Ultrahigh magnetic induction oriented silicon steel strip for low-frequency transformer and preparation method of ultrahigh magnetic induction oriented silicon steel strip

Abstract

The invention belongs to the technical field of silicon steel materials, and discloses an ultrahigh-magnetic-induction oriented silicon steel strip for a low-frequency transformer and a preparation method of the ultrahigh-magnetic-induction oriented silicon steel strip. A casting blank is subjected to hot rolling, primary cold rolling, decarburization annealing, nitriding, secondary cold rolling, magnesium oxide coating and annealing; a casting blank is prepared from the following components in percentage by mass: 0.02 percent to 0.065 percent of C, 2.7 percent to 3.7 percent of Si, 0.04 percent to 1.1 percent of Mn, 0.002 percent to 0.01 percent of S, 0.015 percent to 0.025 percent of N, 0.030 percent to 0.040 percent of Als and 0.01 percent to 0.3 percent of Cu. According to the method, aluminum nitride is used as an inhibitor, the inhibitor is formed by nitriding an initial alloy component, the sum of the nitrogen content and the nitriding amount in the initial component is about 500 ppm, and the obtained ultrahigh-magnetic-induction oriented silicon steel strip without the island crystal structure and with B800 larger than or equal to 1.95 T is suitable for machining of a 50 / 3 Hz low-frequency transformer iron core.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon steel material preparation, and specifically relates to an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer and a preparation method thereof. Background Art

[0002] As a new transmission method suitable for large-capacity long-distance transmission and grid connection, low-frequency transmission (50 / 3 Hz) has more technical and economic advantages than industrial frequency (50 Hz) AC transmission and flexible DC transmission, and has therefore received widespread attention. However, low-frequency transmission also faces huge challenges, such as key equipment such as low-frequency transformers, circuit breakers, and inverters. At present, low-frequency transformers are still made of conventional industrial frequency transformer cores and windings. The transformer core is made of high magnetic induction oriented silicon steel with a magnetic induction value of B 800 Most of them are 1.88-1.92 T. Under the premise of maintaining the transformer's induced electromotive force and magnetic flux density unchanged, the number of transformer turns and the cross-sectional area of ​​the core are inversely proportional to the frequency. That is, when the transformer operates at low frequency, in order to avoid magnetic saturation, the number of transformer turns and the cross-sectional area of ​​the core are larger than those at the power frequency, resulting in an increase in the volume, weight, and cost of the low-frequency transformer. Studies have shown that the cost of the transformer will increase by about 70%, which seriously restricts the economic efficiency of the flexible low-frequency power transmission technology. Therefore, in order to improve the overexcitation capacity of the low-frequency transformer and reduce its volume and weight, it is urgent to develop B 800 Ultra-high magnetic induction oriented silicon steel of ≥1.95 T is used to increase the design magnetic flux density of the low-frequency transformer core, thereby reducing the weight and volume of the core.

[0003] Japanese Patent Publication No. 6-88174, No. 7-166240, and Chinese Patent Application No. 201310666117.9 describe the preparation technology of ultra-high magnetic induction oriented silicon steel, which mainly reduces the deviation angle of Gauss grain orientation by adding trace alloy elements such as bismuth, lead, and tin during steelmaking, and controls the deviation angle within the range of ≤3°, thereby improving the magnetic induction value (B 800 ≥1.95T). However, the addition of bismuth and other elements will reduce the quality of the magnesium silicate bottom layer of the oriented silicon steel finished strip and the adhesion of the coating. It will also increase the size of the secondary recrystallized grains and the width of the 180° magnetic domain, which is not conducive to loss. At the same time, the addition of trace alloy elements will also increase the production cost.

[0004] The magnetic induction value of oriented silicon steel is not only related to the orientation deviation angle of Gaussian grains, but also to the proportion of Gaussian grains per unit area. The higher the proportion of Gaussian grains, the higher the magnetic induction value. "Island crystal" is a kind of structure that is easy to exist after high-temperature annealing of high-magnetic induction oriented silicon steel. Most of the grains are island-shaped, and the grain size is about 0.5mm-5mm. Figure 1As shown by the black arrows in the figure. During the high-temperature annealing process, the surface inhibitor will mature, resulting in a decrease in the inhibitory force. Some of the surface grains will gradually grow normally. When the grain size is large enough, it is difficult for the abnormally grown Gaussian grains in the secondary recrystallization process to swallow it up, and eventually "island crystals" will remain. The orientation characteristics of these "island crystals" are basically non-Gaussian orientations that are not easy to magnetize, resulting in a decrease in the proportion of Gaussian grains per unit area, deteriorating the magnetic properties, and the magnetic induction value B 800 Therefore, if the "island crystal" structure is eliminated and the proportion of the Goss grain structure is increased, it will be beneficial to the improvement of the magnetic induction value.

