JP6468208B2 - Powder for annealing separator, method for producing the same, and grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a powder used for an annealing separator for producing a grain-oriented electrical steel sheet that does not have a film mainly composed of forsterite on the surface, and for an annealing separator that contributes to complete filmlessness in the grain-oriented electrical steel sheet. The present invention relates to a powder, a manufacturing method thereof, and a grain-oriented electrical steel sheet.

  Production of grain-oriented electrical steel sheets is generally performed by subjecting a steel slab adjusted to a predetermined component composition to hot rolling, annealing, and cold rolling, followed by recrystallization annealing followed by finish annealing. . Of the above steps, the finish annealing step requires annealing at a high temperature of 1200 ° C. or higher. Therefore, an annealing separator mainly composed of magnesium oxide powder is applied to prevent coil seizure. Is customary.

In addition to the above role as an annealing separator, magnesium oxide reacts with an oxide layer mainly composed of silica that forms on the steel sheet surface during decarburization annealing prior to finish annealing to form a forsterite coating. Precipitation (such as AlN, MnS, MnSe, Si ₃ N ₄ , TiN, TiC, etc.) is removed from the steel sheet after finish annealing. And has the role of purification.

  The above forsterite coating works as a binder that improves the adhesion between the overcoated phosphate insulating coating and the steel plate, and improves the magnetic properties by applying tension to the steel plate. There is also.

  However, while the forsterite film has an excellent adhesion improving effect, it disturbs the interface structure between the ground iron and the film, so that the tension effect on the iron loss is offset. In order to avoid this, Patent Document 1 discloses that the roughness of the interface between the steel sheet surface and the coating is reduced, that is, the iron core of the material is greatly reduced by smoothing the surface of the ground iron and applying the tension. Techniques for reducing are disclosed. As the annealing separator mainly composed of magnesium oxide, those having good reactivity are usually used in order to form forsterite densely and uniformly on the steel sheet surface.

  However, such an annealing separator is inconvenient for smoothing the steel plate surface. Therefore, Patent Document 2 discloses a technique using an annealing separator obtained by adding 2 to 40 parts by weight of an alkali or alkaline earth metal chloride to 100 parts by weight of magnesium oxide. Patent Document 3 discloses a technique that does not form forsterite by using alumina as an annealing separator.

Japanese Patent Publication No.52-24499 JP-A-64-62476 JP 2003-268450 A

  However, none of the above-mentioned techniques has solved the problem that a small amount of oxide remains after finish annealing, and in order to obtain a mirror-like smooth surface, an acid with hydrofluoric acid is used. Processes such as washing and electropolishing are necessary, and the manufacturing cost is very high.

  The present invention has been developed in view of the above circumstances, and the amount of oxide remaining after finish annealing is extremely small, and without adding a process such as pickling with an acid containing hydrofluoric acid or electropolishing, it is in a mirror state. An object is to obtain a powder for annealing separator that contributes to obtaining a grain-oriented electrical steel sheet having a smooth surface and a grain-oriented electrical steel sheet having a smooth surface.

Now, in order to solve the above-mentioned problems, the present inventors have intensively investigated and studied the techniques of Patent Document 2 and Patent Document 3.
As a result, the technique described in Patent Document 2 uses magnesium oxide prepared to form a forsterite film equivalent to the conventional one, and therefore has a high forsterite film forming ability, and the decomposition of SiO ₂ by chlorides. It was found that even if it was attempted to prevent the formation of silicate compounds by promoting the above, the effect of inhibiting 100% could not be obtained.

  In the technique described in Patent Document 3, it is considered that when alumina is applied as a slurry, moisture brought into the steel sheet has an adverse effect. Patent Document 3 considers this point and claims that in claim 2, “the amount of water brought in after applying and separating an annealing separator mainly composed of alumina in a water slurry state is 1.5% or less” is 1.5. % Or less is still inadequate, and it has been found that oxides are generated on the surface of the steel sheet by high-temperature annealing due to the introduced moisture.

First, the inventors changed the idea of not forming forsterite as much as possible, which is the idea in Patent Document 3. That is, the development of a new technology was attempted on the assumption that the formation of oxides due to the introduced moisture is inevitable. Here, assuming the formation of an oxide, the technical idea of Patent Document 2 is to inhibit the reaction between magnesia for forming a forsterite film at a high temperature and SiO ₂ that is a steel sheet surface oxide. The focus was on SiO ₂ .

