JPH1030123A - Production of thin grain oriented silicon steel sheet having extremely high magnetic flux density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably produce a thin grain oriented silicon steel sheet having extremely high magnetic flux density by applying, after degreasing, specific decarburizing annealing to a cold rolled sheet of silicon steel containing Al and N for grain oriented silicon steel sheet and controlling picking loss. SOLUTION: A silicon steel slab for grain oriented silicon steel sheet, containing Al and N as inhibitor components and having a composition containing, e.g. 0.03-0.09% C, 2.0-4.5% Si, 0.05-0.15% Mn, 0.01-0.04% Al, and about 0.004-0.012% N, is used as a stock. After hot rolling, final cold rolled sheet thickness is regulated to <=0.20mm by means of two or more times of cold rolling including process annealing. After degreasing, decarburizing annealing is applied, and then, after the application of a separation agent at annealing, final finish annealing is performed. At the time of producing this thin grain oriented silicon steel sheet, the average temp. raise rate between 400 and 800 deg.C at the decarburizing annealing is regulated to (5 to 25) deg.C/s and also decarburizing annealing conditions are regulated, and, at the time of successive pickling, pickling loss, under the pickling conditions of, e.g. 5% HCl, 60 deg.C, and 60sec, is controlled to (0.1 to 0.4)g/m<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention proposes a method for manufacturing a grain-oriented electrical steel sheet having a particularly high magnetic flux density, which is used for an iron core such as a transformer.

[0002] Grain-oriented electrical steel sheets are mainly used as soft magnetic materials for core materials of transformers and other electric equipment, and are required to have good magnetic properties in terms of excitation properties and iron loss. Such a grain-oriented electrical steel sheet generates secondary recrystallization in the final finish annealing step, and causes {110} on the steel sheet surface.
Good magnetic properties can be obtained by developing a so-called Goss grain structure having a <001> axis in the plane and rolling direction. Therefore, in order to obtain good magnetic properties, it is important that the <001> axis, which is the axis of easy magnetization, is highly aligned in the rolling direction, and a product having an extremely high magnetic flux density can be obtained by containing AlN, MnSe, or the like as an inhibitor. Can be obtained.

However, on the other hand, as the sheet thickness decreases, secondary recrystallization tends to be incomplete due to subtle changes in conditions in decarburizing annealing and finish annealing, and as a result, magnetic properties become unstable and high It has become difficult to stably obtain a product having a magnetic flux density, and improvement thereof has been desired.

[0004]

2. Description of the Related Art Heretofore, as a method of manufacturing a thin product,
For example, JP-A-1-316421 (a method for producing a thin high magnetic flux density unidirectional magnetic steel sheet by a single-stage cold rolling method) discloses a method for controlling the contents of Al, N and AlN. In the official gazette (a method of manufacturing a thin high magnetic flux density unidirectional magnetic steel sheet by a single-stage cold rolling method), a method of controlling the Al, N, and AlN contents and controlling the finish rolling conditions of hot rolling is proposed and disclosed. Have been. Also, Japanese Patent Publication No. Sho 62-56927 (a method for producing a low iron loss unidirectional silicon steel sheet having excellent surface properties) and Japanese Patent Application Laid-Open No. 63-72825 (a low iron loss unidirectional silicon steel sheet having excellent surface properties) Proposed and disclosed is a method of regulating the distribution of the rolling reduction of the two cold rollings and controlling the temperature rising rate and the cooling rate of the intermediate annealing. However, even with these methods, in the case of a thin product with a final plate thickness of 0.20 mm or less, secondary recrystallization becomes unstable due to the difference in the surface state after decarburization annealing, and high magnetic flux density It was difficult to obtain a stable product.

