A method for decarburization annealing control of oriented silicon steel

Abstract

The application discloses a kind of oriented silicon steel decarburization annealing control methods, the control method is completed by the control of the atmosphere established by decarburization section flow to oxidation section;The control is the control of the setting control of annealing furnace chimney and the control of atmosphere monitoring in furnace.This application is a kind of oriented silicon steel decarburization annealing control method, by adjusting chimney, under the premise of guaranteeing process requirement furnace pressure, it greatly reduces the protective gas flow, reduces energy consumption;By changing the original heating section to oxidation section furnace protective gas flow direction, eliminate the influence of oxidation section atmosphere on decarburization section dew point, significantly improve the stability of decarburization section dew point;By increasing oxygen analyzer, furnace pressure gauge and related safety interlock in inlet sealing chamber.The safety hazard after the cancellation of annealing furnace entrance chimney is eliminated.

Description

Technical Field

[0001] This invention belongs to the field of decarburization annealing production line in the production process of grain-oriented silicon steel in metallurgical machinery / heating technology, and specifically relates to a method for controlling the decarburization annealing of grain-oriented silicon steel. Background Technology

[0002] Decarburization annealing is a necessary process in the production of grain-oriented silicon steel. It needs to complete decarburization, initial recrystallization, and oxide layer formation, and sometimes nitriding is also required. The process requirements are very strict. The decarburization process has a significant impact on the bottom layer quality and magnetic properties of the final product. Therefore, the furnace temperature, atmosphere, and dew point of decarburization annealing must be strictly controlled during production. The design and process parameters of the decarburization annealing furnace are core technologies in the production of grain-oriented silicon steel.

[0003] Figure 1 This is a schematic diagram of a commonly used decarburization annealing unit for grain-oriented silicon steel. Figure 1 As shown, the strip steel (1) undergoes decarburization annealing through the heating section (2), decarburization section (3), oxidation section (4), and nitriding section (5), and is cooled through the cooling section (6). The annealing furnace is equipped with an inlet sealing chamber (7) and an outlet sealing chamber (8) at the inlet and outlet. Nitrogen gas is introduced into the sealing chamber through a nitrogen spray beam (7.1) for sealing. The decarburization section (3) and oxidation section (4) are equipped with several gas mixing stations (2.1) to mix N2, H2, and H2O gases. Each gas mixing station is configured according to process requirements and the mixed gas is introduced into the furnace through a nozzle or spray beam (2.2). A set of chimneys (9) is provided at the front of the heating section (2), between the oxidation section (4) and the nitriding section (5), and between the nitriding section (5) and the cooling section (6) for the isolation and exhaust of the furnace atmosphere. Dew point meters (3.1) are provided at the rear of the decarburization section and the rear of the oxidation section to detect the dew point of the decarburization section in the furnace.

[0004] It should be noted that: 1) The decarburization, primary recrystallization, and oxide layer formation processes of oriented silicon steel are usually not strictly distinguishable. For example, decarburization mainly completes the decarburization process, while oxidation is also present; 2) The nitriding section is required for the production of oriented silicon steel using second-phase particles such as Al (Si, N) as inhibitors. Other processes may not require the nitriding process, i.e., the nitriding section may be unnecessary; 3) The nitriding section, cooling section, and some existing rapid heating systems and waste gas recovery systems of the decarburization annealing furnace have not been changed in this invention, and therefore will not be described in detail.

[0005] The main functions of each furnace section are as follows: ① Heating section: Rapidly heats the cold-rolled strip to the target temperature of approximately 800℃. Rapid heating is beneficial for the formation of an ideal texture and has a significant impact on the magnetic properties of the product. ② Decarburization section: Removes carbon from the strip to below 0.003%, ensuring that high-temperature annealing forms a perfect secondary recrystallization structure and preventing magnetic aging in the final product. ③ Oxidation section: Forms an oxide layer mainly composed of SiO2 and FeSiO4. During high-temperature annealing, the oxide layer reacts with MgO to form a dense Mg2SiO4 underlayer, while simultaneously completing the initial recrystallization. ④ Nitriding section: Nitriding obtains an appropriate amount of Al (Si, N) and other second-phase particle formation inhibitors. ⑤ Cooling section: Cools the strip to below 90℃.

