JPH05295440A - Production of grain-oriented silicon steel sheet using rapidly solidified thin cast slab - Google Patents

Abstract

PURPOSE:To obtain a grain-oriented silicon steel sheet excellent in magnetic properties and improved in brittleness by applying hot rolling to a thin cast slab under specific conditions in a manufacturing method where a rapidly solidified thin cast slab of a steel with a specific composition free from the effect of inhibitor is used and nitriding treatment is included. CONSTITUTION:A plate of a steel having a composition consisting of, by weight, 0.025-0.100% C, 1.0-4.7% Si, 0.006-0.045% acid-soluble Al, 0.0030-0.0130% N, and the balance Fe, is cold-rolled once or is cold-rolled twice or more while process-annealed between the cold rolling stages to the final sheet thickness. In the process for subjecting the resulting steel sheet to decarburizing annealing, to the application of a separation agent at annealing, and to finish annealing for secondary recrystallization, nitriding treatment is applied to the steel sheet in any of the stages in the range after the production of the cast slab and before the initiation of secondary recrystallization in finish annealing, by that the grain-oriented silicon steel sheet can be obtained. In this method, the cast slab solidified by regulating the cooling velocity in the (alpha+gamma) two phase coexistent region at the time of casting to >=8.5 deg.C/sec is subjected to hot rolling at 900-1300 deg.C at 3-60% draft.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a unidirectional electrical steel sheet which is a soft magnetic material used as an iron core material for electric equipment.

[0002]

2. Description of the Related Art A unidirectional electrical steel sheet has a steel sheet surface of {11
It is composed of crystal grains having a so-called Goss orientation (which uses Miller index and is expressed as {110} <001>) having a <001> axis in the rolling direction on the 0} plane and is used as a soft magnetic material for a transformer or a generator. Used for iron cores. The unidirectional electrical steel sheet is required to have good magnetic characteristics and good iron loss characteristics.

The quality of the magnetization characteristic is evaluated by the level of the magnetic flux density induced in the iron core under a constant applied magnetic field. The grain-oriented electrical steel sheet with high magnetic flux density is
It is obtained by highly aligning the crystal grain orientations with {110} <001>. The quality of the iron loss characteristic is evaluated based on the amount of power loss consumed as heat energy when a predetermined AC magnetic field is applied to the iron core. Factors such as magnetic flux density, plate thickness, specific resistance, and crystal grain size influence the quality of iron loss characteristics. The grain-oriented electrical steel sheet with high magnetic flux density is
While making it possible to miniaturize electrical equipment,
It is very preferable because it provides good iron loss characteristics.

By the way, the unidirectional electrical steel sheet has a {110} <001> orientation obtained by subjecting a steel sheet having a final thickness by a suitable combination of hot rolling, cold rolling and annealing to high temperature finish annealing. It is obtained by so-called secondary recrystallization in which the primary recrystallized grains that it has grow selectively. Secondary recrystallization is due to the presence of fine precipitates, such as MnS, AlN, MnSe, etc. in the steel sheet before secondary recrystallization, or the presence of grain boundary segregation type elements such as Sn, Sb, P. To be achieved. The fine precipitates or grain boundary segregation-type elements in these steel plates are
0} <001> orientation other than primary recrystallized grain growth is suppressed,
It has a function of selectively growing {110} <001> oriented grains. Such an effect of suppressing grain growth is generally called an inhibitor effect. Therefore, the priority issue of research and development in this technical field is what kind of precipitate or grain boundary segregation type element is used to stabilize the secondary recrystallization, and the existence of accurate {110} <001> oriented grains. How to achieve their proper state of existence, in order to increase the proportion.

At present, there are three types of typical industrially produced grain-oriented electrical steel sheets. The first technique is
M. F. It is a manufacturing method by a double cold rolling method disclosed in Japanese Patent Publication No. 30-3651 by Littmann, in which MnS functions as an inhibitor.

The second technique is AlN + MnS disclosed in Japanese Patent Publication No. 40-15644 by Taguchi and Sakakura.
80% of the final cold rolling that causes
This is a manufacturing method performed under the application of the above-mentioned strong reduction rate. The third technique is MnS (or MnSe) + S disclosed in Japanese Patent Publication No. 51-13469.
It is a production method by the double cold rolling method in which b is made to function as an inhibitor.

In all of these techniques, the heating temperature of the slab prior to hot rolling is set to 126 in the first technique as a means for finely dispersing and uniformly precipitating precipitates.
0 ° C or higher, in the second technique, as disclosed in JP-A-48-51852, it depends on the amount of Si in the material, but 1350 ° C in the case of 3% Si. As disclosed in Japanese Unexamined Patent Publication No. 51-20716, by heating the cast slab to an extremely high temperature of 1230 ° C. or higher, or 1320 ° C. in the embodiment where a high magnetic flux density can be obtained, it exists in a coarse state. The precipitate is once made into a solid solution and then finely dispersed and precipitated during the subsequent hot rolling or heat treatment.

