JP3247154B2 - Melting method of non-oriented electrical steel sheet with excellent magnetic properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detoxifying fine MnS, which is harmful to iron loss characteristics, using an oxide. a melting method of the non-oriented electrical steel sheet which contained than 0%.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for higher efficiency of electrical equipment in the context of worldwide power and energy saving. For this reason, even non-oriented electrical steel sheets widely used for core materials such as rotating machines and small and medium-sized transformers are increasingly required to have excellent magnetic properties, especially low iron loss. Is coming.

[0003] Precipitates such as MnS and AlN are important factors influencing the magnetic properties of non-oriented electrical steel sheets. That is, fine MnS or AlN precipitated in the hot rolling step.
However, it hinders the growth of crystal grains at the time of finish annealing or at the time of strain relief annealing at a customer, and greatly deteriorates iron loss characteristics. In order to reduce the number of fine MnS precipitated in the hot rolling process, it is necessary to reduce S as much as possible at the melting stage, and to reduce Mn before hot rolling.
It is conceivable that S is precipitated to form a coarse aggregate and reduce the number.

[0004] Of the above, the former corresponds to the thorough desulfurization in the secondary refining process from the hot metal pretreatment, but inevitably causes a significant increase in the cost of smelting. When desulfurization is performed in the secondary refining process, A
The use of a strong deoxidizing element such as 1 is premised, but it is necessary to take measures to prevent fine precipitation of AlN. For example, JP-A-54-16
As described in Japanese Patent No. 3720, by adding B in Al deoxidation, N is fixed as BN and A
Although there is a method of suppressing fine precipitation of 1N, there is a concern that BN itself may cause magnetic deterioration. In addition, in Al deoxidation, cluster-like Al ₂ O ₃ is generated, which causes iron loss to deteriorate.

On the other hand, as described in Japanese Patent Application Laid-Open No. 3-104844, 1000 to 50,000 oxides having a diameter of 0.5 to 5 μm per 1 cm ² are provided, so that oxides before hot rolling can be obtained. There is a method of coarsely depositing MnS around the oxide, but this method alone cannot provide a sufficient effect when the deoxidation method or the composition of the steel ingot is variously changed. In particular, when the Si concentration is higher than 0.6%, a sufficient effect cannot be obtained by this method alone. When the Si concentration is high as described above, the primary deoxidizing power becomes strong.
Controlling the composition of the individual oxides is extremely important because the amount of secondary deoxidation products is reduced. That is, it is necessary to control not only the number of oxides but also the composition of the oxide on which MnS is easily precipitated.

In the method of deoxidizing with Si, as disclosed in Japanese Patent Application Laid-Open No. 1-152239, SiO ₂ ,
M based on the total weight of the three types of inclusions, MnO and Al ₂ O ₃
The weight ratio of nO is 15% or less, and SiO ₂
Discloses a method for preventing the formation of a low-melting oxide with high spreadability by setting the weight ratio of the compound to 75% or more. However, when the Si concentration is higher than 0.6%,
As described above, since the amount of the secondary deoxidation product is reduced, it is necessary to control the oxide so that MnS is easily precipitated. However, oxides in which the proportion by weight of MnO is 15% or less are MnO.
Since S hardly precipitates, this method has not been able to obtain a sufficient effect.

According to a report described in Material and Process, Vol. 4, page 283, MnO in oxides
It is shown that MnS precipitates preferentially at a high concentration. However, for this purpose, it is necessary to make the Mn concentration much higher than the Si concentration in the molten steel, so that manganese silicate with high ductility is produced and MnS precipitation is promoted, but the produced oxide itself is However, there is a problem that the grain growth is inhibited.

[0008]

DISCLOSURE OF THE INVENTION The present invention is intended to reduce the cost of smelting when low sulfurization is carried out,
In addition to solving the problem of fine precipitation of AlN when using a strongly deoxidizing element such as the above, and the problem of magnetic deterioration due to BN in the method described in JP-A-54-163720, In the methods described in JP-A-104844 and JP-A-1-152239, it was possible to solve the problem that a sufficient effect was not obtained when the deoxidation method and the composition of the steel ingot were variously changed. An object of the present invention is to provide a method for melting a non-oriented electrical steel sheet having excellent magnetic properties.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method for producing C by weight.
Is 0.01% or less, Mn is 0.1% or more and 2.0% or less,
Si is 0.6% or more and 2.0% or less, Al is 0.010%
Hereinafter, P contains 0.15% or less and S contains 0.01% or less .
(MnO) and (Si) in the total oxides of the steel sheet.
0 ₂₎ concentration ratios expressed in percent by weight of, (% MnO) /
(% Si0 ₂₎ as an electromagnetic steel is 0.15 to 0.45
Upon the melting plate, decarburization that by the vacuum degassing furnace
Then , with the dissolved oxygen concentration being 200 ppm or more , Mn
Was added prior to, and characterized by adding pull-out continues, the Si so that the ratio of 0.2 to 1.0 as Mn / Si
This is a method for melting non-oriented electrical steel sheets having excellent magnetic properties .