Therefore, as a result of repeated researches focused on magnesium oxide, the inventors
1) The action of boron is large in promoting the formation of a forsterite film at high temperatures,
2) The present inventors have found that the presence of boron is largely involved in the adhesion between the coating formed at high temperature and the ground iron.
The present invention is based on the above findings.
That is, the gist of the present invention is as follows.

(1) A powder for an annealing separator containing 0.04 mass% or more and 0.30 mass% of boron and containing magnesium oxide as a main component,
An annealing separator powder, wherein the proportion of tetracoordinate boron in the boron is 50% or more.

(2) The powder for annealing separator as described in (1) above, wherein phosphorus is contained in an amount of 0.03 to 0.30% by mass in terms of P ₂ O ₅ .

(3) The annealing separator powder according to (1) or (2) above, wherein the 325 mesh sieve residue in the magnesium oxide powder is 1.0% by mass or less.

(4) Magnesium oxide content is 95% by mass or more, The annealing separator powder according to (1) to (3) above.

(5) Firing a raw material containing one or both of magnesium hydroxide and magnesium carbonate and boron, and then
A method for producing an oxidized powder for an annealing separator, wherein the tetracoordinate boron ratio is adjusted by adjusting the humidity of the fired product.

(6) The raw material of the powder for annealing separator according to (5) above, wherein the raw material contains one or both of the magnesium hydroxide and the magnesium carbonate in a total of 80% by mass or more. Production method.

(7) The above raw material contains 0.04% by mass or more and 0.30% by mass or less of the boron, and the proportion of tetracoordinate boron in the boron is 50% by mass or more. The manufacturing method of the powder for annealing separators as described in 6).

(8) A grain-oriented electrical steel sheet characterized by having no coating mainly composed of forsterite on the steel sheet surface by the annealing separator powder according to any one of (1) to (4) above.

(9) The grain-oriented electrical steel sheet according to (8) above, wherein the thickness is 0.05 mm or more and 0.23 mm or less.

  According to the present invention, a grain-oriented electrical steel sheet having a smooth surface in a mirror state, which does not require a process such as pickling with an acid containing hydrofluoric acid or electropolishing, has a low manufacturing cost, and has good magnetic properties. Can be obtained.

Hereinafter, experimental results that led to the present invention will be described.
First, a sample was manufactured as follows.
As a starting material, vapor phase high purity ultrafine powder magnesia 2000A manufactured by Ube Materials Co., Ltd. was used. Its purity was very high at 99.98%.

This starting material was hydrated with pure water to obtain a magnesium hydroxide slurry. To this magnesium hydroxide slurry, boric acid (H ₃ BO ₃ ) is added after annealing to be adjusted to a desired boron concentration, and the magnesium hydroxide slurry is squeezed with a filter press, A magnesium oxide cake was obtained.

  100 g of this magnesium hydroxide cake is put in an alumina crucible and baked in the air in the temperature range of 1000 ° C to 1500 ° C for 30 minutes after the electric furnace reheats in an electric furnace (SPX1518T-17 manufactured by Marusho Electric). After cooling in the furnace as it was, pulverization was performed. The amount of boron and the 4-coordinate boron ratio (4-coordinate boron / (3-coordinate boron + 4-coordinate boron)) of the powder thus prepared are shown in Table 1.

  The amount of boron was analyzed by high-frequency inductively coupled plasma (ICP) after magnesium oxide was dissolved in acid. The tetracoordinate boron ratio was measured by DD / MAS method using ECA600 manufactured by JEOL at Toray Research Center, Inc. Measurement was performed at a pulse width of 1.0 μsec (30 ° pulse), a repetition waiting time of 3.0 s, a saturated boric acid aqueous solution (external reference 19.49 ppm) as a reference material, and a sample rotation speed of 15.0 kHz at room temperature. .

  Calculation of the abundance ratio of tricoordinated boron and tetracoordinated boron can be accurately performed by waveform separation, but as a simpler calculation method, the peak derived from tricoordinated boron, from 6 ppm to 6 ppm -6 ppm was calculated as a peak derived from tetracoordinate boron, and the area was integrated to calculate the ratio.

