JPH055126A - Production of nonoriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To produce a nonoriented silicon steel sheet reduced in iron loss, having high magnetic flux density, and excellent in magnetic properties. CONSTITUTION:A hot rolled plate having a chemical composition consisting of, by weight, 0.006-0.020% C, 3.5-4.5% (Si+Al), <=0.005% (Ti+Nb+Zr+V/10), 0.1-2% Mn, <=0.001% S, <=0.002% N, <=0.003% O, and the balance Fe with inevitable impurities or a hot rolled plate having a chemical composition containing, besides the above components, 0.1-2% Mn is heated up to >=800 deg.C and cooled at >=10 deg.C/s cooling rate to undergo hot rolled plate annealing. Subsequently, a cold rolled steel sheet cold-rolled to the prescribed thickness is heated up to 900-1100 deg.C at <=10 deg.C/s temp. rise rate and successively subjected to decarburizing annealing at <=900 deg.C, by which C content is regulated to <=0.003%. The decarburizing annealing can be done by subjecting the steel sheet, after cold rolled sheet annealing, to temporary cooling down to room temp. and then to reheating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-oriented electrical steel sheet having excellent magnetic properties, which is used for iron core materials such as motors.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are magnetic materials used as iron cores for motors and the like. In recent years, non-oriented electrical steel sheets have been made of low iron to reduce the power loss and size of equipment. There is a strong demand for improvement in magnetic properties such as loss and higher magnetic flux density.

In order to improve the magnetic properties, in addition to techniques such as increasing the electric resistance and increasing the crystal grain size after final annealing to some extent, the <100> axis, which is the easy axis of magnetization, is set in the direction of magnetization. Alignment, it is important to reduce the <111> axis, which is the hard axis of magnetization, from the magnetization direction, that is, it is important to control the texture, and for electromagnetic steel sheets used in equipment such as motors, <100 A texture in which the> axis is non-directionally distributed in the plate surface and the <111> axis is not in the plate surface is most suitable.

Conventionally, as a method for obtaining such a texture, there has been known a melt quenching method, a cross rolling method, or a method of utilizing surface energy in the production of a non-oriented electrical steel sheet. Further, Japanese Patent Laid-Open No. 2-54720 discloses a method of heating annealing after cold rolling to an Ac ₃ transformation point or higher and cooling at a cooling rate of 10 ° C./min or higher.

However, each of the above methods for obtaining a texture in which <100> axes are densely integrated in the in-plane direction has the following problems. For example, the molten metal quenching method can obtain only an extremely thin sheet, and the electromagnetic steel sheet has a poor space factor and is difficult to punch. In the cross rolling method, it is extremely difficult to roll in a coil shape, and the productivity is poor. The method utilizing surface energy requires annealing at high temperature for a long time, which increases the manufacturing cost. Further, the method described in Japanese Patent Application Laid-Open No. 2-54720, in which annealing is performed at the Ac ₃ transformation point or higher, the Ac ₃ transformation point becomes extremely high in the case of a component system having a high Si content, or _{Since the 3} transformation point itself disappears, it cannot be applied to steel of such a composition system.

[0006]

An object of the present invention is to solve the above problems. That is, an object of the present invention is to provide a method capable of industrially and inexpensively producing a non-oriented electrical steel sheet excellent in magnetic properties having a texture in which <100> axes are densely integrated in the in-plane direction. To provide.

[0007]

The inventors of the present invention suppress the development of the <111> axis in the in-plane direction of the sheet in a high (Si + Al) system having a high electric resistance and a low eddy current loss, and suppress the development of the <100> axis. As a result of investigating the method of improving the magnetic properties by developing the alloy, the (Si + Al) hot-rolled sheet with a limited composition was annealed under certain conditions to determine the grain size before cold rolling. It has been found that the magnetic properties can be greatly improved by increasing the amount and allowing the solid solution C to remain during the cold rolling and the subsequent recrystallization annealing.

The gist of the present invention based on the above findings is the following manufacturing methods.

% By weight, C: 0.006 to 0.020%, Si
+ Al: 3.5 to 4.5%, (Ti + Nb + Zr + V / 10): 0.005
% Or less, Mn: 0.1 to 2%, S: 0.001% or less, N: 0.00
2% or less, O: 0.003% or less, balance: Fe and a hot rolled sheet with a chemical composition consisting of unavoidable impurities are heated to 800 ° C or more, then cooled at a cooling rate of 10 ° C / s or more, and then to a predetermined thickness. After cold rolling, the temperature rise rate of 10 ℃ / s or more is 900
A method for producing a non-oriented electrical steel sheet, which comprises heating to ~ 1100 ° C, followed by decarburization annealing at a temperature of 900 ° C or less until the C content becomes 0.003% or less.

