JPH0718335A - Manufacture of electromagnetic steel sheet having excellent magnetic property - Google Patents

Abstract

PURPOSE:To provide a manufacturing method of an electromagnetic steel sheet having little anisotropy in magnetic property. CONSTITUTION:A steel slab containing <=0.010% C, 1.5 to 4.0% Si, 1.0 to 4.0% Mn, <=0.01% S, less than 0.003% sol.Al and 0.001 to 0.010% N is treated by the following (1) to (5) in which the electromagnetic steel sheet with low iron loss and excellent balance between magnetic properties in the rolling direction and in the direction orthogonally crossing with the rolling direction is manufactured. (1) Hot rolling process. (2) Cold rolling process continuously following the hot rolling or after annealing following the hot rolling. (3) First crystallizing process by continuous annealing. (4) Second crystallizing process by keeping for 4 to 100 hours in a temp. range of 800 to 950 deg.C in an N2 containing atmosphere. (5) Purifying process by keeping for 4 to 100 hours in a temp. range of 800 to 1000 deg.C in an H2 atmosphere. Thus, the electromagnetic steel sheet having iron loss anisotropy of <=2.0 and low iron loss in both of the rolling direction and the direction orthogonally crossing with rolling direction is obtained.

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 an electromagnetic steel sheet having excellent magnetic properties as an iron core material for a large rotating machine.

[0002]

2. Description of the Related Art In iron cores for large rotating machines such as generators and large motors, it is important to balance the magnetic properties of the steel sheet in the rolling direction (L direction) and the rolling orthogonal direction (C direction). Generally, high-grade non-oriented electrical steel sheets and grain-oriented electrical steel sheets are used.

However, when a non-oriented electrical steel sheet is used, the magnetic properties in the L direction cannot be said to be sufficient, and improvement of this property is a problem. On the other hand, when the grain-oriented electrical steel sheet is used, the anisotropy of magnetic properties is strong and the magnetic properties in the L direction are excellent, but the magnetic properties in the C direction are extremely poor. is not. In addition, the production of grain-oriented electrical steel sheets requires decarburization annealing and finish annealing at a high temperature of around 1200 ° C, which makes the cost extremely high.

Several proposals have been made to solve the above problems. For example, in JP-A-5-9666, C: 0.01% or less, Si: 1.5 to 3.0%, Mn: 1.0 to 3.
Decarburization annealing or high temperature exceeding 1050 ° C is performed by performing annealing for secondary recrystallization in a nitrogen-containing atmosphere using a steel sheet manufactured from a steel slab containing 0% and acid-soluble Al: 0.003 to 0.015%. A method for producing a grain-oriented electrical steel sheet having good magnetic properties at low cost without annealing has been shown.

However, this method is not intended to eliminate the drawback of the grain-oriented electrical steel sheet in which the magnetic properties in the C direction are extremely poor.

Japanese Unexamined Patent Publication (Kokai) No. 5-70833 discloses hot rolling at a slab heating temperature of 1150 to 1250 ° C., followed by cold rolling 1 to 2 times including intermediate annealing, followed by decarburizing annealing. ,
After that, a method for producing an electrical steel sheet having an excellent balance of anisotropy of magnetic properties is shown, in which cold rolling is performed at a reduction rate of 0.5 to 5.0% if necessary and continuous annealing is performed.

However, in this case as well, although the anisotropy is reduced as compared with the general grain-oriented electrical steel sheet, the C / L (C
The iron loss W _15/50 in the direction is divided by that in the L direction), and the anisotropy is not sufficiently improved. Moreover, this method requires decarburization annealing and, depending on the case, 2-3 times of cold rolling, and does not have a sufficient cost reduction effect.

[0008]

The object of the present invention is to provide a C / L of iron loss of 2.0 or less, no extreme anisotropy, and a low iron loss in both the L and C directions. An object of the present invention is to provide a method of manufacturing an electromagnetic steel sheet having excellent magnetic properties as an iron core material for a machine at low cost.

[0009]

The gist of the present invention resides in the following manufacturing method.

% By weight, C: 0.010% or less, Si: 1.5 to 4.0
%, Mn: 1.0 to 4.0%, S: 0.01% or less, acid-soluble Al: 0.0
A steel slab containing less than 03% and N: 0.001 to 0.010%, the balance being Fe and unavoidable impurities, is processed in the following steps to have a low iron loss and a direction perpendicular to the rolling direction. Manufacturing method of magnetic steel sheet with excellent balance of magnetic properties of.

