JP6888603B2 - 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 having excellent magnetic properties, which is suitable for use as an iron core material of a transformer or the like.

Electrical steel sheets are soft magnetic materials widely used as iron cores for transformers, motors, etc. In particular, grain-oriented electrical steel sheets are highly integrated in the {110} <001> orientation, which is called the Goss orientation. Since it has excellent magnetic characteristics, it is mainly used for large transformers. In order to reduce the no-load loss (energy loss) of the transformer, it is necessary for the grain-oriented electrical steel sheet to have a low iron loss. In order to reduce this iron loss, conventional methods such as reducing the plate thickness and increasing the Si content, improving the orientation of the crystal orientation, applying tension to the steel sheet, smoothing the surface of the steel sheet, and refining the secondary recrystallization structure, etc. Means have been used.

Among these, as a technique for finely granulating the secondary recrystallization structure, many methods have been disclosed, such as a method of rapid heating during decarburization annealing and a method of rapid heat treatment immediately before decarburization annealing to improve the primary recrystallization texture. There is. For example, Patent Document 1 states that immediately before decarburizing and annealing a strip rolled to a final plate thickness, the oxygen potential PH ₂ O / PH ₂ is 700 at 100 ° C./s or higher in a non-oxidizing atmosphere of 0.2 or lower. A technique for obtaining a grain-oriented electrical steel sheet having low iron loss by rapidly heating to a temperature of ° C. or higher is disclosed.

Further, in Patent Document 2, the oxygen concentration in the atmosphere is set to 500 ppm or less, and the temperature is rapidly heated to 800 to 950 ° C. at a heating rate of 100 ° C./s or more, and then rapidly heated to a temperature of 800 to 950 ° C., which is lower than the temperature of 775 to 840. A technique for obtaining a grain-oriented electrical steel sheet having low iron loss by holding at a temperature of ° C. and then decarburizing and annealing at a temperature of 815 to 875 ° C. is disclosed.

Further, Patent Document 3 states that the temperature range of 600 ° C. or higher in the decarburization annealing step is heated to a temperature of 800 ° C. or higher at a heating rate of 95 ° C./s or higher, and the atmosphere in this temperature range is appropriately controlled. Discloses a technique for obtaining a grain-oriented electrical steel sheet having excellent coating properties and magnetic properties.

Further, in Patent Document 4, the amount of AlN in the hot strip is limited to 25 ppm or less by setting it to Nas AlN, and heating is performed at a heating rate of 80 ° C./s or more to a temperature of 700 ° C. or more during decarburization annealing. A technique for obtaining a grain-oriented electrical steel sheet with low iron loss is disclosed.

These technical ideas of rapid heating suppress the development of γ fibers (<111> // ND orientation) that are preferentially formed at normal heating rates by raising the temperature to near the recrystallization temperature in a short time. It is understood that the primary recrystallization texture is modified by promoting the generation of the {110} <001> structure that is the core of the secondary recrystallization, and the crystal grains after the secondary recrystallization are reduced. ing.

Many of these methods for improving the primary recrystallization texture by rapid heating uniquely define the rate of temperature rise in the temperature range from room temperature to approximately 700 ° C. or higher. It is known that the next recrystallized grains become finer and the iron loss is improved.

However, the rapid heating technique has a problem that variations in magnetic characteristics, which are considered to be caused by temperature unevenness of the steel sheet during heating, are scattered. Therefore, in order to reduce the variation in magnetic characteristics, the direction is to perform the retention treatment for a short time at the intermediate temperature during the rapid heating once (Patent Document 5) or a plurality of times (Patent Document 6). A method for manufacturing an electromagnetic steel sheet is disclosed.

