JPS58747B2 - Low iron loss unidirectional silicon steel sheet and its manufacturing method - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a unidirectional silicon steel plate with high magnetic flux density and low core loss, and a method for manufacturing the same. Conventionally, unidirectional silicon steel sheets each have (110) grains.
It has been said that those in the (001) direction are better. Therefore, when manufacturing unidirectional silicon steel sheets, various methods are adopted to bring all grains close to the (110) [0OL) orientation, and as a result, today the iron loss is 11
0watts/kg (17KG, 50Hz, plate thickness 0-3
Those exhibiting a low level of around 0-3O are produced industrially. However, in order to obtain a unidirectional silicon steel sheet with even lower core loss, it has been found through research by the present inventors that there is a limit to simply bringing the crystal structure closer to the (110)(001) orientation. The present inventors have already found that when the [001] axis has an angle to the rolling surface rather than the ideal (110) [001] orientation, a material with lower iron loss that is superior to the conventional one can be obtained. . That is, the essential feature of the present invention is that the [001] axis is inclined within a range of approximately 4° or less with respect to the rolling surface. As a specific manufacturing method, the steel plate surface is given a minute curvature extending in a direction crossing the rolling direction in the final plate thickness step before application of an annealing separator, and then subjected to secondary and secondary recrystallization annealing. This is due to the fact that this minute curvature is corrected in the process. In addition, the present inventors applied linear microstrain to the steel plate surface having a linear glassy surface coating on the surface of the steel plate having a glassy surface coating after completion of the secondary recrystallization obtained by the method described above. By this method, the inventors have invented that an iron loss that is even lower than that obtained by the above-mentioned method can be obtained. The specific manufacturing method is as follows. During or after the above-described microcurvature correction process, a linear micro-strain is applied via the glassy surface coating formed on the surface of the steel sheet. The application method is, for example, a method in which a load is applied to a rotor made of a small ball made of a hard substance, and the ball is rotated while pressing it against the surface of the steel plate to draw a line.Details of the present invention are as follows. The basic basis for completing this invention is based on the following experimental facts discovered by the present inventors. 3%5i based on the knowledge that subdivision of magnetic domain width is important for improving iron loss.
-Ideal (1,10)(0) of C00II axis of Fe single crystal
As a result of forming a deviation angle β from the 011t direction and examining the relationship between this deviation angle β and iron loss, the fact shown in FIG. 1 was confirmed. Here, the deviation angle β is the inclination angle of the [001-] axis of the m crystal close to the (11,0) COO11 orientation from the rolling surface (crystal surface). FIG. 1 shows the relationship between the deviation angle β and the iron loss at 50 Hz and 17 KG. As is clear from Fig. 1, the iron loss value of the unidirectional silicon steel sheet strongly depends on the deviation angle β, and the iron loss value is lowest when the [001] axis is inclined at approximately 2 degrees with respect to the rolling surface. It becomes. When the deviation angle β is less than 2°, the iron loss value increases as it approaches 0°, and reaches its maximum value at the ideal (110) (0011 orientation). The loss value is thick. Therefore, in order to obtain a steel plate with qualitatively excellent low core loss, the grain size should be β-0.5 to 4.0°, preferably 1 to 3 ( 001) It can be seen that forming a structure having an axial inclination angle.The fundamental idea of this invention is as follows: To narrow the width of the 180° magnetic domain, and within this 180° magnetic domain, Low iron loss can be obtained by minimizing the presence of circulating magnetic domains other than magnetic domains.The 180° subdivision of magnetic domains occurs due to the fact that the C001,) axis is inclined with respect to the rolling surface. This is done to lower the magnetostatic energy due to the surface magnetic pole. Circulating magnetic domains also occur to lower the magnetostatic energy due to the surface magnetic pole, but these tend to disappear due to the tension along the [001) axis. Therefore, ( 001,) The state in which the axis is tilted 1 or more with respect to the rolling surface and the recirculating magnetic domain is almost eliminated by further application of tension is the state in which the 180° magnetic domain subdivision is greatest and the lowest core loss can be obtained. This is possible.The surface film that is finally formed on the surface during the manufacturing process of grain-oriented silicon steel sheets provides tension to the steel sheet, which has the same effect as external tension, so that the [001] axis is aligned with the rolling surface. This is a necessary condition for the subdivision of 800 magnetic domains. By applying micro-strain to the steel plate whose (001) axis is inclined with respect to the rolling surface, the iron loss can be further reduced. (Figure 2). Figure 2 shows the effects of tension and microstrain on the iron loss of a 3%5i-Fe single crystal. The horizontal axis is the (0011 axis) Indicates the angle of inclination to the surface2
