JPH04337033A - Method for controlling additive quantity of oxygen in grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To obtain a steel sheet having superior external appearance characteristics and excellent in magnetic properties by regulating, at last, one of a steel-sheet temp. and atmospheric dew point in a furnace and regulating the additive quantity of oxygen in a steel sheet to a value showing the prescribed emissivity at the time of applying decarburizing annealing to a grain- oriented silicon steel sheet. CONSTITUTION:A grain-oriented silicon steel sheet is subjected to decarburizing annealing or to nitriding successively to decarburizing. In this decarburizing annealing method, the relationship between the radiant quantity in the steel sheet and the additive quantity of oxygen in the steel sheet is previously determined, and the emissivity of the steel sheet for attaining the prescribed oxygen quantity is determined. Then, at least, one of the temp. of the steel sheet and atmospheric dew point in a furnace is regulated, by which the emissivity for attaining the prescribed oxygen quantity is obtained. By this method, the additive quantity of oxygen in the steel sheet can be constantly secured, and the steel sheet excellent in external appearance characteristics and magnetic properties can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the amount of oxygen added during decarburization annealing in which a grain-oriented electrical steel sheet is decarburized or subsequently nitrided to form an inhibitor.

0002

[Prior Art] Grain-oriented electrical steel sheets are mainly used for transformers,
It is used as an iron core material for electrical equipment such as generators, and it is important that it has good magnetic excitation characteristics and iron loss characteristics. Normally, grain-oriented electrical steel sheets are produced by hot-rolling a silicon steel slab containing 2 to 4% Si, annealing the hot-rolled sheet if necessary, and then cold-rolling it once or twice or more with an intermediate annealing in between. A cold-rolled sheet with the final thickness was obtained, and then decarburized annealed, an annealing separator containing MgO as the main component was applied, and final annealing was performed to produce secondary recrystallized grains with Goss orientation. It is produced by developing the glass, removing impurities such as S and N, and forming a glass film. Furthermore, flattening annealing and insulation coating treatment are performed as necessary.

[0003] In order for secondary recrystallization to occur during final annealing, it is necessary to have a fine inhibitor such as AlN, MnS, MnSe, etc. that suppresses the growth of primary recrystallized grains up to the secondary recrystallization temperature range. It has been known. By the way, in the manufacturing process of grain-oriented electrical steel sheets, for example, 0.02 to 1.00% of C is contained in order to control the crystal structure of the steel, but the C present in the product does not affect the magnetic properties. To avoid deterioration, decarburization annealing is performed after cold rolling to the final thickness.

[0004] Although the main purpose of decarburization annealing is to remove C as described above, in this annealing, C is further incidentally used to form a glass film by reaction with the annealing separator MgO in the subsequent final annealing. An oxide film containing SiO2 is formed on the surface of the steel sheet, and primary recrystallization also occurs. Normally, in decarburization annealing, a humid atmosphere gas containing H2 is used, and the formula (1)
, (2), decarburization and oxygen addition are performed.

[0005] H2O +C→H2 +CO2 (1)H
2O +M→MO+H2 (2) However, M: Metal decarburization and oxygen addition are important factors that determine the magnetic properties and coating quality of grain-oriented electrode steel sheets. As shown in the publication, the amount of decarburization and the amount of oxygen added were controlled by the degree of oxidation of the atmospheric gas.

[0006]

[Problems to be Solved by the Invention] On the other hand, oxygen addition is easily affected by the surface properties of the steel sheet such as roughness and dirt due to surface reactions, and even if the atmospheric gas composition on the supply side is kept constant, decarburization cannot be achieved. In some cases, the amount of oxygen added after annealing was not constant. Thus, in decarburization annealing, it is not easy to control the amount of oxygen added. In view of these conventional problems, the present invention stabilizes grain-oriented electrical steel sheets with good glass coating and magnetic properties by adding a desired amount of oxygen during decarburization annealing or decarburization annealing that is followed by nitriding. The purpose is to obtain

[0007]

[Means for Solving the Problems] The gist of the present invention is to detect the emissivity of the steel plate and determine its value in advance in a decarburization annealing method in which a grain-oriented electrical steel sheet is decarburized or nitrided after decarburization. Find the emissivity of the steel plate to obtain the specified amount of oxygen by inserting it into the relationship between the emissivity of the steel plate and the amount of added oxygen, and then adjust the temperature of the steel plate or the dew point of the furnace atmosphere to obtain the emissivity. A method for controlling the amount of oxygen added to a grain-oriented electrical steel sheet, which comprises adjusting at least one of the elements.

[0008]

[Operation] The present invention will be explained in detail below. FIG. 1 shows a decarburization annealing furnace, in which a grain-oriented electrical steel sheet rolled to the final thickness is decarburized prior to final annealing. Reference numeral 1 denotes a decarburization and oxygen addition zone provided in the decarburization annealing furnace, into which a humid gas containing H2 is supplied through an atmosphere supply gas pipe 2. On the other hand, the steel plate 3 is introduced into the furnace through the sealing device 4, and the moisture in the humid gas reacts with the carbon in the steel plate, resulting in carbonation.
At the same time as O is generated and decarburized, the surface of the steel sheet is oxidized and S
An oxide layer containing iO2 is formed, providing the basis for the coating.

