JPH062041A - Stable production of grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To produce a middle grade grain-oriented silicon steel sheet having not so high B8 of magnetic properties without causing sensitivity to the change in hot rolling heating temp. CONSTITUTION:At the time of producing a grain-oriented silicon steel sheet by using a steel having a composition consisting of, by weight, 2-7% Si, 0.03-0.08% C, 0.01-0.07% Al, 0.003-0.013% N, 0.05-0.45% Mn, and the balance Fe with inevitable impurities as a starting material and controlling slab heating temp. to <=1280 deg.C, S content is regulated to 0.01-0.05%, by which the diameter of primary recrystallized grains is controlled. By this method, the inexpensive middle grade grain-oriented silicon steel sheet can be produced.

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 grain-oriented electrical steel sheet used for an iron core of electric equipment such as a transformer.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are soft magnetic materials used for transformer cores and the like. The characteristic required for the iron core of the transformer is that the iron loss, which is the magnetic energy loss during voltage conversion, is small. In order to reduce iron loss, methods such as adding Si and adjusting the texture are applied to the steel sheet for electromagnetic steel sheets.

When alternating current magnetization is applied to a steel sheet, an induced current flows in the steel sheet. Since the source of Joule heat generated by this current is magnetic energy, reduction of Joule heat, that is, reduction of induced current leads to reduction of iron loss. When Si is added, the electric resistance of the steel sheet increases and the induced current decreases. Therefore, Si is generally added to the magnetic steel sheet.
In addition, Fe or Fe-Si forming a body-centered cubic lattice
The alloy has different magnetization characteristics depending on the orientation of the lattice. This property is called magnetic anisotropy, and in the case of Fe or Fe-Si alloy, the <100> direction is the best in terms of the magnetization characteristic in terms of Miller index. Therefore, if the crystal grains are magnetized in the <100> direction, a predetermined magnetic flux density can be obtained with a small magnetizing force, and the magnetic energy loss per one cycle of magnetization is also small. Therefore, aligning the <100> orientation of the crystal grains of the steel sheet with the magnetization direction leads to reduction of iron loss.

Thus, the Fe--Si alloy crystal grains <1
A steel sheet whose 00> orientation is aligned with the rolling direction by texture control is called a grain-oriented electrical steel sheet. The texture control at this time utilizes a grain growth phenomenon using fine precipitates called secondary recrystallization. The metallurgical conditions required for secondary recrystallization are
It is a crystal grain size and texture of primary recrystallized grains, and fine precipitates called inhibitors. The texture during primary recrystallization is generally the final orientation after secondary recrystallization (11
0) <001> (referred to as Goss orientation) is incorporated into the grains to have a (111) <112> orientation.

The inhibitor functions to suppress the growth of crystal grains up to a temperature at which the Goss orientation preferentially grows.
Precipitates used for this purpose include MnS, Al
N, MnSe, etc. are used. In addition, the inhibitor can be made by adjusting the composition at the steelmaking stage and controlling the dispersed state by rolling or annealing, or by making nitriding during the process.

On the other hand, the primary recrystallized grain size is controlled so that the secondary recrystallized orientation is optimum and that the secondary recrystallized orientation is directed to the correct Goss orientation as much as possible. The primary recrystallization grain size is determined by the temperature of the primary recrystallization annealing (decarburization annealing substitutes for this) and the state of precipitates precipitated during the primary recrystallization. Therefore, for example, if the decarburization annealing temperature is fixed as an operating condition during production, it is difficult to obtain a stable and uniform secondary recrystallization state unless the dispersed state of the precipitate is kept constant.

The state of the precipitate until the decarburization annealing depends on the components and the dissolution and precipitation behavior up to that point. For example, a large number of large precipitates are present when the melting is small in the upper step, but a large number of small precipitates are present when the melting is intense. When the decarburization annealing temperature is the same, the latter has a smaller crystal grain size. Therefore, if the distribution of precipitates in the steel sheet is not uniform, the secondary recrystallized state will also be uneven.

[0008]

In the present invention, when the magnetic properties of the grain-oriented electrical steel sheet are not required to be so high, the primary recrystallized grain size is appropriately controlled so that the grain size is stable and uniform rather than high magnetism. The present invention proposes a method for producing a grain-oriented electrical steel sheet which causes secondary recrystallization.

[0009]

Means for Solving the Problems A grain-oriented electrical steel sheet is
When slab heating is performed at a low temperature of 80 ° C. or lower, it becomes difficult to secure the inhibitor strength. Therefore, the inhibitor strength must be ensured by adjusting the components or nitriding immediately before secondary recrystallization.

The inventor of the present invention measured the change in the primary recrystallized grain size (hereinafter referred to as the primary grain size) when the slab heating temperature was changed. FIG. 1 shows the change in the primary particle size of component A in Table 1.
2 shows the change in the primary particle size of the component B.

