JPH0826397B2 - Finishing annealing method for grain-oriented silicon steel sheet - Google Patents

Description

The present invention relates to a method for finish annealing a grain-oriented silicon steel sheet. More specifically, a grain-oriented silicon steel sheet having a forsterite coating and excellent magnetic properties can be obtained. A finish annealing method.

[Conventional technology]

It is indispensable that the grain-oriented silicon steel sheet has excellent magnetic properties such as magnetic flux density and iron loss, and that a good forsterite film is formed. The grain-oriented silicon steel sheet is obtained by utilizing the secondary recrystallization phenomenon to develop crystal grains having a so-called Goss orientation having a (110) plane in the rolling surface and a [001] axis in the rolling direction. In the finish annealing that causes this secondary recrystallization, the oxide film containing SiO ₂ formed by decarburizing annealing on the surface of the steel sheet reacts with the annealing separating agent containing MgO as a main component to form a forsterite film.

Finish annealing of grain-oriented silicon steel sheet is performed by cold rolling to a final sheet thickness, then decarburizing annealing and applying an annealing separating agent to the steel sheet, for example, as disclosed in JP-A-56-62925. It is performed in a state.

By the way, considering the heating that the coil receives in the finish annealing, the coil is placed in the annealing furnace in one or more stages with the hollow part of the coil in the vertical direction, covered with a muffle, and heated by a heating device such as a burner, electricity, or a heater. Be heated. When heated, most of the heat transfer is the radiation between the coil and the muffle, and the heat flow component in the coil thickness direction (radial direction of the coil) through the inner and outer peripheral surfaces of the coil is overwhelmingly large, The heat flow component in the coil width direction through the end is small. On the other hand, the heat conductivity in the thickness direction of the coil is slow because it is heat conduction through the annealing separator, and the heat conductivity in the width direction of the coil is fast because it is the grain-oriented silicon steel plate itself. As a result, when the coil is heated, temperature deviation occurs between the outer winding portion, the inner winding portion, and the intermediate portion of the coil. Further, as described above, the annealing separator is applied to the grain-oriented silicon steel sheet, but this inevitably contains magnesium hydroxide (Mg (OH) ₂ ). This magnesium hydroxide is thermally decomposed during the heating of finish annealing and releases water vapor, but since the annealing coil has the temperature deviation as described above,
The amount of water vapor released varies depending on the position in the coil. The forsterite film formed on the surface of the steel sheet is affected by this, and it is difficult to form a good forsterite film over the entire length or width of the coil. Further, the temperature deviation in the coil has a bad influence on the development of secondary recrystallization, which is one of the causes of the variation in the magnetic characteristics.

Conventionally, there is a finish annealing method for improving the magnetic flux density and the iron loss by performing the finish annealing of the grain-oriented silicon steel sheet in three steps of pre-annealing at about 830 ° C, subsequent slow heating secondary recrystallization annealing, and purification annealing. It has been proposed (JP-A-58-221227).

Further, in Japanese Examined Patent Publication No. 57-34351, after the completion of room temperature retention at 800 to 920 ° C, the atmosphere for finish annealing is switched from neutral gas to H ₂ gas, and the atmosphere during heating to 1150 to 1250 ° C and soaking Set the dew point of gas to -20 ℃ to + 20 ℃ respectively
The average dew point in contact with the steel strip during the entire 1250 ° C annealing is + 10 ° C or less, and the annealing time at a dew point higher than + 10 ° C is within 5 hours, and the forsterite film has a fine structure to improve adhesion and appearance. It is proposed to try.

[Problems to be solved by the invention]

With these, some effects may be exhibited, but since finish annealing is performed in a coil shape, it is unavoidable that temperature deviation occurs due to the position in the coil, and the circulation of atmospheric gas in the coil In reality, it is not performed sufficiently, and is rarely performed. Therefore, it is impossible to eliminate the occurrence of variations in the magnetic characteristics and the forsterite film in the coil.

[Means for solving problems]

It is an object of the present invention to provide a finish annealing method capable of providing a grain-oriented silicon steel sheet having high quality and little variation in the magnetic properties and the forsterite coating over the entire length and width of the coil. The gist is that a grain-oriented silicon steel plate is cold-rolled to a specified plate thickness, then decarburized and annealed to form a steel plate surface.
Forming an oxide layer containing SiO ₂ and applying an annealing separator containing magnesia oxide as a main component to the steel sheet, and performing finish annealing, unwinding a grain-oriented silicon steel sheet from a coil and passing it in a plate shape. In the same furnace, annealing and coiling the directional silicon steel sheet passed through the coil and annealing in a coil shape are performed.
A finish annealing method for grain-oriented silicon steel sheets, which is characterized in that they are performed in combination.

