Normalizing control method and production method of high-magnetic-induction oriented silicon steel

Abstract

This invention discloses a normalizing control method and production method for high magnetic induction oriented silicon steel, which involves normalizing and annealing hot-rolled coils at different temperature stages: the first normalizing temperature is 1135~1140℃, and the normalizing time is 55~70s; the second normalizing temperature is 1130~1135℃, the dew point is controlled to be positive, and the normalizing time is 20~30s; the third normalizing temperature is 930~940℃, the dew point is controlled to be positive, and the normalizing time is 55~75s; the fourth cooling temperature is 860~870℃, and the cooling time is 8~15s. This invention, through an improved normalizing process, achieves more complete nitride solidification at normalizing temperatures above 1130°C under a fixed furnace atmosphere dew point, while simultaneously reducing nitride solidification time: the first normalizing stage is reduced to below 70 seconds, with a minimum of 55 seconds; the second normalizing stage is reduced to below 30 seconds. During the cooling process at approximately 930-940°C, finer AlN precipitation is more uniform, and the AlN precipitation time after 930-940°C is reduced to below 75 seconds, with a minimum of 55 seconds. This invention significantly shortens the normalizing time, improves normalizing production efficiency, and increases production capacity by controlling the uniformity of the grain size on the surface of the normalized hot-rolled plate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of steel, and particularly relates to a normalizing control method and production method of high-magnetic-induction oriented silicon steel with high production efficiency. BACKGROUND

[0002] Due to the sharp Goss texture preferred orientation characteristics of the grain of the oriented silicon steel finished product, the oriented silicon steel is easily magnetized in the rolling direction and can obtain a high saturation magnetic induction. The oriented silicon steel is widely used in the production of transformer cores in the industry due to the characteristics. The higher the saturation magnetic induction obtained by the oriented silicon steel, the lower the iron loss under a specific magnetic induction. The transformer core made of the oriented silicon steel with excellent magnetic properties has low loss, which is important for reducing the energy loss of the transformer equipment, improving the quality, volume and manufacturing cost of the transformer equipment.

[0003] From the product magnetic properties, the oriented silicon steel with a magnetic induction (B 800 ) of 1.88T or more is called high-magnetic-induction oriented silicon steel. From the production process characteristics, the oriented silicon steel prepared by the low-temperature slab heating method (referred to as "low-temperature oriented silicon steel", the hot-rolled slab heating temperature is 1200℃ or less).

[0004] In order to achieve the purpose of low-temperature slab heating, the low-temperature high-magnetic-induction oriented silicon steel preparation process uses AlN with a low solid solution temperature as the main inhibitor. Through appropriate composition design, the casting slab heating temperature can be reduced to 1200℃ or less. The low-temperature slab reheating technology includes "inherent inhibitor method" and "acquired inhibitor method". The "inherent inhibitor method" forms the inhibitor required for secondary recrystallization before cold rolling. In addition to the main AlN, Cu2S, MnSe and other precipitated phases and Sn, Sb and other segregation elements are added as auxiliary inhibitors to replace MnS with a high solid solution temperature. Through high-temperature short-time heating and holding at 1100℃-1150℃, the unstable secondary particle phase is dissolved, the number of γ phases in the steel strip is more, and the solid solubility of nitrides in the γ phase is 10 times larger than that in the α phase. Then, slow cooling to 900℃ realizes the precipitation of a large number of fine and dispersed inhibitors, so that enough fine and dispersed second phase is obtained to inhibit the grain growth before secondary recrystallization. The "acquired inhibitor method" is a method for obtaining the inhibitor required for producing high-magnetic-induction oriented silicon steel after decarburization annealing and before high-temperature annealing secondary recrystallization. It includes coating a nitride promoter before entering the high-temperature annealing furnace or coating a nitrogenizing agent containing CrN and MnN to realize nitriding during the high-temperature annealing process. However, due to the non-uniformity of the obtained nitrides and the instability of the finished product performance, the method is not widely used. The most widely used process measure is to add a gas nitriding treatment section after the decarburization furnace, and complete the nitriding treatment by using N2 and H2 mixture to form (Al, Si)N on the surface of the steel strip to ensure the inhibitor amount for inhibiting the abnormal growth of secondary recrystallization.

