CN116855877A - Method for controlling oxidation product proportion of Hi-B steel decarburization annealing plate - Google Patents

Abstract

The invention discloses a method for controlling the proportion of oxidation products of a decarburization annealing plate of Hi-B steel, which establishes a relation between the dew point temperature of a decarburization annealing process and the proportion of the oxidation products through the hydrogen-water partial pressure ratio, and realizes the control of the proportion of the oxidation products of the decarburization annealing plate through the control of the dew point temperature of the decarburization annealing. The dew point temperature and the proportion of oxidation products are related by the following relation: dew point temperature and partial pressure ratio P _H2O /P _H2 A relationship between; oxygen content and partial pressure ratio P at decarburization annealing temperature _H2O /P _H2 A relationship between; oxygen contentAnd oxidation product Fe ₂ SiO ₄ And SiO ₂ Relationship between them. The invention realizes the corresponding relation between the decarburization annealing dew point temperature and the proportion of oxidation products, so that the abstract oxide layer becomes more visual; changing the control of the decarburization annealing oxidation product ratio from qualitative to quantitative; laying foundation for forming good glass film bottom layer.

Description

A method to control the proportion of oxidation products in Hi-B steel decarburized annealed plates

Technical field

The invention belongs to the technical field of cold-rolled oriented silicon steel, and in particular relates to a method for controlling the proportion of oxidation products of Hi-B steel decarburized annealed plates.

Background technique

Oriented silicon steel has an extremely strong Gaussian texture {110}<001>, that is, the <001> direction of almost all grains is parallel to the rolling direction of the strip, and the {110} crystal plane is parallel to the rolling surface, so it has Best magnetization properties. It is used to make the core of a transformer. Under the working conditions of a directional magnetic field, its extremely high magnetic induction and extremely low iron loss can significantly save materials and electrical energy. Oriented silicon steel is generally divided into two types: ordinary oriented silicon steel (CGO steel) and high magnetic induction oriented silicon steel (Hi-B steel). The oriented silicon steel produced by two cold rolling methods is ordinary oriented silicon steel, and the high magnetic induction steel produced by one cold rolling method. Inductively oriented silicon steel is called Hi-B steel. Before decarburization annealing, CGO steel generally contains 0.03% to 0.05% C. Different from CGO steel, the mass fraction of C in Hi-B steel is around 0.06% to 0.075%.

Before decarburization and annealing of grain-oriented silicon steel, a certain carbon content can ensure that 10% to 25% austenite appears in the strip during hot rolling. The existence of the two-phase structure of ferrite and austenite can cause crystallization during hot rolling deformation. The particles are small and uniform, and the appearance of austenite structure is conducive to the dissolution of the inhibitor A1N. If the carbon content in the steel matrix is too low, the grains will grow significantly during high-temperature heating, and the structure after hot rolling will become very coarse and extremely uneven. After C has completed its role in ensuring that the hot-rolled structure is fine and uniform, it is necessary to remove excess carbon through decarburization annealing to decarburize the C in the steel to less than 30 ppm to ensure that it is in a single ferrite during high-temperature annealing in the future. phase, develop a perfect secondary recrystallization structure and remove S and N in the steel, eliminating the magnetic aging of the product.

During decarburization and annealing, the Fe element on the surface of the steel strip will oxidize with water vapor to form FeO, but the oxidizing ability of water vapor is not enough to directly oxidize the Fe element into Fe ₂ O ₃ . In addition to the oxidation of C and Fe, the Si element on the surface of the steel strip is more easily oxidized by water vapor to form dense SiO ₂ . The generated SiO ₂ particles and FeO synthesize fayalite 2FeO·SiO ₂ . After the decarburization annealing process is completed, an oxide layer mainly composed of SiO ₂ , FeO, 2FeO·SiO ₂ , etc. will be formed on the surface of the steel strip. This oxide layer is the matrix for the subsequent process to generate a magnesium silicate glass film. When Fe ₂ SiO4/SiO ₂ =0.16~0.68, the quality of the bottom layer formed is good. During purification annealing, the sulfur in the steel will not enter the oxide film prematurely, maintaining strong inhibition and good magnetism. When the content of Fe ₂ SiO ₄ in the oxide film is too high and the content of SiO ₂ is low, the thickness of the underlying layer formed will be uneven and point-like exposed substrate defects will easily occur. However, if the content of Fe ₂ SiO ₄ is too small, the underlying layer formed will be uneven and due to oxidation. The total oxygen content in the film is too low, and the adhesion of the bottom layer deteriorates.

