JPH0569909B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to so-called medium to high-grade non-oriented electrical steel sheets with a Si content of 1.0 to 4.0%, particularly non-oriented electrical steel sheets with small anisotropy of magnetic properties in the plane of the rolled plate. It is related to. (Prior Art) Non-oriented electrical steel sheets are mainly used as iron core materials for motors and transformers, and are classified into types according to sheet thickness and iron loss value according to the JIS standard (revised C-2552). Iron loss represents the heat loss that occurs when iron is magnetized.Of course, the smaller the value, the better, but the grade is selected depending on the purpose, such as economic efficiency and the size of the equipment. Generally, as equipment becomes larger, the amount of heat generated by iron loss increases in proportion to its volume, while the amount of heat dissipated is only proportional to its surface area, making it difficult to cool the equipment. For this reason, the larger the equipment, the more materials with low iron loss are required. Iron loss is dominated by two factors: eddy current loss and hysteresis loss. Eddy current loss is a loss due to eddy currents induced by magnetization, and depends on the plate thickness and the electrical resistance of the steel. The thinner the plate thickness, the better, but if it is too thin, problems such as the labor-intensive work of laminating the iron core will occur, so JIS specifies three types: 0.65, 0.50, and 0.35 mm. The higher the electrical resistance of steel, the better, and Si is often used as an alloying element because it has a large electrical resistance increase rate per unit addition amount and is inexpensive. This is why electrical steel sheets are also called silicon steel sheets; the higher the Si content, the lower the iron loss, resulting in higher-grade electrical steel sheets. For similar purposes, Al and
Mn and the like are also added as necessary. On the other hand, the hysteresis loss becomes smaller as the number of fine precipitates and grain boundaries that impede movement of domain walls during the magnetization process decreases. Therefore, it is important to grow crystal grains using steel of as high a purity as possible. Ti, Nb, V, and the like produce fine carbonitrides, and these precipitates inhibit crystal grain growth, resulting in significant deterioration of magnetic properties. For this reason, the addition of these carbonitride-forming elements to electrical steel sheets is strictly limited. Al is also fine AlN
It is generally not added to low-grade electrical steel sheets because it produces similar negative effects. In medium to high-grade electrical steel sheets, Al is added to increase electrical resistance.
In this case, a large amount of 0.1% or more is usually added.
By coarsening the precipitates, adverse effects on hysteresis loss are avoided. In other words, it is generally accepted that Al should not be added at all or, conversely, should be added in a large amount. On the other hand, it has been reported that when boron (B) is added, good magnetic properties can be obtained even if the Al content is less than 0.1% (for example,
59-20731). The reason is not clear, but
It is said that it is necessary to balance it in a certain relationship with the amount of nitrogen (N) in steel. That is, considering that a B/N ratio in the range of 0.5 to 2.5 is considered appropriate, it is presumed that there is a close relationship with the precipitation of BN. In this case, it is said that if the Al content is 0.1% or more, it will only increase the price and the effect of adding B will not be sufficiently obtained. As described above, although B is a nitride-forming element, it is considered to be an element that has relatively little adverse effect on magnetic properties, but its actions and effects have not been fully clarified. So-called medium to high-grade non-oriented electrical steel sheets with low iron loss are particularly required to have small in-plane anisotropy of magnetic properties. In other words, in the iron core of a motor or transformer, lines of magnetic force flow in various directions within the board surface, so if the magnetic properties are poor in a certain direction, this will affect the performance of the entire device. Evaluation of the magnetic properties of non-oriented electrical steel sheets is usually done by
This is done using average values in the rolling direction (L direction) and the direction perpendicular to it (T direction), but when it comes to medium to high-grade electrical steel sheets, it is dangerous to design equipment using only average values. Even if the average value of iron loss is within the control range of the grade, if the difference between the L direction and the T direction is large, the performance of the equipment will be affected by the characteristics in the bad direction. In general, compared to the L direction, T
Usually, the magnetic properties in the direction are poor. In the case of low-grade non-oriented electrical steel sheets, the level of iron loss is high, so some anisotropy is not a problem, but for medium to low iron loss
In high-grade non-oriented electrical steel sheets, even a slight anisotropy difference becomes relatively large and becomes a problem. Non-oriented electrical steel sheets are originally used on the premise that they have no anisotropy. On the other hand, in the case of grain-oriented electrical steel sheets, the magnetic properties in the L direction are maximized by aligning the crystal grains in a specific direction and maximizing anisotropy using secondary recrystallization. This is an improved version. Devices using grain-oriented electrical steel sheets are designed to utilize only the characteristics in the L direction.
