JPH09263908A - Nonoriented silicon steel sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a nonoriented silicon steel sheet low in the content of Si and excellent in magnetic properties and to provided a method for producing the same. SOLUTION: This nonoriented silicon steel sheet excellent in magnetic properties has a compsn. contg., by weight, <=0.01% C, 0.05 to 1.0% Si, 0.05 to 1.0% Mn, <=0.15$% P, <=0.005% S, 0.008 to 0.02% 0 (oxygen), <0.002% sol. Al, 0.003 to 0.018% Ca, and the balance Fe with inevitable impurities. As for the method for furthermore improving its magnetic properties, in the producing process in which a steel slab is subjected to hot rolling, cold rolling, annealing or the like to form into a final product, the coiling temp. in the hot rolling is regulated to >=650 deg.C, or the coiling temp. in the hot rolling is regulated to <650 deg.C, and hot rolled sheet annealing before the cold rolling is executed at 650 to 1,000 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties, which is widely used as an iron core of electric equipment, and a method for producing the same. For non-oriented electrical steel sheets, the steel sheet manufacturer performs finish annealing after cold rolling, and the user side does not perform annealing in particular, a full process material used for the iron core, and the user side performs punching and annealing. However, the present invention is applicable to any of these cases.

[0002]

2. Description of the Related Art Magnetic steel sheets used for iron cores of electric equipment include non-oriented electrical steel sheets and grain-oriented electrical steel sheets. The grain-oriented electrical steel sheet is mainly used for electric power transformers, whereas the non-oriented electrical steel sheet is widely used for general-purpose motors, small motors and small transformers. Some electric devices, such as generators, convert rotational energy into electrical energy, and transformers, such as those that change voltage to a form that is easy to use, or motors that rotate electrical energy and other machinery. There is something that can be converted into dynamic energy. In equipment that performs such energy conversion, it is necessary to suppress wasteful loss of energy such as heat generation as low as possible, and the iron core used for it has low loss and high efficiency, that is, low iron loss and high magnetic flux density. Required.

Iron loss of electromagnetic steel sheets is divided into eddy current loss and hysteresis loss. Since the eddy current loss decreases as the electric resistance increases, in order to obtain a non-oriented electrical steel sheet with low iron loss, Si is usually contained in a large amount, which has the effect of increasing the electric resistance. However, the addition of Si tends to lower the magnetic flux density, and the addition of Si not only raises the cost, but also hardens the steel and increases the deformation resistance of rolling.

On the other hand, in the case of a non-oriented electrical steel sheet, the hysteresis loss decreases as the crystal grain size of the steel sheet increases if the chemical composition such as Si is the same. However, since the eddy current loss tends to increase as the crystal grain size increases,
It is said that there is an optimum crystal grain size at which the iron loss shows the minimum value.
However, the optimum crystal grain size is considerably larger than that obtained by a general manufacturing method by cold rolling several tens of percent or more and subsequent annealing. Therefore, in ordinary non-oriented electrical steel sheets, various measures have been taken in consideration of economic efficiency so that the crystal grain size after annealing is as large as possible in order to reduce iron loss.

In a non-oriented electrical steel sheet having a low Si content level, in order to make crystal grain growth during annealing as easy as possible, it is possible to reduce fine precipitates that inhibit grain growth. For example, as in the invention disclosed in JP-A-63-195217, sol. Al (acid-soluble Al) is added in an amount of 0.001 to 0.0
The production amount of fine AlN is reduced to 05% (weight%: "%" is omitted for the following description).

S also becomes a sulfide-based precipitate such as MnS and inhibits grain growth. In order to make the finely precipitated MnS harmless by changing its form, for example, JP-A-63-10
No. 3023 discloses that in a low Si non-oriented electrical steel sheet, the ratio of the Ca and S contents (Ca / S) is 0.3 to 2.0.
The invention of the method of adding Ca is shown. in this case,
In order to avoid the damage caused by the precipitation of fine AlN, sol.Al
It is kept below 0.002%. Further, in the invention of Japanese Patent Laid-Open No. 3-126845, even if Al is sufficiently added, Ca is 0.001
In the range of up to 0.005% and Ca / S in an amount of 0.1 to 1.5, fine precipitation of MnS is suppressed, AlN is precipitated and aggregated with CaS as a nucleus, and moreover,
It is said that the B type inclusions of Al ₂ O ₃ can be changed to C type inclusions to improve the magnetic characteristics.

