JP4677765B2 - Directional electrical steel sheet with chromeless coating and method for producing the same - Google Patents

Description

The present invention, core loss increased upon forming a coating film containing no chromium on the surface of the square oriented electrical steel sheet, to prevent the inevitable coating defects occurring, the tension applied to the steel sheet along with improving the surface coating properties It is about the method of improving.

  In general, in a grain-oriented electrical steel sheet, a coating is applied to the surface thereof in order to provide insulation, workability, rust prevention, and the like. Such a film is usually composed of a base film mainly composed of forsterite formed at the time of final finish annealing and a phosphate-based topcoat film formed thereon. Since these coatings are formed at high temperatures and have a low coefficient of thermal expansion, there is a large difference in the coefficient of thermal expansion between the steel sheet whose temperature has dropped to room temperature and the film, thereby imparting tension to the steel sheet. Therefore, it is effective in reducing iron loss. Therefore, the coating is desired to have a function of imparting as high tension as possible to the steel sheet.

  Conventionally, various proposals have been made for coatings in order to satisfy the above-mentioned various characteristics. For example, Patent Document 1 has a film mainly composed of magnesium phosphate, colloidal silica and chromic anhydride, and Patent Document 2 has a film mainly composed of aluminum phosphate, colloidal silica and chromic anhydride. Proposed.

  By the way, due to the recent increase in interest in environmental conservation, there is an increasing demand for products that do not contain harmful substances such as chromium and lead. In the field of grain-oriented electrical steel, a method for forming a film that does not contain chromium. Development was desired. However, if chromium is not used, quality problems such as significant loss of moisture absorption and loss of iron loss due to a decrease in tension occur, so it was not possible to add no chromium. Here, the deterioration of moisture absorption resistance of the coating means that the coating absorbs moisture in the atmosphere, and this moisture is partially liquefied, resulting in a thin film thickness or a portion without the coating. And the rust prevention property is deteriorated.

As a method for solving this problem, Patent Document 3 discloses a method of applying a coating liquid composed of colloidal silica, aluminum phosphate, boric acid and sulfate. This method resulted in an improvement in iron loss and an improvement in moisture absorption resistance due to a tension effect similar to that of a conventional chromium-containing coating.
However, the improvement of the iron loss and moisture absorption resistance by this method varies in the effect, and in some cases, the iron loss and moisture absorption resistance may be deteriorated to a problematic level. Such variations in quality are significant even within the same coil, and non-uniform portions must be removed using a rewinding line, resulting in a large yield loss and pressure on the operation of the rewinding line. It was the main cause of lowering.

Further, regarding the coating film not containing chromium, Patent Document 4 discloses a method of adding a boric acid compound instead of a chromium compound, Patent Document 5 discloses a method of adding an oxide colloid, and Patent Document 6 discloses a metal organic acid. Each method of adding a salt is disclosed, but the effect of improving hygroscopicity and iron loss varies greatly within the coil by any of the techniques, so that a complete solution has not been achieved.
Japanese Examined Patent Publication No. 56-52117 Japanese Patent Publication No.53-28375 Japanese Patent Publication No.57-9631 Japanese Patent Application Laid-Open No. 2000-169973 JP 2000-169972 A JP 2000-178760 A

  Therefore, the present invention has been made in view of the above circumstances, and even when a coating containing no chromium is applied to a grain-oriented electrical steel sheet, it has a high resistance to the same level as a steel sheet on which a chromium-containing coating is formed. It aims at providing the grain-oriented electrical steel sheet with a chromeless film which implement | achieves a hygroscopic property and a low iron loss together with the manufacturing method.

The inventors have found that the effect of improving the moisture absorption resistance and the iron loss varies in the coating film not containing chromium described in the above-mentioned Patent Document 3 because there are some disturbance factors and the desired characteristics cannot be achieved. I thought and carried out an enormous experiment to find out the cause. As a result, it was found that variations occur depending on the titanium content in the ceramic base film formed after the final finish annealing. This titanium penetrates into the coating film by the decomposition of titanium oxide used for the annealing separator auxiliary agent during the final finish annealing. Titanium oxide is often used because it promotes film formation and is effective for making titanium penetrate into the base film to form a strong base film.
The following describes the experiments that led to this finding.

