JP2003313645A - Non-oriented silicon steel plate and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-oriented silicon steel plate of which the magnetic characteristics can be improved and the product performance can be stabilized simultaneously by applying magnetic annealing to the plate, and its production method. <P>SOLUTION: The non-oriented silicon steel plate has the content of C: 0.004% or less, Si: 0.1-1.0%, Mn: 0.2-0.6%, sol.Al: less than 0.0006%, P: 0.03-0.2%, S: 0.035% or less, N: 0.004% or less, O (oxygen): 0.0025-0.012% in mass percent, and the ratio (MnO/FeO) of MnO and FeO content (mass percent) in inclusion in steel is 2 or less. The plate can be manufactured by employing the mass ratio (added Al amount/added Si amount) of 0.85 or less for Al and Si added into molten steel after finish decarbonization conducted at vacuum degassing apparatus. <P>COPYRIGHT: (C)2004,JPO

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, more specifically, after shipping, it is punched by a user, assembled into an iron core, and then subjected to magnetic annealing for improving magnetic properties. The present invention relates to a non-oriented electrical steel sheet (so-called semi-processed material) to be applied, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Magnetic steel sheets, which are the materials for iron cores used in transformers and motors, have been required to have high magnetic properties such as low iron loss and high magnetic flux density. Therefore, many electromagnetic steel sheets having high magnetic properties and methods for manufacturing the same have been proposed.

In Japanese Patent Laid-Open No. 63-195217, Si: 0.1-
1.0%, Mn: 1.5% or less, sol.Al: 0.001 to 0.005%, and the ratio of the mass of MnO to the total mass of three kinds of inclusions of SiO ₂ , MnO, and Al ₂ O ₃ in steel is 15 A magnetic steel sheet having a low iron loss of less than 100% is disclosed.

In Japanese Patent Laid-Open No. 7-150248, Si:
0.1-1.0%, Mn: 1.5% or less, sol.Al: 0.0005-0.001%
And the content of MnO in the inclusions is 15% or less,
₂ Magnetic steel sheets with a low iron loss having a content of 75% or more have been proposed.

Further, in JP-A-10-147849, mass%, Si: 0.05 to 0.55%, Mn: 0.1% or more, and M
n-Si ≦ 0.5%, including Al: 0.004% or less, Mn in inclusions
A non-oriented electrical steel sheet in which the ratio MnO / SiO _{2 of} O mass% to SiO ₂ mass% is 0.3 or less is proposed, and it is said that a magnetic steel sheet excellent in surface shape with few scale defects can be obtained.

These techniques improve the magnetic properties by appropriately controlling the chemical composition of the steel material in addition to the chemical composition of the steel material, and show the proper range of the SiO ₂ content and MnO content in the inclusions. Has been done.

However, in recent years, energy saving has become an important issue, and electric equipment having higher efficiency than ever has been demanded. Therefore, an electromagnetic steel sheet having higher magnetic properties than ever before is required. Further, if the magnetic properties of the manufactured electromagnetic steel sheet are not stable, the product yield is lowered and the cost of the electromagnetic steel plate is increased, so that stable performance (magnetic properties) is also important.

As described above, it is becoming more and more important to secure magnetic characteristics that are higher and more stable than ever before. However, the conventional technology cannot sufficiently meet such requirements. It was

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-oriented electrical steel sheet which enhances magnetic properties by performing magnetic annealing and at the same time stabilizes product performance, and a manufacturing method thereof.

[0010]

The gist of the present invention resides in the following (1) non-oriented electrical steel sheet and the following (2) manufacturing method thereof.

(1) C: 0.004% or less, Si:
0.1-1.0%, Mn: 0.2-0.6%, sol.Al: less than 0.0006%,
P: 0.03 to 0.2%, S: 0.035% or less, N: 0.004% or less, O (oxygen): 0.0025 to 0.012%, the balance consisting of Fe and unavoidable impurities, in inclusions present in steel A non-oriented electrical steel sheet having a MnO / FeO ratio of MnO / FeO of 2 or less. Here, “O” indicating the oxygen content means “TO”.

(2) Manufacture of non-oriented electrical steel sheet made from a slab made by continuous casting of molten steel with rough decarburization in a converter, final decarburization with a vacuum degassing device, and then composition adjustment A method of adding Al and Si to molten steel after the final decarburization.
The manufacturing method of the non-oriented electrical steel sheet according to (1) above, wherein the mass ratio (additional Al amount / additional Si amount) is 0.85 or less.