Japanese Unexamined Patent Publication No. 07-062436 Japanese Unexamined Patent Publication No. 10-298653 Japanese Unexamined Patent Publication No. 2003-027194 Japanese Unexamined Patent Publication No. 10-130729 Japanese Unexamined Patent Publication No. 2014-025106 Japanese Unexamined Patent Publication No. 2015-183189

In the techniques disclosed above, in many cases, a heating rate of about 100 to 300 ° C./s is regarded as rapid heating, and as a comparison, a heating rate of about 20 to 50 ° C./s is evaluated as a conventional condition. ing.
However, when the inventors performed decarburization annealing at a heating rate exceeding 300 ° C./s to verify the effect of rapid heating, when the heating rate was extremely high at 400 ° C./s or more, the magnetic flux density. A new problem has emerged. That is, although rapid heating was originally developed for the purpose of reducing iron loss, when the magnetic flux density deteriorates, the iron loss also deteriorates, so that the expected iron loss reduction effect cannot be obtained. Became clear.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to have magnetic characteristics, particularly iron loss characteristics, even when the heating rate at the time of decarburization annealing is extremely high. The purpose is to propose a method for producing an excellent grain-oriented electrical steel sheet.

In order to solve the above problems, the inventors have made extensive studies focusing on the effect of the temperature rise pattern of decarburization annealing on the magnetic characteristics. As a result, when a short-time retention treatment is performed at an intermediate temperature during temperature rise by rapid heating of decarburization annealing, the heating rate is changed before and after the intermediate temperature, specifically, from room temperature to intermediate temperature. By slowing the temperature rise rate in the low temperature range and increasing the temperature rise rate in the high temperature range above the intermediate temperature, it is possible to stably obtain a directional electromagnetic steel plate with low iron loss without causing a decrease in magnetic flux density. , And have come to develop the present invention.

That is, the present invention contains C: 0.02 to 0.10 mass%, Si: 2.0 to 8.0 mass% and Mn: 0.02 to 1.0 mass%, and the balance is derived from Fe and unavoidable impurities. A steel material having the same composition is hot-rolled to obtain a hot-rolled plate, and if necessary, hot-rolled plate is annealed, and then cold-rolled once or two or more times with intermediate annealing sandwiched between them to make a final plate. It consists of a series of steps in which a thick cold-rolled sheet is subjected to decarburization annealing that also serves as primary recrystallization annealing, then an annealing separator mainly composed of MgO is applied to the surface of the steel sheet, and finish annealing including purification treatment is performed. In the method for producing a directional electromagnetic steel sheet, a retention treatment is performed in which the decarburization annealing is held at an arbitrary intermediate temperature of 300 ° C. or higher and 500 ° C. or lower for 0.1 to 5.0 seconds when the temperature is raised from room temperature to 700 ° C. Then, when heating again, the average temperature rise rate from room temperature to the intermediate temperature is set to 200 ° C./s or less, and the average temperature rise rate from the intermediate temperature to 700 ° C. after the retention treatment is 400 ° C./s. We propose a method for manufacturing a directional electromagnetic steel sheet, which is characterized by having s or more.

In the method for producing a directional electromagnetic steel plate of the present invention, when the decarburization annealing is performed at an arbitrary soaking temperature of 800 ° C. or higher, the average heating rate from 750 ° C. to the soaking temperature is 10 ° C./s or less. It is preferable to do so.

Further, in the method for producing grain-oriented electrical steel sheets of the present invention, it is preferable that the average heating rate from room temperature to the intermediate temperature is 150 ° C./s or less when the temperature is raised by decarburization annealing.

Further, the steel material of the present invention preferably further contains at least one inhibitor-forming component of the following groups A and B in addition to the above component composition.
Note: Group A; Al: 0.005 to 0.050 mass% and N: 0.003 to 0.020 mass%
Group B; Se: 0.003 to 0.030 mass% and S: 0.002 to 0.03 mass%, one or two selected

Further, the steel material of the present invention preferably further contains at least one component of the following groups C and D in addition to the above component composition.
Description-Group C: One or more selected from Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass% and P: 0.005 to 0.50 mass%-D Group; Ni: 0.01 to 1.50 mass%, Sb: 0.005 to 0.50 mass%, Sn: 0.005 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, Mo: 0. One or more selected from 005 to 0.100 mass%, B: 0.0002 to 0.0025 mass% and Nb: 0.0010 to 0.0200 mass%

According to the present invention, when performing a short-term retention treatment at an intermediate temperature during temperature rise by rapid heating of decarburization annealing, the temperature rise rate before and after the intermediate temperature is optimized to achieve high magnetic flux density and low magnetic flux density. Directional iron loss direction It becomes possible to stably manufacture an electromagnetic steel sheet. Therefore, according to the present invention, it is possible to provide a grain-oriented electrical steel sheet suitable as an iron core material for a transformer or the like.

