JP3295008B2 - Manufacturing 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 for producing a non-oriented electrical steel sheet having excellent magnetic properties, and in particular, by controlling the composition and morphology of precipitates and inclusions in the steel sheet.
It is intended to improve the iron loss characteristics advantageously.

[0002]

2. Description of the Related Art In general, the most important characteristic of non-oriented electrical steel sheets is iron loss, which greatly depends on the recrystallized grain size obtained by finish annealing after cold rolling. In order to obtain a product with low iron loss, it is basically necessary to increase the crystal grain size. The lowest iron loss is
It is known that it can be obtained when the recrystallized grain size is 150 to 250 μm.

[0003] Here, the growth of crystal grains is greatly affected by the second phase dispersed in the steel, ie, precipitates and inclusions, and is greatly influenced by the components, size distribution, and dispersion state. Therefore, in order to recrystallize to such a particle size, it is effective to reduce fine precipitates such as nitrides and sulfides as much as possible.

[0004] However, at the current level of industrial technology, it is extremely difficult to melt high-purity steel in which precipitates and inclusions in the steel are reduced to such an extent that the grain growth is not affected, and general-purpose practical materials are used. In the production of steel, the problem of cost cannot be neglected, and it is substantially impossible to melt such high-purity steel.

[0005] For this reason, some precipitates and inclusions remain in the steel inevitably, resulting in the deterioration of the magnetic properties. In particular, when precipitates having a relatively low solid solution temperature such as MnS and AlN are formed, they are once dissolved in the process of slab heating, hot-rolled sheet annealing, recrystallization annealing after cold rolling, etc., and then cooled. The fine precipitates are re-precipitated finely at a stage, and since such fine precipitates have a very large effect of suppressing grain growth, the magnetic properties are remarkably deteriorated.

As means for avoiding this solid solution and reprecipitation,
There is a method of lowering the slab heating temperature, the hot rolled sheet annealing temperature, and the recrystallization annealing temperature after cold rolling. However, although lowering the slab heating temperature has the effect of preventing solid solution of precipitates, it also lowers the hot rolling temperature, which not only makes rolling difficult, but also makes the hot rolled sheet unrecrystallized. Since the grain size is small even if a part remains or is recrystallized, the texture of the product sheet is deteriorated by subsequent cold rolling and recrystallization, which is not preferable for the product characteristics of the non-oriented electrical steel sheet. Similarly, in the method of lowering the annealing temperature of the hot-rolled sheet, recrystallization and grain growth become insufficient, and deterioration of the texture of the product sheet is inevitable.
Further, when the recrystallization annealing temperature is lowered, the grain growth rate is rather lowered due to the low temperature, and a sufficient grain size cannot be obtained with a limited annealing time. As described above, there is a limit in obtaining a product having good magnetic properties without dissolving and re-precipitating a precipitate, and no particular effect can be expected.

As a means for avoiding the adverse effects of precipitates, there is a method of controlling the form of precipitates. As such a method of controlling the form of precipitates, S in steel is converted to REM sulfide, Sb sulfide, or the like. Method of fixing as a precipitate having a high solid solution temperature (JP-A-51-62115)
Method for fixing S using Ca (Japanese Patent Publication No. 58-17248,
JP-B-58-17249 and JP-A-59-74213),
Method of adding Zr (Japanese Patent Publication No. 1-52448, JP-A-51-6)
0624)

[0008] However, in order to obtain a sufficient effect by these methods, it is necessary to add a large amount of expensive auxiliary materials, which raises a problem of an increase in product cost. Not only that, REM sulfide is (REM, Mn, Al, Si) (O, S)
In addition to the fact that it takes a very complicated precipitation form as described above, it is difficult to float during melting and has a disadvantage that it remains in a large amount in steel. Therefore, even though the solid solution temperature of REM sulfide (mainly Ce sulfide) alone is high, it is actually a composite precipitate, and partially solid solution and reprecipitate.

Also, in the method using Ca, since the precipitate takes a very complicated form such as Al (O, N) + (Ca, Mn) (S, O), similarly, the grain growth also takes place. On the other hand, it is hard to say that it is completely harmless, and this has been a problem particularly in the production of high-grade non-oriented electrical steel sheets aimed at low iron loss. In particular, Japanese Unexamined Patent Publication No.
According to JP-74213, in ladle refining of molten steel smelted in a steelmaking furnace, first, Si and Al are added and deoxidized sufficiently, and a Ca alloy and a desulfurization flux are mixed and added to the deoxidized molten steel. Although a method of desulfurizing by using the method has been proposed, a sufficient effect has not been obtained for high cost.

