JPS63277718A - 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 to form a steel sheet, subjecting this steel sheet to primary recrystallization annealing which doubles as decarburization under specific conditions, and successively applying secondary recrystallization annealing. CONSTITUTION:A silicon-steel slab is hot-rolled and the hot-rolled steel plate is annealed and subjected to removal of surface scales, which is cold-rolled twice, while process-annealed between the cold-rolling stages, so as to be finished into a steel sheet of 0.23mm final thickness. A coil of this steel sheet is subjected to primary recrystallization annealing which doubles as decarburization by dividing both coil ends 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 at a temp. in the range of 550-750 deg.C for 10sec-10min in the course of temp. rise by means of a continuous furnace where heaters are dividedly disposed in a coil-width direction and the temp. rise at the coil width end can be inhibited by means of a heat-removing device for cooling, by which >=10 deg.C local difference in temp. is provided to the subsequent secondary recrystallization annealing initiation, and, under a temp. gradient larger than the above-mentioned difference, secondary recrystallization annealing is carried out from a region having high initial temp. of secondary recrystallization.

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 and electric motors, are high magnetic flux density obtained at a constant magnetization force, and a high magnetic flux density that can be obtained at a constant magnetization force. The core loss is low when Typically, these representative values are magnetic flux density B at a magnetizing force of 800 A/m.

(T: Tesla) and magnetic flux density 1.70T, frequency 50
Iron loss W+t/5o (W/kg) at Hz 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.
After hot rolling a material in which trace amounts of inhibitor-forming elements such as Mn, S, Se+Sb, AI, Sn, N, and B are added to low carbon steel containing 5wt
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 (11(1<001>
Excellent magnetic properties are obtained by highly accumulating the steel in different directions and by removing impurities from the steel plate through subsequent purification annealing.

At this time, the orientation of the secondary recrystallized grains is (110) <OOI>
The magnetic flux density of the steel sheet increases as it accumulates in the steel sheet, 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. 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, magnetic domain refining technology by introducing physical local strain (for example,
8-26410), it has become possible to obtain low iron loss without particularly making the secondary grains finer, so the direction of technological development is leaning toward improving magnetic flux density.

In this regard, in Japanese Patent Publication No. 58-50295, a unidirectional temperature gradient is applied during secondary recrystallization, and (1,101<001
A method for obtaining high magnetic flux density by selectively growing secondary grains in the > orientation has been disclosed. This method utilizes a phenomenon unique to secondary recrystallization, in which the nucleation rate of secondary grains is high at relatively high temperatures, while the grain growth rate is high at low temperatures. By heating while applying a temperature gradient, the grains grow to a large extent, thereby improving the directionality of the steel sheet as a whole.

(Problem to be Solved by the Invention) However, in the above method, no improvements have been made to the secondary grains that are generated first, so the properties of the sheet metal body are determined by the orientation of the secondary grains that are generated first. The problem remains that a high B10 value cannot always be obtained because the B10 value is largely influenced by chance, so to speak.

This invention advantageously solves the above problem by first nucleating (110) <001>, that is, Goss oriented grains under a high probability, and then preferentially growing secondary grains in this orientation. The purpose of the present invention is to propose an advantageous method that can stably produce a grain-oriented silicon steel sheet in which the orientation of secondary grains is highly aligned with the Goss orientation and thus has a high magnetic flux density.

(Means for Solving the Problems) From the above-mentioned viewpoints, the inventors systematically conducted research on nucleation and grain growth.

As a result, it was found that (110) <oot> orientation of secondary recrystallized grains generated by nucleation from regions with strong restraining force is generally excellent; Since the temperature at which recrystallization starts (Ts++) is higher, when normal annealing is performed, Ts
3. The primary recrystallized structure is eroded by the grain growth of poorly oriented crystal grains nucleated from the low l region (1
10) It was found that it is difficult to expect the nucleation of secondary grains with good orientation in the <ool> direction.

Here, the secondary recrystallization temperature refers to the temperature at which the decarburized primary recrystallization annealed sheet is annealed for 20 hours in a temperature gradient furnace with a temperature gradient of 750 to 1050°C after the final cold rolling. The temperature at which the recrystallization region changes to the secondary recrystallization region is used as an index.

In contrast, by consciously changing the suppressing force due to the texture or inhibitor within the surface of the steel sheet, we move from the high 'rsi region where the suppressing force is stronger to the direction where the suppressing force is weaker.
If grains were allowed to grow while giving a temperature gradient larger than T□, nucleation occurred in the region with high T and R (11
0) <ool> It was found that secondary grains with good orientation could be stably grown.