[0010]

According to the present invention, in order to increase the MnO concentration in the oxide, the oxygen concentration before deoxidation and the order of addition of the deoxidizing agent can be adjusted to the appropriate values for the Si concentration and the Mn concentration as the deoxidizing agent. Is based on the discovery that the precipitation of MnS can be promoted without increasing the concentration balance of manganese silicate to a detrimentally spreadable manganese silicate. This is 1
Regardless of the secondary deoxidation product and the secondary deoxidation product, it was considered that the number of oxides should be a certain amount or more, and MnS was deposited unless the Mn concentration was much higher than the Si concentration. This is a significant departure from previous findings that no effective manganese silicate is produced.

The present invention is described in principle as follows. In other words, when Si reacts with the FeO-MnO-based deoxidized oxide generated by the prior addition of Mn, it changes into FeO-MnO-SiO ₂ -based oxide, but this reduction reaction (reverse In view of the above, the driving force of the reaction for producing SiO ₂ ) is the activity difference between SiO ₂ having an activity of 1 and the activity of SiO ₂ in the oxide, which is in equilibrium with Si in molten steel. Thus, activity of SiO ₂ in the oxide and the SiO ₂ concentration of the oxide is an SiO ₂ saturation also increased 1
Therefore, there is no driving force for the reaction, and the reduction reaction does not proceed any further. For this reason, even if it is a condition presumed from calculation that equilibrium is completely reduced to SiO ₂ , the starting point is the FeO—MnO-based deoxidation product generated by Mn predeoxidation. The oxide is not pure SiO ₂ but Mn as FeO—MnO—SiO ₂ based oxide.
O will remain. However, when the amount of SiO ₂ generated by this reaction is small, the dissolved oxygen concentration does not sufficiently decrease, and deoxidation proceeds by generating pure SiO ₂ elsewhere. This means that it is important to generate a large amount of FeO—MnO-based deoxidation products before adding Si.

According to this principle, thermodynamically pure S
Even under the condition that only iO ₂ is generated, it is possible to generate a MnO-containing oxide that effectively acts on the precipitation of MnS by strictly controlling the deoxidation conditions. Manganese silicate produced by such a method is composed of Mn in the oxide.
The melting point is high due to the low concentration of O, and there is almost no adverse effect on the magnetic properties of the oxide itself as compared with manganese silicate, which is formed under thermodynamic equilibrium conditions and has a high melting point and a high melting point, and thus has high ductility . Conversely, when investigating the locations of the elements in the oxide, the MnO-containing oxide produced based on the present principle shows that even when the MnO concentration is low, a phase in which MnO is concentrated exists at the outer peripheral portion of the oxide. , MnS
This is extremely advantageous for the precipitation of.

According to a detailed experiment by the present inventors, the following requirements must be satisfied in order to form a large number of oxides with MnO remaining based on this principle. After the decarburization treatment in a vacuum degassing furnace, Mn is added in advance with the dissolved oxygen concentration kept at 200 ppm or more. Subsequently, Si should be added in a ratio of 0.2 to 1.0 as Mn / Si. Al content should be 0.010% by weight or less.

