JPH10237606A - Nonoriented silicon steel sheet reduced in iron loss after magnetic annealing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the precipitation of fine VN, AlN, and MnS and to reduce iron loss after magnetic annealing by adding specific amounts of Zr and regulating the additive quantities of Al and Mn to values in specific ranges, respectively, in a silicon steel sheet containing V and S. SOLUTION: The composition of the nonoriented silicon steel sheet consists of, by weight, <=0.005% C, <=1.0% Si, 0.3-1.5% Mn, <=0.003% Al, <=0.2% P, <=0.015% (including 0%) S, <=0.005% (including 0%) N, 0.001-0.02% V, 0.01-0.05% Zr, and the balance essentially Fe with inevitable impurities. This steel sheet is produced by applying degassing treatment to a molten steel blown in a converter to regulate it into prescribed composition, successively applying casting and hot rolling to the molten steel, subjecting the resultant steel plate to cold rolling once or to cold rolling two or more times while applying process annealing between cold rolling stages to the prescribed sheet thickness, and then carrying out final annealing. By this method, the silicon steel sheet having high magnetic flux density can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a non-oriented electrical steel sheet having a low iron loss after magnetic annealing.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are classified into full-process materials and semi-process materials according to their manufacturing methods. Among them, the full process material is to obtain predetermined magnetic characteristics by finish annealing on the steel maker side, and the semi-process material is to obtain predetermined magnetic characteristics by performing strain relief annealing after punching in a customer. Things. In the semi-process material, since the crystal grains grow simultaneously with the removal of the processing strain during the strain relief annealing, the iron loss can be further reduced. For this reason, the strain relief annealing is also called “magnetic annealing”.

[0003] However, since this magnetic annealing is usually performed at a temperature of 800 ° C or less, low iron loss cannot be achieved if fine precipitates that inhibit grain growth are present in the steel. Among these precipitates, fine precipitates such as MnS and AlN inhibit grain growth and significantly reduce iron loss. In order to reduce the number of fine MnS precipitated during the hot rolling step, it is necessary to reduce the amount of MnS dissolved in the steel during hot rolling. As a method of reducing the amount of MnS, for example, a method of reducing S as much as possible in the smelting stage can be cited. However, this method requires a thorough desulfurization in the steelmaking stage, which leads to a significant cost increase.

[0004] In addition to MnS and AlN, VN finely precipitated during magnetic annealing also markedly impairs grain growth and deteriorates iron loss, so that it is clear that it is necessary to reduce the amount of V in the steel sheet. As a method for detoxifying this VN,
JP-A-3-20413 proposes a technique for preventing the precipitation of VN by defining the V and N contents in steel as V: 0.01% or less and N: 0.005% or less. However, only by specifying the V content, as described in the specification of the patent, the iron loss W _15/50 after magnetic annealing of 0.30% Si steel.
Is 4.9 W / kg (approximately), and it is not possible to sufficiently reduce iron loss.

[0005] Further, since V is mixed in from the ore, it is necessary to sort out ore with a low amount of V mixed in order to reduce V, resulting in a significant increase in cost.

In order to suppress the precipitation of VN, V,
In addition to the method of reducing the amount of N, there is also a method of adding N and fixing N as AlN. However, when a small amount of Al is added in a range of less than 0.1%, although precipitation of VN is prevented, AlN precipitated during hot rolling impairs the grain growth, so that the grain growth during magnetic annealing is suppressed. Does not improve. On the other hand, Al
When added in an amount of 0.1% or more, the grain growth is improved, but the cost is inevitably increased.

On the other hand, various methods have been proposed for producing non-oriented electrical steel sheets using Zr to improve grain growth.

For example, JP-A-64-4454 discloses that
There is disclosed a technique for suppressing the fine precipitation of AlN and reducing iron loss by adding Zr to steel of 3.5% or less of Si and 0.01 to 0.10% of Al. However, in Al deoxidation, there is a concern that the production of Al ₂ O ₃ may cause iron loss deterioration, and it is difficult to completely suppress the precipitation of AlN.