In other words, grain-oriented electrical steel sheets and non-oriented electrical steel sheets generally have different uses. In order to reduce iron loss in non-oriented electrical steel sheets, as mentioned above, efforts have been made to reduce eddy current loss by adding alloying elements such as Si, and to reduce hysteresis loss by increasing the purity of the steel. . However, when it comes to medium to high-grade non-oriented electrical steel sheets, it is difficult to obtain the desired low iron loss using only these means.
Various methods are being studied to control the texture (orientation of crystal grains) by adding special alloying elements or modifying manufacturing conditions. In the case of a non-oriented electrical steel sheet, it is not possible to form a strong texture like that of a grain-oriented electrical steel sheet, but it is possible to form a texture that is aligned in the {100} direction, which is the axis of easy magnetization, to some extent. However, although conventional methods can improve the average value of magnetic properties, they often have the fatal drawback of increasing in-plane anisotropy. In other words, in conventional texture control, the overall properties are improved by improving the properties in the L direction, and the properties in the T direction are improved.
The directional characteristics often remain almost unchanged or even slightly degraded. In this way, although it is desired to reduce the in-plane anisotropy of medium to high-grade non-oriented electrical steel sheets with low iron loss, we have developed an effective means to achieve this. The current situation is that this is not the case. (Problems to be Solved by the Invention) In view of the above circumstances, the present invention aims to provide a medium to high-grade non-oriented electrical steel sheet with small in-plane anisotropy and low iron loss. be. (Means for Solving the Problems) The present inventor conducted a detailed study on the effects of various alloy elements constituting electrical steel sheets. As a result, it has been found that the above object can be achieved by keeping the content of each component including Si and Al within an appropriate range, and then adding B within a certain content range. The gist of the present invention resides in the following non-oriented electrical steel sheet. In weight%, C: 0.005% or less, Si: more than 1.0% and less than 4.0%, Mn: more than 0.1% and less than 1.5%, P: 0.1% or less, S: 0.002% or less, Al: more than 0.10% and less than 1.0%. N: 0.004% or less, B: more than 0.0003% and less than 0.0015%, and the balance is Fe and inevitable impurities. A non-oriented electrical steel sheet with small in-plane anisotropy. Conventionally, it has been thought that B exerts its effect through BN precipitation, and emphasis has been placed on its relationship with N content. That is, it is necessary to add B in an amount sufficient to chemically equivalently fix N to some extent (preferably, an amount sufficient to completely fix N). Therefore, in this case, B basically functions to fix N in the same way as Al, but the BN in the precipitate is
It has less negative impact on magnetic properties than AlN, so it is only used for electrical steel sheets. Although the details of precipitates when Al and B are added in combination are not fully clarified, it is thought that AlN precipitates with BN as the nucleus, and as a result, even in steels with relatively low Al content. It is understood that the precipitation of fine AlN is suppressed and the magnetic properties are improved. In response, the present inventors focused on and studied the effect of B addition on anisotropy, targeting medium to high-grade electrical steel sheets with high Si and Al contents. the result,
They discovered that when a small amount of B is added to high-Al steel with an Al content exceeding 0.10%, the anisotropy of magnetic properties is significantly reduced. In this case, N is almost completely fixed by Al, and the solid solution N is substantially close to zero, so it is considered that the effect of B is due to the solid solution B. Although the detailed mechanism is still unknown,
Probably due to segregation of solid solution B at grain boundaries, etc.
It is presumed that the process of cold rolling and subsequent recrystallization annealing contributes to the formation of a texture with low anisotropy. (Function) Hereinafter, the function and effect of the alloying elements in the electrical steel sheet of the present invention will be explained together with the reason for limiting the content. C: C is an element that forms carbides and deteriorates all magnetic properties, so it is desirable to reduce it as much as possible. Especially to prevent magnetic aging,
Must be less than 0.005% and even 0.003
% or less. Si: The Si content is set to exceed 1.0% in order to obtain the core loss necessary for a medium to high-grade non-oriented electrical steel sheet.
If Si is less than 1.0%, eddy current loss will be large and iron loss will not be as low as the target. On the other hand, if Si is contained in an amount of 4.0% or more, cold rolling properties are significantly deteriorated. Mn: Mn is contained in an amount exceeding 0.1% to prevent hot embrittlement caused by S. Mn is also effective in increasing electrical resistance and reducing eddy current loss.
However, if the Mn content exceeds 1.5%, the steel will become brittle and the growth of crystal grains will deteriorate, so it should be less than this. P: P is 0.1% for the purpose of adjusting strength and increasing electrical resistance.
