JPH10102144A - Manufacturing method of non-oriented electrical steel sheet with excellent magnetic properties - Google Patents

Abstract

[PROBLEMS] To provide a method for inexpensively manufacturing a non-oriented electrical steel sheet having a high degree of integration of {100} planes parallel to the steel sheet surface and having excellent magnetic properties. SOLUTION: C: 0.005% or less, Si: 0.1 to 7%, M
n: 0.05-4%, P: 0.1% or less, S: 0.05% or less, A
l: A production method in which steel consisting of 2% or less, the balance of Fe and unavoidable impurities is hot-rolled at 700 ° C. or more and continuously annealed at 800 ° C. or more at a temperature at which austenite transformation does not occur. Further, a manufacturing method in which the sheet is rolled to a thickness of twice or less the thickness of the final product, cold-rolled to the thickness of the final product, and then subjected to the above-described continuous annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a non-oriented electrical steel sheet having excellent magnetic properties.

[0002]

2. Description of the Related Art Electrical steel sheets are roughly classified into grain-oriented electrical steel sheets and non-oriented electrical steel sheets. The grain-oriented electrical steel sheet has the <001> axis, which is the axis of easy magnetization of the crystal, integrated in the rolling direction, and has excellent magnetic properties when a magnetic field is applied in the rolling direction. On the other hand, the non-oriented electrical steel sheet is <001>
The axis is distributed in various directions in the plane of the steel sheet, and there is a small difference in magnetic properties depending on the magnetization direction in the plane of the steel sheet.

[0003] Conventionally, there has been a demand for improvements in magnetic properties (low iron loss, high magnetic flux density, etc.) of magnetic steel sheets. In particular, non-oriented magnetic steel sheets have been used in large quantities, and improving their performance is an important issue. is there. Means for reducing iron loss in non-oriented electrical steel sheets include Si
There are methods such as increasing the content to increase the specific resistance, adjusting the crystal grain diameter to an optimum value by reducing the impurity elements of the steel, and reducing the thickness of the steel sheet.

[0004] However, the magnetic flux density decreases as the Si content increases, and the effect of controlling the crystal grain size is limited. For this reason, control of texture is indispensable for realizing both reduction of iron loss and improvement of magnetic flux density. The ideal texture of the non-oriented electrical steel sheet is ideally a {100} texture in which the {100} planes of the crystal are accumulated parallel to the steel sheet surface, and several proposals have been made to realize this. ing.

There is a method of developing {100} texture by utilizing surface energy during recrystallization annealing. For example, a silicon steel sheet with a thickness of 0.15 mm or less
This is a method of preferentially growing crystal grains having a {100} plane parallel to the plate surface when annealing at 00 ° C. or more, using a difference in surface energy as a driving force. However, this method requires an extremely thin steel plate and also requires high-temperature annealing, which is not economical.

[0006] JP-A-1-319632 discloses C, N, Si.
, Mn-containing steel sheet having a thickness of about 0.35 mm is annealed in vacuum to form a decarburized layer in which {100} texture is accumulated on the surface, and then decarburization and decarburization of the surface in a decarburization and denitrification atmosphere. A method has been proposed in which a nitride layer is developed up to the center of the thickness.

[0007] The intensity of the degree of accumulation of the texture is determined by the ratio of the X-ray reflection intensity from a random orientation such as a powder sample to the X-ray reflection intensity from the orientation of the sample (hereinafter referred to as "random specific intensity"). ). When using any of the above methods, the {100} area density is 30
It is possible to obtain a material having an extremely high integration degree twice or more. But,
It is difficult to produce these stably and economically.

[0008] US Pat. No. 3,163,564 discloses a trace amount of Al.
Is proposed to grow the crystal grains of {100} <001> orientation by performing cross-rolling for rolling in the longitudinal direction and the width direction on the silicon steel to which the steel is added, and then performing final annealing at a high temperature for a long time. Have been. However, this method also lacks mass productivity and economy.

Japanese Patent Application Laid-Open No. Sho 53-31515 discloses that a steel sheet essentially containing no C is gradually cooled after heating to a γ single phase region and utilizing the γ-α transformation during cooling. A method of integrating {100} planes has been proposed. However, in this method, the degree of {100} texture development is weak.