C: 0.045mass%, Si: 3.25mass%, Mn: 0.07mass% and Se: 0.02mass%, with the balance being iron and unavoidable impurity composition, heated at 1380 ° C for 30 minutes, hot After rolling to 2.2 mm thickness by rolling and then hot-rolled sheet annealing at 950 ° C for 1 minute, after finishing to a final sheet thickness of 0.23 mm by cold rolling with intermediate annealing at 1000 ° C for 1 minute, Decarburization annealing was performed at 850 ° C. for 2 minutes. Thereafter, an annealing separator consisting of 100 parts by mass of magnesium oxide, 0 to 20 parts by mass of titanium oxide and 1 part by mass of strontium sulfate is applied to the surface of the steel sheet on both sides at 12 g / m ² , and dried and subjected to final finish annealing. did. Final annealing is at 100% humidity atmosphere of H ₂ in the region of 1150 ° C. from 850 ° C., the ratio PH ₂ 0 / PH ₂ of the steam partial pressure to the hydrogen partial pressure _{(PH 2) (PH 2 0} ) from 0.001 Changed to 0.2. Thereafter, the unreacted annealing separator was removed.

  The steel plate thus obtained was sheared to a size of 300 mm × 100 mm and subjected to magnetic measurement with an SST (Single Sheet Tester) tester. At the same time, a part of the steel sheet was sampled, the amount of titanium intrusion into the base film was measured by chemical analysis, and the measured value was converted to the basis weight per both surfaces of the steel sheet.

Then, after carrying out phosphoric acid pickling, 50 parts by mass of aluminum phosphate, 40 parts by mass of colloidal silica, 5 parts by mass of boric acid and 10 parts by mass of manganese sulfate described in the above-mentioned Patent Document 3 as a coating treatment liquid. A coating agent having a blending ratio was applied to both surfaces of the steel sheet at a dry weight of 10 g / m ² and then baked at 800 ° C. for 2 minutes in a dry N ₂ atmosphere. For comparison, coating and baking were similarly performed using a coating solution comprising 50 parts by mass of aluminum phosphate, 40 parts by mass of colloidal silica, and 10 parts by mass of chromic anhydride.

  The steel plate thus obtained was again subjected to magnetic measurement with an SST testing machine. Further, a dissolution test of P was also performed. That is, in the P dissolution test, three 50 mm × 50 mm test pieces were immersed in 100 ° C. distilled water for 5 minutes and boiled to elute P from the coating surface and quantitatively analyze the P. The P elution amount serves as a standard for discriminating the easiness of dissolution of the film by moisture, and the moisture absorption resistance can be evaluated. Further, regarding the corrosion resistance of the coating, a 50 mm × 100 mm test piece was exposed to an atmosphere at a temperature of 50 ° C. and a humidity of 50% for 50 hours, and then rust generated on the steel sheet was evaluated as an area ratio.

  The above measurement and evaluation results are shown in FIG. 1, FIG. 2, and FIG. 3, respectively, organized by the relationship between the rust occurrence rate, the magnetic properties, the P elution amount, and the titanium content of the underlying film after the final finish annealing.

First, as shown in FIG. 1, when a chromium-containing coating is used, the overall rust generation rate is low, and the dependency of the rust generation rate on the content of the underlying film titanium is also low. However, if the titanium content of the base film is less than 0.02 g / m ² or more than 0.4 g / m ² , the rust generation rate tends to be slightly deteriorated.
On the other hand, in the coating containing no chromium, the rust occurrence rate is high in many areas. However, when the titanium content of the base film is in the range of 0.05 to 0.5 g / m ² , it shows good corrosion resistance, Inferior performance is obtained.

This is the same for the iron loss and the amount of elution of P. As shown in FIGS. 2 and 3, even if the coating does not contain chromium, the titanium content of the base film is within the range of 0.05 to 0.5 g / m ^2. If present, excellent iron loss and durability improvement effects equivalent to those of the coating film containing chromium were observed.

