JPH09143559A - Production of high magnetic flux density grain-oriented silicon steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high magnetic flux density grain-oriented silicon steel sheet using a stock having low C regions in the surface layer parts. SOLUTION: In the method for producing a grain-oriented silicon steel shseet in which a slab contg., by weight, 0.03 to 0.10% C, 2.5 to 4.5% Si, 0.02 to 0.15% Mn, 0.01 to 0.05% S, 0.01 to 0.04% acid soluble Al and 0.003 to 0.015% N, and the balance Fe with inevitable impurities is used as the stock, which is subjected to hot rolling and precipitation annealing, is thereafter subjected to cold rolling at >=50% final cold rolling draft for one time or ∞ two times including process annealing and is moreover subjected to decarburizing annealing and finish annealing, the slab surface layer contg. 0.005% <= the internal layer C to the surface layer C <= 0.03% and contg. the other elements similarly to the above is provided on both sides by 5 to 25% per side. By providing sufficiently low C regions on both sides of the stab surface parts by 5 to 30% per side, the Goss nuclei before secondary recrystallization increase to stabilize secondary recrystallization and to improve its magnetic properties.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a grain-oriented electrical steel sheet using a material having a low C region in the surface layer portion.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are used as iron core materials for electrical equipment such as transformers, and must have good magnetic excitation characteristics and iron loss characteristics. Moreover, in recent years, the market demand for low iron loss materials with particularly low energy loss has been increasing.

A steel sheet having a high magnetic flux density has a low iron loss and a small iron core, and is a very important development target.
This unidirectional electrical steel sheet having a high magnetic flux density has a {110} <001> orientation (goss orientation) by finish annealing a steel sheet that has been made a final sheet thickness from a hot rolled sheet by appropriate cold rolling and annealing. It is obtained by so-called secondary recrystallization in which secondary recrystallized grains are selectively grown.

In the secondary recrystallization, fine precipitates such as MnS, AlN, MnSe and Cu ₂ are contained in the steel sheet before the secondary recrystallization.
This is achieved by the presence of S, BN, (Al, Si) N, etc., or the presence of grain boundary segregation type elements such as Sn, Sb. These precipitates and grain boundary segregation type elements are
JBMay and Tnrnbull (Trans.Met.Soc.AIME 212 (1958)
As described in P.769 / 781), the growth of primary recrystallized grains other than the {110} <001> orientation is suppressed in the finish annealing step, and the {110} <001> oriented grains are selectively grown. It has a function to let.

Such a grain growth suppressing effect is generally called an inhibitor effect. Therefore, the important issue of research and development in this field is what kind of precipitates or grain boundary segregation type elements are used to stabilize the secondary recrystallization, and the exact proportion of {110} <001> oriented grains. How to achieve those proper existence states in order to enhance

In particular, recently, since there is a limit to the control of the altitude of {110} <001> orientation in the method using one kind of precipitate, some advantages can be obtained by deeply clarifying the advantages and disadvantages of each precipitate. Combining things organically,
Development of technology that enables stable manufacture of products with higher magnetic flux density and lower cost is underway.

At present, there are three types of typical industrially produced grain-oriented electrical steel sheets, each of which has advantages and disadvantages. The first technology is MFLittmnann
It is a double cold rolling process using MnS disclosed in Japanese Patent Publication No. 30-3651, and the obtained secondary recrystallized grains are stably developed, but high magnetic flux density cannot be obtained.

The second technique is Taguchi et al.
This is a process shown in Japanese Patent No. 15644, in which the final cold rolling using AlN + MnS is performed at a high pressure reduction rate of 80% or more, and a high magnetic flux density can be obtained, but strict control of manufacturing conditions is required in industrial production. It

The third technique is the Japanese Patent Publication No. 51-
MnS (and / or Mn
This is a process for producing a silicon steel containing Se) + Sb by a double cold rolling process. A relatively high magnetic flux density can be obtained, but harmful and expensive elements such as Sb and Se are used. Since it is a cold rolling method, the manufacturing cost is high.