On the other hand, Japanese Patent Application Laid-Open No. 6-192847 (Decarburization of grain-oriented silicon steel sheet / management method of primary recrystallized sheet) discloses a decarburization method.
There has been proposed a method of evaluating the surface condition of the secondary recrystallized plate by the dissolution loss by pickling and controlling the loss. However, in this method, when the thickness of the final cold-rolled sheet is reduced, the dispersion is large, and it is not always possible to obtain a stable and good secondary recrystallization, and it is difficult to stabilize the magnetic properties.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to propose a method for producing a thin grain-oriented electrical steel sheet having a thickness of 0.20 mm or less using AlN as an inhibitor that can stably obtain an extremely high magnetic flux density. I do.

[0007]

The gist of the present invention is as follows.

[0008] Using a silicon steel slab for grain-oriented electrical steel sheets containing Al and N as a raw material, hot rolling is performed, and cold rolling is performed two or more times with intermediate annealing to obtain a final cold rolled sheet thickness of 0.20.
mm or less, then, after degreasing, after decarburizing annealing, to produce thin grain-oriented electrical steel sheets by a series of steps of applying an annealing separator and then performing final finish annealing, heating in the decarburizing annealing step The average heating rate in the temperature range from 400 ° C to 800 ° C is in the range of 5 ° C / s to 25 ° C / s, and
A method for producing a thin grain-oriented electrical steel sheet having an extremely high magnetic flux density, characterized in that the decarburizing annealing conditions are adjusted to control the amount of pickling loss of the steel sheet after the decarburizing annealing under predetermined pickling conditions within a specific range (first method). invention).

5% of steel sheet after decarburization annealing Hcl ・ 60 ℃ ・ 60
The method for producing a thin grain-oriented electrical steel sheet having an extremely high magnetic flux density according to the first aspect of the invention, wherein the pickling loss under the condition of pickling for 2 seconds is in the range of 0.1 to 0.4 g / m ² (second invention).

Here, the decarburizing annealing conditions include, in addition to the heating temperature and the holding time, in particular, the cleanliness of the steel sheet surface after degreasing as pretreatment conditions for the cold rolled sheet, and the atmosphere as the heating conditions.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an experimental example which has achieved the present invention will be described below. Material: C: 0.068
wt% (hereinafter simply expressed as%) Si: 3.2%, solAl:
0.028%, N: 0.0080%, Se: 0.024%, Sb: 0.029%
And a steel ingot containing 0.05% of Cu:
After being heated to a temperature of 50 ° C., it was hot-rolled to obtain hot-rolled sheets having a thickness of 2.3 mm and 1.5 mm. Then, after hot-rolled sheet annealing at 1000 ° C for 3 minutes, two cold rollings with an intermediate annealing at 1000 ° C for 2 minutes are performed, and from 2.3mm to 0.23mm and from 1.5mm to 0.15mm, respectively. Finished to the final thickness.

Thereafter, these cold-rolled sheets were subjected to decarburization and primary recrystallization annealing at 840 ° C. for 4 minutes in a wet hydrogen atmosphere. At that time, the atmosphere is changed the oxidation degree P (H ₂ O) / P (H ₂ ) in the range of 0.3 to 0.6 by controlling the dew point with H ₂ as 50%, and further, from 400 ° C. to 800 ° C. Was changed in the range of 3 ° C./s to 40 ° C./s.

These decarburized annealed sheets are coated with an annealing separator containing MgO as a main component and rapidly heated to a temperature of 800 ° C. at a rate of 50 ° C./h, and from a temperature of 800 ° C. to 1200 ° C. at a rate of 10 ° C./h. Final finish annealing was performed by gradually heating to obtain a product plate.

The magnetic flux density (B ₈ ) of each of the product sheets thus obtained was measured, and the loss of pickling by pickling was measured for the annealed decarburized sheet. The pickling conditions were: pickling solution: 5% Hcl, solution temperature: 60 ° C., and pickling time: 60 seconds.

FIGS. 1 and 2 show graphs of the relationship between the amount of pickling loss of the decarburized annealed plate and the magnetic flux density (B ₈ ) of the product plate when the product plate thickness is 0.23 mm and 0.15 mm, respectively. Show. The pickling loss was represented by the weight loss (g / m ² ) per 1 m ² of the steel sheet surface area.

