JP6375692B2 - Non-oriented electrical steel sheet and manufacturing method thereof, hot-rolled sheet for non-oriented electrical steel sheet and manufacturing method thereof - Google Patents

Description

  The present invention relates to a non-oriented electrical steel sheet having excellent high-frequency iron loss, which is suitable as a material for motor cores, particularly motor cores that are driven at high speed and high frequency, such as hybrid cars and electric cars, and particularly contains Si and Al. Non-oriented electrical steel sheet with high specific resistance using steel with increased amount, especially non-oriented electrical steel sheet with improved workability at the time of punching motor cores and its manufacturing method, and heat with improved cold rollability The present invention relates to a rolled sheet, a manufacturing method thereof, and a method of manufacturing a non-oriented electrical steel sheet using the hot rolled sheet.

In recent years, the spread of hybrid vehicles and electric vehicles has been remarkable. Drive motors used for these are increasing in speed and driven at high frequencies by inverters. With high-speed rotation and high-frequency driving, non-oriented electrical steel sheets for motor cores are required to reduce high-frequency iron loss.
The most effective way to reduce eddy current loss, which accounts for most of the high-frequency iron loss of non-oriented electrical steel sheets, is to reduce the thickness of the sheet. High specific resistance due to has become prominent.

  Si is the most effective alloy element added for the purpose of increasing the specific resistance, and the addition cost is cheaper than other elements, so it is most commonly used. Furthermore, since the magnetostriction constant in the <100> direction becomes 0 when the Si content is 6.5%, it is very effective in reducing noise in electrical equipment, improving the permeability of steel sheets, and reducing hysteresis loss.

  Al is also effective as an alloying element other than Si. Al has the advantage of improving the specific resistance at the same added amount as compared with Si, but has an advantage that the increase in hardness is less than that of Si. Furthermore, Mn and Cr are elements that increase the specific resistance, but the effect of improving the specific resistance at the same addition amount is about ½ compared to Si and Al, and are rarely added for the purpose of increasing the specific resistance. .

  On the other hand, when Si and Al are added, the strength of the steel sheet is increased and cured. In order to use a non-oriented electrical steel sheet as a motor core, it is necessary to punch into a predetermined shape. However, when a steel sheet having high hardness is punched, the wear of the mold becomes severe. When the mold is worn, dripping or burrs are generated on the punched end face, and the mold must be frequently replaced, which causes a serious problem in terms of cost and productivity.

In order to solve such a problem, a technique for suppressing an increase in the hardness of a steel sheet by adding an alloy element has been proposed. For example, in Patent Document 1, Cr: 0.2-3% is added to steel containing Si: 1-3.5% and Al: 0.1-3% to improve punching workability. However, the effect is not sufficient in a steel plate having a higher Si content.
Patent Document 2 discloses a hard oxide inclusion such as alumina for steel containing Si: 0.1 to 7%, Al: 0.01 to 3%, and Mn: 0.1 to 2%. Has been disclosed as a starting point for cracking during punching by dispersing the steel inside the steel plate, and the technology to improve punching workability is disclosed, but hard oxide inclusions affect the magnetic properties. Therefore, it is difficult to uniformly disperse the steel sheet.

  Furthermore, as a problem in steel plate manufacture, it is generally mentioned that rolling at room temperature becomes difficult due to embrittlement when Si exceeds 2%. In particular, motor core materials that emphasize the efficiency of electric vehicles, etc., are generally annealed before cold rolling to improve magnetic properties, and then recrystallized and grain grown. Further embrittlement makes cold rolling difficult.

  In order to suppress cracking during cold rolling due to embrittlement, it is effective to raise the temperature during rolling and to roll at a temperature equal to or higher than the ductility / brittle transition temperature of the steel sheet. For example, Patent Document 1 discloses a technique for raising the temperature to a ductile / brittle transition temperature of 60 ° C. or higher by induction heating or the like before cold rolling of a silicon steel sheet. Patent Document 2 discloses a method of performing rapid heating before cold rolling. However, as the amounts of Si and Al increase, the ductile / brittle transition temperature rises to 100 ° C. or higher, which makes heating difficult.

