JP3446257B2 - Non-oriented electrical steel sheet with excellent iron loss properties after strain relief annealing - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-Si non-oriented electrical steel sheet having an excellent iron loss characteristic, and is particularly intended to improve grain growth during strain relief annealing.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets have been widely used as iron core materials for electric equipment such as motors, generators and small transformers. The demand for low iron loss is increasing.

The three main factors that determine the iron loss of a non-oriented electrical steel sheet are the following specific resistance, texture and grain size. When the specific resistance (Si + Al) content is increased, the specific resistance is increased and the iron loss is decreased, but the increase of (Si + Al) is merely a grade upgrade and is not the purpose of the present invention.

As a texture improving method, a method of coarsening the grain size before cold rolling and a method of adding Sb and Sn are known.

Crystal grain size The crystal grain size at which iron loss (W _15/50 ) is the smallest is 100 to
It is known to be 150 μm. Usually, low Si (Si ≦
The grain size of 1.2 wt% (hereinafter simply referred to as%) non-oriented electrical steel sheet is 10 to 30 μm at the time of shipment, but the grain grows by the subsequent strain relief annealing (usually 750 ° C x 2 h). , Iron loss becomes smaller. Therefore, to reduce iron loss, it is particularly important to improve grain growth during strain relief annealing. Factors that inhibit grain growth include fine sulfides, nitrides, oxides, etc. in steel. In order to reduce these, conventionally, use of desulfurization flux (removal of S), Ar
Degassing (removal of N) and deoxidation of Al (removal of oxides) by gas reflux are generally performed. Furthermore, as a method of reducing fine nitrides, in a non-oriented electrical steel sheet with Si: 0.1 to 1.0%, deoxidizing with only Si to reduce the total Al content.
A method of setting 0.007% or less (Japanese Patent Publication No. Sho 56-43294),
A method has been proposed in which Al is made 0.15 to 0.60% to coarsen nitrides and reduce oxides (JP-A-61-119652).

Further, in JP-A-63-195217, the composition of inclusions is MnO / SiO ₂ + MnO + Al ₂ O ₃ ≦ 0.15, sol.Al: 0.00
A method of reducing ductile inclusions harmful to grain growth to non-ductile inclusions by setting the content to 1 to 0.005% is disclosed. However, in order to control the inclusions described above, it is necessary to adjust Mn at the time of tapping the converter, but the treatment at the tapping of the converter is not only poor in the yield of Mn but also vacuum degassing. The predictive value of the Mn concentration is lower than that of the time adjustment. Therefore, as a readjustment process of Mn concentration, in the vacuum degassing process
It often becomes necessary to input Mn. However, since Mn introduced in the vacuum degassing step forms ductile inclusions and deteriorates iron loss, it was not possible to stably obtain low iron loss by this method.

Further, in Japanese Patent Laid-Open No. 3-249115, Si-
As a technique for reducing ductile inclusions by deoxidizing Mn, Mn (55.6
+ 34.5 × Si) × S (%) is added, but
Such deoxidation using only Si-Mn has a problem that nozzle clogging easily occurs during casting.

[0008]

Therefore, there has been a demand for the development of an inexpensive magnetic steel sheet which can stably obtain a low iron loss even by adjusting Mn during vacuum degassing. The present invention advantageously responds to the above-mentioned requirements, and even by adjusting Mn during vacuum degassing, a ductile inclusion that inhibits grain growth is not formed, and a stable low iron loss is obtained after stress relief annealing. The purpose is to propose a non-oriented electrical steel sheet that can be manufactured.

[0009]

That is, this invention is
C: 0.010% or less, Si: 0.01 to 1.2%, P: 0.20% or less, S: 0.01% or less, TO: 0.020% or less, N:
Contains 0.0050% or less, contains Mn in a range satisfying the following formula [Mn] ² /[Si]≦0.45, and further contains sol.Al: 8 ppm or less, and the balance is substantially Fe composition. This is a non-oriented electrical steel sheet (first invention) having excellent iron loss characteristics after stress relief annealing.

The present invention also provides C: 0.010% or less, S
i: 0.01 to 1.2%, P: 0.20% or less, S: 0.01% or less, TO: 0.020% or less, N: 0.0050% or less,
In addition, Mn is contained in a range that satisfies the following formula [Mn] ² /[Si]≦0.45, and further contains sol.Al: 8 ppm or less and sol.Al + Ti: 20 ppm or less, and the balance is substantially Fe. It is a non-oriented electrical steel sheet (second invention) excellent in iron loss characteristics after stress relief annealing, which is characterized by the following composition.