[0005] In summary, the magnetic induction value of oriented silicon steel can be increased by adding trace alloy elements, but it also brings disadvantages. Therefore, it is necessary to provide a new preparation technology for ultra-high magnetic induction oriented silicon steel strip. Summary of the invention The present invention aims to solve the technical problem of low magnetic induction value of oriented silicon steel in the prior art, and aims to provide an ultra-high magnetic induction oriented silicon steel strip for low-frequency transformers and a preparation method thereof. The ultra-high magnetic induction oriented silicon steel strip for low-frequency transformers prepared by the method has a magnetic induction value of ≥1.95T and is suitable for processing low-frequency transformer cores.

[0006] To achieve the above object, the technical solution adopted by the present invention is: The first aspect of the present invention provides a method for preparing an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer, comprising: The ingot is hot-rolled, cold-rolled once, decarburized, nitrided, cold-rolled twice, coated with magnesium oxide, and annealed to obtain an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer; The ingot includes, by mass percentage, C: 0.02%~0.065%, Si: 2.7%~3.7%, Mn: 0.04%~1.1%, S: 0.002%~0.01%, N: 0.015%~0.025%, Als: 0.030%~0.040%, Cu: 0.01%~0.3%, and the rest are iron and unavoidable impurity elements.

[0007] Furthermore, the process parameters of hot rolling are: hot rolling temperature is 1150-1200°C, and final rolling temperature is ≥1050°C.

[0008] Furthermore, the process parameters of the primary cold rolling are: rolling reduction rate is 55%-70%, the front tension stress of the strip is 50-150 KN, and the back tension stress of the rolling roller is 50-100 KN.

[0009] Furthermore, the thickness of the strip after the first cold rolling is 0.63-0.945 mm.

[0010] Furthermore, the process parameters of the decarburization annealing are: annealing temperature is 800-880°C, annealing time is 5-10min, and annealing atmosphere is a mixed atmosphere of wet N2 and H2 with a dew point temperature of 20-35°C.

[0011] Furthermore, the volume ratio of N2 to H2 is 1:3.

[0012] Furthermore, the process parameters of nitriding are: the nitriding atmosphere is a mixed atmosphere of dry N2, H2 and NH3, the nitriding temperature is 700-750°C, and the nitriding amount is 250-350 ppm.

[0013] Furthermore, the volume ratio N2:H2:NH3=1:3:2.

[0014] Furthermore, the process parameters of the secondary cold rolling are: rolling reduction rate is 65%-75%, the front tension stress of the strip is 50-100 KN, and the back tension stress of the rolling roller is 60-100 KN.

[0015] Furthermore, the annealing includes three stages. The first stage is kept at 840-860 °C for 10-30 min; the second stage is kept at 1040-1060 °C for 5-10 h, and the third stage is kept at 1200-1250 °C for 10-20 h.

[0016] Further, heating to 840-860°C at a heating rate of 200-300°C / h; Heat to 1040-1060℃ at a rate of 15-35℃ / h; Heat to 1200-1250 ℃ at a heating rate of 50-200 ℃ / h.

[0017] Furthermore, the annealing atmosphere in the first stage and the annealing atmosphere in the second stage are nitrogen-hydrogen mixed gases; The annealing atmosphere in the third stage is hydrogen.

[0018] Furthermore, the annealing atmosphere in the first stage is a nitrogen-hydrogen mixed gas with a volume ratio of N2:H2=1:1; The annealing atmosphere in the second stage is a nitrogen-hydrogen mixture with a volume ratio of N2:H2=3:1; The annealing atmosphere in the third stage is hydrogen.

