JP2014193790A - MgO FOR ANNEALING SEPARATING AGENT - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide MgO for annealing separating agents which enables stable production of grain oriented silicon steel having a uniform and high-quality forsterite coat even when used as an annealing separating agent after baking in a rotary kiln.SOLUTION: MgO for annealing separating agents has a CAA40% of 60-100 s, CAA80% of 150-300 s and a BET specific surface area of 12-35 m/g and contains 0.2-1.0 mass% of CaO, 0.01-0.04 mass% of Cl and 0.15-0.50 mass% of P in terms of PO. Preferably, the MgO is formed by baking Mg(OH)of a BET specific surface area of 10-25 m/g, and the P content in terms of PO[PO](mass%) and the Cl content(mass%) meet equation (1): [PO]≥125[Cl]-9.95[Cl]+0.348.

Description

  The present invention relates to MgO for annealing separator, and specifically relates to MgO for annealing separator suitable for an annealing separator used for finish annealing of grain-oriented electrical steel sheets.

  A so-called grain-oriented electrical steel sheet is obtained by hot rolling a steel slab adjusted to a predetermined component composition, and subjecting it to hot-rolled sheet annealing as necessary to form a hot-rolled sheet once or coldly sandwiched between two or more times. It is generally manufactured by rolling into a cold-rolled sheet, followed by decarburization annealing, finish annealing, and then flattening annealing. In the above manufacturing method, an annealing separator mainly composed of magnesia (MgO) is applied to the surface of the decarburized and annealed steel sheet in order to prevent the steel sheets wound around the coil from fusing with each other in finish annealing at a high temperature for a long time. To be done.

Here, the MgO applied to the surface of the steel sheet reacts with SiO _{2 on the} surface layer of the steel sheet in finish annealing to form a forsterite (Mg ₂ SiO ₄ ) -based film. In addition, MgO also affects the precipitation behavior of the inhibitor in the steel in the above reaction process, and therefore has a great influence on the magnetic properties of the product plate through secondary recrystallization. Therefore, in order to obtain a grain-oriented electrical steel sheet having excellent coating properties and magnetic properties, it is important to use optimum MgO.

  By the way, in recent years, in order to reduce the manufacturing cost of the grain-oriented electrical steel sheet, the material coil has been increased in size. In addition, in order to reduce the manufacturing cost of MgO, switching from the conventional method using a muffle furnace to the method using a rotary kiln is being promoted. As a result, as compared with the conventional case, there is a problem that variation in coating characteristics in the coil longitudinal direction and width direction of the grain-oriented electrical steel sheet becomes large, resulting in coating failure. Here, the film defect means a point defect (bare spot), an appearance defect such as blackening or white film formation, a non-uniform appearance such as a black streak pattern, or a poor adhesion of the film. .

In order to solve the above problem, Patent Document 1 proposes a method of blending MgO for annealing separator with highly active MgO. This is to compensate for the demerit that the activity distribution of the rotary kiln made of MgO is narrow, and by using MgO having a wide activity distribution, an attempt is made to obtain a steel sheet having uniform coating properties and excellent magnetic properties. Patent Document 2 proposes a technique for improving both magnetic properties and film properties by controlling the specific surface area and crystallites of Mg (OH) ₂ which is a raw material of MgO made by rotary kiln. Patent Document 3 proposes a technique for improving the coating characteristics by optimizing the contents of Ca, P, Si and S in MgO.

JP2008-260668 Japanese Patent No. 4192283 Japanese Patent No. 3761867

  However, even if these techniques are applied, the problems of the rotary kiln made MgO have not yet been completely solved. In particular, in order to increase the production of grain-oriented electrical steel sheets, when the time for decarburization annealing and finish annealing is shortened, there is a problem that the coating characteristics are likely to deteriorate in part of the length direction and width direction of the coil. there were.

