JPH05171284A - Method for producing grain-oriented silicon steel sheet having excellent magnetic properties and insulating film quality - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel excellent in magnetic properties and film characteristics by specifying the degree of oxidation of the atmosphere in a decarburizing annealing stage and also specifying the degree of oxidation of the atmosphere in a finish annealing stage. CONSTITUTION:After a stock for grain-oriented silicon steel sheet is subjected to final cold rolling, decarburizing annealing is performed and then a separation agent at annealing is applied and finishing annealing is done. At this time, the degree of oxidation (pH20/pH2) of the atmosphere in the decarburizing annealing stage is kept at 0.20-0.75. Subsequently, the degree of oxidation of the atmosphere in the finish annealing stage after the application of a separation agent at annealing, composed essentially of MgO, is regulated to <=0.20. By this method, the grain-oriented silicon steel sheet excellent in the quality of an insulating film 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 producing grain-oriented silicon steel.

[0002]

2. Description of the Related Art Grain-oriented silicon steel is subjected to decarburization annealing that also serves as primary recrystallization, decarburization, and surface oxidation after the final cold rolling.
After applying an annealing separator containing MgO as a main component, finish annealing is performed. And, in general, the atmosphere of the decarburization annealing step has an oxidation degree (=
PH ₂ O / PH ₂ ) is kept constant, and as shown in Japanese Patent Publication No. 57-1575, the degree of oxidation in the rear region is made smaller than that in the front region.

In finish annealing, a coil obtained by applying a slurry annealing separator containing MgO as a main component and drying it after decarburizing annealing is annealed in a batch system. The purpose of finish annealing is secondary recrystallization, film formation and purification. A heat pattern as shown in FIG. 1A or 1B is generally adopted.

[0004]

By the way, the problem with the above-mentioned finish annealing is that MgO is not heated near 300 to 500 ° C during heating.
That is, the dehydration reaction occurs, the degree of oxidation in the atmosphere increases, and the surface layer of the steel sheet is peroxidized. When the surface of the steel sheet is excessively oxidized, (1) oxidative decomposition of inhibitors such as MnSe and AlN occurs, the effect of suppressing crystal growth is reduced, and the magnetic properties are deteriorated. In addition, (2) oxide such as SiO ₂ is excessively generated in the surface layer,
It causes deterioration of coating properties. Also, (3) it is possible to reduce the oxidation degree only in the rear region in the decarburizing annealing process and reduce the oxidation during finish annealing, but it is difficult to reduce the oxidation degree only in the rear region in a continuous furnace. In addition, the cost of passing the strip twice is increased. Further, even if the surface oxidation during decarburization annealing is mild, if the surface layer is oxidized again by the finish annealing in the next step,
It is inevitable that its effect will decrease.

It is an object of the present invention to solve the above problems and provide a method for producing a grain-oriented silicon steel sheet having excellent magnetic properties and insulating film quality.

[0006]

In order to solve the above-mentioned problems, the present invention is one in which decarburization annealing is carried out in an atmosphere within a certain range, and the oxidation degree of finishing annealing which is the next step is lowered to a certain value or less. Is. That is, the present invention, after the final cold rolling of the grain-oriented electrical steel sheet, subjected to decarburization annealing, and then applying an annealing separating agent to perform finish annealing, the degree of oxidation of the atmosphere of the decarburization annealing step (PH ₂ O / PH ₂ ) in the range of 0.20 to 0.75, and then the degree of oxidation of the atmosphere in the finish annealing step after applying the annealing separator containing MgO as the main component was set to 0.20 or less. This is a method for producing a grain-oriented silicon steel sheet having excellent quality.

[0007]

[Operation] According to the present invention, the decarburization annealing is performed at an oxidation degree (PH ₂ O /
PH ₂ ) in an atmosphere of 0.2 to 0.75, then M
Apply an annealing separator containing gO as a main component. The surface layer of the internal oxide layer formed by decarburization annealing reduces the degree of oxidation during finish annealing to 0.
It is considered that when the ratio is 20 or less, it is improved, and thereafter the quality of the glass film is improved, so that the film properties are better than those of the conventional method. When the degree of oxidation in the finish annealing step is higher than 0.2, the improvement effect is small as shown in FIG. The reason for limiting the degree of oxidation of the atmosphere in the decarburization annealing process to the range of 0.2 to 0.75 is that if it is less than 0.2, sufficient decarburization cannot be achieved, while 0.75
If it is over, the oxide film will be too thick, and the degree of oxidation during finish annealing
This is because a good glass film will not be formed even if it is kept at 0.20 or less.

[0008]

Example: Si 3.3%, C 0.060%, Mn 0.070%, Al 0.0
25%, N 0.0070%, Se 0.020% The balance was made of Fe, and a hot-rolled steel sheet for grain-oriented silicon steel sheet having a thickness of 2.2 mm was rolled to 0.23 mm by two cold rolling processes with intermediate annealing. The cold-rolled steel was subjected to decarburization annealing in a hydrogen stream at 840 ° C for 120 seconds soaking. At this time, the degree of oxidation in the furnace was maintained between 0.6 and 0.7. After decarburization annealing, apply MgO and finish annealing as shown in Fig. 1 (a).
Pattern A was used. The following three experimental conditions were used. (1) The atmosphere gas during heating of the finish annealing to 800 ° C is N ₂ /
H ₂ was used at a ratio of 70/30 and was blown at a flow rate of 0.2 Nm ³ / hr · t. At this time, the degree of oxidation was 0.11 or less. (2) As a comparison, the atmosphere gas is N ₂ 100% gas is 0.2 Nm ³ / hr
・ Blow off at a flow rate of t. The dew point rose to about 25 ℃.
At this time, the degree of oxidation was low at PH _{2 and} high at 3.2. (3) Decarburization annealing was performed at 840 ° C for 120 seconds in an atmosphere with an oxidation degree of 0.60 to 0.70, and then treated at 840 ° C for 30 seconds with an oxidation degree of 0.1, and finish annealing was performed under the conditions of (2). It was

In the latter half of these three levels of finish annealing in hydrogen
It was kept at 1200 ° C for 5 hours and cooled. The magnetic properties and coating properties are shown in Table 1.

[0010]

[Table 1]

By the method of the present invention, it was possible to obtain a grain-oriented silicon steel sheet having good magnetic properties and coating properties. In addition, as a means for reducing the degree of oxidation during finish annealing, another method of increasing the flow rate of the blowing gas is also effective.

[0012]

According to the present invention, decarburization annealing is performed in a certain range of atmosphere, and thereafter, the degree of oxidation of the finish annealing atmosphere is set to 0.20 or less to produce grain oriented silicon steel excellent in magnetic characteristics and coating characteristics. I was able to do it.

[Brief description of drawings]

FIG. 1 shows an example of a heat pattern for finish annealing.

FIG. 2 is a graph showing the relationship between the degree of oxidation in the atmosphere during finish annealing and the film characteristics.

Claims (1)

[Claims] 1. When the final cold rolling of the grain-oriented electrical steel sheet is followed by decarburization annealing, and then the annealing separator is applied and finish annealing is performed, the degree of oxidation (PH ₂ O / PH) in the atmosphere of the decarburizing annealing step is set. ₂ )
Is maintained in the range of 0.20 to 0.75, and then the degree of oxidation of the atmosphere in the finish annealing process after applying the annealing separator containing MgO as the main component is adjusted.
A method for producing a grain-oriented silicon steel sheet having excellent magnetic properties and insulating film quality characterized by being 0.20 or less.