Further, the above three types of techniques have the following problems in common. In other words, all of the above techniques are techniques for controlling the precipitates finely and uniformly, and the slab heating temperature prior to hot rolling is 1260 ° C. or higher in the first technique.
In the second technique, as shown in Japanese Patent Laid-Open No. 48-51852, depending on the amount of raw material Si, 1350 in the case of 3% Si.
In the third technique, as shown in Japanese Patent Application Laid-Open No. 51-20716, the precipitates that are coarsely present by extremely high temperatures such as 1230 ° C. or higher, and 1320 ° C. in the example in which a high magnetic flux density was obtained. Is once made into a solid solution and then precipitated during the subsequent hot rolling or heat treatment.

Increasing the slab heating temperature increases the energy used during heating, lowers the yield due to the generation of slag, and lowers the facility operating rate due to the increased frequency of repairs to the heating furnace. Further, JP-B-57-41526. As disclosed in the publication, there is a problem that a continuous cast slab cannot be used because a linear secondary recrystallization defect occurs.

However, more important than such a cost problem is that linear secondary recrystallization failure occurs when measures such as increasing Si content and reducing product thickness are taken to improve iron loss. However, the technology based on the high temperature slab heating method has no hope for improving iron loss in the future.

On the other hand, in the technique disclosed in Japanese Examined Patent Publication No. 61-60896, by reducing S in the steel, the secondary recrystallization is extremely stable, and a high Si thin product is made possible. However, this technique has a problem in the stability of the magnetic flux density in factory production on a mass production scale.
Although an improved technique as disclosed in Japanese Patent Publication No. 2-40315 has been proposed, it has not been completely solved until now.

On the other hand, by performing decarburization annealing after hot rolling and before cold rolling to increase the recrystallization region of the plate surface layer portion, the layer with a large amount of goss nuclei in the primary recrystallized plate is increased and secondary recrystallization is performed. Stabilization and improvement of magnetism are disclosed in JP-A-59-232227 and JP-A-61-117215. However, it is inefficient to decarburize such a thick plate before cold rolling in a continuous line, and there is a problem that decarburization is insufficient or the productivity is remarkably reduced.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide a stable and excellent magnetic property producing method for a grain-oriented electrical steel sheet (particularly a thin material) which has been difficult to produce as described above. That is.

[0016]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventors have found that in a method for producing a grain-oriented electrical steel sheet containing a known inhibitor element in a slab, a slab surface layer part is formed. It has been found that by having a sufficiently low C region on both sides of 5% or more and 30% or less on one side, the number of Goss nuclei before secondary recrystallization increases, and secondary recrystallization stabilizes and magnetic properties are improved. .

The gist of the present invention is as follows. (1) C: 0.03 to 0.10% by weight ratio, Si:
2.5-4.5%, Mn: 0.02-0.15%, S:
0.01-0.05%, acid-soluble Al: 0.01-0.
04%, N: 0.003 to 0.015% inclusive, balance F
Using a slab consisting of e and unavoidable impurities as a raw material, after hot rolling and precipitation annealing, one final cold rolling reduction of 50% or more or two or more cold rollings including an intermediate annealing is performed, and further decarburization annealing is performed. In the method of manufacturing a grain-oriented electrical steel sheet for performing finish annealing, 0.005% ≦ inner layer C−surface layer C ≦ 0.03.
%, Other elements are contained in the same manner as described above on the surface of the cast slab on both sides of 5% or more and 25% or less on both sides.

(2) The final cold rolling reduction of the material is 80
The method according to (1), which is at least%. (3) C: 0.03 to 0.10% by weight ratio, Si:
2.5-4.5%, Mn: 0.02-0.15%, acid-soluble Al: 0.01-0.04%, N: 0.003-
The method according to (1), wherein a molten steel containing 0.015% and at least one of Sb: 0.01 to 0.15% and S, Se: 0.01 to 0.05% is used.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
It is generally known that, during the production of a grain-oriented electrical steel sheet, secondary recrystallization is performed from near the surface of the sheet thickness during finish annealing. This is an inhibitor (Al) that suppresses the growth of other oriented grains during the secondary recrystallization until the Goss oriented grains grow.
It is considered that the precipitates (N, MnS, etc.) deteriorate from near the surface of the sheet thickness due to Ostwald growth of the precipitates, denitrification, etc. during finish annealing.