[0011]

[Table 1]

The magnetic properties of the product after the secondary recrystallization are determined by the relationship between the primary particle size and the strength of the inhibitor. For example, when it is not necessary to increase the magnetic flux density of the product after secondary recrystallization so much, it is necessary to reduce the primary particle size and to reduce the fluctuation of the primary particle size with respect to the fluctuation of the primary recrystallization temperature. There is. As shown in FIG. 1 and FIG. 2, it was found that depending on the component system, both the size and the fluctuation of the primary recrystallized grain size are small with respect to the fluctuation of the slab heating temperature.

That is, as shown in FIGS. 1 and 2, Al is added in an amount of 300 to secure the inhibitor necessary for secondary recrystallization.
It has been found that when the content of S is approximately ppm, the one having a higher S content, that is, the one shown in FIG.

The present invention has been made on the basis of this finding, and as a result of further experiments, it is possible to manufacture an inexpensive grain-oriented electrical steel sheet, although the magnetic flux density is not so high, under the following conditions. I found it. That is, the gist of the present invention is, by weight%, Si: 2 to 7%, C: 0.03 to 0.
08%, Al: 0.01 to 0.07%, N: 0.003
.About.0.0130%, Mn: 0.05 to 0.45%, and smelting steel containing the balance Fe and unavoidable impurities,
After forming a steel ingot or slab by casting, hot rolling, cold rolling, decarburization annealing and subsequent annealing separating agent application, followed by high temperature finish annealing, in the method for producing a grain-oriented electrical steel sheet, the S content is 0.01 % Or more and 0.05% or less, and the slab heating temperature is 1280 ° C. or less, which is a stable method for producing a grain-oriented electrical steel sheet.

Further, according to the present invention, after hot rolling and before the end of cold rolling, one or more annealings are performed at 900 ° C to 1250 ° C.
Nitriding until the secondary recrystallization occurs after decarburization annealing, and the amount of nitrogen after nitriding is 150 pp.
It is included that it is m or more and 300 ppm or less.

First, the reasons for limiting the components will be described. S
When i is less than 2%, iron loss characteristics cannot be sufficiently obtained, and good secondary recrystallization was not obtained, so i was set to 2% or more. If it exceeds 7%, the product becomes extremely brittle,
Since processing such as slitting and punching becomes difficult, it was set to 7% or less.

If C is less than 0.03%, the magnetic properties cannot be obtained because the orientation of secondary recrystallization is poor, and if it exceeds 0.08%, decarburization annealing takes a long time and the cost is low. However, it is 0.03% or more and 0.08% or less.

Al is necessary as an inhibitor-forming element during secondary recrystallization. If it is less than 0.01%, stable secondary recrystallization cannot be obtained, and even if it is obtained, the magnetic properties are poor. If the content exceeds 0.07%, a large amount of Al ₂ O ₃ is formed on the surface of the steel sheet during finish annealing, which not only impairs the appearance of the coating film but also adversely affects the iron loss characteristics.

N combines with Al to form AlN,
Acts as an inhibitor of secondary recrystallization. If it is less than 0.003%, it is insufficient to secure the amount of the inhibitor,
If it exceeds 0.0130%, a crack called a blister on the surface of the steel sheet is caused to impair the characteristics.

Mn fixes the solid solution S and prevents hot cracking due to S segregation. MnS is also a precipitate that is effective as an inhibitor. If it is too large, the balance of the inhibitor will be lost and the amount of oxygen adhered to the decarburized annealed plate will be excessive, impairing the film formation.

In the present invention, the role of S is important.
In the material of the present invention, when the amount of S is small, the magnetic properties of the product are high and excellent, but the primary particle size varies somewhat due to fluctuations in slab heating. However, when the S content is 0.010% or more, the magnetic characteristics of the product are not so high, but the influence of the slab heating temperature is reduced. On the other hand, if the amount is too large, the balance of the inhibitor is lost or segregation is caused to cause variations in properties within the steel sheet.

In order to reduce the load of hot rolling, especially heating, the slab heating temperature is set to 1280 ° C. or lower. Since the melting point of the steel containing Si is lowered, if the temperature is too high, extreme oxidation of the surface of the steel sheet, partial melting or the like will occur. Therefore, the lower the temperature, the better. Moreover, since the heating furnace used in the manufacturing process of ordinary steel can be shared, it is advantageous in production.

When the slab heating temperature is low, the amount of solid solution and reprecipitation of the precipitate is small. Therefore, the inhibitor strength is weakened. At this time, forming AlN by nitriding as a means for reinforcing the inhibitor is advantageous for secondary recrystallization. At this time, some Al and N must be contained in the steel composition. AlN often precipitates extremely finely when re-deposited as a solid solution, and the precipitation state changes greatly with a slight difference in temperature history. Therefore, for example, when the slab heating temperature becomes high, fine AlN increases in the stages of cold-rolled sheet and decarburized sheet, and the primary recrystallized grains become finer.

