JP2001294998A - Nonoriented silicon steel sheet excellent in corrosion resistance and high frequency magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonoriented silicon steel sheet combining excellent corrosion resistance with excellent high frequency magnetic properties, particularly suitable for high frequency use, and increased in industrial value. SOLUTION: The nonoriented silicon steel sheet excellent in corrosion resistance and high frequency magnetic properties has a composition consisting of 2.5-10 mass % Si, 1.5-20 mass % Cr, C and N in amounts reduced to <=0.0010 mass % and <=0.0050 mass %, respectively, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet, and more particularly to a steel sheet having excellent corrosion resistance and high-frequency magnetic properties.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are known as magnetic materials, and are frequently used mainly in various types of iron cores for commercial frequencies. However, when the operating frequency is higher than the commercial frequency, there is a disadvantage that the iron loss of a normal non-oriented electrical steel sheet whose Si content is 3.5 wt% or less increases. For example, in recent years, in electrical equipment, products adopting an inverter system have been increasing for higher efficiency and power saving, and a high-frequency reactor is used for such inverter equipment. Since these high-frequency reactors are usually used in the frequency range of 10 kHz or more, it is difficult to use conventional non-oriented electrical steel sheets because they generate a large amount of heat. there were.

[0003] In order to improve high frequency iron loss, it is important to increase the specific resistance of steel, and generally, a method of increasing the content of Si or Al has been adopted. However, when the contents of Si and Al are increased, the workability is deteriorated, and it is difficult to produce the same by a usual method. Techniques for improving the manufacturability include a method of hot rolling under high temperature and low pressure described in JP-A-61-166923 for a high silicon steel sheet,
There is a method based on the diffusion and infiltration treatment of Si described in Japanese Patent Application Laid-Open No. 2-227078. However, both technologies have high S
i, It did not essentially improve the brittleness inherent in Al steel, and the products produced therefrom had extremely poor workability and were difficult to process into reactor core. Further, the former technique disclosed in Japanese Patent Application Laid-Open No. 61-166923 requires fine adjustment of the rolling structure to apparently improve the brittleness of the alloy, and strict control is required in the manufacturing process. Since it must be performed, it is difficult to produce industrially stably. On the other hand, the latter technique disclosed in JP-A-62-227078 uses a special diffusion infiltration method, which is extremely disadvantageous in terms of cost in the case of industrial production. It is disadvantageous for high-frequency iron loss because it becomes coarse.

[0004] In fact, a steel sheet containing 6.5 mass% of Si exists as a high Si material by diffusion and infiltration of Si, and is used as a reactor core for an inverter air conditioner, but its growth is about 5%. However, since punching and bending are difficult with a normal method, strip-shaped steel plates are laminated to produce a reactor core. If bending and punching are possible in the usual way, punched and laminated cores such as wound cores and EI cores can be manufactured,
Significantly contributes to the reduction of the processing cost.

A technique of adding Cr to increase the specific resistance of steel without increasing the amount of Si is disclosed in JP-A-11-22909.
No. 5 publication. However, the content of Si is not beyond the range of ordinary silicon steel sheets, and is intended for electric vehicle motor core materials,
The usable frequency range also corresponds to a frequency of less than 1 kHz, similar to conventional silicon steel sheets for high frequency applications,
As a material used for high frequencies of 10 kHz or more, sufficient high-frequency magnetic characteristics have not been obtained.

[0006]

As described above, in the prior art, increasing the specific resistance until it can be used for a high frequency of 10 kHz or more has not been performed except for the use of Si and Al. At present, it has not been attempted to improve the brittleness inherent in the high Si, Al steel material itself, which has increased the specific resistance of the steel. In addition, although high-frequency non-oriented electrical steel sheets for high frequency use are required to have good corrosion resistance depending on the application, they cannot be said to have sufficient corrosion resistance in the prior art.

In view of the above, the present invention has
By improving the brittleness of Si steel, it facilitates production and improves the workability of the product, and thus has both high specific resistance, good punching workability and bending workability, and also has excellent corrosion resistance and excellent high-frequency magnetic properties The purpose is to propose a non-oriented electrical steel sheet.

[0008]

Means for Solving the Problems The present inventors have proposed Fe-Si alloys and the like.
After conducting research and development on Fe-Si-Al alloys to achieve both high resistivity and good workability of the alloys, we gained the knowledge that coexistence of Cr is effective and obtained the results. It is disclosed in JP-A-11-343544. That is, in the Fe-Si alloy and the Fe-Si-Al alloy, it has been thought that toughness deteriorates as Cr is added. However, even when the content of Si is 3 mass% or more, C and It has been found that, by sufficiently reducing the N content and then adding a certain amount or more of Cr, rather high toughness can be obtained.

