JPH05148532A - Manufacture of grain oriented silicon steel sheet having excellent magnetic characteristic and insulating film quality - Google Patents

Abstract

PURPOSE:To manufacture a grain oriented electric steel sheet having excellent magnetic characteristic and insulating film by specifying dew points and oxidizing degrees at the front part zone and the rear part zone of a decarbon- annealing process at the time of decarbon-annealing the grain oriented electric steel sheet after the last cold-rolling. CONSTITUTION:After a hot-rolling, annealing and cold-rolling are executed to the grain oriented silicon steel slab to finish this slab into the sheet, decarbon- annealing is executed in H2-N2 mixed gas atmosphere and successively, after coating annealing-separating agent substantially containing MgO, a finish annealing is executed. By making 40-60 deg.C the dew point and <=0.3 the oxidizing degree PH20/PH2 in the atmosphere at the front part zone of the decarbon- annealing and 40-75 deg.C the dew point and 0.3-0.6 the oxidizing degree (PH2O/PH2) in the atmosphere at the rear part zone, the grain oriented electric steel sheet having excellent qualities of the magnetic characteristic and the insulating film is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decarburizing and annealing a grain-oriented electrical steel sheet, and more particularly to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and insulating film quality.

[0002]

2. Description of the Related Art After the final cold rolling in the manufacturing process of grain-oriented silicon steel sheet, so-called decarburization annealing which also serves as primary recrystallization, decarburization and surface oxidation is performed. Japanese Patent Publication No. 57-1575 proposes a method of dividing this decarburization annealing into a front region and a rear region, and increasing the degree of oxidation (PH ₂ O / PH ₂ ) of the atmosphere in the front region higher than that in the rear region. ing.

On the other hand, as a method for improving the magnetic properties of grain-oriented silicon steel sheet, a method described in JP-B-59-32526 and a method for increasing the amount of Si in the raw material components and correspondingly increasing the amount of C and JP-B-55-55. -119126, γ in hot rolling
Method of precipitating 3% or more of phase ── To adopt this method,
It is known that it is necessary to increase the amount of material C.

When the above-mentioned prior art relating to the decarburizing and annealing atmosphere is applied to a material having a high C content before decarburizing and annealing, a sufficiently low value is obtained.
Before decarburization to (0.003% or less), since the degree of oxidation in the front region is high, a thick oxide film is formed on the surface of the steel sheet, and subsequent decarburization hardly progresses. If finish annealing is performed in a state where the amount of C after decarburization annealing is not sufficiently low, there is a problem that secondary recrystallization is likely to be incomplete and a product having good magnetic properties cannot be obtained.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems by improving a decarburizing annealing method, and to provide a method for producing a grain-oriented electrical steel sheet excellent in both magnetic properties and insulating film quality. It is what

[0006]

Means for Solving the Problems That is, in the present invention, when decarburizing annealing is performed after the final cold rolling of grain-oriented electrical steel sheet, the dew point (dp) of the atmosphere in the front region of the decarburizing annealing step is set. 40 ~
The degree of oxidation (PH ₂ O / PH ₂ ) is set to 65 or less, the dew point (dp) of the atmosphere in the rear region is set to 40 to 75 ° C., and the degree of oxidation (PH ₂ O / PH ₂ ) is set to 0.3. It is a method for producing a grain-oriented electrical steel sheet excellent in both magnetic properties and the quality of the insulating film, which is characterized in that

[0007]

In the conventional decarburization annealing method, the high degree of oxidation (PH ₂ O / PH ₂ ) in the atmosphere in the front region of the annealing step is the reason why decarburization does not proceed sufficiently. First, in order to lower the degree of oxidation in the front area and to secure a certain amount of water necessary for decarburization, the dew point (dp) is set relatively high and decarburization is performed while suppressing the formation of surface oxide film as much as possible. Was made to progress sufficiently. On the other hand, over the entire heat cycle of decarburization annealing, when treated in an atmosphere with the same low degree of oxidation as the front area, the amount of surface oxidation is small, and the adhesion of the vitreous insulating film formed by finish annealing in the next step Since the uniformity and the uniformity of the surface appearance are inferior, the degree of oxidation of the atmosphere in the rear region was made higher than that in the front region to obtain a predetermined amount of oxidation.