  There is also a means for reducing brittleness during rolling by adding an alloy element. For example, Patent Document 5 discloses a material having excellent high-frequency characteristics and excellent rolling properties by adding 1.5 to 20% of Cr to a material having Si: 2.5 to 10% and Al: 5% or less. A technique for obtaining the above is disclosed. Further, as an improvement of this technique, Patent Document 6 further describes Ni and Cu as elements that further reduce C and N to 0.005% or less to lower the ductile-brittle transition temperature and improve workability. A technique for further adding is disclosed. However, it is not sufficient to drastically solve problems such as ear cracks by improving the cold rollability only by adding alloy elements and reducing impurities.

  Furthermore, in Patent Document 7, a molten steel containing Si: 4 to 10%, Al: 0.04 to 2%, and the like is super-quenched and directly cast into a thin strip, and the thin strip is annealed. Although a technique for obtaining a high silicon steel ribbon having no lattice and excellent workability and magnetic properties has been disclosed, it is not suitable for implementation on an industrial scale.

JP 61-15919 A JP-A-2-303620 JP 2002-356718 A Japanese Patent Laid-Open No. 10-251754 JP-A-11-343544 JP 2001-279327 A Japanese Patent Publication No. 61-15136

  The present invention provides a non-oriented electrical steel sheet capable of improving the workability at the time of punching a motor core in a non-oriented electrical steel sheet using high Si-Al steel, and a method for producing the same, and a high Si-Al steel. An object of the present invention is to provide a hot-rolled sheet for producing a non-oriented electrical steel sheet capable of producing a non-oriented electrical steel sheet using steel while suppressing brittle fracture in cold rolling, and a method for producing the hot-rolled sheet.

In order to solve the above-mentioned problems, the present inventors diligently studied means for reducing the hardness of the high-Si steel sheet. As a result, DO ₃ ordered clusters are generated in the cooling process after annealing, which affects the increase in hardness of the steel sheet after annealing, and the size of the clusters is set to 100 nm or less. It has been found that by using a material to which Ni or Ni is added, it is possible to suppress an increase in hardness of the steel sheet when the Si content is increased and to suppress embrittlement.
And as a result of further examination, it is possible to improve the punchability by applying this knowledge to the non-oriented electrical steel sheet used as a product after cold rolling annealing, and to apply to the hot rolled steel sheet as an intermediate product Thus, it was confirmed that the rollability during the subsequent cold rolling could be improved, and the present invention was achieved.

The gist of the present invention made as a result of such examination is as follows.
(1) Steel composition is mass%,
C: 0.01% or less,
Si: 2.0% to 7.0%,
Al: 0.3% to 10.0%,
Mn: 0.2% to 2.0%
P: 0.1% or less,
S: 0.005% or less Ni: 0.1 to 5% and Cu: 0.1 to 3% of one or two kinds, the balance is made of Fe and inevitable impurities, DO ₃ rules in the steel sheet Non-oriented electrical steel sheet, wherein the size of the cluster is 100 nm or less.

(2) The slab having the steel composition described in (1) above is hot-rolled, hot-rolled sheet annealed and cold-rolled, or cold-rolled without performing hot-rolled sheet annealing, and finish annealing. In producing the non-oriented electrical steel sheet according to (1) above,
In the cooling process of the finish annealing, it is held for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. or less, and then 600 ° C. or less is cooled to at least 250 ° C. or less at a cooling rate of 60 ° C./sec or more. A method for producing a non-oriented electrical steel sheet.
(3) The non-oriented electrical steel sheet according to claim 1 is manufactured by hot rolling, hot-rolled sheet annealing, cold rolling, and finish annealing of the slab having the steel composition described in (1) above. When doing
In the cooling process of the hot-rolled sheet annealing, it is held for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. or less, and then 600 ° C. or less is cooled to at least 250 ° C. or less at a cooling rate of 60 ° C./sec or more. A method for producing a non-oriented electrical steel sheet.
(4) The non-oriented electrical steel sheet according to claim 1 is produced by hot rolling, hot-rolled sheet annealing, cold rolling, and finish annealing of the slab having the steel composition described in (1) above. When doing
In the cooling process of the hot-rolled sheet annealing, it is maintained for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. or less, and then 600 ° C. or less is cooled to at least 250 ° C. or less at a cooling rate of 60 ° C./sec or more. In the annealing cooling process, the temperature is maintained for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. or less, and then 600 ° C. or less is cooled to at least 250 ° C. or less at a cooling rate of 60 ° C./sec or more. Method for producing an electrical steel sheet.

