TWI551694B - Nonoriented electromagnetic steel sheet with excellent high frequency core loss property - Google Patents

Description

Non-directional electromagnetic steel sheet with excellent high frequency iron loss characteristics

The present invention relates to a non-oriented electrical steel sheet excellent in high frequency iron loss characteristics.

A motor for a hybrid automobile or an electric automobile is driven in a high frequency range of 400 Hz to 2 kHz from the viewpoint of miniaturization and high efficiency. For the non-oriented electrical steel sheet used in the core material of such a high-frequency motor, it is desirable that the iron loss at a high frequency is low.

In order to reduce iron loss at high frequencies, it is effective to reduce the thickness of the plate and increase the specific resistance. However, the method of reducing the thickness of the sheet has a problem that not only the processing is difficult due to the decrease in the rigidity of the material, but also the productivity is lowered due to an increase in the number of punching hours or the loading man-hour. On the other hand, the method of increasing the specific resistance does not have the above-described disadvantages, and therefore it is preferable as a method of reducing the high-frequency iron loss.

In order to increase the specific resistance, it is effective to add Si. However, since Si is an element having a large solid solution strengthening ability, there is a problem that the material is hardened as the amount of addition of Si increases, and the rolling property is lowered. As a means of solving the above problems One of them is a method of adding Mn instead of Si. Since Mn has a small solid solution strengthening ability compared with Si, it is possible to reduce high-frequency iron loss while suppressing a decrease in manufacturability.

As a technique for effectively utilizing the effect of adding Mn described above, for example, Patent Document 1 discloses that it contains 0.5% by mass (% by mass) to 2.5% by mass of Si, 1.0% by mass to 3.5% by mass of Mn, and 1.0% by mass. 3.0% by mass of Al non-oriented electrical steel sheet. Further, Patent Document 2 discloses a non-oriented electrical steel sheet containing 3.0% by mass or less of Si, 1.0% by mass to 4.0% by mass of Mn, and 1.0% by mass to 3.0% by mass of Al.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2002-47542

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2002-30397

However, the techniques disclosed in Patent Document 1 and Patent Document 2 have a problem in that hysteresis loss increases as the amount of Mn added increases, and a desired iron loss reduction effect cannot be obtained.

The present invention has been made in view of the above problems in the prior art, and an object thereof is to provide a non-oriented electrical steel sheet having stable and excellent high-frequency iron loss characteristics even when a large amount of Mn is contained.

In order to solve the above problems, the inventors of the present invention have focused on the impurity components contained in the steel sheet and have studied it intensively. As a result, it has been found that the high frequency iron loss characteristic of steel having a high Mn addition amount is deteriorated due to the presence of Bi contained as an impurity, and therefore, The present invention has been developed by suppressing the content of Bi and stably reducing the high-frequency iron loss even if the Mn content is high.

The present invention is a non-oriented electrical steel sheet comprising: 0.005 mass% or less of C, 1.5 mass% to 4 mass% of Si, 1.0 mass% to 5% by mass of Mn, and 0.1 mass% or less of P. 0.005 mass% or less of S, 3% by mass or less of Al, 0.005 mass% or less of N, and 0.0030 mass% or less of Bi, and the remainder is a component composition of Fe and unavoidable impurities.

The non-oriented electrical steel sheet according to the present invention is characterized by further comprising one or two selected from the group consisting of 0.0005 mass% to 0.005 mass% of Ca and 0.0002 mass% to 0.005 mass% of Mg, in addition to the above-described component composition.

Further, the non-oriented electrical steel sheet according to the present invention is characterized by further comprising one or two selected from the group consisting of 0.005 mass% to 0.05 mass% of Sb and 0.0005 mass% to 0.05 mass% of Sn in addition to the above-described component composition. .

Moreover, the non-oriented electrical steel sheet according to the present invention is characterized by further containing 0.0005 mass% to 0.0030 mass% of Mo in addition to the above component composition.

Moreover, the non-oriented electrical steel sheet according to the present invention is characterized in that the content of Ti is 0.002% by mass or less.

According to the present invention, by suppressing the content of Bi contained as an impurity, even if the amount of Mn added is high, a non-oriented electrical steel sheet having excellent high-frequency iron loss characteristics can be stably produced with good productivity.

Fig. 1 is a graph showing the effect of the inclusion of Bi on the relationship between the Mn content and the high-frequency iron loss W _10/400 .

Fig. 2 is a graph showing the relationship between the Bi content and the high frequency iron loss W _10/400 .

First, an experiment which is an opportunity for development of the present invention will be described.

