JPH07116515B2 - Method for producing unidirectional silicon steel sheet having excellent magnetic properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a method for producing a unidirectional silicon steel sheet having excellent magnetic characteristics, and particularly proposes a method capable of improving both magnetization characteristics and iron loss characteristics. To do.

<Prior Art> A unidirectional silicon steel sheet is mainly used as an iron core of a transformer or other electric equipment, but it is required to have excellent magnetic characteristics and magnetic loss characteristics. In recent years, due to progress in manufacturing technology of silicon steel sheets, for example, with unidirectional silicon steel sheets having a plate thickness of 0.23 mm, magnetization characteristics B _{10 to} 1.90 T, iron loss W _{17/50 to} 0.
Excellent products such as 90w / kg can be produced in process.

The material having such excellent magnetic properties is composed of crystal grains in which the [001] direction, which is the easy axis of iron, is highly aligned with the rolling direction of the steel sheet. The formation of such crystal grains is such that during the final annealing in the manufacturing process of unidirectional silicon steel sheet, the crystal grains of (110) [001] orientation, which are so-called Goss grains, are sufficient as secondary recrystallized grains. It is achieved by growing and developing.

As a basic requirement for sufficiently growing the secondary recrystallized grains in the (110) [001] orientation, in the secondary recrystallization process (11
0) The presence of an inhibitor that strongly suppresses the growth of crystal grains having an unfavorable crystal orientation other than the [001] orientation, and that the sharply aligned secondary recrystallized grains of the (110) [001] orientation are sufficiently developed. It is well known that the formation of a recrystallized texture suitable for the above is required.

Fine inhibitors such as MnS and MnSe are generally used as inhibitors. In addition to these fine precipitates,
As disclosed in Japanese Patent Publication No. 51-13469 (Patent No. 839079) and Japanese Patent Publication No. 54-32412 (Patent No. 998277), Sb, As, Bi, Pb, Sn, etc., or Japanese Patent Publication No. 56-
The effect of the inhibitor is also strengthened by adding a grain boundary segregation type element such as Mo described in Japanese Patent No. 4613 together.

Regarding the formation of an appropriate recrystallized texture, conventionally, the method of appropriately combining the process conditions of hot rolling and cold rolling has been adopted, and even in complicated processes such as performing intermediate cold annealing twice, cold rolling is performed. It is for this purpose that it has been adopted, but further, as described in Japanese Patent Publication No. 56-38652, the present inventors,
800 for both decarburization and recrystallization on a cold-rolled sheet finished to the final thickness
According to the method of adding annealing (hereinafter referred to as recrystallization annealing) which is held for 30 seconds or more for 10 minutes in the temperature range of 600 to 650 ° C before decarburization annealing performed at a temperature of about ℃, it is more preferable. It was disclosed that the formation of recrystallized texture was obtained.

Thus, regarding the steel sheet having an inhibitor for suppressing the grain growth and a suitable recrystallization texture, the above-mentioned Japanese Patent Publication No. 51-
13469, JP 54-32412 and JP 56-
In the final finishing annealing, which is an indispensable requirement in any case according to the description of 38652 publication, by applying a method of holding for 10 hours or more at a temperature near approximately 850 ° C at which secondary recrystallization develops, The secondary recrystallized grains with sharp (110) [001] orientation can selectively grow sufficiently and a unidirectional silicon steel sheet having a high magnetic flux density can be manufactured.

However, when the method of recrystallization annealing for improving the recrystallization texture according to the last-mentioned Japanese Patent Publication No. 56-38652 is attempted to be carried out on an industrial production scale, the following problems occur. That is, the recrystallization for the purpose of holding for 30 seconds to 10 minutes in the temperature range of 600 to 650 ° C., which is applied to the final cold-rolled sheet obtained through the complicated and various steps of the unidirectional silicon steel sheet. As for annealing, the magnetic flux density is 1.92T at B ₁₀ value.
In some cases, it exhibits instability, but it is unstable, and secondary recrystallized grains become large and coarse with an increase in the B ₁₀ value, resulting in insufficient iron loss and low iron loss. It was difficult to obtain a product stably and reliably.

<Problems to be Solved by the Invention> An object of the present invention is to improve the above method and industrially stably produce a unidirectional silicon steel sheet having excellent magnetization characteristics and iron loss characteristics. To provide.

<Means for Solving the Problems> That is, the present invention is, by weight%, C: 0.02 to 0.1%, Si: 2.5 to
Contains 4.0%, Mn: 0.05 to 0.1%, Se: 0.01 to 0.03%, balance
A silicon steel slab consisting of Fe and unavoidable impurities is heated to 1300 ° C or higher, hot-rolled, and then subjected to intermediate annealing 2
After carrying out cold rolling twice to obtain a specified final thickness, decarburization annealing is applied, then an annealing separator containing MgO as a main component is applied, and then final finishing including secondary recrystallization annealing and purification annealing. In the method for manufacturing a unidirectional silicon steel sheet comprising a series of annealing steps, the secondary recrystallization annealing is performed by holding at a temperature 5 to 25 ° C. higher than the secondary recrystallization start temperature for 5 to 20 hours, and then secondary A unidirectional silicon steel sheet with excellent magnetic properties, characterized in that it is kept for about 20 hours or more near the recrystallization start temperature, or for 40 hours or more at a temperature 5 to 15 ° C lower than the secondary recrystallization start temperature. Is a manufacturing method.

