JPS5943814A - Method for refining molten steel in ladle in manufacture of non-oriented electrical steel sheet with small iron loss - Google Patents

Abstract

PURPOSE:To manufacture the titled electrical steel sheet by adding a deoxidizer contg. Si and Al to deoxidize well molten steel, adding an alloy consisting of rare earth elements and a flux for desulfurization to the deoxidized molten steel, and carrying out ladle refining including vacuum degassing. CONSTITUTION:A deoxidizer contg. Si and Al is added to molten steel manufactured in a steel manufacturing furnace to deoxidize well the molten steel, and the molten steel is well agitated to separate the deoxidation products. To the deoxidized molten steel are added 0.1-2kg/t rare earth element or alloy consisting of >=2 kinds of rare earth elements and 1-20kg/t flux for desulfurization such as lime, soda ash, NaOH or KOH, and ladle refining including vacuum degassing is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ladle refining method for producing non-oriented electrical steel sheets with low iron loss, and in particular to obtain cold-rolled non-oriented electrical steel sheets with excellent iron density and iron loss values. We propose a method of molten steel treatment that is particularly effective for reducing inclusions and precipitates.

The most important characteristic of non-oriented electrical steel sheets is low iron loss. This iron loss depends on the recrystallized grain size obtained by finish annealing after cold rolling, and it is known that the lowest iron loss is obtained when the recrystallized grain size is 150 to 25011. In order to recrystallize to such a grain size, it is necessary to control fine precipitates such as nitrides and sulfides to an extremely low level. Among these precipitates, nitrides are present in the steel.
By containing 15% or more of AJ, l? Since N can be precipitated with a relatively large grain size, there is little interference with recrystallization grain growth during final annealing. On the other hand, for sulfides, if rare earth elements or Oa are added as an alloying element, the sulfides are thermodynamically stable and do not undergo solid solution reprecipitation, or can be fixed as relatively large precipitates. It is reported in JP-A-51-62115 or JP-A-55-2494 that it is effective in improving the iron loss value.
No. 2 has already been proposed and is publicly known.

However, in the field of high-grade electrical steel sheets, in order to further improve the iron loss value, it is necessary to obtain the most ideal recrystallized grain size and to reduce inclusions and precipitates in the matrix structure as much as possible. become. The iron loss value of a non-directional high-grade electromagnetic plate is composed of magnetic wear P: loss and eddy current loss, and the ratio thereof is 6 to 7:4 to 3, and the contribution of hysteretic contact loss is large.

It is known that to reduce the above eddy current loss without affecting the iron loss value, it is possible to increase the content of Sl and A/ to reduce the electrical resistance of the steel plate base by t-1'. but,
If S1+A/' exceeds 4 inches, cracks will occur during cold rolling, so there is a limit to reducing eddy current loss.On the other hand,
Since hysteresis loss increases due to inclusions and precipitates in the hexabase structure, their formation must be suppressed.

In other words, these inclusions and precipitates act as obstacles to the movement of the domain wall, increasing hysteresis loss. These inclusions and precipitates are formed by oxides as well as nitrides and sulfides, and in order to improve the iron loss value of high-grade non-oriented electrical steel sheets, it is necessary to N, S, and O in the sheathed molten copper to suppress oxides.
It is necessary to reduce the

The present invention is a technology developed in view of the above-mentioned current state of the industry with the aim of overcoming the disadvantages1). When refining the molten steel in a ladle, first add a deoxidizing agent using 5i-Ar to fully deoxidize the molten steel. A ladle sheath of molten steel used for the production of non-oriented electrical steel sheet with low core loss, characterized in that the alloy consisting of the following is added together with desulfurization flux and subjected to vacuum degassing treatment;V ladle refining.
) 11 method configuration. The details of the configuration will be explained below.

In general, 'R8' material for non-oriented electrical steel sheets is produced by decarburizing desulfurized hot metal in a smelting furnace and then using a ladle at the top of the fcti process. 11. As a ladle refining method, vacuum Kozue ρ1! is preferable, and after first sufficiently decarburizing by rimmed treatment, Sl and AI! is added to deoxidize, and the molten steel is sufficiently stirred to separate the deoxidized products. It is necessary to keep the S content in molten steel sufficiently low during hot metal desulfurization, but resulfurization may occur due to pollution from the smelting furnace, and currently it is not possible to obtain a satisfactory low-sulfur molten steel. be. Therefore, Sl and A
After deoxidation by /', desulfurization is sometimes tried by adding desulfurization flux, but the S concentration (S≦lOppm) is obtained to ensure the core loss value of high-grade non-oriented electrical steel sheet. In order to do this, it is necessary to add a large amount of desulfurization flux,
In that case, there was a drawback that deoxidation did not proceed sufficiently.

Therefore, in the ladle refining of the molten lees obtained in a steelmaking furnace, first, after sufficient deoxidation with Sl and L', rare earth elements are added to reduce dissolved S, and at the same time, the necessary minimum amount of desulfurization is carried out. By desulfurizing dissolved S by adding flux in combination, the desulfurization flux promotes flotation and separation of rare earth sulfides and sulfides that are generated and suspended in molten steel due to the addition of rare earth elements. This is a method in which deoxidation is followed by desulfurization.

The method of the present invention will be explained in further detail below. Rare earth elements have a strong affinity for oxygen, and in order to effectively desulfurize, it is necessary to sufficiently deoxidize the molten steel and remove the deoxidized products from the system in advance. Therefore, prior to the addition of rare earth elements,
Sit. and A/ are added to molten steel to sufficiently deoxidize it, and then rare earth elements are added to the deoxidized molten steel.

