JPS63277713A - 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 a silicon-steel slab, by cold-rolling twice or more under specific conditions, while process-annealing between the cold rolling stages, to form a cold-rolled sheet of the final thickness, and by successively applying decarburization and primary recrystallization annealing and then secondary recrystallization annealing and purification annealing to the above steel sheet. CONSTITUTION:A silicon-steel slab is hot-rolled, and this hot-rolled plate is annealed and subjected to descaling of surface scales, and then the first cold rolling is applied to the above plate. Subsequently, the resulting cold-rolled sheet is process-annealed in a continuous annealing furnace where heaters are dividedly disposed in a width direction and temp. differences can be provided in a sheet-width direction and is annealed by providing a temp. gradient so that temps. of the steel sheet are regulated to 1,000 deg.C at the central part and 400 deg.C at both ends, respectively, which is then subjected to the second cold rolling so as to be finished to 0.23mm final sheet thickness. Successively, after carrying out decarburization and primary recrystallization annealing, an annealing and separation agent is applied to the above steel sheet, which is then subjected to secondary recrystallization annealing by providing >=10 deg.C difference in the initiation temp. of secondary recrystallization between the central part and both ends of the steel sheet, followed by purification 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 representative values include magnetic flux density B (T: Tesla) at a magnetizing force of 800 A/m, and iron loss -1? at a magnetic flux density of 1.70 T and a frequency of 50 Hz. /,. (W/kg) is 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.
Low carbon steel containing 5wtχ (hereinafter simply referred to as χ) contains trace amounts of Mn, S, Se, Sb, Sn, A1. After hot rolling the material to which inhibitor-forming elements such as N and B are added,
After cold rolling once or twice or more with intermediate annealing in between, the cold rolled steel sheet is subjected to primary recrystallization annealing that also serves as decarburization, and then subjected to secondary recrystallization treatment in the final finishing annealing step. The secondary recrystallized grains are defined as (110)<001> by
Good magnetic properties are obtained by highly accumulating the steel in the orientation and removing impurities in the steel plate 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) This invention advantageously solves the above-mentioned problems, without the need for particularly complicated temperature control.
The object of the present invention is to propose an advantageous manufacturing method for grain-oriented silicon steel sheets that can easily obtain high magnetic flux density by preferentially and selectively growing secondary grains in the <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.

That is, this invention hot-rolls a silicon-containing steel slab, then cold-rolls it two or more times with intermediate annealing to obtain the final thickness, and then decarburizes and primary recrystallization annealing, Then, in manufacturing a unidirectional silicon steel sheet through a series of steps of secondary recrystallization annealing and purification annealing, the intermediate annealing is performed at an annealing temperature that is continuous or stepwise in the longitudinal direction or width direction of the steel sheet. Manufacture of unidirectional silicon steel sheet with excellent magnetic properties, which consists of imparting a temperature difference of 10°C or more to the secondary recrystallization start temperature in subsequent secondary recrystallization annealing by subjecting it to varying conditions. It's a method.

This invention will be specifically explained 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 nucleating the (110) <001> orientation preferentially, the magnetic flux is highly concentrated in the (110) <001> orientation by selectively growing grains in the other orientation. A secondary recrystallized structure with high density is obtained.

However, in the conventional unidirectional silicon steel sheet, the (110) <001> oriented grains could not be sufficiently selectively grown 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
The temperature ranges from 0 to 1100"C, but the specific temperature of the steel sheet is determined by its components and manufacturing process. Here, the secondary crystallization start temperature is the temperature at which the decarburized and primary recrystallization annealed sheet is heated to a certain temperature after the final cold rolling. The temperature at which secondary recrystallized grains are generated when the material is held for 20 hours at However, in this invention, prior to the secondary recrystallization annealing, the manufacturing conditions are modified to
The secondary recrystallization start temperature is set to have a temperature difference of 10"C or more and within 200°C within the steel sheet, and the secondary grains with the (110) <001> orientation are first preferentially extracted from the region where the secondary recrystallization temperature is low. The main feature is that the secondary grains are eroded by the secondary grains in the (110) <001> orientation to cause the grains to grow to a huge size, thereby completing the secondary recrystallization before secondary grains are generated in other areas. be.

