JPH05117752A - Method for producing grain-oriented silicon steel sheet having excellent repeated bending properties - Google Patents

Abstract

(57) [Summary] [Structure] During the final finishing annealing process during the production process of grain-oriented silicon steel sheet, the hydrogen gas flow rate should be 0.3 Nm ³ / h ・ t or more in the temperature range of at least 950 to 1050 ° C during the heating process. To do. [Effect] The amount of N in the steel and the coating is reduced, and the cyclic bending property is improved.

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 silicon steel sheet, and more particularly to improving its repeated bending characteristics.

[0002]

2. Description of the Related Art In the final finish annealing of a grain-oriented silicon steel sheet, usually, as shown in FIG. 3 (a), each coil 1 is covered with an inner case 2, and a set of 4 coils is used. It is carried out by passing through a continuous tunnel furnace in which the furnace temperature in each section as shown in FIG. In FIG. 3, reference numeral 3 is a coil pedestal, 4 is a sand seal, 5 is a hydrogen gas supply pipe, and 6 is an annular continuous tunnel furnace.

By the way, the grain-oriented silicon steel sheet is required to have excellent magnetic properties as well as good repeated bending properties.
For that purpose, it is necessary to reduce impurities, especially N and S, in the final product. Figure 1 shows the relationship between the amount of N in steel and the number of repeated bends until fracture. The number of repeated bends increases as the amount of N decreases, and if the amount of N in steel is 7 ppm or less, the radius of curvature Under severe machining conditions of 5 mm and a bending angle of 90 °, 4 or more bends are guaranteed.

Here, denitrification in the process of manufacturing the grain-oriented silicon steel sheet is carried out at the time of finish annealing as is clear from the view shown in FIG. 950 to 1050 during finish annealing
H ₂ is used as an atmospheric gas during ℃, N + 3 / 2H ₂ → NH ₃
By the gas phase release by the reaction of ↑, N is expelled from the system and de-N
I do.

As a method of promoting such denitrification, the applicant company previously described in Japanese Patent Publication No. 58-32216, 950 to 1050 ° C.
While raising the temperature range of at an average rate of 5 to 15 ° C / h,
A method of heating in H ₂ atmosphere was proposed. In addition, based on the finding that N penetrates into the steel during the cooling process of final finish annealing, in JP-B-62-56206, after the holding temperature, the cooling atmosphere up to 600 ° C. is set to Ar alone or H ₂ and Ar. It was proposed that the mixed gas atmosphere is maintained and the internal pressure is maintained at a pressure higher than the outer pressure of the inner case by ₂ mmH ₂ O or more.

[0006]

[Problems to be Solved by the Invention] However, Japanese Patent Publication Sho 58
In the method disclosed in Japanese Patent No. 32216-, since the temperature rising rate is slow,
There was a problem in terms of productivity. Further, in Japanese Patent Publication No. 62-56206, N penetrates into a steel plate when the N concentration in the coating is high. Therefore, it is important to reduce the N concentration in the coating. The material could not be covered. The present invention advantageously solves the above-mentioned problems, and effectively promotes the gas phase release of N and reduces the amount of N in the steel and the coating, thereby advantageously improving the repetitive bending property. The purpose of the present invention is to propose a method for manufacturing a heat-resistant silicon steel sheet.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention increases the amount of hydrogen gas blown in a temperature range where the de-N reaction is active and accelerates the NH ₃ gas produced by the de-N reaction. By purging the crab out of the system, the de-N reaction is promoted. That is, according to the present invention, a hot-rolled silicon-containing steel hot-rolled sheet is pickled, and then cold-rolled once or twice with intermediate annealing, to obtain a final sheet thickness, followed by decarburization and primary recrystallization annealing. Then, after applying an annealing separating agent containing MgO as a main component, in producing a grain-oriented silicon steel sheet by a series of steps of performing final finishing annealing, in the final finishing annealing using hydrogen gas as an atmospheric gas, Set the hydrogen gas flow rate in the temperature range of at least 950 to 1050 ℃.
It is a method for producing a grain-oriented silicon steel sheet having excellent repeated bending properties, which is 0.3 Nm ³ / h · t or more.

