JPH04218622A - Production of grain-oriented silicon steel sheet excellent in magnetic property and adhesive strength of film - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel sheet excellent in magnetic properties and adhesive strength of film by regulating the furnace atmosphere in the course of temp. rise to a nonoxidizing atmosphere at the time of applying decarburizing annealing to a silicon-containing steel stock. CONSTITUTION:A silicon-containing steel stock of about 3.28% Si content is hot-rolled, and the resulting plate is cold-rolled once or is cold-rolled twice or more while process- annealed between the cold rolling stages so as to be formed to the final sheet thickness. Subsequently, the resulting cold rolled steel sheet is subjected to decarburizing annealing and further to finish annealing. At this time, in the above decarburizing annealing, the furnace atmosphere in the course of temp. rise until a decarburizing soaking temp. of about 750-900 deg.C is reached is regulated to nonoxidizing atmosphere. As the above atmosphere, a dry gas, such as Ar, He, N2, and H2, is used. In the course of soaking after temp. rise, the atmosphere is regulated to wet-gas atmosphere. By this method, the grain-oriented silicon steel sheet improved in iron loss and magnetic flux density and excellent in adhesive strength of film, external appearance, and space factor can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for producing grain-oriented electrical steel sheets with excellent magnetic properties and coating properties.

0002

[Prior Art] Grain-oriented electrical steel sheets are mainly used as cores of transformers, and as core materials, they have low electromagnetic core loss.
In addition, it is required to have high magnetic flux density and interlayer resistance, and mechanically, it must have a high space factor and good adhesion of the insulating film.

[0003] This method for producing grain-oriented electrical steel sheets uses an inhibitor necessary for secondary recrystallization, such as MnS, MnSe
, After heating and hot rolling a grain-oriented electrical steel slab containing AlN, etc., annealing is performed as necessary, and cold rolling is performed once or twice or more with intermediate annealing in between to form a final product board. After thickening and then decarburizing annealing, the steel plate is coated with MgO.
It is manufactured by applying an annealing separator such as, and then performing final annealing. In this process, the purpose of decarburization annealing is to give the steel plate 0.01
0 to 0.100% The amount of C contained is 0.003%
To improve the magnetic properties to the following extent, to properly primary recrystallize the cold-rolled steel sheet, and to cause appropriate secondary recrystallization in the subsequent final annealing, and to add SiO2, etc. to the surface layer of the steel sheet. It is to generate an oxide film which is the main component. This oxide film reacts with MgO, an annealing separator, in the final annealing process as shown in the following formula: SiO2+2MgO→Mg2SiO4 to form a forsterite film (Mg2SiO4).

[0004] This forsterite coating is usually used together with an overcoat such as phosphate coated on top of this coating to improve the electrical insulation of the steel sheet and to provide tension to the steel sheet to improve its magnetic properties. It has a certain effect. The forsterite coating must have good adhesion to the steel plate and be thin and uniform; otherwise, the coating may peel off when the steel plate is bent or cut, and the magnetic properties and space factor may deteriorate. do. As mentioned earlier, the forsterite film is formed by the reaction between the oxide film such as SiO2 produced during the decarburization annealing process and the annealing separator MgO, so the properties of the forsterite film depend on the annealing separator. In addition to the characteristics, it is greatly influenced by the properties of the oxide film produced during decarburization annealing. In other words, the decarburization annealing process has an important meaning in forming a good forsterite film.

[0005] The decarburization process is carried out at a soaking temperature of 750 to 900°C in a wet mixed gas atmosphere mainly containing H2 and N2, that is, in an oxidizing atmosphere. Conventional techniques include, for example, a method of controlling the dew point of the annealing atmosphere to 50 to 75°C as disclosed in JP-A-59-185725, and a method disclosed in JP-A-54-160514.
The degree of oxidation P (PH2
A known method is to set O)/P(H2) to 0.15 or more in the first half of decarburization and to 0.75 or less in the second half and lower than the first half.

[0006]

[Problems to be Solved by the Invention] However, as mentioned above, even if the degree of oxidation of the oxidizing atmosphere is controlled, it is not always possible to produce a forsterite film with sufficiently satisfactory electromagnetic and mechanical properties. There wasn't.