[0005] In the preparation of low-temperature, high-magnetic-induction grain-oriented silicon steel, the state of the primary crystallization and precipitate inhibitors varies. The uniformity of the primary crystallization leads to different abilities for secondary recrystallization and abnormal growth. To achieve more uniform primary grains, hot-rolled plates must undergo a normalizing stage to make the microstructure more uniform, increase the number of crystalline grains on the upper and lower surfaces after normalizing, and simultaneously promote grain growth and coarsening of ALN solid solution, thus strengthening the crystalline phase structure. Generally, normalizing at 1100℃ for more than 70 seconds can gradually dissolve the inhibitor nitrides. During the solution treatment, maintaining a humid atmosphere in the furnace is crucial. The stronger the decarburization ability, the thicker the ferrite thickness on the steel strip surface, and the greater the number of γ-phase phases in the steel strip. The solid solubility of nitrides in the γ-phase is 10 times greater than in the α-phase. Under the condition of a certain ferrite thickness, the normalizing holding time can be shortened, improving the normalizing production efficiency.

[0006] However, if the temperature and time are not properly controlled during the normalizing process: for example, if the steel strip temperature does not reach the ALN solution temperature, insufficient ALN nitride dissolution will occur, preventing subsequent secondary recrystallization; or if the steel strip temperature exceeds the ALN solution temperature for too short a time, insufficient nitride dissolution will result in excessively small normalized grains, and other non-Gaussian oriented grains will also grow to a certain extent, making them difficult to completely engulf, resulting in poor overall texture orientation and reduced magnetic induction in the final product. To control the matching relationship between heating rate, normalizing temperature, and time to obtain optimal performance, various manufacturers have implemented relevant measures and improvements to the normalizing process, but all have shortcomings.

[0007] In actual production, the common practice is to use a longer holding time (more than 70 seconds) during the heating process to reach the normalization temperature of 1100℃ to ensure the time for ALN to solidify; at the same time, the precipitation of coarse ALN after 900℃ takes more than 70 seconds, resulting in low normalization efficiency.

[0008] For example, Chinese patent application CN105177444A discloses a normalizing control method for producing low-temperature high-magnetic-induction grain-oriented silicon steel. After conventional hot rolling, a two-stage normalizing process is performed: the temperature T of the steel plate in the first stage is controlled according to the Al content in the hot-rolled coil, and held for 20-30 seconds; then the temperature of the steel plate is reduced to 890-910℃ to begin the second stage of normalizing, and held for 100-120 seconds to obtain good magnetic properties. This method results in a low steel plate temperature before the start of the second stage of normalizing, leading to uneven nitride precipitation during the normalizing stage. This makes it impossible to obtain high-magnetic-induction grain-oriented silicon steel with a maximum magnetic induction B8(T) > 1.920, and also results in low production efficiency and energy consumption.

[0009] Chinese patent application CN103074476A discloses a method for producing high-magnetic-induction oriented silicon steel strips through a three-stage normalizing and tempering process. The normalizing and tempering is performed in three stages: the first stage temperature is controlled at 1050–1150℃, the second stage temperature at 1050–950℃, and the third stage temperature at 950–800℃, to obtain high-magnetic-induction oriented silicon steel. However, due to the lower temperature in the second stage, the normalized surface grains do not grow sufficiently, making it impossible to obtain high-magnetic-induction oriented silicon steel with a maximum magnetic induction B8(T) > 1.920. Furthermore, the method suffers from low production efficiency and high energy consumption. Summary of the Invention

[0010] The technical problem this invention aims to solve is to provide a normalizing control method and production method for high-magnetic-induction grain-oriented silicon steel, addressing the shortcomings of existing technologies. This invention, through an improved normalizing process, achieves more complete nitride dissolution at normalizing temperatures above 1130°C while maintaining a fixed furnace atmosphere dew point, and simultaneously reduces nitride dissolution time: the first normalizing time is reduced to below 70 seconds, with a minimum of 55 seconds, and the second normalizing time is reduced to below 30 seconds. During the cooling process at approximately 930-940°C, fine AlN precipitation is more uniform, and the AlN precipitation time after 930-940°C is reduced to below 75 seconds, with a minimum of 55 seconds. By controlling the uniformity of the surface grains in the normalized hot-rolled plate, the normalizing time is significantly shortened, normalizing production efficiency is improved, and production capacity is increased.