It is a graph which shows the influence which the temperature rise pattern at the time of decarburization annealing _{has on the magnetic flux density B 8 of the grain-oriented electrical steel sheet.} It is a graph which shows the influence which the temperature rise pattern at the time of decarburization annealing _{has on the iron loss W 17/50 of a grain-oriented electrical steel sheet.}

The experiment that triggered the development of the present invention will be described.
<Experiment 1>
A steel slab containing C: 0.055 mass%, Si: 3.18 mass%, and Mn: 0.12 mass% is produced by continuous casting, heated to a temperature of 1400 ° C., and then hot-rolled to have a plate thickness of 2. .2 mm hot-rolled plate, hot-rolled plate annealed at 1050 ° C for 60 seconds, then cold-rolled to an intermediate plate thickness of 1.5 mm, after intermediate annealing at 1130 ° C for 100 seconds. The final cold rolling was performed to obtain a cold rolled plate having a plate thickness of 0.23 mm. _Then, the dew point at 50vol% H ₂ -50vol% _N 2 is in a humid atmosphere at 60 ° C., was subjected to a decarburization annealing serving also as a primary recrystallization annealing of 850 ° C. × 120 seconds. At this time, the retention treatment is carried out at an intermediate temperature of 500 ° C. during the temperature rise for 1 second, and the average temperature rise rate from room temperature (25 ° C.) to 500 ° C. and the average temperature rise rate from 500 ° C. to 700 ° C. after the retention treatment. Was changed in various ways. The average heating rate from room temperature (25 ° C.) to 500 ° C. is the average heating rate obtained by dividing the temperature difference of 475 ° C. by the required heating time including the retention treatment time. The temperature was raised at 50 ° C./s from 700 ° C. to 750 ° C. and at 5 ° C./s from 750 ° C. to 850 ° C., which is the soaking temperature. Then, an annealing separator mainly containing MgO is applied, dried, and then heated from room temperature to 1200 ° C. at about 20 ° C./hour to complete secondary recrystallization, and then at 1200 ° C. under a hydrogen atmosphere. Was subjected to finish annealing, which was subjected to a purification treatment of holding for 10 hours, to obtain a product plate.

A sample was taken from the product plate obtained as described above, and the magnetic properties were measured by the Epstein test method described in JIS C2550-1: 2011. The relationship between the obtained magnetic flux density B ₈ and the temperature rise pattern is shown in FIG. 1, and the relationship between the iron loss W _17/50 and the temperature rise pattern is shown in FIG. From these figures, when the average rate of temperature rise on the side (from 500 ° C to 700 ° C) higher than the intermediate temperature of 500 ° C is 400 ° C / s or higher, the side lower than the intermediate temperature (room temperature (25 ° C)). The magnetic characteristics change greatly depending on the temperature rise rate condition from to 500 ° C., and by setting the average temperature rise rate on the lower temperature side than the intermediate temperature to 200 ° C./s or less, the conventional whole period (room temperature (25)) It can be seen that magnetic characteristics equal to or higher than those in the case where the average temperature rise rate is about 200 ° C./s) can be obtained from (° C.) to 700 ° C.). In particular, by setting the heating rate from room temperature (25 ° C.) to 500 ° C. to 150 ° C. or lower, excellent iron loss characteristics can be obtained.

As shown in the results of this experiment, when the average temperature rise rate on the higher temperature side (from 500 ° C to 700 ° C) than the intermediate temperature is 400 ° C / s or more, the temperature on the lower side than the intermediate temperature (room temperature (25 ° C) to 500 ° C) The reason why the magnetic characteristics change significantly depending on the average temperature rise rate condition (up to) is not sufficiently clear at this time, but the inventors think as follows.

As described above, the effect of rapid heating during decarburization annealing suppresses the development of γ fibers (<111> // ND orientation) that are preferentially formed at a normal heating rate of about 50 ° C./s. Low iron loss by reducing the crystal grains after secondary recrystallization through modification of the primary recrystallization texture, such as promoting the generation of the {110} <001> structure that is the core of secondary recrystallization. It means that the conversion will be achieved. Therefore, it is expected that the effect of grain refinement after the secondary recrystallization will be more exerted by increasing the rate of temperature rise from 500 ° C. to 700 ° C. at which recrystallization starts.

