A method for producing grain-oriented silicon steel with control of point-like precipitates

Abstract

The application belongs to the technical field of oriented silicon steel production, and discloses a production method of oriented silicon steel for controlling point-like crystallization defects. In the decarburization annealing section of the production method, the protective gas inlet is arranged only in the front region of the decarburization section and the rear region of the decarburization section, the inlet of the protective gas is regulated, and the water-hydrogen partial pressure ratio of different parts in the furnace satisfies a specific formula; the nitriding section is processed in two stages, the first-stage nitriding temperature is 750-850 DEG C, and the duration is 10-30 s; the second-stage nitriding temperature is 850-950 DEG C, and the duration is 20-40 s; through the above measures, the occurrence rate of the point-like crystallization defects is significantly reduced, the defect length accounts for less than 6% of the length of the steel coil, and is reduced by more than 10% compared with the conventional production process.

Description

Technical Field

[0001] This invention belongs to the field of grain-oriented silicon steel production technology, specifically relating to a method for producing grain-oriented silicon steel that controls point-like crystallization defects. Background Technology

[0002] Grain-oriented silicon steel is an essential soft magnetic alloy material in the power, electronics, and military industries. Currently, domestic processes for producing grain-oriented silicon steel can be categorized into intrinsic inhibitor methods and acquisition-type inhibitor methods based on the type of inhibitor used. The intrinsic inhibitor method uses MnS as an inhibitor, with the slab heating temperature exceeding 1300℃, and is commonly referred to as high-temperature grain-oriented silicon steel technology. The acquisition-type inhibitor method utilizes gas nitriding to form AlN as an inhibitor before secondary recrystallization. This method reduces the solid solubility of the precipitated phase elements, lowering the hot-rolled slab heating temperature to between 1100 and 1200℃, hence it is also known as low-temperature grain-oriented silicon steel technology. Because the low-temperature slab heating production method solves many metallurgical and manufacturing problems, low-temperature grain-oriented silicon steel technology has become a hot topic in grain-oriented silicon steel manufacturing and research. However, the surface quality of low-temperature grain-oriented silicon steel products still needs improvement. The most typical surface defect is point-like crystallization, which has a high incidence rate and seriously affects the overall product quality.

[0003] The formation of dot-like crystallization is complex, and in production practice, it has been found to be mainly affected by subsequent processes such as decarburization annealing, nitriding, and high-temperature annealing. Decarburization annealing is one of the key steps in the production of grain-oriented silicon steel. Its main function is to remove carbon from the steel matrix through a reaction in an oxidizing atmosphere, while simultaneously forming a SiO2 oxide layer on the steel plate surface. Following subsequent nitriding and MgO coating, the MgO and SiO2 on the steel plate surface will form a Mg2SiO4 underlayer during the subsequent high-temperature annealing process. This underlayer protects the steel plates from sticking together during high-temperature annealing and provides a good adhesion carrier for the coating of the insulating coating on the finished product. Therefore, the rationality of the oxide layer structure in the decarburization stage is crucial for a product free of surface defects.

[0004] Furthermore, due to the inherently low-temperature oriented silicon steel having fewer inhibitors, nitriding is required after the decarburization process. However, the infiltrated nitrogen will eventually overflow during high-temperature annealing, damaging the oxide layer or the underlying layer. The nitrogen overflow process and the underlying layer formation process occur simultaneously. If the underlying layer is too thick and dense, nitrogen overflow will be hindered, eventually penetrating the underlying layer and overflowing, leading to the formation of one type of dot-like crystallization (referred to as: dot crystallization I). If the formed underlying layer is too thin or porous, the nitrogen overflow will weaken the local adhesion of the underlying layer, causing it to detach, resulting in another type of dot-like crystallization (referred to as: dot crystallization II).

[0005] Although small in size, point-like crystal deposits can lead to a decrease in local insulation performance, thus failing to meet the high insulation requirements of transformer cores. Therefore, controlling the occurrence of point-like crystal deposits is essential. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the shortcomings of existing technologies by providing a method for producing grain-oriented silicon steel that controls point-like crystallization defects. This method involves adjusting the water-hydrogen partial pressure ratio (P) at different locations within the furnace during the decarburization annealing process. H2O / P H2 By altering the oxide layer structure and optimizing the nitriding process, the occurrence of point-like crystallization defects during high-temperature annealing can be controlled.

[0007] To address the technical problem presented in this invention, this invention provides a method for producing grain-oriented silicon steel that controls point-like crystallization defects, comprising the following steps:

[0008] 1) Smelt and continuously cast according to the chemical composition of grain-oriented silicon steel to obtain slabs;

[0009] 2) After heating, hot rolling, normalizing, and cold rolling, slabs are used to obtain cold-rolled strip steel;

[0010] 3) Perform decarburization annealing;

[0011] 4) Nitriding treatment is performed, followed by coating with MgO and drying;

[0012] 5) Perform high-temperature annealing;

[0013] 6) Perform stretching and leveling annealing, apply an insulating coating, and obtain the oriented silicon steel finished product.

[0014] In the above scheme, the chemical composition of the oriented silicon steel by weight percentage is as follows: Si: 3.31-3.6%, C: 0.05-0.075%, Mn: 0.05-0.12%, P: 0.01-0.05%, S: 0.005-0.01%, N: 0.005-0.009%, Cr: 0.02-0.2%, Cu: 0.1-0.2%, Al: 0.0306-0.0330%, with the balance being Fe and unavoidable impurities.