[0011] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0012] A method for producing high magnetic induction grain-oriented silicon steel, comprising the following steps in sequence:

[0013] 1) After smelting and continuous casting into billets, the billet heating temperature is controlled at 1160~1180℃;

[0014] 2) After conventional hot rolling, cooling, and coiling;

[0015] 3) Normalizing and annealing of hot-rolled coils at different temperature stages:

[0016] The first normalization temperature is 1135~1140℃, and the normalization time is 55~70s;

[0017] The second normalizing temperature is 1130~1135℃, the dew point is controlled at the positive dew point, and the normalizing time is 20~30s;

[0018] The normalization temperature for the third stage is 930~940℃, the dew point is controlled at the positive dew point, and the normalization time is 55~75ss;

[0019] The fourth stage of cooling has a temperature of 860~870℃ and a cooling time of 8~15s.

[0020] 4) Perform cold rolling on a rolling mill to a thickness range of 0.2~0.3mm, generally not exceeding 0.282mm;

[0021] 5) After alkaline washing, decarburization annealing is performed: the decarburization annealing atmosphere is a mixture of gas with a moisture dew point of 40~55° and a N2:H2 ratio of 1:1 (volume ratio), the decarburization temperature is 830~845°C, the decarburization annealing time is 90~140s, and the carbon content at the end of the decarburization annealing is controlled to be no higher than 0.0010%;

[0022] 6) Nitriding annealing: The nitriding annealing atmosphere is a mixture of N2:H2 = 1:3 (volume ratio) with a moisture dew point of 30~40°C. The nitriding temperature is 830~890°C, and the nitriding time is 20~50s. The increase in nitrogen content of the steel strip after nitriding compared to the nitrogen content of the billet is controlled to be 0.020~0.025wt%.

[0023] 7) High-temperature annealing with atmosphere changes at different temperature stages:

[0024] a. Heat to 700~730℃ and hold for 2~2.5h to remove the bound water in the MgO layer on the surface of the steel strip;

[0025] b. Heating: Based on the determined secondary recrystallization temperature of 1080~1090℃, during the heating process before 1080~1090℃, control the heating rate of the steel strip at 30~35℃ / h, and use a pure N2 atmosphere during the heating process.

[0026] c. When the temperature reaches the secondary recrystallization temperature of 1080~1090℃, the high-temperature annealing atmosphere is changed from pure nitrogen to a mixed gas of N2:H2=1:(2.8~3) (volume ratio), and held at this temperature for 1.8~2.5h; continue heating and raising the temperature to 1160~1250℃ at a rate of 10~25℃ / h under the mixed gas atmosphere of N2:H2=1:(2.8~3) (volume ratio);

[0027] 8) After high-temperature annealing, stretching and leveling annealing and coating with an insulating layer are carried out to obtain the finished grain-oriented silicon steel.

[0028] The method for producing high magnetic induction oriented silicon steel by controlling the normalization temperature described above in this invention applies to steel grades with the following composition and weight percentage content: C 0.05%~0.065%, Si 3.1~3.4%, Als 0.022~0.032%, Mn 0.08~0.09%, N 0.0060~0.0090%, S 0.0040~0.0070%, Sn 0.030~0.045%, Cr 0.020~0.120%, with the remainder being Fe and unavoidable inclusions.

[0029] The high magnetic induction oriented silicon steel prepared by the above method of the present invention has a finished product thickness of no more than 0.3 mm, a maximum magnetic induction B8(T) between 1.920 and 1.925, and a minimum iron loss P. 17 (W / kg) reaches between 0.825 and 0.97.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] This invention, through an improved normalizing process, achieves more complete nitride dissolution at normalizing temperatures above 1130℃ under a fixed furnace atmosphere dew point, while simultaneously reducing nitride dissolution time: the first normalizing time is reduced to below 70s, with a minimum of 55s, and the second normalizing time is reduced to below 30s. During the cooling process at approximately 930-940℃, fine AlN precipitation is more uniform, and the AlN precipitation time after 930-940℃ is reduced to below 75s, with a minimum of 55s. By controlling the uniformity of surface grains in the normalized hot-rolled plate, the normalizing time is significantly shortened, improving normalizing production efficiency and increasing capacity. The high magnetic orientation silicon steel produced by this invention exhibits stable performance and can achieve a yield of over 1.920T. Attached Figure Description

[0032] Figure 1 This is a micrograph of the high magnetic induction oriented silicon steel produced by this invention. Detailed Implementation

[0033] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the present invention is not limited to the following embodiments.