When adding these rare earth elements, it is important to secure the amount of rare earth elements necessary to reduce the dissolved S in the molten steel to the equilibrium S# degree, specifically 0.1 to 2 kf.
/l of rare earth element is added. Normally, in the production of non-oriented silicon steel, the S concentration of molten steel is reduced to 100 when desulfurizing hot metal.
Since ladle refining is performed after reducing the amount to about ppm, assuming that the reaction efficiency of rare earth elements with S is about 50 parts, the ratio is 2 to 9 parts.
1 of rare earth elements is required. Further, even if the initial S concentration of molten steel is low, no effect in water washing can be expected if the addition amount is less than 0.1 kp/.

After adding the rare earth element, the molten steel is sufficiently stirred to allow the reaction with dissolved S to occur completely. Rare earth elements are dissolved S
and reacts with oxides floating in molten steel, producing sulfides (Ce
S, LaS) l>or oxysulfide (CeO2,'
La5s), but these sulfides 22
22 Alternatively, oxysulfides have a high density and have a small density difference with respect to the molten steel, so the surfacing wall thickness 11 cannot be expected to form much, and they migrate into the molten steel.

Next, a desulfurization flux is added to desulfurize dissolved S that has not reacted with the rare earth element. The desulfurization fluxes used here are lime (CaO), (CaF 2 ), soda ash (N
' 2 COa ), caustic soda (NaOH), caustic potash (KOH), etc., commonly used known species (white ones, or composites thereof may be used.Calcium carbide (Oa C2) il''j:, main form In this case, it is not desirable because it causes recarburization of the molten steel and deteriorates the electromagnetic properties of the immature steel plate.As a desulfurization flux, lime ((, aO), etc., which is solid at a temperature of 2 degrees Celsius) is not desirable. When using calcium fluoride (CF), iron oxide (Fe208), limestone (C
It is effective to use a mixture of one or more types of desulfurization flux such as ``COa''.The desulfurization flux added to molten steel reacts with dissolved S to form sulfides, and the flux is also formed by the flux. The sulfur arsenides or excessively present flux adsorb and coalesce with the rare earth element sulfides or oxysulfides that were formed earlier and are too dense to float in the molten steel. Hanging reduces the density of the upper surface and increases the floatability, rapidly promoting the de-semination of molten steel or ")".

The amount of desulfurization flux to be added is to ensure the amount necessary to accelerate desulfurization, but it is not suitable if it is added in excess and increases the amount of oxygen in the molten steel. Specifically, desulfurization flux of [~2 (,1 kV/t) is added. If the amount of flux added is less than 1 kV/t, the desulfurization effect described above is not sufficient. In this case, the oxygen concentration in the steel increases, which actually deteriorates the electromagnetic properties of the product.

Next, the present invention will be explained in detail.

Example IS Desulfurized hot metal with an S concentration of 0.004% was blown in a 280-ton bottom blowing converter, and the molten steel components were c: o, oa to 0.
06'1, Si: tr, Mn: 0,10~
0.20%, P: 0.007-0.015, S:
Section 0.002-0.004, 0:400-6 (10
Melting steel with ppm composition? ! (3 charges), and this molten steel is decarburized using an RH degassing device, and RH degassed ladle refining is carried out under the conditions shown in 1. I got it. Next, the molten steel was formed into a slab by continuous U-shaping, and hot rolled to obtain a hot rolled plate. After dredging these hot-rolled sheets, they were subjected to two consecutive annealing sessions (
A cold-rolled plate with a finishing thickness of 0.85 tntm was obtained by rolling for 9 hours and subjected to continuous annealing for V-finishing. Δ, 13.0 Electromagnetic 114 obtained for 3-phase steel plate. The gender is shown in Table 2 (,
Ta. From this table, it can be seen that compared to Method A in which a rare earth element alloy and desulfurization flux were added in combination in the present invention example, and Method B or C in which a rare earth element alloy or desulfurization flux was added alone as a comparative example, the results were significantly improved. It turns out that it is excellent.

Example 2 Desulfurized hot metal with an S concentration of 0.004% was blown in a 90-ton top-bottom blowing converter. After out-of-furnace scouring in which decarburization and degassing are carried out in the equipment for -1- minutes and addition of rare earth alloys, a portion of the charge is subjected to lime-based desulfurization using a ladle immersion lance, as shown in Table 8. Flux was blown in with Ar gas. Each molten steel was continuously cast to form a slab, which was then hot rolled and once cold rolled to a 0.
Finish annealing was performed using a cold-rolled plate with a finish thickness of 5 m and a finish thickness of 17 m.

Method D -y f) (7) What are the electromagnetic properties of the product sheets obtained for the four steel types? It is shown in Mo4. From this, it can be seen that method G of the present invention, in which a rare earth element alloy and desulfurization flux are added in combination, has significantly superior electromagnetic properties to those of E and F compared to the comparative methods.

Table 2 Electromagnetic properties of product plate -90- Table 4 Electromagnetic properties of product plate As explained above, according to the present invention, the most preferable recrystallized grain size can be adjusted, and inclusions and precipitates in the matrix structure can be adjusted. Can it be significantly reduced? C) It has the effect of facilitating the production of non-oriented high-grade electrical steel sheets with low iron loss.

Claims (1)

[Claims] 1. When preparing ladle & Ij of molten steel melted in a steelmaking furnace used for manufacturing non-oriented electrical steel sheets with low core loss, first, Sl.
A deoxidizing agent using A/' is added to fully deoxidize, and the alloy consisting of one or more rare earth elements is added to the deoxidized molten steel along with desulfurization flux to perform vacuum degassing treatment. 1. A ladle refining method for molten steel used for manufacturing non-oriented electrical steel sheets with low iron loss, characterized by carrying out ladle refining including molten steel.