JPH1112654A - Manufacture of grain oriented silicon sheet having excellent magnetic characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent magnetic characteristic by specifying the annealing condition before the final cold rolling, holding a nitride in a solid solution state and cooling and controlling the diameter equivalent to the average circle of the primary recrystallized grain in the primary recrystallized sheet to finely deposit the inhibitor mainly consisting of AlN. SOLUTION: The cold rolling including annealing is applied, and the primary and secondary recrystallizing annealing are applied at >= the attained temperature of 700 deg.C to the silicon steel strip containing, by mass, 2.0-6.5% Si, 0.004-0.03% Al, 0.001-0.01% N. In the annealing process before the final cold rolling, the temperature is risen up to the temperature zone satisfying the formula to dissociate and enter into solid solution the nitride containing Al. Thereafter, the average cooling speed at 850-650 deg.C is held at >=20 deg.C/sec to hold the nitride in the solid solution state and cool. AlN is finely deposited until the starting of the primary recrystallization in the primary recrystallizing annealing after that. The diameter equivalent to the average circle of the primary recrystallized grain in the cross section of the primary recrystallization annealed sheet is controlled to <=8 μm.

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, and more particularly, to a method for stably obtaining higher magnetic properties.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are mainly used as iron cores for transformers and other electric equipment, and it is basically important to have excellent magnetic properties such as magnetic flux density and iron loss in order to meet such applications. . Therefore, what is important in the production of a grain-oriented electrical steel sheet is that the orientation of crystal grains subjected to secondary recrystallization in the so-called finish annealing step is highly integrated in the {110} <001> orientation, the so-called Goss orientation. It is.

In order to effectively promote the accumulation of such secondary recrystallized grains, first, a dispersed phase called an inhibitor which selectively inhibits the growth of primary recrystallized grains is uniformly and properly dispersed. It is important to form them in a suitable size. As such inhibitors, substances such as MnS, MnSe and AlN which are sulfides, selenides and nitrides and have low solubility in steel are mainly used. For this reason, conventionally, in slab heating before hot rolling, a method of performing high-temperature heating to completely dissolve the inhibitor and finely dispersing the inhibitor in the process from the hot rolling step to the secondary recrystallization is known. Has been taken. In addition, Sb, Sn, As, Bi,
Components such as B, Pb, Ce, Cu and Mo have also been used as inhibitors.

The second condition is to control the primary recrystallized grain structure and texture formed by a combination of one or more times of cold rolling and one or more times of annealing. It is in. In particular, since the primary recrystallized grain diameter is inversely proportional to the secondary recrystallization driving force, small primary recrystallized grains can be obtained stably, and the inhibitory force of the above-mentioned inhibitor is stably maintained at a high level. It becomes important.

[0005] Therefore, conventionally, in the process of manufacturing a grain-oriented electrical steel sheet, a slab having a thickness of 100 to 300 mm is heated to a temperature of 1250 ° C or more to completely dissolve the inhibitor component, and then hot-rolled by hot rolling. The hot-rolled sheet is subjected to cold rolling at least once or two or more times with intermediate annealing to obtain a final cold-rolled sheet thickness, then decarburized annealing, coated with an annealing separator, and then subjected to a second re-rolling. Means for applying a final finish annealing for the purpose of crystallization and purification are common.

As a method for precipitating AlN in these steps, as disclosed in Japanese Patent Publication No. 46-23820 (heat treatment method for high magnetic flux density electromagnetic steel sheet), etc., in the annealing step before final cold rolling, A method of partially dissolving and dissolving AlN to precipitate AlN finely in the subsequent cooling process, or finely forming AlN in the cooling process of hot rolling or the subsequent heating step of annealing is generally used. The value of the crystal grain diameter is generally about 9 to 9 as shown in Japanese Patent Publication No. 6-84524 (primary recrystallization annealing method for grain-oriented electrical steel sheets).
A range of 30 μm was usual.

Therefore, in order to cause complete primary recrystallization and stably obtain a primary recrystallization particle size of 8 μm or less, a larger amount of an inhibitor component should be added, or the precipitation state of a finer inhibitor should be reduced. It is necessary to achieve this, but for the former, the addition of a larger amount of the inhibitor component naturally has a limit because it requires a higher slab heating temperature, and also for the latter, the cooling process after hot rolling or annealing. It was difficult to stably obtain fine primary recrystallized grains, for example, there was a limit to the miniaturization of the inhibitor formed by the method.

