JP2001348652A - Nonoriented silicon steel sheet and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an inexensive silicon steel sheet having a characteristic of being small in core loss, and to provide its production method. SOLUTION: This nonoriented silicon steel sheet has a composition containing, by weight, <=0.01% C, 0.05 to 3.5% Si, <=1% Mn, <=1% Sol.Al, <=0.02% Cu, <=0.02% S, <=0.3% P, 0.01 to 0.2% Zr and 0.0005 to 0.025% Ca, and the balance substantially Fe, in which Ca inclusions dispersed into the steel contain at least either O or S, Zr inclusions contain at least N among N and C, and the total weight of each inclusion of CaO, CaS and Zr (N, C) is >=50% to the weight of all inclusions.

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 a method for producing the same, and more particularly, to a method for determining the form and size of nitride precipitates, sulfide precipitates and oxide precipitates in a steel sheet. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet having excellent iron loss characteristics by controlling, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are used as iron core materials for electric equipment such as motors and transformers. recent years,
With the demand for more energy-saving properties, it has been desired that iron core materials be further reduced in iron loss. Generally, since iron loss is considered to be the sum of eddy current loss and hysteresis loss, reduction of eddy current loss and hysteresis loss has been attempted to reduce iron loss of non-oriented electrical steel sheets. Methods for reducing eddy current loss include Si and Al.
Generally, a method of adding an alloying element such as to steel to increase electric resistance is used. Further, as a method of reducing the hysteresis loss, optimization of the crystal grain size and control of precipitates and inclusions in steel are generally performed.

[0003]

However, when alloying elements such as Si and Al are increased, the magnetic flux density decreases with an increase in the content, and the deformation resistance during rolling increases. Due to this, the manufacturability is reduced, so that it is difficult to further reduce the eddy current loss under the current situation where these component elements are added to almost the upper limit.

In order to reduce the hysteresis loss, it is common practice to manufacture the steel sheet so that the crystal grain size is about 150 to 250 μm. When it is present, the growth of crystal grains is inhibited,
It is difficult to make the target particle size uniform. Therefore, an attempt is made to reduce impurity elements in order to reduce fine precipitates and inclusions, and to make the precipitates and inclusions harmless by controlling the form and size of the precipitates and inclusions themselves. Have been.

[0005] Low iron loss by reducing impurity elements is disclosed in, for example, JP-A-59-74258, and its effect is clearly shown. However, the impurity control values require the operation of iron and steel at the highest level, and cannot be said to be industrially suitable at present.

The reduction of iron loss by controlling the morphology of precipitates is disclosed, for example, in Japanese Patent Application Laid-Open No. H11-12699, in which reduction of iron loss is achieved by controlling oxides and sulfides. However, since fine nitrides may be precipitated, the improvement effect varies. The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an inexpensive electromagnetic steel sheet having a characteristic of small iron loss and a method for manufacturing the same.

[0007]

The first means for solving the above-mentioned problems is as follows: C: 0.01% or less and Si: 0.05% by weight.
3.5%, Mn: 1% or less, Sol. Al: 1% or less, Cu: 0.02
%, S: 0.02% or less, P: 0.3% or less, Zr: 0.01 ~
0.2%, Ca: 0.0005-0.025%, with the balance being substantially
Non-oriented electrical steel sheet made of Fe, dispersed in steel
The Ca inclusions contain at least one of O and S, and the Zr inclusions contain at least N of N and C, and CaO, Ca
The non-oriented electrical steel sheet according to claim 1, wherein the sum of the weights of the S and Zr (N, C) inclusions is 50% or more of the total inclusion weight (claim 1).

[0008] A second means for solving the above problems is as follows.
C: 0.01% or less by weight%, Si: 0.05 to 3.5 wt%, Mn: 1
% Or less, Sol. Al: 1% or less, Cu: 0.02% or less, S: 0.02%
%, P: 0.3% or less, Zr: 0.01 to 0.2%, Ca: 0.0005
This is a method for producing a non-oriented electrical steel sheet containing about 0.025% by weight, and the balance substantially consisting of Fe, wherein the oxygen content in the steel is adjusted to 0.01% by weight or less by adjusting the components in a converter and a vacuum degassing apparatus. A method for producing a non-oriented electrical steel sheet, characterized by adding a Ca source and a Zr source in this order to the molten steel until casting is completed (Claim 2).

