JP6624180B2 - Grain-oriented electrical steel sheet and its manufacturing method - Google Patents

Description

  The present invention relates to a grain-oriented electrical steel sheet and a method for producing the same. Specifically, the present invention relates to a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties when manufactured into a transformer, and a method for manufacturing the same.

  Since the grain-oriented electrical steel sheet is mainly used as a core material of a transformer, it is strongly required that the grain-oriented electrical steel sheet has excellent magnetic properties, especially low iron loss. For this reason, grain-oriented electrical steel sheets are conventionally subjected to decarburizing annealing also serving as primary recrystallization annealing on a cold-rolled Si-containing steel sheet, and applying an annealing separator mainly containing MgO, followed by secondary annealing in finish annealing. It is manufactured by a method in which recrystallization is caused and crystal grains are highly aligned in a {110} <001> direction (a so-called Goss direction). The above-mentioned finish annealing is performed by batch annealing performed in a state wound in a coil, because it requires about 10 days including the annealing for secondary recrystallization and the purification treatment for raising the temperature up to about 1200 ° C. I have.

During the finish annealing, a sub-scale mainly composed of SiO ₂ formed on the steel sheet surface during decarburization annealing and an annealing separator mainly composed of MgO applied to the steel sheet surface after decarburization annealing are composed of 2MgO + SiO ₂ → Mg. ₂ The reaction of SiO ₄ occurs, and a vitreous forsterite film is formed on the surface of the steel sheet. The above forsterite film has an effect of imparting tensile stress to the surface of the steel sheet and improving magnetic properties in addition to imparting insulation and corrosion resistance, and therefore is required to be uniform and excellent in adhesion.

  However, when the film thickness is too thick, the space factor decreases, and when used as a transformer, the stacking thickness becomes too thick to increase the size. As a result, copper loss increases, or conversely, the size is reduced to a predetermined size. For this reason, there is a problem that the number of stacked sheets is reduced and iron loss increases. Therefore, it is also required to reduce the film thickness as much as possible.

  Further, the forsterite film is formed so as to bite into the inside of the base iron, and thereby mechanically adheres to the steel sheet surface. However, when the unevenness at the interface between the ground iron and the coating becomes severe, residual magnetization is generated in the unevenness, and the hysteresis loss increases. Therefore, there is a trade-off relationship between the coating adhesion and the hysteresis loss, and it has been difficult to achieve a balance between the two.

  In addition, although the technology of forming an insulating coating directly on the steel sheet surface without forming a forsterite coating has also been developed, at this time, it is difficult to secure the coating adhesion, and the insulation and withstand voltage characteristics, Corrosion resistance is also insufficient. Therefore, the need for a grain-oriented electrical steel sheet having a forsterite film is still high.

  As a technique for improving the space factor, Patent Literature 1 describes a technique in which Ba is added to a non-hydratable oxide as an annealing separator. Patent Document 2 discloses a technique for forming a film in which the Young's modulus and the coefficient of linear expansion satisfy certain conditions.

JP-A-9-118922 JP-A-6-248465

However, in the method of Patent Document 1, although the space factor is high because no undercoat is formed, the adhesion of the coating, insulation, corrosion resistance, and the like are insufficient. Further, the method of Patent Document 2 has a problem that the coating is easily peeled off because the coating tension is high and the film thickness is thin.
Thus, a grain-oriented electrical steel sheet having good adhesion, low iron loss (trans iron loss) when supplied to a transformer, and a high space factor has not been obtained.

  The present invention has been made in view of the above circumstances, and has an object to provide a grain-oriented electrical steel sheet having a high space factor in addition to having excellent film adhesion and reduced transformer iron loss. And

The present inventors have intensively studied to solve the above-mentioned problems. As a result, by forming a base coat so that the surface has irregularities and then smoothing the surface, in addition to having excellent coat adhesion and reduced transformer iron loss, a high space factor is obtained. It has been found that a grain-oriented electrical steel sheet can be obtained.
In order to achieve the above object, an appropriate amount of alkaline earth metal is contained in the annealing separator, and after finish annealing, the surface of the formed undercoat is thinly ground. , Sb, Sn and P were found to be important in the steel.

Hereinafter, an experiment which led to the present invention will be described.
(Experiment)
A steel containing 0.068% by mass of C, 3.41% by mass of Si, 0.07% by mass of Mn, 0.030% by mass of Al, and 0.008% by mass of N was melted and made into a steel material (steel slab) by a continuous casting method. Then, heated to 1410 ℃, hot-rolled to a hot-rolled sheet with a thickness of 2.2 mm, subjected to hot-rolled sheet annealing at 1050 ℃ × 60 seconds, and then subjected to primary cold rolling to 1.7 mm of the intermediate sheet thickness After performing an intermediate annealing at 1100 ° C. for 80 seconds, a cold-rolled sheet having a final sheet thickness of 0.23 mm was obtained by rolling in a warm region at 200 ° C.

Next, decarburization annealing was performed at 830 ° C. for 100 seconds in a humid atmosphere of 50 vol% H ₂ -50 vol% N ₂ and a dew point of 57 ° C.
Thereafter, it contains titanium oxide and sodium hydroxide, and the remainder is an annealing separator for magnesium oxide, containing 5 mass% of titanium oxide in terms of Ti, 40 mass ppm of sodium hydroxide in terms of Na, and having a Ca concentration of 0.2 mass. % And 3.2% by mass or less of an annealing separator mainly composed of magnesium oxide, which was applied to the surface of the steel sheet and dried. When the impurities of titanium oxide and sodium hydroxide were analyzed, the concentrations of Ca and other alkaline earth metals were all below the detection limit.