[0019] A second aspect of the present invention provides an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer, wherein the magnetic induction value of the oriented silicon steel strip is ≥1.95T.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The method for preparing ultra-high magnetic induction oriented silicon steel strip provided by the present invention adopts a technical route of one-time cold rolling + decarburization annealing + nitriding + secondary cold rolling, which is different from the one-time cold rolling + decarburization annealing + nitriding process route of traditional low-temperature oriented silicon steel. The method of one-time cold rolling + decarburization annealing + secondary cold rolling adopted in the present invention can help to increase the proportion of Gaussian texture, overcome the one-time cold rolling of traditional low-temperature oriented silicon steel, the reduction rate reaches more than 87%, which is easy to cause the proportion of Gaussian grains to decrease, and at the same time is conducive to the deterioration of the magnetic properties of the Gaussian {110} <227> , Brass {110} <112> The increase in the proportion of textures can easily lead to the problem of reduced magnetic induction value of the strip after high-temperature annealing. In the present invention, aluminum nitride inhibitor is obtained by combining initial nitrogen component + nitriding, and the total nitrogen content is about 500ppm. Compared with the aluminum and nitrogen content in conventional low-temperature hot-rolled oriented silicon steel components, the present invention reduces production costs by increasing aluminum and nitrogen elements to replace trace alloying elements such as bismuth and tin. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low-frequency transformers provided by the present invention adopts low-temperature hot rolling while omitting the normalization process after conventional low-temperature hot rolling, which can shorten the process flow.

[0021] Furthermore, the present invention performs nitriding treatment before secondary cold rolling to increase the nitrogen content in the strip and form a large number of inhibitor particles such as silicon nitride and silicon aluminum nitride. The particles are fragmented during the secondary cold rolling, which plays a role in further refining the grains in the subsequent primary recrystallization process.

[0022] Furthermore, the method for preparing ultra-high magnetic induction oriented silicon steel strip provided by the present invention omits the primary recrystallization annealing process before high-temperature annealing, and directly coats magnesium oxide for high-temperature annealing after secondary cold rolling. In the first stage of high-temperature annealing, the temperature is raised to 800°C by a rapid heating method to allow primary recrystallization to occur. In the second stage of high-temperature annealing, a slow heating method is used to fully ensure that unstable inhibitor particles such as silicon nitride and silicon aluminum nitride are converted into stable aluminum nitride inhibitor particles, inhibiting the growth of the grain size of the matrix structure. After reaching 1050°C and maintaining the temperature for 5-10 hours, the Gaussian grains undergo secondary recrystallization. In the third stage of high-temperature annealing, a pure hydrogen atmosphere is used to purify impurities such as nitrogen and sulfur in the strip, and at the same time, the secondary recrystallization is further improved, and finally an oriented silicon steel strip without "island crystal" structure is obtained.

[0023] The present invention increases the aluminum and nitrogen elements in the initial components, adjusts the process route, controls and refines the grain size multiple times during the whole preparation process, improves the grain size stability of the matrix structure, and finally obtains an oriented silicon steel strip without "island crystal" structure. The magnetic induction value of the strip is ≥1.95T, which is suitable for processing low-frequency transformer cores.

[0024] Furthermore, the final rolling temperature is controlled at ≥1050°C to increase the amount of aluminum nitride inhibitor particles precipitated in the initial hot-rolled plate, thereby refining the grain size of the hot-rolled plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of "island crystal" in the secondary recrystallization structure in the prior art; Figure 2 is the secondary recrystallization structure diagram of Example 1; Figure 3 is the secondary recrystallization structure diagram of Example 2; Figure 4 is the secondary recrystallization structure diagram of Example 3; Figure 5 is the secondary recrystallization structure diagram of Example 4; Figure 6 is the secondary recrystallization structure diagram of Example 5; Figure 7 is the secondary recrystallization structure diagram of Example 6; Figure 8 is the secondary recrystallization structure diagram of Comparative Example 1; Fig. 9 This is the secondary recrystallization structure diagram of Comparative Example 2. DETAILED DESCRIPTION

[0026] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0027] If no specific experimental steps or conditions are specified in the examples, the experiments can be carried out according to the conventional experimental steps or conditions described in the literature in the art.

[0028] The invention discloses a method for preparing an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer, comprising the steps of smelting → hot rolling → primary cold rolling → decarburization annealing → nitriding → secondary cold rolling → coating magnesium oxide → high temperature annealing.

[0029] Specifically, the chemical composition of the ingot after smelting, by mass percentage, is mainly C: 0.02%~0.065%, Si: 2.7%~3.7%, Mn: 0.04%~1.1%, S: 0.002%~0.01%, N: 0.015%~0.025%, Als: 0.030%~0.040%, Cu: 0.01%~0.3%, and the rest is iron and unavoidable impurity elements.

