JP6079092B2 - Method for producing grain-oriented electrical steel sheet having a thickness of 0.12 to 0.25 mm - Google Patents

Description

  The present invention relates to a grain-oriented electrical steel sheet used mainly for iron cores such as transformers and generators, and a method for manufacturing the same.

  A grain-oriented electrical steel sheet containing Si and highly oriented in the {110} <001> orientation (Goss orientation) or {100} <001> orientation (Cube orientation) should exhibit excellent soft magnetic properties. Therefore, it is widely used as a core material for various electric devices used in the commercial frequency range. In general, it is important for grain-oriented electrical steel sheets used in such applications to have a low W17 / 50 (W / kg), which is an iron loss when magnetized to 1.7 T at a frequency of 50 Hz. In other words, the power loss of generators and transformers can be greatly reduced by using materials with low values of W17 / 50, so the development of materials with low iron loss has been strongly demanded year by year.

  As a further reduction in iron loss, the trend is toward reducing eddy current loss with a thin plate material, and the need for products with a plate thickness of 0.25 mm or less is increasing compared to the conventional product centered on a plate thickness of 0.30 mm. It is in the direction of being.

  When the plate thickness is reduced, the Ostwald growth during finish annealing of precipitates called inhibitors and the oxidative decomposition reaction on the surface are more likely to affect secondary recrystallization, and the pinning force against the grain growth of primary recrystallized grains of the inhibitor. If excessively lost, a defective structure called Poor Grain Growth (hereinafter referred to as PGG) that does not cause secondary recrystallization is formed, leading to significant iron loss deterioration.

  In order to solve such a problem, Patent Document 1 discloses that Ni is added to refine the structure, and Sb and a trace amount of B are added to increase the expression stability of secondary recrystallization. Has been.

  In Patent Document 2, the secondary recrystallized grain size is controlled to be constant by adjusting the rolling reduction ratio of the first and second cold rolling according to the amount of material B of 1 ppm or less. Techniques for producing low iron loss products are disclosed.

  However, even with the technique of Patent Document 1, there is a problem that iron loss is greatly deteriorated due to PGG type defects at the end portions in the longitudinal direction such as the outer winding and inner winding of the coil during finish annealing. It was. In addition, the technique of Patent Document 2 is a technique in a system that does not use AlN as an inhibitor, and the effect thereof is an orientation failure (Unfavorable Grain growth, (Hereinafter referred to as UFG), the system using AlN as an inhibitor has not been sufficiently studied.

Japanese Patent No. 3357601 Japanese Patent Laid-Open No. 10-245630

  Therefore, the problem of the present invention is that a directional electrical steel sheet that stably develops secondary recrystallization even in a directional electrical steel sheet having a thickness of 0.12 to 0.25 mm, and has low and uniform iron loss in a product coil, and its It is to propose a manufacturing method.

The present invention has the following features.
[1] As component composition, C: 0.04-0.12 mass%, Si: 1.5-5.0 mass%, Mn: 0.01-1.0 mass%, one or two selected from S and Se: total 0.005-0.05 mass %, Sol.Al: 0.010 to 0.027 mass%, N: 0.0040 to 0.0110 mass%, sol.Al/N: 1.50 to 2.50, B: 1.2 mass ppm or less,
A steel slab containing the remainder Fe and inevitable impurities is heated to a temperature of 1250 ° C or higher, and then hot-rolled, hot-rolled sheet annealed, and cooled twice or more sandwiching one or intermediate annealing. A method of producing a grain-oriented electrical steel sheet having a thickness of 0.12 to 0.25 mm, characterized by performing cold rolling to obtain a cold-rolled sheet having a final thickness, primary recrystallization annealing, finish annealing, and further flattening annealing .
[2] The heating process during the finish annealing is maintained at 750 to 875 ° C. for 10 to 200 hours, and then the heating rate of 900 to 1150 ° C. is set to 5 ° C./hr or more. A method for producing grain-oriented electrical steel sheets having a thickness of 0.12 to 0.25 mm.
[3] In addition to the above component composition, the above [1] or [2] further containing 0.002 to 1.0 mass% of one or more selected from Sb, Sn, Ni, Cu, and Mo 2. A method for producing a grain-oriented electrical steel sheet having a thickness of 0.12 to 0.25 mm.
[4] A grain-oriented electrical steel sheet obtained by the production method according to any one of [1] to [3].