  The steel sheet was subjected to a secondary recrystallization annealing and a finish annealing including a purification treatment at 1200 ° C. for 7 hours in a hydrogen atmosphere to form a base coat. Then, an unreacted annealing separating agent was removed, and further, a particle size The surface roughness of the base coat was variously changed by grinding the surface of the base coat with a brush roll having 100, # 240 (JIS R6001) abrasive grains. Thereafter, a coating liquid was applied to the surface of the undercoating film so as to have a coating thickness of 1 μm after baking, and flattening annealing was performed at 800 ° C. for 30 seconds while baking the coating liquid.

  The steel sheet thus obtained was evaluated for the space factor, film adhesion, and rust generation rate by a corrosion test, and a 1 MVA (megavolt amp) transformer was manufactured using the steel sheet. Loss (trans iron loss) was measured. The measurement results are shown in FIGS. 1 to 9 in relation to the Ca concentration of the agent during annealing separation. Here, the coating adhesion was evaluated by performing a strain relief annealing at 800 ° C. for 2 hours and then bending with a round bar to evaluate a minimum diameter at which the coating did not peel. Also, after removing the coating film by alkali washing the steel sheet, using a surface roughness meter, while measuring the arithmetic average roughness Ra of the undercoat surface, observing the undercoat cross-section by SEM observation, The film thickness was measured. Specifically, the arithmetic average roughness Ra was measured three times with a measuring length of 10 mm in the direction perpendicular to the rolling direction from the center of the base film surface in the width direction using a stylus-type roughness meter, and the average value was calculated. I took it. The space factor was calculated by a method specified in JIS C2550.

From FIG. 1, it can be seen that the surface roughness of the undercoat increases as the Ca concentration in the annealing separator increases, and that the arithmetic average roughness Ra decreases by grinding. From FIGS. 2 and 3, even if the Ca concentration in the separating agent is changed without grinding, the maximum film thickness and the minimum film thickness of the base film do not change significantly. As the height increased, the maximum film thickness tended to increase, and the minimum film thickness tended to decrease.
did.

  Further, the thickness of the undercoat film was investigated in a specific thickness range. That is, the relationship between the Ca concentration of the annealing separator and the film thickness in the range of 0.05 to 0.5 μm and in the range of 2.0 to 3.5 μm was investigated. Here, the reason why the film thickness is in the range of 0.05 to 0.5 μm and the film thickness is in the range of 2.0 to 3.5 μm is to evaluate unevenness of the coating-base iron interface. That is, since the outermost surface of the undercoat is almost flat by grinding, the thick portion (ie, 2.0 to 3.5 μm thick) has the coating penetrating into the steel plate and the thin portion (ie, (0.05 to 0.5 μm thick) indicates that the steel sheet is raised near the outermost layer. When the thick portion and the thin portion coexist in this way, the contact between the coating and the ground iron becomes dense, and the adhesion of the coating increases due to the anchor effect.

  FIG. 4 shows the “line segment ratio in which the film thickness is in the range of 0.05 to 0.5 μm” in the undercoat. The “line segment ratio in which the film thickness is in the range of 0.05 to 0.5 μm” is obtained by measuring a line segment ratio in which the film thickness is in the range of 0.05 to 0.5 μm from a cross-sectional SEM photograph. The measurement magnification was 2000 times, and the measurement was performed three times for a length of 100 μm, and the average value was obtained. As shown in FIG. 4, the value was approximately 0% regardless of the Ca concentration without grinding, but it can be seen that the ratio of line segments tends to increase as the Ca concentration increases with grinding.

  Similarly, FIG. 5 shows the results obtained by measuring the “line segment ratio at which the film thickness is in the range of 2.0 to 3.5 μm”. As shown in FIG. 5, the “line segment ratio at which the film thickness is in the range of 2.0 to 3.5 μm” became almost constant regardless of the Ca concentration without grinding, but sharply when the Ca concentration was low after grinding. And tended to increase as the Ca concentration increased.

  Next, regarding the transformer iron loss shown in FIG. 6, an optimum value is found for the Ca concentration, and it can be seen that the iron loss is most improved in the range of 0.3 to 2.2% by mass. This tendency is further enhanced by grinding, and it can be seen that excellent transformer iron loss is obtained in the above Ca concentration range.

  In FIG. 7, the optimum value of the Ca concentration is also recognized for the bending peeling diameter indicating the film adhesion. In particular, in a region where the Ca concentration is high, the deterioration in adhesion became remarkable by grinding. Although the rust generation rate by the corrosion resistance test shown in FIG. 8 was almost 0% in the region where the Ca concentration was low, the rust generation rate was increased by increasing the Ca concentration and further grinding. It can be seen that the space factor shown in FIG. 9 decreases as the Ca concentration increases, but is significantly improved by grinding.

From the above results, the present inventors concluded that the reason why iron loss is improved by adding a very small amount of Ca to the annealing separator and performing light grinding after finish annealing and further reducing the coating film thickness to 1 μm is described. I think as follows.
First, Ca ions as impurities in the MgO crystal of the annealing separation agent cut the bond between Si—O of amorphous SiO ₂ , thereby increasing the mobility of SiO ₂ and promoting the concentration of the surface layer. is there. In the absence of Ca ions, the surface layer concentration of SiO ₂ progresses slowly, so that iron also diffuses at the same time, making it difficult for surface stress to occur. As a result, unevenness at the interface with the ground iron is reduced. On the other hand, when Ca ions are added, the surface layer of SiO ₂ is rapidly concentrated, so that a compressive stress is generated and the interface is likely to be deformed.

