JP6866869B2 - Manufacturing method of grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet, and more particularly to a method for manufacturing a grain-oriented electrical steel sheet which has a high magnetic flux density and can obtain a grain-oriented electrical steel sheet which can be suitably used as an iron core material of a transformer.

The grain-oriented electrical steel sheet is a soft magnetic material used as an iron core material for transformers and generators, and has a texture in which the <001> orientation, which is the easy axis of iron magnetization, is highly aligned in the rolling direction of the steel sheet. There is. Such textures are formed by performing purification annealing with secondary recrystallization during the manufacturing process of grain-oriented electrical steel sheets. Here, the secondary recrystallization refers to a phenomenon in which crystal grains in the {110} <001> orientation, which are so-called Goth orientations, are preferentially grown in a huge manner.

As a typical method for causing the above-mentioned secondary recrystallization, there is a method using a precipitate called an inhibitor. In this method, crystal grain growth during the annealing step is controlled by dispersing precipitates such as AlN, MnS, and MnSe in the steel, and finally, crystal grains having a Goss orientation are selectively grown.

The method using the above-mentioned inhibitor has been widely used in the production of grain-oriented electrical steel sheets because it is possible to stably develop secondary recrystallized grains. However, in order to finely disperse the inhibitor in the steel, it is necessary to perform slab heating at a high temperature of 1300 ° C. or higher in advance to dissolve the inhibitor component once. Further, since the inhibitor element remaining in the steel after the secondary recrystallization causes deterioration of the magnetic properties of the grain-oriented electrical steel sheet, purification annealing is performed in a high temperature of 1100 ° C. or higher and a controlled atmosphere. It is necessary to remove the inhibitor element from the ground iron.

Therefore, in order to solve the problems caused by the use of inhibitors as described above, a method of manufacturing grain-oriented electrical steel sheets without using inhibitors (inhibitorless method) has been proposed (for example, Patent Document 1, Patent Document 1, 2).

The inhibitorless method is a technique for expressing secondary recrystallization by using more purified steel and controlling the texture. Specifically, by demonstrating the grain boundary orientation difference angle dependence of the grain boundary energy of the crystal grain boundary at the time of primary recrystallization, the crystal grains having the Goss orientation are secondarily recrystallized without using an inhibitor. It becomes possible to make it. Such an effect is called a texture inhibition effect.

Japanese Unexamined Patent Publication No. 2000-129356 Japanese Unexamined Patent Publication No. 2001-040449

In the inhibitorless method, since it is not necessary to finely disperse the inhibitor in the steel, it is not necessary to perform the high temperature slab heating which is indispensable when the inhibitor is used. Therefore, the inhibitorless method has a great advantage not only in terms of manufacturing cost but also in terms of maintenance of manufacturing equipment.

However, the inhibitorless method has a problem that it is difficult to stably produce a grain-oriented electrical steel sheet having good magnetic characteristics. Therefore, there is a need for a method for manufacturing grain-oriented electrical steel sheets, which is an inhibitorless method excellent in terms of cost and can manufacture grain-oriented electrical steel sheets having more excellent magnetic characteristics, specifically, high magnetic flux density. Has been done.

The present invention has been made in view of the above circumstances, is an inhibitorless method excellent in terms of cost, and is a method for manufacturing a grain-oriented electrical steel sheet capable of manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density. The purpose is to provide.

As a result of repeated studies to solve the above problems, the inventors have controlled the slab heating conditions and the annealing conditions immediately before the final cold rolling in the production of grain-oriented electrical steel sheets. It has been found that the magnetic flux density of the finally obtained grain-oriented electrical steel sheet can be improved.

Here, an example of an experiment that led to the above findings will be described. In this experiment, a plurality of grain-oriented electrical steel sheets were prepared under different manufacturing conditions based on the inhibitorless method, and the magnetic properties of the obtained grain-oriented electrical steel sheets were evaluated. The specific procedure will be described below. In the following experiments, grain-oriented electrical steel sheets were manufactured by a one-time method in which cold rolling was performed only once.

First, molten steel was prepared by vacuum melting to obtain a steel slab. As the steel slab, by mass%,
C: 0.045%,
Si: 3.4%,
Mn: 0.06%,
Al: 0.0060%,
N: 0.0025%,
S: 0.0010%,
Se: Contains 0.0010%
A steel slab having a component composition in which the balance was composed of Fe and unavoidable impurities was used.

The steel slab was heated to a slab heating temperature of 1250 ° C. and maintained at the slab heating temperature for the soaking time shown in Table 1. Then, hot rolling was performed to obtain a hot-rolled steel sheet having a thickness of 2.0 mm. Then, the hot-rolled steel sheet was annealed by hot-rolled steel sheet. In the hot-rolled sheet annealing, the hot-rolled steel sheet was heated to an annealing temperature of 1050 ° C., kept at the annealing temperature for a holding time of 30 seconds, and then cooled. The residence time for staying in the temperature range of 1030 to 900 ° C. during the cooling was as shown in Table 1. The average cooling rate in the temperature range between 900 ° C. and 350 ° C. was 30 ° C./s.