  For the measurement of the tetracoordinate boron ratio, ECA600 is not necessarily used, and any NMR measurement apparatus having a magnetic field strength equivalent to 600 MHz at another hydrogen resonance frequency can be obtained from the NMR spectrum obtained by measurement. It can be calculated in the same manner as

From the results in Table 1, it can be seen that the higher the firing temperature, the higher the tetracoordinate boron ratio. This is because H ₃ BO ₃ incorporated into magnesium hydroxide before firing is tri-coordinated as shown in Fig. 7 of Materials Transactions, vol. 54, No. 9, (2013) P.1809. This is considered to be due to the fact that it exists and then gradually becomes four-coordinated with firing.

  Furthermore, the tetracoordinate boron ratio is controlled by performing humidity adjustment such as drying or moisture absorption treatment on the fired product after firing. That is, a desired tetracoordinate boron ratio can be obtained by subjecting the fired product to a drying treatment or a moisture absorption treatment. As preferable conditions for humidity control, the drying treatment is performed at 100 ° C. to 400 ° C. (more preferably 100 ° C. to 300 ° C.), and the moisture absorption treatment is performed at 10 ° C. to 50 ° C. (more preferably 20 ° C. to 40 ° C.). As the treatment time, a drying treatment time or a moisture absorption treatment time is appropriately selected so that a desired tetracoordinate boron ratio is obtained.

  For example, Table 2 shows powders for annealing separator containing No. 5 magnesium oxide as the main component in Table 1 subjected to drying treatment at 200 ° C. for 6 hours to 48 hours. Table 3 shows the results of moisture absorption treatment of No. 2 magnesium oxide in Table 1 which was left in a room at 22 ° C. and 70% humidity for 1 to 42 days.

  From the results in Table 2, it was found that the tetracoordinate boron ratio can be lowered by drying at 200 ° C. Specifically, the 4-coordinate boron ratio could be reduced from 60% to 55% by drying the No. 5 magnesium oxide in Table 1 for 24 hours.

  The results in Table 3 also revealed that the tetracoordinate boron ratio can be increased by leaving it indoors as a moisture absorption treatment. Specifically, the four-coordinate boron ratio could be increased from 48% to 82% by moisture absorption treatment of No. 2 magnesium oxide in Table 1 for 14 days.

Next, the steel sheet slab containing C: 0.045% by mass, Si: 3.25% by mass, Mn: 0.070% by mass, Al: 80ppm, N: 40ppm, S: 20ppm is heated to a temperature of 1200 ° C and then hot. The steel sheet was rolled to form a hot-rolled sheet coil having a thickness of 2.0 mm. Next, it was cold-rolled with a tandem rolling mill to a final cold-rolled sheet thickness of 0.23 mm. Thereafter, decarburization annealing is performed for 90 seconds at a soaking temperature of 850 ° C., and an annealing separator mainly composed of magnesium oxide shown in Tables 1 to 3 is applied and wound into a coil shape. After heat-treating at a temperature of ℃ / h and finish annealing at 1200 ° C for 20 hours, the annealing separator was removed with a brush. Thereafter, smooth annealing was performed at 800 ° C. for 30 seconds in a non-oxidizing atmosphere of N ₂ 98% -H ₂ 2%.

The magnetic flux density B ₈ , iron loss W _17/50 , oxygen content of the steel sheet, boron content, and repeated bending characteristics of the sample thus obtained were investigated. For magnetic flux density and iron loss, a tensile stress of 10 MPa was mechanically applied to the steel sheet, and the test was conducted in accordance with the JISC2550-1 Epstein test. The amount of oxygen in the steel sheet was measured by an inert gas melting infrared absorption method, and the amount of boron (B) was measured by a methyl borate-distilled curcumin spectrophotometric method. The repeated bending characteristics were measured using the method of JISC2550 (2000).

Table 4 shows the magnesia powder used in the experiment and its 4-coordinated boron ratio, the boron content of the magnesia powder (mass%), the magnetic flux density B ₈ , the iron loss W _17/50 , the oxygen content of the steel sheet and the boron content (mass ppm) ), Showing repeated bending properties.
As shown in Table 4, when the amount of boron is small (No. 1-3) and when the tetracoordinate boron ratio is low (No. 1-1, No. 1-2, No. 2-5), the steel plate There is a large amount of oxygen remaining (namely, surface oxide = residual forsterite film) and the iron loss is inferior. When the amount of boron is too large (No. 1-4), boron remains in the steel sheet, resulting in an increase in iron loss and a decrease in the number of repeated bending.