As is clear from FIG. 1, in the case of a product having a plate thickness of 0.23 mm, a good correlation is recognized between the pickling weight loss and the magnetic flux density, and the magnetic flux density increases as the pickling weight loss increases. Has deteriorated. On the other hand, in the case of a thin product with a thickness of 0.15 mm, there is no correlation as in the case of a thickness of 0.23.
As is clear from FIG. 7, the dependence of the magnetic flux density on the pickling loss changes depending on the heating rate during the decarburizing annealing.

That is, in the case of a thin product having a sheet thickness of 0.15 mm, if the heating rate during decarburization annealing is 25 ° C./s or less, the magnetic flux density can be controlled by reducing the amount of pickling. B ₈ ) While high flux density products of ≧ 1.92T can be obtained,
If the heating rate exceeds 25 ° C./s, it can be seen that it is difficult to obtain a high magnetic flux density product.

Therefore, attention is paid to the rate of temperature rise during decarburization annealing and the amount of pickling loss of the decarburized annealed plate, and the results of the relationship between these and the magnetic flux density (B ₈ ) are shown in FIGS. 3 and 4. FIG.
Fig. 4 shows the case where the product plate thickness is 0.23 mm, and Fig. 4 shows the case where the product plate thickness is 0.15 mm. In both cases, the heating rate during the decarburization annealing, the pickling loss of the decarburized annealing plate, and the magnetic flux density of the product plate ( ₁₈ is a graph showing the relationship with B ₈ ).

From these figures, when the product thickness is 0.23 mm (FIG. 3), it is possible to obtain a product having a good magnetic flux density by controlling the pickling loss of the decarburized annealed plate within a specific range. However, if the product thickness is 0.15mm (Fig. 4), it is possible to obtain a product with good magnetic flux density unless the heating rate range during decarburization annealing is regulated in addition to the acid washing loss. Can not,
Specifically, the pickling weight loss of the decarburized annealed plate under 5% Hcl at 60 ° C. for 60 seconds in the pickling condition is set in the range of 0.1 to 0.4 g / m ² ,
In addition, when the average heating rate between the temperatures of 400 to 800 ° C. during the decarburizing annealing is in the range of 5 to 25 ° C./s, the magnetic flux density (B ₈ )
It is clear that a thin product having a good secondary recrystallization of more than 1.92 T can be obtained.

Next, the manufacturing process and component composition of the thin grain-oriented electrical steel sheet to which the present invention is applied will be described below. Molten steel smelted by a conventionally used steelmaking method is cast by a continuous casting method or an ingot-making method, and a silicon steel slab is interposed, if necessary, through a sizing process. The component composition of the silicon steel slab at this time is listed below.

[0021] SolAl and N are essential as inhibitor-forming components for producing good secondary recrystallization.
These are finely dispersed as AlN before secondary recrystallization and have a strong inhibitory effect on the growth of crystal grains. For this purpose, the content of solAl is important to be 0.01% or more, but if it exceeds 0.04%, the precipitates are coarsened and the suppressing power is reduced, so the range of 0.01 to 0.04% is good. If the N content is less than 0.004%, the AlN content is insufficient, and if it exceeds 0.012%, blisters may be generated in the product.
The range of 004 to 0.012% is good.

C is an important component for improving the hot-rolled structure, but if it is too large, decarburization becomes difficult.
A range of 0.03 to 0.09% is preferred.

Si is a component useful for increasing electric resistance and reducing iron loss. However, if it is too large, it becomes difficult to perform cold rolling. Therefore, the content of Si is preferably in the range of 2.0 to 4.5%.

Further, Mn, S and Se may be contained as an inhibitor-forming component. Mn and S and Se are MnS and Mn
It forms an inhibitor such as Se and is effective as an inhibitor for reinforcing AlN. If Mn is too large, it is difficult to form a solution, so the content is preferably in the range of 0.05 to 0.15%. In order to precipitate MnS and MnSe, the contents of S and Se are set individually and individually. In the case of combined use, the total range is preferably 0.01 to 0.04%.