[0015] In the above scheme, the heating temperature of the slab is 1120~1190℃.

[0016] In the above scheme, the hot rolling is to a thickness of 2.2 to 2.8 mm.

[0017] In the above scheme, the normalization is a two-stage normalization, with the first stage normalization temperature at 1100-1150℃ and the time at 10-30s, and the second stage normalization temperature at 850-950℃ and the time at 10-30s.

[0018] In the above scheme, the cold rolling is carried out in one rolling process, with intermediate passes performing effective rolling at 180-250°C.

[0019] In the above scheme, the finished thickness of the cold-rolled strip steel is 0.23 to 0.3 mm.

[0020] In the above scheme, the decarburization annealing is carried out at a constant temperature of 800-900℃ for a duration of 1-3 minutes.

[0021] In the above scheme, the protective gas for decarburization annealing is a humidified mixture of N2 and H2, with a total flow rate of 400-600 m³ / h. 3 / h.

[0022] In the above scheme, the protective gas inlet for decarburization annealing is set in two areas: the front area of ​​the decarburization section and the rear area of ​​the decarburization section. No protective gas inlet is set in other areas.

[0023] Furthermore, the length of the front zone of the decarburization section accounts for 1 / 4 to 1 / 3 of the length of the decarburization annealing furnace.

[0024] Furthermore, the length of the rear zone of the decarburization section accounts for 1 / 4 to 1 / 3 of the length of the decarburization annealing furnace.

[0025] Furthermore, the protective gas inlets inside the front zone of the decarbonization section are arranged at intervals of 3 to 4 meters.

[0026] Furthermore, the protective gas inlets inside the rear zone of the decarbonization section are arranged at intervals of 1.5 to 2 meters.

[0027] Furthermore, the protective gas flow rate in the front zone of the decarburization section is less than that in the rear zone of the decarburization section, causing the gas to flow from the rear zone to the front zone in the opposite direction to the running direction of the steel strip.

[0028] Furthermore, the protective gas flow rate in the pre-decarbonization zone accounts for 1 / 4 to 1 / 3 of the total flow rate.

[0029] Furthermore, the protective gas flow rate in the downstream zone of the decarbonization section accounts for 2 / 3 to 3 / 4 of the total flow rate.

[0030] Furthermore, each of the head of the front zone of the decarbonization section and the tail of the rear zone of the decarbonization section is provided with an isolator, and the opening ratio of the front and rear isolators is (2~3):1, where the opening ratio refers to the proportion of the open area to the total area.

[0031] Furthermore, the humidification temperature of the protective gas in the pre-decarbonization zone is 0–10°C, and the hydrogen content is 50–75%.

[0032] Furthermore, the humidification temperature of the protective gas in the post-decarbonization zone is 60–75°C, and the hydrogen content is 40–60%.

[0033] In the above scheme, a set of detection points, numbered from 1 to n, are arranged from the front end to the rear end of the decarburization annealing furnace. The detection points start 2-5m from the front end of the furnace and are arranged at fixed lengths every 8-10m thereafter, satisfying 12 ≤ n ≤ 18. Through these measures, the water-hydrogen partial pressure ratio at any detection point in the furnace satisfies the formula: 0.00205i 2 +0.0054i+0.1351≤P i ≤2.317×10 -4 i 3 -0.00836i 2 +0.1118i+0.303, where i represents the detection point number, P i This represents the water-hydrogen partial pressure ratio measured at detection point i.

[0034] In the above scheme, the O content in the steel after decarburization annealing is 500-1100 ppm.

[0035] In the above scheme, the nitriding treatment is a two-stage process. The first stage of nitriding is performed at a temperature of 750–850°C for 10–30 seconds. The second stage of nitriding is performed at a temperature of 850–950°C for 20–40 seconds.

[0036] Furthermore, the atmosphere for the first stage of nitriding is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.3–0.7, a N2 to H2 volume ratio of 1:(1–3), and an NH3 flow rate of 2–4 m³ / s. 3 / h.

[0037] Furthermore, the atmosphere for the second stage of nitriding is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.001–0.05, a N2 to H2 volume ratio of 1:(1–3), and an NH3 flow rate of 7–10 m³ / s. 3 / h.

[0038] In the above scheme, the total N content in the steel after nitriding treatment is 180-300 ppm.

[0039] In the above scheme, the high-temperature annealing process is as follows: first, the temperature is rapidly raised to 700-750°C, and a N2 and H2 mixture with a volume ratio of 1:(1-3) is introduced and kept at this temperature for 15-20 hours; then, the temperature is slowly raised to 1170-1210°C and kept at this temperature for 20-30 hours in a 100% H2 atmosphere; then, the temperature is lowered to 500-600°C and then air-cooled to room temperature.

[0040] Furthermore, the rapid heating rate is ≥50℃ / h, the slow heating rate is 15~17℃ / h, and the cooling rate is 12~30℃ / h.