On the other hand, in recent years, the demand for energy saving has been further increased, and in order to respond to this demand, a process capable of more stably obtaining a high level of suppressing power is required.

[0009]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems. According to a novel idea, an inhibitor mainly composed of AlN is deposited very finely to obtain a stable and favorable solution. It is an object of the present invention to propose a method for manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties for use in generating secondary recrystallization.

[0010]

As a result of various experiments, the inventors have found that in the conventional process, AlN is precipitated in the annealing step before hot rolling or the subsequent final cold rolling, and in the subsequent heat treatment step. It has been found that, until it is decomposed during the finish annealing, the inhibitory power is gradually reduced by Ostwald ripening, basically without completely forming a solid solution. Further, it was also found that the method of dissolving AlN as a solid solution during annealing and then precipitating AlN during the cooling process has a problem that the distribution of AlN precipitated becomes non-uniform.

As a result of intensive investigations based on these findings, it was found that the temperature of the annealing step before the final cold rolling was sufficiently raised to a high temperature to completely dissolve the entire amount of AlN, and then the AlN was dissolved in the cooling step. By precipitating AlN on the dislocations introduced in the subsequent cold rolling without precipitation, before the recovery and recrystallization of the structure occurs, extremely fine
It has been clarified that AlN can be uniformly deposited and a high suppressing power can be obtained. The gist of the present invention based on the above findings is as follows.

Si: 2.0 to 6.5 mass%, Al: 0.004 to
Using a silicon steel strip containing 0.03 mass% and N: 0.001 to 0.01 mass% as a raw material, the steel sheet is subjected to one or more cold rolling steps of appropriately annealing, and is subjected to a primary recrystallization annealing at an ultimate temperature of 700 ° C. or more. Then, when producing a grain-oriented electrical steel sheet by successively or separately performing secondary recrystallization annealing, in the annealing step before final cold rolling, the material temperature T (° C.) is set to the value of the above Al content.
The value of mass% Al and the content of N is expressed as mass% N. The temperature is raised to a temperature range that satisfies the following equation (1) to dissociate the nitride containing Al as a solid solution.
The average cooling rate between temperatures up to 650 ° C is 20 ° C / s or more, the nitride is kept in a solid solution state, cooled, and then subjected to primary recrystallization annealing through primary recrystallization annealing. Manufacture of grain-oriented electrical steel sheets with excellent magnetic properties, wherein AlN is finely precipitated before the start of crystallization and the average equivalent circle diameter of primary recrystallized grains in the cross section of the primary recrystallized annealed sheet is 8 μm or less. Method (first invention).

[0013] The amount of precipitated Al before final cold rolling is reduced to 60 masspp.
The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to the first invention, wherein the grain is controlled to be less than m (second invention).

After the final cold rolling, the cold rolled sheet is kept in a temperature range of 450 ° C. or more and 650 ° C. or less for 20 seconds or more, and then
The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to the first invention or the second invention, wherein the second recrystallization annealing is performed (third invention).

[0015] The magnetic properties according to the first, second or third invention, wherein the steel sheet is subjected to nitriding of N: 10 mass ppm or more after the end of the final cold rolling until the start of the secondary recrystallization. A method for producing a grain-oriented electrical steel sheet having an excellent (fourth invention).

Although the present invention has been made mainly with respect to a method for producing a grain-oriented electrical steel sheet, it is also applicable to the production of a grain-oriented electrical steel sheet utilizing a similar secondary recrystallization phenomenon. 1. When adopting a method in which the primary recrystallization annealing and the secondary recrystallization annealing are performed during the same annealing, when employing a low-temperature slab heating method, and further for manufacturing a product to be subjected to various magnetic domain refining treatments. Is applicable.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The reason for limiting the component composition of a material for a grain-oriented electrical steel sheet, ie, a silicon steel strip, to which the present invention is applied, and the preferred range will be described below.

C: 0.10 mass% or less (hereinafter simply expressed as%) C is a component useful not only for uniformly dispersing the composition during hot rolling and cold rolling, but also for developing Goss-oriented crystal grains. Desirably, it is present even in trace amounts. However, when the content exceeds 0.10%, decarburization becomes difficult, and the accumulation of Goss-oriented crystal grains is disturbed. Therefore, the upper limit of the content is not necessarily limited to 0.10%. It is desirable to do.

