JPH0649607A - Grain-oriented silicon steel sheet and its production - Google Patents

Abstract

PURPOSE:To provide a grain-oriented silicon steel sheet low in core loss and to provide its producing method. CONSTITUTION:(1) The grain-oriented silicon steel sheet contains <=0.01% C, 2.0 to 3.0% Si, >3.0 to 4.0% Mn, <=0.01% S, 0.003 to 0.015% acid soluble Al and <=0.010% N. (2) The steel slab in (1) (the content of N is regulated to 0.001 to 0.010%) is treated by the following steps of executing hot rolling; subjecting it to cold rolling for one or >=two times including process annealing as is hot- rolled or after being subjected to annealing after the hot rolling; allowing primary recrystallization to occur by continuous annealing; holding it to 825 to 925 deg.C for 7 to 100hr and allowing secondary recrystallization to occur; and holding it to >925 to 1050 deg.C for 4 to 100hr and purifying it. The grain-oriented silicon steel sheet low in core loss can be produced. Furthermore, the stock of this silicon steel sheet is excellent in cold workability as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented electrical steel sheet widely used as a core material for transformers, generators and electric motors, and a method for manufacturing the grain-oriented electrical steel sheet.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are soft magnetic materials having a crystal orientation mainly called {110} <001> orientation called Goss orientation and having extremely excellent excitation characteristics and iron loss characteristics in the rolling direction. is there. This material is generally manufactured through the following steps. A slab of low carbon steel containing about 3.0% of Si is hot-rolled and then annealed (annealed hot-rolled sheet) and then cold-rolled once or twice with an intermediate annealing. After the final plate thickness, continuous decarburization annealing is performed to perform primary recrystallization, then an annealing separator is applied to prevent seizure, and the coil is wound up and further 1100 to 1200 ° C.
Finish annealing at ultra high temperature.

The purpose of finish annealing is to generate secondary recrystallization to form a texture that is integrated in the Goss orientation, and to precipitate precipitates called inhibitors (nitriding) used to generate secondary recrystallization. Thing). In the present invention, the former is called the first finish annealing, and the latter is called the second finish annealing. The second finish annealing for removing this precipitate is
It is also called purification annealing, and can be said to be an essential step in order to obtain good magnetic properties together with the first finish annealing that causes secondary recrystallization.

The grain-oriented electrical steel sheet produced by the above production method requires a special process such as continuous decarburization annealing or ultra-high temperature finish annealing at 1100 ° C. or more in the production process, which is extremely costly. It will be expensive.

In order to solve this cost problem, various researches and developments have been made in the past.

For example, the present inventors have previously described that the chemical composition is Si: 0.5 to 2.5%, Mn: 1.0 to 2.0%, sol.Al: 0.003 to
0.015%, C: 0.01% or less, N: 0.001 to 0.010%
The inventors have invented a grain-oriented electrical steel sheet which is mainly characterized by containing, and a method for producing the grain-oriented electrical steel sheet, which enables low-temperature annealing without the need for decarburizing annealing (see Japanese Patent Laid-Open No. 1-119644). This method
Omission of continuous decarburization annealing and reduction of finish annealing temperature can greatly contribute to the reduction of the manufacturing cost of grain-oriented electrical steel sheet.

[0007]

In recent years, with the trend of energy saving to be further enhanced, it has been strongly demanded that the core loss of grain-oriented electrical steel sheets be further reduced.

An object of the present invention is to provide a grain-oriented electrical steel sheet having a low iron loss and a method for producing the same, which aims to further improve the electrical steel sheet and the method for producing the same disclosed in JP-A-1-119644. With the goal.

[0009]

The gist of the present invention resides in the grain-oriented electrical steel sheet and its manufacturing method as described below.

(1) By weight%, C: 0.01% or less, Si: 2.0-
3.0%, Mn: more than 3.0% to 4.0%, S: 0.01% or less,
An grain-oriented electrical steel sheet comprising acid-soluble Al: 0.003 to 0.015% and N: 0.010% or less, and the balance being Fe and inevitable impurities.

(2)%: C: 0.01% or less, Si: 2.0-
3.0%, Mn: more than 3.0% to 4.0%, S: 0.01% or less,
Acid-soluble Al: 0.003 to 0.015% and N: 0.001 to 0.010%
A method for producing a grain-oriented electrical steel sheet, comprising: treating a slab of steel containing Fe and unavoidable impurities in the balance in the following steps.

