JPH05186825A - Production of nonoriented silicon steel sheet reduced in iron loss - Google Patents

Abstract

PURPOSE:To produce a nonoriented silicon steel sheet extremely reduced in iron loss and suitable for iron core material without causing troubles, such as breakage, at the time of cold working. CONSTITUTION:A slab of a steel having a composition which consists of, by weight, <=0.005% C, 3.0-4.0% Si, 2.2-8.0% Mn, <=0.020% P, <=0.005% S, 0.10-2.00% Al, <=0.005% N, and the balance Fe with inevitable impurities and where Si(%)+Al(%) -0.5XMn(%)<=2.0 is satisfied is hot-rolled, cold-rolled once or cold-rolled twice or more while process-annealed between cold rolling stages, where at least one cold rolling is done at 70-300 deg.C steel sheet temp., and further annealed continuously. Annealing can be done before cold rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a non-oriented electrical steel sheet having extremely low iron loss, which is widely used as an iron core material for transformers, generators and electric motors.

[0002]

2. Description of the Related Art The magnetic performance of a non-oriented electrical steel sheet is generally represented by iron loss and magnetic flux density. In particular, the grade of a material is almost determined by the magnitude of iron loss. By using an electromagnetic steel sheet having a low iron loss as an iron core material, a temperature rise of an electric device due to heat generation of the iron core can be suppressed and the efficiency of the device can be improved. Therefore, there is an extremely strong demand for a low iron loss material.

Iron loss is generally divided into two iron loss components, hysteresis loss and eddy current loss. It is known that these iron loss components change due to metallurgical factors such as the crystal grain size of the steel sheet, the amount of precipitates, the texture and the electrical resistance (specific resistance) of the steel sheet. To reduce the iron loss, The following metallurgical factors are controlled.

Regarding the crystal grain size, the hysteresis loss decreases as the grain size increases, but the eddy current loss increases, so there is an appropriate grain size that minimizes the iron loss. However, it is known that the proper particle diameter changes depending on the excitation frequency, and the higher the frequency, the smaller the proper particle diameter. Therefore, the proper particle diameter is selected according to the frequency used. For example, 50
100 to 200 μm for excitation at commercial frequencies up to 60 Hz
It is said that the grain size before and after is the proper grain size, and in a high-grade non-oriented electrical steel sheet with low iron loss, the finish annealing conditions are selected so that the grain size falls within this range.

Precipitates impede the movement of the domain wall and increase the hysteresis loss, and also prevent the crystal grains from growing to an appropriate grain size in the finish annealing, thereby causing an increase in iron loss.
Therefore, S and N that form precipitates such as sulfides and nitrides
Efforts have been made to reduce as much as possible.

Regarding the texture, by increasing the accumulation of {100} and {110} orientations that include the easy axis of magnetization in the plate surface and decreasing the {111} and {211} orientations that do not include the easy axis of magnetization, hysteresis can be obtained. We are trying to reduce losses.

An increase in the specific resistance of the steel sheet reduces eddy current loss and is therefore extremely effective in reducing iron loss. Generally Si
Although the specific resistance of the steel sheet is increased by the addition of 3% by weight, if the content exceeds 3% by weight (hereinafter, "%" means "% by weight"), the workability of the steel sheet deteriorates and cold rolling is performed. Occasionally, breakage easily occurs, and it is extremely difficult to manufacture a steel sheet having a Si content exceeding 3%. Al is also an element that has a large effect of increasing the specific resistance, but since it also deteriorates the workability like Si, the addition amount is limited. Therefore, in the present situation, Si and Al are contained within the range of 4% or less of Si (%) + Al (%) to increase the specific resistance of the steel sheet to improve the iron loss.

[0008]

However, with the recent trend toward higher efficiency of electrical equipment, the demand for low iron loss of non-oriented electrical steel sheets has become stronger and stronger. The demand cannot be sufficiently met only by controlling the metallurgical factors which have been conventionally performed such as optimization of the crystal grain size, reduction of precipitates and increase of specific resistance. Increasing the specific resistance of the steel sheet is an effective means to reduce the eddy current loss and surely reduce the iron loss.However, regarding the increase of the specific resistance due to the increase of Si and Al contents, cold rolling property From the perspective of.

The present invention has been made in view of such circumstances, and an object thereof is to provide a method for producing a non-oriented electrical steel sheet which has extremely low iron loss and is excellent in cold workability. To do.

