JP2013047382A - Method of producing grain-oriented electromagnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing an ultrathin grain-oriented electromagnetic steel sheet exhibiting uniform and extremely low iron loss in a product coil thereof.SOLUTION: The method of producing a grain-oriented electromagnetic steel sheet comprises carrying out processes of hot rolling, cold rolling, primary recrystallization annealing, and finish annealing of a steel slab containing, in mass%, C: 0.04 to 0.12%, Si: 1.5 to 5.0%, Mn: 0.01 to 1.0%, sol. Al: 0.010 to 0.040%, N: 0.004 to 0.02% and, S and Se: 0.005 to 0.05% in total. In the steel slab, the ratio of the amount of the sol. Al and N (sol. Al/N) and the thickness d (mm) of the steel sheet at the time of the secondary recrystallization annealing satisfies the relation: 4d+1.52≤sol. Al/N≤4d+2.32. In the heating process of the finish annealing, the steel sheet before the secondary recrystallization is kept at a temperature of 775 to 875°C for 40 to 200 hours and subsequently heated at a temperature raising rate of 10 to 60°C/hour through a temperature range of 875 to 1,050°C to carry out the secondary recrystallization and the purification treatment.

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 directionality of ultrathin and low iron loss with a thickness of 0.15 to 0.23 mm. The present invention relates to a method for manufacturing an electromagnetic steel sheet.

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.

  To deal with 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 0.15 to 0.23 mm after the final cold rolling, even if the technique disclosed in the above prior art is applied, the secondary re-rolling is still performed in a part of the coil. There is a problem that crystal defects occur and the yield decreases.

  Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, stably cause secondary recrystallization even in an ultrathin grained electrical steel sheet having a thickness of 0.15 to 0.23 mm, The object is to propose an advantageous method for producing a grain-oriented electrical steel sheet having uniform iron loss in the coil and extremely low iron loss.

  In order to elucidate the cause of unstable secondary recrystallization behavior in a directional electrical steel sheet with a thin plate thickness, the inventors are in the middle of secondary recrystallization annealing when finishing annealing the steel sheet after primary recrystallization annealing. The steel sheet was taken out and the precipitation state of the inhibitor and the growth state of the crystal grains were investigated. As a result, in the heating process of finish annealing, the inhibitor is coarsened and the ability to suppress crystal grain growth is reduced. 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, and the surface layer The coarsening of the 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 0.15 to 0.23 m, the above-described inhibitor is coarse. It has been clarified that the decrease in the ability to suppress crystal grain growth due to crystallization and the progress of coarsening of surface grains are the main causes of secondary recrystallization failure.

  In view of this, the inventors have established a method for ensuring sufficient driving force required for secondary recrystallization by suppressing the growth of primary recrystallized grains and stably causing secondary recrystallization over the entire coil length. We further examined it with the idea that it might be possible. As a result, depending on the product sheet thickness, that is, the final sheet thickness d after cold rolling, the sol. In the heating process of finish annealing, the ratio of the content of Al and N (sol.Al/N) is controlled to an appropriate range so that the grain size of the central layer of the steel plate thickness is suitable for secondary recrystallization. The steel sheet before secondary recrystallization is kept at a predetermined holding temperature for a predetermined time to equalize the temperature in the coil, and then rapidly heated at a temperature rising rate of 10 to 60 ° C./hr to reduce the grain size of the steel sheet surface layer. It has been found that by controlling to an appropriate range, secondary recrystallization can be stably expressed over the entire length of the coil, and a grain-oriented electrical steel sheet having a uniform and extremely low iron loss over the entire length of the coil can be obtained. .