Below, the experimental results that form the basis of the present invention will be explained. Now, the inventors have investigated the relationship between the Si, Mn, Al concentrations and the iron loss of the low Si non-oriented electrical steel sheet, and obtained the following results. FIG. 1 shows [Mn] ² / [Si] and 750 for non-oriented electrical steel sheets of various Si and Mn concentrations in which Mn was adjusted only after Al deoxidation in vacuum degassing.
The result of having investigated about the relationship with the core loss after the stress relief annealing of 2 degreeC is shown. For any steel sheet, sol.Al: 2-5 p
pm and Ti: It was 6-7 ppm. As is clear from the figure, when [Mn] ² / [Si] increases, especially when it exceeds 0.45,
It was found that iron loss increased sharply. From the observation of the cross section of the plate after strain relief annealing with a scanning electron microscope (SEM), the iron loss defect material is fine grain and has extremely poor grain growth property compared with the good material, and the ductile inclusion extending in the rolling direction. It turned out that there are many. Therefore, it is considered that these inclusions inhibited the grain growth.

Next, FIG. 2 shows the results by examining the relationship between the sol.Al concentration and the iron loss of the non-oriented electrical steel sheet containing Si: 0.2%, Mn: 0.2% and Ti: 5 to 7 ppm. . The Mn concentration was adjusted mainly during tapping of the converter, and metallic Mn was added during vacuum degassing only when the Mn concentration was below 0.2% by sampling and analysis during vacuum degassing. . As is clear from the figure, when the sol.Al concentration is low, the iron loss is good, but when the sol.Al concentration exceeds 8 ppm, the iron loss is increased especially when Mn is added during vacuum degassing. Causing variability,
Low iron loss could not be obtained stably.

As described above, although the sol.Al concentration has a great influence on the iron loss, it was newly found that not only the sol.Al concentration but also the Ti concentration significantly affects the iron loss.
Fig. 3 shows Si: 0.2%, Mn: 0.2%, sol.Al: 1-8 ppm.
The relationship between the (sol.Al + Ti) concentration and the iron loss of the non-oriented electrical steel sheet containing Cr is investigated and the results are shown. The Mn concentration was adjusted mainly during tapping of the converter, and metallic Mn was added during vacuum degassing only when the Mn concentration was below 0.2% by sampling and analysis during vacuum degassing. . As is clear from the figure, when the (sol.Al + Ti) concentration is low, the iron loss is good, but when the (sol.Al + Ti) concentration exceeds 20 ppm, especially when Mn is added during vacuum degassing. The iron loss varied, and low iron loss could not be stably obtained.

The Mn is generally adjusted at the time of tapping of the converter, or before or after Al deoxidation in vacuum degassing. However, the metal Mn or Fe-Mn alloy is vacuumed during degassing. When sol.Al exceeds 8 ppm or (sol.Al + Ti) concentration exceeds 20 ppm, the same sol.Al concentration, ( It was revealed that the iron loss was deteriorated even when the sol.Al + Ti) concentration was compared.

Next, Table 1 shows the analysis results of iron loss and inclusions after stress relief annealing of three types of non-oriented electrical steel sheets containing Si: 0.12% and Mn: 0.22%. The Mn concentration was adjusted during vacuum degassing. In addition, the composition analysis of inclusions is performed by an energy dispersive X-ray analyzer (EDX).
Five inclusions were randomly selected.

[0016]

[Table 1]

As is clear from the table, sol.Al is 8 ppm.
, Or (sol.Al + Ti) exceeds 20ppm, not only SiO ₂ rich non-ductile inclusions but also Al ₂ O ₃ and
Many ductile inclusions containing about 20% TiO ₂ were found.

From the above results, when the Mn concentration is adjusted during vacuum degassing, [Mn] ² / [Si] is set to 0.45 or less, and the sol.Al concentration or (sol.Al + Ti) concentration is adjusted. It was found that the reduction reduces the number of ductile inclusions, and as a result, the grain growth during strain relief annealing is improved and a non-oriented electrical steel sheet with low iron loss can be stably obtained. .

Since Ti is a nitride-forming element, it has been conventionally considered desirable to reduce Ti to improve iron loss. However, Ti alone has a small adverse effect on iron loss, and rather, by coexistence with sol.Al, SiO ₂ -MnO
It was newly found that inclusions become ductile, resulting in poor grain growth and iron loss deterioration, thus leading to the present invention.

[0020]

The reason why the component composition is limited to the above range in the present invention will be described below. C: 0.010% or less If C exceeds 0.010%, the magnetic characteristics are deteriorated due to C precipitation, so the C content is limited to 0.010% or less. Si: 0.01 to 1.2% Si is a useful element that increases the specific resistance and decreases the iron loss, but since the increase of Si increases the cost, in the present invention,
It was limited to the range of 0.01 to 1.2%. P: 0.20% or less P effectively contributes to the improvement of punchability, but the content is 0.20%.
%, The cold rolling property deteriorates, so the content was limited to 0.20% or less. S: 0.01% or less S is finely precipitated together with Mn and hinders grain growth. Therefore, the S content is preferably as small as possible. In the present invention, S is limited to 0.01% or less. T.O: 0.020% or less O inhibits grain growth as an oxide, so it is desirable that it is as small as possible. In the present invention, it is limited to 0.02% or less. N: 0.0050% or less N inhibits grain growth as a nitride, so it is desirable that the amount is as small as possible. In the present invention, N is limited to 0.0050% or less.

