JP5988027B2 - Method for producing ultrathin grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet mainly used for iron cores such as transformers and generators. Specifically, the thickness of the grain-oriented electrical steel sheet having a thickness of 0.20 mm or less and an extremely thin and low iron loss. It relates to a manufacturing method.

A grain-oriented electrical steel sheet containing Si and highly oriented in the {110} <001> orientation (Goss orientation) or {100} <001> orientation (Cube orientation) has excellent soft magnetic properties. Therefore, it is widely used as a core material for various electric devices used in the commercial frequency range. The grain-oriented electrical steel sheet used for such applications is generally required to have a low iron loss W _17/50 (W / kg) representing magnetic loss when magnetized to 1.7 T at a frequency of 50 Hz. . The reason is that the efficiency of the generator and the transformer can be greatly improved by using an iron core material having a low W _17/50 value. Therefore, development of materials with low iron loss has been increasingly demanded.

  The iron loss of an electrical steel sheet is represented by the sum of hysteresis loss that depends on crystal orientation and purity, and eddy current loss that depends on sheet thickness, specific resistance, magnetic domain size, and the like. Therefore, as a method of reducing the iron loss, the degree of integration of the crystal orientation is increased to improve the magnetic flux density, the hysteresis loss is reduced, the Si content is increased to increase the electric resistance, or the thickness of the steel plate is increased. There are known methods for reducing the eddy current loss by reducing the eddy current or by subdividing the magnetic domain.

  Among these iron loss reduction methods, with respect to the method of improving the magnetic flux density, for example, in Patent Document 1 and Patent Document 2, Ni is added in a method of manufacturing a grain-oriented electrical steel sheet using AlN as an inhibitor and Ni By adding Sb within a predetermined range according to the amount added, an extremely strong inhibitory effect on the growth of primary recrystallized grains can be obtained, improving the primary recrystallized grain texture and making secondary recrystallized grains finer It is disclosed that the average in-plane deviation angle in the rolling direction from the {110} <001> orientation can be reduced and the iron loss can be greatly reduced.

  In addition, as a method for reducing the plate thickness, a rolling method and a chemical polishing method are known, but the method of thinning by chemical polishing has a large decrease in yield, and for production on an industrial scale. Not suitable. For this reason, a rolling method is exclusively used as a method for reducing the plate thickness. However, when the sheet thickness is reduced by rolling, there is a problem that secondary recrystallization in finish annealing becomes unstable and it is difficult to stably manufacture a product having excellent magnetic properties.

  For this problem, for example, in Patent Document 3, in addition to the combined addition of Sn and Se, in the manufacture of a thin unidirectional electrical steel sheet characterized by AlN as the main inhibitor and the final cold rolling under strong pressure, According to Patent Document 4, Nb is added in the method of manufacturing a thin unidirectional electrical steel sheet having a thickness of 0.20 mm or less, because an excellent iron loss value can be obtained by adding Cu and / or Sb. It has been proposed that fine dispersion of carbonitrides is promoted by this to strengthen the inhibitor and improve the magnetic properties. Patent Document 5 discloses that the thickness of the hot-rolled sheet is reduced, the coil winding temperature is lowered, and the finish annealing pattern is controlled appropriately, so that the thin film having excellent magnetic properties can be obtained by one cold rolling. Patent Document 6 discloses a method of manufacturing a grain-oriented electrical steel sheet, in which a sheet thickness of a hot-rolled coil is set to 1.9 mm or less to produce a grain-oriented electrical steel sheet of 0.23 mm or less by a single cold rolling method. A method has been proposed.

Japanese Patent No. 3357601 Japanese Patent No. 3357578 Japanese Patent Publication No. 07-017956 Japanese Patent Laid-Open No. 06-025747 Japanese Patent Publication No. 07-042507 Japanese Patent Laid-Open No. 04-341518

  As a method of reducing the iron loss of the grain-oriented electrical steel sheet, it is effective to apply the above-described conventional technique, reduce the sheet thickness by rolling, and reduce the eddy current loss. However, in the ultrathin grain-oriented electrical steel sheet having a thickness of 0.12 to 0.20 mm after the final cold rolling, even if the technique disclosed in the above prior art is applied, the secondary recycle is still performed in a part of the coil. There is a problem that crystal defects occur and the yield decreases.

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to stably cause secondary recrystallization even in an ultrathin grained electrical steel sheet having a thickness of 0.12 to 0.20 mm, and to produce a product coil It is to propose an advantageous method for producing a grain-oriented electrical steel sheet having a uniform iron loss and a very low iron loss.

  In order to elucidate the cause of unstable secondary recrystallization behavior in a grain-oriented electrical steel sheet with a thin plate thickness, the inventors have made a steel sheet in the middle of secondary recrystallization when finish annealing the steel sheet after primary recrystallization annealing. And the inhibitor precipitation state and crystal grain growth state were investigated. As a result, in the temperature raising process of finish annealing, the inhibitor is coarsened and the ability to suppress crystal grain growth is reduced, and in the temperature region of 875 ° C. or higher, the inhibitor component is oxidized and disappeared due to the surface oxidation of the steel sheet, The coarsening of the surface layer grains occurs, in particular, the tendency becomes remarkable at 975 ° C. or more, and in the ultrathin grain-oriented electrical steel sheet having a thickness of 0.12 to 0.20 mm, It has been clarified that the decrease in crystal grain growth inhibiting power due to coarsening and the progress of coarsening of surface grains are the main causes of secondary recrystallization failure.