[0006] To prevent explosions caused by outside air entering the decarburizing annealing furnace along with the running strip, the atmosphere in the decarburizing annealing furnace flows from the oxidation section to the heating section, and then exits through the chimney at the inlet of the heating section. A small portion flows to the chimney after the oxidation section. The protective gas flow in the nitriding section flows to the chimney between the oxidation and nitriding sections and between the nitriding and cooling sections. The protective gas flow in the cooling section flows to the chimney between the nitriding and cooling sections. The furnace atmosphere flow direction is as follows: Figure 1 As indicated by the dashed arrow.

[0007] To ensure successful decarburization and the formation of an ideal Fe2SiO4 layer, the decarburization section P is usually... H2O / P H2 Controlled between 0.1 and 0.7, P in the oxidation section H2O / P H2 Controlled within 0.7–1.0. Decarbonization stage P H2O / P H2 This not only affects the decarburization efficiency of the strip steel and the structure of the oxide layer formed during the decarburization process, but also the ratio of Fe2SiO4 and SiO2 formed in the oxidation section, and also affects the initial recrystallization process; consequently, it affects the surface quality and magnetic properties of the final product after high-temperature annealing. Therefore, the decarburization section P H2O / P H2 Stable control is extremely critical. Under current technological conditions, increasing the P in the decarbonization section is achieved by increasing the protective gas flow rate in both the oxidation and decarbonization sections. H2O / P H2 Stability.

[0008] The shortcomings of existing technology:

[0009] As illustrated in the example above, the commonly used decarburization annealing methods and equipment for grain-oriented silicon steel currently have the following two problems:

[0010] Energy consumption is relatively high. In order to ensure the relative stability of the atmosphere flow and the dew point in the decarbonization and oxidation sections, a large amount of protective gas must be introduced.

[0011] The dew point in the decarburization section fluctuates significantly. The protective gas in the furnace flows from the oxidation section to the decarburization section. Since the dew point is higher in the oxidation section and lower in the decarburization section, a small fluctuation in the dew point in the oxidation section leads to a significant increase in the fluctuation in the decarburization section. Furthermore, the dew point in the decarburization section is also affected by factors such as the composition of the incoming strip steel, strip decarburization, and oxidation reactions. This significant fluctuation in the dew point in the decarburization section results in unstable decarburization efficiency and an unstable oxide layer structure formed in the decarburization and oxidation sections. This leads to poor process stability and inconsistent quality of the bottom layer of the product.

[0012] The invention application with application number CN92113560.2 discloses "a continuous annealing furnace for the production of electrical steel plates", which consists of a preheating furnace, a heating furnace, a soaking furnace, etc. The annealing furnace is divided into two sections. The front section is purged with a wet protective atmosphere for decarburization annealing, and the rear section is purged with a dry protective atmosphere for improving magnetic properties annealing. The front and rear sections are separated by an isolation device.

[0013] The invention application with application number CN 201610187806.5 discloses "a method for monitoring the gas flow and distribution in a decarburizing annealing furnace for oriented silicon steel", including an inlet section and an outlet section; the method includes the following steps: determining the amount of substance N of the gas introduced into the inlet and outlet sections of the decarburizing annealing furnace for oriented silicon steel; determining the amount of decarburization Tc of the decarburizing annealing furnace for oriented silicon steel per unit time; using a gas analyzer to measure the volume ratio of CO and CO2 in the gas in the inlet section of the decarburizing annealing furnace for oriented silicon steel and the volume ratio of CO and CO2 in the gas in the outlet section and the volume ratio of CO and CO2 in the outlet section and the volume ratio of CO and CO2 in the outlet section; determining the gas distribution coefficient λ of the inlet section of the decarburizing annealing furnace for oriented silicon steel according to the model formula; when λ > 1, it is judged that furnace gas backflow has occurred; otherwise, it is judged that the gas flow in the furnace is normal. Summary of the Invention

[0014] To address the above problems, this invention provides a decarburization annealing method for grain-oriented silicon steel, the specific technical solution of which is as follows:

[0015] A method for controlling decarburization annealing of grain-oriented silicon steel, characterized in that:

[0016] The control method is achieved by controlling the flow of the protective atmosphere from the decarbonization section to the oxidation section.

[0017] The control measures include the configuration control of the annealing furnace chimney and the control of the furnace atmosphere monitoring.

[0018] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0019] The aforementioned control over the setting of the annealing furnace chimney specifically includes:

[0020] At least one chimney shall be installed between the oxidation section and the nitriding section of the annealing furnace, and between the nitriding section and the cooling section.

