JPH0888114A - Manufacture of nonoriented flat rolled magnetic steel sheet - Google Patents

Abstract

PURPOSE: To provide a method of manufacturing a nonoriented flat rolled magnetic steel sheet whose iron loss is low especially in a high-frequency use and whose workability is good. CONSTITUTION: A slab as steel in which C in 0.010% or lower, Si in 2.0 to 3.25%, Mn in 0.1 to 2.5%, P in 0.02% or lower, N in 0.006% or lower, Al in 1.5 to 2.5% and B in 0 to 0.0050% are contained, in which Si (in %)+Al(in %)>=4.5 and Si (in %)+0.5A (in %)<4.0 are satisfied and whose remaining part is composed of Fe and of unavoidable impurities is hot-rolled. After that, in the method of manufacturing a nonoriented flat rolled magnetic steel sheet, a hot-rolled plate is annealed, a cold-rolling operation at a rolling rate of 40 to 80%, an intermediate annealing operation at 650 to 1000 deg.C and a cold-rolling operation at a rolling rate of 40 to 80% are performed, and, after that, a finish annealing operation is performed so as to lower an iron loss. Without using a special production installation, it is possible to manufacture the nonoriented flat rolled magnetic steel sheet whose cold workability and stamping workability are excellent and whose iron loss in a high-frequency region is low.

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 a low iron loss, which is widely used as an iron core for electric equipment, and is particularly suitable for an iron core for electric equipment used under high frequency conditions. The present invention relates to a method for manufacturing a non-oriented electrical steel sheet.

[0002]

2. Description of the Related Art As an environment surrounding electrical equipment, it has been long since the demand for efficient, compact and lightweight equipment, and more efficient inverter control has begun to spread. By increasing the frequency, the efficiency is improved and the size can be reduced.
Among electric devices currently used at commercial frequencies, it is expected that the number of applications of high frequencies will increase in the future.

Therefore, electrical equipment with low energy loss under high frequency conditions is required, and electromagnetic steel sheets used for the iron core are also required to have low iron loss in the high frequency range.

Iron loss of electromagnetic steel sheets increases as the frequency increases. This is because the iron loss is composed of the sum of the hysteresis loss and the eddy current loss, and both increase depending on the applied frequency. In particular, since the eddy current loss increases in proportion to the square of the frequency, most of the iron loss in the high frequency region is the eddy current loss. That is, suppressing eddy current loss leads to suppressing high frequency iron loss.

Conventionally, as a method for reducing this eddy current loss, the electrical resistance of the steel sheet has been increased and the thickness of the steel sheet has been reduced. Addition of Si for the purpose of increasing electric resistance is more effective than any other element, but if Si is added in an amount of 4% or more, not only becomes hard but also becomes extremely brittle. Therefore, the cold rolling method of the steel sheet in the usual industrial process is apt to cause cracks, and in addition, it becomes more difficult to manufacture if the thin sheet thickness is required.

It has been known for a long time that when Si is added to steel in an amount of about 6.5%, the magnetostriction becomes almost zero, the magnetic permeability exhibits a maximum, and the hysteresis loss is remarkably reduced. In addition, a large amount of Si is added. Since it is added, the electrical resistance increases,
In the Fe-Si system, the material has the best magnetic characteristics. Although a molten metal ultra-quenching method and a siliconizing method have been developed as a method for manufacturing such a high Si content steel sheet, special manufacturing equipment is required.

A method for producing such a high Si steel sheet having poor workability by rolling is disclosed in Japanese Patent Application Laid-Open No. 62-103321, in which a crystal is formed by applying high pressure in the low temperature range of hot rolling. We are trying to reduce the grain size and suppress cracking during cold rolling. However, in order to exhibit good magnetic properties in the product steel sheet, it must be annealed sufficiently to increase the crystal grain,
If this happens, it becomes an extremely brittle product that is difficult to process, and if this is to be processed, special tools and equipment are required.

