JPH1161260A - Manufacture of nonoriented silicon steel sheet with low iron loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacture of a nonoriented silicon steel sheet reduced in iron loss at a low cost. SOLUTION: A steel, having a composition consisting of, by weight, <=0.005% C, <=4.0% Si, 0.05-1.0% Mn, <=0.1% P, <=0.005% (including 0%) N, <=0.001% (including 0%) S, <=1.0% Al, and the balance essentially Fe, is hot-rolled, pickled, subjected to hot rolled plate annealing in an atmosphere having >=20% partial pressure of nitrogen and -20 to 10 deg.C dew point, successively cold-rolled to prescribed sheet thickness, and then finish-annealed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a non-oriented electrical steel sheet having a low iron loss and used for electric equipment and the like.

[0002]

2. Description of the Related Art In recent years, electromagnetic steel sheets having high magnetic flux density and low iron loss have been demanded from the viewpoint of energy saving and miniaturization of electric equipment. Since magnetic steel sheets are used in layers, it is important to control their surface properties. From this viewpoint, medium- and high-grade non-oriented magnetic steel sheets with a Si + Al content of about 1-3% It is common to perform hot-rolled sheet annealing in a non-oxidizing atmosphere containing nitrogen.

[0003]

However, in the middle and high grade materials subjected to such hot-rolled sheet annealing, the formation of surface layer fine grains is observed in the finish-annealed sheet.
For this reason, it is the present situation that the iron loss is not sufficiently reduced.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a method of manufacturing an electromagnetic steel sheet having low iron loss at low cost.

[0005]

The gist of the present invention is to reduce the S content in steel to a predetermined value or less and to set the atmosphere of the hot-rolled sheet annealing in a predetermined range so that the surface layer portion of the steel sheet generated during hot-rolled sheet annealing is formed. Is to suppress nitriding of the steel, thereby reducing iron loss.

[0006] That is, the above-mentioned problem is expressed by:
005% or less, Si: 4.0% or less, Mn: 0.05 to 1.0%, P: 0.1
%, N: 0.005% or less (including 0), S: 0.001% or less (including 0), Al: 1.0% or less, and the balance substantially consisting of Fe is subjected to hot rolling. After pickling, hot-rolled sheet annealing is performed in an atmosphere with a nitrogen partial pressure of 20% or more and a dew point of -20 ° C or more and 10 ° C or less, and subsequently cold-rolled to a predetermined sheet thickness, followed by finish annealing. The problem is solved by a method for producing a non-oriented electrical steel sheet having a low iron loss, which is characterized by being applied.

[0007] Here, "the balance is substantially Fe" means that those containing other trace elements fall within the scope of the right within a range not to impair the features of the present invention. In the following description, all percentages indicating the composition of steel mean weight%,
ppm also means ppm by weight.

(History leading to the invention, S content, and reasons for limiting the atmosphere of hot-rolled sheet annealing) The present inventors have investigated in detail the factors that form fine nitrides observed on the surface layer during the finish annealing. As a result, it is evident that significant nitriding progresses in the surface layer of the steel sheet during hot-rolled sheet annealing, and this nitrided layer is inherited until the time of finish annealing to form fine-grained surface layers, impeding the reduction of iron loss. became.

Accordingly, the present inventors have conducted intensive studies on a technique for suppressing nitriding. As a result, it has been found that the dew point is controlled to -20 ° C to 10 ° C in an atmosphere containing 20% or more of nitrogen during hot-rolled sheet annealing. It was found that nitriding was suppressed by this and iron loss after finish annealing was greatly reduced.

First, in order to investigate the effect of surface fine particles on iron loss, C: 0.0025%, Si: 2.85%, Mn: 0.20%,
S: 1 to 16 ppm, P: 0.01%, Al: 0.31%, N: 0.0021%
Was melted in a laboratory, hot-rolled, and then pickled. Subsequently, the hot rolled sheet was subjected to a dew point of −30 ° C., 25% N ₂ −75% H ₂ , 50
% H ₂ -50% N ₂ and 830 in 90% N ₂ -10% H ₂ atmosphere
The sheet was annealed at 300C for 3 hours. Thereafter, the sheet is cold-rolled to a sheet thickness of 0.5 mm, and 850 ° C. to 110% in a 25% H ₂ -75% N ₂ atmosphere.
Finish annealing was performed at 0 ° C. × 1 min.