(5) A hot-rolled sheet for producing the non-oriented electrical steel sheet according to (1) by cold rolling,
Steel composition is mass%,
C: 0.01% or less,
Si: 2.0% to 7.0%,
Al: 0.3% to 10.0%,
Mn: 0.2% to 2.0%
P: 0.1% or less,
S: 0.005% or less,
It contains one or two of Cu: 0.1 to 3% and Ni: 0.1 to 5%, the balance is made of Fe and inevitable impurities, and the size of the DO ₃ ordered cluster in the steel sheet is 100 nm or less. A hot-rolled sheet for non-oriented electrical steel sheets.

(6) When manufacturing the hot-rolled sheet for non-oriented electrical steel sheets according to claim 5 by hot-rolling the slab composed of the steel composition described in (5) above and performing hot-rolled sheet annealing.
In the cooling process of the hot-rolled sheet annealing, it is held for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. or less, and then 600 ° C. or less is cooled to at least 250 ° C. or less at a cooling rate of 60 ° C./sec or more. The manufacturing method of the hot-rolled sheet for non-oriented electrical steel sheets.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to provide the non-oriented electrical steel sheet which improved the workability at the time of the motor core punching of high Si-Al steel by a simple means, cooling of the material with high content of Si and Al is possible. Since a non-oriented electrical steel sheet can be obtained by suppressing brittle fracture in hot rolling, a non-oriented electrical steel sheet having a high specific resistance and excellent high-frequency iron loss can be manufactured more stably. Become.

It is a figure which shows typically the relationship between the amount of Al addition in a Fe-2Si alloy, and the hardness of a steel plate. It is a figure which compares and shows the relationship between Cu addition amount in the Fe-2Si alloy, and the hardness of a steel plate by the presence or absence of heat processing.

Hereinafter, embodiments of the present invention will be described in detail.
When Si or Al is added to steel, the hardness of the steel increases. When a steel sheet having a high hardness is punched, the mold is severely worn, and there is a problem that the height of burrs generated on the punched end surface of the steel sheet increases. In addition, the critical stress required for slip deformation is increased, and movable dislocations are not introduced during cold rolling, generating twins. Twins are known to be the starting point of brittle fracture, and for this reason, steel with a large amount of Si or Al is susceptible to brittle fracture in cold rolling.

The present inventors investigated the relationship between the Si and Al amounts and the hardness of the alloys by increasing the amounts of Si and Al in Fe—Al based alloys and Fe—Si—Al based alloys. As an example, FIG. 1 is a schematic diagram showing changes in hardness (HV) when the Al content is increased in an Fe-2% Si alloy.
As shown in FIG. 1, as the Al content is increased, the hardness increase tends to saturate gradually, but the Al content starts to increase again from about 4%, and when the Al content is around 8%, the regular phase is reached. A sudden increase in hardness was observed due to the appearance of.

The increase in hardness up to about 4% is due to the solid solution strengthening of Al, and it is expected that a gradual increase in hardness will continue until a regular phase appears, as shown by the dotted line in FIG. However, it was found that the hardness increased abnormally before the regular phase appeared.
Therefore, the cause of such an abnormal increase in hardness was investigated. When the Fe-2Si-6Al alloy in the hardness increasing region was rapidly cooled from the molten state to prepare a rapidly cooled sample, and the rapidly cooled sample was observed in detail by TEM, a DO ₃ ordered cluster having a particle size of about 200 nm was found. Observed.

Conventionally, it has not been reported that DO ₃ ordered clusters appear from a low Al content stage, but we proceeded with investigations assuming that an abnormal increase in hardness would occur due to the appearance of such ordered phases. .

Therefore, first, a means for suppressing the increase in hardness by reducing the size of the DO ₃ ordered cluster was examined.
Since the regular transformation is a diffusion type transformation, it is possible to suppress the generation of the ordered phase by creating an irregular phase state in the cooling process of finish annealing after cold rolling and quenching from that state. As a result of repeated experiments under the idea of whether or not there is an increase in hardness by making the size of the DO ₃ ordered cluster to be 100 nm or less, and over 600 ° C. during cooling after annealing, 700 ° C. It was found that the cluster size can be suppressed to a small value even if a regular phase is formed by holding for 10 seconds or more below and rapidly cooling the temperature range from 600 ° C. to at least 250 ° C.

