JPS63277712A - Manufacture of grain-oriented silicon steel sheet excellent in magnetic characteristic - Google Patents

Abstract

PURPOSE:To manufacture a grain-oriented silicon steel sheet excellent in magnetic flux density, by hot-rolling and cold-rolling a silicon-steel slab, by subjecting the resulting steel sheet to decarburization and primary recrystallization annealing under specific conditions, and then by applying secondary recrystallization annealing. CONSTITUTION:A silicon-steel slab is hot-rolled and successively subjected to single cold rolling or to two-time or more cold rollings, while process-annealed between the cold rolling stages, so as to be worked into a cold-rolled steel sheet of the final sheet thickness. Subsequently, at the time of applying decarburization and primary recrystallization annealing, the above steel sheet is placed into a continuous annealing furnace in which heaters are dividedly disposed and temp. differences can be provided in a sheet-width direction and then decarburization and primary recrystallization annealing are carried out by dividing into a region where temp. is raised at >=10 deg.C/sec temp.-rise rate and a region where temp. is raised at <=10 deg.C/sec temp.-rise rate or holding is applied for 10sec-10min in a temp. range of 550-750 deg.C in the course of temp. rise, so that annealing is carried out by providing >=10 deg.C temp. difference to the initial temp. of the secondary recrystallization at the time of subsequent secondary recrystallization annealing.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a unidirectional silicon steel sheet with excellent magnetic properties, and aims to advantageously improve magnetic flux density among the magnetic properties. .

(Prior art) The properties required of unidirectional silicon steel sheets, which are mainly used as core materials for transformers, are that they have a high magnetic flux density at a constant magnetization force, and a high magnetic flux density at a constant magnetization force. The iron loss is low when the iron is given. Typically, these typical values are: magnetic flux density Be (T: Tesla) at magnetizing force of 800 A/m and iron loss at magnetic flux density of 1.70 T, frequency 50) + 2 (W/kg).
has been adopted.

In order to improve magnetic properties including both of these properties,
Much research has been carried out to date, and considerable results have been obtained, particularly through improvements in the composition of materials, hot and cold rolling methods, heat treatment methods, etc.

Conventional unidirectional silicon steel sheets usually have Si: 2.5 to 4.
After hot rolling a material in which trace amounts of inhibitor-forming elements such as Mn, S, Se+Sb, Sn, 8L, N, and B are added to low carbon steel containing 5 wt% (hereinafter simply indicated as χ), it is rolled once. Alternatively, by performing two or more cold rollings with intermediate annealing in between, performing primary recrystallization annealing that also serves as decarburization on the cold rolled steel sheet, and then performing secondary recrystallization treatment in the final finishing annealing step. The next recrystallized grain is (110)<
Good magnetic properties are obtained by highly accumulating the steel in the 001> direction and removing impurities in the steel sheet through subsequent purification annealing.

At this time, the orientation of the secondary recrystallized grains is (110) <001>
The magnetic flux density of the steel sheet becomes higher as it accumulates, but on the other hand, it tends to form huge secondary grains, the magnetic domain width within the grains increases, and the iron loss characteristics tend to deteriorate due to an increase in eddy current loss. So 2
Various efforts have been made to refine the secondary grains,
For example, in Japanese Patent Application Laid-Open No. 60-89521, recrystallization promotion regions and retardation regions are alternately provided to increase the nucleation of secondary grains and prevent their growth, thereby making the secondary grains finer and improving iron loss. A method is proposed. However, in recent years, with the establishment of magnetic domain refining technology through the introduction of physical local strain, it has become possible to obtain low iron loss without particularly making the secondary grains finer, so the direction of technological development is to improve magnetic flux density. leaning towards

In this regard, in Japanese Patent Publication No. 58-50295, a unidirectional temperature gradient is applied during secondary recrystallization, and (110) <001
A method for obtaining high magnetic flux density by selectively growing secondary grains in the > orientation has been disclosed. However, this method cannot be called practical because temperature control is extremely difficult.

(Problems to be Solved by the Invention) The present invention advantageously solves the above problems, and eliminates the need for particularly complicated temperature control.
It is an object of the present invention to propose an advantageous method for manufacturing a grain-oriented silicon steel sheet that can easily obtain a high magnetic flux density by selectively growing secondary grains with a 001> orientation.