[0010]

Means for Solving the Problems The inventors of the present invention have made various studies on methods of increasing the specific resistance and reducing the iron loss without deteriorating the workability, and have obtained the following findings.

The steel sheet contains more than 3% Si,
(%) + Al (%) is 4% or more, Si (%) + Al
By adding Mn in the range of (%) − 0.5 × Mn (%) ≦ 2.0, deterioration of workability is suppressed, and it is possible to manufacture a non-oriented electrical steel sheet with extremely low iron loss.

Moreover, Mn is an element that increases the specific resistance of the steel sheet like Si, and is also effective in reducing iron loss.
Even if (%) + Al (%) is less than 4%, Si (%) + Al
By adding Mn in the range of (%)-0.5 x Mn (%) ≤ 2.0, it is possible to manufacture a non-oriented electrical steel sheet having a smaller iron loss than the conventional high-grade non-oriented electrical steel sheet.

After the chemical composition of the steel is set to the above-mentioned composition or by further performing cold rolling at least once at a steel plate temperature of 70 to 300 ° C.,
It can be manufactured without causing troubles such as breakage due to deterioration of workability during cold rolling.

The present invention was made on the basis of the above findings, and the gist thereof is "C: 0.005% or less, Si: 3.0-.
4.0%, Mn: 2.2 to 8.0%, P: 0.020% or less, S: 0.
005% or less, Al: 0.10 to 2.00%, N: 0.005% or less,
And, Si (%) + Al (%) − 0.5 × Mn (%) ≦ 2.0,
The balance is hot-rolled steel slab consisting of Fe and unavoidable impurities, and the obtained steel sheet is hot-rolled or annealed after hot-rolling, and then cold-rolled once or twice with intermediate annealing. Roll at least once cold rolling 70 ~ 300 ℃
The method for producing a non-oriented electrical steel sheet, which is characterized in that it is performed at the steel sheet temperature, followed by continuous annealing.

Incidentally, in JP-A-64-225, C: 0.01%
Below, Si: 2.0 to 3.5%, Mn: 0.1 to 10.0%, P: 0.20
% Or less, Al: 0.10 to 1.50%, B: 0.008% or less, that is, Si, Al and Mn are contained in the same manner as the magnetic steel sheet of the present invention.
A method of manufacturing a high tensile strength non-oriented electrical steel sheet having a high content of is proposed. However, this steel sheet is intended for high strength, and elements such as P and B, which are not so effective in reducing iron loss, are added, and the iron loss is at the level of medium-to-low grade non-oriented electrical steel sheet. is there. Further, in the present invention, the balance of Si, Al and Mn contents of the steel slab is taken into consideration in order to improve the workability, but such an idea is recognized in the invention of JP-A-64-225. Therefore, the obtained steel sheet is considered to have poor cold rolling property.

[0016]

The function and effect of each constituent element of the present invention will be described below.

I. Composition of steel slab or product C and N: Since C and N in the product adversely affect iron loss, both C and N are 0.005% or less, preferably
It should be 0.003% or less. The reason is that C and N remaining in the product stage become carbonitrides and hinder the movement of the domain wall, thus increasing iron loss.

Regarding C, 0.005% at the stage of steel slab
Even if it exceeds C, C
The content can be 0.005% or less. However, since an oxide layer is formed on the surface layer of the steel sheet during decarburization annealing and the magnetic properties are deteriorated, it is effective to decarburize at the steelmaking stage so that the C content in the steel slab is 0.005% or less.

Si: Si is an element having a great influence on the magnetic properties, and as the content increases, the specific resistance of the steel sheet increases, the eddy current loss decreases, and the iron loss decreases. But 4.0
If the content exceeds%, the workability is remarkably reduced and cold rolling becomes difficult. On the other hand, if the content is less than 3.0%, the specific resistance of the steel sheet is low, and a non-oriented electrical steel sheet with low iron loss cannot be manufactured. Therefore, the Si content is 3.0 to 4.0%.