Step of performing hot rolling After hot rolling, or after annealing after hot rolling,
Process of cold rolling Process of causing primary recrystallization by continuous annealing Process of maintaining secondary temperature in the temperature range of 800 to 950 ° C for 4 to 100 hours in an atmosphere containing N ₂ and causing secondary recrystallization in H ₂ atmosphere Process of purifying by holding in the temperature range of 800 to 1000 ° C. for 4 to 100 hours The moderate anisotropy of magnetic properties aimed by the present invention is due to the influence of the texture formed by secondary recrystallization during annealing. It is a thing. In this secondary recrystallization, crystal grains with a Goss orientation indicated by Miller index {110} <001> selectively grow under the condition that crystal grain growth is suppressed by precipitates generally called inhibitors. It is a phenomenon.

In a normal grain-oriented electrical steel sheet, the inhibitor effect of precipitates is extremely strong, and secondary recrystallization with a high degree of Goss orientation integration occurs. Therefore, in this case, the magnetic characteristic in the L direction is remarkably good, but that in the C direction is extremely deteriorated.

The present invention is based on the following findings. That is, by controlling the respective contents of Si and Mn and controlling the atmosphere of the secondary recrystallization annealing, relatively weak inhibitor precipitates are generated and the degree of integration of the secondary recrystallization in the Goss orientation is optimized. The difference between the magnetic properties in the C and C directions is small, and the average magnetic properties in the L and C directions are high.

[0014]

The reason why the chemical composition, the manufacturing process and the manufacturing conditions of the steel slab to which the method of the present invention is applied are limited as described above will be explained. Hereinafter,% means% by weight.

(1) Composition of slab C: 0.010% or less C in the product adversely affects iron loss, so the C content must be 0.010% or less, preferably 0.005% or less at the slab stage. This is because C remaining in the product stage forms carbides, which become obstacles for domain wall movement and increase iron loss.

Si: 1.5 to 4.0% Si is an element having a great influence on the magnetic properties, and as its content increases, the electrical resistance of the steel sheet increases and the eddy current loss decreases, resulting in a decrease in iron loss. To do. However, if the Si content exceeds 4.0%, the workability deteriorates and cold rolling becomes difficult. On the other hand, if it is less than 1.5%, the electrical resistance of the steel sheet is low,
Iron loss cannot be reduced. Therefore, the range of Si content is 1.5
It was set to ~ 4.0%.

Mn: 1.0 to 4.0% Mn is an element effective for increasing the electric resistance of the steel sheet as with Si, but if the Mn content is less than 1.0%, its effect is small.

Mn is an inhibitor precipitate (A
L, Si, Mn) nitride is formed, and secondary recrystallization annealing is an element indispensable for forming a texture capable of obtaining magnetic properties having appropriate anisotropy, which is the aim of the present invention. This action is also Mn
Since it becomes remarkable when the content is 1.0% or more, from this aspect as well 1.
It was set to 0% or more.

On the other hand, if the Mn content exceeds 4.0%, the dispersed state of (Al, Si, Mn) nitride formed in steel becomes unsuitable, and good magnetic properties cannot be obtained. Therefore, the range of Mn content was 1.0 to 4.0%.

S: 0.01% or less S combines with Mn to form MnS. In the present invention, as a main inhibitor precipitate that controls the texture during annealing,
(Al, Si, Mn) nitride is used. Therefore, since MnS is not used as an inhibitor unlike general grain-oriented electrical steel sheets, it is not necessary to contain a large amount of S. If a large amount of MnS particles remain in the steel at the product stage, iron loss will be deteriorated. Therefore, the S content is set to 0.01% or less. In addition,
From the viewpoint of reducing iron loss, 0.005% or less is desirable.

Acid-soluble Al (sol.Al): Less than 0.003% When Al is contained, the formation of MnSiN ₂ is hindered, the precipitate changes to (Al, Si, Mn) nitride, and the inhibitor effect becomes too strong. Therefore, the desired texture cannot be obtained during the secondary recrystallization. Such adverse effect of Al is 0.003 as sol.Al content.
%, It becomes remarkable, so less than 0.003%.