Furthermore, the effect of the additive element was also investigated. As a result, it has been found that the addition of Cu or Ni further suppresses clustering of the DO ₃ ordered phase and suppresses an increase in steel sheet hardness. FIG. 2 shows the results of investigating the effect of Cu addition on the hardness in the case where the cold-rolled sheet was held and heated as described above while being cooled and rapidly cooled without being held. .
As shown in FIG. 2, it can be seen that when the heat treatment as described above is performed, the effect of suppressing the increase in hardness of Cu is greater.

The present invention thus made will be described in detail below.
First, a non-oriented electrical steel sheet of the present invention and a hot-rolled sheet manufactured in the course of manufacturing the non-oriented electrical steel sheet (this hot-rolled sheet is referred to as a non-oriented electrical steel sheet). The reason for limiting the component composition range of) will be described. In addition,% of element content means the mass%.

  The Si content is 2 to 7%. Si increases the specific resistance of the steel sheet and reduces high-frequency iron loss by reducing eddy current loss. If it is less than 2%, the increase in specific resistance is small and the effect of reducing iron loss is small. On the other hand, if it is less than 2%, the wear of the mold in the punching process is not so remarkable, and the brittle fracture in the cold rolling is not so remarkable, so it is out of the scope of the present invention. If it exceeds 7%, not only does the saturation magnetic flux density of the steel sheet decrease significantly, but even if the present invention is used, punching and cold rolling become difficult, so the upper limit is made 7%.

The A1 content is 0.3 to 10%. Al, like Si, increases the specific resistance of the steel sheet and reduces high-frequency iron loss. Although the specific resistance improvement effect at the same addition amount is lower than that of Si, since the increase in hardness is small compared to Si, by replacing a part of Si with Al, the increase in the hardness of the steel sheet is suppressed, and the specific resistance is reduced. Can be improved. The amount of Al added is desirably 0.3% or more from the viewpoint of deoxidation at the steel making stage and suppression of fine precipitation of nitride. If it exceeds 10%, the saturation magnetic flux density of the steel sheet is significantly reduced, so the upper limit is made 10%.
The effect of the present invention is more exhibited in a region where 2Si + Al is 8% or more, which generally makes cold rolling and punching more difficult.

  The Mn content is 0.2-2%. Although Mn also has a small effect margin, it increases the specific resistance of the steel sheet. Moreover, 0.2% or more is desirable from a viewpoint of suppressing the fine precipitation of sulfide. Even if the content exceeds 2%, the effect of increasing the specific resistance is small compared to Si and A1, and conversely, the demerits such as lowering the saturation magnetic flux density of the steel sheet become significant, so the upper limit is limited to 2%.

Furthermore, 1 type or 2 types of Cu and Ni are contained in the range of Cu: 0.1 to 3%, Ni: 0.1 to 5%.
In the steel sheet that is kept at a temperature range of more than 600 ° C. and 700 ° C. or less for 10 seconds or more and then cooled to at least 250 ° C. at a cooling rate of 60 ° C./sec or more at a cooling rate of 60 ° C./sec or more in the cooling process of finish annealing by Cu addition The formation of DO ₃ ordered clusters is suppressed, and the hardness of the steel sheet after finish annealing is reduced. Ni addition has the same effect. As an amount that can achieve the object, 0.1% or more is added. However, even if adding over 3% for Cu and over 5% for Ni, not only the effect of reducing the hardness is saturated, but also the saturation magnetic flux density is lowered, so the value is made the upper limit respectively.

C, S, and N are impurity elements for the non-oriented electrical steel sheet, and the smaller the number, the better.
The C content is 0.005% or less. C precipitates as carbides in the steel and degrades crystal grain growth and iron loss. If it exceeds 0.005%, the deterioration of crystal grain growth and the deterioration of iron loss become remarkable, so it is limited to 0.005% or less. Furthermore, in order to suppress magnetic aging, 0.003% or less is desirable. Although a minimum is not specifically limited, It is difficult to make it 0.001% or less with a normal manufacturing method.

