JP2006104530A - Method for producing nonoriented silicon steel sheet having excellent magnetic property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonoriented silicon steel sheet having higher magnetic flux density and lower core loss compared with those of the conventional one. <P>SOLUTION: The nonoriented silicon steel sheet is produced by subjecting a steel having a composition comprising, by mass, 0.01 to 0.2% C, ≤3% Si, 0.05 to 3.0% Mn, ≤1% Al and ≤0.005% N, and P, S and Se restrained into the range satisfying the inequality of P+100×S+300×Se≤0.5, and the balance Fe with inevitable impurities to a series of steps of hot rolling, hot rolled sheet annealing, rolling to a final sheet thickness and decarburizing annealing and finish annealing, wherein the hot rolled sheet annealing is performed in the temperature range of an Ac<SB>3</SB>point or higher. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an advantageous method for producing a non-oriented electrical steel sheet suitable for use in a motor, an EI core iron core material, and the like.

  In recent years, with increasing needs for energy saving, there is an increasing demand for higher motor efficiency. In order to achieve high motor efficiency, it is essential to improve the performance of the electrical steel sheet used as the core material. Therefore, there is a strong demand for electrical steel sheets with higher magnetic flux density and lower iron loss than ever before. ing.

In order to increase the magnetic flux density of the electrical steel sheet, it is effective to coarsen the crystal grains before cold rolling, and therefore a technique for performing annealing by imparting a skin pass to the hot-rolled steel sheet (for example, Patent Document 1). Or the technique (for example, patent document 2) which performs high temperature winding after hot rolling and performs self-annealing with the heat which a steel strip holds is proposed.
In addition, a technique (for example, Patent Document 3) for improving magnetic properties by causing secondary recrystallization before cold rolling to make crystal grains coarse has been proposed.

Japanese Examined Patent Publication No. 45-22211 Japanese Patent Publication No.57-43132 JP-A-3-21258

However, in recent years, a material having a higher magnetic flux density has been demanded from the strong demand for higher motor efficiency as described above.
The present invention was developed in view of the above-mentioned actual situation, and an object thereof is to provide an advantageous method for producing a non-oriented electrical steel sheet having a high magnetic flux density and a low iron loss as compared with the prior art and excellent in magnetic properties. And

As a result of intensive studies to solve the above problems, the inventors have obtained the following knowledge.
(a) Conventionally, from the viewpoint of magnetic properties, it was better that the amount of C in steel was small. However, according to the study by the inventors, rather, the amount of C in steel was rather increased, and hot-rolled sheet A structure in which cementite is finely dispersed in ferrite during annealing is advantageous for improving magnetic properties.
(b) Moreover, if P, S, and Se in steel are regulated to an appropriate range, stable decarburization annealing becomes possible, and aging deterioration of iron loss is effectively suppressed.
(c) Furthermore, when combined with warm rolling, the magnetic flux density is further improved.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
(1) In mass%,
C: 0.01-0.2%
Si: 3% or less,
Mn: 0.05-3.0%
Al: 1% or less and N: 0.005% or less, and P, S and Se are represented by the following formula:
P + 100 × S + 300 × Se ≦ 0.5
A series of steel materials with a composition of Fe and inevitable impurities in the balance, hot-rolled, hot-rolled sheet annealed, rolled to the final thickness, and then decarburized and finish annealed. A method for producing a non-oriented electrical steel sheet having excellent magnetic properties, characterized by performing hot-rolled sheet annealing in a temperature range of Ac ₃ or higher when producing a non-oriented electrical steel sheet by a process.

(2) In mass%,
C: 0.01-0.2%
Si: 3% or less,
Mn: 0.05-3.0%
Al: 1% or less and N: 0.005% or less, and P, S and Se are represented by the following formula:
P + 100 × S + 300 × Se ≦ 0.5
A series of steel materials with a composition of Fe and inevitable impurities in the balance, hot-rolled, hot-rolled sheet annealed, rolled to the final thickness, and then decarburized and finish annealed. When producing non-oriented electrical steel sheets by the process, the hot rolling annealing is performed in the temperature range of Ac ₃ points or higher, and then the hot rolling is performed in the temperature range of 70 to 400 ° C. A method for producing an excellent non-oriented electrical steel sheet.

(3) In the above (1) or (2), the decarburization annealing is performed under conditions of dew point: 10 to 40 ° C., annealing temperature: 700 to 900 ° C., and annealing time: 30 to 3600 s. A method for producing a non-oriented electrical steel sheet having excellent characteristics.

