JP2018066061A - Directional electromagnetic steel sheet, and manufacturing method thereof - Google Patents

Abstract

A grain-oriented electrical steel sheet having a high space factor in addition to having excellent film adhesion and reduced transformer iron loss. A grain-oriented electrical steel sheet having a base coating on the surface of the steel plate and having a coating coating on the base coating, the arithmetic average roughness Ra at the interface between the base coating and the coating coating. 0.25 μm or less, and the undercoat has a maximum film thickness of 3.50 μm or less, a minimum film thickness of 0.05 μm or more, a line segment ratio of 2% or more in a region of film thickness of 2.0 μm or more and 3.5 μm or less, and a film thickness. The line segment ratio in the region of 0.05 μm or more and 0.5 μm or less is 2% or more, and the thickness of the coating film is 2 μm or less. [Selection] Figure 1

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 film properties when manufactured into a transformer, and a method for manufacturing the same.

  The grain-oriented electrical steel sheet is mainly used as a core material of a transformer, so that it is strongly required to have excellent magnetic properties, particularly low iron loss. Therefore, the grain-oriented electrical steel sheet is conventionally subjected to decarburization annealing that also serves as primary recrystallization annealing on the cold-rolled Si-containing steel sheet, and after applying an annealing separator mainly composed of MgO, secondary annealing is performed in finish annealing. Recrystallization occurs, and the crystal grains are manufactured by a method that highly aligns the {110} <001> orientation (so-called Goth orientation). The above-mentioned finish annealing requires about 10 days in total including annealing for secondary recrystallization and purification treatment for raising the temperature to a maximum of about 1200 ° C. Therefore, it is usually performed by batch annealing performed in a state of being wound around a coil. Yes.

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

  However, when the film thickness becomes too thick, the space factor decreases, and when used as a transformer, the stacking thickness becomes too thick and the size increases, resulting in an increase in copper loss or conversely within a predetermined size. Therefore, there arises a problem that the iron loss increases by reducing the number of stacked sheets. Therefore, it is also required to make the film thickness as thin as possible.

  Further, the forsterite film is formed so as to penetrate into the inside of the ground iron, and is thereby mechanically bonded to the steel plate surface. However, when the unevenness at the interface between the ground iron and the coating becomes severe, residual magnetization occurs in the uneven portion, and thus the hysteresis loss increases. Therefore, the film adhesion and the hysteresis loss are in a trade-off relationship, and it has been difficult to achieve both of them.

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

  In addition, as a technique for improving the space factor, Patent Document 1 describes a technique of using a non-hydratable oxide as an annealing separator and adding Ba thereto. Patent Document 2 describes a technique for forming a film that satisfies certain conditions of Young's modulus and linear expansion coefficient.

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

However, the method of Patent Document 1 has a high space factor because a base film is not formed, but has insufficient film adhesion, insulation, corrosion resistance, and the like. In addition, the method of Patent Document 2 has a problem in that the film is easily peeled off because the film tension is high and the film thickness is thin.
Thus, a grain-oriented electrical steel sheet having good adhesion, low iron loss (transformer iron loss) when applied to a transformer, and high space factor has not been obtained.

  The present invention has been made in view of the above circumstances, and an object thereof is 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 problems. As a result, by forming an undercoat so that the surface has irregularities and then smoothing the surface, in addition to having excellent film adhesion and reduced transformer iron loss, a high space factor It has been found that a grain-oriented electrical steel sheet is obtained.
In order to achieve the above-mentioned problem, an appropriate amount of alkaline earth metal is contained in the annealing separator, and after finishing annealing, the surface of the formed undercoat is ground thinly. It has also been found that it is important to contain Sb, Sn and P in the steel.