[0021] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0022] The control of the furnace atmosphere monitoring specifically includes:

[0023] An oxygen analyzer is installed inside the sealed inlet chamber.

[0024] Furnace pressure gauges are installed in the inlet sealed chamber, the heating section, and the oxidation section respectively;

[0025] Oxygen levels are monitored by using an oxygen analyzer in conjunction with L1.

[0026] By using a furnace pressure gauge in conjunction with L1, the furnace pressure in the inlet sealing chamber, heating section, and oxidation section can be monitored separately.

[0027] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0028] When the oxygen content received in real time by L1 is greater than 1%, the gas mixing station is shut down and the nitrogen passage from the inlet sealing chamber to the furnace is opened; otherwise, the nitrogen passage is shut down and the gas mixing station is operated.

[0029] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0030] The furnace pressure from the inlet sealing chamber to the oxidation section is set in a progressively decreasing manner.

[0031] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0032] The furnace pressure difference between the inlet sealing chamber and the heating section is monitored and regulated based on the benchmark that the furnace pressure in the inlet sealing chamber is 30-60 Pa greater than the furnace pressure in the heating section.

[0033] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0034] The furnace pressure difference between the heating section and the oxidation section is monitored and adjusted based on the benchmark that the furnace pressure in the heating section is 5-15 Pa greater than that in the oxidation section.

[0035] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0036] When the nitrogen passage from the inlet sealed chamber to the furnace is opened, the flow rate of nitrogen introduced is 1000-3000 m³ / h. 3 / h.

[0037] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0038] The monitoring and adjustment of the furnace pressure difference between the inlet sealing chamber and the heating section is carried out by adjusting the amount of nitrogen gas introduced into the inlet sealing chamber in conjunction with the furnace pressure gauge located in the inlet sealing chamber.

[0039] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0040] The monitoring and adjustment of the furnace pressure difference between the heating section and the oxidation section is carried out by establishing feedback control with this reference as the control target through furnace pressure gauges set in the heating section and the oxidation section respectively, in conjunction with L1.

[0041] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0042] One to three chimneys are installed between the oxidation section and the nitriding section of the annealing furnace;

[0043] One to three chimneys are installed between the nitriding section and the cooling section.

[0044] According to the present invention, a method for controlling decarburization annealing of grain-oriented silicon steel is characterized in that:

[0045] The decarburization annealing control method is applied to oriented silicon steel cold-rolled sheets with a carbon content of 0.03-0.05 wt% and a cold-rolled thickness of 0.15-0.5 mm.

[0046] This invention discloses a method for controlling the decarburization annealing of grain-oriented silicon steel. By altering the flow direction of the protective atmosphere between the decarburization and oxidation sections, it eliminates the impact of atmospheric fluctuation differences between the oxidation and decarburization sections on the dew point fluctuations in the decarburization section. This significantly improves the dew point stability of the decarburization section, and the resulting reduction in the need for an inlet chimney further reduces costs, thus resolving the conflict between furnace pressure and dew point control and cost. This method also eliminates the influence of the oxidation section atmosphere on the dew point of the decarburization section by adjusting the chimney and changing the original protective gas flow direction from the heating section to the oxidation section. Compared to commonly used grain-oriented silicon steel decarburization annealing units and control methods, the method of this invention reduces the protective gas flow rate from the heating section to the oxidation section by approximately 15-35%, significantly improves the dew point stability of the decarburization section for producing products of the same specifications, and significantly reduces oxygen content fluctuations after decarburization annealing. The final product's bottom layer quality stability is significantly improved. In summary, this invention significantly reduces the protective gas flow rate and energy consumption by adjusting the chimney while ensuring the furnace pressure required by the process. It also alters the original protective gas flow direction from the heating section to the oxidation section, eliminating the influence of the oxidation section atmosphere on the dew point of the decarburization section and significantly improving the dew point stability of the decarburization section. Furthermore, by adding an oxygen analyzer, furnace pressure gauge, and related safety interlocks to the inlet sealing chamber, it eliminates the safety hazards associated with removing the annealing furnace inlet chimney. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of an existing decarburization annealing unit in the background art of this invention;

[0048] Figure 2 This is a schematic diagram of the decarburization annealing unit of the present invention.