[0010]

As described above, in order to obtain good magnetic properties in a non-oriented electrical steel sheet,
It is necessary to ensure sufficient grain growth, and it is important to control the precipitates affecting the grain growth. However, up to now, an effective and inexpensive production method at an industrial level has not been developed. The present invention advantageously solves the above-mentioned problems, and controls the sulfide-based inclusions inexpensively and effectively as compared with the prior art, thereby improving the grain growth and thereby further improving the iron loss characteristics. It is an object of the present invention to propose an advantageous method for producing a non-oriented electrical steel sheet that has achieved an improvement.

[0011]

The details of the invention will be described below. By the way, the present inventors examined the addition amount of Ca alloy and the mixing ratio of Ca alloy and desulfurization flux. As described in Japanese Patent Application Laid-Open No. 59-74213,
Even without adding a large amount of Ca alloy as much as 1 kg per
It has been found that if the mixing ratio of the alloy and the desulfurization flux is restricted to an appropriate range, the maximum effect can be obtained with less than 1 kg / t. The present invention is based on the above findings.

That is, the present invention provides: C: 0.01 wt% or less, Si: 3.5 wt% or less, Mn: 1.5 wt% or less, Al: 2.5 wt% or less, S: 0.01 wt% or less, P: 0.1 wt% or less After forming molten steel having a composition containing, into a slab by continuous casting, hot rolling, cold rolling and then finish annealing to produce a non-oriented electrical steel sheet, until the completion of continuous casting, Ca alloy And desulfurization flux are mixed and desulfurized.At this time, the addition amount of Ca alloy is 0.2 kg / t or more and less than 1.0 kg / t, and the addition ratio of Ca alloy and desulfurization flux is weight ratio. A method for producing a non-oriented electrical steel sheet having excellent magnetic properties, characterized by restricting the range of 0.50 ≦ Ca alloy / desulfurization flux ≦ 5.0.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be specifically described based on experimental results which have led to the present invention. FIG. 1 shows the results of an investigation on the effect of the addition ratio of the Ca alloy and the flux on iron loss improvement when the addition amount of the Ca alloy is 3.0, 0.9, and 0.5 kg / t. The iron loss ratio on the vertical axis is defined as 1.0, with the iron loss W _15/50 when the addition amount of Ca alloy is 0.5 kg / t and the addition amount ratio of Ca alloy and flux is 1: 1.
The ratio to this is shown. As is clear from FIG.
Particularly good iron loss characteristics are obtained when the addition amount of the alloy is less than 1 kg / t and the Ca alloy / flux addition amount ratio is 0.5 to 5.0.

Next, FIG. 2 shows the results of a study on the relationship between the Ca alloy addition amount and the iron loss characteristics when the Ca alloy / flux addition amount ratio is 0.3. As is clear from the figure, particularly good iron loss characteristics were obtained when the addition amount of the Ca alloy was 0.2 kg / t or more and less than 1.0 kg / t.

Although the reason why the present invention reduces iron loss has not always been clearly elucidated,
The inventors consider as follows. That is, by keeping the Ca alloy addition amount to a small amount of less than 1 kg / t, Ca precipitates harmful to the magnetic properties remaining in the final product can be suppressed to a minimum, and the addition ratio of the Ca alloy to the flux can be minimized. It is considered that by restricting to an appropriate range, the finest precipitation of the most harmful sulfides was hardly minimized.

Next, the reason why the material components are limited to the above ranges in the present invention will be described. C: 0.01 wt% or less C expands the γ region and lowers the α-γ transformation point. During annealing, the γ phase is formed in the form of a film at the α grain boundary to suppress the growth of the α grains, so that C must be basically reduced. Also, C content should be 0.01 wt% or less because it contains a large amount of α-phase stabilizing elements such as Si and Al, and causes aging deterioration of iron loss characteristics even when γ-phase is not generated in all temperature ranges. There is. The lower limit is not particularly limited, but is preferably 0.0005 wt% or more from the viewpoint of cost and the like.

Si: 3.5 wt% or less Si is a useful element that increases the specific resistance of steel and reduces iron loss, and changes the content according to target magnetic properties.
However, at the same time, the hardness is increased and the cold rollability is deteriorated. Therefore, the upper limit is set to 3.5 wt%. Although the lower limit is not particularly defined, it is 0.05 from the viewpoint of increasing the specific resistance.
It is desirable to contain at least wt%.

Al: 2.5 wt% or less Al, like Si, is an element that increases the specific resistance of steel and reduces iron loss, and changes the content according to target magnetic properties. However, when the content is large, the lubricity with the mold decreases during continuous casting, and casting becomes difficult. Therefore, the upper limit is set to 2.5 wt%.

Mn: 1.5 wt% or less Mn also has the effect of increasing the specific resistance of the steel and reducing iron loss, though not as much as that of Si and Al, and also has the effect of improving hot rolling properties. However, if contained in large amounts, the cold rollability deteriorates, so the upper limit was set to 1.5 wt%.

