JPH0625381B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a grain-oriented electrical steel sheet having {110} <001> as a main orientation.

[Conventional technology]

The grain-oriented electrical steel sheet is mainly used for the iron core of a transformer, and generally contains about 3% (weight%, the same below) of Si, which is excellent in rolling direction excitation characteristics and iron loss characteristics. Came.

However, in recent years, demands for magnetic characteristics have been diversified along with the diversification of electric devices, and severe conditions such as low cost and higher saturation magnetic flux density as compared with existing 3% Si products have come to be imposed. It was

Against this background, in recent years, low Si soft magnetic materials having a low carbon content have come to the spotlight. Low carbon,
The low Si material has a simpler manufacturing process for forming grain-oriented electrical steel sheets than the high Si materials described above, and has a high possibility of cost reduction, and in particular, the Si content is low in the magnetic flux density. Is expected to have very good performance.

However, on the other hand, it is said that it is extremely difficult to give a remarkable directionality to this kind of material, and in fact, in the technology of the commonly known range, a material that can be put to practical use in terms of magnetic properties is manufactured. It was impossible.

Therefore, there is a need for a technique capable of producing a grain-oriented electrical steel sheet having an extremely low carbon over a wide range of Si content including a low Si region (substantially 0 to 4%), and its development is desired. Came.

In order to meet this demand, the present inventors have previously found a method for producing a grain-oriented electrical steel sheet to which an extremely small amount of Al is added,
Proposed (JP-A-61-91329, JP-A-62-834)
No. 21, hereinafter referred to as a prior application). This is basically an extremely low temperature in the case of producing a grain-oriented electrical steel sheet by subjecting a hot-rolled steel sheet to annealing for performing primary recrystallization after cold rolling and finish annealing for performing secondary recrystallization. By adding an extremely small amount of Al to the carbon material steel and precipitating AlN in an appropriate shape and distribution before finish annealing, this is used as an inhibitor that suppresses the grain growth of primary recrystallized grains. This is to stably generate secondary recrystallization in annealing. In this method, decarburization annealing in the middle of the normally required steps can be omitted, and also finish annealing can generate secondary recrystallization by low temperature annealing in the α region, so that cost reduction is possible. is there. In addition, the fact that secondary recrystallization is possible by low-temperature annealing means that secondary recrystallization can occur without problems even in low-Si steel that cannot be annealed at high temperature due to the α-γ transformation. This is also a great advantage.

[Problems to be solved by the invention]

Although the method of the prior application is effective as described above, it has become clear from the subsequent experiments that it is not always satisfactory in practical use. That is, in this method, since the appropriate range of the Al content is narrow, it is difficult to adjust the Al amount in steel making, and it is practically difficult to maintain a good precision ratio. In addition, the stability of secondary recrystallization in finish annealing has a feeling that it is not enough, and is not always sufficient.

The present invention relates to an improvement of the method of the above-mentioned prior application, and provides a method for producing a grain-oriented electrical steel sheet which effectively eliminates the above-mentioned drawbacks while making use of the advantages of the method.

[Means for solving problems]

The inventors of the present invention applied A in steelmaking when applying the method of the prior application.
As a result of continuous experiments and research in order to find an effective means for improving the appropriate ratio and improving the stability of secondary recrystallization in finish annealing, the following findings were obtained.

It is necessary to stabilize the oxygen level in the molten steel at a low level in order to increase the appropriate ratio of Al. Then, as a means for stabilizing the oxygen level at a low level, the addition of Ti, which has a stronger deoxidizing power than Al, is effective.

The addition of Ti also effectively contributes to the stabilization of secondary recrystallization. However, if the added amount is too large, it becomes necessary to raise the secondary recrystallization temperature, which results in a cost reduction.

The present invention is based on the above findings and has as its gist the following manufacturing method.

C 0.01% or less, Si 4.0% or less, Mn 1.5% or less, P 0.2% or less, S 0.015% or less, Sol. A
0.003 to 0.015%, N 0.0010 to 0.0
100%, Ti 0.005 to 0.015%, the balance is F
e and a hot rolled steel sheet consisting of inevitable impurities,
With or without hot-rolled sheet annealing at 0 to 1000 ° C, one cold rolling or two or more cold rolling steps with intermediate annealing are performed to obtain the final sheet thickness, and then 650 to 950.
A method for producing a grain-oriented electrical steel sheet, which comprises performing continuous annealing at a temperature of 800 ° C. and then performing finish annealing at a temperature of 800 to 950 ° C. to cause secondary recrystallization.