A hot-rolled sheet having the chemical composition described above is
After heating to 800 ° C or higher, it is cooled at a cooling rate of 10 ° C / s or higher, then cold-rolled to a predetermined thickness, and then heated to 900 to 1100 ° C at a heating rate of 10 ° C / s or higher, Once cooled to room temperature, reheated to a temperature below 900 ° C to reduce the C content.
A method for producing a non-oriented electrical steel sheet, which comprises performing decarburization annealing until the content becomes 0.003% or less.

[0011]

In the present invention, the chemical composition of the hot rolled sheet will be described below.
The reason for limiting the conditions of the annealing of the hot rolled sheet, the annealing of the cold rolled sheet and the decarburizing annealing as described above will be described. In addition, "%" regarding a component content means "weight%."

A) Chemical Composition of Hot Rolled Sheet It is important that C: C is present as a solid solution C during cold rolling and recrystallization annealing. 0.006% for that
It is necessary to contain the above. When C is contained in an amount of 0.006% or more, it can be present as solid solution C during cold rolling and recrystallization annealing, so that the development of the <111> axis in the plate surface direction can be suppressed. However, if too much is added, the amount of solid solution C does not change, and in addition, cementite becomes present during annealing, which hinders grain growth. Further, excessive addition also prolongs the final decarburization annealing. In the present invention, the C content is reduced to 0.003% or less in the final decarburization annealing so as not to deteriorate the magnetic properties. However, when the C content of the hot rolled sheet as the starting material exceeds 0.020%, the grain growth is It will be hindered and it will take a long time to decarburize. Therefore, the C content is set to 0.006 to 0.020%.

Si and Al: Si and Al are deoxidizing agents,
Further, it is added in order to increase the electric resistance value to lower the iron loss, and further to raise the transformation point to enable decarburization annealing at a high temperature of 900 ° C or higher. To do that, Si +
3.5% or more of Al is required. However, the amount of Si + Al is 4.5
%, Not only the magnetic flux density is lowered, but also the steel becomes brittle. Therefore, the amount of Si + Al was set to 3.5-4.5%.

Ti, Nb, Zr and V: Ti, Nb, Zr because these elements easily combine with carbon to form carbides and deteriorate the magnetic properties as well as reduce the effective solid solution C.
And the total of V / 10 was 0.005% or less. The reason why only V is set to 1/10 times is that the carbide forming ability corresponds to 1/10 times that of the other three elements.

Mn: Mn not only has the effect of increasing the electric resistance value and promoting the decrease of iron loss, but also has the function of desulfurization. In order to obtain these effects, it is necessary to contain at least 0.1%. However, if a large amount is added, the magnetic flux density will be lowered, so the content was made 0.1 to 2%.

S: S forms fine sulfide-based precipitates and deteriorates the magnetic properties, so the content is made 0.001% or less.

Since N: N also forms fine nitride-based precipitates and deteriorates the magnetic properties, the content thereof is set to 0.002% or less.

O: O forms an oxide and deteriorates the magnetic properties like S and N, so its content is 0.003%.
Below. It is desirable to keep it to 0.002% or less.

B) Annealing of Hot Rolled Sheet The purpose of this annealing is to increase the grain size of the hot rolled sheet and to make C a solid solution.

To this end, a hot-rolled sheet having the above chemical composition is
It is necessary to anneal under the conditions of heating at a temperature of 800 ° C or higher and cooling at a cooling rate of 10 ° C / s or higher. Heating temperature is 800 ℃
If it is lower, the grain size of the hot-rolled sheet does not become sufficiently large. When the cooling rate is less than 10 ° C./s, carbide precipitates during cooling, so solid solution C cannot be present during cold rolling and during recrystallization annealing thereafter.

C) Annealing of Cold Rolled Sheet The purpose of this annealing is to recrystallize the cold rolled steel sheet and grow the crystal grains. For that purpose, it is necessary to anneal under the condition of heating to a temperature of 900 to 1100 ° C. at a temperature rising rate of 10 ° C./s or more. At a heating rate slower than 10 ° C / s, carbide is precipitated before recrystallization, and it is not possible to suppress the development of <111> axis in the in-plane direction. Iron loss does not decrease because the crystal grains do not grow sufficiently at heating temperatures lower than 900 ° C. 11
At heating temperatures higher than 00 ° C, the Ac ₃ transformation point is exceeded,
It becomes difficult to control the texture, and even if the Ac ₃ transformation point is not exceeded, grain growth occurs remarkably, and the iron loss rather deteriorates.