FIG. 1 shows the relationship between the iron loss W _15/50 of the sample thus obtained. Where the magnetic measurement is 25cm
This was performed by the Epstein method.

From FIG. 1, S is 10 pp at any nitrogen partial pressure.
It can be seen that a significant reduction in iron loss is achieved when the distance is set to m or less. This is because grain growth was improved by reducing the amount of S. From the above, in the present invention, S is 10
ppm or less, more preferably 5 ppm or less.

However, if S is set to 10 ppm or less,
Reduction of iron loss is gradual, and iron loss is 2.
It cannot be less than 4W / Kg.

On the other hand, when the nitrogen partial pressure increases, the attained level of iron loss shifts to a higher iron loss side. The rate of iron loss degradation is S
> 10 ppm, even if the nitrogen partial pressure is increased from 25% to 90%,
From about 3.1 W / Kg to about 3.3 W / Kg, which is about 0.2 W / Kg. In the range of S ≦ 10 ppm, from about 2.4 W / Kg to about 2.8 W / Kg, which is as large as 0.4 W / Kg. .

The present inventors consider that the reason why the reduction of iron loss is inhibited by the extremely low S material having S of 10 ppm or less may be due to unknown factors other than MnS. Was used to observe the structure. As a result, in the region of S> 10 ppm, the nitrided layer was slight, while in the region of S ≦ 10 ppm, a remarkable nitrided layer was recognized.
In the region of S> 10 ppm, no significant difference was observed in the degree of nitriding even when the partial pressure of nitrogen in the atmosphere gas was changed from 25% to 75%. On the other hand, when S ≦ 10 ppm, when the nitrogen partial pressure in the atmosphere gas was changed from 25% to 75%, a remarkable nitride layer was formed on the surface layer in accordance with the increase in the nitrogen partial pressure.

As described above, the relationship between the amount of S in steel and the surface nitriding,
The present inventors further consider the influence of the atmospheric nitrogen partial pressure on these relationships as follows. That is, S is easily concentrated on the surface and the grain boundaries, and its diffusion rate is relatively high. Therefore, S segregates on the surface in the initial process of hot-rolled sheet annealing. As a result, even when the nitrogen partial pressure in hot-rolled sheet annealing is high, S segregated on the surface serves as a barrier for the nitrogen adsorption reaction. The lower limit value of S to be a barrier for the nitrogen adsorption reaction is in principle an extremely small amount sufficient to cover the surface, and S> 10 found experimentally.
The ppm range corresponds to this. On the other hand, in the region where S ≦ 10 ppm, the effect of suppressing nitrogen adsorption by S is reduced, and it is considered that nitriding is more likely to occur than in the region where S> 10 ppm.

The degree of such nitriding has a strong relationship with the partial pressure of nitrogen in the atmosphere gas. As the partial pressure of nitrogen increases, the amount of nitrogen contributing to the nitriding reaction increases. As a result, a nitride layer corresponding to the nitrogen partial pressure is formed in a region of S ≦ 10 ppm, particularly without an adsorption barrier.

The present inventors have thought that the nitrided layer at the surface portion is formed mainly during hot-rolled sheet annealing and may hinder the growth of crystal grains at the time of finish annealing to suppress a reduction in iron loss. As a countermeasure, ideally, it is desirable to perform vacuum annealing of hot-rolled sheet annealing or annealing in a non-oxidizing atmosphere (100% hydrogen atmosphere, 100% Ar atmosphere, etc.) that does not contain nitrogen. It is not realistic due to problems.
Therefore, the inventors have found that the general annealing atmosphere of nitrogen-
When annealing in a hydrogen mixed gas, measures were taken to prevent nitriding.

Then, as a result of a detailed study of the surface nitridation method in place of S, it was concluded that if an oxide film was formed before the nitride layer was formed, the oxide film would serve as a barrier. It was studied to perform annealing at a high dew point such that an oxide film was positively formed during sheet annealing.