Hereinafter, each constituent element of the present invention will be described specifically and in detail.

First, the reasons for limiting the steel composition of the hot-rolled steel sheet used are as follows.

C: When the amount of C in the steel exceeds 0.01%, unfavorable phenomena in magnetic characteristics such as deterioration of iron loss and deterioration of magnetic aging become remarkable. Therefore, C is set to 0.01% or less.

It should be noted that the lower the C value, the more advantageous it is in terms of magnetic properties, so the lower limit is not specified.

Incidentally, the conventional grain-oriented electrical steel sheet usually contains about 0.03 to 0.06% of C at the stage of the material (hot rolled sheet), which is the process after cold rolling. The amount of product C is reduced by decarburization annealing. C during the process
This is because it is thought that the inclusion will help improve the magnetism of the final product, but the present invention provides excellent magnetic properties without such inclusion of C, and it is necessary to include C in the raw steel. Absent. Rather, decarburization annealing, which is economically disadvantageous in order to reduce costs, is omitted, so decarburization is performed at the steelmaking stage to reduce the C content in advance to an extremely low value of 0.01% or less, which is the final C content. It is necessary to keep it.

Si: Si is an element that has a dominant influence on the magnetic properties. Generally, as the Si content increases, the iron loss tends to improve, and the saturation magnetic flux density tends to worsen.
The performance as an electromagnetic steel plate is basically determined by the selection of this Si content.

The present invention aims to obtain good magnetic properties over a wide range of Si content so as to meet various requirements, but cold rolling becomes difficult at Si 4.0%. Therefore, the upper limit of Si is set to 4.0%.

The lower limit is not specified so that a sufficiently high magnetic flux density can be realized if necessary.

Mn: Effective for adjusting hardness for improving punchability, and in this sense, it is particularly useful for low Si steel. Also S
Although not as great as i, it also has the effect of increasing the electrical resistance of the steel sheet and reducing the iron loss. However, if the content exceeds 1.5%, the product becomes brittle. Therefore, 1.5% was made the upper limit.

The lower limit is not specified because there is no particular problem in terms of magnetic properties even at the unavoidable impurity level.

P: Since it has the effect of increasing hardness and punching property,
It is useful in the case of low Si steel, but if it exceeds 0.2%, cold rolling property is impaired. From this, 0.2%
The upper limit was set to allow the addition.

The lower limit of P is not set because there is no particular problem with P inevitable impurity levels.

S: In the present invention, AlN is used as an inhibitor that suppresses crystal grain coarsening before secondary recrystallization. MnS is usually used as the inhibitor, but since it is not used as the main inhibitor, it is not necessary to add a large amount of S. Rather, the addition of a large amount of S leads to an increase in the secondary recrystallization temperature. From this, S was set to 0.015% or less.
The present invention does not prevent utilization of MnS as an auxiliary inhibitor by adding S within the range of 0.015% or less.

Sol. Al: an element necessary for forming AlN that suppresses the grain growth of primary recrystallized grains, and the definition of the amount of addition thereof has an extremely important meaning in the present invention.

If the content of Al is Sol. 0.003 to 0.01 in terms of Al amount
Below 5%, the absolute amount of AlN as an inhibitor is insufficient and no sufficient effect can be expected, while above 5%, the amount of inhibitor becomes too large and the distribution This is because the morphology is not suitable and stable secondary recrystallization cannot be obtained by low temperature finish annealing.

N: An element that is indispensable for forming AlN as an inhibitor, and is required to be at least 0.0010% or more in that sense. However, if the content exceeds 0.0100%, it is meaningless in terms of inhibitor effect. Therefore, N is set to 0.0010 to 0.0100%.

Ti: A component characterizing the present invention. As described above, Ti is used for improving the Al suitability in steelmaking and for ensuring the stability of secondary recrystallization during finish annealing.

FIG. 1 shows the results of investigating the influence on the magnetic characteristics (magnetic flux density) by changing the Ti amount. The test material is C0.002
%, Si 0.8%, Mn 0.25%, P 0.013%,
S 0.005%, Sol. Al 0.006-0.008
%, N 0.0030 to 0.0036% with various amounts of Ti, and 2.1 mm thick hot-rolled sheet of such composition was cold-rolled to 0.35 mm thickness and then at 750 ° C. for 20 minutes. After continuous annealing for 25 seconds, 85% in an atmosphere of 25% H ₂ + 75% N ₂
It is the result of investigating the magnetic flux density in the rolling direction of the obtained annealed material by performing finish annealing at 0 ° C. for 10 hours.

