JP5712626B2 - 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 having excellent iron loss characteristics.

  The grain-oriented electrical steel sheet is a soft magnetic material that is widely used as a core material for transformers, and is required to have excellent magnetic properties, in particular, excellent iron loss properties (low iron loss). As a material satisfying such characteristics, a grain-oriented electrical steel sheet in which {110} <001> orientation called Goth orientation is highly integrated in the rolling direction on the steel plate surface by causing secondary recrystallization has been developed. As is well known, it is put into practical use.

  As a method for highly accumulating the {110} <001> orientation in the rolling direction on the steel plate surface, a method of controlling secondary recrystallization using precipitates called inhibitors is common. However, if precipitates (inhibitors) remain in the product steel sheet, it will lead to deterioration of the magnetic properties. Therefore, after recrystallization by secondary annealing, so-called purification annealing is performed to remove impurities by high-temperature annealing. Has been done. For example, this purification annealing is performed under conditions of high temperature and long time so that annealing at a temperature of 1100 to 1250 ° C. is required for 3 hours or more in order to reduce the nitrogen concentration in the steel sheet to 0.0020 mass% or less. It is necessary to do in.

Thus, it has been studied to lower the annealing temperature in the purification annealing. For example, Patent Document 1 discloses that a cold-rolled sheet containing Al and N as an inhibitor is secondarily recrystallized, and then a nitrogen partial pressure in an atmosphere containing hydrogen gas is set to 0.10 atm. A purification annealing method for removing inhibitors in a steel sheet by performing purification annealing at a temperature of 0 ° C. is disclosed. Further, Patent Document 2 discloses that in the second half of finish annealing in which C of the steel material is reduced to 0.01% by weight or less and secondary recrystallization is completed, in a H ₂ atmosphere at a temperature of 925 ° C. to 1050 ° C. A technique for reducing C + N to 0.0020% by weight or less without requiring decarburization annealing is disclosed.

  Recently, a so-called inhibitorless technique has been proposed in which secondary recrystallization is caused using a material not containing an inhibitor to develop goth-oriented grains (see, for example, Patent Document 3). This technology eliminates the inhibitory component as much as possible, and reveals the grain boundary orientation angle dependence of the grain boundary energy of the primary recrystallized grain boundary, thereby enabling secondary recrystallization without using an inhibitor. To grow goth-oriented grains. This method does not require the step of removing the inhibitor after the secondary recrystallization, so there is no need for purification annealing, and there is no need to finely disperse the inhibitor in the steel, so no high-temperature slab heating is required. This is an advantageous method in terms of cost and equipment maintenance.

Japanese Patent Laid-Open No. 11-158557 JP 05-009666 A JP 2000-129356 A

  By the way, in recent years, further reduction of iron loss has been demanded for the purpose of energy saving. Therefore, in addition to the technology to purify the impurities (inhibitor components) and the inhibitorless technology, as a technology to further reduce iron loss, a coating with a different coefficient of thermal expansion from that of the steel plate is formed at a high temperature to apply tension to the steel plate. In addition, techniques for magnetic domain subdivision have been developed. By applying these techniques, the iron loss of grain-oriented electrical steel sheets has been improved to a considerably low level. However, in recent years, from the viewpoint of protecting the global environment, the demand for energy saving is becoming stronger, and further reduction of iron loss is required for grain oriented electrical steel sheets.

  However, there is a manufacturing problem in order to further reduce the iron loss with the above technique. For example, a technique for imparting tension to a steel sheet has been developed as a coating capable of imparting high tension, such as TiN coating, but requires special processing equipment and is not practical. In addition, magnetic domain refinement technology has been proposed in a variety of ways, including physical groove formation and thermal distortion such as lasers, plasma flames, and electron beams. Therefore, special processing equipment and processes different from those of the above manufacturing are required, which complicates the manufacturing process and increases the manufacturing cost.

  The present invention has been made in view of the above-described problems of the prior art, and the purpose thereof is a directional electromagnetic wave that can efficiently improve iron loss without requiring special equipment or processes. The object is to propose an advantageous method of manufacturing a steel sheet.

  In order to solve the above-mentioned problems, the inventors focused on the manufacturing process after finish annealing, and conducted intensive studies. As a result, the conventional purification annealing or inhibitorless technology is further improved, that is, after performing the conventional finish annealing, it is found that a large iron loss reduction can be realized by performing additional annealing under more appropriate conditions, The present invention has been completed.