Hereinafter, experiments that led to the present invention will be described.
(Experiment)
C: 0.068% by mass, Si: 3.41% by mass, Mn: 0.07% by mass, Al: 0.030% by mass, N: 0.008% by mass Steel was melted and made into a steel material (steel slab) by continuous casting. After heating to 1410 ° C, hot rolled to a hot rolled sheet with a thickness of 2.2 mm, after subjecting to 1050 ° C x 60 seconds of hot rolled sheet annealing, primary cold rolled to an intermediate sheet thickness of 1.7 mm Then, after intermediate annealing at 1100 ° C. × 80 seconds, a cold rolled sheet having a final sheet thickness of 0.23 mm was obtained by rolling in a warm region of 200 ° C.

Next, decarburization annealing was performed by holding 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, titanium oxide and sodium hydroxide are contained, and the balance is an annealing separator of magnesium oxide. Titanium oxide is contained in an amount of 5 mass% in terms of Ti, sodium hydroxide is contained in an amount of 40 mass ppm in terms of Na, and the Ca concentration is 0.2 mass. An annealing separator having a main component of magnesium oxide varied in a range of not less than% and not more than 3.2% by mass was applied to the steel sheet surface and dried. When impurities of titanium oxide and sodium hydroxide were analyzed, the concentrations of Ca and other alkaline earth metals were both below the detection limit.

  The steel sheet was subjected to secondary recrystallization annealing and finish annealing including purification treatment at 1200 ° C. for 7 hours in a hydrogen atmosphere to form a base film, and then the unreacted annealing separator was removed. The surface roughness was variously changed by grinding the surface of the undercoat with a brush roll having abrasive grains of 100 and # 240 (JIS R6001). Thereafter, the coating liquid was applied to the surface of the undercoat so that the coating thickness after baking was 1 μm, and the coating liquid was baked and planarization annealing was performed at 800 ° C. for 30 seconds.

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

1 that the Ca concentration in the annealing separator increases, the surface roughness of the undercoat increases, and the arithmetic average roughness Ra decreases by grinding. In addition, as shown in FIGS. 2 and 3, if grinding is not performed, the maximum film thickness and the minimum film thickness of the undercoat are not greatly changed even if the Ca concentration in the separating agent is changed. As the value increased, the maximum film thickness tended to increase and the minimum film thickness tended to decrease.
did.

  Furthermore, the specific film thickness range was investigated about the film thickness of a base film. That is, the relationship between the film thickness of 0.05 to 0.5 μm and the film thickness of 2.0 to 3.5 μm was investigated with respect to the Ca concentration of the annealing separator. Here, the reason why the film thickness is in the range of 0.05 to 0.5 [mu] m and the film thickness is in the range of 2.0 to 3.5 [mu] m is to evaluate the unevenness at the film-base metal interface. That is, since the outermost surface of the base film is almost flat by grinding, the thick part (that is, 2.0 to 3.5 μm thickness) is penetrated to the inside of the steel plate, and the thin part (that is, the part is thin) 0.05 to 0.5 μm thickness) indicates that the steel plate is raised to the vicinity of the outermost layer. Thus, when the thick part and the thin part are mixed, the contact between the coating and the ground iron becomes dense, and the adhesion of the coating is enhanced by 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 base film. This “line segment ratio in which the film thickness is in the range of 0.05 to 0.5 μm” is obtained by measuring the line segment ratio in which the film thickness is in the range of 0.05 to 0.5 μm from the 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 taken. As shown in FIG. 4, it was about 0% regardless of the Ca concentration without grinding, but it can be seen that, when grinding, the line segment ratio tends to increase as the Ca concentration increases.

  Similarly, what was measured for “the line segment ratio in which the film thickness is in the range of 2.0 to 3.5 μm” is shown in FIG. As shown in FIG. 5, the “line segment ratio in which the film thickness is in the range of 2.0 to 3.5 μm” is a substantially constant value regardless of the Ca concentration without grinding. However, when the Ca concentration is low after grinding, Tended to increase as the Ca concentration increased.

  Next, with respect to the transformer iron loss shown in FIG. 6, the optimum value is recognized in the Ca concentration, and it can be seen that the iron loss is most improved in the range of 0.3 to 2.2 mass%. When grinding, this tendency is further strengthened, and it can be seen that excellent transformer iron loss is obtained in the above Ca concentration range.

