Method for improving quality and consistency of oriented electrical steel glass film bottom layer

Abstract

The invention discloses a method for improving the quality and consistency of an oriented electrical steel glass film. The method comprises the following steps: controlling the temperature rise rate of decarburization, nitriding and annealing to be 200-400 DEG C / s; the partial pressure ratio P (H2O) / P (H2) of the decarburization nitriding annealing atmosphere is controlled to be 0.20-0.30; the oxygen content of decarburization, nitriding and annealing is controlled to be 500-800 ppm; the hydration rate of the magnesium oxide coating is controlled to be less than 2.0; and in the high-temperature annealing process, in the annealing temperature range of 700-1200 DEG C, the heating rate is controlled to be less than 8 DEG C / h or heat preservation treatment is carried out for more than 15 hours. Through the implementation of the method, the oriented electrical steel product glass film is compact, has no defects such as dot-shaped crystal leakage and the like, meanwhile, the uniformity is good, the quality of the head glass film, the middle glass film and the tail glass film is uniform and consistent in the length direction of the steel coil, the proportion of surface degraded products caused by the defects of the bottom layer of the glass film is reduced to 20% or below from existing 40% or above, and the quality and the uniformity of the glass film are obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology for grain-oriented electrical steel, and specifically relates to a method for improving the quality and consistency of the bottom layer of grain-oriented electrical steel glass film. Background Technology

[0002] Grain-oriented electrical steel is an important soft magnetic material, mainly used as transformer core material, and widely applied in power transmission and distribution industries such as transformers. It is typically prepared using secondary recrystallization. Although this product is a polycrystalline silicon steel sheet, its grain orientation and easy magnetization direction are aligned with the Miller index. <100> The product, like single-crystal silicon steel, possesses excellent magnetic properties.

[0003] The surface of grain-oriented electrical steel has a high-resistivity thin film, mainly used to prevent the transmission of eddy currents within the iron core between the electrical steel sections. It also helps reduce transformer energy consumption and protects electrical equipment. The film is mostly divided into inner and outer parts. The outer layer is an insulating coating, while the inner (bottom) layer is a glass film formed by the reaction of MgO with the oxides on the surface of the electrical steel. This reaction occurs during the high-temperature annealing process that leads to secondary recrystallization. The glass film is generally ≤2μm thick and mainly consists of magnesium olivine (Mg2SiO4) particles.

[0004] The quality of the glass film underlayer of grain-oriented electrical steel determines the surface quality of the steel. Because the outer insulating coating is applied during the stretching, leveling, and annealing process, the factors affecting its quality are relatively singular, resulting in a relatively stable coating quality. However, numerous factors influence the glass film underlayer, including surface oxides, magnesium oxide and additives, and the high-temperature annealing process. Furthermore, the glass film control process overlaps with the product's magnetic property control process. The decarburization and nitriding annealing process for controlling oxides also controls the initial recrystallization and increases nitrogen and carbon content, while the high-temperature annealing process for glass film formation controls secondary recrystallization. Therefore, glass film control is complex and has always been a challenging and hot topic in the control of grain-oriented electrical steel, leading to research focused on optimizing composition, adjusting the oxide layer, and preparing magnesium oxide and additives.

[0005] Chinese patents CN112522613A and CN103695620A disclose high-magnetic-induction oriented silicon steel with excellent underlying quality and its production method. The main method is to form a dense oxide layer on the surface of silicon steel by re-oxidation after decarburization annealing and nitriding treatment, thereby improving the surface quality of the product.

[0006] Japanese Patent Application Publication No. 59-226115 discloses that by adding 0.003-0.1 wt% of Mo to the composition, controlling the partial pressure ratio P(H2O) / P(H2) in the annealing atmosphere to 0.30-0.50, and controlling the (Fe2SiO4) / (SiO2) ratio in the oxide layer to 0.05-0.45, point defects in magnesium olivine films can be suppressed and surface quality improved.