The present invention developed on the basis of the above findings includes C: 0.04 to 0.12 mass%, Si: 1.5 to 5.0 mass%, Mn: 0.01 to 1.0 mass%, sol. Al: 0.010-0.040 mass%, N: 0.004-0.02 mass%, one or two selected from S and Se: a total of 0.005-0.05 mass%, with the balance being Fe And a steel slab having a component composition consisting of inevitable impurities is heated to 1250 ° C. or higher, and then hot-rolled to form a hot-rolled sheet having a thickness of 1.8 mm or more. In a method for producing a grain-oriented electrical steel sheet comprising a series of steps of forming a cold-rolled sheet having a final thickness of 0.15 to 0.23 mm by rolling, performing primary recrystallization annealing, and then finishing annealing, the sol. The ratio of the content of Al and N (sol. Al / N) and the final thickness d (mm) are the following formula (1):
4d + 1.52 ≦ sol. Al / N ≦ 4d + 2.32 (1)
And the steel sheet is kept at a temperature of 775 to 875 ° C. for 40 to 200 hours in the heating process of the finish annealing, and then a temperature range of 875 to 1050 ° C. is heated at a heating rate of 10 to 60 ° C./hr. This is a method for producing a grain-oriented electrical steel sheet characterized by the following.

  The steel slab in the method for producing a grain-oriented electrical steel sheet according to the present invention further includes Ni: 0.1 to 1.0 mass%, Cu: 0.02 to 1.0 mass%, and Sb: 0.0. 1 type or 2 types or more chosen from 01-0.10 mass% are contained, It is characterized by the above-mentioned.

  Further, the steel slab in the method for producing a grain-oriented electrical steel sheet of the present invention is one or two selected from Ge, Bi, V, Nb, Te, Cr, Sn and Mo in addition to the above component composition. It contains 0.002 to 1.0 mass% of seeds or more in total.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention heats between 200 and 700 ° C. in the heating process of the primary recrystallization annealing at a temperature rising rate of 50 ° C./s or more, and between 250 and 600 ° C. The temperature is kept isothermal for 1 to 10 seconds.

  The grain-oriented electrical steel sheet manufacturing method of the present invention is characterized in that, at any stage after cold rolling, a groove is formed on the steel sheet surface in a direction crossing the rolling direction and subjected to magnetic domain refinement treatment. To do.

  Further, the grain-oriented electrical steel sheet manufacturing method of the present invention performs the magnetic domain fragmentation treatment by irradiating the surface of the steel sheet with the insulating coating continuously or intermittently in the direction intersecting the rolling direction. It is characterized by giving.

  According to the present invention, by controlling the value of (sol.Al/N) in the steel material (slab) to an appropriate range according to the product plate thickness (final plate thickness), the inhibitor during secondary recrystallization annealing is performed. The steel sheet before the secondary recrystallization was kept at a predetermined temperature for a predetermined time during heating in the finish annealing to make the temperature in the coil uniform. After that, the temperature is rapidly raised to the secondary recrystallization temperature to suppress the coarsening of the steel sheet surface layer grains, so that secondary recrystallization can be stably expressed over the entire length of the coil, and the iron loss characteristics are excellent. It becomes possible to manufacture a grain-oriented electrical steel sheet with a high yield.

Magnetic flux density _B 8: is a graph showing the range of 1.90T or higher final thickness d and the resulting (sol.Al/N). It is a graph which shows the relationship between the temperature increase rate between 850-1050 degreeC in finish annealing, and the guaranteed value in a coil of iron loss _{W17 / 50} .

First, the experiment that led to the development of the present invention will be described.
<Experiment 1>
As shown in Table 1, C: 0.07 mass%, Si: 3.4 mass%, Mn: 0.07 mass%, Se: 0.015 mass%, Ni: 0.3 mass%, Cu: 0.03 mass% and Sb: 0.04 mass%, and sol. Seven types of steel slabs having component compositions in which the ratio of the content of Al and N (sol. Al / N) was changed in a range of 2.10 to 3.56 were hot-rolled to obtain a sheet thickness of 2. A hot rolled coil of 4 mm, annealed at 900 ° C. for 40 seconds, pickled, first cold rolled to a thickness of 1.5 mm, intermediate annealed at 1150 ° C. for 80 seconds, and a temperature of 170 ° C. After cold-rolling into cold-rolled coils with various plate thicknesses in the range of 0.12 to 0.25 mm, degreased, and 850 ° C. × 2 minutes in a wet hydrogen atmosphere of 60 vol% H ₂ -40 vol% N ₂ A primary recrystallization annealing was also applied to decarburize the steel.