The present inventors conducted the following tests in order to solve the above-mentioned problems. The test method is as follows. In the following, “%” indicating the chemical composition and inclusion composition of steel means “mass%”. The content of chemical components or inclusions in steel is the amount expressed in "mass%".

First, the magnetic properties are enhanced by magnetic annealing,
In order to find the chemical composition and the composition of inclusions that the electrical steel sheet that stabilizes product performance should satisfy, C: less than 0.002%, S
Steel containing i: 0.2-0.8%, Mn: 0.25-0.5%, sol.Al: less than 0.0006%, P: 0.09%, S: 0.005-0.02%, N: less than 0.003%, O: 0.0025-0.015% 200 kg was melted in the laboratory to obtain a steel ingot. The composition of inclusions in the steel was changed by arbitrarily changing the amounts of addition of Al, Si, and Mn, the timing of addition, and the holding time during melting.

A steel piece having a thickness of 15 mm was cut out from this steel ingot and subjected to soaking at 1200 ° C. for 1 hour. After that, it is rolled in 3 passes and hot-finish rolled at 850 ° C to obtain a thickness of 3 mm.
Of hot rolled steel sheet. Next, both sides of this hot-rolled steel sheet are ground to a thickness of 2.3 mm, and further cold-rolled to a thickness of 0.5 mm.
Cold rolled steel sheet. This cold rolled steel sheet was rapidly heated to 750 ° C. and annealed for 30 seconds to obtain a non-oriented electrical steel sheet.

From this steel plate, a 30 mm × 100 mm test piece was prepared.
Half of them were punched in parallel with the rolling direction and the other half were punched perpendicularly to the rolling direction, and magnetic annealing was performed at 750 ° C. for 2 hours.

Regarding the test piece thus obtained,
Using an Epstein tester, magnetic properties (iron loss) were measured according to the method specified in JIS C2550. Further, inclusions in the steel were extracted by the Br-methanol method, the elements contained therein were analyzed, and the composition of the inclusions was analyzed by EPMA observation to investigate the relationship between the composition of the inclusions and the magnetic properties.

FIG. 1 is a diagram showing the relationship between the SiO ₂ content in inclusions and iron loss (W _15/50 ). The relationship between the SiO ₂ content and the iron loss is unclear, and even if the SiO ₂ content is the same, the variation in the iron loss is large. From this result, it can be seen that it is difficult to surely improve the magnetic properties of the product and to stabilize the product performance to improve the yield even if only the SiO ₂ content is used as an index.

FIG. 2 shows the MnO content in the inclusions and the iron loss (W
_15/50 ) FIG. MnO content is 15
%, The iron loss may be low, and the MnO content may be high even if the MnO content is less than 15%. As with the SiO ₂ content, there is a limit in using the MnO content as an index. Recognize.

FIG. 3 shows the ratio of the content of MnO to the content of SiO _{2 in} the inclusions (MnO / SiO ₂ ) and the core loss (W
_15/50 ). Also in this case MnO
As with the case of the content or the content of SiO ₂ , a clear relationship cannot be obtained.

As described above, the conventionally proposed Mn
If an index based on O content or SiO ₂ content is used,
It is considered difficult to reliably reduce the iron loss due to variations in magnetic properties (iron loss).

Therefore, the present inventors further investigated the effect of inclusions on the magnetic properties (iron loss).

Conventionally, when investigating the relationship between the composition of inclusions and the magnetic characteristics, SiO ₂ , MnO and Al ₂ O ₃ in the inclusions were investigated.
Attempts have been made to sort out and examine the test results, focusing only on this. However, as a result of the inventors performing extraction of inclusions in steel by the Br-methanol method and analysis of elements contained therein, and EPMA observation, as described below,
In steel containing less than 0.0006% of l.Al, FeO is present as a fourth component in the inclusions.
It was found that the existing state (abundance ratio) of O and MnO greatly affects the iron loss.

Sol.Al contained in the steel ingot used in the test
Is less than 0.0006%, but the inclusions generated at this time are Si
It was confirmed to consist of O ₂ , MnO, Al ₂ O ₃ and 1-10% FeO. The presence of FeO is presumed to be due to the low Al content in the steel, which is a deoxidizing element.