The amount of S is 0.003% or less by mass%. S precipitates in the steel as sulfides and degrades crystal grain growth and iron loss. If it exceeds 0.003%, the deterioration of crystal grain growth and the deterioration of iron loss become remarkable, so it is limited to 0.003% or less. Although a minimum is not specifically limited, It is difficult to make it 0.0005% or less with a normal manufacturing method.
The amount of N is 0.003% or less by mass. If N exceeds 0.003%, blister-shaped surface defects called blisters are generated, so the N content is limited to 0.003% or less. Although a minimum is not specifically limited, It is difficult to make it 0.001% or less with a normal manufacturing method.

  The above is the basic composition of steel used as a raw material, but other additive elements may be included for the purpose of improving magnetic properties. As this example, Sn, Sb, and Cr can each be contained in the range of 0.20 mass% or less.

In the steel plate of the present invention, in addition to the steel composition as described above, the size of the DO ₃ ordered cluster existing in the steel plate after annealing is specified.
It is well known that a DO ₃ ordered phase appears when the amount of Si or Al added to Fe is increased. The present inventors have confirmed that there is a situation in which the DO ₃ ordered phase appears in a cluster state even when the addition amount is smaller than the addition amount of Si or Al in which the DO ₃ ordered phase appears on the phase diagram. It was inferred that it contributed to the increase in the rolling strength, the cold rolling property, and the punching property. The appearance of such DO ₃ ordered clusters is thought to be due to the formation of minute regions having high concentrations due to fluctuations in the concentrations of Si and Al in the steel. Based on further detailed investigation, it was confirmed that such fluctuations are likely to occur during holding in a specific temperature range, particularly during the cooling process from a high temperature where Si and Al are in solution, and the characteristics and In addition to determining the allowable cluster size in relation to the above, the thermal history that enables control of the cluster size was identified.

In the present invention, the size is defined as 100 nm or less from the above examination results. Since the size of the DO ₃ regularized cluster is preferably as small as possible, no lower limit is set.
The size of DO ₃ ordering clusters to equivalent circle diameter of DO ₃ ordered clusters found from TEM observation.
It should be noted that the regularized cluster defined in the present invention needs to sense a delicate arrangement at the atomic level, and should be observed with great care in TEM observation. In particular, it is often necessary to narrow the electron beam diameter to the nano order.

In the present invention, as described above, the steel composition is adjusted so that excellent high-frequency iron loss can be obtained, and then the steel sheet has a structure in which the size of the DO ₃ ordered cluster is regulated. By realizing the steel sheet after cold rolling, a non-oriented electrical steel sheet with improved workability when punching the motor core can be obtained. Moreover, the hot rolled sheet which can suppress the brittle fracture | rupture in cold rolling can be obtained by implement | achieving in the stage of the hot rolled sheet after hot rolling.
Next, a method for producing such a non-oriented electrical steel sheet will be described.
First, after explaining the overall process, heat treatment for suppressing the size of the DO ₃ ordered cluster will be described.

The steel composed of the above components is cast into a slab, re-ripened and hot-rolled into a hot-rolled sheet. Alternatively, a thin slab manufactured by a rapid solidification method may be hot-rolled to form a hot-rolled sheet. Casting and hot rolling conditions are not particularly limited.
The obtained hot-rolled sheet may be subjected to cold rolling without being subjected to hot-rolled sheet annealing, or may be subjected to hot-rolled sheet annealing for the purpose of improving magnetic properties. The hot-rolled sheet annealing is performed without any problem in continuous annealing or batch annealing, and is performed under conditions of temperature and time at which a crystal grain size suitable for improving magnetic properties can be obtained, usually at 850 to 1100 ° C. for 30 seconds or more.

The hot-rolled sheet thus manufactured is then subjected to cold rolling.
Cold rolling is usually performed by levers or tandem, but levers mills such as Sendzimer mill are preferred because high magnetic flux density can be obtained.
The product sheet thickness after cold rolling is preferably 0.1 to 0.35 mm from the viewpoint of reducing high-frequency iron loss. In the cold rolling to obtain the product sheet thickness, one or more intermediate annealings may be sandwiched.

After making the product thickness by cold rolling, finish annealing is performed. In the finish annealing, a sufficient temperature for obtaining recrystallization and grain growth is necessary, and it is usually performed at 800 to 1100 ° C.
After finish annealing, a coating for the purpose of insulation is usually applied and baked. The effect of the present invention is not hindered by any of all organic, all inorganic, and a mixture of organic and inorganic coatings.