[0034] The steel composition and its weight percentage content applicable to this invention are as follows: C 0.05%~0.065%, Si 3.1~3.4%, Als 0.022~0.032%, Mn 0.08~0.09%, N 0.0060~0.0090%, S 0.0040~0.0070%, Sn 0.030~0.045%, Cr 0.020~0.120%, with the remainder being Fe and unavoidable inclusions.

[0035] This invention provides a method for producing high magnetic induction oriented silicon steel, the steps of which are as follows:

[0036] 1) After smelting and continuous casting into billets, the billet heating temperature is controlled at 1160~1180℃;

[0037] 2) After conventional hot rolling, cooling, and coiling;

[0038] 3) Normalizing and annealing of hot-rolled coils at different temperature stages:

[0039] The first normalization temperature is 1135~1140℃, and the normalization time is 55~70s;

[0040] The second normalizing temperature is 1130~1135℃, the dew point is controlled at the positive dew point, and the normalizing time is 20~30s;

[0041] The normalization temperature for the third stage is 930~940℃, the dew point is controlled at the positive dew point, and the normalization time is 55~75s;

[0042] The fourth stage of cooling has a temperature of 860~870℃ and a cooling time of 8~15s.

[0043] 4) Perform cold rolling on a rolling mill to a thickness range of 0.2~0.3mm, generally not exceeding 0.282mm;

[0044] 5) After alkaline washing, decarburization annealing is performed: the decarburization annealing atmosphere is a mixture of N2:H2 = 1:1 with a moisture dew point of 40~55°C, the decarburization temperature is 830~845°C, the decarburization annealing time is 90~140s, and the carbon content at the end of the decarburization annealing is controlled to be no higher than 0.0010%;

[0045] 6) Nitriding annealing: The nitriding annealing atmosphere is a mixture of N2:H2 = 1:3 with a moisture dew point of 30~40°C. The nitriding temperature is 830~890°C, and the nitriding time is 20~50s. The increase in nitrogen content of the steel strip after nitriding compared to the nitrogen content of the billet is controlled to be 0.020~0.025wt%.

[0046] 7) High-temperature annealing with atmosphere changes at different temperature stages:

[0047] a. Heat to 700℃~730℃ and hold for 2~2.5h to remove the bound water in the MgO layer on the surface of the steel strip;

[0048] b. Heating: Based on the determined secondary recrystallization temperature of 1080~1090℃, during the heating process before 1080~1090℃, control the heating rate of the steel strip at 30~35℃ / h, and use a pure N2 atmosphere during the heating process.

[0049] c. When the temperature reaches the secondary recrystallization temperature of 1080~1090℃, the high-temperature annealing atmosphere is changed from pure nitrogen to a mixed gas of N2:H2=1:(2.8~3), and held at this temperature for 1.8~2.5h; continue heating and raising the temperature to 1160~1250℃ at a rate of 10~25℃ / h under the mixed gas atmosphere of N2:H2=1:(2.8~3);

[0050] 8) After high-temperature annealing, stretching and leveling annealing and coating with an insulating layer are carried out to obtain the finished grain-oriented silicon steel.

[0051] Example 1

[0052] The high magnetic orientation silicon steel smelted in this embodiment has the following composition and weight percentage: C 0.056%, Si 3.25%, Al 0.030%, Mn 0.087%, N 0.0072%, S 0.006%, Sn 0.035%, Cr 0.120%, with the remainder being Fe and unavoidable inclusions. The production steps are as follows:

[0053] 1) After smelting and continuous casting into billets, the billet heating temperature is controlled at 1160~1180℃;

[0054] 2) After conventional hot rolling, cooling, and coiling;

[0055] 3) Normalizing and annealing of hot-rolled coils at different temperature stages:

[0056] The first normalization temperature is 1135℃, and the normalization time is 70s;

[0057] The second normalizing temperature is 1130℃, the dew point is controlled at the positive dew point, and the normalizing time is 30s;

[0058] The normalization temperature for the third stage is 930℃, the dew point is controlled at the positive dew point, and the normalization time is 70s.

[0059] The fourth stage of cooling has a temperature of 860℃ and a cooling time of 15 seconds.