Besides fine precipitates of nitride and sulfide, oxide-based inclusions also hinder the growth of crystal grains. It is said that the presence of oxide-based inclusions having a low softening temperature is elongated and dispersed during rolling, which hinders crystal grain growth during annealing. On the other hand, for example, Japanese Patent Laid-Open No. 7-
No. 150248 discloses that inclusions in steel such as SiO ₂ , MnO and A
The ratio of the weight of MnO to the total weight of the three types of l ₂ O ₃ is
If the content of SiO ₂ is regulated to 15% or less and the weight ratio of SiO ₂ is regulated to 75% or more, the inclusions will be spherical, and if so, the effect of suppressing the crystal grain growth is small, so an invention is proposed that grain growth is improved. ing.

Such precipitates or inclusions of N, S or O (oxygen) not only finely disperse and hinder grain growth, but also the presence thereof hinders domain wall movement during magnetization. Increases hysteresis loss and deteriorates magnetic properties. Therefore, the mixing of these impurity elements must be suppressed as low as possible.

[0009] S can be reduced by the treatment of hot metal or molten steel, and N can be reduced by removing as much as possible from the atmosphere after denitrification by vacuum treatment of molten steel. However, with respect to oxygen, since C, which is another element particularly deteriorating the magnetic properties, is decarburized as gaseous CO by vacuum treatment of molten steel, it is unavoidable to remain to some extent. In order to obtain a sound ingot, this oxygen is stabilized by adding a deoxidizing agent such as sol.Al or Si, that is, deoxidized, and becomes an oxide inclusion. Although the form of O remaining in the steel varies depending on the type of deoxidizer, the timing of addition, the treatment method, etc., the total amount of oxygen in the steel does not change significantly after vacuum treatment. Further, oxide inclusions such as SiO ₂ , MnO and A
Even if the composition ratio of l ₂ O ₃ has a great influence on the growth of crystal grains, if the steel composition such as the content of Al or Si is limited,
It may be difficult to make the composition of these inclusions into a preferable state.

[0010]

SUMMARY OF THE INVENTION The present invention focuses on the fact that the morphology of oxide inclusions in steel influences the improvement of magnetic properties, and the magnetic properties are improved by changing the morphology. An object of the present invention is to provide a non-oriented electrical steel sheet having a low content and a method for producing the same.

[0011]

[Means for Solving the Problems] The inventors of the present invention decarburized steel in the steelmaking stage to make the C content 0.01% or less, Si 1.0% or less, S 0.005% or less, and sol.Al 0.002% or less. It was discovered that the pure iron-based non-oriented electrical steel sheet often had inferior magnetic properties. It is considered that the sol.Al content was suppressed to a low level to suppress the fine precipitation of AlN, and the influence of the sulfide-based precipitates was reduced, so that the inhibition of crystal grain growth could be reduced. Nevertheless, it was presumed that the poor magnetic properties and poor crystal grain growth were due to the morphology of the oxide inclusions.

However, when the Si content is lowered, sol.A
It is not easy to stably control the morphology of oxide-based inclusions in steel containing a small amount of Mn and containing a relatively large amount of Mn. Under such restrictions on the chemical composition of steel, it was found that the addition of Ca is effective as a result of various studies on the effect of the additive elements and the heat treatment including the steelmaking conditions.