  The present invention has been made in view of the above problems in the prior art, and its purpose is to have a uniform and high-quality forsterite film even when MgO fired in a rotary kiln is used as an annealing separator. An object of the present invention is to provide MgO for an annealing separator that can stably produce a heat-resistant electrical steel sheet.

  The inventors diligently studied a means for solving the above problems. As a result, by optimizing the content of trace components contained in rotary kiln MgO and the MgO manufacturing process, it is possible for an annealing separator capable of stably producing a grain-oriented electrical steel sheet having a uniform and high-quality coating. The present inventors have found that MgO can be obtained and have completed the present invention.

That is, the present invention is CAA 40%: 60 to 100 seconds, CAA 80%: 150 to 300 seconds, BET specific surface area: 12 to 35 m ² / g, CaO: 0.2 to 1.0 mass%, Cl: 0 .01～0.04Mass% and _P: a MgO for annealing separator containing 0.15～0.50Mass% in P 2 _{O 3} conversion.

Annealing separator for MgO of the present _invention, P content of P 2 _{O 3} in terms _{[P 2} O 3] and (mass%) content of Cl and (mass%), but the following (1);
[P ₂ O ₃ ] ≧ 125 [Cl] ² −9.95 [Cl] +0.348 (1)
It is characterized by satisfying.

The MgO for annealing separator of the present invention is characterized by firing Mg (OH) ₂ having a BET specific surface area of 10 to 25 m ² / g.

The MgO for annealing separator of the present invention is characterized in that it contains 50 mass% or more of MgO obtained by firing Mg (OH) ₂ having a BET specific surface area of 10 to 25 m ² / g.

  According to the present invention, even when inexpensive rotary kiln-made MgO is used as an annealing separator, a grain-oriented electrical steel sheet having uniform and high-quality coating properties can be stably produced, so that high-quality directionality is achieved. It is possible to provide an electromagnetic steel sheet at a low cost.

It is Cl concentration and _P 2 _{O 3} concentration contained in the MgO is a graph showing the effect on film quality.

In order to solve the problem that MgO produced by firing Mg (OH) ₂ in a rotary kiln, that is, the forsterite film characteristic formed on the steel sheet surface is not stable, MgO was produced under various conditions, and this was applied to an annealing separator, and the following experiment was conducted to investigate the effect on the coating properties of grain-oriented electrical steel sheets.

  C: 0.07 mass%, Si: 3.3 mass%, Mn: 0.070 mass%, acid-soluble Al: 0.022 mass%, N: 0.0080 mass%, Se: 0.015 mass% and Sb: 0.025 mass% A steel slab containing the composition of Fe and the inevitable impurities in the balance is heated at 1400 ° C. for 30 minutes, and then hot-rolled to form a hot-rolled sheet having a sheet thickness of 2.3 mm at 1050 ° C. × 60 seconds. After hot-rolled sheet annealing, the first cold rolling is performed with an intermediate sheet thickness of 1.5 mm. After the intermediate annealing at 1100 ° C. for 45 seconds, the second cold rolling is performed with a final sheet thickness of 0.22 mm. It was a sheet.

Thereafter, the cold-rolled sheet was decarburized and annealed at 840 ° C. for 30 seconds in a mixed atmosphere of (H ₂ + N ₂ + H ₂ O), and then an annealing separator mainly composed of MgO was applied to the steel sheet surface and dried. Then, finish annealing was performed. The MgO is obtained by firing Mg (OH) ₂ having various specific surface areas in a rotary kiln, and when used as an annealing separator, TiO ₂ : 6 parts by mass was added as an agent.
The steel sheet after the final finish annealing is then subjected to a flattening annealing at 800 ° C. for 30 seconds, which is used for shape correction and baking of a tension coating mainly composed of phosphate and colloidal silica. It was.