[0010]

An object of the present invention is to provide a method for inexpensively manufacturing a non-oriented electrical steel sheet having a high degree of integration of {100} planes parallel to the steel sheet surface and having excellent magnetic properties.

[0011]

The gist of the present invention resides in the following methods (1) to (3) for producing a non-oriented electrical steel sheet having excellent magnetic properties. In addition, the following percentages of the chemical composition mean% by weight.

(1) By weight%, C: 0.005% or less, Si
: 0.1 to 7%, Mn: 0.05 to 4%, P: 0.1% or less,
S: 0.05% or less, Al: 2% or less, steel consisting of Fe and unavoidable impurities is hot-rolled at 700 ° C. or more, pickled, and then continuously annealed at 800 ° C. or more at a temperature at which austenite transformation does not occur. A method for producing a non-oriented electrical steel sheet having excellent magnetic properties.

(2) C: 0.005% or less by weight%, Si
: 0.1 to 7%, Mn: 0.05 to 4%, P: 0.1% or less,
S: 0.05% or less, Al: 2% or less, steel consisting of the balance of Fe and unavoidable impurities to a thickness of twice or less the final product
Excellent magnetic properties characterized by hot rolling at 700 ° C or higher, cold rolling to the final product thickness after pickling, and continuous annealing at 800 ° C or higher at a temperature at which austenite transformation does not occur. Manufacturing method of non-oriented electrical steel sheet.

(3) In the hot rolling, the steel being rolled is heated to a higher temperature to continue the rolling, or hot-rolled to an intermediate thickness and wound, and then the wound steel sheet of intermediate thickness is wound. The method for producing a non-oriented electrical steel sheet having excellent magnetic properties according to claim 1 or 2, wherein the method is hot rolling again while heating the sheet.

The {100} texture is known as a rolled texture, and particularly develops remarkably when cold rolling a Si-containing steel. However, when recrystallization annealing is performed after cold rolling, the {100} texture crystals are eroded by the {111} texture crystals due to a low recrystallization rate. For this reason, even if a hot-rolled steel sheet is cold-rolled and annealed under normal conditions, the {100} area density of the steel sheet is ultimately only about 1.5 at most in terms of random specific strength. .

The inventors of the present invention hot-rolled and annealed the Si-containing steel to form a highly integrated {100} texture having a random specific strength of about 6 in the central part of the sheet thickness, and the magnetic flux in that part. The density was found to be extremely high. It is presumed that recrystallization does not occur even if annealed because the hot-rolled steel sheet has small working strain, and the hot-rolled texture remains.

Further, a method for producing a steel sheet having a desired thickness without deteriorating these characteristics has been found. If necessary, a hot-rolled steel sheet having a desired thickness can be obtained by providing a temperature compensating means in the middle or by performing re-heating and hot rolling again. Further, if necessary, the sheet thickness is reduced by applying a slight cold reduction and annealing to the {100} texture obtained by annealing the hot rolling.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In implementing the present invention, the form and the range of conditions and the reasons for setting them will be described below. In addition, all indications of the following chemical compositions are% by weight.

(A) Chemical composition of a steel sheet C: Since remaining in a product has an adverse effect on iron loss, it is preferable to reduce the chemical composition. For this reason, the C content is set to 0.005% or less.

Si: As the content increases, the electric resistance of the steel increases, the eddy current loss decreases, and the iron loss increases. 6.5% of Si
In the case where it is included, the magnetostriction is eliminated, and the magnetic properties become extremely good. However, as the Si content increases, the steel becomes harder and more brittle, and particularly, cold rolling becomes more difficult.

In the present invention, hot rolling is performed to a position close to the product sheet thickness, so that rolling can be easily performed even with a Si content of 3% or more. As the range in which rolling is possible, the upper limit of Si of the present invention is 7%. The lower limit is 0.1 to secure the iron loss level required for the minimum grade of non-oriented electrical steel sheets.
%.