  The iron loss was determined to be 0.85 W / kg or less considering the magnetic flux density (1.91-1.93T). The number of repeated bendings was 10 or more. The analytical value (mass ppm) of B was judged to be good when it was less than 20 mass ppm, and the analytical value (mass ppm) of oxygen was judged to be good when it was 20 mass ppm or less.

Next, the reasons for limiting the respective constituent requirements of the present invention will be described.
The powder for annealing separator mainly composed of magnesium oxide for grain-oriented electrical steel sheet according to the present invention contains boron in an amount of 0.04 mass% to 0.30 mass% (preferably 0.05 mass% to 0.20 mass%). . If the boron content is less than 0.04% by mass, the oxygen remaining rate after finish annealing becomes high, and consequently the iron loss is inferior. If it exceeds 0.30% by mass, B penetrates into the steel sheet during finish annealing to form Fe ₂ B, resulting in an increase in iron loss and a decrease in the number of repeated bending.

  Further, the ratio of tetracoordinate boron in boron is 50% or more (preferably 55% or more and 95% or less). That is, when the tetracoordinate boron ratio is lower than 50%, the forsterite film forming ability at high temperature is improved, the adhesion between the steel sheet and the film is improved, and the separation agent removing process after annealing is mechanically performed with a brush or the like. Film removal cannot be facilitated, surface residue increases, and iron loss increases.

There are various methods for adjusting the tetracoordinate boron ratio. For example, as shown in Tables 1 to 3 above, the method for adjusting the firing temperature, etc., and adjustment by operations such as drying and moisture absorption after firing. In addition, a method in which a compound having a known 4-coordination ratio (eg, Mg ₂ B ₂ O ₅ , MgB ₆ O ₁₀ , Mg ₃ B ₂ O _6, etc.) is conceivable.

The annealing separator powder may further contain phosphorus (P) in an amount of 0.03% by mass or more and 0.30% by mass or less in terms of P ₂ O ₅ . B contributes to film reactivity at high temperatures, while P has a function to improve film reactivity at low temperatures. Therefore, by adding P, the film formation amount at a low temperature is controlled to be constant, thereby reducing the influence of steel plate oxidation due to moisture brought in, and improving the film formation controllability by controlling B more. Can do. When P is less than 0.03% by mass in terms of P ₂ O ₅ , the improvement effect cannot be obtained, and when the addition amount is large, the improvement effect and cost increase are not balanced, so the addition amount is 0.30 mass% or less. It is preferable. In addition to the above, in the powder for annealing separator, impurities that volatilize as Igloss (ignition loss), mainly moisture, carbon dioxide gas, organic matter, impurities such as CaO, SiO ₂ , Al ₂ O ₃ May also be included.

  The annealing separator powder mainly composed of magnesium oxide of the present invention is produced by firing the raw material, and the main raw material includes magnesium hydroxide and magnesium carbonate. B and P are preferably adjusted in advance at the raw material stage by addition or purification. In general, the cake is in the form of a cake containing a large amount of moisture before baking, but the moisture content is desirably 20% or less of the cake weight (that is, 80% or more as a raw material solid content).

  Magnesium oxide produced by firing is preferably adjusted in particle size by pulverization. The particle size is preferably 1.0% by mass or less with a 325 mesh sieve residue. If the sieve residue exceeds 1.0% by mass, it may cause the surface of the steel sheet to be pressed, and it may take time to install a sieve during the manufacturing process of the electrical steel sheet to prevent it. The reason why 325 mesh (aperture 45 μm) is used for the sieve is that the relationship between the size of the coarse particles and the coating thickness of the annealing separator is just right from the viewpoint of preventing the scratches after annealing.

  Various impurities such as Ca, Si, Fe, Al, S, Na may be inevitably mixed in the powder depending on the manufacturing process. Therefore, in order to reduce the variation in the characteristics as much as possible, the annealing separator The content of magnesium oxide in the powder for use is preferably 95% by mass or more.