Steel is melted in the laboratory to form a steel block, and hot rolling is performed, and hot rolling sheet annealing at 1000 ° C × 30 sec is performed in a 100 vol% N ₂ environment, followed by cold rolling. A cold-rolled sheet having a thickness of 0.30 mm and a finish annealing of 1000 ° C × 30 sec in a 20 vol% H _{2 -} 80 vol% N ₂ atmosphere, the steel containing 0.0016 mass% of C, 3.35 mass% Si, 0.013 mass% of P, 0.0004% by mass of S, 1.4% by mass of Al, and 0.0018 mass% of N steel are used as a base, and Mn is allowed to be in a range of 0.1% by mass to 5.2% by mass. Change is added to it.

The symbol of Fig. 1 is the relationship between the above experimental results and the relationship between the amount of addition of Mn and the iron loss W _10/400 . From the above results, it is understood that when Mn is less than 1% by mass, the iron loss decreases as the amount of Mn added increases, and when Mn is 1% by mass or more, the iron loss decreases, and when Mn exceeds 4% by mass, iron The damage increases. In order to investigate the cause, a steel sheet containing 2% by mass of Mn was observed by a transmission electron microscope (TEM), and as a result, granular Bi was observed at a grain boundary.

Therefore, in order to further investigate the influence of Bi on the magnetic properties, the steel was melted in the laboratory, and a cold rolled annealed sheet was prepared in the same manner as the above experiment, and the iron loss W _{10/400 was} measured, and the steel was 0.0014 mass. % of C, 3.33 mass% of Si, 1.2 mass% of Al, 0.014 mass% of P, 0.0006 mass% of S, 0.0020 mass% of N and a content of Bi of 0.0010 mass% or less are used as a matrix, and The Mn is added in various amounts within a range of 0.1% by mass to 5.2% by mass.

The experimental results thus obtained are indicated by the ▲ symbol in FIG. From the above results, it is understood that in the cold-rolled annealed sheet using the high-purity steel having reduced Bi, the amount of Mn added is increased, and the iron loss is lowered with respect to the steel sheet indicated by the ● symbol. Further, when a steel sheet containing 2% by mass of Mn was observed by TEM, no granular Bi was observed in the grain boundary. From the above results, it is presumed that the increase in iron loss caused by an increase in the amount of added Mn in the steel sheet of the above-mentioned symbol is due to an increase in hysteresis loss due to fine precipitation of Bi.

On the other hand, in the steel sheet having less than 1% by mass of Mn, although the effect of improving the iron loss obtained by the decrease in Bi was observed, the reason was small, and the reason was not sufficiently clarified, but it was considered that the cause was increased. In the steel having the Mn content, the driving force for grain growth is lowered by the solute drag of Mn, and therefore the grain growth is likely to be greatly affected by the presence of a trace amount of Bi.

Bi is usually an impurity that is mixed in from scrap. With the increase in the use ratio of scrap in recent years, not only the amount of incorporation is gradually increasing, but also the unevenness of the incorporation is gradually increasing. It is considered that the increase in the Bi content as described above does not become a major problem in the electromagnetic steel sheet having a low Mn content, but is high in the Mn content. In steel, since the grain growth property is lowered by the solute drag of Mn, it is greatly affected by a small amount of Bi.

Next, in order to investigate the influence of the Bi content on the iron loss, the steel was melted in the laboratory, and a cold rolled annealed sheet having a thickness of 0.30 mm was produced in the same manner as the above experiment, and the iron loss W _{10/400 was} measured. The steel is based on a steel containing 0.0022% by mass of C, 3.20% by mass of Si, 1.7% by mass of Mn, 1.3% by mass of Al, 0.014% by mass of P, 0.0005% by mass of S, and 0.0020% by mass of N. Further, the content of Bi is changed in a range of a trace amount (trace, tr.) to 0.0045 mass%, and is added thereto.

In Fig. 2, the above experimental results are expressed as the relationship between the Bi content and the iron loss W _10/400 . As is apparent from the above-described FIG. 2, when the Bi content is 0.0030% by mass or less (30 ppm by mass or less), the iron loss is largely lowered. The reason for this is considered to be that the grain growth property is improved by reducing Bi. From the above results, it is understood that in order to suppress the adverse effect of Bi on the grain growth, it is necessary to reduce the content of Bi to 0.0030% by mass or less. The present invention is based on the above novel insights.

Next, the chemical composition of the non-oriented electrical steel sheet of the present invention will be described.

C: 0.005 mass% or less

C is an element which forms a carbide with Mn. When the amount exceeds 0.005 mass%, the amount of the Mn-based carbide increases and the grain growth is inhibited. Therefore, the upper limit is made 0.005 mass%. It is preferably 0.002% by mass or less.