The present invention will be described in detail below. INDUSTRIAL APPLICABILITY The present invention is widely used in a method for manufacturing a grain-oriented silicon steel sheet,
It is not necessary to specify the steel components of the grain-oriented silicon steel sheet and the manufacturing conditions from cold rolling to a predetermined sheet thickness, decarburization annealing, and application of the annealing separator. For example, in finish annealing, Al is used as an inhibitor to induce secondary recrystallization.
Known materials such as N, MnS, MnSe, and BN are used, and if necessary, C
Elements such as u, Sn, Cr, Ni, Mo, Sb and P are contained. As for the manufacturing conditions, the slab is hot-rolled and annealed and then decarburized once or twice or more by intermediate rolling and then cold-rolled to a predetermined final plate thickness. The decarburization annealing decarburizes the grain-oriented silicon steel sheet and forms an oxide layer containing SiO ₂ on the surface of the steel sheet. Next, water is added to an annealing separating agent containing MgO as a main component to suspend the mixture to form a slurry, which is applied onto the above-mentioned steel sheet by a roll coater or the like. The application of the annealing separator is not limited to the above, and may be performed by, for example, an electrostatic coating method,
A known method is adopted.

When the annealing separator is applied in the form of a slurry, the grain-oriented silicon steel sheet is heated in a drying furnace at, for example, about 200 ° C. to remove the attached water from the slurry of the annealing separator on the steel sheet. As a heating device for removing water, there are methods such as radiant tube heating, induction heating, direct heating, resistance heating, far infrared heating, and microwave heating, and any device may be used.

 Next, finish annealing is performed.

The finish annealing is not performed in a coil shape from the beginning to the end as in the conventional case, but is performed by rolling a grain-oriented silicon steel sheet from a coil and annealing it while passing it in a plate in an annealing furnace. It is characterized in that the coiling and annealing is performed in combination in the same furnace. Hereinafter, the features of finish annealing will be described in detail with reference to the drawings.

First, the coil 1 is loaded into the annealing apparatus shown in FIG. 1, and the coil 1 is rolled up from the reel 2 in the form of a strip (strip) to the reel 3 and heated, and then the coil 1 is placed on the steel plate. Water of crystallization is removed from the applied annealing separator magnesium hydroxide. This removal reaction is carried out at about 380 ° C to about 500 ° C according to the reaction formula of Mg (OH) ₂ → MgO + H ₂ O, but since it is a plate-like plate, the removal of crystal water is complete and It is made uniform over the entire width and length of the steel plate.

In the annealing apparatus of FIG. 1, reference numeral 4 is an intermediate furnace wall, which is useful for dividing the inside of the furnace and facilitating atmosphere control, temperature control, and the like. The reels 2 and 3 are connected to a rotation driving device (not shown). The atmosphere gas supply device 5 is provided in each zone and supplies a desired gas such as H ₂ , N ₂ or Ar into the furnace.

After the removal of water of crystallization is achieved, a heating action is further applied to the strip,
When heated above 850 ° C, the generation of nuclei that are the source of secondary recrystallization occurs. Also in this case, the steel sheet is uniformly heated over the entire width and the entire length without causing temperature deviation, and the atmosphere gas supply device 5 and the intermediate furnace wall 4 are used to make the gas of the atmosphere in the furnace in contact with the steel sheet. Since the composition such as the mixing ratio of N ₂ and H ₂ and the dew point can be controlled arbitrarily according to the temperature, the production of secondary recrystallization nuclei is stabilized in combination with the good contact between the steel sheet and the atmosphere, and The degree of orientation integration can be made extremely high. For example, when heated to 950 ° C, nuclei of secondary recrystallization occur everywhere on the steel sheet, and above that temperature secondary recrystallization starts, but only the (110) plane and the Goss orientation of the (001) axis In order to preferentially grow the N ₂ gas, the atmosphere gas is limited to N ₂ gas, and N is strengthened as an inhibitor in the steel sheet from the N ₂ gas in the vapor phase, so that a grain-oriented silicon steel sheet with extremely uniform orientation can be obtained. As described above, since the atmosphere gas can be accurately controlled according to the temperature, annealing by passing a sheet greatly contributes to improvement and stabilization of magnetic characteristics.

