JPH03104844A - Nonoriented silicon steel sheet excellent in magnetic characteristics and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the nonoriented silicon steel sheet in which fine MnS harm ful to iron loss properties is made harmless by the use of oxides by forming it from the compsn. contg. each prescribed amt. of C, Si and Mn, in which the content of Al or Zr is limited in accordance with a deoxidizing system in the steel and in which the number of the oxides having prescribed diameter or above is specified. CONSTITUTION:The nonoriented silicon steel sheet excellent in magnetic characteristics contg., by weight, <=0.01% C, 0.1 to 2.0% Si and 0.1 to 1.5% Mn, contg. <=0.1% Al or <=0.05% Zr according to a deoxidizing system in the steel and satisfying the following condition is offered. Namely, as for the above condition, the number of oxides having 0.5 to 5mum diameter in the steel is lim ited to 1000 to 5000 pieces per cm<2>. In this way, the excellent nonoriented silicon steel sheet having less core loss than that in the one by a conventional technique can be obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention uses an oxide to eliminate fine Mn particles that are harmful to iron loss characteristics.
The present invention relates to a non-oriented electrical steel sheet with excellent iron loss characteristics, which is characterized by rendering S harmless.

(Prior Art) In recent years, there has been a strong demand for higher efficiency in electrical equipment amidst the worldwide movement to save electricity and energy.

For this reason, there is an increasing demand for non-oriented electrical steel sheets, which are widely used as core materials for rotating machines and small and medium-sized transformers, to have excellent magnetic properties, especially low iron loss. It's coming.

M is an important factor that influences the magnetic properties of non-oriented electrical steel sheets.
Examples include precipitates such as nS, A, and QN, and B-based inclusions. In other words, fine MnS and A precipitated during the hot rolling process.
! l N 1A II 2 0 A clusters and B-based inclusions that spread during rolling inhibit the growth of grains during finish annealing or strain relief annealing at the customer, and significantly reduce iron loss characteristics. to deteriorate.

In order to reduce the number of fine MnS that precipitates in the hot rolling process, it is possible to reduce S as much as possible in the melting stage, and to precipitate MnS before hot rolling to aggregate and coarsen the pieces to reduce the number. .

Of these, for the former, ultra-high purity refining can be considered from the welding preliminary treatment to the secondary refining process, but this will inevitably lead to an increase in the melting cost. Furthermore, when considering desulfurization in the secondary refining process, the use of a strong deoxidizing element such as Aρ is a prerequisite, but it is necessary to take measures to prevent fine precipitation of AρN.

As described in Japanese Patent Application Laid-Open No. 54-163720, l? In deoxidation, by adding B,
There is a method of fixing N as BN to suppress fine precipitation of AρN, but there is a concern that BN itself may cause magnetic deterioration. In addition, in A,9 deoxidation, cluster-like A,1
? 20a is generated and causes deterioration of iron loss.

On the other hand, in the method of deoxidizing with Si,
It is considered that inclusions spread during rolling can be reduced by regulating the ratio of S 50 a and MnO-based inclusions, as disclosed in Japanese Patent No. 239, and this has been shown to be quite effective.

(Problems to be Solved by the Invention) However, the above-mentioned prior art does not mention conditions for effectively coagulating and coarsening MnS.

The present inventors focused on the conditions of oxides as precipitation nuclei of MnS, and as a result of elucidating and examining them based on many experimental results, we found that by appropriately controlling the size and number of oxides, He also invented an excellent non-oriented electrical steel sheet with low iron loss.

(Means for Solving the Problems) The present inventors have conducted extensive research in an attempt to utilize oxides in order to control the precipitation of MnS in non-oriented electrical steel sheets. As a result, in the steel ingot, especially 0.5u
By leaving a large number of oxides with a size of n or more and 5tEn or less, MnS is coagulated and precipitated using these oxides as nuclei, and the number of fine MnS precipitates is greatly reduced, resulting in extremely excellent iron loss characteristics tn ( It was discovered that grain-oriented electrical steel sheets can be obtained.