[0007] Chinese patent CN106319174A discloses an annealing release agent for improving the quality of the underlayer of high-magnetic-induction oriented silicon steel heated at low temperatures, reducing glass film defects and improving adhesion and resistance. Japanese patent No. 54-14567 discloses adding Cu, Sn, Ni, Co, or their compounds to the release agent, while Japanese patent No. 60-243282 discloses adding TiO2, SnS, SrS, CuS, etc., to the release agent to improve glass film quality. Furthermore, Japanese patents Nos. 4-329829 and 4-329830 disclose adding Cr, Sb, or Cr, Sn, and Sb to the composition design, resulting in smaller fluctuations in the surface oxide layer and a stable underlayer and good surface quality in the final finished glass film.

[0008] In the industrial production of grain-oriented electrical steel, annealing is typically performed in coils within a ring furnace or bell furnace to complete secondary recrystallization, generate a glass film underlayer, and remove sulfur and nitrogen elements. This process generally takes more than 120 hours, resulting in poor uniformity of the coil, significant differences in performance between the beginning and end of the coil, and substantial variations in the quality of the glass film underlayer. Although Chinese patent CN108004376A discloses a method for producing low-temperature, high-magnetic-induction grain-oriented silicon steel with uniform longitudinal magnetic properties, thus improving the uniformity of the product's magnetic properties, research on improving the uniformity of the glass film underlayer has not yet been published. Summary of the Invention

[0009] To address the aforementioned technical problems in the prior art, this invention provides a method for improving the quality and consistency of the underlying layer of an oriented electrical steel glass film, comprising:

[0010] (1) The heating rate range for decarburization and nitriding annealing of oriented electrical steel is controlled within the range of 200-400℃ / s;

[0011] (2) The partial pressure ratio P(H2O) / P(H2) of the decarburizing and nitriding annealing atmosphere for oriented electrical steel is controlled within the range of 0.20-0.30;

[0012] (3) The oxygen content of the decarburized and nitrided annealed oriented electrical steel is controlled within the range of 500-800 ppm;

[0013] (4) The hydration rate of the magnesium oxide coating is controlled to be <2.0;

[0014] (5) In the high-temperature annealing process of oriented electrical steel, the heating rate is controlled to be <8℃ / h within the annealing temperature range of 700-1200℃; or, the heat preservation treatment is carried out for >15h within the annealing temperature range of 700-1200℃.

[0015] Preferably, in the above-mentioned method for improving the quality and consistency of grain-oriented electrical steel glass film, the heating rate range of decarburization and nitriding annealing of grain-oriented electrical steel is controlled within 200-320℃ / s; the oxygen content range of decarburization and nitriding annealing of grain-oriented electrical steel is controlled within 550-700ppm; the hydration rate of magnesium oxide coating is controlled within <1.7; and the heating rate of grain-oriented electrical steel during high-temperature annealing is controlled within the annealing temperature range of 700-1150℃ within the range of 700-1150℃ within the range of annealing temperature for >20h, or a heat preservation treatment is performed within the annealing temperature range of 700-1150℃ for >20h.

[0016] As an optional implementation, in the above method for improving the quality and consistency of grain-oriented electrical steel glass film, the heating rate range of decarburization and nitriding annealing of grain-oriented electrical steel is controlled to be 250-300℃ / s.

[0017] As an optional implementation, in the above method for improving the quality and consistency of grain-oriented electrical steel glass film, the partial pressure ratio P(H2O) / P(H2) of the decarburizing and nitriding annealing atmosphere of the grain-oriented electrical steel is controlled in the range of 0.28-0.30.

[0018] As an optional implementation, in the above method for improving the quality and consistency of grain-oriented electrical steel glass film, the oxygen content of the grain-oriented electrical steel after decarburization, nitriding, and annealing is controlled within the range of 600-710 ppm.

[0019] As an optional implementation, in the above-mentioned method for improving the quality and consistency of grain-oriented electrical steel glass film, in the high-temperature annealing process of grain-oriented electrical steel, the heating rate is controlled to be <8℃ / h within the annealing temperature range of 750-1000℃; or, a heat preservation treatment of >15h is performed within the annealing temperature range of 750-1000℃.