Next, after applying and drying an annealing separator mainly composed of MgO on the surface of the steel sheet after the primary recrystallization, the steel plate is heated up to 850 ° C. in a N ₂ atmosphere at a heating rate of 20 ° C./hr, and 850 ° C. And then at a temperature rising rate of 20 ° C./hr, between 850 and 1150 ° C. in a mixed atmosphere of 25 vol% N ₂ -75 vol% H ₂ and between 1150 and 1200 ° C. in an H ₂ atmosphere. After heating and heating at 1200 ° C for 10 hours in an H ₂ atmosphere, secondary recrystallization annealing for cooling below 800 ° C in an N ₂ atmosphere and finish annealing that combines purification treatment are performed. did. Next, after removing the unreacted annealing separator from the surface of the steel sheet after the above-mentioned finish annealing, an insulating coating mainly composed of aluminum phosphate and colloidal silica was formed to obtain a product coil.

Samples for magnetic measurement were taken from five locations of 0 m, 1000 m, 2000 m, 3000 and 4000 m in the longitudinal direction of the product coil having a total length of about 4000 m thus obtained, and the magnetic flux density B ₈ at a magnetizing force of 800 A / m was measured. The value with the lowest magnetic flux density in the coil is the guaranteed value in the coil, and the highest value is the good value in the coil. The results are also shown in Table 1. Further, FIG. 1 shows the range of the plate thickness d and (sol.Al/N) at which the magnetic flux density B _{8 is} 1.90 T or more. Here, the magnetic flux density B ₈ is an effective index for determining that secondary recrystallization has occurred properly. The high guaranteed value of B _{8 in} the coil indicates that the secondary recrystallization is uniformly performed in the coil. It indicates that crystals are occurring.

From these results, the value of (sol.Al/N) in the steel material (slab) is controlled within an appropriate range according to the thickness (final thickness) at the time of secondary recrystallization annealing. , The following formula (1);
4d + 1.52 ≦ sol. Al / N ≦ 4d + 2.32 (1)
It can be seen that by controlling so as to satisfy the above, secondary recrystallization occurs over the entire length of the coil and the magnetic characteristics are improved.

<Experiment 2>
C: 0.07 mass%, Si: 3.4 mass%, Mn: 0.07 mass%, sol. Hot rolling a steel slab containing Al: 0.020 mass%, N: 0.007 mass%, Se: 0.015 mass%, Ni: 0.3 mass%, Cu: 0.03 mass% and Sb: 0.04 mass% And a hot rolled coil having a thickness of 2.4 mm, annealed by hot rolling at 900 ° C. for 40 seconds, pickled, and first cold-rolled to a thickness of 1.5 mm, and intermediate annealing at 1150 ° C. for 80 seconds. Then, it was warm-rolled at a temperature of 170 ° C. to obtain a cold rolled coil having a final sheet thickness of 0.20 mm, degreased, and then 850 ° C. × 2 minutes in a wet hydrogen atmosphere of 60 vol% H ₂ -40 vol% N ₂ A primary recrystallization annealing was also applied to decarburize.

Next, after applying and drying an annealing separator mainly composed of MgO on the steel sheet surface after the primary recrystallization, heating up to 850 ° C. in a N ₂ atmosphere at a heating rate of 20 ° C./hr, As shown in Table 2, up to 1200 ° C. and 25 vol% N ₂ between 850 ° C. and 1150 ° C. in the heating pattern of A to G with the presence or absence of the retention treatment at 850 ° C. and the heating rate between 850 and 1050 ° C. mixed atmosphere of -75vol% _{H 2,} between 1150 to 1200 ° C. is heated under an atmosphere of _{H 2} addition, after the soaking treatment of 1200 ° C. × 10 hours under an atmosphere of _{H 2 N 2} atmosphere a 800 ° C. or less The secondary recrystallization annealing that is cooled at the bottom and the finish annealing that combines the purification treatment were performed. Next, after removing the unreacted annealing separator from the surface of the steel sheet after the above-mentioned finish annealing, an insulating coating mainly composed of aluminum phosphate and colloidal silica was formed to obtain a product coil.