In order to significantly shorten the time from deoxidation to injection, a large number of oxides of the above size are present in the steel, and MnS is agglomerated and precipitated using these oxides as nuclei, reducing the number of fine MnS precipitates. It was found that the iron loss characteristics of non-oriented electrical steel sheets were significantly improved.

Experiments have shown that in order to leave a large number of oxides of this size in steel, it is necessary to keep the time from injecting molten steel to completing solidification after adding a deoxidizing agent to within 3 minutes, preferably within 60 seconds. This is what I found.

The present invention will be explained in detail below.

If this oxide is smaller than 0.5 m, it will adversely affect core loss for the same reason as fine MnS. Also, if it is larger than 5-, it becomes a precipitation nucleus of MnS.
, the main purpose cannot be achieved.

In terms of the number of oxides of the relevant size, 10 per 1c
It has been experimentally found that it is very effective to have 00 or more in steel. On the other hand, if it exceeds 50,000 pieces,
Oxides aggregate and accumulate in the injection nozzle, causing nozzle blockage and making stable operation impossible.

In the production of non-oriented electrical steel sheets, when deoxidizing the molten metal, the methods of deoxidizing with Aj7 and the method of deoxidizing with Aj81 are common, but the oxides as deoxidized products are Those that are generated during the process and already exist in molten steel (primary deoxidation products)
and those that crystallize as the solubility product decreases during solidification and cooling (secondary deoxidation products).

Among these, the secondary deoxidation products are Mn, S, due to solidification segregation.
M
It tends to become a precipitation nucleus of nS. It has been experimentally found that the size of this secondary deoxidized material is mostly 51 or less.

Therefore, in order to increase the number of oxides as precipitation nuclei of MnS, it is effective to utilize secondary deoxidation products. When using a deoxidizing agent such as S1, which has a relatively weak deoxidizing power and a large temperature dependence of the solubility product, the amount of secondary deoxidizing products is large (it is possible to act as precipitation nuclei of MnS).

Furthermore, when the content of Sl is the same, it is effective to increase the amount of secondary deoxidation products by increasing the temperature when injecting into the mold and increasing the solubility product. When the injection temperature is low,
The amount of primary deoxidation products that are generated in the molten steel stage before injection and grows to a larger size increases, and the amount of secondary deoxidation products decreases accordingly.

However, by increasing the injection temperature, the proportion of secondary deoxidation products that are effective as precipitation nuclei of MnS increases if the cooling rate is about the same as that of the current continuous casting machine.

For example, it has been found that by increasing the injection temperature by 20°C from 1560°C, the secondary deoxidation product increases by about 40%.

It is also possible to increase the number of oxide particles by adding oxide powder of the above-mentioned size to molten steel before injection, and to use it as precipitation nuclei of MnS. It has been found that some of the added oxide powders coalesce with each other and float to the surface, but the remaining oxide powders of the same size remain in the steel ingot. It goes without saying that it is advantageous from the viewpoint of the cleanliness of the steel to reduce as much as possible the oxides of 5 or more and the inclusions that spread during rolling.

On the other hand, in the method of shortening the retention time after deoxidation, A
When using a strong deoxidizing element like fI, the amount of secondary deoxidation products is very small, but if the molten steel is poured into the mold immediately after deoxidation, the time for growth and flotation separation of the primary deoxidation products can be reduced. is reduced, and a large number of oxides of the relevant size remain in the steel, which is effective.

If molten steel is held for more than 3 minutes after deoxidation, oxides, which are deoxidation products, will grow and become large, and most of them will float and separate. By specifying the holding time after deoxidation, the oxide is injected into the mold before it grows and floats to separate, so that a large number of oxides that become MnS precipitation nuclei are present in the steel.

This square is particularly effective when strong deoxidizing elements An, Zr, etc. are used as a deoxidizing agent. It has been experimentally found that the present invention is effective even when using a relatively weak deoxidizing agent like S1, but the effect is smaller than when using a strong deoxidizing element. This is because in the case of S1 deoxidation, the secondary deoxidation products that crystallize during solidification and cooling account for a large proportion of the oxides of 5 μm or less, so the influence of the holding time after deoxidation is small. think. However, even in the case of Sl deoxidation, practical effects can be expected, so it is included in the present invention.