FIG. 4 shows Mn with respect to FeO content in inclusions.
It is a figure which shows the relationship between the ratio (MnO / FeO) of O content, and iron loss ( _W15 / ₅₀ ). It can be seen that when MnO / FeO exceeds 2 and becomes high, the iron loss becomes large, and when it is 2 or less, the iron loss is small and stable. This is for FeO
When MnO is relatively large, the inclusions have a low melting point, and the inclusions are likely to become large, so that iron loss is considered to deteriorate.

The invention described in (1) above was made based on the knowledge obtained by the above-mentioned test.

Next, in order to examine a method for efficiently controlling the MnO content and the FeO content in the inclusions, which are indispensable for obtaining the above-mentioned non-oriented electrical steel sheet of the present invention, the following tests are conducted. went.

180 kg of molten steel is melted in a vacuum melting furnace, the molten steel temperature is set to 1600 ° C., P: 0.03 to 0.2%, S: 0.003 to 0.035
%, N: 0.004% or less. After that, the melting atmosphere is Ar gas, decarburization is performed by reducing the pressure to 670 Pa,
C: less than 0.004%, O: 0.04 to 0.08%.

After that, Al, Si and Mn are added, and sol.
l: 0.0006% or less, Si: 0.1 to 1.0%, Mn: 0.2 to 0.6%. At that time, the relationship between the amounts of Al, Si and Mn added to the molten steel and the composition of the inclusions was investigated, and further the relationship between MnO / FeO in the inclusions was investigated. Al, Si and Mn are all deoxidizing elements,
Since the composition of Al ₂ O ₃ , SiO ₂ , and MnO in the inclusions is determined, the composition of the inclusions can be controlled by adjusting the addition amount of these deoxidizing elements, and in particular, the electromagnetic steel sheet of the present invention described above. FeO and MnO, which were noted in Section 3, are easily reduced by Al and Si.
This is because it was considered that the addition amounts of Al and Si were more important than the addition amount of.

The test results are shown in FIG. FIG. 5 is a diagram showing the relationship between the ratio of the added amount (mass) of Al and Si and MnO / FeO in the inclusions. From this result, Al added amount / Si added amount (hereinafter,
By setting "R") to 0.85 or less, MnO / Fe
It can be seen that O can be controlled. When R is higher than 0.85, the amount of Al added is excessive with respect to the amount of inclusions, and when the amount of Al is large, the reduction of FeO easily proceeds and the FeO content becomes low. Therefore, MnO / FeO tends to be high. That is, MnO in inclusions specified in the electromagnetic steel sheet of the present invention
In order to control / FeO to 2 or less, the ratio of the added amount of Al and Si added to the molten steel after the decarburization (corresponding to the final decarburization described below) performed under the above-mentioned reduced pressure is 0.85 or less It needs to be adjusted.

As described above, the inventors of the present invention stably manufacture MnO / FeO by adjusting the amount of Al added and the amount of Si added in the smelting process when producing the electromagnetic steel sheet described in (1) above. I found that I could control it. The method for manufacturing a non-oriented electrical steel sheet according to the present invention described in (2) above is based on this finding.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION First, in the non-oriented electrical steel sheet of the present invention described in (1) above, the reason why the chemical composition of the steel sheet and the composition of inclusions are limited as described above will be explained.

C: 0.004% or less C precipitates as carbides and deteriorates the magnetic properties of the steel sheet. Therefore, the lower the content, the better. In particular, the content is 0.00
When it exceeds 4% and becomes high, magnetic aging occurs, so the content of C is made 0.004% or less. In order to suppress the growth of (111) crystallographically oriented grains, which is not desirable for magnetic properties,
The content is preferably 0.0003% or more.

Si: 0.1 to 1.0% Since Si increases the specific resistance of the steel sheet, the higher the content, the smaller the iron loss. However, when the Si content exceeds 1% and becomes high, a nitride is formed, which causes the iron loss to deteriorate, so the content is made 1.0% or less. On the other hand, S
If the i content is less than 0.1%, the deoxidation during steelmaking becomes weak, and the FeO content in inclusions tends to increase, and the above-mentioned MnO / Fe
Since the control of O becomes impossible, the lower limit of Si content is 0.1%.
And

Mn: 0.2 to 0.6% Mn also has the effect of increasing the specific resistance of the steel sheet, so the higher the Mn content is, the better. If the Mn content is less than 0.2%, MnS
Finely precipitates and disperses and the magnetic properties are significantly deteriorated.
The Mn content needs to be 0.2% or more. On the other hand, M
When the n content exceeds 0.6%, the cost increases while the increase in the effect becomes less significant, so Mn
The upper limit of the content is 0.6%.