The test pieces for magnetic measurement were taken from five places in the longitudinal direction of 0 m, 1000 m, 2000 m, 3000 m and 4000 m of the product coil having a total length of about 4000 m thus obtained, and the magnetic flux density B ₈ and the magnetic flux density at a magnetizing force of 800 A / m. The iron loss value W _17/50 per mass at an amplitude of 1.7 T and 50 Hz was measured, and the worst B ₈ and W _17/50 values in the coil were measured as guaranteed values in the coil and the best B ₈ in the coil. _And the value of W _17/50 was regarded as a good value in the coil, and the results are also shown in Table 2. Further, FIG. 2 shows the relationship between the heating rate between 850 and 1050 ° C., the guaranteed value in the coil of the magnetic flux density B ₈ and the iron loss W _17/50 , and the good value in the coil.

From these results, the heating pattern A in which the holding treatment for 50 hours was not performed at 850 ° C. during the heating of the finish annealing and the heating pattern B having a low heating rate of 5 ° C./hr between 850 to 1050 ° C. Because the secondary recrystallization is not uniform, the guaranteed value in the coil is poor. However, after the above retention treatment, the secondary recrystallization is stable in the heating patterns C to G that are rapidly heated at a heating rate of 10 ° C./hr or more. It can be seen that the magnetic properties are improved over the entire length in the coil. However, the magnetic properties are slightly deteriorated at a temperature rising rate of 100 ° C./hr (heating pattern G).
The present invention has been made based on the above findings.

Next, the component composition of the steel 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 annealing may cause insufficient decarburization, 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%.

sol. Al / N
In the present invention, depending on the final thickness (product thickness) d (mm) of cold rolling, the sol. To optimize the ratio of Al and N content (mass%), specifically, the following formula (1);
4d + 1.52 ≦ sol. Al / N ≦ 4d + 2.32 (1)
It is important to make it contain so that a relationship may be satisfy | filled.
As shown in FIG. 1, when the value of (sol.Al/N) is large, the inhibitory force of AlN as an inhibitor is not sufficient, leading to the coarsening of crystal grains in the surface layer and the central layer of the steel sheet. End up. On the other hand, when (sol.Al/N) is small, grains having a large angular difference from the Goss orientation also secondary recrystallize, so that the magnetic flux density after secondary recrystallization decreases, iron loss This is because it increases.
In addition, the value of (sol.Al/N) is set to the final plate thickness d (mm) and the sol. In order to optimize in accordance with the Al content, the N content may be adjusted by performing nitriding before the secondary recrystallization.

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%.

In addition to the above components, the grain-oriented electrical steel sheet of the present invention may further contain one or more selected from Ni, Cu and Sb.
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%.

In addition to the above components, the 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 as an inhibitor auxiliary component. , And can be contained in the range of 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 processes in which cold rolling is performed more than once, primary recrystallization annealing is performed, and finish annealing is performed that combines secondary recrystallization annealing and purification treatment.
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 above slab reheating, hot rolling and hot rolled sheet with a thickness of 1.8 mm or more (coil. Here, the reason for limiting the hot rolled sheet thickness to 1.8 mm or more is to shorten the rolling time, This is to reduce the temperature difference in the rolling direction of the hot-rolled steel sheet, and the hot rolling conditions are not particularly limited as long as they are performed according to a conventional method.

The hot-rolled sheet (hot-rolled coil) obtained by hot rolling is then subjected to hot-rolled sheet annealing as necessary, and then pickled and cold-rolled twice or more with one or intermediate annealing in between. Thus, a cold-rolled sheet (cold-rolled coil) having a final thickness is obtained.
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 cold rolling described above, aging between passes or warm rolling may be applied.