  As a result of further studies, the inventors have added (1) Ni, Cu and Sb in combination, and sol. By controlling the ratio of Al to N (sol.Al/N) within an appropriate range, it is possible to suppress a decrease in the inhibitory power of the inhibitor in the temperature raising process of finish annealing, and (2) secondary re-generation in the temperature raising process of finish annealing. By holding for a predetermined time in the temperature range of 775 to 875 ° C. before crystallization occurs, it is possible to suppress the surface grain coarsening due to steel plate surface oxidation at 875 ° C. or higher, and therefore apply these findings. Thus, it has been found that secondary recrystallization occurs stably over the entire length of the coil, and it is possible to manufacture an ultrathin grain-oriented electrical steel sheet having uniform iron loss in the coil and extremely low iron loss.

The present invention developed based on the above knowledge is C: 0.04-0.12 mass%, Si: 1.5-5.0 mass%, Mn: 0.01-1.0 mass%, Ni: 0.10-1 0.0 mass%, sol. Al: 0.010-0.040 mass%, N: 0.004-0.02 mass%, Cu: 0.02-1.0 mass%, Sb: 0.01-0.10 mass%, S and Se 1 type or 2 types selected: A steel slab containing 0.005 to 0.05 mass% in total and the balance being Fe and inevitable impurities is heated to a temperature of 1250 ° C. or higher, and then hot-rolled to obtain a plate thickness A hot-rolled sheet with a thickness of 1.8 mm or more is cold-rolled once or twice with an intermediate annealing in between to form a cold-rolled sheet with a final sheet thickness of 0.12 to 0.20 mm, subjected to primary recrystallization annealing, and finish annealing. In the manufacturing process of the grain-oriented electrical steel sheet comprising a series of processes, the sol. The Al / N value is in the range of 2.0 to 2.8, and the steel plate before secondary recrystallization in finish annealing is held in the temperature range of 775 to 875 ° C. for 40 to 200 hours , and then 10 to 60 ° C. A method for producing a grain- oriented electrical steel sheet, characterized by heating to a secondary recrystallization temperature range at a rate of temperature rise of / hr, is proposed.

  The method for producing a grain-oriented electrical steel sheet according to the present invention further includes one or more selected from Ge, Bi, V, Nb, Te, Cr, Sn, and Mo in addition to the above component composition in a total of 0. It is characterized by containing 0.002 to 1.0 mass%.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet of this invention heats between 200-700 degreeC in the heating process of the said primary recrystallization annealing with the temperature increase rate of 50 degrees C / s or more.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet of this invention is hold | maintained isothermally for 1 to 10 seconds in any temperature between 250-600 degreeC in the heating process of the said primary recrystallization annealing.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention is characterized in that a magnetic domain refinement process is performed on the steel sheet surface after the final cold rolling.

  According to the present invention, the addition amount of Ni, Cu and Sb, and the sol. By controlling the value of Al / N within an appropriate range, it is possible to suppress a decrease in the inhibitory power of the inhibitor before secondary recrystallization in finish annealing, and the steel plate temperature before secondary recrystallization in finish annealing is in a certain temperature range. Therefore, it is possible to suppress the coarsening of the surface layer grains and stably generate secondary recrystallization. Therefore, a high magnetic flux density ultrathin grain-oriented electrical steel sheet having excellent iron loss characteristics can be obtained at a high yield. Can be manufactured.

The effect of sol. On the fluctuation in the coil of iron loss W _17/50 . It is a figure which shows the influence of the heating pattern at the time of Al / N, an additive element (Ni, Cu, Sb) and finish annealing. Sol on the coil fluctuation of the magnetic flux density _{B 8.} It is a figure which shows the influence of the heating pattern at the time of Al / N, an additive element (Ni, Cu, Sb) and finish annealing.

Hereinafter, experiments that have led to the development of the present invention will be described.
Contains C: 0.07 mass%, Si: 3.4 mass%, Mn: 0.07 mass%, Ni: 0.3 mass%, Cu: 0.03 mass%, Sb: 0.04 mass% and Se: 0.015 mass% And sol. Four types of steel (No. 1 to 4 in Table 1) with Al / N changed in the range of 1.8 to 3.1, C: 0.07 mass%, Si: 3.4 mass%, Mn: 0 .07 mass%, sol. Three types of steels containing Al: 0.027 mass%, N: 0.01 mass% and Se: 0.015 mass%, and further changing the contents of Ni, Cu and Sb (Nos. 5 to 7 in Table 1) )), And hot rolled into a hot rolled coil with a thickness of 2.4 mm, and then subjected to hot rolled sheet annealing at 900 ° C. for 40 seconds, pickled and cold rolled. An intermediate cold-rolled sheet having a thickness of 1.5 mm was subjected to intermediate annealing at 1150 ° C. for 80 seconds, and then warm-rolled at 170 ° C. to obtain a cold-rolled sheet having a final thickness of 0.17 mm.

Thereafter, the cold-rolled sheet was degreased and subjected to primary recrystallization annealing also serving as decarburization at 850 ° C. for 2 minutes in a wet hydrogen atmosphere composed of H ₂ : 60 vol% and N ₂ : 40 vol%, An annealing separator mainly composed of MgO was applied to the surface of the steel sheet and subjected to finish annealing for secondary recrystallization.
The finish annealing is performed at a temperature of 850 ° C. after heating up to 850 ° C. at a rate of temperature increase of 20 ° C./hr in an N ₂ atmosphere and then performing no holding (FA pattern 1). Heating was performed at two levels of conditions (FA pattern 2) for 50 hours of retention treatment, and then between 850 and 1150 ° C. in a mixed atmosphere of N ₂ : 25 vol% and H ₂ : 75 vol%, and 1150 to 1200 ° C. during the under an _{H 2} atmosphere, heating rate of 20 ° C. / hr, further, subjected to soaking treatment of 1200 ° C. × 10 hours in an _{H 2} atmosphere, cooled, and 800 ° C. or less N _It was performed under the condition of cooling under _two atmospheres.
The steel sheet subjected to finish annealing was used as a product plate by removing an unreacted annealing separator and then applying an insulating coating composed mainly of aluminum phosphate and colloidal silica.