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 between the secondary recrystallization temperatures of the steel sheet, the secondary recrystallization grain size can be maintained while maintaining a high magnetic flux density. IIJ control of the crystal structure is also possible.

Although various methods can be considered for controlling the secondary recrystallization start temperature in the manufacturing process, in the present invention, research has been focused on the annealing temperature during intermediate annealing.

As a result, it was found that there is a relationship as shown in FIG. 1 between the intermediate annealing temperature and the secondary recrystallization start temperature.

Figure 1 shows the transition of the secondary recrystallization start temperature when the temperature during intermediate annealing performed between the first and second cold rolling was varied in the manufacturing process of grain-oriented silicon steel sheets. This is an example, and as is clear from the figure, when the intermediate annealing temperature changes, the secondary recrystallization start temperature also changes accordingly.

Therefore, by locally changing the intermediate annealing temperature of the steel sheet, it is possible to provide local differences in the secondary recrystallization start temperature.

That is, by forming regions with different annealing temperatures continuously or stepwise in the width direction or longitudinal direction of the steel sheet during intermediate annealing, regions with different secondary recrystallization start temperatures are formed, and the intermediate annealing temperature is high. Secondary grains with (110) <001> orientation are generated preferentially from the region where the secondary recrystallization start temperature is low, and secondary grains are generated in the region where the intermediate annealing temperature is low and therefore the secondary recrystallization start temperature is high. By first causing the secondary grains with the (110) <001> orientation to cause grain growth, secondary recrystallization in the desired orientation can be completed in the width direction or length direction.

By the way, in order to fully obtain this effect, the temperature must be 2.
A difference in the next recrystallization start temperature must be given to the steel plate.

This is because the effect is small below 10° C., and the desired effect cannot be obtained. In order to make a difference of 10°C or more in the secondary recrystallization start temperature, a temperature gradient of 200"C/m is required when the annealing temperature is changed continuously, and a temperature gradient of 200"C/m is required when the annealing temperature is changed stepwise. , the temperature difference between adjacent areas is 1
It is important that the temperature be 00°C or higher.

As a method of providing such a temperature difference during intermediate annealing,
There is a method as follows.

For example, a continuous furnace with a large temperature difference in the width direction of the sheet may be used, or the annealing temperature may be varied along the length of the coil. Furthermore, the latest method is to heat only a desired part of the steel plate to a high temperature using a local heating device such as laser heating. Furthermore, it is also possible to use a box-type annealing furnace instead of the continuous annealing furnace as described above to effectively utilize the temperature difference during coil annealing.

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

In other words, it contains 4.5% or less of Si, and contains Mn, S, Se, //! as trace addition elements. , N,
B, Sn, Cu, M.

A material containing at least one type of Nb and the like is melted and made into a hot-rolled plate using a normal steel-making method or hot-rolling method, or a recently developed direct plate-making method is used. The plate material is made into a plate material with a thickness of approximately 5 m, hot rolled plate annealed as necessary, then cold rolled two or more times including the above-mentioned special intermediate annealing to obtain the final plate thickness, and decarburized annealed as necessary. Then, after applying an annealing separator, 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, it is necessary to maintain the temperature at the lowest temperature at which the secondary recrystallization starts or to start the secondary recrystallization. 10' from the lowest temperature to completion
It is desirable to heat at a temperature increase rate of C/h or less.