Further, Japanese Patent Application Laid-Open No. 3-104844 discloses that Zr is used for steel having a content of Si: 0.1 to 2.0% and Al: 0.1% or less.
A technique for suppressing precipitation of MnS and reducing iron loss by adjusting the number of oxides in steel to 0.05% or less. However, in the deoxidation method of this technique in which the number of oxides in steel serving as precipitation nuclei of MnS is adjusted to make MnS harmless, Zr is consumed as ZrO _{2, and} as a result, V is mixed. In this case, N cannot be fixed as ZrN, and generation of VN cannot be suppressed. Therefore, as described in the specification of this publication, the iron loss W _15/50 of 0.30% Si steel after magnetic annealing is about 4.7 W / kg, and a sufficient decrease in iron loss during magnetic annealing is shown in FIG. However, if the amount of V mixed is large, the characteristics are expected to further deteriorate.

[0010] Further, Japanese Patent Application Laid-Open No. 3-264619 discloses that, on the premise of direct rolling, Si: 0.1 to 1.2% and Al: 0.2%.
There is disclosed a technique for suppressing the precipitation of MnS and reducing iron loss by adding Zr to steel of 5% or less.

However, under the conditions of this technique, as described in this specification, in addition to the addition of Zr, 0.29% Si
Even if B is added to -0.025% Al steel to suppress the precipitation of AlN, the iron loss W15 / ₅₀ after magnetic annealing is 5.02W / kg, and a sufficient reduction in iron loss has not been achieved. However, sufficient detoxification of fine precipitates has not been achieved.

As described above, in any of the conventional techniques, it is possible to sufficiently detoxify VN, MnS, and AlN inevitably contained in steel and obtain a non-oriented magnetic steel sheet having low iron loss at low cost. Can not.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is an object of the present invention to effectively suppress precipitation of VN, MnS, and AlN which impair grain growth. Accordingly, it is an object to obtain a non-oriented electrical steel sheet having low iron loss after magnetic annealing at low cost.

[0014]

The gist of the present invention is to suppress the precipitation of fine VN, AlN, and MnN by adding Zr and further adjusting the addition amount of Al and Mn, and thus, after magnetic annealing. Is to reduce iron loss.

[0015] That is, the above-mentioned problem is expressed by:
% Or less, Si: 1.0% or less, Mn: 0.3 to 1.5%, Al: 0.003
%, P: 0.2% or less, S: 0.015% or less (including 0), N: 0.005% or less (including 0), V: 0.001-0.
The problem is solved by a non-oriented electrical steel sheet having a low iron loss after magnetic annealing, characterized by containing 02% and Zr: 0.01 to 0.05%, with the balance substantially consisting of Fe and unavoidable impurities.

Here, "the balance substantially consists of Fe and unavoidable impurities" means that other trace elements may be contained as long as the effects of the present invention are not impaired. In particular, those to which Sn, Sb, etc. are added in order to further improve the magnetic properties are also included in the category of “the remainder substantially consists of Fe and unavoidable impurities”.

(Circumstances leading to the invention) In order to realize the above object, the present inventors have studied a method of reducing iron loss after magnetic annealing in an electromagnetic steel sheet containing V and S, and as a result, Zr was added. Fine V by adjusting the addition amount of Al, Mn
It has been found that precipitation of N, AlN, and MnS can be suppressed, and iron loss after magnetic annealing is reduced. Hereinafter, the present invention will be described in detail based on experimental results.

(Reason for limiting Zr) First, in order to confirm the effect of suppressing the precipitation of VN by Zr, C = 0.030% and Si = 0.30%.
%, Mn = 0.80%, P = 0.100%, S = 0.050%, Al = 0.
0020%, N = 0.030%, V = 0.005%, Zr = tr.
% Was melted in a laboratory and cast to obtain a slab. These slabs are hot-rolled, pickled, cold-rolled to a thickness of 0.5 mm, subjected to finish annealing at 750 ° C. × 1 min,
Magnetic annealing at 0 ° C. × 2 hours was performed.

FIG. 1 shows the iron loss W _15/50 of these samples after magnetic annealing. Here, the magnetic properties were measured using a 25 cm Epstein test piece. From FIG. 1, the iron loss W after the magnetic annealing is shown.
It can be seen that _15/50 is greatly affected by the amount of Zr added. In the case of tr. Zr steel, the iron loss _W15 / ₅₀ after magnetic annealing is 5.2 W /
kg, but the iron loss is reduced by adding 0.01% or more of Zr, and the iron loss W _15/50 is 4.4 W / kg. On the other hand, when Zr exceeds 0.05%, the iron loss increases.