[0049] Figure 1 middle:

[0050] 1-Strip steel;

[0051] 2-Heating stage;

[0052] 2.1 - Gas mixing station;

[0053] 2.2 - Spray nozzle or spray beam;

[0054] 3-Decarbonization stage;

[0055] 3.1-Dew point meter;

[0056] 4-Oxidation segment;

[0057] 5-Nitriding section;

[0058] 6-Cooling section;

[0059] 7-Inlet sealed chamber;

[0060] 7.1 - Nitrogen spray beam in the inlet sealing chamber;

[0061] 8-Exit sealing chamber;

[0062] 9-Chimney.

[0063] Figure 2 middle:

[0064] 1-Strip steel;

[0065] 2-Heating stage;

[0066] 2.1 - Gas mixing station;

[0067] 2.2 - Spray nozzle or spray beam;

[0068] 2.3 - Furnace pressure gauge for the heating section;

[0069] 3-Decarbonization stage;

[0070] 3.1-Dew point meter;

[0071] 4-Oxidation segment;

[0072] 4.1 Oxidation section furnace pressure gauge;

[0073] 5-Nitriding section;

[0074] 6-Cooling section;

[0075] 7-Inlet sealed chamber;

[0076] 7.1 - Nitrogen spray beam in sealed chamber;

[0077] 7.2 - Oxygen analyzer for inlet sealed chamber;

[0078] 7.3 - Inlet sealing chamber pressure gauge;

[0079] 8-Exit sealing chamber;

[0080] 9-Chimney. Detailed Implementation

[0081] The decarburization annealing control method for oriented silicon steel according to the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0082] A method for controlling decarburization annealing of grain-oriented silicon steel.

[0083] The control method is achieved by controlling the flow of the protective atmosphere from the decarbonization section to the oxidation section.

[0084] The control measures include the configuration control of the annealing furnace chimney and the control of the furnace atmosphere monitoring.

[0085] in,

[0086] The aforementioned control over the setting of the annealing furnace chimney specifically includes:

[0087] At least one chimney shall be installed between the oxidation section and the nitriding section of the annealing furnace, and between the nitriding section and the cooling section.

[0088] in,

[0089] The control of the furnace atmosphere monitoring specifically includes:

[0090] An oxygen analyzer is installed inside the sealed inlet chamber.

[0091] Furnace pressure gauges are installed in the inlet sealed chamber, the heating section, and the oxidation section respectively;

[0092] Oxygen levels are monitored by using an oxygen analyzer in conjunction with L1.

[0093] By using a furnace pressure gauge in conjunction with L1, the furnace pressure in the inlet sealing chamber, heating section, and oxidation section can be monitored separately.

[0094] in,

[0095] When the oxygen content received in real time by L1 is greater than 1%, the gas mixing station is shut down and the nitrogen passage from the inlet sealing chamber to the furnace is opened; otherwise, the nitrogen passage is shut down and the gas mixing station is operated.

[0096] in,

[0097] The furnace pressure from the inlet sealing chamber to the oxidation section is set in a progressively decreasing manner.

[0098] in,

[0099] The furnace pressure difference between the inlet sealing chamber and the heating section is monitored and regulated based on the benchmark that the furnace pressure in the inlet sealing chamber is 30-60 Pa greater than the furnace pressure in the heating section.

[0100] in,

[0101] The furnace pressure difference between the heating section and the oxidation section is monitored and adjusted based on the benchmark that the furnace pressure in the heating section is 5-15 Pa greater than that in the oxidation section.

[0102] in,

[0103] When the nitrogen passage from the inlet sealed chamber to the furnace is opened, the flow rate of nitrogen introduced is 1000-3000 m³ / h. 3 / h.

[0104] in,

[0105] The monitoring and adjustment of the furnace pressure difference between the inlet sealing chamber and the heating section is carried out by adjusting the amount of nitrogen gas introduced into the inlet sealing chamber in conjunction with the furnace pressure gauge located in the inlet sealing chamber.

[0106] in,

[0107] The monitoring and adjustment of the furnace pressure difference between the heating section and the oxidation section is carried out by establishing feedback control with this reference as the control target through furnace pressure gauges set in the heating section and the oxidation section respectively, in conjunction with L1.

[0108] in,

[0109] One to three chimneys are installed between the oxidation section and the nitriding section of the annealing furnace;

[0110] One to three chimneys are installed between the nitriding section and the cooling section.

[0111] in,

[0112] The decarburization annealing control method is applied to oriented silicon steel cold-rolled sheets with a carbon content of 0.03-0.05 wt% and a cold-rolled thickness of 0.15-0.5 mm.