Si: 2.0 to 6.5% Si is effective in increasing the specific resistance of the steel sheet and reducing iron loss, but when the content exceeds 6.5%, the cold rolling property is impaired.
On the other hand, if the content is less than 2.0%, not only the specific resistance is reduced, but also the crystal orientation is randomized by α → γ transformation during the final refining annealing performed for secondary recrystallization and purification, and No iron loss reduction effect can be obtained.
Therefore, its content is in the range of 2.0 to 6.5%.

Mn: 0.02 to 0.12% Mn is not necessarily limited, but is preferably contained at least about 0.02% in order to prevent hot embrittlement. However, if the content is too large, the magnetic properties are degraded, so the upper limit is preferably set to about 0.12%.

The constituents of AlN as an inhibitor are:
The upper and lower limits of Al and N are determined for the following reasons. Al: 0.004 to 0.03% When the content of Al is too small, the absolute amount of the inhibitor becomes insufficient, and when the content is too large, AlN at a temperature that can be industrially heated can be obtained.
Can not be completely solid-dissolved, so its content is 0.00
The range is 4 to 0.03%. N: 0.001 to 0.01% The upper and lower limits of N of the silicon steel strip, which is the starting material, are determined for the same reason as for Al, and the content is 0.001 to 0.01%.
Range.

Further, in the present invention, it is effective to increase the inhibitor by nitriding the steel sheet between the end of the final cold rolling and the start of the secondary recrystallization, and the amount of nitriding at that time is preferably 10 ppm or more. .

Further, in the present invention, MnS, MnSe, CuSx, CuSex and the like may be used as the precipitation inhibitor, and in this case, it is possible to use together with AlN. Also,
It can be used in combination with a grain boundary segregation inhibitor, and each works effectively. Examples of these inhibitor components include Sb, Sn, As, Bi, B, Pb, Ce, Ti, Cu and Mo in addition to S and Se described above, and one or more of these may be used in combination. It is possible. The preferred range of the content of these components is generally in the range of 0.001 to 0.2%.

Next, the manufacturing process conditions of the present invention will be described below. Molten steel adjusted to the above component composition obtained by conventional steelmaking method is cast by continuous casting method or ingot-making method,
If necessary, the slab is sandwiched between the slabs, and then hot-rolled through a slab heating process to obtain a silicon steel strip as a raw material. As the slab heating, any of generally-used high-temperature heating and low-temperature heating can be applied.

Using the silicon steel strip as a raw material, the steel sheet is subjected to one or more cold rolling steps of appropriately annealing such as hot-rolled sheet annealing and intermediate annealing to obtain a final cold-rolled sheet thickness. In the annealing step before the final cold rolling, the material temperature T (° C.) was set to the value of the Al content of the material, and the values of mass% Al and N were set to ma.
The temperature is raised to a temperature range satisfying the following formula (1) expressed as ss% N to dissociate all the nitride containing Al as a solid solution, and then average cooling between 850 ° C and 650 ° C in the subsequent cooling process Cooling at a rate of 20 ° C./s or more while maintaining the nitride in a solid solution state, and before the first recrystallization in the first recrystallization annealing performed through final cold rolling, The essence is to finely precipitate and make the average diameter of the primary recrystallized grains in the cross section of the primary recrystallized annealed plate 8 μm or less. T (° C)> -5570 / log (mass% Al x mass% N) -273 (1)

In the annealing before the final cold rolling, it is necessary to raise the temperature of the material to at least a temperature exceeding the above-mentioned formula (1) in order to completely dissolve the AlN. Fine AlN precipitates cannot be obtained, resulting in a coarse primary recrystallized structure. Also, in the cooling process after the solid solution heating, if the cooling is not performed in accordance with the above conditions, some coarse AlN
Precipitates and causes the same problem.

Further, the amount of precipitated Al of the material before the final cold rolling after the solid solution heating of AlN is preferably less than 60 ppm. For this analysis, JP-A-6-11805 (electrolyte for analysis of precipitates and inclusions in steel materials) in which ICP analysis is carried out by dissolving in a mixed acid solution of nitric acid and hydrochloric acid after electrolytic extraction filtration is used. Good.

After the final cold rolling, primary recrystallization annealing is performed. However, if the primary recrystallization annealing temperature is too low, the primary recrystallization will not be completed, so it is necessary to heat to at least 700 ° C. On the other hand, however, an excessively high temperature treatment is not preferable in order to obtain a primary recrystallized grain size of 8 μm or less, and the upper limit thereof is preferably about 900 ° C.