  In FIG. 7, the optimum value for the Ca concentration is also observed for the bending peel diameter indicating the film adhesion. In particular, in the region where the Ca concentration is high, the deterioration of the adhesion becomes significant by grinding. 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, but the rust generation rate increased by increasing the Ca concentration and further grinding. The space factor shown in FIG. 9 decreases as the Ca concentration increases, but it can be seen that it is significantly improved by grinding.

From the above results, the inventors of the present invention have the reason why iron loss is improved by adding a very small amount of Ca in the annealing separator and performing light grinding after finish annealing and further reducing the coating film thickness to 1 μm. I think as follows.
First, Ca ions as impurities in the MgO crystal of the annealing separation agent break the bond between amorphous SiO ₂ and Si—O, thereby increasing the mobility of SiO ₂ and promoting surface concentration. is there. When there is no Ca ion, the surface layer concentration of SiO ₂ proceeds slowly, so that iron diffusion also occurs at the same time, and surface stress is less likely to occur. As a result, the 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 compressive stress is generated and interface deformation is likely to occur.

  Thus, in the state in which the unevenness is formed on the base film, the film is not easily peeled off when bending stress is applied, so that the adhesion is ensured. However, if a large amount of Ca ions are 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 Ca concentration with respect to film adhesion.

  In addition, when the underlying film with the irregularities formed was ground, there was no change in the bending adhesion when the Ca concentration was low. However, when the Ca concentration exceeded 2.2% by mass, the deterioration of the adhesion became significant. It was. This is presumably because the Ca concentration is increased and the unevenness of the base film is emphasized, and a portion where the ground iron is exposed when such a film is ground.

  Regarding the iron loss, it can be said that there is an optimum range of Ca concentration. First, in the case of a very small amount of Ca concentration, it is considered that the adhesion of the film is enhanced, and as a result, the tension on the steel sheet due to the 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, the number of stacked sheets when the transformer is assembled decreases, and the iron loss is considered to have increased. By grinding the convex portions on the surface of the undercoat film, the space factor is improved, and as a result, iron loss is also reduced.

Regarding the rust generation rate, when the Ca concentration is low, rust is hardly generated, but when the Ca concentration is high, the rust generation rate is increased. This is presumably because the coating thickness was reduced to 1 μm in this experiment. That is, when the Ca concentration is low, the unevenness on the surface of the undercoating film is small, but by increasing the Ca concentration, the unevenness increases, 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 deteriorates. Even when the surface of the base coating is ground, part of the iron is exposed at the convex portions of the coating surface. Even if it coats on this, since there is no undercoat, it will peel off partially. And it seems that the corrosion resistance of this part deteriorates.
These findings are not limited to Ca, but are the same for all alkaline earth metals, and the applicable range is exactly the same. Alkaline earth metal ions have a function of promoting surface concentration by increasing the mobility of SiO ₂ by cutting bonds between Si—O of amorphous SiO ₂ .

  Therefore, first, by adding a predetermined amount of alkaline earth metal such as Ca, unevenness of the coating is moderately applied, moderate tension is applied to the ground iron, and 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 the space factor from decreasing and to prevent the corrosion resistance from deteriorating.

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

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

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

2. % By mass
C: 0.020% to 0.080%,
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 steel material having an inevitable impurity component composition, sandwiching one cold rolling or intermediate annealing 2 Cold-rolled steel sheet having a final sheet thickness by performing cold rolling more than once,
Subjecting the cold-rolled steel sheet to decarburization annealing,
On the surface of the steel sheet, an annealing separator containing MgO: 50% by mass or more and alkaline earth metal in an amount of 0.3% by mass to 2.2% by mass in terms of metal is applied,
Thereafter, finish annealing is performed to form a base film, and then the surface arithmetic average roughness Ra is 0.25 μm or less, the film thickness maximum part is 3.50 μm or less, and the film thickness minimum part is 0.05 μm or more, After adjusting the line segment ratio of 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 of 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 film having a thickness of 2 μm or less is formed by applying and baking a coating liquid.