In order to increase the electric resistance, a method of adding a large amount of Al, which has almost the same effect as adding Si, can be considered.
In the grain-oriented electrical steel sheet, the addition of Al to the electrical steel sheet has a metal structure (110 <001> texture) in which each crystal grain is preferentially oriented in the 110 <001> orientation. It has been studied for a long time because it is easy to obtain <001> texture. 100 <001> A steel sheet with an increased texture improves the magnetic properties in the plane direction of the sheet, and is not biased in a specific direction, so it is said to be ideal for non-oriented electrical steel sheets used for motors, etc. However, in reality, it has not been put to practical use because of the balance between the manufacturing cost and the improvement in characteristics.

In addition to adding Si, increase the electric resistance,
Fine AlN that obstructs the movement of the domain wall and deteriorates the magnetization characteristics
In order to prevent the precipitation of Al, 1% or less of Al is often added to non-oriented electrical steel sheets. Japanese Patent Application Laid-Open No. 3-24251 proposes that Al is more positively added to this Si-added steel. Si for this
A non-oriented electrical steel sheet with an Al content of 1.5% to 8% at 3.3% or less is proposed. If the Si content is lowered and the Al content is increased, the workability is improved and the magnetic properties are improved.
00 <001> The organization is said to be easy to develop. This publication introduces, as a precedent reference, the case where Al: 0.3-1.5% is added to Si: 2.5-3.5% of French patent application No. 2,316,338. With this Si content, when Al exceeds 1.5%, the alloy becomes extremely extreme. It points out that it becomes brittle.

Although it is known that an increase in the amount of Si added increases the electrical resistance and obtains the performance particularly suitable for use in the high frequency region, the workability of the material is significantly deteriorated. As a countermeasure, it is possible to add Al without increasing the amount of Si. However, there is a limit to ensuring workability while sufficiently increasing the electric resistance.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is possible to manufacture steel sheets under the conditions that can be realized with the current equipment, and to punch product steel sheets. It is intended to provide a method for manufacturing a non-oriented electrical steel sheet which is easy to process and has excellent magnetic properties, and particularly has a low iron loss in a high frequency range.

[0012]

DISCLOSURE OF THE INVENTION The inventors of the present invention have found that non-directional electromagnetic waves having excellent magnetic properties, particularly in the high frequency range, and having good cold rollability during manufacturing and punching properties of steel sheet products. As a result of extensively studying a number of experiments on the method for manufacturing a steel sheet, the following new findings were obtained.

(A) In order to suppress eddy current loss to reduce high-frequency iron loss, as a result of studying addition of Si, which has an effect of increasing electric resistance equivalent to that of Si, in addition to Si, an appropriate amount was found. It was found that by adding Al in combination, good magnetic characteristics can be obtained in the high frequency range.

(B) In order to obtain equivalent magnetic properties, the workability was better when Al was added in combination rather than when Si was added alone. However, if the addition amount of Al also increases, the workability deteriorates and the improvement effect is limited. As a result of various investigations on the effect of the composite addition on the workability and magnetic properties, it has been revealed that there is a range of the composite addition having improved magnetic properties and good workability.

(C) If Mn is added in addition to the composite addition of Si and Al, the crack resistance during cold rolling and punching is improved, and if the addition amount is increased, the workability is impaired. It was found that the magnetic characteristics at high frequencies were improved.

(D) As a method of manufacturing a steel sheet using a material to which Si, Al and Mn are added in combination, the steps of hot rolling, cold rolling → intermediate annealing → cold rolling → final annealing may be performed. It was optimal for obtaining a favorable texture.

(E) Further, in addition to the above (d), the magnetic property is further improved by a process in which hot-rolled sheet annealing is performed before cold rolling after hot rolling. It was found that it is also effective in suppressing ridging when it becomes a problem.

Based on these findings, (1)% by weight
C: 0.010% or less, Si: 2.0 to 3.25%, Mn:
0.1 to 2.5%, P: 0.02% or less, S: 0.006% or less,
N: 0.006% or less, Al: 1.5 to 2.5% and B: 0 to
Contains 0.0050% and Si (%) + Al (%) ≧
A steel slab satisfying 4.5 and Si (%) + 0.5 Al (%) <4.0 with the balance being Fe and inevitable impurities is hot-rolled and then cold-rolled at a rolling rate of 40 to 80%, Then, an intermediate annealing is performed at 650 to 1000 ° C., and after cold rolling with a rolling rate of 40 to 80%, finish annealing is performed, and a method for producing a non-oriented electrical steel sheet with low iron loss, and (2) above (1) After hot rolling a steel slab having the composition described in 1.
Annealing is performed at 650 to 1000 ° C, cold rolling is performed at a rolling rate of 40 to 80%, then intermediate annealing is performed at 650 to 1000 ° C, and further finish annealing is performed after cold rolling at a rolling rate of 40 to 80%. The invention of a method for producing a non-oriented electrical steel sheet having a low iron loss is completed.

