RU2650469C2 - Non-oriented magnetic steel sheet with excellent high frequency iron loss characteristics - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy, specifically to a non-oriented electrical steel sheet used for making cores of high-frequency motors. Sheet is made of steel of the following chemical composition, wt%: C: not more than 0.005, Si: 1.5–4, Mn: from more than 3.0 to not more than 5.0, P: not more than 0.1, S: not more than 0.005, Al: no more than 3, N: not more than 0.005, Bi: 0.0002–0.003, Ti: not more than 0,002, the balance is Fe and inevitable impurities.

EFFECT: stable high frequency iron loss characteristics.

5 cl, 2 dwg, 1 tbl

Description

FIELD OF THE INVENTION

The invention relates to a sheet of non-textured electrical steel with excellent loss in iron at a high frequency.

Prior art

The engine for hybrid cars and electric vehicles operates in the high-frequency range from 400 Hz to 2 kHz in terms of miniaturization and high efficiency. The non-textured electrical steel sheet used in the core material of such a high frequency motor should preferably have low iron loss at high frequency.

Effective in reducing losses in iron at high frequency is a decrease in sheet thickness and an increase in resistivity. However, the method of reducing the sheet thickness is complicated by a decrease in productivity, not only because the processing of the material is difficult due to a decrease in its rigidity, but also because of an increase in the number of stampings or stacking stages. On the contrary, the method of increasing the resistivity does not have the above drawback, so that it is preferred as a method of reducing losses in iron at a high frequency.

The addition of Si is effective in increasing the resistivity. However, Si is an element with significant solid-solution hardening ability, so there is a problem in that the material hardens with an increase in the added amount of Si, which impairs rolling ability. As a means of solving this problem, there is a way to add Mn instead of Si. Since Μn has little solid-solution hardening ability compared to Si, high-frequency iron loss can be reduced while suppressing performance degradation.

For example, as a method using the above effect of adding Mn, Patent Document 1 discloses a non-textured electrical steel sheet containing Si: 0.5-2.5 wt.%, Mn: 1.0-3.5 wt.% And Al : 1.0-3.0 wt.%. Also, Patent Document 2 discloses a non-textured electrical steel sheet containing Si: not more than 3.0 wt.%, Mn: 1.0-4.0 wt.% And Al: 1.0-3.0 wt.%.

Prior art documents

Patent documents

Patent Document 1: JP-A-2002-47542

Patent Document 2: JP-A-2002-30397

Summary of the invention

The problem solved by the invention

However, the problem with the methods disclosed in Patent Documents 1 and 2 is that the hysteresis loss increases with the added amount of Mn and, therefore, the desired effect of reducing iron loss cannot be achieved.

The invention is made taking into account the above problem inherent in the prior art, and its task is to create a sheet of non-textured electrical steel with suitable stable losses in iron at a high frequency, even if a large amount of Mn is introduced.

The solution of the problem

The inventors conducted various studies of the impurity ingredients included in the steel sheet to solve the above problem. As a result, it was found that the deterioration of losses in iron at a high frequency of steel with the addition of a large amount of Mn depends on the presence of Bi, which is an impurity, and, therefore, losses in iron at a high frequency can be stably reduced by suppressing the Bi content even at a high content Mn, therefore, the invention has been completed.

The present invention is based on the above data and is a sheet of non-textured electrical steel with a chemical composition, including C: not more than 0.005 wt.%, Si: 1.5-4 wt.%, Mn: 1.0-5 wt.%, P : not more than 0.1 wt.%, S: not more than 0.005 wt.%, Al: not more than 3 wt.%, N: not more than 0.005 wt.%, Bi: not more than 0.0030 wt.%, Ti: not more than 0.002 and the rest of Fe and inevitable impurities.

A non-textured electrical steel sheet according to the invention is characterized in that it contains one or two elements of Ca: 0.0005-0.005 wt.% And Mg: 0.0002-0.005 wt.% In addition to the above chemical composition.

Also, a non-textured electrical steel sheet in accordance with the invention is characterized in that it further comprises one or two elements of Sb: 0.0005-0.05 wt.% And Sn: 0.0005-0.05 wt.% In addition to the above chemical composition.

In addition, a sheet of non-textured electrical steel in accordance with the invention is characterized in that it further comprises Mo: 0.0005-0.0030 wt.% In addition to the above chemical composition.

In addition, a sheet of non-textured electrical steel in accordance with the invention is characterized by a Ti content of not more than 0.002 wt.%.