Observation of the structures of these samples showed that the average crystal grain size of the tr. Zr steel was 20 μm or less, whereas the crystal grains became coarse when the Zr addition amount was 0.01% or more. I was It was also found that when the amount of Zr added was 0.05% or more, the grain growth was reduced.

The reason why the grain growth after magnetic annealing differs depending on the amount of Zr added as described above is considered as follows.

In tr. Zr steel, fine VN precipitates during magnetic annealing, and this VN inhibits grain growth. However, when Zr is added at 0.01% or more, Zr has a nitride forming ability as compared with V. Since it is large, N is fixed as relatively coarse ZrN, and fine VN does not precipitate during magnetic annealing, so that grain growth is improved.

However, if the amount of Zr added is less than 0.01%, Zr will be consumed as ZrO ₂ , so
Cannot be fixed, and the precipitation of VN cannot be suppressed. On the other hand, if the amount of Zr added is 0.05% or more, precipitates increase, so that the grain growth cannot be improved.

From the above results, Zr is made 0.01% or more and 0.05% or less.

(Reason for limiting Al) Next, in order to investigate the effect of the amount of Al on iron loss, C = 0.0025%, Si = 0.30%, Mn
= 0.80%, P = 0.100%, S = 0.0050%, N = 0.0030
%, V = 0.005%, Zr = 0.030%, and Al is tr.
A slab was obtained by lab melting and casting steel that had been changed to 7%. These slabs were hot-rolled and then pickled, then the hot-rolled sheets were cold-rolled to a thickness of 0.5 mm, subjected to finish annealing at 750 ° C. × 1 min, and further subjected to magnetic annealing at 750 ° C. × 2 hours.

FIG. 2 shows the iron loss W _15/50 of these samples after magnetic annealing. Here, the magnetic properties were measured using a 25 cm Epstein test piece. FIG. 2 shows that when the Al content is 0.003% or less, the iron loss W _15/50 decreases to 4.4 W / kg or less. When the structures of these samples were observed with an optical microscope, it was found that the structures became finer as the amount of Al increased. In order to investigate the cause of the decrease in grain growth, SEM observation of the steel sheet after magnetic annealing was performed. As a result, AlN was observed at Al> 0.003%. From this, it is considered that the decrease in grain growth at Al> 0.003% is due to the precipitation of AlN.

From the above results, the content of Al is set to 0.003% or less. As described above, even in the case of steel to which Zr is added, AlN precipitates when the amount of Al added increases, and even if the precipitation of VN is suppressed, the magnetic properties after magnetic annealing cannot be improved. That is, Zr
In order to make V harmless, control of the amount of Al added is a very important factor.

(Reasons for Limiting Other Components) Hereinafter, the reasons for limiting other components in the present invention will be described.

C: C is set to 0.005% or less to cause magnetic aging and deteriorate magnetic properties.

Si: Si is an element that reduces iron loss with an increase in the amount of addition, but if it exceeds 1.0%, the magnetic flux density decreases, so the upper limit is made 1.0%.

Mn: Mn is a very important element because it precipitates S in steel as MnS. FIG. 3 shows a MnS solubility curve at 1200 ° C. FIG. 3 shows that the amount of MnS re-dissolved during hot rolling increases as the amount of Mn decreases. This re-dissolved MnS precipitates finely during hot rolling, especially Mn <0.30%
In such a case, MnS to be finely precipitated increases, and it is difficult to improve the grain growth. Therefore, the lower limit of Mn is 0.30%. Further, the upper limit of Mn is set to 1.5% from the viewpoint of lowering the magnetic flux density.

P: P is an element necessary for improving the punching property of the steel sheet, but if it exceeds 0.2%, the steel sheet becomes brittle, so that the content of P is set to 0.2% or less.

S: S binds to Mn and precipitates finely as MnS, and inhibits grain growth. Therefore, the upper limit is 0.015%.