  In the state where the unevenness is formed on the undercoat, the coating is sunk into the ground iron when a bending stress is applied, so that the undercoat is not easily peeled off, and the adhesion is secured. However, if a large amount of Ca ions is present, the reaction of MgO itself is suppressed, resulting in poor film formation and poor adhesion. From the above points, it can be said that there is an optimum range of the Ca concentration for the coating adhesion.

  Furthermore, when the undercoating with irregularities was ground, the bending adhesion did not change when the Ca concentration was low, but the adhesion deteriorated remarkably when the Ca concentration exceeded 2.2 mass%. Was. This is considered to be because the Ca concentration was increased and the unevenness of the underlying film was emphasized, and a portion where the ground iron was exposed when such a film was ground was generated.

  Regarding iron loss, it can be said that there is an optimum range of Ca concentration. First, in the case of a very small Ca concentration, it is considered that the adhesion of the coating film is enhanced, and the tension applied to the steel sheet by the coating film is effectively applied, so that the iron loss is improved. On the other hand, if the Ca concentration is too high, the unevenness of the undercoat increases, and the space factor decreases. As a result, it is considered that the number of stacked transformers is reduced and the iron loss is increased. By grinding the projections on the surface of the base coat, the space factor is improved, and as a result, iron loss is also reduced.

Regarding the rust generation rate, when the Ca concentration was low, almost no rust was generated, but when the Ca concentration was high, the rust generation rate increased. This is considered to be because the thickness of the coating was reduced to 1 μm in this experiment. That is, when the Ca concentration is low, the irregularities on the surface of the undercoating film are small. However, when the Ca concentration is increased, the irregularities increase, and when the coating liquid is applied thinly, a part of the undercoating film is exposed. Since Fe is also contained in the undercoat, the corrosion resistance of this portion is deteriorated. Even when the undercoating film surface is ground, part of the base iron is exposed at the projections of the coating film surface. Even if a coating is applied thereon, it will be partially peeled off because there is no underlying film. Then, it is considered that the corrosion resistance of this portion is deteriorated.
These findings are not limited to Ca, but are the same for alkaline earth metals in general, and their compatible ranges were completely the same. Alkaline earth metal ions have the function of increasing the mobility of SiO ₂ and promoting the concentration of the surface layer by cutting the bond between Si—O of amorphous SiO ₂ .

  Therefore, first, by including a predetermined amount of an alkaline earth metal such as Ca, the unevenness of the coating is moderately applied, and a proper tension is applied to the ground iron, and the adhesion of the coating is improved. Next, the roughness is reduced by grinding the outermost surface of the undercoat, and the space factor is increased. Further, by reducing the coating film thickness, it is possible to prevent a decrease in the space factor and prevent deterioration of corrosion resistance.

  By using a steel plate as described above and pumping up the transformer, it is possible to secure a sufficient number of stacked sheets even if the stacking thickness is constant due to size restrictions. As a result, when magnetizing to a predetermined magnetic flux density, the magnetization amount Can be improved without excessively increasing the iron loss.

  As described above, the present invention relates to a method for reducing the unevenness of the surface of the undercoat film and reducing the thickness of the coating film, thereby ensuring the adhesion of the film and reducing the transformer iron loss and increasing the space factor. It is a suggestion.

The present invention has been completed based on the above experimental results after further study, and the gist configuration thereof is as follows.
1. A grain-oriented electrical steel sheet having a base coat on the surface of a steel sheet and having a coating coat on the base coat,
Arithmetic average roughness Ra at the interface between the undercoat and the coating film is 0.25 μm or less,
The undercoating has a maximum thickness of 3.50 μm or less, a minimum thickness of 0.05 μm or more, and a line segment ratio of 2 μm or more and 3.5 μm or less in a region of 2 μm or more and a thickness of 0.05 μm or more and 0.5 μm or less. Area ratio is 2% or more,
A grain-oriented electrical steel sheet having a coating film thickness of 2 μm or less.

2. In mass%,
C: 0.020% or more and 0.080% or less,
One cold rolling or intermediate annealing is performed on a steel material containing Si: 2.50% or more and 4.50% or less and Mn: 0.03% or more and 0.30% or less, with the balance being Fe and a component composition that is an unavoidable impurity 2 Cold-rolled steel sheet having a final thickness by performing cold rolling more than once,
Decarburizing the cold rolled steel sheet,
An annealing separator containing 50% by mass or more of MgO and 0.3% by mass or more and 2.2% by mass or less of alkaline earth metal in terms of metal is applied to the surface of the steel sheet,
Thereafter, a base coat is formed by performing finish annealing, and then, for the base coat, the arithmetic average roughness Ra of the surface is 0.25 μm or less, the maximum thickness is 3.50 μm or less, and the minimum thickness is 0.05 μm or more. After adjusting the line segment ratio in the region where the film thickness is 2.0 μm or more and 3.5 μm or less to 2% or more and the line segment ratio in the region where the film thickness is 0.05 μm or more and 0.5 μm or less to 2% or more, A method for producing a grain-oriented electrical steel sheet, in which a coating liquid is applied and baked to form a coating film having a thickness of 2 μm or less.