This invention is based on the knowledge of J.2.

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 and primary recrystallization annealing. , followed by secondary recrystallization annealing and then purification annealing.
- In manufacturing °ζ unidirectional silicon steel sheet through a series of steps, in the decarburization and primary recrystallization annealing process,
A region heated at a heating rate of 10°C/s or more, and 10'
The temperature is raised at a temperature increase rate of less than C/'S or is in the middle of heating5
By dividing the area into a region where the temperature range is 50 to 750°C for 10 seconds or more and less than 10 minutes, a local difference of 10°C or more is given to the subsequent secondary recrystallization start temperature of the steel plate,
Then, under a temperature gradient larger than the difference in the secondary recrystallization start temperatures, gradient annealing is performed to start the secondary recrystallization from the region where the secondary recrystallization start temperature is high. This is a method for manufacturing a unidirectional silicon steel sheet.

This invention will be specifically explained below.

The steel that is the object of this invention is subjected to secondary recrystallization for the purpose of increasing the parallelism between the <001> axis and the rolling direction, and more preferably, by magnetic domain refining technology, the iron loss is significantly improved, and the steel is used in electrical equipment, etc. There are no particular restrictions on the composition of the unidirectional silicon steel sheets used, and all steels currently used industrially are included.

That is, it contains 4.5% or less of Si, and trace amounts of Mn + S and AI + Se l necessary for the occurrence of secondary recrystallization.
The composition contains at least one inhibitor component such as B and Nb.

This type of silicon steel sheet is made into a steel slab by ingot method or continuous casting method, which is hot rolled, then cold rolled once or twice or more including intermediate annealing, and then decarburized. ,1
It is manufactured by performing secondary recrystallization annealing and final annealing (secondary recrystallization and purification annealing). When finishing annealing a coiled or laminated steel plate, an annealing separator is applied in advance.

In short, in this invention, conventionally used or developed known manufacturing processes can be applied, but it is necessary to give the steel plate a TSM gradient before secondary recrystallization.

Various methods can be considered to control the secondary recrystallization start temperature by changing the suppressing force within the sheet surface at the stage before the secondary recrystallization, but in this invention, the heating conditions during decarburization annealing are We have conducted repeated research with a focus on

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.

That is, during decarburization annealing, by forming regions with different heating conditions continuously or stepwise in the width direction or longitudinal direction of the steel sheet, regions with different secondary recrystallization start temperatures are formed, and the decarburization annealing is performed. Preferentially (secondary grains with 1101<001> orientation are generated from the region where the temperature rise rate is slow or the secondary recrystallization start temperature is high with appropriate intermediate holding, and the temperature is rapidly raised by decarburization annealing. (110) <00 before secondary grains are generated in the region where the secondary recrystallization start temperature is low.
By causing the secondary grains in the 1> orientation to cause grain growth, secondary recrystallization in the desired orientation can be completed in the width direction or the length direction. In order to sufficiently obtain the above effect, it is necessary to give the steel sheet 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 can be ensured.

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

For example, a cooling nozzle is installed 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 raise the temperature in two stages. There are two methods: one method is to set the temperature, and locally perform normal rapid heating; another method is to divide the steel sheet into two or more parts and partially annealing them under the above conditions, each time giving a difference in the secondary crystallization start temperature of the steel sheet.

Next, secondary recrystallization annealing is performed, but in this secondary recrystallization annealing, secondary recrystallization is started from a region where T'si is high under a temperature gradient larger than the TiN gradient applied as described above. It is important to perform inclined annealing so that the

The temperature gradient in such inclined annealing is desirably 2° C. or more per 1 cm of unit length.

After that, it was heated to 1100-1250℃15 in a dry hydrogen atmosphere.
Purification annealing is performed for about 25 hours.

The above-mentioned finish annealing is carried out industrially in a type that processes coiled copper strips, but it is also a continuous type in which a single steel plate (including cut plates) or a stack of steel plates is continuously annealed. has also been proposed, and both types can be used in this invention.

Furthermore, the temperature gradient can be easily achieved by providing a zone with a temperature gradient in the furnace, and the direction of the temperature gradient can be the width direction, length direction, or any other arbitrary direction of the steel plate. It may be.

The magnetic properties can be effectively improved by performing such a series of treatments, but in this invention, after purification annealing, an ultra-thin tension-applying film is formed on the surface of the steel sheet, thereby improving the magnetic properties. Further improvements can also be made.