Further, Sb (0.005 to 0.20%), Cu (0.02 to 0.20%), and Sn (0.02%), which are known as inhibitor reinforcing components.
~ 0.30%), Ge (0.01 ~ 0.30), Ni (0.02 ~ 0.20%)
And Mo (0.01 to 0.05%) may be contained alone or in combination.

Next, after the silicon steel slab having such a composition is hot-rolled, if necessary, hot-rolled sheet annealing is carried out, and 0.20 or more cold rolling is carried out two or more times with intermediate annealing.
A cold-rolled sheet with a final thickness of not more than mm. If the rolling reduction in the final cold rolling is less than 80%, the orientation of the secondary recrystallized grains is deteriorated, and if it exceeds 95%, the secondary recrystallization becomes difficult.
A range of 80-95% is preferred.

Then, after decarburizing annealing conforming to the present invention is performed, an annealing separator containing MgO as a main component is applied, followed by final finish annealing to obtain a product sheet.

As described above, the decarburizing annealing is performed by increasing the average heating rate in the temperature range from 400 ° C. to 800 ° C. during heating by 5%.
C./s to 25.degree. C./s, and it is necessary to adjust the pre-treatment conditions after degreasing and the decarburization annealing conditions such as heating atmosphere to control the pickling weight loss under specified pickling conditions within a specific range. And

In the above series of steps, for a material having a final cold rolled sheet thickness of 0.20 mm or less, the pickling loss of the decarburized annealed sheet is controlled within a specific range in order to obtain a good magnetic flux density on the product sheet. The reasons for doing so are described below.

In the above-described experimental example, the decarburized annealed sheet obtained under the same conditions as those for measuring the loss in pickling was dried in dry N ₂ .
Annealing was performed at 900 ° C. for 20 hours, and the amount of nitriding was measured. As a result, it was found that the smaller the pickling loss, the lower the amount of nitriding. It is considered that the magnitude of the nitriding amount during the annealing indicates the reactivity with the atmosphere on the steel sheet surface, that is, the activity. And, in this highly active material, excessive nitridation occurs during the secondary recrystallization annealing,
For this reason, when the inhibitor becomes stronger than the appropriate grain growth suppressing power, the grain size of the primary recrystallized grains before the secondary recrystallization in the initial stage of annealing is excessively suppressed, and therefore, the orientation is poor.
This gives room for secondary recrystallized grains to appear.

Further, it is considered that when the activity is high, the amount of additional oxidation during the secondary recrystallization annealing increases. If the amount of additional oxidation is large, iron oxide or iron silicate is formed on the surface to prevent the formation of forsterite, so that a coarse and poorly adhered film is formed. Further oxidation is an inhibitor
It causes oxidation of AlN and MnSe, etc., which causes a decrease in the ability to suppress grain growth.

In any case, the increase in the activity of the steel sheet surface is 2
Specifying the pickling weight loss in the optimum range in order to optimize the activity of the surface of the decarburized annealed sheet is an extremely effective means for improving the magnetic properties because it makes the generation of the secondary recrystallization unstable. You can see that.

However, as is clear from the graph of the relationship between the amount of pickling loss and the amount of nitriding using the heating rate during decarburization annealing as a parameter in FIG. 5 plotted from the results of the nitriding amount measurement, the amount of pickling loss decreases. Accordingly, the variation in the amount of nitriding increases with the increase in the amount of nitriding. It can be seen that the variation is due to the difference in the rate of temperature rise during the decarburizing annealing.

Although the reason for this is not necessarily clear, the above experimental results show that when the plate thickness is 0.20 mm or less, the magnetic properties are good when the heating rate is 5 to 25 ° C./s. It is considered that the composition, structure, etc. of the oxide on the steel sheet surface change depending on the difference in the heating rate.