[0113] Working process and principle

[0114] First, a brief overview of the solution of the present invention is given below:

[0115] The original decarburization annealing furnace structure and atmosphere control methods were adjusted as follows:

[0116] 1. Eliminate the inlet chimney of the annealing furnace. The number of chimneys in the annealing furnace is reduced from 3 to 2. A smaller amount of nitrogen and hydrogen protective gas can meet the atmosphere requirements of the decarburization and annealing sections, thus reducing production energy consumption.

[0117] 2. By changing the atmosphere flow direction from the heating section to the oxidation section, the influence of the oxidation section atmosphere on the decarburization section dew point is eliminated, thereby improving the process stability of the decarburization dew point and making the bottom layer quality of the product more stable.

[0118] Specifically:

[0119] The different elemental compositions, thicknesses, and decarburization annealing rates of oriented silicon strip steel require different decarburization and oxidation processes. The difference lies in the method of adjusting the chimney. This invention alters the original flow direction of the protective gas in the furnace from the heating section to the oxidation section, eliminating the influence of the oxidation section atmosphere on the decarburization section dew point and improving the process stability of the decarburization dew point. A schematic diagram of the grain-oriented silicon steel decarburization annealing unit of this invention is shown below. Figure 2 As shown in the diagram, 1 represents strip steel; 2 represents the heating section; 2.1 represents the gas mixing station; 2.2 represents the nozzle or spray beam; 2.3 represents the furnace pressure gauge in the heating section; 3 represents the decarburization section; 3.1 represents the dew point meter; 4 represents the oxidation section; 4.1 represents the furnace pressure gauge in the oxidation section; 5 represents the nitriding section; 6 represents the cooling section; 7 represents the inlet sealing chamber; 7.1 represents the nitrogen spray beam in the sealing chamber; 7.2 represents the oxygen analyzer in the inlet sealing chamber; 7.3 represents the furnace pressure gauge in the inlet sealing chamber; 8 represents the outlet sealing chamber; and 9 represents the chimney. Figure 2As shown in the figure, the strip steel (1) undergoes decarburization annealing through the heating section (2), decarburization section (3), oxidation section (4), and nitriding section (5), and is cooled through the cooling section (6). A set of chimneys (9) is provided between the oxidation section (4) and the nitriding section (5), and between the nitriding section (5) and the cooling section (6), for the isolation and exhaust of the furnace atmosphere. Several gas mixing stations (2.1) are provided from the heating section (3) to the oxidation section (4) to mix N2, H2, and H2O. Each gas mixing station prepares the mixed gas according to the process requirements and introduces it into the furnace through the nozzle or spray beam (2.2). A dew point meter (3.1) is provided at the rear of the decarburization section to detect the dew point in the decarburization section of the furnace. An oxygen analyzer (7.2) and a furnace pressure gauge (7.3) are provided in the inlet sealing chamber (7), a furnace pressure gauge (2.3) is provided in the heating section, and a furnace pressure gauge (4.1) is provided at the rear of the oxidation section.

[0120] The main improvements in the above settings are as follows:

[0121] Reduce energy consumption: Eliminate the inlet chimney of the annealing furnace. The number of chimneys in the annealing furnace is reduced from three to two, which can significantly reduce the amount of protective gas while ensuring the furnace pressure required by the process.

[0122] Improving dew point stability in the decarburization section: The gas from the heating section to the oxidation section mainly flows from the heating section to the chimney between the oxidation and nitriding sections. The furnace atmosphere flow direction is as follows... Figure 2 As shown by the dashed arrow, this method eliminates the influence of the oxidation zone atmosphere on the dew point of the decarburization zone. The furnace pressure in the heating zone and the latter part of the oxidation zone is used as a reference to control the furnace airflow; the furnace pressure in the heating zone is higher than that in the oxidation zone, with a pressure difference of 5–15 Pa.

[0123] Addressing safety issues arising from the change in atmosphere flow:

[0124] The inlet sealing chamber and the heating section are equipped with furnace pressure gauges. The furnace pressure in the inlet sealing chamber is greater than that in the heating section, with a pressure difference greater than 30-50 Pa. The pressure difference is controlled by adjusting the sealing of the inlet sealing chamber and the flow rate of nitrogen gas entering the sealing chamber.