In addition, in this experiment, a short-time retention process is adopted at an intermediate temperature during rapid heating. As described above, this process is considered to be indispensable for stabilizing the magnetic characteristics, and this action preferentially causes the release of the strain in the <111> // ND rolling stable direction in which the strain tends to accumulate. By suppressing the recrystallization of the orientation, it is considered that the number of recrystallized grains of the <111> // ND orientation generated from the rolled structure of the <111> // ND orientation is reduced. However, if the rate of temperature rise in a low temperature range such as room temperature to 500 ° C. is high, the time for solid solution C to move in the steel is short, and it becomes difficult to fix the dislocations introduced by rolling with C. As a result, during the retention process at an intermediate temperature, the strain is excessively released to form a recovered structure, which adversely affects the orientation after recrystallization and the subsequent secondary recrystallization. However, by slowing the temperature rise rate in the low temperature range, the dislocations are fixed at C and become difficult to move, and the strain release and residual balance during the retention process at the intermediate temperature are balanced, and the magnetic characteristics are improved. It is considered to be.

Considering such a mechanism, in the ultra-rapid heating of 400 ° C./s or more, the retention treatment time during the temperature rise needs to be shorter than the time (1 to 10 seconds) described in Patent Document 5. I think that the. Further, in order for C to effectively act on the fixation of dislocations, it is considered sufficient if the amount of C in the material is 0.02 mass% or more. Further, for the above-mentioned reason, the present invention is intended for a case where the temperature rising rate from the retention treatment temperature (intermediate temperature) to 700 ° C. is extremely high, and when the temperature rising rate in this temperature range is less than 400 ° C./s. Exclude the target.

Next, the component composition that the steel material (slab) used for producing the grain-oriented electrical steel sheet of the present invention should have will be described.
C: 0.02 to 0.10 mass%
As described above, if C in the material is less than 0.02 mass%, the effect of fixing dislocations by C does not appear, which adversely affects the magnetic properties. On the other hand, if it exceeds 0.10 mass%, it becomes difficult to reduce the magnetic aging of the product plate to 0.005 mass% or less, which is not a problem, by decarburization annealing. Therefore, C is in the range of 0.02 to 0.10 mass%. Preferably, it is in the range of 0.025 to 0.08 mass%.

Si: 2.0 to 8.0 mass%
Si is an element necessary for increasing the specific resistance of steel and improving iron loss, but if it is less than 2.0 mass%, the above effect cannot be sufficiently obtained, while if it exceeds 8.0 mass%, it cannot be sufficiently obtained. , The workability of steel deteriorates, making it difficult to roll and manufacture. Therefore, Si is in the range of 2.0 to 8.0 mass%. Preferably, it is in the range of 2.5 to 4.0 mass%.

Mn: 0.02-1.0 mass%
Mn is an element necessary for improving hot workability, but if it is less than 0.02 mass%, the above effect cannot be sufficiently obtained, while if it exceeds 1.0 mass%, the magnetic flux density of the product plate is high. Will decrease. Therefore, Mn is in the range of 0.02 to 1.0 mass%. Preferably, it is in the range of 0.05 to 0.30%.