[0060] 4) Perform cold rolling on a rolling mill to a thickness of 0.282 mm;

[0061] 5) After alkaline washing, decarburization annealing is performed: the decarburization annealing atmosphere is a mixture of N2:H2 = 1:1 with a moisture dew point of 48°C, the decarburization temperature is 830°C, the decarburization annealing time is 95~100s, and the carbon content at the end of the decarburization annealing is controlled to be no higher than 0.0010%;

[0062] 6) Nitriding annealing: The nitriding annealing atmosphere is a mixture of N2:H2 = 1:3 with a moisture dew point of 34°C. The nitriding temperature is 835°C, and the nitriding time is 25~30s. The increase in nitrogen content of the steel plate after nitriding compared to the nitrogen content of the billet is controlled to be 0.020~0.025wt%.

[0063] 7) High-temperature annealing with atmosphere changes at different temperature stages:

[0064] a. Heat to 730℃ and hold for 2 hours to remove the bound water in the MgO layer on the surface of the strip steel;

[0065] b. Heating: Based on the determined secondary recrystallization temperature of 1080℃, during the heating process before 1080℃, the heating rate of the steel strip is controlled at 30℃ / h, and a pure N2 atmosphere is used during the heating process.

[0066] c. When the temperature reaches the secondary recrystallization temperature of 1080℃, the high-temperature annealing atmosphere is changed from pure nitrogen to a mixed gas of N2:H2=1:(2.8~3), and held at this temperature for 2.0h; continue heating and raising the temperature to 1195~1200℃ at a rate of 16℃ / h under the mixed gas atmosphere of N2:H2=1:(2.8~3);

[0067] 8) After the high-temperature annealing is completed, stretching and leveling annealing and coating with an insulating layer are carried out to obtain the finished grain-oriented silicon steel with a thickness of about 0.3 mm.

[0068] Comparative Example 1: The normalization temperature for the four stages was fixed, but the holding time (i.e., the normalization time for the first to third stages and the cooling time for the fourth stage) differed from that of Example 1; all other steps were the same. Testing revealed that the maximum magnetic induction B8 and the minimum iron loss P of Example 1 and Comparative Example 1 were... 17 As shown in Table 1.

[0069] Table 1

[0070]

[0071] Example 2

[0072] The high magnetic orientation silicon steel smelted in this embodiment has the following composition and weight percentage content: C 0.056%, Si 3.25%, Al 0.030%, Mn 0.087%, N 0.0072%, S 0.006%, Sn 0.035%, Cr 0.120%, with the remainder being Fe and unavoidable inclusions. The production steps are as follows:

[0073] 1) After smelting and continuous casting into billets, the billet heating temperature is controlled at 1160~1180℃;

[0074] 2) After conventional hot rolling, cooling, and coiling;

[0075] 3) Normalizing and annealing of hot-rolled coils at different temperature stages:

[0076] The first normalization temperature is 1135℃, and the normalization time is 65s;

[0077] The second normalizing temperature is 1130℃, the dew point is controlled at the positive dew point, and the normalizing time is 28s;

[0078] The normalization temperature for the third stage is 930℃, the dew point is controlled at the positive dew point, and the normalization time is 65s.

[0079] The fourth stage of cooling has a temperature of 860℃ and a cooling time of 13 seconds.

[0080] 4) Perform cold rolling on a rolling mill to a thickness of approximately 0.215 mm;

[0081] 5) After alkaline washing, decarburization annealing is performed: the decarburization annealing atmosphere is a mixture of N2:H2 = 1:1 with a moisture dew point of 48°C, the decarburization temperature is 830°C, the decarburization annealing time is 95~100s, and the carbon content at the end of the decarburization annealing is controlled to be no higher than 0.0010%;

[0082] 6) Nitriding annealing: The nitriding annealing atmosphere is a mixture of N2:H2 = 1:3 with a moisture dew point of 34°C. The nitriding temperature is 835°C, and the nitriding time is 25~30s. The increase in nitrogen content of the steel plate after nitriding compared to the nitrogen content of the billet is controlled to be 0.020~0.025wt%.

[0083] 7) High-temperature annealing with atmosphere changes at different temperature stages:

[0084] a. Heat to 730℃ and hold for 2 hours to remove the bound water in the MgO layer on the surface of the strip steel;

[0085] b. Heating: Based on the determined secondary recrystallization temperature of 1080℃, during the heating process before 1080℃, the heating rate of the steel strip is controlled at 30℃ / h, and a pure N2 atmosphere is used during the heating process.