  According to the present invention, a non-oriented electrical steel sheet having a high magnetic flux density and a low iron loss can be obtained. Therefore, when the electrical steel sheet of the present invention is used, for example, high efficiency induction motors and high efficiency of EI cores can be obtained. Greatly contribute to

Hereinafter, the experimental results that led to the present invention will be described. Unless otherwise specified, “%” in relation to ingredients means mass%.
First, in order to investigate the influence of hot-rolled sheet annealing conditions on magnetic flux density, C: 0.02%, Si: 0.35%, Mn: 0.05%, Al: tr, N: 0.002%, P: 0.05%, S: 0.0020 % And Se: tr, with the balance being Fe and inevitable impurities, steel is vacuum melted, hot-rolled, and then annealed at 800 to 1150 ° C. for 30 s, and then the thickness: Cold-rolled (25 ° C.) to 0.5 mm. Subsequently, decarburization annealing was performed in an atmosphere of 20 vol% H ₂ −80 vol% N ₂ , dew point: 35 ° C. and 800 ° C. for 60 s, and further 850 ° C. and 10 s in a 25 vol% H ₂ −75 vol% N ₂ atmosphere. Finish annealing was performed.

In FIG. 1, the result of having investigated about the relationship between hot-rolled sheet annealing temperature and magnetic flux density is shown.
It can be seen from the figure that the magnetic flux density is greatly improved when the hot-rolled sheet annealing temperature is 1000 ° C. or higher.

In order to investigate this cause, the structure of the steel sheet after hot-rolled sheet annealing was observed.
As a result, in the material subjected to hot-rolled sheet annealing at a temperature of 1000 ° C. or higher, prior austenite grain boundaries were observed, and a structure in which cementite was finely dispersed in ferrite was obtained.
From the results of such structure observation, it is considered that the structure was austenite at the hot-rolled sheet annealing stage at 1000 ° C. or higher.

Therefore, the Ac ₃ transformation point of this material was investigated by measuring the coefficient of thermal expansion during a temperature rise of 30 ° C./s using a Formaster tester. As a result, the Ac ₃ point of this material was found to be 1000 ° C.
From this, the above-mentioned structure is austenite region at the time of hot-rolled sheet annealing by performing hot-rolled sheet annealing at Ac ₃ points or more, and it becomes finer due to a decrease in the solubility amount of C accompanying γ → α transformation at the time of cooling. It is thought that a lot of cementite was precipitated.

The reason why the magnetic flux density is improved by annealing a material containing a relatively large amount of C under the above conditions is not clearly clarified, but there is a second phase of cementite. Thus, recrystallization from around the cementite occurs, and it is considered that a texture favorable to the magnetic flux density was formed.
Such cementite is once dissolved in steel by subsequent decarburization annealing and then removed from the steel.

Next, the inventors examined C: 0.002 to 0.2%, Si: 0.35%, Mn: 0.2%, Al: tr, N: 0.002%, P: 0.05%, S in order to investigate an appropriate amount of C. : Steel containing 0.0020% and Se: tr, the balance being Fe and inevitable impurities, vacuum-melted, hot-rolled and annealed at 1150 ° C for 30s, then cold rolled (25 ° C.) and warm rolling (150 ° C.), respectively, to a thickness of 0.5 mm. Subsequently, according to the amount of C, decarburization annealing is performed in an atmosphere of 20 vol% H ₂ −80 vol% N ₂ , dew point: 35 ° C. at 800 ° C. for 60 to 1200 s, and further 25 vol% H ₂ −75 vol% N ₂ Finish annealing was performed at 850 ° C for 10 s in the atmosphere.

FIG. 2 shows the results of examining the influence of the C amount of hot-rolled sheet and the rolling temperature after hot-rolled sheet annealing (hereinafter referred to as final rolling temperature) on the magnetic flux density.
First, focusing on the C content of the hot-rolled sheet, it can be seen that the magnetic flux density is improved when the C content is 0.01% or more. The reason for this is considered to be that when the C content is less than 0.01%, cementite that affects the texture does not precipitate even when hot-rolled sheet annealing is performed at the Ac ₃ transformation point or higher.
Next, focusing on the final rolling temperature, it can be seen that the magnetic flux density is further improved by performing warm rolling.