[0019]

The operation and effect and the reason for limitation will be described below for each constituent element of the method of the present invention.

(1) Chemical composition of raw material slab or product steel sheet (1) C content The presence of C significantly deteriorates the magnetic properties, and the allowable range is 0.010% or less, but if it can be further reduced, the magnetic properties will improve. Therefore, it is preferably 0.005% or less.

(2) Si content Si is an element that greatly affects the magnetic properties, and the iron loss of the steel sheet decreases as the content increases. This is mainly because the electrical resistance increases and the eddy current loss decreases. However, if the Si content exceeds 3.25%, cold rolling becomes difficult and the punchability also deteriorates. on the other hand,
If the content is less than 2.0%, the reduction of iron loss is insufficient. Therefore, the Si content range is 2.0 to 3.25%.

(3) Mn content In order to reduce the influence of S, which is one of the unavoidable impurity elements, it is necessary to add at least 0.1%. The addition of Mn to some extent is effective in reducing cracks in the coil edge portion during cold rolling. This is considered to be because the solid solution of Mn suppressed coarsening of the crystal grain size during hot rolling, and improved the ductility during cold rolling. Further, if the addition amount is increased, the magnetic properties are improved without impairing the cold workability. However, excessive addition makes the material too hard, so it is not preferable to exceed 2.5%.

For this reason, the addition range of Mn should be 0.2
Although it is set to ~ 2.5%, it is preferable to set it to 0.6 to 2.5% especially when the magnetic characteristics at high frequencies are taken into consideration.

(4) S content S is preferable because it is combined with Mn in steel to form MnS precipitates and deteriorates magnetic properties and ductility. The limit for exerting the effect of the present invention is 0.006% or less, preferably 0.003% or less.

(5) Amount of Al Al has an effect of increasing electric resistance which is almost equal to that of Si. Therefore, as a result of investigating the improvement of the magnetic characteristics and the deterioration of the workability by adding Al to the place where the Si content is contained up to the upper limit which does not impair the workability, the effect of improving the high frequency magnetic characteristics is more than the increase in the electric resistance. It was found that the workability was better than that in the case where the electrical resistance was increased to the same extent only by the amount of Si. The optimum amount of Al added depends on the amount of Si, and if it is 1.5% or less, sufficient magnetic properties cannot be obtained. On the other hand, addition of a large amount of Al tends to increase the magnetostriction, and in particular, when it exceeds 2.5%, it remarkably increases. Magnetostriction is said to be a cause of noise, and moreover, an increase in magnetostriction also causes an increase in hysteresis loss. For this reason, the range of addition of Al is 1.5 to 2.5%.

(6) N content N combines with Al to form fine AlN precipitates, which impairs magnetic properties. Therefore, the lower the better.
0.006% is the upper limit of tolerance.

(7) Amount of B It is not necessary to add B, but if it is added, cracks during processing,
In particular, it is effective in preventing cracks during processing where stress is rapidly applied. When added: 0.0003% or more is preferable, 0.0020%
If the content is above, the effect is saturated, and if it is more than 0.0050%, it becomes brittle.

(8) Combined effect of Si and Al As described above, by adding Mn to the combined addition of Si and Al, the magnetic characteristics and workability are improved, and more sufficient magnetic characteristics are obtained within the range of the addition amount. To secure the
The amount and the amount of Al must be Si (%) + Al (%) ≧ 4.5. However, from the viewpoint of deterioration of cold workability such as cracks during cold rolling or cracks during punching of product steel sheet, there is a limit to the increase in Si and Al contents, and it is necessary to maintain sufficient workability. , Si (%) + 0.5Al (%) <4.0.