Mn: [Mn] ² /[Si]≦0.45 When the amount of Mn exceeds 0.45 in [Mn] ² / [Si], Mn was adjusted during vacuum degassing as shown in FIG. 1 above. In this case, ductile inclusions are generated and grain growth is inhibited, so
It is limited to the above range. sol.Al: 8 ppm or less Al is added for deoxidation, but as shown in Fig. 2, when sol.Al exceeds 8 ppm, ductile inclusions are generated by Mn adjustment during vacuum degassing, As grain growth is hindered,
Limited to 8 ppm or less. In addition, in order to reduce the sol.Al to 8 ppm or less, it is necessary to pay close attention to the amount of Al mixed from iron alloy such as Fe-Si. Before adding Al, the free O concentration in the molten steel is measured with an oxygen probe in advance, and the amount of Al is controlled so that it does not become excessive. Furthermore, it is preferable to adjust the basicity of the slag as small as possible.

Sol.Al + Ti: 20 ppm or less As shown in FIG. 3 and Table 1, Ti and sol.Al additively participate in the formation of ductile inclusions and inhibit grain growth. Therefore, Ti and sol. The total amount of Al is not likely to take 20
Limited to below ppm. Since Ti is mixed in from ferroalloy, etc., it is necessary to limit the mixing with the utmost care as in the case of Al.

Next, a preferred method for producing the inventive steel will be described. Steel is usually melted by using a converter and a vacuum degassing device. Conventionally, Mn is added, for example, when tapping the converter.
Fe-Mn alloy (300kg for 100t converter)
The amount of Mn added during vacuum degassing was reduced. Therefore, most of the Mn that was put into the steel when tapping the converter was MnO, and the yield of Mn was extremely poor. In this respect, in the present invention, the addition of the Fe-Mn alloy at the time of tapping of the converter is reduced (100 kg) or eliminated, and the Mn adjustment is mainly performed during vacuum degassing, so the yield is improved, and the Mn concentration The rate also improves.

Then, a slab is formed by a continuous casting method or an ingot-slabbing rolling method, and then a hot rolling method according to a conventional method is used.
Finish a hot rolled sheet with a sheet thickness of 2.0 to 3.0 mm. The plate thickness is not limited to this size. Then, if necessary, hot-rolled sheet annealing for improving the texture of the product is performed, and after cold rolling to a predetermined sheet thickness, final annealing is performed, and then an insulating coating is formed by a known method. To do.

[0025]

Example A slab for non-oriented electrical steel sheets having the composition shown in Table 2 was manufactured by a converter-vacuum degassing-continuous casting process. Mn adjustment was performed after Al deoxidation during vacuum degassing. Then, after heating the slab to 1150 ° C., it was hot-rolled to a thickness of 2.0 mm, then cold-rolled to a thickness of 0.5 mm, finish-annealed at 750 ° C. for 10 seconds, and then an insulating coating was applied. Further, strain relief annealing was performed at 750 ° C. for 2 hours. Table 2 also shows the results of examining the components of the product thus obtained, the grain size after the stress relief annealing, and the magnetic properties.

[0026]

[Table 2]

As is clear from the table, in the steel according to the present invention, good iron loss was obtained after the strain relief annealing even by adding Mn in vacuum degassing having a high yield ratio of Mn.

[0028]

Thus, according to the present invention, the amount of Mn, the amount of sol.Al, and the amount of Ti in steel are respectively [Mn] ² / [Si].
≤ 0.45, sol.Al: 8ppm or less and (sol.Al + Ti):
By controlling to 20 ppm or less, good iron loss can be stably obtained after stress relief annealing.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between [Mn] ² / [Si] and iron loss after stress relief annealing.

FIG. 2 is a graph showing the relationship between sol.Al concentration and iron loss after stress relief annealing.

FIG. 3 is a graph showing the relationship between (sol.Al + Ti) concentration and iron loss after stress relief annealing.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Nabeshima, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Works Ltd. Technical Research Division (56) Reference JP-A-3-104844 (JP, A) JP Flat 3-249115 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (2)

(57) [Claims] 1. C: 0.010 wt% or less, Si: 0.01 to 1.2 wt.
%, P: 0.20 wt% or less, S: 0.01 wt% or less, TO: 0.020 wt% or less, N: 0.0050 wt% or less,
In addition, Mn is contained in a range that satisfies the following formula [Mn] ² /[Si]≦0.45, and further contains sol.Al: 8 ppm or less, and the balance is substantially Fe composition. Non-oriented electrical steel sheet with excellent iron loss characteristics after stress relief annealing. 2. C: 0.010 wt% or less, Si: 0.01 to 1.2 wt.
%, P: 0.20 wt% or less, S: 0.01 wt% or less, TO: 0.020 wt% or less, N: 0.0050 wt% or less,
In addition, Mn is contained in a range that satisfies the following formula [Mn] ² /[Si]≦0.45, and further contains sol.Al: 8 ppm or less and sol.Al + Ti: 20 ppm or less, and the balance is substantially Fe. A non-oriented electrical steel sheet having excellent iron loss characteristics after stress relief annealing, which is characterized by the composition