From the above experimental results, when a coating containing no chromium was formed, the present inventors inferred the influence of the titanium content of the base film on the hygroscopicity, magnetic properties, and corrosion resistance of the chromiumless coating as follows.
First, the underlying film is generally a ceramic polycrystalline body mainly composed of forsterite, but titanium concentrates in the grain boundaries of the ceramic particles to increase the grain boundary strength and improve the characteristics of the underlying film. There is work. When the penetration amount of titanium into the coating is reduced, the strength of the base film is weakened, so that it partially peels off. Even if the coating is applied in such a state, it is considered that this partial peeling weakens the tension effect or lowers the protection against the atmosphere and reduces the iron loss improvement effect due to hygroscopicity, corrosion resistance and tension.

  On the contrary, when the penetration amount of titanium into the base film is too large, titanium is present in places other than the grain boundaries of the ceramic particles. This is mainly incorporated into forsterite and has the effect of promoting acid solubility. Therefore, when a phosphate-based film is applied on such a base film, the forsterite particles are etched and partly dissolved by the coating solution, resulting in a thin part in the base film, which also absorbs moisture. , Corrosion resistance and tension effect will deteriorate.

  From the above, in order to obtain excellent film properties, it is important to optimize the titanium content in the base film.

  Here, when the film containing chromium is compared with the film not containing chromium, the chromium-containing film traps free P and enters into the bonding of Si, O and P in the coating. Strengthening the moisture resistance and corrosion resistance, and improving iron loss due to tension, but when using a film that does not contain chromium, the effect of strengthening the film is less than that of the film containing chromium, Even if it is uneven, corrosion resistance and the like are impaired. Therefore, in the case of a coating that does not contain chromium, it is necessary to more strictly control the amount of oxygen in the base film.

  Further, when a conventionally used coating solution containing chromium is applied, chromium is also a highly corrosive element, so that the etching effect of the underlying film becomes stronger than the coating containing no chromium. Therefore, when a chromium-containing coating is applied, the etching effect becomes too strong and dissolution of the coating proceeds, so it is necessary to reduce the titanium content. Therefore, the higher the titanium content, the better.

  In view of the above, the coating film not containing chromium has a great influence on the product quality due to the penetration of titanium in the base film, and has an optimum value on the side where the amount of penetration of titanium is larger than the coating film containing chromium. It will be.

Conventionally, coatings that do not contain chromium have had the problem of large variations in quality within the coil. However, the above-mentioned findings have revealed the cause of this quality variation and countermeasures. That is, the non-uniform quality in the coil is due to the difference in the interlayer atmosphere inside the coil during box annealing. In the coil inner winding portion, generally, the surface pressure due to the thermal expansion of the coil is increased, and thereby the gas generated in the interlayer is likely to stay. The generated gas is mainly hydrated water brought in by MgO, the main ingredient of the annealing separator, and when this water vapor stays in the atmosphere, titanium dioxide, the additive of the separating agent, reacts with MgO and moisture to produce an intermediate product. And penetration into the steel sheet surface is promoted. Then, the penetration amount of titanium in the base film is larger in the inner winding portion than in the outer winding portion, and as a result, the titanium content in the base film is larger in the outer winding portion than in the coil inner winding portion. The appropriate range shown in FIG. Thus, since the difference in the amount of intrusion of titanium occurs, it is considered that the quality of the chromeless coating having a strong dependency on the amount of intrusion of titanium varies. Therefore, in order to prevent this, the ratio PH ₂ 0 / PH ₂ , which is the atmospheric oxidizing property during the final finish annealing, is kept within a certain range at the lowest possible level so as to eliminate the atmospheric difference between the inner winding portion and the outer winding portion. It is necessary to fit.

This invention is made | formed based on the above knowledge, The summary structure is as follows.
(1) A grain- oriented electrical steel sheet having a phosphate-based tension-imparting film containing no chromium via a ceramic base film on the surface of the steel sheet, and containing Si: 2.0 to 4.0 mass% The slab is hot-rolled and then cold-rolled once or multiple times with intermediate annealing to finish to the final thickness, followed by primary recrystallization annealing, and then the annealing separation with magnesia as the main component on the steel plate surface After the final finish annealing after applying the agent, in a series of steps of forming a phosphate-based tension-imparting film containing no chromium, magnesium oxide: 100 parts by mass and titanium dioxide: 1 part by mass or more and 12 parts by mass The ratio of the steam partial pressure (PH ₂ 0) to the hydrogen partial pressure (PH ₂ ) in an atmosphere in the temperature range of at least 850 ° C. to 1150 ° C. of the final finish annealing is applied PH ₂ 0. / PH ₂ below 0.06 and previous The titanium content in the base film is 0.05 g / m ² or more and 0.5 g per both sides of the steel plate , obtained by adjusting PH ₂ 0 / PH ₂ in the temperature range of at least 50 ° C. to 0.01 to 0.06. / M ² or less grain-oriented electrical steel sheet with a chromeless coating.