ing. Tension was applied in the longitudinal direction of the sample, and minute strains were applied at intervals of 5 mm in the direction perpendicular to the longitudinal direction using a ballpoint pen with a diameter of 0.6 mm. In the figure, there is no tension or strain (−〇−), only tension is applied (−・−), and only strain is applied (−−○'
−−), if the tension is applied after applying strain (−＊−
). From the figure, it can be seen that the decrease in iron loss due to strain becomes larger as the angle of the (ool,) axis with respect to the rolling surface is smaller, regardless of whether there is tension or not. In addition, regardless of whether there is distortion or not, the reduction in iron loss due to tension reaches its maximum when the angle of inclination is about 2°, and decreases even if the angle is larger or smaller than this angle. When tension is applied after strain is introduced, the iron loss force is lower than under any other condition, but the lowest iron loss is obtained when the inclination angle is about 1°. FIG. 3 shows an electron micrograph of the magnetic domain pattern of a sample to which tension was applied and minute strain was applied in the same manner as in FIG. 2. Figure 3a shows a comparative example in which neither tension nor microstrain is applied, and Figure 3a shows a sample with a load of 1.5kg/mm2 in the longitudinal direction (horizontal direction in the drawing).
FIG. 3C is an example in which only a small amount of tension is applied, and FIG. 3D is an example in which tension is applied after a small amount of strain is applied (in the vertical direction in the figure). From the comparative observation of the magnetic domain shapes in Figure 3a and c, the effect of reducing iron loss due to microstrain is that the 180° magnetic domain width decreases due to strain and the generation of auxiliary magnetic domains mainly consisting of 180° magnetic domains. This is thought to contribute to the reduction of iron loss. In other words, auxiliary magnetic domains are likely to be generated due to the demagnetizing field due to magnetic poles near the strain line and local internal strain (this contributes to the subdivision of the 180° magnetic domain in the demagnetized state, and furthermore, the auxiliary magnetic domain near the strain line participates in magnetization. This is thought to be due to the fact that the 180° magnetic domain in the magnetized state is narrowed substantially, which is completely different from the case of the tension shown in Figure 3. Therefore, as shown in Figure 3 d, the strain applied to the sample When tension is applied, the iron loss exhibits an inclination angle dependence as if the strain effect and tension effect were acting separately.Next, the method for manufacturing the unidirectional silicon steel sheet according to the present invention will be described. 001] A method for periodically forming an inclination of an axis with respect to a rolling surface is described.This invention is a method for periodically forming an inclination of an axis with respect to a rolling surface. Completely different from a strip coil shape, a steel plate with a wave shape is created after the steel plate has reached its final thickness and is given a wave shape extending in a direction crossing the rolling direction, and after the above-mentioned secondary recrystallization annealing is performed. As mentioned above, this allows the (001, l axis to be tilted within ±4.0° or less, preferably within the range of ±0.3 to 3°, with respect to the rolling surface. It is possible to obtain a structure close to the above-mentioned ideal structure of the crystal grains consisting of the unidirectional silicon steel sheet, and the iron loss of the unidirectional silicon steel sheet can be reduced to an extremely low level. Silicon steel sheets can be produced by obtaining a steel ingot with an appropriate composition by an electric furnace method, an open hearth method, or a converter method, soaking this steel in a soaking furnace, and forming it into a slab by blooming or as described above. The molten steel obtained by the steel manufacturing method is continuously cast directly, or after continuous casting, a preliminary rolling process is added to form slabs, and these slabs are hot rolled to an intermediate thickness to obtain hot rolled sheets. The hot-rolled sheet is pickled and, if so, heat treated at this stage, and then cold-rolled usually twice with intermediate annealing in between.