Al: Al, like Si, is an element effective for increasing the specific resistance of the steel sheet and has the effect of reducing iron loss. However, when the content exceeds 2.0%, the workability of the steel sheet deteriorates, and when the content is less than 0.1%, the iron loss reducing effect is small, and AlN formed by combining with N is finely precipitated, resulting in the growth of crystal grains. Content is 0.10 to 2.00% because it suppresses iron loss and interferes with domain wall movement and prevents iron loss from decreasing.
And

Mn: Mn is an element effective for causing α-γ transformation in high Si and high Al steel sheets such as electromagnetic steel sheets produced by the method of the present invention. The occurrence of transformation promotes the refinement and homogenization of the structure during hot rolling, and as a result, the workability during cold rolling is improved. Whether or not the above α-γ transformation occurs depends on the balance between the contents of Si and Al which are ferrite forming elements and Mn which is an austenite forming element, and Si (%) + Al (%)-0.5Mn (%) It is necessary for Mn to be included so that ≦ 2.0 for the transformation to occur. In order to satisfy this formula, if the contents of Si and Al are the lower limit values defined in the present invention, respectively, Si (%) + Al
Since (%) = 3.1%, it is necessary to contain 2.2% or more of Mn, and when the contents of Si and Al are the upper limits defined by the present invention, the required Mn content is 8.0
% Or more. On the other hand, Mn, like Si and Al, is an element effective in increasing the specific resistance of the steel sheet, and for the purpose of reducing iron loss, it is essential to contain Mn in an amount of 2.2% or more. Further, if the Mn content exceeds 8.0%, the cold workability deteriorates. Therefore, the Mn content is 2.2 to 8.0%, and Si (%) + Al
It is necessary to satisfy the condition of (%)-0.5Mn (%) ≤ 2.0.

P: P is an element that easily segregates at grain boundaries and embrittles the steel sheet. In the steel of the present invention having a high workability of high Si, Al and Mn contents, the P content is It is necessary to keep it below 0.020%. If possible, 0.015% or less is desirable.

S: S is an element which forms MnS together with Mn, inhibits the growth of crystal grains during the final continuous annealing, and interferes with the domain wall movement to prevent the reduction of iron loss.
If it exceeds, the adverse effect is great. Therefore, its content is
It is 0.005% or less, preferably 0.002% or less.

II. Hot Rolling The raw steel slab has the above composition. This may be molten steel that has been melted in a converter, an electric furnace, or the like, and if necessary subjected to vacuum degassing or the like, slabs made by continuous casting, or slab-rolled ingots. ..

There are no particular restrictions on the hot rolling conditions, but it is preferable that the heating temperature is 1100 to 1250 ° C. and the finishing temperature.
It is 700-900 ℃.

III. Hot Rolled Sheet Annealing, Cold Rolling and Intermediate Annealing A steel sheet (hot rolled sheet) obtained by hot rolling is annealed as it is or after hot rolling (hot rolled sheet annealing), By cold rolling one or more times, it is rolled to a predetermined product plate thickness.

The hot-rolled sheet annealing is effective for improving the texture of the final product and obtaining good magnetic properties. When hot-rolled sheet annealing is performed by continuous annealing, soaking in the temperature range of 700 to 1000 ° C is preferable, and when performing box annealing, soaking in the temperature range of 650-950 ° C is desirable.

If the temperature of the steel sheet during cold rolling is raised to 70 ° C. or higher, the workability of the steel sheet is improved and the fracture during rolling is significantly reduced. The higher the temperature of the steel sheet, the greater the effect of improving the cold rolling property, but rolling at a temperature exceeding 300 ° C is not preferable because the surface of the steel sheet is oxidized. Therefore, cold rolling
At a steel plate temperature of 70 to 300 ° C.

When performing cold rolling a plurality of times, it is desirable to heat the steel sheet to the above temperature range for each cold rolling before rolling. At least the plate thickness before cold rolling
If it is 1.0 mm or more, it is necessary to perform cold rolling at the above steel plate temperature. However, when the sheet thickness is less than 1.0 mm, at least one cold rolling among multiple cold rolling performed at a steel sheet temperature of 70 to 300 ° C is effective in preventing breakage trouble during rolling. Is recognized.

When performing cold rolling a plurality of times, an annealing process is sandwiched between them. This intermediate annealing is preferably performed in the temperature range of 700 to 1000 ° C.

Heating of the steel sheet during cold rolling may be carried out, for example, by induction heating with a high frequency, direct current heating in which an electric current is directly applied to the steel sheet using a roll as an electrode, or heating in an annealing furnace. Not limited.

IV. Continuous Annealing After Cold Rolling In order to develop a good texture, primary recrystallization by rapid heating is necessary, and therefore continuous annealing is effective. The annealing temperature is preferably 700 to 1050 ° C.

In the step after the continuous annealing, an insulating coating may be applied if necessary, as in the case of manufacturing a normal non-oriented electrical steel sheet.