The test pieces for magnetic measurement were collected from a total of five positions in the coil longitudinal direction 0 m, 1000 m, 2000 m, 3000 m and 4000 m of the product coil having a total length of 4000 m obtained in this way, and the method described in JIS C2550, The iron loss W _17/50 and the magnetic flux density B ₈ were measured, and among these measured values, the worst value was the guaranteed value in the coil, and the best value was the good value in the coil. And shown in FIG. 1 and FIG.

From FIG. 1 and FIG. 2, the good value in the coil showing the best value in the coil is the same as that of the iron loss W _17/50 and the magnetic flux density B ₈ . Al / N, additive elements (Ni, Cu, Sb) and finish annealing are not affected by the heating pattern and show almost the same good value, but the guarantee in the coil shows the worst value in the coil For values, see sol. It can be seen that there are significant changes depending on the heating pattern of Al / N, additive elements (Ni, Cu, Sb), and finish annealing.

  For example, sol. No. 2 having Al / N values of 2.1 and 2.7 and containing appropriate amounts of Ni, Cu and Sb. 2 and no. Steel No. 3 shows an excellent value of the magnetic property of the guaranteed value in the coil at the same level as the good value in the coil in the FA pattern 2 held at 850 ° C. for 50 hours. In contrast, sol. Steels with FA pattern 1 that have Al / N values of 1.8 and 3.1, do not contain appropriate amounts of Ni, Cu and Sb, or were not held at 850 ° C. for 50 hours (No. In 1, 4 to 7), the guaranteed value in the coil is greatly inferior to the good value in the coil.

Therefore, in order to investigate this cause, when finish annealing the steel sheet after the primary recrystallization annealing, the steel sheet in the middle of the secondary recrystallization annealing was taken out and the precipitation state of the inhibitor and the growth state of the crystal grains were investigated. As a result, sol. When the inhibitory force of the inhibitor changes with the value of Al / N and the addition amount of Ni, Cu and Sb, and when holding for 50 hours at 850 ° C. in the heating process of finish annealing, Of the coarsening of the resin is suppressed, and accordingly, sol. In addition to controlling the Al / N value within the appropriate range and adding Ni, Cu and Sb in appropriate amounts, the steel plate before secondary recrystallization is maintained in a certain temperature range for a predetermined time during the heating process of finish annealing. Thus, it was found that a grain-oriented electrical steel sheet having no fluctuation in the coil and having excellent magnetic properties can be produced.
The present invention has been made based on the above findings.

Next, the component composition of the steel slab used as the raw material of the grain-oriented electrical steel sheet according to the present invention will be described.
C: 0.04 to 0.12 mass%
C is an element useful for uniform refinement of the structure during hot rolling and cold rolling and development of Goss orientation, and it is necessary to contain at least 0.04 mass%. However, if added over 0.12 mass%, decarburization may be insufficient due to primary recrystallization annealing, and the magnetic properties may deteriorate. Therefore, C is set to a range of 0.04 to 0.12 mass%. Preferably it is the range of 0.05-0.10 mass%.

Si: 1.5-5.0 mass%
Si is an element that increases the specific resistance of the steel sheet and contributes effectively to the reduction of iron loss. From the viewpoint of securing good magnetic properties, Si is contained in an amount of 1.5 mass% or more in the present invention. On the other hand, addition exceeding 5.0 mass% significantly impairs cold workability. Therefore, Si is set to a range of 1.5 to 5.0 mass%. Preferably it is the range of 2.0-4.0 mass%.

Mn: 0.01 to 1.0 mass%
Mn is an element effective for improving hot workability and preventing surface flaws during hot rolling, and in order to obtain such an effect, it is necessary to contain 0.01 mass% or more. However, when it is added exceeding 1.0 mass%, the magnetic flux density is lowered. Therefore, Mn is set to a range of 0.01 to 1.0 mass%. Preferably it is the range of 0.04-0.2 mass%.

sol. Al: 0.010-0.040 mass%
Al is an essential element constituting AlN which is an inhibitor. If the Al content is less than 0.010 mass%, the amount of AlN precipitated during hot rolling or during the temperature rising process of hot-rolled sheet annealing is insufficient, and the inhibitor effect cannot be obtained. On the other hand, if added in excess of 0.040 mass%, the precipitated inhibitor becomes complex and coarse, and conversely, the suppressive power decreases. Therefore, in order to sufficiently obtain the inhibitor effect of AlN, Al is sol. It is necessary to make it into the range of 0.010-0.040 mass% with Al. Preferably it is the range of 0.02-0.03 mass%.

N: 0.004 to 0.02 mass%
N, like Al, is an essential element constituting AlN, which is an inhibitor. However, since this N can be added after performing a nitriding treatment in the cold rolling process, it may be contained at 0.004 mass% or more in the slab stage. However, when nitriding is not performed in the cold rolling process, it is necessary to contain 0.005 mass% or more. On the other hand, when N is added in excess of 0.02 mass%, blistering may occur in hot rolling. Therefore, N is set to a range of 0.004 to 0.02 mass%. Preferably it is the range of 0.005-0.01 mass%.

S and Se: 0.005-0.05 mass% in total
S and Se are indispensable elements that are required for fine precipitation of Cu ₂ S, Cu ₂ Se, and the like in combination with AlN. For this purpose, in the present invention, it is necessary to contain 0.005 mass% or more alone or in total. However, if added over 0.05 mass%, the precipitates become coarse. Therefore, S and Se are made into the range of 0.005-0.05 mass% individually or in total. Preferably it is the range of 0.01-0.03 mass%.