Next, the secondary recrystallization is performed. This is done in the process of heating the steel sheet, for example, from 980 ° C to 1050 ° C. This process is also possible in the strip state, but since it takes a long time, for example, 1 to 2 hours, after the nuclei of secondary recrystallization are expressed,
It is desirable to wind the reel 3 into a coil and process the coil.

During the finish annealing, a forsterite film is formed concurrently with the occurrence of secondary recrystallization. The formation of a forsterite film is performed by a reaction between an oxide layer containing SiO ₂ on the surface of a steel sheet and an annealing separating agent containing MgO as a main component, as is well known. This reaction starts, for example, near 1000 ° C. and the dew point of the atmospheric gas is 10 to
Since the reaction can be promoted in the range of −20 ° C., when the steel plate is rewound into a coil shape on the reel 3, H ₂ O content is supplied so that the dew point of the atmosphere becomes a desired value. The present invention has a great advantage that such control of the atmospheric conditions can be performed accurately and uniformly over the entire width and length of the steel sheet.

It takes a relatively long time to form the forsterite film and to remove impurities in the steel sheet, so that it is preferable to perform the purification in a coil state. In this case, the atmosphere gas is H ₂
It is preferable to increase the amount of H ₂ or only H ₂ gas.

As described above, according to the present invention, in order to perform the final finish annealing by combining the processing in the coil shape while passing the steel sheet in the plate shape, the temperature and the atmosphere are required to be metallurgically required. Since it can be arbitrarily made, it is possible to obtain a grain-oriented silicon steel sheet having excellent magnetic properties and a uniform insulating film over the entire width and length of the steel sheet.

〔Example〕

 Next, examples of the present invention will be described.

A slab containing Si3.2%, S0.02%, Mn0.07%, AlN0.028%, N0.009% was hot-rolled to a thickness of 3 mm and annealed at 1120 ° C for 3 minutes. Then, it was cold rolled to a final thickness of 0.3 mm. Next, continuous decarburization annealing was performed at 850 ° C. for 3 minutes in an atmosphere consisting of dew point 40 ° C. and H ₂ 50%, and then this grain-oriented silicon steel sheet was coated with a slurry annealing separator by a roll coater. Next, the steel sheet coated with the annealing separator was heated in a drying furnace until the steel sheet temperature reached 200 ° C. to remove attached water, and was wound into a coil. Weight of solid after removing water is 8g / m
It was ² (one side). Then, put it into the final annealing furnace, pass the steel plate through the coil while unwinding the coil from the reel 60
The mixture was heated to 0 ° C. to remove the water of crystallization of magnesium hydroxide in the annealing separator. The atmosphere was H ₂ 75%, N ₂ 25%, and the dew point was 5 ° C. Subsequently, the strip was heated to 950 ° C to develop secondary recrystallization nuclei, and the atmosphere gas was set to N ₂ in the furnace at 950 ° C or less. Next, the steel plate is wound into a coil on a reel 3 and heated to 1000 ° C. to cause secondary recrystallization, and the atmosphere gas is switched to H ₂ + N ₂ to humidify the dew point.
The temperature was raised to 10 ° C to form a film of forsterite. Furnace temperature
The temperature was set to 1100 ° C and the coil was soaked for 10 hours. After that, the atmosphere gas was supplied to H ₂ gas alone and annealed at 1100 ° C. for 40 hours to remove N and S, which are harmful components, from the steel sheet. The characteristics of the front end portion, the middle portion, and the rear end portion of the coil of the grain-oriented silicon steel sheet after annealing were investigated and averaged to obtain the results shown in Table 1. In the comparison method, finish annealing was performed in the conventional coil shape.

[Effects of the Invention] As can be seen from these results, according to the present invention, the magnetic flux density B ₁₀ and the iron loss W _17/50 are excellent, the forsterite film has excellent adhesion, and there is no defect and the appearance is good. That is, a grain-oriented silicon steel sheet having excellent magnetic characteristics and coating characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus for performing finish annealing of the present invention. 1 ... coil, 2 ... reel, 3 ... reel, 5 ... atmosphere gas supply device.

Claims (1)

[Claims] 1. A grain-oriented silicon steel sheet is cold-rolled to a predetermined thickness and decarburized and annealed to form an oxide layer containing SiO ₂ on the surface of the steel sheet.
When applying an annealing separator having a magnesia oxide as a main component to the steel sheet and performing finish annealing, the grain-oriented silicon steel sheet is rolled off from a coil and annealed while passing in a plate shape, and A finish annealing method for a grain-oriented silicon steel sheet, characterized in that the steel sheets are wound in a coil shape and annealed in a coil shape in combination in the same furnace.