JP6132103B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet that is suitable for use as a core material of a transformer.

  Oriented electrical steel sheet is a soft magnetic material mainly used as a core material for transformers and generators, and has a crystal structure in which the <001> orientation, which is the easy axis of iron, is highly aligned with the rolling direction of the steel sheet. There is a feature in doing. Such a texture is formed through secondary recrystallization that preferentially grows grains of {110} <001> orientation, so-called Goss orientation, in finish annealing at the end of the manufacturing process. The

  As a method of causing secondary recrystallization, a method of preferentially recrystallizing grains having Goss orientation during finish annealing using precipitates called inhibitors is generally used. No. 1 proposes a method using AlN or MnS as an inhibitor, and Patent Document 2 proposes a method using MnS or MnSe as an inhibitor, which has already been put into practical use. The method using these inhibitors is an extremely useful method for stably developing secondary recrystallized grains, although it is necessary to reheat the slab to a high temperature of 1300 ° C. or higher. Furthermore, in order to reinforce the action of these inhibitors, Patent Document 3 discloses a method of adding Pb, Sb, Nb and Te, and Patent Document 4 discloses Zr, Ti, B, Nb, Ta, V, Cr. And a method of adding Mo is disclosed.

  Furthermore, Patent Document 5 contains acid-soluble Al (sol. Al) in an amount of 0.010 to 0.060 mass%, and slab reheating temperature is suppressed to a low temperature, and nitriding is performed in an appropriate nitriding atmosphere in a decarburization annealing process. There has been proposed a method in which (Al, Si) N is precipitated during the secondary recrystallization by treatment, and this is used as an inhibitor. However, (Al, Si) N finely disperses in steel and functions effectively as an inhibitor. However, since the strength of the inhibitor is determined by the Al content, the accuracy of Al in steelmaking is not sufficient. However, there is a problem that a sufficient grain growth inhibiting power may not be obtained. Note that. Many techniques have been proposed in which (Al, Si) N or AlN is precipitated by performing nitriding in the course of such a manufacturing process, and these are used as inhibitors. Recently, the slab reheating temperature is 1300 ° C. The manufacturing method etc. which exceed are also proposed.

  On the other hand, Patent Document 6 discloses a technique in which goss-oriented crystal grains are secondarily recrystallized and grown using a so-called inhibitorless material that does not contain an inhibitor-forming component. Since this method does not require the inhibitor to be finely dispersed in steel, the technique using the inhibitor does not require reheating of the slab, which is essential, and has great advantages in terms of energy cost and equipment cost.

Japanese Patent Publication No. 40-015644 Japanese Patent Publication No.51-013469 Japanese Patent Publication No. 38-008214 JP-A-52-024116 Japanese Patent No. 2782086 JP 2000-129356 A

  However, in the method for producing a grain-oriented electrical steel sheet using an inhibitorless material as disclosed in Patent Document 6, an inhibitor having a function of suppressing grain growth of primary recrystallized grains and aligning the grain sizes to a certain size Therefore, the crystal grain size of the steel sheet after primary recrystallization may fluctuate greatly or a non-uniform grain size distribution may occur even if the process conditions and material components are slightly changed. For this reason, in the manufacturing method of the inhibitorless grain-oriented electrical steel sheet proposed until now, there exists a problem that it is not easy to implement | achieve a favorable magnetic characteristic stably.

  The present invention has been made in view of the above-described problems in the method of manufacturing an inhibitorless grain-oriented electrical steel sheet, and its object is to avoid the high-temperature reheating of the slab and to provide a stable and stable magnetic field. The object is to propose a method for stably producing a grain-oriented electrical steel sheet having characteristics.

Inventors repeated earnest examination toward the solution of the said subject. As a result, as a steel material, high temperature reheating of the slab is avoided by using steel according to the inhibitorless component in which Al is reduced to less than 0.0100 mass% (100 massppm). By precipitating silicon nitride (Si ₃ N ₄ ) instead of AlN, this silicon nitride functions as an inhibitor of normal grain growth, ie, an inhibitor, and further optimizes the hot-rolled sheet annealing conditions, thereby performing primary recrystallization. It has been found that a grain-oriented electrical steel sheet having good magnetic properties can be produced industrially stably by increasing the ratio of high energy grain boundaries in the steel sheet after annealing, leading to the development of the present invention.