[0086] c. When the temperature reaches the secondary recrystallization temperature of 1080℃, the high-temperature annealing atmosphere is changed from pure nitrogen to a mixed gas of N2:H2=1:(2.8~3), and held at this temperature for 2.0h; continue heating and raising the temperature to 1195~1200℃ at a rate of 16℃ / h under the mixed gas atmosphere of N2:H2=1:(2.8~3);

[0087] 8) After high-temperature annealing, stretching and leveling annealing and coating with an insulating layer are performed to obtain the finished grained silicon steel with a thickness of 0.23mm.

[0088] Comparative Example 2: The normalization temperature was fixed for four stages, but the holding time differed from that in Example 2; all other steps were the same. Testing revealed that the maximum magnetic induction B8 and minimum iron loss P of Example 2 and Comparative Example 2 were... 17 As shown in Table 2.

[0089] Table 2

[0090]

[0091] Example 3

[0092] The high magnetic orientation silicon steel smelted in this embodiment has the following composition and weight percentage content: C 0.056%, Si 3.25%, Al 0.030%, Mn 0.087%, N 0.0072%, S 0.006%, Sn 0.035%, Cr 0.120%, with the remainder being Fe and unavoidable inclusions. The production steps are as follows:

[0093] 1) After smelting and continuous casting into billets, the billet heating temperature is controlled at 1160~1180℃;

[0094] 2) After conventional hot rolling, cooling, and coiling;

[0095] 3) Normalizing and annealing of hot-rolled coils at different temperature stages:

[0096] The first normalization temperature is 1135℃, and the normalization time is 60s;

[0097] The second normalizing temperature is 1130℃, the dew point is controlled at the positive dew point, and the normalizing time is 25s;

[0098] The normalization temperature for the third stage is 930℃, the dew point is controlled at the positive dew point, and the normalization time is 60s.

[0099] The fourth stage of cooling has a temperature of 860℃ and a cooling time of 10 seconds.

[0100] 4) Perform cold rolling on a rolling mill to a thickness of approximately 0.215 mm;

[0101] 5) After alkaline washing, decarburization annealing is performed: the decarburization annealing atmosphere is a mixture of N2:H2 = 1:1 with a moisture dew point of 48°C, the decarburization temperature is 830°C, the decarburization annealing time is 95~100s, and the carbon content at the end of the decarburization annealing is controlled to be no higher than 0.0010%;

[0102] 6) Nitriding annealing: The nitriding annealing atmosphere is a mixture of N2:H2 = 1:3 with a moisture dew point of 34°C. The nitriding temperature is 835°C, and the nitriding time is 25~30s. The increase in nitrogen content of the steel plate after nitriding compared to the nitrogen content of the billet is controlled to be 0.020~0.025wt%.

[0103] 7) High-temperature annealing with atmosphere changes at different temperature stages:

[0104] a. Heat to 730℃ and hold for 2 hours to remove the bound water in the MgO layer on the surface of the strip steel;

[0105] b. Heating: Based on the determined secondary recrystallization temperature of 1080℃, during the heating process before 1080℃, the heating rate of the steel strip is controlled at 30℃ / h, and a pure N2 atmosphere is used during the heating process.

[0106] c. When the temperature reaches the secondary recrystallization temperature of 1080℃, the high-temperature annealing atmosphere is changed from pure nitrogen to a mixed gas of N2:H2=1:(2.8~3), and held at this temperature for 2.0h; continue heating and raising the temperature to 1195~1200℃ at a rate of 16℃ / h under the mixed gas atmosphere of N2:H2=1:(2.8~3);

[0107] 8) After the high-temperature annealing is completed, stretching and leveling annealing and coating with an insulating layer are carried out to obtain the finished grain-oriented silicon steel with a thickness of about 0.23 mm.

[0108] Comparative Example 3: The normalization temperature was fixed for four stages, but the holding time differed from that in Example 3; all other steps were the same. Testing revealed that the maximum magnetic induction B8 and minimum iron loss P of Example 3 and Comparative Example 3 were... 17 As shown in Table 3.