Si: 1.5% by mass to 4% by mass

Si is an element which effectively increases the specific resistance of steel and reduces iron loss, and therefore is added in an amount of 1.5% by mass or more. On the other hand, when the addition exceeds 4% by mass, the magnetic flux density decreases, so the upper limit is made 4% by mass. The lower limit of Si is preferably 2.0% by mass, and the upper limit is 3.0% by mass.

Mn: 1.0% by mass to 5% by mass

Mn does not greatly impair the workability, but effectively increases the specific resistance of the steel to reduce the iron loss. In the present invention, it is an important component and is added in an amount of 1.0% by mass or more. In order to further obtain the iron loss reducing effect, it is preferable to add 1.6% by mass or more. On the other hand, when the addition exceeds 5% by mass, the magnetic flux density is lowered, so the upper limit is made 5% by mass. The lower limit of Mn is preferably 2% by mass, and the upper limit is 3% by mass.

P: 0.1% by mass or less

P is an element having a large solid solution strengthening ability. When the content is more than 0.1% by mass, the steel sheet is too hard and the manufacturability is lowered. Therefore, it is limited to 0.1% by mass or less. It is preferably 0.05% by mass or less.

S: 0.005 mass% or less

When S is an unavoidable impurity, when the content exceeds 0.005 mass%, grain growth is inhibited by precipitation of MnS, and iron loss is increased. Therefore, the upper limit is made 0.005 mass%. It is preferably 0.001% by mass or less.

Al: 3 mass% or less

Similarly to Si, Al is an element which effectively increases the specific resistance of steel and reduces iron loss. When the addition exceeds 3% by mass, the magnetic flux density decreases, so the upper limit is 3% by mass. It is preferably 2% by mass or less. However, if the content of Al is less than 0.1% by mass, Since fine AlN is precipitated to inhibit grain growth and increase iron loss, the lower limit is preferably made 0.1% by mass.

N: 0.005 mass% or less

N is an unavoidable impurity that permeates into the steel from the atmosphere. When the content is large, the grain growth is inhibited by the precipitation of AlN, and the iron loss is increased. Therefore, the upper limit is limited to 0.005 mass%. It is preferably 0.003 mass% or less.

Bi: 0.0030% by mass or less

In the present invention, Bi is an important management element which adversely affects the high-frequency iron loss characteristics. As is apparent from Fig. 2 above, if the content of Bi exceeds 0.0030% by mass, the iron loss increases sharply. Therefore, Bi is limited to 0.0030% by mass or less. It is preferably 0.0010% by mass or less.

The non-oriented electrical steel sheet of the present invention preferably contains any one or two of Ca and Mg in addition to the above-described component composition.

Ca: 0.0005 mass% to 0.005 mass%

Ca is an element which forms a sulfide and is coarsely precipitated by precipitation with Bi, thereby effectively suppressing the adverse effects of Bi and reducing iron loss. In order to obtain the above effects, it is preferred to add 0.0005 mass% or more. However, when the addition exceeds 0.005 mass%, the amount of precipitation of CaS becomes excessive and the iron loss increases, so the upper limit is preferably made 0.005 mass%. More preferably, the lower limit of Ca is 0.001% by mass, and the upper limit is 0.004% by mass.

Mg: 0.0002% by mass to 0.005% by mass

Mg is an element which forms an oxide and is coarsely formed by precipitation with Bi, thereby effectively suppressing the adverse effects of Bi and reducing iron loss. In order to obtain the above effects, it is preferred It is added in an amount of 0.0002% by mass or more. However, it is difficult to add more than 0.005 mass%, and the random addition only causes an increase in cost. Therefore, the upper limit is preferably made 0.005 mass%. More preferably, the lower limit of Mg is 0.001% by mass, and the upper limit is 0.004% by mass.

Moreover, it is preferable that the non-oriented electrical steel sheet of the present invention contains the following components in addition to the above-described component composition.

Sb: 0.0005 mass% to 0.05 mass%, Sn: 0.0005 mass% to 0.05 mass%

Since Sb and Sn have an effect of improving the texture and increasing the magnetic flux density, they can be added separately or in combination of 0.0005 mass% or more. More preferably, it is 0.01% by mass or more. However, when the addition of more than 0.05% by mass causes embrittlement of the steel sheet, the upper limit is preferably made 0.05% by mass. More preferably, the lower limit of Sb and the lower limit of Sn are 0.01% by mass, respectively, and the upper limit of Sb and the upper limit of Sn are respectively 0.04% by mass.