[0125] The inlet sealing chamber is equipped with an oxygen analyzer to increase the safety interlock of oxygen content detection value. The prerequisite for hydrogen to be introduced into the gas mixing station is that the oxygen content is less than 1%. In addition, when the oxygen content in the inlet sealing chamber is greater than 1% when hydrogen is introduced into the mixing station, the protective gas in the annealing furnace is immediately purged with high-pressure nitrogen.

[0126] Example

[0127] Example 1:

[0128] Cold-rolled sheets of grain-oriented silicon steel with a carbon content of 0.03–0.05 wt% and a thickness of 0.23 mm are produced using... Figure 2 Device.

[0129] like Figure 2As shown, the cleaned strip steel (1) undergoes decarburization annealing in the heating section (2), decarburization section (3), oxidation section (4), and nitriding section (5), and is cooled in the cooling section (6). A set of chimneys (7) is provided between the oxidation section (4) and the nitriding section (5), and between the nitriding section (5) and the cooling section (6), for the isolation and exhaust of the furnace atmosphere. Several gas mixing stations (8) are provided from the heating section (3) to the oxidation section (4) to mix N2, H2, and H2O. Each gas mixing station is configured according to the process requirements and the mixed gas is introduced into the furnace through nozzles or spray beams (9). Dew point meters (10) are provided at the rear of the decarburization section and the rear of the oxidation section to detect the dew point in the furnace. The gas mixing station in the decarburization section is equipped with a dew point feedback controller (11), which can adjust the dew point set value of the gas mixing station in the decarburization section in real time. A furnace pressure gauge (12) is provided at the rear of the heating section (2) and the oxidation section (4) to control the atmosphere flow from the heating section (2) to the oxidation section (4).

[0130] The protective gas flow rate of the heating section and decarbonization section mixing station is 200 m3 / h, and the hydrogen ratio is 80%.

[0131] The total flow rate of the nitrogen-hydrogen mixture at the oxidation section mixing station is 300 m³ / h, with a hydrogen content of 80%.

[0132] The dew point setting for the oxidation section mixing station is 65.0–70.0℃, and the dew point for the oxidation section is 63.0–68.0℃.

[0133] The furnace pressure at the end of the heating and oxidation sections is used as a reference to control the airflow inside the furnace. The furnace pressure in the heating section is lower than that at the end of the oxidation section, with a pressure difference of 5 to 15 Pa. The protective gas flows from the heating section to the chimney between the oxidation and nitriding sections.

[0134] The inlet sealing chamber and the heating section are equipped with furnace pressure gauges. Protective nitrogen is introduced into the inlet sealing chamber at a flow rate of 120 m3 / h. The furnace pressure in the inlet sealing chamber is greater than that in the heating section, with a pressure difference of about 50 Pa.

[0135] The furnace pressure values ​​at the end of the heating and oxidation sections are used as references to control the airflow inside the furnace. The furnace pressure in the heating section is greater than that in the oxidation section, with a pressure difference of about 10 Pa.

[0136] The annealing temperature was 850℃. After decarburization and annealing, MgO was applied, and the strip was dried and coiled. After decarburization and annealing, the residual carbon content of the strip was measured to be 3–15 ppm, and the oxygen content was 650–750 ppm.

[0137] The steel coils were heated to 1200℃ in a ring furnace under a 25% N2 + 75% H2 atmosphere, and then held at that temperature for 24 hours in a 100% H2 atmosphere before cooling. After high-temperature annealing, the surface of the steel plate was treated, and then uncoiled in a hot stretching unit. After coating with an insulating coating and leveling annealing, a finished product with good magnetic properties and uniform bottom layer quality was obtained.

[0138] Table 1

[0139]

[0140] As shown in Table 1, compared with the currently commonly used decarburization annealing unit for oriented silicon steel, after using this solution, the protective gas flow rate from the heating section to the oxidation section is reduced from 700 m³ / s. 3 / h decreased to 500m 3 Energy consumption per ton of steel was significantly reduced. The dew point fluctuation in the decarburization stage decreased from ±2.0℃ to ±0.3℃, and the oxygen content control range after decarburization annealing decreased from ±200ppm to ±50ppm. The final product showed significantly reduced bright spot defects, more uniform plate color, and a lower bottom-layer re-judgment rate from 9.31% to 2.63%, resulting in significantly improved quality stability.

[0141] Example 2:

[0142] Cold-rolled sheets of grain-oriented silicon steel with a carbon content of 0.03–0.05 wt% and a thickness of 0.18 mm are produced using... Figure 2 Device.

