JP3456295B2 - Melting method of steel for non-oriented electrical steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention
Related to the melting of low-Si non-oriented electrical steel sheets.
Particularly stable improvement of grain growth after strain relief annealing
And clogged nozzles in pots and tundishes during melting
The present invention proposes a smelting method that can prevent the occurrence of smelting. [0002] Non-oriented electrical steel sheets are used for motors, generators,
Widely used as core material for electrical equipment such as small transformers
In recent years, in particular, these electric devices have
There is a growing demand for lower iron loss for efficiency.
The main factor that determines the iron loss of non-oriented electrical steel sheet is Si + Al
And the crystal grain size. For the content of Si + Al, increase them
Then, the specific resistance increases and the iron loss decreases, but the amount of Si + Al increases
Is merely an upgrade (cost increase).
It is not the object of the invention. On the other hand, when the component compositions are the same,
The larger the crystal grain size, the smaller the iron loss.
Iron loss (W_15/50) Is 100 to 15
It is known to be in the range of 0 μm. Usually low Si
(Si ≦ 1.0 wt%) non-oriented electrical steel sheet at shipping
Although the crystal grain size is 10 to 30 μm, the subsequent strain relief annealing
The crystal grains grow by 750 ° C x 2 hours) and the iron loss is small.
It becomes. Therefore, in order to reduce iron loss,
It is important to improve the growth of crystal grains during dulling.
is there. [0005] [Prior Art] Si: 1.0 wt% or less of non-oriented electrical steel sheet
Factors that inhibit the growth of crystal grains include fine sulfur in steel.
There are compounds, nitrides and oxides. Of these, sulfides
In addition, Mn is contained at 0.1 wt% or more to make MnS coarser.
Detoxify or use desulfurizing flux during refining
S is made harmless by reducing S. Ma
As for nitrides, Al is contained in steel in the range of 0.1-1.0 wt%.
Relatively large size AlN
Precipitates as a crystal to reduce the suppression of grain growth
(For example, JP-A-55-97426, JP-A-50-98423)
JP, JP-A-51-151215). However, when the Si content is 1.0 wt% or less,
In the case of low-grade electrical steel sheets, low price is an essential condition
Therefore, the addition of Al as described above causes an increase in cost. this
Therefore, the content of Al is suppressed to 0.007 wt% or less,
Iron loss by preventing precipitation of fine AlN
There has been proposed a method (for example, Japanese Patent Publication No. 48-3055).
JP-A-53-109815), the Al content is low.
If not, a large amount of oxygen in the steel is inevitably
Oxide-based inclusions are generated, and the inclusions have a low melting point
In the case of an existing object, the inclusion exists in a state of extending in the rolling direction.
There is a problem of inhibiting the growth of crystal grains. [0007] Such oxides are disclosed in
No. 195217 (Non-directional electromagnetic with low iron loss after magnetic annealing
Steel plate) and JP-A-1-152239 (iron loss after magnetic annealing)
0.1 to 1.0 wt% Si
%, Mn 1.5 wt% or less, sol.Al 0.001 to 0.005 wt%
In non-oriented electrical steel sheets, the inclusion of SiO_Two, MnO,
Al_TwoO_ThreeOf MnO weight to total weight of three types of inclusions
Less than 15%, SiO_TwoWeight ratio of 75% or more
To reduce grain growth by making inclusions non-ductile
A method for weakening the force and reducing the iron loss has been proposed and disclosed. However, the content of MnO in inclusions is reduced to 15 wt% or less.
To increase the amount of sol.Al and SiBut, Al amount
Is more than 0.003 wt%, N in steel is more than 20ppm
If fine AlN precipitates at the grain boundaries,
The problem that growth is hindered and iron loss cannot be reduced
is there. On the other hand, Al content is 0.001 wt% or more,0.003 wt% or less
If it is too low, the oxygen content in the steel must be highToMore
Oxide inclusions are generated. And Al with respect to Si concentration
If the concentration is high, as indicated in the above-mentioned prior application patent
In addition, the inclusions in the steel have a low melting point composition and extend during hot rolling.