Then, in order to investigate the influence of the final rolling temperature on the magnetic flux density, the inventors next made C: 0.02%, Si: 0.35%, Mn: 0.18%, Al: tr, N: 0.0018%, P: 0.05. %, S: 0.0020% and Se: tr, with the balance being Fe and inevitable impurities, steel was melted in vacuum, hot-rolled, and then annealed at 1150 ° C for 30s, Sheet thickness: Rolling was performed at a rolling temperature of 20 to 400 ° C. to 0.5 mm. Subsequently, decarburization annealing was performed in an atmosphere of 20 vol% H ₂ -80 vol% N ₂ , dew point: 35 ° C. at 800 ° C. for 60 s, and further 850 ° C., 10 s in a 25 vol% H ₂ -75 vol% N ₂ atmosphere. Finish annealing was performed.

FIG. 3 shows the result of examining the relationship between the final rolling temperature and the magnetic flux density.
As shown in the figure, it can be seen that the magnetic flux density is greatly improved by setting the rolling temperature to 70 ° C. or higher.
Thus, the reason why the magnetic flux density is improved by making the final rolling warm is considered to be that a texture favorable to magnetic properties has developed due to dynamic strain aging during rolling.

  By the way, since the El core, the motor, etc. are used for a long period of 10 years or more, it is necessary that the magnetic characteristics do not change with time. As the time-dependent change of the electromagnetic steel sheet, there is a magnetic aging in which C in the steel precipitates as cementite during long-term use, thereby inhibiting the domain wall movement and increasing the iron loss. For this evaluation, an aging treatment is generally performed at 150 ° C. for about 100 hours, and the iron loss after the aging treatment is measured and judged.

Then, in order to investigate the change with time of the steel sheet, C: 0.03%, Si: 0.33%, Mn: 0.2%, Al: tr, N = 0.002%, P: 0.11%, Se: tr and S: 0.003% Steel grade A and S: 0.005% steel grade B were vacuum melted, hot-rolled and then subjected to hot-rolled sheet annealing at 1150 ° C for 30 seconds, and then plate thickness: 0.5 ° C to 150 ° C And warm rolling. Subsequently, decarburization annealing was performed in an atmosphere of 20 vol% H ₂ -80 vol% N ₂ , dew point: 35 ° C. at 800 ° C. for 60 s, and further 850 ° C., 10 s in a 25 vol% H ₂ -75 vol% N ₂ atmosphere. Finish annealing was performed.

Thereafter, each steel plate obtained was subjected to an aging treatment at 150 ° C. for 100 hours, and then the iron loss was measured. In each steel sheet, the iron loss W _15/50 before aging treatment was 4.4 W / kg.
As a result, the iron loss W _15/50 of steel type A was 4.5 W / kg, while the iron loss W _15/50 of steel type B was deteriorated to 5.4 W / kg.

From this, it can be seen that in steel type B, the iron loss is remarkably increased by the aging treatment.
When investigating the material structure to investigate this cause, fine cementite was observed in steel type B, the precipitation of cementite was the cause of the deterioration of the magnetic properties, and cementite was precipitated during the aging treatment. It became clear that
In addition, as a result of component analysis of the product plate, it was found that steel type B had a C content of 0.007% and was not fully decarburized.

The cause of the decarburization failure in the steel with high S as described above is considered as follows.
That is, since S is an element that is easily segregated, S segregates around the cementite precipitated during hot-rolled sheet annealing, delays the solid solution of cementite during decarburization annealing, and the surface segregated S It is considered that decarburization did not sufficiently proceed because the adsorption of oxygen to the steel was suppressed and the oxidation reaction of C in the steel did not proceed.
Even in such a state, the cementite remaining by the subsequent high-temperature finish annealing is dissolved in the steel, so that no adverse effects due to the decarburization failure appear immediately after the finish annealing. However, if used for a long period of time, the solid solution C precipitates as cementite in the steel, so the magnetic properties deteriorate.

From this, there is a concern that segregation-type elements other than S, such as P and Se, inhibit the decarburization reaction.
Then, in order to investigate about the relationship between the amount of S, P, Se and the iron loss after aging treatment, the inventors then made C: 0.03%, Si: 0.32%, Mn: 0.18%, Al: tr, N: 0.002% steel with various changes of S, P, Se was vacuum melted, hot-rolled, and then subjected to hot-rolled sheet annealing at 1150 ° C for 30s. Then, warm rolling was performed. Subsequently, decarburization annealing was performed in an atmosphere of 20 vol% H ₂ -80 vol% N ₂ , dew point: 35 ° C. at 800 ° C. for 60 s, and further 850 ° C., 10 s in a 25 vol% H ₂ -75 vol% N ₂ atmosphere. After finishing annealing, after further aging treatment at 150 ° C. for 100 hours, the iron loss was measured.

