a small surface roughness, there were few twinning traces as a whole, and there were many crystal grains in which no twinning was observed. Normally, when a secondary recrystallized sheet is rolled and then annealed, grains with an orientation very close to the {110} <001> orientation are generated from the original secondary grains to form a primary recrystallized structure. These crystal grain boundaries are formed at low-angle grain boundaries, and it is difficult for grains to grow during annealing.On the other hand, when a certain temperature is reached, only a few crystals with different orientations are generated near the original secondary grain boundary. A secondary recrystallized structure is formed by being engulfed by the grains. On the other hand, in a sample in which many twins are generated in the original secondary grains, crystal grains having different orientations from the surroundings are likely to be generated from the twins. When such crystal grains are present, abnormal grain growth can be suppressed when annealing is performed at a high temperature. If the amount of twins is too large, the total {110} <001> accumulation will be reduced when primary recrystallization occurs. However, if twins are present appropriately, {110} <001 > Suppression of secondary recrystallization during high temperature annealing is suppressed without significantly reducing the degree of integration. By defining the surface roughness before rolling this time, moderate twins are formed during rolling, and secondary annealing can be performed even if high temperature annealing is performed without significantly reducing {110} <001> accumulation during annealing. It is thought that the material which is hard to crystallize could be obtained.

As mentioned above, this invention was made | formed based on the said experimental result and knowledge, and the summary is as follows.
[1] An ultrathin silicon steel plate having a thickness of 0.03 to 0.10 mm obtained by re-rolling a unidirectional silicon steel secondary recrystallized plate containing Si: 2 to 4% by mass, and in a nitrogen atmosphere, After heat treatment at 1100 ° C for 1 minute, the ratio of coarse grains whose maximum grain width exceeds 5 times the plate thickness is 15% or less and B8 / Bs is 0.85 or more Thin silicon steel sheet.
However, the ratio of the coarse grains is the area ratio of the coarse grains to the entire crystal plate surface, and B8 / Bs is the ratio of the magnetic flux density B8 and the saturation magnetic flux density Bs when excited with a magnetizing force of 800 A / m in the rolling direction.
[2] A unidirectional silicon steel secondary recrystallized plate containing Si: 2 to 4% by mass and B8 / Bs of 0.9 or more is subjected to mechanical polishing or chemical corrosion, and the unidirectional The thin film is characterized in that the arithmetic average Ra of the roughness of the surface of the secondary recrystallized steel plate is 0.6 μm or more and less than 3.5 μm, and then rolled to a plate thickness of 0.03 to 0.10 mm at a rolling reduction of 60 to 90%. A method for producing a silicon steel sheet.
However, B8 / Bs is the ratio of the magnetic flux density B8 and the saturation magnetic flux density Bs when excited in the rolling direction with a magnetizing force of 800 A / m.
[3] In a unidirectional silicon steel secondary recrystallized plate containing, by mass%, Si: 2 to 4%, B8 / Bs of 0.9 or more, with the forsterite film removed or without the forsterite film, Annealing is performed in a humid atmosphere, and an internal oxide layer having a thickness of 1 μm or more is formed on the surface of the unidirectional silicon steel secondary recrystallized plate, and then the internal oxide layer is removed by chemical corrosion. A method for producing an ultrathin silicon steel sheet, characterized in that the arithmetic average Ra is 0.6 μm or more and less than 3.5 μm, and then rolled to a sheet thickness of 0.03 to 0.10 mm at a rolling reduction of 60 to 90%.
However, B8 / Bs is the ratio of the magnetic flux density B8 and the saturation magnetic flux density Bs when excited in the rolling direction with a magnetizing force of 800 A / m.
[4] Production of ultra-thin silicon steel sheet according to [2] or [3], wherein after the rolling, the temperature range from room temperature to 1100 ° C. is further heated at a rate of temperature increase of 15 ° C./s or more. Method.

  In this specification, “%” and “ppm” indicating the components of steel are mass% and mass ppm, respectively.

  According to the present invention, an ultrathin silicon steel sheet suitable for a continuous siliconization process in which the treatment is performed at 1100 ° C. or higher can be obtained according to the present invention. Then, by subjecting the ultrathin silicon steel sheet of the present invention to a siliconization process, it is possible to provide a silicon steel sheet having a higher magnetic flux density and lower high frequency and low iron loss than in the past.