Many inclusions extending in the rolling direction exist
However, the inclusions hinder the growth of crystal grains. Also, by lowering the Al concentration with respect to the Si concentration,
When making non-ductile inclusions, use ferro silicon during melting.
After the addition, a large amount of SiO_TwoIs produced,
It can cause clogging of the tundish nozzle
At times, there is a problem that a great hindrance occurs. [0010] SUMMARY OF THE INVENTION The present invention
Sol.Al 0.003 wt
% Or less to prevent the precipitation of fine AlN at the grain boundaries,
Also, by preventing the formation of low melting point ductile inclusions,
To improve the growth of crystal grains,
Straightening without clogging the tundish nozzle
Non-oriented silicon steel excellent in economy with small iron loss after annealing
The purpose is to propose a smelting method for sheet steel.
You. [0011] That is, the present invention provides
This was done to solve the problem
The configuration is as follows. C: 0.01 wt% or less and Si: 0.05% or more, 1.0 wt% or less And Mn is expressed in wt% in relation to Si.
Per amount (% Mn)^Two /(%Si)≦0.30
Including and further sol.Al: 0.003 wt% or less, P: 0.10 wt% or less, S: 0.01 wt% or less, totalO: 0.020 wt% or less and N: 0.01 wt% or less, Of the amount of Al added to the molten steel before the addition of Si when smelting steel containing
By adjustment, oxygen activity a expressed in wt% of molten steel before Si addition
_O To,Less than 0.015soAnd within the range satisfying the following equation (1).
Smelting method for non-oriented electrical steel sheet characterized by controlling
Law.                           〔Record〕      0.7 <(% Si) ・ a_O ^Two /Ten ^{-30110 / (T + 273) +11.4}    ----- (1)         However,         (% Si): Si content of steel expressed in wt%           T: Temperature of molten steel with Si added, expressed in ° C [0013] The following is a description of the experimental results on which the present invention is based and the results thereof.
The operation of will be described. The inventors have found that low Si (0.1 to 1.0)
(wt%) and low-sol.Al (≦ 0.003 wt%) non-oriented electrical steel sheet
, Mn and Al concentrations of steel, operating conditions during smelting and after strain relief annealing
A number of experiments and surveys were conducted on iron loss in
Results were obtained. 0.10 wt%, 0.40 wt% and 0.80 w% of Si
t% and eachReStrangeTsuAnd N: 0.010 to 0.00
Mn in the range of 2 wt% (% Mn)^Two /(%Si)≦0.30
Satisfies the relationship ofLaSol.Al content changed
Temperature of each non-oriented electrical steel sheet: 750
° C, time: iron loss after strain relief annealing for 2 hours (W_15/50 )
Inspected. These results are summarized in FIG. Figure 1 is so
l. Graph showing the relationship between Al content and iron loss after strain relief annealing
is there. As is apparent from FIG. 1, the Al content increases.
However, when the sol.Al content exceeds 0.003 wt%, the iron loss increases.
Stable and low iron loss
Will not be able to. For poor iron loss materials (materials with large iron loss)
A large number of AlNs are precipitated, and the average
As a result of measuring the crystal grains, a material with good iron loss (material with small iron loss)
Has an average crystal grain size of 50 μm or more,
The average grain size of the good material is as small as 20 μm.
The difference in the growth of crystal grains during annealing affects iron loss.
I understand. Next, 0.10 wt%, 0.40 wt% of Si and
 0.80 wt% different from each other, and sol.Al:
0.003 wt% or less and N: 0.010 wt% or less
To (% Mn)^Two/ Non-directional each with changed (% Si)
Temperature of 750 ° C for 2 hours
Iron loss after annealing (W_15/50)investigated. These results
FIG. Figure 2 is (% Mn)^Two/ (% Si) and strain
It is a graph which shows the relationship with the iron loss after annealing. As is apparent from FIG. 2, the iron loss is (% Mn)
^TwoStrong correlation with / (% Si), (% Mn)^Two/ (% Si)
Increase, especially when the value exceeds 0.30, the iron loss is remarkably large.