(9) Inevitable Impurity Elements Any unavoidable impurity elements other than the above-mentioned elements deteriorate the magnetic characteristics, so the smaller the amount, the more preferable. However, the elements that have a great influence particularly on the magnetic characteristics and workability, For example, O, Ti, Nb, V, etc. require careful attention.

(2) Manufacturing conditions (a) Hot rolling The slab used for hot rolling may be either a continuously cast slab or a slab of slabs, and the slab obtained by continuous casting may be directly rolled. Then, the slab once cooled may be reheated. Although the hot rolling conditions are not particularly limited, it is desirable that the slab heating temperature is 1200 ° C or lower and the finishing temperature is 750 to 850 ° C in view of magnetic characteristics.

Although the winding temperature is not particularly limited, the magnetic characteristics tend to improve as the temperature increases. However, when the winding temperature is increased, the oxide layer on the surface increases and it becomes difficult to remove it. However, in the method of annealing a hot rolled sheet according to claim 2, it should be wound at a low temperature, preferably 6
It shall be below 00 ℃.

(B) Cold Rolling In order to obtain excellent magnetic properties, the hot rolled steel sheet is cold rolled, then annealed to be sufficiently recrystallized, and further cold rolled to finish the thickness of the final product. The first cold rolling is called primary cold rolling, and the cold rolling after the intermediate annealing is called secondary cold rolling. By cold rolling twice with an intermediate anneal, the magnetic properties of the final product are improved, but this is 110% less than the plate thickness of the final product by one cold pressing at high pressure. 001> bearing and 1
This is because a texture that is favorable for magnetic properties such as the <001> orientation easily develops.

The reduction ratio of cold rolling is set to 40 to 80% for both the primary cold pressure and the secondary cold pressure. However, if the reduction ratio is out of this range, sufficient magnetic properties cannot be obtained.

The cold rolling may be carried out at room temperature, but may be carried out by heating the steel sheet to 350 ° C. or lower from the viewpoint of preventing cracking. 3
If the temperature exceeds 50 ° C, it becomes difficult to control the shape of the steel sheet during rolling, and it is necessary to use rolling oil with special properties.

(C) Intermediate Annealing By intermediate annealing, the material is recrystallized and softened,
Cold rolling cracks can be prevented in the secondary cold rolling, and a magnetically favorable texture can be developed.
The method of annealing may be either box annealing or continuous annealing, and there is no particular limitation on the soaking time as long as the temperature is reached.

When the annealing temperature is lower than 650 ° C., recrystallization does not proceed sufficiently and the effect of annealing cannot be obtained. On the other hand, if the annealing temperature exceeds 1000 ° C., the crystal grains become too coarse and cracks are likely to occur during cold rolling. Therefore, the intermediate annealing temperature was set to 650 to 1000 ° C. 650 to 900 for box annealing
In the case of continuous annealing, 750 to 1000 ° C is desirable.

(D) Finish annealing After finishing to a predetermined plate thickness by secondary cold pressure, finish annealing is performed to obtain a magnetic steel sheet as a product. The conditions are not particularly limited as long as the recrystallization is sufficiently performed and the crystal grains are appropriately grown, but the annealing temperature is preferably 700 ° C to
It is 1250 ° C.

If necessary, a thin film may be applied and baked on the surface for the purpose of insulation, rust prevention, or improvement of punching workability.

(E) Annealing of Hot-rolled Sheet In the above-mentioned manufacturing process, if the hot-rolled sheet is annealed before the cold rolling after the hot rolling, the magnetic characteristics can be further improved. It is considered that this is because a magnetically favorable texture easily develops. Further, by performing the hot-rolled sheet annealing, it is possible to reduce ridging, which is an uneven defect generated on the surface. Ridging lowers the space factor of the laminated core of the final product and deteriorates its magnetic properties, and is not preferable in terms of appearance as a steel sheet product.

The hot-rolled sheet annealing temperature for obtaining such effects is 650 ° C. to 1000 ° C., and the holding time is not particularly limited as long as the material reaches this temperature. If the annealing temperature is less than 650 ° C, recrystallization is insufficient and the magnetic properties are not improved, and if it exceeds 1000 ° C, the crystal grains become too coarse and the mechanical properties deteriorate, which is effective in suppressing cracking and ridging. Disappear. In order to fully exhibit these effects, 700 to 900 ° C is desirable.