Sol.Al: 0.0006% or less Al is an element effective for deoxidizing steel, but since it is easy to form nitrides and the like, the lower the content, the better. Further, the content thereof is set to 0.0006% or less because it causes variations in magnetic properties.

P: 0.03 to 0.2% When P exceeds 0.2% and becomes high, the embrittlement of the steel becomes remarkable,
If it is less than 0.03%, the punching property deteriorates. Therefore, P
Content of 0.03 to 0.2%.

S: 0.035% or less When S exceeds 0.035% and becomes high, MnS is formed and iron loss is not sufficiently improved, so the content is made 0.035% or less. Desirably, it is 0.008% or less.

N: 0.004% or less N forms a nitride with Si, Mn, Al, Ti, etc. and hinders grain growth during magnetic annealing, so the content is made 0.004% or less. Note that, similarly to C, the content thereof is preferably 0.0003% or more in order to suppress the growth of (111) crystallographically oriented grains which are not preferable for magnetic properties.

O (oxygen): 0.0025 to 0.012% O forms an oxide in steel and suppresses the growth of crystal grains, so its content is made 0.012% or less. Desirably 0.0
It is 085% or less. On the other hand, if the O content is set to less than 0.0025%, the deoxidizing cost increases, so the lower limit of the content is made 0.0025%.

The electrical steel sheet of the present invention contains the above-mentioned components, the other components are Fe and unavoidable impurities mixed in during the manufacturing process, and further, Mn relative to the content of FeO in the inclusions.
A steel sheet having an O content ratio MnO / FeO of 2 or less. The MnO / FeO content in the inclusions is set to 2 or less because the iron loss after magnetic annealing is small and stable, as described above. The lower limit of MnO / FeO is not particularly limited, but Mn
As described above, since it is contained at least 0.2%, the MnO in the inclusions is not completely nonexistent, and MnO / Fe
0 is not included in the range where O is 2 or less.

Next, regarding the method for producing a non-oriented electrical steel sheet according to the present invention described in (2) above, a converter, an RH type vacuum degassing apparatus (hereinafter abbreviated as RH) and a continuous casting machine are used. The case of manufacturing will be described as an example.

After the molten steel that has been subjected to refining such as decarburization and desulfurization in the converter is tapped from the converter into the ladle, the ladle is moved to RH. Finish decarburization is performed under reduced pressure at RH to reduce the C content in molten steel to 0.004% or less. Al and Si are deoxidizing elements, and if these elements are added before RH decarburization, the decarburization rate will be significantly reduced, so they are not added during this final decarburization treatment.

After decarburization at RH, the S and P contents in the molten steel are adjusted, and Al, Si and Mn are added. When S and P are added to the molten steel, they may be added before or after the addition of Al, Si and Mn.

Mn may be added at any time after decarburization at RH.

Al and Si may be added at the same time, but it is desirable to add Si before adding Al. If earlier addition of Al, alumina inclusions or FeO-MnO-Al ₂ O ₃ inclusions is produced, thereafter, be added to Si, Si may be deoxidizing force weaker than Al, FeO-MnO -Al ₂ O ₃ Fe inclusions in
FeO and Mn in the inclusions are reduced because the reduction rate of FeO and MnO by Si decreases due to the decrease in O and MnO activities.
It becomes difficult to control the O content in a short time, and the processing time must be lengthened. On the other hand, if Al is added after Si is added, since Al has a stronger deoxidizing power, the reaction rate is faster and the treatment can be performed in a shorter time. However, with either method,
As described above, the accuracy of inclusion control (that is, control of MnO / FeO in inclusions) is improved by adding R (Al addition amount / Si addition amount) so as to be 0.85 or less.

Subsequently, the molten steel having the adjusted composition is cast by a continuous casting machine to obtain a slab, which is hot-rolled and then cold-rolled to obtain an electromagnetic steel sheet.