With respect to the product coil thus obtained, the appearance of the film was visually inspected in the final inspection process, and the occurrence length rate (film defect rate) of film defects such as point defects and black streaks was investigated.
In addition, from the portion with the most inferior coating appearance, test pieces having a length of 280 mm × width of 30 mm with the length direction being the rolling direction are collected, and the test pieces are wound around round bars having various diameters at intervals of 5 mm The adhesiveness of the coating was evaluated by determining the minimum diameter that does not peel off.

FIG. 1 shows, as an example of the above experimental results, the influence of the contents of Cl and P contained in MgO (P is a P ₂ O ₃ converted value) on the film properties. From this figure, the P content is optimized according to the Cl content. Specifically, the P ₂ O ₃ converted value of P [P ₂ O ₃ ] and the Cl content are as follows. (1) formula;
[P ₂ O ₃ ] ≧ 125 [Cl] ² −9.95 [Cl] +0.348 (1)
It was clarified that the grain-oriented electrical steel sheet having excellent coating quality can be produced even with MgO subjected to rotary kiln firing by controlling to satisfy the above.

The reason for this is not yet clear at present, but the above effect cannot be obtained when CaO is low. Therefore, P and Cl form a compound such as Ca ₅ (PO ₄ ) ₃ Cl. And, since it has the effect of mitigating the adverse effect of CaO that inhibits the reaction of the coating, it is believed that MgO was activated and the coating quality was improved over the entire length of the coil. In order to eliminate the adverse effects of CaO, simply reducing CaO causes the film formation reaction to proceed excessively, and on the other hand, point defects are generated, making it impossible to obtain a uniform film.

Table 1 shows the influence of the BET specific surface area of Mg (OH) ₂ that is a raw material of MgO on the coating quality. From Table 1, it can be seen that by controlling the BET specific surface area of Mg (OH) ₂ in the range of 10 to 25 m ² / g, both the film defect rate and the adhesion are remarkably improved. The reason for this is that MgO is known to inherit the raw material Mg (OH) ₂ hexagonal disk shape, but if the specific surface area of the raw material Mg (OH) ₂ is increased, P and Cl are concentrated. Since the MgO on the hexagonal disk surface where P and Cl are concentrated starts the reaction at the initial stage of finish annealing, the coating reaction is started at a low temperature by the concentration of P and Cl, and the coating quality is further improved. Conceivable.

In addition, it is not indispensable that MgO fired by rotary kiln according to the present invention strictly inherits the shape of the raw material Mg (OH) ₂ hexagonal disk, and even if the shape is somewhat broken, a sufficient effect can be obtained. . The reason is that the concentration of P and Cl supplements the activation of MgO.

In Table 1, No. 10 is an example in which MgO produced from Mg (OH) ₂ having a specific surface area of more than 25 m ² / g was used as an annealing separator. I could not. This is considered to be caused by the fact that the specific surface area of Mg (OH) ₂ is so large that the particle diameter of the obtained MgO becomes too small, causing aggregation.

The MgO of the present invention will be further described. It is necessary that the CAA is 40%: 60 to 100 seconds, the CAA is 80%: 150 to 300 seconds, and the BET specific surface area is 12 to 35 m ² / g. Here, the above-mentioned CAA (Critic Acid Activity, citric acid activity) is an index value indicating the reaction activity of citric acid and MgO, and CAA 40% and CAA 80% are at a temperature of 30 ° C. and 0.4 N, respectively. Time until final reaction when 40 mass% and 80 mass% of the final reaction equivalent of MgO are respectively administered in the citric acid aqueous solution, stirred, and reacted (time until citric acid is consumed and the solution becomes neutral) The activity is expressed by the reaction time.

  Here, the reason why the values of CAA 40% and CAA 80% of MgO of the present invention are 60 to 100 seconds and 150 to 250 seconds, respectively, is that when each CAA value is less than the above lower limit value, the reactivity is too strong. Since forsterite is generated rapidly, many point-like defects are generated in the film. Conversely, when each CAA value exceeds the above upper limit value, the reactivity is too weak to generate forsterite. This is because the adhesion of the coating is lowered. Preferred CAA 40% and CAA 80% are in the range of 70 to 90 seconds and 170 to 230 seconds, respectively.