Ni: 0.10 to 1.0 mass%
Ni is an element that co-segregates with Sb at the grain boundary, promotes the segregation effect of Sb, and inhibits the coarsening of the inhibitor, so it is contained in an amount of 0.10 mass% or more. However, if added over 1.0 mass%, the texture after the primary recrystallization annealing deteriorates, which causes the magnetic properties to deteriorate. Therefore, Ni is set in the range of 0.10 to 1.0 mass%. Preferably it is the range of 0.10-0.50 mass%.

Cu: 0.02-1.0 mass%
Cu is an essential element constituting Cu ₂ S and Cu ₂ Se. In an ultrathin grain-oriented electrical steel sheet, when the inhibitor is MnS or MnSe, the suppressive force decreases during finish annealing, and secondary recrystallization becomes unstable. On the other hand, when the inhibitor is Cu ₂ S, Cu ₂ Se and is added together with Ni and Sb, the inhibitor's inhibitory power is unlikely to decrease. Therefore, in this invention, it is essential to add 0.02 mass% or more of Cu. However, if the content exceeds 1.0 mass%, the inhibitor becomes coarse. Therefore, Cu is set to a range of 0.02 to 1.0 mass%. Preferably it is the range of 0.04-0.5 mass%.

Sb: 0.01-0.10 mass%
Sb is an element necessary for segregating on the surface of the precipitated inhibitors AlN, Cu ₂ S, Cu ₂ Se, MnS, and MnSe, and suppressing the coarsening of the inhibitors. Such an effect can be obtained by addition of 0.01 mass% or more. However, if it is added in excess of 0.10 mass%, the decarburization reaction is hindered and the magnetic properties are deteriorated. Therefore, Sb is set to a range of 0.01 to 0.10 mass%. Preferably it is the range of 0.02-0.05 mass%.

2.0 ≦ sol. Al / N ≦ 2.8
The grain-oriented electrical steel sheet according to the present invention has a sol. The ratio of the Al content (mass%) and the N content (mass%) is the following formula:
2.0 ≦ sol. Al / N ≦ 2.8
It is necessary to satisfy and contain.
sol. When Al / N is larger than 2.8, fine AlN is decomposed to form an oxide, so that the inhibitory force of AlN as an inhibitor is not sufficient, and the surface grain is coarsened. On the other hand, if it is less than 2.0, the grain growth is strongly suppressed, and the Goss oriented grains do not grow to a sufficient size necessary for good secondary recrystallization, so that the magnetic characteristics are deteriorated. Note that sol. Even if the value of Al / N is within the range of the above formula, if Ni and Sb are not added, AlN becomes coarse during finish annealing and secondary recrystallization failure occurs. Therefore, it is necessary to add Ni and Sb in order to satisfy the above formula.

In addition to the above component composition, the grain-oriented electrical steel sheet of the present invention further includes one or more selected from Ge, Bi, V, Nb, Te, Cr, Sn and Mo as an inhibitor auxiliary component. It can be made to contain in 0.002 to 1.0 mass% in total.
All of these elements form precipitates and segregate on the grain boundaries and the surface of the precipitates to perform an auxiliary function of strengthening the suppression force. In order to obtain such an action, it is necessary to contain one or more of these elements in a total of 0.002 mass%. However, it is because the addition exceeding 1.0 mass% leads to embrittlement and poor decarburization of steel. Therefore, it is preferable to contain the said element in the range of 0.002-1.0 mass% in total.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
In the method for producing a grain-oriented electrical steel sheet according to the present invention, after reheating the steel slab adjusted to the above-described component composition, hot rolling is performed, and hot-rolled sheet annealing is performed as necessary. It consists of a series of steps of cold rolling at least times, primary recrystallization annealing, and finish annealing.
As long as the steel slab contains the above-described component composition of the present invention, the production method is not particularly limited and can be produced under generally known production conditions.
The steel slab is then reheated to a temperature of 1250 ° C. or higher and then subjected to hot rolling. This is because when the reheating temperature is less than 1250 ° C., the added element does not dissolve in the steel. In addition, the method of reheating can use well-known methods, such as a gas furnace, an induction heating furnace, and an electric furnace. Moreover, the conditions of hot rolling should just be conventionally well-known conditions, and there is no restriction | limiting in particular.

  After the slab reheating, hot rolling is performed to obtain a hot rolled sheet having a thickness of 1.8 mm or more. Here, the reason for limiting the thickness of the hot-rolled sheet to 1.8 mm or more is to shorten the rolling time and reduce the temperature difference in the rolling direction of the hot-rolled steel sheet. In addition, the hot rolling conditions may be performed according to a conventional method, and there is no particular limitation.

The hot-rolled sheet obtained by hot rolling is then subjected to hot-rolled sheet annealing as necessary, and then pickled, and the final sheet thickness is obtained by cold rolling at least once with one or intermediate annealing in between. Cold-rolled sheet.
The hot-rolled sheet annealing and intermediate annealing are preferably performed at a temperature of 800 ° C. or higher in order to recrystallize using strain introduced by hot rolling or cold rolling. In addition, it is preferable to quench the cooling in the annealing at a predetermined cooling rate to increase the amount of solute C in the steel because it has an effect of increasing the nucleation frequency of secondary recrystallization. Moreover, it is more preferable to hold | maintain in a predetermined temperature range after rapid cooling, since a fine carbide precipitates in steel and the said effect is heightened. Of course, in the above cold rolling, aging between passes or warm rolling may be applied.