In the present invention, during the hot-rolled sheet annealing or the finish annealing after cold rolling, a heat treatment is performed such that the size of the DO ₃ ordered clusters generated in the steel sheet is 100 nm or less (this heat treatment is referred to as “DO ₃ ordered cluster suppression”). May be described as “heat treatment”.
In hot-rolled sheet annealing, after being heated and held at a necessary temperature and time, in the cooling process, it is held for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. or less, and then 600 ° C. or less is 60 ° C./sec or more. Cool to at least 250 ° C. or less at the cooling rate.
Similarly, even in the finish annealing after cold rolling, in the cooling process, the temperature is maintained in the temperature range of more than 600 ° C. and not more than 700 ° C. for 10 seconds or more, and then 600 ° C. or less is at least 250 ° C. at a cooling rate of 60 ° C./sec or more. Cool to below.

  The reason why each holding temperature is set to a temperature range of more than 600 ° C. and not more than 700 ° C. is that an irregular state is reached within that range. The holding time is set to 10 seconds or more in order to make the steel sheet structure in an irregular phase state. Even if the holding time is lengthened, the effect is saturated, so holding for a long time is not necessary, and a holding time of about 60 seconds is sufficient.

After holding for a predetermined time, 600 ° C. or lower is cooled at a cooling rate of 60 ° C./sec or higher. This is because if the rapid cooling is not started at least at 600 ° C., and if the cooling is not performed at a cooling rate of 60 ° C./sec or more, the regular transformation starts, and DO ₃ ordered clusters having a size exceeding 100 nm remain. Although the upper limit of the cooling rate is not particularly defined, the rate at which cooling can be performed without burdening the facility is 300 ° C./sec.
This quenching temperature range is at least up to 250 ° C. This is because the regular transformation starts unless it is rapidly cooled to this temperature.

By performing such heat treatment, the size of the DO ₃ ordered cluster can be suppressed to 100 nm, there is also a synergistic effect due to the addition of Cu and Ni, an increase in the hardness of the steel sheet can be suppressed, and the cold workability of the steel sheet can be reduced. improves.

This DO ₃ ordered cluster-suppressing heat treatment can be applied in the following aspects (a) to (c), for example, in the manufacturing process of the non-oriented electrical steel sheet, thereby obtaining industrial merit corresponding to each. it can.
(A) A DO ₃ ordered cluster-suppressing heat treatment is applied only in finish annealing after cold rolling.
(B) DO ₃ regularized cluster suppression heat treatment is performed only by hot-rolled sheet annealing.
(C) A DO ₃ ordered cluster-suppressing heat treatment is performed in both hot-rolled sheet annealing and finish annealing after cold rolling.

In the case of (a), the raw material is hot-rolled, hot-rolled sheet annealed as necessary, cold-rolled into a cold-rolled sheet, and DO ₃ ordered cluster-suppressed heat treatment during finish annealing of the cold-rolled sheet Apply. As a result, a non-oriented electrical steel sheet with improved workability when punching products such as motor cores can be obtained.
In this case, since steel having a high Si or Al content is used, the hot-rolled sheet has high hardness and is easily cracked. Therefore, it may be essential to perform cold rolling at a temperature equal to or higher than the ductility / brittle transition temperature of the steel sheet (that is, warm rolling).

In the case of (b), the material is hot-rolled, hot-rolled sheet annealed, cold-rolled and finish-annealed, and subjected to DO ₃ ordered cluster suppression heat treatment on the hot-rolled sheet in the middle.
As a result, the rollability of cold rolling performed thereafter is improved, and cold rolling can be performed while suppressing brittle fracture even if the cold rolling temperature is not particularly high. Of course, it goes without saying that the cold rolling property is further improved by applying a higher cold rolling temperature after applying the DO ₃ ordered cluster suppressing heat treatment in the hot rolled sheet annealing.

In this case, in finish annealing after cold rolling, the heat treatment is performed under general conditions such as air cooling after holding at high temperature without performing DO ₃ ordered cluster suppression heat treatment. The effect of suppressing the size of the broken DO ₃ ordered cluster is continuously maintained even after cold rolling, and the improvement effect on the product punchability is exhibited as in the case (a). However, in this case, the effect of improving the punchability is smaller than that obtained by heat treatment with regularized cluster suppression in finish annealing.
This is presumably because a small proportion of the clusters controlled to a minute size breaks the structure during the high temperature holding of the finish annealing, and the structure is reconstructed during the cooling process of the finish annealing. Even when intermediate annealing is performed in the middle of cold rolling, the characteristics of clusters formed by hot-rolled sheet annealing disappear, and the remaining invention effects in the final product tend to be small.