(two-time cold rolling method), ′ or - cold rolling method only (
- double cold rolling method) to achieve the final standard thickness. This is produced by decarburizing annealing and then annealing at a high enough temperature to cause secondary recrystallization. Conventional annealing, which is performed at a high enough temperature to cause secondary recrystallization, is usually performed to prevent seizure between steel plates, to form a strong insulating film, and to purify impurities contained in steel plates.
The target is those that are coated with a so-called annealing separator such as gO on the surface of the steel plate after the above-mentioned decarburization annealing and then wound into a coil shape, or those that are pro-eutectoid to a predetermined length and laminated in a sheet shape. It was done as such. On the other hand, there is also a method of secondary recrystallization by continuously heating a steel plate coated with the above-mentioned annealing separator at a high temperature for a predetermined time while it is still in a band shape. However, in either case, secondary recrystallization annealing was performed on the steel sheet in a flat state. In this invention, the shape of the steel sheet in secondary recrystallization annealing is made to have a minute curvature extending in a direction crossing the rolling direction, and the curvature is flattened after the completion of secondary recrystallization. It can significantly lower iron loss compared to silicon steel sheets, and has a silicon content of 0 to 4.0.
% to the final product plate thickness, and then decarburization annealing and secondary recrystallization annealing. The purpose is to straighten the steel plate having the above-mentioned minute curvature into a flat plate after secondary recrystallization annealing. Typical examples of the shape of the steel sheet in secondary recrystallization annealing are shown in FIGS. 4a and 4b. As shown in these figures, it is necessary to have a wavy shape extending in a direction intersecting the rolling direction of the steel plate. Generally, it is practical to give a steel plate the sinusoidal curvature shown in FIG. 4a from the viewpoint of ease of forming and correction. In this case, θ is 0.5 to 4.0°, preferably 1 to 3°, and P is required to be smaller than the secondary recrystallized grains. Even if θ is smaller than 0.5° or larger than 4°,
Alternatively, even if P is made larger than the secondary recrystallized grain size, iron loss cannot be significantly improved. The reason for this is clear from FIG. 1, which shows the principle of this invention. - To give a steel plate a curvature extending in a direction intersecting the rolling direction, rolling, pressing, etc. may be used. For example, there is a method of imparting minute curvatures to a steel plate using a pair of rolls having minute curvatures extending in a direction intersecting the circumferential direction of the steel plate, or a method of imparting minute curvatures to a steel plate using a press having a die having minute curvatures carved thereon. Regarding the timing of forming, it is practical to carry out the forming at the cold rolling or warm rolling stage, but depending on the case, it may be carried out during or after the decarburizing annealing. After applying an annealing separator if necessary, the slightly curved steel plate is wound into a coil in the form of a band, and subjected to secondary recrystallization annealing in a box-shaped annealing furnace. - Secondary recrystallization annealing may be carried out in a continuous annealing furnace during unwinding and winding of the steel sheet in the form of a strip. In this invention, it is necessary to perform a step of flattening the slightly curved steel plate after the secondary recrystallization annealing. The methods of micro-curvature straightening include rolling, roller leveler, tension,
A normal method such as pressing (at room temperature) may be used. (The flattened steel plate may be used as is, but generally internal strain due to shape correction and surface machining is present in the steel plate and deteriorates the magnetic properties, so it is usually 600~
It is preferable to perform so-called strain relief annealing, which is heated to a temperature of 1200°C. Note that the above-described shape straightening of the steel plate may be performed in a strain relief annealing furnace together with strain relief annealing, and it is practical to use a hot leveler in a continuous strain relief annealing furnace. In this way, the iron loss value of the unidirectional silicon steel sheet can be lowered by giving the steel plate a slight curvature to the final thickness, performing secondary recrystallization annealing, and flattening the steel plate by straightening the minute curvature. Do what you want to do. Industrially, the above-mentioned application of minute curvature to a steel plate is carried out using a roll having a minute curvature carved into its circular surface. When the steel plate that has been given a slight curvature in this way is subjected to secondary recrystallization annealing and then flattened, the [001] axis becomes
There will be cars that are periodically tilted within a range of ±4° or less. in this way

The annealed steel plate whose [00] axis is periodically inclined in the range of ±4° or less is also given a slight strain, which is a feature of the present invention. As mentioned above, this steel plate has an insulating glass film formed on it, and when strain is applied to this film,

[00]
The iron loss value on the low iron loss side can be achieved synergistically with the shaft inclination effect. Next, a list of specific methods for imparting minute strain will be listed. For example, as mentioned above, a line is drawn by rotating a rotor made of a small ball surrounded by a hard substance and pressing it against the surface of a steel plate while applying a load.Rotate the small ball. Therefore, strain can be applied to the base steel without causing scratches on the surface of the steel plate, including the glassy coating.The appropriate diameter of the sphere is about 0.2 to 10112771. -J is 10~300μ
It is m. If it is larger than this, the strain area will become too wide (and the iron loss will increase on the contrary.