Effect of the invention

According to the invention, it is possible to stably produce a non-textured electrical steel sheet with excellent iron loss at a high frequency by reducing the Bi content as an impurity, even if the added amount of Mn is high.

Brief Description of the Drawings

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

FIG. 2 is a graph illustrating the relationship between Bi content and iron loss at high frequency W _10/400 .

The implementation of the invention

First, the experiment leading to the invention will be described.

Steel containing C: 0.0016 wt.%, Si: 3.35 wt.%, P: 0.013 wt.%, S: 0.0004 wt.%, Al: 1.4 wt.% And N: 0. 0018 wt.%, And with the addition of varying amounts of Mn in the range of 0.1-5.2 wt.%, They are melted in the laboratory and formed into a hot-rolled steel ingot, annealed in the hot zone at 1000 ° C in an atmosphere of 100% about. N ₂ for 30 seconds, cold rolling to obtain a cold-rolled sheet with a thickness of 0.30 mm and subjected to final annealing at 1000 ° C atmosphere of 20% vol. H ₂ - 80% vol. N ₂ for 30 seconds.

In FIG. 1, the symbol • represents the above experimental results as the ratio between the added amount of Mn and the iron loss W _10/400 . As can be seen from these results, when Mn is less than 1 wt.%, Iron loss decreases with increasing added amount of Mn, but the decrease in iron loss becomes insignificant with an amount of not less than 1 wt.%, And iron loss increases when exceeding 4 wt. % In this case, when examining a steel sheet containing 2 wt.% Mn with TEM, granular Bi at grain boundaries is observed.

In order to further study the effect of Bi on the magnetic properties of steel, prepared by adding various amounts of Mn in the range of 0.1-5.2 wt.% To high-purity steel containing C: 0.0014 wt.%, Si: 3.33 wt. %, Al: 1.2 wt.%, P: 0.014 wt.%, S: 0.0006 wt.%, Ν: 0.0020 wt.% And Bi: not more than 0.0010 wt.%, Smelted in the laboratory and formed into a cold-rolled annealed sheet in the same manner as in the above experiment for measuring iron loss W _10/400 .

The experimental results thus obtained are represented by the ▲ symbol in FIG. 1. As can be seen from these results, the iron loss decreases with an increase in the added amount of Mn in the cold-rolled annealed sheet made of high-purity steel with a reduced Bi content, compared with the steel sheet represented by the symbol •. When a steel sheet containing 2 wt.% Mn is examined by TEM, granular Bi is not detected at the grain boundaries. Based on this fact, it is assumed that the increase in iron losses associated with the increase in the added amount of Mn in the steel sheet, indicated by the symbol •, is caused by the increase in hysteresis losses due to finely dispersed precipitates of Bi.

In a steel sheet containing less than 1 wt.% Mn, the effect of improving losses in iron due to a decrease in Bi is observed, but its proportion is insignificant. Although the reason is not clear enough, it is believed that the driving force for grain growth is reduced due to the impurity inhibition of Mn in steel with a high Mn content and, therefore, the presence of finely dispersed Bi significantly influences.

Bi, as a rule, is an impurity coming from scrap so that not only the quantity increases, but also its change gradually becomes large due to an increase in the share of scrap use in recent years. Such an increase in Bi content is not a big problem in low Mn electrical steel sheets, but high Mn steel is believed to be highly dependent on a small amount of Bi, since grain growth is reduced by impurity inhibition of Mn.

To check the effect of Bi content on iron loss, steel obtained by adding various amounts of Bi ranging from traces to 0.0045 wt.% To steel containing C: 0.0022 wt.%, Si: 3.20 wt.%, Mn : 1.7 wt.%, Al: 1.3 wt.%, P: 0.014 wt.%, S: 0.0005 wt.% And N: 0.0020 wt.%, Melted in the laboratory and molded as cold rolled annealed sheets of 0.30 mm thick in the same manner as in the above experiment for measuring iron loss W _10/400 .

In FIG. 2 shows the above experimental results in the form of a ratio between the Bi content and iron loss W _10/400 . As can be seen from FIG. 2, iron loss is significantly reduced when the Bi content is not more than 0.0030 wt.% (Not more than 30 wt. Ppm). It is believed that this is due to the fact that grain growth is improved by reducing the Bi content. This fact confirms that the Bi content must be reduced to not more than 0.0030 wt.% To suppress the negative effect of Bi on grain growth. The invention is based on the above new data.

Below will be described the chemical composition of the sheet of non-textured electrical steel in accordance with the invention.