D) Decarburization Annealing Since the method of the present invention is characterized by recrystallization and grain growth in the state containing solid solution C, decarburization annealing must always be performed after recrystallization and grain growth. .. In this decarburization annealing, the amount of C in the steel is reduced to 0.003% or less and the magnetic properties are enhanced. In the present invention, this decarburization annealing may be performed after the annealing of the cold-rolled sheet, that is, after the high temperature steel sheet after annealing is cooled to the decarburization annealing temperature without cooling to room temperature, once cooled to room temperature. Then, it may be reheated to the decarburization annealing temperature. However, in all cases, decarburization annealing at a temperature higher than 900 ° C causes grain growth more than necessary, and a texture that is disadvantageous to magnetic properties is generated. You need to do the following: Even if the temperature of decarburization annealing is 900 ° C or less, if the decarburization annealing is finished at a stage where the carbon content in the steel does not reach 0.003% or less, the steel sheet after decarburization annealing undergoes magnetic aging and magnetic properties. Deteriorates. If the cold-rolled sheet is annealed and then cooled to room temperature, it may be punched and then decarburized and annealed.

[0023]

Example 1 Steels having the chemical compositions shown in Table 1 were melted and made into slabs, which were then hot rolled into hot rolled sheets having a thickness of 2.3 mm.

After pickling these hot-rolled steel sheets, the temperature of the hot-rolled steel sheet was set to 60 at 900 ° C.
It was heated for sec, cooled to room temperature at a cooling rate of 15 ° C / s, and then cold rolled to a thickness of 0.5 mm. Then, the obtained cold-rolled sheet was heated to 1000 ° C at a heating rate of 20 ° C / s, held at this temperature for 60 seconds, and then cooled to room temperature, and subsequently in a H ₂ + Ar mixed atmosphere with a dew point of + 30 ° C. 60 mi at a temperature of 700 ° C
Decarburization annealing was performed while maintaining n.

A test piece was cut out from the thus-obtained magnetic steel sheet, and its magnetic characteristics were investigated. The results are shown in Table 2.

The magnetic properties were investigated for iron loss and magnetic flux density. The investigation was conducted using test pieces taken from the respective electromagnetic steel sheets in two directions, the rolling direction and the direction perpendicular to the rolling direction.
Commercial frequency according to Epstein test of S C2550
Performed in an alternating magnetic field of 50 Hz

[0027]

[Table 1]

[0028]

[Table 2]

From Table 2, all of the magnetic steel sheets produced by the method of the present invention have a thickness of 0.5 mm and the iron loss (W _15/50 ) is 2.3 W / k.
It can be seen that below g, the magnetic flux density (B ₅₀ ) is 1.65 T or more, indicating excellent magnetic properties. On the other hand, if the component composition is out of the range specified in the present invention, the magnetic properties are poor. In the comparative example of Sample No. 2, the C content was lower than 0.006%, and the iron loss and the magnetic density were poor because the texture which was inconvenient for the magnetic properties developed. In the comparative example of sample No. 3, the amount of C was more than 0.020%, decarburization was insufficient, and after decarburization, the amount of C was 0.003% or more.
Since iron is included, iron loss is bad. Comparative example of sample No.5
The (Si + Al) content is lower than 3.5%, and it is not possible to expect an increase in eddy current due to an increase in electrical resistance, resulting in poor iron loss. Comparative example of sample No.6
The (Si + Al) content was higher than 4.5% and fracture occurred during cold rolling.

In the comparative example of sample No. 8, the Mn content is higher than 2.0% and therefore the magnetic flux density is low. The comparative example of sample No. 10 is
The content of (Ti + Nb + Zr + V / 10) exceeds 0.005%, the solid solution C is reduced, and fine carbides harmful to the magnetic properties are generated, resulting in poor core loss and magnetic flux density. sample
In the comparative example of No. 11, the S content exceeds 0.001%, and the iron loss is poor because fine precipitates harmful to the magnetic properties are formed. In the comparative example of sample No. 12, the N content exceeds 0.002%, and the iron loss is poor because fine precipitates harmful to the magnetic properties are generated.
In the comparative example of Sample No. 13, the O content exceeds 0.003%, and the iron loss is poor because an oxide harmful to the magnetic properties is generated.