The step of performing hot rolling, as hot rolling, or after annealing after hot rolling,
A step of performing cold rolling once or twice or more with intermediate annealing sandwiched between them, a step of causing primary recrystallization by continuous annealing, and a secondary recrystallization that is maintained at a temperature range of 825 to 925 ° C for 7 to 100 hours. The first finish annealing step to be caused to occur, and the second finish annealing step of purifying by holding in the temperature range above 925 ° C and up to 1050 ° C for 4 to 100 hours.

Iron loss is roughly divided into two types of loss components, hysteresis loss and eddy current loss, and reduction of iron loss is achieved by reducing these two iron loss components. In order to reduce the hysteresis loss, it is effective to increase the degree of integration in the Goss orientation and reduce the content of impurities. On the other hand, in order to reduce the eddy current loss, it is effective to increase the specific resistance of the steel plate and reduce the plate thickness. However, with regard to the improvement of the degree of integration in the Goth direction and the reduction of the content of impurities, the improvement has been progressing to the point of almost the limit. Although there is still room for iron loss improvement due to thinner sheet thickness, higher manufacturing costs cannot be avoided with thinner sheet thickness.

The increase in resistivity is generally made by increasing the Si content. However, if the Si content is increased, the cold workability of the steel sheet deteriorates and cold rolling becomes difficult, so in practice 3.3%.
It is difficult to add more than Si. The aforementioned Japanese Patent Laid-Open No. 1-1196
It is from this point of view that the upper limit of the Si content of the electrical steel sheet disclosed in Japanese Patent Publication No. 44 is limited to 2.5%. Therefore, increasing the Si content to increase the resistivity is also reaching its limit.

However, the inventors of the present invention have disclosed in Japanese Unexamined Patent Publication No. 1-11961.
As a result of examining a method of increasing the specific resistance and reducing the iron loss without deteriorating the cold workability, based on the electromagnetic steel sheet shown in Japanese Patent Publication No. 44, the following findings were obtained.

(A) Even if the Si content is more than 2.5%, the deterioration of cold workability is suppressed and the finish annealing during finish annealing is suppressed by containing Mn in the range of more than 3.0% and up to 4.0%. The development of secondary recrystallization is stabilized.

(B) Moreover, Mn has an action of increasing the specific resistance of the steel sheet like Si, and is an extremely effective element for reducing iron loss.

(C) In the case of such a high Si and high Mn steel, in order to generate the secondary recrystallization, 825 in the first half of the finish annealing.
It is effective to maintain the temperature in the temperature range of 〜 925 ℃ for 7 to 100 hours and then to remove the nitride that becomes the inhibitor, in the latter half of the finish annealing, it is effective to purify in the temperature range up to 1050 ℃ and over 925 ℃. Is.

The present invention has been made based on these new findings.

[0020]

The function and effect of each constituent of the present invention will be described below.

I Composition of Steel Slab and Product Steel Sheet as Material (a) C: C in the product adversely affects iron loss when the content thereof is large. That is, basically, the smaller the content of C in the product, the better the magnetic properties obtained. The reason for this is that C remaining at the product stage forms carbides, which serve as obstacles for domain wall movement and increase iron loss. Therefore, C in the product is 0.01% or less, preferably
It should be 0.005% or less. However, if the C content is set to 0.01% or less at the stage of the steel slab used as the raw material, the amount of harmful carbides will be reduced, so even if the continuous annealing for primary recrystallization is not decarburization annealing, the finish There is no adverse effect on the desired secondary recrystallization during annealing. Further, it is possible to reduce the content of C to a desired low value during the purification annealing performed in the latter half of the finish annealing. Therefore, the C content in the stage of the steel slab is 0.01% or less.

(B) Si: Si is an element having a great influence on the magnetic properties, and as the content thereof increases, the specific resistance of the steel sheet increases, so that the eddy current loss decreases, and as a result, the iron loss decreases. To do.

However, if the content exceeds 3.0%, the saturation magnetic flux density is lowered, so 3.0% was made the upper limit. on the other hand,
If the content is less than 2.0%, the specific resistance of the steel sheet is low, and the grain-oriented electrical steel sheet with low iron loss, which is the target of the present invention, cannot be manufactured. Therefore, it is appropriate that the Si content is in the range of 2.0 to 3.0%.