[0109] Table 3

[0110]

[0111] Example 4

[0112] The high magnetic orientation silicon steel smelted in this embodiment has the following composition and weight percentage content: C 0.056%, Si 3.25%, Al 0.030%, Mn 0.087%, N 0.0072%, S 0.006%, Sn 0.035%, Cr 0.120%, with the remainder being Fe and unavoidable inclusions. The production steps are as follows:

[0113] 1) After smelting and continuous casting into billets, the billet heating temperature is controlled at 1160~1180℃;

[0114] 2) After conventional hot rolling, cooling, and coiling;

[0115] 3) Normalizing and annealing of hot-rolled coils at different temperature stages:

[0116] The first normalization temperature is 1135℃, and the duration is 55 seconds.

[0117] The second normalizing temperature is 1135℃, the dew point is controlled at the positive dew point, and the normalizing time is 20s;

[0118] The normalization temperature for the third stage is 940℃, the dew point is controlled at the positive dew point, and the normalization time is 55s.

[0119] The fourth stage of cooling has a temperature of 870℃ and a cooling time of 8 seconds.

[0120] 4) Perform cold rolling on a rolling mill to a thickness of 0.215 mm;

[0121] 5) After alkaline washing, decarburization annealing is performed: the decarburization annealing atmosphere is a mixture of N2:H2 = 1:1 with a moisture dew point of 48°C, the decarburization temperature is 830°C, the decarburization annealing time is 95~100s, and the carbon content at the end of the decarburization annealing is controlled to be no higher than 0.0010%;

[0122] 6) Nitriding annealing: The nitriding annealing atmosphere is a mixture of N2:H2 = 1:3 with a moisture dew point of 34°C. The nitriding temperature is 835°C, and the nitriding time is 25~30s. The increase in nitrogen content of the steel plate after nitriding compared to the nitrogen content of the billet is controlled to be 0.020~0.025wt%.

[0123] 7) High-temperature annealing with atmosphere changes at different temperature stages:

[0124] a. Heat to 730℃ and hold for 2 hours to remove the bound water in the MgO layer on the surface of the strip steel;

[0125] b. Heating: Based on the determined secondary recrystallization temperature of 1080℃, during the heating process before 1080℃, the heating rate of the steel strip is controlled at 30℃ / h, and a pure N2 atmosphere is used during the heating process.

[0126] c. When the temperature reaches the secondary recrystallization temperature of 1080℃, the high-temperature annealing atmosphere is changed from pure nitrogen to a mixed gas of N2:H2=1:(2.8~3), and held at this temperature for 2.0h; continue heating and raising the temperature to 1195~1200℃ at a rate of 16℃ / h under the mixed gas atmosphere of N2:H2=1:(2.8~3);

[0127] 8) After high-temperature annealing, stretching and leveling annealing and coating with an insulating layer are performed to obtain the finished grained silicon steel with a thickness of 0.23mm.

[0128] Comparative Example 3: The normalization temperature was fixed for four stages, but the holding time differed from that in Example 4; all other steps were the same. Testing revealed that the maximum magnetic induction B8 and minimum iron loss P of Example 4 and Comparative Example 4 were... 17 As shown in Table 4.

[0129] Table 4

[0130]

[0131] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for producing high magnetic induction oriented silicon steel, comprising the steps of smelting, continuous casting into billets, slab heating, hot rolling and coiling, normalizing annealing, cold rolling, and annealing, characterized in that: Normalizing and annealing of hot-rolled coils at different temperature stages: The first normalization temperature is 1135~1140℃, and the normalization time is 55~70s; The second normalizing temperature is 1130~1135℃, the dew point is controlled at the positive dew point, and the normalizing time is 20~30s; The normalization temperature for the third stage is 930~940℃, the dew point is controlled at the positive dew point, and the normalization time is 55~75s; The fourth stage of cooling has a temperature of 860~870℃ and a cooling time of 8~15s; The annealing process includes decarburization annealing, nitriding annealing, and high-temperature annealing. The high-temperature annealing involves changing the atmosphere at different temperature stages, and the specific process is as follows: a. Heat to 700~730℃ and hold for 2~2.5h to remove the bound water in the MgO layer on the surface of the strip steel; b. Heating: Based on the determined secondary recrystallization temperature of 1080~1090℃, during the heating process before 1080~1090℃, the heating rate of the steel strip is controlled at 30~35℃ / h, and a pure N2 atmosphere is used during the heating process. c. When the temperature reaches the secondary recrystallization temperature of 1080~1090℃, the high-temperature annealing atmosphere is changed from pure nitrogen to a mixed gas of N2:H2=1:(2.8~3.2), and held at this temperature for 1.8~2.5h; continue heating and raising the temperature to 1160~1250℃ at a rate of 10~25℃ / h under the mixed gas atmosphere of N2:H2=1:(2.8~3.2); The steel composition and its weight percentage content applicable to the production method are as follows: C 0.05%~0.065%, Si 3.1~3.4%, Als 0.022~0.032%, Mn 0.08~0.09%, N 0.0060~0.0090%, S 0.0040~0.0070%, Sn 0.030~0.045%, Cr 0.020~0.120%, with the remainder being Fe and unavoidable inclusions.

