JP4839766B2 - Method for producing grain-oriented electrical steel sheet having excellent coating properties and annealing separator for grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet having good coating properties, particularly uniform coating appearance and peeling resistance, and an annealing separator for a grain-oriented electrical steel sheet suitable for use in producing such grain-oriented electrical steel plates. .

Production of grain-oriented electrical steel sheets is generally carried out by subjecting a steel slab adjusted to a predetermined composition to hot rolling, annealing, cold rolling, recrystallization annealing, and final finishing annealing. . Of these manufacturing processes, in final finish annealing, it is usual to apply an annealing separator mainly composed of magnesia in order to prevent coil seizure during annealing at a high temperature of 1200 ° C.
In addition to the role of the annealing separator described above, this magnesia forms a forsterite film by reacting with an oxide layer mainly composed of silica that forms on the surface of the steel sheet during decarburization annealing performed before final finish annealing. There is also a function to make it.

The forsterite film formed as described above not only works as a kind of binder to adhere the phosphate-based insulating coating to be coated with the base metal part, but also provides magnetic properties by applying tension to the steel sheet. There is a function of improving and uniforming the appearance of the steel sheet coating film, and the role of this annealing separator is great.
In addition, the reactivity of the annealing separator has a great influence on the appearance of the coating. If the reactivity is too high, point-like defects occur in the coating. Will be exposed.

For this reason, various methods have been proposed in order to improve film properties.
For example, Patent Document 1 proposes a method for improving film properties by optimizing the expected value and standard deviation of values obtained by observing the reaction of magnesia and citric acid over time.
Patent Document 2 proposes a method for improving the film characteristics by keeping the gas adsorption isotherm curve of magnesium oxide within an appropriate range.
However, it has been found that even when an annealing separator whose citric acid activity and gas adsorption isotherm curves are adjusted to appropriate ranges is applied to the steel sheet, the film stability may be lacking.
JP 2004-353054 A JP-A-10-88240

All the technologies that have been proposed so far have been proposed under the implicit assumption that the forsterite formation reaction is a solid-phase reaction between silica and magnesia.
The essence of the present invention is to improve the film stability by abandoning this fixed idea and examining the contribution of the gas phase reaction in the forsterite formation reaction.

  Now, as a result of intensive studies on the contribution of the gas phase reaction in the forsterite formation reaction, the inventors have found that there is a correlation between the stability of the film properties and the gas phase reactivity of the annealing separator, The present invention has been completed.

That is, the gist configuration of the present invention is as follows.
(1) A steel slab containing Si: 2 to 4 mass% is hot-rolled, subjected to final cold rolling after hot-rolled sheet annealing, and then primarily recrystallized and annealed with MgO as the main component on the steel sheet surface. In the method of manufacturing a grain-oriented electrical steel sheet comprising a series of steps of performing final finish annealing after applying an annealing separator,
Regarding the physical properties of the annealing separator, the surface fluorescent X-ray Mg intensity ratio A (A = I (no application) / I () when the final finish annealing is performed by separating the steel sheet coated with the annealing separator and the uncoated steel sheet by 5 mm. A method for producing a grain-oriented electrical steel sheet having excellent coating properties, characterized by using an annealing separator whose value is evaluated in the application step)) and whose value satisfies the range of 0.5 ≦ A ≦ 1.5.

(2) The annealing separator contains magnesia: 100 parts by mass, one or more selected from Ca compound, Sr compound and Ba compound at 3 parts by mass or less in terms of the metal A method for producing a grain-oriented electrical steel sheet according to the above (1), characterized in that:

(3) A annealing separator mainly comprised of MgO, the annealing separator of the separating 5mm steel plates of coated steel sheet and a non-coated surface fluorescent X-rays when subjected to final finish annealing Mg intensity ratio A ( A = I (no application) / I (application)) satisfies the range of 0.5 ≦ A ≦ 1.5.