The present inventors have discovered that the amount of oxygen added during decarburization annealing is greatly influenced by the emissivity of the grain-oriented electrical steel sheet, and that there is a certain relationship between them. This will be explained with reference to an experimental example. Cold rolled to final plate thickness 0.25 mm C: 0.062%, Si: 3.0%, Mn: 0
．． 085%, S: 0.018%, Al: 0.02
6%, N: 0.0066% grain-oriented electrical steel sheet was used as a test material in the decarburization annealing furnace shown in Fig. 1 at a temperature of 830 to 850 °C.
The steel sheets were decarburized and annealed using wet H2 gas with a dew point of 55 to 70° C. while varying the emissivity. At this time, in the rear part 1-1 of the decarburization/oxygenation zone 1, the emissivity of the steel plate was detected using an emissivity meter 5, and a sample was sampled from the steel plate after decarburization and annealing to measure the amount of oxygen addition. FIG. 2 shows the relationship between the measured oxygen addition amount and the emissivity of the sample. As shown in this figure, it was found that the relationship between the emissivity of the steel plate and the amount of oxygen added after decarburization annealing is almost proportional, and it is possible to accurately estimate the amount of oxygen added by detecting the emissivity of the steel sheet. There was found.

[0010] Furthermore, the relationship between the emissivity of the steel sheet and the amount of oxygen added after decarburization annealing is such that the grain-oriented electrical steel sheet contains Sn, Cu,
Similarly, there is a nearly proportional relationship even in the case where elements such as Cr, B, Sb, and Mo are added. Furthermore, the emissivity of the steel plate can be changed by the dew point of the atmosphere during decarburization annealing and the temperature of the steel plate. For example, the emissivity can be lowered by increasing the dew point and lowering the steel plate temperature within the decarburization possible range.

[0011] The relationship between the emissivity of the steel plate and the amount of oxygen added after decarburization annealing is determined in advance and stored in the decarburization annealing control device 10, so that the radiation detected by the emissivity meter 5 during decarburization annealing is The rate is input into the controller 10 and inserted into the stored relationship to estimate the amount of oxygen added. This estimated oxygen addition amount and the target oxygen addition amount of the grain-oriented electrical steel sheet are compared by the control device 10, and if there is a deviation, the dew point or heating of the atmospheric gas passed through the atmosphere supply gas pipe 2 is adjusted to eliminate the deviation. The temperature of the steel plate is changed by controlling the device 9. As a result, the target oxygen addition amount can always be obtained, and a grain-oriented electrical steel sheet with good coating appearance and excellent magnetic properties can be obtained.

The present invention can also be applied to cases in which decarburization and oxygen addition are performed in a decarburization annealing furnace that is also equipped with nitriding treatment subsequent to decarburization annealing. After the decarburization treatment, an annealing separator containing MgO as a main component was applied using a coating device 6, and after drying in a drying oven 7, the coil was wound up 8 and final annealed. the result,
A grain-oriented electrical steel sheet with good coating appearance and excellent magnetic properties was obtained.

[0013]

[Example] A slab having the composition and structure shown in Table 1 was heated under the conditions shown in the table and hot-rolled to a thickness of 1.6 mm, and this hot-rolled plate was cold-rolled to a thickness of 0.23 mm. And so.

[0014]

[Table 1]

Next, the cold-rolled plate is inserted into a decarburization annealing furnace, and
Under an atmosphere consisting of 75% H2 and 25% N2 15
Decarburization was performed for 5 seconds. During decarburization annealing, the emissivity of the steel plate is detected, and the detected value is applied to the pre-memorized relationship between the emissivity of the steel plate and the amount of oxygen added, and the dew point and plate are adjusted so that the desired amount of oxygen is added. Annealing was performed by adjusting the temperature. Next, the material (sample Nos. 5 to 9) heated to a low temperature slab was heated to 750°C x 3
Nitriding treatment was performed using NH3 for 0 seconds in an atmosphere of 75% H2, 25% N2, and a dew point of -10°C. Next, an annealing separator containing MgO as a main component was applied to the steel plate, and final annealing was performed at 1200°C for 20 hours. The magnetic properties and coating properties of the obtained grain-oriented electrical steel sheet were measured, and the results are shown in Table 2.
Shown below.

[0016]

[Table 2]

[0017] In the examples of the present invention, as shown in Tables 1 and 2, the amount of added oxygen could be kept approximately constant, and as a result, good surface properties could be obtained.

[0018]

As described above, according to the present invention, it is possible to stably obtain a grain-oriented electrical steel sheet having a good coating appearance and excellent magnetic properties.

[Brief explanation of drawings]

FIG. 1 is a schematic partial sectional view showing an example of equipment for carrying out the method of the present invention.

FIG. 2 is a diagram showing the relationship between the emissivity of the steel plate in the decarburization completion zone and the amount of added oxygen.

[Explanation of symbols]

1...Decarburization/oxygenation zone 2...Atmosphere supply gas pipe 3...Steel plate 4...Sealing device 5...Emissivity meter 6...Coating device 7...Drying oven 8... Winder 9...Heating device 10...Control device

Claims (1)

[Claims] [Claim 1] In a decarburization annealing method in which a grain-oriented electrical steel sheet is decarburized or nitrided after decarburization, the emissivity of the steel sheet is detected, and the emissivity and oxygen addition amount of the steel sheet are determined in advance. The method is characterized in that the emissivity of the steel plate to obtain a predetermined amount of oxygen is determined by inserting it into the relationship between Method for controlling the amount of oxygen added to grain-oriented electrical steel sheets.