Increasing the heating temperature of the slab increases the energy used during heating, lowers the yield due to the generation of molten slag called Noro, and increases the maintenance frequency of the heating furnace, which increases maintenance costs. In addition to problems such as an increase and a decrease in equipment operating rate, as disclosed in Japanese Patent Publication No. 57-41526, secondary recrystallization failure occurs, so various types of continuous cast slabs can be used. It is necessary to take measures for
As disclosed in Japanese Patent Laid-Open No. 58-58, when the product plate thickness is made thin, there is a problem that this secondary recrystallization defect is further increased. As a technique for solving these problems caused by high-temperature heating of a slab and reducing macrosegregation in the slab during solidification, Japanese Patent Application Laid-Open No. 3-613 filed by the present inventors.
There is a technique disclosed in Japanese Patent No. 26. according to it,
By using a thin slab obtained at a solidification rate of 8.5 ° C./sec or more as a starting material, a hot rolling process starting from high temperature heating can be omitted, and macro segregation of the slab during solidification can be reduced. It is said that it will be effective for improvement. However, in the slab of this technique, the grain size of the slab is larger than that of the recrystallized structure formed by hot working, and the slab is inferior to the conventional hot-rolled sheet in terms of brittleness, and there is a problem in stripability.

[0009]

DISCLOSURE OF THE INVENTION According to the present invention, a steel sheet is nitrided at any stage from the production of the slab to the start of secondary recrystallization in finish annealing without the production of an inhibitor during the heating of the slab. In the method for producing a grain-oriented electrical steel sheet based on the formation of a precipitate necessary for secondary recrystallization, a product having a high magnetic flux density by realizing extremely stable secondary recrystallization. In addition to improving the brittleness peculiar to the thin slab and at the same time combining with hot rolling for the purpose of improving the structure, a lower cost process using the thin slab as a material is realized. It is an object of the present invention to provide a method for producing a grain-oriented electrical steel sheet capable of producing a product having good magnetic properties at low cost.

[0010]

The main points of the present invention are as follows. By weight, C: 0.025-0.
100%, Si: 1.5 to 4.7%, acid-soluble Al:
0.006-0.045%, N: 0.0030-0.0
Steel plate containing 130% and the balance being substantially Fe,
One or two or more cold rolling processes including intermediate annealing to obtain the final plate thickness, followed by decarburization annealing, application of an annealing separator, and then finishing annealing for the purpose of secondary recrystallization. Therefore, in the manufacturing method of the unidirectional electrical steel sheet in which the steel sheet is nitrided at any stage from the production of the cast slab to the start of the secondary recrystallization in the finish annealing, in the (α + γ) two-phase coexisting region at the time of casting, Manufacture of unidirectional electrical steel sheet characterized by subjecting a slab solidified at a cooling rate of 8.5 ° C./sec or more to hot rolling with a reduction rate of 3 to 60% in a temperature range of 900 to 1300 ° C. Method.

The present invention will be described in detail below. First,
Although it is a component, if C is less than 0.025%, secondary recrystallization becomes unstable, and if C is too much, decarburization annealing time becomes long and it is not economical, so it was made 0.100% or less. If Si is less than 1.5%, the electric resistance is low and it is difficult to obtain good iron loss characteristics, so the content is made 1.5% or more. On the other hand, if Si exceeds 4.7%, cracks become large during cold rolling of the steel sheet, so the content is made 4.7% or less.

Al and N are 0.006% as acid-soluble Al in order to secure AlN necessary for stabilizing secondary recrystallization.
As described above, N is required to be 0.0030% or more. If the acid-soluble Al exceeds 0.045%, the AlN of the hot-rolled sheet becomes inadequate and the secondary recrystallization becomes unstable.
Below. When N exceeds 0.0130%, blisters on the surface of the steel sheet called blister occur, so that it is 0.
It was set to 0130% or less.

Other components may be contained within a range not departing from the basic idea of the present invention. Molten steel containing these components is cast into a slab. In the present invention, (α +
γ) The cooling rate in the two-phase coexistence region is 8.5 ° C./sec or more. In the conventional continuous casting process that outputs a slab having a thickness of 150 to 300 mm, a cooling rate of 8.5 ° C / sec or more cannot be achieved, and the cooling rate is almost 15 ° C / min (0.2
It was around 5 ° C / sec). In order to achieve a cooling rate of 8.5 ° C./sec or more, a process for directly obtaining a ribbon by casting is required. The higher the cooling rate, the smaller the component segregation, which is preferable. However, in order to obtain a high magnetic flux density, it is necessary to have a high cold rolling rate, so that the thickness of the cast ribbon is naturally limited. A higher cooling rate in the casting process is more effective in suppressing the component segregation, but it is 8.5 ° C / sec.
A cooling rate of 10 is sufficient.

The reduction temperature of the cast slab after casting, which is a feature of the present invention, is preferably 900 to 1300 ° C, particularly preferably 1000 to 1250 ° C. From the viewpoint of simplifying the process, it is preferable to perform the reduction of the cast piece after casting immediately after casting, but it is also possible to reheat the cast piece to a predetermined temperature in terms of metallurgy.
If the rolling temperature is less than 900 ° C, recrystallization after rolling does not occur, and it is insufficient for improving the brittleness of the slab. If it exceeds 1300 ° C, coarsening of crystal grains occurs during recrystallization after rolling, rather This temperature range is preferable because the brittleness of No. 1 deteriorates.