(2) Hot rolling is applied to a steel slab containing Si: 2.0 to 4.0 mass%, and then cold rolling is performed once or multiple times sandwiching intermediate annealing to finish to the final plate thickness, and then primary recrystallization annealing is performed. Then, after applying final annealing after applying an annealing separator mainly composed of magnesia to the steel plate surface, the directionality is determined by a series of steps to form a phosphate-based tension-imparting film that does not contain chromium. In producing the electrical steel sheet, an annealing separator containing magnesium oxide: 100 parts by mass and titanium dioxide: 1.0 part by mass or more and 12.0 parts by mass or less is applied, and at a temperature range of at least 850 ° C. to 1150 ° C. of the final finish annealing. Ratio of water vapor partial pressure (PH ₂ 0) to hydrogen partial pressure (PH ₂ ) in the atmosphere PH ₂ 0 / PH ₂ is 0.06 or less, and PH ₂ 0 / adjust the PH ₂ to 0.01 or more than 0.06 Method for producing a chromeless a coated oriented electrical steel sheet characterized by Rukoto.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where the film which does not contain chromium is applied, the grain-oriented electrical steel sheet which was excellent in both the magnetic characteristic and the film characteristic can be provided stably.

Next, the reason why each constituent element of the present invention is limited will be described in detail.
First, the steel sheet which this invention makes object does not ask | require steel grade especially if it is a raw material for grain-oriented electrical steel. This electromagnetic steel slab is hot-rolled by a known method, finished to the final sheet thickness by cold rolling multiple times with one or more intermediate annealings, then subjected to primary recrystallization annealing, and an annealing separator is applied. Apply final finish annealing. At this time, a titanium content of the final finish underlying film after annealing essential to control such that the 0.05 g / m ² or more 0.5 g / m ² or less.

  In order to control the titanium content of the undercoat within this range, first, Si: 2.0 to 4.0 mass% is contained as a component. That is, when the Si content is less than 2.0 mass%, the iron loss is deteriorated, while when it exceeds 4.0 mass%, the rollability is lowered. The balance may be composed of iron and inevitable impurities, but if necessary, 0.02 to 0.10 mass% for C and AlN as an inhibitor to improve the primary recrystallization structure and improve the magnetic properties. 0.01 to 0.03 mass% for Al and 0.006 to 0.012 mass% for N. When MnS or MnSe is used as an inhibitor, 0.04 to 0.20 mass% for Mn and 0.01 to 0.03 mass% for S or Se, Cu, Ni as auxiliary inhibitors When Mo, Cr, Bi, Sb and Sn are used singly or in combination, 0.01 to 0.2 mass% can be contained.

  The steel slab having such a component composition is heated and then hot-rolled, subjected to one time or a plurality of cold rolling sandwiching intermediate annealing to finish the final thickness, and then subjected to primary recrystallization annealing. Thereafter, the final finish annealing is performed after applying the annealing separator. In this annealing separator, titanium dioxide is contained in an amount of 1.0 to 12.0 parts by mass with respect to 100 parts by mass of magnesium oxide. That is, when the content of titanium dioxide is less than 1.0 part by mass, the amount of intrusion of titanium is too small. On the other hand, when the content is more than 12 parts by mass, the amount of infiltration of titanium is too large, which is not suitable.

The temperature range from 850 ° C. to 1150 ° C. in the final finish annealing is an important region for determining the subsequent penetration amount of titanium into the steel plate surface. Here, the ratio PH ₂ 0 / PH ₂ is adjusted to 0.06 or less by containing H ₂ in the atmosphere. If the ratio PH ₂ 0 / PH ₂ in this atmosphere exceeds 0.06, titanium penetrates too much into the underlying film and the difference in oxidization between the inner and outer coil portions of the coil becomes too great, resulting in a coil Uniform titanium penetration between layers is not achieved.