In the case of (c), in the step of hot rolling the material, annealing the hot rolled sheet, cold rolling to form a cold rolled sheet, and finishing annealing the cold rolled sheet, the hot rolled sheet annealing and the cold rolled sheet are performed. A DO ₃ ordered cluster-suppressing heat treatment is applied to both finish annealing.
Thereby, the size of the DO ₃ ordered cluster can be suppressed by controlling the hot-rolled sheet annealing, the cold rolling property of the steel sheet can be improved, and the product punching property can be improved by the same control in the finish annealing.

As described above, in the present invention, the steel composition is adjusted so that excellent high-frequency iron loss can be obtained, and then the steel sheet has a structure in which the size of the DO ₃ ordered cluster is regulated. By realizing the steel sheet after cold rolling, a non-oriented electrical steel sheet with improved workability when punching the motor core can be obtained. Moreover, the hot rolled sheet which can suppress the brittle fracture | rupture in cold rolling can be obtained by implement | achieving in the stage of the hot rolled sheet after hot rolling.
Hereinafter, such embodiments of the present invention will be described in detail by way of examples. These examples are examples for confirming the effects of the present invention, and do not limit the present invention.

Using a slab composed of the composition shown in Table 1 (remainder Fe and inevitable impurities), hot-rolled to produce a hot-rolled sheet having a thickness of 2 mm, and kept at 950 ° C. for 60 seconds without hot-rolled sheet annealing The steel sheet was annealed and cold-rolled to a thickness of 0.35 mm.
In addition, the cooling conditions after annealing in the hot-rolled sheet annealing were the following seven conditions, and Table 2 lists the numbers. A1 to A3 are conditions suitable for the present invention, and A4 to A6 are conditions not suitable for the present invention. A7 is an example of cooling without performing the DO ₃ ordered cluster suppression heat treatment.

A1: Air-cooled from the annealing temperature, held at 650 ° C. for 30 seconds, and then cooled to 200 ° C. at a cooling rate of 70 ° C./sec.
A2: Air-cooled from the annealing temperature, held at 610 ° C. for 60 seconds, and then cooled to 600 ° C. or lower to room temperature at a cooling rate of 100 ° C./sec.
A3: Air-cooled from the annealing temperature, held at 650 ° C. for 30 seconds, and cooled from that temperature to room temperature at a cooling rate of 70 ° C./sec.
A4: Air-cooled from the annealing temperature, held at 710 ° C. for 60 seconds, and then cooled to 600 ° C. or lower to room temperature at a cooling rate of 70 ° C./sec.
A5: Air-cooled from the annealing temperature, held at 590 ° C. for 60 seconds, and cooled from that temperature to room temperature at a cooling rate of 70 ° C./sec.
A6: Air-cooled from the annealing temperature, held at 650 ° C. for 60 seconds, and then cooled below 600 ° C. to room temperature at a cooling rate of 50 ° C./sec.
A7: Hold at 950 ° C. for 60 seconds, and air-cooled from that temperature to room temperature.

The size of the DO ₃ ordered cluster was measured using the nanobeam diffraction method for 10 observation regions of 1 μm × 1 μm of each sample obtained from the obtained hot-rolled plate and annealed plate before cold rolling, and averaged them. The size of the DO ₃ ordered cluster was determined.
Furthermore, the cold rolling property of the hot-rolled sheet was evaluated by the number of cracks due to brittleness generated at the edge of the steel sheet during rolling from 2 mm to 0.35 mm. The obtained results are shown in Table 2.

From Tables 1 and 2, it was confirmed that when the content of Ni and Cu and the size of the DO ₃ ordered cluster satisfy the scope of the present invention, improvement in cold rollability can be ensured.

Using a slab composed of the composition shown in Table 1 (remainder Fe and inevitable impurities), hot rolled to produce a hot rolled sheet having a thickness of 2 mm, and subjected to hot rolled sheet annealing at 950 ° C. for 60 seconds; Cold rolled to a thickness of 35 mm. After cold rolling, finish annealing was performed at 1000 ° C. for 60 seconds.
In addition, the cooling conditions after annealing in hot-rolled sheet annealing and cold-rolled sheet finish annealing are the above seven conditions, and Table 3 lists the numbers.