Next, l. A method for producing 1,000 ton scale molten steel using a continuous casting machine will be explained.

When molten steel is deoxidized using a pot, the molten steel at the final stage of casting has already been deoxidized for several 10 minutes, and most of the oxides float and separate, which acts effectively as a precipitation site for MnS. Due to the insufficient number of oxides, sufficient magnetic properties cannot be obtained. Therefore, we continuously pour molten steel in a tundish or continuous casting machine, and control the addition rate of deoxidizing agent according to the casting speed so that all molten steel completes solidification within 3 minutes after deoxidation.
By producing a thin cast slab, it is possible to increase the number of oxides that effectively serve as MnS precipitation sites, and the magnetic properties are improved.

The most desirable deoxidizer is one that produces a large number of secondary deoxidation products, such as S+, unless there is a problem with cleanliness, but if the size and number of oxides can be controlled as described above, T
Strong deoxidizing elements such as I, Aj, and Zr can be used.

Next, the reasons for limiting the steel components of the present invention will be described.

C is a harmful component that increases core loss and causes magnetic aging, so it should be kept at 0.010% or less.

As is well known, S1 is a component that has the effect of reducing iron loss, and in order to exhibit this effect, it must be 0. It is necessary to contain I% or more. On the other hand, if the content increases, the magnetic flux density decreases, the rolling operation deteriorates, and furthermore, the cost increases, so it is set to 2.0% or less.

Mn also has the effect of increasing specific resistance and lowering iron loss, and for this purpose it is necessary to contain it in an amount of 0.1% or more. On the other hand, as the content increases, the ferrite 1,1 austenite transformation temperature decreases, making it impossible to maintain a sufficiently high annealing temperature and requiring long-term annealing at a relatively low temperature, which reduces productivity. Since it deteriorates, it should be 1.5% or less.

Aρ is necessary when used as a deoxidizing agent, but if its content exceeds 0.1%, it causes a decrease in magnetic flux density and an increase in cost, so it is set to 0.1% or less. However, for the deoxidizing effect, it is necessary to contain 0.005% or more.

Zr is also necessary when used as a deoxidizing agent, but in consideration of high cost, the content is set to 0.05% or less. However, for the deoxidizing effect, it is necessary to contain 0.005% or more.

P is a necessary component to increase the hardness of steel and improve its punchability, but if its content exceeds 0.15%,
Since the steel becomes brittle and rolling workability and workability deteriorate, 0.
15% or less.

Components other than those mentioned above are iron and unavoidable impurity elements.

(Example 1) Two steel ingots for non-oriented electrical steel sheets containing the components shown in Table 1 were
Manufactured using a 0kg scale high frequency vacuum melting furnace, then hot rolled and cold rolled to a thickness of 0.50m.
Final annealing was performed at ℃ for 30 seconds, and further annealed at 750℃
Magnetic annealing was performed for 2 hours.

As a result of investigating the oxide particle size distribution and MnS precipitation status of the steel ingot, observing the crystal grains of the product sheet, and measuring the iron loss characteristics, it was found that the steel ingot contains 0. oxide of 1
000 pieces/C1 or more has a very small amount of fine MnS precipitated, large crystal grains after magnetic annealing, and a very low iron loss W15/50 of 4.5 W/kg.

The results are summarized in Table 2.

In the present invention, A, B, and C are deoxidized with Si, AJ7, and Zr, respectively, and A is the one in which the injection temperature is increased by 30°C. B,
C are Aρ2 0 a and Z r O 2 respectively
The number of oxide particles of 0.5 μs or more and 5 μs or less is 1600 per CD.

DE was prepared by deoxidizing Sl and l), respectively, in a comparative method. In addition, for F, add 5 1 0 2 oxide powder before injection, and 800 oxide powder of the above size per 10
However, the injection nozzle was blocked and casting was extremely difficult.