However, if the content exceeds this range, cold rollability will deteriorate. S: S produces sulfide-based precipitates and deteriorates magnetic properties, so it is best to suppress it to 0.002% or less. Al: Generally, medium to high-grade non-oriented electrical steel sheets often contain 0.1% or more for the purpose of increasing electrical resistance and coarsening AlN, but in the present invention, in addition to these effects, N is completely fixed. , B is contained in an amount exceeding 0.10% in order to fully exhibit its effects. On the other hand, if the content exceeds 1.0%, the effect will be saturated and the price will only increase, so the content should be less than this. N: Since N forms nitrides and impairs magnetic properties, the content should be 0.004% or less, preferably 0.002% or less. B: B is 0.0003 to reduce the anisotropy of magnetic properties.
% or more. If it is less than 0.0003%, the amount of solid solution B will be insufficient and the anisotropy will increase. On the other hand, if the content exceeds 0.0015%, not only the effect of reducing anisotropy is saturated, but also the overall magnetic properties tend to deteriorate due to an increase in precipitates. The effect of adding a small amount of B on reducing the anisotropy of the magnetic properties is only effective when the Al content is high. That is, by sufficiently adding Al as described above,
It is also essential to add a small amount of B. Usually, it is appropriate to contain B in a range of 0.0008 to 0.0012%. The electrical steel sheet of the present invention having the composition as described above can be manufactured by the following method. The slab heating temperature in the hot rolling process is 1100~
The temperature should be within the range of 1250℃. Low temperature heating is better to prevent deterioration of magnetic properties due to fine precipitation of MnS, but in order to ensure hot rolling finishing temperature, the temperature cannot be lowered too low. A temperature of about 1150 to 1200°C is suitable. The hot rolling finishing temperature should be higher, preferably 800℃ or higher.
The temperature shall be 850℃ or higher. It is better to wind it at a high temperature,
A suitable winding temperature is 550 to 650°C, taking into account pickling properties. After hot rolling, the hot rolled sheet is annealed at 750°C or higher, preferably 850°C or higher, in order to recrystallize the worked structure of the hot rolled sheet. However, if this temperature becomes too high, the crystal grains will become coarse and cracks will easily occur during the next cold rolling, so it is better to keep it below 1050°C. Usually, continuous annealing is carried out at 900 to 1000°C for 5 minutes or less, but box annealing at 800 to 900°C may also be used. The reduction ratio of cold rolling is in the range of 60-90%. From the viewpoint of magnetic properties, it is appropriate to perform a one-time cold rolling process with a reduction of about 75 to 85%. When placing importance on reducing iron loss, cold rolling including intermediate annealing may be performed two or more times. It is desirable that the final annealing be performed at 850°C or higher for 3 minutes or less using a continuous annealing method. (Example) Steel having the composition shown in Table 1 was melted in a laboratory and made into a thin plate with a thickness of 0.5 mm in the next manufacturing process. In other words, the heating temperature for hot rolling is 1150℃, and the finishing temperature for rolling is 850℃.
After rolling, the material was air cooled to 600°C, and then placed in a furnace maintained at 600°C for furnace cooling. This is a heat treatment equivalent to winding a hot-rolled coil. The thickness of the hot-rolled plate was 2.3 mm, and after pickling, it was further heat-treated at 950°C for 3 minutes. This is done to recrystallize the structure of the hot rolled sheet. Steel with a high Si content tends to leave processed structures in hot-rolled sheets, and the surface shape deteriorates during cold rolling, which is why hot-rolled sheets are heat-treated in this way. Thereafter, it was cold rolled to a thickness of 0.5 mm at a reduction rate of 78%. After recrystallizing the cold-rolled sheet at 950° C. for 1 minute, specimens were punched out from the L direction and the T direction, and their magnetic properties were measured. The measurement results are shown in Table 2. The present invention (a, d,
It is clear that the difference between the L direction and the T direction is small in both cases, and the average characteristics are also excellent. On the other hand, even steels with high Al content, steels that do not contain B (B, E, and J), and even steels with B added,
Steels with low Al content (C and L) have large anisotropy, and the object of the present invention is not achieved. Also,
In steel (F) with too much B content, the magnetic anisotropy becomes slightly large and the average value becomes poor.

【table】

[Table] (Note): * indicates that it is outside the scope specified by the present invention.

[Table] (Effects of the Invention) The non-oriented electrical steel sheet of the present invention has extremely small anisotropy of magnetic properties within the sheet plane, and can be manufactured at low cost. The electrical steel sheet of the present invention greatly contributes to improving the performance of motors, transformers, etc. as iron core materials.

Claims (1)

[Claims] 1% by weight, C: 0.005% or less, Si: more than 1.0% and less than 4.0%, Mn: more than 0.1% and less than 1.5%, P:
0.1% or less, S: 0.002% or less, Al: more than 0.10%
A non-oriented electrical steel sheet with small in-plane anisotropy, characterized in that it contains less than 1.0%, N: 0.004% or less, B: more than 0.0003% and less than 0.0015%, and the remainder consists of Fe and inevitable impurities.