Next, the hot-rolled steel sheet after annealing was subjected to cold rolling to obtain a cold-rolled steel sheet having a final plate thickness of 0.23 mm. The rolling temperature in the cold rolling was 100 ° C.

Next, the obtained cold-rolled steel sheet was subjected to primary recrystallization annealing, which also served as decarburization annealing. The primary recrystallization _{annealing, 50% H 2 -50% N} 2, carried out under a humid atmosphere with a dew point of 50 ° C., and the heating rate in the temperature elevation section 500-680 ° C. and 200 ° C. / s.

An annealing separator mainly composed of MgO was applied to the surface of the cold-rolled steel sheet after the primary recrystallization annealing, and then purified annealing accompanied by secondary recrystallization was performed. In the purified annealing, it was retained at 1200 ° C. for 5 hours in a hydrogen atmosphere.

Next, in order to correct the shape of the steel sheet, the cold-rolled steel sheet after purification annealing was subjected to flattening annealing at 830 ° C. for 30 seconds to obtain a grain-oriented electrical steel sheet.

In order to evaluate the magnetic properties of the obtained grain-oriented electrical steel sheet, the magnetic flux density when excited at 800 A / m: B ₈ (T) was measured by the method specified by JIS C 2550. The measurement results are as shown in Table 1.

As can be seen from the results in Table 1, in the production of grain-oriented electrical steel sheets by the inhibitorless method, the soaking time t (minutes) in the slab heating step is P _t or less defined by the following equation (1), and When the residence time staying in the temperature range of 103 to 900 ° C. for 10 seconds or more in the cooling process of hot-rolled sheet annealing, good magnetic characteristics can be obtained.
P _t = 800 [C] -5 [Si] + T / 25 ... (1)
However, in the formula (1), [C] is the C content (mass%) in the steel slab, and [Si] is the Si content (mass%) in the steel slab.

The reason why the magnetic flux density is improved in this way is not completely clear, but it is considered as follows.

In the conventional production of grain-oriented electrical steel sheets, the soaking time in slab heating before hot rolling is generally about 120 minutes. On the other hand, when the soaking time in the slab heating is shortened as in the above experiment, the austenite (γ) phase aggregation during the slab heating is suppressed, and the γ phase can be dispersed.

Further, in the cooling process of hot-rolled sheet annealing, the γ phase can be sufficiently contracted by lengthening the residence time in the temperature range of 103 to 900 ° C.

In this way, the soaking time in slab heating is shortened to suppress the aggregation of the γ phase, and the residence time in the hot rolled plate annealing is shortened to make the γ phase finer, so that the micro is micro after hot rolled plate annealing. The structure can be in a state in which the non-diffusion transformation phase generated by the transformation of the γ phase is finely dispersed.

When such a hot-rolled steel sheet is cold-rolled, the finely dispersed non-diffusion transformation phase acts as a starting point of shear deformation, so that the number of nucleation sites of {411} oriented grains increases. Since the {411} oriented grains have the effect of increasing the secondary recrystallization orientation selectivity of the ideal Goss orientation, as a result of the increase in the {411} oriented grains, the final grain of the grain-oriented electrical steel sheet is obtained. It is considered that the magnetic characteristics have improved.

As described above, in the inhibitorless method, since the crystal grains having the Goss orientation are secondarily recrystallized by controlling the texture, the texture affects the magnetic properties as compared with the case where the inhibitor is used. The impact is much greater. Therefore, in the method of the present invention that does not use an inhibitor, a high magnetic property improving effect can be obtained by controlling the production conditions as described above.

In the above experiment, since the grain-oriented electrical steel sheet was manufactured by using the one-time method in which cold rolling was performed only once, the microstructure of the steel sheet to be subjected to cold rolling was formed before the cold rolling. It is affected by the conditions of hot-rolled sheet annealing. However, when cold rolling is performed twice or more, it is affected by the conditions of intermediate annealing performed immediately before the final cold rolling (final cold rolling). Therefore, when the last cold rolling of one or more cold rollings is defined as final cold rolling, and the annealing performed immediately before the final cold rolling is defined as final cold rolling pre-annealing, the above is defined. It is important to control the conditions of final pre-roll annealing.

The present invention has been made based on the above findings, and its gist structure is as follows.