FIG. 4 shows the result of examining the relationship between the amount of S, P, Se and iron loss, with (P + 100 × S + 300 × Se) as a parameter.
As shown in the figure, it is understood that the iron loss is reduced when the parameter (P + 100 × S + 300 × Se) is 0.5 or less.
The reason for this is considered to be that by reducing these elements, cementite is easily dissolved in steel during decarburization annealing, and decarburization proceeds.

Next, the preferred component composition range of the steel in the present invention will be described.
C: 0.01 to 0.2%
In the present invention, at the time of hot-rolled sheet annealing, at least 0.01% of C is required in order to finely disperse cementite in ferrite and form a texture suitable for magnetic flux density. Preferably it is 0.15% or more. However, if the amount of C exceeds 0.2%, it takes a long time for decarburization and unnecessarily increases the cost. Therefore, the upper limit of the amount of C is set to 0.2%.

Si: 3% or less
Si is an effective element for increasing the specific resistance of the steel sheet, but if it exceeds 3%, not only annealing beyond the Ac ₃ point becomes difficult, but the deformation resistance of the hot-rolled sheet increases and cold rolling is performed. Becomes difficult. For this reason, the upper limit of the amount of Si was made into 3%.

Mn: 0.05-3.0%
Mn needs to be contained in an amount of 0.05% or more in order to prevent red hot brittleness during hot rolling. However, if it exceeds 3.0%, the magnetic flux density is lowered, so 0.05 to 3.0% was set.

Al: 1% or less
Al, like Si, is an effective element for increasing the specific resistance. However, if it exceeds 1%, the Ac ₃ point becomes high, and it becomes difficult to anneal in the austenite region in hot-rolled sheet annealing. Was 1%. In addition, this Al can also be abbreviate | omitted as needed.

N: 0.005% or less N is 0.005% or less because if N exceeds 0.005%, the amount of nitride increases and iron loss increases.

(P + 100 × S + 300 × Se) ≦ 0.5
As shown in FIG. 4, when the amount of S, P, and Se in the steel exceeds 0.5 by the parameter (P + 100 × S + 300 × Se), decarburization does not proceed stably, and as a result, sufficiently low iron Since it is difficult to obtain a loss, the amount of S, P, and Se is limited to 0.5 or less by a parameter (P + 100 × S + 300 × Se).

Although the basic components have been described above, in the present invention, Sb, Sn, Ni, Cr, Co, Cu, and the like can be appropriately added from the viewpoint of improving the magnetic characteristics.
The preferable addition range of these elements is as follows.
Sb: 0.005-0.05%
Sn: 0.005-0.1%
Ni: 0.1-5%
Cr: 0.5-5%
Co: 0.1-10%
Cu: 0.01 to 1%

Next, the manufacturing method of the non-oriented electrical steel sheet according to the present invention will be described.
The non-oriented electrical steel sheet of the present invention is not particularly limited as long as the components, hot-rolled sheet annealing conditions, and warm-rolling conditions are within a predetermined range, and may be a normal method.
That is, in order to obtain the steel sheet of the present invention, the molten steel blown in the converter is degassed and adjusted to a predetermined component, followed by casting and hot rolling. At this time, the finish annealing temperature and the coiling temperature at the time of hot rolling do not need to be particularly defined, and may be normal.

Next, hot rolling is performed after hot rolling. This hot-rolled sheet annealing temperature is set to a temperature equal to or higher than the Ac ₃ transformation point determined by the components.
This is because, if the hot-rolled sheet annealing temperature is lower than the Ac ₃ transformation point, as shown in FIG. 1, good magnetic flux density improvement cannot be expected. Although the upper limit of the hot-rolled sheet annealing temperature is not particularly limited, it is preferable to set the temperature to about 1250 ° C. or less because annealing at an excessively high temperature unnecessarily increases costs.
Moreover, although the hot-rolled sheet annealing time is not particularly limited, a stable structure before cold (warm) rolling can be obtained by annealing for 10 seconds or more.

Subsequently, the steel sheet is rolled to the final thickness in the cold or warm state, and the magnetic flux density can be further improved by rolling at a particularly high temperature of 70 to 400 ° C.
That is, as shown in FIG. 3, the magnetic flux density is greatly improved when the rolling temperature is 70 ° C. or higher. Therefore, the lower limit of the temperature during warm rolling was set to 70 ° C. More preferably, it is 100 ° C. or higher. Note that even if the warm rolling temperature exceeds 400 ° C., there is an effect of improving the magnetic flux density, but since the cost is unnecessarily increased, the upper limit of the temperature during the warm rolling is set to 400 ° C.