C: 0.0026%, Si: 2.70%, Mn: 0.20%,
P: 0.020%, Al: 0.30%, S: 0.0004%, N: 0.0020
% Was melted in a laboratory, hot rolled, and then pickled.
Subsequently, the hot-rolled sheet was placed at 830 ° C. in an atmosphere with a dew point of −30 ° C. and −5 ° C. and a nitrogen partial pressure of 0 to 100% (the remaining hydrogen).
The sheet was subjected to hot rolled sheet annealing for 3 hours. Thereafter, the sheet was cold-rolled to a sheet thickness of 0.5 mm and subjected to finish annealing at 900 ° C. for 1 minute in a 25% H ₂ -75% N ₂ atmosphere.

As a result, as shown in FIG.
℃, compared with the conventional method when the dew point is -30 ℃, the iron loss is improved when the nitrogen partial pressure in the atmosphere gas is 20% or more, especially the nitrogen partial pressure atmosphere of 40% or more. Among them, the effect of the improvement was remarkable.

When the structure after annealing of the hot-rolled sheet was observed in detail, when the annealing was performed at a dew point of −30 ° C., a nitride layer was formed on the surface of the sample after the annealing of the hot-rolled sheet, and the nitrogen content was low. Increasing the pressure increased the degree of nitridation. However, when annealing was performed at a dew point of −5 ° C., the degree of the surface nitride layer was reduced, and in particular, intense nitriding in a high nitrogen partial pressure atmosphere of 40% or more tended to be suppressed. Therefore, it is considered that the reason why the iron loss deterioration during the finish annealing is suppressed at the dew point of -5 ° C and the nitrogen partial pressure of 20% or more is due to the nitridation suppression effect described above.

On the other hand, when the nitrogen partial pressure was less than 20%, improvement in iron loss was not recognized even when the dew point was increased. This is presumably due to the fact that, although the rate of deterioration of iron loss in the surface oxide layer is smaller than that of nitride, the effect cannot be ignored. In other words, in an atmosphere where the nitrogen partial pressure is low and nitriding is relatively gentle, there is no iron loss deterioration due to nitriding, so that iron loss due to oxidation cannot be ignored, and as a result, the iron loss level is the same as when the dew point is -30 ° C. It is thought that it became.

From the above results, it has been clarified that in an atmosphere where the nitrogen partial pressure is 20% or more, nitriding can be prevented by increasing the dew point. In order to further examine the appropriate range of the dew point, the dew point was raised from -40 ° C to +10
C., hot-rolled sheet annealing was performed while changing the nitrogen partial pressure to 0-100% (remainder hydrogen), and then cold-rolled to a sheet thickness of 0.5 mm.
Finish annealing was performed at 900 ° C. for 1 minute in an atmosphere of 5% H ₂ -75% N ₂ to evaluate iron loss.

FIG. 3 shows the results. In FIG. 3, the numbers in the circles indicate the iron loss value (W _15/50 ) after the finish annealing. As can be seen from FIG. 3, when the dew point is −20 ° C. or higher, the iron loss is improved when the nitrogen partial pressure in the atmosphere gas is set to 20% or higher, and especially when the nitrogen partial pressure is 40% or higher. The effect was significant.

However, when the dew point exceeds + 10 ° C., although there is no problem in the magnetic properties, a large amount of oxide is formed on the surface of the steel sheet, which is liable to cause a surface property defect called a pickup. The gas atmosphere during hot-rolled sheet annealing should have a nitrogen partial pressure of 20% or more and a dew point of -20 ° C to 10 ° C.

(Other Reasons for Limiting Components) Next, the reasons for limiting the components will be described. C: C is 0.005% or less because of the problem of magnetic aging. Mn: Mn is 0.1% to prevent red hot brittleness during hot rolling.
It is required to be not less than 05%, but if it is not less than 1.0%, the magnetic flux density is reduced. Si: Si is an effective element for increasing the specific resistance of the steel sheet. However, if it exceeds 4.0%, the magnetic flux density decreases with a decrease in the saturation magnetic flux density, so the upper limit is set to 4.0%. P: P is an element necessary for improving the punching property of the steel sheet. However, if the content exceeds 0.1%, the steel sheet becomes brittle, so that the content is set to 0.1% or less. N: N is set to 0.005% or less because when N content is large, the precipitation amount of AlN increases, and even when AlN becomes coarse, the grain growth decreases and the iron loss increases. Al: When Al is added in a small amount, it generates fine AlN and deteriorates the magnetic properties. However, if it is 1.0% or more, the magnetic flux density is reduced, so the upper limit is 1.0% or less.