In order to clarify the effect of adding Ca and its limit, C: 0.002 to 0.005%, Si: 0.2 to 0.3%,
Mn: 0.2-0.3%, P: 0.07-0.08%, S: 0.003%
Below, based on the content of Al: 0.002% or less, oxygen is produced in the laboratory by laboratory melting of steel with varying Ca content aiming at three levels of high, medium, and low contents. A 0.5 mm thick electrical steel sheet was prototyped under the manufacturing process and conditions simulating the above. These steel plates were used to cut out the prescribed test pieces from the steel plates and then subjected to strain relief annealing at 700 ° C for 2 hours, and JIS-
Magnetic properties were measured by a test method using an Epstein frame according to C-2550.

FIG. 1 shows the test results plotting the relationship between the Ca content and the iron loss of magnetic properties. As is clear from this, when the oxygen content is too high or too low, there is little or no effect of improving the magnetic properties, but when the oxygen content is within a specific range, Ca 0.
It can be seen that the iron loss is remarkably reduced when the content is around 01%.

The addition of Ca to steel is usually done by adding MnS in the steel.
It is carried out for the purpose of controlling the existence form of sulfide-based inclusions. Also in electromagnetic steel sheets, Japanese Patent Publication No. 58-17249 and
JP-B-63-103023 or JP-A-3-126845
Although the invention of adding Ca is disclosed in Japanese Patent Laid-Open Publication No. 2005-242242, both of them regulate the range of Ca / S and aim at controlling the morphology of sulfides. On the other hand, as a result of adding it for the purpose of changing the form of an oxide, not a sulfide, it was found that the magnetic properties of a low Si non-oriented electrical steel sheet can be stably improved. In these steel sheets in which oxygen and Ca were present in appropriate amounts, the crystal grains after annealing were sufficiently grown, and it was clear that the improvement in magnetic properties was due to the improvement in crystal grain growth.

When a magnetic steel sheet is produced from a steel having such a composition, a final product having good magnetic properties can be obtained even if the conventional conditions such as hot rolling, cold rolling and annealing are adopted. By setting the coiling temperature at the time of hot rolling to be higher, the magnetic characteristics can be further improved. Also,
It was also confirmed that the magnetic properties of the final product can be further improved by suppressing the coiling temperature of hot rolling to a low value and then annealing the hot rolled sheet before cold rolling.

The present invention has been completed based on the above findings, and its gist is as follows.

(1) C: 0.01% or less, Si:
0.05 to 1.0%, Mn: 0.05 to 1.0%, P: 0.15% or less,
S: 0.005% or less, O (oxygen): 0.008 to 0.02%, sol.
Al: less than 0.002%, and Ca: 0.003 to 0.018%
And the balance is Fe and inevitable impurities, which is a non-oriented electrical steel sheet with excellent magnetic properties.

(2) In the manufacturing process in which a steel slab is hot-rolled, cold-rolled, and annealed to obtain a final product, the coiling temperature for hot-rolling is 650 ° C. or higher. )
Manufacturing method of non-oriented electrical steel sheet.

(3) In a manufacturing process in which a steel slab is hot-rolled, hot-rolled sheet annealed, cold-rolled, and annealed to obtain a final product, the rolling temperature of the hot-rolling is set to less than 650 ° C, and the cold-rolling is performed. The method for producing a non-oriented electrical steel sheet according to the above (1), characterized in that the preceding hot-rolled sheet annealing is performed at 650 to 1000 ° C.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting each factor and condition in implementing the present invention will be described below.

(1) C C is an element that greatly deteriorates the magnetic properties, so the less it is, the better it is in the steel sheet of the product, and it is limited to 0.010% or less as the limit at which no significant adverse effect appears. At the stage of decarburization or deoxidation of molten steel by vacuum treatment, if the C in the molten steel is too low, depending on the ultimate vacuum degree, the amount of oxygen cannot be reduced to 0.02% or less, so some residual amount is desirable. However, in the process of manufacturing the slab into the final electrical steel sheet, decarburization due to the atmosphere may occur in the annealing step, for example, and therefore it may be reduced. Therefore, the lower limit of the C content as a chemical composition of the electrical steel sheet is particularly regulated. do not do.