That is, the present invention, C: 0.002~0.08mass%, Si: 2.0~ 4.5 mass% and Mn: containing 0.005~1.0mass%, sol. Al is less than 0.0150 mass%, N is less than 0.0100 mass%, S and Se are each reduced to less than 0.0050 mass%, and a slab having a composition composed of Fe and unavoidable impurities as the balance is 1250 ° C. or less. After reheating to temperature, hot rolled to hot rolled sheet, hot rolled sheet annealed, cold rolled twice or more with one or more intermediate sandwiches in between to make a cold rolled sheet of final thickness, decarburized Directional electromagnetics consisting of a series of processes in which primary recrystallization annealing that also serves as annealing is performed, nitriding is performed during or after decarburization annealing, and then an annealing separator is applied to the surface of the steel sheet and finish annealing is performed. In the steel sheet manufacturing method, the soaking temperature in the hot-rolled sheet annealing is set to 800 to 1100 ° C., the average heating rate between 200 ° C. and the soaking temperature in the heating process is set to 5 ° C./s or more, and after the primary recrystallization. steel sheet The ratio of the total grain boundaries of the grain boundary of misorientation angle 20 to 45 ° and less than 65%, directionality, characterized in that the range of 0.0050～0.1000Mass% intensifying窒量in the nitriding treatment A method for manufacturing electrical steel sheets is proposed.

Method for producing a grain-oriented electrical steel sheet of the present invention, the thickness of the hot-rolled sheet t _{h (mm),} a total rolling reduction of hot finish rolling when the R _{f (%),} the t _h and R _f Is the following formula (1):
t _h > −0.0571 × R _f +7.2 (1)
It is characterized by hot rolling to satisfy the above.

  Moreover, in addition to the said component composition, the said slab used for the manufacturing method of the grain-oriented electrical steel sheet of this invention is further Ni: 0.010-1.50 mass%, Cr: 0.01-0.50 mass%, Cu: 0. 0.01 to 0.50 mass%, P: 0.005 to 0.50 mass%, Sn: 0.005 to 0.50 mass%, Sb: 0.005 to 0.50 mass%, Bi: 0.005 to 0.50 mass %, Mo: 0.005 to 0.100 mass%, Te: 0.005 to 0.050 mass%, and Nb: 0.0010 to 0.0100 mass%. Features.

According to the present invention, by utilizing nitriding technology, silicon nitride (Si ₃ N ₄ ) instead of AlN functions as an inhibitor, and the hot-rolled sheet annealing conditions are optimized, and the high energy of the steel sheet after primary recrystallization annealing Since the inhibitor function can be enhanced by increasing the grain boundary ratio, there is no need to reheat the slab to a high temperature, and a grain-oriented electrical steel sheet having excellent magnetic properties can be provided inexpensively and industrially stably. Is possible.

Misorientation angle in the steel sheet after primary recrystallization is a graph showing the relationship between the grain boundary ratio of 20 to 45 ° (%) and the final annealing after the magnetic properties B _{8 (T).} It is a graph which shows the influence of the rolling reduction of hot finish rolling, and hot-rolled sheet thickness which the orientation difference angle in a steel plate after primary recrystallization has on the grain boundary ratio (%) of 20-45 degrees.

First, the experiment that led to the development of the present invention will be described.
C: 0.055 mass%, Si: 3.25 mass%, Mn: 0.15 mass%, sol. A slab containing Al: 0.0065 mass%, N: 0.0040 mass%, S: 0.0034 mass%, and Se: 0.0010 mass% was manufactured by a continuous casting method, and after reheating to a temperature of 1180 ° C, Hot rolled to various plate thicknesses of 1.2 to 3.0 mm. Thereafter, these hot-rolled sheets were subjected to hot-rolled sheet annealing at various heating rates, soaking temperatures, and soaking times, and then cold rolled to finish cold-rolled sheets having a final thickness of 0.27 mm. . Under the present circumstances, the steel plate temperature in cold rolling was changed at various temperature in the range of room temperature-300 degreeC. Here, the thickness of the hot-rolled sheet, the hot-rolled sheet annealing conditions, and the cold-rolled conditions were variously changed in order to change the crystal orientation distribution of the steel sheet after primary recrystallization (decarburization annealing).