In the steel material (slab) of the present invention, the balance other than the above components is Fe and unavoidable impurities. However, in the present invention, in addition to the above basic components, at least one inhibitor-forming component of the following groups A and B can be contained in order to stably express secondary recrystallization.
Group A; Al: 0.005 to 0.050 mass% and N: 0.003 to 0.020 mass%
Group B; When an inhibitor is used to generate one or two secondary recrystallizations selected from Se: 0.003 to 0.030 mass% and S: 0.002 to 0.03 mass%. When AlN is used as an inhibitor (AlN system), when one or two types selected from MnS and MnSe are used (MnS / MnSe system), and when both of the above inhibitors are used in combination (AlN + MnS. It can be selected from any of MnSe type).
Specifically, in the case of the AlN system, it is preferable to contain Al and N in the range of Al: 0.005 to 0.050 mass% and N: 0.003 to 0.020 mass%, respectively. Further, in the case of the MnS / MnSe system, it is preferable to contain one or two kinds selected from Se: 0.003 to 0.030 mass% and S: 0.002 to 0.03 mass%. In the case of AlN + MnS / MnSe system, in addition to Al: 0.005 to 0.050 mass% and N: 0.003 to 0.020 mass%, Se: 0.003 to 0.030 mass% and S: 0. It is preferable to contain one or two kinds selected from .002 to 0.03 mass%. When the addition amount is less than the above lower limit amount, the inhibitory effect cannot be sufficiently obtained, while when the addition amount exceeds the above upper limit amount, the precipitated inhibitor remains undissolved during slab heating, and the inhibitory effect is reduced. , Secondary recrystallization becomes unstable and sufficient magnetic properties cannot be obtained.

Further, the steel material (slab) of the present invention can contain at least one component of the following groups C and D in addition to the above components.
Description-Group C: One or more selected from Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass% and P: 0.005 to 0.50 mass%-D Group; Ni: 0.01 to 1.50 mass%, Sb: 0.005 to 0.50 mass%, Sn: 0.005 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, Mo: 0. One or more selected from 005 to 0.100 mass%, B: 0.0002 to 0.0025% and Nb: 0.0010 to 0.0200 Cr, Cu and P, which are elements of group C, are , All of which are elements having an effect of reducing iron loss, and are among Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, and P: 0.005 to 0.50 mass%. One or more selected species can be contained alone or in combination. When the content of each element is less than the above lower limit value, the above magnetic characteristic effect cannot be sufficiently obtained, while when the content exceeds the above upper limit value, the development of secondary recrystallized grains is suppressed and the magnetic characteristics are deteriorated. It will deteriorate.

Further, the elements of Group D, Ni, Sb, Sn, Bi, Mo, B and Nb, are all elements having an effect of improving the magnetic flux density, and Ni: 0.01 to 1.50 mass%, Sb: 0.005 to 0.50 mass%, Sn: 0.005 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, Mo: 0.005 to 0.100 mass%, B: 0.0002 to 0. One or more selected from 0025mass% and Nb: 0.0010 to 0.0200mass% can be added alone or in combination. When the content of each element is less than the above lower limit value, the effect of improving the magnetic characteristics is not sufficiently obtained, while when the content exceeds the above upper limit value, the development of secondary recrystallized grains is suppressed and the magnetic characteristics Will deteriorate.

Next, the method for manufacturing the grain-oriented electrical steel sheet of the present invention will be described.
The steel material used for producing the directional electromagnetic steel sheet of the present invention is a steel material obtained by melting a steel having the above-mentioned composition by a conventional refining process and then using a conventionally known ingot-lump rolling method or continuous casting method. (Slab) may be produced, or a thin slab having a thickness of 100 mm or less may be produced by a direct casting method.

The slab is heated by a usual method and hot-rolled. The slab heating before hot rolling is heated to about 1400 ° C. when the inhibitor forming component is contained, while heating to a temperature of 1250 ° C. or less when the inhibitor component is not contained. When heating to a high temperature such as 1400 ° C., it is desirable to adopt an induction heating method from the viewpoint of heating efficiency. Further, when the inhibitor-forming component is not contained, hot rolling may be performed immediately after casting without heating. Further, in the case of thin slabs, hot rolling may be performed as in the case of slabs, or hot rolling may be omitted and the process may proceed as it is.

Next, the hot-rolled plate obtained by the above-mentioned hot rolling is annealed by hot-rolled plate, if necessary. In order to obtain good magnetic properties, the annealing temperature of the hot-rolled plate is preferably 800 ° C. or higher and 1150 ° C. or lower. If the hot-rolled plate annealing temperature is less than 800 ° C., the band structure formed by hot rolling remains, making it difficult to obtain a sized primary recrystallization structure and inhibiting the development of secondary recrystallization. There is a risk of On the other hand, if the hot-rolled plate annealing temperature exceeds 1150 ° C., the crystal grains after the hot-rolled plate annealing may become too coarse and the primary recrystallization structure of the sized grains may not be obtained.