C: not more than 0.005 wt.%

C is an element forming a carbide with Mn. When the content exceeds 0.005 wt.%, The amount of Mn-based carbide increases, preventing grain growth, so that the upper limit is 0.005 wt.%. Preferably it is not more than 0.002 wt.%.

Si: 1.5-4 wt.%

Si is an element effective to increase the resistivity of steel and reduce losses in iron and is added in an amount of at least 1.5 wt.%. While when it is added in an amount exceeding 4 wt.%, The magnetic flux density decreases, so that the upper limit is 4 wt.%. Preferably, the lower limit of the Si content is 2.0 wt.%, While its upper limit is 3.0 wt.%.

Mn: 1.0-5 wt.%

Mn is a component effective in increasing the resistivity of steel and reducing losses in iron without a significant deterioration in workability, and plays an important role in the invention so that it is added in an amount of not less than 1.0 wt.%. To obtain the additional effect of reducing iron loss, the addition of at least 1.6 wt.% Is preferred. While when it is added in an amount exceeding 5 wt.%, The magnetic flux density decreases, so that the upper limit is 5 wt.%. Preferably, the lower limit of the Mn content is 2 wt.%, While its upper limit is 3 wt.%.

P: not more than 0.1 wt.%

Ρ is an element having a significant ability for solid solution hardening, but when it is contained in an amount in excess of 0.1 wt.%, The steel sheet is significantly hardened, which reduces productivity, so that it is limited to not more than 0.1 wt.%. Preferably it is not more than 0.05 wt.%.

S: not more than 0.005 wt.%

S is an unavoidable impurity. When it is contained in an amount in excess of 0.005 wt.%, MnS precipitates impede grain growth and increase iron loss, so that the upper limit is 0.005 wt.%. Preferably it is not more than 0.001 wt.%.

Al: not more than 3 wt.%

Al is an element effective in increasing the resistivity of steel to reduce iron loss like Si. When added in an amount exceeding 3 wt.%, The magnetic flux density decreases, so that the upper limit is 3 wt.%. Preferably, the content is not more than 2 wt.%. However, when the Al content is less than 0.1 wt.%, Finely divided AlN precipitates inhibit grain growth and increase iron loss, so that the lower limit is preferably 0.1 wt.%.

N: not more than 0.005 wt.%

N is an unavoidable impurity penetrating from air into steel. When the content is large, AlN precipitation inhibits grain growth with an increase in iron loss, so that the upper limit is limited to 0.005 wt.%. Preferably it is not more than 0.003 wt.%.

Bi: not more than 0.0030 wt.%

Bi is an important element, the content of which must be controlled in the invention, since it negatively affects the loss in iron at a high frequency. When the Bi content exceeds 0.0030 wt.%, As can be seen from FIG. 2, iron loss increases sharply. Thus, the Bi content is limited to not more than 0.0030 wt.%. Preferably it is not more than 0.0010 wt.%.

The non-textured electrical steel sheet according to the invention preferably contains one or two elements of Ca and Mg in addition to the above chemical composition.

Ca: 0.0005-0.005 wt.%

Ca is an element effective for the formation of sulfide and coarsening by co-excretion with Bi, to suppress the harmful effects of Bi and reduce iron loss. To achieve this effect, it is preferable to add in an amount of not less than 0.0005 wt.%. However, when it is added in an amount in excess of 0.005 wt.%, The amount of CaS precipitates becomes too large and the iron loss increases, so that the upper limit is preferably 0.005 wt.%. More preferably, the lower limit of the Ca content is 0.001 wt.% And its upper limit is 0.004 wt.%.

Mg: 0.0002-0.005 wt.%

Mg is an element effective for the formation of oxide and coarsening by co-isolation with Bi, to suppress the harmful effects of Bi and reduce iron loss. To achieve this effect, it is preferable to add in an amount of not less than 0.0002 wt.%. However, adding an amount in excess of 0.005 wt.% Is difficult and leads to an increase in cost, so that the upper limit is preferably 0.005 wt.%. More preferably, the lower limit of the Mg content is 0.001 wt.% And its upper limit is 0.004 wt.%.

Also, a non-textured electrical steel sheet according to the invention preferably further comprises the following ingredients in addition to the above chemical composition.

Sb: 0.0005-0.05 wt.%, Sn: 0.0005-0.05 wt.%

Sb and Sn have the effect of improving texture to increase the magnetic flux density, so that they can be added in an amount of at least 0.0005 wt.% Individually or in a mixture. More preferably, the content of each is at least 0.01 wt.%. However, when added in an amount exceeding 0.05 wt.%, Brittleness of the steel sheet occurs, so that the upper limit is preferably 0.05 wt.%. More preferably, the lower limit of the content of each of Sb and Sn is 0.01 wt.% And its upper limit is 0.04 wt.%.