In order to investigate the relationship between the reduction temperature and the effect of improving the brittleness of cast slabs, the inventors of the present invention, C: 0.070% by weight, S
i: 3.25%, acid-soluble Al: 0.028%, Tot
alN: 0.0067%, the balance of molten steel consisting essentially of Fe from about 1500 ° C to about 1000 ° C at 600 ° C
It was cast at a cooling rate of / min to form a 2.0 mm thick slab, and after casting, these plates were rolled at a rolling reduction of about 25%. The temperature of the plate during this rolling was set to 850 to 1300 ° C., and improvement in brittleness of the cast piece by reduction was investigated. The brittleness evaluation of the slab was performed by the repeated bending test of JIS C2550. The results are shown in Table 1. In consideration of stripability, it is essential that the number of repeated bendings is 4 times or more, preferably 5 times or more. Therefore, as shown in the table, the number of repeated bendings of 4 times or more is 900 to 1300 ° C. It was defined as the rolling temperature.

[0016]

[Table 1]

The rolling reduction in this case is 3 to 60%, preferably 5 to 40%. If it is less than 3%, the brittleness of the cast slab is not sufficiently improved by the reduction, and if it exceeds 60%, the facility cost required for the strong reduction in the hot is increased, which is an advantage of the present invention, so that the low cost process can be realized. It is not suitable because it is impossible. This cast ribbon is directly cold-rolled to obtain the final plate thickness. To obtain products with high magnetic flux density, 8
It is suitable to carry out cold rolling in which 0% or more, preferably 88% or more, of strong reduction is applied.

The material having the final plate thickness is then subjected to decarburization annealing for a short time in a wet hydrogen atmosphere. Then, an annealing separator is applied to this decarburized annealed plate. Then, finish annealing for the purpose of secondary recrystallization is performed. In the present invention, either one of a method of annealing the decarburized and annealed steel sheet for a short time in an atmosphere having a nitriding ability, or a method of nitriding during temperature rising during finish annealing and before the start of secondary recrystallization, or It is essential to form a nitride effective for secondary recrystallization by combining both.

Since the latter is annealed in the state of laminated steel sheets or in the state of strip coil,
Since it is difficult to perform nitriding in the atmosphere, it is effective to add a compound having a nitriding ability to the annealing separator for uniform nitriding.

[0020]

【Example】

Example 1 By weight, C: 0.070%, Si: 3.25%, acid-soluble Al: 0.028%, Total N: 0.0067.
%, And the balance of molten steel consisting essentially of Fe from approximately 1500 ° C. to approximately 1000 ° C. at 600 ° C./min (10 ° C./s
It was cooled at a cooling rate of ec), and a plate having a thickness of 2.1 to 3.1 mm was cast. Immediately after casting, these plates were rolled to a plate thickness of 2.0 mm. The temperature of the plate during this rolling is approximately 1100.
It was ℃. This plate was annealed at 1120 ° C. for 2.5 min, cold-rolled to 0.2 mm, decarburized annealed at 810 ° C., and applied with 5% ferromanganese nitride added to MgO as an annealing separator. Finish annealing was performed at 1200 ° C. for 20 hours. As a comparative example, molten steel of the same composition was cast at the same solidification rate, and a slab having a plate thickness of 2.0 mm was used as a starting material, and the following steps were the same as those of the present invention.

Table 2 shows the magnetism and secondary recrystallization state of the samples of the present invention and the comparative example at this time, and the result of the repeated bending test of the cast piece performed according to JIS C2550.

[0022]

[Table 2]

[0023]

According to the present invention, a ribbon can be directly obtained from molten steel by casting, and a unidirectional electrical steel sheet having excellent magnetic properties can be obtained by a simple process using the ribbon as a cold rolled material. it can.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Kosuge 1 Fuji-machi, Hirohata-ku, Himeji-shi, Hyogo Shin Nippon Steel Co., Ltd. Hirohata Works

Claims (1)

[Claims] 1. By weight, C: 0.025 to 0.100.
%, Si: 1.5 to 4.7%, acid-soluble Al: 0.00
6 to 0.045%, N: 0.0030 to 0.0130%
The steel sheet which contains, and has the balance substantially made of Fe is subjected to cold rolling once or twice or more including intermediate annealing to obtain a final sheet thickness, and then decarburizing annealing, and applying an annealing separator,
In the process of performing finish annealing for the purpose of secondary recrystallization, production of unidirectional electrical steel sheet in which nitriding treatment of the steel sheet is performed at any stage from the production of cast slab to the start of secondary recrystallization in finish annealing. In the method, during casting (α + γ)
One direction characterized by subjecting a slab solidified at a cooling rate in a two-phase coexistence region of 8.5 ° C./sec or more to hot rolling with a reduction rate of 3 to 60% in a temperature region of 900 to 1300 ° C. For manufacturing high-performance electrical steel sheet.