2. The method for producing high magnetic induction oriented silicon steel according to claim 1, characterized in that: Alkali washing is performed before decarburization annealing. The decarburization annealing atmosphere is a mixture of N2:H2=1:1 with a moisture dew point of 40~55°. The decarburization temperature is 830~845°C and the decarburization annealing time is 90~140s. The carbon content at the end of the decarburization annealing is controlled to be no higher than 0.0010%.

3. The method for producing high magnetic induction oriented silicon steel according to claim 2, characterized in that: The nitriding annealing atmosphere is a mixture of gas with a moisture dew point of 30~40° and a N2:H2 ratio of 1:

3. The nitriding temperature is 830~890°C, the nitriding time is 20~50s, and the increase in nitrogen content of the steel strip after nitriding compared to the nitrogen content of the billet is controlled to be 0.020~0.025wt%.

4. The method for producing high magnetic induction oriented silicon steel according to claim 1, characterized in that: The steps include: 1) After smelting and continuous casting into billets, the billet heating temperature is controlled at 1160~1180℃; 2) After conventional hot rolling, cooling, and coiling; 3) Normalizing and annealing of hot-rolled coils at different temperature stages: The first normalization temperature is 1135~1140℃, and the normalization time is 55~70s; The second normalizing temperature is 1130~1135℃, the dew point is controlled at the positive dew point, and the normalizing time is 20~30s; The normalization temperature for the third stage is 930~940℃, the dew point is controlled at the positive dew point, and the normalization time is 55~75s; The fourth stage of cooling has a temperature of 860~870℃ and a cooling time of 8~15s; 4) Perform cold rolling on a rolling mill to a thickness not exceeding 0.3 mm; 5) After alkaline washing, decarburization annealing is performed: the decarburization annealing atmosphere is a mixture of N2:H2 = 1:1 with a moisture dew point of 40~55°C, the decarburization temperature is 830~845°C, the decarburization annealing time is 90~140s, and the carbon content at the end of the decarburization annealing is controlled to be no higher than 0.0010%; 6) Nitriding annealing: The nitriding annealing atmosphere is a mixture of N2:H2 = 1:3 with a moisture dew point of 30~40°C. The nitriding temperature is 830~890°C, and the nitriding time is 20~50s. The increase in nitrogen content of the steel strip after nitriding compared to the nitrogen content of the billet is controlled to be 0.020~0.025wt%. 7) High-temperature annealing with atmosphere changes at different temperature stages: a. Heat to 700~730℃ and hold for 2~2.5 hours; b. Heating: Based on the determined secondary recrystallization temperature of 1080~1090℃, during the heating process before 1080~1090℃, control the heating rate of the steel strip at 30~35℃ / h, and use a pure N2 atmosphere during the heating process. c. When the temperature reaches the secondary recrystallization temperature of 1080~1090℃, the high-temperature annealing atmosphere is changed from pure nitrogen to a mixed gas of N2:H2=1:(2.8~3), and held at this temperature for 1.8~2.5h; continue heating and raising the temperature to 1160~1250℃ at a rate of 10~25℃ / h under the mixed gas atmosphere of N2:H2=1:(2.8~3); 8) After the high-temperature annealing is completed, the post-finishing process is carried out to obtain the finished grain-oriented silicon steel.

5. The high magnetic induction oriented silicon steel produced by the method according to any one of claims 1 to 4, characterized in that: The finished product thickness does not exceed 0.3mm, the maximum magnetic induction B8 reaches between 1.920 and 1.925T, and the minimum iron loss P 17 It reaches 0.825~0.97W / kg.

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