[0030] Main parameters of hot rolling process: hot rolling the ingot to obtain hot rolled plate, the hot rolling temperature is 1150-1200 ℃, the final rolling temperature is ≥1050 ℃, and the thickness of the hot rolled plate is about 2.1 mm.

[0031] One cold rolling: The hot-rolled plate is subjected to one cold rolling to obtain the strip after one cold rolling, the rolling reduction rate is 55%-70%, the front tension stress of the strip is 50-150KN, the back tension stress of the rolling roller is 50-100 KN, and the strip thickness is 0.63-0.945mm.

[0032] Decarburization annealing: Decarburization annealing is performed on the strip after the first cold rolling to obtain the strip after decarburization annealing; the annealing temperature is 800-880 ℃, the annealing time is 5-10 min, the annealing atmosphere is a wet N2+H2 mixed atmosphere (the volume ratio of N2 to H2 atmosphere is 1:3), and the dew point temperature is 20-35 ℃.

[0033] Nitriding: The strip after decarburization annealing is nitrided to obtain a strip after decarburization annealing; the nitriding atmosphere is a mixed atmosphere of dry volume ratio N2:H2:NH3=1:3:2, the nitriding temperature is 700-750 °C, and the nitriding amount is 250-350 ppm.

[0034] Secondary cold rolling: The strip after decarburization annealing is subjected to secondary cold rolling to obtain the strip after secondary cold rolling; the rolling reduction rate is 65%-75%, the front tension stress of the strip is 50-100 KN, and the back tension stress of the rolling roller is 60-100 KN.

[0035] Magnesium oxide coating: Magnesium oxide is coated on the strip after secondary cold rolling with a thickness of 0.5-1.5 μm; High temperature annealing: The strip coated with magnesium oxide is subjected to high temperature annealing to obtain ultra-high magnetic induction oriented silicon steel strip for low-frequency transformers. The high temperature annealing is divided into three stages. In the first stage, the strip is heated to 840-860°C at a heating rate of 200-300°C / h and kept warm for 10-30 min. The annealing atmosphere is a nitrogen-hydrogen mixture with a volume ratio of N2:H2=1:1; in the second stage, the strip is heated to 1040-1060°C at a heating rate of 15-35°C / h and kept warm for 5-10 h. The annealing atmosphere is a nitrogen-hydrogen mixture with a volume ratio of N2:H2=3:1; in the third stage, the strip is heated to 1200-1250°C at a heating rate of 50-200°C / h and kept warm for 10-20 h. The annealing atmosphere is pure hydrogen.

[0036] The following are specific embodiments.

[0037] Example 1 This embodiment provides a method for preparing an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer, the steps of which are as follows: The original ingot is smelted to obtain an ingot, and the ingot is hot-rolled, cold-rolled once, decarburized, nitrided, cold-rolled twice, coated with magnesium oxide and annealed to obtain an ultra-high magnetic induction oriented silicon steel strip for low-frequency transformers; The chemical composition of the ingot by mass percentage is mainly C: 0.02%~0.065%, Si: 2.7%~3.7%, Mn: 0.04%~1.1%, S: 0.002%~0.01%, N: ~0.015%, Als: 0.030%~0.040%, Cu: 0.01%~0.3%, and the rest are iron and unavoidable impurity elements.

[0038] Hot rolling: The hot rolling temperature is 1150℃, the final rolling temperature is ≥1050℃, and the thickness of the hot rolled plate is about 2.1mm.

[0039] One cold rolling: the rolling reduction rate is 55%, the front tension stress of the strip is 50KN, the back tension stress of the rolling roller is 50KN, and the strip after one cold rolling is obtained, and the strip thickness is 0.945mm.

[0040] Decarburization annealing: annealing temperature is 880°C, annealing time is 5 min, annealing atmosphere is wet N2+H2 mixed atmosphere (atmosphere ratio is 1:3), and dew point temperature is 35°C.

[0041] Nitriding: The nitriding atmosphere is a dry N2:H2:NH3=1:3:2 mixed atmosphere, the nitriding temperature is 750℃, and the nitriding amount is ~350ppm.

[0042] Secondary cold rolling: the rolling reduction rate is 75%, the front tension stress of the strip is 50KN, the back tension stress of the rolling roller is 60KN, and the strip after secondary cold rolling is obtained.