(2) Si As the content of Si increases, the electrical resistance of steel increases and it is effective in reducing iron loss. However, on the other hand, as the content increases, the magnetic flux density decreases, so in order to secure a sufficient magnetic flux density, the upper limit of the content is 1.0%. Also, sol.Al
Of less than 0.002% does not increase the amount of MnO, the deoxidizing effect of Si is important, and at least 0.05% or more is required for this purpose. Therefore, Si
Content range of 0.05 to 1.0%.

(3) Mn In the present invention, the content of Mn is adjusted mainly for the purpose of suppressing cracking during hot rolling due to the presence of S, that is, hot embrittlement, and reducing grain growth inhibition. In order to obtain this effect, it is necessary to contain at least 0.05% Mn. Since Mn content increases electric resistance, it is also significant in reducing iron loss, but its effect is smaller than that of Si,
Even if the content of S is increased, the effect of suppressing the harmful effects of S is saturated, and increasing the content of S causes an increase in cost.
0.75%

(4) P P is one of the impurities that are inevitably mixed in the steel, but in the case of a low Si non-oriented electrical steel sheet, the electrical resistance is increased, the hardness is increased, and the punchability is increased. Since it has the effect of improving However, since it tends to embrittle steel, its content should be at most 0.15%. The lower limit is not particularly limited, but the desirable content is 0.02% or more for the purpose of improving hardness.

(5) Since S S deteriorates the magnetic properties due to the inhibition of crystal grain growth due to the formation of fine sulfide-based precipitates and the formation of inclusions, the smaller the content, the better. The maximum limit is 0.005%, which does not significantly affect the magnetic properties.

(6) sol.Al (acid-soluble Al) Al is added to molten steel as a deoxidizing agent for obtaining sound cast pieces. Although a part of the deoxidized product floats by the addition, the balance forms oxide inclusions, and the excess Al is sol.A.
It remains in the steel as l. Since sol.Al easily forms fine precipitates of AlN, and if the amount increases, it hinders crystal grain growth and domain wall movement, so it should be made as small as possible, and its upper limit is made less than 0.0020%.

By limiting the amount of sol.Al to a low level, the formation of AlN can be suppressed even if a large amount of N is contained, but the presence of Si and Mn may cause harmful Si--Mn--N-based fine precipitates. Will occur. Therefore, the amount of N mixed as impurities should be reduced as much as possible, and 0.005%
It is desirable to do the following.

(7) Oxygen The amount of oxygen in the steel is set to 0.008 to 0.02%. If it exceeds 0.02%, the amount of oxide inclusions becomes too large, and no matter how the form is changed, the adverse effect on the magnetic properties cannot be suppressed. In addition, manufacturing problems such as melting damage of refractories and nozzles often occur, so the content is limited to 0.02% or less.
On the other hand, if it becomes too low, the improvement effect by the addition of Ca becomes small as shown in FIG. The reason for this is not clear, but since the crystal grain size does not increase, it is presumed that the coarsening or detoxification of the oxide due to the addition of Ca was insufficient. Therefore, the lower limit of oxygen content should be
It is 0.008%.

In order to adjust the oxygen content to 0.008 to 0.02%, deoxidation by CO generation under reduced pressure during molten steel vacuum treatment is utilized,
The ultimate vacuum and the processing time are controlled so that the amount of C in the molten steel is desirably 0.002 to 0.005%. The ultimate vacuum is preferably about 0.01 atm, but even at about 0.05 atm, it can be reduced to the required oxygen amount range by lengthening the treatment time. After that, Al is preferably added, and then Si and Mn are added to adjust the steel composition. Before vacuum treatment of molten steel,
Or, the addition of Al for the purpose of heating deoxidation during vacuum treatment is avoided as much as possible. This is because if Al is added before the completion of deoxidation by vacuum treatment, the amount of oxygen will not fall within the target range, and the improvement effect due to the addition of Ca will not be obtained.