[0009] Based on such technology, the inventors have conducted intensive studies with the aim of further improving the corrosion resistance, and as a result, C has been particularly improved.
It has been found that by reducing the content to 0.0010 mass% or less, the corrosion resistance is significantly improved.

The present invention is based on the above findings. That is, according to the present invention, the content of Si is 2.5 to 10% by mass and
Contains 1.5 to 20 mass%, and contains C and N respectively.
A non-oriented electrical steel sheet which is reduced to 0.0010 mass% or less and 0.0050 mass% or less, with the balance being Fe and unavoidable impurities, and having excellent corrosion resistance and high-frequency magnetic properties.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Regarding the magnetic properties of a non-oriented electrical steel sheet according to the present invention, a synergistic effect on the increase of the specific resistance can be obtained by adding Cr simultaneously with Si or Si and Al. As a result, iron loss, especially in the high frequency
Only, or can be significantly reduced as compared to an alloy system containing Si and Al.

Further, the material having a high specific resistance so far has a poor rolling property, and the thickness is reduced only to about 0.5 mm by the ordinary rolling method. It has also been said that simply reducing the thickness does not allow a sufficient reduction in iron loss due to hysteresis loss. However, as a result of the inventors' earnest research, as in the present invention, by controlling the components and purity,
The effect of the high-frequency iron loss characteristics when the thickness is reduced can be promoted.

Further, by setting the content of C to 0.0010 mass% or less, the generation of Cr carbide harmful to corrosion resistance is reduced, and a passive film made of Cr oxide is firmly formed on the surface of the steel sheet as in the case of stainless steel. While the details are unknown, the synergistic effect with Si improves the corrosion resistance of the passivation film, so that good corrosion resistance comparable to stainless steel can be obtained. FIG. 1 shows the results of a corrosion resistance test performed on steels other than C having the component composition of the steel sheet of the present invention and various C contents. As shown in FIG.
It can be seen that by setting the content to not more than mass%, the corrosion resistance is remarkably improved.

Hereinafter, the present invention will be described in detail. First,
The reason for limiting the component composition range in the non-oriented electrical steel sheet of the present invention will be described. Cr is a basic alloying element that greatly improves the specific resistance of steel by synergistic effect with Si, reduces iron loss in high frequency range, and further improves corrosion resistance. Even in the case of Si content, it is extremely effective for obtaining toughness to the extent that ordinary rolling is possible, and from that viewpoint, 2 mass% or more is required. When the amount of Si is smaller than the above case, workability can be ensured even if the Cr amount is further reduced, but in order to exhibit the effect of improving workability by containing Cr, and to make the specific resistance of steel 60 μΩcm or more. , 1.5 mass% or more of Cr is essential. On the other hand, 20ma
If the content exceeds ss%, the effect of improving toughness is saturated and the cost is increased. Therefore, the range of the Cr content is 1.5 mass%.
Not less than 20 mass%, preferably not less than 2 mass% and 10 ma
ss% or less, more preferably 3 mass% or more and 7 mass% or less.

Although Si alone increases the specific resistance of steel, it is a component that is effective for significantly increasing the specific resistance by a synergistic effect with Cr, and particularly for reducing iron loss in a high frequency range. . If the amount of Si is less than 2.5 mass%, even if Cr is used in combination, it is not possible to obtain a specific resistance of 60 μΩcm or more without sacrificing the magnetic flux density, so that good high frequency magnetic characteristics cannot be obtained. On the other hand, if the content exceeds 10 mass%, the toughness until normal rolling cannot be ensured even when Cr is contained, so the content range of Si is 2.5 mass% or more and 10 mass% or less, preferably 2.5 mass% or more. , 7 mass% or less, more preferably 3.5 mass% or more and 5 mass% or less.

Since C is a component that deteriorates the toughness of the Fe—Cr—Si based alloy, it is preferable to reduce C as much as possible. Moreover, by reducing C, the corrosion resistance can be remarkably improved. Therefore, in the present invention,
C content is set to 0.0010 mass% or less.

Since N deteriorates the toughness of the Fe—Cr—Si based alloy, it is preferable to reduce N as much as possible. The allowable amount of N is high toughness in the case of the amounts of Cr, Si and Al according to the present invention. It is necessary to keep the content to 0.005 mass% or less in order to secure Preferably, it is 0.003 mass% or less, more preferably 0.1 mass%.
0015 mass% or less is good.