  Moreover, as an annealing separation agent for grain-oriented electrical steel sheets, in addition to the above powder containing magnesium oxide as a main component, a known substance such as titanium oxide can be mixed as an auxiliary agent.

  The steel plate used in the present invention is not particularly limited as long as it is a grain-oriented electrical steel plate. Usually, such a grain-oriented electrical steel sheet is obtained by first hot rolling a steel slab containing silicon by a known method and finishing it to a final thickness by one or multiple cold rolling sandwiching intermediate annealing. It is manufactured by subjecting it to recrystallization annealing and then applying an annealing separating agent, followed by final finishing annealing.

In addition, as the thickness of the steel sheet decreases, the proportion of the surface that contributes to the performance of the steel sheet increases, so the influence of the surface specularity on the iron loss also increases, and the characteristics required for the powder for annealing separators are also increased. Get higher. Therefore, the annealing separator powder of the present invention is more suitable than the conventionally known annealing separator powders, particularly when applied to a steel sheet having a thin plate thickness.
[Example]

Example 1
Nacalai Tesque's basic magnesium carbonate (MgCO ₃ ) ₄ Mg (OH) ₂ xH ₂ O was used as a starting material, which was slurried with pure water and then borax (Na ₂ B ₄ O ₅ (OH) ₄ · 8H ₂ O) and magnesium metaphosphate were mixed to obtain desired B and P concentrations as the powder after firing. This slurry was squeezed with a filter press to obtain a cake. The cake moisture content was 3%. Next, the cake was put into an alumina crucible and fired at a temperature and time shown in Table 5 in a box furnace in the air. After firing, this was pulverized to adjust the particle size to obtain a powder for an annealing separator. Table 5 shows the results of investigating the tetracoordinate boron ratio, the boron content, and the P content in the boron content of the powder thus obtained.

Next, steel containing C: 0.06% by mass, Si: 2.95% by mass, Mn: 0.07% by mass, Se: 0.015% by mass, Sb: 0.015% by mass and Cr: 0.03% by mass, the balance being Fe and inevitable impurities The slab is heated at 1350 ° C for 40 minutes, then hot rolled to a thickness of 2.6mm, then hot-rolled sheet annealed at 900 ° C and 60s, followed by intermediate annealing at 1050 ° C and 60s. Cold rolled to a final thickness of 0.23 mm. Then, decarburization annealing was performed, and the powder listed in Table 5 was applied as an annealing separator, heated to 1200 ° C at a rate of 25 ° C / h, and subjected to finish annealing that was held at 1200 ° C for 20 hours. Removed. Thereafter, smooth annealing was performed at 800 ° C. for 30 seconds in a non-oxidizing atmosphere of N ₂ 98% -H ₂ 2%.

Table 5 shows the results of measuring the magnetic flux density B ₈ , iron loss W _17/50 , oxygen content, boron content, and repeated bending characteristics for the _grain- oriented electrical steel sheet produced according to the above. The magnetic flux density and iron loss were tested according to the JISC2550-1 Epstein test by mechanically applying a tensile stress of 10 MPa to the steel sheet. The amount of oxygen in the steel sheet was measured by an inert gas melting infrared absorption method, and B was measured by methyl borate distillation separation curcumin absorptiometry. The repeated bending characteristics were measured using the method of JISC2550 (2000). The number of repeated bendings was determined to be 10 or more. The analytical value (mass ppm) of B was judged to be good when it was less than 20 mass ppm, and the analytical value (mass ppm) of oxygen was judged to be good when it was 20 mass ppm or less.

As shown in Table 5, if the powder contains boron in an amount of 0.04 mass% or more and 0.30 mass% or less and the tetracoordinate boron ratio is 50% or more, the amount of residual oxygen and iron loss after finish annealing are low, The appearance is highly uniform and the number of repeated bending can be increased. Furthermore, by including 0.03% by mass or more of P in terms of P ₂ O ₅ , a much lower oxygen residual amount can be obtained.

(Example 2)
Nacalai tex magnesium chloride hexahydrate was dissolved in pure water kept at 25 ° C. to obtain a saturated aqueous solution. This was reacted with calcium hydroxide to obtain magnesium hydroxide. The magnesium hydroxide thus obtained was washed with filtered water and again poured into pure water to obtain a magnesium hydroxide slurry. Predetermined amounts of sodium borate and calcium phosphate were added to the magnesium hydroxide slurry so that the desired B concentration and P concentration were obtained after firing.