[0041] In the above scheme, the temperature of the leveling annealing is 800-900℃.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] This invention addresses two main issues. First, by controlling the water-hydrogen partial pressure ratio at different locations within the furnace during decarburization annealing, the oxide layer formed on the steel strip surface exhibits different structural characteristics, ensuring the release of nitrogen from the outer and inner rings and the formation of a good underlying layer during subsequent high-temperature annealing. Second, by optimizing the nitriding process, it satisfies both rapid nitriding and inhibitor stabilization requirements, while delaying and reducing nitrogen release and its damage to the oxide layer during high-temperature annealing. Through these measures, the incidence of point-like crystallization defects is significantly reduced, and the defect length accounts for less than 6% of the steel coil length, a reduction of more than 10% compared to conventional production processes. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the decarburization annealing section in Example 1.

[0045] Figure 2 This is a schematic diagram showing the correspondence between partial pressure ratio and defects under constant water-hydrogen partial pressure ratio conditions. Detailed Implementation

[0046] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0047] Each embodiment of the present invention is manufactured according to the following process, including the following steps:

[0048] 1) The chemical composition of grain-oriented silicon steel, by weight percentage, is as follows: Si: 3.31–3.6%, C: 0.05–0.075%, Mn: 0.05–0.12%, P: 0.01–0.05%, S: 0.005–0.01%, N: 0.005–0.009%, Cr: 0.02–0.2%, Cu: 0.1–0.2%, Al: 0.0306–0.0330%, with the balance being Fe and unavoidable impurities; slabs are obtained by smelting and continuous casting according to the chemical composition of grain-oriented silicon steel.

[0049] 2) The slab is heated to 1120-1190℃ and hot-rolled to a thickness of 2.2-2.8mm; then it undergoes a two-stage normalizing process, with the first stage at 1100-1150℃ for 10-30s and the second stage at 850-950℃ for 10-30s; cold rolling is performed in one pass with intermediate passes at 180-250℃ to obtain a cold-rolled strip with a finished thickness of 0.23-0.3mm.

[0050] 3) Cold-rolled strip steel is decarburized and annealed at a constant temperature of 800–900℃ for 1–3 minutes; the protective gas for decarburization annealing is a humidified mixture of N2 and H2, with a total flow rate of 400–600 m³ / min. 3 / h; The protective gas inlet for decarburization annealing is set in two areas: the front area and the rear area of ​​the decarburization section. The length of the front area accounts for 1 / 4 to 1 / 3 of the length of the decarburization annealing furnace, and the length of the rear area accounts for 1 / 4 to 1 / 3 of the length of the decarburization annealing furnace.

[0051] The protective gas inlets in the front zone of the decarbonization section are arranged at intervals of 3-4m, with the protective gas flow rate accounting for 1 / 4 to 1 / 3 of the total flow rate. The humidification temperature of the protective gas is 0-10℃, and the hydrogen content is 50-75%. The protective gas inlets in the rear zone of the decarbonization section are arranged at intervals of 1.5-2m, with the protective gas flow rate accounting for 2 / 3 to 3 / 4 of the total flow rate. The humidification temperature of the protective gas is 60-75℃, and the hydrogen content is 40-60%. An isolator is provided at the head of the front zone and the tail of the rear zone, with the opening ratio of the isolators in the front and rear zones being (2-3):1.

[0052] A set of detection points, numbered from 1 to n, is set up from the front to the back of the decarburization annealing furnace. The detection points start 2-5 meters from the front of the furnace and are then spaced 8-10 meters apart at fixed intervals, ensuring that 12 ≤ n ≤ 18. Through these measures, the water-hydrogen partial pressure ratio at any detection point in the furnace satisfies the formula: 0.00205i 2 +0.0054i+0.1351≤P i ≤2.317×10 -4 i 3 -0.00836i 2 +0.1118i+0.303, where i represents the detection point number, P i This represents the water-hydrogen partial pressure ratio measured at detection point i;

[0053] After decarburization annealing, the oxygen content in the steel is 500–1100 ppm;

[0054] 4) Perform a two-stage nitriding treatment. The first stage nitriding temperature is 750–850℃, the duration is 10–30 seconds, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.3–0.7. The volume ratio of N2 to H2 is 1:(1–3), and the NH3 flow rate is 2–4 m³ / s. 3 / h; The second stage nitriding temperature is 850–950℃, the duration is 20–40s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.001–0.05, the volume ratio of N2 to H2 is 1:(1–3), and the NH3 flow rate is 7–10 m³ / h. 3 / h;

[0055] After nitriding, the total nitrogen content in the steel is 180–300 ppm, then MgO is coated and dried;

[0056] 5) Perform high-temperature annealing. First, rapidly heat the temperature to 700-750℃ at a heating rate of ≥50℃ / h, introduce a N2 and H2 mixture with a volume ratio of 1:(1-3), and hold for 15-20h. Then, slowly heat the temperature to 1170-1210℃ at a heating rate of 15-17℃ / h, and hold for 20-30h in a 100% H2 atmosphere. Subsequently, cool the temperature to 500-600℃ at a cooling rate of 12-30℃ / h, and then air cool to room temperature.

[0057] 6) Perform stretching and leveling annealing at 800-900℃, apply an insulating coating, and obtain the finished grain-oriented silicon steel product.

[0058] Example 1 (Original Example 3)

[0059] A method for producing grain-oriented silicon steel with controlled point-like crystallization defects includes the following steps:

[0060] 1) The chemical composition of grain-oriented silicon steel, by weight percentage, is: Si: 3.45%, C: 0.058%, Mn: 0.09%, P: 0.02%, S: 0.008%, N: 0.007%, Cr: 0.1%, Cu: 0.2%, Al: 0.0320%, with the balance being Fe and unavoidable impurities; slabs are obtained by smelting and continuous casting according to the above chemical composition.