[0007]

[Means for Solving the Problems] The present invention is based on the prior art, in which annealing was performed in the above-mentioned oxidizing atmosphere during the temperature raising process of decarburization annealing, and an oxide film was formed on the surface of the steel sheet even during the temperature raising process. This was developed as a result of intensive research from the viewpoint that the oxide film produced at this time has a negative effect on the formation of a high-quality forsterite film, and it has been developed to make the atmosphere in the furnace non-oxidizing during the heating process during decarburization annealing. This is based on the new knowledge that by doing so, it is possible to obtain a grain-oriented electrical steel sheet with excellent magnetic properties, adhesion, etc., which has never existed before.

[0008] That is, the present invention uses a silicon-containing steel material,
Unidirectional silicon is produced through a series of steps of hot rolling, then cold rolling once or twice or more including intermediate annealing to obtain the final thickness, decarburizing annealing, and final annealing. This is a method for producing grain-oriented electrical steel sheets with excellent magnetic properties and film adhesion, which involves making the furnace atmosphere non-oxidizing during the temperature raising process during decarburization annealing.

[0009] Below, the experimental results that led to this invention will be explained. Conventional decarburization annealing technology
During the heating process up to the decarburization soaking temperature of 750 to 900 °C, the oxidation degree P(PH2O)/P(H2) is approximately 0.10.
It was annealed in an oxidizing atmosphere of ~0.80. This temperature raising process took about 30 seconds to 5 minutes, and therefore the steel plate was oxidized even during this time. Such a steel plate surface oxide film that is formed at a temperature lower than the decarburization soaking temperature not only inhibits decarburization during soaking during decarburization annealing, but also has a negative effect on the oxide film after decarburization annealing. The experiment was conducted based on the assumption that this would be the case. As a result, compared to the conventional annealing method where annealing is performed in an oxidizing atmosphere from the temperature raising stage, annealing in a non-oxidizing atmosphere during the temperature raising stage not only improves iron loss and magnetic flux density, but also improves the coating. It has been newly discovered that adhesion, appearance, and even space factor are improved.

0010

[Operation] The following may be the reason why the properties are improved by making the heating process non-oxidizing. In other words, when annealing is performed in an oxidizing atmosphere from the heating process as in the conventional method, an oxide film is generated even during the heating process at a temperature lower than the soaking temperature. It is thought that the coating has a negative effect on forsterite formation and magnetic properties. On the other hand, if the heating process is performed in a non-oxidizing atmosphere as in the method of this invention, an oxide film different from that of the conventional method is formed, and this is thought to have a favorable effect on the magnetic properties and film properties.

[0011] The steel plate subjected to decarburization annealing of the present invention is
A slab of electrical steel sheet containing inhibitors such as MnS, MnSe, AlN, etc. is hot-rolled, annealed as necessary, and then cold-rolled once or twice or more including intermediate annealing to reduce the thickness of the final product. When this steel plate is decarburized and annealed, the temperature is raised in a non-oxidizing atmosphere.

Specifically, an inert gas such as Ar or Ne, a neutral gas such as N2, or a reducing gas such as H2 is used. Since these gases may contain moisture, it is necessary to use sufficiently dry dry gases. After the steel plate is heated, it is soaked, and the soaking temperature may be a normal decarburization annealing temperature. The atmosphere during soaking is usually a humid gas such as H2 or H2+N2, and the oxidation degree is P(PH2O)/P(
H2) may have an oxidation degree of about 0.10 to 0.80, but the oxidation degree in the second half of soaking may be lower than this. Furthermore, even if a part of the first half of the soaking is non-oxidizing after the temperature raising process, the effects of the present invention can be recognized as long as the decarburization effect is not hindered. When changing the annealing atmosphere between the temperature raising process and the soaking process, there is a method, for example, of installing a partition plate or the like in the furnace to prevent mixing of atmospheric gases. The cooling process after soaking may be carried out by any known method since the film formation has already been completed. After the decarburization annealing, an annealing separator containing MgO 2 as a main component is applied, followed by final annealing at about 1200° C., and a top coating is applied as necessary to produce a product.