3. The above-mentioned component further contains one or more of P: 0.005% or more and 0.20% or less, Sb: 0.005% or more and 0.200% or less, and Sn: 0.005% or more and 0.50% or less by mass%. The method for producing a grain-oriented electrical steel sheet according to the above.

4. The component composition further includes, in mass%,
4. The method for producing a grain-oriented electrical steel sheet according to the above item 2 or 3, comprising Al: 0.010% to 0.040% and N: 0.003% to 0.012%.

5. The component composition further comprises:
In mass%,
5. The method for producing a grain-oriented electrical steel sheet according to any one of the above items 2 to 4, comprising Se: 0.003% or more and 0.030% or less and / or S: 0.002% or more and 0.030% or less.

6. The component composition further comprises:
In mass%,
Ni: 0.01% or more and 1.50% or less,
Cr: 0.01% or more and 0.50% or less,
Cu: 0.01% or more and 0.50% or less,
Bi: 0.005% or more and 0.100% or less,
Mo: 0.005% or more and 0.100% or less,
B: 0.0002% or more and 0.0025% or less,
Te: 0.0005% or more and 0.0100% or less,
Nb: 0.001% or more and 0.010% or less,
V: 0.001% or more and 0.010% or less,
6. The method for producing a grain-oriented electrical steel sheet according to any one of the above items 2 to 5, comprising one or more selected from among Ti: 0.001% to 0.010% and Ta: 0.001% to 0.010%.

  ADVANTAGE OF THE INVENTION According to this invention, in addition to having excellent film adhesion and reduced transformer iron loss, a grain-oriented electrical steel sheet having a high space factor can be provided.

4 is a graph showing the relationship between the Ca concentration in the annealing separator and the arithmetic average roughness of the undercoat. It is a graph which shows the relationship between the Ca density | concentration in an annealing separating agent, and the maximum film thickness of an undercoat. It is a graph which shows the relationship between the Ca density | concentration in an annealing separating agent, and the minimum film thickness of an undercoat. It is a graph which shows the relationship between Ca density | concentration in an annealing separating agent, and film thickness: The line segment ratio of 0.05 to 0.5 micrometer. It is a graph which shows the relationship between Ca density | concentration in an annealing separating agent, and film thickness: The line segment ratio of 2.0 to 3.5 micrometers. It is a graph which shows the relationship between Ca concentration in an annealing separating agent, and trans iron loss. It is a graph which shows the relationship between the Ca density | concentration in an annealing separating agent, and a bending peeling diameter. It is a graph which shows the relationship between the Ca density | concentration in an annealing separating agent, and a rust generation rate. It is a graph which shows the relationship between the Ca concentration in an annealing separating agent, and a space factor.

The present invention has a base coat on the surface of the steel sheet, a grain-oriented electrical steel sheet having a coating film on the base coat,
Arithmetic average roughness Ra at the interface between the undercoat and the coating film is 0.25 μm or less,
The undercoating has a maximum thickness of 3.50 μm or less, a minimum thickness of 0.05 μm or more, and a line segment ratio of 2 μm or more and 3.5 μm or less in a region of 2 μm or more and a thickness of 0.05 μm or more and 0.5 μm or less. The line segment ratio of the region of 2% or more,
The coating film has a thickness of 2 μm or less;
It is characterized by. In the present invention, when simply referred to as the film thickness, it is the film thickness of the undercoat film (forsterite film).
Hereinafter, description will be given for each requirement for the above-described undercoating.

[Arithmetic average roughness Ra: 0.25 μm or less]
If the interface between the undercoat film and the coating film, in other words, the arithmetic average roughness Ra of the undercoat surface exceeds 0.25 μm, the unevenness is too large and the space factor decreases. Therefore, the arithmetic average roughness Ra is set to 0.25 μm or less, preferably 0.20 μm or more and 0.24 μm or less.
Incidentally, as the roughness meter for obtaining the arithmetic mean roughness, any commercially available roughness meter such as a laser type or a stylus type may be used. The method of calculating the arithmetic average roughness is as described in JIS B0601.

[Maximum thickness and minimum thickness]
If the maximum thickness of the undercoat is more than 3.50 μm, not only the sufficient effect of improving the space factor is not obtained, but also the corrosion resistance is deteriorated. If the minimum value of the film thickness is less than 0.05 μm, the forsterite film is too thin and the base iron is partially exposed, resulting in a film defect. Therefore, the maximum thickness is set to 3.50 μm or less, and the minimum thickness is set to 0.05 μm or more. The maximum part of the film thickness is preferably 2.90 μm or more and 3.30 μm or less. The minimum thickness part is preferably 0.08 μm or more and 0.35 μm or less.

  Here, the film thickness can be evaluated by an optical microscope or an electron microscope. A sample was cut out from the center of the coil plate in the width direction, and the C cross section (cross section parallel to the plate width direction) was observed at 2,000 times using an electron microscope, and the maximum and minimum values in the range of 100 μm in length were measured. To evaluate. The measurement is performed three times, and the average value is defined as the maximum thickness portion and the minimum thickness portion, respectively. In measuring the film thickness, the so-called anchor portion released from the upper surface of the film was not taken into consideration, and the film thickness of only the film not released was measured.

[Thickness: line segment ratio in the range of 0.05 to 0.5 μm and film thickness: line segment ratio in the range of 2 to 3.5 μm]
The line segment ratio in the thickness range of 0.05 to 0.5 μm is 2% or more, and the line segment ratio in the film thickness range of 2 to 3.5 μm is 2% or more. When the thickness falls within this range, a thick portion and a thin portion are introduced, and due to the unevenness, the adhesion between the steel sheet base iron and the coating film is ensured. The thickness can be measured by the same method as described above.