[0061] 2) The slab is heated to 1150℃ and hot-rolled to a thickness of 2.5mm; then it undergoes two-stage normalizing, with the first stage normalizing temperature at 1130℃ for 20s and the second stage normalizing temperature at 900℃ for 20s; cold rolling is carried out in one rolling process, with intermediate passes undergoing effective rolling at 210℃, to obtain a finished cold-rolled strip with a thickness of 0.23mm.

[0062] 3) Cold-rolled strip steel is decarburized and annealed at a constant temperature of 860℃ for 1 minute; the protective gas for decarburization annealing is a humidified mixture of N2 and H2 with a total flow rate of 500 m³ / min. 3 / h; The protective gas inlet for decarburization annealing is set in two areas: the front area and the rear area of ​​the decarburization section. The length of the front area accounts for 1 / 4 of the length of the decarburization annealing furnace, and the length of the rear area accounts for 1 / 3 of the length of the decarburization annealing furnace.

[0063] The protective gas inlets in the front zone of the decarbonization section are arranged at 3m intervals, with the protective gas flow rate accounting for 1 / 3 of the total flow rate. The humidification temperature of the protective gas is 7℃, and the hydrogen content is 50%. The protective gas inlets in the rear zone of the decarbonization section are arranged at 2m intervals, with the protective gas flow rate accounting for 2 / 3 of the total flow rate. The humidification temperature of the protective gas is 70℃, and the hydrogen content is 55%. There is one isolator at the head of the front zone and one at the tail of the rear zone of the decarbonization section. The opening ratio of the isolators in the front and rear zones is 3:1, with the front zone isolator opening at 75% and the rear zone isolator opening at 25%.

[0064] A set of detection points, numbered 1 to 17, is arranged from front to back inside the decarburization annealing furnace. The detection points begin 2m from the front end of the furnace and are spaced 8m apart thereafter. After the above process measures, the water-hydrogen partial pressure ratio P at any detection point i inside the furnace is measured. i All satisfy the formula: 0.00205i 2 +0.0054i+0.1351≤P i ≤2.317×10 -4 i 3 -0.00836i 2 +0.1118i +0.303;

[0065] The measured results of the partial pressure ratio of water and hydrogen at each detection point are as follows:

[0066] Detection point number i 1 2 3 4 5 6 7 8 9 <![CDATA[Water hydrogen partial pressure ratio P i > 0.24 0.28 0.32 0.37 0.43 0.5 0.56 0.63 0.68 Detection point number i 10 11 12 13 14 15 16 17 <![CDATA[Water-hydrogen partial pressure ratio P i > 0.72 0.76 0.81 0.84 0.86 0.87 0.88 0.87

[0067] After decarburization annealing, the oxygen content in the steel was 956 ppm.

[0068] 4) A two-stage nitriding process is performed. The first stage nitriding temperature is 800℃, the duration is 20s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.5, a N2 to H2 volume ratio of 1:3, and an NH3 flow rate of 4m³ / h. 3 / h; The second stage nitriding temperature is 920℃, the duration is 40s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.005, a N2 to H2 volume ratio of 1:3, and an NH3 flow rate of 8m³ / h. 3 / h;

[0069] After nitriding, the total nitrogen content in the steel was 226 ppm. Then, MgO was coated and dried.

[0070] 5) Perform high-temperature annealing. First, rapidly heat the temperature to 700℃ at a heating rate of 70℃ / h, introduce a N2 and H2 mixture with a volume ratio of 1:2, and hold for 20h. Then, slowly heat the temperature to 1190℃ at a heating rate of 15℃ / h, hold for 20h in a 100% H2 atmosphere, and then cool the temperature to 500℃ at a cooling rate of 25℃ / h, and then air cool to room temperature.

[0071] 6) Perform stretching and leveling annealing at 860℃, apply an insulating coating, and obtain the oriented silicon steel finished product.

[0072] Comparative Example 1

[0073] Comparative Example 1 follows the same steps as Example 1, except that:

[0074] 1) The decarburization section is not divided into zones, and the nozzles are evenly arranged at 3m intervals throughout the section; the layout of the detection points is the same as in Example 1, but the water-hydrogen partial pressure ratio at each detection point is 0.55±0.05; the O content in the steel after decarburization annealing is 920ppm.

[0075] 2) The nitriding temperature is 860℃, the duration is 60s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.40, a N2 to H2 volume ratio of 1:3, and an NH3 flow rate of 6m³ / h. 3 / h; After nitriding, the total N content in the steel is 215ppm.

[0076] Example 2 (Original Example 1)

[0077] A method for producing grain-oriented silicon steel with controlled point-like crystallization defects includes the following steps:

[0078] 1) The chemical composition of grain-oriented silicon steel, by weight percentage, is: Si: 3.5%, C: 0.060%, Mn: 0.095%, P: 0.02%, S: 0.008%, N: 0.009%, Cr: 0.2%, Cu: 0.1%, Al: 0.0325%, with the balance being Fe and unavoidable impurities; smelting and continuous casting are carried out according to the above chemical composition to obtain slabs;

[0079] 2) The slab is heated to 1190℃ and hot-rolled to a thickness of 2.2mm; then it undergoes two-stage normalizing, with the first stage normalizing temperature at 1150℃ for 10s and the second stage normalizing temperature at 950℃ for 10s; cold rolling is carried out in one rolling process, with intermediate passes undergoing effective rolling at 242℃ to obtain a finished cold-rolled strip with a thickness of 0.23mm.