The present invention is described in detail below.
The object of the present invention is an ultrathin silicon steel plate having a thickness of 0.03 to 0.10 mm obtained by rerolling a unidirectional silicon steel secondary recrystallized plate containing Si :: 2 to 4%. In addition, after heat treatment at 1100 ° C. for 1 minute in a nitrogen atmosphere, the ratio of coarse grains where the maximum width of crystal grains exceeds 5 times the plate thickness is 15% or less, and B8 / Bs is 0.85 That's it. However, the ratio of the coarse grains is the area ratio of the coarse grains to the entire crystal plate surface, and B8 / Bs is the ratio of the magnetic flux density B8 and the saturation magnetic flux density Bs when excited with a magnetizing force of 800 A / m in the rolling direction. (Hereafter, this ratio is abbreviated as B8 / Bs). These are the most important requirements in the present invention.
Si: 2-4%
If the amount of Si in the material is small, the amount of raw material SiCl ₄ gas used will increase during the silicidation process, and the cost will increase due to the prolonged silicidation process, so the lower limit is set to 2%. In addition, if the Si content increases, rolling becomes difficult, so the upper limit of the Si content is 4%.
Thickness 0.03-0.10mm
If the plate thickness is less than 0.03 mm, the manufacturing cost increases and the man-hours for assembling the iron core increase, which is not desirable. On the other hand, when the plate thickness exceeds 0.10 mm, the high-frequency iron loss increases.
In the siliconization treatment in a continuous line, heat treatment is required at 1100 ° C or higher for 1 minute or longer. Therefore, if the ratio of coarse particles after heat treatment under these conditions is 15% or less, the bending workability after the siliconization treatment can be ensured. In addition, if the plate thickness is 0.1 mm or less, it is possible to produce a 6.5% silicon steel sheet with sufficiently good characteristics by immersion or diffusion treatment within 1200 minutes at 1200 ° C. or less, preferably after heat treatment at 1200 ° C. for 30 minutes. The ratio of coarse particles is 15% or less.

B8 of 3% Si non-oriented electrical steel sheet obtained by primary recrystallization of cold-rolled sheet with B8 / Bs of 0.85 or more is around 1.45T, and the 6.5% Si steel sheet currently industrially produced is also made of this material. Used. By the way, the core dimensions of the reactor and the like are designed using this B8 as an index. In order to reduce the size of the iron core, it is required to increase the B8 of the material. The core downsizing, as a whole reactor, has strong user needs because it has many secondary improvement effects such as a reduced amount of windings and improved copper loss and reduced material costs for the case. However, the improvement of B8 of about several percent is absorbed in the cost of design change, so to obtain a substantial improvement effect, it is necessary to improve B8 by 20% or more.
3% Si material B8 is equivalent to 1.73T or more. Therefore, in the present invention, B8 / Bs of the material suitable for the siliconization treatment is set to 0.85 or more. The reason why the ratio B8 / Bs with the saturation magnetic flux density Bs is used instead of B8 is that this does not depend on the amount of material Si.

  By using the ultrathin silicon steel sheet as described above, the conventional ultrathin silicon steel sheet produced by re-rolling the unidirectional silicon steel secondary recrystallized sheet generates coarse grains at 1100 ° C or higher and decreases B8. Therefore, while being unsuitable as a material for siliconization, the present invention provides an excellent material for siliconization in which even if annealing is performed at 1100 ° C. or higher, the ratio of coarse particles is small and there is almost no decrease in B8.

Next, the manufacturing method of the ultra-thin silicon steel plate of this invention is demonstrated.
A unidirectional silicon steel secondary recrystallized plate containing, by mass%, Si: 2 to 4% and B8 / Bs of 0.9 or more is subjected to mechanical polishing or chemical corrosion, and the unidirectional silicon steel The arithmetic average Ra of the roughness of the secondary recrystallized sheet surface is set to 0.6 μm or more and less than 3.5 μm, and then rolled to a sheet thickness of 0.03 to 0.10 mm at a rolling reduction of 60 to 90%. Alternatively, the unidirectional silicon steel secondary recrystallized plate containing, by mass%, Si: 2 to 4% and B8 / Bs of 0.9 or more is annealed in a wet atmosphere, and the unidirectional silicon steel secondary recrystallization is performed. An internal oxide layer with a thickness of 1 μm or more is formed on the crystal plate surface, then the internal oxide layer is removed by chemical corrosion, the arithmetic average Ra of the surface roughness is 0.6 μm or more and less than 3.5 μm, and then the reduction rate Roll to 60-90% to plate thickness 0.03-0.10mm. Preferably, after the rolling, a heat treatment is further performed at a temperature increase rate of 15 ° C./s or more in a temperature range from room temperature to 1100 ° C.