[0043] Coating with magnesium oxide: Magnesium oxide is coated on the strip after the first cold rolling with a thickness of 0.5-1.5 μm to avoid adhesion.

[0044] High temperature annealing: In the first stage, the temperature is heated to 850°C at a heating rate of 200°C / h and kept for 10 minutes. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=1:1; in the second stage, the temperature is heated to 1050°C at a heating rate of 15°C / h and kept for 5 hours. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=3:1; in the third stage, the temperature is heated to 1200°C at a heating rate of 50°C / h and kept for 10 hours. The annealing atmosphere is pure hydrogen.

[0045] See also Figure 2 It can be seen that this embodiment eliminates the "island crystal" structure and increases the proportion of the Gossian grain structure.

[0046] Example 2 This embodiment provides a method for preparing an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer, the steps of which are as follows: Smelting: By mass percentage, the main chemical components are C: 0.02%~0.065%, Si: 2.7%~3.7%, Mn: 0.04%~1.1%, S: 0.002%~0.01%, N: ~0.025%, Als: 0.030%~0.040%, Cu: 0.01%~0.3%, and the rest are iron and unavoidable impurity elements.

[0047] Hot rolling: The hot rolling temperature is 1200℃, the final rolling temperature is ≥1050℃, and the thickness of the hot rolled plate is about 2.1mm.

[0048] One cold rolling: the rolling reduction rate is 70%, the front tension stress of the strip is 150KN, the back tension stress of the rolling roller is 100KN, and the strip after the one cold rolling is obtained, and the strip thickness is 0.63mm.

[0049] Decarburization annealing: annealing temperature is 800℃, annealing time is 10min, annealing atmosphere is wet N2+H2 mixed atmosphere (atmosphere ratio is 1:3), and dew point temperature is 20℃.

[0050] Nitriding: The nitriding atmosphere is a dry N2:H2:NH3=1:3:2 mixed atmosphere, the nitriding temperature is 700℃, and the nitriding amount is ~250ppm.

[0051] Secondary cold rolling: the rolling reduction rate is 65%, the front tension stress of the strip is 100KN, the rear tension stress of the rolling roller is 100KN, and the strip after secondary cold rolling is obtained.

[0052] Coating with magnesium oxide: Magnesium oxide is coated on the strip after the first cold rolling with a thickness of 0.5-1.5 μm to avoid adhesion.

[0053] High temperature annealing: High temperature annealing is divided into three stages. In the first stage, the temperature is heated to 850°C at a heating rate of 300°C / h and kept warm for 30 minutes. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=1:1; in the second stage, the temperature is heated to 1050°C at a heating rate of 35°C / h and kept warm for 10 hours. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=3:1; in the third stage, the temperature is heated to 1200°C at a heating rate of 200°C / h and kept warm for 20 hours. The annealing atmosphere is pure hydrogen.

[0054] See also Figure 3 It can be seen that this embodiment eliminates the "island crystal" structure and increases the proportion of the Gossian grain structure.

[0055] Example 3 This embodiment provides a method for preparing an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer, the steps of which are as follows: Smelting: By mass percentage, the main chemical components are C: 0.02%~0.065%, Si: 2.7%~3.7%, Mn: 0.04%~1.1%, S: 0.002%~0.01%, N: ~0.020%, Als: 0.030%~0.040%, Cu: 0.01%~0.3%, and the rest are iron and unavoidable impurity elements.

[0056] Hot rolling: The hot rolling temperature is 1150℃, the final rolling temperature is ≥1050℃, and the thickness of the hot rolled plate is about 2.1mm.

[0057] One cold rolling: the rolling reduction rate is 65%, the front tension stress of the strip is 120KN, the back tension stress of the rolling roller is 80KN, and the strip after the one cold rolling is obtained, and the strip thickness is 0.735mm.

[0058] Decarburization annealing: annealing temperature is 850℃, annealing time is 8min, annealing atmosphere is wet N2+H2 mixed atmosphere (atmosphere ratio is 1:3), and dew point temperature is 25℃.

[0059] Nitriding: The nitriding atmosphere is a dry N2:H2:NH3=1:3:2 mixed atmosphere, the nitriding temperature is 730℃, and the nitriding amount is ~300ppm.

[0060] Secondary cold rolling: the rolling reduction rate is 65%, the front tension stress of the strip is 70KN, the back tension stress of the rolling roller is 70KN, and the strip after secondary cold rolling is obtained.