[0020] Compared with the prior art, the method of the present invention for improving the quality and consistency of oriented electrical steel glass film has the following advantages and beneficial effects:

[0021] This invention starts with the decarburization and nitriding annealing and high-temperature annealing processes. By adjusting the heating rate of decarburization and nitriding annealing of oriented electrical steel, the partial pressure ratio of the annealing atmosphere P(H2O) / P(H2), the oxygen content, the hydration rate of the magnesium oxide coating, and the heating rate or holding temperature of high-temperature annealing, the glass film of the oriented electrical steel product is dense and free of defects such as point-like crystal leakage. At the same time, it has good uniformity, and the quality of the glass film is uniform from the beginning, middle and end along the length of the steel coil. This solves the problems of point-like crystal leakage and poor uniformity of the beginning, middle and end of the oriented electrical steel glass film in the prior art. The proportion of surface degradation products caused by defects in the bottom layer of the glass film is reduced from more than 40% to less than 20%, and the quality and uniformity of the glass film are significantly improved. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] This invention studies the factors affecting the uniformity of the bottom layer of magnesium silicate glass film for electrical steel, determines the influence of the surface oxide layer, magnesium oxide and additives, and high-temperature annealing process on the quality of the glass film, and proposes a method to improve the quality and consistency of the bottom layer of oriented electrical steel glass film by starting with decarburization and nitriding annealing and high-temperature annealing processes. This method aims to solve the problem of poor uniformity of the bottom layer of oriented electrical steel glass film, especially the problem of poor uniformity of glass film quality at the beginning, middle and end of the steel coil length direction.

[0024] Specifically, the method of the present invention for improving the quality and consistency of oriented electrical steel glass film includes:

[0025] (1) The heating rate range for decarburization and nitriding annealing of oriented electrical steel is controlled within the range of 200-400℃ / s;

[0026] (2) The partial pressure ratio P(H2O) / P(H2) of the decarburizing and nitriding annealing atmosphere for oriented electrical steel is controlled within the range of 0.20-0.30;

[0027] (3) The oxygen content of the decarburized and nitrided annealed oriented electrical steel is controlled within the range of 500-800 ppm;

[0028] (4) The hydration rate of the magnesium oxide coating is controlled to be <2.0;

[0029] (5) In the high-temperature annealing process of oriented electrical steel, the heating rate is controlled to be <8℃ / h within the annealing temperature range of 700-1200℃; or, the heat preservation treatment is carried out for >15h within the annealing temperature range of 700-1200℃.

[0030] Preferably, in the method for improving the quality and consistency of grain-oriented electrical steel glass film of the present invention, the heating rate range of decarburization and nitriding annealing of grain-oriented electrical steel is controlled within 200-320℃ / s; the oxygen content range of decarburization and nitriding annealing of grain-oriented electrical steel is controlled within 550-700ppm; the hydration rate of magnesium oxide coating is controlled within <1.7; and the heating rate of grain-oriented electrical steel during high-temperature annealing is controlled within the annealing temperature range of 700-1150℃ within the annealing temperature range of <6℃ / h, or a heat preservation treatment of >20h is performed within the annealing temperature range of 700-1150℃.

[0031] The following detailed embodiments and comparative examples further illustrate the method of the present invention for improving the quality and consistency of oriented electrical steel glass films.

[0032] Example 1

[0033] The heating rate for decarburizing and nitriding annealing of oriented electrical steel is controlled at 300℃ / s, the partial pressure ratio of the annealing atmosphere in the furnace P(H2O) / P(H2) is controlled at 0.30, and the oxygen content on the surface of the steel strip after annealing is controlled at 640ppm. By controlling the temperature of the magnesium oxide drying furnace, the hydration rate of the magnesium oxide coating is adjusted to 1.67. In the high-temperature annealing process, the heating rate is controlled at 5℃ / h within the annealing range of 750-1000℃.

[0034] Example 2

[0035] The heating rate for decarburizing and nitriding annealing of oriented electrical steel is controlled at 300℃ / s, the partial pressure ratio of the annealing atmosphere in the furnace P(H2O) / P(H2) is controlled at 0.28, and the oxygen content on the surface of the steel strip after annealing is controlled at 600ppm. By controlling the temperature of the magnesium oxide drying furnace, the hydration rate of the magnesium oxide coating is adjusted to 1.55. In the high-temperature annealing process, the heating rate is controlled at 5℃ / h within the annealing range of 750-1000℃.