Contents of the invention

The purpose of the present invention is to provide a method for controlling the proportion of oxidation products in a Hi-B steel decarburization annealed plate. By controlling the decarburization annealing dew point temperature, it is ensured that the oxides Fe ₂ SiO ₄ and SiO in the oxide layer formed by the decarburization annealing are The composition ratio of ₂ lays the foundation for forming a good bottom layer of magnesium silicate glass film, improves the point-like exposed substrate defects of the finished oriented silicon steel plate, and improves the surface quality.

In order to achieve the purpose of the invention, the technical solutions adopted by the present invention are as follows:

A method for controlling the proportion of oxidation products in decarburized annealed plates of Hi-B steel. The relationship between the decarburization annealing process dew point temperature and the proportion of oxidation products is established through the hydrogen water pressure ratio. By controlling the decarburization annealing dew point temperature, it is achieved To control the proportion of oxidation products of the decarburization annealing plate, the dew point temperature and the proportion of oxidation products are connected through the following relationship;

1) The relationship between dew point temperature and partial pressure ratio P _H2O /P _H2 .

2) At the decarburization annealing temperature, the relationship between the oxygen content and the partial pressure ratio P _H2O /P _H2 ; the relationship between the oxygen content and the oxidation products Fe ₂ SiO ₄ and SiO ₂ .

Further, the mass percentages of the chemical components of the Hi-B steel are as follows: C: 0.043% to 0.073%, Si: 2.60% to 3.80%, Mn: 0.0018% to 0.0180%, S: 0.002% to 0.009%, P: 0.0023% to 0.0180%, Als: 0.009% to 0.0750%, N: 0.0023% to 0.0100%, and the rest is Fe and inevitable impurities.

Further, the ratio of Fe ₂ SiO ₄ /SiO ₂ in the decarburized annealed plate is controlled between 0.16 and 0.68.

Further, the decarburization annealing atmosphere of the cold-rolled plate is: wet 75% H ₂ + 25% N ₂ with a humidification tank temperature ranging from 30 to 80°C; the decarburization annealing temperature is: 830 to 850°C; the decarburization annealing time For: 2~3min.

Further, decarburization annealing and nitriding treatment are carried out on the same continuous furnace production line. The nitriding process is: carried out in a 75% H ₂ + N ₂ atmosphere containing 2% to 15% dry NH ₃ at 700 to 810°C. Nitriding treatment for 10 to 50 seconds. The decarburized annealed plate is coated with MgO release agent after nitriding annealing.

Beneficial effects of the present invention:

(1) Controlling the oxide layer through decarburization annealing dew point temperature is simple and easy to operate;

(2) The corresponding relationship between the decarburization annealing dew point temperature and the proportion of oxidation products is realized, making the abstract oxide layer more intuitive;

(3) Through calculation, the control of the proportion of decarburization annealing and oxidation products is changed from qualitative to quantitative;

(4) Precise control of the oxide layer lays the foundation for the formation of a good bottom layer of glass film;

(5) Effectively reduce the number of point-like exposed substrate defects.

Description of the drawings

Figure 1 shows the relationship between dew point temperature and partial pressure ratio P _H2O /P _H2 ;

Figure 2 shows the relationship between oxygen content and partial pressure ratio P _H2O /P _H2 at 850°C;

Figure 3 shows the relationship between the oxygen content at 850°C and the oxidation products Fe ₂ SiO ₄ and SiO ₂ .

Detailed ways

It should be noted that, as long as there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The described embodiments are only some of the embodiments of the present invention, but not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application or uses. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

1. The process of producing oriented silicon steel using the control method of the present invention

1. Composition and preliminary process

(1)Ingredients

The mass percentages of Hi-B steel elements are shown in Table 1 below, and the rest are Fe and impurities.

Table 1 Mass percentage of Hi-B steel elements, wt%

(2) Technology

Cold-rolled plates with a thickness of 0.27mm are made using smelting, continuous casting, hot rolling, normalization and one-time cold rolling processes.

2. Decarburization annealing process and oxide ratio control in the oxide layer.

(1) Decarburization annealing process

The decarburization annealing atmosphere of the cold-rolled plate is: wet 75% H ₂ + 25% N ₂ with a humidification tank temperature range of 40 to 70°C; the decarburization annealing temperature is: 850°C; the decarburization annealing time is: 2.5 minutes.

(2) Control the oxide layer structure of the decarburization plate

In order to find the relationship between the dew point temperature and the proportion of oxidation products, the following Thermo-Calc thermodynamic calculation is performed:

1) The relationship between the dew point temperature and the partial pressure ratio P _H2O /P _H2 . The calculation results are shown in Figure 1.