Since the inhibitor deterioration from the plate surface is interface-limited, if the inhibitor strength before the secondary recrystallization annealing is the same, the thinner the material is, the more easily the inhibitor is deteriorated near the surface of the plate, and the better Goss orientation is obtained. Secondary recrystallization of grains becomes difficult. On the other hand, if an attempt is made to make the inhibitor strength in the vicinity of the plate surface during secondary recrystallization appropriate, the inhibitor strength inside the plate becomes too strong, and secondary recrystallization becomes difficult.

As a result of repeated studies, by increasing the Goss-rich layer before secondary recrystallization by having a sufficiently low C region on both surfaces of the cast slab surface layer portion of 5% or more and 25% or less on one surface, It has been found industrially that secondary recrystallization is stable and magnetic properties are improved. Note that this effect is more remarkable for thin products. FIG. 1 shows the effect of improving the magnetism by lowering the carbon content in the surface layer.

Next, the reason why the steel composition and manufacturing conditions are limited as described above in the present invention will be explained. 0.005% ≦ inner layer C-surface layer so as to increase the Goss-rich layer near the surface layer before secondary recrystallization and stabilize the secondary recrystallization of the product thin material to obtain excellent magnetic properties. C ≦ 0.03
%, Other elements are specified to have a cast slab surface layer portion on both sides, which is the same as the inner layer.

The lower limit of C of the inner layer portion is 0.03% so that the γ phase is appropriately generated and the fine dispersion of the precipitate is good, and the upper limit is set to 0.10% unless decarburization becomes difficult. To do. The thickness ratio of the surface layer of the decarburized slab is limited to 5% or more and 25% or less on one side, which is near the region where secondary recrystallization occurs.

On the other hand, regarding the elements described below, the same component amounts were used both in the slab and in the surface layer. Si has a lower limit of 2.5% in order to improve iron loss, but if it is too much, it easily cracks during cold rolling, making it difficult to process, so the upper limit is 4.5%.
And

Further, the following components are impurities used as a precipitation dispersed phase for secondary recrystallization, and they must be contained in appropriate amounts for effective action. That is, Mn:
0.02-0.15%, S: 0.01-0.05%, acid-soluble Al: 0.01-0.04%, N: 0.003-
0.015%, Sb: 0.01 to 0.15%, Se:
By properly combining two or more kinds of 0.01 to 0.05%, it is possible to obtain secondary recrystallization having a high degree of Goss orientation grain integration. In addition, at least one kind of Cu and Sn may be added so as to be 1.0% or less for the purpose of strengthening the inhibitor.

Next, this cast slab is hot-rolled and further 950
After annealing at ˜1200 ° C. for 30 seconds to 30 minutes, a final cold rolling reduction of 80% or more is performed once or two or more times of cold rolling including intermediate annealing is performed, and a final plate having a thickness of 200 μm or less is obtained. Be thick.

Thereafter, decarburization annealing is performed in a wet hydrogen atmosphere,
Furthermore, by applying an annealing separator such as MgO and performing secondary annealing and finishing annealing at 1100 ° C. or more for purification, a thin unidirectional electrical steel sheet having a high magnetic flux density is manufactured.

[0028]

【Example】

(Example 1) A continuous magnetic ingot A having a surface layer thickness ratio of 10% is formed by forming a static magnetic field in the full width of the slab perpendicular to the casting direction and supplying molten steel containing the steel components shown in Table 1 with this as a boundary. , B, C were obtained. The steel ingot D was prepared by a usual method of supplying molten steel having a single component. Next, these steel ingots
After heating at 50 ° C for 1 hour, hot rolling, 2.3mm, 1.7m
A hot-rolled sheet with a thickness of 1.2 mm was prepared.

Next, these hot-rolled sheets were annealed at 1050 ° C. for 5 minutes, further pickled and cold-rolled to 0.3
The thickness was 0 to 0.15 mm (cold rolling reduction rate 87.0%). Next, this cold rolled sheet was decarburized and annealed in wet hydrogen, MgO powder was applied, and then high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. As shown in Table 2, the results of magnetic measurement of this product plate show that the inventive materials A and B have better magnetic properties than the comparative materials C and D, especially in the case of thin materials of 0.22 mm or less. Was obtained.