μ, usually about 1 μ. The above includes slight distortion! This is an example of a method for drawing lines, and the purpose can also be achieved by, for example, drawing a line while rotating a small disk under a load. Alternatively, a line may be drawn by sliding a round object (such as the ball or disc pad mentioned above) or a round object onto the steel plate without causing any scratches. The amount of strain that is effective for reducing iron loss is about the size that can be observed as dislocation pits. In addition, the strain can be applied to either one or both sides of the steel plate (through the vitreous coating. The need to apply the strain through the vitreous coating is as follows. MgO applied before annealing
It is made of Si and other materials contained in the steel sheet, and in addition to preventing seizure during final annealing, it also serves to reduce iron loss by applying tension to the surface of the steel sheet. Next, describe the direction of the linear microstrain. Figure 5a shows the iron loss (W171) when magnetizing in the rolling direction (L direction) with respect to the angle α between the wire direction and the rolling direction when a minute strain is applied to one side of the steel sheet from above the glassy coating.
50). When α is 10°, the iron loss actually deteriorates, but it decreases as α increases, and when α is 30°, it shows an improvement rate of 5% or more, and when α is 45°, it shows an improvement rate of 10% or more. Therefore, in order to significantly improve iron loss, α is: 3
Preferably 0° or more 1. In other words, α is suitably 45° or more. In the case of a wound core, it is sufficient to consider the iron loss in the L direction7
J' - Direction perpendicular to the rolling direction (C direction) depending on the application
The iron loss when the magnetization is 1 or more is also important. The iron loss in the C direction can be improved by decreasing α, contrary to the L direction. From FIG. 4, it can be seen that it is appropriate to pull in the force direction of, for example, 30° to 80° in consideration of improving one characteristic in both directions. Also, the shape of the line does not necessarily have to be straight (although the object of the present invention can be achieved even if the line is curved, zigzag, wavy, or intersects). 39. Next, discuss the appropriate spacing of microdistortion. Figure 6 (plate thickness 0.30 mm) shows a ball with a diameter of 0.7 mm placed on a glassy coating approximately 1 μ thick and rolled in the C direction without applying a load of 200 g to induce linear strain. When, the relationship between line spacing and iron loss is shown. It can be seen that the optimal spacing is 265 to 5 when 200P is used. Also, the optimal spacing changes depending on the load, and the ball preload ″−0,
7m7! In the case of , the optimal spacing increases as the load increases. Since the optimal spacing varies depending on the magnitude of strain, it should be determined on a case-by-case basis depending on the method of introduction, the thickness of the glassy coating, etc., and is not limited to the above example. However, in the case of micro-distortion by the method of the present invention that does not leave any scratches, the optimum spacing is 1 m7IL or more. In order to apply micro-strain in a continuous line, steel plates (strips)
It is better to apply tension to the steel sheet. This is not only to support the load necessary to apply strain to the steel plate, but also to promote the effect of applying strain. The coating usually has a thickness of 1 to 3μ on one side, and this thickness is most suitable for introducing minute strain.However, if it is less than 5μ, it is possible to apply strain to the steel base without damaging the coating. The step of imparting micro-strain, which is a feature of the present invention, may be inserted in any of the post-processes as long as it is after completing the secondary recrystallization. For example, it may be performed immediately after final annealing, or It may be performed after the foot-footing step. Also, if a continuous finish annealing method is adopted, it may be performed during the cooling process. However, it should be applied at a temperature of 800°C or lower, preferably 700°C or lower. Steel plates can be made into products as is, but usually they are coated with a phosphoric acid-based or organic compound as a secondary coating to increase insulation before being made into final products.During coating, the temperature of the steel plate is 800℃ or less. It is preferable that the heating is carried out at a temperature of 700° C. or higher.Ultraviolet curable resin is suitable for this purpose.Examples will be explained below.Example I C; 0.052%, Si;2. 95%, Mn; 0.08