Subsequently, the cold-rolled sheet was subjected to primary recrystallization annealing performed at 50 vol% H ₂ -50 vol% N ₂ in a humid atmosphere having a dew point of 60 ° C. and also performing decarburization annealing at 840 ° C. for 80 seconds.
Next, the cross-sectional structure of the steel sheet after primary recrystallization was measured for the grain boundary orientation difference angle by EBSP over the range of plate thickness x length 5 mm, and the ratio of grain boundaries having an orientation difference angle of 20 to 45 ° was calculated. .
Next, after immersing in a salt bath of 500 ° C. using isonite as a main raw material for 30 minutes to perform nitriding treatment, it was washed with water, and an annealing separator mainly composed of MgO was applied to the steel sheet surface, followed by secondary recrystallization. Then, the finish annealing which hold | maintains at 1200 degreeC for 5 hours under a hydrogen atmosphere was given.

Test pieces were collected from the steel sheet after finish annealing thus obtained, and the magnetic flux density B ₈ (magnetic flux density (T) when excited at 800 A / m) was measured by the method described in JIS C2550.
FIG. 1 shows the measurement results. From this result, in the steel sheet after primary recrystallization, when the ratio of the grain boundary having a misorientation angle of 20 to 45 ° is 65% or more, the magnetic flux density B ₈ is seen to be a more 1.90T.

As described above, the inventors consider the reason why the magnetic properties are improved by increasing the ratio of grain boundaries having an orientation difference angle of 20 to 45 ° as follows.
Grain boundaries with misorientation angles of 20 to 45 ° are C.I. G. According to the experimental data by Dunn et al. (AIME Transaction, Vol. 88 (1949) P. 368), it is a high energy grain boundary. This high energy grain boundary has a random structure with a large free space within the grain boundary. Grain boundary diffusion is a phenomenon in which atoms move through the grain boundary, and the diffusion space (diffusion rate) is larger in the high energy grain boundary where the free space in the grain boundary is larger.
Here, considering the case where the steel sheet is subjected to nitriding treatment, the temperature is low during nitriding treatment, so nitrogen forms iron nitride on the steel sheet surface and does not diffuse so much inside the steel sheet. It is considered that nitrogen diffuses at the time of temperature increase in finish annealing.
In the above-mentioned finish annealing, after causing secondary recrystallization at a temperature of 800 ° C. or higher, the temperature is usually raised to a high temperature of about 1200 ° C. in order to form a forsterite film or to purify it. When not applied, since there is no inhibitor, normal grains grow before secondary recrystallization occurs, and the driving force of secondary recrystallization decreases.
However, when nitriding is performed, the iron nitride formed on the steel sheet surface by nitriding is decomposed before secondary recrystallization occurs, and nitrogen diffuses into the steel sheet through high energy grain boundaries. Then, silicon nitride is deposited on the grain boundaries. This precipitate expresses a pinning effect, suppresses the coarsening of the particle size during temperature rise, and functions as an inhibitor, so that it is possible to suppress a reduction in driving force of secondary recrystallization. In particular, when the high energy grain boundary is 65% or more, the diffusion of nitrogen is promoted, and the above pinning effect is expressed early in the finish annealing, so that the inhibitor function is more effectively expressed and is close to the ideal orientation. Goss by oriented grains selectively to secondary recrystallization, presumably with improved magnetic flux density B _8.

  And the said effect is thought to be expressed by the component system which reduced the impurity element like an inhibitor free raw material. This is because the impurity elements present in steel tend to segregate at the grain boundaries, particularly at high energy grain boundaries, and therefore when there are many impurity elements, the diffusion coefficient of the high energy grain boundaries differs greatly from other grain boundaries. Because it will disappear. That is, the technique of the present invention is a technique that exhibits an effect for the first time by using an inhibitor-free material.

  Here, in the above experiment, the hot rolling conditions, the hot-rolled sheet annealing conditions, and the cold-rolling conditions were variously changed. From this result, the ratio of the high-energy grain boundaries having a misorientation angle of 20 to 45 ° was increased to 65% or more. In order to raise, it turns out that it is necessary to make the soaking temperature of hot-rolled sheet annealing into the range of 800-1100 degreeC, and to raise the temperature increase rate until it reaches the said soaking temperature 5 degree-C / s or more. It was. Here, the said temperature increase rate is defined by the average temperature increase rate between 200 degreeC and soaking temperature.