The hot rolling conditions may be the same as those used in the production of ordinary magnetic steel sheets, but the finishing temperature of hot rolling is preferably 800 to (880 + 50 × [% Si]) ° C. (The above [% Si] represents the Si content of the steel plate). If the finishing temperature is less than 800 ° C, the microstructure will become a fine unrecrystallized structure and the magnetic flux density will decrease, resulting in (880 + 50 × [% Si]) ° C.
This is because if it is higher than 1.0, a fine structure is generated due to A ₃ transformation, and the magnetic flux density tends to decrease. The cold rolling, the heat treatment to be performed thereafter, and the like may be performed under commonly used conditions.

[0049]

Example: 230 t of molten steel decarburized and desulfurized in a converter was tapped into a ladle, and the ladle was moved to an RH type vacuum degassing device.
After finishing decarburization treatment under reduced pressure at RH and setting the C content in molten steel to 0.004% or less, the S content in molten steel is 0.018%.
~ 0.021%, P content 0.089-0.092%, Mn content 0.2
Adjusted to 5 to 0.3%. After adjusting the components, Al and Si were added almost at the same time, and R (Al addition amount / Si addition amount) was changed in the range of 0.12 to 1.98. If the molten steel temperature is low,
Oxygen gas was applied and the temperature rising process was performed.

The molten steel after the above treatment was made into a slab (slab) by a continuous casting machine. This slab is heated to 1200 ° C in a heating furnace and hot-rolled at a finishing temperature of 860 to 870 ° C, with a thickness of 2.5 mm.
And Then, it was cold rolled to 0.5 mm and finish annealed at 770 ° C. After finishing annealing, an insulating film of about 0.2 μm was applied.

A 28 cm Epstein test piece was taken from this steel sheet, magnetically annealed at 750 ° C. for 2 hours in a nitrogen atmosphere, and then subjected to magnetic properties (iron loss W _15/50 by the method specified in JIS C 2550). ) Was measured, and at the same time, the composition of inclusions was examined by extracting inclusions in steel by the Br-methanol method and analyzing the elements contained therein.

Table 1 shows the measurement results of the chemical composition of steel (steel plate), R (Al addition amount / Si addition amount), MnO / FeO in inclusions and iron loss.

[0053]

[Table 1]

If it has the chemical composition defined by the electromagnetic steel sheet of the present invention of the above (1) and MnO / FeO is 2 or less,
It can be seen that the iron loss is small. Also, MnO / Fe
It has been confirmed that the condition that O is 2 or less can be achieved by the method of the present invention in which the mass ratio R of Al and Si added to the molten steel after finish decarburization is 0.85 or less.

[0055]

INDUSTRIAL APPLICABILITY The non-oriented electrical steel sheet of the present invention can be magnetically annealed to enhance the magnetic properties and stabilize the product performance. This electromagnetic steel sheet can be easily manufactured by the method of the present invention.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the content of SiO _{2 in} inclusions and iron loss.

FIG. 2 is a diagram showing a relationship between MnO content in inclusions and iron loss.

FIG. 3 is a diagram showing the relationship between the ratio of the content of MnO to the content of SiO _{2 in} the inclusions (MnO / SiO ₂ ) and the iron loss.

FIG. 4 is a diagram showing the relationship between the ratio of the content of MnO to the content of FeO in the inclusions (MnO / FeO) and the iron loss.

FIG. 5 is a diagram showing a relationship between a mass ratio of Al and Si (amount of Al added / amount of Si added) and MnO / FeO added during molten steel refining.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01F 1/16 H01F 1/16 A (72) Inventor Yoshihiko Higuchi 4-53-3 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal industry Co., Ltd. F term (reference) 4K013 AA04 BA08 BA14 EA19 EA28 FA02 5E041 AA02 CA02 CA04 NN01

Claims (2)

[Claims] 1. In mass%, C: 0.004% or less, Si: 0.1-1.
0%, Mn: 0.2-0.6%, sol.Al: less than 0.0006%, P: 0.0
3 to 0.2%, S: 0.035% or less, N: 0.004% or less, O: 0.
[0025] The content of MnO / FeO in the inclusions present in the steel (% by mass), MnO / FeO, is 2 or less. Non-oriented electrical steel sheet. 2. A method for producing a non-oriented electrical steel sheet using a slab as a raw material, which is obtained by roughly decarburizing in a converter, performing final decarburization in a vacuum degassing device, and then continuously casting molten steel whose composition has been adjusted. In addition, the mass ratio of Al and Si added to the molten steel after the final decarburization (added Al amount / added Si amount) is 0.85 or less, and the non-oriented electrical steel sheet according to claim 1, Production method.