[0013]

[Example] Example 1 C: 0.040%, Si: 3.28%, Mn: 0
．． 070%, Se: 0.020% and Sb: 0
．． After hot rolling, a grain-oriented electrical steel sheet material containing 0.025% was cold-rolled twice with intermediate annealing at 975° C. for 2 minutes to a final sheet thickness of 0.23 mm. This steel plate was then subjected to decarburization annealing under the conditions described below. Condition A: The temperature was raised from room temperature to 820°C in 50 seconds, then soaked at 820°C for 2 minutes, and then cooled. The annealing atmosphere was a wet mixed gas of 55% hydrogen and 45% nitrogen with a dew point of 60°C. Condition B: Temperature raising, soaking, and cooling are the same as condition A, and non-oxidizing N2 gas is used as the annealing atmosphere during the heating process, and after soaking, the humidity is 55% hydrogen and 45% nitrogen with a dew point of 60°C. A mixed gas was used.

[0014] Next, these decarburized annealed plates were coated with an annealing separator mainly composed of MgO, and then subjected to final annealing at 1200°C, and then a top coating mainly composed of phosphate and colloidal silica was applied. It was made into a product. The thus obtained product had an iron loss W of 17/50 at 1.7 T and 50 Hz, and a magnetic flux density B of the magnetic field of 800 A/m.
8. Table 1 shows the results of an investigation regarding the bending adhesion of the coating, the space factor of the product, and the appearance of the coating. The bending adhesion of the coating was determined by winding an Epstein test piece around a round bar with a diameter of 10 to 50 mm (5 mm intervals) and determining the minimum diameter at which the coating did not peel off.

[0015]

As is clear from the same table, under condition B, in which non-oxidizing N2 gas was used in the temperature raising process of decarburization annealing, both magnetic flux density and iron loss were superior to conventional condition A, and the adhesion of the coating was improved. Condition B according to the present invention is also superior in terms of space factor. Regarding the appearance of the coating, in Condition A, which is the conventional method, some forsterite coating defects called bare spots, which are approximately 1 mm in diameter, were seen scattered on some steel plates, whereas in Condition B, a uniform forsterite coating was observed. Condition B was superior in terms of the appearance of the film.

Example 2 C: 0.071%, Si: 3.18%, Mn: 0
．． 08%, Se: 0.021%, Al: 0.02
The electromagnetic steel slab containing N: 5% and N: 0.008% was hot rolled and then cold rolled into a cold rolled plate with a final thickness of 0.23 mm. Next, this steel plate is subjected to the following conditions C,
Decarburization annealing was performed in step D. Condition C: Raise the temperature from room temperature to 850°C in 60 seconds, 8
The mixture was soaked at 50°C for 80 seconds, then at 870°C for 45 seconds, and then cooled. The atmosphere was 850℃, 80℃ from the start of temperature rise.
A wet mixed gas of 90% H2 and 10% N2 with a dew point of 70° C. was used until soaking for seconds. In the second half of soaking at 870°C for 45 seconds, a gas with the same gas composition but with a dew point lowered to 15°C was used. Condition D: Same as Condition C, but dry Ar gas was used for the temperature raising process.

[0018] These steel plates were then coated with an annealing separator containing MgO as the main component, and then subjected to final annealing at 1200°C, and the magnetic properties and coating properties were investigated in the same manner as in Example 1. The results are shown in Table 2. Shown below.

[0019]

As shown in Example 1, excellent magnetic properties and film properties were obtained under decarburization condition D in which a non-oxidizing atmosphere was used during the heating process.

[0021]

[Effects of the Invention] Thus, according to the present invention, magnetic properties,
It is now possible to manufacture grain-oriented electrical steel sheets with excellent coating properties.
When used as a transformer core, it can improve the efficiency of the transformer.

Claims (1)

[Claims] [Claim 1] A silicon-containing steel material is hot-rolled, then cold-rolled once or twice or more including intermediate annealing to obtain the final thickness, and then subjected to decarburization annealing and further finished. In manufacturing grain-oriented silicon steel sheets through a series of annealing processes, the furnace atmosphere during the temperature rising process during decarburization annealing is made non-oxidizing. A method for manufacturing grain-oriented electrical steel sheets.