  The final thickness (product thickness) of the grain-oriented electrical steel sheet of the present invention is in the range of 0.15 to 0.23 mm. If the plate thickness exceeds 0.23 mm, the driving force of secondary recrystallization becomes excessive, and the dispersion of secondary recrystallized grains from the Goss orientation increases. On the other hand, when the thickness is less than 0.15 mm, secondary recrystallization becomes unstable or the ratio of the insulating film relatively increases and the magnetic flux density decreases, and it is difficult to roll and manufacture. Because it becomes.

The cold-rolled sheet with 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, wound around a coil, Finish annealing is performed to raise the crystal and purify it.
Here, the primary recrystallization annealing is performed at a temperature increase rate of 50 ° C./s or more at 200 to 700 ° C. in the heating process, and is isothermal for 1 to 10 seconds at any temperature between 250 to 600 ° C. It is preferable to hold it. By applying this rapid heating and holding treatment, the recrystallization after the secondary recrystallization is made finer, so that it is possible to obtain a grain-oriented electrical steel sheet with low iron loss and small variations in iron loss values. It is.

  In the primary recrystallization annealing, in order to adjust the value of (sol.Al/N) to an appropriate range, the nitriding treatment may be performed as necessary. Apart from the primary recrystallization annealing, A nitriding treatment step may be added between after cold rolling and before finish annealing.

  Before the primary recrystallization annealing, the cold-rolled sheet may be subjected to a magnetic domain refinement process in which grooves are formed by etching on the steel sheet surface in order to reduce iron loss of the product sheet. 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.

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.

  The finish annealing is the most important step in the production method of the present invention. Usually, the finish annealing is performed at a temperature of about 1200 ° C. at the maximum, which combines the secondary recrystallization annealing and the purification annealing, but in the method of manufacturing the grain-oriented electrical steel sheet of the present invention, in the temperature raising process of the finish annealing. It is necessary to hold for 40 to 200 hours in a temperature range of 775 to 875 ° C. before secondary recrystallization. The reason is as follows.

  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.

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 higher, 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.

  The rate of temperature increase up to 1050 ° C. following 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 excessively high, the sharpness of the secondary recrystallized grains in the Goss orientation decreases and the magnetic properties may deteriorate, so the upper limit is set to 60 ° C./hr. Further, the rate of temperature increase from 1050 ° C. to the maximum temperature is preferably 5 ° C./hr or more from the viewpoint of economy, while it is preferably 100 ° C./hr or less from the viewpoint of uniformizing the temperature in the coil. preferable.

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. It is preferable to suppress the coarsening of the film. Further, when Ni is added, segregation of Sb is promoted, so that the suppressive force of Cu ₂ S and Cu ₂ Se is further reinforced, and the inhibitory force of the inhibitor can be kept high.

As the atmosphere gas in the final annealing, it is used N _{2, H} 2, _Ar or a mixed gas thereof, generally at the temperature of 850 ° C. or less of the heating process and cooling process, N ₂ is, higher temperatures Then, H ₂ or a mixed gas of H ₂ and N ₂ or H ₂ and Ar is used.

  The steel sheet that has been subjected to finish annealing is used as a product plate after removing the unreacted annealing separator on the surface of the steel sheet, and then applying and baking an insulating coating solution or performing flattening annealing as necessary. In order to reduce the iron loss, it is preferable to use a tension coating as the insulating coating. In addition, in order to reduce iron loss to the steel plate after finish annealing, a known magnetic domain subdivision treatment is performed in which a continuous or intermittent irradiation with an electron beam or a laser, or linear distortion is imparted with a protruding roll. May be applied. In addition, when a forsterite film is not formed on the steel sheet surface by finish annealing, the steel sheet surface is further mirror-finished or subjected to grain orientation selection process by NaCl electrolysis, etc., and then a tension film is further formed. And it is good also as a product board.