In addition, since it is important to precipitate AlN finely on dislocations before the first recrystallization, the rate of temperature rise is reduced during the first recrystallization annealing,
It is extremely effective to stabilize the effect of the present invention by using a technique such as maintaining the temperature in a temperature range of 450 ° C. or more and 650 ° C. or less for 20 seconds or more. Further, in order to make the extremely fine nitride formed by this method exist during the secondary recrystallization annealing, nitriding (N: 10 ppm or more) is performed by a known method before the start of the secondary recrystallization. Means are also very effective.

After the primary recrystallization annealing, secondary recrystallization annealing is performed according to a conventional method to obtain a product. However, if necessary, the product may be subjected to insulation coating or flattening treatment to obtain a product.

[0031]

【Example】

Example 1 C: 0.05%, Si: 3.25%, Mn: 0.07%, S: 0.02%, A
l: A molten steel containing 0.020% and N: 0.007%, with the balance being mainly Fe, is continuously cast into a slab having a thickness of 220 mm, and this slab is heated to a temperature of 1260 ° C in a gas-fired furnace. Then, after heating to a temperature of 1380 ° C. in an induction heating furnace, hot rolling was performed to obtain a hot-rolled sheet (silicon steel strip) having a sheet thickness of 2.5 mm.

Using this hot-rolled sheet as a material, it is subjected to hot-rolled sheet annealing at 1000 ° C./40 s, then primary cold-rolled to a sheet thickness of 1.8 mm, and as annealed at 1190 ° C./100 s before final cold-rolling. Was subjected to water cooling (T> 1172 ° C. calculated from the equation (1)), followed by secondary cold rolling to a final cold-rolled sheet thickness of 0.23 mm.

After that, when the cold-rolled sheet was subjected to primary recrystallization annealing combined with decarburization at 780 ° C. for 110 seconds, a primary recrystallized sheet having an average equivalent circle diameter of 6.2 μm was obtained.
Up to a temperature of 25 ° C./h in an atmosphere of nitrogen: hydrogen = 1: 3
The secondary recrystallization annealing was performed at a heating rate of. As a result of examining the magnetic flux density of the product thus obtained, an excellent value of B ₈ : 1.953 T was obtained.

On the other hand, the magnetic flux density B ₈ of the product treated under the same conditions as above except that the final pre-cold-rolling annealing, that is, the intermediate annealing temperature was 1130 ° C., was 1.855 T.

Example 2 C: 0.05%, Si: 3.25%, Mn: 0.07%, S: 0.02%, A
l: 0.020% and N: 0.0078%, the remainder being mainly cast of molten steel consisting mainly of Fe to form a slab with a thickness of 220 mm, and heating this slab to a temperature of 1280 ° C in a gas-fired furnace. Hot rolling was performed to obtain a hot-rolled sheet (silicon steel strip) having a thickness of 2.5 mm.

Using this hot rolled sheet as a material, hot rolled sheet annealing at 950 ° C./40 s is performed, then primary cold rolling is performed to a sheet thickness: 1.8 mm, and annealing at 1250 ° C./100 s is performed before final cold rolling. After the intermediate annealing (T> 1213 ° C. calculated from the equation (1)), the steel sheet was water-cooled and subjected to secondary cold rolling to a final cold-rolled sheet thickness of 0.23 mm.

Thereafter, the cold rolled sheet was subjected to AlN at 580 ° C. for 60 seconds.
Following the precipitation annealing, the primary recrystallization annealing combined with decarburization at 830 ° C for 70 s was performed.
A secondary recrystallized plate was obtained, and subsequently heated to a temperature of 1160 ° C. in an atmosphere of nitrogen: hydrogen = 1: 3 at a temperature increasing rate of 20 ° C./h.
The secondary recrystallization annealing was performed, and the magnetic flux density of the obtained product was examined. As a result, an excellent value of B ₈ : 1.957 T was obtained.

On the other hand, in the case of annealing before the final cold rolling, that is, the treatment under the same conditions as above except that the intermediate annealing temperature was changed, precipitation of the material before the final cold rolling after the intermediate annealing was performed.
The Al content, the primary recrystallized grain size of the primary recrystallized plate, and the magnetic flux density of the product were measured.

The results of these measurements are shown in FIGS. FIG. 1 is a graph showing the effect of the intermediate annealing temperature on the amount of precipitated Al after intermediate annealing, FIG. 2 is a graph showing the relationship between the intermediate annealing temperature and the average primary recrystallization grain size, and FIG. It is a graph which shows the influence of intermediate annealing temperature.