Although the amount of impurities other than C and N is not particularly limited, it is important to limit the amount of impurities to the following ranges in order to maintain good magnetic properties and workability similarly to general silicon steel. S is 0.005 mass% or less, preferably 0.002 mass% or less, and more preferably 0.001 mass% or less. O is 0.00
5 mass% or less, preferably 0.003 mass% or less, more preferably 0.0015 mass% or less. V is 0.005% or less, preferably 0.002% or less, more preferably 0.0015% or less.
% Or less is good. In addition, it is preferable to reduce La, Mg, and the like as much as possible.

In the steel sheet of the component of the present invention, reducing the sheet thickness promotes the effect of improving the high-frequency iron loss characteristics. However, in order to obtain the effect of the reduction in thickness, the sheet thickness should be 0.4 mm or less. It is effective to do. However, in order to make it thinner than 0.01 mm, not only the production cost becomes higher, but also extra care must be taken in handling the steel sheet, and the cost of product production becomes higher. mm or less is preferable. More preferably, it is 0.02 to 0.25 mm.

In order to achieve excellent high-frequency iron loss, it is necessary to increase the specific resistance. In the steel of the present invention, it is desirable that the steel has a resistivity of at least 60 μΩcm or more. If the specific resistance is lower than 60 μΩcm, a desired high-frequency iron loss cannot be obtained even if the sheet thickness is reduced. Therefore, in the present invention, the specific resistance is preferably set to 60 μΩcm or more.

The steel sheet of the present invention has an average crystal grain size of 5 μm
As described above, the thickness is preferably 100 μm or less. The iron loss in the high frequency range has a large ratio of eddy current loss, and this eddy current loss can be reduced by reducing the average crystal grain size of the steel sheet. That is, by setting the average crystal grain size of the steel sheet to 100 μm or less, the iron loss characteristics in a high frequency range can be further improved. If the average crystal grain size exceeds 100 μm, iron loss in the high frequency range is particularly deteriorated, and desired iron loss characteristics cannot be obtained.If the average crystal grain size is less than 5 μm, control is not performed in normal production. In the present invention, the upper limit of the average crystal grain size is limited because it is difficult to obtain a grain-sized structure and the magnetic properties deteriorate.
It is desirable to set the lower limit to 100 μm or less and the lower limit to 5 μm or more.

The non-oriented electrical steel sheet of the present invention can be manufactured by the following method. The alloy material adjusted to the component composition range described above can be made into a slab by continuous casting or ingot-bulking rolling. In addition, a thin slab can be manufactured by using a thin slab continuous casting method. The obtained slab is subjected to hot rolling after heating and holding, or as in the CC-DR method (a method of directly feeding and rolling after continuous casting) or an HCR method (a method of keeping the temperature after continuous casting). It can be subjected to hot rolling without heating while maintaining the sensible heat during continuous casting.

The steel of the present invention has good rolling workability since the amount of carbon is reduced as much as possible. Therefore, a means for heating and holding the slab from the continuous casting to the hot rolling is unnecessary. In hot rolling, by rolling as thinly as possible, workability in the next step of cold rolling or warm rolling, ie, rollability, can be improved. This is based on the new finding that in the case of the Fe-Cr-Si-based alloy composition of the present invention, the surface portion of the hot-rolled sheet has higher toughness than the central portion and has excellent workability. is there. The thickness of the hot rolled sheet for that purpose is 3 mm or less, preferably 2.
5 mm or less, more preferably 2.0 mm or less.

After the hot rolling, if necessary, hot rolled sheet annealing is performed. By performing the hot-rolled sheet annealing, the texture of the rolled material is improved, which advantageously works to improve the iron loss characteristics. The hot-rolled sheet annealing conditions include, for example, a temperature of 700 to 1100
C. for 1 second to 2 hours. When the annealing temperature is high or the annealing time is long, the annealing effect is saturated and further improvement of the iron loss characteristics cannot be expected and causes a cost increase.When the annealing temperature is low or the annealing time is short. Since the effect of improving the iron loss characteristics is small, it may be determined within the above range in consideration of these effects.