N: If the content of N is large, the precipitation amount of ZrN increases, the grain growth is reduced, and the iron loss increases, so that N is set to 0.005% or less.

V: In the present invention, the precipitation of VN is prevented by Zr, so that mixing of up to 0.02% is acceptable.
However, if it exceeds 0.02%, it precipitates as VC and inhibits grain growth, so the upper limit is made 0.02%.

It should be noted that addition of Sb and Sn for improving the magnetic properties may be performed without any problem.

(Manufacturing method) The non-oriented magnetic steel sheet according to the present invention can be manufactured by a normal method for manufacturing a non-oriented magnetic 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. Hot-rolled sheet annealing after hot rolling may be performed, but is not essential. Next, final cold-rolling or cold-rolling two or more times with intermediate annealing to obtain a predetermined sheet thickness is performed, followed by final annealing. As for the hot rolling conditions and the annealing conditions, well-known conditions for manufacturing a non-oriented electrical steel sheet can be appropriately selected and used.

[0038]

EXAMPLE After steel was blown in a converter, degassing treatment was performed to adjust the components to the predetermined components shown in Table 1 and then cast.
Next, this slab is heated at a slab heating temperature of 1200 ° C. for 1 hour,
Hot rolling was performed to a thickness of 2.0 mm. In this case, the finishing temperature was 800 ° C. and the winding temperature was 675 ° C. Next, the hot-rolled sheet is pickled, cold-rolled to a sheet thickness of 0.5 mm, subjected to a finish annealing at 750 ° C. × 1 min, and further 750 ° C. ×
Magnetic annealing was performed for 2 hours. Magnetic properties were measured using 25 cm Epstein specimens. Table 1 also shows the magnetic properties of each steel sheet.

[0039]

[Table 1] In Table 1, No. 1 to No. 8 have the components of the present invention. In any of these, the iron loss W _15/50 is 4.
34 W / kg with or less, 1.726 T or more high magnetic flux density B ₅₀ is obtained. Naturally, the iron loss W _15/50 and the magnetic flux density B ₅₀ are lower when the Si level is 0.7% than when the Si level is 0.4%.

The steel sheet No. 9 has a high iron loss W _15/50 because C exceeds the range of the present invention.

In the steel sheet No. 10, since the range of Si exceeds the range of the present invention, the iron loss W _15/50 is low, but the magnetic flux density B ₅₀ is also low.

In the steel sheet No. 11, since the range of Mn is lower than the range of the present invention, the iron loss W _15/50 is high.
In contrast, steel No.12, because the range of Mn is higher than the scope of the present invention, the magnetic flux density B ₅₀ is low.

The steel sheet No. 13 has a high iron loss W _15/50 because the range of S exceeds the range of the present invention.

The steel sheet No. 14 has a high iron loss W _15/50 because the range of Al exceeds the range of the present invention.

The No. 15 steel plate and the No. 16 steel plate each have a high iron loss W _15/50 because the range of Zr is below or above the range of the present invention.

The steel sheet No. 17 has a high iron loss W _15/50 because the range of V is larger than the range of the present invention.

From these examples, it can be seen that when the steel sheet components are controlled within the range of the present invention, a non-oriented electrical steel sheet having a low iron loss after magnetic annealing and a high magnetic flux density can be obtained.

[0048]

As described above, according to the present invention, a steel sheet having low iron loss after magnetic annealing can be obtained. The non-oriented electrical steel sheet according to the present invention is suitable for use as an electrical material requiring low iron loss.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of Zr and iron loss after magnetic annealing.

FIG. 2 is a graph showing the relationship between the amount of Al and iron loss after magnetic annealing.

FIG. 3 is a diagram showing a solubility curve of MnS.

Claims (1)

[Claims] (1) C: 0.005% or less, Si: 1.0% by weight
%, Mn: 0.3 to 1.5%, Al: 0.003% or less, P: 0.
2% or less, S: 0.015% or less (including 0), N: 0.005
% Or less (including 0), V: 0.001 to 0.02%, Zr: 0.01 to
Non-oriented electrical steel sheet with low iron loss after magnetic annealing, characterized by containing 0.05% and the balance substantially consisting of Fe and unavoidable impurities.