Then, after performing decarburization annealing according to the amount of C in steel, finish annealing for obtaining predetermined magnetic properties is performed to obtain a product. Here, suitable conditions for decarburization annealing are annealing temperature: 700 to 900 ° C., annealing time: 30 to 3600 s, and dew point: 10 to 40 ° C.
This is because if the decarburization annealing temperature is less than 700 ° C., decarburization is insufficient, while if it exceeds 900 ° C., internal oxidation proceeds and causes an increase in iron loss.
Further, if the decarburization annealing time is less than 30 s, decarburization is insufficient, while if it exceeds 3600 s, the cost is unnecessarily increased.
Furthermore, if the dew point is less than 10 ° C, decarburization becomes insufficient. On the other hand, if it exceeds 40 ° C, internal oxidation proceeds and iron loss increases.

Steels with the composition shown in Table 1 were melted by converter blowing and degassing, and after continuous casting, the resulting slab was heated at 1200 ° C for 1 h, and then hot rolled to a thickness of 2.6 mm. did. The hot rolling finishing temperature was 830 ° C and the winding temperature was 610 ° C.
Next, after hot-rolled sheet annealing under the conditions shown in Table 2, the sheet thickness is rolled to cold (25 ° C) or warm (50-350 ° C) to 0.5 mm, and then decarburized under the conditions shown in Table 2 as well. Annealing and finish annealing were performed to obtain a non-oriented electrical steel sheet.
The magnetic properties were obtained for the magnetic steel sheet thus obtained. Magnetic measurement was performed using a 25 cm Epstein test piece.
In addition, after the magnetic measurement, after aging treatment at 150 ° C. for 100 hours, the magnetic measurement was performed again.
The obtained measurement results are also shown in Table 2.
In addition, Ac ₃ point in a table | surface was calculated | required by measuring the thermal expansion coefficient at the time of heating a sample at 30 degrees C / s with a four master test machine.

As is clear from Table 2, all of the invention examples in which the steel components and the hot-rolled sheet annealing conditions were controlled within the appropriate range of the present invention were obtained in combination with a high magnetic flux density and a low iron loss. When warm rolling was used, even better magnetic properties could be obtained.
On the other hand, in any of the comparative examples in which one or both of the steel component and the hot-rolled sheet annealing condition deviate from the appropriate range of the present invention, at least either the magnetic flux density or the iron loss is not sufficient, and compared with the inventive example. Only inferior magnetic properties were obtained.

It is a figure which shows the relationship between hot-rolled sheet annealing temperature and magnetic flux density. It is a figure which shows the relationship between C amount in steel, and magnetic flux density. It is a figure which shows the relationship between final rolling temperature and magnetic flux density. It is a figure which shows the relationship between the amount of S, P, and Se and the iron loss after an aging treatment by using (P + 100 * S + 300 * Se) as a parameter.

Claims (3)

% By mass
C: 0.01-0.2%
Si: 3% or less,
Mn: 0.05-3.0%
Al: 1% or less and N: 0.005% or less, and P, S and Se are represented by the following formula:
P + 100 × S + 300 × Se ≦ 0.5
A series of steel materials with a composition of Fe and inevitable impurities in the balance, hot-rolled, hot-rolled sheet annealed, rolled to the final thickness, and then decarburized and finish annealed. A method for producing a non-oriented electrical steel sheet having excellent magnetic properties, characterized by performing hot-rolled sheet annealing in a temperature range of Ac ₃ or higher when producing a non-oriented electrical steel sheet by a process. % By mass
C: 0.01-0.2%
Si: 3% or less,
Mn: 0.05-3.0%
Al: 1% or less and N: 0.005% or less, and P, S and Se are represented by the following formula:
P + 100 × S + 300 × Se ≦ 0.5
A series of steel materials with a composition of Fe and inevitable impurities in the balance, hot-rolled, hot-rolled sheet annealed, rolled to the final thickness, and then decarburized and finish annealed. When producing non-oriented electrical steel sheets by the process, the hot rolling annealing is performed in the temperature range of Ac ₃ points or higher, and then the hot rolling is performed in the temperature range of 70 to 400 ° C. A method for producing an excellent non-oriented electrical steel sheet.   3. Non-directional excellent in magnetic characteristics, characterized in that decarburization annealing is performed under conditions of dew point: 10 to 40 ° C., annealing temperature: 700 to 900 ° C., and annealing time: 30 to 3600 s. Method for producing an electrical steel sheet.

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