Mn: The content of Mn is set to 0.05% or more in order to fix S in the steel as sulfide to prevent hot embrittlement. Mn, like Si, increases the electrical resistance of steel, and is therefore effective in reducing eddy current loss. However, if Mn is added excessively, rolling becomes difficult and the α / γ transformation point decreases. The final continuous annealing in the production method of the present invention needs to be performed in a temperature range where austenite transformation does not occur in order to maintain a texture. If the α / γ transformation point is too low, the annealing temperature in the final continuous annealing step is restricted, which is not preferable. In order to avoid this, the upper limit of the Mn content is set to 4%.

P: The effect of reducing the eddy current loss by increasing the electric resistance of the steel, and the effect of improving the punching property at the customer by hardening the steel. However, if it is contained excessively, it segregates at the ferrite grain boundaries and embrittles the steel. In particular, in steels in which Si exceeds 1%, the embrittlement of P poses a problem. For this reason, P can be contained as needed. When it is contained, the upper limit is 0.1%.

S: It is a harmful element to the magnetic properties, and it is desirable that the amount is small. Therefore, the upper limit is set to 0.05%.

As in the case of Al: Si, when the content increases, the electric resistance of the steel increases, the eddy current loss decreases, and the iron loss improves.
On the other hand, Al ₂ O ₃ inclusions inhibit the growth of crystal grains and impair iron loss. For this reason, Al is not an essential element, and may be contained as necessary. Even when Al is contained, if it is contained excessively, the rollability deteriorates. Therefore, A
l The upper limit of the content is 2%.

(B) Manufacturing Step The most desirable method for manufacturing the non-oriented electrical steel sheet having excellent magnetic properties according to the present invention is to hot roll a steel having the composition described in the above item (a).
Thereafter, it is manufactured through the steps of pickling, annealing, and coating. If the desired thickness cannot be obtained only by hot rolling, hot rolling is performed to a thickness of twice or less the thickness of the final product, and then cold rolling is performed to the thickness of the final product. , Annealed and coated.

Hot rolling: Hot rolling is preferably carried out to the thickness of the final product. Alternatively, hot rolling may be performed to a thickness of not more than twice the thickness of the final product. If the thickness after hot rolling exceeds twice the thickness of the final product, the {100} texture is undesirably weakened in the subsequent cold rolling and annealing.

Hot rolling must be completed above the recrystallization temperature. For this reason, the rolling end temperature is set to 700 ° C. or more. Although the rolling start temperature is not particularly limited, it is desirable to start rolling at a high temperature because the temperature decreases during rolling.
There is no special limitation on the winding temperature. However, if the winding temperature is too high, the scale may be excessively formed.

There are three types of hot rolling methods applied to the production method of the present invention. a. Rolling is performed by a normal hot rolling mill. b.
Means for heating the steel is provided in the middle of the plurality of hot rolling mills, and the steel being rolled is reheated to complete the hot rolling. c. Rolled by a normal hot rolling mill, taken up once, pickled, and then heated using a rolling facility equipped with a means for heating the steel on the entry side, while rewinding the steel on the entry side and heating again at 700 ° C or higher. Hot rolling.

The method (a) has a short manufacturing process and is rich in economy, but the rollable sheet thickness is limited. This method can be applied when the thickness of the final product is relatively large. The methods b and c are preferably applied when a steel sheet having a thickness that is difficult to roll by ordinary hot rolling is required.

Means for heating the steel by the methods b and c are as follows:
Any method capable of rapidly heating steel may be used, and the present invention does not specify the means. Examples include an electric heating method in which the steel is heated by using the electric resistance of the steel itself through a direct current through the steel through an energizing roll, and an induction heating method in which an induction current is generated in the steel by using an induction coil to heat the steel. Conceivable. These methods are preferable because the equipment is compact, rapid heating is possible, and the plate to be heated is not excessively oxidized.

Pickling: The scale on the plate surface is removed by a usual method. There are no particular restrictions on the pickling equipment and conditions.

Cold rolling: Cold rolling can be omitted if hot rolling can be performed to the thickness of the final product. In this case, annealing can be performed immediately after pickling. In order to adjust the flatness and shape of the plate, skin pass rolling at a rolling reduction of about 0.1% or shape correction by a leveler or the like may be performed. These may be applied before pickling.