[0008]

[Function] In finish annealing of grain-oriented silicon steel sheet, 950
De-N reaction in the temperature range of up to 1050 ℃ (N + 3/2 H ₂ → NH ₃ ↑)
Becomes active. The reason is that the atmosphere changes to hydrogen and the temperature becomes high. In this respect, when the temperature exceeds 1050 ° C., the formation of a forsterite film starts and a strong film is formed on the surface layer of the steel sheet, so N in steel decreases but N remains in the film and is not released to the outside of the system. In order to accelerate the de-N reaction, the amount of reaction H ₂ is increased and at the same time the product N
It is essential to quickly discharge the H ₃ gas out of the system. However, increasing the supply amount of the H ₂ gas satisfies these conditions and promotes denitrification.

Table 1 shows N in steel (steel + film) when the H ₂ gas circulation flow rate in the inner case was variously changed.
The result of having investigated about the amount of middle N and the frequency | count of repeated bending is shown.

[0010]

[Table 1]

As is clear from the above table, the amount of H ₂ gas is 0.3
In the range of Nm ³ / h · t or more, N in steel is 7 ppm or less, and good repeated bending properties are obtained. The improvement effect is particularly large when the H ₂ gas amount is 0.4 Nm ³ / h · t or more.

As a material to which the present invention is applied, any conventionally known material of grain-oriented silicon steel sheet is suitable. The manufacturing method may be according to a conventional method and is not particularly limited. However, in the final finish annealing, it is important to set the flow rate of hydrogen gas to 0.3 Nm ³ / h · t or more in the temperature range of at least 950 to 1050 ° C during the heating process. The reason why the temperature range is limited to the range of 950 to 1050 ° C. is that the de-N reaction is particularly active in this temperature range. The reason for limiting the hydrogen gas flow rate to 0.3 Nm ³ / h · t or more is that if this value is not satisfied, it is not possible to expect a sufficiently satisfactory improvement in repeated bending properties. The conventional amount of hydrogen gas supplied is
It was only about 0.2 Nm ³ / h · t.

[0013]

Example: Si: 3.2%, silicon steel material containing 2.0%,
After hot-rolling to thickness, 0.3 times by cold-rolling twice with intermediate annealing
The final plate thickness was mm. Next, this cold-rolled steel sheet was subjected to decarburization annealing at 820 ° C. for 3 minutes in wet hydrogen, then an annealing separating agent containing MgO as a main component was applied thereto, and then subjected to final annealing. For final finish annealing, 900 ° C to 0.2 Nm ³
A hydrogen gas atmosphere was started by injecting hydrogen gas of / h · t, and the amount of hydrogen gas supplied was increased to 0.4 Nm ³ / h · t in the temperature range of 950 to 1050 ° C. At 1050 ° C or higher, the amount of hydrogen gas was returned to 0.2 Nm ³ / h · t, and the temperature was maintained at 1180 ° C for 5 hours.

The amount of N in steel and the amount of N in (steel + film) of the product plate thus obtained were 5 ppm and 10 ppm, respectively, and the number of repeated bendings until breakage was 20 times. Also, as a result of applying the same treatment to 100 coils, there was no product that failed repeated bending.

[0015]

As described above, according to the present invention, at least 950 to 1050 is used in the temperature rising process of the final finish annealing of grain-oriented silicon steel sheet.
By setting the hydrogen gas flow rate in the temperature range of 50 ° C. to 0.3 Nm ³ / h · t or more, it is possible to obtain a grain-oriented silicon steel sheet having remarkably excellent repeated bending characteristics.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the N content in steel and the number of repeated bendings.

FIG. 2 is a graph showing the behavior of N during final finish annealing.

FIG. 3 is a diagram showing a procedure for finish annealing of a directional silicon steel coil.

[Explanation of symbols]

 1 coil 2 inner case 3 coil cradle 4 sand seal 5 hydrogen gas supply pipe 6 annular continuous tunnel furnace

Claims (1)

[Claims] 1. A hot-rolled silicon-containing steel hot-rolled sheet is pickled, and then cold-rolled once or twice with intermediate annealing, to a final thickness, and then decarburized and primary recrystallization annealing. Then, after applying an annealing separator containing MgO as a main component, and then performing a final finishing annealing to manufacture a grain-oriented silicon steel sheet, in the final finishing annealing using hydrogen gas as an atmosphere gas, A method for producing a grain-oriented silicon steel sheet having excellent repeated bending properties, characterized in that a hydrogen gas flow rate is set to 0.3 Nm ³ / h · t or more in a temperature range of at least 950 to 1050 ° C.