(C) Mn: Mn is an element effective in causing α-γ transformation in an extremely low carbon steel slab of high Si such as the steel of the present invention and the steel to which the method of the present invention is applied. Yes,
The occurrence of this transformation promotes the refinement and homogenization of the structure of the hot-rolled sheet during hot rolling, and as a result, the secondary recrystallization with a high degree of integration in the Goss orientation is stabilized by the first finish annealing. In addition, the cold workability of high Si steel is improved.

The occurrence of α-γ transformation is determined by the balance of the contents of Si, which is a ferrite-forming element, and Mn, which is an austenite-forming element. Therefore, the contents of Si and Mn must be adjusted in relation to each other. Si content above 2.0-3.0
%, If Mn exceeds 3.0%,
A suitable α-γ transformation in the hot rolled sheet can be generated.

Mn is also an element effective for increasing the specific resistance of the steel sheet, like Si, and is the lower limit content of Si of 2.0.
%, By adding Mn in excess of 3.0%, the same specific resistance as in the case where Si alone is included in 3.5% is obtained. This degree of specific resistance is an essential condition for reducing iron loss by increasing the specific resistance of the steel sheet, which is the target of the present invention, and from this aspect also, it is necessary to contain Mn in excess of 3.0%. However, when the content exceeds 4.0%, the saturation magnetic flux density is lowered similarly to Si, so 4.0% was made the upper limit.

(D) S: S combines with Mn to form MnS. In the present invention, AlN, (Al, S
i) N, (Al 2, Si, Mn) N nitrides are used. Therefore, since MnS is not used as a main inhibitor unlike general grain-oriented electrical steel sheets, it is not necessary to add a large amount of S. If a large amount of MnS particles remain in the steel at the product stage, iron loss will deteriorate. Further, in the method of the present invention, the upper limit of the finish annealing temperature is as low as 1050 ° C., and therefore the desulfurization effect cannot be expected in the purification annealing. Therefore, the S content is 0.01% or less in both the product and the steel slab as the raw material. From the viewpoint of reducing iron loss, it is desirable to set it to 0.005% or less.

(E) Acid-soluble Al (sol.Al): Al is a major inhibitor that plays an important role in the occurrence of secondary recrystallization.
It is an important element that forms nitrides such as AlN, (Al, Si) N, and (Al 2, Si, Mn) N. In order to obtain a proper inhibitor effect, 0.003% or more of sol.Al is necessary. But,
If the sol.Al content exceeds 0.015%, the amount of the inhibitor will be too large and the dispersion state will be inadequate, and stable secondary recrystallization will not occur.

(F) N: N is an element necessary for forming the above-mentioned nitride as an inhibitor, and an appropriate amount thereof is present in the steel until secondary recrystallization is completed. Is an essential element. If it is less than 0.001% in the steel slab stage, the desired inhibitory effect cannot be obtained because the precipitation amount of nitride is too small, while if it exceeds 0.010%, the effect is saturated. The range is appropriate.

When the content of N in the product increases, the iron loss is adversely affected. In other words, basically, the smaller the content of N in the product, the better the magnetic properties obtained. The reason for this is that N remaining at the product stage forms a nitride, which acts as an obstacle for domain wall movement and increases iron loss. Therefore, N in the product must be 0.010% or less. Furthermore, 0.006% or less is desirable.
However, if the above range is set at the stage of the steel slab, it is possible to reduce the N content to a desired low value during the purification annealing performed in the latter half of the finish annealing.

II Manufacturing Process (a) First Process (Hot Rolling): The slab of the raw steel has the above composition. This is a molten steel that has been melted in a converter, electric furnace, etc. and, if necessary, vacuum degassed, etc.
It may be either a slab made by a continuous casting method or an ingot and slabbing rolled.

There are no particular restrictions on the conditions of hot rolling, but it is preferable that the heating temperature is 1150 to 1270 ° C. and the finishing temperature is 7
It is in the range of 00 to 900 ° C.

(B) Second step (cold rolling): The hot rolled steel sheet is cold-rolled once or plural times 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. .

If the hot-rolled sheet is annealed by continuous annealing, 700
When soaking at ˜1100 ° C. for 10 seconds to 5 minutes and box annealing, it is desirable to soaking at 650 to 950 ° C. for 30 minutes to 24 hours. When performing cold rolling a plurality of times, an annealing process is sandwiched in between. This intermediate annealing is preferably performed in the temperature range of 700 to 1000 ° C. Further, in order to obtain a good primary recrystallized structure by continuous annealing, the reduction ratio of the final cold rolling should be set as
40 to 90% is desirable, and more specifically 70 to 90% is effective.