An inorganic organic film having a thickness of 0.7 μm was applied to the obtained cold-rolled annealed plate after finish annealing, and magnetic properties (iron loss W _10/1000 , magnetic flux density B ₅₀ ) were measured. Further, for cold-rolled annealed plates, the Vickers hardness (load 100 g) of each plate surface is measured, and 10 observation regions of 1 μm × 1 μm of each sample obtained from the annealed plates are subjected to DO ₃ rules using a nanobeam diffraction method. The size of the clustered cluster was measured, and the size of the DO ₃ regularized cluster obtained by averaging them was determined.
In addition, a cold-rolled annealed sheet coated with an inorganic organic film was punched into a ring-shaped sample with an inner diameter of 70 mm and an outer diameter of 100 mm with a clearance of 10%, and the number of punches when the burr height of the sample after punching exceeded 50 μm The punching workability of the cold-rolled annealed plate was evaluated.
The obtained results are shown in Table 3.

From Tables 1 and 3, when the content of Ni and Cu and the size of the DO ₃ ordered cluster satisfy the scope of the present invention, a sufficient number of punches can be obtained after securing excellent high frequency characteristics. It was confirmed that it could be secured.

Claims (6)

Steel composition is mass%,
C: 0.01% or less,
Si: 2.0% to 7.0%,
Al: 0.3% to 10.0%,
Mn: 0.2% to 2.0%
P: 0.1% or less,
S: 0.005% or less,
One or two of Ni: 0.1-5% and Cu: 0.1-3% are contained, the balance consists of Fe and inevitable impurities, and the size of the DO ₃ ordered cluster in the steel sheet is 100 nm or less A non-oriented electrical steel sheet characterized by being. The slab comprising the steel composition according to claim 1 is hot-rolled, hot-rolled sheet annealed and cold-rolled, or cold-rolled without hot-rolled sheet annealing, and finish-annealed. When manufacturing the non-oriented electrical steel sheet according to 1,
In the cooling process of the finish annealing, it is held for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. or less, and then 600 ° C. or less is cooled to at least 250 ° C. or less at a cooling rate of 60 ° C./sec or more. A method for producing a non-oriented electrical steel sheet. When producing the non-oriented electrical steel sheet according to claim 1 by hot rolling, hot-rolled sheet annealing, cold rolling, and finish annealing the slab comprising the steel composition according to claim 1,
In the cooling process of the hot-rolled sheet annealing, it is maintained for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. A method for producing a non-oriented electrical steel sheet. When producing the non-oriented electrical steel sheet according to claim 1 by hot rolling, hot-rolled sheet annealing, cold rolling, and finish annealing the slab comprising the steel composition according to claim 1,
In the cooling process of the hot-rolled sheet annealing, it is maintained for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. or less, and then 600 ° C. or less is cooled to at least 250 ° C. or less at a cooling rate of 60 ° C./sec or more. In the annealing cooling process, the temperature is maintained for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. or less, and then 600 ° C. or less is cooled to at least 250 ° C. or less at a cooling rate of 60 ° C./sec or more. Method for producing an electrical steel sheet. A hot rolled sheet for producing the non-oriented electrical steel sheet according to claim 1 by cold rolling,
Steel composition is mass%,
C: 0.01% or less,
Si: 2.0% to 7.0%,
Al: 0.3% to 10.0%,
Mn: 0.2% to 2.0%
P: 0.1% or less,
S: 0.005% or less,
It contains one or two of Cu: 0.1 to 3% and Ni: 0.1 to 5%, the balance is made of Fe and inevitable impurities, and the size of the DO ₃ ordered cluster in the steel sheet is 100 nm or less. A hot-rolled sheet for non-oriented electrical steel sheets. When the slab comprising the steel composition according to claim 5 is hot-rolled and hot-rolled sheet annealed to produce a hot-rolled sheet for non-oriented electrical steel sheets according to claim 5,
In the cooling process of the hot-rolled sheet annealing, it is maintained for 10 seconds or more in a temperature range of more than 600 ° C. and 700 ° C. The manufacturing method of the hot-rolled sheet for non-oriented electrical steel sheets.

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