After the hot rolling or, if necessary, after the hot-rolled sheet annealing, the hot-rolled scale is removed by pickling or shot blasting, and then cold rolling or warm rolling is performed.
Since the toughness of the hot-rolled sheet is improved by adjusting the material components and the purity, the sheet can be further rolled warm or cold to make a sheet having a thickness of 0.4 mm or less. Generally, when the thickness is reduced,
It is well known that eddy current loss is advantageously suppressed, especially at high frequencies, resulting in low iron loss. However, conventionally, a material having a high specific resistance has poor rollability, and may be 0.5% by a normal rolling method.
The thickness was reduced only to about mm. It has also been said that simply reducing the thickness does not allow a sufficient reduction in iron loss due to hysteresis loss. In this regard, in the present invention, the effect of high-frequency iron loss characteristics when the thickness is reduced can be promoted by adjusting the material components and the purity. In order to obtain such an effect of thickness reduction, it is effective to make the plate thickness 0.4 mm or less. However, to make it thinner than 0.01mm,
Due to industrial unreasonability, the range of plate thickness is 0.01 to 0.4 mm,
Preferably, it is defined as 0.02 to 0.25 mm.

The above-described cold rolling and warm rolling are performed by one rolling or two or more rollings including intermediate annealing.
Performing the intermediate annealing has an advantageous effect on the improvement of the magnetic properties through the improvement of the texture of the rolled material. Further, the workability of the cold rolling and the warm rolling can be improved. The condition of the intermediate annealing is, for example, at a temperature of 600 to 1100 ° C for a time of 1 second to 10
Minute range. When the annealing temperature is low or the annealing time is short, the effect of improving the iron loss characteristics is small, and when the annealing temperature is high or the annealing time is long, the annealing effect is saturated and the iron loss characteristics can be further improved. Since it is not possible and causes a cost increase, it is sufficient to set the above range within consideration of these effects. Here, cold rolling and warm rolling are preferably performed at the lowest possible temperature in terms of cost. When performing warm rolling, it is desirable to set the temperature to about 300 ° C. or less.

After cold rolling and warm rolling, finish annealing is performed, and an insulating film is further applied to obtain a product. The conditions for the finish annealing and the conditions for forming the insulating coating may be the same as those commonly used for ordinary electromagnetic steel sheets and electromagnetic stainless steel sheets. Further adjusting the material components and / or
Alternatively, by controlling the temperature conditions of the finish annealing, the average crystal grain size can be reduced to 100 μm or less.

[0028]

EXAMPLE A steel containing the composition shown in Table 1 and the remainder consisting of Fe and unavoidable impurities was smelted, slab-formed by continuous casting, reheated, and hot-rolled to a thickness of 2.0 mm by hot rolling. It was a rolled sheet. After removing the scale of these hot rolled sheets,
Cold rolling was performed to a sheet thickness of 0.35 mm, and intermediate annealing was performed at a temperature of 800 ° C. for 10 seconds in a hydrogen / nitrogen mixed atmosphere. These steel sheets are further cold-rolled to a thickness of 0.1 mm, and
The final annealing for 2 seconds was performed in a hydrogen / nitrogen mixed atmosphere to provide an insulating film. The obtained product is cut into Epstein samples, and the magnetism is measured according to JIS C 2550 (1975).
Table 2 shows the results. The rollability is marked with ◎,
One or more cracks at one or more places per 5 m
The mark and the sheet that was broken and could not be rolled were marked X. For corrosion resistance, a salt spray test in accordance with JIS Z2371 was performed for 2 hours. The results are shown in Table 2. The mark ◎ indicates that the area of rust generated on the plate surface was 10% or less, and △ indicates that it exceeded 10% and was 50% or less.
If the mark exceeds 50%, the evaluation is indicated by the mark x.

[0029]

[Table 1]

[0030]

[Table 2]

From the results shown in Table 2, the C content was 0.0010 mass%.
In the following examples, it is understood that the rolling property is good and the corrosion resistance is remarkably improved.

[0032]

As described above, the non-oriented electrical steel sheet of the present invention has both excellent corrosion resistance and high-frequency magnetic properties.
It is particularly suitable for high frequency applications, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between C content and corrosion resistance.

Continued on the front page (72) Inventor Masaki Kono 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. (Without address) Inside the Mizushima Works, Kawasaki Steel Corporation (72) Inventor Masaaki Kawano 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama None) Inside of Mizushima Works, Kawasaki Steel Corporation (72) Inventor Atsuto Honda 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture (No address) Inside of Mizushima Works, Kawasaki Steel Corporation F-term (reference) 5E041 AA02 AA19 CA01 NN01

Claims (1)

[Claims] (1) 2.5 to 10 mass% of Si and 1.5 to 20 mass% of Cr
%, And C and N are reduced to 0.0010 mass% or less and 0.0050 mass% or less, respectively, and the balance is composed of Fe and inevitable impurities. steel sheet.