The cold-rolled sheet having the final thickness is then degreased and subjected to primary recrystallization annealing that also serves as decarburization annealing, and then an annealing separator is applied to the surface of the steel sheet and wound into a coil shape. Finish annealing that causes next recrystallization.
In addition, in order to reduce the iron loss of a product board, the said cold-rolled board may perform the magnetic domain refinement | purification process which forms a groove | channel by etching in the steel plate surface, in order to reduce the iron loss of a product board. Further, the cold-rolled plate may be subjected to a known magnetic domain refinement process, for example, a spot-like local heat treatment or chemical process for generating fine crystal grains, before secondary recrystallization.
Furthermore, in the primary recrystallization annealing, it may be performed as a nitriding treatment if necessary. In addition to the primary recrystallization annealing, a nitriding treatment step is added between the cold rolling and the finish annealing. May be.

  The texture improving effect as described above can be obtained by satisfying the above conditions and performing normal primary recrystallization annealing. However, in addition to the above, the number of Goss orientation grains in the primary recrystallized plate texture can be increased by increasing the heating rate between 200 and 700 ° C in the heating process of primary recrystallization annealing to 50 ° C / s or more. Since the secondary recrystallized grains can be made finer, the iron loss characteristics can be further improved.

  The reason is that the driving force that causes primary recrystallization is the strain energy accumulated by rolling (introduction of dislocations), the amount of which depends on the crystal orientation, and the <111> // ND orientation is the highest, Goss orientation is relatively low. Therefore, it is known that the <111> // ND orientation is easy to recrystallize, and the Goss orientation is difficult to recrystallize. In the heating process of primary recrystallization annealing, the rolling structure recovers from a relatively low temperature, and the accumulated strain energy of dislocations is released at a stretch above a certain temperature range, and nucleation and growth of primary recrystallized grains occur.

  Here, as described above, the purpose of the rapid heating technique is to bring the Goss orientation grains, which are essentially difficult to recrystallize at a normal heating rate, to a high temperature range while maintaining the accumulated strain energy. It is to facilitate recrystallization. Therefore, in order to facilitate recrystallization, the temperature range for rapid heating is in the range of 200 to 700 ° C. where recovery of the rolling structure after cold rolling occurs and recrystallization nuclei occur. Is important, and by rapidly heating the temperature range at 50 ° C./s or more, the above-mentioned Goss orientation grain recrystallization promotion effect can be obtained. This is because when the heating rate is less than 50 ° C./s, the rolling structure is easily recovered and cannot be suppressed. In addition, this temperature increase rate is a temperature increase rate excluding the isothermal holding time described below.

  In addition, in the heating process of primary recrystallization annealing, the inventors, in addition to the rapid heating described above, a temperature range before primary recrystallization nuclei are generated, specifically, 250 to 600 ° C. at which dislocations can move sufficiently. The number of Goss orientation grains in the primary recrystallized plate texture is increased by maintaining the temperature isothermally in the temperature range, applying a moderate recovery process, and optimizing the strain energy accumulated in the rolled structure. It has been found that the secondary recrystallized grains can be refined to further improve the iron loss characteristics.

Although the reason why the iron loss characteristics are improved by performing the recovery process during the heating is not yet fully clarified, the inventors consider as follows.
As described above, the accumulated strain energy of dislocations has crystal orientation dependence, and the <111> // ND orientation has the highest strain energy in the rolled structure. A high strain energy means a high recovery ability, and therefore the recovery proceeds most in the <111> // ND orientation in a temperature range where primary recrystallization nuclei are not generated. Therefore, by performing the recovery process in a temperature range (250 to 600 ° C.) in which the dislocations before the primary recrystallization nuclei can easily move, the recrystallization advantage of the original <111> // ND orientation is lost. Therefore, the recrystallization superiority of the desired Goss orientation can be relatively improved. It should be noted that the recovery treatment time in the temperature range is not effective even if it is too short, while on the other hand, it is difficult to cause primary recrystallization by reducing the driving force of primary recrystallization in any crystal orientation in a long time. Become. Therefore, the retention time for the recovery process is preferably in the range of 1 second to 10 seconds.

Further, as the annealing separator applied to the steel sheet surface, a known one can be used, but it is preferable to use properly depending on whether or not a forsterite film is formed on the steel sheet surface. For example, the above-mentioned film is formed. In some cases, it is preferable to use an annealing separator having MgO as a main component. On the other hand, if it is desired to mirror the surface of the steel sheet, an annealing separator such as an Al ₂ O ₃ system that does not form a film is preferably used.

  In addition, the finish annealing is the most important step in the production method of the present invention, which is usually performed at a temperature of about 1200 ° C. at the maximum for both secondary recrystallization annealing and purification annealing. That is, the method for producing a grain-oriented electrical steel sheet according to the present invention is characterized in that, in the temperature raising process of the finish annealing, it is held for 40 to 200 hours in a temperature range of 775 to 875 ° C. before secondary recrystallization.

  Usually, the secondary recrystallization occurs at a temperature around 1000 ° C., but in the temperature range exceeding 875 ° C., the inhibitor component is oxidized and the primary recrystallized grains of the steel sheet surface layer become coarse. And this coarsening of the surface primary recrystallized grains causes a secondary recrystallization failure in the grain-oriented electrical steel sheet having a thin plate thickness.

As a result of repeated research on a solution to this problem, the inventors have retained the steel sheet before secondary recrystallization in a temperature range of 775 to 875 ° C. for 40 to 200 hours, whereby primary recrystallization of the surface layer is performed. It has been found that grain coarsening is suppressed. If the holding time is less than 40 hours, the primary recrystallized grains in the surface layer become coarse, secondary recrystallization failure occurs, and the magnetic properties deteriorate. On the other hand, when the holding time exceeds 200 hours, the primary recrystallized grains are coarsened as a whole, and grains other than the Goss orientation are also coarsened, so that secondary recrystallization hardly occurs and the magnetic properties are deteriorated.
The holding treatment before the secondary recrystallization may be held at a specific temperature between 775 and 875 ° C. for 40 to 200 hours, or between 775 and 875 ° C. over 40 to 200 hours. It may be.