Thus, in the production of grain-oriented electrical steel sheets according to the present invention, the amount of B remaining in the slab is reduced, the sol.Al/N ratio is limited, and further, the temperature holding treatment during the finish annealing and the subsequent heating process By appropriately controlling the heating rate, a thin grain-oriented electrical steel sheet having a thickness of 0.25 mm or less can obtain a uniform grain-oriented electrical steel sheet with low iron loss over the entire length of the coil.

It is the figure which showed the influence on the product magnetic characteristic of the amount of B remaining in a slab, and sol.Al/N ratio.

Hereinafter, the experimental results that are the basis of the present invention will be described.

(Experiment 1)
As test materials, steels A to T having different B contents and sol.Al/N ratios were used. Each chemical component is as shown in Table 1.

The steel slabs (thickness 230 mm) described above were each heated to 1400 ° C., finished to a sheet thickness of 2.0 mm by hot rolling, finished hot rolling at 960 ° C., and then wound around a coil at 530 ° C. Next, the hot-rolled coil was subjected to hot-rolled sheet heating to 1020 ° C., pickled, and then made an intermediate thickness of 1.5 mm by cold rolling, and then subjected to intermediate annealing at 1070 ° C. × 30 seconds. These coils were pickled and then cold rolled at a temperature of 180 ° C. to finish to a final thickness of 0.20 mm. Thereafter, linear grooves in the direction perpendicular to the rolling direction for magnetic domain subdivision were applied by electrolytic treatment under conditions of a depth of 15 μm and a width of 150 μm. After that, primary recrystallization annealing was also performed in a dew point: 60 ° C. (50% N ₂ + 50% H ₂ ) atmosphere which also served as decarburization annealing at 850 ° C. for 120 seconds. Thereafter, a magnesia-based annealing separator was applied to the surface of the steel sheet and then wound around a coil.

Then, as finish annealing, heating was performed at a rate of 10 ° C./hr from 800 ° C. during heating to 1150 ° C. in an atmosphere of 75% H ₂ + 25% N ₂ . Further, a purification treatment was performed by soaking at 1150 ° C. for 5 hours in H ₂ . After the finish annealing, after removing the unreacted annealing separator, a glass-based tension coat made of colloidal silica and magnesium phosphate was applied and baked to obtain a product.

  Table 2 and FIG. 1 show the results of measuring the iron loss W17 / 50 of the coil outer winding, the longitudinal central division (middle winding), and the inner winding of the finish annealing coil thus obtained. In Figure 1, ○ indicates that the value of W17 / 50 for all of the outer, middle, and inner volumes is 0.80 W / kg or less, and × indicates W17 / for any of the outer, middle, and inner volumes. Indicates that a value of 50 is greater than 0.80 W / kg. Here, the measurement of the iron loss was evaluated according to the method described in JIS C 2550. The coil outer winding and inner winding are portions excluding several turns of the outermost or innermost defective portion.

  As can be seen from Fig. 1, B is reduced to 1.2 mass ppm or less, and sol.Al/N is controlled to 1.50-2.50, so finish annealing coil outer winding, longitudinal center division (middle winding), and inner winding are also good. It has been found that excellent magnetic properties can be obtained.

(Experiment 2)
Further, for steel H in Table 1, after completing the primary recrystallization annealing in the same manner as in Experiment 1, the holding temperature during heating during finish annealing is 700 to 880 ° C., and the holding time is 0 to 250 hours. Further, the experiment for changing the subsequent heating rate from 900 to 1150 ° C. to 2.5 ° C./hr to 50 ° C./hr was carried out under 11 conditions shown in Table 3. After the final annealing, the unreacted annealing separator was removed, and then a glass-based tension coat made of colloidal silica and magnesium phosphate was applied and baked to obtain a product.