In order to form such an ultra-thin film, first remove non-metallic substances from the surface of the steel sheet after purification annealing, and then perform chemical polishing or electrolytic polishing to reduce the smoothness of the steel sheet surface to a centerline average roughness Ra of 0. The diameter shall be 4 μm or less. This is because if the roughness is greater than this, no improvement in iron loss can be expected even if the next extremely thin coating is applied.

Next, T is deposited using a vapor deposition method such as CVD or PVD (ion blating or ion imbuing).
i, Nb, Si, V, Cr, AI+Mn+B, Ni, C
o, Mo, Zr, Ta+11f, - nitride and/
Or carbide AltSi+Mn, Mg+Zn
An extremely thin film consisting mainly of at least one type of +Ti oxide is firmly formed on the surface of the steel sheet.

In addition to doffing, the material for the coating may be doffed,
Any material may be used as long as it has a low coefficient of thermal expansion and firmly adheres to the steel plate.

Further, if necessary, a tension-applied low thermal expansion top insulating film is preferably applied according to a conventional method, and magnetic domain refining techniques such as laser irradiation, plasma jet irradiation, electrical discharge machining, scribing method, and ballpoint pen processing method are applied.

(Function) When a steel plate is heated while applying a temperature gradient larger than the gradient of TS, l from a region where Ts, l is high, the edge of the steel plate first rises to a temperature above TsR, and a small amount of grains with good orientation occur. Nuclei are generated to form a secondary recrystallized region.

At this time, the temperature is increased to T5 until the first grain is nucleated. It is desirable to keep the temperature as low as possible without raising the temperature too much.

A region in which the primary recrystallized structure and the secondary recrystallized structure are mixed resides in a narrow range between the secondary recrystallized region and the region that has not yet reached TiN. As the temperature of the steel sheet rises, the warped region continues to move toward the lower temperature side, and the secondary recrystallization region expands accordingly, causing grain growth.

As mentioned above, grain growth in secondary recrystallization occurs at a lower temperature than the nucleation temperature, so when heating without applying a temperature gradient, the heating rate should be excessive (large variations in , TS, and I). As long as there is no new nucleation, no new nucleation will occur during the process, and the first crystal orientation grains will grow toward the low temperature side.At this time, there is a gradient in T and R, and the growth direction of the crystal grains will be Ts. , a region with low I, that is, a region where the suppressing force is weak, has the characteristic that grain growth becomes more stable and rapid.Throughout this growth, the temperature in the boundary region between primary recrystallization and secondary recrystallization remains relatively low. remains constant.

The inventors created steel sheets in which the TSR changes continuously by modifying the annealing process during decarburization and primary recrystallization annealing, and then applied these steel sheets to the T and R gradients in the high TSR region. The difference in TSR between both ends of the steel plate is 5℃11.
After preparing samples at three levels, 0°C and 20°C, these steel plates were treated with T3. O'C/cm and 1°C/cm, respectively, with the high I region as the high temperature side.

Finish annealing was performed by applying a temperature gradient of 2°C/cm and 5°C/cm.

The results of investigating the magnetic flux density of the thus obtained product plate are shown in the table below.
It has been found that when 3R is 10° C. or more higher than other parts and the temperature gradient is 2° C./cm or more, a remarkable effect is seen in improving B.

When secondary recrystallization progresses while applying a temperature gradient,
The temperature at which secondary recrystallization occurs is not constant depending on the type of steel sheet and heating conditions, and the temperature range cannot be limited, but for example, in the case of grain-oriented silicon steel sheet with MnSe and sb as inhibitors, it is 850 ~ It is within the range of 1000°C, and in this invention, it is sufficient to provide a temperature gradient in this boundary region, and before and after that, the conventional processing conditions may be used, and of course, even if a temperature gradient is provided. good.

In this way, it became possible to stably obtain unidirectional silicon steel sheets with excellent magnetic properties and magnetic flux density.

Although the mechanism by which the method of this invention causes local differences in the secondary recrystallization start temperature of the steel sheet is not clear, the inventors believe that by changing the heating conditions during decarburization annealing,
It is believed that the above effect was obtained due to the difference in the crystal texture.

(Example) Example I C: 0.045%, St: 3.40%, Mn:
0.065%, Se: 0.022%, Sb: 0
．． A silicon steel hot-rolled sheet containing 0.025% and Mo: 0.011%, with the remainder having a composition of Fe excluding unavoidable impurities, was annealed, and after descaling, it was annealed twice, including intermediate annealing. After cold rolling to a thickness of 0.23 mm, samples A and B were divided into four parts.

C and D.