When the Ti addition amount is in the range of 0.005 to 0.02%,
The magnetic flux density is stable at a high level. This is {11
This is because secondary recrystallization having 0} <001> as the main orientation was stably generated. Although the stabilization of such secondary recrystallization has not been fully clarified yet, an appropriate amount of Ti or carbonitrides or sulfides of Ti cooperates with AlN as a main inhibitor to produce an appropriate primary recrystallized grain. It is considered that this is because the grain growth suppressing effect is exerted, and the secondary recrystallization is stably generated in annealing at a relatively low temperature of 850 ° C.

In the figure, when the Ti content is less than 0.005%,
A large variation in magnetic flux density was observed, while 0.02%
There is no variation in the magnetic flux density in the range of the voice,
The value itself is low. This is because if it is less than 0.005%, the distribution and amount of AlN as an inhibitor cannot be stably obtained, and if it is 0.02%, the grain growth suppressing effect of the primary recrystallized grains becomes too strong, and 850 It is considered that this secondary recrystallization did not occur in the low temperature annealing at about ℃.

From the following, Ti is set to a range of 0.005 to 0.02%.

It should be noted that Ti alone has no significant effect on iron loss in the amount of the steel of the present invention when Ti alone is used. However, in the range of the present invention, secondary recrystallization is stably generated, so that the iron loss is reduced.

Ti also contributes to the improvement of the appropriateness ratio of Al in steel making, but this is because the added Ti fixes oxygen in the molten steel and stabilizes the level of free oxygen at a low level, and as a result, the stopping ratio of added Al becomes stable. It is due to Such an effect is
It will be fully exhibited at the Ti level of 0.005 to 0.01%.

○ Next, the manufacturing process will be described.

The method of the present invention basically uses a hot-rolled steel sheet that conforms to the above-mentioned component conditions, cold-rolls this, and then performs continuous annealing (annealing after cold rolling), followed by finish annealing. Then, if necessary, annealing at the stage of hot-rolled sheet is added.

Each step will be described below.

Annealing of hot-rolled sheet If the Si content in the material steel exceeds 1.5%, the problem of ridging occurs.

Hot-rolled sheet annealing is to cope with this, and is performed as necessary. The hot-rolled sheet annealing is preferably continuous annealing.

Regarding the annealing temperature, if it is less than 700 ° C, the effect of preventing ridging is not sufficient, and if it exceeds 1000 ° C, the grain size becomes coarse and it becomes difficult to carry out cold rolling. Therefore, 700-10
It should be in the range of 00 ° C.

The process for obtaining the hot rolled sheet is not particularly limited. The conventional method is to go through the processes of converter melting, continuous casting, and hot rolling, but the same process can be applied to the present invention.

Cold rolling One or two or more cold rollings are performed. When the rolling is performed twice, an intermediate annealing step for softening is sandwiched between cold rolling. The condition of the intermediate annealing is 700 to 95.
0 ° C is common.

○ Annealing after cold rolling In order to generate stable secondary recrystallization, an appropriate state (distribution and morphology) of AlN as an inhibitor and a primary recrystallization texture are required. This is achieved by annealing after cold rolling.

The annealing after cold rolling requires rapid heating annealing, and continuous annealing is suitable for this.

As the annealing condition, it is desired that the heating rate is 5 ° C./S or more. If the annealing temperature is less than 650 ° C., the effect of annealing cannot be obtained, and if it exceeds 1000 ° C., problems occur in the distribution of AlN and the grain size of primary recrystallization. Therefore, in the present invention, the range is limited to 650 to 1000 ° C. It should be noted that this annealing needs to be in the α region, so the upper limit temperature of the low Si steel is determined by the α-γ transformation temperature,
In some cases, the temperature is below ℃.

○ Finishing Annealing In the present invention, stable secondary recrystallization is caused by finishing annealing at a low temperature by optimizing the components, and in the finishing annealing, so-called purification annealing at a high temperature of 1000 ° C or higher is not performed. This leads to cost reduction.