1. 1. By mass%
C: 0.020 to 0.10%,
Si: 2.0-6.5%,
Mn: 0.005-1.00%,
Al: less than 0.010%,
N: less than 0.0050% S: less than 0.0050%, and Se: less than 0.0050%, including
A steel slab having a component composition in which the balance is composed of Fe and unavoidable impurities is subjected to slab heating.
The heated steel slab is hot-rolled to form a hot-rolled steel sheet.
The hot-rolled steel sheet is annealed by hot-rolled steel sheet, and then the hot-rolled steel sheet is annealed.
The hot-rolled steel sheet after annealing is subjected to one cold-rolling or two or more cold-rolling sandwiching an intermediate annealing to obtain a cold-rolled steel sheet.
The cold-rolled steel sheet is subjected to primary recrystallization annealing that also serves as decarburization annealing.
An annealing separator is applied to the surface of the cold-rolled steel sheet after the primary recrystallization annealing.
The cold-rolled steel sheet was subjected to purification annealing accompanied by secondary recrystallization, and then subjected to purification annealing.
A method for producing a grain-oriented electrical steel sheet, in which the cold-rolled steel sheet after purification annealing is flattened and annealed.
In the slab heating, the steel slab is heated to a slab heating temperature T (° C.) of 1280 ° C. or lower and maintained at the slab heating temperature T for a soaking time t (minutes), and the soaking time t is as follows. It is less than or equal to P defined by equation (1), and is less than or equal to P.
When the last cold rolling of the one or two or more cold rollings is defined as final cold rolling, and the annealing performed immediately before the final cold rolling is defined as final cold rolling pre-annealing, respectively.
In the final pre-cooling annealing, the steel plate is heated to an annealing temperature of 1030 to 1150 ° C., held at the annealing temperature for a holding time of 10 to 180 seconds, cooled, and 1030 to 1030 during the cooling. The residence time staying in the temperature range of 900 ° C. is 10 seconds or more.
The rolling temperature in the final cold rolling is 100 to 300 ° C.
A method for producing a grain-oriented electrical steel sheet, wherein the heating rate in the temperature rising section of 500 to 680 ° C. in the primary recrystallization annealing is 100 to 400 ° C./s.
P _t = 800 [C] -5 [Si] + T / 25 ... (1)
However, in equation (1), [C] is the C content (mass%) in the steel slab, and [Si] is the Si content (mass%) in the steel slab.

2. In the final pre-cold annealing,
The method for manufacturing a grain-oriented electrical steel sheet according to 1 above, wherein the average cooling rate in the temperature range between 900 ° C. and 350 ° C. is 20 ° C./s or more.

3. 3. In the final pre-cold annealing,
The method for manufacturing a grain-oriented electrical steel sheet according to 2 above, wherein the average cooling rate in the temperature range between 700 ° C. and 350 ° C. is 35 ° C./s or more.

4. When the component composition is mass%,
Cr: 0.01-0.50%,
Cu: 0.01-0.50%,
Ni: 0.01-0.50%,
Bi: 0.005 to 0.50%,
B: 0.0002 to 0.0025%,
Nb: 0.0010 to 0.0100%,
Sn: 0.010 to 0.400%,
Sb: 0.010 to 0.150%,
The direction according to any one of 1 to 3 above, further comprising 1 or 2 or more selected from the group consisting of Mo: 0.010 to 0.200% and P: 0.010 to 0.150%. Manufacturing method of electrical steel sheet.

According to the present invention, a grain-oriented electrical steel sheet having a high magnetic flux density can be manufactured by an inhibitorless method excellent in terms of cost.

Next, the method of carrying out the present invention will be specifically described.

[Steel slab]
In the present invention, the steel slab used for manufacturing the grain-oriented electrical steel sheet needs to have the above-mentioned component composition. Therefore, first, the reason for limiting the component composition in the present invention will be described. In addition, "%" regarding a component composition shall mean "mass%" unless otherwise specified.

C: 0.020 to 0.10%
C is an element necessary for controlling the microstructure of the steel sheet. If the C content is less than 0.020%, the γ phase does not precipitate during slab heating, which makes it difficult to control the structure, and as a result, the magnetic flux density decreases. Therefore, the C content is 0.020%, preferably 0.025% or more. On the other hand, if C remains in the finally obtained grain-oriented electrical steel sheet, it causes deterioration of magnetic properties due to magnetic aging. Therefore, in the production of grain-oriented electrical steel sheet, primary recrystallization annealing that also serves as decarburization annealing is performed. The C content is reduced. However, if the C content of the steel slab is higher than 0.10%, the C content cannot be sufficiently reduced even by decarburization annealing. Therefore, the C content of the steel slab is 0.10% or less, preferably 0.050% or less. The C content in the finally obtained grain-oriented electrical steel sheet is not particularly limited, but is preferably 0.005% or less from the viewpoint of suppressing magnetic aging.

Si: 2.0-6.5%
Si is an element necessary for increasing the specific resistance of steel and improving iron loss. In order to obtain the above effect, the Si content is set to 2.0% or more, preferably 2.5% or more. On the other hand, if the Si content exceeds 6.5%, the workability of the steel deteriorates and rolling becomes difficult. Therefore, the Si content is 6.5% or less, preferably 4.5% or less.

Mn: 0.005-1.00%
Mn is an element required to obtain good hot workability. In order to obtain the above effect, the Mn content is 0.005% or more, preferably 0.03% or more. On the other hand, when the Mn content exceeds 1.00%, the magnetic flux density of the finally obtained grain-oriented electrical steel sheet decreases. Therefore, the Mn content is 1.00% or less, preferably 0.20% or less.