Mo: 0.0005-0.0030 wt.%

Mo has the effect of coarsening the resulting carbide to reduce losses in iron, and preferably it is added in an amount of not less than 0.0005 wt.%. However, when it is added in an amount in excess of 0.0030 wt.%, The amount of carbide becomes too large and the iron loss is slightly increased, so the upper limit is preferably 0.0030 wt.%. More preferably, the lower limit of the Mo content is 0.0010 wt.% And its upper limit is 0.0020 wt.%

Ti: not more than 0.002 wt.%

Ti is an element forming carbonitride. When the content is high, the amount of carbonitride precipitates becomes too large, resulting in limited grain growth, which increases the loss in iron. In the invention, therefore, the Ti content is preferably limited to not more than 0.002 wt.%. More preferably, it is not more than 0.001 wt.%.

The remainder of the composition, in addition to the above ingredients, sheet of non-textured electrical steel in accordance with the invention consists of Fe and inevitable impurities. However, other elements may be contained within, not violating the effect and effect of the present invention.

Next will be described a method of manufacturing a sheet of non-textured electrical steel in accordance with the invention.

In the method for manufacturing a non-textured electrical steel sheet according to the invention, the conditions are not particularly limited, except that the chemical composition of the steel sheet is controlled in the range defined in the invention, and the sheet can be manufactured under the same conditions as a conventional non-textured sheet electrical steel. For example, a steel sheet can be made by a process in which steel with a chemical composition according to the invention is melted, for example, in a converter, a degasser, and the like. to obtain the initial steel material (slab) using the continuous casting method or by rolling an ingot in a crimping stand, hot rolling, annealing in the hot zone, if necessary, single cold rolling or double or multiple cold rolling with intermediate annealing between them to a given sheet thickness and subsequent final annealing.

Examples

The steel of the chemical composition shown in Table 1 is melted in a converter, degassed by blowing and continuously poured into a slab that is heated at 1100 ° C for 1 hour, subjected to hot rolling at a final rolling temperature of 800 ° C, wound into a roll at a temperature of 610 ° C to produce a hot-rolled sheet 1.8 mm thick. Then annealing is carried out in the hot zone at 1000 ° C of a hot-rolled sheet in an atmosphere of 100% vol. N ₂ for 30 seconds and cold rolling to obtain a cold-rolled sheet 0.35 mm thick, which is subjected to final annealing at 980 ° C in an atmosphere of 20% vol. H ₂ - 80% vol. N ₂ for 15 seconds to obtain a cold-rolled and annealed sheet.

From such a cold-rolled and annealed sheet, Epstein test specimens are cut out in width: 30 mm × length: 280 mm in the rolling direction and in the direction perpendicular to the rolling direction in order to measure iron loss W _10/400 and magnetic flux density B ₅₀ in accordance with JIS C2550, respectively. These results are also shown in table 1.

As can be seen from table 1, steel sheets of the chemical composition according to the invention, in particular steel sheets with a low Bi content, are characterized by excellent losses in iron, regardless of the high Mn content.

Claims (5)

1. A sheet of non-textured electrical steel with a chemical composition, including wt.%: C: not more than 0.005, Si: 1.5-4, Mn: more than 3.0 and not more than 5.0, P: not more than 0.1 , S: not more than 0.005, Al: not more than 3, N: not more than 0.005, Bi: 0.0002-0.0030, Ti: not more than 0.002 and the rest Fe and inevitable impurities. 2. A non-textured electrical steel sheet according to claim 1, which further comprises one or two elements of Ca: 0.0005-0.005 wt.% And Mg: 0.0002-0.005 wt.% In addition to the above chemical composition. 3. A sheet of non-textured electrical steel according to claim 1, which further comprises one or two elements of Sb: 0.0005-0.05 wt.% And Sn: 0.0005-0.05 wt.% In addition to the above chemical composition. 4. A sheet of non-textured electrical steel according to claim 2, which further comprises one or two elements of Sb: 0.0005-0.05 wt.% And Sn: 0.0005-0.05 wt.% In addition to the above chemical composition. 5. A sheet of non-textured electrical steel according to any one of paragraphs. 1-4, which additionally contains Mo: 0.0005-0.0030 wt.% In addition to the above chemical composition.

Images