The present invention developed on the basis of the above findings is directed to using a steel material containing C: 0.01 to 0.08 mass%, Si: 2.0 to 8.0 mass%, and Mn: 0.005 to 1.0 mass%. In the manufacturing method of heat- resistant electrical steel sheets, the highest temperature is achieved by the final annealing that causes secondary recrystallization to form a forsterite film, or the final annealing that causes secondary recrystallization to form a forsterite film and purifies it. A grain-oriented electrical steel sheet characterized by being subjected to additional annealing at a temperature of 950 to 1200 ° C. and a soaking time of 3 hours or more after the temperature is once lowered to 800 ° C. or less after being applied at 1100 ° C. or higher. It is a manufacturing method.

  In the manufacturing method of the grain-oriented electrical steel sheet of the present invention, the steel material further includes Al: 0.01 to 0.065 mass% and N: 0.005 to 0.012 mass% as an AlN-based inhibitor component in addition to the above component composition. And / or S: 0.005 to 0.03 mass% and Se: 0.005 to 0.03 mass% as a MnS · MnSe-based inhibitor component.

  Moreover, the steel material in the method for producing a grain-oriented electrical steel sheet according to the present invention further includes Al, N, S, and Se in addition to the above component composition, Al: 0.0100 mass% or less, N: 0.0050 mass% or less, It contains S: 0.0050 mass% or less and Se: 0.0050 mass% or less.

  Moreover, in addition to the said component composition, the said steel raw material in the manufacturing method of the grain-oriented electrical steel sheet of this invention is further Ni: 0.03-1.50 mass%, Sn: 0.01-1.50 mass%, Sb: 0.005-1.50 mass%, Cu: 0.03-3.0 mass%, P: 0.03-0.50 mass%, Mo: 0.005-0.10 mass%, and Cr: 0.03-1. 1 type or 2 types or more selected from 50 mass% are contained.

  According to the present invention, since it is possible to improve the iron loss characteristics without requiring special processing equipment and manufacturing processes, it is possible to stably provide a grain-oriented electrical steel sheet having excellent iron loss characteristics at low cost. Is possible.

Is a graph showing the relationship between the additional annealing temperature after finish annealing and the magnetic flux density B _8. It is a graph which shows the relationship between the additional annealing temperature after finish annealing, and the iron loss _{W17 / 50} . It is a graph which shows the relationship between the additional annealing time after finish annealing and iron loss _{W17 / 50} .

Inventors conducted the following experiment in order to investigate whether iron loss could be reduced by performing another annealing after finishing annealing.
<Experiment 1>
Epstein from the center in the longitudinal direction and the center in the width direction of the directional electrical steel sheet coil having a thickness of 0.27 mm subjected to finish annealing that is soaked at 1200 ° C. after secondary recrystallization and less distortion due to finish annealing After 10 sets of test pieces were cut out and subjected to flattening annealing at 750 ° C. × 5 hr, the magnetic flux density (B ₈ ) at a magnetizing force of 800 A / m and the iron loss (W ₁₇ at AC 50 Hz and 1.7 T excitation conditions). _{/ 50} ).
Thereafter, additional annealing was performed again at 800 to 1250 ° C. for 5 hours in an H ₂ atmosphere, and then the magnetic properties were measured under the same conditions as described above.

Figure 1 is a additional annealing temperature shows the effect on the magnetic flux density B _8. From this figure, it can be seen that the magnetic flux density B ₈ is improved by 0.002 T or more at any additional annealing temperature, but in particular, the improvement margin tends to increase as the additional annealing temperature becomes higher.
FIG. 2 shows the effect of additional annealing temperature on iron loss W _17/50 . From this figure, the iron loss W _17/50 is improved at any additional annealing temperature, but when the additional annealing is performed at a temperature range of 950 to 1200 ° C., an improvement cost of 0.02 W / kg or more is further obtained. It can be seen that an improvement margin of 0.03 W / kg or more is obtained in the range of 1000 to 1100 ° C. Therefore, in order to acquire an iron loss reduction effect, it is necessary to perform additional annealing temperature in the range of 950-1200 degreeC, Preferably it is understood that it is the range of 1000-1100 degreeC.

As described above, the reason why there is an appropriate additional annealing temperature that improves the magnetic properties, particularly the iron loss properties, is not yet clear enough at present, but is considered as follows.
In FIG. 2, the iron loss characteristics are improved at all additional annealing temperatures. Of these, the improvement in the iron loss characteristics recognized at 900 ° C. or less is 750 ° C. × 5 hr performed before the additional annealing. It is considered that the curved shape left after the flattening annealing was eliminated by the additional annealing.