(Example 2) Two steel ingots for non-oriented electrical steel sheets containing the components shown in Table 3 were
Manufactured using a 0 kg scale high frequency vacuum melting furnace, then hot rolled and cold rolled to a thickness of 0.50 + o + s.
Final annealing was performed at 50°C for 30 seconds, and further annealing was performed at 750°C.
Magnetic annealing was performed at ℃ for 2 hours.

As a result of investigating the oxide particle size distribution and MnS precipitation status of the steel ingot, observing the crystal grains of the product plate, and determining the iron loss characteristics, we found that the holding time after deoxidation is 30 seconds as in the present invention. The amount of fine MnS precipitated in the steel ingot is very small, the crystal grains are large after magnetic annealing, and the iron loss W is 4.4 W/
Very low weight (kg).

15/50 The results are summarized in Table 4.

In the present invention, the retention times for A, A, and C after deoxidation are 2 minutes, 30 seconds, and 30 seconds, respectively. The deoxidation methods are (a) Aρ deoxidation, and (c) Sl deoxidation. 2 and E are respectively Aj) deoxidation;
This is a conventional method of Si deoxidation.

Table 4 Deoxidizer Killing Oxide Iron I
Aρ 2 minutes 1300 4.8 shots Ro AN 30 seconds 1800 4.6 Meiha Sj 30 seconds 3000 4.4 Next law Ho Sl 60 minutes 800 5
．． 1 (Note 1) The number of oxides is 0.5 or more 5 per 1c.
The number of oxides with the following size (Note 2) Iron loss is the iron loss after magnetic annealing (W/kg) (Note 3)
Killing tiile is a non-directional electromagnetic fv4Ifi. 100 tons of molten steel is cast using a continuous casting machine, then hot rolled, then cold rolled to a thickness of 0.50 mm, finish annealed at 750 ° C. for 30 seconds, and
Magnetic annealing was performed at 750°C for 2 hours. The deoxidizer is AJI
I was used to directly cast a thin slab with a thickness of lOm+i in a tundish immediately before pouring the molten steel, depending on the casting speed (method P).

For comparison, we hot-rolled a slab obtained by deoxidizing it in a pot,
Then, after cold rolling to a thickness of 0.50 mm, it was rolled at 750°C for 30 minutes.
Finish annealing was performed for seconds, and magnetic annealing was further performed at 750° C. for 2 hours (Q method). Oxide ablation distribution of slab, M
As a result of investigating the nS precipitation situation, observing the crystal grains of the product plate, and measuring the iron loss characteristics, we found that the casting method of the present invention (P method), which significantly shortens the time to complete solidification after deoxidation, Piece of fine M
The amount of nS precipitated is very small, the crystal grains after magnetic annealing are large, and the iron loss W is very low at 4.6 W/kg.

:5/50 The results are summarized in Table 6.

(Effects of the Invention) As described above, according to the present invention, by appropriately controlling the size and amount of the oxide, it is possible to significantly improve the iron loss after magnetic annealing.

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Claims (1)

[Claims] 1. C: 0.01% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.1% or more and 1.5% or less, and deoxidation of steel. Depending on the method, in a non-oriented electrical steel sheet containing Al: 0.1% or less or Zr: 0.05% or less, the balance being iron and unavoidable impurity elements, the oxide in the steel has a diameter of 0.5 μm.
Items with a size of 5 μm or less are 10 per 1 cm^2.
A non-oriented electrical steel sheet with excellent magnetic properties, characterized in that the number of particles is 00 or more and 50,000 or less. 2. C: 0.01% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.1% or more and 1.5% or less, and depending on the steel deoxidation method, Al Zr: 0.1% or less, or Zr: 0.05% or less, with the balance consisting of iron and unavoidable impurity elements, is hot rolled, then cold rolled and finish annealed. A method for producing a non-oriented electrical steel sheet with excellent magnetic properties, characterized in that when deoxidizing molten steel, casting and solidification are completed within 3 minutes after adding a deoxidizing agent. 3. A non-oriented electrical steel sheet with excellent magnetic properties according to claim 1 or 2, which contains P: 0.15% or less by weight.