  Table 3 shows the results of measuring the iron loss W17 / 50 of the coil outer winding, the longitudinal central division (middle winding), and the inner winding of the finish annealing coil thus obtained. As shown in Table 3, when the temperature is held at 750 to 875 ° C for 10 to 200 hours and the heating rate at 900 to 1150 ° C is set to 5 ° C / hr or more, the coil outer winding and the longitudinal central division (middle winding) It was found that even better magnetic properties can be obtained in both the inner volume and the inner volume.

(Experiment 3)
Further, for steels U to Y shown in Table 4, Sb, Sn, Ni, Cu, and Mo are added and manufactured under the same manufacturing conditions as in condition 3 of Experiment 2, and the coil outer winding of the finish annealing coil is similarly performed. The iron loss W17 / 50 of the longitudinal central division (middle volume) and the inner volume was measured. The results obtained are shown in Table 5. As shown in Table 5, the characteristics of the steel added with Sb, Sn, Ni, Cu, and Mo were further improved with respect to Condition 3 of Comparative Experiment 2.

The cause of the above improvement in magnetism according to the present invention is not completely clear, but is considered as follows.
In the manufacture of thin grain-oriented electrical steel sheets with a thickness of 0.25 mm or less, the inhibitor components are easily decomposed during finish annealing, and the growth of primary recrystallized grains cannot be pinned, resulting in a good secondary recycle. PGG defects that do not provide a crystal structure and excessive addition of an inhibitor component cause UFG defects that deteriorate the orientation selectivity of secondary recrystallization and deteriorate the iron loss of the product. It tends to decline.

  On the other hand, in the present invention, the influence of the ratio of trace amounts of B, sol. As described above, B had an effect on the PGG failure at the end of the annealed coil because AlN, which is the main inhibitor component in the system containing Al, and BN formed by combining B with N , It becomes a competitive relationship with respect to bonding with N, the precipitation amount and precipitation form as AlN changes, and conditions such as temperature and atmosphere such as outermost winding and innermost winding that are unsteady parts of finish annealing are likely to fluctuate It is thought that a sudden change in the precipitation state occurred, leading to PGG failure. Therefore, in the present invention, B is reduced to 1.2 mass ppm or less and sol.Al/N is controlled to 1.50 to 2.50. By regulating the ratio of B, sol.Al, and N in this way, the occurrence of PGG at the end of the coil in the longitudinal direction, such as the outer winding and inner winding of the finish annealing, is suppressed, and stable recrystallization is achieved. Therefore, it becomes possible to manufacture a grain-oriented electrical steel sheet having a low and uniform iron loss in the product coil.

  Furthermore, holding in the heating process of finish annealing has the effect of stabilizing the expression of secondary recrystallization by promoting the formation of secondary recrystallization nuclei, and also promotes the homogenization of the temperature of the entire coil. It is believed that this contributes to suppression of temperature variations in the coil during the subsequent heating process. The regulation of the heating rate seems to cause the occurrence of secondary recrystallization while moderately inhibiting the decomposition of the inhibitor.

  About Sb, Sn, Ni, Cu, and Mo, it is thought that PGG is suppressed by the effect which assists the effect of an inhibitor.

  In the present invention, the reason for limiting the component composition range is as follows.

C: 0.04-0.12 mass%
C is an element useful for uniform refinement of the structure during hot rolling and cold rolling and the development of Goss orientation, and it is necessary to contain at least 0.04 mass% or more. However, if added over 0.12 mass%, decarburization annealing may cause a shortage of decarburization, and the magnetic properties may deteriorate, so the content is made 0.12 mass% or less. Therefore, C is in the 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, the 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 in the range of 2.0 to 4.0 mass%.

Mn: 0.01-1.0 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, if added over 1.0 mass%, the magnetic flux density decreases. 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%.