[0061] Coating with magnesium oxide: Magnesium oxide is coated on the strip after the first cold rolling with a thickness of 0.5-1.5 μm to avoid adhesion.

[0062] High temperature annealing: In the first stage, the temperature is heated to 850°C at a heating rate of 250°C / h and kept warm for 20 minutes. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=1:1; in the second stage, the temperature is heated to 1050°C at a heating rate of 30°C / h and kept warm for 8 hours. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=3:1; in the third stage, the temperature is heated to 1200°C at a heating rate of 150°C / h and kept warm for 15 hours. The annealing atmosphere is pure hydrogen.

[0063] See also Figure 4 It can be seen that this embodiment eliminates the "island crystal" structure and increases the proportion of the Gossian grain structure.

[0064] Example 4 This embodiment provides a method for preparing an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer, the steps of which are as follows: Smelting: By mass percentage, the main chemical components are C: 0.02%~0.065%, Si: 2.7%~3.7%, Mn: 0.04%~1.1%, S: 0.002%~0.01%, N: ~0.018%, Als: 0.030%~0.040%, Cu: 0.01%~0.3%, and the rest are iron and unavoidable impurity elements.

[0065] Hot rolling: The hot rolling temperature is 1180℃, the final rolling temperature is ≥1050℃, and the thickness of the hot rolled plate is about 2.1mm.

[0066] One cold rolling: the rolling reduction rate is 70%, the front tension stress of the strip is 90KN, the back tension stress of the rolling roller is 70KN, and the strip after the one cold rolling is obtained, and the strip thickness is 0.630mm.

[0067] Decarburization annealing: annealing temperature is 840℃, annealing time is 10min, annealing atmosphere is wet N2+H2 mixed atmosphere (atmosphere ratio is 1:3), and dew point temperature is 20℃.

[0068] Nitriding: The nitriding atmosphere is a dry N2:H2:NH3=1:3:2 mixed atmosphere, the nitriding temperature is 750℃, and the nitriding amount is ~320ppm.

[0069] Secondary cold rolling: the rolling reduction rate is 65%, the front tension stress of the strip is 70KN, the back tension stress of the rolling roller is 70KN, and the strip after secondary cold rolling is obtained.

[0070] Coating with magnesium oxide: Magnesium oxide is coated on the strip after the first cold rolling with a thickness of 0.5-1.5 μm to avoid adhesion.

[0071] High temperature annealing: In the first stage, the temperature is heated to 850°C at a rate of 200°C / h and kept warm for 25 minutes. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=1:1; in the second stage, the temperature is heated to 1050°C at a rate of 25°C / h and kept warm for 10 hours. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=3:1; in the third stage, the temperature is heated to 1200°C at a rate of 50°C / h and kept warm for 10 hours. The annealing atmosphere is pure hydrogen.

[0072] See also Figure 5 It can be seen that this embodiment eliminates the "island crystal" structure and increases the proportion of the Gossian grain structure.

[0073] Example 5 This embodiment provides a method for preparing an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer, the steps of which are as follows: Smelting: By mass percentage, the main chemical components are C: 0.02%~0.065%, Si: 2.7%~3.7%, Mn: 0.04%~1.1%, S: 0.002%~0.01%, N: ~0.018%, Als: 0.030%~0.040%, Cu: 0.01%~0.3%, and the rest are iron and unavoidable impurity elements.

[0074] Hot rolling: The hot rolling temperature is 1170℃, the final rolling temperature is ≥1050℃, and the thickness of the hot rolled plate is about 2.1mm.

[0075] One cold rolling: the rolling reduction rate is 60%, the front tension stress of the strip is 70KN, the back tension stress of the rolling roller is 90KN, and the strip after one cold rolling is obtained, and the strip thickness is 0.80mm.

[0076] Decarburization annealing: annealing temperature is 860℃, annealing time is 6min, annealing atmosphere is wet N2+H2 mixed atmosphere (atmosphere ratio is 1:3), and dew point temperature is 20℃.

[0077] Nitriding: The nitriding atmosphere is a dry N2:H2:NH3=1:3:2 mixed atmosphere, the nitriding temperature is 750℃, and the nitriding amount is ~320ppm.

[0078] Secondary cold rolling: the rolling reduction rate is 65%, the front tension stress of the strip is 70KN, the back tension stress of the rolling roller is 70KN, and the strip after secondary cold rolling is obtained.