(8) Ca Addition in the presence of an appropriate amount of oxygen improves the magnetic characteristics. Its optimum content range is as shown in FIG.
It is 0.003 to 0.018%. When it exceeds 0.018%, the effect disappears because Ca hardly dissolves in Fe.
It is considered that when it is present in excess, it is present in the form of inclusions, which hinders the growth of crystal grains and adversely affects the magnetic properties. Further, it is considered that the reason why the ratio is less than 0.003 is not good because the effect of controlling the morphology of oxide inclusions is reduced.
As can be seen from FIG. 1, a more desirable range is 0.006 to 0.017% from the effect of improving iron loss.

(9) Winding temperature of hot rolling Generally, in the manufacturing process of a normal non-oriented electrical steel sheet which is hot rolled, cold rolled, and annealed to obtain a final product, the winding temperature of hot rolling is used. When the temperature is raised, the effect of improving the magnetic characteristics can be obtained. Low Si content reduces sol.Al,
In the steel of the present invention in which Ca is added to improve the crystal grain growth property, increasing the coiling temperature is particularly effective. Therefore, as a method for further improving the magnetic properties of the steel of the present invention, the coiling temperature is set to 650 ° C or higher.

The higher the winding temperature, the better the magnetic properties, so the upper limit is not specified, but there is a natural limit due to the finishing temperature, coil deformation, and frequent scale generation due to oxidation. The magnetic properties are improved by increasing the coiling temperature because the precipitation of sulfides and nitrides is promoted by the oxide inclusions changed by the addition of Ca as the nuclei, and their detoxification proceeds further. It is thought to be because of this. 650
If the temperature is lower than 0 ° C, the improvement effect is small because the detoxification is insufficient.

(10) Annealing of hot-rolled sheet Annealing after hot rolling and before cold rolling further improves the magnetic properties of the final product. In that case, the coiling temperature for hot rolling shall be less than 650 ° C and the annealing temperature shall be 650-1000 ° C. The reason why the coiling temperature is lower than 650 ° C is that the effect of annealing becomes more remarkable. This seems to be because the dispersed state of precipitates and the like during low-temperature winding accelerated the change during annealing. The reason why the annealing temperature is limited is that the effect is insufficient at less than 650 ° C, and the crystal grains become coarser at more than 1000 ° C and cracks may occur during cold rolling. It should be noted that, as long as the material temperature reaches the above range for annealing, the annealing method and heating time are not specified, but it is desirable to use the box annealing method at 650 to 800 ° C for about 30 min to 10 h for continuous heating. In the annealing method, it is 10s to 5 at 750 to 1000 ℃.
The heating is about min. As described above, the annealing before cold rolling is particularly effective for improving the magnetic properties in the steel of the present invention, as described above, because harmful nitrides and sulfides are precipitated due to oxides whose shape is changed by the addition of Ca. It is thought that this is due to the promotion of.

[0035]

【Example】

[Example 1] Using steels having the chemical compositions shown in Table 1, in each case, heating to 1200 ° C and hot rolling to finish to a thickness of 1.8 mm,
It was wound at about 670 ° C. After descaling, it was cold-rolled to a thickness of 0.5 mm and annealed at 850 ° C for 1 min to obtain a magnetic steel sheet. Based on the method described in JIS-C-2550, a test piece having a width of 30 mm and a length of 280 mm was punched out and the magnetic properties were investigated using an Epstein frame. Table 1 shows the measurement results of the iron loss W _15/50 (W / kg) at a frequency of 50 Hz and a maximum magnetic flux density of 1.5 T, and the magnetic flux density B ₅₀ (T) at a magnetizing force of 5000 A / m. Show.