In addition, when manufacturing Mg (OH) ₂ by rotary kiln baking like MgO of this invention, the value of CAA can be adjusted by changing the baking temperature of a rotary kiln. On the other hand, MgO produced by firing in a muffle furnace is characterized by having a wide activity distribution. Therefore, it is usual that the values of CAA 40% and CAA 80% are largely separated. It is difficult to obtain the effects of the present invention.

On the other hand, the reason why it is necessary to control the specific surface area of MgO in the range of 12~35m ² / g, when the value of the specific surface area is less than ^12m 2 / g, since the reactivity with the subscale is reduced, When the coating film becomes a white film and the adhesion is reduced. On the contrary, when it exceeds 35 m ² / g, the reaction with the subscale proceeds rapidly, and many point-like defects are generated in the coating film. Because it becomes like this. A preferred specific surface area is in the range of 15 to 30 m ² / g.

The MgO of the present invention must contain (add?) Ca, Cl, and P as trace elements in the following ranges.
CaO: 0.2 to 1.0 mass%
Since CaO is a component having an effect of adjusting the film forming reaction, it is necessary to control it within the range of 0.2 to 1.0 mass%. When CaO is less than 0.2 mass%, the reaction proceeds excessively, so that a large number of point defects are generated in the film and the effect of adding Cl or P described later cannot be obtained. On the other hand, if it exceeds 1.0 mass%, the amount of film formation is insufficient, so that the film becomes a white film and the adhesiveness decreases. Preferably it is the range of 0.2-0.5 mass%.

Cl: 0.01-0.04 mass%
Since Cl is a component having an effect of promoting a film forming reaction, it is necessary to control it within a range of 0.01 to 0.04 mass%. When Cl is less than 0.01 mass%, the reaction becomes insufficient, so that the film becomes a white film and the adhesion is lowered. On the contrary, when the upper limit is exceeded, the reaction becomes excessive, and a large number of point defects are generated in the film. Preferably it is the range of 0.02-0.03 mass%.

_P: P 2 _{O 3} 0.15~0.50mass% in terms of
Since P is a component having an effect of promoting the film forming reaction, it is necessary to control it in the range of 0.15 to 0.50 mass% in terms of P ₂ O ₃ . When P is less than 0.15 mass% in terms of P ₂ O ₃ , the reaction becomes insufficient, and a uniform coating cannot be obtained over the entire length of the coil. On the other hand, when it exceeds 0.50 mass%, the reaction becomes excessive, so that the magnetic characteristics and film characteristics of the entire coil are deteriorated. Preferably it is the range of 0.25-0.40 mass%.

In addition, MgO of the present invention has a P content equivalent to P ₂ O ₃ [P ₂ O ₃ ] and a Cl content represented by the following formula (1):
[P ₂ O ₃ ] ≧ 125 [Cl] ² −9.95 [Cl] +0.348
It is preferable to contain and satisfy. This is because, as shown in FIG. 1, good film quality can be ensured within a range satisfying the above formula.

In addition, MgO of the present invention may contain, in addition to the above-described components such as B, SO ₃ , F, I, Br, etc., which are conventionally known as auxiliary agents added to the annealing separator, in a total amount of 20 mass%. You may contain below.

Further, MgO of the present invention is produced by firing Mg (OH) ₂ in a rotary kiln, but it is more excellent when the value of the specific surface area of the raw material Mg (OH) ₂ is 10 to 25 m ² / g. The effect of improving the coating quality can be obtained. When the specific surface area of Mg (OH) ₂ is less than 10 m ² / g, the sinterability of MgO increases, it becomes difficult to obtain desired characteristics, and the coating tends to be non-uniform. On the other hand, when it exceeds 25 m ² / g, the particle diameter of the obtained MgO becomes too small and agglomerates, and troubles are likely to occur when the annealing separator is applied. More preferably, it is the range of 13-22 m < ² > / g, More preferably, it is the range of 15-22 m < ² > / g.