It turned out to be harder. Inclusion composition of iron loss defective material is Mn
Low melting point ductile inclusions with high O concentration.
Exists as ductile inclusions that are largely stretched in the
You. Also, as a result of examining the average crystal grain size after strain relief annealing,
The average crystal grain size of iron loss good material is more than 50μm.
Therefore, the average crystal grain size of the iron loss defective material is as small as 30 μm or less.
The difference in crystal grain growth during strain relief annealing
It can be seen that the value is affected. Normal,At the smelting stage of steel for non-oriented electrical steel sheets
The C content of non-oriented electrical steel sheet is 0.010 wt% or less.
Ferro after decarburization by vacuum degassing
Silicon is added for deoxidation. Therefore, in the molten steel before the addition of ferrosilicon,
If the oxygen activity of the ferro silicon is high, the yield of ferrosilicon
Not only bad, but also a large amount of SiO_TwoInclusions are formed,
Fruit, ladle-tundish or tundish-
Clogging of nozzles between fluids.
Cause inhibition. On the other hand, sol.Al: 0.003 wt% or less
If the oxygen activity is reduced by adding
It is found that there is a problem that too large
Revealed. Therefore, considering these results, further experiments
went. The results of these experiments are described below. SiTo0.10wt%, 0.20wt% and 0.30wt%
Each containing different (% Mn)^Two / (% Si): 0.30
wt% or less, sol.Al: 0.003 wt% or less and N: 0.010 wt%
% At the stage of melting steel for non-oriented electrical steel sheets
After the decarburization treatment by vacuum degassing treatment, Al is added and
The oxygen activity in molten steel before adding ferrosilicon
It was measured with an oxygen probe using an electrolyte. Then obtained
Hot rolled and cold rolled steel slabs
Non-oriented electrical steel sheet is subjected to strain relief annealing, and then iron loss (W
_15/50 ) Was measured. These results are shown in FIGS.
Shown in Fig. 3 shows Si: 0.10wt% material before ferrosilicon addition
Between oxygen activity of steel and iron loss after strain relief annealing at 750 ° C for 2 hours
FIG. 4 is a graph showing the state of engagement and nozzle clogging, and FIG.
i: Oxygen activity and 750 before adding 0.20 wt% ferrosilicon
 Relationship between iron loss after strain relief annealing for 2 hours and nozzle
FIG. 5 is a graph showing the state of clogging, and FIG.
Oxygen activity before ferrosilicon addition and strain at 750 ° C for 2 hours
Relationship between iron loss after annealing and occurrence of nozzle clogging
It is a graph shown. As can be seen from these figures, any Si
Even in contentA = (% Si) ・ a_o ^Two /Ten ^{-30110 / (T + 273) +11.4} As the value of 0.7 increases, the iron loss decreases significantly,
Also, a_o Above 150 wtppm causes nozzle clogging
However, it was found that the iron loss gradually increased. Also,
Of the above ingotA = (% Si) ・ a_o ^Two /Ten ^{-30110 / (T + 273) +11.4} With good iron loss exceeding 0.7 and poor iron loss below 0.7
As a result of investigating the average grain size after strain relief annealing,
The average crystal grain size of all good materials is 80μm or more, and iron loss is poor.
Is significantly larger than that of 50 μm. This was before
As mentioned above, the iron loss good material is the crystal grain during strain relief annealing.
It is considered that the growth greatly reduced iron loss. About these poor iron loss materials and good iron loss materials
The shapes and compositions of the investigated inclusions are shown in FIGS.
You. FIG. 6 shows the shape and composition of inclusions of the iron loss defective material.
The graph and FIG. 7 show the shape and composition of inclusions of iron loss good material.
It is a graph shown. The shape of inclusions should be observed by SEM.