N: 0.001 to 0.010% N is an element necessary for forming an inhibitor nitride. If the N content is less than 0.001% in the slab stage, the amount of nitride precipitation is insufficient, and the desired inhibitor effect cannot be obtained. On the other hand, if it exceeds 0.010%, the effect is saturated. Therefore, the range of N content in the slab stage is 0.001 to 0.010.
%.

(2) Manufacturing Process and Manufacturing Conditions The raw material steel slab has the above composition. This is either a slab made by continuous casting of molten steel that has been melted in a converter, an electric furnace, etc. and, if necessary, vacuum degassed, or slabs made by slabbing and rolling. But it's okay.

(A) Second Step (Hot Rolling) The hot rolling conditions are not particularly limited, but the heating temperature is preferably 1100 to 1270 ° C. and the finishing temperature is 700 to 950 ° C.

(B) First Step (Hot Rolled Sheet Annealing, Cold Rolling) The hot rolled sheet is cold rolled to a predetermined product sheet thickness. At this time, annealing (so-called hot rolled sheet annealing) may be performed before the start of cold rolling. This hot-rolled sheet annealing is effective in optimizing the dispersion state of precipitates, promoting homogenization of the microstructure by recrystallization of the hot-rolled sheet, and stabilizing the occurrence of secondary recrystallization.

When the hot-rolled sheet is annealed continuously, it is 750-
600 at the time of soaking at 1100 ℃ for 10 seconds to 5 minutes and box annealing
It is desirable to soak at 850 ℃ for 30 minutes to 24 hours.

(C) First step (continuous annealing before finish annealing,
Primary Recrystallization Annealing) In order to generate stable secondary recrystallization in finish annealing described later, primary recrystallization by rapid heating is necessary. For this reason, continuous annealing is effective, and the annealing temperature is 700 to 1000 ° C.
Is desirable.

(D) Second Step (First Annealing in Finish Annealing, ie, Secondary Recrystallization Annealing) Finishing annealing is the first half annealing (first annealing) for the purpose of secondary recrystallization, and thereafter. Annealing (second annealing) for the purpose of removing (purifying) the precipitates.

In order to generate secondary recrystallization having an appropriate degree of Goth orientation integration, it is important to appropriately control the inhibitor strength in the temperature range in which secondary recrystallization occurs.

In the secondary recrystallization annealing, keeping the temperature in the temperature range of 800 to 950 ° C. for 4 to 100 hours is the reason why the most suitable inhibitor strength is obtained in this temperature range and the secondary recrystallization is appropriately accumulated in the Goss orientation. This is because crystals are generated. If the temperature is less than 800 ° C, the effect of the inhibitor, that is, the grain growth suppressing force is too strong and secondary recrystallization does not occur. On the other hand, in the temperature range above 950 ° C, the inhibitor strength is too weak to cause secondary recrystallization, and only the growth of normal primary recrystallized grains proceeds.

If the holding time in the temperature range of 800 to 950 ° C. is less than 4 hours, the secondary recrystallization is not sufficient. on the other hand,
Retaining more than 100 hours is meaningless and economically disadvantageous. For these reasons, the condition of the secondary recrystallization annealing is set to 800 ~
The temperature was maintained at 950 ° C for 4 to 100 hours.

The atmosphere for the secondary recrystallization annealing needs to be a nitrogen-containing atmosphere. This is because in the case of a nitrogen-containing gas, nitriding of the steel sheet due to the atmospheric gas occurs, the amount of MnSiN ₂ precipitated increases, an appropriate inhibitor effect occurs, and secondary recrystallization that appropriately accumulates in the Goss orientation occurs. . However, secondary recrystallization occurs in the 100% H ₂ atmosphere.
The denitrification reaction proceeds in the temperature range of 800 to 950 ℃, MnSiN ₂ is gradually reduced, and the inhibitor effect is too weak to cause secondary recrystallization.

The desirable nitrogen content range is 5% by volume.
100% with the balance hydrogen.

This is because if the nitrogen content is less than 5% by volume, the nitriding reaction may not proceed sufficiently and the inhibitor strength may be weakened.

(E) First Step (Second Annealing in Finish Annealing, that is, Purification Annealing) The presence of precipitates (MnSiN ₂ ) as an inhibitor is an essential condition for the occurrence of secondary recrystallization. However, the precipitate hinders the movement of the domain wall, which is harmful to the magnetic properties.