[0080] 3) Cold-rolled strip steel is decarburized and annealed at a constant temperature of 810℃ for 3 minutes; the protective gas for decarburization annealing is a humidified mixture of N2 and H2 with a total flow rate of 600 m³ / min. 3 / h; The protective gas inlet for decarburization annealing is set in two areas: the front area and the rear area of ​​the decarburization section. The length of the front area accounts for 1 / 4 of the length of the decarburization annealing furnace, and the length of the rear area accounts for 1 / 4 of the length of the decarburization annealing furnace.

[0081] The protective gas inlets in the front zone of the decarbonization section are arranged at 3m intervals, with the protective gas flow rate accounting for 1 / 3 of the total flow rate. The humidification temperature of the protective gas is 0℃, and the hydrogen content is 50%. The protective gas inlets in the rear zone of the decarbonization section are arranged at 1.5m intervals, with the protective gas flow rate accounting for 2 / 3 of the total flow rate. The humidification temperature of the protective gas is 70℃, and the hydrogen content is 52%. There is one isolator at the head of the front zone and one at the tail of the rear zone of the decarbonization section. The opening ratio of the isolators in the front and rear zones is 2:1, with the front zone isolator opening at 70% and the rear zone isolator opening at 35%.

[0082] A set of detection points, numbered 1 to 18, is arranged from front to back inside the decarburization annealing furnace. The detection points begin 5m from the front end of the furnace and are spaced 10m apart thereafter. After the above process measures, the water-hydrogen partial pressure ratio P at any detection point i inside the furnace is measured. i All satisfy the formula: 0.00205i 2 +0.0054i+0.1351≤P i ≤2.317×10 -4 i 3 -0.00836i 2 +0.1118i +0.303;

[0083] The measured results of the partial pressure ratio of water and hydrogen at each detection point are as follows:

[0084] Detection point number i 1 2 3 4 5 6 7 8 9 <![CDATA[Water-hydrogen partial pressure ratio P i > 0.15 0.17 0.25 0.28 0.35 0.39 0.48 0.53 0.61 Detection point number i 10 11 12 13 14 15 16 17 18 <![CDATA[Hydrogen partial pressure ratio P i > 0.71 0.79 0.83 0.81 0.86 0.85 0.89 0.91 0.92

[0085] After decarburization annealing, the oxygen content in the steel is 945 ppm;

[0086] 4) A two-stage nitriding process is performed. The first stage nitriding temperature is 750℃, the duration is 10s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.7. The volume ratio of N2 to H2 is 1:3, and the NH3 flow rate is 2m³ / h. 3 / h; The second stage nitriding temperature is 850℃, the duration is 40s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.001, a N2 to H2 volume ratio of 1:2, and an NH3 flow rate of 10m³ / h. 3 / h;

[0087] After nitriding, the total nitrogen content in the steel is 240 ppm. Then, MgO is coated and dried.

[0088] 5) Perform high-temperature annealing. First, rapidly heat the temperature to 750℃ at a heating rate of 50℃ / h, introduce a N2 and H2 mixture with a volume ratio of 1:1, and hold for 15h. Then, slowly heat the temperature to 1170℃ at a heating rate of 16℃ / h, hold for 20h in a 100% H2 atmosphere, and then cool the temperature to 500℃ at a cooling rate of 12℃ / h, and then air cool to room temperature.

[0089] 6) Perform stretching and leveling annealing at 800℃, apply an insulating coating, and obtain the finished grain-oriented silicon steel product.

[0090] Comparative Example 2

[0091] Comparative Example 2 follows the same steps as Example 2, except that:

[0092] 1) The decarburization section is not divided into zones, and the nozzles are evenly arranged at 3m intervals throughout the section; the layout of the detection points is the same as in Example 1, but the water-hydrogen partial pressure ratio at each detection point is 0.45±0.05; the O content in the steel after decarburization annealing is 956ppm.

[0093] 2) The nitriding temperature is 850℃, the duration is 50s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.20, a N2 to H2 volume ratio of 1:3, and an NH3 flow rate of 8m³ / kg. 3 / h; After nitriding, the total N content in the steel is 220ppm.

[0094] Example 3 (Original Example 2)

[0095] A method for producing grain-oriented silicon steel with controlled point-like crystallization defects includes the following steps:

[0096] 1) The chemical composition of grain-oriented silicon steel, by weight percentage, is: Si: 3.31%, C: 0.05%, Mn: 0.05%, P: 0.01%, S: 0.01%, N: 0.007%, Cr: 0.15%, Cu: 0.1%, Al: 0.0310%, with the balance being Fe and unavoidable impurities; smelting and continuous casting are carried out according to the above chemical composition to obtain slabs;

[0097] 2) The slab is heated to 1120℃ and hot-rolled to a thickness of 2.8mm; then it undergoes two-stage normalizing, with the first stage normalizing temperature at 1100℃ for 30s and the second stage normalizing temperature at 850℃ for 30s; cold rolling is carried out in one rolling process, with intermediate passes undergoing effective rolling at 185℃ to obtain a finished cold-rolled strip with a thickness of 0.3mm.