Furthermore, it is also important to adjust the atmospheric ratio PH ₂ 0 / PH ₂ to a range of 0.01 or more and 0.06 or less in a temperature range of at least 50 ° C. of the temperature range from 850 ° C. to 1150 ° C. That is, when the ratio PH ₂ 0 / PH ₂ here is higher than 0.01, titanium can easily enter the steel sheet surface to improve the quality. After such atmosphere control, purification annealing is subsequently performed, and at the same time, the formation of the base film is completed.

Chromium after removing the unreacted annealing separator and pickling with phosphoric acid, etc., after the titanium content of the base film after final finish annealing is 0.05 to 0.5 g / m ² per both sides of the steel plate by the above process Apply a phosphate coating solution that does not contain
As the coating liquid component, a conventionally known one, for example, a coating liquid composed of colloidal silica and aluminum phosphate, boric acid and sulfate described in Patent Document 3 described above, or described in Patent Document 4 described above. Can be used in any coating solution, such as those containing borated inclusions, those containing oxide colloids described in Patent Document 5, and those containing metal organic acid salts described in Patent Document 6. is there. Moreover, it is also possible to improve sticking resistance by adding inorganic mineral particles such as silica and alumina to these coating solutions. The basis weight of the coating solution is 4 to 15 g / m ^{2 on} both sides of the steel plate. That is, if it is less than 4 g / m ² , the interlayer resistance is lowered, and if it is more than 15 g / m ² , the occupational graduation is lowered.

  After this coating liquid is applied and dried, flattening annealing is also performed for baking. In addition, although the conditions of planarization annealing are not specifically limited, As for annealing temperature, it is desirable to set it as the soaking time of about 2-120 second in the temperature range of 700 to 950 degreeC. If the annealing temperature is less than 700 ° C or the soaking time is shorter than 2 seconds, flattening will be insufficient, resulting in poor yield due to shape defects, while the temperature exceeds 950 ° C or soaking time. If the time is longer than 120 seconds, the effect of the flattening annealing is too strong, resulting in creep deformation and deterioration of the magnetic properties. Therefore, the above range is preferable.

A steel slab having components of C: 0.06 mass%, Si: 3.3 mass%, Mn: 0.07 mass%, Se: 0.02 mass%, Al: 0.03 mass% and N: 0.008 mass% is hot-rolled, and then 1050 A 0.23mm-thick decarburized annealed sheet obtained by performing two final cold rollings with intermediate annealing for 1 minute at 850 ° C, followed by decarburizing annealing at 850 ° C for 2 minutes, and magnesia 100 as an annealing separator. Applying powder added by changing the amount of titanium oxide with respect to part by mass, performing final finish annealing with various temperature patterns, and then removing the unreacted annealing separator, so that the titanium of the underlying film Steel plates with different contents were prepared. After the phosphoric acid pickling treatment, the component composition is in the ratio of dry solid to solid content, colloidal silica: 50 mass%, magnesium phosphate: 40 mass%, manganese sulfate: 9.5 mass% and fine powder silica particles: 0.5 mass% The coating solution to be applied was applied at a coating amount of 10 g / m ^{2 on} both surfaces of the steel plate. Incidentally, the magnetic flux density of the final finish steel sheet after annealing was both at B ₈ 1.92 (T). Then, 30 seconds at 850 ° C., subjected to baking treatment of dry N ₂ atmosphere.

Table 1 shows the results of investigation of various properties of the steel sheet thus obtained. In addition, the titanium content of the base film was converted to a basis weight by a value measured by chemical analysis.
As shown in the table, according to the description in the above-mentioned Patent Document 1, the titanium content of the base film is in the range of 0.05 to 0.5 g / m ² even under the condition that Mn sulfate is simply used instead of chromic anhydride. It can be seen that good film properties and iron loss can be obtained.

The titanium content of the base film after final finish annealing, which was processed by the methods of conditions No. 5 and 9 of Example 1, was 0.18 g / m ² and 0.04 g / m ² , and the magnetic flux density was B ₈ , both of which were 1.92 ( After removing the unreacted annealing separator from the steel plate T), and then subjecting it to a phosphoric acid pickling treatment, the component composition is in the proportion of dry solids, colloidal silica: 50 mass%, various primary phosphorus A coating liquid comprising 40 mass% of an acid salt compound and 9.5 mass% of an inorganic compound and 0.5 mass% of fine powder silica particles is applied at 10 g / m ^{2 on} both sides of the steel plate, and then baked in a dry N ₂ atmosphere. It was applied at ℃ and 30 seconds.