The MgO for annealing separator of the present invention does not necessarily use 100 mass% of MgO produced by controlling the specific surface area of the raw material Mg (OH) ₂ within the above range, and adjusts the slurry viscosity and MgO cohesiveness. Therefore, it can be used by mixing with MgO having other characteristics. That is, the effect of the present invention can be obtained by containing 50 mass% or more of MgO obtained by adjusting the specific surface area of the raw material Mg (OH) ₂ to the above range. More preferably, it is 70 mass% or more.

MgO produced as described above is appropriately added and mixed with a known auxiliary agent such as TiO ₂ and applied to the surface of the steel sheet before finish annealing. As a method of applying, a conventionally known method such as a method of applying / drying after slurrying and a method of electrostatic coating can be used.
The steel sheet after application of the annealing separator is then wound around a coil and subjected to finish annealing. In this finish annealing, secondary recrystallization, forsterite film formation, and purification of impurities in the steel are performed, and basic characteristics as a grain-oriented electrical steel sheet are imparted.
The steel sheet after finish annealing is then subjected to flattening annealing that combines shape correction, insulation coating application, and baking, as necessary, after removing the unreacted annealing separator. The grain-oriented electrical steel sheet may be subjected to magnetic domain refinement by a method such as groove formation, laser irradiation, plasma jet irradiation, or electron beam irradiation.

C: 0.065 mass%, Si: 3.4 mass%, Mn: 0.065 mass%, acid-soluble Al: 0.024 mass%, N: 0.0085 mass%, Se: 0.018 mass%, and Sb: 0.020 mass% The slab for grain-oriented electrical steel sheet, the balance of which is composed of Fe and inevitable impurities, is heated at 1400 ° C. for 80 minutes, and then hot-rolled to obtain a hot-rolled sheet having a thickness of 2.2 mm at 1075 ° C. * Hot rolled sheet annealing for 60 seconds, intermediate sheet thickness of 1.5 mm by first cold rolling, intermediate annealing at 1100 ° C. for 45 seconds, final plate thickness of 0.22 mm by second cold rolling The cold-rolled sheet was used.
Thereafter, the cold-rolled sheet was subjected to decarburization annealing at 840 ° C. for 30 seconds in a mixed atmosphere of (H ₂ + N ₂ + H ₂ O), and then the annealing separator mainly composed of MgO shown in Table 2 was used. After applying and drying, finish annealing was performed. The above MgO is obtained by rotary kiln firing of Mg (OH) ₂ having various specific surface areas, and when used as an annealing separator, As the agent, TiO ₂ : 7 parts by mass and SrSO ₄ : 2 parts by mass were added.
The steel sheet after the finish annealing is then subjected to flattening annealing at 800 ° C. for 30 seconds, which serves as shape correction and baking of a tension coating mainly composed of phosphate and colloidal silica, and a product plate (coil) did.

With respect to the product coil thus obtained, the appearance of the film was visually inspected in the final inspection process, and the occurrence ratio of the film defects (film defect rate) was investigated.
In addition, a test piece having a length of 280 mm and a width of 30 mm with the rolling direction as the rolling direction is taken from the portion having the most inferior coating appearance, and the test piece is wound around a round bar having various diameters at intervals of 5 mm, and the coating is peeled off. The adhesion of the film was evaluated by determining the minimum diameter that was not used.