[0009] In this specification, "the remainder is substantially F
"is composed of e", unless the effects of the present invention are lost.
Those containing other trace elements are included in the scope of the present invention. Unless otherwise specified, all percentages indicating the components of steel are% by weight.

(Process leading to the invention and reason for limiting inclusions) The present inventors have studied the detoxification of impurity elements by using relatively inexpensive special elements without resorting to extreme purification. In addition, it has been found that harmful fine precipitates that significantly affect recrystallization and grain growth during the annealing process after cold rolling can be almost completely rendered harmless by appropriate use of steelmaking inclusions.

If the magnetic steel sheet contains a large number of fine nitride precipitates such as AlN of less than 1 μm, sulfides such as MnS, and oxides such as Al ₂ O ₃ , the grain growth is poor and iron It is generally known that the loss characteristics are also poor. The present inventors have conducted intensive studies with the aim of reducing the number of fine precipitates and fine inclusions, and found that when Zr is added to steel, fine nitride precipitates in the steel sheet are reduced. I found it.

However, the effect is easily affected by the amounts of O and S in the steel, and when deoxidation and desulfurization are insufficient, the iron loss value of the steel sheet is inferior to that of the steel sheet to which Zr is not added. The reason is that Zr, which has excellent nitride forming ability, is easily bonded to O and S,
It was presumed that this was because O ₂ and ZrS were generated and the fixation of nitrogen by Zr was insufficient, and fine nitride precipitates such as AlN were generated.

In view of the above, in order to prevent oxidation and sulfidation of Zr, a steel in which Ca, which is a stronger deoxidizing agent and desulfurizing agent than Zr, was added prior to Zr at the slab casting stage was manufactured. The result may be steel with very low iron loss value depending on the amount added,
In the steel sheet, it was found that Ca inclusions were mainly O and S, Zr inclusions were mainly N, and the size of the inclusions was 1 μm or more in average particle size.

That is, a steel sheet having good iron loss characteristics includes CaO and CaS inclusions having an average grain size of 1 μm or more, and Zr
(N, C) inclusions are present. Ca and O, S or Zr and N,
O, S, N, C are Ca
O, CaS, and Zr (N, C) are fixed, and even during strain relief annealing, Al, which is caused by N, S, etc. of CaO, CaS, Zr (N, C)
Fine precipitates such as N and MnS are hardly formed, and the size of the inclusions rarely decreases.

In addition, CaO, CaS inclusions, and Zr (N, C) inclusions are likely to become precipitation sites for fine precipitates such as AlN due to re-solid solution or nitrogen absorbed from the atmosphere. And precipitates are compounded, and fine precipitates are rarely precipitated alone. FIG. 1 shows the results of investigation of the relationship between the ratio (%) of the sum of the weights of CaO, CaS, and Zr (N, C) inclusions to the total inclusion weight and iron loss. Chemical composition: C: 0.002%, Si: 0.2
%, Mn: 0.2%, Sol. Al: 0.1-0.2%, S: 0.004%,
P: 0.07% or less, Zr: tr. To 0.15%, Ca: tr. To 0.0015
% Or less.

The sheet thickness is 0.5 mm, which shows the magnetic properties after strain relief annealing. The iron loss characteristics were measured by an Epstein test method, and the particle size of inclusions was investigated by a method of polishing and etching a cross section of a steel sheet and then observing with a SEM or an optical microscope. In the case where the inclusions are complexed, the particle size of the composite inclusions was taken as the particle size of the inclusions. Also the weight of inclusions
Classification by% was performed by combining extraction residue analysis in addition to ordinary chemical analysis.