As described above, the reason why the coarsening of the primary recrystallized grains in the surface layer is suppressed by holding in the temperature range of 775 to 875 ° C. for 40 to 200 hours is considered as follows.
In the manufacture of grain-oriented electrical steel sheets using AlN as an inhibitor, AlN decomposes at a temperature of about 920 ° C. or more, resulting in coarsening of primary recrystallized grains in the surface layer. Here, in order to suppress the decomposition of AlN before starting secondary recrystallization, it is necessary to quickly raise the temperature to the secondary recrystallization temperature range, but in coil annealing, in the initial heating stage Since the rate of temperature increase is slow, the decomposition of AlN cannot be suppressed, leading to the coarsening of primary recrystallized grains in the surface layer. Therefore, by performing a retention treatment at a predetermined temperature for a predetermined time before heating to the recrystallization temperature, the temperature distribution in the coil becomes uniform, and the rate of temperature increase in the temperature range where AlN decomposes increases. The coarsening of the primary recrystallized grains before the next recrystallization can be suppressed.

  In addition, the temperature increase rate after the retention treatment is preferably 10 ° C./hr or more, and more preferably 20 ° C./hr or more. However, if the rate of temperature increase is too high, the sharpness of the secondary recrystallized grains in the Goss orientation decreases, and the magnetic properties may be deteriorated. Therefore, the upper limit is preferably about 60 ° C./hr. .

In addition, if it is going to fully perform said holding | maintenance process, there exists a possibility that MnS and MnSe which are inhibitors other than AlN may coarsen, and suppression power may fall. Therefore, in the present invention, Cu ₂ S or Cu ₂ Se whose inhibitory power is hardly reduced is used as an inhibitor, and Sb is added, and Sb is segregated on the surface of the precipitated Cu ₂ S or Cu ₂ Se inhibitor. Suppresses the coarsening. Furthermore, since the segregation of Sb is promoted when Ni is added, the inhibitory power of Cu ₂ S and Cu ₂ Se is further reinforced, and the inhibitory power of the inhibitor can be kept high.

Note that N ₂ , H ₂ , Ar, or a mixed gas thereof is used as the atmospheric gas in the above-described finish annealing. Generally, N ₂ is a temperature higher than that in the heating process and the cooling process at a temperature of 850 ° C. Then, H ₂ or a mixed gas of H ₂ and N ₂ or H ₂ and Ar is used.

  Then, after finishing the unreacted annealing separator on the surface of the steel sheet, the finish-annealed steel sheet is coated with an insulating coating and baked or flattened annealed as necessary to obtain a product plate. The insulating coating is preferably a tension coating in order to reduce iron loss. In addition, in order to reduce iron loss to the steel sheet after finish annealing, a known magnetic domain subdivision is applied in which a plasma jet, laser irradiation, or electron beam irradiation is linearly applied, or linear distortion is imparted by a protruding roll. Processing may be performed. In addition, when the forsterite film is not formed on the steel plate surface by finish annealing, the steel plate surface is further mirror-finished or subjected to grain orientation selection processing by NaCl electrolysis, etc., and further subjected to tension coating. It is good also as a product board.

C: 0.07 mass%, Si: 3.4 mass%, Mn: 0.07 mass%, sol. Al: 0.022-0.027 mass%, N: 0.005-0.009 mass%, Ni: 0.3 mass%, Cu: 0.03 mass%, Sb: 0.04 mass% and Se: 0.015 mass% Containing, sol. Twelve kinds of steel slabs having a component composition in which the value of Al / N is changed in the range of 1.6 to 3.1 are hot-rolled to form a hot-rolled sheet having a thickness of 2.4 mm, and 900 ° C. × 40 After hot-rolled sheet annealing for 2 seconds, pickling, cold-rolling and intermediate sheet thickness: 1.5 mm, intermediate annealing of 1150 ° C. × 80 seconds, and warm-rolling at a temperature of 170 ° C. Final plate thickness: 0.17 mm cold rolled plate. Then, after performing a degreasing treatment to the cold-rolled _sheet, H 2: 60 vol% and _N 2: was subjected to primary recrystallization annealing, which also serves as a 40 vol% of the wet 850 ° C. × 2 minutes decarburization under a hydrogen atmosphere. A part of the cold-rolled sheets was subjected to a magnetic domain refinement process in which grooves on the steel sheet surface having a width of 180 μm × depth of 15 μm and extending in the direction perpendicular to the rolling direction were formed at intervals of 5 mm in the rolling direction.
Then, after applying as an annealing separator mainly composed of MgO on the steel sheet surface, the temperature was raised from room temperature to 850 ° C. at 20 ° C./hr in an N ₂ atmosphere, and subsequently maintained at 850 ° C. for 50 hours. Then, the temperature was raised between 20 ° C. and 1150 ° C. in a mixed atmosphere of N ₂ : 50 vol% + H ₂ : 50 vol%, and between 1150 and 1200 ° C. in an H ₂ atmosphere at 20 ° C./hr, respectively. After finishing soaking at 1200 ° C. for 10 hours in an H ₂ atmosphere, cooling is started, and cooling at 800 ° C. or lower in an N ₂ atmosphere is performed, and finish annealing that combines secondary recrystallization annealing and purification annealing is performed. gave. The steel sheet after the finish annealing was prepared by removing unreacted annealing separating agent and then applying and baking a tension coat composed of 50 mass% colloidal silica and magnesium phosphate.