%, S; 0.009%, 5olAl: 0.026%, S
e: A steel ingot containing 0.126% was bloomed and rolled to obtain a slab, and this slab was heated and hot rolled to obtain a hot rolled plate having a thickness of 2.3 mm. Hot-rolled plate annealed at 1150°C for 2 minutes, then pickled, 0.29m
It was cold rolled to m. At this stage, the cold-rolled sheet was divided into three parts, and minute curvatures shown in FIG. 4a were imparted to the steel sheet in parts 1 and 2 by a roll having a minute curvature extending in a direction intersecting the circumferential direction on the roll surface. The minute curvature in the steel plate at this time is the wave height shown in Figure 4 =
50 x 10", pitch -0.5 cm. Part 3, where the coil was divided during the cold rolling stage, retained its shape. These three cold rolled sheets were decarburized and annealed, respectively. Then, the steel sheet surface was decarburized and annealed. After applying MgO to the steel sheet, secondary recrystallization annealing was performed. After washing the steel sheets after secondary recrystallization annealing, these steel sheets were stacked and strain relief annealing was performed while applying pressure to correct minute curvatures. Then, on one side of the second sample (with a glassy coating),
A ball having a diameter of 0.7 mm was rolled in contact with the steel plate under a load of 2001, and linear strain was applied by sweeping the ball linearly in a direction perpendicular to the rolling direction at an interval of 5 mm. The magnetism of these three samples in the rolling direction was , and an improvement in iron loss was observed. Example 2 C: 0.055%, Si: 2.95%, Seed: 0.089
%, S; 0.026%, 5olAl; 0.028, N;
For a hot rolled sheet with a thickness of 2.3 mm containing 0.0065%, 1150
After hot-rolled sheet annealing for 2 minutes at ℃, pickling and then
．． It was cold rolled to 29 mm. At this stage, the cold-rolled sheet was divided into three parts, and parts 1 and 2 were subjected to slight curvature at a warm temperature (550° C. for 30 seconds) in the same manner as in the previous example. In this case, the wave height was 25 x 10-6 m and the pitch was 5. Part 3, which was divided at the cold rolling stage, retained its shape after being subjected to the same heat treatment as Parts 1 and 2 (550°C x 30 seconds). These three cold rolled sheets were decarburized and annealed in the same manner as in Example 1, followed by secondary recrystallization annealing and shape correction annealing. After that, a ball with a diameter of 0.5 mm was rolled on one side of the second sample (with a glassy coating) in contact with the steel plate under a load of 30 oz, and the ball was swept linearly in a direction perpendicular to the rolling direction at an interval of 5 mm. Added linear distortion. As for the magnetism in the rolling direction of these three samples, improvement in iron loss was observed as in Example 1 with a hole.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the inclination angle β of the (001) axis with respect to the rolling surface and iron loss, FIG. 2 is a diagram showing the effect of applying minute strain on the β angle and iron loss, and FIG. 3a. b, e, and d are electron micrographs showing the influence of microstrain and tension on the magnetic domain shape; Fig. 4 a, b are profile diagrams of microcurvature; Figs. Diagram showing improvement rate, Figure 6a. b is a diagram showing the relationship between minute strain application interval and iron loss.

Claims (1)

[Claims] 1. A silicon steel plate on which an insulating coating is formed, having a [001] axis inclined at 4° or less with respect to the rolling surface, and containing 4% or less Si and having a microstrain applied to the steel plate from above the coating. Contains low iron loss unidirectional silicon steel plate. 2. In the process before applying the annealing separator, a slight curvature is imparted to the final thickness steel plate in the direction crossing the rolling direction, and then a unidirectional silicon steel plate is manufactured through a normal treatment process including a corrective annealing process, A method for producing a low iron loss unidirectional silicon steel sheet, which is characterized by imparting a slight strain to the surface of the product.