FIG. 1 shows that the ratio (%) of the sum of the inclusion weights of CaO, CaS, and Zr (N, C) to the total weight of the inclusions rapidly decreases when approaching 50%. CaO, Ca
Since each of the S and Zr (N, C) inclusions tends to be larger than 1 μm, the inclusions do not themselves deteriorate the grain growth, and also serve as precipitation sites for other fine precipitates and suppress fine precipitates. On the other hand, when the proportion of the total inclusion weight is 50% or more, it is considered that the grain growth is improved and the iron loss value is reduced. Thereby, in the claimed invention, CaO, CaS, Z
r (N, C) Add the weight of each inclusion to 50
% Or more.

As described above, by specifying the main constituent impurity elements of Zr and Ca inclusions, the growth of the crystal grains of the steel sheet is improved, and the fine precipitates which are likely to become the pinning sites of the domain wall are formed. Can be reduced, and magnetic characteristics centering on iron loss characteristics can be improved. In FIG. 1, the values on the horizontal axis of the measurement points within the range of the present invention are 50
%, 56%, 65% and 80%.

Next, the reasons for limiting the steel components of the present invention will be described. (Reason for limiting chemical components) C: 0.01% or less C is a harmful component from the viewpoint of magnetic properties, and it is preferable to reduce it as much as possible. Si: 0.05% or more and 3.5% or less Si has the effect of increasing the electrical resistance of steel and reducing iron loss, but the effect is not exhibited unless 0.05% or more is added. In addition, as the magnetic flux density decreases as the content increases,
Since workability deteriorates, the upper limit is set to 3.5% or less. Mn: 1% or less Mn is added as a deoxidizing agent and for suppressing hot brittleness due to S. However, as the content increases, the magnetic flux density decreases and the workability deteriorates.
%.

Sol. Al: 1% or less Al also contributes as a deoxidizing agent and, like Si, increases the specific resistance of steel and reduces iron loss, but conversely, as the content increases, the magnetic flux density decreases. Therefore, the upper limit is set to 1%. S: 0.02% or less Among the impurity components, it is an element that needs to be particularly reduced. If the content exceeds 0.02.%, The effect of reducing iron loss by controlling inclusions decreases. Therefore, the S content is set to 0.02% or less. P: 0.3% or less P can be contained because it is effective for improving iron loss, but if it exceeds 0.3%, the workability is significantly affected, so it is limited to 0.3% or less. Cu: 0.02% or less Cu is a component that easily forms fine precipitates as sulfides, so the upper limit was made 0.02%.

Zr: 0.001 to 0.2% Zr forms an inclusion represented by Zr (N, C), has an effect of fixing nitrogen and carbon in steel and preventing formation of fine precipitates. However, if too much, the magnetic flux density decreases,
Since the processability is reduced, the optimal component range is from 0.01 to
0.2%. Ca: 0.0005 to 0.025% Ca is added to form stable inclusions of CaO and CaS at high temperature and bind Zr, which has a large deoxidizing power, to nitrogen. But,
Since excessive addition leads to deterioration of mechanical properties, the optimum range is 0.0005 to 0.025%.

(Manufacturing method) The non-oriented electrical steel sheet according to claim 1 can be manufactured by the following method. After vacuum processing and degassing steel melted in a converter or electric furnace, Si source, Al source,
After adding a Mn source and confirming a decrease in oxygen, a Ca source is added. After that, further decrease in oxygen and decrease in S were confirmed,
Zr is added and casting is performed subsequently. Thus, the inclusions are controlled to be very stable. Subsequent steps may be the same as the steps for manufacturing a normal magnetic steel sheet. In particular, with regard to cold rolling, since N, S, O, and C are already fixed, and fine precipitates are hardly generated at low temperatures, it is possible to use either the single cold pressure method or the double cold pressure method. Good. Also, if the final annealing is performed in a reducing atmosphere which is usually performed, it is possible to obtain an electromagnetic steel sheet having good low iron loss characteristics.