If the sheet is too thick without hot rolling, or if there is a problem with the accuracy of the sheet thickness, cold rolling is performed. Since the essential point of the production method of the present invention is to utilize the hot rolled texture, the {100} texture must not be broken by the cold rolling. For this reason, the rolling reduction in the cold state is set to 50% or less. The cold rolling reduction is preferably 20% or less, more preferably 10% or less, in order to maintain a higher {100} texture.

Continuous annealing: The steel sheet after pickling or the steel sheet after cold rolling is subjected to pretreatment such as degreasing and washing as required, and then subjected to continuous annealing to remove processing strain and grow grains. This reduces the hysteresis loss. For this purpose, it is necessary to perform annealing at a high temperature, and the minimum temperature is set to 800 ° C. The upper limit of the annealing temperature is a temperature at which α / γ transformation does not occur. This temperature depends on the chemical composition of the steel sheet, for example,
The temperature is 960 ° C for steel with 2.3% Si and 1.7% Mn.

In the conventional method in which the cold rolling reduction exceeds 50%, a {111} recrystallized texture is obtained by annealing at a high temperature after cold rolling. However, when the cold rolling reduction is limited to 50% or less as in the production method of the present invention, the generation of recrystallization nuclei on the {111} plane during annealing is small, and the {100} texture is hardly eaten by silkworms. After recrystallization is completed, the volume fraction is large # 10
The {0} crystal grains eat the {111} crystal grains into silkworms {1}
The 00 ° plane may be stronger.

After the continuous annealing, an insulating coating is usually applied. The type of the insulating coating and the conditions for baking the paint are not specially defined and are arbitrary.

Texture of final product: The {100} plane X-ray reflection integrated intensity at the center of the thickness of the final product manufactured according to the manufacturing method of the present invention is 3 or more as a random specific intensity.

[0039]

【Example】

[Example 1] Steel A having the chemical composition shown in Table 1 was melted in a vacuum, and a steel ingot was forged into a 30 mm thick slab.

[0040]

[Table 1]

After holding this at 1200 ° C. for 30 minutes, the width is 100 m
m, thickness 2.3mm, 1.8mm, 1.2mm, 0.80mm, 0.60mm, 0.
It was hot rolled into a 50 mm steel plate. The rolling end temperature was 850 ° C. These steel sheets were pickled, and steel sheets having a thickness other than 0.50 mm were cold-rolled to a thickness of 0.50 mm. From these cold-rolled steel sheets, a ring-shaped specimen having an outer diameter of 45 mm and an inner diameter of 33 mm was punched out with a press, and this specimen was subjected to a first re-simulation simulating continuous annealing held in a salt bath at 900 ° C. for 1 minute. Crystal annealing was performed.
The magnetic properties of the annealed ring-shaped specimen and the random specific strength of the {100} texture were measured. The results are shown in Table 2.

[0042]

[Table 2]

In sample No. 1, which was rolled to a thickness of the final product by hot rolling, the {100} texture had the highest random specific strength,
Good magnetic properties. When the cold reduction rate is high, especially
If it exceeds 50%, the random specific strength is remarkably reduced and the magnetic properties are inferior.

Example 2 After steel B having the chemical composition shown in Table 1 was melted in a vacuum, a steel ingot was forged to produce a 30 mm thick slab. After holding this at 1250 ° C for 30 minutes, the rolling end temperature
Hot rolling was performed at 830 ° C. to obtain a steel plate having a width of 100 mm and a thickness of 2.3 mm. After this was pickled, a second hot rolling was performed using a rolling mill provided with an induction heating device for heating the steel sheet on the entrance side, and then these were pickled and cold rolled. Table 3 shows the sheet thickness after the second hot rolling, the rolling end temperature, the sheet thickness after the cold rolling, and the cold rolling reduction.

[0045]

[Table 3]

From a cold-rolled steel sheet, a ring-shaped specimen having an outer diameter of 45 mm and an inner diameter of 33 mm was punched out with a press, and 900 μm
Annealing was performed to simulate continuous annealing held in a salt bath at 1 ° C for 1 minute. The magnetic properties of the annealed ring-shaped specimen and the random specific strength of the {100} texture were measured.
The results are shown in Table 3.