(Means for solving the problem) Now, the inventors have found that the above problem can be solved (as a result of extensive research, it is possible to recrystallize a steel sheet by secondary recrystallization without particularly controlling the temperature gradient during secondary recrystallization. It was found that by controlling the crystal initiation temperature, it is possible to preferentially grow secondary grains in the (110) <001> orientation, and as a result, a high magnetic flux density can be obtained.

This invention is based on the above knowledge.

In other words, the present invention hot-rolls a silicon-containing steel slab, then cold-rolls it once or twice or more with an intermediate annealing in between to obtain the final thickness, and then decarburizes it and anneales it for primary recrystallization. In the method for producing a unidirectional silicon steel sheet, which consists of a series of steps in which the steel sheet is subjected to decarburization and primary recrystallization annealing, 1.
Area heated at a heating rate of 0″C/s or more and 10°C
The temperature is raised at a temperature increase rate of less than /s, or the temperature is raised in the middle of 550
By dividing the temperature range between 10 seconds and less than 10 minutes in the temperature range of ~750°C, a temperature difference of 10°C or more is given to the secondary recrystallization start temperature in the subsequent secondary recrystallization annealing. This is a method of manufacturing a unidirectional silicon steel sheet with excellent magnetic properties.

This invention will be explained in detail below.

First, the background to the elucidation of this invention will be explained.

Conventionally, when increasing the frequency of nucleation of secondary grains in order to make them finer in order to reduce iron loss, the deviation from the (110) <001> orientation increases, making it impossible to avoid a decrease in magnetic flux density. However, by performing the secondary recrystallization treatment to maintain a uniform annealing temperature, it is possible to preferentially generate nuclei in the (110) <001> orientation, thus increasing the number of secondary grains without impairing the magnetic flux density. It has made miniaturization possible. In order to improve the magnetic flux density, after preferentially nucleating the (110) <001> orientation, the nucleates are further selectively grown with respect to the other grains, resulting in a high degree of accumulation in the (110) <001> orientation. A secondary recrystallized structure with high magnetic flux density is obtained.

However, in the conventional unidirectional silicon steel sheet, it has not been possible to sufficiently selectively grow grains in the <001> orientation due to the high frequency of nucleation of secondary grains.

In this regard, the inventors' research showed that (110) <
By locally shifting the timing of nucleation in the 001> orientation, it is possible to selectively grow the (110) <001> oriented grains that were generated earlier, thus obtaining a secondary recrystallized structure with an extremely high magnetic flux density. It has been determined that this is possible.

The secondary recrystallization start temperature of grain-oriented silicon steel sheets is usually 80
Although it is in the range of 0 to 1100°C, the specific temperature of the steel sheet is determined by its components and manufacturing process. Here, the secondary recrystallization start temperature is defined as the temperature at which secondary recrystallized grains are generated when the decarburized and primary recrystallized annealed plate is held at a constant temperature for 20 hours after the final cold rolling. Normally, secondary recrystallization can be completed by performing annealing at a temperature equal to or higher than the secondary recrystallization start temperature for a long time, but in this invention, prior to secondary recrystallization annealing, manufacturing conditions are devised. In addition, the secondary recrystallization start temperature of the steel sheet is made to have a temperature difference within the steel sheet of 10° C. or more and within 200° C., and first, the region with the lower secondary recrystallization temperature is preferentially (110) <001> Secondary grains with the orientation are generated, and before secondary grains are generated in other areas, the secondary grains with the above (110) <001> orientation are eroded to cause huge grain growth, thereby completing the secondary recrystallization. A major feature is that it allows

At this time, the size of the secondary recrystallized grains depends on the distribution state of the secondary recrystallization temperature, so by controlling the temperature difference in the secondary recrystallization temperature of the steel sheet, the secondary recrystallization grain size is
It also becomes possible to control the subsequent recrystallization structure.

Various methods can be considered for controlling the secondary recrystallization start temperature in the manufacturing process, but in the present invention, research has been focused on the temperature raising conditions during decarburization annealing.

As a result, it was found that there is a relationship as shown in FIGS. 1 and 2 between the temperature raising conditions for decarburization annealing and the secondary recrystallization start temperature.