[0023]

EXAMPLES (Examples and Comparative Examples) Steel having a chemical composition of the present invention and steel having a chemical composition outside the range specified by the present invention were subjected to degassing treatment after being blown in a converter, and a predetermined component source was obtained. After addition and adjustment, casting was performed. At that time, addition of each component was performed according to the procedure described in the above (manufacturing method). However, in the comparative example, at least one of Zr and Ca was not added. Table 1 shows the component values of these steels in the ladle.

[0024]

[Table 1] Table of chemical analysis values of steels subjected to the present invention and those outside the present invention

The slab after casting is heated to 1200 ° C., the finishing temperature is 850 to 900 ° C., the winding temperature is 650 to 700 ° C., and the thickness is 2.3 m.
m and hot-rolled and pickled. Continue to add this hot rolled sheet
Cold rolled to 0.5 mm, 900% in an atmosphere of 75% H ₂ -25% N ₂
Finish annealing was performed at 1 ° C. × 1 minute. For this sample, 25cm
An Epstein test piece was prepared, and the iron loss value (W _15/50 ) and the magnetic flux density (B ₅₀ ) were measured.

Further, the size and number of CaO, CaS, and Zr (N, C) inclusions were determined by observing the cross section of the steel material with an optical microscope and an SEM. In addition, by performing extraction analysis, Ca
The ratio (%) of the sum of the weights of O, CaS, and Zr (N, C) inclusions to the total inclusion weight was determined. Table 2 summarizes the analysis results.

[0027]

[Table 2] Table 2. Iron loss value of steel material according to the present invention and comparative conditions
Ratio of the sum of the weights of CaO, CaS, and Zr (N, C) inclusions to the total inclusion weight (%) As is clear from Table 2, in the example in which Zr was added after Ca was added, the weight of each inclusion of CaO, CaS, and Zr (N, C) was 5%.
0% or more, indicating a lower value in iron loss (W _15/50 ) than the comparative example.

[0028]

As described above, the non-oriented electrical steel sheet of the present invention can achieve low iron loss by an inexpensive manufacturing method without using a special manufacturing process. The non-oriented electrical steel sheet of the present invention is suitable for use in applications requiring low iron loss, such as motors and iron cores of transformers.

[Brief description of the drawings]

FIG. 1 shows the sum of the weights of CaO, CaS, and Zr (N, C) inclusions,
It is a figure which shows the relationship between the ratio (%) with respect to the total inclusion weight, and iron loss value _W15 / ₅₀ (W / Kg).

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Atsushi Chino, Inventor 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Yoshihiko Ono 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Date Inside the Honko Co., Ltd. (72) Inventor Akira Hirata 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Honkan Co., Ltd. F-term (reference) 4K013 AA04 BA08 BA16 EA18 EA25 5E041 AA02 AA11 AA19 CA02 CA04 HB09

Claims (2)

[Claims] 1. C: 0.01% or less by weight%, Si: 0.05% or less
3.5%, Mn: 1% or less, Sol.Al: 1% or less, Cu: 0.02%
Hereinafter, S: 0.02% or less, P: 0.3% or less, Zr: 0.01 to 0.2
%, Ca: 0.0005 to 0.025%, the balance being substantially Fe
Non-oriented electrical steel sheet consisting of
Inclusions include at least one of O and S, and Zr inclusions include at least N of N and C, and include CaO, Ca
Non-oriented electrical steel sheet characterized in that the sum of the weights of S and Zr (N, C) inclusions is 50% or more based on the weight of all inclusions. 2. C: 0.01% or less by weight%, Si: 0.05 to
3.5wt%, Mn: 1% or less, Sol.Al: 1% or less, Cu: 0.02
%, S: 0.02% or less, P: 0.3% or less, Zr: 0.01 ~
0.2%, Ca: 0.0005-0.025%, with the balance being substantially
This is a method for producing non-oriented electrical steel sheets made of Fe, in which a molten steel with the oxygen content in the steel adjusted to 0.01% by weight or less by adjusting the components in a converter and a vacuum degassing apparatus is used. ,
A method for producing a non-oriented electrical steel sheet, characterized in that Zr sources are added in order.