S and Se: 0.005 to 0.05 mass% in total
S and Se are indispensable elements necessary for finely precipitating 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 precipitate becomes coarse. Therefore, S and Se are individually or in total in the range of 0.005 to 0.05 mass%. Preferably it is the range of 0.01-0.03 mass%.

sol.Al: 0.010-0.027mass%
sol.Al is acid-soluble Al and is an essential element constituting AlN that is an inhibitor. If it is less than 0.010 mass% as sol.Al, the amount of AlN deposited during hot rolling or the heating process of hot-rolled sheet annealing is insufficient, and the inhibitor effect cannot be obtained. On the other hand, if added in excess of 0.027 mass%, the inhibitor that precipitates becomes composite coarsened, and conversely the inhibitory power decreases. Therefore, in order to sufficiently obtain the inhibitor effect of AlN, it is necessary to make the range of 0.010 to 0.027 mass% with sol.Al.

N: 0.0040 to 0.0110 mass%
N, like Al, is an essential element that constitutes the inhibitor AlN. If N is less than 0.0040 mass%, the amount of the inhibitor component is insufficient. On the other hand, when N is added in an amount exceeding 0.0110 mass%, there is a risk of causing blistering in hot rolling. Therefore, N is set to a range of 0.0040 to 0.0110 mass%.

sol.Al/N: 1.50-2.50
sol.Al/N is an index that defines the amount and form of AlN as an inhibitor. If it is less than 1.50, the amount of precipitated AlN is insufficient, and the effect of the inhibitor cannot be obtained. On the other hand, if it exceeds 2.50, the coarsening of the inhibitor during finish annealing tends to proceed. Therefore, sol.Al/N is in the range of 1.50 to 2.50.

B: 1.2 mass ppm or less
B is an element that may combine with N to form BN. As described above, B exceeds 1.2 mass ppm, because a PGG defect in which a secondary recrystallized structure cannot be obtained at the end of the coil occurs when it exceeds 1.2 mass ppm. Preferably it is the range of 0.8 mass ppm or less.

  The balance is Fe and inevitable impurities. However, in addition to these component elements, the following alloy elements can be added as necessary.

One or more selected from Sb, Sn, Ni, Cu, and Mo: 0.002 to 1.0 mass% in total
Any of these elements forms a precipitate or segregates on the grain boundary or the surface of the precipitate 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, addition exceeding 1.0 mass% leads to embrittlement and poor decarburization of steel, so it is set to 1.0 mass% or less. Therefore, it is preferable to contain the above elements in the range of 0.002 to 1.0 mass% in total.

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 to heat a steel slab adjusted to the above-described composition to 1250 ° C. or higher, then hot-roll and cold-roll one or more times with intermediate annealing. , Primary recrystallization annealing, finish annealing, and further, a series of steps for performing flattening annealing. In the above, it is also preferable to perform hot-rolled sheet annealing as necessary.

In finish annealing, it is preferable to first hold for 10 to 200 hours in the temperature range of 750 to 875 ° C. during the heating process. The holding temperature range was set to 750 to 875 ° C because the effect of generating Goss orientation nuclei was insufficient at a temperature lower than 750 ° C, and the decomposition of the inhibitor was excessively promoted at a temperature higher than 875 ° C. Because there are cases. The retention time is set to 10 to 200 hours because the effect of producing Goss azimuth nuclei is insufficient when the retention time is less than 10 hours, and the decomposition of the inhibitor is excessively promoted when it exceeds 200 hours.
Furthermore, it is preferable to control the heating rate of 900 to 1150 ° C. to 5 ° C./hr or more. The reason why the temperature is set to 5 ° C./hr or more is that if the temperature is less than 5 ° C./hr, the inhibitor is excessively decomposed during the secondary recrystallization. Subsequent to this, a purification annealing for removing impurities is performed, followed by cooling to complete the finish annealing.