Further, in order to more stably increase the ratio of high energy grain boundaries having an orientation difference angle of 20 to 45 °, the relationship between the reduction ratio of the finish rolling in hot rolling and the hot rolled sheet thickness is within an appropriate range. , namely, the plate thickness of the hot-rolled sheet _t h (mm), when a total reduction ratio of the hot finish rolling was set to _R f (%), the _{t h} and _{R f} is represented by the following formula (1);
t _h > −0.0571 × R _f +7.2 (1)
It was also found that it is effective to perform hot rolling to satisfy the above condition.

Figure 2 is a finish rolling reduction ratio R _f and the plate thickness t _h of the hot-rolled plate, shows the effect on the ratio of the high-energy grain boundaries of misorientation angle 20 to 45 °. In FIG. 2, the high energy grain boundary ratio of 69% is that the range in which good characteristics with a magnetic flux density B ₈ of 1.94 T or more were obtained in the above experiment is 69 to 85%. Because.

Next, the component composition of the steel material (slab) used for manufacture of the grain-oriented electrical steel sheet of the present invention will be described.
C: 0.002-0.08 mass%
If C is less than 0.002 mass%, the grain boundary strengthening effect is lost, the slab is cracked, and surface defects occur, which hinders production. On the other hand, if it exceeds 0.08 mass%, it will be difficult to reduce to 0.005 mass% or less at which no magnetic aging occurs due to decarburization annealing. Therefore, C is in the range of 0.002 to 0.08 mass%. Preferably it is the range of 0.01-0.05 mass%.

Si: 2.0 to 8.0 mass%
Si is an element necessary for increasing the specific resistance of steel and reducing iron loss. If the effect is less than 2.0 mass%, it is not sufficient. On the other hand, if it exceeds 8.0 mass%, the workability is lowered and it is difficult to roll and manufacture. Therefore, Si is set to a range of 2.0 to 8.0 mass%. Preferably it is the range of 2.5-4.5 mass%.

Mn: 0.005 to 1.0 mass%
Mn is an element necessary for improving the hot workability of steel. If the effect is less than 0.005 mass%, it is not sufficient. On the other hand, if it exceeds 1.0 mass%, the magnetic flux density of the product plate is lowered. Therefore, Mn is set to a range of 0.005 to 1.0 mass%. Preferably it is the range of 0.02-0.20 mass%.

  As components other than C, Si, and Mn, it is necessary to reduce Al, N, S, and Se as inhibitor forming components as much as possible. In the present invention, Al is sol. A steel material is used in which Al is less than 0.0150 mass%, N is less than 0.0100 mass%, and S and Se are each reduced to less than 0.0050 mass%. Preferably, for Al, sol. Al is less than 0.0100 mass%, and N is less than 0.0050 mass%.

  In addition to the above components, the steel material used in the present invention is for the purpose of improving iron loss, Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu: 0.01 -0.50 mass%, P: 0.005-0.50 mass%, Sn: 0.005-0.50 mass%, Sb: 0.005-0.50 mass%, Bi: 0.005-0.50 mass%, You may contain 1 type or 2 types chosen from Mo: 0.005-0.100mass%, Te: 0.005-0.050mass% and Nb: 0.0010-0.0100mass%. When the amount of each element added is less than the lower limit, the effect of reducing iron loss is small. On the other hand, when the upper limit is exceeded, the magnetic flux density is lowered and the magnetic properties are deteriorated. However, among the above components, P, Sn and Sb are easily segregated at the grain boundaries and have a great influence on the present invention. Therefore, when added, the upper limit of these elements is 0.10 mass%. Is desirable, more desirably 0.05 mass%.

  The balance other than the above components is Fe and inevitable impurities. However, as long as the effect of the present invention is not impaired, it does not refuse to contain components other than those described above.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
The steel material (slab) used in the production method of the present invention is produced by a generally known continuous casting method or ingot-bundling rolling method after melting the steel having the component composition described above by a normal refining process. It is preferable to do. Moreover, you may manufacture a thin cast piece of 100 mm or less by a direct manufacturing method.
In addition, since it is difficult to add the arbitrary addition component mentioned above in the middle of a manufacturing process, it is preferable to add at the molten steel stage.

  The slab produced as described above is then reheated and subjected to hot rolling. However, the component system of the present invention does not require high-temperature reheating to dissolve the inhibitor, so that the slab is reheated. The temperature can be a low temperature of 1250 ° C. or lower.