3. The component further contains one or more of P: 0.005% to 0.20% and Sb: 0.005% to 0.200% and Sn: 0.005% to 0.50% by mass%. The manufacturing method of the grain-oriented electrical steel sheet of description.

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

5. The component composition further includes:
% By mass
Se: 0.003% or more and 0.030% or less and / or S: 0.002% or more and 0.030% or less, The manufacturing method of the grain-oriented electrical steel sheet in any one of said 2 to 4.

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

  According to the present invention, it is possible 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.

It is a graph which shows the relationship between Ca density | concentration in an annealing separation agent, and arithmetic mean roughness of a base film. It is a graph which shows the relationship between Ca density | concentration in an annealing separation agent, and the maximum film thickness of a base film. It is a graph which shows the relationship between Ca density | concentration in an annealing separation agent, and the minimum film thickness of a base film. It is a graph which shows the relationship between Ca density | concentration in an annealing separation agent, and film thickness: 0.05 to 0.5 micrometer line segment ratio. It is a graph which shows the relationship between Ca density | concentration in an annealing separator, and a film thickness: Line segment ratio of 2.0 micrometers or more and 3.5 micrometers or less. It is a graph which shows the relationship between Ca density | concentration in an annealing separation agent, and trans iron loss. It is a graph which shows the relationship between Ca density | concentration in an annealing separation agent, and a bending peeling diameter. It is a graph which shows the relationship between Ca density | concentration in an annealing separation agent, and a rust incidence. It is a graph which shows the relationship between Ca density | concentration in an annealing separation agent, and a space factor.

The present invention has a base coating on the surface of the steel sheet, and in the grain-oriented electrical steel sheet having a coating coating on the base coating,
Arithmetic mean roughness Ra at the interface between the undercoat and the coating film is 0.25 μm or less,
The base coating has a maximum thickness of 3.50 μm or less, a minimum thickness of 0.05 μm or more, a line segment ratio of 2% or more and a thickness of 0.05 μm or more and 0.5 μm or less. The line segment ratio of the area is 2% or more,
The coating film thickness is 2 μm or less,
It is characterized by. In the present invention, the term “film thickness” simply refers to the film thickness of the base film (forsterite film).
Hereafter, it demonstrates for every requirement regarding the above-mentioned undercoat.

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

[Maximum film thickness and minimum film thickness]
If the maximum thickness of the undercoat is more than 3.50 μm, not only a sufficient space factor improvement effect can be obtained, but also the corrosion resistance deteriorates. 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. For this reason, the maximum film thickness portion is set to 3.50 μm or less and the minimum film thickness portion is set to 0.05 μm or more. The maximum thickness portion is preferably 2.90 μm or more and 3.30 μm or less. The minimum film thickness portion is preferably 0.08 μm or more and 0.35 μm or less.

  Here, the film thickness can be evaluated with an optical microscope or an electron microscope. A sample is cut out from the central part of the coil plate width direction, and the C cross section (cross section parallel to the plate width direction) is observed at 2000 times using an electron microscope, and the maximum and minimum values in the range of 100 μm in length are measured. To evaluate. The measurement is performed three times, and the average values are taken as the maximum film thickness portion and the minimum film thickness portion, respectively. When measuring the film thickness, the so-called anchor part released from the upper surface of the film was not taken into consideration, and the film thickness of only the non-free film was measured.

[Film 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 range of 0.05 to 0.5 μm is 2% or more, and the line segment ratio in the range of film thickness 2 to 3.5 μm is 2% or more. By being in this range, a thick part and a thin part are introduced, and the adhesion between the steel sheet steel and the coating film is ensured by the unevenness. In addition, the measuring method of a film thickness can be calculated | required by the method similar to the above.

  Here, the reason why the line segment ratio is defined for the film thickness range of 0.05 to 0.5 μm and the film thickness range of 2 to 3.5 μm is that the unevenness of the interface between the coating and the base iron is thereby evaluated. . The upper limit of the line segment ratio in both regions is not particularly limited, but is desirably 40% or less because unevenness increases excessively and magnetic characteristics deteriorate.