Figure 1 shows an example of the transition of the secondary recrystallization start temperature when the temperature increase rate during decarburization annealing is changed in the manufacturing process of grain-oriented silicon steel sheets. As is clear, there is a difference in the secondary recrystallization start temperature when the temperature increase rate during decarburization annealing reaches 10° C./s.

In addition, Figure 2 shows an example of the secondary recrystallization start temperature when a short holding treatment is performed during the temperature rise during decarburization annealing. By holding at 550 to 750°C for 10 seconds or more, the secondary recrystallization start temperature is higher than when holding is not performed.

Therefore, as described above, by changing the heating rate during the temperature raising process of decarburization annealing or by performing a holding treatment for a short time, it is possible to give local differences to the secondary recrystallization start temperature of the steel sheet.

In other words, during decarburization annealing, by forming regions with different heating conditions in the width direction or longitudinal direction of the steel sheet in a continuous or stepwise manner, regions with different secondary recrystallization start temperatures are formed. Secondary grains with the (110) <001> orientation are generated preferentially from the region where the secondary recrystallization start temperature is rapidly raised, and the temperature rise rate during decarburization annealing is slow or the temperature is maintained appropriately midway. (110) <0 before secondary grains are generated in the region where the secondary recrystallization start temperature is high.
By feeding silkworms with secondary grains in the 01> direction,
By causing huge grain growth, secondary recrystallization in a desired orientation can be completed in the width direction or length direction. In order to fully obtain the above effects, it is necessary to give the steel sheets a difference in secondary recrystallization start temperature of 10'C or more. This is because if the temperature is less than 10''C, the effect is small and the desired effect cannot be obtained.

Here are some of the temperature increase conditions for decarburization annealing: a temperature increase rate of 10℃
By holding the temperature at 550 to 750° C. for 10 seconds to 10 minutes, the predetermined temperature difference for starting secondary recrystallization is ensured.

The following methods can be used to vary the heating conditions during decarburization annealing.

For example, a cooling nozzle is provided in the furnace heating zone and low-temperature atmospheric gas is applied to a part of the steel plate to control the heating conditions, or a local heating device such as laser heating is used to remove heat from the entire furnace or a two-stage heating zone is used. There are two methods: one method is to set the temperature, and perform local rapid heating, and another is to divide the steel plate into two or more parts and partially annealing them under the above conditions, respectively, to give a difference in the secondary recrystallization start temperature of the F8 plate. .

The main steps in this invention are as described above, but for other steps, conventional manufacturing steps may be applied.

That is, it contains 4.5% or less of Si, and also contains Mn, S, Se, Aj2. N,
B, Sn, Cu, M.

A material containing at least one type of Nb, etc. is melted and made into a hot-rolled sheet using a normal steel-making method or hot-rolling method, or a recently developed direct sheet-making method is used to produce a hot-rolled sheet with a diameter of 1.0 to 3°. The plate is made into a plate material with a thickness of about 5 mm, hot-rolled plate annealed as necessary, then cold rolled once or twice or more including intermediate annealing to obtain the final plate thickness, subjected to the above-mentioned decarburization annealing, and then annealed. After applying the separating agent, annealing is performed to complete secondary recrystallization. At this time, in order to generate secondary recrystallization from a place where the secondary recrystallization start temperature is low and obtain a predetermined high magnetic flux density,
Maintain the temperature at the lowest temperature at which secondary recrystallization begins, or
It is desirable to heat at a temperature increase rate of 10''C/h or less from the minimum temperature at which the next recrystallization begins until the completion of the recrystallization.

After that, a purifying annealing is performed at 1150'C or more, and then a flattening annealing is performed if it is necessary to remove the coil curls, and sometimes a strong coating is applied to produce a product.

Furthermore, this invention takes advantage of its characteristic extremely high magnetic flux density and combines magnetic domain refining technology using lasers, plasma jets, etc., and special surface treatments such as mirror polishing and ion brating to achieve extremely low iron loss. It is also possible to produce unidirectional silicon steel sheets. In other words, the method of the present invention can be said to be a manufacturing method that can more effectively utilize the effects of the recently developed ultra-low iron loss method described above.

(Function) Although the mechanism by which this invention method causes local differences in the secondary recrystallization start temperature of steel sheets has not yet been clearly elucidated, the inventors believe that the temperature increase conditions for decarburization annealing It is believed that by changing the , a difference occurs in the primary recrystallized texture, and that this produces the above effect.