The present invention relates to the production of grain-oriented electrical steel sheets by the inhibitorless method. Therefore, it is necessary to reduce the amounts of the inhibitor-forming components Al, N, S, and Se in the steel slab as much as possible. Specifically, the content of each of the above elements is in the following range.

The Al content is less than 0.010%, preferably less than 0.007%. The N content is less than 0.0050%, preferably less than 0.0040%. The S content is less than 0.0050%, preferably less than 0.0030%. The Se content is less than 0.0050%, preferably less than 0.0030%.

However, since Al has a high oxygen affinity, the amount of dissolved oxygen in the steel can be reduced by adding a small amount of Al in the steelmaking process, and as a result, oxide-based inclusions leading to deterioration of characteristics can be reduced. Therefore, in order to obtain the above effect, Al can be added within the range of the above content.

In the present invention, a steel slab containing each of the above elements and having a component composition in which the balance is composed of Fe and unavoidable impurities is used. In one embodiment of the present invention, a steel slab having a component composition consisting of only the above elements, the remaining Fe, and unavoidable impurities can also be used.

In addition to the above-mentioned elements, the above-mentioned component composition can be arbitrarily added.
Cr: 0.01-0.50%,
Cu: 0.01-0.50%,
Ni: 0.01-0.50%,
Bi: 0.005 to 0.50%,
B: 0.0002 to 0.0025%,
Nb: 0.0010 to 0.0100%,
Sn: 0.010 to 0.400%,
Sb: 0.010 to 0.150%,
It may further contain 1 or 2 or more selected from the group consisting of Mo: 0.010 to 0.200% and P: 0.010 to 0.150%.

Each of the above elements has an action of improving the magnetic characteristics of the grain-oriented electrical steel sheet, but if the content is lower than the above lower limit value, a sufficient effect of improving the magnetic characteristics cannot be obtained. On the other hand, when the content exceeds the above upper limit value, the development of secondary recrystallized grains is suppressed, so that the magnetic characteristics are rather deteriorated.

As the steel slab, any steel slab can be used without particular limitation as long as it has the above-mentioned composition. The method for producing the steel slab is not particularly limited, and the steel slab can be produced by any method. For example, a steel slab can be produced by an ingot forming method or a continuous casting method using molten steel adjusted to a predetermined composition. Further, a thin slab having a thickness of 100 mm or less can be produced by using a direct casting method, and this can be used as a steel slab. Since it is difficult to add each of the above-mentioned elements in the intermediate process, it is preferable to add each element at the stage of molten steel.

[heating]
Prior to hot rolling, the steel slab is subjected to slab heating. In the slab heating, the steel slab is heated to a slab heating temperature T (° C.) of 1280 ° C. or lower, and maintained at the slab heating temperature T for a soaking time t (minutes).

-Slab heating temperature: 1280 ° C. or less In the conventional technique using an inhibitor, it is necessary to raise the slab heating temperature in order to dissolve the inhibitor component, but in the present invention, the slab heating temperature is set because the inhibitor is not used. It doesn't have to be high. Therefore, the slab heating temperature is set to 1280 ° C. or lower so that hot rolling can be performed without any problem. On the other hand, the lower limit of the slab heating temperature is not particularly limited, but is preferably 1150 ° C. or higher.

-Heat soaking time t: P _t or less Further, the heat soaking time t (minutes) in the slab heating is set to P _t or less defined by the following equation (1).
P _t = 800 [C] -5 [Si] + T / 25 ... (1)
However, in the formula (1), [C] is the C content (mass%) in the steel slab, and [Si] is the Si content (mass%) in the steel slab.

As described above, in the present invention, by shortening the soaking time in slab heating, a microstructure in which the γ phase is dispersed is formed, and as a result, an texture suitable for selective growth of Goss oriented grains is obtained. Can be done. However, the amount of γ phase is affected by the C content and Si content of the steel slab. Specifically, C increases the γ phase amount and Si decreases the γ phase amount. The smaller the amount of γ-phase, the greater the influence of the dispersion of γ-phase on the texture, so that the slab heating needs to be shortened. Therefore, by setting the soaking time t to be equal to or less than the above P value in consideration of the influences of not only the soaking time T but also the C content and the Si content, the dispersion state of the γ phase is optimized and finally. The magnetic properties of the grain-oriented electrical steel sheet obtained in the above can be improved.

[Hot rolling]
Next, the steel slab heated to the slab heating temperature is hot-rolled to obtain a hot-rolled steel sheet. The conditions for hot rolling are not particularly limited, and the hot rolling can be performed under any conditions.

[Annealed hot-rolled plate]
Next, the hot-rolled steel sheet is annealed. In the present invention, it is necessary to control the conditions of final pre-cold annealing annealing as described later. In the next cold rolling step, in the case of the one-time method in which cold rolling is performed only once, since the hot-rolled sheet annealing corresponds to the final cold-rolled pre-annealing, the hot-rolled sheet annealing is carried out under specific conditions. There is a need. On the other hand, when cold rolling is performed twice or more, the final cold rolling is the final cold rolling among the two or more cold rollings, so that the intermediate annealing before the final cold rolling is final. Corresponds to annealing before cold rolling. Therefore, in that case, it is necessary to carry out the intermediate annealing under specific conditions, but the conditions for hot-rolled sheet annealing are not particularly limited and can be carried out under any conditions. The specific conditions for final annealing before annealing will be described later.