On the other hand, in the case of a thin material having a plate thickness of 0.20 mm or less, the same amount of the material reacts with nitrogen or oxygen at the surface layer as compared with a relatively thick material such as 0.23 mm or 0.30 mm. However, even if the surface is nitrided or oxidized, it is assumed that their concentration in the whole steel sheet becomes high and more sensitively affects magnetic properties and the like.

The composition of the oxide on the surface of the steel sheet
Due to subtle changes in the structure or the like, the reactivity of the surface with nitrogen and oxygen is subtly changed, and these changes are not detected as the magnitude of the pickling loss. Therefore, it is considered that in the range where the pickling loss is small, the nitriding amount changes due to the difference in the heating rate.

Therefore, when manufacturing a thin grain-oriented electrical steel sheet having a sheet thickness of 0.20 mm or less, it is necessary to regulate the rate of temperature rise during decarburizing annealing in addition to controlling the pickling loss of the decarburized annealing sheet. You can see that.

Here, when the heating rate is higher than 25 ° C./s,
A change in the composition and structure of the oxide on the surface results in a high activity state, which increases the reactivity with the atmosphere, resulting in poor secondary recrystallization. On the other hand, when the temperature is lower than 5 ° C./s, the recrystallized grains of the primary recrystallization in the early stage of the decarburization annealing become too large, and the nuclei of the secondary recrystallization generated thereby cannot eat the primary recrystallized grains.
Secondary recrystallization becomes unstable.

In the above experimental example, 5% HCl / 60 ° C.
The optimum pickling weight loss range under which the magnetic flux density of the product plate is good under the pickling conditions for 60 seconds was 0.1 to 0.4 g / m ² , but this optimum pickling weight loss range depends on the type of acid, temperature, and time. It naturally changes depending on pickling conditions such as As the type of the acid, HNO ₃ and H ₂ SO ₄ can be used in addition to Hcl.
Other pickling conditions using these acids include temperature: 50-90.
C, time: about 30 to 200 seconds is good.

Even when the pickling conditions are changed as described above,
By controlling the pickling weight loss within the optimum range determined by the respective pickling conditions, a product having good magnetic properties can be obtained.
In addition, the optimal pickling loss basically varies depending on the composition of the steel. However, as mentioned above, a good 2
Within the preferred range of the chemical components required to cause the next recrystallization, the change of each component within those ranges has little effect on the pickling weight loss, and it is considered that there is no problem.

[0041]

【Example】

Example 1 C: 0.065%, Si: 3.35%, solAl: 0.029%, N: 0.
0080%, Mn: 0.077% and S: 0.038%, the balance being substantially Fe composition.
After hot-rolled sheet annealing, which was quenched after heating at 00 ° C. for 3 minutes, a cold-rolled sheet having a sheet thickness of 0.20 mm was obtained by performing two cold rollings with intermediate annealing at 1100 ° C. for 2 minutes. Then degrease, 84
After decarburizing annealing at 0 ° C. for 4 minutes, MgO to which 5% of TiO ₂ was added was applied as an annealing separator, followed by final finish annealing to obtain a product sheet.

In the above decarburizing annealing step, 400 to 800
The average rate of temperature rise in the temperature range of
° C / s, and the degree of oxidation P (H ₂ O) of the atmosphere in the heating zone
/ P (H ₂ ) was varied to 0.35, 0.45 and 0.55, respectively.

Then, for each decarburized annealed plate, 5% Hc
l ・ The pickling loss under the pickling conditions of 60 ° C for 60 seconds was measured respectively, and nitriding annealing at 850 ° C for 20 hours in a dry N ₂ atmosphere was performed to determine the increase in the amount of nitrogen in the steel after nitriding annealing. Each was examined as the amount of nitriding. For each product plate, the magnetic flux density (B ₈ ) was measured by an Epstein test, and the formation state of secondary recrystallization was examined from the pickled macrostructure.

Table 1 summarizes these decarburizing annealing conditions and investigation results.