[0143] like Figure 2 As shown, the cleaned strip steel (1) undergoes decarburization annealing in the heating section (2), decarburization section (3), oxidation section (4), and nitriding section (5), and is cooled in the cooling section (6). A set of chimneys (7) is provided between the oxidation section (4) and the nitriding section (5), and between the nitriding section (5) and the cooling section (6), for the isolation and exhaust of the furnace atmosphere. Several gas mixing stations (8) are provided from the heating section (3) to the oxidation section (4) to mix N2, H2, and H2O. Each gas mixing station is configured according to the process requirements and the mixed gas is introduced into the furnace through nozzles or spray beams (9). Dew point meters (10) are provided at the rear of the decarburization section and the rear of the oxidation section to detect the dew point in the furnace. The gas mixing station in the decarburization section is equipped with a dew point feedback controller (11), which can adjust the dew point set value of the gas mixing station in the decarburization section in real time. A furnace pressure gauge (12) is provided at the rear of the heating section (2) and the oxidation section (4) to control the atmosphere flow from the heating section (2) to the oxidation section (4).

[0144] The protective gas flow rate of the heating section and decarbonization section mixing station is 250 m3 / h, and the hydrogen ratio is 80%.

[0145] The total flow rate of the nitrogen-hydrogen mixture at the oxidation section mixing station is 350 m³ / h, with a hydrogen content of 80%.

[0146] The dew point setting for the oxidation section mixing station is 68.0–72.0℃, and the dew point for the oxidation section is 65.0–69.0℃.

[0147] The furnace pressure at the end of the heating and oxidation sections is used as a reference to control the airflow inside the furnace. The furnace pressure in the heating section is lower than that at the end of the oxidation section, with a pressure difference of 5 to 15 Pa. The protective gas flows from the heating section to the chimney between the oxidation and nitriding sections.

[0148] The inlet sealing chamber and the heating section are equipped with furnace pressure gauges. Protective nitrogen is introduced into the inlet sealing chamber at a flow rate of 120 m3 / h. The furnace pressure in the inlet sealing chamber is greater than that in the heating section, with a pressure difference of about 50 Pa.

[0149] The furnace pressure values ​​at the end of the heating and oxidation sections are used as references to control the airflow inside the furnace. The furnace pressure in the heating section is greater than that in the oxidation section, with a pressure difference of about 10 Pa.

[0150] The annealing temperature was 850℃. After decarburization and annealing, MgO was applied, and the strip was dried and coiled. After decarburization and annealing, the residual carbon content of the strip was measured to be 3–10 ppm, and the oxygen content was 705–795 ppm.

[0151] The steel coils were heated to 1200℃ in a ring furnace under a 25% N2 + 75% H2 atmosphere, and then held at that temperature for 24 hours in a 100% H2 atmosphere before cooling. After high-temperature annealing, the surface of the steel plate was treated, and then uncoiled in a hot stretching unit. After coating with an insulating coating and leveling annealing, a finished product with good magnetic properties and uniform bottom layer quality was obtained.

[0152] Table 2

[0153]

[0154] As shown in Table 2, compared with the currently commonly used decarburization annealing unit for oriented silicon steel, the protective gas flow rate from the heating section to the oxidation section is reduced from 700 m³ / s to 700 m³ / s. 3 / h decreased to 600m 3 Energy consumption per ton of steel was significantly reduced. The dew point fluctuation in the decarburization stage decreased from ±2.0℃ to ±0.3℃, and the oxygen content control range after decarburization annealing decreased from ±170ppm to ±45ppm. The final product showed significantly reduced bright spot defects, more uniform plate color, and a lower bottom-layer rejection rate of 22.8% to 5.65%, resulting in significantly improved quality stability.

[0155] This invention discloses a method for controlling the decarburization annealing of grain-oriented silicon steel. By altering the flow direction of the protective atmosphere between the decarburization and oxidation sections, it eliminates the impact of atmospheric fluctuation differences between the oxidation and decarburization sections on the dew point fluctuations in the decarburization section. This significantly improves the dew point stability of the decarburization section, and the resulting reduction in the need for an inlet chimney further reduces costs, thus resolving the conflict between furnace pressure and dew point control and cost. This method also eliminates the influence of the oxidation section atmosphere on the dew point of the decarburization section by adjusting the chimney and changing the original protective gas flow direction from the heating section to the oxidation section. Compared to commonly used grain-oriented silicon steel decarburization annealing units and control methods, the method of this invention reduces the protective gas flow rate from the heating section to the oxidation section by approximately 15-35%, significantly improves the dew point stability of the decarburization section for producing products of the same specifications, and significantly reduces oxygen content fluctuations after decarburization annealing. The final product's bottom layer quality stability is significantly improved. In summary, this invention significantly reduces the protective gas flow rate and energy consumption by adjusting the chimney while ensuring the furnace pressure required by the process. It also alters the original protective gas flow direction from the heating section to the oxidation section, eliminating the influence of the oxidation section atmosphere on the dew point of the decarburization section and significantly improving the dew point stability of the decarburization section. Furthermore, by adding an oxygen analyzer, furnace pressure gauge, and related safety interlocks to the inlet sealing chamber, it eliminates the safety hazards associated with removing the annealing furnace inlet chimney.