  Table 2 shows the results of investigating various properties of the steel sheet thus obtained. In any of the coating liquids not containing chromium described in Patent Documents 3 to 6 described above, excellent magnetic properties and coating properties are obtained by controlling the titanium content of the base film within an appropriate range.

After passing through the decarburization annealing process similarly to Example 1, the coil which apply | coated the annealing separator containing 8 mass parts titanium dioxide with respect to 100 mass parts of magnesia was divided into 2, and box annealing was performed, respectively. At that time, the annealing atmosphere was changed from 850 ° C. to 1150 ° C. under two conditions of the atmosphere ratio PH ₂ 0 / PH ₂ of 0.05 and 0.12.
Next, after the final finish annealing, the coil was washed with phosphoric acid, and then a coating solution was applied, followed by a heat flattening treatment at 800 ° C. for 30 seconds. Thereafter, samples were taken from the inside, inside and outside of the coil, and the magnetic properties and the coating properties were evaluated. The evaluation results are shown in Table 3.

As can be seen from the table, the quality of the product processed under the condition of the atmosphere ratio PH ₂ 0 / PH ₂ of 0.12 tends to be deteriorated as a whole and the quality difference between the inner volume and the outer volume is significant. When the ratio PH ₂ 0 / PH ₂ is 0.05, uniform magnetic characteristics and film characteristics can be obtained over the entire length of the inner winding to the outer winding.

It is a graph which shows the relationship between the titanium content in the base film of a final finish annealing board, and a rust incidence. It is a graph which shows the relationship between the titanium content in the base film of a final finish annealing board, and the measurement result of an iron loss. It is a graph which shows the relationship between titanium content in a base film of a final finish annealing board, and hygroscopicity.

Claims (2)

A grain- oriented electrical steel sheet having a phosphate-based tension-imparting film containing no chromium via a ceramic base film on the surface of the steel sheet, and heat applied to a steel slab containing Si: 2.0 to 4.0 mass% Apply intermediate rolling, perform cold rolling multiple times with one or more intermediate annealings, finish to the final sheet thickness, then perform primary recrystallization annealing, and then apply an annealing separator containing magnesia as the main component to the steel sheet surface Then, after performing final finish annealing, in a series of steps to form a phosphate-based tension-imparting film not containing chromium, magnesium oxide: 100 parts by mass and titanium dioxide: 1 part by mass to 12 parts by mass applying an annealing separating agent containing, final finish vapor partial pressure to hydrogen partial pressure (PH ₂₎ at ambient temperature range from at least 850 ° C. to 1150 ° C. annealing (PH ₂ 0) of the ratio PH ₂ 0 / PH ₂ 0.06 or less and the temperature The titanium content in the underlying film is 0.05 g / m ² or more and 0.5 g / m on both sides of the steel sheet , obtained by adjusting PH ₂ 0 / PH ₂ in the temperature range of at least 50 ° C. to 0.01 to 0.06. A grainless electrical steel sheet with a chromeless coating, characterized by being ² or less. Si: Steel slab containing 2.0 to 4.0 mass% is hot-rolled, subjected to cold rolling of one time or multiple times sandwiching intermediate annealing and finished to the final sheet thickness, and then subjected to primary recrystallization annealing, After applying final annealing after applying an annealing separator containing magnesia as the main component to the steel sheet surface, the grain-oriented electrical steel sheet is formed by a series of steps to form a phosphate-based tension-imparting film that does not contain chromium. In production, an annealing separator containing magnesium oxide: 100 parts by mass and titanium dioxide: 1 part by mass to 12 parts by mass is applied, and hydrogen in an atmosphere in a temperature range of at least 850 ° C. to 1150 ° C. of final finish annealing the ratio PH ₂ 0 / PH ₂ of the steam partial pressure (PH ₂ 0) to 0.06 for the partial pressure (PH _2), and the PH ₂ 0 / PH ₂ in the temperature range over at least 50 ° C. of the temperature range Adjust to 0.01 or more and 0.06 or less Method for producing a chromeless a coated oriented electrical steel sheet characterized.

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