(Production Method) In the present invention, the production process other than the hot-rolled sheet annealing may be a method for producing a normal non-oriented electrical steel sheet. That is, the molten steel blown in the converter is degassed and adjusted to a predetermined component, and subsequently casting and hot rolling are performed. The finish annealing temperature and the winding temperature at the time of hot rolling do not need to be particularly specified, and may be in a normal range.
After hot-rolled sheet annealing after hot-rolling, final annealing is performed after a predetermined thickness is obtained by one cold rolling or two or more cold rolling steps including intermediate annealing.

[0029]

EXAMPLES The steels shown in Table 1 were cast into a given component after being degassed after being blown in a converter,
After the slab was heated at 1160 ° C. for 1 hour, hot rolling was performed to a thickness of 2.0 mm. Hot rolling finishing temperature is 800 ℃, winding temperature is 6
The temperature was set to 10 ° C., and hot-rolled sheet annealing was performed under the conditions shown in Table 1. Next, the hot-rolled sheet was pickled, cold-rolled to a sheet thickness of 0.5 mm, and then annealed under the finish annealing conditions shown in Table 1. Magnetic measurements were performed using 25 cm Epstein specimens. Table 1 also shows the magnetic properties of each steel sheet.

[0030]

[Table 1]

From this, it can be seen that when the atmosphere of the hot-rolled sheet annealing is controlled within a predetermined range, a steel sheet with low iron loss after finish annealing can be obtained.

The steel sheets No. 9 and No. 10 and the steel sheets No. 25 and No. 26 have lower nitrogen partial pressures than the range targeted in the present invention, and have low iron loss. .

The steel sheets of No. 11 and the steel sheets of No. 22, No. 23 and No. 24 have a dew point outside the range of the present invention, and thus have a lower iron loss than the steel sheets manufactured according to the present invention. It is getting bigger.

[0034] The No. 12 steel plate and the No. 27 steel plate have an S content outside the range of the present invention, and thus have a higher iron loss than the steel plate manufactured by the present invention.

[0035]

As described above, in the present invention, C: 0.005% or less, Si: 4.0% or less, Mn:
0.05 to 1.0%, P: 0.1% or less, N: 0.005% or less (including 0), S: 0.001% or less (including 0), Al: 1.0% or less, with the balance being substantially Fe After hot rolling and pickling steel, the nitrogen partial pressure is more than 20% and the dew point is-
Since hot-rolled sheet annealing is performed in an atmosphere of 20 ° C or more and 10 ° C or less, and then cold-rolled to a predetermined thickness, and then finish-annealed, magnetic steel sheets with low iron loss can be manufactured at low cost. Can be.

This steel sheet is suitable for being widely used for applications requiring low iron loss such as electric materials.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of S in steel and iron loss.

FIG. 2 is a view showing a relationship between a hot-rolled sheet annealing atmosphere and iron loss after finish annealing.

FIG. 3 is a diagram showing the relationship between the dew point and the nitrogen partial pressure during hot-rolled sheet annealing and iron loss after finish annealing.

Claims (1)

[Claims] 1. C: 0.005% or less, Si: 4.0% by weight%
Mn: 0.05 to 1.0%, P: 0.1% or less, N: 0.005%
Or less (including 0), S: 0.001% or less (including 0), Al:
Steel containing 1.0% or less, with the balance being substantially Fe,
After hot rolling and pickling, hot rolled sheet annealing was performed in an atmosphere having a nitrogen partial pressure of 20% or more and a dew point of -20 ° C or more and 10 ° C or less, and then cold-rolled to a predetermined sheet thickness. A method for producing a non-oriented electrical steel sheet having a low iron loss, which is followed by finish annealing.