In addition, composition analysis is an energy dispersive X-ray analyzer
(EDX) to randomly select inclusions and perform
MnO-SiO_Two−Al_TwoO _ThreeThe total amount of these is 100
%. As is clear from these figures,A = (% Si) ・ a_o ^Two /Ten ^{-30110 / (T + 273) +11.4} The inclusion composition of iron loss defective material with a value of 0.7 or less is MnO, Al_TwoO_Three  Dark
Low melting with high degree of stretching in hot rolling during hot rolling
Many exist as ductile inclusions of points. For this reason,
These inclusions hindered grain growth during strain relief annealing.
it is considered as. On the other hand,A = (% Si) ・ a_o ^Two /Ten ^{-30110 / (T + 273) +11.4} Inclusion exceeds 0.7_TwoHigh concentration
Non-ductile inclusions that exist as fine, granular inclusions
ing. Therefore, growth of crystal grains after strain relief annealing is suppressed.
It is probable that this was prevented. Also, a_oIs more than 150 wt ppm
Between tundish and between tundish and mold
As a result of investigating the inside of the_TwoWas packed in large quantities. This
It is considered that the molten steel stopped flowing. From the above results, C: 0.010 wt% or less and
And Si: 0.05-1.0 wt%, and Mn is related to Si
For content expressed in wt%, (% Mn)^Two / (% Si) ≦
Contained within the range satisfying 0.30, and sol.Al: 0.003 wt
%, P: 0.01 wt% or less, S: 0.01 wt% or less, to
tal O: 0.020 wt% or less and N: 0.010 wt% or less
Of Al to molten steel before Si addition during smelting of steel for non-oriented electrical steel sheets
By adjusting the amount of addition, the oxygen activity expressed in wt% of the molten steel
Quantity a_o To,Less than 0.015so,And 0.7 <(% Si) ・ a_o ^Two /Ten ^{-30110 / (T + 273) +11.4} By controlling to a range that satisfies the formula
Can prevent clogging, and it is more inexpensive and non-directional
Core loss after strain relief annealing in conductive electrical steel products
It became clear what we could do. Next, in the present invention other than the above description,
The reasons for limiting the component composition will be described. C: 0.010 wt% or less If C exceeds 0.010 wt%, the magnetic properties due to the precipitation of C
Degradation occurs. Therefore, the C content is 0.010 wt% or less.
Below. Si: 0.05 to 1.0 wt% Si is a useful component that increases specific resistance and reduces iron loss.
However, an increase in Si increases costs. Therefore,
In the invention of the above, the content is set to 0.05 wt% or more and 1.0 wt% or less.
I do. P: 0.10 wt% or less P is an effective component for increasing the strength of the steel sheet.
If the content exceeds wt%, brittleness of the steel sheet will increase markedly.
The upper limit of the amount is 0.10 wt%. S: 0.01 wt% or less Since S precipitates finely with Mn and inhibits grain growth,
It is desirable to have as little as possible. This invention is acceptable
The upper limit is 0.01 wt%. Total O: 0.020 wt% or less total O is vacuum degassing to prevent nozzle clogging
Before deoxidizing material (ferrosilicon) addition after decarburization
It is important to keep the dissolved oxygen concentration low. That
Therefore, the content is necessarily 0.020 wt% or less. N: 0.010 wt% Formation of fine AlN that inhibits grain growth after strain relief annealing
To prevent this, 0.010 wt% or less is required. Accordingly
And its content should be 0.010 wt% or less. [0034] [Examples] 0.1 wt%, 0.4 wt%, 0.8 wt% of Si
The slab for non-oriented electrical steel sheets
-Made by a continuous casting process. C: 0.03wt
%, P: 0.01 wt% or less, S: molten steel with 0.01 wt% or less
n in a converter, during tapping, or in a vacuum degassing unit.
The ferromanganese was added to adjust the Mn concentration. So
After that, the molten steel is subjected to CO decarburization treatment by a vacuum
The concentration was adjusted. Next, adjust the amount of Al
After various changes in the oxygen activity of steel, ferro silicon
And adjust the Si concentration.
And cast it into Next, each slab is stripped by a hot rolling mill.
Thickness: Rolled to 2.0mm, then cold rolled.