  The steel sheet that has been annealed is then stripped of the unreacted annealing separator on the surface of the steel sheet, and if necessary, is coated and baked with an insulating coating, and is subjected to planarization annealing to obtain a product plate. The insulating coating is preferably a tension coating in order to reduce iron loss. In addition, in order to reduce iron loss, a well-known magnetic domain refinement process is performed in which the steel sheet after finish annealing is linearly subjected to plasma jet, laser irradiation, or electron beam irradiation, or linear distortion is imparted by a protruding roll. You may give it. Moreover, when forming a physical groove | channel for magnetic domain subdivision, it is effective to carry out after the last cold rolling. Also, if the forsterite film is not formed on the steel plate surface by finish annealing, the steel plate surface is further mirror-finished or subjected to grain orientation selection treatment with NaCl electrolysis, etc. Good.

  Steel slabs 1-7 having the composition shown in Table 6 are hot-rolled to form a hot-rolled sheet with a thickness of 2.0 mm, subjected to hot-rolled sheet annealing at 950 ° C. for 20 seconds, and then pickled. , Cold rolled to a sheet thickness of 1.4 mm, subjected to an intermediate annealing of 1050 ° C. × 60 seconds, pickled and cold rolled to a final sheet thickness of 0.12, 0.18, 0.23 mm Cold-rolled sheets of various thicknesses were used. Here, a groove for subdividing the magnetic domain having a depth of 15 μm and a width of 200 μm was further formed by an electrochemical method. Then, degreased the cold-rolled sheet, subjected to primary recrystallization annealing that also serves as decarburization 820 ° C. × 2 minutes in a wet hydrogen atmosphere, after applying an annealing separator mainly composed of MgO on the steel sheet surface, Steels 1 to 4 were uniformly heated from 800 ° C. to 1150 ° C. in the finish annealing at 10 ° C./hr. On the other hand, about 5-7, after hold | maintaining processing at 800 degreeC of the heating process of finish annealing for 30 hours, between 900 degreeC-1150 degreeC was heated at 18 degreeC / hr. Thereafter, purification annealing was performed at 1200 ° C. for 5 hours. The steel sheet after the finish annealing was prepared by removing unreacted annealing separator and applying and baking a tension coat composed of colloidal silica and magnesium phosphate.

  Table 7 shows the measurement results of iron loss at both ends (outer winding, inner winding) and the center dividing point (middle winding) of the coil thus obtained. The iron loss was measured by evaluating the iron loss W17 / 50 at a magnetic flux density of 1.7 T and a frequency of 50 Hz according to the method described in JIS C 2550. Here, both ends of the coil are portions excluding several turns of the outermost or innermost defective portion.

From Table 7, the coils 5 to 7 of the present invention example had a low and uniform iron loss over the entire length of the coil as compared with the comparative example 1.

Claims (2)

As component composition, C: 0.04-0.12 mass%, Si: 1.5-5.0 mass%, Mn: 0.01-1.0 mass%, one or two selected from S and Se: total 0.005-0.05 mass%, sol A steel slab containing Al: 0.010 to 0.027 mass%, N: 0.0040 to 0.0110 mass%, sol.Al/N: 1.50 to 2.50, B: 1.2 mass ppm or less, with the balance being Fe and inevitable impurities , Heated to a temperature of 1250 ° C or higher, then hot-rolled, cold-rolled twice or more with one or more intermediate annealings to obtain a cold-rolled sheet with the final thickness, primary recrystallization annealing , heating process wherein the seven hundred fifty to eight hundred seventy-five ° C. in 10 to 200 hours retention to above specification and the heating rate of the followed 900~1150 ℃ 5 ℃ / hr or higher annealing, further, be subjected to a flattening annealing at a thickness 0.12 to 0.25 Manufacturing method of mm-oriented electrical steel sheet. In addition to the chemical composition further, Sb, Sn, Ni, Cu, according to claim 1, characterized in that it contains 0.002～1.0Mass% in total of one or two or more selected from among Mo A method for producing grain-oriented electrical steel sheets having a thickness of 0.12 to 0.25 mm.

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