(Example) Example I C: 0.044%, Si: 3.35%, Mn:
0.065%, Se? 0.20%, Sb: 0.0
A silicon steel hot-rolled sheet containing 23% and Mo: 0.011%, with the remainder essentially having a composition of Fe, is hot-rolled and descaled, then cold-rolled twice with an intermediate annealing in between. After that, a cold-rolled plate with a final thickness of 0.23 mm was obtained, and then divided into four parts to give samples A, B, C, and D.

Samples A and B were heated at a heating rate of 20°C/s, while Samples C and D were heated in a continuous annealing furnace controlled so that the heater was divided in the width direction of the plate to provide a temperature difference in the width direction of the plate. Using, full width: 1000mm central part of the coil 3o
III1 width is 20℃/S, and both ends are 5℃/S
Then, the temperature was raised to 830°C, and after decarburization treatment for 2 minutes, an annealing separator was applied, followed by secondary recrystallization annealing at 835°C for 160 hours, followed by purification annealing at 1190°C for 7 hours. In samples C and D, the secondary recrystallization start temperature at the center of the coil is 835°C, while that at both ends is 890°C.
Met.

Thereafter, samples B and D were subjected to magnetic domain refining treatment by laser irradiation.

Table 1 shows the results of investigating the magnetic properties of each product board thus obtained.

Note that the magnetic properties of both samples were almost the same in the width direction.

Table 1 Example 2 C: 0.055%, Si: 3.45%, Mn:
0.080%, S: 0.025%, Af: 0.
029% and N: 0.0082%, with the remainder being substantially Fe.
0.23 by one cold rolling after hot-rolled plate annealing at 'C.
After finishing the sample to 1 mm, it was divided into four parts to form samples A to D.

Samples A and B were heated to 835°C at a heating rate of 17°C/s.
On the other hand, samples C and D were heated using a furnace that could locally heat them by laser heating, with a total width of 1000 mm.
940 s width at the center of the coil is 650°C during heating
After holding for 1 minute, both ends of the coil are sample A.

The temperature was raised to 835°C under the same conditions as B, and after decarburization annealing for 2 minutes, an annealing separator was applied, and then the temperature was raised from 800°C to 1000°C at a rate of 7°C/h. After completing the recrystallization, purification annealing was performed at 1200° C. for 10 hours. The secondary recrystallization start temperature at both ends of Samples A, B, C, and D was 840°C1, and that at the center of Sample C9D was 885°C.

After that, for samples B and D, after mirror-finishing the surfaces, CV
A TiN film was formed on the mirror-finished surface by step D.

Table 2 shows the results of investigating the magnetic properties of each product board thus obtained.

Note that the magnetic properties of both samples were almost the same in the width direction.

Table 2 (Effects of the invention) Thus, according to this invention, the magnetic properties, especially the magnetic flux density B
It is possible to produce unidirectional silicon steel sheets with high IO,
Furthermore, by combining magnetic domain refining technology and special surface treatment technology, it is possible to obtain a unidirectional silicon steel sheet with excellent iron loss characteristics.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between temperature increase rate and secondary recrystallization start temperature during decarburization annealing, and Figure 2 is a graph showing the holding time, temperature, and secondary recrystallization start temperature during temperature increase during decarburization annealing. It is a graph showing the relationship with temperature. Patent Applicant: Kawasaki Steel Co., Ltd. 1st Calculation Private Degree ('C/s)

Claims (1)

[Claims] 1. A silicon-containing steel slab is hot-rolled, then cold-rolled once or twice or more with intermediate annealing to achieve the final thickness, and then decarburized and subjected to primary In a method for producing a unidirectional silicon steel sheet, which consists of a series of steps of recrystallization annealing, then secondary recrystallization annealing, and purification annealing, when decarburizing and primary recrystallization annealing is performed on the steel sheet, A region heated at a heating rate of 10°C/s or more, and 1
The temperature is raised at a temperature increase rate of less than 0°C/s or in the middle of heating5
A temperature difference of 10°C or more is provided to the secondary recrystallization start temperature in the subsequent secondary recrystallization annealing by dividing it into a region where the temperature range is 50 to 750°C for 10 seconds or more and less than 10 minutes. A method for manufacturing a unidirectional silicon steel sheet with excellent magnetic properties.