[Cold rolling]
Next, the hot-rolled steel sheet after annealing is subjected to cold rolling to obtain a cold-rolled steel sheet. The cold rolling may be performed only once (one-time method), or may be performed twice or more. When cold rolling is performed twice or more, intermediate annealing is performed between each cold rolling step. For example, in the case of the two-time method in which cold rolling is performed twice, hot-rolled sheet annealing, first cold rolling, intermediate annealing, and second cold rolling may be performed in this order.

As described above, when cold rolling is performed twice or more, the intermediate annealing performed immediately before the last cold rolling among the two or more cold rollings corresponds to the final pre-rolling annealing. .. Therefore, the final pre-cold annealing annealing needs to be performed under the conditions described later. On the other hand, the conditions for intermediate annealing other than the final cold pre-rolling annealing (for example, the first intermediate annealing when cold rolling is performed three times) are not particularly limited and can be performed under any conditions.

-Rolling temperature in final cold rolling: 100-300 ° C
The rolling temperature in the last cold rolling (final cold rolling) of the one or more cold rollings is 100 ° C. to 300 ° C. As a result, the recrystallized texture can be changed to improve the magnetic properties. Here, the rolling temperature in the final cold rolling refers to the highest temperature among the exit temperature of each pass constituting the final cold rolling.

Further, it is also effective to perform the aging treatment in the range of 100 to 300 ° C. once or a plurality of times during the cold rolling in order to further improve the magnetic characteristics. If the temperature is higher than 300 ° C., the shape will be poor and rolling will be difficult.

[Primary recrystallization annealing]
・ Temperature rise rate: 100 to 400 ° C / s
Next, the obtained cold-rolled steel sheet is subjected to primary recrystallization annealing that also serves as decarburization. In the primary recrystallization annealing, the rate of temperature rise in the temperature rise section of 500 to 680 ° C. is set to 100 to 400 ° C./s from the viewpoint of controlling the recrystallization texture. When the temperature rising rate is less than 100 ° C./s, the {110} azimuth grains decrease and the magnetic characteristics deteriorate. On the other hand, when the temperature rising rate exceeds 400 ° C./s, the {411} directional grains become excessive, and the magnetic characteristics are rather deteriorated. It is more preferable that the temperature rising rate is 350 ° C./s or less.

The annealing temperature in the primary recrystallization annealing is not particularly limited, but from the viewpoint of improving the decarburization property, the annealing temperature is preferably 800 ° C. or higher and 900 ° C. or lower. Similarly, from the viewpoint of improving the decarburization property, it is preferable to make the annealing atmosphere a moist atmosphere.

[Application of annealing separator]
Then, an annealing separator is applied to the surface of the cold-rolled steel sheet after primary recrystallization annealing. The annealing separating agent is not particularly limited, and any composition can be used. For example, when importance is attached to iron loss, it is preferable to use an annealing separator containing MgO, which is a forsterite forming component. By applying an annealing separator containing MgO to the surface of the steel sheet and then performing purification annealing, a secondary recrystallization structure is developed and a forsterite film is formed on the surface of the steel sheet. As the annealing separator, it is preferable to use an annealing separator mainly composed of MgO.

On the other hand, when emphasizing punching workability, it is preferable to use an annealing separator that does not contain MgO, which is a component that forms forsterite. When an annealing separator containing no MgO is used, a forsterite film is not formed, and as a result, punching workability is improved. Examples of the annealing separator containing no MgO include an annealing separator containing either one or both of silica and alumina. When applying these annealing separators, it is effective to perform electrostatic coating that does not bring in moisture. Further, a heat-resistant inorganic material sheet (silica, alumina, mica) may be used.

[Purified annealing]
Then, purification annealing with secondary recrystallization is performed. The purification annealing can be carried out under any conditions without particular limitation, but the annealing temperature is preferably 800 ° C. or higher for the expression of secondary recrystallization. Further, from the viewpoint of reliably completing the secondary recrystallization, it is preferable to hold the annealing temperature (holding temperature) of 800 ° C. or higher for 20 hours or longer.

Generally, in the purification annealing step, a forsterite film is formed by the reaction between the oxide present on the surface of the steel sheet and the annealing separator. It is not necessary to form a forsterite film. When the forsterite film is not formed, the holding temperature in the purified annealing is preferably 850 to 950 ° C. In that case, the purification annealing can be completed only by holding at the holding temperature. On the other hand, when forming a forsterite film for improving iron loss and reducing transformer noise, it is preferable to raise the temperature to 1100 to 1300 ° C.

After the purification annealing, it is preferable to remove the annealing separator adhering to the surface of the steel sheet. The method of removal is not particularly limited, and for example, one or two or more selected from the group consisting of washing with water, brushing, and pickling can be used.