The hot-rolled plate after hot-rolling or after hot-rolling plate annealing is cold-rolled once or cold-rolled two or more times with intermediate annealing sandwiched between them to obtain a cold-rolled plate having a final plate thickness. When the intermediate annealing is carried out, the annealing temperature is preferably 900 ° C. or higher and 1200 ° C. or lower. If the intermediate annealing temperature is less than 900 ° C., the recrystallized grains become finer, the Goss nuclei in the primary recrystallized structure decrease, and the magnetic properties of the product plate may deteriorate. On the other hand, if the temperature exceeds 1200 ° C., the crystal grains become too coarse as in the case of hot-rolled sheet annealing, and there is a risk that a primary recrystallized structure of sized grains cannot be obtained.
From the viewpoint of improving the recrystallization texture and further improving the magnetic properties, the final cold rolling, which is the final plate thickness, employs warm rolling in which the steel plate temperature is raised to 100 ° C. to 300 ° C. and rolled. Is effective.

The cold-rolled plate having the final plate thickness is then subjected to decarburization annealing, which is the most important step in the present invention, which also serves as primary recrystallization annealing. For the reason mentioned above, the temperature rise pattern in decarburization annealing is the average temperature rise rate in the temperature interval from room temperature (25 ° C) to 700 ° C, and from room temperature to any temperature (intermediate temperature) of 300 ° C or more and 500 ° C or less. After heating at 200 ° C./s or less and holding at the intermediate temperature for a short time of 0.1 to 5.0 seconds, the average temperature rise rate from the intermediate temperature after the retention treatment to 700 ° C. It is necessary to heat at 400 ° C./s or higher.

Here, the reason why the intermediate temperature for the retention treatment is set to 300 ° C. or higher and 500 ° C. or lower is that strain release is insufficient below 300 ° C., while recrystallization starts when the temperature exceeds 500 ° C. .. The reason why the retention process is set to 0.1 to 5.0 seconds is that if it is less than 0.1 seconds, the effect of the retention process is not sufficient, while if it exceeds 5.0 seconds, the strain is released. This is because it becomes a recovery organization.

From the viewpoint of the mechanism of occurrence of the effect, the retention process may be performed once or a plurality of times, but in the case of a plurality of times, the total holding time must be within the above range. Further, the temperature fluctuation during the retention process is preferably controlled in the range of −20 ° C./s to + 20 ° C./s.

Further, the average temperature rise rate from room temperature to an arbitrary temperature (intermediate temperature) of 300 ° C. or higher and 500 ° C. or lower needs to be 200 ° C./s or lower, but as can be seen from FIG. When the average heating rate up to the intermediate temperature between ~ 500 ° C. is 150 ° C./s or less, better magnetic characteristics can be obtained. However, if the heating rate in this section is slow, the processing time becomes long, so from the viewpoint of operability, the average heating rate is preferably 20 ° C./s or more. Here, the average heating rate from room temperature to the intermediate temperature is the average heating rate obtained by dividing the temperature difference by the required heating time including the retention treatment time.

Further, in the present invention, the average heating rate from the intermediate temperature to 700 ° C. after the retention treatment needs to be 400 ° C./s or more, but is preferably 600 ° C./s or more. The upper limit of the heating rate in this temperature section depends on the heating equipment, but is about 1250 ° C./s in consideration of economic efficiency.

The soaking temperature in decarburization annealing is preferably 800 ° C. or higher and 900 ° C. or lower from the viewpoint of sufficient decarburization. However, the rate of temperature rise from 700 ° C. to the soaking temperature is not particularly limited. The average heating rate from 750 ° C. to the soaking temperature is preferably 10 ° C./s or less from the viewpoint of ensuring a longer decarburization time.

Further, the atmosphere at the time of decarburization annealing is preferably a moist atmosphere from the viewpoint of ensuring decarburization, and more preferably 30 ° C. or higher at the dew point. Similarly, from the viewpoint of ensuring decarburization, the atmosphere _{preferably contains hydrogen gas (H 2} ), and the concentration thereof is more preferably 5 vol% or more and 70 vol% or less.