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

Next, a suitable component composition in the grain-oriented electrical steel sheet of the present invention will be described. In the present specification, “%” representing the content of each component element means “% by mass” unless otherwise specified.
[Ingredient composition]
C: 0.020% or more and 0.080% or less When C is less than 0.020%, the grain boundary strengthening effect due to C is lost, and defects such as cracks in the slab are produced. On the other hand, if it exceeds 0.080%, it becomes difficult to reduce to 0.005% or less, which does not cause magnetic aging, by decarburization annealing. Therefore, C is in the range of 0.020% or more and 0.080% or less. Preferably it is 0.025% or more and 0.075% or less of range.

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. On the other hand, if it exceeds 4.50%, the workability deteriorates, and it becomes difficult to produce by rolling. Therefore, Si is set in the range of 2.50% to 4.50%. Preferably it is 2.80% or more and 4.00% or less of range.

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%, it is not sufficient. On the other hand, if it exceeds 0.30%, the magnetic flux density of the product plate decreases. Therefore, Mn is set in the range of 0.03% to 0.30%. Preferably it is 0.04% or more and 0.20% or less of range.

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

For components other than Si, C, and Mn, a more advantageous effect can be obtained by including one or more of Sb, Sn, and P as surface segregation elements. This is because when these elements segregate on the surface during the finish annealing, the Fe concentration in the coating decreases when the forsterite of the base coating is formed. As a result, rust prevention and insulation are maintained even if the film thickness of the undercoat is reduced by subsequent grinding. Furthermore, even if the base iron is exposed by grinding, the adhesion between the coating and the base iron is maintained by the action of these segregating elements.
In order to obtain the above effects, each of Sb, Sn, and P is preferably 0.005% or more. On the other hand, if Sb exceeds 0.500% and Sn and P exceed 0.200%, there is a concern about cracks in rolling and fractures resulting from this, so it is preferable that the upper limit is 0.500% for Sb and 0.200% for Sn and P. .

Further, the following components may be contained depending on whether or not an inhibitor is used in order to cause secondary recrystallization.
First, when an inhibitor is used to cause secondary recrystallization. For example, when an AlN-based inhibitor is used, Al and N are changed to Al: 0.010% or more and 0.040% or less, N: 0.003% or more and 0.012%, respectively. It is preferable to make it contain in the following ranges.

  When using an MnS / MnSe-based inhibitor, the amount of Mn described above and one or two of S: 0.002% to 0.030% and Se: 0.003% to 0.030% are included. Is preferred. If the amount of each additive is less than the above lower limit value, the inhibitor effect is not sufficiently obtained. On the other hand, if the amount exceeds the upper limit value, the inhibitor component remains undissolved during slab heating, resulting in a decrease in magnetic properties. AlN and MnS / MnSe inhibitors may be used in combination.

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

  In the present invention, for the purpose of improving magnetic properties, 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 more selected from the following and Ta: 0.001% or more and 0.010% or less can be appropriately contained.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
[Casting-Heating]
After the steel having the above-described composition is melted by a conventional refining process, a slab is produced by a conventionally known ingot-bundling rolling method or continuous casting method, and the slab is hot-rolled to produce a steel material. (Hot-rolled sheet) may be manufactured, or after manufacturing a thin cast piece with a thickness of 100 mm or less by direct casting method, it is made into a steel material by hot rolling or without hot rolling. . The slab or thin slab is heated according to a conventional method. For example, when it contains an inhibitor component, it is heated to about 1350 ° C., whereas when it does not contain an inhibitor component, it is heated to a temperature of 1300 ° C. or less.

[Hot rolling]
After the heating, it is subjected to hot rolling. In addition, when not containing an inhibitor component, you may hot-roll immediately, without heating after casting. Moreover, in the case of a thin slab, it may be hot-rolled, or the hot-rolling may be omitted and the process may proceed as it is. 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 should be in the range of 1.0 to 4.0 mm. desirable.