[0031]

Example 2 A steel having the same chemical composition as the steel type A shown in Table 1 was melted to form a slab, which was then hot rolled into a hot-rolled sheet having a thickness of 2.3 mm.

After pickling these hot-rolled sheets, hot-rolled sheet annealing, cold rolling, cold-rolled sheet annealing and decarburization annealing were carried out under the conditions shown in Table 3. Cold-rolled sheet annealing was performed in a 100% H ₂ atmosphere with a dew point of −40 ° C., and decarburization annealing was performed in a H ₂ + N ₂ mixed atmosphere with a dew point of + 35 ° C. Further, decarburization annealing was continuously performed after cooling the cold rolled sheet without cooling to room temperature.

From the magnetic steel sheet thus obtained, Example 1
The test pieces were cut out from the same two directions as above, and the magnetic properties were investigated by the same test method. The results are also shown in Table 3.

[0034]

[Table 3]

As is apparent from Table 3, the electromagnetic steel sheet of Sample No. 14 produced by the method of the present invention has a thickness of 0.5 mm and an iron loss of
(W _15/50 ) is less than _2.3 W / kg, magnetic flux density (B ₅₀ ) is 1.65
It has excellent magnetic properties of T or more. On the contrary,
If the manufacturing conditions are outside the range specified in the present invention, the magnetic properties are inferior. The comparative example of Sample No. 15 which was not decarburized and annealed was
Iron loss is poor because a large amount of carbide remains, which hinders the improvement of magnetic properties. The heating temperature during annealing of cold-rolled sheet is 900
In the comparative example of sample No. 16 whose temperature is lower than ℃, grain growth does not occur so much and iron loss is poor. The heating temperature during annealing of cold-rolled sheet is 1000
In the comparative example of Sample No. 17 higher than ℃, remarkable grain growth occurs and iron loss is poor. Temperature rise rate during annealing of cold-rolled sheet is 10 ℃ /
In the comparative example of Sample No. 18 which is slower than s, the cementite is precipitated before recrystallization and a texture which is disadvantageous to the magnetic properties is generated, so that the iron loss and the magnetic flux density are poor. In the comparative example of Sample No. 19 in which the cooling rate in hot-rolled sheet annealing was slower than 10 ° C / s, cementite was precipitated during cooling and solid solution C was decreased,
During the subsequent cold rolling and annealing of the cold rolled sheet, the iron loss and the magnetic flux density were poor because a texture which was unfavorable to the magnetic properties was generated. In the comparative example of Sample No. 20 in which the heating rate in hot-rolled sheet annealing is lower than 800 ° C / s, recrystallization and grain growth were not sufficient, and the magnetic properties were deteriorated during the subsequent cold rolling and cold-rolled sheet annealing. Both iron loss and magnetic flux density are poor due to the formation of various textures.

[0036]

As described above, according to the method of the present invention, a non-oriented electrical steel sheet having a low iron loss, a high magnetic flux density and excellent magnetic characteristics can be produced at a low cost on an industrial scale.

Claims (1)

[Claims] [Claim 1] C: 0.006 to 0.020% by weight, Si + A
l: 3.5 to 4.5%, (Ti + Nb + Zr + V / 10): 0.005%
Below, Mn: 0.1 to 2%, S: 0.001% or less, N: 0.002
%, O: 0.003% or less, balance: Fe and a hot-rolled sheet of a chemical composition consisting of inevitable impurities are heated to 800 ° C. or higher and then cooled at a cooling rate of 10 ° C./s or higher, and then to a predetermined thickness. After cold rolling to 900-1 at a heating rate of 10 ℃ / s or more
A method for producing a non-oriented electrical steel sheet, which comprises heating to 100 ° C. and subsequently decarburizing and annealing at a temperature of 900 ° C. or lower until the C content becomes 0.003% or less. 2. A hot-rolled sheet having the chemical composition according to claim 1,
After heating to 00 ℃ or more, it is cooled at a cooling rate of 10 ℃ / s or more, then cold-rolled to a predetermined thickness, and then heated to 900 ~ 1100 ℃ at a heating rate of 10 ℃ / s or more, Once cooled to room temperature, it is reheated to a temperature below 900 ℃ and the C content is 0.0
A method for producing a non-oriented electrical steel sheet, which comprises performing decarburization annealing until the content becomes 03% or less.