<Operation> Each requirement that constitutes the present invention will be described in detail based on experimental results.

% By weight, C: 0.042%, Si: 3.35%, Mn: 0.071%, Se: 0.020
%, Sb: 0.025%, the unidirectional silicon steel slab consisting of the balance Fe and unavoidable impurities was heated at 1400 ° C., and then conventionally known hot rolling was performed to form a hot rolled sheet with a thickness of 2.0 mm, 100
The material was decarburized and annealed by normalizing at 0 ℃ for 30 seconds and cold rolling twice with intermediate annealing to obtain a final plate thickness of 0.23mm. First, its secondary recrystallization starting temperature ( _TSR )
Was measured.

T _SR is 800 to 900 in a furnace having a temperature gradient of 5 to 10 ° C. / cm
After annealing at a temperature of 50 ° C. for 50 hours, observation of the macrostructure shows the temperature at which secondary recrystallization occurs.

For unidirectional silicon steel manufactured by the double cold rolling method, _TSR
Is around 850 ℃ ± 30 ℃, which differs slightly depending on the material. Particularly excellent production of finished products of the magnetic properties, that it is necessary to retention at T _SR known empirically. In this experimental material, T _SR = 840 ° C. Therefore, when final finishing annealing was performed while changing the holding temperature variously, the results shown in FIG. 1 were obtained. That is, it can be understood that the iron loss shows the best value by holding it by T _SR , but not necessarily the best value for B ₁₀ . As described above, it was difficult to simultaneously satisfy the best values of W _{17/50 for} the magnetization characteristic B ₁₀ and the _core loss characteristic in the conventional final finish annealing by maintaining the constant temperature.

In Fig. 1, one of the reasons why the best value of B ₁₀ and iron loss do not match is considered to be that the secondary particle size increases with B ₁₀ and eddy current loss increases.

The present inventors have further advanced the research on such secondary recrystallization process. Figure 2 shows B when the holding time is changed.
_{Shows 10} changes. After the normal holding, purification annealing of impurities by high temperature hydrogen annealing at 1200 ° C. continues, but the purification annealing is omitted here to clarify the secondary recrystallization behavior. The higher B ₁₀ corresponds to the development and growth of secondary grains in the Goss orientation, and the higher the B ₁₀ is, the higher the orientation accumulation in the rolling direction becomes. ing. Similar to the primary recrystallization process, in the secondary recrystallization as well, there is an incubation period until the rapid growth of the Goss grains, which greatly varies depending on the holding temperature. When kept at 880 ° C, the incubation period is short, and the secondary recrystallization is completed in about 20 hours, but the reached B ₁₀ is less than that kept at 850 ° C. It is considered that this is because secondary recrystallization occurs at the same time even in an orientation slightly deviated from the Goth orientation. on the other hand
When kept at 830 ° C, the incubation period was long and secondary recrystallization was not completed even after 100 hours. Therefore, in the retention of T _SR or less, the secondary recrystallization is not completed during the holding at the constant temperature, and the secondary recrystallization is performed in the subsequent high temperature hydrogen annealing process. _It is thought to cause ₁₀ drops.

It is well known that during secondary recrystallization, fine precipitates such as MnSe function as inhibitors in order to prevent normal grain growth at the other position during the growth of Goss grains. It is said that the Ostwald growth of the precipitate progresses, and the secondary recrystallization explosively proceeds with the deterioration of the function.

Although there is no clear evidence, it is considered that the secondary recrystallized goss grains have started to grow to some extent during the incubation period and that the growth rate increases with the Ostwald growth of the inhibitor. Therefore, during the incubation period, a large number of highly oriented Goss grains can be grown to a critical size capable of secondary recrystallization to obtain a fine secondary recrystallized structure with highly oriented orientation. In order to increase the growth driving force, holding at a high temperature is more effective to some extent, but since the growth rate rapidly increases, relatively large secondary grains are likely to be formed, which is not preferable for improving iron loss.

The present inventors attempted to hold the temperature at a slightly high temperature during the incubation period at the time of holding the constant temperature, and then slowly progress the growth at a low temperature. Fig. 3 shows the magnetic characteristics when the temperature is maintained above T _{SR in the} initial period of constant temperature maintenance. The various conditions are shown in the upper right of the figure. It was found that good results were obtained for both B ₁₀ and W _17/50 by this method, as compared to the usual constant temperature maintenance at T _SR (840 ° C) (see Fig. 1). Particularly, the range where ΔT is 5 to 20 ° C. is preferable. Due to the limit of temperature control accuracy in actual operation, _TSR retention includes a variation of ± 2 to 3 ° C.