Next, the present invention will be described in more detail based on experimental results. Fig. 1 shows that the steel sheet composition before decarburization annealing is
C: 0.045%, Si: 3.05%, Mn: 0.05%, Se: 0.012%,
Sb: 0.03% of a 0.23 mm thick steel plate was annealed under the conditions shown in the figure, interrupted in the middle, and the C concentration of the steel plate pulled out from the furnace was investigated. From the figure, the degree of oxidation of the atmosphere of the annealing front is low, and in the example of the present invention with a high dp, at the time of the front annealing, the degree of oxidation of the front atmosphere is higher than that of decarburization in a suitable range. In the comparative example where the degree of oxidation is high, or the degree of oxidation and dp are both low, it is understood that decarburization has not progressed to a suitable range not only after the front annealing but also after the rear annealing.

FIG. 2 is similar to FIG. 1 in that C: 0.07%, Si:
3.20%, Mn: 0.06%, Se: 0.015%, Sb: 0.020%, A
l: 0.03%, N: 0.007% containing steel plate (0.23mm thickness)
The amount of surface oxidation increase after decarburization annealing is shown by the amount per 1 m _{2 of the} total amount of both sides of the steel sheet. In the invention examples having a high degree of oxidation in the rear atmosphere, the amount of oxidation increase in the preferable range was It can be seen that in the comparative example of low degree, the increase in oxidation amount is small.

Next, the reasons for limiting the decarburization annealing atmosphere will be described.
Regarding the front region, when the oxidation degree exceeds 0.3 and when dp is lower than 40 ° C, the C concentration after decarburization annealing does not decrease to a suitable range, and when dp exceeds 65 ° C, the oxidation degree is increased.
Since it is greater than 0.3, the degree of oxidation is 0.3 or less dp is 40 to 65 ° C
Limited to In the rear region, if the degree of oxidation exceeds 0.6, the amount of increased oxidation becomes excessive, deteriorating the magnetic properties of the product. If the degree of oxidation is less than 0.3 or dp is less than 40 ° C., the amount of increased oxidation cannot be obtained in the preferred range. Also, dp is 75
When the temperature exceeds ℃, the degree of oxidation exceeds 0.6.
~ 0.6, dp limited to 40 ~ 75 ℃.

As for the annealing time of the front region and the rear region, depending on the degree of oxidation of the atmosphere, the C concentration in the steel in the preferable range is obtained in the front region, and the amount of surface oxidation increase in the preferable region is obtained in the rear region. All you have to do is choose the time you can spend The steel sheet targeted by the present invention has C: 0.03 to 0.10% and Si: 2.8 to 4.5% as components.
It is a raw material for grain-oriented silicon steel sheet, containing any of the elements contained for suppressing crystal grain growth.

The degree of oxidation is adjusted by changing the atmosphere to H ₂ --N ₂ or H ₂
-Ar mixed gas is used by adjusting the mixing ratio and dp.

[0013]

EXAMPLE A grain-oriented silicon steel sheet containing the components shown in Table 1 was cast, hot-rolled, annealed, and cold-rolled to a thickness of 0.23 mm, and then in a H ₂ —N ₂ mixed gas. 84 under the atmospheric conditions shown in
Decarburization annealing was performed at 0 ° C, then a separating agent mainly containing MgO was applied, and finish annealing was performed.

At the time of finish annealing, for materials Nos. 1 to 4, after holding at 870 ° C. for 30 Hr in Ar gas, 1200 in H ₂ gas.
750 ℃ in N ₂ gas for 10Hr, material No. 5-10
After holding at ℃ 20Hr, annealing condition of 1200 ℃ 10Hr in H ₂ gas was applied. Table 3 shows the magnetic properties and insulating film evaluation of the obtained product. From the table, it is clear that the conditions for good magnetic properties and good evaluation of the insulating film of all the materials are D, E and F corresponding to the present invention.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

According to the present invention, it becomes possible to stably manufacture a product having good magnetic properties and an insulating film.

[Brief description of drawings]

FIG. 1 is a diagram showing changes in C% in steel during decarburization annealing.

FIG. 2 is a diagram showing the amount of increase in oxidation after decarburization annealing.

Claims (1)

[Claims] 1. When decarburizing annealing is performed after the final cold rolling of the grain-oriented electrical steel sheet, the dew point (dp) of the atmosphere in the front region of the decarburizing annealing step is set to 40 to 65 ° C. and the oxidation degree ( PH ₂ O / PH ₂ )
0.3 or less, and the dew point (dp) of the atmosphere in the rear area is 40 or less.
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and insulating film quality, characterized in that the degree of oxidation (PH ₂ O / PH ₂ ) is set to 0.3 to 0.6 at a temperature of up to 75 ° C.