  Moreover, it is thought that another factor is working in the temperature range of 950 to 1200 ° C. in which the iron loss is greatly improved. That is, from the results of EBSD (Electron Backscatter Diffraction) observation and SEM observation of the cross section of the steel sheet after additional annealing, rearrangement of GN dislocations within the crystal grains and changes in the smoothness of the interface between the steel sheet and the forsterite film occurred. It has been suggested that If the cause is the former, the effect is as if the crystal grains have been reduced by appropriate rearrangement of dislocations (dislocations arranged in a line: polygonization), and if the cause is the latter, pinning of domain wall motion occurs. It seems that the effect which became difficult is related. The iron loss improvement effect due to such a cause is obtained at 950 ° C. or higher. However, as the annealing temperature increases, the impurity element diffuses from the coating into the steel, and the reverse effect of deteriorating iron loss occurs. Therefore, it is considered that there was an additional annealing temperature range optimal for iron loss improvement.

<Experiment 2>
Six sets of Epstein test pieces were cut out from a 0.23 mm-thick directional electrical steel sheet coil having a groove for magnetic domain refinement, which was subjected to finish annealing consisting of secondary recrystallization annealing and purification annealing at 1180 ° C. As for the 5 sets, additional annealing was performed by changing the holding time by 1 hr in the range of 1 to 5 hr at a temperature of 1050 ° C. while keeping the coil shape without performing flattening annealing. The sample was used for comparison without additional annealing. Next, after applying the insulating coating made of 60 mass% colloidal silica and aluminum phosphate to the test piece after the additional annealing and the test piece for comparison, after baking at 800 ° C. also for flattening annealing, AC 50 Hz, The iron loss W _17/50 was measured under an excitation condition of _1.7T .
The result of the measurement is shown in FIG. From FIG. 3, when the holding time is 2 hours or less, the iron loss reduction effect cannot be obtained. Therefore, in order to obtain the iron loss improvement effect by the additional annealing, it is necessary to secure the soaking time for 3 hours or more. I understand.
The present invention has been developed based on the above novel findings.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
The method for producing a grain-oriented electrical steel sheet according to the present invention is characterized in that additional annealing is further performed on the grain-oriented electrical steel sheet after finish annealing, and the manufacturing conditions until finish annealing and the manufacturing conditions after additional annealing are particularly important. It is not limited and a conventionally well-known method can be used.

However, in order to obtain a grain-oriented electrical steel sheet having excellent magnetic properties, it is necessary to use a steel slab containing C, Si and Mn as basic components in the following range. In addition, about the melting method of steel, and the manufacturing method of a steel slab, what is necessary is just to follow a conventional method and it does not ask | require in particular.
C: 0.01-0.08 mass%
C is an element necessary for improving the texture at the time of primary recrystallization, and in order to obtain the effect, it is necessary to contain 0.01% by mass or more. On the other hand, if the amount of C added exceeds 0.08 mass%, it is difficult to reduce to 0.0050 mass% or less at which demagnetization annealing does not cause magnetic aging. Therefore, C is in the range of 0.01 to 0.08 mass%.

Si: 2.0 to 8.0 mass%
Si is an element effective for increasing the electrical resistance of steel and improving iron loss. However, if the content is less than 2.0 mass%, a sufficient effect of reducing iron loss cannot be obtained. On the other hand, if it exceeds 8.0 mass%, the workability is remarkably lowered and it is difficult to roll and manufacture, and the magnetic flux density is also lowered. Therefore, Si is set to a range of 2.0 to 8.0 mass%.

Mn: 0.005 to 1.0 mass%
Mn is an element necessary for improving hot workability. However, if the content is less than 0.005 mass%, the above effect cannot be obtained. On the other hand, if the content exceeds 1.0 mass%, the magnetic flux density decreases. To come. Therefore, Mn is set to a range of 0.005 to 1.0 mass%.

  In the grain-oriented electrical steel sheet according to the present invention, when an inhibitor is used to cause secondary recrystallization, for example, when an AlN-based inhibitor is used, Al and N are each changed to Al: 0.01-0. 065 mass% and N: 0.005 to 0.012 mass% are preferably included. When a MnS · MnSe-based inhibitor is used, Se and / or S is changed to S: 0.005 to 0.005, respectively. It is preferable to make it contain in the range of 03mass%, Se: 0.005-0.03mass%.

  On the other hand, when an inhibitor is not used for causing secondary recrystallization, the inhibitor components Al, N, S and Se are Al: 0.0100 mass% or less, N: 0.0050 mass% or less, S : 0.0050 mass% or less, preferably Se: 0.0050 mass% or less.