Total length obtained in this way: From the 4000 m product coil, magnetic test specimens were collected from a total of 5 locations of 0 m, 1000 m, 2000 m, 3000 m and 4000 m in the longitudinal direction of the coil, and the method described in JIS C2550 was used. Then, the iron loss W _17/50 and the magnetic flux density B ₈ are measured, and the worst iron loss W _17/50 and the magnetic flux density B ₈ among the five measurement results are set as guaranteed values in the coil. It is shown in Table 3.

From Table 3, while adding appropriate amounts of Ni, Cu and Sb, sol. It can be seen that by controlling the value of Al / N in the range of 2.0 to 2.8, a _grain- oriented electrical steel sheet having excellent iron loss W _17/50 and magnetic flux density B ₈ can be obtained over the entire length of the coil. In particular, those obtained by subjecting a cold-rolled sheet to magnetic domain refinement have extremely good magnetic properties.

A steel slab of A to I having the component composition shown in Table 4 is hot-rolled to form a hot-rolled sheet having a thickness of 2.4 mm, annealed at 900 ° C. for 40 seconds, and then pickled. And cold-rolled to an intermediate thickness of 1.5 mm, subjected to intermediate annealing at 1150 ° C. for 80 seconds, and then warm-rolled at a temperature of 170 ° C. to obtain a final thickness of 0.17 mm. Cold-rolled sheet was used. Thereafter, the cold-rolled sheet is degreased and subjected to primary recrystallization annealing that also serves as decarburization at 850 ° C. × 2 minutes in a wet hydrogen atmosphere of H ₂ : 60 vol% + N ₂ : 40 vol%. After coating as an annealing separator as a component, the temperature was raised from room temperature to 850 ° C. at 20 ° C./hr in an N ₂ atmosphere, and subsequently, a holding treatment was performed at 850 ° C. for 50 hours. The temperature was raised at 20 ° C./hr in an N ₂ atmosphere for 1 ° C. and 1250 to 1200 ° C. in an H ₂ atmosphere, and after soaking at 1200 ° C. for 10 hours in an H ₂ atmosphere, Cooling was started, and finish annealing was performed, in which secondary recrystallization annealing and purification annealing were performed at 800 ° C. or lower in an N ₂ atmosphere. The steel sheet after the finish annealing was prepared by removing the unreacted annealing separator and applying and baking a tension coat composed of 50 mass% colloidal silica and magnesium phosphate.

Total length obtained in this way: From the 4000 m product coil, magnetic test specimens were collected from a total of 5 locations of 0 m, 1000 m, 2000 m, 3000 m and 4000 m in the longitudinal direction of the coil, and the method described in JIS C2550 was used. Then, the iron loss W _17/50 and the magnetic flux density B ₈ are measured, and the worst iron loss W _17/50 and the magnetic flux density B ₈ among the five measurement results are set as guaranteed values in the coil. This is also shown in Table 4.

From Table 4, steels A to I to which any one of Ge, Bi, V, Nb, Te, Cr, Sn, and Mo is added in an appropriate range are compared with steel A that does not contain those elements. It can be seen that the iron loss W _17/50 is improved.

C: 0.07 mass%, Si: 3.4 mass%, Mn: 0.07 mass%, sol. Steel slab having a component composition containing Al: 0.027 mass%, N: 0.010 mass%, Ni: 0.3 mass%, Cu: 0.03 mass%, Sb: 0.04 mass% and Se: 0.015% Is hot-rolled to obtain a hot-rolled sheet having a thickness of 2.4 mm, subjected to hot-rolled sheet annealing at 900 ° C. for 40 seconds, pickled, and cold-rolled to obtain an intermediate thickness of 1.5 mm. A cold-rolled sheet was subjected to intermediate annealing at 1150 ° C. for 80 seconds and warm-rolled at a temperature of 170 ° C. to obtain a final cold-rolled sheet having a thickness of 0.17 mm. Thereafter, the cold-rolled sheet was degreased and subjected to primary recrystallization annealing also serving as decarburization at 850 ° C. for 2 minutes in a wet hydrogen atmosphere of H ₂ : 60 vol% + N ₂ : 40 vol%. Was applied as an annealing separation agent containing as a main component, and finish annealing was performed which served as secondary recrystallization annealing and purification annealing.
In addition, the above-mentioned finish annealing is roughly divided into a temperature rising process,
(A) The temperature is raised from room temperature to 850 ° C. at 20 ° C./hr in an N ₂ atmosphere, and subsequently maintained at 850 ° C. for 20 hours, 30 hours, 40 hours, 50 hours, 100 hours, 200 hours or 300 hours. 7 conditions of A to G (temperature increase pattern A)
(B) Room temperature to 750 ° C., 775 ° C., 825 ° C., 875 ° C. or 900 ° C. is heated at 20 ° C./hr in an N ₂ atmosphere, and subsequently maintained at that temperature for 50 hours. 5 conditions (temperature rise pattern B),
(C) The temperature was raised from room temperature to 775 ° C. at 20 ° C./hr in an N ₂ atmosphere, and subsequently from 775 ° C. to 850 ° C. for 30 hours, 40 hours, 50 hours, 100 hours, 200 hours or 300 hours. 6 conditions (temperature increase pattern C) of M to R that are heated at a constant temperature increase rate over time,
And then up to 1150 ° C. in a mixed atmosphere of N ₂ : 25 vol% + H ₂ : 75 vol% and between 1150 and 1200 ° C. in an H ₂ atmosphere at 20 ° C. / The temperature was increased by hr, and further, a soaking process was performed at 1200 ° C. for 10 hours in an H ₂ atmosphere. Then, cooling was started, and cooling was performed at a temperature of 800 ° C. or lower in an N ₂ atmosphere. The steel sheet after the finish annealing was prepared by removing the unreacted annealing separator and applying and baking a tension coat composed of 50 mass% colloidal silica and magnesium phosphate.