[Hot rolled sheet annealing]
The hot-rolled sheet or thin cast slab obtained by hot rolling is subjected to hot-rolled sheet annealing as necessary. In order to obtain good magnetic properties, the annealing temperature of this hot-rolled sheet annealing is preferably in the range of 800 to 1150 ° C. If it is less than 800 degreeC, the band structure formed by hot rolling will remain, it will become difficult to obtain the primary recrystallized structure of grain size, and the development of secondary recrystallization will be inhibited. On the other hand, when the temperature exceeds 1150 ° C., the grain size after hot-rolled sheet annealing becomes too coarse, and it becomes difficult to obtain a primary recrystallized structure of sized particles. Further, the soaking time is not necessarily required, and the temperature can be lowered as it is at the highest temperature reached. The upper limit of time for soaking is preferably up to about 5 minutes.

[Cold rolling]
The hot-rolled sheet (including the above-mentioned thin cast slab) after hot-rolling or after hot-rolled sheet annealing is subjected to one or more cold rollings or two or more cold rollings sandwiching the intermediate annealing to obtain the final sheet thickness. Cold-rolled sheet. The annealing temperature of the intermediate annealing is preferably in the range of 900 to 1200 ° C. When the temperature is lower than 900 ° C., the recrystallized grains after the intermediate annealing tend to become finer, and the Goss nuclei in the primary recrystallized structure tend to decrease and the magnetic properties of the product plate tend to deteriorate. On the other hand, when the temperature exceeds 1200 ° C., the crystal grains become too coarse as in the case of hot-rolled sheet annealing, and it becomes difficult to obtain a primary recrystallized structure of grain size. The intermediate annealing time is preferably about 2 to 150 seconds. Note that cold rolling includes rolling in a warm region (warm rolling).

  In addition, cold rolling (final cold rolling) with a final sheet thickness is performed by increasing the steel plate temperature during cold rolling to 100 to 300 ° C, or at a temperature of 100 to 300 ° C during the cold rolling. In order to improve the primary recrystallization texture and to improve the magnetic properties, it is effective to apply the aging treatment once or plural times.

[Decarburization annealing]
The cold-rolled sheet having the final thickness is then subjected to decarburization annealing that also serves 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 it is less than 700 ° C. or less than 30 seconds, decarburization is insufficient, and the primary recrystallized grain size is too small, so that the magnetic properties deteriorate. On the other hand, if it exceeds 900 ° C. or more than 300 seconds, the primary recrystallized grain size becomes too large and the magnetic properties deteriorate.

By this decarburization annealing, a subscale is formed on the surface layer. This oxygen basis weight of the subscale is not specified, it is desirable to suppress to 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 to apply stress between the steel sheet surface layer and the center layer. However, if the oxygen basis weight is large, the unevenness of the undercoat becomes severe due to the compressive stress of the surface during finish annealing. The iron loss is deteriorated. On the other hand, if the amount is too small, the film formation amount is insufficient.

[Application of annealing separator]
An annealing separator is applied after the decarburization annealing. At this time, a compound containing at least 50% by mass of MgO as a main component of the annealing separator and containing an alkaline earth metal is contained in the annealing separator 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 on the undercoat, and if it is too large, the irregularities become excessive and iron loss deteriorates. Moreover, when there are too few, an unevenness | corrugation will decrease too much and film adhesiveness will fall. For this reason, content of the compound containing alkaline-earth metal shall be said range.

  Alkaline earth metal may be introduced in a small amount in MgO or other additives, and separately in hydroxides, sulfates, carbonates, nitrates, borates, oxides, chlorides, sulfides. It may be added as a compound such as a product. In addition, when a plurality of alkaline earth metals are contained, the total sum thereof falls within the above range. In addition to these, various conventionally known additives can be used as the annealing separator. 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 It is a thing. Only one of these may be added, or a plurality of these may be mixed and added.

[Finish annealing]
After application of the annealing separator, finish annealing is performed with the steel sheet wound in a coil shape, and a secondary recrystallized structure highly accumulated in the Goss orientation is developed, and a base film (forsterite film) is formed. .