(4) The annealing separator contains magnesia: 100 parts by mass, one or more selected from Ca compound, Sr compound and Ba compound is contained in 3 parts by mass or less in terms of the metal. The annealing separator for grain-oriented electrical steel sheets according to (3) above, characterized in that:

  According to the present invention, it is possible to stably obtain a grain-oriented electrical steel sheet having good coating film adhesion, excellent in coating characteristics, and having no change in color tone or occurrence of point defects.

Hereinafter, the present invention will be specifically described.
First, the experimental results that led to the present invention will be described.
The inventors have found that a coil for grain-oriented electrical steel sheet is produced using the techniques described in the above-mentioned Patent Document 1 and Patent Document 2, and that there is a coil to be subjected to the coating characteristic stability. Specifically, uneven coating color tone in the coil due to inferior film formability and bending peel diameter degradation, and conversely point defects due to too good film formability were observed.

As the inventors proceeded with various studies on the cause of the above-mentioned defects, conventionally, the reaction between silica and magnesia was thought to be mainly a solid-phase reaction, so the contribution of the gas-phase reaction was completely considered. I thought that it was not, and started research from this viewpoint.
That is, the inventors conducted the following experiment paying attention to the gas phase reactivity in the annealing separator.

As an annealing separator, magnesia with good coating stability and magnesia with poor coating were prepared, and one of two steel plates (100mm x 100mm) with an internal oxide layer of silica by decarburization annealing. The above annealing separator was applied, and the other was not applied. The coating amount was 12.5 g / m ^{2 on} both sides. These two steel sheets are stacked as shown in Fig. 1 through a 5mm wide ring (inner diameter: 80mm, outer diameter: 81mm) ring (spacer) made by processing steel sheets of the same material, and from room temperature to 1200 ° C. The temperature was increased at a rate of 25 ° C./h, and then final finish annealing was performed at 1200 ° C. for 20 h. During this annealing, the annealing atmosphere was H _{2 in} the temperature range of 1000 ° C. or higher, and N ₂ was the others.
In addition, FIG. 2 is the figure which shifted from one steel plate and was seen from the top, in order to demonstrate the lamination | stacking state of two steel plates intelligibly. In FIGS. 1 and 2, reference numeral 1 is an annealing separator-uncoated steel sheet, 2 is an annealing separator-coated steel sheet, 3 is a ring (spacer), number 4 is an annealing separator-uncoated surface, and number 5 is annealing separation. The agent application surface is shown.

The sample after annealing was disassembled, and the obtained two steel sheets were washed with water, and then subjected to surface X-ray fluorescence analysis and FT-IR analysis.
FIG. 3 shows the Mg count numbers of the magnesia-coated surface and the non-coated surface when various magnesias are used. In the figure, ◯ indicates magnesia with good film stability, and x indicates magnesia with poor film stability.
As shown in the figure, magnesia with good film stability has a surface fluorescent X-ray Mg intensity ratio A (A = I (no application) / I (application)) in the range of 0.50 ≦ A ≦ 1.50. there were.
In contrast, in magnesia where A <0.50, point defects were observed. On the other hand, magnesia with A> 1.50 was inferior in film color uniformity.

Next, the measurement result of surface FT-IR is shown in FIG.
The position of the arrow in the figure is the peak of forsterite, and it can be seen that forsterite is formed not only on the magnesia-coated surface but also on the non-coated surface.
In addition, since no film formation was observed in the portion masked by the spacer, it is clear that Mg was diffused in the gas phase from the magnesia-coated surface to the magnesia-uncoated surface.

From the above experimental results, when the fluorescent X-ray Mg intensity ratio is low, it is considered that the forsterite formation reaction is mainly caused by the solid-phase reaction because of the gas-phase reaction << solid-phase reaction. That is, since it is considered that the steel plate and magnesia are in a point contact state, the solid phase reaction is considered to proceed from the contact point. Then, there is a portion where the reaction has progressed for each contact point, and it is presumed that point defects are likely to occur.
On the other hand, a high fluorescence X-ray Mg intensity ratio means that vapor phase reaction is active, but Mg is evaporated much. Therefore, if this value is too high, it is considered that the residence state of the Mg vapor between the coil layers differs between the coil edge portion and other portions, and the coating uniformity is lost.