[0036]

[Table 1]

In Test No. 6, since the Si content is high, the iron loss is low,
The magnetic flux density does not increase. In Test Nos. 7, No. 8, No. 9 and No. 10, Mn, Ca, Al and oxygen exceeded the ranges defined by the present invention, respectively, and all the crystal grain growth after annealing was not good. This is the reason why the iron loss is large and the magnetic flux density is low. In the test No. 10 using steel with high oxygen content, the nozzle was clogged, the surface defects of the product increased, and a product that could be shipped could not be obtained. In Test Nos. 11 and 12, the oxygen or Ca content was lower than the range defined by the present invention, and the oxide inclusions inhibited the grain growth. Test No. 13, which had an excessively high P content, cracked during cold rolling and was discontinued from commercialization. In Test No. 14, it is considered that S was too high and the magnetic properties were not improved. Compared to these,
Test No. 1 to which each chemical composition satisfies the range defined in the present invention
It can be seen that the No. 5 steel plate exhibits excellent magnetic properties.

Example 2 Using the slabs of steel C, steel K and steel L whose chemical compositions are shown in Table 1, the winding temperature at the time of hot rolling was changed and the obtained hot rolled steel sheet was descaled. It was post-cold rolled to a thickness of 0.5 mm and annealed at 700 ° C for 30 s to obtain a magnetic steel sheet. A test piece with a width of 30 mm and a length of 280 mm was cut out from these steel sheets, subjected to strain relief annealing at 750 ° C. for 2 hours, and then the magnetic properties were investigated by an Epstein test based on JIS-C-2550. Table 2 shows the results of the winding temperature and magnetic properties of each test piece during hot rolling.

[0039]

[Table 2]

Steel C of the invention has a coiling temperature of 650 during hot rolling.
It can be seen that iron loss is further improved by making the temperature higher than ° C. However, in the case of steel K or steel L having a chemical composition outside the range defined by the present invention, some improvement effect can be recognized by increasing the coiling temperature, but the obtained characteristics are far inferior to those of steel C. It is a thing.

Example 3 Steel C whose chemical composition is shown in Table 1
And the slab of steel K, the winding temperature during hot rolling
After descaling the obtained hot-rolled steel sheet at 550 to 560 ℃, annealed at various temperatures, cold rolled to 0.5 mm thickness, and annealed at 850 ℃ for 1 min to obtain a magnetic steel sheet. . The magnetic properties of the obtained steel sheet were measured in the same manner as in Example 1. The results are shown together in Table 3.

[0042]

[Table 3]

In the steel having the chemical composition defined in the present invention, the magnetic properties of the obtained electromagnetic steel sheet are greatly improved by the low coiling temperature and the hot rolled sheet annealing at 650 ° C. or higher. However 1000
Even if it is annealed at a temperature higher than ℃, the effect is saturated, and it only increases meaningless loss such as an increase in energy cost and frequent occurrence of surface defects.

[0044]

INDUSTRIAL APPLICABILITY According to the present invention, by controlling the amount of oxygen and changing the form of oxide inclusions in steel by adding Ca, it is possible to reduce iron loss without using expensive alloying elements or special manufacturing processes. The present invention provides a low Si non-oriented electrical steel sheet and a method for producing the same, in which magnetic characteristics of high magnetic flux density are stably obtained.
It is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between Ca content and total oxygen content in a low Si electromagnetic steel sheet and iron loss of magnetic characteristics.

Claims (3)

[Claims] 1. In weight%, C: 0.01% or less, Si: 0.05
~ 1.0%, Mn: 0.05 ~ 1.0%, P: 0.15% or less, S:
0.005% or less, O (oxygen): 0.008 to 0.02%, sol.A
l: less than 0.002% and Ca: 0.003 to 0.018%,
The balance is Fe and inevitable impurities, which is a non-oriented electrical steel sheet with excellent magnetic properties. 2. A coiling temperature of hot rolling is set to 650 ° C. or higher in a manufacturing process of hot rolling, cold rolling, and annealing a steel slab to obtain a final product. Manufacturing method of non-oriented electrical steel sheet. 3. In a manufacturing process in which a steel slab is hot-rolled, hot-rolled sheet annealed, cold-rolled, and annealed to obtain a final product, the coiling temperature of the hot-rolling is set to less than 650 ° C. before cold-rolling. The method for producing a non-oriented electrical steel sheet according to claim 1, wherein the hot rolled sheet annealing is performed at 650 to 1000 ° C.