[0041]

【Example】

[Example 1] Sample steels having the compositions shown in Table 1 were melted in a high frequency heating vacuum melting furnace, and the steel pieces were heated to 1150 ° C and then hot rolled at a finishing temperature of 800 ° C to obtain a thickness of 2.3 mm. The hot-rolled sheet of was produced. This is the primary cold rolling and 0.80 at a reduction rate of 65%.
After rolling to a thickness of mm, intermediate annealing was performed by box annealing at 750 ° C for 1 hour or more, and secondary cold rolling with a reduction rate of 56% was performed to a thickness of 0.35 mm. The test piece in which cracking occurred in cold rolling was hot-rolled at 300 ° C to a predetermined plate thickness.

The rolled steel sheet was annealed at 1000 ° C. for 1 minute, and then punched at room temperature to make the rolling direction and the direction perpendicular to the rolling longitudinal direction, width 30 mm, length 280.
An Epstein magnetic property measurement test piece of mm was prepared. As for the test piece in which cracking occurred during punching, a test piece was prepared by electrical discharge machining.

Using these test pieces, after performing stress relief annealing at 800 ° C. for 2 hours, magnetic properties were measured. In general, non-oriented electrical steel sheets are measured for iron loss at a commercial frequency of 50 to 60 hertz, but in order to know the performance at high frequencies, iron loss at 400 hertz was measured. The results of these series of tests are also shown in Table 1. As for the magnetic characteristics, the lower the iron loss and the higher the magnetic flux density is, the better the iron loss is W10 / 400.
(Iron loss when magnetized to 1.0 Tesla (T) at a frequency of 400 Hz) is 16.0 or less, and magnetic flux density B8 (magnetic flux density when magnetized in a magnetic field of 800 A / m) is 1.40 or more.

Steel type A satisfying all the conditions defined in the present invention
In addition to exhibiting good magnetic properties, Nos. To E had good workability without cracking during cold rolling or punching at room temperature.

For steel types K to N, Si (%) + Al (%) is
The value was below 4.5, and the magnetic properties of the steel sheets produced from them had large iron loss and the required performance was not obtained.

Further, Si (%) + 0.5Al (%) is 4.0
Steel sheets manufactured from steel types F to J and P exceeding 5% have low iron loss and good magnetic properties, but cracks occur in cold rolling, and fine cracks occur from the edge portion during punching. did.

Steel types O and P having an amount higher than that specified in the present invention have large magnetostriction and are not practical.

As described above, the steel types A to E are extremely excellent materials in terms of characteristics, manufacturing and workability.

[0049]

[Table 1]

[Example 2] In order to know the influence of the amount of Mn, as shown in Table 2, steels C and D used in Example 1 were made to have the same amounts of Si and Al, but different amounts of Mn. C1
.About.C3 and D1 to D4 were melted in a high frequency heating vacuum melting furnace, a test piece having a plate thickness of 0.35 mm was prepared under the same process and conditions as in Example 1, and magnetic properties were investigated by the same method. The results of these tests are shown in Table 2.

Iron loss decreases as the amount of Mn increases,
If too much, it becomes hard and it becomes difficult to carry out cold rolling reduction. Steel types C3 and D4 in which the amount of Mn exceeds the range of the present invention are
The thickness could not be reduced by the primary and secondary cold rolling at room temperature.

[0052]

[Table 2]

[Example 3] Using the steel types C and C1 used in Examples 1 and 2, a hot rolled sheet having a plate thickness of 2.3 mm was finished in the same manner as in Example 1, and then shown in Table 3. like,
Primary cold rolling, intermediate annealing and secondary cold rolling,
Finished to a 0.35 mm thick steel plate. Both the primary and secondary cold rolling were performed at room temperature, and the intermediate annealing was performed at 850 ° C for 1 hour. After the secondary cold rolling, test pieces were prepared in the same manner as in Example 1 and magnetic measurements were performed.

In the primary or secondary cold rolling, the steel sheets manufactured with the rolling reduction outside the range of the present invention have target magnetic properties (iron loss W15 / 400 ≦ 16.0 and magnetic flux density B).
8 ≧ 1.40) was not reached. Further, under the condition 7 in which it was attempted to finish the target plate thickness by one cold rolling without intermediate annealing, cracking occurred during cold rolling.