[0098] 3) Cold-rolled strip steel is decarburized and annealed at a constant temperature of 850℃ for 1.5 minutes; the protective gas for decarburization annealing is a humidified mixture of N2 and H2 with a total flow rate of 400 m³ / min. 3 / h; The protective gas inlet for decarburization annealing is set in two areas: the front area and the rear area of ​​the decarburization section. The length of the front area accounts for 1 / 3 of the length of the decarburization annealing furnace, and the length of the rear area accounts for 1 / 3 of the length of the decarburization annealing furnace.

[0099] The protective gas inlets in the front zone of the decarbonization section are arranged at 4m intervals, with the protective gas flow rate accounting for 1 / 4 of the total flow rate. The humidification temperature of the protective gas is 10℃, and the hydrogen content is 75%. The protective gas inlets in the rear zone of the decarbonization section are arranged at 2m intervals, with the protective gas flow rate accounting for 3 / 4 of the total flow rate. The humidification temperature of the protective gas is 60℃, and the hydrogen content is 45%. There is one isolator at the head of the front zone and one at the tail of the rear zone of the decarbonization section. The opening ratio of the isolators in the front and rear zones is 2:1, with the front zone isolator opening at 70% and the rear zone isolator opening at 35%.

[0100] A set of detection points, numbered 1 to 12, is arranged from front to back inside the decarburization annealing furnace. The detection points begin 5m from the front end of the furnace and are spaced every 10m thereafter. After the above process measures, the water-hydrogen partial pressure ratio P at any detection point i inside the furnace is measured. i All satisfy the formula: 0.00205i 2 +0.0054i+0.1351≤P i ≤2.317×10 -4 i 3 -0.00836i 2 +0.1118i +0.303;

[0101] The measured results of the partial pressure ratio of water and hydrogen at each detection point are as follows:

[0102] Detection point number i 1 2 3 4 5 6 <![CDATA[Hydrogen partial pressure ratio P i > 0.2 0.25 0.29 0.32 0.36 0.41 Detection point number i 7 8 9 10 11 12 <![CDATA[Water-hydrogen partial pressure ratio P i > 0.45 0.48 0.5 0.53 0.55 0.57

[0103] After decarburization annealing, the oxygen content in the steel is 720 ppm;

[0104] 4) A two-stage nitriding process is performed. The first stage nitriding temperature is 850℃, the duration is 20s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.3, a N2 to H2 volume ratio of 1:1, and an NH3 flow rate of 4m³ / h. 3 / h; The second stage nitriding temperature is 950℃, the duration is 20s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.05, the volume ratio of N2 to H2 is 1:3, and the NH3 flow rate is 7m³ / h. 3 / h;

[0105] After nitriding, the total nitrogen content in the steel was 192 ppm. Then, MgO was coated and dried.

[0106] 5) Perform high-temperature annealing. First, rapidly heat the temperature to 700℃ at a heating rate of 70℃ / h, introduce a N2 and H2 mixture with a volume ratio of 1:3, and hold for 15h. Then, slowly heat the temperature to 1210℃ at a heating rate of 17℃ / h, hold for 30h in a 100% H2 atmosphere, and then cool the temperature to 500℃ at a cooling rate of 12℃ / h, and then air cool to room temperature.

[0107] 6) Perform stretching and leveling annealing at 890℃, apply an insulating coating, and obtain the oriented silicon steel finished product.

[0108] Comparative Example 3

[0109] The other steps in Comparative Example 3 are the same as in Example 3, except that:

[0110] 1) The decarburization section is not divided into zones, and the nozzles are evenly arranged at 3m intervals throughout the section; the layout of the detection points is the same as in Example 1, but the water-hydrogen partial pressure ratio at each detection point is 0.35±0.05; the O content in the steel after decarburization annealing is 680ppm.

[0111] 2) The nitriding temperature is 850℃, the duration is 40s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.40, a N2 to H2 volume ratio of 1:3, and an NH3 flow rate of 10m³ / h. 3 / h; After nitriding, the total N content in the steel is 205ppm.

[0112] Example 4

[0113] A method for producing grain-oriented silicon steel with controlled point-like crystallization defects includes the following steps:

[0114] 1) The chemical composition of grain-oriented silicon steel, by weight percentage, is: Si: 3.55%, C: 0.065%, Mn: 0.08%, P: 0.02%, S: 0.01%, N: 0.0085%, Cr: 0.11%, Cu: 0.15%, Al: 0.0332%, with the balance being Fe and unavoidable impurities; slabs are obtained by smelting and continuous casting according to the above chemical composition.

[0115] 2) The slab is heated to 1170℃ and hot-rolled to a thickness of 2.6mm; then it undergoes two-stage normalizing, with the first stage normalizing temperature at 1140℃ for 20s and the second stage normalizing temperature at 910℃ for 20s; cold rolling is carried out in one rolling process, with intermediate passes undergoing effective rolling at 212℃ to obtain a finished cold-rolled strip with a thickness of 0.27mm.

[0116] 3) Cold-rolled strip steel is decarburized and annealed at a constant temperature of 825℃ for 2.5 minutes; the protective gas for decarburization annealing is a humidified mixture of N2 and H2 with a total flow rate of 600 m³ / min. 3 / h; The protective gas inlet for decarburization annealing is set in two areas: the front area and the rear area of ​​the decarburization section. The length of the front area accounts for 1 / 3 of the length of the decarburization annealing furnace, and the length of the rear area accounts for 1 / 4 of the length of the decarburization annealing furnace.