Next, the decarburized and annealed steel sheet was dried by applying an annealing separator mainly composed of MgO to the surface of the steel sheet in order to prevent fusion of the steel sheets during annealing and to form a forsterite film. After that, finish annealing including secondary recrystallization annealing and purification treatment is performed.

The annealing temperature of the finish annealing is preferably maintained at a temperature of 800 ° C. or higher for 20 hours or longer in order to develop and complete secondary recrystallization. Further, in the case of removing impurities in the steel to improve the magnetic properties or forming a forsterite film, the temperature is further raised to 1180 ° C. or higher after the secondary recrystallization is completed. , It is preferable to carry out a purification treatment in which the temperature is maintained at the temperature for 3 hours or more in a hydrogen atmosphere.

The steel sheet after finish annealing is washed with water, brushed, pickled, etc. to remove the unreacted annealing separator adhering to the surface of the steel sheet, and then flattened and annealed to correct the shape, thereby reducing iron loss. Is valid for.

When the steel sheets of the present invention are laminated and used, in order to improve iron loss, it is preferable to coat the surface of the steel sheets with an insulating film in the above-mentioned flattening annealing or the steps before and after the above-mentioned flattening annealing, and more iron. In order to reduce the loss, it is preferable to use a tension applying film as the insulating film. Further, in forming the insulating coating, it is preferable to coat the coating after depositing an inorganic substance on the surface of the steel sheet via a binder or by a physical vapor deposition method or a chemical vapor deposition method. As a result, a film having excellent film adhesion and a large iron loss reducing effect can be obtained.

C: 0.035 mass%, Si: 3.53 mass%, Mn: 0.06 mass%, Al: 0.032 mass%, Se: 0.019 mass% and N: 0.009 mass%, and the balance is Fe and unavoidable. A steel slab having a component composition composed of target impurities is heated to a temperature of 1420 ° C. and then hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.7 mm, and then the hot-rolled plate is subjected to 1050 ° C. × 50 seconds. After annealing the hot-rolled plate, it was cold-rolled to finish a cold-rolled plate having a final plate thickness of 0.23 mm.
Then, the cold-rolled _sheet, the dew point at 50vol% H ₂ -50vol% _N 2 is in a humid atmosphere at 60 ° C., was subjected to a decarburization annealing serving also as a primary recrystallization annealing of 840 ° C. × 120 seconds. At this time, a retention treatment is performed in which the temperature is maintained at 500 ° C. during the temperature rise for 0.3 seconds, and the average temperature rise rate from room temperature (25 ° C.) to the above 500 ° C. and the average from 500 ° C. to 700 ° C. after the retention treatment. The rate of temperature rise was variously changed as shown in Table 1. The average heating rate from room temperature (25 ° C.) to 500 ° C. is a value obtained by dividing the temperature difference of 475 ° C. by the required heating time including the retention treatment time. Further, the temperature rising rate from 700 ° C. to 750 ° C. was set to 40 ° C./s, and the heating rate from 750 ° C. to the soaking temperature (840 ° C.) was variously changed as shown in Table 1.
Next, the steel sheet after decarburization and annealing is coated and dried with an annealing separator mainly composed of MgO, and then the temperature is raised from room temperature at an average temperature rise rate of 15 ° C./hour under a nitrogen atmosphere for secondary recrystallization. After the above was completed, the temperature was further raised to 1180 ° C., and the product plate was subjected to finish annealing in which the temperature was maintained at the temperature for 4 hours in a hydrogen atmosphere for purification treatment.

A sample was taken from the product plate thus obtained, the magnetic properties were measured by the Epstein test method described in JIS C2550-1: 2011, and the results are also shown in Table 1. From the table, it can be seen that the steel sheets manufactured under the conditions conforming to the present invention are all _{excellent in magnetic flux density B 8} and iron loss W _17/50.