Further, the grain-oriented electrical steel sheet of the present invention is further provided with Ni: 0.03-1.50 mass%, Sn: 0.01-1.50 mass%, Sb in addition to the above component composition for the purpose of improving magnetic properties. : 0.005 to 1.50 mass%, Cu: 0.03 to 3.0 mass%, P: 0.03 to 0.50 mass%, Mo: 0.005 to 0.10 mass%, and Cr: 0.03 to 1 One or two or more selected from .50 mass% may be contained.
Ni is an element useful for improving the magnetic properties by improving the hot-rolled sheet structure. However, if the amount is less than 0.03 mass%, the above effect is small. On the other hand, if it exceeds 1.50 mass%, the secondary recrystallization becomes unstable and the magnetic characteristics deteriorate. Sn, Sb, Cu, P, Mo, and Cr are elements useful for improving the magnetic properties, but any of them is less effective in improving the magnetic properties if it is less than the above lower limit value, but exceeds the above upper limit values. In addition, since the development of secondary recrystallized grains is inhibited, it is preferable to contain them in the above ranges.
The balance other than the above components is Fe and inevitable impurities.

  After the steel slab whose component composition has been adjusted to the above appropriate range, the slab is re-heated, hot-rolled, and hot-rolled sheet annealed as necessary, in accordance with a conventional method. After cold rolling to a cold-rolled sheet of the final sheet thickness, the cold-rolled sheet is subjected to primary recrystallization annealing also serving as decarburization, and after applying an annealing separator, secondary recrystallization and purification are performed. For this purpose, a grain-oriented electrical steel sheet is obtained by performing finish annealing. In addition, although decarburization can be performed by making the said primary recrystallization annealing into a humid atmosphere, you may perform separately.

The purification annealing after the secondary recrystallization annealing in the finish annealing described above requires that the highest temperature be 1100 ° C. or higher when an inhibitor is used for the secondary recrystallization, and the soaking time is 3 hours or more. It is preferable to do this. This is because if the temperature is lower than 1100 ° C., the precipitate cannot be decomposed and diffused to the surface of the steel sheet, so that sufficient purification cannot be obtained.
On the other hand, when an inhibitor is not used for secondary recrystallization, purification annealing is not necessarily required if nitrogen or the like can be sufficiently reduced. However, in order to form a good forsterite film, the temperature is 1100 ° C. or higher. High temperature annealing is required.

The method for producing a grain-oriented electrical steel sheet according to the present invention is characterized in that, following the above-described finish annealing, for the purpose of improving iron loss characteristics, additional annealing is performed for 3 hours or more at a soaking temperature of 950 to 1200 ° C. is there. When the annealing temperature is less than 950 ° C. or exceeds 1200 ° C., as shown in FIG. 2, the iron loss improvement effect is limited, and a sufficient effect cannot be obtained.
Further, if the soaking time is less than 3 hr, a sufficient iron loss reduction effect cannot be obtained as shown in FIG. The upper limit of the soaking time is not specified, but excessive annealing for longer periods may lead to wasted heat energy and damage to the annealing furnace, or may reduce productivity and increase manufacturing costs. Therefore, it is preferably 24 hours or less.

  This additional annealing needs to be performed after the finish-annealed coil is once cooled to 800 ° C. or lower. After the finish annealing, the same iron loss improvement effect is not recognized only by extending the holding time of the finish annealing without sufficiently lowering the temperature. This is because when the forsterite film is completely formed and tension is applied to the steel sheet to some extent by cooling and then heated again, the tension relaxes and rearrangement of GN dislocations (polygonization) occurs. This is probably because the forsterite film has a change in anchor shape (improved smoothness) and the conditions for improving the characteristics are satisfied.

Note that the additional annealing of the present invention can be performed using the furnace used for the finish annealing as it is once it can be cooled. Further, as the atmospheric gas during the additional annealing, it is desirable to use a gas having a high heat transfer coefficient from the viewpoint of increasing the temperature of the coil uniformly in a short time and increasing the productivity, for example, H ₂ gas or H ₂ mixed gas. Is preferably used.

  After that, the additionally annealed coil may be made into a product coil by a known method. For example, a product coil is formed by applying and baking a colloidal silica and a tensile insulating coating made of a phosphate such as magnesium phosphate or aluminum phosphate. Alternatively, planarization annealing may be further performed.

  According to the present invention, since additional annealing can be performed using the furnace used for finish annealing, a grain-oriented electrical steel sheet having excellent iron loss characteristics can be obtained without requiring new processing equipment and manufacturing processes. It becomes possible to manufacture stably and inexpensively.