Claims

1. A method for controlling decarburization annealing of grain-oriented silicon steel, characterized in that: The control method is achieved by controlling the flow of the protective atmosphere from the decarbonization section to the oxidation section. The control refers to the control of the annealing furnace chimney setup in conjunction with the control of the furnace atmosphere monitoring. The aforementioned control over the setting of the annealing furnace chimney specifically includes: At least one chimney shall be installed between the oxidation section and the nitriding section of the annealing furnace, and between the nitriding section and the cooling section.

2. The method for controlling decarburization annealing of grain-oriented silicon steel according to claim 2, characterized in that: The control of the furnace atmosphere monitoring specifically includes: An oxygen analyzer is installed inside the sealed inlet chamber. Furnace pressure gauges are installed in the inlet sealed chamber, the heating section, and the oxidation section respectively; Oxygen levels are monitored by using an oxygen analyzer in conjunction with L1. By using a furnace pressure gauge in conjunction with L1, the furnace pressure in the inlet sealing chamber, heating section, and oxidation section can be monitored separately.

3. The method for controlling decarburization annealing of grain-oriented silicon steel according to claim 2, characterized in that: When the oxygen content received in real time by L1 is greater than 1%, the gas mixing station is shut down and the nitrogen passage from the inlet sealing chamber to the furnace is opened; otherwise, the nitrogen passage is shut down and the gas mixing station is operated.

4. The method for controlling decarburization annealing of grain-oriented silicon steel according to claim 2, characterized in that: The furnace pressure from the inlet sealing chamber to the oxidation section is set in a progressively decreasing manner.

5. The method for controlling decarburization annealing of grain-oriented silicon steel according to claim 4, characterized in that: The furnace pressure difference between the inlet sealing chamber and the heating section is monitored and regulated based on the benchmark that the furnace pressure in the inlet sealing chamber is 30-60 Pa greater than the furnace pressure in the heating section.

6. The method for controlling decarburization annealing of grain-oriented silicon steel according to claim 4, characterized in that: The furnace pressure difference between the heating section and the oxidation section is monitored and adjusted based on the benchmark that the furnace pressure in the heating section is 5-15 Pa greater than that in the oxidation section.

7. The method for controlling decarburization annealing of grain-oriented silicon steel according to claim 3, characterized in that: When the nitrogen passage from the inlet sealed chamber to the furnace is opened, the flow rate of nitrogen introduced is 1000-3000 m³ / h. 3 / h.

8. The method for controlling decarburization annealing of grain-oriented silicon steel according to claim 5, characterized in that: The monitoring and adjustment of the furnace pressure difference between the inlet sealing chamber and the heating section is carried out by adjusting the amount of nitrogen gas introduced into the inlet sealing chamber in conjunction with the furnace pressure gauge located in the inlet sealing chamber.

9. The method for controlling decarburization annealing of grain-oriented silicon steel according to claim 6, characterized in that: The monitoring and adjustment of the furnace pressure difference between the heating section and the oxidation section is carried out by establishing feedback control with this reference as the control target through furnace pressure gauges set in the heating section and the oxidation section respectively, in conjunction with L1.

10. The method for controlling decarburization annealing of grain-oriented silicon steel according to claim 1, characterized in that: One to three chimneys are installed between the oxidation section and the nitriding section of the annealing furnace; One to three chimneys are installed between the nitriding section and the cooling section.

11. The method for controlling decarburization annealing of grain-oriented silicon steel according to claim 1, characterized in that: The decarburization annealing control method is applied to oriented silicon steel cold-rolled sheets with a carbon content of 0.03~0.05wt% and a cold-rolled thickness of 0.15-0.5mm.

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