Next, as an effect when an alkaline earth metal compound is added to the annealing separator, a case where strontium hydroxide is added will be described as an example. In addition, 1 mass part of strontium hydroxide was added with respect to 100 mass parts of magnesia in conversion of metal Sr.
As shown in FIG. 5, it was found that the surface fluorescence X-ray Mg intensity ratio A was higher after the addition than before the addition.
At this time, since the fluorescent X-ray Sr intensity of the non-coated surface was higher than that of the coated surface, it is estimated that Sr and Mg were vapor-phase diffused together on the non-coated surface.

Hereinafter, the reasons for limiting the constituent requirements of the present invention will be described.
First, the suitable component composition range of the grain-oriented electrical steel sheet targeted in the present invention will be described.
Si is a useful element that contributes effectively to improving iron loss by increasing electrical resistance. However, if the content is less than 2 mass%, a sufficient iron loss reduction effect cannot be obtained. On the other hand, if it exceeds 4 mass%, the workability deteriorates, so the Si amount is 2 to 4 mass%.

There is no restriction | limiting in particular about another component, All the components conventionally used for the grain-oriented electrical steel sheet adapt advantageously. For example, the following component composition is recommended.
That is, it contains C: 0.02 to 0.1 mass% and Mn: 0.02 to 0.2 mass%, and if necessary, Se: 0.001 to 0.03 mass%, Sb: 0.01 to 0.08 mass%, Al: 0.001 to 0.04 mass%, N: 0.001 to 0.012 mass%, S: 0.001 to 0.03 mass%, Cu: 0.05 to 0.2 mass, Sn: 0.005 to 0.4 mass%, Cr: 0.02 to 0.08 mass%, Mo: 0.01 to 0.1 mass%, P: 0.01 It is a composition containing at least one selected from -0.03 mass% and Bi: 0.001-0.04 mass%.

The steel slab having the above component composition is hot-rolled, subjected to hot-rolled sheet annealing, and then subjected to final cold rolling to finish the final plate thickness. These may be known methods. Next, primary recrystallization annealing, secondary recrystallization annealing, and purification annealing are performed. In primary recrystallization annealing or secondary recrystallization annealing, it also serves as decarburization annealing.
After the decarburization annealing, an annealing separator mainly composed of magnesia is applied to the steel sheet surface. As such an annealing separator, the surface fluorescent X-ray Mg intensity ratio A (A = I (no application) / I (application) when the final finish annealing is performed by separating the coated steel sheet and the uncoated steel sheet by 5 mm. It is important to use a value that satisfies the range of 0.5 ≦ A ≦ 1.5 when evaluated in ()).
Here, when the surface fluorescent X-ray Mg intensity ratio A is A <0.5 when the final finish annealing is performed with a separation agent-coated steel plate and an uncoated steel plate separated by 5 mm, point defects are formed in the coating, whereas A> At 1.5, the coating color uniformity and bending peel diameter are poor.

Furthermore, in the annealing separator, one or more selected from Ca compound, Sr compound and Ba compound is contained in 3 parts by mass or less in terms of metal relative to 100 parts by mass of magnesia. It is effective to increase the intensity ratio A.
Here, when the addition amount of Ca compound, Sr compound and Ba compound with respect to 100 parts by mass of magnesia exceeds 3 parts by mass, the cross-sectional structure of the film is changed and the peel resistance is deteriorated. In addition, since the addition effect will be scarce when there is too little addition amount of each above-mentioned compound, it is preferable to contain these compounds 0.2 mass part or more in conversion of the said metal.