C: 0.05 mass%, Si: 3.0 mass%, Mn: 0.02 mass%, Al: 0.02 mass%, N: 0.01 mass%, S: 0.005 mass% and Se: 0.01 mass% A steel slab containing an inhibitor component is hot-rolled according to a conventional method, cold-rolled to obtain a cold-rolled sheet having a final thickness of 0.27 mm, and then subjected to primary recrystallization annealing that also serves as a decarburization according to a conventional method. 7 coils of a grain oriented electrical steel sheet coated with an annealing separator mainly composed of MgO and then subjected to finish annealing including secondary recrystallization annealing and purification annealing that maintains soaking temperature at 1200 ° C. for 10 hours. Got ready. Among these, 6 coils remain in the coil shape, and the annealing temperature is set to 4 levels of 900 ° C., 1050 ° C., 1200 ° C. and 1250 ° C. in an atmosphere of H ₂ : 70 vol% + N ₂ : 30 vol%, and the soaking time is 1 hr. Additional annealing was carried out by changing to two levels of 5 hr, and the remaining one coil was used as a reference coil without additional annealing. Thereafter, an insulating coat made of 60 mass% colloidal silica and aluminum phosphate was applied to each of the coils, and baked at 800 ° C. to obtain product coils.

The Epstein test piece was cut out from the longitudinal center and the width center of each product coil thus obtained, the iron loss W _17/50 was measured, and the results are shown in Table 1 together with the annealing conditions. From Table 1, it can be seen that the iron loss W _17/50 is improved by 0.02 W / kg or more in the product coil additionally annealed under the conditions suitable for the present invention after finish annealing (purification annealing).

Various steel slabs having the composition shown in Table 2 are hot-rolled according to a conventional method, cold-rolled to obtain a cold-rolled sheet having a final thickness of 0.30 mm, and primary recrystallization annealing also serving as decarburization Then, after applying an annealing separator mainly composed of MgO, finish annealing including secondary recrystallization annealing and purification annealing was performed under the conditions shown in Table 2 to obtain a grain-oriented electrical steel sheet. The grain-oriented electrical steel sheet was produced in two coils under each condition. Next, one of the two coils is subjected to additional annealing under the conditions shown in Table 2 in the atmosphere of 100 vol% H ₂ while maintaining the coil shape, and the remaining one coil is additionally annealed. Without application, an insulating coating made of 60 mass% colloidal silica and aluminum phosphate was applied to the steel sheet surface, and baked at 800 ° C. to obtain a product coil.

The Epstein test piece was cut out from the longitudinal center and the width center of each product coil thus obtained, the iron loss W _17/50 was measured, and the results are shown in Table 2 together with the annealing conditions.
From Table 2, it can be seen that a directional electrical steel sheet having excellent iron loss characteristics is obtained in a product coil that is additionally annealed to a directional electrical steel sheet having a composition suitable for the present invention under conditions suitable for the present invention. .

Claims (4)

In the method for producing a grain-oriented electrical steel sheet using a steel material containing C: 0.01 to 0.08 mass%, Si: 2.0 to 8.0 mass% and Mn: 0.005 to 1.0 mass%,
After performing secondary recrystallization and finishing annealing to form a forsterite film, or causing secondary recrystallization to form a forsterite film and purifying finishing annealing at a maximum attained temperature of 1100 ° C. or higher , A method for producing a grain-oriented electrical steel sheet, wherein the temperature is once lowered to 800 ° C. or less, and then subjected to additional annealing at a soaking temperature of 950 to 1200 ° C. and a soaking time of 3 hours or more. In addition to the above component composition, the steel material further includes Al: 0.01 to 0.065 mass% and N: 0.005 to 0.012 mass%, and / or MnS / MnSe inhibitor component as an AlN inhibitor component. 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, comprising: S: 0.005 to 0.03 mass% and Se: 0.005 to 0.03 mass%. In addition to the above component composition, the steel material further includes Al, N, S, and Se: Al: 0.0100 mass% or less, N: 0.0050 mass% or less, S: 0.0050 mass% or less, and Se: 0.0050 mass. % Or less is contained, The manufacturing method of the grain-oriented electrical steel sheet according to claim 1 characterized by things. In addition to the above component composition, the steel material further includes Ni: 0.03-1.50 mass%, Sn: 0.01-1.50 mass%, Sb: 0.005-1.50 mass%, Cu: 0.00. 03-3.0 mass%, P: 0.03-0.50 mass%, Mo: 0.005-0.10 mass%, and Cr: 0.03-1.50 mass% The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the grain-oriented electrical steel sheet is contained.

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