(C) Third step (continuous annealing before finish annealing,
Primary Recrystallization Annealing): In order to generate stable secondary recrystallization in the finish annealing described below, primary recrystallization annealing by rapid heating is necessary in the preceding step, and continuous annealing is effective for this purpose. The annealing temperature is preferably 700 to 1000 ° C.

(D) Fourth Step (First Annealing in Finish Annealing, Secondary Recrystallization Annealing): The finishing annealing step is the first half annealing (first annealing for the purpose of generating secondary recrystallization). Annealing) and the following
It is divided into the subsequent annealing (second annealing) for the purpose of removing (purifying) precipitates described in (e).

In order to generate the secondary recrystallization having a high degree of integration in the Goss orientation, it is important to appropriately control the effect of the inhibitor, that is, the strength, in the temperature range where the secondary recrystallization occurs. The first annealing in the finish annealing, 825 ~ 925 ℃
The temperature is kept at 7 to 100 hours for the reason that the most suitable inhibitor strength is obtained in this temperature range and the secondary recrystallization having a high degree of integration in the Goss orientation occurs. 825 ° C
When the amount is less than the above, the inhibitory effect on the crystal grain growth is too strong and secondary recrystallization does not occur. On the other hand, in the temperature range above 925 ° C, the inhibitor effect is weak, so secondary recrystallization with a low degree of integration in the Goss orientation occurs, or primary recrystallized grains coarsen due to normal grain growth.

The holding time for generating the selective growth of the Goss orientation in the range of 825 to 925 ° C. is not sufficient if it is less than 7 hours, while holding for more than 100 hours is meaningless and economically disadvantageous. . For these reasons, the first half of the first annealing of the finish annealing process is performed with the purpose of producing 825
It was decided to hold at 925 ° C for 7 to 100 hours. It is desirable that this annealing be performed in an atmosphere containing 5 to 50% of N ₂ . This is to prevent the nitride acting as an inhibitor from being reduced by denitrification and the secondary recrystallization becoming unstable. A more positive meaning is to increase the precipitation amount of the nitride that serves as an inhibitor due to the absorption of nitrogen from the annealing atmosphere to generate secondary recrystallization having a high degree of integration in the Goss orientation.

(E) Fifth step (second finish annealing in finish annealing, purification annealing): The nitride acting as an inhibitor is harmful in terms of magnetic properties after secondary recrystallization occurs. Therefore, a purification annealing step for denitrifying and removing this is necessary. For this purpose, in the second finish annealing, the atmosphere is replaced with H ₂ 100% and the purification annealing is carried out by maintaining the temperature range above 925 ° C and up to 1050 ° C for 4 to 100 hours.

This denitrifying effect is not sufficient at a temperature of 925 ° C. or lower, while if it exceeds 1050 ° C., the effect of removing nitrides is saturated, so it is meaningless. At least 4 hours is required to maintain the denitrification reaction properly.
Retention for more than 00 hours is unnecessary and economically unprofitable. Therefore, the second finish annealing (purification annealing) is
4 to 100 in the temperature range from 925 ℃ to 1050 ℃
I decided to hold it for a while.

Applying an annealing separating agent for preventing seizure during annealing before finish annealing is the same as in the usual method for producing grain-oriented electrical steel sheet. As a process after the finish annealing, after removing the annealing separator as in the case of the ordinary grain-oriented electrical steel sheet, an insulating coating is applied or flattening annealing is performed if necessary.

[0043]

【Example】

(Test 1) The slabs of steels A, B, C and D having the compositions shown in Table 1 obtained by continuous casting after melting in a converter, adjusting the components by vacuum treatment, and heating temperature 1250 ° C, finishing temperature It was hot rolled at 840 ℃ and finished to 2.0mm thickness. These test steels have significantly increased specific resistance compared to general grain-oriented electromagnetic steel sheets (with a specific resistance of approximately 50 μΩ ・ cm) in order to achieve low iron loss, and they have substantially the same specific resistance. The balance of the contents of Si and Mn is changed so that the specific resistance is obtained.