What is important in the subsequent hot rolling is that when the thickness of the hot rolled sheet is t _h and the total rolling reduction of the hot finish rolling is R _f , the following equation (1):
t _h > −0.0571 × R _f +7.2 (1)
And hot rolling. By satisfying this condition, it becomes easy to control the ratio of high energy grain boundaries having an orientation difference angle of 20 to 45 ° in the primary recrystallized structure within the range of the present invention.

Next, the hot-rolled sheet obtained by hot rolling is subjected to the most important hot-rolled sheet annealing in the present invention.
In order to set the ratio of high energy grain boundaries having an orientation angle angle of 20 to 45 ° in the steel sheet after the primary recrystallization to 65% or more, the hot rolled sheet annealing is performed at a soaking temperature in the range of 800 to 1100 ° C. It is necessary to heat at a heating rate (average heating rate between 200 ° C. and soaking temperature) at 5 ° C./s or higher when heating to the soaking temperature. If the soaking temperature is less than 800 ° C., recrystallization is insufficient and a band-like structure remains, resulting in poor texture after primary recrystallization, and the above effect cannot be obtained. On the other hand, when the soaking temperature exceeds 1100 ° C., the crystal grains become too coarse, and it becomes difficult to obtain a primary recrystallized structure of sized particles. A preferable soaking temperature is in the range of 900 to 1050 ° C.
Further, when the rate of temperature rise is less than 5 ° C./s, the recovery proceeds before recrystallization, so that the band-like structure tends to remain and the above effect cannot be obtained. Preferably, it is heating between 200-600 degreeC with the average temperature increase rate of 15 degrees C / s or more.
The soaking time in the hot-rolled sheet annealing is preferably 5 seconds or more from the viewpoint of increasing the ratio of high energy grain boundaries.

  The hot-rolled sheet subjected to the above-mentioned hot-rolled sheet annealing is then made into a cold-rolled sheet with a final sheet thickness by cold rolling at least once with one or two intermediate sandwiches. When performing the said intermediate annealing, it is preferable to make annealing temperature into the range of 900-1200 degreeC. If it is less than 900 ° C., the recrystallized grains become too fine, the Goss orientation nuclei in the primary recrystallized structure decrease, and the magnetic properties deteriorate. On the other hand, when it exceeds 1200 ° C., the grain size becomes excessively coarse as in the case of hot-rolled sheet annealing, and it becomes difficult to obtain a primary recrystallized structure of sized particles.

  In addition, cold rolling (final cold rolling) to be the final plate thickness employs warm rolling in which the steel plate temperature is increased to 100 to 300 ° C. from the viewpoint of increasing the ratio of high energy grain boundaries, It is effective to perform an aging treatment one or more times at a temperature of 100 to 300 ° C. during rolling, and it is also effective to increase the reduction ratio of the final cold rolling to 81% or more.

The cold-rolled sheet rolled to the final sheet thickness is then subjected to primary recrystallization annealing that also serves as decarburization annealing.
In this primary recrystallization annealing, it is necessary to set the ratio of high energy grain boundaries having a misorientation angle of 20 to 45 ° in the steel sheet after annealing to 65% or more. Preferably it is 69 to 85% of range.
From the viewpoint of ensuring decarburization, it is preferable that the soaking temperature is in the range of 800 to 900 ° C. and the atmosphere is an oxidizing wet atmosphere. In addition, it is not this limitation when C content of the steel raw material to be used is 0.005 mass% or less which does not require decarburization.
Moreover, in order to prevent the temperature increase rate in the primary recrystallization annealing from randomizing the texture and reducing the ratio of the high energy grain boundaries, the upper limit is preferably set to 200 ° C./s.

The decarburized and annealed steel sheet is then subjected to nitriding treatment. The method of nitriding is not particularly limited as long as the amount of nitriding can be controlled. For example, a method of performing gas nitridation in an NH ₃ atmosphere with a coil form, or a continuous strip by introducing a running strip into the NH ₃ atmosphere. In particular, a method of performing gas nitriding, a salt bath nitriding method having higher nitriding ability than the gas nitriding method, or the like can be used.