As the Ca compound, Sr compound, and Ba compound, carbonates, hydroxides, sulfates, sulfides, and the like of the metals can be used.
The method of adjusting the surface fluorescent X-ray Mg intensity ratio is that the intensity ratio tends to decrease by increasing the firing temperature in the process of firing the raw magnesium hydroxide to magnesia. And a method of adjusting in the form of the raw material because the strength ratio tends to be increased by increasing the aspect ratio of the raw material before firing.
Furthermore, as described above, the surface fluorescent X-ray Mg intensity ratio can also be increased by adding a Ca compound, an Sr compound and a Ba compound to the annealing separator.

  After finish annealing, shape correction is performed by flattening annealing. Furthermore, in order to improve the iron loss, it is effective to provide an insulating coating that imparts tension to the steel sheet surface.

Example 1
C: 0.06 mass%, Si: 2.95 mass%, Mn: 0.07 mass%, Se: 0.015 mass%, Sb: 0.015 mass% and Cr: 0.03 mass%, the balance being Fe and inevitable impurities A steel slab is heated at 1350 ° C for 40 minutes, hot rolled to a thickness of 2.6 mm, and then subjected to hot rolling of 900 ° C for 60 s, followed by cold sandwiching an intermediate annealing of 1050 ° C for 60 s A final thickness of 0.30 mm was obtained by rolling. Next, after the primary recrystallization annealing, magnesia with different surface fluorescent X-ray Mg intensity ratio A (A = I (no application) / I (application)) measured by the same method as in FIG. 1 was applied. Then, after finishing annealing to raise the temperature to 1200 ° C. at a rate of 25 ° C./h, flattening annealing was performed.

Thereafter, the bending peel diameter was measured over the entire length of the coil, and the presence or absence of coating defects was investigated.
Here, it is judged that the coating properties are good because the bending peel diameter is 40 mm or less, no noticeable color tone change is observed in the transverse width direction and the longitudinal direction, and the area where the coating point defects are generated is The case of less than 1%.
The survey results are shown in Table 1.

  As shown in the table, when an annealing separator that satisfies the range of 0.5 ≦ A ≦ 1.5 in the surface fluorescent X-ray Mg intensity ratio A (A = I (no coating) / I (coating)) is used, It can be seen that a favorable coating property is obtained in which the bending peel diameter is 40 mm or less, no noticeable color tone change is observed in the coil width direction and the longitudinal direction, and the area of occurrence of coating point defects is less than 1% of the coil. .

Example 2
Steel slab containing C: 0.045 mass%, Si: 3.25 mass%, Mn: 0.070 mass%, Al: 80 ppm, N: 40 ppm and S: 20 ppm, with the balance being Fe and inevitable impurities, 1200 ° C After heating, a hot rolled sheet coil having a thickness of 2.2 mm was obtained by hot rolling. The hot rolled sheet was subjected to hot rolled sheet annealing at 1000 ° C. for 30 seconds, and then the scale on the surface of the steel sheet was removed. Next, a cold rolled sheet having a final sheet thickness of 0.30 mm was obtained by cold rolling using a tandem rolling mill. Then, after applying primary recrystallization annealing that is held at a soaking temperature of 860 ° C. for 90 seconds, an annealing separator mainly composed of MgO is applied, and then heated up to 1200 ° C. at a rate of 25 ° C./h. After finishing annealing, flattening annealing was performed.
At this time, magnesia having different surface fluorescent X-ray Mg intensity ratios A (A = I (no application) / I (application)) measured by the same method as in FIG. 1 was applied as an annealing separator.

Thereafter, the bending peel diameter was measured over the entire length of the coil, and the presence or absence of coating defects was investigated.
The survey results are shown in Table 2.

  As is apparent from the table, the surface fluorescent X-ray Mg intensity ratio A (A = I (no coating) / I (coating)) is bent by using an annealing separator that satisfies the range of 0.5 ≦ A ≦ 1.5. With a peel diameter of 40 mm or less, no remarkable change in color tone was observed in the width direction and longitudinal direction of the coil, and good film characteristics were obtained in which the area where defects on the film were formed was less than 1% of the coil.