Mo: 0.0005 mass% to 0.0030 mass%

Since Mo has an effect of coarsening the formed carbide to reduce iron loss, it is preferably added in an amount of 0.0005 mass% or more. However, when 0.0030% by mass or more is added, the amount of carbides is excessively increased, and the iron loss is increased. Therefore, the upper limit is preferably made 0.0030% by mass. More preferably, the lower limit of Mo is 0.0010% by mass, and the upper limit is 0.0020% by mass.

Ti: 0.002% by mass or less

Ti is an element which forms a carbonitride. When the content is large, the amount of precipitation of the carbonitride is excessively increased to inhibit grain growth, and the iron loss is increased. Therefore, in the present invention, Ti is preferably limited to 0.002% by mass or less. More preferably, it is 0.001% by mass or less.

Further, in the non-oriented electrical steel sheet of the present invention, the remainder other than the above components is Fe and unavoidable impurities. However, it is allowed to contain other elements as long as it does not impair the effects of the present invention.

Next, a method of producing the non-oriented electrical steel sheet of the present invention will be described.

When the method for producing a non-oriented electrical steel sheet according to the present invention is produced by setting the chemical composition of the steel sheet within the above-described range of the present invention, the other conditions are not particularly limited, and the ordinary non-oriented electrical steel sheet can be used. Manufactured under the same conditions. For example, it can be produced by using a converter furnace or a degassing treatment apparatus or the like to perform ingots on steels suitable for the composition of the present invention, and by continuous casting or ingot casting (ingot casting) After the steel raw material (slab) is formed by block rolling or the like, hot rolling is performed, and hot-rolled sheet annealing is performed as needed, followed by one cold rolling or interleaving intermediate annealing twice. The above-described cold rolling is formed into a predetermined thickness, and then the finished annealing is performed.

[Examples]

The molten steel blown by the converter was degassed and cast into steel having the composition shown in Table 1, and then continuously cast to prepare a slab, and a slab of 1100 ° C × 1 hr was produced. After the heating, hot rolling was carried out at a hot rolling end temperature of 800 ° C, and coiled at a temperature of 610 ° C to prepare a hot rolled sheet having a thickness of 1.8 mm. Next, the hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000 ° C for 30 sec in a 100 vol% N ₂ atmosphere, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.35 mm, and at 20 vol% H ₂ - In an 80 vol% N ₂ environment, finish annealing at 980 ° C × 15 sec was carried out to prepare a cold rolled annealed sheet.

From the thus obtained cold-rolled annealed sheet, an Epstein test piece having a width of 30 mm and a length of 280 mm was cut out from the rolling direction and the direction perpendicular to the rolling direction, and the iron loss W _10/400 and the magnetic flux density B _{50 were} measured in accordance with JIS C2550. The results are shown in Table 1-1 to Table 1-2.

As is understood from Table 1-1 to Table 1-2, the steel sheet satisfying the composition of the present invention, particularly the steel sheet having reduced Bi, is excellent in high-frequency iron loss characteristics although the Mn content is high.

Claims (9)

A non-oriented electrical steel sheet comprising: 0.005 mass% or less of C, 1.5 mass% to 4 mass% of Si, 1.0 mass% to 5% by mass of Mn, 0.1 mass% or less of P, and 0.005 mass% or less of S. 3% by mass or less of Al, 0.005 mass% or less of N, and 0.0030 mass% or less of Bi, and the remainder is a component composition of Fe and unavoidable impurities. The non-oriented electrical steel sheet according to the first aspect of the invention, which further comprises, in addition to the component composition described above, one selected from the group consisting of 0.0005 mass% to 0.005 mass% of Ca and 0.0002 mass% to 0.005 mass% of Mg. Or two. The non-oriented electrical steel sheet according to the first or second aspect of the invention, further comprising, in addition to the component composition, Sb and 0.0005 mass% to 0.05 mass% of Sn selected from 0.0005 mass% to 0.05 mass% One or two of them. The non-oriented electrical steel sheet according to the first or second aspect of the invention, wherein the non-oriented electrical steel sheet further contains 0.0005 mass% to 0.0030 mass% of Mo in addition to the component composition. The non-oriented electrical steel sheet according to claim 3, which further contains 0.0005 mass% to 0.0030 mass% of Mo in addition to the above component composition. The non-oriented electrical steel sheet according to the first or second aspect of the invention, wherein the content of Ti is 0.002% by mass or less. A non-oriented electrical steel sheet according to claim 3, wherein The content of Ti is 0.002% by mass or less. The non-oriented electrical steel sheet according to claim 4, wherein the content of Ti is 0.002% by mass or less. The non-oriented electrical steel sheet according to claim 5, wherein the content of Ti is 0.002% by mass or less.