A steel slab having the composition of components A to N shown in Table 3 was hot-rolled according to a conventional method to form a hot-rolled coil having a thickness of 2.4 mm, and subjected to hot-rolled sheet annealing at 900 ° C. for 40 seconds, Pickling, primary cold rolling to a sheet thickness of 1.5 mm, intermediate annealing at 1150 ° C. for 80 seconds, followed by warm rolling at a temperature of 170 ° C. and a cold rolled coil with a final sheet thickness of 0.17 mm It was. Subsequently, after degreasing the cold-rolled coil, primary recrystallization annealing was performed which also served as a decarburization process at 850 ° C. for 2 minutes in a wet hydrogen atmosphere of 60 vol% H ₂ -40 vol% N ₂ . Next, after applying and drying an annealing separator mainly composed of MgO on the surface of the steel sheet, after heating to 850 ° C. at a heating rate of 40 ° C./hr in an N ₂ atmosphere, and holding at 850 ° C. for 50 hours. , subsequently, at a heating rate of 20 ° C. / hr, up from 850 to 1,150 ° C. under 100 vol% _{N 2} atmosphere, to 1150 to 1200 ° C. was heated under an atmosphere of _{H 2} addition, 1200 ° C. × under _{a H 2} atmosphere The soaking was performed for 10 hours, and then finish annealing was performed to cool 800 ° C. or lower in an N ₂ atmosphere. Next, after removing the unreacted annealing separator from the surface of the steel plate subjected to the above-mentioned finish annealing, an insulating film mainly composed of magnesium phosphate and colloidal silica was formed to obtain a product coil.

The test pieces for magnetic measurement were collected from a total of five locations in the longitudinal direction of 0 m, 1000 m, 2000 m, 3000 m and 4000 m of the product coil having a total length of about 4000 m thus obtained, and the iron loss value W at a magnetic flux density of 1.7 T was obtained. _17/50 was measured, and among the above five iron losses, the worst value was the guaranteed value in the coil, and the best value was the good value in the coil. The results are also shown in Table 3.
From Table 3, one or more selected from Ni, Cu and Sb, or, in addition, one or more selected from Ge, Bi, V, Nb, Tb, Cr, Sn and Mo can be added to add iron. It can be seen that the loss characteristics are further improved, and that if the (sol.Al/N) is removed, the iron loss characteristics are greatly deteriorated.

C: 0.07 mass%, Si: 3.4 mass%, Mn: 0.07 mass%, sol. A steel slab having a composition containing Al: 0.018 mass%, N: 0.007 mass%, Se: 0.015 mass%, Ni: 0.3 mass%, Cu: 0.03 mass%, and Sb: 0.04 mass%. , Hot rolled into a 2.4 mm thick hot rolled coil, annealed at 900 ° C. for 40 seconds, pickled, and first cold rolled to a thickness of 1.5 mm at 80 ° C. at 1150 ° C. After intermediate annealing for 2 seconds, the steel sheet was warm-rolled at a temperature of 170 ° C. to obtain a cold-rolled coil having a final thickness of 0.17 mm. Next, the cold-rolled coil is divided into two, and after one is subjected to a magnetic domain refinement treatment 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 sheet surface at intervals of 5 mm in the rolling direction. without applying the domain refining _treatment, in a humidified atmosphere of _{50vol% H 2 -50vol% N 2} , it was subjected to primary recrystallization annealing, which also serves as a decarburization annealing. In addition, the heating until reaching 840 ° C. in the primary recrystallization annealing is performed by changing the rate of temperature increase from 200 ° C. to 700 ° C. in a range of 20 to 200 ° C./s as shown in Table 4. It was. The heating rate between 200-700 ° C is constant, and the temperature is maintained at 450 ° C during the heating for 0.5-3 seconds. In addition, some coils are retained. There wasn't.