Total length obtained in this way: From the 4000 m product coil, magnetic test specimens were collected from a total of 5 locations of 0 m, 1000 m, 2000 m, 3000 m and 4000 m in the longitudinal direction of the coil, and the method described in JIS C2550 was used. Then, the iron loss W _17/50 and the magnetic flux density B ₈ are measured, and the worst iron loss W _17/50 and the magnetic flux density B ₈ among the five measurement results are set as guaranteed values in the coil. Table 5 shows.

  From Table 5, it can be seen that the magnetic properties are greatly improved by holding for 40 to 200 hours in the temperature range of 775 to 875 ° C. before secondary recrystallization occurs. It can also be seen that it is preferable to hold at a constant temperature for the same holding time.

C: 0.07 mass%, Si: 3.4 mass%, Mn: 0.07 mass%, Al: 0.018 mass%, N: 0.007 mass%, Se: 0.04 mass%, Ni: 0.3 mass%, Cu : A steel slab having a composition containing 0.03 mass% and Sb: 0.04 mass% is hot-rolled to form a hot-rolled coil having a thickness of 2.4 mm, and hot-rolled sheet annealing is performed at 900 ° C for 40 seconds. Application, pickling, primary cold rolling to a sheet thickness of 1.5 mm, intermediate annealing held at 1150 ° C. for 80 seconds, and then warm rolling at a temperature of 170 ° C. to give a final sheet thickness of 0.17 mm. A rolled coil was used. Next, the cold-rolled coil is divided into two parts, and one is subjected to a magnetic domain refinement process in which a groove having a width of 180 μm and extending in a direction perpendicular to the rolling direction is formed on the steel plate surface at intervals of 5 mm in the rolling direction. Was subjected to primary recrystallization annealing also serving as decarburization annealing in a wet atmosphere of 50 vol% H ₂ -50 vol% N ₂ without being subjected to magnetic domain refinement treatment.
The heating up to 840 ° C. in the primary recrystallization annealing varies in various ways within the range of 20 ° C./s to 200 ° C./s, as shown in Table 6, at a rate of temperature increase from 200 ° C. to 700 ° C. I let you. However, the temperature rising rate was constant, and the condition was maintained at 450 ° C. during the heating for 0.5 seconds to 3 seconds. Some conditions were not retained.
Then, after applying an annealing separator mainly composed of MgO to the steel sheet surface, the steel plate was heated to 850 ° C. at a heating rate of 20 ° C./hr in an N ₂ atmosphere, and maintained at 850 ° C. for 50 hours. in raising rate 40 ° C. / hr, up to 850-1150 ° C. under a mixed atmosphere of _{50vol% N 2 -50vol% H 2} , up to 1150 to 1200 ° C. was heated under an atmosphere of _{H 2} addition, _{H 2} atmosphere at After soaking at 1200 ° C. for 10 hours, secondary recrystallization annealing (finish annealing) was performed in which 800 ° C. or lower was cooled in an N ₂ atmosphere. Subsequently, after removing the unreacted annealing separator from the surface of the steel plate subjected to finish annealing, a tension coating liquid composed of 50 mass% colloidal silica and magnesium phosphate was applied and baked to obtain a product coil.

The product coils (total length: about 4000 m) thus obtained were collected from a total of five locations in the longitudinal direction: 0 m, 1000 m, 2000 m, 3000 m, and 4000 m, and magnetic test specimens were collected and iron at a magnetic flux density of 1.7 T. The loss value W _17/50 was measured and the average value was obtained.
The results of the above measurements are shown in Table 6 with classification according to the presence or absence of magnetic domain fragmentation. From this table, by performing the heating process in the primary recrystallization annealing while satisfying the conditions of the present invention, the iron loss characteristics (W _17/50 ) are greatly improved, especially when the magnetic domain subdivision treatment is performed. It can be seen that the iron loss improvement effect is remarkable.

Claims (5)

C: 0.04-0.12 mass%,
Si: 1.5 to 5.0 mass%,
Mn: 0.01 to 1.0 mass%,
Ni: 0.10 to 1.0 mass%,
sol. Al: 0.010 to 0.040 mass%,
N: 0.004 to 0.02 mass%,
Cu: 0.02-1.0 mass%,
Sb: 0.01-0.10 mass%,
One or two selected from S and Se: a steel slab containing 0.005 to 0.05 mass% in total, the balance being Fe and unavoidable impurities is heated to a temperature of 1250 ° C. or higher, Hot rolled to a thickness of 1.8 mm or more by cold rolling and cold rolled to a final thickness of 0.12 to 0.20 mm by cold rolling one or more times with intermediate annealing. In the manufacturing process of grain-oriented electrical steel sheet consisting of a series of steps of crystal annealing and finish annealing,
Sol sol. The Al / N value is in the range of 2.0 to 2.8, and the steel plate before secondary recrystallization in finish annealing is held in the temperature range of 775 to 875 ° C. for 40 to 200 hours , and then 10 to 60 ° C. A method for producing a grain- oriented electrical steel sheet, wherein the steel sheet is heated to a secondary recrystallization temperature range at a rate of temperature rise of / hr . In addition to the above component composition, the composition further contains one or more selected from Ge, Bi, V, Nb, Te, Cr, Sn and Mo in a total amount of 0.002 to 1.0 mass%. The manufacturing method of the grain-oriented electrical steel sheet according to claim 1. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, wherein heating is performed at a temperature rising rate of 50 ° C / s or more between 200 to 700 ° C in the heating process of the primary recrystallization annealing. The directionality according to any one of claims 1 to 3, wherein the temperature is kept isothermal for 1 to 10 seconds at any temperature between 250 to 600C in the heating process of the primary recrystallization annealing. A method for producing electrical steel sheets. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein after the final cold rolling, a magnetic domain refinement process is performed on the steel sheet surface.

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