[0055]

[Table 3]

Example 4 Using the steel types C and C1 used in Examples 1 and 2, a hot rolled sheet having a plate thickness of 2.3 mm was finished in the same manner as in Example 1, and then primary cold rolling was performed. The reduction rate of 65% was changed to 65%, the temperature of intermediate annealing was changed, and
Secondary cold rolling with a reduction rate of 56% was performed to finish to mm.
The intermediate annealing was a continuous annealing for 1 minute soaking. When the intermediate annealing temperature was as high as 1030 ℃, cracking occurred in the secondary cold rolling.
This was probably because the annealing temperature was too high and the crystal grains became coarse and brittle. After the secondary cold rolling, soaking was performed for 1 minute at 1000 ° C., and the magnetic characteristics were investigated in the same manner as in Example 1.

The results are summarized in Table 4. When the temperature of the intermediate annealing was too low, sufficient magnetic properties could not be obtained.

[0058]

[Table 4]

[Embodiment 5] Using the steel types C and C1 used in Embodiments 1 and 2, a hot-rolled sheet having a thickness of 2.3 mm was finished in the same manner as in Embodiment 1, and then shown in Table 5. Annealing of the hot rolled sheet was carried out under the conditions. Then, after undergoing primary cold rolling, intermediate annealing, and secondary cold rolling in the same steps and conditions as in Example 1, 10
Annealing was performed at 00 ° C. for 1 minute to prepare a test piece, and the magnetic field measurement and the space factor test specified in JIS C2550 were performed.

Condition 11 shown in Table 5 is an example of the present invention in which hot-rolled sheet annealing is not performed, and is shown as a comparison. In condition 12, the hot-rolled sheet annealing temperature is used, but the effect is not exhibited because the temperature is insufficient. These two conditions do not correspond to claim 2 of the present invention, and the effect of hot-rolled sheet annealing is not obtained, but they are included in claim 1, and a sufficient value is obtained as magnetic characteristics. ing.

Under the condition 13 in which the hot-rolled sheet was annealed under the conditions corresponding to claim 2 of the present invention, not only the magnetic properties were improved, but also the space factor was improved. However, under condition 14 where the annealing temperature was too high, it became brittle and cracked during cold rolling.

[0062]

[Table 5]

[0063]

According to the method of the present invention, it is possible to improve the magnetic properties of the electrical steel sheet, particularly to reduce the iron loss in the high frequency region without deteriorating the cold workability. Therefore, it becomes possible to manufacture such a low-loss non-oriented electrical steel sheet without using special equipment and to process the product steel sheet into a required shape.

[0064]

Claims (2)

[Claims] 1. By weight%, C: 0.010% or less, Si: 2.0
~ 3.25%, Mn: 0.1-2.5%, P: 0.02% or less, S:
0.006% or less, N: 0.006% or less, Al: 1.5 to 2.5%
And B: contains 0 to 0.0050% and Si (%) + A
l (%) ≧ 4.5 and Si (%) + 0.5Al (%) <
A slab of steel satisfying 4.0 and balance of Fe and unavoidable impurities is hot-rolled, cold-rolled at a rolling rate of 40 to 80%, then annealed at 650 to 1000 ° C., and A method for producing a non-oriented electrical steel sheet with low iron loss, which comprises performing finish annealing after cold rolling with a rolling rate of 40 to 80%. 2. By weight%, C: 0.010% or less, Si: 2.0
~ 3.25%, Mn: 0.1-2.5%, P: 0.02% or less, S:
0.006% or less, N: 0.006% or less, Al: 1.5 to 2.5%
And B: contains 0 to 0.0050% and Si (%) + A
l (%) ≧ 4.5 and Si (%) + 0.5Al (%) <
4.0, with the balance being Fe and unavoidable impurities, the steel slab was hot-rolled,
Annealed at 00 ℃, cold rolled at a rolling rate of 40-80%,
Then, intermediate annealing was performed at 650 to 1000 ℃, and the rolling rate was 40%.
A method for manufacturing a non-oriented electrical steel sheet with low iron loss, which is obtained by performing finish annealing after cold rolling to -80%.