After that, a purifying annealing is performed at a temperature of 1150° C. or higher, and then a flattening annealing is performed if it is necessary to remove curls in the coil, and sometimes a strong coating is further 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 the steel sheet has not yet been clearly elucidated, the inventors believe that the mechanism by which the secondary recrystallization start temperature of the steel sheet is locally caused by the method is maintained at a low temperature during intermediate annealing. In some areas, the recrystallization due to intermediate annealing is insufficient, resulting in a state similar to that of the one-step method, and it is thought that this causes a difference in the texture after the first recrystallization, and this is the reason for the above effect. ing.

(Example) Example I C: 0.045%, Si: 3.45%, Mn:
0.070%, Se: 0.025% and Sb:
A hot-rolled silicon steel sheet containing 0.023% Fe with the remainder being substantially Fe is annealed, descaled, first cold rolled, and then intermediate annealed. For this purpose, we used a continuous annealing furnace in which the heater was divided in the width direction and controlled to give temperature differences in the width direction of the plate.Total width: 100
The 40 mm width at the center of the 0 mm coil was annealed at a temperature gradient of 1000° C., while both ends of the coil were annealed at a temperature gradient of 400° C., and then cold rolled for the second time to a finished thickness of 0.23 mm.

After that, decarburization annealing was performed at 825°C for 2 minutes, an annealing separator was applied, and the temperature was kept at 840°C for 70 hours.
After completing the next recrystallization, purification annealing was performed at 1200° C. for 110 hours.

At this time, the secondary recrystallization start temperature at the center of the coil is 840
℃, while the temperature at both ends of the coil was 920°C.

The results of investigating the magnetic properties of the thus obtained product plate (symbol C) are shown in Table 1 below.

The same table also shows the results of an investigation on a product (symbol A) obtained by uniformly performing intermediate annealing at 1000° C. according to the conventional method. Furthermore, the magnetic properties when these steel plates were subjected to magnetic domain refining treatment by plasma jet (symbols B and D) are also shown.

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

Table 1 Example 2 C: 0.053%, Si: 3.25%, Mn:
0.084%, S2 0.027%, Aj! 70.0
30% and N: 0.0080%, with the remainder being substantially Fe. After the first cold rolling, intermediate annealing was performed in the same manner as in Example 1. Using a furnace, heat a coil with a total width of 1000 au at 500°C from one end to the center, and the other end 25mm wide at 105°C.
It was annealed at a temperature gradient of 0° C., and then cold-rolled for the second time to a thickness of 0.23 mm. After that, decarburization annealing was performed at 835°C for 3 minutes, an annealing separator was applied, and the temperature was raised between 800 and 1000°C at a rate of 5°C/h to complete secondary recrystallization. Later 11
Purification annealing was performed at 80°C for 12 hours. At this time 500℃
The secondary recrystallization start temperature of the coil width end annealed at 930
℃1 The secondary recrystallization start temperature at one end was 860°C.

The results of investigating the magnetic properties of the thus obtained product plate (symbol C) are shown in Table 2 below.

The same table also shows the investigation results for a product (symbol A) obtained by uniformly performing intermediate annealing at 1050° C. according to the conventional method. Furthermore, the same table also lists the magnetic properties of these steel plates (symbols B and D) whose surfaces were mirror-finished and then coated with a TiN film by ion blating.

Note that the magnetic properties 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
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 the drawing]

FIG. 1 is a graph showing the relationship between intermediate annealing temperature and secondary crystal initiation temperature.

Claims (1)

[Claims] 1. A silicon-containing steel slab is hot rolled, then cold rolled two or more times with intermediate annealing to obtain the final thickness, and then decarburized and primary recrystallization annealed. In manufacturing a grain-oriented silicon steel sheet through a series of steps in which a grain-oriented silicon steel sheet is subjected to a secondary recrystallization annealing and then a purification annealing, the intermediate annealing is performed at an annealing temperature that is continuous or Unidirectional properties with excellent magnetic properties characterized by providing a temperature difference of 10°C or more to the secondary recrystallization start temperature in the subsequent secondary recrystallization annealing by applying the process under conditions that change stepwise. Method of manufacturing silicon steel sheet.