Among these conditions, conditions for generating a large amount of MnO-based oxides before the addition of Si, and when the concentration of dissolved oxygen at the time of prior addition of Mn is less than 200 ppm, formation of MnO-based oxides after addition of Mn. Since the number of FeO—MnO-based oxides is reduced, pure SiO ₂
Is generated in a large amount, and the amount of the oxide containing MnO that effectively works for the precipitation of MnS is insufficient. If dissolved oxygen is high,
Although it is advantageous as a condition for forming the MnO-based oxide, the content is preferably 900 ppm or less in order to prevent a problem that the cleanliness of the molten steel is deteriorated by generating more than necessary. Is a condition for appropriately controlling the composition of the oxide generated after reacting with Si. That is, the FeO—MnO—SiO ₂ -based oxide generated by the above reaction mechanism has a MnO concentration in the oxide higher than a certain value and a MnO
It is necessary to effectively act as a precipitation nucleus of S and not to make the manganese silicate rich in spreadability harmful to magnetism by not extremely lowering the melting point. Mn
/ Si is smaller than 0.2, Mn in the oxide
Since the O concentration is low, it does not effectively act on the precipitation of MnS. Conversely, if the O concentration is higher than 1.0 , the MnO concentration in the produced oxide becomes too high, causing ductility and causing harmful manganese silicate. Become. On the other hand, the condition of MnS
This is a condition for optimizing the composition of manganese silicate, which serves as a precipitation nucleus of manganese. That is, when Al is higher than 0.010%, FeO—Mn generated after Mn addition is added.
The O-based oxide does not eventually become manganese silicate, but becomes alumina silicate having a very low manganese concentration, and thus does not effectively act as MnS precipitation nuclei.

Si is 0.1% to reduce iron loss
However, if the content is less than 0.6%, the primary deoxidizing power is weak, and a large amount of the secondary deoxidizing product is crystallized. Characteristics are obtained. If it is higher than 2%, the magnetic flux density decreases,
The rolling operation is deteriorated, and the cost is further increased.

As can be seen from the above, the most important point of the present invention is that the composition of the oxide is such that MnS is easily precipitated.
On the other hand, while making MnO a high manganese silicate, the MnO concentration is increased more than necessary, and a harmful manganese silicate with high malleability is not formed. FIG. 1 shows the concentration ratio between MnO and SiO ₂ in the total oxides of the steel sheet and the Mn in the slab.
It shows the relationship with the S crystallization rate and the iron loss value after magnetic annealing in an electrical steel sheet. The concentration ratio expressed in% by weight (% M
(nO /% SiO ₂ ) is smaller than 0.15,
The crystallization ratio of MnS in the slab is small and the iron loss is high.
Even when it is larger than 45, the iron loss is high because the manganese silicate starts to have ductility. Here, the total oxide composition is determined by, for example, dissolving a part of the steel sheet with an iodine alcohol solution and analyzing the extraction residue. The MnS crystallization rate was defined as a comparison between the sulfur content crystallized as MnS by chemical analysis as SasMnS and the total sulfur concentration (TotalS) (ΔS
asMnS / Total S｝ × 100). % M
When nO /% SiO ₂ is smaller than 0.15, the magnetic properties are poor because the number of manganese silicates having a high MnO concentration effective for MnS precipitation is small, and efficient crystallization of MnS at the slab stage. This is because the concentration of the dissolved sulfur is high because it does not occur, and a large amount of fine MnS precipitates after hot rolling and hinders crystal grain growth. On the other hand, when it is larger than 0.45, the MnO concentration in the manganese silicate becomes too high, so that the melting point of the oxide decreases and starts to have ductility. This is because they are present and hinder coarsening of crystal grains.

Further, when the method according to the present invention is used, Si
Is less than 0.6%,
It is possible to manufacture a product having high magnetic properties equal to or higher than the product obtained by the method described in Japanese Patent No. 04844.

Next, the reasons for limiting other steel components of the present invention will be described. C is a harmful component that increases iron loss and causes magnetic aging. Mn has the effect of increasing the specific resistance and reducing the iron loss. For this purpose, Mn must be contained in an amount of 0.1% by weight or more. On the other hand, when the content increases, the ferrite / austenite transformation temperature decreases, so that the temperature during annealing cannot be sufficiently increased, and long-time annealing at a relatively low temperature is required,
Since the productivity deteriorates, the content is set to 2.0% by weight or less.

P is a component necessary for increasing the hardness of the steel and improving the punching property. However, if the content exceeds 0.15%, the steel becomes brittle and the rolling workability and workability deteriorate. 0.15% by weight or less. S is crystallized as MnS in the slab stage to render it harmless. However, as long as the Mn concentration is within the above-mentioned range, even when the present invention is used, when S is more than 0.01% by weight, it is not sufficient. Since it is difficult to make the particles harmless, the content is set to 0.01% by weight or less.