For A and B, a continuous furnace was used in which the heater was divided in the width direction of the coil and a cooling heat removal device was used to suppress the temperature rise at the ends of the coil width, and the total width was 10.
One end of the 00m coil with a width of 30fflI1 was heated at 7''C/s, and the other end was heated at 23°C/s to perform decarburization and primary recrystallization annealing for 2 minutes.

On the other hand, in samples C and D, the temperature was uniformly raised across the entire width of the coil at 22° C./S. At this time, the temperature at which the secondary recrystallization started was 890°C when the temperature was raised at 7°C/s.
, D was 840°C. In FIG. 3, the distribution of the secondary recrystallization start temperature across the width direction is shown by a solid line.

Next, after applying an annealing separator to each steel plate, using a box-type annealing furnace equipped with a heating heater and a cooling device on the end face of the coil, the side where the secondary recrystallization start temperature is higher is 890°C, and the opposite side is 820°C. After raising the temperature as shown above and holding it for 30 hours, the temperature was raised at 5° C./h for 10 hours while maintaining the temperature gradient, and then purification annealing was performed at 1200″C for 10 hours.

For samples B and D, after removing the insulation coating,
After chemical polishing in 3% HF and H2O2 solution to give a mirror finish, heat treatment is performed in a mixed gas atmosphere of CH gas, Nt gas, and TiC1m gas, and Ti is applied to the steel plate surface by CVD.
A (C,N) layer was formed with a thickness of 0.5μ#I.

The results of investigating the magnetic properties of the thus obtained product plate are shown in the table below.

In addition, the magnetic properties were all the same in the width direction.

Example 2 C: 0.056%, Si: 3.30%, Mn:
0.079%, Se: 0.025%, Al:
Contains 0.031% and N: 0.0081%,
A silicon steel hot-rolled sheet having a composition of Fe with the remainder excluding unavoidable impurities is annealed and then cold-rolled to a 0.23
After finishing it to a thickness of mm, it was divided into four parts A to D.

For samples A and B, in a furnace equipped with a local heating zone using an infrared heater at the front stage, only the center 40 strokes of a coil with a total width of 1000 mm were first held at 600°C for 30 seconds, and then heated to 19°C in a normal heating zone. /s to 835°C to perform decarburization annealing.

On the other hand, samples C and D have a coil width of 19”C/
Similar decarburization and primary recrystallization annealing was performed by uniformly heating to 835° C. at s.

At this time, the temperature at which the secondary crystallization starts at the center of the coil is 940℃1
On the other hand, the temperature in other parts and the comparative material was 870°C. The distribution of secondary crystal initiation temperatures across the width direction of samples A and B is shown in FIG. 3 by a broken line.

Next, after applying an annealing separator to each sample, a coil box furnace with cooling plates at both ends of the coil was used to heat the high temperature part to 8.
The coil was heated at 8°C/h from 00°C to 1000°C with a temperature gradient of 100°C between the center and both ends of the coil, and then purified annealed at 1200°C for 13 hours.

For samples B and D, a laser was further used to roll 9 cm perpendicularly to the rolling direction at an energy density of 21 J/cm2.
Magnetic domain refining processing was performed using pitch.

The results of investigating the magnetic properties of each product board thus obtained are shown in the table below.

In addition, the magnetic properties of both samples were almost the same in the width direction.

(Effect of the invention) Thus, according to this invention, the magnetic flux density BIl is 2.0T.
It is possible to produce a unidirectional silicon steel sheet with an extremely high magnetic flux density close to 100%, and furthermore, by combining surface treatment with laser treatment or CVD, 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 crystal start temperature during decarburization annealing, and Figure 2 is a graph showing the relationship between holding time and temperature during temperature increase during decarburization annealing and secondary crystal start temperature. FIG. 3 is a diagram showing the secondary crystallization start temperature distribution across the plate width direction in Examples 1 and 2.

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 After recrystallization annealing, 2
In manufacturing unidirectional silicon steel sheets through a series of steps of secondary recrystallization annealing and then purification annealing,
Areas that are heated at a heating rate of 550 to 750°C, or areas that are heated at a heating rate of less than 10°C/s or 550 to 750°C during heating.
A local difference of 10°C or more is given to the subsequent secondary recrystallization start temperature of the steel plate by dividing the steel plate into a region where the temperature range is maintained for 10 seconds or more but less than 10 minutes, and then the secondary recrystallization is performed. Unidirectional silicon with excellent magnetic properties, characterized by performing gradient annealing to start secondary recrystallization from a region where the secondary recrystallization start temperature is high under a temperature gradient greater than the difference in starting temperatures. Method of manufacturing steel plates. 2. The method according to claim 1, wherein the temperature gradient in inclined annealing is 2° C. or more per 1 cm of unit length.