[Table 1]

The secondary recrystallized state in Table 1 is indicated by a circle when secondary recrystallization is almost complete, and a triangle when 20 to 50% of unrecrystallized fine particles remain. The case where more than 50% of unrecrystallized fine grains were present was marked with x. As is clear from Table 1, all of the applicable examples of the present invention show high magnetic flux densities.

Example 2 C: 0.070%, Si: 3.25%, solAl: 0.025%, N: 0.
0080%, Mn: 0.073% Se: 0.038% and Sb: 0.026%
, The balance being substantially Fe composition: 1.8 mm
Hot-rolled sheet is heated at 1000 ° C for 3 minutes, then quenched, and then cold-rolled twice with intermediate annealing at 1100 ° C for 2 minutes. And afterwards,
After degreasing, as it is, as well as applying 1% and 3% of Na ₃ PO ₄ as equivalents to dirt and impurities on the steel sheet surface, decarburizing annealing at 840 ° C. for 4 minutes, and adding 5% of TiO ₂ MgO was applied as an annealing separator, and then subjected to final finish annealing to obtain a product sheet.

In the above decarburization annealing step, 400 to 800
The average rate of temperature rise in the temperature range of 4 ° C. was changed to 4, 11, 20, and 35 ° C./s, respectively.
(H ₂ O) / P (H ₂ ) was kept constant at 0.45. Then, the same investigation as in Example 1 was conducted for each decarburized annealed plate and each product plate.

Table 2 summarizes these decarburizing annealing conditions and investigation results.

[Table 2] As is apparent from Table 2, all of the applicable examples of the present invention show high magnetic flux densities.

[0049]

According to the present invention, in the production of a thin grain oriented silicon steel sheet using an AlN-based inhibitor, in the decarburization annealing step, the average heating rate range is regulated and the decarburization annealing conditions are adjusted. The purpose of the present invention is to control the pickling loss of the decarburized annealed sheet within a specific range. According to the present invention, it is possible to stably produce a thin grain-oriented electrical steel sheet having an extremely high magnetic flux density.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the pickling loss of a decarburized annealed plate and the magnetic flux density (B ₈ ) of a product plate when the product plate thickness is 0.23 mm.

FIG. 2 is a graph showing the relationship between the pickling loss of a decarburized annealed plate and the magnetic flux density (B ₈ ) of a product plate when the product plate thickness is 0.15 mm.

FIG. 3 is a graph showing a relationship between a heating rate during decarburization annealing, a reduction in pickling of a decarburized annealed plate, and a magnetic flux density (B ₈ ) of the product plate when the product plate thickness is 0.23 mm.

FIG. 4 is a graph showing a relationship between a heating rate during decarburization annealing, a pickling loss of a decarburized annealed sheet, and a magnetic flux density (B ₈ ) of the product sheet when the product sheet thickness is 0.15 mm.

FIG. 5 is a graph showing the relationship between the amount of pickling loss and the amount of nitriding using the heating rate during decarburizing annealing as a parameter.

Claims (2)

[Claims] 1. Using a silicon steel slab for a grain-oriented electrical steel sheet containing Al and N as a raw material, hot rolling is performed, and cold rolling is performed two or more times with intermediate annealing to obtain a final cold rolled sheet thickness of 0.20. mm
Then, after degreasing, after decarburizing annealing, to produce a thin grain-oriented electrical steel sheet by a series of steps of applying an annealing separator and then performing final finish annealing, in the decarburizing annealing step, The average rate of temperature rise in the temperature range from 400 ° C to 800 ° C is in the range of 5 ° C / s to 25 ° C / s, and the decarburizing annealing conditions are adjusted to obtain a predetermined pickling condition of the steel sheet after decarburizing annealing. A method for producing a thin grain-oriented electrical steel sheet having an extremely high magnetic flux density, wherein the pickling loss is controlled within a specific range. 2. The magnetic flux density according to claim 1, wherein the steel sheet after decarburizing annealing has a pickling loss of 5% HCl at 60 ° C. for 60 seconds in a pickling condition of 0.1 to 0.4 g / m ² . A method for manufacturing extremely thin, grain-oriented electrical steel sheets.