[0079] Coating with magnesium oxide: Magnesium oxide is coated on the strip after the first cold rolling with a thickness of 0.5-1.5 μm to avoid adhesion.

[0080] High temperature annealing: In the first stage, the temperature is heated to 840°C at a heating rate of 200°C / h and kept warm for 30 minutes. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=1:1; in the second stage, the temperature is heated to 1040°C at a heating rate of 25°C / h and kept warm for 10 hours. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=3:1; in the third stage, the temperature is heated to 1200°C at a heating rate of 50°C / h and kept warm for 20 hours. The annealing atmosphere is pure hydrogen.

[0081] See also Figure 6 It can be seen that this embodiment eliminates the "island crystal" structure and increases the proportion of the Gossian grain structure.

[0082] Example 6 This embodiment provides a method for preparing an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer, the steps of which are as follows: Smelting: By mass percentage, the main chemical components are C: 0.02%~0.065%, Si: 2.7%~3.7%, Mn: 0.04%~1.1%, S: 0.002%~0.01%, N: ~0.018%, Als: 0.030%~0.040%, Cu: 0.01%~0.3%, and the rest are iron and unavoidable impurity elements.

[0083] Hot rolling: The hot rolling temperature is 1200℃, the final rolling temperature is ≥1050℃, and the thickness of the hot rolled plate is about 2.1mm.

[0084] One cold rolling: the rolling reduction rate is 55%, the front tension stress of the strip is 130KN, the back tension stress of the rolling roller is 60KN, and the strip after the one cold rolling is obtained, and the strip thickness is 0.90mm.

[0085] Decarburization annealing: annealing temperature is 880℃, annealing time is 7min, annealing atmosphere is wet N2+H2 mixed atmosphere (atmosphere ratio is 1:3), and dew point temperature is 20℃.

[0086] Nitriding: The nitriding atmosphere is a dry N2:H2:NH3=1:3:2 mixed atmosphere, the nitriding temperature is 750℃, and the nitriding amount is ~320ppm.

[0087] Secondary cold rolling: the rolling reduction rate is 65%, the front tension stress of the strip is 70KN, the back tension stress of the rolling roller is 70KN, and the strip after secondary cold rolling is obtained.

[0088] Coating with magnesium oxide: Magnesium oxide is coated on the strip after the first cold rolling with a thickness of 0.5-1.5 μm to avoid adhesion.

[0089] High temperature annealing: In the first stage, the temperature is heated to 860°C at a heating rate of 200°C / h and kept for 10 minutes. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=1:1; in the second stage, the temperature is heated to 1060°C at a heating rate of 25°C / h and kept for 5 hours. The annealing atmosphere is a nitrogen-hydrogen mixture with a ratio of N2:H2=3:1; in the third stage, the temperature is heated to 1250°C at a heating rate of 50°C / h and kept for 10 hours. The annealing atmosphere is pure hydrogen.

[0090] See also Figure 7 It can be seen that this embodiment eliminates the "island crystal" structure and increases the proportion of the Gossian grain structure.

[0091] Comparative Example 1 This comparative example refers to Example 1, except that the hot rolling temperature is 1100°C, the final rolling temperature is 1000°C, and the nitriding amount is 150 ppm.

[0092] See also Figure 8It can be seen that the "island crystal" structure is not eliminated after high temperature annealing in this comparative example.

[0093] Comparative Example 2 This comparative example refers to Implementation 4, except that the first cold rolling reduction rate is 85%; and the second cold rolling reduction rate is 55%.

[0094] See also Fig. 9 It can be seen that the "island crystal" structure was not eliminated after temperature annealing in this comparative example.

[0095] Table 1 Example "island crystal" organizational proportion and magnetic properties

[0096] It can be seen from Table 1 that the ultra-high magnetic induction oriented silicon steel strip for low-frequency transformer prepared by the present invention does not contain "island crystal" structure, and the magnetic induction value B 800 The maximum reaches 1.959T.

[0097] In the present invention, aluminum nitride is used as an inhibitor, and the source of the inhibitor is composed of the initial alloy component + nitriding, and the sum of the nitrogen content in the initial component and the nitriding amount is about 500 ppm. After hot rolling, primary cold rolling, decarburization, nitriding, secondary cold rolling, high temperature annealing and other processes, the grain size of the hot rolling structure, the structure after decarburization annealing and the surface structure during high temperature annealing are refined, and finally B without "island crystal" structure is obtained. 800 ≥1.95 T ultra-high magnetic induction oriented silicon steel strip.