A steel slab having the component composition shown in Table 2 and having the balance of Fe and unavoidable impurities is heated to a temperature of 1320 ° C. and then hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.0 mm, and then The hot-rolled plate was annealed at 1070 ° C. for 80 seconds and cold-rolled to finish a cold-rolled plate having a final plate thickness of 0.20 mm. Then, the cold-rolled _sheet, with _{50vol% H 2 -50vol% N 2} , under a humid atmosphere with a dew point of 55 ° C., was subjected to a decarburization annealing serving also as a primary recrystallization annealing of 825 ° C. × 120 seconds. At this time, a retention treatment is performed in which the temperature is maintained at 300 ° C. during the temperature rise for 3.0 seconds, and the average temperature rise rate from room temperature (25 ° C.) to the above 300 ° C. is 100 ° C./s and from 300 ° C. after the retention treatment. The temperature was heated up to 700 ° C. at an average heating rate of 500 ° C./s. The average heating rate from room temperature (25 ° C.) to 500 ° C. is a value obtained by dividing the temperature difference of 275 ° C. by the required heating time including the retention treatment time. Further, heating was performed at an average heating rate of 25 ° C./s from 700 ° C. to 750 ° C., and at an average heating rate of 3 ° C./s from 750 ° C. to the soaking temperature (840 ° C.).
The steel sheet after decarburization and annealing is coated and dried with an annealing separator mainly composed of MgO, and then kept at a temperature of 900 ° C. for 50 hours in a nitrogen atmosphere to complete secondary recrystallization, and then further. The temperature was raised to 1250 ° C., and the product plate was subjected to finish annealing in which the temperature was maintained at the temperature for 10 hours for purification treatment.

A sample was taken from the product board thus obtained, the magnetic properties were measured by the Epstein test method described in JIS C2550-1: 2011, and the results are also shown in Table 2. From the table, it can be seen that the steel sheets manufactured under the conditions conforming to the present invention using the materials having the component composition conforming to the present invention are all _{excellent in the magnetic flux density B 8} and the iron loss W _17/50.

Claims (5)

Steel containing C: 0.02 to 0.10 mass%, Si: 2.0 to 8.0 mass% and Mn: 0.02 to 1.0 mass%, and having a component composition in which the balance is Fe and unavoidable impurities. The material is hot-rolled to obtain a hot-rolled plate, and if necessary, hot-rolled plate is annealed, and then cold-rolled once or two or more times with intermediate annealing in between to obtain a cold-rolled plate with the final plate thickness. , After performing decarburization annealing that also serves as primary recrystallization annealing, an annealing separator mainly containing MgO is applied to the surface of the steel sheet, and finish annealing including purification treatment is performed. Manufacture of directional electromagnetic steel sheet. In the method
When the decarburization annealing raises the temperature from room temperature to 700 ° C., it is held at an arbitrary intermediate temperature of 300 ° C. or higher and 500 ° C. or lower for 0.1 to 5.0 seconds, and then heated again at room temperature. The average temperature rise rate from the intermediate temperature to the intermediate temperature is 200 ° C./s or less, and the average temperature rise rate from the intermediate temperature to 700 ° C. after the retention treatment is 400 ° C./s or more. Manufacturing method of directional electromagnetic steel plate. The direction according to claim 1, wherein when the decarburization annealing is performed at a soaking temperature of 800 ° C. or higher, the average heating rate from 750 ° C. to the soaking temperature is 10 ° C./s or less. Manufacturing method of electromagnetic steel plate. The method for producing a directional electromagnetic steel plate according to claim 1 or 2, wherein the average temperature rising rate from room temperature to the intermediate temperature at the time of raising the temperature of the decarburization annealing is 150 ° C./s or less. The steel material according to any one of claims 1 to 3, wherein the steel material further contains at least one inhibitor-forming component of the following groups A and B in addition to the component composition. Manufacturing method of grain-oriented electrical steel sheet.
Note: Group A; Al: 0.005 to 0.050 mass% and N: 0.003 to 0.020 mass%
Group B; Se: 0.003 to 0.030 mass% and S: 0.002 to 0.03 mass%, one or two selected The direction according to any one of claims 1 to 4, wherein the steel material further contains at least one component of the following groups C and D in addition to the component composition. Manufacturing method of electrical steel sheet.
Description-Group C: One or more selected from Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass% and P: 0.005 to 0.50 mass%-D Group; Ni: 0.01 to 1.50 mass%, Sb: 0.005 to 0.50 mass%, Sn: 0.005 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, Mo: 0. One or more selected from 005 to 0.100 mass%, B: 0.0002 to 0.0025 mass% and Nb: 0.0010 to 0.0200 mass%

Images