The arithmetic average Ra (hereinafter referred to as Ra) of the surface roughness before re-rolling is the most important point in the present invention.
Usually, Ra is 0.2 to 0.4 μm when the film of the secondary recrystallization plate is removed by pickling. When the surface roughness of the secondary recrystallized plate is increased, the {110} <001> orientation accumulation degree of the primary recrystallized structure obtained when rolling and annealing is considered to decrease. There has never been an idea to do. However, in the present invention, Ra before re-rolling is set to 0.6 μm or more and 3.5 μm or less. By setting Ra before rolling to 0.6 μm or more and 3.5 μm or less, generation of coarse grains when re-rolling and annealing at 1100 ° C. or more can be suppressed, and B8 can be maintained at a relatively high value.
To adjust the surface roughness, mechanical polishing or chemical corrosion may be used, or an internal oxide layer of 1 μm or more is formed on the surface of the secondary recrystallized plate without forsterite or once the film is removed. After that, it may be chemically corroded.

Since the rolling reduction is 60 to 90%, the arithmetic average Ra of the surface roughness is set to 0.6 μm or more and less than 3.5 μm before rolling and rolling to a sheet thickness of 0.03 to 0.10 mm, and then rolling is performed again. When the rolling reduction is less than 60%, the primary recrystallized structure in annealing is low in the {110} <001> orientation, and sufficient B8 cannot be obtained. On the other hand, even if it exceeds 90%, the accumulation of the primary recrystallized structure after annealing in the {110} <001> orientation decreases, and B8 decreases. The plate thickness is set to 0.03 to 0.10 mm for the reason described above.

A temperature range from room temperature to 1100 ° C is heated at a rate of temperature increase of 15 ° C / s (preferred conditions).
When the re-rolled sheet was annealed, it was recognized that the larger the rate of temperature rise, the smaller the coarse grain ratio at high temperatures. Specifically, it is desirable that the heating rate is 15 ° C./s or more.

The re-rolled ultrathin silicon steel plate may be recrystallized by passing through a continuous annealing line, and then may be subjected to a siliconizing process by blowing Si-based reaction gas into the furnace without cooling.
The siliconization treatment can be performed according to a conventional method. The concentration of SiCl ₄ gas is not particularly limited, but is preferably about 5% to 50%. If it is too low, the reactivity is poor and it is difficult to obtain the effects of the present invention. If it is too high, excess gas will be used, resulting in poor economic efficiency.

After removing the insulating film by pickling and removing the unidirectional silicon steel secondary recrystallized plate (B8 / Bs = 1.93T) with a thickness of 0.30mm which contains Si: 3.2% and the balance is essentially Fe Samples with different surface roughness Ra were prepared by polishing the surface with emery paper with grain roughness # 60-600. Next, it was cold-rolled to a thickness of 0.086 mm. The ultrathin silicon steel sheet obtained as described above was heated at a heating rate of 18 ° C./s in 100% N ₂ and annealed at 1100 ° C. for 1 minute and 1200 ° C. for 30 minutes. B8 was evaluated. The microstructure of the sample surface was observed to determine the coarse particle ratio. The coarse particle ratio is obtained by pickling the steel plate surface with a solution containing hydrochloric acid and then taking a photograph to measure the number and size of coarse particles having a particle size of 5 times or more, that is, a particle size of 400 μm or more. Was divided by the area of the observation field. Table 4 shows the obtained results.

  Table 4 shows that for Ra ≤ 0.5 μm, the ratio of coarse grains after rerolling and annealing greatly exceeds 15%, and the value of B8 is low, whereas in the samples with Ra of 0.9 to 2.1 μm, coarse grains are almost Not recognized, B8 showed a high value of 1.75T or higher. In the sample with Ra = 3.7 μm, coarse particles were not seen, but B8 was as low as 1.64T. In annealing at 1200 ° C. for 30 minutes, coarse grains tended to increase slightly compared to annealing at 1100 ° C. for 1 minute, but the results were almost the same.

The insulating film was pickled and removed from a unidirectional silicon steel secondary recrystallized plate (B8 / Bs = 0.91) having a thickness of 0.30 mm containing Si: 3.2% and the balance being substantially Fe. At this time, the surface roughness was Ra = 0.4 μm. Next, after removing some samples, the samples were further pickled with 10% nitric acid (50 ° C), 10% hydrochloric acid (80 ° C), or 10% sulfuric acid (80 ° C) for 30 seconds to 5 minutes. The surface roughness was measured again. Subsequently, it was cold-rolled to a thickness of 0.075 mm, annealed in 100% N ₂ at the temperature and time shown in Table 5, and then subjected to surface structure observation and B8 evaluation in the same manner as in Example 1. The results obtained are shown in Table 5.

  From Table 5, many coarse grains were generated in the sample with the surface roughness Ra <0.6 μm before re-rolling, whereas almost no coarse grains were observed when Ra ≧ 0.6 μm. Further, it was confirmed that B8 also showed a high value when Ra ≧ 0.6 μm.