[0034]

[Example 1] A steel slab having the composition shown in Table 1 obtained by melting in a converter, adjusting the components by vacuum treatment, and then continuously casting was hot-rolled at a heating temperature of 1180 ° C and a finishing temperature of 830 ° C. 2.3 mm
Finished thick. These test steels are general high-grade non-oriented electrical steel sheets (with a specific resistance of approximately 50-60 μΩ) in order to reduce iron loss.
・ The specific resistance is significantly increased compared to the (cm), and the balance of Si, Al, and Mn is variously changed so that the specific resistance is almost the same.

However, for comparison, only the hot-rolled sheet of Test No. 6 had a specific resistance equivalent to that of a general high-grade non-oriented electrical steel sheet.

Next, descaling is performed by pickling, and
After carrying out box annealing type hot rolled sheet annealing in which it was soaked at 50 ° C. for 4 hours, it was further cold rolled to a thickness of 0.50 mm. Heating of the steel sheet during cold rolling is performed by charging the steel sheet (coil) into a box annealing furnace before heating and rolling, and the steel sheet temperature during cold rolling is in the range of 100 to 120 ° C. And

As a result, the hot-rolled sheets of Test Nos. 1 to 3, which deviate from the composition range defined by the present invention, cracked or ruptured from the edge portion of the steel sheet during cold rolling, and thus had a predetermined sheet thickness. Could not be cold rolled. On the other hand, test numbers 4 and 5 within the composition range specified in the present invention
The hot-rolled sheet of No. 1 could be cold-rolled to a predetermined sheet thickness without breaking. Further, the hot-rolled sheet of test number 6, which is a comparative material having a low specific resistance, could be cold-rolled.

[0038]

[Table 1]

[0039]

Example 2 The cold-rolled sheets (0.50 mm thick) of test numbers 4, 5 and 6 obtained in Example 1 were subjected to continuous annealing in which they were soaked at 970 ° C. for 1 minute, and then their magnetic properties were measured. The results are shown in Table 2.
Shown in.

As shown in Table 2, the cold-rolled sheets of Test Nos. 4 and 5 within the composition range defined by the present invention have increased specific resistance as compared with the cold-rolled sheet of Test No. 6 as a comparative material. Correspondingly good iron loss values were shown.

[0041]

[Table 2]

[0042]

[Example 3] C: 0.0025%, Si: 3.12%, Mn: 5.11%,
P: 0.009%, S: 0.0009%, Al: 1.05%, N: 0.0020
% Steel slab having a chemical composition within the range defined by the present invention is hot-rolled at a heating temperature of 1200 ° C. and a finishing temperature of 810 ° C.,
Finished to 2.3mm thickness. After descaling this hot rolled sheet by pickling, it was heated to various temperatures shown in Table 3 by induction heating during cold rolling and cold rolled to a thickness of 0.50 mm. Table 3 also shows the occurrence ratio of breakage troubles during the cold rolling.

From the results shown in Table 3, when the steel sheet temperature was lower than 70 ° C., although the occurrence ratio was low, the breaking trouble occurred.
When the steel sheet temperature was 70 ° C or higher, there were almost no fracture problems.

The coils obtained by cold rolling without causing breakage trouble were subjected to continuous annealing at 970 ° C. for 1 minute and then magnetic measurements were performed. W _15/50 ) was 2.05 to 2.15 W / kg, and the magnetic flux density (B ₅₀ ) was in the range of 1.61 to 1.62 T, and extremely good characteristics were obtained.

[0045]

[Table 3]

[0046]

According to the method of the present invention, the iron loss is extremely low,
A non-oriented electrical steel sheet suitable as an iron core material can be manufactured without causing trouble such as breakage during cold rolling.

[0047]

Claims (1)

[Claims] 1. By weight%, C: 0.005% or less, Si: 3.0-
4.0%, Mn: 2.2 to 8.0%, P: 0.020% or less, S:
0.005% or less, Al: 0.10 to 2.00%, N: 0.005% or less, and Si (%) + Al (%)-0.5 x Mn (%) ≤ 2.0
Then, the rest is hot-rolled a steel slab consisting of Fe and unavoidable impurities, and the obtained steel sheet is annealed as it is or after hot-rolling, once or twice or more with intermediate annealing. Cold rolling, at least one cold rolling 70-30
A method for manufacturing a non-oriented electrical steel sheet, which comprises performing the steel sheet temperature of 0 ° C. and then performing continuous annealing.