  Here, the reason why the line segment ratio is defined for the range of the film thickness: 0.05 to 0.5 μm and the range of the film thickness: 2 to 3.5 μm is that the unevenness of the interface between the coating film and the ground iron is evaluated. . Note that the upper limit of the line segment ratio in both regions is not particularly limited, but is preferably set to 40% or less because the magnetic properties are degraded due to excessive increase in unevenness.

[Coating film]
The thickness of the coating film is 2 μm or less in order to prevent the interlayer resistance from deteriorating and to improve the space factor. On the other hand, if the film thickness is less than 0.2 μm, corrosion resistance and insulation properties become problems. Therefore, the thickness is preferably 0.2 μm or more.

Next, a preferred component composition in the grain-oriented electrical steel sheet of the present invention will be described. In this specification, "%" representing the content of each component element means "% by mass" unless otherwise specified.
[Component composition]
C: 0.020% or more and 0.080% or less If C is less than 0.020%, the grain boundary strengthening effect by C is lost, and defects that hinder production, such as cracks in slabs, occur. On the other hand, when the content exceeds 0.080%, it becomes difficult to reduce the content to 0.005% or less at which magnetic aging does not occur by decarburizing annealing. Therefore, C is in the range of 0.020% to 0.080%. Preferably it is in the range of 0.025% or more and 0.075% or less.

Si: 2.50% or more and 4.50% or less Si is an element necessary for increasing the specific resistance of steel and reducing iron loss. If this effect is less than 2.50%, it is not sufficient, while if it exceeds 4.50%, the workability is reduced and it is difficult to manufacture by rolling. Therefore, the content of Si is set in the range of 2.50% to 4.50%. It is preferably in the range of 2.80% to 4.00%.

Mn: 0.03% or more and 0.30% or less Mn is an element necessary for improving the hot workability of steel. If this effect is less than 0.03%, the effect is not sufficient, while if it exceeds 0.30%, the magnetic flux density of the product plate decreases. Therefore, Mn is in the range of 0.03% to 0.30%. Preferably, it is in the range of 0.04% or more and 0.20% or less.

  The basic components in the present invention are as described above, and the balance is Fe and inevitable impurities. Examples of such unavoidable impurities include impurities unavoidably mixed from raw materials and manufacturing facilities.

Further, for components other than Si, C and Mn, more advantageous effects can be obtained by including one or more of Sb, Sn and P as surface segregating elements. That is, when these elements are segregated on the surface during the finish annealing, when the forsterite of the base coat is formed, the Fe concentration in the coat decreases. As a result, even if the thickness of the base coat is reduced by subsequent grinding, rust prevention and insulation are maintained. Furthermore, even if the ground iron is exposed by grinding, the action of these segregating elements maintains the adhesion between the coating and the ground iron.
In order to obtain the above effects, it is preferable that each of Sb, Sn and P is 0.005% or more. On the other hand, if Sb exceeds 0.500% and Sn and P exceed 0.200%, the upper limit is preferably 0.500% for Sb and 0.200% for Sn and P, since there is a concern about cracking during rolling and rupture due to it. .

Further, the following components may be contained depending on whether an inhibitor is used or not to cause secondary recrystallization.
First, in the case where an inhibitor is used to cause secondary recrystallization, for example, when an AlN-based inhibitor is used, Al and N are respectively converted to Al: 0.010% to 0.040%, N: 0.003% to 0.012%. It is preferable to contain it in the following range.

  When an MnS · MnSe-based inhibitor is used, the above-mentioned amount of Mn and one or two of S: 0.002% to 0.030% and Se: 0.003% to 0.030% are contained. Is preferred. If the amount of each addition is less than the above lower limit, the inhibitor effect cannot be sufficiently obtained, while if it exceeds the upper limit, the inhibitor component remains undissolved during slab heating, resulting in a decrease in magnetic properties. The AlN-based and MnS / MnSe-based inhibitors may be used in combination.

  On the other hand, when an inhibitor is not used to cause secondary recrystallization, the contents of Al, N, S, and Se, which are the above-described inhibitor-forming components, are reduced as much as possible, and Al: less than 0.010%, N: 0.003 %, S: less than 0.002%, and Se: preferably less than 0.003%.

  In the present invention, Ni: 0.01% to 1.50%, Cr: 0.01% to 0.50%, Cu: 0.01% to 0.50%, Bi: 0.005% to 0.100%, Mo: 0.005% to 0.100%, B: 0.0002% to 0.0025%, Te: 0.0005% to 0.0100%, Nb: 0.001% to 0.010%, V: 0.001% to 0.010%, Ti: 0.001% to 0.010% One or two or more selected from the following and Ta: 0.001% or more and 0.010% or less can be appropriately contained.

Next, a method for producing a grain-oriented electrical steel sheet according to the present invention will be described.
[Casting-heating]
After smelting a steel having the above-mentioned composition by a conventional refining process, a slab is manufactured by a conventionally known ingot-bulking rolling method or a continuous casting method, and the slab is subjected to hot rolling to obtain a steel material. (Hot rolled sheet) may be manufactured, or a thin slab with a thickness of 100 mm or less is manufactured by a direct casting method and then hot rolled or made into a steel material without hot rolling . The slab or the thin slab is heated to a temperature of about 1350 ° C. when it contains an inhibitor component, and is heated to a temperature of 1300 ° C. or less when it does not contain an inhibitor component.