Si: Containing 3.2%, unidirectional silicon steel secondary recrystallized plate (B8 / Bs = 0.91) having no forsterite film substantially comprising Fe, 850 ° C., dew point 40-50 ° C., Heat treatment was performed for 10 to 30 seconds in a 60% H ₂ + 40% N ₂ atmosphere. The thickness of the internal oxide layer was confirmed by SEM observation after etching the sample cross section.
The heat-treated sample was immersed in a 10% H ₂ NO ₃ solution heated to 40 ° C. for 3 minutes to remove the internal oxide layer, and then the surface roughness was measured. Note that Ra before the formation of the internal oxide layer was 0.3 μm. Next, the sample was cold-rolled to a thickness of 0.065 mm, and then annealed in 100% N ₂ at the temperature and time shown in Table 6, followed by surface texture observation and B8 evaluation in the same manner as in Example 1. went. The results obtained are shown in Table 6.

  From Table 6, if the thickness of the internal oxide layer is 1 μm or more and then pickled and removed, sufficient surface roughness can be obtained, and almost no coarse particles are observed even after high-temperature annealing at 1100 ° C. or 1200. It was found to show B8.

After changing the surface roughness of the secondary recrystallized plate by mechanical polishing in Example 1, the rerolled steel plate was heated at a heating rate of 16 ° C / s, and then was subjected to silicification / diffusion for 7 minutes at 1150 ° C. The 6.5% silicon steel sheet was processed.
The obtained 6.5% silicon steel sheet was subjected to structure observation, B8 measurement, and workability evaluation by being wound around a round bar having a different diameter in the same manner as in Example 1. The results obtained are shown in Table 7.

  From Table 7, it can be seen that when the surface roughness before re-rolling Ra ≧ 0.6 μm, the coarse grain ratio is 15% or less, and a material showing high B8 / Bs without deterioration in workability can be obtained.

  The ultra-thin silicon steel sheet of the present invention has excellent high-frequency characteristics and is suitable for a continuous siliconization process in which processing is performed at 1100 ° C. or higher. Therefore, the ultra-thin silicon steel sheet is suitable for various uses as a core material mainly for transformers, motors, reactors, etc. Can be used.

It is a figure which shows the relationship between heat processing temperature, magnetic flux density B8, and a coarse grain ratio. It is a figure which shows the relationship between the surface roughness Ra before re-rolling, a coarse grain ratio, and B8 / Bs when annealing at 1150 degreeC for 2 minutes after re-rolling to 0.080 mm.

Claims (4)

An ultrathin silicon steel sheet having a thickness of 0.03 to 0.10 mm obtained by rerolling a unidirectional silicon steel secondary recrystallized sheet containing Si: 2 to 4% by mass%, in a nitrogen atmosphere at 1100 ° C., The ultrathin silicon steel sheet with a ratio of coarse grains whose maximum width of crystal grains exceeds 5 times the plate thickness after heat treatment under 1 minute condition is 15% or less and B8 / Bs is 0.85 or more .
However, the ratio of the coarse grains is the area ratio of the coarse grains to the entire crystal plate surface, and B8 / Bs is the ratio of the magnetic flux density B8 and the saturation magnetic flux density Bs when excited with a magnetizing force of 800 A / m in the rolling direction. A unidirectional silicon steel secondary recrystallized plate containing, by mass%, Si: 2 to 4% and B8 / Bs of 0.9 or more is subjected to mechanical polishing or chemical corrosion, and the unidirectional silicon steel An arithmetic average Ra of the roughness of the secondary recrystallized sheet surface is 0.6 μm or more and less than 3.5 μm, and then rolled to a sheet thickness of 0.03 to 0.10 mm at a rolling reduction of 60 to 90%. Production method.
However, B8 / Bs is the ratio of the magnetic flux density B8 and the saturation magnetic flux density Bs when excited in the rolling direction with a magnetizing force of 800 A / m. In a wet atmosphere in a unidirectional silicon steel secondary recrystallized plate containing, by mass%, Si: 2 to 4%, B8 / Bs of 0.9 or more, with the forsterite film removed or without the forsterite film Annealing is performed to form an internal oxide layer having a thickness of 1 μm or more on the surface of the unidirectional silicon steel secondary recrystallized plate, and then the internal oxide layer is removed by chemical corrosion. Is made to be 0.6 μm or more and less than 3.5 μm, and then rolled to a sheet thickness of 0.03 to 0.10 mm at a rolling reduction of 60 to 90%.
However, B8 / Bs is the ratio of the magnetic flux density B8 and the saturation magnetic flux density Bs when excited in the rolling direction with a magnetizing force of 800 A / m.   4. The method for producing an ultrathin silicon steel sheet according to claim 2, wherein after the rolling, the temperature range from room temperature to 1100 ° C. is further heated at a temperature rising rate of 15 ° C./s or more. 5.

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