Then, after applying an annealing separator mainly composed of MgO to the steel sheet surface, the steel was heated to 850 ° C. at a heating rate of 20 ° C./hr in an N ₂ atmosphere and subjected to a holding treatment at 850 ° C. for 50 hours. The mixture is heated to 1200 ° C. at a heating rate of 40 ° C./hr with a mixed atmosphere of 50 vol% N ₂ -50 vol% H ₂ up to 850-1150 ° C. and an H ₂ atmosphere up to 1150-1200 ° C., and further under an H ₂ atmosphere Was subjected to soaking at 1200 ° C. for 10 hours, followed by finish annealing in which 800 ° C. or lower was cooled in an N ₂ atmosphere. Next, after removing the unreacted annealing separator from the surface of the steel plate after the above-mentioned finish annealing, a tension coating solution composed of 50 mass% colloidal silica and magnesium phosphate is applied and baked to form an insulating coating, and a product coil It was.

Test pieces for magnetic measurement were collected from a total of five locations in the longitudinal direction of 0 m, 1000 m, 2000 m, 3000 m and 4000 m of the product coil having a total length of about 4000 m thus obtained, and the iron loss value W _{17 at} a magnetic flux density of 1.7 T was obtained. _{/ 50} was measured and the average value was determined.
The results of the above measurement are shown in Table 4 with classification according to whether or not the magnetic domain fragmentation treatment was performed. From Table 4, in addition to optimizing the heating conditions for the finish annealing, the iron loss characteristics are further improved by performing the holding treatment in the heating process in the primary recrystallization annealing, in particular, the magnetic domain refinement treatment was performed. It can be seen that the iron loss improvement effect in the case is remarkable.

Claims (6)

C: 0.04-0.12 mass%, Si: 1.5-5.0 mass%, Mn: 0.01-1.0 mass%, sol. Al: 0.010-0.040 mass%, N: 0.004-0.02 mass%, one or two selected from S and Se: a total of 0.005-0.05 mass%, with the balance being Fe And a steel slab having a component composition consisting of inevitable impurities is heated to 1250 ° C. or higher, and then hot-rolled to form a hot-rolled sheet having a thickness of 1.8 mm or more. In the manufacturing method of the grain-oriented electrical steel sheet comprising a series of steps of performing a final annealing after a primary recrystallization annealing after forming a cold rolled sheet having a final thickness of 0.15 to 0.23 mm by rolling,
The sol. The ratio of the content of Al and N (sol.Al/N) and the final thickness d (mm) satisfy the following formula (1), and
A direction in which the steel sheet is held at a temperature of 775 to 875 ° C. for 40 to 200 hours in the heating process of the finish annealing, and then a temperature range of 875 to 1050 ° C. is heated at a temperature rising rate of 10 to 60 ° C./hr. Method for producing an electrical steel sheet.
4d + 1.52 ≦ sol. Al / N ≦ 4d + 2.32 (1) The steel slab is selected from Ni: 0.1 to 1.0 mass%, Cu: 0.02 to 1.0 mass%, and Sb: 0.01 to 0.10 mass% in addition to the component composition. It contains 1 type (s) or 2 or more types, The manufacturing method of the grain-oriented electrical steel sheet of Claim 1 characterized by the above-mentioned. In the steel slab, in addition to the component composition, one or more selected from Ge, Bi, V, Nb, Te, Cr, Sn, and Mo are added in a total amount of 0.002 to 1.0 mass%. It contains, The manufacturing method of the grain-oriented electrical steel sheet of Claim 1 or 2 characterized by the above-mentioned. Heating at 200 to 700 ° C. in the heating process of the primary recrystallization annealing at a temperature rising rate of 50 ° C./s or more and maintaining isothermal at any temperature between 250 to 600 ° C. for 1 to 10 seconds. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3. 5. The magnetic domain refinement process according to claim 1, wherein a groove is formed in a direction crossing the rolling direction on the steel sheet surface at any stage after the cold rolling to perform a magnetic domain refinement process. A method for producing grain-oriented electrical steel sheets. 5. The magnetic domain fragmentation treatment is performed by irradiating an electron beam or a laser continuously or intermittently in a direction intersecting the rolling direction on the surface of the steel sheet on which the insulating coating is formed. A method for producing a grain-oriented electrical steel sheet according to item 1.

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