If the temperature of this finish annealing is less than 800 ° C., sufficient secondary recrystallization does not occur, and good magnetic properties cannot be expected. Again 9
Not only is annealing above 50 ° C. unnecessary, but the cost also rises. Further, in the case of low Si steel, it may be in the γ region at 950 ° C or higher, and at this time, secondary recrystallization does not occur. Therefore, the annealing temperature is 800 to 95.
Specified at 0 ° C.

〔Example〕

For the hot rolled sheets of various components shown in Table 1, cold rolling under the conditions shown in the table → continuous annealing → finish annealing (atmosphere: No. 1 to 10 is 5
0% H ₂ + 50% N ₂ , Nos. 11 to 16 are 25% H ₂ +
75% N ₂ , Nos. 17 and 18 are 75% H ₂ + 25% N ₂
Annealing for 4 h in the initial soaking, then soaking is 100% H
Switched to ₂ . ) Was given. However, for Nos. 17 and 18, hot-rolled sheet annealing was performed under the conditions shown in the table before cold rolling.

The magnetic properties (iron loss, magnetic flux density) in the rolling direction of the obtained finished annealed material were measured. The measurement is JIS C255
It depends on 0.

The results are shown in the right column of the table.

The test results will be described.

○ Nos. 1 to 4 are examples in which the finish annealing temperature was changed with the same composition (within the range of the present invention). It ’s off. ”
No. 1 and No. 4 are significantly inferior in iron loss and magnetic flux density as compared with the proper Inventive Examples Nos. 2 and 3 at the same temperature. This is because the secondary recrystallization did not occur. In the case of No. 4, since the annealing was the γ region annealing, the secondary recrystallization did not occur.

○ No. 5 is an example of the present invention in which the Si content is 0.3%, and Si0.1
%, The magnetic flux density is slightly lower than that of the present invention examples Nos. 2 and 3, but the core loss is better by that amount. Magnetic properties with a higher level of balance of both properties are obtained.

○ In No. 6 to No. 9, the manufacturing conditions were fixed within the scope of the present invention and Sol. In the example in which only the amount of Al is changed, Sol. No. 6 in which the amount of Al deviates from a low level and No. 9 in which the amount of Al deviates from a high level, secondary recrystallization is not obtained, and magnetic properties (iron loss, magnetic flux density) are higher than those of Inventive Examples Nos. 7 and 8. It was markedly inferior.

○ No. 10 is an example of the present invention having a Si content of 0.6%. When this is also compared with examples 2 and 3 of the present invention, the magnetic flux density is slightly lower, but the iron loss is improved, The overall performance is high.

○ Nos. 11 to 16 are those in which the amount of Ti added was changed while keeping other conditions constant. Insufficient, it was not possible to obtain good iron loss and magnetic flux density as in Invention Examples Nos. 12 to 15.

○ No. 17 and 18 have a Si content of 2.1%,
This is an example of the present invention of 3.2%. For example, when compared with the example 14 of the present invention in which the amount of Si is 0.8%, the magnetic flux density tends to be somewhat low, but a considerable improvement is recognized in the iron loss. Good magnetic properties are realized.

〔The invention's effect〕

As is clear from the above description, the method of the present invention has a low Si content.
It is possible to stably manufacture a high-performance grain-oriented electrical steel sheet having good iron loss and magnetic flux density over a wide range including the region. Moreover, by adding Ti to the raw material steel, it becomes possible to maintain the appropriate ratio of Al at the time of steelmaking.

[Brief description of drawings]

FIG. 1 is a plot diagram showing the results of investigating the influence of Ti on the magnetic flux density.

Claims (2)

[Claims] 1. C. 0.01% or less by weight%, Si4.0
% Or less, Mn 1.5% or less, P 0.2% or less, S0.0
15% or less, Sol. Al 0.003 to 0.015%,
N 0.0010-0.0100%, Ti 0.005-
A hot-rolled steel sheet with 0.02% and the balance being Fe and inevitable impurities is made into a final sheet thickness by one cold rolling or two or more cold rolling steps with intermediate annealing, and then 650 to 1
Perform continuous annealing at 000 ° C, then 800-950
A method for manufacturing a grain-oriented electrical steel sheet, which comprises subjecting a secondary annealing to a secondary annealing at ℃. 2. Hot-rolled steel sheet 700-1000 before cold rolling
The method for producing a grain-oriented electrical steel sheet according to claim 1, characterized in that annealing is performed at ℃.