[Hot rolling]
After the above heating, it is subjected to hot rolling. When no inhibitor component is contained, hot rolling may be performed immediately after casting without heating. In the case of thin cast slabs, hot rolling may be performed, or hot rolling may be omitted and the process may proceed to the subsequent steps. Although not particularly limited, the rolling end temperature of hot rolling is 700 to 1100 ° C., the coil winding temperature is 300 to 650 ° C., and the thickness after hot rolling may be in the range of 1.0 to 4.0 mm. desirable.

[Hot rolled sheet annealing]
The hot rolled sheet or thin slab slab obtained by hot rolling is subjected to hot rolled sheet annealing as necessary. The annealing temperature of the hot-rolled sheet annealing is preferably in the range of 800 to 1150 ° C. in order to obtain good magnetic properties. If the temperature is lower than 800 ° C., a band structure formed by hot rolling remains, making it difficult to obtain a primary recrystallized structure of sized particles, and hindering the development of secondary recrystallization. On the other hand, when the temperature exceeds 1150 ° C., the grain size after annealing of the hot-rolled sheet becomes too large, and it is also difficult to obtain a primary recrystallized structure having a uniform size. Further, the soaking time is not always necessary, and the temperature can be lowered as it is at the highest temperature. The upper limit of the time for soaking is preferably up to about 5 minutes.

[Cold rolling]
The hot-rolled sheet (including the above-mentioned thin slab) after hot rolling or hot-rolled sheet annealing is subjected to one or more cold-rolling operations including one-time cold rolling or intermediate annealing to obtain a final sheet thickness. Cold rolled sheet. The annealing temperature of the intermediate annealing is preferably in the range of 900 to 1200 ° C. If the temperature is lower than 900 ° C., the recrystallized grains after the intermediate annealing tend to be fine, and the Goss nuclei in the primary recrystallized structure tend to be reduced, so that the magnetic properties of the product sheet tend to deteriorate. On the other hand, when the temperature exceeds 1200 ° C., as in the case of hot-rolled sheet annealing, the crystal grains become too coarse, and it becomes difficult to obtain a primary recrystallized structure of sized grains. Further, the intermediate annealing time is preferably set to about 2 to 150 seconds. The cold rolling includes rolling in a warm region (warm rolling).

  In addition, the cold rolling (final cold rolling) to be the final thickness can be performed by increasing the steel sheet temperature during cold rolling to 100 to 300 ° C, or the temperature of 100 to 300 ° C during the cold rolling. Applying the aging treatment one or more times is effective for improving the primary recrystallization texture and improving the magnetic properties.

[Decarburizing annealing]
After that, the cold-rolled sheet having the final thickness is subjected to decarburization annealing also serving as primary recrystallization annealing. The decarburization annealing temperature is in the range of 700 to 900 ° C, and the decarburization annealing time is in the range of 30 to 300 seconds. If the temperature is less than 700 ° C. or less than 30 seconds, decarburization is insufficient, and the primary recrystallized particle size is too small, so that the magnetic properties deteriorate. On the other hand, if the temperature exceeds 900 ° C. or 300 seconds, the primary recrystallized grain size becomes too large, so that the magnetic properties deteriorate.

By this decarburizing annealing, a sub-scale is formed on the surface layer. Although the basis weight of oxygen of this subscale is not specified, it is desirable to keep it in a low range of 0.5 to 1.2 g / m ² . Since SiO ₂ in the subscale has a low density, it has a function of applying a stress between the steel sheet surface layer and the center layer. However, if the oxygen basis weight is large, the undercoat film becomes rough due to the compressive stress of the surface during the finish annealing. And iron loss deteriorates. Conversely, if the amount is too small, the amount of the formed film is insufficient.

[Application of annealing separator]
After the decarburizing annealing, an annealing separating agent is applied. At this time, a compound containing at least 50% by mass or more of MgO as a main component of the annealing separating agent and containing an alkaline earth metal is contained in the annealing separating agent in an amount of 0.3 to 2.2% by mass in terms of the metal. This is an amount necessary for appropriately forming irregularities in the undercoating. If the amount is too large, the irregularities become too severe and iron loss deteriorates. On the other hand, if the amount is too small, the unevenness becomes too small, and the adhesion of the film is reduced. For this reason, the content of the compound containing an alkaline earth metal is in the above range.

  As a method for introducing the alkaline earth metal, a small amount may be contained in MgO or other additives, and hydroxide, sulfate, carbonate, nitrate, borate, oxide, chloride, sulfide, etc. It may be added as a compound such as a substance. When a plurality of kinds of alkaline earth metals are contained, the sum of them is within the above range. In addition, as an annealing separator, various conventionally known additives can be used in addition to the above. For example, oxides, hydroxides, sulfates, carbonates, nitrates, borates, chlorides and sulfides such as Mn, Mo, Fe, Cu, Zn, Ni, Al, K, Li, Ti, Na and Sb. Things. These may be added alone or in a mixture of a plurality of types.

[Finish annealing]
After applying the annealing separating agent, finish annealing is performed while the steel sheet is wound in a coil shape to develop a secondary recrystallized structure highly integrated in the Goss orientation and to form a base film (forsterite film). .