Test Nos. 7 to 7 manufactured under the conditions specified in the present invention
In No. 12, the {100} texture was remarkably developed, and the random specific strength was 5 or more, indicating good magnetic properties. Trial number 7
Was rolled to the thickness of the final product in the second hot rolling, so that cold rolling was omitted and annealing was performed. This steel sheet had the best magnetic properties. On the other hand, in Test Nos. 14 and 15, the cold reduction was too high and the {100} texture was impaired, so that the magnetic properties were deteriorated. Test No. 13 in which the second hot-rolling finishing temperature was as low as 480 ° C. was in a so-called cold-rolled state, in which the {100} texture was damaged during annealing and the magnetic properties were damaged.

Example 3 Steels A to A having the chemical compositions shown in Table 1
After vacuum melting of J, the steel ingot was forged into a 30 mm thick slab. After holding them at 1200 ° C. for 30 minutes, they were hot rolled into a 2.3 mm thick and 100 mm wide plate at a rolling end temperature of 850 ° C. These hot rolled sheets were allowed to cool to room temperature and then rolled to a thickness of 0.60 mm while reheating to 900 ° C. using a rolling mill provided with a current-carrying heating device on the entry side. Rolling end temperature is 80
It was 0 ° C.

At this time, hot cracking occurred in steel H because Mn was too low. Therefore, the subsequent processing was abandoned. The remaining hot-rolled steel sheet was pickled and cold-rolled to a thickness of 0.50 mm. At this time, since the P content was too high, a crack was generated from the steel sheet end of the steel I. Therefore, the subsequent treatment of steel I was abandoned.

Outer diameter 45 mm, inner diameter
A 33 mm ring-shaped specimen was punched out with a press, and the ring-shaped specimen was subjected to annealing simulating continuous annealing in a salt bath at 850 ° C. for 1 minute.

The results of the magnetic measurement of these specimens were as follows:
Table 4 shows the measurement results of the random specific strength of the 0 ° texture.

[0052]

[Table 4]

In the case of steels A to G and J, $ 10
An extremely good {100} texture was formed with a {0} plane density of 7 or more in random specific strength. Steels A to F exhibited good magnetic properties, but steel G deteriorated magnetic properties due to too high C, and steel J deteriorated magnetic properties due to a large amount of MnS precipitated due to high S.

When the method of the present invention was used, a steel sheet having a thickness of 0.50 mm was obtained even with a high Si steel C, which is usually difficult to roll, and its magnetic properties were good.

[0055]

According to the method of the present invention, the {100} plane density parallel to the plate surface has a texture of 3 or more in terms of random specific strength, and is excellent in both magnetic properties such as magnetic flux density and iron loss. A non-oriented electrical steel sheet having high performance and a non-oriented electrical steel sheet suitable for high Si and high frequency applications can be easily manufactured.

Claims (3)

[Claims] (1) C: 0.005% or less, Si: 0.1% by weight
-7%, Mn: 0.05-4%, P: 0.1% or less, S: 0.05
% Or less, Al: 2% or less, the balance consisting of Fe and unavoidable impurities is hot-rolled at 700 ° C. or more, pickled,
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties, characterized by continuously annealing at a temperature at which austenite transformation does not occur at 0 ° C or higher. 2. In% by weight, C: 0.005% or less, Si: 0.1%
-7%, Mn: 0.05-4%, P: 0.1% or less, S: 0.05
%, Al: less than 2%, the balance of Fe and unavoidable impurities is hot-rolled at 700 ° C. or more to a thickness of less than twice the thickness of the final product. A method for producing a non-oriented electrical steel sheet having excellent magnetic properties, characterized by cold rolling and continuous annealing at a temperature of 800 ° C. or higher where austenite transformation does not occur. 3. The hot rolling is carried out by heating the steel being rolled to increase the temperature and continuing the rolling, or hot rolling to an intermediate thickness and winding it, and then unwinding the wound steel plate of the intermediate thickness. The method for producing an omnidirectional magnetic steel sheet having excellent magnetic properties according to claim 1 or 2, wherein the method is hot rolling again while heating.