Therefore, after the secondary recrystallization is completed,
It is necessary to remove the precipitate by purification. The denitrification annealing performed for this purpose is a purification annealing step.

To promote the denitrification reaction, an H ₂ atmosphere is used.
It is necessary to anneal for 4 to 100 hours in the temperature range of 800 to 1000 ° C in (pure hydrogen atmosphere in the industrial sense). 800
If the temperature is less than ℃, the denitrification reaction does not proceed, while if the temperature exceeds 1000 ℃, the denitrification effect is saturated, which is economically disadvantageous.

When the refining annealing time is less than 4 hours, sufficient denitrification is not performed. On the other hand, holding for more than 100 hours is meaningless because the denitrification effect is almost saturated.

The application of the annealing separating agent before the finish annealing for preventing the seizure during the annealing is the same as in the case of the production of the ordinary grain-oriented electrical steel sheet. Similarly, in the step after finish annealing, after removing the annealing separating agent, an insulating coating is applied or flattening annealing is performed if necessary.

[0040]

【Example】

(Test 1) After melting in a converter and adjusting the components by vacuum treatment,
C: 0.0032%, Si: 2.63%, Mn: 2.12 obtained by continuous casting
%, S: 0.005%, sol.Al: 0.0008%, N: 0.0045%, with the balance being Fe and inevitable impurities, a steel slab heated to 1220 ° C and hot rolled at a finishing temperature of 835 ° C. The plate thickness is 2.3mm.

Next, after descaling by pickling, 70
After carrying out box annealing type hot-rolled sheet annealing of soaking at 0 ° C. for 1 hour, it was cold-rolled to 0.35 mm and primary recrystallized by continuous annealing at 875 ° C. for 30 seconds. Then, after applying an annealing separator, finish annealing was performed under the conditions shown in Table 1.

[0042]

[Table 1]

In the finish annealing, the temperature is raised to the soaking temperature of the secondary recrystallization annealing at a heating rate of 40 ° C./h, the atmosphere is switched to the purification annealing condition after completion of the soaking of the secondary recrystallization annealing, and the annealing is performed at 40 ° C./h. The temperature was raised to the soaking temperature of the purification annealing at a heating rate of h, and after soaking of the purification annealing was completed, it was cooled to room temperature at a cooling rate of 40 ° C / h.

Next, after removing the annealing separating agent, continuous annealing for flattening soaking for 30 seconds at 800 ° C. was performed, and a coating was applied to obtain a product. Epstein test pieces were sampled from these products and magnetic measurements were performed in the L and C directions. The Epstein test piece was subjected to the magnetic measurement without performing the stress relief annealing like the general full-process non-oriented electrical steel sheet. The results of these measurements are shown in Table 2.

[0045]

[Table 2]

Test No. 1 and Test No. 4 in which the soaking temperature of the secondary recrystallization annealing is outside the range defined by the present invention, and the atmosphere of the secondary recrystallization annealing outside the range defined by the present invention is 100.
In the test No. 5 in which% H ₂ was used, the C / L ratio was small because secondary recrystallization was not performed, but the magnetic properties in the L direction were not improved, and the magnetic properties in both L and C averages were also inferior. .

In Test No. 6 in which the atmosphere of all the steps of finish annealing was a nitrogen-containing atmosphere, the iron loss was deteriorated because purification was not performed.

Test No. 2 satisfying the conditions defined in the present invention,
In No. 3, the difference between the magnetic properties in both the L and C directions is small, and the average magnetic properties in both directions are also good.

(Test 2) A hot-rolled sheet having a plate thickness of 2.3 mm was finished in the same manner as in Test 1 using 5 types of steels having the chemical compositions shown in Table 3. These sheets were annealed at 860 ° C. for 1 minute in a continuous annealing method, hot-rolled and then descaled by pickling, and then cold-rolled to a thickness of 0.35 mm.

[0050]

[Table 3]

These cold-rolled sheets were subjected to primary annealing by continuous annealing with uniform heating at 875 ° C. for 30 seconds, and then an annealing separator was applied to finish annealing. The finish annealing is a soaking temperature of secondary recrystallization annealing at a heating rate of 40 ° C / h in an atmosphere of 50% H ₂ + 50% N ₂ 880
The temperature is raised to ℃ and after heating for 8 hours, the atmosphere is heated to 100% H ₂
Switch to, and carry out purification annealing with soaking for 24 hours,
Then, it was cooled to room temperature at a cooling rate of 40 ° C / h.