[0036] Example 3

[0037] The heating rate for decarburizing and nitriding annealing of oriented electrical steel was controlled at 300℃ / s, the partial pressure ratio of the annealing atmosphere in the furnace, P(H2O) / P(H2), was controlled at 0.28, and the oxygen content on the surface of the steel strip after annealing was controlled at 620ppm. The hydration rate of the magnesium oxide coating was adjusted to 1.56 by controlling the temperature of the magnesium oxide drying furnace. In the high-temperature annealing process, the annealing temperature was held at 950℃ for 24 hours.

[0038] Example 4

[0039] The heating rate for decarburizing and nitriding annealing of oriented electrical steel is controlled at 250℃ / s, the partial pressure ratio of the annealing atmosphere in the furnace P(H2O) / P(H2) is controlled at 0.30, and the oxygen content on the surface of the steel strip after annealing is controlled at 710ppm. By controlling the temperature of the magnesium oxide drying furnace, the hydration rate of the magnesium oxide coating is adjusted to 1.43. In the high-temperature annealing process, the heating rate is controlled at 5℃ / h within the annealing range of 750-1000℃.

[0040] Example 5

[0041] The heating rate for decarburizing and nitriding annealing of oriented electrical steel is controlled at 250℃ / s, the partial pressure ratio of the annealing atmosphere in the furnace P(H2O) / P(H2) is controlled at 0.30, and the oxygen content on the surface of the steel strip after annealing is controlled at 680ppm. By controlling the temperature of the magnesium oxide drying furnace, the hydration rate of the magnesium oxide coating is adjusted to 1.76. In the high-temperature annealing process, the heating rate is controlled at 7℃ / h within the annealing range of 750-1000℃.

[0042] Example 6

[0043] The heating rate for decarburizing and nitriding annealing of oriented electrical steel was controlled at 250℃ / s, the partial pressure ratio of the annealing atmosphere in the furnace, P(H2O) / P(H2), was controlled at 0.30, and the oxygen content on the surface of the steel strip after annealing was controlled at 700ppm. The hydration rate of the magnesium oxide coating was adjusted to 1.64 by controlling the temperature of the magnesium oxide drying furnace. In the high-temperature annealing process, the annealing temperature was held at 950℃ for 18 hours.

[0044] Comparative Example 1

[0045] The heating rate for decarburizing and nitriding annealing of oriented electrical steel is controlled at 200℃ / s, the partial pressure ratio of the annealing atmosphere in the furnace P(H2O) / P(H2) is controlled at 0.45, and the oxygen content on the surface of the steel strip after annealing is controlled at 970ppm. By controlling the temperature of the magnesium oxide drying furnace, the hydration rate of the magnesium oxide coating is adjusted to 1.65. In the high-temperature annealing process, the heating rate is controlled at 12℃ / h within the annealing range of 750-1150℃.

[0046] Comparative Example 2

[0047] The heating rate for decarburizing and nitriding annealing of oriented electrical steel is controlled at 200℃ / s, the partial pressure ratio of the annealing atmosphere in the furnace P(H2O) / P(H2) is controlled at 0.45, and the oxygen content on the surface of the steel strip after annealing is controlled at 1020ppm. By controlling the temperature of the magnesium oxide drying furnace, the hydration rate of the magnesium oxide coating is adjusted to 2.28. In the high-temperature annealing process, the heating rate is controlled at 12℃ / h within the annealing range of 750-1150℃.

[0048] Comparative Example 3

[0049] The heating rate for decarburizing and nitriding annealing of oriented electrical steel is controlled at 200℃ / s, the partial pressure ratio of the annealing atmosphere in the furnace P(H2O) / P(H2) is controlled at 0.36, and the oxygen content on the surface of the steel strip after annealing is controlled at 910ppm. By controlling the temperature of the magnesium oxide drying furnace, the hydration rate of the magnesium oxide coating is adjusted to 1.82. In the high-temperature annealing process, the heating rate is controlled at 12℃ / h within the annealing range of 750-1150℃.