Next, Fig. 4 shows the result when the temperature was held at T _SR or lower after being kept at a high temperature. Although the retention of T _SR or less takes time until the completion of secondary recrystallization, the ultimate magnetic properties are excellent.
In order to obtain a product with higher characteristics, it is advantageous to extend the time to some extent. From the figure, it is possible to carry out on an industrial scale by securing at least 40 hours after holding at a high temperature if it is 5 to 15 ° C below T _SR .

Hereinafter, the reasons for limiting the components of the material applied to the present invention will be described.

C is an essential element for homogenizing the crystal structure of the steel sheet and forming a recrystallized texture with a high degree of integration of the (110) [001] orientation in the hot rolling and cold rolling processes, and achieves this purpose. To achieve this, 0.02% or more is required. On the other hand, if it exceeds 0.10%, it is difficult to decarburize sufficiently by the short decarburization annealing that is usually performed by continuous annealing. In this case, if C remains in the product, iron loss Since the properties deteriorate significantly, the upper limit is limited to 0.10% or less from the limit of industrial decarburization annealing. For this reason, C is limited to the range of 0.02 to 0.10%.

If Si is lower than 2.5%, the sufficiently low iron loss value aimed at by the present invention cannot be realized, and if it exceeds 4.0%, it becomes brittle, and it is difficult to perform ordinary industrial rolling with poor cold workability. Therefore, it is limited to within the range of 2.5 to 4.0%.

Both Mn and Se are added as inhibitors to suppress the growth of primary recrystallized grains during final annealing (110).
It is an element necessary for sharply developing secondary recrystallized grains in the [001] orientation. However, Mn: 0.05-0.10%, Se 0.01-
If the amount deviates from the range of 0.03% and becomes excessive or insufficient, sufficient growth of secondary recrystallized grains cannot be expected, and the desired excellent magnetic characteristics cannot be obtained. Therefore, the range is limited to the above range.

<Example> In weight%, C: 0.040%, Si: 3.38%, Mn: 0.68%, Se: 0.021
%, Sb: 0.026%, and the rest of the unidirectional silicon steel material slab consisting of Fe and unavoidable impurities was reheated at 1400 ° C for 10 minutes, and then a hot-rolled sheet having a thickness of 2.0 mm was obtained. After normalizing at 1000 ℃ for 30 seconds, after pickling, insert intermediate annealing at 1000 ℃ for 1 minute 2
A final plate thickness of 0.23 mm was obtained by the cold rolling method. 600 ℃ 1 minute, 820
℃ after the primary recrystallization annealing, which also serves as a 2-minute decarburization by 2 DanHitoshinetsu method, and coated with an annealing separator mainly comprised of MgO, first T _SR
Was 850 ° C. Magnetic properties of these materials having the same charge are shown when secondary recrystallization annealing is performed under the conditions as shown in Table 1 and then purified annealing in H ₂ at 1200 ° C. and 5 Hr is performed. As is clear from Table 1, in the examples of the present invention, both B ₁₀ and W _17/50 were superior to those of the comparative examples.

<Effects of the Invention> As described above, according to the method of the present invention, it is possible to obtain a unidirectional silicon steel sheet which is extremely excellent in both the magnetization characteristics and the iron loss characteristics.

[Brief description of drawings]

Fig. 1 is a graph showing the effect of final holding temperature on magnetic properties, Fig. 2 is a graph showing the effect of holding time on B ₁₀ , and Fig. 3 is an explanatory diagram showing the effect of high temperature holding on magnetic properties. FIG. 4 is a graph showing the relationship between the retention time of T _SR or less after the retention of T _SR or more and B ₁₀ .

Claims (2)

[Claims] 1. In weight%, C: 0.02 to 0.1%, Si: 2.5 to 4.0%,
After heating a silicon steel slab containing Mn: 0.05 to 0.1% and Se: 0.01 to 0.03% and the balance Fe and unavoidable impurities to 1300 ° C or higher, hot rolling is performed, and then intermediate annealing is performed twice. After cold rolling to a specified final plate thickness, decarburization annealing is applied, and then an annealing separator containing MgO as a main component is applied, followed by final finishing annealing including secondary recrystallization annealing and purification annealing. In the method for manufacturing a unidirectional silicon steel sheet comprising a series of steps, the secondary recrystallization annealing is performed at a temperature 5 to 25 ° C. higher than the secondary recrystallization start temperature for 5 to 20 hours, and then 2
A method for producing a unidirectional silicon steel sheet having excellent magnetic properties, which is characterized by holding the material at a temperature of the next recrystallization start for 20 hours or more. 2. The secondary recrystallization annealing according to claim 1,
Excellent magnetic properties, characterized by holding at a temperature 5 to 25 ° C higher than the starting temperature of secondary recrystallization for 5 to 20 hours, and then holding at a temperature 5 to 15 ° C lower than the starting temperature of secondary recrystallization for 40 hours or more. Method for producing a unidirectional silicon steel sheet.