2) The relationship between oxygen content and partial pressure ratio P _H2O /P _H2 at 850°C. The calculation results are shown in Figure 2;

3) The relationship between oxygen content and oxidation products Fe ₂ SiO ₄ and SiO ₂ at 850°C. The calculation results are shown in Figure 3.

By controlling the dew point temperature, the proportion of oxidation products can be controlled. The ratio of Fe ₂ SiO ₄ /SiO ₂ in the decarburized annealed plate is controlled between 0.16 and 0.68, which can form a good magnesium silicate bottom layer and reduce the point-like exposure of the substrate in the finished plate. defect.

(3) Nitriding and coating with MgO release agent

Decarburization annealing and nitriding treatment are carried out on the same continuous furnace production line. The nitriding process is: nitriding treatment for 30 seconds at 770°C in a 75% H ₂ + N ₂ atmosphere containing 6% NH ₃ dry. The decarburized annealed plate is coated with MgO release agent after nitriding annealing.

3. High temperature annealing and subsequent processes

After high-temperature annealing, apply an insulating coating on the hot drawing flat annealing line to make the finished product, and detect point-like substrate defects on the surface of the finished board.

2. Comparison between Examples and Comparative Examples of the Method for Controlling the Ratio of Oxidation Products of the Invention

By comparing the proportions, the proportion of oxidation products corresponding to the decarburization annealing dew point temperature is compared, and the impact on point-like exposed substrate defects. The comparison results between Examples and Comparative Examples are shown in Table 2.

Table 2 Comparison between Examples and Comparative Examples

From the comparison in Table 2, it can be seen that the method of the present invention can control the ratio of Fe ₂ SiO ₄ and SiO ₂ generated by decarburization annealing, lay the foundation for the formation of a good magnesium silicate bottom layer, and can effectively reduce spot dew. Proportion of substrate defects.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, but not to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features can be equivalently replaced; and these modifications or substitutions do not deviate from the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention. scope.

Claims (5)

1. A method for controlling the proportion of oxidation products of a decarburization annealing plate of Hi-B steel, which is characterized in that the relation between the dew point temperature of a decarburization annealing process and the proportion of the oxidation products is established through the hydrogen-water partial pressure ratio, the control of the proportion of the oxidation products of the decarburization annealing plate is realized through the control of the dew point temperature of the decarburization annealing, and the relation between the dew point temperature and the proportion of the oxidation products is established through the following relation;

1) Dew point temperature and partial pressure ratio P _H2O /P _H2 A relationship between;

2) Oxygen content and partial pressure ratio P at decarburization annealing temperature _H2O /P _H2 A relationship between; oxygen content and oxidation product Fe ₂ SiO ₄ And SiO ₂ Relationship between them.

2. The method for controlling the oxidation product proportion of a Hi-B steel decarburization annealed sheet according to claim 1, wherein the Hi-B steel comprises the following chemical components in percentage by mass: c:0.043% -0.073%, si:2.60 to 3.80 percent of Mn:0.0018 to 0.0180 percent, S:0.002% -0.009%, P:0.0023% -0.0180%, als:0.009% -0.0750%, N:0.0023 to 0.0100 percent, and the balance of Fe and unavoidable impurities.

3. A method for controlling the oxidation product ratio of a decarburized annealed Hi-B steel sheet according to claim 1, wherein Fe is contained in the decarburized annealed sheet ₂ SiO ₄ /SiO ₂ The ratio of (2) is controlled to be 0.16-0.68.

4. The method for controlling the oxidation product ratio of a decarburization annealed sheet of Hi-B steel according to claim 1, wherein the decarburization annealing atmosphere of the cold rolled sheet is: wet 75% H with a humidifying tank temperature in the range of 30-80 DEG C ₂ +25％N ₂ The method comprises the steps of carrying out a first treatment on the surface of the The decarburization annealing temperature is: 830-850 ℃; the decarburization annealing time is: 2-3 min.

5. The method for controlling the oxidation product ratio of a decarburized annealed Hi-B steel sheet according to claim 1, wherein the decarburization annealing and the nitriding treatment are carried out in the same continuous furnace line, and the nitriding process comprises: contains 2 to 15 percent of NH ₃ Dry 75% H ₂ +N ₂ Nitriding treatment is carried out for 10-50 seconds at 700-810 ℃ in the atmosphere; the decarburization annealed sheet is nitrided and annealed and then coated with a MgO separating agent.