The annealing temperature for the finish annealing is preferably 800 ° C. or higher for the purpose of secondary recrystallization, and preferably 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 of N ₂ , H ₂ and Ar, or a mixed atmosphere of two or more thereof, the purification temperature is 1100 to 1250 ° C., and the time is about 1 to 40 hours. Done with heat.
The steel sheet after 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 are included.

[Surface grinding]
The steel plate coil after finish annealing is then subjected to water washing, brushing, pickling, etc. to remove the unreacted annealing separator adhering to the steel plate surface. In addition, it is important in the present invention to perform surface grinding such as light grinding or blasting at any stage until the coating liquid is applied. By adding an alkaline earth metal to the annealing separator, it is possible to increase the unevenness of the cross section of the underlying film and improve the film adhesion, but on the other hand, this unevenness degrades the space factor, so grinding To remove the protruding part.

  Specific methods of surface grinding include abrasive brush grinding in which abrasive grains are put into a nylon brush roll, and blasting such as microblasting and fine shot blasting, and any means can be used. Surface roughness can be reduced by reducing the particle size of these abrasive grains and particles. Further, in brush grinding, the surface roughness can be reduced by increasing the rotation speed of the brush or passing a plurality of passes, and in blasting, the projection density is increased or the projection pressure is reduced.

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

[Application of coating solution]
After the surface of the undercoat is prepared by surface grinding as described above, a coating solution is applied, and after baking, a final product is obtained. By preparing the surface of the base film, the film thickness of the coating film 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.
Any coating solution may be used as long as it is a known coating solution used for coating the surface of the electrical steel sheet.

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

Other manufacturing conditions may follow the general manufacturing method of a grain-oriented electrical steel sheet.
The grain-oriented electrical steel sheet of the present invention produced in this way has a high space factor, so it can achieve low iron loss when processed into a transformer, EI core, etc., and has excellent corrosion resistance and interlayer resistance. Steel plate can be obtained.

Example 1
A steel slab having a mass composition of C: 0.070%, Si: 3.43%, Mn: 0.08%, P: 0.03%, the balance being Fe and inevitable impurities is produced by continuous casting, After being heated to a temperature, hot rolled to a hot rolled sheet with a thickness of 2.4 mm, subjected to hot rolled sheet annealing at 1000 ° C. for 50 seconds, and then with an intermediate thickness of 1.8 mm by primary cold rolling, After intermediate annealing at 1100 ° C. for 20 seconds, secondary cold rolling was performed to finish a cold rolled sheet having a final sheet thickness of 0.27 mm and decarburized annealing. In the decarburization annealing, the amount of oxygen was controlled by holding 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.

Next, as an annealing separator, powder containing MgO as the main ingredient, TiO ₂ in 2% by mass in terms of Ti, and various alkaline earth metal compounds in the amounts shown in Table 1 in terms of alkaline earth metals The body was made into a slurry and applied to the surface of the steel sheet and dried. Further, finish annealing accompanied by a purification treatment at 1200 ° C. for 10 hours was performed to form a base film. The atmosphere of the finish annealing was H _{2 at} 1200 ° C. holding for purification, and N ₂ at the time of temperature increase and temperature decrease.

  A fine shot blast was applied to the base film of the steel sheet subjected to the above treatment to change the surface state, and then the coating liquid was applied. At this time, the coating amount was changed to adjust the coating film thickness, and coating and baking were performed to obtain a final product. With respect to the product plate thus obtained, the rust generation rate, space factor, bending peel diameter indicating film adhesion, and transformer iron loss indicating corrosion resistance were measured according to the measurement method described above. The measurement results are shown in Table 1. Various film thicknesses of the undercoat were also measured according to the measurement method described above. 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 film adhesion and reduced iron loss is obtained.