[Flatration annealing]
Next, the cold-rolled steel sheet after purification annealing is subjected to flattening annealing. By the flattening annealing, the shape of the steel sheet can be corrected and the iron loss can be reduced.

[Insulation coating]
Although not essential in the present invention, an insulating coating can be formed on the surface of the grain-oriented electrical steel sheet. By providing the insulating coating, it is possible to reduce the iron loss when the grain-oriented electrical steel sheets are laminated and used. The insulating coating can be formed, for example, before or after flattening annealing. The material of the insulating coating is not particularly limited, and a coating made of any insulating material can be used, and an inorganic coating is generally used.

The method for forming the insulating coating is not particularly limited, and for example, a method of applying a coating treatment liquid, a physical vapor deposition method, a chemical vapor deposition method, or the like can be used. When the method of applying the coating treatment liquid is used, the coating treatment liquid can be baked by applying the coating before the flattening annealing and then performing the flattening annealing. The composition of the coating treatment liquid is not particularly limited, but for example, a treatment liquid containing phosphate and silica can be used.

[Magnetic domain subdivision processing]
Further magnetic domain subdivision treatment can be performed in order to further reduce iron loss. The method of the magnetic domain subdivision treatment is not particularly limited, and any method can be used. Examples of the magnetic domain subdivision treatment method include a method of introducing at least one of thermal strain and impact strain by irradiating the surface of the obtained directional electromagnetic steel sheet with a laser, an electron beam, plasma, or the like, or in the middle of a manufacturing process. For example, a method of forming a groove on the surface of a steel sheet by mechanical processing or etching after cold rolling can be mentioned.

[Conditions for final cold pre-annealing]
In the present invention, the grain-oriented electrical steel sheet is manufactured by sequentially performing each step as described above. At that time, in the final pre-cold annealing annealing, the steel sheet is heated to an annealing temperature of 103 to 1150 ° C., kept at the annealing temperature for a holding time of 10 to 180 seconds, and cooled. Then, the residence time of staying in the temperature range of 1030 to 900 ° C. during the cooling is set to 10 seconds or more. The reason will be described below.

Here, the "final cold rolling" refers to the last cold rolling of the one or two or more cold rollings. For example, in the case of the one-time method in which cold rolling is performed only once, the one-time cold rolling is the final cold rolling. In the case of the two-time method in which cold rolling is performed twice, the second cold rolling is the final cold rolling.

Further, here, the “annealing before final cold rolling” refers to the annealing performed immediately before the “final cold rolling” defined as described above. For example, in the case of the one-time method in which cold rolling is performed only once, the hot-rolled sheet annealing performed before the one cold rolling is the final cold-rolled pre-annealing. Further, in the case of the two-time method in which the cold rolling is performed twice, the intermediate annealing performed between the first cold rolling and the second cold rolling is the final cold pre-rolling annealing.

Annealing temperature: 1030 to 1150 ° C
The annealing temperature (maximum temperature reached) in the final pre-rolling annealing is set to 1030 ° C. or higher, preferably 1040 ° C. or higher in order to completely recrystallize the structure formed by hot rolling. On the other hand, if the annealing temperature exceeds 1150 ° C., the crystal grains after annealing become coarse, which is extremely disadvantageous in realizing the subsequent primary recrystallization structure of granulation. Therefore, the annealing temperature is set to 1150 ° C. or lower, preferably 1100 ° C. or lower.

Retention time: 10 to 180 seconds As described above, in the final pre-rolling annealing, it is necessary to completely recrystallize the structure formed by hot rolling. If the holding time maintained at the annealing temperature in the final pre-cold annealing is less than 10 seconds, there is a high possibility that unrecrystallized portions remain. Further, when the annealing temperature is 103 to 1150 ° C., if the annealing temperature is held for 180 seconds, recrystallization is completely completed, so that further holding is not necessary. Therefore, the holding time is set to 180 seconds or less.

Dwelling time of 1030 to 900 ° C .: 10 seconds or more By ensuring a dwelling time of staying in the temperature range of 1030 to 900 ° C. in the cooling process of pre-anneal annealing, the γ phase is refined and finally obtained. The magnetic flux density of the grain-oriented electrical steel sheet can be improved. Therefore, the residence time is set to 10 seconds or more. The residence time is preferably 20 seconds or more. On the other hand, the upper limit of the residence time is not particularly limited. However, if the residence time exceeds 180 seconds, the effect of refining the γ phase is saturated and the productivity is lowered. Therefore, the residence time is preferably 180 seconds or less.

The cooling from 900 ° C. to 350 ° C. in the cooling process of final pre-cooling annealing is not particularly limited and can be performed at an arbitrary speed. However, from the viewpoint of controlling the texture and further improving the magnetic characteristics, it is preferable that the average cooling rate in the temperature range between 900 ° C. and 350 ° C. is 20 ° C./s or more.

Further, even in the above temperature range, the average cooling rate in the temperature range of 700 ° C. to 350 ° C. can be set to 35 ° C./s or less.