Rolled to 0.5 mm, finish annealing at 750 ° C for 10 seconds
Thereafter, an insulating coating was formed. After that, temperature: 750 ℃, hour
Period: Strain relief annealing was performed for 2 hours. Obtained in this way
Of each product, oxygen activity before addition of ferrosilicon, strain
Grain size and magnetic properties after pre-annealing,
Table 1 summarizes the results of surveys, such as nozzle clogging.
You. [0035] [Table 1]As is clear from Table 1, the present invention
A suitable example of this would be nozzle clogging during casting.
The average grain size of the product after strain relief annealing should be 80 μm or more.
Non-oriented electrical steel with low iron loss
It can be seen that a plate is obtained. [0037] According to the present invention, the composition of the components is specified,
Oxygen activity in molten steel by adjusting the amount of Al added before the addition of Si during manufacturing
This is a method of melting steel for non-oriented electrical steel sheets that controls
Thus, according to the present invention, nozzle clogging during casting is prevented.
Non-directional electromagnetic with low iron loss after strain relief annealing
Steel sheet can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between sol.Al content and iron loss after strain relief annealing. FIG. 2 is a graph showing a relationship between (% Mn) ² / (% Si) and iron loss after strain relief annealing. Fig. 3 Relationship between oxygen activity of Si: 0.10 wt% material before ferrosilicon addition and iron loss after strain relief annealing at 750 ° C for 2 hours.
6 is a graph showing a state of occurrence of nozzle clogging. Fig. 4 Relationship between oxygen activity before addition of ferrosilicon of 0.20 wt% material and iron loss after strain relief annealing at 750 ° C for 2 hours.
6 is a graph showing a state of occurrence of nozzle clogging. Fig. 5 Relationship between oxygen activity before addition of ferrosilicon of Si = 0.20 wt% material and iron loss after strain relief annealing at 750 ° C for 2 hours,
6 is a graph showing a state of occurrence of nozzle clogging. FIG. 6 is a graph showing the shape and composition of inclusions of poor iron loss material. FIG. 7 is a graph showing the shape and composition of inclusions of a good iron loss material.

Continuation of the front page (56) References JP-A-6-73510 (JP, A) JP-A-1-152239 (JP, A) The Japan Institute of Metals, Lecture / Modern Metallurgy Refining Edition 1 “Steel Refining” , Japan, The Japan Institute of Metals, June 25, 1995, 14-16, Japan Society for the Promotion of Science, Steelmaking 19th Committee, Revision and supplementation of recommended equilibrium values for steelmaking reactions, Japan, Japan Society for the Promotion of Science, Steelmaking 19th Committee, November 1, 1984, 38, 114, 131 Slag atlas, Germany, 1981, 61 Fujisawa et al., Equilibrium relationship between molten steel and deoxidation products in Mn-Si-Al complex deoxidation, Iron and steel, Japan , 1977, No. 63, No. 9, 1494-1503 (58) Fields investigated (Int. Cl. ⁷ , DB name) C21C 7/00 B22D 11/00 C22C 38/00 303 C22C 38/06

Claims (1)

(57) [Claims] [Claim 1] C: 0.01% by weight or less and Si: 0.05% or more and 1.0% by weight or less, and Mn is represented by wt% in relation to Si. The amount is included in the range that satisfies (% Mn) ² / (% Si) ≦ 0.30, and sol.Al: 0.003 wt% or less, P: 0.10 wt% or less, S: 0.01 wt% or less, totalO: 0.020 wt% or less and N: 0.01 wt% or less, in the step of melting the steel containing, by adjusting the amount of Al added to the Si-added before the molten steel, the oxygen activity a _O expressed by wt% of Si added before the molten steel, less than 0.015, And a method for melting steel for non-oriented electrical steel sheets, wherein the steel is controlled so as to satisfy the following expression (1). [Symbol] 0.7 <(% Si) · a O 2/10 -30110 / (T + 273) +11.4 ----- (1) provided that, (% Si): Si content in steel expressed by wt% T : Temperature of molten steel with Si added, expressed in ° C