[0098] In the present invention, no additional trace alloying elements such as bismuth, lead, and tin are added. Instead, the ratio of aluminum and nitrogen elements in the original alloy components is increased, and aluminum nitride inhibitor particles required for partial high-temperature annealing are formed during the hot rolling process. The preparation process route is adjusted, and the grain size is controlled and refined for multiple times during the entire preparation process. Then, nitriding treatment is performed to further increase the nitrogen content in the strip, increase the number of inhibitor particles, avoid the growth of surface grains during high-temperature annealing, and finally eliminate the "island crystal" structure. The ratio of Gaussian grain structure is increased by eliminating the "island crystal" structure. The obtained ultra-high magnetic induction oriented silicon steel is suitable for the processing of 50 / 3 Hz low-frequency transformer cores, reduces the volume and weight of the transformer, and saves costs.

[0099] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing ultra-high magnetic induction oriented silicon steel strip for low-frequency transformer, characterized in that: include: The ingot is hot-rolled, cold-rolled once, decarburized, nitrided, cold-rolled twice, coated with magnesium oxide, and annealed to obtain an ultra-high magnetic induction oriented silicon steel strip for a low-frequency transformer; The ingot includes, by mass percentage, C: 0.02%~0.065%, Si: 2.7%~3.7%, Mn: 0.04%~1.1%, S: 0.002%~0.01%, N: 0.015%~0.025%, Als: 0.030%~0.040%, Cu: 0.01%~0.3%, and the rest are iron and unavoidable impurity elements.

2. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 1, characterized in that: The process parameters of hot rolling are: hot rolling temperature is 1150-1200 ℃, and the final rolling temperature is ≥1050 ℃.

3. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 1, characterized in that: The process parameters of the primary cold rolling are: rolling reduction rate is 55%-70%, the front tension stress of the strip is 50-150KN, and the back tension stress of the rolling roller is 50-100 KN.

4. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 1, characterized in that: The thickness of the strip after the first cold rolling is 0.63-0.945 mm.

5. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 1, characterized in that: The process parameters of decarburization annealing are: annealing temperature is 800-880 ℃, annealing time is 5-10 min, annealing atmosphere is a mixed atmosphere of wet N2 and H2 with a dew point temperature of 20-35 ℃.

6. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 5, characterized in that: The volume ratio of N2 to H2 is 1:

3.

7. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 1, characterized in that: The process parameters of nitriding are: the nitriding atmosphere is a mixed atmosphere of dry N2, H2 and NH3, the nitriding temperature is 700-750 ℃, and the nitriding amount is 250-350 ppm.

8. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 7, characterized in that: Volume ratio N2:H2:NH3=1:3:

2.

9. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 1, characterized in that: The process parameters of secondary cold rolling are: rolling reduction rate is 65%-75%, the front tension stress of the strip is 50-100 KN, and the back tension stress of the rolling roller is 60-100 KN.

10. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 1, characterized in that: Annealing includes three stages. The first stage is kept at 840-860 ℃ for 10-30 min; the second stage is kept at 1040-1060 ℃ for 5-10 h; and the third stage is kept at 1200-1250 ℃ for 10-20 h.

11. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 10, characterized in that: Heat to 840-860 ℃ at a heating rate of 200-300 ℃ / h; Heat to 1040-1060℃ at a rate of 15-35℃ / h; Heat to 1200-1250 ℃ at a heating rate of 50-200 ℃ / h.

12. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 10, characterized in that: The annealing atmosphere in the first stage and the annealing atmosphere in the second stage are nitrogen-hydrogen mixed gases; The annealing atmosphere in the third stage is hydrogen.

13. The method for preparing ultra-high magnetic induction oriented silicon steel strip for low frequency transformer according to claim 10, characterized in that: The annealing atmosphere in the first stage is a nitrogen-hydrogen mixture with a volume ratio of N2:H2=1:1; The annealing atmosphere in the second stage is a nitrogen-hydrogen mixture with a volume ratio of N2:H2=3:1; The annealing atmosphere in the third stage is hydrogen.

14. An ultra-high magnetic induction oriented silicon steel strip for low frequency transformer prepared according to the method according to any one of claims 1 to 13, characterized in that: The magnetic induction value of the oriented silicon steel strip is ≥1.95T.

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