From the viewpoint of reducing thermal energy, the timing of the nitriding treatment is preferably performed continuously after decarburization annealing without lowering the steel plate temperature to room temperature, but after decarburization annealing, after cooling to room temperature, Nitriding treatment may be performed again.
The amount of increase in nitrogen amount (nitrification increase amount) by nitriding is preferably in the range of 0.0050 to 0.1000 mass% (50 to 1000 massppm). If the nitrogen increase is less than 0.0050 mass%, the amount of silicon nitride deposited is too small and the effect of improving the magnetic properties is not sufficiently obtained. On the other hand, if it exceeds 0.1000 mass%, the amount of silicon nitride deposited becomes excessive, Secondary recrystallization may not occur. Desirably, it is in the range of 0.0200 to 0.0700 mass%.

  The steel sheet subjected to nitriding treatment is then applied with an annealing separator mainly composed of MgO on the steel sheet surface, and then subjected to finish annealing to develop a secondary recrystallized structure and to form a forsterite film. The finish annealing temperature is preferably 800 ° C. or higher in order to develop secondary recrystallization, and is preferably maintained at the above temperature for 20 hours or more in order to complete the secondary recrystallization. Further, in order to form a forsterite film or to perform a purification treatment, it is preferable to raise the temperature to about 1200 ° C. after completing the secondary recrystallization.

  The steel sheet after finish annealing is then subjected to flattening annealing for shape correction and iron loss property improvement after washing, brushing, pickling, etc. to remove the annealing separator remaining on the steel sheet surface. Is preferred.

  In addition, when using it, laminating | stacking a steel plate, in order to improve an iron loss, it is preferable to coat | cover an insulating film on the steel plate surface before or after the said planarization annealing. Moreover, in order to reduce iron loss more, it is preferable that the said insulating film is a tension | tensile_strengthening type thing which provides tension | tensile_strength to the steel plate surface. In addition, when the insulating film is formed, a method of applying a tension-imparting film via a binder or a method of applying an inorganic substance on a steel sheet surface by physical vapor deposition or chemical vapor deposition is adopted. A film having excellent properties and a remarkable effect of reducing iron loss can be obtained.

  Furthermore, in order to further reduce the iron loss, it is preferable to perform a magnetic domain refinement process. As a method of subdividing the magnetic domain, a linear groove or strain region is formed on the final product plate by roller processing or the like, or an electron beam, laser, plasma jet, etc. is irradiated to form a linear shape. The method of introducing the thermal strain region or the impact strain region, or the method of forming grooves in the surface of the cold-rolled plate rolled to the final plate thickness by etching or the like in the subsequent steps can be used.

C: 0.045 mass%, Si: 3.21 mass%, Mn: 0.08 mass%, sol. A slab containing Al: 0.0080 mass%, N: 0.0035 mass%, S: 0.0034 mass% and Se: 0.0010 mass% was manufactured by a continuous casting method, and after reheating to a temperature of 1230 ° C, A hot rolled sheet having a sheet thickness of 2.4 mm (reduction ratio 94.0%) was finished by hot finish rolling.
Thereafter, the hot-rolled sheet is heated to a soaking temperature at the rate of temperature increase shown in Table 1 and subjected to hot-rolled sheet annealing that is held for 45 seconds, and then cold-rolled to obtain a final sheet thickness of 0.27 mm. Finished in a sheet.
Next, primary recrystallization annealing was performed at 55 vol% H ₂ -45 vol% N ₂ in a humid atmosphere with a dew point of 60 ° C., which also served as decarburization annealing at 840 ° C. for 90 seconds.
At this time, a sample was taken from the steel sheet after the primary recrystallization, and the cross section was measured by EBSP over a range of plate thickness (0.27 mm) × length 5 mm to obtain an orientation difference distribution of grain boundaries. From this, the ratio of high energy grain boundaries with an orientation difference angle of 20 to 45 ° was calculated.
Thereafter, the steel sheet after the primary recrystallization was subjected to nitriding treatment for 240 seconds at 550 ° C. in an atmosphere of 80 vol% N ₂ +20 vol% NH ₃ .
Next, after applying and drying an annealing separator mainly composed of MgO on the surface of the steel sheet after the nitriding treatment, the secondary recrystallization is performed, and then a finishing treatment is performed by holding at 1230 ° C. for 2 hours in a hydrogen atmosphere. Annealed to give a product plate.

And thus the product plate from the specimen obtained was in collected, the magnetic flux density was measured B ₈ by the method described in JIS C2550.
The obtained results are also shown in Table 1. From the table, it can be seen that the magnetic flux density B ₈ : 1.90 T or more is stably obtained in the grain-oriented electrical steel sheet manufactured under conditions suitable for the present invention.