As is apparent from these figures, in the temperature range in which the annealing before final cold rolling, ie, the intermediate annealing temperature satisfies the above equation (1), the amount of precipitated Al is small before final cold rolling (see FIG. 1) It can be seen that the primary recrystallized grain equivalent to an average circle becomes fine grains of 8 μm or less (FIG. 2), and the magnetic flux density of the product (FIG. 3) is extremely excellent.

Example 3 C: 0.05%, Si: 3.25%, Mn: 0.05%, S: 0.01%, A
Continuously cast molten steel containing l: 0.014% and N: 0.007%, with the balance being mainly Fe, to form a slab with a thickness of 220 mm. This slab was heated to 1190 ° C in a gas-fired furnace, Rolled and hot-rolled with a thickness of 2.5 mm (silicon steel strip)
And

Using this hot rolled sheet as a material, annealing before final cold rolling at 1190 ° C./80 s, that is, after the hot rolled sheet annealing (T> 1116 ° C. calculated from the equation (1)), then cold rolling once Finished to a final cold-rolled sheet thickness: 0.27 mm by the method. Then on this cold rolled sheet
Primary recrystallization annealing combined with decarburization at 780 ° C for 110 s was performed, and nitriding was performed in an atmosphere containing ammonia to N: 0.022%. Obtained. Subsequently, the temperature is raised to a temperature of 1160 ° C. in an atmosphere of nitrogen: hydrogen = 1: 3 at a rate of 25 ° C./h 2
Next recrystallization annealing was performed to obtain a product.

The magnetic flux density B ₈ of the product thus obtained is 1.
It showed an excellent value of 961 T.

[0044]

According to the present invention, in manufacturing a grain-oriented electrical steel sheet, the annealing conditions before final cold rolling are specified, the nitride is kept in a solid solution state, cooled, and the first recrystallized sheet is cooled. According to the present invention, an average equivalent circle diameter of the next recrystallized grains is controlled. According to the present invention, a high-order suppressing force can be stably obtained, and an industrially extremely high-magnetic grain-oriented electrical steel sheet can be stably obtained. Can be. Further, since the present invention can be applied to a low-temperature slab heating method, it is effective in reducing energy costs in a manufacturing process.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of intermediate annealing temperature on the amount of precipitated Al after intermediate annealing.

FIG. 2 is a graph showing a relationship between an intermediate annealing temperature and a primary recrystallization average particle size.

FIG. 3 is a graph showing the effect of an intermediate annealing temperature on magnetic properties.

Claims (4)

[Claims] [Claim 1] Si: 2.0 to 6.5 mass%, Al: 0.004 to 0.4 mass%.
Using a silicon steel strip containing 03 mass% and N: 0.001 to 0.01 mass% as a raw material, it is subjected to at least one cold rolling step of appropriately annealing, and after primary recrystallization annealing at an ultimate temperature of 700 ° C or more, In order to manufacture a grain-oriented electrical steel sheet by successively or separately performing secondary recrystallization annealing, in the annealing step before final cold rolling, the material temperature T (° C.) is set to the above Al content value by mass% Al and Mass value of N content
The temperature is raised to a temperature range that satisfies the following formula (1), expressed as N, to dissociate and dissolve the nitride containing Al for a moment, and the average cooling rate between 850 ° C. and 650 ° C. in the subsequent cooling process is
At a temperature of 20 ° C./s or more, the nitride is kept in a solid solution state and cooled, and then AlN is finely precipitated before the start of primary recrystallization in primary recrystallization annealing performed through final cold rolling. The average circle equivalent diameter of the primary recrystallized grains in the cross section of the primary recrystallized annealed plate was 8
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, characterized in that the grain size is not more than μm. [Note] T (° C)> -5570 / log (mass% Al x mass% N) -273 (1) 2. The amount of precipitated Al before final cold rolling is reduced to 60 mass ppm.
The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the grain size is controlled to be less than. 3. After the final cold rolling, the cold rolled sheet is heated to 450 ° C. or more,
The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1 or 2, wherein the primary recrystallization annealing is performed after the temperature is maintained at a temperature of 650 ° C or less for 20 seconds or more. 4. The magnetic properties according to claim 1, 2, or 3, wherein the steel sheet is subjected to nitriding of N: 10 mass ppm or more after the end of the final cold rolling until the start of the secondary recrystallization. Manufacturing method of grain-oriented electrical steel sheet.