S: 0.01 wt% or less S is an element to be reduced as much as possible because it forms precipitates and inclusions and inhibits grain growth. The present invention uses Ca alloy for desulfurization and makes S harmless by controlling the precipitation form of S. However, when the residual amount in steel is large, the number of particles of inclusions increases, and Ca for fixing
If the content is relatively insufficient, the proportion of MnS in the inclusions increases, which also has an adverse effect on the grain growth. Therefore, the content of S was reduced to 0.01 wt% or less.

P: 0.1 wt% or less P, although not as effective as Si or Al, has the effect of increasing the specific resistance of steel and reducing iron loss, and also has a texture after cold rolling recrystallization due to grain boundary segregation. To improve the magnetic flux density. However, if added excessively, the amount of grain boundary segregation increases, which rather inhibits grain growth and degrades iron loss. Therefore, the content is set to 0.1 wt% or less.

Although the essential components have been described above, various other known elements can be added. For example, B, Ni, Cu, Sn, Bi and
Ge or the like can be added.

As the Ca alloy to be used, a wire-like material in which calcium metal is covered with an iron hoop, or a calcium-silicon alloy whose particle size has been adjusted to a size suitable for injection, are suitable. On the other hand, lime (CaO), calcium fluoride (Ca
F), soda ash (Na ₂ CO ₃ ), and other commonly used well-known materials are suitable.

Next, the manufacturing method will be described. In the present invention, the manufacturing method is not particularly limited, and a conventionally known method can be applied. The slab heating temperature is 1000
It is preferable that the temperature is set to not less than ° C. This is because when the heating temperature is 1000 ° C. or higher, further growth of crystal grains can be expected by Ostwald ripening.

[0025]

[Example] C: 0.003 wt%, Si: 2.8 wt%, Mn: 0.2 wt%
%, Al: 0.3% by weight and P: 0.04% by weight, the balance being substantially Fe, steel was melted by a converter and vacuum degassing, and the thickness was 215 mm by continuous casting. Width: 1000
mm slab. At this time, Ca alloy ( CaSi ) , CaO, C
A mixture of a desulfurization flux containing a mixture of aF as a main component at a ratio shown in Table 1 was added.
Desulfurized to wt%. Then, in a normal gas heating furnace 1100 ℃
After hot-rolling, a hot-rolled sheet having a thickness of 2.5 mm was formed by hot rolling. Then, after subjecting the hot-rolled sheet to annealing at 1000 ° C for 60 seconds, the cold-rolled sheet having a thickness of 0.5 mm is formed by one cold rolling, and then subjected to recrystallization annealing at 820 ° C for 60 seconds to obtain a product sheet. did. The results of examining the magnetic properties of the product plate thus obtained are also shown in Table 1.

[0026]

[Table 1]

As is clear from the table, in each case of desulfurization under the conditions according to the present invention, an excellent iron loss value was obtained as compared with the conventional case.

[0028]

Thus, according to the present invention, by controlling the mixing ratio of the Ca alloy and the desulfurization flux to an appropriate range, the addition of a small amount of the Ca alloy of less than 1.0 kg / t causes the adverse effect of the sulfide inclusions. Therefore, a non-oriented electrical steel sheet excellent in iron loss characteristics under favorable grain growth properties can be obtained at low cost.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the addition ratio of a Ca alloy and a flux on iron loss improvement.

FIG. 2 is a graph showing a relationship between a Ca alloy addition amount and iron loss characteristics.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI C21C 7/076 C21C 7/076 A C21D 8/12 C21D 8/12 A C22C 38/00 303 C22C 38/00 303U 38/06 38 / 06 H01F 1/16 H01F 1/16 A (58) Fields investigated (Int. Cl. ⁷ , DB name) C21C 7/064 B22D 11/00 B22D 11/108 C21C 7/00 C21C 7/04 C21C 7 / 076 C21D 8/12 C22C 38/00 C22C 38/06 H01F 1/16

Claims (1)

(57) [Claims] 1. A composition containing: C: 0.01 wt% or less, Si: 3.5 wt% or less, Mn: 1.5 wt% or less, Al: 2.5 wt% or less, S: 0.01 wt% or less, P: 0.1 wt% or less. The molten steel to be slab by continuous casting, hot rolling, cold rolling and then finish annealing to produce a non-oriented electrical steel sheet, Ca alloy and desulfurization flux until the completion of continuous casting Is desulfurized by mixing and adding, and at that time, the addition amount of the Ca alloy is 0.2 kg / t or more and less than 1.0 kg / t, and the addition amount ratio between the Ca alloy and the desulfurization flux is 0.50 ≦ Ca alloy /
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties, characterized in that desulfurization flux is regulated within a range of ≤5.0.