Slabs having various component compositions shown in Table 2 were manufactured by a continuous casting method, reheated to a temperature of 1150 ° C., then hot-rolled into 30 mm sheet bars, and hot-finished by 2.7 mm ( The sheet was finished into a hot-rolled sheet having a reduction ratio of 91.0%.
Thereafter, the heating rate between 200 to 600 ° C. is set to 17 ° C./s and the heating rate between 200 to 950 ° C. is set to 10 ° C./s and heated to a soaking temperature. gave.
Next, the hot-rolled sheet was cold-rolled to a thickness of 1.7 mm, subjected to intermediate annealing at 1100 ° C. for 45 seconds, and then warm-rolled at a temperature of 100 ° C. to a final thickness of 0.23 mm. Finished in cold rolled sheet.
Next, primary recrystallization annealing was performed at 60 vol% H ₂ -40 vol% N ₂ in a humid atmosphere with a dew point of 64 ° C. and also performing decarburization annealing at 850 ° C. for 100 seconds.
At this time, a sample was taken from the steel sheet after the primary recrystallization, and the cross section was measured by EBSP over a range of plate thickness (0.27 mm) × length 5 mm to obtain an orientation difference distribution of grain boundaries. From this, the ratio of high energy grain boundaries with an orientation difference angle of 20 to 45 ° was calculated.
Thereafter, the steel sheet after the primary recrystallization was subjected to a nitriding treatment that was held at 800 ° C. for 30 seconds in an atmosphere of 90 vol% N ₂ +5 vol% H ₂ +5 vol% NH ₃ .
Next, after applying and drying an annealing separator mainly composed of MgO on the surface of the steel sheet after the nitriding treatment, secondary recrystallization is performed, and then a finishing treatment is performed by maintaining at 1200 ° C. for 10 hours in a hydrogen atmosphere. Annealed to give a product plate.

And thus the product plate from the specimen obtained was in collected, the magnetic flux density was measured B ₈ by the method described in JIS C2550.
The obtained results are also shown in Table 2. From the table, it can be seen that the magnetic flux density B ₈ : 1.92 T or more is stably obtained in the grain-oriented electrical steel sheet manufactured under the conditions suitable for the present invention.

  The technique of the present invention can also be used as a method of increasing the surface hardness by nitriding or increasing the strength itself.

Claims (3)

C: 0.002~0.08mass%, Si: 2.0~ 4.5 mass% and Mn: containing 0.005~1.0mass%, sol. Al is less than 0.0150 mass%, N is less than 0.0100 mass%, S and Se are each reduced to less than 0.0050 mass%, and a slab having a composition composed of Fe and unavoidable impurities as the balance is 1250 ° C. or less. After reheating to temperature, hot rolled to hot rolled sheet, hot rolled sheet annealed, cold rolled twice or more with one or more intermediate sandwiches in between to make a cold rolled sheet of final thickness, decarburized Directional electromagnetics consisting of a series of processes in which primary recrystallization annealing that also serves as annealing is performed, nitriding is performed during or after decarburization annealing, and then an annealing separator is applied to the surface of the steel sheet and finish annealing is performed. In the manufacturing method of the steel sheet,
The soaking temperature in the hot-rolled sheet annealing is set to 800 to 1100 ° C., and the average heating rate between 200 ° C. and the soaking temperature in the heating process is set to 5 ° C./s or more. Production of grain- oriented electrical steel sheet, characterized in that the ratio of grain boundaries of ˜45 ° to the whole grain boundaries is 65% or more , and the nitriding amount in the nitriding treatment is in the range of 0.0050 to 0.1000 mass%. Method. The thickness of the hot-rolled sheet t _{h (mm),} when the total rolling reduction of hot finish rolling and R _{f (%),} hot to the t _h and R _f satisfies the following formula (1) rolling The method for producing a grain-oriented electrical steel sheet according to claim 1.
T _h > −0.0571 × R _f +7.2 (1) In addition to the above component composition, the slab further includes Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, and P: 0.005. 0.50 mass%, Sn: 0.005-0.50 mass%, Sb: 0.005-0.50 mass%, Bi: 0.005-0.50 mass%, Mo: 0.005-0.100 mass%, Te The directional electromagnetic wave according to claim 1, comprising one or more selected from: 0.005 to 0.050 mass% and Nb: 0.0010 to 0.0100 mass%. A method of manufacturing a steel sheet.

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