[0117] The protective gas inlets in the front zone of the decarbonization section are arranged at 4m intervals, with the protective gas flow rate accounting for 1 / 3 of the total flow rate. The humidification temperature of the protective gas is 5℃, and the hydrogen content is 55%. The protective gas inlets in the rear zone of the decarbonization section are arranged at 1.5m intervals, with the protective gas flow rate accounting for 2 / 3 of the total flow rate. The humidification temperature of the protective gas is 66℃, and the hydrogen content is 45%. There is one isolator at the head of the front zone and one at the tail of the rear zone of the decarbonization section. The opening ratio of the isolators in the front and rear zones is 3:1, with the front zone isolator opening at 75% and the rear zone isolator opening at 25%.

[0118] A set of detection points, numbered 1 to 15, is arranged from front to back inside the decarburization annealing furnace. The detection points begin 5m from the front end of the furnace and are spaced every 10m thereafter. After the above process measures, the water-hydrogen partial pressure ratio P at any detection point i inside the furnace is measured. i All satisfy the formula: 0.00205i 2 +0.0054i+0.1351≤P i ≤2.317×10 -4 i 3 -0.00836i 2 +0.1118i +0.303;

[0119] The measured results of the partial pressure ratio of water and hydrogen at each detection point are as follows:

[0120] Detection point number i 1 2 3 4 5 6 7 8 <![CDATA[Water hydrogen partial pressure ratio P i > 0.17 0.2 0.25 0.29 0.35 0.42 0.48 0.54 Detection point number i 9 10 11 12 13 14 15 <![CDATA[Water-hydrogen partial pressure ratio P i > 0.61 0.68 0.74 0.79 0.84 0.86 0.85

[0121] After decarburization annealing, the oxygen content in the steel is 842 ppm;

[0122] 4) A two-stage nitriding process is performed. The first stage nitriding temperature is 800℃, the duration is 15s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.6, a N2 to H2 volume ratio of 1:2, and an NH3 flow rate of 4m³ / h. 3 / h; The second stage nitriding temperature is 890℃, the duration is 35s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.002, a N2 to H2 volume ratio of 1:2, and an NH3 flow rate of 10m³ / h. 3 / h;

[0123] After nitriding, the total nitrogen content in the steel was 223 ppm. Then, MgO was coated and dried.

[0124] 5) Perform high-temperature annealing. First, rapidly heat the temperature to 750℃ at a heating rate of 60℃ / h, introduce a N2 and H2 mixture with a volume ratio of 1:3, and hold for 20h. Then, slowly heat the temperature to 1200℃ at a heating rate of 15℃ / h, hold for 20h in a 100% H2 atmosphere, and then cool the temperature to 500℃ at a cooling rate of 20℃ / h, and then air cool to room temperature.

[0125] 6) Perform stretching and leveling annealing at 870℃, apply an insulating coating, and obtain the oriented silicon steel finished product.

[0126] Comparative Example 4

[0127] The other steps in Comparative Example 4 are the same as in Example 4, except that:

[0128] 1) The decarburization section is not divided into zones, and the nozzles are evenly arranged at 3m intervals throughout the section; the layout of the detection points is the same as in Example 1, but the water-hydrogen partial pressure ratio at each detection point is 0.50±0.05; the O content in the steel after decarburization annealing is 830ppm.

[0129] 2) The nitriding temperature is 840℃, the duration is 50s, and the nitriding atmosphere is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.30, the volume ratio of N2 to H2 is 1:3, and the NH3 flow rate is 8m³ / h. 3 / h; After nitriding, the total N content in the steel is 219ppm.

[0130] The occurrence of defects on the surface of the oriented silicon steel products obtained in Examples 1-4 and Comparative Examples 2-4 was monitored, and the results are as follows:

[0131] Grouping Steel coil length Longitudinal length of dot-like crystals Longitudinal defect ratio Defect reduction rate Example 1 8056 m 330m 4.10％ 35.17％ Comparative Example 1 3200m 8150m 39.26％ / Example 2 9150m 180m 1.97％ 13.82％ Comparative Example 2 9500m 1500m 15.79％ / Example 3 11550m 450m 3.90％ 56.57％ Comparative Example 3 11080m 6700m 60.47％ / Example 4 6850m 350m 5.11％ 53.05％ Comparative Example 4 7050m 4100m 58.16％ /

[0132] The above data shows that by using the production method of the present invention, by controlling the water-hydrogen partial pressure ratio in different parts of the furnace during the decarburization annealing process, the oxide layer formed on the surface of the steel strip exhibits different structural characteristics. Furthermore, by optimizing the nitriding process, the incidence of point-like crystallization defects is significantly reduced, and the proportion of defect length to the length of the steel coil is less than 6%, which is more than 10% lower than that of conventional production processes.

[0133] Long-term experiments revealed that when a constant partial pressure gas is uniformly introduced into the furnace, under different constant partial pressure ratios, the finished steel coils after high-temperature annealing all exhibited point-like crystallization defects at the edges or center. Figure 2 For example, the protective gas inlets for decarburization annealing are distributed throughout the entire decarburization section, evenly spaced at 3m intervals. A constant partial pressure ratio of protective gas is uniformly introduced, and multiple sets of tests are conducted under different partial pressure ratio conditions. The outer 500m section of the steel coil is taken for observation and evaluation. Each shape in the figure represents a partial pressure ratio setting. It can be seen from the figure that a large proportion of point-like crystallization defects will be generated regardless of the constant partial pressure ratio condition, indicating that a specific distribution of partial pressure ratio is required to obtain a completely defect-free surface.