Example 3
Contains C: 0.06 mass%, Si: 2.95 mass%, Mn: 0.070 mass%, Se: 0.015 mass%, Sb: 0.015 mass% and Cr: 0.03 mass%, the balance being Fe and inevitable impurities A steel slab is heated at 1350 ° C for 40 minutes, hot rolled to a thickness of 2.6 mm, and then subjected to hot rolling of 900 ° C for 60 s, followed by cold sandwiching an intermediate annealing of 1050 ° C for 60 s A final thickness of 0.30 mm was obtained by rolling. Next, after the primary recrystallization annealing, the surface fluorescent X-ray Mg intensity ratio A (A = I (no application) / I (application)) measured by the same method as in FIG. After applying an annealing separator added with various Ca compounds, Sr compounds and Ba compounds shown in (1) above, and performing a finish annealing that raises the temperature to 1200 ° C. at a rate of 25 ° C./h, flattening annealing was performed.

Thereafter, the bending peel diameter was measured over the entire length of the coil, and the presence or absence of coating defects was investigated.
The survey results are shown in Table 3.

  As shown in the table, even when the surface fluorescence X-ray Mg intensity ratio A of magnesia, which is the main component of the annealing separator, is 0.30, an appropriate amount of Ca compound, Sr compound, and Ba compound is added to the annealing separator. It can be seen that good film properties can be obtained by controlling the surface fluorescent X-ray Mg intensity ratio A in the range of 0.5 ≦ A ≦ 1.5.

It is a figure (figure seen from the side) explaining the stacking method of the steel plate at the time of test plate annealing. It is a figure explaining the stacking method of the steel plate at the time of test-plate annealing (the figure seen from the top shifted). It is a figure which shows the relationship between the fluorescent material X-ray Mg of the separating agent application surface after annealing, and a non-application surface. It is a figure which shows the surface infrared reflection spectrum of the separating agent application surface after annealing, and a non-application surface. It is a figure which shows the influence which addition of strontium hydroxide has on the fluorescent X-ray Mg intensity ratio (A).

Explanation of symbols

1 Steel plate without annealing separator 2 Steel plate with annealing separator 3 Ring (spacer)
4 Annealing separation agent non-application surface 5 Annealing separation agent application surface

Claims (4)

A steel slab containing Si: 2 to 4 mass% is hot-rolled, subjected to final cold rolling after hot-rolled sheet annealing, and then subjected to primary recrystallization annealing, followed by an annealing separator mainly composed of MgO on the steel sheet surface. In the manufacturing method of grain-oriented electrical steel sheet consisting of a series of steps of performing final finish annealing after applying
Regarding the physical properties of the annealing separator, the surface fluorescent X-ray Mg intensity ratio A (A = I (no application) / I () when the final finish annealing is performed by separating the steel sheet coated with the annealing separator and the uncoated steel sheet by 5 mm. A method for producing a grain-oriented electrical steel sheet having excellent coating properties, characterized by using an annealing separator whose value is evaluated in the application step)) and whose value satisfies the range of 0.5 ≦ A ≦ 1.5.   The annealing separator contains one or more selected from Ca compound, Sr compound and Ba compound with respect to 100 parts by mass of magnesia at 3 parts by mass or less in terms of the metal. The method for producing a grain-oriented electrical steel sheet according to claim 1, characterized in that: A annealing separator mainly comprised of MgO, the annealing separator of the separating 5mm steel plates of coated steel sheet and a non-coated surface fluorescent X-rays when subjected to final finish annealing Mg intensity ratio A (A = I (No coating) / I (coating)) satisfies the range of 0.5 ≦ A ≦ 1.5.   The annealing separator contains one or more selected from Ca compound, Sr compound and Ba compound with respect to 100 parts by mass of magnesia at 3 parts by mass or less in terms of the metal. The annealing separator for grain-oriented electrical steel sheets according to claim 3 characterized by the above-mentioned.

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