[0020]

【Example】

(Example 1) Example 1 was performed by the following steps. A non-oriented electrical steel sheet containing the components shown in Table 1 was manufactured using a high-frequency vacuum melting furnace of a 20 kg scale, and then hot-rolled.
After cold rolling to a thickness of 50 mm, finish annealing was performed at 800 ° C. for 30 seconds, and further magnetic annealing was performed at 750 ° C. × 2 hours.

Table 1 shows the results. From this,% MnO /% SiO ₂ in the total oxide composition from 0.15 to 0.
It can be seen that the comparative example steel sheets e, f, and g, which are outside the range of 45, have high iron loss values and are inferior in magnetic properties.

[0022]

[Table 1]

Example 2 Example 2 was performed by the following steps. 20 kg of non-oriented electrical steel sheet containing the components shown in Table 2
It is manufactured using a high-frequency vacuum melting furnace of a scale, then hot-rolled, cold-rolled to a thickness of 0.50 mm, and then
Finish annealing was performed for 2 seconds, and then magnetic annealing was performed at 750 ° C. × 2 hours. Here, in the vacuum melting furnace, after controlling the dissolved oxygen concentration by mixing and dissolving iron oxide together with electrolytic iron, first, a predetermined amount of Mn was charged, and then a predetermined amount of Si was charged. Observe the oxide particle size distribution of the steel ingot with an optical microscope.
The MnS precipitation was evaluated by the number per cm ² , and the MnS precipitation state was defined as the ratio of the sulfur content crystallized as MnS by chemical analysis as SasMnS and the total sulfur concentration (TotalS) (Ｍｎ (SasMnS) / (TotalS)｝ × 1
00) was investigated. In addition, observation of crystal grains of the product plate and measurement of iron loss characteristics were performed.

[0024]

[Table 2]

[0025]

[Table 3]

Table 3 shows the results of the investigation. From this, Mn /
H having an Si content of less than 0.2 or an Al concentration of 0.010
% Of J and K having a dissolved oxygen concentration of 200 ppm or less before the addition of Mn have a low MnS crystallization ratio and poor electromagnetic characteristics. Also,
I having Mn / Si greater than 1.0 has a large MnS crystallization rate, but an extensible oxide appears, so that the electromagnetic characteristics are deteriorated. Further, even when the same component as A in the embodiment of the present invention is used, L in which the deoxidation order is Si predeoxidation has a low MnS crystallization ratio due to a low MnO concentration ratio in the oxide, resulting in low electromagnetic characteristics. bad.

Example 3 Example 3 was performed by the following steps. First, about 350 tons of molten steel for non-oriented electrical steel sheets was melted in a converter, and then vacuum degassed with DH. After degassing, Mn, S
i was added and deoxidized. Finally, the composition was controlled to the composition shown in Table 4, and then cast using a continuous casting machine. After that, hot rolling,
After cold rolling to a thickness of 0.50 mm, finish annealing was performed at 800 ° C. for 30 seconds, and magnetic annealing was performed at 750 ° C. × 2 hours. The results are shown in Table 5, and the same results as in Examples 1 and 2 were obtained in the actual process.

[0028]

[Table 4]

[0029]

[Table 5]

[0030]

According to the present invention, any S
Even in a non-oriented electrical steel sheet having an i-concentration, it is possible to produce a non-oriented electrical steel sheet excellent in magnetic properties characterized by detoxifying fine MnS harmful to iron loss properties using an oxide. became.

[Brief description of the drawings]

FIG. 1 shows a relationship between a concentration ratio of MnO and SiO ₂ in all oxides of a steel sheet, a crystallization ratio of MnS in a slab, and a relationship between an iron loss value of a magnetic steel sheet after magnetic annealing.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C21C 7/00 C22C 38/00 C22C 38/06

Claims (1)

(57) [Claims] 1. C: 0.01% or less, Mn: 0.1 to 2.0%, Si: 0.6 to 2.0%, Al: 0.010% or less, P: 0. 15% or less, S: see contains 0.01% or less, in the total oxides of the steel sheet, as MnO and Si0 concentration ratio expressed ₂ in weight percent,% MnO /% Si0 ₂ 0.15 to 0.45 To melt electrical steel sheets
After the decarburization treatment in a vacuum degassing furnace, the dissolved oxygen
Mn is added in advance in a state of not less than 00 ppm,
Subsequently, Si is converted to a ratio of 0.2 to 1.0 as Mn / Si.
Excellent magnetic properties characterized by being added as
A method for melting non-oriented electrical steel sheets.