  The magnesium hydroxide slurry thus prepared is squeezed into a cake with a filter press, and then calcined at 1000 ° C. for 40 minutes in an alumina crucible to obtain powders A and B, and further calcined at 1400 ° C. for 40 minutes. C and D were obtained. The particle size was adjusted by pulverization after firing. The obtained powders A and B were subjected to a moisture absorption treatment at 25 ° C. and 80% humidity for the number of days shown in Table 6, and the powders C and D were further dried at 200 ° C. for the time shown in Table 6. Went. Table 6 shows the results of investigating the tetracoordinate boron ratio, the boron content, and the P content in the boron contained in the powder thus obtained.

Next, the steel sheet slab containing C: 0.045% by mass, Si: 3.25% by mass, Mn: 0.070% by mass, Al: 80ppm, N: 40ppm, S: 20ppm is heated to a temperature of 1200 ° C and then hot. The steel sheet was rolled to form a hot-rolled sheet coil having a thickness of 2.0 mm. Next, it was cold-rolled with a tandem rolling mill to a final cold-rolled sheet thickness of 0.20 mm. Thereafter, decarburization annealing is performed for 90 seconds at a soaking temperature of 850 ° C., and a mixture of 100 g of the powder shown in Table 6 and 5.0 g of titanium oxide is applied as an annealing separator and wound into a coil shape. After heat-treating to 1200 ° C at 25 ° C / h and finishing annealing at 1200 ° C for 20 h, the annealing separator is removed with a brush, and then N ₂ 98% -H ₂ 2% in a non-oxidizing atmosphere Smooth annealing was performed at 800 ° C. for 30 seconds.

Table 6 shows the results of investigating the magnetic flux density B ₈ , iron loss W _17/50 , oxygen content, boron content, and repeated bending characteristics of the _grain- oriented electrical steel sheet manufactured according to the above. For magnetic flux density and iron loss, a tensile stress of 10 MPa was mechanically applied to the steel sheet, and the test was conducted in accordance with the JISC2550-1 Epstein test. The oxygen content of the steel sheet was measured by an inert gas melting infrared absorption method, and B was measured by methyl borate distillation separation curcumin absorptiometry. The repeated bending characteristics were measured using the method of JISC2550 (2000). The number of repeated bendings was determined to be 10 or more. The analytical value (mass ppm) of B was judged to be good when it was less than 20 mass ppm, and the analytical value (mass ppm) of oxygen was judged to be good when it was 20 mass ppm or less.

As shown in Table 6, the powder contains 0.04 mass% or more and 0.30 mass% or less of boron, and its 4-coordinate boron ratio is 50% or more, so that the amount of residual oxygen and iron loss after finish annealing are low. The appearance uniformity is high and the number of repeated bending can be increased. Furthermore, by including 0.03% by mass or more of P in terms of P ₂ O ₅ , a much lower oxygen residual amount can be obtained.

Claims (6)

A powder for an annealing separator having a magnesium oxide content of 95% by mass or more and containing 0.04% by mass to 0.30% by mass of boron,
An annealing separator powder, wherein the proportion of tetracoordinate boron in the boron is 55 to 95%. _{2. The} powder for annealing separator according to claim 1, wherein phosphorus is contained in an amount of 0.03 to 0.30 mass% in terms of P ₂ O ₅ .   The powder for annealing separator according to claim 1 or 2, wherein a 325 mesh sieve residue in the magnesium oxide powder is 1.0 mass% or less. A method for producing a powder for an annealing separator according to claim 1, wherein a raw material containing one or both of magnesium hydroxide and magnesium carbonate and boron is fired, and thereafter
A method for producing a powder for an annealing separator, wherein the tetracoordinate boron ratio is adjusted by adjusting the humidity of the fired product.   The said raw material contains 80 mass% or more in total of any one or both of the said magnesium hydroxide and the said magnesium carbonate, The manufacturing method of the powder for annealing separators of Claim 4 characterized by the above-mentioned. The annealing according to claim 4 or 5, wherein the raw material contains 0.04 mass% or more and 0.30 mass% or less of the boron, and the proportion of tetracoordinate boron in the boron is 55 to 95%. Method for producing powder for separating agent .