This is the content shown as the difference between the solid line and the broken line in FIGS. When S is added, MnS begins to precipitate. Since MnS is not so severely refined by solid solution reprecipitation, the variation in the primary particle diameter due to the difference in thermal history is small. That is, in FIG. 1, the distance between the solid line and the broken line is narrower than that in FIG. 2, and the amount of change with respect to the primary recrystallization temperature is smaller. Further, since MnS becomes a precipitation nucleus when AlN is re-precipitated, when MnS is present, AlN is present in the form of complex precipitation with MnS, and the fine precipitation amount is reduced. That is, when the amount of S in the steel is increased, the characteristic instability factor due to the thermal history variation in the upper process is reduced.

When the hot rolled sheet is annealed, the texture of the steel sheet is optimized and the magnetic flux density is increased. This effect is particularly remarkable when annealed at 900 ° C. or higher. At this time, the magnetic fluctuation tends to be suppressed, but when the slab heating temperature fluctuation is extremely large, for example, it is difficult to suppress the fluctuation only by annealing the hot rolled sheet. In addition, the hot-rolled sheet annealing condition itself may change, and the present invention also exhibits the effect at this time.

[0026]

【Example】

 (Example 1)

[Table 2]

The slabs having the components shown in Table 2 were heated at 1150 ° C.
After heating at 1200 ° C and 1250 ° C, hot rolling to a plate thickness of 2.0 mm, annealing at 880 ° C (Table 3) and 1120 ° C for 30 seconds (Table 4) followed by pickling, 0.22 mm Cold rolled to 830 ℃ × 11 in a humid atmosphere with a dew point of 60 ℃
Annealing is performed for 0 seconds, and then annealing is performed in an atmosphere containing NH ₃ so that the nitrogen content is about 180 ppm (A material: 184 ppm,
B material: 179 ppm, C material: 175 ppm, D material: 181 pp
After m), an annealing separator containing MgO as a main component was applied, and high temperature annealing at 1200 ° C. for 20 hours was performed.

The values of the magnetic flux density at this time are shown in Tables 3 and 4. From the table, the material A has a high B8, but the magnetic characteristics change a little when the slab heating temperature changes greatly. On the other hand, B,
It is understood that the C and D materials have a slightly low B8, but their change is small. That is, although the B8 is not as high as the A material in the material of the present invention, the change in magnetism is small with respect to the fluctuation in the slab heating temperature. From the comparison between Table 3 and Table 4, a similar tendency is observed regardless of the hot-rolled sheet annealing temperature.

[0029]

[Table 3]

[0030]

[Table 4]

[0031]

EFFECTS OF THE INVENTION According to the present invention, a manufacturing method that is insensitive to fluctuations in the hot rolling heating temperature can be realized for the production of a mid-grade grain-oriented electrical steel sheet in which the magnetic property B8 is not so high.

[Brief description of drawings]

FIG. 1 is a table showing the relationship between the slab heating temperature when S is sufficiently contained and the primary recrystallized grain size during decarburization annealing.

FIG. 2 is a table showing the relationship between the slab heating temperature when the amount of S is small and the primary recrystallized grain size during decarburization annealing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunari Yoshitomi 1-1 Tobahata-cho, Tobata-ku, Kitakyushu City Nippon Steel Co., Ltd. Yawata Works (72) Inventor Yoshiyuki Ushigami 20-1 Shintomi, Futtsu-shi Shinnihon Steel Engineering Co., Ltd.

Claims (4)

[Claims] 1. By weight%, Si: 2 to 7%, C: 0.03 to 0.08%, Al: 0.01 to 0.07%, N: 0.003 to 0.0130%, Mn. : Steel containing 0.05 to 0.45% and the balance Fe and unavoidable impurities is melted and cast into a steel ingot or slab, which is then hot rolled, cold rolled, decarburized and subsequently decarburized. In the method for producing a grain-oriented electrical steel sheet, wherein high temperature finish annealing is performed after applying an annealing separator, the amount of S is 0.01% or more and 0.05% or less, and the slab heating temperature is 1280 ° C or less. Stable manufacturing method for high-performance electrical steel sheet. 2. The directional electromagnetic field according to claim 1, wherein annealing is performed once or twice or more between 900 ° C. and 1250 ° C. after hot rolling and before completion of cold rolling. Stable manufacturing method of steel sheet. 3. The stable production method of a grain-oriented electrical steel sheet according to claim 1, wherein nitriding is performed after decarburization annealing until secondary recrystallization occurs. 4. The amount of nitrogen after nitriding is 150 ppm or more and 30 or more.
It is 0 ppm or less, The stable manufacturing method of the grain-oriented electrical steel sheet of Claim 1 or 2 or 3 characterized by the above-mentioned.