Next, after hot-rolled sheet annealing with uniform heating at 880 ° C. for 1 minute using a continuous annealing furnace, descaling by pickling and rolling to 0.30 mm thickness by one cold rolling. Tried. As a result, in steels A and B having a composition outside the composition range defined by the present invention, cracks were formed from the steel plate edge portion during cold rolling, or fractures occurred, so that the steel sheet was cold-rolled to a predetermined thickness. Could not be rolled. On the other hand, Steel C and Steel D having the composition range defined in the present invention could be cold-rolled to a predetermined plate thickness without cracks or fractures.

[0045]

[Table 1]

(Test 2) A 0.30 mm-thick cold-rolled steel sheet obtained from Steel C and Steel D was subjected to a non-decarburizing atmosphere (50% N ₂ +50).
% H ₂ with a dew point of −20 ° C. or lower), and was temporarily recrystallized by continuous annealing at 870 ° C. for 30 seconds. Next, after annealing separating agent coated, with _{10% N 2 + 90% H} 2 atmosphere, subjected to a first finishing annealing for 24 hours soaking temperature was raised to 870 ° C., subsequently 100% H ₂ atmosphere And a second finishing annealing (purification annealing) was performed in which the material was soaked at 930 ° C. for 24 hours and then cooled in the furnace.

The magnetic properties of the steel sheet thus obtained are as follows: in steel C, iron loss W _17/50 = 1.10 W / kg, magnetic flux density B ₈
= 1.78T, and in Steel D, the iron loss W _17/50 = 1.12W / kg and the magnetic flux density B ₈ = 1.78T, which were extremely good.

(Test 3) Composition within the range defined by the present invention,
C: 0.0045%, Si: 2.85%, Mn: 3.14%, S: 0.0006
%, Sol.Al: 0.010%, N: 0.0045%, balance Fe
A slab of steel E consisting of and impurities was melted and hot-rolled in the same manner as in Test 1, and finished to a thickness of 1.8 mm.

Next, after descaling by pickling,
After hot-rolled sheet annealing using a box annealing furnace that soaks at 00 ° C for 1 hour, it is cold-rolled to a thickness of 0.30 mm in a non-decarburizing atmosphere (50% N ₂
+ 50% H ₂ and dew point -15 ℃ or less) at 890 ℃
It was temporarily recrystallized by continuous annealing for soaking for a second. Next, after annealing separating agent coated, with _{10% N 2 + 90% H} 2 atmosphere, subjected to a first finishing annealing for 24 hours soaking temperature was raised to 870 ° C., subsequently 100% H ₂ atmosphere At the temperature shown in Table 2
A second finish annealing (purification annealing) was performed in which the furnace was cooled after the uniform heating for a time.

The magnetic properties of the steel sheet thus obtained are also shown in Table 2. In all cases, good magnetic property characteristics were obtained irrespective of the temperature condition of the purification annealing, but particularly good in tests No. 3 and No. 4 which satisfy all the conditions defined in the present invention.

[0051]

[Table 2]

[0052]

According to the steel of the present invention and the method for manufacturing the same, it is possible to manufacture a grain-oriented electrical steel sheet which has a low iron loss and is suitable for use as a core material or a magnetic shield material for transformers, generators and electric motors. You can Furthermore, the material of this electromagnetic steel sheet is also excellent in cold workability. Since the method of the present invention does not include a decarburization annealing step and a finishing annealing step at an ultrahigh temperature that require a long time, it also contributes to a reduction in manufacturing cost.

Claims (2)

[Claims] 1. By weight%, C: 0.01% or less, Si: 2.0 to 3.0
%, Mn: more than 3.0% to 4.0%, S: 0.01% or less, acid-soluble Al: 0.003 to 0.015% and N: 0.010% or less, and the balance is Fe and inevitable impurities. Grain-oriented electrical steel sheet. 2. By weight%, C: 0.01% or less, Si: 2.0 to 3.0
%, Mn: more than 3.0% to 4.0%, S: 0.01% or less, acid-soluble Al: 0.003 to 0.015% and N: 0.001 to 0.010%, and the balance being a steel slab consisting of Fe and inevitable impurities. A method for manufacturing a grain-oriented electrical steel sheet, comprising the steps of: The step of performing hot rolling, as hot rolling, or after annealing after hot rolling,
A step of performing cold rolling once or twice or more with intermediate annealing sandwiched between them, a step of causing primary recrystallization by continuous annealing, and a secondary recrystallization that is maintained at a temperature range of 825 to 925 ° C for 7 to 100 hours. The first finish annealing step to be caused to occur, and the second finish annealing step of purifying by holding in the temperature range above 925 ° C and up to 1050 ° C for 4 to 100 hours.