[0030]

[Table 1]

[0031]

[Table 2]

(Example 2) By forming a static magnetic field in the entire width of the slab perpendicular to the casting direction and supplying molten steel containing the steel components shown in Table 3 as a boundary, continuous steel ingots E, F, G
I got Further, the steel ingot H was prepared by a usual method of supplying molten steel having a single component. Next, these steel ingots were heated and hot rolled into hot-rolled sheets of 2.3 mm, 1.7 mm, and 1.2 mm thickness.

Next, these hot-rolled sheets were annealed at 1050 ° C. for 5 minutes, further pickled and cold-rolled to 0.3
The thickness was 0 to 0.15 mm (cold rolling reduction rate 87.0%). Next, this cold rolled sheet was decarburized and annealed in wet hydrogen, MgO powder was applied, and then high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. As shown in Table 4, the results of magnetic measurement of this product plate show that the inventive materials E and F show better magnetic properties than the comparative materials G and H, especially in the case of thin materials of 0.22 mm or less. Was obtained.

[0034]

[Table 3]

[0035]

[Table 4]

(Example 3) By forming a static magnetic field in the entire width of the slab perpendicular to the casting direction and supplying molten steel containing the steel components shown in Table 5 as a boundary, continuous steel ingots I, J, K
I got Further, the steel ingot L was prepared by a usual method of supplying molten steel having a single component. Next, these steel ingots were heated and hot-rolled into hot-rolled sheets having a thickness of 1.7 mm.

Next, these hot-rolled sheets were annealed at 1050 ° C. for 5 minutes, further pickled and then cold-rolled to 0.3
The thickness was 0 to 0.15 mm (cold rolling reduction rate 90.0%). Next, this cold rolled sheet was decarburized and annealed in wet hydrogen, MgO powder was applied, and then high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. As shown in Table 6, the results of magnetic measurement of this product plate show that the inventive materials I and J have better magnetic properties than the comparative materials K and L, especially in the case of thin materials of 0.22 mm or less. Was obtained.

[0038]

[Table 5]

[0039]

[Table 6]

[0040]

EFFECTS OF THE INVENTION According to the present invention, in a method for producing a grain-oriented electrical steel sheet containing a known inhibitor element in a slab, a sufficient low C region is provided on both surfaces of the cast slab surface layer portion at 5% or more and 30% or less. By having it, the Goss nuclei before the secondary recrystallization increase, and the secondary recrystallization becomes stable and the magnetic characteristics are improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the reduction of carbon content in the surface layer and the magnetic characteristics of a thin material having a plate thickness of 0.15 mm.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01F 1/16 H01F 1/16 B

Claims (3)

[Claims] 1. By weight ratio, C: 0.03-0.10%, Si: 2.5-4.5%, Mn: 0.02-0.15%, S: 0.01-0. 05%, acid-soluble Al: 0.01 to 0.04%, N: 0.003 to 0.015%, and a slab composed of the balance Fe and unavoidable impurities is used as a material, and after hot rolling and precipitation annealing, final In a method for producing a unidirectional electrical steel sheet, wherein cold rolling is performed once with a cold rolling reduction of 50% or more or twice or more including intermediate annealing, and further decarburization annealing and finish annealing are performed. C-surface layer C ≤ 0.03%, other elements are contained in the same manner as described above on the slab surface layer portion on one side 5% or more and 25% or less on both sides, a method for producing a high magnetic flux density unidirectional electrical steel sheet . 2. The method according to claim 1, wherein the final cold rolling reduction of the material is 80% or more. 3. By weight ratio, C: 0.03-0.10%, Si: 2.5-4.5%, Mn: 0.02-0.15%, acid-soluble Al: 0.01- 0.04%, N: 0.003 to 0.015%, Sb: 0.01 to 0.15% and S, Se: 0.01
The method according to claim 1, wherein molten steel containing at least one of 0.05 to 0.05% is used.