JP3387937B2 - Method for producing grain-oriented silicon steel sheet excellent in both magnetic properties and insulating film quality - Google Patents

Description

Description: 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 to manufacture a grain-oriented electrical steel sheet having both excellent magnetic properties and insulating film quality. It is about the method. [0002] During the production process of grain-oriented silicon steel sheets, after the final cold rolling, so-called decarburization annealing, which also serves as primary recrystallization, decarburization and surface oxidation, is performed. Japanese Patent Publication No. Sho 57-1575 proposes a method in which the decarburizing annealing is divided into a front region and a rear region, and the degree of oxidation of the atmosphere in the front region (PH ₂ O / PH ₂ ) is made higher than that in the rear region. ing. On the other hand, as a method for improving the magnetic properties of a grain-oriented silicon steel sheet, there is a method disclosed in Japanese Patent Publication No. 59-32526 in which the amount of Si in the material component is increased and the C amount is increased accordingly. -119126, γ in hot rolling
Method of precipitating 3% or more phase. To use this method,
It is necessary to increase the amount of material C, for example. [0004] If the above-mentioned prior art relating to the decarburizing annealing atmosphere is applied to a material having a high C content before decarburizing annealing, a sufficiently low value is obtained.
Before decarburization (less than 0.003%), the degree of oxidation in the front region is high, so that a thick oxide film is formed on the surface of the steel sheet, and decarburization hardly proceeds thereafter. If the finish annealing is performed in a state where the carbon content after the decarburizing annealing is not sufficiently low, there is a problem that secondary recrystallization tends to be incomplete, and a product having good magnetic properties cannot be obtained. [0005] The present invention solves the above-mentioned problems by improving the decarburizing annealing method, and provides a method for producing a grain-oriented electrical steel sheet having both excellent magnetic properties and insulating film quality. The purpose is to do so. That is, according to the present invention, when the grain-oriented electrical steel sheet material is subjected to decarburization annealing after final cold rolling, the dew point of the atmosphere in the front region of the decarburization annealing step ( dp) 40 ~
65 ° C., the degree of oxidation (PH ₂ O / PH ₂ ) is 0.3 or less, the dew point (dp) of the atmosphere in the rear region is 40 to 75 ° C., and the degree of oxidation (PH ₂ O / PH ₂ ) is 0.3. This is a method for producing a grain-oriented electrical steel sheet having both excellent magnetic properties and excellent quality of an insulating film, characterized by being set to 0.6. 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 a cause of insufficient decarburization. The present invention firstly lowers the degree of oxidation in the front region, and in order to secure a predetermined amount of water required for decarburization, while keeping the dew point (dp) relatively high, while suppressing the formation of a surface oxide film as much as possible. The decarburization was advanced sufficiently. On the other hand, when the treatment is carried out in the same low oxidation degree atmosphere as in the front region over the entire heat cycle of the decarburization annealing, the amount of surface oxidation is small, and the adhesion of the vitreous insulating film formed by the finish annealing in the next step is reduced. Since the properties and the uniformity of the surface appearance are inferior, the degree of oxidation of the atmosphere in the rear region is set 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. Figure 1 shows that the steel sheet components before decarburization annealing
C: 0.045%, Si: 3.05%, Mn: 0.05%, Se: 0.012%,
This is the result of examining the C concentration of the steel sheet drawn out of the furnace after annealing a 0.23 mm-thick steel sheet with Sb: 0.03% under the conditions shown in FIG. From the figure, the oxidation degree of the atmosphere in the front part of the annealing is low and the dp is high in the example of the present invention. In the comparative examples where the degree of oxidation is high or the degree of oxidation and dp are both low, it can be seen that decarburization has not progressed to a suitable range not only after the end of the front annealing but also after the end of the rear annealing. FIG. 2 shows, similarly to FIG. 1, C: 0.07%, Si:
3.20%, Mn: 0.06%, Se: 0.015%, Sb: 0.020%, A
l: Steel sheet containing 0.03%, N: 0.007% (0.23mm thickness)
The surface oxidation weight gain after decarburization annealing which was indicated by an amount per 1 m ₂ of steel sheet both sides total, the higher the invention examples of degree of oxidation of the rear atmosphere, compared to oxidation weight gain of the preferred range can be obtained, oxide It can be seen that the comparative example having a low degree of oxidation has a small amount of increase in oxidation. Next, the reasons for limiting the decarburizing annealing atmosphere will be described.
Regarding the front region, when the degree of oxidation 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 degree of oxidation decreases.
Since it is larger than 0.3, the oxidation degree should be 0.3 or less.
Limited to. In the rear region, when the degree of oxidation exceeds 0.6, the amount of oxidation increases excessively, deteriorating the magnetic properties of the product. On the other hand, when the degree of oxidation is less than 0.3 or dp is less than 40 ° C., it is not possible to obtain a suitable range of increase in oxidation. Dp is 75
If the temperature exceeds ℃, the oxidation degree exceeds 0.6.
~ 0.6, dp limited to 40-75 ° C. According to the degree of oxidation of the atmosphere, the annealing time in the front region and the rear region is determined to be within a suitable range for the C concentration in steel in the front region and in a suitable range for the surface oxidation increase in the rear region. You just have to choose the time you want. The steel sheet targeted by the present invention has C: 0.03 to 0.10% and Si: 2.8 to 4.5% as components.
This is a material for grain-oriented silicon steel sheets containing, regardless of the element to be contained for suppressing crystal grain growth. To adjust the degree of oxidation, the atmosphere is H ₂ -N ₂ or H ₂
This is performed by adjusting the mixture ratio and adjusting the dp as a mixed gas of -Ar. 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 mixed in an H ₂ -N ₂ mixed gas. , 84 under the atmospheric conditions shown in Table 2.
Decarburization annealing at 0 ° C. was performed, and then a separating agent mainly composed of MgO was applied and finish annealing was performed. At the time of finish annealing, materials Nos. 1 to 4 were maintained at 870 ° C. for 30 hours in Ar gas and then 1200 hours in H ₂ gas.
℃ 10Hr, for material No.5-10, 750 in N ₂ gas
After holding at 20 ° C for 20 ° C, annealing conditions of 1200 ° C for 10 hours in H ₂ gas were applied. Table 3 shows the magnetic properties and the evaluation of the insulating film of the obtained product. From the table, it is clear that the conditions for favorable evaluation of the magnetic properties of the product and the evaluation of the insulating film are D, E and F corresponding to the present invention. [Table 1] [Table 2] [Table 3] According to the present invention, it is possible to stably produce a product having good magnetic properties and insulating film.

[Brief description of the drawings] FIG. 1 is a diagram showing a change in C% in steel during decarburizing annealing. FIG. 2 is a diagram showing an increase in oxidation after decarburization annealing.

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Claims (1)

(57) [Claims] [Claim 1] When performing decarburization annealing after final cold rolling of grain-oriented electrical steel sheet material, the dew point (dp) of the atmosphere in the front region of the decarburization annealing step is set to 40. Up to 65 ° C and the degree of oxidation (PH ₂ O / PH ₂ )
0.3 or less, and the dew point (dp) of the atmosphere in the rear area is 40
To to 75 ° C., and the oxidation degree (PH ₂ O / PH ₂₎ of 0.3-0.6 and a manufacturing method are both excellent grain-oriented electrical steel sheet quality magnetic properties and the insulating film, characterized by.