The annealing temperature in the finish annealing is preferably set to 800 ° C. or higher for the appearance of secondary recrystallization, and is preferably set to 1100 ° C. or lower for completing the secondary recrystallization. Thereafter, in order to form a forsterite film, it is preferable to raise the temperature to about 1200 ° C. as a purification treatment. The finish annealing may be performed under known conditions. For example, the atmosphere may be any one of N ₂ , H _2, and Ar, or a mixed atmosphere of two or more of them, the purification temperature is 1100 to 1250 ° C., and the time is about 1 to 40 hours. Done with heat.
The steel sheet after the finish annealing contains C: 40 mass ppm or less, Si: 4.5 mass% or less, and Mn: 0.3 mass% or less, and the steel material contains Al, S, Se, and N. In this case, Al: 50 mass ppm or less, S: 20 mass ppm or less, Se: 20 mass ppm or less, and N: 30 mass ppm or less.

[Surface grinding]
After the finish annealing, the steel sheet coil is subjected to water washing, brushing, pickling or the like to remove the unreacted annealing separating agent attached to the steel sheet surface. Further, it is important in the present invention to perform surface grinding such as light grinding or blasting at any stage before the application of the coating liquid. By adding an alkaline earth metal to the annealing separator, the effect of increasing the unevenness of the cross-section of the undercoating and improving the adhesion of the coating can be obtained. Removes the protruding portion.

  Specific methods of surface grinding include abrasive brush grinding in which grinding abrasive grains are put into a nylon brush roll, and blast processing such as microblasting and fine shot blasting, but any means is not required. By reducing the particle size of these abrasive grains and particles, the surface roughness can be reduced. The surface roughness can also be reduced by increasing the rotation speed of the brush or passing through a plurality of passes in brush grinding, and by increasing the projection density or reducing the projection pressure in blasting.

  By shaving the surface of the undercoat by the above method, the line segment ratio of the forsterite film in the range of 3.50 μm or less at the maximum part, 0.05 μm or more at the minimum part, and 0.05 to 0.5 μm in the minimum part is 2%. The above and the line segment ratio in the range of the film thickness of 2 to 3.5 μm are processed to 2% or more.

[Application of coating liquid]
After preparing the surface of the base coat by surface grinding as described above, a coating liquid is applied, dried and baked to obtain a final product. By performing the surface preparation of the undercoat, the thickness of the coating can be reduced without impairing the corrosion resistance, and the space factor can be improved. In order to prevent the interlayer resistance from deteriorating and improve the space factor, the thickness of the coating film is set to 2 μm or less.
The coating liquid may be any known coating liquid used for coating the surface of an electromagnetic steel sheet.

[Magnetic domain subdivision processing]
In order to further reduce iron loss, it is possible to perform a magnetic domain refining process. As a treatment method, a method of forming a groove in a steel plate after secondary recrystallization, which is generally performed, and thermal or impact strain in a linear or dot form by laser irradiation or electron beam irradiation. A method of introducing a groove, a method of forming a groove by etching a surface of a steel sheet in an intermediate step, such as a steel sheet cold-rolled to a final thickness, and the like can be used.

Other manufacturing conditions may be in accordance with a general method for manufacturing a grain-oriented electrical steel sheet.
The grain-oriented electrical steel sheet of the present invention thus manufactured has a high space factor, so that it can achieve low iron loss when processed into a transformer or an EI core, and has excellent corrosion resistance and interlayer resistance. Steel sheet can be obtained.

(Example 1)
By mass%, a steel slab having a composition of 0.070% C, 3.43% Si, 0.08% Mn, 0.03% P, and the balance Fe and unavoidable impurities was produced by a continuous casting method, After being heated to a temperature, hot-rolled to form a hot-rolled sheet having a thickness of 2.4 mm, and subjected to hot-rolled sheet annealing at 1000 ° C x 50 seconds, and then to an intermediate sheet thickness of 1.8 mm by primary cold rolling, After performing intermediate annealing at 1100 ° C. × 20 seconds, secondary cold rolling was performed to finish a cold-rolled sheet having a final sheet thickness of 0.27 mm, followed by decarburizing annealing. The decarburizing annealing was controlled at 840 ° C. for 100 seconds in a humid atmosphere of 50 vol% H ₂ -50 vol% N ₂ and a dew point of 50 to 65 ° C. to control the amount of oxygen.

Next, as an annealing separating agent, a powder containing MgO as a main component, TiO ₂ in an amount of 2% by mass in terms of Ti, and various alkaline earth metal-containing compounds in an amount shown in Table 1 in terms of alkaline earth metal was added. The body was formed into a slurry, applied to the surface of a steel sheet, and dried. Further, a finish annealing with a purification treatment at 1200 ° C. for 10 hours was performed to form a base coat. The atmosphere for the finish annealing was H ₂ when the temperature was kept at 1200 ° C. for purifying treatment, and N ₂ when the temperature was raised and lowered.

  After applying a fine shot blast to the base coat of the steel sheet subjected to the above treatment to change the surface state, a coating liquid was applied. At this time, the coating thickness was adjusted by changing the coating amount, and coating and baking were performed to obtain a final product. With respect to the product plate thus obtained, a rust generation rate indicating corrosion resistance, a space factor, a bending peeling diameter indicating film adhesion, and a transformer iron loss were measured according to the above-described measurement methods. Table 1 shows the measurement results. In addition, various film thicknesses of the undercoat were also measured according to the above-described measurement method. From Table 1, it can be seen that according to the present invention, a grain-oriented electrical steel sheet having a high space factor in addition to having excellent coating adhesion and reduced iron loss is obtained.