The measurement results are also shown in Table 2. “Gray uniform” described in the coating appearance column of Table 2 indicates the state in which the coating quality is the best, “slightly non-uniform” indicates the next best state, and “black non-uniform” indicates the black streak. The state in which a pattern such as “a point-like defect occurs” indicates a state in which the ground iron is exposed in a point shape.
From the results in Table 2, it can be seen that even with MgO subjected to rotary kiln firing, by satisfying the conditions of the present invention, a grain-oriented electrical steel sheet having excellent coating quality over the entire length of the product coil can be obtained.

C: 0.055 mass%, Si: 3.2 mass%, Mn: 0.065 mass%, Se: 0.020 mass%, Sb: 0.027 mass% and Cu: 0.03 mass%, the balance being Fe and inevitable A slab for grain-oriented electrical steel sheets comprising a component composition of mechanical impurities is heated at 1400 ° C. for 30 minutes and then hot rolled to form a hot-rolled sheet having a thickness of 2.4 mm, and hot-rolled sheet annealing at 1000 ° C. for 60 seconds is performed. After the application, the first cold rolling was performed to obtain an intermediate sheet thickness of 0.6 mm, and after the intermediate annealing at 1000 ° C. for 60 seconds, the second cold rolling was performed to obtain a cold rolled sheet having a final sheet thickness of 0.22 mm.
Thereafter, the cold-rolled sheet was subjected to decarburization annealing at 840 ° C. for 30 seconds in a mixed atmosphere of (H ₂ + N ₂ + H ₂ O), and then an annealing separator mainly composed of MgO shown in Table 3 was applied. After drying, finish annealing was performed. The above MgO has a specific surface area different from A, B2 Type: the ^{(A 7.2m 2 /g,B:16.3m 2 / g} ) of Mg _{(OH) 2} was obtained as a rotary kiln calcination MgO, Table 3 is mixed at a ratio of A: B shown in FIG. 3, and when used as an annealing separator, TiO ₂ : 3 parts by mass, MgSO ₂ as an auxiliary agent with respect to 100 parts by mass of the above MgO. ₄ : 2 parts by mass were added.
The steel sheet after the finish annealing is then subjected to flattening annealing at 800 ° C. for 30 seconds, which is used for shape correction and baking of a tension coating mainly composed of phosphate and colloidal silica. did.

With respect to the product coil thus obtained, the appearance of the film was visually inspected in the final inspection process, and the occurrence ratio of the film defects (film defect rate) was investigated.
In addition, a test piece having a length of 280 mm and a width of 30 mm with the rolling direction as the rolling direction is taken from the portion having the most inferior coating appearance, and the test piece is wound around a round bar having various diameters at intervals of 5 mm, and the coating is peeled off. The adhesion of the film was evaluated by determining the minimum diameter that was not used.

The results of the above measurements are also shown in Table 3. From Table 3, it can be seen that a grain-oriented electrical steel sheet having a remarkably excellent coating quality can be obtained under the condition that the specific surface area contains a large amount of MgO obtained by rotary kiln firing of Mg (OH) ₂ of B suitable for the present invention.

Claims (4)

CAA 40%: 60 to 100 seconds, CAA 80%: 150 to 300 seconds,
BET specific surface area: 12-35 m ² / g,
CaO: 0.2~1.0mass%, Cl: 0.01~0.04mass % and _{P: P} 2 _{O 3} annealing separator for MgO containing 0.15～0.50Mass% in terms of. P content of P ₂ O ₃ in terms _{[P 2} O 3] and (mass%) content of Cl and (mass%), but annealed according to claim 1, characterized in that satisfies the following formula (1) MgO for separating agent.
[P ₂ O ₃ ] ≧ 125 [Cl] ² −9.95 [Cl] +0.348 (1) The MgO for annealing separator according to claim 1 or 2, wherein Mg (OH) ₂ having a BET specific surface area of 10 to 25 m ² / g is fired. The MgO for annealing separator according to claim 1 or 2, which contains 50 mass% or more of MgO obtained by baking Mg (OH) ₂ having a BET specific surface area of 10 to 25 m ² / g.

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