[0134] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for producing grain-oriented silicon steel with controlled point-like crystallization defects, characterized in that, Includes the following steps: 1) Smelt and continuously cast according to the chemical composition of grain-oriented silicon steel to obtain slabs; 2) The slab is heated to 1120~1190℃ and hot-rolled to a thickness of 2.2~2.8mm; then it undergoes a two-stage normalizing process, with the first stage at 1100~1150℃ for 10~30s and the second stage at 850~950℃ for 10~30s; finally, it is cold-rolled to obtain a cold-rolled strip with a finished thickness of 0.23~0.3mm. 3) Decarburization annealing is carried out at a constant temperature of 800~900℃ for 1~3 minutes; the protective gas for decarburization annealing is a humidified N2 and H2 mixture with a total flow rate of 400~600 m³ / min. 3 / h; The protective gas inlet for decarburization annealing is only set in two areas: the front zone and the rear zone of the decarburization section. The front zone and the rear zone of the decarburization section each account for 1 / 4 to 1 / 3 of the length of the decarburization annealing furnace. A set of detection points, numbered from 1 to n, is set up from the front to the back of the decarburization annealing furnace. The detection points start 2-5 meters from the front of the furnace and are then spaced at fixed intervals of 8-10 meters, ensuring that 12 ≤ n ≤ 18. Through these measures, the water-hydrogen partial pressure ratio at any detection point in the furnace satisfies the formula: 0.00205i 2 +0.0054i+0.1351≤P i ≤2.317×10 -4 i 3 -0.00836i 2 +0.1118i+0.303, where i represents the detection point number, P i This represents the water-hydrogen partial pressure ratio measured at detection point i; 4) Perform a two-stage nitriding treatment. The first stage nitriding temperature is 750~850℃, and the duration is 10~30s. The second stage nitriding temperature is 850~950℃, and the duration is 20~40s. After that, coat with MgO and dry. 5) Perform high-temperature annealing; 6) Perform stretching and leveling annealing, apply an insulating coating, and obtain the oriented silicon steel finished product.

2. The method for producing grain-oriented silicon steel with controlled point-like crystallization defects according to claim 1, characterized in that, The protective gas inlets inside the front zone of the decarbonization section are arranged at intervals of 3-4m. The protective gas flow rate accounts for 1 / 4 to 1 / 3 of the total flow rate. The humidification temperature of the protective gas is 0-10℃, and the hydrogen content is 50-75%.

3. The method for producing grain-oriented silicon steel with controlled point-like crystallization defects according to claim 1, characterized in that, The protective gas inlets inside the rear zone of the decarbonization section are arranged at intervals of 1.5 to 2 meters. The protective gas flow rate accounts for 2 / 3 to 3 / 4 of the total flow rate. The humidification temperature of the protective gas is 60 to 75°C, and the hydrogen content is 40 to 60%.

4. The method for producing grain-oriented silicon steel with controlled point-like crystallization defects according to claim 1, characterized in that, Each of the front section of the decarbonization section and the rear section of the decarbonization section is provided with an isolator, and the opening ratio of the front and rear isolators is (2~3):

1.

5. The method for producing grain-oriented silicon steel with controlled point-like crystallization defects according to claim 1, characterized in that, The atmosphere for the first stage of nitriding is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.3 to 0.7, a N2 to H2 volume ratio of 1:(1 to 3), and an NH3 flow rate of 2 to 4 m³ / s. 3 / h.

6. The method for producing grain-oriented silicon steel with controlled point-like crystallization defects according to claim 1, characterized in that, The atmosphere for the second stage of nitriding is a mixture of NH3 + N2 + H2 with a water-to-hydrogen partial pressure ratio of 0.001 to 0.05, a N2 to H2 volume ratio of 1:(1~3), and an NH3 flow rate of 7~10 m³ / s. 3 / h.

7. The method for producing grain-oriented silicon steel with controlled point-like crystallization defects according to claim 1, characterized in that, The high-temperature annealing process is as follows: first, the temperature is rapidly increased to 700~750℃, and a N2 and H2 mixture with a volume ratio of 1:(1~3) is introduced and kept at this temperature for 15~20h; then the temperature is slowly increased to 1170~1210℃ and kept at this temperature for 20~30h in a 100% H2 atmosphere; then the temperature is reduced to 500~600℃ and then air-cooled to room temperature.

8. The method for producing grain-oriented silicon steel with controlled point-like crystallization defects according to claim 7, characterized in that, The rapid heating rate is ≥50℃ / h, the slow heating rate is 15~17℃ / h, and the cooling rate is 12~30℃ / h.

9. The method for producing grain-oriented silicon steel with controlled point-like crystallization defects according to claim 1, characterized in that, The chemical composition of grain-oriented silicon steel by weight percentage is as follows: Si: 3.31~3.6%, C: 0.05~0.075%, Mn: 0.05~0.12%, P: 0.01~0.05%, S: 0.005~0.01%, N: 0.005~0.009%, Cr: 0.02~0.2%, Cu: 0.1~0.2%, Al: 0.0306~0.0330%, with the balance being Fe and unavoidable impurities.

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