After removing the annealing separator, the steel sheet thus obtained was continuously annealed at 800 ° C. for 30 seconds for soaking, and coated to obtain a product. Epstein test pieces were sampled from these products and magnetic measurements were performed in the L and C directions. The magnetic properties were investigated in the same manner as in Test 1 using these products. The results are shown in Table 4.

[0053]

[Table 4]

In the test numbers 7 and 9 in which the contents of Mn and Si were out of the ranges defined by the present invention, respectively, secondary recrystallization did not occur, and the anisotropy was small, but the magnetic characteristics in the L direction were small. Inferior In the test number 11 in which the Al content exceeds the upper limit defined in the present invention, the inhibitor effect is too strong, and secondary recrystallization in which the degree of integration in the Goss direction is too high occurs, so that the magnetic properties in the L direction are good, It is remarkably inferior in the C direction and has large anisotropy. On the other hand, in Test No. 8 and Test No. 10 satisfying the conditions defined in the present invention, the anisotropy of the magnetic characteristics is relatively small, and the magnetic characteristics in the L and C directions are both excellent and excellent.

(Test 3) C: 0.0045%, Si: 3.08, obtained by melting in a converter, adjusting the components by vacuum treatment, and then continuously casting.
%, Mn: 2.56%, S: 0.003%, sol.Al:0.001%, N: 0.0
A steel slab containing 045% and the balance of Fe and inevitable impurities was heated to 1210 ° C. and hot-rolled at a finishing temperature of 845 ° C. to finish a plate thickness of 2.1 mm.

Next, after descaling by pickling, cold rolling was performed to a thickness of 0.50 mm, and primary recrystallization was performed by continuous annealing at 875 ° C. for 30 seconds soaking. Next, after applying the annealing separator, finish annealing was performed under the conditions shown in Table 5.

In the finish annealing, the temperature was raised to 880 ° C. which is the soaking temperature of the secondary recrystallization annealing at a heating rate of 40 ° C./h, the atmosphere was switched to 100% H ₂ after completion of the soaking for 16 hours, and further, Purification annealing with soaking was performed for 24 hours, and then cooled to room temperature at a cooling rate of 40 ° C / h.

Next, after removing the annealing separator, continuous annealing was performed at 800 ° C. for 30 seconds for soaking and flattening, and a coating was applied to obtain a product. The magnetic properties were investigated in the same manner as in Test 1 using these products. The results of these measurements are also shown in Table 5.

[0059]

[Table 5]

In the test No. 13 in which the atmosphere of the secondary recrystallization annealing is outside the conditions defined by the present invention, the secondary remake does not occur and although the anisotropy is small, the improvement of the magnetic properties in the L direction is not observed.
The magnetic properties of both L and C averages are also poor. In Test No. 12, which satisfies the conditions defined by the present invention, the difference in the magnetic properties in both the L and C directions is small, and the average magnetic properties in both directions are also good.

[0061]

According to the method of the present invention, the C / L of iron loss is
It is possible to manufacture at low cost an electromagnetic steel sheet having an anisotropy of 2.0 or less and having a low level of iron loss in both the L and C directions.

Claims (1)

[Claims] 1. By weight%, C: 0.010% or less, Si: 1.5 to 4.0
%, Mn: 1.0 to 4.0%, S: 0.01% or less, acid-soluble Al: 0.0
A steel slab containing less than 03% and N: 0.001 to 0.010%, the balance being Fe and unavoidable impurities, is processed in the following steps to have a low iron loss and a direction perpendicular to the rolling direction. Manufacturing method of magnetic steel sheet with excellent balance of magnetic properties of. Process of hot rolling, as hot rolling, or after annealing after hot rolling,
Process of cold rolling Process of causing primary recrystallization by continuous annealing Process of maintaining secondary temperature in the temperature range of 800 to 950 ° C for 4 to 100 hours in an atmosphere containing N ₂ and causing secondary recrystallization in H ₂ atmosphere Process of keeping the temperature in the temperature range of 800-1000 ℃ for 4-100 hours and purifying