Cooling in the temperature range below 350 ° C. can be arbitrarily performed. For example, it may be allowed to cool to room temperature.

When the cold rolling is performed twice or more, the intermediate annealing before the final cold rolling may be performed under the above conditions, and the hot rolling plate annealing can be performed under any conditions. For example, hot-rolled plate annealing can be performed under the conditions of a soaking temperature of 900 to 1150 ° C. and a soaking time of 10 seconds or more.

Next, the present invention will be described in more detail based on Examples. The following examples show a suitable example of the present invention, and the present invention is not limited to the above examples.

(Example 1)
A grain-oriented electrical steel sheet was manufactured by a one-time method according to the procedure described below, and its magnetic properties were evaluated.

-Slab heating, hot rolling First, steel slabs having the composition shown in Tables 2 and 3 were manufactured by a continuous casting method. Next, the steel slab was heated under the conditions shown in Tables 4 and 5 (slab heating). Then, the heated steel slab was hot-rolled to obtain a hot-rolled steel sheet having a plate thickness of 2.3 mm.

-Hot-rolled sheet annealing Next, the hot-rolled steel sheet was annealed on the hot-rolled steel sheet under the conditions of an annealing temperature of 1050 ° C. and a holding time of 40 seconds. The cooling conditions after the lapse of the holding time in the hot-rolled plate annealing were as shown in Tables 4 and 5.

・ Cold rolling (1 time method)
Further, the hot-rolled steel sheet (hot-rolled sheet) after annealing of the hot-rolled sheet was subjected to one cold rolling to obtain a cold-rolled steel sheet having a thickness of 0.27 mm. The rolling temperature in the cold rolling was as shown in Tables 4 and 5. In this embodiment, as described above, the one-time method in which cold rolling is performed only once is adopted, and intermediate annealing is not performed. Therefore, the cold rolling corresponds to the final cold rolling, and the hot-rolled plate annealing corresponds to the final cold pre-rolling annealing.

-Primary recrystallization annealing The cold-rolled steel sheet was subjected to primary recrystallization annealing that also served as decarburization annealing. Said primary recrystallization annealing is 70 seconds at _{850 ℃, 52% H 2 -48} % N 2, were carried out under a humid atmosphere with a dew point of 60 ° C.. The rate of temperature rise in the temperature range of 500 to 680 ° C. in the temperature rise process of the primary recrystallization annealing was as shown in Tables 4 and 5.

-Application of annealing separator After the primary recrystallization annealing, an annealing separator mainly composed of MgO was applied to the surface of the steel sheet.

Next, the steel sheet coated with the annealing separator was subjected to purification annealing accompanied by secondary recrystallization. In the purification annealing, the steel sheet was retained at 1225 ° C. for 10 hours in a hydrogen atmosphere.

After that, the cold-rolled steel sheet after the purification annealing was subjected to flattening annealing at 800 ° C. for 40 seconds to obtain a grain-oriented electrical steel sheet.

-Measurement of magnetic flux density The B8 (magnetic flux density when excited at 800 A / m) of the obtained grain-oriented electrical steel sheet was measured by the method described in JIS C2550. The obtained B8 values are also shown in Tables 4 and 5.

As is clear from the results shown in Tables 2 to 5, the grain-oriented electrical steel sheets satisfying the conditions of the present invention had good magnetic properties.

(Example 2)
A grain-oriented electrical steel sheet was manufactured by a two-step method according to the procedure described below, and its magnetic properties were evaluated.

-Slab heating, hot rolling First, steel slabs having the component compositions shown in Tables 6 and 7 were produced by a continuous casting method. Next, the steel slab was heated under the conditions shown in Tables 8 and 9 (slab heating). Then, the heated steel slab was hot-rolled to obtain a hot-rolled steel sheet having a plate thickness of 2.5 mm.

-Hot-rolled sheet annealing Next, the hot-rolled steel sheet was annealed on the hot-rolled steel sheet under the conditions of an annealing temperature of 1000 ° C. and a holding time of 40 seconds. The cooling conditions after the lapse of the holding time in the hot-rolled plate annealing were as shown in Tables 8 and 9.

・ Cold rolling (double method)
Further, the hot-rolled steel sheet (hot-rolled sheet) after the hot-rolled sheet was annealed was subjected to cold rolling twice with intermediate annealing sandwiched between them. Specifically, the first cold rolling was first carried out to make the sheet thickness of the steel sheet 1.5 mm, and then intermediate annealing was carried out under the conditions of annealing temperature: 1080 ° C. and holding time: 30 seconds. After the intermediate annealing, the second cold rolling was performed to obtain a cold-rolled steel sheet having a plate thickness of 0.23 mm. In this embodiment, as described above, a one-time method in which cold rolling is performed twice is adopted. Therefore, the second cold rolling corresponds to the final cold rolling, and the intermediate annealing corresponds to the final cold pre-annealing. The rolling temperature in the second cold rolling (final cold rolling) was as shown in Tables 8 and 9.