(Example 2)
A steel slab having the component composition shown in Table 2 and the remainder having a component composition of Fe and unavoidable impurities was produced by a continuous casting method, heated to a temperature of 1380 ° C., and then hot-rolled to obtain a sheet thickness. A 2.0 mm hot-rolled sheet was subjected to hot-rolled sheet annealing at 1030 ° C. × 10 seconds, and then cold-rolled to obtain a cold-rolled sheet having a final sheet thickness of 0.23 mm. Thereafter, decarburization annealing was performed. The decarburization annealing was maintained at 840 ° C. for 100 seconds in a humid atmosphere of 50 vol% H ₂ -50 vol% N ₂ and a dew point of 55 ° C.

Next, as an annealing separator, MgO is used as a main component, TiO ₂ is converted into 2% in terms of Ti, and Ba sulfate is converted in terms of Ba. After drying, the substrate was subjected to finish annealing with a purification treatment at 1220 ° C. for 4 hours to form a base coat. The atmosphere of the finish annealing was H ₂ when the temperature was kept at 1220 ° C. for purifying, and Ar when the temperature was raised and lowered.

After changing the surface condition by grinding the undercoat film of the steel plate subjected to the above treatment with a nylon brush roll containing # 360 abrasive grains, further adjust the coating amount of the coating liquid so that the film thickness becomes 1.0 μm. Then, coating and baking were performed to obtain a final product. With respect to the product plate thus obtained, a rust generation rate indicating corrosion resistance, a space factor, a bending peeling diameter indicating film adhesion, and a transformer iron loss were measured according to the above-described measurement methods. Table 3 shows the measurement results. In addition, various film thicknesses of the undercoat were also measured according to the above-described measurement method. Table 3 shows that according to the present invention, in addition to having excellent coating adhesion and reduced transformer iron loss, a grain-oriented electrical steel sheet having a high space factor is obtained.
As described above, the grain-oriented electrical steel sheet according to the present invention can control the unevenness of the base coat, reduce iron loss, and obtain a high space factor without impairing various coat properties.

Claims (6)

In mass%,
C: 0.0040% or less,
Si: 2.50% to 4.50% and
Mn: 0.03% or more and 0.30% or less
And the balance has a component composition having Fe and unavoidable impurities,
A grain-oriented electrical steel sheet having a base coat on the surface of a steel sheet and having a coating coat on the base coat,
Arithmetic average roughness Ra at the interface between the undercoat and the coating film is 0.25 μm or less,
The undercoat film has a maximum film thickness of 3.50 μm or less, a minimum film thickness of 0.05 μm or more, and a line segment ratio of 2% or more and 3.5 μm or less in a region of 2.0 μm or more and 3.5 μm or less and a film thickness of 0.05 % or less. The line segment ratio in the region of μm or more and 0.5 μm or less is 2% or more and 5.3% or less ,
A grain-oriented electrical steel sheet having a coating film thickness of 2 μm or less. In mass%,
C: 0.020% or more and 0.080% or less,
One cold rolling or intermediate annealing is performed on a steel material containing Si: 2.50% or more and 4.50% or less and Mn: 0.03% or more and 0.30% or less, with the balance being Fe and a component composition that is an unavoidable impurity 2 Cold-rolled steel sheet having a final thickness by performing cold rolling more than once,
Decarburizing the cold rolled steel sheet,
An annealing separator containing 50% by mass or more of MgO and 0.3% by mass or more and 2.2% by mass or less of alkaline earth metal in terms of metal is applied to the surface of the steel sheet,
Thereafter, a base coat is formed by performing finish annealing, and then, for the base coat, the arithmetic average roughness Ra of the surface is 0.25 μm or less, the maximum thickness is 3.50 μm or less, and the minimum thickness is 0.05 μm or more. The line segment ratio in the region where the film thickness is 2.0 μm or more and 3.5 μm or less is 2% or more and 5.6% or less, and the line segment ratio in the region where the film thickness is 0.05 μm or more and 0.5 μm or less is 2% or more and 5.3% or less . After the adjustment, a coating solution is applied to the surface of the base coat and baked to form a coating having a thickness of 2 μm or less. The component further contains one or more of P: 0.005% or more and 0.20% or less, Sb: 0.005% or more and 0.200% or less, and Sn: 0.005% or more and 0.50% or less by mass%. 3. The method for producing a grain-oriented electrical steel sheet according to item 1. The component composition further includes, in mass%,
4. The method for producing a grain-oriented electrical steel sheet according to claim 2, wherein Al: 0.010% to 0.040% and N: 0.003% to 0.012%. 5. The component composition further comprises:
In mass%,
The method for producing a grain-oriented electrical steel sheet according to any one of claims 2 to 4, comprising Se: 0.003% or more and 0.030% or less and / or S: 0.002% or more and 0.030% or less. The component composition further comprises:
In mass%,
Ni: 0.01% or more and 1.50% or less,
Cr: 0.01% or more and 0.50% or less,
Cu: 0.01% or more and 0.50% or less,
Bi: 0.005% or more and 0.100% or less,
Mo: 0.005% or more and 0.100% or less,
B: 0.0002% or more and 0.0025% or less,
Te: 0.0005% or more and 0.0100% or less,
Nb: 0.001% or more and 0.010% or less,
V: 0.001% or more and 0.010% or less,
The method for producing a grain-oriented electrical steel sheet according to any one of claims 2 to 5, comprising one or more selected from among Ti: 0.001% to 0.010% and Ta: 0.001% to 0.010%. .

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