(Example 2)
A steel slab having the composition shown in Table 2 with the balance being Fe and inevitable impurities is produced by a continuous casting method, heated to a temperature of 1380 ° C., and then hot-rolled to obtain a plate thickness A hot-rolled sheet of 2.0 mm was subjected to hot-rolled sheet annealing at 1030 ° C. for 10 seconds, and then cold-rolled to finish a cold-rolled sheet having a final sheet thickness of 0.23 mm. Thereafter, decarburization annealing was performed. The decarburization annealing was held 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 the main ingredient, TiO ₂ is 2% in terms of Ti, and Ba sulfate is in terms of Ba. After drying, finish annealing was further performed with a purification treatment at 1220 ° C. for 4 hours to form a base coating. The atmosphere of the finish annealing was H ₂ when the purification treatment was held at 1220 ° C., and Ar when the temperature was raised and lowered.

After changing the surface condition by grinding the base film of the steel plate after the above treatment with a nylon brush roll containing # 360 abrasive grains, the coating amount of the coating liquid is adjusted so that the film thickness becomes 1.0 μm. Then, application and baking were performed to obtain a final product. With respect to the product plate thus obtained, the rust generation rate, space factor, bending peel diameter indicating film adhesion, and transformer iron loss indicating corrosion resistance were measured according to the measurement method described above. The measurement results are shown in Table 3. Various film thicknesses of the undercoat were also measured according to the measurement method described above. From Table 3, it can be seen that according to the present invention, in addition to having excellent film adhesion and reduced transformer iron loss, a grain-oriented electrical steel sheet having a high space factor is obtained.
Thus, the grain-oriented electrical steel sheet according to the present invention can reduce the iron loss by controlling the unevenness of the base coating without impairing various coating properties, and can obtain a high space factor.

Claims (6)

A grain-oriented electrical steel sheet having an undercoat on the surface of the steel sheet, and having a coating film on the undercoat,
Arithmetic mean roughness Ra at the interface between the undercoat and the coating film is 0.25 μm or less,
The base coating has a maximum thickness of 3.50 μm or less, a minimum thickness of 0.05 μm or more, a line segment ratio of 2% or more and a thickness of 0.05 μm or more and 0.5 μm or less. The line segment ratio of the area is 2% or more,
A grain-oriented electrical steel sheet having a coating film thickness of 2 μm or less. % By mass
C: 0.020% to 0.080%,
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 steel material having an inevitable impurity component composition, sandwiching one cold rolling or intermediate annealing 2 Cold-rolled steel sheet having a final sheet thickness by performing cold rolling more than once,
Subjecting the cold-rolled steel sheet to decarburization annealing,
On the surface of the steel sheet, an annealing separator containing MgO: 50% by mass or more and alkaline earth metal in an amount of 0.3% by mass to 2.2% by mass in terms of metal is applied,
Thereafter, finish annealing is performed to form a base film, and then the surface arithmetic average roughness Ra is 0.25 μm or less, the film thickness maximum part is 3.50 μm or less, and the film thickness minimum part is 0.05 μm or more, After adjusting the line segment ratio of 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 of 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 film having a thickness of 2 μm or less is formed by applying and baking a coating liquid. The component further contains one or more of P: 0.005% to 0.20% and Sb: 0.005% to 0.200% and Sn: 0.005% to 0.50% by mass%. The manufacturing method of the grain-oriented electrical steel sheet described in 1. The component composition is further mass%,
The method for producing a grain-oriented electrical steel sheet according to claim 2 or 3, comprising Al: 0.010% to 0.040% and N: 0.003% to 0.012%. The component composition further includes:
% By mass
The method for producing a grain-oriented electrical steel sheet according to any one of claims 2 to 4, comprising Se: 0.003% to 0.030% and / or S: 0.002% to 0.030%. The component composition further includes:
% By mass
Ni: 0.01% or more and 1.50% or less,
Cr: 0.01% or more and 0.50% or less,
Cu: 0.01% to 0.50%,
Bi: 0.005% to 0.100%,
Mo: 0.005% or more and 0.100% or less,
B: 0.0002% to 0.0025%,
Te: 0.0005% or more and 0.0100% or less,
Nb: 0.001% or more and 0.010% or less,
V: 0.001% to 0.010%,
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 Ti: 0.001% to 0.010% and Ta: 0.001% to 0.010%. .

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