-Primary recrystallization annealing The cold-rolled steel sheet was subjected to primary recrystallization annealing that also served as decarburization annealing. Said primary recrystallization annealing is 150 seconds at _{840 ℃, 55% H 2 -45} % N 2, were carried out under a humid atmosphere with a dew point of 60 ° C.. The rate of temperature rise in the temperature range of 500 to 680 ° C. in the temperature rise process of the primary recrystallization annealing was as shown in Tables 8 and 9.

-Application of annealing separator After the primary recrystallization annealing, an annealing separator mainly composed of MgO was applied to the surface of the steel sheet.

Next, the steel sheet coated with the annealing separator was subjected to purification annealing accompanied by secondary recrystallization. In the purified annealing, the steel sheet was retained at 1200 ° C. for 10 hours in a hydrogen atmosphere.

After that, the cold-rolled steel sheet after the purification annealing was subjected to flattening annealing at 830 ° C. for 40 seconds to obtain a grain-oriented electrical steel sheet.

-Measurement of magnetic flux density The B8 (magnetic flux density when excited at 800 A / m) of the obtained grain-oriented electrical steel sheet was measured by the method described in JIS C2550. The obtained B8 values are also shown in Tables 8 and 9.

As is clear from the results shown in Tables 6 to 9, the grain-oriented electrical steel sheets satisfying the conditions of the present invention had good magnetic properties.

Further, from the results of Examples 1 and 2 above, by controlling the conditions of final cold rolling and final cold rolling pre-annealing as defined in the present invention, excellent magnetic properties can be obtained regardless of the number of cold rollings. It can be seen that a grain-oriented electrical steel sheet having is obtained.

Claims (4)

By mass%
C: 0.025 to 0.10%,
Si: 2.0-6.5%,
Mn: 0.005-1.00%,
Al: less than 0.010%,
N: less than 0.0050% S: less than 0.0050%, and Se: less than 0.0050%, including
A steel slab having a component composition in which the balance is composed of Fe and unavoidable impurities is subjected to slab heating.
The heated steel slab is hot-rolled to form a hot-rolled steel sheet.
The hot-rolled steel sheet is annealed by hot-rolled steel sheet, and then the hot-rolled steel sheet is annealed.
The hot-rolled steel sheet after annealing is subjected to one cold-rolling or two or more cold-rolling sandwiching an intermediate annealing to obtain a cold-rolled steel sheet.
The cold-rolled steel sheet is subjected to primary recrystallization annealing that also serves as decarburization annealing.
An annealing separator is applied to the surface of the cold-rolled steel sheet after the primary recrystallization annealing.
The cold-rolled steel sheet was subjected to purification annealing accompanied by secondary recrystallization, and then subjected to purification annealing.
A method for producing a grain-oriented electrical steel sheet, in which the cold-rolled steel sheet after purification annealing is flattened and annealed.
In the slab heating, the steel slab is heated to a slab heating temperature T (° C.) of 1280 ° C. or lower and maintained at the slab heating temperature T for a soaking time t (minutes), and the soaking time t is as follows. It is less than or equal _{to P t} defined by Eq. (1).
When the last cold rolling of the one or two or more cold rollings is defined as final cold rolling, and the annealing performed immediately before the final cold rolling is defined as final cold rolling pre-annealing, respectively.
In the final pre-cooling annealing, the steel plate is heated to an annealing temperature of 1030 to 1150 ° C., held at the annealing temperature for a holding time of 10 to 180 seconds, cooled, and 1030 to 1030 during the cooling. The residence time staying in the temperature range of 900 ° C. is 10 seconds or more.
The rolling temperature in the final cold rolling is 100 to 300 ° C.
A method for producing a grain-oriented electrical steel sheet, wherein the heating rate in the temperature rising section of 500 to 680 ° C. in the primary recrystallization annealing is 100 to 400 ° C./s.
P _t = 800 [C] -5 [Si] + T / 25 ... (1)
However, in equation (1), [C] is the C content (mass%) in the steel slab, and [Si] is the Si content (mass%) in the steel slab. In the cooling process of the final cold pre-annealing
The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein the average cooling rate in a temperature range between 900 ° C. and 350 ° C. is 20 ° C./s or more. In the cooling process of the final cold pre-annealing
The method for manufacturing a grain-oriented electrical steel sheet according to claim 2, wherein the average cooling rate in the temperature range between 700 ° C. and 350 ° C. is 35 ° C./s or less. When the component composition is mass%,
Cr: 0.01-0.50%,
Cu: 0.01-0.50%,
Ni: 0.01-0.50%,
Bi: 0.005 to 0.50%,
B: 0.0002 to 0.0025%,
Nb: 0.0010 to 0.0100%,
Sn: 0.010 to 0.400%,
Sb: 0.010 to 0.150%,
Mo: 0.010-.200% and P: further seen contains one or more selected from the group consisting of 0.010 to 0.150%,
The method for producing grain-oriented electrical steel sheets according to claim 1, wherein in the cooling process of the final pre-cooling annealing, the average cooling rate in the temperature range between 900 ° C. and 350 ° C. is 18 ° C./s or more.