[0050] Comparative Example 4

[0051] The heating rate for decarburizing and nitriding annealing of oriented electrical steel is controlled at 200℃ / s, the partial pressure ratio of the annealing atmosphere in the furnace P(H2O) / P(H2) is controlled at 0.45, and the oxygen content on the surface of the steel strip after annealing is controlled at 870ppm. By controlling the temperature of the magnesium oxide drying furnace, the hydration rate of the magnesium oxide coating is adjusted to 1.79. In the high-temperature annealing process, the heating rate is controlled at 10℃ / h within the annealing range of 750-1150℃.

[0052] The main process parameters of Examples 1-6 and Comparative Examples 1-4, and the corresponding proportion of surface-degraded oriented electrical steel products due to defects in the glass film underlayer are summarized in the table below:

[0053] In summary, the method of the present invention for improving the quality and consistency of grain-oriented electrical steel glass films starts with the decarburization and nitriding annealing and high-temperature annealing processes. By adjusting the heating rate of the decarburization and nitriding annealing of grain-oriented electrical steel, the partial pressure ratio of the annealing atmosphere P(H2O) / P(H2), the oxygen content, the hydration rate of the magnesium oxide coating, and the heating rate or holding temperature of the high-temperature annealing, the grain-oriented electrical steel glass films are dense, free from defects such as point-like crystal leakage, and have good uniformity. Along the length of the steel coil, the quality of the glass films at the beginning, middle, and end is uniform. This solves the problems of point-like crystal leakage and poor uniformity at the beginning, middle, and end of the grain-oriented electrical steel glass films in the prior art. The proportion of surface-degraded products caused by defects in the bottom layer of the glass film is reduced from more than 40% to less than 20%, and the quality and uniformity of the glass film are significantly improved.

[0054] It should be noted that, unless otherwise specified, the terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, when a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum. Further, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Moreover, when multiple ranges are provided to describe features, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0055] It should also be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A method for improving the quality and consistency of grain-oriented electrical steel glass films, characterized in that, include: (1) The heating rate range for decarburization and nitriding annealing of oriented electrical steel is controlled within the range of 200-400℃ / s; (2) The partial pressure ratio P(H2O) / P(H2) of the decarburizing and nitriding annealing atmosphere for oriented electrical steel is controlled within the range of 0.20-0.30; (3) The oxygen content of the decarburized and nitrided annealed oriented electrical steel is controlled within the range of 500-800 ppm; (4) The hydration rate of the magnesium oxide coating is controlled to be <2.0; (5) In the high-temperature annealing process of oriented electrical steel, the heating rate is controlled to be <8℃ / h within the annealing temperature range of 700-1200℃; or, the heat preservation treatment is carried out for >15h within the annealing temperature range of 700-1200℃.

2. The method for improving the quality and consistency of grain-oriented electrical steel glass film as described in claim 1, characterized in that, The heating rate range for decarburizing and nitriding annealing of oriented electrical steel is controlled within 200-320℃ / s; the oxygen content range for decarburizing and nitriding annealing of oriented electrical steel is controlled within 550-700ppm; the hydration rate of the magnesium oxide coating is controlled within <1.7; during high-temperature annealing of oriented electrical steel, the heating rate range is controlled within annealing temperature of 700-1150℃ within the range of 700-1150℃ within the range of annealing temperature of >20h, or a heat preservation treatment is performed within annealing temperature of 700-1150℃ for >20h.

3. The method for improving the quality and consistency of grain-oriented electrical steel glass film as described in claim 1, characterized in that, The heating rate range for decarburizing and nitriding annealing of oriented electrical steel is controlled within 250-300℃ / s.

4. The method for improving the quality and consistency of grain-oriented electrical steel glass film as described in claim 1, characterized in that, The partial pressure ratio P(H2O) / P(H2) of the decarburizing and nitriding annealing atmosphere for oriented electrical steel is controlled within the range of 0.28-0.

30.

5. The method for improving the quality and consistency of grain-oriented electrical steel glass film as described in claim 1, characterized in that, The oxygen content of oriented electrical steel after decarburization, nitriding, and annealing is controlled within the range of 600-710 ppm.

6. The method for improving the quality and consistency of grain-oriented electrical steel glass film as described in claim 1, characterized in that, In the high-temperature annealing process of grain-oriented electrical steel, the heating rate is controlled to be <8℃ / h within the annealing temperature range of 750-1000℃; or, the heat treatment is carried out for >15h within the annealing temperature range of 750-1000℃.

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